Broadband all-optical isolator based on all-passive graded index

We propose an all optical isolator based on a passive nonlinear graded refractive index. The proposed optical isolator is fully passive and also cavity-less based structure which causes the suggested isolator to operate in a wide frequency rang. The transmission contrast between the forward and backward directions is 81.9 dB and also the transmission intensity is large at the desirable ports. Moreover, the proposed isolator can simultaneously support two incident ports without altering the structure in the forward direction and works as a 2 × 1 optical isolator. Furthermore, the graded waveguide can be easily realized and fabricated by GaAs-based waveguide in the infrared optical frequency regime.