CN105180800B - The high optics sub-structure of auto-collimation grating interferometer - Google Patents

Abstract

A highly optically subdivided structure of a self-collimating grating interferometer, comprising: a scale grating, a first reflector and a second reflector; the measurement beam is first incident on the scale grating at a near Littrow angle, and is diffracted by the scale grating , the diffracted light with a diffraction order of -1 is in the first plane, and the -1 order diffracted light is incident on the first reflector, and is still in the first plane after being reflected by the first reflector, and is again nearly The Littrow angle is incident on the scale grating, so that the measurement beam is reflected back and forth between the scale grating and the first reflector, and finally perpendicularly incident on the second reflector, the measurement beam returns along the original optical path, and the whole structure forms a self-collimation structure. The invention increases the optical subdivision multiple to N times, adopts near Littrow angle incident, can make the design and manufacture of the scale grating easier, increases the number of times the measurement beam is diffracted by the scale grating, that is, increases the multiple of the optical subdivision of the grating interferometer .

Description

High Optical Subdivision Structure of Self-collimating Grating Interferometer

technical field

The invention relates to a grating interferometer, in particular to a high optical subdivision structure of the self-collimating grating interferometer, which can greatly increase the optical subdivision multiple of the grating interferometer.

Background technique

There are currently two main types of instruments for micro-nano precision displacement measurement: laser interferometer and grating interferometer. Laser interferometer is based on wavelength and can obtain high resolution, but its application is limited because the wavelength is easily affected by factors such as environment and light source. The grating interferometer just makes up for the shortcomings of the laser interferometer. It uses the grating period as the reference, and the measurement results are basically not affected by the environment and wavelength. It has been widely used in processing machine tools, robots, biomedical and other fields.

Whether it is a laser interferometer or a grating interferometer, its resolution depends on the optical subdivision multiple and the electronic subdivision multiple. Since the electronic subdivision is limited by the optical subdivision signal, in the case of the same electronic subdivision, the higher the optical subdivision multiple, the higher the measurement resolution. Currently typical grating interferometer systems, such as the patent US5574558 of Heidenhain, the patent US5038032 of Canon of Japan, the patent US5442172 of IBM, etc., the optical subdivision multiple is not high, generally 2 or 4 times. Therefore, it is of great significance to increase the optical subdivision multiple. The present invention can theoretically increase the optical subdivision factor infinitely under the condition that the grating efficiency is sufficiently high, and solves the problem of low subdivision factor of the current grating interferometer.

Contents of the invention

The purpose of the present invention is to solve the problem of low optical subdivision multiples of the current grating interferometer, and propose a high optical subdivision structure for the self-collimation grating interferometer, which can make the measuring beam diffracted by the grating scale many times, thereby Greatly increase the optical subdivision multiple of the grating interferometer system.

Principle of the present invention is as follows:

The principle of the grating interferometer is to use the grating Doppler frequency shift to calculate the displacement of the grating scale. The grating Doppler frequency shift is either obtained by the number of fringe movements formed by the interference of the measuring beam and the reference beam, or by the interference of two measuring beams. The number of fringe moves is obtained. The measuring beam is a beam diffracted by the grating scale, and the reference beam is a beam not diffracted by the grating scale.

The high optical subdivision structure of the self-collimating grating interferometer of the present invention makes the measurement beam of the grating interferometer incident on the grating scale at a near Littrow angle, and the Littrow angle can be obtained by the following formula,

Where λ is the wavelength of the measuring beam, and d is the grating period.

