Exposure apparatus, exposure method, apparatus for manufacturing holographic optical elements, and method for manufacturing holographic optical elements

Abstract

To accurately measure the diffraction efficiency of holographic optical elements during exposure. [Solution] An exposure apparatus used to expose a volume hologram 5 comprises a laser light source 6 that irradiates the volume hologram 5 with first light, which is light in a predetermined wavelength band, in order to detect the diffraction efficiency of the volume hologram 5 during exposure, a power meter 8 that detects the amount of light of the first light, and a power meter 9 that detects the amount of light of the second light, which is the first light diffracted by the volume hologram 5.

Description

Technical Field

[0001] The present disclosure relates to an exposure apparatus, an exposure method, a manufacturing apparatus for a holographic optical element, and a manufacturing method for a holographic optical element.

Background Art

[0002] Conventionally, an exposure apparatus for manufacturing a holographic optical element has been known. For example, the interference exposure apparatus of Patent Document 1 includes a first laser light source for exposure and a second laser light source for monitoring. In Patent Document 1, light is irradiated from the second laser light source onto a recording material, and the light intensity of the light diffracted by the recording material is monitored to create a desired diffraction grating (holographic optical element).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in Patent Document 1, since the diffraction efficiency of the holographic optical element is measured (monitored) only by the light intensity of the light diffracted by the recording material among the light irradiated from the second laser light source, if the amount of light irradiated by the second laser light source fluctuates, the diffraction efficiency of the holographic optical element cannot be accurately measured. As a result, the diffraction efficiency of the holographic optical element varies.

[0005] For example, if the output of the second laser light source fluctuates by about ±1%, the diffraction efficiency of the holographic optical element will also fluctuate by about ±1%. In this case, it cannot be used in applications where high quality standards for the holographic optical element are required. For example, in the case of automotive applications, the variation in diffraction efficiency needs to be kept to about ±3%, and if the diffraction efficiency of the holographic diffracting element fluctuates by about ±1%, it will have a significant impact on its quality.

[0006] Therefore, the object of this disclosure is to provide an exposure apparatus, an exposure method, a manufacturing apparatus for a holographic optical element, and a method for manufacturing a holographic optical element that can accurately measure the diffraction efficiency of a holographic optical element during exposure. [Means for solving the problem]

[0007] To achieve the above objective, an exposure apparatus according to one embodiment of the present disclosure is an exposure apparatus used for exposing a holographic optical element, comprising: a light source that irradiates the holographic optical element with first light, which is light in a predetermined wavelength band, in order to detect the diffraction efficiency of the holographic optical element during exposure; a first detector that detects the amount of the first light; and a second detector that detects the amount of second light, which is the first light diffracted by the holographic optical element. [Effects of the Invention]

[0008] According to this disclosure, the diffraction efficiency of a holographic optical element during exposure can be accurately measured. [Brief explanation of the drawing]

[0009] [Figure 1] A side view of the exposure apparatus according to the first embodiment. [Figure 2] A flowchart illustrating the operation of the exposure apparatus according to the first embodiment. [Figure 3] A graph showing an example of the change in diffraction efficiency in a volume hologram according to the first embodiment. [Figure 4] A side view of the exposure apparatus according to the second embodiment. [Figure 5] A flowchart illustrating the operation of the exposure apparatus according to the second embodiment. [Figure 6] A graph showing an example of the change in the predicted diffraction efficiency in a volume hologram according to the second embodiment. [Figure 7] A graph showing an example of the change in diffraction efficiency in a volume hologram according to the second embodiment. [Figure 8] A graph showing an example of the change in the amount of light from the laser beam irradiated onto the volume hologram according to the second embodiment. [Figure 9] A side view of the exposure apparatus according to the third embodiment. [Figure 10] A graph showing an example of the change in the predicted diffraction efficiency in a volume hologram according to the third embodiment. [Figure 11] A flowchart illustrating the operation of the exposure apparatus according to the third embodiment. [Figure 12] A graph showing an example of the change in diffraction efficiency in a volume hologram according to the third embodiment. [Figure 13] A graph showing an example of the change in the amount of bleaching light irradiated onto a volume hologram according to the third embodiment. [Figure 14] A side view of the exposure apparatus according to the fourth embodiment. [Figure 15] A flowchart illustrating the operation of the exposure apparatus according to the fourth embodiment. [Figure 16] A graph showing an example of the change in diffraction efficiency in a volume hologram according to the fourth embodiment. [Figure 17] A graph showing an example of the change in the amount of laser light irradiated onto a volume hologram according to the fourth embodiment. [Figure 18] A graph showing an example of the change in the amount of bleaching light irradiated onto a volume hologram according to the fourth embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the present disclosure will be described in detail based on the drawings. The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its applications, or its uses in any way. In the following description, the same parts are denoted by the same reference numerals, and detailed descriptions thereof are omitted as appropriate.

[0011] Note that the volume hologram (volume hologram 5) used in the present disclosure is different from a two-dimensional diffraction grating in which fine periodic irregularities are arranged on the surface, and a refractive index distribution is three-dimensionally recorded in a sine wave shape in the volume. By controlling the direction, period, and amplitude of the refractive index difference of this sine wave, light distribution control of the volume hologram becomes possible. In the present disclosure, for the sake of convenience of explanation, the refractive index distribution recorded in the volume hologram is assumed to be sine wave-shaped, but the refractive index distribution recorded in the volume hologram is not limited to sine wave-shaped and may be other shapes or complex ones.

[0012] Also, an exposure method and a method for manufacturing a holographic optical element are realized by the exposure apparatus described below.

[0013] (First Embodiment) (Overall Configuration of Exposure Apparatus) FIG. 1 is a side view of an exposure apparatus according to the first embodiment. In FIG. 1, the irradiation direction of the laser beam L3 is the X direction, the laser beam L2 (object beam) is the Y direction, and the direction perpendicular to the X direction and the Y direction (the depth direction of the paper surface) is the Z direction. Also, in FIG. 1, the light irradiated from the laser light sources 1 and 6 is indicated by dashed arrows.

