Analysis and design of unidirectional erbium-doped waveguide ring lasers

This paper examines the possibility of fabricating unidirectional erbium-doped waveguide ring lasers (EDWRLs) without the use of optical isolators and analyzes factors affecting directionality in such lasers. The analysis is carried out using numerical simulations based on a rate-propagation equation model. Two methods of obtaining unidirectional operation are investigated: feeding back radiation by external retro-reflector and employing integrated intra-cavity Bragg grating with an asymmetric profile. Tendency to unidirectional operation of the ring laser due to one-side pumping is also discussed in conjunction with the other methods. It is shown that counter-directional wave suppression of more than 20 dB can be attained using principles of EDWRL design elaborated in this paper.