Typical L-type photonic crystal (PC) microcavities have a dynamic range of approximately 3-4 orders of magnitude in biosensing. We experimentally demonstrated that multiplexing of PC sensors with different geometry can achieve a wide dynamic range covering 6 orders of magnitude with potential for 8 or more orders with suitable optimization.
We present progress towards the development of novel hybrid photonic-phononic oscillator technologies in both nanoscale silicon photonics and in fiber optic systems. These systems utilize traveling-wave photon-phonon couplings involving both stimulated Brillouin scattering processes (SBS). We explore numerous geometries that have enabled large forward-SBS processes in nanoscale silicon waveguides for the first time, and examine new approaches to achieving integrated Brillouin based signal processing.
We examine the physics of traveling-wave photon-phonon coupling within nanoscale silicon waveguides and explore a host of new Brillouin-based signal processing technologies enabled by tailorable stimulated Brillouin processes in silicon photonics. Theoretical analysis of Brillouin coupling at sub-wavelength scales is presented, revealing that strong light-boundary interactions produce large radiation pressures mediated Brillouin nonlinearities. Experimental results demonstrating stimulated Brillouin scattering in silicon waveguides for the first time are also presented, revealing 1000 times larger forward stimulated Brillouin gain coeffcients than any prior system.
We develop a general framework of evaluating slow-light performance using Stimulated Brillouin Scattering (SBS) in optical waveguides via the overlap integral between optical and elastic eigen-modes. We show that spatial symmetry of the optical force dictates the selection rules of the excitable elastic modes. By applying this method to a rectangular silicon waveguide, we demonstrate the spatial distributions of optical force and elastic eigen-modes jointly determine the magnitude and scaling of SBS gain coefficient in both forward and backward SBS processes. We further apply this method to inter-modal SBS process, and demonstrate that the coupling between distinct optical modes is necessary to excite elastic modes with all possible symmetries.
We review the physics of photon-phonon coupling in guided wave systems, and discuss new opportunities for
information transduction aorded by nanoscale connement of light and phonons within a novel class of optome-
chanical waveguide systems. We present a fundamental analysis of optical forces generated through nanoscale
light-matter interactions, and use these insights to develop new approaches for broadband signal processing via
optomechanics. Recent experimental results will also be discussed.
Recent advance in controlling optical forces using nanostructures suggests that nanoscale optical waveguides are capable
of generating coherent acoustic phonons efficiently through a combination of radiation pressure and electrostriction. We
discuss the critical roles of group velocity in such processes. This photon-phonon coupling would allow an acoustic
intermediary to perform on-chip optical delay with a capacity 105 greater than photonic delay lines of the same size.
We present two photonic crystal enabled platforms, exhibiting novel active optical
phenomena. First, using a detailed theoretical and numerical analysis, we show how
a Purcell-effect inspired nonlinear nanophotonic scheme could enable optimal and
compact THz sources via optical difference frequency generation. Second, we show
how electromagnetic one-way edge modes analogous to quantum Hall edge states,
originally predicted by Raghu and Haldane in gyroelectric photonic crystals, can
appear in more general settings. In gyromagnetic YIG photonic crystals operating at
microwave frequencies, time-reversal breaking is strong enough that the effect is
readily observable. We present our experimental results on this novel
We present a new treatment of optical forces, revealing that the forces in virtually all optomechanically variable
systems can be computed exactly and simply from only the optical phase and amplitude response of the system.
This treatment, termed the response theory of optical forces (or RTOF), provides conceptual clarity to the
essential physics of optomechanical systems, which computationally intensive Maxwell stress-tensor analyses
leave obscured, enabling the construction simple models with which optical forces and trapping potentials can
be synthesized based on the optical response of optomechanical systems. A theory of optical forces, based
on the optical response of systems, is advantageous since the phase and amplitude response of virtually any
optomechanical system (involving waveguides, ring resonators or photonic crystals) can be derived, with relative
ease, through well-established analytical theories. In contrast, conventional Maxwell stress tensor methods
require the computation of complex 3-dimensional electromagnetic field distributions; making a theory for the
synthesis of optical forces exceedingly difficult. Through numerous examples, we illustrate that the optical forces
generated in complex waveguide and microcavity systems can be computed exactly through use of analytical
scattering-matrix methods. When compared with Maxwell stress-tensor methods of force computation, perfect
agreement is found.
