Fiber integrated modulated underwater long-range optical detection system

Abstract

The present application relates to the technical field of underwater optical imaging, and particularly relates to a fiber integrated modulation underwater long-distance optical detection system, a laser illumination optical module is used for emitting two beams of light with an included angle to an underwater target water area, the two beams of light form spatially varying interference fringes in the target water area to produce alternating bright and dark illumination light; a Scheimpflug imaging optical module is used for shooting the target water area under the illumination light according to the Scheimpflug imaging condition to obtain an underwater spatial image; and a circuit control core group is used for controlling the laser illumination optical module to emit the two beams of light and collecting the underwater spatial image from the Scheimpflug imaging optical module. The present application introduces a fiber integrated modulation optical fiber interferometer structure as an optical source output regulation module, so that the outgoing light beams form an angle to realize spatial interference, effectively improves the regulation of the light source part of the traditional Scheimpflug imaging laser radar, effectively reduces the size and weight, and has the advantages of low cost and stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of underwater optical imaging, and particularly relates to a fiber integrated modulation underwater long-distance optical detection system. BACKGROUND

[0002] The existing underwater detection technology can be divided into in-situ detection technology and sampling off-line detection technology. Compared with the off-line sampling detection of limited samples, the in-situ detection in a complex wide range such as deep sea has more value. Among the many in-situ detection technologies, not only can the actual information of the water sample be detected online, but some can also search and explore the geological and mineral resources of the seabed and the ocean floor. In this process, the increasing application requirements put forward higher requirements on the information acquisition range and capacity of the underwater detection technology.

[0003] The in-situ detection technology method based on acoustics and optics has more practical value in a large range of complex and variable water environments. Although the acoustic detection method can achieve lower transmission loss in water, it still lags behind the optical detection method in the resolution limit. Among the existing various underwater high-resolution optical detection technologies, the active excitation type underwater optical detection technology has better environmental background resistance and application potential in turbid water and deep sea dark environment. However, the current active detection technology is always difficult to be effectively applied due to the problems of high cost, large size, complex system and other issues of the gate selection type hardware. At the same time, although the current Shashima imaging lidar technology is low in cost, the regulation and control ability of the continuous laser illumination light source is poor, and the signal analysis still relies on the direct collection of traditional image sensors. The signal-to-noise ratio of long-distance detection is poor, and it is difficult to break through the limit of traditional underwater detection distance. SUMMARY

[0004] Therefore, the present application aims to provide a fiber integrated modulation underwater long-distance optical detection system, which improves the regulation and control of the existing Shashima imaging lidar light source part, introduces a fiber integrated modulation optical fiber interferometer structure as a light source output regulation and control module, and relies on the fiber integrated modulation optical fiber interferometer structure to increase the regulation and control of the traditional Shashima imaging lidar light source part, effectively reduce the size and weight, and have the advantages of low cost and stability.

[0005] To achieve the above purpose, the technical scheme of the present application is as follows:

[0006] The application discloses an underwater long-distance optical detection system integrated with fiber modulation, which comprises a laser illumination optical module, a Schlieren imaging optical module and a circuit control core group.

[0007] Further, the laser illumination optical module comprises a laser unit, a first laser arm and a second laser arm; the first laser arm and the second laser arm receive laser from the laser unit and emit laser to the target water area at an included angle, so that the two beams of light form spatially varying interference fringes in the target water area.

[0008] Further, the laser unit comprises a laser light source and a light source fiber splitter; the light source fiber splitter splits the laser from the laser light source into first laser and second laser, and transmits the first laser into the first laser arm and the second laser into the second laser arm.

[0009] Further, the first laser arm comprises a first fiber splitter and a first fiber collimator group; the first fiber collimator group comprises a plurality of first fiber collimators arranged in parallel; the first fiber splitter splits the first laser, and inputs the split laser into the corresponding first fiber collimator; and the first fiber collimator emits the collimated laser into the target water area.

[0010] Further, the second laser arm comprises a piezoelectric ceramic structure, a second fiber splitter and a second fiber collimator group; the second fiber collimator group comprises a plurality of second fiber collimators arranged in parallel and having the same number as the first fiber collimators; the light exit angle between the first fiber collimators and the second fiber collimators satisfies the condition of forming spatially varying interference fringes; the second fiber splitter splits the second laser, and inputs the split laser into the corresponding second fiber collimator; and the second fiber collimator emits the collimated laser into the target water area; the optical fibers between the light source fiber splitter and the second fiber splitter are wound on the piezoelectric ceramic structure; the piezoelectric ceramic structure adjusts the stretching and shrinking of the wound optical fibers, changes the arm length of the second laser arm, and further adjusts the light and dark change of the illumination light.

