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Chalcogenide Glass IR Fibers Produced At Amorphous Materials
For Application In The 1 - 12 µm Wavelength Range
Amorphous Materials, Inc. (AMI) developed a unique process and draw tower design (see figure 1) to draw, clad and plastic coat chalcogenide glass fibers. Core diameters are closely controlled within the range of < 100 µm to as much as 1000 µm. Continuous drawing of fibers in lengths of 100 meters for large core diameters to thousands of meters for the very small core diameters is easily accomplished. The efficiency of the process leads to low cost fiber for the user. AMI has sold fiber commercially since 1990.
Fibers from chalcogenide glasses in a number of different glass systems were prepared and evaluated relative to attenuation, strength and flexibility. A glass composition from the As - Se - Te system was selected to provide the mid IR fibers. The fibers, designated Cl, show less than 1 db/m 2-10 µm and have a bend to break radius ranging from I cm for 750 µm core diameter to 0.1 cm for 100 µm fibers. The AM produced Cl fibers are the basis for a number of IR chemical sensors currently produced and sold commercially.
The process was also used to produce fibers, designated C2, from As 2S3 glass. The C2 fibers cover the wavelength range from the visible through the near infrared, 0.7 - 7 µm. The C2 fiber also has the ability to transmit large amounts of laser light.
Internal transmission plots typical for Cl and C2 fiber as measured using our Perkin Elmer Paragon 1000 FTIR are shown in figures 2 & 3. The plots do not include corrections for Fresnel reflection losses. Maximum transmission for Cl fiber is 60 % and 69 % for C2. The curves are generated when light is transmitted through a fiber 1.5 m in length and ratioed against a background measured through a fiber 0.5 min length. Fresnel reflections are thus ratioed out. Wavelengths below 1.5 µm are not shown in the C2 spectrum because of the instrument limitations. The plots show that Cl fiber is below 1 db/m from 2 to 10 µm while C2 fiber is below 1 db/m 1.5 - 6.5 µm. To check the validity of the FTIR results, laser light transmission is measured for 1 m of both types of fiber and the attenuation calculated. A tunable C02 laser emitting at 9.27 µm is used for the Cl fiber while a CO
laser emitting at 5.25 µm is used for the C2 fiber. The values are then marked on the curves for comparison to the FTIR curves. The laser transmission values are usually less than the attenuation indicated by the FTIR scan.
Figure 4 illustrates how Cl and C2 fiber can be used for chemical sensing in the sample area of a FTIR. Simple piano/convex AMTIR lenses are used to focus energy into the fiber end and return the energy at the end of the fiber back into the optical path of the instrument. Also shown is a similar application using either a rod or plate extruded from AMTIR-l or the glasses used for Cl or C2 fiber.
One area of interest in IR fibers has been the ability to transmit laser light from the C02 laser in amounts sufficient for laser surgery, welding and other applications. However, for selenium based glass fibers, only modest amounts of energy, less than 10 watts, have been transmitted before the fiber bums into. The problem is not just absorption and generation of heat. The limit is related to the thermal change in refractive index. When laser light is transmitted and absorbed down the length of the fiber a large positive value of index change leads to thermal lensing followed by melting and vaporization of the glass. With careful techniques, a 1000 µm Cl fiber can be used to transmit 5 -10 watts of laser power at 5.25 µm or 9.27 µm.
The situation is different for C2 fiber. Our measurements show the thermal change in refractive index for AS2S3 is essentially zero. Thermal lensing does not occur in C2 fibers. For this reason, energy in excess of 100 watts emitted from a CO laser has been reported to have been transmitted through a 700 µm fiber. Additionally, the low attenuation of 0.1-0.2 db/m at 5.25 µm has been confirmed in AM C2 fiber. A 1000 µm core C2 fiber should be capable of transmitting 100 watts of 5.25 µm energy emitted from a CO laser.
The chalcogenide glass fibers C 1 and C2 produced at AMI are chemically inert. Not attacked by moisture, Cl and C2 are unaffected by weak acids and bases while resistant to attack by most organic solvents. The fibers do not darken when exposed to visible light containing ultra violet.
| CORE GLASS | As-Se-Te (Cl) | As2S3 (C2) | ||||||
| Glass Transition Temperature °C | 136 | 180 | ||||||
| Softening Point °C | 170 | 208 | ||||||
| Thermal Expansion DL/Lx106/ºC | 23.5 | 21.4 | ||||||
Refractive Index
|
Value
|
Value
|
||||||
| Thermal Change in Index xl05/°C | +3 | ± 0.9 |
| @ 5.25 µm, db/m | 0.2-0.4 | 5<10 w | 0.2-0.4 > 100 w |
| @ 9.27 µm, db/m | 0.2-0.4 | 5<10 w | ---- |
| @ l0.6 µm, db/m | 4-5 | 5 w | ---- |
| lOOO µm Core | 4 | 62,000 | 4 | 44,000 |
| 750 µm Core | 1 | 68,000 | 3 | 45,000 |
| 500 µm Core | 0.8 | 70,000 | 1.7 | 56,000 |
| <l00 µm Core | 0.1 | 133,000 | 0.1 | 122,000 |
( Measurements courtesy of Tom Loretz of CES)
Numerical Aperture* 0.6-0.7 (± 40-50°) O.5-O.6 (± 35-40°)
(Measured at the 90 % point using variable iris while detecting energy from a heated surface. Large value results because of Fresnel reflection I refraction at oblique angles of incidence by the high refractive index core glass.)
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| SPOOLED FIBER | FIBER CONNECTOR |
| Quantity in meters | 1000 µm Core | 750 µm Core | 500 µm Core | 250 µm Core | 100 µm Core |
| 1-10 | $250 | $200 | $140 | $100 | $30 |
| 50 | $70 | $50 | $35 | $25 | $7 |
| >100 | $40 | $30 | $20 | $16 | $4 |
* Available cabled in most any length, 1-50 meters, jacketed in nylon tubing inside flexible stainless steel, $15/m
* Both ends polished, add $50
* Connectors both ends, stainless SMA, add $60
Pricing:
CONTACT: Greg Whaley
PH: 001-972-494-5624 FAX: 001-972-272-7971 E-mail GregWhaley@aol.com
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