Receiving unit and water body scattered light measuring device

Abstract

The invention discloses a receiving unit and a water body scattered light measuring device.The receiving unit comprises a first receiving module, the first receiving module comprises a Fourier lens and at least one first optical fiber, and the optical axis of the Fourier lens extends in the first direction so that a laser beam penetrating through a water body can be focused to a focus; the receiving end surface of each first optical fiber is positioned on the focal plane, and the radius of the focal plane corresponds to the average scattering angle of the scattered light received by the first optical fiber; the average scattering angles corresponding to the at least two first optical fibers are different. The water body scattered light measuring device adopts the receiving unit and the time division multiplexing technology, so that a single detector can measure water body scattered light with different scattering angles. By adopting the technical scheme, compared with the prior art, the receiving unit is lower in cost, and the water body scattered light measuring device is better in adaptability to particle size distribution of different water bodies.

Description

Technical Field

[0001] The present application relates to the field of water scattered light optical detection, and in particular to a receiving unit and a water scattered light measuring device. Background Art

[0002] Water scattering distribution refers to the directional distribution of scattered light intensity caused by the interaction of incident light with suspended particles, bubbles, phytoplankton, and other substances in the water. This distribution is primarily described by the volume scattering function (VSF) of the water. Water scattering distribution measurement plays an important role in marine science and environmental monitoring, and has been widely used in areas such as remote sensing of water color, research on marine particulate matter properties, analysis of plankton communities and carbon cycles, and marine pollution monitoring. Key methods for measuring water scattering distribution include mechanical rotational measurement and fixed-angle synchronous measurement using array detectors.

[0003] Prior art methods focus forward scattered light from water at varying scattering angles onto circles of varying radii on the Fourier lens' focal plane using a Fourier lens. Silicon ring detectors are then used to detect the scattered light. Specifically, the silicon ring detectors create circular sector detection windows corresponding to the circles of varying radii on the focal plane to directly detect the scattered light intensity and output an analog electrical signal. As the size of the particles in the water increases, the scattered light becomes more concentrated on circles with smaller focal plane radii. For example, for a particle size of 459 microns, 90% of the scattered light will be concentrated within a scattering angle range greater than 0 and less than or equal to 0.032 degrees. This necessitates a very small area for the sector detection windows corresponding to these small angles, otherwise the detector's permissible light intensity range will be easily exceeded. Furthermore, when detecting water with varying particle size distributions, the silicon ring detectors must be replaced, otherwise the individual sector detection windows will be difficult to adjust to the detector's permissible light intensity range. Consequently, the same silicon ring detector is not very adaptable to the particle size distribution of the water. Since the silicon ring detector combines the light receiving unit and the detection unit into one and is extremely difficult to process, the cost is very high. It also needs to be replaced according to the particle size distribution of different water bodies, which causes great inconvenience to water body detection. Summary of the Invention

[0004] The purpose of this application is to overcome the above-mentioned defects or problems in the background technology and to provide a receiving unit and a water scattered light measuring device, wherein the receiving unit has a lower cost than the prior art and the water scattered light measuring device has better adaptability to the particle size distribution of different water bodies.

[0005] In order to achieve the above objectives, the following technical solutions are adopted:

[0006] The first technical solution relates to a receiving unit, which is used to receive scattered light formed by a laser beam passing through a water body along a first direction. The characteristic of the receiving unit is that it includes a first receiving module, which includes: a Fourier lens, whose optical axis extends along the first direction to focus the laser beam passing through the water body to a focal point; and at least two first optical fibers, the receiving end face of each first optical fiber is located in the focal plane, and the distance between the center point of the receiving end face of the first optical fiber and the focus is defined as the focal plane radius of the first optical fiber, and the focal plane radius corresponds to the average scattering angle of the scattered light received by the first optical fiber; the average scattering angles corresponding to at least two first optical fibers are different.

[0007] The second technical solution is based on the first technical solution, wherein first optical fibers with corresponding same average scattering angles form a first optical fiber group, the first optical fiber groups are arranged according to the focal plane radius, and the ratio of the larger value to the smaller value of the focal plane radius in all adjacent first optical fiber groups is the same.

[0008] The third technical solution is based on the first technical solution, wherein the first receiving module further includes a first fixing member for fixing the receiving end of each first optical fiber, and the first fixing member is provided with a through hole penetrating along the first direction at the focus.

