Rugged telemetry system for coiled-tubing earth drilling

Abstract

The development of a rugged optical fiber telemetry system for coiled-tubing earth-drilling is described. The transmitter and receiver of the telemetry system are located on the surface. A high temperature fiber cable connects a serial array of downhole modulators with the surface. Each modulator consists of an intrinsic fiber Bragg grating (FBG) fixed to a piezoelectric transducer (PZ). Each modulating signal causes a PZ to stretch its attached FBG, shifting the wavelength of the light reflected by the grating. The wavelength shift of the grating-reflected light is detected at the output using a Mach-Zehnder interferometer.