Engineering the Mode Coupling in Microrings for Laser and Sensor Applications (Lynford L Goddard)

00:54:03
https://www.youtube.com/watch?v=jMT54AGraUE

Zusammenfassung

TLDRIn this talk, the speaker presents the work done by their group on reflective micro ring resonators over eight years at the University of Illinois. They explain the principles of these devices, including the coupling of different modes within the micro ring, and how this engineering leads to applications in laser mirrors and biosensing. The presentation covers experimental results demonstrating single wavelength operation, the simulation and design processes using tools like COMSOL and MATLAB, and the advantages over traditional structures such as linear Bragg reflectors including smaller size and better performance. Applications also include the detection of biomolecules using plasmonics based whispering gallery mode sensors. The speaker concludes by discussing future directions in developing low threshold lasers and optimizing fabrication processes, emphasizing the collaborative efforts that made the work possible.

Mitbringsel

  • 🔬 Reflective micro ring resonators improve sensing capabilities.
  • 🔄 Mode coupling enhances laser output and minimizes noise.
  • ⚙️ Simulation tools like COMSOL and MATLAB aid design processes.
  • 🌟 Applications include single wavelength lasers and biosensing.
  • 🔍 Plasmonic sensors detect small biomolecules effectively.
  • 🔧 Collaboration and funding were key to research success.
  • ⚖️ Balancing design for high sensitivity vs. resonance quality factor.
  • 📏 Smaller devices reduce fabrication variation sensitivity.
  • ♻️ Temperature affects refractive index, changing resonances.
  • 📈 Future work includes improving fabrication and developing new designs.

Zeitleiste

  • 00:00:00 - 00:05:00

    The speaker expresses gratitude to the i optics organizing committee and introduces the topic of micro ring resonators, focusing on mode coupling for applications in sensing. The presentation will cover motivations, simulations, experimental results, and applications.

  • 00:05:00 - 00:10:00

    The traditional micro ring resonators utilize constructive interference for light coupling, but the speaker's group has innovated with reflective designs that incorporate gratings to enhance reflection spectra. The outline includes motivation, methods, results, and applications.

  • 00:10:00 - 00:15:00

    The speaker discusses the motivation behind studying reflective micro ring resonators, highlighting the efficiency, size reduction, and benefits over traditional linear Bragg reflectors, particularly in terms of power tuning and elimination of side lobes.

  • 00:15:00 - 00:20:00

    The design and fabrication of these reflective micro ring resonators are presented, including the use of simulations to understand light behavior and coupling mechanisms. The effective coupling theory guides the device design for optimal resonance properties.

  • 00:20:00 - 00:25:00

    The speaker discusses experimental results demonstrating high reflection capabilities and precise resonance control using their reflective micro ring designs, showcasing their potential for practical applications in lasers and sensors.

  • 00:25:00 - 00:30:00

    Applications of the reflective micro ring resonators are explored, emphasizing their use as mirrors for lasers, achieving single wavelength operation through careful design and mode selection in the resonators.

  • 00:30:00 - 00:35:00

    The speaker introduces integrated devices, such as the single wavelength integrated ring laser, highlighting how mode coupling and engineering can lead to improved performance in lasing operations.

  • 00:35:00 - 00:40:00

    The summary touches on the development of hybrid sensing platforms, where micro ring resonators interact with plasmonic nanostructures to enable highly sensitive detection of biomolecules through mode coupling effects.

  • 00:40:00 - 00:45:00

    The presentation concludes with the focus on future advancements, including exploring plasmonic antennas and optimizing laser designs to enhance sensitivity and performance in sensing applications.

  • 00:45:00 - 00:54:03

    Acknowledgments are given to the research team's efforts and funding sources, with an invitation for questions from the audience.

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Video-Fragen und Antworten

  • What are reflective micro ring resonators used for?

    They are used in applications such as sensing and laser technologies.

  • How has the speaker's group contributed to this field?

    They engineered mode coupling in reflective micro ring resonators, leading to several innovative results.

  • What simulation tools are mentioned in the presentation?

    COMSOL and MATLAB were used for simulation and design.

  • What are the benefits of reflective micro ring resonators over traditional designs?

    They offer smaller size, reduced sensitivity to fabrication variations, and less noise in laser output.

  • What is the significance of mode coupling in these devices?

    Mode coupling allows for selective reflection and reduces unwanted resonances, enhancing performance.

  • What experimental results were discussed?

    The results include the demonstration of single wavelength reflectors and laser operations.

  • What are the applications of plasmonics based whispering gallery mode sensors?

    They are used for detecting small biomolecules binding to the sensor surface.

  • What is the advantage of using a reflective micro ring as a laser mirror?

    It allows narrow operating bandwidth and higher efficiency in semiconductor lasers.

  • How does temperature affect the resonator structure?

    Temperature changes affect the refractive index and can shift resonance wavelengths.

  • What future work is mentioned for the reflective micro rings?

    The group is looking at further optimizing fabrication processes and developing new designs for enhanced performance.

