A method for precisely measuring optical wave parameters based on cross-polarization effect

Abstract

The application discloses a kind of based on the optical wave parameter precision measurement method of cross polarization effect, comprising: step 1, the polarized light of polarization direction as horizontal direction is as incident light to be illuminated to dielectric, and cross polarization effect occurs when reflecting on dielectric interface;Step 2, make reflected light pass through the polarizer, and adjust the polarizer, the central light intensity of reflected light after passing through the polarizer becomes 0, and record the initial angle of the light transmission direction of polarizer and vertical direction at this time;Step 3, the physical quantity to be measured is introduced to incident light, then adjust the polarizer again, when the central light intensity of reflected light becomes 0, record the angle ψ of the change of polarizer from initial angle;Step 4, the change amount of incident light polarization direction after introducing the physical quantity to be measured is calculated according to ψ, and then the physical quantity to be measured is calculated.The optical wave parameter measurement method of the application is simple, low in cost, but the small change of the physical quantity to be measured can be accurately measured.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, and in particular to a method for precise measurement of optical wave parameters based on the cross-polarization effect. Background Technology

[0002] Light is an electromagnetic wave with a specific wavelength, frequency, and energy. Its wave properties include amplitude, wavelength, frequency, polarization, phase, and direction of propagation, making it widely used in lighting, imaging, measurement, information, and communication, and playing a significant role in agriculture, industry, and national defense. For example, crop growth depends primarily on amplitude or intensity, and most optical instruments are based on this; high-precision spectrometers can be made based on wavelength or frequency; and optical devices such as lenses can be made based on phase.

[0003] Measuring the wave parameters of light waves is fundamental to the development of optical applications. Typically, measuring the direction of incident and refracted light allows for the measurement of a material's refractive index. However, existing measurement methods have many shortcomings. For example, measuring light intensity is easily affected by background light; spectrometers, while highly accurate, are expensive; conventional instruments for measuring polarization or phase rely on angle measurements, but general angle measuring instruments have limited accuracy, typically not exceeding 0.01°. In recent years, new sensing methods have been proposed, such as using high-frequency signals for measurement through signal modulation to eliminate background noise interference. Although this can achieve higher accuracy (10^(-4) to 10^(-6) degrees), the systems are complex and require lock-in amplifiers, resulting in high costs. To date, achieving a simple, low-cost, and highly accurate method for measuring light wave parameters remains a crucial problem that urgently needs to be solved. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a precise measurement method for changes in optical wave parameters based on the cross-polarization effect, which can significantly improve the accuracy of measuring minute changes in optical wave parameters. This method features a simple and low-cost device; it also offers high and adjustable accuracy, requiring only conventional angle measuring instruments (accuracy 10). -2 It can amplify changes in light wave parameters by more than 10,000 times (degrees); it has a wide range of applications and can measure minute changes in light wave parameters such as polarization, phase, and propagation direction.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for precise measurement of optical wave parameters based on cross-polarization effect includes the following steps:

[0007] Step 1: Polarized light with a horizontal polarization direction is used as incident light to illuminate the dielectric, and cross-polarization effect occurs when it is reflected at the dielectric interface.

[0008] Step 2: Pass the reflected light through the analyzer and adjust the analyzer so that the center light intensity of the reflected light after passing through the analyzer becomes 0. Record the initial angle between the transmission direction of the analyzer and the vertical direction at this time.

[0009] Step 3: Introduce the physical quantity to be measured into the incident light, and then readjust the analyzer. When the center light intensity of the reflected light becomes 0, record the angle ψ that the analyzer changes from the initial angle at this time.

[0010] Step 4: Calculate the change in the polarization direction of the incident light after the introduction of the physical quantity to be measured based on ψ, and then calculate the physical quantity to be measured.

[0011] The aforementioned method for precise measurement of optical wave parameters based on cross-polarization effect refers to the change in the direction of the polarization angle of the incident light as the physical quantity to be measured.

[0012] The method for precise measurement of optical wave parameters based on cross-polarization effect, wherein step 4 includes:

[0013] The polarization direction of the incident light is calculated using the following formula. :

[0014]

[0015] Where θ is the incident angle of the incident light, and the incident angle remains constant throughout the measurement process, obtained by the following formula:

[0016]

[0017] n is the refractive index of the dielectric.

