JPH06282212A - Hologram preparation method - Google Patents

Abstract

PURPOSE:To provide a hologram preparation method capable of preparing a hologram of large area even with light having a short coherent distance. CONSTITUTION:Regarding a hologram preparation method where object light 4 having a coherent distance D and reference light 5 are used as a two-beam interference system for the exposure of a hologram 15, diffraction gratings 14a and 14b are arranged in the optical path of at least one of the object light 4 and reference light 5 at a position where light is vertically incident, or at a position where a light diffraction angle and an incident angle to the hologram 15 are unequal. Thereafter, the object light 4 and the reference light 5 transmitted through the gratings 14a and 14b, and so set as to have an approximately equal optical path length L, are used for emission to exposure surface 15a, thereby preparing the hologram 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram producing method used in the field of optical couplers, decorative holograms and the like.

[0002]

2. Description of the Related Art Various conventional methods for creating holograms have been devised. For example, there is one disclosed in the 18th Micro Optics Research Conference lecture paper under the title of "Holographic lens for semiconductor laser". this is,
When a hologram lens for a semiconductor laser is created by using an Ar laser, an aberration occurs due to a difference in wavelength, but we have proposed a method of correcting such an aberration by using a convex lens when creating the hologram lens. is there. That is, when the hologram lens 2 is created by exposing the hologram lens with an object light of a certain wavelength at the time of creation, and the hologram lens 2 is exposed with the reproduction light 1 having a wavelength different from the exposure wavelength as shown in FIG. Aberration, which is called negative spherical aberration, has the opposite tendency to that of aberration. Therefore, in order to correct such aberration, a convex lens is used when the hologram lens 2 is created. In addition to this convex lens, there is also a method of making a correction in advance using a parallel plate, that is, a method of giving an offsetting aberration to the hologram lens 2 for exposure and making a correction.

FIG. 8 proposes a method of generating a wave having a predetermined spherical aberration by using the plano-convex lens 3. Now, by passing the focused object light 4 through the plano-convex lens 3, negative spherical aberration is added to the spherical wave focused on the point P. By irradiating the hologram dry plate 6 with the reference light 5 as divergent light by crossing such light waves once, it is possible to obtain light for hologram production having a positive spherical aberration when viewed from the dry plate. In this way, the plano-convex lens 3 can be used to correct aberrations, and moreover, it can be realized with a simple optical system.

FIG. 9 proposes a method of using the parallel plate 7 to generate a predetermined spherical aberration. A positive spherical aberration can be generated by transmitting the object light 4 which is a focused spherical wave to the parallel flat plate 7, whereby the aberration can be corrected by a simple optical system.

[0005]

FIG. 10 shows a state in which a large area hologram is created by exposing the surface of a hologram material 9 formed on a hologram substrate 8 with object light 4 and reference light 5. Is shown. In this case, when the exposure is performed using a normal gas laser, the coherence length is short, and therefore the optical path lengths La and Lb are different between the left and right regions of the exposure surface 9a (in La, the optical path length of the reference light 5 is smaller. The optical path length of the object light 4 is longer than the optical path length of the object light 4, and in Lb, the optical path length of the object light 4 is longer than the optical path length of the reference light 5). The optical path length B of a region with low coherence that cannot be obtained appears, and a uniform hologram cannot be obtained (hatched region indicates the coherent region D, and Q indicates that both optical path lengths are equal). . Therefore, in general, an etalon is added to the gas laser to increase the coherence length. However, the light intensity is reduced, and such an etalon is very expensive.

Further, as a conventional method for producing a hologram lens, there is a method in which an object light and a reference light are exposed by different optical paths by using a light flux interference method. However, in this case, a problem arises when a hologram lens having a large NA (numerical aperture) is exposed. That is, it is necessary to use a lens having a large NA on the side of the object light 4, whereby the object light becomes light that rapidly expands. In the case of such light, the reference light must be incident at a very large incident angle, and a large light diameter must be used to make a hologram lens having the same length and width. A large space is required when these are configured with a mirror optical system and exposed. FIG. 11 shows a configuration example of the mirror optical system. The object light 4 is focused by the objective lens 11 held by the objective lens holder 10,
Exposure surface 9 of hologram material 9 through pinhole 12
A is exposed. On the other hand, the reference light 5 is reflected by the mirror 13 to expose the exposure surface 9a.

Further, in a hologram lens having a large NA, a large aberration occurs when the reproduction wavelength and the exposure wavelength are different, and it becomes difficult to completely correct the aberration. By making the reproduction wavelength and the exposure wavelength equal, this aberration can be made extremely small. However, even in such a case, since the hologram lens is usually formed on a thick transparent substrate,
Aberration occurs. Even if the hologram lens is supposed to have a beam diameter of about 1 μm without aberration, the thickness of the substrate is 1 to 2 mm.
If there is a certain degree, it is not uncommon for the beam diameter to be about 0.1 to 0.2 mm.

[0008]

According to a first aspect of the present invention, there is provided a hologram forming method in which a hologram is exposed by a two-beam interferometry method using an object light having a short coherence length and a reference light. A diffraction grating is arranged in the optical path of at least one of the object light or the reference light at a position where the incident angle of light is perpendicular or the incident angle to the hologram is not equiangular, and the diffraction grating is transmitted. The hologram is created by exposing the exposure surface with the object light and the reference light whose optical path lengths are substantially equal to each other.

According to the second aspect of the present invention, a hologram is formed by exposing a hologram by a two-beam interferometry method using a spherical wave object light that diverges or converges and a reference light that diverges or converges in parallel. In the creation method, a plane diffraction grating is arranged in the spherical wave of the object light, and an exposure surface is exposed using the object light transmitted through the plane diffraction grating and the reference light diffracted by the plane diffraction grating. Then, the hologram was created.

According to the third aspect of the present invention, a hologram produced by exposing a hologram by a two-beam interferometry method using a diverging or converging spherical wave object light and a parallel light or a slowly diverging or converging reference light. In the manufacturing method, a diffraction element in which a diffraction grating for object light and a diffraction grating for reference light are formed on the same substrate in a light flux of a certain width is arranged, and is diffracted by the diffraction grating for object light of this diffraction element. The hologram is created by exposing the exposure surface with the object light and the reference light diffracted by the reference light diffraction grating.

According to a fourth aspect of the present invention, a hologram formed on a transparent substrate is exposed by a two-beam interferometry method using the divergent light object light having the same exposure wavelength and the same reproduction wavelength and the reference light. In the hologram creating method, the diffraction element is arranged at the same position as the light having the reproduction wavelength at the time of reproduction in the optical path on the exposure surface side of the convergence point of the object light and transmitted through the diffraction element. The hologram is created by exposing the exposed surface with the object light having the exposure wavelength and the reference light.

[0012]

According to the present invention, by arranging the diffraction grating in the optical path of the object light or the reference light, it becomes possible to freely set the incident angle and the diffraction angle depending on the shape of the grating. . Further, even with a laser light source that can only emit light with a short coherence length, it is possible to uniformly create a large area hologram with a high spatial frequency.

According to the second aspect of the invention, it is possible to set the incident angle and the diffraction angle of the plane diffraction grating to be non-equal, and the plane diffraction grating is equivalent to a half mirror. Since it has, it becomes possible to set up an in-line type optical system.

According to the third aspect of the invention, it is possible to combine and shape the object light and the reference light with one diffractive element.

According to the present invention, when the exposure wavelength and the reproduction wavelength are the same, when the same object as the one through which the light passes during reproduction is inserted from the convergence point of the object light to the exposure surface side and exposed, the reproduction is performed. It is possible to cancel the aberrations at the time.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the invention described in claim 1 will be described with reference to FIGS. In addition, the related art (FIGS. 7 to 11)
The description of the same parts as those of the reference) is omitted, and the same parts are denoted by the same reference numerals.

The reason why the large area hologram cannot be exposed by the laser having a short coherence length as described in the above-mentioned conventional example (see FIG. 10) is that the optical path length La of the reference light 5 is at each point on the exposure surface 9a. And the optical path length Lb of the object light 4 are significantly different, and in order to solve this, the optical path length of the reference light 5 and the optical path length of the object light 4 may be made equal depending on the location.

Therefore, the present embodiment relates to a hologram forming method in which a hologram is exposed by the two-beam interference method using the object light 4 and the reference light 5 having a short coherence length, and the light is perpendicular to the hologram. A diffraction grating is arranged in the optical path of at least one of the object light 4 and the reference light 5 at a position where the incident angle or the diffraction angle of the light and the incident angle to the hologram are non-equal, and the optical path length is transmitted through this diffraction grating. A hologram is created by exposing the exposure surface with the object light 4 and the reference light 5 whose both (hereinafter, referred to as optical path length) are set to be substantially equal.

