JP2004145315A - Optical element and method of modulating optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element and a method of modulating the optical element in which the dimensional accuracy of the whole optical element is enhanced, the optical characteristic is homogenized and the freedom of selecting materials is enhanced. <P>SOLUTION: The method of modulating the optical element is characterized by the fact that the optical characteristic of the optical element is modulated by varying the diameter of columnar members by giving a force to the columnar members in a direction perpendicular to the arranging direction of the columnar members of the optical element which is formed by including a plurality of columnar members which are periodically arranged and a pair of supporting members which are arranged in the direction perpendicular to the arranged direction of the columnar members and interposing the columnar members and which optical element has a periodical structure in which the refractive index distributes periodically. The dimensional accuracy of the whole optical element is enhanced, the optical characteristic is homogenized and the freedom of selecting materials is enhanced. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an optical element and a method for modulating an optical element.

In recent years, a new artificial crystal called “photonic crystal” in which substances having different refractive indexes are periodically arranged at intervals of about a wavelength has been proposed (E. Yablonovitch, Phys. Rev. Lett., 58 (1987) 2059-2062). ), Attention. This artificial crystal exhibits unique optical characteristics, such as the band gap of light and apparent refractive index anomalies caused by the so-called photonic band structure, similar to the band structure of semiconductors. Therefore, research and development as an optical element have been actively conducted.
One of the things that attracts attention in these researches and developments is an active optical element. This is an element whose optical characteristics can be actively controlled not only at the time of design but also from outside during use, and is expected to be applied to a wide range of fields such as a variable filter and an optical switch.

As such prior art, Patent Document 1 proposes a method of controlling a refractive index distribution in a fiber by arranging an actuator around a fiber diffraction grating and expanding and contracting the actuator to apply tension to the fiber. I have.
Patent Document 2 proposes a method in which a substance such as a piezoelectric element or the like whose refractive index and transmittance is externally controllable is introduced into a crystal, and the periodicity of the crystal is disturbed by expansion and contraction of the substance and a change in characteristics. .
Patent Document 3 proposes a method of controlling the lattice spacing by applying external pressure to a photonic crystal.
JP-A-10-253829 JP-A-2001-091911 International Publication Number WO02 / 27384

However, these conventional techniques have the following problems.
Since the method of expanding and contracting the optical fiber changes the one-dimensional periodic structure arranged in the light incident direction, in addition to a member that generates expansion and contraction force, for example, a piezoelectric body, a transmission member for transmitting the force to the fiber is used. This is necessary, and there is a problem that the control accuracy of the lattice spacing is affected by the material, arrangement, connection state, and the like of these transmission members.
Although the apparent refractive index abnormality as described above appears in a two-dimensional or more periodic structure, applying a force in two or more directions via a transmission member further complicates the apparatus.
The method of incorporating a means for disturbing the crystal structure in the photonic crystal has many drawbacks in that many operation steps are required at the time of fabrication, which increases the complexity and limits the usable materials.

In the method of changing the crystal structure by applying pressure to the photonic crystal from the outside, the photonic crystal has a periodic refractive index distribution shown in FIG. 5 (vertical parallel lines in FIG. 5 indicate the period). When the nick crystal is deformed by applying pressure from the vertical direction, as shown in FIG. 6, the amount of deformation is accumulated from the central portion to the peripheral portion, and the shape of the entire crystal is greatly distorted. In addition, non-uniformity of characteristics occurs due to a portion in the crystal. Further, the change of the refractive index distribution, the change of the period, and the change of the phase within one cycle are mixed, and it is difficult to control.

Therefore, the present invention solves the above-described problems, improves the dimensional accuracy of the entire optical element, has uniform optical characteristics, and enables a high degree of freedom in material selection and modulation of the optical element. It is intended to provide a method.

