CN115250144B - Visual coupling and large dynamic range crosstalk testing method and device for multi-core optical fiber - Google Patents
Visual coupling and large dynamic range crosstalk testing method and device for multi-core optical fiber Download PDFInfo
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Abstract
The invention discloses a method and a device for testing visual coupling and large dynamic range crosstalk of a multi-core optical fiber, 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 size of the reverse illumination light covers the whole cladding of the tail end of the multi-core optical fiber, the reverse illumination light can be respectively transmitted in a plurality of different fiber cores of the multi-core optical fiber and can illuminate the multi-core optical fiber, and the reverse illumination light and the coupling incident light reflected from the head end of the multi-core optical fiber are received by a camera together in a front section optical path, so that the coupling process is visualized. When the coupling of a certain fiber core of the multi-core optical fiber is completed, the large dynamic range crosstalk test can be realized by measuring the output light field intensity diagram of the fiber core under different input light power and camera exposure time. The invention has the advantages of clear and visible coupling whole process dynamic state, coupling precision reaching micron level, random switching of the measured multi-core optical fiber, convenient and accurate coupling adjustment and the like in the coupling of the multi-core optical fiber and the 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 visual coupling and large dynamic range crosstalk test of a multi-core optical fiber.
Background
In recent years, due to explosive growth in demand for communication capacity, space division multiplexing technology is one of candidate technologies for coping with increasing communication capacity. Space division multiplexing technology based on special optical fibers includes two transmission technologies of transmitting a plurality of different spatial orthogonal modes in the 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 cores of multi-core optical fibers. The multi-core optical fiber has very wide application prospect because crosstalk among channels of different fiber cores is very small, so that signal quality of each channel can be ensured when a plurality of fiber cores transmit information simultaneously. In addition, the multi-core optical fiber has wide application in the fields of optical fiber sensing and the like because of special fiber core distribution.
In various applications of multi-core fibers, it is desirable to couple the light beam into different cores of the multi-core fiber for propagation. Since the core size of a multicore fiber is often on the order of microns, the coupled-in light needs to be very tightly aligned to the core and the spot size cannot be much larger than the core size to prevent the spot from affecting other cores on the same cladding. The coupling and crosstalk testing methods of the multi-core optical fiber at present are numerous and can be summarized into two types. One of the methods is to realize fanning-in and fanning-out of a multi-core optical fiber through the schemes of optical fiber fusion tapering, optical fiber corrosion, integrated waveguide and the like; the other is to converge the beam or array of beams in free space through an objective lens or lenses so that the beam is coupled into the core of the multi-core fiber. The second method can be used for randomly switching the tested multi-core optical fiber, so that the method has the advantage of not needing to perform process operations such as fusion coupling tapering and the like in each coupling test, and can be suitable for wider multi-core optical fiber testing application scenes. However, coupling from the millimeter-scale dimension of the free-space beam through the objective lens or lens to the micrometer-scale dimension of the multicore fiber core often suffers from misalignment and spot size variation. For these problems, most researchers can only determine the coupling condition of the input end of the multi-core optical fiber approximately by the optical power and the optical field distribution of the output end of the multi-core optical fiber. However, the lack of a visualization process for coupling in to the core makes the coupling and testing of the multi-core fiber cumbersome. Therefore, establishing a visual system, which can clearly see the position of the light spot incident on the fiber core and the size relationship between the light spot and the fiber core during the coupling and large dynamic range crosstalk test of the multi-core optical fiber, becomes an important challenge.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method and a device for testing visual coupling and large dynamic range crosstalk of a multi-core optical fiber, and aims to establish a visual system as a judging basis of a coupling effect when the multi-core optical fiber is coupled, and the aim is to build the visual system by using as few devices as possible, so that the relation of the positions of light spots incident on a fiber core and the sizes of the light spots and the fiber core can be clearly seen when the multi-core optical fiber is coupled and the large dynamic range crosstalk is tested.
In order to achieve the above-mentioned objective, in one aspect, the present invention provides a method for visual coupling and crosstalk testing in a large dynamic range of a multi-core optical fiber, where a forward incident coupled beam is converged by a high power objective lens and is incident on a surface of a head end of the multi-core optical fiber, and a backward illumination beam with a larger divergence angle is converged by a low power objective lens and is incident on a surface of a tail end of the multi-core optical fiber, so that a light spot size covers an entire cladding. The position of different fiber cores can be marked by the illumination light beams transmitted reversely through the fiber cores, and all fiber cores illuminated by the illumination light beams transmitted reversely and light spots reflected by the incident light beams at the front end on the surface of the optical fiber can be seen by observing the fiber cores at the front end through a camera. The position of the head end of the optical fiber is finely adjusted according to the real-time image observed by the front-end camera, when the light spot is seen to be incident on the target fiber core and the light spot size is matched with the fiber core size, 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, respectively recording the output light field intensity graph of the target fiber core under the conditions of low power light input, low camera exposure time and high power light input and high camera exposure time, and realizing the multi-core fiber crosstalk test with a large dynamic range through gray value comparison.
