CN111562649A - A vortex light dispersion compensation fiber - Google Patents

Abstract

The invention relates to a vortex optical dispersion compensating optical fiber, which is applied to the technical fields of optical fiber communication and optical signal processing. The existence of dispersion greatly limits the appearance and application range of nonlinear effects. The present invention provides an optical fiber technical solution that can be used to realize dispersion compensation. Confined to propagate in the annular region, the refractive index contrast and thus the dispersion properties of the fiber can be changed by changing the materials of the annular region and the cladding, and the above-mentioned cross-sectional structure does not change along the length of the fiber. The beneficial effects of the invention are as follows: the optical fiber has a large negative dispersion in a certain wavelength range, and the adjustment of the size of the negative dispersion and the wavelength range can be realized by properly adjusting the ring position, the ring width and the fiber material. The maximum negative dispersion can be increased by appropriately increasing the core-cladding refractive index contrast, inter-ring distance and ring width.

Description

A vortex light dispersion compensation fiber

technical field

The invention relates to a vortex optical ring fiber, in particular to a ring fiber with dispersion compensation characteristics. It is used in technical fields such as optical fiber communication and optical signal processing.

Background technique

Vortex light has a unique field distribution. There is a phase singularity at the center, and the light intensity at the singularity is zero. The light wave phase is spirally distributed in the direction perpendicular to the propagation direction, and has orbital angular momentum. Vortex light is divided into polarized vortex light and phase vortex light. Polarized vortex light consists of radial vector beam TM ₀₁ and angular vector beam TE ₀₁ two modes, phase vortex light is also called orbital angular momentum (OAM) vortex light, OAM mode It can be expressed as OAM _l,m , where l (l=±1,±2,±3...) is the topological charge and m is the radial order corresponding to the intensity distribution of the modes in the radial direction. For OAM modes propagating in a fiber, the vector eigenmodes can be composed by the following relationship:

和

两种模式线性组合而成

涡旋光可作为一种不同于相位、偏振的传输光信息的载体，这意味着涡旋光为信息传输提供了新的维度以及拓展了新的信道。For example, when the topological charge number is 1, the OAM vortex light is given by

and

Linear combination of the two modes

Vortex light can be used as a carrier for transmitting optical information different from phase and polarization, which means that vortex light provides a new dimension for information transmission and expands new channels.

When light is transmitted in an optical fiber, the chromatic dispersion of the optical fiber is a major obstacle that limits its transmission quality. The longer the transmission distance, the greater the dispersion effect, which will lead to intersymbol crosstalk, which will increase the bit error rate and reduce the information transmission efficiency. and distance. In order to minimize the dispersion loss and improve the performance of the fiber, it is necessary to use a dispersion compensation fiber with negative dispersion, and improve the performance of the fiber by periodically balancing the positive dispersion of the fiber. Fibers used for dispersion compensation include Bragg fiber and photonic crystal fiber. In 2003, TD Engeness et al. in "Dispersion tailoring and compensation by modalinteractions in OmniGuide fibers", Optics express, 11, 1175-1196 (2003) proposed a Bragg fiber that introduces defect layers into periodic multilayers, which utilizes TE ₀₁ The mode produces a large negative dispersion, but according to its principle, the actual transmission loss may not be very low. In 2015, J.Hsu et al. proposed a wavelength-tunable dispersion of a hybrid structure in "Wavelength-tunabledispersion compensating photonic crystal fibers suitable for conventional/coarse wavelength division multiplexing systems", Journal of LightwaveTechnology, 33, 2240-2245 (2015). The compensation photonic crystal fiber has a large negative dispersion coefficient, but the manufacturing process of the photonic crystal fiber is complicated and the cost is high.

SUMMARY OF THE INVENTION

In view of the above situation, the present invention provides a vortex light dispersion compensation fiber with large negative dispersion, aiming to transmit vortex light and simplify the structure of the fiber with large negative dispersion characteristics.

The technical scheme adopted in the present invention is specifically:

The vortex light dispersion compensating fiber with large negative dispersion includes a fiber core and an optical fiber cladding sheathed outside the fiber core. an annular region and an outer fiber cladding, the first annular region, the inter-ring cladding and the second annular region are sequentially arranged between the core and the outer fiber cladding from inside to outside ; wherein: the core, the first layer of annular region, the inter-ring cladding, the second layer of annular region, the outer fiber cladding refractive index n ₁ , n ₂ , n ₃ , n ₄ , n ₅ satisfies the value of n ₁ , n ₃ , n ₅ is smaller than the value of n ₂ , n ₄ Under the condition that the above-mentioned refractive index distribution is satisfied, it can be a combination of materials such as germanium-doped silica, Schott glass, As ₂ S ₃ and the like.

