In this chapter we discuss recent advances in silicon photonics research at the National Research Council Canada. We review our work on first implementations of subwavelength grating structures in silicon waveguides, including efficient fiber-chip coupling structures, and anti-reflective and high-reflectivity structures formed at the SOI waveguide facets. Silicon planar waveguide spectrometer chips are introduced, namely a high-resolution arrayed waveguide grating spectrometer and the first planar waveguide Fourier-transform spectrometer with a largely increased light gathering capability. Finally, we review our work in developing silicon-wire biological sensors with excellent surface sensitivity, ultracompact sensor designs, and new waveguide geometries that allow these sensors to be densely arrayed for compatibility with conventional microarray spotters. These sensors provide a practical route to the development of label-free micro-array biochips for multi-analyte monitoring.

The spectral characteristics of a ring resonator made of Si photonic wires are modeled using mode expansion of super-modes 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.

We report a compact high-resolution arrayed waveguide grating (AWG) interrogator system designed to measure the relative wavelength spacing between two individual resonances of a tilted fiber Bragg grating (TFBG) refractometer. The TFBG refractometer benefits from an internal wavelength and power reference provided by the core mode reflection resonance that can be used to determine cladding mode perturbations with high accuracy. The AWG interrogator is a planar waveguide device fabricated on a silicon-on-insulator platform, having 50 channels with a 0.18 nm wavelength separation and a footprint of 8 mmx8 mm. By overlaying two adjacent interference orders of the AWG we demonstrate simultaneous monitoring of two widely separated resonances in real time with high wavelength resolution. The standard deviation of the measured wavelength shifts is 1.2 pm, and it is limited by the resolution of the optical spectrum analyzer used for the interrogator calibration measurements.

We review recent advances in silicon photonic arrayed waveguide grating and sub-wavelength grating devices developed at the NRC Canada. We present three original microspectrometer concepts, namely a compact 50 channel AWG microspectrometer with a spectral resolution of 1 A and a total chip size of 8 x 8 mm", a Fourier- transform AWG with a markedly increased light gathering capability compared to conventional AWG devices, and an AWG with a resolution significantly increased by inserting a triangular photonic crystal waveguide region in the phased array. Various new sub-wavelength grating waveguide structures will also be presented, including monolithic fibre-chip couplers, anti-reflective waveguide facets and mirrors.

The Local Oxidation of Silicon (LOCOS) technique is used to define optical rib waveguides in silicon-on-insulator (SOI) material. This process, commonly used for device isolation in purely microelectronic CMOS processes, results in a nearly planar surface suitable for integrating optical and electronic components on the same chip. Optical mode simulation was used to determine rib geometries suitable for single-mode propagation and minimizing birefringence in the 1550 nm optical telecommunications band. Test devices were then fabricated in SOI material with a Si film thickness near 3 mu m. Growth of a 1 mu m field oxide by wet oxidation yielded a 0.5 mu m rib height. As-drawn rib widths ranged from 3 mu m to 5 mu m, giving final rib widths ranging from 2 mu m to 4 mu m after oxidation. Cutback optical testing of 3 mu m drawn width ribs showed the loss to be less than 1 dB/cm at 1555 nm. Unbalanced Mach-Zehnder interferometers with Y-splitter junctions were also fabricated and tested with input wavelength swept from 1470 to 1580 nm and showed an extinction of 6-10 dB, demonstrating the ability of the LOCOS rib technique to produce more complex waveguide devices.

We review the design considerations and experimental results of a novel design of polarization insensitive ring resonators in silicon-on-insulator (SOI) ridge waveguides. The polarization insensitive coupling is achieved using a multi-mode-interference (MMI) coupler. Cladding stress-induced birefringence is used to correct the round trip phase difference between the TE and TM polarizations. Experimental demonstration is presented for such ring resonators fabricated on SOI with 1.5 ?m Si waveguide core layer. For resonators with radius R = 200 ?m, polarization insensitive operation is achieved in both the resonance wavelength and linewidth over a ~ 4 nm wavelength range using a 7.5 ?m × 84 ?m MMI coupler and 0.8 ?m thick oxide cladding with -250 MPa stress, with the resonance wavelength shifts between TE and TM polarizations less than 3 pm. The quality factor Q of ~ 15,000 and free-spectral range (FSR) of 0.46 nm is measured. For resonators with a smaller radius of 50 ?m, similar FRS of 1.3 nm and extinction of 13 dB are observed for TE and TM, although the resonance wavelengths are shifted, in agreement with the theoretical prediction. By choosing the proper combination of the cladding stress and thickness, zero-birefringence condition can be achieved for resonators of different cavity lengths.

A ring resonator in SOI photonic wire waveguides is demonstrated using a compact MMI coupler with 3mum x 9 mum footprint as the coupling element. We achieved high bandwidth of 0.25 nm, and a quality factor Q of ~ 6000 for rings with a radius of 50 mum. Unlike directional coupler based rings, these resonators have a wavelength independent Q and extinction ratio over more than 30 nm wavelength range, and there is no loss penalty for increasing the bandwidth. Compared to their directional coupler based counterparts, these resonators also have less demanding fabrication requirements and are compatible with high speed signal processing and optical delay lines.