机械工程助力半导体纤维光子学

Glass optical fibres have had a tremendous impact on modern society,not only changing the way we communicate and share information on a global scale,but also how we sense,monitor,and manufacture using light-based technologies.Predominantly fashioned from silica glass,commercial optical fibres owe their ubiquity to decades of efforts in optimizing the fabrication techniques to minimize transmission losses,principally within the telecommunications wavelength bands[1].However,the intrinsic properties of silica glass,such as its transmission window,nonlinear coefficients,and the absence of electronic functionality,have limited the use of these fibres in some applications.Thus,alongside these efforts,fibre fabrication teams have continued to explore alternative material systems that can help to lift some of these limitations and extend the reach of optical fibres and their applications.

Raman amplification at 2.2μm in silicon core fibers with prospects for extended mid-infrared source generation

Raman scattering provides a convenient mechanism to generate or amplify light at wavelengths where gain is not otherwise available.When combined with recent advancements in high-power fiber lasers that operate at wavelengths~2μm,great opportunities exist for Raman systems that extend operation further into the mid-infrared regime for applications such as gas sensing,spectroscopy,and biomedical analyses.Here,a thulium-doped fiber laser is used to demonstrate Raman emission and amplification from a highly nonlinear silicon core fiber(SCF)platform at wavelengths beyond 2μm.The SCF has been tapered to obtain a micrometer-sized core diameter(~1.6μm)over a length of 6 cm,with losses as low as 0.2 dB cm^(−1).A maximum on-off peak gain of 30.4 dB was obtained using 10 W of peak pump power at 1.99μm,with simulations indicating that the gain could be increased to up to~50 dB by extending the SCF length.Simulations also show that by exploiting the large Raman gain and extended mid-infrared transparency of the SCF,cascaded Raman processes could yield tunable systems with practical output powers across the 2–5μm range.

Post-fabrication phase trimming of Mach–Zehnder interferometers by laser annealing of germanium implanted waveguides

We demonstrate a novel high-accuracy post-fabrication trimming technique to fine-tune the phase of integrated Mach–Zehnder interferometers, enabling permanent correction of typical fabrication-based phase errors. The effective index change of the optical mode is 0.19 in our measurement, which is approximately an order of magnitude improvement compared to previous work with similar excess optical loss. Our measurement results suggest that a phase accuracy of 0.078 rad was achievable with active feedback control.

Hot-wire chemical vapor deposition low-loss hydrogenated amorphous silicon waveguides for silicon photonic devices

We demonstrate low-loss hydrogenated amorphous silicon(a-Si:H) waveguides by hot-wire chemical vapor deposition(HWCVD). The effect of hydrogenation in a-Si at different deposition temperatures has been investigated and analyzed by Raman spectroscopy. We obtained an optical quality a-Si:H waveguide deposited at 230°C that has a strong Raman peak shift at 480 cm^(-1), peak width(full width at half-maximum) of 68.9 cm^(-1), and bond angle deviation of 8.98°. Optical transmission measurement shows a low propagation loss of 0.8 dB/cm at the1550 nm wavelength, which is the first, to our knowledge, report for a HWCVD a-Si:H waveguide.

Low-loss silicon core fibre platform for mid-infrared nonlinear photonics

Broadband mid-infrared light sources are highly desired for wide-ranging applications that span free-space communications to spectroscopy.In recent years,silicon has attracted great interest as a platform for nonlinear optical wavelength conversion in this region,owing to its low losses(linear and nonlinear)and high stability.However,most research in this area has made use of small core waveguides fabricated from silicon-on-insulator platforms,which suffer from high absorption losses of the use of silica cladding,limiting their ability to generate light beyond 3μm.Here,we design and demonstrate a compact silicon core,silica-clad waveguide platform that has low losses across the entire silicon transparency window.The waveguides are fabricated from a silicon core fibre that is tapered to engineer mode properties to ensure efficient nonlinear propagation in the core with minimal interaction of the mid-infrared light with the cladding.These waveguides exhibit many of the benefits of fibre platforms,such as a high coupling efficiency and power handling capability,allowing for the generation of mid-infrared supercontinuum spectra with high brightness and coherence spanning almost two octaves(1.6-5.3μm).