A kind of temperature measuring device and method based on optical fiber
Technical field
The present invention relates to a kind of full optical fiber interference fields of measurement, are based on seven core fibres and optical fiber ball pair in particular to one kind
Claim the thermometry of Mach-Zender interferometer.
Background technique
In recent years, fibre optical sensor is detecting temperature, pressure, the physical quantitys such as curvature, refractive index and Biochemistry measurement field
Concern by more and more researchers.For fibre optical sensor because of its electromagnetism interference, risk is small, compact dimensions, weight
Gently, the at low cost and splendid characteristic of flexibility, with the adaptability of height in some special environment, so as to tested
Physical parameter is accurately monitored.A kind of space interference of light system is proposed in 19th-century from roentgen Mach and Zeng Deer
Since system, researcher realizes the measurement of a variety of physical quantitys with different optical fiber mach-zhender structures.Mach-Zehnder is dry
The type fibre optical sensor of relating to has the characteristics that simple and light, to be easy to production, high sensitivity, sensing wavelength range big, for a long time with
Come be researchers at home and abroad concern emphasis direction.Compared to space optical path, waveguide coupling or the cascade horse of fiber coupler
Conspicuous-once moral interference system, integrated full optical fiber interference device were more convenient and easily fabricated.In recent years, optical fiber mode
Formula interference, which is formed by Mach-Zehnder interferometer, becomes research hotspot, and the two-way of interference is formed in this Mach-Zehnder interferometer
Light corresponds to two different transmission modes in optical fiber.For common single mode optical fiber, a kind of generally only transmission of basic mode
Mode, researcher pass through dislocation welding, drawing cone, non-single mode optical fiber welding, thin-core fibers, photonic crystal fiber, hollow-core fiber
The methods of be to realize Mach-Zehnder interference, and realize certain physics using its feature by basic mode energy coupling into cladding mode
The measurement of amount.
With the development of optical fiber structure design and manufacture craft, seven core fibres are not only applicable to fiber optic communication, because it has
The characteristics of interference condition is good, high sensitivity is used for sensory field by domestic and foreign scholars.Wherein, G.Salceda-Delgado is proposed
Interference structure based on seven cores is used for curvature sensing/monitoring, and "-seven cores of single mode-single mode " type has been built based on seven core fibres
Mach-Zehnder interference sensing structure, although the sensitivity of structure sensing is strong, the linear pass of wave length shift and Curvature varying
Tie up to curvature it is smaller when show be not obvious.Zhou Song et al. proposes " single mode-- seven cores of multimode-multi-mode-single mode " temperature sensing knot
Structure, can accurately measure 800 DEG C of test temperature, sensitivity and measurement range compared to traditional sensor has large increase,
But the structure needs the splicing parameter of rationally control multimode fibre, it is more demanding to process.
Summary of the invention
The present invention provides the thermometry of a kind of seven core fibres and optical fiber ball asymmetric Mach-Zender that interferometer, institute
It is high to state small measuring all -fiber Mach Zehnder interference structural volume, sound construction and measurement accuracy.
The present invention is realized by following technical solution:
A kind of temperature measuring device based on optical fiber, including interference structure, which is characterized in that the interference structure includes the
The end of one single mode optical fiber and the second single mode optical fiber, first single mode optical fiber and the second single mode optical fiber is melted and molded as bead
Shape forms single mode optical fiber-- seven core fibres of bead-bead-single mode optical fiber using one section of seven core fibre connection between two beads
Structure;
First single mode optical fiber is connected with wide spectrum light source, and the second single mode optical fiber is connected with spectrum recorder.
It is further to improve, the wide spectrum light source be laser pump (ing) excite doped fiber generate spontaneous radiation wide spectrum optical or
The spontaneous generation wide spectrum optical of laser diode.
It is further to improve, the small ball's diameter that first single mode optical fiber and the second single mode optical fiber end are melt into is 200~
400um。
Further to improve, the length of seven core fibre is 9mm.
Further to improve, the first single mode optical fiber is connect by FC/APC connector with wide spectrum light source.
Further to improve, the second single mode optical fiber is connect by FC/APC connector with spectrum recorder.
A kind of thermometry based on optical fiber, which comprises the following steps:
Step 1) single mode optical fiber-- seven core fibres of bead-bead-single mode optical fiber structure interference structure is built, and connect
Wide spectrum light source and spectrum recorder;
Step 2) interference structure is put into the temperature calibration case of temperature controllable;
Step 3) temperature level is gradually changed, the interference transmission spectrum under different temperatures is recorded, it is right to draw interference spectrum trough institute
The curve that the optical wavelength answered changes with temperature level;
Step 4) interference structure is placed at temperature to be measured, it can be calculated according to interference spectrum to testing temperature.
It is further to improve, optical wavelength corresponding to the interference spectrum trough vary with temperature curve negotiating linear fit or
Person's least square method is fitted.
The method for the principle of interference measurement temperature that the invention proposes a kind of using light, all -fiber Mach-in the present invention
Zeng Deer interference structure is small in size, sound construction and measurement accuracy are high.
