JP2001251004A - Light amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a problem caused by the fact that the conventional light amplifier is not effective for wavelength dispersion compensation, especially tertiary dispersion compensation, and therefore cannot contribute to the extension is distance and increase in speed of an optical communication system. SOLUTION: A tertiary dispersion compensation element is assembled in a light amplifier to allow the light amplifier to perform both amplification and wavelength dispersion compensation, which increases the possibility of the extension is distance and increase in speed of an optical communication system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier, and more particularly, to chromatic dispersion (hereinafter simply referred to as chromatic dispersion) caused by various causes in optical communication using an optical fiber for a transmission line.
The present invention relates to an optical amplifier that incorporates a chromatic dispersion compensating element (hereinafter, also simply referred to as a dispersion compensating element) that can compensate for dispersion.

[0002]

2. Description of the Related Art In optical communication using an optical fiber for a communication transmission line, there is a demand for a longer distance of the communication transmission line and a higher communication bit rate with the development of the utilization technology and the expansion of the use range. In such an environment, chromatic dispersion generated when transmitting an optical fiber becomes a serious problem, and various attempts have been made to compensate for chromatic dispersion. At present, secondary chromatic dispersion is a major problem, and various compensations have been proposed, some of which have been effective.

However, as the demand for optical communication becomes higher, it is not enough to compensate only for secondary chromatic dispersion during transmission, and compensation for tertiary chromatic dispersion is becoming an issue.

[0004] A conventional method of compensating secondary chromatic dispersion will be described below with reference to FIGS. 4 and 5.

FIG. 5 shows a single mode optical fiber (hereinafter, also referred to as SMF), a dispersion compensating fiber, and a DS.
FIG. 3 is a diagram illustrating dispersion-wavelength characteristics of F (dispersion shift fiber). In FIG. 5, reference numeral 601 denotes the dispersion of SMF.
A graph showing the wavelength characteristic, 602 is a graph showing the dispersion-wavelength characteristic of the dispersion compensating fiber, and 603 is a graph showing the dispersion-wavelength characteristic of the DSF, with the vertical axis representing the dispersion and the horizontal axis representing the wavelength.

As apparent from FIG. 5, in the SMF, the dispersion increases as the wavelength of the light input to the fiber increases from 1.3 μm to 1.8 μm, and in the dispersion compensation fiber, the wavelength of the input light is 1. Dispersion decreases as the length increases from 2 μm to 1.7 μm. In the DSF, as the wavelength of the input light increases from 1.2 μm to 1.55 μm, the dispersion decreases, and the wavelength increases from 1.55 μm to 1.55 μm.
The dispersion increases with increasing length to 8 μm. And
The DSF has a characteristic that when the wavelength of the input light is around 1.55 μm, the dispersion is almost constant with respect to a change in the wavelength.

FIG. 4 is a diagram for explaining a method of compensating for the second-order chromatic dispersion. FIG. 4A shows a wavelength-time (time) characteristic.
FIG. 3B is a diagram illustrating an example in which second-order chromatic dispersion compensation is performed using an SMF and a dispersion compensating fiber, and FIG. 3C is a diagram illustrating a transmission line including only an SMF.

In FIG. 4, reference numerals 501 and 511 denote graphs showing the characteristics of the signal light before being input to the transmission line.
Is an SMF, 530 is a transmission line constituted by the SMF 531, 502 and 512 are graphs showing characteristics of signal light output from the transmission line 530, 521 is a dispersion compensating fiber, 522 is an SMF, and 520 is a dispersion fiber. Compensating fiber 52
1 and SMF 522, respectively, and 503 and 513 are graphs showing the characteristics of the signal light output from the transmission line 520. Reference numerals 504 and 514
Is a graph showing the characteristics of the signal light when the signal light is subjected to a desirable third-order dispersion compensation described later according to the present invention, and almost coincides with the graphs 501 and 511. Graphs 501, 502, 503, and 504 are graphs with the vertical axis representing wavelength and the horizontal axis representing time (or time), respectively, and graphs 511, 512, 513, and 514.
Is a graph in which the vertical axis represents intensity and the horizontal axis represents time (or time). Reference numerals 524 and 534 are transmitters, and reference numerals 525 and 535 are receivers.