In this structure, the ring width of the annular region of the first layer is larger than the annular width of the annular region of the second layer in the cross-section of the optical fiber. On the basis that the refractive index of the annular region is higher than that of the cladding region, the mode is confined to the two annular regions. Under certain refractive index contrast and structural parameters, the effective refractive index of the vortex light in the first annular region varies with wavelength. The decrease is faster than that of the effective refractive index in the annular region of the second layer, the refractive indices of the same mode in the two rings are close to each other at a certain wavelength, and strong mode coupling occurs near this wavelength, forming a composite mode that is a symmetric mode and an opposing mode. Symmetric modes, symmetric modes have negative dispersion and anti-symmetric modes have positive dispersion. The vortex light dispersion compensating fiber with large negative dispersion according to the present invention adopts a symmetrical mode with large negative dispersion.

The beneficial effects of the present invention are as follows: by selecting the materials of the annular region and the core cladding layer, and appropriately adjusting the width of the annular region or the positions of the two annular regions, the size of the maximum negative dispersion of different modes and the wavelength range can be adjusted. Numerical calculation results show that by appropriately increasing the distance between the two annular regions (r ₃ -r ₁ ), the negative dispersion can be increased, and the wavelength range with large negative dispersion can be tightened. Appropriate adjustment of the width of the annular region of the first layer can change the wavelength of the maximum negative dispersion.

Description of drawings

Figure 1 is a schematic structural diagram of the cross-section of the optical fiber of the present invention.

2 shows the dispersion of TE ₀₁ , TM ₀₁ and HE ₂₁ modes as a function of wavelength when r ₁ =1 μm, r ₂ =2 μm, r ₃ =12 μm, and r ₄ =12.6 μm in the fiber structure of the present invention.

3 is the variation of the dispersion of the TE ₀₁ mode with wavelength, r ₂ and r ₄ when r ₁ =1 μm and r ₃ =10 μm in the fiber structure of the present invention.

Fig. 4 is the variation of the dispersion of the TE ₀₁ mode with wavelength, r ₃ and r ₄ values when r ₁ =1 μm and r ₂ =2 μm in the fiber structure of the present invention.

FIG. 5 shows the variation of the dispersion of HE ₂₁ , HE ₃₁ , HE ₄₁ and HE ₆₁ with wavelength in the optical fiber structure of the present invention.

In the figure: 1. Fiber core; 2. First layer annular area; 3. Inter-ring cladding; 4. Second layer annular area; 5. Outer fiber cladding;

r ₁ . The core radius; r ₂ . The radius of the annular region of the first layer; r ₃ . The radius of the inter-annular cladding; r ₄ . The radius of the annular region of the second layer.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings:

Example 1:

The vortex light dispersion compensating fiber with large negative dispersion of the present invention is shown in FIG. 1 , including a core 1 from the inside to the outside, a first annular region 2, an inter-annular cladding 3, a second annular region 4, an outer The optical fiber cladding 5 has refractive indices n ₁ , n ₂ , n ₃ , n ₄ , and n ₅ respectively, and the first-layer annular region 2 and the second-layer annular region 4 are concentric high-refractive-index rings with a refractive index greater than In other regions, the refractive index distribution satisfies n ₁ =n ₃ =n ₅ , n ₂ =n ₄ , and n ₁ <n ₂ , and the optical fiber material may be germanium-doped silica or Schott glass when the above-mentioned refractive index distribution is satisfied , As ₂ S ₃ and other materials, the higher-order OAM mode can also have a large negative dispersion through adjustment. In this embodiment, the material of the annular region is silica material with a molar concentration of germanium-doped 40 mol%, the material of the core cladding is silica, and the above-mentioned cross-sectional structure does not change along the length direction of the optical fiber.

When r ₁ =1 μm, r ₂ =2 μm, r ₃ =12 μm, and r ₄ =12.6 μm, the variation of dispersion of TE ₀₁ , TM ₀₁ and HE ₂₁ modes with wavelength is shown in FIG. 2 . It can be seen from the figure that the vortex light of different modes transmitted in the optical fiber of the present invention can achieve large negative dispersion.

Fig. 3 is a graph showing the variation of dispersion with wavelength of the TE ₀₁ mode corresponding to different r ₂ and r ₄ values when r ₁ =1 μm and r ₃ =10 μm. As can be seen from the figure, the wavelength range where the negative dispersion is located can be selected by adjusting r ₂ and r ₄ , that is, the width of the annular region.

FIG. 4 is a graph showing the variation of the dispersion with wavelength of the TE ₀₁ mode corresponding to different r ₃ and r ₄ values when r ₁ =1 μm and r ₂ =2 μm. As can be seen from the figure, by adjusting r ₃ and r ₄ , that is, the distance between the two annular regions, the size of the maximum negative dispersion of the fiber and the bandwidth with negative dispersion can be changed under the condition that the wavelength is basically unchanged.

