Quasi-single-mode VCSEL / hollow-core optical fiber coupling optical fiber, coupling interface and manufacturing method

Abstract

According to the quasi-single-mode VCSEL / hollow-core optical fiber coupling optical fiber, the coupling interface and the manufacturing method, the coupling optical fiber comprises a small-outer-diameter optical fiber section, a first optical fiber section, a high-order mode filtering optical fiber section and a second optical fiber section, the small-outer-diameter optical fiber section supports few-mode transmission at the wavelength of 850 nm, and the diameter of a fiber core of the small-outer-diameter optical fiber section is close to the aperture of a light outlet hole of a quasi-single-mode VCSEL; the inner diameter of the first optical fiber section is the same as that of the small-outer-diameter optical fiber section, and the outer diameter of the first optical fiber section is larger than that of the small-outer-diameter optical fiber section; the working wave band of the high-order mode filtering optical fiber section is the same as that of the quasi single-mode VCSEL, and the high-order mode filtering optical fiber section is in single-mode transmission in the wave band; the tail end of the second optical fiber section is processed through the conical thermal diffusion core, so that the fundamental mode field diameter of the second optical fiber section is gradually expanded to be matched with the hollow-core optical fiber mode field diameter. According to the invention, through a unique all-fiber structure, signal light of the 850nm quasi-single-mode VCSEL is coupled into a hollow-core fiber link in a low-delay, low-dispersion and low-loss manner.

Description

Technical Field

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

[0002] In the past decade, data centers and networks have become an indispensable support platform for many Internet applications (such as search engines, online interactive maps, social networks, video streaming, and the Internet of Things), and the information transmission capabilities within data centers have been rapidly improved. For example, the two-way transmission bandwidth of Google's data center cluster has increased 1,000 times in the past decade.

[0003] The surge in data traffic has also brought about a strong demand for high-speed, low-latency intensity modulation / direct detection (IM / DD) optical transmission technology. For IM-DD, traditional quartz fiber links have insurmountable intrinsic barriers in terms of delay, 850nm band dispersion and loss. Antiresonant hollow-core fibers with near-single-mode characteristics are increasingly attracting attention from academia and industry because of their good low channel noise, tolerance to high laser power and reduced complexity of digital signal processing.

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

[0005] In terms of dispersion, the chromatic dispersion of optical fiber comes from both the material and the waveguide. Since the dispersion of air material can be basically ignored, the chromatic dispersion of antiresonant hollow core fiber is about 2-3ps / nm / km within the spectrum window, which is 6-8 times lower than that of G.652.D fiber in the C band and 30-50 times lower than that of quartz fiber in the 850nm band. In IM / DD systems, since dispersion compensation is usually not performed, low dispersion will help alleviate the power selective fading caused by dispersion. The lower dispersion slope also further reduces the difficulty and complexity of dispersion compensation, and increases the total number of channels that can be wavelength-division multiplexed in the full band.

[0006] In terms of loss, with the advancement of drawing technology, antiresonant hollow-core optical fiber has surpassed the lowest loss of quartz optical fiber in the entire spectrum. The typical loss of OM4 quartz optical fiber in the 850nm band is 2.3dB / km, while the latest drawn antiresonant hollow-core optical fiber has reached the level of 0.33dB / km in this band.

[0007] In the information transmission within the data center, three interconnection technologies have been used to optimize bandwidth costs and energy efficiency: the first is the copper wire connecting the server in the rack to the top switch, with a typical transmission distance of less than a few meters; the second is the short-distance optical interconnection based on parallel multi-mode fiber (MMF) or the optical transceiver based on parallel single-mode fiber (SMF), which is used to connect the top switch to the aggregation layer switch, with a typical transmission distance of 100 meters. The third is the coarse wavelength division multiplexing (CWDM) transmission link based on SMF, which is used to connect the aggregation layer switches or the aggregation switch to the backbone switching layer network, with a transmission distance of up to 1 km.

[0008] For the second interconnection technology, the 850nm vertical-cavity surface-emitting laser (VCSEL) has the advantages of low cost, small size and compact structure. The VCSEL-MMF-IMDD combination has been 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 optical fiber links can no longer achieve distortion-free transmission of optical pulses. It is necessary to abandon the 850nm VCSEL light source and adopt the more expensive third technology, namely SMF-based coarse wavelength division multiplexing (CWDM). This technology uses 1310nm wavelength edge-emitting lasers and externally modulated optical signal loading solutions, which not only greatly increases the transmission cost, but also occupies valuable space resources inside the data center.

