CN106773586A - Based on single-mode fiber without lens Jones matrixes holographic measurement and imaging system - Google Patents
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Abstract
The invention discloses it is a kind of based on single-mode fiber without lens Jones matrixes holographic measurement and imaging system,Including two LASER Light Sources of fiber coupling,Each light source is divided into intensity identical multichannel light by optical fiber splitter,It is fixed on corresponding structure of fiber_optic after per the transmission of Lu Guangjing length identicals single-mode fiber,So that each light source wherein all the way light as illumination light introduce sample arm,By testing sample,Obtain the object light of off-axis digital holography,If remaining main line light introduces reference path,By the reference light after polarization as off-axis gaussian beam,The superposition light field of reference light and object light passes through image recording sensor,Obtain the amplitude comprising Object light wave,The four-way Jones matrix hologram of phase and polarization information,Simple structure of the present invention,The one step surveying of the two-dimentional Jones matrixes parameter that Polarization-Sensitive dielectric space is differentiated can be realized.
Description
Technical Field
The invention relates to a lensless Jones matrix holographic measurement and imaging system based on single-mode optical fibers.
Background
Polarization is one of the fundamental properties of light, and one important phenomenon associated with polarization is that light passing through polarization sensitive media, or after reflection from such media, undergoes a change in polarization state. This variation depends on the polarization transformation properties of the medium and can be characterized by its transmission matrix. The accurate measurement of the transmission matrix parameters of the polarization sensitive material has important significance for revealing the internal structure or birefringence property of the material, representing the complex modulation property of an optical device, finding the physical mechanism of the interaction of light and a substance and the like.
Two main forms describing the transmission matrix of polarization sensitive materials are the Mueller and Jones matrices, respectively. The intensity-based Mueller matrix form is adopted by most conventional polarization-based techniques, but it does not describe the field properties of light polarization and does not directly preserve the phase information of light. The Jones matrix method can directly describe the complex amplitude information of the light field. In general, the measurement of the Jones matrix is more complex than the Mueller matrix because the Jones matrix of a typical material contains at least four complex parameters associated with different polarization states of the input and output beams.
Recently, some polarization imaging techniques based on the holographic principle are proposed, and these methods can obtain a spatially resolved two-dimensional jones matrix, but all require adjusting the polarization element multiple times or using additional equipment to control the rotation of the polarization device, which increases the complexity of the system and reduces the stability and measurement accuracy of the system.
Chinese patent 2014104949275 discloses a method for measuring a two-dimensional jones matrix in one step, which greatly improves the measurement efficiency, and uses an optical device which is simpler than the conventional method, but the used method has certain inherent defects: the used measuring optical path is based on Mach-Zehnder interference, so that the requirement on the adjustment precision of the optical path is high, more optical elements are required, and the measurement can be only limited on a specific measuring platform.
Recently, Yang et al (document 1) proposed a one-step measurement method using an orthogonal shear grating, but the method is also based on mach-zehnder interference, and further uses a large number of lenses and mirrors, and the adjustment of the measurement optical path is complicated.
In summary, the existing jones matrix measurement and imaging technology based on the holographic principle needs to adjust the polarization element for multiple times or use a complex measurement light path to realize one-step measurement, which increases the requirement on the light path adjustment precision, reduces the stability of the system, and limits the application range of the measurement system.
Document 1: T.D. Yang, K.park, Y.G.Kang, K.J.Lee, B.M.Kim, and Y.Choi, "Single-shot digital logic microprocessor for qualifying a scientific-resolved joint matrix of biological experiments," Opt.express 24(25), 29302-.
Disclosure of Invention
The invention provides a lensless Jones matrix holographic measurement and imaging system based on single-mode optical fiber, which is designed based on the principles of optical fiber and lensless off-axis Fresnel holography, two optical fiber splitters are used for generating a plurality of reference and illumination light beams required by the off-axis holography, the emergent end of the optical fiber is fixed on a specially designed optical fiber support, and four-channel angular multiplexing of the hologram can be realized only by three beam splitting prisms.
