JPH0323914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for manufacturing an in-line hologram lens.

Hologram lenses include in-line hologram lenses and off-axis hologram lenses. The principles of recording and reproducing methods for these two types of hologram lenses will be briefly explained below.

First, the off-axis hologram lens will be explained. As shown in Figure 1, the hologram recording medium
On the recording surface (photosensitive surface) r of the HR, a recording object wave beam (spherical wave beam) A and a recording reference wave beam (plane wave or spherical wave A beam) B is irradiated to record an off-axis hologram lens portion HL', which is formed of an interference image and has a circular or inert circular shape, for example. Note that a description of the development process for the recording surface r will be omitted here. Further, the recording object wave beam A is a beam that is created using an optical lens, converges at a point P, and then diverges. Further, both beams A and B are produced from laser beams from the same laser light source. Thus, off-axis hologram lens OX-L
is created.

To reproduce this off-axis hologram lens OX-L, as shown in Figure 2, the recording medium HR
If a reproduced reference wave beam B' similar to beam B is irradiated onto the off-axis hologram lens part HL' on the extension of the recorded reference wave beam B in FIG. 1 from the surface opposite to the recording surface r, A reproduced object wave beam A' focused on point P' is reproduced from the recording surface r side. still,
Unlike in Fig. 2, if the reproduction reference wave beam is irradiated from the recording surface r side of the recording medium HR in the same way as the recording reference wave beam B in Fig. 1, it will diverge on the extension of the recording object wave beam A in Fig. 1. The reproduced object wave beam is reproduced from the surface of the recording medium HR opposite to the recording surface r.

Next, the inline hologram lens will be explained. As shown in Figure 3, the hologram recording medium
A recording object wave beam (spherical wave beam A) and a recording reference wave beam (plane wave or spherical wave beam) B whose optical axes coincide or are parallel to each other in the normal direction, that is, inline with each other, are placed on the recording surface r of the HR. In-line hologram lens part HL consisting of interference image by illumination
Record. Other details are the same as in FIG. In this way, the in-line hologram lens IN-L is created.

To reproduce this in-line hologram lens IN-L, as shown in FIG. 4, a beam is emitted from the surface of the recording medium HR opposite to the recording surface r on the extension of the recorded reference wave beam B in FIG. The reproduced reference wave beam B′ similar to B is transmitted to the inline hologram lens section.
When HL is irradiated, a reproduced object wave beam A' is reproduced which is focused on point P' from the recording surface r side. In this case as well, the diverging object wave beam can be reproduced by irradiating the reproduction reference wave beam onto the hologram recording medium HR from its recording surface r. Others are the same as in FIG. 2.

The hologram lens made as described above is small and lightweight, and by arbitrarily selecting the mother lens for creating the object wave beam, the desired shape can be obtained.
It is possible to obtain a lens with NA (numerical aperture) and a working distance close to each other, and it is also possible to mass-produce lenses with the same characteristics through replication.

By the way, for example, the objective lens used in the optical signal reproducing head of an optical signal reproducing device is N.
A fairly large lens is used, and conventionally, optical lenses consisting of a large number of lenses, similar to the objective lenses of microscopes, have been widely used. However, such an objective lens cannot be expected to be small and lightweight, and therefore, especially when using focusing servo, a considerable amount of mechanical energy is required to move the objective lens up and down, and the servo device is complicated. It becomes large.

From this point of view, it is highly preferable to use the above-mentioned hologram lens as the objective lens of the optical signal reproducing head. However, among hologram lenses, off-axis hologram lenses are not very desirable to be used as objective lenses in optical signal reproducing heads due to the following points.

One reason for this is that, as mentioned above, the objective lens is moved up and down by the focusing servo, so the reproduced reference wave beam must also be moved up and down in parallel at the same time to ensure that it irradiates the lens part of the off-axis hologram lens. There is. In the case of an in-line hologram lens, if the optical axis is parallel to the normal line of the in-line hologram lens section, the moving direction of the lens will match the direction of the reproduction irradiation wave beam, so this is not necessary.

The other reason is that the off-axis hologram lens is rotated around three orthogonal axes with an accuracy of about ±0.5° relative to the reproduced reference wave beam, and the focal point of the reproduced object wave beam and its optical axis are adjusted. It is necessary to adjust the lens so that it is in the desired position, which is extremely troublesome to adjust, especially when the NA of the lens is large. In the case of an inline hologram lens, such adjustment is not very difficult.