1 and 2 show a specific example thereof.
First, in FIG. 1, the deflection gratings 14a and 14b as diffraction gratings are arranged in the respective optical paths at positions where the object light 4 and the reference light 5 are vertically incident. Then, exposure of the hologram 15 in which the optical path lengths L (corresponding to the above-described optical path lengths La and Lb) of the object light 4 and the reference light 5 which pass through and cross the deflection gratings 14a and 14b are set to be substantially equal to each other. The surface 15a was exposed. The hologram 15 is composed of the hologram substrate 8 as shown in FIG. 11 and the hologram material 9 formed on the substrate.

Therefore, in this way, the deflection grating 1
By deflecting the optical paths using 4a and 14b, the optical path lengths L of the object light 4 and the reference light 5 can be made equal, and thereby the hologram 15 having a large area can be exposed with good coherence. The hatched area D in FIG. 1 indicates the coherence area).

In FIG. 2, a condenser lens 16 is arranged in the optical path of the object light 4, a grating 17 as a diffraction grating is arranged in the optical path of the reference light 5, and this grating 17 is used.
The exposure surface 15a is located at a position where the diffraction angle of 1 and the angle of incidence on the hologram 15 are not equiangular. Thus, the grating 17 can freely set the diffraction angle from the grating and the incident angle to the exposure surface 15a depending on the characteristics of the grating, so that the light can be deflected in a narrow space in an efficient direction. . Therefore, the optical path length L of the object light 4 and the reference light 5 can be set to be equal at any position on the exposure surface 15a, so that a hologram 15 having a large area can be formed even when a laser having a short coherence length is used. can do.

Next, an embodiment of the invention described in claim 2 will be described with reference to FIG. The description of the same parts as those in the first aspect of the present invention will be omitted, and the same reference numerals will be used for the same parts.

When a hologram lens having a large numerical aperture as described in the above-mentioned conventional example is exposed, the incident angle of light becomes large and the space becomes large, which makes exposure arrangement difficult. When the incident angle becomes steep, strict accuracy is required during exposure. Further, even at the time of reproduction, the spatial frequency becomes high and the amount of aberration changes depending on the incident angle, and strict accuracy is required for the arrangement. In order to be able to perform exposure with a compact structure and with a low degree of accuracy, it is advisable to irradiate the object light 4 and the reference light 5 in-line. However, it is impossible to use a normal mirror because the incident angle and the reflection angle are equal, and even if a half mirror is used, a large NA is required.
The exposure of the lens will cause a collision.

Therefore, in this embodiment, the hologram 15 is exposed by the two-beam interference method using the object light 4 of the spherical wave that diverges or converges and the reference light 5 that collimates or diverges or converges gently. In the hologram creating method described above, as shown in FIG. 3, a plane diffraction grating 18 is arranged in the optical path of the object light 4 of the spherical wave diverging from the objective lens 11, and the object light 4 transmitted through the plane diffraction grating 18 and its The hologram 15 is created by exposing the exposure surface 15a with the reference light 5 diffracted by the plane diffraction grating 18.

By disposing the plane diffraction grating 18 in the optical path of the object light 4 in this way, the reference light 5 incident on the plane diffraction grating 18 at a steep angle can be diffracted in the same direction as the optical axis of the object light 4. You can Therefore, since the diffraction angle and the incident angle to the hologram 15 can be freely set depending on the structure of the diffraction grating, an in-line type optical system can be set. Further, in this case, by using the gradient index hologram as the diffraction grating, the object light 4 is also transmitted to some extent, and interference exposure becomes possible.

Next, an embodiment of the invention described in claim 3 will be described with reference to FIG. The description of the same parts as those in the first and second aspects of the present invention is omitted, and the same parts are designated by the same reference numerals.

This embodiment relates to a hologram forming method in which a hologram is exposed by a two-beam interference method using object light of a spherical wave that diverges or converges and reference light that collimates or gently diverges or converges. It is a thing.
In this case, as shown in FIG. 4, the diffraction element 20 in which the object light diffraction grating 20a and the reference light diffraction grating 20b are formed on the same substrate in the light beam 19 having a constant width is arranged. Then, the exposure surface 15a is exposed by using the two lights separated into the object light 4 diffracted by the object light diffraction grating 20a of the diffractive element 20 and the reference light 5 diffracted by the reference light diffraction grating 20b. The hologram 15 was created by exposing. Therefore, in this way, one diffractive element 2
Since the object light 4 and the reference light 5 can be combined and shaped at 0, it is possible to create a hologram lens having a simple structure with a small space and a high NA.

Next, an embodiment of the invention described in claim 4 will be described with reference to FIGS. 5 and 6. The description of the same parts as those in the first to third aspects of the present invention is omitted, and the same parts are designated by the same reference numerals.

