阅读说明：本技术 一种用于角速度测量的光学系统 (Optical system for measuring angular velocity ) 是由 董毅 张艳玲 田娅 于 2019-11-28 设计创作，主要内容包括：本发明的用于角速度测量的光学系统,包括激光光源、第一分光棱镜、偏振分束镜、第二分光棱镜、螺旋相位片和四分之一波片,经第一分光棱镜后的透射光和反射光分别形成信号光和参考光；螺旋相位片将信号光转化为涡旋光,偏振分束镜完全透射的参考光与偏振分束镜完全反射的涡旋信号光汇成一路光束,汇成一路光束的信号光与参考光经第二偏振片后偏振方向相同,并发生光外差干涉。本发明的用于角速度测量的光学系统,通过转动第一半波片,可对透过第二半波片之后的信号光与透过第一偏振片之后的参考光的光强比进行调节,以使汇成一束的涡旋信号光与参考光的光强比相等,此时干涉衬比度最大,光电探测器所检测到的差分电信号信噪比最高。(The optical system for measuring the angular velocity comprises a laser light source, a first light splitting prism, a polarization beam splitter, a second light splitting prism, a spiral phase plate and a quarter wave plate, wherein transmitted light and reflected light passing through the first light splitting prism respectively form signal light and reference light; the spiral phase plate converts the signal light into vortex rotation, the reference light completely transmitted by the polarization beam splitter and the vortex signal light completely reflected by the polarization beam splitter are converged into a light beam, the signal light and the reference light which are converged into the light beam are polarized in the same direction after passing through the second polarizing plate, and light heterodyne interference is generated. According to the optical system for measuring the angular velocity, the light intensity ratio of the signal light after passing through the second half-wave plate and the reference light after passing through the first polaroid can be adjusted by rotating the first half-wave plate, so that the light intensity ratio of the vortex signal light and the reference light which are converged into one beam is equal, the interference contrast is the largest at the moment, and the signal-to-noise ratio of the differential electric signal detected by the photoelectric detector is the highest.)

1. An optical system for measuring angular velocity comprises a laser light source (1), a first light splitting prism (5), a polarization beam splitter (9), a second light splitting prism (14), a spiral phase plate (8) and a quarter wave plate (10), wherein a first half wave plate (4) is arranged between the laser light source and the first light splitting prism, the laser light source is used for generating linearly polarized laser, the laser light generated by the laser light source is irradiated on the first light splitting prism after the polarization direction of the laser light is rotated by the first half wave plate, and transmitted light and reflected light after passing through the first light splitting prism respectively form signal light and reference light; the method is characterized in that: a second half-wave plate (6) is arranged between the first beam splitter prism and the spiral phase plate, a first polarizing plate (12) is arranged between the first beam splitter prism and the polarization beam splitter, and a second polarizing plate (13) is arranged between the polarization beam splitter and the second beam splitter prism; the signal light transmitted by the first beam splitting prism is irradiated on a spiral phase plate (8) after rotating the polarization direction through a second half-wave plate, and the spiral phase plate converts the signal light into vortex optical rotation with the angular quantum number of l; the vortex light converted by the spiral phase plate is irradiated on a polarization beam splitter (9), the polarization beam splitter enables the vortex rotation irradiated on the polarization beam splitter to be completely transmitted, the completely transmitted vortex light vertically irradiates on a rotating body to be detected (11) after passing through a quarter-wave plate, the vortex light is reflected by the rotating body to be detected and passes through the quarter-wave plate again, the polarization direction of the vortex light rotates for 90 degrees relative to the initial vortex rotation, and the rotated vortex light is irradiated on the polarization beam splitter (9) and is totally reflected;

the reference light formed by reflection of the first light splitting prism (5) changes the polarization direction through the first polarizing film (12), and after the light intensity is adjusted, the reference light irradiates on the polarization beam splitter (9), and the reference light irradiating on the polarization beam splitter is transmitted; the reference light completely transmitted by the polarization beam splitter and vortex signal light completely reflected by the polarization beam splitter are converged into one light beam, the signal light converged into the one light beam and the reference light are polarized in the same direction after passing through a second polarizing film (13) and perform light heterodyne interference, the interfered light beam irradiates a second light splitting prism, and the photoelectric detector is used for detecting a difference frequency signal of the signal light and the reference light.

