JPH11265139A - Method for making multilayer volume hologram - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a multilayer volume hologram which does not require the alignment of a volume hologram and is excellent in optical characteristic by exposing the volume hologram being an n-th layer by the interference of luminous flux from a light source with diffracted light diffracted by the volume hologram where a diffraction grating has been already formed. SOLUTION: Photosensitive film for the volume hologram 14B being the 2nd layer is laminated so as to be positioned on the light source side with reference to the volume hologram 1A. Thereafter, it is exposed by using a laser beam whose wavelength is short with reference to the wavelength of the beam exposing the hologram 1A as the exposing laser beam 15. Then, the center part area of the volume hologram being the 2nd layer corresponding to the center part area of the volume hologram 1A is uniformly exposed and the light is straight advanced to be transmitted therethrough, and the volume hologram 1B is formed by making the laser beam 15 interfere with the diffracted light diffracted by the volume hologram 1A in the peripheral part area of the volume hologram being the 2nd layer corresponding to the peripheral part area of the hologram 1A where the diffraction grating is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a multilayer volume hologram in which a plurality of volume holograms reflecting a specific wavelength region are stacked.

[0002]

2. Description of the Related Art The bandwidth of the wavelength to be diffracted (diffraction efficiency is 50
There is a multilayer volume hologram in which a plurality of volume holograms are stacked to form a multilayer structure in order to widen the bandwidth of% (hereinafter referred to as a diffraction wavelength bandwidth). Conventionally, this multilayer volume hologram is manufactured by laminating and bonding a plurality of volume holograms separately manufactured.

However, in the above-described manufacturing method in which a plurality of separately manufactured volume holograms are laminated and bonded, when applied to an optical element requiring positional accuracy, for example, an aperture control element such as a CD or a DVD, the alignment is difficult. However, there is a drawback that the cost is increased because the number of steps for performing UV treatment with a mask is required.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method for producing a multilayer volume hologram having excellent optical characteristics.

[0005]

According to the present invention, there is provided a method for producing a multilayer volume hologram in which a plurality of volume holograms are laminated, wherein the first layer of the photosensitive film for volume hologram is irradiated with a laser beam to obtain a predetermined diffraction grating. Is formed, and the second layer of the volume hologram photosensitive film is disposed on the light source side with respect to the first layer of the volume hologram on which the predetermined diffraction grating is formed. A method for producing a multilayer volume hologram, comprising irradiating a photosensitive film with a laser beam to form a predetermined diffraction grating to produce a multilayer volume hologram.

Further, when exposing the k-th layer (k is a natural number not less than 2 and not more than n) volume hologram of an n-layer (n is a natural number not less than 3) multilayered volume hologram element, the k-th layer volume hologram element is exposed. The photosensitive film and the volume hologram of at least one of the first to (k-1) th layers are used for the volume hologram of the kth layer with respect to the volume hologram of at least one of the first to (k-1) th layers. In a state where the photosensitive film is arranged and laminated on the light source side, the k-th layer of the photosensitive film for volume hologram is irradiated with laser light to form a predetermined diffraction grating to produce a multilayer volume hologram. Provided is a method for manufacturing a multilayer volume hologram.

Further, the present invention provides a method for producing a multilayer volume hologram as described above, wherein the refractive index difference of the exposed volume hologram is increased each time the exposure of one layer of volume hologram is completed. Thereby, a multilayer volume hologram having high diffraction efficiency and a wide diffraction wavelength bandwidth can be obtained.

Further, the diffraction efficiency of the diffraction wavelength band of the (n-1) th layer volume hologram in which the wavelength for exposing the volume hologram of the nth layer is shifted from the wavelength of the hologram of the (n-1) th layer in which the refractive index difference is enhanced and the diffraction wavelength band shifts is the maximum. And a method for producing the above-mentioned multilayer volume hologram having the same wavelength or center wavelength. Thereby, the exposure efficiency of the n-th layer is increased.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, when exposing a first layer of a volume hologram, a photosensitive film for a volume hologram is irradiated with a laser beam having a wavelength to be reflected, and is placed on the side opposite to the light source. When the light reflected by the mirror and the light flux from the light source interfere with each other to form a diffraction grating, and when exposing the second and subsequent n-th volume holograms, the diffraction gratings 1 to 1 are already formed. After laminating the volume hologram of the (n-1) th layer and the photosensitive film for the volume hologram of the nth layer for newly forming a diffraction grating,
-1) The volume hologram in which the diffraction grating of the layer is already formed is used as a reflection mirror, and the light flux from the light source is
The diffraction grating is formed by interfering with the diffracted light diffracted by the volume hologram in which the diffraction gratings of the (n-1) th layer are already formed.

