CN102829729A - Method for aliasing polarizations of high-gain laser displacement sensor - Google Patents

Abstract

The invention relates to a method for aliasing the polarizations of a high-gain laser displacement sensor, which comprises a double-frequency laser, a photoelectric conversion circuit, a singlechip, a piezoelectric ceramics and a piezoelectric ceramics drive circuit, wherein the double-frequency laser comprises a laser gain tube, an output mirror and an anti-reflection window, the outer part of the output mirror is provided with a Wollaston prism which is vertical to the laser transmission direction, and a first photoelectric detector and a second photoelectric detector are correspondingly arranged along the light-emitting direction of the Wollaston prism respectively; the Wollaston prism is formed by adhering a first right-angle prism and a second right-angle prism along the inclined planes, the optical axes of the first right-angle prism and the second right-angle prism are vertical to each other and are vertical to the face normal of an incident face; and the method is characterized in that the Wollaston prism, the first photoelectric detector and the second photoelectric detector are used as a whole to rotate at the angular velocity of omega by taking the laser which is sent out by the double-frequency laser as an axis, and an x light and a y light which are sent out by the Wollaston prism are respectively received by the first photoelectric detector and the second photoelectric detector. The method can be widely applied in the laser displacement measured signal processing process.

Description

A polarization aliasing method for high-gain laser displacement sensors

technical field

The invention relates to an optical signal processing method of a laser displacement sensor, in particular to a polarization mixing method of a high-gain laser displacement sensor.

Background technique

As shown in Figure 1, when the laser displacement sensor is used for displacement measurement, when the output power of the dual-frequency laser is small (low gain), during the process of voltage rise and voltage drop of the piezoelectric ceramic, due to the change of the cavity length, the o light and The order of appearance of e-light is significantly different. O-light and e-light have two points with equal light intensity in each half-wavelength period, which are called high light intensity point and low light intensity point. When the high light intensity point and low light intensity point When the vertical gap between strong points is large, the circuit signal processing is relatively easy. For example: the patent number is ZL200910076308.3, and the Chinese patent titled "1152nm wavelength helium-neon laser nanometer measuring ruler" uses an infrared laser with an output light of 1152nm wavelength as the core of the displacement sensor, so that the resolution is constant. , the range can be expanded to more than 100mm, and the high gain of the infrared laser is used to realize non-contact measurement. As shown in Figure 2, the circuit signal processing process is as follows: one of the curves is the power tuning curve of light o, and the other curve is the power tuning curve of light e. The vertical gap between strong points G is relatively large. A~E in the figure indicate that a complete period of light output bandwidth is divided into four equal parts, that is, AB=BC=CD=DE. In order to facilitate signal processing, at high light intensity points A threshold H is set between F and low light intensity point G, and only the signals above the threshold H are processed to realize displacement measurement. Among them, the AB segment only has o light, BC is a mixed light of o light and e light, and CD only has e Light, DE is the no-light area, A~E means that the cavity mirror moves λ/2, then the four equal divisions represent λ/8 respectively, that is, four subdivisions within half a wavelength are realized.

From the actual measurement point of view, for the displacement measurement system with low dual-frequency laser power, on the general straightness level of the guide rail, the dual-frequency laser can emit light within the range of 10-20mm of cavity mirror movement, and the light intensity is unstable; continue to increase When moving the range, the dual-frequency laser cannot emit light. Therefore, in actual measurement, a dual-frequency laser with a higher output power should be selected for displacement measurement. Light o light and e light cannot be significantly separated at adjacent high and low light intensity points, especially when the output power of the dual-frequency laser is large, the light intensity of adjacent high and low light intensity points may be very similar, As a result, when the signal is processed by using the method of setting the threshold value of the nanoscale ruler, it is easy to cause miscounting, thereby causing a large measurement error. As shown in Figure 3, by zooming in on the power tuning curve shown in Figure 3, the signal voltages at the two points of equal light intensity in one cycle are not completely equal, but have a certain voltage difference. In Figure 1, the absolute voltage difference values of two adjacent equal-intensity points are similar, just because the overall amplitude of the signal in Figure 3 is relatively large, and the amplitudes of the two equal-intensity points are relatively close, so if two adjacent equal-intensity points can be made The voltage difference remains the same and the overall amplitude of the signal is greatly reduced, so that the high and low light intensity points can be significantly separated.

Contents of the invention

In view of the above problems, the purpose of the present invention is to provide a kind of when adopting high-power dual-frequency laser to carry out displacement measurement, can make the adjacent high and low light intensity points of o-light and e-light output by dual-frequency laser significantly separate, effectively A Polarization Aliasing Method for High-Gain Laser Displacement Sensors Avoiding Large Measurement Errors.

角度，经所述渥拉斯顿棱镜输出的x光和y光分别被所述第一光电探测器和第二光电探测器接收。In order to achieve the above object, the present invention adopts the following technical solutions: a polarization mixing method for a high-gain laser displacement sensor, which includes a dual-frequency laser, a photoelectric conversion circuit, a single-chip microcomputer, piezoelectric ceramics, and a piezoelectric ceramic drive circuit. The high-frequency laser includes a laser gain tube, an output mirror and an anti-reflection window. A Wollaston prism perpendicular to the laser propagation direction is arranged on the outside of the output mirror, and a first photodetector and the second photodetector; the Wollaston prism is formed by bonding the first right-angle prism and the second right-angle prism along the inclined plane, and the light of the first right-angle prism and the second right-angle prism The axes are perpendicular to each other and are all perpendicular to the surface normal of the incident surface; it is characterized in that: the Wollaston prism, the first photodetector and the second photodetector are taken as a whole and the laser light emitted by the dual-frequency laser is The axis is rotated by an angle ω so that the two orthogonal linearly polarized lights that are vertically incident on the first right-angle prism through the dual-frequency laser, wherein the vibration direction of one polarized light forms an angle ω with the optical axis of the first right-angle prism, The vibration direction of the other polarized light is aligned with the optical axis of the first rectangular prism

angle, the x-ray and y-ray outputted by the Wollaston prism are respectively received by the first photodetector and the second photodetector.

The x-ray is the mixed light of two orthogonal linearly polarized lights emitted by the dual-frequency laser, that is, the mixed light of o light and e light, the mixing ratio is k, k=sin ² ω, and the y light is o The mixed light of light and e light, the mixing ratio is 1-k.

The value range of ω is: 0≤ω≤180.

The dual-frequency laser adopts a helium-neon dual-frequency laser with a wavelength of 1152nm.

角度，此时双频激光器输出两线偏振光发射到旋转后的渥拉斯顿棱镜，经渥拉斯顿棱镜输出的x光和y光分别被第一光电探测器和第二光电探测器接收，因此本发明在不增加任何系统成本和电路复杂度的前提下，使得一个周期内相邻高、低两等光强点的电压差保持不变，信号的整体幅度大幅缩小，从而使相邻高、低两等光强点的电压差在信号整体中占有较大的比例，使得相邻高、低等光强点显著分开，方便了信号处理，有效避免了由于两个等光强点在整体信号中距离过近导致误计数引起的测量误差，大大提高了激光位移测量系统的精度和稳定性。本发明可以广泛应用于激光位移测量的信号处理过程中。The present invention has the following advantages due to the adoption of the above technical scheme: the present invention rotates the Wollaston prism, the first photodetector and the second photodetector as a whole with the laser output by the dual-frequency laser as the axis by an angle of ω, so that Two orthogonal linearly polarized lights that are vertically incident on the first rectangular prism through the dual-frequency laser, the vibration direction of one polarized light is at an angle ω with the optical axis of the first rectangular prism, and the vibration direction of the other polarized light is with the first rectangular prism The optical axis becomes

At this time, the dual-frequency laser outputs two linearly polarized lights and sends them to the rotated Wollaston prism, and the x-ray and y-ray output by the Wollaston prism are respectively received by the first photodetector and the second photodetector , so the present invention keeps the voltage difference between the adjacent high and low light intensity points in one cycle without increasing any system cost and circuit complexity, and the overall amplitude of the signal is greatly reduced, so that the adjacent The voltage difference between the high and low light intensity points occupies a large proportion in the overall signal, which makes the adjacent high and low light intensity points significantly separated, which facilitates signal processing and effectively avoids the problem caused by two equal light intensity points The measurement error caused by miscounting caused by the short distance in the overall signal greatly improves the accuracy and stability of the laser displacement measurement system. The invention can be widely used in the signal processing process of laser displacement measurement.

