James McCord

Infrared imaging with fiber optic bundles

Efforts have resumed to improve the image quality of infrared imaging bundles formed at AMI using the ribbon stacking method. The C4 glass has been used to reduce core size, increase packing density and improve flexibility. Ribbons are formed from unclad fiber wound on a drum with pitch, ribbon count and spacing between ribbons computer controlled. A small portion of each ribbon is compressed and fused using thin, dilute Epoxy. Unfortunately, the Epoxy, serving as a clad, absorbs most all the LWIR energy making the bundles unsuited for 8-12 μm cameras. The ribbons are removed from the drum and stacked, one on top of the other observing proper orientation to form the bundle. A typical 1 meter bundle is formed from 50-70 count ribbons for a total of 2500-4900 fibers, made from 2.5-4.9 Km of C4 fiber. Typical core diameters are 60-80 μm. Active surface area ranges from 60-70%. Infrared resolution images formed using a NIR tube camera equipped with a special relay lens demonstrates the resolution limit for the bundle. Currently, the limit is about 10 lp/mm. The bundle end is imaged in the 3-5 μm Agema 210 camera using an Amtir 1 F/1 meniscus, coated 3-5 μm. Video images taken in natural light of an individual, easily recognizable at 50 feet, will be shown. Results of careful evaluation carried out at Lockheed Martin in Orlando using a high performance Raytheon Galileo camera will be presented.

Amorphous Materials Molded IR Lens Progress Report

Amorphous Materials began in 2000 a joint program with Lockheed Martin in Orlando to develop molding technology required to produce infrared lenses from chalcogenide glasses. Preliminary results were reported at this SPIE meeting by Amy Graham1 in 2003. The program ended in 2004. Since that time, AMI has concentrated on improving results from two low softening glasses, Amtir 4&5. Both glasses have been fully characterized and antireflection coatings have been developed for each. Lenses have been molded from both glasses, from Amtir 6 and from C1 Core glass. A Zygo unit is used to evaluate the results of each molded lens as a guide to improving the molding process. Expansion into a larger building has provided room for five production molding units. Molded lens sizes have ranged from 8 mm to 136 mm in diameter. Recent results will be presented

Production of infrared-transmitting chalcogenide glasses

Chalcogenide glasses have been produced commercially for use in infrared systems for almost 50 years. Only three glass compositions in the western world have been produced and used in ton quantities: As2S3, Ge33As12Se55, and Ge28Sb12Se60. Production of these three compositions at Amorphous Materials will be discussed. Physical properties of the glasses will be compared and related to the properties of other IR optical materials. Drawing of chalcogenide glass fibers at Amorphous Materials will be described.

Improved imaging bundles developed by Amorphous Materials

Efforts have been underway for several years at AMI to develop a ribbon stacking method to fabricate infrared imaging bundles from chalcogenide glass fibers. Bundles have been formed drawing fibers from an As-Se-Te glass (Cl) and from As2S3 glass (C2). Fiber core diameter has been limited to 100 ?m or greater due to the low tensile strength of chalcogenide glasses. Glass cladding adds strength to the fiber but results in low active area (25-35%) and coarse images. Use ofunclad fiber increases packing density ( active area 50-70%,) and improves infrared camera images. Recently, a new As-Se glass, designated C4, was developed at AMI, that can be drawn into flexible fibers with core diameters of 50-60 ?m. Bundles formed from stacked ribbons ofunclad fiber produce infrared camera images markedly improved over previous bundles. Imagery using C4 bundles made with small core unclad fibers and a Cl bundle made with glass clad 140 ?m core fibers, are compared. Images for both bundles made using a low sensitivity 3-5?m camera are compared to those made using a very sensitive 3-5 ?m radiometer camera.

Fabrication of a 10-m-length IR imaging bundle from arsenic trisulfide glass fibers

Amorphous Materials (AMI) has been engaged for several years in developing a process suitable for forming coherent imaging bundles from small diameter chalcogenide glass fibers. Currently, in a SBIR II program funded by the Navy Air Warfare Center at Patuxent River, Md., efforts are directed towards forming a bundle 10 meters in length from arsenic trisulfide glass fibers using the stacked ribbon method. A drum 10 meters in circumference was constructed on which to wind the ribbons. The fiber core diameter goal is 50 micrometer. The bundle will be 7 mm square with an active fiber area greater than 50% and an overall transmission goal of 50%. Anti-reflection coatings on both ends are provided using the AMI coating facility. A unique method of forming imaging bundles will be discussed. Images formed during evaluation will be shown.

Production of arsenic trisulfide glass

At one time, arsenic trisulfide (As2S3) glass was the only IR optical material produced commercially for infrared optical systems. The glass was produced by the tons from the 50s into the 70s. However, as the emphasis shifted to the long wavelength 8 - 12 micrometer passive optical systems, the glass fell out of favor and production worldwide ceased. The production processes used were open systems which led to environmental concerns that also contributed to the decisions to cease production. In the 1990s, Amorphous Materials (AMI) became interested in the glass in part because of the reported ability of As2S3 glass fibers to transmit large amounts (greater than 100 watts) of laser power. A closed process which eliminated environmental concerns was developed to produce the glass. Major emphasis was in producing glass for IR fibers. Use for imaging systems was limited. Now, however, a trend has developed to produce imaging systems based on focal plane array technology which operate in the 3 - 5 micrometer wavelength region. A demand once again has been created for the glass. The method used at AMI to produce the glass is presented. Efforts to reduce absorption through purification of the elements are described. Properties of the glass are reviewed.

Progress report: fabrication of coherent IR glass fiber bundles

The results of attempts to fabricate coherent imaging IR glass fiber bundles have been described previously. The stacked ribbon method was used. The need to use smaller diameter fibers, more evenly packed was pointed out. Better methods to evaluate the optical performance of the bundle need to be developed. Results of continued efforts to improve are described.

Applications of infrared-transmitting chalcogenide glasses

Amorphous Materials produces for IR applications three chalcogenide glass compositions: As2S3, Ge33As12Se55 designated AMTIR 1, and Ge28Sb12Se60 designated AMTIR 3. Methods of production will be discussed. AMTIR 1 and AMTIR 3 were used extensively in FLIR systems. Amorphous Materials produces thousands of small sensor lenses for non contact temperature measuring devices. Drawing of chalcogenide glass fibers at Amorphous Materials will be described. Chemical sensing is the main application. Currently, the fabrication of coherent fiber imaging bundles is under development. Extrusion of glass rods for chemical sensing will be mentioned.

Laser-power delivery using chalcogenide glass fibers

During the last 15 years, numerous programs have been carried out in the U.S., UK, France, Japan, Israel and Russia aimed at providing a flexible chalcogenide glass fiber suited for delivery of power from a carbon dioxide laser emitting at 10.6 micrometer. The success of these programs has been modest at best with output power limited to 10 watts or less. The purpose of this paper is to examine chalcogenide glasses used for fiber from a thermal lensing standpoint.

Fabrication of chalcogenide glass rods and tubes by processor-controlled extrusion techniques

AMI is engaged in a number of programs to produce infrared transmitting fiber and lenses using AMTIRR materials, for commercial and military purposes. Through adaptation of Computer Engineering Services (authors prior company) conventional silicate glass extrusion technology, it is possible to fabricate fire polished rods and tubes of virtually any cross-sectional geometry. Diameters between about 3 mm and 75 mm and lengths as great as 1000 mm have been achieved. Extrusion is similar in many respects to fiber optic draw technology and requires precise control of feed and draw parameters, via the use of microprocessor systems. Internal homogeneity of the starting material is completely retained. This paper discusses the effort to date and describes product applications.