[0011] Further, the Schlieren imaging optical module comprises an image sensor and an imaging lens group, wherein light beams from the target water area pass through the imaging lens group into the image sensor to be imaged to obtain an underwater space image; a plane where a target surface of the image sensor is located, a central plane of the imaging lens group, and a longitudinal plane of the target water area converge at a point.

[0012] Further, the circuit control core group comprises an industrial computer and a piezoelectric ceramic control driver; the industrial computer is configured to control the laser light source to emit laser light and receive the underwater space image from the image sensor; and the piezoelectric ceramic control driver is configured to control the piezoelectric ceramic structure to adjust the expansion and contraction of the wrapped optical fiber.

[0013] Further, the water-tight shell structure comprises a cylindrical support shell, an imaging receiving optical window, and an outgoing laser illumination window; the imaging receiving optical window and the outgoing laser illumination window are arranged on the cylindrical support shell; the cylindrical support shell is configured to place and seal the laser illumination optical module, the Schlieren imaging optical module, and the circuit control core group; the laser light emitted by the laser illumination optical module is configured to irradiate the target water area through the outgoing laser illumination window; and the light beams generated by the target water area are configured to enter the Schlieren imaging optical module through the imaging receiving optical window.

[0014] Compared with the prior art, the present application can achieve the following beneficial effects:

[0015] (1) In the fiber integrated modulation underwater long-distance optical detection system, the advantages of the fiber integrated modulator and the Schlieren imaging are fully combined, the compactness, flexible layout, and integrated modulation operability of the fiber interferometer are combined with the high relative aperture and large tilt depth of the Schlieren imaging, the limitation of the signal-to-noise ratio degradation of the long-distance detection oblique backscattering is broken through, and the spatial dynamic structure illumination of the laser light source in the spatial depth direction is realized by using low-cost fiber components, thereby improving the poor regulation and insufficient resolution of the traditional Schlieren imaging illumination light source;

[0016] (2) In the fiber integrated modulation underwater long-distance optical detection system, the double-fiber collimator is arranged obliquely to realize dynamic structure illumination of the target water area in the depth direction, and the high-speed modulation of the piezoelectric ceramic can effectively improve the signal-to-noise ratio degradation of the Schlieren imaging underwater long-distance optical detection system;

[0017] (3) In the fiber integrated modulation underwater long-distance optical detection system, the water-tight shell structure meets the requirements of wide and narrow transverse observation range, and the use requirements in the shallow water area, turbid water body, or deep-sea high-pressure environment; and the high stability of the fiber integrated device and the Schlieren imaging system module can realize high reliability, high stability, and long service life of the underwater application. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The illustrations are shown schematically in the drawings where:

[0019] Figure 1 Structure diagram of the fiber integrated modulation underwater long-distance optical detection system according to the embodiments of the present application;

[0020] Figure 2 Structure diagram of the laser illumination optical module according to the embodiments of the present application;

[0021] Figure 3 Working principle diagram of the fiber integrated modulation underwater long-distance optical detection system according to the embodiments of the present application.

[0022] Explanation of reference signs:

[0023] 1, laser light source; 2, light source fiber optical splitter; 3, first fiber optical splitter; 4, first fiber collimator; 5, piezoelectric ceramic structure; 6, second fiber optical splitter; 7, second fiber collimator; 8, image sensor; 9, imaging lens group; 10, industrial computer; 11, piezoelectric ceramic control driver; 12, cylindrical support shell; 13, imaging receiving optical window; 14, outgoing laser illumination window. DETAILED DESCRIPTION

[0024] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but do not constitute limitation to the present application.

[0025] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0026] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" and the like can be explicitly or implicitly included one or more. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0027] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0028] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0029] As shown in Figure 1 and Figure 2 The fiber integrated modulation underwater long-distance optical detection system described in the embodiments of the present application includes a laser illumination optical module, a Zernike imaging optical module, a circuit control core group and a water-tight housing structure. The laser illumination optical module is used to emit two beams of light with an included angle to the underwater target water area, and the two beams of light form spatially varying interference fringes in the target water area, producing alternating bright and dark illumination light. The Zernike imaging optical module is used to shoot the target water area under the illumination light according to the Zernike imaging condition, and obtain the underwater space image. The circuit control core group is used to control the laser illumination optical module to emit two beams of light, and collect the underwater space image from the Zernike imaging optical module. The water-tight housing structure is used to seal the laser illumination optical module, the Zernike imaging optical module and the circuit control core group.

