JPH11142896A - Variable branching ratio type optical branching device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To be able to change a light branching ratio steplessly and to improve the branching ratio accuracy. SOLUTION: A bidirectional birefringent material layer has a unidirectional periodic structure by alternate repetition, and a polarized light of 45 ° with respect to the periodic repetition direction feels a difference in the refractive index of each layer, and a polarized light perpendicular to this is. In order to avoid the difference in the refractive index of each layer,
The structure birefringent element 2 configured by selecting the refractive index and the orientation direction of the birefringent material layer of the type, and the outgoing light L2 of the structural birefringent element 2 disposed on the emission side of the structure birefringent element 2 S
A polarization splitting element 3 that separates the polarized light Ls and the P-polarized light Lp and guides the S-polarized light Ls and the L-polarized light Lp to the emission units 3a and 3b, respectively. By changing the angle, the incident light L1
Can be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable branching ratio type optical branching device capable of branching the power of incident light with a variable branching ratio.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional branching ratio variable type optical branching device 100 disclosed in JP-A-1-116523. The optical branching device 100 couples an optical coupling portion 101a of an optical fiber coupler 101 made by fusing, polishing, or bonding a part of two single mode optical fibers to a temperature / temperature.
Substance 102 whose refractive index changes according to a physical quantity such as pressure
, And the periphery thereof is covered with a heater 103.

According to the optical branching device 100, the amount of heat generated from the heater 103 is controlled by changing the voltage of the power supply 104, and when the temperature around the optical coupling portion 101a changes, the refractive index of the optical coupling portion 101a changes. Then, the light coupling state between the two cores changes, and is finally observed as a change in the light branching ratio.

Another similar technique is disclosed in Japanese Patent Application Laid-Open No. 2-31804.
No. 6,086,045.

[0005]

However, the optical branching device 100 has a problem that it is difficult to precisely control the refractive index of the optical coupling portion 101a, and it is difficult to obtain an accurate light branching ratio.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a variable branching ratio type optical branching device capable of changing the branching ratio of light steplessly and improving the branching ratio accuracy. .

[0007]

In order to achieve the above object, the invention according to claim 1 has a unidirectional periodic structure in which two types of birefringent material layers are alternately repeated, and is formed at 45 ° with respect to the periodic repetition direction. Of the two types of birefringent material layers are selected so that polarized light perceives the difference in the refractive index of each layer, and polarized light perpendicular thereto does not perceive the difference in the refractive index of each layer. Structural birefringent element provided rotatably around the incident site, with one of the two side surfaces exposed of each layer as the incident surface and the other as the exit surface, and the structural birefringent element A plurality of light-emitting portions disposed on the light-emitting side and opposed to the plurality of light-receiving portions; separating the light emitted from the structural birefringent element into S-polarized light and P-polarized light; And a polarization separation element for guiding light to each It is characterized in.

Therefore, according to the first aspect of the present invention, incident light having a random polarization component can be converted into emission light having only one-way polarization component by making it incident on the structural birefringent element. By adjusting the rotation angle of the birefringent element, it is possible to convert the birefringent element into emission light having a polarization component in an arbitrary direction. These conversions can be performed with almost no light energy loss by using a structural birefringent element.

The incident light that has entered the structural birefringent element is interconverted between S-polarized light and P-polarized light according to the set rotation angle of the element, and then exits the element and enters the polarization splitting element. . Further, the S-polarized light and the P-polarized light that have entered the polarization splitting element are separated in the same element, guided to each of the plurality of emission sections, and emitted from each emission section to the opposing light receiving section.
The branching ratio of the power of the light emitted to each light receiving section can be changed steplessly by the stepless change of the rotation angle of the structural birefringent element, and the set rotation angle of the structural birefringent element. Can be determined accurately.

According to a second aspect of the present invention, there is provided a variable branching ratio type optical branching device according to the first aspect, wherein the structural birefringent element is one of two types of birefringent material layers. The layer has a thickness t1, a refractive index n01 for each component of ordinary light and extraordinary light.
And ne1 and the optical axis are set to 45 with respect to the period repetition direction.
And the other material layer has a thickness t2, a refractive index n0 for each component of ordinary light and extraordinary light.
2 and ne2, and the optical axis are set to be oriented at 90 ° to the optical axis of the one material layer, and t1 + t2ｔλ (where λ: wavelength of incident light) n01 = ne2, n02 ≠ ne1 Δnd = λ / 2 (where Δn = | nper−npar |, npe
r: a refractive index in a direction perpendicular to the periodic repetition direction, and npar: a refractive index in a direction parallel to the periodic repetition direction).

