Device and method for measuring and improving seed light coupling efficiency in photonic crystal fiber

Abstract

The invention provides a device and method for measuring and improving seed light coupling efficiency in a photonic crystal fiber, the device comprises a seed source, a seed light coupling module, a photonic crystal fiber, a pump light coupling module, a measuring module and an adjusting module, and the measuring module comprises a CCD camera and a power meter. The CCD camera is used for acquiring the amplified end face near-field light spot of the output end of the photonic crystal fiber in real time; the power meter is used for measuring the power of laser output by the photonic crystal fiber. The adjusting module determines the fiber core area power and the total power of the end face near-field light spots, calculates the core-to-package ratio, and adjusts the seed optical coupling module to adjust the core-to-package ratio to the maximum, so that the seed optical coupling efficiency in the photonic crystal fiber reaches the maximum. According to the invention, real-time imaging and analysis can be carried out on the light spot output by the optical fiber through the CCD camera, the coupling state is visually presented, and the measurement uncertainty caused by small hole positioning errors and alignment deviation is avoided, so that the effective coupling efficiency of seed light is accurately improved.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of optoelectronic technology, in particular to a device and method for measuring and improving seed light coupling efficiency in a photonic crystal fiber. BACKGROUND

[0002] Due to its special microstructure design, the photonic crystal fiber has a large mode field, high gain and single-mode transmission capability, and can realize near-diffraction-limited high beam quality output while maintaining a large mode field area, which is suitable for large-power high-beam-quality picosecond pulse amplification.

[0003] Based on the spatial coupling mode, when the seed light is amplified by the photonic crystal fiber, the coupling degree of the seed light has a decisive influence on the efficiency of laser amplification and the beam quality after amplification. Among them, the core / clad power ratio (CCR) is an important parameter for measuring the effective coupling degree of the seed light in the photonic crystal fiber. If the coupling is poor, the beam will produce mode distortion, resulting in power loss, unstable signal, and even damage to the optical fiber in severe cases. On the contrary, when the coupling reaches the optimal state, the beam energy is concentrated in the core of the photonic crystal fiber, which is beneficial to achieve higher output power, stable beam quality and long-life reliable operation. Therefore, in the process of building a spatial light path of a laser amplifier, optimizing the coupling of the seed light is a key step to improve the performance of the system, which requires precise mode field matching and beam alignment to achieve the optimal coupling effect.

[0004] Due to the large mode field and regular air hole microstructure characteristics of large-size photonic crystal fibers (such as rod-shaped photonic crystal fibers), the use of traditional fiber fusion will cause air hole collapse, so it is not possible to directly fuse them with the seed source in experiments, therefore the fiber rod is usually provided with an end cap with an anti-reflection coating on the end face, and a free-space lens group is used to couple the seed light and the pump light. The lens group coupling has very strict requirements on the position and focal length of the lens, not only the appropriate focal length needs to be selected according to the mode field parameters, but also the position of the lens group needs to be adjusted in multiple degrees of freedom to realize the coordinated cooperation between multiple optical elements, so as to achieve the maximum coupling efficiency.

[0005] When seed light enters the photonic crystal fiber core by spatial coupling, the simplest way to improve the effective coupling efficiency is to use a small hole to block the cladding light, only measure the power of the core area and make it as large as possible. However, without using a lens group to amplify the output spot, the imaging resolution is limited due to the small size of the original spot, and it is difficult to distinguish the core and the cladding, so it is difficult to judge the coupling state. The method of blocking the cladding light with a small hole has many inconveniences and limitations in actual operation. Because the spot size is close to the aperture size of the small hole, a slight deviation of the small hole in space will cause the blocking of the core light or the misrecognition of the cladding light. The aperture size of the small hole needs to be accurately selected according to the size of the fiber core. If the aperture size of the small hole is too small, the core mode energy will be truncated, and if the aperture size of the small hole is too large, the cladding light cannot be effectively shielded. Therefore, the aperture size of the small hole directly affects the accuracy of the results. Secondly, the installation and alignment of the small hole in space are also extremely critical. The position of the small hole needs to be adjusted by a multi-dimensional adjustment frame to adjust the spatial position and angle, so that it is aligned with the optical axis, and it is ensured that only the power of the core area is intercepted. A slight deviation in this process may cause measurement errors.

