JP2001320328A - Optical communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems in the conventional methods that wavelength dispersion occurs in a signal transmitted on an optical fiber which brings about large disturbance in an optical communication, in which communication bit rate is >=10 Gbps, >=20 Gbps in particular and is not solved, even though various methods and elements for dispersion compensation have been proposed. SOLUTION: A plurality of elements capable of performing dispersion compensation by utilizing the group velocity delay time-wavelength characteristics are serially connected to produce an optical dispersion compensation element, where bandwidth is large and the peak of group velocity delay time is large, and the tertiary dispersion compensation of an optical signal of a wide wavelength band, including an 1,460 to 1,640 nm wavelength band, is performed by using the optical dispersion compensation element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system using an optical fiber for a communication transmission line, wherein the wavelength of signal light is 1460-1.
More specifically, the present invention relates to an optical communication method in a communication wavelength band including a range of 640 nm, and more specifically, to compensate for chromatic dispersion generated in an optical signal transmitted through a transmission path mainly including an optical fiber, thereby enabling high-speed and long-distance transmission. To an optical communication method.

In the following description of the present invention, chromatic dispersion is simply referred to as dispersion, optical dispersion compensation is also simply referred to as dispersion compensation, and optical dispersion compensating element is simply referred to as dispersion compensating element.

According to the present invention, an element capable of compensating for a second- or higher-order dispersion (to be described later) that occurs in optical communication using an optical fiber as a transmission path (hereinafter, an element capable of changing the second-order dispersion, or Similarly, an element capable of performing tertiary dispersion compensation described later is also referred to as an element capable of changing tertiary dispersion or an element capable of changing tertiary dispersion. ). More specifically, in the present invention, a dispersion compensating element capable of compensating for third- or higher-order dispersion or a dispersion compensating element capable of performing second- or third-order dispersion compensation is used. The dispersion compensating element used in the present invention may be only the above-described third-order dispersion compensating element, or may include a unit for changing an incident position of incident light on an incident surface described later. In some cases, it is possible to perform not only the second-order or higher dispersion compensation but also the second-order dispersion compensation, and it may be mounted in a case. In some cases. The dispersion compensating element used in the present invention includes all of these forms, and can take various forms according to purposes such as use and sale.

In the present invention, an element capable of performing dispersion compensation by itself or a part of an element capable of performing dispersion compensation (for example, a specific part on one wafer as an element capable of performing dispersion compensation) is used. The elements are collectively referred to as elements that can perform dispersion compensation unless it is particularly necessary to distinguish them.

In the present invention, the second-order dispersion compensation is described in FIG.
(A) to compensate for the slope of the dispersion of the wavelength-time characteristic curve described later ”, and the third-order dispersion compensation means“ compensating the wavelength-time characteristic curve described later with reference to FIG. Compensating for bending ".

[0006]

2. Description of the Related Art Hereinafter, the term "chirp" used in the present invention will be described.
Is mainly used to mean “group velocity delay” or “wavelength dispersion (hereinafter, also referred to as dispersion)”.

In optical communication using an optical fiber, long-distance transmission represented by a submarine cable is performed on a communication transmission line. .5G (giga) b
ps (bits per second) is not enough, 10 Gbps,
Attempts have been made to use signal light having a high bit rate such as 20 Gbps, 40 Gbps,.... In such an environment, it is known that the pulse causes a nonlinear phenomenon such as spreading, distortion, cracking, and sub-pulses because the refractive index and the speed are different depending on the spectral components of the signal light and the changing speed of the pulse. ing. This nonlinear phenomenon causes the pulse width of the signal light input to the transmission path to decrease,
It becomes remarkable as the rate of change of pulse intensity increases,
The change in the signal light pulse increases. In other words, in the case of high-speed communication in which the pulse width of the signal light is reduced and the rate of change of the pulse intensity is increased, the dispersion generated in the signal light is strongly affected by the nonlinear phenomenon in which the waveform changes according to the change speed of the light intensity. Therefore, normal communication cannot be performed.

FIGS. 9A and 9B are diagrams for explaining the intensity and wavelength of signal light when performing long-distance transmission. FIG. 9A shows a communication bit rate of 2.5 Gbps, and FIG.
FIG. 2C is a diagram illustrating optical communication at Gbps, and FIG. 2C is a diagram illustrating optical communication at 40 Gbps. Here, whether the input signal is on or off is determined based on a predetermined critical value such as a so-called eye diagram (eye mode), that is, a threshold. Symbols 7a, 7b and 7c indicate communication bit rates of 2.5 Gbps, 10 Gbps and 40 Gbps, respectively.
In the spectrum of the Gbps signal light, the vertical axis represents the light intensity and the horizontal axis represents the wavelength. Reference numerals 71a, 72a and 73a denote transmission waveforms at a communication bit rate of 2.5 Gbps, 71b and 7
2b, 73b are transmission waveforms at a communication bit rate of 10 Gbps, 71c, 72c, 73c are transmission waveforms at a communication bit rate of 40 Gbps, and reference numerals 71a1, 72a1,.
73a1, 71b1, 72b1, 73b1, 71c1,
72c1 and 73c1 are transmission waveforms 71a and 72c, respectively.
a, 73a, 71b, 72b, 73b, 71c, 72
c and 73c are waveforms received after being transmitted through an optical fiber or an optical fiber transmission system (hereinafter, also referred to simply as an optical fiber when no particular distinction is required) at the above communication bit rate. The light intensity and the horizontal axis are time, and in each waveform, the waveform portion on the left side of the figure is transmitted or received first.

In the conventional 2.5 Gbps optical communication, an optical signal is input to an optical fiber (hereinafter, also referred to as incident light).
Since the signal light has a gradual change in pulse intensity and a wide pulse width, the influence of non-linear phenomena is small and can be treated as a substantially linear phenomenon. The intensity and the wavelength of the signal light incident on the optical fiber during long-distance transmission slightly change as shown in FIG. 9A, but when two or more signal lights are continuously transmitted. However, the signal light transmitted through the optical fiber can be accurately received without taking into account the influence of the nonlinear phenomenon without causing a change that influences the discrimination of each signal light.

Next, in a conventional 10 Gbps optical communication system, the signal light incident on the optical fiber has a sudden change in pulse intensity and a narrow pulse width. Due to the increase in the light intensity change rate and the communication speed, non-negligible dispersion occurs to change the refractive index, and as a result, the spectral waveform and time waveform of the signal light change. For example, the refractive index and the wavelength change depending on the speed. The intensity and wavelength of the signal light incident on the optical fiber during long-distance transmission change, for example, as shown in FIG.
When transmitting more than one signal light, a phenomenon may occur in which one signal and the subsequent signal overlap until it is impossible to determine the identification, and it is necessary to accurately receive the signal light incident on the optical fiber. There was a problem that it could not be done.

Conventionally, this problem has been solved by using a component that does not easily generate chirp, for example, a filter in which a dielectric multilayer film filter is formed into a rectangular wave filter, a 1.5 μm
Fiber of a material that does not generate chirp with respect to wavelength,
By using a fiber with expanded core area, etc.
Several attempts have been made, such as an attempt to reduce chirp and accurately receive signal light incident on an optical fiber.

In high-speed communication at 40 Gbps, the signal light incident on the optical fiber has a more rapid change in pulse intensity and a narrower pulse width of 1/4 of 10 Gbps. The intensity and wavelength of the signal light incident on the optical fiber during long-distance transmission vary greatly as shown in FIG. 9C, and almost all of the signal light incident on the optical fiber is received. There was a problem that I could not do it. This problem is hardly solved at present and it is predicted that the optical fiber itself must be changed.

In order to clarify the present invention for solving such a conventional problem, a conventional second-order dispersion compensation method will be described with reference to FIGS.

FIG. 8 is a diagram illustrating the dispersion-wavelength characteristics of a single mode optical fiber (hereinafter, also referred to as SMF), a dispersion compensating fiber, and a dispersion shift fiber (hereinafter, also referred to as DSF). 8, reference numeral 601 is a graph showing the dispersion-wavelength characteristic of the SMF, 602 is a graph showing the dispersion-wavelength characteristic of the dispersion compensating fiber, and 603 is D
5 is a graph showing SF-dispersion-wavelength characteristics, in which the vertical axis represents dispersion and the horizontal axis represents wavelength.

