Quantum Cascade Laser Array Research Articles

Nitrous oxide quartz-enhanced photoacoustic detection employing a broadband distributed-feedback quantum cascade laser array

We present a gas sensing system based on quartz-enhanced photoacoustic spectroscopy (QEPAS) employing a monolithic distributed-feedback quantum cascade laser (QCL) array operated in a pulsed mode as a light source. The array consists of 32 quantum cascade lasers emitting in a spectral range from 1190 cm−1 to 1340 cm−1. The optoacoustic detection module was composed of a custom quartz tuning fork with a prong spacing of 1 mm, coupled with two micro-resonator tubes to enhance the signal-to-noise ratio. The QEPAS sensor was validated by detecting the absorption of the P- and R-branches of nitrous oxide. The measurements were performed by switching the array QCLs in sequence while tuning their operating temperature to retrieve the fine structure of the two N2O branches. A sensor calibration was performed, demonstrating a linear responsivity for N2O:N2 concentrations from 1000 down to 200 parts-per-million. With a 10 s lock-in integration time, a detection sensitivity of less than 60 parts-per-billion was achieved permitting the monitoring of nitrous oxide at global atmospheric levels.

Mid-infrared quantum cascade laser arrays with electrical switching of emission frequencies

We present a design of quantum cascade laser arrays made of ridge-waveguide devices in which the emission frequency can be electrically switched between several specified values. Our approach relies on fabricating multiple independently-biased distributed feedback grating sections along the laser ridge waveguides. Switchable single-mode lasing from the laser facet is achieved by balancing the injection pumping of the different grating sections. Our method provides a robust solution that can increase the tuning bandwidth of the quantum cascade laser arrays without increasing the size of the array emission aperture.

Chirped coupled ridge waveguide quantum cascade laser arrays with stable single-lobe far-field patterns

Power scaling in a broad area quantum cascade laser (QCL) tends to deteriorate beam quality with the emission of a multiple-lobe far-field pattern. In this paper, we demonstrate a coupled ridge waveguide QCL array consisting of five elements with chirped geometry. In-phase mode operation is secured by managing supermode loss with properly designed geometries of ridges. A single-lobe lateral far-field with a near diffraction limited beam pattern was obtained in the whole current dynamic range. The devices were fabricated with the wet and dry etching method. The regrowth technique of the InP:Fe insulation layer and InP:Si waveguide layer was employed. Such a structure has the potential to optimize the beam quality of the recently reported high-power broad-area QCL with a reduced cascade number.

Tapered Quantum Cascade Laser Arrays Integrated with Talbot Cavities

Power scaling in broad area quantum cascade laser (QCL) usually leads to the deterioration of the beam quality with an emission of multiple lobes far-field pattern. In this letter, we demonstrate a tapered QCL array integrated with Talbot cavity at one side of the array. Fundamental supermode operation is achieved in the arrays with taper straight-end connected to the Talbot cavity. Lateral far-field of the fundamental supermode shows a near diffraction limited beam divergence of 2.7°. The output power of a five-element array is about three times as high as a single-ridge laser with an emission wavelength of around 4.8 μm. However, arrays with the taper-end connected to the Talbot cavity always show a high-order supermode operation whatever Talbot cavity length is.

Multi-wavelength sampled Bragg grating quantum cascade laser arrays

A multi-wavelength sampled Bragg grating (SBG) quantum cascade laser array operating between 7.32 and 7.85 μm is reported. The sampling grating structure, which can be analyzed as a conventional grating multiplied by a sampling function, is fabricated by holographic exposure combined with optical photolithography. The sampling grating period was varied from 8 to 32 μm, and different sampling order (−1st, −2nd, and −3rd order) modes were achieved. We propose that higher-order modes with optimized duty cycles can be used to take full advantage of the gain curve and improve the wavelength coverage of the SBG array, which will be beneficial to many applications.