[0006] In summary, due to the small size of the core and the divergence of the laser itself, the size of the small hole is difficult to determine and not easy to align, which is easy to introduce measurement errors. Therefore, how to accurately measure and improve the effective coupling efficiency of spatial seed light in photonic crystal fiber is a technical problem that needs to be solved in the field. SUMMARY

[0007] The purpose of the present application is to provide a device and method for measuring and improving the coupling efficiency of seed light in photonic crystal fiber.

[0008] The first aspect of the present application provides a device for measuring and improving the coupling efficiency of seed light in photonic crystal fiber, comprising:

[0009] a seed source, a seed light coupling module, a photonic crystal fiber, a pump light coupling module, a measurement module and an adjustment module;

[0010] The seed source is configured to provide seed light.

[0011] The seed light coupling module is configured to adjust the polarization direction of the seed light and focus the seed light into the photonic crystal fiber.

[0012] The pump light coupling module is configured to generate pump light and focus the pump light into the photonic crystal fiber.

[0013] The measurement module comprises a CCD camera and a power meter. The CCD camera is configured to acquire the amplified end face near field spot of the output end of the photonic crystal fiber in real time. The power meter is configured to measure the power of the output laser of the photonic crystal fiber.

[0014] The adjusting module is configured to obtain the end face near-field light spot, determine a core area power and a total power of the end face near-field light spot, and calculate a core-cladding ratio according to the core area power and the total power, and adjust the seed light coupling module to adjust the core-cladding ratio to be maximum.

[0015] In some embodiments of the present application, the seed light coupling module comprises, in sequence, a first half-wave plate, an isolator, a second half-wave plate, a first mirror, a second mirror, a seed light coupling lens, and a first dichroic mirror.

[0016] The first half-wave plate and the second half-wave plate are configured to adjust a polarization direction of the seed light.

[0017] The isolator is configured to isolate the backward-propagating laser light to prevent the laser light from damaging the seed source.

[0018] The first mirror and the second mirror are configured to reflect the seed light to adjust a direction of the seed light.

[0019] The seed light coupling lens is configured to focus and couple the seed light into a core of the photonic crystal fiber.

[0020] The first dichroic mirror is configured to transmit the seed light and reflect the pump light.

[0021] In some embodiments of the present application, the first mirror and the second mirror are both 45°

[0022] full reflection mirrors.

[0023] In some embodiments of the present application, the first dichroic mirror is a 20° seed light transmitting dichroic mirror.

[0024] In some embodiments of the present application, the pump light coupling module comprises, in sequence, a pump light focusing lens, a second dichroic mirror, a third dichroic mirror, a pump light collimating lens, and a pump light source.

[0025] The pump light source is configured to generate pump light.

[0026] The pump light collimating lens is configured to collimate the pump light.

[0027] The third dichroic mirror is configured to transmit the pump light and reflect residual laser light to protect the pump light source.

[0028] The second dichroic mirror is configured to transmit the seed light and reflect the pump light.

[0029] The pump light focusing lens is configured to focus the pump light into the photonic crystal fiber and collimate the amplified laser light obtained after amplifying the seed light.

[0030] In some embodiments of this application, both the second dichroic mirror and the third dichroic mirror are 20°.

[0031] Seed-transmitting dichroic mirror.

[0032] In some embodiments of this application, the measurement module further includes:

[0033] A wedge-shaped mirror is used to guide part of the laser to the CCD camera in order to obtain the magnified near-field spot at the output end of the photonic crystal fiber.

[0034] The laser focusing lens, together with the pump light focusing lens, constitutes a magnifying glass system, which is used to enlarge the spot size at the end face of the photonic crystal fiber.

