CN115250144A - Multi-core optical fiber visual coupling and large dynamic range crosstalk testing method and device - Google Patents
Multi-core optical fiber visual coupling and large dynamic range crosstalk testing method and device Download PDFInfo
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Abstract
The invention discloses a method and a device for testing multi-core optical fiber visual coupling and large dynamic range crosstalk, and belongs to the field of optical communication and information optics. The method uses a beam of reverse illumination light to be input from the tail end of the multi-core optical fiber, the reverse illumination light covers the whole cladding of the tail end of the multi-core optical fiber in size, can be respectively transmitted in a plurality of different fiber cores of the multi-core optical fiber and illuminates the fiber cores, and coupled incident light reflected from the head end of the optical fiber and a front section of optical path are received by a camera together, so that the coupling process is visualized. When the coupling of a certain fiber core of the multi-core optical fiber is completed, the crosstalk test with a large dynamic range can be realized by measuring the output optical field intensity diagram of the fiber core under different input optical powers and camera exposure time. The invention has the advantages of clear and visible coupling whole process dynamic state, micron-level coupling precision, random switching of the tested multi-core fiber, convenient and accurate coupling adjustment and the like in the multi-core fiber coupling and large dynamic range crosstalk test, thereby having great application potential.
Description
Technical Field
The invention belongs to the field of optical communication and information optics, and particularly relates to a method and a device for testing multi-core optical fiber visual coupling and large dynamic range crosstalk.
Background
In recent years, due to an explosive increase in demand for communication capacity, the space division multiplexing technique is one of the candidates for coping with the increasing communication capacity. The spatial division multiplexing technology based on special optical fibers comprises two transmission technologies of transmitting a plurality of different spatial orthogonal modes in the fiber cores of optical fibers (few-mode optical fibers, annular core optical fibers and the like) supporting a plurality of modes and transmitting different information by using different fiber cores of multi-core optical fibers. The multi-core optical fiber has the advantages that crosstalk among different fiber core channels is small, signal quality of each channel when a plurality of fiber cores transmit information at the same time can be guaranteed, and the multi-core optical fiber has a wide application prospect. In addition, the multi-core optical fiber has a wide application in the fields of optical fiber sensing and the like because of the special core distribution of the multi-core optical fiber.
In various applications of multi-core fibers, it is necessary to couple light beams into different cores of the multi-core fiber for propagation. Since the core size of a multicore fiber is often in the order of microns, the coupling input light needs to be very strictly aligned with the core, and the light spot size cannot be much larger than the core size, so as to prevent the light spot from affecting other cores on the same cladding. At present, the coupling and crosstalk test methods of the multi-core optical fiber are many, and can be summarized into two types. One of the methods is to realize fan-in and fan-out of the multi-core optical fiber by adopting the schemes of optical fiber melting tapering, optical fiber corrosion, integrated waveguide and the like; the other is the convergence of a beam or an array of beams in free space through an objective lens or lens so that the beams are coupled into the cores of the multicore fiber. The second method has the advantage that the tested multi-core fiber can be switched at will, so that the process operations such as fused coupling tapering and the like are not required to be carried out in each coupling test, and the method can be applied to wider multi-core fiber testing application scenarios. However, coupling from the millimeter-scale dimension of the free-space beam through an objective lens or lens to the micron-scale dimension of the multicore fiber core often suffers from misalignment and spot size variation. At present, most researchers can only roughly judge the coupling condition of the input end of the optical fiber according to the optical power and the optical field distribution of the output end of the multi-core optical fiber. However, the lack of visualization process for coupling the input to the core makes the coupling and testing of the multicore fiber cumbersome. Therefore, it becomes an important challenge to establish a set of visualization system, so that the position of the fiber core where the light spot is incident and the size relationship between the light spot and the fiber core can be clearly seen in the coupling and large dynamic range crosstalk test of the multi-core fiber.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method and a device for testing the multi-core optical fiber visual coupling and the large dynamic range crosstalk, aims to establish a visual system during the multi-core optical fiber coupling as a judgment basis for the coupling effect, aims to establish the visual system by using devices as few as possible, and can clearly see the position of a light spot incident on a fiber core and the size relation between the light spot and the fiber core during the multi-core optical fiber coupling and large dynamic range crosstalk test.
