JP2004170448A - Polarized light splitting element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarized light splitting element which has higher reliability while its cost is suppressed low. <P>SOLUTION: The polarized light splitting element 10 is manufactured on the assumption that it is used as, for example, OLPF. The difference between refractive indexes no and ne to ordinary light and extraordinary light included in incident light LI is used to separate by a separation width S and transmit them. Its thickness t is determined according to specifications that the polarized light splitting element 10 needs to have and the crystal axis angle ϕ is determined according to the determined specifications. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polarization separation element manufactured using a birefringent material for separating ordinary light and extraordinary light contained in incident light.
[0002]
[Prior art]
In recent years, the digitization of information is progressing at a remarkable rate. Accordingly, in the field of music and movies, for example, digitized information is recorded on recording media such as CDs and DVDs and sold, or distributed via communication networks such as the Internet. In the field of image recording, devices that record digital image information, such as DVC (digital video camera) and DSC (digital still camera), are generally used.
An optical device for converting an optical signal into an electric signal used in such an apparatus is required to satisfy optical specifications and to reduce costs. At present, as the optical device, a CCD (Charge Coupled Device) in which portions for accumulating electric charges according to the amount of light (hereinafter referred to as “cells”) are regularly arranged is widely used.
In a CCD, it is known that a moire phenomenon occurs when the spatial frequency of a captured image (here, an optical signal) matches the cell arrangement pitch. An optical low-pass filter (OLPF) is used to reduce such moire phenomenon. The OLPF is configured to birefringently split light incident thereon so that an optical signal does not match the cell arrangement pitch. Birefringence of light is performed by using a substrate obtained by cutting a birefringent material (birefringent material) such as quartz in a specific crystal axis direction. The substrate is a polarization separation element.
By birefringence, ordinary light and extraordinary light included in the incident light are separated. The relationship between the pitch (separation width) S at which the polarization separation element separates them and the thickness t (mm) of the polarization separation element is generally represented by the following equation (1).
S = ((b ² −a ² ) / 2c ² ) · sin (2φ) · t (1)
Here, a = 1 / ne (refractive index of extraordinary light), b = 1 / no (refractive index of ordinary light), and φ is an angle between incident light and a crystal axis (optical axis, for example, z axis in the case of quartz). This is a certain crystal axis angle (°).
As is apparent from the equation (1), the maximum separation efficiency, that is, the maximum separation width S with respect to the thickness t is obtained at φ = about 45 ° in the case of quartz. For this reason, the ordinary OLPF polarization separation element is manufactured at φ = 45 °. When manufactured at that angle, the thickness t needs to be set to about 0.41 mm to make the separation width S 24 μm.
[Patent Document 1] JP-A-2000-56268 [Patent Document 2] JP-A-10-186284
[Problems to be solved by the invention]
The OLPF is arranged in front of an optical device such as a CCD, that is, on the light incident side. The light incident by the shooting must be focused on the device. For this reason, conventionally, in order to satisfy the two specifications of the separation width and the optical path length, an optical path length required by bonding a glass material that is not a birefringent material to a thin polarization separation element (for example, quartz) is conventionally used. Was secured.
However, when such bonding is performed, the number of processing steps increases, and the reliability of the OLPF itself decreases. Naturally, an increase in the number of processing steps causes an increase in cost. For this reason, the OLPF using the conventional polarization separation element has a problem that the manufacturing cost is high and its reliability is low.
An object of the present invention is to provide a polarization separation element having higher reliability while suppressing costs.
[0004]
[Means for Solving the Problems]
The modified separation elements according to the first and second aspects of the present invention are presumed to be manufactured using a birefringent material in order to separate ordinary light and extraordinary light contained in incident light. It is manufactured in.
The polarization separation element of the first aspect is formed such that the thickness in the direction in which the incident light is incident is adjusted to the specifications required for the light separation element, and the angle between the incident light and the crystal axis of the birefringent material is the thickness. , And the width to separate ordinary light from extraordinary light.
It is desirable that the required specifications include at least one of the actual thickness in the direction in which the incident light is incident and the optical thickness in the direction.
In the polarization splitting element according to the second aspect, the angle between the incident light and the crystal axis of the birefringent material is determined such that the efficiency of separating the ordinary light and the extraordinary light is maximized, and a value that is not close to the maximum. The thickness in the direction to be made is determined according to the width at which the ordinary light and the extraordinary light are to be separated at an angle.
