Rare-earth doped single-mode fiber lasers, amplifiers and devices

It is the current widespread use of single-mode optical fiber for telecommunications and the ready availability of high-power semiconductor pump lasers which have recently stimulated interest in single-mode fiber lasers and amplifiers. Until recently, lasing in glass fibers has been carried out in multimode devices. Using a new manufacturing process we have shown that single-mode fibers with rare-earth dopant concentrations up to 900 ppm can be made without compromising the low losses (<1 dB/km) which are characteristic of telecommunications fibers. It is thus now possible to construct a wide range of active fiber devices and sensors which exploit the numerous fiber components available, such as four-port couplers, ring-resonators, polarisers and filter