E-band dispersion compensating optical fiber

Abstract

The invention belongs to the technical field of optical fiber communication, and discloses an E-band dispersion compensation optical fiber, comprising a central air hole, a first high-refractive index solid ring, a first low-refractive index solid ring, a second high-refractive index solid ring and a second low-refractive index solid ring; the central air hole has a refractive index of n1=1, and a first diameter d1<1360nm; the first high-refractive index solid ring has a refractive index of n2, and a first ring width L1 of 3.5-4.4μm; the first low-refractive index solid ring has a refractive index of n3, and a second ring width L2>1460nm; the second high-refractive index solid ring has a refractive index of n4, and a third ring width L3<L1; the second low-refractive index solid ring has a refractive index of n3, and a second diameter d2 of 125±1μm; n4>n2>n3>n1. The invention can make the optical fiber have a large absolute value of negative dispersion at the E-band working wavelength, and the coupling loss with the front-end single-mode optical fiber is low, ensuring that the limiting loss and the bending loss will not deteriorate.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and more specifically, relates to an E-band dispersion compensating optical fiber. Background Art

[0002] As a signal transmission medium, single-mode optical fiber is widely used in the field of communications. However, the accumulation of positive dispersion inside it will cause the signal pulse to be broadened. Using dispersion-compensating optical fiber with large negative dispersion to compensate for the accumulated positive dispersion in the front-end single-mode optical fiber is one of the methods to improve the performance of the communication system.

[0003] A commonly used technical solution to achieve large negative dispersion characteristics is coaxial dual-core dispersion-compensating optical fiber. This solution includes an inner core, an inner cladding, an outer core, and an outer cladding from the center of the optical fiber to the outside. The upper limit of the refractive index value of the inner core mode is greater than the upper limit of the refractive index value of the outer core mode, and the lower limit of the refractive index value of the inner core mode is equal to or less than the lower limit of the refractive index value of the outer core mode. Therefore, the refractive index value of the inner core mode is greater than the refractive index value of the outer core mode, and the slope of the curve of the refractive index of the inner core mode with wavelength is greater than the slope of the curve of the refractive index of the outer core mode with wavelength. Under the premise that the slope difference between the curves of the refractive index of the inner and outer core modes with wavelength is large (slope mismatch), adjust the refractive index values ​​of the inner and outer core modes so that they intersect at a certain wavelength (numerical matching), but the two curves separate rapidly at other wavelengths. According to the coupled mode theory, the closer the mode refractive index values ​​are, the stronger the mode coupling is. The coupling is strong near the intersection point and weak at other wavelengths, resulting in a sudden change in the refractive index of the inner and outer core modes only at the intersection point, and then the curve of the refractive index of the entire mode changing with wavelength is folded near this point, resulting in large negative dispersion.

[0004] The current optical communication system is mainly concentrated in the S band, C band and L band. With the development of 5G, attempts to use E band communication have begun, so there is also a demand for E band dispersion compensation fiber. However, the E band (1360-1460nm) has a shorter wavelength than the existing communication band. If the conventional coaxial dual-core dispersion compensation fiber is constructed, and only its structural parameters are optimized, the working wavelength is blue-shifted to the E band, and the absolute value of the negative dispersion value of the inner core mode at the working wavelength, the coupling loss between the fiber and the front single-mode fiber, and the limitation and bending loss of the fiber will deteriorate sharply. How to eliminate the contradiction between the working wavelength position of the dispersion compensation fiber and the absolute value of the negative dispersion value of the inner core mode at the working wavelength, the coupling loss between the fiber and the front single-mode fiber, the limitation and bending loss of the fiber, and the opposite requirements of the fiber parameters, and obtain a good performance E band dispersion compensation fiber is a technical problem that needs to be solved in this field. Summary of the invention

[0005] The present invention solves the problem that an E-band dispersion compensating optical fiber with good performance cannot be obtained in the prior art by providing an E-band dispersion compensating optical fiber.

[0006] The present invention provides an E-band dispersion-compensating optical fiber, which comprises, from the center of the optical fiber outward, a central air hole, a first high-refractive-index solid ring, a first low-refractive-index solid ring, a second high-refractive-index solid ring, and a second low-refractive-index solid ring;

[0007] The refractive index of the central air hole n1=1, and the first diameter d1<1360nm;

[0008] The refractive index of the first high-refractive-index solid ring is n2, and the first ring width L1 is in the range of 3.5 to 4.4 μm;

[0009] The refractive index of the first low-refractive-index solid ring is n3, and the second ring width L2 is greater than 1460 nm;

[0010] The refractive index of the second high refractive index solid ring is n4, and the third ring width L3<L1;

[0011] The refractive index of the second low-refractive-index solid ring is n3, and the second diameter d2 is in the range of 125±1 μm;

[0012] Among them, n4﹥n2﹥n3﹥n1.

[0013] Preferably, the central air hole and the first high refractive index solid ring serve as the inner core of the optical fiber, the first high refractive index solid ring and the first low refractive index solid ring serve as the inner cladding of the outer core of the optical fiber, the second high refractive index solid ring serves as the outer core of the optical fiber, and the second low refractive index solid ring serves as the outer cladding of the outer core of the optical fiber.

[0014] Preferably, the upper limit of the refractive index of the inner core mode of the optical fiber is: The lower limit of the refractive index of the outer core mode of the optical fiber is:

[0015] Preferably, the first diameter d1 is in the range of 1.1 to 1.3 μm.

[0016] Preferably, the first ring width L1 is in the range of 3.8 to 4.2 μm.

[0017] Preferably, the second ring width L2 is in the range of 8.0 to 10.0 μm.

[0018] Preferably, the third ring width L3 is in the range of 3.0 to 3.5 μm.

[0019] Preferably, the refractive index n2 of the first high-refractive-index solid ring is in the range of 1.010n3 to 1.011n3.

[0020] Preferably, the refractive index n4 of the second high-refractive-index solid ring is in the range of (n2+0.00005) to (n2+0.00015).

[0021] Preferably, the first low-refractive-index solid ring and the second low-refractive-index solid ring are both made of pure quartz glass material.

