III-V/silicon photonic integrated circuits (ICs) promise to enable low cost and miniature optical sensors for trace-gas detection, bio-sensing and environmental monitoring. A lot of these applications can benefit from the availability of photonic ICs beyond the telecommunication wavelength range. The 2 μm wavelength range is of interest for spectroscopic detection of many important gases and blood constituents. In this contribution we will present 2 μmwavelength-range III-V/silicon photonic ICs consisting of tunable laser sources, photodetectors and silicon waveguide circuits. Silicon waveguides with a loss of ~0.5 dB/cm are obtained in a well-established silicon photonics platform. Based on the waveguides, low insertion loss (2-3 dB) and low crosstalk (25-30 dB) arrayed waveguide gratings (AWGs) are realized for the 2.3 μm wavelength range. Active opto-electronic components are integrated on the photonic IC by the heterogeneous integration of an InP-based type-II epitaxial layer stack on silicon. III-V-on-silicon 2.3 μm range distributed feedback (DFB) lasers can operate up to 25 °C in continuous-wave regime and shows an output power of 3 mW. By varying the silicon grating pitch, a DFB laser array with broad wavelength coverage from 2.28 μm to 2.43 μm is achieved. III-V-on-silicon photodetectors with the same epitaxial layer stack exhibit a responsivity of 1.6 A/W near 2.35 μm. In addition, we also report a 2 μm range GaSb/silicon hybrid external cavity laser using a silicon photonic IC for wavelength selective feedback. A wavelength tuning over 58 nm and side mode suppression ratio better than 60 dB is demonstrated.
We demonstrate the extension of the wavelength range of InP- and GaSb-based buried tunnel junction VCSELs using type-II quantum wells. The InP-based devices emit at 2.5 μm and operate in continuous-wave (CW) up to 20°C, with a maximum single-mode output power above 500 μW. They exhibit a continuous electro-thermal tuning range of 5.2 nm. The GaSb-based devices emit up to 4 μm and operate in CW and pulsed mode until -7°C and 45°C, respectively. The maximum single-mode CW output power is 175 μW. A mode-hop free electro-thermal tuning of ~19 nm is achieved. These VCSELs are highly promising for gas sensing applications.
The short-wave infrared wavelength range (2-3 μm) is attractive for applications in gas sensing and next-generation communication systems. Photodetectors and wavelength (de)multiplexers are key components that have to be developed for these systems. In this contribution, we report the integration of InGaAs/GaAsSb type-II quantum well photodetectors and spectrometers on the silicon photonics platform. In this photodetector epitaxial layer stack, the absorbing active region consists of 6 periods of W-shaped quantum wells, which can also be used to realize lasers. The efficient coupling between silicon waveguides and quantum well photodetectors is realized by tapered III-V waveguides. The photodetectors have a very low dark current of 12 nA at -0.5 V bias at room temperature. The devices show a responsivity of 1.2 A/W at 2.32 μm wavelength, and higher than 0.5A/W over the 2.2-2.4 μm wavelength range. On the silicon-on-insulator platform we also demonstrate high performance short-wave infrared spectrometers. 8-channel spectrometers in the 2.3-2.4 μm range with a resolution of 5nm and 1.4nm are demonstrated, showing a cross-talk below -25 dB and an insertion loss lower than 3 dB.
Type-II light sources on InP substrate are an innovative concept for wavelengths ranging from 2 μm to the mid-IR. The concept is using the type-II band alignment between GaInAs and GaAsSb to exceed the limitation of type-I devices. Since the first demonstration of InP type-II heterostructure lasers above 2.3 μm in 2012, we have extended the emission wavelength to 2.7 μm. Furthermore, a drastic reduction in threshold current density down to 104 A/cm<sup>2</sup> per QW at infinite length was achieved (at 2.5 μm), which represents an improvement by more than a factor of two. Additionally CW operation up to 30°C and up to 80°C pulsed is presented. Furthermore, LEDs for 3.5μm peak emission wavelength and up to 86 μW output power are shown.
We present different concepts for long wavelength buried tunnel junction VCSELs for the spectroscopically important range above 2 μm. This includes GaSb-based laser using GaInAsSb quantum wells, InP-based lasers with V-shaped quantum wells and InP-based lasers using type-II quantum wells. For InP-based devices, emission wavelengths up to 2.36 μm are presented, with single-mode output powers of roughly 500 μW and side-mode suppression ratios of more than 30 dB. GaSb-based VCSELs are presented with single-mode emission at 2.6 μm, a side-mode suppression ratio of more than 20 dB and a peak output power of 400 μW.
GaSb-based type-I quantum-well lasers, emitting in the spectral range from 2 to 4 μm are promising light sources for
various trace gas sensing systems by means of tunable diode laser absorption spectroscopy (TDLAS). Excellent device
performance has been achieved so far in the spectral range from 2 to 3 μm, however, room-temperature operation above
3 μm is much more difficult to achieve. In this work we demonstrate the extension of room-temperature operation
wavelength of GaSb-based type-I lasers up to 3.73 μm by implementation of high-quality quinternary AlGaInAsSb