A novel lensed fiber employing a wedge-shaped graded-index fiber (GIF) is proposed. The characteristic of coupling loss as a function of the aspect ratio is numerically investigated. When the aspect ratio is seven,the coupling loss of a wedge-shaped GIF and a conventional wedge-shaped SMF are 0.22 dB and 0.60 dB, respectively, and when the aspect ratio is 13, they are 0.5 dB and 2.4 dB. The tolerance to laser diode (LD)-fiber displacement is also numerically investigated, and it is confirmed that the proposed fiber has larger tolerance than a conventional wedge-shaped single-mode fiber (SMF). The performance of the new lensed fiber is also experimentally verified.
Hidehiko Yoda and Kazuo Shiraishi, "A New Scheme of a Lensed Fiber Employing a Wedge-Shaped Graded-Index Fiber Tip for the Coupling Between High-Power Laser Diodes and Single-Mode Fibers," J. Lightwave Technol. 19, 1910- (2001)