[0022] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0023] The E-band dispersion compensating optical fiber provided by the present invention comprises five parts, which are sequentially from the center of the optical fiber outward, a central air hole, a first high-refractive index solid ring wrapping the central air hole and concentric with the central air hole, a first low-refractive index solid ring wrapping the first high-refractive index solid ring and concentric with the central air hole, a second high-refractive index solid ring wrapping the first low-refractive index solid ring and concentric with the central air hole, and a second low-refractive index solid ring wrapping the second high-refractive index solid ring and concentric with the central air hole: the refractive indexes of the central air hole, the first high-refractive index solid ring, the first low-refractive index solid ring, the second high-refractive index solid ring and the second low-refractive index solid ring are n1, n2, n3, n4, and n3 respectively, and n4>n2>n3>n1; the first high-refractive index solid ring in the present invention is in the shape of a circular ring, and the diameter of the central air hole located inside the first high-refractive index solid ring is smaller than the lower limit wavelength of the E-band 1360nm, so the overall structure formed by the first high-refractive index solid ring and the central air hole is the inner core of the present invention. The above scheme allows part of the energy of the inner core mode to be retained in the first high refractive index solid ring, and part of the energy to diffuse into the central air hole, that is, the field distribution of the inner core mode in the inner core is affected by the first high refractive index solid ring and the central air hole. Therefore, the upper limit of the refractive index of the inner core mode of the optical fiber is jointly determined by the refractive index of the first high refractive index solid ring and the refractive index of air, and is related to the field distribution: at short wavelengths, less energy enters the central air hole, then the central air hole part has a weak effect, the first high refractive index solid ring part has a strong effect, and the upper limit of the refractive index of the inner core mode is high; at long wavelengths, more energy enters the central air hole, then the central air hole part has a strong effect, the first high refractive index solid ring part has a weak effect, and the upper limit of the refractive index of the inner core mode is low. Since the field distribution of the inner core mode in the inner core gradually enters the central air hole as the wavelength redshifts, the upper limit of the refractive index of the inner core mode will decrease as the wavelength redshifts. In the present invention, the ring width of the first low refractive index solid ring located inside the second high refractive index solid ring is greater than the upper limit wavelength of the E band 1460nm, so the second high refractive index solid ring portion is the outer core of the present invention, and the optical fiber structures located on the inner and outer sides thereof respectively constitute its cladding. Since the refractive index of the second high refractive index solid ring is higher than the refractive index of the first high refractive index solid ring, the inner cladding of the outer core can be regarded as a structure of two claddings consisting of the first low refractive index solid ring and the first high refractive index solid ring.Part of the energy of the outer core mode diffused into the inner cladding is distributed in the first low refractive index solid ring, and the other part of the energy is distributed in the first high refractive index solid ring, that is, the field distribution of the outer core mode in the inner cladding is affected by the first low refractive index solid ring and the first high refractive index solid ring. Therefore, the lower limit of the refractive index of the outer core mode is determined by the refractive index of the first low refractive index solid ring and the refractive index of the first high refractive index solid ring, and is related to the field distribution: at short wavelengths, less energy enters the first high refractive index solid ring, then the first high refractive index solid ring part has a weak effect, the first low refractive index solid ring part has a strong effect, and the lower limit of the refractive index of the outer core mode is low; at long wavelengths, more energy enters the first high refractive index solid ring, then the first high refractive index solid ring part has a strong effect, the first low refractive index solid ring part has a weak effect, and the lower limit of the refractive index of the outer core mode is high. Since the field distribution of the outer core mode in the inner cladding changes with the redshift of the wavelength, the lower limit of the refractive index of the outer core mode increases with the redshift of the wavelength. Through the organic effect of the above series of technical solutions, the present invention eliminates the contradiction between the working wavelength position of the dispersion-compensating optical fiber and the absolute value of the negative dispersion value of the inner core mode at the working wavelength, the coupling loss between the optical fiber and the front-end single-mode optical fiber, the limitation and bending loss of the optical fiber, and the opposite requirements of the optical fiber parameters. The present invention not only achieves the blue shift of the working wavelength to the E band, but also ensures that the absolute value of the negative dispersion value of the optical fiber at the working wavelength is large, the coupling loss with the front-end single-mode optical fiber is low, and the limitation and bending loss are low. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the cross section and refractive index of an E-band dispersion-compensating optical fiber provided by the present invention;

[0025] Figure 2 A curve showing the variation of the refractive index values ​​of the inner and outer core modes of an E-band dispersion compensating optical fiber as a function of wavelength provided in Example 1 of the present invention;

[0026] Figure 3 A curve showing the variation of the dispersion value of the inner core mode of an E-band dispersion compensating optical fiber with the wavelength provided in Example 1 of the present invention;

[0027] Figure 4 A curve showing the variation of the refractive index values ​​of the inner and outer core modes of an E-band dispersion compensating optical fiber as a function of wavelength provided in Example 2 of the present invention;

[0028] Figure 5 A curve showing the variation of the dispersion value of the inner core mode of an E-band dispersion compensating optical fiber with the wavelength provided in Example 2 of the present invention;

[0029] Figure 6 A curve showing the variation of the refractive index values ​​of the inner and outer core modes of an E-band dispersion compensating optical fiber as a function of wavelength provided in Example 3 of the present invention;

[0030] Figure 7 A curve showing the variation of the dispersion value of the inner core mode of an E-band dispersion compensating optical fiber with the wavelength provided in Example 3 of the present invention. DETAILED DESCRIPTION

[0031] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0032] See also Figure 1 The present invention provides an E-band dispersion-compensating optical fiber, the working wavelength of which is 1360-1460 nm, and which includes, from the center of the optical fiber outward, a central air hole, a first high-refractive-index solid ring, a first low-refractive-index solid ring, a second high-refractive-index solid ring, and a second low-refractive-index solid ring;

[0033] The refractive index of the central air hole n1=1, and the first diameter d1<1360nm;

[0034] The refractive index of the first high-refractive-index solid ring is n2, and the first ring width L1 is in the range of 3.5 to 4.4 μm;

[0035] The refractive index of the first low-refractive-index solid ring is n3, and the second ring width L2 is greater than 1460 nm;

[0036] The refractive index of the second high refractive index solid ring is n4, and the third ring width L3<L1;

[0037] The refractive index of the second low-refractive-index solid ring is n3, and the second diameter d2 is in the range of 125±1 μm;

[0038] Among them, n4﹥n2﹥n3﹥n1.

