JP2002243935A - Dispersion compensator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersion compensator which is a transmission type, small in size and inexpensive, which has a large dispersion quantity to be compensated, and which can continuously vary the dispersion quantity by easy operation. SOLUTION: The compensator has a multilayered film structure of dielectric materials consisting of a first dielectric material region, a second dielectric material region and a thin film between these regions. The first dielectric material region is produced by alternately laminating first dielectric thin films having the thickness as about 1/4 of the wavelength of the incident light in the first medium and second dielectric thin films each having the refractive index different from that of the first dielectric material and having the thickness as about 1/4 wavelength of the incident light in the second medium. The second dielectric material region is produced by alternately laminating third dielectric thin films each having the thickness as about 1/4 wavelength of the incident light in the third medium and fourth dielectric thin films each having the refractive index different from that of the third dielectric material and having the thickness as about 1/4 wavelength of the incident light in the fourth medium. The thin film between the above regions is a fifth dielectric thin film having the thickness as about 1/2 of the wavelength of the incident light in the fifth medium. In this structure, the dispersion value can be continuously varied by using such property that the dispersion almost linearly and continuously varies from positive to negative with respect to the wavelength in a high transmittance region formed almost in the center of the high reflection region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dispersion compensator,
In particular, the present invention relates to a compact and inexpensive dispersion compensator capable of continuously changing the amount of dispersion from positive to negative.

[0002]

2. Description of the Related Art In recent years, in long-distance, large-capacity optical fiber communication, dispersion compensation for correcting distortion of a transmission waveform has become a very important technical problem. The principle of dispersion compensation is to shape a signal waveform by guiding an optical pulse signal into a medium having the amount of dispersion: -D having the opposite sign to the amount of dispersion received during optical fiber transmission: D. .

At present, the dispersion compensation includes a dispersion compensating optical fiber, an optical fiber grating, an AWG (Arra
yed Waveguide Grating) A dispersion compensator or the like is used. However, all of them have problems that the size is large and expensive, and it is difficult or impossible to adjust the dispersion compensation amount by continuously changing it.

[0004] In addition, as a small-sized one, a reflection type etalon, such as a GT interferometer, is used to compensate, but the amount of dispersion that can be corrected is small and the reflection type is used. Had various restrictions.

On the other hand, a structure that enables dispersion compensation by using a dielectric multilayer film in a transmission type has been proposed in, for example, Japanese Patent Application Laid-Open No. 10-48567 (Japanese Patent No. 2902996). Since this is a thin film structure, it is very small, low cost,
It has various advantages, such as stability and good compatibility with other devices.

[0006]

However, in a conventional dispersion compensator using a dielectric multilayer film of a transmission type, the value of the compensable dispersion amount is almost fixed, and the value of the dispersion amount is continuously changed. That was impossible.

[0007] Therefore, the problem to be solved by the present invention is that it is of a transmission type with a dielectric multilayer structure, is small and inexpensive, has a sufficiently large compensating amount of dispersion, and is capable of continuously increasing the amount of dispersion by a simple operation. It is another object of the present invention to provide a dispersion compensator that can be varied in the range.

[0008]

SUMMARY OF THE INVENTION The present invention, which provides means for solving the above-mentioned problems, comprises a first dielectric thin film having a thickness of about 1/4 of a wavelength of incident light in the medium. And a second dielectric thin film having a refractive index different from that of the first dielectric and having a film thickness of about 1/4 of the wavelength of the incident light in the medium, which is alternately laminated. A third dielectric region comprising a thickness of about 1/4 of the wavelength of the incident light in the medium, and
The dielectric thin film, the refractive index of the third dielectric is different,
And the film thickness is about 1/4 of the wavelength of the incident light in the medium.
A second dielectric region formed by alternately laminating a fourth dielectric thin film made of, sandwiched between the first and second dielectric regions,
And the film thickness is about 1/2 of the wavelength of the incident light in the medium.
In the dielectric multilayer structure consisting of the fifth dielectric thin film consisting of, in the high transmittance region formed almost at the center of the high reflection region on the spectrum, the dispersion value is almost linear with wavelength from positive to negative. The variance value can be continuously varied by utilizing the fact that the variance changes continuously. The present invention may further have the following configurations.

