A quasi-single-mode VCSEL / hollow-core fiber coupling fiber, coupling interface and manufacturing method

Abstract

This invention discloses a quasi-single-mode VCSEL / hollow-core fiber coupling optical fiber, coupling interface, and fabrication method. The coupling fiber includes a thin-diameter outer diameter fiber segment, a first fiber segment, a higher-order mode filtering fiber segment, and a second fiber segment. The thin-diameter outer diameter fiber segment supports few-mode transmission at a wavelength of 850nm, and its core diameter is close to the aperture diameter of the quasi-single-mode VCSEL. The inner diameter of the first fiber segment is the same as that of the thin-diameter outer diameter fiber segment, but its outer diameter is larger. The higher-order mode filtering fiber segment operates in the same wavelength band as the quasi-single-mode VCSEL and transmits in single-mode at this wavelength. The end of the second fiber segment is treated with a tapered heat-diffusion core to gradually expand its fundamental mode field diameter to match that of the hollow-core fiber. This invention, through a unique all-fiber structure, couples the signal light from an 850nm quasi-single-mode VCSEL into a hollow-core fiber link with low delay, low dispersion, and low loss.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber communication, and specifically relates to a quasi-single-mode VCSEL / hollow fiber coupling interface suitable for short-distance high-speed data transmission. Background Technology

[0002] Over the past decade, data centers and networks have become indispensable supporting platforms for numerous internet applications, such as search engines, online interactive maps, social networks, video streaming, and the Internet of Things, with information transmission capabilities within data centers experiencing rapid growth. For example, the bidirectional transmission bandwidth of Google's data center clusters has increased 1,000 times in the past ten years.

[0003] The surge in data traffic has also created a strong demand for high-speed, low-latency intensity modulation / direct detection (IM / DD) optical transmission technology. For IM-DD, traditional silica fiber links face insurmountable intrinsic barriers in terms of latency, 850nm band dispersion, and loss. Meanwhile, antiresonant hollow fiber, with its near-single-mode characteristics, is attracting increasing attention from academia and industry due to its excellent low channel noise, tolerance to high laser power, and ability to reduce the complexity of digital signal processing.

[0004] In terms of time delay, the basic principle of traditional solid fiber light guiding is total internal reflection between the fiber core and cladding (both of which are composed of silicon dioxide molecules). The complete overlap of light waves with silicon dioxide causes the speed of light in the fiber to be about 1 / 3 slower than the speed of light in a vacuum. In contrast, the light waves in hollow fiber hardly overlap with the quartz glass, and its speed of light is almost equal to the speed of light in a vacuum.

[0005] Regarding dispersion, fiber chromatic dispersion originates from both the material and the waveguide. Since air material dispersion is negligible, the chromatic dispersion of antiresonant hollow-core fiber is approximately 2-3 ps / nm / km within the spectral window. This is 6-8 times lower than G.652.D fiber in the C-band and 30-50 times lower than silica fiber in the 850nm band. In IM / DD systems, since dispersion compensation is typically not performed, low dispersion helps mitigate power selective fading caused by dispersion. A lower dispersion slope further reduces the difficulty and complexity of dispersion compensation, increasing the total number of channels that can be wavelength division multiplexed across the entire band.

[0006] In terms of loss, with the advancement of drawing technology, anti-resonant hollow fiber has achieved the lowest loss of silica fiber across the entire spectrum. The typical loss of OM4 silica fiber in the 850nm band is 2.3dB / km, while the latest drawn anti-resonant hollow fiber has reached a level of 0.33dB / km in this band.

[0007] In data center internal information transmission, three interconnect technologies have been used to optimize bandwidth costs and energy efficiency: First, copper cables connecting servers within a rack to top-level switches, with typical transmission distances of less than a few meters; second, short-distance optical interconnects based on parallel multimode fiber (MMF) or optical transceivers based on parallel single-mode fiber (SMF), used to connect top-level switches to aggregation layer switches, with typical transmission distances up to 100 meters; and third, coarse wavelength division multiplexing (CWDM) transmission links based on SMF, used to connect aggregation layer switches between each other or between aggregation switches and the backbone switching layer network, with transmission distances up to 1 kilometer.

[0008] For the second interconnect technology, the 850nm Vertical-Cavity Surface-Emitting Laser (VCSEL) offers advantages such as low cost, small size, and compact structure. The VCSEL-MMF-IMDD combination has proven to be the optimal solution for data transmission within this distance range. For longer transmission distances, due to the high dispersion and high loss characteristics of quartz glass at 850nm wavelength, traditional fiber optic links cannot achieve distortion-free transmission of optical pulses. Therefore, the 850nm VCSEL light source must be abandoned in favor of the more expensive third technology: Coarse Wavelength Division Multiplexing (CWDM) based on SMF. This technology uses a 1310nm side-emitting laser and an externally modulated optical signal loading scheme, which not only significantly increases transmission costs but also occupies valuable space resources within the data center.