In order to achieve the purpose, the invention adopts the following technical scheme:
a lens-free Jones matrix holographic measurement and imaging system based on single-mode fibers comprises two laser light sources coupled by the single-mode fibers, wherein each light source is divided into multiple paths of light with the same intensity through a fiber splitter, and each path of light is transmitted through the single-mode fibers with the same length and then fixed on a corresponding fiber support, so that one path of light of each light source is introduced into a sample light path as illumination light to obtain off-axis digital holographic object light; introducing the rest of the light into a reference light path, and using the light after linear polarization as off-axis holographic reference light; and recording the superposed light field of the reference light and the object light by an image sensor to obtain a four-channel Jones matrix hologram containing the amplitude, the phase and the polarization information of the object light. And carrying out data processing on the recorded hologram by using a data processing system to obtain the amplitude and phase distribution of all four matrix parameters of the two-dimensional Jones matrix of the sample.
Further, the optical fiber splitter is a 1 × 3 optical fiber splitter, and divides each laser light source into three beams with the same intensity.
Furthermore, the emergent ends of the two paths of light of the sample light path are placed on different optical fiber supports.
Furthermore, two paths of light of the sample light path are converted into right-handed circularly polarized light and left-handed circularly polarized light to irradiate on a sample to be measured after passing through the polarization beam splitter prism and the quarter wave plate with the optical axis direction forming 45 degrees with the horizontal direction.
Furthermore, in the reference light path, the emitting ends of one path of light from different laser light sources are jointly placed on the optical fiber support with the center sharing the object light path.
Furthermore, the position of the light emitting end of the reference light path can be adjusted in one dimension on the support so as to change the included angle between the light emitting end of the reference light path and the object light.
Furthermore, different light rays of the reference light path are converted into linearly polarized light through a polarization beam splitter prism to serve as off-axis holographic reference light, horizontal polarized light and vertical polarized light are respectively formed, the reference light and object light are overlapped together on a recording plane after passing through a non-polarization beam splitter prism, an overlapped light field is recorded by an image sensor, and a four-channel Jones matrix hologram containing the amplitude, the phase and the polarization information of the object light wave is obtained.
Further, the cross section of the optical fiber support through which the light rays forming the vertically polarized light pass is a circle with a gap of 1/4 area, the gap is located at 0-90 degrees, and different light rays of the two light sources are arranged on different sides of the gap.
Further, the cross section of the optical fiber support through which the light rays forming the horizontally polarized light pass is a circle with a gap of 1/4 area, the gap is located at 135-45 degrees, and different light rays of the two light sources are arranged on different sides of the gap.
Further, the center of the fiber support of the reference light path and the point source of the sample light path are spatially and symmetrically distributed relative to the corresponding polarization splitting prism and the corresponding non-polarization splitting prism.
Further, the obtained Jones matrix of the measured sample isAnd is
Wherein,Cmn(m, n ═ 1,2) denotes illumination light wave S when no object is placedmAnd a reference light wave RmnComplex amplitude distribution of interference field on recording surface on which sensor is located, YmnFor complex amplitude distribution, IFrZAnd { } is to perform inverse Fresnel diffraction transformation with the diffraction distance z, and z is the distance between the sample to be measured and the image sensor.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention can realize one-step measurement of two-dimensional Jones matrix parameters of polarization sensitive medium spatial resolution;
(2) the method is based on lens-free Fresnel diffraction holography, multiple beams of reference light and object light required by the method are separated by using the optical fiber branching unit, four-channel angular multiplexing of the hologram is realized, and four matrix parameters can be obtained through one-time measurement;
(3) the invention is a Fresnel holographic design without lens, the light path is simple and easy to adjust, and the influence of lens aberration is avoided; based on the design of the optical fiber, the number of used optical elements is greatly reduced, the system cost is reduced, and the system is easy to realize;
(4) the invention has compact structure, easy integration, is suitable for integral carrying and movement, is beneficial to further optimizing and developing an integrated and portable system, and is suitable for measuring the complex Jones matrix diagram and dynamic polarization imaging of the polarization sensitive material in real time.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 is a schematic structural view of the present invention;
