Abstract

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 M 2 = 500 in the slow axis and M 2 = 4 in the fast axis is converted successfully into a symmetric circular beam with a beam quality of M 2 = 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 µm) fiber for a 2-W LD array. We extend the experiments to a higher-power source with higher asymmetric beam qualities of M 2 = 3000 and M 2 = 4. By slightly bending the GI10000 (10000 means a core diameter of 10,000 µm) fiber, we have succeeded in generating a symmetric beam with a improved beam quality of M 2 = 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.

© 2002 Optical Society of America

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References

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  1. J. R. Leger, W. C. Goltsos, “Geometrical transformation of linear diode-laser arrays for longitudinal pumping of solid-state lasers,” IEEE J. Quantum Electron. 28, 1088–1100 (1992).
    [CrossRef]
  2. S. Yamaguchi, T. Kobayashi, Y. Saito, K. Chiba, “Collimation of emissions from a high-power multistripe laser-diode bar with multiprism array coupling and focusing to a small spot,” Opt. Lett. 20, 898–900 (1995).
    [CrossRef] [PubMed]
  3. W. A. Clarkson, D. C. Hanna, “Two-mirror beam-shaping technique for high-power diode bars,” Opt. Lett. 21, 375–377 (1996).
    [CrossRef] [PubMed]

1996 (1)

1995 (1)

1992 (1)

J. R. Leger, W. C. Goltsos, “Geometrical transformation of linear diode-laser arrays for longitudinal pumping of solid-state lasers,” IEEE J. Quantum Electron. 28, 1088–1100 (1992).
[CrossRef]

Chiba, K.

Clarkson, W. A.

Goltsos, W. C.

J. R. Leger, W. C. Goltsos, “Geometrical transformation of linear diode-laser arrays for longitudinal pumping of solid-state lasers,” IEEE J. Quantum Electron. 28, 1088–1100 (1992).
[CrossRef]

Hanna, D. C.

Kobayashi, T.

Leger, J. R.

J. R. Leger, W. C. Goltsos, “Geometrical transformation of linear diode-laser arrays for longitudinal pumping of solid-state lasers,” IEEE J. Quantum Electron. 28, 1088–1100 (1992).
[CrossRef]

Saito, Y.

Yamaguchi, S.

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Figures (11)

Fig. 1
Fig. 1

Schematic drawing of beam-equalizing techniques with GI fiber optics.

Fig. 2
Fig. 2

Schematic drawing of typical GI fiber optics showing input and output beam distributions.

Fig. 3
Fig. 3

Required optimum beam diameter as a function of input beam quality in the slow axis.

Fig. 4
Fig. 4

Experimental setup for the beam equalizing of LD beam with GI1200 fiber optics.

Fig. 5
Fig. 5

Beam shape of LD at the output of a 5m long GI1200 fiber optics.

Fig. 6
Fig. 6

Output-beam quality as a function of displacement of GI1200 fiber in (a) x, parallel to the slow axis and y, parallel to the fast axis; and (b) z, parallel to the optic axis directions from the location of the best quality of 175 achieved.

Fig. 7
Fig. 7

Output-beam quality as a function of length of GI1200 fiber.

Fig. 8
Fig. 8

Beam shape of LD beam at the output of GI1200 fiber with the length of (a) 111.5, (b) 224, and (c) 550 mm.

Fig. 9
Fig. 9

Experimental setup for the beam equalizing of LD beam with GI10000 fiber optics.

Fig. 10
Fig. 10

Beam shape of LD beam at the output of a straight GI10000 fiber.

Fig. 11
Fig. 11

Beam shape of LD beam at the output of a GI10000 fiber having a bend with a curvature of 2 m. The input beam is off-centered by (a) -1mm, (b) 0 mm (centered), and (c) +1 mm.

Tables (2)

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Table 1 Change in the Output-Beam Qualities with Respect to the Displacement in x (Parallel to the Slow Axis), y (Parallel to the Fast Axis), and z (Parallel to the Optic Axis) Axes

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Table 2 Beam Symmetric Degree Defined by the Diameter Ratio between the Orthogonal Planes

Equations (2)

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ϕx=2Mx2ϕcλπ2n0Δn1/21/2,
ϕy= 2My2ϕcλπ2n0Δn1/21/2,

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