JPH07209517A - Polarized beam splitter - Google Patents

Abstract

PURPOSE:To realize a polarized beam splitter enhanced in laser beam resistance and excellent in optical characteristics. CONSTITUTION:A polarized beam splitter having a third alternate multilayer film 3 obtained by laminating five low-refractiveindex layers of SiO2 and five high-refractive-index layers of TiO2 at the center of the film thickness second and fourth alternate multilayer films 2 and 4 formed by laminating five low- refractive-index layers of SiO2 and five high-refractive-index layers of ZrO2 and first and fifth multilayer films 1 and 5 obtained by laminating four low- refractive-index layers of SiO2 and four high-refractive-index layers of Al2O3 are provided on a substrate B1. Since the low-refractive-index Al2O3 is used as the high-refractive index layer close to the surface on the incident laser beam side, the laser beam resistance is improved, and an excellent optical characteristic is secured by using high-refractive-index TiO2 in the high- refractive-index layer at the center of film thickness.

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 used for high power laser light and the like.

[0002]

2. Description of the Related Art A polarization beam splitter transmits a P component of light incident on an alternate multilayer film and reflects the S component to divide the light into two parts. The high refractive index layer and the low refractive index layer are alternately arranged. Known are a prism type in which laminated alternating multilayer films are sandwiched by a pair of prisms, and a plate type in which an incident angle of a plane wave with respect to an alternating multilayer film provided on a flat plate-shaped substrate is 60 degrees or more. . Among them, the plate-type polarization beam splitter uses TiO ₂ as the material for the high refractive index layer and SiO ₂ as the material for the low refractive index layer to prevent wavelength variations, wavelength shifts, or variations in the finished state of each product. A device is devised to prevent the decrease in the transmittance of the P component caused by the phenomenon (Japanese Patent Laid-Open No. 62-
299907), or when a high refractive index substance and a low refractive index substance are alternately layered, TiO is used as the material of the high refractive index layer.
By alternately laminating ₂ and ZnS or by laminating both of them with a constant film thickness, the adhesion to the substrate and the controllability of the film thickness are improved (JP-A-63-116107).
(See Japanese Patent Laid-Open Publication No.) or a film structure of M (SiO ₂ / Ti
O ₂ ) / N (SiO ₂ / ZrO ₂ ), a laser reflecting mirror having improved laser resistance (Japanese Patent Laid-Open No. 2-2047).
No. 02) or a low refractive index layer of MgF ₂ and CeO ₂
Alternatively, a laser beam polarizer having a high-refractive index layer of ZnS and having a film structure symmetrical with respect to the center of the entire film thickness and having an incident angle of 60 degrees (see US Pat. No. 3,622,225).
Etc. have been developed.

[0003]

However, according to the above-mentioned prior art, a laser that can obtain a stable extinction ratio in a relatively wide wavelength range has a low laser resistance and is improved so that the laser resistance becomes high. Requires complicated film thickness control, and a slight film thickness deviation may lead to a decrease in extinction ratio, resulting in insufficient optical characteristics and high manufacturing cost.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a polarizing beam splitter which has high laser resistance, excellent optical characteristics, and is inexpensive. Is.

[0005]

In order to achieve the above object, the polarization beam splitter of the present invention comprises a high refractive index layer and a low refractive index layer alternately stacked in the center of the entire film thickness. A central layer and at least a pair of symmetrical layers composed of a high refractive index layer and a low refractive index layer, which are alternately laminated at substantially symmetrical positions with the central layer sandwiched, are provided, and each of the pair of symmetrical layers is provided. The high refractive index layer has a lower refractive index than each of the high refractive index layers of the central layer.

[0006]

The strength of the electric field energy generated by the S component of the light incident on the polarization beam splitter is larger as it is closer to the surface of the polarization beam splitter, and when the strength of the electric field energy is large, the absorption amount also increases. Therefore, by using a material having a lower refractive index than each high refractive index layer of the central layer for each high refractive index layer of each symmetric layer located outside the central layer, the absorption amount is reduced and the laser proof strength is improved. By using a material having a high refractive index for each high refractive index layer of the layer, excellent optical characteristics are ensured with a small number of layers.

