JP2001021860A - Half-value width variable liquid etalon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal etalon which is capable of changing a half-value width, is capable of dealing with a change in the number of channels and is small in size. SOLUTION: This liquid crystal etalon is constituted by oppositely arranging substrates, each formed by laminating transparent electrodes 4, a reflection film 3 and a liquid crystal alignment layer 8 on a glass substrate 2, in such a manner the reflection surfaces of the reflection films 3 are paralleled to each other and sealing liquid crystals between the substrates. The reflection films 3 of the half width variable liquid crystal etalon described above are constituted by arraying plural reflection film pieces 3a to 3c varying in reflectivity and the reflection film pieces 3a to 3c of the same reflectivity are arranged to face each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal etalon, and more particularly to a liquid crystal etalon capable of changing a half-value width of transmitted light by using a WDM.
The present invention relates to a liquid crystal etalon suitable for (wavelength multiplexing) optical communication.

[0002]

2. Description of the Related Art In recent years, WDM optical communication systems have become widespread in order to increase the speed and capacity of information communication. In this WDM optical communication system, information is simultaneously transmitted from a transmitting side through an optical fiber using light of a plurality of wavelengths, and the receiving side selectively receives information by transmitting light of a specific wavelength through a wavelength selection filter. I do. One such wavelength selection filter is a liquid crystal etalon. As shown in FIG. 5, the liquid crystal etalon 10 has a pair of substrates in which a reflection film 12, a transparent electrode 13, and a liquid crystal alignment film 14 are sequentially formed on a glass substrate 11 so that the reflection films 12 are parallel to each other. Then, a space formed thereby is filled with a liquid crystal 15, sealed with a spacer 16 and a sealant 17, and a non-reflective film 18 is formed on the other surface of the glass substrate 11. The light enters from the anti-reflection film 18 of one substrate, passes through the liquid crystal 15, and is emitted from the anti-reflection film 18 of the other substrate. that time,
By applying a voltage between the transparent electrodes, the orientation of the liquid crystal 15 is changed to change the refractive index for incident light,
Select the transmitted light.

On the other hand, a so-called multi-channel transmission in which the number of channels to be multiplexed within a certain frequency range (the wavelength interval of light to be transmitted) is changed and transmitted is attempted. It is necessary to use different light, and at the same time, it is necessary to change the half value width of the transmitted light also in the wavelength selection filter. However, in the conventional liquid crystal etalon 10, the reflection film 12 is formed to have a uniform thickness, and its reflectance is constant. Therefore, the half width cannot be changed.
In order to support multi-channel transmission, a plurality of liquid crystal etalons 10 having different reflectivities of the reflection film 12 must be used. If the accuracy and stability of the wavelength of the light source on the transmitting side are not high, the wavelength and intensity of the light incident on the wavelength selection filter will vary. The strength needs to be compensated. However, the conventional liquid crystal etalon cannot cope with such a problem for the reasons described above.

As a technique for changing the half width of transmitted light, for example, Japanese Patent Laid-Open Publication No. Sho 51-94956 discloses an acousto-optic effect utilizing the interaction between ultrasonic waves and light. Describes a filter using anomalous Bragg diffraction in which are orthogonal to each other. In this acousto-optic filter, light is made incident on an acousto-optic element such as PbMoO ₄ in a state where ultrasonic waves are propagated. At this time, by changing the frequency of the ultrasonic wave propagated to the acousto-optic element, the diffraction state of the incident light is changed to emit light having different diffraction angles. Since the difference in the diffraction angle at this time corresponds to the difference in the half width, the half width can be controlled by the frequency of the ultrasonic wave.
However, this acousto-optic filter has a problem that the optical axis is different for each outgoing light, and thus there is a problem that a deviation from the optical axis of the optical fiber occurs and the transmission characteristic is largely changed, which is not suitable for actual use. Moreover, in this acousto-optic filter, the optical elements such as the lens and the slit must be arranged apart from the acousto-optic element, and the device becomes relatively large.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a small-sized liquid crystal etalon which can change the half width and can cope with a change in the number of channels. The purpose is to do.

[0006]

In order to achieve the above object, the present invention is directed to a method of forming a substrate comprising a glass substrate on which a transparent electrode, a reflective film and a liquid crystal alignment film are laminated, wherein the reflective surfaces of the reflective films are parallel to each other. And a liquid crystal etalon configured by sealing liquid crystal between the substrates, wherein the reflective film is configured by aligning a plurality of reflective film pieces having different reflectances, and Provided is a half-width variable liquid crystal etalon, wherein reflective film pieces having the same reflectance are arranged to face each other.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 shows one substrate 1 (hereinafter referred to as a liquid crystal etalon one-sided substrate) 1 constituting the liquid crystal etalon of the present invention. As shown in the figure, the liquid crystal etalon one-sided substrate 1 has a reflection film 3 and a liquid crystal alignment film 8 formed on one surface of a glass substrate 2 via a transparent electrode 4 and a non-reflection film 6 on the other surface. It is formed and formed. Then, a pair of the liquid crystal etalon single-sided substrates 1 are arranged facing each other so that the reflection surfaces of the reflection films 3 are parallel to each other as shown in FIG.
The space formed by this is filled with liquid crystal and sealed with a spacer and a sealant to form a liquid crystal etalon. Further, a lead wire for external connection (not shown) is connected to the transparent electrode 4. In the above description, any material may be used for forming each member, for example, a quartz plate can be used as the glass substrate 2, and the transparent electrode 4 may be a deposited film of ITO (indium tin oxide). it can. The liquid crystal is generally a nematic liquid crystal.