FIGS. 2(a) and 2(b) are schematic structural views of a fiber optic mount of the present invention;
FIG. 3 is a schematic diagram of an optical fiber-based off-axis Fresnel holographic recording system according to the present invention;
FIG. 4(a) is a four-channel angular division multiplexed hologram recorded during the experiments of the present invention;
FIG. 4(b) is an enlarged view of the rectangular area in FIG. 4 (a);
spatial frequency Spectrum of hologram of FIG. 4(c)
FIGS. 5(a) - (b) are respectively the amplitude and phase distributions of experimentally measured Jones matrix parameters;
fig. 5(c) - (d) are amplitude and phase distributions of corresponding theoretical calculations of jones matrix parameters under the same parameters; from left to right are: j. the design is a squarexx,Jxy,JyxAnd Jyy；。
FIG. 6 is a sample of stressed PMMA of the present invention, with the circular area being the illuminated area;
FIGS. 7(a) - (d) are respectively the Jones matrix parameter J in the measurement results of PMMA samplexx,Jxy,JyxAnd JyyThe amplitude distribution of (a);
FIGS. 7(e) - (h) are phase distributions of corresponding Jones matrix parameters in the measurements of PMMA samples;
FIGS. 8(a) - (d) are Jones matrix parameters J of the measurement results of the mica sheet samples, respectivelyxx,Jxy,JyxAnd JyyThe amplitude distribution of (a);
fig. 8(e) - (h) are phase distributions of corresponding jones matrix parameters of the measurement results of the mica sheet samples;
FIGS. 8(i) - (j) are phase distributions of two characteristic values of the measurement results of the mica sheet sample;
fig. 8(k) is the phase retardation distribution of the mica sheet sample in two eigenvector directions.
The specific implementation mode is as follows:
the invention is further described with reference to the following figures and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
As described in the background art, in the polarization imaging technology based on the holographic principle in the prior art, there is a need to adjust the polarization element for many times, or to use a complicated measurement optical path to realize one-step measurement, which increases the requirement for the optical path adjustment precision, reduces the stability of the system, and limits the application range of the measurement system.
In an exemplary embodiment of the present application, an experimental setup of a measurement system is shown in fig. 1. Two single-mode fiber-coupled laser diodes LD1 and LD2 are used as light sources, each of which is split into three beams of equal intensity by a 1 × 3 fiber splitter (FS1 and FS 2). Three beams of light separated from each optical fiber splitter are transmitted by single-mode optical fibers (Nufern 630-HP) with the same length and then are fixed on corresponding optical fiber supports (FH 1-FH4 in figure 1) through optical fiber ceramic sleeve cores, and are used as a light source of off-axis holography, one beam of the three beams of light is used as illumination light to be introduced into a sample light path, and the other two beams of light are used as reference light to be introduced into a reference light path.
In the sample light path, the illumination light S from two different light sources1(from light source LD1, fixed on support FH 1) and S2(from light source LD2, fixed on frame FH 2), after passing through polarizing beam splitter PBS1 and quarter-wave plate QWP whose optical axis direction forms 45 degrees with horizontal direction, it is converted into right-handed and left-handed circularly polarized light to irradiate on the object. The light rays emerging from the object are the object light of the off-axis digital hologram.
In the reference path, the remaining light R is split from two fiber splitters11、R12(from light source LD1) and R21、R22(from a light source LD2) with its exit end respectively placed on fiber supports FH3 and FH4 whose centers share the same path with the object light, wherein R is11And R21Placed on a support FH3, R12And R22The position of the light emitting end can be adjusted in one dimension on the bracket, the adjusting direction is shown by arrows in fig. 2(a) and 2(b), and the included angle between the light emitting end and the object light can be changed through the adjustment of the position.
It should be noted that the centers of the fiber supports FH3 and FH4 and the point sources S1 and S2 are spatially symmetrically distributed with respect to the PBS1, the PBS2, and the non-polarizing beam splitter prism NPBS. The rays of the reference light path are converted into linearly polarized light through a polarization beam splitter PBS2 to serve as reference light of off-axis holography, wherein R is11And R21Is horizontally polarized light, R12And R22Is vertically polarized light. Finally, the reference light and the object light are superposed together on a recording plane after passing through a non-polarization beam splitter (NPBS), and a superposed light field IS recorded by an Image Sensor (IS) to obtain the amplitude, the phase and the polarization of the object light waveA four-channel jones matrix hologram of information. In FIG. 1, d IS the distance between the illumination light point source S1 or S2 and the sample, and z IS the distance between the sample to be measured and the image sensor IS.
