[Show abstract][Hide abstract] ABSTRACT: We propose a method for soliton formation in whispering-gallery-mode (WGM)
resonators through input phase modulation. Our numerical simulations of a
variant of the Lugiato-Lefever equation suggest that modulating the input phase
at a frequency equal to the resonator free-spectral-range and at modest
modulation depths provides a deterministic route towards soliton formation in
WGM resonators without undergoing a chaotic phase. We show that the generated
solitonic state is sustained when the modulation is turned off adiabatically.
Our results support parametric seeding as a powerful means of control, besides
input pump power and pump-resonance detuning, over frequency comb generation in
WGM resonators. Our findings also help pave the path towards ultra-short pulse
formation on a chip.
[Show abstract][Hide abstract] ABSTRACT: A systematic study of the limit of detection (LOD) in resonance-based silicon photonic lab-on-chip sensors is presented. The effects of the noise, temperature fluctuations, and the fundamental thermodynamic limit of the resonator are studied. Wavelength noise is identified as the dominant source of noise, and an efficient technique for suppressing this noise is presented. A large ensemble of statistical data from the transmission measurements in a laser-scanning configuration on five silicon nitride (SiN) microrings is collected to discuss and identify the sources of noise. The experimental results show that the LOD is limited by a 3σ wavelength noise of 1.8 pm. We present a sub-periodic interferometric technique, relying on an inverse algorithm, to suppress this noise. Our technique reduces the wavelength noise by more than one order of magnitude to an ensemble average of 3σ = 120 fm, for a resonator quality factor (Q) of about 5×10^4 without any temperature stabilization or cooling. This technique is readily amenable to on-chip integration to realize highly accurate and low-cost lab-on-chip sensors.
[Show abstract][Hide abstract] ABSTRACT: Optical switches are among the essential building blocks in optical networks due to their unique role in routing data. In this Letter, for the first time to our knowledge, we have exploited a high-quality factor (Q) optical microresonator combined with the well-known irreversible dielectric breakdown phenomenon to introduce a simple field-programmable on/off optical switch. This simple unit can be thought of as a building block for more complex optical systems with different functionalities. By using this simple unit we have demonstrated an optical field-programmable 2×2 switch. After the device is programmed by the user, no external electrical signal is needed to maintain the state of the device. The same approach can readily be adopted to design a field-programmable arbitrary N×N optical switch.
[Show abstract][Hide abstract] ABSTRACT: We have designed interlayer grating couplers with single/double metallic reflectors for Si/SiO2/SiN multilayer material platform. Out-of-plane diffractive grating couplers separated by 1.6 μm thick buffer SiO2 layer are vertically stacked against each other in Si and SiN layers. Geometrical optimization using genetic algorithm coupled with electromagnetic simulations using two-dimensional (2D) finite element method (FEM) results in coupler designs with high peak coupling efficiency of up to 89% for double- mirror and 64% for single-mirror structures at telecom wavelength. Also, 3-dB bandwidths of 40 nm and 50 nm are theoretically predicted for the two designs, respectively. We have fabricated the grating coupler structure with single mirror. Measured values for insertion loss and 3-dB bandwidth in the fabricated single-mirror coupler confirms the theoretical results. This opens up the possibility of low-loss 3D dense integration of optical functionalities in hybrid material platforms.
[Show abstract][Hide abstract] ABSTRACT: We investigate polarization cross-coupling between modes of microring resonators and waveguides due to structural asymmetries. We experimentally demonstrate the coupling between a double-layer SOI waveguide fundamental TM mode and microring higher-order radial TE modes.
[Show abstract][Hide abstract] ABSTRACT: Monolayer graphene sheet has been integrated on top of small disk optical resonator in SOI platform. Electro-optic interaction between graphene and whispering gallery mode of the cavity has been demonstrated and studied for modulation application.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate the possibility of forming ultra-compact, field-configurable, and low-power resonance-based passive integrated photonic structures based on charge accumulation in a high-quality multilayer material platform comprising Si/SiO2/Si layers prepared through direct bonding of SOI wafers.
[Show abstract][Hide abstract] ABSTRACT: We present mechanically-tunable microdisk resonators using electrostatic actuation in double-layer-SOI material platform. The possibility of achieving resonance wavelength shifts as-high-as 5.5 nm/volt and 1.35 nm/nm over a wavelength tuning range of 35 nm is demonstrated.
[Show abstract][Hide abstract] ABSTRACT: We develop a model for silicon-on-insulator microresonators with magnesiothermically-formed porous silicon cladding possessing three-dimensional interconnected pores. Investigation of waveguide design and geometrical parameters indicates an optimized areal mass sensitivity of ~ 0.2 pm/(pg/mm2).
[Show abstract][Hide abstract] ABSTRACT: We present a novel bilayer plasmonic nanoantenna array, utilizing lattice plasmon waves to increase the sensitivity in SERS process. Using this nanostructure, we performed SERS measurements of proteins in a very low concentration.
[Show abstract][Hide abstract] ABSTRACT: A full biosensor system based on referenced and spectrally multiplexed arrays of silicon nitride microrings with glycoprotein receptors is demonstrated. Underlying system design guidelines and fundamental noise limits of the device are discussed.
[Show abstract][Hide abstract] ABSTRACT: Repeatability of resonance detection for on-chip microring resonators is systematically studied. An efficient interferometric method is presented to improve the accuracy by more than one order of magnitude in an 8 nm bandwidth, without any temperature control.