[0039] The central air hole and the first high refractive index solid ring serve as the inner core of the optical fiber, the first high refractive index solid ring and the first low refractive index solid ring serve as the inner cladding of the outer core of the optical fiber, the second high refractive index solid ring serves as the outer core of the optical fiber, and the second low refractive index solid ring serves as the outer cladding of the outer core of the optical fiber.

[0040] The upper limit of the refractive index of the core mode of the optical fiber is: The lower limit of the refractive index of the outer core mode of the optical fiber is:

[0041] In a preferred embodiment, the first diameter d1 is in the range of 1.1 to 1.3 μm, the first ring width L1 is in the range of 3.8 to 4.2 μm, the second ring width L2 is in the range of 8.0 to 10.0 μm, and the third ring width L3 is in the range of 3.0 to 3.5 μm. The refractive index n2 of the first high-refractive-index solid ring is in the range of 1.010n3 to 1.011n3, the refractive index n4 of the second high-refractive-index solid ring is in the range of (n2+0.00005) to (n2+0.00015), the first low-refractive-index solid ring and the second low-refractive-index solid ring are both made of pure quartz glass material, and n3 is 1.45732.

[0042] The present invention not only realizes the blue shift of the working wavelength to the E band, but also ensures that the absolute value of the negative dispersion value of the optical fiber at the working wavelength is large, the coupling loss with the front-end single-mode optical fiber is low, and the restriction and bending losses are low.

[0043] The present invention is described in detail below.

[0044] The technical solution provided by the present invention can solve the following three technical problems at the same time:

[0045] 1. When the working wavelength is blue-shifted to the E band, the absolute value of the negative dispersion value of the inner core mode at the working wavelength is large.

[0046] From the perspective of numerical matching of the refractive index of the inner and outer core modes, the refractive index of the first low-refractive-index solid ring of the present invention is equal to the refractive index of the second low-refractive-index solid ring, that is, the initial lower limits of the refractive index values ​​of the inner and outer core modes are equal. On this basis, on one hand, the present invention adopts a scheme in which the inner core is composed of the first high-refractive-index solid ring and the central air hole with a diameter less than the lower limit wavelength of the E band 1360nm, so that the upper limit of the refractive index value of the inner core mode is jointly determined by the refractive index of the first high-refractive-index solid ring and the refractive index of air. Since the refractive index value of air is much smaller than the refractive index values ​​of other parts of the optical fiber, the introduction of an air hole in the center of the optical fiber has the effect of reducing the refractive index of the inner core, reducing the upper limit of the refractive index value of the inner core mode, and then reducing the refractive index value of the inner core mode, so that the refractive index value of the inner core mode decreases along the wavelength redshift curve, which is conducive to the working wavelength moving to the E band. On the other hand, the present invention adopts a scheme that the refractive index of the second high refractive index solid ring is greater than the refractive index of the first high refractive index solid ring, which can increase the upper limit of the refractive index of the outer core mode, and then increase the refractive index value of the outer core mode, so that the refractive index value of the outer core mode increases with the wavelength redshift curve, which is conducive to the working wavelength moving to the E band. In addition, the refractive index of the second high refractive index solid ring of the present invention is greater than the refractive index of the first high refractive index solid ring, the design of the width of the first high refractive index solid ring, and the combined effect of reducing the width of the first low refractive index solid ring can also increase the refractive index value of the outer core mode, so that the refractive index value of the outer core mode increases with the wavelength redshift curve, which is conducive to the working wavelength moving to the E band. The reason is that the inner cladding of the outer core of the present invention is composed of the first low refractive index solid ring and the first high refractive index solid ring, so that the lower limit of the refractive index value of the outer core mode is jointly determined by the refractive index of the first low refractive index solid ring and the refractive index of the first high refractive index solid ring. The refractive index values ​​of the first low-refractive index solid ring and the second low-refractive index solid ring on both sides of the outer core are equal, while the refractive index value of the first high-refractive index solid ring is greater than the refractive index value of the first low-refractive index solid ring. Therefore, the first high-refractive index solid ring has the effect of increasing the refractive index of the inner cladding of the outer core, so that the lower limit of the refractive index of the outer core mode is increased. When light is incident from the first high-refractive index solid ring with a smaller refractive index to the second high-refractive index solid ring with a larger refractive index, total reflection will not occur, so the second high-refractive index solid ring cannot be used as part of the inner core cladding. Therefore, the outer core does not have the effect of increasing the refractive index of the inner core cladding, and will not increase the lower limit of the refractive index of the inner core mode. The combined effect of the above-mentioned schemes for regulating the refractive index values ​​of the inner and outer core modes ensures that the curve of the refractive index value of the inner core mode with the red shift of the wavelength and the curve of the refractive index value of the outer core mode with the red shift of the wavelength can intersect at a certain wavelength in the E band. The refractive index values ​​of the inner and outer core modes match near the intersection (the values ​​are equal or close), which satisfies one of the conditions for the resonance of the inner and outer core modes at the working wavelength.

