JPS61294480A - Hologram lattice recording method - Google Patents

Abstract

PURPOSE:To record a hologram lattice by setting each of two luminous fluxes which interfere with each other, as a parallel luminous flux, fixing a recording medium, and displacing an interference area of two luminous fluxes to be interfered with, in the lattice array direction. CONSTITUTION:An interference fringe by two luminous fluxes is generated in an interference area, and a direction of a bright part and a dark part of a linear shape is parallel to the upper and lower directions in an interference area 200. When a plane mirror 52 is moved to the right from said state, a parallel luminous flux L0 is also displaced to the right, by which two luminous fluxes L1, L2B inputted to a recording medium 100 are also moved in parallel to the right at the same speed. Accordingly, the interference area 200 moves to the right, namely, in the lattice array direction of a linear hologram lattice to be recorded. In this way, an exposure is executed and the linear hologram lattice being an interference fringe pattern is recorded to the recording medium 100, and thereafter, by performing a necessary processing such as a development, etc. to the recording medium 100, a desired linear hologram lattice can be obtained.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a hologram grating recording method.

(Prior Art) A hologram grating recording method is known in which a linear hologram grating is recorded by causing two coherent beams of light to interfere with each other on a photosensitive recording medium.

FIG. 4 shows an example of an optical system for implementing a conventionally known hologram grating recording method. Below, we will explain the outline of hologram grating recording based on this example.
In addition, one problem to be solved by the present invention will be described.

In FIG. 4, numeral 10 is a laser light source, numeral 12 is a shutter, and numerals 14, 18, 26, and 32 are plane mirrors.

Reference numeral 16 is a half mirror 1. Reference numeral 20 is an objective lens.

Reference numerals 24 and 30 indicate a collimator lens, 34 a mask, and 100 a photosensitive recording medium, respectively.

The photosensitive recording medium 100 is, for example, one in which a photoresist layer is provided on a substrate such as glass, a photoconductive thermoplastic photoreceptor, a silver salt film, or the like.

The mask 34 is a light shielding plate having an opening that matches the shape of the linear hologram grating to be recorded.

It is placed close to the surface of the recording medium 100.

Now, when the shutter 12 is opened, the laser light source 10
The coherent light emitted from the mirror enters the half mirror 16 via the plane mirror 14, where part of it is reflected and the other part is transmitted. In this way, two coherent beams of light are obtained.

The light reflected by the half mirror 16 becomes a parallel light beam whose diameter is expanded by the objective lens 20 and the collimator lens 24, and enters the plane @26.

On the other hand, the light transmitted through the half mirror 16 is reflected by the plane mirror 18, and is incident on the plane mirror 32 as a parallel beam whose diameter is enlarged by the objective lens 28 and the collimator lens 30.

The parallel beams of light reflected by the plane mirrors 26 and 32 are, respectively,
The light enters the recording medium 100 through the mask 34 at a predetermined angle of incidence, interferes on the recording medium 100, and produces interference fringes. After exposing the recording medium 100 to the interference fringes for a required time, the shutter 12 is closed and the recording medium 100 is subjected to necessary processing such as development, thereby obtaining a linear hologram grating. This linear hologram grating is identical to the pattern of the interference fringes described above.

The above-mentioned pattern of interference fringes is one in which linear bright areas and dark areas are arranged alternately, parallel to each other, and periodically. The direction in which the bright or dark areas are arranged is called the lattice arrangement direction.

Note that the lattice directions of the linear hologram grating obtained as described above are the direction orthogonal to one drawing in FIG.
The grating arrangement direction is the horizontal direction in the drawing, and the lattice constant of the linear hologram grating is determined by the wavelength of the laser beam and the recording medium 100.
It is determined by the respective incident angles of the two light beams incident on .

Now, in this conventional hologram grating recording method,
There are the following problems.

In other words, the lenses and plane mirrors that make up the recording optical system,
If chips, dust, scratches, etc. are attached, all of these chips, dust, scratches, etc. will be recorded as a hologram image (three-dimensional image) on the recording medium 100, which is a recording material.

In this way, if clumps, dust, scratches, etc. are recorded as a hologram image, they will be reproduced as noise around the main beam diffracted by this hologram grating, and the value of the diffraction grating will be significantly reduced. Not only dirt attached to the optical system and scratches on the optical system, but also scattered light from the plane mirror, lens periphery, etc. enter the recording medium and are recorded as a hologram, which becomes noise during reproduction.

(Objective) Therefore, the present invention aims to provide a novel hologram grating recording method that solves such problems.

(composition) The present invention will be explained below.

The hologram grating recording method of the present invention is characterized by the following points.

That is, each of the two light beams that interfere with each other on the recording medium is made into a parallel light beam, and the recording medium is fixed.

The interference region of the two light beams to interfere is displaced in the grating arrangement direction.

This will be explained below using a specific example.

FIG. 1 shows an example of an optical system for implementing the present invention. In order to avoid complexity, the same reference numerals as in FIG. 4 described above are used for the laser light source, mask, and recording medium. This point also applies to FIGS. 2 and 3, which will be described later.

Now, in FIG. 1 (1), 40.42.52.56, 58.60 are plane mirrors, 44 is an objective lens, 46 is a collimator lens, and 54 is a half mirror.
are shown respectively.

In addition, in FIG. 1 (II), reference numeral 34' indicates the mask 3.
4 opening is shown.

In the optical system shown in FIG. 1, the parts other than the plane mirror 52 are fixed, but the plane mirror 52 is movable in the left and right directions in the drawing by a moving mechanism (not shown). A shutter is provided between the plane @40, but this shutter is not shown.

Now, the light from the laser light source 10 enters the objective lens 44 via the plane mirrors 40 and 42, and is expanded in diameter and made into a parallel light beam by the objective lens 44 and the collimator lens 46. The cross-sectional shape of this parallel light beam is approximately circular. After being reflected by the plane @52, this light beam is split by a half mirror 54 into transmitted light and reflected light. The light reflected by the half mirror 54 enters the recording medium 100 via the plane mirror 58. On the other hand, half mirror
The light transmitted through 54 is on plane 1! ! 56 and 60 one after another and enter the recording medium 100. These two beams of light are incident on the same position on the recording medium loo. Since the cross-sectional shape of each light beam is approximately circular, the area where the two light beams overlap is.

It has an elliptical shape close to a circle as shown by the reference numeral 200 in the first figure (■). This area 200 is called an interference area of two beams of light.

Now, the interference fringes due to the two light beams are generated in the interference region, and the directions of the linear bright and dark regions are the interference region 200 (the first
In figure (■), it is parallel to the vertical direction of figure 1.

Now, when the plane @52 is moved in the direction of the arrow, that is, to the right from the state shown in FIG.
The light beam L2 also moves in parallel to the right at the same speed. Therefore, the interference region 200 (FIG. 1 (■)) moves to the right, that is, in the grating arrangement direction of the linear hologram grating to be recorded. Exposure is thus performed and a linear hologram grating is recorded as an interference fringe pattern on the recording medium 100. Thereafter, by performing necessary processing such as development on the recording medium 100, a desired linear hologram grating can be obtained. can.

FIG. 2 shows another example of an optical system for carrying out the present invention. 6 The same reference numerals as in FIG. 1 are used to avoid confusion. As in Figure 1,
A shutter (not shown) is provided between the laser light source 1o and the plane mirror 4°.

By the objective lens 44 and collimator lens 46,
The parallel light beam whose diameter has been expanded enters the spherical lens 62 and is focused on point P. Then, at point P, the plane mirror 64
The light is reflected by the spherical lens 66 and returned to a parallel beam of light. That is, point P becomes the common focus of the spherical lenses 62,66. The optical path after the spherical lens 66 is the same as the example shown in FIG. The plane @64 is movable around an axis passing through point P and perpendicular to the drawing, and this plane @64
When rotated counterclockwise, the interference area moves to the recording medium 1.
00, the recording medium 100 moves to the right in FIG.
to expose.

FIG. 3 shows yet another example of an optical system for implementing the present invention. In this figure as well, the same reference numerals as in FIG. 1 are used for parts that are not likely to be confused. As in the case of Fig. 1, the laser light source 10 and the plane @
A shutter (not shown) is provided between the collimator lens 40 and the collimator lens 6. The light transmitted through the collimator lens 46 becomes a parallel beam of light, is reflected by the plane mirror 70, is divided into two parts by the half mirror 72, and is reflected by the half mirror 72. The portion that passes through the half mirror 72 is reflected by the plane @74 and enters the recording medium 100.

If the half mirror 72 and the plane mirror 74 are integrally moved upward in FIG. 3, the interference region will also be displaced upward with respect to the recording medium 100 in FIG. 3, and the recording medium 100 will be exposed.

In addition, in the hologram grating recording method of the present invention, the interference fringe pattern is determined by the relative relationship between the wavefronts of the two beams in the interference region, and even if the interference region is displaced by the movement of the two beams, the interference fringe pattern will not change. The recording medium itself does not have a relative speed with respect to the recording medium. In the above explanation, a flat recording medium was taken as an example, but the present invention is also applicable even if the recording medium surface is curved. .

In addition, in the recording apparatus shown in FIG. 1, the plane fi52.56
゜58, 60. The half mirror 54 may be integrally displaced to the right for recording.

(Effects) According to the present invention, a novel hologram grating recording method can be provided.

In this recording method, two beams of light are made to interfere on the recording medium,
Since the recording medium is exposed while displacing the interference region caused by this interference in the lattice arrangement direction of the linear hologram grating to be recorded on the recording medium, there may be dust or dirt attached to the recording optical system, or Even if there are scratches or scattered lights, they are always in motion relative to the recording medium and are therefore not recorded as a hologram. Therefore, this recording method records a hologram grating with extremely low noise. can do.

In addition, since laser light has a Gaussian intensity distribution with the optical axis as the axis of symmetry, when trying to make the light intensity distribution uniform on the recording medium using conventional recording methods, it is difficult to achieve a two-dimensional transmittance distribution. However, in the recording method of the present invention, since the interference region is displaced in the grating arrangement direction, a correction plate having a one-dimensional transmittance distribution (a correction plate having the two-dimensional transmittance distribution described above) must be used. (can be produced more cheaply and easily than the conventional method), it is possible to perform uniform exposure over the entire exposure area simply by making the light intensity distribution in the lattice direction uniform.

Alternatively, by performing hologram grating recording while changing the displacement speed of the interference region, it is also possible to change the exposure amount in the direction of the interference region displacement and provide a desired diffraction efficiency distribution in the grating arrangement direction. . The present invention can be used to create diffraction gratings used in spectrometers, hologram grating disks used in optical scanning, gratings for demultiplexing and combining optical ICs, gratings used in DFB lasers, and the like. Note that the shape of the interference region is arbitrary as long as hologram recording is possible.

[Brief explanation of drawings]

1 is a diagram showing one example of an optical system for implementing the present invention, FIG. 2 is a diagram showing another example of an optical system for implementing the present invention, and FIG. 3 is a diagram showing an example of an optical system for implementing the present invention. FIG. 4 is a diagram illustrating another example of an optical system for implementing the conventional technique. 10... Laser light source, 44... Objective lens,
45...half mirror, 46...collimator lens, 52...plane mirror, 100...recording medium, 200...interference area.

Claims (1)

[Claims] A method for recording a linear hologram grating by causing two coherent beams of light to interfere with each other on a photosensitive recording medium, the method comprising: converting each of the two beams of light that interferes on the recording medium into a parallel beam of light; A holographic grating recording method, comprising: fixing the recording medium and displacing the interference region of the two light beams in the grating arrangement direction.