An optical fiber is the transmission medium within FOC systems. Here, optical fiber is the crystal clear and stretchy filament which transmits the light from a transmitter end to a receiver end. When the optical signal enters at the transmitter end of fi. An optical fiber is the transmission medium within FOC systems. Here, optical fiber is the crystal clear and stretchy filament which transmits the light from a transmitter end to a receiver end. When the optical signal enters at the transmitter end of fiber then optical communication system transmits to the end of the receiver using the optical fib. In the FOC system, the light source like an LED or laser diode is used as a transmitter. The main function of a light source like LED / Laser is to change an electrical signal into the light signal. These light sources are small semiconductor devices which efficiently converts electrical signal to light signal. These light sources require connectio. The fiber optic transmitter uses sources based on several criteria's like diodes, DFB laser, FP lasers, VCSEL, etc. The main function of these sources is to changes from an electrical signal to an optical signal. All these are semiconductor devices. The LEDs & VCSELs are made-up on semiconductor wafers to produce light from the outside of the chip,. In the FOC system, a photodetector can be used as a receiver. The main function of the receiver is to change an optical data signal back to an electrical signal. This is a semiconductorphotodiode in photodetector in current FOC system. This is a small device generally fabricated jointly with electrical circuitry to form an IC package to offer conne.