A tuneable laser is a very important device which has a wide range of applications such as, wavelength-division-multiplexing networks, optical sensors, spectroscopy, wavelength protection, ﬁbre-optic gyroscope, and testing of optical components and instruments. Tuneable fibre lasers, which consist of an optical fibre cavity and wave-guided gain medium, have recently attracted great interest.
Fibre lasers exhibit several intrinsic advantages over traditional lasers: (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 tuneable high-power 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 tuneable fibre 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, current fibre lasers, especially multi-wavelength fibre lasers, suffer from limited tuneability and flexibility, poor stability, and narrow operation ranges.
Two main aspects related to the development of tuneable single/multi-wavelength fibre lasers are currently under intensive investigation at our centre; 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 has particular limitations.
A multi-wavelength tuneable fibre laser based on the use of an Opto-VLSI processor in conjunction with different optical amplifiers has experimentally been demonstrated by our centre’s researchers. The Opto-VLSI processor can simultaneously select any part of the gain spectrum from each optical amplifier into its associated fibre ring, leading to a multiport tuneable fibre laser source. In particular, we have experimentally demonstrated a 3-port tuneable fibre laser source, where each output wavelength of each port can independently be tuned within the C-band with a wavelength step of about 0.05nm. Experimental results have demonstrated a laser linewidth as narrow as 0.05nm and an optical side-mode-suppression-ratio (SMSR) of about 35dB having excellent stability at room temperature and output power uniformity less than 0.5dB over the whole C-band.