JPS5858525A - Optical switch - Google Patents

Abstract

PURPOSE:To obtain an optical switch of high efficiency which is easy to manufacture and operates on low electric power by providing an optical transmission medium of which the refractive index changes with temp. in the opposing part of a pair of waveguides of which the end parts oppose to each other specially on a substrate, and providing a heating electrode between the waveguides. CONSTITUTION:A Ti is diffused on a substrate 1 consisting of a dielectric crystal consisting of an LiNbO3 to form waveguides 2a, 2b of which the end parts are spaced by l1. An electrode 3 of a length l2(l2>=l1) consisting of an Ni-Cr alloy is provided in the opposed part of the waveguides 2a, 2b to form a switching area 1a. While no electric conduction is performed at the electrode 3, the light waves propagating in the waveguide 2a deflects toward the inside of the substrate 1 as shown by an alternate long and short dash line in a switching area 1a where the refractive index is small, and the light waves arriving at the waveguide 2b are slight but when electric conduction is performed at the electrode 3, the refractive index of the area 1a is increased by the heating, and the strong light is emitted from the waveguide 2. Thus the optical switch which is easy to manufacture and operates on low electric power is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical switch that utilizes the property that the refractive index (depending on the temperature) of a crystal material changes.

In the field of optical information processing such as optical fiber communications, optical memory devices, and optical printers, devices that control the direction of light and turn on and off the passage of light are essential. Optical switches used as devices of this type are required to have low crosstalk, easy switching with low power, high switching speed, and low cost. By the way, some conventional optical switches utilize an acoustic optical effect or an electro-optical effect. FIG. 3 is a schematic perspective view of an optical switch O using the electro-optic effect. This light switch is
On the surface of the substrate 60 made of a crystal material such as LiNb0j,
A T1 diffusion layer is formed by Tit diffusion to form a cite waveguide 7. Then, one part of this waveguide 7 K Tie! A prism 1o consisting of a prism 1o is mounted, and an insulating layer Ill of Sin or Ajρ8 is laminated on the other part, and three parallel planar electrodes sas 8b, gc ? b The substrates 60 are arranged in parallel at the center in the width direction so that their longitudinal directions coincide with the longitudinal direction of the substrate 6. Each of these electrodes 8m, 8b, 8
Terminals c are connected to terminals 9m, 9b, and 9c, respectively, and a DC voltage can be applied between terminals 9a and 9c and terminal 9b. When a light wave is made to enter the waveguide 7 through the prism 10i, the light wave propagates through the waveguide 7 toward the formation position of the electrode 81 and the like.

Then, when a voltage is applied between the center electrode 8b and the electrodes ga and ge on both sides thereof, an electric field is formed that increases the refractive index of the portion directly below the electrode 8b in the waveguide 7.
The light wave is focused and propagated directly under the central electrode 8b,
The light is emitted from the end of the waveguide 7 on the electrode 8b side. On the other hand, electrode 8
b and electrode 8&.

When the polarity of the voltage applied between 8C and 8C is reversed, the light wave propagates through the slab-shaped waveguide 71 while being dispersed to the left and right when viewed from above in the light traveling direction, and is emitted from near the end of the electrode 8b of the waveguide 7. The intensity of the light waves generated decreases significantly. In this way, the electrode 8b
The intensity of the light wave emitted from the specific position W of the waveguide 7 changes depending on the polarity and intensity of the voltage applied between the electrodes 8a, gc, and 0, thereby forming an optical switch.

However, in this case, since the waveguide 7 is in the form of a d'Z slab, the propagation direction changes depending on the direction of incidence and the position of incidence of the incident light wave on the waveguide 7, so the switching characteristics fluctuate, resulting in a highly efficient optical switch. It's difficult to make it look funny. Also, electric & 8a.

To completely suppress the propagation loss of light waves for 8b and 8c.

It is necessary to provide the insulating layer 11t, and the waveguide 7Fi
Since it needs to be shaped like a wide slab, it is almost impossible to convert the light wave into a single mode. Furthermore, an electrode 8a.

The relative shape of 8b and 8c is that of a machine ship, which makes it difficult to form, and there are other disadvantages such as the need to use a DC power source as a power source.

On the other hand, in the multiplication table switch using the acousto-optic effect,
PbMo0. , using crystalline materials such as Teal.

Furthermore, it is extremely expensive because it uses a transducer that converts electrical signals into ultrasonic waves. Furthermore, since a large amount of high power is required to drive one light/switch, there is a problem in that there are restrictions on how it can be used.

