P. Dowd et al., LINEWIDTH NARROWED VERTICAL-CAVITY SURFACE-EMITTING LASERS FOR MILLIMETER-WAVE GENERATION BY OPTICAL HETERODYNING, IEEE journal of selected topics in quantum electronics, 3(2), 1997, pp. 405-408
Narrow beat-note linewidths as low as 190 kHz have been obtained by op
tically heterodyning two vertical-cavity surface-emitting lasers (VCSE
L's) whose linewidths are minimized by optical feedback, Narrow line o
peration has been achieved stably at frequencies up to a detector limi
ted value of 25 GHz for both free space and fiber-loop arrangements.