We present the development of Ge-on-Si waveguide-based devices for low-noise mid-infrared absorption spectroscopy of aqueous solutions, targeting wavelengths between 6 and 10 μm, that are able to reduce the relative intensity noise which is a key roadblock when measuring tiny analyte absorptions masked by a large background matrix absorption. The sensor uses a pair of integrated thermo-optic switches to continuously switch light between a reference waveguide and a sensor waveguide, so that common noise components can be cancelled out, even when the light source and photodetector are not integrated on the same chip.
We review our recent results on modulators and detectors for the 2μm range, which may become very relevant for future communications, and on the development of mid-IR broadband devices for sensing applications. We show Mach-Zehnder and Michelson based modulators operating at data rates up to 25 Gb/s and Ge based detectors operating up to 12.5 Gb/s. For longer wavelengths relevant for sensing applications, we present broadband waveguides and splitters, waveguide integrated bolometers, and the realisation of a mid-infrared sensor.
This work describes the integration of mid-infrared (MIR) silicon photonics with PDMS microfluidics to perform absorption spectroscopy of IPA-water solutions. The MIR spectral region contains strong absorption bands for many molecules, and photonic devices operating in the MIR can be used in many sensing applications. In this work a preliminary demonstration of a silicon-on-insulator (SOI) device is carried out in which the transmission spectra of different concentrations of water-IPA solutions are measured at wavelengths between 3.725 μm and 3.888 μm. A PDMS microfluidic channel is integrated with the waveguides in order to improve the repeatability of sample handing, reduce reagent volumes and prevent evaporation of the analyte. A microfluidic channel with 3000 x 100 μm cross-section and 30 mm length is bonded to a SOI chip comprising 500 nm thick rib waveguides and a 2 μm thick SiO2top cladding isolating the waveguide mode from the analyte. Trenches were patterned into the SiO2 cladding to create sensing windows of varying lengths (10 μm to 3mm) along different waveguides. The devices were used to detect an expected IPA absorption peak at 3.77 μm, and concentration as low as 3% IPA in water (by volume) was detected. Further work will focus on increasing the sensitivity of the measurement by using increased interaction lengths, reduction of noise and instability, and on the detection of drugs using transmission measurements over a broader wavelength range.
In this paper we present silicon and germanium-based material platforms for the mid-infrared wavelength region and we report several active and passive devices realised in these materials. We particularly focus on devices and circuits for wavelengths longer than 7 micrometers.
Group IV platforms can operate at longer wavelengths due to their low material losses. By combining graphene and Si and Ge platforms, photodetection can be achieved by using graphene’s optical properties and coplanar integration methods. Here, we presented a waveguide coupled graphene photodetector operating at a wavelength of 3.8 μm.
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