Static Simulations Of Optical Phased Arrays With Function Spacing Distribution

On-chip OPAs have a wide range of applications in the fields of LIDAR,holographic video displays,free-space communication,and image projection.By using SOI platform with CMOS technology,such an integrated system can be easy to implement.However,when it comes to the uniform array capable of wide-range beam steering,the inter-element spacing should be less than half of the operation wavelength to avoid the grating lobes.As a result,there is strong coupling between adjacent waveguides,which distorts the far field patterns.Placing the waveguide positions irregularly is one of the solutions to relax the half-wavelength separation requirement,while allowing narrow FWHM and low grating lobes,at the cost of increasing the side lobe intensities.Moreover,OPAs with lower number of elements can simplify the control and circuitry,which are built easily and at lower cost.Nonetheless,the lateral array sizes generally decrease when the counts of the waveguides are lower,along with that the FWHMs increase and hence the precisions decrease.In this paper,in order to obtain a comparative FWHM with fewer elements,we have put forward a design methodology based on SOI platform.In the output array,the spacings are very large to make up for the lower waveguide count and prevent the strong coupling.Besides,they are in function distribution to suppress the grating lobes and further compress the main lobe.The main content of the thesis includes:(1)Describe the far-field characteristics and side-lobe improvement methods of the ideal OPA.Review of beam analysis method derived from BPM and their scopes of application.Use the theory of ray optics and wave optics to deduce the propagation characteristics of the slab waveguide and explain the coupling phenomenon.(2)Using the improved EIM to reduce the dimension of waveguide structure,we simulate the single-mode waveguide,MMI coupler and S shaped waveguide respectively.Then,the corresponding structures are designed.(3)The discrete components are combined into a 1×8 OPA on the SOI platform.Based on the symmetric and asymmetric structures,the direct and indirect determinationmethods are used to arrange the waveguide locations.Then,the far field patterns are simulated respectively.The side lobe suppression ratio can reach at least 18.90% under the limited FWHM condition.(4)Using the 1×16 OPA structure,the cosine function is taken as an example.Starting from the most common function expression,the influence of different key parameters on the performance of the far field is studied.Moreover,the side lobe suppression ratio of 17.82% and the FWHM of 0.81o can be obtained at the same time.