In the conventional SMF, as shown by a graph 601 in FIG. 5, the dispersion increases as the wavelength of the signal light increases from 1.3 μm. This causes a group velocity delay. In the transmission path 530 constituted by the SMF, the signal light is greatly delayed on the long wavelength side as compared with the short wavelength side during transmission.
It becomes as shown in. For example, in high-speed long-distance transmission, the changed signal light may not be able to be received as an accurate signal because it overlaps the preceding and following signal lights.

In order to solve such a problem, conventionally, dispersion is compensated (hereinafter, also referred to as correction) by using a dispersion compensating fiber as shown in FIG. The conventional dispersion compensating fiber solves the problem of SMF in which the dispersion increases as the wavelength increases from 1.3 μm. Therefore, as shown by a graph 602 in FIG. 5, the dispersion increases as the wavelength increases from 1.3 μm. Is made to decrease.
The dispersion compensating fiber is, for example, a transmission line 5 shown in FIG.
As shown at 20, the dispersion compensating fiber 5 is connected to the SMF 522.
21 can be connected and used. The transmission line 520
Then, the signal light has a longer delay on the long wavelength side than on the short wavelength side in the SMF 522, and has a longer delay on the short wavelength side than the long wavelength side in the dispersion compensating fiber 521, so that as shown in graphs 503 and 513, 502 and 51
The change can be suppressed more than the change shown in FIG.

However, in the above-mentioned conventional secondary chromatic dispersion compensating method using a dispersion compensating fiber, the chromatic dispersion of the signal light transmitted through the transmission line is represented by the state of the signal light before input to the transmission line, that is, a graph. It is not possible to compensate for dispersion up to the shape of 501, and the limit is to compensate for the shape of graph 503. As shown in the graph 503, the center of the wavelength of the signal light is not delayed as compared with the short wavelength side and the long wavelength side, and only the short wavelength side and the long wavelength side of the signal light are delayed. Ripple occurs as shown. This ripple is considered to be due to third-order wavelength dispersion. As described above, the conventional method of compensating for the second-order chromatic dispersion cannot sufficiently compensate for the chromatic dispersion and cannot receive an accurate signal overlapping with the preceding and succeeding signal lights. Was.

The DSF is designed to reduce second-order dispersion for light having a wavelength of 1.55 μm.
Third-order dispersion compensation is not possible.

The communication bit rate is set to 10 Gbps.
In order to increase the speed to s, 20 Gbps, 40 Gbps, etc., it is said that not only the conventional fiber but also the fiber itself needs to be newly developed, and there is concern that the total cost of building a communication system will be extremely high. Have been.

As shown in FIG. 6, an optical fiber having a dispersion-wavelength characteristic indicated by reference numeral 401 has been developed in order to improve dispersion in long-distance or high-speed optical communication. Attempts have been made to use a compensating fiber denoted by reference numeral 402 having characteristics opposite to those of the optical fiber denoted by reference numeral 401 to increase the speed and lengthen the communication.

However, even when the fiber shown in FIG. 6 is used, it is difficult to compensate up to the graph indicated by reference numeral 504 in FIG. 4, and only slightly improves the degree of compensation in the graph indicated by reference numeral 503.

However, in high-speed communication and long-distance communication, third-order dispersion is increasingly recognized as a major problem, and compensation of third-order dispersion is becoming an important problem. However, it has been difficult to realize a long-distance communication transmission path and high-speed communication.

In long-distance transmission, an optical amplifier is inserted every several tens of kilometers to amplify a signal and perform long-distance transmission. The amplifier used therein has a third-order dispersion as referred to in the present invention. No compensation is taken into account.

