Sensitivity of grating-coupled surface emitters to length-induced phase variations

The longitudinal mode structure of a two-gain section, three-grating surface emitting laser is studied as a function of length-induced phase variations. It is found that several mode hops occur in the course of changing the length of one of the gain sections by one grating period. Although the number of mode hops can be reduced by optimizing the design, stable, single-mode laser operation appears to require control of the optical length of each gain and grating section to better than one wavelength.<
>