1. An optical displacement sensor, characterized by, include according to the same central line sets gradually:

a light source module (1) for generating a non-uniform light field;

the movable positioning scale (2) is provided with a periodic micro-nano structure and is used for generating surface plasma waves under the irradiation of the non-uniform optical field and mutually interfering to form a near-field interference image;

an imaging module (3) for converting the near-field interference image into a far-field imaging image;

and the imaging detector (4) is used for converting the optical field intensity of the far-field imaging graph into an electric signal so as to realize displacement measurement.

2. Optical displacement sensor according to claim 1, characterized in that the light source module (1) comprises a laser light source (11) and a focusing objective (12), the laser light source (11) being adapted to generate non-uniform incident light; the focusing objective (12) is used for carrying out focusing treatment on the non-uniform incident light to form a convergent non-uniform light field.

3. Optical displacement sensor according to claim 2, characterized in that the structure of the focusing objective (12) is variable in order to form a non-uniform light field with different spot sizes.

4. Optical displacement sensor according to claim 3, characterized in that the movable positioning scale (2) comprises a light-transmissive substrate (21) and a metal film (22) on the light-transmissive substrate (21), the periodic micro-nano-structures being located on the metal film (22); the contact surface of the metal film (22) and the light-transmitting substrate (21) is always positioned at the focal plane of the focusing objective lens (12) in the moving process of the movable positioning scale (2) and is also positioned at the focal plane of the imaging module (3).

5. Optical displacement sensor according to claim 4, characterized in that the material of the light-transmitting substrate (21) is quartz or glass.

6. The optical displacement sensor according to claim 4, wherein the micro-nano structure comprises a plurality of nano-scale scribing pairs, and the nano-scale scribing pairs are sequentially arranged on the metal film with a period of micrometer scale.

7. Optical displacement sensor according to claim 4, characterized in that the material of the metal film (22) is gold or silver.

8. An optical displacement detection system, comprising:

a light source module (1) for generating a non-uniform light field;

the movable positioning scale (2) is connected with an object to be detected and used for generating surface plasma waves under the irradiation of the non-uniform light field and interfering with each other to form a near-field interference image;

an imaging module (3) for converting the near-field interference image into a far-field imaging image;

an imaging detector (4) for converting the optical field intensity of the far-field imaging map into an electrical signal for displacement measurement;

the computer module (5) is used for analyzing the change condition of the light field intensity according to the electric signal so as to obtain the displacement of the object to be detected;

the light source module (1), the movable positioning scale (2), the imaging module (3) and the imaging detector (4) are arranged according to the same central line.

Background

The displacement sensor is a sensing device for sensing the relative displacement, and is widely applied to the fields of machining, precision manufacturing, industrial automation and the like. Conventional displacement sensors can be broadly classified into strain-type displacement sensors, magnetostrictive displacement sensors, and grating displacement sensors according to their operating principles. The strain displacement sensor mainly utilizes the resistance strain effect of metal, calculates corresponding deformation and displacement according to the change of resistance values, and has larger nonlinearity, so that the repeated positioning precision can only reach tens of microns. The magnetostrictive displacement sensor mainly utilizes the magnetostrictive principle, and accurately measures the position by generating a strain pulse signal through the intersection of two different magnetic fields, and the repeated positioning precision of the magnetostrictive displacement sensor can reach the micron level generally. The grating displacement sensor detects the displacement by using the change of moire fringes formed by the measurement grating and the reference grating, and the highest repeated positioning precision can reach a submicron level.

With the great improvement of the requirements for precision machining and fine measurement, the requirements of people on the precision and the range of displacement measurement are higher and higher. For example, in the process of processing a micro-nano optical device, the designed micro-nano structure is usually one tenth or even smaller than the working wavelength, so the processing precision needs to reach or even be better than the nano scale. For example, in the alignment process of super-resolution lithography, the repeated positioning accuracy needs to be much smaller than the minimum feature size in lithography, so that the repeated positioning accuracy of nanometer level is also the most basic requirement. In recent years, a displacement sensor and a displacement control system based on piezoelectric ceramics have attracted much attention, and can realize positioning accuracy of a nanometer level or less by utilizing electrostrictive properties of ceramic materials. However, the displacement measurement range of piezoceramic materials is usually only in the order of hundreds of microns, and the measurement range is very limited.

