JPS6329737A - Optical wavelength selecting element - Google Patents

Abstract

PURPOSE:To make incident light again incident on an optical resonator even if the polarized state o the incident light intersects the oriented direction of liquid crystal so as to realize variable selecting operations, by installing an optical rotator having a reflecting layer in part of the plate of incident light. CONSTITUTION:Two base plates 1, on which ferroelectric multilayer film filters 2, transparent electrodes 3, and orientation processing agent layers 4 are succes sively formed, respectively, are arranged in a state where the layers 4 are faced to each other and liquid crystal 5 is enclosed between the base plates 1. The two filters 2 form an optical resonator. A Farady rotator 12 and reflecting mirror 11 which provide a rotation of 45 deg.+90 deg.Xk (k: an integer) to transmitted light are formed on the base plate 1 on the incident side of optical signals. When such constitution is used, incident light is made incident to a light receiving system 9 through an incident-light fiber 7, lens system 8, and optical resonator. The light reflected by the optical resonator is passed the rotator 12 twice after it is reflected by the mirror 11. Therefore, the light is again made incident to the resonator, with its polarized direction being turned by 90 deg.+180 deg.Xk. Nonselected optical signals are emitted from the rotator 12 after the above-mentioned reflection is repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used as a duplexer or filter for optical communication equipment. In particular, the present invention relates to an optical wavelength selection element that selects and outputs an optical signal of a predetermined wavelength from wavelength-multiplexed optical signals.

[Conventional technology]

FIG. 10 is a diagram showing an example of a conventional optical wavelength selection element that selectively outputs an optical signal of a predetermined wavelength from optical signals wavelength-multiplexed using an optical resonator (Japanese Patent Application No. 19685-1982). "Optical wavelength selection element").

The optical wavelength selection element shown in FIG. 10 has an optical resonator configured by opposing mirrors made of a dielectric multilayer filter 2 fabricated on a transparent fused silica glass substrate 1, and has optical properties ( The structure is such that liquid crystal 5 whose refractive index changes is sealed. Reference number 3 is a transparent electrode, reference number 6
is a power source connected to the transparent electrode 3 and applying an electric field to the liquid crystal 5. Reference number 4 is an alignment agent that determines the orientation direction of the liquid crystal 5, and the liquid crystal 5 is given parallel alignment in the same direction on the remelted silica glass substrate 1 by the alignment agent 4. The optical signal is input from the input optical fiber 7 via the lens system 8, and the optical signal output from the optical wavelength selection element is input to the light receiving system 9.
is incident on the

With such a configuration, the liquid crystal 5 uses the fact that the optical path length changes depending on the applied voltage and its resonant frequency changes, so that among the optical signals incident in the form of a beam, the optical signal with the resonant wavelength corresponding to the applied voltage is can be transmitted, and can be operated as a variable optical wavelength selection element.

[Problems to be Solved by the Invention] However, in such a conventional optical wavelength selection element, the variable optical wavelength can only be changed when the polarization state of the incident light is linearly polarized light in the same direction as the alignment direction of the liquid crystal 5. Operates as a selection element.

For example, when selectively outputting an optical signal with wavelength λ,
By appropriately setting the applied voltage when the polarization state of the incident optical signal and the alignment direction of the liquid crystal 5 are in the same direction,
Although the dielectric multilayer filter 2 can be transmitted through the optical resonator arranged facing each other (Fig. 1), when the alignment direction of the liquid crystal 5 is orthogonal to the polarization state of the incident light, Wavelength selectivity could not be obtained (12th
figure).

On the other hand, by making the optical signal enter through a polarizing plate,
There is a method to maintain the wavelength selectivity of the optical wavelength selection element by changing the polarization state of the incident light to linear polarization, but in actual optical signal transmission, the polarization state of the incident light varies greatly, and the polarization state may vary depending on the polarization state. Since the subsequent light intensity varies, signal components may be lost in the light intensity modulated optical signal. Furthermore, the technique of controlling polarization and converting incident polarized light into linearly polarized light involves control using a complicated optical system, and therefore has the problem of increased loss.

The present invention solves these conventional problems,
It is an object of the present invention to provide an optical wavelength selection element without polarization dependence.

