Optical amplifier

摘要

An optical amplifier comprises an input optical fiber (402) for receiving a light signal at a predetermined wavelength to be amplified; a first pump light source (408); first wave division multiplexing means (407) for focusing light from the first pump source (408) into a first end of a doped optical fiber (404) without blocking light at the wavelength of the light signal to be amplified, the doped optical fiber forming a loop and being pumpable by the first pump light source (408). Means are provided for coupling light exiting a second end of the doped optical fiber into an output optical fiber (410); as are optical isolation means (406) for restricting the direction of travel of light in the doped optical fiber (404). The optical isolation means (406) is located between the first and second ends of the doped optical fiber (404).