A compact, low-loss and wavelength insensitive Y-junction for submicron silicon waveguides. The design was performed using FDTD and particle swarm optimization (PSO). The device was fabricated in a 248 nm CMOS line. Measured average insertion loss is 0.28±0.02 dB across an 8-inch wafer. The device footprint is less than 1.2 μm×2 μm, orders of magnitude smaller than MMI and directional couplers.

Compact and low loss Y-junction for submicron silicon waveguide

This paper reviews developments in cascaded microresonator-based matrix switches for silicon photonic interconnection networks in many-core computing applications. Specifically, we emphasize our recently proposed 5 times 5 matrix switch comprising two-dimensionally cascaded microring resonator-based electrooptic switches coupled to a waveguide cross-grid on a silicon chip. The cross-grid adopts low-loss low-crosstalk multimode-interference-based waveguide crossings. Such a microresonator-based matrix switch offers nonblocking interconnections among multiple inputs and multiple outputs, with the key merits of i) a tens to hundreds of micrometers-scale footprint, ii) gigabit/second-scale data transmission, iii) nanosecond-speed circuit-switching, iv) 100-muW-scale DC power consumption per link, and v) large-scale integration for networks-on-chips applications. We analyze in detail the microring resonator-based cross-grid switch design for high-data-rate signal transmission in the context of our proposed 5 times 5 matrix switch. We also study the feasibility of large-scale integration of the matrix switch. We report proof-of-concept experiments of a single cross-grid switch element and a 2 times 2 matrix switch, propose design guidelines, and discuss future engineering challenges.

Cascaded Microresonator-Based Matrix Switch for Silicon On-Chip Optical Interconnection

Silicon photonics has experienced phenomenal transformations over the last decade. In this paper, we present some of the notable advances in silicon-based passive and active optical interconnect components, and highlight some of our key contributions. Light is also cast on few other parallel technologies that are working in tandem with silicon-based structures, and providing unique functions not achievable with any single system acting alone. With an increasing utilization of CMOS foundries for silicon photonics fabrication, a viable path for realizing extremely low-cost integrated optoelectronics has been paved. These advances are expected to benefit several application domains in the years to come, including communication networks, sensing, and nonlinear systems.

Recent advances in silicon-based passive and active optical interconnects

Aluminum nitride (AlN) is an appealing nonlinear optical material for on-chip wavelength conversion. Here we report optical frequency comb generation from high-quality-factor AlN microring resonators integrated on silicon substrates. By engineering the waveguide structure to achieve near-zero dispersion at telecommunication wavelengths and optimizing the phase matching for four-wave mixing, frequency combs are generated with a single-wavelength continuous-wave pump laser. Further, the Kerr coefficient (n2) of AlN is extracted from our experimental results.

Optical frequency comb generation from aluminum nitride microring resonator

We design a resistive heater optimized for efficient and low-loss optical phase modulation in a silicon-on-insulator (SOI) waveguide and characterize the fabricated devices. Modulation is achieved by flowing current perpendicular to a new ridge waveguide geometry. The resistance profile is engineered using different dopant concentrations to obtain localized heat generation and maximize the overlap between the optical mode and the high temperature regions of the structure, while simultaneously minimizing optical loss due to free-carrier absorption. A 61.6 μm long phase shifter was fabricated in a CMOS process with oxide cladding and two metal layers. The device features a phase-shifting efficiency of 24.77 ± 0.43 mW/π and a −3 dB modulation bandwidth of 130.0 ± 5.59 kHz; the insertion loss measured for 21 devices across an 8-inch wafer was only 0.23 ± 0.13 dB. Considering the prospect of densely integrated photonic circuits, we also quantify the separation necessary to isolate thermo-optic devices in the standard 220 nm SOI platform.

Efficient, compact and low loss thermo-optic phase shifter in silicon

Bistability (BS) and self-pulsation (SP) phenomena in silicon microring resonators (MRR) with intense CW light injection are studied. Several nonlinear optical effects including Kerr effect, two-photon absorption, free carrier absorption and free carrier dispersion are taken into account. The threshold optical intensity of BS and SP is derived from the coupled mode theory and a linear stability analysis method. The influences of MRR's parameters (carrier lifetime, linear loss and radius) and light injection conditions (input power, wavelength detuning) on the characteristics of SP (modulation depth and oscillating frequency) are analyzed and discussed. It is shown that, SP occurs only if the carrier lifetime ranges from several ps to several-hundred ps and the input light intensity is higher than 10⁶W/cm². The modulation depth of SP can be as large as 8dB and the associated oscillating frequency is in the range from several GHz to beyond 10 GHz.

Bistability and self-pulsation phenomena in silicon microring resonators based on nonlinear optical effects

Study on inverse taper based mode transformer for low loss coupling between silicon wire waveguide and lensed fiber

Low power 2 × 2 thermo-optic SOI waveguide switch fabricated by anisotropy chemical etching

Optical bistability (BI) and self-pulsation (SP) in high-$Q$ silicon microring resonators (MRRs) induced by thermo-optical (TO) effect and other nonlinear effects are theoretically studied with coupled mode theory and linear stability analysis method. It is found that the boundaries for both BI and SP are mainly restricted by two counteracting effects: free carrier dispersion effect and TO effect. If the refractive index changes of a MRR caused by these two effects are on the same order of magnitude, the output power will exhibit much more complicated dependence on the input power and wavelength, namely, input-power-dependent multi-BI and multi-SP regions will exist at certain input wavelength range. The controllability of multi-BI and multi-SP phenomena by the input power and input wavelength could be very useful in all-optical nonlinear devices.

Multibistability and self-pulsation in nonlinear high- Q silicon microring resonators considering thermo-optical effect

Optical bistability and self-pulsation (SP) in silicon microring resonators (MRRs) are experimentally observed. The waveforms and frequencies of SP can be controlled by changing input light power and its wavelength, and the region of SP can be modulated readily by applying a reverse voltage on the PN junction embedded in the MRR. These phenomena are theoretically studied by adopting the coupled-mode theory and linear stability analysis method for differential equations, with theoretical results fitting well with the experimental ones.

Shaowu Chen

Papers

Bistability and self-pulsation phenomena in silicon microring resonators based on nonlinear optical effects

Study on inverse taper based mode transformer for low loss coupling between silicon wire waveguide and lensed fiber

Low power 2 × 2 thermo-optic SOI waveguide switch fabricated by anisotropy chemical etching

Multibistability and self-pulsation in nonlinear high- Q silicon microring resonators considering thermo-optical effect

Experimental observations of thermo-optical bistability and self-pulsation in silicon microring resonators