[0009] Due to the unique light-guiding mechanism of antiresonant hollow core 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 100 meters. VCSEL-HCF-IMDD is expected to replace the third transmission solution currently used in data centers. It is not only superior to SMF-CWDM interconnection in terms of cost, but also due to the good structural compactness of VCSEL and HCF (Hollow Core Fiber), it can achieve high spatial integration interface configuration, and the space utilization rate will far exceed the SMF-CWDM solution. In addition, thanks to the low energy consumption of VCSEL and the low latency characteristics of HCF, the new interconnection technology can also greatly improve the signal transmission capacity and speed.

[0010] However, there are many challenges in the efficient coupling of VCSEL-HCF. Due to the large difference between the aperture of the light-emitting hole of VCSEL and the mode-field diameter (MFD) of HCF, the coupling between the two requires special design. There are currently two existing coupling methods: first, a coreless fiber and a graded-index fiber of a certain length are fused on the end face of HCF. The graded-index fiber is responsible for adjusting the mode field diameter of the light beam to reduce the coupling loss. The coreless fiber between the graded-index fiber and the HCF is used as an axial interval to control the focal position of the converged light beam. However, since this method places high precision requirements on the length and specifications of the optical fiber, the production cost is too high to be applied in practice. Second, a combination of multiple lenses is used to change the mode field diameter and focal position of the light beam by adjusting the lens specifications and spacing. The lens coupling method also brings high costs, and the optical path adjustment also places high requirements on the operator's ability and experience, and takes up a lot of space. In short, the current coupling interface technology is not suitable for efficient coupling of the all-fiber structure of VCSEL-HCF. Summary of the invention

[0011] In order to solve the above problems existing in the prior art, the embodiments of the present application propose a quasi-single-mode VCSEL / hollow-core fiber coupling fiber, coupling interface and manufacturing method. Through a unique all-fiber structure, the signal light of the 850nm quasi-single-mode VCSEL is coupled into the hollow-core fiber link with low latency, low dispersion and low loss. In this design, the all-fiber structure not only greatly saves space resources, but also can expand the transmission capacity by connecting multiple links.

[0012] The technical solution adopted by the present invention is:

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

[0014] A thin outer diameter optical fiber segment, used for coupling with the light output hole of the quasi-single mode VCSEL, wherein the thin outer diameter optical fiber segment supports few-mode transmission at a wavelength of 850 nm, and the core diameter thereof is close to the aperture of the light output hole of the quasi-single mode VCSEL;

[0015] a first optical fiber segment connected to the optical fiber segment with a small outer diameter, wherein the inner diameter of the first optical fiber segment is the same as the inner diameter of the optical fiber segment with a small outer diameter, and the outer diameter of the first optical fiber segment is larger than the outer diameter of the optical fiber segment with a small outer diameter;

[0016] a high-order mode filtering fiber segment, coupled to the first fiber segment, the high-order mode filtering fiber segment having the same operating band as the quasi-single-mode VCSEL and single-mode transmission in the band, an inner diameter of the high-order mode filtering fiber segment being different from the inner diameter of the first fiber segment, and an outer diameter of the high-order mode filtering fiber segment being close to the outer diameter of the first fiber segment;

[0017] A second optical fiber segment is coupled to the high-order mode filtering optical fiber segment. The inner diameter and outer diameter of the second optical fiber segment body are the same as those of the first optical fiber segment. The second optical fiber segment supports few-mode transmission at a wavelength of 850nm. The end of the second optical fiber segment is processed by a tapered heat diffusion core so that the fundamental mode mode field diameter is gradually expanded to match the hollow core optical fiber mode field diameter.

[0018] Optionally, the main bodies of the first optical fiber segment and the second optical fiber segment are both Corning SMF-28 optical fibers.

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

[0020] Optionally, the high-order mode filtering optical fiber segment is CS780 optical fiber produced by Changfei Company.

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

[0022] According to a 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 shell as described in the first aspect above, wherein the shell 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 optical fibers have multiple fibers corresponding to the light output holes of multiple quasi-single-mode VCSELs; the shell is provided with a positioning pin, and the position of the positioning pin matches the position of the positioning hole arranged on the installation plane of the light output holes of the multiple quasi-single-mode VCSELs.

