JP2002214430A - Optical dispersion compensating element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide an optical dispersion compensating element having such superior group velocity retardation time-wavelength characteristics that it can perform satisfactory dispersion compensation, particularly tertiary dispersion compensation even in a wide wavelength range in which a conventional element cannot be put to practical use as a miniature element easy to use, ensuring a small loss and having high reliability in a state suitable for mass production. SOLUTION: The miniature highly stable optical dispersion compensating element ensuring a small loss and usable in a wide band is obtained by disposing multilayer films having dispersion compensating function on the opposite faces of a substrate capable of transmitting signal light in such a way that the planes of incidence confront each other. Dispersion compensation is performed by reflecting signal light a plurality of times between the opposite multilayer films.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In the following description of the present invention, optical dispersion compensation is simply referred to as dispersion compensation, optical dispersion compensation element is also simply referred to as dispersion compensation element, and optical dispersion compensation method is simply referred to as dispersion compensation method. It is also called a compensation method.

[0002] The present invention uses an optical fiber (hereinafter, simply referred to as an optical fiber) for a transmission path,
The signal light is not limited to this. For example, it can compensate second-order or higher (hereinafter described) chromatic dispersion (hereinafter, also simply referred to as dispersion) generated in optical communication using light having a wavelength of about 1.55 μm or the like. Element (hereinafter, an element capable of compensating secondary dispersion is also referred to as an element capable of changing secondary dispersion, or a secondary dispersion compensating element. An element capable of compensating for tertiary dispersion described later. Similarly, the element which can change the tertiary dispersion, or
Also called a third-order dispersion compensating element. ).

[0003] The dispersion compensating element of the present invention may be the above-described third-order dispersion compensation, may be configured to be capable of secondary dispersion compensation, or may be mounted in a case. In some cases, it may be a so-called chip or wafer that is not mounted on a case.

[0004] The dispersion compensating element of the present invention includes all of these forms, and can take various forms in accordance with the status of use or the purpose of sale.

In the present invention, the second-order dispersion compensation is described in FIG.
(A) to compensate for the dispersion gradient 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 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 range of use. Under such an environment, dispersion generated when transmitting an optical fiber becomes a serious problem, and various attempts have been made to compensate for dispersion. At present, quadratic 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 dispersion during transmission, and compensation for tertiary dispersion is becoming an issue.

A conventional second-order dispersion compensation method will be described below with reference to FIGS.

FIG. 14 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). Referring to FIG.
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, 603 is a graph showing the dispersion-wavelength characteristic of the DSF, and the vertical axis represents the dispersion.
5 is a graph in which the horizontal axis represents wavelength.

As apparent from FIG. 14, in the SMF, the dispersion increases as the wavelength of light input (hereinafter also referred to as “incident”) to the fiber increases from 1.3 μm to 1.8 μm, and the dispersion compensating fiber is increased. In, the dispersion decreases as the wavelength of the input light (hereinafter, also referred to as incident light) increases from 1.3 μm to 1.8 μm. In the DSF, the dispersion decreases as the wavelength of the input light increases from 1.2 μm to around 1.55 μm, and the wavelength of the input light becomes 1.55 μm.
The dispersion increases as the length increases from around m 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. 13A and 13B are diagrams mainly illustrating a second-order dispersion compensation method. FIG. 13A shows the wavelength-time characteristic and the light intensity-time characteristic, and FIG. 13B shows the dispersion in the transmission line using the SMF. FIG. 3C is a diagram illustrating a transmission example in which second-order dispersion compensation is performed using a compensating fiber, and FIG. 4C is a diagram illustrating a transmission example in a transmission path including only an SMF.

In FIG. 13, reference numerals 501 and 511 denote graphs showing the characteristics of the signal light before being input to the transmission line.
0 indicates a transmission path constituted by the SMF 531;
2 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 SMF 522, 503 and 5
13 is a graph showing the characteristics of the signal light output from the transmission line 520 after the signal light having the characteristics shown in the graphs 501 and 511 is transmitted through the transmission line 520. Symbols 504 and 5
Reference numeral 14 denotes the characteristic of the signal light when the signal light having the characteristics shown in the graphs 501 and 511 is transmitted through the transmission line 520 and output from the transmission line 520, and after the desired third-order dispersion compensation described below is performed by the present invention. FIG.
Almost coincides with 1 and 511. 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 are graphs in which the vertical axis represents light intensity and the horizontal axis represents time (or time). Reference numerals 524 and 534 are transmitters, 525 and 5
35 is a receiver.

As described above, in the conventional SMF, the dispersion increases as the wavelength of the signal light increases from 1.3 μm to 1.8 μm.
This causes group velocity delay due to dispersion. 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. 13B, dispersion is compensated (or also referred to as correction) using a dispersion compensating fiber.

A conventional dispersion compensating fiber has a wavelength of 1.3.
In order to solve the problem of SMF in which the dispersion increases as the length increases from μm to 1.8 μm, as described above, the dispersion is reduced as the wavelength increases from 1.3 μm to 1.8 μm. Have been.

The dispersion compensating fiber can be used by connecting a dispersion compensating fiber 521 to an SMF 522, for example, as shown by a transmission line 520 in FIG. In the transmission line 520, the signal light is delayed more on the long wavelength side than on the short wavelength side in the SMF 522, and the dispersion compensating fiber 52
As shown in graphs 503 and 513, the short wavelength side of FIG.
The change amount can be suppressed smaller than the changes shown in 02 and 512.

However, in the above-described conventional method of compensating for the second-order chromatic dispersion using the 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 to the shape of the graph 503 is the limit. 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.

[0018] These phenomena are becoming serious problems such as the inability to accurately receive signals as the need for longer transmission distances and higher communication speeds in optical communication increases.

For example, if the communication bit rate is 10 Gbps
s (10 Gigabits per second) or higher,
These phenomena are considerably worried, and particularly as a very serious problem in communication at a communication bit rate of 40 Gbps or more.

In such high-speed communication,
It is considered difficult to use the conventional optical fiber communication system. For example, it is necessary to change the material of the optical fiber itself, and this is a serious problem from the economic viewpoint of system construction.

[0021]

It is difficult to perform such a dispersion compensation only by a second-order dispersion compensation, and a third-order or higher dispersion compensation is required.

Conventionally, DS has been used as an optical fiber in which second-order dispersion is reduced for light having a wavelength of around 1.55 μm.
F, but in this fiber, as described above with reference to FIGS.
As is clear from the characteristics described above, the third-order dispersion compensation, which is an object of the present invention, cannot be performed.

In realizing high-speed communication and long-distance communication of optical communication, third-order dispersion is gradually recognized as a major problem, and compensation thereof is becoming an important issue. Many attempts have been made to solve the third-order dispersion compensation problem, but no third-order dispersion compensation element or compensation method that can sufficiently solve the conventional problems has yet to be put into practical use.

The multilayer film such as a dielectric material proposed by the present inventors as an example of the optical dispersion compensating element used for the above-mentioned third-order dispersion compensation succeeds in the third-order dispersion compensation and greatly increases the conventional optical communication technology. I was able to move forward.

However, for example, if the communication bit rate is 40
In order to ideally perform third-order dispersion compensation when the speed is increased, such as Gbps or 80 Gbps, or to sufficiently perform third-order dispersion compensation in a multi-channel optical communication, it is necessary to use 2 A dispersion compensating element capable of sufficiently compensating the second and third-order or higher dispersion is desired.

As one of the proposals, the present inventors have proposed a third-order dispersion compensator capable of adjusting the wavelength band of the group velocity delay and the delay time of the group velocity delay.
In particular, as one method of inexpensively putting a third-order or higher-order dispersion compensating element suitable for the wavelength of each channel into practical use, a wavelength-variable (that is, a dispersion-compensating target wavelength selectable) dispersion compensating element is proposed by the present inventors. Suggested by

However, it is extremely difficult to obtain a dispersion compensating element having a group velocity delay time-wavelength characteristic that can perform sufficient dispersion compensation in a sufficiently wide wavelength range by using these dispersion compensating elements alone.

As a method of obtaining a dispersion compensating element having a group velocity delay time-wavelength characteristic capable of performing good dispersion compensation over a wide wavelength range, an element capable of performing dispersion compensation proposed by the present inventors is called a signal. There is a method of connecting a plurality of light beams in series in an optical path of light. In this case, if elements capable of performing dispersion compensation are connected in series via, for example, an optical fiber collimator having an optical fiber and a lens, the shape and dimensions of the dispersion compensation element as a whole become large, and the loss is further reduced. It will be multiplied. Therefore, depending on the use conditions of the dispersion compensating element, it is a big problem how the loss of the dispersion compensating element can be reduced.

Further, when it is necessary to change the dispersion compensation according to the dispersion state of the signal light, the light dispersion compensating element must be changed. However, it is very difficult to change the content of the optical dispersion compensating element in a wide wavelength band of 30 nm and 40 nm.

A plurality of elements capable of performing dispersion compensation are connected in series in the optical path, and for example, 30 nm
In the case of configuring an optical dispersion compensating element that can be used in a wide wavelength band as described above, it is desired to realize a method of configuring a dispersion compensating element that has a small loss and is easy to use.

To solve this problem, the inventors of the present invention solve the problem by using at least one set of a pair of optical dispersion compensating elements arranged with their incident surfaces facing each other. Type optical dispersion compensator was proposed.
As a result, the loss reduction and miniaturization of the optical dispersion compensating element have been greatly improved.

However, when using a plurality of sets of a pair of optical dispersion compensating elements arranged with the incident surfaces facing each other, or when using another place of the same element, any one of the pair of optical dispersion compensating elements is used. Since the optical fiber collimator is used when the light emitted from the optical fiber is again incident on the optical dispersion compensating element, the size and the loss increase depending on the specifications required for the optical dispersion compensating element.

The present invention has been made in view of the above points, and it is an object of the present invention to provide sufficient dispersion compensation over a wide wavelength range which has not been practically used in the past, and particularly, tertiary dispersion compensation. To provide an optical dispersion compensator having excellent group velocity delay time-wavelength characteristics that can perform the above operation in a small size, easy to use, low loss, high reliability, suitable for mass production, and inexpensively. It is in.

