High-precision light spot test system and method based on spatial imaging system

Abstract

A high-precision light spot test system and method based on a space imaging system. The test system comprises: a wide-spectrum light source (1), an optical fiber (2), a light source focusing lens (3),

Description

The present invention belongs to the technical field of optics and optical communications, and particularly relates to a high-precision light spot size test system and method based on a spatial imaging system. BACKGROUND In recent years, development of 5G communication has driven rapid upgrades in the optical communication technology, which also pose challenges, particularly in terms of energy consumption and performance ratio. In optical communications, part of energy loss arises at a photonic switching interface. Due to differences in mode field sizes of light in different material media, modes of emission light spots mismatch during energy exchange, and part of the light becomes scattered light, thereby resulting in low coupling efficiency, increasing energy consumption of system, and reducing a signal-to-noise ratio of communication. Accurate measurement of emission light spots of the structure significantly helps to further improve coupling efficiency of optical interfaces through engineering design. However, in the prior art, sizes of the emission light spots are hardly accurately measured usually due to two primary reasons as follows: On the one hand, designed emission light spots of the structure differ from prepared emission light spots of the structure due to differences in materials, processes, environments, and the like. On the other hand, an actual size of emission light spots is not directly related to a size of an emission facet, indicating that an exact size of emission light spots cannot be determined simply by observing near-field light spots and facet characteristics. At present, there is a lack of accurate measurement solutions. SUMMARY In order to solve the above problems, the present invention provides a high-precision light spot size test system and method based on a spatial imaging system, which is widely applicable to measuring light spot sizes of micron-scale light-emitting elements. In order to achieve the above objective, the present invention provides a technical solution as follows: A high-precision light spot size test method based on a spatial imaging system, including the following steps: SI, selecting appropriate parameters selecting a high-magnification objective lens, a Fourier lens and an imaging lens whose parameters satisfy conditions of 2f0 tan(sin-1 NA) fc / fp <Lx and 2fo tan(sin-1 NA)fc / fF <LY , where fo is an equivalent focal length of the high-magnification objective lens, NA is a numerical aperture of the high-magnification objective lens, fc is a focal length of the imaging lens, fF is a focal length of the Fourier lens, Lx is a horizontal size of a photosensitive surface of a CCD camera, Ly is a vertical size of the photosensitive surface of the CCD camera, and a maximum diameter of a back-focal-plane image of the high-magnification objective lens remains within a range of receiving by the CCD camera; and a real image magnification ( / c ■ fF) / (fi ■ fo) causes an area of projecting a specimen onto the CCD camera after magnification to be smaller than an area of the CCD camera; S2, installing and calibrating a test system when the test system includes a Kohler lens, an iris, and a secondary focusing lens, the following steps are included: installing the test system, connecting an optical fiber to a light source, sequentially arranging a tube lens for light source and a beam splitter on an optical path introduced by the optical fiber from near to far, arranging the high-magnification objective lens and a six-axis carrier platform on a reflection path of the beam splitter, sequentially arranging the Fourier lens, the secondary focusing lens, the imaging lens, a variable neutral density filter, and the CCD camera on a transmission path of the beam splitter from near to far, and connecting the CCD camera to a computer; loading a silver-coated mirror onto the six-axis carrier platform, where an optical path sequence is as follows: the optical fiber^-the tube lens for light source^the beam splitter^the high-magnification objective lens^-the silver-coated mirror—>the high-magnification objective lens^the beam splitter—>the Fourier lens—>the secondary focusing lens—>the imaging lens^the variable neutral density filter—>the CCD camera; adjusting a distance between the six-axis carrier platform and the high-magnification objective lens such that an image displayed on the computer is a focused image on a surface of the silver-coated mirror; removing the secondary focusing lens; adjusting the variable neutral density filter such that maximum image brightness obtained by the computer is close to saturation; recording the image and measuring horizontal and vertical widths at the image brightness of 1 / e2 denoted as Xi pixels and Yi pixels; when the test system does not include the Kohler lens, the iris, and the secondary focusing lens, the following steps are included: installing the test system, where the Fourier lens is not arranged; connecting the optical fiber to the light source, sequentially arranging the tube lens for light source and the beam splitter on an optical path introduced by the optical fiber from near to far, arranging the high-magnification objective lens and the six-axis carrier platform on a reflection path of the beam splitter, sequentially arranging the imaging lens, the variable neutral density filter, and the CCD camera on a transmission path of the beam splitter from near to far, and connecting the CCD camera to the computer; loading the silver-coated mirror onto the six-axis carrier platform, where an optical path sequence is as follows: the optical fiber—>the tube lens for light source^the beam splitter^the high-magnification objective lens^the silver-coated mirror—>the high-magnification objective lens—>the beam splitter^the imaging lens^the variable neutral density filter—► the CCD camera; adjusting a distance between the six-axis carrier platform and the high-magnification objective lens such that an image displayed on the computer is a focused image on a surface of the silver-coated mirror; adding the Fourier lens between the beam splitter and the imaging lens; adjusting the variable neutral density filter such that maximum image brightness obtained by the computer is close to saturation; recording the image and measuring horizontal and vertical widths at the image brightness of 1 / e2 denoted as Xi pixels and Yi pixels; S3, testing the specimen when the test system includes a Kohler lens, an iris, and a secondary focusing lens, the following steps are included: loading the specimen onto a specimen stage, installing the test system, connecting the optical fiber to the light source, sequentially arranging the tube lens for light source, the Kohler lens and the beam splitter on an optical path introduced by the optical fiber from near to far, arranging the high-magnification objective lens and the six-axis carrier platform on a reflection path of the beam splitter, sequentially arranging the Fourier lens, the secondary focusing lens, the imaging lens, the variable neutral density filter, and the CCD camera on a transmission path of the beam splitter from near to far, arranging the iris between the Fourier lens and the secondary focusing lens, allowing the optical path to pass through an aperture on the iris, and connecting the CCD camera to the computer; where an optical path sequence is as follows: the optical fiber—>the tube lens for light source—>the Kohler lens^the beam splitter—>the high-magnification objective