Room-temperature Quantum Cascade Research Articles

Millimeter-wave generation with a room-temperature nonlinear quantum cascade laser

Millimeter-wave difference frequency generation is reported for a dual-wavelength mid-infrared quantum cascade laser operating at room temperature. To overcome a low mid-infrared-to-terahertz conversion efficiency below 1 THz, a long-wavelength, high-performance mid-infrared quantum cascade laser structure with higher nonlinear susceptivity is adopted. By designing the efficient allocation of mid-infrared pumps to two sections of fabricated distributed feedback grating, a closely separated dual-wavelength (λ1 ∼ 13.53 μm and λ2 ∼ 13.39 μm) laser oscillation was obtained. Consequently, a millimeter-wave emission at a frequency of 231 GHz was successfully observed at room temperature.

Fast-sweeping continuous wave quantum cascade laser operating in an external cavity with polygon mirror.

We report a continuous wave room temperature quantum cascade laser operating in an external cavity in the Littrow configuration with a 10-facet polygon mirror rotating at 24,000 RPM. The quantum cascade laser emission is swept across ∼1520 - 1625 cm-1 wavenumber range in less than ∼45 µs with a sweep repetition rate of 4 kHz. The measured maximum output power at the laser gain maximum, 15°C and 0.86 A driving current is ∼90 mW; the estimated average output power across the 45 µs wavenumber sweep is ∼50 mW. Through its sweep, the laser emits on the sequential Fabry-Perot longitudinal modes of the laser chip cavity with the mode separation of ∼0.5 cm-1. The linewidth of the emitting modes is less than ∼0.05 cm-1. Spectral measurements of the infrared absorption features of a 10 µm thick layer of acetophenone and water vapor in the air have demonstrated the capability of obtaining spectral data in less than 45 µs.

Room‐temperature quantum cascade laser packaged module at ∼8 μm designed for high‐frequency response

A high-speed, room-temperature quantum cascade laser packaged module emitting at 8.14 μm is presented. The cavity length of the laser is as small as 0.5 mm, and the threshold current at 298 K is 110 mA. A matching printed circuit board is inserted into the packaged module to reduce the RC constant. As a result, the rectification response of packaged module is relatively flat upto 2 GHz and the –3 dB cut-off frequency is increased from 0.9 to 2.2 GHz.

Watt-level, high wall plug efficiency, continuous-wave room temperature quantum cascade laser emitting at 7.7µm.

In this article, a InP based strain-balanced In0.58Ga0.42As/In0.47Al0.53As quantum cascade laser emitting at 7.7µm is reported. The active region is based on a slightly-diagonal bound to continuum design with 50 cascade stages and a low voltage defect Δinj of 96 meV. By optimizing the active region and waveguide structure, the waveguide loss αw of 1.18cm-1 are obtained, which contribute to a high wall-plug efficiency (WPE) of 9.08% and low threshold current of only 1.09 kA/cm2 in continuous-wave(CW) operation at 293K. The maximum single facet output power of 1.17W in CW operation and 2.3W in pulsed operation are measured at 293K. The narrow ridge and buried ridge structure epi-side-down-mounted on the diamond heatsink improved the heat dissipation of the device. A beam of pure zero order mode and a broad external-cavity tuning range from 7.16µm to 8.16µm are also achieved.

Room temperature quantum cascade laser with ∼31% wall-plug efficiency

In this article, we report the demonstration of a quantum cascade laser emitting at λ ≈ 4.9 μm with a wall-plug efficiency of ∼31% and an output power of ∼23 W in pulsed operation at room temperature with 50 cascade stages (Ns). With proper fabrication and packaging, this buried ridge quantum cascade laser with a cavity length of 5 mm delivers more than ∼15 W output power, and its wall-plug efficiency exceeds ∼20% at 100 °C. The experimental results of the lasers are well in agreement with the numerical predictions.

Room temperature quantum cascade lasers with 22% wall plug efficiency in continuous-wave operation.

We report the demonstration of quantum cascade lasers (QCLs) with improved efficiency emitting at a wavelength of 4.9 µm in pulsed and continuous-wave (CW) operation. Based on an established design and guided by simulation, the number of QCL-emitting stages is increased in order to realize a 29.3% wall plug efficiency (WPE) in pulsed operation at room temperature. With proper fabrication and packaging, a 5-mm-long, 8-µm-wide QCL with a buried ridge waveguide is capable of 22% CW WPE and 5.6 W CW output power at room temperature. This corresponds to an extremely high optical density at the output facet of ∼35 MW/cm2, without any damage.

High power continuous wave operation of single mode quantum cascade lasers up to 5 W spanning λ∼3.8-8.3 µm.

In this work, we report high power continuous wave room-temperature operation single mode quantum cascade lasers in the mid-infrared spectral range from 3.8 to 8.3 µm. Single mode robustness and dynamic range are enhanced by optimizing the distributed feedback grating coupling design and the facet coatings. High power single mode operation is secured by circumventing the over-coupling issue and spatial hole burning effect. Maximum single-facet continuous-wave output power of 5.1 W and wall plug efficiency of 16.6% is achieved at room temperature. Single mode operation with a side mode suppression ratio of 30 dB and single-lobed far field with negligible beam steering is observed. The significantly increased power for single mode emission will boost the QCL applications in long-range free-space communication and remote sensing of hazardous chemicals.

