Linewidth reduction by coupled phase-shift distributed-feedback lasers

A coupled phase-shift distributed-feedback structure is proposed to achieve narrow-linewidth laser emission. Its mode properties are analysed and the narrowest linewidth is calculated taking into account the spatial hole burning effect. It is found that, by coupling two DFB laser units, the linewidth can be made as narrow as 0.1 MHz, which is an order of magnitude improvement over the value for the conventional distributed-feedback laser structure.