JP2853663B2 - Integrated optical circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical circuit, and more particularly, to an integrated optical circuit that forms an optical control device using an optical waveguide provided in a substrate.

[0002]

2. Description of the Related Art In recent years, as optical communication systems have been put into practical use, larger-capacity, higher-performance optical communication systems have been desired, and light control elements such as higher-speed light wave modulators and optical switches have become necessary. ing. In particular, for a waveguide type optical circuit that performs control using an optical waveguide provided in a substrate,
For example, Okayama et al.
Further, as described by Nishimoto et al. In "Optics", Vol. 1, No. 8, pp 521, it is possible to integrate many optical circuits in one element by using ordinary photolithography technology. A matrix optical switch used for optical switching or optical cross-connect as an optical device utilizing this feature includes a plurality of optical switch elements, for example, 1 × 2 or 2 × 2 switches in parallel and according to the required number of channels. It is configured by connecting in tandem. As an optical switch element, a Mach-Zehnder interferometer having a phase shifter between two 3 dB couplers, a directional coupler, and a digital optical switch that performs an optical switch by giving a refractive index change to each branch of a Y branch Is generally used.

[0003] The optical wiring constituting these optical switch elements and the optical wiring for connecting the respective optical switch elements are optically connected to the switching elements constituting the optical switch elements, or the optical switch elements formed and arranged are arranged. In general, a bent optical waveguide is used for optical connection to each other. For this reason, in order to reduce the size of the optical switch element and the integrated optical circuit including the optical switch element, it is desirable that the bend radius of the bend optical waveguide be as small as possible within a range where excess radiation loss is small. As a method for reducing the radiation loss of the bent optical waveguide, a technique has been proposed in Japanese Patent Application Laid-Open No. 7-212655 in which the film formation and diffusion of Ti on a LiNbO ₃ substrate are repeated a plurality of times.

[0004]

In such an integrated optical circuit, when a directional coupler or a Mach-Zehnder type interference system is used for the optical switch element, the optical wiring and the direction to the 3 dB coupler in the optical switch element are controlled. It is desirable that the optical wiring to the sex coupler is also coupled by a bent optical waveguide having a bending radius as small as possible. For this reason, conventionally, optical wiring is performed between optical switch elements or within an optical switch element by using an optical waveguide having a minimum bend radius with almost no radiation loss in the optical waveguide. In the coupler section described above, excessive loss may occur between the bent optical waveguide and the coupler section. Therefore, conventionally, an optical wiring is formed by an optical waveguide having a bend radius that does not cause excessive loss in a coupler section in an optical switch element, and an optical wiring between optical switch elements is formed by using an optical waveguide having the same bend radius. Therefore, the area occupied by the optical waveguide between the optical switch elements is particularly large, which has been an obstacle to further miniaturizing the integrated optical circuit.

It is known that the operating voltage of an optical switch element using a directional coupler or a Mach-Zehnder interference system decreases as the electrode length increases. Reducing the operating voltage in this manner is preferable because it is difficult to configure a high-voltage circuit capable of high-speed operation when performing high-speed operation. However, when the electrode length is increased, it becomes more difficult to reduce the size of the optical switch element or the integrated optical circuit in combination with the increase in the area occupied by the bent optical waveguide.

An object of the present invention is to provide an integrated optical circuit which is small in size, has low loss, and can operate at low voltage.

[0007]

According to the present invention, an optical waveguide for guiding an optical signal to a substrate made of a translucent material, and an optical control device for controlling the intensity or propagation direction of light are formed. In an integrated optical circuit in which an optical waveguide and an optical control device are optically connected, the optical control device is
With respect to the radius of curvature of the internally curved optical waveguide to be configured,
The light control device is more distant than the partially bent optical waveguide.
Externally bent light guide of the optical waveguide located on the
It is characterized in that the curvature radius of the wave path is formed small . Further, it is preferable that the direction of the connection between the internal bent optical waveguide included in the light control device and the external bent optical waveguide connected to the light control device is the same.

