Building blocks for mid-IR programmable light source based on GaSb-based amplified spontaneous emission sources and μm-scale Silicon-on-Insulator waveguide photonics Jukka Viheriälä 1 , Matteo Cherchi 2 , Heidi Tuorila 3 , Nouman Zia 3 , Eero Koivusalo 3 , Samu-Pekka Ojanen 3 , Pentti Karioja 2 and Mircea Guina 3 1 Faculty of Natural Sciences and Engineering, Tampere University, 33720 Tampere, Finland 2 VTT Technical Research Centre of Finland Ltd, Finland 3 Optoelectronics Research Center, Physics Unit, Tampere University, 33720 Tampere, Finland e-mail:jukka.viheriala@tuni.fi ABSTRACT Industrial and environmental sensing applications require compact, robust and cost effective mid-IR light sources for multiline spectroscopy. An essential feature of such source is the ability to generate multiple-emission lines on demand, i.e. in a programmable fashion. Building blocks for an integrated programmable light sources operating 2 to 3 μm wavelength band are presented. Our approach is based on μm-scale Silicon-on-Insulator technology and GaSb-based quantum well broadband emitter demonstrates. In particular, we focus on presenting state-of-the-art developments of amplified spontaneous emission sources emitting within 2 μm to 2.65 μm quantum-wells and present their application as semiconductor optical amplifiers. Progress towards emission at 3 μm using GaInAsSb/AlGa(In)AsSb quantum wells in single-transvers-mode superluminescent LEDs is also discussed. Moreover, performance merits for various circuit elements prepared using micron-scale Silicon-on- insulator technology are described; these include waveguides with low propagation and bend losses and echelle gratings for wavelength selection. Keywords: Silicon Photonics, mid-IR, superluminescent diodes, semiconductor optical amplifiers, GaSb-laser, spectroscopy 1. INTRODUCTION The wavelength region 2–3 μm is well known for its use in the spectroscopic sensing due to the strong molecular absorption of some important gases, such as CO [1] , CO2 [2], NH3 [3], N2O [4], and it is also relevant for detection of complex molecules from liquids [5]. More and more spectroscopic applications are realized with multi-line methods combined with artificial intelligence to allow better discrimination between complex mixtures of species [5]; this calls for development of light source with capability to switch its emission to match different emission lines. From application perspective, increasing environmental awareness, and new applications for example related to food safety, creates a demand for affordable and compact spectroscopic measurements systems with increased functionality, making mid-IR (laser) market one of the fastest growing sectors in photonics [6]. Here we present a toolkit to build miniaturized light sources based on hybrid integration of III-V light sources on silicon photonic circuits, exploiting their complementarity. The silicon photonics platform is based on micron- scale Silicon-on-Insulator (SOI) technology utilizing large core 3 μm thick waveguides with low propagation and bending loss ensuring also very good mode matching between SOI-waveguides and III-V waveguides. Light sources and amplifiers are produced using molecular beam epitaxy (MBE) for fabrication of GaInAsSb/AlGa(In)AsSb – quantum wells, ensuring emission in the 2–3 μm band. In particular, we present state- of-the-art mid-IR superluminescent diodes (SLEDs) and low loss waveguide technology. These building blocks are discussed in a context of programmable light source, where silicon photonic filters select specific lines from the wide emission spectrum provided by SLEDs. Nevertheless, similar building blocks could as well be used to build smart laser sources through suitable feedback configurations. 2. High power superluminescent diodes for 1.9 μm to 2.65 μm wavelength band The SLED-architecture is based on single mode ridge waveguide technology utilizing tailored gain provided by GaInAsSb QWs placed within AlGa(In)AsSb waveguide and barrier layers. Further details of fabrication are given in references [7], [8]. This material system can be used to provide broad range of wavelength by tailoring compositions of QWs and barriers to obtain favourable QW confinement and strain profile. For longer wavelengths both Auger recombination and carrier leakage from QW increase limiting achievable output power of the source. These mechanisms can, to some extent, be countered by chip design utilizing double pass gain scheme or by driving conditions [8] of SLED allowing to achieve milliwatt-level amplified spontaneous emission sources up to