Single-mode Fiber-optic Sensor Research Articles

Single-mode fiber-based reflex sensor for internal surface in-line measurement of small products

Abstract This paper describes experiments concerning dimension and surface shape measurement with a single-mode fiber-optic sensor and improvement of the measurement principle. The sensor probe was well designed with a small structure and a compensation network. The novel optical fiber probe arrangement as well as the possibilities for complex measurement problems is explained by measuring an internal screw thread as an example. The size of the fiber-based sensor probe is about 5 mm, which is very suitable for the internal surface measurement of small precision products. The experimental results show that the measurement uncertainty of the internal screw thread minor diameter can reach ±10 μm, and the stability of the measurement system is better than 0.1%. Compared the measurement results obtained by the developed sensor system with those by a Universal Tool Maker’s Microscope, the measurement results of an external screw thread are satisfactory. The maximum deviation of the thread pitch measurement is about 1 μm, and that of the major diameter measurement is better than 3 μm.

Shape measurement based on fiber-optic technique for complex internal surface

Reverse engineering based on fiber-optic technique is a very new topic in CAD/CAM fields. A novel single-mode fiber-optic sensor is presented based on the principle of beam reflection to implement the digitizing of complex surface shape. The fibers in the sensor probe are arranged like a spoke with eight symmetrically cross-arranged receiving fibers and one centered emitting fiber. Thus, the sensor can compensate for the offsets caused by fluctuations of surface reflectivity and light power and is fit for application under rough and formidable conditions with noncontact, fast shape measurement. A prototype was developed based on the simulation results to verify the feasibility. With the GRIN lens on the exit end of the single-mode emitting fiber, the lateral resolution was greatly improved compared with former multimode fiber-optic displacement sensors. Preliminary experiments indicated that the estimated uncertainty of displacement measurement was better than ±2 μm, and the uncertainty of ±5.6 μm can be obtained when measuring a MJ20×1.5 thread.

Rayleigh scattering optical frequency correlation in a single-mode optical fiber

The bichromatic optical frequency correlation function for Rayleigh backscattering from a pulse of laser light propagating along a single-mode optical fiber has been calculated and measured. It is shown that the optical correlation frequency, Dnu(c) , is equal to the reciprocal of pulse width T(w) . These results are important for the development of wavelength diversity techniques for the reduction of coherent Rayleigh noise in distributed Rayleigh backscattering single-mode optical fiber sensors.

Polarization effects on single-mode optical fiber sensors

In a conventional circular cross-section single-mode fiber, built-in and induced birefringences remove the degeneracy and make the fiber a two-Eigenmode system. We have constructed the first all-fiber interferometric sensor system and have performed preliminary studies on the effects of birefringence in these interferometers. Theoretical analysis and experimental data supporting this analysis are presented for the 3-dB coupler and all-fiber interferometer sensor.