Room-temperature THz-QCL source

The room temperature THz-QCL is currently under development.

Nanotechnology for next generation ICT, non-destructive inspection/analysis, and astronomy


The terahertz (THz) spectral range has considerable potential for application in numerous fields, including communications, non-destructive imaging, spectroscopy, and biological engineering. One major obstacle preventing widespread commercial deployment of this technology is the lack of a compact and mass-producible high-performance semiconductor source operating in the THz range. As shown in figure 1, on the low-frequency side (from the electron device), Resonant tunnel diode (RTD) oscillators have operated at room temperature. On the other hand, on the high frequency side (from the optical device), THz quantum cascade lasers (THz-QCL) have been reported; however, they require a cryogenic-cooling.

Figure 1 Room-temperature semiconductor THz sources (Output power vs Frequency)

Quantum cascade lasers (QCLs) are semiconductor light emitting device (Figure 2(a)). This light sources are one of the best known devices created by engineering of electron wavefunctions in semiconductor heterostructures grown by molecular beam epitaxy or metal organic vapor phase epitaxy crystal growth techniques. Unlike devices based on band-to-band transitions, the electrical and optical properties of QCLs, such as optical transition energy and dipole moment, upper and lower laser states lifetimes, and electron transport are determined by their heterostructure design. The working principle is shown in Figure 2(b). Over the past two decades, QCLs have become the most attractive semiconductor sources in the mid-infrared and terahertz regions. THz QCLs nevertheless still require cryogenic cooling for operation.

Figure 2 (a)Quantum cascade laser device

(b)Working principle of QCL

An alternative approach to THz generation from QCLs is based on intracavity difference-frequency generation (DFG) in a dual-wavelength mid-IR QCL. These devices, known as THz DFG-QCLs, use a mid-IR QCL active region engineered to exhibit a giant intersubband nonlinear susceptibility χ(2) for an efficient THz DFG process (Figure 3). Upon application of bias current, THz DFG-QCLs produce two mid-IR pump frequencies as well as the THz frequency, that corresponds to the difference of the mid-IR pump frequencies, via the intra-cavity nonlinear mixing process in the device active region. The optical nonlinearity of the DFG-QCL active region does not require population inversion across the THz transition. As a result, THz DFG-QCLs can operate at room temperature, unlike THz QCLs. THz DFG-QCLs are currently the only electrically-pumped, monolithic, mass-producible semiconductor sources operable at room temperature.

Figure 3 Schematics of working principle of THz QCL source based on nonlinear optical effect

In our group, by using our original concept “Anticross DAU active region (Figure 4(a)),” we achieved mW-level output power at room temperature . THz output power can be detected with room-temperature THz thermo-electric detector. Also, ultra-broadband THz emission spectrum spanning over one octave (Figure 4(b)) have been obtained based on the DAU active region, and as a result, we have successfully demonstrated THz imaging with these THz sources.

Figure 4 (a) AnticrossDAU structure

(b) Typical characteristics of room-temperature broadband THz nonlinear QCL device

Figure 5 Spectroscopic imaging using broadband THz-QCL source (Polyethylene, D-histidine, DL-histidine, reprint from Reference 4)

Future applications

The THz frequency range is very important for many applications, such as imaging, chem/bio sensing, heterodyne detection, and spectroscopy. In the field of ICT, ultra-broadband wireless communications are expected for short distance applications, while long-distance transmission is difficult due to strong water absorption.
In the field of nondestructive testing and analysis, THz frequency-range radiation has been used to demonstrate imaging of objects that are opaque at optical frequencies. There are many THz applications, including screening of chemical substances, nondestructive imaging for industrial material and historical arts object. By building a compact imaging system using THz nonlinear QCLs, much research on THz imaging technology will be performed in the future.


In the field of astronomy, THz frequency signal is very important since interstellar gas and dust can be detected in this frequency range. With the fine structure line of interstellar gases, the star formation process can be investigated. For these purposes, an astronomical receiver requires a compact local oscillator. Since THz nonlinear QCL sources can generate single frequency THz signal, it will be used as a LO to analyze a THz wave signal coming from space.

Our researcher received the 24th Optics and Quantum Electronics Achievement Award (Hiroshi Takuma Award)

Dr. Kazuue Fujita of Central Research Laboratory has received this award, which is given by the Japan Society of Applied Physics to honor those who have made outstanding achievements in the field of optics and quantum electronics.


