Abstract

Tapered fiber bundles are often used to combine the output power of several semiconductor lasers into a multimode optical fiber for the purpose of pumping fiber lasers and amplifiers. It is generally recognized that the brightness of such combiners does not exceed the brightness of the individual input fibers. We report that the brightness of the tapered fibers (and fiber bundles) depends on both the taper ratio and the mode-filling properties of the beams launched into the individual fibers. Brightness, therefore, can be increased by selection of sources that fill a small fraction of the input fiber’s modal capacity. As proof of concept, we present the results of measurements on tapered fiber-bundle combiners having a low-output étendue. Under low mode-filling conditions per input multimode fiber (i.e., fraction of filled modes ≤ 0.29), we report brightness enhancements of 8.0 dB for 19 × 1 bundles, 6.7 dB for 7 × 1 bundles, and 4.0 dB for 3 × 1 combiners. Our measured coupling efficiency variations of ∼1%–2% among the various fibers in a given bundle confirm the uniformity and quality of the fabricated devices.

© 2004 Optical Society of America

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References

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  1. W. A. Clarkson, D. C. Hanna, “Two mirror beam-shaping technique for high-power diode bars,” Opt. Lett. 21, 375–377 (1996).
    [CrossRef] [PubMed]
  2. P. Y. Wang, A. Gheen, Z. Wang, “Beam shaping technology for laser diode arrays,” in Laser Beam Shaping III, F. M. Dickey, S. C. Holswade, D. L. Shealy, eds., Proc. SPIE4770, 131–135 (2002).
    [CrossRef]
  3. D. M. Brown, “High-power laser diode beam combiner,” Opt. Eng. 42, 3086–3087 (2003).
    [CrossRef]
  4. J. Berger, D. F. Welch, W. Streifer, D. R. Scifres, N. J. Hoffman, J. J. Smith, D. Radecki, “Fiber-bundle coupled, diode end-pumped Nd: YAG laser,” Opt. Lett. 13, 306–308 (1988).
    [CrossRef] [PubMed]
  5. H. Zbinden, J. E. Balmer, “Q-switched Nd: YLF laser end pumped by a diode-laser bar,” Opt. Lett., 15, 1014–1016 (1990).
    [CrossRef] [PubMed]
  6. D. J. DiGiovanni, A. J. Stentz, “Tapered fiber bundles for coupling light into and out of cladding-pumped fiber devices,” U.S. patent5,864,644 (26January1999).
  7. B. G. Fidric, V. G. Dominic, S. Sanders, “Optical couplers for multimode fibers,” U.S. patent6, 434,302 B1 (13August2002).
  8. 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]
  9. Y. F. Li, W. Y. Lit, “Transmission properties of a multimode optical-fiber taper,” J. Opt. Soc. Am. A 2, 462–468 (1985).
    [CrossRef]
  10. D. H. McMahon, “Efficiency limitations imposed by thermodynamics on optical coupling in fiber-optic data links,” J. Opt. Soc. Am. 65, 1479–1482 (1974).
    [CrossRef]
  11. M. C. Hudson, “Calculation of the maximum optical coupling efficiency into multimode optical waveguides,” Appl. Opt. 13, 1029–1033 (1975).
    [CrossRef]

2003 (1)

D. M. Brown, “High-power laser diode beam combiner,” Opt. Eng. 42, 3086–3087 (2003).
[CrossRef]

1996 (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]

1990 (1)

1988 (1)

1985 (1)

1975 (1)

1974 (1)

Balmer, J. E.

Berger, J.

Brown, D. M.

D. M. Brown, “High-power laser diode beam combiner,” Opt. Eng. 42, 3086–3087 (2003).
[CrossRef]

Clarkson, W. A.

DiGiovanni, D. J.

D. J. DiGiovanni, A. J. Stentz, “Tapered fiber bundles for coupling light into and out of cladding-pumped fiber devices,” U.S. patent5,864,644 (26January1999).

Dominic, V. G.