The present invention provides an optical element and a modulation method of the optical element configured as follows.
The optical device of the present invention is formed to include a plurality of columnar members that are periodically arranged, and a pair of support members that are arranged in a direction perpendicular to the arrangement direction of the columnar members and sandwich the columnar member. An optical element having a periodic structure in which the refractive index is periodically distributed, and means for applying a force in a direction perpendicular to the arrangement direction from the support member to the columnar member to deform the columnar member. Features.
Further, the present invention is formed including a plurality of columnar members arranged periodically, and a pair of support members that are arranged in a direction perpendicular to the arrangement direction of the columnar members and sandwich the columnar member, The optical characteristics of the optical element are changed by applying a force to the columnar member in a direction perpendicular to the arrangement direction of the columnar member to change the diameter of the columnar member with respect to the optical element having a periodic structure in which the refractive index is periodically distributed. This is also a method for modulating an optical element, characterized by modulating.

According to the present invention, there is provided an optical element of an optical element and a method of modulating the optical element, which can increase the dimensional accuracy of the entire optical element, have uniform optical characteristics, and can increase the degree of freedom in material selection. Can be realized.

In the embodiment of the present invention, by applying the above configuration, independent columnar members made of a deformable material are periodically arranged, and a two-dimensional photonic crystal is formed by sandwiching the columnar members with a supporting member. The support member has rigidity such that deformation is negligible, and fixes the periodic arrangement with the columnar member interposed therebetween. The support member and the upper and lower bottom surfaces of the columnar member are fixed with an adhesive. Alternatively, only one of the upper and lower bottom surfaces may be bonded, and the columnar member may be supported only by pressure without bonding to both bottom surfaces. In that case, however, the external force applied to the columnar member via the support member is only pressure, and tension is not transmitted.

ア ク チ ュ エ ー タ An actuator for applying a mechanical external force to the crystal in a direction perpendicular to the support member surface is attached to the crystal, and the actuator is driven to apply a vertical force to the columnar member via the support member. This changes the height of the columnar member and the diameter and cross-sectional area of the column near the middle between the upper and lower bottom surfaces. That is, when pressure is applied from the upper and lower support members, the cross-sectional area of the columnar member increases near the center, and the cross-sectional area decreases when tension is applied. The ratio of the change in the cross-sectional area to the applied force is determined by the height and the cross-sectional shape of the columnar member, and the Young's modulus and Poisson's ratio, which are material constants.

The support member is made of a material having sufficient rigidity with respect to the columnar member. Therefore, the force is effectively used to deform the columnar member. Since the columnar member is fixed to the support member, the arrangement period does not change.
The change in the cross-sectional area changes the distribution of the refractive index within one period of the periodic array, thereby causing a change in the photonic band structure. This makes it possible to adjust optical characteristics of the photonic crystal, such as light reflection and refraction.
Further, according to the above configuration, since the optical characteristics can be adjusted by changing only the diameter of the columnar member, even in a case where the area is particularly large, uniform deformation can be performed while maintaining the accuracy of the entire dimension. Thus, the properties of the entire crystal after the adjustment can be made uniform.

Further, according to the above configuration, there is little restriction on members, the degree of freedom in selecting a material is increased, and it is possible to appropriately select a material that simplifies the manufacturing process.
In addition, by forming the support member from a piezoelectric material, a force can be directly applied to the columnar member using the support member itself as an actuator.
In the present invention, the columnar members are arranged apart from each other, but the gap portion is made of another material that does not hinder the deformation of the columnar member, such as a gas, a liquid, a gel-like material, or a resin having high flexibility. It may be filled.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a device configuration of the optical device according to the present embodiment. As shown in FIG. 1, an actuator 101 made of a piezoelectric element and a photonic crystal 105 are stacked and housed in a housing 106. The operation direction of the actuator 101 is the normal direction of the surface of the substrate 104, and causes the photonic crystal 105 to expand and contract in the same direction. The housing 106 has two holes with the photonic crystal 105 interposed therebetween to secure an optical path.
The laser light from the optical fiber 110 enters the element through one hole, passes through the photonic crystal 105, passes through the other hole, and enters the light receiver 109. The light receiver 109 includes a photodiode, and sends the intensity of the incident light to the control circuit 107. The control circuit 107 calculates a control amount and sends it to the drive circuit 108 to drive the actuator 101 so that a laser beam having a predetermined intensity is incident on the light receiver 109.