[0047] From the mismatch angle of the slope of the redshift curve of the inner and outer core modes refractive index with wavelength, the inner core of the present invention is composed of a first high refractive index solid ring and a central air hole with a diameter less than the lower limit wavelength of the E band 1360nm, so that (1) when the wavelength of light is less than the diameter of the air hole, the energy of the inner core mode is mainly concentrated in the first high refractive index solid ring, and the energy diffused into the central air hole is very small. The refractive index value of the inner core mode takes the refractive index value of the first high refractive index solid ring as the upper limit, so its value is relatively high; (2) when the wavelength of light is greater than the diameter of the air hole, the energy distributed in the first high refractive index solid ring becomes less, and the energy diffused into the central air hole becomes more. The refractive index value of the inner core mode takes the average of the refractive index value of the first high refractive index solid ring and the refractive index value of air converted by area (hereinafter referred to as the inner core average refractive index) as the upper limit. Since the refractive index value of air is much smaller than the refractive index value of other parts of the optical fiber, the inner core average refractive index value is smaller than the refractive index value of the first high refractive index solid ring. Therefore, compared with when the wavelength of light is less than the diameter of the air hole, the refractive index value of the inner core mode is significantly reduced at this time. The combined effect of (1) and (2) increases the absolute value of the slope of the inner core mode refractive index versus wavelength redshift curve, which increases the absolute value difference between the slopes of the inner and outer core mode refractive index versus wavelength redshift curves, which is conducive to achieving the maximum mismatch between the slopes of the inner and outer core mode refractive index versus wavelength redshift curves. The inner cladding of the outer core of the present invention is composed of a first low-refractive index solid ring and a first high-refractive index solid ring, so that (3) when the wavelength of light is short, the energy of the outer core mode diffuses to the first low-refractive index solid ring more, and diffuses to the first high-refractive index solid ring less, and the refractive index value of the outer core mode takes the refractive index value of the first low-refractive index solid ring as the lower limit, so its value is relatively low; (4) when the wavelength of light is long, the energy of the outer core mode diffuses to the first low-refractive index solid ring less, and diffuses to the first high-refractive index solid ring more, and the refractive index value of the outer core mode takes the average of the refractive index value of the first low-refractive index solid ring and the refractive index value of the first high-refractive index solid ring converted by area (hereinafter referred to as the average refractive index of the inner cladding of the outer core) as the lower limit. Since the refractive index value of the first high-refractive index solid ring is greater than the refractive index value of the first low-refractive index solid ring, the average refractive index value of the inner cladding is less than the refractive index value of the first low-refractive index solid ring, so compared with the case where the wavelength of light is short, the refractive index value of the outer core mode is significantly increased at this time. The combined effect of (3) and (4) reduces the absolute value of the slope of the outer core mode refractive index versus wavelength redshift curve, increases the absolute value difference of the slope of the inner and outer core mode refractive index versus wavelength redshift curve, and is conducive to achieving the maximum mismatch of the slope of the inner and outer core mode refractive index versus wavelength redshift curve. The above-mentioned schemes for regulating the absolute value of the slope of the inner and outer core mode refractive index versus wavelength redshift curve have a combined effect, increasing the absolute value difference of the slope of the inner and outer core mode refractive index versus wavelength redshift curve (i.e., achieving the maximum mismatch of the slope of the inner and outer core mode refractive index versus wavelength redshift curve).Due to the mismatch in the slope of the redshift curves of the refractive index of the inner and outer core modes versus wavelength, the energy of the inner and outer core modes converts from an incompletely coupled state to a resonant state faster (i.e., when approaching the working wavelength, the redshift curves of the refractive index of the inner and outer core modes versus wavelength rapidly approach each other, causing the difference between the two to decrease rapidly), thereby enhancing the coupling strength of the inner and outer core modes at the working wavelength.

[0048] From the perspective of enhancing the coupling between the inner and outer core modes, the first high refractive index solid ring of the present invention is in the shape of a circular ring, the inner side of which is adjacent to a central air hole with a diameter less than 1360nm, the lower limit wavelength of the E band, and the outer side is adjacent to the first low refractive index solid ring, so that the boundary conditions on the inner and outer sides of the first high refractive index solid ring are different. Since the refractive index value of air is much smaller than the refractive index value of the first low refractive index solid ring, the field distribution of the inner core mode in the first high refractive index solid ring is offset to one side of the first low refractive index solid ring, which is conducive to enhancing the coupling between the inner and outer core modes. The width of the second high refractive index solid ring of the present invention is smaller than the width of the first high refractive index solid ring, and the refractive index values ​​of the first low refractive index solid ring and the second low refractive index solid ring on both sides of the outer core are equal. Since the refractive index value of the first high refractive index solid ring is smaller than the refractive index value of the second high refractive index solid ring, the average refractive index value of the inner cladding is greater than the refractive index value of the second low refractive index solid ring. Therefore, the scheme that the energy of the outer core mode is easily diffused inward can weaken the outer core's ability to limit light, so that the field distribution of the second high refractive index solid ring is offset to the side of the first low refractive index solid ring, which is conducive to enhancing the coupling of the inner and outer core modes. The scheme of reducing the width of the first low refractive index solid ring of the present invention can reduce the distance between the inner core and the outer core, which is conducive to enhancing the coupling of the inner and outer core modes. Under the conditions of simultaneously satisfying the numerical matching of the refractive index and the slope mismatch between the inner core mode and the outer core mode, the above scheme ensures that the inner and outer core modes can be coupled at the working wavelength, so that the inner and outer core modes can resonate at the working wavelength, thereby enhancing the coupling strength between the inner and outer core modes at the working wavelength, and increasing the absolute value of the large negative dispersion value of the inner core mode at the working wavelength.

[0049] Second, when the working wavelength is blue-shifted to the E band, the coupling loss between the inner core mode and the front single-mode optical fiber at the working wavelength is low.

[0050] The design of the width of the first high-refractive-index solid ring of the present invention ensures that the diameter of the inner core formed by the central air hole and the first high-refractive-index solid ring matches the core diameter of the front single-mode optical fiber in numerical value. On the basis of the core diameter numerical matching, the diameter of the central air hole of the present invention is smaller than the scheme of 1360nm, the lower limit wavelength of the E band, and the optical energy can diffuse into the central air hole at the working wavelength. Therefore, the central air hole has little effect on the Gaussian distribution of the inner core mode field, further ensuring the mode field matching of the inner core mode and the front single-mode optical fiber mode. Therefore, the inner core composition scheme of the present invention can reduce the coupling loss with the front single-mode optical fiber.

[0051] 3. When the operating wavelength is blue-shifted to the E-band, the confinement and bending losses of the inner core mode at the operating wavelength are low.

[0052] The scheme of the present invention for achieving the blue shift of the working wavelength to the E band does not rely on the reduction of the inner core diameter, nor does it rely on the reduction of the refractive index value of the first high refractive index solid ring and the increase of the refractive index value of the first low refractive index solid ring, and therefore will not deteriorate the limiting loss and bending loss of the inner core mode.

