CN107728403B - A Wavelength Converter from 1.55μm to 2μm - Google Patents

Abstract

A wavelength converter of 1.55 μm band to 2 μm band, comprising a first wavelength division multiplexer having an input port for inputting pulse light of 1.55 μm band inputted to the wavelength converter, a tellurate photonic crystal fiber for realizing group velocity matching, a second wavelength division multiplexer having an output port for outputting pulse light of 1.55 μm band, and a coupler having an input port for inputting continuous light of 2 μm band, an output port for outputting pulse light of 1.55 μm band as an output of the wavelength converter, the tellurate photonic crystal fiber being connected between the first input output port and the third input output port, the second input output port being connected to a fifth input output port, the fourth input output port being connected to a sixth input output port. In the cross phase modulation, the group velocity matching and the high nonlinearity of the wavelength converter overcome the walk-off effect between two wavelengths, and ensure the high efficiency of the cross phase modulation.

Description

A Wavelength Converter from 1.55μm to 2μm

technical field

The invention relates to the field of optical fibers, more specifically, to a wavelength converter from 1.55 μm to 2 μm.

Background technique

With the development of communication technology and people's strong demand for information interaction, all-optical communication network technology has undoubtedly become the main force of global communication. The rapid development of optical communication network has made its capacity increase exponentially in the past few decades, and there have been many breakthroughs in technology, including low-loss single-mode transmission fiber, erbium-doped fiber amplifier, wavelength division multiplexing, etc. For long-distance and high-capacity transmission, most work has been carried out in the C-band communication window (1530nm ~ 1565nm), where the optical fiber transmission loss is the smallest, and low noise amplification can be obtained, and advanced modulation format signaling allows efficient increase in this limited bandwidth. capacity. However, the bandwidth-distance product of capacity transfer is ultimately limited by fiber nonlinearity. Today's telecommunications networks are rapidly pushing to their capacity limits due to exponential growth in internet traffic, raising concerns about a potential future "capacity crunch". Therefore, the existing 1.55μm band (1530-1565nm) optical fiber communication system has approached the limit of transmission capacity, and one of the effective means to solve this problem is to open up a new optical transmission band. With the rapid development of related technologies in the 2μm band and the huge gain bandwidth (1.8μm-2.1μm) provided by thulium-doped fiber amplifiers (TDFA), the 2μm band has great potential to become the next optical fiber transmission window. 2um band (1.8μm～2.3μm) light has a high absorption peak for molecules such as carbon dioxide and water, so it belongs to the human eye-safe band and has a wide range of applications in various fields, such as eye-safe lidar, laser scalpel, material Processing and shaping, fiber optic sensors, etc.

Tellurite glass has the advantages of high refractive index, high nonlinear refractive index coefficient, high rare earth doping concentration, high expansion coefficient, low phonon energy, low melting point, good stability, corrosion resistance and unique magneto-optical properties. Used in lasers, nonlinear devices, etc.

In the wavelength division multiplexing system of the all-optical network, the wavelength conversion technology is one of the key technologies, and it is also one of the effective means to solve the capacity limitation of the optical transmission band. The wavelength conversion is to transfer the information carried by one wavelength to another wavelength. to transfer. The wavelength conversion technology based on cross-phase modulation can also be used for intensity modulation to generate mode-locking. Existing technologies use dispersion-shifted fiber to achieve wavelength conversion based on cross-phase modulation. However, the existing dispersion-flattened fiber mainly achieves near-zero dispersion flatness in the 1.55 μm band, and values are taken at intervals in the 1.55 μm band, so it can be used The number of wavelengths is very limited; in cross-phase modulation, due to the walk-off effect, the existing technology cannot extend the 1.55 μm band to the 2 μm band by using dispersion-shifted fibers.

Contents of the invention

The technical problem to be solved by the present invention is to solve the technical problem of the controllable wavelength of cross-band group velocity matching between 1.55 μm and 2 μm bands in the prior art and insufficient cross-phase modulation and walking in large-span wavelength conversion based on cross-phase modulation. In order to solve the technical defect of interference from the off-center effect, a wavelength converter from the 1.55 μm band to the 2 μm band is provided.

In order to solve the technical problem, the present invention provides a wavelength converter from 1.55 μm to 2 μm, including a first wavelength division multiplexer, a tellurate photonic crystal fiber for group velocity matching, a second wavelength division A multiplexer and a coupler; the first wavelength division multiplexer has a first input and output port, a second input and output port, and an input port for accessing pulsed light in the 1.55 μm band input to the wavelength converter, the first The two-wavelength division multiplexer has a third input and output port, a fourth input and output port, and an output port for outputting pulsed light in the 1.55 μm band. Band pulsed light is used as the output port, the fifth input-output port and the sixth input-output port of the wavelength converter, and the tellurate photonic crystal fiber is connected between the first input-output port and the third input-output port. The second input and output terminal is connected to the fifth input and output terminal, and the fourth input and output terminal is connected to the sixth input and output terminal.

In the wavelength converter of the present invention, the structure and connection relationship of each part of the wavelength converter is also limited by the flow direction of the following signals:

The signal flow direction of the pump light pulse in the 1.55 μm band is: the first wavelength division multiplexer, tellurate photonic crystal fiber, the second wavelength division multiplexer, and then flows out;

The flow of light in the 2μm band entering the coupler is divided into two paths, one path is: coupler, first wavelength division multiplexer, tellurate photonic crystal fiber, second wavelength division multiplexer, and then flows back to the coupling The other path is: coupler, second wavelength division multiplexer, tellurate photonic crystal fiber, first wavelength division multiplexer, and then flow back to the coupler.

In the wavelength converter of the present invention, the tellurate photonic crystal fiber has a core and a cladding both made of a base material 60TeO2-20PbO-20PbCl2, and the base material has a A plurality of air holes arranged parallel to the axis of the photonic crystal fiber; on any cross-section of the tellurate photonic crystal fiber: the plurality of air holes are distributed in multiple layers along the axis of the tellurate photonic crystal fiber, each The air holes in the layer are arranged in a regular hexagon, the distance between the centers of any two adjacent air holes is P=4μm±0.25μm, and the diameter d1 of each air hole in the innermost layer ranges from 3.0 to 3.7μm , the diameter difference of any air hole in the innermost layer is within 0.5 μm, and the diameter d of the remaining air holes is 3 μm±0.5 μm, or the distance P between the centers of any two adjacent air holes is in the range of 3.80～ 4.15μm, the distance between the centers of any two adjacent air holes is within 0.725μm, the diameter d1 of the innermost air hole is 3.3μm±1.45μm, and the diameter d of the remaining air holes is 3μm±1.45 μm; the base material surrounded by the circle formed between the cores of the innermost air holes forms the core, and other base materials and all air holes form the cladding.

In the wavelength converter of the present invention, in each regular hexagon, there is an air hole at the intersection between any two adjacent sides.

In the wavelength converter of the present invention, the distance between the centers of any two adjacent air holes is P=4 μm, the diameter d1 of each air hole in the innermost layer is equal, and the range of d1 is 3.0 to 3.7 μm, and the rest The diameter d of the air hole is 3 μm, or the distance between the centers of any two adjacent air holes is equal, P is 3.80-4.15 μm, the diameter d1 of the innermost air hole is 3.3 μm, and the diameter of the remaining air holes The diameter d is 3 μm.

In the wavelength converter of the present invention, the diameter of the innermost air hole and the distance between the centers of any two adjacent air holes are further determined by the diameter of the innermost air hole and any two adjacent air holes The ratio K of the distance between the hole centers is limited, and the range of K is 72% to 92%.

In the wavelength converter of the present invention, for any one of the tellurate photonic crystal fibers, the core diameter is within 2P _min ~ 2P _max , where P _min and P _max respectively represent the tellurate photonic crystal The minimum and maximum distances between the centers of two adjacent air holes in an optical fiber.

In the wavelength converter of the present invention, the light in the 2 μm wavelength band is specifically light with a wavelength of 2.025 μm.

In the wavelength converter of the present invention, the first wavelength division multiplexer, the tellurate photonic crystal fiber, the second wavelength division multiplexer and the coupler are connected to form a ring, and the length of the optical fiber contained in the ring conforms to the following formula :

π＝2Pγ ₁₂ L

In the formula, P is the input signal power, L is the fiber length, and _γ12 is the nonlinear coefficient related to cross-phase modulation.

