The pore water pressure sensor based on Sagnac interferometer with polarization-maintaining photonic crystal fiber for the geotechnical engineering

The pore water pressure sensors with the six-hole suspended-core polarization-maintaining photonic crystal fiber (SC-PM-PCF) and commercial polarization-maintaining photonic crystal fiber (PM-PCF) are designed based Sagnac interferometer and calibrated in the laboratory. According to the theoretical analysis and calibration results, the transmission spectrum is very sensitive to the pore water pressure. It is found that the wavelength of the spectrum has a good linear relationship with variances of the surrounding pore water pressure, and the coefficient of wavelength–pressure of the commercial PM-PCF is 304.41 kPa/nm with the length of 35 cm as the sensing element while the coefficient of the SC-PM-PCF is 254.75 kPa/nm with the length of 100 cm. Finally, the two PM-PCF sensors are applied and compared with the conventional Pore water Pressure Transducers (PPTs) in a physical model test. It is found that measurements of the PM-PCF sensors are in good agreement with the results measured by the conventional PPTs.     

Application of blue laser direct-writing equipment for manufacturing of periodic and aperiodic nanostructure patterns

This study presents the novel development of low cost, highly efficient blue laser direct-writing equipment for using mask-less laser lithography to manufacture periodic and aperiodic nanostructure patterns. The system includes a long-stroke linear motor precision stage (X, Y), a piezoelectric nano-precision stage (Y, θz), a 3-DOF (degrees of freedom) laser interferometer measurement system, and a blue laser direct-writing optical system. The 3-DOF laser interferometer measurement system gives the control system feedback for displacement (X, Y, θz) of the equipment. The laser processing equipment consists of a blue laser direct-writing optical head, a field-programmable gate array (FPGA) alignment interface, and an optical head servo controller. The optical head operates at a wavelength of 405 nm. Processing the nanostructures on thermo-reaction inorganic resists with precise control of the laser intensity, taking advantage of the threshold effect to exceed the limitations of optical diffraction, and reduces the nanostructure hole size. The equipment can be used to fabricate various periodic nanostructure patterns, aperiodic nanostructure patterns, and two-dimensional patterns. The equipment positioning accuracy is within 50 nm at a speed of 50 mm/s, and the minimum critical dimension can be achieved about 100 nm or so.     

Nano force sensing using symmetric double stage micro resonator

A new approach is proposed to improve a graphical approach with considering intensity coupling loss coefficients in the analytical derivation of the optical transfer functions for a symmetric double stage vertically coupled microring resonator. An optimum transmission coupling condition is determined with considering terms of couplers intensity loss which leads to low insertion loss of 1.2 dB, finesse of 1525, the out of band rejection ratio of 61.8 dB. The resonating system is used as an optical force sensing system to make the benefit of the accuracy of measurements in micro and nano scales. The sensitivity of proposed force sensor in terms of wavelength-shift is 33 nm/nN and the limit of detection is 1.6 × 10⁻² nN. The proposed sensing system has the advantages of self-calibration and the low power consumption due to the low intensity.     

Measurement of CFRP elastic modulus based on FBG reflectance spectrum analysis

Based on fiber Bragg grating (FBG) reflectance spectrum analysis, one novel method to measure the elastic modulus of carbon fiber reinforced plastics (CFRP) is proposed. Basic theory of the novel method is that CFRP uniform cantilever beam produces linear gradient strain which leads to FBG reflectance spectrum broadening under external loadings. Calculation model of the basic theory is put forward and validated by finite element method (FEM) simulation. In order to obtain actual data about the relationship between elastic modulus and FBG reflectance spectrum, experiment of CFRP uniform cantilever beam under external loadings is implemented. The experiment spectrum corresponding to external weight 20 g is chosen as the specimen to explain data processing procedure by self-adaptive method. 3 dB bandwidth and center wavelength of FBG are selected as the reference indexes in the procedure. Elastic modulus of CFRP which is used in the experiment is extracted and its value is 6.617 GPa. To validate the correctness of the elastic modulus, contrastive analyses between transmission matrix theory calculation and experiment spectrums with external weights 5 g and 10 g are also carried out. Absolute errors of 3 dB bandwidth and center wavelength in the comparison are all less than 5 pm which prove the feasibility and correctness of this novel elastic modulus measurement method.     

Subpixel edge location method proposed to improve the performance of optical fiber spherical coupling probe during dimensional measurement of micro-cavities with high aspect ratio

A subpixel edge location method based on orthogonal Jacobi–Fourier moments is proposed in this paper to improve the performance of optical fiber spherical coupling probe during dimensional measurement of micro-cavities with high aspect ratio. The effectiveness of the proposed method is proved through the performance test of a micro-hole measuring machine with optical spherical coupling probe. Test results indicate that a blind micro-hole of 400 μm in diameter can be experimentally measured at the depth of 2000 μm with a repeatability of 40 nm and an extremity resolution of 42 nm.     