Technical solution of the present invention is as follows:

A high optical subdivision structure of a self-collimating grating interferometer is characterized in that its composition includes: a scale grating, a first reflector and a second reflector;

Let the first plane be the plane formed by the measuring light beam and the scale grating lines, the second plane be the plane formed by the scale grating normal and the scale grating lines, the first plane and the second plane between The angle is the Littrow angle, and the third plane is the plane formed by the scale grating normal and the grating vector;

The reflective surface of the first reflector is perpendicular to the first plane, and the reflective surface of the second reflector is perpendicular to the direction of the diffracted light diffracted by the scale grating for the Nth time, where 2N is the measuring beam being measured by the scale The total number of diffractions for grating diffraction;

The measuring beam is first incident on the scale grating at a near Littrow angle, and is diffracted by the scale grating. The diffracted light with a diffraction order of -1 is in the first plane, and the -1 order diffracted light is incident on the The first reflector is still in the first plane after being reflected by the first reflector, and is incident on the scale grating at a near Littrow angle again, so that the measuring beam is reflected back and forth between the scale grating and the first reflector, After finally being perpendicularly incident on the second reflector, the measuring beam returns along the original optical path, and the whole structure forms a self-collimating structure.

The near Littrow angle means that the measurement beam in the first plane deviates from the third plane by an angle.

Further, the present invention also includes: a third reflecting mirror and a fourth reflecting mirror;

The third reflector and the first reflector are mirror-symmetrical with respect to the plane perpendicular to the scale grating, and the fourth reflector and the second reflector are symmetrical with respect to the scale The plane perpendicular to the grating is axisymmetric;

The two measuring beams are mirror-symmetrical with respect to the plane perpendicular to the scale grating, and respectively incident on the scale grating for the first time at a near Littrow angle, and are diffracted by the scale grating, and the diffracted light with a diffraction order of -1 is In the first plane, the -1-order diffracted light is respectively incident on the first reflector and the third reflector, and is still in the first plane after being reflected by the first reflector and the third reflector, and is again nearly The Littrow angle is incident on the scale grating, so that the measurement beam is reflected back and forth between the scale grating and the first reflector, the scale grating and the third reflector, and finally perpendicularly incident on the second reflector and the fourth reflector respectively , the measuring beam returns along the original optical path respectively, and the whole structure forms a self-collimating structure.

In particular, the present invention is applicable to the self-collimating grating interferometer whose interference fringes are formed by two beams of measuring light, as long as the third reflector and the fourth reflector are added, the placement of the third reflector and the fourth reflector is the same as The placement of the first and second mirrors is exactly the same. The first measurement beam is reflected back and forth between the scale grating and the first reflector, and finally enters the second reflector perpendicularly and returns along the original optical path; the second measurement beam is reflected back and forth between the scale grating and the third reflector and finally It is perpendicularly incident on the fourth reflector and returns along the original optical path.

In particular, the small angles by which the measurement beam deviates from the third plane at each incidence near the Littrow angle may or may not be equal.

In particular, the present invention adopts near-Littrow angle incidence, and may also adopt near-multiple Bragg angle incidence. The m-th Bragg angle is,

where m is the diffraction order.

Compared with prior art, technical effect of the present invention:

The invention makes the measurement light beam incident on the scale grating at a near Littrow angle, and the measurement light beam is diffracted by the scale grating for multiple times through the reflection mirror, so as to achieve the effect of high optical subdivision. According to the grating Doppler frequency shift effect, it can be seen that the incident beam undergoes N times-1 order diffraction on the scale grating, which will generate N times Doppler frequency shift to the measuring beam, which can increase the optical subdivision multiple to N times. In particular, the present invention adopts near Littrow angle incidence, which can make the design and manufacture of the scale grating easier, because the grating is easy to obtain high diffraction efficiency when the Littrow angle is incident, which means that the number of diffractions of the measuring beam through the scale grating can be increased , that is, to increase the multiple of the optical subdivision of the grating interferometer. In particular, the present invention adopts only two mirrors to design a high optical subdivision structure, which is simple in structure and economical.