[0053] According to the structure, parameters and working principle of the optical fiber of the present invention, when the wavelength of light approaches 0 (in the short-wave limit), the energy of the inner core mode is mainly concentrated in the first high-refractive index solid ring, so the refractive index value of the inner core mode takes the refractive index value n2 of the first high-refractive index solid ring as the upper limit; when the wavelength of light approaches ∞ (in the long-wave limit), most of the energy of the inner core mode enters the air hole. At this time, the energy of the inner core mode is evenly distributed in the first high-refractive index solid ring and the central air hole, so the refractive index value of the inner core mode is the average refractive index value converted by area of ​​the refractive index value of the first high-refractive index solid ring and the refractive index value of air. (where n1 = 1) is used as the upper limit. Therefore, the upper limit of the refractive index of the inner core mode increases with the wavelength blue shift, and the value range is: When the wavelength of light approaches 0 (in the short-wave limit), the energy of the outer core mode is mainly concentrated in the second high-refractive-index solid ring, and the energy that partially diffuses into the inner cladding is mainly distributed in the first low-refractive-index solid ring, so the refractive index value of the outer core mode takes the refractive index value n3 of the first low-refractive-index solid ring as the lower limit; when the wavelength of light approaches ∞ (in the long-wave limit), most of the energy diffused into the inner cladding enters the first high-refractive-index solid ring. At this time, the energy of the outer core mode in the inner cladding is evenly distributed in the first low-refractive-index solid ring and the first high-refractive-index solid ring, so the refractive index value of the outer core mode is the average refractive index value converted by area using the refractive index values ​​of the first low-refractive-index solid ring and the first high-refractive-index solid ring. As the lower limit. Therefore, the lower limit of the refractive index of the outer core mode increases with the wavelength redshift, and the value range is:

[0054] The technical effects of the above-mentioned structures and parameters of the present invention are as follows.

[0055] (1) The center of the optical fiber is a circular central air hole, which will produce the following technical effects:

[0056] a. Since the refractive index of air n1 is much smaller than the refractive index of other parts of the optical fiber, the introduction of an air hole in the center of the optical fiber has the effect of reducing the refractive index of the inner core, reducing the upper limit of the refractive index of the inner core mode from n2 to This reduces the refractive index value of the inner core mode, so that the refractive index value of the inner core mode decreases along the wavelength redshift curve, which is beneficial for the refractive index value matching wavelength (working wavelength) of the inner and outer core modes to blueshift to the E band.

[0057] b. The refractive index difference n2-n1 between the first high refractive index solid ring and the inner air is greater than the refractive index difference n2-n3 between the first high refractive index solid ring and the outer first low refractive index solid ring, so that the field distribution of the inner core mode in the first high refractive index solid ring is offset toward the first low refractive index solid ring, which is beneficial to enhance the coupling between the inner and outer core modes.

[0058] (2) The refractive index n2 of the first high-refractive-index solid ring is greater than the refractive index n3 of the first low-refractive-index solid ring, which will produce the following technical effects: the refractive index difference n2-n3 between the first high-refractive-index solid ring and the first low-refractive-index solid ring on the outside is large, ensuring that the limiting loss and bending loss of the inner core mode are low.

[0059] (3) The first high refractive index solid ring width L1 is in the range of 3.5 to 4.4 μm, which will produce the following technical effects:

[0060] a. Make the inner core diameter d1+2L1 within the diameter range of the single-mode optical fiber, ensuring that the inner core diameter d1+2L1 matches the core diameter of the front-end single-mode optical fiber in terms of value, which is beneficial to reducing the coupling loss with the front-end single-mode optical fiber.

[0061] b. The diameter of the inner core d1+2L1 is large, which ensures low limiting loss and bending loss of the inner core mode.

[0062] c. Increase the area ratio of the first high refractive index solid ring and the first low refractive index solid ring, so that the average refractive index of the inner cladding of the outer core Increase, and then increase the refractive index value of the outer core mode, so that the refractive index value of the outer core mode increases with the wavelength redshift curve, which is beneficial to the blue shift of the refractive index value matching wavelength (working wavelength) of the inner and outer core modes to the E band.

[0063] (4) The first high refractive index solid ring wraps the central air hole with a diameter d1 smaller than the lower limit wavelength of the E band 1360nm. The combined effect of the two will produce the following technical effects:

[0064] a. It is determined that the inner core of the present invention is composed of a first high-refractive index solid ring and a central air hole.

[0065] b. Part of the energy of the inner core mode is retained in the first high refractive index solid ring, and part of the energy is diffused into the central air hole. Since the energy of the inner core mode distributed in the air hole increases with the wavelength redshift, the upper limit of the refractive index of the inner core mode decreases with the wavelength redshift, which increases the absolute value of the slope of the curve of the refractive index of the inner core mode versus the wavelength redshift, and increases the absolute value difference in the slope of the curve of the refractive index of the inner and outer core modes versus the wavelength redshift, which is conducive to achieving the maximum mismatch in the slope of the curve of the refractive index of the inner and outer core modes versus the wavelength redshift, thereby enhancing the coupling strength of the inner and outer core modes at the working wavelength.

[0066] c. Allows light energy to diffuse into the central air hole at the working wavelength, so the central air hole has little effect on the Gaussian distribution of the inner core mode field, ensuring the mode field matching between the inner core mode and the front-end single-mode fiber mode, which is beneficial to reducing the coupling loss with the front-end single-mode fiber.

[0067] (5) The first low refractive index solid ring width L2 is greater than the upper limit wavelength of the E band 1460nm, which will produce the following technical effects:

[0068] a. It is determined that the second high refractive index solid ring portion is the outer core of the present invention, and the optical fiber structures on both the inner and outer sides thereof may constitute its cladding.

[0069] b. Reducing the width L2 of the first low-refractive-index solid ring will reduce the distance between the inner core and the outer core, which is beneficial to enhancing the coupling between the inner and outer core modes.

[0070] c. Reducing the width L2 of the first low-refractive-index solid ring will increase the area ratio of the first high-refractive-index solid ring and the first low-refractive-index solid ring, making the average refractive index of the inner cladding of the outer core Increase, and then increase the refractive index value of the outer core mode, so that the refractive index value of the outer core mode increases with the wavelength redshift curve, which is beneficial to the blue shift of the refractive index value matching wavelength (working wavelength) of the inner and outer core modes to the E band.

