CN109357693A - A kind of detection system and method for low reflected energy fiber grating - Google Patents
A kind of detection system and method for low reflected energy fiber grating Download PDFInfo
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- CN109357693A CN109357693A CN201810322484.XA CN201810322484A CN109357693A CN 109357693 A CN109357693 A CN 109357693A CN 201810322484 A CN201810322484 A CN 201810322484A CN 109357693 A CN109357693 A CN 109357693A
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Abstract
The present invention provides a kind of detection methods of low reflected energy fiber grating, this method is suitable for fiber grating detection and measuring system, the system are made of wideband light source, high-speed optical switch one, attenuator one, circulator, optical cable, fiber grating, attenuator two, high-speed optical switch two, tracking filter, (FBG) demodulator, logic controller.Use two high-speed optical switches, high-precision temporal scalable is carried out to transmitting light and reflected light, and utilize tracking filter, specific band filtering processing is carried out to fiber grating reflected light, in conjunction with ambient noise suppression technology, it can be achieved that low reflected energy optic fiber grating wavelength stablizes identification and apart from precise measurement.The features such as technology has structure simple, low cost, detection accuracy is high.
Description
Technical field
The present invention relates to a kind of detection methods of low energy reflection fiber grating, belong to fiber optic communication and fiber grating
Sensor field is, it can be achieved that detection and identification to low energy reflection fiber grating.
Background technique
With the continuous development of optical fiber sensing technology, fiber grating is widely used, and is widely used in a variety of physics and is measured
The sensory field of amount and communication links etc..Fiber grating detection system is primarily limited to the dynamic response of (FBG) demodulator at present
Can, signal demodulation and noise management technique so that the use of fiber grating is limited, such as remote, or have big attenuation
Occasion causes the detection and identification of low energy reflection fiber grating in use, the reflected energy value due to fiber grating is lower
It is difficult.
In the prior art, two fiber-optic grating sensors, wavelengt demodulator, dense wavelength division demultiplexer and light are needed
Electric explorer etc. forms multi-channel optical fibre raster sensor, to realize the detection to sensor.This device, not only tunes
Technical costs is high, and system complex.Also there are other alternatives in the prior art, for example use wideband light source, uses in pairs
The fiber grating that is cascaded realize the linear relationship of wavelength change reflect fiber grating, detected to realize.More than
Device and detection method when detecting, pass through the optical fiber for including a large amount of fiber-optic grating sensor between multiple gratings
Often there is crosstalk, and its detection range is limited, cannot be advantageously applied in complicated long-distance optical fiber raster grid.
Other prior art includes: to realize in the optical fiber with big fiber-optic grating sensor to optical fiber
The detection of grating, by way of two pairs of SOA high speed optoelectronics switches of setting and signal generator, using time division multiplexing and wavelength-division
It is multiplexed the mode combined, realizes the detection that a large amount of light are thought with grating sensor, still, this set-up mode system structure is multiple
It is miscellaneous, and it is easy the factors such as be bent, lost by environment and optical fiber itself and is influenced, cause the curve detected to be overlapped mutually
Seriously, it to influence the detection accuracy of sensor, and be easy to cause and misreads.
Based on above-mentioned problems of the prior art, if can be recognized more under the premise of not increasing too big investment
Remote FBG by the utilization rate for effectively improving FBG (FBG) demodulator and reduces cost.