[0035] In some embodiments of this application, the seed source provides seed light with an average power ≥5W, a repetition frequency of 1MHz, a pulse width ≥500fs, and a wavelength of 1030nm~1040nm.

[0036] A second aspect of this application provides a method for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber, based on the apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber as described in the first aspect above, the method comprising:

[0037] The seed source provides seed light;

[0038] The seed light coupling module adjusts the polarization direction of the seed light and focuses and couples the seed light into the photonic crystal fiber.

[0039] The pump light coupling module generates pump light and focuses the pump light into the photonic crystal fiber;

[0040] The power meter measures the power of the laser output from the photonic crystal fiber, and the seed optical coupling module is adjusted to maximize the power of the output laser.

[0041] The CCD camera acquires the magnified near-field light spot at the output end of the photonic crystal fiber in real time.

[0042] The adjustment module acquires the near-field spot on the end face, determines the core region power and total power of the near-field spot on the end face, calculates the core-to-cladding ratio based on the core region power and total power, adjusts the seed optical coupling module, and adjusts the core-to-cladding ratio to the maximum, so that the seed optical coupling efficiency in the photonic crystal fiber reaches the maximum.

[0043] Compared to existing technologies, the device provided in this application for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber includes: a seed source, a seed optical coupling module, a photonic crystal fiber, a pump optical coupling module, a measurement module, and an adjustment module. The measurement module includes a CCD camera and a power meter. The CCD camera is used to acquire the magnified near-field spot at the output end of the photonic crystal fiber in real time; the power meter is used to measure the power of the laser output from the photonic crystal fiber. The adjustment module acquires the near-field spot at the end end, determines the core region power and total power of the near-field spot, calculates the core-to-cladding ratio based on the core region power and total power, and adjusts the seed optical coupling module to maximize the core-to-cladding ratio, thereby maximizing the seed optical coupling efficiency in the photonic crystal fiber. This application enables real-time observation of the seed light coupling spot in a photonic crystal fiber using a CCD camera. Compared to the method of using a pinhole to limit the power of the fiber core region, the CCD camera can perform real-time imaging and analysis of the fiber output spot, accurately define the fiber core region, and intuitively present the coupling state. This avoids measurement uncertainties caused by pinhole positioning errors and alignment deviations, thereby accurately improving the effective coupling efficiency of the seed light in the photonic crystal fiber. Attached Figure Description

[0044] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this disclosure. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0045] Figure 1 A schematic diagram of the structure of an apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber, provided in this disclosure, is shown.

[0046] Figure 2 A flowchart is shown illustrating a specific method for measuring and improving the effective coupling efficiency of seed light in a photonic crystal fiber, as provided in this disclosure. Detailed Implementation

[0047] Embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0048] The accompanying drawings illustrate various structural schematics according to embodiments of the present disclosure. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0049] In the context of this disclosure, when a layer / element is referred to as being "above" another layer / element, the layer / element may be directly above the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "above" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0050] This application provides an apparatus and method for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber, which will be described below with reference to the accompanying drawings.

[0051] Please refer to Figure 1 This document illustrates a schematic diagram of a device for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber, as provided in an embodiment of this application. Figure 1 As shown, the device includes: a seed source 100, a seed optical coupling module 200, a photonic crystal fiber 300, a pump optical coupling module 400, a measurement module 500, and an adjustment module (not shown in the figure).

[0052] The seed source 100 is used to provide seed light. Specifically, the seed source provides seed light with an average power ≥ 5W, a repetition frequency of 1MHz, a pulse width ≥ 500fs, and a wavelength of 1030nm~1040nm.

[0053] The seed light coupling module 200 is used to adjust the polarization direction of the seed light and focus and couple the seed light into the photonic crystal fiber.

[0054] like Figure 1 As shown, the seed light coupling module 200 includes: a first half-wave plate 201, an isolator 202, a second half-wave plate 203, a first reflector 204, a second reflector 205, a seed light coupling lens 206, and a first dichroic mirror 207 arranged sequentially.