Further, recording an output light field intensity graph of the coupling input light beam under the conditions of the first input light power and the first camera exposure time, and calculating the output power of the coupling fiber core by using the gray value of the coupling fiber core output light field in the light 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, dividing the gray value of the output light field of other fiber cores in the light field by the incident light power change multiplying power and the camera exposure time change multiplying power in the two measurements, and calculating to obtain crosstalk light output power of other fiber cores; the first input optical power is smaller than the first camera exposure time, and the second input optical power is smaller 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, the measured dynamic range depends on the highest gray value and the lowest gray value range received by the camera pixel point and the input light power change range and the camera exposure time change range in the two measurements, and therefore, 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 of the two measurements.
As an improvement of the technical scheme, when the output power of other fiber cores is measured under the conditions of the second input optical power and the second camera exposure time, the light beams output by the coupling fiber cores are shielded or attenuated by utilizing a space optical method, and the crosstalk light beams output by the other fiber cores are received without being influenced, so that the higher input optical power is allowed on the premise that the camera is prevented from being damaged by the output light field of the coupling fiber cores with over-high power, and the dynamic range of the crosstalk test is further improved.
As an improvement of the technical scheme, the method further comprises the step of additionally introducing a beam of forward illumination light to illuminate the cladding of the multi-core optical fiber from the forward direction, and the forward illumination light is used for imaging the cladding of the end face of the input end of the multi-core optical fiber, so that the visual coupling effect is improved, and the crosstalk testing accuracy is improved.
The invention further 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 outgoing end mechanical fixing piece, 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 directly passes through the first beam splitter, is converged by the first objective lens and is incident on the cladding surface of the head end of the multi-core optical fiber arranged on the optical fiber coupling platform, the reverse illumination light beam directly passes through the second beam splitter and is converged by the second objective lens and then covers the whole cladding surface of the tail end of the multi-core optical fiber, the light beam reversely propagates along different fiber cores of the multi-core optical fiber, is reflected by the first beam splitter after being amplified by the first objective lens at the head end of the optical fiber, and is converged by the first lens, so that the reverse illumination light is received by the first camera, and the positions of different fiber cores are marked by 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 passing through the first lens, so that the first camera can see the distribution of fiber cores and the incidence position of light spots on the surface of the optical fiber, and the displacement of the head end of the multi-core optical fiber can be finely adjusted easily according to the image of the first camera so as to achieve the best coupling effect. Meanwhile, the tail end of the multi-core optical fiber is connected to the mechanical fixing piece, and the output optical field can be seen at the second camera after being reflected by the second beam splitter and converged by the second lens. After the coupling of the target fiber core is completed, respectively recording the output light field intensity graph of the target fiber core under the conditions of low power light input, low camera exposure time and high power light input and high camera exposure time, and realizing the multi-core fiber crosstalk test with a large dynamic range through gray value comparison.
Wherein 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 the first beam splitter of the device, and the effect of the third beam splitter is to combine an incident coupling beam and a newly added front-end forward illumination beam to a coaxial state, and the forward illumination beam can image a cladding of the end face of the input end of the multi-core optical fiber, so that the visual coupling effect is improved, and the crosstalk testing accuracy is improved. The size of the forward illumination beam at the front end is larger, the divergence angle of the forward illumination beam is finely adjusted, the forward illumination beam is converged by the first objective lens and then covers the surface of the cladding at the head end of the whole multi-core optical fiber, so that the visible position of the first camera is more than the cores and the incident light spots of the multi-core optical fiber in the technical scheme, and the cladding of the multi-core optical fiber, and the supplement ensures that a visualization system is more perfect and rich.
As an improvement of the technical scheme, in a free space optical path of an output optical field of the multi-core optical fiber, a space optical method is utilized, and when high input optical power and high camera exposure time are measured, a small barrier or a miniature attenuation sheet is inserted, so that only coupled fiber core output light beams are shielded or attenuated, and crosstalk light beams of other fiber core light beams are received by a second camera without being influenced, and the dynamic range of crosstalk test can be further improved.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1. compared with the traditional multi-core optical fiber coupling system, the system visualizes the coupling process, can assist an operator to quickly and simply finish any multi-core optical fiber coupling alignment, and improves the coupling effect.