Summary of the invention
In order to solve above-mentioned problems of the prior art, the invention proposes a kind of low reflected energy fiber gratings
Detection and identifying system and method, be greatly improved the detecting distance and accuracy of identification of fiber grating, expand fiber grating
Usable range.Specifically, the present invention provides following technical schemes:
On the one hand, the present invention provides a kind of low reflected energy fiber grating detection system, the system includes: broadband
Light source, high-speed optical switch one, attenuator one, circulator, optical cable, fiber grating string, attenuator two, high-speed optical switch two, tracking
Filter, (FBG) demodulator and logic controller；
The wideband light source, high-speed optical switch one, attenuator one are connected with circulator；The (FBG) demodulator, tracking filter
Device, high-speed optical switch two, attenuator two are connected with circulator；The circulator is connected with optical cable, and the fiber grating is placed in light
In the optical fiber of cable；The logic controller respectively with wideband light source, high-speed optical switch one, attenuator one, attenuator two, high speed
Photoswitch two, tracking filter are connected with (FBG) demodulator, and carry out logic control to these components；The fiber grating string is by more
The fiber grating of a different wave length forms, and concatenation is in a fiber.
Preferably, emit light by described high-speed optical switch a pair to be controlled, form the detection of one section of fixed pulse width
Light, then by control high-speed light open the light two make-and-break time delay, the selective reflected light received after sometime delay
Pulse.Different time delays then corresponds to different reflective distances.
Preferably, wideband light source is sent out according to the distance of different detection ranges by the attenuator one, attenuator two
Light intensity out is adjusted, so that (FBG) demodulator can receive suitable reflective light intensity.
Preferably, logic controller reads the optical power signals that (FBG) demodulator detects in real time, according to the optical power signals
Power in real time adjust attenuator one and attenuator two attenuation amplitude, by feedback control, so that (FBG) demodulator can obtain always
Stable optical power is got, so that the stability and accuracy of identification can be improved.
Preferably, wave-length coverage of the logic controller according to surveyed fiber grating, the filtering of dynamic regulation tracking filter
Parameter filters out the noise signal outside optic fiber grating wavelength range, improves the signal-to-noise ratio of system.
Preferably for the fiber grating with low reflected energy, attenuator one and attenuator two are reduced by dynamic
Attenuation value increases the optical power of incident light and reflected light, improves identification sensitivity of the system to low reflected energy grating.
Preferably, the (FBG) demodulator is controlled by logic controller, according to wavelength model locating for fiber grating detected
It encloses, dynamic adjusts the wavelength detection parameter of (FBG) demodulator, guarantees the detectivity at target wavelength much higher than at other wavelength
Sensitivity, further increase the detection sensitivity of system.
Preferably, using the reflected light signal of fiber Bragg grating (FBG) demodulator acquisition fiber grating, and it is converted into electric signal, and
Judge whether there is the reflectance signature of fiber grating in reflected impulse that this section receives, to judge whether there is light at the distance
Fine grating, has such as detected grating, by the relative time delay time of two photoswitches, that is, can determine the distance of the grating.
Preferably, by adjusting the on off delay of different high-speed optical switches two, each different location of optical cable is connected
Continuous detection, completes the identification and ranging of fiber grating on whole optical fiber.
Preferably, the optical power signals that fiber Bragg grating (FBG) demodulator detects are read in real time by logic controller, according to detection
The power of signal adjusts the attenuation amplitude of attenuator one and attenuator two in real time, by feedback control, so that (FBG) demodulator always may be used
To get stable optical power, so that the stability and accuracy of identification can be improved.
Preferably, logic controller can be according to the wave-length coverage of surveyed fiber grating, the filter of dynamic regulation tracking filter
Wave parameter may filter that the noise signal outside optic fiber grating wavelength range, to improve the signal-to-noise ratio of system.
Preferably for the fiber grating string with low reflected energy, such as remote fiber grating string, pass through logic
Controller dynamic reduces the optical power that attenuator one increases incident light, improves the reflected energy value of fiber grating, system can be improved
Identification sensitivity to low reflected energy grating.
Preferably for the fiber grating string with low reflected energy, such as remote fiber grating string, pass through logic
Controller dynamic reduces the optical power that attenuator two increases reflected light, and identification spirit of the system to low reflected energy grating can be improved
Sensitivity.
