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arXiv · 2304.11146

Second order add/drop filter with a single ring resonator

Matteo Cherchi·Fei Sun·Markku Kapulainen·Tapani Vehmas·Mikko Harjanne·Timo Aalto
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Abstract

We show theoretically and experimentally how a flat-top second-order response can be achieved with a self-coupled single add-drop ring resonator based on two couplers with different splitting ratios. The resulting device is a 1x1 filter, reflecting light back in the input waveguide at resonating wavelengths in the passbands, and transmitting light in the output waveguide at all other non-resonating wavelengths. Different implementations of the filter have been designed and fabricated on a micron-scale silicon photonics platform. They are based on compact Euler bends - either U-bends or L-bends - and Multi-Mode Interferometers as splitters for the ring resonators. Different finesse values have been achieved by using either 50:50 MMIs in conjunction with 85:15 MMIs or 85:15 MMIs in conjunction with 95:05 double MMIs. Unlike ordinary lowest order directional couplers, the MMIs couple most of the power in the cross-port which make them particularly suitable for the topology of the self-coupled ring, which would otherwise require a waveguide crossing. Experimental results are presented, showing good agreement with simulations. The proposed devices can find applications as wavelength-selective reflectors for relatively broad-band lasers or used as 2x2 add-drop filters when two exact replicas of the device are placed on the arms of a Mach-Zehnder interferometer.

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Matteo Cherchi, Fei Sun, Markku Kapulainen, Tapani Vehmas, Mikko Harjanne, Timo Aalto. 2023-04-21. Second order add/drop filter with a single ring resonator. https://doi.org/10.1117/12.2252146

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