2. The optical fiber arranged 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 can be used as a system for testing multi-core optical fibers, and the system can be used for coping with a plurality of different multi-core optical fibers.
3. The invention forms an amplifying system through the front high-power objective lens and the lens, so that the micron-scale optical fiber core position is calibrated, and the micron-scale coupling accuracy can be realized.
4. The invention provides a visual large dynamic range inter-core crosstalk test method, which comprises the steps of firstly recording the output power of a coupling fiber core which is not overexposed under the conditions of low input optical power and low exposure time, and then recording the crosstalk optical power of other fiber cores under the conditions of overexposure of the output light of the coupling fiber core under the conditions of high input optical power and high exposure time, so that the overexposure problem caused by the excessively high light intensity during the large dynamic range test can be effectively avoided.
5. The invention can realize the coupling of various different beam arrays to the multi-core optical fiber, and some special beam array coupling is a 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 method for testing visual coupling and large dynamic range crosstalk of a multi-core optical fiber according to the present invention.
Fig. 2 is a schematic structural diagram of a multi-core optical fiber visual coupling and large dynamic range crosstalk testing device provided by the invention.
FIG. 3 shows the real-time coupling recorded by the first camera 9 when the device of FIG. 2 is used to implement an embodiment of the five-core optical fiber, where (a) covers the front-end coupling input light, and only inputs the rear-end reverse illumination light, and the core distribution recorded by the camera; (b) The coupling input light and the reverse illumination light are all turned on, and the coupling is regulated to enable the light beam to be incident on the middle fiber core and the recorded image is obtained when the size of the light beam is matched; (c) Is a real-time image recorded when the coupled beam is laterally (x-axis direction in fig. 1) misaligned with the central core; (d) Is a real-time image recorded when the coupled beam is longitudinally misaligned (y-axis direction in fig. 1) with the central core; (e) Is a real-time image recorded when the coupled beam is not aligned with the central core in both the lateral and longitudinal directions (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 is not at the most appropriate position.
FIG. 4 is a partial result of measuring a five-core optical fiber crosstalk matrix using the apparatus of FIG. 2 provided by the present invention, wherein (a) is the front-end core profile recorded using the first camera 9; (b) Is a 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 adjusting light beam is coupled into the middle fiber core; (d) The output light field of the central fiber core is adjusted when the light intensity of the coupling input light is weaker and the exposure time of the second camera 11 is lower; (e) The coupled-in light is adjusted to be in a state of stronger light intensity, and the second camera 11 is in a state of higher exposure time, so that the light field is output from the central fiber core.
Fig. 5 is all results of measuring a five-core fiber crosstalk matrix using the apparatus of fig. 2 provided by the present invention. Wherein the five images in (a) are in turn real-time images recorded by the first camera 9 when the coupling positions are adjusted so that the light beams are input along five different cores; (b) The output light field recorded by the second camera 11 when the input coupling light is weak (12 dB attenuation applied) and the exposure time is short (0.1 ms) is sequentially shown for the above-mentioned different core input conditions; (c) The five graphs in (a) are sequentially the output light fields recorded by the second camera 11 when the input coupling light is strong (0 dB attenuation is applied) and the exposure time is long (10 ms) under the different fiber core input conditions; (d) And the middle is a five-core optical fiber crosstalk matrix obtained according to the image measurement.
Fig. 6 is a schematic structural diagram of an improved multi-core fiber visual coupling and large dynamic range crosstalk testing apparatus provided by the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not interfere 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 comprises the following specific embodiments:
The multi-core optical fiber to be coupled and tested for large dynamic range crosstalk is shown in the figure, input coupling light is input from the head end of the optical fiber on the right side, reverse illumination light is input reversely from the tail end of the optical fiber, and as can be seen from the figure, the reverse illumination light covers all the fiber cores, so that all the fiber cores have reverse transmission of illumination light. The optical fiber is received by the camera together with the light spot which is incident on the head end of the multi-core optical fiber and reflected back, so that a real-time image of the light spot coexisting with each fiber core can be seen at the camera, and the position of the optical fiber is finely adjusted according to the image so as to achieve the best coupling effect.
