Optical fiber with a small slope of the dispersion in the frequency domain erbium amplifier

 

(57) Abstract:

Optical fibre is used in systems with wavelength division multiplexing channels, working with alloyed erbium fiber amplifier. Fiber has chromatic dispersion, the absolute value of which is in the range of wavelengths from 1530 to 1565 nm greater than 0.8 PS/(nmkm), and the slope of the dispersion is less than 0.05 PS/(nm2km). The optical fiber has a loss not exceeding 0,20 dB/km, and relatively little sensitive to bending, the effective area of its cross section exceeds 50 μm2. The optical fiber has a Central core of transparent material with a maximum refractive index n, and deposited outside the layer forming the shell material with a refractive index of nl. Central vein has a ring of transparent material with a minimum refractive index of n3that is less than n2. The refractive indices must satisfy the following conditions: 0,50 <(n-n2)/n2< 0,70 - 0,30 <(n-n2)/n2< -0,05. Examples of the use of fibers with a small slope variance at both positive and negative dispersion. Provided the us in particular fibers, which are intended for use in systems with multiplexing (SU-systems).

Background of the invention

Optical signaling lately finds more widespread in communication technology due to the extremely wide bandwidth, which has an optical fiber. The bandwidth of optical fiber having a thickness of the hair and are made of high quality glass, provides the possibility of simultaneous transmission fiber of thousands of phone calls and hundreds of television signals transmitted through different channels. The bandwidth of the optical fiber increases in SIOUX systems that are working with several different wavelengths of the channels are combined into a single fiber. However, in SU-system arise from nonlinear interactions between channels, such as 4-photon mixing, which significantly reduce the throughput of the system. The fundamental solution to this problem is proposed in U.S. patent 5327516 (hereinafter patent ' 516), which describes the optical fiber, which reduces such nonlinear interaction by introducing a small amount of chromatic dio sent over one fiber in the SU system, increases and the optical power or the load on the fiber. When increasing the power increase is also nonlinear effects. Therefore, it is advisable that the optical fiber has created a small chromatic dispersion in each channel of the SU system.

Recently managed to significantly improve the quality of the glass (almost pure silicon dioxide SiO2), which is used for the manufacture of optical fibers. In 1970, it was considered that an acceptable loss for optical fiber is about 20 dB/km, whereas today these losses usually do not exceed 0,25 dB/km it is Known that theoretically minimal loss for optical fiber approximately 0.16 dB/km at a wavelength of approximately 1550 nanometers (nm). Successful development of optical communication was facilitated by the fact that this wavelength lies in the range of operating wave erbium doped fiber amplifiers, which for this reason were the main from practically used optical amplifiers. In such amplifiers are erbium ions, which are doped optical fiber, "pumping" energy in the first wavelength range (i.e., the wave length of 980 nm) and release it in the second wavelength range (i.e., in the wavelength range from 1530 to 1565 nm), when iniciat the opportunity to gain a wide spectrum of optical signals and, therefore, are the major components of the SU-systems. Currently, there are various ways to transmit optical signals, including the transfer method of one terabyte of information per second (Tbit = 1000 GB), based on the use of twenty-five (25) adjacent channels with independent modulation of each of the two polarized modes per channel. However, all currently known designs of optical fibers are characterized by a large difference of the chromatic dispersion in the working wavelength range of erbium amplifier, which causes problems with the creation of the SU-systems operating in the wavelength range from 1530 to 1565 nm (the range of operating wavelengths of erbium amplifier).

Recently, great efforts were taken to create the design of the optical fibers having a flat characteristic dispersion in a wide wavelength range and transmit signals with the wavelengths and 1310, and 1550 nm. However, such fibers with "straightened characteristic dispersion" is not widely used and proved to be uneconomical because of the large bending losses and tight tolerances on the accuracy of manufacture.