Simultaneous interferometric measurement of the absolute thickness and surface shape of a transparent plate using wavelength tuning Fourier analysis and phase shifting

The absolute optical thickness and surface shape of optical devices are considered as the fundamental characteristics when designing optical equipment. The thickness and surface shape should be measured simultaneously to reduce cost. In this research, the absolute optical thickness and surface shape of a 6–mm-thick fused silica transparent plate of diameter 100 mm was measured simultaneously by a three-surface Fizeau interferometer. A measurement method combining the wavelength tuning Fourier and phase shifting technique was proposed. The absolute optical thickness that corresponds to the group refractive index was determined by wavelength tuning Fourier analysis. At the beginning and end of the wavelength tuning, the fractional phases of the interference fringes were measured by the phase shifting technique and optical thickness deviations with respect to the ordinary refractive index and surface shape were determined. These two kinds of optical thicknesses were synthesized using the Sellmeier equation for the refractive index of fused silica glass, and the least square fitting method was used to determine the final absolute optical thickness distribution. The experimental results indicate that the all the measurement uncertainties for the absolute optical thickness and surface shape were approximately 3 nm and 35 nm, respectively.     

Verification of the positioning accuracy of industrial coordinate measuring machine using optical-comb pulsed interferometer with a rough metal ball target

An optical-comb pulsed interferometer was developed for the positioning measurements of the industrial coordinate measuring machine (CMM); a rough metal ball was used as the target of the single-mode optical fiber interferometer. The measurement system is connected through a single-mode fiber more than 100 m long. It is used to connect a laser source from the 10th floor of a building to the proposed measuring system inside a CMM room in the basement of the building. The repetition frequency of a general optical comb is transferred to 1 GHz by an optical fiber-type Fabry–Pérot etalon. Then, a compact absolute position-measuring system is realized for practical non-contact use with a high accuracy of measurement. The measurement uncertainty is approximately 0.6 μm with a confidence level of 95%.     

Plasmonic effect of silver nanoparticles on the upconversion emissions of Sm3+-doped sodium-borosilicate glass

The effect of the localized surface plasmon resonance (SPR) on optical absorption and photoluminescence of Sm³⁺-doped sodium borosilicate glass containing reduced silver nanoparticles (NPs) is reported (Ag⁺ → Ag⁰). The interaction of ultraviolet light by metallic NPs and its effect on the optical properties of samarium in proposed glass were investigated by absorption and photoluminescence spectra analysis. The existence of the NPs was pursued by transmission electron microscopy technique, revealing the existence of Ag NPs with average size of ∼8–14 nm. The largest enhancement was achieved for emission at 561 nm. Such improvements were attributed and discussed by enhanced electric field around metallic NPs and energy transfer (ET) between Sm³⁺ ions and silver NPs.     

Surface roughness measurement based on fiber optic sensor

The multi-wavelength fiber sensor for measuring surface roughness and surface scattering characteristics were investigated. In this paper, specimens with different surface roughness were analyzed by using 650 nm, 1310 nm and 1550 nm laser as the light source, respectively. The working distance of 2 mm was chosen as the optimum measurement distance. The experimental results indicate that multi-wavelength fiber sensor can accurately measure surface roughness, and can effectively reduce the unsystematic error. The light scattering intensity ratio has a good linear relationship with the surface roughness. The minimum relative error of the surface roughness is 2.92%, the maximum relative error is 13.4%, and the average relative error is about 7.48%. The accuracy for measuring surface roughness by multi-wavelength fiber sensor is about twice as large as that by single-wavelength fiber sensor.     

Optical fiber distributed temperature sensor using short term Fourier transform based simplified signal processing of Raman signals

A simplified technique using short term Fourier transform to reduce the errors in distributed temperature measurement with a Raman scattering based optical fiber sensor system is presented. The two main sources of errors are differential attenuation to anti-Stokes and Stokes signal by fiber and local change in Stokes due to change in temperature. The proposed technique compensates these errors and extracts correct temperature profile in spite of practical difficulties encountered in applying the theoretical concept. Moreover proposed technique is less complex, self-reliant, can tolerate variation in laser power, requires less dead zone and suits automation using embedded solution. Results of measurement carried out, using the system developed at RRCAT, Indore, for two hot zones having spatial width of 1.9 m (kept at 56 °C) and 1.5 m (kept at 78 °C), located at 47 m and 85 m respectively, show that these parameters can be recovered with significantly small errors.     