An adaptive Kalman filtering algorithm based on back-propagation (BP) neural network applied for simultaneously detection of exhaled CO and N2O.

A compact high-resolution spectroscopic sensor using a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser (QCL) was demonstrated for simultaneous measurements of exhaled carbon monoxide (CO) and nitrous oxide (N2O). The sampling pressure was optimized to improve the sensitivity, the optimal pressure was determined to be 150 mbar based on an optical density analysis of simulated and measured absorption spectra. An adaptive Kalman filtering algorithm based on back-propagation (BP) neural network was developed and proposed for real-time exhaled breath analysis in order to perform fast and high precision on-line measurements. The detection limits (1σ) of 1.14 ppb and 1.12 ppb were experimentally achieved for CO and N2O detection, respectively. Typical concentrations of exhaled CO and N2O from smokers and non-smokers were analyzed. The experimental results indicated that the state-of-the-art CW-QCL based sensor has a great potential for non-invasive, on-line identification and quantification of biomarkers in human breath.

High-power, continuous-wave, phase-locked quantum cascade laser arrays emitting at 8 µm.

We report a room-temperature eight-element phase-locked quantum cascade laser array emitting at 8 µm with a high continuous-wave power of 8.2 W and wall plug efficiency of 9.5%. The laser array operates primarily via the in-phase supermode and has single-mode emission with a side-mode suppression ratio of ~20 dB. The quantum cascade laser active region is based on a high differential gain (8.7 cm/kA) and low voltage defect (90 meV) design. A record high wall plug efficiency of 20.4% is achieved from a low loss buried ridge type single-element Fabry-Perot laser operating in pulsed mode at 20 °C.

ZnO-based terahertz quantum cascade lasers

High-power terahertz sources operating at room-temperature are promising for many applications such as explosive materials detection, non-invasive medical imaging, and high speed telecommunication. Here we report the results of a simulation study, which shows the significantly improved performance of room-temperature terahertz quantum cascade lasers (THz QCLs) based on a ZnMgO/ZnO material system employing a 2-well design scheme with variable barrier heights and a delta-doped injector well. We found that by varying and optimizing constituent layer widths and doping level of the injector well, high power performance of THz QCLs can be achieved at room temperature: optical gain and radiation frequency is varied from 108 cm −1 @ 2.18 THz to 300 cm −1 @ 4.96 THz. These results show that among II–VI compounds the ZnMgO/ZnO material system is optimally suited for high-performance room-temperature THz QCLs.

Mid-infrared broadband superluminescent light emitter arrays

Mid-infrared (MIR) room-temperature (RT) and continuous-wave (CW) broadband quantum cascade superluminescent light emitters (QCSLEs) have emerged as ideal broadband light sources for a number of applications of biomedical imaging, security inspection, and gas detection. It is quite challenging to attain a RT-CW output power up to milliwatt level due to the very low efficiency of the spontaneous emission in the intersubband transitions in QCSLEs. In this work, for the first time to the best of our knowledge, a compact light emitter array is realized by integrating several single emitters exhibiting a very high RT-CW power of 2.4mW, which is attributed to the sufficient low reflectivity provided by the waveguide structure that includes three sections with a short straight part adjacent to a tilted stripe and to a J-shaped waveguide, and the two-phonon resonance QC active structure. This advancement is certainly a big step forward to the applications of broadband light sources towards MIR photonics.

Quantum cascade laser based absorption spectroscopy for direct monitoring of atmospheric N2O isotopes

A compact high-resolution spectroscopic sensor using a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser (QCL) operating at 4.6 μm, is employed for simultaneous detection of three main isotopic species (14N15N16O, 15N14N16O and 14N14N16O). To enable a high-precision analysis of N2O isotopic species at ambient mixing ratios, a liquid nitrogen-free preconcentration unit is built to trap and load atmospheric N2O. The absorption spectra of 14N15N16O, 15N14N16O, and 14N14N16O between 2188.6 cm−1 and 2189 cm−1 are measured, and the respective ratios of the rare to the abundant isotopologues abundances are demonstrated. Moreover, spectroscopic parameters of pressure-broadening coefficient for selected absorption lines have been determined, and a good agreement is obtained by comparing with HITRAN database.

Room-temperature quantum cascade superluminescent light emitters with wide bandwidth and high temperature stability.

