JP2002318354A - Light waveform shaping device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light waveform shaping device which can sufficiently vary chromatic dispersion characteristics. SOLUTION: Plastic photonic crystal 2 is formed by incorporating micro spheres or air bubbles of silica or barium titanate in a gel of a substance and used as a dispersing medium which gives chromatic dispersion to input light. When the photonic crystal 2 is applied with an external force by an external force applying means 3 constituting a chromatic dispersion control means, the photonic crystal 2 deforms and its photonic band structure and chromatic dispersion characteristics accompanying the band structure easily vary. Consequently, the light wavelength shaping device is actualized which can sufficiently vary the chromatic dispersion characteristics by the application of the external force.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveform shaping device using a photonic crystal.

[0002]

2. Description of the Related Art A semiconductor single crystal is a substance in which specific atoms are periodically and regularly arranged. The electron propagation characteristics in such a semiconductor single crystal are determined by the type of atoms constituting the crystal and the atomic spacing of the arrangement. That is, the electron propagation characteristics in the semiconductor single crystal indicate a band structure having an energy band gap generated due to the wave nature of the electrons and the periodic potential due to the constituent atoms.

[0003] On the other hand, a photonic crystal has a band structure for light, similar to the above band structure for electrons, and has a structure similar to that of Yablonovich.
It is a three-dimensional structure proposed by Mr. et al. In a photonic crystal, a band structure with respect to light is generated by the wave property of light and a periodic structure in which substances having a refractive index difference, which is a potential difference with respect to light, are arranged at a period about the wavelength of light.

[0004] In a photonic crystal, the light propagation characteristics are limited by the constraints on the wave nature of light due to its three-dimensional structure. That is, in a photonic crystal, there is a photonic band gap, which is an energy band gap for light, and light in a specific wavelength band cannot propagate through the crystal. Show properties. Fabry-Perot interferometers, multilayer mirrors, and the like are also zero-dimensional or one-dimensional photonic crystals.

Conventionally, various photonic crystals have been proposed. For example, there is a type in which particles of submicron size are arranged at a cycle of about the wavelength of light. In the case of a microwave band, a type in which polymer spheres as particles are arranged in a space is known.

In addition, a method in which a polymer microsphere is solidified in a metal and then the polymer sphere is chemically dissolved to form a periodic minute space in the metal, and a hole is formed in the metal at regular intervals. And a solid material in which a region having a different refractive index from the surroundings is formed using a laser, and a photopolymerizable polymer processed into a groove shape using a lithography technique.

[0007]

The photonic crystals formed by these processes are produced with high precision in order to generate a photonic band gap. Then, once the crystal structure is determined, the photonic crystal has a photonic band structure uniquely determined according to the structure.

On the other hand, such a photonic crystal has a wavelength dispersion characteristic corresponding to the photonic band structure because transmission characteristics and reflection characteristics at different wavelengths differ depending on the band structure. It is considered that this wavelength dispersion characteristic can be applied to an optical waveform shaping device or the like. However, in such an optical waveform shaping device, since the photonic band structure of the photonic crystal cannot be sufficiently changed, the wavelength dispersion characteristics cannot be made variable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an optical waveform shaping device capable of sufficiently changing chromatic dispersion characteristics.

[0010]

In order to achieve the above object, an optical waveform shaping device according to the present invention provides an optical waveform shaping device for generating a predetermined chromatic dispersion for input light within a predetermined wavelength band. A dispersion medium comprising a plastic photonic crystal having a photonic band structure and a wavelength dispersion characteristic having a different refractive index for each wavelength, and having a wavelength dispersion characteristic changed by applying an external force or an external field. And a wavelength dispersion control means for maintaining or changing the wavelength dispersion characteristics of the photonic crystal.

In the above-described optical waveform shaping device, a plastic photonic crystal is used as a dispersion medium for generating wavelength dispersion for input light. At this time, if the photonic crystal is deformed by applying an external force through the wavelength dispersion control means, the photonic band structure (photonic band gap) changes greatly, and the wavelength dispersion characteristics (group velocity or group velocity dispersion) of the photonic crystal are changed. Characteristic) can be changed sufficiently.

Also, when an external field is applied via the chromatic dispersion control means, the photonic band structure and the chromatic dispersion characteristics can be similarly changed. As such an external field, for example, there are fields such as an electric field, a magnetic field, a force, and a temperature field that change the refractive index and the position of the periodic structure in the photonic crystal.

In such an optical waveform shaping device, even when the volume of the photonic crystal itself is reduced, the optical waveform can be effectively shaped, so that the entire device can be reduced in size.

Further, the photonic crystal is characterized in that the photonic band gap in the photonic band structure is formed so as to have a wavelength near the wavelength of the input light. With such a wavelength configuration, it is possible to generate sufficient chromatic dispersion for the input light and to efficiently shape the optical waveform.

Further, it is characterized in that the input light is configured to pass through the photonic crystal a plurality of times and to be output. According to such a configuration, the chromatic dispersion generated in the input light can be increased.

As a configuration for transmitting light a plurality of times as described above, for example, in addition to a photonic crystal which is a dispersion medium, a pair of reflecting means arranged to form a reciprocating optical path passing through the photonic crystal may be used. An optical output means installed on the reciprocating optical path and configured to be able to switch between light output from the reciprocating optical path and output to the reciprocating optical path or output to the output optical path to the outside of the apparatus. It is preferable to further include As the light output means, for example, there is a configuration in which a switchable polarization element such as a Pockels cell and a polarization beam splitter are combined.

Further, as the photonic crystal, two photonic crystals capable of passing input light and having one wavelength dispersion characteristic positive and the other wavelength dispersion characteristic negative with respect to the wavelength of the input light are used. Is used. Thus, various optical waveforms can be shaped by combining photonic crystals having wavelength dispersion characteristics of opposite signs.