In the wavelength converter of the present invention, the coupler is a 3dB coupler.

The implementation of the present invention has the following beneficial effects: in the cross-phase modulation of the wavelength converter of the present invention, group velocity matching and high nonlinearity overcome the walk-off effect between two wavelengths, ensuring the high efficiency of cross-phase modulation; and The structure of the tellurite photonic crystal fiber used is simple. Except for the innermost air hole, the diameter of the air holes in each layer is the same, the arrangement is simple, the drawing is relatively simple, and the outer air can be adjusted appropriately according to the manufacturing process and fusion process. The diameter and spacing of the holes have almost no influence on the characteristics of the optical fiber, and the group velocity matching of any wavelength in the 1.55 μm and 2 μm bands can be realized by adjusting the structure of the photonic crystal fiber of the present invention.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

Figure 1 is a graph showing the variation of the refractive index of 60TeO ₂ -20PbO-20PbCl ₂ tellurate glass with wavelength;

Fig. 2 is a two-dimensional sectional view of the basic structure of a tellurate photonic crystal fiber in a wavelength converter of the present invention;

Fig. 3 (a) is in the structure of Fig. 2, P=4 μ m, d=3 μ m, d1=3.3 μ m and the fundamental mode field diagram of 1.55 μ m when the effective refractive index is 2.0832;

Figure 3(b) is the fundamental mode field of 2.025 μm when P=4 μm, d=3 μm, d1=3.3 μm and effective refractive index is 2.069 in the structure of Figure 2;

Fig. 4 is under the condition of P = 4 μm d = 3 μm, the group velocity of tellurate photonic crystal fibers with different diameters d1 of air holes in the first layer varies with wavelength and the schematic diagram of the group velocity matching process;

Fig. 5 is under the condition of P = 4 μm d = 3 μm, the effective refractive index of tellurate photonic crystal fiber with different diameter d1 of the air hole in the first layer varies with wavelength;

Fig. 6 is a graph showing the group velocity of a tellurate photonic crystal fiber with wavelength varying with P=4 μm d=3 μm d1=3.3 μm;

Fig. 7 is a graph showing the variation of dispersion with wavelength of a tellurate photonic crystal fiber with P=4 μm d=3 μm d1=3.3 μm;

Fig. 8 is a graph showing the change of the wavelength matching the group velocity of 1.55 μm with the diameter d1 of the air holes in the first layer under the condition of P=4 μm d=3 μm;

Fig. 9 is a graph showing the change of the wavelength matching the group velocity of 1.55 μm with the hole spacing P under the condition of d=3 μm d1=3.3 μm;

Fig. 10 is a wavelength conversion model diagram based on cross-phase modulation in a wavelength converter based on group velocity matching photonic crystal fiber;

Fig. 11(a) is a 1.55 μm input pulse waveform diagram at the input end during wavelength conversion, and Fig. 11(b) is a 2.025 μm output pulse waveform diagram at the output end during wavelength conversion.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation manners of the present invention will now be described in detail with reference to the accompanying drawings.

The base material used in a tellurate photonic crystal fiber designed by the present invention is 60TeO ₂ -20PbO-20PbCl ₂ (TLX), and its refractive index is calculated by using three Sellmeier equations:

n ² (λ)＝1+B ₁ λ ² /(λ ² -C ₁ )+B ₂ λ ² /(λ ² -C ₂ )+B ₃ λ ² /(λ ² -C ₃ )

Where λ is the wavelength in μm, B _i (i=1,2,3) and C _i (i=1,2,3) are coefficients, and the six coefficients corresponding to TLX glass are: B ₁ =1.212, B ₂ =2.157, B ₃ =0.1891, C ₁ =6.068×10 ^-2 , C ₂ =7.068×10 ^-4 , C ₃ =45.19. The refractive index of TLX is very high, and its refractive index versus wavelength curve is shown in Figure 1. The tellurate material 60TeO ₂ -20PbO-20PbCl ₂ (TLX) used in the present invention has a nonlinear refractive index as high as 5×10 ^-19 m ² /W, about 20 times that of silica glass, and due to the The structure is variable, and the dispersion, nonlinear coefficient, group velocity, etc. of the photonic crystal fiber can be adjusted by adjusting the structural parameters of the photonic crystal fiber, so as to achieve a fiber structure that meets the requirements.

