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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (30 June 2013)

Special Issue Editor

Guest Editor
Prof. Dr. Alexander W. Koch

Technische Universität München, Institute for Measurement Systems and Sensor Technology (MST), Munich, Germany
Website | E-Mail
Phone: 00498928923344
Interests: optical fiber sensors; optomechatronic measurement technology; laser- and video-based perception; environmental monitoring; multisensory systems; speckle-holographic measurement techniques; laser measurement systems; FTIR spectroscopy; image processing

Special Issue Information

Dear Colleagues,

The field of optomechatronics provides synergistic effects of optics, mechanics and electronics for efficient sensor development. Optical sensors for the measurement of mechanical quantities, equipped with appropriate electronic signal (pre)processing have a wide range of applications, from surface testing, stress monitoring, thin film analysis to biochemical sensing. The aim of this special issue is to provide an overview of actual research and innovative applications of optomechatronics in sensors. Papers addressing, inter alia, optical sensor principles, fiber-optic sensors, electronic speckle pattern interferometry, surface analysis, thin film measurement, FGB sensors, and biochemical sensors are welcome.

Prof. Dr.-Ing. Dr. h.c. Alexander W. Koch
Guest Editor

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed Open Access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs).

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Keywords

  • optical sensor
  • fiber-optic sensor
  • speckle effect monitoring
  • surface analysis
  • thin film measurement
  • fiber-Bragg grating sensor
  • biochemical sensor


Published Papers (19 papers)

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Editorial

Jump to: Research, Other

Open AccessEditorial Introduction to the Special Issue on “Optomechatronics”
Sensors 2014, 14(4), 6302-6304; doi:10.3390/s140406302
Received: 15 March 2014 / Accepted: 28 March 2014 / Published: 31 March 2014
PDF Full-text (110 KB) | HTML Full-text | XML Full-text
Abstract
The field of optomechatronics combines the synergistic effects of optics, mechanics and electronics for efficient sensor development. Optical sensors for the measurement of mechanical quantities, equipped with appropriate electronic signal (pre)processing have a wide range of applications, from surface testing, stress monitoring, and
[...] Read more.
The field of optomechatronics combines the synergistic effects of optics, mechanics and electronics for efficient sensor development. Optical sensors for the measurement of mechanical quantities, equipped with appropriate electronic signal (pre)processing have a wide range of applications, from surface testing, stress monitoring, and thin film analysis to biochemical sensing. The aim of this special issue is to provide an overview of current research and innovative applications of optomechatronics in sensors. [...] Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available

