STRAIN-RATE SENSOR-BASED ON IN-FIBER DOPPLER VELOCIMETRY

An optical fiber strain-rate sensor based on in-line Doppler velocimet ry is developed using a 3x3 coupler with a large path imbalance Mach-Z ehnder interferometer for passive demodulation of Doppler wavelength s hifts. A model is developed that relates the strain rate in an optical fiber to the corresponding Doppler wavelength shifts. The strain rate obtained by differentiating strain from a Michelson strain sensor mou nted on the piezoelectric transistor (PZT) cylinder shows good agreeme nt with the strain rate directly obtained from the Doppler-based strai n-rate sensor. The Doppler-based strain-rate sensor is also bonded to a Hopkinson pressure bar in an attempt to detect the stress waves prop agation. It is shown that the higher the strain rate of stress wave, t he easier it is to couple into the lead-in/out fiber. (C) 1998 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(98)01705-X].