As apparent from FIG. 8, in the SMF, the dispersion increases as the wavelength of light input to the fiber increases from 1.3 μm, and in the dispersion compensating fiber, the wavelength of the input light changes from 1.3 μm to 1.3 μm. Dispersion decreases with increasing length to 8 μm. In the DSF, the wavelength of the input light is 1.
The dispersion decreases as the wavelength increases from 2 μm to around 1.55 μm, and the dispersion increases as the wavelength of the input light increases from around 1.55 μm to 1.8 μm. In DSF, in conventional optical communication at a communication bit rate of about 2.5 Gbps (2.5 gigabits per second), dispersion does not cause a problem in optical communication when the wavelength of input light is around 1.55 μm.

FIGS. 7A and 7B are diagrams mainly illustrating a method of compensating for the second-order dispersion. FIG. 7A shows the wavelength-time characteristics and the light intensity.
(B) shows an example of transmission on a transmission line on which secondary dispersion compensation is performed using an SMF and a dispersion compensation fiber, and (C) shows a transmission characteristic.
FIG. 3 is a diagram for explaining an example of transmission on a transmission line configured only with SMF.

In FIG. 7, reference numerals 501 and 511 denote graphs showing the characteristics of the signal light before being input to the transmission line.
Denote transmission paths constituted by SMF531, 502 and 512
Is a graph showing the characteristics of the signal light output from the transmission line 530 when the signal light having the characteristics shown in the graphs 501 and 511 is transmitted through the transmission line 530, and 520 is the dispersion compensating fiber 5
21 and SMF522, and 503 and 513 are graphs showing the characteristics of the signal light output from the transmission line 520 when the signal light having the characteristics shown in the graphs 501 and 511 are transmitted through the transmission line 520. is there. Reference numerals 504 and 514 indicate the case where the signal light having the characteristics shown in the graphs 501 and 511 is transmitted through the transmission path 520 and output from the transmission path 520, and then the desired third-order dispersion compensation described later is performed by the present invention. 5 is a graph showing characteristics of signal light, and almost coincides with graphs 501 and 511. Further, graphs 501, 502, 503, and 504 are graphs in which the vertical axis represents wavelength and the horizontal axis represents time (or time). Graphs 511, 512, 513, and 514 respectively represent light intensity on the vertical axis and horizontal axis. Is a graph of time (or time). Reference numerals 524 and 534 are transmitters, 525
And 535 are receivers.

In the conventional SMF, as described above, the dispersion increases as the wavelength of the signal light increases from 1.3 μm, so that a group velocity delay due to the dispersion occurs in high-speed communication or long-distance transmission. In the transmission line 530 constituted by the SMF, the signal light is delayed more on the long wavelength side than on the short wavelength side during transmission, and the graphs become as shown in graphs 502 and 512. For example, in high-speed communication and long-distance transmission, the changed signal light may not be able to be received as an accurate signal by overlapping with the preceding and following signal lights.

In order to solve such a problem, conventionally,
For example, as shown in FIG. 7B, dispersion is compensated (hereinafter, also referred to as correction) using a dispersion compensating fiber. The conventional dispersion compensating fiber solves the problem of SMF in which the dispersion increases as the wavelength increases from 1.3 μm, and as described above, the dispersion decreases as the wavelength increases from 1.3 μm. It is made. Also,
The dispersion compensating fiber can be used, for example, by connecting the dispersion compensating fiber 521 to the SMF 522 as shown by the transmission line 520 in FIG. In the transmission line 520,
As shown in graphs 503 and 513, the signal light has a longer delay on the longer wavelength side than on the shorter wavelength side in the SMF 522 and a greater delay on the shorter wavelength side than the longer wavelength side in the dispersion compensating fiber 521. And the amount of change can be suppressed smaller than the changes shown in FIGS.

However, in the above-mentioned conventional secondary chromatic dispersion compensation method using a dispersion compensating fiber, the chromatic dispersion of the signal light transmitted through the transmission line is determined by the state of the signal light before being input to the transmission line, that is, Dispersion compensation cannot be performed up to the shape of the graph 501, and compensation is limited to the shape of the graph 503. As shown in the graph 503, in the conventional secondary chromatic dispersion compensation method using the dispersion compensating fiber, the central wavelength light of the signal light is not delayed as compared with the short wavelength light and the long wavelength light. Only the light of the components on the shorter wavelength side and the longer wavelength side than the light of the central wavelength component of the signal light is delayed. Then, a ripple may be generated in a part of the graph as shown in a graph 513.

[0021]

In the case where the occurrence of chirp is reduced by using the above-mentioned method, the cost of parts is increased, or a situation where the single mode cannot be maintained due to the expansion of the core area occurs. Problems such as an increase in light loss in a communication transmission line due to leakage of light from a bent portion of the fiber have occurred. In addition, due to the small chirp generated by transmission over a long distance, it is impossible to cope with high-speed communication.
Even if the chirp can be transmitted and received without any problem in the optical communication up to the bps band, in the optical communication using the 20 Gbps or 40 Gbps band, even if the chirp is reduced using the conventional method, the transmission and the reception become so large that the communication becomes impossible. It is a big problem that a chirp that hinders the operation is generated.

However, this solution has not been found at present, and it is predicted that as a countermeasure, the fiber itself must be changed to cope with the problem. As a result, the accumulated fiber and related components of optical communication have been required to undergo major changes, and conventional methods and equipment may not be usable, resulting in large social and economic losses. ing.

The present invention has been made in view of the above point, and an object of the present invention is to consider the wavelength of signal light in consideration of optical communication wavelength bands called L band, C band, S band, and the like. In the communication wavelength band including the wavelengths before and after the wavelength band of 1460 to 1640 nm,
It is an object of the present invention to provide a communication method capable of solving the above-mentioned problem in long-distance communication.

More specifically, an optical dispersion compensator is provided so as to have a group velocity delay time-wavelength characteristic capable of compensating for the above-mentioned dispersion occurring in communication over a wavelength band of several tens of nm which has not been practically used in the past. An inexpensive, reliable, and compact communication system that composes an element and uses the optical dispersion compensating element to compensate for the dispersion of the entire signal light before splitting the signal light for each receiving station of each terminal. An object of the present invention is to provide an optical communication method.

In order to achieve the object of the present invention, an optical communication method according to the present invention has several embodiments, each having features.

[0026]

A feature of the optical communication method of the present invention is that in an optical communication system using an optical fiber for a communication transmission line, signal light transmitted through the optical fiber is wavelength-separated for each receiving channel. Before, chromatic dispersion (hereinafter simply,
(Also referred to as dispersion) through an optical dispersion compensating element capable of compensating for at least the third-order dispersion of the entire signal light to be transmitted. A plurality of elements capable of performing dispersion compensation can be connected in series along a communication path of signal light to perform dispersion compensation by acting as the optical dispersion compensation element. An optical dispersion compensating element constituted by connecting a plurality of elements capable of performing dispersion compensation in series along a communication path of signal light can be used.

In the example of the optical dispersion compensating element used in the optical communication method according to the present invention, the optical dispersion compensating element constituted by connecting a plurality of elements capable of performing the dispersion compensation in series is provided with the incident light. In the wavelength range of 1460 to 1640 nm, the group velocity delay time-wavelength characteristic curve has at least one extreme value.

Then, in the example of the typical optical dispersion compensating element used in the optical communication method of the present invention, 1460 to 164
It is characterized in that the group velocity delay time-wavelength characteristic curve has one extreme value in the wavelength range of 0 nm.

In the multilayer film used for at least one of the elements capable of performing dispersion compensation, which constitutes the optical dispersion compensating element used in the optical communication method of the present invention, at least two layers having different light reflectances from each other. It has a reflection layer and at least one light transmission layer formed between the reflection layers.

The multilayer film has at least one cavity formed by two reflection layers and a light transmission layer formed between the reflection layers.

In the optical communication method according to the present invention, the number of cavities of each multilayer film of the at least two dispersion compensating elements constituting the optical dispersion compensating element is different.

