Fiber optic transmission systems transmit information from one location to another by sending optical energy through glass fiber. Fiber optic cables are used in telephony, cable television, local area networks, industry and medicine. Information is encoded on the energy by modulating either its power or spectrum. In these systems it is often necessary to monitor the average optical power being carried by a transmission fiber. Average optical power is a useful indicator of system performance, and thus is often used for maintenance and control purposes. The proper utilization of fiber optic systems requires precise instruments for measuring optical power and testing the integrity of optical circuits. Optical power meters may comprise a photodiode which outputs an electrical current proportional to the optical power of an input optical beam, an I/V amplifier which converts the output current of this photodiode to a voltage, a variable-gain amplifier which amplifies the output voltage of this I/V amplifier, and an A/D converter which converts the output voltage of this variable gain amplifier to a digital signal.
