Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1986-06-23
1988-09-06
Willis, Davis L.
Optics: measuring and testing
By particle light scattering
With photocell detection
250227, 356358, G01B 902
Patent
active
047688807
ABSTRACT:
A technique and system for accurate determination of differential propagation delays in fiber-optic circuits. The method includes providing a sinusoidally modulated optical signal to each of two waveguides defining optical paths. The optical signals received from the optical paths are combined to form a reference output signal which has a null waveform whenever the propagation delay between the optical signals contains an odd number of half periods of the optical signal waveforms. The difference in the sinusoidal modulation frequency producing a first and second null or constant waveform in the reference signal is determined. This difference value between adjacent frequencies forming the null or constant waveforms comprises the inverse of the difference of signal propagation delay in the two optical paths. Accuracy is improved by measuring the sinusoidal modulation frequencies corresponding to first and second waveforms which are not formed by adjacent frequencies. The difference between those nonadjacent frequencies is divided by the difference in the reference waveform orders of the null reference waveforms to obtain the inverse of the differential propagation delay. Further accuracy is achieved by measuring at least one of the waveform nulls at a high waveform order. Still further accuracy is achieved by monitoring the reference waveforms on a network analyzer and using a frequency synthesizer to more precisely match and identify the modulation frequencies corresponding to the null reference signal waveforms. A system is disclosed for implementing this technique optionally using optical sources having a short coherence length. Mathematical relationships are disclosed for use with measured values in obtaining further improved accuracy.
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Brooks Janet L.
Kim Byoung Y.
Shaw Herbert J.
Tur Moshe
Koren Matthew W.
The Board of Trustees of the Leland Stanford Junior University
Willis Davis L.
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