The method for manufacturing a polarization separation element of the present invention is a method used for manufacturing a polarization separation element for separating ordinary light and extraordinary light contained in incident light. Determined according to the specifications required for the separation element, the angle between the incident light and the crystal axis of the birefringent material used to manufacture the polarization separation element depends on the thickness, and the width to separate ordinary light from extraordinary light Then, the birefringent material is processed so as to satisfy the determined thickness and angle, thereby producing a polarization beam splitting element.
In the present invention, the thickness in the direction in which the incident light is incident is formed according to the required specification, and the crystal axis of the incident light and the birefringent material is determined according to the thickness and the width to separate the ordinary light from the extraordinary light. (Crystal axis angle) is determined. As a result, the crystal axis angle is determined to be a value at which the efficiency of separating ordinary light and extraordinary light is maximum, and a value that is not in the vicinity thereof. The polarization splitting element is manufactured in a form determined according to the following.
Even if a polarization splitting element is manufactured by adjusting the crystal axis angle to any appropriate angle and adjusting its thickness, the required specifications (for example, actual thickness, Alternatively, it is possible to satisfy the optical thickness alone. It is possible to avoid the necessity of bonding another material and the like, and by avoiding this, the number of processing steps is reduced, and the cost of other materials and the like is suppressed. As a result, it is possible to further improve the reliability of the polarization separation element (here, one or more polarization separation elements including the OLPF) are suppressed.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating a polarization separation element according to the present embodiment.
The polarization separation element 10 is manufactured on the assumption that it is used as, for example, an OLPF. Due to the difference in the refractive indexes no and ne for the ordinary light and the extraordinary light included in the incident light L, they are separated and transmitted by a separation width S. The thickness t is determined according to the specifications required for the polarization beam splitter 10, and the crystal axis angle φ is determined according to the determined specifications.
[0006]
FIG. 2 is a diagram for explaining a method of manufacturing the polarization beam splitter according to the present embodiment. Hereinafter, the production method will be described in detail with reference to FIG.
Before describing a method of manufacturing a polarization beam splitter according to the present embodiment, a conventional method of manufacturing a polarization beam splitter will be described with reference to FIGS. 2 (a) and 2 (b).
As shown in FIG. 2A, the conventional polarization separation element 31 is manufactured at a crystal axis angle φ = 45 ° at which the separation efficiency is maximized. That is, in order to realize the desired separation width S, the thickness t in the incident direction of the incident light L is manufactured to be minimum. As a result, as shown in FIG. 2B, the glass material 32 was bonded to the polarization separation element 31 in order to secure a necessary optical path length.
On the other hand, as described above, the thickness t of the polarization beam splitter 10 according to the present embodiment is determined according to the specification required, and the crystal axis angle φ is determined according to the specification. Unlike the related art, the crystal axis angle φ is not fixed, and an appropriate one is determined (selected) as appropriate. For this reason, the angle φ is usually different from 45 °.
[0007]
Now, assuming that the crystal axis angle φ based on the specifications is 9 °, as shown in FIG. 2C, it is needless to say that the polarization separation element 21 having the same thickness t as the conventional polarization separation element 31 is desired. Cannot be obtained. Therefore, as shown in FIG. 2D, the thickness t1 is adjusted so that the desired separation width S can be obtained at the angle φ = 9 °.
In FIG. 2D, the polarization splitting element 10 is divided into two parts 21 and 22 by broken lines. The portion 21 corresponds to the portion of the polarization beam splitting element 21 shown in FIG. 2C (therefore, the same sign is used), and the portion 22 corresponds to the portion added to the polarization beam splitting element 21.
There are usually specifications required for the thickness t1 of the polarization beam splitter 10 shown in FIG. Therefore, in practice, the crystal axis angle φ is determined so that a desired separation width S is obtained when the thickness satisfying the specification is t1. In this way, the necessity of attaching the glass material 32 to the polarization separation element 10 is eliminated.
If the bonding of the glass material to the polarization separation element is avoided, the reliability of the polarization separation element 10 is greatly improved as compared with the case where the bonding is performed. Since the step of performing bonding is unnecessary, and it is not necessary to prepare the glass material 32 to be bonded, not only the cost can be reduced by reducing the number of processing steps, but also materials other than the birefringent material (glass material or adhesive) can be used. , Etc.) and the costs required for processing and processing are also reduced. From these facts, it is possible to improve reliability and reduce costs. As is well known, quartz, which is a birefringent material, has a property of easily growing in the Z-axis direction. For this reason, when the crystal axis angle φ becomes small, it becomes possible to take out more large-sized polarized light separating elements from a small rough which requires a short growth time. For this reason, not only the manufacturing cost but also the cost of procuring the birefringent material can be further reduced.
