JP2862423B2 - Polarizing beam splitter - Google Patents

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.

[0002]

2. Description of the Related Art Conventionally, a polarizing beam splitter has been used in fields such as application of optical disk technology to separate light such as laser light having various polarization components into an s-polarization component and a p-polarization component. . This type of polarizing beam splitter includes a high refractive index dielectric thin film and a low refractive index dielectric thin film alternately stacked between two prisms, a Nicol prism using a birefringent crystal, and a Gran-Thompson. There are prisms and the like.

[0003]

A polarizing beam splitter using a birefringent crystal prism has an advantage of excellent polarization characteristics, but has a problem that a birefringent crystal is expensive. In addition, a polarizing beam splitter using a dielectric multilayer film has a problem that it is necessary to stack multiple dielectric layers in order to improve polarization characteristics, and it is difficult to manufacture the polarizing beam splitter.

Accordingly, the present invention provides a polarizing beam splitter which is easy to manufacture and inexpensive.

[0005]

According to the present invention, a metal film and a film having the same thickness laminated on both surfaces of the metal film are provided.
First and second dielectric layers having the same refractive index ;
A first wave number matching element provided to match the wave number of incident light and the wave number of surface plasmon on the surface of the metal layer excited by the light, And a second wave number matching element provided in the polarization beam splitter.

[0006]

[0007]

When the refractive index and thickness of a metal layer, the refractive index and thickness of a dielectric layer, and the refractive index of a wave number matching element such as a prism are appropriately selected, p-polarized light of a certain wavelength can be obtained. When the light enters the dielectric layer from the incident side prism at a certain incident angle larger than the total reflection angle, surface plasmons are excited at the interface between the metal layer and the dielectric layer. In this case, the s-polarized component of the incident light does not excite surface plasmons and is larger than the total reflection angle, so that the s-polarized component is totally reflected at the prism bottom surface on the incident side.

[0008] The excited surface plasmon propagates on the surface of the metal layer. If, for example, the incident side and the output side are symmetrical, p-polarized light is emitted from the wave number matching element, for example, a prism on the output side by re-radiation. If the thickness and refractive index of the layer are appropriately selected, almost all of the p-polarized light component of the incident light can be re-emitted.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a polarizing beam splitter according to the present invention.

FIG. 1 is a sectional view schematically showing the structure of an embodiment of a polarizing beam splitter according to the present invention.
FIG. 4 is a cross-sectional view showing the operation of the polarizing beam splitter according to the present invention.

The polarizing beam splitter has a dielectric layer 1 between two wave number matching elements, prisms 10 and 14.
The metal layer 12 sandwiched between 1 and 13 is sandwiched. As the prisms 10 and 14, for example, a LaSF9 right-angle prism made of light refractive index glass is used.
Reference numerals 1 and 13 are formed of a SiO ₂ (silicon dioxide) film having a thickness of about 0.7 μm. The metal layer 12 is formed of an Ag film 12 having a thickness of about 10 nm.

In the polarizing beam splitter having such a structure, the SiO ₂ film 13, the Ag film 12, and the SiO ₂ film 11 are directly laminated on the prism 14, and the L
It is manufactured by pressing and fixing the aSF9 right angle prism 10.

At this time, the SiO ₂ film and the Ag film are formed by RF magnetron sputtering. SiO ₂ film is SiO ₂ in the target, the discharge gas with Ar,
Gas flow rate about 10 ccm, gas pressure about 2 Pa, input power about 4
The film was formed at a speed of about 2.3 nm / s.
Met. The Ag film uses Ag as a target and N ₂ as a discharge gas, and has a gas flow rate of about 3 ccm and a gas pressure of about 0.1 cm.
A film is formed at 2 Pa and an input power of about 5 W, and a film forming speed is about 0.4.
nm / s.

In the polarizing beam splitter having such a configuration, the refractive index and the thickness of the metal layer, the refractive index and the thickness of the dielectric layer, and the refractive index of the prism are appropriately selected. As shown in FIG. 2, a p-polarized laser beam 20 of a certain wavelength is transmitted from the incident side prism 10 to the total reflection angle θc.
When the light enters the dielectric layer 11 at a certain incident angle θ larger than that, long-distance surface plasmons are excited at the interface between the metal layer 12 and the dielectric layer 11.

Generally, light incident from the outside has a total reflection angle θ.
When the light is incident at a certain incident angle θ larger than c, the electromagnetic field of the incident light is not completely reflected at the reflecting surface (the boundary surface between the dielectric layer 11 and the metal layer 12), and the electromagnetic field of the incident light is at a distance from the reflecting surface. On the other hand, an electromagnetic wave that attenuates exponentially exists and oozes out of the reflection surface. The wave number of this electromagnetic wave is k = (n _p ω / c)
(N _p is the refractive index of the prism, ω is the angular frequency of the incident light, and c is the speed of light).
(When the wave number k and angular frequency ω of the electromagnetic wave match those of the surface plasmon), the long-range surface plasmon having the same wave number and angular frequency as the above wave number k and angular frequency ω is resonantly excited. And the resulting energy dissipation lowers the reflectivity. In this case, the s-polarized component of the incident light does not excite long-range surface plasmons,
In addition, the prism 10 on the incident side is larger than the total reflection angle.
Is totally reflected on the bottom surface of the prism 21 and exits from the other surface of the prism 21 as emission light 21.

