JPS60122981A - Preparation of hologram - Google Patents

Abstract

PURPOSE:To prepare a hologram having no injurious ghost image by providing a mask for cutting off other light than an object light or a reference light from two holograms, with regard to a preparation of the hologram which uses reproduced lights of two holograms as the object light and the reference light. CONSTITUTION:Parallel laser luminous fluxes 38, 40 are made incident on a reference wave use hologram 42 and an object wave use hologram 43 formed on a base body 37, respectively, becom a reference wave luminous flux 33 and an object wave luminous flux 34, are emitted through masks 39, 41 provided on the base plate 37, made incident to a hologram sensitized material 32 on a base plate 28 through a mask 35 provided on the base plate 28, a formed interference fringe is recorded, and a hologram is prepared. Since the mask 35 is provided, unnecessary transmitting luminous fluxes 39, 41 and higher order diffracted luminous fluxes 50, 51 generated from the hologams 42, 43 are cut off, therefore, a hologram having no injurious ghost image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for producing a hologram, and more particularly to a method for producing a hologram in which an object beam and a reference beam are obtained by hologram reproduction.

[Prior art]

A hologram lens can be obtained by creating a hologram of a point light source using the hosography technique. Hologram lenses have the advantage of being flat, thin film lenses with a thickness of several microns, and the ability to mass-produce a large number of lenses on the same flat plate using the step-de-and-repeat method. .

For this reason, a hologram lens is used as an optical element in an optical system that uses laser light, such as a condenser lens in an optical head of an optical disk device or a collimation lens for converting a diverging light beam from a semiconductor radar into a parallel light beam. It is proposed to do so.

The optical system of the optical head section of an optical disk device focuses the signals recorded on the back side of the disk substrate, a glass plate that is usually about 1.1 m thick, on the front side of the disk substrate so that the signals are read through the disk substrate. A light hologram lens is arranged. The hologram lens is placed with an air gap of about one gourd from the disk substrate to prevent collisions due to disk shaking, and a cover glass or protective layer of an appropriate thickness is provided to prevent dust from adhering. I am forced to do it.

FIG. 1 shows an optical system for producing a hologram lens used in this □-like optical system. In the figure, a part of monochromatic light 2 emitted from a laser light source 1 passes through a semi-transparent mirror 3, is reflected by a reflecting mirror 4, and is condensed into a pinhole 16 by a microscope objective lens 15. The transmitted light passes through the collimation lens 17, becomes a parallel light beam 18, passes through the parallel plate 9, and enters the hologram sensitive material 11 coated on the hologram substrate lo. This is the reference light. On the other hand, the light beam reflected by the semi-transparent mirror 3 is reflected by the reflecting mirror 5.
It is reflected by the microscope objective lens 7.
The light that is focused on the pinhole 8 and transmitted through the pinhole 8 becomes a diverging light beam 12, which is transmitted through the parallel plate 9 and then passed through the hologram sensitive material 1.
1. This is object light. The object beam 12 becomes a divergent beam with spherical aberration on the parallel plate 9, and this and the reference beam form interference fringes at the position of the hologram sensitive material 11, and this interference fringe is recorded on the hologram sensitive material 11. - By developing this, a hologram lens can be obtained.

When using the hologram lens thus produced, a laser beam having the same wavelength as that used during production is made to enter the hologram 11 as a parallel light beam in the same corner layer as the parallel light beam 18 but in the opposite direction.

The light diffracted by the hologram 11 becomes a convergent light beam with the spherical aberration given to the object beam at the time of fabrication, and after passing through the cover f lath and the disk substrate, it reaches the position corresponding to the pinhole 8 at the time of fabrication of the hologram. A light spot appears.

In this way, by using light of the same wavelength during fabrication and use, it is possible to perform complete wavefront reconstruction with substantially no aberration using the hologram lens.

In particular, when a volume type phase hologram is fabricated using dichromate gelatin as the hologram sensitive material 11, the diffraction efficiency of the hologram can be improved to almost 100%, and the light utilization efficiency is sufficiently high. Become.

