JPS63169615A - Optical waveguide gate element - Google Patents

Abstract

PURPOSE:To improve the consistency with other waveguides and to improve light confinement effect and layout freedom by forming a gate element of a quartz single-mode ridge type optical waveguide whose periphery is covered completely with a clad layer. CONSTITUTION:An optical waveguide core which becomes the quart single-mode ridge type optical waveguide forming a branch structure 5, arm optical waveguides 4a and 4b, and a confluence structure 6 on a buffer layer 3 with a low refractive index is covered with a clad layer 3 laminated on a layer 2 with a low refractive index including even the top surface. The gate element is composed of the single-mode ridge type waveguide whose periphery is covered completely with the clad layer and easily coupled easily and excellently with high consistency with other optical waveguides such as an optical fiber. The light confinement effect of the optical waveguide is high and the degree of freedom of layout is increased; and a sharp curvature angle is selected to reduce the size of the circuit and also facilitate integration.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical waveguide gate element. More specifically,
The present invention relates to the configuration of a novel element that can be advantageously used as an optical switch in fields such as optical communication and optical information processing.

Conventional technology Optical waveguide gate devices are devices that cut and break optical signals propagating through optical fibers and various optical waveguides, and there are many types, including those that operate mechanically and those that utilize various optical effects. The following configuration has been proposed.

FIG. 5 shows the structure of a known optical waveguide gate element that utilizes the electro-optic effect or thermo-optic effect to realize optical switch operation without moving parts.

This optical waveguide gate element includes an optical circuit 20 formed on an optical waveguide formed on a substrate 10, and an electrode 30 provided close to a part of the optical circuit for controlling the refractive index of the optical waveguide.
It is composed of.

In such an optical waveguide gate element, the optical circuit 20 is L+N
It is generally formed by a buried optical waveguide formed by thermally diffusing Ti into a bO3 substrate or adding Ag by ion exchange to a multicomponent glass substrate. The optical circuit 20 includes a human power port 11 and a human power port 11.
A branching section 12 that branches an optical signal incident on the branching section 12 into two, two arm optical waveguides 13a and 13b that respectively propagate the optical signals branched at the branching section 12, and further an arm optical waveguide 13.
It is formed of an optical mixing section 14 that combines optical signals propagated through channels a and 13b into one, and an output port 15. Note that the electrodes 30 are provided on the arm optical waveguides 13a and 13b, respectively. That is, in order to avoid attenuation of propagating light in the waveguide due to total optical absorption, the electrode 30 connects the arm optical waveguide 13a, Generally, it is formed directly above 13b.

The optical signal incident on this optical waveguide gate element is transmitted to the branching section 12.
branched into two optical signals at each arm optical waveguide 13a,
After propagating through 13b, the signals are combined again in the mixer 14 and output. At this time, the optical lengths of the arm optical waveguides 13a and 113b are completely equal, or the phase difference of the propagating light at the output end of the arm optical waveguide is 2nπ (N=0.1.2·
), the optical signals are combined in the same phase in the mixer 14 and output to the output port 15. That is,
Since an optical signal substantially equivalent to the input optical signal is output, this state is "ON" when considered as an optical switch.

On the other hand, when the scale difference of the optical signal at the output end of the arm optical waveguide is (2n+1)π, optical signals of opposite phases are combined in the mixing section 14, and no optical signal is output. This state becomes "OFF".

In this way, in this optical waveguide gate element, by supplying power to one of the electrodes 30, the refractive index of the arm waveguide in contact with that electrode is changed, and the substantial optical length of the arm waveguide is controlled. .

When the waveguide is formed of LiNbO3, the refractive index of the waveguide section is changed by applying an electric field through the electrode 30 and utilizing the electro-optic effect.

Although not shown, in this case, a pair of electrodes sandwiching one optical waveguide are required.