Detailed description of the invention
Fig. 1 shows seven core fibres and optical fiber ball asymmetric Mach-Zender that interferometer temperature measurement knot according to the present invention
Structure schematic diagram;
Fig. 2 shows seven core fibres and optical fiber ball asymmetric Mach-Zender that interference welding schematic diagram;
Fig. 3 shows seven core fibres and optical fiber ball asymmetric Mach-Zender that interference structure and optical transport schematic diagram.
Fig. 4 shows the curve and linear relationship that interference spectrum in one embodiment of the invention changes with temperature level.
Specific embodiment
As depicted in figs. 1 and 2: 1 is wide spectrum light source in Fig. 1, and 2 be interference structure, mounted in the scale of thermometer of a temperature-controllable
Determine in case, 3 be spectrum recorder, and 4 be transmission fiber, and 5 use thermometer for calibration or comparison.
In Fig. 2, the left side is single mode optical fiber and seven core fibre end face sectional views, and 7 fibre cores of seven core fibre are by one
Central core and 6 away from 35 μm of the central core peripheral fibre core groups compositions in regular hexagon.What is selected in the present embodiment is
Seven core fibre of SM-7C1500 (6.1/125) model of fibercore company, seven core fibre length are 9mm.
As shown in figure 3, all -fiber Mach Zehnder interference structure includes the first single mode optical fiber 6 and the second single mode optical fiber 10,
The end of first single mode optical fiber 6 and the second single mode optical fiber 10 is melted and molded as coccoid (7 and 9), bead 7 and bead 9
Between connected using one section of seven core fibre 8.
All -fiber Mach Zehnder interference structure fabrication process: first single mode optical fiber is melted at one end using optical fiber splicer
It is connected into spherical structure, is made another spare;Again by seven core fibres and the single mode optical fiber welding for having spherical structure, a fixed length is measured
It spends (choosing 9mm in the present embodiment) and seven core fibres is truncated using optical fiber cutter, then be fused into another single mode optical fiber ball end
Symmetrical structure forms the fibre-optic waveguide of " SMF-ball-SCF-ball-SMF ".
The working principle of the sensor are as follows: wide spectrum optical enters single mode optical fiber, is transmitted in the form of optical fiber basic mode, by first
When optical fiber ball 7, launching efficiency is improved, and at mutation, a part of core mode, which is excited in covering, forms cladding mode, along packet
Layer continues to transmit, and another part continues to propagate along the fibre core of seven core fibres 8, when reaching second optical fiber spherical structure 9, coupling effect
Rate significantly improves, and cladding mode is again coupled into fibre core, is interfered with core mode, forms Mach-Zehnder interference.
Output transmission spectral intensity can indicate after Mach-Zehnder structure interferes are as follows:
In formula, k1And k2The respectively coefficient of coup of the transmission light when optical fiber spherical structure 7 and 9 transmits, η is cladding mode
Transmission loss, IinIt is the light intensity of input light, Δ φ is the transmission through seven core fibre of interlude, the phase of core mode and cladding mode
Potential difference
Since the propagation constant between different mode is different, after propagating same distance, different modes can generate phase
Poor core mode and the phase difference of cladding mode generation are
When the interference effect that phase difference meets Δ φ=(2m+1) π (m is positive integer) Shi Fasheng destructive interference structure is saturating
Penetrating spectrum trough wavelength may be expressed as:
In formula, Δ neffEffective refractive index for core mode and m rank cladding mode is poor, and L is the length of interferometer, and N is indicated
The coefficient of phase difference when transmission spectrum is in trough.
Temperature sensing test is carried out using the transmission spectrum trough peak value drift of interferometer, when interferometer is influenced by temperature,
The variation of optical path difference occurs for optical fiber at interference structure, and transmission spectrum can drift therewith.
Fig. 4 (a) is the transmission spectrum of fiber interference structure under different temperatures, is followed successively by 50 DEG C, 59 DEG C, 66.5 from left to right
DEG C, 75.5 DEG C, 84 DEG C, 93.3 DEG C, 101.2 DEG C, 110.5 DEG C, 117.7 DEG C, the curve of spectrum at 126.4 DEG C.As can be seen that with
The raising of temperature, interference spectrum is mobile to long wave length direction, carries out peak-seeking to the optical wavelength trough of spectrum trough, and by peak-seeking
Value and spectral depth record and analyze the variation of temperature, this group of data are carried out with the linear fit of least square method, it is known that,
Interference spectrum valley value varies with temperature linear variation.Temperature-wavelength formula is as follows:
In formula, m is damping peak order, and L is seven core fibre length, KTFor the coefficient of temperature and the relationship of wavelength change.
Therefore the sensing characteristics be can use and carry out temperature test.
The calibration of temperature sensitivity coefficient:
Interference structure is put into temperature calibration case, records a spectrum at interval of 5 DEG C of variations, interfere the wavelength of trough with
The raising of temperature is to long wave length direction drift.As shown in Fig. 4 (b), the linearity reaches 0.9855, and spectral depth is basically unchanged.Root
The temperature at interference structure can be calculated by the corresponding wavelength of measurement spectrum trough according to the linear relationship.
The match parameter of associated fiber of the present invention is as shown in the table: