System and method for accurate loop length determination in fiber-optic sensors and signal processors

US4768880A · kind A · utility

Assignee

• The Board of Trustees of the Leland Stanford Junior University · US

Inventors

• Moshe Tur · Nes Ziona, IL
• Byoung Y. Kim · Menlo Park, US
• Janet L. Brooks · Mountain View, US
• Herbert J. Shaw · Stanford, US

Key dates

• Filing date: Jun 23, 1986
• Grant date: Sep 6, 1988
• Expiry date: Jun 23, 2006

Classification

• Technology area (CPC G): Physics
• CPC primary: G01D5/35303
• WIPO field: Measurement
• WIPO sector: Instruments

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 accu…