JP2017122766A - Polarization beam splitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarization beam splitter capable of increasing utilization efficiency of light.SOLUTION: There are provided: a first prism 2 which has an upper surface and a lower surface having right triangle shapes, a first side surface 2c1 connecting oblique sides of the upper surface and the lower surface, and second and third side surfaces 2c2, 2c3 connecting sides other than oblique sides of the upper surface and the lower surface; a second prism 3 which has virtually the same shape as the first prism 2 and has fourth to sixth side surfaces 3c4 to 3c6 corresponding to the first to third side surfaces 2c1 to 2c3; and a polarization separation film 4 provided between the third side surface 2c3 and the sixth side surface 3c6. In the state that the second side surface 2c2 and the fifth side surface 3c5 are positioned on the same side, the third side surface 2c3 and the sixth side surface 3c6 are bonded. A first antireflection film 5a is provided in a region of an incident part 2c1A of the first side surface 2c1 and is not provided in a region of a first reflection part 2c1B of the first side surface 2c1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a polarizing beam splitter.

  Conventionally, polarization beam splitters are widely used in optical communication devices and the like. For example, Patent Document 1 below discloses a polarizing beam splitter in which two prisms are bonded. The two prisms have the same shape and have a right triangle cross section. The internal angles of the right triangle are 90 degrees, less than 30 degrees, and 60 degrees or more, respectively. The two prisms are bonded so that the polarization beam splitter has an isosceles triangular cross-sectional shape. A polarization separation film is formed on the surface on which the two prisms are bonded.

  Incident light enters from the incident surface and is polarized and separated by the polarization separation film. Each polarized light that has undergone polarization separation is reflected on the inner surface of the prism and emitted from the exit surface.

JP-A-7-306314

  In recent years, there has been a demand for further increasing the light utilization efficiency. In the polarization beam splitter described in Patent Document 1, since the two prisms have the shape as described above, the polarized light is easily totally reflected on the inner surface of the prism. However, it has been difficult to sufficiently increase the light utilization efficiency.

  An object of the present invention is to provide a polarization beam splitter that can improve the light utilization efficiency.

  The polarizing beam splitter according to the present invention includes an upper surface and a lower surface having a hypotenuse and a right triangle shape including two sides other than the hypotenuse, a first side surface connecting the upper and lower hypotenuses, and an upper surface. And a first prism having a second side surface and a third side surface respectively connecting sides other than the oblique sides of the lower surface, and the first side surface having substantially the same shape as the first prism. A second prism having a fourth side surface corresponding to the second side surface, a fifth side surface corresponding to the second side surface, a third side surface corresponding to the third side surface, a third side surface of the first prism, and a second side surface. And a polarization separation film provided between the sixth side surface of the prism. A polarized beam in which the third side surface of the first prism and the sixth side surface of the second prism are joined in a state where the second side surface and the fifth side surface are located on the same side. In the splitter, the incident light passes through the incident portion on the first side surface, enters the first prism, is reflected by the polarization separation film, and is transmitted through the polarization separation film. The first polarized component separated by the polarized light component and reflected by the polarized light separating film is reflected by the first reflecting portion on the first side surface in the first prism, and the first outgoing light on the second side surface. The second polarized light component that has exited from the light source and transmitted through the polarization separation film is reflected by the second reflecting part on the fourth side surface within the second prism, and exits from the second light emitting part on the fifth side surface. Is configured to do. The first antireflection film is provided in the region of the incident portion on the first side surface, and is not provided in the region of the first reflection portion on the first side surface.

  The second antireflection film is provided in the region of the first emission part on the second side surface, and the third antireflection film is provided in the region of the second emission part on the fifth side surface. Preferably it is.

  The angle formed by the first side surface and the third side surface is preferably 25 degrees or more and 35 degrees or less. More preferably, the angle formed by the first side surface and the third side surface is 30 degrees.

  According to the polarizing beam splitter of the present invention, the light utilization efficiency can be increased.

It is a top view of the polarizing beam splitter which concerns on the 1st Embodiment of this invention. It is a perspective view of the 1st prism in the 1st Embodiment of this invention. It is a top view of a polarization beam splitter when the angle which the 1st side and the 3rd side make is small. It is a top view of a polarization beam splitter when the angle which the 1st side and the 3rd side make is large. It is a top view of the polarizing beam splitter which concerns on the modification of the 1st Embodiment of this invention. It is a top view of the polarizing beam splitter which concerns on the 2nd Embodiment of this invention.

