Next-generation fiber-optic communication systems require dramatically increased complexity that cannot be obtained using discrete optical components. Silicon photonics has a unique capacity of handling complexity. We review our recent progress in high-speed silicon photonic transmitters and space-division multiplexers to scale the capacity of fiber-optic networks towards terabits-per-second (Tb/s) per optical interface and petabits-per-second (Pb/s) per transmission link.
In this work, we address a chip-scale polarimeter in which the measurement frame remains optimal over a wavelength range of 200 nm in the presence of Gaussian and Poisson shot noise. The optimization includes equalized variances of each Stokes parameter, and minimal equally weighted variance. The proposed device contains only four photodetectors, which is the minimum number required for full-Stokes reconstruction. It includes broadband asymmetric power splitters and phase shifters. Notably, the broadband phase shifters are designed based on the subwavelength grating waveguides.
We discuss recent progress and challenges in realizing Bragg-grating devices on the submicron silicon-on-insulator platform for next-generation optical communications applications, such as on-chip optical interconnects and signal processing. In particular, we focus on grating-assisted, wavelength-selective couplers, known as contra-directional couplers (contra-DCs). In contrast to conventional two-port Bragg gratings operating in the reection mode, contra-DCs are four-port devices with very weak backreections and, therefore, can be easily integrated with other photonic components on a chip. In order to provide a reliable on-chip wavelength-division multiplexing (WDM) solution for high-speed optical interconnects, we have developed high-performance add-drop filters and, furthermore, wavelength multiplexers/demultiplexers with combined advantages of at-top responses, low insertion loss (< 1 dB), and low crosstalk (< -23 dB). These WDM devices are ultra-compact and highly tolerant to temperature uctuations (up to ±50 °C), showing great potential for large-scale integration and low-power consumption. We further discuss a novel four-port Bragg photonic resonator for high-speed, low-power optical switching. Using a coupler-chirped design with uniform Bragg gratings, we have recently achieved an on-chip, continuously tunable photonic delay line with low insertion loss. These system-orientated devices indicate great potential for large-scale integration of Bragg-grating-defined functions using CMOS-compatible silicon photonics technology.
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.
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.
Silicon photonics is poised to revolutionize biosensing applications, specifically in medical diagnostics. Optical sensors can be designed to improve clinically-relevant diagnostic assays and be functionalized to capture and detect target biomarkers of interest. There are various approaches to designing these sensors - improving the devices' performance, increasing the interaction of light with the analyte, and matching the characteristics of the biomolecules by using architectures that complement the biosensing application. Using e-beam lithography and standard foundry processes, we have investigated Transverse Magnetic (TM) and Transverse Electric (TE) disk and ring resonators. TM devices hold the potential for higher sensitivity and large-particle sensing capabilities due to the increased penetration distance of light into the analyte. In addition, devices such as slot wavegguide Bragg grating sensors have shown high sensitivities and high quality factors and may present advantages for specific biosensing applications. These devices have been investigated for wavelengths around λ=1550 nm (conventional wavelength window in fiber-optic communication) and λ=1220 nm, where the water absorption is greatly decreased, offering improved limits of detection. Using reversibly bonded PDMS microfluidic flow cells, the performance and bio-detection capabilities of these devices were characterized. Comparing binding performance across these devices will help validate architectures suitable for biological applications. The most promising sensors for each application will then be identified for further study and development. This paper will discuss the sensors' comparative advantages for different applications in biosensing and provide an outlook for future work in this field.
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.
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.
A silicon racetrack resonator modulator, based on phase-match control, is proposed. The device is comprised of a straight
waveguide evanescently coupled to a ring resonator in the shape of a racetrack. A PN junction, formed in the straight
waveguide, is used to control the degree of phase-match in the coupler. Consequently, the coupling, and hence the power
transmission, is controlled by the voltage across the PN junction. The predicted free spectral range and switching voltage are,
respectively, 0.4 nm and 7.5 Volt, while the device dimensions are approximately 0.7 mm by 0.15 mm. The device behavior
is analyzed using two different analytic approaches for the coupling, the results of which are compared to numerical
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.
A 1550 InGaAsP-InP multiple-quantum-well (MQW) transistor laser is numerically modeled. The proposed
structure has a deep-ridge waveguide and asymmetric doping profile in the base (i.e. only the part below
QWs of the base is doped) which provides good optical and electrical confinement and effectively reduces the
lateral leakage current and optical absorption. The important physical models and parameters are discussed and
validated by modeling a conventional ridge-waveguide laser diode and comparing the results with the experiment.
The simulation results of the transistor laser demonstrate a low threshold (< 10 mA) and a > 25 % slope efficiency
with the current gain of 2 ~ 4. The optical saturation and voltage-controlled operation are also demonstrated.