Vinh Q. Nguyen

Fabrication of low-loss IR-transmitting Ge/sub 30/As/sub 10/Se/sub 30/Te/sub 30/ glass fibers

Improved purification and processing techniques have been utilized to fabricate Ge/sub 30/As/sub 10/Se/sub 30/Te/sub 30/ glass fibers with a minimum loss of O.11 dB/m at 6.6 /spl mu/m. This is the lowest loss reported for any telluride glass fiber in the infrared region. Furthermore, the fibers exhibit less than 1 dB/m loss between 5.25 and 9.5 /spl mu/m. >

Fabrication of long lengths of low-loss IR transmitting As/sub 40/S/sub (60-x)/Se/sub x/ glass fibers

Teflon clad and As/sub 40/S/sub 60/ glass clad As/sub 40/S/sub 55/Se/sub 5/ fibers transmitting in the 1-6 /spl mu/m wavelength region have been fabricated in lengths of about 50 m and with minimum losses of 0.098 and 0.65 dB/m, respectively. Short lengths of the Teflon clad fiber possessed a minimum loss of 0.047 dB/m. While current fiber losses are dominated by extrinsic scattering and absorption, the calculated theoretical minimum loss is estimated to be 3.6 dB/km at 5.3 /spl mu/m and is limited by the contribution from the weak absorption tail. Improvements in the purification and processing of the glasses into the optical fibers are required to reduce the losses further.

Fabrication of single-mode chalcogenide optical fiber

Long lengths (>150 m) of single-mode chalcogenide optical fiber were fabricated by a double crucible technique. Single-mode transmission through 10 m of continuous fiber was demonstrated using an F-center laser at 2.7 /spl mu/m. The optical loss of this fiber was measured by a standard cutback technique using an FTIR spectrometer and also using an F-center laser, A minimum loss of less than 1 dB/m was obtained.

Infrared evanescent-absorption spectroscopy with chalcogenide glass fibers

We have used telluride glass fibers fabricated in house to measure the evanescent-absorption spectra of water, methanol, ethanol, isopropanol, acetone, ethanoic acid, hexane, and chloroform. Furthermore, detection limits of less than 2 vol. % solute were obtained for mixtures of water and methanol, ethanol, isopropanol, acetone, and ethanoic acid. Techniques to reduce the detection limits are discussed.

Structural investigation of chalcogenide and chalcohalide glasses using Raman spectroscopy

Abstract HV- and HH-polarized Raman spectra of the chalcogenide glasses Ge 30 As 10 Se (60− x ) Te x (25⩽ x ⩽35) and the chalcohalide glasses Ge 30 As 10 Se 30 Te (30− y ) I y (0⩽ y ⩽30), Ge 30 As 10 Se 35 Te (25− z ) I z (0⩽ z ⩽20) were investigated. For the chalcogenide glasses, the main structural units include [AsSe 3− x Te x ] mixed pyramidal units, [GeSe 4− x Te x ] mixed tetrahedral units, and Ge–Te–Ge chains. The substitution of iodine for tellurium in the chalcohalide glasses results in the formation of Ge–I, As–I, and Se–I bonds which break up the three-dimensional network. The main structural units for the chalcohalide glasses are [AsSe x Te y I z ] mixed pyramidal units where x + y + z =3, [GeSe x Te y I z ] mixed tetrahedral units where x + y + z =4, and GeSe 3/2 I mixed tetrahedral units. The symmetry properties of these structural units has been determined through the dependence of the depolarization ratio on the frequency shift.

Development of low-loss IR transmitting chalcogenide glass fibers

We have fabricated long lengths of low loss sulphide and telluride glass fibers for the 1 - 6 and 3 - 12 micrometers regions, respectively. Minimum losses for core/clad fibers are approximately 0.6 and 0.7 dB/m, respectively, while core-only fibers have exhibited losses of about 0.1 dB/m. The measurements have been performed on long lengths, typically 7 - 50 meters. Fiber strengths are reasonable for many short length applications, but improved processing will lead to stronger fibers for long length applications. These fibers are candidates for chemical sensors and for IR laser power delivery.

Infrared optical fibers and their applications

Chalcogenide glass fibers based on sulphide, selenide, telluride and their rare earth doped compositions are being actively pursued at the Naval Research Laboratory (NRL) as well as world-wide. Great strides have been made in reducing optical losses using improved chemical purification techniques, but further improvements are needed in both purification and fiberization technology to attain the theoretical optical losses. Despite this, current singlemode and multimode chalcogenide glass fibers are enabling numerous applications. Some of these applications include laser power delivery, chemical sensing, scanning near field microscopy/spectroscopy, and fiber IR sources/lasers and amplifiers.

Measurement of bulk absorption coefficients of chalcogenide and chalcohalide glasses at 10.6 μm using CO2 laser calorimetry

Abstract The bulk absorption coefficients of chalcogenide and chalcohalide glasses at 10.6 μm have been measured using CO2 laser calorimetry. The results indicate that processing of as-received chemicals is necessary to lower the impurity oxide content of the glasses and consequently the absorption coefficient at 10.6 μm.

Chalcogenide glasses containing tellurium for IR fiber optics

We have fabricated stable chalcogenide glasses containing up to 35 at. % tellurium and these glasses do not exhibit crystallization upon reheating up to the fiber draw temperature. The physical properties such as Tg, packing density, and Vickers Hardness decreases while the mass density and CTE increase with Te content and these are attributed to the weaker delocalized metallic-bonding character introduced with Te. We have drawn unclad fibers with a minimum attenuation of 0.11 dB/m at 6.6 micrometers which represents the lowest loss reported for a chalcogenide glass containing high levels of Te. Preliminary core/clad fibers have been drawn with a minimum loss of 0.7 dB/m at 6.6 micrometers . Improvements in glass quality and processing will lead to lower losses. We also present data demonstrating the use of unclad fibers for evanescent sensing of numerous organic and inorganic liquids and their mixtures in the 3-12 micrometers region.

New moldable glasses for multispectral optics (Conference Presentation)

There is a strong desire to reduce size and weight of single and multiband IR imaging systems in ISR operations on hand-held, helmet mounted or airborne platforms. NRL is developing new IR glasses that transmit from 0.9 to < 12 µm in wavelength, with refractive index ranging from 2.38 to 3.17, to expand the glass map and provide compact solutions to multispectral imaging systems. These glasses were specifically designed to have comparable glass molding temperatures and thermal properties so that they can be laminated and co-molded into optics with reduced number of air-glass interfaces (lower Fresnel reflection losses). These new NRL glasses also have negative or very low dn/dT, making it easier to athermalize the optical system. Our multispectral optics designs using these new materials demonstrate reduced size, complexity and improved performance. The glass database is now available for distribution. Some of the NRL glasses are also available commercially. This presentation will cover discussions on the new optical materials, multispectral designs, as well fabrication and characterization of new optics.