Using a validated transmission model for the optimization of bundled fiber optic displacement sensors

A Wide-Range Displacement Sensor Based on Plastic Fiber Macro-Bend Coupling

This paper proposes the strategy of fabricating an all fiber wide-range displacement sensor based on the macro-bend coupling effect which causes power transmission between two twisted bending plastic optical fibers (POF), where the coupling power changes with the bending radius of the fibers. For the sensor, a structure of two twisted plastic fibers is designed with the experimental platform that we constructed. The influence of external temperature and displacement speed shifts are reported. The displacement sensor performance is the sensor test at different temperatures and speeds. The sensor was found to be satisfactory at both room temperature and 70 °C when the displacement is up to 140 mm. The output power is approximately linear to a displacement of 110 mm–140 mm under room temperature and 2 mm/s speed at 19.805 nW/mm sensitivity and 0.12 mm resolution. The simple structure of the sensor makes it reliable for other applications and further utilizations, promising a bright future.

An Optical Fiber Lateral Displacement Measurement Method and Experiments Based on Reflective Grating Panel

An optical fiber sensing method based on a reflective grating panel is demonstrated for lateral displacement measurement. The reflective panel is a homemade grating with a periodic variation of its refractive index, which is used to modulate the reflected light intensity. The system structure and operation principle are illustrated in detail. The intensity calculation and simulation of the optical path are carried out to theoretically analyze the measurement performance. A distinctive fiber optic grating ruler with a special fiber optic measuring probe and reflective grating panel is set up. Experiments with different grating pitches are conducted, and long-distance measurements are executed to accomplish the functions of counting optical signals, subdivision, and discerning direction. Experimental results show that the proposed measurement method can be used to detect lateral displacement, especially for applications in working environments with high temperatures.

Timing parameter optimization for comparison experiments of TSIM

The optimization problem of an absolute radiometer's timing parameters is investigated for comparison experiments of Total Solar Irradiance Monitor (TSIM). Comparison experiments were performed to establish the TSIM's contact with other space radiometers for measuring total solar irradiance (TSI). Since the comparison experiments had to be performed on a tight schedule under the impact of weather conditions, the measurement parameters for the comparison experiments were selected carefully using optimized solutions of timing parameters. The optimized solutions were identified by a genetic algorithm (GA) based on a thermal model of an absolute radiometer. The thermal model includes terms of heat radiation, air conduction, etc. Fitness value function and constraints of GA are constructed using the thermal model. The experimental results indicate that the selected measurement parameters are sufficient to implement accurate calibration of TSI, providing more opportunities for solar observation.

Understanding the effects of Doppler phenomena in white light Fabry-Perot interferometers for simultaneous position and velocity measurement

In static tests, low-power (<5 mW) white light extrinsic Fabry-Perot interferometric position sensors offer high-accuracy (μm) absolute measurements of a target's position over large (cm) axial-position ranges, and since position is demodulated directly from phase in the interferogram, these sensors are robust to fluctuations in measured power levels. However, target surface dynamics distort the interferogram via Doppler shifting, introducing a bias in the demodulation process. With typical commercial off-the-shelf hardware, a broadband source centered near 1550 nm, and an otherwise typical setup, the bias may be as large as 50-100 μm for target surface velocities as low as 0.1 mm/s. In this paper, the authors derive a model for this Doppler-induced position bias, relating its magnitude to three swept-filter tuning parameters. Target velocity (magnitude and direction) is calculated using this relationship in conjunction with a phase-diversity approach, and knowledge of the target's velocity is then used to compensate exactly for the position bias. The phase-diversity approach exploits side-by-side measurement signals, transmitted through separate swept filters with distinct tuning parameters, and permits simultaneous measurement of target velocity and target position, thereby mitigating the most fundamental performance limitation that exists on dynamic white light interferometric position sensors.

High sensitivity fiber optic angular displacement sensor and its application for detection of ultrasound

In this paper, we report on the development of an intensity-modulated fiber-optic sensor for angular displacement measurement. This sensor was designed to present high sensitivity, linear response, and wide bandwidth and, furthermore, to be simple and low cost. The sensor comprises two optical fibers, a positive lens, a reflective surface, an optical source, and a photodetector. A mathematical model was developed to determine and simulate the static characteristic curve of the sensor and to compare different sensor configurations regarding the core radii of the optical fibers. The simulation results showed that the sensor configurations tested are highly sensitive to small angle variation (in the range of microradians) with nonlinearity less than or equal to 1%. The normalized sensitivity ranges from (0.25×V(max)) to (2.40×V(max)) mV/μrad (where V(max) is the peak voltage of the static characteristic curve), and the linear range is from 194 to 1840 μrad. The unnormalized sensitivity for a reflective surface with reflectivity of 100% was measured as 7.7 mV/μrad. The simulations were compared with experimental results to validate the mathematical model and to define the most suitable configuration for ultrasonic detection. The sensor was tested on the characterization of a piezoelectric transducer and as part of a laser ultrasonics setup. The velocities of the longitudinal, shear, and surface waves were measured on aluminum samples as 6.43, 3.17, and 2.96 mm/μs, respectively, with an error smaller than 1.3%. The sensor, an alternative to piezoelectric or interferometric detectors, proved to be suitable for detection of ultrasonic waves and to perform time-of-flight measurements and nondestructive inspection.

Dynamics of a noncontacting, white light Fabry-Perot interferometric displacement sensor

A white light extrinsic Fabry-Perot interferometer is implemented as a noncontacting displacement sensor, providing robust, absolute displacement measurements with micrometer accuracy at a sampling rate of 10 Hz. This paper presents a dynamic model of the sensing cavity between the sensor probe and the nearby target surface using a Fabry-Perot etalon approach obtained from straightforward electromagnetic field formulations. Such a model is important for system characterization, as the dynamically changing cavity length imparts a Doppler shift on any signals circulating within the sensing cavity. Contrary to previously published results, Doppler-induced shifting within the low-finesse sensing cavity is shown to significantly distort the measurement signal as recorded by the sensor. Experimental and simulation results are compared, and the direct effects of cavity dynamics on the measurement signal are analyzed along with their indirect impact on sensor performance. This document has been approved by Los Alamos National Laboratory for unlimited public release (LA-UR 12-00301).