Fig. 7: Comparison of the acceptance (divergence) angles of the plastic optical fibres with spherical or conical microlenses, with red paths representing the light emitted directly from the bare end of plastic optical fibres, and green paths representing the light emitted from microlenses.

a The spherical microlens has a larger acceptance angle than the flat-end optical fibre (i.e., φ3 > φ1). b The conical microlens has a smaller acceptance angle (i.e., φ2 < φ1). Therefore, the use of conical microlenses can effectively narrow the acceptance angle