2. The optical system for angular velocity measurement according to claim 1, characterized in that: a holophote (2) and a beam expander (3) are sequentially arranged between the laser source (1) and the first half-wave plate (4), linearly polarized laser emitted by the laser source is reflected by the holophote and then irradiates the beam expander (3), and the beam expander realizes beam expansion of the laser; a right-angle prism (7) is arranged between the second half-wave plate (6) and the spiral phase plate (8), and the signal light entering and exiting from the right-angle prism has opposite propagation directions and is strictly parallel.

3. The optical system for angular velocity measurement according to claim 1 or 2, characterized in that: the photoelectric detector comprises a first photoelectric detector (17) and a second photoelectric detector (18), signal light and reference light are converted into the same polarization direction through a second polarizing film (13) and interfere with each other, transmitted light irradiated on a second beam splitter prism (14) by the interfered light beams is focused through a first focusing lens (15) and then irradiated on the first photoelectric detector (17), and reflected light of the second beam splitter prism is focused through a second focusing lens (16) and then irradiated on the second photoelectric detector (18).

4. The optical system for angular velocity measurement according to claim 1 or 2, characterized in that: the first half wave plate (4), the second half wave plate (6), the first polarizer (12) and the second polarizer (13) can be adjusted in a rotating mode.

5. The optical system for angular velocity measurement according to claim 3, characterized in that: if the number of angular quanta of the spiral phase plate is l, and a difference frequency signal obtained after random noise is filtered by the first photoelectric detector (17) and the second photoelectric detector (18) is delta f, the following conditions are met:

from equation (1):

wherein l is the angular quantum number of the spiral phase plate, and Δ f is the frequency of the difference frequency signal measured by the detector.

Technical Field

The present invention relates to an optical system for measuring angular velocity, and more particularly, to an optical system for measuring angular velocity by using a frequency shift phenomenon in which vortex light is irradiated on a rotating object.

Background

Vortex is one of the most common phenomena in nature and is commonly found in classical macroscopic systems such as water, clouds, and cyclones. A number of theories and experiments confirm that vortices also exist in the light wave field. The vortex light is singular light with a spiral wave front structure, and the center of the light beam of the vortex light is provided with a phase singularity, so that the light intensity of the cross section of the vortex light is distributed in an annular hollow shape. Vortex rotation, which is a form of wave motion, has orbital angular momentum due to a helical phase structure. In 1992, professor Allen of british physicist originally demonstrated that orbital angular momentum of vortex rotation has quantum properties, with each photon carrying an angular momentum of lh.

Like the doppler effect of sound waves, the relative motion of the light source and the object also has the doppler effect. The propagation direction of the light and the velocity direction of the object to be measured cannot be perpendicular, and is therefore also referred to as the linear doppler effect. In 2013, Martin P.J. Lavery, a British scholar and Camelo Rosales-Guzman, a Spanish scholar, respectively, demonstrated experimentally the rotational Doppler effect of vortex rotation for the first time, almost at the same time, and were used to measure angular velocity. Both groups use a Spatial Light Modulator (SLM) to generate vortex rotation for rotational doppler velocimetry. Similar methods are adopted by research groups such as Beijing university of science and technology, Western-style university of transportation and the like in China to generate vortex rotation.

By utilizing the SLM method, the position, the size and the number of angular quantum can be controlled by controlling the hologram displayed on the SLM through a computer, so that the method has higher flexibility. However, the SLM is limited in its further popularization and application by the disadvantages of high price, complex control system, reflective operation mode, etc. Another common method is to generate a vortex beam using a spiral phase plate. The spiral phase plate adopts a transmission type working mode, the conversion efficiency is high, and the transmission light propagation direction is not deflected. Compared with the SLM, the volume is smaller, the structure is simpler, and the space occupied by the whole measuring system is expected to be further reduced through design.

