JPH10239520A - Polarized beam splitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of part items of a polarized beam splitter so as to miniaturize the whole structure and to reduce the cost, by joining a double refracting member integrally into the reflected light passing position of a light transmissible member provided with a splitter face for splitting a beam into transmitted light and reflected light. SOLUTION: The light transmissible member 3 formed of a triangle prismatic body of glass or the like, and a double refracting member 1 formed of a triangle prismatic body of crystal material with a double refracting characteristic such as sapphire are jointed by bringing the slant faces into contact with each other, and the slant face is made a splitter face 2. The members 1, 3 are arranged so that the optical axis of the double refracting member 1 is extended in the transmitted direction of an optical signal 21. The optical signal 21 entering from the double refracting member 1 side passes as it is along the optical axis of the crystal material and is split into transmitted light and reflected light at the splitter face 2. When the reflected light passes again in the double refracting member 1, the reflected light is split into normal light and abnormal light, and the normal light and abnormal light are respectively propagated at different refractive indexes so as to be split into two polarized light 21a, 21b orthogonal to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing beam splitter having a function of separating a light beam such as an optical signal and separating the separated light beam by a plane of polarization.

[0002]

2. Description of the Related Art In recent years, information transmission using optical signals has been widely used in fields such as optical disks, optical cards, optical sensors using lasers, and optical communications. In these apparatuses, a polarization separation element having a function of separating an optical signal by a plane of polarization is used.

[0003] For example, in the reflection of light on the surface of a substance, there is an optical rotation phenomenon (Kerr effect) that rotates the plane of polarization, and in a substance that transmits light, an optical rotation phenomenon occurs when transmitted.
An optical disc or an optical sensor uses a polarization separation element to read information using this phenomenon.

Also, in the field of optical communication, it is necessary to separate or combine polarizations in order to properly use signal light depending on the plane of polarization of light and to control the transmission characteristics of signal light according to the plane of polarization. A polarization splitting element is used.

[0005] Here, as shown in FIG. 5, the schematic structure of an optical disk reading device, an optical signal 20 emitted from a laser diode 14 passes through a beam splitter 11, is reflected by an optical disk 17, and is reflected by the optical signal. 21 is reflected again by the beam splitter 11, and the reflected light is split into two polarized lights 21 a and 21 b by the polarization splitting element 12.
Photodetectors 15 and 16 respectively detect the light. That is, the information on the optical disk 17 is read by detecting the optical rotation phenomenon of the optical signal 21 reflected by the optical disk 17 by the photodetectors 15 and 16.

FIG. 4A shows a detailed structure of the beam splitter 11 and the polarization splitting element 12. The beam splitter 11 is formed by joining two translucent members 3, 3 each formed of a triangular prism body made of glass to each other at an inclined surface to form the inclined surface 2 as a splitter surface 2.
Is Si between two glass translucent members 3 ', 3'.
Polarization separation film 4 made of a dielectric multilayer film such as O ₂ and TiO ₂
Are bonded together. Then, the polarization splitting element 12 is joined to a position where the reflected light of the beam splitter 11 passes, thereby forming a polarization beam splitter.

For this reason, when the optical signal 21 reflected by the optical disk 17 enters the beam splitter 11, a part of the signal is transmitted, but the rest is reflected by the splitter surface 2. The reflected optical signal 21 is split by the polarization splitting film 4 of the polarization splitting element 12 into two orthogonal polarizations 21a and 21b.

In order to achieve the same effect, FIG.
As shown in (b), a Wollaston prism 13 using a crystal material can be arranged instead of the polarization separation element 12. This Wollaston prism 13
It is made of a crystal material having birefringence characteristics. The incident optical signal 21 is separated into normal light oscillating in a direction parallel to the optical axis of the crystal and extraordinary light oscillating in a direction perpendicular to the optical axis. , Each propagate according to a different refractive index,
The light is separated into two polarized lights 21a and 21b orthogonal to each other.

[0009]

In recent years, these optical elements have been required to be reduced in size and cost.
On the other hand, the polarization beam splitter as shown in FIG. 4 requires two elements, the beam splitter 11, the polarization splitting element 12, and the Wollaston prism 13, so that the overall size becomes large and miniaturization is difficult. In addition, the cost was increased, and the above required characteristics could not be satisfied.

In particular, in the case of using the Wollaston prism 13 shown in FIG. 4B, if the Wollaston prism 13 is made smaller in order to reduce the size of the whole, the polarization 21a,
There has been a problem that the separation angle of 21b is reduced and the polarization separation function is reduced.

Further, as shown in FIG. 4A, when polarization separation is performed using the polarization separation film 4, there is a problem that a high polarization separation function cannot be obtained.

