Longitudinal periodic structure optical fiber geometric parameter detection system and method

Abstract

The invention provides a system and a method for detecting geometric parameters of an optical fiber with a longitudinal periodic structure. The system comprises an optical fiber clamp used for fixing a test part of the optical fiber to be detected in optical fiber refractive index matching oil in a space image imaging device; the light source is used for emitting test light to the collecting lens through the optical fiber bundle, and the test light is focused into a focused light spot through the collecting lens and then is sequentially emitted to the space image imaging device and the detection device; the space image imaging device is used for moving along the axis direction of the to-be-tested optical fiber based on a preset moving speed after the test light passes through a test part in the optical fiber refractive index matching oil so as to form an optical imaging signal corresponding to the test part; and the detection device is used for acquiring geometric parameters of the periodic structure in the to-be-detected optical fiber according to the optical imaging signal. According to the invention, the detection device can accurately obtain the periodic structure geometric parameters of the to-be-detected optical fiber, and the detection precision and reliability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of special optical fiber testing, and particularly to a detection system and method for geometric parameters of an optical fiber with a longitudinal periodic structure. Background Art

[0002] The geometric size parameters of an optical fiber are key indicators for evaluating the performance of the optical fiber, and have an important impact on the optical transmission efficiency and insertion loss of the optical fiber.

[0003] Currently, the commonly used image gray-scale method obtains the geometric size parameters of the optical fiber by collecting the end-face image of the optical fiber and performing data processing. However, for special optical fibers with an axially periodic distribution structure in the spatial dimension, the image gray-scale method based on the end-face cannot effectively measure the periodic pitch parameters inside the special optical fiber, and currently, there is no reliable test method to accurately measure these parameters.

[0004] Therefore, there is an urgent need for a detection system and method for geometric parameters of an optical fiber with a longitudinal periodic structure to solve the above problems. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides a detection system and method for geometric parameters of an optical fiber with a longitudinal periodic structure.

[0006] The present invention provides a detection system for geometric parameters of an optical fiber with a longitudinal periodic structure, including an optical fiber fixture, a light source, a spatial image imaging device, and a detection device, wherein: The optical fiber fixture is used to fix the test part of the optical fiber to be tested in the optical fiber refractive index matching oil in the spatial image imaging device. The optical fiber to be tested is composed of a main core and side cores, and the side cores form a periodic structure around the main core in a preset pitch distribution manner. The coating layer of the test part has been stripped off; the refractive index of the optical fiber refractive index matching oil is determined based on the refractive index of the cladding of the optical fiber to be tested; The light source is used to emit test light to a condenser lens through an optical fiber bundle. After the test light is focused into a focused spot by the condenser lens, it is sequentially emitted to the spatial image imaging device and the detection device; The spatial image imaging device is used to move along the axis direction of the optical fiber to be tested at a preset moving rate after the test light passes through the test part in the optical fiber refractive index matching oil, so as to form an optical imaging signal corresponding to the test part; The detection device is used to obtain the geometric parameters of the periodic structure in the optical fiber to be tested according to the optical imaging signal; Wherein, the light source, the condenser lens, and the spatial image imaging device are on the same optical axis.

[0007] According to a geometric parameter detection system for a longitudinally periodic structure optical fiber provided by the present invention, a diaphragm is arranged on the optical axis between the condenser lens and the spatial image imaging device, and the diaphragm is used to adjust the amount of light of the focused spot emitted to the spatial image imaging device.

[0008] According to a geometric parameter detection system for a longitudinally periodic structure optical fiber provided by the present invention, the detection device includes a photodetector and a driving integrated control device, wherein: The photodetector is used to receive the optical imaging signal sent by the image imaging device and convert the optical imaging signal into a corresponding electrical signal; The driving integrated control device is used to obtain the geometric parameters of the periodic structure in the optical fiber to be measured according to the periodic characteristics corresponding to the electrical signal.

[0009] According to a geometric parameter detection system for a longitudinally periodic structure optical fiber provided by the present invention, the spatial image imaging device includes a first objective lens and a second objective lens. The first objective lens and the second objective lens are on the same optical axis, and the fiber refractive index matching oil is adsorbed in the objective lens gap between the first objective lens and the second objective lens, wherein: The first objective lens is used to perform a first magnification process on the focused spot emitted by the condenser lens and emit the focused spot after the first magnification process to the fiber refractive index matching oil; The second objective lens is used to perform a second magnification process on the focused spot after the first magnification process in the test part in the fiber refractive index matching oil to generate an optical imaging signal corresponding to the test part.

[0010] According to a geometric parameter detection system for a longitudinally periodic structure optical fiber provided by the present invention, a first linear displacement stage is arranged on the first objective lens, and a second linear displacement stage is arranged on the second objective lens, wherein: The first linear displacement stage and the second linear displacement stage are used to adjust the spatial position between the first objective lens and the second objective lens along the axis direction of the optical fiber to be measured according to the control instruction sent by the driving integrated control device, so as to obtain the geometric parameters corresponding to at least one periodic structure of the optical fiber to be measured.

[0011] According to a geometric parameter detection system for a longitudinally periodic structure optical fiber provided by the present invention, a focusing lens and a band-pass filter are further arranged between the second objective lens and the photodetector, wherein: The band-pass filter is used to perform denoising processing on the optical imaging signal to obtain a denoised optical imaging signal; The focusing lens is used to perform focusing processing on the denoised optical imaging signal to obtain a target optical imaging signal; The photodetector is also used to convert the target optical imaging signal into the corresponding electrical signal.