[0014] As shown in FIG. 1, the exposure apparatus according to the first embodiment includes a laser light source 1 (exposure laser light source), a branching mirror 2, mirrors 3 and 4, a volume hologram 5 (holographic optical element), a laser light source 6 (monitor laser light source), a beam splitter 7 (optical element), a power meter 8 (first detector), a power meter 9 (second detector), a control device 10 (prediction device), and a shutter 11. Note that the volume hologram 5 is a volume hologram exposed (manufactured) by this exposure apparatus.

[0015] Laser light source 1 is a light source that irradiates the branching mirror 2 with laser light L1 (parallel light, third light). Laser light source 1 is a highly coherent laser light source. Therefore, even if the laser light L2 and L3 are separated by the branching mirror 2 (described later) and have the same optical path length, it is possible to generate optical interference between them. In addition, laser light L1 has the characteristics of linear polarization, and if the polarization ratio is insufficient, the polarization direction may be controlled by inserting a wave plate or polarizer.

[0016] A shutter 11 is provided between the laser light source 1 and the branching mirror 2 to block the laser beam L1. The laser light source 1 and the shutter 11 operate in response to signals from the control device 10. The shutter 11 may be integrated with the laser light source 1.

[0017] Furthermore, an optical system for making the laser beam L1 parallel light may be provided between the laser light source 1 and the branching mirror 2. For example, a focusing lens and a collimating lens may be provided between the laser light source 1 and the branching mirror 2. In this case, the focusing lens focuses the laser beam L1 from the laser light source 1 and makes it diffuse light. The collimating lens then makes the laser beam L1, which has been diffused by the focusing lens, parallel light.

[0018] The branching mirror 2 splits the laser light L1 emitted from the laser light source 1 into two beams. Specifically, the branching mirror 2 splits the laser light L1 into laser light L2 (object light) and laser light L3 (reference light). For example, the branching mirror 2 is composed of a polarizing beam splitter, which reflects the linearly polarized light in the first polarization direction (laser light L2, e.g., S-polarized light) of the laser light L1 and transmits the linearly polarized light in the second polarization direction (laser light L3, e.g., P-polarized light).

[0019] Mirror 3 is a mirror that reflects the laser light L2 reflected by the branched mirror 2. As shown in Figure 1, mirror 3 is formed in a planar shape. The laser light L2 is reflected by mirror 3 and irradiated onto the volume hologram 5. Note that mirror 3 may also be curved.

[0020] Mirror 4 is a mirror that reflects the laser light L3 that has passed through the branched mirror 2. As shown in Figure 1, mirror 4 is formed in a planar shape. The laser light L3 is reflected by mirror 4 and irradiated onto the volume hologram 5. Note that mirror 4 may also be curved.

[0021] The volumetric hologram 5 is a volumetric hologram that is exposed (manufactured) by this exposure apparatus. The volumetric hologram 5 comprises a photopolymer 5a and a substrate 5b. The photopolymer 5a is formed of, for example, an optical material whose refractive index changes when exposed to visible light. The substrate 5b is a flat plate with high transmittance, and for example, quartz or optical glass can be used.

[0022] In this embodiment, when the volume hologram 5 is exposed, interference fringes (refractive index distribution) are formed on the photopolymer 5a by irradiating the volume hologram 5 with laser light L2 (object light) and laser light L3 (reference light). That is, the volume hologram 5 is exposed by irradiating it with laser light L2 and L3. Subsequently, the volume hologram 5 is treated by irradiating it with ultraviolet light to prevent the formed interference fringes from changing. In this way, the volume hologram 5 is manufactured.

[0023] As shown in Figure 1, the laser beams L2 and L3, when irradiated onto the volume hologram 5, may be parallel, divergent, or focused. For example, by making mirrors 3 and 4 curved, or by placing optical elements such as lenses before and after mirrors 3 and 4, it is possible to make mirrors 3 and 4 emit divergent or focused light. Also, in Figure 1, the laser beams L2 and L3 are irradiated onto the volume hologram 5 such that the angle between their irradiation directions is 90°, but this is not limited to this, and the angle between their irradiation directions can be any degree. In addition, the laser beam L2 may be irradiated from the front (or back) side of the volume hologram 5, and the laser beam L3 may be irradiated from the back (or front) side of the volume hologram 5.

[0024] The laser light source 6 is a light source that irradiates the beam splitter 7 with laser light L4. The laser light L4 is light in a wavelength range that does not affect the diffraction efficiency of the volume hologram 5 when irradiated onto the volume hologram 5 during exposure (for example, light in the infrared wavelength range of approximately 800 nm to 1500 nm). The laser light source 6 is a light source for detecting the diffraction efficiency of the volume hologram 5 during exposure. At this time, the laser light L4 is incident on the volume hologram 5 from an angle that satisfies the Bragg angle condition so as to diffract with respect to the volume hologram 5. Note that the laser light L4 irradiated by the laser light source 6 may be light in a wavelength range other than the above.

[0025] The beam splitter 7 splits (divides) the laser light L4 emitted from the laser light source 6 into two beams. Specifically, the beam splitter 7 splits the laser light L4 into laser beams L5 and L6. Alternatively, a half-mirror may be used instead of the beam splitter 7. Any other optical element that can split the laser light L4 emitted from the laser light source 6 into two beams may be used.

[0026] Power meters 8 and 9 are, for example, power meters that measure the amount of light received. Note that power meters 8 and 9 can be any detectors that can detect the light intensity of laser beams L5 and L7, respectively.

[0027] The power meter 8 receives the laser light L5 that has been split by the beam splitter 7 and outputs data indicating the light intensity of the received laser light L5 to the control device 10.