In the dispersion compensator, 80% or more of the spectral component of the incident light for which dispersion compensation is performed falls within the high transmittance region formed substantially at the center of the high reflection region.

In the dispersion compensator, by tilting the dispersion compensator with respect to the incident light so as to change the transmission center wavelength of the dispersion compensator relative to the wavelength of the incident light, the incident light is subjected to the main dispersion compensation. It is possible to continuously change the amount of dispersion received while passing through the vessel.

The dispersion compensator has a structure having spatially different transmission center wavelengths by spatially continuously changing the thickness of each of the multilayer films constituting the dispersion compensator. The transmission center wavelength of the dispersion compensator is relatively changed with respect to the wavelength of the incident light by changing the place where the incident light passes above, and the amount of dispersion that the incident light receives while passing through the dispersion compensator is changed. It is possible to change continuously.

In the dispersion compensator, the amount of dispersion is controlled by changing the temperature of the dispersion compensator, thereby changing the refractive index of the material constituting the dispersion compensator, and changing the transmission center wavelength.

[0013] In the dispersion compensator, each layer or any layer of the substrate or the multilayer film constituting the dispersion compensator is made of an optically active semiconductor material having an optical amplification function by excitation.
An optical amplification effect can be exhibited by pumping by light excitation or current injection.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to clarify the above and other objects, features and advantages of the present invention, embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

According to the present invention, there is provided a narrow-band transmission type wavelength filter having a dielectric multilayer structure, wherein in a narrow-band transmission wavelength region formed substantially at the center of a high-reflection region, the amount of dispersion received by light transmitted therethrough is a wavelength. By making use of the fact that an area that changes almost linearly and continuously from positive to negative is formed, and by continuously changing the amount of dispersion given to incident light in that wavelength range, This is to compensate for the amount of dispersion of the values.

The dispersion compensator according to the present invention is characterized in that the first dielectric thin film (111) having a film thickness of about / 4 of the wavelength in the medium of the incident light and the first dielectric are: The refractive index is different and the film thickness is about the wavelength of the incident light in the medium.
A first dielectric region (first dielectric multilayer film) in which second dielectric thin films (112) each composed of 1/4 are alternately laminated.
(110), a third dielectric thin film (131) having a thickness of about / 4 of the wavelength of the incident light in the medium, a refractive index of the third dielectric is different, and A second dielectric region (a second dielectric multilayer) in which fourth dielectric thin films (132) each having a thickness of about 1/4 of the wavelength of the incident light in the medium are alternately laminated. Membrane) (130) and the first
Dielectric region (110) and the second dielectric region (13)
0), and the fifth dielectric thin film (1) having a thickness of about の of the wavelength of the incident light in the medium.
20), and in a high transmittance region formed substantially at the center of the high reflection region on the spectrum, the dispersion value changes from positive to negative, and
Utilizing the fact that it changes substantially linearly and continuously, by continuously changing the amount of dispersion given to the incident light in the wavelength region, it is configured to compensate for the amount of dispersion of an arbitrary value. I have.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; FIG. 1 is a diagram showing the configuration of one embodiment of the present invention. As shown in FIG. 1, the basic configuration of a dispersion compensator according to one embodiment of the present invention includes a dielectric thin film 111 having a thickness of 1/4 of a wavelength in a medium of incident light, and a dielectric thin film 111. And a second dielectric thin film 1 having a refractive index different from that of the incident light and having a thickness of 1/4 of the wavelength of the incident light in the medium.
A first dielectric region (first dielectric multilayer film) 110 formed by alternately laminating the first and second thin films 12 and a dielectric thin film 131 having a thickness of 1/4 of the wavelength of the incident light in the medium. And the dielectric thin film 131 has a refractive index different from that of the dielectric thin film 131 and has a thickness of 1/4 of the wavelength in the medium of the incident light.
Are alternately laminated, a second dielectric region (second dielectric multilayer film) 130, a first dielectric region (first dielectric multilayer film) 110, and a second dielectric region ( A second dielectric multi-layered film) and a dielectric having a film thickness of 1/2 (or n + 1/2, where n is a positive integer) of the wavelength of the incident light in the medium. It has a dielectric multilayer structure including the thin film 120.

