A low-magnification double-telecentric microscope imaging objective system and its application

Abstract

The present invention discloses a low-magnification double-telecentric microscopic imaging objective lens system and its application. From the object side to the image side, along the direction of light incidence, the system comprises a flat low-pass filter, a front objective lens group consisting of a biconvex spherical positive lens, a rear objective lens group consisting of a meniscus spherical positive lens and the same lens as the front objective lens group, and an aperture stop is placed at the image-side focal plane of the front objective lens group and the object-side focal plane of the rear objective lens group to form a double-telecentric imaging optical path. The low-magnification double-telecentric microscopic imaging objective lens system provided by the present invention has the advantages of high resolution, low distortion, good imaging performance, simple and compact structure, and low cost. Its imaging performance reaches the diffraction limit, and it can achieve fine imaging of the end face of a ribbon optical fiber and high-precision alignment when the magnification is ≤1X. It can also accurately identify the type of 4-16 core ribbon optical fibers, meeting the use requirements of a core-aligned ribbon optical fiber fusion splicer.

Description

Technical Field

[0001] The patent of this invention relates to optical imaging technology, a low-magnification double-telecentric microscopic imaging objective system and its application, specifically to a microscopic optical imaging objective that can image the end face of a ribbon optical fiber onto a CMOS chip with high definition, and is used for ribbon optical fiber identification and high-precision alignment. Background Art

[0002] Fiber fusion splicers are primarily used for the construction and maintenance of optical cables in optical communications, hence the name "cable fusion splicer." Their general operating principle is to use a high-voltage arc to fuse two optical fiber sections, while simultaneously using a high-precision motion mechanism to gently advance the two fibers into a single strand, thereby coupling the fiber mode fields. With the rapid development of optical communications and advancements in related technologies, ribbon fiber fusion splicers, specifically designed for splicing ribbon fibers, have gained significant demand in recent years. They are used by major operators, engineering companies, enterprises, and institutions for optical cable line construction, line maintenance, emergency repair, production and testing of optical fiber components, and research and teaching at scientific research institutions.

[0003] The characteristic of ribbon fiber is that it is wider than a single optical fiber, and each ribbon can contain 4, 8, 12, or 16 optical fibers. The spacing between the optical fibers in the ribbon is 0.28mm (for 4 and 8) and 0.3mm (for 12 and 16), and they are arranged neatly and have flatness in the vertical direction. 12-core flat fiber is the most widely used ribbon fiber. Ordinary single-core communication optical fiber is a cylindrical material composed of quartz crystal material with a diameter of 0.125mm, while the 12-core ribbon fiber is flat and 3mm wide. Its overall splicing requires that all 12 core fibers be spliced at the same time and heat-shrunk for protection. The final splicing point is about the same size as the single-core fiber splicing point, giving full play to the characteristics of fast and convenient splicing of ribbon fiber. Core alignment is currently the most popular alignment method for fiber fusion splicers. Its quality depends on the performance of its high-precision microscopic imaging objective. To achieve low splice loss, the fiber cores must be aligned with high precision. This requires a high-precision optical microscopic imaging objective to perform high-quality imaging of the two fiber end faces to be aligned, while also enabling fiber type identification and high-precision alignment to ensure fiber splice quality. This high-performance microscopic imaging objective requires a large relative aperture and high resolution; limitations imposed by specific optical paths make it difficult for ordinary imaging objectives to simultaneously meet these requirements. Ensuring that the ribbon fiber image can be recognized by the system is a challenging task. A clear image of the largest 12-core ribbon fiber can be formed on the chip's photosensitive surface. Furthermore, determining the three-dimensional alignment of the two ribbon fibers in space requires observing the fibers in two mutually perpendicular directions. This requires the design of a specialized microscope objective lens with both a sufficient field of view and a certain depth of field. Therefore, the objective lens's magnification is limited. Considering image distortion and clarity, and considering that the fiber fusion splicer is a portable tool, the optical system must be compact, limiting the size of the objective lens. The objective lens's magnification is no greater than 1x.