Further, in addition to the photonic crystal, which is a dispersion medium, an optical device for inputting light output from an input light passing through the photonic crystal and performing a predetermined conversion, and a light output from the optical device. And a wavelength dispersion element that generates a wavelength dispersion opposite to that of the photonic crystal. As for the wavelength dispersion element provided at the subsequent stage of the optical device, a photonic crystal may be used similarly to the dispersion medium at the previous stage.

The chromatic dispersion control means is characterized in that the chromatic dispersion control means includes external force applying means for applying an external force to the photonic crystal. There are various external force applying means.

For example, there is a configuration in which a container for storing a photonic crystal is further provided, and the external force applying means applies a pressure as an external force in a certain direction to the photonic crystal stored in the container. In this case, the photonic crystal can be held by the outer wall of the container, and deformation due to a force other than a desired external force can be suppressed, and the direction of the deformation can be restricted.

At this time, it is preferable that at least a part of the outer wall of the container is made transparent or a transparent window is provided in this part. In this case, the input light is introduced into the photonic crystal via an outer wall or window portion transparent to the input light, but the photonic crystal is held by the outer wall of the container, so that the number of parts can be reduced. .

Preferably, the container is formed by processing a semiconductor substrate, and the external force applying means is a piezoelectric element formed on the semiconductor substrate and deforming in response to an electric input. . In this case, a photonic crystal is arranged in a container such as a concave portion formed in a semiconductor substrate, and a piezoelectric element is formed on the semiconductor substrate. The whole can be reduced in size.

The external force applying means is a hollow member which can be deformed so as to change its inner diameter, and the photonic crystal is arranged in the hollow member. Since the hollow member is deformed so as to change the inner diameter, the photonic crystal is deformed in accordance with this deformation so as to expand and contract in the longitudinal direction of the hollow member. Input light is input from one end of the photonic crystal in the longitudinal direction, and output light is output from the other end. Therefore, in this case, the spread of light in the radial direction can be suppressed, and a decrease in the intensity of output light per unit area can be suppressed.

Further, there is a configuration in which the external force applying means is a piezoelectric element which is deformed in response to an electric input. In this case, since an external force is applied to the photonic crystal when the piezoelectric element is deformed by an electric input, a system for performing an electric input based on a specific measured value or the like can be configured.

The external force applying means may be a pressing mechanism for pressing the photonic crystal in response to a manual input. In this case, the external force can be manually adjusted in the measurement system.

Further, the apparatus further comprises feedback means for measuring a physical quantity which changes in accordance with the photonic band structure of the photonic crystal, and controlling retention or change of the chromatic dispersion characteristic by the chromatic dispersion control means based on the measured value. Features. When a desired chromatic dispersion characteristic is obtained, a physical quantity that changes according to the corresponding photonic band structure can be measured, and the operation of the chromatic dispersion control means can be controlled by the feedback means. For example, when the chromatic dispersion control means includes an external force applying means,
The application of the external force by the external force applying means is controlled.

Further, the apparatus further comprises a heater for heating the photonic crystal, and a temperature sensor for measuring the temperature of the photonic crystal, wherein the heating by the heater is controlled based on the temperature measured by the temperature sensor. In this case, since the heating is performed while measuring the temperature of the photonic crystal with a temperature sensor, the temperature of the photonic crystal can be set to a desired value, preferably a substantially constant value, and the temperature of the photonic band structure and the wavelength dispersion characteristic can be increased. Can be suppressed.

As a photonic crystal used in the optical waveform shaping device, there is a photonic crystal characterized by containing a plurality of silica or barium titanate microspheres in a gel substance. Further, the photonic crystal may include a plurality of microspaces formed in a gel-like substance. In these cases, a plastic photonic crystal that can easily deform the photonic crystal can be obtained.

The wavelength dispersion controlling means may include an external field applying means for applying an external field to the photonic crystal. There are various external field applying means.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the optical waveform shaping device according to the present invention will be described below in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.

FIG. 1 is a block diagram schematically showing an embodiment of an optical waveform shaping device according to the present invention. This optical waveform shaping device is an optical waveform shaping device that gives desired wavelength dispersion to input light having a wavelength within a predetermined wavelength band and shapes the optical waveform. In an optical waveform shaping device, an optical waveform is shaped by a dispersion medium having a wavelength dispersion characteristic having a different refractive index for each wavelength within a predetermined wavelength band.

The optical waveform shaping device shown in FIG.
Photonic crystal 2 which is a dispersion medium installed on a base 1
Pressurizing / depressurizing device 3 which is an external force applying means for applying an external force to the photonic crystal 2 (increasing or decreasing the external force)
And is configured. A first optical element 5 is provided on the input side of the photonic crystal 2, and a second optical element 6 is provided on the output side. The optical elements 5 and 6 on the input side and the output side are respectively installed as necessary, and a configuration in which neither is installed may be adopted.

The photonic crystal 2 has a photonic band structure and a wavelength dispersion characteristic corresponding to the photonic band structure according to the crystal structure. The photonic crystal 2 is plastic and, as described later, is deformed with high accuracy by the application of an external force, and its wavelength dispersion characteristic changes according to the deformation. That is, when the photonic crystal 2 is deformed by application of an external force in the pressurizing / depressurizing device 3, the photonic band structure and the corresponding wavelength dispersion characteristics change.

The pressurizing / depressurizing device 3 is controlled by an external pressure control device 4 which is an external force control means. The external pressure control device 4 accurately controls the magnitude of the external force and the application time.
In the present embodiment, the pressurizing / depressurizing device (external force applying means) 3 and the external pressure control device 4 constitute a chromatic dispersion control means for maintaining or changing the chromatic dispersion characteristics of the photonic crystal 2.

