CN102980601B - Demodulating device and method for optical fiber Young interference optical path difference based on low coherent interference - Google Patents

Abstract

The invention discloses a demodulating device for an optical fiber Young interference optical path difference based on low coherent interference. The demodulating device comprises a wideband light source, a 3dB coupler, a sensing interferometer, a demodulating interferometer, a calibration interferometer and a line array camera, wherein a multimode optical fiber is adopted in a light path formed by the components in sequence for optical signal transmission. A demodulating method mainly comprises the steps of optical path difference sensing, optical path difference demodulating and optical path difference calibration. Compared with the prior art, the demodulating device and the method integrate modes of space scanning and time scanning to conduct low coherent interference optical path difference demodulating; no mechanical movement is available; the stability is high; compared with the time scanning, the demodulating precision is not affected by moving precision of a scanning motor; the nano-level high precision demodulating can be realized; the optical path difference calibration of an overall system is realized by adjusting the optical path difference; in addition, a nano displacement platform is adopted to control the output optical path difference effectively; an optical path difference demodulating interval of the overall system is amended; and with the adoption of an optical fiber interferometer structural form, the system adjustment is facilitated and the working stability is high.

Description

Based on optical fiber Mechanical Study On Young Interference optical path difference demodulating equipment and the method for low coherence interference

Technical field

The present invention relates in sensory field of optic fibre, particularly relate to a kind of optical path difference demodulation method and device.

Background technology

Low coherence interference technology is used for its principle of optical path difference demodulation and is, demodulated interferential instrument optical path difference and sensing interferometer optical path difference is utilized to carry out scan matching, under the condition that both optical path differences are strictly mated, export the strongest low coherence interference signal, realize the high precision demodulation of optical path difference to be measured finally by the mode of accurately locating low coherence interference signal envelope peak value.

Low coherence interference technology mainly contains time scan formula and spacescan formula as optical path difference demodulation method.Time scan formula is that optical path difference changes scanning in time.As (Parallel demodulation system andsignal-processing method for extrinsic Fabry-Perot interferometer and fiber Bragg gratingsensors such as Junfeng Jiang, Optics Letters, 2005,30:604-606) by the movement of a wherein arm of Electric Machine Control Michelson interferometer, carry out optical path scanning, thus match optical path difference to be measured.Spacescan formula is that optical path difference linearly distributes along locus, utilizes line-scan digital camera to receive the spacescan realizing optical path difference.As J.Schwider (White-lightFizeau interferometer, Applied Optics, 1997,36:1433-1437) in 1997, Fizeau white light interferometer structure is proposed, the wedge utilizing Fizeau interferometer to form realizes optical path difference space distribution.(the Marshall such as Marshall, R., et al., A novel electronically scanned white-light interferometer using aMach-Zehnder approach.Lightwave Technology, Journal of, 1996.14 (3): 397-402) proposed to adopt Mach-Zehnder interferometer structure to realize the space distribution of optical path difference in 1996.

Although time scan formula measurement range is large, there is mechanical motion in system, if Long-Time Service stability and measuring accuracy all affect by it, measuring accuracy is relatively low can only in micron dimension.Spacescan formula mechanical is moved, and Long-Time Service stability is high, and its demodulation accuracy mainly affects by line-scan digital camera pixel number, and measuring accuracy can reach nanometer scale.But spatial light path difference sweep limit limits by system architecture, and measurement range is little.

Summary of the invention

For overcoming the deficiencies in the prior art, the present invention proposes a kind of optical fiber Mechanical Study On Young Interference optical path difference demodulating equipment based on low coherence interference and method, carry out the demodulation of low coherence interference optical path difference in conjunction with spacescan mode and time scan mode, optical path difference demodulation method of the present invention also can be used for realizing high-precision sensing and the demodulation that displacement, pressure, strain, temperature, refractive index etc. can be converted into the physical quantity of optical path difference change.

