High-speed integrated silicon germanium optical modulator with 3 GHz bandwidth in the 5-9 µm wavelength range

Mid-infrared spectroscopy is a powerful technique for identifying chemical and biological substances, increasing the demand for compact and cost-effective integrated systems. In this context, integrated electro-optic modulators are essential to implement advanced techniques such as synchronous detection or dual-comb spectroscopy. In this paper, we present a waveguide-integrated electro-optic modulator operating in a broad spectral range from 5 to 9 µm wavelength, based on a Schottky diode embedded in a graded silicon germanium waveguide. By using the free-carrier plasma absorption effect, the device achieves an extinction ratio of up to 1.9 dB at a wavelength of 9 µm. Two different methods have been used to evaluate the device speed. In both cases, high-speed operation up to 7 GHz is obtained, while the optical bandwidth is estimated to be around 3 GHz. These results represent a significant step forward in both the development of characterization techniques and in the performance of mid-IR integrated modulators, paving the way for high-performance on-chip spectroscopic systems.