Spatial and polarization division multiplexing harnessing on-chip optical beam forming

TL;DR

This paper introduces a novel on-chip spatial and polarization multiplexing method using evanescent coupling between guided modes and free-propagating beams, significantly enhancing bandwidth and performance of integrated optical transceivers.

Contribution

It presents a new approach based on evanescent coupling for spatial and polarization multiplexing, demonstrating high-performance links with broad bandwidths using standard silicon photonics technology.

Findings

Achieved -35 dB crosstalk bandwidth of 180 nm for two-polarization link.

Demonstrated -20 dB crosstalk bandwidth of 195 nm for three-mode link.

Error-free transmission at 40 Gbps for multiple signals with minimal power penalties.

Abstract

On-chip spatial and polarization multiplexing have emerged as a powerful strategy to boost the bandwidth of integrated optical transceivers. State-of-the-art multiplexers require accurate control of the relative phase or the spatial distribution among different guided optical modes, seriously compromising the bandwidth and performance of the devices. To overcome this limitation, we propose a new approach based on the coupling between guided modes in integrated waveguides and optical beams free-propagating on the chip plane. The engineering of the evanescent coupling between the guided modes and free-propagating beams allows spatial and polarization multiplexing with state-of-the-art performance. To demonstrate the potential and versatility of this approach, we have developed a two-polarization multiplexed link and a three-mode multiplexed link using standard 220-nm-thick silicon-on-insulator technology. The two-polarization link shows a measured -35 dB crosstalk bandwidth of 180 nm, while the three-mode link exhibits a -20 dB crosstalk bandwidth of 195 nm. These bandwidths cover the S, C, L, and U communication bands. We used these links to demonstrate error-free transmission (bit-error-rate < 10-9) of two and three non-return-to-zero signals at 40 Gbps each, with power penalties below 0.08 dB and 1.5 dB for the two-polarization and three-mode links respectively. The approach demonstrated here for two polarizations and three modes is also applicable to future implementation of more complex multiplexing schemes.