[0007]

Embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) FIG. 1 is a schematic view showing a film structure of a polarization beam splitter according to the first embodiment.
This is an S layer in which four layers are alternately laminated on the surface of the substrate B _1.
Low refractive index layer 1a of iO ₂ and high refractive index layer 1b of Al ₂ O ₃
And a second alternating multilayer film layer _{2 comprising} a low refractive index layer 2a made of SiO ₂ and a high refractive index layer 2b made of ZrO ₂ , which are alternately laminated on each five layers. And a low-refractive-index layer 3 of SiO ₂ alternately laminated on each of the five layers
a third alternate multilayer film layer 3 made of a and TiO ₂ of high refractive index layer 3b, SiO ₂ stacked five layers alternately thereon
The consists of a low refractive index layer 4a and ZrO ₂ in the high refractive index layer 4b 4 alternating multilayer film 4 and further the low refractive index layer 5a of SiO ₂ stacked by four layers alternately thereon Al ₂ It has a fifth alternating multilayer film layer 5 consisting of a high refractive index layer 5b of O ₃ . That is, the second and fourth alternating multilayer films having the same film structure as the pair of first symmetrical layers sandwiching the third alternating multilayer film layer 3 which is the central layer arranged in the center of the entire film thickness. The layers 2 and 4 are arranged, and the first and fifth alternating multilayer film layers 1 and 5 of the same film structure, which are a pair of second symmetrical layers, are arranged on the outer side thereof, and the entire film structure is _{4 (SiO 2 / Al 2 O} 3) / 5
(SiO ₂ / ZrO ₂ ) / 5 (SiO ₂ / TiO ₂ ) /
5 (SiO ₂ / ZrO ₂ ) / 4 (SiO ₂ / Al ₂ O
₃ ) / Air symmetrical Nd-YAG laser fundamental wave (wavelength 1064
nm) for the polarizer.

The optical film thickness of the low refractive index layers 1a and 5a of SiO ₂ of the first and fifth alternate multilayer film layers 1 and 5 is 268.
nm, the optical film thickness of each high refractive index layer 1b, 5b of Al ₂ O ₃ is 269 nm, and the second and fourth alternating multilayer film layers 2, 4
Each of the SiO ₂ low refractive index layers 2a and 4a has an optical film thickness of 27
The optical film thickness of the high refractive index layers 2b and 4b of 3 nm and each ZrO ₂ is 274 nm, and each SiO of the third alternate multilayer film layer 3 is 3 nm.
Optical thickness of the optical thickness and the high refractive index layer 3b of the TiO ₂ in the _second low refractive index layer 3a is 271nm none. Also,
The low refractive index layer and the high refractive index layer each have an oxygen partial pressure of 0.5.
The film was formed in an atmosphere of ˜3 × 10 ⁻⁴ Torr, and the vapor deposition rate was 0.5 to 5.0 Å / sec.

The refractive index n (of Al ₂ O ₃ forming the high refractive index layers of the first and fifth alternating multilayer films 1 and 5 located on the outermost side with the third alternate multilayer film layer 3 as the center. A) and the refractive index n (Z) of ZrO ₂ forming each high refractive index layer of the second and fourth alternating multilayer film layers 2 and 4 located inside thereof and the third alternating multilayer film layer 3 of The refractive index n (T) of TiO ₂ forming each high refractive index layer has a relationship of n (A) <n (Z) <n (T), and the refractive index n (T) of TiO ₂ is the highest, Al ₂ O
Refractive index of ₃ n (A) is the lowest.

In general, a material having a higher refractive index has a larger absorption amount of laser light, and therefore has a lower laser resistance.

Further, the S of the laser light incident on the polarizing film is
The component is reflected light, and the intensity of the electric field energy generated in the polarizing film by this is larger as it is closer to the surface of the polarizing film, and the intensity of the electric field energy is larger, as shown by the curve (b) in FIG. The absorption amount tends to increase and the laser proof strength tends to decrease. The curve (a) shows the intensity of electric field energy due to the P component which is transmitted light.