Description of drawings

为o光，为e光；横坐标表示时间，单位s，纵坐标为信号电压，单位V，折线表示为压电陶瓷（PZT）电压上升和下降的过程；Figure 1 is the power tuning curve when the output laser power of the dual-frequency laser is small, where

for o light, It is e light; the abscissa represents time, the unit is s, the ordinate is the signal voltage, the unit is V, and the broken line represents the process of rising and falling of piezoelectric ceramic (PZT) voltage;

Fig. 2 is a schematic diagram of an existing signal counting processing method, the abscissa represents time, the unit is s, and the ordinate is the signal voltage, the unit is V;

为o光，

为e光；横坐标表示时间，单位s，纵坐标为信号电压，单位V，折线表示为压电陶瓷电压上升和下降的过程；Figure 3 is the power tuning curve when the output laser power of the dual-frequency laser is relatively high.

for o light,

is e-light; the abscissa represents time, the unit is s, the ordinate is the signal voltage, the unit is V, and the broken line represents the process of the piezoelectric ceramic voltage rising and falling;

Fig. 4 is a schematic structural diagram of an existing high-gain laser displacement sensor system;

表示第一直角棱镜光轴方向平行于纸面，“·”表示第二直角棱镜光轴方向垂直于纸面；Fig. 5 is the structural representation of Wollaston prism in the embodiment of the present invention,

Indicates that the optical axis direction of the first rectangular prism is parallel to the paper surface, and "·" indicates that the optical axis direction of the second rectangular prism is perpendicular to the paper surface;

Figure 6 is a schematic diagram of the power tuning curve of x-ray and y-ray when k is 0, "·" is x-ray, is the y light, the abscissa indicates the change of the cavity length, the unit is nm, and the ordinate is the light intensity, dimensionless;

为y光，横坐标表示腔长变化，单位nm，纵坐标为光强，无量纲；Figure 7 is a schematic diagram of the power tuning curve of x-ray and y-ray when k is 0.1, "·" is x-ray,

is the y light, the abscissa indicates the change of the cavity length, the unit is nm, and the ordinate is the light intensity, dimensionless;

为y光，横坐标表示腔长变化，单位nm，纵坐标为光强，无量纲；Figure 8 is a schematic diagram of the power tuning curve of x-ray and y-ray when k is 0.2, "·" is x-ray,

is the y light, the abscissa indicates the change of the cavity length, the unit is nm, and the ordinate is the light intensity, dimensionless;

Figure 9 is a schematic diagram of the power tuning curve of x-ray and y-ray when k is 0.3, "·" is x-ray, is the y light, the abscissa indicates the change of the cavity length, the unit is nm, and the ordinate is the light intensity, dimensionless;

为y光，横坐标表示腔长变化，单位nm，纵坐标为光强，无量纲；Figure 10 is a schematic diagram of the power tuning curve of x-ray and y-ray when k is 0.4, "·" is x-ray,

is the y light, the abscissa indicates the change of the cavity length, the unit is nm, and the ordinate is the light intensity, dimensionless;

为y光，横坐标表示腔长变化，单位nm，纵坐标为光强，无量纲。Figure 11 is a schematic diagram of the power tuning curve of x-ray and y-ray when k is 0.45, "·" is x-ray,

