Multimode-enabled silicon photonic delay lines: break the delay-density limit
Shihan Hong, Long Zhang, Jiachen Wu, Yingying Peng, Linyan Lyu, Yinpeng Hu, Yiwei Xie, Daoxin Dai
Abstract
Abstract Integrated optical delay lines have become imperative to meet the growing demand as large aperture antennas and high number of subarrays required for microwave beamforming, high-speed optical communication, and integrated quantum photonics. It is very challenging to achieve large delay ranges, small footprints, and broad bandwidths simultaneously due to the strong trade-off between the propagation loss and the group refractive index of optical waveguides. In this paper, we propose and experimentally demonstrate multimode-enabled silicon photonic delay line for the first time, which breaks the delay-density limit of singlemode waveguide spirals, towards a broadband, mm 2 -scale, and ultra-large time delay. By demonstrating low-loss-propagation possibilities for different polarizations and modes, we introduce a novel multimode delay unit by integrating the mode (de)multiplexers and the ultralow-loss multimode waveguide spiral supporting the TE 0 , TE 1 , and TE 2 modes propagating in parallel. The measured propagation losses for the TE 0 , TE 1 , and TE 2 modes are 0.2 dB/cm, 0.31 dB/cm, and 0.49 dB/cm, respectively. In this way, the highest line delay-density of 376.9 ps/cm and low delay loss of 0.004 dB/ps are achieved. Furthermore, we implement a 7-bit tunable multimode photonic delay line and experimentally demonstrate an ultra-large delay range of 12.7 ns with a delay resolution of 100 ps and within an ultra-compact footprint of 3.85 mm 2 , enabling a delay density over 3299 ps/mm 2 , showing the largest delay range and the highest delay density among on-chip delay lines reported to date, to the best of our knowledge.