[Means for solving problems]

In the present invention, an optical rotator is provided in a part of the incident side of the optical resonator, and a specific polarization state of the incident light is perpendicular to the orientation direction of the optically anisotropic medium. It is characterized by passing through an optical rotator and making it enter or re-enter the optical resonator.

That is, the first invention of the present invention provides an optical wavelength selection element in which an optically anisotropic medium is sealed inside an optical resonator and includes means for changing the voltage applied to the optically anisotropic medium according to a selected wavelength. An optical rotator having a reflective layer is attached to a part of the light incident surface of the optical resonator, and the non-attached part of the optical rotator is used as a light incident part.

The optical rotator is 45° + 90° x k (k
is an integer).

A second aspect of the present invention is an optical wavelength selection element in which an optically anisotropic medium is sealed inside an optical resonator and includes means for changing the voltage applied to the optically anisotropic medium according to a selected wavelength. A polarization splitting element is provided on the light incidence surface of the optical resonator, and between the polarization splitting element and the optical resonator, one polarized light separated by the polarization splitting element is provided with a polarized light that is the same as the other polarized light. It is characterized by the insertion of an optical rotator that changes the polarization state.

The optical rotator is 90°+180”xk(
It is preferable to have a structure that provides rotation (k is an integer).

[For production]

In the first aspect of the present invention, an optical rotator having a reflective layer is attached to a part of the incident surface of an optical resonator, and an optical signal is made incident at a predetermined angle of incidence from the non-attached part. When the polarization state of the light is parallel to the orientation direction of the optically anisotropic medium, the wavelength selectivity of the optical resonator enables variable selection operation, and the polarization state of the incident light is parallel to the orientation direction of the optically anisotropic medium. If the beam is perpendicular to the orientation direction of the beam, it passes through an optical rotator having a reflective layer and re-enters the optical resonator, thereby enabling a variable selection operation.

In the second aspect of the present invention, the incident light is separated by a polarization separation element into a polarization component that is variably selected and a polarization component that is not variably selected, and the light of the polarization component that is not variably selected is transmitted through an optical rotator. By rotating and injecting the optical resonator into the optical resonator, variable selection operation can be made possible.

Note that in the first aspect of the present invention, the polarization separation element is not required by utilizing the polarization separation function that the light valve oscillator itself has.

As described above, the first invention and the second invention of the present invention can eliminate the polarization dependence of the optical wavelength selection element without causing optical power loss.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram showing a first embodiment of the first invention of the present invention. In FIG. 1, the arrangement of a fused silica glass substrate 1, a dielectric multilayer filter 2, a transparent electrode 3, an alignment agent 4, a liquid crystal 5, and a power source 6 is the same as in the conventional structure, and they are arranged facing each other. The two dielectric multilayer filters 2 constitute an optical resonator. The incident light enters the optical resonator at a predetermined angle of incidence via the incident optical fiber 7 and the lens system 8, and a light receiving system 9 is provided at an opposing position.

The first feature of the present invention is that a reflecting mirror 1) is provided on the fused silica glass substrate 1 on the incident side of the optical signal, and a mirror 1) is provided on the fused silica glass substrate 1 on the incident side of the optical signal.
It has a configuration in which a Faraday rotator 12 that gives a rotation of 90°Xk (k is an integer) is attached.

That is, among the incident light, the light reflected by the optical resonator formed by the opposing dielectric multilayer filters 2 passes through the Faraday rotator 12, is reflected by the reflecting mirror 1), and passes through the Faraday rotator 12 again. and guided into an optical resonator. Therefore, the light reflected by the optical resonator passes twice through the Faraday rotator 12 at 45°+90°×, thereby having its polarization rotated by 90°+180″xk, and enters the optical resonator again.

Here, if the polarized light is reflected again when re-entering the optical resonator after being rotated to 90° + 180°, the light is not reflected based on the polarization state, but is reflected due to the voltage applied to the liquid crystal 5. Since this is a selective optical signal, even if this light is subsequently incident on the optical resonator, it will simply be reflected repeatedly. In order to prevent such repeated incidence, it is preferable to make the size of the reflecting mirror 1) smaller than the size of the Faraday rotator 12.

The ratio is determined by the size of the optical wavelength selection element, the angle of incidence of the incident beam, and the size of the spot.

