Page 215 - Chalcogenide Glasses for Infrared Optics

IR Imaging Bundles Made fr om Chalcogenide Glass Fibers 191

A second evaluation of the bundle was carried out at Lockheed
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Martin in Orlando by Rich LeBlanc. A high-performance Galileo
camera was used. A nearly 1:1 optical relay coupled the bundle to the
camera. The acceptance angle (half angle) for the bundle was mea-
sured as 30°. Using the good camera and a 1:1 relay, individual fibers
were resolved. Some were dark and presumed broken. The limiting
resolution was about 10 lp/mm. Resolution target elements were
clearly imaged. A clear up-close facial image was made as well as
images of vehicles in a parking lot. The effort demonstrated that if the
relay lens were chosen to fill the view with the bundle image and the
objective lens were of good quality selected for the bundle applica-
tion, AMI bundles would produce useful infrared images.
Some of this effort to improve bundle image performance was
made after the U.S. Navy bundle program began. Improvement of
bundle construction techniques would be valuable later on. There
was much to be done in the program before any attempt to make a
bundle 10 m long could begin. First, we had to wait many months
until a drum with a circumference of 10 m could be designed, built,
delivered, and put in operation.
In summary, AMI developed methods to produce infrared imaging
bundles using the stacked ribbon method. The fibers could be glass
clad, but due to the nature of the clad glass, the process was too slow.
In addition, the cladding reduced the percentage of active area. Use
of C4 glass improved imagery because we could draw flexible small-
diameter fibers. However, in fusing the fibers to form the ribbons, a
thin epoxy solution was used. As the oblique rays entered the bundle,
the 8- to 12-µm energy was lost. AMI bundles were good for use with
the NIR (1.5-µm) camera, the MWIR (3- to 5-µm) camera, but not the
LWIR (8- to 12-µm) camera.

8.3 Goals of the Navy SBIR 10-m IR Imaging
Bundle Program
The goal of this Phase II program was for Amorphous Materials
6
(AMI) to provide for the Navy with an infrared imaging bundle made
from arsenic trisulfide glass fibers, 10 m long, to be used to transmit
infrared images from optical elements on the surface of an aircraft to
a sensitive 3- to 5-µm camera suitably located within. Arsenic trisulfide
glass was chosen because it transmits red light, the NIR and the
MWIR 3- to 5-µm light used in Navy imaging systems. The method
used to form the bundle was to be based on the AMI ribbon stacking
method. Modification of the method would be required to accommo-
date use of a drum with a circumference of 10 m. The drum would
have to be designed, constructed, installed, and put in operation
before a single 10-m bundle could be made. The fiber-optic imaging
bundle was to have a 7-mm × 7-mm cross-sectional format made with