The present invention has been made in view of the above points, and is easy to manufacture, can operate with low power without being restricted by a driving power source, and can easily convert light waves into a single mode. Aims to provide full efficiency light switch. The present invention was made based on the novel idea of utilizing the temperature dependence of the refractive index of crystalline materials, in addition to the conventional optical switch concept of utilizing the electro-optic effect or acousto-optic effect of crystalline materials. . Therefore, the optical switch of the present invention does not require that the plane of polarization of the light wave be polarized in a specific direction unlike conventional switches that utilize the electro-optic effect, and therefore can operate even with white light. The optical switch according to the present invention includes a pair of waveguides formed on the surface of a substrate such that their end portions face each other with an appropriate distance M apart from each other, and at least the pair of waveguides on the surface of the substrate face each other. a switching region formed of an optical transmission medium whose refractive index changes depending on temperature; and a heating electrode formed between the pair of waveguides along the switching region. It is. In this case, St.
O, or A40. By forming an insulating layer consisting of, for example, the heating electrode on this insulating layer, it is possible to reduce the loss of light waves propagating in the switching region into the metal (heating electrode). Since the length of the portion along the switching region can be set to be extremely short, the propagation loss of light waves is small, so in this case it is not necessarily necessary to provide an insulating layer. Further, the pair of waveguides are formed of an optical transmission medium having a higher refractive index than the substrate and the switching region.

Preferably, the switching region is formed of an optical transmission medium whose refractive index increases with increasing temperature.

LtNbol, LtTaO, TaOx as a crystal material #'i such as quartz.

Its refractive index has temperature dependence, and it has the property of having a high culm waste refractive index with a high temperature sum. When light passes through a boundary between substances with different refractive indexes, K.

A refraction phenomenon occurs such that the angle of refraction (the angle between the direction perpendicular to the boundary and the light beam) becomes smaller in a substance with a high refractive index. Therefore, if a part of the waveguide is missing in the middle and the missing part is occupied by an optical transmission medium whose refractive index is smaller than the refractive index of the waveguide but whose refractive index is temperature dependent,
The light wave propagating through the waveguide enters the missing portion with a small refractive index and is dispersed in all directions, and the light wave that reaches the opposing waveguide and enters it has an extremely weak intensity.

However, when the missing part between the waveguides is heated to raise the temperature and increase the refractive index, the refractive index of the missing part becomes as high as the refractive index of the waveguide, so to speak. This means that a new waveguide connecting the two has been formed. Therefore, the light waves are not dispersed in this portion, and extremely high-intensity light waves are emitted from the output end of the waveguide. The present invention has been made based on this knowledge. That is, by providing a heating electrode along the missing part between the waveguides, heating the missing part by applying electricity, and turning this part into a waveguide with a high refractive index, it is possible to turn on the electricity to the heating electrode.・
This constitutes an optical switch that corresponds to turning off and connecting/shorting the waveguide.

Hereinafter, one specific embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic perspective view showing one embodiment of the present invention, and FIG. 2 is a longitudinal cross-sectional view taken along the line ■--■ of FIG.

The substrate 1 is made of LiNb0. It is cut so that the crystal Iz axis direction is the thickness direction, and waveguides 2a and 2bi are formed by rt2 diffusion on the surface of this substrate 10. The waveguide 2& on the light wave input side and the waveguide 2b on the output side are formed to be fully aligned in the longitudinal direction, and their opposing ends are separated by tl, and the opposing portion of this tl is located on the substrate. It is occupied by LiNb0°, which is the constituent material of 1 and which is not subjected to Ti diffusion. Tl=i The diffused waveguides 2a and 2b are connected to the substrate l including the opposing portions between the waveguides.
In particular, the refractive index is higher by approximately o, o t s for extraordinary light in which the electric field direction is biaxial.

In addition, the diffusion depth of Tl is several μs' (for example, about 2.4 lines), and the thickness is sufficient to propagate light waves of two modes, 1M41 and TMl, in the thickness direction of the waveguides 2m and 2b. However, it is of course possible to achieve the intended purpose of the present invention even if the waveguides 2m and 2b are formed so that a single mode light wave can be propagated in the thickness direction and the width direction.

A heating electrode 3 is formed on the surface of the portion of the substrate 1 where the waveguides 2 and 2b are opposed, with both ends of the heating electrode 3 in the longitudinal direction slightly overlapping the opposite end of the waveguides 2& and 2b. . The heating electrode 3 is made of a FiNi-Cr alloy and is formed by vapor deposition. (≧
t1) is led out approximately perpendicularly from the longitudinal end of the substrate 1.
It is connected to a terminal section 4.4 formed on the surface of the terminal 4, and is further connected to a suitable power source 5 such as a terminal @4, 4#i, a DC power source, or a commercial frequency AC power source.