It is now known optical fiber with a small slope of the dispersion in the range of operating wavelengths of arbieto the 259-260, published in OFC '95 Technical Digest article titled "Dispersion-shifted single-mode fiber for high-bit-rate and multiwavelength systems. This fiber consists of an outer ring made from a material with high refractive index, and is located inside the Central wire made from a material with low refractive index. In this fiber, however, the optical loss due to the specified profile of the refractive index, are at a wavelength equal to 1550 nm, about 0,22 dB/km, which is at least ten percent (10%) than theoretically achievable value losses. In addition, if the proposed article solution and allows you to create a fiber with a negative chromatic dispersion and a low slope in the range of operating wavelengths of erbium amplifier, you can create a fiber with positive chromatic dispersion and the same small slope in the wavelength range it is not possible.

Thus, at the present time, there is still not solved the problem of creating an optical fiber, which would be suitable for operation in the wavelength range of erbium amplifier and which is characterized by: 1) optical loss at a wavelength equal to 1550 nm, less than 0 is e 0.8 PS/(nmkm) and (3) small slope of the chromatic dispersion [lesser of 0.05 PS/(nm2km)].

Summary of the invention

Problems inherent in presently known optical fibers, are solved using the proposed according to the invention the optical fiber, the absolute value of the chromatic dispersion greater than 0.8 PS/(nmkm) for all wavelengths in the range from 1530 to 1565 nm. The optical fiber has a Central core of transparent material with a maximum refractive index of n1and covering the outside with a transparent shell of material with a refractive index of n2. Central vein has a ring of transparent material, the minimum refractive index of n3which was less than a refractive index of n2. To ensure that the fiber had a low loss and a small slope of the dispersion in the wavelength range in length from 1530 to 1565 nm, the refractive index must satisfy the following conditions:

0,50 < (n1- n2)/n2<0,70 and

0,30 < (n3- n2)/n2< -0,05

In one of the following, the invention proposes an optical fiber having positive chromatic dispersion. The slope of the dispersion of this fiber is about +0,043 PS/(power of one round rings of doped fluorine material, located between germanium alloy core and an outer shell of pure silicon dioxide. The refractive index of the ring is less than the refractive index of the outer shell.

In another discussed below variant of the invention proposes an optical fiber with a negative chromatic dispersion. The slope of this fiber is also about +0,043 PS/(nm2km) across the range of wavelengths from 1530 to 1565 nm, and the formation of the profile of the refractive index is carried out with the help of two round rings, made of a material with a specific refractive index and located between the Central housing of doped germanium material and the outer shell of pure silicon dioxide. The first round of the ring is adjacent to the Central vein and are made of doped fluorine material, which has a refractive index less than that of the outer shell. The second round ring adjacent to the outer shell and is made of doped germanium material, which has a refractive index greater than that of the outer shell. The second o-ring is used to increase the effective cross-sectional area of the fiber has an average value of optical loss at a wavelength of, equal to 1550 nm, not more than 0,20 dB/km, and in comparison with other fibers virtually no bending losses. In addition, the effective cross-sectional area of the fiber exceeds 50 μm2.

Brief description of drawings

The design proposed in the invention of the optical fiber and the principle of its operation is discussed in detail in the description below, with reference to the accompanying drawings on which is shown:

in Fig. 1 - General view of the known from the prior art optical fiber with two layers of protective coating,

in Fig. 2 - graphics depending on the wavelength, the total chromatic dispersion of the fiber with straightened characteristic dispersion and its components that depend on material properties and characteristics of the waveguide,

in Fig. 3A is a cross section without coating the optical fiber with multiple layers of materials with different refractive indices,

Fig. 3B is a profile of the refractive index proposed in the invention is a fiber with positive dispersion,

Fig. 3B is a profile of the refractive index proposed in this invention is a fiber with negative dispersion,

Fig. 4 - graphics depending on the wavelength of total chromatic, depending on material properties and characteristics of the waveguide,

Fig. 5 - graphics chromatic dispersion proposed in the present invention the optical fiber with positive and negative dispersion, indicating a change of the dispersion in a more narrow range of wavelengths that lie in the wavelength range of erbium amplifier

Fig. 6 is a General view of a cable containing several groups proposed in the present invention the optical fiber, and

Fig. 7 diagram 4-channel SU-system in which to transmit information used optical fibers with positive and negative dispersion and erbium doped fiber amplifiers.