From the above, it can be seen that an in-line hologram lens is suitable as an objective lens for an optical signal reproducing head.

The recording method of the in-line hologram lens has been briefly explained with reference to FIG. 3, but will be explained more specifically with reference to FIG. 5. An in-line hologram is created by irradiating a recording object wave beam A and a recording reference wave beam B, whose optical axes coincide on the normal line, onto a circular area of the recording surface (photosensitive surface) r of the hologram recording medium HR to form an interference image. Record the lens part HL. In this case, both beams A and B are generated from a laser beam from a laser light source LS.

The recording object wave beam A is created as follows. Laser beam (plane wave beam) from laser light source LS
A part of the wave is made incident on the mother lens (optical convex lens) L ₁ through two beam splitters SP ₁ - SP ₂ , and the spherical wave is focused at a point P (corresponding to the rear focal point of the lens L ₁ ) and then diverges. A beam is obtained and is designated as a recording object wave beam A. Further, the recording reference wave beam B is created as follows. A part of the laser beam from the laser light source LS is reflected by the beam splitter SP ₁ , and the reflected laser beam is reflected by two mirrors M ₁ - M ₂ and then enters the auxiliary lens (optical convex lens) L ₂ . The output beam is focused on the central point Q on the beam splitter SP ₂ (corresponding to the back focal point of the lens L ₂ ), and the beam splitter
The reflected diffused beam from SP ₂ is made incident on the mother lens L ₁ , and the beam emitted from the lens L ₁ is defined as a recording reference wave beam (parallel plane wave beam) B.

By the way, this inline hologram lens
The NA of IN-L depends on the NA of the mother lens _L1 . Therefore, this inline hologram lens
When IN-L is used as the objective lens of the above-mentioned optical signal reproducing head, the NA of the in-line hologram lens IN-L must be made considerably large, and in that case, it is natural that the lenses L ₁ and L ₂
Also, one with a large NA must be used.

However, if ordinary optical lenses are used as the lenses L ₁ and L ₂ , a lens consisting of a large number of lens sets like the objective lens of a microscope must be used, but as the NA increases, the focus of the lenses L ₁ and L ₂ becomes smaller. is located inside the lens barrel, making the recording method of the in-line hologram lens shown in FIG. 5 impossible.

Therefore, in order to solve this problem, a beam splitter is provided facing the hologram recording medium, and an optical lens consisting of a large number of lenses is provided as an objective lens on the opposite side of the beam splitter. A laser beam is made incident on the objective lens, the diverging output beam is made to irradiate a hologram recording medium through a beam splitter as a recording object wave beam, and the recording reference wave beam created by making the laser beam incident on an auxiliary lens is generated as described above. A recording method using an in-line hologram lens with a large NA has been proposed, in which the beam is reflected by a beam splitter and irradiated onto a hologram recording medium (Japanese Patent Laid-Open No. 147339-1982).
(see issue).

However, in such a recording method, the recording object wave beam (spherical wave beam) from the objective lens
passes through the beam splitter, so it is subject to aberration. In order to avoid this, it is necessary to use a special objective lens to correct aberrations to the recording object wave beam, or to provide a similar beam splitter during playback. This is not very desirable in practical terms.

In view of this, the present applicant has previously proposed a manufacturing method that can easily produce an in-line hologram lens with a large numerical aperture (NA).

An example of the method for manufacturing the in-line hologram lens will be described below with reference to FIG. An off-axis hologram lens OX-L, which is made using a recording object wave beam and a recording reference wave beam that are off-axis to each other, is used as a mother lens (objective lens). This off-axis hologram lens
The manufacturing method of OX-L, especially its recording method, will be described later with reference to FIG. This off-axis hologram lens OX-L is a hologram recording medium consisting of a glass substrate BS and a photosensitive layer (recording layer) K on the glass substrate BS.
A circular off-axis hologram lens portion HL' is recorded in the center of the photosensitive layer K of HR ₂ , and is further formed by performing the development process described below.
In this case, off-axis hologram lens OX−
L is photosensitive when the lens portion HL' of the photosensitive layer K is irradiated with a reproduced reference wave beam (a plane wave or a spherical wave beam, here a plane wave beam) at an angle of approximately 45 degrees to the normal line from the substrate BS side. It has an optical axis on the normal line from the layer K side, and is made to reproduce a reproduced object wave beam that is focused at a point P.

