A microscopic imaging objective lens and imaging method for fiber core identification of optical fiber fusion splicer

Abstract

The present invention discloses a microscopic imaging objective lens and an imaging method thereof for fiber core identification of an optical fiber fusion splicer. It adopts a coaxial transmission optical imaging structure, and along the incident direction of light, it is sequentially composed of a front group consisting of a concave-convex spherical positive lens and a meniscus spherical negative lens glued together, and a rear group consisting of a double convex spherical positive lens, a meniscus spherical negative lens and a meniscus spherical thick positive lens separated. The imaging objective lens provided by the present invention has the advantages of high resolution, small distortion, good imaging performance, short optical tube length, low processing cost, simple and compact structure, etc. Its imaging performance reaches the diffraction limit, and the resolution is as high as 2μm, which is much higher than the fiber end face diameter size of 10μm; the magnification reaches 5 times, and the fiber end face can be finely imaged, high-precision alignment can be achieved, and the fiber type can be accurately identified; at the same time, it solves the problems of large fusion loss and unstable fusion in the prior art, and meets the use requirements of the core alignment type optical fiber fusion splicer.

Description

Technical Field

[0001] The present invention relates to a high-precision microscopic imaging objective lens and an imaging method thereof for fiber core identification and alignment of an optical fiber fusion splicer, and in particular to a microscopic optical imaging lens and an imaging method thereof, which can magnify the end face of a large-aperture optical fiber by a high factor and image it onto a detector photosensitive surface with high quality for fiber core identification and high-precision alignment. Background Art

[0002] Fiber fusion splicer is a basic equipment used in the field of optical communication. It is mainly used to connect various optical fibers and perform heat shrink protection on the connection points. It can be widely used in various optical cable line construction, line maintenance, emergency repair projects, as well as coherent optical communication, interferometric fiber optic sensors and optoelectronic switching technology. It can also be used for production testing of optical fiber devices. According to the different alignment methods, fiber fusion splicers can be divided into two categories: cladding alignment type and core alignment type. The core alignment type fiber fusion splicer adopts a core detection system. Its working principle is shown in the attached Figure 1 , mainly composed of an illumination light source, a plane reflector, a high-performance microscopic imaging objective lens, a CCD detector, a drive motor, etc. The light beam emitted by the light source is first incident on the plane reflector, and then incident on the end faces of the two optical fibers that need to be aligned after being deflected by two plane reflectors. The two end faces are respectively deflected by two surfaces of the same prism and then incident on the same light path. After being aberration-free and highly magnified by a high-performance microscopic imaging objective lens, the image is formed on the CCD detector. According to the different grayscales of the image, a certain algorithm is used to drive the motor through the control circuit to achieve focusing and alignment of the optical fiber, and the image is displayed on the screen through the display system.

[0003] The quality of the core-aligned fiber fusion splicer depends on the performance of its high-precision microscopic imaging objective lens. In order to achieve low fusion loss, the fiber core must be aligned with high precision, and it must be equipped with a high-precision optical microscopic imaging objective lens to perform high-quality imaging of the two fiber end faces to be aligned, while achieving fiber type identification and high-precision alignment to ensure the quality of fiber fusion. This high-performance microscopic imaging objective lens not only requires a large relative aperture and high resolution; it is also required to have a high method magnification due to special use requirements; it is also required to have a large field of view due to specific optical path restrictions. It is difficult for ordinary imaging objective lenses to simultaneously meet the field of view requirements and large relative aperture, and it is even more difficult to obtain a high magnification, and the imaging performance is difficult to meet the requirements of the core-aligned fiber fusion splicer. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a high-precision microscopic imaging objective lens and an imaging method thereof which have a large relative aperture, high resolution, excellent imaging performance, a simple and compact structure and good stability and are used for fiber core identification and alignment of an optical fiber fusion splicer.

[0005] The technical solution for achieving the purpose of the invention is to provide a microscopic imaging objective lens for fiber core identification of an optical fiber fusion splicer, which adopts a coaxial transmission optical imaging structure, including a front group consisting of a double-cemented lens group, a double convex spherical positive lens and a rear group consisting of two double-separated meniscus spherical lenses; the double-cemented lens group is formed by cementing a concave-convex spherical positive lens of the double-cemented lens and a meniscus spherical negative lens of the double-cemented lens; along the incident direction of light, the concave-convex spherical positive lens of the double-cemented lens, the meniscus spherical negative lens of the double-cemented lens, the double convex spherical positive lens, the meniscus spherical negative lens of the rear group and the meniscus spherical thick positive lens are sequentially arranged, and the focal lengths of the optical lens elements correspond to f’ 11 , f’ 12 , f’ 2. f’ 3. f’ 4. The normalized range of the focal length relative to the imaging objective is: 0.55≤ f’ 11 ≤0.65、-1.0≤ f’ 12 ≤-0.85, 1.10≤ f’ 2≤1.45、-2.10≤ f’ 3≤-1.81、8.45≤ f’ 4≤9.05; the aperture stop is located on the biconvex spherical positive lens, and the objective lens is symmetrical about the aperture stop; the front double cemented lens group is bent toward the incident direction of the light and faces away from the front surface of the biconvex spherical positive lens; the rear surface of the biconvex spherical positive lens faces away from the front surface of the meniscus spherical negative lens of the rear group; the two meniscus spherical lenses of the rear group both face away from the incident direction of the light.