In the example of the optical dispersion compensating element used in the optical communication method of the present invention, the thickness of at least one laminated film constituting at least one of the multilayer films is parallel to a light incident surface of the multilayer film. It is characterized in that an optical dispersion compensating element using a multilayer film which changes in an in-plane direction in a cross section (hereinafter also referred to as an in-plane direction) is used.

[0033] In the multilayer film in which the film thickness changes in at least one direction in the incident plane, there are at least two film thickness changing directions.

In the example of the optical dispersion compensating element used in the optical communication method according to the present invention, at least one element constituting the optical dispersion compensating element capable of performing dispersion compensation may be arranged such that the direction in the incident plane Adjusting means for adjusting the film thickness of at least one laminated film of the multilayer film by engaging with an element capable of performing dispersion compensation having a multilayer film whose film thickness is changed, or It is characterized in that means for changing the incident position of light on the incident surface is provided.

The extreme value of the group velocity delay time-wavelength characteristic curve of the optical dispersion compensating element used in the optical communication method of the present invention is the minimum value of the peak value of the dispersion of each signal light generated by the transmission line mainly including the optical fiber. It is characterized by not being larger than the value.

In the present invention, the difference between the wavelength giving the extreme value of the group velocity delay time-wavelength characteristic curve of the optical dispersion compensating element and the wavelength giving the minimum peak value of the dispersion of each signal light is obtained. It is characterized by being within 6 nm.

In the optical dispersion compensating element used in the optical communication method of the present invention, the multilayer film, which is a component of at least one of the elements capable of performing dispersion compensation, used in the optical dispersion compensating element has a structure in which an incident light is reflected. When considered as an optical path length (hereinafter, also simply referred to as an optical path length) for light having a center wavelength λ, the film thickness of each layer of the multilayer film (hereinafter, also simply referred to as a film thickness or a film thickness) is λ / 4. A multilayer film having a thickness in a range of an integral multiple of ± 1% (hereinafter, also referred to as an integral multiple of λ / 4, or an almost integral multiple of λ / 4); a layer having a higher refractive index at a quarter of λ (hereinafter, referred to as a thickness of ４ times ± 1% of λ ± 1%) (hereinafter, also referred to as a layer H) ) And a layer having a thickness of 1/4 times λ and a lower refractive index (hereinafter, also referred to as a layer L). H is Si, Ge, T
It is characterized by being formed of a layer made of any one of iO ₂ , Ta ₂ O ₅ and Nb ₂ O ₅ .

In the optical dispersion compensating element used in the optical communication method of the present invention, the layer L is formed using a material having a lower refractive index than the material used for the layer H. A typical example is characterized in that the layer L is formed of a layer made of SiO ₂ .

Then, in order to achieve the object of the present invention,
In the example of the optical dispersion compensating element used in the optical communication method of the present invention, at least one kind of multilayer films A to H described later can be used as the multilayer film.

That is, each of the multilayer films A to H described below has at least five types of laminated films having different optical properties (that is, at least five types of laminated films having different optical properties such as light reflectance and film thickness). 5 layers), the multilayer film has at least three types of reflective layers including at least two types of reflective layers having different light reflectances from each other, and at least two types of reflective layers in addition to the three types of reflective layers. One light-transmitting layer, and one layer of each of the three types of reflective layers and each one of the two light-transmitting layers are alternately arranged, and the multilayer film is one of the ones in the thickness direction of the film. In order from the side, a first layer that is a first reflection layer, a second layer that is a first light transmission layer, a third layer that is a second reflection layer, a fourth layer that is a second light transmission layer, It is composed of a fifth layer that is a third reflective layer, and the multilayer film A is
A layer in which the five stacked films, that is, the first to fifth layers are combined one by one in the order of layer H and layer L in order from one side in the thickness direction of the multilayer film (hereinafter, also referred to as HL layer). Say)
(A layer obtained by combining the layer H1 layer and the layer L1 layer is referred to as an HL layer 1 set; the same applies hereinafter), a first layer formed by stacking the layers H and H,
A layer formed by stacking two layers of layer H. Hereinafter, also referred to as a layer of HH), a second layer constituted by laminating 10 sets
The third layer is formed by laminating seven sets of layers and HL layers.
Layer, a fourth layer configured by stacking 38 sets of HH layers,
The layer L is a multilayer film composed of a fifth layer formed by laminating one layer and 13 sets of HL layers, and a multilayer film B is laminated with 10 sets of the HH layers of the multilayer film A. Instead of the second layer formed as described above, the second layer is “in order from one side in the thickness direction of the film” in the same direction as that of the multilayer film A, three sets of HH layers, and the layer L (I.e., a layer formed by laminating two layers L. Hereinafter, a layer formed by combining two layers L.
LL layer), 3 sets of HH layers,
A multilayer film formed of a laminated film formed by laminating two sets of LL layers and one set of HH layers in this order;
In place of the fourth layer formed by laminating 38 sets of the HH layers of the multilayer film A or B, the multilayer film C is replaced by a “film” in the same direction as in the case of the multilayer film A. From one side in the thickness direction ”, three sets of HH layers, three sets of LL layers, three sets of HH layers, three sets of LL layers,
3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers,
3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers,
The HH layer is a multilayer film formed by laminating two sets of layers in this order, and the multilayer film D is the multilayer film of the five layers, that is, the first to fifth layers are the multilayer films. The first layer and the LL layer, which are formed by laminating five sets of layers (hereinafter also referred to as LH layers) in which layers L and H are combined one by one in this order from one side in the thickness direction of A second layer formed by stacking seven sets, a third layer formed by stacking one layer H and seven sets of LH layers, and a fourth layer formed by stacking 57 sets of LL layers. And a layer H, which is a multilayer film composed of a fifth layer formed by laminating one layer and 13 sets of LH layers, and a multilayer film E is defined as the five-layer laminated film, that is, the first layer. To a fifth layer, a first layer formed by laminating two sets of HL layers in order from one side in a thickness direction of the multilayer film; , A third layer formed by laminating one layer L and six sets of HL layers, and a 24 layer set of HH layers. And a multilayer L formed by laminating a fourth layer, a single layer L, and a fifth layer formed by laminating 13 sets of HL layers. One layer
Instead of the second layer formed by laminating four sets, the second layer has three sets of HH layers “in order from one side in the thickness direction of the film” in the same direction as that of the multilayer film E. , 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 2 sets of HH layers, 1 set of LL layers, and 1 set of HH layers. Instead of the fourth layer formed by laminating 24 sets of the HH layers of the multilayer film E or F, the fourth layer is a multilayer film formed of a multilayer film formed by: 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, in order from one side in the thickness direction of the film in the same direction as the multilayer film E,
3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers,
The multi-layered film is formed by laminating two sets of HH layers, one set of LL layers, and one set of HH layers in this order. The film, that is, the first to fifth layers are formed by laminating four sets of LH layers and laminating nine sets of LL layers in order from one side in the thickness direction of the multilayer film. Second
A third layer formed by laminating one set of layers H and six sets of LH layers, a fourth layer formed by laminating 35 sets of LL layers, and one set of layers H and one set of LH. The layer is a multilayer film formed by a fifth layer formed by laminating 13 sets.

[0041]

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 convenience of description of the present invention, the magnification may be partially changed in the drawings, and the drawings used for the description of the present invention may not always be similar to the actual product or the description. In addition, in each of the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

FIG. 1 is a diagram for explaining a method of compensating dispersion caused by communication using an optical fiber as a transmission line by an optical dispersion compensating element. Reference numeral 1101 denotes a signal light of a signal light remaining after compensating for secondary dispersion. A group velocity delay time-wavelength characteristic curve showing cubic dispersion, 1102 is a group velocity delay time-wavelength characteristic curve of the dispersion compensating element, 1103 is the dispersion of the signal light having the dispersion characteristic of the curve 1101, and the dispersion of the curve 1102 is Compensation target wavelength band λ _{1 to} λ ₂ after being compensated by a dispersion compensating element having characteristics.
The vertical axis represents the group velocity delay time and the horizontal axis represents the wavelength.

FIGS. 2 to 4 are views for explaining an optical dispersion compensating element used in the optical communication method of the present invention. FIG. 2 is a sectional view of a multilayer film described later, and FIG. FIG. 4 is a group velocity delay time-wavelength characteristic curve of the multilayer film.

