Query: injection locking  of a terahertz quantum cascade laser to a telecommunications

Candidate papers:

abstract: High resolution spectroscopy not only can identify atoms and molecules but also can provide detailed information on their chemical and physical environment and relative motion. In the terahertz frequency region of the electromagnetic spectrum, where many molecules have fundamental vibrational modes, there is a lack of powerful sources with narrow linewidths that can be used for absorption measurements or as local oscillators in heterodyne detectors. The most promising solid state source is the THz frequency quantum cascade laser (QCL) however, the linewidth of this compact semiconductor laser is typically too broad for many applications, and its frequency is not directly referenced to primary frequency standards. In this work, we injection lock a QCL operating at 2 THz to a compact fiber based telecommunications wavelength frequency comb, where the comb line spacing is referenced to a microwave frequency reference. This results in the QCL frequency locking to an integer harmonic of the microwave reference, and the QCL linewidth reducing to the multiplied linewidth of the microwave reference, <100 Hz. Furthermore, we perform phase resolved detection of the locked QCL and measure the phase noise of the locked system to be 75 dBc/Hz at 10 kHz offset from the 2 THz carrier.
author_names: Joshua R Freeman

Lalitha Ponnampalam

Haymen Shams

Reshma A Mohandas

Cyril C Renaud

Paul Dean

Lihang Li

Alexander Giles Davies

Alwyn J Seeds

Edmund H Linfield
title: Injection locking of a terahertz quantum cascade laser to a telecommunications wavelength frequency comb
year: 2017

abstract: Quantum Cascade lasers (QCLs) relying on intersubband transitions in semiconductor quantum well structures, show very short carrier lifetimes of the order of picoseconds [1] As a consequence, relaxation oscillations remain over damped up to modulation frequencies of several tens of GHz [2] enabling efficient amplitude modulation of the gain medium in this frequency range. These properties make QCLs ideally suited for RF injection locking. We demonstrate that the round trip frequency of THz QCLs, as observed from the beatnote, can be injection locked by RF modulating the bias current. Within a certain locking range we observe mutual phase locking of approximately 20 longitudinal modes for significantly lower RF powers than in previous studies [3] Apart from injection locking, we demonstrate beatnote control by means of an external cavity.
author_names: P Taeschler

Andres Forrer

David Stark

T Olariu

Mattias Beck

Jerome Faist

Giacomo Scalari
title: Low RF Power Injection Locking and Beatnote Control of Terahertz Quantum Cascade Laser Frequency Combs
venue: 2019 Conference on Lasers and Electro Optics Europe European Quantum Electronics Conference (CLEO/Europe EQEC)
year: 2019

abstract: Absolute frequency and phase control of a coherent terahertz (THz) source is desirable for high resolution spectroscopy of atoms and molecules, coherent communications and advanced imaging techniques. Here we report on the phase control of a 2.0 THz quantum cascade laser (QCL) The QCL is optical injection locked (OIL) to an infrared frequency comb, which is generated by the successive modulation of a 'C band' laser in a recirculating fibre loop. A stable microwave source defines the spacing between the comb lines resulting in the QCL being locked to an integer harmonic of the microwave frequency; the reference frequency. Within the locking range the frequency of the injection locked QCL is locked to the reference frequency, whereas the phase of the QCL undergoes a 'p' phase shift across the locking range. In this work, we control the phase of the QCL by introducing a phase lock loop to the OIL system to provide feedback to the QCL current forming an optical injection phase locked loop. This has several advantages over the bare OIL system: (1) the underlying frequency of the QCL is stabilised so that the QCL remains within the locking range for long periods of time. (2) The QCL frequency and phase track the microwave frequency so that the QCL may be tuned with extremely high precision. (3) By changing the locking point for the PLL the phase of QCL relative to the reference frequency could be controlled within a range 0.4p, limited by the PLL, with a constant amplitude.
author_names: Reshma Anamari Mohandas

