Abstract

We demonstrate a broadband $2\times 2$ 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 $\sim 22\mathrm{mm}$, exhibits an $\sim 85\mathrm{nm}$ bandwidth for an extinction ratio (ER) higher than 15 dB and a maximum ER of $\sim 35\mathrm{dB}$ 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.

© 2017 Optical Society of America

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