The dielectric thin films 111 and 131 are made of a high refractive index medium.
Quality (in this example, Si has a refractive index of about 3.5)
The optical film thickness is λc / 4 (where λc is the incident light for dispersion compensation)
, The dielectric thin films 112 and 132 have low refractive indices.
Medium (in this example, SiO₂And the refractive index is about 1.5).
Has an optical film thickness of λc / 4, the first dielectric region 110 and the second
Dielectric thin film 120 serving as an intermediate layer between dielectric regions 130
Is a low refractive index medium (SiO ₂) Whose optical thickness is λc /
2. Here, the optical film thickness is defined as the thickness of light in the medium.
It refers to the size for the wavelength. The refractive index of the medium is nr
In this case, the optical film thickness for one wavelength means that the wavelength of the incident light is λ.
Then, λ / nr is obtained.

For example, the medium is glass (SiO ₂ ) having a refractive index of 1.5.
, The optical film thickness λ for one wavelength with respect to incident light having a wavelength λ of 1.5 μm (micrometer) is λ / nr = 1.5 / 1.5
= 1 μm.

The optical thickness λ / 2 is half the thickness, and the optical thickness λ / 4 is half the thickness.

Therefore, the multilayer film structure shown in FIG. 1 is the same structure as a general narrow band transmission type wavelength filter, and the present invention utilizes this as a dispersion compensator.

In this case, the dielectric thin film 120 having an optical thickness of λc / 2 located at the center of the multilayer structure is not necessarily limited to the optical thickness of λc / 2. , (N + 1/2) λc (n is zero or a natural number)
May be used.

In the embodiment of the present invention shown in FIG. 1, the multilayer film structure has a dielectric thin film (three layers of Si 111, two layers of dielectric thin film (SiO ₂ ) 112, and a thin layer of dielectric thin film (Si) 13).
1 is composed of three layers, the dielectric thin film (SiO ₂ ) 132 is composed of two layers, and the dielectric thin film (SiO ₂ ) 120 is composed of one layer, that is, a total of 11 layers. The dielectric multilayer on both sides of the dielectric film thin (SiO ₂ ) 120 Membrane 110,
Although 130 has a symmetric structure, the structures of the dielectric multilayer films 110 and 130 on both sides of the intermediate dielectric thin film 120 are not necessarily required to be symmetric. That is, the materials of the films forming the dielectric multilayer films 110 and 130 on both sides may be different, or the dielectric multilayer films 110 and 13 may be different.
The number of layers of 0 may be different from each other.

In the present invention, the dielectric multilayer film 11 on both sides is used.
It is sufficient that the center wavelengths of the Bragg reflections of 0 and 130 match. That is, any material may be used as long as the optical film thickness of each layer is λc / 4. However, it is preferably transparent.

FIG. 2 is a diagram showing the operation principle of the dispersion compensator of the embodiment of the present invention having the structure shown in FIG.
2A shows the relationship (solid line) between the wavelength (horizontal axis) and the transmittance (left vertical axis), and the relationship (dashed line) between the wavelength (horizontal axis) and the phase shift amount (right vertical axis). ) Shows the relationship between the wavelength (horizontal axis) and the amount of dispersion (wavelength dependence of the group velocity of optical pulses) (vertical axis).

The multilayer structure shown in FIG. 1 is structurally
Because it is the same as a normal narrow band transmission type wavelength filter,
As shown in FIG. 2A, at the transmission center wavelength λc,
Transmittance is maximum (theoretically 10 if there is no absorption by the medium)
0%).

The amount of dispersion given to the light passing through this wavelength range by the multilayer structure according to one embodiment of the present invention is shown in FIG.
As shown in (B), it becomes zero at the center wavelength λc of the transmission region, but takes a continuous value from the negative dispersion amount on the short wavelength side to the positive dispersion amount on the long wavelength side, hand,
There is a wavelength range that changes almost linearly.

The maximum value of the amount of dispersion and the wavelength region in which the value of the amount of dispersion changes linearly can be arbitrarily designed depending on the type of medium and the number of layers of the multilayer film.

The amount of dispersion that can be compensated is, for example, as shown in FIG. 1, a maximum of ± 0.2 ps / nm for a single dispersion compensator composed of all 11 layers of Si / SiO _2. Is calculated to be about 5 nm. For example, to compress a linear chirped light pulse with a pulse width of about 1.5 ps (picoseconds) and a spectral width of about 2.5 nm (nanometers) to 1.0 ps by dispersion compensation,
Although a dispersion amount of 0.2 ps / nm is required, this can be realized by one dispersion compensator according to the embodiment of the present invention described above.