[0034]

SUMMARY OF THE INVENTION In order to achieve the object of the present invention, an optical dispersion compensating element according to the present invention is an optical dispersion compensating element which is capable of compensating chromatic dispersion by using an optical fiber for communication using a communication transmission line. A dispersion compensating element, a substrate capable of transmitting incident light, a multilayer film formed on at least a pair of opposing surfaces of the substrate, and an incident light incident portion provided on the substrate; The multilayer film formed on the pair of opposing surfaces can compensate for wavelength dispersion of light incident from the substrate side.

In the optical dispersion compensating element according to the present invention, each of the multilayer films formed on the pair of opposing surfaces has at least two reflective layers and at least a multilayer film formed at a position sandwiched between the pair of reflective layers. A single light transmitting layer, and the reflectance of the reflection layer constituting the multilayer film with respect to the incident light becomes maximum or maximum as the layer becomes closer to the layer farther from the substrate. The multi-layer film is characterized in that the multilayer film is formed so as to gradually increase up to the point where a value layer appears.

The light dispersion compensating element of the present invention provides a greater effect by disposing an antireflection film on the incident light incident portion of the substrate.

An example of the optical dispersion compensating element of the present invention is such that the incident light incident on the substrate from the incident light incident portion of the substrate is at least one of the multilayer films formed on the pair of opposing surfaces. The multi-layer film is characterized in that the multi-layer film is arranged so as to perform dispersion compensation by repeating the alternate incidence on the other multi-layer film a plurality of times.

In the optical dispersion compensating element of the present invention, a light emitting portion can be provided on the substrate at a position different from the position of the incident light incident portion, and a light emitting portion is provided outside the substrate and near the light emitting portion. It is possible to adopt a structure in which a reflector is arranged, and the reflector can be a Faraday rotator reflector.

In the example of the optical dispersion compensating element of the present invention,
The substrate may have a structure in which a reflector for the incident light is provided at a position different from the position of the incident light incident portion, and the reflector may be a 100% reflective film.

An example of the optical dispersion compensating element of the present invention is such that the incident light incident on the substrate from the incident light incident portion of the substrate alternately passes through the inside of the substrate to the multilayer film formed on the opposing surface of the substrate. The same as the optical path from the incident light incidence part to the reflector after the incident light is subjected to dispersion compensation and travels through the substrate to reach the reflector, and is reflected by the reflector. It is characterized in that the light reaches the incident light incident part through an optical path and exits from the incident light incident part.

In the example of the optical dispersion compensating element of the present invention, at least two light emitting portions are provided on the substrate at positions different from the position of the incident light incident portion, and at least one near the light emitting portion is provided. A reflector may be disposed at least, and at least one of the reflectors is a Faraday rotator reflecting mirror, so that the signal light traveling in the substrate is received in the process of performing dispersion compensation in the multilayer film. The change that occurs in the polarization component of the signal light can be minimized.

An example of the optical dispersion compensating element of the present invention is such that at least one of the reflectors is incident on the reflector and travels through the substrate (hereinafter, also referred to as incident light A). Can be a reflector that reflects the incident light A in a direction different from the direction opposite to the direction in which the light has traveled, and at least one of the reflectors is a light that enters the reflector (hereinafter, referred to as a light).
(Referred to as incident light B) is a reflector that reflects the incident light B in a direction opposite and parallel to the direction in which the incident light B travels.

An example of the light dispersion compensating element according to the present invention is characterized in that an antireflection film is provided on the emission section.

In the optical dispersion compensating element of the present invention, the substrate may be provided with at least one incident light incident portion different from the incident light incident portion.

A great effect can be brought about by forming the substrate of the optical dispersion compensating element of the present invention from optically isotropic materials.

When the substrate of the light dispersion compensating element of the present invention is made of glass, the light dispersion compensating element suitable for mass production can be obtained.

In the optical dispersion compensating element of the present invention, it is preferable that the reflectance of the reflection layer having the maximum or maximum reflectance constituting the multilayer film formed on the substrate is 99.5% or more. Greater effects can be obtained by setting the reflectance to 8% or more, and it is most preferable that the maximum or maximum reflectance is set to 100%.

In the example of the light dispersion compensating element of the present invention, by making at least one reflecting surface of the reflector movable, the element can be used for a wide range of purposes with good characteristics.

Further, in an example of the optical dispersion compensating element of the present invention, the thickness of at least one laminated film constituting at least one multilayer film is such that an in-plane direction in a cross section parallel to a light incident surface of the multilayer film is provided. (Hereinafter, also referred to as a change in film thickness) in each of the at least one pair of the opposing multilayer films. The thickness of at least one light transmitting layer is configured to be different from each other in a changing direction, or the thickness of at least one light transmitting layer of each of the at least one pair of the multilayer films disposed to face each other is reduced. By configuring the optical dispersion compensating elements to change in opposite directions, various characteristics of the optical dispersion compensating element can be realized.

The optical dispersion compensating element of the present invention is characterized in that it is an optical dispersion compensating element capable of mainly compensating for third-order dispersion.

In the example of the optical dispersion compensating element of the present invention,
The shape of the optical dispersion compensating element in the vicinity of the extreme value of the group velocity delay time-wavelength characteristic curve can be asymmetric.

[0052]

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 in the description of 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. 1 is a diagram for explaining a method of compensating dispersion generated in communication using an optical fiber for a transmission line by an optical dispersion compensating element. Reference numeral 1101 denotes a second-order dispersion of signal light transmitted through the transmission line. 1103 is a group velocity delay time-wavelength characteristic curve showing the third order dispersion of the signal light remaining after the above, and 1102 is a group velocity delay time-wavelength characteristic curve of the optical dispersion compensating element capable of compensating the third order dispersion. Is a group velocity delay time-wavelength characteristic curve between the compensation target wavelength bands λ1 to λ2 after compensating the dispersion of the signal light having the dispersion characteristic of the curve 1101 with the dispersion compensating element having the dispersion characteristic of the curve 1102,
The vertical axis is the group velocity delay time, and the horizontal axis is the wavelength.

FIGS. 2 to 4 show the respective optical dispersion compensating elements used in the present invention (in the present invention, the element itself capable of performing dispersion compensation and the element constituted by them are widely referred to as an optical dispersion compensating element. Due to the above-mentioned necessity, for example, each element constituting the composite type optical dispersion compensating element of the present invention may be referred to as an optical dispersion compensating element. When it is not particularly necessary to distinguish the compensating element alone, the optical dispersion compensating element alone or the optical dispersion compensating element may be referred to as the optical dispersion compensating element alone. When it is necessary to distinguish between the elements, the element may be referred to as an optical dispersion compensating element alone, and as described later, the optical dispersion compensating element is composed of a plurality of elements capable of performing dispersion compensation. Place In the case where the element itself capable of performing dispersion compensation as a constituent element is described or defined, it is also referred to as an element capable of performing dispersion compensation.) FIG. 2 is a cross-sectional view of a multilayer film described later, FIG. 3 is a perspective view of a multilayer film having a changed thickness, and 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 a tertiary light dispersion compensating element used in the present invention. In FIG. 2, reference numeral 100 denotes a multilayer film as an example of the optical dispersion compensating element used in the present invention, 101 denotes an arrow indicating the direction of incident light, 102 denotes an arrow indicating the direction of output light,
03 and 104 are reflective layers having a reflectance of less than 100% (hereinafter referred to as “reflective layers”).
Reference numeral 105 denotes a reflection layer having a reflectivity of 98 to 100%, reference numerals 108 and 109 denote light transmission layers (hereinafter, also simply referred to as transmission layers), and reference numerals 111 and 112 denote cavities. Reference numeral 107 denotes a substrate, for example,
BK-7 glass is used.

The reflectivity R (103), R (104), R (105) of each of the reflection layers 103, 104, 105 in FIG.
R (103) ≦ R (104) ≦ R (105). It is preferable in terms of mass production that the reflectance of each reflective layer be set to be different from each other at least between adjacent reflective layers with the light transmitting layer interposed therebetween. That is, the central wavelength λ of the incident light is from the side where the incident light is incident toward the thickness direction of the multilayer film.
Is formed so that the reflectance of each reflective layer with respect to It is particularly preferable that the reflectance of each reflective layer with respect to the light having the wavelength λ is 60% ≦ R (103) ≦ 77.
%, 96% ≦ R (104) ≦ 99.8%, 98% ≦ R
(105), R (103), R (10)
4) By configuring so as to satisfy the magnitude relationship of R (105), a group velocity delay time-wavelength characteristic curve as shown in FIGS. 4 and 5 described later can be obtained. And R
It is more preferable that (103) <R (104) <R (105), and if R (105) is close to 100% or 1
It is more preferably set to 00%, and the performance of the optical dispersion compensating element used in 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 each of the reflective layers so that the intervals are different when considering the optical path length between the adjacent reflective layers. Preferably, the design condition of the reflectance of each reflective layer can be relaxed, and the film thickness is one quarter of the wavelength λ.
(I.e., a film having a thickness of an integral multiple of λ / 4) can form a multilayer film used in the tertiary light dispersion compensating element used in the present invention. A third-order optical dispersion compensating element having excellent properties can be provided at low cost.

The unit film of the multilayer film has a wavelength λ.
It is described that the error is most preferably almost zero, but as described above, within a range of an error allowable in film formation in mass production, λ /
4, specifically, λ / 4 ± 10% (however, this does not mean that the thicknesses of all the films may simultaneously vary in the direction of large errors within ± 10%, but some Even if the film thickness of the film is within ± 10% and the error fluctuates in a large direction, many other films vary within ± 3% or cancel each other's bad influence on characteristics. ,
Meaning within a range not to impair the gist of the present invention,
Depending on the specification, it may mean a narrower error range as described later. ) Means the film thickness of λ / 4 in the present invention, and when the film thickness of λ / 4 ± 1% is implemented as the film thickness of λ / 4, the present invention has a particularly great effect in this range. Emit. In particular, the thickness of the unit film is λ / 4 ±
By setting it to 0.5% (λ / 4 in this case means λ / 4 without error), it is possible to form a highly reliable multilayer film with little variation without impairing mass productivity.
An optical dispersion compensating element as described later with reference to FIGS. 5 and 7 to 9 can be provided at low cost.

The multilayer film of the present invention has a thickness of λ.
There is a part that the unit film of / is formed by lamination, but this is to form a multilayer film by repeating the method of forming one unit film and then forming the next unit film. However, the present 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 in time. For example, it is included in a multilayer film composed of a laminated film having a film thickness that is an integral multiple of λ / 4. Then, some of the multilayer films of the present invention can be formed 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 thickness of the multilayer film 100 is changed in the in-plane direction of the multilayer film 100 in FIG.

