GE/SIGE PHOTONIC DEVICES FOR THE LONG MID-INFRARED

With the recent progress in integrated silicon photonics technology and the recent development of efficient quantum cascade lasers (QCL), there is now a very good opportunity to investigate new gas sensors offering very high sensitivity, high selectivity (multi-gas sensing, atmosphere analysis) and low cost thanks to integration on planar Si substrates. Gas sensing generally requires a tunable source continuously covering the whole operational range of the QCL stack. This paper presents the design, fabrication and characterization of Array Waveguide Grating (AWG) devices aiming at the simultaneous detection of several gas using arrays of QCL sources. We have developed a new platform based on Ge cores surrounded by thick Si80Ge20 layers. The index difference between the core and the cladding is around 0.5 on the 3-13 mu m spectral range. The core has a typical cross section of 2.5 x 2.5 mu m and is surrounded by 6 mu m thick SiGe cladding layers. As test vehicle device, we designed a 35 inputs multiplexer working in the 9.5 mu m operation range (1050-1250 cm(-1)). The design was carried out to match the inputs of a Distributed Feed-Back-QCL array. Preliminary measurements on the waveguide showed losses in the 3.5 dB/cm range. AWG devices were fabricated and tested. They showed results in good agreement with the modeling. An almost flat transmission over a full 200 cm(-1) operational range was obtained, with a peak-to-valley modulation of -5dB.