Phase-compensated ultra-sensitive polarimetric interferometer

Abstract

The application discloses a phase compensation supersensitive polarizing interferometer, and belongs to the technical field of optical interference measurement, which comprises a first polarizer, a birefringent crystal, a compensator, a birefringent sample, a second polarizer and a converging component arranged in sequence, wherein the incident light is polarized by the first polarizer to form linearly polarized light, the linearly polarized light is divided into two beams of linearly polarized light with orthogonal polarization by the birefringent crystal, one of the two beams of linearly polarized light propagates through the compensator, the transmission light of the birefringent sample is analyzed by the second polarizer, the two beams of light transmitted by the second polarizer are converged by the converging component and interfere to form the polarizing interferometer. The birefringent crystal is used to divide one beam of polarized light into two beams of light with orthogonal polarization, and the compensator is used to compensate the phase of one of the two beams of linearly polarized light emitted by the birefringent crystal, so that the interference fringes are split, the sensitivity is greatly improved, and the problems in the prior art are solved.

Description

Technical Field

[0001] This invention relates to a phase-compensated ultrasensitive polarizing interferometer, belonging to the field of optical interferometry technology. Background Technology

[0002] Birefringence measurement technology has wide applications in physics, medicine, and engineering research, such as measuring electromagnetic field distribution, material optical coefficients, biomass concentration, and internal stress distribution of objects. Furthermore, it can be used to design precision optical components such as ultrafast optical switches and permanent optical memories, and to map the internal birefringence distribution of these components. Currently, the requirements for birefringence measurement in these fields are no longer limited to obtaining rough birefringence distributions, but rather focus more on measuring weak birefringence, improving measurement accuracy, speed, range, and other performance parameters, as well as miniaturizing the measurement system.

[0003] Currently, there are various methods for measuring birefringence. Based on different measurement principles, the main methods include the quarter-wave plate polarization transformation method, modulation method, and polarization interferometry. The quarter-wave plate polarization transformation method is the most classic birefringence measurement system and is widely used in birefringence detection and analysis. The detection light source passes sequentially through a polarizer, sample, quarter-wave plate, and analyzer. The polarization angle is measured by rotating the waveplate or analyzer, thus achieving birefringence measurement. This method is simple in structure and accurate, but the measuring device must insert a waveplate, and the analyzer or waveplate needs to be rotated during measurement, limiting measurement accuracy and sensitivity. Modulation measurement methods include electro-optic modulation, magneto-optic modulation, acousto-optic modulation, and terahertz modulation, which are characterized by high speed and high frequency, but their structure is relatively complex and costly. The polarization interferometry method utilizes the interference caused by the phase difference between two linearly polarized beams. By observing the interference fringes, the magnitude of the birefringence of the sample can be calculated. It allows for relatively intuitive observation of the optical path difference of the sample, but its accuracy and sensitivity are poor. Therefore, improving the sensitivity of polarizing interferometers has become a pressing technical problem that needs to be solved. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a phase-compensated ultrasensitive polarized interferometer. It uses a birefringent crystal to split a beam of polarized light into two beams of orthogonal polarization, and uses a compensator to perform phase compensation on one of the linearly polarized beams emitted from the birefringent crystal, thereby improving the sensitivity and solving the problems existing in the prior art.

[0005] The present invention discloses a phase-compensated ultrasensitive polarizing interferometer, comprising a first polarizer, a birefringent crystal, a birefringent sample, and a second polarizer arranged sequentially. Incident light is polarized by the first polarizer to form linearly polarized light. The linearly polarized light is split into two orthogonally polarized beams by the birefringent crystal. One beam propagates through a compensator, which performs phase compensation on the one beam. The two beams are then incident on the birefringent sample. The transmitted light from the birefringent sample is analyzed by the second polarizer. The two beams transmitted through the second polarizer are converged by a converging component and interfere to form the polarizing interferometer.

[0006] Furthermore, a detection system is provided behind the converging component. The detection system is used to detect the interference fringe drift of the polarizing interferometer or to detect the light intensity change caused by the interference fringe drift, thereby realizing the detection of the difference in refractive index between the two beams of light in the birefringent sample.

[0007] Furthermore, the incident light is monochromatic or polychromatic.

[0008] Furthermore, the converging component is a converging lens, and the two beams of light transmitted by the second polarizer are converged by the converging lens and interfere with each other.

[0009] Furthermore, the first polarizer and the second polarizer are one or more of the following: dichroic polarizer, crystal polarizing prism, and Brewster polarizer.

[0010] Furthermore, the birefringent crystal is a positive crystal, and the compensator is located in the outgoing light path of the o-ray in the birefringent crystal.

[0011] Furthermore, the birefringent crystal is a negative crystal, and the compensator is located in the outgoing light path of the e-ray in the birefringent crystal.

[0012] Furthermore, the compensator has two light-transmitting surfaces, from which light enters and exits sequentially. The phase delay of the light propagating through the compensator is adjusted by regulating the incident angle of the light onto the compensator.

[0013] Furthermore, the birefringent sample has two parallel light-transmitting surfaces, and the optical axis of the birefringent sample is parallel to the light-transmitting surfaces.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] This invention discloses a phase-compensated ultrasensitive polarized interferometer. It utilizes a birefringent crystal to split a beam of polarized light into two orthogonally polarized beams. A compensator is used to compensate the phase of one of the linearly polarized beams emitted from the birefringent crystal. Due to material dispersion, the interference fringes split, resulting in two interference fringes of the same order. When measuring the birefringence of a sample using these split interference fringes, if the resonant wavelength is near the critical wavelength for fringe splitting, the theoretical sensitivity limit is infinite. Compared to traditional polarized interferometers, the sensitivity is greatly improved, and the measurement accuracy is also enhanced, thus solving the problems encountered in existing technologies. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the phase-compensated ultrasensitive polarizing interferometer of the present invention;

[0017] Figure 2 This is a side view of the birefringent crystal used in the phase-compensated ultrasensitive polarizing interferometer of the present invention;

[0018] Figure 3 This is an optical path diagram of light propagation through the compensator in the phase-compensated ultrasensitive polarizing interferometer of the present invention;

[0019] Figure 4 This is a graph showing the variation of the phase difference between two beams with wavelength in the phase-compensated ultrasensitive polarizing interferometer of this invention;

[0020] Figure 5 This is a distribution diagram of interference fringes with wavelength in the phase-compensated ultrasensitive polarizing interferometer of the present invention;

[0021] In the figure: 1. Incident light ray; 2. First polarizer; 3. Birefringent crystal; 4. Compensator; 5. Birefringent sample; 6. Second polarizer; 7. Converging component; 8. Detection system. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0023] Example 1:

[0024] like Figure 1As shown, the phase-compensated ultrasensitive polarized interferometer of the present invention includes, in sequence, a parallel beam, a first polarizer 2, a birefringent crystal 3, a compensator 4, a birefringent sample 5, a second polarizer 6, a converging component 7, and a detection system 8. The parallel beam is polarized by the first polarizer 2 and becomes linearly polarized. The linearly polarized beam is split into two orthogonally polarized beams by the birefringent crystal 3. After the phase of one of the linearly polarized beams is compensated by the compensator 4, the two beams are incident on the birefringent sample 5. The transmitted light from the birefringent sample 5 is detected by the second polarizer 6. The two beams transmitted by the second polarizer 6 are converged by the converging component 7 and interfere. The drift of the interference fringes is analyzed by the detection system 8, and the birefringence of the sample can be measured.

[0025] To further illustrate the above embodiments, parallel light can be monochromatic light or polychromatic light.

[0026] To further illustrate the above embodiments, the first polarizer 2 and the second polarizer 6 can be dichroic polarizers, crystal polarizing prisms, Brewster polarizers, but are not limited to these polarizing devices. All devices capable of polarizing and detecting the incident light 1 are suitable for the present invention.

[0027] To further illustrate the above embodiments, if the birefringent crystal 3 is a positive crystal, the compensator 4 is located in the outgoing light path of the o-ray in the birefringent crystal 3; if the birefringent crystal 3 is a negative crystal, the compensator 4 is located in the outgoing light path of the e-ray in the birefringent crystal 3.

[0028] Figure 2 This is a side view of the birefringent crystal 3 used in the phase-compensated ultrasensitive polarizing interferometer of the present invention. The dashed line in the figure represents the optical axis direction of the birefringent crystal 3, which is parallel to the plane of the paper. θ represents the angle between the optical axis direction of the birefringent crystal 3 and the light-transmitting surface of the birefringent crystal 3.

[0029] To further illustrate the above embodiment, the compensator 4 has two light-transmitting surfaces, and the incident light 1 enters and exits from the two surfaces in sequence.