In a preferred embodiment of the present invention, in the light control device, the phase shift section and the coupler section are connected by an internally bent optical waveguide, and an electrode constituting the phase shift section is provided on at least a part of the internally bent optical waveguide. Extended to Further, the light control device is configured as an optical switch element, and a matrix switch is configured by the plurality of optical switch elements and the plurality of optical waveguides.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of one embodiment of the present invention, and is an example in which a 4 × 4 matrix switch is configured. Four Mach-Zehnder interference systems 1 are provided as optical switch elements.
Are connected to each other by an externally bent optical waveguide 2 to form 4 × 4
A matrix switch is configured. In the Mach-Zehnder interference system 1, the phase shifter section 11 and the coupler section 12 are optically connected by an internally bent optical waveguide 13, and the internally bent optical waveguide 13 is connected to the coupler section 12 and the internally bent optical waveguide 1.
3 with a bend radius that does not cause excessive loss. On the other hand, the external bend optical waveguide 2 used for optical wiring between the optical switch elements is formed with a minimum bend radius in which bend excess loss is sufficiently small. In this case, the minimum bend radius of the internal bend optical waveguide 13 of the optical switch element 1 is set to be larger than the minimum bend radius of the external bend optical waveguide 2 between the optical switch elements 1.

According to this structure, a bent optical waveguide having a minimum bend radius that does not cause excessive loss is used as the external bend optical waveguide 2 for optically connecting the optical switch elements 1 with each other. Since the inner bend optical waveguide 13 in the optical switch element 1 is smaller than the minimum bend radius, the excess loss between the coupler section 12 and the inner bend optical waveguide 13 in each optical switch element 1 does not occur. The area occupied by the external bent optical waveguide 2 between the optical switch elements 1 can be reduced, the overall dimensions of the integrated optical circuit can be reduced, and the size can be reduced. On the other hand, when the maximum length of the optical circuit is limited by the wafer size or the like, the length of the optical switch element 1 is maximized by minimizing the length of the optical wiring between the optical switch elements 1. Can be Therefore, the length of the phase shifter section 11 in the Mach-Zehnder optical switch element 1 can be lengthened accordingly, and the operating voltage can be reduced.

FIG. 2 is a diagram showing one example of the phase shifters 11 and 3 of the Mach-Zehnder switch element 1. As shown in FIG.
The dB coupler section 12 is optically connected by an internal bending optical waveguide 13, and the bending radius of the internal bending optical waveguide 13 is made larger than the bending radius of the external bending optical waveguide 2 for optically connecting the optical switch elements 1. . Then, the electrodes 14 and 15 formed on the phase shifter section 11 are extended to the internal bent optical waveguide 13. This allows
The effective length of the phase shifter 11 can be increased, and the operating voltage can be reduced. Conversely, when the length of the optical switch element 1 is constant, the length of the phase shifter section 11 is reduced by increasing the bending radius of the internal bending optical waveguide 13, As described above, by extending the electrodes 14 and 15 to a part of the internally bent optical waveguide 13, the substantial length of the phase shift other portion 11 hardly changes, and the optical switch element can be hardly increased without increasing the operating voltage. Can be reduced.

The same applies to the case where a directional coupler or a digital switch is used for an optical switch element. In addition, between the optical switch element and the optical wiring for optically connecting the optical switch elements, coupling of two bent optical waveguides having different bending radii occurs, but this portion is formed by matching the directions of the waveguides and smoothly coupling them. Excess loss is suppressed.