In the multilayer structure of the dispersion compensator according to one embodiment of the present invention, the maximum amount of dispersion that can be compensated is determined by the refractive index of the material constituting the multilayer film and the total number of the multilayer films. That is, the larger the difference between the refractive indices of the two types of materials constituting the dielectric multilayer film and the greater the total number of multilayer films (the total number of layers), the larger the maximum amount of dispersion that can be compensated.

However, when the maximum dispersion amount is increased, the wavelength band that can be compensated becomes narrower. That is, there is a trade-off between the maximum dispersion amount and the wavelength band.

FIG. 3 shows the total number of layers (horizontal axis) and the maximum amount of dispersion obtained (left vertical axis;
FIG. 6 is a diagram illustrating a relationship (unit: ps / nm) (black circles) and a relationship (dispersion-compensated wavelength band (right vertical axis; unit nm)) (solid squares). Referring to FIG. 3, it can be seen that the maximum dispersion amount obtained increases as the number of layers of the multilayer film increases, but the wavelength range becomes narrower.

Therefore, in the dispersion compensator according to one embodiment of the present invention, when obtaining a wide band, the obtained maximum dispersion amount is sacrificed to some extent.

The band can be broadened by gradually changing the optical film thickness of the multilayer films 110 and 130 on both sides and chirping the center wavelength of Bragg reflection. The amount will be smaller.

In order to form a multilayer structure according to an embodiment of the present invention, the multilayer structure is formed on a substrate transparent to incident light. This is because the multilayer film itself has a film thickness of less than 10 μm even when 10 layers are laminated, and mechanical strength cannot be maintained as it is. FIG. 1 shows, as one embodiment of the present invention, a structure in which a substrate is laminated on a substrate 140 (having any thickness) such as glass or semiconductor transparent to incident light. In this case, it is preferable to apply an anti-reflection coating 150 (anti-reflection film) on the surface of the substrate 140 on the side opposite to the multilayer film (the light entrance / exit surface). In the case where the light emitting device is manufactured in a state where the reflection from the end surface of the substrate 140 remains, it is calculated by the calculation that the light causes a multiple reflection between the end surface of the substrate 140 and the multilayer film, thereby adversely affecting the dispersion characteristics. Has been confirmed.

Next, a method of continuously changing the amount of dispersion with respect to incident light in the dispersion compensator having the structure shown in FIG. 1 will be described. The simplest and most realistic method will be described as an example of a method for continuously changing the variance.

FIG. 4 is a diagram for explaining the second embodiment of the present invention, and is a schematic diagram showing the principle of continuously changing the amount of dispersion.

Referring to FIG. 4, in the second embodiment of the present invention, the angle of the dispersion compensator (dispersion compensation filter) 1 having the structure shown in FIG. It is possible to shift the transmission center wavelength. The optical signal (incident light) 2 incident on the end surface (light incident surface) of the dielectric multilayer film 110 in FIG.
The position of the dispersion compensator 1 is set so as to form a predetermined angle with respect to the direction.

If the transmission center wavelength changes relative to the incident light, the amount of dispersion that the incident light undergoes during transmission also changes. Therefore, by variably controlling the incident angle, fine adjustment of the amount of dispersion becomes possible.

In the multilayer structure shown in FIG.
As shown in (2), by rotating the incident angle by 20 degrees, it is possible to shift the dispersion characteristics to the shorter wavelength side by about 20 nm.

FIG. 5 is a graph showing calculation results for explaining the principle of the second embodiment of the present invention, and shows the relationship between the incident angle (horizontal axis) and the amount of dispersion (vertical axis). FIG. In FIG. 5, p (black circle) and s (black square) indicate the directions of polarization. Referring to FIG. 5, it can be seen that the value of the amount of dispersion can be controlled with respect to the incident angle.