In order to achieve the above object, the present invention provides a method for testing the visual coupling and the large dynamic range crosstalk of a multi-core fiber, in which a forward incident coupled light beam is converged by a high power objective lens and incident on the surface of the head end of the multi-core fiber, and simultaneously, a backward illumination light beam with a larger divergence angle is converged by a low power objective lens and incident on the surface of the tail end of the multi-core fiber, so that the light spot size covers the whole cladding. The positions of different fiber cores can be marked by the reversely transmitted illumination light beams through the fiber cores, and all the fiber cores illuminated by the reverse illumination light beams and light spots reflected by the front-end incident light beams on the surface of the optical fiber can be seen by observing the front end by using a camera. The position of the head end of the optical fiber is finely adjusted according to a real-time image observed by the front-end camera, when a light spot is observed to be incident on a target fiber core and the size of the light spot is matched with that of the fiber core, the best light beam incident coupling effect is achieved, and the coupled fiber core can be quickly switched according to the front-end camera. After the coupling of the target fiber core is completed, the output optical field intensity graphs of the target fiber core under the conditions of low-power light input, low-camera exposure time, high-power light input and high-camera exposure time are respectively recorded, and the multi-core fiber crosstalk test in a large dynamic range is realized through gray value comparison.
Further, recording an output optical field intensity diagram of the coupled input light beam under the conditions of the first input optical power and the first camera exposure time, and calculating the output power of the coupled fiber core by using gray values of an output optical field of the coupled fiber core in the optical field; recording an output light field intensity graph of the coupled input light beam under the conditions of second input light power and second camera exposure time, and calculating crosstalk light output power of other fiber cores by dividing gray values of output light fields of other fiber cores in the light field by incident light power change multiplying power and camera exposure time change multiplying power in two times of measurement; the first input optical power is less than the first camera exposure time, and the second input optical power is less than the second camera exposure time;
the measured crosstalk value is obtained by calculating the output power difference value of the coupling fiber core and other fiber cores, and the measured dynamic range depends on the highest gray value and the lowest gray value range received by the pixel point of the camera and the input light power change range and the camera exposure time change range in the two measurements, so that the dynamic range of the crosstalk test can be effectively improved by adjusting the input light power change range and the camera exposure time change range in the two measurements.
As an improvement of the above technical solution, when measuring the output powers of other fiber cores under the conditions of the second input optical power and the second camera exposure time, the spatial optical method is used to shield or attenuate the light beam output by the coupling fiber core, while the crosstalk light beams output by other fiber cores are received unaffected, so as to allow higher input optical power on the premise of preventing the camera from being damaged by the optical field output by the coupling fiber core with too high power, thereby further improving the dynamic range of the crosstalk test.
As an improvement of the above technical solution, the method further includes additionally introducing a beam of forward illumination light to illuminate the cladding of the multi-core fiber from the forward direction for imaging the cladding on the input end face of the multi-core fiber, thereby improving the effect of visual coupling and improving the crosstalk test accuracy.