Example 2:

The structure of the vortex optical dispersion compensation fiber in this embodiment is shown in FIG. 1 , including an inner-to-outer fiber core 1 , a first-layer annular region 2 , an inter-annular cladding 3 , a second-layer annular region 4 , and an outer fiber cladding layer. 5. The refractive indices are respectively n ₁ , n ₂ , n ₃ , n ₄ , and n ₅ , the first-layer annular region 2 and the second-layer annular region 4 are concentric high-refractive-index rings, and the refractive index distribution satisfies n ₁ =n ₃ =n ₅ , n ₂ =n ₄ , n ₁ <n ₂ . In this embodiment, the material used is Schott glass, the material of the annular region is SF57 glass, the refractive index of this material is 1.80 at a wavelength of 1550 nm, the core cladding material is SF2 glass, and the refractive index of this material is 1.62 at a wavelength of 1550 nm , the above-mentioned cross-sectional structure does not change along the length of the fiber.

Fig. 5 shows the variation of dispersion of HE ₂₁ , HE ₃₁ , HE ₄₁ and HE ₆₁ with wavelength. The parameters of each mode in the figure are, HE ₂₁ : r ₁ =1μm, r ₂ =1.7μm, r ₃ =5μm, r ₄ = 5.6 μm; HE ₃₁ : r ₁ =1 μm, r ₂ =1.95 μm, r ₃ =5 μm, r ₄ =5.6 μm; HE ₄₁ : r ₁ =1 μm, r ₂ =1.95 μm, r ₃ =5 μm, r ₄ =5.4 μm; HE ₆₁ : r ₁ =1 μm, r ₂ =3 μm, r ₃ =5 μm, r ₄ =5.6 μm. It can be seen from the figure that the higher-order mode vortex light transmitted in the optical fiber of the present invention can achieve a larger negative dispersion.

Further, the fiber core 1 with a circular cross-section can also be designed as an elliptical fiber core, or the fiber core can be filled with air, and the vortex light dispersion compensation can be realized by design.

There are many options and combinations of optical fiber materials capable of realizing dispersion compensation in the present invention, so any further expansion including the present invention also belongs to the protection scope of the present invention.

The embodiments of the present invention have been described above in detail with reference to the accompanying drawings, and the accompanying drawings here are used to provide a further understanding of the present invention. However, the scope of protection of the present invention is not limited to the disclosed embodiments, and is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and there are more variations with larger negative dispersion in the fibers of the present invention. Higher-order vortex light modes. Therefore, any changes that belong to the technical concept of the present invention and are merely obvious changes to the technical solution shall belong to the protection scope of the present invention.

Claims (9)

1. A vortex light dispersion compensating fiber, characterized in that: the fiber core has two concentric annular regions, and the refractive index of the fiber is higher than that of the cladding. 2 . The vortex light dispersion compensation fiber according to claim 1 , wherein the fiber comprises a fiber core and a fiber cladding sheathed outside the fiber core, and the fiber cladding comprises a first-layer annular region, an annular The inter-cladding layer, the second-layer annular region and the outer fiber cladding layer; the first-layer annular region, the inter-ring cladding layer, and the second-layer annular region are sequentially arranged on the fiber core and the outer fiber cladding from the inside to the outside between layers; the refractive indices n ₁ , n ₂ , n ₃ , n ₄ , and n ₅ of the core, the first annular region, the inter-annular cladding, the second annular region, and the outer fiber cladding satisfy : The values of n ₁ , n ₃ , and n ₅ are smaller than the values of n ₂ and n ₄ . 3 . The vortex light dispersion compensation fiber according to claim 2 , wherein the ring width of the annular region of the first layer on the cross-section of the optical fiber is larger than that of the annular region of the second layer. 4 . 4. The vortex optical dispersion compensating fiber according to claim 1, 2 or 3, characterized in that: by appropriately increasing the distance r ₃ -r ₁ between the two annular regions, the negative dispersion can be increased, and there is a large negative dispersion by tightening The wavelength range of ; where r ₃ is the width of the cladding between the rings, and r ₁ is the width of the core. 5 . The vortex light dispersion compensation fiber according to claim 4 , wherein the fiber material is germanium-doped silica or Schott glass or As ₂ S ₃ . 6 . 6 . The vortex optical dispersion compensation fiber according to claim 5 , wherein the material of the first annular region and the second annular region is germanium-doped silica, and the core cladding material is silica. 7 . 7 . The vortex light dispersion compensation fiber according to claim 5 , wherein the material of the first annular region and the second annular region is SF57 glass, and the material has a refractive index of 1.80 at a wavelength of 1550 nm; The layer material is SF2 glass, which has a refractive index of 1.62 at a wavelength of 1550 nm. 8. The vortex light dispersion compensation fiber according to claim 1 or 2, wherein the fiber core is an elliptical core. 9 . The vortex light dispersion compensation fiber according to claim 8 , wherein the core is filled with air. 10 .

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