Multi-directional controllable electro-optical switch based on grating coupler

Abstract

In this paper, based on a lithium niobate thin film (LNTF) photonic integration platform, addressing the difficulties of high microwave loss and restricted optical signal transmission direction in traditional electro-optic modulators, a multi-directional controllable electro-optical switch structure based on a grating coupler is proposed and designed. By cascading three directional couplers and a grating-assisted contra-directional coupler (GACDC), and combining the low-loss transmission characteristics of tapered waveguide and bent waveguide, a multi-directional controllable optical switch is constructed to support forward and reverse transmission of optical signals. Due to the problem of metal absorption and high microwave loss induced by tiny electrode gaps in LNTF electro-optic modulators, traveling wave electrodes with micro-structures were designed to overcome this limitation. Simulation verification with the input of TE₀ mode light with a wavelength of 1550 nm shows that the coupling efficiencies of the output ports (Port₆, Port₉, Port₁₁, and Port₁₂) reach 0.828, 0.830, 0.748, and 0.750, corresponding to insertion losses of 0.82 dB, 0.81 dB, 1.26 dB, and 1.25 dB, respectively. The insertion loss of the GACDC within the device is only 0.56 dB, and the inverse crosstalk is as low as −21 dB; the transmission response of the TE₀ polarization mode is higher than −1.3 dB at the download port in the wavelength range from 1548 to 1553 nm. The flexible output of optical signals from different ports is realized by dynamically modulating the optical signal paths through electrode groups. This study provides a low-loss, multi-directional controllable solution for high-density photonic integrated circuits.