Monolithic single mode interband cascade lasers with wide wavelength tunability

Abstract

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].

The Interband Cascade Laser

“…The same team reported cw single-mode lasing to 0 • C at λ = 5.2 µm [119], and later to 6.0 µm by growing on an InAs substrate [101]. A two-segment grating provided single-mode emission spanning 158 nm, effectively covering the entire ICL gain spectrum, although the tuning was not continuous [120].…”

Interband Cascade Laser Arrays for Simultaneous and Selective Analysis of C1–C5 Hydrocarbons in Petrochemical Industry

“…Additionally, the flexibility of such a laser array could be further increased by incorporating waveguides with extended wavelength tuning capability. 23…”

Widely tunable 23 μm III-V-on-silicon Vernier lasers for broadband spectroscopic sensing

“…Besides, widely tunable laser sources are also suited to detect the broad absorption features of bio-molecules. For the >3 µm mid-infrared wavelength range, widely tunable GaSb-based interband cascade lasers and InP-based quantum cascade lasers have been realized by employing sampled gratings as a Vernier filter [16,17]. In the 2-2.5 µm range, GaSb-based semiconductor lasers coupled to an external diffraction grating used for wavelength selection have shown wide tunability [16][17][18].…”

“…For the >3 µm mid-infrared wavelength range, widely tunable GaSb-based interband cascade lasers and InP-based quantum cascade lasers have been realized by employing sampled gratings as a Vernier filter [16,17]. In the 2-2.5 µm range, GaSb-based semiconductor lasers coupled to an external diffraction grating used for wavelength selection have shown wide tunability [16][17][18]. But the use of a bulky diffraction grating and mechanical controller as the wavelength selection mechanism make these external cavity lasers expensive and difficult to use for portable sensing systems.…”