The heating electrode 3 is energized to heat the substrate 1 directly under the p-heating electrode 3 through resistance heat generation. That is, due to the heat generated by energizing the heating electrode 30 of length t3, the area shown by the broken line in FIG. 2 is heated, and the refractive index of this area increases and becomes a waveguide. , since the refractive index remains at a low value, the waveguides 2a and 2b are short-circuited, and the broken line region is the switching region [1 m
It will function as

Therefore, the length of the switching region 1a is 2 m, 2 m of the waveguide.
It is determined by the distance t between b and the length t of the heating electrode 3, but this affects the S/N ratio as an optical switch.

That is, when the heating electrode 3 is not energized, the light waves that have propagated through the waveguide 2 enter the switching region 1m and are dispersed in the left and right direction and toward the inside of the substrate 1 when viewed from above in the direction of propagation. This is because the longer the length of the switching region 1a of the light wave incident on the waveguide 2b, the smaller the noise. on the other hand.

From the point of view of practicality as an optical switch, the S/N ratio must be 10 to 20 dB, preferably 20 dB or more.
For this tl or 1. (1, ≧11> is several hundred μ
It is necessary to set it to about 1 (for example, 400 tones). By the way, the light wave propagating through the switching chain acid 1&t- formed into a waveguide propagates into the heating electrode 3 formed on the surface of the switching region 1a.

In order to avoid loss of output light quantity.

An insulating layer 1 made of 5i01 or ll1Atρ8 may be formed on the switching region la, and the heating electrode 3t may be formed on this insulating layer. However, as described above, when tl or t is short, on the order of several 100 μs+, the propagation loss of the light wave is negligibly small, so it is not necessarily necessary to provide an insulating layer. Furthermore, if a Ni-Cr alloy is used as the material for the heating electrode 3,
Since the heat capacity is small and the heating efficiency is high, it is possible to increase the switching speed, but it is not necessary to use such a material for the terminal section 4 or the lead-out section connecting the terminal section 4 and the heating electrode 3. Rather, it is better to use a material with low heating efficiency (low electrical resistance), such as μ or Au, because the substrate directly below it is heated and its refractive index increases, causing light waves propagating through waveguides -2m and 2b to leak. This is preferable in order to avoid the possibility of

In the optical switch configured as described above, when the heating electrode 3 is not energized, light waves such as TM light propagating in the X-axis direction of the waveguide 2ak enter the switching region 11 having a small refractive index. Its direction of travel is bent,
The particles are deflected and dispersed in the left-right direction when viewed from above in the direction of travel, and toward the inside of the substrate 1 as shown by the dashed line in FIG. Therefore, only a small amount of light waves reach the opposing waveguide 2bK, and the intensity of the light waves emitted from the waveguide 2b is extremely weak.

When electricity is applied to the heating electrode 3, the heating electrode 3 generates resistance heat, and the switching region 1a immediately below the heating electrode 3 is heated. and.

The temperature in the switching region 1 rises and the refractive index increases, and the switching region 1a has a higher refractive index than other parts of the substrate 1, and becomes a waveguide. As a result, the waveguide 2
a and 2b are connected, and the light wave propagating through the waveguide 2a reaches the waveguide 2b, as shown by the second middle arrow, without being scattered in one breath of the switching region, and the light wave propagates through the waveguide Zbi.
Emits light with high intensity.

In this way, the intensity of the light wave emitted from the waveguide 2b can be controlled with a high S/N ratio by turning on and off the power supply to the heating electrode 3. Moreover, since the heat capacity of the heating electrode 3 and the switching region 1a is small, the switching speed is l
It is fast at less than m5ec. Furthermore, since the power source 5 causes the heating electrode 3 to generate heat through resistance, it may be an AC power source.
The voltage applied to the heating electrode 3 may be less than or equal to Fi20/root. This applied voltage can be further reduced by appropriately setting the material and shape of the heating electrode 3. If it were to be configured using As shown in the figure, it has a long plate shape, and there is no need to arrange multiple electrodes in parallel in the width direction of the waveguide like in an optical switch that uses the electro-optic effect, so the shape is simple and easy to form. be.

