Broadband continuous single-mode tuning of a short-cavity quantum-cascade VECSEL


Changing the length of a laser cavity is a simple technique for continuously tuning the wavelength of a laser but is rarely used for broad fractional tuning, with a notable exception of the vertical-cavity surface-emitting laser (VCSEL)1,2. This is because, to avoid mode hopping, the cavity must be kept optically short to ensure a large free spectral range compared to the gain bandwidth of the amplifying material. Terahertz quantum-cascade lasers are ideal candidates for such a short cavity scheme as they demonstrate exceptional gain bandwidths (up to octave spanning)3 and can be integrated with broadband amplifying metasurfaces4. We present such a quantum-cascade metasurface-based vertical-external-cavity surface-emitting laser (VECSEL) that exhibits over 20% continuous fractional tuning of a single laser mode. Such tuning is possible because the metasurface has subwavelength thickness, which allows lasing on low-order Fabry–Pérot cavity modes. Good beam quality and high output power are simultaneously obtained.

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Fig. 1: Metasurface cavity design and electromagnetic simulations.
Fig. 2: Measurement results on longitudinal mode m = 4 with 19% fractional tuning at 77 K.
Fig. 3: Measurement results on longitudinal mode m = 2 with 25% fractional tuning at 77 K.

Data availability

The data that support the plots within this study are available from the corresponding author upon reasonable request.


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This work was supported by the National Science Foundation (NSF) (1150071, 1407711, 1711892) and the National Aeronautics and Space Administration (NASA) (NNX16AC73G). Microfabrication was performed at the UCLA Nanoelectronics Research Facility, and wire bonding was performed at the UCLA Center for High Frequency Electronics. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the US DOE Office of Science. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, a wholly owned subsidiary of Honeywell International, for the US DOE’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in this article do not necessarily represent the views of the US DOE or the United States Government.

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C.A.C. and B.S.W. conceived of the idea. C.A.C. derived the experimental strategy, fabricated the devices, performed the measurements and analysed the data. J.L.R. performed the molecular beam epitaxy growth. C.A.C. and B.S.W. co-wrote the manuscript. All work was done under the supervision of B.S.W.

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Correspondence to Benjamin S. Williams.

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Supplementary Information

Supplementary details, Figs. 1–6 and refs. 1–4.

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Curwen, C.A., Reno, J.L. & Williams, B.S. Broadband continuous single-mode tuning of a short-cavity quantum-cascade VECSEL. Nat. Photonics 13, 855–859 (2019).

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