The realization of room-temperature (RT) mid-infrared (MIR) broadband light sources is fundamentally interesting and highly desirable for a number of applications. Recently, superluminescent light emitters (SLEs) based on quantum cascade (QC) structures have emerged as excellent candidates among mid-infrared broadband light sources. However, it is challenging to achieve RT-QCSLEs due to the very low efficiency of the spontaneous emission in the intersubband transitions. Here, we demonstrate the realization of a set of ~5 μm RT-SLEs under continuous wave (CW) or quasi-CW (10% duty circle) operation by using a two-phonon resonant QC active region and monolithic integrated waveguide structures. In addition, with the design of an inclined tapered cavity, the SLEs exhibit high milliwatt power, large spectral width of more than 200 cm-1 and good temperature characteristic. These demonstrated results are believed to be a big step forward to the applications of broadband MIR semiconductor light sources.

Erratum: “High photoresponse in room temperature quantum cascade detector based on coupled quantum well design” [Appl. Phys. Lett. 109, 261107 (2016)

First Page

High photoresponse in room temperature quantum cascade detector based on coupled quantum well design

We report high photoresponse measured in a room temperature quantum cascade detector (QCD) based on a coupled quantum well design that operates with a peak response wavelength of 5.4 μm. The coupled quantum well design is expected to produce higher photocurrents when compared with device active regions that use a combination of simple quantum wells. The coupled quantum well QCD demonstrated high responsivity of 22 mA/W at room temperature with a commonly used 45° wedge-based light coupling configuration. Application of a waveguide configuration to the proposed QCD yielded an elevated responsivity of ∼130 mA/W and a specific detectivity (D*) of 1.1 × 108 cm W−1 Hz1/2 at room temperature.

Ultra-broadband room-temperature terahertz quantum cascade laser sources based on difference frequency generation.

We present ultra-broadband room temperature monolithic terahertz quantum cascade laser (QCL) sources based on intra-cavity difference frequency generation, emitting continuously more than one octave in frequency between 1.6 and 3.8 THz, with a peak output power of ~200 μW. Broadband terahertz emission is realized by nonlinear mixing between single-mode and multi-mode spectra due to distributed feedback grating and Fabry-Perot cavity, respectively, in a mid-infrared QCL with dual-upper-state active region design. Besides, at low temperature of 150 K, the device produces a peak power of ~1.0 mW with a broadband THz emission centered at 2.5 THz, ranging from 1.5 to 3.7 THz.

Simultaneous atmospheric CO, N2O and H2O detection using a single quantum cascade laser sensor based on dual-spectroscopy techniques

A single continuous wave (CW) room-temperature (RT) quantum cascade laser (QCL) sensor based on dual spectroscopic techniques was demonstrated and developed for simultaneous measurement of atmospheric carbon monoxide (CO), nitrous oxide (N2O) and water vapor (H2O). The newly developed detection scheme combines the benefits of absolute concentration measurements using calibration-free direct absorption spectroscopy (DAS) with higher sensitive wavelength modulation spectroscopy (WMS), which offers the possibility of calibration-free trace gases concentration detection with a 3–4 fold improvement in measurement precision and a significant decrease in optimal signal averaging time. By using the DAS calibrated WMS-2f detection scheme, Allan deviation analysis indicates that measurement precision of 1.64ppb for CO, 1.15ppb for N2O and 50.4ppm for H2O was achieved with a 1-s integration time, which can be further improved to 0.21ppb, 0.18ppb and 5.65ppm by averaging up to 75s.

High-speed, room-temperature quantum cascade detectors at 4.3 μm

We present high-speed, room-temperature operated 4.3 μm quantum cascade detectors. The devices are processed as square mesas with 50 Ω coplanar access line and air-bridge connector. The high frequency features are explored using microwave rectification technique and a RLC circuit model. The -3 dB cutoff frequency is experimentally 9 GHz and 4 GHz for 20×20 μm2 and 50×50 μm2 detectors, respectively. The equivalent circuit analysis shows that a second order filter feature governs the devices. Higher cutoff frequency can be achieved by eliminate the parasitics further.

Generation of Kerr combs centered at 4.5 μm in crystalline microresonators pumped with quantum-cascade lasers.

We report on the generation of mid-infrared Kerr frequency combs in high-finesse CaF2 and MgF2 whispering-gallery-mode resonators pumped with continuous-wave room-temperature quantum cascade lasers. The combs were centered at 4.5 μm, the longest wavelength to date. A frequency comb wider than one half of an octave was demonstrated when approximately 20 mW of pump power was coupled to an MgF2 resonator characterized with quality factor exceeding 10(8).

Simultaneous measurement of NO and NO(2) by dual-wavelength quantum cascade laser spectroscopy.

The concept of a multi-wavelength quantum cascade laser emitting at two or more spectrally well-separated wavelengths is highly appealing for applied spectroscopy, as it allows detecting several species with compact and cost-efficient optical setups. Here we present a practical realization of such a dual-wavelength setup, which is based on a room-temperature quantum cascade laser emitting single-mode at 1600 cm-1 and 1900 cm-1 and is thus well-suited for simultaneous NO and NO2 detection. Operated in a time-division multiplexed mode, our spectrometer reaches detection limits of 0.5 and 1.5 ppb for NO2 and NO, respectively. The performance of the system is validated against the well-established chemiluminescence detection while measuring the NOx emissions on an automotive test-bench, as well as upon monitoring the pollution at a suburban site.