Air velocity transducer based on long-period fiber grating
Technical field
The invention mainly relates to sensory field of optic fibre and optic communication passive device field, more particularly to are based on long period optical fiber
The air velocity transducer of grating.
Background technique
With the rapid development of Fibre Optical Communication Technology, optical fiber sensing technology since after the 1970s also rise,
Become the new force in numerous sensing technologies.And fiber grating therein has manufacturing technology mature, is easily attached, anti-electricity
Magnetic disturbance, light-weight, small in size advantage, additionally due to fiber grating is for environmental parameter, (refractive index, temperature, stress are curved
Song, distortion etc.) variation it is more sensitive, therefore fiber grating is widely applied in sensory field of optic fibre.Optical fiber passes at present
Sensor can vibrate, speed, humidity, a variety of physical quantitys such as angle measure temperature, pressure.
Optical fiber sensing technology can be mainly divided into two aspects of modulation technique and demodulation techniques, and modulation technique is exactly in environment
Variable is to the process of physical parameter in optical fiber, and demodulation techniques are then the mistakes for trying to obtain useful information from brewed signal
Journey.
It is divided according to modulation system, fiber grating air velocity transducer can be divided into hot-wire and bending-type, hot-wire wind
Fast sensor utilizes pump light source heating optical fiber surface, is changed by the temperature on fiber grating surface to achieve the effect that modulation.
And bending-type then pass through fiber grating bending change its structure achieve the effect that modulation.Above two structure has respective lack
Point, hot-wire array sensor also need pump light source to provide heating other than needing signal optical source.And bending-type wind speed senses
For device in order to improve sensitivity, the structure of bending part is often very fragile, is easily damaged.
Wave length type and power-type, wave length type wind can be then divided by dividing fiber grating air velocity transducer according to demodulation mode
Fast sensor obtains final wind speed by the offset of measured waveform wavelength, and power-type is measured by the change of output power
Wind speed size.Most air velocity transducers is based on wave length type air velocity transducer at present, although reason essentially consists in power-type biography
Sensor demodulation is simple but its sensitivity is bad.But at the same time, there is also demodulation mode difficulties for wave length type air velocity transducer
The shortcomings that.
In short, current fiber-optic grating sensor still remains, structure is complicated, and demodulation is difficult, and fiber grating is easy to damage,
The not high disadvantage of sensitivity.
Summary of the invention
Structure is complicated, demodulation is difficult in order to overcome existing for current fiber grating air velocity transducer, and fiber grating is easy to damage
The shortcomings that, simple, demodulation that the present invention provides a kind of structures is used easily based on the air velocity transducer of long-period fiber grating
Power demodulation is bent with fibre-optical bending instead of fiber grating.
The technical solution adopted by the present invention to solve the technical problems is:
A kind of air velocity transducer based on long-period fiber grating, including input optical fibre, input LPFG, output optical fibre, painting
Coating and fibre reflector, the input optical fibre are doubly clad optical fiber, and the input LPFG is located at the fibre core of the input optical fibre
Interior, the output optical fibre is single mode optical fiber, and the coat is located at the outer surface of the output optical fibre, the fibre reflector position
In in the distal end faces of the output optical fibre.
Further, the fibre reflector is formed by carrying out plating high-reflecting film in end face, and the coat is to use
High-index material coating.
Further, the high-reflecting film is metal film or deielectric-coating, and the coating material is that refractive index is greater than single-mode optics
The high refractive index resins of fine cladding index, the coating material include but is not limited to tetrafunctional urethane acrylate.
The production method of the input LPFG includes but is not limited to ultraviolet light (UV), CO2Pulse laser write-in, electric arc are write
Enter, femto-second laser pulse write-in and the methods of Mechanical Method.
Technical concept of the invention are as follows: signal light is transferred to by input LPFG by input optical fibre, it will be fine by input LPFG
In the inner cladding optically coupling to input optical fibre in core.Inner cladding mode subsequently enters in the covering of output optical fibre, output optical fibre
It can be bent under the action of the forces of the wind, cladding mode can be consumed at this time, while coat exacerbates this loss situation, into
And improve the sensitivity of whole system.Subsequent dump energy advances at fibre reflector, is reflected, is returned at this
Reverse transfer in the covering of output optical fibre is returned, and is lost again, dump energy can be coupled once again after entering input LPFG
Enter in fibre core, can then be detected.Actual wind speed can be obtained in variation by measuring power.
