Fiber curvature sensor based on spherical-shape structures and long-period grating

A novel curvature sensor based on optical fiber Mach–Zehnder interferometer (MZI) is demonstrated. It consists of two spherical-shape structures and a long-period grating (LPG) in between. The experimental results show that the shift of the dip wavelength is almost linearly proportional to the change of curvature, and the curvature sensitivity are −22.144 nm/m⁻¹ in the measurement range of 5.33–6.93 m⁻¹, −28.225 nm/m⁻¹ in the range of 6.93–8.43 m⁻ and −15.68 nm/m⁻¹ in the range of 8.43–9.43 m⁻¹, respectively. And the maximum curvature error caused by temperature is only −0.003 m⁻¹/°C. The sensor exhibits the advantages of all-fiber structure, high mechanical strength, high curvature sensitivity and large measurement scales.     

Temperature self-compensation fiber-optic pressure sensor based on fiber Bragg grating and Fabry–Perot interference multiplexing

A high performance multiplexed fiber-optic sensor consisted of diaphragm-based extrinsic Fabry–Perot interferometer (DEFPI) and fiber Bragg grating (FBG) is proposed. The novel structure DEFPI fabricated with laser heating fusion technique possesses high sensitivity with 5.35 nm/kPa (36.89 nm/psi) and exhibits ultra-low temperature dependence with 0.015 nm/°C. But the ultra-low temperature dependence still results in small pressure measurement error of the DEFPI (0.0028 kPa/°C). The designed stainless epoxy-free packaging structure guarantees the FBG to be only sensitive to temperature. The temperature information is created to calibrate the DEFPI's pressure measurement error induced by the temperature dependence, realizing effectively temperature self-compensation of the multiplexed sensor. The sensitivity of the FBG is 10.5 pm/°C. In addition, the multiplexed sensor is also very easy to realize the pressure and the temperature high-precise high-sensitive simultaneous measurement at single point in many harsh environmental areas.     

I–V characteristics of a methanol concentration sensor for direct methanol fuel cell (DMFC) by using catalyst electrode of Pt dots

In this work, the methanol sensors were fabricated by using Pt dot catalyst electrode and the level of electrochemical response was analyzed. This kind of sensors can be applicable to sensing the methanol concentration in real-time. When we measured the methanol sensor with 5 nm of Pt dot, we could get 2.00 × 10⁻⁶, 3.06 × 10⁻⁶ and 6.25 × 10⁻⁶ A of electric current value for the methanol concentration of 1, 2 and 3 mole, respectively. The measured voltage was 1 V. To optimize the sensitivity level of Pt dot catalyst electrode, the electrodes were made in H-grid shape. The distance between electrode branches was designed to be 80, 150 and 300 μm, respectively. When we measured the electric current–voltage characteristics of methanol sensor with 2 M of methanol, it was 3.06 × 10⁻⁶, 2.02 × 10⁻⁶ and 1.50 × 10⁻⁶ A, for 80, 150 and 200 μm, respectively. Thus it is suggested that more efficient response of methanol sensing is possible when the distance between electrodes is reduced.     

Device linearity improvement and current enhancement utilizing high-to-low doping-channel FETs

We report device linearity improvement and current enhancement in both a heterostructure FET (HFET) and a camel-gate FET (CAMFET) using InGaAs/GaAs high-low and GaAs high-medium-low doped channels, respectively. In an HFET, a low doped GaAs layer was employed to build an excellent Schottky contact. In a GaAs CAMFET, a low doped layer together withn⁺andp⁺layers formed a high-performance majority camel-diode gate. Both exhibit high effective potential barriers of >1.0 V and gate-to-drain breakdown voltages of >20.0 V (atI_g=1.0 mA mm⁻¹). A thin, high doped channel was used to enhance current drivability and to improve the transconductance linearity. A 2×100 μm²HFET had a peak transconductance of 230 mS mm⁻¹and a current density greater than 800 mA mm⁻¹. The device had a transconductance of more than 80 percent of the peak value over a wide drain current range of 200 to 800 mA mm⁻¹. A 1.5×100 μm²CAMFET had a peak transconductance of 220 mS mm⁻¹and a current density greater than 800 mA mm⁻¹. Similarly, the device had a transconductance of more than 80 percent of the peak value over a wide drain current range of 160 to 800 mA mm⁻¹. The improvement of device linearity and the enhancement of current density suggest that high-to-low doped-channel devices for both an HFET and a CAMFET are suitable for high-power large signal circuit applications.     