In summary, the conventional displacement sensor is limited by factors such as sensitivity, repeated positioning accuracy or measurement range, and cannot meet the actual requirement. Therefore, designing a displacement sensor with a wide measurement range and high accuracy plays an extremely important role in ultra-precision machining and ultra-precision measurement.

Disclosure of Invention

In order to solve the above problems in the prior art, the present invention provides an optical displacement sensor and an optical displacement detection system. The technical problem to be solved by the invention is realized by the following technical scheme:

an optical displacement sensor, comprising, arranged in sequence according to a common centre line:

the light source module is used for generating a non-uniform light field;

the movable positioning scale is provided with a periodic micro-nano structure and is used for generating surface plasma waves under the irradiation of the non-uniform optical field and mutually interfering to form a near-field interference image;

the imaging module is used for converting the near-field interference image into a far-field imaging image;

and the imaging detector is used for converting the optical field intensity of the far-field imaging graph into an electric signal so as to realize displacement measurement.

In one embodiment of the present invention, the light source module includes a laser light source for generating non-uniform incident light and a focusing objective lens; the focusing objective lens is used for carrying out focusing treatment on the non-uniform incident light to form a converged non-uniform light field.

In one embodiment of the invention, the focusing objective is structurally variable to facilitate the formation of a non-uniform light field with different spot sizes.

In one embodiment of the invention, the movable positioning scale comprises a light-transmitting substrate and a metal film positioned on the light-transmitting substrate, and the periodic micro-nano structure is positioned on the metal film; the contact surface of the metal film and the light-transmitting substrate is always positioned on the focal plane of the focusing objective lens in the moving process of the movable positioning scale and is also positioned on the focal plane of the imaging module.

In one embodiment of the invention, the material of the light-transmitting substrate is quartz or glass.

In an embodiment of the invention, the micro-nano structure comprises a plurality of nano-scale line pairs, and the nano-scale line pairs are sequentially arranged on the metal film in a micron-scale period.

In one embodiment of the present invention, the material of the metal thin film is gold or silver.

Another embodiment of the present invention also provides an optical displacement detection system, including:

the light source module is used for generating a non-uniform light field;

the movable positioning scale is connected with an object to be detected and used for generating surface plasma waves under the irradiation of the non-uniform light field and interfering with each other to form a near-field interference image;

the imaging module is used for converting the near-field interference image into a far-field imaging image;

an imaging detector for converting the optical field intensity of the far field imaging map into an electrical signal for displacement measurement;

the computer module is used for analyzing the change condition of the light field intensity according to the electric signal so as to obtain the displacement of the object to be detected;

the light source module, the movable positioning scale, the imaging module and the imaging detector are arranged according to the same central line.

The invention has the beneficial effects that:

the optical displacement sensor provided by the invention utilizes the characteristic that the interference fringe intensity of surface plasma waves under the irradiation of a non-uniform light field is easily influenced by the change of the center of the light field and the periodic micro-nano structure arranged in the movable positioning scale, simultaneously realizes the displacement measurement requirements of wide range and high precision, has the advantages of non-contact, high stability and the like, and can be widely applied to the fields of ultra-precision displacement measurement, ultra-precision machining and manufacturing and the like.

The present invention will be described in further detail with reference to the accompanying drawings and examples.

Drawings

Fig. 1 is a schematic structural diagram of an optical displacement sensor according to an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a positioning scale provided in an embodiment of the present invention;

FIG. 3 is a near-field interferogram of a plasmon wave at different positions provided by embodiments of the present invention;

FIG. 4 is a far-field image of interference fringes of plasma waves at different positions according to an embodiment of the present invention;

FIG. 5 is a graph of the relationship between the lateral displacement of the positioning scale and the contrast of light intensity in the far-field interferogram according to an embodiment of the present invention;

fig. 6 is a schematic structural diagram of an optical displacement sensing detection system according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.

Example one

Referring to fig. 1, fig. 1 is a schematic structural diagram of an optical displacement sensor according to an embodiment of the present invention, which includes:

a light source module 1 for generating a non-uniform light field;

the movable positioning scale 2 is provided with a periodic micro-nano structure and is used for generating surface plasma waves under the irradiation of the non-uniform optical field and mutually interfering to form a near-field interference image;

the imaging module 3 is used for converting the near-field interference image into a far-field imaging image;

and the imaging detector 4 is used for converting the optical field intensity of the far-field imaging graph into an electric signal so as to realize displacement measurement.