[0030] In some embodiments, the laser illumination optical module comprises a laser unit, a first laser arm and a second laser arm. The first laser arm and the second laser arm receive laser from the laser unit and emit laser to the target water area at an angle, so that the two beams of light form spatially varying interference fringes in the target water area. In the present application, the first laser arm and the second laser arm form an integrated fiber-optic interferometer modulation structure, the light emitted by the first laser arm and the second laser arm forms a certain angle in the target water area, and the two beams of light emitted strictly overlap in the target water area, so that spatially varying interference fringes are formed in the target water area, and the target water area is illuminated by the light with clear and dark bands.

[0031] The laser unit comprises a laser light source 1 and a light source fiber-optic splitter 2. The light source fiber-optic splitter 2 splits the laser from the laser light source 1 into a first laser and a second laser, and transmits the first laser into the first laser arm and the second laser into the second laser arm.

[0032] As shown in Figure 2 The first laser arm comprises a first fiber-optic splitter 3 and a first fiber-optic collimator set. The first fiber-optic collimator set comprises a plurality of first fiber-optic collimators 4 arranged in parallel. The first fiber-optic splitter 3 splits the first laser and inputs the split laser into the corresponding first fiber-optic collimator 4. The first fiber-optic collimator 4 emits the collimated laser into the target water area. It should be noted that the length of the first laser arm is defined as the length of the transmission path of the light beam from the light source fiber-optic splitter 2 to the first fiber-optic collimator 4.

[0033] As shown in Figure 2As shown, the second laser arm includes a piezoelectric ceramic structure 5, a second fiber optic splitter 6, and a second fiber collimator group, which includes a plurality of second fiber collimators 7 arranged in parallel and in the same number as the first fiber collimators 4, and the light exit angles between the first fiber collimators 4 and the second fiber collimators 7 satisfy the condition of forming spatially varying interference fringes. The length of the second laser arm is defined as the length of the transmission path of the light beam from the light source fiber splitter 2 to the second fiber collimator 7, consistent with the length of the first laser arm. The second fiber optic splitter 6 splits the second laser light and inputs the split laser light into the corresponding second fiber collimator 7, and the second fiber collimator 7 shoots the collimated laser light into the target water body region. The optical fibers between the light source fiber splitter 2 and the second fiber optic splitter 6 are wound on the piezoelectric ceramic structure 5, and the piezoelectric ceramic structure 5 adjusts the expansion and contraction of the wound optical fibers to change the length of the second laser arm, thereby dynamically and accurately adjusting and controlling the length difference between the first laser arm and the second laser arm, and adjusting the brightness variation of the illumination light. In other embodiments, the optical fibers connected to the first fiber collimator 4 and the second fiber collimator 7 of the light source fiber splitter 2 can be wound on the piezoelectric ceramic structure 5 at the same time, but it is necessary to ensure that the expansion and contraction amounts of the optical fibers in the two laser arms are inconsistent during the piezoelectric expansion of the piezoelectric ceramic structure 5, so that the modulation function of the interferometer modulation structure formed by the first laser arm and the second laser arm can be effectively realized, and fiber integrated modulation can be realized. The arrangement of the first fiber collimator group and the second fiber collimator group in the present application does not increase the number of piezoelectric ceramic structures 5, which can effectively compensate for the problem of narrow exit light path and narrow detectable target water body region in the transverse direction. The parallel arrangement of the fiber collimators in the first fiber collimator group and the second fiber collimator group effectively avoids the appearance of additional interference fringes, which brings confusion to image analysis. In addition, to improve the differential modulation of the increased number of channels, the first fiber collimator and the second fiber collimator that form an angle with the output light can be set as a group of fiber collimators, and the interference optical path differences between different groups of fiber collimators are different. At the same time, each optical element in the laser illumination optical module is wavelength-dependent. Since the transmission loss in the water body is the lowest for blue-green light, its attenuation coefficient is generally about 0.4 dB / m, so blue-green light band laser light source 1 should be selected in the usual working condition, and other corresponding waveband laser light source 1 can be used in special working scenarios and biological phototaxis analysis requirements.