[0018] The method for precise measurement of optical wave parameters based on cross-polarization effect, wherein the physical quantity to be measured is a small change in the direction of the incident light, and step 3, introducing the physical quantity to be measured into the incident light, includes:

[0019] The incident angle of the incident light is changed, but the change in the incident angle must be such that the incident light undergoes cross-polarization when reflected at the dielectric interface.

[0020] The method for precise measurement of optical wave parameters based on cross-polarization effect, wherein step 4 includes:

[0021] The incident angle θ is calculated using the following formula:

[0022]

[0023] in The polarization direction of the incident light is known and remains constant throughout the measurement.

[0024] The method for precise measurement of optical wave parameters based on cross-polarization effect, wherein the physical quantity to be measured is phase delay, and step 3, introducing the physical quantity to be measured into the incident light includes:

[0025] A phase delay to be measured is introduced into the incident light in a polarized state, wherein the phase delay is introduced into a direction that makes an angle of 45° with the polarization direction of the incident light, thereby changing the polarization state of the incident light from linear polarization to elliptical polarization.

[0026] Then, the incident light in the elliptic polarization state is converted back into the linear polarization state, so that the polarization direction angle of the incident light becomes the sum of the original polarization direction and the elliptic angle in the elliptic polarization state.

[0027] Then, the polarization direction of the converted linearly polarized incident light is changed so that the polarization direction of the incident light when it irradiates the reflecting medium is an elliptic angle.

[0028] The method for precise measurement of optical wave parameters based on cross-polarization effect, wherein step 4 includes:

[0029] The phase delay δ is calculated using the following formula:

[0030]

[0031] Where n is the refractive index of the dielectric.

[0032] The technical advantages of this invention are that its optical wave parameter measurement method is simple and low-cost. The measurement of the cross-polarization effect utilizes the reflection of light on a dielectric surface, and the apparatus is simple. The main experimental components are a dielectric block and a pair of polarizers, resulting in low cost. The optical wave parameter variation measurement method of this invention has high accuracy. When the incident angle meets the conditions, the resulting cross-polarization effect will cause a change in ψ compared to... Or the change in θ is much larger. Therefore, the incident polarization angle Even a small change in the incident angle θ can lead to a significant change in ψ, which can be used for precise measurement. Or θ, thereby enabling precise measurement of minute changes in light wave parameters. The method for measuring changes in light wave parameters in this invention has adjustable precision; simply changing the incident angle to make the cross-polarization rotation more drastic allows for the measurement of minute changes in light wave parameters, i.e., the polarization angle. Alternatively, a tiny change in the incident angle θ can lead to a larger change in ψ, thus allowing for more precise measurement of changes in optical wave parameters. The polarization minute change measurement method of this invention can measure minute changes in any optical wave parameter. It only requires suitable devices or systems to convert the minute changes in the parameters of the optical wave to be measured into the angle of the polarization direction of the incident light. Alternatively, a change in the incident angle θ can lead to the amplified ψ, from which minute changes in light wave parameters can be derived. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the optical path structure for measuring polarization or propagation direction changes based on the cross-polarization effect, provided in an embodiment of the present invention. Reference numerals: 1-polarizer, 2-reflecting medium, 3-analyzer, 4-laser beam analyzer.

[0035] Figure 2 The image shows a horizontally polarized incident light and a reflected cross-polarized light spot pattern provided in an embodiment of the present invention.

[0036] Figure 3 The graph showing the variation of the detection angle with the incident polarization angle is provided for an embodiment of the present invention.

[0037] Figure 4 The graph showing the change of the detection angle with the incident angle is provided for an embodiment of the present invention.

[0038] Figure 5 This is a schematic diagram of the optical path structure for measuring phase delay based on cross-polarization effect, provided in an embodiment of the present invention. Reference numerals: 1-Polarizer, 2-Phase delayer, 3-Quarter-wave plate, 4-Half-wave plate, 5-Reflecting medium, 6-Polarizer, 7-Laser beam analyzer.

[0039] Figure 6 A schematic diagram of the polarization state at various points along the optical path for measuring phase delay, provided in an embodiment of the present invention.

[0040] Figure 7 The graphs provided in this embodiment of the invention show the variation of the detection angle with phase delay and the amplification factor of the detection angle with phase delay. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0042] The embodiments of the present invention are implemented based on the following principles:

[0043] First, the measuring device used in the embodiments of the present invention includes an incident beam, a polarizer, a dielectric block placed on a rotating stage, an analyzer, and a laser beam analyzer arranged in sequence.