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Untertitel
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Automatisches Blättern:
  • 00:00:05
    Thank You Hasan and also thank you to
  • 00:00:08
    the rest of the i optics organizing
  • 00:00:10
    committee for giving me the opportunity
  • 00:00:11
    to share some of the results that my
  • 00:00:14
    group has had in my Kron resonators over
  • 00:00:17
    the past Wow eight eight years I've been
  • 00:00:21
    at Illinois now this is my ninth year
  • 00:00:22
    and very early in our in our development
  • 00:00:26
    as a group we got interested in the
  • 00:00:28
    theory and application of reflective my
  • 00:00:30
    crane resonators and so we'll talk today
  • 00:00:32
    about how we engineer the mode coupling
  • 00:00:35
    between the different modes and the
  • 00:00:37
    micro ring so that we can have
  • 00:00:38
    applications and sensing and amazing so
  • 00:00:42
    brief outline um I'm going to talk about
  • 00:00:44
    some motivation there's the traditional
  • 00:00:46
    my crowing resonator that many of you
  • 00:00:48
    are familiar with basically light
  • 00:00:50
    couples in from a waveguide into a micro
  • 00:00:52
    resonator and based on constructive
  • 00:00:54
    interference the field intensity builds
  • 00:00:56
    up inside the ring so our group started
  • 00:00:59
    looking at reflective micron resonators
  • 00:01:01
    where we put our grading inside the ring
  • 00:01:02
    so that we can generate a reflection
  • 00:01:04
    spectrum I'll talk about some of the
  • 00:01:07
    simulation design tools on basically our
  • 00:01:09
    methods of using comsol to simulate
  • 00:01:12
    two-dimensional cross sections of the
  • 00:01:15
    mode profile using finite element method
  • 00:01:17
    I'll talk about the work that we did to
  • 00:01:20
    develop a cylindrical couple mode theory
  • 00:01:22
    so that we can understand how the
  • 00:01:24
    different modes of the micro ring
  • 00:01:26
    coupled to each other and how we can
  • 00:01:28
    engineer the spectra by doing the
  • 00:01:30
    Selective coupling I'll talk about the
  • 00:01:32
    results that we have four passive
  • 00:01:34
    microwave resonators how we design in
  • 00:01:35
    fabricated structures in silicon nitride
  • 00:01:38
    using silicon dioxide cladding the
  • 00:01:40
    measurement of these devices so that we
  • 00:01:43
    can calculate the spectra of the
  • 00:01:45
    transmitted and also the reflected
  • 00:01:48
    properties of the device and I'll show
  • 00:01:51
    some experimental results where we
  • 00:01:52
    demonstrated single wavelength
  • 00:01:53
    reflectors based on our micro ring
  • 00:01:56
    design next I'll go into some
  • 00:01:59
    applications so the first part of the
  • 00:02:01
    talk will be mostly about the theory of
  • 00:02:03
    these devices and gives some basic
  • 00:02:05
    fabrication results the second part of
  • 00:02:07
    the talk will go into the applications
  • 00:02:09
    so we want to be able to use these
  • 00:02:10
    devices as micro these pet these
  • 00:02:13
    reflective my crowing mirrors as laser
  • 00:02:16
    mirrors so
  • 00:02:16
    replacing the linear bragg reflector
  • 00:02:18
    with this compact micro ring based
  • 00:02:21
    reflector and we show experimental
  • 00:02:24
    results of how we did monolithic active
  • 00:02:26
    and passive integration of a device on a
  • 00:02:29
    gallium arsenide substrate I'll then get
  • 00:02:32
    into our work in single wavelength
  • 00:02:34
    integrated mic releasers it's nice to
  • 00:02:38
    have good acronyms so we call this
  • 00:02:40
    device the swirl single wavelength
  • 00:02:42
    integrated ring laser I'll talk about
  • 00:02:44
    how we can engineer the loss of the
  • 00:02:47
    different modes based on mode coupling
  • 00:02:51
    and then show some fabrication results
  • 00:02:53
    and experimental results about how we
  • 00:02:55
    can choose the specific resonance the
  • 00:02:57
    specific as a middle order of the
  • 00:02:59
    resonant for lazing finally I'll go into
  • 00:03:04
    the application and sensing on so our
  • 00:03:06
    group is interested in making a
  • 00:03:09
    plasmonics based whispering gallery mode
  • 00:03:11
    based micro ring sensors so this hybrid
  • 00:03:15
    sensor allows us to detect small
  • 00:03:18
    biomolecules as it binds to the surface
  • 00:03:21
    so the structure consists of this
  • 00:03:24
    silicon microsphere surrounded by these
  • 00:03:27
    gold nanoparticles which we call
  • 00:03:29
    epitopes and based on the design of the
  • 00:03:32
    dimensions of the epitopes relative to
  • 00:03:34
    the design of the whispering gallery
  • 00:03:36
    mode we can engineer coupling between
  • 00:03:38
    the isolated my crowing resonator on
  • 00:03:41
    formed by the whispering gallery mode
  • 00:03:43
    and the plasmonics chain ring resonator
  • 00:03:45
    formed by these epitopes and will show
  • 00:03:47
    that based on the device dimensions we
  • 00:03:50
    essentially get something like mode anti
  • 00:03:53
    crossing or abandoned I crossing where
  • 00:03:55
    we generate the symmetric and
  • 00:03:56
    anti-symmetric modes and in this very
  • 00:03:59
    small variation in the radius we can get
  • 00:04:03
    significantly significant changes in the
  • 00:04:06
    resonance on shift due to binding events
  • 00:04:10
    okay so let's talk about the motivation
  • 00:04:12
    so why do we want to study reflective my
  • 00:04:15
    crowing resonators so when you look at a
  • 00:04:17
    semiconductor laser on typically the end
  • 00:04:19
    facets are made by linear Bragg
  • 00:04:21
    reflectors so alternating high and low
  • 00:04:23
    refractive index materials and you make
  • 00:04:26
    these quarter wavelength long for each
  • 00:04:28
    section
  • 00:04:29
    and this is a well-known reflection
  • 00:04:31
    spectrum profile which has a maximum in
  • 00:04:33
    the reflection when the wavelength is
  • 00:04:36
    exactly such that the thicknesses lab
  • 00:04:38
    Dover for for each layer so you can
  • 00:04:40
    design these high reflective mirrors on
  • 00:04:42
    some of the disadvantages of the linear
  • 00:04:45
    dbr is that it's very long in order to
  • 00:04:48
    get a high reflectivity and narrow line
  • 00:04:50
    with you have to make it longer so the
  • 00:04:52
    width in frequency is inversely
  • 00:04:55
    proportional to the length of the dbr so
  • 00:04:57
    if you want to improve the narrowness of
  • 00:05:01
    this reflection spectrum by a factor of
  • 00:05:02
    10 you need it to be 10 times as long
  • 00:05:05
    there's also an issue when you start
  • 00:05:07
    making these gratings to the millimeter
  • 00:05:09
    to centimeter size in that you get
  • 00:05:11
    fabrication non-uniformities so across
  • 00:05:13
    the wafer on the pitch that you're able
  • 00:05:16
    to achieve the refractive index the
  • 00:05:18
    device dimensions when you fabricate
  • 00:05:20
    these devices it becomes less uniform as
  • 00:05:23
    it spreads out there is also the issue
  • 00:05:26
    of these side lobes so the side lobes
  • 00:05:28
    are actually additional modes that can
  • 00:05:30
    lays in your spectrum they add noise in
  • 00:05:33
    the overall laserperformance and so
  • 00:05:35
    although you get the main output power
  • 00:05:37
    at the peak of the reflection spectrum
  • 00:05:39
    you also generate light at these other
  • 00:05:41
    unwanted wavelengths which produces
  • 00:05:44
    laser noise so our group had a very
  • 00:05:47
    simple idea our idea was just take the
  • 00:05:49
    linear dbr and roll it into itself and
  • 00:05:52
    make a ring dbr and we didn't really
  • 00:05:54
    fully understand all the great benefits
  • 00:05:57
    that you can have just by doing this our
  • 00:05:59
    main motivation was we wanted to make a
  • 00:06:01
    smaller device so after we started
  • 00:06:03
    simulating these structures we found
  • 00:06:05
    some really nice properties so the main
  • 00:06:07
    goal was we wanted to make it smaller
  • 00:06:09
    but in addition to this because it's
  • 00:06:12
    smaller it's less sensitive to way for
  • 00:06:14
    scale variations so I'm only patterning
  • 00:06:16
    a grating over a 60 or 70 micron
  • 00:06:19
    diameter ring instead of a few
  • 00:06:22
    millimeters two centimeters long and I
  • 00:06:24
    can achieve the same amount of
  • 00:06:26
    reflection power from my very compact
  • 00:06:29
    structure that I could from this very
  • 00:06:30
    long device so if I want to tune the
  • 00:06:33
    structure if I do something like
  • 00:06:35
    temperature tuning in the first case I
  • 00:06:37
    have to temperature tune the entire
  • 00:06:38
    length of the dbr whereas in this case I
  • 00:06:41
    only have two temperature to in a very
  • 00:06:42
    small micro
  • 00:06:43
    resonator so there's less power required
  • 00:06:45
    for tuning probably the biggest benefit
  • 00:06:48
    of the structure is that there are no
  • 00:06:50
    side lobes so these side lobes exist
  • 00:06:53
    because of the fact that the linear
  • 00:06:56
    grading has a finite length and so this
  • 00:06:59
    finite length introduces zeros into the
  • 00:07:02
    summation that you would get from adding
  • 00:07:04
    up the reflectivities because this ring
  • 00:07:07
    is periodic when you add up the
  • 00:07:08
    reflections from multiple passes around
  • 00:07:11
    the ring it becomes an infinite sum and
  • 00:07:15
    this infinite sum does not have zeros so
  • 00:07:17
    as a results there are no side lobes in
  • 00:07:19
    the reflection profile and you'll get a
  • 00:07:21
    much cleaner laser output if you use
  • 00:07:25
    this as a reflective mirror so um let's
  • 00:07:29
    look at how we discuss these things on
  • 00:07:33
    so we have lights in a waveguide that
  • 00:07:35
    couples to a ring on we form the ring
  • 00:07:37
    just by bending the waveguide into ring
  • 00:07:39
    shape we can easily fabricate one
  • 00:07:41
    dimensional or two dimensional arrays of
  • 00:07:43
    these ring resonators on chip through
  • 00:07:45
    standard even lithography a single micro
  • 00:07:48
    ring resonator will have equally spaced
  • 00:07:50
    resonant modes at each one of these
  • 00:07:52
    wavelengths that's resonant essentially
  • 00:07:54
    you have an integer multiple of
  • 00:07:56