Preferably, the optical power that the reflection light obtains at fiber Bragg grating (FBG) demodulator are as follows:
Wherein, z is the position where fiber grating, Pg(z,λg) be fiber grating reflection signal, r (z, λg) it is reflection
Coefficient, Pi(λ) is the optical power distribution of incident light, this power is the function of wavelength X, Ps(z,λs) it is backward scattered in optical fiber
Penetrate signal, a (x, λg) be positive propagation unit length loss factor, d (x, λ) is back-scattering light unit length decaying system
Number, these three parameters are all using wavelength and distance as variable, λgIt is the center reflection wavelength of fiber grating to be measured.
System terminates the reflected energy in the light energy received comprising fiber grating with after to scattered in fiber Bragg grating (FBG) demodulator
Penetrate energy.In actual measurement, in order to more accurately react the reflection characteristic of fiber grating, removed from total reflection power backward
The optical power of scattering, back scattering optical power are determined by following formula:
In formula (2), k (λ) is fibre scattering coefficient, is the function of wavelength X, and a is the fiber core radius of optical fiber, Pi(λ) is
Input optical power spectrum, vgFor the light propagation group velocity in optical fiber.
Preferably, the optical power of the rear orientation light of fiber grating is calculated according to formula (2), it is total by what is received
Optical power subtracts the optical power of rear orientation light, and the optical power of fiber grating reflection can be obtained.
On the other hand, the present invention also provides a kind of low reflected energy fiber grating detection method, the method is applied to
It detects in the optical path with fiber grating string, which comprises
Step 1, setting high-speed optical switch one, high-speed optical switch two are converted incident light by high-speed optical switch one
For the detection light with fixed pulse width, the high-speed optical switch one opens a set time T；
Step 2, the detection light are reflected at each fiber grating, are formed reflected light, are controlled the high-speed optical switch
After two with the specific delays time, a set time T is opened, and receive the reflected light；It is incident in the delay time
The half of the transmission range of light in a fiber, the as distance of one-time detection；
The reflected light received is converted to electric signal by step 3, is demodulated to the reflected light received,
And carry out fiber grating string identification；
If step 4 identifies that this time the distance of detection is the fiber grating string institute with the presence of fiber grating string
Distance.
Preferably, the distance range according to the reflected light signal, detection that detect adjusts attenuation amplitude, to improve
The optical power of the reflected light.
Preferably, the wave-length coverage according to locating for the optical wavelength range of work and fiber grating string to be detected,
Dynamic adjustment filtering parameter, so that its centre frequency is at the wavelengths centered frequency of work, bandwidth meets the light to be detected
Fine grating string wave-length coverage.
The advantageous effects of the above technical solutions of the present invention are as follows:
1, the relative time delay of light is shone and received using high-speed optical switch control, and segmentation detection is carried out to the grating on optical fiber,
Can effectively avoid multiple fiber grating reflected lights mutually identify caused by superimposed crosstalk it is difficult；
2, by the reflection signal of the single fiber grating of reception of high-speed optical switch selectivity, low reflection can be effectively improved
The signal-to-noise ratio of the transmitting signal of the fiber grating of energy value, improves discrimination and accuracy, can effectively realize it is remote or have compared with
The identification and ranging of big attenuation grating；
3, measure fiber grating distance by shining and receiving light relative time delay, controlled by the high-precision time and when
Between measure, the accuracy of fiber grating ranging can be improved；
Detailed description of the invention
Fig. 1 is schematic structural view of the invention；
Fig. 2 is optical grating construction schematic diagram of the invention；
Fig. 3 is low reflected energy fiber grating reflectogram schematic diagram.
Wherein, in Fig. 1: 1- wideband light source, 2- high-speed optical switch one, 3- attenuator one, 4- circulator, 5- optical cable, 6- light
Fine grating string, 7- attenuator two, 8- high-speed optical switch two, 9- tracking filter, 10- (FBG) demodulator, 11- logic controller；
In Fig. 2,6-1- optical cable, 6-2,6-3,6-4 are fiber grating；
In Fig. 3: 3-1- fiber grating reflection spectrum.