[0004] The Chinese patent publication number is "CN110824682A", and the name is "A microscopic imaging objective lens for fiber core identification in an optical fiber fusion splicer and an imaging method thereof". It specifically discloses "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 the light, according to The next step is a double cemented concave-convex spherical positive lens, a double cemented meniscus spherical negative lens, a double convex spherical positive lens, a rear group of meniscus spherical negative lenses, and a meniscus spherical thick positive lens... " The comparative document uses a "negative + positive" type of large-field image-side telecentric optical path, which can ensure that the optical system has a relatively small size and mass, but the system magnification can only be greater than 1X, and the general magnification is 4X to 10X. This system is mostly used in single-core optical fiber fusion splicers and is difficult to apply to ribbon optical fiber fusion splicers. Summary of the Invention

[0005] The low-magnification bi-telecentric microscopic imaging objective lens provided by the present invention offers high resolution, minimal distortion, excellent imaging performance, a simple and compact structure, and low cost. Its imaging performance reaches the diffraction limit, with a magnification of 0.5x. It enables precise imaging of fiber ribbon end faces, high-precision alignment, and accurate identification of 12-core fiber ribbon types, meeting the requirements of core-aligned fiber ribbon fusion splicers. Furthermore, due to the bi-telecentric optical path between the object and image sides, it offers a large depth of field, facilitating lens assembly and adjustment in the fusion splicer.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] On the one hand, the present application provides a low-magnification bi-telecentric microscopic imaging objective system, which includes a low-pass filter, a front objective lens group, and a rear objective lens group in sequence from the object side to the image side along the incident direction of light; wherein,

[0008] The front objective lens group includes a first biconvex spherical positive lens;

[0009] The rear objective lens group includes a meniscus spherical positive lens and a second biconvex spherical positive lens.

[0010] The second biconvex spherical positive lens is arranged on the side close to the image side;

[0011] An aperture stop is further provided between the front objective lens group and the rear objective lens group, and a low-magnification double telecentric imaging optical path is formed by placing the aperture stop at the image-side focal plane of the front objective lens group and the object-side focal plane of the rear objective lens group.

[0012] As a preferred solution, the low-pass filter is a double-sided polished plane mirror, wherein the side facing away from the object is coated with a dielectric anti-reflection film, so that the transmittance τ of the flat low-pass filter is ≤10%.

[0013] As a preferred embodiment, the first biconvex spherical positive lens and the second biconvex spherical positive lens are lenses with the same structure, and the curvature radius of the curved surface close to the object side is 18 to 20 mm, the curvature radius of the curved surface close to the image side is: -25 to -40 mm, and the focal length of the positive lens is 13 to 18 mm.

[0014] As a preferred solution, the curvature radius of the curved surface of the meniscus spherical positive lens close to the object side is -40 to -60 mm, the curvature radius of the curved surface close to the image side is -10 to -15 mm, and the focal length of the positive lens is 18 to 22 mm.

[0015] As a preferred solution, the first biconvex spherical positive lens, the second biconvex spherical positive lens and the meniscus spherical positive lens have a refractive index greater than 1.7 and an Abbe number less than 50.

[0016] On the other hand, the present application provides an application of a low-magnification bi-telecentric microscopic imaging objective system in optical fiber fusion identification and alignment, characterized in that it includes the following steps:

[0017] The fiber fusion splicer lighting system irradiates 625nm light onto the optical fiber. After passing through the optical fiber, the light irradiates the low-pass filter to ensure that the optical fiber imaging on the chip has reasonable light energy.

[0018] The light passing through the low-pass filter is incident on the biconvex spherical positive lens to form the front objective lens group;

[0019] Then it is converged by a double convex spherical positive lens, and outputs a concentrated energy and high resolution converging beam to its image focal plane;

[0020] The aperture stop is placed on the double convex spherical image focal plane, the object focal plane of the rear objective lens group coincides with the double convex spherical image focal plane, and the entire objective lens system is symmetrical about the aperture stop;

[0021] The converged light beam obtained above is incident on the rear objective lens group, passes through the meniscus spherical positive lens and the second double convex spherical positive lens in sequence, and after the optical aberration is corrected by the objective lens system, a magnified fiber image is obtained on the photosensitive surface of the detector.

[0022] As a preferred solution, the magnification obtained on the photosensitive surface of the detector is ≤1X.

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] The object of the present invention is to provide a low-magnification bi-telecentric microscopic imaging objective lens with the advantages of high resolution, small distortion, good imaging performance, simple and compact structure and low cost.

[0025] The low-magnification bi-telecentric microscopic imaging objective provided by the present invention is applied to a core-aligned ribbon optical fiber fusion splicer. Its imaging performance reaches the diffraction limit. It can achieve fine imaging of the end face of the ribbon optical fiber and high-precision alignment when the magnification is ≤1X. It can also accurately identify the type of 4-16-core ribbon optical fibers, meeting the use requirements of the core-aligned ribbon optical fiber fusion splicer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure is a schematic diagram of the structure of a low-magnification bi-telecentric microscope imaging objective lens of the present invention.