Hereinafter, light of all wavelengths is transmitted at a high linear transmittance in the central region including the optical axis (hereinafter referred to as the central region), and in the peripheral region not including the optical axis (hereinafter referred to as the peripheral region). A method of manufacturing a multilayer volume hologram applied to an aperture control element having a function of diffracting light of one or more wavelengths and changing an optical path will be specifically described.

First, the volume hologram of the first layer (hereinafter referred to as the first layer)
When exposing the volume hologram), the peripheral region forming the diffraction grating of the photosensitive film for the volume hologram was masked, and UV light was irradiated so that light was transmitted so that only the central region would go straight. After that, when the mask is removed and a laser beam of a wavelength desired to be selectively reflected is irradiated, light reflected by a mirror placed on the side opposite to the light source in the peripheral region interferes with a light beam from the light source. A diffraction grating is formed. Thereafter, the first volume hologram in which the diffraction grating is formed in the peripheral region is irradiated with UV light, so that the peripheral region in which the diffraction grating is formed is also exposed. Even if the peripheral region where the diffraction grating of the exposed first volume hologram is formed is subsequently irradiated with laser light, the diffraction is not formed because the exposure is almost stopped (this UV light or the like is irradiated). Here, stopping the exposure is referred to as a fixing process).

Next, when exposing the n-th volume hologram after the second layer (hereinafter referred to as the second volume hologram),
As one method, there is a method of exposing the volume hologram of the n-th layer to the volume hologram of the first to (n-1) layers in a state where only the fixing process is performed and the processing such as heat treatment is not applied to the volume hologram of the first to (n-1) layers (hereinafter, first Exposure method).

When exposing the second layer of the volume hologram in the first exposure method, the second layer of the volume hologram photosensitive film and the second layer of the volume hologram are exposed to light. After the functional film is laminated so as to be located on the light source side with respect to the first volume hologram, the diffraction wavelength band of the second layer volume hologram is equal to the first wavelength.
So that it partially overlaps the diffraction wavelength band of the volume hologram of
When a laser beam having a wavelength included in the diffraction wavelength band of the first volume hologram and having a wavelength different from the wavelength of the laser beam exposing the first volume hologram is irradiated and exposed, a central portion of the first volume hologram is exposed. In the central region of the second layer volume hologram corresponding to the region, the irradiated laser beam is transmitted and exposed, but the second layer volume hologram corresponding to the peripheral region of the first layer hologram. In the peripheral region, the irradiated laser light and the diffracted light diffracted by the diffraction grating of the first volume hologram interfere to form a diffraction grating. Thereafter, a fixing process is performed on the diffraction grating to stop the exposure.

Similarly, in the case of exposing the volume holograms of the third and subsequent layers to the nth layer, the volume hologram photosensitive film of the nth layer and the volumes of the first to (n-1) th layers in which the diffraction grating has already been formed are similarly exposed. Hologram (1 to 1 where the diffraction grating is already formed)
(N-1) The volume hologram of the layer is hereinafter referred to as an exposed volume hologram), and the n-th layer volume hologram photosensitive film is laminated on the light source side with respect to the exposed volume hologram. Exposure is performed by irradiating the exposed volume hologram with laser light having a wavelength different from the wavelength of the laser light that has been exposed such that the diffraction wavelength band of the n-th layer volume hologram partially overlaps the diffraction wavelength band of the exposed volume hologram. In the central region of the n-th layer volume hologram corresponding to the central region of the exposed volume hologram, the irradiated laser light is transmitted and exposed, but corresponds to the peripheral region of the exposed volume hologram. In the peripheral region of the n-th layer volume hologram, the irradiated laser light and the diffracted light diffracted by the diffraction grating of the exposed volume hologram interfere. Diffraction grating is formed Te. afterwards,
The fixing process is performed on the diffraction grating to stop the exposure.

Here, instead of making the wavelength of the laser beam used for exposing the exposed volume hologram and the wavelength of the laser beam exposing the n-th layer volume hologram different, a laser beam having the same wavelength is used in a different diffraction wavelength band. Irradiation may be performed with the incident angle changed as described above.

After that, when a treatment for sensitizing a difference in refractive index due to thermal polymerization or the like is performed on the volume hologram of the laminated n layers,
The pigment inside the hologram is decomposed and decolorized, and the angle formed by the diffraction grating formed by the shrinkage of the hologram changes, the diffraction wavelength bandwidth is widened, and the diffraction efficiency is improved. The processing for sensitizing the difference is hereinafter referred to as sensitization processing, and the volume hologram subjected to the sensitization processing is hereinafter referred to as a sensitized volume hologram.)