[0044] After the measurement process begins, the polarization direction of the light to be measured is adjusted to the horizontal direction using a polarizer; when the light is reflected at the interface of the medium, a cross-polarization effect occurs, and the cross-polarized light generated is detected by an analyzer; then it is propagated to a beam analyzer to detect the split spot.

[0045] Assume the polarization direction of the incident beam makes an angle with the horizontal direction. The incident light is incident from air at an angle θ onto a reflecting medium with a refractive index of n. Therefore, the incident light can be represented as... Where E0 is the amplitude distribution.

[0046] Cross-polarization occurs during reflection from a dielectric surface, meaning that one type of polarized light induces orthogonally polarized reflected light. Specifically, for light reflected along the wave vector... The reflected polarization field of an incident plane wave in the direction of is:

[0047]

[0048] Among them, the reflection coefficients of horizontally and vertically linearly polarized plane waves are R0 and R1, respectively. p and R s , It is incident polarized light (E ix E iy The spatial spectrum of the reflected light in the above equation. By performing an inverse Fourier transform, the spatial distribution of the reflected light (E) can be obtained. rx E ry ).

[0049] Let the reflected light pass through the analyzer, and let the angle ψ between its transmission direction and the perpendicular direction be , then the output light is E. ψ =E rx sinψ+E ry cosψ. When only the cross-polarized component passes through the analyzer, the central intensity of the outgoing light is equal to 0 because the original polarization component is blocked, i.e., E. ψ = 0. Therefore, we can solve for:

[0050]

[0051] According to equation (ii) above, when the denominator approaches zero, that is, the angle of incidence approaches...

[0052]

[0053] hour, Even a very small value can yield a huge ψ value. That is, incident polarization... A tiny change in θ can lead to a huge change in ψ. Similarly, a tiny change in θ can also lead to a huge change in ψ. This is the angular amplification effect caused by cross-polarization. Therefore, this effect can be used to accurately measure the incident polarization azimuth angle. Or, by measuring the change in the incident angle θ, one can measure minute changes in the parameters of the light wave.

[0054] The specific measurement steps are as follows:

[0055] (1) First, use a polarizer to rotate the polarization direction of the incident light to horizontal. Then, in a suitable manner, convert the minute changes in the parameters of the light wave to be measured into the polarization direction of the incident light. Or the change in the incident angle θ;

[0056] (2) When the beam is reflected on the surface of the dielectric block, a cross-polarization effect occurs. After the reflected light passes through the analyzer, the cross-polarization component it produces is detected and observed by the beam analyzer.

[0057] (3) Adjust the analyzer until the intensity at the center of the light spot is observed to be zero, and record the angle ψ between the light transmission direction of the analyzer and the vertical direction.

[0058] (4) Substitute the value of ψ into the above equation (ii) to calculate the incident polarization direction. Or the value of the propagation direction θ.

[0059] The following are specific detection examples for detecting different physical quantities.

[0060] Example 1: Measuring minute changes in polarization direction

[0061] Figure 1 This is a schematic diagram of an experimental setup for measuring minute changes in polarization based on the cross-polarization effect, provided in an embodiment of the present invention. The setup includes: 1-polarizer, 2-dielectric block, 3-analyzer, and 4-laser beam analyzer. The incident light source is a laser source; the dielectric is a glass block with a refractive index n = 1.515 and a smooth surface, placed on a rotating stage; the analyzer is a Glan laser polarizer.

[0062] The direction change of the polarization angle of the incident light wave is measured. Figure 1 The experimental setup shown is described, and the specific experimental steps are as follows:

[0063] (1) Adjust the polarizer so that the polarization direction of the incident beam is horizontal. The beam is transmitted to the surface of the glass block. Adjust the turntable so that the incident angle is θ = 56°, which is close to the angle value of 56.5725° in equation (iii) of the glass material.

[0064] (2) When light is reflected from the glass surface, it undergoes cross-polarization and then passes through the analyzer. The transmission direction of the rotating analyzer is perpendicular to the horizontal plane. A beam analyzer shows that the intensity of the reflected light at the center is zero, as can be seen... Figure 2 The two split light spots in the middle.

[0065] (3) Adjust the polarizer again to change the polarization of the incident light by a small angle. Next, rotate the analyzer until the reflected light is observed to be two split spots with zero central intensity. Record the change in the transmission direction of the analyzer relative to (2), i.e., the angle ψ with the vertical direction.

[0066] (4) Substituting the included angle ψ into equation (ii), the polarization change can be calculated. The value of .