In the present embodiment, the light source module 1 includes a laser light source 11 and a focusing objective 12, the laser light source 11 is used for generating non-uniform incident light; the focusing objective 12 is used for focusing the non-uniform incident light to form a convergent non-uniform light field.

Further, the non-uniform optical field in this embodiment can be any light beam with non-uniform intensity. Preferably, in this embodiment, a gaussian beam emitted by a laser is used as an incident light, and is converged by a focusing objective lens to form a gaussian beam with a smaller beam waist radius.

It should be noted that the structure of the focusing objective lens 12 in this embodiment is variable, so as to form a non-uniform optical field with different spot sizes, thereby meeting the detection requirements in various scenes.

Further, the movable positioning scale 2 comprises a light-transmitting substrate 21 and a metal film 22 located on the light-transmitting substrate 21, and the periodic micro-nano structure is located on the metal film 22.

The material of the transparent substrate 21 is quartz or glass, which mainly plays a role of support. The material of the metal thin film 22 is gold or silver.

Preferably, the present embodiment forms the positioning scale using a quartz substrate and an Au metal thin film.

Specifically, the movable positioning scale 2 is disposed vertically directly below the focusing objective lens 12 so that the converged non-uniform incident light field can be vertically irradiated onto the metal thin film 22. Here, the movable positioning scale 2 may be configured to move in the X or Y direction according to the detection requirement, and the present embodiment is described by taking lateral movement in the X direction as an example. During the movement of the positioning scale, the contact surface of the metal film 22 with the transparent substrate 21 is always located at the focal plane of the focusing objective 12 and at the same time at the focal plane of the imaging module 3, i.e. at the position indicated by the dashed line in fig. 1.

Referring to fig. 2, fig. 2 is a schematic structural diagram of a positioning scale provided in an embodiment of the present invention, where a micro-nano structure includes a plurality of nano-scale line pairs, and the nano-scale line pairs are sequentially arranged on a metal film at a micron-scale period to perform an accurate positioning function.

Specifically, when a pair of nano-scale lines is in an incident optical field, the plasmon wave of the metal surface may form interference fringes on both sides of the pair of lines. The intensity and position of the interference fringes have strong sensitivity to the phase of an incident beam, if the center of the reticle pair is not coincident with the center of an incident light field, the intensity of surface waves generated by the two reticles is different, and the intensity of the surface wave interference fringes on the two sides of the reticle pair is different.

Referring to fig. 3, fig. 3 is a diagram of a near-field interference pattern of a plasmon wave at different positions according to an embodiment of the present invention, wherein (a) the diagram is a surface plasmon wave interference pattern when a scribe line pair center coincides with a gaussian beam center, and (b) the diagram is a surface plasmon wave interference pattern after the scribe line pair has moved to the right by 50 nm. As can be seen from the graph (a), when the center of the scribed line coincides with the center of the gaussian beam, the intensities of the left and right stripes are the same; it can be seen from the graph (b) that the intensity of the fringes on the left is significantly greater than the intensity of the fringes on the right after the pair of lines has moved to the right, and thus the intensity of the interference fringes is accurately modulated by the position of the pair of lines.

It should be noted that, for the number of the nano-scale line pairs, the adaptability can be increased according to the actual measurement range, when one group of the line pairs moves out of the incident light spot, the adjacent other group of the line pairs enters the incident light field, so that the continuous precise positioning can be performed, and the displacement sensing function with large range and high precision can be realized.

Further, since the near-field interference fringes cannot be directly measured and displayed, the imaging module 3 is used to magnify and image the near-field interference fringes onto the imaging detector 4 to obtain a far-field imaging graph.

Specifically, the imaging module 3 in the present embodiment is mainly implemented by a microscope objective. Referring to fig. 4, fig. 4 is a far-field image of interference fringes of plasma waves at different positions according to an embodiment of the present invention.

Wherein, the graph (a) is a far-field imaging graph when the reticle is aligned to the center of an incident light field, and the intensities of the left and right stripes of the far-field imaging graph are the same; when the reticle is shifted to the right by 50nm, the far field image is as shown in (b), and it can be seen that the intensity of the left and right fringes is obviously different, and the left fringe near the center of the light field has greater light intensity.

Then, the variation of the light field intensity is analyzed to obtain the displacement information.