The present invention proposes a kind of optical fiber Mechanical Study On Young Interference optical path difference demodulating equipment based on low coherence interference, this demodulating equipment comprises wideband light source, three-dB coupler, sensing interferometer, demodulated interferential instrument, corrects interferometer and line-scan digital camera, multimode optical fiber is adopted to carry out optical signal transmission between the light path that each parts sequentially form, it is characterized in that, described sensing interferometer adopts Michelson interferometer, and demodulated interferential instrument adopts optical fiber Young's interferometer and corrects interferometer and adopts the adjustable Mach Zehnder interferometer of optical path difference:

The light that wideband light source sends is divided into two-way light by 2 × 2 three-dB couplers, two-way light is respectively by crossing Michelson interferometer arm and No. two arms, and after being reflected by Michelson interferometer arm reflection end face and No. two arm reflection end faces respectively, again by 2 × 2 three-dB coupler synthesis light beams, and be transferred to 2 × 1 three-dB couplers, light is divided into two-way by 2 × 13dB coupling mechanism again, is respectively Mach Zehnder interferometer arm and No. two arms; The optical path difference means for correcting be present on Mach Zehnder interferometer arm comprises the first GRIN Lens, the second GRIN Lens, nanometer displacement platform: the Space Collimation light beam exported by the first GRIN Lens, after propagating a segment distance in atmosphere, get back among multimode optical fiber by the second GRIN Lens, mobile nanometer displacement platform changes the aerial propagation distance of Space Collimation light beam, thus regulates Mach Zehnder interferometer optical path difference; Mach Zehnder interferometer two-arm optical fiber connector side by side, is fixed by fiber array, forms optical fiber Young's interferometer; Fiber end face overlaps with the cylindrical mirror focal plane after fiber array, and received by line-scan digital camera by the light of cylindrical mirror compression in light belt, the optical path difference on line-scan digital camera receiving plane linearly distributes, and realizes the scanning of optical path difference spatial linear.

Described demodulated interferential instrument replaces with optical fiber Fabry-Perot interferometer: the light along Optical Fiber Transmission reflects in optical fiber Fabry-Perot interferometer fiber end face generating portion, is formed with reference to reflected light; Transmitted light by with fiber end face distance, delta L ₂catoptron reflection after be again coupled to optical fiber, form sensory reflex light, after reflected light and sensory reflex light compositing light beam, contain 2 Δ L ₂optical path difference information, change catoptron distance fiber end face distance, namely change optical path difference sensing amount.

According to the photosensitive requirement of line-scan digital camera, described wideband light source selects white LED light source, Halogen lamp LED, xenon lamp or ASE light source.

Described three-dB coupler selects multi-module optical fiber coupler, and described line-scan digital camera selects linear array CCD camera.In addition, according to selection light source spectral band, select other line-scan digital cameras, have linear array CMOS, linear array Gallium indium arsenide photodetector.

The invention allows for a kind of optical fiber Mechanical Study On Young Interference optical path difference demodulation method based on low coherence interference, it is characterized in that, the method comprises the following steps:

Step one, the light sent by wideband light source is divided into two-way light by 2 × 2 three-dB couplers, respectively through Michelson interferometer arm and No. two arms, after two-way light is reflected by Michelson interferometer arm reflection end face and No. two arm reflection end faces respectively, again by 2 × 2 three-dB couplers synthesis light beams; Optical path difference information 2 Δ L will be there is in reflected light ₁be transferred to 2 × 1 three-dB couplers, realize optical path difference sensing;

Step 2, is divided into two-way by the reflected light in step one by 2 × 1 three-dB coupler light, obtains light path corresponding to two-arm respectively through Mach Zehnder interferometer arm and No. two arms; Following operation is performed: after the Space Collimation light beam that the first GRIN Lens exports propagates a segment distance in atmosphere by being present in the optical path difference means for correcting that Mach Zehnder interferometer arm is made up of the first GRIN Lens, the second GRIN Lens, nanometer displacement platform, get back among multimode optical fiber by the second GRIN Lens, mobile nanometer displacement platform changes the aerial propagation distance of Space Collimation light beam, thus regulates Mach Zehnder interferometer arm light path; Through aforementioned operation, output optical signal and optical path difference information thereof;

