High-nonlinearity photonic crystal fiber and optical fiber amplifier

Abstract

The invention relates to a high-nonlinearity photonic crystal fiber and an optical fiber amplifier, the fiber comprises a core layer and cladding layers, the cladding layers comprise an inner cladding layer and an outer cladding layer, the high-nonlinearity photonic crystal fiber is characterized in that the refractive index profile of the core layer is in alpha power exponential function distribution, the distribution index alpha of the core layer is 2.0-8.0, the radius a of the core layer is 0.8-2 microns, and the refractive index alpha of the core layer is 2.0-8.0. The maximum relative refractive index difference delta 1max is 2-5%, the inner cladding layer is an air hole dot matrix inner cladding layer, the outer cladding layer is arranged outside the inner cladding layer, and the outer cladding layer is a pure silicon dioxide glass outer cladding layer. According to the invention, the large refractive index difference between the high refractive index core layer and the low refractive index air hole cladding is beneficial to improving the binding ability of the fiber core to light on one hand and promoting the reduction of the effective mode field area of the optical fiber on the other hand, thereby improving the nonlinear performance. The gradient high-nonlinearity photonic crystal fiber provided by the invention is mainly used in the field of communication and can be used as an optical gain medium of an optical fiber amplifier, and a corresponding device has the advantages of low noise, high gain and the like.

Description

Technical Field

[0001] The invention relates to a highly nonlinear photonic crystal optical fiber and an optical fiber amplifier, belonging to the technical field of optical fibers. Background Art

[0002] Under specific conditions, highly nonlinear optical fibers can produce a variety of nonlinear effects, including self-phase modulation, soliton splitting, four-wave mixing, and stimulated Raman scattering. Their unique optical properties have given them broad commercial and scientific value in areas such as supercontinuum generation, optical frequency combs, wavelength division multiplexing systems, broadband tunable light sources, soliton communications, and Raman amplifiers. However, conventional quartz optical fibers exhibit a low nonlinear coefficient at 1550 nm, making it difficult to meet the critical parameter requirements of optical fiber amplifiers in the communication band. The key challenge is to develop optical fiber media with higher nonlinear coefficients in the 1550 nm band.

[0003] For quartz optical fiber, the nonlinearity of the optical fiber can be improved to a certain extent through material regulation or structural design. Chinese patent CN1721896A designs a high nonlinear quartz optical fiber that can achieve more than 10W in the 1550nm band. - 1 km -1 The nonlinear coefficient of the fiber is 6W. Compared with traditional quartz fiber, the nonlinear performance has been significantly improved, but it still cannot meet the high nonlinear requirements of related fields. In contrast, the rich adjustable factors of microstructured fiber provide more options for the design of high nonlinear fiber. The literature [Gilles Mélin.et.al.Photonic Crystal Fibers.(2008)SPIE.Vol.6990,699003] designed a photonic crystal fiber based on a germanium-doped fiber core and achieved a nonlinear coefficient of 6W. -1 km -1 Microstructured fibers offer a wide range of design options for highly nonlinear fibers due to their small effective area and high Raman gain performance. The flexible structural arrangement of microstructured fibers can provide more design options for highly nonlinear fibers. However, from a manufacturing perspective, the precise proportions, small capillary apertures, and unique arrangement positions lead to technical challenges in implementing highly nonlinear microstructured fibers, including process tolerances and positional fixation. Consequently, most microstructured highly nonlinear fibers exist only at the design level, lacking readily manufacturable high-nonlinear microstructured fibers.