Research

Jump to: Editorial, Other

Open AccessArticle On-Line Thickness Measurement for Two-Layer Systems on Polymer Electronic Devices
Sensors 2013, 13(11), 15747-15757; doi:10.3390/s131115747
Received: 25 September 2013 / Revised: 24 October 2013 / Accepted: 11 November 2013 / Published: 18 November 2013
Cited by 2 | PDF Full-text (699 KB) | HTML Full-text | XML Full-text
Abstract
During the manufacturing of printed electronic circuits, different layers of coatings are applied successively on a substrate. The correct thickness of such layers is essential for guaranteeing the electronic behavior of the final product and must therefore be controlled thoroughly. This paper presents
[...] Read more.
During the manufacturing of printed electronic circuits, different layers of coatings are applied successively on a substrate. The correct thickness of such layers is essential for guaranteeing the electronic behavior of the final product and must therefore be controlled thoroughly. This paper presents a model for measuring two-layer systems through thin film reflectometry (TFR). The model considers irregular interfaces and distortions introduced by the setup and the vertical vibration movements caused by the production process. The results show that the introduction of these latter variables is indispensable to obtain correct thickness values. The proposed approach is applied to a typical configuration of polymer electronics on transparent and non-transparent substrates. We compare our results to those obtained using a profilometer. The high degree of agreement between both measurements validates the model and suggests that the proposed measurement method can be used in industrial applications requiring fast and non-contact inspection of two-layer systems. Moreover, this approach can be used for other kinds of materials with known optical parameters. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle Satellite Angular Velocity Estimation Based on Star Images and Optical Flow Techniques
Sensors 2013, 13(10), 12771-12793; doi:10.3390/s131012771
Received: 20 July 2013 / Revised: 13 September 2013 / Accepted: 17 September 2013 / Published: 25 September 2013
Cited by 6 | PDF Full-text (571 KB) | HTML Full-text | XML Full-text
Abstract
An optical flow-based technique is proposed to estimate spacecraft angular velocity based on sequences of star-field images. It does not require star identification and can be thus used to also deliver angular rate information when attitude determination is not possible, as during platform
[...] Read more.
An optical flow-based technique is proposed to estimate spacecraft angular velocity based on sequences of star-field images. It does not require star identification and can be thus used to also deliver angular rate information when attitude determination is not possible, as during platform de tumbling or slewing. Region-based optical flow calculation is carried out on successive star images preprocessed to remove background. Sensor calibration parameters, Poisson equation, and a least-squares method are then used to estimate the angular velocity vector components in the sensor rotating frame. A theoretical error budget is developed to estimate the expected angular rate accuracy as a function of camera parameters and star distribution in the field of view. The effectiveness of the proposed technique is tested by using star field scenes generated by a hardware-in-the-loop testing facility and acquired by a commercial-off-the shelf camera sensor. Simulated cases comprise rotations at different rates. Experimental results are presented which are consistent with theoretical estimates. In particular, very accurate angular velocity estimates are generated at lower slew rates, while in all cases the achievable accuracy in the estimation of the angular velocity component along boresight is about one order of magnitude worse than the other two components. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Figures

