Optical nonreciprocity with large bandwidth in asymmetric hybrid slot waveguide coupler

On-chip broadband optical nonreciprocal transmission based on asymmetric hybrid slot waveguide (HSW) coupler is proposed. Filled with flint glass LaSF-010 and organic material DDMEBT in slots, respectively, two branches of an asymmetric HSW coupler have very distinct nonlinear coefficients, yet very close effective indexes. Since asymmetric coupler with low linear mismatch has a large free spectral range, the results show that our device has a 10-dB nonreciprocal transmission bandwidth (NTB) as large as about 66 nm corresponding to 80-mW operating power. The NTB could be even larger when the incident power is raised. This indicates over two orders of magnitude enhancement compared to previous on-chip passive schemes. Owing to the large NTB, the device also functions properly for sub-picosecond pulses. Our scheme paves a path toward practical all-optical nonreciprocal applications.