Ring-Assisted Mach-Zehnder Interferometer Switch with Multiple Rings per Switch Element

Wavelength-selective switches have been proposed for datacenter use to enhance their scalability and to help in meeting ever-increasing traffic demands. We have previously demonstrated a 4 x 4 ring-based crossbar silicon photonic switch in which each cross-point contained three ring pairs to partition the free spectral range (FSR) into three equal regions to reduce wavelength tuning range per ring pair- thereby reducing both the tuning power consumption and stress on the rings-while maintaining full routing flexibility. However, the question of scalability remains for the crossbar switch in which 96 signal pads-routed to each ring-are required to fully control it. The pad count scales by 2M N-2 for an N x N switch with M ring pairs. In this paper we present a 4-port silicon photonic ring-assisted Mach-Zehnder interferometer (RAMZI) switch, fabricated in the AIM Photonics process, with multiple-sized rings per switching elements in a Benes network configuration to reduce the number of electrical pads required to 36 signal pads. The switch is 500 mu m x 3mm in size and is packaged on a custom PCB. In such a switch, the pad count scales by 2M(N log(2) N - N). Another advantage the RAMZI switch has over the crossbar switch is that the loss through the switch is not path-dependent due to its balanced path configuration. In the crossbar switch, the difference between the shortest and longest paths is 2(N - 1) switching elements.