Disclosure of Invention

The present invention has been made to overcome the above-mentioned drawbacks of the prior art, and provides an optical system for angular velocity measurement.

The optical system for measuring the angular velocity comprises a laser light source, a first light splitting prism, a polarization beam splitter, a second light splitting prism, a spiral phase plate and a quarter wave plate, wherein a first half wave plate is arranged between the laser light source and the first light splitting prism; the method is characterized in that: a second half-wave plate is arranged between the first light splitting prism and the spiral phase plate, a first polaroid is arranged between the first light splitting prism and the polarization beam splitter, and a second polaroid is arranged between the polarization beam splitter and the second light splitting prism; the signal light transmitted by the first beam splitting prism is irradiated on the spiral phase plate after rotating the polarization direction through the second half-wave plate, and the spiral phase plate converts the signal light into vortex rotation with the angular quantum number of l; the vortex light converted by the spiral phase plate is irradiated on the polarization beam splitter, the polarization beam splitter enables the vortex optical rotation irradiated on the polarization beam splitter to be completely transmitted, the completely transmitted vortex light vertically irradiates on a rotator to be tested after passing through a quarter-wave plate, the vortex light is reflected by the rotator to be tested and passes through the quarter-wave plate again, the polarization direction of the vortex light rotates by 90 degrees relative to the initial vortex optical rotation, and the rotated vortex light irradiates on the polarization beam splitter and is totally reflected;

the reference light formed by reflection of the first light splitting prism is irradiated on the polarization beam splitter after the polarization direction of the reference light is changed by the first polaroid and the light intensity is adjusted, and the reference light irradiated on the polarization beam splitter is completely transmitted; the reference light completely transmitted by the polarization beam splitter and the vortex signal light completely reflected by the polarization beam splitter are converged into one light beam, the signal light converged into the one light beam and the reference light pass through the second polaroid and have the same polarization direction, light heterodyne interference is generated, the interfered light beam irradiates the second beam splitter prism, and the photoelectric detector is used for detecting a difference frequency signal of the signal light and the reference light.

According to the optical system for measuring the angular velocity, the total reflector and the beam expander are sequentially arranged between the laser light source and the first half-wave plate, linear polarization laser emitted by the laser light source is reflected by the total reflector and then irradiates the beam expander, and the beam expander expands the laser; a right-angle prism is arranged between the second half-wave plate and the spiral phase plate, and the signal light incident and emergent from the right-angle prism has opposite propagation directions and is strictly parallel.

The optical system for measuring the angular velocity comprises a first photoelectric detector and a second photoelectric detector, signal light and reference light are converted into the same polarization direction through a second polaroid and interfere with each other, transmitted light irradiated on a second beam splitter prism by the interfered light beams is irradiated on the first photoelectric detector after being converged by a first converging lens, and reflected light of the second beam splitter prism is irradiated on the second photoelectric detector after being converged by a second converging lens.

The optical system for measuring the angular velocity is characterized in that the first half wave plate, the second half wave plate, the first polaroid and the second polaroid can be rotationally adjusted.

The optical system for measuring the angular velocity of the invention is that the angular quantum number of the spiral phase plate is set as l, and the difference frequency signal obtained after the random noise is filtered by the first photoelectric detector and the second photoelectric detector is set as delta f, so that the following requirements are met:

from equation (1):

wherein l is the angular quantum number of the spiral phase plate, and Δ f is the frequency of the difference frequency signal measured by the detector.

