Laser transmitter is an optical communication system, which utilizes the light signal to carry information, requires optical transmitters to generate optical signals, fiber optics transmission media, and optical receivers to detect optical signals. Semiconductor lasers are developed to fulfill requirements for the application of optical communication systems, and these are prerequisites as light sources in compact optical transmitter modules. Laser transmitters are applied to optical communication systems of various classes, such as high-capacity transmission using either the time division multiplexing technique at very high bit rates or the wavelength division multiplexing technique with many wavelength channels, as well as LAN and access network systems where more cost-effective components are required.