[0027] Figure 2 Schematic diagram of the working principle of a specific embodiment of the present invention.

[0028] Figure 3 This is an MTF diagram in a specific embodiment of the present invention.

[0029] Figure 4 This is the diffuse pattern in a specific embodiment of the present invention.

[0030] Figure 5 4 is a field curvature distortion diagram in a specific embodiment of the present invention.

[0031] Figure 6 This is an imaging optical path diagram in a specific embodiment of the present invention.

[0032] Among them: 10- flat low-pass filter, 20- front objective lens group, 30- aperture stop, 40- rear objective lens group, 401- second biconvex spherical positive lens, 402- meniscus spherical positive lens. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] See also Figure 1-2 The present invention provides a technical solution: a low-magnification bi-telecentric microscopic imaging objective system, characterized in that: from the object side to the image side, along the incident direction of light, it includes a low-pass filter, a front objective lens group and a rear objective lens group in sequence; wherein,

[0035] The front objective lens group includes a first biconvex spherical positive lens;

[0036] The rear objective lens group includes a meniscus spherical positive lens and a second biconvex spherical positive lens, wherein the second biconvex spherical positive lens is arranged on the side close to the object side;

[0037] An aperture stop is further provided between the front objective lens group and the rear objective lens group, and a low-magnification double telecentric imaging optical path is formed by placing the aperture stop at the image-side focal plane of the front objective lens group and the object-side focal plane of the rear objective lens group.

[0038] An application of a low-magnification bi-telecentric microscopic imaging objective system in optical fiber fusion identification and alignment is characterized by comprising the following steps:

[0039] The fiber fusion splicer lighting system irradiates 625nm light onto the optical fiber. After passing through the optical fiber, the light is irradiated onto the low-pass filter to ensure that the optical fiber imaging on the chip has reasonable light energy. The function of the low-pass filter is to reduce the energy of the light passing through and suppress the background brightness of the chip image surface from the light that does not pass through the optical fiber.

[0040] The light passing through the low-pass filter is incident on the biconvex spherical positive lens to form the front objective lens group;

[0041] Then it is converged by a double convex spherical positive lens, and outputs a concentrated energy and high resolution converging beam to its image focal plane;

[0042] The aperture stop is located on the image-side focal plane of the biconvex spherical lens. The object-side focal plane of the rear objective lens group coincides with the image-side focal plane of the biconvex spherical lens. The entire objective lens system is symmetrical about the aperture stop. In this way, the principal rays of the object and image sides are parallel to the optical axis, combining the advantages of the object-side telecentric and image-side telecentric optical paths. Both object-side distortion and image-side distortion are eliminated, reducing objective lens distortion.

[0043] The converged light beam obtained above is incident on the rear objective lens group, passes through the meniscus spherical positive lens and the second double convex spherical positive lens successively, and after the optical aberration is corrected by the objective lens system, a magnified optical fiber image is obtained on the photosensitive surface of the detector, and the magnification obtained on the photosensitive surface of the detector is ≤1X.

[0044] The specific parameters of each lens are shown in the following objective lens parameter table. The flat low-pass filter is a double-sided polished plane mirror, the surface facing away from the object is coated with a dielectric anti-reflection film, so that the flat low-pass filter has a transmittance τ ≤ 6% (625 ± 20 μm), a thickness of 1.0 ± 0.1 mm, and is made of H-K9L material. The front objective lens group consists of a biconvex spherical positive lens, the curvature radius of the surface of which is close to the object is 19. The rear objective lens assembly consists of a positive spherical meniscus lens and the same lens elements as the front objective assembly. The meniscus lens has a curvature radius of -54.09mm on the object side and a curvature radius of -11.934mm on the image side, with a positive focal length of 19.44mm. The refractive indices of the biconvex spherical positive lens and the meniscus lens are 1.806105 / 1.772501, respectively, and their Abbe numbers are 41.02 / 49.61.

[0045] The optical parameters of this embodiment are shown in Table 1. The system parameters implemented are as follows: optical conjugate distance (distance from the object plane to the image plane TTL) 50 mm, object working distance 12.5 mm, mechanical back focus 7 mm, operating wavelength 625 ± 20 μm, and image plane size 1443.2 μm × 1082.5 μm.