The invention provides a multi-core optical fiber visual coupling and large dynamic range crosstalk testing device, which comprises a first beam splitter, a first objective lens, an optical fiber coupling platform, a multi-core optical fiber, an optical fiber emergent end mechanical fixing part, a second objective lens, a second beam splitter, a first lens, a first camera, a second lens and a second camera. The incident coupling light beam penetrates through the first beam splitter in a perpendicular mode, the incident coupling light beam is converged through the first objective lens and enters the cladding surface of the head end of the multi-core optical fiber placed on the optical fiber coupling platform, the backward illumination light beam penetrates through the second beam splitter in a perpendicular mode, the second objective lens is used for converging the backward illumination light beam and then covers the whole cladding surface of the tail end of the multi-core optical fiber, the light beam propagates in the backward mode along different fiber cores of the multi-core optical fiber, the head end of the optical fiber is amplified through the first objective lens and then is reflected through the first beam splitter, the first lens is used for converging the backward illumination light beam, and therefore the backward illumination light beam is received by the first camera, and the positions of the different fiber cores are calibrated through the first camera. Meanwhile, the reflected light beam of the incident coupling light beam incident on the surface of the head end of the optical fiber passes through the first beam splitter and is received by the first camera after the first lens, so that the first camera can see the fiber core distribution and the position of the light spot incident on the surface of the optical fiber, and the displacement of the head end of the multi-core optical fiber can be easily finely adjusted according to the image of the first camera to achieve the best coupling effect. Meanwhile, the tail end of the multi-core optical fiber is connected to the mechanical fixing piece, and is reflected by the second beam splitter, the second lens converges, and the output light field can be seen in the second camera. After the coupling of the target fiber core is completed, the output optical field intensity graphs of the target fiber core under the conditions of low-power light input, low-camera exposure time, high-power light input and high-camera exposure time are respectively recorded, and the multi-core fiber crosstalk test in a large dynamic range is realized through gray value comparison.
The first lens is preferably a high power objective lens, and the second lens is preferably a low power objective lens.
As an improvement of the technical scheme, a third beam splitter is added in front of a first beam splitter of the device, the third beam splitter has the function of combining the incident coupling light beams and the newly added front-end forward illumination light beams to be in a coaxial state, the forward illumination light beams can image a cladding on the end face of the input end of the multi-core optical fiber, and therefore the visual coupling effect is improved, and the crosstalk test accuracy is improved. The size of the front-end forward illumination light beam is larger, the divergence angle of the front-end forward illumination light beam is finely adjusted, the forward illumination light beam covers the surface of the cladding at the head end of the whole multi-core optical fiber after being converged by the first objective lens, and therefore the forward illumination light beam can be seen at the first camera not only through each fiber core and an incident light spot of the multi-core optical fiber in the technical scheme, but also through the cladding of the multi-core optical fiber, and the visual system is more complete and abundant due to the supplement.
As an improvement of the above technical solution, in a free space optical path of the multi-core optical fiber output optical field, when measuring high input optical power and high camera exposure time, a small-sized barrier or a micro-attenuation sheet is inserted by using a space optical method, so that only the coupling fiber core output light beam is shielded or attenuated, and the crosstalk light beams of other fiber core light beams are received by the second camera without being affected, thereby further improving the dynamic range of the crosstalk test.
Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:
1. compared with the traditional multi-core optical fiber coupling system, the system enables the coupling process to be visualized, can assist an operator to quickly and simply complete any multi-core optical fiber coupling alignment, and improves the coupling effect.
2. The optical fiber placed on the optical fiber coupling platform can be switched at will, new optical fiber coupling can be realized quickly after each switching, the optical fiber coupling platform can be used as a multi-core optical fiber testing system, and the system can be used for dealing with various multi-core optical fibers.
3. According to the invention, the front-end high-power objective lens and the lens form an amplification system, so that the position of the fiber core of the optical fiber with the micron scale is calibrated, and the micron-scale coupling precision can be realized.
4. The invention provides a visual testing method for crosstalk between cores with a large dynamic range.
5. The invention can realize the coupling of various different light beam arrays to the multi-core optical fiber, and the special light beam array coupling is the necessary input condition of the multi-core optical fiber communication system or the sensing system, thereby showing the expandability of the invention.
Drawings
Fig. 1 is a schematic diagram of a multi-core optical fiber visual coupling and large dynamic range crosstalk testing method provided by the present invention.