 Award-Winning Achievements: Engineering research on Quantum Cascade Lasers and its development to room temperature terahertz semiconductor source


Hiroshi Takuma Award


  1. K. Fujita, S. Hayashi, A. Ito, T. Dougakiuchi, M. Hitaka, and A. Nakanishi. "Broadly tunable lens-coupled nonlinear quantum cascade lasers in the sub-THz to THz frequency range." Photonics Research Vol. 10, no. 3 pp. 703-710, 2022.
  2. A. Nakanishi, K. Akiyama, S. Hayashi, H. Satozono, and K. Fujita. "Spectral imaging of pharmaceutical materials with a compact terahertz difference-frequency generation semiconductor source." Analytical Methods Vol. 13, no. 46 pp. 5549-5554, 2021.
  3. A. Nakanishi, S. Hayashi, H. Satozono, and K. Fujita. "Polarization imaging of liquid crystal polymer using terahertz difference-frequency generation source." Applied Sciences Vol. 11, no. 21 pp. 10260, 2021.
  4. A. Nakanishi, S. Hayashi, H. Satozono, and K. Fujita, “Spectroscopic Imaging with an Ultra-Broadband (1–4 THz) Compact Terahertz Difference-Frequency Generation Source,” Electronics, Vol. 10, pp. 336, 2021.
  5. L. Consolino, M. Nafa, M. De Regis, F. Cappelli, ... and K. Fujita, “Direct Observation of Terahertz Frequency Comb Generation in Difference-Frequency Quantum Cascade Lasers,” Applied Sciences, Vol. 11, no.4 pp. 1416, 2021.
  6. Shohei Hayashi, Akio Ito, Masahiro Hitaka, and Kazuue Fujita, “Room temperature, single-mode 1.0 THz semiconductor source based on long-wavelength infrared quantum-cascade laser,” Applied Physics Express Vol. 13, pp. 112001, 2020.
  7. Atsushi Nakanishi, Hiroshi Satozono, and Kazuue Fujita, “Detection of single human hairs with a terahertz nonlinear quantum cascade laser,” Applied Optics Vol. 59, pp. 9169-9173, 2020.
  8. Atsushi Nakanishi, Shohei Hayashi, Hiroshi Satozono, and Kazuue Fujita, “Temperature-Insensitive Imaging Properties of a Broadband Terahertz Nonlinear Quantum Cascade Laser,” Applied Sciences Vol. 10, pp. 5926, 2020.
  9. Kazuue Fujita, Shohei Hayashi, Atsushi Nakanishi, Akio Ito, Masahiro Hitaka, and Tatsuo Dougakiuchi, "Sub-terahertz and terahertz generation in long-wavelength quantum cascade lasers," Nanophotonics Vol. 8, pp. 2235-2241, 2019.
  10. Masahiro Hitaka, Tatsuo Dougakiuchi, Akio Ito, Kazuue Fujita, Tadataka Edamura, "Stacked quantum cascade laser and detector structure for a monolithic mid-infrared sensing device," Applied Physics Letters Vol. 115, pp. 161102, 2019.
  11. Atsushi Nakanishi, Kazuue Fujita, Kazuki Horita, and Hironori Takahashi, "Terahertz imaging with room-temperature terahertz difference-frequency quantum-cascade laser sources," Optics express Vol. 27, pp.1884-1893, 2019.
  12. Jae Hyun Kim, Seungyong Jung, Yifan Jiang, Kazuue Fujita, Masahiro Hitaka, Akio Ito, Tadataka Edamura, and Mikhail A. Belkin, "Double-metal waveguide terahertz difference-frequency generation quantum cascade lasers with surface grating outcouplers," Applied Physics Letters Vol. 113, pp.161102, 2018.
  13.  Kazuue Fujita, Seungyong Jung, Yifan Jiang, Jae Hyun Kim, Atsushi Nakanishi, Akio Ito, Masahiro Hitaka, Tadataka Edamura, and Mikhail A. Belkin, "Recent progress in terahertz difference-frequency quantum cascade laser sources (Invited Review Article)," Nanophotonics Vol. 7, pp.1795-1817, 2018.