[0009] The fourth technical solution relates to a water body scattered light measuring device, which includes: a transmitting unit, which emits a laser beam suitable for passing through a water body in a first direction, wherein the laser beam is a pulsed laser beam; a receiving unit, which is described in any one of the first to third technical solutions; all first optical fibers are receiving optical fibers, and corresponding receiving optical fibers with the same average scattering angle form a receiving optical fiber group; the length of each receiving optical fiber in a receiving optical fiber group including more than two receiving optical fibers is the same; each receiving optical fiber group is correspondingly defined with a connecting optical fiber and an optical fiber length; wherein, the connecting optical fiber corresponding to the receiving optical fiber group including more than two receiving optical fibers is defined as the combined optical fiber to which the output end of the first combiner is connected after all the receiving optical fibers of the receiving optical fiber group are combined into one by the first combiner; the connecting optical fiber corresponding to the receiving optical fiber group including only one receiving optical fiber is defined as the receiving optical fiber in the receiving optical fiber group; the optical fiber length of the receiving optical fiber group including more than two receiving optical fibers is defined as the sum of the length of any receiving optical fiber in the receiving optical fiber group and the length of the combined optical fiber; the optical fiber length of the receiving optical fiber group including only one receiving optical fiber is defined as Defined as the length of the connecting optical fiber in the receiving optical fiber group; the optical fiber lengths of all receiving optical fiber groups are different, the receiving optical fiber groups are arranged according to the optical fiber lengths, the ratio of the absolute value of the difference in optical fiber lengths of adjacent receiving optical fiber groups to the speed of light is greater than the pulse width of the pulsed laser beam, and the ratio of the absolute value of the difference in optical fiber lengths of two receiving optical fiber groups with the largest difference in optical fiber lengths to the speed of light is less than the pulse interval period of the pulsed laser beam; an adjustment unit, which includes an optical attenuator arranged corresponding to the receiving optical fiber group, the optical attenuator is serially connected to the corresponding connecting optical fiber and is used to adjust the dynamic light intensity of the scattered light; a second combiner, whose input end is connected to all connecting optical fibers to combine all connecting optical fibers into one; its output end is connected to the optical fiber to be tested; a single-photon detector, whose input end is connected to the optical fiber to be tested to receive the scattered light signal output by the second combiner and output a counting signal corresponding to the detection time point; and a collection unit, which is connected to the single-photon detector to collect the counting signal output by the single-photon detector corresponding to the detection time point, and count the counting signal according to the period corresponding to the average scattering angle within each pulse interval period.

[0010] The fifth technical solution is based on the fourth technical solution, wherein the receiving unit also includes a second receiving module, the second receiving module includes at least one second optical fiber; the receiving end face of the second optical fiber is oriented toward a point on the path of the pulsed laser beam in the water body, and a first angle is formed between the direction of the receiving end face of the second optical fiber and the first direction, and the first angle corresponds to the average scattering angle of the scattered light received by the second optical fiber; the average scattering angle corresponding to any second optical fiber is greater than the average scattering angle corresponding to all first optical fibers; all second optical fibers are also receiving optical fibers.

[0011] The sixth technical solution is based on the fifth technical solution, wherein the second receiving module also includes a second fixing member for fixing the receiving end of each second optical fiber, the second fixing member is provided with an angle limiting hole arranged corresponding to the second optical fiber, and the second angle limiting hole extends along the direction of the receiving end face of the second optical fiber to limit the receiving angle of the receiving end face of the second optical fiber.

[0012] The seventh technical solution is based on the fifth technical solution, wherein the average scattering angle range corresponding to all first optical fibers is greater than 0 degrees and less than 11 degrees; the average scattering angle range corresponding to all second optical fibers is greater than or equal to 11 degrees and less than 180 degrees.

[0013] The eighth technical solution is based on any one of the fourth to seventh technical solutions, which also includes an optical power meter, which is used to detect the power of the laser beam after passing through the water body.

[0014] The ninth technical solution is based on any one of the fourth to seventh technical solutions, wherein the emitting unit includes a laser and a collimator, the laser emits pulsed laser, and the collimator receives the pulsed laser and forms a pulsed laser beam after collimation and expansion.

[0015] Compared with the prior art, the above solution has the following beneficial effects:

[0016] In the first technical solution, the fan-shaped detection window of the silicon ring detector is replaced by the first optical fiber located in the focal plane through the receiving end face to receive scattered light at different scattering angles, thereby separating the receiving unit from the detection unit, reducing the cost of the receiving unit. Even if the receiving unit needs to be replaced for different water bodies, the replacement cost is greatly reduced. At the same time, the receiving unit in the first technical solution is conducive to regulating the scattered light intensity of each receiving optical fiber group by adjusting the optical attenuator of the unit, so that the receiving unit of the first technical solution has greater adaptability to water bodies with different particle size distributions. Even if the receiving unit in the first technical solution needs to increase the receiving area for forward scattered light at a larger angle, it only needs to increase the number of first optical fibers located at the same focal plane radius accordingly, so replacement and deployment are more convenient. At the same time, the use of optical fibers to receive scattered light from water bodies can reduce temperature sensitivity and improve system stability, and is particularly suitable for harsh climatic conditions such as high ocean temperatures.

