A true single longitudinal mode distributed feedback (DFB) fiber laser will be developed. The first and only, a preliminary demonstration of this laser has just been published, but it is not truly single frequency. We shall develop and commercialize the world's first DFB fiber laser with Bragg gratings written directly onto the core of the fiber. We shall implement an innovative external technique to introduce and control a halp-pi phase shift into the middle of the grating and this would allow only a single frequency to exist at the Bragg wavelength. Phase I will prove the feasibility of the idea, which will be very easy to control and use in large scale manufacturing. Producing the required shift by writing two different gratings has not been attempted and may well prove to be very difficult. With further development in Phase II, this practical, rugged and low-cost fiber laser will have the following characteristics: true single longitudinal mode, high powers in the 50-100 mW range, low relative intensity noise, very narrow linewidth in the tens of kilohertz range. This DFB fiber laser will have a better frequency stability than either a semiconductor diode laser or a distributed Bragg-end-reflector fiber laser because of its increased side-mode separation and suppression. Further, packaging will be easy because fiber lasers are simple and fiber-compatible, and output powers can be scaled up with the pump power and by making the fiber more efficient. The DFB fiber laser also has a wavelength that can be determined to an accuracy of <0.1 nm; this is not possible in DFB laser diodes. The DFB fiber laser will have large scale applications in dual-use technologies, including optical CATV networks, high capacity WDM communication systems, fiber optic sensors and spectroscopy systems. For WDM systems, many tens of channels can be multiplexed and system capacity increased substantially. There is an urgent need to develop and fabricate pressure and temperature tolerant pigtailed DFB lasers for WDM in fiber optic data links at specified pre-selected wavelengths in the 1520-1560 nm range. Our laser will be able to meet these specifications.
Keywords: Distributed Feedback Rare-Earth Fiber Laser Single Frequency Laser