is the y light, the abscissa represents the change of the cavity length, the unit is nm, and the ordinate is the light intensity, which is dimensionless.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 4, the structure of the laser displacement sensor adopted in the present invention is basically the same as the laser displacement sensor adopted in the 1152nm wavelength helium-neon laser nanoscale ruler disclosed in the prior art, and it includes a dual-frequency laser, a photoelectric conversion circuit, a single-chip microcomputer and a piezoelectric ceramic drive circuit; the dual-frequency laser includes a laser gain tube 1, an output mirror 2 is set at one end of the laser gain tube 1, an anti-reflection window 3 is set at the other end, and a polarization splitter perpendicular to the laser propagation direction is set outside the output mirror 2 The prism 4 is respectively provided with a first photodetector 5 and a second photodetector 6 corresponding to the light output direction of the polarization splitter prism 4; a birefringent crystal 7 and a cavity mirror 8 are sequentially provided on the outside of the anti-reflection window 3 along the laser propagation direction , the outer side of the cavity mirror 8 is fixed with a piezoelectric ceramic (PZT) 9, the piezoelectric ceramic 9 is connected to the positive and negative poles of the piezoelectric ceramic drive circuit 10, and the output laser of the dual-frequency laser is emitted to the polarization beam splitter prism 4 through the output mirror 2 , the horizontally polarized light and the vertically polarized light that are perpendicular to each other output by the polarization beam splitter prism 4 are respectively received by the first photodetector 5 and the second photodetector 6 and sent to the two input terminals of the photoelectric conversion circuit 11, and the photoelectric conversion circuit 11 will The received optical signal is processed and sent to the single-chip microcomputer 12, and the single-chip microcomputer 12 controls the piezoelectric ceramic driving circuit 10 to drive the piezoelectric ceramic 9 to work.

As shown in Figure 5, among the present invention, the polarizing beam splitter prism 4 adopts the Wollaston prism 4, and the Wollaston prism 4 is a rectangular prism formed by bonding the first right-angle prism 41 and the second right-angle prism 42 along the inclined plane, The optical axes of the first right-angle prism 41 and the second right-angle prism 42 are perpendicular to each other and the surface normal of the incident surface (MN plane). The first right-angle prism 41 and the second right-angle prism 42 are both made of calcite crystal. The two orthogonal linearly polarized lights emitted by the dual-frequency laser are incident on the first right-angled prism 41 of the Wollaston prism 4, and when the vibration directions of the two linearly polarized lights are parallel to or perpendicular to the MN plane of the first right-angled prism 41, the two Orthogonal linearly polarized light is strictly separated. When the vibration direction of the two linearly polarized lights forms another angle β (β≠0 or 90) with the optical axis of the first right-angle prism, the two orthogonal linearly polarized lights pass through the Wollaston prism After 4, they failed to separate, but mixed in the two beams of light in different proportions.

According to the principle of orthogonally polarized laser light, every time the cavity mirror 8 moves half a wavelength, the laser light intensity output by the output mirror 2 fluctuates for a period, and the laser output by the cavity mirror 8 is a mixed light of o light and e light, and the o light and e light The light is mixed in unequal proportions to form two other beams of light: x-ray and y-ray. The x-ray contains part of o-light and e-light, and the y-ray also contains part of o-light and e-light. Assume that the mixing ratio is k (0≤k≤ 1) When o light enters x-ray, then o-ray with a ratio of (1-k) enters y-ray; similarly, e-ray with a ratio of k enters y-ray, and e-ray with a ratio of (1-k) enters x-ray, Then the light intensity of x-ray and y-ray is expressed as:

I _x/y ＝k×I _o/e +(1-k)×I _e/o

角度，此时双频激光器输出两线偏振光发射到旋转后的渥拉斯顿棱镜4，经渥拉斯顿棱镜4输出的x光和y光分别被第一光电探测器5和第二光电探测器6接收，其中x光为o光与e光的混合光，混合比例为k，y光为o光与e光的混合光，混合比例为1-k，k＝sin²ω，夹角ω的大小可以根据实验需要进行确定，只要将一个周期内相邻的高、低两个等光强点分开即可。According to the above principle, the present invention rotates the Wollaston prism 4, the first photodetector 5 and the second photodetector 6 as a whole by an angle of ω (0≤ω≤180) with the laser output by the dual-frequency laser as the axis, so that Two orthogonal linearly polarized lights that are vertically incident on the first rectangular prism 41 through the dual-frequency laser, wherein the vibration direction of one polarized light is at an angle ω with the optical axis of the first rectangular prism 41, and the vibration direction of the other polarized light is with the first rectangular prism 41. The optical axis of rectangular prism 41 is

At this time, the dual-frequency laser outputs two linearly polarized lights and sends them to the rotated Wollaston prism 4, and the x-ray and y-ray output by the Wollaston prism 4 are respectively detected by the first photodetector 5 and the second photoelectric detector 5. Detector 6 receives, wherein x-ray is the mixed light of o light and e light, the mixing ratio is k, y light is the mixed light of o light and e light, the mixing ratio is 1-k, k=sin ² ω, the included angle The size of ω can be determined according to the needs of the experiment, as long as the adjacent high and low points of equal light intensity within a period are separated.