The input light within a predetermined wavelength band whose optical waveform is to be shaped is incident on the photonic crystal 2 via the first optical element 5. At this time, chromatic dispersion according to the chromatic dispersion characteristics of the photonic crystal 2 occurs for the input light propagating in the photonic crystal 2. The light having the desired wavelength dispersion and shaped into an optical waveform is emitted from the photonic crystal 2 and output as output light to the outside of the optical waveform shaping device via the second optical element 6.

The plastic photonic crystal 2 used in the optical waveform shaping device will be described. FIG. 2 is a perspective view illustrating an example of the photonic crystal 2.

This photonic crystal 2 is a gel-like substance 2
G contains a plurality of silica or barium titanate microspheres (optical microcrystals) 2B. This photonic crystal 2 is plastic and can be easily deformed.
The microspheres 2B are regularly and uniformly arranged in the material 2G at a period about the wavelength of light.

The interval between the microspheres 2B is set to, for example, about half to one-fourth of the wavelength in accordance with the wavelength band of the input light whose optical waveform is to be shaped. With this crystal structure, a photonic band structure is generated in the photonic crystal 2. In addition, since the gel is easily deformed by an external force, the crystal structure of the photonic crystal 2 and therefore the photonic band structure thereof are easily changed. Due to this change, the wavelength dispersion characteristic for light passing through the photonic crystal 2 also changes. The microsphere 2B and the substance 2G have different refractive indices, and both are transparent to the selected light wavelength or have an appropriate transmittance.

For example, a material obtained by mixing a sol material with an ultraviolet curable resin and irradiating it with ultraviolet light to form a gel can obtain the above-mentioned gel-like substance 2G. A typical UV-curable resin is a mixture of acrylamide with a crosslinking agent and a photopolymerization initiator, and many of them are conventionally known. In addition, since the number of periodic structures of the microspheres 2B may be about 50, the photonic crystal 2 sufficiently functions with an element having a size of about 100 μm square at the maximum.

Another example of the photonic crystal 2 is a photonic crystal 2 having the configuration shown in FIG. 2 in which the microspheres 2B arranged in the gel material 2G are replaced with microspaces. Is also good. As a specific minute space, a configuration in which a plurality of bubbles are arranged in the gel material 2G can be used. Such a photonic crystal 2 can also be easily deformed by an external force.

In the optical waveform shaping device described above, a plastic photonic crystal 2 is used as a dispersion medium for generating wavelength dispersion with respect to input light. At this time, if the photonic crystal 2 is deformed by applying an external force through the wavelength dispersion control means including the external force applying means 3 and the external pressure control device 4, the photonic band structure (photonic band gap) changes greatly, 2 can sufficiently change the wavelength dispersion characteristic (group velocity or group velocity dispersion characteristic).

That is, by using the photonic crystal 2 capable of changing the photonic band structure by applying an external force, the optical elements 5 and 6 on the input side and the output side are used.
Thus, an optical waveform shaping device in which the wavelength dispersion characteristics between the wavelengths sufficiently changes is obtained.

As described later, such a plastic photonic crystal has characteristics such as a larger wavelength dispersion characteristic than ordinary glass or the like and a change (tuning) property in a wavelength region caused by crystal plasticity. Therefore, it has many advantages as compared with wavelength dispersion elements such as prisms, diffraction gratings, and glass blocks used in conventional optical waveform shaping devices.

For example, in such an optical waveform shaping device, even when the volume of the photonic crystal 2 itself is reduced, the optical waveform can be effectively shaped as described above. Therefore, if this photonic crystal 2 is used, the size of the device can be reduced. Note that the photonic crystal 2 may have elasticity.

In a conventional chromatic dispersion element such as a prism, chromatic dispersion is greatly affected by the incident direction and angle of input light to the element. For example, in the case of a diffraction grating, when the number of gratings per unit length and the cut angle of the grating are determined, the wavelength dispersion characteristics are uniquely determined. Therefore, light can be incident from any direction or light can be incident many times. It is difficult to adopt such a configuration. On the other hand, when the photonic crystal 2 is used, various configurations are possible.

When a photonic crystal having no plasticity is used, the photonic band structure is changed by changing the temperature of the crystal or irradiating the crystal with high-intensity light to generate a nonlinear optical effect. Is possible. However, when the band structure is controlled by the temperature, there is a problem that the response is slow. Further, in the case of controlling by light irradiation, there is a problem that a high-intensity excitation light is required and optical deterioration of the crystal occurs. Further, in any of the control methods, the obtained variable range is narrow.

On the other hand, according to the plastic photonic crystal in which the photonic band structure is changed by applying an external force, the photonic band structure and the wavelength dispersion characteristic can be easily changed in a sufficient variable range. Becomes

The photonic band structure and wavelength dispersion characteristics generated in the photonic crystal 2 will be specifically described with reference to examples.

FIG. 3 is a graph showing the wavelength (nm) dependence of light transmittance (arbitrary constant) in a photonic crystal having a multilayer structure, that is, a dichroic mirror. The input light is white light. In this graph, a transmission characteristic is obtained in which the transmittance of light near a wavelength band of 400 nm is lower than the surrounding wavelength band, corresponding to the photonic band gap generated in the photonic crystal. Note that this graph is not based on the photonic crystal 2 having the above-described configuration, but when the microspheres 2B are completely arranged at equal intervals, the optical characteristics of the microspheres 2B in a specific direction are shown in FIG.
Is the same as that shown in FIG.

A photonic crystal having such a photonic band structure exhibits a characteristic wavelength dispersion characteristic corresponding to the band structure (for example, see Arnout Imhof et al.
l., Phys. Rev. Lett. vol.83, p.2942 (1999) ").
That is, since the photonic crystal has different transmission characteristics and reflection characteristics at different wavelengths depending on the band structure, the refractive index of light in the photonic crystal at different wavelengths, that is, the wavelength dispersion of the light propagation speed (phase velocity, group velocity) differs. Has characteristics.

