Optical system and preform analysis system

Abstract

The invention is applicable to the field of optical measuring instruments, and provides an optical system and a preform analysis system.The optical system comprises a non-diffraction light beam generation module used for generating a first non-diffraction light beam with the width at the center of a non-diffraction area being the first width; the reflection module is used for reflecting the first non-diffraction light beam to the width adjustment module; the width adjusting module is used for focusing the incident first non-diffracting light beam and generating a second non-diffracting light beam of which the width at the center of the non-diffracting region is a second width; wherein the second width is smaller than the first width, and the second diffraction-free light beam is used for irradiating the preform rod so as to determine the geometric parameters of the preform rod. Based on the technical scheme provided by the invention, the phenomena of light beam diffraction and interference between high-order diffraction light and zero-order diffraction light can be avoided, the scanning accuracy of the preform rod is greatly improved, the quality control of the preform rod is effectively improved, and the quality of an optical cable is further greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measuring instruments, and in particular relates to an optical system and a preform rod analysis system. Background Art

[0002] Optical fiber is the abbreviation of optical fiber (fiber that can conduct light), which is a fiber made of glass or plastic that can be used as a light transmission tool. Optical fiber is obtained by a series of treatments on optical fiber preforms, which are usually made by processes such as axial vapor deposition (VAD), outside chemical vapor deposition (OVD), and plasma activated chemical vapor deposition (PCVD). Figure 1 This is an example of the production of conventional preform rods. Figure 1 As shown, the germanium compound and the silicon compound are burned and gasified before vapor deposition. During the deposition process, the preform is fixed on a bracket and rotates at a certain speed, and the combustion material reciprocates at a certain speed relative to the preform. Usually, the rotation speed and the reciprocating speed are constant. The finished preform is obtained in this way. However, since the rotation speed and the reciprocating speed are constant, the thickness of each layer of the preform is also constant. This situation causes periodic fluctuations in the doping concentration, that is, the doping concentration is uneven, resulting in periodic stripes 16 on the preform. Figure 2 yes Figure 1 An example of periodic fringes produced by the preform in FIG. Figure 2 As shown, regular periodic stripes 16 can be seen on the end surface of the preform rod.

[0003] Optical fiber is an important component of optical cable, and the geometric parameters of optical fiber preform have a great influence on the performance of optical cable. Therefore, the geometric parameters of optical fiber preform must be strictly measured before the preform is drawn. At present, the detection method of optical fiber preform is mainly through preform analyzer. The preform analyzer obtains the deflection information of the light beam after each lateral movement by scanning the optical fiber preform horizontally, and uses the deflection information to obtain the geometric parameters of the optical fiber preform. However, when using the preform analyzer to Figure 1 When analyzing the preform in the fiber optic cable, the light beam excited by the preform will diffract, and the high-order diffraction light will interfere with the zero-order diffraction light, resulting in the inability to accurately obtain the geometric parameters of the optical fiber preform, affecting the quality control of the preform and seriously reducing the quality of the optical cable. Summary of the invention

[0004] In order to solve the problem that the existing preform analysis has beam diffraction and beam interference, the geometric parameters of the preform cannot be accurately obtained, which affects the quality control of the preform and seriously reduces the quality of the optical cable, the present invention provides an optical system and a preform analysis system. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0005] In a first aspect, the present invention provides an optical system, comprising: a diffraction-free beam generating module, used to generate a first diffraction-free beam whose width at the center of a diffraction-free area is a first width; a reflection module, used to reflect the first diffraction-free beam to a width adjustment module; the width adjustment module, used to focus the incident first diffraction-free beam to generate a second diffraction-free beam whose width at the center of the diffraction-free area is a second width; wherein the second width is smaller than the first width, and the second diffraction-free beam is used to irradiate onto a preform to determine the geometric parameters of the preform.

[0006] In some embodiments, the second width is greater than a radius of a core layer of the preform rod.

[0007] In some embodiments, the width adjustment module includes: a first focusing lens for focusing the incident first non-diffraction light beam to generate a focused light beam; and a second focusing lens for focusing the focused light beam to generate the second non-diffraction light beam.