Open AccessArticle Static Hyperspectral Fluorescence Imaging of Viscous Materials Based on a Linear Variable Filter Spectrometer
Sensors 2013, 13(9), 12687-12697; doi:10.3390/s130912687
Received: 25 June 2013 / Revised: 29 August 2013 / Accepted: 13 September 2013 / Published: 23 September 2013
Cited by 6 | PDF Full-text (279 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a low-cost hyperspectral measurement setup in a new application based on fluorescence detection in the visible (Vis) wavelength range. The aim of the setup is to take hyperspectral fluorescence images of viscous materials. Based on these images, fluorescent and non-fluorescent
[...] Read more.
This paper presents a low-cost hyperspectral measurement setup in a new application based on fluorescence detection in the visible (Vis) wavelength range. The aim of the setup is to take hyperspectral fluorescence images of viscous materials. Based on these images, fluorescent and non-fluorescent impurities in the viscous materials can be detected. For the illumination of the measurement object, a narrow-band high-power light-emitting diode (LED) with a center wavelength of 370 nm was used. The low-cost acquisition unit for the imaging consists of a linear variable filter (LVF) and a complementary metal oxide semiconductor (CMOS) 2D sensor array. The translucent wavelength range of the LVF is from 400 nm to 700 nm. For the confirmation of the concept, static measurements of fluorescent viscous materials with a non-fluorescent impurity have been performed and analyzed. With the presented setup, measurement surfaces in the micrometer range can be provided. The measureable minimum particle size of the impurities is in the nanometer range. The recording rate for the measurements depends on the exposure time of the used CMOS 2D sensor array and has been found to be in the microsecond range. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle A High-Temperature Fiber Sensor Using a Low Cost Interrogation Scheme
Sensors 2013, 13(9), 11653-11659; doi:10.3390/s130911653
Received: 16 June 2013 / Revised: 24 August 2013 / Accepted: 29 August 2013 / Published: 4 September 2013
Cited by 3 | PDF Full-text (481 KB) | HTML Full-text | XML Full-text
Abstract
Regenerated Fibre Bragg Gratings have the potential for high-temperature monitoring. In this paper, the inscription of Fibre Bragg Gratings (FBGs) and the later regeneration process to obtain Regenerated Fiber Bragg Gratings (RFBGs) in high-birefringence optical fiber is reported. The obtained RFBGs show two
[...] Read more.
Regenerated Fibre Bragg Gratings have the potential for high-temperature monitoring. In this paper, the inscription of Fibre Bragg Gratings (FBGs) and the later regeneration process to obtain Regenerated Fiber Bragg Gratings (RFBGs) in high-birefringence optical fiber is reported. The obtained RFBGs show two Bragg resonances corresponding to the slow and fast axis that are characterized in temperature terms. As the temperature increases the separation between the two Bragg resonances is reduced, which can be used for low cost interrogation. The proposed interrogation setup is based in the use of optical filters in order to convert the wavelength shift of each of the Bragg resonances into optical power changes. The design of the optical filters is also studied in this article. In first place, the ideal filter is calculated using a recursive method and defining the boundary conditions. This ideal filter linearizes the output of the interrogation setup but is limited by the large wavelength shift of the RFBG with temperature and the maximum attenuation. The response of modal interferometers as optical filters is also analyzed. They can be easily tuned shifting the optical spectrum. The output of the proposed interrogation scheme is simulated in these conditions improving the sensitivity. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle Spectral-Domain Measurements of Birefringence and Sensing Characteristics of a Side-Hole Microstructured Fiber
Sensors 2013, 13(9), 11424-11438; doi:10.3390/s130911424
Received: 10 July 2013 / Revised: 12 August 2013 / Accepted: 27 August 2013 / Published: 28 August 2013
Cited by 10 | PDF Full-text (643 KB) | HTML Full-text | XML Full-text
Abstract