FIG. 7 shows a conventional erbium-doped fiber amplifier (hereinafter referred to as E) as a typical optical amplifier.
Reference numeral 700 denotes a conventional EDFA, reference numeral 701 denotes an input port, reference numeral 702 denotes an input-side isolator, reference numeral 703 denotes an optical fiber doped with Er (hereinafter, also referred to as EDF), and reference numeral 704 denotes an input to the EDF 703. An excitation light source such as a laser diode for exciting the signal light input from the input port 701;
DM, 706 is an output side isolator, 707 is an optical fiber (for example, SMF), and 708 is an output port.

The operation of the optical amplifier 700 will be described below with reference to FIG. Since the state of polarization inside the amplifier is well known, a further explanation is omitted.

Referring to FIG. 7, a WDM
Excitation light having a wavelength, for example, 1.48 μm, emitted toward 705 is sent from WDM 705 to EDF 703. The signal light having a wavelength of, for example, 1.55 μm
When the signal light is input to the EDF 703 from 1 through the isolator 702, the signal light is amplified in the EDF 703. E
The signal light amplified by the DF 703 is output from the output port 708 via the WDM 705 and the isolator 706.

[0021]

[Problems to be solved by the present invention] However, FIG.
Does not include the function of compensating for dispersion.

On the other hand, as described above, conventional second-order dispersion compensation cannot cope with high-speed and long-range communication, and third-order dispersion is becoming a major problem. This problem of dispersion has become so serious that it is necessary to change the optical fiber itself, which is the basis of the optical communication system, when trying to increase the communication distance and speed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide an optical amplifier having a dispersion compensation function that can be used for high-speed communication and long-distance communication, and to provide an optical amplifier in a current optical communication system. The purpose of the present invention is to greatly increase the limits of long-distance and high-speed communication, and to realize high-speed, long-distance communication such as 40 Gbps.

[0024]

In order to achieve the object of the present invention, an optical amplifier according to the present invention comprises an input section (hereinafter also referred to as an input terminal) and an output section (hereinafter also referred to as an output terminal) of the optical amplifier. ), A component capable of performing dispersion compensation (hereinafter, also referred to as a dispersion compensation element) is disposed. Further, an erbium-doped fiber amplifier (hereinafter, also referred to as EDFA) can be used as the optical amplifier.

In order to enhance the effect of the present invention, a secondary dispersion compensating element or
One or both of the secondary dispersion compensating elements are used.

As an example of a secondary dispersion compensating element which is a dispersion compensating element incorporated in the optical amplifier of the present invention, a dispersion compensating optical fiber can be mentioned. Further, as an example of a tertiary dispersion compensating element which is a dispersion compensating element incorporated in the optical amplifier of the present invention, a multi-layer dispersion compensating element such as a dielectric multi-layer film, or an air combining the multi-layer film element and an air gap. Gap type dispersion compensating elements and the like can be given.

In order to enhance the effect of the present invention, the optical amplifier of the present invention is characterized in that a gain equalizer and a saturable absorber are arranged between the input terminal and the output terminal.

In the optical amplifier of the present invention, the shape of the characteristic curve of the group velocity delay time-wavelength characteristic of the dispersion compensating element and the wavelength at the peak value of the characteristic curve (hereinafter also referred to as peak wavelength) are variable. And an adjusting means for adjusting the characteristic curve and the peak wavelength. And the adjusting means is manual, electric means such as a motor,
It can be adjusted not only by optical means such as a prism, but also from the outside of the case of the optical amplifier, and based on any electrical or optical information signal (for example, chirp information). You can also adjust automatically. Then, information of the peak wavelength and the group velocity delay time to be adjusted or adjusted by the adjusting means can be detected and displayed by a monitor.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. Each drawing used in the description schematically shows the size, shape, arrangement relationship, and the like of each component so that the present invention can be understood. For the sake of convenience of the present invention, there is a case where the magnification is partially changed for illustration, and the drawings used for describing the present invention may not necessarily be similar to the actual product or description of the embodiment. In addition, in each of the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

FIG. 2 is a diagram illustrating an optical amplifier according to the present invention. 2, reference numeral 200 denotes an optical amplifier, 201 denotes an input port, 202 denotes a gain adjuster (gain equalizer), 203 and 207 denote isolators, and 204 denotes an ED.
F, 205 is an excitation light source, 206 is a WDM, 208, 20
9 is a dispersion compensating element, 210 is a saturable absorber (hereinafter also referred to as SA), and 211 is an output port.