[0006] The present invention discloses a microscopic imaging objective lens for fiber core identification of an optical fiber fusion splicer. The material refractive indices of the concave-convex spherical positive lens, the biconvex spherical positive lens, and the meniscus spherical thick positive lens of the double glued lens correspond to: n 11 , n 2. n 4, the value range is 1.50≤ n 11 = n 2= n 4≤1.71; the material refractive indexes of the meniscus spherical negative lens of the double cemented lens and the meniscus spherical negative lens of the rear group correspond to: n 12 , n 3, the value range is 1.73≤ n 12 = n 3≤1.96.

[0007] The present invention provides a microscopic imaging objective lens for fiber core identification of an optical fiber fusion splicer, wherein the value range of the entrance pupil diameter is D≥14mm, the value range of the numerical aperture NA is NA≥0.2; the field of view is 2.5mm, the magnification is 5 times; and the tube length is less than 40mm.

[0008] The technical solution of the present invention also includes providing an imaging method of a microscopic imaging objective lens for fiber core identification of an optical fiber fusion splicer, the steps of which are as follows:

[0009] (1) The light emitted from the end face of the optical fiber is incident on the front double-cemented lens group, which is composed of a concave-convex spherical positive lens of the double-cemented lens and a meniscus spherical negative lens of the double-cemented lens; the double-cemented lens group is bent toward the end face of the optical fiber, receives the light beam emitted from the end face of the optical fiber with a large aperture angle, and eliminates the spherical aberration and chromatic aberration of the double-cemented lens group, and outputs a divergent light beam with concentrated energy and high resolution;

[0010] (2) The divergent light beam obtained in step (1) is incident on a biconvex spherical positive lens, the aperture stop is located on the biconvex spherical positive lens, and the objective lens is symmetrical about the aperture stop to reduce the distortion of the objective lens; the two optical surfaces of the biconvex spherical positive lens are placed back to back with the optical surface closest to the adjacent optical group, and the light beam obtained by the front group is converged and relayed to form an image, so as to obtain a converged light beam with a small optical path difference between the on-axis and off-axis light and a high concentricity;

[0011] (3) The converged light beam obtained in step (2) is incident on a rear group consisting of two double-separated meniscus spherical lenses. The meniscus spherical negative lens in the rear group diverges the incident light beam and then makes it incident nearly parallel to the meniscus spherical thick positive lens. After fine correction of optical aberrations, a 5-fold magnified fiber end face image is obtained on the detector photosensitive surface.

[0012] Compared with the prior art, the present invention adopts an optimized coaxial transmission optical structure and adopts different bending directions of lenses at different positions along the light line, thereby overcoming the design difficulty of large relative aperture, large imaging field and high magnification imaging lens, and realizing the aberration correction of large field and large relative aperture lens; at the same time, high magnification is realized by adopting different optical focal lengths of each lens in the front group and the rear group. Thus, high-precision alignment of the end faces of the two optical fibers to be fused is ensured, fusion loss is reduced, and fusion efficiency and quality are guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the working principle of the optical fiber fusion splicer;

[0014] Figure 2 It is an imaging optical path diagram of a high-precision microscopic imaging objective lens for fiber core identification and alignment of an optical fiber fusion splicer provided by an embodiment of the present invention;

[0015] Figure 3 It is a ray tracing point diagram of a high-precision microscopic imaging objective lens for fiber core identification and alignment of an optical fiber fusion splicer provided by an embodiment of the present invention;

[0016] Figure 4 It is an energy concentration curve of a high-precision microscopic imaging objective lens for fiber core identification and alignment of an optical fiber fusion splicer provided by an embodiment of the present invention;

[0017] Figure 5 It is a distortion curve of a high-precision microscopic imaging objective lens for fiber core identification and alignment of an optical fiber fusion splicer provided in an embodiment of the present invention;

[0018] Figure 6 It is a modulation transfer function curve of a high-precision microscopic imaging objective lens for fiber core identification and alignment of an optical fiber fusion splicer provided by an embodiment of the present invention.