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

[0025] A thin outer diameter solid core optical fiber segment is arranged to be coupled with a light output hole of a quasi-single mode VCSEL;

[0026] Filter out the high-order mode components in the optical fiber in the quasi-single-mode VCSEL operating band;

[0027] Low-loss coupling between solid-core fiber segments and hollow-core fibers;

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

[0029] Optionally, the step of setting the solid core optical fiber segment to be coupled with the quasi-single-mode VCSEL light output hole specifically includes:

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

[0031] A section of Corning's SMF-28 optical fiber was immersed in hydrofluoric acid to etch it to reduce the outer diameter of the optical fiber;

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

[0033] The step of low-loss coupling the solid-core optical fiber segment with the hollow-core optical fiber specifically comprises:

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

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

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

[0037] A single-mode optical fiber with VCSEL working band is set in the middle of Corning's SMF-28 optical fiber;

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

[0039] The beneficial effects of the present invention are:

[0040] Some embodiments of the present invention collect the output light of a quasi-single-mode VCSEL by using an optical fiber segment with a suitable core diameter and a thin outer diameter, thereby improving the efficiency of the output light entering the optical fiber; by setting a high-order mode filtering optical fiber segment that has the same operating band as the quasi-single-mode VCSEL and is single-mode transmitted in this band, the high-order mode of the signal light transmitted in the optical fiber can be filtered out, which is an effective measure to ensure the stability of the beam coupling efficiency and the absence of inter-mode dispersion interference in the long-distance transmission of the IMDD signal; through the tapered heat diffusion core technology, the fundamental mode mode field diameter of the solid core optical fiber is expanded to a level that matches the mode field diameter of the hollow core optical fiber, thereby reducing the loss of signal light entering the hollow core optical fiber link.

[0041] Some embodiments of the present invention can greatly improve the coupling efficiency by coupling the output optical signal of a quasi-single-mode VCSEL through an optical fiber with a core diameter of 8.2 μm. The optical fiber with a core diameter of 8.2 μm has a similar aperture to the light output hole of the quasi-single-mode VCSEL.

[0042] Some embodiments of the present invention reduce the outer diameter of the collection optical fiber segment by means of hydrofluoric acid corrosion to reduce the effect of blocking at the edge of the optical fiber end face on coupling. The advantage of this method is that the corrosion of the optical fiber cladding by hydrofluoric acid will not affect the optical fiber core.

[0043] Some embodiments of the present invention use Changfei Company's CS780 optical fiber as the high-order mode filtering fiber segment. When the multi-mode optical signal passes through the high-order mode filtering fiber segment, the high-order mode components therein will be filtered out by the optical fiber cladding, thereby ensuring the stability of the beam coupling efficiency and the absence of inter-modal dispersion interference in 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 can reduce the coupling loss between Corning's SMF-28 optical fiber and hollow core optical fiber by changing the fundamental mode field diameter of Corning's SMF-28 optical fiber using tapered heat diffusion core technology.

[0045] In some embodiments of the present invention, the optical fiber end face of the prepared tapered heat diffusion core is polished and / or coated to form an anti-reflection film, which can reduce the reflection loss at a wavelength of 850nm and improve the coupling efficiency.

[0046] In some embodiments of the present invention, the arrangement of quasi-single-mode VCSEL / hollow-core fiber coupling fibers is determined by the arrangement of the light output holes of the 850nm quasi-single-mode VCSEL, and then a quasi-single-mode VCSEL / hollow-core fiber coupling interface is formed, and the transmission capacity can be expanded by connecting the fibers of multiple links; the rapidity of coupling is improved by adding positioning holes at the 850nm quasi-single-mode VCSEL end. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0048] Figure 1 850nm quasi-single-mode VCSEL-HCF transmission link schematic diagram of an embodiment of the present invention;

[0049] Figure 2 is a cross-sectional view of an 850nm quasi-single-mode VCSEL according to an embodiment of the present invention;

[0050] Figure 3 is a cross-sectional view of a hollow-core optical fiber according to an example of an embodiment of the present invention;

[0051] Figure 4 is a cross-sectional view of an untreated Corning SMF-28 optical fiber according to an embodiment of the present invention;

[0052] Figure 5 Schematic diagram of possible blocking of the edge of the optical fiber end face when the Corning SMF-28 optical fiber is coupled to the VCSEL light output hole according to an embodiment of the present invention.

