InAlAs/InGaAs-MSM photodetectors based on optical cavity using metallic mirrors: THz frequency operation, high quantum efficiency and high saturation current

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Free induction decay signals stimulated by photomixing

International audienceAn optically driven photoconductor device is electrically pulsed to provide a powerful pulse around 206 GHz. The pulsed radiation polarizes the OCS gas which emits a free induction decay signal that is observed after the end of the pulse. This is the first step in the development of a photonic chirped pulsed spectrometer

Short bends using curved mirrors in silicon waveguides for terahertz waves

International audienceDielectric waveguides are capable of confining and guiding terahertz waves along sub-wavelength sized structures. A small feature size allows for a denser integration of different photonic components such as modulators, beam-splitters, wavelength (de)multiplexers and more. The integration of components on a small scale requires bending of the waveguides. In this paper we demonstrate a very short silicon 90°-bend, based on total internal reflection on an elliptically curved outer facet and a rounding of the inner corner joining two waveguides, with an average loss of 0.14 dB per bend in the 600-750 GHz range

Millimeter-long travelling wave photoconductors for THz generation by photomixing

International audienceIn this communication we present the development of a travelling wave photoconductor for THz generation by photomixing. It is based on a silicon nitride optical waveguide coupled to a membrane-supported low-temperature-grown GaAs photoconductor embedded in a coplanar waveguide. The frequency response of a 1-mm-long structure, measured up to 100 GHz by using the beatnote produced by two 780-nm-DFB lasers, shows the expected travelling wave signature consisting in a 6-dB-decrease ending at ~50 GHz when the contribution of the backward travelling wave is fully cancelled, following by a constant level up to ~100 GHz

Development of a millimeter-long Travelling wave THz photomixer

International audienceTHz sources based on the optical-heterodyne (photo)mixing in an ultrafast photodetector are very promising since they operate at room temperature, are potentially compact, cost-efficient and, above all, are widely frequencytunable. However, their widespread use is currently hampered by available power levels in the µW range at THz frequencies. We present here a travelling wave structure, with millimeter level coherence length at THz frequencies opening the way to large active area (~4000 µm 2) photomixing devices capable of handling optical pump power beyond 1 W well beyond the capabilities of standard lumped-element devices using small active areas (<50 µm 2) needed to maintain a capacitance level (<10 fF) compatible with THz operation. It is based on a silicon nitride waveguide coupled to a membrane-supported lowtemperature-grown GaAs photoconductor embedded in a coplanar waveguide. Milliwatt power levels up to 1 THz and still above 1 µW up to 4 THz are expected according to the optoelectronics model of this device elaborated in this study. Experimentally, the frequency response of a 1-mm-long structure, measured up to 100 GHz by using the beatnote produced by two 780-nm-DFB lasers, shows clearly the expected travelling wave signature consisting in a 6-dB-decrease ending at ~50 GHz when the contribution of the backward travelling wave is fully cancelled, following by a constant level up to ~100 GHz. The experimental demonstration of operation in the travelling wave regime is a first step towards the fulfillment of the original promises of this concept in terms of power level and frequency bandwidth

Over-wavelength pitch sized diffraction gratings for augmented reality applications

International audienceWaveguide based optical combiners for augmented reality (AR) glasses are integrating several surface relief gratings (SRG) whose pitch sizes can be as small as 200 nm for the blue wavelength. All SRG components exploit the first diffraction order to couple in and out or to deviate the light. We present SRG using higher diffraction orders featuring over-wavelength pitch sizes. Our gratings use the edge wave (EW) diffraction phenomenon to steer light in the preferred far field direction