    wavelengths fitting inside the
  • 00:07:58
    circumference of the ring so when this
  • 00:08:00
    has a constructive interference such
  • 00:08:02
    that i have an integer multiple on the
  • 00:08:04
    power in the ring will build up and all
  • 00:08:07
    the power gets lost in the ring instead
  • 00:08:09
    of being transmitted so when I'm off
  • 00:08:10
    resonance the light goes into the ring
  • 00:08:12
    and then it destructively interferes and
  • 00:08:14
    the light couples back out when I'm on
  • 00:08:16
    resonance the light couples into the
  • 00:08:18
    ring and it keeps circulating until it
  • 00:08:20
    builds up in strength and eventually
  • 00:08:22
    it's absorbed inside the ring so add a
  • 00:08:26
    single resonance there's actually two
  • 00:08:28
    degenerate modes the two degenerate
  • 00:08:30
    modes are the counter propagating modes
  • 00:08:31
    so there's one that's going clockwise
  • 00:08:33
    one that's going counterclockwise and
  • 00:08:35
    these have the exact same resonance
  • 00:08:37
    frequency it's the key that we're going
  • 00:08:39
    to do with our engineered mode coupling
  • 00:08:40
    is we're going to couple the clockwise
  • 00:08:43
    and the counterclockwise propagating
  • 00:08:44
    modes to be able to form standing wave
  • 00:08:47
    modes so the standing wave modes are
  • 00:08:49
    going to allow us to have high
  • 00:08:50
    reflection in our device so we study the
  • 00:08:53
    reflective micro ring resonators using s
  • 00:08:55
    parameters
  • 00:08:56
    we do the simple calculation in matlab
  • 00:08:58
    we model our system as we have power
  • 00:09:01
    coming in and there's a certain amount
  • 00:09:02
    or electric field coming in we have a
  • 00:09:04
    certain amount of electric field
  • 00:09:06
    circulating in the ring there's a
  • 00:09:07
    reflective element which you can write
  • 00:09:09
    in terms of a scattering matrix with
  • 00:09:11
    reflection and transmission coefficients
  • 00:09:13
    and what you can calculate is as a
  • 00:09:15
    function of the wavelength normalized by
  • 00:09:17
    the free spectral range of the device
  • 00:09:19
    what is the overall reflection of this
  • 00:09:22
    structure as a function of the
  • 00:09:25
    reflection that you put the reflection
  • 00:09:28
    coefficient of the element that you put
  • 00:09:30
    inside this ring so we get a profile
  • 00:09:33
    that looks like this so this is a plot
  • 00:09:35
    so for a fixed amount of coupling into
  • 00:09:37
    the ring for a fixed amount of loss we
  • 00:09:39
    generate one of these plots and this
  • 00:09:41
    plot allows us to design the type of
  • 00:09:43
    reflective element that we put in the
  • 00:09:45
    ring so that we get an overall
  • 00:09:47
    reflection spectrum that's useful for a
  • 00:09:49
    device so as an example if I wanted to
  • 00:09:52
    design a structure that reflects exactly
  • 00:09:54
    at this one wavelength and doesn't
  • 00:09:57
    reflect it any of the other resonances
  • 00:09:59
    what I need to do is I need to construct
  • 00:10:01
    a wavelength dependent reflector inside
  • 00:10:04
    the ring that goes through the maximum
  • 00:10:06
    in this curve here and goes through
  • 00:10:08
    nulls at all these other resonances if I
  • 00:10:11
    can construct such a device then the
  • 00:10:14
    overall structure will have one
  • 00:10:15
    reflection peak in it and all the other
  • 00:10:18
    resonances will be non reflective so I
  • 00:10:21
    want to construct a device that has this
  • 00:10:23
    particular reflection profile it's
  • 00:10:25
    reflective in this case it's like five
  • 00:10:28
    percent reflection on at this one
  • 00:10:31
    wavelength and then it has no reflection
  • 00:10:33
    at these other wavelengths and so if I
  • 00:10:37
    can construct such a device than the can
  • 00:10:39
    the combined response of the overall
  • 00:10:41
    ring plus reflector will have high
  • 00:10:43
    reflectivity at my design wavelength and
  • 00:10:45
    then i'll have the suppressed
  • 00:10:47
    reflectivity at the other resonances so
  • 00:10:50
    at these other residences the field
  • 00:10:52
    wants to build up and become stronger
  • 00:10:54
    because it's a resonant condition but at
  • 00:10:56
    the same time this element is becoming
  • 00:10:58
    non-reflective so as a result the
  • 00:11:00
    overall reflection will be very small so
  • 00:11:03
    how do i construct something that has
  • 00:11:05
    this profile it turns out that if i put
  • 00:11:07
    exactly half the grade
  • 00:11:10
    filled with this linear dbr then I get
  • 00:11:12
    these reflection nodes so in the linear
  • 00:11:15
    DVR it's a bad thing but when I combine
  • 00:11:17
    it into the ring I get the exact
  • 00:11:19
    spectrum that I want and it turns out
  • 00:11:21
    that if this is exactly half then I get
  • 00:11:23
    the nulls at exactly the resonance
  • 00:11:25
    wavelength of the other residences so
  • 00:11:28
    this combined structure gives us high
  • 00:11:30
    reflectivity at the design wavelength
  • 00:11:31
    and no reflection or in this case minus
  • 00:11:34
    40 DB in terms of reflection at the
  • 00:11:36
    other resonances so if i zoom in I can
  • 00:11:40
    see I have a nice reflection at that one
  • 00:11:42
    wavelength the transmission goes down
  • 00:11:44
    and then at the other residences the
  • 00:11:46
    reflection is zero so this will form the
  • 00:11:49
    basis of a single wave length mirror so
  • 00:11:51
    if I want to make a laser and I want it
  • 00:11:53
    to be operating at a single wavelength
  • 00:11:54
    if I put this device as the output or as
  • 00:11:58
    the awe as the high reflectivity mirror
  • 00:12:01
    in my laser cavity then this structure
  • 00:12:03
    will reflect and give me lazing
  • 00:12:05
    condition at this one resonant
  • 00:12:08
    wavelength and all the other wavelengths
  • 00:12:10
    will be not able to laze because the
  • 00:12:12
    loss going from the mirror is going to
  • 00:12:14
    be very high because it has very low
  • 00:12:17
    reflectivity overall so now let's shift
  • 00:12:21
    into on the simulation and design tools
  • 00:12:23
    that we use so our group does quite a
  • 00:12:26
    bit of modeling depending on what
  • 00:12:28
    program we use we combine comsol
  • 00:12:30
    modeling we also do modeling and matlab
  • 00:12:32
    we're collaborating with professor Jim
  • 00:12:35
    scroop to do a computational fe m so we
  • 00:12:38
    have all these different simulation and
  • 00:12:40
    design tools so I'll talk about our
  • 00:12:42
    simplified versions of the of the tools
  • 00:12:45
    so in order to design a general my
  • 00:12:49
    crowing reflector on we want fast and
  • 00:12:52
    accurate simulations the challenge was
  • 00:12:54
    simulating a micro ring resonator is
  • 00:12:56
    that since the dimensions are very large
  • 00:12:58
    compared to the wavelength and since the
  • 00:13:01
    dimensions are it's a three-dimensional
  • 00:13:03
    structure you need a lot of memory and
  • 00:13:05
    you need a lot of computational power to
  • 00:13:07
    be able to accurately simulate it with a
  • 00:13:09
    brute force method so one of the
  • 00:13:11
    quickest things that you can do is
  • 00:13:13
    notice that the modes have it as a
  • 00:13:15
    mutual dependence of the form e to the j
  • 00:13:18
    nu five so taking off this azimuthal
  • 00:13:20
    dependence allows you to reduce the
  • 00:13:23
    problem
  • 00:13:23
    from a three-dimensional problem into a
  • 00:13:25
    two-dimensional problem and so typically
  • 00:13:27
    we simulate the mood profile in this
  • 00:13:29
    two-dimensional constant five plane
  • 00:13:31
    where we plot as a function of radius
  • 00:13:33
    and a function of Z the mode profile so
  • 00:13:36
    this tiny blocks here is the core
  • 00:13:39
    surrounded by some cladding material and
  • 00:13:41
    then based on the way that we fabricate
  • 00:13:43
    it we actually have some more unwanted
  • 00:13:45
    material at the side so in order to
  • 00:13:49
    study the effect of the gratings that
  • 00:13:51
    we're putting on our structure what we
  • 00:13:53
    wanted to do is developed a develop a
  • 00:13:56
    cylindrical coordinate coupled mode
  • 00:13:58
    theory so a couple mode theory is well
  • 00:14:00
    known in a Cartesian coordinates is very
  • 00:14:02
    easy to write down on well I should say
  • 00:14:04
    very easy in the sense that you have to
  • 00:14:06
    look up a bunch of papers and then it
  • 00:14:07
    becomes very easy to write down but what
  • 00:14:10
    we wanted to do is we wanted to study
  • 00:14:11
    the coupling between the clockwise and
  • 00:14:14
    the counterclockwise amplitudes of the
  • 00:14:18
    mode so what we developed well we write
  • 00:14:21
    out Maxwell's equations we do a whole
  • 00:14:22
    bunch of algebra we simplify it using
  • 00:14:24
    these approximations and we get a
  • 00:14:26
    differential equation that talks about
  • 00:14:28
    the coupling of the forward and the
  • 00:14:29
    backward propagating modes this coupling
  • 00:14:32
    matrix on what you have to do is you
  • 00:14:34
    have to calculate the electric and
  • 00:14:35
    magnetic fields and then compute various
  • 00:14:37
    integrals of the electric and magnetic
  • 00:14:39
    field tangential and parallel components
  • 00:14:42
    / cross sectional areas so in this paper
  • 00:14:45
    you can figure out what these integrals
  • 00:14:47
    you have to compute is but basically all
  • 00:14:49
    you need to do is simulate the
  • 00:14:50
    two-dimensional cross sectional profile
  • 00:14:52
    for electrical magnetic fields and then
  • 00:14:53
    calculate a bunch of integrals based on
  • 00:14:56
    that and this allows you to figure out
  • 00:14:57
    how do the forward and the backward
  • 00:14:58
    waves a couple to each other so we
  • 00:15:03
    verified this with fim simulations so
  • 00:15:06
    the FM simulation that we did was a two
  • 00:15:08
    dimensional simulation so the method
  • 00:15:10
    that we developed is good to run in 3d
  • 00:15:13
    however the commercial software we're
  • 00:15:15
    validating it against doesn't have
  • 00:15:16
    enough memory to simulate in 3d so we do
  • 00:15:18
    the simulation in 2d where this is the
  • 00:15:21
    same structure in the out-of-plane
  • 00:15:24
