Broad-band optical parametric gain on a silicon photonic chip

TLDR: Net on/off gain over a wavelength range of 28 nm is demonstrated through the optical process of phase-matched four-wave mixing in suitably designed SOI channel waveguides, allowing for the implementation of dense wavelength division multiplexing in an all-silicon photonic integrated circuit.

Abstract: The development of silicon-compatible optical components that simultaneously amplify and process a broad range of wavelength channels is critical for future data communication technology based on photonic chips. Until now, such devices have only been able to amplify a single wavelength channel. Now, using nanoscale silicon waveguides designed for the purpose, Foster et al. have achieved broadband amplification. The key is the exploitation of a nonlinear optical effect known as four-wave mixing. This process can also be used for other all-optical functions previously only possible in extended lengths of optical fibre. Phase-matched four-wave mixing can take place with high efficiency in a suitably designed silicon waveguide — this advance could allow for the implementation of dense wavelength channels for optical processing in an all-silicon photonic chip. Developing an optical amplifier on silicon is essential for the success of silicon-on-insulator (SOI) photonic integrated circuits. Recently, optical gain with a 1-nm bandwidth was demonstrated using the Raman effect1,2,3,4,5,6,7,8,9, which led to the demonstration of a Raman oscillator10,11, lossless optical modulation12 and optically tunable slow light13. A key strength of optical communications is the parallelism of information transfer and processing onto multiple wavelength channels. However, the relatively narrow Raman gain bandwidth only allows for amplification or generation of a single wavelength channel. If broad gain bandwidths were to be demonstrated on silicon, then an array of wavelength channels could be generated and processed, representing a critical advance for densely integrated photonic circuits. Here we demonstrate net on/off gain over a wavelength range of 28 nm through the optical process of phase-matched four-wave mixing in suitably designed SOI channel waveguides. We also demonstrate wavelength conversion in the range 1,511–1,591 nm with peak conversion efficiencies of +5.2 dB, which represents more than 20 times improvement on previous four-wave-mixing efficiencies in SOI waveguides14,15,16,17. These advances allow for the implementation of dense wavelength division multiplexing in an all-silicon photonic integrated circuit. Additionally, all-optical delays18, all-optical switches19, optical signal regenerators20 and optical sources for quantum information technology21, all demonstrated using four-wave mixing in silica fibres, can now be transferred to the SOI platform.