[0017] In the second technical solution, since the particle size distribution in nature and industrial fields often spans several orders of magnitude and usually conforms to a normal distribution, in order to enable the water scattered light measurement device to provide a measurement range from submicron to millimeter level, ensure balanced resolution within the measurement range, and ensure sufficient measurement accuracy for large particles (small scattering angle) and small particles (larger scattering angle), the focal plane radius corresponding to the average scattering angle of the first optical fiber group is set to be exponentially distributed, which is more conducive to improving the resolution within a larger measurement range.

[0018] In the third technical solution, the first fixing member is provided with a through hole extending along the first direction at the focus, which allows the laser beam focused by the Fourier lens to pass through the through hole, thereby preventing the laser beam from affecting the reception of small-angle scattered light signals when hitting the first fixing member.

[0019] In the fourth technical solution, first, the dynamic range of the scattered light intensity is adjusted by an optical attenuator corresponding to the receiving optical fiber group. Compared with the prior art method of setting the scattered light intensity by the fan-shaped detection window area of the silicon ring detector, it has greater adaptability to water bodies with different particle size distributions. Secondly, by setting the pulsed laser beam, the optical fiber length, and the second combiner, time-division multiplexing of scattered light at different scattering angles is achieved, laying the foundation for detecting multi-angle scattered light with only one detector, avoiding the need to calibrate parameters such as sensitivity, dark current, response time, and linear range for each detector when using multiple detectors, and also avoiding the high requirements for the response time of multiple different detectors. It should be noted that it is precisely because of the use of receiving optical fibers that time-division multiplexing can be achieved by changing the optical fiber length. Therefore, time-division multiplexing technology is based on the receiving unit in the first technical solution. In the prior art, silicon ring detectors are unable to achieve time-division multiplexing technology. Thirdly, by detecting the time-division multiplexed scattered light signal through a single-photon detector, a counting signal corresponding to the detection time point can be directly output, thereby avoiding the silicon ring detector in the existing technology outputting multiple analog signals, so the anti-interference ability is stronger and the accuracy is higher.

[0020] In the fifth technical solution, the second receiving module is suitable for detecting scattered light signals with larger scattering angles. Because the second receiving module also uses optical fiber to receive scattered light, it can be used together with the receiving fiber of the first receiving module to use an optical attenuator to control the dynamic range of light intensity. It can also use time-division multiplexing technology with the receiving fiber of the first receiving module, allowing a single detector to detect scattered light signals at various scattering angles, from small to large. Conventional silicon ring detectors, on the other hand, are unable to detect backscattered light signals, and are even unable to detect forward scattered light signals at larger scattering angles. Therefore, the fifth technical solution significantly improves its adaptability to water bodies with different particle size distributions.

[0021] In the sixth technical solution, the second fixing member limits the receiving angle of the second optical fiber through the angle-limiting hole, so that the scattered light signal received by the second optical fiber has a better correspondence with the average scattering angle.

[0022] In the eighth technical solution, an optical power meter is installed to measure the optical power of the laser beam after it passes through the water. This power can be compared with the output power of the laser beam to obtain the beam attenuation coefficient, which represents the scattering and absorption of light by the water. This allows for a rapid measurement of water turbidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solution of the embodiment, the following briefly introduces the drawings required for use:

[0024] Figure 1 Schematic diagram of the structure of the scattered light measuring device in the embodiment;

[0025] Figure 2 Schematic diagram of the principle of the Fourier lens in the embodiment;

[0026] Figure 3 This is a schematic structural diagram of the first fixing member in the embodiment;

[0027] Figure 4 This is a schematic structural diagram of the second receiving module in the embodiment;

[0028] Figure 5 FIG. 4 is a schematic diagram of a combining structure of a receiving optical fiber group including more than two receiving optical fibers in an embodiment.

[0029] Description of main reference numerals:

[0030] 1. Transmitting unit; 2. Receiving unit; 3. Adjusting unit; 4. Second combiner; 5. Single-photon detector; 6. Acquisition unit; 7. Calculation unit; 8. Optical power meter; 11. Laser; 12. Collimator; 21. First receiving module; 22. Second receiving module; 211. Fourier lens; 212. First optical fiber; 213. First fixing member; 214. Through hole; 221. Second optical fiber; 222. Second fixing member; 223. Angle-limiting hole; 31. Optical attenuator; 91. Receiving optical fiber; 92. First combiner; 93. Combined optical fiber; A. Sample cell; B. Optical axis; C. Focal plane; D. Focus; r, focal plane radius; f, focal length; θ, angle of incidence. DETAILED DESCRIPTION

[0031] In the claims and the description, unless otherwise defined, the terms "first", "second" or "third", etc. are intended to distinguish different objects rather than to describe a specific order.

[0032] In the claims and the specification, unless otherwise specified, the terms "center", "transverse", "longitudinal", "horizontal", "vertical", "top", "bottom", "inside", "outside", "up", "down", "front", "back", "left", "right", "clockwise", "counterclockwise" and the like to indicate directions or positional relationships are based on the directions and positional relationships shown in the accompanying drawings and are only for the convenience of simplifying the description, and do not imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction.

[0033] In the claims and description, unless otherwise specified, the term "fixed connection" or "fixed connection" should be understood in a broad sense, that is, any connection method in which there is no displacement relationship or relative rotation relationship between the two parties, that is, including non-detachable fixed connection, detachable fixed connection, integral connection, and fixed connection through other devices or elements.

[0034] In the claims and the description, unless otherwise defined, the terms "include", "have" and their variations mean "including but not limited to".

[0035] In the claims and the description, unless otherwise defined, the term "provided with" means that the technical feature thereafter is part of the technical feature therefor.

[0036] In the claims and description, unless otherwise defined, the term "Fourier lens" refers to a lens that is suitable for focusing parallel light incident along the optical axis onto a focal point where the focal plane intersects the optical axis, and is suitable for focusing incident light having the same angle with the optical axis onto a circle with the focal point as its center, where the radius of the circle is the focal plane radius, and the focal plane radius r = ftanθ, where f is the focal length of the first lens and θ is the angle between the incident light and the optical axis.

[0037] In the claims and the specification, unless otherwise defined, the term "first direction" refers to an emission direction of a laser beam as parallel light.

[0038] The phrase "a receiving fiber group comprising two or more receiving fibers" in the claims and the specification does not necessarily mean that all receiving fiber groups must include such a group. This application permits all receiving fiber groups to include only one receiving fiber. However, when a receiving fiber group includes two or more receiving fibers, the corresponding limitations and definitions apply.

[0039] The technical solutions in the embodiments will be described clearly and completely below with reference to the accompanying drawings.

[0040] See also Figure 1 , Figure 1 FIG. 2 shows a device for measuring scattered light from a water body in an embodiment. Figure 1 As shown, the water scattered light measuring device includes a transmitting unit 1, a receiving unit 2, an adjusting unit 3, a second combiner 4, a single photon detector 5, a collecting unit 6, a calculating unit 7 and an optical power meter 8.

[0041] Transmitting unit 1 includes a laser 11 and a collimator 12. Laser 11 emits pulsed laser light in the blue-green wavelength band suitable for passing through water. The pulsed laser light has a pulse width and a pulse interval period. Collimator 12 is connected to laser 11 via an optical fiber. It receives the pulsed laser light and collimates and expands it to form a pulsed laser beam. The pulsed laser beam is emitted in a first direction and is a parallel beam. The pulsed laser beam passes through water A in the first direction and interacts with the water to form scattered light.

[0042] The receiving unit 2 includes a first receiving module 21 and a second receiving module 22 .

[0043] The first receiving module 21 includes a Fourier lens 211 , at least two first optical fibers 212 , and a first fixing member 213 .

[0044] See also Figure 2 , Figure 2 A Fourier lens 211 is shown. A Fourier lens is suitable for focusing parallel light incident along optical axis B onto focal point D, where focal plane C intersects optical axis B. It is also suitable for focusing incident light at the same angle of incidence θ relative to optical axis B onto a circle centered on focal point D. The radius of this circle is the focal plane radius r, where r = ftanθ, where f is the focal length of the first lens and θ is the angle between the incident light and the optical axis. In this embodiment, Fourier lens 211 is positioned in front of water body A along a first direction, with optical axis B of Fourier lens 211 extending along the first direction, so that the laser beam passing through water body A is focused onto focal point D.

[0045] See also Figure 2 and Figure 3 , Figure 2 and Figure 3 FIG. 2 shows the first optical fiber 212 and the first fixing member 213 in this embodiment. Figure 2 and Figure 3 As shown, the first optical fiber 212 adopts a single-mode optical fiber with a diameter of 10 μm. The number of first optical fibers 212 is at least 2. In this embodiment, the number of first optical fibers 212 is 36. The receiving end face of each first optical fiber 212 is located at the focal plane C of the Fourier lens 211. The distance between the center point of the receiving end face of the first optical fiber 212 and the focus D is the focal plane radius r of the first optical fiber 212. The focal plane radius r corresponds to the average scattering angle θ of the water scattered light received by the first optical fiber 212. Specifically, since the receiving end face of the first optical fiber 212 is located in the air, the average scattering angle θ of the water scattered light received by the first optical fiber 212 and the focal plane radius r conform to the following rules:

[0046] θ=θ1, sinθ1=(sinθ2) / 1.33, r=ftanθ2, where θ1 is the scattering angle of water and θ2 is the scattering angle of air.

[0047] The average scattering angle θ of the water scattered light received by the first optical fiber 212 and the particle size d suitable for measurement conform to the following rules:

[0048] θ = 4 / (k·d), where k = 2π / λ, and λ is the wavelength of the laser beam.

[0049] In this embodiment, the wavelength of the laser beam λ is 532 nm, and the focal length f of the Fourier lens 211 is 125 mm.

[0050] The average scattering angle θ corresponding to at least two first optical fibers 212 is different. In this embodiment, the first optical fibers 212 with the same corresponding average scattering angle θ form a first optical fiber group, and the first optical fiber groups are arranged according to the focal plane radius r. The ratio of the larger value to the smaller value of the focal plane radius r in all adjacent first optical fiber groups is the same, which is 1.18. In this embodiment, each first optical fiber group includes only one first optical fiber 212. Of course, in other embodiments, the first optical fiber group may include at least two first optical fibers 212, and each first optical fiber 212 in the same first optical fiber group has the same focal plane radius r. In this embodiment, the line segment between the center point of the receiving end face of two adjacent first optical fibers 212 and the focus D forms an acute angle, so that the receiving end faces of the 36 first optical fibers 212 are as follows. Figure 3 The arrangement shown is, of course, in other embodiments, the first optical fibers may also be arranged in a straight line.

[0051] Specifically, in this embodiment, the relationship between the focal plane radius r of the first optical fiber 212 and the air scattering angle θ2, the water scattering angle θ1, and the particle size d suitable for measurement is shown in Table 1.

[0052] Table 1: Relationship between the focal plane radius r of each first optical fiber 212 and the air scattering angle θ2, the water scattering angle θ1 and the particle size d suitable for measurement:

[0053]

[0054]

[0055] As shown in Table 1, in this embodiment, the first receiving module 21 is suitable for receiving water scattered light with a minimum scattering angle of 0.032° and a maximum scattering angle of 10.678°. Accordingly, the first receiving module 21 is suitable for detecting particles with a particle size d in the range of 1.36 μm to 459 μm.

[0056] like Figure 3As shown, the first fixing member 213 is used to fix the receiving end of each first optical fiber 212. The first fixing member 213 is disc-shaped and fixed relative to the Fourier lens 211. The disc surface of the first fixing member 213 facing the Fourier lens 211 is located on the focal plane C of the Fourier lens 211. The first fixing member 213 has a through hole 214 extending in a first direction at the focal point D. The diameter of the through hole 214 is 50 μm. The through hole 214 is used to allow the laser beam focused by the Fourier lens 211 to pass through.

[0057] See also Figure 4 , Figure 4 FIG. 2 shows the second receiving module 22 in this embodiment. Figure 4 As shown, the second receiving module 22 includes at least one second optical fiber 221 and a second fixing member 222. The receiving end face of the second optical fiber 221 faces a point on the path of the pulsed laser beam in the water body A, and the direction of the receiving end face of the second optical fiber 221 forms a first angle with the first direction, and the first angle corresponds to the average scattering angle θ of the scattered light received by the second optical fiber 221. In this embodiment, the receiving end faces of the second optical fibers 221 are evenly distributed on an arc with a sector angle of 11° to 179°. The radius of the arc is 80 mm. The center of the arc is located in the water body A and on the optical axis B of the Fourier lens 211. In this embodiment, one second optical fiber 221 is arranged every 1°, for a total of 169. The second fixing member 222 is semi-annular and is used to fix all the second optical fibers 221. The second fixing member 222 is provided with an angle-limiting hole 223 corresponding to each second optical fiber 221. The angle-limiting hole 223 extends in the direction of the receiving end face of the corresponding second optical fiber 221 to limit the receiving angle of the receiving end face of the second optical fiber 221. In this embodiment, the angle-limiting hole 223 has a diameter of 0.1 mm and a depth of 20 mm, resulting in a receiving angle of 0.57° for the second optical fiber 221.

[0058] As can be seen from the above description, the average scattering angle θ corresponding to any second optical fiber 221 is greater than the average scattering angle θ corresponding to all first optical fibers 212. In this embodiment, the scattering angle range of water scattered light suitable for all first optical fibers 212 is 0.032° to 10.678°, and the scattering angle range of water scattered light suitable for all second optical fibers 221 is 11° to 179°. In other embodiments, the average scattering angle range corresponding to all first optical fibers is greater than 0° and less than 15°; the average scattering angle range corresponding to all second optical fibers is greater than or equal to 10° and less than 180°. However, in all cases, the rule that the average scattering angle θ corresponding to any second optical fiber 221 is greater than the average scattering angle θ corresponding to all first optical fibers 212 must be followed.

[0059] In this embodiment, all first optical fibers 212 and all second optical fibers 221 are receiving optical fibers 91. The corresponding receiving optical fibers 91 with the same average scattering angle θ form a receiving optical fiber group; the lengths of the receiving optical fibers 91 in a receiving optical fiber group including more than two receiving optical fibers 91 are the same; each receiving optical fiber group is correspondingly defined with a connecting optical fiber and an optical fiber length; wherein, the connecting optical fiber corresponding to the receiving optical fiber group including more than two receiving optical fibers 91 is defined as the combined optical fiber 93 connected to the output end of the first combiner 92 after all the receiving optical fibers 91 of the receiving optical fiber group are combined into one by the first combiner 92; the connecting optical fiber corresponding to the receiving optical fiber group including only one receiving optical fiber 91 is defined as the receiving optical fiber 91 in the receiving optical fiber group; The fiber length of a receiving fiber group with more than one receiving fiber 91 is defined as the sum of the length of any receiving fiber 91 in the receiving fiber group and the length of the combined fiber 92; the fiber length of a receiving fiber group including only one receiving fiber 91 is defined as the length of the connecting fiber in the receiving fiber group; the fiber lengths of all receiving fiber groups are different, and the receiving fiber groups are arranged according to the fiber lengths. The ratio of the absolute value of the difference in the fiber lengths of adjacent receiving fiber groups to the speed of light is greater than the pulse width of the pulsed laser beam, and the ratio of the absolute value of the difference in the fiber lengths of the two receiving fiber groups with the largest difference in fiber length to the speed of light is less than the pulse interval period of the pulsed laser beam. In this embodiment, each receiving fiber group includes only one receiving fiber. However, in other embodiments, each receiving fiber group is allowed to include at least two receiving fibers.

[0060] See also Figure 5 , Figure 5 FIG. 1 shows the combining structure of the receiving optical fiber group when the receiving optical fiber group includes at least two receiving optical fibers 91. Figure 5 As shown, when the receiving fiber group includes at least two receiving fibers, the receiving fiber group has a combining structure. The combining structure includes all the receiving fibers 91 of the receiving fiber group, a first combiner 92, and a combining fiber 93. Specifically, the input end of the first combiner 92 is connected to all the receiving fibers 91 of the receiving fiber group, and the output end of the first combiner 92 is connected to the combining fiber 93 corresponding to the receiving fiber group. The function of the first combiner 92 is to combine all the receiving fibers 91 in the receiving fiber group into one. When the receiving fiber group includes at least two receiving fibers, the general way to change the fiber length is to adjust the length of the combining fiber 93.

[0061] It should be noted that in this embodiment, the connecting optical fibers and optical fiber lengths corresponding to the receiving optical fiber group are defined only for the purpose of accurate description, and it is not necessary to provide additional connecting optical fibers outside the receiving optical fiber group.

[0062] like Figure 1As shown, the adjustment unit 3 includes an optical attenuator 31 corresponding to the receiving fiber group. The optical attenuator 31 is connected in series with the corresponding connecting fiber and is used to adjust the dynamic optical intensity of the scattered light. The term "connected in series" here means that the optical fiber connected to the input end and the optical fiber connected to the output end of the optical attenuator 31 are both considered connecting fibers. In other words, when the receiving fiber group includes at least two receiving fibers 91, the optical fibers before and after the optical attenuator 31 are both considered to be combined fibers. When the receiving fiber group includes only one receiving fiber 91, the optical fibers before and after the optical attenuator 31 are both considered to be receiving fiber 91.

[0063] like Figure 1 As shown, the input end of the second combiner 4 is connected to all the connected optical fibers to combine all the connected optical fibers into one, and the output end thereof is connected to the optical fiber to be tested.

[0064] like Figure 1 As shown, the single-photon detector 5 is connected to the optical fiber to be tested to receive the scattered light signal output by the second combiner 4 and output a counting signal corresponding to the detection time point.

[0065] like Figure 1 As shown, the acquisition unit 6 is connected to the single-photon detector 5 to collect the counting signal corresponding to the detection time point output by the single-photon detector 5, and within each pulse interval period, the counting signal is statistically analyzed according to the period corresponding to the average scattering angle θ to establish a high-resolution time distribution histogram, thereby obtaining the signal intensity data corresponding to each average scattering angle θ.

[0066] like Figure 1 As shown, the calculation unit 7 inverts the particle size distribution of the water body A based on the signal intensity data corresponding to each average scattering angle θ obtained by the acquisition unit 6.

[0067] like Figure 1 As shown, the optical power meter 8 is used to detect the power of the laser beam after passing through the water body A. In this embodiment, the optical power meter 8 is arranged behind the through hole 214 of the first fixing member 213 to detect the power of the laser beam passing through the through hole 214 .