The invention has the beneficial effects that: the invention relates to an optical system for measuring angular velocity, wherein linear polarized laser generated by a laser source is split into signal light and reference light by a first half-wave plate after rotating the polarization direction, the signal light is converted into vortex rotation by a spiral phase plate after rotating the polarization direction by a first half-wave plate, the vortex light irradiates on a rotating body to be measured by a quarter-wave plate, the vortex light is reflected and then passes through the quarter-wave plate again to enable the polarization direction of the vortex rotation to rotate 90 degrees relative to the initial vortex rotation, the rotated vortex light is converged into a light beam with the reference light after being totally reflected by a polarization beam splitter, the signal light converged into the light beam and the reference light are rotated to the same polarization direction by a second polarizer to generate interference, and a photoelectric detector realizes the measurement of the angular velocity of the rotating body by detecting a difference frequency signal of the signal light and the reference light.

According to the optical system for measuring the angular velocity, under the condition that the beam splitting ratio of the first beam splitter prism is constant, the light intensity ratio of the signal light after passing through the second half-wave plate and the reference light after passing through the first polarizer can be adjusted by rotating the first half-wave plate, so that the light intensity ratio of the vortex signal light and the reference light which are converged into one beam is equal, the light intensity ratio of the signal light and the reference light which are finally interfered is also 1:1, the polarization directions of the reference light and the signal light are the same, the light intensity is equal, the interference contrast ratio is the largest at the moment, and the signal-to-noise ratio of the differential electric signal detected by the photoelectric detector is the highest.

Drawings

Fig. 1 is a schematic diagram of an optical system for angular velocity measurement of the present invention.

In the figure: the device comprises a laser light source 1, a total reflector 2, a beam expander 3, a first half-wave plate 4, a first beam splitter 5, a second half-wave plate 6, a right-angle prism 7, a spiral phase plate 8, a polarization beam splitter 9, a quarter-wave plate 10, a rotating body to be tested 11, a first polaroid 12, a second polaroid 13, a second polaroid 14, a first condensing lens 15, a second condensing lens 16, a first photoelectric detector 17 and a second photoelectric detector 18.

Detailed Description

The invention is further described with reference to the following figures and examples.

As shown in fig. 1, a schematic diagram of an optical system for angular velocity measurement according to the present invention is shown, which is composed of a laser light source 1, a total reflection mirror 2, a beam expander 3, a first half-wave plate 4, a first beam splitter 5, a second half-wave plate 6, a right-angle prism 7, a spiral phase plate 8, a polarization beam splitter 9, a quarter-wave plate 10, a first polarizer 12, a second polarizer 13, a second beam splitter 14, a first condenser lens 15, a second condenser lens 16, a first photodetector 17, and a second photodetector 18, and optical elements in all the same directions have coaxial centers. Holophote 2, beam expander 3 and first half wave plate 4 set gradually between laser source 1 to first spectroscope 5, laser source 1 sends linear polarization laser, linear polarization laser that laser source 1 sent is after the reflection of holophote 2, the beam expanding of beam expander 3 again, then shine on first half wave plate 4, the polarization direction of the rotatory laser of first half wave plate 4, laser after the rotatory polarization direction is shone on first spectroscope 5, the laser is as signal light and reference light respectively through the transmission light and the reverberation of first spectroscope 5, the beam splitting ratio of first spectroscope 5 can be selected as 1: 1.

the second half-wave plate 6 is positioned between the first beam splitter prism 5 and the right-angle prism 7, the spiral phase plate 8 is positioned between the right-angle prism 7 and the polarization beam splitter 9, and the quarter-wave plate 10 is positioned between the polarization beam splitter 9 and the rotating body 11 to be measured. The signal light transmitted by the first beam splitter prism 5 firstly rotates the polarization direction through the second half-wave plate 6, the laser light becomes P polarized light shown in the figure, the P polarized signal light is irradiated on the spiral phase plate 8 in an antiparallel light mode through twice total reflection of the right-angle prism 7, the spiral phase plate 8 converts the linear polarized signal light into vortex light with the angular quantum number of l, and the vortex light is irradiated on the polarization beam splitter 9. The placing mode of the polarization beam splitter 9 meets the requirement of full transmission of vortex optical rotation irradiated on the polarization beam splitter 9, the vortex optical rotation of full transmission is perpendicularly irradiated on the rotating body 11 to be detected through the quarter-wave plate 5, the rotation of the rotating body 11 to be detected can cause the vortex optical rotation to generate frequency shift, the vortex optical rotation is reflected by the rotating body 11 to be detected and passes through the quarter-wave plate 10 again, the polarization direction of the vortex optical rotation is 90 degrees after rotating relative to the initial vortex optical rotation, namely, P polarized light is converted into S polarized light, and the vortex optical rotation in the S polarization direction can be totally reflected after being irradiated on the polarization beam splitter.