  14.  Kazuue Fujita, Akio Ito, Masahiro Hitaka, Tatsuo Dougakiuchi, and Tadataka Edamura. "Development of THz light sources based on QCL technology." In Quantum Sensing and Nano Electronics and Photonics XV, Vol. 10540, pp. 105401J. International Society for Optics and Photonics, 2018.
  15.  Luigi Consolino, Seungyong Jung, Annamaria Campa, Michele De Regis, Shovon Pal, Jae Hyun Kim, Kazuue Fujita et al., "Spectral purity and tunability of terahertz quantum cascade laser sources based on intracavity difference-frequency generation," Science advances Vol. 3, pp. e1603317, 2017.
  16.  Kazuue Fujita, Akio Ito, Masahiro Hitaka, Tatsuo Dougakiuchi, and Tadataka Edamura, "Low-threshold room-temperature continuous-wave operation of a terahertz difference-frequency quantum cascade laser source," Applied Physics Express Vol. 10, pp. 082102, 2017.
  17.  Tatsuo Dougakiuchi, Kazuue Fujita, Toru Hirohata, Akio Ito, Masahiro Hitaka, and Tadataka Edamura, "High photoresponse in room temperature quantum cascade detector based on coupled quantum well design," Applied Physics Letters Vol. 109, pp. 261107, 2016.
  18.  Kazuue Fujita, Masahiro Hitaka, Akio Ito, Masamichi Yamanishi, Tatsuo Dougakiuchi, and Tadataka Edamura, "Ultra-broadband room-temperature terahertz quantum cascade laser sources based on difference frequency generation," Optics express Vol. 24, pp. 16357-16365, 2016.
  19.  Kazuue Fujita, Masahiro Hitaka, Akio Ito, Tadataka Edamura, Masamichi Yamanishi, Seungyong Jung, and Mikhail A. Belkin, "Terahertz generation in mid-infrared quantum cascade lasers with a dual-upper-state active region," Applied Physics Letters Vol. 106, pp. 251104, 2015.
  20.  Masamichi Yamanishi, Tooru Hirohata, Syohei Hayashi, Kazuue Fujita, and Kazunori Tanaka, "Electrical flicker-noise generated by filling and emptying of impurity states in injectors of quantum-cascade lasers," Journal of Applied Physics Vol. 116, pp. 183106, 2014.
  21.  Tatsuo Dougakiuchi, Kazuue Fujita, Atsushi Sugiyama, Akio Ito, Naota Akikusa, and Tadataka Edamura, "Broadband tuning of continuous wave quantum cascade lasers in long wavelength (> 10μm) range," Optics express Vol. 22, pp. 19930-19935, 2014.
  22.  Bo Meng, Masamichi Yamanishi, Christian Pflügl, Kazuue Fujita, Federico Capasso, and Qi Jie Wang, "Investigation of tunable single-mode quantum cascade lasers via surface-acoustic-wave modulation," IEEE Journal of Quantum Electronics Vol. 49, pp. 1053-1061, 2013.
  23.  Romain Blanchard, Tobias S. Mansuripur, Burc G€okden, Nanfang Yu, Mikhail Kats, Patrice Genevet, Kazuue Fujita, Tadataka Edamura, Masamichi Yamanishi, and Federico Capasso, "High-power low-divergence tapered quantum cascade lasers with plasmonic collimators,"Appl. Phys. Lett., Vol. 102, pp.191114 -1-191114 -5, 2013.
  24.  Pietro Malara, Romain Blanchard, Tobias S. Mansuripur, Aleksander K. Wojcik, Alexey Belyanin, Kazuue Fujita, Tadataka Edamura, Shinichi Furuta, Masamichi Yamanishi, Paolo de Natale, and Federico Capasso, "External ring-cavity quantum cascade lasers," Appl. Phys. Lett., Vol. 102, No.14, 141105-1-141105-5, 2013.
  25.  Kazuue Fujita, Masamichi Yamanishi, Shinichi Furuta, Atsushi Sugiyama, and Tadataka Edamura, "Extremely temperature-insensitive continuous-wave quantum cascade lasers," Appl. Phys. Lett., Vol.101, No.18, pp.181111-1-181111-4, 2012.
  26.  Kazuue Fujita, Masamichi Yamanishi, Shinichi Furuta, Kazunori Tanaka, Tadataka Edamura, Tillmann Kubis, and Gerhard Klimeck," Indirectly pumped 3.7 THz InGaAs/InAlAs quantum-cascade lasers grown by metal-organic vapor-phase epitaxy," Optics Express, Vol. 20, pp.20647-20658, 2012.