Fig. 2 is a schematic structural diagram of a multi-core optical fiber visual coupling and large dynamic range crosstalk testing apparatus provided by the present invention.
FIG. 3 is a real-time coupling situation recorded by the first camera 9 when the apparatus of FIG. 2 is used to implement the five-core optical fiber, wherein (a) is the fiber core distribution situation recorded by the camera when the front-end coupling input light is covered and only the back-end backward illumination light is input; (b) The coupling input light and the reverse illumination light are all started, and the coupling is adjusted to enable the light beams to be incident on the middle fiber core and to be recorded when the sizes are matched; (c) Is a real-time image recorded when the coupled beam is misaligned laterally (x-axis direction in fig. 1) with respect to the central core; (d) Is a real-time image recorded when the coupled beam is not longitudinally (y-axis direction in fig. 1) aligned with the central core; (e) Is a real-time image recorded when the coupled beam is misaligned with the central core both laterally and longitudinally (in the x-axis and y-axis directions in fig. 1); (f) Is a real-time image recorded when the coupled beam axial (optical axis direction in fig. 2 and z-axis direction in fig. 1) adjustment has not reached the most suitable position.
FIG. 4 is a partial result of a five-core fiber crosstalk matrix measured using the apparatus of FIG. 2 provided by the present invention, where (a) is the front-end core profile recorded using the first camera 9; (b) Is the corresponding distribution of the different core outputs recorded by the second camera 11; (c) Is a real-time image recorded by the first camera 9 when the light beam is adjusted to be coupled and input into the middle fiber core; (d) Adjusting the output light field of the central fiber core when the light intensity of the coupled input light is weak and the exposure time of the second camera 11 is low; (e) The coupling input light is adjusted to be in the output light field of the central fiber core when the light intensity is stronger and the exposure time of the second camera 11 is higher.
FIG. 5 is a graph of all results of measuring a five-core fiber crosstalk matrix using the apparatus of FIG. 2 provided by the present invention. The five images in (a) are real-time images recorded by a first camera 9 when the coupling position is adjusted to enable light beams to enter along five different fiber cores in sequence; (b) The five diagrams in the middle are sequentially the output optical fields recorded by the second camera 11 under the conditions of the input of the different fiber cores and weak input coupling light (applying 12dB attenuation) and short exposure time (0.1 ms); (c) The five diagrams in the middle are sequentially the output light fields recorded by the second camera 11 under the different fiber core input conditions when the input coupling light is strong (0 dB attenuation is applied) and the exposure time is long (10 ms); (d) The five-core optical fiber crosstalk matrix obtained according to the image measurement is shown in the figure.
Fig. 6 is a schematic structural diagram of an improved multi-core optical fiber visual coupling and large dynamic range crosstalk testing apparatus provided by the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, the present invention provides a method for testing visual coupling and large dynamic range crosstalk of a multi-core optical fiber, which has the following specific implementation:
the figure shows that the multi-core optical fiber to be coupled and tested for the large dynamic range crosstalk is input with the input coupling light from the head end of the right optical fiber, and the reverse illumination light is input from the tail end of the optical fiber in the reverse direction. The light spot and the light spot reflected by the head end of the multi-core optical fiber are received by the camera together with the input coupling light, so that the real-time image of the light spot and each fiber core can be seen at the camera, and the position of the optical fiber is finely adjusted according to the image to achieve the best coupling effect.