We experimentally characterized a birefringent side-hole microstructured fiber in the visible wavelength region. The spectral dependence of the group and phase modal birefringence was measured using the methods of spectral interferometry. The phase modal birefringence of the investigated fiber increases with wavelength, but
[...] Read more.
We experimentally characterized a birefringent side-hole microstructured fiber in the visible wavelength region. The spectral dependence of the group and phase modal birefringence was measured using the methods of spectral interferometry. The phase modal birefringence of the investigated fiber increases with wavelength, but its positive sign is opposite to the sign of the group modal birefringence. We also measured the sensing characteristics of the fiber using a method of tandem spectral interferometry. Spectral interferograms corresponding to different values of a physical parameter were processed to retrieve the spectral phase functions and to determine the spectral dependence of polarimetric sensitivity to strain, temperature and hydrostatic pressure. A negative sign of the polarimetric sensitivity was deduced from the simulation results utilizing the known modal birefringence dispersion of the fiber. Our experimental results show that the investigated fiber has a very high polarimetric sensitivity to hydrostatic pressure, reaching –200 rad x MPa–1 x m–1 at 750 nm. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle A Refractive Index Sensor Based on the Resonant Coupling to Cladding Modes in a Fiber Loop
Sensors 2013, 13(9), 11260-11270; doi:10.3390/s130911260
Received: 23 July 2013 / Revised: 2 August 2013 / Accepted: 16 August 2013 / Published: 23 August 2013
Cited by 6 | PDF Full-text (399 KB) | HTML Full-text | XML Full-text
Abstract
We report an easy-to-build, compact, and low-cost optical fiber refractive index sensor. It consists of a single fiber loop whose transmission spectra exhibit a series of notches produced by the resonant coupling between the fundamental mode and the cladding modes in a uniformly
[...] Read more.
We report an easy-to-build, compact, and low-cost optical fiber refractive index sensor. It consists of a single fiber loop whose transmission spectra exhibit a series of notches produced by the resonant coupling between the fundamental mode and the cladding modes in a uniformly bent fiber. The wavelength of the notches, distributed in a wavelength span from 1,400 to 1,700 nm, can be tuned by adjusting the diameter of the fiber loop and are sensitive to refractive index changes of the external medium. Sensitivities of 170 and 800 nm per refractive index unit for water solutions and for the refractive index interval 1.40–1.442, respectively, are demonstrated. We estimate a long range resolution of 3 × 10−4 and a short range resolution of 2 × 10−5 for water solutions. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle 3D Finite Element Model for Writing Long-Period Fiber Gratings by CO2 Laser Radiation
Sensors 2013, 13(8), 10333-10347; doi:10.3390/s130810333
Received: 1 July 2013 / Revised: 6 August 2013 / Accepted: 8 August 2013 / Published: 12 August 2013
Cited by 3 | PDF Full-text (786 KB) | HTML Full-text | XML Full-text
Abstract
In the last years, mid-infrared radiation emitted by CO2 lasers has become increasing popular as a tool in the development of long-period fiber gratings. However, although the development and characterization of the resulting sensing devices have progressed quickly, further research is still
[...] Read more.
In the last years, mid-infrared radiation emitted by CO2 lasers has become increasing popular as a tool in the development of long-period fiber gratings. However, although the development and characterization of the resulting sensing devices have progressed quickly, further research is still necessary to consolidate functional models, especially regarding the interaction between laser radiation and the fiber’s material. In this paper, a 3D finite element model is presented to simulate the interaction between laser radiation and an optical fiber and to determine the resulting refractive index change. Dependence with temperature of the main parameters of the optical fiber materials (with special focus on the absorption of incident laser radiation) is considered, as well as convection and radiation losses. Thermal and residual stress analyses are made for a standard single mode fiber, and experimental results are presented. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Figures

