Narrow-linewidth and tunable fiber lasers

Morkel, P.R. (1993) Narrow-linewidth and tunable fiber lasers. In, Digonnet, M.J.F. (ed.) Rare-Earth-Doped Fibre Lasers and Amplifiers. (Optical Engineering Series, 37) Marcel Dekker, pp. 281-318.

Record type: Book Section

Abstract

1. Introduction
2. Line-narrowed fiber laser devices
Integral fiber reflective Bragg grating lasers
Intra-cavity etalon laser
3. Tunable, line narrowed fiber laser devices
Ring lasers using wavelength selective couplers
Tunable lasers using bulk-optic components
a) Mechanical tuning
b) Electronic tuning
4. Single frequency fiber lasers
Integral fiber reflective Bragg grating laser
Interferometric cavity laser
Injection locked laser
Travelling-wave laser
5. Summary

Introduction: fiber laser devices based on rare-earth ions incorporated into various glass types have generated considerable interest as narrow linewidth sources, and a number of research groups have published results in this area. Inherent compatibility with optical fiber transmission and sensing media are an obvious attraction for the use of fiber laser devices as sources in fiber communication and sensor applications where narrow linewidths are required. In particular, potential future coherent optical communication systems using wavelength division multiplexing (WDM) will require tunable, narrow-line laser sources. The broad lineshapes associated with rare-earth-doped glass media allow tunable fiber laser sources to be fabricated. The strong optical confinement associated with single-mode fiber laser media enables substantial gain to be obtained over a large fraction of the total emission lines, for both 3-level and 4-level transitions, and hence broad tunability is possible. The potential exists therefore for tunable, narrow linewidth and single longitudinal-mode fiber sources which could find wide application in the field of optical fiber communications and sensors. The ability to convert emission from laser diode pump sources which can be of low modal and temporal quality into highly coherent, low-noise laser emission is an attractive feature of rare-earth lasers in general. The ultimate aim of the development of narrow linewidth fiber laser devices is to provide rugged and stable narrow linewidth or single frequency sources, pumped by a semiconductor laser diode with the capacity of rapidly electronic tunability. Also at low cost! A challenging target certainly, although as will be seen in this chapter, all of the above requirements have been addressed to some extent in various fiber laser devices developed to date. The cost issue has yet to be addressed, although the relative ease of fabrication of bulk quantities of fiber laser gain media (see chapter I: Fiber fabrication), along with expected high yields in device fabrication indicate that low cost devices can be expected. A single device offering all of the above characteristics has yet to be developed although considering the relative youth of modem single-mode fiber laser technology, progress in this field to date has been substantial.