Pablo C. Pureza

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.

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.

Very large temperature-induced absorptive loss in high Te-containing chalcogenide fibers

The change in the absorption loss relative to room temperature of the infrared (IR)-transmitting Ge/sub 15/As/sub 35/Se/sub (50-x)/Te/sub x/ glass fibers in the temperature range of -110/spl deg/C/spl les/T/spl les/110/spl deg/C was investigated. The attenuation increased significantly at T/spl ges/40/spl deg/C. This is mainly attributed to thermally activated free carriers associated with the semimetallic character of the Te atom. For /spl lambda//spl les/4.2 /spl mu/m, the loss due to electronic and free-carrier absorption was strongly affected by temperature. In the wavelength region of 5-11 /spl mu/m, the loss was mainly due to free-carrier absorption. Beyond /spl lambda//spl ges/11 /spl mu/m, multiphonon absorption dominated the loss spectrum at T/spl les/60/spl deg/C while free-carrier absorption contributed mainly to the total loss at T/spl ges/80/spl deg/C.

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 spatial filtering capabilities of single mode infrared fibers

Spatial filtering is necessary to achieve deep nulls in optical interferometer and single mode infrared fibers can serve as spatial filters. The filtering function is based on the ability of these devices to perform the mode-cleaning function: only the component of the input field that is coupled to the single bound (fundamental) mode of the device propagates to the output without substantial loss. In practical fiber devices, there are leakage channels that cause light not coupled into the fundamental mode to propagate to the output. These include propagation through the fiber cladding and by means of a leaky mode. We propose a technique for measuring the magnitude of this leakage and apply it to infrared fibers made at the Naval Research Laboratory and at Tel Aviv University. All measurements are performed at 10.5 μm wavelength.

Effect of heating on the optical loss in the As-Se glass fiber

The increase in the optical loss of the IR-transmitting arsenic-selenide glass fiber in the temperature range of 150/spl deg/C /spl ges/T/spl ges/ 20/spl deg/C was investigated. Between the wavelength region of 1.3 and 8 /spl mu/m, there is a small increase in the loss in which the contribution of free-carrier absorption is small. At high temperature T=150/spl deg/C and /spl lambda//spl ges/8 /spl mu/m, both the free-carrier and multiphonon absorption contributed to the total loss. From a practical perspective, the As-Se fiber loss increases only slightly under normal operating temperatures and so can still be used for many applications.

Fabrication of As-S and As-Se optical fiber with low hydrogen impurities using tellurium tetrachloride (TeC1 4 )

Arsenic sulfide (As-S) and arsenic selenide (As-Se) glass optical fibers typically possess extrinsic absorption bands in the infrared wavelength region associated with residual hydrogen and oxygen related impurities, despite using purified precursors. We report a purification process based on the addition of 0.1 wt%tellurium tetrachloride (TeCl4) to the glass. During melting, the chlorine from TeCl4 reacts with the hydrogen impurities to produce volatile products (e.g. HCl) that can be removed by subsequent dynamic distillation. The processing conditions have been modified accordingly to give low H-S (1.5 dB/m) and low H-Se (0.2 dB/m) impurity content.

IR fiber optics development at the Naval Research Laboratory

We report the first technology demonstration of the use of an IR fiber cable in an IRCM system for missile jamming. The IR fiber cable contains sulphide glass fibers which possess low loss, high strength and high threshold to laser damage. The fiber cable was used to transmit the output from a laser operating in the 2 - 5 micrometers atmospheric window to a Jam Head located remote from the laser. The demonstration was successful and fiber cable performed remarkably well and without damage.

Raman amplification in As-Se fiber

We have demonstrated Raman amplification in small core As-Se fiber. We observed over 20 dB of gain in a 1.1-meter length of fiber pumped by a nanosecond pulse of approximately 10.8 W peak power at 1.50 micrometers . The peak of the Raman gain was shifted by approximately 230 cm-1 to 1.56 micrometers . The Raman gain coefficient is estimated to be about 2.3 x 10-11 m/W, over 300 times greater than that of silica. The large Raman gain coefficient coupled with the large IR transparency window of these fibers shows promise for development of As-Se Raman fiber lasers and amplifiers in the near, mid and long IR spectral regions.