[0012]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a birefringent member integrally joined to a translucent member having a splitter surface for separating beam light into transmitted light and reflected light, at a position where the reflected light passes. To form a polarization beam splitter.

Further, according to the present invention, the translucent member and the birefringent member are formed of a material having substantially the same refractive index, and a translucent adhesive having substantially the same refractive index is provided therebetween. It is characterized by being joined by.

[0014]

According to the present invention, the translucent member and the birefringent member are joined, and the beam splitter and the Wollaston prism are integrated, so that the number of parts can be reduced, the whole can be reduced in size, and the cost can be reduced. In addition, since the crystal material can be formed relatively large, the polarization separation function can be improved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram of the polarization beam splitter 10 as viewed from the side in the transmission direction of the optical signal 21. The polarizing beam splitter 10 is formed by joining a translucent member 3 made of a triangular prism made of glass or the like and a birefringent member 1 made of a triangular prism made of a crystalline material by contacting their slopes with each other. Is the splitter surface 2.

The birefringent member 1 is made of a crystalline material having birefringent characteristics such as sapphire and lithium borate. Here, the crystal material having birefringence characteristics is a material having different refractive indexes depending on normal light vibrating in a direction parallel to the optical axis of the crystal and extraordinary light vibrating in a direction perpendicular to the optical axis. . Then, the polarization beam splitter 10
In the example, the birefringent member 1 is arranged such that the optical axis of the birefringent member 1 is oriented in a direction in which the optical signal 21 is transmitted (vertical direction in the drawing).

Since the optical signal 21 incident from the birefringent member 1 is in the direction along the optical axis of the crystal material, it passes through as it is, and is separated into transmitted light and reflected light by the splitter surface 2. Then, the reflected light passes through the birefringent member 1 again, but at this time, because it passes in a direction crossing the optical axis at a certain angle, it is separated into normal light and extraordinary light, and propagates with different refractive indexes. The two mutually orthogonal polarizations 2
It can be separated into 1a and 21b.

Next, an example in which the polarization beam splitter 10 is applied to an optical disk reader will be described. FIG.
As shown in (2), the optical signal 20 emitted from the laser diode 14 passes through the polarizing beam splitter 10 and is reflected by the optical disk 17, and the reflected optical signal 21 is again incident on the polarizing beam splitter 10, and the reflected light is As described above, the light is separated into two polarized lights 21a and 21b, and is detected by the photodetectors 15 and 16, respectively.

At this time, as described above, the birefringent member 1 of the polarizing beam splitter 10 has an optical axis whose optical axis is
Since they are arranged so as to match the transmission direction of 21, the transmitted optical signals 20, 21 can be transmitted as they are, and only the reflected light can be separated into two polarized lights 21a, 21b.

As described above, the polarization beam splitter 10 of the present invention can separate the optical signal 21 into the transmitted light and the reflected light, and can further separate the reflected light into two polarized lights 21a and 21b. In addition, the polarization beam splitter 10 does not require two elements as in the conventional structure shown in FIG. 4 and only needs to have the same dimensions as the conventional beam splitter 11, so that the size can be significantly reduced, and Can be cost. In addition, since the birefringent member 1 made of a crystalline material can be formed relatively large, the polarization separation function can be improved.

Next, another embodiment of the present invention will be described.

The polarization beam splitter 10 shown in FIG.
The translucent member 3 made of glass or the like and the birefringent member 1 made of a crystal material are both joined as a quadrangular prism. However, unlike the embodiment of FIG. It is formed in. Then, the optical signal 21 is
When transmitting, only the optical signal transmitted through the light transmitting member 3 and reflected by the splitter surface 2 passes through the birefringent member 1 made of a crystalline material and is separated into two polarized lights 21a and 21b. ing. In this case, since the transmitted light of the optical signal 21 does not pass through the birefringent member 1 made of a crystalline material,
It is not necessary to determine the direction of the optical axis of the crystal material.

The polarization beam splitter 10 of the present invention described above.
In the above, the crystal material forming the birefringent member 1 may be any material having birefringence characteristics, and most single crystal bodies can be used. In particular, from the viewpoints of refractive index, transmittance, and cost, quartz , Sapphire, rutile, calcite, lithium niobate, lithium tantalate, lithium tetraborate (LB
O), KTP, ADP and the like are suitable. In the case of producing these crystal materials, a single crystal having a predetermined shape and crystal orientation can be obtained by immersing and pulling up seed crystals in each molten raw material by EFG method or the like.

