The three most commonly used wavelengths of light in fiber optics are 850nm, 1310nm, and 1550nm. After transmission through the optical fiber, the receiving interface converts the optical signals into electrical signals using a photodetector diode and. This light was transmitted approximately 700 ft. away, converted back to voice for the recipient to hear, and is now believed to be the first instance of wireless transmission of speech. Not surprisingly, this method was initially too difficult to use over longer distances due to the transmission. An optical module usually consists of an optical transmitting device (TOSA, including a laser), an optical receiving device (ROSA, including a photodetector), functional circuits,main control circuit board (PCBA), housing and optical (electrical) interface and other components. Photonic systems are usually analyzed in terms of individual photons, although wave methods still. The operating wavelength of an optical module is a range measured in nanometers (nm). Gray optical modules typically operate in the range of 850.