CN1588141A - Photon crystal optical fiber - Google Patents

Abstract

The invention relates to a photonic crystal fiber. It contains a core and a cladding, which is characterized in that the core is the central solid area of the fiber background material; the cladding is an area surrounded by uniform air holes around the core, and the air holes are periodically arranged in the fiber background material. That is, every adjacent three air holes form an equilateral triangle; several rings of air holes in the cladding close to the core are arranged in a regular hexagonal shape in the fiber background material to form an inner cladding, and the rest are farther away from the core. The annular area surrounded by the periodic arrangement of distant air holes in the optical fiber background material constitutes the outer cladding; the air holes in the inner cladding are smaller than the air holes in the outer cladding. The optical fiber provided by the invention can realize relatively flat dispersion characteristics in a wide wavelength range. This optical fiber is suitable for making various optical devices and used as transmission optical fiber.

Description

Photonic crystal fiber

Technical field:

The invention relates to a photon crystal fiber, in particular to a photon crystal fiber with flat dispersion in a wide wavelength range.

technical background:

In the past ten years, photonic crystal fiber has attracted the attention of scientists all over the world because of its many excellent properties. Photonic crystal fiber, also known as holey fiber or microstructure fiber, is characterized by the fact that the refractive index of the cladding is periodically modulated by the wavelength order. This modulation is generally achieved by introducing axially elongated air holes into silica glass. The fiber core consists of a defect that breaks the periodicity of the refractive index modulation. Relative to the effective refractive index of the cladding, if the core is made of a low refractive index material (such as air), this fiber guides light through the band gap principle, which requires strict arrangement of the air holes in the cladding. Another type of photonic crystal fiber has a higher core refractive index, so light transmission can be achieved through total internal reflection. This type of fiber does not require very precise periodic arrangement of air holes in the cladding, so it is easier to manufacture.

Photonic crystal fibers have many excellent characteristics different from traditional fibers, such as: single-mode transmission (endless single-mode) can be achieved at any wavelength, and the dispersion and mode field area of the fiber can be flexibly controlled by changing the size of the air hole and the hole spacing. Implement very weak or strong nonlinear effects. In addition, high birefringence properties can be achieved through the asymmetry of the air hole arrangement. However, changing the size of the air hole and hole spacing can only make the dispersion-wavelength curve flatter in a narrow wavelength range.

These excellent characteristics of photonic crystal fiber make it play a great role in the field of optical communication. High dispersion photonic crystal fiber can be used for dispersion compensation, and strong nonlinear or strong birefringent photonic crystal fiber can be used to make various optical devices, especially It is the improvement of the production technology that has gradually reduced the loss of the fiber, making it possible to use it as a transmission fiber. Therefore, in order to meet the requirements of the WDM system, it is very necessary to develop a photonic crystal fiber with flat dispersion in a wide wavelength range.

Invention content:

The object of the present invention is to provide a photonic crystal fiber capable of flattening dispersion in a wide wavelength range.

To achieve the above object, the present invention adopts the following technical solutions:

A photonic crystal fiber, comprising a core and a cladding, is characterized in that the core is the central solid region of the optical fiber background material; the cladding is the area surrounding the periphery of the core with air holes uniformly distributed, and the air holes appear in the fiber background material Periodically arranged, that is, every adjacent three air holes form an equilateral triangle; several rings of air holes in the cladding close to the fiber core are arranged in a regular hexagonal band in the fiber background material to form the inner cladding, and the rest The annular area surrounded by the periodic arrangement of the air holes farther from the fiber core in the fiber background material constitutes the outer cladding; the air holes in the inner cladding are smaller than the air holes in the outer cladding.

The air holes in the inner cladding layer are arranged in 1-4 turns.

The above-mentioned ratio (d _{1 /} d 2 ) of the inner cladding air hole diameter (d ₁ ) to the outer cladding air hole diameter (d ₂ ) is 0.1-0.9.