FIGS. 4A to 4C are graphs showing an example of the wavelength dispersion characteristics of the photonic crystal (see the above-mentioned document). In these graphs, each horizontal axis is indicated by frequency (10 ¹⁵ rad / s),
This corresponds to the wavelength of the input light. These graphs were obtained using unfixed photonic crystals formed in the solution.

FIG. 4A is a graph showing the wavelength dependence of the transmittance of the photonic crystal. In this graph, FIG.
As in the case of the graph of FIG.
(Near 4 × 10 ¹⁵ rad / s), a photonic band structure in which the transmittance is reduced is obtained.

On the other hand, the wavelength dispersion characteristics of the photonic crystal corresponding to this photonic band structure are shown in FIG.
(B) and (c). FIG. 4B shows the delay time Δt (ps, corresponding to the group delay) obtained when the input light passes through the photonic crystal, and FIG.
Indicates group velocity dispersion parameter β ₂ (ps ² / m, corresponding to group velocity dispersion). Here, in these two graphs, each point in the graph indicates an actually measured value, and a solid line indicates a calculated value theoretically analyzed.

As shown in the graphs of FIGS. 4B and 4C, the photonic crystal exhibits wavelength dispersion characteristics according to the photonic band structure. Therefore, by using a photonic crystal having such wavelength dispersion characteristics as a dispersion medium of an optical waveform shaping device, it becomes possible to shape an optical waveform of input light. In particular, the value of the chromatic dispersion in the photonic crystal is about two to three orders of magnitude larger than that of ordinary glass or the like, so that the chromatic dispersion can be imparted with high efficiency and the optical waveform can be shaped thereby.
Further, since a sufficient wavelength dispersion can be obtained even if the volume of the photonic crystal as the dispersion medium is reduced, the size of the apparatus can be reduced.

Specifically, the photonic crystal is shown in FIG.
As shown in the graphs of (b) and (c), a large chromatic dispersion is exhibited near the photonic band gap. Therefore, the photonic crystal used in the optical waveform shaping device includes:
It is preferable to use one formed such that the wavelength of the photonic band gap in the photonic band structure is near the wavelength of the input light. With such a wavelength configuration, it is possible to generate sufficient chromatic dispersion for the input light and to efficiently shape the optical waveform.

Next, the variability of the photonic band structure and the wavelength dispersion characteristics of the photonic crystal will be described.

FIG. 5 is a graph showing the wavelength (nm) dependence of the light reflectance (arbitrary constant) of a photonic crystal having a multilayer structure, that is, a dichroic mirror. FIG.
5A is a graph when no external force is applied to the dichroic mirror, and FIG. 5B is a graph when pressure (external force) is applied in the compression direction so that 1% lattice distortion occurs in the mirror vertical direction. FIG. 5C is a graph in the case where pressure is applied in the spreading direction so that 1% lattice distortion occurs in the mirror vertical direction.

Note that pressure can be applied so that lattice distortion occurs along the mirror surface. Further, the graph of FIG. 5A corresponds to the transmittance graph shown in FIG. 3 or FIG. Although this graph is not based on the photonic crystal 2 having the above-described configuration, the tendency of the change in the optical characteristics is the same.

According to these graphs, the reflection intensity peak when no external force is applied has a wavelength λc = 1500 n
m (FIG. 5A). On the other hand, when 1% compression strain is applied, the wavelength λc is 1480 nm.
(FIG. 5 (b)) and shift to the shorter wavelength side, while 1%
Is applied, the wavelength λc is 1520 nm.
The degree (FIG. 5C) is shifted to the longer wavelength side.

That is, when a slight lattice distortion due to an external force is introduced into the photonic crystal, the photonic band structure changes due to a change in the crystal structure in the crystal, and the obtained transmission characteristics and reflection characteristics change with the wavelength of the input light. Change with respect to Further, as described above with reference to FIGS. 4A to 4C, the wavelength dispersion characteristics of the photonic crystal show a large wavelength dispersion near the photonic band gap, and the photonic band structure, particularly, the position of the photonic band gap. Depends heavily on

As described above, by applying an external force to the plastic photonic crystal by the chromatic dispersion control means to introduce lattice distortion, the chromatic dispersion characteristics can be changed with respect to the wavelength. Therefore, according to the optical waveform shaping device having the configuration shown in FIG. 1, an optical waveform shaping device capable of sufficiently changing the wavelength dispersion characteristics is realized.

Hereinafter, a preferred example of the optical waveform shaping device according to the above embodiment will be described.

FIG. 6 is a block diagram showing a first embodiment of the optical waveform shaping device. In this embodiment, the external force applying means 3
A pressing plate 30 and a piezoelectric element (piezo element) 31 are used. In response to this, a variable voltage power supply 41 is used as the external pressure control device 4. Thereby, in the present embodiment, the holding plate 30, the piezoelectric element 31, and the power source 41
Constitutes a chromatic dispersion controller.

In the configuration shown in FIG. 6, a holding plate 30 is disposed above photonic crystal 2, and holding plate 30 holds photonic crystal 2 together with base 1. The upper surface of the piezoelectric element 31 is fixed to the base 1, and the lower surface of the piezoelectric element 31 is
It is fixed to 0.

Here, when a voltage is applied to the piezoelectric element 31 from the power supply 41, the piezoelectric element 31 moves in a direction perpendicular to the surface of the base 1 in accordance with the voltage applied from the power supply 41 and its change. Go to At this time, since the distance between the holding plate 30 fixed to the piezoelectric element 31 and the base 1 changes, the photonic crystal 2 is deformed so as to extend along the optical path, and its photonic band structure and wavelength dispersion are changed. The characteristics change. In this embodiment, the window material 10 is provided on the light input surface and the light output surface of the photonic crystal 2 respectively.
Is pasted.