In the case of the first exposure method, the number of sensitization steps is only one, which is the minimum number of steps. In the conventional method of separately producing and stacking a plurality of volume holograms, the hologram is necessary for the whole volume hologram. The step of irradiating UV light with a mask for exposing the central region that has been exposed can be omitted for the second and subsequent layers,
Further, since no alignment is required when the layers are stacked, the fabrication is facilitated, and the cost is reduced.

Depending on the material of the volume hologram photosensitive film and the manufacturing conditions, the sensitizing treatment may shift the diffraction wavelength band by several nm to about 30 nm. The wavelength may be corrected by the shift amount according to the respective conditions, and exposure may be performed.

Another method of exposing the volume holograms of the second and subsequent layers is as follows. Each time the exposure and fixing of the volume holograms of the first to (n-1) layers are completed, the sensitization process is applied to each volume hologram. And then exposing the n-th layer volume hologram (hereinafter referred to as a second exposure method).

In the second exposure method, the first volume hologram is prepared by a method different from that of the first exposure method, and when the second layer is exposed, a diffraction grating is already formed and fixed. After subjecting the treated first volume hologram to sensitization, a second layer of the photosensitive film for volume hologram, and the sensitized first volume hologram,
After laminating the second layer volume hologram photosensitive film on the light source side with respect to the sensitized first volume hologram, the diffraction wavelength band of the second layer volume hologram is first. Is included in the diffraction wavelength band of the sensitized first volume hologram so as to partially overlap the diffraction wavelength band of the volume hologram, and
Is irradiated with a laser beam having a wavelength different from the wavelength of the laser beam to which the volume hologram is exposed, the photosensitivity for the second layer corresponding to the central region of the sensitized first volume hologram is obtained. In the central region of the film, the irradiated laser beam is transmitted straight through and exposed, and in the peripheral region of the photosensitive film for the second layer of the volume hologram corresponding to the peripheral region of the sensitized volume hologram, The diffracted light diffracted by the sensitized volume hologram and the irradiated laser light interfere with each other to form a diffraction grating. Thereafter, a fixing process is performed on the diffraction grating to stop the exposure.

Similarly, when exposing the volume holograms of the third and subsequent layers to the n-th layer, the sensitization process is performed on the volume holograms of the first to (n-1) th layers on which the diffraction grating has already been formed and the fixing process has been performed. Is performed, the n-th layer photosensitive film for volume hologram and the sensitized 1st to (n-1) layer volume hologram are combined with the n-th layer volume hologram photosensitive film. After laminating the sensitized volume hologram so as to be positioned on the light source side, the diffraction wavelength band of the n-th layer volume hologram partially overlaps the diffraction wavelength band of the (n-1) th layer volume hologram. As described above, when included in the diffraction wavelength band of the sensitized volume hologram, and exposed by irradiating with a laser beam having a wavelength different from the wavelength of the laser beam exposed to the sensitized volume hologram, Sensitized volume hologram In the central region of the n-th layer photosensitive film for a volume hologram corresponding to the central region of the above, the irradiated laser beam is transmitted straight and exposed, and corresponds to the peripheral region of the sensitized volume hologram. In the peripheral region of the n-th layer photosensitive film for volume hologram, the diffraction light diffracted by the sensitized volume hologram and the irradiated laser light interfere with each other to form a diffraction grating.
Thereafter, a fixing process is performed on the diffraction grating to stop the exposure.

Here, instead of making the wavelength of the laser beam used for exposing the sensitized volume hologram different from the wavelength of the laser beam exposing the n-th layer volume hologram, a laser beam having the same wavelength is converted into a diffraction wavelength band. Irradiation may be performed by changing the angle of incidence so that is different.

In the second exposure method, the number of sensitization steps is increased as compared with the first exposure method. However, the step of irradiating UV light, which is an advantage of the first exposure method, can be omitted for the second and subsequent layers. ,
In addition to the feature that the alignment is not required at the time of lamination, the fabrication becomes easy, and the volume holograms of the first to (n-1) th layers have already been subjected to the sensitization process when the n-th layer volume hologram is exposed. Since the diffraction wavelength bandwidth is wide and the diffraction efficiency is large, the exposure efficiency is improved as compared with the first exposure method, the diffraction wavelength bandwidth is widened, and the optical characteristics of the stacked volume holograms are uniform. This is preferable because a volume hologram can be realized.