lens^the specimen—>the high-magnification objective lens—>the beam splitter^the Fourier lens^the iris^the secondary focusing lens^the imaging lens^the variable neutral density filter^the CCD camera; adjusting a distance between the six-axis carrier platform and the high-magnification objective lens such that an image displayed on the computer is a real image reflected on a surface of the specimen; locating vicinity of a light-emitting part of the specimen through the reflected real image; allowing the specimen to self-illuminate, and removing the beam splitter from the optical path, where the optical path sequence is changed to the specimen—>the high-magnification objective lens^-the Fourier lens^-the iris-—*the secondary focusing lens—>the imaging lens^the variable neutral density filter—»the CCD camera; further moving the specimen to center and focus a light spot seen by the CCD camera; changing a size of the iris to limit an imaging range to only the vicinity of the light spot; removing the secondary focusing lens, and adjusting the variable neutral density filter such that maximum image brightness obtained by the computer is the same as that of a calibrated image; recording the image and measuring horizontal and vertical widths at the image brightness of 1 / e2 denoted as X2 pixels and Y2 pixels; when the test system does not include the Kohler lens, the iris, and the secondary focusing lens, the following steps are included: loading the specimen onto the specimen stage, where the Fourier lens is not arranged; connecting the optical fiber to the light source, sequentially arranging the tube lens for light source and the beam splitter on an optical path introduced by the optical fiber from near to far, arranging the high-magnification objective lens and the six-axis carrier platform on a reflection path of the beam splitter, sequentially arranging the imaging lens, the variable neutral density filter, and the CCD camera on a transmission path of the beam splitter from near to far, and connecting the CCD camera to a computer; where an optical path sequence is as follows: the optical fiber^the tube lens for light source^-the beam splitter^-the high-magnification objective lens^the specimen—>the high-magnification objective lens^the beam splitter^the imaging lens^the variable neutral density filter^the CCD camera; adjusting a distance between the six-axis carrier platform and the high-magnification objective lens such that an image displayed on the computer is a real image reflected on a surface of the specimen; locating vicinity of a light-emitting part of the specimen through the reflected real image; allowing the specimen to self-illuminate, and removing the beam splitter from the optical path, where the optical path sequence is changed to the specimen—>the high-magnification objective lens^the imaging lens—>the variable neutral density filter—>the CCD camera; further moving the specimen to center and focus a light spot seen by the CCD camera; adding the Fourier lens between the beam splitter and the imaging lens; adjusting the variable neutral density filter such that maximum image brightness obtained by the computer is the same as that of a calibrated image; recording the image and measuring horizontal and vertical widths at the image brightness of 1 / e2 denoted as X2 pixels and Y2 pixels; S4, performing data processing By comparing calibration data with tested data, calculating a horizontal divergence angle sin-1 (— ■ NA) of the specimen, a horizontal diameter A / (trsin-1 (— ■ NA]) of a corresponding Gaussian light spot, a vertical divergence angle sin-1 ■ NA^, and a vertical diameter A / ^tt sin-1 ■ NA^ of the corresponding Gaussian light spot. Further, the following step is further included: measuring a far-field image size of the specimen according to intensity distribution of Fourier images of the specimen. The present invention further provides a high-precision light spot size test system based on a spatial imaging system, and the test system includes a broadband light source, an optical fiber, a tube lens for light source, a beam splitter, a high-magnification objective lens, a six-axis carrier platform, a Fourier lens, an imaging lens, a variable neutral density filter, a CCD camera, and a computer; the broadband light source is connected to the optical fiber, the tube lens for light source and the beam splitter are sequentially arranged on an optical path introduced by the optical fiber from near to far, the high-magnification objective lens and the six-axis carrier platform are arranged on a reflection path of the beam splitter, the Fourier lens, the imaging lens, the variable neutral density filter, and the CCD camera are sequentially arranged on a transmission path of the beam splitter from near to far, and the CCD camera is connected to the computer; and the optical fiber introduces light from the broadband light source into the test system; the tube lens for light source is configured to collimate light emitted by the broadband light source through the optical fiber; the beam splitter is configured to combine a reflection path and a transmission path into one optical path in front of the high-magnification objective lens; the high-magnification objective lens is configured to collect light from all emission directions of the specimen; the six-axis carrier platform is configured to load the specimen; the Fourier lens is configured to focus a back-focal-plane image of the high-magnification objective lens and perform optical Fourier transform on a near-field light spot to obtain a corresponding far-field image; the imaging lens is configured to form a focused real image on the CCD camera; the variable neutral density filter is configured to reduce light transmittance; and the computer is configured to receive and process images from the CCD camera. Further, a Kohler lens, an iris, and a secondary focusing lens are further included: the Kohler lens is arranged between the tube lens for light source and the beam splitter, the iris and the secondary focusing lens are arranged between the Fourier lens and the imaging lens and located on a transmission path of the beam splitter, the iris is located at a position where a rear focus of the Fourier lens and a front focus of the secondary focusing lens are overlapped, and the transmission path passes through an aperture on the iris; and the Kohler lens is configured to form a Kohler illumination system in front of the high-magnification objective lens and enlarge an illumination range of the high-magnification objective lens; the iris is configured to filter out scattered light; and the secondary focusing lens is configured to focus a back-focal-plane image of the Fourier lens and realize a wavefront at a position where the iris is located, which facilitates adjustment of a filtering range. Further, the tube lens for light source, the Kohler lens, the Fourier lens, the secondary focusing lens and the imaging lens are all aspherical lenses, an anti-reflection coating with a corresponding wavelength is to be coated on both sides of the lens, and a diameter of the lens is not less than 1 inch but not greater than 2 inches; and parameters of the high-magnification objective lens, the Fourier lens and the imaging lens are to satisfy conditions of 2 / 0 tan(sin-1 NA) fc / fp <Lx, ?fo tan(sin-1 NA) fc / fr <LY, where Lx and Ly denote horizontal and vertical sizes of the CCD camera. Further, a measurement parameter of the specimen is a divergence angle is <9<sin lNA . Further, the beam splitter is a thin-film beam splitter or a block beam splitter, and is coated with an anti-reflection coating with a corresponding wavelength on both sides thereof, with a splitting ratio of 50:50, and functions to combine a reflection path and a