[0030] To further illustrate the above embodiments, Figure 3 This is the optical path diagram of light propagation through compensator 4 in the phase-compensated ultrasensitive polarized interferometer of the present invention. By adjusting the incident angle α of light incident on compensator 4, the phase delay of light propagation through compensator 4 can be adjusted, thereby realizing dynamic adjustment of phase compensation.

[0031] To further illustrate the above embodiments, the birefringent sample 5 has two parallel light-transmitting surfaces, the optical axis of the birefringent sample 5 is parallel to the light-transmitting surfaces, and the two beams of orthogonally polarized light emitted from the birefringent crystal 3 are perpendicularly incident on the light-transmitting surfaces of the birefringent sample 5.

[0032] To further illustrate the above embodiment, the two beams of light transmitted through the second polarizer 6 are converged by a converging lens and interfere. When the two beams of light meet, their phase difference... It can be represented as:

[0033]

[0034] Where λ is the wavelength of light, Δ(λ) is the optical path difference between the two beams, and n o (λ), n e (λ) represents the refractive index of the o-ray and e-ray with wavelength λ in the birefringent crystal 3, respectively; l1 and l2 represent the path lengths of the o-ray and e-ray with wavelength λ in the birefringent crystal 3, respectively; l3 represents the thickness of the compensator 4; n pc (λ) is the refractive index of compensator 4, l4 is the thickness of the birefringent sample, and δn sa (λ) represents the difference in refractive index between the o-ray and e-ray with wavelength λ in the birefringent sample, and m represents the interference order.

[0035] In birefringent sample 5, the difference in refractive index between the o-ray and e-ray with wavelength λ changes slightly, d(δn). sa (λ) will cause a dλ shift in the resonant wavelength of the interference fringes. Due to this wavelength shift, dispersion will cause changes in the refractive indices of the o-ray and e-ray in the birefringent crystal 3, respectively (dn). o (λ) / dλ)dλ、(dn e (λ) / dλ)dλ, where dn o (λ) / dλ、dn e (λ) / dλ are the dispersion coefficients of the o-ray and e-ray with wavelength λ in the birefringent crystal 3, respectively. Dispersion also causes a change in the refractive index of the compensator 4 (dn). pc (λ) / dλ)dλ, where dn pc (λ) / dλ is the dispersion coefficient of compensator 4 for light with wavelength λ. In the case of weak birefringence, neglecting the dispersion of o-ray and e-ray in birefringent sample 5, the differential form of equation (1) can be expressed as follows:

[0036]

[0037] The sensitivity of a polarizing interferometer is defined as dλ / d(δn) sa According to formula (2), the sensitivity RIS can be expressed as:

[0038]

[0039] If the thickness l1 of the birefringent crystal 3 and the angle θ are known, by selecting the thickness l3 of the compensator 4, the denominator of formula (3) can be made to approach zero, thereby obtaining ultra-high sensitivity, and the theoretical sensitivity limit approaches infinity. Material dispersion plays a key role in enhancing the sensitivity of the polarizing interferometer.

[0040] The specific application of this embodiment is as follows:

[0041] Preferably, Iceland spar is selected as the birefringent crystal 3, and barium fluoride is selected as the compensator 4. Since Iceland spar is a negative crystal, the barium fluoride sheet is located in the e-ray emission path of the Iceland spar crystal. When the thickness of the Iceland spar crystal is 10 mm, the angle θ between the optical axis of the Iceland spar crystal and the light transmission surface of the crystal is 45 degrees, the thickness of the barium fluoride sheet is 3.605 mm, and the birefringent sample 5 is pure water with a light transmission path length of 3 mm. Figure 4 The phase difference between the two beams of the phase-compensated ultrasensitive polarizing interferometer of this invention Curve a represents the phase difference without birefringence, as the wavelength λ changes. From Figure 4 It can be seen that the phase difference between the two beams does not change monotonically with wavelength, but rather two wavelengths exhibit the same phase difference. This means that two wavelengths have the same interference order, causing the interference fringes to split. Applying a terahertz wave to pure water causes birefringence within the water. Assume the difference in refractive index between the o-ray and e-ray in the water is d(δn). sa (λ))=10 -5 RIU, Phase difference between two beams in a polarizing interferometer The variation with wavelength λ is as follows Figure 4 As shown by curve b in the figure.