Usually, the hologram lens is formed on a transparent substrate. When convergent light or divergent light is transmitted through such a substrate, aberration occurs and it is impossible to realize a small spot diameter without aberration. Further, if the exposure wavelength and the reproduction wavelength are different, it is difficult to completely remove the aberration by the conventional method because the NA is high. From such a thing,
It is preferable that the exposure wavelength and the reproduction wavelength are equal wavelengths, but still the aberration due to the parallel plate cannot be removed.

Therefore, in this embodiment, the hologram formed on the transparent substrate is exposed by the two-beam interference method using the object light 4 having the same exposure wavelength and reproduction wavelength and diverging light and the reference light 5. In the hologram creation method created by
It is the same as the reproduction light 21 having the reproduction wavelength at the time of reproduction shown in FIG. 5B passing through the optical path on the exposure surface side of the convergence point P of the object light 4 as shown in FIG. 5A. The diffractive element 22 was arranged at the position. Then, using the object light 4 having the exposure wavelength and the reference light 5 which have passed through the diffraction element 22, the exposure surface 1
The hologram lens 23 can be created by exposing the hologram lens 5a. This hologram lens 23 is composed of a parallel plate type transparent hologram substrate 24 and a hologram material 9.

In this case, the hologram lens 2 created
The value of 3 may be the same as the value at the time of exposure when the value obtained by multiplying the refractive index and the thickness. For example, assuming that the refractive index of the hologram lens 23 at the time of reproduction in FIG. 5B is n and the thickness is d, FIG.
When the hologram lens 23 has an index of refraction of n ₁ and a thickness of d ₁ at the time of exposure, a parallel plate of n × d = n ₁ × d ₁ is used. Therefore, when the exposure wavelength and the reproduction wavelength are the same, the same optical element as the parallel plate hologram lens 23 through which light passes during reproduction is inserted on the exposure surface side from the convergence point P of the object light 4 for exposure. By this, the aberration at the time of reproduction can be canceled out, and thereby a high performance aberration-free hologram element can be produced.

Another specific example will be described with reference to FIG. The optical element through which the reproduction light 21 passes at the time of reproduction as shown in FIG. 5B is not limited to a transparent parallel plate type element, and light may be passed through elements having various shapes. For example, when the prism-shaped transparent hologram substrate 25 as shown in FIG. 6B is used, the hologram lens having no aberration is obtained by inserting and exposing the same position on the object light 4 side as during reproduction. 23 can be exposed. Therefore, the hologram lens 23 is created by using the divergent light for the object light 4 in this way, and the same element as the optical element that passes through at the time of reproduction is previously installed at the exposure surface on the exposure surface side of the convergence point P of the object light 4. The hologram lens 23 having no aberration can be formed by using the hologram lens 23 in actual use.

[0033]

According to the first aspect of the present invention, there is provided a hologram producing method of exposing a hologram by a two-beam interference method using an object light having a short coherence length and a reference light,
A diffraction grating is arranged in the optical path of at least one of the object light or the reference light at a position where the light is vertically incident or at a position where the diffraction angle of the light and the incident angle to the hologram are non-equal. Since the hologram is created by exposing the exposure surface using the object light and the reference light that are both transmitted and the optical path lengths are substantially equal to each other,
The angle of incidence and the angle of diffraction can be set freely by the shape of the grating, which makes it possible to equalize the optical path lengths of the reference light and the object light on the exposure surface, and even for a laser with a short coherence length A hologram can be created by exposure.

According to a second aspect of the present invention, a hologram is formed by exposing a hologram by a two-beam interferometry method using a diverging or converging spherical wave object light and a parallel light or a gently diverging or converging reference light. In the creation method,
A plane diffraction grating is arranged in the spherical wave of the object light, and the hologram is formed by exposing the exposure surface using the object light transmitted through the plane diffraction grating and the reference light diffracted by the plane diffraction grating. Since it was created, the incident angle and the diffraction angle of the plane diffraction grating are set to be non-equal,
Moreover, since the plane diffraction grating has an equivalent property like a half mirror, it is possible to set an in-line type optical system and perform interference exposure.

According to a third aspect of the present invention, a hologram is formed by exposing a hologram by a two-beam interference method using a diverging or converging spherical wave object light and a parallel light or a diverging or converging reference light. In the creation method,
A diffraction element in which a diffraction grating for object light and a diffraction grating for reference light are formed on the same substrate in a light flux having a constant width is arranged, and the object light diffracted by the diffraction grating for object light of this diffraction element and the Since the hologram is created by exposing the exposure surface using the reference light diffracted by the reference light diffraction grating, it is possible to combine and shape the object light and the reference light with one diffractive element. This makes it possible to produce a hologram lens having a high NA without taking up a simple space.