FIG. 3 is a schematic diagram of a four-channel Fresnel holographic recording system. According to the experimental design, all the reference light and the illumination light can be considered to be emitted from different point sources coplanar in space, where S1 and S2 represent illumination light point sources (in this schematic, S1 and S2 are coincident in space), and R is11、R12、R21And R22Four reference light point sources are shown. The plane of the point sources is at a distance d from the sample plane. The arrows in the figure indicate the polarization state of the exiting light beam.
Setting the x axis of the system as horizontal direction, setting the y axis as vertical direction, and using the coordinate (x axis) of the plane where the sample to be measured is located and the coordinate of the recording surface where the image sensor is locatedo,yo) And (x, y) the coordinates of the image plane after hologram reconstruction are represented by (x)i,yi) And (4) showing. According to the jones matrix theory, the jones matrix for any sample can be expressed as:
here Jxx、Jxy、JyxAnd JyyIs the jones matrix parameter of the sample. In the sample light path, two light beams emitted from point sources S1 and S2 pass through PBS1 and QWP, become right circularly polarized light and left circularly polarized light respectively, and irradiate on a sample, and if the light field distribution after passing through the sample is represented as O1And O2The object light emerging from the rear surface of the sample can then be expressed as the jones vector:
here, theRepresents O1And O2Non-coherent superposition of1And A2Is the complex constant of the illumination light, λ is the wavelength of the illumination light wave, and d is the distance between the point source plane and the object plane. The object light emitted from the sample surface reaches the recording plane where the image sensor is located after the space transmission distance z, the transmission process meets the Fresnel diffraction of the light in the free space, and the corresponding Fresnel diffraction formula is as follows:
wherein: o isz(x, y) represents an object light field distribution on the recording surface; o (x)o,yo) Representing the distribution of the emergent light field on the sample surface; here with the symbol Frz{ } denotes Fresnel diffraction with a diffraction distance z. Substituting equation (2) into equation (3) can further express the object optical field distribution on the recording surface as:
wherein:
on the other hand, the reference light wave can be considered as coming from the point source plane (x)mn,ymn) A spherical wave emitted by a point, where (m, n ═ 1, 2). Under the condition of fresnel approximation, the four beams of reference light incident on the recording surface can be expressed as:
finally, the interference field generated by the object light and the total reference light on the recording surface can be expressed as:
wherein:
Y11＝A1R11 *(Jxx'+iJxy')
Y12＝A1R12 *(Jyx'+iJyy')
Y21＝A2R21 *(Jxx'-iJxy')
Y22＝A2R22 *(Jyx'-iJyy') (9)
the symbol "+" in equations (7) and (9) represents a complex conjugate operator. Y in the formula (7)mn(m, n-1, 2) represents a group with an object light OmzAnd reference light RmnThe associated complex amplitude distribution. In addition, because the off-axis holographic recording mode is adopted, Y can be directly reproduced by a method of carrying out spatial filtering on the recorded hologrammn(m,n＝1,2。)
Albeit YmnThe (m, n-1, 2) term can be directly recovered from the recorded hologram, but the resulting Y can be seen from equation (9)mn(m, n ═ 1,2) is not directly equal to the jones matrix quantity J desired to be measuredxx、Jxy、JyxAnd Jyy. Here by Y11How to explain from Y is an examplemnAnd (m, n is 1,2) recovering the Jones matrix parameters to be detected. Substituting equations (5) and (6) into equation (9) can result in:
in equation (10), the coordinate x with the reference light point source11And y11The associated phase factor can be eliminated by conventional off-axis holographic reconstruction methods, so equation (10) can be further simplified as:
x 'here'o＝xo(z+d)/d，y′o＝yo(z+d)/d，xi＝x′o/M，yi＝y′o/M，ziZ (z + d)/d and M (z + d)/d. M ═ z + d)/d, and is the magnification of the system. In addition, equation (11) also shows the amplified jones matrix parameters Jxx+iJxyAnd Y11The relation between the diffraction distance and the diffraction distance satisfies the relation of Fresnel diffraction:
thus can be aligned to Y11Diffraction distance ziInverse Fresnel diffraction transformation of to Jxx+iJxyNamely:
here symbolDenotes a diffraction distance ziInverse fresnel diffraction transformation of (1). For Y in formula (9)12，Y21And Y22The same conclusion can be reached by analyzing the terms:
where C ismn(m, n ═ 1,2) denotes illumination light wave S when no object is placedmAnd a reference light wave RmnThe complex amplitude distribution of the interference field on the recording surface on which the sensor is located. Complex amplitude distribution Y in equations (13) and (14)mnDivided by corresponding CmnCan effectively remove the system noise and the additional background phase influence generated in the off-axis holography.