    directions so a two-dimensional
  • 00:15:26
    simulation of this reflective micro ring
  • 00:15:29
    and you can see that we have these nice
  • 00:15:30
    standing wave generated from sending
  • 00:15:34
    light in and then having it highly
  • 00:15:36
    ected and we get very good agreement
  • 00:15:38
    between the finite element method in
  • 00:15:40
    comsol and our cylindrical coupled
  • 00:15:41
    million theory next we wanted to look at
  • 00:15:45
    some nonlinear effects so we wanted to
  • 00:15:47
    study the self-heating dynamics that
  • 00:15:49
    occur in micro resonators so basically
  • 00:15:52
    as you send power into this micro ring
  • 00:15:55
    the amplitude builds up in strength
  • 00:15:56
    because we have constructive
  • 00:15:58
    interference and this increase in power
  • 00:16:00
    that's circulating inside the ring
  • 00:16:01
    there's this tiny bit of absorption that
  • 00:16:04
    causes heating of the ring which changes
  • 00:16:06
    the refractive index which therefore
  • 00:16:08
    shifts the resonances so we wanted to
  • 00:16:10
    study the time domain evolution of the
  • 00:16:13
    optical properties of the Ring so we
  • 00:16:16
    developed time domain coupled mode
  • 00:16:17
    theory plus a lump thermal circuit model
  • 00:16:20
    so we have these equations which are
  • 00:16:22
    just the standard coupled mode theory in
  • 00:16:25
    the time domain plus there's this
  • 00:16:27
    thermal model where we consider that the
  • 00:16:29
    core is the source of heat so when the
  • 00:16:32
    light is propagating in the core of the
  • 00:16:34
    waveguide if there's absorption there's
  • 00:16:36
    a certain amount of heat generated given
  • 00:16:38
    by alpha Q there's a certain amount of
  • 00:16:40
    heat that's generated in the cladding
  • 00:16:42
    which is oxide given by 1 minus alpha Q
  • 00:16:44
    and then there's thermal resistance
  • 00:16:46
    between the core and the cladding
  • 00:16:48
    between the cladding and the substrate
  • 00:16:49
    and these are also heat sick these are
  • 00:16:52
    also heat storage materials so there's a
  • 00:16:55
    thermal capacitance from the core to the
  • 00:16:57
    substrate and from the cladding to the
  • 00:16:59
    substrate and we get an equivalent
  • 00:17:00
    circuit model that looks like this so
  • 00:17:02
    there are heat sources and there are
  • 00:17:04
    compassed ences and resistances in the
  • 00:17:06
    structure and you can calculate the
  • 00:17:08
    temperature at different parts of the
  • 00:17:10
    device based on this model you can then
  • 00:17:12
    predict what happens if I sit at a
  • 00:17:15
    specific wavelength relative to the
  • 00:17:17
    resonance and i put in a pulse of
  • 00:17:19
    optical energy so this pulse of optical
  • 00:17:22
    energy essentially in this graph on we
  • 00:17:25
    have this turning off and so there's a
  • 00:17:28
    certain time constant in which this
  • 00:17:30
    decays so we get a certain time response
  • 00:17:33
    that we measured experimentally and
  • 00:17:34
    validated with our simulation ok so now
  • 00:17:39
    let's talk about the structures that we
  • 00:17:41
    fabricate and how we test them so on our
  • 00:17:44
    general setup we have a tunable laser
  • 00:17:46
    isolator polarization controller so we
  • 00:17:48
    can control the
  • 00:17:49
    zation whether we launch te or TM
  • 00:17:51
    polarized light into our device under
  • 00:17:53
    test this polarizer ensures that the
  • 00:17:55
    polarization is lined to the direction
  • 00:17:57
    that we want we have a reference arm
  • 00:18:00
    that measures the power that we're
  • 00:18:01
    putting in a circulator so that we can
  • 00:18:03
    send the light to the device under test
  • 00:18:05
    and the reflective power gets measured
  • 00:18:06
    by the reflection detector and then the
  • 00:18:09
    transmitted power goes to the
  • 00:18:10
    transmitted detector and on each of
  • 00:18:12
    these fibers are lens tips so that we
  • 00:18:15
    can focus light from the fiber into this
  • 00:18:17
    mic rowing resonator chip and I'll
  • 00:18:19
    explain how we were able to achieve
  • 00:18:21
    these measurement results of having a
  • 00:18:23
    single reflection peak so our structure
  • 00:18:27
    consists of silicon nitride core on a
  • 00:18:30
    grown thermal oxide of of sio2 on a
  • 00:18:35
    silicon substrate and so we designed
  • 00:18:37
    this using the simulation methods I
  • 00:18:40
    previously described we fabricated these
  • 00:18:42
    structures with ebm lithography so
  • 00:18:44
    thanks to Edmond and some of the others
  • 00:18:46
    in the MNT all clean room for helping us
  • 00:18:48
    with the fabrication so you can see the
  • 00:18:50
    microwave resonator the scale bar is
  • 00:18:52
    about 15 microns and we made different
  • 00:18:54
    types of indentations to form our
  • 00:18:56
    reflectors so in this case we made 50
  • 00:18:59
    nanometer indentations in the waveguide
  • 00:19:01
    with in this case we have a waveguide
  • 00:19:03
    that's here and then we have a separate
  • 00:19:05
    grading structure so the evanescent tale
  • 00:19:08
    of the mode in this waveguide couples
  • 00:19:11
    with the grading that's on the separate
  • 00:19:13
    region and then we measure the
  • 00:19:15
    reflection and transmission setup or
  • 00:19:17
    spectra with our setup so the design
  • 00:19:20
    wavelength so when we did the first run
  • 00:19:23
    of devices on we didn't have accurate
  • 00:19:25
    numbers for the refractive index of
  • 00:19:27
    silicon nitride or for silicon dioxide
  • 00:19:29
    that we were depositing so our first
  • 00:19:32
    design we wanted to get wavelengths
  • 00:19:34
    being 1550 because that's the center
  • 00:19:36
    wavelength for the c-band which is the
  • 00:19:38
    wavelength that has the minimum loss in
  • 00:19:40
    optical fiber but our first set of
  • 00:19:43
    devices came out at 1,500 instead of
  • 00:19:46
    1550 and the main source of error was
  • 00:19:48
    the refractive indices that we assume so
  • 00:19:51
    we were assumed that the value of the
  • 00:19:52
    refractive index of silicon nitride was
  • 00:19:54
    too it turns out that it's 1.98 and that
  • 00:19:57
    very small change of one percent is
  • 00:20:02
    enough to shift some
  • 00:20:03
    portion of the spectrum there are some
  • 00:20:04
    other errors in the dimensions and the
  • 00:20:06
    values of the refractive index of the
  • 00:20:08
    core of the cladding that also
  • 00:20:10
    contributed to the shift so what we did
  • 00:20:13
    was ok so the wavelength that we wanted
  • 00:20:16
    was incorrect so how can we accurately
  • 00:20:18
    measure the wavelength or the refractive
  • 00:20:21
    indices of our devices well one thing to
  • 00:20:23
    notice is that the resonance wavelengths
  • 00:20:26
    depend very critically on whether it's
  • 00:20:28
    te or TM polarized light so you get
  • 00:20:31
    different effective indices for
  • 00:20:33
    different modes of propagation and based
  • 00:20:35
    on these resonance locations the
  • 00:20:38
    difference between te and TM and also
  • 00:20:41
    the geometry the free spectral range
  • 00:20:42
    which is the separation between adjacent
  • 00:20:46
    resonances the free spectral range plus
  • 00:20:49
    the te and TM dependencies these
  • 00:20:51
    determine where these resonances lined
  • 00:20:54
    up so we measure for a single micron
  • 00:20:56
    resonator the positions of these
  • 00:20:58
    resonances and from this we can infer
  • 00:21:01
    the refractive index attractive indices
  • 00:21:03
    of the core in the cladding material so
  • 00:21:05
    we get a measurement of 34 resonance
  • 00:21:07
    wavelengths we form it into a vector and
  • 00:21:10
    then we have to somehow resolve the
  • 00:21:13
    ambiguity that occurs in micro
  • 00:21:15
    resonators so there's no way to tell
  • 00:21:17
    from the spectrum whether this is the
  • 00:21:19
    200th mode or the 200 first as a methyl
  • 00:21:21
    mode but with a reflective structure we
  • 00:21:24
    know that this particular resonance
  • 00:21:26
    corresponds to the 200th mode so by
  • 00:21:28
    using the reflection peak we're able to
  • 00:21:31
    resolve the mode ambiguity and based on
  • 00:21:33
    that we can then say okay this is the
  • 00:21:35
    200 both this is the 199 this 198 197
  • 00:21:39
    and so forth and we can uniquely
  • 00:21:40
    identify each mode so in order to
  • 00:21:44
    calculate the parameters in our model
  • 00:21:48
    what we did was we linearize the
  • 00:21:50
    relationship between what we measured
  • 00:21:52
    and what our initial guesses based on
  • 00:21:54
    the model we calculated based on the
  • 00:21:56
    model the sensitivity matrix the
  • 00:21:58
    sensitivity matrix tells us how much
  • 00:22:00
    does the predicted wavelength change
  • 00:22:02
    when I change a parameter such as the
  • 00:22:04
    width of the ring or the refractive
  • 00:22:06
    index of the core or the refractive
  • 00:22:08
    index of the cladding so based on our
  • 00:22:10
    measured values of the wavelength our
  • 00:22:12
    initial simulation based on our initial
  • 00:22:15
    guesses for the parameter
  • 00:22:16
    this allows us to solve for how much we
  • 00:22:18
    have to adjust the parameters so that we
  • 00:22:21
    get an agreement between our measured
  • 00:22:23
    data and our predicted simulation so we
  • 00:22:26
    want to minimize this so we minimize the
  • 00:22:29
    difference of this equaling zero so we
  • 00:22:32
    do a singular value decomposition to
  • 00:22:34
    find the parameters it turns out that
  • 00:22:36
    although we have 34 measured parameters
  • 00:22:38
    there are only four the rank of this
  • 00:22:42
    matrix s is only four so we can only
  • 00:22:45
    accurately determine four parameters in
  • 00:22:47
    our model and the key parameters are the
  • 00:22:49
    refractive indices of the quorum of the
  • 00:22:51
    cladding the thickness of the core and
  • 00:22:53
    also the chromatic dispersion so the
  • 00:22:55
    reason that we only have a rank of four
  • 00:22:57
    is that when you look at the spectrum
  • 00:22:59
    it's pretty much determined by te versus
  • 00:23:02
    TM and also the free spectral range all
  • 00:23:04
    these other resonances all agree with if
  • 00:23:07
    I give you those four quantities like