The signal light input from the input port 201 to the optical amplifier 200 is adjusted by the gain adjuster 202 and then transmitted from the pump light source 205 through the WDM 206 to the EDF.
Due to the effect of the excitation light input to the
Amplified at 4. The amplified signal light is supplied to the dispersion compensating element 2
08 and 209 can compensate for chromatic dispersion. Further, the SA 210 provided after the dispersion compensating elements 208 and 209 has a low light transmittance when the intensity of the input light is less than a certain intensity, and the light intensity becomes higher than a certain intensity. In this case, the light transmittance is rapidly increased.

Then, the dispersion compensating elements 208 and 209
Various dispersion compensating elements can be used depending on the purpose and application.

Hereinafter, as an example of a third-order dispersion compensating element (hereinafter also referred to as a third-order dispersion compensating element) used in the optical amplifier of the present invention, a dispersion compensating element using a dielectric multilayer film shown in FIG. 3 will be described. .

That is, the dispersion compensating element using the multilayer film used in the optical amplifier of the present invention has an optical path length for the light having the central wavelength of the incident light, where λ is the central wavelength of the incident light. ) (Hereinafter, referred to as
Simply called film thickness or film thickness) is 1/4 of λ
It has at least seven laminated films that are integral multiples of (λ / 4), and is formed such that the multilayer film has at least four light reflecting layers (hereinafter, also simply referred to as reflecting layers) for incident light. It is characterized in that an element having a multilayer film is used as a third-order chromatic dispersion compensating element.

In order to enhance the effect of the present invention, in the tertiary dispersion compensating element used in the present invention, at least seven laminated films constituting the multilayer film (hereinafter, except when it is particularly necessary to distinguish them) , The multilayer film and the laminated film may be collectively referred to as a multilayer film), and seven effective layers are formed such that a reflection layer and a light transmission layer (hereinafter, also simply referred to as a transmission layer) are alternately formed. Constitute. Then, four reflective layers and three transmissive layers are used.
Form a layer. Then, when considered as an optical path length between the layers, each interval is configured such that at least adjacent intervals are not equal, and particularly preferably, all intervals are not equal.

The tertiary dispersion compensating element used in the optical amplifier of the present invention is characterized by having three cavities having different resonance (resonance) wavelengths.

In the tertiary dispersion compensating element used in the optical amplifier of the present invention, the seven-layer multilayer film is formed by sequentially ordering the seven layers from the first side, the second layer, and the second layer from one side in the thickness direction of the multilayer film. Three layers,
When referred to as the fourth, fifth, sixth, and seventh layers, the reflecting layers are the first, third, fifth, and seventh layers, and the reflectances thereof are R1, R3, and R5, respectively. , R7, R1 ≦ R
It is characterized in that 3 ≦ R5 ≦ R7.

As an example of the third-order dispersion compensating element used in the optical amplifier of the present invention, the multilayer film has a thickness of ４ of λ.
And a layer having a higher refractive index (layer H) and a layer (layer L) having a thickness of 1/4 times λ and a lower refractive index (layer L). The film is composed of three layers (hereinafter, also referred to as LH layers or LH films) in which layers L and H are combined in this order from one side in the thickness direction of the multilayer film.
Layers formed by set lamination, layers obtained by combining layers L and L (hereinafter, also referred to as LL layers or LL films)
, A layer constituted by stacking 32 sets, one layer H and one layer LH
, A layer configured by stacking 43 sets of LL layers, a layer configured by stacking one layer H and eight sets of LH layers. , LL layer 1
A multilayer film formed by each layer of a layer constituted by laminating 8 sets, a layer constituted by laminating one layer H and a layer constituted by 15 sets of LH layers can be given.

