Abstract

When a single-mode fiber is used at a wavelength below the cutoff wavelength, the fiber guides second-order modes, which travel at different phase velocities from the fundamental mode. Periodically stressing this two-mode fiber once per beat length can cause coherent coupling between the modes. Such a modal coupler has been developed and is described here. Coupling to one of the second-order modes has been achieved, leaving less than −40-dB residual power in the fundamental mode. Two couplers have been mounted on a single strand of fiber to construct a Mach–Zehnder interferometer with better than a 30-dB on/off ratio. The coupler is polarization sensitive and can be used as an in-line polarizer. A 36-dB extinction ratio between polarizations has been observed.

© 1984 Optical Society of America

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References

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  1. R. C. Youngquist, J. L. Brooks, H. J. Shaw, “A birefringent-fiber polarization coupler,” Opt. Lett. 8, 656–658 (1983).
    [CrossRef] [PubMed]
  2. S. E. Miller, “On solutions for two waves with periodic coupling,” Bell Syst. Tech. J. 47, 1801–1822 (1968).
  3. R. C. Alferness, L. L. Buhl, “Waveguide electro-optic polarization transformer,” Appl. Phys. Lett. 38, 655–657 (1981).
    [CrossRef]
  4. D. Gloge, “Weakly guiding fibers,” Appl. Opt. 10, 2252–2258 (1971).
    [CrossRef] [PubMed]
  5. Y. Katsuyama, “Single-mode propagation in 2-mode region of optical fiber by using mode filter,” Electron. Lett. 15, 442–444 (1979).
    [CrossRef]
  6. H. C. Lefevre, “Single-mode fibre fractional wave devices and polarisation controllers,” Electron. Lett. 16, 778–780 (1980).
    [CrossRef]
  7. D. Marcuse, Light Transmission Optics, 2nd ed. (Van Nostrand Reinhold, New York, 1982).

1983 (1)

1981 (1)

R. C. Alferness, L. L. Buhl, “Waveguide electro-optic polarization transformer,” Appl. Phys. Lett. 38, 655–657 (1981).
[CrossRef]

1980 (1)

H. C. Lefevre, “Single-mode fibre fractional wave devices and polarisation controllers,” Electron. Lett. 16, 778–780 (1980).
[CrossRef]

1979 (1)

Y. Katsuyama, “Single-mode propagation in 2-mode region of optical fiber by using mode filter,” Electron. Lett. 15, 442–444 (1979).
[CrossRef]

1971 (1)

1968 (1)

S. E. Miller, “On solutions for two waves with periodic coupling,” Bell Syst. Tech. J. 47, 1801–1822 (1968).

Alferness, R. C.

R. C. Alferness, L. L. Buhl, “Waveguide electro-optic polarization transformer,” Appl. Phys. Lett. 38, 655–657 (1981).
[CrossRef]

Brooks, J. L.

Buhl, L. L.

R. C. Alferness, L. L. Buhl, “Waveguide electro-optic polarization transformer,” Appl. Phys. Lett. 38, 655–657 (1981).
[CrossRef]

Gloge, D.

Katsuyama, Y.

Y. Katsuyama, “Single-mode propagation in 2-mode region of optical fiber by using mode filter,” Electron. Lett. 15, 442–444 (1979).
[CrossRef]

Lefevre, H. C.

H. C. Lefevre, “Single-mode fibre fractional wave devices and polarisation controllers,” Electron. Lett. 16, 778–780 (1980).
[CrossRef]

Marcuse, D.

D. Marcuse, Light Transmission Optics, 2nd ed. (Van Nostrand Reinhold, New York, 1982).

Miller, S. E.

S. E. Miller, “On solutions for two waves with periodic coupling,” Bell Syst. Tech. J. 47, 1801–1822 (1968).

Shaw, H. J.

Youngquist, R. C.

Appl. Opt. (1)

Appl. Phys. Lett. (1)

R. C. Alferness, L. L. Buhl, “Waveguide electro-optic polarization transformer,” Appl. Phys. Lett. 38, 655–657 (1981).
[CrossRef]

Bell Syst. Tech. J. (1)

S. E. Miller, “On solutions for two waves with periodic coupling,” Bell Syst. Tech. J. 47, 1801–1822 (1968).

Electron. Lett. (2)

Y. Katsuyama, “Single-mode propagation in 2-mode region of optical fiber by using mode filter,” Electron. Lett. 15, 442–444 (1979).
[CrossRef]

H. C. Lefevre, “Single-mode fibre fractional wave devices and polarisation controllers,” Electron. Lett. 16, 778–780 (1980).
[CrossRef]

Opt. Lett. (1)

Other (1)

D. Marcuse, Light Transmission Optics, 2nd ed. (Van Nostrand Reinhold, New York, 1982).

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Figures (5)

Fig. 1
Fig. 1

The first six guided modes of a cylindrically symmetric fiber assuming that the core and cladding indexes are approximately equal. Arrows indicate the direction of the electric field.

Fig. 2
Fig. 2

Squeezing a fiber on one side with a square ridge will produce an asymmetric deformation of the fiber. This allows coupling to occur at the beginning and at the end of the deformation between the fundamental and second-order modes. The ridge is half a beat length long.

Fig. 3
Fig. 3

Modal coupler. Plastic ridges are used to produce periodic pressure regions in the fiber.

Fig. 4
Fig. 4

Schematic diagram of the experimental setup used to evaluate the modal coupler.

Fig. 5
Fig. 5

Theoretical curve of the power coupling versus wavelength of a 30-ridge device using conventional coupled-mode theory. The triangles and circles show the experimentally measured coupling between the fundamental and second-order modes of the vertical and horizontal polarizations, respectively.

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