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Title: Tuning a microcavity-coupled terahertz laser

Abstract

Tunable oscillators are a key component of almost all electronic and photonic systems. Yet, a technology capable of operating in the terahertz (THz)-frequency range and fully suitable for widescale implementation is still lacking. This issue is significantly limiting potential THz applications in gas sensing, high-resolution spectroscopy, hyper-spectral imaging, and optical communications. The THz quantum cascade laser is arguably the most promising solution in terms of output power and spectral purity. In order to achieve reliable, repeatable, and broad tunability, here we exploit the strong coupling between two different cavity mode concepts: a distributed feedback one-dimensional photonic resonator (providing gain) and a mechanically actuated wavelength-size microcavity (providing tuning). The result is a continuously tunable, single-mode emitter covering a 162 GHz spectral range, centered on 3.2 THz. Our source has a few tens of MHz resolution, extremely high differential efficiency, and unprecedented compact and simple design architecture. By unveiling the large potential that lies in this technique, our results provide a robust platform for radically different THz systems exploiting broadly tunable semiconductor lasers.

Authors:
; ;  [1]; ; ; ;  [2];  [3]
  1. NEST, CNR-Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa (Italy)
  2. School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom)
  3. Dipartimento di Fisica, Università degli Studi di Pisa, Largo Pontecorvo 6, 56127 Pisa (Italy)
Publication Date:
OSTI Identifier:
22486297
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 107; Journal Issue: 26; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; FEEDBACK; GAIN; GHZ RANGE 100-1000; IMPURITIES; MHZ RANGE; OSCILLATORS; POTENTIALS; RESONATORS; SEMICONDUCTOR LASERS; SPECTROSCOPY; STRONG-COUPLING MODEL; TUNING