FIG. 2 is a diagram schematically illustrating a cross section of a multilayer film used as an example of the third-order dispersion compensating element of the present invention.
2, reference numeral 100 denotes a multilayer film as an example of the optical dispersion compensating element of the present invention, 101 denotes an arrow indicating the direction of incident light,
102 is an arrow indicating the direction of the emitted light, 103 and 104 are reflection layers having a reflectance of less than 100% (hereinafter also referred to as reflection films), 105 is a reflection layer having a reflectance of 98 to 100%, 10
Numerals 8 and 109 are light transmitting layers, and 111 and 112 are cavities. The optical dispersion compensating element 100 has two cavities 111
It can also be said to be a two-cavity type including Reference numeral 107 denotes a substrate, for example, using BK-7 glass.

The reflectances R (103), R (104), and R (105) of each of the reflection layers 103, 104, and 105 in FIG.
R (103) ≦ R (104) ≦ R (105). Then, it is preferable in terms of mass production that the reflectance of each layer is set to be different from each other at least between adjacent reflective layers with the light transmitting layer interposed therebetween. That is, the reflective layers are formed such that the reflectance of each reflective layer with respect to the center wavelength λ of the incident light gradually increases from the side where the incident light is incident toward the thickness direction of the multilayer film. Then, the reflectance of each reflection layer with respect to the light having the wavelength λ is 60% ≦ R (103) ≦ 77%,
96% ≦ R (104) ≦ 99.8%, 98% ≦ R (10
For the range of 5), the above R (103), R (10)
4) By configuring so as to satisfy the relationship of R (105), a group velocity delay time-wavelength characteristic curve as shown in FIGS. 5 and 6 described below can be obtained. And R (10
3) It is more preferable that R <104 (R) <R (105), and R (105) approaches 100% or 100%.
Is more preferable, and the performance of the optical dispersion compensation element of the present invention can be further enhanced.

In order to make the optical dispersion compensating element of the present invention easier to manufacture, it is necessary to select the conditions for forming the respective reflective layers so that the intervals when considering the optical path length between the adjacent reflective layers are different. More preferably, the design accuracy of the reflectance of each reflective layer can be relaxed, and a combination of unit films whose film thickness is a quarter of the central wavelength λ of the incident light (a film having a film thickness of an integral multiple of λ / 4) Thus, for example, a multilayer film used for a tertiary dispersion compensation element of the present invention can be formed, and a dispersion compensation element having high reliability and excellent mass productivity can be provided at low cost.

The thickness of the unit film of the multilayer film has a wavelength λ.
Which is described as one-fourth of
It means λ / 4 within the range of an error allowable in the formation of a film in mass production, and specifically, λ / 4 ± 3%, preferably λ / 4 ± 1%. The present invention exhibits a particularly large effect even in this range. Therefore, in the present invention, the film thickness in this range is defined as a thickness of λ / 4. In particular,
When the thickness of the unit film is λ / 4 ± 0.5% (λ /
4 means [lambda] / 4 without error), thereby making it possible to form a highly reliable multilayer film with little variation without impairing mass productivity, as will be described later with reference to FIGS. An optical dispersion compensating element can be provided at low cost.

In the present invention, the thickness of the multilayer film is λ /
Although it is described that the unit film of No. 4 is formed by lamination, it is possible to form a multilayer film by repeating a method of forming one unit film and then forming the next unit film. The invention is not limited to this, and in general, a film having a thickness of an integral multiple of λ / 4 is often formed continuously, and such a multilayer film is naturally the object of the multilayer film of the present invention. Then, the multilayer film of the present invention can be formed by using a film forming step of continuously forming the reflection layer and the transmission layer.

FIG. 3 is a view for explaining an example in which the film thickness of the multilayer film 100 is changed in an in-plane direction of a later-described incident surface 220 of the multilayer film 100 of FIG.

In FIG. 3, reference numeral 200 denotes a multilayer film as an example of the optical dispersion compensating element of the present invention, 201 denotes a first reflective layer, 202 denotes a second reflective layer, and 203 denotes a third reflective layer.
05 is a substrate, 206 is a first light transmitting layer, 207 is a second light transmitting layer, 211 is a first cavity, 212 is a second cavity, 220 is a light incident surface, and 230 indicates the direction of incident light. Arrow, 240, arrow indicating the direction of the emitted light, 250
Is an arrow indicating a first film thickness change direction, 260 is an arrow indicating a second film thickness change direction, and 270 and 271 are arrows indicating a direction in which an incident position of incident light is moved.

In FIG. 3, for example, on a substrate 205 made of BK-7 glass or the like, a third reflective layer 203,
A second light transmission layer 207, a second reflection layer 202, a first light transmission layer 206, and a first reflection layer 201 are sequentially formed.

The thickness of the first light transmitting layer 206 changes in the direction indicated by the arrow 250 in FIG. 3 (the thickness gradually increases from right to left in the figure), and the second light transmitting layer 206 changes. The multilayer film is formed such that the thickness of 207 changes in the direction indicated by arrow 260 (the thickness gradually increases from the near side to the far side in the figure). The thickness of the first to third reflective layers is
When the wavelength when the resonance wavelength of the first and second cavities coincides with the center wavelength λ of the incident light,
The reflectance of each of the second and third reflective layers is R (103),
The film is formed so as to satisfy the conditions of R (104) and R (105).

FIG. 4 shows incident light from the direction of an arrow 230 in FIG. 3 on an incident surface 220 of a multilayer film (hereinafter also referred to as a light dispersion compensating element) 200 as an example of the light dispersion compensating element of the present invention. , The outgoing light is obtained in the direction of arrow 240, and the incident position of the incoming light is set to the arrow 270 in FIG.
Alternatively, it illustrates the manner in which the group velocity delay time-wavelength characteristic curve changes when moving in the direction of 271.

FIG. 4 shows the positions of incidence 280-2 in FIG.
82 shows a group velocity delay time-wavelength characteristic curve when incident light having a center wavelength λ is incident, and the vertical axis shows the group velocity delay time;
The horizontal axis is the wavelength.

Reflecting layers 201 to 203 and light transmitting layer 20
When the incident position of the incident light on the incident surface 220 is moved in the direction indicated by the arrow 270 by appropriately selecting the conditions for changing the film thickness in the directions indicated by the arrows 250 and 260 of FIGS. While maintaining the shape of the delay time-wavelength characteristic curve in substantially the same shape, the band center wavelength λ _{0 of} the group velocity delay time-wavelength characteristic curve (for example, the group velocity delay time-wavelength having a substantially symmetrical shape in FIG. 4) Characteristic curve 280
1), and when the incident position is moved in the direction indicated by the arrow 271 from the position, the wavelength λ ₀ hardly changes, and the group velocity delay time-wavelength characteristic curve Is changed to the curve 281 in FIG.
1, 2812. Each curve in FIG. 4 is obtained when the thickness of each film is monotonically increased in the directions of arrows 250 and 260 in FIG.

The band center wavelength λ ₀ in the curves 2801 to 2812 is set, for example, at an appropriate wavelength in the graph of FIG. 4 according to the purpose of dispersion compensation.
It may be set to approximately the center value of the wavelength range of the curve shown in FIG. 4, or may be appropriately determined according to the purpose of dispersion compensation. In addition, it is natural that the correspondence between the wavelengths of the respective characteristic points of the curves, such as the respective extreme wavelengths between the curves 2801 to 2812, is checked in advance, etc., without being described here.

Thus, for example, first, the band center wavelength λ corresponding to the center wavelength λ of the incident light to be dispersion-compensated
_The arrow 270 indicates the incident position of the incident light so that ₀ is matched.
And the shape of the group velocity delay time-wavelength characteristic curve used for dispersion compensation in accordance with the content of compensation to be dispersion-compensated, that is, in accordance with the dispersion state of the incident light. The incident position is, for example, 280 in the direction indicated by the arrow 271 in FIG.
By selecting each point as shown by ~ 282,
The dispersion compensation required for the signal light can be effectively performed.

