Nonlinear wave mixing in optical microresonators offers a route to chip-level optical frequency combs with many promising applications. The properties of the combs generated depend crucially on the interaction between nonlinearity and dispersion. This paper will discuss our research on Kerr comb generation in silicon nitride chip-scale microresonators, with an emphasis on distinct features observed in the normal and anomalous dispersion regimes. The topics covered include comb initiation, comb coherence and mode-locking, power conversion efficiency, and second-harmonic involved comb generation.
Microcavity structures have recently found utility in chemical/biological sensing applications. The appeal of these structures over other refractive index-based sensing schemes, such as those based on surface plasmon resonance, lies in their potential for producing a highly sensitive response to binding events. High-Q devices, characterized by sharp line widths, are extremely attractive for sensing applications because the bound analyte provides an increased optical pathlength, thus shifting the resonant frequency of the device. In this work, we design and simulate resonant microrings using full-wave finite element models. In addition to structure design, integration of the biological recognition element on the resonator is also considered. This is equally important in dictating the sensitivity of the sensing device. To this end, we take a four-step theoretical approach to optimizing the sensor. We begin by using FEM analysis to obtain the characteristic resonant wavelength, line width, and quality factor for bare ring resonators absent of surface functionalization. Next, we simulate the structure with a biorecognition element attached to the surface. The third step is to model the functionalized microring to mimic the interaction with the target analyte. At each step, we derive the transmission spectra, electric field distributions and coupling efficiencies, as well as wavelength dependence using empirical data for the refractive indices of biorecognition element and analyte. Finally, the geometry of the microrings is optimized in conjunction with the constituent material properties and the recognition chemistry using FEM combined with an optimization algorithm to maximize the sensitivity of the integrated biosensor.
Using laser direct writing in combination with chemical vapor deposition to produce nanometer scale electronics holds several advantages over current large scale photolithography methods. These include single step electrical interconnect deposition, mask-less patterning, and parallel processing. When taken together they make quick production of individualized electronic circuits possible. This work demonstrates the ability of combining laser direct write and chemical vapor deposition to produce silicon wires a few hundred nanometers wide. Optimized parameters will be discussed, with a particular emphasis paid to the laser-material interactions. The feasibility for electronic applications will be shown by examining the deposition formation on a silicon dioxide surface without degrading the surface's integrity, and by evaluating the resistivity of the deposited silicon wires.
Proc. SPIE. 7764, Nanoengineering: Fabrication, Properties, Optics, and Devices VII
KEYWORDS: Diffraction, Continuous wave operation, Femtosecond phenomena, Silicon, Chemical vapor deposition, Semiconductor lasers, Scanning electron microscopy, Transmission electron microscopy, Zone plates, Laser systems engineering
Direct writing using a femtosecond laser provides an accurate, repeatable and efficient means of creating
nanoscale lines for electronic applications circumventing the standard fabrication methods that require
expensive masks and numerous processing steps. Femtosecond laser writing makes these nanoscale lines by
using a phase zone plate to focus the laser pulse onto a silicon substrate in a chemical vapor deposition
chamber flowing silane. The silane is decomposed onto the narrow heated area of the substrate as the laser
scans across leaving behind a thin line of silicon deposition. This manufacturing technique utilizes a high
precision optical metrology system and a high precision motion control system to make this nanomanufacturing
possible. It has been shown to successfully make as many as 100 silicon lines on the order of a few hundred nanometers in width. The size and crystal structure of these lines are characterized using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).
We describe a method of detecting nanometer-level gap and tip/tilt alignment between a focusing zone plate mask and a
silicon substrate using interferometric-spatial-phase-imaging (ISPI). The zone plate mask is used to generate submicrometer
focused light spot to induce silicon nanowire growth in a CVD process. ISPI makes use of diffracting fringes
from gratings and checkerboards fabricated on the mask to determine the correct gapping distance for the focusing zone
plates. The method is capable of detecting alignment inside a gas-flow chamber with variable pressure.
Supercontinuum based sources and measurement techniques are developed, enabling optical ultra-broadband studies of nano-scale photonic crystal devices and integrated photonic circuits over 1.2 - 2.0 micron wavelength range. Experiments involving 1-D periodic photonic crystal microcavity waveguides and 3-D periodic photonic crystals with embedded point defects are described. Experimental findings are compared with rigorous electromagnetic simulations.
The majority of photonic crystals developed till-date are not dynamically tunable, especially in silicon-based structures. Dynamic tunability is required not only for reconfiguration of the optical characteristics based on user-demand, but also for compensation against external disturbances and relaxation of tight device fabrication tolerances. Recent developments in photonic crystals have suggested interesting possibilities for static small-strain modulations to affect the optical characteristics [1-3], including a proposal for dynamic strain-tunability . Here we report the theoretical analysis, device fabrication, and experimental measurements of tunable silicon photonic band gap microcavities in optical waveguides, through direct application of dynamic strain to the periodic structures . The device concept consists of embedding the microcavity waveguide  on a deformable SiO2 membrane. The membrane is strained through integrated thin-film piezoelectric microactuators. We show a 1.54 nm shift in cavity resonances at 1.56 um wavelengths for an applied piezoelectric strain of 0.04%. This is in excellent agreement with our modeling, predicted through first-order semi-analytical perturbation theory  and finite-difference time-domain calculations. The measured microcavity transmission shows resonances between 1.55 to 1.57 um, with Q factors ranging from 159 to 280. For operation at infrared wavelengths, we integrate X-ray and electron-beam lithography (for critical 100 nm feature sizes) with thin-film piezoelectric surface micromachining. This level of integration permits realizable silicon-based photonic chip devices, such as high-density optical filters and spontaneous-emission enhancement devices with tunable configurations.
This paper explores the optical characteristics of one-dimensional (1D) and two-dimensional (2D) photonic crystals (PhC) as spectral control components for use in thermophotovoltaic (TPV) systems. 1D PhC are used as optical filters while 2D PhC are used as selective thermal emitters. A Si/SiO2 1D PhC is fabricated using low-pressure chemical vapor deposition (LPCVD). The measurement and characterization of this structure is presented. A 2D hexagonal PhC of periodic holes is fabricated using interference litography and reactive ion etching (RIE) process. Our results predict that a TPV system utilizing a 2D PhC selective emitter and 1D Si/SiO2 PhC optical filter promises significant performance improvements over conventional TPV system architectures.