[0012] According to a longitudinal periodic structure optical fiber geometric parameter detection system provided by the present invention, the magnification of the first objective lens is at least 20 times, and the spatial numerical aperture of the first objective lens is greater than 0.38; the magnification of the second objective lens is at least 50 times, and the spatial numerical aperture of the second objective lens is greater than 0.68; the objective lens gap between the first objective lens and the second objective lens is less than 700 um.

[0013] According to a longitudinal periodic structure optical fiber geometric parameter detection system provided by the present invention, the optical fiber fixture includes a first V-groove and a second V-groove, wherein: The first V-groove and the second V-groove are used to press both ends of the optical fiber to be measured through a pressing block, so that the test part of the optical fiber to be measured is fixed in the optical fiber refractive index matching oil.

[0014] According to a longitudinal periodic structure optical fiber geometric parameter detection system provided by the present invention, the light source is a broadband light source, which is used to emit visible light or near-infrared band light as the test light.

[0015] The present invention also provides a longitudinal periodic structure optical fiber geometric parameter detection method based on the above longitudinal periodic structure optical fiber geometric parameter detection system, including: After determining that the test part of the optical fiber to be measured is fixed in the optical fiber refractive index matching oil in the spatial image imaging device, a test light is sent to the test part through a light source; Based on the spatial image imaging device, obtain the optical imaging signal corresponding to the test part after the test light passes through the test part in the optical fiber refractive index matching oil; Based on the detection device, convert the optical imaging signal into an electrical signal, and obtain the geometric parameters of the periodic structure in the optical fiber to be measured according to the periodic characteristics corresponding to the electrical signal.

[0016] The longitudinal periodic structure optical fiber geometric parameter detection system and method provided by the present invention fix the optical fiber to be measured in the optical fiber refractive index matching oil of the spatial image imaging device through the optical fiber fixture, and then send the test light to the condenser through the light source, and after focusing, it is sequentially projected onto the imaging device and the detection device. After the test light passes through the test part, the imaging device moves along the optical fiber axis at a preset rate to form an optical imaging signal, so that the detection device can accurately obtain the geometric parameters of the periodic structure of the optical fiber to be measured, improving the detection accuracy and reliability. Description of the Drawings

[0017] To more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] Figure 1 Schematic diagram of the radial end face of the periodic structure optical fiber provided by the present invention; Figure 2 Schematic diagram of the axial geometric structure of the periodic structure optical fiber provided by the present invention; Figure 3 Schematic diagram of the structure of the geometric parameter detection system for the longitudinal periodic structure optical fiber provided by the present invention; Figure 4 Schematic diagram of the flow of the geometric parameter detection method for the longitudinal periodic structure optical fiber provided by the present invention; Reference numerals: 101: Cladding; 102: Main core; 103: Side core; 301: Optical fiber fixture; 302: Light source; 303: Spatial image imaging device; 304: Detection device; 305: Optical fiber to be measured; 306: Optical fiber refractive index matching oil; 307: Optical fiber bundle; 308: Condensing lens; 309: Diaphragm; 310: Focusing lens; 311: Band-pass filter; 3041: Photoelectric detector; 3042: Driving integrated control device; 3031: First objective lens; 3032: Second objective lens; 3033: First linear displacement stage; 3034: Second linear displacement stage; 3035: First motor controller; 3036: Second motor controller; 3037: Rotation controller; 3038: Rotatable V-groove; 3011: First V-groove; 3012: Second V-groove; 3013: Pressing block. Detailed implementation manners

[0019] To make the objectives, technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention in conjunction with the drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments in the present invention fall within the scope of protection of the present invention.

[0020] The features of the terms "first" and "second" in this application may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise specified, the meaning of "a plurality" is two or more.

[0021] In the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this application.

[0022] In the description of this application, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0023] The geometric dimension parameters of an optical fiber are key indicators in evaluating the performance of the optical fiber, and they have a significant impact on the performance of the optical fiber such as optical transmission efficiency and insertion loss. In the traditional optical fiber structure, the design is relatively simple and usually consists of only two parts, namely the core and the cladding. For this conventional structure, the commonly used image gray-scale method at present is an effective means, which can accurately obtain the geometric dimension parameters of the optical fiber by collecting the image of the end face of the optical fiber and through a series of data processing.

[0024] However, with the continuous development of optical fiber technology, some special optical fibers with an axially periodic distribution structure in the spatial dimension have emerged as the times require. Figure 1 The schematic diagram of the radial end face of the periodic structure optical fiber provided by the present invention is as Figure 1 shown. The end face structure of such special optical fibers is more complex. In addition to the cladding 101, there are also two optical cores, namely the main core 102 and the side core 103. The main core 102 is located at the center of the optical fiber, while the side core 103 is distributed around the main core 102 with a certain periodic pitch. Figure 2 The schematic diagram of the axial geometric structure of the periodic structure optical fiber provided by the present invention can be referred to Figure 2As shown, this periodic pitch structure P (whose form may include but is not limited to sine, cosine, square wave, etc.) plays a unique role in the optical fiber design principle. It is equivalent to introducing an equivalent bending radius around the main core 102. This design enables the high-order mode in the main core 102 to be coupled to the side core 103 at the edge. Once the high-order mode is coupled from the main core 102 to the side core 103, its energy will produce bending loss due to the periodic structure of the side core 103, and then radiate out of the optical fiber. In this way, the low-order mode can be retained in the side core 103, thereby achieving single-mode transmission of the main core 102 through an equivalent bending radius without using a bending tool. Therefore, the size of the periodic pitch directly determines the size of the equivalent bending radius, which in turn affects the bending loss performance, and ultimately determines whether the main core 102 can achieve single-mode transmission.

