In this work, single-mode distributed feedback (DFB) interband cascade laser (ICL) devices with record short wavelength emission below 2.8 μm are presented. Pulsed measurements based on broad area laser devices with a cavity of 2 mm length and 150 μm width showed threshold current densities of 383 A/cm2 at T = 20 °C and a characteristic temperature T0 of 67 K. Fabricated DFB devices were operated in continuous wave mode at room temperature, with threshold currents of 57 mA and demonstrated side mode suppression ratios of larger than 25 dB. The devices showed current tuning ranges of 7 nm and total (including drive current and temperature) tuning ranges of 12 nm, with respective tuning rates of 21 nm/W, 0.13 nm/mA and 0.29 nm/K. Using the full spectral gain bandwidth of the underlying ICL material, single-mode DFB emission was observed within a wavelength range of 150 nm utilizing different DFB grating periods.
Monolithic two-section interband cascade lasers offering a wide wavelength tunability in the wavelength range around 3.7 µm are presented. Stable single mode emission in several wavelength channels was realized using the concept of binary superimposed gratings and two-segment Vernier-tuning. The wavelength selective elements in the two segments were based on specially designed lateral metal grating structures defined by electron beam lithography. A dual-step dry etch process provided electrical separation between the segments. Individual current control of the segments allowed wavelength channel selection as well as continuous wavelength tuning within channels. A discontinuous tuning range extending over 158 nm in up to six discrete wavelength channels was achieved. Mode hop free wavelength tuning up to 14 nm was observed within one channel. The devices can be operated in continuous wave mode up to 30 °C with output powers of 3.5 mW around room temperature.Interband cascade laser (ICL) technology has granted access to the mid-infrared wavelength region from 3 to 6 µm with low threshold powers [1-4], enabling for example novel high-speed, highsensitivity tunable laser absorption spectroscopy (TLAS) applications [5,6]. These require single mode laser emission, which can be achieved by a grating structure providing distributed feedback (DFB) [7,8]. The spectral bandwidth of sensors based on conventional DFB lasers is however limited by the current-induced tuning range of these devices, which is usually on the order of a few nanometers. Laser sources with increased tunability offer new possibilities for spectroscopic applications, for example the simultaneous detection of several gas species with a single sensor. An increased accessible spectral range also allows base line determination in the detection of molecules with broad absorption features, e.g. complex hydrocarbons. One way to achieve wider tunability is given by the use of a multiplexing schemes based on multiple individual DFB lasers at selected wavelengths [9]. However, this approach is expensive and limited by rapidly increasing complexity. Another approach based on external cavity (EC) setups [10] is of limited use for industrial applications due to the lack of ruggedness, the rather large size and high cost of EC based setups. A monolithic solution that is compact, rugged and that provides high tuning speeds is given by a multi-segment laser device with aperiodic grating structures. Several competitive approaches exist like sampled gratings [11,12] and binary superimposed gratings (BSGs) [13]. In this paper BSG structures were used because of the increased coupling strength compared to alternative solutions. In addition, BSG structures allow rather readily the selection of arbitrary combinations of wavelengths within the gain area. Corresponding designs with varying numbers of segments have been demonstrated at shorter emission wavelengths based on conventional diode laser gain media [14][15][16][17].
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The detection and measurement of hydrocarbons is of high interest for a variety of applications, for example within the oil & gas industry from extraction throughout the complete refining process, as well as for environmental monitoring and for portable safety devices. This paper presents a highly sensitive, selective and robust tunable laser analyzer that has the capability to analyze several components in a gas sample stream. More specifically, a multi-gas system for simultaneous detection of C1 to iC5 hydrocarbons, using a room temperature distributed feedback interband cascade laser array, emitting in the 3.3 micrometer band has been realized. It combines all the advantages of the tunable laser spectroscopy method for a fast, sensitive and selective in-line multicomponent tunable laser analyzer. Capable of continuous and milliseconds fast monitoring of C1-iC5 hydrocarbon compositions in a process stream, the analyzer requires no consumables (e.g. purging, carrier gas) and no in-field calibration, enabling a low cost of ownership for the analyzer. The system was built, based on an industrial GasEye series platform and deployed for the first time in field at Preem refinery in Lysekil, Sweden in autumn 2018. Results of the measurement campaign and comparison with gas chromatography instrumentation is presented.
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