  • 00:23:09
    the resonance location of one of the
  • 00:23:11
    residences for TE plus the free spectral
  • 00:23:13
    range for TE the resonance wavelength
  • 00:23:15
    for TM plus a free spectral range for TM
  • 00:23:17
    those four parameters pretty much
  • 00:23:18
    determine these entire spectra so the
  • 00:23:21
    rank of our measured or of our singular
  • 00:23:25
    matrix s is only four so we're able to
  • 00:23:28
    achieve very accurate results for our
  • 00:23:31
    model parameters for four parameters so
  • 00:23:33
    we determine refractive index of the
  • 00:23:35
    core with a precision of of essentially
  • 00:23:39
    four decimal places the cladding to
  • 00:23:41
    three decimal places and then the core
  • 00:23:43
    thickness to it looks like one decimal
  • 00:23:45
    place and the dispersion to essentially
  • 00:23:48
    hundred percent it's not very well it's
  • 00:23:51
    not very accurate we also measured these
  • 00:23:55
    resonances as we change the temperature
  • 00:23:56
    so when you change the temperature
  • 00:23:58
    there's a change in the refractive index
  • 00:23:59
    due to the thermal optic effect so these
  • 00:24:02
    resonances we tracked as a function of
  • 00:24:04
    temperature and by measuring a best-fit
  • 00:24:06
    slope and also modeling the effect of te
  • 00:24:09
    and TM we're able to extract the thermal
  • 00:24:12
    optic coefficients of silicon nitride
  • 00:24:14
    and silicon dioxide so this is a method
  • 00:24:16
    that allows us to figure out what's
  • 00:24:19
    going on in our device geometry and our
  • 00:24:22
    device parameters from observations of
  • 00:24:24
    the resonances of the ring the reason
  • 00:24:26
    that this method is very accurate is
  • 00:24:28
    because we can determine the resin
  • 00:24:30
    wavelength of the Ring two on the order
  • 00:24:32
    of like one picometer in a measurement
  • 00:24:35
    that has 15 50 nanometers so it's
  • 00:24:37
    essentially about six or seven digits of
  • 00:24:39
    precision that we can measure these
  • 00:24:41
    residents wavelengths lambda so then the
  • 00:24:43
    question is how precisely can we model
  • 00:24:46
    the structures and it turns out that we
  • 00:24:47
    can extract several digits of precision
  • 00:24:49
    in our parameters both for the
  • 00:24:51
    parameters at room temperature and also
  • 00:24:54
    their dependency on temperature so based
  • 00:24:58
    on these new values we fixed all the
  • 00:24:59
    designs so now that we know the actual
  • 00:25:01
    refractive indices we constructed a
  • 00:25:04
    second generation of devices and we hit
  • 00:25:06
    exactly the wavelength that we want so
  • 00:25:08
    we were targeting 1549 we got 1549 or
  • 00:25:11
    retargeting 1550 we got 15 49.6 so
  • 00:25:15
    within point for nanometers of our
  • 00:25:16
    target wavelength by having very
  • 00:25:19
    accurate model parameters on these
  • 00:25:22
    ripples these are due to the end effects
  • 00:25:25
    from the fiber and also from the facet
  • 00:25:27
    of the of the chip so by doing a
  • 00:25:30
    model-based data interpretation so
  • 00:25:32
    basically you have a measurement you
  • 00:25:33
    model the entire system not just the
  • 00:25:36
    micro ring but also the end facets and
  • 00:25:38
    so forth you can extract the effective
  • 00:25:41
    reflection of just the ring itself and
  • 00:25:44
    you get this red dotted line and if you
  • 00:25:47
    compare this DVR structure that's in a
  • 00:25:50
    ring to what you get from the linear DVR
  • 00:25:52
    you can see two things one we've gotten
  • 00:25:54
    rid of the ripples so there aren't these
  • 00:25:56
    these ripples in the spectrum but also
  • 00:25:59
    the roll-off is much faster so this
  • 00:26:02
    device will be better for single mode
  • 00:26:04
    operation so we achieved 93% reflection
  • 00:26:08
    point for nanometer full with half max
  • 00:26:09
    and the overall structure is 70 times
  • 00:26:12
    smaller than the conventional dbr
  • 00:26:14
    structures that you find in the
  • 00:26:16
    semiconductor laser we got rid of the
  • 00:26:18
    side lobes and we also have a faster
  • 00:26:19
    roll off ok so now I'm going to move
  • 00:26:23
    into the applications so the first
  • 00:26:25
    application they'll talk about is how we
  • 00:26:27
    make a single wave well how do we
  • 00:26:29
    integrate an active laser with a passive
  • 00:26:31
    microwave mirror so what we want to
  • 00:26:34
    achieve is a device that has a single
  • 00:26:36
    wavelength of lazing and lazing being
  • 00:26:38
    determined by the passive section which
  • 00:26:40
    has the micronian grading
  • 00:26:43
    late mirror so the advantage of this
  • 00:26:47
    micro ring reflector is that it has a
  • 00:26:49
    very narrow reflection bandwidth this
  • 00:26:51
    narrow reflection bandwidth means that
  • 00:26:52
    the device will lays in a very specific
  • 00:26:54
    wavelength and this specific wavelength
  • 00:26:57
    allows us to use this reflective micron
  • 00:26:59
    resonator as the mirror for a single
  • 00:27:02
    mode laser device so we're trying to
  • 00:27:04
    make a compact replacement for the
  • 00:27:06
    linear distributed bragg reflectors that
  • 00:27:08
    you find in conventional semiconductor
  • 00:27:10
    diode lasers there's another advantage
  • 00:27:14
    of using passive mirrors so this is if
  • 00:27:17
    you look at the theory shallow towns
  • 00:27:19
    theory and also study on the henry line
  • 00:27:23
    with enhancement factor there is a
  • 00:27:25
    benefit of having a wavelength dependent
  • 00:27:27
    mirror if you lock your laser to the
  • 00:27:30
    right side of the resonance peak and you
  • 00:27:32
    have this wavelength dependent mirror
  • 00:27:34
    you can reduce the line width by this
  • 00:27:36
    factor f c squared compared to a plain
  • 00:27:38
    laser and so if you want to make a laser
  • 00:27:41
    that's useful for spectroscopy so that
  • 00:27:43
    you can have precise wavelengths in your
  • 00:27:45
    measurement then the line width becomes
  • 00:27:47
    a limiting factor and so being able to
  • 00:27:49
    reduce the line width is a very
  • 00:27:50
    important goal of making the
  • 00:27:53
    semiconductor laser diodes so having a
  • 00:27:57
    wavelength dependent mirror which is
  • 00:27:58
    what we have from our reflective micro
  • 00:28:00
    ring so we have this nice wavelength
  • 00:28:03
    dependent mirror so there's a very sharp
  • 00:28:05
    change in the reflection as I very the
  • 00:28:07
    wavelength this will make a light a nice
  • 00:28:09
    mirror that locks the wavelength of the
  • 00:28:11
    laser so this laser that we constructed
  • 00:28:14
    it has a amplification section so
  • 00:28:17
    there's a gain section there's this
  • 00:28:18
    optional phase section and then you have
  • 00:28:20
    this passive section where on you're not
  • 00:28:23
    injecting current and so there's going
  • 00:28:24
    to be less noise because this mirror is
  • 00:28:27
    going to serve as a wavelength lock for
  • 00:28:29
    your laser so the goal is to achieve a
  • 00:28:31
    single a single wavelength out of our
  • 00:28:34
    device now there's another application
  • 00:28:37
    which is if you put these two structures
  • 00:28:39
    instead of having a single wavelength in
  • 00:28:41
    the reflection spectrum if you can
  • 00:28:43
    generate a coma of reflection peaks and
  • 00:28:45
    you can do that by putting a single
  • 00:28:46
    notch then you can have two different
  • 00:28:49
    free spectral range for the mirror
  • 00:28:51
    reflective atif and by aligning these up
  • 00:28:54
    using the vernier effects essentially
  • 00:28:56
    if I have a set of resonances here and I
  • 00:28:58
    have a different spacing when I get one
  • 00:29:01
    of these to align then that's going to
  • 00:29:02
    be the wavelength that lazes and then I
  • 00:29:05
    just need to make a very small shift in
  • 00:29:07
    one of the mirrors to line up a
  • 00:29:09
    different resonance and that gives me a
  • 00:29:11
    large tuning so I can get quasi
  • 00:29:14
    continuous tuning over a large
  • 00:29:15
    wavelength range by using the vernier
  • 00:29:17
    effect if I can get the free spectral
  • 00:29:19
    range to be different for the two
  • 00:29:21
    different mirrors so this is one
  • 00:29:23
    application we're interested in we
  • 00:29:24
    haven't fabricating these devices I'll
  • 00:29:26
    talk about this device because we have
  • 00:29:29
    that fabricated so in order to integrate
  • 00:29:32
    active sections with passive sections on
  • 00:29:35
    we have to do a bit of work in the
  • 00:29:37
    device design and fabrication so we have
  • 00:29:39
    these two we have this material which
  • 00:29:41
    has grown for us by epitaxial growth
  • 00:29:44
    MOCVD growth by a company called epi
  • 00:29:47
    works in champaign on so we have the
  • 00:29:49
    conventional gallium arsenide core
  • 00:29:52
    surrounding indium gallium arsenide
  • 00:29:54
    quantum well and then we have this
  • 00:29:56
    indium gallium phosphide etch stop layer
  • 00:29:57
    in these two locations we have this
  • 00:30:00
    undoped aluminum gallium arsenide bottom
  • 00:30:02
    plotting and then we have n-type and
  • 00:30:04
    p-type aluminum gallium arsenide to form
  • 00:30:07
    the separate confinement hetero
  • 00:30:09
    structure so that we can separately
  • 00:30:10
    confine electrons and optical fields and
  • 00:30:14
    then what we're going to do is normally
  • 00:30:17
    this quantum well we'll be in the very
  • 00:30:18
    center of the core we're going to shift
  • 00:30:20
    it up slightly so that in one section of
  • 00:30:22
    the Vice we keep the full length so that
  • 00:30:24
    this is the active section in this other
  • 00:30:27
    section of the device we're going to
  • 00:30:28
    etch away all this material including
  • 00:30:30
    the quantum well and so without the
  • 00:30:32
    quantum well this section becomes a
  • 00:30:33
    passive section so it works as a
  • 00:30:36
    transparent waveguide that's made of
  • 00:30:38
    just gallium arsenide so what we need to
  • 00:30:41
    do is we need to go from this active
  • 00:30:43
    section which has the quantum well and
  • 00:30:44
    has the mode sitting way up here to this
  • 00:30:47
    passive section where the mode is going
