Page 216 - Chalcogenide Glasses for Infrared Optics

192 Cha pte r Ei g h t

fibers with a core diameter of 50 µm. The active fiber area goal was to
be 70 percent and with the use of antireflection coatings reach an overall
transmission goal of 50 percent in the 3- to 5-µm band. Many problems
would have to be solved. Specific objectives are listed here:
1. Reduce the core diameter into the 40- to 50-µm range.
2. Using the ribbon pressing tool, increase the packing density
of the fibers to attain the 70 percent goal.
3. Expend considerable effort to develop a reliable method to
purify sulfur to be used to produce low-absorption As S
2 3
glass. Our goal is an attenuation of 1 dB/m for water at
2.92 µm and 5 dB/m at 4 µm due to hydrogen sulfide as
measured with the FTIR. Attenuation in the fiber will also be
measured by laser transmission using the 5.25-µm emission
of the CO laser. Another Navy goal is 0.1 dB/m at 2.44 µm.
4. Absorption-free transmission of an arsenic trisulfide fiber is
only 69 percent. Fresnel reflection losses must be minimized
considering the optical path is 10 m. Establishment of an AMI
antireflection coating capability for imaging bundles will be
required.
5. The optical performance of the bundles will be evaluated
using a resolution target as a critical test. Good-quality relay
and objective ir lenses designed to couple the bundles to the
ir camera and the image to the bundle will be required to
produce useful images. The designs are to be made by Gary
Wiese of Panoptics. AMI will fabricate and coat the lenses.

8.4 The Navy Phase II 27-Month Program
AMI developed the technology and built a facility capable of producing
for the U.S. Navy ir coherent FO imaging bundles 10 m in length for
use with IRFPA (infrared focal plane array) cameras. Results of efforts
directed toward the specific goals listed above are discussed below in
the order listed.

8.4.1 The 1-m C2 Imaging Bundles
The fabrication of 1-m fiber-optic bundles was used to develop tech-
niques and make decisions suitable to drawing and stacking ribbons
on the 10-m drum. The drum was not delivered and put in operation
until more than one-half of the 27 months had passed. A total of nine
bundles were made during the program, four in Phase I and five in
Phase II. The last, bundle 9, was made and evaluated in August 1997,
the seventh month of the program. An attempt to reduce core size by
changing the exit port size was ineffective. We were able to draw 50-µm