transmission path into one optical path in front of the high-magnification objective lens. Further, a magnification M of the high-magnification objective lens is not less than 40, a numerical aperture (NA) is not less than 0.5 but less than 1, and a surface thereof is coated with an anti-refl ection coating with a corresponding wavelength. Further, the iris has an aperture ranging from 0.1 mm to 10 mm, and functions to filter out scattered light through spatial filtering to increase a signal-to-noise ratio for testing. Further, the broadband light source is a halogen lamp with a wavelength covering visible light to near-infrared; the optical fiber is usually a multimode optical fiber with a diameter of less than 1 mm; and the variable neutral density filter has a variable neutral density ranging from 0.1 to 4. The present invention has the following beneficial effects: 1. The present invention accurately derives a size of Gaussian light spot by measuring a far-field divergence angle of the light spot emitted by a device under test, and solves the problems including large errors in light spot measurement caused by inability to accurately locate a waist position of Gaussian beam, complexity of measuring with an instrument (measuring by just moving a robotic arm), and the like. 2. The test system of the present invention enables highly-free measurement within a large range, and characteristics of the specimen can be satisfied by adjusting corresponding measurement parameters. The measured light spot size ranges from sub-millimeter to submicron, and the wavelength range covers visible light to near-infrared, which is far superior to the prior art. 3. The present invention is widely applicable to light spot measurement of micron-scale light emitting elements including active photonic devices such as lasers and superluminescent diodes, and passive photonic devices such as optical fibers, optical waveguides, and photonic chips. A measurement error is not greater than 5%, and the present invention is of great application value for optics-related scientific research and engineering development. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an optical path assembly in a high-precision light spot size test system based on a spatial imaging system provided by the present invention. FIG. 2 is a schematic diagram of optical path parameters of a high-precision light spot size test system based on a spatial imaging system provided by the present invention. FIG. 3 is a schematic diagram of a Fourier image formed by reflecting light on a CCD camera through a silver-coated mirror obtained through calibration of a test system before testing of the present invention, where Xi and Yi represent 1 / e2 widths in horizontal and vertical directions of the image. FIG. 4 is a schematic diagram of a real image of a specimen (shown as a small-mode-field optical fiber) captured by reflecting light on a CCD camera during specimen testing of the present invention. FIG. 5 is a schematic diagram of a Fourier image of a specimen (shown as a small-mode-field optical fiber) captured by self-illuminating on a CCD camera during specimen testing of the present invention, where X2 and Y2 represent 1 / e2 widths in horizontal and vertical directions of the image. FIG. 6 is a schematic diagram of intensity distribution (horizontal or vertical) of Fourier images of a specimen (a mirror and a small-mode-field optical fiber) captured during specimen testing of the present invention, where a far-field image size of the specimen is accurately measured according to the figure. Reference numerals in the figures: 1-broadband light source; 2-optical fiber; 3-tube lens for light source; 4-Kohler lens; 5-beam splitter; 6-high-magnification objective lens; 7-specimen; 8-six-axis carrier platform; 9-Fourier lens; 10-iris; 11-secondary focusing lens; 12-imaging lens; 13-variable neutral density filter; 14-CCD camera; 15-computer; / s-focal length of tube lens for light source; / K-focal length of Kohler lens; / i-focal length of Fourier lens; / i-focal length of secondary focusing lens; Jc-focal length of imaging lens; Di-any distance greater than 0; and D2-any distance greater than 0. DETAILED DESCRIPTION OF EMBODIMENTS The technical solutions provided by the present invention are described in detail below with reference to specific examples. It is to be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. As shown in FIGs. 1-2, the present invention provides a high-precision light spot size test system based on a spatial imaging system. A test object in this example is a small-mode-field optical fiber, and a system structure includes: a broadband light source 1, an optical fiber 2, a tube lens 3 for light source, a Kohler lens 4, a beam splitter 5, a high-magnification objective lens 6, a specimen 7, a six-axis carrier platform 8, a Fourier lens 9, an iris 10, a secondary focusing lens 11, an imaging lens 12, a variable neutral density filter 13, a CCD camera 14, and a computer 15. The test system applies a corresponding test logic method to achieve overall testing. Specifically, in this example, the broadband light source 1 is a halogen lamp with a wavelength covering visible light to near-infrared (300 nm to 2 pm). The broadband light source 1 is used as a light source for calibrating the test system and as an illumination source for measuring a specimen. The optical fiber 2 is a multimode optical fiber with a diameter of 200 pm (usually less than 1 mm), and the optical fiber 2 introduces light from the broadband light source 1 into the test system as a starting point of an entire optical path. The tube lens 3 for light source, the Kohler lens 4, the Fourier lens 9, the secondary focusing lens 11 and the imaging lens 12 are all aspherical lenses, a wavelength of an anti-reflection coating coated on both sides of the lens is 1050-1700 nm (alternatively 400-700 nm or 650-1050 nm), and a diameter of the lens is I inch (preferably not less than 1 inch and not greater than 2 inches). The tube lens 3 for light source is configured to collimate light emitted by the broadband light source 1 through the optical fiber 2. The Kohler lens 4 is configured to form a Kohler illumination system in front of the high-magnification objective lens 6, enlarge an illumination range of the high-magnification objective lens 6, and facilitate search of a specimen. The Fourier lens 9 is configured to focus a back-focal-plane image of the high-magnification objective lens 6 and perform optical Fourier transform on a near-field light spot to obtain a corresponding far-field image. The secondary focusing lens 11 is configured to focus a back-focal-plane image of the Fourier lens 9 and realize a wavefront at a position where the iris 10 is located, which facilitates adjustment of a filtering range. The imaging lens 12 is configured to form a focused real image on the CCD camera 14. In this example, focal lengths of the tube lens 3 for light source, the Kohler lens 4, the Fourier lens 9, the secondary focusing lens 11 and the imaging lens 12 are / s=50 mm, / K=200 mm, / F=150 mm, ^=50 mm, and^=300 mm. The above focal lengths are provided for illustrative purposes only, and focal lengths of the above lenses are selected according to requirements. The beam splitter 5 is to be a thin-film beam splitter or a block beam splitter, and is coated with an anti-reflection coating with a wavelength of 1200 nm to 1600 nm on both sides thereof. In this example, the beam splitter 5 has a splitting ratio of 50:50, and functions to combine a reflection path and a transmission path into one optical path in front of the high-magnification objective lens 6. The high-magnification objective lens 6, by virtue of its high numerical aperture (NA) characteristics, maximizes light collection