[0008] In some embodiments, a focal length of the first focusing lens is greater than a focal length of the second focusing lens, and the focal length of the second focusing lens is positively correlated with the second width.

[0009] In some embodiments, the spacing between the first focusing lens and the second focusing lens is the sum of a first distance and a second distance, wherein the first distance refers to a distance having a numerical value equal to the focal length of the first focusing lens, and the second distance refers to a distance having a numerical value equal to the focal length of the second focusing lens.

[0010] In some embodiments, the diffraction-free beam generating module includes: a laser, a beam expander, and an axle lens, wherein the laser is used to emit a Gaussian beam; the beam expander is used to increase the beam diameter of the Gaussian beam and reduce the divergence angle of the Gaussian beam to generate a beam expansion light ring; and the axle lens is used to convert the beam expansion light ring into the first diffraction-free beam.

[0011] In some embodiments, the reflection module is a total reflection mirror.

[0012] In a second aspect, the present invention further provides a preform analysis system, comprising: a platform, an optical system as described in the first aspect above and arranged on the platform, a detection module and an analysis module arranged on the platform; the optical system is used to scan the preform up and down along the direction perpendicular to the axial direction of the preform with a second non-diffraction light beam under the drive of the platform, wherein the non-diffraction area of ​​the second non-diffraction light beam is located in the rod core layer of the preform, and the center of the non-diffraction area of ​​the second non-diffraction light beam is aligned with the axis of the preform; the detection module is used to receive the non-diffraction light beam excited by the preform, and obtain the displacement information of the non-diffraction light beam according to the energy of the non-diffraction light beam, and send the displacement information of the non-diffraction light beam to the analysis module, wherein the displacement information of the non-diffraction light beam refers to the distance information of the non-diffraction light beam offset from the optical axis; the analysis module is used to determine and output the geometric parameters of the preform using the displacement information of the non-diffraction light beam.

[0013] In some embodiments, the detection module includes: a linear camera, wherein the linear camera is used to receive the diffraction-free light beam, and when the energy of the diffraction-free light beam is greater than a preset threshold, obtain the displacement information of the diffraction-free light beam, and send the displacement information of the diffraction-free light beam to the analysis module.

[0014] In some embodiments, the preform is fixedly placed in a matching liquid container, and the refractive index of the matching liquid in the matching liquid container is the same as the refractive index of the cladding of the preform.

[0015] The present invention has the following beneficial technical effects:

[0016] (1) Use a non-diffraction beam to scan the preform rod. The exciting beam is still a non-diffraction beam, which avoids beam diffraction and the interference between high-order diffraction light and zero-order diffraction light. It greatly improves the accuracy of preform rod scanning, effectively improves the quality control of preform rods, and thus greatly improves the quality of optical cables.

[0017] (2) It can avoid the need to replace other lasers or use multiple lasers when scanning with longer wavelengths or multi-wavelength beams, which causes the system to be complex and costly. It has the advantages of greatly reducing investment costs, avoiding the introduction of human errors, and being easier to operate.

[0018] (3) The traditional analysis method needs to calculate the wavelength based on the preform stripes, and needs to find the position where the peak positions of the diffraction stripes of the two wavelength beams in the detector are consistent. In the present invention, a non-diffraction beam is used for scanning, and the obtained beam is a non-diffraction beam. There is no problem of beam diffraction and beam interference, that is, there is no need to find the position where the peak position of the diffraction stripes is consistent. This method does not require additional calculations, and the calculation process is consistent with the traditional calculation method, which has the characteristics of low computational complexity.

[0019] (4) The traditional analysis method has certain requirements on the width of the preform stripes due to the problems of beam diffraction and beam interference. However, the beam obtained by the present invention does not have the problems of beam diffraction and beam interference, and thus there is no need to limit the width of the preform stripes, which can effectively improve the production efficiency of the preform.

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a sample diagram of the production of conventional preforms;

[0022] Figure 2 yes Figure 1 Example of periodic stripes produced by the preform in ;

[0023] Figure 3 is a structural block diagram of an optical system provided by an embodiment of the present invention;

[0024] Figure 4 is a schematic diagram of generating a non-diffraction light beam provided by an embodiment of the present invention;

[0025] Figure 5 is a schematic diagram of the composition of an optical system provided by an embodiment of the present invention;

[0026] Figure 6 is a cross-sectional schematic diagram of the incoherent irradiance of the second non-diffraction light beam in the X direction captured by the linear camera provided by an embodiment of the present invention;

[0027] Figure 7 is a cross-sectional schematic diagram of the incoherent irradiance in the X direction when a portion of the second non-diffracted light beam is incident on a preform provided by an embodiment of the present invention;

[0028] Figure 8 is a cross-sectional schematic diagram of the incoherent irradiance in the X direction when the second non-diffraction light beam provided by an embodiment of the present invention is completely incident on the preform;

[0029] Fig. 9 Schematic diagram of a preform analysis system provided in an embodiment of the present invention.

[0030] Description of reference numerals:

[0031] 1-He-Ne laser; 2-beam expander; 3-conical lens; 4-first non-diffraction beam; 5-total reflection mirror; 6-first focusing lens; 7-second focusing lens; 8-cladding of preform; 9-core layer of preform; 10-matching liquid container; 11-matching liquid; 12-platform; 13-third focusing lens; 14-cylindrical lens; 15-linear camera; 16-preform stripes; 17-thin light ring; 18-preform axis; 19-optical axis; 20-center position of the non-diffraction area of ​​the second non-diffraction beam. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0033] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0034] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0035] Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in the claims. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0036] In view of the problem that the existing preform analysis has beam diffraction and beam interference, the geometric parameters of the preform cannot be accurately obtained, which affects the quality control of the preform and thus seriously reduces the quality of the optical cable, the present invention provides an optical system and a preform analysis system. Based on the technical solution proposed by the present invention, the geometric parameters of the preform can be accurately obtained, the quality control of the preform can be effectively improved, and the quality of the optical cable can be greatly improved.

[0037] Now combined Figure 3 The technical solution proposed in the present invention is described in detail. Figure 3 is a structural block diagram of an optical system provided by an embodiment of the present invention. Figure 3 As shown, the optical system includes: a diffraction-free beam generating module, used to generate a first diffraction-free beam with a first width at the center of the diffraction-free area; a reflection module, used to reflect the first diffraction-free beam to the width adjustment module; the width adjustment module, used to focus the incident first diffraction-free beam to generate a second diffraction-free beam with a second width at the center of the diffraction-free area; wherein the second width is smaller than the first width, and the second diffraction-free beam is used to irradiate the preform to determine the geometric parameters of the preform.

[0038] Here, the geometric parameters of the preform include: cladding thickness, core radius, concentricity, verticality and refractive index distribution.

[0039] Here, the non-diffraction light beam can be a Bessel light beam. As a typical non-diffraction light beam, the Bessel light beam appears as a central light beam and a series of concentric rings in the transverse light field, in which the energy of each lobe is approximately equal. The non-diffraction light beam maintains the transverse light intensity distribution, that is, after encountering an opaque obstacle, it can also restore to the original transverse light intensity distribution. Moreover, when the non-diffraction light beam is transmitted in space, the scattering effect in the non-uniform medium is much smaller than that of the Gaussian light beam. Using a non-diffraction light beam for scanning detection will greatly improve the detection accuracy. Figure 4 FIG. 1 is a schematic diagram of generating a non-diffraction light beam provided by an embodiment of the present invention. Figure 4 As shown, a collimated Gaussian beam with uniform intensity is generated by a laser source. The laser beam passes through an axicon lens 3 (also called an axicon lens or a conical prism), and is reflected and refracted inside the axicon lens to generate a non-diffracting beam. The non-diffracting beam converges and then diverges along the optical axis. The radius of the Gaussian beam is R, the bottom angle of the axicon lens 3 is α, and the non-diffracting area of ​​the non-diffracting beam is prism-shaped, and the length of the non-diffracting area is represented by L. diff The width of the non-diffraction zone at the center is represented by w, the ring thickness is represented by H, and the ring diameter of the non-diffraction beam is represented by R L , the angle between the light ring of the undiffracted light beam and the optical axis is expressed as β.

