JPH07218722A - Optical beam splitter - Google Patents

Abstract

PURPOSE:To provide a beam splitter which branches light of 1 to 6% of an incident angle 45 deg. with lower dependency on polarization. CONSTITUTION:This beam splitter has reflection sepn. films 6 which are composed of multilayered films formed by alternately depositing high-refractive index layers 2, 4 and low-refractive index layers 3, 5 both consisting of dielectric substances by evaporation and have no dependency on polarization corresponding to light of the incident angle 45 deg. on one surface of a transparent optical substrate 1 and antireflection films 11 which are composed of multilayered films formed by alternately depositing high-refractive index layers 7, 9 and low- refractive index layers 8, 10 consisting of dielectric substances by evaporation and correspond to the 45 deg. incident light on the other surface of the transparent optical substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam splitter used in an optical communication system, and more particularly to a beam splitter used to split monitor light from signal light of various devices in such a system.

[0002]

2. Description of the Related Art A beam splitter of this type extracts about 5% of light from a signal line in order to monitor the signal light. As this beam splitter, there is provided a beam splitter called BK-7 in which a dielectric film such as TiO2 or SiO2 is alternately deposited on a glass substrate.

[0003]

According to this structure, there is a problem that the optical branching characteristic has polarization dependency, and the amount of reflected light changes depending on the polarization state of the incident light. On the other hand, there are some that are designed to have a low polarization dependence, but there is a problem that the amount of transmitted light to the amount of reflected light is 1: 1 to 1:10 and the branching ratio is so large that it is not suitable for monitor branching. .

Here, another condition that the beam splitter should have is that it is desirable to form branched light which is obtained by reflecting light having an incident angle of 45 ° at a right angle.

The present invention has been made in consideration of the above points, and an object of the present invention is to provide a beam splitter which splits 1% to 6% of light having an incident angle of 45 ° with low polarization dependence. To do.

[0006]

To achieve the above object, in the present invention, a high refractive index layer and a low refractive index layer, both made of a dielectric material, are alternately formed on one surface of a transparent optical substrate according to claim 1. A non-polarization-dependent reflection separation film which is composed of a vapor-deposited multilayer film and corresponds to light having an incident angle of 45 °, and a high refractive index layer and a low refractive index layer made of a dielectric material on the other surface of the transparent optical substrate. 3. A beam splitter provided with an antireflection film corresponding to 45 ° incident light, which is constituted by a multilayer film in which and are alternately deposited, and the reflection separation film in the beam splitter according to claim 1 is a high beam splitter. TiO2 is used as a material for forming the refractive index layer, and SiO2 is used as a material for forming the low refractive index layer. TiO2: 0.0
7λ to 0.11λ, SiO2: 0.08λ to 0.19
λ, TiO2: 0.25λ to 0.29λ, SiO2:
The beam splitter configured by stacking at least four layers so as to have an optical film thickness of 0.28λ to 0.31λ, and the antireflection film in the beam splitter according to claim 3 having a high refractive index. TiO2 as the material for forming the low refractive index layer, and SiO2 as the material for forming the low refractive index layer, TiO2: 0.1.lambda.
11λ, SiO2: 0.08λ to 0.10λ, TiO2
: 0.25λ to 0.27λ, SiO2: 0.28λ to
The present invention provides a beam splitter composed of at least four layers stacked so that the optical film thickness becomes 0.31λ.

[0007]

According to the structure of claim 1, a part of the light incident at an incident angle of 45 ° with respect to the reflective separation film disposed on one surface of the transparent optical substrate is reflected and separated in the right angle direction, and most of the light is separated. It penetrates through the transparent optical substrate. The light incident on the substrate passes through the antireflection film provided on the other surface of the transparent optical substrate and is emitted. The reflected and separated light and the transmitted and emitted light are both reflected by the reflection / separation film having a low polarization dependence or transmitted through such an antireflection film, so that the predetermined light is output regardless of the polarization state of the incident light. Output light is obtained.

According to a second aspect of the present invention, the reflective separation film is formed of at least 4 layers each of which has a predetermined thickness of TiO2 and SiO2.
By configuring each layer of the film,
6% is branched.

According to a third aspect of the present invention, the antireflection film is formed of at least 4 layers of TiO2 and SiO2 each having a predetermined thickness.
Reflection of the amount of incident light is reduced by constituting each film of the layer.