In FIG. 3, reference numeral 200 denotes a multilayer film as an example of a light dispersion compensating element used in the present invention, and 201 denotes a first film.
202, a second reflective layer, 203, a third reflective layer, 205, a substrate, 206, a first light transmitting layer, 207, a second light transmitting layer, 211, a first cavity, 212 Is a second cavity, 220 is a light incident surface, 230 is an arrow indicating the direction of incident light, 240 is an arrow indicating the direction of output light,
Reference numeral 250 denotes an arrow indicating the first film thickness change direction, and 260 denotes the second film thickness change direction.
Arrows 270 and 271 indicate the direction in which the incident position of the incident light is moved.

In FIG. 3, a substrate 20 made of, for example, BK-7 glass (trade name of Schott, Germany) or the like is used.
5, a third reflection layer 203 and a second light transmission layer 20
7, the second reflective layer 202, the first light transmitting layer 206, the first
Are sequentially formed.

The thickness of the first light transmitting layer 206 in the in-plane direction (the film thickness, the same applies hereinafter) changes so as to change in the direction indicated by the arrow 250 in FIG.
The multilayer film is formed such that the thickness in the in-plane direction changes in the direction indicated by the arrow 260. 1st to 3rd
The thickness and the configuration of the reflection layer are such that the wavelength when the resonance wavelengths of the first and second cavities coincide is the center wavelength λ of the incident light.
, The reflectances of the first, second, and third reflective layers are R (103), R (104), and R (105).
That is, the reflection layer 201,
02 and 203 are R (201) and R (2
02) and R (203), R (201) ≦ R
The film is formed to have a film thickness that satisfies (202) ≦ R (203).

The first reflective layer 201 shown in FIG. 3 is formed on an appropriate substrate capable of transmitting incident light, and the first transparent layer 206 and the second reflective layer 201 are formed thereon. 20
2, the second transmission layer 207 and the third reflection layer 203 are formed in this order, and the reflectance of each reflection layer is R (201) ≦ R
The effect of the present invention can be exhibited even if it is configured so that (202) ≦ R (203). In this case, light incident on the multilayer film is incident from the substrate side.

FIG. 4 shows that incident light is incident on the incident surface 220 of the multilayer film 200 as an example of the optical dispersion compensating element of the present invention in the direction of arrow 230 in FIG. The following describes how the group velocity delay time-wavelength characteristic curve changes when the incident position of the incident light is moved in the direction of the arrow 270 or 271 in FIG. 3 as described later.

FIG. 4 shows a group velocity delay time-wavelength characteristic curve when incident light having a center wavelength λ is incident on the incident positions 280 to 282 in FIG. 3, the vertical axis represents the group velocity delay time, and the horizontal axis represents the group velocity delay time. Wavelength.

By appropriately selecting the conditions for changing the film thickness in the directions indicated by arrows 250 and 260 of the reflection layers 201 to 203 and the light transmission layers 206 and 207 in FIG. When the position is moved in the direction indicated by the arrow 270, the band center wavelength λ0 of the group velocity delay time-wavelength characteristic curve (for example, FIG. 4
(The wavelength giving an extreme value in the group velocity delay time-wavelength characteristic curve 2801 having a substantially symmetrical shape) changes, and when the incident position is moved from each position in the direction indicated by the arrow 271, the wavelength .lambda.0 is a value in substantially the same range, and the shape of the group velocity delay time-wavelength characteristic curve can be changed like the curves 2811 and 2812 in FIG. 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, 2811 and 2812 is set, for example, at an appropriate wavelength in the graph of FIG. 4 for the purpose of dispersion compensation.
For example, 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. Also, curves 2801 to 2812 and curve 2801
It is natural that the correspondence between the characteristic points of the curve such as the extremal wavelength between the curves 2811 and 2812 and the shape of the curve such as the curve between the curves 2811 and 2812 need not be described in advance. is there.

As described above, for example, first, the band center wavelength λ corresponding to the center wavelength λ of the incident light to be dispersion-compensated
In order to make 0 coincide, the incident position of the incident light is indicated by an arrow 270.
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, the dispersion state of the incident light, is determined, for example, as shown in FIG. Select from each curve, etc., and
By selecting the incident position in the direction indicated by the arrow 271 as, for example, each point indicated by reference numerals 280 to 282, the dispersion compensation required for the signal light can be effectively performed.

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

Although the "element capable of performing dispersion compensation" used in the present invention has been described with reference to FIGS. 2 to 4, if the "element capable of performing dispersion compensation" is used, The fact that the third-order dispersion can be compensated to some extent is apparent from the description of the curves in FIGS. Also,
As can be clearly understood from the above description, the "element capable of performing dispersion compensation" itself can also be a light dispersion compensation element constituting the composite light dispersion compensation element of the present invention.

However, the wavelength bandwidth of the dispersion compensation that can be compensated by the “element capable of performing the dispersion compensation” alone is, for example, 1.5 times for the signal light whose wavelength is around 1.55 μm.
nm, the extreme value of group velocity delay time is 3-6ps
(Picoseconds) in many cases, and by changing the configuration conditions of the multilayer film, the group velocity delay time-wavelength characteristic curve having a bandwidth of about 0.5 to 3 nm and a peak value of the group velocity delay time of about 2 to 10 ps is obtained. Can be realized. However, the wavelength band of the dispersion compensation is set to 10n in order to correspond to the optical communication of many channels.
When the width is widened to m or 30 nm, the peak value of the group velocity delay time becomes an extremely small value, and it is difficult to obtain the group velocity delay time enough to sufficiently perform dispersion compensation, and it is easy to use for actual communication and widely used. Further improvement is desirable for use. Therefore, the present invention will be described in more detail with reference to FIGS.

FIG. 5 is a diagram for explaining a method of improving the group velocity delay time-wavelength characteristic by using a plurality of elements capable of performing dispersion compensation as described above.
FIG. 5A shows the group velocity delay time-wavelength characteristic when only one element capable of performing dispersion compensation is used in the present invention.
(B) shows that the shape of the group velocity delay time-wavelength characteristic curve is almost the same,
Two devices capable of performing dispersion compensation having different wavelengths (hereinafter also referred to as extreme values) giving an extreme value are connected in series along the optical path of the incident light (hereinafter, along the optical path of the incident light). The connection of two in series is also referred to as simply connecting two in series. The same applies to the case of three in series, four in series, etc.) The group velocity delay time of the optical dispersion compensating element used in the present invention -Wavelength characteristics, FIG. 5 (C) shows group velocity delay time-
FIG. 5 shows the group velocity delay time-wavelength characteristic of the optical dispersion compensating element used in the present invention in which three elements capable of performing dispersion compensation having different extremal wavelengths having substantially the same shape of the wavelength characteristic curve are connected in series. In D), one of the three elements connected in series and capable of performing dispersion compensation can perform dispersion compensation in which the shape of the group velocity delay time-wavelength characteristic curve and the extreme value wavelength are different from those of the other two elements. It is a graph which respectively shows the group velocity delay time-wavelength characteristic of the optical dispersion compensating element used in the present invention in which three elements having the characteristics as shown in the figure are connected in series. The horizontal axis is the wavelength. And
The basis of the optical dispersion compensation method of the present invention is, for example, as shown in FIG.
For example, a composite type optical dispersion compensating element as described later with reference to FIGS. 7 and 8 is constructed by using the optical dispersion compensating element having the characteristics shown in FIGS. In an appropriate place such as an optical transmission line with a compensating element, for example, a signal light such as an amplifier, a receiver, a wavelength demultiplexer, and various devices such as a relay station connected in series to an optical fiber or provided in the transmission line. And compensating the dispersion of the signal light by making the signal light incident on the optical dispersion compensating element.

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. A group velocity delay time-wavelength characteristic curve when two elements that can perform dispersion compensation with different shapes of characteristic curves and different extreme wavelengths are connected in series;
Reference numeral 311 denotes a group velocity delay time-wavelength characteristic when three elements capable of performing dispersion compensation having substantially the same group velocity delay time-wavelength characteristic curve and different extremal wavelengths used in the present invention are connected in series. Curve 312 indicates that one of three elements connected in series and capable of performing dispersion compensation performs dispersion compensation in which the shape of the group velocity delay time-wavelength characteristic curve and the extreme value wavelength are different from those of the other two elements. 5 is a group velocity delay time-wavelength characteristic curve when three elements having the characteristics shown in FIG. In FIG. 5A, the symbol a indicates the bandwidth of the wavelength band to be compensated for dispersion, and b indicates the magnitude of the extreme value of the group velocity delay time (hereinafter, also simply referred to as the extreme value). Curves 302-307
309 and the extreme value of the group velocity delay time are almost the same, and the curve 308 shows that the bandwidth of the wavelength band to be compensated for dispersion is narrower than the curves 307 and 309 and the extreme value of the group velocity delay time. Is a large group velocity delay time-wavelength characteristic curve. The extreme wavelengths of the curves 301 to 309 are as follows:
As shown, each is different.

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
The bandwidth of the wavelength band to be dispersion-compensated is about 1.8 times, and the extreme value of the group velocity delay time of the group velocity delay time-wavelength characteristic curve 311 is equal to that of one element capable of performing dispersion compensation. The bandwidth of the wavelength to be dispersion-compensated is about 2.3 times that of the case, and about 2.5 times that of a single element capable of performing dispersion compensation. In FIG. 5D, the group velocity delay time−
The extreme value of the group velocity delay time of the curve of the wavelength characteristic curve 312 is about three times as large as the case of each of the elements 307 and 309 capable of performing dispersion compensation. This is about 2.3 times that in the case of one element 307 and 309 respectively.

The extreme value of the group velocity delay time of the group velocity delay time-wavelength characteristic curve of the element capable of performing dispersion compensation using the multilayer film described with reference to FIGS. The bandwidth varies depending on the configuration conditions of each reflection layer and each light transmission layer of the multilayer film.
The dispersion compensation target wavelength band such as the curve 307 in (D) 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 can be realized by, for example, combining a group velocity delay time-wavelength characteristic curve in which the bandwidth of the wavelength band is narrow but the extreme value of the group velocity delay time is large.

