High efficiency optical coupler for a small photo acceptance area photodiode used in the high speed plastic optical fiber communication

A high efficiency optical coupler has been developed for high speed plastic optical fiber communication. The coupler was designed for a small photo acceptance area photodiode based on the shape of compound parabolic concentrator. The theoretical efficiency of the coupler for graded index plastic optical fiber (GI-POF) was simulated with ray trace simulation, and the coupling loss was calculated less than 0.4 dB. The coupler was batch fabricated in a glass substrate using sand blast technique. The reflection layer of reflectance 90% was formed by Gold/Nickel mirror plating method. The coupler was bonded with a custom designed high speed PIN photodiode. The photocurrent was 20% higher than the current of a ball lens type PIN photodiode. The cut-off frequency was over 1 Gbps at reverse bias of 1.5 V.