Addressing the programming challenges of practical interferometric mesh based optical processors.

We demonstrate a novel mesh of Mach-Zehnder interferometers (MZIs) for programmable optical processors. We thoroughly analyze the benefits and drawbacks of previously known meshes and compare our newly proposed mesh with these prior architectures, highlighting its unique features and advantages. The proposed mesh, referred to as Bokun mesh, is an architecture that merges the attributes of the prior topologies Diamond and Clements. Similar to Diamond, Bokun provides diagonal paths passing through every individual MZI enabling direct phase monitoring. However, unlike Diamond and similar to Clements, Bokun maintains a minimum optical depth leading to better scalability. Providing the monitoring option, Bokun's programming is faster improving the total energy efficiency of the processor. The performance of Bokun mesh enabled by an optimal optical depth is also more resilient to the loss and fabrication imperfections compared to architectures with longer depth such as Reck and Diamond. Employing an efficient programming scheme, the proposed architecture improves energy efficiency by 83% maintaining the same computation accuracy for weight matrix changes at 2 kHz.

Broadband polarization/mode insensitive 3-dB optical coupler for silicon photonic switches.

In this work, we experimentally demonstrate a four-mode polarization/mode insensitive 3-dB coupler based on an adiabatic coupler. The proposed design works for the first two transverse electric (TE) modes and the first two transverse magnetic (TM) modes. Over an optical bandwidth of 70 nm (1500 nm to 1570 nm), the coupler exhibits at most 0.7 dB insertion loss with a maximum crosstalk of -15.7 dB and a power imbalance not worse than 0.9 dB. A multimode photonic switch matrix using this optical coupler is proposed simultaneously exploiting wavelength division multiplexing (WDM), polarization division multiplexing (PDM), and mode division multiplexing (MDM). Based on the coupler experimental measurements, the switching system loss is estimated to be 10.6 dB with crosstalk limited by the MDM (de)multiplexing circuit.