The present invention is characterized in that the reflection film 3 is constituted by arranging a plurality of reflection film pieces having different reflectivities. Each reflective film piece is not particularly limited as long as it has a different reflectance, but may have the following configuration, for example. For the sake of explanation, as shown in FIG. 1, it is assumed that the reflection film 3 is composed of three reflection film pieces I, II and III indicated by reference numerals 3a to 3c. For example, the reflection film 3 is made of the same material,
It is composed of three reflective film pieces 3a to 3c having different thicknesses (thickness: reflective film piece I <reflective film piece II <reflective film piece III). The reflection film pieces 3a to 3c are provided on the underlayers 5a to 5c made of silicon oxide or the like, on which titanium oxide, silicon oxide,
A film made of a dielectric material such as tantalum oxide can be formed by vapor deposition so as to have different thicknesses. Alternatively, a thin film made of these dielectric materials may be appropriately combined, and the number of layers may be changed to form a multilayer film. The reflectivity of each of the reflective film pieces 3a to 3c can be changed more variously. become. However, if the thicknesses of the reflective film pieces 3a to 3c are different, the opposing reflecting surfaces will not be parallel when the liquid crystal etalon is assembled, and the gap length (the distance between the reflecting surfaces) in the liquid crystal etalon surface ) Are not the same. Therefore, the thickness of each of the base layers 5a to 5c corresponding to each of the reflection film pieces 3a to 3c is adjusted so that all the reflection film pieces 3a to 3c constituting the reflection film 3 have the same height.

Further, the film forming material of each of the reflective film pieces 3a to 3c or, in the case of a multilayer film, the number of laminations is made the same, and by changing the order of the layers, the respective reflectances can be changed with the same film thickness. . In this case, it is not necessary to change the thickness of the underlayers 5a to 5c, and the respective reflective film pieces 3a to 3c may be formed directly on the transparent electrode 4 without the underlayers 5a to 5c. When assembling the liquid crystal etalon,
The respective reflective film pieces 3a to 3c of the opposing liquid crystal etalon one-sided substrate 1 are arranged in the formation region of the reflective film 3 of each liquid crystal etalon one-sided substrate 1 so that those having the same reflectance face each other.

In the liquid crystal etalon, usually, substrates are arranged to be opposed to each other in a plane direction in order to form a connection region between the transparent electrode 4 and the lead wire for external connection. Along with this, the portion where the reflective films overlap, that is, the light transmission area is also reduced. Therefore, as shown in FIG. 2, the area of the transparent electrode 4 is enlarged using a glass substrate 2 having a large area as one liquid crystal etalon one-side substrate constituting the liquid crystal etalon, and the connection portion with the external connection lead wire is formed. It is preferable to secure them. As shown in FIG. 1, the reflection film 3 is composed of three reflection film pieces 3a to 3c having different reflectivities, and the base layers 5a to 5c.
c is adjusted so that the reflecting surfaces have the same height. A liquid crystal alignment film 8 is formed on the reflection film 3. Then, the liquid crystal etalon one-sided substrate shown in FIG. 1 and the liquid crystal etalon one-sided substrate shown in FIG. 2 are arranged so that the pieces of the reflective film having the same reflectance face each other to form a liquid crystal etalon. According to such a configuration, it is not necessary to shift the substrates in the plane direction, and the area of the reflection film 3 can be directly used as the transmission area. At this time, the transparent electrode 4 divides the formation region of the reflection film 3 by the insulating portion 7, and sets the reflection film formation region of one of the substrates to the ground potential via transfer to the transparent electrode portion outside this region. To provide a potential difference between the transparent electrodes on both substrates.

In a Fabry-Perot resonator (etalon) in which two reflecting mirrors are arranged in parallel, the half-width Δν of the transmitted light depends on the reflectance R of the reflecting surface constituting the reflecting mirror as follows: It is known that approximation can be made as in equation (1), and that Δν decreases as R increases.

[0012]

(Equation 1)

In the above equation (1), c is the speed of light, L
Is a gap length (distance between reflection surfaces). Therefore, by configuring the reflective film 3 with the plurality of reflective film pieces 3a to 3c having different reflectivities as described above, the incident position on the reflective film 3 with respect to the light incident on the liquid crystal etalon, that is, the reflective film piece 3a ~
The half width of the transmitted light can be changed according to 3c. According to the above principle, according to the liquid crystal etalon of the present invention, the half width of the transmitted light can be controlled by changing the incident position of the incident light in the plane. Moreover, at that time, there is no need to use other optical elements such as a lens and a slit as in the related art, and the apparatus does not increase in size.