from all emission directions of the specimen 7, and focuses light at a specific angle to a corresponding position of the back-focal-plane of the high-magnification objective lens 6 through optical Fourier transform, such that a position-intensity distribution diagram of a near-field image is transformed into an angleintensity distribution diagram of a far-field image, which enables to analyze a divergence angle of the light spot. A magnification M of the high-magnification objective lens 6 is to be not less than 40, a numerical aperture (NA) is not less than 0.5 but less than 1, and a surface thereof is to be coated with an anti-reflection coating with a corresponding wavelength (400-700 nm or 650-1050 nm or 1050-1700 nm). In this example, the magnification of the high-magnification objective lens 6 is 40, with an equivalent focal length / o=2 mm, and an NA of 0.5 mm, and a surface thereof is coated with an anti-refl ection coating with a wavelength of 1050-1700 nm. The six-axis carrier platform 8 is configured to load the specimen 7, and six-axis degrees of freedom thereof correspond to vertical and rotational coordinate axes in a Cartesian coordinate system. Fine tuning accuracies of the six-axis carrier platform 8 in linear and rotational directions are not less than 1 pm / graduation and 1 arcmin / graduation. In this example, the specimen 7 is a small-mode-field optical fiber, a measurement parameter is defined as a divergence angle ^<sin4M4, and a central wavelength is N The iris 10 has an aperture ranging from 0.1 mm to 10 mm, and functions to filter out scattered light through spatial filtering to increase a signal-to-noise ratio for testing. During installation of a test system, the iris 10 is located at a position where a rear focus of the Fourier lens 9 and a front focus of the secondary focusing lens 11 are overlapped. The variable neutral density filter 13 has a variable neutral density ranging from 0.1 to 4, and functions to reduce light transmittance, prevent damage to the CCD camera 14 receiving excessive energy, and equalize image brightness. the CCD camera 14 is optimized for a specific wavelength, with an operating range of 900 nm to 2000 nm, a dynamic range greater than 30 dB, and a resolution of horizontal X pixels * vertical Y pixels (which is to be greater than 300*200). In this example, the resolution is 400*300, and a size of the CCD camera 14 is Lx*Ly=12 mm*9 mm. the CCD camera 14 is configured to capture the near-field image and the far-field image of the specimen 7. The computer 15 is connected to the CCD camera 14, is optionally installed with control and image capture software matched with the CCD camera 14, and outputs images for later data processing. The present invention further provides a high-precision light spot size test method based on a spatial imaging system, and the method includes the following steps: SI, select appropriate parameters Selected parameters of the high-magnification objective lens 6, the Fourier lens 9 and the imaging lens 12 are to satisfy conditions of 2f0 tan(sin-1 NA) fc / fp <Lx and 2f0 tan(sin-1 NA) fc / fF <LY, with an aim to ensure that a maximum diameter of the back-focal-plane image of the high-magnification objective lens 6 remains within a range of receiving by the CCD camera 14; and ( / c • fF) / (fi ■ f0) is a real image magnification, and an area of projecting the specimen 7 onto the CCD camera 14 after magnification is to be smaller than an area of the CCD camera 14. S2, install and calibrate the test system The test system is installed as shown in FIG. 1, and optical elements are placed at designated positions as shown in FIG. 2, where the Kohler lens 4 is not arranged. The optical fiber 2 is connected to the broadband light source 1 to introduce light from the broadband light source 1 into the test system, the tube lens 3 for light source and the beam splitter 5 are sequentially arranged on an optical path introduced by the optical fiber 2 from near to far, the high-magnification objective lens 6 and the six-axis carrier platform 8 are arranged on a reflection path of the beam splitter 5, the Fourier lens 9, the secondary focusing lens 11, the imaging lens 12, the variable neutral density filter 13, and the CCD camera 14 are sequentially arranged on a transmission path of the beam splitter 5 from near to far, and the CCD camera 14 is connected to the computer 15. A silver-coated mirror is loaded onto the six-axis carrier platform 8. The broadband light source 1 is turned on, and as shown in FIG. 2, an optical path sequence is as follows: the optical fiber 2^-the tube lens 3 for light source^-the beam splitter 5^-the high-magnification objective lens 6^-the silver-coated mirror^-the high-magnification objective lens 6^the beam splitter 5—The Fourier lens 9^the secondary focusing lens 11—The imaging lens 12^The variable neutral density filter I3^the CCD camera 14. A distance between the six-axis carrier platform 8 and the high-magnification objective lens 6 is adjusted such that an image displayed on the computer 15 is a focused image on a surface of the silver-coated mirror; the secondary focusing lens 11 is removed; the variable neutral density filter 13 is adjusted such that maximum image brightness obtained by the computer 15 is close to saturation, as shown in FIG. 3; and the image is recorded and horizontal and vertical widths at the image brightness of 1 / e2 are measured and denoted as Xi pixels and Yi pixels. System calibration before testing aims to determine maximum ranges Xi and Yi of divergence angle, and angular resolutions per pixel, i.e., sin4(A4 / Xi) and sin \NA / Yi), are calculated and determined. S3, test the specimen The small-mode-field optical fiber of the specimen 7 is loaded onto a specimen stage, and the test system is installed as shown in FIG. 1. The optical fiber 2 is connected to the broadband light source 1 to introduce light from the broadband light source 1 into the test system, the tube lens 3 for light source, the Kohler lens 4 and the beam splitter 5 are sequentially arranged on an optical path introduced by the optical fiber 2 from near to far, the high-magnification objective lens 6 and the six-axis carrier platform 8 are arranged on a reflection path of the beam splitter 5, the Fourier lens 9, the secondary focusing lens 11, the imaging lens 12, the variable neutral density filter 13, and the CCD camera 14 are sequentially arranged on a transmission path of the beam splitter 5 from near to far, the iris 10 is arranged between the Fourier lens 9 and the secondary focusing lens 11, the optical path passes through an aperture on the iris 10, and the CCD camera 14 is connected to the computer 15. As shown in FIG. 2, an optical path sequence is as follows: the optical fiber 2^the tube lens 3 for light source^the Kohler lens 4^the beam splitter 5—►the high-magnification objective lens 6^the specimen 7^-the high-magnification objective lens 6^the beam splitter 5^the Fourier lens 9^the iris lO^the secondary focusing lens l l^the imaging lens 12—>the variable neutral density filter 13—>the CCD camera 14. A distance between the six-axis carrier platform 8 and the high-magnification objective lens 6 is adjusted such that an image displayed on the computer 15 is a real image reflected on a surface of the specimen 7; vicinity of a light-emitting part of the specimen 7 is located through the reflected real image, as shown in FIG. 4; the specimen 7 is allowed to selfilluminate, the beam splitter 5 in the optical path is removed (a foldable beam splitter is optionally used, and the beam splitter 5 is removed from the optical path by simply folding the beam splitter 5), and the optical path sequence is changed to the specimen 7^ the high-magnification objective lens 6^-the Fourier lens 9^the