As the translucent member 3, borosilicate glass such as crown glass (BK7) or flint glass or other glass is used. And the splitter surface 2
It is obtained by forming a slope at a predetermined angle with respect to the transmitted optical signal 21 in a part of the light transmitting member 3.

Further, for bonding the birefringent member 1 and the light-transmitting member 3, it is preferable to use an adhesive such as a light-transmitting thermosetting adhesive or an ultraviolet-setting adhesive. When the birefringent member 1 and the translucent member 3 are joined, the joining surface of both is a smooth surface having a surface roughness (Ra) of 0.001 μm or less, and the adhesive is applied to a thickness of 0.5 mm or less. And joined so that

In the present invention, the birefringent member 1, the translucent member 3, and the
It is preferable that the refractive indices of the adhesives be substantially equal to each other, so that optical interference and surface reflection can be prevented with respect to an optical signal passing through the bonding surface.

Although the crystal material forming the birefringent member 1 has two refractive indices, the difference between them is small, so that the refractive index may be substantially equal to either one. In addition, “substantially match” means that the difference between the maximum value and the minimum value of the three types of refractive index is 0.
05 or less.

Further, the polarization beam splitter 10 of the present invention
Is suitably used not only for the optical disk reader shown in FIG. 2 but also for signal separation of optical cards, optical sensors using lasers, processing of optical signals for optical communication (isolators, demultiplexers, multiplexers), etc. can do.

[0030]

EXAMPLE As an example of the present invention, a polarizing beam splitter 10 shown in FIG. 1 was manufactured. A crown glass having a refractive index of 1.55 is used as the translucent member 3, a lithium tetraborate crystal having a refractive index of 1.56 is used as the birefringent member 1, and an ultraviolet curable adhesive having a refractive index of 1.55 is used as an adhesive. To obtain a polarizing beam splitter 10 having an overall size of 3 × 3 × 3 mm.

When an element having the same function as that of the conventional structure shown in FIG. 4A is formed, the overall size becomes 3 × 3 × 4 mm, and the polarizing beam splitter 10 of the present invention is miniaturized. We can see that we can do it.

Further, the polarization beam splitter 10 of the present invention
In response, an optical signal 21 having a wavelength of 780 nm is incident, the reflected light on the splitter surface 2 is separated into two polarized lights 21a and 21b, and each is detected by a photodetector. 21b was found to be detectable.

Further, as described above, since the refractive indices of the birefringent member 1, the translucent member 3 and the adhesive are made substantially the same, the bonding surface of the polarizing beam splitter 10 and the bonding surface with other optical components are formed. Optical interference and surface reflection could be prevented without the need for an antireflection coating.

[0034]

As described above, according to the present invention, a light-transmitting member having a splitter surface for separating an optical signal into transmitted light and reflected light, and a crystal material arranged at a position through which the reflected light passes. A birefringent member is joined and integrated to form a polarizing beam splitter, so that the beam splitter and the Wollaston prism are integrated, so the number of parts can be reduced and the whole can be reduced in size and cost can be reduced. Can be formed relatively large, so that the polarization separation function can be improved.

Further, according to the present invention, the translucent member and the birefringent member are joined with a translucent adhesive, and the refractive indexes of the translucent member, the birefringent member, and the translucent adhesive are determined. Are substantially matched, surface reflection and optical interference can be prevented.

Accordingly, a small-sized, low-cost, high-performance polarizing beam splitter can be constructed.

[Brief description of the drawings]

FIG. 1 is a side view showing a polarizing beam splitter of the present invention.

FIG. 2 is a schematic view showing an optical disk reading device using the polarization beam splitter of the present invention.

FIG. 3 is a side view showing another embodiment of the polarizing beam splitter of the present invention.

FIGS. 4A and 4B are side views showing a conventional polarizing beam splitter.

FIG. 5 is a schematic diagram showing a conventional optical disk reading device.

[Explanation of symbols]

 1: Birefringent member 2: Splitter surface 3: Translucent member 10: Polarizing beam splitter 11: Beam splitter 12: Polarization splitting element 13: Wollaston prism 14: Laser diode 15: Photodetector 16: Photodetector 17: Optical disk 20: Light Signal 21: Optical signal 21a: Polarized 21b: Polarized

Claims (2)

[Claims] A polarizing beam splitter comprising a light transmitting member having a splitter surface for separating a light beam into transmitted light and reflected light, and a birefringent member joined and integrated at a position where the reflected light passes. 2. The method according to claim 1, wherein the light-transmitting member and the birefringent member are formed of a material having substantially the same refractive index, and are joined with a light-transmitting adhesive having substantially the same refractive index. The polarizing beam splitter according to claim 1, wherein: