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Light diffraction method and diffraction device, diffraction grating used for them, and position encoder device

外国特許コード F110005363
整理番号 K01407WO
掲載日 2011年9月5日
出願国 アメリカ合衆国
出願番号 56148904
公報番号 20060152808
公報番号 7466487
出願日 平成16年7月1日(2004.7.1)
公報発行日 平成18年7月13日(2006.7.13)
公報発行日 平成20年12月16日(2008.12.16)
国際出願番号 JP2004009342
国際公開番号 WO2005003823
国際出願日 平成16年7月1日(2004.7.1)
国際公開日 平成17年1月13日(2005.1.13)
優先権データ
  • 特願2003-270002 (2003.7.1) JP
  • 2004JP009342 (2004.7.1) WO
発明の名称 (英語) Light diffraction method and diffraction device, diffraction grating used for them, and position encoder device
発明の概要(英語) A principle of blazing that is effective even in the resonance domain.
Light (51) is made incident on a diffraction grating so that specular resonance can occur in two or more light scattering units including, for example, bispheres (11a, 21a; 12a,22a), and by the specular resonance, a fraction of diffracted light 52 that is diffracted by the first layer (1) and the second layer (2) is selectively enhanced.
It also becomes possible to tune a blazing condition by a control signal from outside.
従来技術、競合技術の概要(英語) BACKGROUND ART
A diffraction grating is generally a one-dimensional periodic array of protrusions having a triangular or rectangular cross-sectional shape.
Depending on the purposes, a two-dimensional periodic array of protrusions or recesses in a pyramidal or rectangular parallelepiped shape also is used as a diffraction grating.
Diffraction gratings are classified roughly into two types, a reflective type and a transmission type.
FIG. 17 is a schematic cross-sectional view illustrating one example of a conventional diffraction grating 101.
When the period of the grating is greater than half the wavelength of incident light 103, generally diffracted lights 104 and 107 are produced on the reflection side and the transmission side.
The angles of these diffracted lights are determined by the wavelength and incident direction of light and the period of grating, so even the light waves that are incident from the same direction can result in diffracted lights in different directions depending on their wavelengths.
This principle is utilized in splitting white light into spectra, detecting only the intensity of light with a predetermined wavelength by a light detection device placed in a predetermined direction, and so forth.
In a reflective diffraction grating, a metal film is coated on the surface, and therefore, light cannot proceed through to the transmission side.
In a transmission diffraction grating, a surface layer 102 for reflecting light is omitted or it is subjected to an anti-reflection coating.
Conventional diffraction gratings have employed the technology of processing its cross section in an appropriate sawtooth shape to attain high diffraction efficiency.
As illustrated in FIG. 17, incident light 103 is divided into reflected lights 105 and refracted lights 106 at a slope of one triangle.
In the case of a reflective diffraction grating, the inclination angle and period of the slopes are determined so that the reflected diffraction light with a wavelength that is required to be diffracted efficiently can proceed in the direction coinciding with that of the reflected light.
In the case of a transmission diffraction grating, its design is conducted so that the direction of desired transmitting diffraction light coincides with that of refracted light.
This optimization of the cross-sectional shape for obtaining high diffraction efficiency is called blazing, and a diffraction grating that is optimized in this way is called a blazed diffraction grating.
The blazing principle discussed above, however, can be applied only to the diffraction grating with a period considerably greater than the wavelength because it utilizes geometrical optical phenomena such as reflection and refraction.
This type of diffraction grating is called a diffraction grating in the scalar domain.
The diffraction grating in the scalar domain may be satisfactory in the case of using a very high diffraction order or in the case where only a very small angle of diffraction is necessary; however, when a low order and a large angle of diffraction are desired, the period and wavelength should be designed to be close values so as to be different by several times at most.
This type of diffraction grating is called a resonance domain diffraction grating.
The resonance domain refers to a domain in which the ratio of grating period p to wavelength lambda is greater than 1 but less than 10 (1<p/lambda <10).
Unlike for the scalar domain (p/lambda >10), no clear design theory of blazing has been offered for the resonance domain.
For this reason, resonance domain diffraction gratings are designed by solving Maxwell's equations as rigorously as possible to search for a desirable cross-sectional shape.