Open AccessArticle Dynamic Sensor Interrogation Using Wavelength-Swept Laser with a Polygon-Scanner-Based Wavelength Filter
Sensors 2013, 13(8), 9669-9678; doi:10.3390/s130809669
Received: 15 April 2013 / Revised: 30 June 2013 / Accepted: 15 July 2013 / Published: 29 July 2013
Cited by 9 | PDF Full-text (484 KB) | HTML Full-text | XML Full-text
Abstract
We report a high-speed (~2 kHz) dynamic multiplexed fiber Bragg grating (FBG) sensor interrogation using a wavelength-swept laser (WSL) with a polygon-scanner-based wavelength filter. The scanning frequency of the WSL is 18 kHz, and the 10 dB scanning bandwidth is more than 90
[...] Read more.
We report a high-speed (~2 kHz) dynamic multiplexed fiber Bragg grating (FBG) sensor interrogation using a wavelength-swept laser (WSL) with a polygon-scanner-based wavelength filter. The scanning frequency of the WSL is 18 kHz, and the 10 dB scanning bandwidth is more than 90 nm around a center wavelength of 1,540 nm. The output from the WSL is coupled into the multiplexed FBG array, which consists of five FBGs. The reflected Bragg wavelengths of the FBGs are 1,532.02 nm, 1,537.84 nm, 1,543.48 nm, 1,547.98 nm, and 1,553.06 nm, respectively. A dynamic periodic strain ranging from 500 Hz to 2 kHz is applied to one of the multiplexed FBGs, which is fixed on the stage of the piezoelectric transducer stack. Good dynamic performance of the FBGs and recording of their fast Fourier transform spectra have been successfully achieved with a measuring speed of 18 kHz. The signal-to-noise ratio and the bandwidth over the whole frequency span are determined to be more than 30 dB and around 10 Hz, respectively. We successfully obtained a real-time measurement of the abrupt change of the periodic strain. The dynamic FBG sensor interrogation system can be read out with a WSL for high-speed and high-sensitivity real-time measurement. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle Temperature-Insensitive Bend Sensor Using Entirely Centered Erbium Doping in the Fiber Core
Sensors 2013, 13(7), 9536-9546; doi:10.3390/s130709536
Received: 3 June 2013 / Revised: 15 July 2013 / Accepted: 17 July 2013 / Published: 23 July 2013
Cited by 4 | PDF Full-text (785 KB) | HTML Full-text | XML Full-text
Abstract
A fiber based bend sensor using a uniquely designed Bend-Sensitive Erbium Doped Fiber (BSEDF) is proposed and demonstrated. The BSEDF has two core regions, namely an undoped outer region with a diameter of about 9.38 μm encompassing a doped, inner core region with
[...] Read more.
A fiber based bend sensor using a uniquely designed Bend-Sensitive Erbium Doped Fiber (BSEDF) is proposed and demonstrated. The BSEDF has two core regions, namely an undoped outer region with a diameter of about 9.38 μm encompassing a doped, inner core region with a diameter of 4.00 μm. The doped core region has about 400 ppm of an Er2O3 dopant. Pumping the BSEDF with a conventional 980 nm laser diode gives an Amplified Spontaneous Emission (ASE) spectrum spanning from 1,510 nm to over 1,560 nm at the output power level of about −58 dBm. The ASE spectrum has a peak power of −52 dBm at a central wavelength of 1,533 nm when not spooled. Spooling the BSEDF with diameters of 10 cm to 2 cm yields decreasing peak powers from −57.0 dBm to −61.8 dBm, while the central wavelength remains unchanged. The output is highly stable over time, with a low temperature sensitivity of around ~0.005 dBm/°C, thus allowing for the development of a highly stable sensor system based in the change of the peak power alone. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle Investigation on Dynamic Calibration for an Optical-Fiber Solids Concentration Probe in Gas-Solid Two-Phase Flows
Sensors 2013, 13(7), 9201-9222; doi:10.3390/s130709201
Received: 3 April 2013 / Revised: 4 July 2013 / Accepted: 15 July 2013 / Published: 17 July 2013
Cited by 6 | PDF Full-text (442 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a review and analysis of the research that has been carried out on dynamic calibration for optical-fiber solids concentration probes. An introduction to the optical-fiber solids concentration probe was given. Different calibration methods of optical-fiber solids concentration probes reported in
[...] Read more.
This paper presents a review and analysis of the research that has been carried out on dynamic calibration for optical-fiber solids concentration probes. An introduction to the optical-fiber solids concentration probe was given. Different calibration methods of optical-fiber solids concentration probes reported in the literature were reviewed. In addition, a reflection-type optical-fiber solids concentration probe was uniquely calibrated at nearly full range of the solids concentration from 0 to packed bed concentration. The effects of particle properties (particle size, sphericity and color) on the calibration results were comprehensively investigated. The results show that the output voltage has a tendency to increase with the decreasing particle size, and the effect of particle color on calibration result is more predominant than that of sphericity. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle An In-Reflection Strain Sensing Head Based on a Hi-Bi Photonic Crystal Fiber