[0028] The laser beam L6 (first beam), split by the beam splitter 7, enters the volume hologram 5. After being diffracted by the volume hologram 5, the laser beam L6 enters (is received by) the power meter 9 as laser beam L7 (second beam). The power meter 9 outputs data indicating the light intensity of the received laser beam L7 to the control device 10.

[0029] The control device 10 is, for example, a computer equipped with a CPU, ROM, RAM, etc. The control device 10 controls the exposure process of the volume hologram 5 based on the data output from the power meters 8 and 9. Specifically, the control device 10 controls the laser light source 1 and the shutter 11 according to the predicted value of the diffraction efficiency of the volume hologram 5 (details will be described later).

[0030] (Regarding the operation of the exposure equipment) Figure 2 is a flowchart showing the operation of the exposure apparatus according to this embodiment.

[0031] First, the control device 10 receives input from the user via an operation unit (not shown in the figure) or the like, specifying the diffraction efficiency of the volume hologram 5 to be created (step S1). At this time, the setting value of the diffraction efficiency of the volume hologram 5 received by the control device 10 is the setting value of the diffraction efficiency of the volume hologram 5 in the green wavelength band (for example, light in the infrared wavelength band of about 800 nm to 1500 nm). The control device 10 then converts the input setting value of the diffraction efficiency of the volume hologram 5 into a setting value of the diffraction efficiency of the volume hologram 5 in the infrared wavelength band (for example, light in the infrared wavelength band of about 800 nm to 1500 nm). The control device 10 uses the converted setting value of the diffraction efficiency of the volume hologram 5 in the infrared wavelength band in the following processing.

[0032] The control device 10 controls each part of the exposure apparatus to start the exposure of the volume hologram 5 (step S2). Specifically, when starting the exposure of the volume hologram 5, the control device 10 controls the laser light source 1 and the shutter 11 so that laser light L1 is emitted from the laser light source 1 and the shutter 11 is in the open state.

[0033] The control device 10 calculates the diffraction efficiency of the volume hologram 5 based on the data output from the power meters 8 and 9 (step S3). Specifically, the control device 10 calculates the diffraction efficiency (first diffraction efficiency) of the volume hologram 5 during exposure based on the data output from the power meters 8 and 9, respectively. The diffraction efficiency of the volume hologram 5 is determined as a value obtained by dividing the amount of laser light L7 (amount of second light) by the amount of laser light L6 (amount of first light). That is, when laser light L4 is irradiated from the laser light source 6, which is a laser light source for monitoring, the diffraction efficiency of the volume hologram 5 is determined as a value obtained by dividing the amount of laser light L7, which is the diffracted light diffracted by the volume hologram 5, by the amount of laser light L6, which is the incident light to the volume hologram 5. In this embodiment, the amount of laser light L7 is included in the data output from the power meter 9. Also, since the amount of laser light L6 is correlated with the amount of laser light L5, the amount of laser light L6 can be measured based on the data output from the power meter 8 (amount of laser light L5).

[0034] However, in Patent Document 1, the diffraction efficiency of the hologram optical element is measured (monitored) based only on the light intensity of the light diffracted by the recording material from the light irradiated from the second laser light source. Therefore, if the amount of light irradiated by the second laser light source fluctuates, the diffraction efficiency of the hologram optical element cannot be accurately measured. As a result, the diffraction efficiency of the hologram optical element will vary.

[0035] For example, if the output of the second laser light source fluctuates by about ±1%, the diffraction efficiency of the holographic optical element will also fluctuate by about ±1%. In this case, it cannot be used in applications where high quality standards for the holographic optical element are required. For example, in the case of automotive applications, the variation in diffraction efficiency needs to be kept to about ±3%, and if the diffraction efficiency of the holographic diffracting element fluctuates by about ±1%, it will have a significant impact on its quality. Therefore, it is necessary to accurately measure the diffraction efficiency of the holographic optical element during exposure.

[0036] Therefore, in this embodiment, the diffraction efficiency of the volume hologram 5 is calculated based on the measured value of the light intensity of the laser light L6, which is the diffracted light diffracted by the volume hologram 5, and the measured value of the light intensity of the laser light L6, which is the incident light to the volume hologram 5. This makes it possible to accurately measure the diffraction efficiency of the holographic optical element during exposure.

[0037] The control device 10 predicts the diffraction efficiency (second diffraction efficiency) of the volume hologram 5 (step S4). Specifically, the control device 10 determines the measured value and change in the diffraction efficiency based on the diffraction efficiency calculated in step S3. Then, the control device 10 uses the measured value + change × coefficient as the predicted value of the volume hologram 5. The coefficient at this time is determined by various implementation results and machine learning (AI), etc.

[0038] The control device 10 determines whether the predicted value of the diffraction efficiency of the volume hologram 5 is equal to or greater than the set value of the diffraction efficiency of the volume hologram 5 (step S5). If the predicted value of the diffraction efficiency of the volume hologram 5 is less than the set value of the diffraction efficiency of the volume hologram 5 (No in step S5), the control device 10 returns to step S3. If the predicted value of the diffraction efficiency of the volume hologram 5 is equal to or greater than the set value of the diffraction efficiency of the volume hologram 5 (Yes in step S5), the control device 10 stops (ends) the exposure of the volume hologram 5 (step S6). Specifically, when stopping the exposure of the volume hologram 5, the control device 10 controls the laser light source 1 and the shutter 11 so that the laser light source 1 stops irradiating laser light L1 (third light) and the shutter 11 is closed. In other words, the control device 10 controls the exposure process of the volume hologram 5 (in this case, stopping (ending) the exposure) according to the calculated diffraction efficiency.

[0039] Subsequently, the volume hologram 5 is irradiated with ultraviolet light to ensure that the formed interference fringes do not change.