[0053] Figure 6 is a cross-sectional view of a Corning SMF-28 optical fiber having an outer diameter of 30 μm after being etched with hydrofluoric acid according to an embodiment of the present invention;

[0054] Figure 7 is a longitudinal schematic diagram of a Corning SMF-28 optical fiber after being etched by hydrofluoric acid according to an embodiment of the present invention;

[0055] Figure 8 is a cross-sectional view of a high-order mode filtering optical fiber segment according to an example of an embodiment of the present invention;

[0056] Fig. 9 It is a schematic diagram of a high-order mode filtering optical fiber segment according to an embodiment of the present invention being fused at both ends with a Corning SMF-28 optical fiber;

[0057] Fig.10 Schematic diagram of performing tapered heat diffusion core processing on Corning's SMF-28 optical fiber according to an embodiment of the present invention;

[0058] Fig.11 It is a schematic diagram of a conical heat diffusion core end face of a Corning SMF-28 optical fiber according to an embodiment of the present invention butted against a hollow core optical fiber;

[0059] Fig.12 Schematic diagram of a quasi-single-mode VCSEL / hollow-core fiber coupling interface according to an embodiment of the present invention;

[0060] Fig.13 It is a schematic diagram of a process for manufacturing a quasi-single-mode VCSEL / hollow-core optical fiber coupling interface according to an embodiment of the present invention.

[0061] Markings in the attached drawings:

[0062] 100-quasi-single-mode VCSEL; 110-light exit hole; 210-quasi-single-mode VCSEL / hollow-core fiber coupling fiber; 211-thin outer diameter fiber segment; 212-first fiber segment; 212'-Corning SMF-28 fiber; 213-high-order mode filter fiber segment; 214-second fiber segment; 215-tapered heat diffusion core; 216-antireflection film; 300-hollow-core fiber; 311-first ceramic ferrule; 312-C sleeve; 313-second ceramic ferrule; 400-receiving end. DETAILED DESCRIPTION

[0063] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0064] This specific embodiment is only an explanation of the present invention, and it is not a limitation of the present invention. After reading this specification, those skilled in the art can make non-creative modifications to this embodiment as needed, but as long as it is within the scope of the claims of the present invention, it is protected by the patent law.

[0065] like Figure 1-Figure 11 As shown, the embodiment of the present application proposes a quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210, including a thin outer 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 outer diameter fiber segment 211 is used to couple with the light exit hole 110 of the quasi-single-mode VCSEL. The thin outer diameter fiber segment 211 supports few-mode transmission at a wavelength of 850nm, and its core diameter is close to the aperture of the light exit hole 110 of the quasi-single-mode VCSEL. The first fiber segment 212 is connected to the thin outer diameter fiber segment 211, and the inner diameter of the first fiber segment 212 is the same as the inner diameter of the thin outer diameter fiber segment 211, and the outer diameter of the first fiber segment 212 is greater than the outer diameter of the thin outer diameter fiber segment 211. The high-order mode filtering fiber segment 213 is coupled to the first fiber segment 212. The high-order mode filtering fiber segment 213 has the same operating band as the quasi-single-mode VCSEL and is single-mode transmission in this band. The inner diameter of the high-order mode filtering fiber segment 213 is different from the inner diameter of the first fiber segment 212, and the outer diameter of the high-order mode filtering fiber segment 213 is close to the outer diameter of the first fiber segment 212. The second fiber segment 214 is coupled to the high-order mode filtering fiber segment 213. The inner diameter and outer diameter of the second fiber segment 214 body are the same as those of the first fiber segment 212. 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 core fiber 300 through the tapered heat diffusion core treatment.

[0066] See also Figure 1 The optical signal is output from the light exit hole 110 of the quasi-single-mode VCSEL 100, and 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-core fiber 300 of the quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 in sequence, and finally output to the receiving end 400 for signal processing and analysis. In the transmission of optical signals, the hollow-core fiber 300 undertakes the main transmission task. The quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 plays the role of reducing the coupling loss between the light source and the optical fiber link and filtering out the high-order mode components in the optical signal.

[0067] In a specific implementation, the quasi-single-mode VCSEL involved has an operating band of 850 nm, and the thin outer diameter optical fiber segment can be Corning's SMF28 single-mode optical fiber after being etched with hydrofluoric acid.