In this embodiment, the three high refractive index materials Al are used.
_{Of the 2} O ₃ , ZrO ₂ , and TiO ₂ , the fifth refractive index layer of the fifth alternating multilayer film layer 5 closest to the surface of the polarizing film is made of Al ₂ O ₃ having the lowest refractive index to form a laser by absorption. The material of the high refractive index layer of the third alternating multilayer film layer 3 which is relatively far from the surface of the polarizing film and is less likely to be affected by the electric field energy is used as the material of the high refractive index layer of TiO _{2 which has} the highest refractive index. By using S, the rising characteristic from the reflection band to the transmission band of the S component is sharp, and the transmission property of the P component is also realized in a wide wavelength region with a good polarization beam splitter with a relatively small number of layers. . That is, according to the present embodiment, it is possible to obtain a polarizing beam splitter having high laser resistance, excellent optical characteristics, and low cost.

[0014] For comparison, a polarization beam splitter film structure by laminating made of a low refractive index layer and the TiO ₂ of SiO ₂ high refractive index layer by respectively 12-layer 12 (SiO ₂ / TiO _2), SiO ₂ 18 layers of low refractive index layers and ZrO ₂ high refractive index layers
(SiO ₂ / ZrO ₂ ) polarization beam splitter,
A film structure 32 (SiO ₂ / Al ₂ layer) in which 32 low refractive index layers of SiO ₂ and 32 high refractive index layers of Al ₂ O ₃ are laminated respectively
O ₃ ) polarization beam splitters are manufactured to obtain samples B, C, and D, respectively, and the polarization beam splitter of this embodiment is referred to as sample A, and the spectral characteristics of samples A to C are shown in FIGS. 3 to 5, respectively. N of each sample A to D
Table 1 shows the measurement results of the laser proof stress of the fundamental wave of the d-YAG laser with respect to the S component and the P component.

[0015]

[Table 1] From this table, it is found that sample A, which is the polarization beam splitter of the present example, has the same laser resistance to the S component as samples C and D of the comparative example, and also has sufficient laser resistance to the P component. I understand.

3 to 5, the polarization beam splitter of the present embodiment shown in FIG. 3 has the same optical characteristic as that of the sample B using only TiO _{2 as} the material of the high refractive index layer shown in FIG. It turns out that it is almost the same.

When the number of the high refractive index layers and the number of the low refractive index layers of the third alternating multilayer film layer 3 of the polarization beam splitter of this embodiment is 5 or more, the optical characteristics are further improved, but the P component. Laser resistance of the
Experiments have shown that the extinction ratio is significantly impaired when the thickness is less than the layer.

As the material for the high refractive index layer, Al ₂
Not only O ₃ , ZrO ₂ and TiO _2, but also HfO ₂ and Ti
O, Y ₂ O ₃ , Ta ₂ O ₅ or the like may be used, or
As materials for the low refractive index layer, other than SiO ₂ , MgF ₂ , Li
It is also possible to use F, Na ₃ AlF ₆ or the like.

(Second Embodiment) A film structure of 3 (SiO ₂ / ZrO ₂₎ is used as a polarizer for an Nd-YAG laser fundamental wave.
₂ ) / 10 (SiO ₂ / TiO ₂ ) / 3 (SiO ₂ / Z
A polarizing film of rO ₂ ) / Air was manufactured. This is TiO
Z is formed on the outer side of the second alternating multilayer film layer which is the central layer composed of 10 pairs of (SiO ₂ / TiO ₂ ) having _two high refractive index layers.
having a high refractive index layer of rO ₂ (SiO ₂ / ZrO ₂ ) 3
The polarizing film is a symmetric alternating multilayer film provided with first and third alternating multilayer films which are a pair of symmetrical layers.

The optical film thickness of the high refractive index layer of TiO ₂ and the optical film thickness of the low refractive index layer of SiO ₂ of the second alternating multilayer film layer, which is the central layer, are both 266 nm (λ / 4). ), And each ZrO of the first and third alternating multilayer films that are symmetrical layers
The optical film thickness of the high refractive index layer of No. ₂ is 266 nm (λ / 4), and the optical film thickness of each low refractive index layer of SiO ₂ is 256 nm.
The low-refractive index layer and the high-refractive index layer were formed in an atmosphere with an oxygen partial pressure of 0.5 to 3 × 10 ⁻⁴ Torr, respectively, and the vapor deposition rate was 0.5 to 5.0 Å / sec. .