In addition, when the optical waveguide is formed of multi-component glass, the electrodes are used as heaters, and the heat generated by applying power to one electrode is used to heat the waveguide, and the waveguide is heated by the thermo-optic effect. Utilizes changes in refractive index.

Problems to be Solved by the Invention However, the conventional optical gate device as described above has the following problems:
There were the following problems.

That is, the optical circuit of the conventional optical gate element is constructed of a buried optical waveguide. However, embedded optical waveguides are generally formed by a thermal diffusion method, an ion exchange method, a light irradiation method, or an ion implantation method, and they are formed by confining light within the layer containing the optical waveguide, that is, in a direction parallel to the substrate. The effect is weak and the optical waveguide cannot be bent with a small radius of curvature.

Therefore, when forming the light branching structure or the light merging structure of the optical gate element, the branching angle or the merging angle cannot be increased. Further, each optical waveguide must be bent in order to provide the necessary spacing between the two arm optical waveguides after branching, but the radius of curvature of this bent waveguide cannot be made small. As described above, conventional optical gate elements are extremely difficult to miniaturize.

Furthermore, in actual use, the optical gate element needs to be connected to other optical waveguides such as optical fibers. However, a buried optical waveguide is an optical waveguide whose material and structure are different from those of optical fibers, etc., and coupling thereof is extremely difficult. Therefore, a reflective bending circuit (E!
tronics Letters, Vol. 21. pp
1020-1021.1985), etc., or that it is difficult to integrate them.

Furthermore, in the above structure, since the electrode metal layer is formed substantially in contact with the optical waveguide, waveguide loss due to light absorption by the metal is also a problem that cannot be ignored.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a novel optical gate element that can be miniaturized or have a high concentration, and is easy to combine with other optical elements and has a lot of versatility. It is about providing.

Means for solving the problem, that is, according to the present invention, a pair of arm optical waveguides each propagating a human-powered optical signal split into two by a branching part, and coupling to the output ends of the pair of arm optical waveguides. and -1
An optical circuit configured by forming an optical waveguide on a flat substrate, including an optical mixing unit that combines optical signals emitted after propagating through the pair of arm optical waveguides into one, and the pair of arm optical waveguides. and electrode means for changing the optical length of the one arm optical waveguide, the optical circuit being further away from the optical waveguide. A silica-based single mode ridge is formed on the planar substrate via a buffer layer having a low refractive index, and further, the upper surface and side surfaces of the optical waveguide are covered with a cladding layer having a lower refractive index than the optical waveguide. An optical waveguide gate element is provided, which is characterized in that it is formed by a type optical waveguide.

Note that the ridge type optical waveguide here refers to GaAs on the substrate.
, H” dosed GaAs5Ti diffused LiNbO
It means an optical waveguide three-dimensionally formed using a waveguide material such as No. 3.

The main feature of the optical waveguide gate Yonago according to the present invention is that its optical circuit is formed by a quartz-based single mode ridge type optical waveguide completely surrounded by a cladding layer.

That is, the ridge type optical waveguide can be formed by an ion etching method or a chemical etching method.
At this time, extremely fine processing is possible by using photolithography technology.

Furthermore, before forming the optical waveguide, a buffer layer is formed between the substrate and the optical waveguide using a material with a refractive index lower than that of the optical waveguide, and a cladding layer made of a material also having a lower refractive index than the optical waveguide is used to guide the optical waveguide. By covering the surface of the waveguide, it is possible to form an optical waveguide with dramatically improved light confinement effect, especially in the direction parallel to the substrate. Therefore, when forming an optical branching structure or an optical merging structure of an optical circuit, it is possible to select a relatively large branching or merging angle, and it is also possible to bend the optical waveguide with a relatively small radius of curvature. Become. In this way, in the optical waveguide gate device according to the present invention, a layout that is advantageous for integration can be selected from a wide range.
-Furthermore, since the optical waveguide is made of quartz-based material, it is possible to
In particular, connection with optical fibers etc. becomes extremely easy.