[0071] (6) The refractive index n4 of the second high refractive index solid ring is greater than the refractive index n2 of the first high refractive index solid ring, which will produce the following technical effects:

[0072] a. It can increase the upper limit of the refractive index of the outer core mode, thereby increasing the value of the refractive index of the outer core mode, so that the value of the refractive index of the outer core mode increases with the red shift curve of the wavelength, which is conducive to the blue shift of the refractive index value matching wavelength (working wavelength) of the inner and outer core modes to the E band.

[0073] b. It is determined that the inner cladding of the outer core of the present invention is composed of a first low-refractive-index solid ring and a first high-refractive-index solid ring.

[0074] c. Since the refractive index of the first high-refractive-index solid ring is greater than that of the first low-refractive-index solid ring, the first high-refractive-index solid ring has the effect of increasing the refractive index of the inner cladding of the outer core, so that the lower limit of the refractive index of the outer core mode is increased from n3 to Then the outer core mode refractive index value is increased, so that the outer core mode refractive index value increases with the wavelength redshift curve, which is conducive to the blue shift of the inner and outer core mode refractive index value matching wavelength (working wavelength) to the E band.

[0075] d. Part of the energy of the outer core mode diffused into the inner cladding is distributed in the first low refractive index solid ring, and the other part of the energy is distributed in the first high refractive index solid ring. Since the energy of the outer core mode distributed in the first high refractive index solid ring increases with the wavelength redshift, the lower limit of the refractive index of the outer core mode increases with the wavelength redshift, which reduces the absolute value of the slope of the curve of the refractive index of the outer core mode versus the wavelength redshift, and increases the absolute value difference in the slope of the curve of the refractive index of the inner and outer core modes versus the wavelength redshift, which is conducive to achieving the maximum mismatch in the slope of the curve of the refractive index of the inner and outer core modes versus the wavelength redshift, thereby enhancing the coupling strength of the inner and outer core modes at the operating wavelength.

[0076] e. The refractive index values ​​of the first low-refractive index solid ring and the second low-refractive index solid ring on both sides of the outer core are equal. Due to the refractive index difference between the second high-refractive index solid ring and the inner cladding, The refractive index difference n4-n3 between the second highest refractive index solid ring and the outer cladding is smaller than that of the second highest refractive index solid ring, so that the field distribution of the second highest refractive index solid ring is offset toward the first low refractive index solid ring, which is beneficial to enhance the coupling between the inner and outer core modes.

[0077] (7) The second high refractive index solid ring width L3 is smaller than the first high refractive index solid ring width L1, which will produce the following technical effects: weakening the outer core's ability to limit light, which is conducive to enhancing the coupling between the inner and outer core modes.

[0078] In addition, compared with the improvement idea of ​​only optimizing the structural parameters of the conventional coaxial dual-core dispersion compensating optical fiber to blue-shift the working wavelength to the E band, the present invention also has the following advantages:

[0079] (1) If the diameter of the inner core of a conventional coaxial dual-core dispersion-compensating optical fiber is reduced, the refractive index value of the inner core mode can be reduced. Under the premise that the refractive index value of the outer core mode remains unchanged as the wavelength redshift curve, the refractive index value of the inner core mode is reduced as the wavelength redshift curve, so that the intersection of the two curves, that is, the working wavelength (that is, the resonance wavelength), is blue-shifted. In order to adjust the working wavelength to 1550nm and enhance the coupling strength at the working wavelength, the diameter of the inner core of a conventional coaxial dual-core dispersion-compensating optical fiber is generally smaller than the diameter of the front-end single-mode optical fiber. The mismatch of the core diameter will increase the loss when the coaxial dual-core dispersion-compensating optical fiber is coupled with the front-end single-mode optical fiber. The solution of further reducing the core diameter to blueshift the working wavelength will lead to an increase in the coupling loss with the front-end single-mode optical fiber. At the same time, when other conditions remain unchanged, an overly small core will lead to an increase in the limiting loss and bending loss of the inner core mode. However, due to the adoption of a different improvement idea, the optical fiber provided by the present invention has a low coupling loss with the front-end single-mode optical fiber, and the limiting loss and bending loss will not deteriorate.

[0080] (2) If the refractive index of the inner core of a conventional coaxial dual-core dispersion-compensating optical fiber is reduced, the upper limit of the inner core mode refractive index can be reduced, so that the inner core mode refractive index value is reduced. Under the premise that the outer core mode refractive index value versus wavelength redshift curve remains unchanged, the inner core mode refractive index value versus wavelength redshift curve is reduced, so that the intersection of the two curves, that is, the working wavelength, is blue-shifted. However, after the inner core refractive index is reduced, the refractive index difference between the inner core and the inner cladding is reduced. On the one hand, the absolute value of the slope of the inner core mode refractive index versus wavelength redshift curve will be reduced. When the absolute value of the slope of the outer core mode refractive index versus wavelength redshift curve remains unchanged, the absolute value difference of the slope of the inner and outer core mode refractive index versus wavelength redshift curves will be reduced, causing the separation speed of the inner and outer core mode refractive index versus wavelength redshift curves to slow down when they are far away from the working wavelength (i.e., the speed of increasing the difference in the values ​​of the two becomes slower), widening the transition band of the energy of the inner and outer core modes from incomplete coupling to the resonant state (i.e., from the large difference in the refractive index values ​​of the inner and outer core modes to the equal refractive index values ​​of the inner and outer core modes), resulting in a decrease in the coupling strength of the inner and outer core modes at the working wavelength, and a decrease in the absolute value of the large negative dispersion value of the inner core mode at the working wavelength. On the other hand, since the limiting loss and bending loss of the inner core mode are inversely proportional to the refractive index difference between the inner core and the inner cladding, this solution will increase the limiting loss and bending loss of the inner core mode. However, due to the adoption of different improvement ideas, the optical fiber provided by the present invention has a large absolute value of negative dispersion at the E-band working wavelength, and the limiting loss and bending loss will not deteriorate.