In FIG. 3, reference numeral 300 denotes a dielectric multilayer film, and 301 denotes a BK as a substrate for forming the dielectric multilayer film.
-7 (glass), 305 is a first reflective layer with 3 LH layers
Reference numeral 304 denotes a second reflective layer, which is a second reflective layer having one layer H and an LH layer therebelow (that is, the layer H of the one layer means the substrate 301 side, hereinafter the same). Reference numeral 303 denotes a third reflection layer, which is formed by laminating one layer H and eight sets of LH layers below the third reflection layer. Reference numeral 302 denotes a fourth reflection layer. It is formed by laminating one set of H and 15 sets of LH layers below it. Reference numeral 308 denotes a first transmission layer formed by stacking 32 sets of LL layers, and 307 denotes a second transmission layer LL.
And 306 is a third transmission layer formed by laminating 18 sets of LL layers. Reference numeral 320 denotes an arrow indicating the direction of light incident on the dielectric multilayer film 300, and reference numeral 330 denotes an arrow indicating the direction of light emitted from the dielectric multilayer film 300.

Reference numeral 311 denotes a first cavity (resonator) between the first reflection layer 305 and the second reflection layer 304;
Reference numeral 312 denotes the second reflection layer 304 and the third reflection layer 3
A second cavity 313 between the third reflection layer 303 and a third cavity between the third reflection layer 303 and the fourth reflection layer 302 is provided.

The LH layer has a thickness of S
a layer L formed of a film formed by ion-assisted deposition of iO ₂ (hereinafter also referred to as an ion-assisted film);
A layer H formed of an ion-assist film of TiO _{2 having} a wavelength of one-half wavelength, and one layer of the ion-assist film (layer L) of SiO ₂ and one layer of the ion-assist film (layer H) of TiO ₂ Are referred to as one set of LH layers. For example, “3 layers of LH are laminated” means “layer L ·
Each layer is 1 in the order of layer H / layer L / layer H / layer L / layer H
It is formed by layer-by-layer ".

Similarly, the LL layer has a thickness of 1/4.
A layer formed by laminating two layers L composed of an ion-assisted film of SiO _{2 having} a wavelength is referred to as one set of LL layers.
Therefore, for example, “stacking 32 sets of LL layers” means “formed by stacking 64 layers L”.

The film thickness of each of the first, second, third and fourth reflection layers is 6/4, 11/4 and 17/4 of λ, respectively.
And the thickness of the first, second, and third transmission layers is 64/4, 86/4, and 3 times λ, respectively.
It is 6/4 times.

The reflectance of the first, second, third, and fourth reflection layers increases in the order of the first, second, third, and fourth reflection layers, and is 52.4% and 95.3, respectively. %, 99.5%, 1
00%.

Each of the above-mentioned reflectances is 3% from the above value.
% Is preferable. Further, in order to mass-produce a dispersion compensating element having excellent dispersion compensating characteristics,
The reflectance of the reflective layer is 50.0% or more and 68.0% or less, and the reflectance of the second reflective layer is 92.0% or more and 99.0%.
And the reflectance of the third reflective layer is 99.0% or more and 9 or more.
It is preferable to set the fourth reflectance to 9.8% or less and the fourth reflectance to 99.8% or more. Under conditions outside this range, it is not easy to provide good dispersion compensating elements in mass production.

The third-order dispersion compensating element using the dielectric multilayer film shown in FIG.
The group velocity delay time-wavelength characteristic when 50 nm incident light is emitted in the direction of arrow 330 shows that the group velocity delay time becomes maximum (peak value) when the wavelength is 1550 nm, and the wavelength is 15
The group velocity delay time decreased regardless of whether the wavelength was shifted from 50 nm to a shorter or longer direction, and the shape of the group velocity delay time-wavelength characteristic curve became similar to a quadratic curve convex upward. The maximum group velocity delay time of the emitted light with respect to the incident light was 7.2 ps (picoseconds), and the bandwidth of the third-order dispersion compensating element was about 2 nm.