In this way, the size of the reflecting mirror 1) can be changed to the Faraday rotator 1
Although it would be ideal to make it smaller than the size of 2,
It is not necessarily limited to this.

FIG. 2 and FIG. 3 are configuration diagrams showing a second embodiment and a third embodiment of the first aspect of the present invention.

The second and third embodiments shown in FIGS. 2 and 3 are configuration examples in which a reflecting mirror 1) is attached to the entire surface of the Faraday rotator 12 in order to facilitate manufacturing. In particular, in the third embodiment shown in FIG.
Since the Faraday rotation photon 12 having the reflecting mirror 1) is pasted on the entire surface of the mirror 1) and the part into which the optical signal is incident is cut through, the manufacturing becomes extremely easy.

4 to 6 are diagrams for explaining the first aspect of the present invention in detail. The operation will be explained below using the first embodiment.

When polarized light (wavelength λ,) in the same direction as the alignment direction of the liquid crystal 5 is incident, the applied voltage is set appropriately to selectively output the light with wavelength λ1, which is similar to the conventional optical wavelength selection element. can be selected by passing it through the dielectric multilayer filter 2 (FIG. 4).

When polarized light (wavelength λI) in a direction perpendicular to the alignment direction of the liquid crystal 5 is incident, the applied voltage is appropriately set to change the wavelength λ,
When selectively outputting the light of Since the polarized light is rotated by 90°+180°×k, it becomes polarized in the same direction as the alignment direction of the liquid crystal 5, and can be passed through the dielectric multilayer filter 2 and selected (FIG. 5).

In addition, when the applied voltage is set to non-select light with wavelength λ, the light reflected at the optical resonator part is returned to the optical resonator by the reflecting mirror 1), regardless of the polarization state of the incident light. Although the light is incident, it is reflected again and disappears to the outside, so that it is not selectively output (FIG. 6).

Here, the reflection path and transmission path of the optical signal shown in FIGS. 4 to 6 are model paths to simplify the explanation of the operation, and are composed of two dielectric multilayer filters 2 facing each other. The actual situation of reflected light and transmitted light by the optical resonator is as follows.

FIG. 7 is a diagram illustrating a situation in which light is reflected or transmitted by an optical resonator.

When light enters an optical resonator made up of two dielectric multilayer filters 2a and 2b facing each other, the light reflected by the dielectric multilayer filter 2a (A) and the dielectric multilayer filter 2
The light (7
)', light reflected by the dielectric multilayer filter 2b and transmitted through the dielectric multilayer filter 2a (a), light reflected by the dielectric multilayer filter 2a and transmitted through the dielectric multilayer filter 2b (a)', Similarly, the reflected light is (7), (a), ・
..., and the transmitted light becomes (a)', (b)',... Therefore, the light reflected by the optical resonator is the sum of (a), (b), . . . , and the transmitted light is the sum of (a)', (b)', .

FIG. 8 is a configuration diagram showing a first embodiment of the second invention of the present invention. In FIG. 8, the arrangement of a fused silica glass substrate 1, a dielectric multilayer filter 2, a transparent electrode 3, an alignment agent 4, a liquid crystal 5, and a power source 6 is the same as in the conventional configuration and the configuration example of the first invention. be.

The second aspect of the present invention is characterized by a configuration in which a polarization splitting element 21 and a Faraday rotator 22 that provides a rotation of 90° + 180° are provided on the fused silica glass substrate 1 on the incident side of the optical signal. be. Reference number 23 is a spacer (
transparent, uniform glass, etc.).

That is, the incident light enters the polarization separation element 21 and is separated into a polarization component that does not perform variable selection and a polarization component that does not perform variable selection, and the light of the polarization component that does not perform variable selection is separated by 90° + 180 The configuration is such that the light of the polarized component subjected to the variable selection operation is made to enter the optical resonator as it is through the spacer 23.

Therefore, when an optical signal is input into an optical resonator,
Since the polarized light is always variably selectively operated, an optical wavelength selection element can be constructed without depending on the polarization state of the incident light.

FIG. 9 is a configuration diagram showing a second embodiment of the second invention of the present invention.