[0068] In this embodiment, the output light of the quasi-single-mode VCSEL is collected by using an optical fiber segment 211 with a suitable core diameter and a thin outer diameter, thereby improving the efficiency of the output light entering the optical fiber; by setting a high-order mode filtering optical fiber segment 213 that has the same working band as the quasi-single-mode VCSEL and is single-mode transmitted in this band, the signal light transmitted in the optical fiber can be filtered out in a high-order mode, which is an effective measure to ensure the stability of the beam coupling efficiency and the absence of inter-mode dispersion interference in the long-distance transmission of the IMDD signal; the fundamental mode mode field diameter of the solid core optical fiber is expanded to a degree matching the mode field diameter of the hollow core optical fiber through the tapered thermal diffusion core technology, thereby reducing the loss of signal light entering the hollow core optical fiber link.

[0069] In some embodiments, the first optical fiber segment 212 and the second optical fiber segment 214 are both mainly Corning SMF-28 optical fibers.

[0070] like Figure 2 As shown in Figure 1, the aperture of the 850nm quasi-single-mode VCSEL light output hole is relatively small, at 8μm. Figure 3 As shown, the core diameter of the hollow-core optical fiber is 30 μm, and the mode field diameter is approximately 70% of the core diameter, about 21 μm, which is much larger than the aperture of the VCSEL light output hole, and the direct alignment coupling loss is extremely large.

[0071] The coupling efficiency can be greatly improved by coupling the single-mode VCSEL output optical signal with an optical fiber with a core diameter of 8 μm. In this embodiment, Corning SMF-28 optical fiber is selected. Figure 4 As shown, the outer diameter of Corning's SMF-28 optical fiber 212' is 125 μm, and the core diameter is about 8.2 μm, which is consistent with the aperture size of the VCSEL light output hole and can be well coupled.

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

[0073] like Figure 5 As shown, when Corning's SMF-28 optical fiber 212' is directly aligned and coupled with the light exit hole 110 of the VCSEL, since the sizes of both are too small, the optical fiber may have a non-zero tilt angle θ relative to the vertical direction of the VCSEL during alignment. Due to the tilt of the optical fiber, there will be an air gap d between the fiber core and the light exit hole 110. The air gap d is proportional to the tilt angle θ and the outer diameter D of the optical fiber. The effect of blocking at the edge of the optical fiber end face on coupling can be reduced by reducing the outer diameter D of the Corning SMF-28 optical fiber.

[0074] In this example, hydrofluoric acid etching is used to reduce the outer diameter of the optical fiber. The advantage of this method is that the corrosion of the optical fiber cladding by hydrofluoric acid will not affect the optical fiber core. Corning's SMF-28 optical fiber is placed in a 40% concentration hydrofluoric acid solution and etched to a thin diameter of 30μm. Cutting is performed in the etched area to ensure that the end face of the optical fiber is flat. The cross section of the thin outer diameter optical fiber segment is as follows: Figure 6 As shown in the figure, the fiber core diameter does not change, and the outer diameter is reduced to 30μm. The longitudinal schematic diagram of Corning's SMF-28 optical fiber after hydrofluoric acid corrosion is shown in the figure. Figure 7 As shown, one end thereof forms a thin outer diameter optical fiber segment 211, and the other end thereof serves as a first optical fiber segment 212.

[0075] In some embodiments, the high-order mode filtering optical fiber segment 213 may be a CS780 optical fiber produced by Changfei Optical Fiber Technology Co., Ltd.

[0076] Currently, commercially available 850nm band VCSELs are all in quasi-single-mode operation, and there are still high-order mode components (LP11) remaining in the optical signal. The presence of high-order mode components will cause inter-mode dispersion interference in IMDD signals during long-distance transmission, affecting the transmission distance and quality of the signal. High-order modes may also be excited at the fiber splicing points and bending points.