[0040] Figure 3 is a graph showing an example of the change in diffraction efficiency in a volume hologram according to the first embodiment. Figure 3 illustrates the diffraction efficiency of volume holograms 51 to 53, which have different materials and thicknesses. In Figure 3, the exposure of volume holograms 51 to 53 is stopped at times t1 to t3, respectively.

[0041] Incidentally, even if the irradiation of exposure light is stopped to terminate the exposure process of a holographic optical element, the change in diffraction efficiency continues for a predetermined period. This is thought to be because the material changes (chemical reactions) in the holographic optical element continue even after exposure is stopped. Furthermore, the change in diffraction efficiency of the holographic optical element differs depending on the material and thickness of the holographic optical element. As a result, the diffraction efficiency of the fabricated holographic optical elements will vary.

[0042] Specifically, as shown in Figure 3, the diffraction efficiency of volume holograms 51-53 begins to increase when exposure starts. Furthermore, the increase in diffraction efficiency in volume holograms 51-53 continues even after exposure is stopped (ended). This is thought to be because material changes (chemical reactions) in the volume hologram continue even after exposure is stopped. In other words, even if exposure is stopped, the diffraction efficiency of a volume hologram does not immediately stop (stabilize). In particular, the change in diffraction efficiency of a volume hologram differs depending on its material and thickness.

[0043] Therefore, in this embodiment, the control device 10 calculates the diffraction efficiency of the volume hologram 5 based on the measurement results of the power meters 8 and 9 (actual measured values ​​of the light intensity of laser beams L6 and L7), predicts the diffraction efficiency of the volume hologram 5 after exposure is stopped according to the calculation result of the diffraction efficiency, and stops the exposure of the volume hologram 5 according to the prediction result. In other words, the control device 10 controls the exposure process of the hologram optical element according to the calculation result of the diffraction efficiency of the volume hologram 5. As a result, even if the volume holograms are made of different materials and thicknesses, a volume hologram with the set diffraction efficiency can be created.

[0044] (First Embodiment) (Overall configuration of the exposure system) Figure 4 is a side view of the exposure apparatus according to the second embodiment. In Figure 4, compared to Figure 1, an attenuator 15 is provided between the laser light source 1 and the branching mirror 2 instead of the shutter 11.

[0045] Specifically, the attenuator 15 is an adjustment device that controls the amount of laser light L1 output from the laser light source 1. The attenuator 15 comprises a λ / 2 wave plate 15a and a polarizing beam splitter 15b.

[0046] The λ / 2 wave plate 15a is a wave plate that changes the polarization direction of incident light. The polarization beam splitter 15b splits the incident light into S-polarized and P-polarized light. When laser light L1 is incident on the λ / 2 wave plate 15a, its polarization direction changes. Subsequently, laser light L1 is split into S-polarized (laser light L1a) and P-polarized (laser light L1b) by the polarization beam splitter 15b. Then, laser light L1a is incident on the splitting mirror 2, and laser light L1b is incident on the power meter 12. The power meter 12 is a power meter that measures the amount of light received, and measures the amount of laser light L1b.

[0047] Here, the λ / 2 wave plate 15a is rotatable about the X direction as its central axis. By rotating the λ / 2 wave plate 15a, the polarization direction of the laser light L1 can be changed, and thus the light intensity of the laser light L1a and laser light L1b can be changed. At this time, the light intensity of the laser light L1a can be determined according to the light intensity of the laser light L1b. The control device 10 can measure the light intensity of the laser light L1 (L1a) according to the measurement result of the power meter 12.

[0048] Alternatively, an ND filter may be provided instead of the attenuator 15. In this case as well, it is still possible to control the light intensity of the laser beam L1.

[0049] Alternatively, the attenuator 15 may be omitted, and the laser light source 1 may be equipped with a light intensity control device that controls the light intensity (output) of the laser light L1. The control device 10 may change the light intensity of the laser light L1 by controlling the light intensity control device.

[0050] The control device 10 controls the exposure process of the volume hologram 5 based on the data output from the power meters 8 and 9. Specifically, the control device 10 controls the attenuator 15 (λ / 2 wave plate 15a) according to the predicted diffraction efficiency of the volume hologram 5.

[0051] (Regarding the operation of the exposure equipment) Figure 5 is a flowchart showing the operation of the exposure apparatus according to the second embodiment.

[0052] First, the control device 10 receives input from the user via an operation unit (not shown in the figure) or the like, specifying the set value for the diffraction efficiency of the volume hologram 5 to be created (step S11). At this time, the set value for the diffraction efficiency of the volume hologram 5 received by the control device 10 is the set value for the diffraction efficiency of the volume hologram 5 in the green wavelength band (for example, light in the infrared wavelength band of about 500 nm to 550 nm). The control device 10 then converts the input set value for the diffraction efficiency of the volume hologram 5 into a set value for the diffraction efficiency of the volume hologram 5 in the infrared wavelength band (for example, light in the infrared wavelength band of about 800 nm to 1500 nm). The control device 10 uses the converted set value for the diffraction efficiency of the volume hologram 5 in the infrared wavelength band in the following processing.

[0053] Furthermore, in step S11, the control device 10 sets a first threshold and a second threshold, which will be described later, in response to the input of a set value for the diffraction efficiency.

[0054] The control device 10 controls each part of the exposure apparatus to start the exposure of the volume hologram 5 (step S12). Specifically, the control device 10 controls the attenuator 15 so that the amount of laser light L1 (L1a) emitted from the laser light source 1 becomes a predetermined value (specifically, it rotates the λ / 2 wave plate 15a).