[0009] Due to the unique light-guiding mechanism of anti-resonant hollow fiber, low latency, low dispersion, and low loss performance can be designed at a wavelength of 850nm, and the transmission distance will no longer be limited to within 100 meters. VCSEL-HCF-IMDD is expected to replace the third transmission solution currently used in data centers. It is not only more cost-effective than SMF-CWDM interconnect, but also, due to the excellent structural compactness of VCSEL and HCF (Hollow Core Fiber), it can achieve a high degree of space integration interface configuration, and the space utilization will be far greater than the SMF-CWDM solution. In addition, thanks to the low power consumption of VCSEL and the low latency characteristics of HCF, the new interconnect technology can also significantly improve signal transmission capacity and speed.

[0010] However, achieving efficient coupling in VCSEL-HCF presents several challenges. Due to the significant difference between the VCSEL's output aperture and the HCF's mode-field diameter (MFD), the coupling between them requires specialized design. Currently, two existing coupling methods exist: First, a fixed-length coreless fiber and a graded-index fiber are fused to the HCF endface. The graded-index fiber adjusts the beam's mode-field diameter to reduce coupling loss, while the coreless fiber between the graded-index fiber and the HCF acts as an axial spacer to control the focal point of the converged beam. However, this method imposes high precision requirements on fiber length and specifications, resulting in excessively high manufacturing costs and hindering practical application. Second, multiple lenses are used, with the beam's mode-field diameter and focal point position altered by adjusting lens specifications and spacing. Lens coupling also incurs high costs, and optical path adjustment demands significant operator skill and experience, while also consuming considerable space. In conclusion, current coupling interface technologies are unsuitable for efficient coupling in the all-fiber structure of VCSEL-HCF. Summary of the Invention

[0011] To address the aforementioned problems in the existing technology, this application proposes a quasi-single-mode VCSEL / hollow-core fiber coupling optical fiber, coupling interface, and fabrication method. Through a unique all-fiber structure, the signal light from an 850nm quasi-single-mode VCSEL is coupled into a hollow-core fiber link with low delay, low dispersion, and low loss. In this design, the all-fiber structure not only significantly saves space resources but also expands the transmission capacity through the interconnection of multiple links.

[0012] The technical solution adopted in this invention is as follows:

[0013] According to a first aspect, the present invention provides a quasi-single-mode VCSEL / hollow-core fiber coupled optical fiber, comprising:

[0014] A thin outer diameter fiber segment is used to couple with the output aperture of a quasi-single-mode VCSEL. The thin outer diameter fiber segment supports few-mode transmission at a wavelength of 850nm, and its core diameter is close to the output aperture diameter of the quasi-single-mode VCSEL.

[0015] A first optical fiber segment is connected to the thin outer diameter optical fiber segment. The inner diameter of the first optical fiber segment is the same as the inner diameter of the thin outer diameter optical fiber segment, and the outer diameter of the first optical fiber segment is larger than the outer diameter of the thin outer diameter optical fiber segment.

[0016] A higher-order mode filtering fiber segment is coupled to the first fiber segment. The higher-order mode filtering fiber segment operates in the same wavelength band as the quasi-single-mode VCSEL and transmits in single-mode in this wavelength band. The inner diameter of the higher-order mode filtering fiber segment is different from the inner diameter of the first fiber segment, and the outer diameter of the higher-order mode filtering fiber segment is close to the outer diameter of the first fiber segment.

[0017] The second fiber segment is coupled to the higher-order mode filtering fiber segment. The inner and outer diameters of the second fiber segment are the same as those of the first fiber segment. It supports few-mode transmission at a wavelength of 850nm. The end of the second fiber segment is treated with a tapered heat-diffusion core so that the fundamental mode field diameter gradually expands to match the mode field diameter of the hollow fiber.

[0018] Optionally, the main body of both the first and second fiber segments is Corning SMF-28 fiber.

[0019] Optionally, the thin outer diameter fiber segment is obtained by etching Corning SMF-28 fiber in a hydrofluoric acid solution to reduce its outer diameter, and then cutting off the end.

[0020] Optionally, the high-order mode filtering fiber segment is a CS780 fiber from Yangtze Optical Fibre and Cable.

[0021] Optionally, the second fiber segment has a tapered heat diffusion core at its end.

