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FIBER OPTICS
The fiberoptic cable is made up of fifty-seven randomly distributed glass fibers. Nineteen of these fibers are 100-micron and are distributed to the VNIR region. The remaining fibers are 200-micron and are evenly divided between the two SWIR regions. All fifty-seven fibers are housed in a plastic sheath. A standard cable has a diameter of 0.19 inches while an all-weather cable has a diameter of 0.27 inches.
The fibers are protected by a metal spiral inside the black cable casing and are free to float inside the metal spiral. If there are kinks in your cable, the fibers are not necessarily damaged. If, however, your cable has been crunched so severely that you are able to see the protective metal spiral, the chances are high that the fibers have been damaged too. Each broken fiber results in a 5% loss of response.
It is also possible to damage fibers by coiling the cable up too tightly. For the short term, the cable can withstand being coiled to a size slightly larger than a baseball. If left in that position for a long time, for example, all week or a month, the fibers are likely to develop longitudinal fractures that will not be detectable. These fractures in the fiber will cause light leakage, resulting in a weaker signal. The fiber optic cables should be stored by hanging them from the spectrometer handle or placing them within the carry case compartment below the spectrometer. The fiber cable should never be stored with a bend of less than a 5" diameter.
The tip of the optical fiber cable is not particularly susceptible to damage so, a tip cover is not crucial unless it is likely to be exposed to mud. Covers can be made by cutting some pieces of eighth-inch shrink tubing to about 1.5" lengths and shrinking them onto the fiber cable tip. They will slide on and off the cable easily.
The all-weather cable can withstand low temperatures whereas the standard cable has a tendency to become brittle causing the fibers in the standard cable can break more readily. Both cables should be coiled to a diameter no less than 5 inches; however, the all-weather cable is much more difficult to bend due to the thicker sheath. These cables are also waterproof however if water is allowed to run down the fiberoptic cable to the instrument, the water will penetrate the unit and can cause damage.
The cables should be coiled and stored in the compartment provided in the bottom of the carrier. All accessories should be removed and stored elsewhere.
 The standard length issued with an instrument is 1.5 meters. This cable has a Numerical Aperture (NA) of 0.22 ± 0.02. The Numerical Aperture decreases with cable length.
Fiberoptic cables can be ordered in a variety of lengths. However, as the length increases, the cable performance decreases. The increased length ultimately results in the loss of response as shown:
 The loss in response is further amplified when “jumper” cables are utilized. Jumper cables are additional fiberoptic cables that can be attached to the fixed cable via a SMA adapter. The loss on the jumpers is largely due to the attenuation at the junction between the built-in cable and the jumper, as shown:
Individual broken fibers will further decrease the response of the cable. Each broken fiber results in approximately a five percent loss in response.
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