Optical fiber telemetry systems for measurement-while-drilling applications

Two rugged optical fiber telemetry systems for coiled-tubing drilling and o ther hostile-environment applications are briefly described. One system is a passive uplink; the other is an active simplex link. The transmitter and receiver of the passive uplink are located on the surface. A high-temperatu re fiber cable connects a serial array of downhole modulators with the surf ace. Each modulator consists of an intrinsic fiber Bragg grating fixed to a piezoelectric transducer. The simplex link consists of commercial off-the- shelf components: a LED, plastic-clad silica fiber, and a Si pin diode. Bot h systems performed well when tested at temperatures to 150 degrees C and a t vibration levels similar to those downhole. The passive uplink system's p erformance was unchanged after being tested in actual drilling operations ( rotating, drilling, and reaming). The active simplex link's performance was unchanged after being tested at peak vibration levels of 20g. The signal-t o-noise ratio of the passive uplink was 108 dB/root Hz. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)02106-1].