Tunable laser module for fibre optic communications: Dissertation

This thesis deals with the design, realisation, and testing of the wavelength tunable 1540-nm laser prototypes that are intended for fibre optic communications. The short external cavity laser uses an electrically controlled silicon micromachined Fabry-Perot interferometer (FPI) device as the tuning element. First, the most common techniques for the diode laser wavelength tuning and applications for these devices are reviewed. Then the ways of coupling laser power into the single-mode (SM) optical fibre are considered and the characteristics of the fibre attachment methods are studied. The design, assembly and testing of three prototypes is introduced. Their discontinuous tuning spans range between 8 and 13 nm and their output power between 100 and 570 µW. The modules produce multimode tuning having an rms spectral width of about 1 nm. In addition, one prototype is capable of single-mode tuning with a side mode suppression ratio of 26 dB. The measured wavelength span is the widest reported single-mode tuning range obtained from a short external cavity Fabry-Perot diode laser without temperature tuning. The laser module can be electrically modulated up to over 600 MHz. The test results show that the FPI-tuned diode lasers can provide a cost-effective solution for optical communication applications. The study also confirms that it is possible to realise the laser-to-SM-fibre coupling using adhesive bonding. Further studies are needed in order to improve the speed and repeatibility of the process together with the reliability of the fibre attachment. In addition, the operational and long-term reliability of the module must be characterised.