As shown in fig. 2, the present invention provides a device for testing visual coupling and large dynamic range crosstalk of a multi-core optical fiber, 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 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 first objective lens 2 is a high power objective lens, and the second objective lens 6 is a low power objective lens. The dashed lines in the figure indicate the direction of the optical axis of the light beam transmission, and the transmission paths of the light input coupled and the light back illuminated in the figure are described below, respectively. The input coupling light is transmitted through the first beam splitter 1, converged by the first objective lens 2, and then is incident on the front end face of the multi-core optical fiber 4 arranged on the optical fiber coupling platform 3, the incident coupling light is reflected at the end face, the reflected light is opposite to the incident light, the reflected 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 the light spot incident on the end face. The back illumination beam has a larger beam size, and after passing through the second beam splitter 7 and the second objective lens 6, it can still cover all the cores at the tail end of the multi-core optical fiber, so that the illumination beam is reversely transmitted from the optical fiber outgoing end mechanical fixing piece to the head end of the multi-core optical fiber placed on the optical fiber coupling platform along all the cores. After exiting from the optical fiber head end, 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 cores can be seen in the field of view of the first camera 9. When the multi-core optical fibers are coupled, the displacement of the optical fiber coupling platform can be adjusted in real time according to the image in the first camera 9, so that the micron-level high-precision coupling effect is achieved. After the coupling adjustment is finished, it is obvious that the input coupling light is transmitted through the multi-core optical fiber 4, exits from the optical fiber exit end mechanical fixing piece 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, the five-core fiber visual coupling and the large dynamic range crosstalk test performed using the device of fig. 2 as an example are graphs of the results recorded at a portion of the first camera 9. Wherein, (a) covers the front end coupling input light, and only inputs the fiber core distribution recorded by the camera when the back end reversely illuminates light; (b) The coupling input light and the reverse illumination light are all turned on, and the coupling is regulated to enable the light beam to be incident on the middle fiber core and the recorded image is obtained when the size of the light beam is matched; (c) Is a real-time image recorded when the coupled beam is laterally (x-axis direction in fig. 1) misaligned with the central core; (d) Is a real-time image recorded when the coupled beam is longitudinally misaligned (y-axis direction in fig. 1) with the central core; (e) Is a real-time image recorded when the coupled beam is not aligned with the central core in both the lateral and longitudinal directions (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 is not at the most appropriate position.
As shown in fig. 4, the device in fig. 2 is used as an example to perform the five-core fiber visual coupling and crosstalk matrix test. Wherein (a) is the front end core profile recorded using the first camera 9; (b) 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) Is a real-time image recorded by the first camera 9 when the adjusting light beam is coupled into the middle fiber core; (d) Is to adjust the output light field of the central fiber core when the light intensity of the coupled-in light is weak (12 dB attenuation is applied to the coupled-in light) and the exposure time of the second camera 11 is low (0.1 ms); (e) Is the output light field of the central core that adjusts the intensity of the coupled-in light to be strong (no attenuation is applied to the coupled-in light, i.e. 0dB attenuation), when the exposure time of the second camera 11 is high (10 ms). Then, the method of calculating the crosstalk from the center core to the other four cores is as follows: firstly, intercepting a light spot of a central fiber core from a light field intensity diagram of the diagram (d), calculating a total gray value of the light spot, and recording the total gray value as I 1; then, light spots of other four fiber cores are intercepted in the light field intensity diagram of (e) in fig. 4, and the total gray values are calculated and respectively marked as I 2,I3,I4,I5, so that the specific crosstalk value can be calculated as follows:
Where XT 1,i represents the i-th core to center core crosstalk value, 32dB from the 12dB input light power difference and 20dB (10 ms/0.1ms = 100 times) camera exposure time difference.
As shown in fig. 5, all results obtained from five-core fiber visual coupling and crosstalk matrix testing were performed using the apparatus of fig. 2 as an example. Wherein, the five images in (a) are real-time images recorded by the first camera 9 when the coupling positions are adjusted to input five different fiber cores in sequence; (b) The output light field recorded by the second camera 11 when the input coupling light is weak (12 dB attenuation applied) and the exposure time is short (0.1 ms) is sequentially shown for the above-mentioned different core input conditions; (c) The five graphs in (a) are sequentially the output light fields recorded by the second camera 11 when the input coupling light is strong (0 dB attenuation is applied) and the exposure time is long (10 ms) under the different fiber core input conditions; (d) The specific test path is consistent with the crosstalk test process of the central fiber core and the other four fiber cores introduced in fig. 4, wherein the crosstalk matrix (unit: dB) of the five-core optical fiber is measured according to the image.