Another method for continuously changing the amount of dispersion will be further described. FIG. 6 is a diagram for explaining a third embodiment of the present invention. As another method for controlling the amount of dispersion, as shown in FIG. 6, a multilayer film (11 in FIG. 1) constituting the dispersion compensator 1 (having the basic configuration shown in FIG. 1) is used.
1, 112, 120, 131, and 132), the thickness of each film is changed spatially continuously, so that a structure having a spatially different transmission center wavelength is obtained. By changing the place where light passes, the transmission center wavelength of the dispersion compensator is relatively changed with respect to the wavelength of the incident light, and the amount of dispersion that the incident light receives while passing through the dispersion compensator is changed. , Continuously changing.

By continuously and spatially changing the thickness of each film of the multilayer film, it is possible to obtain a spatial distribution of a film thickness of about 1% in an ordinary sputtering apparatus or vacuum evaporation apparatus which forms a film forming apparatus. If possible, it can be easily realized.

In FIG. 6, the dielectric multilayer films 110, 1
30, the thickness of each thin film of the dielectric thin film 120 of the intermediate layer is set to a different value at one end of the thin film and at the other end opposite to the one end, and the cross-sectional shape of the multilayer structure on the substrate 140 is one end. In the present invention, the distribution of the film thickness is not limited to such a spatial distribution.

As another method of controlling the amount of dispersion, a configuration utilizing the temperature dependence of the refractive index of the material constituting the dispersion compensator may be used. For example, if the refractive index of the material forming the dielectric thin film changes with temperature, the optical film thickness also changes, so that the transmission center wavelength also changes. That is, the amount of dispersion can be controlled by controlling the temperature of the dispersion compensator.

As a comparative example, a transmission type dispersion compensator having a dielectric multilayer structure described in Japanese Patent No. 2902996 (Japanese Patent Application No. 8-204487) and a dispersion compensator according to the present invention will be described below. The difference will be described. Both the dispersion compensator disclosed in Japanese Patent No. 2902996 (Japanese Patent Application No. 8-204487) and the dispersion compensator according to the present invention have the same basic structure of a dielectric multilayer film. That is, in both cases, a known narrow-band transmission wavelength filter is used.

However, the dispersion compensator disclosed in Japanese Patent No. 2902996 (Japanese Patent Application No. 8-204487) (comparative example) is not shown in FIG.
As shown in (A), the dispersion compensator according to the present invention has a narrow spectral width located almost at the center of the reflective region, while using a wide spectral transmission region adjacent to the high reflective region. A transmission area is used. FIG. 7 is based on FIG. 9 of the drawings of Japanese Patent No. 2902996,
FIG. 7B is a calculation result of the secondary phase dispersion in the transmission region adjacent to the long wavelength side of the high reflection region.

In the dispersion compensator of the comparative example, as shown in FIG. 7A, a wide-band transmission region formed on both sides of the high-reflection region is used in order to increase the wavelength band for performing dispersion compensation to some extent. In this case, when compensating for down-chirp, the transmission region on the long wavelength side of the high reflection region is used, and when compensating for up-chirp, the transmission region on the short wavelength side of the high reflection region is used. The wavelength range to be used differs depending on the sign (positive or negative) of the dispersion to be compensated.

On the other hand, the dispersion compensator according to the present invention can compensate for any positive to negative charging amount in the same wavelength region because the transmission region located substantially at the center of the reflection region is used. .

If the dispersion compensator according to the present invention requires a wide wavelength band, the number of layers of the multilayer film may be reduced as described above. However, the obtained maximum dispersion amount becomes smaller accordingly.

Therefore, in the dispersion compensator according to the present invention, it is necessary to put the spectral component of the optical signal whose dispersion is to be compensated into the transmission region located substantially at the center of the reflection region.

In calculation, the power spectrum component of the optical signal
It has been found that dispersion compensation is sufficiently possible if 80% or more is in this region (the transmission region located substantially at the center of the reflection region).

Next, as a fourth embodiment of the present invention, a dispersion compensator having optical amplification characteristics will be described. FIG.
FIG. 13 is a diagram for explaining a fourth embodiment of the present invention, and is a diagram illustrating a configuration of a dispersion compensator having an optical amplification effect. FIG.
According to the fourth embodiment of the present invention, in the fourth embodiment of the present invention, the substrate 140 having the multilayer structure of the dispersion compensator, the dielectric multilayer films 110 and 130, or the intermediate dielectric thin film 12 is formed.
A dispersion compensator having an optical amplification effect is realized by using an optically active material for 0 or any of the films and providing optical amplification by pumping by optical excitation or current injection. Light 3 is obtained.