Specific embodiment
To keep the technical problem to be solved in the present invention, technical solution and advantage clearer, below in conjunction with attached drawing and tool
Body embodiment is described in detail.Those skilled in the art should know following specific embodiments or specific embodiment are
The present invention is the set-up mode for the series of optimum that specific summary of the invention is explained further and enumerates, and those set-up modes
Between can be combined with each other or it is interrelated use, unless clearly proposing some of them or a certain in the present invention
Specific embodiment or embodiment can not be associated setting or be used in conjunction with other embodiments or embodiment.Meanwhile
Following specific embodiments or embodiment is only as the set-up mode optimized, and the protection model of the invention not as restriction
The understanding enclosed.
It additionally needs, it is noted that proposed by the invention for improving each of low reflected energy Grating examinations effect
Embodiment or method can carry out any combination or be applied in combination, for example, can will wherein it is any two or more
Kind of adjustment mode is used in combination with, to improve detection effect and system accuracy, can also only with single mode therein,
These above-mentioned combinations are split, and are regarded as falling under the scope of the present invention.
Below by way of each specific embodiment, it is described in detail to of the invention for preferred embodiment.With
Under each design parameter numerical value involved in each specific embodiment, only illustratively uses, to facilitate to present invention implementation
The explanation of mode is not intended as the restriction of the scope of the present invention.
Embodiment 1
In a specific embodiment, described the present invention provides a kind of low reflected energy fiber grating detection system
System includes: wideband light source, high-speed optical switch one, attenuator one, circulator, optical cable, fiber grating string, attenuator two, high speed
Photoswitch two, tracking filter, (FBG) demodulator and logic controller；
The wideband light source, high-speed optical switch one, attenuator one are connected with circulator；The (FBG) demodulator, tracking filter
Device, high-speed optical switch two, attenuator two are connected with circulator；The circulator is connected with optical cable, and the fiber grating is placed in light
In the optical fiber of cable；The logic controller respectively with wideband light source, high-speed optical switch one, attenuator one, attenuator two, high speed
Photoswitch two, tracking filter are connected with (FBG) demodulator, and to wideband light source, high-speed optical switch one, attenuator one, attenuator two,
These components of high-speed optical switch two, tracking filter and (FBG) demodulator carry out logic control；The fiber grating string is by multiple and different
The fiber grating of wavelength forms, and concatenation is in a fiber.
Preferably, emit light by described high-speed optical switch a pair to be controlled, form the detection of one section of fixed pulse width
Light, then by control high-speed light open the light two make-and-break time delay, the selective reflected light received after sometime delay
Pulse.Different time delays then corresponds to different reflective distances.
Preferably, wideband light source is sent out according to the distance of different detection ranges by the attenuator one, attenuator two
Light intensity out is adjusted, so that (FBG) demodulator can receive suitable reflective light intensity.
Preferably, logic controller reads the optical power signals that (FBG) demodulator detects in real time, according to the optical power signals
Power in real time adjust attenuator one and attenuator two attenuation amplitude, by feedback control, so that (FBG) demodulator can obtain always
Stable optical power is got, so that the stability and accuracy of identification can be improved.
Preferably, wave-length coverage of the logic controller according to surveyed fiber grating, the filtering of dynamic regulation tracking filter
Parameter filters out the noise signal outside optic fiber grating wavelength range, improves the signal-to-noise ratio of system.
Preferably for the fiber grating with low reflected energy, attenuator one and attenuator two are reduced by dynamic
Attenuation value increases the optical power of incident light and reflected light, improves identification sensitivity of the system to low reflected energy grating.
Preferably, the (FBG) demodulator is controlled by logic controller, according to wavelength model locating for fiber grating detected
It encloses, dynamic adjusts the wavelength detection parameter of (FBG) demodulator, guarantees the detectivity at target wavelength much higher than at other wavelength
Sensitivity, further increase the detection sensitivity of system.