A cross-sectional view of a tellurate photonic crystal fiber designed in the present invention is shown in FIG. 2 . The fiber structure is composed of a core structure and a cladding structure. The photonic crystal fiber consists of a base material and air holes arranged on the base material throughout the length of the fiber. There are six layers of air holes arranged in a regular hexagon. Each air hole is arranged parallel to the axis of the tellurate photonic crystal fiber. The hole spacing P (the distance between the center of the air holes) between adjacent air holes is equal, the diameter of the first layer of air holes is d ₁ , the diameter of the remaining air holes is d, the cladding diameter D = 57 μm, the substrate The material is 60TeO ₂ -20PbO-20PbCl ₂ (TLX). The core structure is the base material TLX surrounded by the first layer of air holes in the base material, that is, the base material surrounded by the circle formed between the innermost air holes forms a core, the core diameter is 2P, and the core The axis of the tellurate photonic crystal fiber is the axis of the tellurate photonic crystal fiber, and other substrate materials and all air holes form the cladding.

可知，对于某种材料，不同ω对应不同n(ω)，所以c/n(ω)不同，即光在波导中传输速度不同。不同传播速度的光在传输时会出现走离，导致脉冲展宽，这对光通信的限制非常大。We start from the original Sellmeier equation

It can be seen that for a certain material, different ω corresponds to different n(ω), so c/n(ω) is different, that is, the transmission speed of light in the waveguide is different. Light with different propagation speeds will have walk-off during transmission, resulting in pulse broadening, which is very restrictive to optical communication.

Mathematically, the dispersion effect of a fiber can be expanded as the Taylor series of the mode transmission constant β at the center frequency _ω0 :

所以可得：in,

So you can get:

In the formula, n _g is the group refractive index, which is _defined according to the ratio of the refractive index to the speed of light _{in two media; v g is} the group velocity, which obviously corresponds to the group refractive index , which describes the propagation velocity of the optical pulse envelope; β ₂ is the group velocity dispersion; β ₃ is the third-order dispersion parameter (TOD).

Dispersion describes the phenomenon of pulse broadening due to the walk-off effect when a beam of light has different wavelengths, different refractive indices, different modes, and different transmission speeds in the waveguide when it reaches the receiving end. In fiber optics, we usually use the dispersion parameter D to replace the group velocity dispersion β ₂ :

In the formula, n _eff replaces n in the original formula, indicating the effective refractive index.

The dispersion controllability of the photonic crystal fiber comes from the change of the refractive index distribution of the fiber section, and the structural change of the photonic crystal fiber changes the refractive index distribution of the fiber section. The tellurate photonic crystal fiber designed in the present invention is a refractive index guided photonic crystal fiber, and light tends to propagate in a high refractive index region. The tellurite material has a large refractive index. The introduction of air holes in the cladding reduces the refractive index of the cladding, confines light to the core region, and the greater the core-cladding refractive index difference, the more light Concentrated in the core area, the effective refractive index of the mode is greater, so for a fiber structure, the effective refractive index of the fundamental mode is the largest, for the structure of P=4 μm d=3 μm d ₁ =3.3 μm in the present invention at 1.55 μm and 2.025 μm The fundamental mode at the wavelength is shown in Fig. 3(a) and Fig. 3(b). By adjusting the structural parameters of the photonic crystal fiber, the refractive index distribution of the photonic crystal fiber section is changed. By increasing P, the distance between the air hole and the fiber core is increased, so that the core refractive index increases, and the core-cladding refractive index As the difference increases, for the same wavelength, the mode field is more concentrated in the center of the fiber core, and the effective refractive index increases; by increasing the diameter of the air hole, the distance between the air hole and the fiber core is reduced, so that the core refractive index decreases, and the fiber The core-cladding refractive index difference decreases. For the same wavelength, the mode field is dispersed in the center of the fiber core, and the effective refractive index decreases. As shown in Figure 5, the effective refractive index decreases with the increase of d1. The dispersion and group velocity of optical fiber are closely related to the change of effective refractive index. For the tellurate photonic crystal fiber designed in the present invention, the diameter and hole spacing of the first layer of air holes have the greatest influence on the distribution of the core refractive index, and the influence of the remaining structural parameters is negligible. In order to make the first layer The adjustment range of the air hole diameter is more free. In the present invention, the hole spacing of all the air holes in the six layers is set to a uniform P, so here we only study the relationship between the first layer of air hole diameter d ₁ and the distance P of all air holes. Influence of dispersion, group velocity, effective refractive index and nonlinear coefficient of photonic crystal fiber.

