Optical fiber Sagnac interferometer which identifies harmonically related nulls in the detected spectrum
US6049506A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jan 29, 1999 |
| Grant date | Apr 11, 2000 |
| Priority date | — |
| Expiry date | Jan 29, 2019 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01D5/35303
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An optical fiber sensing system (20) applies spectral analysis to time-varying disturbances in the output optical power from a Sagnac interferometer. In particular, harmonically related null frequencies in the spectrum (402) of the output optical power from the Sagnac interferometer are used to uniquely determine the location of a disturbance along a fiber cable (50). An optical signal having relatively high coherence is fed into a splitter (25), which creates a pair of subsignals that are sent in opposite directions around a common optical path. The splitter is effective to recombine the subsignals after they have traveled around the common path. The location of the disturbance is determined by the formula: ##EQU1## z is the distance between the locations of the disturbance and the splitter; PA1 2L is the length of the common path; PA1 c is the speed of light; PA1 n.sub.e is the effective index of refraction of the optical fiber path experienced by the subsignals; and PA1 .OMEGA..sub.0 is the fundamental frequency associated with harmonically related nulls in the spectrum. Preferably, the sensing system is embedded within a communication system (60), which operates at wavelengths …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.