Toward Compact and Real-Time Terahertz Dual-Comb Spectroscopy Employing a Self-Detection Scheme

We present homogeneous quantum cascade lasers (QCLs) emitting around 3 THz which display bandwidths up to 950 GHz with a single stable beatnote. Devices are spontaneously operating in a harmonic comb state, and when in a dense mode regime they can be injection locked at the cavity roundtrip frequency with very small RF powers down to -55 dBm. When operated in the electrically unstable region of negative differential resistance, the device displays ultra-broadband operation exceeding 1.83THz (∆f /f = 50%) with high phase noise, exhibiting self-sustained, periodic voltage oscillations. The low CW threshold (115 A· cm −2 ) and broadband comb operation (∆f /f = 25%) make these sources extremely appealing for on-chip frequency comb applications.arXiv:1912.00890v1 [physics.optics]

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“…Therefore, the presented active region design can serve as a building block towards broadband, on-chip, octave-spanning THz QCL combs. 40…”

Section: Resultsmentioning

confidence: 99%

Photon-Driven Broadband Emission and Frequency Comb RF Injection Locking in THz Quantum Cascade Lasers

et al. 2020

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“…To characterize the actual performance of the achromatic metalens, a QCL was used as a broadband coherent THz source, [4,87,88] which emits linearly polarized light in a wavelength range from 114.5 to 120 µm. The experimental setup and method can be found in the supplementary materials.…”

Section: Resultsmentioning

confidence: 99%

“…Terahertz (THz) optics has great potential applications in security examination, [1] biological research, [2] communications, [3] spectroscopy, [4] etc. Conventional optical elements available for In the present work, an approach of realizing broadband achromatic sub-diffraction focusing has been proposed utilizing both dispersion engineering and amplitude modulation.…”

Section: Introductionmentioning

confidence: 99%

Broadband Achromatic Sub‐Diffraction Focusing by an Amplitude‐Modulated Terahertz Metalens

Zhao

Dai

et al. 2020

Advanced Optical Materials

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THz focusing and imaging include bulky dielectric refractive lenses and parabolic mirrors. Due to the diffraction effect, the resolution of conventional optics is limited by the Abbe diffraction limit (DL) of 0.5λ/NA, [5] where λ and NA are working wavelength and numerical aperture (NA), respectively. Recently, there has been a growing interest in developing far-field super-resolution optical devices, which can achieve point-spread-function (PSF) of size smaller than the Abbe DL without evanescent waves [6] at a distance far beyond the near-field regime. [7,8] Based on the concept of superoscillation, [9-11] a variety of sub-diffraction or super-resolution optical devices have been demonstrated either theoretically or experimentally, including scalar super-resolution metalenses [12-22] and vector super-resolution metalenses. [23-33] Such super-resolution devices have been successfully shown great potential in labelfree super-resolution microscopy [13,21,34,35] and super-resolution telescope. [36] However, most previously reported super-resolution metalenses only work at one single wavelength [37] or several designed discrete wavelengths, [38,39] while broadband achromatic metalenses working in the visible [40-42] and nearinfrared spectrum [43-46] as well as THz regime [47] are restricted by the Abbe DL. To achieve a broadband super-resolution imaging, recently, a broadband super-resolution scheme was proposed and experimentally demonstrated by adopting the combination of a super-oscillatory binary phase filter and a conventional bulk achromatic refractive convex lens. [48] Up to now, it is still a great challenge to realize a sub-diffraction achromatic metalens with a continuous broad bandwidth. To achieve broadband achromatic super-resolution focusing, similar to the conventional optics, dispersion compensation is required to ensure that the wave of different wavelengths is focused at the same focal point. In addition, wave front engineering is also required to achieve the super-resolution PSF. Recent fast development of metasurfaces [49-54] provides effective ways to manipulate the amplitude, [55,56] phase, [57-61] polarization [30,33,62-66] and dispersion properties [67,68] of light waves. To achieve wave front shaping without influences on dispersion, one possible way is to realize broadband achromatic super-resolution by adopting amplitude modulation. Conventionally, pupil filters [69-78] can be used to achieve super-resolution in traditional optical systems. Recently, there are growing interests in developing super-resolution metalenses for applications of focusing and imaging. On one hand, various sub-diffraction metalenses have been demonstrated; however, most of them only work at a single wavelength or multiple discrete wavelengths. On the other hand, the previously reported broadband achromatic metalenses are diffraction-limited, or their focal spots are larger than the corresponding Abbe diffraction limit, 0.5λ/NA, where λ and NA are the lens working wavelength and numerical aperture. In the present wo...

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“…However, while QCL-FC-based DCS setups have been successfully adopted in the mid-IR [43,44], the THz region is lagging behind. After the first attempts of a proof-of-principle acquisition of an etalon signal simulating a molecular absorption [45], or of a low resolution spectrum of ammonia gas, dual-comb THz setups have been developed for pioneering hyperspectral imaging [46], self-detection schemes [47] and time resolved spectroscopy on molecular gas mixtures [48]. At the same time, a hybrid dual-comb spectrometer based on a OR-and a QCL-FC has been recently demonstrated [49], merging the sensitivity allowed by a 4 mW [23] THz QCL, with the accuracy of the absolute frequency scale, provided by the referenced OR-FC.…”

Section: Applications and Perspectivesmentioning

confidence: 99%

Toward new frontiers for terahertz quantum cascade laser frequency combs

et al. 2020

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Broadband, quantum-engineered, quantum cascade lasers (QCLs) are the most powerful chip-scale sources of optical frequency combs (FCs) across the mid-infrared and the terahertz (THz) frequency range. The inherently short intersubband upper state lifetime spontaneously allows mode proliferation, with large quantum efficiencies, as a result of the intracavity four-wave mixing. QCLs can be easily integrated with external elements or engineered for intracavity embedding of nonlinear optical components and can inherently operate as quantum detectors, providing an intriguing technological platform for on-chip quantum investigations at the nanoscale. The research field of THz FCs is extremely vibrant and promises major impacts in several application domains crossing dual-comb spectroscopy, hyperspectral imaging, time-domain nanoimaging, quantum science and technology, metrology and nonlinear optics in a miniaturized and compact architecture. Here, we discuss the fundamental physical properties and the technological performances of THz QCL FCs, highlighting the future perspectives of this frontier research field.

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Toward Compact and Real-Time Terahertz Dual-Comb Spectroscopy Employing a Self-Detection Scheme

Cited by 60 publications

References 30 publications

Photon-Driven Broadband Emission and Frequency Comb RF Injection Locking in THz Quantum Cascade Lasers

Photon-Driven Broadband Emission and Frequency Comb RF Injection Locking in THz Quantum Cascade Lasers

Broadband Achromatic Sub‐Diffraction Focusing by an Amplitude‐Modulated Terahertz Metalens

Toward new frontiers for terahertz quantum cascade laser frequency combs

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