Fabricating a diffraction grating that is blazed as designed has not yet been so easy to date, even for the one in the scalar domain with a large period.
In every age, the best precision processing technology at the time has been employed for the fabrication of diffraction gratings, and consequently, diffraction gratings always have been expensive elements that can be manufactured only by exclusive people.
In earlier times, precision processing machines called ruling engines were used, and such equipment that can produce high-quality diffraction gratings was limited even in the world.
Although many of them have been replaced with optical interference exposure techniques, highly sophisticated techniques such as special ion etching and precision replication are required for achieving accurate blaze shapes, and the manufacturers that have such techniques are still limited.
JP 2001-91717A discloses a diffraction grating in which microspheres are stacked to form a close-packed structure.
Light is made incident on this diffraction grating so that the Mie resonance condition in each sphere and the Bragg condition originating from the periodic structure of the spheres can be satisfied at the same time.
The publication describes an example in which light is incident from the direction -48 deg. inclined from the direction normal to a layer (z-axis direction) toward a close-packed array direction in a plane of microspheres (a y-axis direction, for example, in the later-described arrangement shown in FIG. 1).
This diffraction grating is obtained by stacking microspheres in a self-assembled manner and can be fabricated relatively easily.
The light diffraction utilizing Mie resonance, however, does not yield high diffraction efficiency.
What has been especially inconvenient in using conventional diffraction gratings is the lack of flexibility of the blazing condition.
Once the incident direction, diffraction direction, period, required wavelength, and required diffraction order are determined, the appropriate blazing shape can be determined easily.
However, when a diffraction grating is used as an optical spectroscope in particular, the diffraction grating is, for example, rotated with respect to the incident light and it must be used even in a condition that falls outside the blazing condition.
For this reason, in designing an optical spectroscope, there has been no other option but to limit its use to a specific wavelength as a typically used wavelength, so it has been only within a certain operational range around the specified wavelength for which high efficiency can be guaranteed.

特許請求の範囲(英語) [claim1]
1. A light diffraction method using a diffraction grating, wherein: the diffraction grating comprises:a first layer containing two or more first light scatterers, two or more of which being periodically arrayed along a first direction and either a) two or more of which being arrayed along a second direction or b) extending along the second direction;
and
a second layer containing two or more second light scatterers respectively corresponding to the two or more first light scatterers, the two or more second light scatterers being disposed at positions shifted from the two or more first light scatterers by a predetermined distance along a predetermined direction in a plane that is other than a plane containing the first direction and the second direction;
the method comprising:making light incident on the diffraction grating so that:in a case of a), the light is incident along a plane containing two or more trajectories selected from trajectories formed by the shifting of the two or more first light scatterers in the predetermined direction;
and
in both cases of a) and b), specular resonance occurs in two or more light scattering units, each comprising one light scatterer selected from the two or more first light scatterers and one of the second light scatterers corresponding to the selected one of the first light scatterers,whereby a fraction of diffracted light that is diffracted by the first layer and the second layer is enhanced selectively by the specular resonance in the two or more light scattering units.
[claim2]
2. The light diffraction method according to claim 1, further comprising the step of changing at least one selected from a relative positional relationship between the first layer and the second layer, and an incident angle of light on the diffraction grating, to change diffracted light that is to be enhanced selectively.
[claim3]
3. The light diffraction method according to claim 1, wherein diffracted light with a single order is enhanced selectively.
[claim4]
4. The light diffraction method according to claim 1, wherein diffracted light in a predetermined wavelength range is enhanced selectively.
[claim5]
5. A light diffraction device comprising: a diffraction grating and a light projecting device, the diffraction grating comprising:a first layer containing two or more first light scatterers, two or more of which being periodically arrayed along a first direction and either a) two or more of which being arrayed along a second direction or b) extending along the second direction;
and
a second layer containing two or more second light scatterers respectively corresponding to the two or more first light scatterers, the two or more second light scatterers being disposed at positions shifted from the two or more first light scatterers by a predetermined distance along a predetermined direction in a plane that is other than a plane containing the first direction and the second direction;
the light projecting device being for making light incident on the diffraction grating so that:in a case of a), the light is incident along a plane containing two or more trajectories selected from trajectories formed by the shifting of the two or more first light scatterers in the predetermined direction;
and
in both cases of a) and b), specular resonance occurs in two or more light scattering units, each comprising one light scatterer selected from the two or more first light scatterers and one of the second light scatterers corresponding to the selected one of the first light scatterers,whereby a fraction of diffracted light that is diffracted by the first layer and the second layer is selectively enhanced by the specular resonance in the two or more light scattering units.
[claim6]
6. The light diffraction device according to claim 5, further comprising a driving device for changing at least one selected from a relative positional relationship between the first layer and the second layer, and an incident angle of light on the diffraction grating.
[claim7]
7. The light diffraction device according to claim 5, further comprising at least one light detection device for detecting diffracted light that has been enhanced selectively.
[claim8]
8. A position encoding device, comprising a light diffraction device according to claim 7, a first member, and a second member, wherein: the first member and the second member are connected to the first layer and the second layer, respectively, andthe at least one light detection device detects the intensity of diffracted light that changes according to relative positions of the first layer and the second layer, to detect the relative positional relationship between the first member and the second member.
[claim9]
9. A diffraction grating comprising: a first layer containing two or more first light scatterers, two or more of which being periodically arrayed along a first direction and either two or more of which being arrayed along a second direction or extend along the second direction;
and
a second layer containing two or more second light scatterers respectively corresponding to the two or more first light scatterers, the two or more second light scatterers being disposed at positions shifted from the two or more first light scatterers by a predetermined distance along a predetermined direction in a plane that is other than a plane containing the first direction and the second direction;wherein the diffraction grating has two or more light scattering units, in each of which one light scatterer selected from the two or more first light scatterers and one of the second light scatters corresponding to the selected one of the first light scatters are disposed adjacent to each other so that incident light can cause specular resonance;
and
the two or more first light scatterers and the two or more second light scatterers respectively in the first layer and the second layer are disposed spaced apart from each other.
[claim10]
10. The diffraction grating according to claim 9, further comprising a first substrate for retaining the two or more first light scatterers, a second substrate for retaining the two or more second light scatterers, and a gap-retaining member for retaining the first substrate and the second substrate so as to be spaced apart from each other.
[claim11]
11. The diffraction grating according to claim 9, further comprising a driving device for changing the relative positional relationship between the first layer and the second layer.
[claim12]
12. A diffraction grating comprising: a first layer containing two or more first light scatterers, two or more of which being periodically arrayed along a first direction and either two or more of which being arrayed along a second direction or extend along the second direction;
and
a second layer containing two or more second light scatterers respectively corresponding to the two or more first light scatterers, the two or more second light scatterers being disposed at positions shifted from the two or more first light scatterers by a predetermined distance along a predetermined direction in a plane that is other than a plane containing the first direction and the second direction;wherein the diffraction grating has two or more light scattering units, in each of which one light scatterer selected from the two or more first light scatterers and one of the second light scatters corresponding to the selected one of the first light scatters are disposed adjacent to each other so that incident light can cause specular resonance;the two or more first light scatterers and the two or more second light scatterers are disposed so as to be in contact with each other;
and
at least one selected from the two or more first light scatterers and the two or more second light scatterers has a shape other than a sphere, or both the two or more first light scatterers and the two or more second light scatterers are spheres but are disposed so as to form a structure other than a close-packed structure.
[claim13]
13. The diffraction grating according to claim 12, wherein the two or more first light scatterers and the two or more second light scatterers are columnar structures extending along the second direction.
[claim14]
14. Light diffraction device comprising a diffraction grating according to claim 9, and an optical component integrated with the diffraction grating.
[claim15]
15. A light diffraction device comprising a diffraction grating according to claim 12, and an optical component integrated with the diffraction grating.
  • 発明者/出願人(英語)
  • MIYAZAKI HIDEKI
  • MIYAZAKI HIROSHI
  • MIYANO KENJIRO
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • NATIONAL INSTITUTE FOR MATERIALS SCIENCE
国際特許分類(IPC)
米国特許分類/主・副
  • 359/576
  • 359/566
  • 359/571
参考情報 (研究プロジェクト等) PRESTO Structural Ordering and Physical Properties AREA
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