Abstract

We present a technique for measuring the modal filtering ability of single mode fibers. The ideal modal filter rejects all input field components that have no overlap with the fundamental mode of the filter and does not attenuate the fundamental mode. We define the quality of a nonideal modal filter Qf as the ratio of transmittance for the fundamental mode to the transmittance for an input field that has no overlap with the fundamental mode. We demonstrate the technique on a 20 cm long mid-infrared fiber that was produced by the U.S. Naval Research Laboratory. The filter quality Qf for this fiber at 10.5  μm wavelength is 1000±300. The absorption and scattering losses in the fundamental mode are approximately 8  dB/m. The total transmittance for the fundamental mode, including Fresnel reflections, is 0.428±0.002. The application of interest is the search for extrasolar Earthlike planets using nulling interferometry. It requires high rejection ratios to suppress the light of a bright star, so that the faint planet becomes visible. The use of modal filters increases the rejection ratio (or, equivalently, relaxes requirements on the wavefront quality) by reducing the sensitivity to small wavefront errors. We show theoretically that, exclusive of coupling losses, the use of a modal filter leads to the improvement of the rejection ratio in a two-beam interferometer by a factor of Qf.

© 2007 Optical Society of America

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References

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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef] [PubMed]
  6. A. Ksendzov, E. Bloemhof, V. White, J. K. Wallace, R. O. Gappinger, J. S. Sanghera, L. E. Busse, W. J. Kim, P. C. Pureza, V. Q. Nguyen, L. D. Aggarwal, S. Shalem, and A. Katzir, "Measurement of spatial filtering capabilities of single mode infrared fibers," Proc. SPIE 6268, 626838 (2006).
    [CrossRef]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef]
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2006 (2)

A. Ksendzov, E. Bloemhof, V. White, J. K. Wallace, R. O. Gappinger, J. S. Sanghera, L. E. Busse, W. J. Kim, P. C. Pureza, V. Q. Nguyen, L. D. Aggarwal, S. Shalem, and A. Katzir, "Measurement of spatial filtering capabilities of single mode infrared fibers," Proc. SPIE 6268, 626838 (2006).
[CrossRef]

P. Haguenauer and E. Serabyn, "Deep nulling of laser light with a single-mode-fiber beam combiner," Appl. Opt. 45, 2749-2754 (2006).
[CrossRef] [PubMed]

2002 (3)

2000 (1)

K. Wallace, G. Hardy, and E. Serabyn, "Deep and stable interferometric nulling of broadband light with implications for observing planets around nearby stars," Nature 406, 700-702 (2000).
[CrossRef] [PubMed]

1979 (1)

R. N. Bracewell and R. H. MacPhie, "Searching for nonsolar planets," Icarus 38, 136-147 (1979).
[CrossRef]

1975 (1)

B. W. Hakki and T. L. Paoli, "Gain spectra in GaAs double-heterostructure injection lasers," J. Appl. Phys. 46, 1299-1306 (1975).
[CrossRef]

1968 (1)

Appl. Opt. (2)

Icarus (1)

R. N. Bracewell and R. H. MacPhie, "Searching for nonsolar planets," Icarus 38, 136-147 (1979).
[CrossRef]

J. Appl. Phys. (1)

B. W. Hakki and T. L. Paoli, "Gain spectra in GaAs double-heterostructure injection lasers," J. Appl. Phys. 46, 1299-1306 (1975).
[CrossRef]

J. Opt. Soc. Am. A (2)

J. Optoelectron. Adv. Mater. (1)

I. D. Aggarwal and J. S. Sanghera, "Development and applications of chalcogenide glass optical fibers at NRL," J. Optoelectron. Adv. Mater. 4, 665-678 (2002).

Nature (1)

K. Wallace, G. Hardy, and E. Serabyn, "Deep and stable interferometric nulling of broadband light with implications for observing planets around nearby stars," Nature 406, 700-702 (2000).
[CrossRef] [PubMed]

Proc. SPIE (1)

A. Ksendzov, E. Bloemhof, V. White, J. K. Wallace, R. O. Gappinger, J. S. Sanghera, L. E. Busse, W. J. Kim, P. C. Pureza, V. Q. Nguyen, L. D. Aggarwal, S. Shalem, and A. Katzir, "Measurement of spatial filtering capabilities of single mode infrared fibers," Proc. SPIE 6268, 626838 (2006).
[CrossRef]

Other (1)

A. W. Snyder and J. D. Love, Optical Waveguide Theory (Chapman and Hall, 1983).

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Figures (6)

Fig. 1
Fig. 1

Planet detection using a two-beam interferometer. Configurations with and without the use of a modal filter (denoted as A and B, respectively) are shown.

Fig. 2
Fig. 2

(a) Experimental setup; (b) stepped mirror; (c) computed field distribution at the fiber's input.

Fig. 3
Fig. 3

Far-field radiation pattern of the NRL fiber. Gaussian fit is also shown.

Fig. 4
Fig. 4

Output intensity versus the NRL fiber position in the focal plane.

Fig. 5
Fig. 5

Output intensity versus the NRL fiber position in the focal plane—one-dimensional scan. The solid curve shows parabolic fit near the minimum. Enlarged section of the plot near the minimum is shown in the inset. The minimum in this particular measurement is 65 DN. We averaged fit results of 88 such measurements to obtain the leakage power.

Fig. 6
Fig. 6

Measurement of absorption in fiber using long coherence length laser. (a) Time dependence of the transmitted intensity during fiber cooling. (b) Parabolic data fit near the last minimum. Five values of I + and I were determined from such fits of successive maxima and minima.

Tables (1)

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Table 1 Design Parameters of the Fiber

Equations (4)

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α l = ln R + ln ( I + 1 / 2 + I 1 / 2 ) ln ( I + 1 / 2 I 1 / 2 ) ,
T F = ( 1 R ) 2 e α l / ( 1 R 2 e 2 α l ) .
R 0 ( 2 / ε ) .
R f P C / P D ( 2 / ε ) ( T F η / T A ) = ( T F η / T A ) R 0 .

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