Abstract
AbstractA room‐temperature mid‐infrared (λ = 9 µm) heterodyne system based on high‐performance unipolar optoelectronic devices is presented. The local oscillator (LO) is a quantum cascade laser (QCL), while the receiver is an antenna coupled quantum well infrared photodetector optimized to operate in a microcavity configuration. Measurements of the saturation intensity show that these receivers have a linear response up to very high optical power, an essential feature for heterodyne detection. By providing an accurate passive stabilization of the LO, the heterodyne system reaches at room temperature the record value of noise equivalent power (NEP) of 30 pW at 9 µm and in the GHz frequency range. Finally, it is demonstrated that the injection of microwave signal into the receivers shifts the heterodyne beating over the large bandwidth of the devices. This mixing property is a unique valuable function of these devices for signal treatment in compact QCL‐based systems.
Highlights
To cite this version: Azzurra Bigioli, Djamal Gacemi, Daniele Palaferri, Yanko Todorov, Angela Vasanelli, et al
No saturation effects appear even at intensities of several kW cm−2, which exceed greatly typical saturation intensity of QWIP structures operating at low temperature.[21,22]
The high temperature prevents the formation of space charge domains and a homogeneous electric field along the structure enables a regime of very high saturation intensity
Summary
The device used in this study is a GaAs/AlGaAs QWIP containing Nqw = 8 quantum wells absorbing at a wavelength of 8.9 μm at room temperature (139 meV).[14] It has been designed with a bound-to-bound structure and has been processed into an array of double-metal patch resonators These resonators provide sub-wavelength electric field confinement and act as antennas.[17,18] An exemplary device is shown, where the 50 × 50 μm array is the collection area of the detector. The thicker active region reduces the ohmic losses of the cavity resulting in a higher cavity quality factor, Q.[19,20] We recall that the fraction of photons absorbed in the quantum wells is the branching ratio between the intersubband absorption factor Bisb and the metal losses, proportional to 1/Q. It can be noticed that a compromise has been reached between Bisb and the metal losses, 1/Q in order to avoid either strong coupling (Bisb → ∞) or to limit the acceptance bandwidth of the detector (Q → ∞).[19]
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