Light beam attenuation coefficient measurement technology based on reflection light path

Abstract

The invention discloses a light beam attenuation coefficient measurement technology based on a reflected light path. A spectrum light source, a color filter, an optical beam splitter, an optical circulator, a measurement light path, a length-adjustable reference light path, a measured medium, a polarization beam splitter, an optical beam combiner, a polarization light switch, a photoelectric detector, a signal acquisition and processing unit, a control unit and an optical switch control unit are adopted. The measurement of the light beam attenuation coefficient follows the white light interference technology, and the influence of background light and stray light is overcome. The polarization light switch is controlled to selectively output the horizontal polarization coherent light or the vertical polarization coherent light, and the horizontal polarization or vertical polarization beam attenuation coefficient of the measured medium can be obtained. The light beam attenuation coefficient of the wide-spectrum light source is measured, and the narrow-band band-stop optical filter is combined, so that the narrow-band spectrum light beam attenuation coefficient corresponding to the narrow-band band-stop optical filter can be obtained.

Description

Technical Field

[0001] The present invention relates to a light beam attenuation coefficient measurement technology based on a reflection light path, and more specifically to a method for measuring the light beam attenuation coefficient by applying the reflection light path and white light interference technology. Background Art

[0002] The beam attenuation coefficient of light in a medium is an inherent optical property of the medium. When a parallel beam of light is transmitted in a homogeneous medium, the transmission characteristics satisfy the Lambert-Beer law: F ( l ) = F 0 × e -μ(λ)l , (1) in, F 0 is the initial luminous flux, l is the wavelength of light, l is the medium length, F is the luminous flux after passing through the medium, m is the beam attenuation coefficient of the medium, also known as the linear attenuation coefficient 。

[0003] According to formula 1, F / F 0 is the transmittance of the medium. l = 1 meter, T = F / F 0 = e -μ The transparency of the medium. In photometry, the transparency of the medium has nothing to do with the external light intensity, but only with the beam attenuation coefficient of the light in the medium. m It is an inherent optical property.

[0004] White light interferometry technology is based on optical interferometers, such as the Michelson interferometer and the Mach–Zehnder interferometer. It has two main characteristics: the light source is a wide spectrum (white light); and the length of the reference arm needs to be dynamically adjusted.

[0005] Because the light source is broadband, interference fringes only appear when the reference and measurement arms are nearly equal in length, meaning all frequencies in the broadband source are nearly coherent. For a constant reference light intensity, the maximum value of the interference fringe envelope is proportional to the intensity of the measurement light.

[0006] The current measurement of beam attenuation coefficient basically adopts a transmissive optical path design, while the present invention adopts a reflective optical path. The present invention applies white light interferometry technology to overcome the influence of background light and stray light in the current measurement of beam attenuation coefficient to a certain extent. Summary of the Invention

[0007] The purpose of the present invention is to provide a light beam attenuation coefficient measurement technology based on a reflection light path to solve the problems raised in the above background technology.

[0008] The present invention includes a wide-spectrum light source, a color filter, an optical beam splitter, an optical circulator, a measuring optical path, a length-adjustable reference optical path, a measured medium, a polarization beam splitter, an optical beam combiner, a polarization light switch, a photodetector, a signal acquisition and processing unit, a control unit, and an optical switch control unit.

[0009] The output light of the wide spectrum light source passes through a color filter and is then split into two paths by an optical beam splitter, one path being the initial measurement light and the other being the initial reference light.

[0010] The measurement light path is composed of an optical circulator and a measurement light emitting lens. The initial measurement light is input from port 1 of the optical circulator. The output light from port 2 of the optical circulator is collimated into a parallel measurement beam by the measurement light emitting lens and then irradiated into the measured medium. The output light from port 3 of the optical circulator is the backscattered light of the measured medium received by the measurement light emitting lens. According to the Lambert-Beer law, it can be obtained: F = β (180°) F 0 × e -μ2R , (2) in β (180°) is the backscattering coefficient of the measured medium, R is the distance between the measured medium and the measuring light emitting lens, 2R That is, measure the arm length.

[0011] The length-adjustable reference light path is composed of a reference light emitting lens and a reference light receiving lens on the same optical axis; the reference light emitting lens collimates the initial reference light into a parallel beam, which is then received by the reference light receiving lens, and the reference light receiving lens outputs the reference light; the distance between the reference light emitting lens and the reference light receiving lens is the reference arm length.