Lalitha Ponnampalam

Lianhe Li

Cyril C Renaud

Alwyn J Seeds

Paul Dean

Edmund H Linfield

Giles Davies

Joshua R Freeman
title: Phase control of a terahertz quantum cascade laser using an optical injection phase lock loop (Conference Presentation)
venue: Novel In Plane Semiconductor Lasers XVIII
year: 2019

abstract: The ability to engineer quantum cascade lasers (QCLs) with ultrabroad gain spectra, and with a full compensation of the group velocity dispersion, at terahertz (THz) frequencies, is key for devising monolithic and miniaturized optical frequency comb synthesizers (FCSs) in the far infrared. In THz QCLs four wave mixing, driven by intrinsic third order susceptibility of the intersubband gain medium, self locks the optical modes in phase, allowing stable comb operation, albeit over a restricted dynamic range ~20% of the laser operational range) Here, we engineer miniaturized THz FCSs, comprising a heterogeneous THz QCL, integrated with a tightly coupled, on chip, solution processed, graphene saturable absorber reflector that preserves phase coherence between lasing modes, even when four wave mixing no longer provides dispersion compensation. This enables a high power (8 mW) FCS with over 90 optical modes, through 55% of the laser operational range. We also achieve stable injection locking, paving the way to a number of key applications, including high precision tunable broadband spectroscopy and quantum metrology.
author_names: Francesco P Mezzapesa

Katia Garrasi

Johannes Schmidt

Luca Salemi

Valentino Pistore

L Li

A G Davies

Edmund H Linfield

Michael Riesch

Christian Jirauschek

Tian Carey

Felice Torrisi

Andrea C Ferrari

Mathias Nest

CNR-Istituto Nanoscienze

Scuola Normale Superiore

School of Electronic

Electrical Engineering

University of Leeds

Department of Electrical

Computer Engineering

Technical University of Munich

Cambridge Graphene Centre

University of Cambridge
title: Terahertz Frequency Combs Exploiting an On Chip, Solution Processed, Graphene Quantum Cascade Laser Coupled Cavity
venue: ACS photonics
year: 2020

abstract: Due to intersubband transitions, the quantum cascade laser (QCL) is free of relaxations and able to work under fast modulations. In this work, the authors investigate the fast modulation properties of a continuous wave (cw) terahertz QCL emitting around 3 THz ~100 mm) Both simulation and experimental results show that the 3 dB modulation bandwidth for the device can reach 11.5 GHz and the modulation response curve is relatively flat upto ~16 GHz. The radio frequency (RF) injection measurements verify that around the laser threshold the inter mode beat note interacts strongly with the RF signal and the laser can be modulated at the round trip frequency of 15.5 GHz.
author_names: Li Gu

Wenjian Wan

Y H Zhu

Zhanglong Fu

Hua Li

Juncheng Cao
title: High frequency modulation and injection locking of terahertz quantum cascade lasers
year: 2017

abstract: Abstract We report a homogeneous quantum cascade laser (QCL) emitting at terahertz (THz) frequencies, with a total spectral emission of about 0.6 THz, centered around 3.3 THz, a current density dynamic range J dr 1.53, and a continuous wave output power of 7 mW. The analysis of the intermode beatnote unveils that the devised laser operates as an optical frequency comb (FC) synthesizer over the whole laser operational regime, with up to 36 optically active laser modes delivering ~200 uW of optical power per optical mode, a power level unreached so far in any THz QCL FC. A stable and narrow single beatnote, reaching a minimum linewidth of about 500 Hz, is observed over a current density range of 240 A/cm2 and even across the negative differential resistance region. We further prove that the QCL FC can be injection locked with moderate radio frequency power at the intermode beatnote frequency, covering a locking range of 1.2 MHz. The demonstration of stable FC operation, in a QCL, over the full current density dynamic range, and without any external dispersion compensation mechanism, makes our proposed homogenous THz QCL an ideal tool for metrological applications requiring mode hop electrical tunability and a tight control of the frequency and phase jitter.
author_names: Alessandra Di Gaspare

