Zhi-Wei Jia

1.8-W Room Temperature Pulsed Operation of Substrate-Emitting Quantum Cascade Lasers

High-power broad area substrate-emitting distributed feedback (DFB) quantum cascade laser emitting at λ ~ 4.6 μm is reported. Proper second-order DFB grating coupling, low waveguide loss mechanism, and epilayer-down mounting bring about a high vertical radiative optical power. The maximum peak power is as high as 1.82 W at 20 ^°C and still 1.22 W at 50 ^°C operated in pulsed mode with a pulsed width of 1 μs and duty cycle of 0.2%. A single-lobed radiation far-field with a divergence angle of 7.9 ^° in the ridge-width direction and two-lobed radiation far-field with a divergence angle of 0.61 ^° in the cavity-length direction are achieved by depositing the high-reflection coatings on both facets. Robust single-mode emission is continuously tunable by the heat sink temperature up to 115 ^°C.

Phase-locked array of quantum cascade lasers with an integrated Talbot cavity

We show a phase-locked array of three quantum cascade lasers with an integrated Talbot cavity at one side of the laser array. The coupling scheme is called diffraction coupling. By controlling the length of Talbot to be a quarter of Talbot distance (Zt/4), in-phase mode operation can be selected. The in-phase operation shows great modal stability under different injection currents, from the threshold current to the full power current. The far-field radiation pattern of the in-phase operation contains three lobes, one central maximum lobe and two side lobes. The interval between adjacent lobes is about 10.5°. The output power is about 1.5 times that of a single-ridge laser. Further studies should be taken to achieve better beam performance and reduce optical losses brought by the integrated Talbot cavity.

High efficiency, single-lobe surface-emitting DFB/DBR quantum cascade lasers.

We demonstrate a surface-emitting quantum cascade laser (QCL) based on second-order buried distributed feedback/distributed Bragg reflector (DFB/DBR) gratings for feedback and outcoupling. The grating fabricated beneath the waveguide was found to fundamentally favor lasing in symmetric mode either through analysis or experiment. Single-lobe far-field radiation pattern with full width at half maximum (FWHM) of 0.18° was obtained along the cavity-length direction. Besides, the buried DFB/DBR grating structure successfully provided an efficient vertical outcoupling mechanism with low optical losses, which manages to achieve a high surface outcouping efficiency of 46% in continuous-wave (CW) operation and 60% in pulsed operation at room temperature. Single-mode emission with a side-mode suppression ratio (SMSR) about 25 dB was continuously tunable by heat sink temperature or injection current. Our work contributes to the realization of high efficiency surface-emitting devices with high far-field beam quality that are significantly needed in many application fields.

Development of Low Power Consumption DFB Quantum Cascade Lasers

We report on the development of λ ~ 4.97 μm continuous-wave operation of substrate emitting distributed feedback quantum cascade lasers. A low threshold power consumption of 1.27 W is obtained at 20 °C, along with an ultralow threshold current density of 0.81 kA/cm² by depositing the high reflection coatings on both facets. Single-lobed far-field radiation pattern with a low divergence angle of about 0.24° × 20.34° is obtained. Reliable single-mode emission with a side-mode suppression ratio about 25 dB is observed among the working temperature range of 10 °C-30 °C.

Phase-locked array of quantum cascade lasers with an intracavity spatial filter

We show a phase-locked array of quantum cascade lasers with an intracavity spatial filter based on the Talbot effect. All the laser arrays show in-phase operation from the threshold current to full power current with a near-diffraction-limited divergence angle. The maximum power is just about 5 times that of a single-ridge laser for an eleven-laser array device and 3 times for a seven-laser array device. The structure was analyzed by using the multi-slit Fraunhofer diffraction theory, showing very good agreement with the experimental results. Considering the great modal selection ability, simple fabricating process, and potential for achieving continuous wave operation, this phase-locked array may be a hopeful solution to obtain higher coherent power.

Improvement of Buried Grating DFB Quantum Cascade Lasers by Small-Angle Tapered Structure

Small-angle tapered waveguide structure combining with the sampled grating was adopted to improve the output power and achieve room temperature continuous-wave (CW) operation of buried grating distributed feedback quantum cascade lasers (DFB QCLs). By utilizing the first-order channel of sampled grating, single-mode DFB QCLs at four different wavelengths were fabricated simultaneously. At 298 K, all four devices can emit more than 130 mW optical power in CW operation. Fundamental transverse mode operation with excellent beam quality was preserved.

High-power phase-locked quantum cascade laser array emitting at λ ∼ 4.6 μm

A phase-locked quantum cascade laser(QCL) array consisting of one hundred elements that were integrated in parallel was achieved at λ ∼ 4.6 μm. The proposed Fraunhofer’s multiple slits diffraction model predicted and explained the far-field pattern of the phase-locked laser array. A single-lobed far-field pattern, attributed to the emission of an in-phase-like supermode, is obtained near the threshold (Ith). Even at 1.5 Ith, greater than 73.3% of the laser output power is concentrated in a low-divergence beam with an optical power of up to 40 W.

Top Grating, Surface-Emitting DFB Quantum Cascade Lasers in Continuous-Wave Operation

We demonstrate room temperature, continuous-wave operation of top grating based surface-emitting distributed feedback quantum cascade lasers at λ ~ 4.8 μm. The second-order metal/semiconductor grating structure allows efficient surface emission for the transverse-magnetic-polarized light. The CW output power from the substrate facet reached 94 mW at 25 °C, with a low threshold current density of 1.21 kA/cm2. Single-mode emission with a side-mode suppression ratio about 30 dB is continuously tunable by the heat sink temperature or injection current. A far-field radiation pattern with a small divergence angle of 0.58° × 16.2° is obtained. Our work may contribute to the fabrication approach for substrate-emitting distributed feedback lasers based on a very simple processing.

Single-Mode Quantum Cascade Laser at

We presented a technique to realize single-mode quantum cascade lasers by simply etching several large-period slots in the ridge, which leads to refractive index perturbations and mirror-loss spectrum variation at different wavelengths stemming from high-order slot feedback. Stable single-mode operation is realized as a result of the reduced mirror-loss at the designed wavelength. A side-mode-suppression-ratio of about 20 dB for all measured temperatures and peak output power of about 500 mW in pulsed operation at room temperature have been achieved.

5.1~\mu \text{m}

A coupled ridge waveguide substrate-emitting quantum cascade laser array operating at