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We design and demonstrate broadband directional couplers that use asymmetric-waveguide based phase control sections, on the silicon-on-insulator platform. Broadband directional couplers with various power splitting ratios, including 10%/90%, 20%/80%, 30%/70%, 40%/60% and 50%/50%, were realized for both transverse electric (TE) and transverse magnetic (TM) modes. Some of the devices exhitbit bandwidths in excess of 100 nm, and all in excess of 75 nm. The footprints of the TE mode couplers are 32 μm ×1.3 μm, or less, and those of the TM mode couplers are 13 μm ×1.3 μm, or less.

We demonstrate the design, fabrication and measurement of integrated Bragg gratings in a compact single-mode silicon-on-insulator ridge waveguide. The gratings are realized by corrugating the sidewalls of the waveguide, either on the ridge or on the slab. The coupling coefficient is varied by changing the corrugation width which allows precise control of the bandwidth and has a high fabrication tolerance. The grating devices are fabricated using a CMOS-compatible process with 193 nm deep ultraviolet lithography. Spectral measurements show bandwidths as narrow as 0.4 nm, which are promising for on-chip applications that require narrow bandwidths such as WDM channel filters. We also present the die-to-die nonuniformity for the grating devices on the wafer, and our analysis shows that the Bragg wavelength deviation is mainly caused by the wafer thickness variation.

We demonstrate fully-etched fiber-waveguide grating couplers with sub-wavelength gratings showing high coupling efficiency as well as low back reflections for both transverse electric (TE) and transverse magnetic (TM) modes. The power reflection coefficients for the TE and TM modes have been significantly suppressed to -16.2 dB and -20.8 dB, respectively. Focusing grating lines have also been used to reduce the footprint of the design. Our sub-wavelength grating couplers for the TE and TM modes show respective measured insertion losses of 4.1 dB and 3.7 dB with 1-dB bandwidths of 30.6 nm (3-dB bandwidth of 52.3 nm) and 47.5 nm (3-dB bandwidth of 81.5 nm), respectively.

We demonstrate, in both theory and experiment, 4-port, electrically tunable photonic filters using silicon contra-directional couplers (contra-DCs) with uniform and phase-shifted waveguide Bragg gratings. Numerical analysis, including both intra- and inter-waveguide couplings, is performed using coupled-mode theory and the transfer-matrix method. The contra-DC devices were fabricated by a CMOS-photonics manufacturing foundry and are electrically tunable using free-carrier injection. A 4-port, grating-based photonic resonator has been obtained using the phase-shifted contra-DC, showing a resonant peak with a 3-dB bandwidth of 0.2 nm and an extinction ratio of 24 dB. These contra-DC devices enable on-chip integration of Bragg-grating-defined functions without using circulators and have great potential for applications such as wavelength-division multiplexing networks and optical signal processing.

Silicon-on-insulator racetrack resonators can be used as multiplexers in wavelength division multiplexing applications. The free spectral range should be comparable to the span of the C-band so that a maximum number of channels can be multiplexed. However, the free spectral range is inversely proportional to the length of the resonator and, therefore, bending losses can become non-negligible. A viable alternative to increase the free spectral range is to use the Vernier effect. In this work, we present the theory of series-coupled racetrack resonators exhibiting the Vernier effect. We demonstrate the experimental performance of the device using silicon-on-insulator strip waveguides. The extended free spectral range is 36 nm and the interstitial peak suppression is from 9 dB to 17 dB.

Silicon photonic resonators, implemented using silicon-on-insulator substrates, are promising for numerous applications. The most commonly studied resonators are ring/racetrack resonators. We have fabricated these and other resonators including disk resonators, waveguide-grating resonators, ring resonator reflectors, contra-directional grating-coupler ring resonators, and racetrack-based multiplexer/demultiplexers. While numerous resonators have been demonstrated for sensing purposes, it remains unclear as to which structures provide the highest sensitivity and best limit of detection; for example, disc resonators and slot-waveguide-based ring resonators have been conjectured to provide an improved limit of detection. Here, we compare various resonators in terms of sensor metrics for label-free bio-sensing in a micro-fluidic environment. We have integrated resonator arrays with PDMS micro-fluidics for real-time detection of biomolecules in experiments such as antigen-antibody binding reaction experiments using Human Factor IX proteins. Numerous resonators are fabricated on the same wafer and experimentally compared. We identify that, while evanescent-field sensors all operate on the principle that the analyte's refractive index shifts the resonant frequency, there are important differences between implementations that lie in the relationship between the optical field overlap with the analyte and the relative contributions of the various loss mechanisms. The chips were fabricated in the context of the CMC-UBC Silicon Nanophotonics Fabrication course and workshop. This yearlong, design-based, graduate training program is offered to students from across Canada and, over the last four years, has attracted participants from nearly every Canadian university involved in photonics research. The course takes students through a full design cycle of a photonic circuit, including theory, modelling, design, and experimentation.

We experimentally demonstrate compact, broadband directional couplers using sub-wavelength gratings for silicon-on-insulator wafers with silicon layers of 220nm. The dispersion properties of the optical modes are engineered using sub-wavelength gratings, which allows broadband operation. Finite-difference time-domain based band structure calculations, with significantly reduced simulation time, were used to analyze the design, which included both the structure and the material dispersions. Compact broadband direction couplers, with device lengths shorter than 14µm, which cover a bandwidth of 100nm, for power splitting ratios of 50/50, 40/60, 30/70, and 20/80, are designed and fabricated for the fundamental transverse electric mode with a central operating wavelength of 1550nm.