Design and fabrication of a biconvex aspherical microlens for maximizing fiber coupling efficiency with an ultraviolet laser diode

- A single bi-convex microlens is proposed to maximizing fiber coupling efficiency.
- The profiles of microlens also focus the Laser diode beam into a small spot size.
- Excimer laser dragging method used to fabricate accurate profiles in the microlens.
- Discrepancy between machining and experiment below 1 μm.
- A small spot size is obtained experimentally and maximizing fiber coupling efficiency successfully.

This paper introduces a biconvex microlens to maximize the light coupling between an edge emitting laser diode (LD) and an optical fiber. Both convex surfaces have different profiles along their x- and y-axis so that the elliptical light beam from an LD can be fed into the core of a fiber. The optimized lens profiles are first simulated by the ray-tracing software Zemax and then fabricated by an excimer laser micromachining system. Focal spot size around 10 μm is achieved experimentally. Light coupling efficiency using this single biconvex microlens is 31.8% and 47.6% for single-mode and multi-mode fiber, respectively.