  27.  Tatsuo Dougakiuchi, Kazuue Fujita, Naota Akikusa, Atsushi Sugiyama,Tadataka Edamura, and Masamichi Yamanishi,"Broadband Tuning of External Cavity Dual-Upper-State Quantum-Cascade Lasers in Continuous Wave Operation," Applied Physics Express, Vol. 4, pp. 102101-1-102101-3, 2011.
  28.  Kazuue Fujita, Shinichi Furuta, Atsushi Sugiyama, Takahide Ochiai, Akio Ito, Tatsuo Dougakiuchi, Tadataka Edamura, and Masamichi Yamanishi, “High-temperature quantum cascade lasers with wide electroluminescence (~600 cm-1), operationg in continuous wave above 100 oC,” Applied Physics Letters, Vol. 98, pp.231102-1-231102-3, 2011.
  29.  Kazuue Fujita, Shinichi Furuta, Tatsuo Dougakiuchi, Atsushi Sugiyama, Tadataka Edamura, and Masamichi Yamanishi, “Extremely broad-gain (Δλ/λ0~0.4), temperature-insensitive (T0~510K) quantum cascade lasers,” Optics Express, Vo. 19, pp.2694-2701, 2011.
  30.  Kazuue Fujita, Masamichi Yamanishi, Tadataka Edamura, Atsushi Sugiyama, and Shinichi Furuta, “Extremely high T0-values (~450 K) of long-wavelength (~15 μm), low-threshold-current-density quantum-cascade lasers based on the indirect pump scheme,” Applied Physics Letters, Vol. 97, pp.201109-1-201109-3, 2010.
  31.  Kazuue Fujita, Tadataka Edamura, Shinichi Furuta, and Masamichi Yamanishi, “High-performance, homogeneous broad-gain quantum cascade lasers based on dual-upper-state design,” Applied Physics Letters, Vol. 96, pp.241107-1-241107-3, 2010.
  32.  Kazuue Fujita, Shinich Furuta, Atsushi Sugiyama, Takahide Ochiai, Tadataka Edamura, Naota Akikusa, Masamichi Yamanishi and Hirofumi Kan, “High-Performanceλ∼ 8.6 μm Quantum Cascade Lasers With Single Phonon-Continuum Depopulation Structures,” IEEE Journal Of Quantum Electronics, Vol. 46, pp.683-688, 2010.
  33.  M. Ishihara, T. Morimoto, S. Furuta, K. Kasahara, N. Akikusa, K. Fujita, and T. Edamura, "Linewidth enhancement factor of quantum cascade lasers with single phonon resonance-continuum depopulation structure on Peltier cooler," Electronics letters Vol. 45, pp. 1168-1169, 2009.
  34.  Kazuue Fujita, Tadataka Edamura, Naota Akikusa, Atsushi Sugiyama, Takahide Ochiai, Shinichi Furuta, Akio Ito, Masamichi Yamanishi, and Hirofumi Kan, "Quantum cascade lasers based on single phonon-continuum depopulation structures," In Novel In-Plane Semiconductor Lasers VIII, Vol. 7230, p. 723016. International Society for Optics and Photonics, 2009.
  35.  Masamichi Yamanishi, Kazuue Fujita, Tadataka Edamura, and Hirofumi Kan, “Indirect pump scheme for quantum cascade lasers: dynamics of electron-transport and very high T0-values,” Optics Express, Vol. 16, pp.20748-20758, 2008.
  36.  Masamichi Yamanishi, Tadataka Edamura, Kazuue Fujita, Naota Akikusa, and Hirofumi Kan, "Theory of the intrinsic linewidth of quantum-cascade lasers: Hidden reason for the narrow linewidth and line-broadening by thermal photons," IEEE Journal of Quantum Electronics Vol. 44, 12-29, (2008).
  37.  K. Fujita, S. Furuta, A. Sugiyama, T. Ochiai, T. Edamura, N. Akikusa, M. Yamanishi, and H. Kan, “Room temperature, continuous-wave operation of quantum cascade lasers with single phonon resonance-continuum depopulation structures grown by metal organic vapor-phase epitaxy,” Applied Physics Letters, Vol. 91, pp.141121-1-141121-3, 2007.

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