AC conduction mechanism and battery discharge characteristics of (PVC/PEO) polyblend films complexed with potassium chloride

New K⁺ ion-conducting polymer blend electrolyte films based on amorphous polymer poly(vinyl chloride) (PVC) and semicrystalline polymer poly(ethylene oxide) (PEO) complexed with KCl salt were prepared using a solution-cast technique. The maximum value of ionic conductivity of a PVC/PEO:KCl (42.5:42.5:15) system is 8.29 × 10⁻⁶ S/cm at 303 K. The absorption edge was found at 4.30 eV for undoped film, while it was observed at 4.03 and 3.93 eV for 10 and 15 wt% KCl doped films, respectively. The direct band gaps for these pure and salt doped PVC/PEO films were found to 4.10, 3.86 and 3.74 eV, respectively, whereas the indirect band gaps were determined as 4.15, 3.72 and 3.64 eV. Transference number values showed that the charge transport in this electrolyte system is predominantly due to ions (t_ion = 0.97). The discharge capacity for PVC/PEO:KCl (42.5:42.5:15) polymer blend electrolyte system is 11 μA/h.     

Cost effective refractive index sensor based on optical fiber micro cavities produced by the catastrophic fuse effect

We propose a refractive index optical fiber sensor based on the micro cavities generated through the fiber catastrophic fuse effect. This sensor was tested in the measurement of solutions with refractive indices ranging from 1.3320 to 1.4280. The linear dependence of the reflection spectra modulation period as function of the surrounding environment refractive index leads to a resolution of 3 × 10⁻⁴ RIU. The proposed sensor is an innovative solution based on optical fiber damaged by the fuse effect, resulting in a cost effective solution.     

Simultaneous distributed measurement of the strain and temperature for a four-point bending test using polarization-maintaining fiber Bragg grating interrogated by optical frequency domain reflectometry

We demonstrate a simultaneous distributed strain and temperature measurement technique with the spatial resolution of 1 mm using fiber Bragg gratings inscribed in a polarization-maintaining and absorption-reducing fiber (PANDA-FBGs) and optical frequency domain reflectometry (OFDR). We conduct four-point bending tests in an environmental chamber. Using high birefringent PANDA-FBGs that are manufactured specifically for the simultaneous measurements, the uniform temperature distributions and the typical strain distribution profiles of the four-point bending tests were successfully obtained. The measurement errors of strain were from −31 με to 19 με, and of temperature were from −0.9 °C to 1.3 °C. The spatial standard deviation was 7.5 με and 0.9 °C. We also discussed the effect of the residual strain of the sensor-bonding procedures and the data averaging.     

Influence of photoelectric stimulation with different spectrum on sliding friction behaviors of locust Oedaleus infernalis Saussure (Orthoptera: Acrididae) on slippery plates

To optimize the method of photoelectric inducement trapping used in swarm locust control, influence of photoelectric stimulation with different spectrums was investigated through sliding test of locusts on PVC plastic plate and zinc plate, and rubbing behaviors of locusts on these plates were observed by means of CCD video monitoring system. Both distinctive slippery ratio and considerable sliding behaviors are exhibited when the peak wavelength of photoelectric stimulation is 460 nm without consideration of slippery plates. Presumably, photoelectric stimulation with such peak wavelength can inspire bio-photoelectric effect of locust much more strongly, and enhance moving activity of locust more effectively, which of it can cause obvious reduction of contact area between locust and slippery plate. Photoelectric stimulation with the spectrum of 460 nm presumably can disturb the forming of mechanical interlock and decrease the adhesive force more obviously. Therefore, friction effect is weakened evidently and much more obvious sliding behaviors are presented. The result supplies a suitable theoretical foundation for the design of photoelectric stimulation sources used in slippery trapping plates to control swarm locusts and other agriculture pests.     

Digital filtering methodology used to reduce scale of measurement effects in roughness parameters for magnetic storage supersmooth hard disks

Roughness of disk media influences the tribological interaction of head-disk interfaces, especially when the intended flying-height is below 5 nm that is required to achieve extremely high-density recording (EHDR). Roughness parameters such as the root-mean-square (RMS) amplitude, however, are influenced by the scale of measurement, such as the scan size. Effects related to scale of measurement such as varying the scan size were investigated and means to reduce such effects were proposed by establishing an “ad hoc” digital filtering procedure. Two types of magnetic disks intended for EHDR were measured by an atomic force microscope (AFM) at various scan dimensions ranging from 0.5 μm × 0.5 μm to 112 μm × 112 μm. The proposed filtering method used the RMS values as a filter design parameter for choosing the appropriate high-pass cutoff wavelength for each scan size. The study revealed the existence of a unique cutoff wavelength that would identify different wavelength regimes and the associated critical scan size in each disk. To substantiate the effectiveness of the proposed filtering method in reducing the scale of measurement effects related to the scan size, other roughness parameters were also calculated subsequent to the filtering procedure. It was found that the proposed filtering scheme effectively reduced the scale of measurement effects in the amplitude parameters (e.g., RMS and the ten-point height variation) and the functional parameters (e.g., material and core void volumes). These parameters exhibited steady-state trends with respect to increasing scan size, indicating reduced scale of measurement effects.     

