Continuous wave operation of terahertz metasurface quantum-cascade VECSEL with a long intra-cryostat cavity

Wu, Yu Sheng; Curwen, Christopher A.; Hayton, D. J.; Reno, John L.; Williams, Benjamin S.

doi:10.1063/5.0107667

Cited by 4 publications

(5 citation statements)

References 33 publications

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“…Another interesting point of comparison is the long-cavity QC-VECSEL in [40]. That VECSEL used an identical metasurface to the 3.4 THz metasurface in Fig.…”

Section: Results: Free Running Behaviormentioning

confidence: 99%

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Phase locking of THz QC-VECSELs to a microwave reference

Curwen¹,

Kawamura²,

Hayton³

et al. 2023

Preprint

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<p>High resolution frequency study and phase-locking have been performed on terahertz quantum-cascade vertical-external-cavity surface-emitting-lasers at 2.5 THz and 3.4 THz. A subharmonic diode mixer is used to downconvert the THz signal to a gigahertz intermediate frequency (IF). Feedback from reflections at the mixer are observed to have a strong influence on the free-running QC-VECSEL frequency stability as a result of efficient coupling to free-space compared to more typical ridge waveguide lasers. Instabilities in feedback result in free-running linewidths of tens of MHz, and at times >100 MHz. The QC-VECSEL IF signal is phase locked to a 100 MHz reference using the bias on the device as a means of error correction. Between 90-95% of the QC-VECSEL signal is locked within 2 Hz of the multiplied RF reference, and amplitude fluctuations on the order of 1-10% are observed, depending on the bias point of the QC-VECSEL. The bandwidth of the locking loop is ~1 MHz. Many noise peaks in the IF signal corresponding to mechanical resonances in the 10 Hz-10 kHz range are observed. These peaks are generally -30 to -60 dB below the main tone, and are below the phase noise level of the multiplied RF reference which ultimately limits the phase noise of the locked QC-VECSEL.</p>

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“…Another interesting point of comparison is the long-cavity QC-VECSEL in [40]. That VECSEL used an identical metasurface to the 3.4 THz metasurface in Fig.…”

Section: Results: Free Running Behaviormentioning

confidence: 99%

“…The 3.5 THz metasurface is identical to that in [10] and [40]. It has a total area of 1.5×1.5 mm 2 , and the central bias area is 0.5 mm in diameter.…”

Section: Metasurface Design and Characterizationmentioning

confidence: 99%

Phase locking of THz QC-VECSELs to a microwave reference

Curwen¹,

Kawamura²,

Hayton³

et al. 2023

Preprint

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show abstract

“…An off‐axis paraboloid (OAP) mirror with a focal length of 12.7 mm is introduced into the VECSEL cavity to reduce the intracavity diffraction loss and enable CW lasing using small metasurfaces in long lasing cavities. [ 21 ] The QC‐metasurface used in this paper is the same one as reported, [ 21 ] with a small bias area of diameter d = 0.4 mm for reduced injection current. It is designed to be resonant at 3.3 THz and consists of an array of ridges of width 12.2 µm repeated with a period of 41.7 µm (Figure 1b).…”

Section: Sample and Experimental Setupmentioning

confidence: 99%

“…In free‐running case, although only single‐mode lasing was observed using the same QC‐device, [ 21 ] we note that the existence of optical feedback can induce multimode operation. [ 29–31 ] Due to the temporally varying small feedback from the scanning Fourier‐transform infrared spectrometer (FTIR, Nicolet 8700) mirrors, we observed more than one lasing mode in the emission spectrum, though their peaks are close to each other which cannot be resolved by the limited FTIR resolution of 7.5 GHz (Figure 1e, see the Supporting Information for more details).…”

Section: Sample and Experimental Setupmentioning

confidence: 99%

“…For example, we have developed an intra‐cryostat focusing VECSEL cavity to reduce the intra‐cavity diffraction loss and enable continuous‐wave (CW) lasing at 3.4 THz with a cavity length of ≈30 mm. [ 21 ] Even though the gain bandwidth of the metasurface used was at least 100 times larger than the free spectral range, only a single lasing mode was observed. This is mainly due to a lack of spatial hole burning within the QC‐VECSEL metasurface which suppresses multimode instabilities, [ 22 ] although it is perhaps compounded by the fact that no effort toward dispersion engineering has yet been attempted.…”

Section: Introductionmentioning

confidence: 99%

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RF Injection Locking of THz Metasurface Quantum‐Cascade VECSEL

Curwen

Shahili

et al. 2023

Laser & Photonics Reviews

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Radiofrequency (RF) injection locking and spectral broadening of a terahertz (THz) quantum‐cascade vertical‐external‐cavity surface‐emitting laser (QC‐VECSEL) is demonstrated. An intracryostat VECSEL focusing cavity design is used to enable continuous‐wave lasing with a cavity length over 30 mm, which corresponds to a round‐trip frequency near 5 GHz. Strong RF current modulation is injected to the QC‐metasurface electrical bias to pull and lock the round‐trip frequency. The injection locking range at various RF injection powers is recorded and compared with the injection locking theory. Moreover, the lasing spectrum broadens from 14 GHz in free‐running mode to a maximum spectral width around 110 GHz with 20 dBm of injected RF power. This experimental setup is suitable for further exploration of active mode‐locking and picosecond pulse generation in THz QC‐VECSELs.

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Harmonic and Subharmonic RF Injection Locking of THz Metasurface Quantum-Cascade VECSEL

Wu,

Schreiber,

Kim

et al. 2024

ACS Photonics

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Harmonic and subharmonic RF injection locking is demonstrated in a terahertz (THz) quantum-cascade verticalexternal-cavity surface-emitting laser (QC-VECSEL). By tuning the RF injection frequency around integer multiples and submultiples of the cavity round-trip frequency, different harmonic and subharmonic orders can be excited in the same device. Modulation-dependent behavior of the device has been studied with recorded lasing spectral broadening and locking bandwidths in each case. In particular, harmonic injection locking results in the observation of harmonic spectra with bandwidths over 200 GHz. A semiclassical Maxwell-density matrix formalism has been applied to interpret QC-VECSEL dynamics, which aligns well with experimental observations.

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Continuous wave operation of terahertz metasurface quantum-cascade VECSEL with a long intra-cryostat cavity

Cited by 4 publications

References 33 publications

Phase locking of THz QC-VECSELs to a microwave reference

Phase locking of THz QC-VECSELs to a microwave reference

RF Injection Locking of THz Metasurface Quantum‐Cascade VECSEL

Harmonic and Subharmonic RF Injection Locking of THz Metasurface Quantum-Cascade VECSEL

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