B. G. Fidric, V. G. Dominic, S. Sanders, “Optical couplers for multimode fibers,” U.S. patent6, 434,302 B1 (13August2002).

Fidric, B. G.

B. G. Fidric, V. G. Dominic, S. Sanders, “Optical couplers for multimode fibers,” U.S. patent6, 434,302 B1 (13August2002).

Gheen, A.

P. Y. Wang, A. Gheen, Z. Wang, “Beam shaping technology for laser diode arrays,” in Laser Beam Shaping III, F. M. Dickey, S. C. Holswade, D. L. Shealy, eds., Proc. SPIE4770, 131–135 (2002).
[CrossRef]

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.

Hoffman, N. J.

Hudson, M. C.

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]

Li, Y. F.

Lit, W. Y.

McMahon, D. H.

Radecki, D.

Sanders, S.

B. G. Fidric, V. G. Dominic, S. Sanders, “Optical couplers for multimode fibers,” U.S. patent6, 434,302 B1 (13August2002).

Scifres, D. R.

Smith, J. J.

Stentz, A. J.

D. J. DiGiovanni, A. J. Stentz, “Tapered fiber bundles for coupling light into and out of cladding-pumped fiber devices,” U.S. patent5,864,644 (26January1999).

Streifer, W.

Wang, P. Y.

P. Y. Wang, A. Gheen, Z. Wang, “Beam shaping technology for laser diode arrays,” in Laser Beam Shaping III, F. M. Dickey, S. C. Holswade, D. L. Shealy, eds., Proc. SPIE4770, 131–135 (2002).
[CrossRef]

Wang, Z.

P. Y. Wang, A. Gheen, Z. Wang, “Beam shaping technology for laser diode arrays,” in Laser Beam Shaping III, F. M. Dickey, S. C. Holswade, D. L. Shealy, eds., Proc. SPIE4770, 131–135 (2002).
[CrossRef]

Welch, D. F.

Zbinden, H.

Appl. Opt. (1)

IEEE J. Quantum. Electron. (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]

J. Opt. Soc. Am. (1)

J. Opt. Soc. Am. A (1)

Opt. Eng. (1)

D. M. Brown, “High-power laser diode beam combiner,” Opt. Eng. 42, 3086–3087 (2003).
[CrossRef]

Opt. Lett. (3)

Other (3)

D. J. DiGiovanni, A. J. Stentz, “Tapered fiber bundles for coupling light into and out of cladding-pumped fiber devices,” U.S. patent5,864,644 (26January1999).

B. G. Fidric, V. G. Dominic, S. Sanders, “Optical couplers for multimode fibers,” U.S. patent6, 434,302 B1 (13August2002).

P. Y. Wang, A. Gheen, Z. Wang, “Beam shaping technology for laser diode arrays,” in Laser Beam Shaping III, F. M. Dickey, S. C. Holswade, D. L. Shealy, eds., Proc. SPIE4770, 131–135 (2002).
[CrossRef]

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Figures (12)

Fig. 1
Fig. 1

Diagram of an N × 1 combiner, fabricated by fusing and tapering a fiber bundle. The beams of N laser diodes (either separate diodes or diodes from an array) enter from the left-hand side. The combined high-brightness beam emerges from the right.

Fig. 2
Fig. 2

Cross-sectional photographs of fused, tapered, and cleaved MM fiber bundles. (a) 3 × 1 combiner; (b) 4 × 1 combiner, (c) 7 × 1 combiner, (d) 19 × 1 combiner. Note that the empty spaces between adjacent fibers have been filled. The different gray levels of individual fibers within the bundle are caused by random illumination of their opposite ends.

Fig. 3
Fig. 3

(a) Side view of the tapered end of the fused, tapered, and cleaved 4 × 1 MM fiber bundle of Fig. 2(b). (b) Cleaved facet of the tapered bundle in (a) is shown fusion-spliced to a MM fiber.