Preferably, using the reflected light signal of fiber Bragg grating (FBG) demodulator acquisition fiber grating, and it is converted into electric signal, and
Judge whether there is the reflectance signature of fiber grating in reflected impulse that this section receives, to judge whether there is light at the distance
Fine grating, has such as detected grating, by the relative time delay time of two photoswitches, that is, can determine the distance of the grating.
Preferably, by adjusting the on off delay of different high-speed optical switches two, each different location of optical cable is connected
Continuous detection, completes the identification and ranging of fiber grating on whole optical fiber.
Preferably, the optical power signals that fiber Bragg grating (FBG) demodulator detects are read in real time by logic controller, according to detection
The power of signal adjusts the attenuation amplitude of attenuator one and attenuator two in real time, by feedback control, so that (FBG) demodulator always may be used
To get stable optical power, so that the stability and accuracy of identification can be improved.
Preferably, logic controller can be according to the wave-length coverage of surveyed fiber grating, the filter of dynamic regulation tracking filter
Wave parameter may filter that the noise signal outside optic fiber grating wavelength range, to improve the signal-to-noise ratio of system.
Preferably for the fiber grating string with low reflected energy, such as remote fiber grating string, pass through logic
Controller dynamic reduces the optical power that attenuator one increases incident light, improves the reflected energy value of fiber grating, system can be improved
Identification sensitivity to low reflected energy grating.
Preferably for the fiber grating string with low reflected energy, such as remote fiber grating string, pass through logic
Controller dynamic reduces the optical power that attenuator two increases reflected light, and identification spirit of the system to low reflected energy grating can be improved
Sensitivity.
Preferably, the optical power that the reflection light obtains at fiber Bragg grating (FBG) demodulator are as follows:
Wherein, z is the position where fiber grating, Pg(z,λg) be fiber grating reflection signal, r (z, λg) it is reflection
Coefficient, Pi(λ) is the optical power distribution of incident light, this power is the function of wavelength X, Ps(z,λs) it is backward scattered in optical fiber
Penetrate signal, a (x, λg) be positive propagation unit length loss factor, d (x, λ) is back-scattering light unit length decaying system
Number, these three parameters are all using wavelength and distance as variable, λgIt is the center reflection wavelength of fiber grating to be measured.
System terminates the reflected energy in the light energy received comprising fiber grating with after to scattered in fiber Bragg grating (FBG) demodulator
Penetrate energy.In actual measurement, in order to more accurately react the reflection characteristic of fiber grating, removed from total reflection power backward
The optical power of scattering, back scattering optical power are determined by following formula:
In formula (2), k (λ) is fibre scattering coefficient, is the function of wavelength X, and a is the fiber core radius of optical fiber, Pi(λ) is
Input optical power spectrum, vgFor the light propagation group velocity in optical fiber.
Preferably, the optical power of the rear orientation light of fiber grating is calculated according to formula (2), it is total by what is received
Optical power subtracts the optical power of rear orientation light, and the optical power of fiber grating reflection can be obtained.
Embodiment 2
In a specific embodiment of the invention, the structure of the embodiment gone out in conjunction with given in Fig. 1 of the present invention, with
The detection method of low reflected energy fiber grating is further described in one specific preferred embodiment.This method is applicable to light
In cable system, in a specific embodiment, as shown in Figure 1, the system includes wideband light source, optical splitter, high-speed optical switch
One, circulator, optical cable, fiber grating string, high-speed optical switch two, fiber Bragg grating (FBG) demodulator and logic controller.It is described to patrol
Volume controller (11) and wideband light source (1), fiber Bragg grating (FBG) demodulator (10), high-speed optical switch one (2), high-speed optical switch two (8),
Attenuator one (3) and attenuator two (7) are connected；Wideband light source (1) is connected with high-speed optical switch one (2)；High-speed optical switch
One (2) are connected with attenuator one (3)；Attenuator one (3) is connected with circulator (4) arrival end；Circulator (4) outlet end and light
Cable (5) is connected；Concatenated fiber grating string (6) on optical cable (5)；Circulator (4) time brings out mouth and is connected with attenuator two (7)；Attenuation
Device two (7) is connected with high-speed optical switch two (8)；High-speed optical switch two (8) is connected with tracking filter (9)；Tracking filter
(9) it is connected with fiber Bragg grating (FBG) demodulator (10).