As is apparent from the shape of the group velocity delay time-wavelength characteristic curve in FIG. 4, tertiary dispersion compensation can be performed using the optical dispersion compensating element of the present invention, for example, using the curve 2801. , The second-order fine dispersion compensation can be performed by using a portion of the curve 2811 or 2812 which is relatively close to a linear component.

As described above with reference to FIGS. 2 to 4, the "element capable of performing a dispersion compensation element" used in the present invention is described.
However, it is clear from the description of each curve in FIG. 4 that the third-order dispersion can be compensated to some extent by using the “element capable of performing the dispersion compensation element”.

However, the wavelength bandwidth of the dispersion compensation that can independently compensate for the “element capable of performing a dispersion compensation element” is:
For signal light having a wavelength near 1.55 μm, 1.5 nm
Before and after, the group velocity delay time is often about 3 ps (picoseconds), and if the wavelength band of dispersion compensation is widened to support optical communication of a plurality of channels, dispersion compensation can be sufficiently performed. It is difficult to obtain the group velocity delay time, and further improvement is desirable for wide and convenient use in actual communication. Therefore, the present invention will be described in more detail with reference to FIGS.

FIG. 5 shows a group velocity delay time obtained by using a plurality of elements capable of performing dispersion compensation as described above.
FIG. 5 is a diagram for explaining a method for improving wavelength characteristics, and FIG.
5A shows a group velocity delay time-wavelength characteristic of one element capable of performing dispersion compensation used in the present invention, and FIG. 5B shows a group velocity delay time-wavelength characteristic curve having almost the same shape. The wavelength (hereinafter, also referred to as an extreme wavelength) that gives the extreme peak value of the speed delay time-wavelength characteristic curve is λ (302) and λ
FIG. 5C shows the group velocity delay time-wavelength characteristic of the optical dispersion compensating element used in the present invention in which two elements capable of performing different dispersion compensation as in (303) are connected in series. FIG. 5D shows a group velocity delay time-wavelength characteristic of the optical dispersion compensating element of the present invention in which three elements capable of performing dispersion compensation having substantially the same wavelength characteristic curve and different extremal wavelengths are connected in series. Is an element capable of performing dispersion compensation having different group velocity delay time-wavelength characteristic curves and different extreme wavelengths.
5 is a graph showing the group velocity delay time-wavelength characteristics of the optical dispersion compensating elements used in the optical dispersion compensation method of the present invention connected in series, wherein the vertical axis represents the group velocity delay time and the horizontal axis represents the wavelength.

In FIG. 5, reference numerals 301 to 309 denote group velocity delay time-wavelength characteristic curves of one element capable of performing dispersion compensation used in the present invention, and 310 denotes group velocity delay time-wavelength used in the present invention. The shape of the characteristic curve is almost the same as the curve 302 and the curve 303, and the extreme value GD (30
2) and the respective extreme wavelength λ giving GD (302)
GD (310) and λ (310) are group velocity delay time-wavelength characteristic curves when two elements capable of performing dispersion compensation with different (302) and λ (303) are connected in series.
Is the extremum and the extremum wavelength of the curve 310, and 311 is the dispersion compensation in which the shape of the group velocity delay time-wavelength characteristic curve used in the present invention is almost the same as the curves 304, 305 and 306 and the extremal wavelengths are different. Group velocity delay time-wavelength characteristic curve when three devices that can be used are connected in series, 312
Is a group velocity delay time-wavelength characteristic when three elements capable of performing dispersion compensation having different shapes and extreme wavelengths are connected in series as shown by curves 307, 308, and 309. It is a curve. In FIG. 5A, reference numeral a denotes a wavelength band to be subjected to dispersion compensation, and b denotes an extreme value of the group velocity delay time.

5B and 5C, the extreme value of the group velocity delay time of the group velocity delay time-wavelength characteristic curve 310 is as follows.
1.6 in the case of one element capable of performing dispersion compensation
Times, the wavelength band for dispersion compensation is about 1.8 times,
The extremum of the group velocity delay time of the group velocity delay time-wavelength characteristic curve 311 is about 2.3 times that of one element, and the wavelength band to be dispersion-compensated is about 2 times that of one element capable of performing dispersion compensation. .5 times. In FIG. 5D, the extreme value of the group velocity delay time of the curve of the group velocity delay time-wavelength characteristic curve 312 is about three times as large as that of one element capable of performing dispersion compensation. Is about 2.3 times that of a single element capable of performing dispersion compensation.

The group velocity delay time of an element capable of performing dispersion compensation using a multilayer film as described in FIG.
The extreme value of the group velocity delay time of the wavelength characteristic curve and the wavelength band to be subjected to dispersion compensation also change depending on the configuration conditions of each reflection layer and each light transmission layer of the multilayer film. For example, curve 30 in FIG.
7, the dispersion compensation wavelength band is relatively wide but the extreme value of the group velocity delay time is not so large. An element capable of performing dispersion compensation having various characteristics, such as a group velocity delay time-wavelength characteristic curve, having an extreme value of the delay time can be realized.

Examples of the multilayer film used for the element capable of performing such dispersion compensation include the multilayer films A to H described in the section for solving the above-mentioned problems. When a device capable of performing dispersion compensation was prepared using the multilayer films A to H, the wavelength was about 1.55.
Extreme value of group velocity delay time is 3 ps for μm signal light
(Picoseconds) and the wavelength band targeted for dispersion compensation is 1.3 to 2.0 n
A group velocity delay time-wavelength characteristic curve of m was realized.

Then, a plurality of elements capable of performing this dispersion compensation are connected in series, and the extreme value of the group velocity delay time is 5 to 50 ps, and the wavelength band for dispersion compensation is 30 to 90 nm.
Optical communication for producing 60 km of signal light corresponding to a communication bit rate of 20 to 100 Gbps including a wavelength band of 1460 to 1640 nm and 6 nm on both sides of the optical dispersion compensating element having various group velocity delay time-wavelength characteristics. As a result, it was possible to perform third-order dispersion compensation, which was completely impossible in the past, and prove that future high-speed and long-distance communication can be improved.

A group of elements that can be used in series and can perform dispersion compensation, such as a group velocity delay time-wavelength characteristic curve in FIG. 4 and a group velocity delay time-wavelength characteristic curve in FIG. 5D. By appropriately selecting the speed delay time-wavelength characteristic curve, not only the third-order dispersion but also the
The following dispersion could also be compensated.

In the example of the optical dispersion compensating element in which at least two elements capable of performing dispersion compensation constituting the optical dispersion compensating element used in the optical communication method of the present invention are connected in series, third-order or higher order dispersion is compensated. Group velocity delay time necessary to realize an optical dispersion compensating element having wavelength characteristics, group velocity delay time-group velocity delay time such that the wavelength characteristic curve has an extreme value in the dispersion compensation target wavelength region- It is desirable to use at least one element having wavelength characteristics and capable of performing dispersion compensation.

Further, in order to more effectively perform dispersion compensation of a communication transmission line, the group velocity delay time as an optical dispersion compensating element is calculated as follows.
It is desirable to improve the wavelength characteristic curve. As one method for this, there is a method of providing a means capable of adjusting the group velocity delay time-wavelength characteristic of an element capable of performing dispersion compensation.

As a method, as described with reference to FIGS. 2 and 3, the thickness of the light-transmitting layer and the reflecting layer of the multilayer film is changed in the in-plane direction of the incident surface to perform dispersion compensation. There is a method of changing a group velocity delay time-wavelength characteristic of an element capable of performing dispersion compensation by changing an incident position of signal light. The means for changing the incident position of the incident light is realized by moving at least one of the optical dispersion compensating element or the incident position itself of the incident light with respect to the position of the incident light. The light dispersion compensating element or the means for moving the incident position can be variously selected depending on the circumstances, such as the circumstances in which the light dispersion compensating element is used, the cost, and the characteristics. For example, a method performed by manual means such as a screw can be used due to the cost or the circumstances of the device, and it can be adjusted for accurate adjustment or when adjustment cannot be performed manually. In order to achieve this, it is effective to use, for example, an electromagnetic step motor or a continuous drive motor, and it is also effective to use a piezoelectric motor using PZT (lead zirconate titanate). In addition, it is possible to easily and accurately select an incident position by using a prism or a two-core collimator that can be combined with these methods, or by selecting an incident position by an optical means such as using an optical waveguide. Can be.