Description of drawings

Figure 1 is a schematic diagram of the high optical subdivision components of the self-collimating grating interferometer

Figure 2 is a schematic diagram of high optical subdivision components of another self-collimating grating interferometer

Fig. 3 is the schematic diagram of embodiment 1 of high optical subdivision components using self-collimating grating interferometer

Fig. 4 is the schematic diagram of embodiment 2 of high optical subdivision components using self-collimating grating interferometer

Fig. 5 is the schematic diagram of embodiment 3 of high optical subdivision components using self-collimating grating interferometer

detailed description

The high optical subdivision structure of the self-collimating grating interferometer of the present invention can be used in the structure of all self-collimating grating interferometers, and the laser light source can adopt a single-frequency laser light source or a dual-frequency laser light source, and the interference signal can be two The measurement beam can also be formed by the interference of the measurement beam and the reference beam. The present invention will be further described below in conjunction with the embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

A highly optically subdivided structure 30 of a self-collimating grating interferometer is shown in FIG. 1 , which is mainly used in a grating interferometer in which measuring beams and reference beams form interference fringes. The structure includes: a grating scale 1 , a first reflector 2 and a second reflector 3 . After the incident light beam 41 of the measuring beam is incident on the scale grating 1 for the first time, it is diffracted by the scale grating 1, and the diffracted light is still in the first plane after being reflected by the first reflector 2, and is incident on the scale grating again at a near Littrow angle 1, so that the measuring beam is reflected back and forth between the scale grating 1 and the first reflector 2, and finally is perpendicularly incident on the second reflector 3, and the measuring beam will return along the original optical path to form an outgoing beam 42. The beam 42 and the beam 41 share the same line, but in the opposite direction. The whole structure forms a self-collimating structure. In particular, the small angles by which the measurement beam deviates from the third plane at each incidence near the Littrow angle may or may not be equal. The outgoing beam 42 of the measurement beam passes through the subsequent grating interference structure and merges with the reference beam to form interference fringes. The Doppler frequency shift can be calculated through the interference fringes, thereby obtaining the displacement of the grating. The characteristic of this structure is that there is only one measurement beam, which can fully reduce the burden of grating design and manufacture, and only need to optimize the diffraction efficiency of the beam in one polarization direction to achieve high diffraction efficiency.

Another highly optically subdivided structure 30 of a self-collimating grating interferometer is shown in FIG. 2 , which is mainly used in a grating interferometer in which two beams of measuring light form interference fringes. The structure includes: a grating scale 1 , a first reflector 2 , a second reflector 3 , a third reflector 4 and a fourth reflector 5 . After the incident light beam 41 of the first measurement beam is incident on the scale grating 1 for the first time, it is diffracted by the scale grating 1, and after being reflected by the first reflector 2, the diffracted light is incident on the scale grating 1 again at a near Littrow angle, so The measurement beam is reflected back and forth between the scale grating 1 and the first reflector 2, and is finally perpendicularly incident on the second reflector 3. The first measurement beam will return along the original optical path to form the outgoing beam 42 of the first measurement beam. The first measurement The outgoing beam 42 of the beam is collinear with the incoming beam 41 of the first measurement beam, but in the opposite direction of propagation. After the incident light beam 43 of the second measurement beam is incident on the scale grating 1 for the first time, it is diffracted by the scale grating 1, and after the diffracted light is reflected by the third reflector 4, it is incident on the scale grating 1 again at a near Littrow angle, so The measurement beam is reflected back and forth between the scale grating 1 and the third reflector 4, and is finally vertically incident on the fourth reflector 5. The second measurement beam will return along the original optical path to form the outgoing beam 44 of the second measurement beam. The second measurement The outgoing beam 44 of the beam is collinear with the incoming beam 43 of the second measurement beam, but in the opposite direction of propagation. The whole structure forms a self-collimating structure. In particular, the small angles by which the measurement beam deviates from the third plane at each incidence near the Littrow angle may or may not be equal. The outgoing beam 42 of the first measuring beam and the outgoing beam 44 of the second measuring beam are combined to form interference fringes after passing through the subsequent structure of the grating interferometer, and the Doppler frequency shift can be calculated through the interference fringes, thereby obtaining the displacement of the grating. The feature of this structure is that it can make full use of the opposite direction of Doppler frequency shift after the two beams of measuring light are diffracted by the scale grating, so that the optical subdivision factor is doubled.