[0055] The control device 10 calculates the diffraction efficiency (first diffraction efficiency) of the volume hologram 5 based on the data output from the power meters 8 and 9 (step S13). Specifically, the control device 10 calculates the diffraction efficiency of the volume hologram 5 during exposure based on the data output from the power meters 8 and 9, respectively. The diffraction efficiency of the volume hologram 5 is determined as the value obtained by dividing the amount of laser light L7 (amount of second light) by the amount of laser light L6 (amount of first light). That is, when laser light L4 is irradiated from the laser light source 6, which is a laser light source for monitoring, the diffraction efficiency of the volume hologram 5 is determined as the value obtained by dividing the amount of laser light L7, which is the diffracted light diffracted by the volume hologram 5, by the amount of laser light L6, which is the incident light to the volume hologram 5. In this embodiment, the amount of laser light L7 is included in the data output from the power meter 9. Also, since the amount of laser light L6 is correlated with the amount of laser light L5, the amount of laser light L6 can be measured based on the data output from the power meter 8 (amount of laser light L5). In other words, in this embodiment, the diffraction efficiency of the volume hologram 5 is calculated based on the measured value of the amount of laser light L6, which is the diffracted light diffracted by the volume hologram 5, and the measured value of the amount of laser light L6, which is the incident light to the volume hologram 5. Therefore, the diffraction efficiency of the holographic optical element during exposure can be accurately measured.

[0056] The control device 10 predicts the diffraction efficiency (second diffraction efficiency) of the volume hologram 5 (step S14). Specifically, the control device 10 determines the measured value and change in the diffraction efficiency based on the diffraction efficiency calculated in step S13. Then, the control device 10 uses the measured value + change × coefficient as the predicted value of the volume hologram 5. The coefficient at this time is determined by various implementation results and machine learning (AI), etc.

[0057] The control device 10 controls the attenuator 15 so that the predicted value of the diffraction efficiency of the volume hologram 5 does not exceed the set value of the diffraction efficiency of the volume hologram 5.

[0058] Specifically, the control device 10 determines whether the predicted value of the diffraction efficiency of the volume hologram 5 is greater than or equal to a first threshold (step S15). If the predicted value of the diffraction efficiency of the volume hologram 5 is less than the first threshold (No. in step S15), the control device 10 controls the attenuator 15 to increase or maintain the light intensity of the laser light L1 according to the first difference (step S16). Specifically, the control device 10 rotates the λ / 2 wave plate 15a to increase or maintain the light intensity of the laser light L1. After step S16, the process returns to step S13.

[0059] If the predicted value of the diffraction efficiency of the volume hologram 5 is greater than or equal to the first threshold (Yes in step S15), the control device 10 controls the attenuator 15 to reduce the amount of laser light L1 according to the first difference (step S17). Specifically, the control device 10 calculates the first difference. The first difference is the ratio (percentage (%)) of the second reference value to the first reference value. The first reference value is the value obtained by subtracting the first threshold from the set value of the diffraction efficiency, and the second reference value is the value obtained by subtracting the predicted value of the diffraction efficiency from the set value of the diffraction efficiency (see Figure 6). The control device 10 rotates the λ / 2 wave plate 15a to reduce the calculated amount of laser light L1.

[0060] The control device 10 determines whether the predicted value of the diffraction efficiency of the volume hologram 5 is greater than or equal to the second threshold (step S18). If the control device 10 determines that the predicted value of the diffraction efficiency of the volume hologram 5 is less than the second threshold (No in step S18), it returns to step S3. If the control device 10 determines that the predicted value of the diffraction efficiency of the volume hologram 5 is greater than or equal to the second threshold (Yes in step S18), it terminates the process. Specifically, the control device 10 controls the laser light source 1 to stop the irradiation of the laser light L1 (i.e., terminates the exposure of the volume hologram 5). For example, the second threshold is set so that the first difference is about 0.1%.

[0061] In other words, the first threshold is a threshold value used to determine whether to maintain, increase, or decrease the amount of laser light L1 irradiated onto the volume hologram 5. The second threshold is a threshold value used to stop the laser light L1 irradiated onto the volume hologram 5, that is, to stop the exposure of the volume hologram 5.

[0062] Subsequently, the volume hologram 5 is bleached to treat (fix / settle) the formed diffraction grating (interference fringes) so that it does not change.

[0063] Figures 6(a) to 6(c) are graphs showing an example of the change in the predicted diffraction efficiency of the volume hologram according to the second embodiment. In Figures 6(a) to 6(c), times t11 to t13 are the times (current time) when the diffraction efficiency of the volume hologram 5 was calculated in step S13. In Figures 6(a) to 6(c), time t14 is the reference time (for example, the time when the diffraction efficiency of the volume hologram 5 stabilizes) when the predicted value of the diffraction efficiency of the volume hologram 5 is calculated in step S14. That is, in the second embodiment, the diffraction efficiency of the volume hologram 5 at time t14 is predicted (step S14) based on the diffraction efficiency of the volume hologram 5 calculated at times t11 to t13 (step S13). Note that in Figures 6(a) to 6(c), time t0 is the time when the exposure of the volume hologram 5 begins.

[0064] Specifically, as shown in Figure 6(a), since the predicted value of the diffraction efficiency of the volume hologram 5 at time t14 is less than the first threshold (No in step S15), the control device 10 maintains (or increases) the light intensity of the laser beam L1 (step S16). As a result, the rate of change of the diffraction efficiency of the volume hologram 5 from time t11 onwards becomes large. Subsequently, as shown in Figure 6(b), since the predicted value of the diffraction efficiency of the volume hologram 5 at time t14 is greater than or equal to the first threshold (Yes in step S15) and less than the second threshold (No in step S18), the control device 10 decreases the light intensity of the laser beam L1 according to the first difference (step S17). As a result, the rate of change of the diffraction efficiency of the volume hologram 5 from time t12 onwards becomes small. Then, as shown in Figure 6(c), since the predicted value of the diffraction efficiency of the volume hologram 5 at time t14 is greater than or equal to the second threshold (Yes in step S18), the control device 10 controls the laser light source 1 to stop the irradiation of the laser beam L1.