[0055] The first half-wave plate 201 and the second half-wave plate 203 are used to adjust the polarization direction of the seed light.

[0056] The isolator 202 is used to isolate the back-propagating laser to prevent the laser from damaging the seed source.

[0057] The first reflector 204 and the second reflector 205 constitute a seed light coupling reflector for reflecting seed light to adjust the direction of seed light; specifically, the first reflector 204 and the second reflector 205 are both 45° total reflection mirrors.

[0058] The seed optical coupling lens 206 is used to focus and couple the seed light into the core of the photonic crystal fiber 300. The focal length of the seed optical coupling lens 206 needs to be matched with that of the photonic crystal fiber, and the focal length of the seed optical coupling lens 206 can be given by the fiber coupling formula. In the formula, D is the diameter of the output light spot of the seed source. MF λ is the mode field diameter of the photonic crystal fiber, and λ is the laser wavelength.

[0059] The first dichroic mirror 207 is used to transmit seed light and reflect pump light. Specifically, the first dichroic mirror 207 is a 20° seed light transmission dichroic mirror. A 20° seed light transmission dichroic mirror is a specially designed optical element, mainly used to achieve high transmittance of seed light at a specific incident angle of 20°, while reflecting light of other wavelengths, thereby playing a role in separating and combining light of different wavelengths in a laser system.

[0060] Photonic crystal fiber 300 can be an aeroGAIN-ROD photonic crystal fiber, with a core diameter of 85μm, a cladding diameter of 260μm, a mode field diameter of 65μm, and a length of 80cm.

[0061] The pump light coupling module 400 is used to generate pump light and focus the pump light into the photonic crystal fiber.

[0062] like Figure 1 As shown, the pump light coupling module 400 includes: a pump light focusing lens 401, a second dichroic mirror 402, a third dichroic mirror 403, a pump light collimating lens 404, and a pump light source 405 arranged sequentially.

[0063] The pump source 405 is used to generate pump light; the pump source 405 may be a semiconductor laser with an output power of 150W and a wavelength of 976nm, and the pump fiber core is 105μm with a numerical aperture.

[0064] NA0.22.

[0065] The pump light collimating lens 404 is used to collimate the pump light.

[0066] The third dichroic mirror 403 is used to transmit pump light and reflect residual laser light to protect the pump light source.

[0067] The second dichroic mirror 402 is used to transmit seed light and reflect pump light. Both the second dichroic mirror 402 and the third dichroic mirror 403 are 20° seed light transmission dichroic mirrors.

[0068] The pump light focusing lens 401 is used to focus the pump light into the photonic crystal fiber and to collimate and amplify the seed light to obtain the laser.

[0069] The measurement module 500 includes a CCD camera 503 and a power meter 504, as well as a wedge mirror 501 and a laser focusing lens 502;

[0070] Wedge mirror 501 is used to guide part of the laser to the CCD camera 503;

[0071] The laser focusing lens 502, together with the pump light focusing lens 401, constitutes a magnifying glass system, which is used to magnify the size of the light spot on the end face of the photonic crystal fiber.

[0072] This application employs a proportional magnifying glass system consisting of two lenses to clearly project the near-field light spot from the fiber end face onto a CCD camera. Software-assisted analysis allows for precise definition of the fiber core region, enabling accurate power calculation and coupling state monitoring. The proportional magnifying glass system comprises a short focal length lens (focal length f1) and a long focal length lens (focal length f2). The first short focal length lens collimates the light spot from the photonic crystal fiber output end face into a parallel beam, while the second lens focuses the parallel beam onto the sensor plane of the CCD camera. The magnification M = f2 / f1, and the imaging size increases linearly with the magnification. The magnification is sufficient to provide adequate spatial resolution for the fiber core and cladding on the CCD image.

[0073] The CCD camera 503 is used to acquire the magnified end face near-field light spot of the output end of the photonic crystal fiber in real time.

[0074] The power meter 504 is used to measure the power of the laser output from the photonic crystal fiber.

