JPS60182425A - Manufacture of optical control system - Google Patents

Abstract

PURPOSE:To manufacture light guides different in refractive indexe in one body by forming partially different-thickness beltlike thin-film patterns which contain metal atoms on a substrate. CONSTITUTION:Part corresponding to input/output light guides 5-8 are covered with a shield plate to vapor-deposit Ti films, and thus light guide patterns 110 are formed of the Ti films which have film thickness t1 at the part of an optical control element and t2 (t2<t1) at parts of the input/output light guides. The gap between the shield plate and substrate is adjusted and the shield plate is moved gradually during vapor deposition to form an optional taper shape. In another way, the thin films are made constant in thickness and then the substrate is heated at different temperatures locally to obtain a refractive index distribution.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a light control element that modulates light waves, switches light paths, etc., and particularly relates to a waveguide type light control device that performs control using an optical waveguide provided in a substrate. This invention relates to a method of manufacturing a circuit.

(Prior art and its problems) As the practical use of optical communication systems progresses, advanced systems with larger capacity and multiple functions are being sought. There is a need to add new functions such as generation of faster optical signals and switching and exchanging optical transmission lines. In current practical systems, optical signals are obtained by directly modulating the injection current of a semiconductor laser or light emitting diode, but with direct modulation, high-speed modulation of several GHz or more is difficult due to effects such as relaxation oscillation. 5There are drawbacks such as difficulty in applying the coherent optical transmission method due to wavelength fluctuations.There is a method to solve this problem [7], but there is a method to use an external optical modulator. The waveguide type optical modulator constructed using the formed guide wavepath has the features of being small, highly efficient, and high speed. On the other hand, an optical switch is used as a means for switching optical transmission lines and providing network switching functions. Optical switches currently in use mechanically move prisms, mirrors, fibers, etc., and have drawbacks such as slow speed, insufficient reliability, and large size making them unsuitable for matrix formation. A waveguide-type optical switch using an optical waveguide is being developed as a means to solve this problem, and has features such as high-speed integration of multiple elements and high reliability.

In particular, materials using ferroelectric materials such as LiNbO3 crystals have features such as low light absorption, low loss, and high efficiency due to a large electro-optic effect. Various types of optical control elements such as coupled optical modulators or switches and total internal reflection optical switches have been reported. When such a waveguide type optical control element is applied to an actual optical communication system, low loss and high speed are required. In the optical waveguide formed by diffusing Ti in LiNbO3 crystal, the wavelength is 0.
A small propagation loss of 1 to 0.2 dB/α has been obtained.

When applied to an actual optical fiber system, it is necessary to sufficiently reduce the coupling loss with the optical fiber, so the optical energy distribution of the propagation mode of the optical waveguide is changed to the optical energy distribution of the propagation mode of the optical fiber. The leading wavepath is created so as to be as close as possible. By the above method, a loss value of 1 to 2 dB has been obtained when an optical waveguide is inserted between optical fibers.On the other hand, in an actual system, an optical control element using the electro-optic effect as described above is used. When used, the operating speed is usually determined by the performance of the drive circuit. Increased drive circuit speed and reduced power consumption,
For miniaturization, it is practically important to reduce the operating voltage of the light control element as much as possible. However, in order to reduce the voltage of the optical control element, it is necessary to concentrate the optical energy of the propagation mode near the electrode where the applied electric field strength is large, and the conditions for this voltage reduction are generally the same as those of the optical fiber mentioned above. This is different from the conditions for reducing coupling loss. The optical energy distribution of a commonly used single mode optical fiber has an intensity of 17e4. Since the width is about 6 to 8 μm, when low-loss coupling is aimed at, the optical energy distribution of the optical waveguide is also selected to be about the above value. This condition is, for example, V Ramaswamy (V, Ramasw)
amy) %7- Le Fist So Alphaness (Ro
C, Alferness), M Dehi/ (M, D
iv 1no) by Electronics Letters Magazine (
Electronics Letters) Vol. 18, No. 1, pages 30 to 31b On the other hand, in order to lower the voltage, the width of the optical energy distribution of the propagation mode of the optical waveguide should be changed by the low-loss coupling with the above-mentioned optical fiber. It is necessary to choose a width that is smaller than the appropriate width. Regarding the trade-off between this low voltage condition and the condition to reduce the coupling loss with the optical fiber, see El Rivière (L, Rivi).
4th International Conference on Integrated Optics and Fiber Communications
erence on IntegrationRted 0pti
csand 0ptical Fiber Commu
nication) Technical Digest 29C
4-4 (pages 362-363).

