JPH0784124A - Beam splitter - Google Patents

Abstract

PURPOSE:To provide the beam splitter of a polarization independent type which has a boundary stable to humidity and hot air and is improved in reliability by using a halfwave plate having a slope and forming first and second branch films respectively on both surfaces of this halfwave plate by vapor deposition or sputtering, thereby forming the beam splitter. CONSTITUTION:This beam splitter is formed by using the halfwave plate having the slope diagonal to a propagation direction of transmitted light and forming the first and second branch films respectively on both surfaces of this halfwave plate by vapor deposition or sputtering. Namely, the beam splitter is formed by mounting the first and second branch films 1 and 2 on both surfaces of the halfwave plate and, therefore, the dependency of the first branch film 1 on polarization and the dependency of the second branch film 2 on polarization are offset and the beam splitter having no dependency on polarization as a whole is obtd. Since the beam splitter is formed by vapor deposition or sputtering of the first and second branch films 1, 2 on both surfaces of the halfwave plate, the boundary is stabilized to moisture, heat, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization-independent beam splitter for splitting one light beam into at least two light beams.

[0002]

In the field of optical communication and optical precision equipment,
A beam splitter is used to split the light beam. For example, in order to monitor the intensity of the signal light transmitted from the optical transmitter, a part of the signal light is branched and taken out and is used by a photodiode to receive the light. For this type of beam splitter, it is required that the polarization ratio of the splitting ratio is small in order to enable highly accurate monitoring, and that it is suitable for downsizing of the device. .

Conventionally, as an example of the beam splitter, as shown in FIG. 3, first and second prisms 11 and 12 each having an inclined surface oblique to the propagation direction of transmitted light,
The first and second branch films 14 and 15 are provided on the slopes of the first and second prisms, respectively, and the half-wave plate 13 sandwiched between the first and second branch films is Some are integrally formed by an adhesive (Japanese Patent Laid-Open No. 5-1.
No. 50114).

[0004]

By the way, in the above-mentioned beam splitter, since the half-wave plate is interposed between the first and second branch films, the polarization dependence of the first branch film and the first The polarization dependence of the two branching films is canceled out, and a beam splitter whose branching ratio does not depend on polarization as a whole can be realized. However, since two prisms and a half-wave plate are bonded together, a bonding surface Is unstable with respect to moisture and heat and lacks reliability.

Further, it is necessary to form a non-reflective film on each of at least five surfaces where light is input to and output from these prisms, in addition to a branch film, and this beam splitter is formed by bonding three members. Therefore, the manufacturing cost is inevitably high. Further, there is a problem that the device to which the beam splitter is applied becomes large. Therefore, an object of the present invention is to provide a beam splitter that solves the above problems.

[0006]

A beam splitter according to the present invention has a sloped surface which is oblique to the propagation direction of transmitted light.
The half-wave plate and the first and second branch films are formed on both surfaces of the half-wave plate by vapor deposition or sputtering, respectively.

In the beam splitter described above, the angle formed by the first branching film and the propagation direction of the light incident on this film is approximately 4 °.
It is characterized in that it is 5 °, and the optical axis of the half-wave plate is located in a plane perpendicular to the propagation direction of the light transmitted therethrough.

[0008] These beam splitters separately receive the light reflected by the first branch film and the light transmitted through the first branch film and reflected by the second branch film and transmitted through the first branch film. Alternatively, it is characterized in that these lights are collectively focused by a lens and received.

The half-wave plate is preferably made of quartz, and the first and second branch films are preferably made of a dielectric single layer film or a dielectric multilayer film.

[0010]

According to the above construction, since the first and second branch films are attached to both surfaces of the half-wave plate respectively, the polarization dependence of the first branch film and the second branch film are prevented. The polarization dependence is canceled out, and a beam splitter having no polarization dependence of the branching ratio as a whole is obtained. Further, since the first and second branch films are formed on both surfaces of the half-wave plate by vapor deposition or sputtering, the interface is stable against moisture and heat, so the reliability is high and the number of elements is high. It has a small size and a simple structure, resulting in a low manufacturing cost and a small size.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a side view showing the configuration of this embodiment, and FIG. 2 is a diagram for explaining the optical path in FIG. In FIG. 1 and FIG. 2, first and second branch films 1 and 2 made of dielectric films are formed on the entrance side and the exit side of a half-wave plate 3 made of quartz, respectively.

