Characterization of single-mode chalcogenide optical fiber for mid-infrared applications

Abstract

Chalcogenide fibers display a wide transmission window ranging from 2-10.6 μm, ideally suited to the development of passive and active mid-infrared (MIR) sensors. They are essential building blocks for the integration and miniaturization of laser-based MIR optical systems for terrestrial, airborne and space-based sensing platforms. Single-mode chalcogenide fibers have only recently become commercially available and therefore performance data and standard reproducible processing techniques have not been widely reported. In this paper we present a method for producing high quality cleaved facets on commercial single-mode As-Se fibers with core and cladding diameters of 28μm and 170μm respectively. The emitted beam profile from these fibers, using the 9.4μm line of a tunable CO 2 laser, showed the presence of leaky cladding modes due to waveguiding conditions created by the protective acrylate jacket. These undesirable cladding modes were easily suppressed by applying a gallium coating on the cladding near both input and output facets. We provide experimental data showing efficient mode suppression and the emission of a circular nearperfect Gaussian beam profile from the fiber. Furthermore, analyses of the beam, acquired by scanning an HgCdTe detector, yielded a 1/e 2 numerical aperture of 0.11 with a full width half maximum divergence of 11° for these fibers. The availability of single-mode MIR fibers, in conjunction with recent advances in room temperature quantum cascade lasers (QCL), could provide compact and light-weight transmitter solutions for several critical defense and nuclear nonproliferation needs.

Mid-Infrared Spectroscopy and Challenges in Industrial Environment

“…To isolate the QCL devices from any kind of inadvertent exposure to high temperature of the process gas, ease of servicing of the laser modules and ensuring Gaussian beam delivery, Chalcogenide glass (ChGs), Flouride glass, Sapphire and Silver Halide fibers were initially used for the transmission of Mid-IR lasers as it has wide optical transmission windows in the IR region. A major challenge with the fibers was their brittle nature and laser feedback due to back reflections from the fiber end which reduces signal-to-noise ratio [13,14]. Last decade has witnessed rapid development of low-loss Hollow Core Waveguides (HCW) for transmission of the Mid-IR beams from the QCLs [15][16][17][18][19].…”

Fiber delivery of mid-IR lasers

“…However, chalcogenide glass fibers have serious drawbacks for use in molecular spectroscopy applications. 6 For example, reflections off the fiber end can cause laser feedback, and cladding modes are supported in these waveguides. Both of these effectively reduce the signal-to-noise ratio in measurement systems.…”