[0081] (3) If the width of the outer core of a conventional coaxial dual-core dispersion-compensating optical fiber is increased, the refractive index value of the outer core mode can be increased. Under the premise that the refractive index value of the inner core mode remains unchanged along the wavelength redshift curve, the refractive index value of the outer core mode increases along the wavelength redshift curve, so that the intersection of the two curves, that is, the working wavelength, is blue-shifted. However, this solution will enhance the outer core's ability to limit light, inhibit the coupling of the inner and outer core modes, and reduce the coupling strength of the inner and outer core modes at the working wavelength, so that the absolute value of the large negative dispersion value of the inner core mode at the working wavelength is reduced. However, due to the adoption of a different improvement idea, the optical fiber provided by the present invention has a negative dispersion with a large absolute value at the E-band working wavelength.

[0082] (4) If the refractive index of the outer core of a conventional coaxial dual-core dispersion-compensating optical fiber is increased, the upper limit of the refractive index of the outer core mode can be increased, so that the value of the refractive index of the outer core mode increases. Under the premise that the value of the refractive index of the inner core mode remains unchanged as the redshift curve of the wavelength, the value of the refractive index of the outer core mode increases as the redshift curve of the wavelength, so that the intersection of the two curves, that is, the working wavelength, blueshifts. However, increasing the upper limit of the refractive index of the outer core mode will increase the absolute value of the slope of the refractive index of the outer core mode as the redshift curve of the wavelength. Under the premise that the absolute value of the slope of the refractive index of the inner core mode as the redshift curve of the wavelength remains unchanged, the absolute value difference of the slope of the refractive index of the inner and outer core modes as the redshift curve of the wavelength will be reduced, causing the separation speed of the refractive index of the inner and outer core modes as the redshift curve of the wavelength to slow down when far away from the working wavelength, widening the transition band from the incomplete coupling of the energy of the inner and outer core modes to the resonant state, resulting in a decrease in the coupling strength of the inner and outer core modes at the working wavelength, so that the absolute value of the large negative dispersion value of the inner core mode at the working wavelength is reduced. However, the present invention adopts a different improvement idea, so that the optical fiber provided by the present invention has a negative dispersion with a large absolute value at the E-band working wavelength.

[0083] (5) If the refractive index of the inner cladding of a conventional coaxial dual-core dispersion-compensating optical fiber is increased, the lower limit of the refractive index of the inner and outer core modes will be increased at the same time, making the values ​​of the refractive index of the inner and outer core modes larger. Because the increase in the refractive index of the outer core mode will cause the working wavelength to blue-shift, while the increase in the refractive index of the inner core mode will cause the working wavelength to red-shift, the effects of the two will offset each other, making it difficult to achieve a large blue shift of the working wavelength. At the same time, this solution will reduce the refractive index difference between the inner core and the inner cladding, as described in (2), which will increase the limiting loss and bending loss of the inner core mode. However, since the present invention adopts a different improvement idea, the limiting loss and bending loss of the optical fiber provided by the present invention will not deteriorate.

[0084] (6) If the width of the inner cladding of a conventional coaxial dual-core dispersion-compensating optical fiber is increased, the refractive index of the inner core mode can be reduced, thereby blueshifting the operating wavelength. The reason is that the refractive index of the inner core of a conventional coaxial dual-core dispersion-compensating optical fiber is greater than that of the outer core, so the outer core can be regarded as the second ring cladding of the inner core. Increasing the width of the inner cladding of a conventional coaxial dual-core dispersion-compensating optical fiber will reduce the average refractive index of the two cladding layers of the inner core (inner cladding + outer core), thereby reducing the lower limit of the refractive index of the inner core mode, thereby reducing the refractive index of the inner core mode and reducing the curve of the refractive index of the inner core mode versus wavelength redshift. Under the premise that the curve of the refractive index of the outer core mode versus wavelength redshift remains unchanged, the curve of the refractive index of the inner core mode versus wavelength redshift decreases, causing the intersection of the two curves, i.e. the operating wavelength, to blueshift. However, the increase in the width of the inner cladding will increase the distance between the inner core and the outer core, resulting in a decrease in the coupling strength of the inner and outer core modes at the operating wavelength, thereby reducing the absolute value of the large negative dispersion value of the inner core mode at the operating wavelength. However, the present invention adopts a different improvement idea, so that the optical fiber provided by the present invention has a negative dispersion with a large absolute value at the E-band working wavelength.

[0085] (7) If the refractive index of the outer cladding of a conventional coaxial dual-core dispersion-compensating optical fiber is increased, the lower limit of the refractive index of the outer core mode can be increased, so that the value of the refractive index of the outer core mode increases. Under the premise that the value of the refractive index of the inner core mode remains unchanged as the wavelength redshift curve, the value of the refractive index of the outer core mode increases as the wavelength redshift curve, so that the intersection of the two curves, that is, the working wavelength blueshifts. However, this solution will reduce the refractive index difference between the inner and outer cores and the outer cladding, resulting in increased bending losses in the inner and outer core modes. At the same time, in order to ensure that the absolute value of the slope of the inner core mode refractive index as the wavelength redshift curve is greater than the absolute value of the slope of the outer core mode refractive index as the wavelength redshift curve, the refractive index of the outer core of the existing coaxial dual-core dispersion-compensating optical fiber is usually smaller than the refractive index of the inner core. Therefore, the refractive index of the outer cladding is difficult to increase significantly due to the limitation of the refractive index of the outer core, and it is difficult to achieve a blueshift of the working wavelength to the E band.

[0086] It can be seen that the present invention can not only achieve the blue shift of the working wavelength to the E band, but also maintain or even improve the absolute value of the negative dispersion value of the optical fiber at the working wavelength, and the performance of parameters such as the coupling loss, limitation and bending loss of the front-end single-mode optical fiber.

[0087] Specifically, the configuration of the inner cladding of the inner core and the outer core proposed in the present invention has a dynamic effect of making the upper limit of the refractive index of the inner core mode and the lower limit of the refractive index of the outer core mode change with the wavelength under the condition that the structural parameters remain unchanged. Based on the configuration scheme of the inner cladding of the inner core and the outer core, the present invention can simultaneously ensure that the numerical matching wavelength (working wavelength) of the refractive index of the inner and outer core modes is blue-shifted to the E band, the slope of the curve of the refractive index of the inner and outer core modes with the red shift of the wavelength is mismatched, and the coupling strength of the inner and outer core modes is high at the working wavelength.

