Abstract

By etching the cladding along several millimeters of circular- or elliptical-core few-mode fiber optics, we gain access to the core and can inject extremely pure modes. The same etching technique allows one to measure the modal purity at the far end of the fiber. Modal purities of −26 dB have been obtained. We also demonstrate a holographic technique that allows all the light of each mode to be focused to an independent spot.

© 1991 Optical Society of America

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References

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  1. J. E. Midwinter, Optical Fibers for Transmission (Wiley, New York, 1979).
  2. P. Facq, P. Fournet, “Observation of tubular modes in multimode graded-index optical fibers,” Electron. Lett. 16, 648–649 (1980).
    [CrossRef]
  3. P. Szczepanek, J. Berthold, “Side launch excitation of selected modes in graded-index optical fibers,” Appl. Opt. 17, 3245–3247 (1978).
    [CrossRef] [PubMed]
  4. F. de Fornel, J. Arnaud, P. Facq, “Microbending effects on monomode light propagation in multimode fibers,” J. Opt. Soc. Am. 73, 661–668 (1983).
    [CrossRef]
  5. S. Shaklan, F. Reynaud, C. Froehly, “Multimode fiberoptic broadband interferometer,” submitted to Appl. Opt. Further references to related techniques can be found in this paper.
  6. F. Louradour, S. Shaklan, “Picosecond display of intermodal coupling matrix at a multimode fiber splice,” Appl. Opt. In press.
  7. M. Spajer, J. Roland, J. Neiras, “Separateurs de modes realises par abrasion d'une fibre optique utilisable dans des capteures interferometriques,” presented at the Ninth European Symposium on Optoelectronics, Opto 89, Paris, 1989.
  8. W. Sorin, B. Kim, H. Shaw, “Phase-velocity measurements using prism output coupling for single- and few-mode optical fibers,” Opt. Lett. 11, 106–108 (1986).
    [CrossRef] [PubMed]
  9. N. S. Kapany, J. J. Burke, Optical Waveguides (Academic, New York, 1972).
  10. L. Eyges, P. Gianino, P. Wintersteiner, “Modes of dielectric waveguides of arbitrary cross sectional shape,” J. Opt. Soc. Am. 69, 1226–1235 (1979).
    [CrossRef]
  11. S. Shaklan, “Measurement of intermodal coupling coefficient in weakly multimode fiber optics,” Electron. Lett. ( 26, 2022– 2024, c1990).
    [CrossRef]
  12. F. Louradour, A. Barthelemy, S. Shaklan, F. Reynaud, “Cross-phase modulation between modes of an optical fiber,” submitted to Opt. Commun.

1990 (1)

S. Shaklan, “Measurement of intermodal coupling coefficient in weakly multimode fiber optics,” Electron. Lett. ( 26, 2022– 2024, c1990).
[CrossRef]

1986 (1)

1983 (1)

1980 (1)

P. Facq, P. Fournet, “Observation of tubular modes in multimode graded-index optical fibers,” Electron. Lett. 16, 648–649 (1980).
[CrossRef]

1979 (1)

1978 (1)

Arnaud, J.

Barthelemy, A.

F. Louradour, A. Barthelemy, S. Shaklan, F. Reynaud, “Cross-phase modulation between modes of an optical fiber,” submitted to Opt. Commun.

Berthold, J.

Burke, J. J.

N. S. Kapany, J. J. Burke, Optical Waveguides (Academic, New York, 1972).

de Fornel, F.

Eyges, L.

Facq, P.

F. de Fornel, J. Arnaud, P. Facq, “Microbending effects on monomode light propagation in multimode fibers,” J. Opt. Soc. Am. 73, 661–668 (1983).
[CrossRef]

P. Facq, P. Fournet, “Observation of tubular modes in multimode graded-index optical fibers,” Electron. Lett. 16, 648–649 (1980).
[CrossRef]

Fournet, P.

P. Facq, P. Fournet, “Observation of tubular modes in multimode graded-index optical fibers,” Electron. Lett. 16, 648–649 (1980).
[CrossRef]

Froehly, C.

S. Shaklan, F. Reynaud, C. Froehly, “Multimode fiberoptic broadband interferometer,” submitted to Appl. Opt. Further references to related techniques can be found in this paper.

Gianino, P.

Kapany, N. S.

N. S. Kapany, J. J. Burke, Optical Waveguides (Academic, New York, 1972).

Kim, B.

Louradour, F.

F. Louradour, S. Shaklan, “Picosecond display of intermodal coupling matrix at a multimode fiber splice,” Appl. Opt. In press.

F. Louradour, A. Barthelemy, S. Shaklan, F. Reynaud, “Cross-phase modulation between modes of an optical fiber,” submitted to Opt. Commun.

Midwinter, J. E.

J. E. Midwinter, Optical Fibers for Transmission (Wiley, New York, 1979).

Neiras, J.

M. Spajer, J. Roland, J. Neiras, “Separateurs de modes realises par abrasion d'une fibre optique utilisable dans des capteures interferometriques,” presented at the Ninth European Symposium on Optoelectronics, Opto 89, Paris, 1989.