[0004] From an application perspective, the lack of highly nonlinear optical fibers in the communications band has limited the application of amplifiers in this band. For example, in Raman fiber amplifiers, where highly nonlinear optical fibers serve as the core gain medium, key parameters such as the nonlinear coefficient significantly impact the gain performance of the Raman amplifier. Existing Raman amplifiers suffer from numerous issues, including limited gain and high noise levels. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a highly nonlinear photonic crystal fiber and a fiber amplifier in view of the deficiencies in the above-mentioned prior art. The fiber has a high nonlinear coefficient and is used in the field of fiber amplifiers, with high gain and low noise effects.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: comprising a core layer and a cladding layer, wherein the cladding layer comprises an inner cladding layer and an outer cladding layer, characterized in that the refractive index profile of the core layer is distributed in an α power exponential function, the core layer distribution index α is 2.0 to 8.0, the radius a is 0.8 to 2 μm, and the maximum relative refractive index difference Δ 1max The inner cladding is an air hole lattice inner cladding, the outer cladding is an outer cladding, and the outer cladding is a pure silica glass outer cladding.

[0007] According to the above solution, the core layer distribution index α is 2.3 to 5.0.

[0008] According to the above solution, the core layer is a silicon dioxide glass layer doped with germanium or bismuth or co-doped with germanium and bismuth.

[0009] According to the above solution, the inner cladding of the air hole lattice is a hexagonal or even-numbered regular polygonal air hole lattice, and the core layer is located at the center of the air hole lattice.

[0010] According to the above solution, the aperture of each air hole in the air hole matrix is the same, and the spacing between adjacent air holes is the same.

[0011] According to the above scheme, the air hole lattice is densely packed and arranged, and the air hole diameter and the distance between adjacent air holes can be flexibly adjusted according to the dispersion property requirements.

[0012] According to the above solution, the distance Λ between adjacent air holes in the inner cladding of the air hole lattice is 2 to 12 μm, and the duty ratio D / Λ is 0.2 to 0.9.

[0013] According to the above solution, the number of regular polygonal layers in the inner cladding of the air hole lattice is 2 to 10.

[0014] According to the above solution, the air hole lattice inner cladding is composed of a pure silica glass substrate layer and an air hole lattice.

[0015] According to the above solution, the outer cladding has a diameter of 100 to 300 μm.

[0016] According to the above scheme, the refractive index distribution formula of the power exponential function is:

[0017]

[0018] Where n1 is the refractive index of the fiber axis; r is the distance from the fiber axis; a is the fiber core radius; α is the distribution index; Δ is the relative refractive index difference between the core center and the outer cladding.

[0019] According to the above scheme, the optical fiber has a power of 18W or more in the 1550nm band. -1 km -1 The nonlinear coefficient of .

[0020] The highly nonlinear photonic crystal optical fiber of the present invention is applied to a backward-pumped optical fiber amplifier as a gain medium of the optical fiber amplifier.

[0021] The beneficial effects of the present invention are: 1. The large refractive index difference between the high-refractive index core layer and the low-refractive index air hole cladding is beneficial to improving the light-binding ability of the fiber core on the one hand, and on the other hand, promoting the reduction of the effective mode field area of the optical fiber, thereby improving the nonlinear performance. 2. The fiber core has a high refractive index and a high nonlinear coefficient, which improves the nonlinear characteristics from the inherent properties of the material and promotes breakthroughs in the optical functions of nonlinear optical fibers. 3. The photonic crystal cladding layout surrounded by the air hole lattice can achieve optical waveguide dispersion regulation with the help of the variable design of the air holes, which is beneficial to the dispersion compensation of optical fibers in different wavelength ranges. 4. The gradient core design can effectively avoid the glass viscosity mismatch caused by the right-angle refractive index mutation and reduce the risk of glass rod explosion during deposition. 5. The preparation process of the present invention relies on a complete PCVD / MCVD deposition process and a photonic crystal fiber preparation process. The process route is mature, the production is stable, and it is easy to mass produce. 6. The gradient high nonlinear photonic crystal fiber provided by the present invention is mainly used in the field of communications and can be used as an optical gain medium for optical fiber amplifiers. The corresponding devices have the advantages of low noise and high gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a radial cross-sectional structural diagram of an optical fiber embodiment of the present invention.

