Design And Optimization Of The Dual-wavelength Optical Isolator Based On Nonreciprocal Phase Shift

Since human society goes into optical information age, photoelectric information system acquire higher integration, faster response speed and wider bandwidth, faster response speed and wider bandwidth. As a main future information carrier and processor of optical information system, all designed optical devices have to face a problem that is how to deal with the reflected light. Optical isolator which can allow light to transport in one direction while forbid reflected light to transport back is the key component of integrated optical system. However, it is adverse to the purpose of pursuing higher integration and wider bandwidth that the optical isolator only work on specific wavelength. In this article we are going to working on how to extend the bandwidth of optical isolator.The Faraday rotation coefficient and index of the magneto-optical materials strongly depend on the wavelength in the infrared range. By adjusting waveguide dispersion dependence of structure parameters to compensate the variation of Faraday rotation coefficient with wavelength, the wavelength-insensitive nonreciprocal phase shifter design can be realized. By referencing the theory of self-imaging effect of directional coupler and the theory of directional coupling, 2x1 multimode interference coupler, 2x2 multimode interference coupler and dualwavelength directional coupler can be designed, Which can achieve 3d B splitting at dualwavelength.Based on these components, we designed two different kinds of dual-wavelength optical isolator based on nonreciprocal phase shift. The first proposal isolator is constituted by 2x2 dual-wavelength multimode interference coupler, wavelength-insensitivity nonreciprocal phase shifter and 2x1 dual-wavelength multimode interference coupler. It shows that the insert loss of designed isolator is 0.30 d B, 0.27 d B, and its isolation is 55.44 d B, 54.95 d B at the wavelength of 1.55μm and 1.31μm respectively, simulated by Beam PROP software and optimization of the parameter of structure.The second one is constituted by dual-wavelength directional coupler, wavelengthinsensitivity nonreciprocal phase shifter and 2x1 dual-wavelength multimode interferenceWe go further to analyze the impact of the structure parameters of directional coupler and multimode interference coupler on the performance of the isolator. We summarize all the analysis and tell the proposed isolators have the advantages of high isolation, low insert loss and mass production.