Neetesh Singh, Ph.D. student (left), and Darren Hudson, project leader. Credit: CUDOS
Scientists from CUDOS’ University of Sydney node (Australia) have designed and demonstrated a small-footprint silicon photonics platform capable of mid-infrared (IR) supercontinuum generation from 2 to 6 µm (Optica, doi: 10.1364/OPTICA.2.000797). The study’s authors say that the platform, which includes low-loss dispersion-engineered silicon-on-sapphire (SOS) nanowires, could someday enable highly sensitive on-chip detection of molecules that are important for health, security screening and environmental sensing.
Silicon is well-known as a platform material for linear and nonlinear integrated photonics, including applications in the telecom window of about 1.5 µm. But expanding the platform’s use into the mid-IR range would open up a new set of applications for spectroscopy, chemical and biological sensing and free-space communications. Previous efforts to create mid-IR silicon-based sensors have been limited to a wavelength range of less than 4 µm because of absorption in the platform’s cladding layer. Non-silicon platforms for generating mid-IR often don’t produce the brightness needed to work effectively as detectors.
Lead authors Neetesh Singh and Darren Hudson and their colleagues used the SOS platform—which was also developed at CUDOS—to demonstrate octave-spanning supercontinuum generation with a continuous spectral range. For this, they used a 1.6-cm-long suspended nanowire with a coupled peak power of 1 kW at 4 µm, with a 320-fs pulse. They minimized propagation loss on the nanowires by chemically reducing surface roughness and improved mode confinement by using a (relatively) wide nanowire.
With further improvements, the SOS platform design may allow scientists to exploit the long wavelength (5 to 6 µm) dispersive wave. And based on theoretical calculations by the CUDOS team, spectral generation beyond 8 µm is possible. In a press release, Singh adds: “The SOS platform now appears to be a promising path forward for integration of electronic and mid-IR photonics on a single device.”
