Design of a 16-channels 2×2 hybrid type wavelength selective crossconnect utilizing a silicon optical switch array

The wavelength selective crossconnect (WXC) is a key component of the reconfigurable optical add/drop multiplexer (ROADM). Waveguide type WXC is difficult to increase the number of ports and channels, and free-space type WXC has a low switching speed of milliseconds. To solve these problems, we have proposed a hybrid type WXC. It has microsecond switching speed, where switching is performed by silicon optical circuit and wavelength division (de)multiplexing is performed by free-space optical system. In this paper, we designed the free-space optics and simulated the transmission spectra of a 16-channel 2×2 hybrid-type WXC using CodeV optical simulator. The thickness and the position of the microlens array to be attached to the silicon optical circuit has been designed. The angle of incidence on the grating coupler was 9 degrees, and the thickness of the lens was 0.53 mm. The center of the microlens array was offset by 60.1 μm from the center of the grating coupler. The distance between the lenses in the free-space optics was optimized for the x-z and y-z planes, respectively. The loss spectra with the light emitted from the grating coupler were simulated for each of the 16 channels. The loss at the center frequency of each channel varies from -0.89 dB to -2.87 dB. The loss can be reduced by optimizing the grating coupler design to be -0.89 dB to -0.91 dB.