Detailed description of the invention

Prerequisites

There are various reasons or mechanisms that limit the bandwidth of the fiber. In multimode fiber, for example, such a mechanism is mode dispersion, which is manifested in the expansion or spreading of light pulses as they pass from one end of the fiber to another. This is due to the fact that through the multimode fiber are hundreds of different fashion signal with a certain wavelength. The combination of the different modes on one end of the fiber is accompanied by tender the ical or linear dispersion. It is generally considered that when the speed of the short-wave radiation exceeds the rate of long-wave radiation, the dispersion has a positive sign.

Fiber can also be used to transfer only the main fashion (LP01) signal with a certain wavelength. Such a fiber is considered to be "single-mode". Bandwidth single-mode fiber is much greater than that of multimode fiber, and the fiber can transmit optical signals with proportionally high velocities. However, single-mode fiber works as a multimode when transmitting signals, the wavelengths of which is less than a critical wavelength LP11that is determined by the radius (a) of the Central veins, refractive index (n) and the relative difference of the refractive index of the Central core and the shell. It is obvious that the reduction of () and (a) is accompanied by a gradual decrease in the number of propagating along the fiber fashion until such time as through the fiber will not be subject to only one mode, the wavelength of which is higher than the critical wavelength LP11. Therefore, the critical wavelength LP11for this fibre should be the magnitude shorter wavelengths, subject to perstering billet of glass with a certain velocity is passed through the furnace. In the furnace the glass is softened and molten end of the rod pulling the fiber through a pulling roller, located in the lower part of the extraction system. (Despite the fact that the diameter of the extruded fibers are thousands of times smaller than the diameter of the shank, the profiles of the refractive index they are the same! ). Since the surface of the glass due to possible abrasion may occur defects in elongated fiber prior to its contact with any surface it is necessary to apply the appropriate floor. Since the application of such coatings should not lead to the appearance of defects on the glass surface during the coating forming the coating material is in a liquid state. The deposited coating should harden quickly enough to the contact glass with the exit roller. To ensure that the coating is hardened within the required period of time, usually use the method of fototerapia, wherein the liquid coating is transformed into a solid under the action of electromagnetic radiation. In Fig. 1 shows an optical fiber 110 with a double coating on the basis of which you can create proposed in the present invention the optical ox is oasea of light of the Central conductor 11 and the outer sheath 14. The diameter of the fiber 10 with the shell is approximately 125 μm. The inner coating 111, known as a primary coating on the fiber 10, and the outer coating 112, known as a secondary coating on the primary coating 111. The secondary coating, which should provide the necessary strength fibers made from a material with a relatively high modulus of elasticity (equal, in particular, 109PA), whereas the primary coating, which should reduce losses due microthiol made of a material with a relatively small modulus of elasticity (equal, in particular, 106PA). The secondary coating is applied on the not yet had time to dry primary coating and after that both coatings simultaneously harden under the action of electromagnetic UV radiation.

In Fig. 2 shows the chromatic dispersion of an optical fiber, in particular straightened feature 23 total dispersion fiber obtained by summing the individual components, which depend on the fiber material and design of the waveguide. (The straightened fibers with characteristic dispersion have zero dispersion at two wavelengths, in particular, 1400 and 1700 nm). Should the Rial, used for the manufacture of optical fibers. Shown on the chart variance 21, which depends on the material of the fiber refers to fiber made of quartz glass. In contrast, the variance 22, which depends on the characteristics of the waveguide is determined by the profile of the refractive index. Unlike the variance, which depends on the material of the fiber, dispersion-dependent characteristics of the waveguide, within certain limits, can always change. Due to the specific shape of the profile of the refractive index and has managed to create an optical fiber with a straightened characteristic dispersion, in which the chromatic dispersion is reduced in a wide wavelength range from 1400 to 1700 nm. Examples of these known fibers with straightened characteristic dispersion fibers are described in U.S. patents 4372647 and 4435040.

In Fig. 3A shows a cross-section not having the cover glass 30, consisting of several layers 31-24, which differ from each other in refractive index and allow you to change the component dispersion fiber, which depends on the characteristics of the waveguide. For fiber, the cross section of which is shown in Fig. 3, is characterized by extreme changes Pokie refractive index occurs smoothly, such fibers are called fibers with smoothly changing the cross section of the refractive index. However, to simplify the description of the present invention further describes an example of an abrupt change in refractive index in the cross section of the fiber. It should be emphasized that the present invention also includes fibers with a smoothly changing the cross section of the refractive index.