[0012] The backscattered light from the measured medium passes through the measuring light polarization beam splitter and is split into horizontally polarized measuring light and vertically polarized measuring light; the reference light passes through the reference light polarization beam splitter and is split into horizontally polarized reference light and vertically polarized reference light.

[0013] The horizontally polarized measurement light and the horizontally polarized reference light are input into the horizontal polarization optical combiner to obtain horizontally polarized coherent light. The vertically polarized measurement light and the vertically polarized reference light are input into the vertical polarization optical combiner to obtain vertically polarized coherent light. The horizontally polarized coherent light and the vertically polarized coherent light are input into the polarization switch.

[0014] The photodetector converts the optical signal output by the polarization switch into a corresponding electrical signal; the signal acquisition and processing unit acquires and processes the electrical signal; and the control unit is responsible for controlling the entire measurement, adjusting the reference arm length by controlling the reference arm length adjustment unit and selecting to output horizontally polarized coherent light or vertically polarized coherent light by controlling the polarization switch.

[0015] According to white light interferometry, when the reference arm and the measuring arm are nearly equal in length, interference fringes appear when all frequencies of light in the broad-spectrum light source approach coherence. For a constant reference light intensity, the maximum value of the interference fringe envelope is proportional to the intensity of the measuring light. Because there is always backscattered light in the measuring light path that matches the length of the reference arm, when the reference arm length is varied at a constant rate, an exponential decay curve corresponding to the Lambert-Beer law is obtained: F = β (180°) F 0 × e -μl , (3) in l is the reference arm length. According to formula 3, the beam attenuation coefficient of the measured medium can be calculated m .

[0016] The polarization switch is controlled to select the output of horizontally polarized coherent light or vertically polarized coherent light. According to the measurement process of formula 3, the attenuation coefficient of the horizontally polarized or vertically polarized light beam of the measured medium can be obtained.

[0017] After measuring the beam attenuation coefficient of the measured medium corresponding to the wide-spectrum light source, a narrow-band rejection filter is added to the color filter and the beam attenuation coefficient of the measured medium is measured again according to the measurement process of Formula 3. By subtracting the two beam attenuation coefficients, the beam attenuation coefficient of the measured medium corresponding to the spectrum of the narrow-band rejection filter can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments of the present invention.

[0019] Figure 1 , Schematic diagram of the light beam attenuation coefficient measurement technology based on the reflected light path of the present invention Figure 2 , the interference signal diagram of the backscattered light and the reference light of the present invention Figure 3 , Spectral characteristics of the wide spectrum light source and narrow band stop filter of the present invention Figure: 1. Broad-spectrum light source, 2. Color filter, 3. Initial signal light, 4. Optical beam splitter, 5. Initial reference light, 6. Initial measurement light, 7. Reference light transmitting lens, 8. Reference light receiving lens, 9. Reference light, 10. Reference arm length adjustment unit, 11. Reference arm length, 12. Optical circulator, 13. Measurement light transmitting lens, 14. Backscattered light from the measured medium, 15. Distance between the measured medium and the measurement light transmitting lens, 16. Reference light polarization beam splitter, 17. Horizontally polarized reference light, 18. Vertically polarized reference light, 19. Measurement light polarization beam splitter, 20. Horizontally polarized measurement light, 21. Vertically polarized measurement light, 22. Horizontally polarized optical beam combiner, 23. Vertically polarized optical beam combiner, 24. Horizontally polarized coherent light, 25. Vertically polarized coherent light, 26. Polarization switch, 27. Photodetector, 28. Signal acquisition and processing unit, 29. Control unit, 30. Optical switch control unit, 31. Exponential decay curve corresponding to the Lambert-Beer law obtained by interfering backscattered light with reference light, 32. Background light and stray light, 33. Spectrum of a broadband light source, 34. Spectrum of a narrowband rejection filter. DETAILED DESCRIPTION

[0020] The present invention aims to provide a technology for measuring the attenuation coefficient of a light beam based on a reflective optical path to address technical problems in related fields. To further clarify the technical problems and technical solutions to be solved by the present invention, the present invention is further described below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0021] The principle of the light beam attenuation coefficient measurement technology based on the reflected light path of the present invention is as follows: Figure 1 shown.