  • 00:30:49
    to sit much lower down in the gallium
  • 00:30:51
    arsenide core so we formed this
  • 00:30:53
    adiabatic horizontal taper where we
  • 00:30:55
    taper the ridge waveguide etch and we
  • 00:30:57
    also taper underneath so that we can
  • 00:30:59
    confine the mode and transition it from
  • 00:31:02
    being centered in the quantum wall
  • 00:31:04
    region to be centered in the core /
  • 00:31:07
    bottom clotting so the mode is going to
  • 00:31:09
    Tran
  • 00:31:09
    position downwards from this active
  • 00:31:11
    region into the passive region and then
  • 00:31:14
    it's going to couple into the reflective
  • 00:31:15
    my crowing resonator which is going to
  • 00:31:17
    serve as a release or mirror so we
  • 00:31:20
    fabricated these structures this is a
  • 00:31:21
    picture of it on where we have the
  • 00:31:24
    active section we have our taper we go
  • 00:31:26
    into the passive section we have our
  • 00:31:27
    reflective my crowing resonator and
  • 00:31:29
    because we don't want any light
  • 00:31:30
    reflecting back from an end facet we
  • 00:31:33
    split out the power so it just
  • 00:31:34
    dissipates into the substrate so our
  • 00:31:37
    output facet is going to be to the side
  • 00:31:39
    this side is just serving as a high
  • 00:31:41
    reflectivity mirror from the structure
  • 00:31:43
    we achieve single mode operations so we
  • 00:31:46
    get lazing at a threshold of about 30
  • 00:31:48
    milliamps for a device that's 1,100 by I
  • 00:31:51
    think this was one micron wide and you
  • 00:31:54
    can see that lazing exists and that we
  • 00:31:56
    have single wavelength operation these
  • 00:31:58
    other notches these are from the
  • 00:32:01
    higher-order resonances of the ring and
  • 00:32:04
    we've effectively suppress them compared
  • 00:32:06
    to the dominant mode that we wanted to
  • 00:32:07
    achieve so the second type of device and
  • 00:32:11
    I should mention on with this structure
  • 00:32:13
    what we do is we have these gratings
  • 00:32:15
    that form a first-order grading so a
  • 00:32:18
    first-order grading the length of the
  • 00:32:20
    section is lamb Dover for long the
  • 00:32:22
    period is lambda over to first order
  • 00:32:24
    grading is designed to reflect light in
  • 00:32:27
    the opposite direction so it if I send
  • 00:32:29
    light in the four direction a lamp first
  • 00:32:32
    order grading will directly couple to
  • 00:32:34
    light in the counter propagating
  • 00:32:36
    direction there's also the second order
  • 00:32:39
    draining and a second or degrading what
  • 00:32:41
    it does is it couples light not only to
  • 00:32:43
    the four direction but it also couples
  • 00:32:46
    light out of the out of the plane of the
  • 00:32:49
    of the direction of the plane and so you
  • 00:32:52
    can generate lossy mirrors if you
  • 00:32:56
    pattern a second order grading so we
  • 00:32:58
    have the swirl device single wavelength
  • 00:33:00
    integrated ring laser and the idea is
  • 00:33:02
    that ordinarily all these modes that
  • 00:33:05
    have different azimuthal mode numbers
  • 00:33:07
    and that are degenerate because they're
  • 00:33:10
    clockwise and counterclockwise
  • 00:33:11
    propagating modes they all had
  • 00:33:14
    degenerate loss so they're all the same
  • 00:33:15
    we increase the loss of all the modes
  • 00:33:18
    except for one and that one mode is the
  • 00:33:20
    one that's going to laze so we can show
  • 00:33:22
    that we can get
  • 00:33:23
    single wavelength operation for a
  • 00:33:25
    specific azimuthal motor and if we
  • 00:33:27
    change the azimuthal mode order of the
  • 00:33:29
    grading we can get a different mode to
  • 00:33:31
    laze so the microcavity laser we want a
  • 00:33:35
    small footprint low threshold off for
  • 00:33:37
    applications like vuitton i agreed and
  • 00:33:39
    grade circuits on ship optical
  • 00:33:41
    interconnects and short distance optical
  • 00:33:43
    communication the micro ring and micro
  • 00:33:45
    disk lasers can be good candidates on
  • 00:33:47
    their small but one of the biggest
  • 00:33:50
    issues with the micro ring in the micro
  • 00:33:51
    disk is that they have many modes so all
  • 00:33:54
    the different azimuthal motors like m is
  • 00:33:56
    equal to 200 201 they all have the same
  • 00:33:59
    amount of loss moreover at a single
  • 00:34:02
    resonance they have to counter
  • 00:34:04
    propagating modes that have the same
  • 00:34:05
    loss so the question is can we engineer
  • 00:34:08
    the mode coupling to select a specific
  • 00:34:11
    lazing mode can we do this by putting a
  • 00:34:14
    grading on our structure to increase the
  • 00:34:15
    loss of all the modes except for one the
  • 00:34:18
    answer is yes and so the way that you do
  • 00:34:21
    this is you form a grading with
  • 00:34:23
    azimuthal mode order m and so that puts
  • 00:34:26
    a perturbation on the cavity of the form
  • 00:34:28
    sign of M Phi what this does is if I
  • 00:34:31
    have the ordinary mode on n for the ring
  • 00:34:35
    and i have the grading with mode m i
  • 00:34:37
    scatter in two modes n plus m and n
  • 00:34:40
    minus m so when you think about what
  • 00:34:42
    happens when i multiply sine of n phi x
  • 00:34:45
    sine of m phi i get the sum and
  • 00:34:47
    difference frequencies and so i generate
  • 00:34:49
    things that radiate into these
  • 00:34:51
    higher-order modes so if i have a
  • 00:34:53
    difference of n minus M equals two what
  • 00:34:56
    I'm going to do is I'm going to couple
  • 00:34:57
    the light from the azimuthal mode n with
  • 00:35:00
    the grading of order m into a mode n
  • 00:35:03
    minus M equals two and since this has
  • 00:35:05
    low azimuthal mode order it's going to
  • 00:35:07
    radiate in all directions and so you can
  • 00:35:09
    see that this is a set this is a this
  • 00:35:12
    corresponds to rotational symmetry to on
  • 00:35:15
    so it radiates and so it has higher loss
  • 00:35:17
    so the radiation modes of small as
  • 00:35:20
    methyl of small azimuthal orders have
  • 00:35:22
    small quality factors so by putting the
  • 00:35:25
    second order grading on the structure i
  • 00:35:27
    can select a specific lazing mode i'm
  • 00:35:30
    going to set m is equal to n and i'm
  • 00:35:32
    going to reduce all the quality factors
  • 00:35:33
    of all the modes except for one mode
  • 00:35:36
    so there's one exception and I keep
  • 00:35:39
    bringing this up but the one exception
  • 00:35:41
    occurs when n is equal to M and the
  • 00:35:43
    electric field is shifted by exactly
  • 00:35:45
    one-quarter wavelength relative to the
  • 00:35:47
    grading so if I have a cosine M Phi
  • 00:35:49
    dependence on Phi and have assigned n
  • 00:35:52
    Phi dependence of the grading when I
  • 00:35:54
    multiply these two together the sine
  • 00:35:57
    times the cosine gives me the sign of
  • 00:35:59
    the double angle I don't get a DC
  • 00:36:01
    component I don't get a low frequency
  • 00:36:03
    component and the low frequency
  • 00:36:05
    component is precisely the component
  • 00:36:06
    that radiates so this one particular
  • 00:36:08
    exception gives me something that
  • 00:36:11
    doesn't radiate and therefore the
  • 00:36:12
    quality factor of this mode is not
  • 00:36:14
    reduced by the presence of the grading
  • 00:36:16
    so I can generate something that doesn't
  • 00:36:18
    radiate it propagates as a or it's a
  • 00:36:21
    standing wave inside the cavity and
  • 00:36:23
    instead if I have the sign fi then sign
  • 00:36:26
    fi x sine and my I get the sum and the
  • 00:36:31
    difference and that radiates so to
  • 00:36:34
    confirm this we did fe m simulations and
  • 00:36:37
    we can see that we have this one
  • 00:36:39
    resonant mode that doesn't radiate this
  • 00:36:41
    one ready radiates like the spherical
  • 00:36:43
    harmonic y 0 0 these ones radiate like
  • 00:36:46
    why LM where L is minus 1 or plus 1 and
  • 00:36:50
    so all the other modes starts radiate
  • 00:36:53
    and so as a function of how deep or how
  • 00:36:56
    strong I make this grading I can see
  • 00:36:58
    that this one mode which is non
  • 00:37:00
    radiating the loss does not change no
  • 00:37:02
    matter how I change the grading whereas
  • 00:37:04
    these other modes the losses increase as
  • 00:37:06
    I increase the strength of the grading
  • 00:37:08
    and so if I have a specific indentation
  • 00:37:10
    sighs I can select this mode compared to
  • 00:37:13
    the other modes so for the device design
  • 00:37:16
    we have a similar structure as before
  • 00:37:18
    except it's has fewer layers than what
  • 00:37:21
    we did for active passive and one of the
  • 00:37:23
    key parameters in terms of this design
  • 00:37:25
    because the light is circulating
  • 00:37:27
    radially is how deep I h24 my ridge
  • 00:37:30
    waveguide if I etch too deep and I etch
  • 00:37:33
    into the quantum well region then i
  • 00:37:35
    create surface defects which is going to
  • 00:37:37
    increase the threshold because i have
  • 00:37:39
    high non-radiative recombination if I
  • 00:37:42
    etch too shallow then the light that's
  • 00:37:44
    propagating the ring can radiate
  • 00:37:45
    radially outwards because there isn't
  • 00:37:48
    tidy
  • 00:37:48
    confinement to guide the mode inside the
  • 00:37:51
    ring so there's a function as a function
  • 00:37:53
    of to how deep I H into the core so the
  • 00:37:56
    core the quantum well is 80 nanometers
  • 00:37:58
    into the core if I etch very close to
  • 00:38:01
    that 80 nanometers then what i get is I
  • 00:38:03
    get very low bending loss and I have
  • 00:38:05
    high quality factor if I don't itch deep
  • 00:38:08
    enough so I'm sitting here then I have
  • 00:38:10
    very high bending loss so 10 inverse
  • 00:38:11
    centimeters is pretty high for a laser
  • 00:38:13
    to operate and so what I want to do is I
  • 00:38:16
    need to edge somewhere between 40 and 80
  • 00:38:19
    nanometers into the core if I edge too
  • 00:38:21
    far I get high threshold because I've
  • 00:38:23
    non-radiative recombination fih too
  • 00:38:25
    shallow i also get high threshold
  • 00:38:26
    because i have a poor optical
  • 00:38:30
    confinement and i have high bending loss
  • 00:38:32
    so we design and pattern these with even