Depending on the material and manufacturing conditions of the photosensitive film for volume hologram, the sensitizing treatment may shift the diffraction wavelength band by about several nm to 30 nm. Exposure may be performed by correcting the wavelength by the shift amount according to each condition.

In particular, when the second exposure method is performed under the condition that the diffraction wavelength band shifts due to the sensitization, the (n-1) after the shift of the sensitized volume hologram by the sensitization is performed. ) When the n-th layer is exposed with a laser beam having a wavelength at which the diffraction efficiency of the diffraction wavelength band of the layer has the maximum value or the same wavelength as the center wavelength, and then this multilayer volume hologram is subjected to a sensitization treatment, In the volume hologram, the diffraction wavelength band is shifted by the sensitization processing, and the wavelength is shifted from the center wavelength or the wavelength at which the diffraction efficiency of the diffraction wavelength band of the (n-1) th layer of the sensitized volume hologram has the maximum value. Hologram having a spectral waveform whose diffraction efficiency and diffraction wavelength bandwidth are almost equal to those of the (n-1) th layer volume hologram. At this time, the exposure efficiency of the n-th layer is almost maximized, which is preferable.

When the n-th layer is exposed in the first and second exposure methods, a diffraction hologram is already formed by exposure, and is subjected to a fixing treatment and, if necessary, a sensitization treatment. The following methods are available for the lamination state and method of the (n-1) -th volume hologram.

First, exposure is performed in a state in which only one arbitrary sheet is laminated, and after all exposures are completed, a method of laminating is performed. Second, exposure is performed in a state in which arbitrary plural sheets are laminated. A method in which a plurality of sets of multilayer volume holograms are produced, and after all the exposures have been completed, a method of stacking the plurality of sets of multilayer volume holograms. Third, one by one, stacking, exposing, fixing and, if necessary, sensitizing When the processing is repeated and the volume hologram is sequentially increased to expose the n-th layer, exposure, fixing, and, if necessary, sensitized 1 to 1 are performed.
A method of exposing in a state where all (n-1) sheets are stacked is possible.

The first and second methods require the step of exposing the n-th layer and then laminating again, whereas the third method requires laminating one by one and exposing, fixing and In such a case, a method of repeatedly performing the sensitization treatment is preferable because there is no step of aligning and stacking later, and the number of assembly steps can be minimized.

FIG. 4 shows the principle of exposure of a multilayer volume hologram according to the present invention, taking a two-layer (n = 2) volume hologram as an example, and FIG. 4 shows the first exposure method and FIG. 5 shows the spectral waveform. The vertical axis indicates the diffraction efficiency, and the horizontal axis indicates the wavelength.

First, the first exposure method will be described.
In FIG. 4, reference numeral 16 denotes a spectral waveform of the diffraction efficiency of the first volume hologram formed by exposing with a laser beam having a wavelength of λ ₁ (nm).

[0031] 17 is irradiated with a laser beam of x ₁ with respect to the wavelength lambda ₁ of the laser beam exposing the first volume hologram (nm) (nm) different wavelength λ ₂ (nm), the lambda ₂
6 is a spectral waveform of diffraction efficiency of a second volume hologram in which a diffraction grating is formed by interfering a laser beam having a wavelength of (nm) with light diffracted by the first volume hologram having 16 spectral waveforms.

Also, 18 and 19 in FIG.
7 shows spectral waveforms of diffraction efficiency after the first and second volume holograms indicated by reference numerals 6 and 17 have been subjected to sensitization processing, and their center wavelengths are respectively λ ₁ (nm) and λ ₂ (n
m) and the diffraction wavelength bandwidths are w ₁ (nm) and w ₂ , respectively.
(Nm). By determining λ ₁ and λ ₂ such that the spectral waveform 18 of the diffraction wavelength of the first volume hologram and the spectral waveform 19 of the diffraction wavelength of the second volume hologram are distributed in an overlapping manner, the bandwidth of the diffraction wavelength is reduced. A wide multilayer volume hologram is realized.

Before and after the sensitization processing, the diffraction efficiency and the diffraction wavelength bandwidth of the second volume hologram are smaller than the diffraction efficiency and the diffraction wavelength bandwidth of the first volume hologram. It is preferable to perform the sensitization process so that the sensitization effect is saturated because the difference between the diffraction efficiencies of the first and second volume holograms and the difference between the diffraction wavelength bandwidths can be reduced.

Assuming that the combined diffraction wavelength bandwidth of the first and second volume holograms subjected to the sensitization processing is W _T (hereinafter referred to as a combined diffraction wavelength bandwidth), the combined diffraction wavelength bandwidth W _T is 2 Is calculated by the logical sum of the diffraction wavelength bandwidths of the two volume holograms, and is expressed as W _T = x ₁ + (w ₁ + w ₂ ) / 2,
When the first and second photosensitive films for a volume hologram are made of the same material and subjected to a sensitization process so that the sensitizing effect of the second volume hologram is saturated, almost w ₁ =
Since w ₂ can be obtained, a multilayer volume hologram having a wider wavelength bandwidth by the difference x ₁ (nm) between the center wavelengths of the spectral waveforms of almost two volume holograms compared to the case of one volume hologram can be obtained.

Next, in the second exposure method, in FIG.
Reference numeral 20 denotes a spectral waveform of the diffraction efficiency of the first volume hologram formed by irradiating a laser beam having a wavelength of λ ₃ (nm). Reference numeral 22 denotes a sensitization process performed on the first volume hologram having the 20 spectral characteristics. Shows the spectral waveform of the diffraction efficiency after
By performing the sensitization treatment, the diffraction wavelength bandwidth is widened (diffraction wavelength bandwidth = w ₃ (nm)), and the diffraction efficiency is also improved.

When exposing the volume hologram of the second layer, the wavelength at which the diffraction efficiency of the diffraction wavelength band of the first volume hologram indicated by the spectral waveform 22 indicates the maximum value or the center wavelength λ ₃ (nm) Is irradiated with laser light having a wavelength λ ₄ (nm) different from x ₂ (nm), the wavelength λ ₄
(Nm) laser light and the light diffracted by the first volume hologram represented by the spectral waveform of 22 interfere with each other, and the central wavelength of the diffraction wavelength band is represented by λ ₄ (nm). A diffraction grating is formed and subjected to a sensitization process, so that the center wavelength is λ ₄ (nm) and the diffraction wavelength bandwidth is w.
It becomes a volume hologram having a spectral waveform indicated by 23 which is ₄ (nm). In this case, synthetic diffraction wavelength band width W _T is W _T
= X ₂ + (w ₃ + w ₄ ) / 2.
When the material of the photosensitive film for volume hologram is the same, it is possible to make w ₃ = w ₄ approximately. Therefore, a multilayer volume hologram having a wider x ₂ (nm) diffraction wavelength bandwidth than that of a single volume hologram. Is obtained.

In the case of performing the exposure by the second exposure method, the diffraction efficiency of the first volume hologram is increased by the sensitization process as compared with the first exposure method. The first advantage is that the diffraction wavelength bandwidth of the first volume hologram is wide because of the advantage of increasing the efficiency, and
Difference x between center wavelengths of diffraction wavelength band of second volume hologram
₂ can be increased (x ₂ > x ₁ ), and furthermore, almost equal characteristics can be obtained along with the diffraction efficiency and the diffraction wavelength bandwidth of the first and second volume holograms, so that there is an advantage that the optical performance can be easily set.

When the exposure is performed by the second exposure method (not shown) under the condition that the diffraction wavelength band is shifted by the sensitization processing, the shift amount of the second volume hologram by the sensitization processing is x _3. (Nm), assuming that the diffraction wavelength bandwidths of the two volume holograms after the sensitization processing are w ₅ and w ₆ respectively,
At this time, the synthetic diffraction wavelength bandwidth W _T is W _T = x ₃ + (w
The ₅ + w ₆₎ / 2.

When the hologram photosensitive film is made of the same material regardless of the central region and the peripheral region, so-called integrally formed films are used. The thickness and the average refractive index become almost the same, and the optical length can be made almost the same. As a material suitable for these volume holograms, a photopolymer, gelatin dichromate, or the like can be used, and a hologram is usually several hundred μm to several mm square in area and several to
It has a thickness of about several tens of μm and has a light diffraction function. As this hologram, a volume hologram such as a Lippmann type can be widely used. Further, as the hologram material, various photosensitive materials such as polyvinyl carbazole, gelatin dichromate, photo resist, photopolymer, and silver salt can be used.

The volume hologram obtained by laminating a plurality of the holograms can be easily formed by sandwiching a plurality of photosensitive films for hologram between two plates having a smooth surface, so that the smoothness of the surface can be easily improved and the hologram is desired to be transmitted. It is preferable because it is possible to prevent the light having the wavelength from being adversely affected on the surface of the aperture control element, and the reliability can be improved at the same time. As the material of the surface substrate, glass or plastic is preferable because of its excellent flatness. As the plastic, polycarbonate, polyolefin, acryl and the like can be used. The substrate and the hologram photosensitive film may be attached to each other with an adhesive layer, and the protective film may be formed on the substrate or the hologram photosensitive film. It is preferable to use a material having a refractive index as close as possible to the hologram and the substrate. In addition, it is preferable to form a non-reflection coating layer on the surface of the substrate, because the transmission efficiency can be increased and return light due to surface reflection can be reduced.