iris 10^-the secondary focusing lens 11 —>the imaging lens 12^the variable neutral density filter 13—>the CCD camera 14; the specimen 7 is further moved to center and focus a light spot seen by the CCD camera 14; a size of the iris 10 is changed to limit an imaging range to only the vicinity of the light spot; the secondary focusing lens 11 is removed, and the variable neutral density filter 13 is adjusted such that maximum image brightness obtained by the computer 15 is the same as that of a calibrated image; and the image is recorded and horizontal and vertical widths at the image brightness of 1 / e2 are measured and denoted as X2 pixels and Y2 pixels, as shown in FIG. 5. S4, perform data processing By comparing calibration data with tested data, it is calculated that a horizontal divergence angle of the specimen 7 is sin 1 • NA^, a horizontal diameter of a corresponding Gaussian light spot is 2 / ( 7i sin-1 (— ■ NA)), a vertical divergence angle is sin-1 (— • NA), and a vertical diameter of the corresponding Gaussian light spot is %l(ii sin-1 ■ NA^ Intensity distribution (horizontal or vertical) of Fourier images of the specimen 7 captured by using the CCD camera 14 is shown in FIG. 6, and a far-field image size of the specimen 7 is accurately measured according to the figure. Repeated experiments show that the above high-precision light spot size test system based on a spatial imaging system is optionally simplified in structure, and the structure includes: a broadband light source 1, an optical fiber 2, a tube lens 3 for light source, a beam splitter 5, a high-magnification objective lens 6, a specimen 7, a six-axis carrier platform 8, a Fourier lens 9, an imaging lens 12, a variable neutral density filter 13, a CCD camera 14, and a computer 15. The test system applies a corresponding test logic method to achieve overall testing. That is, the Kohler lens 4, the iris 10, and the secondary focusing lens 11 in the test system are removed, and remaining components are installed still with reference to FIGs. 1 and 2. The simplified system also enables to measure a size of light spot, but the difficulty of locating a target increases due to removal of the Kohler lens 4, and measurement is affected by scattered light, such that operational difficulty and measurement errors are greatly increased than those of the test system installed with all components. As the high-precision light spot size test system is simplified, corresponding test methods are also simplified. Specifically, the present invention provides a light spot size test method based on a simplified high-precision light spot size test system, steps 1 and 4 of the method are the same as steps 1 and 4 of the above high-precision light spot size test method based on a spatial imaging system, and steps 2 and 3 are as follows: S2, install and calibrate the test system The test system is installed as shown in FIG. 1, and optical elements are placed at designated positions as shown in FIG. 2, where the Kohler lens 4, the Fourier lens 9, the iris 10, and the secondary focusing lens 11 are not arranged. The optical fiber 2 is connected to the broadband light source 1 to introduce light from the broadband light source 1 into the test system, the tube lens 3 for light source and the beam splitter 5 are sequentially arranged on an optical path introduced by the optical fiber 2 from near to far, the high-magnification objective lens 6 and the six-axis carrier platform 8 are arranged on a reflection path of the beam splitter 5, the imaging lens 12, the variable neutral density filter 13, and the CCD camera 14 are sequentially arranged on a transmission path of the beam splitter 5 from near to far, and the CCD camera 14 is connected to the computer 15. A silver-coated mirror is loaded onto the six-axis carrier platform 8. The broadband light source 1 is turned on, and as shown in FIG. 2, an optical path sequence is as follows: the optical fiber 2^the tube lens 3 for light source—>the beam splitter 5—>the high-magnification objective lens 6^the silver-coated mirror—>the high-magnification objective lens 6—>the beam splitter 5—>the imaging lens 12—»the variable neutral density filter 13^the CCD camera 14. A distance between the six-axis carrier platform 8 and the high-magnification objective lens 6 is adjusted such that an image displayed on the computer 15 is a focused image on a surface of the silver-coated mirror; the Fourier lens 9 is added between the beam splitter 5 and the imaging lens 12; the variable neutral density filter 13 is adjusted such that maximum image brightness obtained by the computer 15 is close to saturation; and the image is recorded and horizontal and vertical widths at the image brightness of 1 / e2 are measured and denoted as Xi pixels and Yi pixels. System calibration before testing aims to determine maximum ranges Xi and Yi of divergence angle, and angular resolutions per pixel, i.e., sin-1(A4 / Xi) and sin'^AA / Yi), are calculated and determined. S3, test the specimen The small-mode-field optical fiber of the specimen 7 is loaded onto a specimen stage, and the Kohler lens 4, the iris 10, the secondary focusing lens 11, and the Fourier lens 9 are not arranged. The optical fiber 2 is connected to the broadband light source 1 to introduce light from the broadband light source 1 into the test system, the tube lens 3 for light source and the beam splitter 5 are sequentially arranged on an optical path introduced by the optical fiber 2 from near to far, the high-magnification objective lens 6 and the six-axis carrier platform 8 are arranged on a reflection path of the beam splitter 5, the imaging lens 12, the variable neutral density filter 13, and the CCD camera 14 are sequentially arranged on a transmission path of the beam splitter 5 from near to far, and the CCD camera 14 is connected to the computer 15. As shown in FIG. 2, an optical path sequence is as follows: the optical fiber 2^-the tube lens 3 for light source^-the beam splitter 5^-the high-magnification objective lens 6 >the specimen 7^-the high-magnification objective lens 6—>the beam splitter 5—>the imaging lens 12^the variable neutral density filter 13—>the CCD camera 14. A distance between the six-axis carrier platform 8 and the high-magnification objective lens 6 is adjusted such that an image displayed on the computer 15 is a real image reflected on a surface of the specimen 7; vicinity of a light-emitting part of the specimen 7 is located through the reflected real image; the specimen 7 is allowed to selfilluminate, the beam splitter 5 in the optical path is removed (a foldable beam splitter is optionally used, and the beam splitter 5 is removed from the optical path by simply folding the beam splitter 5), and the optical path sequence is changed to the specimen 7—>the high-magnification objective lens 6—>the imaging lens 12—>the variable neutral density filter 13^-the CCD camera 14; the specimen 7 is further moved to center and focus a light spot seen by the CCD camera 14; the Fourier lens 9 is added between the beam splitter 5 and the imaging lens 12; the variable neutral density filter 13 is adjusted such that maximum image brightness obtained by the computer 15 is the same as that of a calibrated image; and the image is recorded and horizontal and vertical widths at the image brightness of 1 / e2 are measured and denoted as X2 pixels and Y2 pixels, as shown in FIG. 5. It is to be noted that the above content is merely used for explaining the technical idea of the present invention, and cannot limit the protection range of the present invention. Those of ordinary skill in the art may also make some improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also fall within the scope of protection determined in the claims of the present invention.