  • 00:38:35
    lithography you can see the grading
  • 00:38:37
    formed in gallium arsenide so this is
  • 00:38:39
    three-five material the passive
  • 00:38:41
    structures were in silicon nitride so
  • 00:38:43
    this is a completely different etch
  • 00:38:45
    process compared to the passive
  • 00:38:46
    structures we put metal on top of it and
  • 00:38:49
    we transfer the pattern with ICP rie on
  • 00:38:53
    we then planarize it with BCB so that we
  • 00:38:56
    can make metal contacts and we have
  • 00:38:58
    separate contacts for the bus waveguide
  • 00:39:00
    and also for the bus waveguide and also
  • 00:39:03
    for the ring section so the left 450
  • 00:39:07
    micron section was pumped so that we can
  • 00:39:09
    get to transparency the center part is
  • 00:39:12
    the part that's lazing the right part is
  • 00:39:13
    unpub so our laser cavity is formed just
  • 00:39:17
    by this section alone it's a circulating
  • 00:39:20
    ring configuration for our laser the bus
  • 00:39:23
    waveguide allows light to couple out
  • 00:39:25
    from the ring into the waveguide and
  • 00:39:27
    this is at transparency so we let light
  • 00:39:29
    come out the left side so as a function
  • 00:39:31
    of the current we can see that we get an
  • 00:39:33
    increase in power and so we have lazing
  • 00:39:34
    threshold at about twenty six milliamps
  • 00:39:37
    when we set n is equal to M equals 7 24
  • 00:39:40
    we get this one resonance as the lazing
  • 00:39:43
    operation when we change the azimuthal
  • 00:39:45
    mode order so that we can see whether
  • 00:39:48
    it's the grating that determines the
  • 00:39:50
    lazing we can see that it shifts exactly
  • 00:39:52
    four orders on to the fourth resonance
  • 00:39:55
    to the right and so we have precise
  • 00:39:57
    control over the wavelength that lazes
  • 00:39:59
    in the structure by defining the
  • 00:40:01
    azimuthal
  • 00:40:02
    getting so the key to getting single
  • 00:40:04
    mode operation we've made structures
  • 00:40:06
    that looked identical to this but
  • 00:40:08
    without the grading without the grading
  • 00:40:10
    you get resonances you get all these
  • 00:40:12
    resonances competing for lazing and it's
  • 00:40:14
    a multi-mode structure but with the
  • 00:40:16
    grading we get single wavelength
  • 00:40:18
    operation so for the final part of the
  • 00:40:22
    talk I'll talk about our work on hybrid
  • 00:40:24
    whispering gallery mode plasmonics n
  • 00:40:26
    ring resonator sensors the ideas I
  • 00:40:28
    mentioned before we have the silicon
  • 00:40:30
    microsphere which is about 30 microns in
  • 00:40:32
    diameter around the perimeter or the
  • 00:40:35
    circumference of it we put these gold
  • 00:40:36
    epitopes which are going to serve as
  • 00:40:38
    plasmonics ain and the gold epitopes
  • 00:40:42
    allow tight field confinement in the
  • 00:40:44
    vicinity and so we're going to try to
  • 00:40:47
    detect the presence of a thyroid
  • 00:40:50
    globulin cancer marker protein attaching
  • 00:40:54
    to these gold epitopes and we see that
  • 00:40:57
    based on the design of the epitopes we
  • 00:41:00
    can couple effectively between the
  • 00:41:01
    whispering gallery mode resonances and
  • 00:41:03
    the plasmonics chainring resonances and
  • 00:41:05
    get the sharp increase in the creation
  • 00:41:07
    of symmetric and anti-symmetric modes
  • 00:41:09
    and this is a result of mode coupling
  • 00:41:11
    between the plasmonics chain and the
  • 00:41:13
    whispering gallery mode resonator so as
  • 00:41:17
    I mentioned we're looking at the TG
  • 00:41:18
    cancer marker protein and so we have
  • 00:41:21
    these gold epitopes which are basically
  • 00:41:23
    gold nanoshells surrounding silicon nano
  • 00:41:27
    scooters and we place these around the
  • 00:41:29
    equator of a whispering gallery mode
  • 00:41:30
    resonator don't ask me how we're going
  • 00:41:33
    to do this experimental II this is a
  • 00:41:34
    simulation work there's a group that we
  • 00:41:37
    collaborated with at NYU and they have
  • 00:41:40
    methods to use optical gradient force to
  • 00:41:42
    trap particles around the perimeter of
  • 00:41:44
    these spheres whether they can get it
  • 00:41:46
    exactly the way that we simulate or not
  • 00:41:48
    is still open question but the point is
  • 00:41:52
    that we're going to trap or place these
  • 00:41:54
    epitopes at these anti nodes of the
  • 00:41:57
    field and in order to simulate the
  • 00:41:59
    structure very efficiently so this
  • 00:42:01
    structure is about 30 micron radius we
  • 00:42:06
    want to simulate using the symmetry that
  • 00:42:08
    exists in the problem so we're going to
  • 00:42:10
    put perfect electric conductors at the
  • 00:42:13
    at the nodes
  • 00:42:15
    perfect magnetic conductors at the
  • 00:42:16
    antinodes and use periodic boundary
  • 00:42:18
    conditions to essentially solve for the
  • 00:42:20
    entire structure so the field is
  • 00:42:23
    localized near the epitope if I change
  • 00:42:25
    the epitope radius slightly then i can
  • 00:42:27
    get distinct coupling regions in this
  • 00:42:29
    hybrid resonator system as I mentioned
  • 00:42:32
    we model this in 3d using periodic
  • 00:42:34
    boundary conditions with pcs at the
  • 00:42:36
    nodes and pmcs at the anti nodes so this
  • 00:42:40
    is what the field distribution looks
  • 00:42:41
    like as I vary the radius so there's a
  • 00:42:44
    lot of parameters in this model so
  • 00:42:46
    there's like the radius of the
  • 00:42:47
    microsphere there's the radius of the
  • 00:42:49
    epitope there's the thickness of the
  • 00:42:50
    gold coating there's the spacing do i
  • 00:42:52
    put these at every single node or every
  • 00:42:54
    other node there's a lot of parameters
  • 00:42:56
    involved so we fix the thickness of the
  • 00:42:58
    epitope at 10 nanometers we also fix the
  • 00:43:02
    position of the epitopes at the anti
  • 00:43:04
    node so that it has the strongest effect
  • 00:43:06
    and we looked at two different cases of
  • 00:43:08
    the radii so when the radius is small 30
  • 00:43:10
    nanometers and when the radius is large
  • 00:43:12
    there's a very small perturbation in the
  • 00:43:15
    mode profile due to the epitope so this
  • 00:43:17
    is the cross sectional view and xion are
  • 00:43:19
    of this section of the field and you can
  • 00:43:23
    see that we have the field polarized in
  • 00:43:25
    Z and the epitope has a very small
  • 00:43:27
    effect on the overall field shape when I
  • 00:43:30
    have radius of 50 I get slight bending
  • 00:43:32
    in the angles of the vectors near the
  • 00:43:34
    epitopes but there isn't a huge change
  • 00:43:36
    in the overall electric field profile
  • 00:43:39
    this however is completely different if
  • 00:43:41
    I tune the radius of the epitope to the
  • 00:43:44
    resonance of the whispering gallery mode
  • 00:43:46
    so when the radius is 40 nanometers the
  • 00:43:48
    plasma McShane ring resonator and the
  • 00:43:50
    whispering gallery mode resonator these
  • 00:43:53
    modes coupled to each other so the
  • 00:43:55
    hybrid wgm pcr are I generate a
  • 00:43:58
    symmetric mode and an anti symmetric
  • 00:44:00
    mode so compared the previous case where
  • 00:44:02
    the electric field profile for the
  • 00:44:04
    microsphere extends very far in Z and is
  • 00:44:07
    spread out in our to this case where
  • 00:44:10
    it's very tightly confined in Z pretty
  • 00:44:12
    much at the locations of the epitopes
  • 00:44:15
    and so the symmetric mode very tightly
  • 00:44:17
    confined the field at that location the
  • 00:44:20
    anti symmetric mode i end up with the
  • 00:44:22
    fields pointing in the opposite
  • 00:44:23
    direction at this location but again i
  • 00:44:25
    have a significant enhancement of the
  • 00:44:26
    field strength at the
  • 00:44:27
    plasmonics chain epitope location
  • 00:44:30
    compared to this diagram so there's a
  • 00:44:32
    significant increase in the optical
  • 00:44:34
    confinement at that location so we
  • 00:44:37
    wanted to understand this behavior on it
  • 00:44:39
    turns out that this is a very simply
  • 00:44:41
    explained as the coupling of two
  • 00:44:43
    separate resonator systems so one is the
  • 00:44:46
    whispering gallery mode the other is the
  • 00:44:48
    plasmonics Ain ring resonator so if you
  • 00:44:50
    model the plasma exchange I itself you
  • 00:44:53
    can see that it has certain field
  • 00:44:54
    localization properties that basically
  • 00:44:57
    confine the field very tightly near the
  • 00:44:59
    plasmonics chain and so when we look at
  • 00:45:01
    modal dispersion what we can plot is as
  • 00:45:04
    a function of the size of this epitope
  • 00:45:07
    on what are the resonance wavelengths of
  • 00:45:10
    the whispering gallery mode and of the
  • 00:45:13
    plasma exchange so the whispering
  • 00:45:15
    gallery mode microsphere it doesn't
  • 00:45:16
    matter what the plasmonics chain is
  • 00:45:18
    doing it has the same resonance
  • 00:45:20
    wavelength so that's this green curve
  • 00:45:21
    here if you look at the plasmonics chain
  • 00:45:24
    ring resonator by itself it has a sharp
  • 00:45:26
    dependence on the radius and so this is
  • 00:45:29
    this black curve here and so initially
  • 00:45:32
    we're expecting the coupling between the
  • 00:45:34
    screen mode and this black mode however
  • 00:45:36
    there's a perturbation and the
  • 00:45:37
    perturbation is very important these
  • 00:45:39
    epitopes from the plasmonics chain ring
  • 00:45:42
    resonator are not isolated they're
  • 00:45:44
    perturbed by the silicon microsphere
  • 00:45:46
    that's sitting in the center so if you
  • 00:45:48
    do a corrected calculation of the plasma
  • 00:45:50
    etching chain ring resonator in the
  • 00:45:53
    presence of the silicon microsphere you
  • 00:45:55
    get this black dotted line and then when
  • 00:45:57
    i look at the mode coupling between the
  • 00:45:59
    black dotted line and the green line i
  • 00:46:01
    generate the symmetric mode which is in
  • 00:46:03
    red and the anti-symmetric mode which is
  • 00:46:05
    in blue and i can understand the
  • 00:46:07
    existence of these two separate curves
  • 00:46:09
    as simply mode coupling between the
  • 00:46:12