[0040] In a possible implementation, the base angle α and the included angle β of the axicon 3 satisfy: nsinα=sin(α+β)≈α+β, where n refers to the refractive index of the axicon 3. Further, the included angle β can be expressed as: β≈(n-1)α. That is, the included angle β can be determined by selecting the known base angle α and the refractive index n.

[0041] In one possible implementation, the length L of the non-diffracting region of the non-diffracting beam is diff satisfy: And, the width w of the non-diffraction beam at the center of the non-diffraction region satisfies: Furthermore, the ring thickness H is equal to the radius R of the Gaussian beam.

[0042] For example, if the base angle of the axon is α, and α is 5°, the radius R of the Gaussian beam is 4 mm, the wavelength is 632.8 nm, the axon material is fused quartz (also known as F_SILICA), and the refractive index of the axon is 1.45702, based on the above parameters, the length L of the non-diffracting area of ​​the corresponding non-diffracting beam is diff It is about 100mm and the width w is 2mm.

[0043] It should be noted that, in the embodiments of the present invention, the type of non-diffracting beam is not limited to Bessel beam, and may also be Eich beam, Mathieu beam or variable curvature beam, etc. Among them, Eich beam has the characteristic of self-acceleration, that is, the characteristic that the beam propagates along a parabolic trajectory in free space, the Eich beam does not diffract in the transverse direction, and has the ability of self-acceleration and self-repair; the cross section of the Mathieu beam has elliptical symmetry and can be described in an elliptical coordinate system; the variable curvature beam has the advantage of propagating at different curvatures while maintaining the non-diffracting characteristic.

[0044] Here, the non-diffraction beam generation module includes: a laser, a beam expander, and an axon, wherein the laser is used to emit a Gaussian beam; the beam expander is used to increase the beam diameter of the Gaussian beam and reduce the divergence angle of the Gaussian beam to generate a beam expansion ring; and the axon is used to convert the beam expansion ring into a first non-diffraction beam. In a possible implementation, the laser is a helium-neon laser.

[0045] It should be noted that the embodiments of the present invention are not limited to using a conical lens to convert the beam expansion ring into a first non-diffracting beam. Exemplarily, when the first non-diffracting beam is a Bessel beam, an axis prism can be used to convert the incident Gaussian beam into a Bessel beam. The working principle of the axis prism is to refract the incident beam expansion ring into a conical wave to form a beam with a Bessel function cross-section; a specially designed diffractive optical element can also be used to modulate the beam expansion ring to produce a Bessel beam, wherein the specially designed diffractive optical element can be generated by precise grating design and manufacture; a spatial light modulator can also be used to convert the beam expansion ring into a Bessel beam through programmed control; a Fourier lens can also be used in combination with an appropriate amplitude or phase mask to generate a Bessel beam using the beam expansion ring on the Fourier plane. Here, the above method can also be used to convert the beam expansion ring into an Eli beam, a Mathieu beam or a variable curvature beam.