Fig. 4
Fig. 4

Profiles of intensity distribution in the far field for the three sources used in our experiments. Source 1: dashed line, calculated; source 2: (○), measured; source 3: (●), measured.

Fig. 5
Fig. 5

Transmission efficiency ηT versus taper ratio R for several N × 1 combiners. (●) N = 19; (▲) N = 7; (■) N = 4; (♦) N = 3. Some of the bundles were overpulled, resulting in a leftward shift of the corresponding data point on this plot. The solid curve is the best fit to the single taper’s efficiency curve measured with source 2 (reproduced from Fig. 9).

Fig. 6
Fig. 6

Cascade of tapered fibers, all having the same taper ratio R, fusion spliced to each other and to 1-m-long pieces of the standard MM fiber on the input and the output sides. The light beam is launched into the 1-m-long input fiber. At the output side, a loop of the 1-m-long fiber is passed through index-matching fluid to remove any light that might be coupled into its cladding. The transmitted light is measured by the photodetector at the end of the output fiber. Although three tapered fibers are shown cascaded in this figure, the actual number in our experiments could be anywhere from one to four.

Fig. 7
Fig. 7

Transmission efficiencies in a cascade of four tapered fibers. The taper ratio for all four fibers is R = 0.26. The light source is a single-mode laser coupled to a 1-m-long MM fiber (source 1). The transmission efficiency of the first stage is ηT ∼47%; the remaining stages show progressively smaller efficiencies. The dashed line marks the 6.8% efficiency level corresponding to the overfilled mode condition.

Fig. 8
Fig. 8

Effect of core offset between the tapered end of one fiber and the untapered entrance facet of the next fiber in the cascade. In configuration A the transmission efficiency ηT is measured for a single taper, offset from the center of the 1-m-long output fiber, as a function of the displacement between the two cores. In configuration B, efficiency is measured for a cascade of two tapered fibers as a function of the core displacement of the first tapered fiber relative to the center of the second. In both cases the taper ratio was R = 0.23. The second curve is magnified by a factor of 4 to aid better visualization.

Fig. 9
Fig. 9

Measured values of ηT versus the taper ratio R for a single tapered fiber in the system of Fig. 6. Light sources 1 (▲) and 2 (■) yield nearly identical patterns of behavior. The measured efficiency for source 3 (●) is substantially less than that of the other sources. Solid curve is the best fit to the data obtained with source 2. Dashed curve is the tapered fiber efficiency under fully overfilled mode launch, R 2 model. Shown at the top of the figure is the number of tapered fibers that can be bundled and fused together to create an output beam equal in diameter to that of a single, standard MM fiber.

Fig. 10
Fig. 10

Open circles (○) show a single taper’s transmission efficiency ηT versus the taper ratio R for a Lambertian source, given by Eq. (5). The dashed curve shows the taper’s transmission efficiency for the overfilled mode launch condition when all modes contribute equally, namely, the R 2 model. The solid circles (●) show the resulting tapered bundle’s transmission improvement (i.e., the combining effect) for a Lambertian source in units of input channels calculated.

Fig. 11
Fig. 11

Overall transmission efficiency versus taper ratio R for a cascade of two tapered fibers in the fusion-spliced chain of Fig. 6. Triangles (▲) show the data obtained with source 1. Squares (■) show the data obtained with source 2. Shown at the top of the figure, is the number N 2 of fibers that can be combined together when two N × 1 combiners are connected in a cascade configuration. Dashed curve represents the cascade transmission for the overfilled mode launch condition, i.e., (R 2)2.

Fig. 12
Fig. 12

Two-stage 9 × 1 combiner, composed of four identical 3 × 1 combiners.

Tables (1)

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Table 1 Source Characteristics and Estimated Number of Modes

Equations (5)

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i=1n AiNAi2in=AoutNAout2.
V22=π2d2w/22/2λ2.
NAR=fsNAst+fmNAmt,
fs=f1+f, fm=11+f.
ηT=NARNAf2,

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