An embodiment of the liquid crystal etalon of the present invention will be described below. Forming a non-reflective film on one side of a quartz substrate having a side of 15 mm, forming an ITO transparent electrode on the other side,
Tantalum oxide and silicon oxide are alternately arranged on the underlayer made of silicon oxide, and the number of laminated layers is changed to obtain three types of reflection film pieces I, II, and III (thickness: reflection film piece I <reflection). Film piece II <reflective film piece III) was formed. At that time, the thicknesses of the corresponding underlayers were adjusted so that the reflection surfaces of the reflection film pieces I, II, and III were at the same height. Then, a liquid crystal alignment film was formed so as to cover the entire surface of the reflection film composed of the reflection film pieces I, II, and III, thereby producing a first substrate having the configuration shown in FIG. When the reflectance was measured for each of the reflection film pieces I, II, and III, a wavelength-reflectance curve shown in FIG. 3 was shown. As shown in the figure, as the film thickness increases, the reflectance for the same wavelength increases. For example, around a wavelength of 1520 nm, the reflectance of the reflective film I is about 97.5%, and the reflectance of the reflective film II is about 97.5%. About 9
8.8%, and the reflectance of the reflective film III is about 99.2%. Further, a non-reflective film is formed on one surface of a quartz substrate having a short side of 20 mm and a long side of 25 mm, and ITO is formed on the other side.
A transparent electrode is formed, and a region where the reflective film of the transparent electrode is formed is partitioned by an insulating portion. The underlayer and the reflective film pieces I, II, and III are formed in the reflective film formation region in the same manner as the first substrate. Was formed, and further, a liquid crystal alignment film was formed to produce a second substrate having the configuration shown in FIG.

Then, the first substrate and the second substrate were arranged such that pieces of the reflective film having the same reflectance faced in parallel, and filled and sealed with a nematic liquid crystal to produce a liquid crystal etalon. As shown in FIG. 4, the liquid crystal etalon is such that incident light having a wavelength of 1550 nm is made incident on the reflective film piece I, thereby transmitting transmitted light having a half value width of 2.31 nm to the reflective film piece II. The transmitted light having a half-value width of 1.61 nm and the transmitted light having a half-value width of 1.33 nm can be obtained by being incident on the reflection film piece III.

Various modifications can be made to the liquid crystal etalon of the present invention. For example, the laminated structure on the glass substrate 2 may be a structure in which the base layers 5a to 5c, the reflective films 3a to 3c, the transparent electrode 4, and the liquid crystal alignment film 8 are laminated in this order from the substrate side.

[0017]

As described above, the liquid crystal etalon of the present invention can change the half width of transmitted light, and can easily cope with the change in the number of channels in WDM optical communication.
In addition, at that time, other optical elements such as a lens and a slit are not required unlike the related art, and the apparatus does not become large.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a liquid crystal etalon one-side substrate constituting a liquid crystal etalon of the present invention.

FIG. 2 is a perspective view of a liquid crystal etalon one-sided substrate used as a pair with the substrate shown in FIG. 1 used in the embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the wavelength and the reflectance of each reflective film piece.

FIG. 4 is a diagram illustrating a half-value width of transmitted light of each light transmitting portion.

FIG. 5 is a sectional view showing a conventional liquid crystal etalon.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal etalon one side substrate 2 glass substrate 3 reflective film 3a, 3b, 3c reflective film piece 4 transparent electrode 5a, 5b, 5c underlayer 6 anti-reflective film 7 insulating part

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masataka Shishido 1500 Onjuku, Susono-shi, Shizuoka Prefecture Yazaki Sogyo Co., Ltd. F-term (reference) 2H088 EA49 HA02 HA03 HA21 MA20

Claims (4)

[Claims] 1. A substrate comprising a glass substrate, on which a transparent electrode, a reflective film and a liquid crystal alignment film are laminated, are arranged facing each other such that the reflective surfaces of the reflective film are parallel to each other, and
A liquid crystal etalon configured by sealing liquid crystal between substrates, wherein the reflective film is configured by aligning a plurality of reflective film pieces having different reflectances, and the reflective film pieces having the same reflectance face each other. A half-width variable liquid crystal etalon characterized by being arranged in a vertical direction. 2. The method according to claim 1, wherein each of the reflection film pieces is made of the same material.
2. The method according to claim 1, wherein the film thicknesses are different.
The described half-width variable etalon. 3. The half-width variable liquid crystal etalon according to claim 1, wherein each of the reflection film pieces is formed by laminating thin layers made of different kinds of materials, and the lamination number and / or lamination order are different. . 4. The half value width variable liquid crystal etalon according to claim 1, wherein each of the reflection film pieces is made of a different material having the same thickness.