CN102162753B - Sensor structure for simultaneously measuring temperature and strain of long period fiber gratings (LPFGs) - Google Patents

Sensor structure for simultaneously measuring temperature and strain of long period fiber gratings (LPFGs) Download PDF

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Publication number
CN102162753B
CN102162753B CN 201010580482 CN201010580482A CN102162753B CN 102162753 B CN102162753 B CN 102162753B CN 201010580482 CN201010580482 CN 201010580482 CN 201010580482 A CN201010580482 A CN 201010580482A CN 102162753 B CN102162753 B CN 102162753B
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temperature
strain
long period
period fiber
sensor
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CN 201010580482
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Chinese (zh)
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CN102162753A (en
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饶云江
汪文华
汤伟锋
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无锡成电光纤传感科技有限公司
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Abstract

The invention provides a sensor structure for simultaneously measuring the temperature and strain of long period fiber gratings (LPFGs). The sensor structure is characterized in that a pair of LPFGs which are written by high-frequency CO2 laser pulse in a fiber and have different periods are selected, namely an LPFG only sensitive to temperature variation and an LPFG sensitive to both temperature variation and strain variation; and the respective variation of the temperature and the strain can be accurately measured by cascading the two LPFGs. The sensor structure has the following prominent advantages: the temperature variation is measured by using the LPFG which has a specific period and is only sensitive to temperature variation, and the variation of the temperature and the strain is measured by using the other LPFG, thus realizing measurement of the two parameters (the temperature and the strain), and providing a scheme for solving the problem of cross sensitivity of the temperature and the strain; and meanwhile, the sensor has the capability of normally working at the high temperature of 750 DEG C and is unnecessary to be specially packaged.

Description

Measure simultaneously the sensor construction of long period fiber grating temperature and strain

Technical field

The invention belongs to technical field of optical fiber sensing, be specifically related to utilize the long period fiber grating of a pair of different cycles to make the sensor construction that sensor is measured temperature and two parameters of strain simultaneously.

Background technology

Long period fiber grating (LPFG) be a kind of can be with the band resistance type optical fiber filter that couples light to covering of specific wavelength, its resonance wavelength can be along with the variation of the parameters such as the temperature of external environment, strain, refractive index and is changed, according to this principle, the variation of resonance wavelength that can be by measuring LPFG realizes the to external world measurement of environmental physics quantitative change.Because LPFG compares and Fiber Bragg Grating FBG (FBG), and is more responsive to the variation of many external physical quantity, and the higher temperature of LPFG ability, so it has very large application prospect aspect Fibre Optical Sensor.

In temperature and strain while fields of measurement, the people such as H.J.Patrick issue paper (IEEE Photon.Tech.Lett., 1996, Vol.8, No.9, pp.1223-1225) strain and temperature simultaneously measuring scheme proposed, but this scheme needs the combination of Fiber Bragg Grating FBG and long period fiber grating, so that the sensor cost is higher, and volume is larger, is unfavorable for integrated.The river is built, publish thesis (Acta Optica, 2003,32 (9): measure when 1063~1066) proposing to have LPFG/EFPI integrating optical fiber sensor to realize temperature and strain such as Rao Yunjiang.Optical grating strain, the temperature simultaneously measuring sensor that Li Aiqun etc. (ZL 200910026403) propose be with two optical fiber Bragg grating encapsulations in special construction, cause the sensor cost higher, processing inconvenience.

In the fiber-optic grating sensor, the existence of temperature and strain cross sensitivity has had a strong impact on the precision of measuring, and therefore research only has great significance to other physical quantitys variation insensitive optical fiber optical grating sensors to a certain physical quantity sensitive.Utilize the combination of this fiber-optic grating sensor and ordinary optic fibre grating sensor just can realize the accurate measurement of multiparameter.

Summary of the invention

The purpose of this invention is to provide a pair of long-period fiber grating sensor, utilize one of them LPFG (long period fiber grating) insensitive and to responsive to temperature to strain, another LPFG measures when realizing temperature and strain temperature and the equal responsive characteristics of strain.And because this sensor is to be formed by two LPFG cascades, LPFG itself has resistant to elevated temperatures characteristic, has the ability that works under 750 ℃ of high temperature.