As shown in fig. 2, the invention provides a multi-core fiber visual coupling and large dynamic range crosstalk testing apparatus, which has the following specific implementation modes:
the device comprises a first beam splitter 1, a first objective lens 2, an optical fiber coupling platform 3, a multi-core optical fiber 4, an optical fiber emergent end mechanical fixing piece 5, a second objective lens 6, a second beam splitter 7, a first lens 8, a first camera 9, a second lens 10 and a second camera 11. The first objective lens 2 is a high power objective lens, and the second objective lens 6 is a low power objective lens. The dotted line in the figure is the optical axis direction of the light beam transmission, and the transmission paths of the input coupling light and the reverse illumination light in the figure are described below respectively. The input coupling light is transmitted through the first beam splitter 1, and is incident to the end face of the head end of the multi-core optical fiber 4 placed on the optical fiber coupling platform 3 after being converged by the first objective lens 2, the incident coupling light is reflected at the end face, the reflected light is opposite to the incident light, the incident coupling light is reflected by the first beam splitter 1 after passing through the first objective lens 2, and is received by the first camera 9 after passing through the first lens 8, so that the camera can see light spots incident on the end face. The backward illumination light beam has a larger size, and can still cover all the fiber cores at the tail end of the multi-core fiber after passing through the second beam splitter 7 and the second objective lens 6, so that the illumination light beam is transmitted backward from the mechanical fixing part at the fiber exit end to the head end of the multi-core fiber placed on the fiber coupling platform along all the fiber cores. The light emitted from the head end of the optical fiber also passes through the first objective lens 2, the first beam splitter 1 and the first lens 8, and is received by the first camera 9, so that the distribution of the fiber core can be seen in the field of view of the first camera 9. When the multi-core optical fiber is coupled, the displacement of the optical fiber coupling platform can be adjusted in real time according to the image in the first camera 9, and a micron-sized high-precision coupling effect is achieved. After the coupling adjustment is completed, obviously, the input coupling light is transmitted through the multi-core optical fiber 4, is emitted from the optical fiber emitting end mechanical fixing part 5, is transmitted through the second objective lens 6, is reflected by the second beam splitter 7 and is converged by the second lens 10, and finally, the output light field is received by the second camera 11.
As shown in fig. 3, a graph of the results recorded by the first camera 9 is obtained by performing five-core fiber visual coupling and large dynamic range crosstalk test using the apparatus in fig. 2 as an example. The fiber core distribution condition recorded by the camera when the coupled input light at the front end is covered and only the backward illumination light at the rear end is input is obtained; (b) Coupling input light and reverse illumination light are all started, and coupling is adjusted to enable the light beams to be incident on the middle fiber core and to be recorded when the sizes are matched; (c) Is a real-time image recorded when the coupled beam is misaligned laterally (x-axis direction in fig. 1) with respect to the central core; (d) Is a real-time image recorded when the coupled beam is not longitudinally (y-axis direction in fig. 1) aligned with the central core; (e) Is a real-time image recorded when the coupled beam is misaligned with the central core both laterally and longitudinally (in the x-axis and y-axis directions in fig. 1); (f) Is a real-time image recorded when the coupled beam axial (optical axis direction in fig. 2 and z-axis direction in fig. 1) adjustment has not reached the most appropriate position.
As shown in fig. 4, the apparatus in fig. 2 is used as an example to perform a five-core optical fiber visual coupling and crosstalk matrix test. Wherein (a) is the front end core profile recorded using the first camera 9; (b) The corresponding distribution of different fiber core outputs recorded by the second camera 11 corresponds to the fiber core distribution of the output end of the five-core optical fiber; (c) The real-time image recorded by the first camera 9 when the light beam is adjusted to be coupled and input into the middle fiber core; (d) Adjusting the output light field of the central fiber core when the light intensity of the coupling input light is weak (12 dB attenuation is applied to the input coupling light) and the exposure time of the second camera 11 is low (0.1 ms); (e) The output optical field of the central fiber core is adjusted when the exposure time of the second camera 11 is high (10 ms) because the coupling input light intensity is strong (no attenuation is applied to the coupling input light, namely 0dB attenuation). The cross talk from the center core to the other four cores is then calculated as follows: firstly, the light spot of the central fiber core is intercepted from the light field intensity diagram of the diagram (d), the total gray value is calculated and is marked as I 1 (ii) a Then, the light spots of the other four fiber cores are cut out from the light field intensity diagram of (e) in FIG. 4, and the total gray values thereof are calculated and respectively marked as I 2 ,I 3 ,I 4 ,I 5 Then the specific crosstalk value can be calculated as:
wherein XT 1,i Representative are the i-th core to center core crosstalk values, 32dB from the 12dB input optical power difference and the 20dB (10 ms/0.1ms =100 times) camera exposure time difference.