Leonardo Viti

Harvey E Beere

David Ritchie

Miriam Serena Vitiello
title: Homogeneous quantum cascade lasers operating as terahertz frequency combs over their entire operational regime
year: 2020

abstract: We demonstrate that the cavity resonance frequency the round trip frequency of terahertz quantum cascade lasers can be injection locked by direct modulation of the bias current using an RF source. Metal metal and single plasmon waveguide devices with roundtrip frequencies up to 35GHz have been studied, and show locking ranges above 200MHz. Inside this locking range the laser round trip frequency is phase locked, with a phase noise determined by the RF synthesizer. We find a square root dependence of the locking range with RF power in agreement with classical injection locking theory. These results are discussed in the context of mode locking operation.
author_names: Pierre Gellie

Stefano Barbieri

Jean-Francois Lampin

Pascal G Filloux

C Manquest

Carlo Sirtori

Isabelle Sagnes

Suraj P Khanna

Edmund H Linfield

Harvey E Beere

David A Ritchie
title: Injection locking of terahertz quantum cascade lasers up to 35GHz via RF amplitude modulation
venue: 35th International Conference on Infrared, Millimeter, and Terahertz Waves
year: 2010

abstract: We demonstrate that the cavity resonance frequency the round trip frequency of terahertz quantum cascade lasers can be injection locked by direct modulation of the bias current using an RF source. Metal metal and single plasmon waveguide devices with roundtrip frequencies up to 35GHz have been studied, and show locking ranges above 200MHz. Inside this locking range the laser round trip frequency is phase locked, with a phase noise determined by the RF synthesizer. We find a square root dependence of the locking range with RF power in agreement with classical injection locking theory. These results are discussed in the context of mode locking operation.
author_names: Pierre Gellie

Stefano Barbieri

Jean-Francois Lampin

Pascal G Filloux

C Manquest

Carlo Sirtori

Isabelle Sagnes

Suraj P Khanna

Edmund H Linfield

Harvey E Beere

David A Ritchie
title: Injection locking of terahertz quantum cascade lasers up to 35GHz via RF amplitude modulation
year: 2010

abstract: It is demonstrated that the cavity resonance frequency the round trip frequency of terahertz quantum cascade lasers can be injection locked by direct modulation of the bias current using an RF source. Metal metal and single plasmon waveguide devices with round trip frequencies up to 35 GHz have been studied, and show locking ranges above 200 MHz. A square root dependence of the locking range with RF power was found to be in agreement with classical injection locking theory. Inside this locking range the laser round trip frequency is phase locked, with a phase noise determined by the RF synthesiser, leading to the generation of modelocked pulses with low timing jitter.
author_names: Pierre Gellie

Jean-Francois Lampin

Carlo Sirtori

Stefano Barbieri
title: RF injection locking of terahertz quantum cascade lasers
year: 2010

abstract: We report on the Doppler free saturation spectroscopy of a molecular transition at 3.3 THz based on a quantum cascade laser and an absorption cell in a collinear pump probe configuration. A Lamb dip with a sub Doppler linewidth of 170 kHz is observed for a rotational transition of HDO. We found that a certain level of external optical feedback is tolerable as long as the free spectral range of the external cavity is large compared to the width of the absorption line. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement OCIS codes: (140.5965) Semiconductor lasers, quantum cascade; (280.4788) Optical sensing and sensors; (300.6320) Spectroscopy, high resolution; (300.6495) Spectroscopy, terahertz. References and links 1. M. S. Vitiello, L. Consolino, S. Bartalini, A. Taschin, A. Tredicucci, M. Inguscio, and P. De Natale, "Quantum limited frequency fluctuations in a terahertz laser," Nat. Photonics 6, 525 528 (2012) 2. J. L. 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author_names: W M

A T

S L

Guo H-T
title: Doppler free spectroscopy with a terahertz quantum cascade laser
year: 2018