Abstract

In the area of rare-earth doped fiber lasers, interest to date has been almost exclusively centered on studying fiber cavities which support only the lowest order spatial mode. We present experimental results which show how the laser output optical spectrum can be dramatically affected by the inclusion of a passive multimode optical fiber section in the laser cavity. Spatial mode beating between the LP₀₁ and LP₁₁ fiber modes in the multimode fiber¹ acts as a filter to allow several well defined wavelengths to oscillate simultaneously. The filtering occurs because the mode field overlap at the multimode/single-mode interfaces determines which wavelengths spatially beat along the length of multimode fiber to give low transmission loss between the single-mode fibers.

© 1994 Optical Society of America