CN206020713U - Double-clad photon crystal optical fibre - Google Patents

Abstract

The utility model discloses a double-clad photonic crystal fiber, which includes a core, an inner cladding and an outer cladding, wherein the fiber body material is fused silica with a refractive index of n ₁ =1.44, the fiber core is composed of a missing air hole, and the inner cladding It is composed of small air holes in the first layer and the second layer, and the outer cladding layer is composed of air holes in the third layer and the fourth layer. After adopting the above scheme, the utility model PCF is composed of double cladding mainly because the double cladding structure not only It reduces the difficulty of coupling, and has unique dispersion characteristics, which is easy to adjust. When d ₁ =0.5μm, the designed fiber can have the lowest loss at λ=1.55μm, reaching 7.39× ^10-6 dB/km, making The PCF can not only be used as dispersion compensating optical fiber, but also realize low-loss transmission.

Description

Double-clad photonic crystal fiber

technical field

The utility model relates to a photonic crystal fiber, in particular to a double-clad photonic crystal fiber.

Background technique

Photonic crystal fiber (PCF), also known as microstructure or holey fiber, is composed of tiny air holes periodically arranged around the core and its surroundings. By changing the size and filling rate of the air holes, the relative refractive index of the cladding and the fiber core can be flexibly adjusted, so as to achieve the confinement effect on light and realize the transmission of light. According to the light guiding mechanism, photonic crystal fiber can be divided into total internal reflection photonic crystal fiber (Total Internal Reflection PCF, TIR-PCF for short) and photonic band gap photonic crystal fiber (Photonic Band Gap PCF, PBG-PCF for short). ). The reason why photonic crystal fibers are widely used in many fields is mainly due to their unique characteristics: no cut-off single mode, controllable mode area, controllable dispersion characteristics in a wide wavelength range, and high nonlinear characteristics as a transmission medium Wait. Although PCF is widely used in various fields based on some unique advantages, its high loss restricts the further development of some applications.

Utility model content

The purpose of the utility model is to provide a dispersion compensation optical fiber with low loss in the band of λ=1.30-1.80 μm.

In order to achieve the above object, the utility model double-clad photonic crystal fiber includes a core, an inner cladding and an outer cladding, wherein the fiber body material is fused silica with a refractive index n ₁ =1.44, and the core is formed by a missing air hole The inner cladding is composed of small air holes in the first and second layers, the outer cladding is composed of air holes in the third and fourth layers, and the angle difference between the outer cladding and the inner cladding is 30°, and the diameter of the air holes in the inner cladding is d ₁ is 0.5-0.7 μm, the diameter d ₂ of the outer cladding air holes is 1.4-1.6 μm, the pitch Λ of the _first and second layers of air holes is 1.3-1.5 μm, the pitch of the second and third layers of air holes Λ ₂ is 1.7-1.8 μm, and the pitch Λ ₃ of the third and fourth layers of air holes is 1.9-2.1 μm.

The diameter d1 of the air hole in the inner cladding layer is 0.5, the diameter _{d2 of} the air hole in the outer cladding layer is 1.5 μm, the pitch Λ1 of the _first and second layers of air holes is 1.5 μm, and the diameter of the second and third layers of air holes is 1.5 μm. The pitch Λ ₂ is 1.75 μm, and the pitch Λ ₃ of the air holes in the third and fourth layers is 2 μm.

The cladding air holes are arranged in a hexagonal shape.

After adopting the above scheme, the utility model PCF is composed of double cladding mainly because the double cladding structure not only reduces the difficulty of coupling, but also has unique dispersion characteristics, which is easy to adjust. When d ₁ =0.5μm, the designed The optical fiber has the lowest loss at λ=1.55μm, reaching 7.39×10 ^-6 dB/km, so that the PCF can not only be used as dispersion compensation optical fiber, but also realize low-loss transmission.

Description of drawings

Fig. 1 is a schematic cross-sectional view of the structure of the utility model.

detailed description

In order to describe the technical content, structural features, achieved goals and effects of the present utility model in detail, the following will be described in detail in conjunction with the embodiments and accompanying drawings.

Please refer to Fig. 1, the double-clad photonic crystal fiber of the present invention comprises fiber core, inner cladding and outer cladding, and wherein, the material of optical fiber body is the fused silica of refractive index n ₁ =1.44, and fiber core is made of a missing air hole The cladding is composed of four layers of hexagonal air holes, the inner cladding is composed of the first and second layers of small air holes, the outer cladding is composed of the third and fourth layers of air holes, and the outer cladding and the inner cladding The layer angles differ by 30°, the diameter d ₁ of the air holes in the inner cladding is 0.5-0.7 μm, the diameter d ₂ of the air holes in the outer cladding is 1.4-1.6 μm, and the pitch Λ ₁ of the air holes in the first and second layers is 1.3-1.5 μm, the pitch Λ ₂ of the second and third layers of air holes is 1.7-1.8 μm, and the pitch Λ ₃ of the third and fourth layers of air holes is 1.9-2.1 μm.

