Study On Polarization Beam Splitter And Thin Film Lithium Niobate Modulator In Optical ADC Chip

Analog-to-Digital Converter(ADC)is a tool that converts analog signals into digital signals.Although the research and development of electrical ADCs have reached maturity,they are limited by the aperture jitter of the sampling clock and the blur of the comparator,and its sampling rate is difficult to increase.The optical ADC can achieve a sampling rate of 100G/s by using optical pulse sampling and wavelength division/time division multiplexing technologies,which can effectively solve the above two major problems and improve the effective number of bits and bandwidth.As far as the current reports are concerned,the OADC chips that can be integrated are still at the stage of continuous improvement of key unit devices.In the key technology of OADC,polarization beam splitter and electro-optic modulator play an important role.For different testing and integration requirements,it is necessary to design a polarization beam splitter and an electro-optical modulator with smaller size and better performance,and perfect it to the device library.In view of this,the paper focuses on polarization beam splitter and electro-optic modulator.The main content of the paper is as follows:1.A new polarization beam splitter based on MMI is proposed,which can greatly reduce the length of the polarization beam splitter by adopting oblique incidence.Through simulation and optimization,the structural parameters of four groups of obliquely incident MMI polarizing beam splitters with better performance are obtained,and compared with the traditional MMI polarizing beam splitters of the same width.Through simulation optimization,two structural parameters with MMI width of 2.85?m and two structural parameters with MMI width of 2.97 ?m were obtained.Among them,when the polarization extinction ratio of the two structural parameters of 2.85?m is greater than 20dB,the operating bandwidth of the TM mode is 82nm and 80nm respectively,and the operating bandwidth of the TE mode is 3 1nm and 30nm;At this time,the operating bandwidth of TM mode is 108nm and 90nm respectively;the operating bandwidth of TE mode is 30nm and 50nm.The performance of the new MMI polarization beam splitter with four structural parameters is similar to that of the traditional MMI polarization beam splitter,but its size is reduced by 55.3%,50.8%,52%,and 55.6%respectively over the length of the traditional MMI polarization beam splitter.2.The optical properties of thin film lithium niobate electro-optic modulators based on two structures based on LNOI materials(SiN ridge waveguide type and LN ridge waveguide type)and two structures based on LN-SOI material(BCB type and SiO2 type)were studied..1)The limiting factor of the SiN ridge waveguide structure is 0.773 at the highest,and the transmission loss is 1.43dB/cm.The limit factor of the LN type structure is 0.803 at the highest,and the transmission loss is 5.59dB/cm.And the two structures are compared,considering the limiting factor and transmission loss comprehensively,the LN type structure is selected.2)The maximum coupling efficiency of the BCB type is 0.757,the limiting factor is 0.587,and the transmission loss is 4.2dB/cm.The maximum coupling efficiency of the SiO2 structure is 0.67,the limiting factor is 0.625,and the transmission loss is 5.27dB/cm.The two structures are compared,combining the limiting factor and transmission loss,and choosing the SiO2 structure.3)The optical characteristics of the LN-type structure and the SiO2-type structure are compared.The LN-type structure is selected by combining the limiting factor(coupling efficiency)and the manufacturing process.The LN-type electric domain structure is theoretically analyzed.The half-wave voltage of the LN-type lithium niobate thin film modulator can be less than 6V,and the higher the limiting factor,the smaller the half-wave voltage.On the other hand,the half-wave voltage and The modulation bandwidth has a mutually restrictive relationship.When the electrode length is increased from 4mm to 10mm,the half-wave voltage is reduced from 10V to 3V,but the 3dB bandwidth is also reduced from 50GHz to 28GHz.