Examples of the multilayer film used in the element capable of performing such dispersion compensation include, for example, the multilayer films A to H described in the section “Means for Solving the Problems”.
Is raised. When an element capable of performing dispersion compensation was prepared using the multilayer films A to H, the wavelength was about 1.
For a signal light of 55 μm, the extreme value of the group velocity delay time is 3
The bandwidth of the wavelength band for dispersion compensation is 1.ps (ps).
A group velocity delay time-wavelength characteristic curve of 3 to 2.0 nm was able to be realized.

Each of the multilayer films A to H has two light transmitting layers (cavities, that is, resonators for incident light) sandwiched between reflective layers in the thickness direction of the film from the incident surface.
That is, the present invention is a multilayer film having two cavities, but the present invention is not limited to this. It is possible to use multilayer films having various structures such as one cavity, three cavities, and four cavities.

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, not only the third-order dispersion but also the second-order fine dispersion remaining after being compensated by the dispersion compensating fiber can be compensated.

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 must be calculated as follows:
It is desirable to make the wavelength characteristic curve more suitable for the purpose of use. As one method for this, there is a method having a means for adjusting the group velocity delay time-wavelength characteristic of an element capable of performing dispersion compensation.

As one method, dispersion compensation can be performed by changing the film thickness of the light transmitting layer and the reflecting layer of the multilayer film in the in-plane direction of incidence as described with reference to FIGS. Changing the incident position of the incident light on the element to change the group velocity delay time-wavelength characteristic of the element capable of performing dispersion compensation. As a means for changing the incident position of the incident light, for example, there is a means for moving at least one of the multilayer film 200 or the incident position itself of the incident light with respect to the position of the incident light. The means for moving the position of the multilayer film or the incident light can be variously selected depending on the circumstances such as the circumstances in which the optical 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. To do
For example, it is effective to use an electromagnetic step motor or a continuous drive motor, and it is also effective to use a piezoelectric motor using PZT (lead zirconate titanate) or the like. 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. Further, by making at least one cavity of the multilayer film, for example, an air (air) gap cavity and making the air gap variable, the group velocity delay time-wavelength characteristic can be changed.

Each layer of the multilayer film constituting the element capable of performing the dispersion compensation which can be used in the optical dispersion compensation element of the present invention was formed by ion-assisted evaporation of SiO _{2 having} a thickness of a quarter wavelength. A layer L formed of a film (hereinafter also referred to as an ion assist film) and a T having a thickness of a quarter wavelength
It is composed of a layer H formed by ion-assisted film a ₂ O _5. The SiO ₂ ion assist film (layer L)
A combination of one layer and one layer of Ta ₂ O ₅ ion-assisted film (layer H) is referred to as a set of LH layers, for example, “LH
"Layer 5 sets of layers" means "layer L, layer H, layer L, layer H, layer L, layer H, layer L, layer H, layer L, layer H, one layer at a time. To form. "

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”.
The same applies to the HH layer.

[0084] 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 Ta ₂ O ₅ Ta ₂ O ₅
Besides, TiO ₂ , Nb ₂ O _{5 and the} like can be used,
Further, the layer H can be formed using Si or Ge in addition to the dielectric material. The composition of the layer L is SiO 2
₂ , the SiO ₂ has the advantage that the layer L can be formed at low cost and with high reliability, but the present invention is not limited to this, and the refractive index of the layer H is lower than that of the layer H. If the layer L is formed of a different material, it is possible to realize an element capable of performing the optical dispersion compensation exhibiting the above effects of the present invention.

Further, although an example in which each of the layers L and H is formed of one type of material has been described, the present invention is not limited to this.
Alternatively, at least one of the layers H may be formed of a different material from other layers of the same kind. Further, an appropriate third layer may be provided in addition to the layer L and the layer H.

In this embodiment, the layers L and H constituting the multilayer film are formed by ion assisted vapor deposition. However, 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.

As the optical dispersion compensating element used in the present invention, a wafer-like element can be appropriately held and used like the multilayer film 200 as the optical dispersion compensating element shown in FIG. In the thickness direction, that is, in the direction of the thickness from the incident surface 220 to the substrate 205, for example, vertically or obliquely, in the form of a chip that is cut into small pieces, for example, into a cylindrical case together with a fiber collimator. The form has various possibilities, for example, it can be mounted and used as a light dispersion compensation element.

FIG. 6 shows in series a plurality of elements capable of performing dispersion compensation proposed by the inventors of the present invention in order to realize a group velocity delay time-wavelength characteristic curve as in the example described in FIG. FIG. 6A shows an example in which two elements capable of performing the dispersion compensation are connected in series along the optical path of signal light to form an optical dispersion compensation element. FIG. 6B shows an example in which three elements capable of performing the dispersion compensation are connected in series to constitute an optical dispersion compensation element.
FIG. 6C shows an optical dispersion compensating element in which two incident positions of incident light are connected in series along the optical path of signal light on a multilayer film whose film thickness changes in the direction of the incident surface. Figure 6
FIG. 6D 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
Reference numerals 0 and 440 denote an optical dispersion compensating element formed by connecting a plurality of elements capable of performing dispersion compensation as described above in series.
11, 412, 421 to 423, 431, 442, 44
3 is an element capable of performing dispersion compensation, 416 is a multilayer film used in an element capable of performing dispersion compensation, 41
5, 4151 to 4154, 426, 4261, 426
2, 436, 4361, 4362, 446, 4461,
4462 is an optical fiber, 413, 4131, 414, 4
141, 424, 425, 434, 435, 444, 4
45 is an arrow indicating the traveling direction of the signal light, 417 is a lens,
418 is a lens 417 and optical fibers 4151 and 41
52 is a two-core collimator, 441 is a case, and 431 is a wafer configured to form a multilayer film having a film thickness varying in the incident plane direction on a substrate so that dispersion compensation can be performed. Elements 432 and 433 are elements that can perform dispersion compensation in the form of a circle. Further, among the optical fibers, reference numerals 415, 4152, 426, 436, 446
Are optical fibers as internal connection parts, 4151, 4
153, 4154, 4261, 4262, 4361, 4
Reference numerals 362, 4461, and 4462 denote optical fibers as external connection parts.

In FIG. 6A, the signal light incident on the element 411 capable of performing dispersion compensation from the optical fiber 4153 in the direction of arrow 413 is subjected to dispersion compensation and the element 411 capable of performing dispersion compensation. From the optical fiber 415, and is incident on the element 412 capable of performing dispersion compensation by being transmitted through the optical fiber 415. The optical fiber 415 exits from the element 412 capable of receiving dispersion compensation and performing dispersion compensation. 4154 is transmitted.

Reference numeral 4112 denotes a portion surrounded by a broken line 4111 of the element 411 capable of performing dispersion compensation, and is a view for explaining the internal structure thereof. The optical fibers 4151 and 4152 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, for example, a group velocity delay time-wavelength characteristic as shown in FIG.
The multilayer film 41 passes through the optical fiber 4151 and the lens 417.
6 is subjected to third-order dispersion compensation, exits from the multilayer film 416, passes through the lens 417 again, enters the optical fiber 4152, travels in the direction of the arrow 4141, and can perform dispersion compensation. Light enters the element 412. In this case, the optical fiber 4152 and the optical fiber 415 are substantially the same fiber, and the optical fiber 4151 and the optical fiber 4153 are also substantially the same. The signal light further subjected to dispersion compensation by the element 412 capable of performing dispersion compensation is emitted from the element 412 capable of performing dispersion compensation,
The optical fiber 4154 travels in the direction indicated by the arrow 414.

The optical dispersion compensating element 410 shown in FIG. 6A has the group velocity delay time-wavelength characteristic shown in FIG. 5B, and the signal light incident on the optical dispersion compensating element 410. Is subjected to dispersion compensation according to the group velocity delay time-wavelength characteristic curve as shown in FIG.
Emitted from 0.

At this time, the optical fiber 4151 is pointed to by the arrow 41.
The signal light traveling in the 31 direction enters the multilayer film 416 via, for example, a two-core collimator 418, is subjected to dispersion compensation, is reflected by the multilayer film 416, and is reflected by the optical fiber 4152.
In the process of being incident on the optical fiber 4151 and exiting in the direction of arrow 4141, the optical fiber 4152 travels in the direction of arrow 4131 with respect to the incident light of the optical dispersion compensating element 410. Light emitted from the element 410 receives coupling loss (also referred to as coupling loss) of about 0.3 to 0.5 dB.
This loss is extremely small as compared with the conventional dispersion compensation using fiber grating. However, if it is desired to perform dispersion compensation with a smaller loss in a wide wavelength band of 15 nm or 30 nm, FIG. Since the number of elements connected in series and capable of performing dispersion compensation increases, the coupling loss becomes a large loss when integrated. For example, when 10 elements capable of performing dispersion compensation are connected in series by the above connection method, a coupling loss of 3 to 30 dB occurs. This loss becomes a serious problem when configuring an optical dispersion compensating element having a wide wavelength bandwidth of 15 nm or 30 nm.

An object of the present invention is to provide a small, stable, and inexpensive optical dispersion compensating element capable of performing dispersion compensation with a small loss even in such a wide wavelength band. It will be described later with reference to FIG.

Before that, the dispersion compensation will be described in more detail to further understand the present invention.

Similarly, also in the optical dispersion compensating element 420 of FIG.
The signal light that has entered the optical dispersion compensating element 420 via the optical fiber 426 firstly enters the element 421 that can perform dispersion compensation, is subjected to dispersion compensation, and then exits, and performs dispersion compensation via the optical fiber 426. In the process of sequentially entering and exiting the elements 422 to 423, for example, FIG.
(C) is subjected to dispersion compensation according to the group velocity delay time-wavelength characteristic curve, and is emitted from the optical dispersion compensation element 420;
The optical fiber 4262 travels in the direction indicated by the arrow 425.

FIG. 6C shows a portion of the “element 431 capable of performing dispersion compensation” formed on the same wafer instead of the elements 411 and 412 capable of performing dispersion compensation in 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 for (A).

However, it is clear from the above description that the way of performing dispersion compensation depends on the group velocity delay time-wavelength characteristic of the element capable of performing dispersion compensation.

FIG. 6 (D) shows a case where elements 442 and 443 capable of performing the same dispersion compensation as in FIG. 6 (A) are incorporated in the same case 441 and along the communication path of the signal light via the optical fiber 446. Optical dispersion compensating element 440 connected in series
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 multilayer film described with reference to FIG. And has means for adjusting the incident position. Although the incident position adjusting means is not shown, the incident position can be adjusted using a control circuit provided in the case 441 and an incident position adjusting means driving circuit controlled by the control circuit. The signal light enters the optical dispersion compensating element 440 via the optical fiber 4461, and exits from the optical dispersion compensating element 440 via the optical fiber 4462.