[0023] Figure 2 Schematic diagram of the refractive index cross section of the optical fiber core layer according to an embodiment of the present invention.

[0024] Figure 3 FIG. 4 is an attenuation spectrum of an optical fiber in one embodiment of the present invention.

[0025] Figure 4 FIG. 4 is a gain diagram of an optical fiber according to an embodiment of the present invention.

[0026] Figure 5 This is a radial cross-sectional structural diagram of another optical fiber embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to the embodiments of the present invention and the accompanying drawings.

[0028] Example 1: Figure 1 、 Figure 2 As shown, it includes a core layer 1 and a cladding layer, wherein the cladding layer includes an inner cladding layer 2 and an outer cladding layer 3, and the refractive index profile of the core layer is distributed in an α power exponential function, wherein the core layer distribution index α is 2.6, the radius a is 1.87 μm, and the maximum relative refractive index difference Δ 1max The core material is a germanium-doped silica glass layer. The inner cladding is an air hole lattice inner cladding, and the air hole lattice inner cladding is a regular hexagonal air hole lattice inner cladding. The number of regular hexagonal layers is 7. The core layer is located at the center of the air hole lattice. The spacing between adjacent air holes in the air hole lattice inner cladding is Λ, 3.3μm, and the duty cycle D / Λ is 0.8. The air hole lattice inner cladding is composed of a pure silica glass base layer and an air hole lattice. Outside the inner cladding is the outer cladding, and the outer cladding is a pure silica glass outer cladding with a diameter of 110μm. This optical fiber can obtain more than 20W in the 1550nm band. -1 km -1 The nonlinear coefficient, and its attenuation value is less than 3dB / km, the attenuation spectrum is as follows Figure 3 The gain effect of this highly nonlinear photonic crystal fiber is shown in Figure 4 As shown in the figure, at an input power of -10dB, the maximum C-band gain can reach 18.1dB and the noise is less than 5.3dB.

[0029] Example 2: The core radius a is 1.5 μm, the core distribution index α is 2.5, and the maximum relative refractive index difference Δ 1max The inner cladding adopts 6 layers of regular hexagonal air hole lattice, the air hole spacing is Λ 2.6μm, the duty cycle is 0.83, and the outer cladding diameter of the optical fiber is 125μm. The optical fiber can be greater than 20W in the 1550nm band. -1 km -1 The nonlinear coefficient is 0 dB, and its attenuation is less than 3 dB / km. At an input power of 0 dB, the maximum C-band gain of the optical fiber can reach 18.8 dB, and the noise is less than 5.9 dB. Other aspects are the same as in Example 1.

[0030] Example 3: The core radius a is 1.25 μm, the core distribution index α is 3.1, and the maximum relative refractive index difference Δ 1max The inner cladding adopts 7 layers of regular hexagonal air hole lattice, the air hole spacing is Λ 4μm, the duty cycle is 0.75, and the outer cladding diameter of the optical fiber is 118μm. The optical fiber can obtain more than 18.7W in the 1550nm band. -1 km -1The nonlinear coefficient is 0.001, and its attenuation is less than 3 dB / km. At an input power of -10 dB, the maximum C-band gain of the optical fiber can reach 15 dB, and the noise is less than 6 dB. Other aspects are the same as in Example 1.

[0031] Example 4: The core radius a is 1.24 μm, the core distribution index α is 3.0, and the maximum relative refractive index difference Δ 1max The optical fiber has a power density of 2.95%, an inner cladding with 6 layers of regular hexagonal air hole lattice, an air hole spacing of 4.6 μm, a duty cycle of 0.88, and an outer cladding diameter of 120 μm. The optical fiber can obtain more than 18.5W in the 1550nm band. -1 km -1 The nonlinear coefficient is 0 dB / km, and its attenuation is less than 3 dB / km. At an input power of 0 dB, the maximum C-band gain of the optical fiber can reach 17.2 dB, and the noise is less than 5.8 dB. Other aspects are the same as in Example 1.

