Toward on-chip mid-infrared chem/bio sensors using quantum cascade lasers and substrate-integrated semiconductor waveguides

Abstract

In this contribution, we discuss progresses on ultra-sensitive chemical sensing in the mid-infrared (MIR; 3-20 μm) spectral regime by combining microfabricated GaAs/Al0.2Ga0.8As waveguides and sensing structures with quantum cascade lasers (QCL). Modern epitaxial grown methods including molecular beam epitaxy (MBE) and metal–organic vapor-phase epitaxy (MOVPE) were applied facilitating epitaxial growth of on-chip MIR GaAs/Al0.2Ga0.8As (6 μm core / 6 μm cladding) semiconductor slab waveguides, which were then structured with reactive ion etching (RIE) and/or focused ion beam milling (FIB) for establishing a variety of substrate-integrated GaAs/Al0.2Ga0.8As waveguide geometries. A distributed feedback (DFB) QCL lasing at a wavelength of 10.3 μm was combined with planar waveguide slabs and strip waveguides, respectively. Exemplary detection of acetic anhydride on strip waveguides (50 μm waveguide width) result in a limit of detection (LOD) of 0.05 pL, which is among the most sensitive direct evanescent field absorption measurements with substrate-integrated waveguides using MIR sensing systems reported to date. The first mid-infrared Mach-Zehnder interferometers (MIR-MZI) was recently design, fabricated, and functionally verified using a broadly tunable quantum cascade laser (tQCL) providing access to a spectral window of 5.78-6.35 μm. Finally, the development of first MIR ring resonators via microfabrication is shown providing an outlook toward next-generation miniaturized MIR sensor devices based on substrate-integrated semiconductor waveguides.