[0046] Here, in the case where the first non-diffraction light beam is a Bessel light beam, since the cross section of the first non-diffraction light beam in the non-diffraction area is a central light beam and a series of concentric rings, the central light beam needs to be scanned horizontally across the preform rod during scanning to record the distance of the central light beam from the optical axis. Although the energy of the first non-diffraction light beam is concentrated in the central area, the surrounding concentric ring light is too wide, which will also affect the measurement results, and cause problems such as complicated subsequent calculation process and difficulty in focusing. The width of the surrounding concentric rings cannot be further reduced by changing the bottom angle and the refractive index of the material. Therefore, it is necessary to use the first focusing lens and the second focusing lens to change the optical path of the first non-diffraction light beam to form a second non-diffraction light beam to reduce the width of the surrounding concentric rings. Specifically, the width adjustment module includes: a first focusing lens, which is used to focus the incident first non-diffraction light beam to generate a focused light beam; a second focusing lens, which is used to focus the focused light beam to generate a second non-diffraction light beam. Among them, the focal length of the first focusing lens is greater than the focal length of the second focusing lens, and the focal length of the second focusing lens is positively correlated with the second width. The spacing between the first focusing lens and the second focusing lens is the sum of a first distance and a second distance, wherein the first distance refers to a distance having a value equal to the focal length of the first focusing lens, and the second distance refers to a distance having a value equal to the focal length of the second focusing lens. In addition, the second width is greater than a radius of the rod core layer of the preform rod.

[0047] Here, the reflection module is a total reflection mirror, which can be placed at an angle of 45° relative to the optical axis 19 .

[0048] Figure 5 Schematic diagram of the composition of the optical system provided by the embodiment of the present invention. Figure 5As shown, a HeNe laser 1 emits a collimated Gaussian beam with uniform intensity. The Gaussian beam is expanded by a beam expander 2 and then enters an axicon 3 to form a first non-diffraction beam 4. The first non-diffraction beam 4 is a Bessel beam. The minimum width of the non-diffraction area of ​​the first non-diffraction beam 4 (i.e., the width at the center of the non-diffraction area) is represented by w1, and the length is L diff1 , the angle between the light ring of the first non-diffraction light beam and the optical axis 19 is β1, the first non-diffraction light beam 4 changes the light path direction through the total reflection mirror 5, enters the first focusing lens 6, and is focused by the first focusing lens 6. The first non-diffraction light beam 4 converges along the optical axis 19 between the first focusing lens 6 and the second focusing lens 7 to form a thin light ring and then diverges into a thick light ring. The thick light ring enters the second focusing lens 7 and is focused again by the second focusing lens 7 to form a second non-diffraction light beam. The light ring thickness of the second non-diffraction light beam is H2, the minimum width of the non-diffraction area of ​​the second non-diffraction light beam is expressed as w2, and the length is L diff2 , the angle between the second non-diffracted light beam and the optical axis is β3.

[0049] In a possible implementation, the diameter of the ring of the first non-diffracted light beam is R L Satisfy the following formula:

[0050]

[0051] Among them, L refers to the straight-line distance from the center of the diffraction-free area of ​​the first diffraction-free light beam 4 along the optical axis 19 to the total reflection mirror 5 and then to the first focusing lens 6, β1 refers to the angle between the halo of the first diffraction-free light beam and the optical axis 19, α refers to the bottom angle of the conical lens 3, and n refers to the refractive index of the conical lens 3.

[0052] In a possible implementation, the divergence angle β2 of the thin light ring satisfies the following formula:

[0053]

[0054] Wherein, H1 refers to the ring thickness of the first non-diffracted light beam, and f1 refers to the focal length of the first focusing lens 6 .

[0055] In one possible implementation, the ring thickness R of the thin ring lf Satisfaction: R lf =f1tanβ1, wherein f1 refers to the focal length of the first focusing lens 6, and β1 refers to the angle between the light ring of the first non-diffracted light beam and the optical axis 19.

[0056] In a possible implementation, the thickness H2 of the light ring of the second non-diffracted light beam satisfies: H2≈2tanβ2*f2, where β2 refers to the divergence angle of the thin light ring, and f2 refers to the focal length of the second focusing lens 7.

[0057] In a possible implementation, the angle β3 between the second non-diffracted light beam and the optical axis satisfies: Among them, R lf refers to the thickness of the thin light ring, and f2 refers to the focal length of the second focusing lens 7.

[0058] In a possible implementation, the length L of the non-diffraction region of the second non-diffraction light beam is diff2 satisfy: Wherein, H2 refers to the halo thickness of the second non-diffracting light beam, and β3 refers to the angle between the second non-diffracting light beam and the optical axis.