[0019] In the figure: 11. Concave-convex spherical positive lens of double cemented lens; 12. Meniscus spherical negative lens of double cemented lens; 2. Biconvex spherical positive lens; 3. Meniscus spherical negative lens; 4. Meniscus spherical thick positive lens. DETAILED DESCRIPTION

[0020] The technical solution of the invention is further specifically described below in conjunction with the accompanying drawings and embodiments.

[0021] Embodiment 1:

[0022] The technical solution of this embodiment is to provide a high-precision microscopic imaging objective lens for fiber core identification and alignment of a fiber fusion splicer, which has an operating band of 780-820 nm, a system numerical aperture of 0.21, and a field of view of 2.5 mm.

[0023] See attached Figure 2 , which is an imaging optical path diagram of a microscope imaging objective lens for fiber core identification and alignment of a fiber fusion splicer provided in this embodiment; the microscope objective lens is composed of a front group of double-cemented lenses, a double-convex spherical positive lens, and two separate meniscus spherical lenses in the rear group. Along the incident direction of light, it is sequentially composed of a concave-convex spherical positive lens 11 of the double-cemented lens; a meniscus spherical negative lens 12 of the double-cemented lens; a double-convex spherical positive lens 2; a meniscus spherical negative lens 3; and a meniscus spherical thick positive lens 4.

[0024] The aperture stop is located on the rear surface of the double convex spherical positive lens 2, the front group double cemented lens and the rear group double separated meniscus spherical lens are located on both sides of the aperture, the objective lens is symmetrical about the aperture stop, and vertical axis aberrations, such as distortion and chromatic aberration of magnification, can be well corrected; the front group double cemented lens is bent toward the incident direction of the light and away from the front surface of the double convex spherical positive lens, and the two negative meniscus lenses in the rear group are both away from the incident direction of the light and also away from the rear surface of the double convex spherical positive lens, which can well control the optical path difference between the on-axis and off-axis point light beams, balance the astigmatism aberration, and obtain good focusing performance.

[0025] The relevant parameters of each lens are as follows: the focal length of the system is 17.96mm, the curvature radii of the front and rear surfaces of the concave-convex spherical positive lens 11 of the double cemented lens, the meniscus spherical negative lens 12 of the double cemented lens, the double convex spherical positive lens 2, the meniscus spherical negative lens 3, and the meniscus spherical thick positive lens 4 are -105.8mm, -7.58mm, -7.58mm, -26.36mm, 18.65mm, -180.21mm, 14.78mm, respectively. mm, 8.45mm, 10.68mm, 8.67mm; along the incident direction of light, the distances of each optical surface are 6.42mm, 0mm, 3.72mm, 4.53mm, 3.78mm, 0.19mm, 3.23mm, 7.25mm, 6.65mm respectively; the refractive index of each lens is 1.68, 1.74, 1.68, 1.74, 1.68 respectively; all lenses are installed in a lens barrel with a length of 35.77mm.

[0026] The imaging method of the microscopic imaging objective lens provided in this embodiment comprises the following steps:

[0027] (1) The light emitted from the fiber end face is incident on the front double-cemented lens group, which is composed of a double-cemented lens with a concave-convex spherical positive lens and a double-cemented lens with a meniscus spherical negative lens. The double-cemented lens group bends toward the fiber end face and receives the light beam emitted from the fiber end face with a large aperture angle. The double-cemented lens group eliminates spherical aberration and chromatic aberration, and outputs a divergent light beam with concentrated energy and high resolution.

[0028] (2) The divergent light beam obtained in step (1) is incident on a biconvex spherical positive lens, the aperture stop is located on the biconvex spherical positive lens, and the objective lens is symmetrical about the aperture stop to reduce the distortion of the objective lens; the two optical surfaces of the biconvex spherical positive lens are placed back to back with the optical surface closest to the adjacent optical group, and the light beam obtained by the front group is converged and relayed to form an image, so as to obtain a converged light beam with a small optical path difference between the on-axis and off-axis light and a high concentricity;

[0029] (3) The converged light beam obtained in step (2) is incident on a rear group consisting of two double-separated meniscus spherical lenses. The meniscus spherical negative lens in the rear group diverges the incident light beam and then makes it incident nearly parallel to the meniscus spherical thick positive lens. After fine correction of optical aberrations, a 5-fold magnified fiber end face image is obtained on the detector photosensitive surface.

[0030] See attached Figure 3, which is the ray tracing point diagram of the high-precision microscopic imaging objective provided by this embodiment, that is, the situation of the target object on its image plane after passing through the microscopic objective. The black circle in the figure is the Airy disk of the imaging objective. It can be seen that the point diagrams at different fields of view of each wavelength on the image plane are very concentrated within the Airy disk, indicating that the imaging objective has achieved the imaging characteristics of the diffraction limit. Figure 4 It can also be seen from the energy concentration curve that the energy concentration of the imaging beam in each field of view on the image plane within a radius of 10 microns is above 80%.