Step 3, the optical fiber connector of Mach Zehnder interferometer arm and No. two arms to be fixed by fiber array side by side, form Young's interferometer: Mach Zehnder interferometer fiber end face overlaps with the cylindrical mirror focal plane after fiber array; Received by line-scan digital camera by the light of cylindrical mirror compression in light belt; Two optical fiber connector spacing are d, and the distance of fiber end face range line array camera is D, the light overlapping region that two-beam outputs to line-scan digital camera produces final interference fringe, and is received by line-scan digital camera; Under d is far smaller than D condition, optical path difference linearly distributes on light overlapping region, meets formula:

Δ＝xd/D，

Wherein x represents corresponding line-scan digital camera position;

Step 4, carries out the correction of interference light path difference, optical path difference is expressed as: Δ '=2 Δ L ₁-(l ₁-l ₂)-xd/D, l ₁, l ₂represent Mach Zehnder interferometer arm and No. two arms respectively;

When Δ '=0, corresponding x position, exports low coherence interference signal envelope peak value; After correction interferometer has adjusted, l ₁-l ₂for constant, x is with Δ L ₁and change, and there is one-to-one relationship, by accurately locating x value, the high precision demodulation of optical path difference to be measured can be realized.

Described step 4 also comprises: regulate the distance l between Mach Zehnder interferometer arm and No. two arm two brachiums ₁-l ₂, realize the interval demodulation of different optical path difference.

Described step one adopts optical fiber Fabry-Perot interferometer to realize optical path difference sensing, and its interference light path difference sensing routine comprises following operation:

The light sent by wideband light source is by 2 × 2 three-dB couplers, and the light along Optical Fiber Transmission reflects in fiber end face generating portion, is formed with reference to reflected light; Transmitted light by with fiber end face distance, delta L ₂catoptron reflection after be again coupled to optical fiber, form sensory reflex light, after reflected light and sensory reflex light compositing light beam, contain 2 Δ L ₂optical path difference information, change catoptron distance fiber end face distance, namely change optical path difference sensing amount.

Compared with prior art, the mode that present invention incorporates spacescan and time scan carries out the demodulation of low coherence interference optical path difference:

1, in demodulated interferential instrument part, adopt Mechanical Study On Young Interference to form the spatial linear distribution scanning of optical path difference, the low coherence interference striped that line-scan digital camera exports after directly receiving optical path scanning, mechanical is moved, and stability is high.Compared to time scan, this Demodulation Systems precision does not affect by scan module mobile accuracy, selective system parameter, realizes the high precision demodulation of nanometer scale;

2, in correction interferometer part, by regulating the optical path difference of a Mach Zehnder interferometer wherein arm, the object that whole system optical path difference is corrected is realized.Effectively controlled the output optical path difference of Mach Zehnder interferometer by high-precision nanometer displacement platform, be added in whole system, the optical path difference demodulation revising whole system is interval;

3, adopt fibre optic interferometer structural shape, system fading margin is convenient, and job stability is high.

Accompanying drawing explanation

Fig. 1 is the optical fiber Mechanical Study On Young Interference optical path difference demodulating equipment figure based on low coherence interference;

Fig. 2 is Michelson sensing interferometer two-arm optical path difference schematic diagram;

Fig. 3 is Fa-Po sensing interferometer two-arm optical path difference schematic diagram;

Fig. 4 is Young demodulated interferential instrument optical path difference space distribution scanning demodulation schematic diagram;

Fig. 5 is the low coherence interference striped normalization simulation light intensity curve that system exports;

Fig. 6 is that Mach Zehnder corrects interferometer two-arm optical path difference correction schematic diagram;

Fig. 7 is system optical path scanning scope and sweep interval correction analysis schematic diagram.