[0059] In a possible implementation, the minimum width w2 of the non-diffraction region of the second non-diffraction light beam satisfies: Where β3 refers to the angle between the second non-diffracted light beam and the optical axis, L diff2 It refers to the length of the non-diffraction region of the second non-diffraction beam.

[0060] Combining the above formula, it can be known that the size of the preform rod is positively correlated with the focal length of the second focusing lens 7. Selecting a suitable focusing lens 7 can effectively reduce the minimum width w2 of the non-diffraction area of ​​the second non-diffraction light beam. When the focal length f1 of the first focusing lens 6 is fixed and the focal length f1 of the first focusing lens 6 is greater than the focal length f2 of the second focusing lens 7, the smaller the focal length f2 of the second focusing lens 7 is, the smaller the minimum width w2 of the non-diffraction area of ​​the second non-diffraction light beam is. If a smaller w2 is required, it can be achieved by increasing the focal length f1 of the first focusing lens 6 and reducing the focal length f2 of the second focusing lens 7. The reduction of w2 is accompanied by L diff2 of reduction.

[0061] By using the optical system provided by the present invention to scan the preform rod, a non-diffraction narrow light beam can be obtained, which means that there is no light beam diffraction and no interference between the high-order diffraction light and the zero-order diffraction light. By using special equipment to collect the non-diffraction narrow light beam, accurate distance information of the light beam deflection optical axis can be obtained, thereby obtaining the geometric parameters of the preform rod with extremely small errors.

[0062] In another embodiment, the present invention further provides a preform analysis system, the system comprising: a platform, an optical system arranged on the platform, a detection module and an analysis module arranged on the platform; the optical system is used to scan the preform up and down along the direction perpendicular to the axial direction of the preform with a second non-diffraction light beam driven by the platform, wherein the non-diffraction area of ​​the second non-diffraction light beam is located in the rod core layer of the preform, and the center of the non-diffraction area of ​​the second non-diffraction light beam is aligned with the axis of the preform; the detection module is used to receive the non-diffraction light beam excited by the preform, and obtain the displacement information of the non-diffraction light beam according to the energy of the non-diffraction light beam, and send the displacement information of the non-diffraction light beam to the analysis module, wherein the displacement information of the non-diffraction light beam refers to the distance information of the non-diffraction light beam offset from the optical axis; the analysis module is used to determine and output the geometric parameters of the preform using the displacement information of the non-diffraction light beam.

[0063] Here, the detection module includes: a linear camera, wherein the linear camera is used to receive the non-diffraction light beam, and when the energy of the non-diffraction light beam is greater than a preset threshold, obtain the displacement information of the non-diffraction light beam, and send the displacement information of the non-diffraction light beam to the analysis module.

[0064] In a possible implementation, the detection module further includes a third focusing lens and a cylindrical lens. The third focusing lens is used to change the excited non-diffraction light beam and modify its optical path direction to be parallel to the optical axis, and the cylindrical lens is used to compress the non-diffraction light beam, and then the compressed non-diffraction light beam is captured by the linear camera.

[0065] Here, since the central beam of the Bessel beam is used to scan the preform, when the central beam has not yet entered the edge of the preform, the concentric rings around the central beam have already been incident on the preform, which will cause errors in detection. Therefore, before obtaining the displacement information of the non-diffraction beam, it is necessary to first determine whether the energy of the beam captured by the linear camera is greater than a preset threshold. If it is greater than, it is considered that the central beam is incident on the preform, and the non-diffraction beam captured by the linear camera appears as a narrow beam with a very steep edge. The displacement information of the non-diffraction beam can be obtained using the beam edge of the narrow beam; if it is less than, it is considered that the central beam has not been incident on the preform, and no operation is performed.

[0066] Here, the preform is fixedly placed in a matching liquid container, and the refractive index of the matching liquid in the matching liquid container is the same as the refractive index of the cladding of the preform.