As the optically active material, GaAs and AlGaAs-based materials, InP and InGaAsP-based semiconductor materials are generally used, but high-molecular compounds such as rare earth-doped glass and polymers can also be used.

In order to impart an optical amplification effect to these materials, if semiconductor materials are used, current injection by photoexcitation or formation of a PN junction is used. When the rare earth is doped glass or polymer, photoexcitation is preferred.

As a current injection type structure made of a semiconductor material, a structure of a surface emitting laser which has been widely known can be applied. However, the point different from the structure of the surface emitting laser is that the thickness of the central layer (corresponding to the active layer in the case of the surface emitting laser) must be set accurately to (n + 1/2) λc (n is zero or a natural number). It is that there is. Normally, in a surface emitting laser, the thickness of the active layer is arbitrary.

In still another embodiment of the present invention, by disposing a plurality of dispersion compensators having different dispersion amounts in series, it is possible to compensate not only linear dispersion but also nonlinear dispersion (higher-order dispersion). Become.

Further, as still another embodiment of the present invention, by forming a dispersion compensator directly on the light emitting surface of a light emitting device such as a laser, the light is compensated for in a form in which chirping inside the laser resonator is compensated. It is also possible to get output.

It should be noted that the present invention is not limited to the above-described embodiments, and that various modifications and corrections can be made by those skilled in the art within the scope of the invention set forth in the appended claims. Of course.

[0060]

As described above, according to the present invention, in a narrow-band transmission type wavelength filter having a dielectric multilayer structure, dispersion is achieved by using a transmission region formed substantially at the center of a high reflection region. By performing the compensation, the dispersion amount can be continuously changed from positive to negative, and there is an effect that a compact and inexpensive dispersion compensator can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of one embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of one embodiment of the present invention.

FIG. 3 is a diagram for explaining the principle of one embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 5 is a diagram showing the principle of a second embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a third exemplary embodiment of the present invention.

FIG. 7 is a diagram for explaining a difference between the present invention and a comparative example.

FIG. 8 is a diagram for explaining a fourth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 dispersion compensator 2 optical signal (incident light) 3 optical signal (output light) 110, 130 dielectric region (dielectric multilayer film) 111, 112, 120, 131, 132 dielectric thin film 120 dielectric thin film (intermediate layer) 140 substrate 150 anti-reflective coating

Claims (16)