In figure, 1, wideband light source, 2, 2 × 2 three-dB couplers, 3, Michelson interferometer No. 1 arm, 4, Michelson interferometer arm reflection end face, 5, Michelson interferometer No. two arms, 6, Michelson interferometer No. 2 arm reflection end faces, 7, 2 × 1 three-dB couplers, 8, Mach Zehnder interferometer arm, 9, Mach Zehnder interferometer No. two arms, 10, first GRIN Lens, 11, second GRIN Lens, 12, Space Collimation light beam, 13, nanometer displacement platform, 14, fiber array, 15, line-scan digital camera, 16, light overlapping region, 17, fiber end face (Fabry-Perot Interferometer first reflecting surface), 18, reflection end face (Fabry-Perot Interferometer second reflecting surface), 19, Fabry-Perot Interferometer first folded light beam, 20, Fabry-Perot Interferometer second folded light beam.21, line-scan digital camera position, 22, Mach Zehnder interferometer optical path difference, 23, Young's interferometer optical path difference, 24, system scan optical path difference, 25, Mach Zehnder interferometer optical path difference distribution curve, 26, Young's interferometer optical path difference distribution curve, the demodulation low coherence interference striped simulation light intensity curve that 27, first optical path difference is corresponding, 28, the demodulation low coherence interference striped simulation light intensity curve that second optical path difference is corresponding, 29, cylindrical mirror.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in detail, if these embodiments exist exemplary content, should not be construed to limitation of the present invention.

Embodiment 1: based on the optical fiber Mechanical Study On Young Interference optical path difference demodulating equipment of low coherence interference

This system element comprises wideband light source, three-dB coupler, sensing interferometer, demodulated interferential instrument, corrects interferometer and the large parts of line-scan digital camera six, adopts multimode optical fiber to carry out optical signal transmission between each parts.

As shown in Figure 1, the light that wideband light source 1 sends is divided into two-way light by 2 × 2 three-dB couplers 2, two-way light is respectively through Michelson interferometer No. 1 arm 3 and No. 2 arms 5, after being reflected by Michelson interferometer No. 1 arm reflection end face 4 and No. 2 arm reflection end faces 6 respectively, again by the 2-in-1 one-tenth light beam of 2 × 2 three-dB coupler, and be transferred to 2 × 1 three-dB couplers 7; Light is divided into two-way by 2 × 1 three-dB couplers 7 again, respectively through Mach Zehnder interferometer arm 8 and No. two arms 9, the optical path difference means for correcting be arranged on Mach Zehnder interferometer No. 1 arm 8 comprises the first GRIN Lens 10, second GRIN Lens 11, nanometer displacement platform 13.The Space Collimation light beam 12 exported by the first GRIN Lens 10, after propagating a segment distance in atmosphere, get back among multimode optical fiber by the second GRIN Lens 11, mobile nanometer displacement platform 13 changes the aerial propagation distance of Space Collimation light beam 12, thus regulates Mach Zehnder interferometer optical path difference.The optical fiber connector of this two-arm side by side, is fixed by fiber array 14, forms optical fiber Young's interferometer.Fiber end face overlaps with cylindrical mirror 29 focal plane after fiber array 14, and the light compressed in light belt by cylindrical mirror 29 is received by line-scan digital camera 15, and the optical path difference on line-scan digital camera 15 receiving plane linearly distributes, and realizes the scanning of optical path difference spatial linear.

Element in above-mentioned demodulating equipment is specially:

Wideband light source, according to the photosensitive requirement of line-scan digital camera, selects white LED light source, Halogen lamp LED, xenon lamp, ASE light source;

Three-dB coupler, selects multi-module optical fiber coupler, plays divided beams and the effect of closing light beam;

Sensing interferometer, produces optical path difference to be measured, selects Michelson interferometer and Fabry-Perot Interferometer as sensing interferometer;

Demodulated interferential instrument, adopts optical fiber Young's interferometer, utilizes its optical path difference spatial characteristics, scan matching optical path difference to be measured.Its optical fiber exports rear end and places cylindrical mirror, and fiber end face is positioned at cylindrical mirror focus place, and cylindrical mirror effect is by optical pressure contracting in a light belt, and raising back end of line array camera is to light signal receiving efficiency;

Correct interferometer: adopt optical path difference adjustable Mach Zehnder interferometer, regulate the sweep limit that to distribute with the demodulated interferential instrument optical path difference correcting rear end, make it cover the variation range of optical path difference to be measured completely;

Line-scan digital camera: select linear array CCD camera.In addition, according to selection light source spectral band, select other line-scan digital cameras, have linear array CMOS, linear array Gallium indium arsenide photodetector is selective.