As shown in Figures 6 to 11, the specific implementation process of the present invention is further described below through specific examples. The dual-frequency laser adopts a helium-neon dual-frequency laser with a wavelength of 1152nm, and by rotating the Wollaston prism 4, the first right-angled prism 41 forms a series of different angles ω with the laser emitted by the dual-frequency laser, so that k=0, 0.1, 0.2, 0.3, 0.4 and 0.45, when the value of the mixing ratio k gradually increases, o light can be observed The adjacent high and low light intensity points from the e-ray are gradually separated. For example, the mixing ratio k of the o-light and e-light in the x-ray is 0.45, and the rotation angle is ω, which is about arcsin0.67082. It can be seen from Figure 11 The absolute voltage difference between adjacent high and low light intensity points has not changed, but the overall signal amplitude is greatly compressed, and the adjacent high and low light intensity points of o light and e light are significantly separated, so that it can be used Existing methods facilitate subsequent processing of the signal.

To sum up, it is further shown by experiments that using the polarization aliasing method of the present invention can not only significantly increase the relative distance between high and low light intensity points, and conveniently adjust the width of each subdivision interval, but also does not change the adjacent The horizontal position of high and low light intensity points is accurate.

Above-mentioned each embodiment is only for illustrating the present invention, and wherein all implementation process etc. of method all can be changed to some extent, every equivalent transformation and improvement carried out on the basis of the technical scheme of the present invention, all should not be excluded from the scope of the present invention. outside the scope of protection.

Claims (5)

1. the polarization aliasing method of a high gain lasers displacement transducer; It comprises two-frequency laser, photoelectric switching circuit, single-chip microcomputer, piezoelectric ceramics and driver circuit for piezoelectric ceramics; Said two-frequency laser comprises laser gain pipe, outgoing mirror and anti-reflection window; Said outgoing mirror arranged outside has the wollaston prism vertical with the laser propagation direction, and the light direction of corresponding said wollaston prism is respectively arranged with first photodetector and second photodetector; Said wollaston prism is to be bonded along the inclined-plane by first right-angle prism and second right-angle prism, and the optical axis of said first right-angle prism and said second right-angle prism is orthogonal and all perpendicular to the face normal of the plane of incidence; It is characterized in that: with said wollaston prism, first photodetector and second photodetector is an anglec of rotation ω with said two-frequency laser emitting laser as a whole; Make the pairwise orthogonal linearly polarized light that impinges perpendicularly on said first right-angle prism through said two-frequency laser; Wherein the direction of vibration of a polarized light becomes the ω angle with the optical axis of said first right-angle prism; The direction of vibration of another polarized light becomes

angle with the optical axis of said first right-angle prism, x light and the y light exported through said wollaston prism are received by said first photodetector and second photodetector respectively.

2. the polarization aliasing method of a kind of high gain lasers displacement transducer as claimed in claim 1; It is characterized in that: the mixed light of the pairwise orthogonal linearly polarized light that said x light is said two-frequency laser outgoing; Be o light and with the mixed light of e light, blending ratio is k, k=sin ²ω, said y light are the mixed light of o light and e light, and blending ratio is 1-k.

3. the polarization aliasing method of a kind of high gain lasers displacement transducer as claimed in claim 1, it is characterized in that: the span of said ω is: 0≤ω≤180.

4. the polarization aliasing method of a kind of high gain lasers displacement transducer as claimed in claim 2, it is characterized in that: the span of said ω is: 0≤ω≤180.

5. like the polarization aliasing method of claim 1 or 2 or 3 or 4 described a kind of high gain lasers displacement transducers, it is characterized in that: it is the He-Ne two-frequency laser of 1152nm that said two-frequency laser adopts wavelength.

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