[0068] In this embodiment, the receiving end face of the first optical fiber 212 located at the focal plane C replaces the fan-shaped detection window of the silicon ring detector to receive scattered light at different scattering angles, thereby separating the receiving unit 2 from the detection unit, reducing the cost of the receiving unit 2. Even if the receiving unit 2 needs to be replaced for different water bodies, the replacement cost is greatly reduced. At the same time, the receiving unit 2 of this embodiment is conducive to regulating the scattered light intensity of each receiving optical fiber group by adjusting the optical attenuator 31 of the unit 3, so that the receiving unit 2 has greater adaptability to water bodies with different particle size distributions. Even if the receiving unit 2 in this embodiment needs to increase the receiving area for forward scattered light at a larger angle, it only needs to increase the number of first optical fibers 212 located at the same focal plane radius r accordingly, so replacement and deployment are more convenient. At the same time, the use of optical fibers to receive scattered light from water bodies can reduce temperature sensitivity and improve system stability, and is particularly suitable for harsh climate conditions such as high ocean temperatures.

[0069] In this embodiment, in order to enable the water scattered light measurement device to provide a measurement range from submicron to millimeter level, ensure balanced resolution within the measurement range, and ensure sufficient measurement accuracy for both large particles (small scattering angle) and small particles (larger scattering angle), the focal plane radius r corresponding to the average scattering angle of the first optical fiber group is set to be exponentially distributed, which is more conducive to improving the resolution within a larger measurement range.

[0070] In this embodiment, the first fixing member 213 is provided with a through hole 214 extending along the first direction at the focal point D, which allows the laser beam focused by the Fourier lens 211 to pass through the through hole 214, thereby preventing the laser beam from affecting the reception of small-angle scattered light signals when hitting the first fixing member 213.

[0071] In this embodiment, the dynamic range of the scattered light intensity is adjusted by the optical attenuator 31 arranged corresponding to the receiving optical fiber group. Compared with the prior art in which the scattered light intensity is set by the fan-shaped detection window area of the silicon ring detector, it has greater adaptability to water bodies with different particle size distributions.

[0072] In this embodiment, by adjusting the pulsed laser beam, fiber length, and second combiner 4, time-division multiplexing of scattered light at different scattering angles is achieved. This paves the way for detecting scattered light at multiple angles using a single detector, eliminating the need to individually calibrate parameters such as sensitivity, dark current, response time, and linear range for each detector when using multiple detectors. This also avoids the high response time requirements for multiple detectors. It should be noted that the use of receiving fiber 91 enables time-division multiplexing by varying the fiber length. Therefore, time-division multiplexing technology is predicated on the receiving unit 2 in this embodiment. In contrast, silicon ring detectors in the prior art are unable to achieve time-division multiplexing technology.

[0073] In this embodiment, the scattered light signal after time division multiplexing is detected by the single photon detector 5, and a counting signal corresponding to the detection time point can be directly output, thereby avoiding the silicon ring detector in the prior art outputting multiple analog signals, so the anti-interference ability is stronger and the accuracy is higher.

[0074] In this embodiment, the second receiving module 22 is suitable for detecting scattered light signals with larger scattering angles. Because the second receiving module 22 also uses optical fiber to receive scattered light, it can be used together with the receiving optical fiber 91 of the first receiving module 21 to control the dynamic range of light intensity using an optical attenuator 31. It can also use time-division multiplexing technology with the receiving optical fiber 91 of the first receiving module 21, thereby enabling a single detector to detect scattered light signals at various scattering angles, from small to large. Conventional silicon ring detectors, on the other hand, are incapable of detecting backscattered light signals, and are even unable to detect forward scattered light signals at larger scattering angles. Therefore, the water scattered light measurement device of this embodiment has significantly improved adaptability to water bodies with different particle size distributions.

[0075] In this embodiment, the second fixing member 222 limits the receiving angle of the second optical fiber 221 through the angle limiting hole 223, so that the scattered light signal received by the second optical fiber 221 has a better correspondence with the average scattering angle θ.

[0076] In this embodiment, by setting up an optical power meter 8 to measure the optical power of the laser beam after passing through the water body, the beam attenuation coefficient can be obtained by comparing it with the output power of the laser beam to characterize the scattering and absorption effect of the water body on light, thereby quickly measuring the turbidity of the water body.

[0077] The above description of the specification and embodiments is used to explain the scope of protection of the present application, but does not constitute a limitation on the scope of protection of the present application.

Claims

1. A receiving unit for receiving scattered light generated by a laser beam passing through water along a first direction, characterized in that: It includes a first receiving module, which includes: a Fourier lens having an optical axis extending in a first direction to focus the laser beam passing through the body of water to a focal point; and At least two first optical fibers, each having a receiving end face located in the focal plane, a distance between a center point of the receiving end face of the first optical fiber and the focal point being defined as a focal plane radius of the first optical fiber, the focal plane radius corresponding to an average scattering angle of scattered light received by the first optical fiber; and at least two first optical fibers having different corresponding average scattering angles.