[0022] The output light of the wide spectrum light source (1) passes through a color filter (2) to obtain an initial signal light (3), which is then split into two paths by an optical beam splitter (4), one path being an initial reference light (5) and the other being an initial measurement light (6).

[0023] The measurement light path is composed of an optical circulator (12) and a measurement light emitting lens (13); the initial measurement light (6) is input from port 1 of the optical circulator (12); the output light from port 2 of the optical circulator (12) is collimated into a parallel measurement beam by the measurement light emitting lens (13), and then irradiated into the measured medium; the output light from port 3 of the optical circulator (12) is the backscattered light (14) of the measured medium received by the measurement light emitting lens (13). According to the Lambert-Beer law, equation (2) can be obtained, where R is the distance between the measured medium and the measuring light emitting lens (15), 2R That is, measure the arm length.

[0024] The length-adjustable reference light path is composed of a reference light emitting lens (7) and a reference light receiving lens (8) on the same optical axis; the reference light emitting lens (7) collimates the initial reference light (5) into a parallel light beam, which is then received by the reference light receiving lens (8), and the reference light receiving lens outputs the reference light (9); the distance between the reference light emitting lens (7) and the reference light receiving lens (8) is the reference arm length (11); and the reference arm length adjustment unit (10) is used to adjust the reference arm length (11).

[0025] After passing through a measuring light polarization beam splitter (19), the backscattered light (14) of the measured medium is split into horizontally polarized measuring light (20) and vertically polarized measuring light (21); after passing through a reference light polarization beam splitter (16), the reference light (9) is split into horizontally polarized reference light (17) and vertically polarized reference light (18).

[0026] The horizontally polarized measurement light (20) and the horizontally polarized reference light (17) are input into a horizontally polarized optical beam combiner (22) to obtain horizontally polarized coherent light (24); the vertically polarized measurement light (21) and the vertically polarized reference light (18) are input into a vertically polarized optical beam combiner (23) to obtain vertically polarized coherent light (25). The horizontally polarized coherent light (24) and the vertically polarized coherent light (25) are input into a polarization switch (26).

[0027] The photodetector (27) converts the optical signal output by the polarization light switch (26) into a corresponding electrical signal; the signal acquisition and processing unit (28) acquires and processes the electrical signal; the control unit (29) is responsible for controlling the entire measurement, and adjusts the reference arm length (11) through the reference arm length adjustment unit (10); and the polarization light switch (26) is controlled by the optical switch control unit (30) to select the output of horizontally polarized coherent light (24) or vertically polarized coherent light (25).

[0028] The interference signal of the backscattered light and the reference light of the present invention is shown in FIG. Figure 2 shown.

[0029] According to the white light interferometry technique, when the reference arm and the measuring arm are close to the same length, interference fringes appear when all the frequencies of light in the wide spectrum light source are close to coherence at the same time. When the intensity of the reference light is constant, the maximum value of the interference fringes envelope is proportional to the intensity of the measuring light. Because there is always backscattered light that matches the length of the reference arm in the measuring light path, when the length of the reference arm is increased uniformly (11) from L arrive L +Δ L When , we can obtain the exponential decay curve corresponding to the Lambert-Beer law: F = β (180°) F 0 × e -μl , l : L~L +Δ L , (4) Equation 4 corresponds to Figure 2 According to curve (31), the beam attenuation coefficient of the measured medium can be calculated. m . Figure 2 The straight line (32) in the figure is the intensity corresponding to the incoherent light signals such as background light and stray light.

[0030] The polarization switch (26) is controlled to select the output of the horizontally polarized coherent light (24) or the vertically polarized coherent light (25). According to the measurement process of formula 4, the attenuation coefficient of the horizontally polarized or vertically polarized light beam of the measured medium can be obtained.

[0031] The spectral characteristics of the wide spectrum light source and narrow band rejection filter of the present invention are shown in FIG. Figure 3 shown.

[0032] The comprehensive spectral characteristics of the wide-spectrum light source (1) and the color filter (2) are (33), and the spectral characteristics of the narrow-band stop filter are (34).

[0033] Measure the attenuation coefficient of the measured medium corresponding to the wide spectrum light source (1) m Then, add a narrow band-stop filter to the color filter. According to the measurement process of formula 3, the beam attenuation coefficient of the measured medium is obtained again. m ; Subtracting the two beam attenuation coefficients can obtain the beam attenuation coefficient of the measured medium corresponding to the spectrum of the narrow-band rejection filter. m .

