We review our recent results on integration of lasers, detectors and microfluidic channels on silicon and germanium based mid-infrared photonic circuits, as well as initial sensing experiments for medical and gas sensing applications. Wideband devices, such as waveguides, couplers, splitters and detectors are required for mid-IR absorption spectroscopy. We show that such Si and Ge devices can operate over large spectral bands.
Femtosecond laser writing offers low-cost and straightforward photonic circuit fabrication compared to planar cleanroom silicon photonics. Here, we propose a compact and robust laser-written methane gas sensor based on a Mach Zehnder interferometer (MZI) in silica. The MZI is to be written in a 1 x 1cm bulk fused silica substrate with the sensing arm adjacent to the glass surface to allow evanescent field interaction with its environment. The optimisation of a styrene acrylonitrile (SAN polymer, n=1.56) surface film is simulated and discussed. Offering enhanced evanescent field in the sensing arm and selectivity to methane. Demonstrations of fabrication of low-stress buildup multi-scan waveguides and directional couplers is presented. The cladding layer thickness is engineered to improve the evanescent field ratio (power in sensitized SAN region to the total mode power) in the sensing arm up to 15% from previously documented laser written MZI sensors, thus overcoming limitations imposed by the low laser-induced index. Surface waveguides are written adjacent to the surface of the sample, improving previously achieved surface proximity for high index waveguides. The proposed sensor will require one writing step, one spin-coating step and the waveguide is mode-matched well to integrate with SMF-28 fibre devices. The sensitive polymer layer could easily be developed for other analytes with sensitivities estimated to be as comparable to similar devices developed on a silicon nitride cleanroom.
A multi-port microcoil resonator magnetic field sensor based on a microfiber coupler coil resonator (MMCR) is presented. The microfiber coupler coil is fabricated by coiling a four-port microfiber coupler with a uniform waist region around a low index support rod. The MMCR is embedded in a low refractive index polymer to increase the robustness and operation stability. The enhanced sensor response to the magnetic field is ascribed to the diverse MMCR response to the light polarization state. The MMCR magnetic field sensor is compact and low cost, and exhibits a magnetic field sensitivity of 37.09 dB/T with an estimated minimum detection limit (DL) of ~ 27 μT.
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