Fig. 3 is a schematic diagram of the principle of the example 1 of the highly subdivided component using the self-collimating grating interferometer. The light source is a dual-frequency laser light source, and the interference signal is formed by the measurement beam and the reference beam. The dual-frequency laser 51 emits orthogonal dual-frequency linearly polarized light, which is split into two beams by the non-polarizing beam splitter 52, and one beam passes through the first analyzer 59 placed at 45 degrees to the orthogonal dual-frequency linearly polarized light to form interference The signal is received by the first photodetector 61 as a reference signal for dual-frequency heterodyne interferometry; the other beam is divided into transmitted P light and reflected S light by a polarizing beam splitter 52, P light is used as a measuring beam, and S light is used as The reference beam and the measuring beam are incident on the high optical subdivision structure 30 of the self-collimating grating interferometer shown in FIG. The outgoing beam 42. The reference beam is vertically incident on the sixth reflector 57 and returns on the original path, and is jointly incident with the beam 42 that passes through the fifth reflector 56 and the polarizing beam splitter prism 53 through the high optical subdivision structure of the self-collimating grating interferometer. Non-polarizing beam splitter 52, the light reflected by the non-polarizing beam splitter 52 of the measuring beam and the reference beam forms an interference signal after passing through the second analyzer 58 placed at 45 degrees, and is received by the second photodetector 60 as a dual-frequency The measurement signal of heterodyne interferometry; the above-mentioned reference signal and measurement signal can be processed by the data acquisition and processing and control unit 62 to obtain the lateral displacement of the scale diffraction grating.

Figure 4 is a schematic diagram of the principle of the example 2 of the high optical subdivision component using the self-collimating grating interferometer. The light source is a dual-frequency laser light source, and the interference signal is formed by two beams of measurement light. The dual-frequency laser 51 emits orthogonal dual-frequency linearly polarized light, which is split into two beams by the non-polarizing beam splitter 52, and one beam passes through the first analyzer 59 placed at 45 degrees to the orthogonal dual-frequency linearly polarized light to form interference signal, and is received by the first photodetector 61 as the reference signal of dual-frequency heterodyne interferometry; the other beam is divided into the transmitted P light and the reflected S light by the polarizing beam splitter 53, respectively by the first quarter wave Plate 54 and the second quarter-wave plate 55 are converted into circularly polarized light, and then enter the high optical subdivision of the self-collimating grating interferometer as shown in Figure 2 through the fifth reflector 56 and the sixth reflector 57 Structure 30, the incident beam 41 of the first measuring beam and the incident beam 43 of the second measuring beam become the outgoing beam 42 of the first measuring beam and the outgoing beam 44 of the second measuring beam after highly optically subdivided structures, the two outgoing beams After passing through the first reflector 56 and the second reflector 57 again, the first quarter-wave plate 54 and the second quarter-wave plate 55 are converted into linearly polarized light orthogonal to the original polarization state, and pass through the polarization beam splitter prism 53 are jointly incident to the second analyzer 58 placed at 45 degrees to form an interference signal, and are received by the second photodetector 60 as the measurement signal of dual-frequency heterodyne interferometry; the above-mentioned reference signal and measurement signal are collected and The processing and control unit 62 processes to obtain the lateral displacement of the scale diffraction grating.