Claims

06 08 251. A high-precision light spot size test system based on a spatial imaging system, characterized by comprising a broadband light source, an optical fiber, a tube lens for light 5 source, a beam splitter, a high-magnification objective lens, a six-axis carrier platform, aFourier lens, an imaging lens, a variable neutral density filter, a CCD camera, and a computer, whereinthe broadband light source is connected to the optical fiber, the tube lens for light source and the beam splitter are sequentially arranged on an optical path introduced by the optical fiber 10 from near to far, the high-magnification objective lens and the six-axis carrier platform arearranged on a reflection path of the beam splitter, the Fourier lens, the imaging lens, the variable neutral density filter, and the CCD camera are sequentially arranged on a transmission path of the beam splitter from near to far, and the CCD camera is connected to the computer; and15 the optical fiber introduces light from the broadband light source into the test system; the tube lens for light source is configured to collimate light emitted by the broadband light source through the optical fiber; the beam splitter is configured to combine a reflection path and a transmission path into one optical path in front of the high-magnification objective lens; the high-magnification objective lens is configured to collect light from all emission 20 directions of the specimen; the six-axis carrier platform is configured to load the specimen;the Fourier lens is configured to focus a back-focal-plane image of the high-magnification objective lens and perform optical Fourier transform on a near-field light spot to obtain a corresponding far-field image; the imaging lens is configured to form a focused real image on the CCD camera; the variable neutral density filter is configured to reduce light 25 transmittance; and the computer is configured to receive and process images from the CCD camera.