[0032] Example 5: The core radius a is 1.4 μm, the core distribution index α is 2.2, and the maximum relative refractive index difference Δ 1max The optical fiber has a power density of 3.02%, an inner cladding with 6 layers of regular octagonal air hole lattice, an air hole spacing of Λ of 3.6μm, a duty cycle of 0.85, and an outer cladding diameter of 115μm. The optical fiber can obtain more than 19.5W in the 1550nm band. -1 km -1 The nonlinear coefficient is 0dB / km, and its attenuation value is less than 3dB / km. At an input power of 0dB, the maximum C-band gain of the optical fiber can reach 18dB, and the noise is less than 6dB. Figure 5 .

[0033] Example 6: Provided is an optical fiber amplifier, which adopts a backward pumping method, and the optical gain medium of the optical fiber amplifier adopts the above-mentioned graded-index high nonlinear photonic crystal fiber (for example, the graded-index high nonlinear photonic crystal fiber described in Examples 1 to 5 can be used).

Claims

1. A highly nonlinear photonic crystal fiber comprising a core layer and a cladding layer, wherein the cladding layer comprises an inner cladding layer and an outer cladding layer, characterized in that The core layer refractive index profile is distributed in an α power exponential function, the core layer distribution index α is 2.0 to 8.0, the radius a is 0.8 to 2 μm, and the maximum relative refractive index difference Δ 1max The inner cladding is an air hole lattice inner cladding, the outer cladding is an outer cladding, and the outer cladding is a pure silica glass outer cladding.

2. The highly nonlinear photonic crystal fiber according to claim 1, characterized in that The core layer distribution index α is 2.3 to 5.

0.

3. The highly nonlinear photonic crystal fiber according to claim 1 or 2, characterized in that The core layer is a silicon dioxide glass layer doped with germanium or bismuth or co-doped with germanium and bismuth.

4. The highly nonlinear photonic crystal fiber according to claim 1 or 2, characterized in that The inner cladding of the air hole lattice is a regular polygonal cladding with six sides or an even number of sides or more, and the core layer is located at the center of the air hole lattice.

5. The highly nonlinear photonic crystal fiber according to claim 1 or 2, characterized in that The aperture of each air hole in the air hole lattice is the same, and the spacing between adjacent air holes is the same, presenting a periodic close-packed arrangement.

6. The highly nonlinear photonic crystal fiber according to claim 5, characterized in that The distance Λ between adjacent air holes in the air hole lattice inner cladding is 2 to 12 μm, and the duty ratio D / Λ is 0.2 to 0.

9.

7. The highly nonlinear photonic crystal fiber according to claim 5, characterized in that The number of regular polygonal layers in the inner cladding of the air hole lattice is 2 to 10.

8. The highly nonlinear photonic crystal fiber according to claim 1 or 2, characterized in that The air hole lattice inner cladding is composed of a pure silicon dioxide glass substrate layer and an air hole lattice.

9. The highly nonlinear photonic crystal fiber according to claim 1 or 2, characterized in that The outer cladding has a diameter of 100 to 300 μm.

10. The highly nonlinear photonic crystal fiber according to claim 1 or 2, characterized in that The refractive index distribution formula of the α power exponential function is: Where n1 is the refractive index of the fiber axis; r is the distance from the fiber axis; a is the fiber core radius; α is the distribution index; Δ is the relative refractive index difference between the core center and the outer cladding.

11. The highly nonlinear photonic crystal fiber according to claim 1 or 2, characterized in that The optical fiber has a power of 18W or more in the 1550nm band. -1 km -1 The nonlinear coefficient of .

12. An optical fiber amplifier, characterized in that The highly nonlinear photonic crystal fiber according to any one of claims 1 to 11 is applied to a backward-pumped optical fiber amplifier as a gain medium of the optical fiber amplifier.

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