We propose a systematic approach to miniaturize magneto-optical device down to a single wavelength scale through the use of photonic crystal resonances. The nonreciprocal transport, typically found in magneto-optics, is highly enhanced in structures with strong field localization. The devices are magnetically biased along the out-of-plane direction (Voigt configuration). An optimized magnetic domain design maximally couples the standing-wave eigenstates in the resonance. As a conceptual demonstration, we demonstrate the design guideline in two-dimensional photonic crystal cavities, which can be readily extended into designing two-dimensional slab structures with the same functionality. A three-port junction circulator containing bismuth-iron-garnet is modeled with finite-difference time-domain schemes and demonstrates a 30dB-isolation bandwidth well over 100GHz.
During the past decade, defect engineering in photonic crystals has successfully miniaturized many optical devices, such as optical filters and lasers, to a sub-wavelength scale. In the field of magneto-optics, previous researches on one-dimensional photonic crystals have demonstrated that magnetic cavities can be used to create Friday rotation in sub-wavelength optical paths, important for integrated optical isolators. In this paper, we study an optical circulator formed of a bismuth-iron-garnet defect infiltrated in a two dimensional silicon photonic crystal. The additional dimension of the field confinement allows further miniaturization and paves the way for monolithic in-plane integration with current integrated optical devices. The magneto-optical defect is constructed to support two doubly-degenerate TE modes and side-coupled to three photonic-crystal waveguides to form a three-port Y-junction circulator. When maximized with geometrically-optimized bismuth-iron-garnet domain, the gyrotropic effects cross couple the two modes and split them into a pair of counter-spinning states. We use the coupled-mode theory to derive the general criterion between the magneto-coupling and resonance decay constant for complete transmission and isolation. Numerical experiments with finite-difference time-domain methods confirmed the coupled mode theory and demonstrate a Y-junction circulator with an isolation ratio greater than 40dB. The design principle for this two dimensional photonic crystal defect can be readily transferred to magneto-optical defects in three dimensional slab photonic crystals. The silicon/air based system has a small footprint of one wavelength squared and good compatibility for integration with other planar optical devices.
We demonstrate a compact optical transducer (~50μm) based on a gold film perforated with a square array of square holes. The lattice constant (separation between nearest holes) is chosen to be a ~1μm to detect refractive index change around (n~1.4) with resonant wavelength (λ~1.5μm). Both reflectance measurement and finite difference time domain (FDTD) simulations are performed to evaluate the performance of the sensors. The responsivity of the resonant wavelength is measured to be Δλ/Δn ~835nm RIU-1 (RIU= refractive index unit). The linewidth and contrast of resonance are compared with different size of holes from experimental measurement and FDTD simulations. Coupled mode theory analysis is also used to understand the change reflectance spectrum as a function of hole width.
While much work has focused on simulation and measurement of plasmon resonances in noble metal nanostructures, usually the simulation tool is used as a confirmation of experimental results. In this work we use a finite difference time domain (FDTD) technique to calculate the plasmon resonance and electric field enhancement of Ag nanoparticles in regular arrays on quartz substrates. Such structures have also been prepared by e-beam lithography, and the plasmon resonance and surface-enhanced Raman scattering strength of arrays with different nanoparticle size and spacing have been investigated. Arrays of cylindrical nanoparticles were fabricated with varying particle size and interparticle spacing. The observed extinction peaks agree very well with the extinction peaks as calculated by FDTD; typically within a few percent. Experimental plasmon peak widths are considerably larger than their ideal values due to inhomogeneous broadening. As expected, the particle array with highest SERS enhancement has its plasmon resonance nearest the laser and Stokes-shifted wavelengths. We believe the FDTD modeling tool is accurate enough to use as a predictive tool for engineering plasmonic nanostructures.