[0022] According to the second aspect, the present invention proposes a quasi-single-mode VCSEL / hollow-core fiber coupling interface, comprising a quasi-single-mode VCSEL / hollow-core fiber coupling fiber and a housing as described in the first aspect above, wherein the housing covers one end of the quasi-single-mode VCSEL / hollow-core fiber coupling fiber coupled to the light output hole of the quasi-single-mode VCSEL, and exposes the end face.

[0023] Optionally, the quasi-single-mode VCSEL / hollow-core fiber coupling has multiple fibers, corresponding to the light output holes of multiple quasi-single-mode VCSELs; the housing is provided with positioning pins, the positions of which match the positions of the positioning holes set on the mounting planes of the light output holes of multiple quasi-single-mode VCSELs.

[0024] According to a third aspect, the present invention proposes a method for fabricating a quasi-single-mode VCSEL / hollow-core fiber coupling interface, used to manufacture the quasi-single-mode VCSEL / hollow-core fiber coupling interface of the second aspect mentioned above, comprising the following steps:

[0025] A thin-diameter solid fiber segment is coupled to the output aperture of the quasi-single-mode VCSEL.

[0026] High-order mode components in optical fibers are filtered out in the working band of quasi-single-mode VCSELs.

[0027] Low-loss coupling is performed between solid fiber segments and hollow fiber segments;

[0028] Fabricate an all-fiber optic coupling interface.

[0029] Optionally, the step of coupling the solid fiber segment with the quasi-single-mode VCSEL output aperture specifically includes:

[0030] Corning SMF-28 fiber was selected as the solid fiber segment;

[0031] A section of Corning SMF-28 optical fiber was immersed in hydrofluoric acid for etching to reduce the outer diameter of the fiber.

[0032] Cutting is performed in the corroded area to ensure a flat fiber end face;

[0033] The specific steps for low-loss coupling between the solid fiber segment and the hollow fiber include:

[0034] One end of Corning SMF-28 optical fiber is gradient heated to form a tapered thermal diffusion core;

[0035] The end face of the prepared conical heat diffusion core is polished and / or coated.

[0036] Optionally, the step of filtering out higher-order mode components in the fiber in the quasi-single-mode VCSEL operating band specifically includes:

[0037] A section of single-mode fiber in the VCSEL operating band is installed in the middle of Corning SMF-28 fiber;

[0038] The Corning SMF-28 fiber was fused with the single-mode fiber in the working band of the VCSEL.

[0039] The beneficial effects of this invention are as follows:

[0040] Some embodiments of the present invention improve the efficiency of output light entering the optical fiber by using optical fiber segments with appropriate core diameter and small outer diameter to collect the output light of a single-mode VCSEL; by setting a high-order mode filtering optical fiber segment with the same operating band as the quasi-single-mode VCSEL and which is used for single-mode transmission in that band, high-order mode filtering can be performed on the signal light transmitted in the optical fiber. This is an effective measure to ensure stable beam coupling efficiency and prevent intermodal dispersion interference of IMDD signals during long-distance transmission; by using tapered thermal diffusion core technology to expand the fundamental mode field diameter of the solid fiber to match that of the hollow fiber, the loss of signal light entering the hollow fiber link is reduced.

[0041] In some embodiments of the present invention, the optical signal output of a single-mode VCSEL is coupled by aligning it with an optical fiber with a core diameter of 8.2 μm, which can greatly improve the coupling efficiency. The optical fiber with a core diameter of 8.2 μm is similar to the aperture of the quasi-single-mode VCSEL.

[0042] Some embodiments of the present invention reduce the outer diameter of the collecting fiber segment by means of hydrofluoric acid corrosion, thereby reducing the impact of the fiber end face edge on coupling. The advantage of this method is that the corrosion of the fiber cladding by hydrofluoric acid does not affect the fiber core.

[0043] Some embodiments of the present invention use YOFC CS780 fiber as the high-order mode filtering fiber segment. When a multimode optical signal passes through the high-order mode filtering fiber segment, the high-order mode components are filtered out by the fiber cladding, ensuring stable beam coupling efficiency and preventing intermodal dispersion interference of the IMDD signal during long-distance transmission, thereby improving the transmission quality and distance of the optical signal.

[0044] Some embodiments of the present invention reduce the coupling loss between Corning SMF-28 optical fiber and hollow optical fiber by using tapered thermal diffusion core technology to change the fundamental mode field diameter of Corning SMF-28 optical fiber.

[0045] Some embodiments of the present invention involve polishing and / or coating the fiber end face of the prepared tapered heat diffusion core to form an antireflection film, which can reduce the reflection loss at 850nm wavelength and improve the coupling efficiency.

[0046] Some embodiments of the present invention determine the arrangement of the quasi-single-mode VCSEL / hollow-core fiber coupling by arranging the output apertures of the 850nm quasi-single-mode VCSEL, thereby creating a quasi-single-mode VCSEL / hollow-core fiber coupling interface. The transmission capacity can be expanded by connecting multiple links. The coupling speed is improved by adding positioning holes at the 850nm quasi-single-mode VCSEL end. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of an 850nm quasi-single-mode VCSEL-HCF transmission link, as exemplified by an embodiment of the present invention.

[0049] Figure 2 This is a cross-sectional view of an 850nm quasi-single-mode VCSEL, as exemplified in an embodiment of the present invention.

[0050] Figure 3 This is a cross-sectional view of a hollow optical fiber as exemplified in an embodiment of the present invention;

[0051] Figure 4 This is an example of an unprocessed Corning SMF-28 optical fiber cross-section from an embodiment of the present invention;

[0052] Figure 5 This is a schematic diagram illustrating the potential obstruction at the fiber end face edge when Corning SMF-28 optical fiber is coupled to the output aperture of a VCSEL, as exemplified by an embodiment of the present invention.

[0053] Figure 6 This is a cross-sectional view of a Corning SMF-28 optical fiber with an outer diameter of 30 μm after being etched with hydrofluoric acid, as exemplified in an embodiment of the present invention.

[0054] Figure 7 This is a longitudinal schematic diagram of a Corning SMF-28 optical fiber after hydrofluoric acid etching, as exemplified in an embodiment of the present invention.

[0055] Figure 8 This is a cross-sectional view of a high-order mode filtering fiber segment, as exemplified in an embodiment of the present invention.

[0056] Figure 9 This is a schematic diagram illustrating the splicing of a high-order mode filtering fiber segment to Corning SMF-28 fiber at both ends, as exemplified in an embodiment of the present invention.

[0057] Figure 10 This is a schematic diagram illustrating the tapered thermal diffusion core treatment of Corning SMF-28 optical fiber, as exemplified by an embodiment of the present invention.

[0058] Figure 11 This is a schematic diagram of the tapered heat-diffusion core end face of Corning SMF-28 optical fiber, as exemplified in an embodiment of the present invention, connected to a hollow-core optical fiber.

[0059] Figure 12 This is a schematic diagram of a quasi-single-mode VCSEL / hollow fiber coupling interface, as exemplified by an embodiment of the present invention.

[0060] Figure 13 This is a schematic diagram illustrating the fabrication process of a quasi-single-mode VCSEL / hollow-core fiber coupling interface, as exemplified in an embodiment of the present invention.

[0061] Labels in the attached diagram:

[0062] 100 - Quasi-single-mode VCSEL; 110 - Optical exit aperture; 210 - Quasi-single-mode VCSEL / hollow-core fiber coupling fiber; 211 - Small outer diameter fiber segment; 212 - First fiber segment; 212' - Corning SMF-28 fiber; 213 - High-order mode filtering fiber segment; 214 - Second fiber segment; 215 - Tapered heat diffusion core; 216 - Antireflection coating; 300 - Hollow-core fiber; 311 - First ceramic ferrule; 312 - C-sleeve; 313 - Second ceramic ferrule; 400 - Receiver end. Detailed Implementation

[0063] The present invention will be further described in detail below with reference to the accompanying drawings.

[0064] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive element, but such modifications are protected by patent law as long as they fall within the scope of the claims of the present invention.

[0065] like Figures 1-11 As shown in the embodiment of this application, a quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 is proposed, including a thin-diameter fiber segment 211, a first fiber segment 212, a high-order mode filtering fiber segment 213, and a second fiber segment 214. The thin-diameter fiber segment 211 is used for coupling with the output aperture 110 of the quasi-single-mode VCSEL. The thin-diameter fiber segment 211 supports few-mode transmission at a wavelength of 850nm, and its core diameter is close to the aperture of the output aperture 110 of the quasi-single-mode VCSEL. The first fiber segment 212 is connected to the thin-diameter fiber segment 211. The inner diameter of the first fiber segment 212 is the same as the inner diameter of the thin-diameter fiber segment 211, and the outer diameter of the first fiber segment 212 is larger than the outer diameter of the thin-diameter fiber segment 211. A high-order mode filtering fiber segment 213 is coupled to the first fiber segment 212. The high-order mode filtering fiber segment 213 operates in the same wavelength band as the quasi-single-mode VCSEL and transmits in single-mode in this band. The inner diameter of the high-order mode filtering fiber segment 213 is different from that of the first fiber segment 212, while the outer diameter of the high-order mode filtering fiber segment 213 is close to that of the first fiber segment 212. A second fiber segment 214 is coupled to the high-order mode filtering fiber segment 213. The inner and outer diameters of the main body of the second fiber segment 214 are the same as those of the first fiber segment 212. Through a tapered heat-diffusion core treatment, the fundamental mode field diameter at the end of the second fiber segment 214 is gradually expanded to match the mode field diameter of the hollow fiber 300.