[Show abstract][Hide abstract] ABSTRACT: Depth-resolved three-dimensional (3D) reconstruction of fluorophore-tagged inclusions in fluorescence tomography (FT) poses a highly ill-conditioned problem as depth information must be extracted from boundary data. Due to the ill-posed nature of the FT inverse problem, noise and errors in the data can severely impair the accuracy of the 3D reconstructions. The signal-to-noise ratio (SNR) of the FT data strongly affects the quality of the reconstructions. Additionally, in FT scenarios where the fluorescent signal is weak, data acquisition requires lengthy integration times that result in excessive FT scan periods. Enhancing the SNR of FT data contributes to the robustness of the 3D reconstructions as well as the speed of FT scans. A major deciding factor in the SNR of the FT data is the power of the radiation illuminating the subject to excite the administered fluorescent reagents. In existing single-point illumination FT systems, the source power level is limited by the skin maximum radiation exposure levels. In this paper, we introduce and study the performance of a multiplexed fluorescence tomography system with orders-of-magnitude enhanced data SNR over existing systems. The proposed system allows for multi-point illumination of the subject without jeopardizing the information content of the FT measurements and results in highly robust reconstructions of fluorescent inclusions from noisy FT data. Improvements offered by the proposed system are validated by numerical and experimental studies.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a compact, thermally reconfigurable reflection suppressor on a silicon-on-insulator (SOI) platform, without reliance on nonreciprocal mechanisms. A reflection suppression ratio of 40 dB is achieved with a footprint of 105 μm in length. The insertion loss of the device is below 0.15 dB, and its total power consumption stays below 20 mW. The operation bandwidth depends on the frequency dependence of the back reflection going into the suppressor, which is predominantly determined by the distance between the device and the source of reflection. In this work, a 20 dB reflection suppression bandwidth of 20.7 GHz was achieved.
[Show abstract][Hide abstract] ABSTRACT: Earth-based telescope array receivers employing optical communications have the potential to fulfill the communication needs of technologically sophisticated, deep-space exploration missions. Atmospheric turbulence is the chief restrictive factor in an optical deep-space channel (ODSC). In this paper, investigation and design of adaptive optics (AO) subsystems are presented for the compensation of the coupled effects of optical turbulence and background noise in telescope array receivers. An end-to-end simulation platform for an ODSC between Mars and Earth is implemented, which incorporates pulse-position modulation (PPM), direct-detection receivers, and detectors with the capability of detection of single photon. The extreme conditions of atmospheric turbulence and background noise are also modeled in the analysis. AO subsystems are incorporated at individual telescopes in the array receiver to mitigate the turbulence effects. The performance of array receivers is evaluated in terms of the probability of error and communication throughput. The analysis in this research depicts that in worst-case turbulence and background noise conditions, inclusion of AO systems results in 8.5 dB performance improvement in communication data rates. The performance improvement of 5.6 dB is achievable in moderate channel conditions. Comparison of performance of array receivers with that of a large monolithic telescope shows that incorporation of AO systems is more feasible in arrays comprising telescopes with relatively smaller diameters.
[Show abstract][Hide abstract] ABSTRACT: We present a new method for modeling and design of photonic crystal nano-beam resonators (PCNBRs) based on cascaded transmission lines. The proposed model provides an accurate estimate of the PCNBRs properties such as resonance wavelength and quality factor (Q) with much smaller computation cost as compared to the brute-force numerical methods. Furthermore, we have developed a straightforward technique for the design of high-Q PCNBRs based on resonance modes with Gaussian electromagnetic field profiles. The results obtained by using the proposed transmission line model are compared against numerical and experimental results and the accuracy of the model is verified. The proposed model provides an insight to silicon cavity design and significantly reduces computational burden.
Journal of Lightwave Technology 01/2014; 32(1):91-98. · 2.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, the interplay of Bragg scattering and local resonance is theoretically studied in a phononic crystal (PnC) structure composed of a silicon membrane with periodic tungsten pillars. The comparison of phononic band gaps (PnBGs) in three different lattice types (i.e., square, triangular, and honeycomb) with different pillar geometries shows that different PnBGs have varying degrees of dependency on the lattice symmetry based on the interplay of the local resonances and the Bragg effect. The details of this interplay is discussed. The significance of locally resonating pillars, specially in the case of tall pillars, on PnBGs is discussed and verified by examining the PnBG position and width in perturbed lattices via Monte Carlo simulations. It is shown that the PnBGs caused by the local resonance of the pillars are more resilient to the lattice perturbations than those caused by Bragg scattering.
Journal of Applied Physics 01/2014; 116(1):013514-013514-7. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We experimentally demonstrate efficient extinction spectroscopy of single plasmonic gold nanorods with exquisite fidelity (SNR > 20dB) and high efficiency light coupling (e. g., 9.7%) to individual plasmonic nanoparticles in an integrated platform. We demonstrate chip-scale integration of lithographically defined plasmonic nanoparticles on silicon nitride (Si<sub>3</sub>N<sub>4</sub>) ridge waveguides for on-chip localized surface plasmon resonance (LSPR) sensing. The integration of this hybrid plasmonic-photonic platform with microfluidic sample delivery system is also discussed for on-chip LSPR sensing of D-glucose with a large sensitivity of ∼ 250 nm/RIU. The proposed architecture provides an efficient means of interrogating individual plasmonic nanoparticles with large SNR in an integrated alignment-insensitive platform, suitable for high-density on-chip sensing and spectroscopy applications.
[Show abstract][Hide abstract] ABSTRACT: We present theoretical and experimental demonstration of two designs to achieve group velocity insensitive coupling of light from a ridge waveguide to a photonic crystal waveguide. We demonstrate an average improvement of 62% in coupling to low group velocity modes and an average coupling enhancement of 11.5% at large group velocities.