Each layer of the multilayer film used for the element capable of performing dispersion compensation constituting the optical dispersion compensating element used in the optical communication method of the present invention is formed by ion-assisted deposition of SiO _{2 having} a quarter wavelength. It is composed of a layer L formed of a formed film (hereinafter also referred to as an ion assist film) and a layer H formed of a ４ ₂ wavelength TiO ₂ ion assist film having a thickness of ４. One layer of the ion-assisted film (layer L) of SiO ₂ and one layer of the ion-assisted film (layer H) of TiO ₂
A combination of layers is referred to as one set of LH layers. For example, “lamination of five sets of LH layers” means “layer L / layer H
Layer L, layer H, layer L, layer H, layer L, layer H, layer L, and layer H in this order.

Similarly, the LL layer has a thickness of 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, “three sets of LL layers are stacked” means “three layers L are formed and stacked”.

[0073] Incidentally, the composition of film forming the layer H, although an example of a dielectric, the present invention is not limited thereto, as the same dielectric material as TiO ₂ in addition to TiO ₂ , Ta ₂ O ₅ , Nb ₂ O _5, etc., and the layer H can be formed using Si or Ge in addition to the dielectric material. When the layer H is formed using Si or Ge, there is an advantage that the layer H can be formed thinner than optical properties. The composition of the layer L is SiO ₂
Although SiO ₂ has an advantage that SiO ₂ has an advantage that the layer L can be formed at low cost and with high reliability, the present invention is not limited to this, and the refractive index is lower than the refractive index of the layer H. If the layer L is formed of a material, an optical dispersion compensating element used in an optical communication method that exhibits the above-described effects of the present invention can be realized.

Further, in this embodiment, the layers L and H constituting the multilayer film are formed by ion-assisted vapor deposition, but the present invention is not limited to this. The present invention exerts a great effect even when a multilayer film formed by the above-mentioned method is used.

The optical dispersion compensating element used in the optical communication method of the present invention is a multilayer film 20 as an optical dispersion compensating element shown in FIG.
0, it is also possible to appropriately hold and use a wafer-shaped object, and to include a necessary part in the incident surface 220 in the thickness direction, that is, in the direction from the incident surface 220 to the substrate 205. It has a variety of possibilities, for example, it can be made into a small chip that is cut vertically, and it can be used as an element that can be mounted on a cylindrical case together with a fiber collimator to perform dispersion compensation. In each case, the main effects described in the present invention are brought.

FIG. 6 is a diagram for explaining an example of an optical dispersion compensating element used in the optical communication method of the present invention. FIG. 6 (A) shows a case where two elements capable of performing the dispersion compensation are connected in series. FIG. 6B shows an example in which an optical dispersion compensating element is formed, FIG. 6B shows an example in which three elements capable of performing the dispersion compensation are connected in series, and FIG. FIG. 6 shows an example in which two points of incidence of signal light are connected in series along the route of signal light on a multilayer film whose film thickness changes in the in-plane direction to form a light dispersion compensating element. D) is a diagram illustrating an example in which the optical dispersion compensating element having the same configuration as that of FIG. 6A is mounted in one case.

In FIG. 6, reference numerals 410, 420, 43
0 and 440 are optical dispersion compensating elements used in the present invention, 411,
Reference numerals 412, 421 to 423, 431, 442, and 443 denote elements capable of performing dispersion compensation, and 416 denotes a multilayer film used for an element capable of performing dispersion compensation.
51, 4152, 426, 436, 446 are optical fibers, 413, 4131, 414, 4141, 424, 4
25, 434, 435, 444, and 445 are arrows indicating the traveling direction of the signal light, 417 is a lens, and 418 is a lens 41.
7 and optical fibers 4151 and 4152, a two-core collimator 441; a case 431; and a multilayer film 431 whose film thickness changes in the direction of the incident surface is formed on a substrate to perform dispersion compensation. The devices 432 and 433 are configured so as to be capable of performing wafer-shaped dispersion compensation, and are “elements that can perform dispersion compensation”.

In FIG. 6A, the signal light incident in the direction of arrow 413 is applied to the element 4 capable of performing dispersion compensation.
11, exits from the element 411 that can perform dispersion compensation by receiving dispersion compensation, and enters the element 412 that can be transmitted through the fiber 415 and perform dispersion compensation.
The light is emitted from the element 412 which can receive the dispersion compensation again and can perform the dispersion compensation.
5 is transmitted.

Reference numeral 4112 is a cross-sectional view for explaining the internal structure of a portion surrounded by a dotted line 4111 of the element 411 capable of performing dispersion compensation. Optical fibers 4151 and 4
The 152 and the lens 417 constitute a two-core collimator 418, and the signal light traveling through the optical fiber 4151 in the direction of the arrow 4131 passes through the lens 417 and enters the multilayer film 416.

The multilayer film 416 has the group velocity delay time-wavelength characteristic shown in FIG.
The signal light incident on the multilayer film 416 through the lens 417 and the lens 417 is subjected to third-order dispersion compensation, passes through the lens 417 again, enters the optical fiber 4152, proceeds in the direction of the arrow 4141, and performs dispersion compensation. Is incident on the element 412 that can be formed. The signal light further subjected to dispersion compensation by the element 412 capable of performing dispersion compensation exits from the element 412 capable of performing dispersion compensation, and exits in the optical fiber 415 in the direction indicated by the arrow 414.

The optical dispersion compensating element 410 used in the optical communication method of the present invention shown in FIG.
The signal light having the group velocity delay time-wavelength characteristic shown and incident on the optical dispersion compensation element 410 is subjected to dispersion compensation according to the group velocity delay time-wavelength characteristic shown in FIG. The light is emitted from the dispersion compensation element 410.

Similarly, in the light dispersion compensating element 420 shown in FIG.
In the process of sequentially entering and exiting the elements 421 to 423 capable of performing dispersion compensation, the signal light incident on 0 corresponds to, for example, a group velocity delay time-wavelength characteristic curve as shown in FIG. After being subjected to dispersion compensation, the light is emitted from the optical dispersion compensating element 420 and travels through the optical fiber 426 in the direction indicated by the arrow 425.

FIG. 6C shows a part of the element 431 capable of performing dispersion compensation formed on the same wafer in place of the elements 411 and 412 capable of performing dispersion compensation of FIG. 6A. 432 and 433 ”are connected in series along the path of the signal light using the optical fiber 436.
This is the same as described in (A). However, it is clear from the above description that the method of performing the dispersion compensation depends on the group velocity delay time-wavelength characteristic of the element capable of performing the dispersion compensation.

FIG. 6D shows an optical dispersion compensating element 440 in which elements 442 and 443 capable of performing the same dispersion compensation as in FIG. 6A are incorporated in the same case 441. Although not shown, the element 443 capable of performing dispersion compensation uses a multilayer film whose thickness changes in the in-plane direction of the incident surface of the multilayer film described with reference to FIG. 3, and adjusts the incident position. Means. Although the incident position adjusting means is not shown, the incident position can be adjusted using a control circuit provided in the case 441.

At present, the wavelength band of optical communication is S-band, C-band
Each company constructs a communication system for each wavelength band called -band and L-band, and the wavelength band of each band seems to be slightly different. For example, the S-band is roughly 1460-1520 nm, the C-band is 1
520-1570 nm, L-band is 1570-164
Like 0 nm. If dispersion compensation can be performed for all the bands, the effect will be extremely large.

Using the optical dispersion compensating element having such a structure, 20 to 100 G in a wavelength band of 1640 to 1646 nm including so-called L-band, C-band and S-band.
An experiment was conducted in which a signal light corresponding to bps was transmitted for 60 km. As a result, extremely good dispersion compensation could be performed, and the loss due to the transmission of the signal light through the light dispersion compensating element was extremely low. . The loss due to one secondary dispersion compensating element using a conventional fiber grating is 10n in light having a wavelength near 1.5 μm.
Even when a wavelength bandwidth of m or less is applied, it can be said that this is extremely excellent as compared with a large value of 3 to 6 dB.