By the way, as a light source in an optical system using a hologram, it is preferable to use a semiconductor radar, which is small, lightweight, and does not require a special modulator. The oscillation wavelength range of such a semiconductor V-de is usually from the near-infrared region to the infrared region (0°7
8 μm or more). Therefore, when manufacturing a hologram lens as described above and reproducing an image using this semiconductor laser, the hologram sensitive material should be 0.78 μm.
It is necessary to use one that has effective sensitivity above m.

A hologram sensitive material sensitive to this wavelength range includes a silver salt sensitive material sensitized to infrared light. However, since the hologram produced using this sensitive material is an absorption type hologram, it has a drawback of having a low diffraction efficiency of several orders of magnitude. Furthermore, although the diffraction efficiency can be improved to some extent by bleaching it, this method also has a limit.

Therefore, it is necessary to adopt a volume type phase hologram for K in order to improve the diffraction efficiency. Typical sensitive materials used to make holograms like this are heavy chromium, mucinase, and latin. However, the effective sensitivity range of this sensitive material is limited to a maximum of 0.55 .mu.m green light as it is, and even if special dye sensitization is carried out (2009), it is not so high that it can be made sensitive to 6 .mu.m red light.

Furthermore, there is no known sensitive material for volume holograms that has effective sensitivity in the near-infrared and infrared regions.

For this reason, a semiconductor laser cannot be used when producing a body phase hologram, and a laser with a shorter wavelength is used. When a hologram manufactured in this way is used in an optical system using a semiconductor laser, the wavelength of the light differs between the time of manufacture and the time of use, so the image cannot be formed without aberration, so in some cases, aberration correction may be necessary. It becomes necessary. When creating a hologram by adding aberrations to the light flux in advance, taking into account aberrations that often occur due to differences in the wavelength of light during use,
It is necessary to create a reference wave and an object wave using independent optical systems and arrange them in a predetermined space. An example of such an optical system is an optical system using a computer generated hologram (CGH).

FIG. 2 is a diagram showing a specific example of using CGH in a hologram production optical system. In the figure, an incident light flux 101 enters a reference wave CGH 1,09 on a substrate 108, a θ-order transmitted light flux 102, a first-order diffraction light flux 33, and a higher-order diffraction light flux 103.
give rise to The first-order diffracted light beam 33 is a reference wave. On the other hand, the incident light beam 104 is similarly applied to the object wave CG on the substrate 111.
The light beam enters H112 and produces a zero-order transmitted light beam 105, a first-order diffraction light beam 34, and a higher-order diffraction light beam 106. The first-order diffracted light beam 34 is an object wave. Both the reference wave light beam 33 and the object wave light beam 34 enter the hologram sensitive material 32 on the hologram substrate 28 and form interference fringes there, and these interference fringes are recorded on the hologram sensitive material 32.

In the figure, 107 and 110 are respectively the incident light beams 10
1 and 104 as reference wave CGH109 and object wave CG
This is a mask to allow the light to enter only the appropriate portion of H112. Further, 113 is a mask for allowing the diffracted light from the CGH to enter only a proper portion of the hologram sensitive material 32. In the optical system shown in this figure, the zero-order transmitted lights 102 and 105 are blocked by the mask 113 and do not reach the hologram sensitive material 32. However, the high-order diffracted light beams 103 and 106 enter the hologram capture 32, and a harmful ghost image is recorded in the fabricated hologram.

Further, in a hologram production optical system such as No. 111J, a parallel plate 9-stroke image is generated immediately in front of the hologram sensitive material 11. That is, a part of the object wave beam 12 is reflected by the second surface of the parallel plate 9 and then the first surface, and a part of the object wave beam 12 is reflected by the surface of the hologram sensitive material 110 and then by the first surface of the parallel plate 9. The light beam 13' reflected by the surface 2 is incident on the hologram sensitive material 11, and a harmful ghost image is recorded. These dust images are reproduced when the hologram lens is used, resulting in the generation of unnecessary ghost light and a decrease in diffraction efficiency.

[Object of the present invention]

In view of the above-mentioned conventional techniques, the present invention aims to produce a hologram without harmful ghost images.

The above objects can be achieved by placing a non-light-transmitting mask at an appropriate position in the hologram production optical system.

[Example of the present invention]

Prior to explaining the contents of the present invention, the principle of Bragg diffraction will be explained with reference to FIGS. 3(a) and (b). It will be explained that it is possible to create a hologram that can satisfy the Bragg condition for the wavelength of light used.

FIG. 3(a) shows Bragg diffraction at wavelength λ1 when the hologram 11 is used. In the figure, when a light ray 21 that is incident on an interference fringe 20 with a pitch dl at an angle φ1 satisfies the Bragg condition, it is diffracted and forms an angle φ! with respect to the interference fringe 20. The light ray 21' is emitted at this point. In this case, the relationship is wavelength λ!
If the refractive index of the hologram sensitive material at
).

(1) Equation f: To create a satisfying interference fringe using light with a wavelength λ2, which is different from the wavelength λl when used, the wavelength λ2
If the refractive index of the hologram sensitive material is k N s, then 2d*sfnφ2=λ! /N Tomi・・・・・・・・・
...The light may be incident at an angle φ2 that satisfies (2). The situation is shown in Fig. 3(b). The pitch of the interference fringes during fabrication was set to d2, which is different from dl during use, in order to take into account changes in the size of the sensitive material during hologram development. ) After development, the hologram produced by the above method has interference fringes with V and T of dl as shown in Figure 3 (8). As shown in FIG. 3(b), light rays 22 and 2 from two directions at an angle φ2 to form interference fringes 20 are
If 2' is incident, a hologram with interference fringes satisfying the Bragg condition can be obtained during use. There is a specific relationship between dl and d2 in equations (1) and (2), but if we set dl=d2 here for simplicity, then equations (1) and (
2) According to the formula, φtooth is S stone φ=((λz/Ns)/(λ
s/Nt))mφt−・(3) is determined. Since 1st gallery is still φ21×1, μ;(λ2/N
*)/(λ1/N i ) as 1 μ・Rang φ11 × 1
need to be satisfied.

As explained above, even if the wavelength of the light when using the hologram is different from the wavelength of the light when producing the hologram, two light beams are incident on each point of the hologram sensitive material from appropriate directions when producing the hologram. In particular, it is possible to produce a hologram that satisfies the Bragg condition at each point during use and can generate diffracted light in a predetermined direction.

Hereinafter, specific examples of the present invention will be described.

FIG. 4 is a diagram showing an optical system when a hologram lens is used in the optical head section of an optical disk device. In the figure, a parallel light beam 26 with a wavelength of λ0 enters a hologram substrate 28, is diffracted by approximately 100 degrees by a hologram 29, passes through a cover glass or protective film 30, is emitted into the air, becomes a convergent light beam 27, and is directed to a disk 31. The light is focused on the back surface 31' of.

FIG. 5 is a diagram showing an optical system for manufacturing a hologram lens used in the optical system of FIG. 4. In the figure, a reference wave beam 33 and an object wave beam 34 having double wavelengths are made incident on a hologram sensitive material 32. Here, the reference wave beam 33 and the object wave beam 34 are determined in accordance with the above-mentioned principle so as to obtain a hologram that can be focused with substantially no aberration by diffraction as shown in FIG. 4 when the hologram is used. Methods for producing such a light beam include a method using a lens system, a method using a computer generated hologram (CGH), and a method combining these two.

The entire method using CGHK will be explained below.

Conventionally, in order to produce a CGH, an enlarged hologram is produced using an X-Y plotter, and the hologram is optically reduced and exposed. However, with this method, errors such as errors in the optical system and its arrangement are introduced into the reduction process, especially when the N is high.
CGH with sufficiently satisfactory performance in hologram A
was not obtained.

However, in recent years, with improvements in semiconductor integrated circuit manufacturing technology, it has become possible to perform fine processing using electron beam exposure (EB exposure). If you use this EB exposure method, you can create fine details on hologram sensitive materials! Since turns can be formed and reduction using an optical system is not necessary, a high-performance CGH can be obtained. EB
Sensitive materials for IK optical CGH include I-methyl methacrylate (P-MMA), poly-t-butyl methacrylate (P-BMA), and poly-methacrylic anhydride (P-MMA).
P-MA・AN) etc. can be used to fabricate submicron gratings.