As shown in fig. 6, the present invention provides an improved device for visual coupling and large dynamic range crosstalk testing of a multi-core optical fiber, 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 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, a second camera 11 and a third beam splitter 12. The dashed lines in the figure indicate the direction of the optical axis of the beam transmission, and the transmission paths of the in-coupled light and the reverse illumination light are identical to those shown in fig. 2, so only the forward illumination light transmission path to which the improved device is added will be described herein. 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 cross section of the head end of the multi-core optical fiber 4, the size of the forward illumination light is relatively large, and the converged light beam can be ensured to cover the whole optical fiber cladding. The illumination light is reflected at the cross-section, passes through the first objective lens 2, the first beam splitter 1, and the first lens 8, and is then received by the first camera 9, where imaging of the cladding is observed. After the forward illumination light is added, the first camera 9 can see the clear fiber cladding, fiber core distribution and incident light spots, and the supplement further improves the effect of the visual system.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the 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:
a beam of coupling input light is input from the head end of the multi-core optical fiber in the forward direction, and a beam of reverse illumination light with the size covering the whole cladding is input from the tail end of the multi-core optical fiber in the reverse direction;
The back illumination light beam propagates along a plurality of fiber cores of the multi-core optical fiber, is output from the head end of the multi-core optical fiber, is received after free space transmission, and is used for calibrating the position distribution of different fiber cores; the coupling input light is received after being reflected on the head end surface of the multi-core optical fiber, and is used for acquiring a real-time image when the coupling input light is incident on the head end surface of the multi-core optical fiber when the multi-core optical fiber is coupled; adjusting the position of the head end surface of the multi-core optical fiber according to the real-time image, so that a coupling input light beam enters a preset coupling fiber core in an incident mode, and the size of a light spot is matched with the size of the fiber core to finish the coupling of a target fiber core;
Recording an output light field intensity graph of the coupling input light beam under the conditions of first input light power and first camera exposure time, and calculating the output power of the coupling fiber core by using the gray value of the coupling fiber core output light field in the light 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, dividing the gray value of the output light field of other fiber cores in the light field by the incident light power change multiplying power and the camera exposure time change multiplying power in the two measurements, and calculating to obtain crosstalk light output power of other fiber cores; the first input optical power is smaller than the second input optical power, and the first camera exposure time is smaller than the second camera exposure time;
The measured crosstalk value is obtained by calculating the output power difference between the coupled 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 optical power change range and the camera exposure time change range in the two measurements.
2. The method for testing visual coupling and large dynamic range crosstalk according to claim 1, wherein when measuring output power of other cores under the conditions of the second input optical power and the second camera exposure time, the light beams output by the coupled cores are shielded or attenuated by using a space optical method, while the crosstalk light beams output by the other cores are received unaffected, so that the higher input optical power is allowed under the premise of preventing the damage of the camera by the output optical field of the coupled cores with too high power, so as to further improve the dynamic range of the crosstalk test.
3. The method of claim 1, further comprising introducing an additional forward illumination beam to illuminate the cladding of the multi-core fiber from the forward direction for imaging the cladding of the input end face of the multi-core fiber.
4. The 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 connected with a first beam splitter (1), converged into a multi-core optical fiber core (4) arranged on an optical fiber coupling platform (3) through a first objective lens (2), output from an optical fiber emergent 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), received by a second camera (11) to output an optical field, and the output optical field received by the second camera (11) is used for optical fiber large dynamic range crosstalk test;
The reverse illumination light part is directly led to a 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, illumination light is output from the optical fiber coupling platform (3), the illumination light is reflected by the first beam splitter (1) through the rear part of the first objective lens (2), and is received by the first camera (9) after being converged by the first lens (8), besides, the coupling input light has partial light reflection at the end face of the multi-core optical fiber (4) and is reversely transmitted, is reflected by the first beam splitter (1) through the rear part of the first objective lens (2), and is received by the first camera (9) after being received by the first lens (8), and the light spots and the fiber cores at the end face of the optical fiber 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 arranged between the optical fiber exit end mechanical fixture (5) and the second beam splitter (7) or the second beam splitter (7) and the second camera (11) such that the light beam output by the coupled core is shielded or attenuated, while the crosstalk light beam output by the other cores is received unaffected for allowing a higher input optical power if the camera is damaged by the excessively powerful coupled core output light field, to further improve the dynamic range of the crosstalk test.
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 a forward illumination beam, the third beam splitter (12) being configured to combine the forward illumination beam with the input coupled beam into a coaxial state, the forward illumination beam being capable of imaging the cladding of the input end face of the multicore fiber.
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