Design And Research Of Integrated Optical ADC Device

The function of Analog-to-Digital Convertor?ADC?is to convert analog signals into digital signals,which is a bridge between analog world and digital world.It is one of the important technical cornerstones in the digital era.It plays an extremely important role in military and civil fields.With the increasing demand for data services,the time jitter of electric ADC and the blurring of comparator,optical ADC has been proposed and widely concerned for it can overcome the obstacles brought by electronic bottleneck and realize the advantages of on-chip integration of optical path.According to the current reports,the integrated optical ADC is still in the stage of continuous improvement of key components.In the process of design and implementation of unit devices,especially in the process of testing,grating couplers used to couple unit devices and test optical fibers play an important role.For different testing requirements,grating couplers with different characteristics need to be designed and perfected to the component library,which is of great significance to the practical application of optical ADC.In view of this,this paper focuses on silicon-based grating couplers.The main contents of this paper are as follows.1.A toe-cutting grating coupler structure is proposed to increase the coupling efficiency of grating coupler.By designing the duty cycle of the grating coupler,the effective refractive index of the grating coupler changes in the form of toe-cutting,which makes the output light field changes from exponential form to near-Gaussian form,reduces the coupling loss between the grating coupler and the optical fiber due to the mode mismatch,and then increases the coupling efficiency.On the premise of satisfying MPW process,through 2D FDTD simulation,the unexposed part of the gratingk1,the increment of the unexposed part?,the period number n and the position of the fiber are optimized respectively.Finally,the coupler with k₁=180 nm,=10 nm,n=12 is obtained.The coupling loss is reduced from-2.8 dB of the ordinary grating coupler to-2.71 dB.2.A chirped grating coupler structure is proposed to increase the bandwidth of the grating coupler.The period of grating coupler is chirped by designing.If each small period is regarded as an independent unit,then for each small period,they have their own central wavelength,and the transmission spectrum of the chirped grating coupler composed of the envelope of the transmission spectrum of these small periods will be broadened,that is,the working bandwidth will be increased.On the premise of satisfying MPW process,the initial period A0 and chirp value?c of chirped grating coupler are optimized by 2D FDTD simulation.Finally,two groups of better 2D results are obtained?compared with the conventional standard grating,the 1dB bandwidth is 47 nm and the 3dB bandwidth is 81 nm?,one of which has A0 of 605 nm,?c of 8 nm,1 dB/3 dB bandwidth of 64/123 nm,and coupling efficiency of-4.01 dB;While the other has ?0 of 605 nm ?c of 12 nm,1 dB/3 dB bandwidth of 78/130 nm,and coupling efficiency of-5.05 dB.Different chirped grating couplers can be selected according to different actual conditions.3.Fabrication and test of grating coupler.The toe-cutting grating coupler and chirped grating coupler are validated and optimized by using 3D FDTD.Finally,the coupling loss of the toe-cutting grating coupler is reduced from-4.14dB to-3.3dB.Compared with the standard grating coupler,the bandwidth of the chirped grating coupler is increased by 26 nm in 1dB and 50 nm in 3dB.On the premise of satisfying MPW,the 3D simulation structure is deduced and plotted,and sent to the factory for processing.Finally,the standard grating coupler is tested using the vertical coupling platform of the laboratory.