When a plurality of stacked volume holograms are manufactured, a plurality of volume hologram elements each having a size of several mm square are formed on a large substrate, and are manufactured by cutting. Is possible, and low cost can be realized, which is preferable.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, two layers (n =
The volume hologram of 2) will be described as an example with reference to the drawings. FIG. 1 is a cross-sectional view of a multi-layer volume hologram configuration aperture control element according to the present invention in a step of producing a first layer volume hologram, and FIG. 2 is a cross-sectional view of the aperture control element in a second layer volume hologram production step. . FIG. 3 is a configuration diagram of an aperture control element having a multilayer volume hologram configuration produced by the production method according to the present invention. FIG. 3A is a cross-sectional view of the aperture control element viewed from a direction perpendicular to the optical axis. Figure,
(2) is a plan view seen from the optical axis direction.

In FIG. 3, reference numeral 1A denotes a volume hologram of the first layer and 1B denotes a volume hologram of the second layer. In the central region b including the optical axis, light having two wavelengths of 650 (nm) and 780 (nm) is used. In the peripheral region a not including the optical axis, a high linear transmittance for light having a wavelength of 650 (nm), and a high linear transmittance for light having a wavelength of 780 (nm). It is composed of an aperture section having a wavelength selectivity and exhibiting a low linear transmittance.

Reference numeral 2 denotes a substrate, and the volume hologram 1
A and B are sandwiched, bonded and integrally assembled to form an aperture control element, thereby improving the surface flatness and simplifying handling and assembling the optical head.

Example 1 A volume hologram of the first layer is shown in FIG.
4A is sandwiched between the substrates 2, and the wavelength 650 (nm) and the wavelength 7
An open UV exposure mask 10 is placed only on the central region where both wavelengths of 80 (nm) are to be transmitted, and UV light 12 is irradiated onto the volume hologram photosensitive film 14A from the direction of the UV exposure mask 10. The central region irradiated with the UV light is uniformly exposed, and the light is transmitted straight.

Next, the mask 10 is removed, and FIG.
The laser beam 13 is applied to the photosensitive film for volume hologram 14A as shown in FIG. 5, and at this time, the reflection mirror 11 for reflecting the laser beam 13 is placed on the opposite side of the photosensitive film for volume hologram 14A with respect to the laser beam 13. When the irradiated laser light 13 and the light reflected by the reflecting mirror 11 are caused to interfere with each other, the central region transmits all the light, and the peripheral region diffracts light in the same wavelength band as the exposed laser light. A hologram 1A is formed. Thereafter, a fixing process is performed on the volume hologram 1A to stop the subsequent exposure.

The wavelength of the laser light to be exposed is 782 (n
When m) is used, the optical characteristic of the volume hologram 1A is that the center wavelength of the diffraction wavelength band in the peripheral region is 782.
(Nm), the maximum value of the diffraction efficiency (hereinafter referred to as peak diffraction efficiency) is about 65%, and the bandwidth where the diffraction efficiency is 50% of the peak diffraction efficiency (hereinafter referred to as half bandwidth) is about 12 (nm). Was.

As shown in FIG. 2A, the volume hologram photosensitive film 14B of the second layer is provided between the substrate 2 and the volume hologram 1A and the substrate 2. Is stacked on the light source side with respect to the volume hologram 1A, and the laser beam 15 to be exposed is shorter by about 5 (nm) than the wavelength at which the volume hologram 1A is exposed.
When exposure is performed using a laser beam having a wavelength of 7 (nm), the central region of the second-layer volume hologram corresponding to the central region of the volume hologram 1A is uniformly exposed, and the light is transmitted straight. In the peripheral region of the second layer volume hologram corresponding to the peripheral region where the diffraction grating of the volume hologram 1A is formed, the laser beam 15 and the diffracted light diffracted by the volume hologram 1A interfere. A hologram is formed, and the center wavelength of the reflection wavelength band is 777.
(Nm), the peak diffraction efficiency is about 35%, the half bandwidth is about 8 (nm), and the volume hologram 1A almost coincides with the central area and the peripheral area as shown in FIG. 2 (2). 1B is formed.