Group Velocity Matching Process

By constantly adjusting the structural parameters, looking for the changing law and changing range of the wavelength matching the 1.55μm group velocity, so as to determine the ratio of the air hole diameter to the hole spacing under the condition that all the air holes have the same diameter and the hole spacing (that is, the ratio of When the void ratio) is 75% to 87%, the wavelength matched with the 1.55μm group velocity is in the 2μm band. Among them, when the distance between all air holes is 4 μm and the diameter of all air holes is 3.3 μm, the group velocity matching between 1.55 μm and 2 μm bands is ideal. Since the diameters of air holes in the second to sixth layers have little effect on the group velocities of group 5, they can be ignored, so only the influence of the diameters of air holes in the first layer is studied here. As shown in Figure 4, determine the spacing of all air holes P=4μm, the diameter of the air holes in the 2nd to 6th layers is d=3μm, change the size of the diameter of the first layer of air holes, the group velocity change and matching wavelength shift corresponding to each structural parameter The situation is obvious. In the band range in Fig. 4, for a certain wavelength, the group velocity decreases with the increase of the diameter of the air hole in the first layer; for a certain structure, the group velocity first increases and then decreases with the wavelength, and the curve is a kind of concave-convex shape. For group velocity matching fiber, in order to achieve group velocity matching, its group velocity vs. wavelength variation curve should be between two matching wavelengths, which is also a judgment method when screening the group velocity matching fiber structure.

Select P=4 μm d=3 μm d1=3.3 μm tellurate photonic crystal fiber designed by the present invention, can obtain its group velocity with wavelength change curve, as shown in Fig. 6, find out and 1.55 μm group velocity matching The wavelength is 2.025μm, and the group velocity is 140.989m·μs ^-1 ; the variation curve of dispersion with wavelength is shown in Figure 7, from which it can be seen that there is a point of zero dispersion between 1.55μm and 2.025μm, and a point of normal dispersion at 1.55μm 2.025μm is in the anomalous dispersion zone, the dispersion difference between the two wavelengths is 78.73ps·nm ^-1 ·km ^-1 , the calculated nonlinear coefficient at 1.55μm is 192.71W ^-1 km ^-1 , and at 2.025μm The nonlinear coefficient is 143.58W ^-1 km ^-1 , it can be seen that the nonlinear coefficient is very large, which has a great effect on its full cross-phase modulation. The reason why the zero dispersion point appears between the group velocity matching wavelengths is that the group velocity must match, and the curve of the group velocity versus wavelength is concave-convex, and the slope of the curve of group velocity versus wavelength between two wavelengths must be zero. , and the group velocity is the reciprocal of β ₁ , β ₂ is the first derivative of β ₁ with respect to ω, and the dispersion parameter D is the first derivative of β ₁ with respect to λ, then there are points where D is 0.

For the structure parameter P=4μm d=3μm d1=3.3μm around the group velocity matching photonic crystal fiber structure, the spacing P of all air holes and the diameter d ₁ of the first layer of air holes were studied respectively, and the group velocity of 1.55μm matching wavelength effects. For different univariate structural parameters, there are two situations: one is, P=4μm, d=3μm, adjust d ₁ , and the matching wavelength varies with the diameter of the air holes in the first layer, as shown in Figure 8. After fitting, we get The formula λ _GVM ＝-0.021d ₁ ² -0.173d ₁ +2.824, λ _GVM ∈(1.9,2.1); the second is, d=3μm, d ₁ =3.3μm, adjust P, the matching wavelength varies with the spacing of all air holes The curve is shown in Figure 9, after fitting, the formula λ _GVM =-0.134P ² +1.643P-2.411, λ _GVM ∈(1.9, 2.1) is obtained. Therefore, a tellurate photonic crystal fiber designed in the present invention can realize group velocity matching between a wavelength of 1.55 μm and any wavelength in the 2 μm band. When P=4 μm and d=3 μm, the adjustment range of d ₁ is 3.0 to 3.7 About; when d=3μm, d ₁ =3.3μm, the adjustment range of P is about 3.8-4.15μm. The diameter of the air holes in layers 2 to 6 can be adjusted appropriately according to the actual process.

Wavelength conversion process based on tellurate photonic crystal fiber in nonlinear loop mirror:

As shown in Figure 10, the wavelength converter from the 1.55 μm band to the 2 μm band in this embodiment includes a first wavelength division multiplexer 101, a tellurate photonic crystal fiber 102 for realizing group velocity matching, a second wavelength division multiplexer With device 103 and coupler 104; The first wavelength division multiplexer 101 has a first input and output terminal (the connection terminal of the upper part of the first wavelength division multiplexer 101 in the figure), a second input and output terminal (the first wavelength division multiplexer 101 in the figure) The connection end of the lower right part of a wavelength division multiplexer 101) and the input port (lower left of the first wavelength division multiplexer 101 in the figure Part of the connection end), the second wavelength division multiplexer 103 has a third input and output port (the connection end of the upper part of the second wavelength division multiplexer 103 in the figure), a fourth input and output port (the second wave in the figure The connection end of the lower left part of the division multiplexer 103) and the output port (the connection end of the lower right part of the first wavelength division multiplexer 103 in the figure) for outputting the 1.55 μm band pulsed light, the coupler 104 has for Access the input port of the continuous light in the 2 μm band (the connection end of the lower left part of the coupler 104 in the figure), the output port for outputting the pulsed light in the 1.55 μm band as the output of the wavelength converter (the lower right part of the coupler 104 in the figure) output port), the fifth input and output port (the output port of the upper left part of the coupler 104 in the figure), and the sixth input and output port (the output port of the upper right part of the coupler 104 in the figure), the tellurate photonic crystal fiber connection Between the first input and output port of the first wavelength division multiplexer and the third input and output port of the second wavelength division multiplexer, the second input and output port of the first wavelength division multiplexer is connected to the fifth The input and output terminals, the fourth input and output ports of the second wavelength division multiplexer are connected to the sixth input and output terminals of the coupler. The coupler 104 is connected with the first wavelength division multiplexer 101 and the second wavelength division multiplexer 103 by optical fiber, and the first wavelength division multiplexer 101 and the second wavelength division multiplexer 103 are also connected by optical fiber connection (the tellurate photonic crystal fiber 102 can be used directly), the first wavelength division multiplexer 101 , the tellurate photonic crystal fiber 102 , the second wavelength division multiplexer 103 and the coupler 104 are connected in a ring. The structure and connection relationship of each part of the wavelength converter is also limited by the flow direction of the following signals: the signal flow direction of the pump light pulse in the 1.55 μm band is: the first wavelength division multiplexer 101, the tellurate photonic crystal The optical fiber 102, the second wavelength division multiplexer 103, and then flow out; the light flow direction of the 2 μm band entering the coupler is divided into two paths, and one path is sequentially: coupler 104, the first wavelength division multiplexer 101, telluric acid The salt photonic crystal fiber 102, the second wavelength division multiplexer 103, and then flow back to the coupler 104, and the other path is: the coupler 104, the second wavelength division multiplexer 103, the tellurate photonic crystal fiber 102, the first A wavelength division multiplexer 101, then flows back to the coupler 104.

When there is no input signal, the continuous light wave passes through the 3dB coupler 104 and is divided into two light beams with the same intensity and propagating in the counterclockwise direction. The counterclockwise transmitted light produces a phase shift of π/2, and then the phase transmission The two beams of light travel along the above-mentioned circular mirror and then return to the 3dB coupler 104, and the light transmitted counterclockwise produces a phase shift of π/2, so the phase difference between the two beams of light is π, Interferometric destructive, no signal output. When the first wavelength division multiplexer 101 inputs an intense pulsed optical signal and enters the loop mirror and propagates in the clockwise direction, cross-phase modulation occurs in the tellurate photonic crystal fiber 102 with continuous waves in two directions. Cross-phase modulation is negligible due to the severe walk-off effect of the CW in the counterclockwise direction from the input pulse. However, due to the group velocity matching of the clockwise continuous wave, the two waves will not have a walk-off effect, which ensures the high efficiency of the cross-phase modulation. When the clockwise continuous wave and the input pulse interleaved phase modulation produces a phase shift of π, at the output end, the phase difference of the continuous wave in the two directions is zero, and the output waveform is the same as the input pulse due to interference and constructive, which is The conversion of the input pulse signal on the continuous wave is realized, that is, the wavelength conversion is realized. If the phase difference is an odd multiple of π, there will be interference and cancellation, and there will be no output waveform.

For the tellurite photonic crystal fiber with P=4μm, d=3μm, and d ₁ =3.3μm in the present invention, the group velocity matching between 1550nm and 2025nm is realized, so we let 1550nm be used as the input optical pulse signal, and 2025nm is used as the continuous wave . In the simulation, under the condition that the loss is 0, the input signal power is P=10W, and the continuous light wave power is 0.01W. In order to realize the phase shift of π generated by the cross-phase modulation, the total length L of the fiber in the ring (including the tellurite photonic crystal fiber 102) must meet the following formula:

π＝2Pγ ₁₂ L

是有效模场面积。非线性系数计算式中与γ₁₂相关的的n₂和A_eff是与交叉相位调制有关的，计算如下：In the formula, P is the input signal power, L is the fiber length, γ ₁₂ is the nonlinear coefficient related to the cross-phase modulation, the calculation formula of the nonlinear coefficient is: γ=2πn ₂ /(λA _eff ), where n ₂ is the nonlinear Refractive index, dependent on the material, usually constant,

is the effective mode field area. The n ₂ and A _eff related to γ ₁₂ in the nonlinear coefficient calculation formula are related to the cross-phase modulation, and the calculation is as follows:

In the formula, F ₁ and F ₂ are the electric field distributions at 1550nm and 2025nm, respectively, and n ₂₁ and n ₂₂ are the nonlinear coefficients at 1550nm and 2025nm, respectively. As for n ₂₁ and n ₂₂ are related to materials, the TLX-based PCF in this paper has only two materials, one is TLX with a nonlinear refractive index of 5×10 ^-19 m ² /W, and the other is air hole air, the nonlinear coefficient is 0. The calculated γ=166.32W ^-1 km ^-1 , so L=0.9445m. So at this time, the simulation results are shown in Figures 11(a) and 11(b). Obviously, the pulse waveform 11(b) of the output light is the same as the input pulse signal 11(a). Since the loss is 0, the output light The pulse power is unchanged, and the conversion of the 1550nm pulse to the 2025nm wavelength is realized.

The example of wavelength conversion in this example is intended to illustrate that the tellurite photonic crystal fiber designed by the present invention has high nonlinearity, and because the group velocity matching ensures the high efficiency of cross-phase modulation, the efficiency of wavelength conversion is improved, and because the matching The most important is the group velocity of 1.55μm, a commonly used communication window, and 2μm, which has the potential to become a next-generation communication window, which provides a method for next-generation optical communication.

Embodiments of the present invention have been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementations, and the above-mentioned specific implementations are only illustrative, rather than restrictive, and those of ordinary skill in the art will Under the enlightenment of the present invention, many forms can also be made without departing from the gist of the present invention and the protection scope of the claims, and these all belong to the protection of the present invention.