[0087]

As described above, the optical communication method according to the present invention has been described in detail with emphasis on the characteristics of the optical dispersion compensating element used in the optical communication method. According to the present invention, FIGS. 5B to 5D are used. By preparing various group velocity delay time-wavelength characteristic curves described above, dispersion compensation of a wide wavelength band called L-band, C-band, and S-band,
Next-order dispersion compensation can be performed by one element. That is, since the dispersion generated in the optical communication transmission line can be effectively compensated for the tertiary dispersion as a whole before being wavelength-separated to each receiving channel, the dispersion compensation for each channel is simplified, and the cost is reduced. High-speed and long-distance communication with high reliability can be realized. The dispersion compensation by the optical dispersion compensating element used in the present invention has a particularly large effect in the third or higher order dispersion compensation, and in addition to the appropriate adjustment of the group velocity delay time-wavelength characteristic, the second order dispersion compensation. Can also be performed.

The greatest effect of the optical communication method of the present invention is that high-speed and long-distance communication using many of the existing optical communication systems has been concerned about the feasibility even if the optical fiber itself is changed. The social and economic effects are enormous in that it is possible to achieve

[Brief description of the drawings]

FIG. 1 is a diagram illustrating optical dispersion compensation according to the present invention.

FIG. 2 is a sectional view of a multilayer film of the present invention.

FIG. 3 is a perspective view of a multilayer film of the present invention.

FIG. 4 is a group velocity delay time-wavelength characteristic curve of the multilayer film of the present invention.

5A and 5B are diagrams illustrating a method of improving group velocity delay time-wavelength characteristics by using a plurality of elements capable of performing dispersion compensation according to the present invention, wherein FIG. Two,
(C) is a graph showing the group velocity delay time-wavelength characteristics of three optical dispersion compensating elements of the present invention in which three elements capable of performing dispersion compensation are connected in series.

6A and 6B are diagrams illustrating an example of an optical dispersion compensating element according to the present invention, wherein FIG. 6A shows two optical dispersion compensating elements, and FIG. 6B shows three optical dispersion compensating elements connected in series; An example in which a compensating element is configured, (C) shows an optical system in which two incident positions of signal light are connected in series along a route of signal light on a multilayer film whose film thickness changes in the in-plane direction of the light. Example of configuring a dispersion compensating element,
(D) is a diagram showing an example in which the optical dispersion compensation element of the present invention is mounted in one case.

FIGS. 7A and 7B are diagrams illustrating a method of compensating for second and third order chromatic dispersion, where FIG. 7A illustrates wavelength-time characteristics and light intensity-time characteristics, and FIGS. FIG.

FIG. 8 is a graph showing dispersion-wavelength characteristics of a conventional optical fiber.

FIG. 9 is a diagram illustrating the intensity and wavelength of signal light when long-distance transmission is performed by a conventional communication method. FIG. 9 is a graph when the communication bit rate is 2.5 Gbps.
(B) is a graph in the case of 10 Gbps, (C) is 40G
It is a graph in the case of bps.

[Explanation of symbols]

100, 200: multilayer film 101, 230: arrow indicating the direction of incident light 102, 240: arrow indicating the direction of emitted light 103, 104, 105, 201, 202, 203: reflecting layer 108, 109, 206, 207: Light transmitting layers 107, 205: substrates 111, 112, 211, 212: cavities 220: light incident surfaces 250, 260: arrows 270, 271 indicating directions of film thickness changes 280, 281, moving directions of incident light incident positions 282: Incident position 1101, 1102, 1103, 2801, 2811
2812, 301 to 312: Group velocity delay time-wavelength characteristic curve 410, 420, 430, 440: Optical dispersion compensation element 411, 412, 421 to 423, 431, 442, 4
43: element capable of performing dispersion compensation 416: multilayer film 415, 4151, 4152, 426, 436, 44
6: Optical fiber 413, 4131, 414, 4141, 424, 42
5,434,435,444,445: Arrow 417: Lens 418: Two-core collimator 441: Case 432,433: Element part capable of performing dispersion compensation 501,502,503,504,511,512,5
13, 514: Graph showing signal light characteristics 520, 530: Transmission line 521: Dispersion compensating fiber 522, 531: SMF 524, 534: Transmitter 525, 535: Receiver 601: SMF dispersion-wavelength characteristic curve 602: Dispersion-wavelength characteristic curve of dispersion compensating fiber 603: Dispersion-wavelength characteristic curve of DSF 7a to 7c, 71a to 71c, 72a to 72c, 73a
~ 73c, 71a1, 71b1, 71c1, 72a1,
72b1, 72c1, 73a1, 73b1, 73c1:
Signal light waveform

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuichi Takushima 2-18-18 Shibafuji, Kawaguchi-shi, Saitama Say K Heights 202 (72) Inventor Mark Kennes Jaboronski 4-6-29 Komaba, Meguro-ku, Tokyo No. K518 (72) Inventor Yuichi Tanaka 3-1-23-1 Niisonanami, Toda City, Saitama Prefecture (72) Inventor Haruki Kataoka 3-1-23 Niisonami, Toda City, Saitama Prefecture Applied Photoelectric Company Laboratory (72) Inventor Kenji Furushiro 3-1-23 Nisonami, Toda City, Saitama Pref.Applied Optoelectronic Laboratory (72) Inventor Shin Shin Higashi 3-1-23 Nisonami, Toda City, Saitama Pref. Laboratory (72) Inventor Kazuya Sato 3-1-23-1 Niisonanami, Toda City, Saitama Prefecture Applied Photoelectric Laboratory (72) Inventor Yamashita Ichiro Toda City, Saitama Prefecture Nizominami 3 chome No. 23 stock company applied photoelectric laboratory F-term (reference) 2H048 GA01 GA07 GA12 GA33 GA51 GA62 5K002 BA02 BA21 CA01 DA02 FA01

Claims (17)

