Patent ID: 7362923
Filing Date: 2008-04-22
Classification: G01M

Abstract:
1. A method for measuring phase shift in an optical fiber, comprising: calculating a maximum expected change in the optical fiber length for a given set of conditions; producing a monitoring signal with a wavelength greater or equal to four times the maximum expected change in the optical fiber length; using the monitoring signal to modulate a light source, thereby producing modulated monitoring light that carries the monitoring signal; feeding the modulated monitoring light into an optical fiber, wherein the monitoring light, after entering the optical fiber, travels through the fiber a distance; after the modulated monitoring light travels the distance through the optical fiber, causing the modulated monitoring light to travel back through the fiber towards the point at which the monitoring light entered the optical fiber; after causing the modulated monitoring light to travel back through the optical fiber, receiving the modulated monitoring light and producing a phase-shifted monitoring signal based on the received modulated monitoring light; and processing the monitoring signal and the phase-shifted monitoring signal to produce a value corresponding to an amount of phase shift.