Thereafter, after fixing the volume hologram 1B of the multi-layer volume hologram composed of the volume holograms 1A and 1B and the substrate 2 to stop the subsequent exposure, it is heated at about 120 ° C. for 120 minutes. As a spectral waveform of a multilayer volume hologram obtained by laminating the volume holograms 1A and 1B, the center wavelength is approximately 780.
A multilayer volume hologram having a bandwidth of about 36 (nm) showing a diffraction efficiency of 90% or more in (nm) was obtained.

[Example 2] In the same manner as in Example 1, the volume hologram of the first layer was obtained by sandwiching the photosensitive film 14A for volume hologram between the substrates 2 in FIG.
A UV exposure mask 10 that is open only in the central region where both wavelengths of 0 (nm) and 780 (nm) are to be transmitted is placed, and UV light 12 is exposed from the direction of the UV exposure mask 10 to the volume hologram photosensitivity. Irradiate the film 14A.
As a result, the central region irradiated with the UV light is uniformly exposed, and the light is transmitted straight.

Next, the mask 10 is removed, and FIG.
The laser beam 13 is applied to the photosensitive film for volume hologram 14A as shown in FIG. 5, and at this time, the reflection mirror 11 for reflecting the laser beam 13 is placed on the opposite side of the photosensitive film for volume hologram 14A with respect to the laser beam 13. When the irradiated laser light 13 and the light reflected by the reflection mirror 11 interfere with each other, the wavelength of the laser light becomes 787 (n
When m) is used, the center wavelength of the diffraction wavelength band is 787 (nm) in the peripheral region, the peak diffraction efficiency is about 65%,
The volume hologram 1A having the characteristic that the half bandwidth is about 12 (nm) is formed.

After fixing the volume hologram 1A and stopping the subsequent exposure, the volume hologram 1A is heated at 120 ° C. for 120 minutes to perform a sensitization process.
87 (nm), the maximum value of the diffraction efficiency is about 96%, and the half bandwidth is about 30 (nm).

Next, the volume hologram of the second layer is shown in FIG.
In (1), the sensitized volume hologram 1A and the second layer of the photosensitive film 14 for volume hologram are provided.
B is laminated between the substrate 2 and the volume hologram 1A and the substrate 2 so that the second layer of the photosensitive film 14B for the volume hologram is positioned on the light source side with respect to the volume hologram 1A, and then is exposed as laser light. Exposure using a laser beam of 772 (nm), which is approximately 15 (nm) shorter than the wavelength at which the volume hologram 1A is exposed, causes the central portion of the second layer volume hologram corresponding to the central region of the volume hologram 1A. The region is uniformly exposed so that light is transmitted straight, and the peripheral region of the second layer volume hologram corresponding to the peripheral region where the diffraction grating of the volume hologram 1A is formed is the laser beam 15. And the diffracted light diffracted by the volume hologram 1A interfere with each other to form a hologram having a center wavelength of 772 (nm) and a peak diffraction efficiency of about 6 %, Half bandwidth of approximately 10 (n
m) and as shown in FIG.
A volume hologram 1B in which the center region and the peripheral region substantially coincide with A is formed.

Thereafter, the volume hologram 1 of the multilayer volume hologram composed of the volume holograms 1A and 1B and the substrate 2
After the subsequent exposure is stopped by performing a fixing process on B, heating at about 120 ° C. for 120 minutes enhances the refractive index difference of the volume hologram 1B, and a multilayer volume hologram in which the volume holograms 1A and 1B are laminated. As a spectral waveform, a multilayer volume hologram having a central wavelength of about 780 (nm) and a diffraction efficiency of 90% or more and a bandwidth of 45 (nm) was obtained.

In the first and second embodiments, a laser beam having a wavelength to be selectively reflected is used as a method of exposing a volume hologram. However, the incident angle of the laser beam is changed so as to satisfy the Bragg condition. It may be exposed.

In the first and second embodiments, since the peripheral region and the central region of the aperture control element are made of the same material, the peripheral region and the central region have substantially the same thickness and the same average refractive index. Due to this, the optical length (refractive index ×
Thickness) was almost the same, and did not adversely affect the light-collecting characteristics on the disk. At this time, the difference in optical length (transmitted wavefront aberration) is such that the RMS (root mean square) in the effective plane is 0.01λ or less, and PV (Peak to Va).
lley) value was also 0.05λ or less (λ = 633).
(Nm)).

With the method described above, the wavelength is 780 (nm).
Has an NA (numerical aperture) of 0.45 and a wavelength of 65
When an aperture control element manufactured so that NA becomes 0.6 with respect to light of 0 (nm) is used for an optical head of CD and DVD, information recorded on a CD disk having a thickness of 1.2 mm is used. Can be reproduced well with little influence of aberration,
A DVD disk having a thickness of 0.6 mm was also successfully reproduced.