According to the second aspect of the present invention, the extraordinary light component of the incident light passes through the structural birefringent element to be emitted as an ordinary light component, thereby obtaining a single linearly polarized light. it can. Therefore, by adjusting the rotation angle of the structural birefringent element, incident light can be converted into outgoing light consisting of linearly polarized light directed in an arbitrary direction, and this outgoing light is converted into S-polarized light and P-polarized light by the polarization splitting element. If the light is separated, the power of the incident light can be split into a plurality of emission portions of the polarization splitting element at an arbitrary split ratio.

According to a third aspect of the present invention, there is provided the optical splitting device of the first or second aspect, wherein the polarization splitting element includes a Savart plate, a polarizing beam splitter, a Rochon prism, and a wollaston. It is characterized by being constituted by a polarization splitting element which does not involve the absorption of one-sided polarized light, such as a ton prism and a Ramipole element.

Therefore, according to the third aspect of the present invention, the degree of freedom in design is increased because the polarization splitting element can be selected from various types of polarization splitting elements that do not involve the absorption of one-sided polarized light.

According to a fourth aspect of the present invention, there is provided an optical branching device according to any one of the first to third aspects, wherein the light receiving section is provided at an input end of an optical fiber. It is a fiber collimator.

Therefore, in the invention according to claim 4, the light emitted from the emission part of the polarization splitting element is transmitted from the fiber collimator to the optical fiber.

[0016]

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

FIG. 1 shows a variable branching ratio type optical branching device 1 according to a first embodiment of the present invention. This optical branching device 1
It is roughly composed of a structural birefringent element 2 provided on the incident side and a polarization splitting element 3 provided on the output side.

The structural birefringent element 2 has a unidirectional periodic structure in which two types of birefringent material layers are alternately repeated, and polarized light of 45 ° with respect to the periodic repetition direction feels a difference in the refractive index of each layer. And it is constituted by selecting the refractive index and the orientation direction of the two types of birefringent material layers so that the polarized light perpendicular to this does not feel the difference in the refractive index of each layer, One of them is an incident surface 2a and the other is an output surface 2b, and is provided rotatable about an incident part 2c.

In the structural birefringent element 2, specifically, as shown in FIG. 3A, one of the two types of birefringent material layers A and B has a thickness t1, an ordinary light and an ordinary light. The refractive indices n01 and ne1 for each component of the extraordinary light and the optical axis a are set to be oriented at 45 ° with respect to the periodic repetition direction C, and the other material layer B has a thickness t2, ordinary light and The refractive indices n02 and ne2 for each component of the extraordinary light, and the optical axis b are set to be oriented at 90 ° with respect to the optical axis a of the one material layer A, and t1 + t2≪λ (where, λ: wavelength of incident light L1) n01 = ne2, n02 ≠ ne1 Δnd = λ / 2 (where Δn = | nper−npar |, npe
r: refractive index in the direction perpendicular to the periodic repetition direction C, npar:
(The refractive index in the direction parallel to the periodic repetition direction C). Where nper,
npar can be expressed by the following equation.

Nper = {(1 / ne1 ² ) t1 + (1 / n02 ² ) t2} ^1/2 npar = {ne1 ² t1 + n02 ² t2} ^1/2 And this structural birefringent element 2 has a cubic shape as a whole. The upper surface in FIG. 3A is used as an incident surface 2a, and the lower surface is used as an output surface 2b.

The thus structured birefringent element 2
According to the above, when the light wave is perpendicularly incident on the incident surface 2a, each polarization component of the incident light L1 has two types of birefringent material layers A and B.
You will feel the average refractive index. That is, FIG.
As shown in (b), the extraordinary light component D is transmitted while maintaining the polarization component as it is because the refractive indexes of the birefringent material layers A and B are set to n01 = ne2. On the other hand, the ordinary light component E has a refractive index n with respect to the birefringent material layer B.
02, to feel the refractive index ne1 with respect to the birefringent material layer A,
Refractive index npe of component F in a direction perpendicular to periodic repetition direction C
The refractive index npar of the component G in the direction parallel to r is different. Therefore, the extraordinary light component D propagates in the structural birefringent element 2 while changing the polarization state.

This structural birefringent element 2 further has Δnd =
Since it is set to λ / 2, the extraordinary light component D becomes an ordinary light component and exits the structural birefringent element 2. Therefore, the structural birefringent element 2 can convert the incident light L1 having a random polarization component into a single linearly polarized light (ordinary light component) and emit it without any energy loss of light.
By adjusting the rotation angle of, linearly polarized light directed to an arbitrary direction can be obtained.