[0025] For this type of special optical fiber, accurate measurement of periodic pitch parameters is particularly important. However, the traditional end-face image grayscale method cannot effectively measure the periodic pitch parameters when faced with such a complex periodic structure. Currently, there is no reliable test method that can accurately measure these key parameters.

[0026] Figure 3 The schematic diagram of the structure of the longitudinal periodic structure optical fiber geometric parameter detection system provided by the present invention is as follows: Figure 3 As shown, the present invention provides a longitudinal periodic structure optical fiber geometric parameter detection system, including an optical fiber clamp 301, a light source 302, a space image imaging device 303 and a detection device 304, wherein: The optical fiber clamp 301 is used to fix the test part of the optical fiber 305 to be tested in the optical fiber refractive index matching oil 306 in the spatial image imaging device 303, wherein the optical fiber 305 to be tested is composed of a main core and a side core, and the side core is a periodic structure formed in a preset pitch distribution manner around the main core, and the coating layer of the test part has been stripped; the refractive index of the optical fiber refractive index matching oil 306 is determined based on the refractive index of the cladding of the optical fiber 305 to be tested; The light source 302 is used to emit test light to the condenser 308 through the optical fiber bundle 307. After the test light is focused into a focused light spot by the condenser 308, it is emitted to the spatial image forming device 303 and the detection device 304 in sequence; The spatial image forming device 303 is used to move along the axis direction of the optical fiber to be tested 305 based on a preset moving speed after the test light passes through the test part in the optical fiber refractive index matching oil 306, so as to form an optical imaging signal corresponding to the test part; The detection device 304 is configured to obtain geometric parameters of the periodic structure in the optical fiber 305 to be measured according to the optical imaging signal; Wherein, the light source 302, the condenser lens 308, and the spatial image imaging device 303 are on the same optical axis.

[0027] In the present invention, the main function of the optical fiber fixture 301 is to firmly fix the test part of the optical fiber 305 to be measured in the optical fiber refractive index matching oil 306 in the spatial image imaging device 303. The optical fiber 305 to be measured is composed of a main core and side cores. Among them, the side cores form a periodic structure around the main core in a preset pitch distribution manner, and the coating layer of the test part has been stripped off so that the test light can directly act on the core structure of the optical fiber. The refractive index of the optical fiber refractive index matching oil 306 is determined according to the cladding refractive index of the optical fiber 305 to be measured, which can reduce the refraction of light at the optical fiber - oil interface and improve the imaging quality.

[0028] The light source 302 is responsible for generating test light and transmitting the test light to the condenser lens 308 through the optical fiber bundle 307. After passing through the condenser lens 308, the test light will be focused into a focused light spot, and this light spot is emitted to the spatial image imaging device 303 and the detection device 304.

[0029] After the test light passes through the test part in the optical fiber refractive index matching oil 306, the spatial image imaging device 303 moves along the axis direction of the optical fiber 305 to be measured based on a preset moving rate to form an optical imaging signal corresponding to the test part. The spatial image imaging device 303 can capture the subtle changes in the internal structure of the optical fiber and convert them into analyzable optical imaging signals. By moving along the optical fiber axis, the structural information of different positions of the optical fiber can be obtained, so as to more comprehensively understand the geometric parameters of the optical fiber.

[0030] The detection device 304 obtains the geometric parameters of the periodic structure in the optical fiber 305 to be measured according to the optical imaging signal. The detection device 304 usually includes image processing and data analysis software, which can identify and analyze the periodic features in the optical imaging signal, so as to extract the geometric parameters of the optical fiber.

[0031] The longitudinal periodic - structure optical - fiber geometric - parameter detection system provided by the present invention fixes the optical fiber to be measured in the optical fiber refractive index matching oil of the spatial image imaging device through the optical fiber fixture, and then emits test light from the light source to the condenser lens. After focusing, the light is sequentially emitted to the imaging device and the detection device. After the test light passes through the test part, the imaging device moves along the optical fiber axis at a preset rate to form an optical imaging signal, enabling the detection device to accurately obtain the geometric parameters of the periodic structure of the optical fiber to be measured, improving the detection accuracy and reliability.

[0032] On the basis of the above embodiments, a diaphragm 309 is provided on the optical axis between the condenser lens 308 and the spatial image imaging device 303, and the diaphragm 309 is used to adjust the amount of light of the focused spot emitted to the spatial image imaging device 303.

[0033] In the present invention, the diaphragm 309 is disposed on the optical axis between the condenser lens 308 and the spatial image imaging device 303. When the test light is emitted from the light source 302 to the condenser lens 308 through the optical fiber bundle 307 and is focused into a focused spot, this focused spot will pass through the diaphragm 309 before reaching the spatial image imaging device 303.

[0034] If the amount of light entering the spatial image imaging device 303 is too large, it may cause the image to be too bright, or even result in image saturation or distortion; while if the amount of light is too small, it may cause the image to be too dark and unable to clearly capture the details of the internal structure of the optical fiber. Therefore, the present invention provides the diaphragm 309 to adjust the amount of light of the focused spot emitted to the spatial image imaging device 303. In an optical system, a diaphragm is a device for controlling the light flux, and it can limit the amount of light passing through by changing the size of its aperture. In the present invention, the diaphragm 309 may be used to adjust the brightness or intensity of the focused spot to ensure that the spatial image imaging device 303 can receive an appropriate amount of light, so as to generate a clear and accurate optical imaging signal.