This has an advantage of 1% if the optical switch can be operated with single mode light waves, which is advantageous for multiplex communications. In other words, if the waveguide is made into a single mode in both the thickness direction and the annular direction, the waveguide width will be less than 5μ, but since the electrode shape is simple, it is easy to form, and the waveguide width can be reduced. However, there are no restrictions on electrode formation, and it is also easy to arrange many optical switches in parallel to form a play.

As described in detail above, the optical switch according to the present invention is easy to manufacture, is not limited by the power source, and can operate with low power. Furthermore, the light wave to be operated is not subject to any restrictions on its polarization state, wavelength, etc., and white light, which was conventionally inoperable, can also be operated. Note that the present invention is not limited to the specific embodiments described above, and various modifications can be made within the technical scope of the present invention. For example, as the material of the substrate 1, various dielectric crystals having a refractive index temperature dependence such as quartz can be used as described above (in addition to LiNb0. The heating electrodes formed on the surface are also formed by Tl diffusion and
Of course, the material is not limited to Ni-Cr alloys. Further ζ
.

The waveguide and the heating electrode (and therefore the switching region) do not have to be straight as in the above embodiment.

It may be formed in a curved manner. Furthermore, it goes without saying that the waveguide and the heating electrode do not necessarily have to have a width dimension of 4-4.

[Brief explanation of drawings]

FIG. 1 is a schematic trunk view showing one embodiment of the present invention, and FIG. 2 is a longitudinal cross-sectional view taken along the line -■ in FIG. 1. FIG. 3 is a schematic perspective view of a conventional optical switch. (Explanation of symbols) l...Substrate 1m...Switching area 2m, 2b...Waveguide 3...Heating electrode patent applicant Ricoh Co., Ltd. - Figure 1 To Figure 2 Figure 3 Procedure Amendment February 19, 1980 Commissioner of the Japan Patent Office Shima 1) Haruki-dono 1 Indication of the case 1982 Patent application "156117" 2. Title of the invention Optical switch 3. Relationship with the person making the amendment Patent applicant 4 , Agent's name (7618) Patent attorney Masaaki Nobu 5, Date of amendment order 6, Number of inventions increased by amendment None Contents of amendment 1, ``Detailed description of the invention'' in the description Correct as shown below. (1) 4th line from 2nd Sada E, tl of “crystal” stop (“
Corrected to "optics." (2) In the 15th and 16th lines from the top of 4t4, Qk that says "it is almost impossible to convert light waves into a single mode" is corrected to "the scope of application is limited." (Page 3315, lines 9-10 from the top, [Light wave unit]
(-Correct the statement "It is easy to create a mode" to tl [It is easy to connect with a multimode optical fiber.") (4) II5! Lines 13 and 14 from the top say "crystal" (5) On the 5th page, lines 18-19 from the top, it says, "-They do not have to be the same, and therefore 1IIIJtI\ is possible even with white light." ``Polarized light is not required, and it can also operate with natural light. Multimode optical fibers are currently being used in the optical information processing field, but the present invention is It has a great advantage in that it can be applied not only to one mode but also to multimode optical fibers.'' 6) Lines 5 to 7 from No. 9 Teishichi, ``To TMe and TM
It has a thickness sufficient to propagate two modes of light waves I, t, and dimensions sufficient to propagate a multimode light beam in the width direction. but,
7) Lines 6 to 8 from the top of No. 14, [This is especially true when the optical switch is made operable for single-mode light waves that are advantageous for multiplex communication.''
This optical switch has a large refractive index change due to heating, making it useful for use in multimode optical fiber communication systems. Correct to "also". 8) In the 18th line from the top of page g14, replace the word "deflection" with "
Polarized light”. . 9) In the 19th line from the top of the 14th line, correct "white light" to 1 "natural light." (10) @15 4th row directly above, r stone J[J,
! =66 purple, corrected to "quartz, ceramic, glass, etc." (11) In the 5th line from the top of the 15th page, correct the phrase "dielectric crystal" to "optical material". that's all

Claims (1)

[Claims] 1. A pair of waveguides formed on the surface of a substrate so that their ends face each other with an appropriate distance apart, and at least the pair of waveguides on the surface of the substrate face each other. A switching region is formed of an optical transmission medium whose refractive index changes depending on temperature. and a heating electrode formed between the pair of waveguides along the switching region. 2. In the above item 1, the optical switch is characterized in that the heating electrode is formed with an insulating layer interposed between the switching region and the switching region. 3. In the above item 1 or 2, The pair of waveguides are formed of an optical transmission medium having a higher refractive index than the substrate and the switching region. An optical switch characterized in that the switching region is formed of an optical transmission medium whose refractive index increases with temperature rise.