[0077] In addition, since Corning's SMF-28 optical fiber is in the few-mode working mode in the 850nm band, the signal light in Corning's SMF-28 optical fiber must be filtered out in high-order modes through a section of 850nm single-mode optical fiber (such as Changfei's CS780 optical fiber). This is an effective measure to ensure the stability of the beam coupling efficiency and the absence of inter-modal dispersion interference in 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 are the refractive indices of the core and cladding, respectively. When the V parameter of an optical fiber is less than 2.405, it is in single-mode operation. In this case, only the fundamental mode can be transmitted, and the transmission loss of other high-order modes is extremely high. For Corning's SMF-28 optical fiber, when the V parameter is 2.405, the cutoff wavelength is 1260nm, and it is in multi-mode operation at 850nm. This embodiment uses the CS780 optical fiber of Changfei Company, such as Figure 8As shown in the figure, the outer diameter of this optical fiber is 125μm, the core diameter is 5μm, and when V=2.405, its cut-off wavelength is 730nm, which meets the single-mode transmission condition at 850nm. When the multi-mode optical signal passes through the CS780 optical fiber of YOFC, the high-order mode components in it will be filtered out through the optical fiber cladding, ensuring the stability of the beam coupling efficiency and the absence of inter-mode dispersion interference in the IMDD signal during long-distance transmission, thereby improving the transmission quality and distance of the optical signal.

[0081] How to fusion splice Corning SMF-28 optical fiber and Changfei CS780 optical fiber Fig. 9 As shown. The main bodies of the first optical fiber segment 212 and the second optical fiber segment 214 are both Corning SMF-28 optical fibers, and the high-order mode filtering optical fiber segment 213 can be Changfei CS780 optical fibers. Due to the large difference in the core diameters of Corning SMF-28 optical fibers and Changfei CS780 optical fibers, the fusion between the optical fibers will cause large losses, and improper fusion will also excite high-order mode components in the optical fibers. However, when the length of the cone area at the fusion of the two optical fibers reaches a certain value, it can be approximately regarded as an adiabatic mode conversion with low losses. When fusing the two optical fibers, the discharge time should be increased. At the same time, the discharge intensity should not be too large. Excessive current will cause core diffusion, increase losses, and excite high-order mode components in the optical fiber. By adjusting the discharge intensity and discharge time, the fusion loss of the two optical fibers can be as low as 0.2dB, and there is no additional reflection at the fusion point.

[0082] It should be noted that quartz optical fiber has 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's SMF-28 and YOFC's CS780 optical fibers in the link should not be too long.

[0083] In some embodiments, Fig.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 surface of the tapered heat diffusion core 215 has an anti-reflection film 216.

[0084] In the specific implementation, Fig.10As shown, the main body of the second optical fiber segment 214 is Corning's SMF-28 optical fiber. Due to the difference in mode field diameter between Corning's SMF-28 optical fiber and hollow core optical fiber, a mode field adapter is required to achieve coupling between the two optical fibers. The end of Corning's SMF-28 optical fiber is heated so that the doped ions in the core of Corning's SMF-28 optical fiber diffuse in the radial direction. The temperature of the heated area is gradually tapered by gradient heating of the optical fiber, forming a tapered heat diffusion core 215. The fundamental mode field diameter of the optical fiber in the tapered area gradually increases until it is consistent with the mode field diameter of the hollow core optical fiber 300. The tapered heat diffusion core technology is used to change the fundamental mode mode field diameter of Corning's SMF-28 optical fiber, and the fundamental mode mode field diameter of Corning's SMF-28 optical fiber is expanded to a degree that matches the mode field diameter of the hollow core optical fiber 300, which can reduce the coupling loss between Corning's SMF-28 optical fiber and the hollow core optical fiber 300.

[0085] On the other hand, when the optical signal enters the hollow core optical fiber from Corning's SMF-28 optical fiber, it can be approximated as propagation from glass to air, which will produce about 0.15dB Fresnel reflection loss, and this reflected light will also cause damage to the laser. In this embodiment, by polishing and / or coating the end face of the prepared tapered thermal diffusion core optical fiber 215 to form an anti-reflection film 216, the reflection loss at a wavelength of 850nm can be reduced and the coupling efficiency can be improved.

[0086] As an example, Fig.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-core optical fiber 300 is that the end of the second optical fiber segment 214 with the tapered heat diffusion core 215 is inserted into the first ceramic ferrule 311, and the hollow-core 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 fibers are placed in the C sleeve 312 for alignment.

[0087] The present invention also provides an embodiment, Fig.12 As shown, it relates to a quasi-single-mode VCSEL / hollow-core fiber coupling interface 200, including the quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 and a shell 220 in the above embodiment, the shell 220 covers one end of the quasi-single-mode VCSEL / hollow-core fiber coupling fiber 210 coupled to the light output hole 110 of the quasi-single-mode VCSEL, and exposes the end face.