By using such a CGH', a desired luminous flux can be obtained. An example of such a hologram production optical system using CGHi is shown in FIG.

In the figure, numerals 38 and 40 are parts of the light beams from a Radhe light source that are made into parallel light beams using a beam expander, etc., and are incident on holograms 42 and 43 formed on a substrate 37, respectively. These two parallel light beams 38 and 40 are shown as a part of one parallel light beam.The parallel light beam 38 represents the light beam incident on the reference wave hologram 42, and the parallel light beam 40 represents the object wave. hologram 4
represents the luminous flux incident on 3. A portion of the light beam incident on the reference wave hologram 42 becomes a transmitted light beam 39, and a portion undergoes first-order diffraction and becomes a reference wave light beam 33. Similarly, a part of the light flux incident on the object wave hologram 43 becomes a transmitted light flux 41, and a part undergoes first-order diffraction and becomes an object wave light flux 34. Interference fringes formed by the reference wave light beam 33 and the object wave light beam 34 within the hologram sensitive material 32 on the hologram substrate 28 are recorded. Here, 35 is a mask that allows the light beam to enter only a predetermined portion of the hologram 36 or the hologram sensitive material 32. Further, 35' is a substrate 3 for blocking unnecessary transmitted light beams 39 and 41 and higher-order diffraction light beams 50 and 51 generated from the reference wave hologram 42 and object wave hologram 43.
Therefore, unnecessary light does not reach the hologram sensitive material 32.

The required hologram grating pitch and its direction can be determined by a grating equation. The coordinate axes are the X axis in the direction perpendicular to the hologram surface, the y axis in the in-plane direction, and the direction cosines of the incident and exit light beams (
1K + ml a nl ) and (t2 + m2
*12) and the pitches of the grating in the y direction and two directions are Py and P3, respectively, then the following relationship holds true.

Py=λe/(Town - Town) ・・・・・・・・・・・・・・・
・・・(4) Pz=λc/(n鵞-re1) ・・・・・・
・・・・・・・・・(5) Here, λ. is the wavelength of the laser beam. The lattice pitch at each point on the cibologram is determined by equations (4) and (5). This grating pitch can be calculated for any point on the hologram, and if we consider a group of curves that smoothly connect the hologram as a whole, this becomes the necessary hologram shape.

FIG. 7 shows the hologram 36 f used in the optical system of FIG. 6 observed from the x-axis direction.

Reference numeral 44 is the origin of the staff member, and 42 and 43 are a reference wave hologram and an object wave hologram, respectively. This hologram can be created with a wavelength of 0 in an optical system as shown in FIG.
．． In order to manufacture a hologram 29 that is used by making an incident parallel light beam 26 of 78 μm incident at an incident angle of 75 degrees, the wavelength of 0.488 μm is set in the manufacturing optical system as shown in FIG.
This is used when the incident light beams 38 and 40 of 2 are incident at an incident angle of 40 degrees. In this design example, the object wave hologram 43 has a bracing pitch of 0.6 to 13.
The number of 0μm lines is 50oO, the size is 4 x 4m, and the reference wave hologram 42 has a grating pitch of 1.7~,
6 μm number of 5600 fins, size 12 x 1.4 fins,
Both values are achievable with CGH using EB exposure.

According to the embodiment of the present invention as described above, unnecessary diffracted light from the fi CGH can be blocked by the mask 35', so in addition to being able to remove yeast images, the degree of freedom in arranging the optical system is further increased. You get the advantage of doing so. That is, the angle Irr between the higher-order diffracted light and the first-order diffracted light, and the angle Irr between the 0th-order transmitted light and 1
Since K is proportional to the angle between the 0th-order transmitted light and the 1st-order diffracted light, in order to prevent inconvenient higher-order diffracted light from entering the hologram sensitive material, K should be as large as possible to the angle between the 0th-order transmitted light and the 1st-order diffracted light.

