[Fiber Humidity Sensor Based on Fiber Bragg Grating Sandwiched in SMS Fiber Structure].

A fiber humidity sensor based on Fiber-Bragg Grating (FBG) sandwiched in single-mode-multimode fiber core-single mode (SMS) fiber structure is proposed and demonstrated. When the surrounding humidity changes, the central wavelength of FBG remains unchanged for it is insensitive to humidity, while the interference spectrum of SMS fiber structure will shift for it is sensitive to the surrounding humidity. Hence, the shift of the SMS fiber structure interference spectrum with humidity could modulate the FBG core mode. Through measuring the reflected power of the FBG core mode the detection of humidity can be realized. The beam propagation of the SMS fiber structure with different lengths of multimode fiber core (MMFC), diameters of MMFC, and surrounding refractive indices are theoretically simulated with beam propagation method. Theoretical simulation indicates that the output core mode power coefficients shift with surrounding humidity of the SMS fiber structure. Experimental results show that the sensor has a linear response to humidity with enhanced sensitivity of 0.06 dBm·(%RH)-1 in the humidity range of 45%~95%RH with length of 35 mm and diameter of 85 µm. The temperature effect of the sensor is also discussed, the temperature sensitivity is 0.008 nm·â„ƒ-1 in the temperature range of 20~80 ℃ and the measurement error of temperature is 0.047% RH·â„ƒ-1. Such cost-effective, high sensitive, and reflective power detection based optical fiber humidity sensor could be used in humidity sensing applications.

Theoretical and experimental study of structural slow light in a microfiber coil resonator.

In this paper, a compact slow-light microfiber coil resonator (MCR) is fabricated and the slow-light properties of it are analyzed and tested. Based on coupled-wave theory, a theoretical model for describing the slow-light propagation in the MCR is established. Experimentally, the MCR slow-light element is fabricated and its relative slow-light time delay is measured. The group velocity of the light pulse in the MCR slow-light element can be reduced to about 0.47c (c is the speed of light in vacuum) and the shape of the light pulse passing through the MCR is well preserved.

Divalent cations and molecular crowding buffers stabilize G-triplex at physiologically relevant temperatures.

G-triplexes are non-canonical DNA structures formed by G-rich sequences with three G-tracts. Putative G-triplex-forming sequences are expected to be more prevalent than putative G-quadruplex-forming sequences. However, the research on G-triplexes is rare. In this work, the effects of molecular crowding and several physiologically important metal ions on the formation and stability of G-triplexes were examined using a combination of circular dichroism, thermodynamics, optical tweezers and calorimetry techniques. We determined that molecular crowding conditions and cations, such as Na(+), K(+), Mg(2+) and Ca(2+), promote the formation of G-triplexes and stabilize these structures. Of these four metal cations, Ca(2+) has the strongest stabilizing effect, followed by K(+), Mg(2+), and Na(+) in a decreasing order. The binding of K(+) to G-triplexes is accompanied by exothermic heats, and the binding of Ca(2+) with G-triplexes is characterized by endothermic heats. G-triplexes formed from two G-triad layers are not stable at physiological temperatures; however, G-triplexes formed from three G-triads exhibit melting temperatures higher than 37°C, especially under the molecular crowding conditions and in the presence of K(+) or Ca(2+). These observations imply that stable G-triplexes may be formed under physiological conditions.

Photoluminescent sensing for acidic amino acids based on the disruption of graphene quantum dots/europium ions aggregates.

A simple mix-and-detect photoluminescence method was developed for the turn-on detection of acidic amino acids. To achieve this, graphene quantum dots (GQDs), which emit both down-conversion and up-conversion photoluminescence were prepared by solvothermal synthesis. The carboxylic acid-rich surface not only increases the water solubility of the prepared GQDs, but also makes Eu(3+)-triggered GQDs aggregation possible, thus causing the photoluminescence quenching of GQDs. The quenched photoluminescence can be recovered by the competition between acidic amino acids and GQDs for Eu(3+). Under optimized conditions, sensitive and specific acidic amino acids quantitation can be achieved by utilizing the changes in either down-conversion or up-conversion photoluminescence. Up-conversion mode gives a little lower detection limit than the down-conversion one. Nearly overlapped calibration curves were obtained for the two acidic amino acids, glutamic acid (Glu) and aspartic acid (Asp), thus suggesting that the proposed method can be used not only for the quantitation of individual acidic amino acids, but also for the detection of total amount of them.

