Output characteristics of organic distributed feedback lasers with varying grating heights

Abstract

In this study, we examine the influence of the corrugation height of surface relief gratings on the output characteristics of organic distributed feedback (DFB) lasers. A series of surface relief gratings with a constant corrugation period (410 nm) and variable corrugation heights ranging from 20 and 80 nm are fabricated by the illumination of a new developed photosensitive azobenzene containing material with an interference pattern. A blend of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo{2,1′,3}-thiadiazol)] and poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] is used as organic laser active material which is deposited by spin-coating onto the grating array. The investigation of the laser output characteristics reveals an increase of the slope efficiency by a factor of 4 from 0.8% to 3.7% due to an increase of the grating height. The laser threshold decreases only slightly from 8.5 μJ/cm2 to 6.0 μJ/cm2 with increasing corrugation height. We interpret this as a result of the change of coupling between light mode and grating. The study helps to relate this to loss mechanisms of the DFB lasing process. This enables a further optimization of the DFB laser design.