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Photonic crystal fiber optic pressure sensor stability

In Electronic Infomation Category: P | on February 09,2012

Abstract: Photonic crystal fiber stability of the sensor in practical engineering applications, has an important influence. This paper analyzes the photonic crystal fiber optic pressure sensor of the basic principles introduced photonic crystal fiber optic pressure sensor system components, from the theoretical analysis of the sensor system relative to the light source wavelength, the output signal light intensity fluctuations and AT24C16AN datasheet and the stability of ambient temperature fluctuations. Photonic crystal fiber optic pressure sensor laser light source output power and AT24C16AN price and wavelength fluctuations, changes in the length of the sensor and AT24C16AN suppliers and the ambient temperature changes and so on affect the stability of the sensor system.

0 Introduction

fiber strain and stress on the environment temperature-sensitive properties can be used to monitor changes in ambient pressure. Photonic crystal fiber (PCF), compared with traditional fiber-optic transmission has a unique optical properties, in a variety of active and passive components play an important role. Pressure sensors in the PCF, PCF for pressure sensitive than ordinary fiber, the temperature-sensitive than ordinary single-mode fiber one order of magnitude, PCF fiber-optic sensors pressure sensors superior than the average. In the PCF pressure sensor for environmental monitoring of the process, if the sensor is not very good stability of the PCF, we can not accurately identify other sources of error, it can not accurately measure the external pressure changes. Therefore, the stability of the sensor has been engineering the most concern, the stability of a fiber optic sensor a major obstacle to practical use. Affect the stability of its own fiber-optic sensors, including fiber-optic sensor structure factors, light performance, the outside temperature changes and manufacturing process.

PCF sensor and pressure sensor with excellent sensing performance in the field of Smart Materials and Structures has broad application prospects, but the stability of the sensor is the key to PCF pressure sensor. In this paper, the pressure sensor system from the PCF laser light source, ambient temperature changes and the composition of the sensor system to discuss other aspects of passive components such as its stability.

1 PCF basic principle of the pressure sensor

pressure sensor system in the PCF, as sensitive element, using the refractive index guided PCF, the optical pulse limit its spread within the core. When the role of external pressure, PCF generated surface stress of each point, in the face of stress points occur under the strain, shear stress and ignore the angular strain in Cartesian coordinates, the normal stress can be expressed as [ x y z], which x, y x and y axes, respectively, suffered the horizontal stress, z or z axis direction indicated by the PCF stress; positive strain can be expressed as [ x y z], which x, y said the PCF transverse strain, z that PCF axial strain. Sensitive components located in the PCF PCF sensor in which the external pressure field pressure f, PCF core diameter d, and PCF-sensitive components of length L, the external pressure acting on the sensor the PCF shown in Figure 1.

1 external pressure acting on the sensor PCF schematic

according to elasticity theory, under pressure in the outside world, PCF core of the three directions will cause stress, the stress can be expressed as:

elastic light according to the theory, PCF in a point of stress and strain produced by the following relationship:

where, Ci, j is the elasticity of PCF. According to elasticity theory can be proved C11 = C22 = C33, C12 = C13 = C21 = C23 = C31 = C32, then the external pressure generated by the PCF under strain and static pressure in the PCF in the relationship between the formation of stress are as follows:

PCF under stress will change the optical properties and lead to an effective refractive index core PCF change, according to the elastic theory of light, the amount of this change can be expressed as follows:

where, n0 is the refractive index of core were not pressure; E is Youngs modulus; Poissons ratio for the silica fiber; p 11, p 12 are the elastic-optic coefficient of PCF.

PCF values ??of physical parameters are as follows: n0 = 1. 47, = 0. 17, E = 7. 3 10 10 < / SUP> Pa, p 11 = 0. 113, p 12 = 0. 252, by virtue of the equation (1) and (4) Calculate the specific core PCF under pressure to change the effective refractive index of the amount.

pressure sensor system in the PCF, the sensor using the refractive index guided PCF, based on optical waveguide theory, optical pulse propagation in PCF after the phase delay from the L volume: < / P>

where, L is the length of the PCF; n for the core refractive index distribution; for the light waves in optical fiber communication wavelength. Under pressure in the outside world, PCF will generate stress, because stress, PCF length, cross-sectional structure and refractive index distribution will fluctuate, and the phase delay caused by fluctuations in the PCF sensor output using a special device to detect This change, and further to detect changes in the external environment pressure, the pressure sensor which is the basic principle of PCF.