[Research on high sensitivity temperature sensor based on Mach-Zehnder interferometer with waist-enlarged fiber bitapers].

Optical fiber sensing technology is one of the very promising techniques in sensing fields. A high sensitivity high temperature sensor based on inline optical fiber Mach-Zehnder(M-Z) interferometer by using standard single mode fiber with two waist-enlarged bitapers is proposed in the present paper. The waist-enlarged bitapers are considered as couplers, the distance between the two bitapers is the sensing arm. The light in the lead-in fiber core couples into the sensing arms' fiber core and cladding by the first bitaper, and then propagate in them. The phase difference between core mode and cladding mode is produced when the light reaches the second bitaper. Then the second bitaper couples the light into the lead-out single-mode fiber to get the interference spectrum. The sensors with different length were fabricated. The relationship between the sensor length and interference period, and the temperature response of the.sensor were studied by experiments. The results show that the 35 mm long sensor has a high sensitivity of 0.115 nm x degrees C(-1) in the range of 30-400 degrees C. The transmission spectrum of the sensor was also analyzed by the fast Fourier transform. It shows that only LP01 mode and LP08 mode propagate in the sensor. Thesensor has advantages of small size, high precision, and immunity to electromagnetic inteference. In addition, it is of easy fabrication, high signal-to-noise ratio, light weight, and high sensitivity, and could be operated under high temperature. This kind of sensor is a good candidate for high temperature measurement of hot gas, oil and gas well logging and other areas.

Stress and temperature sensitivity of photonic crystals resonant cavity.

The temperature and stress characteristic of photonic band gap structure resonant cavities with square and graphite lattice have been studied by finite-difference time-domain method. The results show that the resonant cavities, both square and graphite lattice, have more and more resonant frequency with the cavity enlarging. And the curves between the resonant frequency and stress have better linearity. When the cavity enlarges enough, the curve between resonant frequency and temperature will become sectionalized line from nonlinear curve. Especially, the temperature sensitivity will be descending as the cavity is enlarging. Nevertheless, once some structures are put in the center of the cavity, the temperature sensitivity will be rising fast for this kind of cavity. Obviously, this character is convenient for us to achieve the specification measurement for temperature and stress.

[Simultaneous measurement of temperature and strain based on long-period fiber grating and Sagnac interferometer spectrum].

A simultaneous measurement system of temperature and strain is proposed and fabricated, which has advantages of low cost and easy structure. The system is formed by combining a long period fiber grating with a polarization-maintaining fiber Sagnac loop. The transmission spectrum of the fiber Sagnac interferometer is modulated by LPFG. The simultaneous measurement of temperature and strain can be realized. The experimental results show that the wavelength of the dip is varied with temperature changing and applied strain on polarization-maintaining fiber, and the intensity of the dip is changed with applied strain on LPFG. The temperature sensitivity of the system is 0.181 81 nm x degrees C(-1), the strain sensitivity of LPFG is 0. 005 283 dB x mu epsilon(-1), and the strain sensitivity of polarization-maintaining fiber Sagnac loop is 0.015 72 nm x mu epsilon(-1). The experimental system indicates that the proposal is feasible and has an application prospect.

[Application of fuzzy comprehensive assessment in risk assessment of water pollution conditions in downriver area of Dahuofang reservoir].

Fuzzy comprehensive model was used to assess water quality state in Hunhe river of Dahuofang reservoir from 1996 to 2004. It was found that the water quality of Hunhe river changed fluctuantly and belonged to II and serious III state besides in 1997, 2001, and 2003. The main pollutants were organic pollutants, oil and ammonia. Concentration of oil and ammonia gradually increased from 1996 to 2004, and COD changed irregularly, while BOD5 decreased.