Several technical revolutions over the last ten years have led to the increasing use of rare earth-doped fiber lasers and amplifiers as a key component of optical communication systems. In this chapter, we review the methods of producing these fibers and the effect of the host composition and the rare earth doping on the quality of the final product. We then review the physics of the dopants and the hosts involved which makes these doped fibers so valuable for optical communications. In the last section, the laser performance itself is summarized; new trends for the future are presented.

Rare Earth-Doped Fiber Lasers and Amplifiers

Tunable laser action has been obtained in Nd3+- and Er3+-doped single-mode fiber lasers. In the case of the Nd3+-doped fiber, an extensive tuning range of 80 nm has been achieved. Tunable CW lasing also has been observed for the first time in an Er3+-doped fiber laser, which has an overall tuning range of 25 nm in the region of \lambda = 1.54 /mu m.

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Tunable single-mode fiber lasers

A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity.

Mode-locked multi-mode fiber laser pulse source

Solid state lasers have undergone a renaissance since the development of reliable and cheap laser diodes which can be used as pump sources. The result is compact, efficient laser sources which are attractive for a wide range of applications. This review summarizes the properties of laser diodes which are advantageous for pumping solid state lasers and describes the diverse laser materials and configurations of solid state lasers reported in the literature.

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Laser diode pumped solid state lasers

We report the first operation of an Nd3+-doped monomode fibre laser oscillating in a single longitudinal mode. The laser incorporated an integral fibre grating used as a narrowband reflector. The lasing linewidth was measured as 1.3MHz FWHM at a wavelength of 1082nm.

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Single-longitudinal-mode operation of an Nd3+-doped fibre laser

We report the efficient operation an Nd3+-doped silica single-mode fibre laser pumped by a GaAlAs laser diode. A CW output power in excess of 1 mW at 1.088 µm has been obtained with a slope efficiency of 33%. Q-switched operation of this device is also reported.

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Efficient diode-pumped CW and Q-switched single-mode fibre laser

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.1 Until recently, lasing in glass fibers has been carried out in multimode devices.2,3 Using a new manufacturing process4 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 filters.

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

An intensity dependent polarisation frequency splitting phenomenon in an Er3+-doped fibre laser operating at 1.55µm has been observed for the first time. The frequency splitting is significant and 530GHz has been measured.

Intensity dependent polarisation frequency splitting in an Er 3+ -doped fibre laser

Fibre lasers represent a new class of active fibre devices with considerable potential for use in telecommunications, sensors and laboratory measurements For these applications the realisation of a practical single-polarisation single-mode (SPSM) fibre laser is of considerable interest In this paper we report an integral fibre polariser technique for making SPSM fibre lasers The corresponding theory, design method and experimental results are also presented It is shown that it is far more efficient to use an intra-cavity polariser than to polarise the output light with an external polariser

Single polarisation fibre lasers using an integral polariser

Fibre lasers are attractive candidates as sources for fibre devices. Certain applications, such as distributed sensing, require short duration pulses of reasonable energy ~1µJ: other applications, for example current monitors, require single polarisation operation. The work reported here demonstrates that both requirements can be met by diode pumped fibre lasers. Results are presented for Nd3+ doped silica fibres, fabricated by the solution doping technique.

J.T. Lin

Papers

Efficient diode-pumped CW and Q-switched single-mode fibre laser

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

Intensity dependent polarisation frequency splitting in an Er 3+ -doped fibre laser

Single polarisation fibre lasers using an integral polariser

Q-switched and single-polarisation operation of a Nd3+-doped fibre laser