Fiber-optic acceleration sensor based on the photoelastic effect

Optical stress sensor based on electro-optic compensation for photoelastic birefringence in a single crystal

An optical stress sensor is proposed by using a single crystal with both electro-optic and photoelastic effects. Different from previous crystal-based stress sensors, the proposed sensor is based on electro-optic compensation for stress-induced birefringence and does not need an additional quarter-wave plate or modulator, because the stress-sensing element is simultaneously used as an electro-optic compensator. Candidate sensing materials include electro-optic crystals of the 3 m symmetry group and all glass with large Kerr coefficients. A primary experiment has demonstrated that the stress-induced birefringence in lithium niobate crystal can be compensated by its electro-optic birefringence. The proposed stress sensor is compact and low cost, and it is possible to achieve closed-loop stress measurement.

Optical fiber accelerometer based on a silicon micromachined cantilever

An intensity-modulated fiber-optic accelerometer based on backreflection effects has been manufactured and tested. It uses a multimode fiber placed at a spherical mirror center, and the beam intensity is modulated by a micromachined silicon cantilever. This device has applications as an accelerometer and vibrometer for rotating machines. It exhibits an amplitude linearity of ±1.2% in the range of 0.1-22 m s(-2), a frequency linearity of ±1% in the range of 0-100 Hz, and a temperature sensitivity of less than 0.03%/°C. The sensor is devoted to a wavelength-division multiplexing network.

Errors introduced by a quarter-wave plate in photoelastic multimode optical fiber sensors

The errors that are introduced by a quarter-wave plate are theoretically evaluated for photoelastic multimode fiber sensors with different configurations. The results indicate that, for the orthogonal and parallel fiber sensors, the error is proportional to the change in the differential retardation of the quarter-wave plate, whereas the error is proportional to the square of the change for the pi/4 fiber sensor.

Fiber-optic sensor for simultaneous and independent measurement of vibration and temperature in electric generators

A fiber-optic sensor designed to operate inside high-power electric plants is presented. The probe is based on a fiber-optic proximity sensor that detects the light intensity modulation induced by an elastic transducer. The nonlinear response of the optical head is exploited in an original manner to obtain the simultaneous and ndependent measurement of temperature and vibration at 100 Hz. The particular working principle provides an intrinsically lead-insensitive response.

Force to frequency conversion by intracavity photoelastic modulation

Force to frequency conversion (FFC) using the photoelastic effect inside a laser cavity is described. Analytic expressions are derived for scale factor, measurement errors, and laser dependent nonlinearity of appropriate instrument transducers. The influence of the laser pushing and pulling effects on linearity is calculated on the basis of the third-order saturation model. Our experiments with a modular test setup (633 nm) demonstrate FFC to be proportional to a high degree over almost 6 decades of input signal range. From 2 x 10(-4) up to 80 N we observed the noise equivalent resolution of 10(-4) N. The frequency response of our test setup was established from dc up to some kilohertz. FFC measurement range and resolution can be extended to 10(-6) N or smaller values by applying improved laser stabilization and miniaturizing the cavity length and size of photoelastic material.