The photonic crystal 105 is produced, for example, as follows. First, in order to improve the transmittance of laser light, a multilayer film is formed on a substrate 104 made of Si by vapor deposition, and a reflective film 102 is formed. Next, PMMA (polymethyl methacrylate) is applied on the reflective film 102, and a periodic structure 103 is formed by X-ray lithography. FIG. 4 shows this as viewed from the direction normal to the surface of the substrate 104 and from the periodic structure 103 side. The individual columnar members forming the periodic structure 103 are isolated, and form a two-dimensional periodic structure on the reflective film 102 in a plane parallel to the substrate 104 surface.
Next, another one in which the reflective film 102 is formed on the substrate 104 made of Si is prepared, and the reflective film 102 is overlaid on the side of the periodic structure 103 made of PMMA. As described above, the photonic crystal 105 in which the periodic structure 103 illustrated in FIG. 2 is sandwiched between the two parallel reflective films 102 and the substrate 104 is formed.

FIG. 3 shows a state in which an external force is applied to the photonic crystal 105 of FIG. 2 in a direction normal to the surface of the substrate 104 and the photonic crystal 105 is compressed in the same direction. The optical characteristics of the photonic crystal 105 change as individual columnar members constituting the periodic structure 103 deform and change in diameter. At this time, since the individual columnar members are isolated, the above-described accumulation of the deformation does not occur in the arrangement plane of the periodic structure 103, and the shape of the entire crystal does not change. The materials of the reflective film 102, the periodic structure 103, the substrate 104, and the like are not limited to the above-described examples. It can be appropriately selected from the suitability and the like. In the present embodiment, a piezoelectric element is used as the actuator 101, but other driving mechanisms such as a feed screw mechanism and a voice coil can be selected. Further, in the present embodiment, the present invention is applied to the adjustment of the transmittance as an optical characteristic, but it is needless to say that the present invention can be applied to other optical characteristics such as a reflectance.

FIG. 2 is a diagram illustrating a device configuration of an optical device according to an embodiment of the invention. FIG. 2 is a diagram illustrating a configuration of an element in an example of the present invention. FIG. 4 is a diagram illustrating an adjustment operation according to the embodiment of the present invention. FIG. 4 is a diagram illustrating a periodic structure according to an embodiment of the present invention as viewed from a direction normal to a substrate surface. FIG. 4 illustrates a problem in a conventional invention. FIG. 4 illustrates a problem in a conventional invention.

Explanation of reference numerals

101: Actuator 102: Reflective film 103: Periodic structure 104: Substrate 105: Photonic crystal 106: Housing 107: Control circuit 108: Driving circuit 109: Light receiver 110: Optical fiber

Claims (8)

A plurality of columnar members arranged periodically,
A pair of support members arranged in a direction perpendicular to the arrangement direction of the columnar members and sandwiching the columnar members,
And an optical element having a periodic structure in which the refractive index is periodically distributed;
Means for applying a force in a direction perpendicular to the arrangement direction from the support member to the columnar member to deform the columnar member;
An optical device, comprising: The optical device according to claim 1, wherein the columnar member is a member whose diameter changes with height due to a force from a direction perpendicular to the arrangement direction. The optical device according to claim 1, wherein the support member is a member having greater rigidity than a columnar member. The optical device according to claim 1, wherein the optical element does not change the period of the periodic structure when the columnar member is deformed. The optical device according to claim 1, wherein at least one of the pair of support members is fixed to an actuator. The optical device according to claim 1, wherein a reflective layer is provided on the support member on the side of the columnar member. 2. The device according to claim 1, wherein at least one of the pair of support members is fixed to a piezoelectric body, and the means for applying the mechanical force includes an electrode disposed on the piezoelectric body, and a circuit device for applying a voltage to the electrode. Optical device. A plurality of columnar members arranged periodically, and a pair of support members arranged in a direction perpendicular to the arrangement direction of the columnar members and sandwiching the columnar member are formed, and the refractive index is periodically adjusted. The optical characteristics of the optical element are modulated by applying a force to the columnar member in a direction perpendicular to the arrangement direction of the columnar member to change the diameter of the columnar member with respect to the optical element having a distributed periodic structure. Modulation method of the optical element.

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