In the above configuration, when the input light enters the photonic crystal 2 through the input side window member 10, the incident light propagates through the photonic crystal 2 and is applied from the external force applying means 3. The chromatic dispersion generated by the chromatic dispersion characteristic determined according to the applied external force is given. And
The light whose desired chromatic dispersion is given and whose optical waveform is shaped is
The light is output as output light through the window member 10 on the output side.

For example, as shown schematically in FIG. 6, it is assumed that an optical pulse having a short time width (for example, femtosecond) is input as input light. Such an input light pulse is
It contains wavelength components spread within a certain wavelength band. When such a light pulse propagates through the photonic crystal 2,
Due to the wavelength dispersion characteristics of the photonic crystal 2, the propagation time differs for each wavelength component.

That is, if the chromatic dispersion is positive, the long wavelength component (for example, a red light beam) propagates quickly and the short wavelength component (for example, a blue light beam) propagates slowly. A spread light pulse is obtained. vice versa,
If the chromatic dispersion is negative, the short-wavelength component propagates earlier and the long-wavelength component propagates later, and an optical pulse that is temporally spread with the short-wavelength component at the top is obtained as output light.

Here, in the photonic crystal 2, as shown in FIGS. 4 (a) to 4 (c), the chromatic dispersion at the two band ends on the short wavelength side and the long wavelength side with respect to the photonic band gap. Is reversed. Therefore, if the photonic crystal 2 and the like are configured so that the wavelength of the photonic band gap in the photonic band structure is close to the wavelength of the input light, and the photonic band structure is adjusted by the external force applying means 3, The shaping of the optical waveform as described above can be performed efficiently.

The external force applying means 3 of this embodiment applies an external force to the photonic crystal 2 by deforming the piezoelectric element 31 by an electric input. A system for inputting can be configured.

Further, the window material 10 is
Is provided, the light input surface and light output surface of the photonic crystal 2 are protected. An optical element such as an optical filter may be used as the window material 10. Further, the window material 10 may be provided on only one of the light input surface and the light output surface.

FIG. 7 is a block diagram showing a second embodiment of the optical waveform shaping device. In this embodiment, the external force applying means 3
The configuration such as is the same as that of the embodiment of FIG. A concave mirror 11 is provided on the light input surface side and the light output surface side of the photonic crystal 2 at a predetermined distance from each other.

In the above configuration, when input light enters the photonic crystal 2 from a predetermined input optical path, the incident light is reflected by the pair of concave mirrors 11 and passes through the photonic crystal 2 a plurality of times. Thereafter, the light is output to a predetermined output optical path as output light.

According to such a configuration, the propagation distance of light in the photonic crystal 2 increases with each pass, so that
The chromatic dispersion given to the input light can be increased. Further, since the photonic crystal 2 required to obtain the desired wavelength dispersion can be small, the size of the device can be reduced.

In FIG. 7, the photonic crystal 2
An optical path of light passing through the inside a plurality of times is schematically illustrated for explanation. Actually, it is necessary to repeat the passage of light in a direction exhibiting the wavelength dispersion characteristic accurately in consideration of each optical path and the crystal orientation of the photonic crystal 2. Further, the reflection means provided on both sides of the photonic crystal is not limited to the concave mirror 11, but a plane mirror or the like may be used.

FIG. 8 is a block diagram showing a third embodiment of the optical waveform shaping device. In the present embodiment, the configuration such as installation of the external force applying means 3 and the window member 10 is the same as that of the embodiment of FIG. Further, in addition to the photonic crystal 2a in the preceding stage, which is a dispersion medium into which the input light is incident, an optical device 71 to which light output by passing the input light through the photonic crystal 2a is input, and an output from the optical device 71. A photonic crystal 2b, which is a wavelength dispersion element (dispersion medium) at a subsequent stage to which the input light is input, is further provided. The configuration of the external force applying means 3 and the like in the photonic crystal 2b in the subsequent stage is the same as that in the photonic crystal 2a in the preceding stage.

In the above configuration, the desired wavelength dispersion is given to the input light by the photonic crystal 2a at the preceding stage. Thereafter, the light from the photonic crystal 2a is subjected to a predetermined conversion in the optical device 71, and a desired wavelength dispersion is given by the subsequent photonic crystal 2b, and the light is output as final output light.

More specifically, for example, the wavelength dispersion characteristic of one photonic crystal 2a with respect to the wavelength of input light is defined as positive (negative), and the wavelength dispersion characteristic of the other photonic crystal 2b is defined as negative (positive) with the opposite sign. It is possible to adopt a configuration in which

At this time, as schematically shown in FIG. 8, the input light pulse having a short time width is converted by the optical device 71 after being chirped by the photonic crystal 2a. Then, by applying the opposite wavelength dispersion to the photonic crystal 2b at the subsequent stage, the time width is shortened again, and the photonic crystal 2b is output as a desired converted output optical pulse.

As described above, by using a configuration in which an optical device and a subsequent wavelength dispersion element are provided in addition to a photonic crystal, or a configuration in which a photonic crystal having wavelength dispersion characteristics of the opposite sign is combined, various optical waveforms can be obtained. Can be shaped. As the optical device 71, various devices such as an optical amplifier, an optical waveform shaping element, and a polarizing element can be applied. For example, when an optical amplifier is applied as the optical device 71, a configuration of a chirp / pulse amplifying device that temporarily widens the input light, amplifies the light once, and performs optical compression again can be adopted.