HR ₁ is a hologram recording medium on which an in-line hologram lens IN-L is to be recorded, and is composed of a glass substrate BS and a photosensitive layer K formed thereon.

And for this hologram recording medium HR ₁ ,
An off-axis hologram lens OX-L, which serves as a mother lens, is made to face each other. That is, in this case, the photosensitive layer K of the hologram recording medium HR ₁ is placed in a predetermined manner so that the photosensitive layer K of the off-axis hologram lens OX-L faces in parallel, and the hologram is placed on the off-axis hologram lens OX-L. Arrange recording medium HR ₁ .

Then, a part of the laser beam (parallel plane wave beam) from the laser light source LS is sent to the beam splitter.
Reflected by SP, the reflected beam is further reflected by mirror M
The reflected beam (parallel plane wave beam) is made incident on the photosensitive layer K from the glass substrate BS side of the off-axis hologram lens OX-L as a reproduced reference wave beam B'. In this way, the off-axis hologram lens OX-L reproduces the reproduced object wave beam A' which is focused at the point P and then diverges, and this is incident on the photosensitive layer K of the hologram recording medium HR ₁ as the recording object wave beam A. do.

On the other hand, a part of the laser beam from the laser light source LS passes through the beam splitter SP, further passes through the off-axis hologram lens OX-L, and is in an in-line relationship with the recording object wave beam A (that is, each optical axis coincides with each other). The recording reference wave beam B is incident on the photosensitive layer K of the hologram recording medium HR ₁ . Thus, a circular in-line hologram lens portion HL is formed at the center of this photosensitive layer K, and by performing a development process to be described later, an in-line hologram lens IN-L is produced.

As shown in FIG. 7, the off-axis hologram lens OX-L is arranged so that the glass substrate BS of _the off-axis hologram lens OX-L as a mother lens is in contact with the photosensitive layer K of the hologram recording medium HR 1 arranged as shown in FIG. -L can also be arranged to perform recording on the in-line hologram lens IN-L. In this case, the reproduction object wave beam A' and the recording object wave beam A become spherical wave beams that diverge from the imaginary point P.

Next, how to make an off-axis hologram lens OX-L used as a mother lens will be explained with reference to FIG. The photosensitive layer K of the holographic recording medium HR ₂ consisting of the photosensitive layer K and the glass substrate BS
Then, a recording object wave beam (spherical wave) is irradiated so that the optical axis coincides with the normal line, and a recording reference wave beam (parallel plane wave beam) is irradiated so that the optical axis has an incident angle of approximately 45° with respect to the normal line. By irradiating B,
A circular off-axis hologram lens portion HL' is recorded in the center of the photosensitive layer K, and then this photosensitive layer K is developed to form an off-axis hologram lens OX-
Get L.

In this case, the recording object wave beam A is created as follows. A part of the laser beam (parallel plane wave beam) from the laser light source LS is sent to the beam splitter SP.
is passed through the auxiliary lens (optical lens) L ₂ to create a spherical wave beam that is focused at point Q (rear focal point of lens L ₂ ) and then diverges, and this beam is sent to the mother lens (objective lens) ( A spherical wave beam is created which is made incident on an optical lens (optical lens (optical lens) _L1 consisting of a large number of lens sets), converges at a point P, and then diverges, and this beam is designated as a recording object wave beam A.

Further, the recording reference wave beam B is created as follows. A part of the laser beam from the laser light source LS is reflected by the beam splitter SP, the reflected beam is reflected by the mirror M, and the reflected beam is used as the recording reference wave beam B.

As the mother lens _L1 , for example, a microscope objective lens with NA of 0.4 or 0.5 is used. Further, the aperture of the off-axis hololens portion HL' is, for example, 2 mm in diameter, and its working distance is, for example, 2.3 mm.
Therefore, in this case, the aperture and working distance of the inline hologram lens section HL of the inline hologram lens IN-L obtained in FIG. 6 are determined by the predetermined distance between the point P in FIG. 6 and the inline hologram lens section HL. .