As mentioned above, conventional optical control elements have the drawback that both low-loss coupling and low-voltage operation cannot be achieved at the same time.

(Objective of the present invention) The object of the present invention is to eliminate the drawbacks of the conventional light control element described above,
An object of the present invention is to provide an optical control circuit that can be coupled to an optical fiber with low loss and can operate at low voltage, and a method for manufacturing the same.

(Structure of the present invention) The method for manufacturing an optical control circuit according to the present invention has two steps. One is to form a thin film pattern containing band-shaped metal atoms with partially different thicknesses on a substrate, and An optical waveguide is formed by heating and diffusing the thin film pattern into the substrate, and an electrode is installed near the optical waveguide formed by diffusing a thicker part of the thin film pattern, and at least One light control element is formed, and a light input/output end surface is formed at an end of an optical waveguide connected to the light control element and formed by diffusing a thin film pattern of the thin film pattern. ing. Another manufacturing method is
Forming a thin film pattern containing band-shaped metal atoms on a substrate,
By heating the substrate partially at different temperatures, the thin film pattern is diffused into the substrate to form an optical waveguide, and an electrode is placed near the optical waveguide formed in the portion heated at a lower temperature during the diffusion. A configuration in which the optical waveguide is installed to form at least one light control element, and is connected to the light control element and forms an optical input/output end face at the end of the optical waveguide formed in the portion where the heating temperature is high during the diffusion. It becomes.

(Detailed explanation of the configuration) In the present invention, as described above, the optical waveguide constituting the light control element and the input/output optical waveguide connecting it to the optical input/output end surface are made to have different refractive indexes. In the input/output optical waveguide section, the refractive index is set to give a propagation light energy distribution close to the optical energy distribution of the optical fiber.
In addition, independently, by setting the refractive index of the optical waveguide constituting the light control element so that the propagation light energy distribution in that part is sufficiently confined near the electrode, low-loss coupling is possible and low-voltage operation is possible. A light control circuit capable of this can be obtained.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a perspective view of a directionally coupled optical control circuit for explaining an embodiment of the method for manufacturing an optical control circuit according to the present invention. In FIG. 1, optical waveguides 2 and 3 with a width of several to several tens of μm and a length of several to several tens of meters are installed on an LtNbos substrate l, which are adjacent to each other with an interval of several μm, and optical waveguides 2 and 3 with a width of several to several tens of μm and a length of several tens of μm are installed on the LtNbos substrate l. Sin was set up to prevent this.

A pair of electrodes 4 are formed via a film (not shown), and these optical waveguides 2 and 3 and the electrodes 4 constitute a reversely coupled optical control element. Further, output optical waveguides 7 and 8 having output ends 17 and 18 on the end face opposite to the input end of the substrate 1 are connected to the output sides of the optical waveguides 2 and 3, respectively. Here, the optical waveguides 2゜3.5, 6, 7,
8 are all formed by thermally diffusing a Ti thin film pattern formed on the surface of the substrate 1 into the substrate l. The refractive index of the optical waveguides 2 and 3 has a distribution in the depth direction as shown in Figure 2 (al), and the maximum refractive index is n. has a distribution of bl in the depth direction, and the maximum refractive index is n, ash, n
, >n.

("I+nt is about 10 to 1O). Also, (
The depths of the distributions of at and (bl are approximately the same. The connecting portions 9 and 10 between the optical waveguides 2.3 and 5.6, 7.8 have a refractive index of It is formed so that it changes in two from the distribution of FIG. 2 (al) to the distribution of FIG.

The above-mentioned optical control circuit can be obtained, for example, by the following manufacturing method. First, LiNb0. An optical waveguide pattern is created on the substrate using ordinary photolithography technology. That is, 7 photoresists are uniformly coated on a ZiNbO substrate, and the photoresist is exposed to light through a photomask having the same shape as the optical waveguide portion shown in FIG. form.

