We report the room-temperature frequency response, in the range 0-220GHz, of GaAs-based QWIP photodetectors operating at 10um. Detectors rely on 2D arrays of patch-antennas, connected to an integrated 50-Ohm coplanar line allowing on-wafer characterization. By difference frequency mixing of two QCLs, we obtain a RF 3dB bandwidth of ~90GHz. The frequency response of devices based on 4 antennas is compatible with a carrier capture-time of ~2.5ps. By replacing the coplanar line with a log-spiral antenna we also demonstrate devices radiating directly in free-space. The perspective of exploiting the latter as QCL-pumped photomixers for the generation of microwave/sub-mm radiation is discussed.
Stable operation is one of the most important requirements for a laser source for high-precision applications. Many efforts have been made to improve the stability of lasers by employing various techniques, e.g., electrical and/or optical injection and phase locking. However, these techniques normally involve complex experimental facilities. Therefore, an easy implementation of the stability evaluation of a laser is still challenging, especially for lasers emitting in the terahertz (THz) frequency range because the broadband photodetectors and mature locking techniques are limited. In this work, we propose a simple method, i.e., relative phase locking, to quickly evaluate the stability of THz lasers without a need of a THz local oscillator. The THz laser system consists of a THz quantum cascade laser (QCL) frequency comb and a single-mode QCL. Using the single-mode laser as a fast detector, heterodyne signals resulting from the beating between the single-mode laser and the comb laser are obtained. One of the heterodyne beating signals is selected and sent to a phase-locked loop (PLL) for implementing the relative phase locking. Two kinds of locks are performed by feeding the output error signal of the PLL, either to the comb laser or to the single-mode laser. By analyzing the current change and the corresponding frequency change of the PLL-controlled QCL in each phase-locking condition, we, in principle, are able to experimentally compare the stability of the emission frequency of the single-mode QCL (fs) and the carrier envelope offset frequency (fCEO) of the QCL comb. The experimental results reveal that the QCL comb with the repetition frequency injection locked demonstrates much higher stability than the single-mode laser. The work provides a simple heterodyne scheme for understanding the stability of THz lasers, which paves the way for the further locking of the lasers and their high-precision applications in the THz frequency range.
Terahertz (THz) wave (frequency range: 0.1-10 THz; 1 THz=1012 Hz) is in the electromagnetic spectrum region between microwave and infrared light, and has important application prospects in the fields of spectral detection, medical imaging, space communication, etc. It has become a hot spot of theoretical and experimental study. When driven by periodic periodic electric fields, electrons in semiconductor superlattices and multiple quantum well structures will exhibit different behaviors, which in turn affect their physical properties such as output current and power. We theoretically studied the transient output power of the optical-injected THz quantum cascade laser (QCL) driven by a time periodic current. It is found that the system displays transient instability. It is found that the transient output power of the QCL exhibits periodic, quasi-periodic, and chaotic oscillation states under the control of external field. The transient dynamic properties of THz QCLs under control of external field open a new way for designing novel THz imaging modality.
Terahertz (1 - 10 THz) quantum-well photodetectors and quantum- cascade lasers have been investigated. The design and projected detector performance are presented together with experimental results on several test devices, all working at photon energies below the optical phonons. Background limited infrared performance (BLIP) operations were observed for all samples (three in total) designed for different wavelengths. For lasers, a set of THz quantumcascade
lasers with identical device parameters except for the doping concentration has been studied. The δ-doping density for each period was varied from 3.2 × 1010 to 4.8 × 1010 cm-2. We observed that the lasing threshold current increased monotonically with doping. Moreover, the measured results on devices with different cavity lengths provided evidence that the free carrier absorption caused waveguide loss also increased monotonically. Interestingly however, the observed maximum lasing temperature displayed an optimum at a doping density of 3.6 × 1010 cm-2.
The optical absorption in semiconductor nanorings under a lateral DC field and a perpendicular magnetic field is numerically simulated by coherent wave approach. The exciton dominated optical absorption is compared with the free-carrier interband absorption to demonstrate the key role of Coulomb interaction between electron and hole. The influence of the lateral DC field and the perpendicular magnetic field on the optical absorption are discussed in detail. It shows that the lateral DC field can significantly enhance the Aharonov-Bohm effect of the neutral excitons in semiconductor nanorings.
Conference Committee Involvement (10)
Infrared, Millimeter-Wave, and Terahertz Technologies XI
13 October 2024 | Nantong, China
Infrared, Millimeter-Wave, and Terahertz Technologies X
15 October 2023 | Beijing, China
Infrared, Millimeter-Wave, and Terahertz Technologies IX
5 December 2022 | Online Only, China
Infrared, Millimeter-Wave, and Terahertz Technologies VIII
10 October 2021 | Nantong, JS, China
Infrared, Millimeter-Wave, and Terahertz Technologies VII
12 October 2020 | Online Only, China
Infrared, Millimeter-Wave, and Terahertz Technologies VI
21 October 2019 | Hangzhou, China
Infrared, Millimeter-Wave, and Terahertz Technologies V
12 October 2018 | Beijing, China
Infrared, Millimeter-Wave, and Terahertz Technologies IV
12 October 2016 | Beijing, China
Infrared, Millimeter-Wave, and Terahertz Technologies III
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