By the equations (13) and (14), the jones matrix parameters of the sample to be measured can be finally given by the following equations:
two single-mode fiber coupled laser diodes with the center wavelength of 650nm are selected as light sources, the output power is 1mW, and the optical fiber connector is a universal 2.5mm connector. The optical fiber used was a 630-HP type single mode fiber from Nufern, USA, with an operating wavelength of 600-770 nm. Experimental data was recorded using a CMOS type image sensor having a pixel size of 6.45um × 6.45um and a pixel number of 1024 × 1024. The distance between the point source and the object is about 95mm, the distance between the object and the CCD recording surface is about 135mm, and the system magnification is about 2.4.
Because of the design based on optical fibers and no lens, the whole system structure is very simple and compact, only a small amount of optical elements such as three beam splitting prisms and a quarter wave plate are used, and the system can be completely concentrated in a portable experimental box of 30cm by 50 cm; the battery-powered laser diode light source also avoids dependence on an external power supply; in addition, because the off-axis holographic optical path without the lens is adopted, the system is easy to adjust, is insensitive to the influences of coaxiality, optical path difference or wavefront distortion and the like, has relatively low requirement on the measurement environment and has better applicability.
Experiments were performed with the above system.
First, jones matrix measurements of the composite polarizer.
The feasibility of the proposed solution was first verified by experiments. The sample used for experimental verification was a composite polarizer (polyvinyl alcohol, PVA) composed of two polarizers with different polarization directions, in which the upper polarizer polarization direction was-18 degrees from the horizontal and the lower one was 27 degrees from the horizontal. FIG. 4(a) is the experimental recordA hologram according to (1). The details of the hologram interference fringes can be observed from the magnified image 4(b), and can be seen as a typical multi-beam interference image. FIG. 4(c) is a spectral diagram of a hologram, in which Y is marked11And Y12Are respectively object light O1And reference light R11、R12Frequency spectrum of interference, Y21And Y22Are respectively object light O2And reference light R21、R22The frequency spectrum after interference, these frequency spectrum terms and Jxx′、Jxy′、Jyx' and Jyy' satisfy equation (9), can be recovered by a spatial filtering algorithm; background dependent spectral term Cmn(m, n ═ 1,2) can also be obtained in a similar way without placing the object.
Recovering the obtained Ymn(m, n ═ 1,2) and Cmn(m, n is 1,2) is substituted into the equations (13) and (14) to perform inverse fresnel diffraction calculation, where the diffraction distance z isi326.8mm, and then substituting the result into equation (15), the Jones matrix parameters of the sample can be calculated. FIGS. 5(a) and 5(b) show the amplitude and phase distributions, respectively, of the parameters of the Jones matrix for this sample, J, from left to rightxx,Jxy,JyxAnd JyyThe parameters, arrows in FIG. 5(a), indicate the polarization directions of different regions of the sample. Wherein J in FIG. 5(b)yyThe phase of (2) is more noisy because its phase is uncertain when the amplitude value is small. In addition, the theoretical calculation is carried out by substituting the known parameters of the sample, and the results of the Jones matrix amplitude and phase obtained by the theoretical calculation are respectively shown in (c) and (d) of FIG. 5, and it can be seen that the theoretical results are basically consistent with the experimental measurement results.
Stress birefringence effect measurement of organic glass
The refractive index characteristics of a transparent solid medium change under the action of pressure or tension, and the phenomenon is called stress birefringence or optical elastic effect. When a transparent isotropic medium is subjected to a mechanical external force, it becomes optically anisotropic, thereby generating a birefringence phenomenon. The birefringence effect generated by the internal stress of the optical element can influence the polarization state of light, and the accurate measurement of the stress birefringence effect of the optical element is the guarantee for ensuring the normal work of a measurement system.