In order to be able to widen the wavelength band to be subjected to dispersion compensation in the dispersion compensating element and the dispersion compensating method using the same according to the present invention, as described above, for example, a multilayer film is used. By connecting a plurality of elements capable of performing dispersion compensation in series in the optical path,
What is necessary is just to constitute the dispersion compensating element as described with reference to FIG. 5, and then to compensate the dispersion using such a dispersion compensating element.

However, as described with reference to FIG. 6, when a plurality of elements capable of performing the dispersion compensation of the present invention are connected using a collimator, if the number of the elements to be connected increases, Optical loss due to the connection is a major problem. Therefore, as a method for greatly reducing the optical loss caused by this connection, the present inventors propose in the present invention a dispersion compensating element using the connection method illustrated in FIGS. 7 and 8.

FIGS. 7A and 7B are views for explaining the composite type optical dispersion compensating element of the present invention. FIG. 7A is a side view, and FIG. The dotted line in FIG. 7 (B) is shown for convenience of explanation of a part that cannot be seen by a part above it.

In FIG. 7, reference numeral 701 denotes a composite type optical dispersion compensating element, and reference numerals 703 and 704 denote the composite type optical dispersion compensating element 7.
01 is an example of an optical dispersion compensating element used in the present invention, in which a plurality of elements capable of performing dispersion compensation used in the present invention are connected in series along the optical path of signal light, as described below. , 710 and 720 are substrates, 711
And 721, a multilayer film formed on the substrate and having the above-described group velocity delay time-wavelength characteristic with respect to the incident light, and 730, a position of an optical path of the incident light described later shown in FIG. , Lines 741-747, 750, 760-
767 is an optical path of incident light, 781 and 782 are optical fibers,
Reference numerals 783 and 784 denote lenses, and reference numerals 708 and 709 denote arrows indicating the direction in which the thickness of the light transmitting layer forming the multilayer film changes. d1 and d2 are intervals at the illustrated positions of the optical dispersion compensating elements 703 and 704, respectively.

The composite type optical dispersion compensating element 701 includes optical dispersion compensating elements 703 and 70
4.

In FIG. 7A, a signal light transmitted through an optical fiber 781 passes through a lens 783 and passes through an optical path 741.
From the light dispersion compensating element 7 constituting the light dispersion compensating element 701
03, is subjected to dispersion compensation at an incident point of the multilayer film 711 (an intersection point of the optical path 741 and the multilayer film 711) as an element capable of performing dispersion compensation and reflected, and passes through the optical path 742 to the optical dispersion compensating element 704. The multilayer film 711 as an element capable of performing dispersion compensation is subjected to dispersion compensation at an incident point of the multilayer film 721 as an element capable of performing dispersion compensation, and then reflected through optical paths 743 to 747.
Alternatively, the light is alternately subjected to dispersion compensation at the incident point 721 and reflected, and further passes through the optical paths 750, 760 to 766, and is reflected and received dispersion compensation at the incident point of the multilayer film 721 or 711, and is combined through the optical path 767. Out of the optical dispersion compensating element 701 of the
82 and is transmitted through an optical fiber 782.

As can be seen from the above description, the optical dispersion compensating elements 703 and 704 can perform dispersion compensation at each signal light incident point (this incident point is both an incident point and a reflection point). Are connected in series along the optical path of the incident light, that is, the signal light.

As shown in FIG. 7A, the light dispersion compensating elements 703 and 704 constituting the composite light dispersion compensating element 701 face each other at a distance d1 on the upper side of the figure and at a distance d2 on the lower side of the figure. It is arranged. In this case, the interval d1 is formed to be narrower than the interval d2, and the light incident through the optical path 741 reaches the optical path 750, the reflection direction is reversed, and sequentially exits from the optical path 767 via the optical paths 760 to 766. . In a preferred example, although not limited to this, the incident angle of the incident light is set to about 5 degrees with respect to the normal of the multilayer film 711, and d1
Is set to 10 mm and the beam diameter of the incident light on the optical path 741 is set to about 1 mm, so that good output light can be obtained from the optical path 767.

The light dispersion compensating elements 703 and 704 have multilayer films 711 and 721 formed on the substrates 710 and 720, respectively. The multilayer films 711 and 721 are formed from the lower side to the upper side in the figure. The direction of change is different from that of FIG. 3 in the case of FIG. 3, but is formed in the same manner as described with reference to FIG. 3 (that is, the thickness of the film varies depending on the location).

As one example, the thickness of each light transmitting layer of the multilayer films 711 and 721 is formed so as to increase in the direction of arrows 708 and 709. Accordingly, the contents of the dispersion compensation that the incident light received at the respective positions of the optical dispersion compensating elements 703 and 704 described with reference to FIG. 7A are different according to the description with reference to FIG. Are different in the shape and the extreme value of the group velocity delay time-wavelength characteristic curve at the position of.

From the optical path 741, the composite type optical dispersion compensating element 7
The signal light which enters the optical signal 01, undergoes dispersion compensation by the optical dispersion compensating elements 703 and 704, and emerges from the optical path 767 is output from the optical path 767 for the same reason as described above with reference to FIG.
As will be described later, the optical dispersion compensating elements 703 and 70
4, dispersion compensation is performed in accordance with the group velocity delay time-wavelength characteristic curve, which is substantially similar to the combined group velocity delay time-wavelength characteristic curve.

In this case, an optical loss occurs when the signal light enters or exits from the optical fiber and when the signal light is reflected after being subjected to dispersion compensation by the optical dispersion compensating element. The former mainly causes coupling loss (loss). The latter mainly causes reflection loss.

In general, the reflection loss is much smaller than the coupling loss, and their properties are different. That is, the reflection loss at the point where dispersion compensation is performed is as follows.
It occurs only in the vicinity of the wavelength giving the extreme value of the group velocity delay time-wavelength characteristic curve at that position (approximately 0.1 dB).
Below), other wavelengths are almost negligible.

A composite type optical dispersion compensating element 70 according to the present invention.
The loss (loss) of the signal light from when the signal light is incident on the optical signal 1 to when the signal light is subjected to dispersion compensation as described above is the reflection loss at each of the incident points (also referred to as reflection points), and has the same content. 6 can be performed as much as possible.
As described above, the coupling loss is greatly reduced as compared with the case where elements capable of performing dispersion compensation are connected in series along the optical path of signal light via an optical fiber and a lens.

FIG. 8 shows another example of the composite type optical dispersion compensating element used in the present invention. In the figure, reference numeral 702 denotes the composite type optical dispersion compensating element of the present invention, 705 denotes a substrate, 706 and 707
Is an optical dispersion compensating element formed on the substrate 705 and composed of a multilayer film having group velocity delay time-wavelength characteristics with respect to incident light as described above, 785 is an arrow indicating the incident direction of signal light, Reference numeral 786 denotes an arrow indicating the emission direction of the signal light. The substrate 705 is formed so that the lower part is gradually thicker than the upper part in the figure, and is formed so as to exhibit the same operation as the operation of the distances d1 and d2 described in FIG.

The thickness of the multilayer film constituting the optical dispersion compensating elements 706 and 707 is changed in the same manner as in FIG. 7A (that is, the thickness of the multilayer film is a multilayer film). (Depending on the position in the film).

In FIG. 8, the signal light incident on the composite type optical dispersion compensating element 702 from the arrow 785 travels in the substrate 705 for the same reason as in FIG. The light enters the optical dispersion compensator 707, undergoes dispersion compensation, is reflected by the multilayer film constituting the optical dispersion compensating element 706 or 707, travels inside the substrate 705, and emerges in the direction of the arrow 786.

The multilayer films and the multilayer films 711 and 721 constituting the optical dispersion compensating elements 706 and 707 are shown in FIGS.
In the same manner as described with reference to FIG. 3, the optical modulator has an effect of performing dispersion compensation on incident light in accordance with the group velocity delay time-wavelength characteristic.

The multilayer films 711 and 721 of FIG. 7A are formed on substrates 710 and 720, respectively, and have at least two reflective layers and at least one light transmitting layer. The reflectance with respect to the center wavelength of the incident light of the reflective layer constituting each multilayer film is higher than that of the reflective layer existing on the incident surface of the incident light on the surface of each multilayer film or the reflective layer closest to the surface of each multilayer film. Each reflection layer is formed such that the next reflection layer provided with the light transmission layer interposed between the reflection layer and the substrate has a higher reflectance. Each multilayer film has at least one reflective layer having a reflectivity of 99.5% or more. From the surface of the multilayer film or the reflective layer closest to the surface,
Each of the reflective layers is arranged such that the reflectance of each of the reflective layers existing between the reflective layers having a reflectance of 99.5% or more closest to the surface of the multilayer film sequentially increases in the direction from the surface toward the substrate. Are formed. The reflection layer is a single reflection layer with the reflection layers on both sides of the light transmission layer interposed therebetween, and the reflectance of each reflection layer means the respective layers H and L constituting the respective reflection layers.
Does not refer to the reflectivity of the unit film, but to the reflectivity of the single reflective layer.

The number of reflective layers and light transmitting layers in each multilayer film in FIG. 7A is, for example, three reflective layers in the case of two reflective layers and one cavity of one light transparent layer. When the light transmitting layer has two layers of two cavities, the reflective layer has four layers and three light transmitting layers have three cavities, and the reflective layer has five layers and four light transmitting layers have four cavities. A form is possible, and a multilayer film is formed and used according to the content of the required dispersion compensation.

The optical dispersion compensating elements 706 and 707 in FIG.
FIG. 7 (A) shows that each of them is composed of a multilayer film, has at least two reflective layers and at least one light transmission layer, and has at least one reflective layer having a reflectivity of 99.5% or more. As in the case, FIG. 7A shows a structure in which the reflectance is sequentially increased from the reflection layer closest to the substrate to the first reflection layer having a reflectance of 99.5% or more. Is different from the case.

In FIG. 7, the optical dispersion compensating element 70
The distances d1 and d2 between 3 and 704 are set to d1 <d2. By setting the difference between d1 and d2 to an appropriate value,
Optical dispersion compensating elements 703 and 704 arranged opposite to each other
As shown in FIG. 7A, the positions of the incident light and the reflected light incident on the
3 and 704 can be on the same side.

