Abstract

We show both theoretically and experimentally that interference fringe signals can always be suppressed to improve the signal-to-noise ratio, provided that the modulation frequency is of the order of the absorption linewidth or higher. Suppression of optical interference fringes by more than 1 order of magnitude and signal-to- noise ratio enhancement of more than 13 dB is demonstrated by use of a proper choice of laser modulation frequency. A further fringe reduction of 10 dB is possible by adjustment of the local oscillator phase.

© 1995 Optical Society of America

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References

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1994 (1)

1989 (1)

1988 (1)

1985 (3)

1983 (1)

1982 (1)

D. T. Cassidy, J. Reid, Appl. Phys. B 29, 279 (1982).
[Crossref]

1980 (2)

Ballik, E. A.

Bjorklund, G. C.

Carlisle, C. B.

Cassidy, D. T.

D. T. Cassidy, J. Reid, Appl. Phys. B 29, 279 (1982).
[Crossref]

Cooper, D. E.

El-Sherbiny, M.

Gallagher, T. F.

Garside, B. K.

Gehrtz, M.

Koga, R.

R. Koga, M. Kosaka, H. Sano, Opt. Laser Technol. 17, 139 (1985).
[Crossref]

Kosaka, M.

R. Koga, M. Kosaka, H. Sano, Opt. Laser Technol. 17, 139 (1985).
[Crossref]

Lenth, W.

Reid, J.

Riris, H.

Sano, H.

R. Koga, M. Kosaka, H. Sano, Opt. Laser Technol. 17, 139 (1985).
[Crossref]

Silver, J. A.

Stanton, A. C.

Tate, D. A.

Wang, L.-G.

Warren, R. E.

Webster, C. R.

Whittaker, E. A.

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Figures (3)

Fig. 1
Fig. 1

In-phase (solid curves) and quadrature (dashed curves) signal for (a) first-harmonic and (b) second-harmonic detection. The local oscillator phase is adjusted to remove interference fringes in the in-phase signal. Modulation parameters are fmτ = 1.3, β = 1, and fmγ = 1.3, where γ is the half-width of the absorption line.

Fig. 2
Fig. 2

Experimental setup. LD, laser diode; PD, photodetector.

Fig. 3
Fig. 3

Measured interference fringe reduction. The two upper traces show the maximum (solid curve) and minimum (dashed curve) interference fringe signals obtained by local oscillator phase tuning for ωmτπ. The lowest trace shows the maximum interference signal with ωmτ ≈ 2π.

Equations (3)

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T ( ω 0 ) ( 1 - R ) [ 1 + R exp ( i ω 0 τ ) ] ,             R 1 ,
I n 4 R J n ( β ω m τ ) f ( ω 0 τ ) f [ n ( ω m t + π / 2 ) ] E 0 2 ,             ω m τ 1 ,
I n 8 R f ( ω 0 τ ) [ 1 2 β sin ( ω m t / 2 ) ] n × cos [ n ( ω m t + ω m τ / 2 ) ] E 0 2 ,             β 1 ,

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