Fig. 5 is a schematic diagram of the principle of the example 3 of the high optical subdivision component using the self-collimating grating interferometer. The light source is a single-frequency laser light source, and the interference signal is formed by two beams of measuring light. The single-frequency laser 71 emits linearly polarized light, which is divided into P light and S light by the polarization beam splitter 53, and is transformed into circularly polarized light by the first quarter-wave plate 54 and the second quarter-wave plate 55 respectively, and then The incident beam 41 of the first measuring beam and the incident beam 43 of the second measuring beam are incident to the high optical subdivision structure 30 of the self-collimating grating interferometer shown in FIG. 2 through the fifth reflector 56 and the sixth reflector 57 After the high optical subdivision structure, it becomes the outgoing beam 42 of the first measuring beam and the outgoing beam 44 of the second measuring beam. The two outgoing beams pass through the fifth reflector 56 and the sixth reflector 57 again, and the first quarter The wave plate 54 and the second quarter wave plate 55 are converted into linearly polarized light orthogonal to the original polarization state, and pass through the polarization beam splitter prism 53, and enter the dotted line frame jointly by the quarter wave plate 72, the non-polarization splitter A beam splitter 73, a first polarizing beam splitter 75, a second polarizing beam splitter 74 (placed at a 45-degree rotation), a first detector 76, a second detector 78, a third detector 77, and a fourth detector 79 The polarized phase-shifting interference photoelectric detection unit forms four detection signals with a phase shift of 90°. Furthermore, the lateral displacement of the scale grating can be obtained by processing the data acquisition and processing and control unit 80 .

Claims (3)

1. A high optical subdivision structure of a self-collimating grating interferometer is characterized in that its composition comprises: a scale grating (1), a first reflector (2) and a second reflector (3); Let the first plane (α) be the plane formed by the measuring beam and the scale grating lines, the second plane (β) be the plane formed by the scale grating normal and the scale grating lines, the first plane and the The included angle of the second plane is the Littrow angle (θ), and the third plane (γ) is the plane formed by the scale grating normal and the grating vector; The reflective surface of the first reflector (2) is perpendicular to the first plane (α), and the reflective surface of the second reflector (3) is perpendicular to the diffracted light diffracted by the scale grating N times direction, where 2N is the total diffraction times of the measurement beam being diffracted by the scale grating; The measuring beam is incident on the scale grating (1) for the first time at a near Littrow angle, and is diffracted by the scale grating (1). The diffracted light with a diffraction order of -1 is in the first plane. The diffracted light is incident on the first reflector (2), is still in the first plane after being reflected by the first reflector, and is incident on the scale grating at a near Littrow angle again, so that the measuring beam is between the scale grating and the The first reflectors are reflected back and forth, and finally, after being vertically incident on the second reflector, the measuring beam returns along the original optical path, and the whole structure forms a self-collimating structure. 2. the high optical subdivision structure of self-collimating grating interferometer according to claim 1, is characterized in that, described near Littrow angle refers to that the measurement beam that is in the first plane deviates from the third plane ( γ) an angle (ε). 3. The high optical subdivision structure of the self-collimating grating interferometer according to claim 1 or 2, is characterized in that also comprising: the third reflecting mirror (4) and the fourth reflecting mirror (5); The third reflector (4) and the first reflector (2) are mirror-symmetrical to the plane perpendicular to the scale grating, and the fourth reflector (5) is symmetrical to the first reflector (2). The second reflecting mirror (3) is mirror-symmetrical with respect to the plane perpendicular to the scale grating; The two measuring beams are mirror-symmetrical with respect to the plane perpendicular to the scale grating, and are first incident on the scale grating (1) at a near Littrow angle respectively, and are diffracted by the scale grating (1), and the diffraction order is The -1 diffracted light is in the first plane, and the -1 order diffracted light is respectively incident on the first reflector (2) and the third reflector (4), and passes through the first reflector and the third reflector After reflection, it is still in the first plane, and is incident on the scale grating again at a near Littrow angle, so that the measuring beam is reflected back and forth between the scale grating and the first reflector, the scale grating and the third reflector, and finally vertically respectively After being incident on the second reflector and the fourth reflector, the measuring light beam returns along the original optical path respectively, and the whole structure forms a self-collimating structure.