The first polarizing plate 12 is disposed between the first beam splitter 5 and the polarization beam splitter 9, the reference light reflected by the first beam splitter 5 is irradiated onto the first polarizing plate 12, and the first polarizing plate 12 rotates the polarization direction of the reference light to convert the reference light into P-polarized light and attenuate the light intensity of the reference light. The reference light in the P polarization direction is irradiated on the polarization beam splitter 9 to be totally transmitted, the totally transmitted reference light and the signal light totally reflected by the polarization beam splitter 9 are converged into a light beam, and at the moment, the signal light converged into the light beam is perpendicular to the polarization direction of the reference light, so that the signal light and the reference light cannot interfere with each other.

The signal light and the reference light are converged into one path of light beam and then irradiated on the second polaroid 13, the second polaroid 13 enables the polarization directions of the signal light and the reference light to be consistent, and interference can be generated after the polarization directions of the signal light and the reference light are consistent. Under the condition that the light intensity of the signal light and the light intensity of the reference light which are converged into one light beam are equal, the polarization directions of the signal light and the reference light are perpendicular to each other, and the transmission direction of the second polarizing film 13 is at a position which forms an included angle of 45 degrees with the polarization directions of the reference light and the signal light, so that the signal light and the reference light which pass through the second polarizing film 13 are not only the same in polarization direction, but also equal in light intensity, the contrast ratio of the signal light and the reference light is optimal at the moment, the interference is most obvious, and the amplitude of the differential alternating current signal detected by the photoelectric detector.

After passing through the second polarizing plate 13, the signal light interferes with the reference light and is irradiated onto the second beam splitter prism 14, the reflected light beam passing through the second beam splitter prism 14 is converged by the second condenser lens 16 and is irradiated onto the second photodetector 18, and the transmitted light beam passing through the second beam splitter prism 14 is converged by the first condenser lens 15 and is irradiated onto the first photodetector 17. The splitting ratio of the second beam splitter prism 14 is 1:1, so that the difference frequency signals detected by the first photodetector 17 and the second photodetector 18 are equal in amplitude and in phase, and random noise in the signals can be filtered by using an opposite phase subtraction method to obtain accurate difference frequency signals.

If the number of angular quanta of the spiral phase plate is l, and a difference frequency signal obtained after random noise is filtered by the first photodetector 16 and the second photodetector 17 is Δ f, then the following conditions are satisfied:

from equation (1):

wherein l is the angular quantum number of the spiral phase plate, and Δ f is the frequency of the difference frequency signal measured by the detector.

The splitting ratio of the first beam splitter prism 5 is 1: under the condition of 1, since the signal light passing through the second half-wave plate 6 is P-polarized light and the reference light passing through the first polarizing plate 12 is also P-polarized light, the transmission direction of the first polarizing plate 12 is determined. Since the vortex light irradiates on the rotating body 11 to be measured and is scattered back, the vortex light has a certain light intensity loss, and therefore, the splitting ratio of the first beam splitter prism 5 is 1:1, if the reference light is not attenuated by the first polarizer 12, the intensity of the reference light is much greater than that of the signal light; at this time, the first half-wave plate 4 should be rotated to change the polarization direction of the reference light reflected by the first beam splitter prism 5, so as to adjust the attenuation of the reference light by the first polarizer 12, and the half-wave plate 6 should be rotated to enhance the light intensity of the signal light, so that the light intensity of the signal light and the reference light is equal when interference occurs.