  Hereinafter, preferred embodiments will be described. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. Moreover, in each drawing, the member which has the substantially the same function may be referred with the same code | symbol.

(First embodiment)
FIG. 1 is a plan view of a polarizing beam splitter according to the first embodiment of the present invention. FIG. 2 is a perspective view of the first prism in the first embodiment.

  As shown in FIG. 1, the polarization beam splitter 1 includes first and second prisms 2 and 3. The first and second prisms 2 and 3 have substantially the same shape. In the present invention, “substantially the same shape” means that the first prism 2 and the second prism 3 do not have to be completely the same shape, and the effects of the present invention can be exhibited. This means that the first prism 2 and the second prism 3 may have different shapes.

  As shown in FIG. 2, the first prism 2 has an upper surface 2a having a right triangle shape. The upper surface 2a has a hypotenuse 2a1 and two sides other than the hypotenuse. In the present embodiment, one of the two sides is the long side 2a3, and the other side is the short side 2a2. The length of the hypotenuse 2a1 is not particularly limited, but is 2.3 mm in the present embodiment.

  The first prism 2 also has a lower surface 2b having the same shape as the upper surface 2a. The first to third side surfaces 2c1 to 2c3 are connected to the upper surface 2a and the lower surface 2b.

  The first side surface 2c1 connects the oblique side 2a1 of the upper surface 2a and the oblique side of the lower surface 2b. The second side surface 2c2 connects the short side 2a2 of the upper surface 2a and the short side of the lower surface 2b. The third side surface 2c3 connects the long side 2a3 of the upper surface 2a and the long side of the lower surface 2b. The angle θ1 formed by the first side surface 2c1 and the third side surface 2c3 is not particularly limited, but is 30 degrees in the present embodiment.

  The second prism also has an upper surface and a lower surface having a right triangle shape. As shown in FIG. 1, the second prism 3 includes a fourth side surface 3c4 corresponding to the first side surface 2c1 of the first prism 2, and a fifth side corresponding to the second and third side surfaces 2c2, 2c3. , Sixth side surfaces 3c5 and 3c6. More specifically, the fourth side surface 3c4 connects the oblique sides of the upper surface and the lower surface. The fifth side surface 3c5 connects the short sides of the upper surface and the lower surface. The sixth side surface 3c6 connects the long sides of the upper surface and the lower surface.

  In the polarization beam splitter 1, the third side surface 2c3 of the first prism 2 and the second prism 3 are arranged so that the second side surface 2c2 and the fifth side surface 3c5 are located on the same side. The sixth side surface 3c6 is joined. The polarization beam splitter 1 has a planar shape of a substantially isosceles triangle.

  The polarization beam splitter 1 includes a polarization separation film 4 provided between the third side surface 2c3 and the sixth side surface 3c6. For example, the polarization separation film 4 is formed on the third side surface 2c3 of the first prism 2, and may be bonded to the sixth side surface 3c6 of the second prism 3 with an adhesive or the like. Alternatively, the polarization separation film 4 may be formed on the sixth side surface 3c6 and bonded to the third side surface 2c3 with an adhesive or the like.

  The polarization separation film 4 is made of, for example, a dielectric multilayer film. The polarization separation film 4 reflects the first polarization component and transmits the second polarization component. In the present embodiment, the first polarization component is S polarization and the second polarization component is P polarization. Note that the first polarization component may be P-polarization and the second polarization component may be S-polarization.

  The first side surface 2c1 of the first prism 2 has an incident portion 2c1A where light enters. A first antireflection film 5a is provided in the region of the incident portion 2c1A. The first side surface 2c1 has a first reflecting portion 2c1B that reflects light in the first prism 2. The first antireflection film 5a is not provided in the region of the first reflecting portion 2c1B.

  The fourth side surface 3c4 of the second prism 3 also has a second reflecting portion 3c4B that reflects the light in the second prism 3.

  The second side surface 2c2 of the first prism 2 has a first emission part 2c2C from which light is emitted. The fifth side surface 3c5 of the second prism 3 has a second emission part 3c5C. The second side surface 2c2 is preferably provided with a second antireflection film 5b at least in the region of the first emitting portion 2c2C. It is preferable that a third antireflection film 5c is also provided on the fifth side surface 3c5 of the second prism 3 at least in the region of the second emitting portion 3c5C. However, as in the present embodiment, the second antireflection film 5b may be provided on the entire surface of the second side surface 2c2. Similarly, a third antireflection film 5c may be provided on the entire surface of the fifth side surface 3c5.

