Takenaka Yushi, Sharma Lalit B, Furuta Keisuke, Kojima Tetsuo, Yasui Koji
Advanced Technology Research and Development Center, Mitsubishi Electric Corporation, 8-1-1, Tsukaguchi-Honmachi, Amagasaki, Hyogo, 661-8661, Japan.
Appl Opt. 2002 Nov 20;41(33):7025-30. doi: 10.1364/ao.41.007025.
We demonstrate a novel method of equalizing a laser diode (LD) beam into a circular beam. This method uses the twist effect of graded index (GI) fiber optics. An asymmetric LD beam with beam qualities of M2 = 500 in the slow axis and M2 = 4 in the fast axis is converted successfully into a symmetric circular beam with a beam quality of M2 = 175. The circular-output beam with 92% coupling efficiency from the fiber input to the fiber output is obtained with a 5-m-long GI1200 (1200 means a core diameter of 1200 microm) fiber for a 2-W LD array. We extend the experiments to a higher-power source with higher asymmetric beam qualities of M2 = 3000 and M2 = 4. By slightly bending the GI10000 (10000 means a core diameter of 10,000 microm) fiber, we have succeeded in generating a symmetric beam with a improved beam quality of M2 = 2000. The average beam quality is preserved when the asymmetric ratio is not high, and the beam quality degradation ratio is investigated up to asymmetric ratios of 750.
