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technology  PICs


Figure 5 a) Cross-section of evanescently coupled InGaAsSb-detector integrated on a silicon waveguide.b) Current-voltage and current-power characteristics for this detector under illumination at 2.25 µm


based completely on III-V semiconductors. We try to address the lack of progress in this area by employing our heterogeneous integration process to develop such circuits. One of the strengths of silicon photonics is its broad transparency window, which stretches from 1 µm to 4 µm. Thanks to this, it should be possible to realize integrated spectroscopic systems combining active III-V devices and silicon-on-insulator passive circuits. Such systems could be incredibly compact, highly affordable and superior to existing products in terms of selectivity and sensitivity.


Fabrication of these systems requires integration of short-wave and mid-wave infrared light sources and photodetectors on top of the silicon waveguide circuit. Our first step towards this was to demonstrate efficient detectors integrated with a silicon-based integrated spectrometer circuit. The detector built for this, which was bonded to a silicon waveguide circuit, had an epilayer stack featuring a 500 nm-thick Ga0.79


In0.21 As0.19 Sb0.81 layer as the


intrinsic absorbing region (see Figure 5). Antimonide layers were grown by the Institut d’Electronique du Sud from the university of Montpellier.


Evanescently coupled detectors fabricated in this way produce a responsivity of 1.4 A/W at 2.3 µm, which is close to the theoretical limit. The detectors have been united with an integrated spectrometer and efficient demultiplexing in up to 16 channels


with a separation of a few nanometres was obtained. We believe this is the first demonstration of a complex PIC operating in this wavelength range. Our next goal is to demonstrate lasers coupled to silicon waveguides operating at these longer wavelengths.


In short, thanks to our development of wafer bonding techniques, we have developed a powerful process for integrating a wide range of III-V active devices on silicon integrated photonic circuits. Our efforts began by demonstrating complex lasers and detectors operating in the telecom range, and now we are starting to unleash the true versatility of the process by pioneering the development of integrated spectrometers working at wavelengths above 2 µm.


Goals for the coming months are improving various aspects of device performance, including thermal behavior, and fabricating lasers operating in the SWIR wavelength range.


 This work has only been possible through the collaboration with many partners within Europe, in particular CEA-LETI, III-V labs, TU/e and IES Montpellier. The work was supported by the EU- projects HELIOS, BOOM, inSPECTRA and MIRACLE.


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Further reading Nature Photonics focus issue on Silicon photonics,August 2010 4491 G.Roelkens et al. III-V/silicon photonics for on-chip and inter-chip optical interconnects,Laser & Photonics reviews p.DOI: 10.1002/lpor.200900033 (2010


60 www.compoundsemiconductor.net March 2013


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