The optical fiber 30 has a Central conductor 31, the nominal refractive index which is equal to n1. Central vein 31 surrounded by the first intermediate layer 32 with a nominal refractive index of n3that in turn surrounded by a second intermediate layer 33 with a nominal refractive index of n4. The second intermediate layer is surrounded by the outer shell 34 with a nominal refractive index of n2. It should be noted that the drawing shown in Fig. 3A, is made not to scale, since the diameter of the outer layer 34 of approximately 125 μm, and the diameter of the Central conductor 31 is less than 7 μm. In addition, it should be emphasized that although in Fig. 3A shows a cross-section of the fiber with four (4) separate layers of glass, in fact, to get shown in Fig. 3B profile of the refractive index IP is"ptx2">

In Fig. 3B shows the profile of the refractive index is made in accordance with the first variant of the present invention is a fiber with positive dispersion with the image of the normalized difference of the refractive index1and2which are defined as follows:

1= (n1-n2)/n2100% and2= (n3-n2)/n2100%.

The necessary qualities of fiber are low loss, small slope variance and a large effective cross-sectional area. It was found that for a fiber with positive dispersion possessed such qualities, values1and2must lie within the following limits:

0,50% <1< a 0.60% and

-0,15% <2< -0,05%

In this embodiment of the invention 1= 0,55% and2= -0,10%. In addition, we offer in this embodiment, the fiber has the following radii of different layers: a1= 3.2 mm and a2= 4.7 µm. Fiber, the profile of the refractive index of which is shown in Fig. 3B, has a Central core of silica doped with germanium doped with fluorine intermediate layer and the outer shell of pure silicon dioxide. However, m the main, what determines all the advantages of the present invention is the relative difference between the refractive indices of its individual layers. For example, the Central core can be made of pure silicon dioxide, and the intermediate layer and the outer shell is made of silicon dioxide with varying degrees of doping with fluorine.

Below is a table of technical characteristics is made in accordance with the present invention is a fiber with positive dispersion. However, it should be noted that the data presented in table do not limit the entire range of the invention fibers and are for illustration purposes only.

The attenuation at 1550 nm of 0.20 dB/km (average)

Modal fiber diameter - 8,40,6 μm (1550 nm)

The eccentricity of the Central veins - < 0.8 μm

The diameter of the outer shell - 125 1 μm

Critical wavelength - <1450 nm (when the sample length 2 m)

Variance - >+0.8 PS/(nmkm) (1530-1565 nm)

The slope of the dispersion - <+0,043 PS/(nm2km) (average)

Microship - < 0.5 dB at 1550 nm (1 bend, 32 mm); < 0.05 dB at 1550 nm (100 turns, 75 mm)

The diameter of the coating - 245 10 μm

Proof test - 100 Kropotov/square inch

In Fig. 3B shows the profile pok is th. It was found that in order for the fiber with negative dispersion possessed the necessary qualities, values1and2must lie within the following limits:

0,60 <1< 0,70,

-0,30 <2< -0,10 and

of 0.05 <3< 0.25 in.

In this embodiment of the invention1= 0,65,2= -0,25 and3= 0,10. In addition, in this embodiment of the invention the proposed fiber has the following radii of various layers: b1= 3,4 µm, b2= 5,2 ám and b3= 7,2 mm. Fiber, the profile of the refractive index of which is shown in Fig. 3B, has a Central core of silica doped with germanium doped with fluorine, the first intermediate layer, doped with germanium, the second intermediate layer and the outer shell of pure silicon dioxide. However, it should be emphasized that the Central vein, and the layers of the outer shell of fiber you can do otherwise, because the main thing that determines all the advantages of the present invention is the relative difference between the refractive indices of its individual layers. For example, the Central core can be made of pure silicon dioxide, and the intermediate layers and the outer shell is made of silicon dioxide with razli in accordance with the present invention is a fiber with negative dispersion. However, it should be noted that the data presented in table do not limit the entire range of the invention fibers and are for illustration purposes only.