[0066] See Figure 1 The optical signal is output from the output aperture 110 of the quasi-single-mode VCSEL 100, and sequentially passes through the thin outer diameter fiber segment 211, the first fiber segment 212, the high-order mode filtering fiber segment 213, the second fiber segment 214, and the hollow fiber 300 of the quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210, before finally being output to the receiving end 400 for signal processing and analysis. In the transmission of the optical signal, the hollow fiber 300 undertakes the main transmission task. The functions of the quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 are to reduce the coupling loss between the light source and the fiber optic link and to filter out high-order mode components in the optical signal.

[0067] In practice, the quasi-single-mode VCSELs involved operate at 850nm, and the thin outer diameter fiber segments can use Corning SMF28 single-mode fiber etched with hydrofluoric acid.

[0068] In this embodiment, by using an optical fiber segment 211 with a suitable core diameter and a small outer diameter to collect the output light of the quasi-single-mode VCSEL, the efficiency of the output light entering the optical fiber is improved. By setting a high-order mode filtering optical fiber segment 213 that is the same as the operating band of the quasi-single-mode VCSEL and is used for single-mode transmission in this band, high-order mode filtering can be performed on the signal light transmitted in the optical fiber. This is an effective measure to ensure stable beam coupling efficiency and prevent intermodal dispersion interference of the IMDD signal during long-distance transmission. By using tapered thermal diffusion core technology to expand the fundamental mode field diameter of the solid fiber to match the mode field diameter of the hollow fiber, the loss of signal light entering the hollow fiber link is reduced.

[0069] In some embodiments, the main body of the first optical fiber segment 212 and the second optical fiber segment 214 is Corning SMF-28 optical fiber.

[0070] like Figure 2 As shown, the 850nm quasi-single-mode VCSEL has a relatively small aperture of 8μm; Figure 3 As shown, the core diameter of the hollow fiber is 30μm, and the mode field diameter is approximately 70% of the core diameter, about 21μm, which is much larger than the aperture of the VCSEL output aperture, resulting in extremely high coupling loss when directly aligned.

[0071] Coupling the output optical signal of a single-mode VCSEL using an 8μm core diameter optical fiber can greatly improve coupling efficiency. In this embodiment, Corning SMF-28 fiber is selected. Figure 4 As shown, Corning's SMF-28 fiber 212' has an outer diameter of 125μm and a core diameter of approximately 8.2μm, which is consistent with the aperture size of the VCSEL, allowing for good coupling.

[0072] In some embodiments, the thin outer diameter fiber segment 211 is obtained by etching Corning SMF-28 fiber in a hydrofluoric acid (HF) solution to reduce its outer diameter and then cutting off the end.

[0073] like Figure 5 As shown, when Corning SMF-28 fiber 212' is directly aligned and coupled with the output aperture 110 of the VCSEL, due to the extremely small size of both, there may be a non-zero tilt angle θ between the fiber and the VCSEL in the vertical direction during alignment. Due to the tilt of the fiber, there will be an air gap d between the fiber core and the output aperture 110. The air gap d is proportional to the tilt angle θ and the outer diameter D of the fiber. The impact of the obstruction at the edge of the fiber end face on the coupling can be reduced by decreasing the outer diameter D of the Corning SMF-28 fiber.

[0074] This example demonstrates reducing the outer diameter of optical fiber using hydrofluoric acid etching. The advantage of this method is that the etching of the fiber cladding by hydrofluoric acid does not affect the fiber core. Corning SMF-28 optical fiber is placed in a 40% concentration hydrofluoric acid solution and etched until a thinner fiber with an outer diameter of 30 μm is achieved. The etched area is then cut to ensure a flat fiber end face. The cross-section of the thinner outer diameter fiber segment is shown below. Figure 6 As shown, the fiber core diameter remains unchanged, while the outer diameter is reduced to 30 μm. A longitudinal schematic diagram of Corning SMF-28 fiber after hydrofluoric acid etching is shown below. Figure 7 As shown, one end forms a thin outer diameter optical fiber segment 211, and the other end serves as the first optical fiber segment 212.

[0075] In some embodiments, the high-order mode filtering fiber segment 213 can be a CS780 fiber from Yangtze Optical Fibre and Cable.

[0076] Currently, commercially available 850nm band VCSELs are all in quasi-single-mode operation, and the optical signal still contains higher-order mode components (LP11). The presence of higher-order mode components can cause intermodal dispersion interference in IMDD signals during long-distance transmission, affecting the transmission distance and quality of the signal. Higher-order modes may also be excited at fiber splices and bends.