[0075] The adjustment module is used to acquire the near-field spot on the end face, determine the core region power and total power of the near-field spot on the end face, calculate the core-packet ratio based on the core region power and total power, and adjust the seed optical coupling module 200 to adjust the core-packet ratio to the maximum.

[0076] This application employs CCD imaging technology to acquire near-field images of the output end of a photonic crystal fiber, and calculates the CCR value based on a predetermined core aperture region, thereby achieving accurate evaluation and optimization of coupling efficiency. The CCR calculation can be given by the formula: In the formula P core P is defined as the core region power of the near-field spot at the end face.total This represents the total power of the near-field spot at the end face.

[0077] Therefore, this application provides a method to improve the effective coupling efficiency when introducing seed light into the core of a photonic crystal fiber via spatial coupling. By introducing a lens group with a certain focal length ratio at the output end of the photonic crystal fiber, the laser output from the core is magnified proportionally and imaged on a CCD. Combined with the known diameter of the photonic crystal fiber core, the size of the magnified core spot in the CCD image can be calculated. If the CCD used supports image analysis software, the manual aperture function in the CCD's image analysis software can be used to accurately calibrate the core area and accurately calculate the core output power. Further comparison with the total power yields the CCR value. If the CCD used does not have a manual aperture function, a physical circular aperture matching the magnification can be introduced in front of the CCD to block the cladding light, allowing only the core area light to pass through the CCD or power meter, thereby achieving indirect measurement of the core power. This method is suitable for scenarios with limited hardware conditions.

[0078] Throughout the entire photonic crystal fiber spatial coupling adjustment process, the CCD provides real-time beam pattern information. By adjusting the optical components in the seed beam coupling path, the beam pattern can be adjusted to achieve a clear, symmetrical, Gaussian distribution. As the coupling state is gradually optimized, the energy percentage in the fiber core region increases, and the CCR reaches its maximum value, indicating that the coupling state has reached its optimal state. Simultaneous observation of coupling quality during the adjustment process improves the accuracy of effective coupling efficiency measurement, providing reliable assurance for system debugging and long-term operation.

[0079] For ease of understanding, this application also provides, as follows: Figure 2 The flowchart shown illustrates a specific method for measuring and improving the effective coupling efficiency of seed light in a photonic crystal fiber. The implementation steps are as follows:

[0080] Step 101: Seed light collimation. By placing two pinhole apertures at the same height as the fiber end cap as references in the optical path, the pitch and yaw angles of the coupling mirrors 204 and 205 are adjusted to change the propagation direction of the seed light, ensuring that the seed light can pass through the center of the two apertures in sequence, thus achieving collimation and laying the foundation for subsequent spatial seed light coupling in photonic crystal fiber;

[0081] Step 102: Positioning and Installation of Photonic Crystal Fiber. Place the photonic crystal fiber into the optical path according to the position defined by the pinhole aperture, ensuring that the seed light is incident at the expected position of the photonic crystal fiber end cap;

[0082] Step 103: Insert and adjust the position of the seed light coupling lens. Focus the seed light onto the incident end face of the photonic crystal fiber 300, and fine-tune the angle and position of the seed light coupling lens 206 to obtain laser output at the output end of the photonic crystal fiber 300 and maximize the output power.

[0083] Step 104: CCD Near-Field Imaging and CCR Measurement. Observe the shape of the output light spot using the CCD camera 503. Magnify the light spot using a magnifying glass system and measure the CCR to obtain the optimal coupling efficiency. Adjust the direction of the output light to the CCD using the pump light focusing lens 401, aligning the end face of the photonic crystal fiber with the image plane of the CCD camera sensor to ensure distortion-free image.

