A device that amplifies an optical signal directly, without the need to convert it to an electrical signal, amplify it electrically, and reconvert it to an optical signal. Note 1: One type of fiber amplifier uses a doped fiber (e.g., a fiber doped with erbium,) which bears the communication signal, and which is optically pumped with a laser having a high-powered continuous output at an optical frequency slightly higher than that of the communication signal. The signal is intensified by Raman amplification. Note 2: Because neither optical-electrical conversion nor electrical amplification takes place, this type of amplifier is well suited for a wide variety of applications, both digital and analog. Note 3: Because this type of amplifier does not require extraordinary frequency (wavelength) control of the pumping laser, it is relatively simple. Synonym Raman amplifier.