The PMMA sample used had a length and width of 20mm, 10mm, a thickness of 1mm, a slit width of 1mm at the center and a depth of 12mm, and the direction of the applied external force was as indicated by the arrow in the figure, and the light was irradiated on the area of the circle in the figure, and the diameter of the area of the circle was 8 mm. Fig. 7 is the Jones matrix measurement of this sample, and fig. 7(a) - (d) and fig. 7(e) - (h) are the amplitude and phase distributions, respectively, for the four parameters. As can be seen from the amplitude distributions of fig. 7(a) - (d), in the background region, i.e., the slit, | Jxx|≈|Jyy|≈1and|Jxy|≈|Jyx| is approximately equal to 0, which is consistent with the theoretical value of the parameter amplitude of the Jones matrix in the isotropic free space; in the sample area, the measured Jones matrix distribution reflects the anisotropic field distribution generated by the external stress, the amplitude contrast of each parameter is very low, and the amplitude of the diagonal parameters of the Jones matrix is basically distributed symmetrically. As can be seen from the phase distributions in fig. 7(e) - (h), the phases of all jones matrix parameters in the sample region have obvious changes, which reflects that the refractive index of the sample is not uniform under the action of the external stress, and the refractive index changes violently near the slit; in addition, the orientation of the fringes in the phase distribution also reflects the spatial orientation change of the birefringence of the sample under the action of external force, revealing that the obvious anisotropy of the sample under stress comes from external stress. Diagonal term (J) of Jones matrix parameter at slitxx、Jyy) Phase value of 0, off-diagonal term (J)xy、Jyx) Is a fragmented and uncertain noise distribution, which is consistent with the polarization response in free space.
The maximum thickness of the mica sheet samples used in the experiments was about 60um, which is much less than the thickness of the PMMA samples used above. Although the thickness of the sample is changed greatly, the system provided by the invention only needs to replace the sample when measuring, and does not need to make other adjustments to the system. Fig. 8(a) - (d) and 8(e) - (h) are respectively the amplitude and phase distributions of the jones matrix of the measured samples.The upper right corner of the measurement area is the free space area where no sample is present, and the measurement result of this area is consistent with the polarization response result of free space. In the region where the mica sample exists, except for the boundary region between layers, the amplitude distribution of each Jones matrix parameter has a low contrast, and the diagonal term (J) of the Jones matrix parameterxx、Jyy) And off-diagonal terms (J)xy、Jyx) Is substantially symmetrical. From the phase distribution of the parameters, it can be seen that there are four different thickness gradients in the sample region, each with a more uniform phase distribution.
The measured spatially resolved jones matrix provides a viable method for further analyzing the birefringence properties of the sample. A typical process is to diagonalize the jones matrix to obtain an eigenvector distribution and corresponding eigenvalues. For each point of the sample, a 2 × 2 complex matrix was constructed from the measured jones matrix elements, and then eigenvectors and corresponding eigenvalues were obtained by matrix diagonalization. When the polarization direction of the input beam is the same as the eigenvector direction, the polarization state of the input beam will remain unchanged after passing through the sample, or no polarization discontinuity will occur, so the direction of the eigenvector is the direction of the principal axis, and the phase difference between the two eigenvalues reveals the birefringence characteristics of the sample. Fig. 8(i) and (j) are phase profiles of two eigenvalues obtained from the measured Jones matrix, respectively, the phase of the eigenvalues representing the additional phase obtained when polarized light parallel to the corresponding principal axis propagates through the sample. The phase difference of the two eigenvalues, as represented in fig. 8(k), represents the phase retardation of light propagating in the sample in the direction of the two eigenvectors, unlike the empty region where the retardation is almost zero, the sample region shows a certain amount of retardation, which verifies the presence of the two refractive indices associated with the two principal axes, i.e. the presence of the birefringence effect. It was also revealed that different birefringence effects exist in regions of different thickness of the sample.