[0084] Before performing CCR measurements, background correction of the CCD is necessary to block the seed light and capture stray light and dark current noise present in the system. These are then removed during subsequent image processing to ensure accurate results. It is crucial to note that if the system state changes during coupling debugging, the background correction operation must be repeated to ensure accurate measurement results. During spot image acquisition, an ND filter can be placed in front of the CCD camera to ensure the output spot is clear and not overexposed. When the CCD has a manual aperture function, this function can be used to directly define the fiber core area for CCR calculation. The size of the manual aperture is determined by the fiber core diameter and the magnification of the magnifying glass system. The final CCR value is calculated from the fiber core power and the total power of the sampled signal within the manual aperture. If the CCD lacks this function, a small aperture matching the magnification can be introduced to block the cladding light, allowing only the fiber core light to pass through, achieving power measurement through physical isolation to indirectly complete the CCR calculation. This method is suitable for coupling optimization of spatial seed light under different test conditions and has good compatibility and adjustability.

[0085] Step 105: Real-time feedback optimization coupling. Based on the near-field image presented by the CCD and the CCR measurement results, the seed light coupling mirrors (204 and 205) and the seed light coupling lens 206 are finely adjusted to maximize the laser energy in the manual aperture, thereby achieving the optimal seed light coupling efficiency.

[0086] The following specific embodiment will further illustrate the above-mentioned apparatus for measuring and improving the seed optical coupling efficiency of photonic crystal fibers.

[0087] Please refer to Figure 1The seed source 100 outputs seed light with a wavelength of 1030-1040 nm, an average power greater than 5 W, a repetition frequency of 1 MHz, and a spot diameter of 2 mm. After the seed light is polarized and its optical path adjusted by half-wave plates (201 and 203), isolator 202, and reflectors (204 and 205), it is focused onto the input end of photonic crystal fiber 300 by seed light coupling lens 206. The photonic crystal fiber used is an aeroGAIN-ROD type photonic crystal fiber with a core diameter of 85 μm, a cladding diameter of 260 μm, and a mode field diameter of 65 μm. The pump light is provided by a 976 nm semiconductor laser and coupled to the cladding of photonic crystal fiber 300 by collimating and focusing lenses (404 and 401). The pump light is separated from the seed light by dichroic mirrors (402 and 403). The system end uses a wedge mirror 501, a magnifying glass system (401 and 502), a CCD camera 503, and a power meter 504 to achieve near-field imaging of the output light spot and precise measurement of coupling efficiency.

[0088] In the seed optical coupling process, the selection of the focal length of the seed optical coupling lens 206 is particularly important, as it must ensure that the waist diameter of the seed beam after focusing matches the mode field diameter of the fiber. In this embodiment, the photonic crystal fiber mode field diameter is 65μm, the seed source output spot diameter is 2mm, and the seed source output laser wavelength is 1030nm. Using the fiber coupling formula, the required focal length of the seed optical coupling lens 206 is calculated to be 100mm.

[0089] For the photonic crystal fiber 300, the core aperture is defined as 90μm. A lens group is used to magnify the light spot on the end face of the photonic crystal fiber. The output coupling lens (pump light focusing lens 401) with a focal length of 30mm is used as the short focal length lens in the magnifying lens group to collimate the output beam. The long focal length lens (laser focusing lens 502) focuses the collimated light onto the CCD camera sensor. In this embodiment, a long focal length lens with a focal length of 200mm is used. The focal length ratio of the two lenses is 6.67, so the light spot is magnified by 6.67 times. The core diameter of 90μm is magnified to about 600μm, and the cladding diameter of 260μm corresponds to about 1734μm after magnification.

[0090] Considering that different CCD cameras have different pixel sizes, to ensure sufficient resolution of the magnified spot, the magnified cladding spot should cover at least a 300×300 pixel area. In this embodiment, a CCD pixel size of 4.4μm and a resolution of 1600×1200 pixels are used. For the above magnifying glass system, the magnified cladding image occupies a 394×394 pixel area in the CCD, and the magnified fiber core area corresponds to approximately 136×136 pixels. Based on the imaging ratio calculation, the 90μm area of ​​the fiber core is magnified to 600μm in the image analysis software, and the diameter of the circular manual aperture or circular pinhole aperture is determined to be 600μm for CCR measurement.