In addition, the laser light sources in Figs. 6, 7, and 8
As the LS, for example, one that generates an argon laser beam (λ = 4880 Å), a krypton laser beam (λ = 6471 Å), a dye laser beam (λ = 6330 Å), a He-Ne laser beam (λ = 6328 Å), etc. is used. obtain. Further, the photosensitive layers K of the hologram recording media HR ₁ and HR _{2 shown in FIGS. 6, 7, and 8} are selected depending on the type of laser beam.

Next, the hologram recording media HR ₁ , HR ₂ and the hologram lens IN-L in FIGS. 6, 7, and 8,
An example of how to make OX-L will be explained. An aqueous gelatin solution containing an appropriate amount of a hardening agent, such as formaldehyde or glyoxal, is maintained at around 40°C, and a 1 mm thick glass substrate and a spinner are similarly maintained at around 40°C. A gelatin aqueous solution is applied onto a glass substrate using this spinner. The coating thickness of this aqueous gelatin solution is such that the thickness after drying is 5 μm for a hologram recording medium for an off-axis hologram lens and 15 μm for an inline hologram lens.
Selected. The aqueous gelatin solution coated on the glass substrate is dried to form a gelatin film that is the base material of the photosensitive layer. Next, a processing step for imparting photosensitivity to this gelatin film will be explained.

To impart photosensitivity to a blue or green beam on a gelatin film, soak the gelatin film in a 2 to 10% by weight aqueous solution of ammonium dichromate for about 10 minutes, then gently pull it up, stand it vertically, and dry it in a dark place. .

To impart photosensitivity to a red beam to a gelatin film, ammonium is added to an aqueous solution containing 2% by weight of ammonium dichromate and 1×10 ^-3 mol/methylene blue dye so that the pH thereof becomes about 10. Thereafter, the gelatin membrane is immersed in this aqueous solution for about 10 minutes, and then dried in a stream of ammonia and dry nitrogen.

In this way, a hologram recording medium having a photosensitive layer K formed on a glass substrate is obtained. Exposure of the photosensitive layer of the hologram recording medium is shown in FIGS. 6 and 7.
The irradiation energy density of the laser beam is approximately 100 to 1000 mJ/cm ² .

A hologram recording medium having an exposed photosensitive layer is immersed in water. If the photosensitive layer has photosensitivity to blue or green beams, it is immersed in running water at about 20°C for about an hour to reduce its photosensitivity to red beams. If you have it, soak it in warm water of about 40℃ for about 30 minutes.
After that, this hologram recording medium was soaked in a 50% aqueous solution of isopropanol for about 10 minutes.
Dip in a 90% aqueous solution for a few seconds, then in a 100% isopropanol solution for about 10 minutes, then quickly dry with warm air. This completes the development process.

Note that the photosensitive layer, which has a gelatin film as its base material, is hygroscopic, and there is a risk that the hologram lens will disappear if left in this state.To prevent this, a cover glass with a thickness of about 150 μm is used as shown in Figure 9. CG is pasted onto the photosensitive layer K using an ultraviolet curing resin. In this way, hologram lenses OX-L and IN-L are obtained. Note that illustration of this cover glass CG is omitted in other figures.

Next, in order to duplicate the slave inline hologram lens IN-L' using the inline hologram lens IN-L obtained in this way as a mother lens, as shown in FIG. The photosensitive layer K of the hologram recording medium HR ₁ ′ to be formed is, for example, a mother inline hologram lens with a diffraction efficiency of 50%.
The hologram recording media HR ₁ and HR ₁ ' are arranged at a predetermined interval so as to face the photosensitive layer K of IN-L at a predetermined interval, and the laser beam from the laser light source LS is directed to the hologram recording medium HR _{1 .} BS side of the glass substrate is irradiated, a part (50%) of which is used as the reproduction reference wave beam B′, and the other part (50%)
is the recording reference wave beam B of the hologram recording medium HR ₁ '. In this way, the reproduced object wave beam A' focused at point P is reproduced from the mother inline hologram lens IN-L, and this is irradiated onto the hologram recording medium _HR1 ' as the recording object wave beam A, and the photosensitive layer K is The hologram lens section HL is recorded.

As shown in FIG. 11, the mother inline hologram lens IN-L is placed in such a way that the glass substrate BS of the mother inline hologram lens IN-L is in contact with the photosensitive layer K of the hologram recording medium HR ₁ ' arranged as shown in FIG. Slave hologram lens IN
−L′ can also be replicated. In this case, the reproduction object wave beam A' and the recording object wave beam A become spherical wave beams that diverge from the imaginary point P.

According to the above-mentioned method for manufacturing an inline hologram lens proposed earlier, an inline hologram lens is manufactured by using a prefabricated off-axis hologram lens as a mother lens, so as long as such a mother lens is obtained, an inline hologram lens can be manufactured. can be easily made.

However, this manufacturing method has the following problems. That is, first, an extra step is required to create an off-axis hologram lens as a mother lens.

The off-axis hologram lens, which serves as a mother lens, is rotated around three orthogonal axes with an accuracy of about ±0.5° relative to the reproduced reference wave beam, so that the focal point and optical axis of the reproduced object wave beam are aligned. It is necessary to adjust it so that it comes to a predetermined position, and the adjustment is extremely troublesome, especially when the NA is large. This is because the distribution of interference fringes of an off-axis hologram lens is not axially symmetrical like that of an in-line hologram lens, but the pitch of the interference fringes changes from large to small in the radial direction.

In addition, since the distribution of interference fringes of an off-axis hologram lens is as described above, interference may occur if the thickness of the photosensitive layer increases in the wet process after exposure to the photosensitive layer using gelatin as the base material. The slope of the cross section of the stripes changes and the characteristics of the lens become distorted. The higher the NA of an off-axis hologram lens, the more the distortion will be severe, and it may even become unusable.

In view of this point, the present invention proposes a manufacturing method that can easily produce an in-line hologram lens without using an off-axis hologram lens as a mother lens.

An example of a method for manufacturing an in-line hologram lens according to the present invention will be described in detail below with reference to FIG.

HR ₁ is a hologram recording medium on which an in-line hologram lens IN-L is to be recorded, and is composed of a glass substrate BS and a photosensitive layer (recording layer) K thereon.

_L1 is an optical element (mother lens) that emits a spherical wave beam, and for example, a microscope objective lens with NA of 0.4 or 0.5 is used.

MR is a total reflection mirror having a small window (light transmitting part) W, BS' is its transparent substrate (glass), MC is a reflective film on its front surface, and NR is a non-reflective film on its back surface. In this example, the small window W is constituted by a through hole bored in the center of the mirror MR.

As shown in Figure 13, the total reflection mirror MR does not have a through hole and has a non-reflective mirror in the center of the reflective film MC.
The small window W may be configured by forming NR'.

Then, the mother lens _L1 is made to face the hologram recording medium _HR1 , and a total reflection mirror MR is arranged between them. The hologram recording medium HR ₁ is arranged so that its photosensitive layer K faces the mother lens L ₁ side. The total reflection mirror MR is arranged obliquely so that its reflection film MC faces the photosensitive layer K of the hologram recording medium HR ₁ . Also, total reflection mirror
A spherical aberration compensating plate (transparent plate) V, which will be described later, is placed between MR and the hologram recording medium HR ₁ so as to be parallel to the hologram recording medium HR ₁ .

Then, at a certain point, a laser beam (parallel plane wave beam) from a common laser light source (for example, an argon, krypton, dye, He-Ne laser light source, etc.) (not shown) is transmitted using a lens (not shown). A spherical wave beam is formed that converges and then diverges, and this diverging spherical wave beam is made incident on the mother lens _L1 to be focused at a point P near the small window W, and then a spherical wave beam without spherical aberration is formed that diverges. , this diverging spherical wave beam is passed through a total reflection mirror MR at a point P so that its optical axis X coincides with the normal line of the compensator V and the photosensitive layer K of the hologram recording medium _HR
The hologram recording medium is passed through the small window W of the recording object wave beam A through the compensation plate V.
The photosensitive layer K of HR ₁ is irradiated.

Furthermore, after changing the direction of the laser beam (a parallel plane wave beam, but a spherical wave beam similar to a plane wave may also be used) from the common laser light source mentioned above using a beam splitter, mirror, etc., this plane wave beam is subjected to total internal reflection. After reflecting on mirror MR, compensating plate V
The recording reference wave beam B is irradiated onto the photosensitive layer K of the hologram recording medium HR ₁ through the recording reference wave beam B. The recording object wave beam A and the recording reference wave beam B are in an in-line relationship, i.e. their respective optical axes X coincide with the normal to the photosensitive layer K of the holographic recording medium HR ₁ , and their respective optical axes make them coincide or have a parallel relationship.

Thus, a circular inline hologram lens portion HL is formed at the center of the photosensitive layer K of this hologram recording medium HR ₁ , and by performing the same development process as described above, the inline hologram lens
IN-L is created.

The diameter of the small window W of the total reflection mirror MR only needs to be within a range through which the recorded object wave beam A can pass, and is sufficiently small so as not to degrade the function of the in-line hologram lens IN-L. In this case, when the diameter of the inline hologram lens part HL is 2 mm,
The diameter of the small window W of the total reflection mirror MR is about 100 μm.

Next, refer to FIG. 14 for an optical information (signal) reproducing device that reproduces recorded information (signals) on an optical recording medium (disc) using an inline hologram lens made by the manufacturing method shown in FIG. 12. In addition, the relationship between the optical recording medium and the spherical aberration compensator V, etc. will also be described. RD is an optical recording medium, DB is a transparent substrate (e.g. vinyl chloride), and RL is a reflective film (layer) formed on the transparent substrate DB so as to cover the entire surface of the pits and lands formed on the bottom surface (e.g. aluminum). GL is a protective film (layer) (for example, PVA) formed to cover the entire lower surface of the reflective film (layer) RL.

Then, the in-line hologram lens IN-L (which becomes an objective lens constituting a part of the reproducing means) obtained by the manufacturing method shown in FIG. In-line hologram lens IN
A reproduced reference wave beam (plane wave beam) B' is irradiated from the glass substrate BS side of -L to the inline hologram lens part HL, and the resulting reproduced object wave beam (focuses on the pit or land of the reflective film (layer) RL). A focused spherical wave beam) A' is irradiated onto the reflective film (layer) RL from the back side of the recording medium RD via the substrate DB as a reproduction beam. Also, this reflective film (layer)
The reflected wave beam from RL is beam A′− beam
Reverse the path of B′ (or B′) to the photoelectric conversion element (this is also possible if the laser light source is a semiconductor laser light source)
The signal is input to and reproduced as an electrical signal.

By the way, as shown in Fig. 14, the recording medium
When optically reproducing RD from the transparent substrate DB side, if the reproduced object wave beam A' is a spherical wave beam without spherical aberration, the spherical wave beam passes through the transparent substrate DB whose thickness as the optical path length is t. This results in the influence of spherical aberration, resulting in a reflected wave beam with spherical aberration.

Therefore, in Fig. 12, a spherical wave beam without spherical aberration is obtained from the mother lens _L1 , and a spherical aberration compensating plate V (if the total reflection mirror MR in Fig. 13 is used, a compensating plate By not providing V and selecting the thickness as the optical path length of the small window W) of the total reflection mirror MR to approximately the above t,
Since the recorded object wave beam A in FIG. 12 becomes a spherical wave beam with spherical aberration, the reproduced object wave beam A' irradiated onto the recording medium RD becomes a beam with spherical aberration, which passes through the transparent substrate DB. Therefore, it is made into an aberration-free beam, and by correcting the spherical aberration of the reproduction beam due to the transparent substrate DB of the recording medium RD, a reflected wave beam free of spherical aberration can be obtained. In this case, the compensating plate V and the recording medium
The actual thickness of RD's transparent substrate DB is 1.1 mm, and the refractive index is approximately 1.5.

Note that when the optical recording medium RD is irradiated with a reproducing beam from the front side thereof, the reproducing beam needs to be substantially aberration-free. In this case, the compensating plate V is not provided.

Next, since the above-mentioned total reflection mirror MR is provided with a small window W, a part of the recording reference wave beam (reflected wave beam) B is missing in this part, but this causes the inline hologram lens IN-L to Explain that it has almost no effect on the production process.

The in-line hologram lens IN-L implemented in the present invention is a type of volume phase hologram, and as shown in FIG. The lattice surface formed by the interference fringes in the inline hologram lens part HL, which consists of the interference fringes formed at K, has a rougher pitch as it approaches the center, that is, the optical axis It becomes secret.

Further, the volume phase hologram has a maximum diffraction efficiency if the Bragg condition is satisfied during reproduction. However, even if a reproduction beam that satisfies the Bragg condition is used, the diffraction efficiency does not necessarily improve. That is, it is well known that there is a restriction on the Q value expressed by the following equation.

Q=2πλd/nΛ ² However, λ is the wavelength of the beam, d is the thickness of the photosensitive layer K (lens portion HL), and n is the photosensitive layer K (lens portion HL).
The refractive index of , Λ is the lattice pitch.

In general, by changing d or Λ, Q
Changing the value changes the intensity of the diffracted beam of each order. In this case, if the Q value is chosen as QÅ1, +
The intensity of the first-order diffracted beam becomes significantly large, and the diffracted beams of other orders are suppressed. This condition of Q Å1 is more easily satisfied as the grating pitch Λ becomes smaller when λ, n, and d are each constant.

FIG. 16 shows an example of the diffraction efficiency distribution of the aperture surface of the inline hologram lens portion HL of the inline hologram lens IN-L. this lens
IN-L was recorded using a krypton laser light source (laser beam wavelength was 6471 Å) and a mother lens with an NA of 0.4. In Fig. 16, a He-Ne laser light source (laser beam wavelength is 6328 Å) is used as a reproduction laser light source, and the thickness d of the inline hologram lens portion HL of this inline hologram lens IN-L is 5 μm and 15 μm.
The curve shows the characteristic of the intensity of the +1st-order diffracted beam with respect to the distance from the radial center of the lens portion HL when According to this, the intensity of the +1st-order diffracted beam at the center of the lens portion HL,
That is, it can be seen that the diffraction efficiency is significantly lower than in other parts.

Therefore, inline hologram lens IN-L
In this case, even if no interference fringes are formed at the center of the lens portion HL due to the deletion of the center of the recording reference wave beam B mentioned above, it will hardly affect the performance as an in-line hologram lens. It turns out there isn't.

According to the manufacturing method of the present invention described above, an in-line hologram lens with high precision can be obtained with great ease. That is, there is no need to make an off-axis hologram lens as a mother lens, and the number of man-hours is reduced. Furthermore, since it is not necessary to use an off-axis hologram lens as a mother lens, a highly accurate in-line hologram lens can be obtained by using a highly accurate mother lens such as a microscope objective lens as an optical element. Furthermore, since a total reflection mirror with a small window is used, both the object wave beam and the reference wave beam can be used for hologram recording without substantially reducing their energy efficiency.

In addition, the optical element emits a spherical wave beam without spherical aberration, and the thickness of the spherical aberration compensator (or the small window of the total reflection mirror) as the optical path length is adjusted to the beam for reproduction of the optical recording medium. By making the thickness substantially equal to the optical path length of the transparent body through which the recording medium passes, a reflected wave beam without spherical aberration can be obtained even if there is a transparent body through which the reproduction beam of the recording medium passes.

[Brief explanation of drawings]

Figures 1 to 4 are explanatory diagrams showing a conventional hologram lens recording and reproducing method, Figure 5 is a layout diagram showing a conventional inline hologram lens recording method, and Figure 6 is a previously proposed inline hologram lens. FIG. 7 is a layout diagram showing an example of a recording method for manufacturing a lens; FIG. 7 is a layout diagram showing another example of a recording method for an in-line hologram lens manufacturing method proposed previously; FIG. A layout diagram showing an example of a recording method for manufacturing an off-axis hologram lens used in
A sectional view showing a hologram lens manufactured using the recording method shown in the figure, FIGS. 10 and 11 are layout diagrams showing a duplication recording method of an inline hologram lens, and FIG. 12 is a method for manufacturing an inline hologram lens according to the present invention. A layout diagram showing an example of the recording method, FIG. 13 is a sectional view of another example of a total reflection mirror,
FIG. 14 is a layout diagram showing a part of the optical information (signal) reproducing device, FIG. 15 is an explanatory diagram of the operation of the in-line hologram lens, and FIG. 16 is a curve diagram. L ₁ is a mother lens as an optical element, MR is a total reflection mirror, W is a small window thereof, A is a recording object wave beam, B is a recording reference wave beam, HR ₁ is a hologram recording medium, BS is a glass substrate, and K is a Photosensitive layer, IN−
L is an inline hologram lens.

Claims (1)

[Claims] 1 Using an optical element that radiates a spherical wave beam and a total reflection mirror having a small window, the spherical wave beam is focused near the small window of the total reflection mirror, and is irradiated onto the hologram recording medium as an object wave beam through the small window. and irradiating the hologram recording medium with a reflected wave beam of the total reflection mirror as a reference wave beam.