In this study, we conduct a comparative analysis of an InAs/InP quantum dot diode laser and an InGaAsP/InP quantum well laser. Both lasers are monolithic, 840 μm long devices. They have a two-part buried heterostructure with 10%/90% reflection coated facets and emit at 1550 nm (quantum dot laser) respectively 1570 nm (quantum well laser). In passive mode-locking operational mode, the larger section of both devices is continuously pumped with forward current, while the second, smaller section (50 μm) is operated with reverse absorber voltage. In self mode-locking operation both sections of the laser are connected and pumped with forward current. Femtosecond pulses have been detected in both operational modes.
Photoconductive emitters and receivers are widely accepted as the best combination for applications requiring broadband and high dynamic range and are nowadays deployed in most commercially available systems. Novel laser sources with higher repetition rate and power levels are a promising route towards further improvements in this area. We present our first steps in this direction by combining state-of-the-art emitters and receivers with an ultra-stable commercial fs laser (MENHIR-1550 SERIES) at 1 GHz repetition rate as the optical source. The output of the laser is amplified and compressed by a commercial fiber amplifier setup. In this experiment, we use 17 mW as the probe beam and 30 mW as the pump beam with a pulse duration of 150 fs, as these are the best operation points for the emitter and receiver available. The emitter is based on iron doped InGaAs in a strip line geometry with an active region of 50 μm x 50 μm while a fiber coupled dipole antenna with a 10 μm gap is used as the receiver. We demonstrate a 1 GHz repetition rate terahertz time-domain spectroscopy (THz-TDS) system with a dynamic range of 73 dB and a bandwidth of 3.5 THz using state-of-the-art THz photoconductive emitter and receiver with a measurement time of 60 s. This result is part of a larger effort to understand the compromises to be realized in terms of repetition rate and average power to take photoconductive emitters and receivers to the next step in dynamic range enhancement.
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