[0091] During the spatial seed light coupling process in photonic crystal fibers, the imaging changes of the output light spot on the CCD are instructive for improving coupling efficiency. Typically, in the initial coupling state, the light spot image exhibits an irregular shape, with low brightness at the center and blurred or high-brightness ring-shaped edges, indicating that the seed light energy is not concentrated in the fiber core, and most of the energy is coupled to the cladding. The Z-axis distance of the output coupling lens can be adjusted first to change the focusing position and achieve mode field matching, gradually changing the light spot from a ring shape to a solid circle. When adjusting the Z-axis position cannot achieve a complete circular image, the XY-axis position of the output coupling lens can be further fine-tuned to move the higher-energy region to the center of the output image. For irregular circular light spots that still exhibit distortion or eccentricity, the front coupling mirror can be fine-tuned to correct the incident direction of the seed light.

[0092] Throughout the adjustment process, a comprehensive judgment should be made based on changes in the near-field spot image and the CCR value. With continuous fine-tuning of the position and angle of the coupling mirror and coupling lens, the spot gradually shrinks towards a symmetrical circle, with increased brightness at the center and decreased brightness at the edges. The overall distribution exhibits a Gaussian distribution, the spot stabilizes in the image center, the edge contour is clear, and the microstructure of the cladding air holes is distinct, indicating that most of the energy enters the fiber core. Finally, after multiple rounds of fine-tuning of the coupling mirror and coupling lens, the fiber core power reaches its maximum value within the manual aperture, and the CCR value also reaches its maximum, indicating that the system has reached its optimal coupling state.

[0093] After the spatial seed light coupling in the photonic crystal fiber reaches its optimal state, pump coupling can be performed to enter the amplification stage. During the pump light coupling process, the pump light is output from the pump source pigtail 405, collimated and focused by lenses 403 and 401 onto the rear cladding region of the photonic crystal fiber. The output end face of the pump source pigtail 405 and the rear end face of the photonic crystal fiber 300 are both placed at the focal point of the lens, while ensuring that the direction of the light output from lens 401 to the CCD camera sensor is perpendicular. It is crucial that the pump be turned on only after the seed light is activated to prevent spontaneous emission due to the lack of seed input. If the system has specific polarization requirements, the polarization direction of the input seed light can be further optimized by adjusting the angle of the second half-wave plate 203 to achieve stable linear polarization amplification performance.

[0094] This application uses a CCD camera to observe the seed light coupling spot of a photonic crystal fiber in real time. Compared with the method of using a pinhole to limit the power of the fiber core area, the CCD camera can perform real-time imaging and analysis of the fiber output spot, accurately define the fiber core area, and intuitively present the coupling state, avoiding measurement uncertainties caused by pinhole positioning errors and alignment deviations.

[0095] Based on the apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber provided in the above embodiments, this application also provides a method for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber, the method comprising:

[0096] The seed source provides seed light;

[0097] The seed light coupling module adjusts the polarization direction of the seed light and focuses and couples the seed light into the photonic crystal fiber.

[0098] The pump light coupling module generates pump light and focuses the pump light into the photonic crystal fiber;

[0099] The power meter measures the power of the laser output from the photonic crystal fiber, and the seed optical coupling module is adjusted to maximize the power of the output laser.

[0100] The CCD camera acquires the magnified near-field light spot at the output end of the photonic crystal fiber in real time.

[0101] The adjustment module acquires the near-field spot on the end face, determines the core region power and total power of the near-field spot on the end face, calculates the core-to-cladding ratio based on the core region power and total power, adjusts the seed optical coupling module, and adjusts the core-to-cladding ratio to the maximum, so that the seed optical coupling efficiency in the photonic crystal fiber reaches the maximum.

[0102] It should be noted that the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0103] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0104] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some communication interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.

[0105] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0106] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0107] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application.