As shown in fig. 5, all the results obtained from the five-core fiber visual coupling and crosstalk matrix test using the apparatus of fig. 2 as an example. The five images in (a) are real-time images recorded by a first camera 9 when the coupling position is adjusted to input five different fiber cores; (b) The five diagrams in the middle are sequentially the output optical fields recorded by the second camera 11 under the conditions of the input of the different fiber cores and weak input coupling light (applying 12dB attenuation) and short exposure time (0.1 ms); (c) The five diagrams in the middle are sequentially the output light fields recorded by the second camera 11 under the different fiber core input conditions when the input coupling light is strong (0 dB attenuation is applied) and the exposure time is long (10 ms); (d) The specific test path of the five-core optical fiber crosstalk matrix (unit: dB) obtained by the image measurement is consistent with the crosstalk test process of the central fiber core and the other four fiber cores introduced in the figure 4.
As shown in fig. 6, the invention provides an improved apparatus for multi-core fiber visual coupling and large dynamic range crosstalk test, and the specific implementation manner is as follows:
the device comprises a first beam splitter 1, a first objective lens 2, an optical fiber coupling platform 3, a multi-core optical fiber 4, an optical fiber emergent end mechanical fixing piece 5, a second objective lens 6, a second beam splitter 7, a first lens 8, a first camera 9, a second lens 10, a second camera 11 and a third beam splitter 12. The dotted line in the figure is the optical axis direction of the light beam transmission, and the transmission paths of the input coupling light and the backward illumination light are the same as those in fig. 2, so that only the transmission path of the forward illumination light added by the improved device will be described here. The forward illumination light is transmitted through the third beam splitter 12, the first beam splitter 1 is converged by the first objective lens 2 and then is incident on the section of the head end of the multi-core fiber 4, the size of the forward illumination light is large, and the converged light beam can be ensured to cover the whole fiber cladding. The illumination light is reflected at the cross section, passes through the first objective lens 2, the first beam splitter 1, the first lens 8 and is then received by the first camera 9, where the imaging of the cladding can be observed. After the forward illumination light is added, the first camera 9 can see clear fiber cladding, fiber core distribution and incident light spots, and the effect of the visualization system is further improved by the supplement.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. A multi-core optical fiber visual coupling and large dynamic range crosstalk testing method is characterized by comprising the following steps:
when a coupled input light is used for being input from the head end of the multi-core optical fiber in the forward direction, a reverse illumination light beam which covers the whole cladding in size is input from the tail end of the multi-core optical fiber in the reverse direction;
the backward illumination light beams are propagated along a plurality of fiber cores of the multi-core optical fiber, then are output from the head end of the multi-core optical fiber, are received after being transmitted in free space, and are used for calibrating the position distribution of different fiber cores; the coupling input light is incident on the surface of the head end of the multi-core optical fiber and is received after being reflected, and the coupling input light is used for acquiring a real-time image when the coupling input light is incident on the surface of the head end of the multi-core optical fiber during the coupling of the multi-core optical fiber; adjusting the position of the surface of the head end of the multi-core optical fiber according to the real-time image to enable the coupling input light beam to enter a preset coupling fiber core, wherein the size of the light spot is matched with the size of the fiber core, and the coupling of the target fiber core is completed;
recording an output light field intensity graph of the coupled input light beam under the conditions of first input light power and first camera exposure time, and calculating the output power of the coupled fiber core by using gray values of an output light field of the coupled fiber core in the light field; recording an output light field intensity diagram of the coupled input light beam under the conditions of second input light power and second camera exposure time, and calculating the crosstalk light output power of other fiber cores by dividing gray values of output light fields of other fiber cores in the light field by incident light power change multiplying power and camera exposure time change multiplying power in two times of measurement; the first input optical power is less than the second input optical power, and the first camera exposure time is less than the second camera exposure time;
the measured crosstalk value is obtained by calculating the output power difference value of the coupling fiber core and other fiber cores, and the measured dynamic range depends on the highest gray value and the lowest gray value range received by the pixel point of the camera and the input light power change range and the camera exposure time change range in two measurements.