[0077] Furthermore, since Corning SMF-28 fiber operates in a few-mode mode at 850nm, it is necessary to filter out the signal light in the Corning SMF-28 fiber by passing through a section of 850nm single-mode fiber (such as YOFC CS780 fiber). This is an effective measure to ensure stable beam coupling efficiency and prevent intermodal dispersion interference of the IMDD signal during long-distance transmission.

[0078] The formula is established based on the normalized frequency parameters of the optical fiber:

[0079]

[0080] Where a is the fiber radius, λ is the wavelength, and n core and n cald These are the refractive indices of the core and cladding, respectively. When the V-parameter of the optical fiber is less than 2.405, it operates in single-mode, meaning only the fundamental mode can transmit, while other higher-order modes suffer extremely high transmission losses. For Corning SMF-28 fiber, with a V-parameter of 2.405, the cutoff wavelength is 1260nm, and it operates in multimode at 850nm. This embodiment uses Yangtze Optical Fibre and Cable's CS780 fiber. Figure 8As shown, this optical fiber has an outer diameter of 125 μm and a core diameter of 5 μm. When V = 2.405, its cutoff wavelength is 730 nm, satisfying the single-mode transmission condition at 850 nm. When a multimode optical signal passes through the YOFC CS780 optical fiber, the higher-order mode components present are filtered out by the fiber cladding, ensuring stable beam coupling efficiency and preventing intermodal dispersion interference of the IMDD signal during long-distance transmission, thus improving the transmission quality and distance of the optical signal.

[0081] The fusion splicing of Corning SMF-28 fiber and Yangtze Optical Fibre and Cable (YOFC) CS780 fiber is as follows: Figure 9 As shown. The main body of the first fiber segment 212 and the second fiber segment 214 is Corning SMF-28 fiber, and the high-order mode filtering fiber segment 213 can be YOFC CS780 fiber. Because the core diameters of Corning SMF-28 fiber and YOFC CS780 fiber differ significantly, fusion splicing between the fibers will cause substantial loss, and improper fusion splicing will also excite high-order mode components in the fiber. However, when the taper length at the fusion splice of the two fibers reaches a certain value, it can be approximated as an adiabatic mode transition with low loss. When fusion splicing the two fibers, the discharge time should be increased, and the discharge intensity should not be too high. Excessive current will cause core diffusion, increasing loss and exciting high-order mode components in the fiber. By adjusting the discharge intensity and discharge time, the fusion loss of the two fibers can be reduced to as low as 0.2 dB, with no additional reflection at the fusion splice point.

[0082] It should be noted that silica optical fibers have severe chromatic dispersion at a wavelength of 850nm. When the walk-off time caused by chromatic dispersion is greater than the pulse timing length of the 850nm quasi-single-mode VCSEL optical signal, the optical signal cannot be transmitted normally in the link. Therefore, the total length of Corning SMF-28 and YOFC CS780 optical fibers in the link should not be too long.

[0083] In some embodiments, such as Figure 10 As shown, the end of the second optical fiber segment 214 has a tapered heat diffusion core 215 obtained by gradient heating, and the end face of the tapered heat diffusion core 215 has an anti-reflection film 216.

[0084] In specific implementation, such as Figure 10As shown, the main body of the second fiber segment 214 is Corning SMF-28 fiber. Due to the difference in mode field diameter between the Corning SMF-28 fiber and the hollow fiber, a mode field adapter is needed to achieve coupling between the two fibers. Heating the end of the Corning SMF-28 fiber causes the doped ions in the fiber core to diffuse radially. Gradient heating of the fiber creates a gradually tapering temperature distribution in the heated region, forming a tapered heat-diffusion core 215. Within this tapered region, the fundamental mode field diameter of the fiber gradually increases until it matches the mode field diameter of the hollow fiber 300. By using the tapered heat-diffusion core technology to change the fundamental mode field diameter of the Corning SMF-28 fiber, expanding it to match the mode field diameter of the hollow fiber 300, the coupling loss between the Corning SMF-28 fiber and the hollow fiber 300 can be reduced.

[0085] On the other hand, when an optical signal enters a hollow-core fiber from Corning SMF-28 fiber, it can be approximated as propagating from glass to air, resulting in approximately 0.15 dB of Fresnel reflection loss. This reflected light can also damage the laser. In this embodiment, by polishing and / or coating the end face of the fabricated tapered heat-diffusing core fiber 215 to form an antireflection coating 216, the reflection loss at 850 nm wavelength can be reduced, and the coupling efficiency can be improved.