Novel bending sensor based on a meniscus shaped beam with LPG

A novel bending sensor based on a long period fiber grating (LPG) is presented. A LPG was glued into a V-shaped groove, which lies on the lower surface of a meniscus shaped beam. It is found that the transmission optical power of the LPG changed linearly with the variation of the bending of the beam. The bending applied on the beam can be measured by detecting the intensity variation of the LPG's resonant dip wavelength. Under a relative large bending measured range from 0 to 7.5 m^?1, the sensitivity of 3.003 dB m^?1 and curvature resolution of 0.001 m^?1 have been achieved for the proposed bending sensor.     

Micro-force measurement of drag on a small flat plate in the presence of a corona discharge

The design of a micro-force sensor suitable for the measurement of corona drag and other low velocity drag studies in a small laboratory wind tunnel facility is described. Example drag data are given for dc corona discharge generated by sharp parallel electrodes mounted on a microscope glass slide with discharge parallel to the air flow. The arrangement simulates two-dimensional flow over a flat plate useful for theoretical analysis. Measurements of free stream wind velocities in the range 0–210 cm/s with attendant drag down to 10⁻⁷ N can be detected in this facility depending on the calibration. The force sensor utilizes two strain gages mounted on a 0.127 mm stainless steel “feeler gage” in a cantilever arrangement. A bridge circuit provides sensitivities in the range 40–250 N/mV using a gravitational calibration technique. Anomalous effects from suspension wires and the interaction of electrostatic forces with the surroundings are discussed.     

A study of cross-gas-flow to stabilize an atmospheric pressure glow plasma in a multi-pin-to-multi-cupped-plane negative corona discharge

In a multi-pin-to-multi-cupped-plane DC negative corona discharge configuration, a stable and diffuse glow discharge controlled by a fast airflow was obtained. This paper investigates the effect of the air gas flow velocity and the electrode structure on the discharge mode transition and the stabilization of the glow discharge by means of electric measurements and emission records. The stabilization mechanism of the glow discharge is discussed. The maximum glow discharge current reached 3.9 mA and the average current density was about 0.7 mA/cm².     

Design and experiment of spectrometer based on scanning micro-grating integrating with angle sensor

A compact, low cost, high speed, non-destructive testing NIR (near infrared) spectrometer optical system based on MOEMS grating device is developed. The MOEMS grating works as the prismatic element and wavelength scanning element in our optical system. The MOEMS grating enables the design of compact grating spectrometers capable of acquiring full spectra using a single detector element. This MOEMS grating is driven by electromagnetic force and integrated with angle sensor which used to monitored deflection angle while the grating working. Comparing with the traditional spectral system, there is a new structure with a single detector and worked at high frequency. With the characteristics of MOEMS grating, the structure of the spectrometer system is proposed. After calculating the parameters of the optical path, ZEMAX optical software is used to simulate the system. According the ZEMAX output file of the 3D model, the prototype is designed by SolidWorks rapidly, fabricated. Designed for a wavelength range between 800 nm and 1500 nm, the spectrometer optical system features a spectral resolution of 16 nm with the volume of 97 mm × 81.7 mm × 81 mm. For the purpose of reduce modulated effect of sinusoidal rotation, spectral intensity of the different wavelength should be compensated by software method in the further. The system satisfies the demand of NIR micro-spectrometer with a single detector.     

Non-incremental interferometric displacement measurement using a laser Doppler sensor with phase coding

The inspection of fast rotating objects with rough surfaces is an important task in the emerging field of process control. However, this is challenging since fast and non-contact inspection techniques with a measurement uncertainty in the nanometer range are often required. We present a novel optical sensor allowing non-incremental interferometric displacement measurement of moving solid state objects with rough surfaces. It features three wavelength coded interference fringe systems which are superposed slightly tilted. The displacement is determined by evaluating the phase shift between the resulting scattered light signals. Experimentally, a measurement uncertainty of 660 nm was obtained. This displacement uncertainty is independent of the lateral object velocity in principle. Due to this unique feature, the sensor can be utilized advantageously for precise displacement and vibration measurements of high speed objects as demonstrated by vibration measurements at a turbo pump shaft rotating with 48 000 rpm.     

A mid-infrared carbon monoxide sensor system using wideband absorption spectroscopy and a single-reflection spherical optical chamber

A mid-infrared carbon monoxide (CO) sensor system based on a dual-channel differential detection method was developed using a broadband light source in the 4.60 µm wavelength region and a single-reflection spherical optical chamber with ∼0.373 m absorption path length. CO detection was realized by targeting the wideband strong absorption lines within 4.55–4.65 µm. A dual-channel pyroelectric detector as well as a self-developed digital signal processor (DSP) based orthogonal lock-in amplifier was employed to process CO sensing signal. A minimum detection limit of ∼0.5 ppm in volume (ppmv) was achieved with a measurement time of 6 s, based on an Allan deviation analysis of the sensor system. The response time (1000 → 0 ppmv) was determined to be ∼7 s for the CO sensor operation. Due to the characteristics of low detection limit, fast response time and high cost performance, the proposed sensor has relatively good prospect in coal-mining operation.     