2. The high-precision light spot size test system based on a spatial imaging system according to claim 1, characterized by further comprising a Kohler lens, an iris and a secondary focusing lens, wherein30 the Kohler lens is arranged between the tube lens for light source and the beam splitter, the iris and the secondary focusing lens are arranged between the Fourier lens and the imaging lens and located on a transmission path of the beam splitter, the iris is located at a position where a rear focus of the Fourier lens and a front focus of the secondary focusing lens are06 08 25overlapped, and the transmission path passes through an aperture on the iris; andthe Kohler lens is configured to form a Kohler illumination system in front of the high-magnification objective lens and enlarge an illumination range of the high-magnification objective lens; the iris is configured to filter out scattered light; and the secondary focusing 5 lens is configured to focus a back-focal-plane image of the Fourier lens and realize a wavefront at a position where the iris is located, which facilitates adjustment of a filtering range.

3. The high-precision light spot size test system based on a spatial imaging system according to claim 1, characterized in that the tube lens for light source, the Kohler lens, the Fourier 10 lens, the secondary focusing lens and the imaging lens are all aspherical lenses, an antireflection coating with a corresponding wavelength is to be coated on both sides of the lens, and a diameter of the lens is not less than 1 inch; and parameters of the high-magnification objective lens, the Fourier lens and the imaging lens are to satisfy conditions of 2f0 ta^sin-1 NA) fc / fF <Lx, 2 f0 ta^sin-1 NA) fc / fF <LY, wherein Lx and Ly denote 15 horizontal and vertical sizes of the CCD camera.

4. The high-precision light spot size test system based on a spatial imaging system according to claim 1, characterized in that a measurement parameter of the specimen is a divergence angle ^sin'bVJ.

5. The high-precision light spot size test system based on a spatial imaging system according 20 to claim 1, characterized in that the beam splitter is a thin-film beam splitter or a block beam splitter, and is coated with an anti-reflection coating with a corresponding wavelength on both sides thereof, with a splitting ratio of 50:50.

6. The high-precision light spot size test system based on a spatial imaging system according to claim 1, characterized in that a magnification M of the high-magnification objective lens 25 is not less than 40, a numerical aperture (NA) is not less than 0.5 but less than 1, and a surface thereof is coated with an anti-reflection coating with a corresponding wavelength.

7. The high-precision light spot size test system based on a spatial imaging system according to claim 2, characterized in that the iris has an aperture ranging from 0.1 mm to 10 mm.