[Claims] A first dielectric thin film having a thickness of about 1/4 of a wavelength of light to be incident in the medium, and a refractive index of the first dielectric thin film different from that of the first dielectric thin film, and A first dielectric region formed by alternately laminating a second dielectric thin film having a wavelength of about 1/4 of the wavelength of the incident light in the medium; A third dielectric thin film consisting of about 1/4 of the wavelength of the light, and a refractive index different from that of the third dielectric, and having a thickness of about 1/4 of the wavelength of the incident light in the medium. A second dielectric region formed by alternately laminating a fourth dielectric thin film, and the first dielectric region and the second dielectric region. And a fifth dielectric thin film having a wavelength of about 波長 of the wavelength of the light to be emitted in the medium. Dispersion compensation characterized by using the fact that the dispersion value changes substantially linearly and continuously from positive to negative wavelengths in the high transmittance region, thereby making the dispersion value continuously variable. vessel. 2. The dispersion compensator according to claim 1, wherein 80% or more of the spectral components of the incident light for which dispersion compensation is performed are:
A dispersion compensator, wherein the dispersion compensator is located in a high transmittance region formed substantially at the center of the high reflection region. 3. The dispersion compensator according to claim 1, wherein the dispersion compensator is inclined with respect to incident light.
With respect to the wavelength of the incident light, the transmission center wavelength of the dispersion compensator is relatively changed, and the amount of dispersion that the incident light receives while passing through the dispersion compensator is continuously changed.
A dispersion compensator that makes it possible. 4. The dispersion compensator according to claim 1, wherein the thickness of each of the dielectric thin films constituting the dispersion compensator is spatially and continuously changed. A structure having spatially different transmission center wavelengths, on the dispersion compensator, changing the location where the incident light passes, and changing the transmission center wavelength of the dispersion compensator relative to the wavelength of the incident light. A dispersion compensator capable of continuously changing an amount of dispersion received while the incident light passes through the dispersion compensator. 5. The dispersion compensator according to claim 1, wherein a temperature of the dispersion compensator is changed to change a refractive index of a material constituting the dispersion compensator, thereby changing a transmission center wavelength. A dispersion compensator characterized by controlling a dispersion amount by changing the dispersion amount. 6. The dispersion compensator according to claim 1, wherein the dielectric multilayer structure of the dispersion compensator is formed on a substrate or each layer of the dielectric multilayer film. Alternatively, a dispersion compensator, wherein one of the layers is made of an optically active semiconductor material having an optical amplification function by excitation, and performs optical amplification by pumping by optical excitation or current injection. 7. A multilayer film structure comprising a dielectric multilayer film having two types of dielectric thin films having different refractive indices alternately arranged on both sides of a dielectric thin film serving as an intermediate layer, The center wavelengths of the Bragg reflections of the dielectric multilayer films on both sides coincide with each other, and the relationship between the wavelength of an optical signal incident from one end of the multilayer film structure and the transmittance and dispersion characteristics indicates that the high reflection region of the spectrum is high. In the high transmittance region formed substantially at the center, the value of the amount of dispersion changes substantially linearly and continuously with respect to the wavelength from one sign to the opposite sign to the one sign. And a dispersion compensator characterized in that the value of the amount of dispersion given to the optical signal in this wavelength region is continuously variable. 8. The optical film according to claim 1, wherein the film thickness is about 1 / the optical film thickness for one wavelength of the incident light.
4, at least first and second dielectric multilayer films in which two types of dielectric thin films having refractive indexes having a relatively high-low relationship are alternately arranged, and the first and second dielectric thin films are provided. Between the dielectric multilayer films, the film thickness is about (n + 1/2) (where n is 0 or a predetermined positive integer) corresponding to the optical film thickness of one wavelength of the incident light, and the refractive index is relatively low. A multi-layer structure in which a dielectric thin film of an intermediate layer is interposed is provided on a substrate, and an optical signal is incident on one end of the multi-layer structure at a predetermined incident angle, and from the end face of the substrate through the multi-layer structure. An optical signal is output, and the amount of dispersion given by the multilayer structure is zero at the center wavelength of the transmission region formed substantially at the center of the high reflection region on the spectrum, and is negative on the short wavelength side with respect to the center wavelength. From the amount of dispersion to the amount of positive dispersion on the long wavelength side is almost linear and continuous with wavelength. Turned into and becomes the value of the dispersion amount to be given to the incident light of the wavelength region as a continuous variable,
A dispersion compensator characterized in that: 9. The dispersion compensator according to claim 8, wherein the end face of the substrate is coated with anti-reflection. 10. An angle of one end of the multilayer structure with respect to incident light is variable, and by varying the incident angle, the value of the amount of dispersion received while the incident light passes through the multilayer structure is continuously changed. 9. The dispersion compensator according to claim 7, wherein the value is changed to: 11. The dispersion compensator according to claim 7, wherein the thickness of at least one dielectric thin film of said multilayer structure has a spatial distribution in an in-plane direction. 12. The film thickness of the dielectric thin film having the multilayer structure is as follows:
Different values are set at one end of the dielectric thin film and the other end opposite to the one end, and the cross-sectional shape of the multilayer film structure on the substrate has a lower shape at one end and a higher shape at the other end. 9. The dispersion compensator according to claim 8, wherein: 13. The dispersion compensator according to claim 7, further comprising means for changing a temperature of the dispersion compensator, as means for changing a refractive index of the dielectric thin film of the multilayer structure. A dispersion compensator characterized in that the value of the amount of dispersion received while incident light passes through the multilayer structure is continuously changed by changing the transmission center wavelength. 14. A substrate on which the multilayer structure is formed or at least one thin film of the multilayer structure is made of an optically active semiconductor material, and photo-excitation or current injection is performed from an end of the substrate. 9. The dispersion compensator according to claim 7, wherein an optical signal optically amplified by pumping is output. 15. A dispersion compensator according to claim 7, wherein a plurality of stages are arranged in series, and said dispersion compensators have different amounts of dispersion, and can compensate for nonlinear dispersion. A dispersion compensator characterized in that: 16. A dispersion compensator comprising the multilayer structure of the dispersion compensator according to claim 7 provided on a light emitting surface of a light emitting element.