Study On Polarization-insensitive Power Splitter/Polarization Rotator Assisted By Subwavelength Gratings

The creation of transistors gave birth to the development of integrated circuits,and human society thus entered the era of microelectronics.The smaller the size of the transistors,the higher their integration and performance.However,the development of integrated circuits has also encountered a bottleneck.The larger the number of integrated silicon circuits per unit space,the greater the amount of heat it generates;at the same time,when the integrated circuit reaches the level of 2 ? 3 nm,the uncertainty of the quantum will limit the behavior of the electrons,which will cause the performance of the transistor to become unstable.Here,the photonic technology with light as the carrier has become an important boost for the development of information technology.Like microelectronic integrated circuits,photonic technology is also aimed at realizing integrated optical circuits.Silicon-based photonics can be compatible with existing mature CMOS manufacturing processes.At the same time,due to the high refractive index difference formed by the silicon core and the silicon dioxide or air cladding layer,the optical signal can be limited to a smaller silicon core.As a result,it is possible to miniaturize silicon-based functional devices and achieve high-density integration on optical chips.Therefore,silicon-based photonics has become an important direction for the development of photonics technology.However,due to the very high refractive index difference between the silicon core and the cladding,SOI optical devices are usually very sensitive to the polarization state of the optical signal,and optical signals with different polarization states may have completely different transmission characteristics in the device.Therefore,it is very important to design photonic devices that are insensitive to polarization or design photonic devices that can control the polarization state of optical signals.This thesis mainly introduces the designed polarization-insensitive power splitter and polarization rotator,with the help of sub-wavelength gratings to realize compact broadband functional equipment.This thesis first introduces the optical properties of silicon-based subwavelength grating structures.When the diffraction effect and reflection effect of the sub-wavelength grating junction are suppressed,it can be equivalent to an anisotropic homogeneous medium.By changing the duty cycle or tilt angle of the sub-wavelength grating,its optical characteristics can be easily changed.In this thesis,we design and optimize the device by introducing a sub-wavelength grating structure.Secondly,the designed polarization-insensitive optical power beam splitter is introduced.By introducing the sub-wavelength grating structure,the coupling intensity of TE and TM mode light in the three-waveguide coupling system is close,so the signal light of the two polarization modes can realize the 3-dB separation function.Theoretical simulation shows that the polarization-insensitive power splitter has an insertion loss of less than 0.9 dB and a reflection loss of less than-30 dB in the operating wavelength range of 1440?1700 nm,and the splitting ratio remains between 0.997 and 1.003.Finally,this thesis introduces the designed compact broadband polarization rotator,which effectively expands the working bandwidth of the device by introducing a subwavelength grating structure on the stepped waveguide.In the wavelength range of1260?1740 nm,the insertion loss of the polarization rotator is less than 0.9 dB,the polarization extinction ratio is greater than 20 dB,and the polarization conversion rate is greater than 0.99.