[0035] In the present invention, the diaphragm 309 not only improves the flexibility and adjustability of the system, but also enables the system to adapt to the requirements of different test conditions and optical fiber types. For example, when testing optical fibers with different diameters or refractive indices, it may be necessary to adjust the aperture size of the diaphragm 309 to ensure the best imaging effect. In addition, the diaphragm 309 can also be used to reduce the entry of stray light or unwanted light into the spatial image imaging device 303, thereby improving the contrast and clarity of the image.

[0036] On the basis of the above embodiments, the detection device 304 includes a photodetector 3041 and a driving integrated control device 3042, wherein: The photodetector 3041 is configured to receive the optical imaging signal sent by the image imaging device 303 and convert the optical imaging signal into a corresponding electrical signal; The driving integrated control device 3042 is configured to obtain the geometric parameters of the periodic structure in the optical fiber 305 to be tested according to the periodic characteristics corresponding to the electrical signal.

[0037] In the present invention, the main function of the photodetector 3041 is to receive the optical imaging signal sent by the spatial image imaging device 303. This optical imaging signal is formed after the test light passes through the test part of the optical fiber 305 to be measured, and it contains detailed information about the internal structure of the optical fiber. The photodetector 3041 can convert the received optical imaging signal into a corresponding electrical signal, and this conversion is achieved based on the photoelectric effect, that is, the optical signal is converted into an electrical signal for subsequent processing and analysis.

[0038] The driving integrated control device 3042 is responsible for receiving the electrical signal converted by the photodetector 3041, and according to the periodic characteristics corresponding to this electrical signal, obtaining the geometric parameters of the periodic structure in the optical fiber 305 to be measured. The periodic characteristics refer to the laws or patterns presented in the electrical signal that correspond to the periodic structure in the optical fiber 305 to be measured. By analyzing and identifying these characteristics, the driving integrated control device 3042 can extract geometric parameters such as the period pitch of the optical fiber.

[0039] In the present invention, the driving integrated control device 3042 also includes data processing and analysis software for further processing and analyzing the electrical signal to improve the accuracy and reliability of parameter acquisition.

[0040] Based on the above embodiments, the spatial image imaging device 303 includes a first objective lens 3031 and a second objective lens 3032. The first objective lens 3031 and the second objective lens 3032 are on the same optical axis. The optical fiber refractive index matching oil 306 is adsorbed in the objective lens gap between the first objective lens 3031 and the second objective lens 3032, where: The first objective lens 3031 is used to perform a first magnification process on the focused light spot emitted by the condenser lens 308, and emit the focused light spot after the first magnification process to the optical fiber refractive index matching oil 306. The second objective lens 3032 is used to perform a second magnification process on the focused light spot after the first magnification process that passes through the test part in the optical fiber refractive index matching oil 306, and generate an optical imaging signal corresponding to the test part.

[0041] In the present invention, the spatial image imaging device 303 is mainly composed of a first objective lens 3031 and a second objective lens 3032. These two objective lenses are on the same optical axis to ensure the accurate transmission of light and the clarity of imaging. Moreover, in the objective lens gap between the first objective lens 3031 and the second objective lens 3032, the optical fiber refractive index matching oil 306 is adsorbed. The function of the optical fiber refractive index matching oil 306 is to reduce the refraction of light at the interface between the optical fiber and the objective lens and improve the imaging quality.

[0042] In the present invention, the main function of the first objective lens 3031 is to perform a first magnification process on the focused light spot emitted by the condenser lens 308. The magnified focused light spot is then emitted into the optical fiber refractive index matching oil 306. Since the refractive index of the matching oil is close to that of the optical fiber cladding, the light refracts less when passing through the interface between the matching oil and the cladding, thus maintaining the clarity and accuracy of the light spot.

[0043] The function of the second objective lens 3032 is to perform a second magnification process on the focused light spot that has undergone the first magnification process at the test site in the optical fiber refractive index matching oil 306. Here, the test site is the part of the optical fiber 305 to be measured where the coating layer has been stripped and immersed in the matching oil. After the magnification process by the second objective lens 3032, an optical imaging signal corresponding to the test site is generated, and this signal contains detailed information about the internal structure of the optical fiber, especially the characteristics of the periodic structure.

[0044] The present invention places the test part of the optical fiber to be measured in the matching oil between the two objective lenses, improving the clarity and accuracy of imaging and providing strong support for subsequent parameter detection.

[0045] Based on the above embodiments, the first objective lens 3031 is provided with a first linear displacement stage 3033, and the second objective lens 3032 is provided with a second linear displacement stage 3034, where: The first linear displacement stage 3033 and the second linear displacement stage 3034 are used to adjust the spatial position between the first objective lens 3031 and the second objective lens 3032 along the axis direction of the optical fiber 305 to be measured according to the control instructions sent by the drive integrated control device 3042, so as to obtain the geometric parameters corresponding to at least one of the periodic structures of the optical fiber 305 to be measured.

[0046] In the present invention, the first objective lens 3031 is provided with a first linear displacement stage 3033, enabling the first objective lens 3031 to perform linear movement along a certain direction; correspondingly, the second objective lens 3032 is provided with a second linear displacement stage 3034, enabling the second objective lens 3032 to also perform linear movement along a certain direction.

[0047] In the present invention, the main function of the first linear displacement stage 3033 and the second linear displacement stage 3034 is to adjust the spatial position between the first objective lens 3031 and the second objective lens 3032. This adjustment is carried out along the axis direction of the optical fiber 305 to be measured, that is, the linear displacement stage can control the movement of the objective lens in the axis direction of the optical fiber.