2. The multi-core fiber visual coupling and large dynamic range crosstalk testing method according to claim 1, wherein when measuring output powers of other fiber cores under the conditions of second input optical power and second camera exposure time, a spatial optical method is used, so that light beams output by the coupled fiber cores are shielded or attenuated, crosstalk light beams output by the other fiber cores are received unaffected, and higher input optical power is allowed on the premise that a camera is prevented from being damaged by an output optical field of the coupled fiber cores with too high power, so as to further improve a dynamic range of crosstalk testing.
3. The method as claimed in claim 1, further comprising introducing a forward illumination beam to illuminate the cladding of the multi-core fiber from the forward direction for imaging the cladding at the input end face of the multi-core fiber.
4. The multi-core optical fiber visual coupling and large dynamic range crosstalk testing device is characterized by comprising a first beam splitter (1), a first objective lens (2), an optical fiber coupling platform (3), a multi-core optical fiber (4), an optical fiber outgoing end mechanical fixing piece (5), a second objective lens (6), a second beam splitter (7), a first lens (8), a first camera (9), a second lens (10) and a second camera (11);
the coupling input light part is directly communicated with a first beam splitter (1), converged into a multi-core optical fiber core (4) placed on an optical fiber coupling platform (3) through a first objective lens (2), output from an optical fiber exit end mechanical fixing piece (5) through optical fiber transmission, collimated by a second objective lens (6), reflected by a second beam splitter (7), converged by a second lens (10) and received by a second camera (11) to obtain an output light field, and the output light field received by the second camera (11) is used for optical fiber large dynamic range crosstalk testing;
the backward illumination light part is directly communicated with the second beam splitter (7), the light field converged by the second objective lens (6) reversely enters the multi-core optical fiber (4) of the optical fiber exit end mechanical fixing piece (5), the cladding of the multi-core optical fiber (4) is completely covered to illuminate all fiber cores, the illumination light is output from the optical fiber coupling platform (3), the part of the illumination light is reflected by the first beam splitter (1) after passing through the first objective lens (2), the illumination light is converged by the first lens (8) and then received by the first camera (9), besides, the coupling input light is partially reflected and reversely transmitted at the end face of the multi-core optical fiber (4), the part of the coupling input light is reflected by the first beam splitter (1) after passing through the first objective lens (2), and then the coupling light is received by the first camera (9) after passing through the first lens (8), and the light spots at the end face of the optical fiber and the fiber cores are used for realizing visual coupling when the coupling is observed at the first camera (9).
5. The device according to claim 4, further comprising a free space shield disposed between the fiber exit end mechanical fixture (5) and the second beam splitter (7) or the second beam splitter (7) and the second camera (11), so that the light beams output by the coupled fiber cores are shielded or attenuated, and the crosstalk light beams output by other fiber cores are received unaffected, thereby allowing higher input optical power on the premise of preventing the camera from being damaged by the optical field output by the coupled fiber cores with too high power, so as to further improve the dynamic range of crosstalk testing.
6. The device according to claim 4, further comprising a third beam splitter (12) arranged at the front end of the first beam splitter (1) and the forward illumination beam, wherein the third beam splitter (12) is used for combining the forward illumination beam and the input coupling beam to a coaxial state, and the forward illumination beam can image the cladding of the input end face of the multi-core optical fiber.
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