This structural birefringent element 2 can be manufactured, for example, by the following method.

That is, a nematic liquid crystal having a refractive index of 1.6 for extraordinary light and a refractive index of 1.3 for ordinary light was heated on a substrate glass while applying an electric field of 45 ° to the periodic repetition direction C while heating the liquid crystal. After orienting the molecules, the molecules are cooled to room temperature and solidified, and the periodic structure of the birefringent material layer A is formed using X-ray lithography and anisotropic etching. Next, a nematic liquid crystal having a refractive index of 1.9 with respect to extraordinary light and a refractive index of 1.6 with respect to ordinary light is sealed between the periodic structures of the birefringent material layer A while being heated. After applying an electric field of −45 ° to align the liquid crystal molecules, the periodic structure of the birefringent material layer B is formed in the same manner as the birefringent material layer A. Then, the structural birefringent element 2 can be obtained by covering the exposed surfaces of the birefringent material layers A and B with a cover glass. This structural birefringent element 2
Preferably, an anti-reflection film is formed on the outer surfaces of the substrate glass and the cover glass to be the entrance surface 2a and the exit surface 2b.

The polarization splitting element 3 is disposed on the output side of the structural birefringent element 2 and is provided at one incident portion 3c and two light receiving portions 4a and 4b where the light L2 emitted from the structural birefringent element 2 enters. And two light emitting portions 3a and 3b facing each other.
Is separated into S-polarized light Ls and P-polarized light Lp, and the S and P-polarized light Ls and Lp are respectively separated into two emission portions 3a and 3b.
, And a polarization beam splitter that guides the light to each of the two. The polarization splitting element 3 is preferably provided with the emission sections 3a, 3
An anti-reflection film is formed on b and the incident part 3c.

Further, two light receiving sections 4a and 4b are provided at the respective input ends of the optical fibers 5a and 5b, and are provided at the output sections 3a and 3b.
Are constituted by fiber collimators provided opposite to each other.

In the optical branching device 1 configured as described above, the incident light L 1 having a random polarization component is incident on the structural birefringent element 2, and becomes S-polarized light and P-polarized light in accordance with the set rotation angle of the element 2. Same element 2 after being interconverted between polarized light
(Emitted light L2) and enters the polarization separation element 3. The outgoing light L2 enters the polarization separation element 3 from the entrance 3c and is separated into S-polarized light Ls and P-polarized light Lp.
The polarized light Ls is reflected by the polarized light separating film 3d and is guided to the emission portion 3a, and the P-polarized light Lp is transmitted through the polarized light separating film 3d and guided to the emitting portion 3b. Then, the S-polarized light Ls and the P-polarized light Lp emitted from the emission units 3a and 3b to the outside of the polarization splitter 3 enter the light receiving units 4a and 4b, respectively.
b, a parallel light beam is efficiently propagated through the optical fibers 5a and 5b and output as outgoing lights L3 and L4, respectively.

FIG. 4 shows the input / output characteristics of the optical branching device 1. FIG. 4 ignores the loss due to the reflection and absorption of each component of the optical branching device 1 as being small, and the straight line α indicates L4 / L1, the straight line β indicates L3 / L1, and L4 / L1 + L3. / L1 = 1 holds. As is clear from FIG. 4, when the structural birefringent element 2 is rotated once, the rotation angles are 0 °, 180 °, 360 °.
Thus, the outgoing light L2 of the same element 2 becomes only the P-polarized light Lp, and the incident light L1 is output as 100% outgoing light L4, and the rotation angle is 90.
At 270 °, the outgoing light L2 of the element 2 becomes only S-polarized light Ls, and the incident light L1 is output as 100% outgoing light L3. When the rotation angle is other than the above-mentioned angle, the outgoing light L2 of the structural birefringent element 2 contains the S-polarized light Ls and the P-polarized light Lp at a ratio according to the set rotation angle of the structural birefringent element 2. L1 is the outgoing light L3 and L4 branched according to the above ratio.
Output as

As described above, the light branching device 1 can change the branching ratio of the incident light L1 steplessly by changing the rotation angle of the structural birefringent element 2 steplessly, and can change the branching ratio. Since the ratio can be accurately determined in accordance with the set rotation angle, a 1 (input) x 2 (output) variable branch ratio type with improved branch ratio accuracy is provided.

Moreover, the optical branching device 1 can not only obtain the incident light L1 as the outgoing light L3 and L4 having a predetermined branching ratio without loss of light energy by the structural birefringent element 2, but also obtain the structural birefringence. By forming an anti-reflection film on the refractive element 2 and the polarization splitting element 3, light loss can be further suppressed, so that the branching ratio accuracy can be further improved.