According to a fourth aspect of the invention, a hologram formed on a transparent substrate is exposed by a two-beam interferometry method using an object light having the same exposure wavelength and a reproduction wavelength and diverging light and a reference light. In the hologram creating method, the diffraction element is arranged at the same position as the light having the reproduction wavelength at the time of reproduction in the optical path on the exposure surface side of the convergence point of the object light and transmitted through the diffraction element. Since the hologram is created by exposing the exposure surface with the object light having the exposure wavelength and the reference light, when the exposure wavelength and the reproduction wavelength are the same, an object through which light passes during reproduction is used. By inserting the same object on the exposure surface side from the convergence point of the object light and exposing it, it is possible to cancel the aberration at the time of reproduction, and thereby it is possible to expose a high-performance aberration-free hologram element. A.

[Brief description of drawings]

FIG. 1 is an optical path diagram showing a hologram producing method according to an embodiment of the present invention.

FIG. 2 is an optical path diagram showing a hologram creating method which is another embodiment of the invention according to claim 1;

FIG. 3 is an optical path diagram showing a hologram creating method which is an embodiment of the invention described in claim 2.

FIG. 4 is an optical path diagram showing a hologram producing method which is an embodiment of the invention described in claim 3;

5A is an optical path diagram showing a hologram forming method according to an embodiment of the invention described in claim 4, and FIG. 5B is an optical path diagram showing a state of reproduction thereof.

6A is an optical path diagram showing a hologram producing method according to another embodiment of the invention described in claim 4, and FIG. 6B is an optical path diagram showing a state at the time of reproduction thereof.

FIG. 7 is an optical path diagram showing a state where aberration occurs during reproduction.

FIG. 8 is an optical path diagram showing a method of correcting aberration using a convex lens.

FIG. 9 is an optical path diagram showing a method of correcting aberration using a parallel plate.

FIG. 10 is an optical path diagram showing a state of performing exposure using a gas laser having a short coherence length.

FIG. 11 is an optical path diagram showing how a hologram lens having a large NA is exposed.

[Explanation of symbols]

 4 Object Light 5 Reference Lights 14a, 14b Diffraction Grating 15 Hologram 15a Exposure Surface 17 Diffraction Grating 18 Planar Diffraction Grating 20 Diffraction Element 20a Object Light Diffraction Grating 20b Reference Light Diffraction Grating 22 Diffractive Coefficient L Optical Path Length

Claims (4)

[Claims] 1. A hologram producing method for producing a hologram by exposing a hologram by a two-beam interference method using an object light and a reference light having a short coherence length, in a position where light is vertically incident or a diffraction angle of the light and the hologram. A diffraction grating is arranged in the optical path of at least one of the object light or the reference light whose angle of incidence to the object is not equiangular, and the object light is transmitted through this diffraction grating and the optical path lengths are set to be substantially equal. And a reference beam for exposing the exposure surface to create the hologram. 2. A hologram producing method for producing a hologram by exposing a hologram by a two-beam interference method using a diverging or converging spherical wave object light and a parallel light or a slowly diverging or converging reference light. A hologram is created by arranging a plane diffraction grating in a spherical wave of light and exposing the exposure surface with the object light transmitted through the plane diffraction grating and the reference light diffracted by the plane diffraction grating. A method for producing a hologram characterized by the above. 3. A hologram creating method for exposing a hologram by a two-beam interference method using a diverging or converging spherical wave object light and a parallel light or a slowly diverging or converging reference light. A diffraction element having an object light diffraction grating and a reference light diffraction grating formed on the same substrate is disposed in the light flux of, and the object light and the reference light diffracted by the object light diffraction grating of the diffraction element A hologram producing method, characterized in that the hologram is produced by exposing the exposure surface with the reference light diffracted by the use diffraction grating. 4. A hologram production method for producing a hologram formed by exposing a hologram formed on a transparent substrate by a two-beam interference method using an object light having an exposure wavelength and a reproduction wavelength which are the same and diverging light, and a reference light. In, the diffraction element is arranged at the same position as the light of the reproduction wavelength at the time of reproduction in the optical path on the exposure surface side of the convergence point of the object light, and the object of the exposure wavelength transmitted through the diffraction element. A hologram creating method, characterized in that the hologram is created by exposing the exposure surface with light and the reference light.