Furthermore, in the structure of the optical waveguide gate element according to the present invention,
Since the electrodes serving as electric field application means or heating means are placed outside the cladding layer, the optical signal propagating within the waveguide is optically blocked from the electrodes by the cladding layer, and the electrode material is This also has the effect of greatly improving the loss of propagating optical signals due to optical absorption.

EXAMPLES The present invention will be described in more detail below with reference to the drawings, but what is disclosed below is only one example of the present invention and does not similarly limit the technical scope of the present invention. ' FIG. 1 is a perspective view showing the structure of an optical waveguide gate element constructed according to the present invention.

This optical waveguide gate element is formed on a Si substrate 1. The optical waveguide core 4 is formed on the Sl substrate 1 with a buffer layer 2 interposed therebetween, and is further covered with a cladding layer 3. In FIG. 1, the front side of the figure (the side where the cross section of the optical waveguide core 4 is visible) is defined as the incident end.

As shown in the figure, the optical waveguide core 4 forms a branching structure 5 after incidence and is coupled to two arm optical waveguides 4a and 4b. is formed.

Furthermore, independent conductor thin film layers 7a, 7b, and 7c are formed on the sides of the arm optical waveguides 4a and 4b, respectively.
In particular, either of the conductor thin film layers 7a, 7c is configured to be energized by a power supply means (not shown).

Such an optical waveguide gate element was manufactured as follows. The manufacturing procedure is schematically shown in Figures 2 (a) to (d).
Shown below.

That is, first, as shown in FIG. 2(a), a buffer layer 2 and an optical waveguide core layer 4' are formed on a Si substrate 1 by a flame direct deposition method using 5ICIA as a raw material and H2 and 02 as combustion gases. A two-layer planar quartz-based optical waveguide film is fabricated. At this time, the thicknesses of the buffer layer 2 and the optical waveguide core layer 4'' were 26 μm and 8 μm, respectively.

Next, the optical waveguide pattern including the optical branching structure 5, the optical combining structure 6, and the arm optical waveguides 4a and 4b is transferred onto the planar optical waveguide by photolithography technology, and as shown in FIG. Unnecessary portions of the core layer 4' are removed by reactive ion etching using as a main component. Note that the width of the optical waveguide core was 8 μm.

Subsequently, as shown in FIG. 2(C), a cladding layer 3 having a thickness of 3 μm is formed on at least the upper surface and side surfaces of the core layer 4 by CVD. In fact, the entire substrate including the optical waveguide core pattern may be covered with a cladding layer, and the fabrication is easy. At this time, the buffer layer 2 and the cladding layer 3 had the same refractive index, and the relative refractive index difference between them and the core layer 4 was 0.3%. The buffer layer 2 and cladding layer 3 thus formed surround the core layer 4 and function as a so-called cladding. Note that the buffer layer 2 also has a function of preventing light passing through the core layer 4 from being absorbed by the Si substrate 1.

On the substrate 1 and optical waveguide 4 thus formed, a second
As shown in Figure (d), a chromium layer 7' is formed by vacuum evaporation, unnecessary parts are removed from this chromium layer 7' by photolithography, and conductor layers 7a, 7b,
Form 7c. In this way, an optical waveguide gate element as shown in FIG. 1 is completed.

There are roughly two types of optical waveguide gate elements. That is, as will be described later, there are two types: a type in which light propagation is blocked when the conductor layer is energized, and a type in which light propagates when the conductor layer is energized.

First, I will discuss the former. The type in which the propagation of light is blocked when electricity is applied to the conductor layer means that the optical lengths of the arm optical waveguides 4a and 4b are equal when no power is applied, or the position of the propagating light at the output end of the arm optical waveguide is the same. Phase difference is 2n
This is a case where π (N=0.1.2...). Therefore, the incident optical signal is branched by the branching structure 5, propagated through the arm optical waveguides 4a and 4b, and then synthesized in the same phase by the optical mixing structure 6, producing an optical signal substantially equivalent to the incident optical signal. Output.