  As shown in FIG. 1, the light A1 as incident light passes through the incident portion 2c1A and enters the first prism 2. The light A1 is separated by the polarization separation film 4 into polarized light P1 that is P-polarized light and polarized light S1 that is S-polarized light. The polarized light S <b> 1 is reflected by the polarization separation film 4. The reflected polarized light S1 is reflected by the first reflecting portion 2c1B of the first side surface 2c1 within the first prism 2, and is emitted from the first emitting portion 2c2C of the second side surface 2c2.

  On the other hand, the polarized light P1 passes through the polarization separation film 4 and enters the second prism 3 from the sixth side surface 3c6. The polarized light P1 is reflected by the second reflecting portion 3c4B of the fourth side surface 3c4 in the second prism 3, and is emitted from the second emitting portion 3c5C of the fifth side surface 3c5.

  The feature of this embodiment is that the first antireflection film 5a is provided in the region of the incident portion 2c1A of the first side surface 2c1, and the first antireflection film 5a is provided in the region of the first reflection portion 2c1B. That is not provided. As a result, the light A1 incident on the first prism 2 is difficult to be reflected at the incident portion 2c1A. Therefore, the light use efficiency can be effectively increased. In addition, since the first antireflection film 5a is not provided in the region of the first reflecting portion 2c1B, the polarized light S1 can be favorably reflected. Therefore, it is difficult for the polarized light S1 to be emitted from the first reflecting portion 2c1B, and the light use efficiency can be further enhanced.

  Since the second antireflection film 5b is provided in the region of the first emission part 2c2C of the second side surface 2c2, the polarized light S1 is not easily reflected on the second side surface 2c2. Since the third antireflection film 5c is also provided in the region of the second emitting portion 3c5C of the fifth side surface 3c5, the polarized light P1 is also difficult to be reflected on the fifth side surface 3c5. Therefore, the light use efficiency can be further increased, and a deviation in intensity at which the polarized light P1 and the polarized light S1 are emitted hardly occurs.

  By the way, as shown in FIG. 3, when the angle θ3 formed by the first side surface 32c1 and the third side surface 32c3 of the first prism 32 is small, it is between the first side surface 32c1 and the third side surface 32c3. The distance becomes shorter. Therefore, the polarized light S3 reflected by the polarization separation film 4 reaches a position closer to the portion where the light A3 is incident on the first side surface 32c1. At this time, when the polarized light S3 reaches the portion where the first antireflection film 5a is provided, the polarized light S3 is emitted from the first side surface 32c1. The emission of the polarized light S3 from the first side surface 32c1 is more likely to occur as the diameter of the light A3 is larger. Therefore, when the diameter of the light A3 is large, it is difficult to increase the light use efficiency.

  Further, the polarized light P3 transmitted through the polarization separation film 4 is reflected on the fourth side surface 33c4 of the second prism 33. Therefore, there is a possibility that a large magnitude may occur in the intensity of the polarized light S3 emitted from the second side surface 32c2 and the polarized light P3 emitted from the fifth side surface 33c5.

  As in the polarizing beam splitter 1 of this embodiment shown in FIG. 1, the angle θ1 formed by the first side surface 2c1 and the third side surface 2c3 is preferably 25 degrees or more. Thereby, even when the diameter of the light A1 is large, the light use efficiency can be effectively increased. In addition, the intensity deviation between the polarized light S1 and the polarized light P1 emitted from the second side surface 2c2 and the fifth side surface 3c5 is less likely to occur.

  More preferably, the angle θ1 is desirably 30 degrees or more. Thereby, the light utilization efficiency can be further increased, and the deviation of the intensity of the polarized light S1 and the polarized light P1 emitted from the second side surface 2c2 and the fifth side surface 3c5 is less likely to occur.