Phase-locked, high power, mid-infrared quantum cascade laser arrays

We demonstrate phase-locked, high power quantum cascade laser arrays, which are combined using a monolithic, tree array multimode interferometer, with emission wavelengths around 4.8 μm. A maximum output power of 15 W was achieved from an eight-element laser array, which has only a slightly higher threshold current density and a similar slope efficiency compared to a Fabry-Perot laser of the same length. Calculated multimode interferometer splitting loss is on the order of 0.27 dB for the in-phase supermode. In-phase supermode operation with nearly ideal behavior is demonstrated over the working current range of the array.

Portable standoff spectrometer for hazard identification using integrated quantum cascade laser arrays from 65 to 11 µm

This article presents new spectroscopic results in standoff chemical detection that are enabled by monolithic arrays of Distributed Feedback (DFB) Quantum Cascade Lasers (QCLs), with each array element at a slightly different wavelength than its neighbor. The standoff analysis of analyte/substrate pairs requires a laser source with characteristics offered uniquely by a QCL Array. This is particularly true for time-evolving liquid chemical warfare agent (CWA) analysis. In addition to describing the QCL array source developed for long wave infrared coverage, a description of an integrated prototype standoff detection system is provided. Experimental standoff detection results using the man-portable system for droplet examination from 1.3 meters are presented using the CWAs VX and T-mustard as test cases. Finally, we consider three significant challenges to working with droplets and liquid films in standoff spectroscopy: substrate uptake of the analyte, time-dependent droplet spread of the analyte, and variable substrate contributions to retrieved signals.

In-water fiber-optic evanescent wave sensing with quantum cascade lasers

The ability of detecting harmful chemicals is an important safety requirement for drinking water systems. An apparatus for in-water chemical sensing based on the absorption of evanescent waves generated by a quantum cascade laser array propagating in a silver halide optical fiber immersed into water is demonstrated. We present a theoretical analysis of the sensitivity of the system and experimentally characterize its real-time response and spectroscopic detection for injection of a sample chemical (ethanol) in a tube containing water.

Proposal for a Monolithic Broadband Terahertz Quantum Cascade Laser Array Tailored to Detection of Explosive Materials

Proposal for a Monolithic Broadband Terahertz Quantum Cascade Laser Array Tailored to Detection of Explosive Materials

Response to “Comment on ‘Phase-locked array of quantum cascade lasers with an intracavity spatial filter’” [Appl. Phys. Lett. 111, 256101 (2017)

Response to “Comment on ‘Phase-locked array of quantum cascade lasers with an intracavity spatial filter’” [Appl. Phys. Lett. <b>111</b>, 256101 (2017)

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.

Multi-gas sensing with quantum cascade laser array in the mid-infrared region

Wide tunable lasers sources are useful for spectroscopy of complex molecules that have broad absorption spectra and for multiple sensing of smaller molecules. A region of interest is the mid-infrared region, where many species have strong ro-vibrational modes. In this paper a novel broad tunable source composed of a QCL DFB array and an arrayed waveguide grating (also called multiplexer) was used to perform multi-species spectroscopy (CO, \(\mathrm{C}_{2}\mathrm{H}_{2}\), \(\mathrm{CO}_{2}\)). The array and the multiplexer are associated in a way to obtain a prototype that is non-sensitive to mechanical vibrations. A 2190–2220 cm\(^{-1}\) spectral range is covered by the chip. The arrayed waveguide grating combines beams to have a single output. A multi-pass White cell was used to demonstrate the efficiency of the multiplexer.

External Cavity Tuning of Coherent Quantum Cascade Laser Array Emitting at ∼7.6 μm**Supported by the National Basic Research Program of China under Grant No 2013CB632801, the National Key Research and Development Program of China under Grant No 2016YFB0402303, the National Natural Science Foundation of China under Grant Nos 61435014, 61627822, 61574136, 61306058 and 61404131, the Key Projects of Chinese Academy

An external cavity quantum cascade laser (QCL) array with a wide tuning range and high output power is presented. The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow configuration. Taking advantage of the single-lobed fundamental supermode far-field pattern, the tuning capability of 30.6 cm−1 is achieved with a fixed injected current of 3.5 A at room temperature. Single-mode emission can be observed in the entire process. The maximum single-mode output power of the external cavity setup is as high as 25 mW and is essential in real applications.

