Laser alignment into single-mode fiber for objective TIRF

The current fiber-coupling scheme involves two adjustable mirrors and the Newport fiber-coupling component (F-91-C1 ), which includes a 40x objective and a fiber chuck for holding FC connector optical fibers (FPH-CA4). The optical fiber that we are currently using is a Newport single-mode fiber specific for 488 nm (F-SA-C-1FC).

Contents

1. Procedure

1. Procedure

1. Initially, steer the laser light through the front and back apertures of the coupling component using the two adjustable mirrors. This can be done with the 40x objective in place. Once laser light is coming through the 40x objective, the fiber chuck containing the fiber can be put into place.
2. Optimization of the light exiting the fiber can now be optimized. It is easiest to obtain light through the fiber with the fiber backed away from the objective. Optimal coupling will occur close in to the objective where the laser light converges. Iteratively adjust the mirrors (first the mirror furthest from the fiber, then the mirror closer to the fiber) followed by adjusting the X and Y controls on the fiber coupling component, which moves the position of the fiber tip. Once maximum power is emitting from the fiber tip, bring the fiber tip closer to the objective and repeat the optimization process.
3. At some point (before the fiber touches the objective) you will achieve maximum coupling. Moving closer to the objective from this point will drop of the coupling efficiency quickly. 60% coupling efficiency is a reasonable goal. The X and Y adjustment knobs can be tightened into place, but do so incrementally so as not to lose the coupling. If coupling is lost, it is easiest to back the fiber out from the objective to restart the process.
4. Once efficient coupling has been achieved, the fiber is connected to the TIRF arm via an FC-connection. The fiber must pass through a protective ring that secures around the connection site via set screws.