By changing the difference between the distances d1 and d2, the positions of the incident light and the reflected light can be on different sides of the optical dispersion compensating elements 703 and 704 arranged opposite to each other. Further, the distances d1 and d2 are set to d.
By setting 1 = d2, the positions of the incident light and the reflected light can be on the opposite sides of the optical dispersion compensating elements 703 and 704 arranged opposite to each other.

FIG. 9 is a graph for explaining a group velocity delay time-wavelength characteristic curve of the composite type optical dispersion compensating element 701 of FIG. 7A. In FIG. 9, reference numeral 801 denotes light dispersion compensating elements 703 and 704 constituting a composite light dispersion compensating element 701.
7 shows a group velocity delay time-wavelength characteristic curve group as a set of each group velocity delay time-wavelength characteristic curve at the incident position of each optical path, and as described by arrows 708 and 709 in FIG. By reversing the direction of the change in the film thickness of 711 and 721, a curve group symmetrical to the left and right is obtained. Code 800
Is a group velocity delay time-wavelength characteristic curve obtained by combining all the curves of the group velocity delay time-wavelength characteristic curve group 801, that is, a group velocity delay time-wavelength characteristic curve of the composite type optical dispersion compensation element 701 according to the present invention. is there.

The characteristic of the group velocity delay time-wavelength characteristic of the composite type optical dispersion compensating element 701 is that it has a larger extreme value and a wider bandwidth than the individual curves of the group velocity delay time-wavelength characteristic curve group 801. In addition to the configuration shown in FIG. 6 in which the optical fiber and the lens are used for coupling,
The loss of light intensity is significantly reduced as described above.

The group velocity delay time-wavelength characteristic curve of FIG. 9 shows that the dispersion compensation wavelength bandwidth value and the group velocity delay time as a compensation amount can be considerably increased as compared with the conventional optical dispersion compensating element. In some communication systems, a wider bandwidth and a larger compensation amount are required. A preferred embodiment of the composite type optical dispersion compensating element of the present invention which can satisfy such a requirement will be described below with reference to FIGS.

FIGS. 10 and 11 are diagrams for explaining a preferred embodiment of the composite type optical dispersion compensating element of the present invention.
FIG. 10A is a model cross-sectional view of a pair of optical dispersion compensating elements 900, each of which is one of the constituent elements of the composite type optical dispersion compensating element of the present invention, in which the incident surfaces are arranged to face each other. )
FIG. 1 shows a pair of optical dispersion compensating elements 900 in which the incident surfaces constituting the composite type optical dispersion compensating element of the present invention are arranged to face each other.
FIG. 11A is a diagram viewed from the direction of the arrow 941 of FIG.
FIG. 11 is a diagram showing a corner cube as an example of the reflector 911 in FIG. 10, and FIG. 11B is a diagram for explaining the corner cube. The dotted line in FIG. 10B shows a portion that cannot be seen because it is below the portion above it for convenience of explanation.

In FIGS. 10 and 11, reference numeral 900 denotes a pair of light dispersion compensating elements 901 in which a pair of incident surfaces constituting a part of the composite type light dispersion compensating element of the present invention are arranged to face each other.
902 and 902 are light dispersion compensating elements alone, 911 to 913 are reflectors, 921 and 922 are optical fibers, 930 to 9
35, 9301-9303, 9311-9313, 93
21 to 9323, 9331 to 9333, 971 to 974
Is an optical path of signal light, 941 is an arrow, 950 and 9500 are corner cubes, and 951 to 953 are corner cubes 9
The inner surface of the cube 960 is 50 reflecting surfaces, and 960 is a cube for explaining the corner cube 950.
Reference numerals 9516 and 961 to 963 are a solid line and a broken line indicating the cutting position of the cube 960.

As shown in FIG. 10A, the single optical dispersion compensating elements 901 and 902 are arranged so that the incident surfaces of the signal light are opposed to each other. 930, enters the incident surface of the optical dispersion compensating element 902, is subjected to dispersion compensation, and is reflected (that is, exits from the optical dispersion compensating element 902);
The light enters the optical dispersion compensating element alone 901 through the optical path 931 and is subjected to dispersion compensation. Similarly, the signal light that has been subjected to dispersion compensation by the optical dispersion compensating element 901 proceeds to an optical path 932, is subjected to dispersion compensation by the optical dispersion compensating element 902, is reflected again, travels to an optical path 933, and The dispersion compensation is performed by the light dispersion compensating element 901 alone, and the light is
34, the light is subjected to dispersion compensation by the dispersion compensating element 902 alone, reflected and proceeds to an optical path 935, and is emitted from a pair of optical dispersion compensating elements 900 arranged with their incident surfaces facing each other and is incident on a reflector 911. Is done. Then, the signal light incident on the reflector 911 is reflected by the reflector 911, and is again directed to the light dispersion compensating element 902 in a direction parallel to and opposite to the optical path 935, and from the optical path 935, for example, as shown in FIG. Incident on an optical path slightly shifted in the depth direction of the optical dispersion compensating element 902 and 901 in the same manner as described above.
Is subjected to dispersion compensation a plurality of times.

When the traveling direction of the signal light described above is viewed from the direction indicated by the arrow 941, as shown in FIG. 10B, the signal light emitted from the optical fiber 921 is
The optical dispersion compensating element 902 enters the optical dispersion compensating element 902, and the optical dispersion compensating element 902 and 901 alternately perform the dispersion compensation a plurality of times as described above. The light is emitted from the simple substance 902, travels along the optical path 9303, and is incident on the reflector 911.

The reflector 911 reflects light incident from the optical path 9303 and emits the light to the optical path 9311. Optical path 9303
And the optical path 9311, as shown in FIG.
1,902 different positions, parallel to each other and in opposite directions.

The signal light reflected by the reflector 911 travels along the optical path 9311 and returns to the optical dispersion compensating element 9 again.
02 and 901, the light travels along the optical path 9312 while the dispersion compensation is performed a plurality of times.
The light emitted from the light source 2 travels along the optical path 9313 and is incident on the reflector 912 of the optical dispersion compensating element 900 disposed on the side opposite to the reflector 911.

The signal light reflected by the reflector 912 is
The optical path 9322 travels along the optical path 9321 while the dispersion compensating elements 902 and 901 perform the dispersion compensation a plurality of times.
Then, the light is emitted from the light dispersion compensating element alone 902, travels along the optical path 9323, and enters the reflector 913.

The signal light reflected by the reflector 913 is
The optical path 9332 travels along the optical path 9331 while the dispersion compensating elements 902 and 901 perform the dispersion compensation a plurality of times.
Then, the light is emitted from the optical dispersion compensating element alone 902, travels along the optical path 9333, and enters the optical fiber 922.

The light dispersion compensating elements 901 and 9 alone
02 can be a mirror (reflection plate), and in this case, the mirror can enter the optical dispersion compensating element a plurality of times to perform the dispersion compensation a plurality of times.

The optical path 9313, the optical path 9321, and the optical path 9
323 and the optical path 9331 are located at different positions, respectively, and are parallel and the traveling directions of light are opposite.

Although FIG. 10 illustrates the case where the signal light enters and exits from the pair of optical dispersion compensating elements in which the incident surfaces are arranged to face each other, the optical dispersion compensating element alone 902 performs the invention. However, the present invention is not limited to this. In some cases, signal light incidence and emission are performed in different optical dispersion compensating elements alone, and by changing the manner in which incident light is incident, the optical dispersion compensating element in which signal light is incident can be changed. In this case, the reflectors 911 to 913 can be changed appropriately.
Can be realized by, for example, arranging them in a pair facing each other in a direction parallel to the arrow 941 in FIG. By forming the reflectors arranged to face each other in an integrated structure or by integrally forming each of the dispersion compensating elements, the size of the light dispersion compensating element is reduced, the reliability is improved, and the mounting is easy. An optical dispersion compensating element with low mass production cost can be provided.

As an example of the reflectors 911 to 913, a corner cube 950 shown in FIG. 11 can be used as the reflector. The corner cube is composed of three mutually orthogonal reflecting surfaces 951, 952, and 953, and a cube 960 shown in FIG.
Is cut at the positions indicated by broken lines 961 to 963. The reflecting surfaces 951 to 953 are
0 is the inner surface of the corner cube cut at the positions indicated by reference numerals 9511 to 9516 (that is, the inner surface of the cube when it is a cube).

Light path 971 to corner cube 950
Is reflected by the reflection surface 951, passes through the optical path 972, enters the reflection surface 952, and is reflected by the reflection surface 952.
Is reflected by the optical path 973 and enters the reflecting surface 953.
The light is reflected by the reflection surface 953, passes through the optical path 964, and is emitted from the corner cube 950.

As an example of downsizing the corner cube 950, the cube 960 can be cut at the positions indicated by broken lines 961 to 963 to form the corner cube 9500. The size of each reflective surface is a corner cube 9
Since it is half of the case of 50, there are restrictions on each optical path,
Basically, it is the same as the case of the corner cube 950.

As described above with reference to FIGS. 7 to 11, a composite type optical dispersion compensating element combining a plurality of optical dispersion compensating elements including at least a pair of optical dispersion compensating elements arranged with their incident surfaces facing each other. And by using it to perform dispersion compensation, the number of lenses and optical fibers for connection is reduced except for the input end and output end of each of the optical dispersion compensating elements configured as described above. However, depending on the configuration, they are not required, and an optical dispersion compensating element with extremely small optical loss, which can perform dispersion compensation even in a wide wavelength band, can be provided at low cost.

In order to utilize the optical dispersion compensating element based on such a technical idea more widely, there is a strong demand for downsizing, high stability, and cost reduction of the element.

The present invention can solve such a problem, and the present invention will be described in more detail below with reference to FIG.

FIG. 12 is a cross-sectional view for explaining an example of a typical optical dispersion compensating element of the present invention. FIG. 12A is a diagram for explaining a part of the processing steps of the optical dispersion compensating element of the present invention. (B) and (C) are diagrams illustrating a light dispersion compensation element of the present invention manufactured by further processing the light dispersion compensation chip processed in the processing step.