[0065] Figure 7 is a graph showing an example of the change in diffraction efficiency in a volume hologram according to the second embodiment. Figure 8 is a graph showing an example of the change in the amount of laser light irradiated onto a volume hologram according to the second embodiment. Figure 7 illustrates the diffraction efficiency of volume holograms 54 to 56, which have different materials and thicknesses. Figure 8 illustrates the amount of laser light L1 irradiated onto volume holograms 54 to 56 (i.e., the sum of the amounts of laser light L2 and laser light L3).

[0066] As shown in Figures 7 and 8, exposure of volume holograms 54-56 begins at time t0. Once exposure begins, the intensity of laser light L1 increases to a predetermined value. After some time has elapsed from time t0, the diffraction efficiency of volume holograms 54-56 begins to increase. Then, towards time t1, the intensity of laser light L1 decreases. Subsequently, bleaching is started on volume holograms 54-56 from time t1. This produces volume holograms with the set diffraction efficiency.

[0067] Incidentally, when manufacturing holographic optical elements, after the exposure of the holographic optical element is stopped (ended), bleaching is performed on the holographic optical element to fix (set) the diffraction grating formed by the exposure. The diffraction efficiency of the holographic optical element also changes during the period from the stop of exposure to the start of bleaching. This is thought to be because material changes (chemical reactions) in the holographic optical element continue even after exposure stops. Furthermore, the change in the diffraction efficiency of the holographic optical element differs depending on the material and thickness of the holographic optical element. As a result, the diffraction efficiency of the manufactured holographic optical elements will vary.

[0068] Therefore, in this embodiment, the control device 10 calculates the diffraction efficiency of the volume hologram 5 based on the measurement results of the power meters 8 and 9 (actual measured values ​​of the light intensity of laser beams L6 and L7), and controls the attenuator 15 (light intensity of laser beam L1) according to the prediction of the diffraction efficiency of the volume hologram 5 after exposure is stopped. As a result, even if the volume holograms are made of different materials and thicknesses, a volume hologram with the set diffraction efficiency can be created.

[0069] Furthermore, the light intensity of laser beam L1, which is the exposure light for the volume hologram, is gradually reduced over time leading up to the start of bleaching. This shortens the period from the end of exposure of the volume hologram to the start of bleaching, thereby suppressing changes in the diffraction efficiency of the volume hologram during that period.

[0070] (Third embodiment) Figure 9 is a side view of the exposure apparatus according to the third embodiment. Compared to Figure 1, the shutter 11 is omitted in Figure 9, and a bleaching light source 13 (third light source) is provided.

[0071] The bleaching light source 13 irradiates the volume hologram 5 with bleaching light L8 to fix (fix) the diffraction grating (interference fringes). For example, the bleaching light source 13 includes at least one of a UV light source and a white light source, which are composed of LEDs or the like.

[0072] In the third embodiment, the control device 10 controls the bleaching light source 13 according to the predicted value of the diffraction efficiency of the volume hologram 5.

[0073] (Regarding the operation of the exposure equipment) Figure 10 is a flowchart showing the operation of the exposure apparatus according to the third embodiment. In Figure 10, compared to Figure 5, step S21 is executed after step S12, and steps S51, S61, S71, and S81 are executed instead of steps S15 to S18. In step S11, the control device 10 sets the third threshold and fourth threshold, which will be described later, according to the input of the set value of the diffraction efficiency.

[0074] In step S21, the control device 10 starts the breaching of the volume hologram 5. Specifically, the control device 10 controls the breaching light source 13 to irradiate the volume hologram 5 with breaching light L8.

[0075] From step S51 onward, the control device 10 controls the bleaching light source 13 so that the predicted value of the diffraction efficiency of the volume hologram 5 (second diffraction efficiency) does not exceed the set value of the diffraction efficiency of the volume hologram 5 (first diffraction efficiency).

[0076] Specifically, the control device 10 determines whether the predicted value of the diffraction efficiency of the volume hologram 5 is greater than or equal to the third threshold (step S51). If the predicted value of the diffraction efficiency of the volume hologram 5 is less than the third threshold (No in step S51), the control device 10 controls the bleaching light source 13 to reduce or maintain the amount of bleaching light L8 (step S61). After step S61, the process returns to step S13.

[0077] If the control device 10 determines that the predicted diffraction efficiency of the volume hologram 5 is greater than or equal to the third threshold (Yes in step S61), it controls the bleaching light source 13 to increase the amount of bleaching light L8 (step S71). Specifically, the control device 10 calculates a first difference. The first difference is the ratio (percentage (%)) of the second reference value to the first reference value. The first reference value is the value obtained by subtracting the third threshold from the set value of the diffraction efficiency, and the second reference value is the value obtained by subtracting the predicted diffraction efficiency from the set value of the diffraction efficiency (see Figure 11).

[0078] The control device 10 determines whether the predicted value of the diffraction efficiency of the volume hologram 5 is greater than or equal to the fourth threshold (step S81). If the control device 10 determines that the predicted value of the diffraction efficiency of the volume hologram 5 is less than the fourth threshold (No in step S81), it returns to step S13. If the control device 10 determines that the predicted value of the diffraction efficiency of the volume hologram 5 is greater than or equal to the fourth threshold (Yes in step S81), it terminates the process. After that, the exposure and bleaching of the volume hologram 5 are completed. For example, the fourth threshold is set so that the first difference is about 0.1%.

[0079] In other words, the third threshold is a threshold used as a criterion for determining whether to maintain, decrease, or increase the amount of bleaching light L8 irradiated onto the volume hologram 5. The fourth threshold is a threshold used as a criterion for stopping this process (the process of increasing the amount of bleaching light L8 irradiated onto the volume hologram 5).

[0080] In steps S61 and S71, if the bleaching light source 13 is composed of a UV light source and a white light source, the control device 10 may control the light intensity of the UV light source and the white light source respectively according to the predicted value of the diffraction efficiency of the volume hologram 5.

[0081] Figures 11(a) to (c) are graphs showing an example of the change in the predicted diffraction efficiency of the volume hologram according to the third embodiment. In Figures 11(a) to (c), times t15 to t17 are the times (current time) when the diffraction efficiency of the volume hologram 5 was calculated in step S3. In Figures 11(a) to (c), time t18 is the reference time when the predicted diffraction efficiency of the volume hologram 5 is calculated in step S14 (for example, the time when the diffraction efficiency of the volume hologram 5 stabilizes). That is, in the second embodiment, the diffraction efficiency of the volume hologram 5 at time t18 is predicted (step S14) based on the diffraction efficiency of the volume hologram 5 calculated at times t15 to t17 (step S13). Note that in Figures 11(a) to (c), time t0 is the time when the exposure of the volume hologram 5 begins.

[0082] Specifically, as shown in Figure 11(a), since the predicted value of the diffraction efficiency of the volume hologram 5 at time t18 is less than the third threshold (No in step S15), the control device 10 maintains (or decreases) the amount of bleaching light L8 (step S61). This increases the rate of change of the diffraction efficiency of the volume hologram 5 after time t15. Subsequently, as shown in Figure 11(b), since the predicted value of the diffraction efficiency of the volume hologram 5 at time t18 is greater than or equal to the third threshold (Yes in step S51) and less than the fourth threshold (No in step S81), the control device 10 decreases the amount of laser light L1 according to the first difference (step S71). This reduces the rate of change of the diffraction efficiency of the volume hologram 5 after time t16. Then, as shown in Figure 11(c), since the predicted value of the diffraction efficiency of the volume hologram 5 at time t18 is greater than or equal to the fourth threshold (Yes in step S81), this process ends.

[0083] Figure 12 is a graph showing an example of the change in diffraction efficiency in a volume hologram according to the third embodiment. Figure 13 is a graph showing an example of the change in the amount of bleaching light irradiated onto a volume hologram according to the third embodiment. Figure 12 illustrates the diffraction efficiency of volume holograms 57-59, which have different materials and thicknesses. Figure 13 illustrates the amount of bleaching light L8 irradiated onto volume holograms 57-59.

[0084] As shown in Figures 12 and 13, exposure of volume holograms 57-59 begins at time t0. After some time has elapsed from time t0, the diffraction efficiency of volume holograms 57-59 begins to increase. Then, at times t2-t4, bleaching of volume holograms 57-59 begins. Finally, at time t5, bleaching of volume holograms 57-59 is completed. This produces volume holograms with the set diffraction efficiency.

[0085] Incidentally, when manufacturing holographic optical elements, after the exposure of the holographic optical element is stopped (completed), bleaching is performed on the holographic optical element to fix (set) the diffraction grating formed by the exposure. The diffraction efficiency of the holographic optical element changes even during bleaching. This is thought to be because the material changes (chemical reactions) in the holographic optical element continue even during bleaching. Furthermore, the change in the diffraction efficiency of the holographic optical element differs depending on the material and thickness of the holographic optical element. As a result, the diffraction efficiency of the manufactured holographic optical elements will vary.

[0086] Therefore, in this embodiment, the control device 10 calculates the diffraction efficiency of the volume hologram 5 based on the measurement results of the power meters 8 and 9 (actual measured values ​​of the light intensity of laser beams L6 and L7), and controls the bleaching light source 13 (light intensity of bleaching light L8) according to the prediction of the diffraction efficiency of the volume hologram 5 after exposure is stopped. As a result, even if the volume holograms are made of different materials and thicknesses, a volume hologram with the set diffraction efficiency can be created.

[0087] Furthermore, the volume hologram is bleached during exposure. This helps to suppress the effects of changes in the diffraction efficiency of the volume hologram during bleaching.

[0088] (Fourth Embodiment) Figure 14 is a side view of the exposure apparatus according to the fourth embodiment. Compared to Figure 4, Figure 14 shows that an additional bleaching light source 13 is provided. The bleaching light source 13 has the same configuration as in the third embodiment.

[0089] In the fourth embodiment, the control device 10 controls the attenuator 15 and the bleaching light source 13 according to the predicted value of the diffraction efficiency of the volume hologram 5.

[0090] (Regarding the operation of the exposure equipment) Figure 15 is a flowchart showing the operation of the exposure apparatus according to the fourth embodiment. In Figure 15, compared to Figure 5, step S21 is executed after step S12, and steps S51, S61, and S71 are executed between steps S17 and S18. Steps S21, S51, S61, and S71 are the same as steps S21, S51, S61, and S71 in Figure 10. That is, from step S15 onward, the control device 10 controls the attenuator 15 and the bleaching light source 13 so that the predicted value of the diffraction efficiency of the volume hologram 5 does not exceed the set value of the diffraction efficiency of the volume hologram 5. In step S11, the control device 10 sets the first threshold, second threshold, and third threshold according to the input of the set value of the diffraction efficiency.

[0091] Figure 16 is a graph showing an example of the change in diffraction efficiency in a volume hologram according to the fourth embodiment. Figure 17 is a graph showing an example of the change in the amount of laser light irradiated onto a volume hologram according to the fourth embodiment. Figure 18 is a graph showing an example of the change in the amount of bleaching light irradiated onto a volume hologram according to the fourth embodiment. Figure 16 illustrates the diffraction efficiency of volume holograms 60 to 62, which are made of different materials and have different thicknesses. Figure 17 illustrates the amount of laser light L1 irradiated onto volume holograms 60 to 62 (i.e., the sum of the amounts of laser light L2 and laser light L3). Figure 18 illustrates the amount of bleaching light L8 irradiated onto volume holograms 60 to 62.

