Libin Zhang

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

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 MRRs 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.

High Efficiency Broadband Polarization Converter Based on Tapered Slot Waveguide

A novel high efficiency broadband polarization converter based on an adiabatic tapered vertical slot waveguide is proposed and analyzed. Unlike previously reported tapered polarization converters, this device converts the first-order TM/TE mode into the first-order TE/TM mode. The structure utilizes a vertical slot waveguide, which only needs a one-mask etching process. The bandwidth is ultrawide, ~100 nm (1500-1600 nm) with a conversion efficiency of > 98%. The total length of the polarization converter is 116 μm, and its minimum fabrication tolerance is acceptable for modern nanofabrication technology.

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

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.

Ultra-compact and fabrication-tolerant polarization rotator based on a bend asymmetric-slab waveguide

We propose and analyze a polarization rotator based on a bend asymmetric-slab waveguide on the silicon-on-insulator platform. The device can be fabricated using standard complementary metal-oxide-semiconductor process involving only two dry etching steps. Compared with the formerly reported polarization rotators based on two-step etching, our introduced device demonstrates a significant improvement for fabrication tolerance. Furthermore, an ultra compact structure of ~5 μm conversion length, an insertion loss of only 0.5 dB, and an extinction ratio of >40 dB for both TE to TM polarization conversion and TM to TE polarization conversion are exhibited. Operation wavelength and the influence of environmental temperature on our device are also discussed.

Design and analysis of polarization splitter based on a horizontal slotted waveguide

We theoretically analyze the effective indices of a horizontal slotted waveguide on SOI platform. Based on the analysis, both polarization independent and strongly birefringent waveguides can be constructed in our proposed waveguide geometry. Utilizing the strongly birefringent waveguide, an ultra-compact polarization splitter based on a directional coupler (DC) was proposed and subsequently optimized by 3D-beam propagation method. The simulation results suggest that the coupling length of the DC could be less than 18 μm, and the maximum polarization crosstalk less than −47 and −37  dB for the cross and bar ports, respectively. Around the 1550 nm operating wavelength, a bandwidth of 30 nm is obtained for the crosstalk less than −20  dB. Finally, the tolerance of the splitter is discussed.