FAC Attach


Automatically attaching fast axis collimator lenses (FAC) to laser diodes

A drawback of semi conductor lasers to classical lasers such as HeNe lasers is their beam profile. Laser diodes present a rather ugly beam profile with a high divergence. Moreover the divergence is very different in the two planes leading to a big astigmatism. The direction with a large divergence angle is called the fast axis compared to the slow axis with a smaller divergence angle.

In order to have a beam which can be used at all the collimation of the laser beam is an unconditional task especially for the fast axis. A lens is placed in front of the laser diode’s facet to collimate the fast axis, hence its name Fast Axis Collimator (FAC). Another lens does the same thing for the slow axis, the Slow Axis Collimator (SAC). For single emitters the FAC and the SAC function can be introduced into a single optical element. For laser diode bars the FAC and SAC usually are separate optics with a single cylindrical type of lens for all emitters as FAC.

The idea is to collect the light as closely to the facet as possible to prevent the beam from getting large while traveling in space. As the goal is to enhance the beam profile and since that beam profile is only accessible when the laser is running the FAC and SAC need to be actively aligned and attached during laser operation.

Due to the complexity of extracting valuable information from a beam profile which can be fed back to some handling system the only way to mount those types of lenses so far was by manually steering the lens in front of the laser diode while observing the beam profile on a monitor.

With the ficonTEC AL500-FAC machine the FAC attachment is being performed fully automatically for the first time. The machine overcomes the drawbacks of unreliable and cost intensive manual processes.

The basic alignment engine of the machine consists of a high precision motion system for all 6 degrees of freedom and a far field camera. As this philosophy is needed for any FAC or SAC lens attachment the AL500-FAC is a standard system with only a little need for customization. The machine is capable of handling single emitter diodes, laser diode bars but also laser diode bar stacks.