INTEGRATED OPTICAL BUFFER

Opt. Express, 27, 11585 (2019)

Trapping light in a photonic integrated circuit can find many applications, such as optical storage, optical-packet switching, optical sensing and microwave photonics. Although there are many ways to implement an integrated optical buffer, such as the use of ring resonators, photonic crystals, Bragg gratings and spiral waveguides, it is still challenging to realize optical buffers with long storage time and low loss. Photonic integrated circuits with small size are of interest for implementing optical buffers. In general, three materials systems are employed to implement integrated optical buffers, silicon, silicon nitride and indium phosphide. However, it is hard to implement optical buffers with a storage time over tens of nanoseconds due to the intrinsic high loss of these materials.

Recently, a low-loss integrated optical buffer based on silica that can offer a long storage time has been proposed and demonstrated by a team led by Dr. Ming Li from the Institute of Semiconductors, CAS. They built an integrated optical buffer based on silica. By connecting four spiral waveguide delay lines with five thermo-optic switches, tunable time delay was achieved. By optimizing the fabrication process and introducing offsets between straight and bending waveguides, the transmission loss of the silica buffer was reduced to 1.08 dB/m. Given that the group refractive index of silica is around 1.46 and the total length of the delay lines in their fabricated chip is about 20 m, the maximum storage time is 100 ns. Moreover, a 10-ns step was accomplished in their experiment by the various combinations of four stair-like delay lines: 10, 20, 30, 40 ns. Their work may provide a valuable reference for fabricating more advanced optical buffers and might have significant impact on signals processing in optical communications networks and microwave photonics systems.

Jianping Yao (University of Ottawa, Ottawa, Canada)

doi: 10.1088/1674-4926/40/5/050205