The availability of silicon photonic integrated circuits (ICs) in the 2–4 μm wavelength range enables miniature optical sensors for trace gas and bio-molecule detection. In this paper, we review our recent work on III–V-on-silicon waveguide circuits for spectroscopic sensing in this wavelength range. We first present results on the heterogeneous integration of 2.3 μm wavelength III–V laser sources and photodetectors on silicon photonic ICs for fully integrated optical sensors. Then a compact 2 μm wavelength widely tunable external cavity laser using a silicon photonic IC for the wavelength selective feedback is shown. High-performance silicon arrayed waveguide grating spectrometers are also presented. Further we show an on-chip photothermal transducer using a suspended silicon-on-insulator microring resonator used for mid-infrared photothermal spectroscopy.

Abstract:The heterogeneous integration of InP-based type-II quantum well photodiodes on silicon photonic integrated circuits for the 2 µm wavelength range is presented. A responsivity of 1.2 A/W at a wavelength of 2.32 µm and 0.6 A/W at 2.4 µm wavelength is demonstrated. The photodiodes have a dark current of 12 nA at −0.5 V at room temperature. The absorbing active region of the integrated photodiodes consists of six periods of a "W"-shaped quantum well, also allowing for laser integration on the same platform.

Silicon photonics is a promising integrated-optics platform for optical communication and sensing applications. Integrating 2-3 μm wavelength widely tunable lasers on silicon photonic integrated circuits enables fully integrated spectroscopic sensors with different potential applications such as multi-species trace gas spectroscopy and bio-molecule detection. Here, we demonstrate a continuous-wave (CW) operated III-V-on-silicon distributed feedback (DFB) laser array covered a broad wavelength range from 2.28 to 2.43 μm. CW operation up to 25°C and an on-chip output power of 2.7 mW in a single mode at 5°C is achieved for lasers operating at 2.35 μm wavelength. Four-channel DFB laser arrays with a continuous tuning range of 10 nm and side mode suppression ratio of 40 dB over the whole range are also presented. This work is a major advance toward chip-scale silicon photonics spectroscopic sensing systems. Gas sensing based on short-wave infrared and mid-infrared absorption spectroscopy has been proven to be a reliable technology for trace-gas measurements with fast response time and a high degree of specificity to the target gas [1,2]. However, most present optical sensors consist of discrete optical components and a bulk gas cell, which limits their viability for applications in portable and economical gas analysis. Integrated photonics platforms offer the potential to realize miniature and low-cost optical gas sensors [3][4][5][6]. As one of the most promising integrated photonics platforms, silicon photonics has been well-developed for optical communication applications during the past decade [7]. In recent years, its applications have been extended to sensing applications, including on-chip spectroscopic sensing [8]. Silicon photonics gas sensors that target different components have been demonstrated, including those that use, e.g., microring resonators [9,10] or spiral waveguides [11] to interact with the gas medium. In these gas sensors, the light from an external laser source is coupled into the silicon chip for the on-chip absorption spectroscopy measurement. The development of fully integrated silicon photonic integrated circuits (PICs) in the 2.3 μm wavelength range enable compact gas sensors with high sensitivity, since many important industrial gases (e.g., NH 3 , CO, and CH 4 ) have strong absorption lines in this wavelength range [12]. It is also valuable for bio-sensing applications, such as non-invasive blood glucose measurements [8,13]. For a compact silicon photonics spectroscopic gas sensor, an integrated and tunable single-mode laser is the key component that should be developed. Recently, heterogeneously integrated III-V-on-silicon Fabry-Perot lasers around 2 μm were realized using strained InGaAs Type I heterostructures [14]. However, the emission wavelength range of laser sources based on the InP-based Type I material is limited to around 2.3 μm [15]. Recently, we demonstrated 2.3x μm heterogeneous III-Von-silicon distributed feedback (DFB) laser sources based on an InP-based Type II heteros...