[0067] (5) Replace the incident angle with an angle value closer to that in equation (iii). Here, we choose 56.5° and 56.57° respectively. Repeat the above steps, record the ψ value, and then substitute it into equation (ii) to calculate the corresponding change in polarization direction.

[0068] like Figure 2 The polarization angle is given. The images show (a) the incident light and (b) the light spot intensity after passing through the analyzer, as observed by a laser beam analyzer. It can be seen that the Gaussian-shaped incident light intensity distribution, after reflection from the interface and passing through the orthogonal analyzer, splits into two lobes, with the central intensity being zero. This is a typical intensity distribution after the cross-polarization effect occurs.

[0069] like Figure 3 The polarization angle of the incident light was drawn. The curves showing the change of the analyzer angle ψ when a small change occurs. Figure (a) shows the theoretical results of formula (ii) for three incident angles of 56°, 56.5°, and 56.57°. It can be seen that: (1) when the incident angle is close to that in formula (iii), the obtained analyzer angle ψ is always smaller than the incident polarization angle. (2) Moreover, the closer the incident angle is to the angle value in equation (iii), the larger the analytical angle ψ is; (3) ψ varies with the incident polarization angle. The changes are generally non-linear, but when... When ψ is smaller The growth is approximately linear.

[0070] use When ψ is smaller Linear increments can be used for precision measurements. For the three incident angles mentioned above, select respectively Within the ranges of 0°~0.01°, 0°~0.001°, and 0°~0.00001°, the magnification of ψ to 0°~0.6°, 0°~0.5°, and 0°~0.14° are 64, 506, and 14362 respectively! Therefore, the closer the incident angle value is to equation (iii), the greater the analytical angle ψ is compared to the incident polarization angle. The higher the magnification, the better. Furthermore, the magnified angles are all on the order of 0.1°, which can be measured using conventional angle measuring tools. Therefore, this method is low-cost, highly accurate, and adjustable.

[0071] Example 2: Measuring minute changes in the direction of incident light propagation

[0072] use Figure 1 The same experimental setup was used. The specific experimental steps are as follows:

[0073] (1) Select an incident angle θ that is close to the angle value in equation (iii) and repeat steps (1)(2)(3) in Example 1.

[0074] (2) Combine the included angle ψ and Substituting the value into equation (ii), the value of the incident angle θ can be calculated.

[0075] (3) Change the incident angle, here the range is selected as 56.5700°~56.5705°, and fix the incident polarization. Repeat the above steps, record the value of ψ, and then substitute it into equation (ii) to find the magnitude of the corresponding incident direction angle θ.

[0076] like Figure 4 The curve showing the change in the cross-polarization angle ψ when the incident direction θ changes slightly is plotted. The figure shows the incident polarization... When the incident angle θ changes with the incident direction θ, according to the theoretical results of formula (ii), it can be seen that for every 0.0001° change in the incident angle θ, the detected angle ψ changes by 0.7760°, which is magnified by 7760 times. Therefore, when the incident angle value is close to that in formula (iii), the change in the detected angle ψ is much larger than the change in the incident angle θ Δθ, and the magnified angle is on the order of 0.1°, which can be measured with inexpensive angle measuring tools. Therefore, this method has high accuracy and low cost; (2) ψ changes with the incident polarization angle The change of ψ is generally nonlinear, but when the change of θ is small, ψ changes approximately linearly with the increase of Δθ, making it suitable for measurement.

[0077] Example 3: Measuring the minute phase delay of light waves

[0078] Figure 5This is a schematic diagram of an experimental setup for measuring phase delay based on cross-polarization effect, provided in an embodiment of the present invention. The setup includes: 1-polarizer, 2-phase delayer, 3-quarter-wave plate, 4-half-wave plate, 5-reflecting medium, 6-polarizer, and 7-laser beam analyzer.

[0079] use Figure 5 The experimental setup shown is described, and the specific experimental steps are as follows:

[0080] (1) Determine the reference for zero phase delay: First, the polarizer adjusts the polarization direction of the incident light wave to an angle of α = φ + 45° with the horizontal plane (polarization state as follows). Figure 6 ①), φ is the angle between the vibration direction of the phase delay to be measured and the horizontal plane; after passing through a quarter-wave plate (fast axis along the α direction) and a half-wave plate (fast axis along the α / 2 direction), the linear polarization azimuth angle is rotated to the horizontal plane; the beam is transmitted to the glass surface, and the rotating medium makes the incident angle θ = 56.573°, which is close to the angle value of equation (iii). The reflection will produce a new polarization component perpendicular to the original polarization. When the reflected light passes through a vertical analyzer, these newly generated polarization components are filtered out, and the beam analyzer observes that the intensity at the center of the spot is zero, presenting two vertically split spots.