A TI film is deposited over the entire surface to a thickness of about 500 to 700 A. Next, cover the portions corresponding to the leading waveguides 5, 6, 7.8 with shielding plates, and further apply approximately 200 to 400 A of Ti.
Deposit the film. After that, by dissolving the photoresist film, tl,
t at the part of the incoming and outgoing cutting edge leading wavepath.

An optical waveguide pattern 110 of a TI film having a film thickness of (tl>h) is formed. The boundary between the film thicknesses t1 and t can be formed into an arbitrary tapered shape by adjusting the distance between the shielding plate and the substrate, or by moving the shielding plate intermittently during vapor deposition.

As shown in Figure 3, the substrate with the Ti film pattern is 1
By heating in a diffusion furnace for about 15 to 10 hours at 000 to 1100'O, an optical waveguide as shown in FIG. 1 described above is formed. This manufacturing method utilizes the fact that the refractive index of the optical waveguide depends on the thickness of the Ti film before diffusion.

A transparent and highly insulating buffer film such as 840 is formed on the light control element portion, and an electrode pattern is formed thereon by foot lithography.

Next, the operation of the optical control circuit shown in FIG. 1 will be explained. The incident light 11 to the input end 15 passes through the input optical waveguide 5 and is guided to the optical waveguide 2 of the directionally coupled light control element.The optical waveguides 2 and 3 are close to each other. The length of - is such that when no pressure is applied to the electrode 4, almost 100% of the energy of the incident light is transferred to the optical waveguide 3.
length, ie, equal to one complete bond length.

Therefore, when the applied voltage is 0, the incident light 11 passes through the optical waveguide 3,
It passes through the output optical waveguide 8 and exits from the output end 18. On the other hand, when a voltage is applied to the electrode 4, the matching of the phase constants of the optical waveguides 2 and 30 propagates due to a change in the refractive index due to the electro-optic effect. , passes through the optical waveguide 2 and the output optical waveguide 7 and is emitted from the output end 17.As described above, the optical path of the incident light is switched depending on the presence or absence of the applied voltage. If you pay attention to the output light 1
2 will be modulated by the voltage waveform applied to the electrode 4. The voltage required for the above-mentioned optical path switching or the voltage required for 100% modulation is smaller as the energy of the propagating light is smaller and confined under the electrode.

In this example, the refractive index of the optical waveguides 2 and 3 is shown in FIG.
The energy distribution of the propagating light is as shown in Figure 2 (
As shown in cl, it becomes smaller and is strongly confined within the leading wavepath. On the other hand, input/output optical waveguides 5, 6, 7 .
8, the refractive index is small as shown in Figure 2 fbl, so the energy distribution of the propagating light is widened as shown in Figure 2 fdl, resulting in low loss in the original fiber at the input and output ends 15, 16° and 17.18°. It is possible to combine.

In this example, as shown in Fig. 3, a manufacturing method was used in which the KTi film thickness was made different between the light control element part and the input/output leading waveguide, but a uniform Ti film thickness was used for both parts, so that the thickness of the KTi film was different during thermal diffusion. Even if the temperature of the part where the input/output optical waveguide is formed is higher than the temperature of the part where the optical control element is formed, an optical control circuit similar to that shown in Fig. 1 can be fabricated. Figure 4 shows the fabrication process described above. An example of the method is shown. FIG. 4 is a cross-sectional view showing the thermal diffusion process, where 20 is a cross section of the diffusion furnace, 1 is L i N1
)O.

The substrate, J3 is a Ti film, and 21 is an additional heater installed close to a portion where an input/output optical waveguide is to be formed. The light is diffused by making the incoming and outgoing blade leading waveguide portions have a higher degree of magnification by several tens of degrees than the light control element portion. Other means for locally heating a part of the substrate as described above include methods such as local high-frequency heating, laser, and annealing using a Furano lamp. In this case, the refractive index distribution of the input/output optical waveguide spreads deeper into the substrate than the portion of the light control element, and the maximum refractive index can also be lowered by about 1O order.

FIG. 5 is a plan view showing a total reflection type 2×2 matrix optical switch for explaining the second embodiment of the method for manufacturing an optical control circuit according to the present invention. Electrodes are formed on the respective intersections of two parallel optical waveguides 31, 32 and two leading waveguides 33, 34 that intersect them at a small angle, forming total internal reflection optical switches 24, 25, 26, 27. and total 2X2
A light switch is configured.