Sensors 2013, 13(7), 8095-8102; doi:10.3390/s130708095
Received: 13 May 2013 / Revised: 13 June 2013 / Accepted: 17 June 2013 / Published: 25 June 2013
Cited by 6 | PDF Full-text (548 KB) | HTML Full-text | XML Full-text
Abstract
A photonic crystal fiber-based sensing head is proposed for strain measurements. The sensor comprises a Hi-Bi PCF sensing head to measure interferometric signals in-reflection. An experimental background study of the sensing head is conducted through an optical backscatter reflectometer confirming the theoretical predictions,
[...] Read more.
A photonic crystal fiber-based sensing head is proposed for strain measurements. The sensor comprises a Hi-Bi PCF sensing head to measure interferometric signals in-reflection. An experimental background study of the sensing head is conducted through an optical backscatter reflectometer confirming the theoretical predictions, also included. A cost effective setup is proposed where a laser is used as illumination source, which allows accurate high precision strain measurements. Thus, a sensitivity of ~7.96 dB/me was achieved in a linear region of 1,200 μe. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle An Optical Fiber Bundle Sensor for Tip Clearance and Tip Timing Measurements in a Turbine Rig
Sensors 2013, 13(6), 7385-7398; doi:10.3390/s130607385
Received: 9 April 2013 / Revised: 16 May 2013 / Accepted: 29 May 2013 / Published: 5 June 2013
Cited by 24 | PDF Full-text (604 KB) | HTML Full-text | XML Full-text
Abstract
When it comes to measuring blade-tip clearance or blade-tip timing in turbines, reflective intensity-modulated optical fiber sensors overcome several traditional limitations of capacitive, inductive or discharging probe sensors. This paper presents the signals and results corresponding to the third stage of a multistage
[...] Read more.
When it comes to measuring blade-tip clearance or blade-tip timing in turbines, reflective intensity-modulated optical fiber sensors overcome several traditional limitations of capacitive, inductive or discharging probe sensors. This paper presents the signals and results corresponding to the third stage of a multistage turbine rig, obtained from a transonic wind-tunnel test. The probe is based on a trifurcated bundle of optical fibers that is mounted on the turbine casing. To eliminate the influence of light source intensity variations and blade surface reflectivity, the sensing principle is based on the quotient of the voltages obtained from the two receiving bundle legs. A discrepancy lower than 3% with respect to a commercial sensor was observed in tip clearance measurements. Regarding tip timing measurements, the travel wave spectrum was obtained, which provides the average vibration amplitude for all blades at a particular nodal diameter. With this approach, both blade-tip timing and tip clearance measurements can be carried out simultaneously. The results obtained on the test turbine rig demonstrate the suitability and reliability of the type of sensor used, and suggest the possibility of performing these measurements in real turbines under real working conditions. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle Soft, Transparent, Electronic Skin for Distributed and Multiple Pressure Sensing
Sensors 2013, 13(5), 6578-6604; doi:10.3390/s130506578
Received: 23 March 2013 / Revised: 19 April 2013 / Accepted: 3 May 2013 / Published: 17 May 2013
Cited by 9 | PDF Full-text (1149 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we present a new optical, flexible pressure sensor that can be applied as smart skin to a robot or to consumer electronic devices. We describe a mechano-optical transduction principle that can allow the encoding of information related to an externally
[...] Read more.
In this paper we present a new optical, flexible pressure sensor that can be applied as smart skin to a robot or to consumer electronic devices. We describe a mechano-optical transduction principle that can allow the encoding of information related to an externally applied mechanical stimulus, e.g., contact, pressure and shape of contact. The physical embodiment that we present in this work is an electronic skin consisting of eight infrared emitters and eight photo-detectors coupled together and embedded in a planar PDMS waveguide of 5.5 cm diameter. When a contact occurs on the sensing area, the optical signals reaching the peripheral detectors experience a loss because of the Frustrated Total Internal Reflection and deformation of the material. The light signal is converted to electrical signal through an electronic system and a reconstruction algorithm running on a computer reconstructs the pressure map. Pilot experiments are performed to validate the tactile sensing principle by applying external pressures up to 160 kPa. Moreover, the capabilities of the electronic skin to detect contact pressure at multiple subsequent positions, as well as its function on curved surfaces, are validated. A weight sensitivity of 0.193 gr−1 was recorded, thus making the electronic skin suitable to detect pressures in the order of few grams. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Figures