Beneficial effects of the present invention are mainly manifested in: 1) being passed at present with the fiber grating wind speed for being bent into modulation principle production
Sensor be easy to cause the damage of fiber grating, and the present invention is not needed through fiber grating flexural measurement wind speed.2) at present with temperature
Degree variation is that the hot-wire array sensor of modulation principle production also needs pump light source in structure other than signal optical source
Heating, and the present invention only needs signal optical source can be driven.3) often exist using wavelength as the fibre optical sensor of demodulation mode at present
The difficult situation of demodulation, the present invention demodulate very simple using power as demodulation mode.4) at present using power as demodulation mode
Fibre optical sensor often haves the shortcomings that sensitivity is not high enough, and the present invention then passes through coating high-index material, with leakage mould
Instead of radiation mode, carry out the sensitivity of strengthen the system.5) part-structure of the present invention uses doubly clad optical fiber, to ensure that cladding mode can
To be transmitted in relatively long distance.
Detailed description of the invention
Fig. 1 is the structural schematic diagram of the air velocity transducer based on long-period fiber grating.
Fig. 2 is specific application example.
Specific embodiment
The invention will be further described below in conjunction with the accompanying drawings.
Referring to Figures 1 and 2, a kind of air velocity transducer based on long-period fiber grating, including input optical fibre 101, input
LPFG102, output optical fibre 103, coat 104, fibre reflector 105.Input LPFG102 is located at the fibre core of input optical fibre 101
Interior, fibre reflector 105 is located on the end face of output optical fibre 103.Coat 104 is located at the outer surface of output optical fibre 103.Input
The fibre core and inner cladding diameter of optical fiber 101 are equal with the fibre core and cladding diameter of output optical fibre 103.
Referring to Fig. 2, a kind of concrete application scene of the air velocity transducer based on long-period fiber grating, including optical fiber are fixed
Fixture 109, light source 110, power meter 111, circulator 112 and target 113, light source 110 are located at the input terminal of circulator 112, wind
Fast sensor is located at the output end of circulator 112, and power meter 111 is located at the reflection end of circulator 112.The spectrum wave of light source 110
It is long to be matched with input LPFG102 resonance wavelength.
Further, input optical fibre 103 be doubly clad optical fiber, fibre reflector 105 be by 103 end face of output optical fibre into
Row plating high-reflecting film is formed, and coat 104 is coated using high-index material, and target 113 is by a kind of lighter in weight, surface
Uniform material is made, and attaches to the position of the optical fiber positioned at air port.
Further, high-reflecting film material is metal or medium, and coating material is the high refraction that refractive index is greater than fibre cladding
Rate resin, coating material include but is not limited to tetrafunctional urethane acrylate.The production method of input LPFG102 includes but not
It is limited to ultraviolet light (UV), CO2The methods of pulse laser write-in, electric arc write-in, femto-second laser pulse write-in and Mechanical Method.Input
The resonance wavelength of LPFG102 is matched with light source 110.
Referring to Figures 1 and 2, the working process and principle of entire device are as follows: firstly, light source 110 is arrived by circulator 112
Up to fibre optical sensor part, by the way that input light 106 is inputted LPFG102 in input optical fibre 101, due to inputting the biography of LPFG102
Band resistance effect is presented in defeated characteristic, and all modes if optical source wavelength selection is correct in fibre core will all be coupled into inner cladding mould
In formula, resonance wavelengthmMeet phase-matching conditionWherein Λ, ncoWithRespectively refer to screen periods, fibre
The effective refractive index of core and the effective refractive index of inner cladding mould.Inner cladding mode subsequently enters in the covering of transmission fiber 103, by
It is located at the phenomenon that air port can be bent under the action of wind-force 108 in 103, cladding mode can be consumed at this time, the journey of consumption
Degree is depending on the micro-bend degree of output optical fibre 103, while coat 104 and the lower presence for hanging target 113 exacerbate this loss
Situation, and then improve the sensitivity of whole system.Subsequent dump energy advances at fibre reflector 105, at this
It is reflected, the covering relaying for returning to output optical fibre 103 resumes defeated, and is once lost again, dump energy becomes 107.
Dump energy 107 can enter input optical fibre 101 later, can be coupled into once again fibre when this portion of energy enters LPFG102
In-core, then can be by being detected in 112 reflection end ingoing power meter 111 of circulator.Since most loss exists
In on power, actual wind speed is can be obtained in the variation by measuring power.