For achieving the above object, the present invention is achieved through the following technical solutions:

Measure simultaneously the sensor construction of long period fiber grating temperature and strain, select high frequency CO 2The a pair of long period fiber grating of the different cycles that laser pulse writes in optical fiber, be respectively one to the long period fiber grating of temperature variation sensitivity, with a long period fiber grating to temperature and the equal sensitivity of strain variation, two long period fiber grating are carried out cascade use, can accurately measure temperature and strain variation separately.

Selected optical fiber is the bend resistant single moded fibers with the nano-rings structure.

The long period fiber grating that writes has following characteristics: the resonance wavelength of the long period fiber grating in the specific period scope is to responsive to temperature and insensitive to strain; The resonance wavelength of the long period fiber grating in the general periodic regime is responsive simultaneously to temperature and strain.

This sensor has the ability that still can work during up to 750 ℃ in environment temperature.

This sensor has the simple characteristics of processing, need not the additional encapsulation processs such as isolated temperature, isolation stress except general protection packaging.

The present invention adopts the long period fiber grating of the different cycles of two cascades to come the variation of sensing external environment temperature and strain, and wherein LPFG1 is only to responsive to temperature, i.e. the variation of its resonance wavelength (Δ λ Res) only relevant with temperature variation (Δ T), can be represented by the formula:

Δλ res-LPFG1=A*ΔT????(1)

LPFG2 is then all responsive to temperature and strain variation (Δ μ ε microstrain), and the variation of resonance wavelength can be expressed as:

Δλ res-LPFG2=B*ΔT+C*Δμε????(2)

In equation (1) and (2), coefficient A, B, C be Resonant Wavelengths of Long Period Fiber Gratings with the coefficient of temperature and strain variation, simultaneous equations (1) and (2) just can solve the variable quantity of temperature and strain.

Long period fiber grating described in the present invention is to utilize high frequency CO 2Laser instrument is the bend resistant single moded fibers in a kind of Novel belt nano-rings structure of release in 2009 in Corning Incorporated On write, these two long period fiber grating have the different cycles, and their cycle be positioned at same interval, to be in same its resonance wavelength of length of an interval period optical fiber grating identical with the character of temperature and strain variation.

Outstanding advantages of the present invention is: with a long period fiber grating feature measurement temperature variation to the temperature variation sensitivity of a specific period, measure the variation of temperature and strain with another long period fiber grating, thereby realize the measurement of temperature and strain biparametric, provided a kind of scheme that solves the temperature strain cross sensitivity.This type sensor has the ability that works under 750 ℃ of high temperature simultaneously, and does not need special package.

Description of drawings

Fig. 1 is the sensor construction synoptic diagram that the present invention adopts;

Fig. 2 is long period fiber grating wiring method among the present invention;

Fig. 3 is the emergent property of the grating of periods lambda=470 μ m;

Fig. 4 is the temperature characteristics of the grating of periods lambda=470 μ m;

Fig. 5 is the emergent property curve of the grating of periods lambda=295 μ m;

Fig. 6 is the temperature characteristics of the grating of periods lambda=295 μ m;

Fig. 7 is the hot properties curve of the grating of periods lambda=468 μ m;

Fig. 8 is temperature and the simultaneously-measured proving installation figure of strain among the present invention.

Embodiment

The below is described in further detail the present invention according to embodiment and accompanying drawing.

Shown in Fig. 1-8, the long period fiber grating that we select is two long period fiber grating of the different cycles that writes at healthy and free from worry bend insensitive optical fiber with the high-frequency CO2 laser pulse.This to the long period fiber grating structure as shown in Figure 1.Among the figure, long period fiber grating 1 and long period fiber grating 2 are two different long period fiber grating of cycle.

1 cycle of long period fiber grating is 470 μ m, and periodicity N=60, harmonic peak wavelength be at 1536.5nm, the grating strain characteristic in this cycle as shown in Figure 3, its harmonic peak is basic not skew under 1500 microstrains; Temperature characteristics as shown in Figure 4, its temperature control is about 0.098nm/ ℃, the linearity is R 2=0.998.