[0086] As an example, such as Figure 11 As shown, the coupling method between the end of the second optical fiber segment 214 with the tapered heat diffusion core 215 and the hollow optical fiber 300 is as follows: the end of the second optical fiber segment 214 with the tapered heat diffusion core 215 is inserted into the first ceramic ferrule 311, the hollow optical fiber 300 is inserted into the second ceramic ferrule 313, and then the first ceramic ferrule 311 and the second ceramic ferrule 313 with optical fiber are both placed into the C sleeve 312 for alignment.

[0087] The present invention also provides an embodiment, such as Figure 12 As shown, a quasi-single-mode VCSEL / hollow-core fiber coupling interface 200 is disclosed, including the quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 and a housing 220 as described in the above embodiment. The housing 220 covers the end of the quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 that is coupled to the light output port 110 of the quasi-single-mode VCSEL, and exposes the end face.

[0088] In some embodiments, the quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 has multiple fibers, corresponding to the light output holes 110 of multiple quasi-single-mode VCSELs; the housing 220 is provided with positioning pins 221, the positions of which match the positioning holes 120 provided on the mounting plane of the light output holes 110 of multiple quasi-single-mode VCSELs.

[0089] like Figure 2 As shown, the size of a single emitting region in an 850nm quasi-single-mode VCSEL is 220×225 (μm²), and multiple emitting regions can be uniformly and closely arranged to form a single emitting panel. On the other side, the outer diameter of the Corning SMF-28 fiber at the coupling end is only 125μm. By rationally arranging the fibers, each of the 110 light-emitting apertures of the 850nm quasi-single-mode VCSEL can be utilized, greatly expanding the data transmission capacity and improving energy efficiency.

[0090] In specific implementation, such as Figure 12 As shown, the arrangement of the quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 is determined by the arrangement of the output aperture 110 of the 850nm quasi-single-mode VCSEL, thereby fabricating the quasi-single-mode VCSEL / hollow-core fiber coupling interface 200. For faster coupling, a positioning hole 120 is added to the 850nm quasi-single-mode VCSEL end, positioned on the mounting plane of the output aperture 110 of the 850nm quasi-single-mode VCSEL. A corresponding positioning pin 221 is fabricated at the coupler interface end. During coupling, the positioning hole 120 and the positioning pin 221 are aligned.

[0091] This invention also relates to a method for fabricating a quasi-single-mode VCSEL / hollow-core fiber coupling interface, used to manufacture the quasi-single-mode VCSEL / hollow-core fiber coupling interface in the above embodiments, and has corresponding technical effects. For example... Figure 13 As shown, it includes steps S10 to S40.

[0092] S10, a solid fiber segment is coupled to the output aperture of the quasi-single-mode VCSEL.

[0093] Step S10 specifically includes:

[0094] S11 uses Corning SMF-28 fiber as the solid fiber segment.

[0095] S12, a section of Corning SMF-28 optical fiber is immersed in hydrofluoric acid for etching to reduce the outer diameter of the optical fiber;

[0096] S13, cut the corroded area to ensure the fiber end face is flat.

[0097] S20 filters out higher-order mode components in optical fibers in the quasi-single-mode VCSEL operating band.

[0098] Step S20 specifically includes:

[0099] S21, install a section of single-mode fiber in the VCSEL operating band in the middle of Corning SMF-28 fiber;

[0100] S22, fusion splice Corning SMF-28 fiber with the single-mode fiber in the working band of the VCSEL.

[0101] In practical implementation, the single-mode fiber in the working band of VCSEL can be the CS780 fiber from Yangtze Optical Fibre and Cable.

[0102] S30 enables low-loss coupling between solid fiber segments and hollow fiber segments.

[0103] Step S30 specifically includes:

[0104] S31, Gradient heating is applied to one end of Corning SMF-28 optical fiber to form a tapered thermal diffusion core;

[0105] S32, Polishing and / or coating the end face of the prepared conical heat diffusion core.

[0106] S40, used to fabricate an all-fiber optic coupling interface.

[0107] Step S40 encapsulates the quasi-single-mode VCSEL / hollow-core fiber coupling fiber created in steps S10 to S30 into a housing to form a quasi-single-mode VCSEL / hollow-core fiber coupling interface of the fiber structure.

[0108] In a quasi-single-mode VCSEL / hollow-core fiber coupling interface, multiple quasi-single-mode VCSEL / hollow-core fiber coupling fibers can be set to connect to the output holes of multiple quasi-single-mode VCSELs respectively, and positioning pins are set to match the positioning holes set on the mounting plane of the output holes of multiple quasi-single-mode VCSELs.

[0109] By performing steps S10-S40, the all-fiber structure coupling interface for the 850nm quasi-single-mode VCSEL to the hollow fiber can be completely fabricated, enabling low-latency, low-dispersion, and low-loss transmission of the 850nm quasi-single-mode VCSEL optical signal.

