JP2006243370A - Interference exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that when a holographic PDLC element is manufactured while an exposure state is monitored by an interference exposure device, it is difficult to end exposure with a proper exposure quantity because of a decrease in monitor level although monitor light in use is short-pulse light or attenuated to low power density since a recording material is exposed to the monitor light so that wavelengths of a light source for exposure and a light source for monitoring are in the same wavelength band. <P>SOLUTION: Coherent light emitted by a laser light source 11 is branched by a luminous flux branching means 14 into two pieces of luminous flux, to which a recording material 16 is exposed from mutually different directions one over the other through deflecting means 15 respectively. One of luminous flux passed through the recording material is made incident on a polarized light conversion section comprising a retardation plate 17 and a mirror 18. Return light from the polarized light conversion section changes in polarizing direction by 90° before being incident on the recording material 16 again and does not contribute to the exposure of the recording material, and diffracted light reaches a monitor detecting element 19. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an interference exposure apparatus including an optical monitor control unit for producing a diffraction grating (hologram).

When producing a diffraction grating (hologram) using an interference exposure apparatus, the exposure state is monitored.
As a method for producing a hologram that does not use an interference exposure apparatus, a method has been proposed in which the oscillation wavelength range of the exposure light source and the monitor light source is different (see, for example, Non-Patent Document 1). The holographic PDLC element of this method is a diffraction grating (hologram) element that diffracts only p-polarized light. The monitor light source has an oscillation wavelength different from that of the exposure light source, and since the recording material is not sensitive at the wavelength of the monitor light source, the recording material is not exposed with the monitor light source. If there is no problem even if the exposure wavelength and the monitor wavelength are different, the exposure optical system with a monitor is very effective.
When the wavelength of the light used for exposure and the wavelength of the monitor light must be in the same wavelength band, the recording material is exposed to the monitor light, so the monitor light is changed to a short pulse light or attenuated to a low power density before being recorded. Needed to be irradiated. For this reason, the sensitivity (monitor level) of the monitor is lowered, and it is difficult to end the exposure with an appropriate exposure amount. Accordingly, among the diffracted light from the diffraction grating by the exposure beam, the diffracted light slightly generated in the orders other than the 0th order and the + 1st order was considered as the monitor light. However, with this method, in the case of an element that diffracts with p-polarized light but does not diffract with s-polarized light, as in the hologram described in Non-Patent Document 1, the exposure beam of the interference exposure method cannot be monitored because it uses s-polarized light. As a method of solving this problem, when the monitor light source is prepared separately from the exposure light source, or when the monitor light source is made common, the emitted light is branched and only the monitor light is rotated by 90 °.

  There are two problems when using a part of the laser beam for exposure as monitor light. One is that the light intensity for exposure decreases. The second is that the wavefront f of the laser beam is degraded due to the branching. When the exposure light intensity decreases, it is necessary to lengthen the exposure time in order to obtain the same exposure amount, which increases the manufacturing cost. As for the degradation of the laser wavefront, a good wavefront can be obtained by using a spatial filter, but the intensity of light from the spatial filter decreases as the wavefront disturbance increases.

Sugawara et al., “Property of Polarization Dependent Holographic Polymer Dispersed Liquid Crystal Device and its Application for Information Display”, p. 161, FIG. 1. International Display Workshops, 2002 Digest

An object of the present invention is to enable interference exposure and monitoring with a single laser light source without sacrificing exposure light intensity.
In addition to the above object, it is an object to be able to divert the wavelength conversion element even when the light source wavelength is changed.
It is another object of the present invention to realize an optical system that can easily receive monitor light.
Another object of the present invention is to realize an optical system that does not need to change the monitor optical system even if the exposure wavelength is changed.
A further object is to increase the light intensity of the monitor light.

