Abstract

A novel technique using an acousto-optic frequency shifter in optical frequency domain imaging (OFDI) is presented. The frequency shift eliminates the ambiguity between positive and negative differential delays, effectively doubling the interferometric ranging depth while avoiding image cross-talk. A signal processing algorithm is demonstrated to accommodate nonlinearity in the tuning slope of the wavelength-swept OFDI laser source.

© 2004 Optical Society of America

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References

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Appl. Phys. Lett. (1)

W. Eickhoff and R. Ulrich, �??Optical frequency domain reflectrometry in single-mode fiber,�?? Appl. Phys. Lett. 39, 693-695 (1981).
[CrossRef]

IEEE Photon. Technol. Lett. (1)

X. Zhou, K. Iiyama, and K. Hayashi, �??Extended-range FMCW reflectometry using an optical loop with a frequency shifter,�?? IEEE Photon. Technol. Lett. 8, 248-250 (1996).
[CrossRef]

J. Lightwave Technol. (2)

J. P. von der Weid, R. Passy, G. Mussi, and N. Gisin, �??On the characterization of optical fiber network components with optical frequency domain reflectometry,�?? J. Lightwave Technol. 15, 1131-1141 (1997).
[CrossRef]

H. Barfuss and E. Brinkmeyer, �??Modified optical frequency domain reflectometry with high spatial resolution for components of integrated optics systems,�?? J. Lightwave Technol. 7, 3-10, (1989).
[CrossRef]

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

Opt. Comm. (1)

A.F. Fercher, C. K. Hitzenberger, G. Kamp, S. Y. El-Zaiat, �??Measurement of intraocular distances by backscattering spectral interferometry,�?? Opt. Comm. 117, 43-48 (1995).
[CrossRef]

Opt. Express (1)

Opt. Lett. (5)

Other (1)

J. G. Proakis and D. G. Manolakis, Digital signal processing, 3rd Ed. (Prentice Hall, New Jersey, 1996), Chap. 5.

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Figures (6)

Fig. 1.
Fig. 1.

A basic configuration of an OFDI system employing a frequency shifter, FS.

Fig. 2.
Fig. 2.

Illustration of coherence range (a) without and (b) with a frequency shift Δf. The frequency shift enables both sides of the coherence range to be used in OFDI, doubling the effective ranging depth (hatched region).

Fig. 3.
Fig. 3.

Experimental setup of the OFDI system. FS: acousto-optic frequency shifter.

Fig. 4.
Fig. 4.

Point spread functions obtained at 7 different depth points for Δf = 0; (a) before and (b) after mapping to linear ν-space.

Fig. 5.
Fig. 5.

Point spread functions obtained at 7 different depth points when Δf = -2.5 MHz; (a) before and (b) after mapping to linear ν-space. The degradation in signal power with depth is no more than 5 dB over the total depth span of 5.8 mm in (b), as opposed to an 11 dB degradation shown in Fig. 4(b) without the frequency shift.

Fig. 6.
Fig. 6.

OFDI images of human lung tissue ex vivo obtained with Δf = 0, A, and Δf = -2.5 MHz, B. Image folding with respect to zero depth, distinct in A, is absent in B where the effective ranging depth is doubled by the frequency shift. Each image consists of 650 vertical x 500 transverse pixels.

Equations (2)

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i s ( t ) = 2 η P r ( t ) P s ( t ) R ( z ) G ( z ) cos [ 4 π c v ( t ) z + ϕ ( z ) + 2 π Δ ft ] dz ,
f s = v 1 2 z c Δ f

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