Embodiment 2: based on the optical fiber Mechanical Study On Young Interference optical path difference method for sensing of low coherence interference

Based on Optical Fiber Michelson Interferometer optical path difference method for sensing as shown in Figure 2, light is divided into two-way by 2 × 2 three-dB couplers 2, be input to Michelson interferometer arm 3 and No. two arms 5 respectively, and after two-arm end face reflects respectively, again synthesize light beam, now, make in light signal, to contain 2 Δ L due to the difference of two brachiums ₁optical path difference information, change the length of wherein one arm, namely change optical path difference sensing amount.Except adopting Optical Fiber Michelson Interferometer, optical fiber Fabry-Perot interferometer is applicable equally, as shown in Figure 3: the light along Optical Fiber Transmission reflects in fiber end face 17 generating portion, is formed with reference to reflected light 19.Transmitted light is again coupled to optical fiber after reflecting with the catoptron 18 of fiber end face 17 distance, delta L2, form sensory reflex light 20, after synthesizing light beam with reference to reflected light 19 and sensory reflex light 20, contain the optical path difference information of 2 Δ L2, change catoptron 18 apart from the distance of fiber end face 17, namely change optical path difference sensing amount.The method is applicable to the sensing of any physical quantity that can be converted into optical path difference change, such as displacement, pressure, temperature, refractive index etc.

Embodiment 3: based on the optical fiber Mechanical Study On Young Interference optical path difference demodulation method of low coherence interference

As shown in Figure 4, optical fiber Young's interferometer two optical fiber connector spacing is d, and the distance of fiber end face range line array camera is D, the light overlapping region 16 that two-beam outputs to line-scan digital camera 15 produces final interference fringe, and is received by line-scan digital camera 15.Under d is far smaller than D condition, optical path difference linearly distributes on light overlapping region 16, meets formula: Δ=xd/D, wherein x represents position.Then demodulation low coherence interference striped normalization light intensity can be expressed as:

$I(\mathrm{\λ},x)={\∫}_{-\∞}^{+\∞}S\left(\mathrm{\λ}\right)\·[1-\cos \left(\frac{2\mathrm{\πxd}/D}{\mathrm{\λ}}\right)]\·[1-\cos \left(\frac{4\mathrm{\π\Δ}{L}_1}{\mathrm{\λ}}\right)]\mathrm{d\λ}---\left(1\right)$

In above formula: λ represents wavelength, x represents corresponding line-scan digital camera position, and d represents optical fiber pitch, and D represents fiber end face and line-scan digital camera distance, Δ L ₁represent to be measured, S (λ) represents light source light spectrum function.

Suppose that the spectrum of light source is Gaussian function, then the low coherence interference striped normalization light intensity curve that exports of above formula (1) as shown in Figure 5, wherein horizontal ordinate represents line-scan digital camera 15 position x, curve 27,28 represents the demodulation low coherence interference striped light intensity curve that two different optical path differences are corresponding respectively, and low coherence interference fringe envelope peak corresponds respectively to line-scan digital camera 15 position x1, x2.X is with Δ L ₁and change, and there is one-to-one relationship, by accurately locating x value, the high precision demodulation of optical path difference to be measured can be realized.

Embodiment 4: based on the optical fiber Mechanical Study On Young Interference optical path difference bearing calibration of low coherence interference

System adopts optical fiber mach Zehnder interferometer to realize optical path difference and corrects, and as shown in Figure 6, Mach Zehnder interferometer arm 8 and No. two arms 9 have corresponding light path respectively.The optical path difference means for correcting be present on an arm 8 is made up of number one GRIN Lens 10, second GRIN Lens 11, nanometer displacement platform 13.The specific practice of optical path difference bearing calibration is: the Space Collimation light beam exported by the first GRIN Lens 10, after propagating a segment distance in atmosphere, get back among multimode optical fiber by the second GRIN Lens 11, mobile nanometer displacement platform 13 changes the aerial propagation distance of Space Collimation light beam 12, thus regulates Mach Zehnder interferometer No. 1 arm light path.Light is by after Mach Zehnder interferometer, and output optical signal adds the optical path difference information of Mach Zehnder interferometer two-arm light path again.The optical path difference of whole system can be expressed as:

