Transverse coupling and front-mirror monitoring for feedback control of laser transmitters

Optical fibers with ends polished 45 degrees to the axis and mounted transversely with respect to injection lasers are shown to have laser-fiber coupling efficiencies comparable with the commonly used hemispherically ended fibers ( approximately 50%). The transverse scheme has the advantage that photodiodes can be mounted to monitor emission from the same mirror of the laser as that to which the fiber is coupled, thus permitting the output power from the fiber to be feedback-stabilized even if the laser develops front/back mirror mistracking. This is accomplished without the customary use of optical taps or additional lenses and mirrors.