The present invention is not limited to the above embodiment, but can be applied to the production of a multilayer volume hologram having no aperture control function. The first exposure method and the second exposure method are not limited to being performed alone, but may be performed in combination. Further, the plurality of volume holograms may have different characteristics. By combining various volume holograms, a multilayer volume hologram having an arbitrary bandwidth (wide band, narrow band) or a diffraction region of various patterns can be obtained. realizable.

[0059]

As described above, according to the present invention,
Using the volume holograms of the first to (n-1) th layers in which the diffraction grating is already formed as a reflection mirror, the light flux from the light source and the first to (n-1) th layers in which the diffraction grating is already formed are used. By exposing the n-th layer volume hologram by the interference with the diffracted light diffracted by the volume hologram of step (a), the step of positioning when bonding can be omitted.
It is easy to manufacture an optical element such as an aperture control element such as D or DVD that requires positional accuracy, and the step of performing UV treatment using a second or subsequent layer mask can be omitted, so that cost can be reduced. is there.

When exposing the n-th layer, a volume hologram which has been subjected to a sensitization treatment such as thermal polymerization is used as the volume hologram of the first to (n-1) -th layers on which the diffraction grating has already been formed. As a result, it is possible to increase the exposure efficiency, and realize a multilayer volume hologram having a wide diffraction wavelength bandwidth and uniform optical characteristics.

[Brief description of the drawings]

FIGS. 1A and 1B are cross-sectional views showing two steps of a method for producing a first-layer volume hologram of the present invention.

FIGS. 2A and 2B are cross-sectional views showing steps of a method for producing a second-layer volume hologram of the present invention.

FIG. 3 is a configuration diagram of an aperture control element having a multilayer volume hologram configuration manufactured by a manufacturing method of the present invention, wherein (1) is a cross-sectional view and (2) is a plan view.

FIG. 4 is a schematic view illustrating a concept of exposure of a volume hologram applied to the first embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating a concept of exposure of a volume hologram applied to a second embodiment of the present invention.

[Description of Signs] 1A, 1B: Volume holograms having different diffraction wavelengths 2: Substrate 10: UV exposure mask 11: Reflection mirror 12: UV light 13: Laser beam for exposing the first layer volume hologram 14A: First layer 14B: photosensitive film for volume hologram of the second layer 15B: laser beam for exposing the volume hologram of the second layer 16, 20: diffraction efficiency of the first volume hologram before sensitization processing Spectral waveform 17, 21: Spectral waveform of diffraction efficiency before sensitization processing of second volume hologram 18, 22: Spectral waveform of diffraction efficiency after sensitization processing of first volume hologram 19, 23: Second volume Spectral waveform of diffraction efficiency after sensitization of hologram

Claims (4)

[Claims] In a method for producing a multilayer volume hologram in which a plurality of volume holograms are laminated, a first diffraction grating is formed by irradiating a first layer of a photosensitive film for a volume hologram with a laser beam, and then forming the predetermined diffraction grating. In a state where the photosensitive film for the second layer volume hologram is arranged and laminated on the light source side with respect to the first layer volume hologram on which the diffraction grating is formed,
A method for producing a multilayer volume hologram, comprising irradiating a second layer photosensitive film for a volume hologram with laser light to form a predetermined diffraction grating to produce a multilayer volume hologram. 2. A method for exposing a k-th layer (k is a natural number not less than 2 and not more than n) volume hologram of an n-layer (n is a natural number not less than 3) multi-layer volume hologram element. The photosensitive film and the volume hologram of at least one of the first to (k-1) th layers are used for the volume hologram of the kth layer with respect to the volume hologram of at least one of the first to (k-1) th layers. In a state where the photosensitive film is arranged and laminated on the light source side, the k-th layer of the photosensitive film for volume hologram is irradiated with laser light to form a predetermined diffraction grating to produce a multilayer volume hologram. A method for producing a multilayer volume hologram. 3. The method for producing a multilayer volume hologram according to claim 1, wherein each time the exposure of the single-layer volume hologram is completed, the difference in refractive index between the exposed volume holograms is enhanced. 4. The diffraction efficiency of the diffraction wavelength band of the volume hologram of the (n-1) th layer in which the wavelength for exposing the n-th layer volume hologram and the refractive index difference are enhanced and the diffraction wavelength band shifts is maximized. The method for producing a multilayer volume hologram according to claim 3, wherein the wavelengths or center wavelengths are equal.