In a specific embodiment, which can specifically be provided that system includes at least one wideband light source
(1), central wavelength 1550nm, bandwidth 20nm；High-speed optical switch one (2), central wavelength 1550nm, three dB bandwidth are
1.5nm；Attenuator one (4) drives optical fiber attenuation device, adjustable range 0-30db for TTL；Circulator (4) be used to reflected light into
Row light splitting；Optical cable (5), the transmission loss for 1550nm or so optical fiber are 0.25dB/km；Fiber grating string (6), Shuo Gezhong
Near a length of 1550nm of cardiac wave, and wavelength does not repeat, the fiber grating of the minimum 0.5nm in wavelength interval；Attenuator two (7), parameter
With attenuator one；High-speed optical switch two (8), central wavelength 1550nm, three dB bandwidth 1.5nm；Tracking filter (9), in
Cardiac wave a length of 1595nm, three dB bandwidth 2nm；Fiber Bragg grating (FBG) demodulator (10), detectable central wavelength are 1550nm, detection
Bandwidth is 20nm；Logic controller (11) is connected with each device and realizes control to it.
Fig. 3 is for the reflectogram of low reflected energy fiber grating, it can be seen that making an uproar in stray light and background in figure
On the signal waveform of sound, it is superimposed with the reflection signal for the fiber grating being an actually-received, as shown in figure medium wave peak.Usually
In real system, for low reflected energy grating, such as distance farther out or among optical fiber there are in the case where larger attenuation,
In the fiber Bragg grating reflected signal that receiving end detects, often very little, meeting be flooded by noise signals such as this land clutters, so away from
It is more difficult to be detected from remoter grating.
In a specific embodiment, the logic controller in system starts light source first and issues incident light, incident light
By high-speed optical switch a period of time, photoswitch is only opened the very short time, such as 500 picoseconds, then will form one section of about 15cm long
Incident light, which can be reflected at each fiber grating, form reflected light.Then, logic controller control is high
After fast photoswitch two is relative to same service time is opened after the time-delay after the service time of high-speed optical switch one
(500 picoseconds) shutdowns.The half of the transmission range of the opening time-delaying time corresponding incident light of two photoswitches in a fiber,
The distance as this time detected.
Then, reflected light signal is converted into corresponding electric signal by fiber Bragg grating (FBG) demodulator, is solved to the light received
It adjusts, and carries out the identification of fiber grating, if identified with the presence of fiber grating, this detection range is the optical fiber light
Distance locating for grid.The fiber Bragg grating reflected signal within the scope of a small distance is only detected every time due to system, thus effectively
Avoid the mutual superimposed crosstalk of the multiple reflection signal of multiple gratings on optical fiber, to reduce the difficulty of signal identification,
Improve accuracy of identification.