[0110] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. The present invention is not limited to the above optional embodiments. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention, regardless of any changes in its shape or structure, should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A quasi-single-mode VCSEL / hollow-core fiber coupled optical fiber, characterized in that, include: A thin outer diameter fiber segment is used to couple with the output aperture of a quasi-single-mode VCSEL. The thin outer diameter fiber segment supports few-mode transmission at a wavelength of 850nm, and its core diameter is close to the output aperture diameter of the quasi-single-mode VCSEL. A first optical fiber segment is connected to the thin outer diameter optical fiber segment. The inner diameter of the first optical fiber segment is the same as the inner diameter of the thin outer diameter optical fiber segment, and the outer diameter of the first optical fiber segment is larger than the outer diameter of the thin outer diameter optical fiber segment. A higher-order mode filtering fiber segment is coupled to the first fiber segment. The higher-order mode filtering fiber segment operates in the same wavelength band as the quasi-single-mode VCSEL and transmits in single-mode in this wavelength band. The inner diameter of the higher-order mode filtering fiber segment is different from the inner diameter of the first fiber segment, and the outer diameter of the higher-order mode filtering fiber segment is close to the outer diameter of the first fiber segment. The second fiber segment is coupled to the higher-order mode filtering fiber segment. The inner and outer diameters of the second fiber segment are the same as those of the first fiber segment. It supports few-mode transmission at a wavelength of 850nm. The end of the second fiber segment is treated with a tapered heat-diffusion core so that its fundamental mode field diameter gradually expands to match the mode field diameter of the hollow fiber. The second optical fiber segment has a tapered heat diffusion core at its end; the end face of the tapered heat diffusion core has an anti-reflection coating.

2. The quasi-single-mode VCSEL / hollow-core fiber coupled optical fiber according to claim 1, characterized in that, The main body of both the first and second fiber segments is Corning SMF-28 fiber.

3. The quasi-single-mode VCSEL / hollow-core fiber coupled optical fiber according to claim 2, characterized in that, The thin outer diameter fiber segment is obtained by etching Corning SMF-28 fiber in hydrofluoric acid solution to reduce its outer diameter, and then cutting off the end.

4. The quasi-single-mode VCSEL / hollow-core fiber coupled optical fiber according to claim 2, characterized in that, The high-order mode filtering fiber segment is a CS780 fiber from Yangtze Optical Fibre and Cable.

5. A quasi-single-mode VCSEL / hollow-core fiber coupling interface, comprising a quasi-single-mode VCSEL / hollow-core fiber coupling fiber and a housing as described in any one of claims 1-4, characterized in that, The housing covers one end of the quasi-single-mode VCSEL / hollow-core fiber coupled to the light output hole of the quasi-single-mode VCSEL, and exposes the end face.

6. A quasi-single-mode VCSEL / hollow-core fiber coupling interface according to claim 5, characterized in that, The quasi-single-mode VCSEL / hollow-core fiber coupling has multiple fibers, corresponding to the light output holes of multiple quasi-single-mode VCSELs; the housing is provided with positioning pins, the positions of which match the positions of the positioning holes set on the mounting planes of the light output holes of multiple quasi-single-mode VCSELs.

7. A method for fabricating a quasi-single-mode VCSEL / hollow-core fiber coupling interface, characterized in that, Includes the following steps: The solid fiber segment is coupled to the output aperture of the quasi-single-mode VCSEL. High-order mode components in optical fibers are filtered out in the working band of quasi-single-mode VCSELs. Low-loss coupling is performed between solid fiber segments and hollow fiber segments; Fabricate an all-fiber optic coupling interface.

8. The method for fabricating a quasi-single-mode VCSEL / hollow-core fiber coupling interface according to claim 7, characterized in that, The specific steps for setting the solid fiber segment to couple with the quasi-single-mode VCSEL output aperture include: Corning SMF-28 fiber was selected as the solid fiber segment; A section of Corning SMF-28 optical fiber was immersed in hydrofluoric acid for etching to reduce the outer diameter of the fiber. Cutting is performed in the corroded area to ensure a flat fiber end face; The specific steps for low-loss coupling between the solid fiber segment and the hollow fiber include: One end of Corning SMF-28 optical fiber is gradient heated to form a tapered thermal diffusion core; The end face of the prepared conical heat diffusion core is polished and / or coated.

9. A method for fabricating a quasi-single-mode VCSEL / hollow-core fiber coupling interface according to claim 8, characterized in that, The steps for filtering out higher-order mode components in the working band of a quasi-single-mode VCSEL specifically include: A section of single-mode fiber in the VCSEL operating band is installed in the middle of Corning SMF-28 fiber; The Corning SMF-28 fiber was fused with the single-mode fiber in the working band of the VCSEL.

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