[0081] (2) Introducing the phase delay to be measured: Let the incident polarized light in (1) pass through a phase delayer, so that the vibration component in the φ direction obtains a small phase delay δ, so that the polarization state becomes an ellipse (polarization state as shown in Figure 1). Figure 6 ②), the ellipse declination angle is Obviously,

[0082] (3) Converting the phase difference into a change in incident polarization: Let the beam pass through the quarter-wave plate in (1), the polarization ellipse becomes linear polarization, and the direction is denoted as . (polarization state such as) Figure 6 ③). Then, let the beam pass through the half-wave plate in (1), and the linear polarization direction is rotated to Direction (polarization state, such as) Figure 6 ④).

[0083] (4) After the beam is reflected from the surface of the medium, its polarization changes. The reflected light passes through the analyzer and is detected and observed by the laser beam analyzer. The analyzer is rotated until the intensity of the reflected light at the center is observed to be zero. The analyzer is then rotated until the rotation is stopped, and the angle ψ between the transmission direction and the perpendicular direction of the analyzer is recorded (the polarization state is as follows). Figure 6 ⑤).

[0084] (5) Substituting the included angle ψ into equation (ii), the polarization change can be calculated. The value of ψ. Repeat the above steps, changing the phase delay device, and measure and record ψ. Then substitute it into the formula. The corresponding phase delay δ is calculated. By fitting multiple sets of data, the measurement accuracy of the experimental method can be further determined.

[0085] like Figure 7 The curves showing the change of the detection angle ψ caused by the phase delay δ according to equation (ii) are plotted. It can be seen that: (1) Figure (a) shows that the obtained detection angle ψ is always much larger than the phase delay δ, because the cross-polarization effect is significant near the angle in equation (iii); (2) Equation (ii) shows that the change of the detection angle ψ with the phase delay δ is generally nonlinear, but Figure (b) shows that when δ is small, ψ changes approximately linearly with δ.

[0086] Based on the linear variation of ψ with δ when δ is small, precise measurement of the phase δ can be performed. For example... Figure 7 As shown in (a) and 7(b), for every 4.2 × 10⁻⁶ increase in phase delay δ, -9 The measured change in ψ value was 0.01°, a magnification of 41,188 times! Moreover, the magnified angle change was on the order of 0.01°, which could be measured using conventional angle measuring instruments. Therefore, this method is highly sensitive to phase changes, has very high measurement accuracy, and the equipment is inexpensive.

[0087] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for precise measurement of optical wave parameters based on cross-polarization effect, characterized in that, Includes the following steps: Step 1: Polarized light with a horizontal polarization direction is used as incident light to illuminate the dielectric, and cross-polarization effect occurs when it is reflected at the dielectric interface. Step 2: Pass the reflected light through the analyzer and adjust the analyzer so that the center light intensity of the reflected light after passing through the analyzer becomes 0. Record the initial angle between the transmission direction of the analyzer and the vertical direction at this time. Step 3: Introduce the physical quantity to be measured into the incident light, and then readjust the analyzer. When the center intensity of the reflected light becomes 0, record the angle by which the analyzer changes from the initial angle. ; Step 4, according to The change in the polarization direction of the incident light after the introduction of the physical quantity to be measured is calculated, and then the physical quantity to be measured is calculated. The physical quantity to be measured is phase delay, and in step 3, introducing the physical quantity to be measured into the incident light includes: A phase delay to be measured is introduced into the incident light in a polarized state, wherein the phase delay is introduced into a direction that makes an angle of 45° with the polarization direction of the incident light, thereby changing the polarization state of the incident light from linear polarization to elliptical polarization. Then, the incident light in the elliptic polarization state is converted back into the linear polarization state, so that the polarization direction angle of the incident light becomes the sum of the original polarization direction and the elliptic angle in the elliptic polarization state. Then, the polarization direction of the converted linearly polarized incident light is changed so that the polarization direction of the incident light when it irradiates the reflecting medium is an elliptic angle.

2. The method for precise measurement of optical wave parameters based on cross-polarization effect according to claim 1, characterized in that, Step 4 includes: The phase delay is calculated using the following formula. : in n denoted as the refractive index of the dielectric.

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