In a specific embodiment, in order to improve the sensitivity of system, enhance to low reflected energy fiber grating
Detectivity automatically can further optimize system parameter, specifically:
Detection for remote grating, the reflection detected by logic control element according to fiber Bragg grating (FBG) demodulator
Optical signal, in conjunction with the distance range detected, dynamic adjusts attenuator one, reduces its attenuation amplitude, to increase the strong of incident light
Degree, the optical power of fiber grating reflected light can be improved in this way, improve the resolution ratio of detection；
Detection for remote grating, the reflection detected by logic control element according to fiber Bragg grating (FBG) demodulator
Optical signal reduces its attenuation amplitude by logic control element dynamic adjustment attenuator two in conjunction with the distance range detected, with
The intensity for increasing reflected light, equally can be improved the resolution ratio of the detection of system；
By the adjustment of two above attenuator parameter, guarantee available to sufficient intensity at fiber Bragg grating (FBG) demodulator
Fiber Bragg grating reflected signal, so as to be identified to signal；
In a specific embodiment, system can wave-length coverage according to work and fiber grating to be detected
Locating wave-length coverage, dynamic adjusts the filtering parameter of tracking filter, so that its centre frequency is in the wavelengths centered of work
At frequency, bandwidth meets the system optic fiber grating wavelength range to be detected.So as to filter out the noise in reflection signal
Signal improves the resolution ratio of system.
Embodiment 3
In another specific embodiment, the present invention also provides a kind of low reflected energy fiber grating detection method,
The method, which is applied to detection, to be had in the optical path of fiber grating string, is readily applicable to such as above-described embodiment 1 and embodiment 2
In given detection system.The described method includes:
Step 1, setting high-speed optical switch one, high-speed optical switch two are converted incident light by high-speed optical switch one
For the detection light with fixed pulse width, the high-speed optical switch one opens a set time T；
Step 2, the detection light are reflected at each fiber grating, are formed reflected light, are controlled the high-speed optical switch
After two with the specific delays time, a set time T is opened, and receive the reflected light；It is incident in the delay time
The half of the transmission range of light in a fiber, the as distance of one-time detection；
The reflected light received is converted to electric signal by step 3, is demodulated to the reflected light received,
And carry out fiber grating string identification；
If step 4 identifies that this time the distance of detection is the fiber grating string institute with the presence of fiber grating string
Distance.
Preferably, the distance range according to the reflected light signal, detection that detect adjusts attenuation amplitude, to improve
The optical power of the reflected light.
Preferably, the wave-length coverage according to locating for the optical wavelength range of work and fiber grating string to be detected,
Dynamic adjustment filtering parameter, so that its centre frequency is at the wavelengths centered frequency of work, bandwidth meets the light to be detected
Fine grating string wave-length coverage.
Preferably, the optical power that the reflection light obtains at fiber Bragg grating (FBG) demodulator are as follows:
Wherein, z is the position where fiber grating, Pg(z,λg) be fiber grating reflection signal, r (z, λg) it is reflection
Coefficient, Pi(λ) is the optical power distribution of incident light, this power is the function of wavelength X, Ps(z,λs) it is backward scattered in optical fiber
Penetrate signal, a (x, λg) be positive propagation unit length loss factor, d (x, λ) is back-scattering light unit length decaying system
Number, these three parameters are all using wavelength and distance as variable, λgIt is the center reflection wavelength of fiber grating to be measured.
System terminates the reflected energy in the light energy received comprising fiber grating with after to scattered in fiber Bragg grating (FBG) demodulator
Penetrate energy.In actual measurement, in order to more accurately react the reflection characteristic of fiber grating, removed from total reflection power backward
The optical power of scattering, back scattering optical power are determined by following formula:
In formula (2), k (λ) is fibre scattering coefficient, is the function of wavelength X, and a is the fiber core radius of optical fiber, Pi(λ) is
Input optical power spectrum, vgFor the light propagation group velocity in optical fiber.
Preferably, the optical power of the rear orientation light of fiber grating is calculated according to formula (2), it is total by what is received
Optical power subtracts the optical power of rear orientation light, and the optical power of fiber grating reflection can be obtained.
The above is a preferred embodiment of the present invention, it is noted that for those skilled in the art
For, without departing from the principles of the present invention, several improvement can also be made, these improvement also should be regarded as this hair
Bright protection scope.