[0088] The present invention is described below with reference to a number of embodiments with specific parameters.

[0089] Embodiment 1:

[0090] The refractive index of the central air hole in Example 1 is n1=1, and its diameter d1=1.22μm; the refractive index of the first high refractive index solid ring is n2=1.0105n3=1.47262186, and its ring width L1=3.9μm; the refractive index of the first low refractive index solid ring is n3=1.45732, and its ring width L2=9.5μm; the refractive index of the second high refractive index solid ring is n4=1.0105n3+0.0001=1.47272186, and its ring width L3=3.18μm; the refractive index of the second low refractive index solid ring is n3=1.45732, and its outer diameter d2=125μm.

[0091] See also Figure 2 When approaching the resonant wavelength near 1413.5nm, the curves of the refractive index values ​​of the inner and outer core modes changing with wavelength quickly approach each other, causing the difference between the two values ​​to decrease rapidly; when moving away from the resonant wavelength, the curves of the refractive index values ​​of the inner and outer core modes changing with wavelength quickly separate, causing the difference between the two values ​​to increase rapidly, causing the coupling between the inner and outer core modes to weaken rapidly in the non-working band and to increase rapidly in the working band, ultimately forming a sudden drop in the refractive index value of the inner core mode in a narrow bandwidth.

[0092] See also Figure 3 According to the dispersion formula, when the refractive index value of the inner core mode suddenly drops in a narrow bandwidth to form a concave, the second-order derivative of the refractive index value of the inner core mode with respect to the wavelength is positive. Therefore, at 1413.5nm, the inner core mode produces a large negative dispersion of -497.5ps / (nm·km).

[0093] Embodiment 2:

[0094] The refractive index of the central air hole in Example 2 is n1=1, and its diameter d1=1.2μm; the refractive index of the first high refractive index solid ring is n2=1.01n3=1.4718932, and its ring width L1=3.9μm; the refractive index of the first low refractive index solid ring is n3=1.45732, and its ring width L2=9.5μm; the refractive index of the second high refractive index solid ring is n4=1.01n3+0.0001=1.4719932, and its ring width L3=3.18μm; the refractive index of the second low refractive index solid ring is n3=1.45732, and its outer diameter d2=125μm.

[0095] See also Figure 4 At the resonant wavelength of 1371nm, the refractive index value of the inner core mode changes with the wavelength curve, so see Figure 5The inner core mode produces a large negative dispersion of -513.6 ps / (nm·km) at 1371 nm.

[0096] Embodiment 3:

[0097] The refractive index of the central air hole in Example 3 is n1=1, and its diameter d1=1.24μm; the refractive index of the first high refractive index solid ring is n2=1.011n3=1.47345162, and its ring width L1=3.9μm; the refractive index of the first low refractive index solid ring is n3=1.45732, and its ring width L2=9.5μm; the refractive index of the second high refractive index solid ring is n4=1.011n3+0.0001=1.47355162, and its ring width L3=3.18μm; the refractive index of the second low refractive index solid ring is n3=1.45732, and its outer diameter d2=125μm.

[0098] See also Figure 6 At the resonant wavelength of 1455.5nm, the refractive index value of the inner core mode changes with the wavelength curve, so see Figure 7 The inner core mode produces a large negative dispersion of -481.2 ps / (nm·km) at 1455.5 nm.

[0099] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. An E-band dispersion compensating optical fiber, characterized in that: The optical fiber includes, from the center to the outside, a central air hole, a first high-refractive-index solid ring, a first low-refractive-index solid ring, a second high-refractive-index solid ring, and a second low-refractive-index solid ring; The refractive index of the central air hole n1=1, and the first diameter d1<1360nm; The refractive index of the first high-refractive-index solid ring is n2, and the first ring width L1 is in the range of 3.5 to 4.4 μm; The refractive index of the first low-refractive-index solid ring is n3, and the second ring width L2 is greater than 1460 nm; The refractive index of the second high refractive index solid ring is n4, and the third ring width L3<L1; The refractive index of the second low-refractive-index solid ring is n3, and the second diameter d2 is in the range of 125±1 μm; Among them, n4﹥n2﹥n3﹥n1.

2. The E-band dispersion compensating optical fiber according to claim 1, characterized in that: The central air hole and the first high refractive index solid ring serve as the inner core of the optical fiber, the first high refractive index solid ring and the first low refractive index solid ring serve as the inner cladding of the outer core of the optical fiber, the second high refractive index solid ring serves as the outer core of the optical fiber, and the second low refractive index solid ring serves as the outer cladding of the outer core of the optical fiber.

3. The E-band dispersion compensating optical fiber according to claim 1, characterized in that: The upper limit of the refractive index of the core mode of the optical fiber is: The lower limit of the refractive index of the outer core mode of the optical fiber is:

4. The E-band dispersion compensating optical fiber according to claim 1, characterized in that: The first diameter d1 ranges from 1.1 to 1.3 μm.

5. The E-band dispersion compensating optical fiber according to claim 1, characterized in that: The first ring width L1 ranges from 3.8 to 4.2 μm.

6. The E-band dispersion compensating optical fiber according to claim 1, characterized in that: The second ring width L2 is in the range of 8.0 to 10.0 μm.

7. The E-band dispersion compensating optical fiber according to claim 1, characterized in that: The third ring width L3 ranges from 3.0 to 3.5 μm.

8. The E-band dispersion compensating optical fiber according to claim 1, characterized in that: The refractive index n2 of the first high-refractive-index solid ring ranges from 1.010n3 to 1.011n3.

9. The E-band dispersion compensating optical fiber according to claim 1, characterized in that: The refractive index n4 of the second high-refractive-index solid ring is in the range of (n2+0.00005) to (n2+0.00015).

10. The E-band dispersion compensating optical fiber according to claim 1, characterized in that: The first low-refractive-index solid ring and the second low-refractive-index solid ring are both made of pure quartz glass material.

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