The wavelength dispersion characteristics of the opposite sign in the two photonic crystals 2a and 2b may be determined, for example, by using a photonic crystal having a different crystal structure or using a photonic crystal having the same crystal structure. A configuration in which the external force applied to each of the band ends on both sides of the gap is controlled can be employed. Further, it is also possible to adopt a configuration in which light passes through one photonic crystal twice, and to give different wavelength dispersions by changing an external force applied to the photonic crystal in each pass.

Further, these two photonic crystals 2a,
The chromatic dispersion characteristic set to 2b is not limited to the reverse sign, and may be set variously according to the purpose. For the wavelength dispersive element added at the subsequent stage, a photonic crystal (dispersion medium)
Not limited to 2b, another wavelength dispersion element such as a prism or a diffraction grating may be used.

FIG. 9 is a block diagram showing a fourth embodiment of the optical waveform shaping device. In this embodiment, the external force applying means 3
The configuration such as is the same as that of the embodiment of FIG. Further, in addition to the photonic crystal 2 which is a dispersion medium for providing wavelength dispersion to the input light, a reflecting mirror 12 which is a pair of reflecting means arranged so as to form a reciprocating optical path passing through the photonic crystal 2, A Pockels cell (polarizing element) 72 and a polarizing beam splitter 73 which are provided on a reciprocating optical path and constitute light output means are further provided.

The optical waveform shaping device of this embodiment has a configuration in which a large wavelength dispersion can be obtained by passing light through the photonic crystal 2 a plurality of times, as in the embodiment of FIG. In particular, by installing light output means including the Pockels cell 72 and the polarization beam splitter 73 in addition to the pair of reflecting mirrors 12, it is possible to realize a plurality of passes of light on the same reciprocating optical path, Is variable.

That is, when input light having a predetermined linear polarization is input from the input optical path to the reciprocating optical path via the polarization beam splitter 73, the Pockels cell 72 is operated when the input light first passes. The plane of polarization of the light is rotated. The light whose polarization plane has been rotated reciprocates in a reciprocating optical path between the two reflecting mirrors 12 and passes through the photonic crystal 2 a plurality of times. Then, the Pockels cell 72 is operated again at a predetermined timing to rotate the polarization plane of the light, and the output light is taken out to the output optical path via the polarization beam splitter 73.

As described above, the light input from the reciprocating optical path is output (transmitted) to the reciprocating optical path again, or
By providing an optical output means capable of switching whether to output (reflect) the output light path to the outside of the device, it is possible to extract the output light after passing the input light through the photonic crystal 2 a desired number of times. Become. In this configuration, the number of times light passes through the photonic crystal 2 can be changed, so that the amount of chromatic dispersion given to input light can be changed. The light output means is not limited to the configuration including the Pockels cell 72 and the polarization beam splitter 73 described above, and various means may be used.

Although the piezoelectric elements 31 are used as the external force applying means 3 in the above-described embodiments of FIGS.
The external force applying means 3 is not limited to the piezoelectric element 31,
Various things may be used.

FIG. 10 is a block diagram showing a fifth embodiment of the optical waveform shaping device. In the present embodiment, the external force applying means 3 shown in FIG. 1 is a pressing mechanism 3 for pressing the photonic crystal 2 in response to a manual input, except that the external pressure control device 4 is manually input. Other configurations are the same as those in FIG. In this case, the pressing mechanism 3 serves as a wavelength dispersion control unit.

The pressing mechanism 3 includes a support plate 32a disposed at a position fixed to the base 1, a screw portion 32b screwed into a screw hole provided in the support plate 32a, and a screw portion 32b.
And a screw feed mechanism comprising a screwdriver head 32c fixed to one end of the screw feeder. The holding plate 30 is in contact with the other end of the screw portion 32b.

In this configuration, when the head 32c is rotated in a predetermined direction, the screw portion 32b moves in the direction of the holding plate 30. Since the lower surface of the holding plate 30 is fixed to the photonic crystal 2 with an adhesive, an external force is applied to the photonic crystal 2 with the rotation of the head 32c, and the photonic crystal 2 is deformed so as to extend along the optical path. . The photonic crystal 2 is plastic, but can be deformed with compressibility and spreadability.

Such an optical waveform shaping apparatus allows manual fine adjustment of an external force in an experimental measurement system.
This apparatus can be applied to basic research on the wavelength dispersion characteristics of photonic crystals.

FIG. 11 is a block diagram showing a sixth embodiment of the optical waveform shaping device. The optical waveform shaping device according to the present embodiment further includes a container 8 for storing a photonic crystal, and the external force applying unit 3 includes a photonic crystal 2 contained in the container 8.
, A pressure as an external force is applied in a certain direction. In this case, the photonic crystal 2 is held by the outer wall of the container 8, and deformation due to a force other than a desired external force can be suppressed, and the direction of the deformation can be limited. FIG.
1 shows a case where the piezoelectric element 31 is used as the external force applying means 3.

Here, at least a part of the outer wall of the container 8, that is, a part including the optical path of the input light is transparent. Alternatively, a transparent window may be provided in this portion.
Input light enters the photonic crystal 2 via the transparent outer wall or window. Similarly, the outer wall portion including the optical path of the output light can be transparent. Since the photonic crystal 2 is held by the outer wall of the container 8, the number of parts required for the device can be reduced.

In the above and following embodiments, a tube type piezoelectric element may be used as the external force applying means 3 of the photonic crystal 2. FIG. 12 is a perspective view showing a main part of a seventh embodiment of an optical waveform shaping device using a tube type piezoelectric element. The piezoelectric element 31 as the external force applying means 3 is a tubular hollow member, which is used as a container 8 and the photonic crystal 2 is disposed inside the container 8. That is, the external force applying means 3 in the present embodiment is a piezoelectric element (hollow member) 31 that can be deformed so that the inner diameter changes.

