Optical communication is a branch of telecommunication in which light is used as signal. Traditionally, the signals through the circuits used to be electrical signals. The need of faster data transfer and large bandwidth became the mother of invention of optical communication, which provides efficient transmission of data over long distances. In this program PSD of ON-OFF Keying signal has been uated.-Optical communication is a branch of telecommunication in which light is used as signal. Traditionally, the signals through the circuits used to be electrical signals. The need of faster data transfer and large bandwidth became the mother of invention of optical communication, which provides efficient transmission of data over long distances. In this program PSD of ON-OFF Keying signal has been　uated.