Fig. 3: Experimental setup and measured system response. | Nature Communications

Fig. 3: Experimental setup and measured system response.

From: Unipolar quantum optoelectronics for high speed direct modulation and transmission in 8–14 µm atmospheric window

Fig. 3

a The modulated signal is generated offline at a lab computer with MATLAB and loaded to the arbitrary waveform generator (AWG). The AWG output is firstly amplified and then combine with a DC bias current at a high-current bias-tee (2 A, 40 GHz), before driving the QCLs. The QCLs are mounted on a Peltier element with thermoelectric cooling (TEC) to configure and stabilize the operational temperature. Two types of detectors, i.e., QCD and QWIP, are mounted 20 cm away from the QCL mount. A pair of f/1” ZnSe collimation lenses are placed between the laser mount and the detector mount to collect the emitted energy focusing on the detectors. For the QWIP, a second bias-tee with a voltage source is connected to provide the bias voltage, whereas for the QCD no bias voltage is required. It’s worth noting that no cooling or temperature control is needed for both types of detectors. The received signal is amplified and captured by a real-time storage oscilloscope (DSO), and the converted digital samples are sent back to the lab computer for demodulation. b The system’s characterized end-to-end S21 amplitude response, including the cascaded frequency response of all the electrical and optoelectronic devices in the setup.

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