Fiber sensor based on Lophine sensitive layer for nitrate detection in drinking water

A new characterization of Lophine as a sensitive layer to measure Nitrate in drinking water is presented in this paper. The characterization was performed with a standard slide and a standard multimode fiber coated with a Lophine sensitive layer (2,4,5-Triphenylimidazol (C₂₁H₁₆N₂)). Spectral characterization has been conducted in the wavelength range from 300 to 1100 nm. We have demonstrated that Lophine can be used as a fiber sensor for the detection of Nitrate in drinking water. The sensing properties of the fiber sensor were analyzed at room temperature. Successful results were achieved when sensing Nitrate in the range between 1 mg/l and 70 mg/l. The response time was 20 ms and the recovery time was 40 ms.     

Second-harmonic laser-coupled optical fiber sensor for pH measurement and corrosion detection based on evanescent field absorption

In the present paper, a laser-coupled optical fiber is introduced for pH sensing of Methyl red solution in the Ethanol solvent. Then it is modified for corrosion detection when it was placed inside a corrosive solution. Second-harmonic (SH) radiation of a microchip Q-switched pulsed Nd:YAG laser operating at λ=532 nm is generated via KTP nonlinear crystal, and it is launched into the fabricated fiber sensor. The provided evanescent field is absorbed by the surrounding environment in the sensing region, and the output intensity of the absorbed laser beam is monitored and recorded in the presence of the different kind of solvents and corrosive solutions. To increase the sensitivity of the pH sensor the fiber-optic probe is coiled and fixed on a Poly Propylene (PP) mount with 6 cm diameter and 10 cm long. The fabricated sensor is then calibrated for pH measurement of unknown media. For corrosion detection, a spin motor is used to uniformly coat a small portion of the fiber designed as U-shaped after its clad was removed by a simple chemical method. It is then electroplated by a very thin Fe–C film to form a corrosion sensor. It is observed that while the concentration of the NH₄Cl solution is changed from 0.068 to 0.125 mol/l and its pH from zero to 14, the output intensity of the launched laser is increased due to the Fe–C film corrosion.     

Detection of influenza A virus using carbon nanotubes field effect transistor based DNA sensor

The carbon nanotubes field effect transistor (CNTFET) based DNA sensor was developed, in this paper, for detection of influenza A virus DNA. Number of factors that influence the output signal and analytical results were investigated. The initial probe DNA, decides the available DNA strands on CNTs, was 10 µM. The hybridization time for defined single helix was 120 min. The hybridization temperature was set at 30 °C to get a net change in drain current of the DNA sensor without altering properties of any biological compounds. The response time of the DNA sensor was less than one minute with a high reproducibility. In addition, the DNA sensor has a wide linear detection range from 1 pM to 10 nM, and a very low detection limit of 1 pM. Finally, after 7-month storage in 7.4 pH buffer, the output signal of DNA sensor recovered 97%.     

Noncontact characterization of glucose by a waveguide microwave probe

We investigate the electromagnetic field interaction with a glucose aqueous solution using a microwave dielectric waveguide probe to evaluate the glucose concentrations. A microwave dielectric waveguide probe allows observation of the small variation of the glucose concentration changes in the range of 0–300 mg/ml by measuring the change of the microwave reflection coefficient. We could observe the effect of concentration change of glucose with a detectable resolution up to 0.5 mg/ml at an operating frequency of about f = 2.0–2.5 GHz. The change of the glucose concentration is directly related to the change of the reflection coefficient due to the electromagnetic interaction between the dielectric waveguide resonator and the glucose aqueous solution. The operational principal is explained by a plane-wave solution model. A glucose biosensor using a microwave dielectric waveguide probe provides a unique approach for glucose monitoring.     

Influence of injection current and temperature on electroluminescence in InGaN/GaN multiple quantum wells

Electroluminescence (EL) spectra of blue InGaN/GaN multiple-quantum-well light-emitting diode (LED) have been investigated over a wide range of injection current (0.001–200 mA) and at various temperatures (6–300 K). Surprisingly, with increasing the injection current the EL peak energy shows an initial blueshift accompanied by a broadening of the EL linewidth at low temperatures (below 30 K). This trend differs from the usual photoluminescence (PL) measurement results, which have shown that with increasing the optical excitation power the PL peak energy gave an initial blueshift accompanied by a narrowing of the PL linewidth at low temperatures. The anomalous current behavior of the EL spectra may be attributed to electron leakage results in the failure of Coulomb screening effect and the relative enhancement of the low-energetic localized state filling at low temperatures and low currents. The electron leakage for the LED is further confirmed by both the current dependence of the EL intensity and the temperature dependence of the EL efficiency.     