  On the other hand, as shown in FIG. 4, when the angle θ4 formed by the first side face 42c1 and the third side face 42c3 of the first prism 42 is large, the fourth side face of the first side face 42c1 and the second prism 43 is the fourth. The distance from the side surface 43c4 becomes longer. Therefore, the polarized light P4 transmitted through the polarization separation film 4 may be emitted from the fifth side surface 43c5 without being reflected by the fourth side surface 43c4. It is easier for the polarized light P4 to be emitted from the fifth side surface 43c5 without reaching the fourth side surface 43c4 as the diameter of the light A4 is larger.

  Similarly, the polarized light S4 reflected by the polarization separation film 4 may be emitted from the second side surface 42c2 without being reflected by the first side surface 42c1. In order to make it difficult to emit the polarized light S4 and P4 as described above, it is necessary to sufficiently lengthen the oblique sides of the upper and lower surfaces of the first and second prisms 42 and 43.

  As in the polarizing beam splitter 1 of the present embodiment shown in FIG. 1, the angle θ1 is preferably 35 degrees or less. Thereby, even when the diameter of the light A1 is large, the light use efficiency can be effectively increased. In addition, the size of the polarizing beam splitter 1 can be reduced.

  More preferably, the angle θ1 is 30 degrees. In the polarization beam splitter 1, the light A1 is incident so that the direction in which the polarized light S1 is emitted from the second side surface 2c2 and the direction in which the polarized light P1 is emitted from the fifth side surface 3c5 are parallel to each other. By setting the angle θ1 to 30 degrees, the light A1 can be incident from an angle perpendicular to the first side surface 2c1. In this case, the reflectance of the first side surface 2c1 of the polarized light P1 and the polarized light S1 included in the light A1 is the same. Accordingly, the intensity deviation between the polarized light P1 and the polarized light S1 is less likely to occur.

  As in the modification of the first embodiment shown in FIG. 5, a fourth antireflection film 25 d may be provided on the fourth side surface 3 c 4 of the second prism 3. The fourth antireflection film 25d is preferably the same antireflection film as the first antireflection film 5a. The second antireflection film 5b is preferably the same antireflection film as the third antireflection film 5c. In this case, the first prism 2 and the first and second antireflection films 5a and 5b, and the second prism 3 and the third and fourth antireflection films 5c and 25d are similarly configured. . Thus, productivity can be effectively increased. Further, even if light is incident from the direction of the fourth antireflection film 25d provided on the fourth side surface 3c4 of the second prism 3, polarization separation can be performed in a state where the light use efficiency is enhanced.

  FIG. 6 is a plan view of a polarizing beam splitter according to the second embodiment.

  The polarization beam splitter 11 is different from the first embodiment in that it includes a third prism 16 joined to the first prism 2 and a position where the first antireflection film 5a is provided. In other respects, the polarizing beam splitter 11 has the same configuration as the polarizing beam splitter 1 of the first embodiment.

  The third prism 16 is an incident portion provided on the first side surface 2 c 1 of the first prism 2. The third prism 16 has seventh to ninth side surfaces 16c7 to 16c9. The seventh side surface 16c7 is an incident surface, and the eighth side surface 16c8 is a reflecting surface. The ninth side surface 16c9 is joined to the first side surface 2c1 of the first prism 2.

  In the present embodiment, the planar shape of a substantially isosceles triangle formed by bonding the first and second prisms 2 and 3 and the planar shape of the third prism 16 have a similar relationship. In the polarization beam splitter 11, the planar shape on which the first and second prisms 2 and 3 are bonded is a substantially equilateral triangle, and the planar shape of the third prism 16 is also a substantially equilateral triangle. The length of the hypotenuse on the upper surface of the first prism 2 is 3.5 mm. The length of one side on the upper surface of the third prism 16 is 1.7 mm. In addition, the magnitude | size of the 1st, 2nd prism 2, 3 and the 3rd prism 16 is not specifically limited.

  The first prism 2 and the third prism 16 are bonded by, for example, an adhesive. The refractive index of the adhesive is preferably substantially the same as the refractive index of the first and third prisms 2 and 16. In addition, the refractive index of the said adhesive agent should just be comparable as the refractive index of the 1st, 3rd prisms 2 and 16, and the range which can exhibit the effect of this invention.

  In the present embodiment, the first antireflection film 5a is not directly provided on the first side surface 2c1. The first antireflection film 5a is provided on the seventh side surface 16c7 of the third prism 16 as the incident portion provided on the first side surface 2c1.