Reynaud, F.

S. Shaklan, F. Reynaud, C. Froehly, “Multimode fiberoptic broadband interferometer,” submitted to Appl. Opt. Further references to related techniques can be found in this paper.

F. Louradour, A. Barthelemy, S. Shaklan, F. Reynaud, “Cross-phase modulation between modes of an optical fiber,” submitted to Opt. Commun.

Roland, J.

M. Spajer, J. Roland, J. Neiras, “Separateurs de modes realises par abrasion d'une fibre optique utilisable dans des capteures interferometriques,” presented at the Ninth European Symposium on Optoelectronics, Opto 89, Paris, 1989.

Shaklan, S.

S. Shaklan, “Measurement of intermodal coupling coefficient in weakly multimode fiber optics,” Electron. Lett. ( 26, 2022– 2024, c1990).
[CrossRef]

F. Louradour, A. Barthelemy, S. Shaklan, F. Reynaud, “Cross-phase modulation between modes of an optical fiber,” submitted to Opt. Commun.

S. Shaklan, F. Reynaud, C. Froehly, “Multimode fiberoptic broadband interferometer,” submitted to Appl. Opt. Further references to related techniques can be found in this paper.

F. Louradour, S. Shaklan, “Picosecond display of intermodal coupling matrix at a multimode fiber splice,” Appl. Opt. In press.

Shaw, H.

Sorin, W.

Spajer, M.

M. Spajer, J. Roland, J. Neiras, “Separateurs de modes realises par abrasion d'une fibre optique utilisable dans des capteures interferometriques,” presented at the Ninth European Symposium on Optoelectronics, Opto 89, Paris, 1989.

Szczepanek, P.

Wintersteiner, P.

Appl. Opt. (1)

Electron. Lett. (2)

P. Facq, P. Fournet, “Observation of tubular modes in multimode graded-index optical fibers,” Electron. Lett. 16, 648–649 (1980).
[CrossRef]

S. Shaklan, “Measurement of intermodal coupling coefficient in weakly multimode fiber optics,” Electron. Lett. ( 26, 2022– 2024, c1990).
[CrossRef]

J. Opt. Soc. Am. (2)

Opt. Lett. (1)

Other (6)

N. S. Kapany, J. J. Burke, Optical Waveguides (Academic, New York, 1972).

J. E. Midwinter, Optical Fibers for Transmission (Wiley, New York, 1979).

S. Shaklan, F. Reynaud, C. Froehly, “Multimode fiberoptic broadband interferometer,” submitted to Appl. Opt. Further references to related techniques can be found in this paper.

F. Louradour, S. Shaklan, “Picosecond display of intermodal coupling matrix at a multimode fiber splice,” Appl. Opt. In press.

M. Spajer, J. Roland, J. Neiras, “Separateurs de modes realises par abrasion d'une fibre optique utilisable dans des capteures interferometriques,” presented at the Ninth European Symposium on Optoelectronics, Opto 89, Paris, 1989.

F. Louradour, A. Barthelemy, S. Shaklan, F. Reynaud, “Cross-phase modulation between modes of an optical fiber,” submitted to Opt. Commun.

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Figures (5)

Fig. 1
Fig. 1

Modal separation and selection: F, ≈ 1-m length of circular-core or elliptical-core fiber; T, etched fiber (diameter ≈ 10 μm, length ≈ 6 mm); W, metal wire to provide slight axial tension on the fiber; O, index-matching paraffin oil; G, glass window in the bottom of the paraffin container; R, rings observed in the far field (arcs for an elliptical-core fiber, as seen in the lower photo); L1, laser beam used to observe rings; L2, collimated laser beam used to inject a single mode. The upper photo is the 7th mode, corresponding to the next-to-last arc of the lower photo.

Fig. 2
Fig. 2

Far-field modes of a step-index fiber supporting seven modes.

Fig. 3
Fig. 3

Far-field modes of a step-index elliptical-core fiber having 2:1 major:minor axis ellipticity. Modes are shown in the order of their appearance as the input beam angle was increased. The notation of Eyges et al.10 is used to identify the modes. The major axis of the fiber is horizontal, resulting in vertically elongated mode lobes.

Fig. 4
Fig. 4

Hologram for collimation of the light from each mode. The hologram is masked to pass the light of one mode at a time. The reference beam angle is changed for each mode. Thus each mode reconstructs a spatially independent point source behind lens L2. L, Argon-ion laser, used at 488 nm; F, elliptical-core fiber supporting 11 modes at 488 nm; O, container of index-matching paraffin oil; T, etched section of the fiber; H, hologram; L1, lens that is moved to change the reference beam (resulting in beams R1 for mode 1, and R2 for beam 2, etc.).

Fig. 5
Fig. 5

Light diffracted by the hologram. Top: just behind the hologram, the diffracted rings of the elliptical core fiber. Middle: the beams converging toward separate points. Bottom: images formed by the hologram.

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