An energy-efficient tie-type architecture for stable and wavelength-tunable SOA-based fiber laser

A new and energy-efficient tie-type architecture for stable and wavelength-tunable semiconductor optical amplifier (SOA)-based fiber ring laser is proposed and experimentally investigated. Here, the tie-type laser configuration is constructed by two Sagnac fiber loops. The proposed laser also can extend the lasing wavelength to longer wavelength (L-band) even only the C-band SOA is used. The proposed tie-type architecture has >5 dB higher output optical power at bias current of 80 mA when compared with the single ring SOA-based fiber laser. In this measurement, the output power, wavelength tuning range, side-mode suppression ratio (SMSR) and output stability of proposed fiber laser have also been analyzed and discussed.     

Spectroscopic ellipsometry measurements on an anisotropic crystal: 6H-SiC

In spectroscopic ellipsometry (SE) measurement, accuracy of optic axis orientation is very important requirement. To reduce the error arising from the uncertainty in optic axis orientation, we applied multiple angles SE measurement performed on 6H-SiC with the optical axis perpendicular to the sample (0 0 0 1) surface in the 300–800 nm wavelength range at room temperature. The refractive indices and extinction coefficients for ordinary and extraordinary were both fitted by Cauchy dispersion model. The obtained results were of great agreement with literatures.     

A handheld mid-infrared methane sensor using a dual-step differential method for additive/multiplicative noise suppression

A miniature mid-infrared (mid-IR) methane (CH₄) sensor system was developed by employing a wide-band wire-source and a semi-ellipsoid multi-pass gas cell. A dual-step differential method instead of the traditional one-step differential method was adopted by this sensor to tune measuring range/zero point and to suppress the additive/multiplicative noise. This method included a first subtraction operation between the two output signals (including a detection signal and a reference signal) from the dual-channel detector and a second subtraction operation on the amplitudes of the first-subtraction signal and the reference signal, followed by a ratio operation between the amplitude of the second-subtraction signal and the reference signal. Detailed experiments were performed to assess the performance of the sensor system. The detection range is 0–50 k ppm, and as the concentration gets larger than 12 k ppm, the relative detection error falls into the range of −3% to +3%. The Allan deviation is about 4.65 ppm with an averaging time of 1 s, and such value can be further improved to 0.45 ppm with an averaging time of 124 s. Due to the cost-effective incandescence wire-source, the small-size ellipsoid multi-pass gas cell and the miniature structure of the sensor, the developed standalone device shows potential applications of CH₄ detection under coal-mine environment.     

Hydrostatic pressure sensor based on a gold-coated thin-core fiber modal interferometer and ripple shift measurement

We propose a hydrostatic pressure sensor based on a gold-coated thin-core fiber modal interferometer (TCFMI). A thin-core fiber is spliced to a single mode fiber forming a single-end fiber modal interferometer (FMI) due to the core mismatch and the fiber end reflection. Relative reflection spectra of TCFMIs based on thin-core fibers with different lengths are investigated. The TCFMI is gold-coated to enhance the optical reflectivity, which also results in the ripple of the relative reflection spectra of TCFMI. A high hydrostatic pressure sensor test system is proposed and the performance of the pressure sensor has been experimentally investigated. A pure-ripple-shift measurement method is used to achieve the demodulation of the sensor. The proposed pressure sensor has a sensing range up to 40 MPa and a sensitivity of 44.8 pm/MPa.     

Development of a liquid stub tuner for the KSTAR ICRF system

A liquid stub tuner was developed to transmit a MW level of RF power continuously in the KSTAR (Korean Superconducting Tokamak Advanced Research) ICRF (ion cyclotron range of frequencies) heating and current drive systems. It is made of a 9–3/16″ coaxial transmission line, and the property of the RF wavelength difference in a liquid and in a gas due to their different dielectric constants is utilized. Silicon oil with a relative dielectric constant of 2.74 was used as the liquid, because of its low vapor pressure and low dielectric loss. The liquid stub tuner components were equipped with electrostatic probes, thermocouples, and a humidity sensor to measure the RF voltages, the liquid temperature, and the humidity in the coaxial transmission line, respectively. The level of the liquid for the liquid stub tuner can be changed from 0 to 2.8 m, which corresponds to 2.0 m mechanical length variation at 30 MHz. The RF power test of the liquid stub tuner was performed with various conditioned silicon oils at 30 MHz to compare the high voltage characteristics among various conditioned silicon oils. The stand-off voltage of 43.82 kV (average) was achieved for the liquid stub tuner during the 300 s operation.