JP2000352609A - Diffraction grating pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pattern with which a preferable white display can be obtained with little influences by the changes in observation conditions by forming a minute region composed of a group of minute cells consisting of diffraction grating having the same direction and specified kinds or more kinds of different spatial frequencies in the pattern. SOLUTION: This pattern consists of a plurality of minute cells consisting of diffraction gratings arranged on the surface of a substrate, with at least one of the spatial frequency of the diffraction gratings, direction of the diffraction gratings or drawing region of the diffraction gratings being changed. The pattern has a minute region composed of a group of minute cells consisting of diffraction gratings having four or more kinds of different spatial frequencies and the same direction. For example, the diffraction gratings have d1 to d4 spatial frequencies (pitches) and the ratio of the line width of the grating represented by the white and black stripes to the grating pitch (corresponding to the peak-valley of a surface relief type diffraction grating) is almost 1:1, however, the gratings are not limited to those.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a pattern expressed by arranging minute cells (dots) made of a diffraction grating on the surface of a substrate.

[0002]

2. Description of the Related Art Since a pattern formed by a diffraction grating has a directional luster that cannot be expressed by ordinary printing techniques, it is widely used for display applications and security products aimed at preventing forgery. Therefore, it is required to produce a more versatile and highly original pattern.

In response to such demands, cells (dots)
2. Description of the Related Art Displays having a diffraction grating pattern constituted by a collection of diffraction gratings are known.

[0004] Incidentally, "cell" and "dot" which are constituent units of a display (pattern) are treated as synonyms, but a nuanced term "cell" which is not restricted by shape (outline) or size, and The product will be referred to as a “diffraction grating pattern”, and the following description will be unified.

[0005] As a method for producing a diffraction grating pattern, a method as exemplified in JP-A-60-156004 is known. According to this method, minute interference fringes (diffraction gratings) due to two-beam interference of laser light are formed at the pitch,
The photosensitive film is successively exposed by changing the direction and the light intensity.

On the other hand, by using an electron beam exposure apparatus instead of a laser and moving the XY stage on which a planar substrate is mounted by computer control, a plurality of minute A method of producing a diffraction grating pattern by arranging various dots has also been proposed. The above method is disclosed in JP-A-2-72320 and U.S. Pat. No. 5,058,992.

As parameters of the diffraction grating pattern, (1) the spatial frequency or the grating interval (grating pitch) of the diffraction grating (2) the direction of the diffraction grating (the direction of the grating) (3) the area where the diffraction grating is formed (diffraction grating cell) According to (1), the color in which the diffraction grating cell looks shiny changes with respect to the fixed point, and according to (2), the direction in which the diffraction grating cell looks shiny changes according to (2). Then, the display pattern (picture) is determined according to (3).

By the way, in such a diffraction grating pattern, characters and the like are often expressed in white from the viewpoint of visibility and the like, and it is important to be able to present stable white under various viewing conditions. is there.

In order to realize a white display by the diffraction grating pattern, three types of diffraction grating cells having spatial frequencies corresponding to the wavelengths of three colors of R, G, and B are used, and a combination thereof is used as a pixel. A technique for displaying white is known.

However, when a pixel for displaying white is composed of the three types of diffraction grating cells as described above, the pixel can be observed as white only under very limited observation conditions. Even a slight shift will be observed as a colored pixel.

The relationship between the wavelength and the incident angle of the illumination light with respect to the diffraction grating, the grating interval of the diffraction grating, and the emission angle of the diffracted light emitted from the diffraction grating is described as follows.

FIG. 3 shows a diffraction grating cell having a wavelength λ at a specific angle.
FIG. 4 is an explanatory diagram showing a state in which diffracted light is observed when monochromatic light is incident. Here, on an arbitrary surface perpendicular to the diffraction grating cell surface, the diffraction phenomenon for an arbitrary order by the diffraction grating cell is expressed by the following equation. d = mλ / (sin α−sin β)

In the above equation, d is the lattice spacing (reciprocal of the spatial frequency) on the surface of interest, m is the diffraction order, and α is the 0th-order diffracted light on the surface (transmitted light or specularly reflected light of FIG. Is the specular reflection light), β
Is the emission angle (diffraction angle) of the first-order diffracted light on the surface.

For example, the direction of a diffracted light in a three-dimensional space can be known by taking the above equation into consideration with respect to an XZ plane and a YZ plane orthogonal to the XY plane of the diffraction grating cell plane. Can be. Usually, the case of first-order diffracted light (that is, m = 1) is considered. The exit angle of the 0th-order diffracted light is the same as the incident angle of the illumination light (in the case of transmission) or only inverted in sign (in the case of reflection).

On the other hand, let us consider normal illumination conditions, that is, illumination of the diffraction grating cell by white light. FIG. 4 is an explanatory diagram illustrating a state in which diffracted light is observed when white light is incident on the diffraction grating cell at a specific angle.

In a hologram or a diffraction grating, since the diffracted light necessarily involves wavelength dispersion, an observer can see the first-order diffracted light at a predetermined wavelength only from one specific direction.
Therefore, as shown in FIG. 4, the first-order diffracted light dispersed for each wavelength is emitted, and the observed color changes to a rainbow color due to the viewpoint moving vertically (in the direction of the grating vector of the diffraction grating) of the observer. In the upper part of the figure, the first-order diffracted light is 600 nm near red.
On the other hand, on the lower side, it is 400 nm which is close to blue. In other words, the diffraction angle β in the above equation is a function of the spatial frequency as well as a function of the wavelength.

Even when white is represented by pixels using diffraction grating cells of three types of spatial frequencies corresponding to the three wavelengths of R, G, and B, specific conditions (incident angle of illumination light, diffraction angle, (Emission angle of light) is observed in white, but if this condition is deviated even a little, the part that should present white is also colored and observed as another color. This is mainly due to the use of R and B wavelengths near both ends of the visible wavelength range when using first-order diffracted light of R, G, and B wavelengths by a diffraction grating.

At this time, when the incident angle or the diffraction angle changes,
Of the first-order diffracted light from the diffraction grating cell that should emit the R and B wavelengths, the wavelength that actually enters the observer's eye is an infrared or ultraviolet wavelength. As a result, the first-order diffracted light out of the visible wavelength range is not recognized, and is expressed color by additive color mixture of the remaining two wavelengths, so that it is far from white.

FIG. 6 is a chromaticity diagram showing the above.
With respect to the color (white) represented by the three wavelengths R, G, and B plotted by ●, the viewing color slightly changed due to slight changes in the viewing conditions, and R ′, G ′, and B ′ plotted with ○.
Shift to the color represented by the three wavelengths. In this case, R '
Is out of the visible wavelength range, and the color represented by the two wavelengths G ′ and B ′ is seen.

The three colors of R, G, and B can be represented by a mixture of all three insides (shaded triangles) having the vertices at the three points plotted by ●, but G ′ and B ′. Only points on these two line segments can be expressed by the two-wavelength color mixture.

The region recognized as “white” is relatively widely distributed near the center (dotted ellipse) on the chromaticity diagram, and light of three or more wavelengths is sensed with almost equal brightness. Then, it is easy to be recognized as “white”. On the other hand, only two wavelengths can be recognized as "white" only under extremely limited conditions.

In practice, even if the wavelength at which the first-order diffracted light is observed does not go outside the infrared or ultraviolet visible wavelength range, the R
When the wavelength is longer than the wavelength of B or shorter than the wavelength of B, a remarkable decrease in human relative luminous efficiency is observed. Therefore, in the white display by the diffraction grating cells of three types of spatial frequencies corresponding to the three wavelengths of R, G, and B, the pixels are viewed as white only in a very limited state.

As described above, in the conventional diffraction grating pattern, it is difficult to recognize a portion where white is desired to be presented as white under various observation conditions, and it is difficult to express an image including white.

[0024]

SUMMARY OF THE INVENTION An object of the present invention is to provide a diffraction grating pattern which is less affected by changes in observation conditions (wavelength dispersion) and realizes a "white display" suitable from the viewpoint of visibility and the like. With the goal.

[0025]

According to the present invention, as pixels constituting an area expressing white, "four or more different spatial frequencies", which are more than three types represented by the conventional R, G, and B, are used. The above-mentioned object is achieved by employing a minute region constituted by a minute cell composed of a diffraction grating.

That is, according to the first aspect of the present invention, a plurality of minute cells made of a diffraction grating are arranged on a substrate surface, and at least one of a spatial frequency of the diffraction grating, a direction of the diffraction grating, and a drawing area of the diffraction grating is provided. Is characterized in that the pattern has a minute region formed by gathering minute cells composed of diffraction gratings having four or more different spatial frequencies in the same direction in the pattern.

