Abstract

A frequency domain optical reflectometer which uses a GaAs interdigital photodetector both for optical detection and for mixing is described. A simple receiver with a postdetection bandwidth of the order of 10 kHz suffices for distance resolution of 10 m with this technique, greatly simplifying the electronics by comparison with pulsed reflectometers or swept frequency reflectometers employing electronic mixing. With available lasers the instrument could detect discrete optical reflections of −57 dB at a distance of 1 km. It is intended for remote measurement of refractive index in fluids, using the Fresnel reflection from a square-cleaved fiber as the sensor.

© 1990 Optical Society of America

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References

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  1. J. P. Legendre, “A Simple Reflectometer Configured to Sense Temperature,” Proc. Soc. Photo-Opt. Instrum. Eng. 566, 321–326 (1986).
  2. R. I. MacDonald, “Frequency Domain Optical Reflectometer,” Appl. Opt. 20, 1840–1844 (1981).
    [CrossRef] [PubMed]
  3. T. T. Tjhung, S. K. Teo, F. V. C. Mendis, B. Selvan, “Refractometry Through Optical Frequency-Domain Reflectometry,” Electron. Lett. 21, 613–614 (1985).
    [CrossRef]
  4. R. I. MacDonald, K. O. Hill, “Avalanche Optoelectronic Downconverter,” Opt. Lett. 7, 83–85 (1982).
    [CrossRef] [PubMed]
  5. A. G. Foyt, F. Leonberger, R. C. Williamson, “InP Optoelectronic Mixers,” Proc. Soc. Photo-Opt. Instrum. Eng. 269, 109–114 (1981).
  6. D. K. W. Lam, R. I. MacDonald, “GaAs Optoelectronic Mixer Operation at 4.5 GHz,” IEEE Trans. Electron. Devices ED-31, 1766–1768 (1984).
    [CrossRef]
  7. C. W. Slayman, L. Figueroa, “Frequency and Pulse Response of a Novel High Speed Interdigital Surface Photoconductor (IDPC),” IEEE Trans. Electron. Devices Lett. EDL-2, 112–114 (1981).
    [CrossRef]
  8. S. R. Forrest, G. L. Tangonan, V. Jones, “Simple 8 × 8 Optoelectronic Crossbar Switch,” IEEE/OSA J. Lightwave Technol. LT-7, 607–614 (1989).
    [CrossRef]
  9. J. P. Dakin, “Multiplexed and Distributed Optical Fibre Sensor Systems,” J. Phys. E 20, 954–967 (1987).
    [CrossRef]

1989

S. R. Forrest, G. L. Tangonan, V. Jones, “Simple 8 × 8 Optoelectronic Crossbar Switch,” IEEE/OSA J. Lightwave Technol. LT-7, 607–614 (1989).
[CrossRef]

1987

J. P. Dakin, “Multiplexed and Distributed Optical Fibre Sensor Systems,” J. Phys. E 20, 954–967 (1987).
[CrossRef]

1986

J. P. Legendre, “A Simple Reflectometer Configured to Sense Temperature,” Proc. Soc. Photo-Opt. Instrum. Eng. 566, 321–326 (1986).

1985

T. T. Tjhung, S. K. Teo, F. V. C. Mendis, B. Selvan, “Refractometry Through Optical Frequency-Domain Reflectometry,” Electron. Lett. 21, 613–614 (1985).
[CrossRef]

1984

D. K. W. Lam, R. I. MacDonald, “GaAs Optoelectronic Mixer Operation at 4.5 GHz,” IEEE Trans. Electron. Devices ED-31, 1766–1768 (1984).
[CrossRef]

1982

1981

R. I. MacDonald, “Frequency Domain Optical Reflectometer,” Appl. Opt. 20, 1840–1844 (1981).
[CrossRef] [PubMed]

C. W. Slayman, L. Figueroa, “Frequency and Pulse Response of a Novel High Speed Interdigital Surface Photoconductor (IDPC),” IEEE Trans. Electron. Devices Lett. EDL-2, 112–114 (1981).
[CrossRef]

A. G. Foyt, F. Leonberger, R. C. Williamson, “InP Optoelectronic Mixers,” Proc. Soc. Photo-Opt. Instrum. Eng. 269, 109–114 (1981).

Dakin, J. P.

J. P. Dakin, “Multiplexed and Distributed Optical Fibre Sensor Systems,” J. Phys. E 20, 954–967 (1987).
[CrossRef]

Figueroa, L.