[Claims] In an optical communication method using an optical fiber for a communication transmission line, signal light transmitted through the optical fiber is subjected to chromatic dispersion (hereinafter, referred to as chromatic dispersion) before being wavelength-separated for each receiving channel.
An optical communication method characterized by passing through an optical dispersion compensating element capable of compensating for only (dispersion), and compensating for at least tertiary dispersion of the entire signal light to be transmitted. 2. The optical communication method according to claim 1, wherein
A plurality of elements capable of performing dispersion compensation, or
At least two parts of the element capable of performing dispersion compensation
(Hereinafter, the element capable of performing the dispersion compensation and the element capable of performing the dispersion compensation are collectively referred to as an element capable of performing the dispersion compensation), and are serially arranged along the communication path of the signal light. An optical communication method, wherein the optical communication method is connected to perform dispersion compensation by functioning as the optical dispersion compensation element. 3. The optical communication method according to claim 1, wherein
An optical communication method, wherein a plurality of elements capable of performing dispersion compensation are connected in series along a signal light communication path as the optical dispersion compensation element. 4. The optical communication method according to claim 2, wherein a plurality of elements capable of performing the dispersion compensation are connected in series, and the optical dispersion compensating element comprises one of the incident lights.
An optical communication method, wherein a group velocity delay time-wavelength characteristic curve has at least one extreme value in a wavelength range of 460 to 1640 nm. 5. The optical communication method according to claim 4, wherein
The optical dispersion compensating element constituted by connecting a plurality of elements capable of performing the dispersion compensation in series is 1460 to 1640n.
An optical communication method, wherein a group velocity delay time-wavelength characteristic curve has one extreme value in a wavelength range of m. 6. The optical communication method according to claim 4, wherein at least one of the devices capable of performing dispersion compensation is a device that performs dispersion compensation using a multilayer film, and the multilayer film is an optical communication device. An optical communication method comprising: at least two reflective layers having different reflectances from each other; and at least one light transmitting layer formed between the reflective layers. 7. The optical communication method according to claim 6, wherein
An optical communication method, wherein at least one of the multilayer films has at least one cavity formed by two reflection layers and a light transmission layer formed between the reflection layers. 8. The optical communication method according to claim 4, wherein at least two dispersion compensating elements constituting said optical dispersion compensating element are used. An optical communication method, wherein the number of cavities of the multilayer film is different. 9. The optical communication method according to claim 4, wherein a thickness of at least one laminated film forming the multilayer film is parallel to a light incident surface of the multilayer film. An optical communication method characterized by using an optical dispersion compensating element using a multilayer film that changes in an in-plane direction in a cross section (hereinafter also referred to as an in-plane direction). 10. The optical communication method according to claim 9, wherein at least one of the at least one multilayer film has a thickness change direction in which a film thickness changes in an incident plane direction of the multilayer film. Characteristic optical communication method. 11. The optical communication method according to claim 9, wherein the adjusting means adjusts the thickness of at least one of the multilayer films by engaging with the element capable of performing the dispersion compensation. Alternatively, there is provided an optical communication method, comprising means for changing a light incident position on an incident surface of the multilayer film. 12. The optical communication method according to claim 5, wherein an extremum of a group velocity delay time-wavelength characteristic curve of the optical dispersion compensating element is a dispersion of each signal light generated by a transmission line mainly including an optical fiber. An optical communication method, wherein the peak value is not larger than a minimum value of the peak value. 13. The optical communication method according to claim 12, wherein the wavelength giving the extreme value of the group velocity delay time-wavelength characteristic curve of the optical dispersion compensating element and the minimum peak value of the dispersion of each signal light. The optical communication method is characterized in that the difference between the wavelengths giving the difference is within 6 nm. 14. The optical communication method according to claim 4, wherein at least one of the optical dispersion compensating elements constituting the optical dispersion compensating element is capable of performing dispersion compensation. When the film is considered as an optical path length for light having a central wavelength λ of incident light (hereinafter, also simply referred to as an optical path length), the film thickness of each layer of the multilayer film (hereinafter, also simply referred to as film thickness or film thickness). Is an integral multiple of λ / 4 ± 1%
(Hereinafter, a film thickness of an integral multiple of λ / 4 ± 1% is also referred to as a film thickness of an integral multiple of λ / 4, or a film thickness of an integral multiple of λ / 4). A thick multilayer film, and
The multilayer film has a film thickness of 1/4 times λ (hereinafter referred to as a film thickness of 倍 times λ in the meaning of 膜厚 times ± 1% of λ), and has a higher refractive index. A layer (hereinafter also referred to as a layer H) and a layer having a film thickness of 倍 of λ and a lower refractive index (hereinafter also referred to as a layer L)
Are combined and a plurality of layers are combined, and the layer H
Is formed of a layer made of any one of Si, Ge, TiO ₂ , Ta ₂ O ₅ , and Nb ₂ O ₅ . 15. The optical communication method according to claim 14, wherein the layer L is formed using a material having a lower refractive index than the material used for the layer H. Method. 16. The optical communication method according to claim 15, wherein said layer L is formed of a layer made of SiO ₂ . 17. The optical communication method according to claim 4, wherein the multilayer film has at least five types of laminated films having different optical properties (ie, light reflectance, film thickness, etc.). Wherein the multilayer film has at least three types of reflective layers including at least two types of reflective layers having different light reflectivities from each other. , Having at least two light transmission layers in addition to the three types of reflection layers, each one of the three types of reflection layers and each one of the two light transmission layers are alternately arranged, The multilayer film is, in order from one side in the thickness direction of the film, a first layer that is a first reflective layer, a second layer that is a first light transmitting layer, and a third layer that is a second reflective layer.
A first layer, a fourth layer as a second light transmitting layer, and a fifth layer as a third reflective layer. Is considered as an optical path length (hereinafter, also simply referred to as an optical path length) with respect to light having a center wavelength λ, the thickness of each layer of the multilayer film (hereinafter, also simply referred to as a film thickness or a film thickness) is λ / 4. Integer multiple of ± 1
% Value (hereinafter, an integral multiple of λ / 4, or λ / 4
And the multilayer film has a thickness of 1/4 times λ (hereinafter, 倍 of λ in the meaning of / times ± 1% of λ). And a layer having a higher refractive index (hereinafter, also referred to as a layer H) and a layer having a lower refractive index of １ times the film thickness of λ (hereinafter, also referred to as a layer L). And the multilayer film A is formed of the five-layer laminated film, that is, the first to fifth layers.
The layer is a layer (hereinafter, referred to as HL) in which one layer is combined with each of layers H and L in order from one side in the thickness direction of the multilayer film.
(A layer obtained by combining the layer H1 layer and the layer L1 layer is referred to as an HL layer 1 set; the same applies hereinafter).
A first layer formed by lamination, a layer obtained by combining layers H and H (that is, a layer formed by laminating two layers H. Hereinafter, H
H) (10 layers).
The third layer is formed by laminating one set of layers L and 7 sets of HL layers, the fourth layer is formed by stacking 38 sets of HH layers, and the third set of layers L is formed of one layer and HL. A multilayer film formed by laminating 13 sets of layers and a fifth layer formed by laminating 13 sets; and a multilayer film B formed by laminating 10 sets of HH layers of the multilayer film A. Instead of two layers, the second layer is a layer obtained by combining three sets of HH layers and a layer L and a layer L in order from one side in the thickness direction of the film in the same direction as that of the multilayer film A (that is, a layer combining the layers L and L). , A layer formed by laminating two layers L (hereinafter, also referred to as LL layer), three sets of HH layers, three sets of LL layers, two sets of LL layers, and one set of HH layers. The multilayer film is formed of a multilayer film, and the multilayer film C includes 38 sets of the HH layers of the multilayer film A or B. Instead of the fourth layer formed as a layer, the fourth layer has three sets of HH layers and LL of LL in order from one side in the thickness direction of the film in the same direction as that of the multilayer film A. 3 sets of layers, 3 sets of HH layers, 3 sets of LL layers,
3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers,
3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers,
The HH layer is a multi-layer film formed by laminating two sets of layers in this order, and the multi-layer film D is a five-layer laminated film, that is, the first to fifth layers.
The layers are layers (hereinafter referred to as LH) in which layers are combined one by one in the order of layer L and layer H from one side in the thickness direction of the multilayer film.
), A first layer formed by stacking five sets of
A second layer formed by stacking seven sets of LL layers, a third layer formed by stacking one layer H and seven sets of LH layers.
Layer, a fourth layer configured by stacking 57 sets of LL layers,
The layer H is a multilayer film composed of a fifth layer formed by laminating one layer and 13 sets of LH layers, and the multilayer film E is a laminated film of the five layers, that is, the first to the first layers. 5
The layers are HL in order from one side in the thickness direction of the multilayer film.
A first layer formed by laminating two sets of HH layers, a second layer formed by laminating 14 sets of HH layers, one layer L and one layer H
HH, a third layer composed of six sets of L layers
Layer L, which is formed by laminating 24 sets of
Layer 13 composed of 13 sets of layers and HL layers
The second layer is a multilayer film formed by laminating 14 sets of the HH layers of the multilayer film E instead of the multilayer film F. In the order from one side in the thickness direction of the film in the same direction as in E, three sets of HH layers, three sets of LL layers, three sets of HH layers, three sets of LL layers, and three sets of HH layers Two sets, one set of LL layers, and one set of HH layers are laminated in this order to form a multilayer film formed of a laminated film, and the multilayer film G is the HH of the multilayer film E or F. Layer 2
Instead of the fourth layer formed by laminating four sets, the fourth layer is composed of three sets of layers of HH and LL in order from one side in the thickness direction of the film in the same direction as the multilayer film E. 3 layers, 3 sets of HH layers, 3 sets of LL layers,
3 sets of HH layers, 3 sets of LL layers, 3 sets of HH layers, 3 sets of LL layers, 2 sets of HH layers,
One set of the LL layer and one set of the HH layer are laminated in this order to form a multilayer film formed of a laminated film. 5
The first layer, L, is formed by laminating four sets of layers L, LH in order from one side in the thickness direction of the multilayer film.
A second layer composed of nine sets of L layers and a layer H
The third layer is formed by laminating six sets of layers and LH layers.
Layer, a fourth layer configured by stacking 35 sets of LL layers,
When the layer H is a multilayer film formed of a fifth layer formed by laminating one layer and 13 sets of LH layers, the multilayer film includes any one of the multilayer films A to H. An optical communication method, comprising: