Effect of far-field structure and angular misalignment on laser coupling.

Fiber coupling measurements have been made on two groups of 1.3 micron Hitachi lasers. The sets consisted of 5 lasers each from lasers that passed and lasers that were rejected during the far-field measurement test. The rejected lasers failed because of beam divergence angles that were excessive and they also exhibited interference type structure in the far-field patterns. The results of these measurements indicate that peak coupled power and alignment tolerance width are not significantly degraded by the presence of the far-field structure. In addition, fiber coupling vs angular misalignment measurements were made on all 10 lasers. These measurements were made to determine the coupling penalty associated with aligning a fiber to a laser with an angular deviation from optimum alignment between the laser source and the single mode fiber. It was found that an 11 degree offset was required to produce a 1 dB reduction in peak coupling, if fiber lateral alignment is allowed following the introduction of the angle.