The attenuation at 1550 nm of 0.20 dB/km (average)

Modal fiber diameter of 8.4 0.6 μm (1550 nm)

The eccentricity of the Central veins - < 0.8 μm

The diameter of the outer shell 125 of 1.0 μm

Critical wavelength - < 1450 nm (when the sample length 2 m)

Variance - <a low of-0.8 PS/(nmkm) (1530-1565 nm)

The slope of the dispersion - < +0,043 PS/(nm2km) (average)

Microship - < 0.5 dB at 1550 nm (1 bend, 32 mm); 0.05 dB at 1550 nm (100 turns, 75 mm)

The diameter of the coating - 245 10 μm

Proof test - 100 Kropotov/square inch

There are many different ways of manufacturing optical fibers. The rod from which the fiber is made, can be as monolithic and composite. The Central cores of the fibers are usually produced by chemical vapor deposition or by one of the methods of chemical deposition, such as an external chemical plating or axial chemical sputtering. The selection of well-known method of manufacture (for example, the method of manufacturing an external single-layer or multi-layer membrane, method of coating, the chromatic dispersion proposed in the present invention the optical fiber. This chart shows how the sum of the variance components 41 and 42 depending from the fiber material and characteristics of the waveguide, it is possible to make the characteristic of the total dispersion of the fiber had a small inclination. It is shown in Fig. 2 for fibers with straightened characteristic dispersion depend on the characteristics of the waveguide component dispersion 22 also has a negative slope, which however, this component of the dispersion so quickly increases with increasing wavelength, which is the total dispersion in this wavelength range the second time becomes zero (at a wavelength of equal to 1700 nm), the characteristic of the total variance 23 within the operating range takes the form of a substantially straightened the curve. In the fiber with a form straightened characteristics of dispersion is the main slice of the fashion signal, which is accompanied by unacceptably large bending loss.

In Fig. 5 shows the characteristic 43-1 chromatic dispersion fiber with positive dispersion, the profile of the refractive index of which is shown in Fig. 3B, and the characteristic 43-2 chromatic dispersion fiber with negative dispersion profile of the expand contents wavelength of 1550 nm; the effective cross-sectional area of the fiber exceeds 50 μm2; absolute dispersion fiber exceeds 0.8 PS/(nmkm) in the wavelength range (1530-1565 nm), employing erbium doped fiber amplifiers. It is very important that each of these fibers is the slope of the dispersion at a wavelength of 1550 nm is about 0,043 PS/(nm2km). With such characteristics (43-1 and 43-2) fiber is most suitable for transmitting signals in SIOUX systems for normal operation which is necessary to ensure low losses in the fiber and having a small dispersion in the working wavelength range of erbium amplifier. (For comparison it may be noted that conventional quartz fiber has zero dispersion at a wavelength of 1310 nm, a dispersion of about +17 PS/(nmkm) at a wavelength of 1550 nm and the slope of the dispersion about 0,095 PS/(nm2km) at a wavelength of 1550 nm).

In Fig. 6 illustrates in greater detail one possible practical embodiment of the structure proposed in the present invention the cable. Optical cable 600 has two groups of optical fibers, which are outside loosely wound thread 606 and form a distinct separate beams. Preferably one of these beams consists of written in U.S. patent 5611016. According to the present invention combining fibers with positive and negative dispersion in a separate beams is preferred, but not mandatory. Fiber bundles are located inside the tube 605, which is made of a dielectric, for example, of polyvinyl chloride or polyethylene. The tube 605 is located inside the sheath of the cable, which consists of absorbing moisture tape 603, plastic shell 601, which in this embodiment is made of polyethylene, and reinforcing elements 602-602, which in this embodiment is made of steel wire or impregnated with epoxy resin and glass fibers. The reinforcing elements are fully or partially prevent the occurrence of stress in optical fibers during installation or during normal operation of the cable 600, the reinforcement of which such items can be made in a variety of well known ways. To remove the cable all shell elements 601-603 you can use terminates in a cable cord thread 604 made of plastic stamps Kevlar. Usually the tube 605 is filled with a filler, which due to its elasticity protects the fiber from appearing in them creating a loss microengines channels (SU system). This system consists of four transmitting devices 71-74, which range from 1530 to 1565 nm modulate four wavelengths four signals with different frequency band. The modulated signals are then combined using a passive device 75 connection with the merger at the output of 4:1 and served in transmitting fiber line 30-1, 30-2, which has optical amplifier 710, preferably made in the form of erbium-doped fiber amplifier. In the form shown in Fig. 7 diagram of a fiber line 30-1 transmission is made in the form having a length of fiber with positive dispersion and line 30-2 is an optical fiber of a certain length with a negative variance. On the receiving end of the transmission line combined signals are split by the demultiplexer 85 depending on the wavelength and four separate signal with different frequency band accepted consumer devices 81-84.