[0067] Now combined Figure 6-Figure 8 Describe the scanning process of the second non-diffracting beam. Figure 6 4 is a cross-sectional schematic diagram of the incoherent irradiance of the second non-diffraction light beam in the X direction captured by the linear camera provided by an embodiment of the present invention. Figure 7It is a cross-sectional schematic diagram of the incoherent irradiance in the X direction when the second non-diffracting light beam is partially incident on the preform provided by an embodiment of the present invention. Figure 8 1 is a cross-sectional schematic diagram of the incoherent irradiance in the X direction when the second non-diffracting light beam provided by an embodiment of the present invention is completely incident on the preform. Figure 6-Figure 8 In the figure, the conical lens material is F_SILICA, the refractive index of the conical lens is 1.45702, the bottom angle is 5°, the radius of the Gaussian beam after expansion is 4 mm, the refractive index of the liquid is 1.514, and the preform is a step-refractive index preform with a radius of 20 mm and a cladding refractive index of 1.526.

[0068] like Figure 6 As shown, the second non-diffraction beam has not yet scanned the preform, and the non-diffraction beam captured on the linear camera shows that the edge positions of the beam are -7.061mm and 7.062mm respectively. The center position of the beam is calculated by calling the deflection function at 0.001mm (approximately equal to 0mm). The center position of the beam is at 0mm, indicating that the beam has no deflection.

[0069] like Figure 7 As shown, when the first non-diffracting beam is a Bessel beam, the preform is scanned using the second non-diffracting beam (i.e., the Bessel beam), and the preform is scanned using the second diffracting beam. Before the central beam of the second non-diffracting beam enters the preform, part of the concentric rings of the second non-diffracting beam enters the preform, and the energy of the concentric rings is significantly lower than the energy of the central beam, so that the beam distribution captured by the linear camera is that the incoherent irradiance at the edge of the beam is much lower than the energy at the center, and the edge of the beam is blurred. In this case, the displacement information of the beam is not collected.

[0070] like Figure 8 As shown, the central beam of the second non-diffraction beam is incident on the preform rod, the edge of the captured halo is steep and clear, and the energy of the halo is greater than the preset threshold. At this time, the edge positions of the beams are -4.249mm and 9.873mm respectively, and the deflection function is called to calculate that the center position of the beam is approximately 2.811mm.

[0071] Fig. 9 Schematic diagram of a preform analysis system provided by an embodiment of the present invention. Fig. 9 As shown, the optical system provided by the present invention is arranged on a platform 12. Driven by the platform 12, the preform placed in the matching liquid container 10 is scanned multiple times with a preset step length in a plane perpendicular to the axis 18 of the preform. Each time the linear camera 15 scans, a set of displacement information of the non-diffraction light beam is obtained.

[0072] After obtaining the displacement information of the non-diffraction light beam, the linear camera 15 sends it to the analysis module for further processing, including: calling the deflection function, calculating the displacement information of the non-diffraction light beam, obtaining the deflection angle of the non-diffraction light beam, and using the deflection angle of the non-diffraction light beam to calculate and obtain the geometric parameters of the preform.

[0073] In view of the problem that the existing preform analysis has beam diffraction and beam interference, the geometric parameters of the preform cannot be accurately obtained, which affects the quality control of the preform and thus seriously reduces the quality of the optical cable, the present invention provides an optical system and a preform analysis system, which have the following effects:

[0074] (1) Use a non-diffraction beam to scan the preform rod. The exciting beam is still a non-diffraction beam, which avoids beam diffraction and the interference between high-order diffraction light and zero-order diffraction light. It greatly improves the accuracy of preform rod scanning, effectively improves the quality control of preform rods, and thus greatly improves the quality of optical cables.

[0075] (2) It can avoid the need to replace other lasers or use multiple lasers when scanning with longer wavelengths or multi-wavelength beams, which causes the system to be complex and costly. It has the advantages of greatly reducing investment costs, avoiding the introduction of human errors, and being easier to operate.