Further, the group velocity delay time of each wavelength of the reflected light obtained by the resonance can be changed by adjusting the thickness of each layer, and the incident light incident on the dielectric multilayer film 300 can be changed. Adjustment is also possible by changing the angle.

The tertiary dispersion compensating element is mainly composed of Si (silicon), Ge (germanium), Ti
O ₂ (titanium dioxide), Ta ₂ O ₅ (tantalum pentoxide),
A layer formed of either Nb ₂ O ₅ (niobium pentoxide) and a material having a lower refractive index than the above materials (typically, SiO ₂ (silicon dioxide) which is advantageous for mass production) It is characterized by having a multilayer film composed of any one or a combination of both.

In order to enhance the effect of the present invention, the layer H is mainly composed of Si, Ge, TiO ₂ , Ta ₂ O.
₅ and Nb ₂ O ₅ , and the layer L is mainly formed of a layer made of a material having a lower refractive index than the material forming the layer H such as SiO ₂ . .

Next, the dispersion compensating element 208 of the present invention,
Another example of the 209 will be described with reference to FIG. The contents of the dispersion compensating elements 208 and 209 can be variously varied.
8 as a secondary dispersion compensating element (hereinafter also referred to as a secondary dispersion compensating element) and a dispersion compensating element 209 as a tertiary dispersion compensating element.

FIG. 1 is a diagram for explaining an example of the third-order dispersion compensating element 209 of FIG. 1, reference numeral 100 denotes a third-order dispersion compensating element, 101 denotes a multilayer film, 102 denotes a first cavity, 103 denotes a second cavity, 104 and 105.
Is a reflection layer having a reflectance of less than 100% (hereinafter, also referred to as a reflection film), and 106 is a reflection layer having a reflectance of about 100%.
3 form the reflector of the dispersion compensating element used in the present invention. Reference numeral 107 denotes a light transmission layer (hereinafter, also simply referred to as a transmission layer), 108 denotes an air layer (air gap), 109 denotes a substrate of the multilayer film 101, 110 denotes a circulator, 111 denotes a screw, and 130 denotes an inside screw for a screw 111. The grooved part, 112 is a motor, and 114 is a holder which holds the part 116 which engages the screw 111 and also holds the substrate 109. 117 and 118 are optical fibers, 115 and 116 are arrows indicating incident light, 119 and 1
Reference numeral 20 denotes an arrow indicating emitted light.

The reflectance R of each of the reflective layers 104 and 105 in FIG.
(104), R (105) and the reflectance RM of the reflector
Is such that R (104) ≦ R (105) ≦ RM.
A holding substrate 113 is attached to the reflector 106, and the substrate 113 is engaged with the right end of the screw 111 as shown in FIG. The screw 1
The motor 11 can change the relative positional relationship with the holder 114 by the motor 112. And the motor 112
By changing the positional relationship between the screw 111 and the holder 114, the reflector 106 and the holder 1 are changed.
14 and the multilayer film 101 engaged therewith, the air gap length (the distance of the air gap, ie,
The distance between the multilayer film 101 and the reflective layer 106 of the reflector)
Can be adjusted. By changing the air gap length, a third-order dispersion compensating element capable of adjusting the group velocity delay time-wavelength characteristic can be realized. Thereby, the usability of the dispersion compensating element of the present invention is further improved, and the mass production cost is further reduced.

In FIG. 1, the multilayer film 101 is a dielectric multilayer film, and is composed of a combination of layers H and L, as in the case of FIG. The substrate 109 is BK-7
The reflection layer 104 formed on the substrate 109 is formed by laminating three sets of LH layers as a first reflection layer, and the reflection layer 105 is formed of a second reflection layer. To form one layer H and a layer above (ie, the substrate 109)
And LH layers are laminated on the reflection layer 104 and the reflection layers 104 and 1.
05, three sets of LL layers are laminated.

The reflectivity of each of the first, second and reflector reflectors increases in the order of the first reflector, the second reflector and the reflector, 90.73%, 95.30%, 9
9.0%.