In FIG. 12A, reference numeral 810 denotes a surface 811a and a surface 811a of a substrate 811 made of, for example, BK-7 glass (trade name of Schott, Germany).
b, a multilayer film 812 capable of compensating the dispersion of the signal light
And 814 to 817 on the wafer in a state where
Is a line indicating an example of a cutting position when the wafer 810 is cut to form the chip 820, 821 is a substrate, 822 and 82
3 is a multilayer film.

In FIGS. 12B and 12C, reference numerals 830 and 8
50 is a light dispersion compensating element of the present invention, 831 and 851 are substrates, 832, 833, 852, and 853 are multilayer films capable of performing dispersion compensation on incident light, 828 and 848 are incident light incident parts, and 829 is Light emitting portion, 834, 835, 854
Denotes an anti-reflection film; 836, a Faraday rotator reflecting mirror as a reflector disposed near the light emitting portion 829;
5 is a 100% reflective film as a reflector, 837 and 857 are optical fibers, 838 and 858 are fiber collimators, 8
Reference numerals 39 and 859 denote lenses constituting a fiber collimator, and reference numerals 840 to 845 and 860 to 865 denote lines indicating optical paths of incident light.

As shown in FIG. 12A, first, the substrate 8
For example, on the pair of opposing surfaces 811a and 811b, multilayer films 812 and 813 having the properties of the optical dispersion compensating element as described with reference to FIGS.
1a and 811b are closer to the incident surface, that is, the reflectance of each of the reflective layers constituting the multilayer films 812 and 813 with respect to the incident light to the incident light is set to the surfaces 811a and 811b. It has a multilayer film 822, 823, which is formed so as to increase sequentially from the nearer reflective layer to the farther reflective layer, and is cut at a predetermined size, for example, at positions indicated by lines 814 to 817. A plurality of chips such as the chip 820 are formed.

Then, as shown in FIG. 12 (B) or (C), the forming portions of the incident light incident portion 828 or 854, the light emitting portion 829, and the reflector forming portion 849 are formed at a predetermined angle. The chip 820 is subjected to processing such as polishing. Then, the antireflection films 834, 835, 854 and the 100% reflection film 855 are formed at the positions shown in the figure, and the Faraday rotator reflection mirror 836 is arranged at a predetermined position.

Next, the operation of the thus-formed optical dispersion compensating element of the present invention will be described.

In FIG. 12B, an optical fiber 837
Is transmitted to the fiber collimator 838
From the lens 839 of the optical dispersion compensating element 830.
The signal light that has entered the optical dispersion compensating element 830 from the incident light incidence unit 828 enters the multilayer film 833 through the optical path 840, undergoes dispersion compensation and is reflected, and enters the multilayer film 832 through the optical path 841 to perform dispersion compensation. The light enters the multilayer film 833 through the optical path 842 and is subjected to dispersion compensation while being reflected. The light travels inside the substrate 831 repeatedly, passes through the optical paths 843 and 844, receives dispersion compensation, and is reflected. The light passes through 845 and exits from the light emitting unit 829, and is reflected by a Faraday rotator reflecting mirror 836 as a reflector, and is reflected by the light emitting unit 829.
From the optical path 845, 844, 843
Through the multilayer film 832 or 833 while being reflected and reflected. The light travels inside the substrate 831 by repeating the above-mentioned process, undergoes dispersion compensation through the optical paths 842 and 841, respectively, is reflected, passes through 840, and enters incident light. The light exits from the unit 828 and enters the optical fiber 837 by optical coupling from the lens 839 of the fiber collimator 838 and is transmitted.

As is clear from the above description, the incident light incident portion 828 is an incident portion when the signal light transmitted through the external transmission path enters the optical dispersion compensating element 830, The portion 829 is provided on the substrate 8 of the light diffusion compensation element 830.
31 is an emission part when the signal light that has traveled while undergoing dispersion compensation inside 31 is emitted from a place different from the incident light incidence part.

In the above example, the signal light is reflected by the Faraday rotator 836, so that the polarization of the signal light is rotated by 90 degrees.
The effect of the signal light incident on the substrate 30 on the polarization component received on the forward path and the influence on the polarization component received on the return path in the substrate cancel each other out, and a great effect is obtained such that the polarization dispersion of the signal light by the multilayer film is eliminated. .

In FIG. 12C, the optical fiber 857
Is transmitted to the fiber collimator 858.
From the lens 859 of FIG.
The signal light incident on the optical dispersion compensating element 850 from the incident light incident portion 848 is incident on the multilayer 853 through the optical path 860, is subjected to dispersion compensation and is reflected, and is incident on the multilayer 852 through the optical path 861 to be dispersion compensated. The light enters the multilayer film 853 through the optical path 862 and is subjected to dispersion compensation and is reflected. The light travels inside the substrate 851 repeatedly, passes through the optical paths 863 and 864, receives dispersion compensation, and is reflected. Then, the light passes through 865, is reflected by a 100% reflective film 855 as a reflector, passes through optical paths 865, 864, 863, undergoes dispersion compensation and is reflected by the multilayer film 852 or 853, and so on. Travels through the optical path 86
The light passes through 860, undergoes dispersion compensation, is reflected, passes through 860, exits from the incident light incident portion 848, enters the optical fiber 857 by optical coupling from the lens 859 of the fiber collimator 858, and is transmitted.

The substrates 811, 821, 831,
If BK-7 glass is used for the 851, a small and stable optical dispersion compensating element can be mass-produced at low cost, but it is clear from the above description that the substrate used in the present invention is not limited to this. It is. If an optically isotropic material is used as the substrate, the present invention can exert a great effect.

By making the reflectors 835 and 855 perpendicular to the optical path, it is possible to reflect the reflected light as light that is parallel to and reverse to the incident light with a particularly simple structure.

Further, a plurality of reflectors are arranged to perform the same operation as the reflectors 911 and 912 in FIG. 10, and the reflector 913 in FIG. 10 performs the same operation as the reflectors 835 and 855 in FIG. A light dispersion compensating element having the same technical concept as that of FIG. 12 can be formed by using the transparent substrate as described above. In this way, the light dispersion compensating element for a wide band and the miniaturization are further promoted. An optical dispersion compensating element can be manufactured.

The angle between the signal light at the incident light incident portion and the incident surface of the incident light incident portion is set so as not to be perpendicular, so that the signal light reflected at the incident surface can be dispersed by the optical dispersion compensating element 830. , 850 and the signal light output after being dispersion-compensated and generating new dispersion. As an example, the dispersion compensation state is measured so that the normal to the incident surface and the incident light have an angle of about 10 degrees, and good results are obtained.

The angle formed between the signal light incident from the incident light incident surface and the normal of the multilayer film in the forward direction of the signal light is 2 degrees.
When a light dispersion compensating element was used, a good dispersion compensation result could be obtained. The angle between the signal light incident from the incident light incident surface and the normal of the multilayer film in the forward direction of the signal light may be 10 degrees. Then, the optical dispersion compensating element of the present invention can be realized even if the angle is further increased. In that case, however, it is necessary to increase the element in order to obtain a predetermined group velocity delay time-wavelength characteristic. .

The reflectivity of the reflective layer having the maximum or maximum reflectivity of the reflective layer of the multilayer film used in the present invention is 99.5.
% Or more, more preferably 99.8% or more, and 1%
Although 00% is particularly preferable, dispersion compensation can be performed even if the reflectance is set to a low value such as 90%. The value of the reflectance can be selected in consideration of required conditions such as the required dispersion compensation specification and cost.

As described above, the optical dispersion compensating element in which a pair of multilayer films capable of performing signal light dispersion compensation are formed on a pair of opposing surfaces of a substrate capable of transmitting light has been described as an example. The present invention is not limited to this, and the present invention also provides a light dispersion compensating element in which a plurality of pairs of opposing surfaces of a substrate capable of transmitting signal light are formed by appropriately forming a multilayer film having opposing incident surfaces and opposing each other. It is included in.

According to the optical dispersion compensating element of the present invention,
It can be applied not only to a wide wavelength band such as 15 nm and 30 nm, but also to a communication system that handles a narrow wavelength band such as 1 nm in optical communication.
The present invention can be applied to a communication system that handles a wavelength band of 10 nm, and in any case, the above-described extremely large effects can be obtained.

As a result of using the optical dispersion compensating element according to the present invention to compensate for dispersion in a communication system for transmitting 60 km at a communication bit rate of 40 Gbps,
In addition to performing excellent dispersion compensation, the loss due to signal light passing through the optical dispersion compensating element is compared to the case where the optical dispersion compensating element is implemented only with a collimator consisting of a lens and an optical fiber. And it was extremely low.

The optical dispersion compensating element of the present invention has been described above. The most notable feature of the optical dispersion compensating element of the present invention is that at least one pair of multilayer films capable of performing dispersion compensation on signal light is provided. On two opposing surfaces of the substrate that can transmit the signal light, the incident surfaces are arranged facing each other, and the signal light is incident on one of the pair of multilayer films arranged opposite to each other,
The dispersion compensation is performed by performing dispersion compensation and incident on the other multilayer film, where the dispersion compensation is performed and reflected, and the incident light is again incident on the one multilayer film and subjected to dispersion compensation and reflected. Is to be repeated multiple times between membranes,
The loss occurring between the time when the signal light is incident on the pair of multilayer films and the time when the signal light is emitted is reduced to only the reflection loss whose loss is much smaller than the coupling loss, without causing the coupling loss. The present invention is capable of performing second- and third-order low-loss dispersion compensation in a wavelength band.

[0164]

As described above, the present invention has been described in detail. According to the present invention, various group velocity delay time-wavelength characteristic curves basically described with reference to FIGS. 5B to 5D are prepared. In doing so, for example, by disposing a multilayer film capable of performing dispersion compensation on at least a pair of opposing surfaces of a substrate that can transmit signal light, such as BK-7 glass, with the incident surfaces facing each other. The connection by the respective internal connection parts described with reference to FIG. 6A is realized by, for example, the reflection of the signal light shown in FIG. 12, and the loss of the signal light at the connection part can be suppressed extremely small. It is possible to provide a stable, small, and inexpensive optical dispersion compensator capable of performing good dispersion compensation, and a stable, small, and inexpensive optical dispersion compensator capable of performing good dispersion compensation for a plurality of channels. . The dispersion compensation by the optical dispersion compensating element of the present invention has a particularly large effect in the third-order dispersion compensation, and also achieves the second-order dispersion compensation by appropriate adjustment of the group velocity delay time-wavelength characteristic. It can be done.

