C. Storey

Extracting coupling and loss coefficients from a ring resonator

A method is developed for extracting the coupling and loss coefficients of ring resonators from the peak widths, depths, and spacings of the resonances of a single resonator. Although the formulas used do not distinguish which coefficient is coupling and which is loss, it is shown how these coefficients can be disentangled based on how they vary with wavelength or device parameters.

Single-mode 2.4 μm InGaAsSb/AlGaAsSb distributed feedback lasers for gas sensing

Single-mode laser diodes on GaSb substrates were developed using InGaAsSb/AlGaAsSb triple quantum well active regions grown by molecular beam epitaxy. The devices were fabricated using lateral Cr gratings, with a grating pitch designed to coincide with a strong absorption feature of HF gas, deposited adjacent to a dry-etched narrow ridge waveguide. High sidemode suppression was achieved, and in 20 °C continuous-wave operation, devices with a 400 μm long cavity provided 9 mW total output power at the 2396 nm target wavelength. High-resolution direct absorption measurements of HF gas agreed with HiTran calculations, yielding an absorption linewidth of 0.030 nm.

Wavelength-Dependent Model of a Ring Resonator Sensor Excited by a Directional Coupler

The spectral characteristics of a ring resonator made of Si photonic wires are modeled using mode expansion of supermodes of the directional coupler. The influence of the coupling coefficient, loss factor and waveguide dispersion on the spectral features are analyzed in detail. The model is then compared with the experimental data of a ring resonator designed for sensing purposes. The model that includes a wavelength dependence on coupling length reproduces the large variations of the envelope of the experimental spectrum, when coupling coefficient cover its full range from 0 to 1. Fitting parameters explain the details of the experimental spectrum and contribute to the sensor optimization, as well as illustrating general guidelines for ring resonator design.

Uniformity of AlGaN ∕ GaN HEMTs Grown by Ammonia-MBE on 2-in. Sapphire Substrate

The uniformity of AlGaN/GaN high electron mobility transistor (HEMT) devices has been studied across a 2-in. wafer. The material was grown by ammonia molecular beam epitaxy (MBE) on a sapphire substrate. The devices exhibit uniformity comparable to that obtained by other growth technologies. Parameters measured include peak current density, transconductance, contact and sheet resistances, gate leakage current, f T and f m a x current collapse under dc, pulsed, and stressed conditions. The effects of wafer bowing on the quality of the contact lithography were explicitly considered. The results indicate excellent potential of ammonia MBE for the growth of commercially useful materials.

Densely folded silicon photonic wire biosensors in ring resonator and Mach-Zehnder configurations

We demonstrate silicon photonic wire evanescent field sensors formed by folding long photonic wire waveguides into dense spiral paths that occupy spot sizes less than 150 mum in diameter, and are hence suitable for biochip array formats. These sensors are incorporated into both ring resonator and Mach-Zehnder interferometer (MZI) interrogation circuits, and tested by monitoring streptavidin protein adsorption. The level of detection is less than 1% of a monolayer in either configuration. Using a balanced MZI design, we show that the sensors can be insensitive to temperature and wavelength, while retaining a very high sensitivity to molecular adsorption.

Single-mode mid-infrared lasers for gas sensing in the 2–4um range

Type-I interband laser diodes were developed for trace gas sensing applications in the 2–4um wavelength range. The devices were grown by molecular beam epitaxy on GaSb substrates using InGaAsSb/Al(In)GaAsSb active regions. Tunable, single-mode lasers were produced using distributed feedback grating processing or by incorporating Fabry-Perot lasers in an external cavity configuration. Sensitive gas detection was demonstrated using these lasers in tunable-diode laser absorption spectroscopy.

Single-mode 2.4μm InGaAsSb/AlGaAsSb distributed feedback lasers for gas sensing

Single-mode laser diodes on GaSb substrates were developed using InGaAsSb/AlGaAsSb triple quantum well active regions grown by molecular beam epitaxy. The devices were fabricated using lateral Cr gratings, with a grating pitch designed to coincide with a strong absorption feature of HF gas, deposited adjacent to a dry-etched narrow ridge waveguide. High sidemode suppression was achieved, and in 20°C continuous-wave operation, devices with a 400μm-long cavity provided 4.5mW total output power at the 2396nm target wavelength. Anti-reflection and high-reflection facet coatings exhibited no deleterious effects on the laser tunability or mode quality, thus allowing the preferential extraction of output power from a single laser facet.

Label-free Evanescent Field Biosensors Using Silicon Photonics Technology

Photonics is playing an increasingly important role in the field of medical diagnostics, genomics and drug discovery. With the advances in molecular biology which gives insight to the processes underlying diseases and drug response, there is a need for new biological sensors to rapidly detect and quantify these processes. Sensing of biological events using planar waveguide evanescent field (EVF) detection offers label-free, high sensitivity, and real time monitoring [1-4]. This is a competing technology with the commercially pervasive SPR (surface plasmon resonance) method, but with the advantage of portability and low cost.