[0031] See attached Figure 5 , is the distortion curve of the high-precision microscopic imaging objective lens provided in this embodiment, the abscissa is the distortion value, and the ordinate represents the field of view. It can be seen that the maximum value is less than 0.3%.

[0032] See attached Figure 6 , is the optical transfer function curve of the high-precision microscopic imaging objective provided by this embodiment, the abscissa is the spatial frequency, and the ordinate is the optical function value. It can be seen that the transfer function value of the optical system at 25lp / mm on the image plane reaches 0.7, and the corresponding object plane can resolve details less than 2μm.

Claims

1. A microscopic imaging objective lens for fiber core identification in an optical fiber fusion splicer, characterized in that: It adopts a coaxial transmission optical imaging structure, including a front group consisting of a double-cemented lens group, a double convex spherical positive lens and a rear group consisting of two double-separated meniscus spherical lenses; the double-cemented lens group is formed by cementing a concave-convex spherical positive lens (11) of the double-cemented lens and a meniscus spherical negative lens (12) of the double-cemented lens; along the incident direction of light, the concave-convex spherical positive lens (11) of the double-cemented lens, the meniscus spherical negative lens (12) of the double-cemented lens, the double convex spherical positive lens (2), the meniscus spherical negative lens (3) of the rear group and the meniscus spherical thick positive lens (4), and the focal lengths of the optical lens elements correspond to f’ 11 , f’ 12 , f’ 2. f’ 3. f’ 4. The normalized range of the focal length relative to the imaging objective is: 0.55≤ f’ 11 ≤0.65、-1.0≤ f’ 12 ≤-0.85, 1.10≤ f’ 2≤1.45、-2.10≤ f’ 3≤-1.81、8.45≤ f’ 4≤9.05; the aperture stop is located on the biconvex spherical positive lens, and the objective lens is symmetrical about the aperture stop; the front double cemented lens group is bent toward the incident direction of the light and faces away from the front surface of the biconvex spherical positive lens; the rear surface of the biconvex spherical positive lens faces away from the front surface of the meniscus spherical negative lens of the rear group; the two meniscus spherical lenses of the rear group both face away from the incident direction of the light; The material refractive indices of the concave-convex spherical positive lens, the biconvex spherical positive lens, and the meniscus spherical thick positive lens of the double cemented lens correspond to: n 11 , n 2. n 4, the value range is 1.50≤ n 11 = n 2= n 4≤1.71; the material refractive indexes of the meniscus spherical negative lens of the double cemented lens and the meniscus spherical negative lens of the rear group correspond to: n 12 , n 3, the value range is 1.73≤ n 12 = n 3≤1.96; The value range of the entrance pupil diameter is D≥14mm, and the value range of the numerical aperture NA is NA≥0.

2.

2. The microscopic imaging objective lens for fiber core identification in an optical fiber fusion splicer according to claim 1, characterized in that: The field of view is 2.5mm and the magnification is 5 times.

3. The microscopic imaging objective lens for fiber core identification in an optical fiber fusion splicer according to claim 1, characterized in that: The tube length is less than 40mm.

4. An imaging method based on the microscopic imaging objective lens for fiber core identification of an optical fiber fusion splicer according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) The light emitted from the end face of the optical fiber is incident on the front double-cemented lens group, wherein the double-cemented lens group is formed by cementing a concave-convex spherical positive lens (11) of the double-cemented lens and a meniscus spherical negative lens (12) of the double-cemented lens; the double-cemented lens group is bent toward the end face of the optical fiber, receives the light beam emitted from the end face of the optical fiber with a large aperture angle, and eliminates the spherical aberration and chromatic aberration of the double-cemented lens group, and outputs a divergent light beam with concentrated energy and high resolution; (2) The divergent light beam obtained in step (1) is incident on a biconvex spherical positive lens (2), the aperture stop is located on the biconvex spherical positive lens, and the objective lens is symmetrical about the aperture stop, thereby reducing the distortion of the objective lens; the two optical surfaces of the biconvex spherical positive lens are placed back to back with the optical surface closest to the adjacent optical group, and the light beam obtained by the front group is converged and relayed for imaging, thereby obtaining a convergent light beam with a small optical path difference between the on-axis and off-axis light rays and a high concentricity; (3) The converged light beam obtained in step (2) is incident on a rear group consisting of two double-separated meniscus spherical lenses. The meniscus spherical negative lens (3) in the rear group diverges the incident light beam and then makes it incident nearly parallel to the meniscus spherical thick positive lens (4). After fine correction of optical aberrations, a 5-fold magnified fiber end face image is obtained on the detector photosensitive surface.

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