Open AccessArticle Using a Fiber Loop and Fiber Bragg Grating as a Fiber Optic Sensor to Simultaneously Measure Temperature and Displacement
Sensors 2013, 13(5), 6542-6551; doi:10.3390/s130506542
Received: 8 April 2013 / Revised: 18 April 2013 / Accepted: 8 May 2013 / Published: 16 May 2013
Cited by 6 | PDF Full-text (463 KB) | HTML Full-text | XML Full-text
Abstract
This study integrated a fiber loop manufactured by using commercial fiber (SMF-28, Corning) and a fiber Bragg grating (FBG) to form a fiber optic sensor that could simultaneously measure displacement and temperature. The fiber loop was placed in a thermoelectric cooling module with
[...] Read more.
This study integrated a fiber loop manufactured by using commercial fiber (SMF-28, Corning) and a fiber Bragg grating (FBG) to form a fiber optic sensor that could simultaneously measure displacement and temperature. The fiber loop was placed in a thermoelectric cooling module with FBG affixed to the module, and, consequently, the center wavelength displacement of FBG was limited by only the effects of temperature change. Displacement and temperature were determined by measuring changes in the transmission of optical power and shifts in Bragg wavelength. This study provides a simple and economical method to measure displacement and temperature simultaneously. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle Remote Interrogation of WDM Fiber-Optic Intensity Sensors Deploying Delay Lines in the Virtual Domain
Sensors 2013, 13(5), 5870-5880; doi:10.3390/s130505870
Received: 6 March 2013 / Revised: 9 April 2013 / Accepted: 3 May 2013 / Published: 7 May 2013
Cited by 7 | PDF Full-text (786 KB) | HTML Full-text | XML Full-text
Abstract
In this work a radio-frequency self-referencing WDM intensity-based fiber-optic sensor operating in reflective configuration and using virtual instrumentation is presented. The use of virtual delay lines at the reception stage, along with novel flexible self-referencing techniques, and using a single frequency, avoids all-optical
[...] Read more.
In this work a radio-frequency self-referencing WDM intensity-based fiber-optic sensor operating in reflective configuration and using virtual instrumentation is presented. The use of virtual delay lines at the reception stage, along with novel flexible self-referencing techniques, and using a single frequency, avoids all-optical or electrical-based delay lines approaches. This solution preserves the self-referencing and performance characteristics of the proposed WDM-based optical sensing topology, and leads to a more compact solution with higher flexibility for the multiple interrogation of remote sensing points in a sensor network. Results are presented for a displacement sensor demonstrating the concept feasibility. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle Optical System Error Analysis and Calibration Method of High-Accuracy Star Trackers
Sensors 2013, 13(4), 4598-4623; doi:10.3390/s130404598
Received: 29 December 2012 / Revised: 27 March 2013 / Accepted: 3 April 2013 / Published: 8 April 2013
Cited by 22 | PDF Full-text (863 KB) | HTML Full-text | XML Full-text
Abstract
The star tracker is a high-accuracy attitude measurement device widely used in spacecraft. Its performance depends largely on the precision of the optical system parameters. Therefore, the analysis of the optical system parameter errors and a precise calibration model are crucial to the
[...] Read more.
The star tracker is a high-accuracy attitude measurement device widely used in spacecraft. Its performance depends largely on the precision of the optical system parameters. Therefore, the analysis of the optical system parameter errors and a precise calibration model are crucial to the accuracy of the star tracker. Research in this field is relatively lacking a systematic and universal analysis up to now. This paper proposes in detail an approach for the synthetic error analysis of the star tracker, without the complicated theoretical derivation. This approach can determine the error propagation relationship of the star tracker, and can build intuitively and systematically an error model. The analysis results can be used as a foundation and a guide for the optical design, calibration, and compensation of the star tracker. A calibration experiment is designed and conducted. Excellent calibration results are achieved based on the calibration model. To summarize, the error analysis approach and the calibration method are proved to be adequate and precise, and could provide an important guarantee for the design, manufacture, and measurement of high-accuracy star trackers. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available
Open AccessArticle Fabrication Quality Analysis of a Fiber Optic Refractive Index Sensor Created by CO2 Laser Machining
Sensors 2013, 13(4), 4067-4087; doi:10.3390/s130404067
Received: 28 December 2012 / Revised: 14 March 2013 / Accepted: 22 March 2013 / Published: 26 March 2013
Cited by 3 | PDF Full-text (721 KB) | HTML Full-text | XML Full-text
Abstract
This study investigates the CO2 laser-stripped partial cladding of silica-based optic fibers with a core diameter of 400 μm, which enables them to sense the refractive index of the surrounding environment. However, inappropriate treatments during the machining process can generate a number
[...] Read more.
This study investigates the CO2 laser-stripped partial cladding of silica-based optic fibers with a core diameter of 400 μm, which enables them to sense the refractive index of the surrounding environment. However, inappropriate treatments during the machining process can generate a number of defects in the optic fiber sensors. Therefore, the quality of optic fiber sensors fabricated using CO2 laser machining must be analyzed. The results show that analysis of the fiber core size after machining can provide preliminary defect detection, and qualitative analysis of the optical transmission defects can be used to identify imperfections that are difficult to observe through size analysis. To more precisely and quantitatively detect fabrication defects, we included a tensile test and numerical aperture measurements in this study. After a series of quality inspections, we proposed improvements to the existing CO2 laser machining parameters, namely, a vertical scanning pathway, 4 W of power, and a feed rate of 9.45 cm/s. Using these improved parameters, we created optical fiber sensors with a core diameter of approximately 400 μm, no obvious optical transmission defects, a numerical aperture of 0.52 ± 0.019, a 0.886 Weibull modulus, and a 1.186 Weibull-shaped parameter. Finally, we used the optical fiber sensor fabricated using the improved parameters to measure the refractive indices of various solutions. The results show that a refractive-index resolution of 1.8 × 10−4 RIU (linear fitting R2 = 0.954) was achieved for sucrose solutions with refractive indices ranging between 1.333 and 1.383. We also adopted the particle plasmon resonance sensing scheme using the fabricated optical fibers. The results provided additional information, specifically, a superior sensor resolution of 5.73 × 10−5 RIU, and greater linearity at R2 = 0.999. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available