Δ′＝2ΔL ₁-(l ₁-l ₂)-xd/D (2)

When Δ '=0, have:

2ΔL ₁＝(l ₁-l ₂)-xd/D (3)

Now, corresponding x position, exports low coherence interference signal envelope peak value.X by 0 to x ₀change, the optical path scanning scope of correspondence system is (l ₁-l ₂) to (l ₁-l ₂)-x ₀d/D.As shown in Figure 7, Young's interferometer carries out optical path scanning for system optical path scanning scope and sweep interval correction analysis, and Mach Zehnder interferometer is introduced optical path difference and is biased, by controlling the bias lighting path difference (l that Mach Zehnder interferometer produces ₁-l ₂), realize the scanning of different optical path difference interval.In addition, by effectively controlling optical path difference amount of bias, make each amount of bias for scanning maximum optical path difference integral multiple, i.e. (l ₁-l ₂)=nx ₀d/D, can make different optical path scanning interval end to end, realizes the object of optical path scanning scope expansion.

Claims (7)

1. the optical fiber Mechanical Study On Young Interference optical path difference demodulating equipment based on low coherence interference, this demodulating equipment comprises wideband light source, three-dB coupler, sensing interferometer, demodulated interferential instrument, corrects interferometer and line-scan digital camera, multimode optical fiber is adopted to carry out optical signal transmission between the light path that each parts sequentially form, it is characterized in that, described sensing interferometer adopts Michelson interferometer, described demodulated interferential instrument adopts optical fiber Young's interferometer, and described correction interferometer adopts the adjustable Mach Zehnder interferometer of optical path difference:

The light that wideband light source sends is divided into two-way light by 2 × 2 three-dB couplers, two-way light is respectively by Michelson interferometer arm and No. two arms, and after being reflected by Michelson interferometer arm reflection end face and No. two arm reflection end faces respectively, again by 2 × 2 three-dB coupler synthesis light beams, and be transferred to 2 × 1 three-dB couplers, light is divided into two-way by 2 × 1 three-dB couplers again, is respectively Mach Zehnder interferometer arm and No. two arms; The optical path difference means for correcting be present on Mach Zehnder interferometer arm comprises the first GRIN Lens, the second GRIN Lens, nanometer displacement platform: the Space Collimation light beam exported by the first GRIN Lens, after propagating a segment distance in atmosphere, get back among multimode optical fiber by the second GRIN Lens, mobile nanometer displacement platform changes the aerial propagation distance of Space Collimation light beam, thus regulates Mach Zehnder interferometer optical path difference; Mach Zehnder interferometer two-arm optical fiber connector side by side, is fixed by fiber array, forms optical fiber Young's interferometer; Fiber end face overlaps with the cylindrical mirror focal plane after fiber array, and received by line-scan digital camera by the light of cylindrical mirror compression in light belt, the optical path difference on line-scan digital camera receiving plane linearly distributes, and realizes the scanning of optical path difference spatial linear.

2. as claimed in claim 1 based on the optical fiber Mechanical Study On Young Interference optical path difference demodulating equipment of low coherence interference, it is characterized in that, described sensing interferometer replaces with optical fiber Fabry-Perot interferometer: the light along Optical Fiber Transmission reflects in optical fiber Fabry-Perot interferometer fiber end face generating portion, is formed with reference to reflected light; Transmitted light by with fiber end face distance, delta L ₂catoptron reflection after be again coupled to optical fiber, form sensory reflex light, after reflected light and sensory reflex light compositing light beam, contain 2 Δ L ₂optical path difference information, change catoptron distance fiber end face distance, namely change optical path difference sensing amount.

3. as claimed in claim 1 or 2 based on the optical fiber Mechanical Study On Young Interference optical path difference demodulating equipment of low coherence interference, it is characterized in that, according to the photosensitive requirement of line-scan digital camera, described wideband light source selects white LED light source, Halogen lamp LED, xenon lamp or ASE light source.

