Phase-locked single-mode terahertz quantum cascade lasers array

We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback(DFB)grating,resulting in nearly five times amplification of the single-mode power.Due to the optimum length of Talbot cavity depends on wavelength,the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry-Perot(F-P)cavities.The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array,enabling phase-locked operation of ridges.We set the spacing between adjacent elements to be 220μm,much larger than the free-space wavelength,ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution.This scheme provides a new approach for enhancing the single-mode power of THz QCLs.

Anti-symmetric sampled grating quantum cascade laser for mode selection

For mode selection in a quantum cascade laser(QCL),we demonstrate an anti-symmetric sampled grating(ASG).The wavelength of the-1-th mode of this laser has been blue-shifted more than 75 nm(~10 cm^(-1))compared with that of an ordinary sampled grating laser with an emission wavelength of approximately 8.6μm,when the periodicities within both the base grating and the sample grating are kept constant.Under this condition,an improvement in the continuous tuning capability of the QCL array is ensured.The ASG structure is fabricated in holographic exposure and optical photolithography,thereby enhancing its flexibility,repeatability,and cost-effectiveness.The wavelength modulation capability of the two channels of the grating is insensitive to the variations in channel size,assuming that the overall waveguide width remains constant.The output wavelength can be tailored freely within a certain range by adjusting the width of the ridge and the material of the cladding layer.

Coupled-ridge waveguide quantum cascade laser array lasing at λ~5μm

In this work,we demonstrated high-power quantum cascade laser(QCL)arrays lasing at λ~5μm by employing an optimized coupled-ridge waveguide(CRW)structure.Five-element QCL arrays were simulated and fabricated through a two-step etching method to extend the CRW structure to a mid-wave infrared regime.A lateral far-field with the main peak near a diffraction-limited intensity curve of about 10°was observed by properly designing a geometric shape of the ridges and interspaces.By introducing a buried 2nd-order distributed feedback(DFB)grating,substrate emission with a radiation power above 1 W at 25℃ is achieved.Single longitudinal mode operation is obtained by changing the temperature of the heatsink with a good linear wavelength tuning coefficient of -0.2 cm^(-1)/K.

Dual-mode distributed feedback quantum cascade laser based on stacked 3D monolithic integration for on-chip multi-channel gas sensing

To facilitate the development of on-chip integrated mid-infrared multi-channel gas sensing systems,we propose a high-power dual-mode(7.01 and 7.5μm)distributed feedback quantum cascade laser based on stacked 3D monolithic integration.Longitudinal mode control is achieved by preparing longitudinal nested bi-periodic compound one-dimensional Bragg gratings along the direction of the cavity length in the confinement layer.Additionally,transverse coherent coupling ridges perpendicular to the cavity length direction are fabricated in the upper waveguide layer to promote the fundamental transverse mode output when all ridges are in phase.Stable dual-wavelength simultaneous emission with a side-mode suppression ratio of more than 20 dB was achieved by holographic exposure and wet etching.The entire spectral tuning range covers nearly 100 nm through joint tuning of the injection current and heat-sink temperature.High peak power and beam quality are guaranteed by the parallel coherent integration of seven-element ridge arrays.The device operates in a fundamental supermode with a single-lobed far-field pattern,and its peak output power reaches 3.36 W in pulsed mode at 20℃.This dual-mode laser chip has the potential for in-situ on-chip simultaneous detection of CH4and C2H6gases in leak monitoring.

14 μm quantum cascade lasers based on diagonal transition and nonresonant extraction

We report In P-based room-temperature high-average-power quantum cascade lasers emitting at 14 μm. Using a novel active region design, a diagonal bound-to-bound lasing transition is guaranteed by efficient electron injection into the upper laser level and fast nonresonant electron extraction through a miniband from the lower laser level. For a 4 mm long and 40 μm wide double channel ridge waveguide laser with 55 stages of the active region, the threshold current density is only 3.13 k A∕cm^2 at room temperature. At 293 K, the maximum singlefacet peak power and average power are up to 830 m W and 75 m W, respectively. The laser exhibits a characteristic temperature T0 of 395 K over a temperature range from 293 to 353 K.