2 PCF pressure sensor system components and the stability analysis

PCF pressure sensor according to the basic principles, we propose the system model shown in Figure 2. The figure, (a) for the sensor system; (b) of the sensor sensitive element, which consists of optical fiber into L1, L2 and export fiber optic sensing element composed of L3; (c) pressure sensor for the PCF signal detection system, which consists of number of detection channels, each channel including the detection beam splitter, delay plate, analyzer and photodetector; (d) for the signal processing unit, which is mainly from the amplifier, filters, analog / digital (A / D) conversion device and computer system. Pressure sensor system PCF light source can be Nd3 +: YAG solid-state lasers or fiber lasers, the laser signal sent through the coupler into the sensor sensitive element PCF, PCF optical pressure sensor output signal through the optical detection system is converted to electrical signals, electrical signals by amplification detected by the computer after filtering process.

Figure 2 PCF pressure sensor system model

of equation (5) the differential, PCF pressure sensor light emitted laser light pulse through the sensor after the phase fluctuations can be expressed as:

(6) shows that the sensor light pulse propagation phase the main factors affecting the volatility of the laser light source wavelength, the refractive index and the length of the PCF sensor fluctuations. If the pressure sensor system in the PCF there is pressure caused by factors other than the transmission pulse phase fluctuations, then these factors, the stability of the sensor system will be affected. The following mainly from the laser light source and ambient temperature sensors both for theoretical analysis.

2. 1 laser light effects

for solid-state laser or fiber laser source, the output pulse has a certain spectral range, will fluctuate around the center wavelength, the wavelength fluctuations can cause pulse phase fluctuations, according to equation (6), the fluctuations can be expressed as:

(7) shows that, PCF light source wavelength sensor system pressure fluctuations will affect the measurement of the external pressure sensor, the sensor measurements with instability. In the PCF pressure sensor to detect the channel from the sensor part of the introduction of the optical pulse optical path difference can be quartz plate into the optical path difference compensation, in the detection channel in order to detect the optical signal intensity of significant change, the sensor detects the channel recording the intensity can be expressed as:

where, I 0 for the detector to monitor the average intensity; is a function associated with the light source spectrum; < / FONT> Os for the sensor system into the optical path difference; Or for the quartz delay plate compensation optical path difference; < / FONT> s for the sensor system into the phase drift; r continuous channel in the ground quartz plate introduced phase shift; Os - Or that the optical path difference decoding system of non-equilibrium quantity; s - r said decoding system of non-equilibrium phase-shift value. (8) shows that, PCF pressure sensor output signal and the spectral width of the laser light source, by? ? Function of the impact of laser light sources affect the spectral shape of the PCF pressure sensor signal measurement stability.

pressure sensor in the PCF, the light source intensity fluctuations directly affect the size of the measured signal, the laser light output pulse power fluctuations can cause the channel output signal to detect the phase fluctuations will inevitably bring to detect channel fluctuations in the output signal, it will also affect the PCF pressure sensor system stability and accuracy. For example, three different systems to detect the channel, I 1, I 2 and I 3 is a three-channel photodetector output signal strength, the phase demodulation of the signal light wave can be expressed as:

where, a 2, a3 are I 2, I 3 two-channel relative to the first channel I 1 1 ratio. (9) shows that the detection system output signal strength fluctuations on the stability of the sensor system also has important implications.

2. 2 of the ambient temperature

PCF pressure sensor if the external environment in which the temperature changes also cause the spread of the PCF light pulse phase change, phase fluctuations of this pressure sensor will not accurately detect PCF external pressure, on the stability of the sensor resulting in harmful effects. Temperature caused by the spread of the PCF optical pulse phase fluctuations in two main areas: effects of thermally induced expansion and thermo-optic effect, can be expressed as:

where, = dL / dT is the thermal expansion coefficient of PCF; a = dn / dT is the thermo-optic coefficient of PCF; T said that the amount of ambient temperature changes. Assume that the light pulse in the vicinity of 1 064 nm wavelength, a = 1. 19 10 - 5 K - 1 , = 0. 55 10 - 6 K - 1 , take the PCF length L = 1 m, L = 1 mm, n = 1. 450 2, < / FONT> T = 0. 1 K. According to equation (10) yields the phase caused by temperature fluctuations in the amount of = 3. 24. The results show that the ambient temperature changes on the PCF pressure sensor system performance stability of the very large.

3 Conclusion

PCF sensor and pressure sensor with excellent sensing performance in the field of Smart Materials and Structures has broad application prospects.

stability of the sensor is a pressure sensor PCF key to its practical applications have a major impact. PCF pressure sensors to improve the environment of constant temperature and enhance the work of the laser light wavelength sensor output power stability, all contribute to the stable pressure sensor PCF. Pressure sensor system in the PCF, PCF sensing element is a core component of its stability and reliability to a large extent determines the stability and reliability of sensors, pressure sensors PCF and constitute all the material, such as couplers, photodetector and amplifier etc should be a good optical, electrical and mechanical long-term stability and temperature coefficient must match in order to make the whole system in the linear working range.

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