Using the full vector finite element method (Finite Element Method, FEM), set the parameters of the photonic crystal fiber, calculate the effective refractive index n _eff of the fundamental mode of the photonic crystal fiber, and analyze it in the broadband range of 1.30～1.80μm Dispersion and loss characteristics within.

The total dispersion of photonic crystal fiber is

Where λ is the propagation wavelength, c is the speed of light in vacuum, n _eff (λ) is the effective refractive index of the fundamental mode, and D _m (λ) is the material dispersion.

An important parameter of optical fiber is the power loss when the optical signal is transmitted in the optical fiber. If P ₀ is the power of the incident fiber, the transmission power

p _T =p ₀ exp(-αL)

In the formula, α is the attenuation coefficient, usually called fiber loss, and L is the length of the fiber.

The loss of photonic crystal fiber follows the definition of traditional silica fiber loss, that is, the attenuation of optical power when the optical signal is transmitted along the optical fiber. The attenuation of different wavelengths is different, and the continuous loss measurement of different wavelengths is called loss spectrum measurement. In practice the loss can usually be expressed using the attenuation coefficient:

The new type of double-cladding photonic crystal fiber (DC-PCF) designed, because the mode light field is mainly distributed near the core, the layer of air holes closest to the core plays an important role in the transmission characteristics of the fiber. effect. The influence of inner cladding air hole diameter d ₁ , outer cladding air hole diameter d ₂ and air hole pitch (Λ ₁ , Λ ₂ , Λ ₃ ) on dispersion and loss is mainly analyzed below.

In this paper, a novel double-clad PCF structure is proposed based on the hexagonal air hole arrangement. Since the PCF dispersion characteristics of this structure are mainly determined by the inner core and the surrounding air hole structure, similar dispersion characteristics can be achieved when the inner cladding structure is the same as that of conventional PCF. The structure of the outer cladding will affect the limit loss, so the loss is reduced by optimizing the structure of the outer cladding. At the same time, it can be seen from the total internal reflection theorem that the periodic structure of the cladding has little effect on the light guiding of the high refractive index core, and it is difficult for a PCF with a regular structure to obtain flat dispersion in a wide band, so this paper uses the diameter of the air hole in the innermost cladding Zoom out to tune the dispersion properties of the fiber.

By reasonably setting the diameter and air hole pitch of the air holes in the inner and outer cladding layers of the PCF, the diameter d ₁ of the air holes in the inner cladding layer is 0.5 μm, the diameter d ₂ of the air holes in the outer cladding layer is 1.5 μm, and the air holes in the first and second layers When the pitch Λ ₁ is 1.5 μm, the pitch Λ ₂ of the second and third layers of air holes is 1.75 μm, and the pitch Λ ₃ of the third and fourth layers of air holes is 2 μm, this PCF can not only realize broadband dispersion compensation but also It has the characteristic of low loss. Numerical results show that the PCF achieves a broadband dispersion compensation effect in the 1.30-1.80μm band, and makes the designed optical fiber limit loss up to 7.39×10 ^-6 dB/km when λ=1.55μm. Therefore, this design provides a reference for the material selection and application of devices based on broadband dispersion compensation photonic crystal fiber, and the low loss characteristics of this design can increase the transmission efficiency of photonic crystal fiber, and provide a certain theory for its practical application in accordance with.

The above is only an embodiment of the present utility model, and does not limit the patent scope of the present utility model. Any equivalent shape or structural transformation made by using the description of the utility model and the contents of the accompanying drawings, or directly or indirectly used in other related Technical fields are all included in the scope of patent protection of the utility model in the same way.

Claims (3)

1. Double-clad photonic crystal fiber, comprising a core, an inner cladding and an outer cladding, characterized in that: the material of the fiber body is fused silica with a refractive index n ₁ =1.44, the core is made of a missing air hole, and the cladding It is four layers of hexagonal air holes, the inner cladding is composed of the first and second layers of small air holes, the outer cladding is composed of the third and fourth layers of air holes, and the angle difference between the outer cladding and the inner cladding is 30° °, the diameter d ₁ of the air holes in the inner cladding is 0.5-0.7 μm, the diameter d ₂ of the air holes in the outer cladding is 1.4-1.6 μm, the pitch Λ ₁ of the air holes in the first and second layers is 1.3-1.5 μm, the second 1. The pitch Λ2 of the third layer of air holes is 1.7-1.8 μm, and the pitch _Λ3 of the _third and fourth layers of air holes is 1.9-2.1 μm. 2. double-clad photonic crystal fiber as claimed in claim 1, is characterized in that: the diameter d ₁ of described inner cladding air hole is 0.5, and the diameter d ₂ of outer cladding air hole is 1.5 μm, first, second The pitch Λ ₁ of the air holes in the first layer is 1.5 μm, the pitch Λ ₂ of the second and third layers of air holes is 1.75 μm, and the pitch Λ ₃ of the third and fourth layers of air holes is 2 μm. 3. The double-clad photonic crystal fiber according to claim 1, characterized in that: the air holes in the cladding are arranged in a hexagonal shape.