2. The receiving unit according to claim 1, wherein: The first optical fibers with the same corresponding average scattering angle form a first optical fiber group. The first optical fiber groups are arranged according to the focal plane radius. The ratio of the larger value to the smaller value of the focal plane radius in all adjacent first optical fiber groups is the same.

3. The receiving unit according to claim 1, wherein: The first receiving module further includes a first fixing member for fixing the receiving end of each first optical fiber, and the first fixing member is provided with a through hole penetrating along the first direction at the focus.

4. A water scattered light measuring device, characterized in that include: a transmitting unit configured to transmit a laser beam suitable for passing through a body of water in a first direction, wherein the laser beam is a pulsed laser beam; A receiving unit as claimed in any one of claims 1 to 3; all first optical fibers are receiving optical fibers, and corresponding receiving optical fibers with the same average scattering angle form a receiving optical fiber group; the lengths of the receiving optical fibers in the receiving optical fiber group including more than two receiving optical fibers are the same; each receiving optical fiber group is correspondingly defined with a connecting optical fiber and an optical fiber length; wherein the connecting optical fiber corresponding to the receiving optical fiber group including more than two receiving optical fibers is defined as the combined optical fiber to which the output end of the first combiner is connected after all the receiving optical fibers of the receiving optical fiber group are combined into one by the first combiner; the connecting optical fiber corresponding to the receiving optical fiber group including only one receiving optical fiber is defined as the receiving optical fiber a receiving optical fiber in a receiving optical fiber group; the optical fiber length of a receiving optical fiber group including two or more receiving optical fibers is defined as the sum of the length of any receiving optical fiber in the receiving optical fiber group and the length of the combined optical fiber; the optical fiber length of a receiving optical fiber group including only one receiving optical fiber is defined as the length of the connecting optical fiber in the receiving optical fiber group; the optical fiber lengths of all receiving optical fiber groups are different, the receiving optical fiber groups are arranged according to the optical fiber lengths, the ratio of the absolute value of the difference between the optical fiber lengths of adjacent receiving optical fiber groups to the speed of light is greater than the pulse width of the pulsed laser beam, and the ratio of the absolute value of the difference between the optical fiber lengths of two receiving optical fiber groups with the largest difference in optical fiber length to the speed of light is less than the pulse interval period of the pulsed laser beam; an adjustment unit, comprising an optical attenuator provided corresponding to the receiving optical fiber group, the optical attenuator being serially connected to the corresponding connecting optical fiber and used for adjusting the dynamic light intensity of the scattered light; A second combiner, whose input end is connected to all the connected optical fibers to combine all the connected optical fibers into one; and whose output end is connected to the optical fiber to be tested; a single-photon detector, the input end of which is connected to the optical fiber to be tested, so as to receive the scattered light signal output by the second combiner and output a counting signal corresponding to the detection time point; and The collecting unit is connected to the single photon detector to collect the counting signal outputted by the single photon detector corresponding to the detection time point, and to count the counting signal during the period corresponding to the average scattering angle in each pulse interval period.

5. The water scattered light measuring device according to claim 4, wherein: The receiving unit further includes a second receiving module, the second receiving module including at least one second optical fiber; a receiving end face of the second optical fiber is oriented toward a point on a path of the pulsed laser beam in the water body, and a first angle is formed between the orientation of the receiving end face of the second optical fiber and the first direction, the first angle corresponding to an average scattering angle of scattered light received by the second optical fiber; The average scattering angle corresponding to any second optical fiber is greater than the average scattering angle corresponding to all first optical fibers; and all second optical fibers are also receiving optical fibers.

6. The water scattered light measuring device according to claim 5, wherein: The second receiving module also includes a second fixing member for fixing the receiving end of each second optical fiber, and the second fixing member is provided with an angle limiting hole arranged corresponding to the second optical fiber, and the second angle limiting hole extends along the direction of the receiving end face of the second optical fiber to limit the receiving angle of the receiving end face of the second optical fiber.

7. The water scattered light measuring device according to claim 5, wherein: The average scattering angle range corresponding to all first optical fibers is greater than 0 degrees and less than 15 degrees; the average scattering angle range corresponding to all second optical fibers is greater than or equal to 10 degrees and less than 180 degrees.

8. The water scattered light measuring device according to any one of claims 4 to 7, wherein: It also includes an optical power meter, which is used to detect the power of the laser beam after passing through the water body.

9. The water scattered light measuring device according to any one of claims 4 to 7, wherein: The emitting unit comprises a laser and a collimator. The laser emits pulsed laser light, and the collimator receives the pulsed laser light and forms a pulsed laser beam after performing collimation and beam expansion.

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