[0048] In the present invention, the movement of the two linear displacement stages is carried out according to the control instructions sent by the drive integrated control device 3042. The drive integrated control device 3042 can send corresponding control instructions to the linear displacement stage according to the detection requirements or imaging effects to adjust the position of the objective lens. In the present invention, as the position of the objective lens changes, it will affect the imaging clarity and focus point, and thus the periodic structural features at different positions inside the optical fiber can be captured. By analyzing these features, geometric parameters of the optical fiber, such as the period pitch, etc., can be extracted.

[0049] In the present invention, the movement processes of the first linear displacement stage 3033 and the second linear displacement stage 3034 are respectively controlled by the first motor controller 3035 and the second motor controller 3036. By driving the linear displacement stage through these two motor controllers, the spatial positions of the first objective lens 3031 and the second objective lens 3032 are adjusted to obtain clear imaging information of the optical fiber in the axial direction.

[0050] When it is necessary to move the position of the objective lens, the drive integrated control device 3042 issues control instructions, and the first motor controller 3035 and the second motor controller 3036 control the movement of the first linear displacement stage 3033 and the second linear displacement stage 3034, thereby driving the movement of the first objective lens 3031 and the second objective lens 3032 to achieve imaging of different axial positions of the test part of the optical fiber 305 to be measured.

[0051] On the basis of the above embodiments, a focusing lens 310 and a band - pass filter 311 are further provided between the second objective lens 3032 and the photodetector 3041, where: The band - pass filter 311 is used to perform denoising processing on the optical imaging signal to obtain a denoised optical imaging signal; The focusing lens 310 is used to perform focusing processing on the denoised optical imaging signal to obtain a target optical imaging signal; The photodetector 3041 is further used to convert the target optical imaging signal into the corresponding electrical signal.

[0052] In the present invention, between the second objective lens 3032 and the photodetector 3041, a focusing lens 310 and a band-pass filter 311 are provided. The main function of the band-pass filter 311 is to denoise the optical imaging signal, that is, to filter out the noise in the optical path system and improve the signal-to-noise ratio of the detection device. During the optical imaging process, due to the influence of various factors (such as the fluctuation of the light source, the scattering of the optical fiber, the interference of the environment, etc.), the imaging signal may contain some noise components. The band-pass filter 311 can selectively allow the optical signal within a specific frequency range to pass through, while suppressing or blocking the noise signals in other frequency ranges, so as to obtain the denoised optical imaging signal and improve the clarity and accuracy of the imaging signal.

[0053] The function of the focusing lens 310 is to focus the denoised optical imaging signal. Since the optical imaging signal may be scattered or diverged during transmission, resulting in the signal not being concentrated or clear enough when reaching the photodetector 3041. The focusing lens 310 can refocus these scattered optical signals onto a point, forming a clearer and more concentrated target optical imaging signal, and improving the reception efficiency and conversion accuracy of the photodetector 3041 for the signal.

[0054] Further, after the photodetector 3041 receives the target optical imaging signal processed by the focusing lens 310, the photodetector 3041 will use the photoelectric effect to convert the optical signal into an electrical signal, and finally display the imaging information in the driving integrated control device 3042.

[0055] Based on the above embodiments, the magnification of the first objective lens 3031 is at least 20 times, and the spatial numerical aperture of the first objective lens 3031 is greater than 0.38; the magnification of the second objective lens 3032 is at least 50 times, and the spatial numerical aperture of the second objective lens 3032 is greater than 0.68; the objective lens gap between the first objective lens 3031 and the second objective lens 3032 is less than 700 um (micrometers).

[0056] In the present invention, the magnification of the first objective lens 3031 is at least 20 times, and the spatial numerical aperture is greater than 0.38. The numerical aperture is an important index to measure the light-gathering ability of the objective lens. The larger the numerical aperture, the more light the objective lens can collect, and the higher the imaging resolution and brightness.

[0057] The magnification of the second objective lens 3032 is at least 50 times. Compared with the first objective lens 3031, it provides a higher magnification, can further magnify the observation object, and enables even finer structures to be clearly captured. The spatial numerical aperture of the second objective lens 3032 is greater than 0.68, which is larger than the numerical aperture of the first objective lens 3031, meaning it can collect more light and provide higher imaging resolution and brightness.

[0058] The objective lens gap between the first objective lens 3031 and the second objective lens 3032 is less than 700 um (micrometers), which is a very small distance. This tight configuration helps reduce light loss and scattering between the objective lenses, improving the imaging quality. In this objective lens gap, there is filled with optical fiber refractive index matching oil. The refractive index of this oil is close to that of the optical fiber cladding, which can reduce the refraction of light between the cladding and the oil, thereby further maintaining the clarity and accuracy of imaging.

[0059] The present invention combines the high numerical aperture and tight objective lens configuration of the first objective lens 3031 and the second objective lens 3032, jointly ensuring the clarity and contrast of imaging, enabling high magnification and high-resolution imaging, and being able to accurately capture and measure the geometric parameters of the periodic structure in the optical fiber.

[0060] Based on the above embodiments, the optical fiber fixture 301 includes a first V-groove 3011 and a second V-groove 3012, where: The first V-groove 3011 and the second V-groove 3012 are used to press both ends of the optical fiber to be measured 305 through a pressing block 3013, so that the test part of the optical fiber to be measured 305 is fixed in the optical fiber refractive index matching oil 306.

[0061] In the present invention, the optical fiber fixture 301 mainly includes a first V-groove 3011 and a second V-groove 3012. The design of these two V-grooves is to adapt to and fix different parts of the optical fiber. There is also a pressing block 3013 on the optical fiber fixture 301, which is a component used to press the optical fiber to ensure its stability during the test.