According to a second aspect of the present invention, there is provided the diffraction grating pattern according to the first aspect, wherein the minute area is a pixel expressing a white color having no color change according to an observation condition.

According to a third aspect of the present invention, there is provided a semiconductor device according to the first or second aspect, wherein the pattern also has a region formed by gathering minute cells made of diffraction gratings having less than four kinds of different spatial frequencies. It is a diffraction grating pattern of description.

A fourth aspect of the present invention is characterized in that four or more different spatial frequencies in the minute area are a combination having observation conditions such that all observed wavelengths are in the visible wavelength area. A diffraction grating pattern according to claim 1.

According to a fifth aspect of the present invention, there is provided a combination of four or more different spatial frequencies in a minute area having an observation condition such that all the observed wavelengths are substantially uniformly distributed in the visible wavelength area. The diffraction grating pattern according to claim 4, wherein:

According to a sixth aspect of the present invention, there is provided an observation condition in which at least one of the four or more different spatial frequencies in the minute region is reproduced at a wavelength outside the visible wavelength region. The diffraction grating pattern according to claim 1, comprising a combination.

According to a seventh aspect of the present invention, the reciprocals of four or more different spatial frequencies in the minute area are formed in such a combination that they are distributed at substantially equal intervals. It is a diffraction grating pattern described in any one of them.

According to the invention of claim 8, the size of the minute area is
The diffraction grating pattern according to claim 1, wherein the diffraction grating pattern has a thickness of 300 μm or less.

<Operation> When white light is incident on the diffraction grating pattern of the present invention, the diffracted light (mainly the first-order diffracted light) causes a small area “expressing white” to be less affected by a change in observation conditions, and to be widely viewed. It is possible to stably observe as white from the region.

As described above, if three or more appropriate wavelengths are simultaneously observed as the first-order diffracted light from the minute area, a sufficient white representation can be obtained, and the observation condition, that is, the incident angle of the illumination light Even if the angle observed by the observer (corresponding to the angle of emergence of the diffracted light) slightly changes, the state in which three or more appropriate wavelengths are simultaneously observed as the first-order diffracted light from the minute area is maintained. Then, sufficient white expression can still be achieved.

In the present invention, minute cells composed of four or more diffraction gratings having different spatial frequencies in the same direction are gathered to constitute a minute region. Even if the first-order diffracted light from the spatial frequency diffraction grating cell is out of the visible wavelength range, white color is realized by the remaining three or more types of spatial frequency diffraction grating cells. In addition, stable white display can be achieved without being affected by changes in observation conditions. (Claims 1 and 2)

Of course, it is possible to express the shading even in white or other colors by a method such as changing the size of the diffraction grating cell in the minute area.

One kind of diffraction grating cell or the like may be arranged in the minute area, and color expression by an arbitrary wavelength by one to three kinds of diffraction gratings can be mixed. Therefore, an arbitrary color image including white can be expressed by using the minute area as a pixel. (Claim 3)

By changing the spatial frequencies of four or more types of diffraction grating cells to a combination having observation conditions such that all observed wavelengths are in the visible wavelength region, slight changes in the observation conditions can be achieved. On the other hand, additive color mixture of three or more wavelengths can always be used, and stable white can be expressed.
(Claim 4)

Further, the four or more different spatial frequencies in the minute region are formed by a combination having observation conditions such that all the observed wavelengths are distributed almost uniformly in the visible wavelength region. As a result, the wavelengths of the diffracted light from the respective diffraction grating cells to be observed are substantially uniformly distributed, and a more stable white color can be expressed. (Claim 5)

In addition, at least one of the four or more different spatial frequencies in the minute region has a diffraction grating of at least one spatial frequency in a combination having an observation condition such that the diffraction grating is reproduced at a wavelength outside the visible wavelength region. by doing,
Even for a relatively large change in viewing conditions, additive color mixture of three or more wavelengths can be used, and it is possible to view white from many viewpoints. (Claim 6)

Also, by making the reciprocals of four or more different spatial frequencies in the minute area be a combination that exists at substantially equal intervals,
The wavelength of the diffracted light from each diffraction grating cell to be observed is almost evenly distributed, achieving stable white color not only for slight changes in observation conditions but also for relatively large changes. It's easy to do. (Claim 7)

In any of the above-described diffraction grating patterns, when the size of the minute region is 300 μm or less, the structure of the minute region can be made inconspicuous. Can be made inconspicuous, and uniform white presentation can be achieved. When displaying an image including white, a high-quality image can be expressed. (Claim 8)

[0044]

FIG. 1 is an explanatory view showing an embodiment of a diffraction grating pattern according to the present invention, in which characters "stop" (white) are formed in the pattern. No diffraction grating cells are arranged around the characters represented in black.

When the inside of the word "stop" in the figure is enlarged, there are four different spatial frequencies as shown in the upper left,
In each direction, a diffraction grating cell having the same size is formed in a minute area, and a character portion is expressed by using this as a pixel.

Since no diffraction grating is formed around the character, when illumination light is incident on the diffraction grating pattern of the present invention, first-order diffraction light is emitted only from the character portion,
By observing this, the brightly lit “stop” character can be recognized. At this time, if three or more types of visible wavelengths are emitted from the minute region as the first-order diffracted light, the observed image is often recognized as white. Here, even if the observation conditions are changed and the incident angle of the illumination light is slightly changed, or if the viewpoint position of the observer is slightly changed, the observed image hardly changes. As described above, the fact that white can be stably presented regardless of observation conditions facilitates identification of an observation image (such as characters).

It is to be noted that the character and its surroundings are inverted so that the pixel composed of the above-mentioned diffraction grating cell is not formed in the character portion, and the pixel is formed in the entire region around the character (portion expressed in black). Accordingly, when the first-order diffracted light is observed, it is possible to recognize a character expressed in black on a white background.

FIG. 2 is an explanatory diagram showing the above “micro area” for displaying white in a further enlarged manner. In the figure,
The diffraction grating has a spatial frequency (pitch) of d1 to d4, and the ratio of the line width of the grating expressed in white and black to the grating pitch (corresponding to the peak-to-valley of the surface relief type diffraction grating) is approximately 1: 1. However, the invention is not so limited.

FIG. 7 is a chromaticity diagram showing the optical characteristics of the "micro area". The minute area in FIG. 2 is a color (white) represented by four wavelengths of A, B, C, and D plotted by ●.
Is equivalent to Due to a slight change in observation conditions, the visual color shifts to a color represented by four wavelengths A ', B', C ', and D' plotted with a circle, and A 'is outside the visible wavelength range (or Even under such a condition, the colors represented by the other three wavelengths (B ′, C ′, D ′) are still recognized as white.

It should be noted that, among the diffraction grating cells having four or more different spatial frequencies, at least one kind of diffraction grating having a spatial frequency is formed of a combination having an observation condition such that the diffraction grating is reproduced at a wavelength outside the visible wavelength range. By doing so, the wavelength of the first-order diffracted light from one diffraction grating cell falls outside the visible wavelength range, and
It is also possible to make the second-order diffracted light have a wavelength within the visible wavelength range. In this case, an additive color mixture of three or more wavelengths can be used not only for a slight change in the viewing conditions but also for a relatively large change, which is effective for viewing in white from many viewpoints.

Further, as shown in FIG. 5, the pattern may also have a region formed by gathering minute cells made of diffraction gratings having less than four types of different spatial frequencies. The figure shows a state in which the periphery of the character "STOP" displayed in white is filled with a diffraction grating cell having a single spatial frequency. This makes it possible, for example, to render the characters white and the surroundings red, but the area where the diffraction grating cells of a single spatial frequency are arranged tends to change color due to changes in viewing conditions. Is clear.

Next, the size of the minute area will be considered. If the minute regions are arranged at an interval equal to or less than the resolution of the observer's eyes, the observer cannot recognize each minute region, and can present a uniform white color in the diffraction grating pattern of the present invention.

On the other hand, when an image is represented by a diffraction grating pattern, an image having a sufficient resolution can be displayed. Of course, even if the observer moves slightly,
The image displayed in white hardly changes. In this way, a part of the image changes color, and the part that wants to increase visibility presents stable white, so that the change in color draws the observer's attention and conveys information on the white display part. Effective display becomes possible.

When an observer with a visual acuity of 1.0 observes at a distance of about 1.0 m, the spacing between the diffraction grating cells is about 300 μm. When the same observer observes at a distance of about 0.3 m, the diffraction grating cell Is about 100 μm, the observer cannot recognize the arrangement structure of the minute area, and can present a sufficiently uniform surface or display an image with a sufficient resolution. Therefore, it is effective that the size of the minute region is 300 μm or less from the viewpoint of display with sufficient uniformity and resolution.

In the above description, a case has been described in which a minute area is formed by minute cells composed of four types of diffraction gratings having different spatial frequencies. However, the present invention is not limited to this. A lattice cell may be used. When many types of spatial frequencies are used, a more stable white color can be observed from a wider range.

In the above description, the first-order diffracted light from the diffraction grating cell has been described. However, if the diffraction efficiency of the second-order or higher-order diffracted light from the diffraction grating is sufficient, the same applies to the diffracted light of the diffraction order. The effect of is obtained.

As the diffraction grating constituting the pattern of the present invention, any type of diffraction grating such as a phase diffraction grating including a surface relief type and an amplitude type diffraction grating based on density expression may be used. From the viewpoint of (light use efficiency), it is preferable to use a blazed diffraction grating or the like. In the case of a mere white display, the diffusion of light is often used. However, in the present invention, since the viewing area can be limited by using a diffraction grating, it is possible to display brighter white (in a specific direction). is there. This effect is particularly remarkable when a highly efficient diffraction grating such as a blazed diffraction grating is used.

In the above description, the density of the image to be expressed is described as being binary. However, the present invention is not limited to this. The density may vary depending on the area of the minute area or the diffraction efficiency of the diffraction grating in the minute area. It is also possible to express an image.

[0059]

As described above, according to the present invention,
Provided is a diffraction grating pattern that is not affected by wavelength dispersion due to changes in observation conditions (incident angle of illumination light, observation direction) and can realize a suitable “white display” from the viewpoint of visibility and the like under relatively wide observation conditions. Is done.

[0060]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of a diffraction grating pattern of the present invention.

FIG. 2 is an explanatory diagram showing, in an enlarged manner, a minute region displaying white (constituting a character “stop” in the pattern of FIG. 1);

FIG. 3 is an explanatory diagram showing a state of observing diffracted light when monochromatic light having a wavelength λ is incident on a diffraction grating cell at a specific angle.

FIG. 4 is an explanatory diagram showing a state in which diffracted light is observed when white light is incident on the diffraction grating cell at a specific angle.

FIG. 5 is an explanatory view showing another embodiment of the diffraction grating pattern of the present invention.

FIG. 6 is a chromaticity diagram showing optical characteristics in a case where white is expressed by a diffraction grating pattern according to a conventional technique (three types of diffraction grating cells).

FIG. 7 shows the structure of the present invention (four or more types of diffraction grating cells).
FIG. 6 is a chromaticity diagram showing optical characteristics when expressing white with a diffraction grating pattern.

Claims (8)

[Claims] 1. A pattern in which at least one of a spatial frequency of a diffraction grating, a direction of a diffraction grating, and a region where a diffraction grating is formed is changed. A diffraction grating pattern, characterized in that the pattern has a minute area formed by gathering minute cells made of diffraction gratings having four or more different spatial frequencies in the same direction. 2. The method according to claim 1, wherein the minute area is a pixel that expresses white without a color change according to an observation condition.
The diffraction grating pattern described in 1. 3. The diffraction grating pattern according to claim 1, wherein the pattern also has a region formed by gathering minute cells made of diffraction gratings having less than four types of different spatial frequencies. . 4. The method according to claim 1, wherein the four or more different spatial frequencies in the minute region are a combination having observation conditions such that all the observed wavelengths are in the visible wavelength region. The diffraction grating pattern according to any one of the above. 5. The method according to claim 1, wherein the four or more different spatial frequencies in the minute region are a combination having observation conditions such that all observed wavelengths are distributed almost uniformly in the visible wavelength region. The diffraction grating pattern according to claim 4, wherein 6. A diffraction grating having at least one spatial frequency among four or more different spatial frequencies in a minute region is formed of a combination having an observation condition such that the diffraction grating is reproduced at a wavelength outside the visible wavelength region. Claim 1.
4. The diffraction grating pattern according to any one of claims 1 to 3. 7. The combination according to claim 1, wherein reciprocals of four or more different spatial frequencies in the minute area are distributed at substantially equal intervals.
The diffraction grating pattern according to any one of the above. 8. The diffraction grating pattern according to claim 1, wherein the size of the minute region is 300 μm or less.