Each of the above-mentioned reflectances is 3% from the above value.
% Is preferable. Further, in order to mass-produce an excellent dispersion compensating element having the characteristics shown in FIG. 3, the reflectance of the first reflective layer should be 85.0% or more.
2.0% or less, and the reflectance of the second reflective layer is 92.0%.
Not less than 98.0% and the reflectance of the reflector is 98.0%.
It is preferable to make the above. For conditions outside this range,
It is not easy to provide such an element as shown in FIG. 3 in mass production.

The motor 112 is made of a piezoelectric material such as PZT (lead zirconate titanate).
By rotating 1 to change the positions of 113 and 114, the air gap length can be adjusted or selected continuously or stepwise.

The air gap length is １ ／ of λ.
It is desirable to adjust for each factor, so that the quality during mass production can be stabilized and the cost can be reduced.

The case where the above third-order dispersion compensating element is used in the optical amplifier 200 of the present invention shown in FIG. 2 will be further described.

In long-distance transmission optical communication such as a submarine cable, as described above, the generation of chirp during transmission, that is, the generation of dispersion is problematic, and it is considered difficult to increase the communication speed.

However, according to the present invention, secondary and tertiary dispersion compensating elements are used for the dispersion compensating elements 208 and 209, respectively, and are disposed at each of the amplifying points in the optical communication transmission system. Since the second and third order dispersion generated in the transmission path or due to amplification can be effectively compensated, the limit of the high speed communication of the communication system is greatly improved.

As the dispersion compensating element, an independent element can be used for each of the second and third orders.
It is also possible to use an element that performs the next and third order dispersion,
In order to increase the level of dispersion compensation,
A large number of tertiary dispersion compensating elements may be connected and used.

[0062]

As described above, by using the optical amplifier of the present invention in an optical communication system using an optical fiber as a transmission line, it is possible to effectively compensate for dispersion generated in signal light during transmission. Because the limitations caused by long-distance transmission of optical communication systems and dispersion of high-speed communication can be greatly expanded, long-distance communication and high-speed communication can be accelerated by using existing systems to speed up some devices. It can be promoted by responding, and its effect on the economic effect and the improvement of the communication ability is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a dispersion compensating element arranged in an optical amplifier according to the present invention.

FIG. 2 is a diagram illustrating an optical amplifier of the present invention.

FIG. 3 is a diagram illustrating an example of a dispersion compensating element arranged in the optical amplifier of the present invention.

FIG. 4 is a diagram for explaining a method of compensating chromatic dispersion;
(B) shows an example in which second-order dispersion compensation is performed using an SMF and a dispersion compensating fiber, and (C) shows an example in which SM is used.
FIG. 3 is a diagram illustrating a transmission path configured only with F.

FIG. 5 is a diagram illustrating dispersion-wavelength characteristics of various optical fibers.

FIG. 6 is a diagram illustrating dispersion-wavelength characteristics of an optical fiber.

FIG. 7 is a diagram illustrating a conventional optical amplifier.

[Explanation of symbols]

100: dispersion compensation element 101: multilayer film 102, 103: cavity 104, 105, 106: reflection layer 107: transmission layer 108: air layer (air gap) 109, 113: substrate 110: circulator 111: screw 112: motor 114: Holder 200: Optical amplifier 201: Input port 202: Gain adjuster 203, 207: Isolator 204: EDF 205: Pump light source 206: WDM 208, 209: Dispersion compensator 210: Saturable absorber (SA) 211: Output port 300: Dielectric multilayer film 301: substrate 302, 303, 304, 305: reflection layer 306, 307, 308: light transmission layer 311, 312, 313: cavity 320, 330: arrow 401, 402: dispersion-wavelength characteristic curve of optical fiber 501, 502, 50 3,504,511,512,5
13, 514: signal light 520: transmission line 521: dispersion compensating fiber 522: SMF 530: transmission line 531: SMF 601 to 603: dispersion-wavelength characteristic curve of optical fiber 701: input port 702, 706: isolator 703: EDF 704 : Excitation light source 705: WDM 707: optical fiber 708: output port

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/16 (72) Inventor Yuichi Takushima 2-18-18 Shiba Fuji, Kawaguchi City, Saitama Prefecture Seike Heights 202 (72) Inventor Mark Kennes Jaboronski K518, 4-6-129 Komaba, Meguro-ku, Tokyo K72 (72) Inventor Yuichi Tanaka 3-1-23-1 Niisonanami, Toda City, Saitama Prefecture (72) Inventor Haruki Kataoka 3-1-23 Niisonanami, Toda City, Saitama Prefecture Applied Optoelectronic Laboratory, Inc. Inventor Kenji Furushiro 3-1-2-3 Niisonanami, Toda-shi, Saitama F-term (Reference) 5F072 AB09 AK06 KK30 PP07 YY17 5K002 AA06 BA02 BA13 CA01 CA05 CA10 CA13 DA05 FA01

Claims (21)

[Claims] 1. An optical amplifier which can be used for optical communication using an optical fiber for a transmission line, wherein an input section (hereinafter also referred to as an input terminal) and an output section (hereinafter, referred to as an input terminal) of the optical amplifier.
An optical amplifier comprising a component (hereinafter, also referred to as a dispersion compensating element) capable of compensating for chromatic dispersion (hereinafter, also referred to simply as dispersion) between output terminals. 2. The optical amplifier according to claim 1, wherein said dispersion compensating element is a secondary dispersion compensating element capable of compensating secondary dispersion. 3. The optical amplifier according to claim 2, wherein said second-order dispersion compensating element is an optical fiber. 4. The optical amplifier according to claim 1, wherein at least a third-order dispersion compensating element is arranged between an input terminal and an output terminal of the optical amplifier. Optical amplifier. 5. The optical amplifier according to claim 1, wherein said optical amplifier is an erbium-doped fiber amplifier (hereinafter, also referred to as EDFA). 6. The optical amplifier according to claim 1, wherein a gain equalizer (gain adjuster) is arranged between an input terminal and an output terminal of the optical amplifier. Optical amplifier. 7. The optical amplifier according to claim 1, wherein a saturable absorber is disposed between an input terminal and an output terminal of the optical amplifier. 8. The optical amplifier according to claim 1, wherein said dispersion compensating element includes a dispersion compensating element composed of a multilayer film. 9. The optical amplifier according to claim 8, wherein said multilayer film is a dielectric multilayer film. 10. The optical amplifier according to claim 8, wherein a thickness and a refractive index of a layer such as a reflection layer and a light transmission layer of the multilayer film depend on a position in a light incident surface of the dispersion compensation element. An optical amplifier characterized by being different. 11. The optical amplifier according to claim 8, wherein said dispersion compensating element has a portion formed of a multilayer film and an air gap. 12. The optical amplifier according to claim 11, wherein said multilayer film is a dielectric multilayer film. 13. The optical amplifier according to claim 1, wherein the dispersion compensation amount of the dispersion compensating element and the center wavelength of the dispersion compensation are variable, and the dispersion compensation amount and the center wavelength of the dispersion compensation are set to be different from each other. An optical amplifier comprising adjusting means for adjusting. 14. The optical amplifier according to claim 13, wherein said adjusting means is manual. 15. The optical amplifier according to claim 13, wherein said adjusting means is a motor. 16. The optical amplifier according to claim 13, wherein the adjustment is performed by at least a part of the dispersion compensating element or a unit that moves a position of incident light along a guide. An optical amplifier, characterized in that: 17. The optical amplifier according to claim 13, wherein said adjusting means is an optical means such as a prism. 18. An optical amplifier according to claim 13, wherein said adjusting means is adjustable from outside the case of the optical amplifier. 19. The optical amplifier according to claim 13, further comprising display means for detecting and displaying the peak wavelength adjusted by said adjusting means with a monitor. amplifier. 20. An optical amplifier according to claim 13, wherein an adjustment amount of the group velocity delay time adjusted by said adjustment means can be detected and displayed by a monitor. . 21. An optical amplifier according to claim 13, wherein said adjusting means is an automatic adjusting means.