In this state, when a current is passed from one end of the thin film conductor 7a to the other end, the thin film conductor 7a generates heat due to electrical resistance, and the temperature of the arm waveguide 4a rises. When the temperature of the arm optical waveguide 4a increases, the refractive index increases due to the thermo-optic effect.

Since the optical length of the optical waveguide is expressed as the product of the physical effective length and the refractive index, in this case, the optical length of the arm optical waveguide 4a is increased. Note that at this time, the thin film conductors 7b and 7c through which current is not flowing act as radiators and radiate heat, so the optical length of the arm waveguide 13b does not change.

In this way, only the optical length of the arm waveguide 4a changes, and 2
When the optical length difference between the main arm optical waveguides 4a and 4b becomes (+A+n)λ [λ: wavelength of signal light] [n: 0 or an integer], the optical signals are combined in opposite phases in the mixing section 6. Therefore, it becomes a radiation mode and does not appear at the output port.

The relationship between the power applied to the conductive thin film and the output optical signal is shown by a solid line in FIG.

From FIG. 3, an OFF state in which the optical output is minimum was obtained at 0.8 W. The specific extinction ratio in the 0N10FF state of optical output is 3
0 dB, the excess insertion loss in the ON state was 3 dB.

Note that the wavelength of the signal light used in this experiment was 1.3 μm.

Furthermore, an optical waveguide gate element of the second type described above, that is, an optical waveguide gate element whose output is turned off when power is supplied to the optical switch, was also fabricated. In this element,
The optical length of arm waveguides 4a and 4b is (+A+n)λ
[λ: Wavelength of signal light] [n: 0 or an integer] A circuit is created in which a difference is provided in advance such that [λ: wavelength of signal light] [n: 0 or an integer]. In this experiment, a difference was set between the signal light wavelength of 1.3 μm and the refractive index of 1.45.

The operation of this optical waveguide gate element is shown by dotted lines in FIG. That is, it can be seen that an OFF state was obtained when the applied power was QW, and an ON state was obtained when the applied power was 0.8W. The extinction ratio and excess insertion loss were approximately the same as in the previous example. Furthermore, since the thin film conductor was formed apart from the side of the optical waveguide, almost no loss due to light absorption by the metal was observed.

Although this embodiment has been described using vacuum-deposited chromium as the thin film conductor, other materials may be used as long as they are conductors that conduct electricity, such as other metals or amorphous silicon.

Further, in this embodiment, an optical waveguide gate element that utilizes the thermo-optic effect due to heat generation of the electrodes has been described, but it is possible to configure an optical waveguide gate element that utilizes the electro-optic effect within the scope of the present invention. Not even. When performing such an operation with the structure shown in FIG. 1, an electric field is applied to either the arm optical waveguide 4a or 4b by using either the electrode 7a or 7b and the central electrode 7C. can do.

Figure 4 shows a 2×
2 Gate Master) An example of the configuration of an IJ sock switch is shown.

This circuit is basically configured with a silica-based ridge type single mode optical waveguide, and includes optical branch circuits 45a145b1 optical waveguide gate elements 46a to 46d1 optical waveguide reflection bending circuit 4
7a to 47e, and optical confluence ports 48a and 48b.

Here, each of the optical gate elements 468 to 46d has the same configuration as the optical gate element shown in FIG. 1, and is of a type that outputs an optical signal when power is applied.

Note that among these adjacent optical gate elements, for example, the thin film conductor 44b of the optical gate element 46b and the thin film conductor 44a of the optical gate element 46a are close to each other with a small distance, but the thin film conductor 44b of the optical gate element 46b and the thin film conductor 44a of the optical gate element 46a are close to each other with a small distance. Since the conductor acts as a heat sink, even if adjacent optical waveguide gate elements operate differently from each other, their influence on each other is extremely small.

In the gate matrix switch configured in this manner, for example, in order to output the optical signal inputted to ① to 01, it is sufficient to turn on only the optical waveguide gate element 46a.

