J. Nguyen

Room temperature continuous wave operation of quantum cascade lasers with watt-level optical power

We demonstrate quantum cascade lasers at an emitting wavelength of 4.6μm, which are capable of room temperature, high power continuous wave (cw) operation. Buried ridge geometry with a width of 9.8μm was utilized. A device with a 3mm cavity length that was epilayer-down bonded on a diamond submount exhibited a maximum output power of 1.3W at room temperature in cw operation. The maximum output power at 80K was measured to be 4W, with a wall plug efficiency of 27%.

Buried heterostructure quantum cascade lasers with high continuous-wave wall plug efficiency

The authors report on the development of λ∼4.7μm strain-balanced InP-based quantum cascade lasers with high wall plug efficiency and room temperature continuous-wave operation. The use of narrow-ridge buried heterostructure waveguides and thermally optimized packaging is presented. Over 9.3% wall plug efficiency is reported at room temperature from a single device producing over 0.675W of continuous-wave output power. Wall plug efficiencies greater than 18% are also reported for devices at a temperature of 150K, with continuous-wave output powers of more than 1W.

Room-temperature continuous-wave operation of quantum-cascade lasers at λ∼4μm

High-power cw λ∼4μm quantum-cascade lasers (QCLs) are demonstrated. The effect of different cavity length and laser die bonding is also investigated. For a high-reflectivity-coated 11-μm-wide and 4-mm-long epilayer-down bonded QCL, cw output powers as high as 1.6W at 80K and 160mW at 298K are obtained, and the cw operation is achieved up to 313K with 12mW. The laser exhibits a threshold current density of 1.96kA∕cm2, a slope efficiency of 737mW∕A, and a maximum wall-plug efficiency of 0.9% under cw mode at 298K. In pulsed mode, a maximum average power of 552mW at 298K is achieved at 45% duty cycle and a characteristic temperature is 176K from 80to393K.

Electrically pumped photonic crystal distributed feedback quantum cascade lasers

We demonstrate electrically pumped, room temperature, single mode operation of photonic crystal distributed feedback (PCDFB) quantum cascade lasers emitting at λ∼4.75μm. Ridge waveguides of 100μm width were fabricated with both PCDFB and Fabry-Perot feedback mechanisms. The Fabry-Perot device has a broad emitting spectrum and a double lobed far-field character. The PCDFB device, as expected, has primarily a single spectral mode and a diffraction limited far field characteristic with a full angular width at half maximum of 2.4°. This accomplishment represents the first step in power scaling of single mode, midinfrared laser diodes operating at room temperature.

High-power λ∼9.5μm quantum-cascade lasers operating above room temperature in continuous-wave mode

We report high-power continuous-wave (cw) operation of λ∼9.5μm quantum-cascade lasers to a temperature of 318K. A high-reflectivity-coated 19-μm-wide and 3-mm-long device exhibits cw output powers as high as 150mW at 288K and still 22mW at 318K. In cw operation at 298K, a threshold current density of 1.57kA∕cm2, a slope efficiency of 391mW∕A, and a maximum wall-plug efficiency of 0.71% are obtained. In pulsed operation, a maximum average power of 317mW is achieved at 49% duty cycle. The emission wavelength in cw mode is shifted from 9.524μm at 288K to 9.547μm at 313K near 1.05A drive current with a temperature tuning coefficient of 0.92nm∕K.

Quantum-cascade lasers operating in continuous-wave mode above 90°C at λ∼5.25μm

We report on the design and fabrication of λ∼5.25μm quantum-cascade lasers (QCLs) for very high temperature continuous-wave (cw) operation. Cw operation is reported up to a maximum temperature of 90°C (363K). Cw output power is reported in excess of 500mW near room temperature with a low threshold current density of 1.4kA∕cm2 at 298K. Room temperature average power of over 540mW is reported at 50% duty cycle. A high thermal conductance (Gth) of 340W∕Kcm2 is reported for cw QCLs. A finite element thermal model is used to investigate the Gth and maximum cw operating temperature of the QCLs.

Optical coatings by ion-beam sputtering deposition for long-wave infrared quantum cascade lasers

The authors report on the development of high-reflection and multilayer antireflection coatings using ion-beam sputtering deposition for long-wave infrared (λ∼9.4μm) quantum cascade lasers. A metallic high-reflection coating structure using Y2O3 and Au is demonstrated to achieve a high reflectance of 96.70%, and the use of a multilayer anti-reflection coating structure using PbTe and ZnO is demonstrated to achieve a very low reflectance of 1.64%. A 170% improvement of peak laser output power and a 169% increase in wall-plug efficiency are reported without any beam steering effects.

Overview of quantum cascade laser research at the Center for Quantum Devices

Over the past several years, our group has endeavored to develop high power quantum cascade lasers for a variety of remote and high sensitivity infrared applications. The systematic optimization of laser performance has allowed for demonstration of high power, continuous-wave quantum cascade lasers operating above room temperature. In the past year alone, the efficiency and power of our short wavelength lasers (λ~4.8 μm) has doubled. In continuous wave at room temperature, we have now separately demonstrated ~10% wallplug efficiency and ~700 mW of output power. Up to now, we have been able to show that room temperature continuous wave operation with >100 mW output power in the 3.8< λ<11.5 μm wavelength range is possible.

Techniques for high-quality SiO2 films

We report on the comparison of optical, structural, and electrical properties of SiO2 using plasma-enhanced chemical vapor deposition and ion-beam sputtering deposition. High-quality, low-temperature deposition of SiO2 by ion-beam sputtering deposition is shown to have lower absorption, smoother and more densely packed films, a lower amount of fixed oxide charges, and a lower trapped-interface density than SiO2 by plasma-enhanced chemical vapor deposition. This high-quality SiO2 is then demonstrated as an excellent electrical and mechanical surface passivation layer on Type-II InAs/GaSb photodetectors. The device performance improved by at least two orders of magnitude in surface resistivity, trap density, and zero-bias resistance-area product. The passivation layer also allows the device the ability to withstand the reflow and curing of underfill epoxy.

Characterization and analysis of single-mode high-power continuous-wave quantum-cascade laser

We measured and modeled the performance characteristics of a distributed-feedback quantum-cascade laser exhibiting high-power continuous-wave (CW) operation in a single spectral mode at λ≈4.8μm and temperatures up to 333K. The sidemode suppression ratio exceeds 25dB, and the emission remains robustly single mode at all currents and temperatures tested. CW output powers of 99mW at 298K and 357mW at 200K are obtained at currents well below the thermal rollover point. The slope efficiency and subthreshold amplified spontaneous emission spectra are shown to be consistent with a coupling coefficient of no more than κL≈4–5, which is substantially lower than the estimate of 9 based on the nominal grating fabrication parameters.