Investigation Of Optical Bistability Based On Silicon Photonic Crystal

Photonic technologies allowing us to deliver large amounts of data at high speed has play a great role in high-speed information transmission and promoting the capacity of the information. Silicon photonic devices are expected to replace the traditional electronic circuit as a result of all-optical operation capable of eliminating power consumption of optical-electrical or electrical-optical conversion at network nodes. Optical nonlinear effect is an effective way to realize all-optical operation, and optical bistability is the versatile foundations for all-optical logic operation and all-optical signal processing. Now Silicon integrated devices towards to the high integration, and photonic crystal are providing convenience as a result of its photonic band structure capable of controlling photonics in micro-scale. Photonic crystal cavity showing strong confinement of light in a tiny region can dramatically enhance light-matter interaction, and the enhanced nonlinear effects in the cavity can decrease the threshold power of the optical bistablity. In this paper, we have done some research on the photonic crystal cavity and its application in optical bistable devices. The results can be summed up in the following aspects:(1) High quality factor(Q) of L3 cavity and H0 cavity are obtained by optimizing the air holes adjacent to the cavity. We have done much work on the silicon photonic crystal device and successfully fabricated the asymmetric-coupled L3 cavity with a high Q of 42360 and the side-coupled H0 cavity with a high Q of 105000.(2) Optical bistability with low threshold of 36.3 μW and large switching contrast of 15 dB in a direct-coupled L3 cavity is realized. The optical bistability generated in the cavity results in the asymmetric shape of the transmission spectrum and the hysteresis curve. The saturable absorption is observed when the input power is a few hundreds of microwatts. Multiple optical nonlinear processes in silicon are employed to analyze the nonlinear behaviors of the cavity and a nonlinear coupled-mode model is accordingly established. The calculated results are in good agreement with the experiment.(3) Optical bistability with an ultralow threshold of 7.8 μW is observed in a side-coupled H0 cavity with a high Q 105000. The redshift of the wavelength and the hysteresis curve are also observed.(4) An asymmetric direct-coupled L3 cavity-waveguide structure are proposed and fabricated. Applying a single step lithography and successive etching, the device can realize optical nonreciprocal transmission in an individual cavity, alleviating the requirement to accurately control the resonance of the cavities. A maximum nonreciprocal transmission ratio(NTR) of 21.1 dB as well as a working bandwidth of 280 pm in the telecommunication band are obtained at a low input power of 76.7 μW. The nonlinear-effect based nonreciprocal device being not a genuine isolator due to limitations of the dynamic reciprocity is experimentally demonstrated firstly.High light of our works can be listed as follows:(1) Large switching contrast of optical bistability is realized and the saturable absorption is observed in a L3 cavity;(2) Ultralow threshold of optical bistable-switching power is observed in a side-coupled H0 cavity;(3) An asymmetric direct-coupled L3 cavity-waveguide structure are proposed,and optical nonreciprocal transmission is first realized in an individual cavity;(4) The nonlinear-effect based nonreciprocal device being not a genuine isolator due to limitations of the dynamic reciprocity is experimentally demonstrated firstly.