Input optical waveguides 37 and 38 having input ends 35 and 36 are connected to the end faces of the LiNbO3 substrate l to the optical waveguides 31 and 32, and LiNb0. Output optical waveguides 41 and 42 having output ends are installed on end faces 39 and 40 of the substrate l facing the above. Here, the optical waveguide 31,
32, 33, 34 are total reflection type optical switches 24, 25, 2, in which the propagating optical energy is strongly confined near the substrate surface.
The thickness of the Ti film was selected to increase the refractive index so that the input/output optical waveguide 37 could operate at low voltage.
．． 38, 41, and 42 have propagation light energy distributions that are the same as the optical energy distributions in the above-mentioned optical fibers so that they can be optically coupled with high efficiency to the single mode optical fibers 43, 44°, and 45.46 connected to their respective end faces. The thickness of the Ti film before diffusion is selected to be smaller than that of the optical waveguides 31, 32, 33, and 34 so as to reduce the refractive index. Also,
Optical waveguides 31, 32, 33, 34 and input/output optical waveguide 37
, 3B.

At the connection portions 41 and 42, the thickness of the Ti film before diffusion is tapered so that the refractive index changes in a tapered manner in the light transmission direction. The operating principle of this embodiment is that by applying a voltage to the electrodes of the total reflection type optical switch at the intersection, the propagating light energy passing through one optical waveguide is reflected and transferred to the other optical waveguide that intersects. , the optical path of the optical signal between the single mode optical fiber 43.44 and the single mode optical fiber 45.46 is switched.

(Effects of the Present Invention) As described above, the present invention provides a method for manufacturing an optical control circuit that can be coupled with optical fibers with low loss and can operate at low voltage. For devices such as branching interference type optical modulators and crossed waveguide type optical switches, it is possible to obtain both low operating voltage characteristics and low loss optical fiber coupling characteristics with a single device, which were conventionally obtained with separate devices. be able to. The substrate material, guiding waveguide shape, electrode shape, etc. used in the present invention are not limited to the above-mentioned examples.
For the optical waveguide, use an optical waveguide using ion exchange or an optical waveguide created by crystal growth, and for the electrode shape, use a traveling waveform electrode that is more suitable for high speed. can do 0

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an optical control circuit for explaining an embodiment of the method for manufacturing an optical control circuit according to the present invention, and FIG. 5 is a perspective view for explaining an embodiment of the method for manufacturing an optical control circuit according to the present invention. Top view of 2×2 matrix light switch, Figures 3 and 4
The figure is a diagram for explaining the method of manufacturing the optical control circuit according to the present invention, and FIG. 2 is a diagram for explaining the principle of the optical control circuit obtained according to the present invention. In the figure, 1 is the substrate, 2, 3, 31, 32, 33, 34
5. is an optical waveguide constituting a light control element; J7,8゜37
．． 38, 41.42 are input/output optical waveguides, 4 is an electrode, 1
1.13 is a diffused Ti film and a thin film.
V= NJ gu4 stomach t yano ゛food Yノ10 薯 4 Figure

Claims (2)

[Claims] (1) forming a thin film pattern containing band-shaped metal atoms with partially different thicknesses on a substrate, heating the substrate to diffuse the thin film pattern into the substrate to form an optical waveguide; At least one light control element is formed by installing an electrode near an optical waveguide formed by diffusing a thicker part of the thin film pattern, and the film of the thin film pattern is connected to the light control element. 1. A method of manufacturing an optical control circuit, comprising forming an optical input/output end face at an end of an optical waveguide formed by diffusing a portion with a small thickness. (2) forming a thin film pattern containing band-shaped metal atoms on a substrate, heating the substrate partially at different temperatures to diffuse the thin film pattern into the substrate to form an optical waveguide; At least one light control element is formed by installing an electrode in the vicinity of the optical waveguide formed in the part where the heating temperature is low during diffusion, and the electrode is connected to the light control element and where the heating temperature is high during the diffusion. 1. A method of manufacturing an optical control circuit, comprising: forming an optical input/output end face at an end of an optical waveguide formed by a section.