[0088] In some embodiments, there are multiple quasi-single-mode VCSEL / hollow-core fiber coupling optical fibers 210 corresponding to the light output holes 110 of multiple quasi-single-mode VCSELs; the housing 220 is provided with a positioning pin 221, and the position of the positioning pin 221 matches the positioning hole 120 set on the installation plane of the light output holes 110 of the multiple quasi-single-mode VCSELs.

[0089] like Figure 2 As shown, the size of a single light-emitting area of ​​the 850nm quasi-single-mode VCSEL is 220×225 (μm2), and multiple light-emitting areas can be evenly and closely arranged to form a light-emitting panel. On the other side, the outer diameter of the Corning SMF-28 optical fiber at the coupling end is only 125μm, and each light-emitting hole 110 of the 850nm quasi-single-mode VCSEL can be utilized by properly arranging the optical fiber, greatly expanding the data transmission capacity and improving energy efficiency.

[0090] In the specific implementation, Fig.12 As shown, the arrangement of the quasi-single-mode VCSEL / hollow-core fiber coupling optical fiber 210 is determined by the arrangement of the light-emitting hole 110 of the 850nm quasi-single-mode VCSEL, thereby manufacturing the quasi-single-mode VCSEL / hollow-core fiber coupling interface 200. For the rapidity of coupling, a positioning hole 120 is added to the end of the 850nm quasi-single-mode VCSEL, which is arranged on the installation plane of the light-emitting hole 110 of the 850nm quasi-single-mode VCSEL, and a corresponding positioning pin 221 is manufactured at the coupler interface end, and the positioning hole 120 is aligned with the positioning pin 221 during coupling.

[0091] The present invention also relates to a method for manufacturing a quasi-single-mode VCSEL / hollow-core optical fiber coupling interface, which is used to manufacture the quasi-single-mode VCSEL / hollow-core optical fiber coupling interface in the above embodiment and has corresponding technical effects. Fig.13 As shown, steps S10 to S40 are included.

[0092] S10, setting the solid core optical fiber segment to be coupled with the light output hole of the quasi-single mode VCSEL.

[0093] Step S10 specifically includes:

[0094] S11, Corning SMF-28 optical fiber was selected as the solid core optical fiber segment;

[0095] S12, immersing a section of Corning SMF-28 optical fiber in hydrofluoric acid corrosion to reduce the outer diameter of the optical fiber;

[0096] S13, cutting is performed in the corroded area to ensure that the end face of the optical fiber is flat.

[0097] S20, filters out the high-order mode components in the optical fiber in the quasi-single-mode VCSEL operating band.

[0098] Step S20 specifically includes:

[0099] S21, a single-mode optical fiber with VCSEL working band is set in the middle of Corning SMF-28 optical fiber;

[0100] S22, fusing the Corning SMF-28 optical fiber with the single-mode optical fiber of the VCSEL working band.

[0101] In a specific implementation, the single-mode optical fiber in the VCSEL working band may be the CS780 optical fiber of Changfei Company.

[0102] S30, low-loss coupling is performed between the solid-core optical fiber segment and the hollow-core optical fiber.

[0103] Step S30 specifically includes:

[0104] S31, gradient heating is performed on one end of Corning's SMF-28 optical fiber to form a tapered heat diffusion core;

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

[0106] S40, fabrication of all-fiber structure coupling interface.

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

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

[0109] Through the operation of steps S10-S40, an all-fiber structure coupling interface of 850nm quasi-single-mode VCSEL and hollow-core optical fiber can be completely manufactured, thereby realizing low-delay, low-dispersion, and low-loss transmission of 850nm quasi-single-mode VCSEL optical signals.

