Spectral confocal displacement measuring head based on double-sided pure phase type diffraction dispersion lens

Abstract

The invention discloses a spectrum confocal displacement measuring head based on a double-sided pure phase type diffraction dispersion lens, which belongs to the technical field of optical measurement, and comprises a lens barrel, an optical fiber interface, a double-sided pure phase type diffraction dispersion lens, a first diffraction surface, a second diffraction surface, an optical fiber and a diaphragm, a double-sided pure phase type diffraction dispersion lens is arranged in the lens barrel and close to the other end of the lens barrel, the double-sided pure phase type diffraction dispersion lens is provided with a first diffraction surface and a second diffraction surface, the first diffraction surface is a light incident surface, the second diffraction surface is a light emergent surface, a diaphragm is arranged at the other end of the lens barrel, and polychromatic light is introduced into the lens barrel through an optical fiber. After passing through the first diffraction surface and the second diffraction surface of the double-sided pure-phase diffraction dispersion lens, dispersion focusing is carried out, and light with different wavelengths is focused at different positions of an optical axis. According to the technical scheme of the invention, the complexity of the measuring head optical system is obviously simplified.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and relates to a spectral confocal displacement probe based on a double-sided pure phase diffraction dispersion lens. Background Art

[0002] Spectral confocal displacement measurement technology is a non-contact absolute displacement measurement technology based on the confocal optical principle. The measured displacement is modulated into peak wavelength change information through a dispersive objective lens, and the peak wavelength is obtained by a spectrometer in combination with the corresponding relationship with the axial distance to calculate the position information of the measured object. The measurement resolution of the spectral confocal displacement sensor can reach nanometers, the measurement frequency can reach tens of thousands of hertz, the detection slope range is large, and the focal spot is small. It can be used for displacement, roughness, thickness and three-dimensional surface scanning measurement.

[0003] Traditional spectral confocal displacement probes use a dispersion lens group to focus the dispersion of a wide-spectrum light source to achieve wavelength-axial position encoding. Generally, a combination of refractive lenses made of materials with different Abbe numbers is used to control parameters such as the starting measurement distance, dispersion range, and numerical aperture. However, the combination structure of multiple refractive lenses increases the size and weight of the spectral confocal displacement probe, and also makes its installation and adjustment complicated. Summary of the invention

[0004] In response to the demand for improvement of the prior art, the present invention proposes a spectral confocal displacement probe based on a double-sided pure phase-type diffraction dispersion lens.

[0005] To achieve the above-mentioned purpose, the present invention proposes a spectral confocal displacement probe based on a double-sided pure phase-type diffraction dispersion lens, which includes a lens barrel, an optical fiber interface, a double-sided pure phase-type diffraction dispersion lens, a first diffraction surface, a second diffraction surface, an optical fiber, and an aperture. One end of the lens barrel is provided with an optical fiber interface for installing the optical fiber, and a double-sided pure phase-type diffraction dispersion lens is provided inside the lens barrel near the other end of the lens barrel. The double-sided pure phase-type diffraction dispersion lens has a first diffraction surface and a second diffraction surface, the first diffraction surface is a light incident surface, and the second diffraction surface is a light exit surface. The other end of the lens barrel is provided with an aperture, wherein complex light is introduced into the lens barrel by the optical fiber, and is dispersed and focused after passing through the first diffraction surface and the second diffraction surface of the double-sided pure phase-type diffraction dispersion lens, and light of different wavelengths is focused at different positions of the optical axis.

[0006] Furthermore, the surface of the first diffraction surface of the double-sided pure phase-type diffractive dispersion lens is an annular step-shaped microstructure.

[0007] Furthermore, the surface of the second diffraction surface of the double-sided pure phase-type diffractive dispersion lens is an annular step-shaped microstructure.

[0008] Compared with the traditional spectral confocal probe, the technical solution proposed by the present invention has the following beneficial effects:

[0009] 1. The spectral confocal probe based on the double-sided pure phase diffraction dispersion lens uses a diffraction lens to directly disperse and focus the point light source emitted by the optical fiber, eliminating the traditional refractive lens group and significantly simplifying the complexity of the optical system of the traditional spectral confocal probe. It has a simple structure, is easy to assemble and adjust, has a small size, is light in weight, and is easy to mass produce.