Since the piezoelectric element 31 is deformed so as to change the inner diameter, the photonic crystal 2 is deformed so as to expand and contract in the longitudinal direction of the hollow piezoelectric element 31 in accordance with the deformation. The input light is input from one end of the photonic crystal 2 in the longitudinal direction, and the output light is output from the other end. Therefore, with such a configuration, the spread of light in the radial direction can be suppressed, and a decrease in the intensity of the output light per unit area can be suppressed.

FIG. 13 is a block diagram showing an eighth embodiment of the optical waveform shaping device. In the optical waveform shaping device of the present embodiment, the window material 10 is provided on each of the light input surface and the light output surface of the photonic crystal 2, and a physical quantity that changes according to the photonic band structure (photonic band gap) of the photonic crystal 2. Is measured, and an optical characteristic measuring device 90 is provided which constitutes feedback means for controlling retention or change of chromatic dispersion characteristics by the chromatic dispersion control means based on the measured value.

In this embodiment, the optical characteristic measuring device 90
The power supply 41 constitutes a feedback unit. The feedback means controls the magnitude of the external force applied to the photonic crystal 2 by the external force applying means 3 in response to the chromatic dispersion control means including the external force applying means 3.

When the wavelength dispersion characteristic of the photonic crystal 2 is set to a desired wavelength dispersion characteristic, a physical quantity, preferably an output light intensity or an output light spectrum, which changes according to the corresponding photonic band structure is measured. Then, the external force applying unit 3 is controlled via the feedback unit including the optical characteristic measuring device 90 and the power supply 41 so that the intensity of the output light or the intensity of the specific wavelength becomes constant.

More specifically, the light whose optical waveform has been shaped by the photonic crystal 2 has its intensity or spectrum measured by the optical characteristic measuring device 90 as output light. Then, the piezoelectric element 31 as a structure control device of the photonic crystal 2 is feedback-controlled via the power supply 41 so that the measurement data satisfies a specific condition.

By this feedback control, it is possible to stabilize the response characteristics of the output light by the photonic crystal 2 and to achieve high accuracy.

The photonic crystal 2 can also be manufactured by using a semiconductor fine processing technology (micro-electromechanical: MEMS technology). For example, the above-described container is formed by processing a semiconductor substrate, and the piezoelectric element 31 is formed on the semiconductor substrate (not shown). in this case,
The photonic crystal 2 is arranged in a container formed on the semiconductor substrate, particularly in the concave portion, and the piezoelectric element 31 is formed on the semiconductor substrate. Can be reduced in size. Of course, a drive circuit for the piezoelectric element 31, a power supply, a photodiode with a wavelength filter, and the like can be further formed in the semiconductor substrate.

The above-described semiconductor fine processing technique is also used, for example, when manufacturing a probe of a scanning tunneling microscope. This probe is provided with a piezoelectric element, but can control expansion and contraction of the piezoelectric element on the order of several nm.

FIG. 14 is a block diagram showing a ninth embodiment of the optical waveform shaping device. The optical waveform shaping device of the present embodiment has
In comparison with the third embodiment, the heater 91, the temperature sensor 92,
The difference is that a heater power supply 93 is provided, and the other configuration is the same as that shown in FIG.

In this optical waveform shaping device, a heater 91 for heating the photonic crystal 2 is provided on the base 1. A temperature sensor 92 for measuring the temperature of the photonic crystal 2 is provided on the base 1. These are all arranged near the photonic crystal 2. The heater power supply 93 controls the power supplied to the heater 91 based on the temperature measured by the temperature sensor 92.

In this embodiment, the temperature of the photonic crystal 2 is heated while the temperature of the photonic crystal 2 is measured by the temperature sensor 92, so that the temperature of the photonic crystal 2 can be set to a desired value, preferably a constant value. . As a result, it is possible to suppress the photonic band structure, for example, the position of the photonic band gap, and the accompanying change in the wavelength dispersion characteristics due to temperature. The heater 91 and the temperature sensor 9
2 can also be made monolithically using MEMS technology.

The optical waveform shaping device according to the present invention is not limited to the above-described embodiments and examples, and various modifications are possible. For example, Fabry-Perot interferometers and multilayer mirrors (dichroic mirrors) are also zero-dimensional or one-dimensional photonic crystals, and plastic photonic crystals 2
As such, such a thing can be applied.

In the above example, the photonic crystal 2 is deformed by applying an external force via the chromatic dispersion control means including the external force applying means. However, the chromatic dispersion control means may be provided with the external field applying means. Is also good. At this time,
By applying an external field via a chromatic dispersion control unit including an external field applying unit, it is possible to similarly change the photonic band structure and the chromatic dispersion characteristics. As such an external field, for example, there are fields such as an electric field, a magnetic field, a force, and a temperature field that change the refractive index and the position of the periodic structure in the photonic crystal.

Also, the soft (plastic) as described above
The photonic crystal 2 will be used in the future to improve the stability of the size and arrangement of the microspheres 2B and the bubbles, mechanical accuracy for improving the controllability, long-term stability of the gel, temperature stability, optical fibers and other optical components. It is expected that further research will be conducted on the connection method with the gel, the gel enclosure, and the external force applying mechanism that can apply the same external force every time.

[0109]

As described above in detail, the optical waveform shaping device according to the present invention has the following effects. That is, according to the optical waveform shaping device that uses a plastic photonic crystal as a dispersion medium and includes a wavelength dispersion control unit including an external force applying unit, the optical waveform shaping that can sufficiently change the wavelength dispersion characteristics The device is realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing an embodiment of an optical waveform shaping device.

FIG. 2 is a perspective view showing an example of a photonic crystal.

FIG. 3 is a graph showing the wavelength dependence of light transmittance in a photonic crystal.

FIG. 4 is a graph showing wavelength dispersion characteristics of a photonic crystal.