[0062] In the present invention, the first V-groove 3011 and the second V-groove 3012 are respectively used to place both ends of the optical fiber to be measured 305. The design of these two V-grooves takes into account the outer diameters of the cladding and coating of the optical fiber to ensure that the optical fiber can be placed tightly and stably in the grooves. For example, the groove depth of the V-groove for placing the cladding is slightly larger than the outer diameter of the cladding, and the groove depth of the V-groove for placing the coating is slightly smaller than the outer diameter of the coating, to ensure that the optical fiber can be firmly placed in the groove without loosening or jumping out.

[0063] The pressing block 3013 is used to press both ends of the optical fiber to be measured 305, making it closely fit in the first V-groove 3011 and the second V-groove 3012. This not only helps fix the optical fiber but also prevents the optical fiber from jumping out of the V-groove due to external interference during the test. Through the pressing of the pressing block 3013, the test part of the optical fiber to be measured 305 can be stably fixed in the optical fiber refractive index matching oil 306. This fixing method ensures that the test part remains stationary during the test, thereby improving the accuracy and stability of imaging.

[0064] Optionally, in the present invention, the spatial image imaging device 303 is further provided with a rotation controller 3037. The rotation controller 3037 is connected to the first V-groove 3011 and the second V-groove 3012 through a rotatable V-groove 3038. During the test, if the imaging of the optical fiber is not in the middle of the screen, it is used to control the rotation of the two V-grooves within a preset rotation range to ensure clear and centered imaging for easy observation and measurement.

[0065] In the present invention, the coated part of the optical fiber 305 to be tested is placed in a rotatable V-groove and fixed by a pressing block 3013. When the rotation angle of the optical fiber needs to be adjusted, the driving integrated control device 3042 controls the rotation of the rotatable V-groove through the rotation controller 3037. During the test, if the imaging of the optical fiber 305 to be tested is not in the middle of the screen, the driving integrated control device 3042 rotates the optical fiber 305 to be tested to a suitable position through the rotation controller 3037 to ensure clear and centered imaging for easy observation and measurement.

[0066] In the present invention, the driving integrated control device 3042 integrates components such as the photodetector 3041, the first motor controller 3035, the second motor controller 3036, and the rotation controller 3037, realizing centralized control and miniaturized design of the entire test device. Each component can work together to improve the test efficiency and accuracy and reduce the space occupied by the device.

[0067] The driving integrated control device 3042 in the present invention further includes measurement software for analyzing and processing the collected data. The measurement software automatically calculates parameters such as the period pitch and displays the results on the screen for convenient viewing and recording by the user. Moreover, after the test is completed, the measurement software calculates the size of the period pitch based on the data collected by the photodetector and compares it with the standard value to determine whether the test result is qualified.

[0068] Based on the above embodiments, the light source 302 is a broadband light source for emitting visible light or near-infrared light as the test light.

[0069] In the present invention, a broadband light source is a light source capable of emitting light in a wide spectral range. Different from a monochromatic light source (such as a laser), the light emitted by a broadband light source contains light of multiple wavelengths, which cover a relatively wide spectral range. The broadband light source in the present invention can emit visible light and near-infrared light. Among them, the visible light wavelength range is between 400 - 700 nanometers; the near-infrared light covers the range from 700 nanometers to 2500 nanometers.

[0070] Furthermore, the emitted visible light or near-infrared light is used as the test light, which is conducted into the optical fiber to be tested and interacts with the periodic structure inside the optical fiber to be tested. By analyzing the results of the interaction between the test light and the optical fiber, key information such as the geometric parameters of the optical fiber can be obtained.

[0071] In the present invention, the light emitted by the light source 301 is conducted through the fiber bundle and focused by the condenser 308 into a smaller light spot. The diameter of the light spot is controlled within the range of about 50 ± 5 mm. By adjusting the opening size of the diaphragm, the amount of light passing through the diaphragm can be controlled, thereby changing the brightness and size of the light spot.

[0072] Figure 4 It is a schematic flow chart of the method for detecting the geometric parameters of the longitudinally periodic structure optical fiber provided by the present invention. As Figure 4 shown, the present invention provides a method for detecting the geometric parameters of the longitudinally periodic structure optical fiber based on the longitudinally periodic structure optical fiber geometric parameter detection system described in the above embodiments, including: Step 401, after determining that the test part of the optical fiber to be tested is fixed in the optical fiber refractive index matching oil in the spatial image imaging device by the optical fiber fixture, send the test light to the test part through the light source.

[0073] In the present invention, after determining that the test part of the optical fiber to be tested has been firmly fixed in the optical fiber refractive index matching oil in the spatial image imaging device by the optical fiber fixture (such as a V-groove fixture), send the test light to the test part of the optical fiber to be tested through the light source (such as a broadband light source). The light emitted by the light source is visible light or near-infrared light, which has a wide spectral range and can cover various periodic structure characteristics that may exist in the optical fiber. The role of the test light is to illuminate the test part of the optical fiber so that the periodic structure inside it can interact with the light, thereby generating optical signals that can be used for imaging and analysis.

[0074] Step 402, based on the spatial image imaging device, obtain the optical imaging signal corresponding to the test part after the test light passes through the test part in the optical fiber refractive index matching oil.