FIG. 2 shows an optical branching device 10 with a variable branching ratio according to a second embodiment of the present invention. This optical branching device 10
Differs only in that two structural birefringent elements are used,
The other configuration is the same as that of the variable branching ratio type optical branching device 1 described above. For this reason, the same components are denoted by the same reference numerals, and detailed description is omitted.

That is, the polarization splitting element 3 in the optical branching device 10 includes two emission parts 3a and 3b and two incidence parts 3c and
3e, and the two structural birefringent elements 2 and 20 are arranged so as to face two incident portions 3c and 3e of the polarization splitting element 3, respectively. . At this time, the polarization splitting element 3 is formed by forming the remaining one side of the same polarization beam splitter as the light splitting device 1 in the incident portion 3e, and the structural birefringent element 20 is the same as the structural birefringent element 2. Like the structural birefringent element 2, it is provided so as to be rotatable about the incident portion 20c. At this time, preferably, the entrance surface 20a and the exit surface 20 of the structural birefringent element 20 are used.
An anti-reflection film is formed on b and the incident part 3e of the polarization separation element 3.

The incident light L10 passing through the structural birefringent element 20 is processed in the same manner as the incident light L1 passing through the structural birefringent element 2. That is, the incident light L10 enters the structural birefringent element 20, and after being mutually converted between S-polarized light and P-polarized light in accordance with the set rotation angle of the element 20,
The light exits from 0 (emitted light L20) and enters the polarization separation element 3. The outgoing light L20 enters the polarization separation element 3 from the entrance 3e and is S-polarized Ls (shown by a double dashed line in FIG. 2) and P-polarized Lp.
(Indicated by a double solid line in FIG. 2) and S
The polarized light Ls is reflected by the polarized light separating film 3d and is guided to the emitting portion 3b, and the P-polarized light Lp is transmitted through the polarized light separating film 3d and guided to the emitting portion 3a. Then, the S-polarized light Ls and the P-polarized light Lp emitted from the emission units 3b and 3a to the outside of the polarization splitter 3 enter the light receiving units 4b and 4a, respectively, and enter the optical fibers 5b and 4b.
5a and output as outgoing lights L4 and L3, respectively. The branching ratio of the outgoing lights L4 and L3 to the incident light L10 can be changed by changing the rotation angle of the structural birefringent element 20. The input / output characteristics at this time are the same as the characteristics shown in FIG.

The S and P polarizations Ls and Lp of the incident light L1 passing through the structural birefringent element 2 are shown by one broken line and solid line in FIG. Output as L3 and L4.

The optical branching device 10 configured as described above
Can determine the branching ratio of the incident lights L1 and L10 independently by the rotation angles of the respective structural birefringent elements 2 and 20. According to the optical branching device 10, when the incident lights L1 and L10 have the same wavelength, the branching ratio of the added power can be freely changed. When the incident lights L1 and L10 have different wavelengths, respectively. Can be changed for the light having the wavelength of

The light branching device 10 can change the branching ratio of the incident lights L1 and L10 steplessly by changing the rotation angles of the structural birefringent elements 2 and 20 steplessly. Since the branching ratio can be accurately determined in accordance with the set rotation angle, a 2 (input) x 2 (output) branching ratio variable type with improved branching ratio accuracy is provided.

FIG. 5 shows one use form of the variable branching ratio type optical branching devices 1 and 10 described above. In this usage mode, the optical branching devices D, E, F, and G, each of which is composed of one of the variable branching ratio type optical branching devices 1 and 10, are connected in series via an optical fiber. Light receiving units d, e, f, g, and h are connected to E, F, and G, respectively (however, the light receiving units g and h are connected to the optical branching device G). According to this usage pattern, the incident light L to each of the light receiving units d, e, f, g, and h
The incident light L1 can be split so that d, Le, Lf, Lg, and Lh are equal.

In the above embodiments, the polarization splitting element 3 is constituted by a polarization beam splitter. However, the present invention is not limited to this, but includes a Savart plate other than a polarization beam splitter, a Rochon prism, a Wollaston prism, a Ramipole. The polarization splitting element can be configured by selecting from within a polarization splitting element that does not involve the absorption of one-sided polarized light, such as an element. In this case, the variable branching ratio type optical branching device can improve the branching ratio accuracy similarly to the above-described embodiment, and can freely select a polarization splitting element as a component according to the purpose of use. As a result, the degree of freedom in design is increased.

