OPERATIONAL VALUE OPERATIONAL VALUE A measure of maintainability that includes the combined effects of item design, quality, installation, environment, operation, maintenance, and repair. OPTICAL ATTENUATOR Absorbing or partially reflecting com- ponent placed in the optical beam to reduce the energy delivered to an optical detector. OPTICAL CARRIER The unmodulated component of light emit- ted by an optical source, suitable for modulation. OPTICAL CONTACT An exact term in optics, signifying the approach of two transparent, index matched bodies so closely (a small fraction of a wavelength) that the discontinuity no longer pro- duces a reflection. Typically, the surfaces of the two bodies must be polished to match each other's form before optical contacting can occur. OPTICAL DETECTOR A transducer that generates an output sig- nal when irradiated with optical power. OPTICAL FIBER Any filament of fiber made of dielectric a mate- rial that guides light, whether or not it is used to transmit signals.