Coherent emission from integrated Talbot-cavity quantum cascade lasers.

We report experimental realization of phase-locked quantum cascade laser (QCL) array using a monolithically integrated Talbot cavity. An array with six laser elements at a wavelength of ~4.8 μm shows a maximum peak power of ~4 W which is more than 5 times higher than that of a single ridge laser element and a slope efficiency of 1 W/A at room temperature. Operation of in-phase coherent supermode has been achieved over the whole dynamic range of the Talbot-cavity QCL. The structure was analysed using a straightforward theoretical model, showing quantitatively good agreement with the experimental results. The reduced thermal resistance makes the structure an attractive approach to achieve high beam quality continuous wave QCLs.

Coupled Ridge Waveguide Substrate-Emitting DFB Quantum Cascade Laser Arrays

A coupled ridge waveguide substrate-emitting quantum cascade laser array operating at $\lambda \sim ~7\mu $ m was presented. Fifteen elements were integrated in parallel to get high peak power and improved beam quality. The device was operating at fundamental supermode with a single-lobed far-field pattern. A narrow divergence angle of 2.9° in the ridge-width direction and 0.36° in the cavity-length direction were obtained by carefullydesigning the coupled ridge waveguide structure.Single-mode emission was observed by employing a buried second-orderdistributed-feedback grating. The peak power of the device was more than 2 W in pulsed operation at room temperature. This letter showed great potential to enlarge the output power of the surface-emitting devices while maintaining good beam quality.

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.

Phase-locked laser arrays through global antenna mutual coupling

Phase locking of an array of lasers is a highly effective method in beam shaping because it increases the output power and reduces the lasing threshold. Here, we show a conceptually novel phase-locking mechanism based on ‘antenna mutual coupling’ in which laser elements interact through far-field radiations with definite phase relations. This allows a long-range global coupling among the array elements to achieve a robust phase locking in two-dimensional laser arrays. The scheme is ideal for lasers with a deep subwavelength confined cavity, such as nanolasers, whose divergent beam patterns could be used to achieve a strong coupling among the elements in the array. We demonstrated experimentally such a scheme based on subwavelength short-cavity surface-emitting lasers at terahertz frequencies. More than 37 laser elements that span over ∼8 λo were phase locked to each other, and delivered up to 6.5 mW (in a pulsed operation) single-mode radiation at ∼3 THz, with a maximum 450 mW A–1 slope efficiency and a near-diffraction-limited beam divergence. Two-dimensional arrays of short-cavity surface-emitting THz quantum cascade lasers are phase-locked to each other via mutual coupling. A directive beam on the order of 10° divergence and a maximum slope efficiency of 450 mW A−1 is achieved.

Single-Mode Quantum Cascade Laser Array Emitting From a Single Facet

We present an array of single-mode quantum cascade lasers operating in the range 8– $9.5~\mu \text{m}$ . The resonator features a pair of distributed Bragg reflectors for the mode selection, together with a second-order extraction grating. The radiation of these substrate emitting devices was combined in a single collector ridge. A proof of principle featured seven laser devices with a coverage of 170 cm $^{-1}$ . The functionality of our approach is corroborated with a set of polarization and near-field measurements confirming the collection of multiple frequencies in a unique ridge.

External cavity coherent quantum cascade laser array

We report on the development of a coherent quantum cascade laser array that consists in the fabrication of multi-stripes array. The main characteristic of this kind of source is that an anti-symmetrical signature with two lobes is obtained in the far field. Taking advantage of this drawback, a grating is aligned with one lobe of the source. Thus a Littrow configuration is designed that permit to obtain a wide tunability of the source. First results are presented and a preliminary test of the source is realized by measurements on acetone.

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.