Novel sub-wavelength silicon photonic waveguides for label-free sensors are demonstrated in this article. We use silicon-on-insulator (SOI) waveguides that consist of sub-wavelength grating (SWG) structures, where the waveguides are made of small silicon arrays (180 × 180 nm<sup>2</sup> rectangles with 60 nm gaps). They are used to form microring and Bragg grating resonators which measure the change of refractive index by monitoring the resonant wavelength shift. Due to the high surface contact area and low optical confinement of the proposed waveguide, the sensitivity (both bulk and surface) can be significantly increased. The bulk sensitivity of 580 nm/RIU for the microring and 610 nm/RIU for the Bragg grating are better than other recently published resonator sensors. Moreover, a standard biological sandwich assay demonstrates an enhanced surface sensitivity of 2050 pm/nm for both devices. Theoretical models and experimental results are investigated, indicating the predominant losses are from the water absorption at 1550 nm and scattering by sidewall roughness.
We demonstrated 2×2 broadband adiabatic 3-dB couplers based on silicon rib waveguides. Functioning as
50/50 optical power splitters, these devices can be used in optoelectronic applications. Fabricated using siliconon-insulator technology, we demonstrated the performance of the adiabatic 3-dB couplers by integrating two couplers into an unbalanced Mach-Zehnder Interferometer (MZI). Measurements of the MZI were made over a 100 nm wavelength range. Extinction ratios in excess of 33.4 dB were obtained over the wavelength range from 1520 nm to 1600 nm, for light injected into Input Port1 and measured at Output Port2, i.e., the cross port response.
A fully-etched grating coupler with improved back re ection and bandwidth is demonstrated in this paper. It can also be made in compact patterns with much smaller footprints than conventional, fully-etched grating couplers with long adiabatic tapers. Sub-wavelength gratings were employed to form the e ective index areas between the major gratings. Our grating has a measured 3-dB bandwidth of 64.37 nm with a back re ection of -14 dB.
Development of large-scale photonic integrated circuits requires an accurate, simple, and space-efficient method for characterizing the optical losses of integrated optical components. Here we present a ring-resonator-based technique for transmission-loss measurement of integrated optical components. Y-branch splitters are used to demonstrate the concept. This measurement techique is based on characterizing the spectral response of a waveguide ring resonator with a number of Y-branches inserted inside the cavity. The measurement accuracy is intrinsically limited by the optical loss of the ring waveguide and is independent of fiber-to-waveguide coupling losses. The devices were fabricated using a CMOS-compatible silicon-on-insulator technology. Our results show that the proposed technique is promising for high-accuracy, high-efficiency characterization of optical losses. Limitations of and potential improvements to the technique are also discussed.
This paper presents a dumbbell shape micro-ring resonator designed for use as a reflective notch filter. Function-ring as a wavelength-selective notch reflector, the device can be used in optoelectronic applications. The device is designed and analyzed using the transfer-matrix method. Fabricated using silicon-on-insulator technology, the dumbbell micro-ring reflector shows a reflective response with a quality factor of ~11,000 and an extinction ratio of 20 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.