In addition, the optical branch circuits 45a, 45b and the optical junction path 18a
A curved waveguide with a slight curvature is normally used for 1b, but like the optical circuit of the optical waveguide gate circuit of the present invention,
By using a ridge-type waveguide with a cladding layer, the radius of curvature can be reduced and the circuit size can be reduced.

Further, by using similar optical waveguides for the reflective bent waveguides 47a to 47e, the entire circuit can be easily highly integrated.

As described above, the optical waveguide gate element of the present invention is suitable for combination integration with other optical circuits, and a more highly functional optical IC can be realized.

Effects of the Invention As detailed above, the optical waveguide gate element according to the present invention has its optical circuit formed by a silica-based single mode guiding path, so that it is compatible with other optical waveguides such as optical fibers in terms of material and structure. It has good consistency and is extremely easy to combine.

In addition, since the optical waveguide is completely surrounded by a cladding layer and uses a wedge-type waveguide structure, the light confinement effect of the optical waveguide is high.
Extremely high degree of freedom in waveguide layout. That is, it is possible to select a small radius of curvature or a steep angle at the bent portion, branched portion, etc. of the optical waveguide, which is extremely advantageous for miniaturizing the circuit.

Due to these advantageous properties, the optical waveguide gate device according to the present invention is suitable for combinatorial integration with other optical circuits,
A more highly functional optical IC can be realized.

Furthermore, since the thin film conductor for driving the optical gate is formed apart from the optical waveguide, there is almost no increase in loss due to metal absorption, and it has excellent characteristics as a gate element, such as low insertion loss.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing the configuration of an optical waveguide gate element constructed according to the present invention, and FIGS. 2(a) to (d) are views of the optical waveguide gate element shown in FIG. 3 is a graph showing the operation of the optical waveguide gate element shown in FIG. 1, and FIG. 4 is a graph showing the operation of the optical waveguide gate element shown in FIG. 1. FIG. 5 is a diagram schematically showing the structure of a 2×2 gate matrix switch constructed using the present invention, and FIG. 5 is a perspective view showing the structure of a conventional optical waveguide gate element. (Main reference numbers) 1... Substrate, 2... Buffer layer, 3... Clad layer, 4... Optical waveguide core, 4'... Optical waveguide core layer, 4a, 4b... Arm Optical waveguide, 5...branch structure, 6...merging structure, 7a, 7b,
7C...Conductor thin film layer, 7'...Chromium layer, 10...Substrate, 11...Manpower port, 12...Branch portion, 13a, 13b
... Arm optical waveguide, 14... Optical mixing section, 15.
... Output boat, 20... Optical circuit, 30... Electrode, 44a, 44b... Thin film conductor, 45a, 45b... Optical branching section,

Claims (4)

[Claims] (1) A pair of arm optical waveguides each propagating an input optical signal split into two by a branching part, and coupled to the output end of the pair of arm optical waveguides and propagating through the pair of arm optical waveguides. an optical circuit formed on a flat substrate, and an optical waveguide including an optical mixing unit that combines the optical signals emitted after the optical signals are combined into one; an optical waveguide gate element provided with electrode means for changing the optical length of the one arm optical waveguide, the optical circuit being provided with a buffer layer having a lower refractive index than the optical waveguide; A silica-based single mode ridge optical waveguide is formed on the planar substrate via the optical waveguide, and the upper and side surfaces of the optical waveguide are covered with a cladding layer having a lower refractive index than that of the optical waveguide. An optical waveguide gate element characterized by: (2) The optical waveguide gate element according to claim 1, wherein the electrode means is a conductive thin film formed on the flat substrate. (3) The optical waveguide gate device according to any one of claims 1 to 2, wherein the electrode means acts as a heater during operation. (4) The optical waveguide gate device according to any one of claims 1 to 3, wherein the electrode means acts as a heat sink when not in operation.