[0075] In the present invention, based on a spatial image imaging device (including components such as a first objective lens, a second objective lens, and fiber optic refractive index matching oil), an optical signal generated by a periodic structure inside the optical fiber is captured and amplified. Specifically, after the test light passes through the test site in the fiber optic refractive index matching oil, it interacts with the periodic structure inside the optical fiber, such as reflection, scattering, or transmission. The optical signals generated by these interactions are captured by the spatial image imaging device and amplified by the first objective lens and the second objective lens to form a clear optical imaging signal. The first objective lens and the second objective lens in the present invention have a high magnification and a high numerical aperture, which can ensure that the axial periodic structure of the optical fiber can be clearly imaged onto the photodetector; at the same time, the precise distance between the objective lenses and the use of the matching oil further improve the accuracy and stability of the imaging.

[0076] Step 403: Based on the detection device, convert the optical imaging signal into an electrical signal, and obtain the geometric parameters of the periodic structure in the optical fiber to be measured according to the periodic characteristics corresponding to the electrical signal.

[0077] In the present invention, based on a detection device (such as a photodetector, a drive integrated control device, etc.), the optical imaging signal can be converted into an electrical signal and further processed and analyzed. Specifically, the optical imaging signal is received by the photodetector and converted into an electrical signal; then, the drive integrated control device processes the electrical signal, extracts the periodic characteristics corresponding to the periodic structure in the optical fiber, and further, according to the periodic characteristics corresponding to the electrical signal, the geometric parameters of the periodic structure in the optical fiber to be measured can be obtained. For example, by measuring the distance between adjacent peaks or valleys in the electrical signal, the period pitch of the optical fiber can be determined. The entire position control accuracy is at the micron level (such as 1um), and the error range is within a very small range (such as within 0.1%), thus ensuring the accuracy of the measurement.

[0078] Finally, through the measurement software in the drive integrated control device, the information of multiple period pitches can be visually displayed, and the geometric parameters of the periodic structure in the optical fiber to be measured can be calculated.

[0079] The method for detecting the geometric parameters of a longitudinally periodic structure optical fiber provided by the present invention fixes the optical fiber to be measured in the fiber optic refractive index matching oil of the spatial image imaging device through a fiber fixture, and then emits test light from a light source to a condenser lens. After being focused, the test light is sequentially directed to the imaging device and the detection device. After the test light passes through the test site, the imaging device moves along the optical fiber axis at a preset rate to form an optical imaging signal, enabling the detection device to accurately obtain the geometric parameters of the periodic structure of the optical fiber to be measured, and improving the detection accuracy and reliability.

[0080] In an embodiment, the process of the method for detecting the geometric parameters of a longitudinally periodic structure optical fiber provided by the present invention is described as a whole. The specific steps are as follows: Step 1: Adjust the relative spacing (i.e., the objective lens gap) between the first objective lens and the second objective lens to 600um ± 50um, and the axial distance to 10mm ± 0.1mm. Then, use a disposable dropper to suck a small amount of matching oil from the matching oil cartridge and drop it into the objective lens gap. The matching oil is adsorbed in the objective lens gap due to surface tension.

[0081] Step 2: Through the zeroing function of the motor controller, zero the position of the motor in the drive integrated control device to zero the position of the objective lens.

[0082] Step 3: Prepare the optical fiber sample to be measured: Take 15 - 20 cm of the optical fiber to be measured, keep 5 - 10 cm of the coating layer unpeeled, peel off the coating layer of the rest part, and wipe the surface of the cladding with anhydrous ethanol.

[0083] Step 4: According to the outer diameters of the cladding and the coating layer of the optical fiber to be measured, select a V - groove fixture that matches the size of the optical fiber. Among them, for the part with the coating layer, select a V - groove fixture with a groove depth slightly smaller than the outer diameter of the coating layer, and for the part with the cladding, select a V - groove fixture with a groove depth slightly larger than the outer diameter of the cladding.

[0084] Step 5: Place the coating layer part of the optical fiber to be measured in the rotatable V - groove fixture and fix it with a pressing block; place the two ends corresponding to the cladding part in the first V - groove and the second V - groove respectively, and immerse the middle part of the cladding in the matching oil in the objective lens gap.

[0085] Step 6: Turn on the white light source, the first linear displacement stage, the second linear displacement stage, the first motor controller, the second motor controller, the rotation controller, the photodetector, and the drive integrated control device in sequence. The broadband light emitted by the white light source is conducted to the focusing lens through the optical fiber bundle, focused by the condenser lens into a light spot with a diameter of about 50 ± 5 mm, and then adjust the size of the light spot through the aperture.

[0086] Step 7: The high magnification and high numerical aperture of the first objective lens and the second objective lens ensure that the axial periodic structure of the optical fiber to be measured can be clearly imaged on the photodetector. The precise spacing between them and the use of the matching oil further improve the accuracy and stability of the imaging.

[0087] Step 8: Through the position control function of the drive integrated control device, move the positions of the first objective lens and the second objective lens with an accuracy of 1um, which is equivalent to moving the optical fiber in the axial direction. Take the starting point of one period as the starting position of the optical fiber. If the imaging is not in the middle of the screen, adjust the position to the middle through the rotation controller.

[0088] Step 9: The periodic structure in the optical fiber under test changes with the moving position and finally returns to the starting point. First, record the starting point. After moving a certain distance from the starting point, if it can return to the original point, it indicates that the optical fiber has passed through a complete cycle. The distance of a complete cycle is the period pitch, generally on the order of sub-millimeters. The overall position control accuracy is 1 μm, and the error range is within 0.1%. The information of multiple period pitches can be displayed in the drive integrated control device. Through the measurement software in the drive integrated control device, taking the peak or valley of a periodic structure as the starting point L1, moving the measurement distance to the next peak or valley L2, and calculating the corresponding distance of L2 - L1, the period pitch of a complete cycle can be obtained, ultimately achieving the precise measurement of the period pitch.

