Page 186 - Chalcogenide Glasses for Infrared Optics

162 Cha pte r Se v e n

10
Amorphous materials
4.6 chalcogenide optical fiber
8 H 2 Se
Clad with glass
Attenuation (dB/m) 6 6.1 5 10.6

4
3.4
2.3
3
6.8 6.4
2

0
1 2 3 4 5 6 7 8 9 10 11 12
Wavelength (µm)
FIGURE 7.5 FTIR measured absorption of AMI C2 fi ber.

core were clad with a nonabsorbing glass in place of the plastic. Note
the absorption level is below 1 dB/m from 3 to 9.5 µm.
Comparing the bending radius to break a fiber was the next test.
The fibers tested were drawn from core glass (Amtir 1 with 2 percent
Te), Amtir 2 (As-Se with no Ge), and C2 glass (As-Se-Te with no Ge).
Workers at Galileo Electro-Optics reported breaking strength results
based on breaking radius, fiber diameter, and Young’s modulus.
Young’s modulus was available from acoustical measurements on
Amtir 1 and the value reduced 10 percent for the Te content. Servo
results were available for Amtir 2 and C2. The process involved
slowly bending the fibers in decreasing radius until they break. Fibers
were taped down to the tangent to circles drawn on a table with
decreasing radius. The AMI results for the same glass fibers were
equal to or higher than the Galileo Electro-Optics results, demonstrating
the AMI process produced strong fibers. Figure 7.6 shows a comparison
of the bend-to-break radius for the three glasses as a function of
fiber diameter. From the figure we find the limiting radius for C2
20-mil core fiber is 0.75 in, 2.8 in for Amtir 2 fiber, and 3.75 in for Te
modified Amtir 1 glass fibers. We may conclude that germanium-
containing glass fibers are the more brittle than those based on
only the As-Se glass. Fibers containing Te along with As-Se in C2
are the most flexible. The addition of Te in the glass composition
adds nondirectional metallic bonding to the covalent As-Se glass
and at the same time increases longer wave transmission because
of increased atomic mass relative to selenium. Addition of clad-
ding to the fibers will improve the strength numbers as well as the