The excited long-range surface plasmon is metal 1
2 surface. If the entrance side and the exit side have a symmetrical structure, the re-radiation will cause p
Polarized light is emitted. Also, by selecting appropriate film thickness conditions and refractive index conditions, almost all of the p-polarized light component of the incident light can be re-emitted.

The polarizing beam splitter that performs such an operation can be easily manufactured as described above, and therefore can be manufactured at low cost.

As shown in FIG. 2, p- and s-polarized He-Ne laser beams were made to enter the LaSF9 right-angle prism of this element, respectively, as shown in FIG. FIG. 4 shows the incident angle dependence of the transmittance of the s-polarized light and the s-polarized light. In FIG. 4, the reflectance of p-polarized light is 0.5%, the reflectance of s-polarized light is 99.9%, and the transmittance of p-polarized light at the incident angle (18.95 degrees) at which the transmittance of the p-polarized component is maximized. Was 92.3% and the transmittance for s-polarized light was 0.1%.
The reason why (reflectance + transmittance) of p-polarized light is less than 100% is due to loss in the metal layer.

When unpolarized monochromatic light is incident on the device at an incident angle of 18.95 degrees, the wavelength dependence of the reflectance of p and s polarized light is shown in FIG. The sex was as shown in FIG. Reflection of p-polarized light due to the fact that the angle of incidence at the bottom of the prism depends on the wavelength due to the wavelength dispersion of the prism and the wave number at the bottom of the prism that excites long-distance surface plasmons due to the wavelength dispersion of the metal and dielectric layers Varies with wavelength.

In the embodiment, an example of an element having a good polarization characteristic at an incident angle of 18.95 degrees is shown. However, the dependence of the polarization characteristic on the incident angle depends on the film thickness condition and the refractive index condition of the metal layer and the dielectric layer. In addition, since the angle of incidence can be changed by selecting the angle of incidence on the prism, it is also possible to manufacture an element having good polarization characteristics when vertically incident on the prism.

In the embodiment, the wavelength is 632.8 nm (He-N
In the case of (e-laser light), an example of an element having good polarization characteristics has been described. For the wavelength dependence of the polarization characteristics, the conditions of the thickness and refractive index of the metal layer and the dielectric layer and the angle of incidence on the prism are selected. Therefore, an element having good polarization characteristics at the wavelength to be used can be manufactured.

[0022]

[0023]

Accordingly, the polarizing beam splitter according to the present invention comprises a metal film and first and second dielectric layers having the same thickness and the same refractive index, which are respectively laminated on both surfaces of the metal film. A first wave number matching element provided on the first dielectric layer to match the wave number of incident light with the wave number of surface plasmons on the surface of the metal layer excited by the light; Since the second wave number matching element provided on the body layer is provided, it is possible to provide a polarization beam splitter which is easy to manufacture and inexpensive.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a configuration of an embodiment of a polarizing beam splitter according to the present invention.

FIG. 2 shows an incident angle θ of the polarization beam splitter shown in FIG.
FIG. 4 is a diagram showing a light path when light is incident on the light source.

FIG. 3 is a diagram showing the incident angle dependence of the reflectance of s-polarized light and p-polarized light when He-Ne laser light is incident on one embodiment of the polarizing beam splitter according to the present invention.

FIG. 4 is an incidence angle dependence of transmittance of s-polarized light and p-polarized light when He-Ne laser light is incident on one embodiment of the polarizing beam splitter according to the present invention.

FIG. 5 is a graph showing the incident wavelength dependence of the reflectance of s-polarized light and p-polarized light in one embodiment of the polarizing beam splitter according to the present invention.

FIG. 6 is a graph showing the dependence of the transmittance of s-polarized light and p-polarized light on the incident wavelength in one embodiment of the polarizing beam splitter according to the present invention.

[Explanation of symbols]

 10,14 right angle prism 11,13 dielectric layer 12 metal layer

──────────────────────────────────────────────────の Continuation of front page (56) References JP-A-60-211403 (JP, A) JP-B-62-40401 (JP, B2) JP-B-6-28361 (JP, B2) 501546 (JP, A) Applied Physics, vol. 41 (4) (1972) pp. 324-337 (58) Field surveyed (Int. Cl. ⁶ , DB name) G02B 5/30 G02B 5/04

Claims (1)

(57) [Claims] 1. A metal film, first and second dielectric layers each having the same thickness and the same refractive index laminated on both surfaces of the metal film, and a first dielectric layer on the first dielectric layer. A first wave number matching element provided for matching a wave number of incident light with a wave number of surface plasmon on the surface of the metal layer excited by the light, and provided on the second dielectric layer. A polarizing beam splitter comprising: a second wave number matching element.