Implementation of on-chip multi-channel focusing wavelength demultiplexer with regularized digital metamaterials

Adiabatic waveguide taper and on-chip wavelength demultiplexer are the key components of photonic integrated circuits. However, these two kinds of devices which were designed by the traditional semi-analytic methods or the brute-force search methods usually have large size. Here, based on the regularized digital metamaterials, a two-channel focused wavelength demultiplexer with a footprint of 2.4 x 10 mu m(2) has been proposed. The designed demultiplexer can directly connect to a grating coupler under the absence of a long adiabatic waveguide taper. The objective first method and the modified steepest descent method are used to design the demultiplexer which splits 1520 nm and 1580 nm light. Experimental results show that the insertion loss of the upper (lower) channel of the demultiplexer is -1.77 dB (-2.10 dB) and the crosstalk is -25.17 dB (-12.14 dB). Besides, the simulation results indicate that the fabrication tolerance of the device can reach +/- 20 nm in etching depth and +/- 10 nm in plane size changing. Benefitted from the extensibility of the design method, other types of ultra-compact focused devices, like mode splitters, mode converters, and power splitters can also be designed. Most importantly, this design method can be used to design devices with more complicated functionalities, such as multi-channel focused wavelength demultiplexers.