A proposal for high-precision fiber optic displacement sensor

2007

In this paper, theoretical and experimental investigation of a novel compact and high-precision (0.2 nm) optical displacement sensor is presented. The sensor operation is based on optical intensity modulation due to diffraction. A circular disk, including a central transmitter and circumferential receivers (8 and 12 configurations), is considered as high precision displacement sensor. Effects of the number of receivers and the reflection coefficient of the receiver's surface on sensitivity of the proposed sensor are investigated. It is shown that with increase of the reflection coefficient of the surface, the sensitivity will increase up to five times compared with the traditional case. It is also demonstrated that there is an excellent agreement between theoretical and experimental results.

2013

Over the last two decades, the fibre optic technology has passed through many analytical stages. Some commercially available fibre optic sensors are being used for automation in mechanical and industrial environments. They are also used for instrumentation and controls. In the present work, a fibre optic displacement sensor is presented. This type of sensor is an intrinsic sensor. In this paper our aim is to study the different results of displacement sensor using fibre optic coupler.

SPIE Proceedings, 1998

A novel low cost interferometric displacement sensor has been developed which tracks distance from the tip of a fiber optic probe. A unique interrogation technique is used which produces a 32-bit phase word, giving the system a dynamic range > 10 9. Therefore, a displacement resolution of < 0.01 nm can be achieved with a full range of 6 mm. The measurement range can be extended beyond 10 m by simply adjusting the digital fringe counter and sacrificing resolution yet maintaining the > 10 9 dynamic range. Demodulation rates of 40 kHz have been achieved which facilitates dynamic measurements. Results from an application to hard disk (HD) profilometry are presented.

Microwave and Optical Technology Letters, 2010

The intensity-modulation-based displacement sensor with two receiving fibers is theoretically and experimentally studied. Themathematical model of the proposed sensor is developed and the simulated responses are obtained to be in a good agreement with the experimental results. Compared with the conventional sensor with only one receiving fiber, the proposed sensor has a better linearity range because it has a larger area to receive the reflected light from the target. However, the sensitivity of both sensors is almost similar. Theproposed sensor has the maximum linearity ranges of 2.5 μm and 0.9 μm at the back and front slopes, respectively. The linearity ranges are improved by about 44% compared with the conventional sensor. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 373–375, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24900

We describe laboratory experiments with a fiber-optic sensor employing a chirped laser that detects, with 20-30 micrometer accuracy, displacements of a remote reflective target at distance of 200-500 mm. The requirements of chirp linearity and laser coherence in order to achieve this sensitivity are elaborated. This sensor can be employed for remotely sensing minute displacements of objects in harsh environments, including cryo-magnets in particle accelerators.

1982

Fibre optics is beginning to find use for sensing purposes. Fibre optic sensors have many interesting features, e.g., their immunity to interference from electrornagnetic fields. The paper briefly discusses different sensor principles. A displacement sensor using multimode, step index fibres is described. Measurement data showing a resolution of 0.05 nm/lHZ in a 150~m linear rallge is gi ven. In this sensor, the light coupling between two fibre ends varies with the position of a movable mirror. A mathematical model of the sensor is presented. Application to pressure sensing is also discussed.

IEEE Transactions on Instrumentation and Measurement, 2000

Light-intensity-modulated displacement sensors are currently extensively used in numerous applications. Most such sensors operate by utilizing a pair of adjacent optical fibers and a reflector. This scheme can provide a good sensing outcome, but its performance can be enhanced with the use of only a single optical fiber. Such displacement sensors have the benefits of higher sensitivity and operating range, because they can efficiently collect more light after a reflectance has occurred. Hence, this paper investigates a single optical fiber that emits and collects light while translating and rotating with respect to the main axis of the optical fiber. The Gaussian light-sensing behavior of these two cases is mathematically modeled, giving sensing characteristics such as linearity and sensitivity. Experimental results are presented for verification and validation of the models.

Some advanced fiber-optic amplitude modulated reflection displacement sensors and refractive index sensors have been developed. An improved three-fiber displacement sensor has been investigated as a refractive index sensor by computer simulations in a large interval of displacement. Some new regularities have been revealed. A reflection fiber-optic displacement sensor of novel configuration, consisting of double optical-pair fibers with a definite angle between the measuring tips of fibers in the pairs has been proposed, designed, and experimentally investigated to indicate and measure the displacement and refractive index of gas and liquid water solutions. The proposed displacement sensor and refractive index sensor configuration improves the measuring sensitivity in comparison with the known measuring methods. The refractive index sensor sensitivity S nsub = 4×10 −7 RIU/mV was achieved. The displacement sensor sensitivity is S sub = 1702 mV/µm in air (n = 1.00027).

Microwave and Optical Technology Letters, 2008

A simple fiber optic displacement sensor based on intensity modulation technique is demonstrated using a bundle multimode plastic fiber as a probe. The sensor consists of a light source, a probe, and photodiode detector. The sensor is capable of measuring displacements of mirror ranging from 0.05 to 2.2 mm using a red light source of wavelength 632.8 nm with maximum output power of 1 mW. The sensitivity of the device is found to be 168.8 mV/mm over 0.05–0.35 mm range and −29.8 mV/mm over 1.05–2.2 mm range. The sensor is highly sensitive at the front slope and very useful for close distance target. The simplicity of the design, high degree of sensitivity, dynamic range and the low cost of the fabrication make it suitable for applications in industries as position control and micro displacement measurement in the hazardous region. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 661–663, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23147

Smart Materials and Structures, 2006

The application of fiber optical sensors (FOSs) in displacement measurement has the advantage that physical contact is not required. In this paper, work is reported consisting of various experiments that have been conducted in order to verify the effect that various parameters might possibly have on the accuracy of FOS displacement measurement. It is to be expected that the texture and reflectivity of the surface of the test piece will affect the sensor's output, as will possibly the thickness of transparent material in front of the reflecting surface. Manufacturers of FOSs caution users on the effect of angularity of the sensor with respect to the surface normal but do not generally provide quantitative information on this topic. In addition, the combined effect of angularity induced from a surface displacement away or toward a stationary sensor is believed to be of interest to experimenters.