    plasmonics ain and the whispering
  • 00:46:13
    gallery mode so the localization of the
  • 00:46:17
    field at this epitopes is stronger when
  • 00:46:20
    we're in the strong coupling regime
  • 00:46:22
    where the radius is close to 40 so when
  • 00:46:25
    I have a TG binding event on one of the
  • 00:46:28
    epitopes I'll get a resonance wavelength
  • 00:46:30
    shift and this is how i'm going to sense
  • 00:46:32
    the TG cancer markers i'm going to look
  • 00:46:34
    at the resonance of the micro ring and
  • 00:46:36
    figure out or of the microsphere and
  • 00:46:38
    figure out has it shifted so at this
  • 00:46:41
    you're 40 nanometers I get a 20
  • 00:46:43
    femtometer shift now you say to yourself
  • 00:46:45
    20 50 meters seems incredibly difficult
  • 00:46:47
    to measure experimentally but it turns
  • 00:46:50
    out that this marker is so small that
  • 00:46:52
    there aren't any other good techniques
  • 00:46:54
    to detect it it's a few nanometers it's
  • 00:46:57
    basically an ellipsoid that's like 10 or
  • 00:47:00
    12 nanometers and one to mention in five
  • 00:47:02
    nanometers in the other dimension and
  • 00:47:03
    the refractive index is pretty much the
  • 00:47:05
    same as a refractive index of the fluid
  • 00:47:07
    that it's in and so as a result any
  • 00:47:09
    other method is not really going to be
  • 00:47:10
    sensitive to the subwavelength type
  • 00:47:12
    structure so this method we get a 20
  • 00:47:15
    femtometer shift for the symmetric mode
  • 00:47:17
    unfortunately when you're looking at a
  • 00:47:19
    micro ring based sensor what's important
  • 00:47:21
    is not only how much of a wavelength
  • 00:47:23
    shift you generate but how narrow are
  • 00:47:26
    the resonances that you're measuring
  • 00:47:27
    because the narrowness of the resonance
  • 00:47:29
    that you're measuring determines the
  • 00:47:31
    error that you can make in determining
  • 00:47:33
    the resonance wavelength so when we
  • 00:47:35
    start increasing the shell radius
  • 00:47:37
    unfortunately the quality factor of the
  • 00:47:38
    ring decreases significantly and so as a
  • 00:47:41
    result it becomes difficult to measure
  • 00:47:43
    the smaller the small shift so there may
  • 00:47:46
    be an optimal point in here depending on
  • 00:47:49
    the instrumentation that you have
  • 00:47:50
    whether you're limited in terms of the
  • 00:47:52
    measurement accuracy of the tunable
  • 00:47:56
    laser of G have where you can trade off
  • 00:47:58
    a larger resonance shift for having a
  • 00:48:01
    wider resonance or you can have a
  • 00:48:03
    smaller residence shift for having a
  • 00:48:05
    narrower resonance so there are a bunch
  • 00:48:08
    of trade-offs in this design and so if
  • 00:48:10
    you look at the case where you place an
  • 00:48:13
    epitope at every single anti node we
  • 00:48:15
    call this the amount of shift you get
  • 00:48:17
    for one epitope per one wavelength or
  • 00:48:20
    one anti node and so that's the largest
  • 00:48:22
    case so you get the biggest resonance
  • 00:48:24
    shift unfortunately you get the smallest
  • 00:48:26
    quality factor if you space them further
  • 00:48:28
    apart and so you put one epitope every
  • 00:48:31
    other anti node then you get a smaller
  • 00:48:33
    resonance shift but you have a higher
  • 00:48:35
    quality factor so if you have just a
  • 00:48:37
    single isolated epitope by itself this
  • 00:48:40
    has a high Q micro ring resonator so the
  • 00:48:43
    advantages that is easy to measure
  • 00:48:45
    wavelength shift the disadvantage is you
  • 00:48:47
    only have one binding site so the
  • 00:48:49
    probability that the TG marker is going
  • 00:48:51
    to attach to that one specific epitope
  • 00:48:53
    that you place is
  • 00:48:54
    very very small and so you have to wait
  • 00:48:56
    a long time to be able to detect this TG
  • 00:48:59
    biomarker if instead you have a certain
  • 00:49:02
    number of coupled epitopes you have a
  • 00:49:03
    lower Q but now you have n times the
  • 00:49:06
    detection frequency because you have
  • 00:49:08
    essentially n sensors distributed around
  • 00:49:11
    your microwave so you wait less time to
  • 00:49:13
    detect this biomarker and so if you
  • 00:49:16
    place them at every single anti node
  • 00:49:18
    then you get the most frequent detection
  • 00:49:21
    and you can still trade off the coupling
  • 00:49:24
    by balancing the effects of sensitivity
  • 00:49:27
    so if I place them at every single node
  • 00:49:29
    or anti node I mean I get very high
  • 00:49:32
    sensitivity but I have low Q if I place
  • 00:49:34
    them every other I have lower
  • 00:49:35
    sensitivity but I have better q so I can
  • 00:49:37
    trade off those two parameters while
  • 00:49:40
    still reducing the detection time
  • 00:49:41
    compared to just having a single
  • 00:49:43
    isolated epitope so in summary we
  • 00:49:47
    presented our work on the development of
  • 00:49:49
    new types of devices that operate based
  • 00:49:51
    on selective mode coupling on this mode
  • 00:49:54
    coupling is sort of an emerging theme
  • 00:49:56
    that's in a lot of our groups research
  • 00:49:58
    basically looking at the existence of
  • 00:50:02
    many different modes and how to engineer
  • 00:50:03
    the coupling between these modes to
  • 00:50:05
    generate the type of devices that you're
  • 00:50:07
    interested in we preserve two types of
  • 00:50:10
    approach one is to couple the modes for
  • 00:50:12
    achieving reflection so first order
  • 00:50:14
    grading gives us nice reflection to a
  • 00:50:16
    second order braiding modifies the
  • 00:50:18
    radiation losses and allows us to
  • 00:50:20
    generate a single wavelength laser we
  • 00:50:23
    developed simulation models the
  • 00:50:24
    cylindrical coupled mode theory on we
  • 00:50:26
    designed and fabricated passive devices
  • 00:50:28
    and we demonstrated single wavelength
  • 00:50:30
    operation this device is also useful for
  • 00:50:32
    allowing us to measure the refractive
  • 00:50:34
    index because it allowed us to determine
  • 00:50:36
    the azimuthal mode order without
  • 00:50:39
    ambiguity on from the symmetry we also
  • 00:50:43
    developed a monolithic integration
  • 00:50:45
    platform so we have active laser devices
  • 00:50:47
    passive microwave reflectors and we show
  • 00:50:50
    that we can integrate these two things
  • 00:50:51
    together we fabricated lasers that have
  • 00:50:54
    these mirrors and showed single
  • 00:50:56
    wavelength lazing single mode lazing we
  • 00:50:58
    also proposed and demonstrated
  • 00:51:00
    engineering the radiation quality factor
  • 00:51:02
    using a second-order grading so that we
  • 00:51:04
    get one particular mode that lazes and
  • 00:51:07
    the other modes are radiated
  • 00:51:08
    radiating we verified this
  • 00:51:10
    experimentally and showed that you can
  • 00:51:12
    control which mode lazes by controlling
  • 00:51:14
    the azimuthal mode order of the grading
  • 00:51:16
    and then in terms of our sensor we
  • 00:51:19
    looked at the distinct coupling regions
  • 00:51:21
    between the whispering gallery mode
  • 00:51:22
    resonator and the plasma McShane ring
  • 00:51:24
    resonator and we showed that you can
  • 00:51:26
    make trade-offs in the sensitivity and
  • 00:51:28
    the detection time and the measurement
  • 00:51:30
    limitations of the quality factor
  • 00:51:32
    there's very strong mode field
  • 00:51:35
    localization and mode splitting that
  • 00:51:37
    occurs if the size of the plasmonics
  • 00:51:39
    chain ring resonator epitopes exactly
  • 00:51:42
    lines up the resonances with the
  • 00:51:43
    residences of the whispering gallery
  • 00:51:45
    mode and we showed the existence of the
  • 00:51:47
    symmetric and the anti-symmetric modes
  • 00:51:49
    at that critical value our future
  • 00:51:52
    outlook on so the reflective micro rings
  • 00:51:54
    with small footprints are going to be
  • 00:51:56
    very useful for semiconductor lasers we
  • 00:52:00
    really want to expand our work in terms
  • 00:52:03
    of making these low threshold laser
  • 00:52:05
    devices and especially for applications
  • 00:52:08
    in sensing and spectroscopy there are
  • 00:52:11
    new designs that our group is studying
  • 00:52:12
    so one example is to have a instead of
  • 00:52:15
    having these epitopes sitting around the
  • 00:52:17
    perimeter of a whispering gallery mode
  • 00:52:20
    structure instead make plasmonics
  • 00:52:22
    antennas on top the surface of our micro
  • 00:52:26
    resonator and so we may be able to
  • 00:52:28
    localize the field very strongly so this
  • 00:52:30
    is the gold plasmonics bowtie structure
  • 00:52:33
    on top of a microwave resonator we may
  • 00:52:36
    be able to tightly confined the optical
  • 00:52:38
    mode in this plasmonics and then if we
  • 00:52:42
    have binding events will have very
  • 00:52:43
    strong shifts in the resonance
  • 00:52:45
    wavelength of the structure and so we
  • 00:52:47
    may be able to enable field localization
  • 00:52:50
    without a huge penalty in the quality
  • 00:52:52
    factor and finally we're also looking at
  • 00:52:55
    practical single mode low threshold
  • 00:52:57
    lasers on with further optimization of
  • 00:53:00
    our fabrication processes there's a lot
  • 00:53:02
    that goes into fabricating a device and
  • 00:53:05
    there's a lot of work in terms of
  • 00:53:07
    developing processing recipes to achieve
  • 00:53:09
    high performance and so we're still
  • 00:53:12
    working on that so for acknowledgments
  • 00:53:15
    none of this work would be possible
  • 00:53:17
    without the excellent effort of the
  • 00:53:19
    graduate students a lot of this work
  • 00:53:21
    was led by a mirror Bobby and young moe
  • 00:53:23
    Kang with contributions from Josephine
  • 00:53:25
    masa and ass on the funding was from
  • 00:53:28
    National Science Foundation the Career
  • 00:53:30
    Award and also matching funds from the
  • 00:53:33
    universally University of Illinois so
  • 00:53:36
    thank you for your attention and I'm
  • 00:53:37
    open for questions
  • 00:53:53
    you
Tags
  • micro ring resonators
  • laser technology
  • sensing
  • mode coupling
  • simulation
  • fabrication
  • biomolecule detection
  • plasmonics
  • semiconductor lasers
  • research development