[0042] Figure 5 The distribution of interference fringes with wavelength in the phase-compensated ultrasensitive polarizing interferometer of this invention is shown. Curve a represents the interference fringes without birefringence; curve b represents the interference fringes with a birefringence of water where the refractive index difference is 1×10⁻⁶. -5 Interference fringes during RIU. From Figure 4 , Figure 5 It can be seen that the interference fringes at m = -126 split. The birefringence of water causes the -126th order interference fringes near the splitting critical point to drift by 11 nm. Based on this, the refractive index measurement sensitivity is calculated to be 1.1 × 10⁻⁶. 6 nm / RIU. By using the aforementioned detection system to detect the drift of interference fringes or the change in light intensity caused by the drift of interference fringes, precise measurement of the phase delay caused by birefringence in birefringent samples can be achieved.

[0043] In the description of this invention, it should be noted that the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0044] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] The phase-compensated ultrasensitive polarized interferometer of the present invention, described above in conjunction with the accompanying drawings, uses a birefringent crystal to split a beam of polarized light into two orthogonally polarized beams. A compensator is used to compensate the phase of one of the linearly polarized beams emitted from the birefringent crystal. Under the influence of material dispersion, the interference fringes split, resulting in two interference fringes of the same order. This improves accuracy and sensitivity, solving problems encountered in the prior art. However, the present invention is not limited to the described embodiments. Variations, modifications, substitutions, and modifications made to the embodiments without departing from the principles and spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A phase-compensated ultrasensitive polarizing interferometer, characterized in that: The system includes a first polarizer (2), a birefringent crystal (3), a compensator (4), a birefringent sample (5), a second polarizer (6), and a converging component (7), arranged sequentially. The incident light (1) is polarized by the first polarizer (2) to form linearly polarized light. This linearly polarized light is then split into two orthogonally polarized beams by the birefringent crystal (3). One of these beams propagates through the compensator (4), which performs phase compensation on the first beam, resulting in two orthogonally polarized beams. Polarized light is incident on a birefringent sample (5). The transmitted light from the birefringent sample (5) is analyzed by a second polarizer (6). The two beams transmitted by the second polarizer (6) are converged by the converging component (7) and interfere to form a polarizing interferometer. When the birefringent crystal (3) is a positive crystal, the compensator (4) is located in the outgoing light path of the o-beam in the birefringent crystal (3). When the birefringent crystal (3) is a negative crystal, the compensator (4) is located in the outgoing light path of the e-beam in the birefringent crystal (3). By adjusting the effective thickness of the compensator (4), the denominator of the sensitivity formula of the polarizing interferometer approaches zero, and the interference fringes split under the action of material dispersion, resulting in two interference fringes with the same order. The sensitivity of the polarizing interferometer theoretically approaches infinity. The sensitivity formula for the polarizing interferometer is: ; in, The wavelength of light For the birefringent sample (5), the wavelength is The difference in refractive index between the o-ray and e-ray, The thickness of the birefringent sample (5) is... , The wavelengths of the birefringent crystal (3) are respectively... The path lengths of the o-ray and e-ray. For the effective thickness of the compensator (4), , The wavelengths of the birefringent crystal (3) are respectively... The dispersion coefficients of o-ray and e-ray, For compensator (4) for wavelength The dispersion coefficient of light, This refers to the interference level.

2. The phase-compensated ultrasensitive polarizing interferometer according to claim 1, characterized in that: The converging component (7) is further provided with a detection system (8) behind it. The detection system (8) is used to detect the interference fringe drift of the polarizing interferometer or to detect the light intensity change caused by the interference fringe drift, so as to realize the detection of the difference in refractive index of the two beams of light in the birefringent sample (5).

3. The phase-compensated ultrasensitive polarizing interferometer according to claim 1, characterized in that: The incident light (1) is monochromatic light or polychromatic light.

4. The phase-compensated ultrasensitive polarizing interferometer according to claim 1, characterized in that: The converging component (7) is a converging lens, and the two beams of light transmitted by the second polarizer (6) are converged by the converging lens and interfere with each other.

5. A phase-compensated ultrasensitive polarizing interferometer according to claim 1, characterized in that: The compensator (4) has two light-transmitting surfaces. Light enters and exits from the two surfaces in sequence. The phase delay of the light propagating through the compensator (4) is adjusted by adjusting the incident angle of the light to the compensator (4).

6. The phase-compensated ultrasensitive polarizing interferometer according to claim 1, characterized in that: The birefringent sample (5) has two parallel light-transmitting surfaces, and the optical axis of the birefringent sample (5) is parallel to the light-transmitting surfaces.

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