By using the optical dispersion compensating element of the present invention, many of the existing optical communication systems can be used, and the social and economic effects are great.

[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 used in the present invention.

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

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

FIG. 5 is a diagram illustrating a method for improving group velocity delay time-wavelength characteristics by using a plurality of elements capable of performing dispersion compensation used in the present invention.

FIG. 6 is a diagram illustrating an example of connection of a light dispersion compensation element.

FIG. 7 is a diagram illustrating an example of a composite type optical dispersion compensation element.

FIG. 8 is a diagram illustrating an example of a composite type optical dispersion compensation element.

FIG. 9 is a graph illustrating a group velocity delay time-wavelength characteristic curve of the composite type optical dispersion compensation element 701.

FIG. 10 is a diagram showing a preferred example of a composite type optical dispersion compensation element.

FIG. 11 is a diagram illustrating an example of a reflector.

FIG. 12 is a diagram illustrating an example of a typical optical dispersion compensating element of the present invention.

FIG. 13 is a diagram illustrating a method of compensating for second and third order chromatic dispersion.

FIG. 14 is a graph showing dispersion-wavelength characteristics of a conventional optical fiber.

[Explanation of symbols]

100, 200, 416, 711, 721, 812, 8
13,822,823,832,833,852,85
3: Multilayer film 101, 230: Arrow indicating the direction of incident light 102, 240: Arrow indicating the direction of outgoing light 103, 104, 105, 201, 202, 203: Reflecting layer 108, 109, 206, 207: Light transmission Layers 107, 205, 705, 710, 720, 811, 8
21, 831, 851: Substrate 111, 112, 211, 212: Cavity 220: Light incident surface 250, 260: Arrow indicating film thickness change direction 270, 271: Direction for moving incident position of incident light 271: Curve adjustment direction 280, 281, 282: incident positions 1101, 1102, 1103, 2801, 2811
2812, 301 to 312: Group velocity delay time-wavelength characteristic curve 410, 420, 430, 440, 703, 704, 7
06,707: Optical dispersion compensation element 411, 412, 421-423, 431, 442, 4
43: Element capable of performing dispersion compensation 415, 4151 to 4154, 426, 4261, 42
62,436,4361,4362,446,446
1,4462,781,782,837,857,92
1,922: Optical fibers 413, 4131, 414, 4141, 424, 42
5, 434, 435, 444, 445: Arrows 417, 783, 784, 839, 859: Lens 418: Two-core collimator 432, 433: Element part capable of performing dispersion compensation 441: Case 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: DSF dispersion-wavelength characteristic curve 701, 702: Composite type optical dispersion compensating element 730: Lines 741-747, 750, 760-767 schematically showing positions of optical paths of incident light. : Optical path 785: arrow indicating incident direction 786: arrow indicating output direction 800: group velocity delay time-wavelength characteristic curve 801: group velocity delay time-wavelength characteristic curve group 810: wafer 811a, 811b: a pair of opposed substrates Surfaces 814 to 817: Line indicating cutting position 820: Chip 828, 848: Incident light incident portion 829: Light output Sections 830, 850: Light dispersion compensating elements 834, 835, 854: Anti-reflection film 836: Faraday rotator reflecting mirror as a reflector 838, 858: Fiber collimator 840-845, 860-865: Optical path 849: Reflector forming section 855 : 100% reflective film 900: a pair of light dispersion compensating elements 901 and 902 with the incident surfaces facing each other 901 and 902: single light dispersion compensating elements 911 to 913: reflectors 930 to 935, 9301 to 9303, 9311 to 93
13, 9321-9323, 9331-9333, 97
1-974: Optical path 941: Arrows 950, 9500: Corner cubes 951-953: Reflection surface 960: Cube 961-963: Dashed line indicating cut surface of cube 960

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuichi Takushima 2-22-7 Hiyoshihoncho, Kohoku-ku, Yokohama City, Kanagawa Prefecture Room 202, Charmant Hiyoshi 202 (72) Inventor Mark Kennes Jaboronsky 8-18 Tokumaru, Itabashi-ku, Tokyo No. 18-208 (72) Inventor Yuichi Tanaka 3-1-23-1 Nishinaminami, Toda City, Saitama Prefecture Co., Ltd.Applied Photonics Laboratory (72) Inventor Haruki Kataoka 3-1-23 Nishinaminami, Toda City, Saitama Prefecture Stock Applied Photovoltaic Laboratory (72) Inventor Kenji Furushiro 3-1-23 Nishinaminami, Toda City, Saitama Prefecture Stock Applied Photonics Laboratory (72) Inventor Shin Higashi 3-1-23 Nishinaminami, Toda City, Saitama Prefecture Stock Applied Photovoltaic Laboratory (72) Inventor Kazuya Sato 3-1-23 Nishinaminami, Toda City, Saitama Pref. Akiya Hiroshi Yaguchi 3-1-23, Niisominami, Toda City, Saitama Prefecture Applied Photoelectric Laboratory, Inc. (72) Inventor Shiro Yamashita 3-1-1, Niisominami, Toda City, Saitama Prefecture F-Term, Applied Optoelectronic Laboratory Reference) 2H048 GA04 GA11 GA22 GA23 GA24 GA34 GA51 GA62 5K002 BA21 CA01 DA02 FA02

Claims (23)

[Claims] An optical dispersion compensating element capable of compensating chromatic dispersion (hereinafter, also simply referred to as dispersion) by using an optical fiber for communication using a communication transmission line, and transmitting incident light. A substrate, a multilayer film formed on at least a pair of opposing surfaces of the substrate, and an incident light incident portion provided on the substrate, and the multilayer film formed on the pair of opposing surfaces is An optical dispersion compensating element capable of compensating for wavelength dispersion of light incident from the substrate side. 2. The optical dispersion compensating element according to claim 1, wherein each of the multilayer films formed on the pair of opposing surfaces is located between at least two reflection layers and the pair of reflection layers. At least one light transmitting layer formed on the substrate, and the reflectivity of the reflective layer constituting the multilayer film with respect to the incident light is changed from a layer closer to the substrate to a layer farther from the substrate. An optical dispersion compensating element, wherein the multilayer film is formed so as to gradually increase until a layer having a maximum or maximum value appears. 3. An optical dispersion compensating element according to claim 1, wherein an anti-reflection film is formed on an incident light incident portion of said substrate. 4. The optical dispersion compensating element according to claim 1, wherein incident light incident on the substrate from an incident light incident portion of the substrate is formed on at least one pair of the opposed surfaces. A light dispersion compensating element, wherein the multilayer film is arranged so as to perform dispersion compensation by repeating alternately entering one of the multilayer films and the other multilayer film a plurality of times. . 5. The light dispersion compensating element according to claim 1, wherein a light emitting portion is provided on the substrate at a position different from a position of the incident light incident portion. A light dispersion compensating element, wherein a reflector is arranged outside the substrate and near the light emitting portion. 6. The light dispersion compensating element according to claim 5, wherein an antireflection film is provided on the light emitting portion, and the reflector is a Faraday rotator reflecting mirror. 7. The light dispersion compensating element according to claim 1, wherein a reflector for the incident light is provided on the substrate at a position different from a position of the incident light incident portion. An optical dispersion compensating element characterized by the above-mentioned. 8. The optical dispersion compensating element according to claim 5, wherein incident light incident on the substrate from an incident light incident portion of the substrate faces the substrate in the substrate. Incident on the multilayer film formed on the surface alternately and subjected to dispersion compensation to advance in the substrate and reach the reflector,
After being reflected by the reflector, the light reaches the incident light incident portion through the same optical path as the optical path from the incident light incident portion to the reflector, and exits from the incident light incident portion. Light dispersion compensating element. 9. The light dispersion compensating element according to claim 1, wherein at least two light emitting portions are provided on the substrate at positions different from the position of the incident light incident portion. A light dispersion compensating element, wherein a reflector is arranged near at least one of the emission sections. 10. The light dispersion compensating element according to claim 9, wherein at least one of the reflectors is a Faraday rotator reflecting mirror. 11. The light dispersion compensating element according to claim 9, wherein at least one of the reflectors is light incident on the reflector and traveling through the substrate (hereinafter, also referred to as incident light A). ), Which is a reflector that reflects the incident light A in a direction different from the direction opposite to the direction in which the incident light A travels. 12. The optical dispersion compensating element according to claim 11, wherein at least one of the reflectors converts light incident on the reflector (hereinafter, also referred to as “incident light B”) as the incident light B progresses. An optical dispersion compensating element, characterized in that it is a reflector that reflects in a direction opposite to and parallel to the direction of the light. 13. The light dispersion compensating element according to claim 9, wherein an anti-reflection film is provided on the light-emitting portion. 14. The optical dispersion compensating element according to claim 1, wherein the substrate has at least one incident light incident part different from the incident light incident part. Light dispersion compensating element. 15. The light dispersion compensating element according to claim 1, wherein the substrate is made of an optically isotropic material. 16. The light dispersion compensating element according to claim 15, wherein the substrate is glass. 17. The optical dispersion compensating element according to claim 2, wherein the reflectance of the maximum or maximum reflectance layer constituting the multilayer film formed on the substrate is 99%. 0.5% or more. 18. An optical dispersion compensating element according to claim 9, wherein at least one reflecting surface of said reflector is movable. 19. The optical dispersion compensating element according to claim 2, wherein the thickness of at least one laminated film forming at least one multilayer film is a light incident surface of the multilayer film. A light dispersion compensating element that changes in an in-plane direction (hereinafter also referred to as an in-plane direction of incidence) in a cross section parallel to (i). 20. The optical dispersion compensating element according to claim 19, wherein a change direction of a film thickness of at least one light transmission layer of each of the at least one pair of opposed multilayer films is different from each other. Characteristic light dispersion compensating element. 21. The optical dispersion compensating element according to claim 20, wherein the thickness of at least one light transmission layer of each of the at least one pair of the multilayer films arranged opposite to each other is opposite to each other. An optical dispersion compensating element characterized by changing. 22. The optical dispersion compensating element according to claim 1, wherein the optical dispersion compensating element is an optical dispersion compensating element capable of mainly compensating for third-order dispersion. Light dispersion compensation element. 23. The optical dispersion compensating element according to claim 1, wherein the optical dispersion compensating element has an asymmetric shape near an extreme value of a group velocity delay time-wavelength characteristic curve. An optical dispersion compensating element characterized by the above-mentioned.