[0008]
The refractive index n of the glass material 32 slightly fluctuates depending on the material, but is about 1.51. In contrast, that of quartz is as high as about 1.54.
For example, the conventional polarization separation element 31 to which the glass material 32 is bonded has a separation width S = 24 μm, and the total thickness (corresponding to the sum of the respective thicknesses of the polarization separation element 31 and the glass material 32) = 1.72 mm (glass material) When 32 minutes = 1.31 mm), the optical thickness of the glass material 32 can be obtained by multiplying the refractive index n by the actual thickness d, so that 1.9781 (= 1.51 × 1.31) mm. Similarly, that of the polarization separation element 31 is 0.6314 (= 1.54 × 0.41) mm. Therefore, the total optical thickness is 2.6095 mm when they are added.
The separation width S = 24 μm and the optical thickness = 2.6095 mm can be satisfied by, for example, setting the crystal axis angle φ to 9.4 °. The actual thickness t at this time is 1.70 (= 2.6095 / 1.54). If there is a required thickness with respect to the actual thickness t instead of the optical thickness, the angle φ may be obtained from Expression (1).
[0009]
Note that the polarization splitting element according to the present embodiment is an example in which the present invention is applied to a polarization splitting element including one substrate, but the present invention is not limited to such a polarization splitting element. is not. For example, it may be applied to one or more polarization splitting elements constituting the OLPF for the purpose of reducing the material (the number of times of bonding) used for the same. Even in such a case, it is possible to realize improvement in reliability and cost reduction in the OLPF.
[0010]
【The invention's effect】
As described above, in the present invention, the thickness in the direction in which the incident light is incident is formed in accordance with the required specifications, and the incident light and the light are combined in accordance with the thickness and the width in which the ordinary light and the extraordinary light are to be separated. An angle between the refraction material and the crystal axis (crystal axis angle) is determined. As a result, the crystal axis angle is determined to be a value at which the efficiency of separating ordinary light and extraordinary light is maximum, and a value that is not in the vicinity thereof. The polarization splitting element is manufactured in a form determined according to the following.
Even if a polarization splitting element is manufactured by adjusting the crystal axis angle to any appropriate angle and adjusting its thickness, the required specifications (for example, actual thickness, Alternatively, the engineering thickness) can be satisfied by itself. The necessity of attaching another material can be avoided, and by avoiding the need, the number of processing steps is reduced, and the cost of other materials is suppressed. Therefore, it is possible to further improve the reliability of the polarization separation element (here, one or more polarization separation elements including the OLPF using the polarization separation element) are suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a polarization beam splitter according to an embodiment.
FIG. 2 is a diagram illustrating a method of manufacturing a polarization beam splitter according to the present embodiment.
[Explanation of symbols]
10 Polarization separation element

Claims (4)

In a polarization separation element manufactured using a birefringent material to separate the ordinary light and the extraordinary light contained in the incident light,
The thickness in the direction in which the incident light is incident is formed in accordance with specifications required for the polarization separation element,
A polarization splitting element, wherein an angle between the incident light and a crystal axis of the birefringent material is determined according to the thickness and a width for separating the ordinary light from the extraordinary light. 2. The polarization separation element according to claim 1, wherein the required specification includes at least one of an actual thickness in a direction in which the incident light is incident and an optical thickness in the direction. In a polarization separation element manufactured using a birefringent material to separate the ordinary light and the extraordinary light contained in the incident light,
The angle between the incident light and the crystal axis of the birefringent material is the maximum efficiency at which the ordinary light and extraordinary light are separated, and is determined to be a value that is not in the vicinity thereof,
A polarization splitting element, wherein a thickness in a direction in which the incident light is incident is determined according to a width at which the ordinary light and the extraordinary light are separated at the angle. A method used for manufacturing a polarization separation element for separating ordinary light and extraordinary light contained in incident light,
The thickness in the direction in which the incident light is incident is determined according to specifications required for the polarization separation element,
The angle between the incident light and the crystal axis of the birefringent material used for manufacturing the polarization separation element is determined according to the thickness, and the width of the ordinary light and extraordinary light to be separated,
The method of manufacturing a polarization beam splitter, wherein the polarization splitter is manufactured by processing the birefringent material so as to satisfy the determined thickness and angle.

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