[0046] surface Curvature radius R(mm) Thickness (mm) Refractive index / Abbe number Remark 1 Infinity 12.50 1.516789 / 64.20 2 Infinity 1.00 3 Infinity 0.45 4 19.860 1.63 1.806105 / 41.02 5 -31.480 14.40 6 Infinity 7.57 7 -54.019 1.53 1.772501 / 49.61 8 -11.934 1.05 9 19.860 1.63 1.806105 / 41.02 10 -31.480 8.30 11 Infinity

[0047] Objective lens parameter table

[0048] Analysis Notes:

[0049] Figure 3 This is a ray tracing spot diagram for the low-magnification bi-telecentric microscope imaging objective system provided by this embodiment, showing the target object on the image plane after passing through the microscope objective. The black circle in the figure represents the Airy disk of the imaging objective. As can be seen, the spot diagrams at different fields of view on the image plane are very concentrated, with the majority of the energy focused within the Airy disk, indicating that this imaging objective has essentially achieved diffraction-limited imaging characteristics.

[0050] Figure 4 This is the distortion curve for the low-magnification bi-telecentric microscopic imaging objective system provided in this embodiment. The horizontal axis represents the distortion value, and the vertical axis represents the field of view. As can be seen, the maximum value is less than 0.8%. Since this system is used for fiber optic imaging recognition and alignment, not measurement applications, the distortion fully meets the requirements.

[0051] Figure 5This is the optical transfer function curve for the low-magnification bi-telecentric microscopic imaging objective system provided by this embodiment. The horizontal axis represents spatial frequency, and the vertical axis represents the optical function value. As can be seen, the optical system's transfer function value reaches 0.5 at 40 lp / mm on the image plane, corresponding to an object plane capable of resolving details less than 2 μm.

[0052] Figure 6 This is an imaging optical path diagram of the low-magnification bi-telecentric microscopic imaging objective system provided in this embodiment.

[0053] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A low-magnification bi-telecentric microscopic imaging objective system, characterized by: From the object side to the image side, along the incident direction of the light, it includes the low-pass filter, the front objective lens group and the rear objective lens group in sequence; among them, The front objective lens group includes a first biconvex spherical positive lens; The rear objective lens group includes a meniscus spherical positive lens and a second biconvex spherical positive lens. The second biconvex spherical positive lens is arranged on the side close to the image side; An aperture stop is further provided between the front objective lens group and the rear objective lens group, and a low-magnification double telecentric imaging optical path is formed by placing the aperture stop at the image-side focal plane of the front objective lens group and the object-side focal plane of the rear objective lens group; The first biconvex spherical positive lens and the second biconvex spherical positive lens have the same structure, and the curvature radius of the curved surface close to the object side is 18-20 mm, the curvature radius of the curved surface close to the image side is: -25 to -40 mm, and the focal length of the positive lens is 13-18 mm; The meniscus spherical positive lens has a curvature radius of -40 to -60 mm on the surface close to the object side and a curvature radius of -10 to -15 mm on the surface close to the image side. The focal length of the positive lens is 18 to 22 mm. The first biconvex spherical positive lens, the second biconvex spherical positive lens and the meniscus spherical positive lens have a refractive index greater than 1.7 and an Abbe number less than 50.

2. A low-magnification bi-telecentric microscopic imaging objective system according to claim 1, characterized in that: The low-pass filter is a double-sided polished plane mirror, wherein the side facing away from the object is coated with a dielectric anti-reflection film, so that the transmittance τ of the flat low-pass filter is ≤10%.

3. The application of a low-magnification bi-telecentric microscopic imaging objective system in optical fiber fusion identification and alignment according to claim 1, characterized in that: The following steps are involved: The fiber fusion splicer lighting system irradiates 625nm light onto the optical fiber. After passing through the optical fiber, the light irradiates the low-pass filter to ensure that the optical fiber imaging on the chip has reasonable light energy. The light passing through the low-pass filter is incident on the biconvex spherical positive lens to form the front objective lens group; Then it is converged by a double convex spherical positive lens, and outputs a concentrated energy and high resolution converging beam to its image focal plane; The aperture stop is placed on the double convex spherical image focal plane, the object focal plane of the rear objective lens group coincides with the double convex spherical image focal plane, and the entire objective lens system is symmetrical about the aperture stop; The converged light beam obtained above is incident on the rear objective lens group, passes through the meniscus spherical positive lens and the second double convex spherical positive lens in sequence, and after the optical aberration is corrected by the objective lens system, a magnified fiber image is obtained on the photosensitive surface of the detector.

4. The application of a low-magnification bi-telecentric microscopic imaging objective system in optical fiber fusion identification and alignment according to claim 3, characterized in that: The magnification obtained on the photosensitive surface of the detector is ≤1X.

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