The electric field energy of the S component of the incident laser light shows a particularly high value in the third alternating multilayer film layer closest to the surface of the polarizing film, as shown by the curve (b) in FIG. The high refractive index layer of the third alternating multilayer film layer has a relatively low refractive index, and therefore, is made of ZrO ₂ having a small absorption, so that there is no fear that the laser resistance will be significantly reduced. First
When the laser proof stress was measured under the same conditions as in the example, S
18 J / cm ^{2 for} the component and 9 J / c for the P component
It was m ² and was found to have sufficient laser resistance.

Further, when the spectral characteristics were examined, it was found that it had a better extinction ratio than the sample B of FIG. 4 as shown in FIG.

The (SiO ₂ / TiO ₂ ) of this embodiment is
It has been proved by experiments that if the number of pairs is set to 10 or more, the optical characteristics are improved, but the laser resistance of the P component is significantly reduced. The other points are the same as those in the first embodiment, and the description thereof will be omitted.

[0024]

Since the present invention is constructed as described above, it has the following effects.

It is possible to realize an inexpensive polarization beam splitter having a high laser resistance and excellent optical characteristics.

[Brief description of drawings]

FIG. 1 is a schematic view showing a film configuration of a polarization beam splitter according to a first embodiment.

FIG. 2 is a graph showing an intensity distribution of electric field energy generated when laser light is incident on the polarization beam splitter of the first embodiment.

FIG. 3 is a graph showing the transmittance for each of the S component and the P component of the first embodiment.

FIG. 4 is a graph showing the transmittances of the S component and P component of sample B of the comparative example.

FIG. 5 is a graph showing the transmittances of the S component and P component of sample C of the comparative example.

FIG. 6 is a graph showing an intensity distribution of electric field energy generated when laser light is incident on the polarization beam splitter according to the second embodiment.

FIG. 7 is a graph showing the respective transmittances of the S component and the P component of the polarization beam splitter of the second embodiment.

[Explanation of symbols]

1 First Alternate Multilayer Film Layer 1a, 2a, 3a, 4a, 5a SiO ₂ Low Refractive Index Layer 1b, 5b Al ₂ O ₃ High Refractive Index Layer 2 Second Alternate Multilayer Film Layer 2b, 4b ZrO ₂ High refractive index layer 3 Third alternating multilayer film layer 3b High refractive index layer of TiO ₂ 4 Fourth alternating multilayer film layer 5 Fifth alternating multilayer film layer

Claims (6)

[Claims] 1. A central layer composed of a high refractive index layer and a low refractive index layer, which are alternately laminated in the center of the entire film thickness, and a plurality of layers are alternately laminated at substantially symmetrical positions with the central layer sandwiched therebetween. A high refractive index layer and a low refractive index layer, and each high refractive index layer of the pair of symmetrical layers has a lower refractive index than each high refractive index layer of the central layer. A polarizing beam splitter characterized in that 2. The polarizing beam splitter according to claim 1, wherein each low refractive index layer of the central layer and each low refractive index layer of the pair of symmetrical layers are made of SiO ₂ . 3. The polarizing beam splitter according to claim 1, wherein each high refractive index layer of the central layer is made of TiO ₂ and each high refractive index layer of the pair of symmetrical layers is made of ZrO _2. . 4. The polarized light according to claim 1, wherein each high refractive index layer of the central layer is made of TiO ₂ and each high refractive index layer of the pair of symmetrical layers is made of Al ₂ O _3. Beam splitter. 5. A T having five central layers each.
high refractive index layer of iO ₂ and SiO _2, low refractive index layer,
A pair of first symmetrical layers consisting of a high-refractive-index layer of ZrO _{2 and} a low-refractive-index layer of SiO ₂ , which are stacked in layers of 5 layers each, are provided on the outer side of the layer, and further on each of the outer sides thereof, there are 4
5. A pair of second symmetrical layers comprising a high-refractive index layer of Al ₂ O _{3 and} a low-refractive index layer of SiO ₂ which are laminated layer by layer are provided. The described polarizing beam splitter. 6. A central layer is a low refractive index layer of the high refractive index layer of TiO ₂ that are stacked one by each 10 layers and SiO _2, the high refractive index layer of ZrO ₂ which are stacked one by each of the three layers on the outside 4. A pair of symmetrical layers composed of a low refractive index layer of SiO ₂ and SiO ₂ are provided.
The polarizing beam splitter according to any one of claims 1.