[0076] (3) The traditional analysis method needs to calculate the wavelength based on the preform stripes, and needs to find the position where the peak positions of the diffraction stripes of the two wavelength beams in the detector are consistent. However, in the present invention, a non-diffraction beam is used for scanning, and the obtained beam is still a non-diffraction beam. There is no problem of beam diffraction and beam interference, that is, there is no need to find the position where the peak position of the diffraction stripes is consistent. This method does not require additional calculations, and the calculation process is consistent with the traditional calculation method, which has the characteristics of low calculation complexity.

[0077] (4) The traditional analysis method has certain requirements on the width of the preform stripes due to the problems of beam diffraction and beam interference. However, the beam obtained by the present invention does not have the problems of beam diffraction and beam interference, and thus there is no need to limit the width of the preform stripes, which can effectively improve the production efficiency of the preform.

[0078] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. An optical system, characterized in that: include: A non-diffraction light beam generating module, used to generate a first non-diffraction light beam having a first width at the center of the non-diffraction area; A reflection module, used for reflecting the first non-diffraction light beam to the width adjustment module; The width adjustment module is used to focus the incident first non-diffraction light beam to generate a second non-diffraction light beam with a second width at the center of the non-diffraction area; wherein the second width is smaller than the first width, and the second non-diffraction light beam is used to irradiate the preform rod to determine the geometric parameters of the preform rod.

2. The optical system according to claim 1, characterized in that The second width is greater than the radius of the rod core layer of the preform rod.

3. The optical system according to claim 1 or 2, characterized in that: The width adjustment module comprises: a first focusing lens, used for focusing the incident first non-diffraction light beam to generate a focused light beam; The second focusing lens is used to focus the focused light beam to generate the second non-diffraction light beam.

4. The optical system according to claim 3, characterized in that The focal length of the first focusing lens is greater than the focal length of the second focusing lens, and the focal length of the second focusing lens is positively correlated with the second width.

5. The optical system according to claim 3, characterized in that The distance between the first focusing lens and the second focusing lens is the sum of a first distance and a second distance, wherein the first distance refers to a distance having a numerical value equal to the focal length of the first focusing lens, and the second distance refers to a distance having a numerical value equal to the focal length of the second focusing lens.

6. The optical system according to claim 1, characterized in that The non-diffraction beam generation module includes: a laser, a beam expander, and an aconic lens, wherein: The laser is used to emit a Gaussian beam; The beam expander is used to increase the beam diameter of the Gaussian beam and reduce the divergence angle of the Gaussian beam to generate a beam expansion ring; The axicon is used to convert the beam expansion ring into the first non-diffraction light beam.

7. The optical system according to claim 1, characterized in that The reflection module is a total reflection mirror.

8. A preform analysis system, characterized in that: The system comprises: a platform, an optical system as described in any one of claims 1 to 7 arranged on the platform, a detection module and an analysis module arranged on the platform; The optical system is used to scan the preform rod up and down along the direction perpendicular to the axial direction of the preform rod using a second non-diffraction light beam under the drive of the platform, wherein the non-diffraction area of ​​the second non-diffraction light beam is located in the rod core layer of the preform rod, and the center of the non-diffraction area of ​​the second non-diffraction light beam is aligned with the axis of the preform rod; The detection module is used to receive the non-diffraction light beam excited by the preform, and obtain the displacement information of the non-diffraction light beam according to the energy of the non-diffraction light beam, and send the displacement information of the non-diffraction light beam to the analysis module, wherein the displacement information of the non-diffraction light beam refers to the distance information of the non-diffraction light beam offset from the optical axis; The analysis module is used to determine and output geometric parameters of the preform by using the displacement information of the non-diffraction light beam.

9. The preform analysis system according to claim 8, characterized in that: The detection module includes: a linear camera, wherein: The linear camera is used to receive the non-diffraction light beam, and when the energy of the non-diffraction light beam is greater than a preset threshold, obtain the displacement information of the non-diffraction light beam, and send the displacement information of the non-diffraction light beam to the analysis module.

10. The preform analysis system according to claim 8, characterized in that: The preform rod is fixedly placed in a matching liquid container, and the refractive index of the matching liquid in the matching liquid container is the same as the refractive index of the cladding of the preform rod.

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