  The light A2 enters the third prism 16 from the seventh side surface 16c7 and is reflected by the eighth side surface 16c8 within the third prism 16. The reflected light A2 is emitted from the ninth side surface 16c9 and is incident on the first prism 2 from the first side surface 2c1 of the first prism 2. The light A2 is polarized and separated as in the first embodiment, and the polarized light S2 and the polarized light P2 are emitted from the second side surface 2c2 and the fifth side surface 3c5.

  Also in the present embodiment, the light use efficiency can be increased as in the first embodiment.

  As in the present embodiment, it is preferable that the planar shape of the substantially isosceles triangle in which the first and second prisms 2 and 3 are bonded and the planar shape of the third prism 16 have a similar relationship. At this time, it is preferable that the third prism 16 is disposed so that the seventh side face 16c7 and the second and fifth side faces 2c2 and 3c5 are parallel to each other. Accordingly, when the light A2 is incident from the direction perpendicular to the seventh side surface 16c7, the direction in which the polarized light S2 and the polarized light P2 are emitted is set to the direction perpendicular to the second side surface 2c2 and the fifth side surface 3c5. Can do. Therefore, it is possible to easily align the direction in which the light A2 is incident and the direction in which the polarized light S2 and the polarized light P2 are emitted.

  Furthermore, since the light A2 is incident on the seventh side surface 16c7 perpendicularly, the intensity of the emitted polarized light S2 and the polarized light P2 is unlikely to shift.

DESCRIPTION OF SYMBOLS 1 ... Polarizing beam splitter 2 ... 1st prism 2a ... Upper surface 2a1 ... Oblique side 2a2 ... Short side 2a3 ... Long side 2b ... Lower surface 2c1-2c3 ... 1st-3rd side surface 2c1A ... Incident part 2c1B ... 1st reflection part 2c2C ... 1st emission part 3 ... 2nd prism 3c4-3c6 ... 4th-6th side surface 3c4B ... 2nd reflection part 3c5C ... 2nd emission part 4 ... Polarization separation films 5a-5c ... 1st-2nd Third antireflection film 11 ... Polarizing beam splitter 16 ... Third prisms 16c7 to 16c9 ... Seventh to ninth side faces 25d ... Fourth antireflection film 32 ... First prisms 32c1 to 32c3 ... First to second 3 side surface 33 ... 2nd prism 33c4, 33c5 ... 4th, 5th side surface 42 ... 1st prism 42c1-42c3 ... 1st-3rd side surface 43 ... 2nd prism 43c4, 43c5 ... 4th Fifth aspect

Claims (4)

An upper surface and a lower surface having a right triangle shape including an oblique side and two sides other than the oblique side, a first side surface connecting the oblique sides of the upper surface and the lower surface, and the upper surface and the lower surface A first prism having second and third side surfaces respectively connecting sides other than the oblique sides;
A fourth side surface having substantially the same shape as the first prism and corresponding to the first side surface; and fifth and sixth side surfaces corresponding to the second and third side surfaces. Having a second prism;
A polarization separation film provided between the third side surface of the first prism and the sixth side surface of the second prism;
The third side surface of the first prism and the sixth side surface of the second prism are arranged so that the second side surface and the fifth side surface are located on the same side. A polarizing beam splitter that is joined,
Incident light passes through the incident portion on the first side surface, enters the first prism, is reflected by the polarization separation film, and is transmitted through the polarization separation film. Separated into polarization components,
The first polarized component reflected by the polarization separation film is reflected by the first reflecting portion on the first side surface in the first prism, and from the first emitting portion on the second side surface. Exit,
The second polarization component transmitted through the polarization separation film is reflected by the second reflecting portion on the fourth side surface in the second prism and is emitted from the second emitting portion on the fifth side surface. Is configured to
A polarizing beam splitter, wherein the first antireflection film is provided in the region of the incident portion on the first side surface and is not provided in the region of the first reflection portion on the first side surface.   A second antireflection film is provided in the region of the first emission portion on the second side surface, and a third antireflection film is provided on the region of the second emission portion on the fifth side surface. The polarizing beam splitter according to claim 1, wherein the polarizing beam splitter is provided on the polarizing beam splitter.   The polarizing beam splitter according to claim 1 or 2, wherein an angle formed by the first side surface and the third side surface is 25 degrees or more and 35 degrees or less.   The polarizing beam splitter according to claim 3, wherein an angle formed by the first side surface and the third side surface is 30 degrees.

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