[0092] As shown in Figures 16 to 18, exposure of volume holograms 60 to 62 begins at time t0. Once exposure begins, the light intensity of laser beam L1 increases to a predetermined value. After some time has elapsed from time t0, the diffraction efficiency of volume holograms 60 to 62 begins to increase. Then, at times t6 to t8, bleaching of volume holograms 60 to 62 begins. Subsequently, the light intensity of laser beam L1 decreases towards time t9. Finally, at time t9, exposure and bleaching of volume holograms 60 to 62 are completed.

[0093] In this embodiment, the control device 10 calculates the diffraction efficiency of the volume hologram 5 based on the measurement results of the power meters 8 and 9 (actual measured values ​​of the light intensity of laser beams L6 and L7), and controls the attenuator 15 (light intensity of laser beam L1) and the bleaching light source 13 (light intensity of bleaching light L8) according to the prediction of the diffraction efficiency of the volume hologram 5 after exposure is stopped. Therefore, even if the volume holograms are made of different materials or have different thicknesses, a volume hologram with the set diffraction efficiency can be created.

[0094] Furthermore, bleaching of the volume hologram is performed during the exposure of the volume hologram. The exposure of the volume hologram is terminated at the same time as the bleaching of the volume hologram is completed. This makes it possible to stop the exposure of the volume hologram and the end of the bleaching at the same time, thereby suppressing changes in the diffraction efficiency of the volume hologram after the exposure of the volume hologram is stopped and during the bleaching.

[0095] In each of the above embodiments, the first threshold and the third threshold may be the same or different. Also, the second threshold and the fourth threshold may be the same or different.

[0096] Furthermore, the above embodiments may be combined as appropriate. For example, the control device 10 may set the timing for stopping the laser light while controlling at least one of the laser light intensity and the bleaching light intensity according to the predicted value of the diffraction efficiency. [Industrial applicability]

[0097] The exposure apparatus of this disclosure can be used when exposing (manufacturing) volume holograms. [Explanation of Symbols]

[0098] 1. Laser light source (second light source) 2-way mirror 3,4 Mirror 5. Volume Hologram (Holographic Optical Element) 6. Laser light source (first light source) 7. Beam splitter (optical element) 8. Power meter (first detector) 9. Power meter (second detector) 10 Control devices (prediction devices, control devices) 11 shutters 12 Power Meters 13. Breaching light source (third light source) 15. Attenuator (adjustment device) 15a λ / 2 wave plate 15b Polarizing Beam Splitter L1 (L1a) Laser light (third light) L6 Laser light (first light) L7 Laser light (second beam) L8 Bleaching Light

Claims

1. An exposure apparatus used to expose a holographic optical element, To detect the first diffraction efficiency, which is the diffraction efficiency of the hologram optical element during exposure, a first light source is provided that irradiates the hologram optical element with first light, which is light in a predetermined wavelength band. A first detector for detecting the amount of light of the first light, An exposure apparatus comprising a second detector for detecting the amount of light of the second light, which is the first light diffracted by the holographic optical element.

2. The exposure apparatus according to claim 1, further comprising an optical element provided in the optical path of the first light from the light source to the holographic optical element for splitting the first light.

3. The system further includes a control device that calculates the first diffraction efficiency based on the detection results of the first and second detectors, and controls the exposure process of the hologram optical element according to the calculated first diffraction efficiency. The exposure apparatus according to claim 1, wherein the control device uses the value obtained by dividing the amount of light of the second light by the amount of light of the first light as the value of the first diffraction efficiency.

4. The exposure apparatus according to claim 1, further comprising a prediction device that calculates the first diffraction efficiency based on the detection results of the first and second detectors, and predicts the second diffraction efficiency, which is the diffraction efficiency of the hologram optical element after exposure is stopped, according to the calculated first diffraction efficiency.

5. The exposure apparatus according to claim 4, wherein the prediction device predicts the second diffraction efficiency according to the value and amount of change of the first diffraction efficiency.

6. A second light source that irradiates the holographic optical element with a third light for exposing the holographic optical element, The exposure apparatus according to claim 4, further comprising a control device that blocks the irradiation of the hologram optical element with the third light according to the prediction result of the computer.

7. The second light is provided in the optical path of the second light from the second light source to the holographic optical element, and further comprises a shutter that blocks the second light, The exposure apparatus according to claim 6, wherein the control device controls the shutter according to the prediction result of the computing device.

8. An exposure method used to expose a holographic optical element, To detect the first diffraction efficiency, which is the diffraction efficiency of the holographic optical element during exposure, the holographic optical element is irradiated with first light, which is light in a predetermined wavelength band. The steps include detecting the amount of light from the first light, An exposure method comprising the step of detecting the amount of light of the second light, which is the first light, diffracted by the holographic optical element.

9. The exposure method according to claim 8, comprising the steps of: calculating the first diffraction efficiency based on the detection results of the light intensity of the first light and the second light; and predicting the second diffraction efficiency, which is the diffraction efficiency of the hologram optical element after exposure is stopped, according to the calculated first diffraction efficiency.

10. A method for manufacturing a holographic optical element, The steps include: exposing the holographic optical element, To detect the first diffraction efficiency, which is the diffraction efficiency of the holographic optical element during exposure, the holographic optical element is irradiated with first light, which is light in a predetermined wavelength band. The steps include detecting the amount of light from the first light, A method for manufacturing a holographic optical element, comprising the step of detecting the amount of light of the second light, which is the first light, diffracted by the holographic optical element.

11. A method for manufacturing a hologram optical element according to claim 10, further comprising the steps of: calculating the first diffraction efficiency based on the detection results of the light intensity of the first light and the second light; and predicting the second diffraction efficiency, which is the diffraction efficiency of the hologram optical element after exposure has been stopped, according to the calculated first diffraction efficiency.

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