The configuration of the second embodiment of the second invention shown in FIG. 9 is as follows:
In the configuration of the first embodiment shown in FIG. 8, a polarization splitting prism 25 is used as a polarization splitting element, and the separated light of the polarization component that does not operate is variably selected by a reflecting mirror 26 and a polarization splitting prism 25.
It is characterized in that the light is made incident on the optical resonator via a Faraday rotator 27 that gives a rotation of 180°.

Here, an example of the dimensions of the optical wavelength selection element of the present invention will be shown.

The diameter of the fused silica glass substrate 1 is 30 mm, and the thickness is lII.
Im, and the thickness of the dielectric multilayer filter 2 is approximately 1-1
The thickness of the transparent electrode 3 and the alignment treatment agent 4 is 1 μm each.
Hereinafter, the thickness of the liquid crystal 5 is 10-.

〔Effect of the invention〕

As explained above, the present invention enables variable selection operation by changing the applied voltage to an optically anisotropic medium (liquid crystal), and further enables wavelength selection regardless of the polarization state of incident light. Can be done. That is, it is possible to selectively output light of a predetermined wavelength from wavelength-multiplexed incident light without depending on its polarization state.

Therefore, the flexibility of the device can be increased, and it can be widely applied to optical signal processing equipment, optical switching equipment, construction of local area networks, etc. using optical demultiplexers and other devices using this device. be.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing a first embodiment of the first invention of the present invention. FIG. 2 is a configuration diagram showing a second embodiment of the first invention of the present invention. FIG. 3 is a configuration diagram showing a third embodiment of the first invention of the present invention. FIG. 4 is a diagram illustrating the operation of the first invention for selected wavelengths (polarized light incident parallel to the alignment direction). FIG. 5 is a diagram illustrating the operation of the first invention for selected wavelengths (polarized light incident perpendicular to the alignment direction). FIG. 6 is a diagram illustrating the operation of the first invention for non-selected wavelengths. FIG. 7 is a diagram illustrating a situation in which light is reflected or transmitted by an optical resonator. FIG. 8 is a configuration diagram showing a first embodiment of the second invention of the present invention. FIG. 9 is a configuration diagram showing a second embodiment of the second invention of the present invention. FIG. 10 is a diagram showing an example of a conventional optical wavelength selection element. Fig. 1) is a diagram explaining the operation of the conventional example for the selected wavelength (polarized light incident parallel to the alignment direction). FIG. 12 is a diagram illustrating the operation of the conventional example for selected wavelengths (polarized light incident perpendicular to the alignment direction). DESCRIPTION OF SYMBOLS 1... Fused silica glass substrate, 2... Dielectric multilayer film filter, 3... Transparent electrode, 4... Alignment treatment agent, 5...
...Liquid crystal, 6...Power source, 7...Incoming optical fiber, 8
...Lens system, 9...Light receiving system, 1)...Reflector,
12... Faraday rotator, 21... polarization separation element, 22... Faraday rotator, 23... spacer,
25...Polarization separation prism, 26...Reflector, 27
...Faraday rotation photon. Patent applicant: Nippon Telegraph and Telephone Corporation 2. -1 agent
Patent Attorney Nao Ide Takashi P. 17 Figure 2 First Embodiment of the Invention Figure 8 Second Invention Second Embodiment Figure 9

Claims (4)

[Claims] (1) An optical wavelength selection element in which an optically anisotropic medium is sealed inside an optical resonator and includes means for changing the voltage applied to the optically anisotropic medium according to a selected wavelength. An optical wavelength selection element characterized in that an optical rotator having a reflective layer is attached to a part of a light incident surface, and the non-attached part of the optical rotator is used as a light incident part. (2) Optical rotator is 45° + 90° x
The optical wavelength selection element according to claim (1), which has a structure that provides rotation k (k is an integer). (3) An optical wavelength selection element in which an optically anisotropic medium is sealed inside an optical resonator and includes means for changing the voltage applied to the optically anisotropic medium according to a selected wavelength. A polarization splitting element is provided on the light incidence plane, and an optical system is provided between the polarization splitting element and the optical resonator to make one polarized light separated by the polarization splitting element the same polarization state as the other polarized light. 1. An optical wavelength selection element characterized in that a optical rotator is inserted. (4) Optical rotator is 90° + 180° with respect to the passing light
The optical wavelength selection element according to claim (3), which has a structure that provides rotation xk (k is an integer).