They mainly consist of optoelectronic components (such as optical transmitters and receivers), functional circuits, and optical interfaces, aiming to achieve the functionalities of optical-to-electrical and electrical-to-optical signal conversion in optical fiber communication. The frequency response characterization of these electrical-to-optical (E/O, modulators sometimes integrated with lasers) and optical-to-electrical (O/E, photo detectors and receivers) converters can be important in terms of such parameters as bandwidth, flatness, phase linearity and group delay. The O2E can be customized to a wide range of wavelengths and is suitable for single mode and multimode applications. As the name suggests it is a modulating device that converts incoming optical signals from a laser source to electrical signals, in data communication systems.