Rafael R. Gattass

All-fiber mid-IR supercontinuum source from 1.5 to 5 µm

An all-fiber supercontinuum source extending from 1.5 to 5 μm has been demonstrated in single-mode step-index As2S3 fiber using a Raman shifted erbium doped mode-locked silica fiber laser pump source. 140 mW broadband power was demonstrated with a spectral intensity variation of 10 dB from 1.9 to 4.4 μm and 20 dB from 1.65 to 4.78 μm.

Review of infrared fiber-based components

The infrared range of the optical spectrum is attractive for its use in sensing, surveillance, and material characterization. The increasing availability of compact laser sources and detectors in the infrared range stands in contrast with the limited development of optical components for this optical range. We highlight developments of infrared components with a particular focus on fiber-based components for compact optical devices and systems.

Infrared Fiber

Fiber-based multimode combiners allow for wavelength and power scaling of laser sources while maintaining a common emission aperture and divergence. For applications in the mid-infrared spectral band, chalcogenide glass optical fibers are one of the few alternatives with high-power beam delivery. We demonstrated a 7 × 1 multimode fiber combiner based on a sulfide-based multimode chalcogenide fiber with 76% per-port transmission. Wavelength combining and power scaling in the mid-infrared are demonstrated through the fiber combiner.

N \times 1

Direct intensity modulation of laser systems in the mid-infrared is marred by instabilities in power output, emission wavelength, and mode profile. In particular, emission characteristics of current implementations of quantum cascade lasers are especially susceptible to modulations in the driving current. We present a broadband mid-infrared variable optical attenuator with large dynamic range and sub-millisecond response time. The modulator has demonstrated 52 dB dynamic range (limited by the detector noise) and frequency response, and has been tested at various wavelength covering 3.5-4.8 μm. The system is composed of a piezoelectric controlled tilt-mirror that images the laser beam into a mid-infrared transmitting optical fiber. The use of broadband anti-reflection optics in the system maintains a high throughput of . Power handling of the system has been confirmed up to 4 W (limited by the laser output power).

Multimode Combiner

We report on development and characterization of square registered infrared imaging bundles fabricated from As2S3fiber for HWIL applications. Bundle properties and cross-talk measurements are presented.

Broadband Watt-Level Mid-Infrared Fiber-Coupled Variable Optical Attenuator

In the visible and near-IR, silica fiber high power lasers, amplifiers, fiber combiners, couplers, fiber optic switches and attenuators have demonstrated impressive performance and have become critical technologies for many applications such as telecommunications, spectroscopy, sensing, laser machining, and directed energy. As mid-IR and long-wave IR applications become more prolific, the need for analogous devices in the IR becomes important. Chalcogenide fiber shows great promise for meeting the source and device needs for applications in the IR. Chalcogenide fiber has a broad transmission range out to 12 μm, depending upon composition, and is ideal for transmission of light in these wavelength ranges. In addition, chalcogenide fibers can be doped with rare earth ions or the high nonlinearity of chalcogenide glasses can be exploited to fabricate sources in the mid and long-wave-IR. In work to date, we have demonstrated an all-fiber broadband supercontinuum source in the mid-IR from 1.9 to 4.8 μm and have scaled up the power to >500 mW in this wavelength range [1]. We have also demonstrated a microchip laser pumped mid-IR supercontinuum source from 3.65 to 4.9 μm [2], IR fiber Raman amplification [3], and broad band mid-IR rare earth doped fiber sources [4]. Passive optical devices that we have demonstrated include chalcogenide fiber based optical attenuators [5], registered coherent imaging bundles [6] and multimode fiber combiners for power and wavelength combining of quantum cascade lasers [7]. In addition, we have developed methods to fabricate high power anti-reflection surface structures on chalcogenide fibers [8], splicing methods for chalcogenide fibers, and cabling and termination methods for fibers to allow the fiber sources and devices to be packaged for applications. Environmental testing and power testing has been performed on chalcogenide fiber and devices to determine the operational limits of these technologies. In this paper, we will review our prior and recent work on chalcogenide based mid-IR sources and devices and the packaging, characterization and applications of these sources and devices.

IR Imaging Bundles for HWIL Testing

Abstract. The bending loss is a critical parameter for packaging, representing a limiting parameter in the minimization of fiber-based devices. For applications in the mid-infrared spectral band, chalcogenide glass optical fibers are one of the few alternatives for high-power beam delivery. We present experimental results for the bending loss of a sulfide-based multimode chalcogenide fiber for a broad range of infrared wavelengths as well demonstrating >5.8  W power handling for a 6.25-mm radius bend.

Chalcogenide fiber based mid-IR sources and applications

Splices between materials with dissimilar thermal expansion and melting points are particularly difficult to create. We have developed a method for splicing YAG single crystal fiber to silica fiber. Optical losses associated with the splices were measured for multimode fibers to be 0.33 dB. The splices display greater than 50 kPsi of tensile strength with reaction bonding at the interface. Study of the elemental composition at the splice interface showed formation of a stable intermediate material that provides mechanical strength to the splice. This is a major step toward developing very high power integrated and compact laser systems based on crystals and glass despite their stark dissimilarities in physical and material properties.

Bend loss in multimode chalcogenide fiber at infrared wavelengths

We report on fabrication and optical properties of double clad single crystal Yb:YAG core fiber. For the first time, net gain is demonstrated in a cladding pumped Yb:YAG single crystal fiber structure.

Fusion splicing of highly dissimilar YAG crystal fiber and silica fiber with reaction bonding

The need for small, robust, and highly selective sensors, for both military and homeland security requirements, is driving the development of portable detectors for hazardous materials. Infrared spectroscopy exhibits high selectivity because the infrared vibrational transitions correlate to the molecular structure and functional groups within the molecule. Small FTIR systems exist as COTS items; however, these systems still require precise moving components to generate the interferogram. A more desirable approach is to build a solid state system with no precision moving parts as required by a typical moving mirror interferometer. This work will describe the design aspects of an optical fiber based mid-infrared FTIR, and focus specifically on the stateof- the-art mid-infrared transmitting optical fibers and the use of an optical fiber supercontinuum source for efficient coupling of light into the system.