C. W. Slayman, L. Figueroa, “Frequency and Pulse Response of a Novel High Speed Interdigital Surface Photoconductor (IDPC),” IEEE Trans. Electron. Devices Lett. EDL-2, 112–114 (1981).
[CrossRef]

Forrest, S. R.

S. R. Forrest, G. L. Tangonan, V. Jones, “Simple 8 × 8 Optoelectronic Crossbar Switch,” IEEE/OSA J. Lightwave Technol. LT-7, 607–614 (1989).
[CrossRef]

Foyt, A. G.

A. G. Foyt, F. Leonberger, R. C. Williamson, “InP Optoelectronic Mixers,” Proc. Soc. Photo-Opt. Instrum. Eng. 269, 109–114 (1981).

Hill, K. O.

Jones, V.

S. R. Forrest, G. L. Tangonan, V. Jones, “Simple 8 × 8 Optoelectronic Crossbar Switch,” IEEE/OSA J. Lightwave Technol. LT-7, 607–614 (1989).
[CrossRef]

Lam, D. K. W.

D. K. W. Lam, R. I. MacDonald, “GaAs Optoelectronic Mixer Operation at 4.5 GHz,” IEEE Trans. Electron. Devices ED-31, 1766–1768 (1984).
[CrossRef]

Legendre, J. P.

J. P. Legendre, “A Simple Reflectometer Configured to Sense Temperature,” Proc. Soc. Photo-Opt. Instrum. Eng. 566, 321–326 (1986).

Leonberger, F.

A. G. Foyt, F. Leonberger, R. C. Williamson, “InP Optoelectronic Mixers,” Proc. Soc. Photo-Opt. Instrum. Eng. 269, 109–114 (1981).

MacDonald, R. I.

Mendis, F. V. C.

T. T. Tjhung, S. K. Teo, F. V. C. Mendis, B. Selvan, “Refractometry Through Optical Frequency-Domain Reflectometry,” Electron. Lett. 21, 613–614 (1985).
[CrossRef]

Selvan, B.

T. T. Tjhung, S. K. Teo, F. V. C. Mendis, B. Selvan, “Refractometry Through Optical Frequency-Domain Reflectometry,” Electron. Lett. 21, 613–614 (1985).
[CrossRef]

Slayman, C. W.

C. W. Slayman, L. Figueroa, “Frequency and Pulse Response of a Novel High Speed Interdigital Surface Photoconductor (IDPC),” IEEE Trans. Electron. Devices Lett. EDL-2, 112–114 (1981).
[CrossRef]

Tangonan, G. L.

S. R. Forrest, G. L. Tangonan, V. Jones, “Simple 8 × 8 Optoelectronic Crossbar Switch,” IEEE/OSA J. Lightwave Technol. LT-7, 607–614 (1989).
[CrossRef]

Teo, S. K.

T. T. Tjhung, S. K. Teo, F. V. C. Mendis, B. Selvan, “Refractometry Through Optical Frequency-Domain Reflectometry,” Electron. Lett. 21, 613–614 (1985).
[CrossRef]

Tjhung, T. T.

T. T. Tjhung, S. K. Teo, F. V. C. Mendis, B. Selvan, “Refractometry Through Optical Frequency-Domain Reflectometry,” Electron. Lett. 21, 613–614 (1985).
[CrossRef]

Williamson, R. C.

A. G. Foyt, F. Leonberger, R. C. Williamson, “InP Optoelectronic Mixers,” Proc. Soc. Photo-Opt. Instrum. Eng. 269, 109–114 (1981).

Appl. Opt.

Electron. Lett.

T. T. Tjhung, S. K. Teo, F. V. C. Mendis, B. Selvan, “Refractometry Through Optical Frequency-Domain Reflectometry,” Electron. Lett. 21, 613–614 (1985).
[CrossRef]

IEEE Trans. Electron. Devices

D. K. W. Lam, R. I. MacDonald, “GaAs Optoelectronic Mixer Operation at 4.5 GHz,” IEEE Trans. Electron. Devices ED-31, 1766–1768 (1984).
[CrossRef]

IEEE Trans. Electron. Devices Lett.

C. W. Slayman, L. Figueroa, “Frequency and Pulse Response of a Novel High Speed Interdigital Surface Photoconductor (IDPC),” IEEE Trans. Electron. Devices Lett. EDL-2, 112–114 (1981).
[CrossRef]

IEEE/OSA J. Lightwave Technol.