[0039]

As described in detail above, according to the present invention, the following effects can be obtained.

That is, according to the first aspect of the present invention,
The power splitting ratio of the output light to the incident light emitted to each light receiving unit can be changed steplessly with almost no energy loss of light due to the stepless change of the rotation angle of the structural birefringent element. It can be determined accurately according to the set rotation angle of the structural birefringent element, whereby the branching ratio accuracy can be improved.

According to the second aspect of the present invention, the condition is set such that the extraordinary light component of the incident light can be converted into the ordinary light component to obtain outgoing light composed of a single linearly polarized light. Since the birefringent element is designed, if the rotation angle of the structural birefringent element is adjusted, the incident light can be accurately converted into the outgoing light composed of linearly polarized light directed in an arbitrary direction. Accuracy can be improved.

According to the third aspect of the present invention, since the polarization splitting element can be selected from various types of polarization splitting elements that do not involve the absorption of one-sided polarized light, the degree of freedom in design can be increased. it can.

According to the fourth aspect of the present invention, the light emitted from the emission part of the polarization splitting element is efficiently transmitted as a parallel light beam to the optical fiber by the fiber collimator, thereby reducing the energy loss of the light. It can be suppressed as much as possible.

[Brief description of the drawings]

FIG. 1 is an operation explanatory view of a variable branching ratio type optical branching device as a first embodiment of the present invention.

FIG. 2 is an operation explanatory view of a variable branching ratio type optical branching device as a second embodiment of the present invention.

FIGS. 3A and 3B are explanatory views of the structure of a structural birefringent element used in the variable branching ratio type optical branching device of FIGS. 1 and 2, wherein FIG. 3A is a perspective view and FIG.

FIG. 4 is a characteristic diagram of the variable branching ratio type optical branching device of FIG. 1;

FIG. 5 is a schematic diagram showing one use mode of the present invention.

FIG. 6 is a schematic explanatory view of a conventional branching ratio variable type optical branching device.

[Explanation of symbols]

 Reference Signs List 1, 1 Variable branching ratio type optical branching device 2, 20 Structural birefringent element 2a, 20a Incident surface 2b, 20b Emissive surface 2c, 20c Incident site 3 Polarization separating element (polarizing beam splitter) 3a, 3b Emission unit 4a, 4b Light receiving section (fiber collimator) 5a, 5b Optical fiber A, B Birefringent material layer C Period repetition direction a, b Optical axis L1, L10 Incident light L2, L20 Outgoing light (of structural birefringent element) Ls S polarized light Lp P Polarization

Claims (4)

[Claims] 1. A bidirectional birefringent material layer having a unidirectional periodic structure formed by alternate repetition, wherein polarized light of 45 ° with respect to the periodic repetition direction senses a difference in the refractive index of each layer, and polarized light perpendicular to this. So that there is no difference in the refractive index of each layer.
The birefringent material layer is formed by selecting the refractive index and the orientation direction of each layer. A structural birefringent element provided so as to be provided, and a plurality of emission sections arranged on the emission side of the structural birefringence element and facing a plurality of light receiving sections, and the emitted light of the structural birefringence element is S-polarized. And P polarization, and S and P
A variable splitting ratio type optical splitting device, comprising: a polarization splitting element for guiding polarized light to each of the plurality of emission units. 2. The optical device according to claim 1, wherein the structural birefringent element has one of two types of birefringent material layers having a thickness of t1, ordinary light, and ordinary light. The refractive indices n01 and ne1 for each component of the extraordinary light, and the optical axis are set to be oriented at 45 ° with respect to the periodic repetition direction.
The other material layer B is set so that the thickness t2, the refractive indices n02 and ne2 for each component of ordinary light and extraordinary light, and the optical axis are oriented at 90 degrees to the optical axis of the one material layer. And t1 + t2≪λ (where λ: wavelength of incident light) n01 = ne2, n02ｎne1 Δnd = λ / 2 (where Δn = | nper−npar |, npe
r: a refractive index in a direction perpendicular to the periodic repetition direction; npar: a refractive index in a direction parallel to the periodic repetition direction). Branching device. 3. The optical branching device according to claim 1, wherein the polarization splitting element includes a Savart plate,
A variable splitting ratio type optical splitting device comprising a polarizing beam splitter, a Rochon prism, a Wollaston prism, a Ramipole element, and other polarization splitting elements that do not involve the absorption of single polarized light. 4. The branching ratio variable optical branching device according to claim 1, wherein the light receiving unit is a fiber collimator provided at an input end of an optical fiber. Variable branching type optical branching device.