Broadband 2 x 2 lithium niobate electro-optic switch based on a Mach-Zehnder interferometer with counter-tapered directional couplers

摘要

We demonstrate a broadband 2 x 2 electro-optic switch based on a Mach-Zehnder interferometer with counter-tapered directional couplers (DCs). The counter-tapered DC is introduced here to replace the conventional one formed with uniform waveguides so that a splitting ratio of 50%: 50% is much easier to be realized over a wide wavelength range and, hence, increase bandwidth of the switch. The proposed switch is fabricated with x-cut lithium niobate by the annealed proton exchange process. A comparison of several experimental devices, fabricated on the same chip with the conventional and different counter-tapered DCs, respectively, confirms the increase of the bandwidth and the improvement of the fabrication tolerance by using the counter-tapered DC. Our fabricated best device, which has a length of similar to 22 mm, exhibits an similar to 85 nm bandwidth for an extinction ratio (ER) higher than 15 dB and a maximum ER of similar to 35 dB at 1563 nm at a driving voltage of 6.0 V. The insertion losses are less than 8.5 dB for all channels. Our proposed optical switch could find applications in wavelength-division-multiplexing optical communication systems. (C) 2017 Optical Society of America