[0034] In other embodiments, the first laser arm can output only one laser beam, and the first fiber splitter 3 in the first laser arm is not needed for splitting, specifically, Figure 1As shown, at this time, the first laser arm includes a first fiber collimator 4, and correspondingly, in the first laser arm, the first laser output by the light source fiber beam splitter 2 is directly emitted into the target water body region after collimation by the first fiber collimator 4. If the first laser arm only outputs one laser beam, at this time, the second laser arm needs to correspond to the first laser arm and only output one laser beam, so that the laser beams output by the first laser arm and the second laser arm form an included angle in the target water body region, thereby forming spatially varying interference fringes. Specifically, the second laser arm includes a fiber ring-wound piezoelectric ceramic structure 5 and a second fiber collimator 7. The second laser output by the light source fiber beam splitter 2 in the laser unit enters the second fiber collimator 7 after winding through the fiber ring, and the second fiber collimator 7 emits the collimated laser into the target water body region.

[0035] The Scheimpflug imaging optical module includes an image sensor 8 and an imaging lens group 9. Wherein, the light beams from the target water body region enter the image sensor 8 through the imaging lens group 9 for imaging to obtain an underwater space image. The Scheimpflug imaging optical module needs to satisfy the Scheimpflug imaging condition, that is, the plane where the target surface of the image sensor 8 is located, the central plane of the imaging lens group 9, and the longitudinal plane of the target water body region converge at a point. The imaging lens group 9 can be a complex imaging lens group composed of multiple lenses, and is not limited to single-lens imaging, but the geometric analysis of its light rays can be analogous to single-lens imaging. A core principle advantage of the Scheimpflug imaging optical module is that it does not need to worry about the imaging depth of field as in traditional imaging lens design. Generally, the imaging depth of field is inversely proportional to the relative aperture of the optical lens, that is, the larger the relative aperture, the smaller the imaging depth of field. In traditional optical systems, this undoubtedly restricts the high-flux light collection and detection capability of underwater scenes. However, in the optical structure of Scheimpflug imaging, the imaging depth of field is related to the longitudinal angle, so the optical lens group of Scheimpflug imaging can achieve the function effect of a larger relative aperture (smaller F number).

[0036] The circuit control core group includes an industrial computer 10 and a piezoelectric ceramic control driver 11. Wherein, the industrial computer 10 is used to control the laser light source 1 to emit laser, and receive the underwater space image from the image sensor 8, and the piezoelectric ceramic control driver 11 is used to control the piezoelectric ceramic structure 5 to adjust the stretching and contraction of the wound fiber.

[0037] The water-tight shell structure includes a cylindrical support shell 12, an imaging receiving optical window 13 and an outgoing laser illumination window 14. The imaging receiving optical window 13 and the outgoing laser illumination window 14 are arranged on the cylindrical support shell 12, and the cylindrical support shell 12 places and seals the laser illumination optical module, the Scheimpflug imaging optical module and the circuit control core group. The laser emitted by the laser illumination optical module irradiates the target water body region through the outgoing laser illumination window 14, and the light beams generated by the target water body region enter the Scheimpflug imaging optical module through the imaging receiving optical window 13.

[0038] In the embodiment of the present application, for engineering consideration in the application process, in the deep sea working condition, the pressure resistance problem needs to be fully considered, the cylindrical support shell 12 is set as a cylindrical structure, the imaging receiving optical window 13 and the outgoing laser illumination window 14 are mainly formed by the acrylic material or sapphire material in the form of a trapezoidal circular truncated cone, and specific design needs to be matched according to the working water depth, and the thickness-diameter ratio is often used as an empirical parameter for calculation and analysis. In addition, in the super-high pressure working environment, the cylindrical support shell 12 of the laser illumination optical module and the Schlieren imaging optical module is designed as a separated double-cylinder structure, so that the difficulty of shell structure design and the requirement of cylinder wall thickness can be reduced. In addition, the imaging receiving optical window 13 and the outgoing laser illumination window 14 are coated with an anti-reflection film matching the wavelength of the laser emitted by the laser light source 1.

[0039] In the embodiment of the present application, the system structure can adopt an offline working mode powered by a built-in battery, or can adopt a tail cable mode for seabed laboratory remote control or water surface platform remote control, but water-tight penetration and water-tight cable arrangement are required.