The above-mentioned ratio (d _{1 /} d 2 ) of the inner cladding air hole diameter (d ₁ ) to the outer cladding air hole diameter (d ₂ ) is 0.2-0.5.

The above optical fiber background material is silica glass material or polymer material.

Compared with the current technology, the present invention has obvious substantive features and advantages: the inner cladding air holes in the present invention are smaller than the outer cladding air holes, and can realize flat dispersion in a wide wavelength range. The optical fiber provided by the invention is suitable for making various optical devices and used as transmission optical fiber.

Description of drawings:

FIG. 1 is a schematic structural diagram of the central part of the cross-sectional view of an embodiment of the present invention, that is, the calculation window area.

FIG. 2 is a mode field distribution diagram of the example in FIG. 1 .

FIG. 3 is a graph of the dispersion curve of the example in FIG. 1 .

Detailed ways:

A preferred implementation example of the present invention is: referring to Fig. 1, Fig. 2 and Fig. 3, there is an air hole missing (silicon dioxide solid) in the fiber core to form a light guide area, and its periphery is surrounded by six smaller air holes 1 The background silica glass 3 forms an inner cladding, and the periodic arrangement of other larger air holes 2 in the background silica glass 3 forms an outer cladding. A periodic arrangement recognized in the technical field is adopted, that is, as shown in FIG. 1 , every three adjacent air holes 1 or 2 form an equilateral triangle, and the distribution of the mode field is shown in FIG. 2 . The air hole diameter d ₂ in the outer cladding is 1.035 microns, and the air hole spacing Λ is 2.3 microns. When the air hole diameter d ₁ of the inner cladding is the same as that of the outer cladding, that is, 1.035 microns, in the wavelength range of 1.0 microns to 2.0 microns, the optical fiber The dispersion changes in the range of 40 to -30, about 70 ps/nm/km. When the inner cladding air hole diameter d ₁ gradually decreases, the high end of the dispersion curve will decrease and the low end will rise. When the inner cladding air hole diameter d ₁ When narrowed down to 0.3 microns, within a bandwidth of 1000 nanometers, the dispersion curve is a horizontal line that is almost maintained at 10 ps/nm/km, truly achieving flat dispersion in a wide wavelength range. But when d ₁ continues to shrink to 0.2 microns, the dispersion curve shows an upward trend in the wavelength range of 1.0-2.0 microns. It can be seen that reducing the size of the air holes in the inner cladding layer to an optimum value (in this example, the optimum d ₁ is 0.3 μm) can achieve broadband dispersion flatness.

Claims (5)

1. a photonic crystal fiber comprises fibre core and covering, it is characterized in that fibre core is the center solid area of optical fiber background material; Covering is the zone of the peripheral uniform airport (1,2) of encirclement fibre core, and airport (1,2) is periodic arrangement in optical fiber background material (3), and promptly every adjacent three airports (1,2) constitute an equilateral triangle; Arrange the belt-like zone that surrounds near the regular hexagon of some circle airports (1) in optical fiber background material (3) of fibre core in the covering and constitute inner cladding, all the other constitute surrounding layer apart from the annular region that the periodic arrangement of fibre core airport far away (2) in optical fiber background material (3) surrounds; Airport in the inner cladding (1) is less than the airport (2) of surrounding layer.

2. photonic crystal fiber according to claim 1, the number of turns that it is characterized in that airport (1) arrangement of inner cladding is the 1-4 circle.

3. photonic crystal fiber according to claim 1 and 2 is characterized in that inner cladding airport (1) diameter (d ₁) and surrounding layer airport (2) diameter (d ₂) ratio (d ₁/ d ₂) be 0.1-0.9.

4. photonic crystal fiber according to claim 3 is characterized in that inner cladding airport (1) diameter (d ₁) and surrounding layer airport (2) diameter (d ₂) ratio (d ₁/ d ₂) be 0.2-0.5.

5. photonic crystal fiber according to claim 1 is characterized in that optical fiber background material (3) is silex glass material or polymeric material.

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