Research On Polarization-independent Silicon-based Mach-Zehnder Electro-optic Modulato

The emergence of 5G,cloud computing,and edge computing in the era of big data has doubled the demand for data traffic.Optical interconnection gradually replaces electrical interconnection for the transmission of information and data.The silicon-based optical interconnection system is an important part of the optical communication network for a long time.Due to the CMOS compatibility,silicon photonic devices attract a lot of attention for its low cost,low power consumption,and strong optical confinement.The silicon-based electro-optical modulator is one of the core optoelectronic devices of the silicon-based optical interconnection system,and it plays an important role in high-speed electro-optical conversion and data transmission.This paper studies the polarization-independent Mach-Zehnder electro-optic modulator based on two-dimensional grating couplers.The purpose of the research is to obtain polarization-independent electro-optic modulator with low insertion loss,high modulation speed.The main contents of this paper are as follows:（1）The two-dimensional apodized grating coupler for complete vertical coupling was studied,and the device was designed and optimized using 3D FDTD.The apodized grating structure greatly improves the coupling efficiency and reduces the parasitic reflection.The experimental results show that the 1 d B bandwidth was 42nm,and the coupling loss was-3.1 d B.The coupler exhibits nearly perfect polarization-independent performance,and the measured PDL in the wavelength range of 1500 nm-1600 nm was less than 0.2 d B.Finally,by analyzing the change in device performance with the change of fiber position and tilting angle,we comprehensively studied the fiber misalignment tolerance of the grating coupler,the additional coupling caused by the fiber misalignment of±2μm and the fiber angle error of±2°The loss was lower than 0.95 d B and 1 d B respectively,and the PDL caused by these two cases was 0.8 d B and 0.55 d B respectively in the worst case.（2）We propose a polarization-independent silicon-based electro-optic modulator structure based on two-dimensional grating couplers.Two devices for single-arm modulation and push-pull modulation with balanced arms are designed and simulated,and 80 Gb/s and 90 Gb/s with OOK modulation are achieved respectively.With a phase shifter length of 2500μm,the extinction ratio of 5.5 d B and 7 d B are obtained.The insertion loss is about-5.2 d B,the modulation efficiency is 2.16 V·cm,and the 3d B electro-optic bandwidth is 24 GHz and 32 GHz.Due to the balanced arms,the optical bandwidth is approximately 25 nm.We also design a polarization-independent electro-optical modulator with unbalanced arm structure（100μm arm length difference）.The T-shaped traveling wave electrode is used for push-pull modulation.With working wavelength of 1555.55 nm,the input optical power of 7 d Bm,and the peak-to-peak voltage V_pp of 6 V,OOK modulation of 100 Gb/s rate and PAM4modulation of 60 Gbaud/s are achieved for a device with 1.5 mm phase shifter length.The extinction ratio is 9.7 d B and 4.22 d B for OOK and PAM4 modulation respectively.Insertion loss of the modulator is only-4.82 d B,while the electro-optical3 d B bandwidth exceeds 40 GHz.