Specifically, referring to fig. 5, fig. 5 is a graph of a relationship between a lateral displacement of a positioning scale and a contrast of light intensity in a far-field interferogram, where an abscissa represents the displacement and an ordinate represents a ratio of left-side interference fringe intensity to right-side interference fringe intensity. In this embodiment, mainly, the transverse displacement when the reticle pair center is aligned with the incident light field center is 0, the displacement value when the scale mark moves rightward is positive, the displacement value when the reticle moves leftward is negative, and the corresponding relationship between the displacement and the fringe intensity ratio is simulated step by step with 10 nm as the step length, as shown in fig. 5. As can be seen from the curves, the ratio of the lateral displacement of the scribing line pair to the left and right stripe intensities shows a very strict linear variation in the range of + -50 nm. Therefore, by analyzing the variation of the light field intensity, the distance of the scribing line from the center of the light field in the transverse direction can be obtained.

In the embodiment, the displacement of the positioning scale relative to the central point of the incident light field is converted into the intensity change of interference fringes received in a far-field imaging device by using the interference characteristic of the metal surface plasma wave and the non-uniform characteristic of the incident light field, and the displacement of the positioning scale relative to the central point of the light field is calculated according to the linear relationship between the intensity change value of the left and right fringes and the displacement.

In addition, the displacement measurement precision can be further improved by selecting the appropriate intensity of the laser light source power, the better power sensitivity of the imaging detector and the incident beam mode. For example, if the power sensitivity of the selected imaging detector is better than one in a thousand, the displacement sensitivity of the displacement sensor provided by the embodiment is better than the nanometer level, and the sub-nanometer level displacement sensitivity and the positioning accuracy are realized.

The optical displacement sensor provided by the invention utilizes the characteristic that the interference fringe intensity of surface plasma waves under the irradiation of a non-uniform light field is easily influenced by the change of the center of the light field and the periodic micro-nano structure arranged in the light receiving module, simultaneously realizes the displacement measurement requirements of wide range and high precision, has the advantages of non-contact, high stability and the like, and can be widely applied to the fields of ultra-precision displacement measurement, ultra-precision machining and manufacturing and the like.

Example two

On the basis of the first embodiment, the present embodiment provides an optical displacement detection system. Referring to fig. 6, fig. 6 is a schematic structural diagram of an optical displacement sensing detection system according to an embodiment of the present invention, which includes:

a light source module 1 for generating a non-uniform light field;

the movable positioning scale 2 is connected with the object to be detected and used for generating surface plasma waves under the irradiation of the non-uniform light field and interfering with each other to form a near-field interference image;

the imaging module 3 is used for converting the near-field interference image into a far-field imaging image;

an imaging detector 4 for converting the optical field intensity of the far field imaging map into an electrical signal for displacement measurement;

the computer module 5 is used for analyzing the change condition of the light field intensity according to the electric signal so as to obtain the displacement of the object to be detected;

the light source module 1, the movable positioning scale 2, the imaging module 3 and the imaging detector 4 are arranged according to the same central line.

Specifically, the optical displacement detection system provided by the present embodiment can be implemented by using the optical displacement sensor provided by the first embodiment, and the working process is as follows:

the non-uniform Gaussian beam generated by the laser is converged by the focusing objective lens to form a Gaussian beam with smaller beam waist radius, the Gaussian beam is vertically incident to a positioning scale with a micro-nano structure, near-field interference fringes of surface plasma waves are formed on the upper surface and the lower surface of the metal film, the near-field interference fringes are imaged on an image surface through the micro objective lens below the scale, and the distance of the scribing line from the center of the optical field in the transverse direction is calculated by the computer module according to the contrast of the intensity of the interference fringes in far-field imaging.

When the object to be measured drives the positioning scale to move transversely below the light source module, the far-field imaging graph of the imaging module also changes periodically, the computer analyzes the change condition of the interference fringe intensity through the output electric signal of the optical displacement sensor, and then the displacement condition of the positioning scale relative to the center of the light field is obtained according to the relationship between the transverse displacement of the positioning scale and the light intensity contrast in the far-field imaging graph shown in fig. 5, so that the displacement condition of the object to be measured is obtained.

Because the intensity of the interference fringes has strong sensitivity to the relative position of the incident beam and the positioning scale, and the periodic micro-nano structure on the positioning scale is enough, the displacement measurement with high precision and wide measuring range can be realized.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.