2 cycles of long period fiber grating are 295 μ m, periodicity N=80, the harmonic peak wavelength is at 1514.7nm, the grating strain characteristic in this cycle as shown in Figure 5, its strain sensitivity is about 2.8pm/ μ ε, strain increases and is heavy and property is relatively good when reducing, and resonance wavelength presents the good linearity with strain variation, its linearity R 2=0.999; Temperature characteristics as shown in Figure 6, its temperature control is about 0.1448nm/ ℃, the linearity is R 2=0.996.Responsive to temperature and strain variation simultaneously.

Make the device of long period fiber grating as shown in Figure 2, comprising: wideband light source 3, high frequency CO 2Laser instrument 4, healthy and free from worry bend insensitive optical fiber 5, spectroanalysis instrument 6.When writing long period fiber grating, high frequency CO 2The pulsewidth of laser instrument is 90 μ s, and frequency is 5kHz, CO 2Laser is focused onto the small spot that diameter is 50 μ m, and average power is 0.45W.

The hot properties of the long period fiber grating that this type sensor is used as shown in Figure 7.Long period fiber grating cycles 468 μ m, periodicity N=60, the harmonic peak wavelength is at 1509.05nm.Among Fig. 7, its temperature control in 100-250 ℃ of interval is about 0.1194nm/ ℃, and the linearity is R 2=0.9998.Its temperature control at 300-750 ℃ is about 0.2084nm/ ℃, and the linearity is R 2=0.9991.High temperature section sensitivity is higher, is keeping the good linearity in various temperature ranges.

Test the device of this sensor as shown in Figure 8, comprising: wideband light source 7; High precision micropositioner 8; Be used for sensor is applied strain; High-accuracy and constant incubator 9 is used for the simulated environment temperature variation; Long period fiber grating 10, spectroanalysis instrument 11 with the present invention's making.

Claims (3)

1. measure simultaneously the sensor construction of long period fiber grating temperature and strain, it is characterized in that, select high frequency CO 2The a pair of long period fiber grating of the different cycles that laser pulse writes in optical fiber, be respectively one to the long period fiber grating of temperature variation sensitivity, with a long period fiber grating to temperature and the equal sensitivity of strain variation, two long period fiber grating are carried out cascade use.
2. the sensor construction of measuring simultaneously long period fiber grating temperature and strain according to claim 1 is characterized in that, selected optical fiber is the bend resistant single moded fibers with the nano-rings structure.
3. the sensor construction of measuring simultaneously long period fiber grating temperature and strain according to claim 1 is characterized in that, two long period fiber grating have the different cycles, and their cycle is positioned at same interval.
CN 201010580482 2010-12-09 2010-12-09 Sensor structure for simultaneously measuring temperature and strain of long period fiber gratings (LPFGs) CN102162753B (en)

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CN103364102B (en) * 2012-04-05 2015-03-18 电子科技大学 Bending-resistant single-LPFG (Long Period Fiber Grating) sensor simultaneously measuring temperature and strain
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CN103411550B (en) * 2013-06-28 2016-07-06 武汉理工大学 Internal combustion engine main bearing inner surface stress and temperature monitoring method based on fiber grating
CN103674085B (en) * 2013-12-16 2016-08-17 西安电子科技大学 The sapphire fiber grating temperature of a kind of U-shape structure and the preparation method of strain gauge
CN103940360B (en) * 2014-04-23 2016-10-05 鲁东大学 A kind of strain monitoring device based on cascade chirped fiber grating
CN103955019B (en) * 2014-04-25 2017-02-01 深圳大学 Expanding type long-period fiber bragg grating based on photonic crystal fiber and manufacturing method of expanding type long-period fiber bragg grating
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CN106524935B (en) * 2016-10-11 2019-01-18 北京信息科技大学 A kind of method of the round trip MZ structure measurement strain of welding long-period fiber grating
CN108827374A (en) * 2018-04-16 2018-11-16 北京工业大学 A kind of tandem hydrogen and oxygen concentration and temperature and humidity measuring system simultaneously

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