[0040] The specific working principle of the system of the present application is as shown in Figure 3 In the traditional underwater Schlieren imaging application process, due to the absorption and scattering of water, the oblique backscattering or reflection signal is gradually weakened, the signal-to-noise ratio is gradually deteriorated, and the underwater detection capability is also correspondingly reduced under the condition of increasing longitudinal distance. Essentially, the signal-to-noise ratios of the near and far distances are quite different, and the dynamic range requirement of the detector is high, and it is difficult to realize the breakthrough of the detection distance in the fixed state of the detector. In the present application, through the integration and modulation of the optical fiber, spatial interference fringes can be formed in the target water area, and through the piezoelectric ceramic driving control, the arm length difference of the two laser arms is changed, and the signal-to-noise ratio change of the target water area is dynamically adjusted. With the modulated signal-to-noise ratio change, the far distance detection problem is solved.

[0041] It should be understood that the various forms of the flow shown above can be used to reorder, add or delete steps. For example, the steps described in the present disclosure can be executed in parallel, in sequence or in different order, as long as the desired results of the technical solutions of the present disclosure can be achieved, which is not limited herein.

[0042] The above specific embodiments do not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An underwater long-range optical detection system with fiber-integrated modulation, characterized in that, The application relates to an underwater laser imaging device. The device comprises a laser illumination optical module, a Scheimpflug imaging optical module, a circuit control core group and a water-tight shell structure. The laser illumination optical module is used for emitting two beams of light with an included angle to a target water body area, forming spatially-varying interference fringes in the target water body area, and generating illumination light with bright and dark areas. The Scheimpflug imaging optical module is used for shooting the target water body area under the illumination light according to the Scheimpflug imaging condition, and obtaining an underwater spatial image. The circuit control core group is used for controlling the laser illumination optical module to emit the two beams of light, and collecting the underwater spatial image from the Scheimpflug imaging optical module.

2. The fiber-integrated modulated underwater long-range optical detection system according to claim 1, wherein, The water-tight shell structure is used for sealing the laser illumination optical module, the Scheimpflug imaging optical module and the circuit control core group.

3. The fiber-integrated modulated underwater long-range optical detection system according to claim 2, wherein, The laser unit comprises a laser light source and a light source fiber splitter.

4. The fiber-integrated modulated underwater long-range optical detection system according to claim 3, wherein, The light source fiber splitter divides the laser from the laser light source into the first laser and the second laser, and transmits the first laser into the first laser arm and the second laser into the second laser arm. The first laser arm comprises a first fiber splitter and a first fiber collimator group. The first fiber splitter divides the first laser, and inputs the divided laser into the corresponding first fiber collimator.

5. The fiber-integrated modulated underwater long-range optical detection system according to claim 4, wherein, The second laser arm comprises a piezoelectric ceramic structure, a second fiber splitter and a second fiber collimator group. The second fiber splitter divides the second laser, and inputs the divided laser into the corresponding second fiber collimator. The piezoelectric ceramic structure adjusts the stretching and contraction of the wound fiber, changes the arm length of the second laser arm, and further adjusts the bright and dark changes of the illumination light. The Scheimpflug imaging optical module comprises an image sensor and an imaging lens group. The light beam from the target water body area passes through the imaging lens group and enters the image sensor to form an image, and an underwater spatial image is obtained. The target surface plane of the image sensor, the central plane of the imaging lens group and the longitudinal plane of the target water body area converge at one point.

6. The fiber-integrated modulated underwater long-range optical detection system according to claim 5, wherein, The circuit control core group comprises an industrial computer and a piezoelectric ceramic control driver; the industrial computer is used for controlling the laser light source to emit laser light and receiving underwater space images from the image sensor; and the piezoelectric ceramic control driver is used for controlling the piezoelectric ceramic structure to adjust the expansion and contraction of the wrapped optical fiber.

7. The fiber-integrated modulated underwater long-range optical detection system according to claim 1, wherein, The watertight shell structure comprises a cylindrical support shell, an imaging receiving optical window and an outgoing laser illumination window, the imaging receiving optical window and the outgoing laser illumination window are arranged in the cylindrical support shell, the cylindrical support shell places and seals a laser illumination optical module, a Schlieren imaging optical module and a circuit control core group, the laser light emitted by the laser illumination optical module irradiates a target water body region through the outgoing laser illumination window, and the light beam generated by the target water body region enters the Schlieren imaging optical module through the imaging receiving optical window.

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