Citation Formats

Castellano, Fabrizio, Bianchi, Vezio, Vitiello, Miriam S., E-mail: miriam.vitiello@sns.it, Li, Lianhe, Zhu, Jingxuan, Linfield, Edmund H., Giles Davies, A., and Tredicucci, Alessandro. Tuning a microcavity-coupled terahertz laser. United States: N. p., 2015. Web. doi:10.1063/1.4938207.
Castellano, Fabrizio, Bianchi, Vezio, Vitiello, Miriam S., E-mail: miriam.vitiello@sns.it, Li, Lianhe, Zhu, Jingxuan, Linfield, Edmund H., Giles Davies, A., & Tredicucci, Alessandro. Tuning a microcavity-coupled terahertz laser. United States. doi:10.1063/1.4938207.
Castellano, Fabrizio, Bianchi, Vezio, Vitiello, Miriam S., E-mail: miriam.vitiello@sns.it, Li, Lianhe, Zhu, Jingxuan, Linfield, Edmund H., Giles Davies, A., and Tredicucci, Alessandro. Mon . "Tuning a microcavity-coupled terahertz laser". United States. doi:10.1063/1.4938207.
@article{osti_22486297,
title = {Tuning a microcavity-coupled terahertz laser},
author = {Castellano, Fabrizio and Bianchi, Vezio and Vitiello, Miriam S., E-mail: miriam.vitiello@sns.it and Li, Lianhe and Zhu, Jingxuan and Linfield, Edmund H. and Giles Davies, A. and Tredicucci, Alessandro},
abstractNote = {Tunable oscillators are a key component of almost all electronic and photonic systems. Yet, a technology capable of operating in the terahertz (THz)-frequency range and fully suitable for widescale implementation is still lacking. This issue is significantly limiting potential THz applications in gas sensing, high-resolution spectroscopy, hyper-spectral imaging, and optical communications. The THz quantum cascade laser is arguably the most promising solution in terms of output power and spectral purity. In order to achieve reliable, repeatable, and broad tunability, here we exploit the strong coupling between two different cavity mode concepts: a distributed feedback one-dimensional photonic resonator (providing gain) and a mechanically actuated wavelength-size microcavity (providing tuning). The result is a continuously tunable, single-mode emitter covering a 162 GHz spectral range, centered on 3.2 THz. Our source has a few tens of MHz resolution, extremely high differential efficiency, and unprecedented compact and simple design architecture. By unveiling the large potential that lies in this technique, our results provide a robust platform for radically different THz systems exploiting broadly tunable semiconductor lasers.},
doi = {10.1063/1.4938207},
journal = {Applied Physics Letters},
number = 26,
volume = 107,
place = {United States},
year = {Mon Dec 28 00:00:00 EST 2015},
month = {Mon Dec 28 00:00:00 EST 2015}
}
  • Electrical laser emission frequency tuning of a three terminal THz quantum cascade laser is demonstrated. A high electron mobility transistor structure is used in a surface plasmon waveguide to modulate the electron density in a channel, controlling the effective refractive index of the waveguide. The threshold current density was modulated by 28% via applying voltage from −3 to 2 V. The observed laser emission frequency shift by electric field was 2 GHz. By using the three terminal devices, pure frequency modulation of the output light is, in principle, achievable.
  • We report observation of strong light-matter coupling in an AlGaAs microcavity (MC) with an embedded single parabolic quantum well. The parabolic potential is achieved by varying aluminum concentration along the growth direction providing equally spaced energy levels, as confirmed by Brewster angle reflectivity from a reference sample without MC. It acts as an active region of the structure which potentially allows cascaded emission of terahertz (THz) light. Spectrally and time resolved pump-probe spectroscopy reveals characteristic quantum beats whose frequencies range from 0.9 to 4.5 THz, corresponding to energy separation between relevant excitonic levels. The structure exhibits strong stimulated nonlinear emissionmore » with simultaneous transition to weak coupling regime. The present study highlights the potential of such devices for creating cascaded relaxation of bosons, which could be utilized for THz emission.« less
  • We present a theoretical analysis of a newly demonstrated semiconductor laser with coupled distributed feedback and Fabry--Perot (DFB-FP) cavities and show that three modes of operation are possible for such a laser. In mode-switched DFB mode, the wavelength can be switched between longitudinal modes on either side of the stopband. In coupled-cavity laser mode, there are successive mode hops inside the stopband. Finally, in continuously tunable distributed Bragg reflector mode, a wide wavelength tuning range (4.8 A) without mode hopping can be obtained. The analysis is general enough to be applied to any laser with a periodic waveguide section, andmore » provides an understanding of the mechanisms and the limits of wavelength tuning in such lasers. This type of laser has very important applications in coherent optical communications.« less
  • Passively mode-locked quantum dot lasers with a grating-coupled external cavity arrangement are investigated. A broad repetition-rate tuning range of fundamental mode-locking from 2 GHz to a record-low frequency of 79.3 MHz is achieved with selecting the wavelength at 1.28 μm. A narrow RF linewidth of ∼25 Hz and an intrinsic linewidth as low as 0.15 Hz are also obtained.
  • The decay dynamics of the classical electromagnetic field in a leaky optical resonator supporting a single mode coupled to a structured continuum of modes (reservoir) is theoretically investigated, and the issue of threshold condition for lasing in presence of an inverted medium is comprehensively addressed. Specific analytical results are given for a single-mode microcavity resonantly coupled to a coupled resonator optical waveguide, which supports a band of continuous modes acting as decay channels. For weak coupling, the usual exponential Weisskopf-Wigner (Markovian) decay of the field in the bare resonator is found, and the threshold for lasing increases linearly with themore » coupling strength. As the coupling between the microcavity and the structured reservoir increases, the field decay in the passive cavity shows nonexponential features, and correspondingly the threshold for lasing ceases to increase, reaching a maximum and then starting to decrease as the coupling strength is further increased. A singular behavior for the 'laser phase transition', which is a clear signature of strong non-Markovian dynamics, is found at critical values of the coupling between the microcavity and the reservoir.« less