Other

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Open AccessLetter An In-situ Real-Time Optical Fiber Sensor Based on Surface Plasmon Resonance for Monitoring the Growth of TiO2 Thin Films
Sensors 2013, 13(7), 9513-9521; doi:10.3390/s130709513
Received: 19 June 2013 / Revised: 12 July 2013 / Accepted: 18 July 2013 / Published: 23 July 2013
Cited by 4 | PDF Full-text (511 KB) | HTML Full-text | XML Full-text
Abstract
An optical fiber sensor based on surface plasmon resonance (SPR) is proposed for monitoring the thickness of deposited nano-thin films. A side-polished multimode SPR optical fiber sensor with an 850 nm-LD is used as the transducing element for real-time monitoring of the deposited
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An optical fiber sensor based on surface plasmon resonance (SPR) is proposed for monitoring the thickness of deposited nano-thin films. A side-polished multimode SPR optical fiber sensor with an 850 nm-LD is used as the transducing element for real-time monitoring of the deposited TiO2 thin films. The SPR optical fiber sensor was installed in the TiO2 sputtering system in order to measure the thickness of the deposited sample during TiO2 deposition. The SPR response declined in real-time in relation to the growth of the thickness of the TiO2 thin film. Our results show the same trend of the SPR response in real-time and in spectra taken before and after deposition. The SPR transmitted intensity changes by approximately 18.76% corresponding to 50 nm of deposited TiO2 thin film. We have shown that optical fiber sensors utilizing SPR have the potential for real-time monitoring of the SPR technology of nanometer film thickness. The compact size of the SPR fiber sensor enables it to be positioned inside the deposition chamber, and it could thus measure the film thickness directly in real-time. This technology also has potential application for monitoring the deposition of other materials. Moreover, in-situ real-time SPR optical fiber sensor technology is in inexpensive, disposable technique that has anti-interference properties, and the potential to enable on-line monitoring and monitoring of organic coatings. Full article
(This article belongs to the Special Issue Optomechatronics) Print Edition available

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