8. The high-precision light spot size test system based on a spatial imaging system according 30 to claim 1, characterized in that the broadband light source is a halogen lamp with a wavelength covering visible light to near-infrared; the optical fiber is usually a multimode optical fiber with a diameter of less than 1 mm; and the variable neutral density filter has a variable neutral density ranging from 0.1 to 4.06 08 259. A high-precision light spot size test method based on a spatial imaging system, using the high-precision light spot size test system of claim 1, characterized by comprising the following steps:SI, selecting appropriate parameters5 wherein the parameters of the high-magnification objective lens, Fourier lens and imaging lens satisfy conditions of 2 f0 tan^sin^1 NA) fc / fp <Lx and 2f0 tan^sin^1 NA) fc / fp <LY, wherein fo is an equivalent focal length of the high-magnification objective lens, NA is a numerical aperture of the high-magnification objective lens, / c is a focal length of the imaging lens, fF is a focal length of the Fourier lens, Lx is a horizontal size of a 10 photosensitive surface of the CCD camera, LY is a vertical size of the photosensitive surface of the CCD camera, and a maximum diameter of a back-focal-plane image of the high-magnification objective lens remains within a range of receiving by the CCD camera; and a real image magnification ( / c ■ fF) / (J) ■ fo) causes an area of projecting a specimen onto the CCD camera after magnification to be smaller than an area of the CCD camera;15 S2, installing and calibrating a test systemwhen the test system comprises a Kohler lens, an iris, and a secondary focusing lens, the following steps are comprised:installing the test system, connecting the optical fiber to the light source, sequentially arranging the tube lens for light source and the beam splitter on an optical path introduced by 20 the optical fiber from near to far, arranging the high-magnification objective lens and the six-axis carrier platform on a reflection path of the beam splitter, sequentially arranging the Fourier lens, the secondary focusing lens, the imaging lens, a variable neutral density filter, and the CCD camera on a transmission path of the beam splitter from near to far, and connecting the CCD camera to a computer; loading a silver-coated mirror onto the six-axis 25 carrier platform, wherein an optical path sequence is as follows: the optical fiber—>the tube lens for light source^the beam splitter—Hhe high-magnification objective lens^-the silver-coated mirror ^-the high-magnification objective lens^-the beam splitter^-the Fourier lens^the secondary focusing lens^the imaging lens^the variable neutral density filter^the CCD camera; adjusting a distance between the six-axis carrier platform and the 30 high-magnification objective lens such that an image displayed on the computer is a focused image on a surface of the silver-coated mirror; removing the secondary focusing lens; adjusting the variable neutral density filter such that maximum image brightness obtained by the computer is close to saturation; recording the image and measuring horizontal and06 08 25vertical widths at the image brightness of 1 / e2 denoted as Xi pixels and Yi pixels;when the test system does not comprise the Kohler lens, the iris, and the secondary focusing lens, the following steps are comprised:installing the test system, wherein the Fourier lens is not arranged; connecting the optical 5 fiber to the light source, sequentially arranging the tube lens for light source and the beam splitter on an optical path introduced by the optical fiber from near to far, arranging the high-magnification objective lens and the six-axis carrier platform on a reflection path of the beam splitter, sequentially arranging the imaging lens, the variable neutral density filter, and the CCD camera on a transmission path of the beam splitter from near to far, and connecting10 the CCD camera to the computer; loading the silver-coated mirror onto the six-axis carrier platform, wherein an optical path sequence is as follows: the optical fiber^the tube lens for light source—>the beam splitter—>the high-magnification objective lens^the silver-coated mirror—>the high-magnification objective lens^the beam splitter^the imaging lens^the variable neutral density filter—>the CCD camera; adjusting a distance between the six-axis15 carrier platform and the high-magnification objective lens such that an image displayed on the computer is a focused image on a surface of the silver-coated mirror; adding the Fourier lens between the beam splitter and the imaging lens; adjusting the variable neutral density filter such that maximum image brightness obtained by the computer is close to saturation; recording the image and measuring horizontal and vertical widths at the image brightness of20 1 / e2 denoted as Xi pixels and Yi pixels;S3, testing a specimenwhen the test system comprises the Kohler lens, the iris, and the secondary focusing lens, the following steps are comprised:loading the specimen onto a specimen stage, installing the test system, connecting the optical 25 fiber to the light source, sequentially arranging the tube lens for light source, the Kohler lensand the beam splitter on an optical path introduced by the optical fiber from near to far, arranging the high-magnification objective lens and the six-axis carrier platform on a reflection path of the beam splitter, sequentially arranging the Fourier lens, the secondary focusing lens, the imaging lens, the variable neutral density filter, and the CCD camera on a 30 transmission path of the beam splitter from near to far, arranging the iris between the Fourierlens and the secondary focusing lens, allowing the optical path to pass through an aperture on the iris, and connecting the CCD camera to the computer; wherein an optical path sequence is as follows: the optical fiber^the tube lens for light source >the Kohler06 08 25lens—>the beam splitter—>the high-magnification objective lens—>the specimen—>the high-magnification objective lens—>the beam splitter—>the Fourier lens—>the iris^the secondary focusing lens^the imaging lens—>the variable neutral density filter—>the CCD camera; adjusting a distance between the six-axis carrier platform and the high-magnification 5 objective lens such that an image displayed on the computer is a real image reflected on a surface of the specimen; locating vicinity of a light-emitting part of the specimen through a reflected real image; allowing the specimen to self-illuminate, and removing the beam splitter from the optical path, wherein the optical path sequence is changed to the specimen—>the high-magnification objective lens—>the Fourier lens^the iris^the secondary 10 focusing lens^the imaging lens^-the variable neutral density filter—»the CCD camera;further moving the specimen to center and focus a light spot seen by the CCD camera; changing a size of the iris to limit an imaging range to only the vicinity of the light spot; removing the secondary focusing lens, and adjusting the variable neutral density filter such that maximum image brightness obtained by the computer is the same as that of a calibrated 15 image; recording the image and measuring horizontal and vertical widths at the imagebrightness of 1 / e2 denoted as X2 pixels and Y? pixels;when the test system does not comprise the Kohler lens, the iris, and the secondary focusing lens, the following steps are comprised:loading the specimen onto the specimen stage, wherein the Fourier lens is not arranged; 20 connecting the optical fiber to the light source, sequentially arranging the tube lens for lightsource and the beam splitter on an optical path introduced by the optical fiber from near to far, arranging the high-magnification objective lens and the six-axis carrier platform on a reflection path of the beam splitter, sequentially arranging the imaging lens, the variable neutral density filter, and the CCD camera on a transmission path of the beam splitter from 25 near to far, and connecting the CCD camera to the computer; wherein an optical path sequence is as follows: the optical fiber—»the tube lens for light source^-the beam splitter^the high-magnification objective lens^the specimen^the high-magnification objective lens^the beam splitter—>the imaging lens^the variable neutral density filter—>the CCD camera; adjusting a distance between the six-axis carrier platform and the high-30 magnification objective lens such that an image displayed on the computer is a real imagereflected on a surface of the specimen; locating vicinity of a light-emitting part of the specimen through a reflected real image; allowing the specimen to self-illuminate, and removing the beam splitter from the optical path, wherein the optical path sequence is06 08 25changed to the specimen^the high-magnification objective lens—>the imaging lens—>the variable neutral density filter—>the CCD camera; further moving the specimen to center and focus a light spot seen by the CCD camera; adding the Fourier lens between the beam splitter and the imaging lens; adjusting the variable neutral density filter such that maximum5 image brightness obtained by the computer is the same as that of a calibrated image; recording the image and measuring horizontal and vertical widths at the image brightness of 1 / e2 denoted as X2 pixels and Y2 pixels;S4, performing data processingby comparing calibration data with tested data, calculating a horizontal divergence angle — ■NA) of the specimen, a horizontal diameter 1 / ( tr sin-1 ( — • NA)) of acorresponding Gaussian light spot, a vertical divergence angle sin-1 (— ■ NA), and a vertical diameter sin-1 ■ Afd))of the corresponding Gaussian light spot.

10. The high-precision light spot size test method based on a spatial imaging system according to claim 9, characterized by further comprising the following steps: measuring a15 far-field image size of the specimen according to intensity distribution of Fourier images of the specimen.

Images