Time-domain addressing of remote fiber-optic interferometric sensor arrays

Abstract

This paper describes and analyzes a particular application of high duty-cycle time-division multiplexing to the separation and identification of signals from an interferometric sensor array. Using the method discussed here, the coherence length of the laser is no longer a severe design constraint. Also, the source phase-induced intensity noise which limits some other multiplexing methods may be overcome, leading to a higher sensitivity. The arrays of all-passive remote sensors exhibit minimal crosstalk between sensors, and have downlead insensitivity. A synthetic heterodyne demodulation technique prevents environmentally induced signal fading. Analysis includes coupling ratios for all directional couplers in the system, signal and noise spectra, minimum detectable phase shift, and the effect of ac coupling on noise and crosstalk. An experimental all-fiber implementation of a two sensor array has yielded a measured sensitivity of approximately 10 prad/& over a range of signal frequencies, and a crosstalk level of better than 55 dB. 0

Performance analysis of a time-division-multiplexed fiber-optic gas-sensor array by wavelength modulation of a distributed-feedback laser

“…The shot-noise current at the detector output is proportional to the square root of the total average optical power at the photodetector. Assuming that an ideal electric switch is used as the demultiplexer and that the switch is synchronized with the optical switch, the root-mean-square ͑rms͒ amplitude of the shot-noise current, after switching ͑demulti-plexing͒, for each individual sensing channel may be expressed as 13 i n,rms ϭ ͩ…”

<title>Laser interferometry: current trends and future prospects (Keynote Paper)</title>

“…23 Such a system can be implemented, as shown in Fig. 3, with a laser diode source which is driven by a gated saw-tooth current to produce pulses during which the laser frequency is ramped linearly.…”

“…20 22 In time-division multiplexing, the optical input is pulsed and each sensor produces an output pulse which is separated in time from the other sensor signals. 23 Such a system can be implemented, as shown in Fig. 3, with a laser diode source which is driven by a gated saw-tooth current to produce pulses during which the laser frequency is ramped linearly.…”

New Design of All-Optical Slow Light TDM Structure Based on Photonic Crystals

“…TDM system has been shown to have many advantages, such as low crosstalk and high sensitivity [12,13], and the system also provides a easier and more useful mean of multiplexing technology. In the multiplexing system, TDM system can transfer multiple signals simultaneously as sub-channels in one communication channel of the same transmission media such as wires or fiber optics.…”