  According to the first aspect of the present invention, a light source that emits a coherent light beam, a light beam branching unit that branches the light beam into a plurality of light beams, a predetermined orientation and a predetermined incident angle with respect to the plurality of light beams as a recording material In the interference exposure apparatus for producing a desired diffraction grating on the recording material, only one predetermined light beam that has passed through the recording material has a polarization vibration plane of 90 °. A polarization conversion unit that converts the light again to enter the recording material, and a light receiving element for monitoring the light beam diffracted by the recording material.

According to a second aspect of the present invention, in the interference exposure apparatus according to the first aspect, the polarization conversion unit includes a phase difference plate that gives a phase of λ / 4 and a mirror.
According to a third aspect of the present invention, in the interference exposure apparatus according to the second aspect, both the one light beam and its return light pass through the retardation plate.
According to a fourth aspect of the present invention, in the interference exposure apparatus according to the third aspect, the retardation plate is a λ / 4 plate.

According to a fifth aspect of the present invention, in the interference exposure apparatus according to the third aspect, the retardation plate is a Fresnel rhombohedron.
According to a sixth aspect of the present invention, in the interference exposure apparatus according to the second aspect, only one of the one light beam and its return light passes through the retardation plate.
According to a seventh aspect of the present invention, in the interference exposure apparatus according to the sixth aspect, the retardation plate is a λ / 2 plate.

According to an eighth aspect of the present invention, in the interference exposure apparatus according to the sixth aspect, the retardation plate is a combination of two Fresnel rhombohedrons.
According to a ninth aspect of the present invention, in the interference exposure apparatus according to any one of the first to eighth aspects, an incident angle of the light beam for monitoring to the recording material is different from any of the incident angles of all exposure light beams. It is characterized by that.

According to a tenth aspect of the present invention, in the interference exposure apparatus according to the first aspect, the polarization conversion unit includes three mirrors.
According to an eleventh aspect of the present invention, in the interference exposure apparatus according to any one of the first to tenth aspects, one of the deflection means is a polarization beam splitter.

According to the present invention, exposure and monitoring can be performed with a single laser light source, and a good diffraction grating can be obtained without sacrificing exposure light intensity and without generating unnecessary interference fringes on the surface of the recording material. Can be made.
In addition to the above effects, since the retardation plate is a Fresnel rhombohedron, the polarization conversion element portion can be used even when the exposure wavelength is changed.
Further, since the incident angle of the monitor light is set to be different from the incident angles of all the exposure light, the diffracted monitor light and the exposure light can be easily separated.
Further, since the polarization conversion element unit is constituted by three mirrors, there is no need to change the polarization conversion element unit even if the exposure wavelength is changed.
Furthermore, since the incident angle of the monitor light to the recording material is the same as the incident angle of one exposure light, the intensity of the monitor light can be increased, and the exposure light and the monitor light are easily separated by the polarization beam splitter. be able to.

FIG. 1 is a diagram for explaining a first embodiment of the present invention.
In the figure, reference numeral 11 is a laser light source, 12 is a spatial filter, 13 is a collimating lens, 14 is a half mirror, 15a and 15b are mirrors, 16 is a recording material, 17 is a λ / 4 plate as a retardation plate, and 18 is A mirror, 19 is a light receiving element, 20 is a control device, and 21 is an electromagnetic shutter.
The outgoing light from the laser 11 is converted into a zero-order beam transverse mode by the spatial filter 12, and the divergent light from the spatial filter 12 is converted into a parallel beam by the collimator lens 13. The parallel light is divided into two by the half mirror 14, and the recording material 16 is irradiated with each beam at a predetermined incident angle using mirrors 15a and 15b as deflection means. The spatial filter 12 includes an objective lens and a pinhole (not shown). The recording material is preferably p-polarized and diffracted with high efficiency. The light emitted from the laser light source 11 is polarized with respect to the recording material as s-polarized light (perpendicular to the paper surface).

FIG. 2 is a diagram for explaining the configuration of the holographic PDLC.
In the figure, reference numeral 22 is a polymer layer, 23 is a liquid crystal layer, 24 is p-polarized light, 25 is a polymer dispersed liquid crystal (hereinafter referred to as holographic PDLC), and 26 is a glass substrate.
As the recording material 16, holographic PDLC as described in Non-Patent Document 1 can be used. In this holographic PDLC 25, as shown in the figure, a polymer layer 22 and a liquid crystal layer 23 are periodically formed, and the refractive index of the polymer and the ordinary light refractive index of the liquid crystal are substantially equal. The liquid crystal is aligned so as to be perpendicular to the wall of the polymer layer 22. Therefore, the s-polarized light does not feel the difference in refractive index between the polymer layer 22 and the liquid crystal layer 23 and does not diffract. However, since the p-polarized light 24 feels a difference between the extraordinary refractive index of the polymer layer 22 and the liquid crystal layer 23, the p-polarized light 24 is diffracted by exhibiting the function of a diffraction grating. Such a holographic PDLC 25 is produced by sandwiching a liquid mixture of a photopolymerizable monomer and a photononpolymerizable liquid crystal between glass substrates 26 and performing interference exposure.

Of the two exposure beams, the recording material transmitted light reflected by the mirror 15b is used as monitor light. The transmitted light is converted into p-polarized return light orthogonal to the incident light (s-polarized light) by the λ / 4 plate 17 and the mirror 18 and is incident on the recording material 16 again. The combination of the λ / 4 plate 17 and the mirror 18 functions as a polarization conversion unit. As shown in FIG. 1, the λ / 4 plate 17 generates a phase of λ / 4 with respect to a predetermined incident angle. Preferably, the incident angle of the monitor light (p-polarized light) to the recording material is the incidence of the exposure beam. Make it different from the corner. The monitor light is diffracted by the recording material and monitored by the light receiving element 19. When the light reception signal reaches a predetermined value, the electromagnetic shutter 21 is closed via the control device 20 to block the exposure beam.
In the present invention, since the transmitted light from one recording material of the exposure beam is diverted to the monitor light, the exposure light intensity is not sacrificed. Further, since the monitor light and the polarization of the exposure beam are orthogonal to each other, unnecessary interference fringes are not generated by the monitor light. For this reason, an unnecessary structure is not produced in the recording material portion by the monitor.
In this embodiment, the two-beam interference exposure is used. However, there is no correlation between the number of exposure beams and the effect of the present invention, and the present invention can be used for multi-beam interference exposure of three or more beams.

FIG. 3 is a diagram for explaining a second embodiment of the present invention.
FIG. 4 is a diagram showing the configuration of the polarization conversion element section.
In both figures, reference numeral 30 denotes a polarization converter, and 31, 32, and 33 denote mirrors. The same parts as those of the first embodiment are denoted by the same reference numerals.
The polarization conversion unit 30 includes three mirrors 31, 32, and 33. The traveling direction of the light incident on the polarization converter 30 is taken as the z axis, and the y axis is taken as the polarization p1 vibration direction. The first mirror 31 reflects incident light in the −y axis direction. At this time, the polarized light p2 of the reflected light is parallel to the z-axis. Light is reflected by the second mirror 32 in the + x direction. This polarization direction is parallel to the z-axis. The light is reflected by the third mirror 33 in the −z direction. At this time, the polarized light is parallel to the x-axis. Therefore, the polarization state can be orthogonalized by the three mirrors. However, the incident light flux and the outgoing light flux in the polarization conversion unit 30 are slightly shifted Δy and Δx both in the vertical direction (y direction) and in the horizontal direction (x direction).
On the other hand, if the angle of the third mirror is adjusted, the polarization oscillation plane can be maintained in the xz plane and the angle from the z axis can be changed. In a polarization conversion unit using a birefringent plate, if the incident angle is different, the phase difference perceived by the light is different, so the emission direction cannot be arbitrarily changed. If it deviates from the specified direction, the polarized light of the emitted light becomes elliptically polarized, and the electric field amplitude component in the same direction as the vibration direction of the incident light remains, causing interference between the monitor light and the exposure light, generating unnecessary optical interference fringes. As a result, a diffraction grating including a ghost is manufactured. However, in this configuration, the direction of the emitted light can be changed only by adjusting the rotation of the third mirror 33 and can be converted into a desired polarization state. Therefore, at least the deviation in the xz plane can be corrected.

FIG. 5 is a diagram for explaining a third embodiment of the present invention. The figure shows only the polarization converter.
In the figure, reference numeral 50 denotes a polarization converter, and 51 denotes a Fresnel rhombohedron.
Only the polarization converter 50 is shown. Except for the polarization conversion section, it may be the same as in FIG.
The polarization conversion unit 50 includes a “Fresnel rhombohedron” 51 that acts as a retardation plate and a mirror 18. When the incident polarized light p1 is parallel to the y axis, the diagonal direction of the end face of the “Fresnel rhombohedron” is arranged to be the y axis (or the x axis). The light emitted after being totally reflected twice by the Fresnel rhombohedron becomes circularly polarized light p2. When the circularly polarized light p3 (circularly polarized light opposite to p2) which is turned back by the mirror 18 is incident on the Fresnel rhombohedron again, the phase difference is further added, and the polarized light p4 of the emitted light becomes parallel to the x axis. “Fresnel rhombohedron” is described in, for example, pages 149 to 151 of “Basics of Optics” (written by Junichi Sakai) published by Corona.

Since the Fresnel rhombohedron gives the phase of polarized light by reflection, it has only a wavelength dependency due to dispersion and can be used in a very wide wavelength range compared to a retardation plate made of a birefringent material. For this reason, even when the laser light source is changed, the polarization conversion element can be used in common.
In the present invention, as in the first embodiment, the transmitted light from one recording material of the exposure beam is diverted to the monitor light, so that the exposure light intensity is not sacrificed. Further, since the monitor light and the polarization of the exposure beam are orthogonal to each other, unnecessary interference fringes are not generated by the monitor light. For this reason, an unnecessary structure is not produced in the recording material portion by the monitor. In this embodiment, the two-beam interference exposure is used. However, there is no correlation between the number of exposure beams and the effect of the present invention, and the present invention can be used for multi-beam interference exposure of three or more beams.

FIG. 6 is a diagram for explaining a modification of the third embodiment. The figure shows only the polarization converter.
In the figure, reference numeral 52 denotes a combination rhombohedron, and 53 and 54 denote mirrors, respectively.
It is composed of a combined rhombohedron 52 combining two Fresnel rhombohedrons and two mirrors 53 and 54. The combination rhombohedron 52 is a combination of two Fresnel rhombohedrons 51 described above, and a phase difference of λ / 2 is generated by four total reflections. For this reason, the polarization vibration plane of the light that has passed through the combination rhombohedron 52 is orthogonal to the incident light. It is folded by two mirrors and is incident on the recording material as monitor light at a predetermined incident angle. According to this configuration, the direction of the emitted light is determined by the two mirrors after the polarization direction of the incident light is converted by 90 °. Since the polarization-converted light is folded back only by the mirror, if the incident surface to the mirrors 53 and 54 is parallel (or perpendicular) to p2, the outgoing light p3 has only a polarization component parallel to the x-axis.
Note that the light beam passing through the combination rhombohedron 52 may be immediately after passing through the recording material or after being reflected by the mirrors 53 and 54.

FIG. 7 is a diagram for explaining a fourth embodiment of the present invention. This figure shows only the recording material and the polarization converter. Other configurations are the same as those in FIG.
In the figure, reference numeral 25 denotes a λ / 2 plate.
The polarization conversion unit includes a λ / 2 plate 25 that is a phase difference plate and two mirrors 18a and 18b. Of the exposure light beams B1 and B2, B1 recording material transmitted light is used as monitor light. The angle formed by the optical axis (slow axis) of the λ / 2 plate and the paper surface is 45 °, and the λ / 2 plate converts the polarization state into a polarization state parallel to the paper surface. This polarized light is again incident on the recording material at a predetermined incident angle by the mirrors 18a and 18b. At this time, since the incident angle is different from the incident angle of the exposure light beam, the diffracted light from the recording material can be easily guided to the light receiving element. The light beam passing through the phase difference plate may be transmitted directly from the recording material or may be reflected by the mirrors 18a and 18b.
In this configuration, since the λ / 2 plate 25 is used as the polarization conversion element, the incident angle of the monitor light to the recording material can be arbitrarily changed.

FIG. 8 is a diagram for explaining a fifth embodiment of the present invention.
In the figure, reference numeral 81 denotes a polarization beam splitter.
In this embodiment, the mirror 15a of the first embodiment shown in FIG. This polarizing beam splitter 81 reflects s-polarized light (vibration plane perpendicular to the paper surface) and transmits p-polarized light (vibration surface parallel to the paper surface). Since the exposure light beam is s-polarized light, it is reflected by the polarization beam splitter 81 and travels toward the recording material. On the other hand, since the monitor light is converted into p-polarized light by the polarization conversion unit including the λ / 4 plate 17 and the mirror 18, the diffracted light diffracted by the recording material passes through the polarization beam splitter.
In this configuration, the incident angle of the light reflected by the polarization converter to the recording material is the same as the incident angle of the exposure light beam. For this reason, the light diffracted by the recording material proceeds so as to follow the optical path of the other exposure beam. By using a polarization beam splitter, the exposure light and the monitor light can be separated. By making the monitor light have the same incident angle as that of one of the exposure lights, the light intensity of the monitor light can be increased.

It is a figure for demonstrating the 1st Example of this invention. It is a figure for demonstrating the structure of holographic PDLC. It is a figure for demonstrating the 2nd Example of this invention. It is a figure which shows the structure of a polarization conversion element part. It is a figure for demonstrating the 3rd Example of this invention. It is a figure for demonstrating the modification of a 3rd Example. It is a figure for demonstrating the 4th Example of this invention. It is a figure for demonstrating the 5th Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Laser light source 16 Recording material 17 (lambda) / 4 board 19 Light receiving element 20 Control part 22 Polymer layer 23 Liquid crystal layer 25 Holographic PDLC
30, 50, 52 Polarization conversion element section

Claims (11)

  A light source that emits a coherent light beam, a light beam branching unit that branches the light beam into a plurality of light beams, and a deflecting unit that irradiates the plurality of light beams to a recording material at a predetermined direction and a predetermined incident angle. In the interference exposure apparatus for producing a desired diffraction grating on the recording material, only one predetermined light beam that has passed through the recording material out of the plurality of light beams is converted into a polarization vibration plane by 90 ° and returned to the recording material again. An interference exposure apparatus comprising: a polarization conversion unit that makes an incident; and a light receiving element that monitors the light beam that is diffracted by the recording material.   The interference exposure apparatus according to claim 1, wherein the polarization conversion unit includes a phase difference plate that gives a phase of λ / 4 and a mirror.   3. The interference exposure apparatus according to claim 2, wherein both the one light beam and its return light pass through the retardation plate.   4. The interference exposure apparatus according to claim 3, wherein the retardation plate is a λ / 4 plate.   4. The interference exposure apparatus according to claim 3, wherein the retardation plate is a Fresnel rhomboid.   3. The interference exposure apparatus according to claim 2, wherein only one of the one light beam and its return light passes through the phase difference plate.   7. The interference exposure apparatus according to claim 6, wherein the retardation plate is a [lambda] / 2 plate.   7. The interference exposure apparatus according to claim 6, wherein the retardation plate is a combination of two Fresnel rhombohedrons.   9. The interference exposure apparatus according to claim 1, wherein an incident angle of a light beam for monitoring to the recording material is different from any of incident angles of all exposure light beams.   The interference exposure apparatus according to claim 1, wherein the polarization conversion unit includes three mirrors.   11. The interference exposure apparatus according to claim 1, wherein one of the deflecting means is a polarization beam splitter.

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