4. as claimed in claim 1 or 2 based on the optical fiber Mechanical Study On Young Interference optical path difference demodulating equipment of low coherence interference, it is characterized in that, described three-dB coupler selects multi-module optical fiber coupler, and described line-scan digital camera selects linear array CCD camera; In addition, according to selection light source spectral band, select other line-scan digital cameras, have linear array CMOS, linear array Gallium indium arsenide photodetector.

5., based on an optical fiber Mechanical Study On Young Interference optical path difference demodulation method for low coherence interference, it is characterized in that, the method comprises the following steps:

Step one, the light sent by wideband light source is divided into two-way light by 2 × 2 three-dB couplers, respectively through Michelson interferometer arm and No. two arms, after two-way light is reflected by Michelson interferometer arm reflection end face and No. two arm reflection end faces respectively, again by 2 × 2 three-dB couplers synthesis light beams; Optical path difference information 2 Δ L will be there is in reflected light ₁be transferred to 2 × 1 three-dB couplers, realize optical path difference sensing;

Step 2, is divided into two-way by the reflected light in step one by 2 × 1 three-dB coupler light, obtains light path corresponding to two-arm respectively through Mach Zehnder interferometer arm and No. two arms; Following operation is performed: after the Space Collimation light beam that the first GRIN Lens exports propagates a segment distance in atmosphere by being present in the optical path difference means for correcting that Mach Zehnder interferometer arm is made up of the first GRIN Lens, the second GRIN Lens, nanometer displacement platform, get back among multimode optical fiber by the second GRIN Lens, mobile nanometer displacement platform changes the aerial propagation distance of Space Collimation light beam, thus regulates Mach Zehnder interferometer arm light path; Through aforementioned operation, output optical signal and optical path difference information thereof;

Step 3, the optical fiber connector of Mach Zehnder interferometer arm and No. two arms to be fixed by fiber array side by side, form Young's interferometer: Mach Zehnder interferometer fiber end face overlaps with the cylindrical mirror focal plane after fiber array; Received by line-scan digital camera by the light of cylindrical mirror compression in light belt; Two optical fiber connector spacing are d, and the distance of fiber end face range line array camera is D, the light overlapping region that two-beam outputs to line-scan digital camera produces final interference fringe, and is received by line-scan digital camera; Under d is far smaller than D condition, optical path difference linearly distributes on light overlapping region, meets formula:

Δ＝xd/D，

Wherein x represents corresponding line-scan digital camera position;

Step 4, carries out the correction of interference light path difference, optical path difference is expressed as: Δ '=2 Δ L ₁-(l ₁-l ₂)-xd/D, l ₁, l ₂represent Mach Zehnder interferometer arm and No. two arms respectively;

When Δ '=0, corresponding x position, exports low coherence interference signal envelope peak value; After correction interferometer has adjusted, l ₁-l ₂for constant, x is with Δ L ₁and change, and there is one-to-one relationship, by accurately locating x value, the high precision demodulation of optical path difference to be measured can be realized.

6. as claimed in claim 5 based on the optical fiber Mechanical Study On Young Interference optical path difference demodulation method of low coherence interference, it is characterized in that, described step 4 also comprises: regulate the distance l between Mach Zehnder interferometer arm and No. two arm two brachiums ₁-l ₂, realize the interval demodulation of different optical path difference.

7., as the optical fiber Mechanical Study On Young Interference optical path difference demodulation method as claimed in claim 5 based on low coherence interference, it is characterized in that, described step one adopts optical fiber Fabry-Perot interferometer to realize optical path difference sensing, and its interference light path difference sensing routine comprises following operation:

The light sent by wideband light source is by 2 × 2 three-dB couplers, and the light along Optical Fiber Transmission reflects in fiber end face generating portion, is formed with reference to reflected light; Transmitted light by with fiber end face distance, delta L ₂catoptron reflection after be again coupled to optical fiber, form sensory reflex light, after reflected light and sensory reflex light compositing light beam, contain 2 Δ L ₂optical path difference information, change catoptron distance fiber end face distance, namely change optical path difference sensing amount.