FIG. 5 is a graph showing a change in wavelength dependence of light reflectivity of a photonic crystal due to an external force.

FIG. 6 is a configuration diagram showing a first embodiment of an optical waveform shaping device.

FIG. 7 is a configuration diagram showing a second embodiment of the optical waveform shaping device.

FIG. 8 is a configuration diagram showing a third embodiment of the optical waveform shaping device.

FIG. 9 is a configuration diagram showing a fourth embodiment of the optical waveform shaping device.

FIG. 10 is a configuration diagram showing a fifth embodiment of the optical waveform shaping device.

FIG. 11 is a configuration diagram showing a sixth embodiment of the optical waveform shaping device.

FIG. 12 is a perspective view showing a main part of a seventh embodiment of the optical waveform shaping device.

FIG. 13 is a configuration diagram showing an eighth embodiment of the optical waveform shaping device.

FIG. 14 is a configuration diagram showing a ninth embodiment of the optical waveform shaping device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base, 10 ... Window material, 11 ... Concave mirror, 12 ... Reflecting mirror,
2, 2a, 2b: plastic photonic crystal, 3: external force applying means (pressurizing / depressurizing device, pressing mechanism), 30: holding plate,
31: piezoelectric element, 32a: support plate, 32b: screw part, 3
2c: screwdriver head, 4: external pressure control device, 41: variable voltage power supply, 5: first optical element, 6: second optical element, 71
... Optical device, 72 ... Pockels cell, 73 ... Polarizing beam splitter, 8 ... Container, 90 ... Optical property measuring device, 91
... heater, 92 ... temperature sensor, 93 ... heater power supply.

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masaomi Takasaka 1126 Nomachi, Ichinomachi, Hamamatsu City, Shizuoka Prefecture F-term in Hamamatsu Photonics Co., Ltd. 2H041 AA21 AB10 AB38 AC02 AC07 AZ00 2H079 AA07 AA12 AA13 BA01 CA04 DA03 EB24 FA01 KA05

Claims (18)

[Claims] 1. An optical waveform shaping device for generating a predetermined chromatic dispersion with respect to input light within a predetermined wavelength band, having a photonic band structure and a wavelength dispersion characteristic having a different refractive index for each wavelength. And a dispersion medium made of a plastic photonic crystal whose wavelength dispersion characteristics change by applying an external force or an external field, and a wavelength dispersion control unit that holds or changes the wavelength dispersion characteristics of the photonic crystal. An optical waveform shaping device, characterized in that: 2. The optical waveform according to claim 1, wherein the photonic crystal is formed such that a wavelength of a photonic band gap in the photonic band structure is near a wavelength of the input light. Shaping equipment. 3. The optical waveform shaping device according to claim 1, wherein the input light is configured to pass through the photonic crystal a plurality of times and to be output. 4. In addition to the photonic crystal as the dispersion medium, a pair of reflecting means arranged so as to form a reciprocating optical path passing through the photonic crystal; Light output means configured to switch between light input from the reciprocating optical path and output to the reciprocating optical path again or output to an output optical path to the outside of the apparatus is further provided. The optical waveform shaping device according to claim 3. 5. The two photonic crystals, each of which allows the input light to pass therethrough and is capable of setting one of the wavelength dispersion characteristics to be positive and the other to be negative with respect to the wavelength of the input light. The optical waveform shaping device according to claim 1, wherein the photonic crystal is used. 6. An optical device for performing predetermined conversion by inputting, in addition to the photonic crystal serving as the dispersion medium, light output from the input light passing through the photonic crystal, and the optical device. The optical waveform shaping device according to any one of claims 1 to 5, further comprising: a chromatic dispersion element that receives light output from the device and generates chromatic dispersion opposite to the photonic crystal. . 7. The optical waveform shaping device according to claim 1, wherein said chromatic dispersion control means includes an external force applying means for applying said external force to said photonic crystal. 8. The photonic crystal according to claim 8, further comprising a container for storing said photonic crystal, wherein said external force applying means applies a pressure in a certain direction to said photonic crystal stored in said container as said external force. The optical waveform shaping device according to claim 7. 9. The optical waveform shaping device according to claim 8, wherein at least a part of an outer wall of the container is made transparent, or a transparent window is provided in this part. 10. The light according to claim 7, wherein said external force applying means is a hollow member deformable so that an inner diameter is changed, and said photonic crystal is disposed inside said hollow member. Waveform shaping device. 11. The optical waveform shaping device according to claim 7, wherein said external force applying means is a piezoelectric element which deforms in response to an electric input. 12. The container is formed by processing a semiconductor substrate, and the external force applying means is a piezoelectric element formed on the semiconductor substrate and deforming in response to an electric input. 9. The method according to claim 8, wherein
The optical waveform shaping device as described in the above. 13. The optical waveform shaping device according to claim 7, wherein said external force applying means is a pressing mechanism for pressing said photonic crystal in response to a manual input. 14. A feedback unit that measures a physical quantity that changes according to the photonic band structure of the photonic crystal and controls holding or change of the chromatic dispersion characteristic by the chromatic dispersion control unit based on the measured value. The optical waveform shaping device according to claim 1, further comprising: 15. A heater for heating the photonic crystal, and a temperature sensor for measuring a temperature of the photonic crystal, wherein heating by the heater is controlled based on the temperature measured by the temperature sensor. The optical waveform shaping device according to any one of claims 1 to 14. 16. The optical waveform shaping according to claim 1, wherein the photonic crystal contains a plurality of silica or barium titanate microspheres in a gel-like substance. apparatus. 17. The optical waveform shaping device according to claim 1, wherein the photonic crystal contains a plurality of minute spaces formed in a gel material. 18. The optical waveform shaping method according to claim 1, wherein said chromatic dispersion control means includes an external field applying means for applying said external field to said photonic crystal. apparatus.