There has been significant interest in the non-orthogonal modes in resonator systems in the context of the excess noise factor in laser cavities. Conventional non-orthogonal modes are created by the gain of the laser cavity during a round trip since gain makes the propagation of light non-unitary. Here, we theoretically demonstrate that these non-orthogonal modes can also be generated in passive photonic crystal systems. We further show that it can have a broader implication in optical resonator systems. In particular, we probe the characteristics of non-orthogonal modes in a resonator system by looking at the transport properties.
We use coupled optical and electronic simulations to investigate design tradeoffs in electrically pumped photonic crystal light emitting diodes. A finite-difference frequency-domain electromagnetic solver is used to calculate the spontaneous emission
enhancement factor and the extraction efficiency as a function of
frequency and of position of the emitting source. The calculated
enhancement factor is fed into an electronic simulator, which solves the coupled continuity equations for electrons and holes and Poisson's equation. We simulate a two-dimensional structure consisting of a photonic-crystal slab with a single-defect cavity, and investigate different pumping configurations for such a cavity.
We propose an optical circulator formed of a magneto-optical cavity in a 2D photonic crystal. With spatially engineered magnetic domain structures, the cavity can be designed to support a pair of counter-rotating states at different frequencies. By coupling the cavity to three waveguides, and by a proper matching of the frequency split of the cavity modes with the coupling strength between the cavity and the waveguide, ideal three-port circulators with complete isolation and transmission can be created. We present a guideline for domain design needed to maximize the modal coupling and operational bandwidth for any given magneto-optical constant.
For applications such as fiber optic networks, wavelength conversion, or extracting information from a predetermined channel, are required operations. All-optical systems, based on non-linear optical frequency conversion, offer advantages compared to present systems based on optical-electronic-optical (OEO) conversion. Thanks to the large nonlinear susceptibility of AlGaAs (d14 = 90pm/V) and mature device fabrication technologies, quasi-phasematched non-linear interactions in orientation-patterned AlGaAs waveguides for optical wavelength conversion have already been demonstrated. However, they require long interaction length (~ centimeters) and a complex fabrication process. Moreover, the conversion efficiency remains relatively low, due to losses and poor confinement. We present here the design and fabrication of a very compact (~ tens of microns long) device based on tightly confining waveguides and photonic crystal microcavities. Our device is inherently phase-matched due to the short length and should significantly increase the conversion efficiency due to tight confinement and high cavity-Q value. We characterized the waveguides, measuring the propagation loss by the Fabry-Perot method and by a variant of the cutback method, and both give a consistent loss value (~5 dB/mm for single-mode waveguides and ~3 dB/mm for multimode waveguide). We also characterized the microcavities measuring the transmission spectrum and the cavity-Q value, obtaining Q's as large as 700.
We present the design and fabrication process for an AlGaAs optical frequency conversion device based on tightly confining waveguides and a Photonic Bandgap Crystal Microcavity. We first theoretically analyze the improvement in non-linear conversion efficiency due to a high confinement cavity, compared to traditional QPM waveguides. The theoretical analysis is supported by finite difference frequency and time domain simulations. The theoretical conversion efficiency estimated with these tools is ~4%/mW for a device ~10 μm long. Influence of sidewall roughness on the Q of the cavity is also analyzed. Then, we describe the fabrication process of our device, which involves molecular beam epitaxy, electron beam lithography and plasma etching.
Photonic crystals are well known for their potentials for confining and guiding light in very small structures. Photonic crystals can also exhibit strong dispersion properties. These properties may offer many exciting opportunities for optical communication applications. In this paper, we discuss some of the basic principles for designing photonic crystal structures for optical communication applications, using examples for applications in polarization mode compensations, and add/drop filtering in wavelength division multiplexing.