S. R. Forrest, G. L. Tangonan, V. Jones, “Simple 8 × 8 Optoelectronic Crossbar Switch,” IEEE/OSA J. Lightwave Technol. LT-7, 607–614 (1989).
[CrossRef]

J. Phys. E

J. P. Dakin, “Multiplexed and Distributed Optical Fibre Sensor Systems,” J. Phys. E 20, 954–967 (1987).
[CrossRef]

Opt. Lett.

Proc. Soc. Photo-Opt. Instrum. Eng.

A. G. Foyt, F. Leonberger, R. C. Williamson, “InP Optoelectronic Mixers,” Proc. Soc. Photo-Opt. Instrum. Eng. 269, 109–114 (1981).

J. P. Legendre, “A Simple Reflectometer Configured to Sense Temperature,” Proc. Soc. Photo-Opt. Instrum. Eng. 566, 321–326 (1986).

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Figures (7)

Fig. 1
Fig. 1

Mixing responsivity r as a function of the bias power delivered to the photodetector. Incident optical power is 60 μW, optical modulation frequency is 100 MHz with a modulation index of 0.5, and local oscillator frequency is 101 MHz.

Fig. 2
Fig. 2

Mixing responsivity r as a function of the average optical power incident on the detector. The laser is modulated at 100 MHz with a modulation index of 0.5 and the photodetector is modulated by a 10-dBm, 101-MHz signal.

Fig. 3
Fig. 3

Mixing responsivity r (solid line, mA/W) and mixing NEP (dashed line, 10−9 W/root Hz) as a function of modulation frequency for GaAs photodetectors with Schottky barrier contacts. The photodetector is modulated by a 0-dBm signal at modulation frequency f pc , while the laser is modulated by a signal at f pc + 1.7 MHz, with a modulation index of 0.7. The average optical power incident on the detector is 45 μW.

Fig. 4
Fig. 4

Experimental arrangement.

Fig. 5
Fig. 5

Comparison of experimental and calculated spectra; (a) detail of a typical discrete reflection, parameters are defined in the text; (b) calculated spectrum with f s = 50, t d = 11 μs, fdiff = 21,278, and Φ = 2.4 rad. It was observed that the sweep oscillator produced a linear sweep for ~98% of the sweep period and a constant voltage for the remainder. The delay in the sweep onset was accounted for in calculating (b) from Eqs. (7) by setting t3 = T s − 37t d . The calculated spectrum agrees well with that observed.

Fig. 6
Fig. 6

Reflections from the end of a fiber immersed in liquids. The sweep parameters are f s = 50 Hz, f s = 10.15 MHz, f d = 9.85 MHz, and t d = 11 μs. The receiver bandwidth is 30 Hz: (a) nliq = 1.33 (water) and (b) nliq = 1.420.

Fig. 7
Fig. 7

Comparison of measured and calculated refractive indices for index matching oils from nliq = 1.33 to nliq = 1.65.

Equations (9)

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r = i rms / P rms .
i ( t ) = K [ v ( t ) ] P ( t ) .
NEP = P rms , noise / r .
f diff = 2 f d f s t d .
x = ( c f diff ) / ( 4 n f f d f s ) ,
x ( t ) = sin ( ω diff t ) 0 < t < T s / 2 - t d , 0 T s / 2 - t d < t < T s / 2 , sin [ ω diff ( t - T s / 2 ) + Φ ] T s / 2 < t < T s - t d , 0 T s - t d < t < T s ,
a m = 1 + cos [ ω ( + ) t 2 - ϑ ] - cos [ ω ( + ) t 1 ] - cos [ ω ( + ) t 3 + ϑ ] ω ( + ) T s + 1 + cos [ ω ( - ) t 2 + ϑ ] - cos [ ω ( - ) t 1 ] - cos [ ω ( - ) t 3 + ϑ ] ω ( - ) T s , b m = sin [ ω ( + ) t 2 + ϑ ] - sin [ ω ( + ) t 1 ] - sin [ ω ( + ) t 3 + ϑ ] ω ( + ) T s - sin [ ω ( - ) t 2 + ϑ ] - sin [ ω ( - ) t 1 ] - sin [ ω ( - ) t 3 + ϑ ] ω ( - ) T s ,
ω ( + ) = ω diff + 2 π f m , ω ( - ) = ω diff + 2 π f m , ϑ = Φ - ω diff T s / 2 , t 1 = T s / 2 - t d , t 2 = T s / 2 , t 3 = T s - t d .
f = c / ( 4 π n f f d ) .

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