Claims

1. A device for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber, characterized in that, include: Seed source, seed optical coupling module, photonic crystal fiber, pump optical coupling module, measurement module, and adjustment module; The seed source is used to provide light to the seeds; The seed light coupling module is used to adjust the polarization direction of the seed light and focus and couple the seed light into the photonic crystal fiber; The pump light coupling module is used to generate pump light and focus the pump light into the photonic crystal fiber; The measurement module includes a CCD camera and a power meter; the CCD camera is used to acquire the magnified near-field spot at the output end of the photonic crystal fiber in real time; the power meter is used to measure the power of the laser output from the photonic crystal fiber. The adjustment module is used to acquire the near-field light spot on the end face, determine the core region power and total power of the near-field light spot on the end face, calculate the core-packet ratio based on the core region power and total power, and adjust the seed optical coupling module to adjust the core-packet ratio to the maximum.

2. The apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber according to claim 1, characterized in that, The seed optical coupling module includes: a first half-wave plate, an isolator, a second half-wave plate, a first reflector, a second reflector, a seed optical coupling lens, and a first dichroic mirror arranged sequentially. The first half-wave plate and the second half-wave plate are used to adjust the polarization direction of the seed light; The isolator is used to isolate the back-propagating laser to prevent the laser from damaging the seed source; The first and second reflectors are used to reflect seed light in order to adjust the direction of the seed light; The seed light coupling lens is used to focus and couple the seed light into the core of the photonic crystal fiber. The first dichroic mirror is used to transmit seed light and reflect pump light.

3. The apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber according to claim 2, characterized in that, Both the first and second reflectors are 45° total reflection mirrors.

4. The apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber according to claim 2, characterized in that, The first dichroic mirror is a 20° seed light transmission dichroic mirror.

5. The apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber according to claim 1, characterized in that, The pump light coupling module includes: a pump light focusing lens, a second dichroic mirror, a third dichroic mirror, a pump light collimating lens, and a pump light source arranged sequentially. The pump light source is used to generate pump light; The pump light collimating lens is used to collimate the pump light; The third dichroic mirror is used to transmit pump light and reflect residual laser light to protect the pump light source; The second dichroic mirror is used to transmit seed light and reflect pump light; The pump light focusing lens is used to focus the pump light into the photonic crystal fiber and to collimate and amplify the seed light to obtain the laser.

6. The apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber according to claim 5, characterized in that, Both the second and third dichroic mirrors are 20° seed-transmitting dichroic mirrors.

7. The apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber according to claim 1, characterized in that, The measurement module further includes: A wedge-shaped mirror is used to guide part of the laser to the CCD camera in order to obtain the magnified near-field spot at the output end of the photonic crystal fiber. The laser focusing lens, together with the pump light focusing lens, constitutes a magnifying glass system, which is used to magnify the size of the light spot on the end face of the photonic crystal fiber.

8. The apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber according to claim 1, characterized in that, The seed source provides seed light with an average power of ≥5W, a repetition frequency of 1MHz, a pulse width of ≥500fs, and a wavelength of 1030nm~1040nm.

9. A method for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber, based on the apparatus for measuring and improving the seed optical coupling efficiency in a photonic crystal fiber according to any one of claims 1 to 8, characterized in that, The method includes: The seed source provides seed light; The seed light coupling module adjusts the polarization direction of the seed light and focuses and couples the seed light into the photonic crystal fiber. The pump light coupling module generates pump light and focuses the pump light into the photonic crystal fiber; The power meter measures the power of the laser output from the photonic crystal fiber, and the seed optical coupling module is adjusted to maximize the power of the output laser. The CCD camera acquires the magnified near-field light spot at the output end of the photonic crystal fiber in real time. The adjustment module acquires the near-field spot on the end face, determines the core region power and total power of the near-field spot on the end face, calculates the core-to-cladding ratio based on the core region power and total power, adjusts the seed optical coupling module, and adjusts the core-to-cladding ratio to the maximum, so that the seed optical coupling efficiency in the photonic crystal fiber reaches the maximum.

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