Diagonal in space of coordinate measuring machine verification using an optical-comb pulsed interferometer with a ball-lens target

This paper presents a new optical method of coordinate measuring machine (CMM) verification. The proposed system based on a single-mode fiber optical-comb pulsed interferometer with a ball lens of refractive index 2 employed as the target. The target can be used for absolute-length measurements in all directions. The laser source is an optical frequency comb, whose repetition rate is stabilized by a rubidium frequency standard. The measurement range is confirmed to be up to 10 m. The diagonals of a CMM are easier to verify by the proposed method than by the conventional artifact test method. The measurement uncertainty of the proposed method is also smaller than that of the conventional method because the proposed measurement system is less affected by air temperature; it achieves an uncertainty of approximately 7 μm for measuring lengths of 10 m. The experimental results show that the measurement accuracy depends on noise in the interference fringe, which arises from airflow fluctuations and mechanical vibrations.     

Gasoline level sensor based on displacement sensor using fiber coupler

A simple and fire safe gasoline level sensor has been designed based on displacement sensor using fiber coupler. The sensing principle is to detect displacement of reflector, which is attached to membrane (reflector displacement device), due to the change of gasoline hydrostatic pressure. The displacement of reflector can be detected using fiber coupler from the change of optical power light reflected by the reflector. Three kinds of reflector displacement device used in this experiment are one-layer, two-layer, and three-layer membrane. The experimental results are 0–180 cm of dynamic range, 100–140 cm of linear range, 3.2 mV/cm of sensitivity, and 0.6 cm of resolution for reflector displacement device with one-layer membrane for emptying the tank process. The hysteresis data for emptying and filling the tank process yields the mean of difference 20% for one-layer membrane.     

Design and characterization of a real-time,wearable, endosomatic electrodermal system

This paper presents the design and characterization of a compact wearable system for long-term assessment of skin potential response, with the aim of monitoring mental stress in a variety of applications. Literature reports that the expected skin potential has peak-to-peak amplitudes of few millivolts in the frequency band [0.1, 10] Hz. The designed system is characterized by a slightly wider bandwidth of [0.08, 40] Hz, and it is based on a 12-bit ADC working with a sampling rate of 200 Sa/s, which can be increased up to 3.5 kSa/s. Data can be continuously acquired for up to 40 h with a battery of 3.7 V/1800 mAh. A Graphical User Interface was also developed for the host computer in .NET framework. The system, to our knowledge the first example of wearable endosomatic electrodermal activity sensor, joins to several skin conductance wearable measuring systems recently proposed in literature, and opens up opportunities for future comparisons of endosomatic and exosomatic responses in real life.The device is thoroughly characterized in accordance with the state-of-the-art of the metrological research in the field.     

Application of two-output port fiber coupler as gasoline level sensor

Detection of gasoline level can be done in a safe and simple way using two output port multimode fiber coupler with a structure of 2 × 2 as a sensor. Two output ports (sensing port) are connected with two reflector displacement device (RDD) and functioned as two probes. These probes are placed on the wall of gasoline tank in a storied and work interchangeably or together depending on setting of these probes. Detection mechanism of the system is based on changes in intensity of reflected light from the reflector RDD that shifts due to changes in level of gasoline (hydrostatic pressure principle). Changes in intensity of light coming into the sensing port are then forwarded to the optical detector. Experiments performed by varying the location of the second probe as 45 cm, 50 cm, and 55 cm above the first probe to detect the level of gasoline in the process of filling and emptying the tank. Experimental results show the process of filling and emptying the tank have small differences of 6% with the dynamic range, the linear region, and resolution are 100 cm, 70 cm, and 0.4 cm respectively. Sensor sensitivity in filling and emptying process of the tank are 2.7 mV/cm and 2.8 mV/cm respectively. These results were the best performance of the sensor, which occurs when the level of the second probe was 55 cm above the first probe.     

Non-contact measurement technique for dimensional metrology using optical comb

This paper proposes a non-contact pulsed interferometer for dimensional metrology using the repetition frequency of an optical frequency comb. A compact absolute-length measuring system is established for practical non-contact measurement based on a single-mode fiber interferometer. The stability and accuracy of the measurements are compared with those from a commercial incremental laser interferometer. The drifts of both systems have the same tendency and a maximum difference is approximately 0.1 μm. Subsequently, preliminary absolute-length measurements up to 1.5 m were measured. The signal-to-noise ratios of the small signals are improved by a frequency-selective amplifier. It is apparent that the noise is rejected, and the intensity of the interference fringes is amplified, achieving a maximum standard deviation of measurement approximately 1 μm. The proposed technique can provide sufficient accuracy for non-contact measurement in applications such as a simple laser-pulse tracking system.