Dan-Yang Yao

High-performance uncooled distributed-feedback quantum cascade laser without lateral regrowth

We demonstrate, uncooled, room-temperature continuous-wave (cw) operation of single-mode distributed-feedback (DFB) quantum cascade lasers (QCLs) emitting around 4.6 μm without lateral regrowth. The effects of cavity length on device performance are studied. A record low threshold electrical power consumption of 2.3 W for the entire laser system with a 1.5-mm-long cavity is realized. For the 2-mm-long laser, high cw output power of 125 mW and very low threshold current density of 0.86 kA/cm2 are obtained. Our devices represent an important step towards using uncooled DFB QCLs in mid-infrared spectral range for practical applications.

Surface emitting quantum cascade lasers operating in continuous-wave mode above 70 °C at λ~ 4.6 μm

We demonstrate surface emitting distributed feedback (DFB) quantum cascade lasers for very high temperature continuous-wave (cw) operation at λ ∼ 4.6 μm. A second-order DFB grating beneath the waveguide provides efficient vertical outcoupling. cw operation is reported up to a temperature of 75 °C. Total output power of 105 mW is obtained with a record low threshold current density of 0.85 kA/cm2 at 10 °C. Single-lobed far-field radiation pattern with a low divergence angle of about 0.17° × 18.7° is achieved. Robust single-mode emission with a side-mode suppression ratio about 30 dB is continuously tunable by the heat sink temperature and injection current.

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.

High power buried sampled grating distributed feedback quantum cascade lasers

A novel index-coupled distributed feedback quantum cascade laser emitting at λ ∼ 4.8 μm is demonstrated by a sampled grating. The coupling coefficient can be almost controlled arbitrarily according to the duty cycle of sampled grating. The additional supermodes caused by the sampled grating can be strongly suppressed by choosing a small sampling period, so that the supermodes are shifted apart from the gain curve. Single-mode emission without any significant disadvantages compared with uniform grating is achieved. Especially, this powerful approach presented here can be applied to achieve the performance with high power and low threshold simultaneously.

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.

Directional collimation of substrate emitting quantum cascade laser by nanopores arrays

We report a beam reshaping phenomena via nanopore array defined on the emission window of a substrate emitting quantum cascade lasers. A pronounced beam divergence reduction by a factor of 6 in the elongated beam direction is achieved. A collimated laser beam with small divergence (2.9° × 0.12°) is observed. These single-mode devices preserve good power and spectral performances at room temperature continuous wave operation. This beam reshaping design is simple to fabricate and able to be adapted for other wavelengths ranging from the visible to mid-infrared regimes, which would open up major opportunities for the control of beam divergence.

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.

Very low threshold operation of quantum cascade lasers

A strain-compensated InP-based quantum cascade laser (QCL) structure emitting at 4.6 μm is demonstrated, based on a two-phonon resonant design and grown by solid-source molecular beam epitaxy (MBE). By optimizing the growth parameters, a very high quality heterostructure with the lowest threshold current densities ever reported for QCLs was fabricated. Threshold current densities as low as 0.47 kA/cm2 in pulsed operation and 0.56 kA/cm2 in continuous-wave (cw) operation at 293 K were achieved for this state-of-the-art QCL. A minimum power consumption of 3.65 W was measured for the QCL, uncooled, with a high-reflectivity (HR) coating on its rear facet.

Design and Fabrication of Six-Channel Complex-Coupled DFB Quantum Cascade Laser Arrays Based on a Sampled Grating

We designed and fabricated a six-channel complex-coupled distributed feedback (DFB) quantum cascade laser arrays based on a sampled Bragg grating. The six-channel DFB laser arrays exhibit a linear tuning range of 74 nm centered at a wavelength of 7.55 μm at room temperature. Robust single-mode emission with a side mode suppression ratio about 20 dB was observed, even at full power. The used sampled grating and reflectivity coating on the back facet lead to the peak output power varying from 55 to 82mW with a small difference in slope efficiency from 100 to 128mW/A.

Index-coupled surface porous grating distributed feedback quantum cascade laser

We report design of special low loss, index-coupled surface porous grating distributed feedback profile by using holographic lithography combined with electro-chemical etching technology. Room temperature continuous-wave (cw) operation of single-mode quantum cascade lasers emitting at λ ∼ 7.6 μm has been achieved. Due to attenuate interplay between the surface plasmon waves and the waveguide waves, the waveguide loss of the lasers is significantly reduced, when compared to conventional surface metal/semiconductor grating devices. This resulted in an improved overall laser performance, such as a reduction of the threshold current density and an increase in cw output power.