As for the optical axis OA of the half-wave plate 3, when light is incident from the branching film 1 at an angle θ, the ordinary component of the transmitted light propagating in the half-wave plate 3 is shifted by θ−θ ′. Follow the axis.
Here, θ ′ is defined by Snell's law sin θ / sin θ ′ = n ′ / n. n is the refractive index of air, and n'is the refractive index of the half-wave plate 3. The light incident on the half-wave plate 3 propagates as ordinary light and extraordinary light separately, and the electric fields of the extraordinary light and the extraordinary light vibrate in a plane (plane A) perpendicular to the traveling direction of the ordinary light. Therefore, the crystal axis OA of the half-wave plate 3 is located on the A plane in order to effectively generate a phase difference between the ordinary light and the extraordinary light. The optical axis OA when viewed from the X direction is a plane (B which includes the incident light and the transmitted light propagating through the half-wave plate 3).
Plane) and the above-mentioned A plane are set to be inclined by 45 ° in the A plane with reference to the intersection line (the A plane and the B plane are not shown).

Next, the optical path of this embodiment will be described. In FIG. 2, light incident on the first branch film 1 from the outside by an optical path at an incident angle of about 45 ° is divided into reflected light (optical path) and transmitted light (optical path). The reflected light on the optical path is extracted as it is as the first branch output. The light transmitted through the optical path has its polarization plane rotated by 90 ° in the half-wave plate 3, enters the second branching film 2, and is divided into reflected light (optical path) and outgoing light (optical path). The reflected light in the optical path is taken out as the second branch output, and the outgoing light in the optical path is taken out as the optical output.

Here, even if the branch films 1 and 2 have different transmittances for the p and s components with respect to the light emitted from the optical path, the difference between the p and s components received by the branch film 1 is caused by the branch film 2. Since it is canceled, it does not depend on the polarization state of incident light. Also,
Regarding the first and second branched lights, the two reflected lights are almost equal to those obtained by exchanging the p and s polarization components thereof with each other, and therefore the sum thereof is almost independent of the polarization of the branch film. In the case of crystal, the optical path difference between optical paths is 1 /
If the thickness of the half-wave plate 3 is about 0.5 mm and the thickness of the half-wave plate 3 is 0.5 mm, the lens is narrowed down to the light receiving surface of the monitor element. The effective diameter of 1 may be 1 to 2 mm.

The amount of reflection of the branch film depends on its thickness or material, and a multilayer film or a single layer film is applied.
As described above, since it is not necessary to impose severe properties on the branch film itself, the design and production of the film are very simple, and a film having stable properties can be obtained.

[0016]

As described above, according to the present invention,
Since the first and second branch films are attached to both surfaces of the half-wave plate respectively, the polarization dependence of the first branch film and the polarization dependence of the second branch film are canceled, and as a whole. A beam splitter having no polarization dependence of the splitting ratio can be obtained. Also, since the first and second branch films are formed by vapor deposition or sputtering on both sides of the half-wave plate, the interface is stable against moisture and heat, improving reliability and further increasing the number of elements. It has a small size and a simple structure, resulting in a low manufacturing cost and a small size.

[Brief description of drawings]

FIG. 1 is a side view showing the configuration of this embodiment.

FIG. 2 is a side view (a) and an X-direction arrow view (b) showing the configuration of the present embodiment.

FIG. 3 is a side view showing a configuration of a conventional example.

[Explanation of symbols]

 1: 1st branch film 2: 2nd branch film 3: 1/2 wave plate 11, 12: Prism 13: 1/2 wave plate 14, 15: Branch film ~: Optical path

Claims (5)

[Claims] 1. A half-wave plate having an inclined surface oblique to the propagation direction of transmitted light, and first and second branch films formed on both surfaces of the half-wave plate by vapor deposition or sputtering. A beam splitter characterized in that 2. The angle formed between the first branching film and the propagation direction of the light incident on the film is approximately 45 °, and the optical axis of the half-wave plate and the propagation direction of the light passing therethrough. The beam splitter according to claim 1, wherein the beam splitter is located in a vertical plane. 3. The light reflected by the first branch film and the light transmitted through the first branch film, reflected by the second branch film, and transmitted through the first branch film are collectively focused by a lens. The beam splitter according to claim 1 or 2, which receives light. 4. The first and second branch films are formed of a dielectric single layer film or a dielectric multilayer film.
4. The beam splitter according to any one of 3 to 3. 5. The beam splitter according to claim 1, wherein the half-wave plate is made of quartz.