[0010] 2. The spectral confocal probe based on the double-sided pure phase diffraction dispersion lens uses two diffraction surfaces to disperse and focus the complex light, and uses the strong dispersion characteristics of the diffraction surface to enable the spectral confocal probe to obtain a larger dispersion range.

[0011] 3. The spectral confocal probe based on the double-sided pure phase diffraction dispersion lens uses an optical modulation element with a pure phase diffraction structure, which improves the diffraction efficiency of the light source compared to the Fresnel zone plate.

[0012] 4. The diffraction lens used in the spectral confocal probe based on the double-sided pure phase diffraction dispersion lens has two diffraction surfaces, which reduces the processing difficulty compared to the diffraction lens with a single diffraction surface of the same numerical aperture. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structure of a spectral confocal displacement probe based on a double-sided pure phase diffraction dispersion lens proposed by the present invention;

[0014] Figure 2 is a focus-wavelength relationship diagram after linear fitting of a specific example proposed by the present invention;

[0015] Figure 3 is a half-section view of the center portion of the first diffraction surface of the double-sided pure phase-type diffractive dispersion lens according to a specific example of the present invention;

[0016] Figure 4 It is a top view of the central part of the first diffraction surface of the double-sided pure phase-type diffraction dispersion lens of the specific example proposed by the present invention.

[0017] Explanation of the numbers in the figure: 1. Lens barrel; 2. Optical fiber interface; 3. Double-sided pure phase-type diffraction dispersion lens; 4. First diffraction surface; 5. Second diffraction surface; 6. Optical fiber; 7. Aperture. DETAILED DESCRIPTION

[0018] The exemplary embodiments of the present disclosure are described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms, and the present disclosure should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0019] See also Figure 1 The present invention provides a spectral confocal displacement probe based on a double-sided pure phase diffraction dispersion lens, wherein the spectral confocal displacement probe based on the double-sided pure phase diffraction dispersion lens comprises a lens barrel 1, An optical fiber interface 2, a double-sided pure phase-type diffraction dispersion lens 3, a first diffraction surface 4, a second diffraction surface 5, an optical fiber 6, and an aperture 7. An optical fiber interface 2 is provided at one end of the lens barrel 1 for installing the optical fiber 6. A double-sided pure phase-type diffraction dispersion lens 3 is provided inside the lens barrel 1 near the other end of the lens barrel 1. The double-sided pure phase-type diffraction dispersion lens 3 has a first diffraction surface 4 and a second diffraction surface 5. The first diffraction surface 4 is a light incident surface, and the second diffraction surface 5 is a light exit surface. An aperture 7 is provided at the other end of the lens barrel 1. The aperture 7 blocks the edge exiting light to constrain the aperture of the exiting light beam. The complex light is introduced into the lens barrel by the optical fiber 6, and is dispersed and focused after passing through the first diffraction surface 4 and the second diffraction surface 5 of the double-sided pure phase-type diffraction dispersion lens 3. Light of different wavelengths is focused at different positions of the optical axis.

[0020] Different from the prior art, the spectral confocal displacement probe uses two diffraction surfaces to disperse and focus the complex light, and utilizes the strong dispersion characteristics of the diffraction surfaces to enable the spectral confocal probe to obtain a larger dispersion range.

[0021] In one embodiment, the interior of the lens barrel has a black coating to reduce stray light.

[0022] In one implementation, after the optical fiber 6 is installed in the optical fiber interface 2 , a broadband light source is emitted from the optical fiber and incident on the double-sided pure phase diffraction dispersion lens 3 .

[0023] Furthermore, the first surface and the second surface of the double-sided pure phase diffractive dispersion lens 3 from left to right are both diffractive surfaces for beam focusing and dispersion. The two diffractive surfaces share the optical focal length, thereby increasing the minimum feature size of each surface and reducing the difficulty of processing.

[0024] Furthermore, the material of the double-sided pure phase-type diffractive dispersion lens 3 is fused quartz, and the double-sided pure phase-type diffractive dispersion lens 3 is a two-step periodic ring structure, and the theoretical diffraction efficiency is 40.5%.

[0025] In one embodiment, the surface of the first diffraction surface 4 of the double-sided pure phase diffractive dispersion lens 3 is an annular step-shaped microstructure. In one embodiment, the surface of the second diffraction surface 5 of the double-sided pure phase diffractive dispersion lens 3 is an annular step-shaped microstructure.

[0026] In one embodiment, the surface diffraction ring radius of the double-sided pure phase diffractive dispersion lens 3 is calculated according to the Fresnel zone plate formula. The Fresnel zone plate formula belongs to the technical content that can be obtained by those skilled in the art from the prior art, and the present invention will not repeat it.

[0027] In one embodiment, the modulation effect of the double-sided pure phase diffraction dispersion lens 3 on white light can be characterized by the relationship between focal length and wavelength. For first-order diffraction, the focal length Inversely proportional to the incident wavelength λ:

[0028] ,

[0029] in, is the central wavelength of the diffractive element, is the central wavelength The corresponding focal length.

[0030] See also Figure 2 The central wavelengths of the two diffraction surfaces of the double-sided pure phase diffraction dispersion lens 3 are , the shortest working wavelength of the double-sided pure phase diffraction dispersion lens 3 is , the longest working wavelength of the double-sided pure phase diffraction dispersion lens 3 is .

[0031] See also Figure 2 , the dispersion range of the double-sided pure phase diffraction dispersion lens 3 on the optical axis is , The wavelength is The focal length of the incident light, The wavelength is The relative error of the wavelength-displacement curve calibration after polynomial fitting is better than 0.022%.

[0032] See also Figure 3 and Figure 4 The two surfaces of the double-sided pure phase diffractive dispersion lens 3 have annular diffraction structures, and the phase difference between adjacent annular zones is 2π.

[0033] Furthermore, the Abbe number of the double-sided pure phase diffractive dispersion lens 3 is ,in is the wavelength of light with a wavelength of 587.6 nanometers, is the wavelength of light with a wavelength of 486.1 nanometers, It is the wavelength of light with a wavelength of 656.3 nanometers.

[0034] Furthermore, the first diffraction surface 4 and the second diffraction surface 5 of the double-sided pure phase diffraction dispersion lens 3 share the focusing and dispersion functions.

[0035] The present invention can realize the function of a spectral confocal probe by only using a single double-sided pure phase diffraction dispersion lens 3, has a large dispersion range, is easy to process in batches, has a small size, is light in weight, is easy to assemble, and has strong practicality.

[0036] The double-sided pure phase diffraction dispersion lens 3 produces a larger dispersion range, which is equivalent to the measurement range of the spectral confocal displacement sensor. Therefore, the spectral confocal displacement sensor using the double-sided pure phase diffraction dispersion lens 3 can meet the measurement requirements of a larger measurement range.

[0037] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A spectral confocal displacement probe based on a double-sided pure phase diffraction dispersion lens, characterized in that: The optical fiber lens comprises a lens barrel (1), an optical fiber interface (2), a double-sided pure phase diffraction dispersion lens (3), a first diffraction surface (4), a second diffraction surface (5), an optical fiber (6), and an aperture (7). One end of the lens barrel (1) is provided with an optical fiber interface (2) for mounting the optical fiber (6). A double-sided pure phase diffraction dispersion lens (3) is provided inside the lens barrel (1) near the other end of the lens barrel (1). The double-sided pure phase diffraction dispersion lens (3) has a first diffraction surface (4) and a second diffraction surface (5). The first diffraction surface (4) is a light incident surface, and the second diffraction surface (5) is a light exit surface. An aperture (7) is provided at the other end of the lens barrel (1). Complex color light is introduced into the lens barrel by the optical fiber (6), and dispersed and focused after passing through the first diffraction surface (4) and the second diffraction surface (5) of the double-sided pure phase diffraction dispersion lens (3). Light of different wavelengths is focused at different positions on the optical axis.

2. The spectral confocal displacement probe based on a double-sided pure phase diffraction dispersion lens according to claim 1, characterized in that: The surface of the first diffraction surface (4) of the double-sided pure phase diffraction dispersion lens (3) is an annular step-shaped microstructure.

3. The spectral confocal displacement probe based on a double-sided pure phase diffraction dispersion lens according to claim 1, characterized in that: The surface of the second diffraction surface (5) of the double-sided pure phase diffraction dispersion lens (3) is an annular step-shaped microstructure.

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