[0010]

1 is a view showing the sectional structure of a beam splitter according to the present invention. In the figure, 1 is a transparent optical substrate, for example, a glass substrate called BK-7. On one surface of the substrate 1, a reflection separation film 6 in which two layers of TiO2 and SiO2 are alternately stacked is arranged, and on the other surface of the substrate 1 in the same manner, two layers of TiO2 and SiO2 are alternately stacked to prevent reflection. The membrane 11 is arranged. Each of these films 6 and 11 has TiO2 on the side in contact with the substrate 1, and the other is SiO
Stagger with 2 In the case of FIG. 1, the outermost layer is SiO2 because it has a four-layer structure.

FIG. 2 shows the optical branching action of the beam splitter thus constructed. When a signal light having a wavelength of 1550 nm is incident from the left side in the figure at an angle of 45 °, 5% of the incident light is reflected by the reflective separation film 6 of the beam splitter in a direction perpendicular to the incident direction. This reflected light is used to monitor the signal light.

95% of the remaining signal light is refracted by the reflection separation film 6 and enters the beam splitter, passes through the substrate 1 and the antireflection film 11 and is refracted on the surface of the antireflection film 11 to be incident to the incident direction. Emit in parallel directions.

FIGS. 3 to 8 show wavelength-to-reflectance characteristics of the beam splitters having the reflection branching ratios of 1, 2, 3, 4, 5 and 6%, respectively, and the center wavelength is 15
It is 50 nm.

First, the characteristic of FIG. 3 is that of a beam splitter having a reflection characteristic of 1%. In this embodiment, BK-7 having a refractive index of about 1.51 is used as a substrate, and TiO2 having a refractive index of 2.25 and SiO2 having a refractive index of 1.46 are provided on one surface thereof.
Are alternately arranged to form four layers. The first layer has an optical film thickness of 0.0978 with respect to light having a wavelength of 1550 nm.
λ, the second layer has the same 0.1050λ, the third layer has the same 0.2672λ, and the fourth layer has the same 0.2838λ.

The characteristic of FIG. 4 is that of a beam splitter having a reflection characteristic of 2%. In this embodiment, BK-7 having a refractive index of about 1.51 is used as a substrate, and TiO2 having a refractive index of 2.25 and SiO2 having a refractive index of 1.46 are alternately arranged on one surface to form four layers. And the first layer has wavelength 1
The optical film thickness for light of 550 nm is 0.0927λ, the second layer is 0.1285λ, and the third layer is 0.26.
72λ, and the fourth layer has the same thickness of 0.2838λ.

The characteristic of FIG. 5 is that of a beam splitter having a reflection characteristic of 3%. In this embodiment, BK-7 having a refractive index of about 1.51 is used as a substrate, and TiO2 having a refractive index of 2.25 and SiO2 having a refractive index of 1.46 are alternately arranged on one surface to form four layers. And the first layer has wavelength 1
The optical film thickness for light of 550 nm is 0.0878λ, the second layer is 0.1465λ, and the third layer is 0.26.
72λ, and the fourth layer has the same thickness of 0.2838λ.

The characteristic of FIG. 6 is that of a beam splitter having a reflection characteristic of 4%. In this embodiment, BK-7 having a refractive index of about 1.51 is used as a substrate, and TiO2 having a refractive index of 2.25 and SiO2 having a refractive index of 1.46 are alternately arranged on one surface to form four layers. And the first layer has wavelength 1
The optical film thickness for light of 550 nm is 0.0838λ, the second layer is 0.1635λ, and the third layer is 0.26.
72λ, and the fourth layer has the same thickness of 0.2838λ.

The characteristic of FIG. 7 is that of a beam splitter having a reflection characteristic of 5%. In this embodiment, BK-7 having a refractive index of about 1.51 is used as a substrate, and TiO2 having a refractive index of 2.25 and SiO2 having a refractive index of 1.46 are alternately arranged on one surface to form four layers. And the first layer has wavelength 1
The optical film thickness for light of 550 nm is 0.0790λ, the second layer is 0.1790λ, and the third layer is 0.26.
72λ, and the fourth layer has the same thickness of 0.2838λ.

The characteristic of FIG. 8 is that of a beam splitter having a reflection characteristic of 6%. In this embodiment, BK-7 having a refractive index of about 1.51 is used as a substrate, and TiO2 having a refractive index of 2.25 and SiO2 having a refractive index of 1.46 are alternately arranged on one surface to form four layers. And the first layer has wavelength 1
The optical film thickness for light of 550 nm is 0.0810λ, the second layer is 0.1867λ, and the third layer is 0.27.
87λ, and the fourth layer has 0.2813λ.

