Tunable Fibre Lasers Based on Optical Amplifiers and an Opto-VLSI Processor

Tunable lasers are currently used in a wide range of applications such as wavelengthdivision-multiplexing networks, optical sensors, spectroscopy, wavelength protection, fiberoptic gyroscope, and testing of optical components and instruments. In particular, tunable fiber lasers, which employ optical fiber cavity and wave-guided gain medium, have recently attracted great interest owing to several intrinsic advantages over traditional lasers, namely: (i) easy manufacture without the need of clean rooms and expensive device packaging; (ii) mechanical flexibility and the ability to withstand bending, thus opening the way for numerous applications in biotechnologies and medical instrumentation; (iii) broadband gain spectrum and high energy efficiency, which are very important features for tunable highpower lasers; (iv) high laser beam quality, ensuring their wide potential applications in material processing, printing, marking, cutting and drilling; (v) robustness, because all optical signals are guided within optical fibres, thus eliminating the need for optical alignment; and (vi) narrow line width which is essential for many applications and hard to achieve for their current counterparts. Benefiting greatly from recent developments in fibre communications, fibre lasers are offering a low-cost alternative to the traditional semiconductor or gain dielectric counterparts. The key features required for tunable fiber lasers include a large number of channels, high-output power, stable operation in power and wavelength, and tuning operation over a wide wavelength range with application-specific wavelength spacing. However, the current fibre lasers, especially multiwavelength fiber lasers, suffer from limited tunability and flexibility, poor stability, and narrow operation ranges. Two main aspects related to the development of tunable single/multiwavelength fibre lasers are currently under intensive investigation; namely, the wavelength selection (or tuning) mechanism, and the used gain media. While these investigations have resulted in significant progress towards the development of commercially viable products each of the current approaches have particular limitations.