[0089] The present invention realizes the precise measurement of the period pitch of the characteristic optical fiber, and has the advantages of simple structure, convenient operation, high test accuracy, and fast test speed.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. However, such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A longitudinal periodic structure optical fiber geometric parameter detection system, characterized in that: It includes an optical fiber fixture, a light source, a space image forming device and a detection device, wherein: The optical fiber clamp is used to fix the test portion of the optical fiber to be tested in the optical fiber refractive index matching oil in the spatial image imaging device, wherein the optical fiber to be tested is composed of a main core and a side core, the side core is a periodic structure formed in a preset pitch distribution manner around the main core, and the coating layer of the test portion has been stripped; the refractive index of the optical fiber refractive index matching oil is determined based on the refractive index of the cladding of the optical fiber to be tested; The light source is used to emit test light to the condenser through the optical fiber bundle, and the test light is focused into a focused light spot by the condenser and then emitted to the spatial image forming device and the detection device in sequence; The spatial image imaging device is used to move along the axis direction of the optical fiber to be tested based on a preset moving speed after the test light passes through the test part in the optical fiber refractive index matching oil, so as to form an optical imaging signal corresponding to the test part; The detection device is used to obtain the geometric parameters of the periodic structure in the optical fiber to be tested according to the optical imaging signal; Wherein, the light source, the condenser and the space image forming device are on the same optical axis.

2. The longitudinal periodic structure optical fiber geometric parameter detection system according to claim 1, characterized in that: The optical axis between the condenser and the aerial image imaging device is provided with an aperture, and the aperture is used to adjust the amount of light of the focused light spot emitted to the aerial image imaging device.

3. The longitudinal periodic structure optical fiber geometric parameter detection system according to claim 2, characterized in that: The detection device includes a photoelectric detector and a drive integrated control device, wherein: The photoelectric detector is used to receive the optical imaging signal sent by the image forming device and convert the optical imaging signal into a corresponding electrical signal; The drive integrated control device is used to obtain the geometric parameters of the periodic structure in the optical fiber to be tested according to the periodic characteristics corresponding to the electrical signal.

4. The longitudinal periodic structure optical fiber geometric parameter detection system according to claim 3, characterized in that: The spatial image imaging device comprises a first objective lens and a second objective lens, wherein the first objective lens and the second objective lens are located on the same optical axis, and the optical fiber refractive index matching oil is adsorbed in the objective lens gap between the first objective lens and the second objective lens, wherein: The first objective lens is used to perform a first amplification process on the focused light spot emitted by the condenser, and emit the focused light spot after the first amplification process to the optical fiber refractive index matching oil; The second objective lens is used to perform a second amplification process on the focused light spot after the first amplification process at the test site in the optical fiber refractive index matching oil, so as to generate an optical imaging signal corresponding to the test site.

5. The longitudinal periodic structure optical fiber geometric parameter detection system according to claim 4, characterized in that: The first objective lens is provided with a first linear translation stage, and the second objective lens is provided with a second linear translation stage, wherein: The first linear translation stage and the second linear translation stage are used to adjust the spatial position between the first objective lens and the second objective lens along the axial direction of the optical fiber to be tested according to the control instructions sent by the drive integrated control device, so as to obtain the geometric parameters corresponding to at least one periodic structure of the optical fiber to be tested.

6. The longitudinal periodic structure optical fiber geometric parameter detection system according to claim 4, characterized in that: A focusing lens and a bandpass filter are also provided between the second objective lens and the photodetector, wherein: The bandpass filter is used to perform denoising on the optical imaging signal to obtain the denoised optical imaging signal; The focusing lens is used to focus the denoised optical imaging signal to obtain a target optical imaging signal; The photodetector is also used to convert the target optical imaging signal into the corresponding electrical signal.

7. The longitudinal periodic structure optical fiber geometric parameter detection system according to claim 4, characterized in that: The magnification of the first objective lens is at least 20 times, and the spatial numerical aperture of the first objective lens is greater than 0.38; the magnification of the second objective lens is at least 50 times, and the spatial numerical aperture of the second objective lens is greater than 0.68; the objective lens gap between the first objective lens and the second objective lens is less than 700um.

8. The longitudinal periodic structure optical fiber geometric parameter detection system according to claim 1, characterized in that: The optical fiber clamp comprises a first V-shaped groove and a second V-shaped groove, wherein: The first V-shaped groove and the second V-shaped groove are used to press the two ends of the optical fiber to be tested through a pressing block so that the test portion of the optical fiber to be tested is fixed in the optical fiber refractive index matching oil.

9. The longitudinal periodic structure optical fiber geometric parameter detection system according to claim 1, characterized in that: The light source is a broadband light source, which is used to emit visible light or near-infrared band light as the test light.

10. A method for detecting geometric parameters of a longitudinal periodic structure optical fiber based on the longitudinal periodic structure optical fiber geometric parameter detection system according to any one of claims 1 to 9, characterized in that: include: After determining that a test portion of the optical fiber to be tested is fixed by an optical fiber clamp to the optical fiber refractive index matching oil in the spatial image imaging device, sending a test light to the test portion through a light source; Based on the spatial image imaging device, an optical imaging signal corresponding to the test part formed after the test light passes through the test part in the optical fiber refractive index matching oil is obtained; Based on the detection device, the optical imaging signal is converted into an electrical signal, and according to the periodic characteristics corresponding to the electrical signal, the geometric parameters of the periodic structure in the optical fiber to be tested are obtained.

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