In summary, the invention provides a lensless holographic imaging system based on optical fibers, which can realize one-step measurement of two-dimensional Jones matrix parameters of polarization sensitive medium spatial resolution. The invention is based on lens-free Fresnel diffraction holography, utilizes the optical fiber branching unit to divide a plurality of beams of reference light and object light required, realizes four-channel angular multiplexing of the hologram, and can measure four matrix parameters at one time. Firstly, the feasibility of the scheme is verified through experimental measurement of the composite polaroid Jones matrix. As an application example of polarization measurement, Jones matrix parameters of a PMMA sample and a mica sheet sample under stress are measured, characteristic value phases along different main shaft directions are further given through a Jones matrix obtained through calculation, and phase delays generated in two directions after polarized light corresponding to the characteristic value phases is transmitted through a medium are further given.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (10)
1. A lens-free Jones matrix holographic measurement and imaging system based on single-mode fiber is characterized in that: the device comprises two laser light sources coupled by single-mode fibers, wherein each light source is divided into multiple paths of light with the same intensity through a fiber splitter, and each path of light is transmitted by the single-mode fibers with the same length and then fixed on a corresponding fiber support, so that one path of light of each light source is introduced into a sample light path as illumination light to obtain off-axis digital holographic object light; and introducing the rest of light into a reference light path, and using the light after linear polarization as off-axis holographic reference light. And recording the superposed light field of the reference light and the object light by an image sensor to obtain a four-channel Jones matrix hologram containing the amplitude, the phase and the polarization information of the object light.
2. The lensless Jones matrix holographic measurement and imaging system of claim 1, wherein: the optical fiber branching unit is a 1 x 3 optical fiber branching unit and divides each laser light source into three beams with the same intensity.
3. The lensless Jones matrix holographic measurement and imaging system of claim 1, wherein: the emergent ends of the two paths of light of the sample light path are placed on different optical fiber supports.
4. The lensless Jones matrix holographic measurement and imaging system of claim 1, wherein: two paths of light of the sample light path are converted into right-handed circularly polarized light and left-handed circularly polarized light to irradiate on a sample to be measured after passing through a polarization beam splitter prism and a quarter wave plate with the optical axis direction forming 45 degrees with the horizontal direction.
5. The lensless Jones matrix holographic measurement and imaging system of claim 1, wherein: in the reference light path, the emergent ends of one path of light from different laser light sources are jointly placed on an optical fiber support with the center sharing the path with the object light.
6. The lensless Jones matrix holographic measurement and imaging system of claim 1, wherein: the position of the light ray emergent end of the reference light path can be adjusted in one dimension on the bracket so as to change the included angle between the light ray emergent end of the reference light path and the object light.
7. The lensless Jones matrix holographic measurement and imaging system of claim 1, wherein: different light rays of the reference light path are converted into linearly polarized light through the polarization beam splitter prism to serve as off-axis holographic reference light, horizontal polarized light and vertical polarized light are respectively formed, the reference light and object light are overlapped together on a recording plane after passing through the non-polarization beam splitter prism, an overlapped light field is recorded by the image sensor, and a four-channel Jones matrix hologram containing the amplitude, the phase and the polarization information of the object light is obtained.
8. The lensless Jones matrix holographic measurement and imaging system of claim 1, wherein: the cross section of the optical fiber support through which the light forming the vertical polarized light passes is a circle with a notch with the area of 1/4, the notch is positioned at 0-90 degrees, and different light of the two light sources are arranged on different edges of the notch;
or the cross section of the optical fiber support through which the light rays forming the horizontal polarized light pass is a circle with a notch with the area of 1/4, the notch is positioned at 135-45 degrees, and different light rays of the two light sources are arranged on different sides of the notch.
9. The lensless Jones matrix holographic measurement and imaging system of claim 1, wherein: the center of the fiber support of the reference light path and the point source of the sample light path are symmetrically distributed relative to the corresponding polarization beam splitter prism and the corresponding non-polarization beam splitter prism in space.
10. The lensless Jones matrix holographic measurement and imaging system of claim 1, wherein: the obtained Jones matrix of the tested sample isAnd is
Wherein,Cmn(m, n ═ 1,2) denotes illumination light wave S when no object is placedmAnd a reference light wave RmnComplex amplitude distribution of interference field on recording surface on which sensor is located, YmnFor complex amplitude distribution, IFrZIn order to perform inverse Fresnel diffraction transformation with a diffraction distance z, z is the distance between the sample to be measured and the image sensor.
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