[0034] It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Those skilled in the art should consider the specification as a whole, and the technical solutions in the various embodiments can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A light beam attenuation coefficient measurement technology based on a reflected light path, characterized by: It consists of a wide-spectrum light source, a color filter, an optical beam splitter, an optical circulator, a measuring optical path, a length-adjustable reference optical path, a measured medium, a polarization beam splitter, an optical beam combiner, a polarization switch, a photodetector, a signal acquisition and processing unit, a control unit, and an optical switch control unit. The output light of the broad spectrum light source is divided into two paths by an optical beam splitter after passing through a color filter, one path being the initial measurement light and the other being the initial reference light; The measurement light path is composed of an optical circulator and a measurement light emitting lens. The initial measurement light is input from port 1 of the optical circulator. The output light from port 2 of the optical circulator is collimated into a parallel measurement beam by the measurement light emitting lens and then irradiated into the measured medium. The output light from port 3 of the optical circulator is the backscattered light of the measured medium received by the measurement light emitting lens. According to the Lambert-Beer law, it can be obtained: Φ = β (180º) Φ 0 × e -μ2R ， (1) in Φ 0 is the initial luminous flux, Φ is the luminous flux after passing through the medium, β (180°) is the backscattering coefficient of the measured medium, R is the distance between the measured medium and the measuring light emitting lens, 2R That is, measuring arm length, μ is the beam attenuation coefficient of the medium, also known as the linear attenuation coefficient; The length-adjustable reference light path is composed of a reference light emitting lens and a reference light receiving lens on the same optical axis; the reference light emitting lens collimates the initial reference light into a parallel beam, which is then received by the reference light receiving lens, and the reference light receiving lens outputs the reference light; the distance between the reference light emitting lens and the reference light receiving lens is the reference arm length; The backscattered light from the measured medium passes through the measurement light polarization beam splitter and is split into horizontally polarized measurement light and vertically polarized measurement light; the reference light passes through the reference light polarization beam splitter and is split into horizontally polarized reference light and vertically polarized reference light. The horizontally polarized measurement light and the horizontally polarized reference light are input into the horizontally polarized optical beam combiner to obtain horizontally polarized coherent light; the vertically polarized measurement light and the vertically polarized reference light are input into the vertically polarized optical beam combiner to obtain vertically polarized coherent light; the horizontally polarized coherent light and the vertically polarized coherent light are input into the polarization switch; The photodetector converts the optical signal output by the polarization switch into a corresponding electrical signal; the signal acquisition and processing unit acquires and processes the electrical signal; the control unit is responsible for controlling the entire measurement, adjusting the reference arm length by controlling the reference arm length adjustment unit, and selecting to output horizontally polarized coherent light or vertically polarized coherent light by controlling the polarization switch; According to white light interferometry, when the reference arm and the measuring arm are nearly equal in length, interference fringes appear when all frequencies of light in the broad-spectrum light source approach coherence. When the intensity of the reference light is constant, the maximum value of the interference fringe envelope is proportional to the intensity of the measuring light. Because there is always backscattered light in the measuring light path that matches the length of the reference arm, when the reference arm length is changed at a constant speed, an exponential decay curve corresponding to the Lambert-Beer law can be obtained: Φ = β (180º) Φ 0 × e -μl ， (2) in l is the reference arm length; according to formula 2, the beam attenuation coefficient of the measured medium can be calculated μ .

2. The light beam attenuation coefficient measurement technology based on a reflective optical path described in claim 1 is characterized in that the polarization switch is controlled to select the output of horizontally polarized coherent light or vertically polarized coherent light. According to the measurement process of Formula 2, the horizontally polarized or vertically polarized light beam attenuation coefficient of the measured medium can be obtained.

3. The light beam attenuation coefficient measurement technology based on a reflective optical path described in claim 1 is characterized in that after measuring the light beam attenuation coefficient of the measured medium corresponding to the wide-spectrum light source, a narrow-band rejection filter is added to the color filter, and the light beam attenuation coefficient of the measured medium is measured again according to the measurement process of Formula 2; by subtracting the two light beam attenuation coefficients, the light beam attenuation coefficient of the measured medium corresponding to the spectrum of the narrow-band rejection filter can be obtained.

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