The invention contemplates the possibility of entering into a discussion of specific options in a variety of changes and improvements, not beyond its capacity. Such advanced and not limiting the invention, may include fiber, in which the profile of the refractive index is connecting to the I), fiber with different width of the layers, the fiber in which to create the same basic shape of the refractive index are different alloying materials, and fiber, which is made not of glass but of appropriate polymeric materials. It should be emphasized that the manufacture of many practically implemented fibers is accompanied by a decrease of the refractive index in the center of the fiber. Such fibers is reduced in the center of the fiber refractive index also apply to the present invention, even despite the fact that the profile of the refractive index differs from the ideal shown in Fig. 3B and 3C.

1. The optical fiber (10) having chromatic dispersion, the absolute value of which is higher than 0.8 PS/(nmkm) for all wavelengths in the range from 1530 to 1565 nm, and containing a Central core of transparent material with a minimum refractive index of n1and the layer forming on the outer surface of the Central core outer shell of transparent material with a minimum refractive index of n2, characterized in that the Central vein has a ring of transparent material with a refractive index of n3and n1> n2&ASS="ptx2">

2. The optical fiber (10) under item 1, in which the slope of the dispersion is less than 0.05 PS/(nm2km) in the wavelength range from 1530 to 1565 nm.

3. The optical fiber (10) p. 2, in which the slope of the dispersion is 0,043 of 0.005 PS/(nm2km) in the wavelength range from 1530 to 1565 nm.

4. The optical fiber (10) under item 1, in which the chromatic dispersion is greater than +0.8 PS/(nmkm) in the wavelength range from 1530 to 1565 nm and whose

0,50 < (n1- n2)/n2< a 0.60 and

-0,15 < (n3- n2)/n2< -0,05.

5. The optical fiber (10) under item 1, in which the chromatic dispersion exceeds of-0.8 PS/(nmkm) in the wavelength range from 1530 to 1565 nm and whose

0,60 < (n1- n2)/n2< 0,70 and

-0,30 < (n3- n2)/n2< -0,20.

6. The optical fiber (10) under item 1, which is enclosed in a cable sheath with the outer plastic shell (601) and forms an optical cable 600.

7. System with multiplexing (SU system) (700), comprising: multiple sources (71-74) optical signals modulated by different wavelengths in the range from 1530 to 1565 nm, the device (75) for combining optical signals at the entrance to the SU-si is th between the device for combining signals and device for the separation and including the first optical fiber (30-1), having chromatic dispersion, the absolute value of which is higher than 0.8 PS/(nmkm) for all wavelengths in the range from 1530 to 1565 nm, and containing a Central core of transparent material with a maximum refractive index of n1and the layer forming on the outer surface of the Central core outer shell of transparent material with a refractive index of n2while the Central vein has a ring of transparent material with a minimum refractive index of n3and n1> n2> n3and

0,50 < (n1- n2)/n2< 0,70 and

-0,30 < (n3- n2)/n2< -0,05.

8. System (700) under item 7, which in the transmission line includes an optical amplifier (710).

9. System (700) under item 8, in which the optical amplifier (710) is an erbium doped fiber amplifier.

10. System (700) under item 7, in which the transmission line includes a second optical fiber (30-2), which is connected in series with the first optical fiber (30-1) and in the wavelength range from 1530 to 1565 nm, the slope of the chromatic dispersion is approximately equal to the slope of the dispersion of the first optical fiber and led

 

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