FIG. 9 shows B used as a substrate in the above embodiment.
It shows the relationship between the incident angle and the reflectance in a glass material called K-7. Looking at a certain polarization plane Rp in this glass material, the reflectance becomes 0% at about 56 °, and the reflectance increases sharply after passing from 0% at 56 ° to a reflectance of about 4% at 0 °. It is a characteristic to do. And, at an incident angle of 45 °, it is about 1% or less. On the other hand, looking at the plane of polarization Rs perpendicular to the plane of polarization Rp, the point is about 4% at an incident angle of 0 °, which is similar to Rp, but the reflectance increases as the incident angle increases. At an incident angle of 45 ° used as a beam splitter, Rp is approximately 1% and Rs is approximately 10%.

FIG. 10 shows the characteristics when the BK-7 material having such characteristics is combined with the low polarization dependent 5% separation reflection film according to the present invention. That is, the reflectance characteristic in this case is such that both Rp and Rs are exactly in the middle of those in FIG. 9, and the reflectance is just 5% at an incident angle of 45 °.

Therefore, it is possible to take out exactly 5% of the signal light for the monitor.

[0023]

Since the present invention is configured as described above, it has various effects.

According to the structure of the first aspect, the reflective separation film and the antireflection film disposed on each surface of the transparent optical substrate are alternately formed of a high refractive index layer and a low refractive index layer made of a dielectric material. Since it is composed of a vapor-deposited multilayer film, it is possible to provide a beam splitter that has almost no polarization dependence and has an appropriate branching ratio for a monitor.

According to the second aspect of the present invention, since each layer of the reflection separation film is formed of at least four layers of TiO2 and SiO2 having a predetermined film thickness, in addition to low polarization dependence, A branching rate of% can be achieved.

Further, according to the third aspect of the invention, since each layer of the antireflection film is composed of at least four layers of TiO2 and SiO2 having a predetermined film thickness, reflection is reduced in addition to low polarization dependence. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a sectional structure of a beam splitter according to the present invention.

FIG. 2 is a diagram showing an optical branching action of a beam splitter according to the present invention.

FIG. 3 is a diagram showing a wavelength vs. reflectance characteristic of a beam splitter having a reflection characteristic of 1%.

FIG. 4 is a diagram showing a wavelength vs. reflectance characteristic of a beam splitter having a reflection characteristic of 2%.

FIG. 5 is a diagram showing a wavelength vs. reflectance characteristic of a beam splitter having a reflectance characteristic of 3%.

FIG. 6 is a diagram showing a wavelength vs. reflectance characteristic of a beam splitter having a reflectance characteristic of 4%.

FIG. 7 is a diagram showing a wavelength vs. reflectance characteristic of a beam splitter having a reflectance characteristic of 5%.

FIG. 8 is a diagram showing a wavelength vs. reflectance characteristic of a beam splitter having a reflectance characteristic of 6%.

FIG. 9 is a characteristic diagram showing a relationship between an incident angle and a reflectance in a glass material called BK-7.

FIG. 10 is a low polarization-dependent 5 according to the present invention for BK-7 material.
The figure which showed the characteristic at the time of combining a% separation reflective film.

[Explanation of symbols]

 1 Substrate 2 TiO2 3 Si02 2 TiO2 5 Si02 6 Reflection Separation Film 7 TiO2 8 Si02 9 TiO2 10 Si022 11 Antireflection Film

Claims (3)

[Claims] 1. A low polarization dependence corresponding to light having an incident angle of 45 °, which is composed of a multilayer film in which a high refractive index layer and a low refractive index layer both made of a dielectric are alternately deposited on one surface of a transparent optical substrate. Reflective separation film, and a reflection film corresponding to 45 ° incident light, which is composed of a multilayer film in which a high refractive index layer and a low refractive index layer made of a dielectric are alternately deposited on the other surface of the transparent optical substrate. Beam splitter with each prevention film. 2. The beam splitter according to claim 1, wherein the reflective separation film is made of T as a material forming a high refractive index layer.
SiO2 is used as a material for forming the low refractive index layer.
2 sequentially from the substrate side: TiO2: 0.07λ to 0.11
λ, SiO2: 0.08λ to 0.19λ, TiO2:
0.25λ to 0.29λ, SiO2: 0.28λ to 0.
A beam splitter formed by stacking at least four layers so as to have an optical film thickness of 31λ. 3. The beam splitter according to claim 1, wherein the antireflection film is made of T as a material forming a high refractive index layer.
SiO2 is used as a material for forming the low refractive index layer.
2 sequentially from the substrate side TiO2: 0.1λ to 0.11
λ, SiO2: 0.08λ to 0.10λ, TiO2:
0.25λ to 0.27λ, SiO2: 0.28λ to 0.
A beam splitter formed by stacking at least four layers so as to have an optical film thickness of 31λ.