Claims (8)

1. A wavelength converter of 1.55 mu m wave band to 2 mu m wave band, which is characterized by comprising a first wavelength division multiplexer, tellurate photonic crystal fiber for realizing group velocity matching, a second wavelength division multiplexer and a coupler; the first wavelength division multiplexer has a first input/output end, a second input/output end and an input port for inputting pulse light of 1.55 mu m wave band to the wavelength converter, the second wavelength division multiplexer has a third input/output port, a fourth input/output port and an output port for outputting pulse light of 1.55 mu m wave band, the coupler has an input port for inputting continuous light of 2 mu m wave band, an output port for outputting pulse light of 1.55 mu m wave band as output of the wavelength converter, a fifth input/output end and a sixth input/output end, the tellurate photonic crystal fiber is connected between the first input/output end and the third input/output port, the second input/output end is connected with the fifth input/output end, the fourth input/output port is connected with the sixth input/output end, the light of 2 mu m wave band is specifically light of 2.025 mu m wave band, and the coupler is a 3dB coupler.

2. The wavelength converter of claim 1, wherein the structure and connection of the sections of the wavelength converter is further defined by the flow direction of the following signals:

the signal flow direction of the pump light pulse with the wave band of 1.55 mu m is as follows: the first wavelength division multiplexer, tellurate photonic crystal fiber, the second wavelength division multiplexer and then flows out;

the flow direction of light of 2 μm wave band entering the coupler is divided into two paths, one path is in sequence: the coupler, the first wavelength division multiplexer, the tellurate photonic crystal fiber and the second wavelength division multiplexer are connected in sequence, and then flow back to the coupler, and the other path is as follows: the device comprises a coupler, a second wavelength division multiplexer, a tellurate photonic crystal fiber, a first wavelength division multiplexer and a back flow to the coupler.

3. The wavelength converter of claim 1, wherein the tellurate photonic crystal fiber has a core and a cladding each made of a base material of 60TeO2-20PbO-20PbCl2, the base material having a plurality of air holes disposed in parallel along the tellurate photonic crystal fiber axis; on any cross section of the tellurate photonic crystal fiber: the air holes are distributed in multiple layers along the axis of the tellurate photonic crystal fiber, the air holes of each layer are arranged into regular hexagons, the distance between the hole centers of any two adjacent air holes is P=4μm+/-0.25 μm, the diameter d1 of each air hole of the innermost layer is 3.0-3.7 μm, the diameter difference of any air hole of the innermost layer is within 0.5 μm, the diameter d of the rest of air holes is 3 μm+/-0.5 μm, or the distance P between the hole centers of any two adjacent air holes is 3.80-4.15 μm, the distance between the hole centers of any two adjacent air holes is within 0.725 μm, the diameter d1 of the air hole of the innermost layer is 3.3 μm+/-1.45 μm, and the diameter d of the rest of air holes is 3 μm+/-1.45 μm; the core is formed by the base material surrounded by circles formed between the centers of the innermost air holes, and the cladding is formed by the other base material and all air holes.

4. A wavelength converter according to claim 3, wherein in each regular hexagon there is an air hole at the intersection between any two adjacent sides.

5. A wavelength converter according to claim 3, wherein the distance between the centers of any two adjacent air holes is P = 4 μm, the diameter d1 of each air hole of the innermost layer is equal, d1 ranges from 3.0 to 3.7 μm, the diameter d of the remaining air holes is 3 μm, or the distance between the centers of any two adjacent air holes is equal, P ranges from 3.80 to 4.15 μm, the diameter d1 of each air hole of the innermost layer is 3.3 μm, and the diameter d of the remaining air holes is 3 μm.

6. A wavelength converter according to claim 3, wherein the diameter of the air holes of the innermost layer and the distance between the centers of any two adjacent air holes are further defined by the ratio K of the diameter of the air holes of the innermost layer to the distance between the centers of any two adjacent air holes, K ranging from 72% to 92%.

7. A wavelength converter according to claim 3, wherein for any one of the tellurate photonic crystal fibers, the size of the core diameter is at 2P _min ～2P _max Within, P _min P _max Respectively represent the minimum value and the maximum value of the distance between the hole centers of two adjacent air holes of the tellurate photonic crystal fiber.

8. The wavelength converter of claim 1, wherein the first wavelength division multiplexer, the tellurate photonic crystal fiber, the second wavelength division multiplexer, and the coupler are connected in a ring, and the length of the optical fiber contained in the ring conforms to the following formula:

π＝2Pγ ₁₂ L

wherein P is input signal power, L is optical fiber length, and gamma ₁₂ Is a nonlinear coefficient associated with cross-phase modulation.

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