However, for this purpose, the grating pitch of the CGH must be made extremely small, which leads to a decrease in diffraction efficiency and an increase in the drawing time during CGH production. Therefore, if the mask 35' is provided as in the embodiment described above, it is possible to block higher-order diffraction light than K, so the grating pitch of the CGH may be large, and the power distribution of the CGH can be made more flexible.

Since the minimum pitch of the CGH grating occurs at the point where the 0th-order transmitted light and the 1st-order diffracted light make the largest angle, in order to increase the minimum pitch, for example, the lower edge of the reference wave CGH 42 in FIG. An optical system may be used that reduces the primary diffraction angle at the upper edge of the object wave CGH 43. An example of such an optical system is shown in FIG. In the figure, the incident light beam 4
7 is focused using the condensing lens 51t and enters the reference wave CGH 42, and the zero-order transmitted light beam 48 is transmitted to the mask 3.
The light is focused on the surface 5' and is blocked, and only the first-order diffracted light beam 33 enters the hologram sensitive material 32 as a reference light. Similarly, the incident light beam 49 is focused using the condensing lens 52 and enters the object wave CGH 43, and the 700th-order transmitted light beam 50 is focused on the surface of the mask 35' and blocked, and the 1st-order diffraction Only the light beam 34 enters the hologram sensitive material 32 as object light. As a result, even if the grating pitch is increased over the entire surface of the 9CGHs 42 and 43 and the angle between the 0th-order transmitted light and the 1st-order diffracted light is decreased, a ghost image will not be recorded.

In this way, according to this embodiment, it is possible to use CGHt uniformly over the entire surface and with a relatively large pitch.
In CGH production, drawing time is shortened and production is facilitated, and the diffraction efficiency of the CGH is improved and the diffraction efficiency is made uniform over the entire surface of the CGH, which is extremely advantageous for hologram production.

In this embodiment, separate condensing lenses 51 and 52 are used for the incident light beams 47 and 49, but the two light beams can also be condensed using a single condensing lens.

In the above embodiment, the reference wave hologram and the object wave hologram are arranged on the same plane, and the light shielding mask for the reference wave and the object wave is also arranged on the same plane. In the invention, the hologram for the reference wave and the hologram for the object wave are disposed on different substrates, and the light-shielding masks can also be provided separately for the reference wave and the object wave, and furthermore, these can be used to create a hologram effect. It can also be installed obliquely to the material surface.

[Effects of the present invention]

According to the hologram manufacturing method of the present invention as described above, no ghost image is recorded on the manufactured hologram.

In addition, in the method of the present invention, the degree of freedom in designing the reference wave hologram and object wave hologram used increases, and furthermore, their production becomes easier.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing a conventional hologram production optical system. Figure 3(a) shows a hologram-based light beam.
FIG. 3(b) is a diagram showing hologram production by light interference. Fig. 4 is a diagram showing the optical system when using the Polodaram lens), Figs. 5, 6, and 8 are diagrams showing the optical system during its manufacture;
This figure is a plan view of a computer-generated hologram used in the optical system of FIG. 6. l: Laser light source, 7.15: Microscope objective lens, 8.1
6: Bin hole, 9: Parallel plate, 10: Hologram substrate, 11: Hologram or hologram sensitive material, 17: Collimation lens, 17-section cylindrical lens, 28:
Hologram substrate, 29: Hologram, 32: Hologram sensitive material, 35° 357: Mask, 36: Hologram, 37
: Substrate, 42: Reference wave hologram, 43: Object one-body wave hologram, 51, 52: Condensing lens, 107, 11
0°113 knee rx, 108, 111: board, 109
: water qgram for reference wave, 112: hologram for object wave. Figure 2 Figure 3 (a) (b) Figure 4

Claims (1)

[Claims] (Li) In a method for producing a hologram using reproduction beams of the first and second holograms as an object beam and a reference beam, the first
and a mask is provided between the second hologram and the hologram sensitive material for blocking light other than the object light or the reference light among the light from the first and WJ2 holograms, respectively. Fabrication method.