[0110] The above content is only used to illustrate the technical solution of the present invention rather than to limit it. The present invention is not limited to the above optional implementation modes. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field, regardless of any changes in its shape or structure, should be included in 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 coupling optical fiber, characterized in that: include: A thin outer diameter optical fiber segment, used for coupling with the light output hole of the quasi-single mode VCSEL, wherein the thin outer diameter optical fiber segment supports few-mode transmission at a wavelength of 850 nm, and the core diameter thereof is close to the aperture of the light output hole of the quasi-single mode VCSEL; a first optical fiber segment connected to the optical fiber segment with a small outer diameter, wherein the inner diameter of the first optical fiber segment is the same as the inner diameter of the optical fiber segment with a small outer diameter, and the outer diameter of the first optical fiber segment is larger than the outer diameter of the optical fiber segment with a small outer diameter; a high-order mode filtering fiber segment, coupled to the first fiber segment, the high-order mode filtering fiber segment having the same operating band as the quasi-single-mode VCSEL and single-mode transmission in the band, an inner diameter of the high-order mode filtering fiber segment being different from the inner diameter of the first fiber segment, and an outer diameter of the high-order mode filtering fiber segment being close to the outer diameter of the first fiber segment; A second optical fiber segment is coupled to the high-order mode filtering optical fiber segment. The inner diameter and outer diameter of the second optical fiber segment body are the same as those of the first optical fiber segment. The second optical fiber segment supports few-mode transmission at a wavelength of 850nm. The end of the second optical fiber segment is processed by a tapered heat diffusion core so that the fundamental mode mode field diameter is gradually expanded to match the hollow core optical fiber mode field diameter.

2. A quasi-single-mode VCSEL / hollow-core fiber coupling optical fiber according to claim 1, characterized in that: The main bodies of the first optical fiber segment and the second optical fiber segment are both Corning SMF-28 optical fibers.

3. A quasi-single-mode VCSEL / hollow-core fiber coupling optical fiber according to claim 2, characterized in that: The thin outer diameter optical fiber segment is obtained by placing Corning's SMF-28 optical fiber in a hydrofluoric acid solution to etch and reduce the outer diameter, and then cutting off the end.

4. The quasi-single-mode VCSEL / hollow-core fiber coupling optical fiber according to claim 2, characterized in that: The high-order mode filtering optical fiber segment is the CS780 optical fiber of Changfei Company.

5. The quasi-single-mode VCSEL / hollow-core fiber coupling optical fiber according to claim 1, characterized in that: The second optical fiber segment has a tapered heat spreading core at its end.

6. 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 claimed in any one of claims 1 to 5, characterized in that: The shell is coated on one end of the quasi-single-mode VCSEL / hollow-core fiber coupling optical fiber coupled with the light-emitting hole of the quasi-single-mode VCSEL, and exposes the end face.

7. A quasi-single-mode VCSEL / hollow-core fiber coupling interface according to claim 6, characterized in that: The quasi-single-mode VCSEL / hollow-core fiber coupling optical fibers are multiple, corresponding to the light output holes of multiple quasi-single-mode VCSELs; the housing is provided with a positioning pin, the position of the positioning pin matches the position of the positioning hole arranged on the installation plane of the light output holes of the multiple quasi-single-mode VCSELs.

8. A method for manufacturing a quasi-single-mode VCSEL / hollow-core fiber coupling interface, characterized in that: The steps include: A solid core optical fiber segment is arranged to be coupled with a light output hole of a quasi-single-mode VCSEL; Filter out the high-order mode components in the optical fiber in the quasi-single-mode VCSEL operating band; Low-loss coupling between solid-core fiber segments and hollow-core fibers; Fabricate an all-fiber structure coupling interface.

9. A method for manufacturing a quasi-single-mode VCSEL / hollow-core fiber coupling interface according to claim 8, characterized in that: The step of setting the solid core optical fiber segment to couple with the quasi-single-mode VCSEL light output hole specifically includes: Corning SMF-28 optical fiber was selected as the solid core optical fiber segment; A section of Corning's SMF-28 optical fiber was immersed in hydrofluoric acid to etch it to reduce the outer diameter of the optical fiber; Cutting is performed in the corroded area to ensure that the fiber end face is flat; The step of low-loss coupling the solid-core optical fiber segment with the hollow-core optical fiber specifically comprises: One end of Corning's SMF-28 optical fiber is gradient heated to form a tapered heat diffusion core; The end surface of the prepared conical heat diffusion core is polished and / or coated.

10. A method for manufacturing a quasi-single-mode VCSEL / hollow-core fiber coupling interface according to claim 9, characterized in that: The step of filtering out the high-order mode components in the optical fiber in the quasi-single-mode VCSEL working band specifically includes: A single-mode optical fiber with VCSEL working band is set in the middle of Corning's SMF-28 optical fiber; The Corning SMF-28 optical fiber is fused with the single-mode optical fiber of the VCSEL working band.

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