Claims (10)
1. a kind of low reflected energy fiber grating detection system, which is characterized in that the system includes: wideband light source, high-speed light
Switch one, attenuator one, circulator, optical cable, fiber grating string, attenuator two, high-speed optical switch two, tracking filter, demodulation
Instrument and logic controller；
The wideband light source, high-speed optical switch one, attenuator one are connected with circulator；The (FBG) demodulator, tracking filter, high speed
Photoswitch two, attenuator two are connected with circulator；The circulator is connected with optical cable, and the fiber grating is placed in the optical fiber of optical cable
In；The logic controller respectively with wideband light source, high-speed optical switch one, attenuator one, attenuator two, high-speed optical switch two,
Tracking filter is connected with (FBG) demodulator, and carries out logic control to these components；The fiber grating string is by multiple and different wavelength
Fiber grating composition, concatenation in a fiber.
2. the system as claimed in claim 1, which is characterized in that light is emitted by described high-speed optical switch a pair and is controlled,
Form the detection light of one section of fixed pulse width, then by control high-speed light open the light two make-and-break time delay, selective reception
Reflection light pulse after being sometime delayed.
3. the system as claimed in claim 1, which is characterized in that by the attenuator one, attenuator two, according to different detections
The distance of distance, the light intensity issued to wideband light source is adjusted, so that (FBG) demodulator can receive suitable reflective light intensity.
4. the system as claimed in claim 1, it is characterised in that: logic controller reads the optical power that (FBG) demodulator detects in real time
Signal adjusts the attenuation amplitude of attenuator one and attenuator two in real time according to the power of the optical power signals, is controlled by feedback
System, so that (FBG) demodulator is available always to arrive stable optical power, so that the stability and accuracy of identification can be improved.
5. the system as claimed in claim 1, it is characterised in that: logic controller according to the wave-length coverage of surveyed fiber grating,
The filtering parameter of dynamic regulation tracking filter filters out the noise signal outside optic fiber grating wavelength range, improves the letter of system
It makes an uproar ratio.
6. the system as claimed in claim 1, it is characterised in that: for the fiber grating with low reflected energy, pass through dynamic
Reduce the attenuation value of attenuator one and attenuator two, increase the optical power of incident light and reflected light, improves system to low reflection energy
Measure the identification sensitivity of grating.
7. the system as claimed in claim 1, it is characterised in that: the (FBG) demodulator is controlled by logic controller, according to being detected
Fiber grating locating for wave-length coverage, dynamic adjust (FBG) demodulator wavelength detection parameter, guarantee the detection at target wavelength
Sensitivity further increases the detection sensitivity of system much higher than the sensitivity at other wavelength.
8. a kind of low reflected energy fiber grating detection method, the method is applied to the optical path that detection has fiber grating string
In, which is characterized in that the described method includes:
Step 1, setting high-speed optical switch one, high-speed optical switch two, by high-speed optical switch one, convert incident light into for
The detection light of fixed pulse width, the high-speed optical switch one open a set time T；
Step 2, the detection light are reflected at each fiber grating, formed reflected light, control the high-speed optical switch two with
After one specific delays time, a set time T is opened, and receive the reflected light；In the delay time, incident light is in light
The half of transmission range in fibre, the as distance of one-time detection；
The reflected light received is converted to electric signal by step 3, is demodulated, is gone forward side by side to the reflected light received
The identification of row fiber grating string；
If step 4, identified with the presence of fiber grating string, this time distance of detection be where the fiber grating string away from
From.
9. according to the method described in claim 8, it is characterized in that, according to detect the reflected light signal, detection away from
From range, attenuation amplitude is adjusted, to improve the optical power of the reflected light.
10. according to the method described in claim 8, it is characterized in that, according to the optical wavelength range of work and to be detected
Fiber grating string locating for wave-length coverage, dynamic adjust filtering parameter so that its centre frequency is in the wavelengths centered of work
At frequency, bandwidth meets the fiber grating string wave-length coverage to be detected.
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