[0013]

EXAMPLE As shown in FIG. 3, an 8 × 8 matrix switch operating in a 1.3 μm band is formed. First, x-cu
A 400 A Ti film is formed on a LiNbO ₃ substrate with tZ-axis propagation, and after 12H diffusion at 1000 ° C.,
By forming a 00A film and diffusing 12H at 1000 ° C.
4A and 4B show the relationship between the bending radius and the bending radiation loss at this time when an optical waveguide satisfying the single mode condition at 31 μm and having a bending radius R of 30 mm or more and having no excessive radiation loss was formed. . When a Mach-Zehnder interference system was formed under the conditions for forming the waveguide, a bending element having a bending radius of 50 mm or more before and after the 3 dB coupler portion and having no excess loss could be formed. 3dB
FIG. 5 shows the relationship between the bending radius before and after the coupler section and the insertion loss of the element. This figure shows the loss of the optical switch element and the bending radiation loss of the bending waveguide included in the optical switch element. As is clear from the figure, when the bending radius is 50 mm or more, the bending radiation loss matches the excess loss of the optical switch element, and there is no excess loss.

In this way, an integrated optical circuit comprising the 8 × 8 matrix switch shown in FIG. 3 was formed. The minimum bending radius of the optical wiring connecting the optical switch elements 1 is 30.
The externally bent optical waveguide 2 of mm and the internal bent optical waveguide of the switching element of the optical switch element 1 composed of a Mach-Zehnder interference system were designed with a bending radius of 50 mm. As a result, the insertion loss of the 8 × 8 switch is 12
It could be reduced to below dB. Further, the electrodes of the phase shifter portion were extended to the inside bent optical waveguide portion as shown in FIG. As a result, a sufficient electrode length could be ensured even if the bending radius of the internal bending optical waveguide of the switching element was increased.

Also, a 4 × 4 matrix switch operating in the 1.5 μm band as shown in FIG. 1 is formed. In this case, a film of Ti is formed at a thickness of 600 A on a LiNbO ₃ substrate of x-cut Z-axis propagation, and after a 12H diffusion at 1000 ° C., a further 600 A film of Ti is formed and a 12H diffusion at 1000 ° C. is repeated twice. An optical waveguide satisfying the single mode condition and having a bending radius of R = 40 mm or more and having no excessive radiation loss was formed. FIG. 6 shows the relationship between the bending radius and the bending radiation loss at this time. When a Mach-Zehnder interference system is formed under the conditions for forming the waveguide, 3 dB
The bending radius of the optical waveguide before and after the coupler is 50 mm
Thus, a switching element without excess loss was formed.

Thus, an integrated optical circuit comprising the 4 × 4 matrix switch shown in FIG. 1 was formed. An externally bent optical waveguide having a minimum bend radius of 40 mm was used for the optical wiring connecting the optical switch elements, and the internal bend optical waveguide of the switching element of the optical switch element composed of a Mach-Zehnder interference system was designed to have a bend radius of 60 mm. As a result, the insertion loss of the 4 × 4 switch is 5.
It could be reduced to 0 dB or less. In addition, the phase shifter section was able to secure a sufficient electrode length even if the bending radius of the switching element was increased by extending the electrode to the internally bent waveguide portion as shown in FIG.

In the above embodiment, x-cutZ-
The description has been made by taking the example of a Ti-diffused optical waveguide on an axially propagated LiNbO ₃ substrate, but the optical wiring between the elements is formed with a minimum bend radius that does not cause excessive bending and excessive loss, and the element generates element excessive loss. Forming with a bend radius that does not have an effect is obvious even if it is applied to an optical waveguide on any substrate. For example, the present invention is applicable to a case where a Z-CutLiNbO ₃ substrate is used, a case where a glass waveguide is used, and a case where a semiconductor waveguide is used. Here, the Mach-Zehnder type optical switch is described as a main example, but it is apparent that the same effect can be expected in a directional coupler or a digital type optical switch which gives a difference in refractive index between the left and right of the Y branch.

[0018]

As described above, the present invention constitutes an optical waveguide for guiding an optical signal provided in an integrated optical circuit.
The curvature radius of the outer curved optical waveguide and the inner curved optical waveguide constituting the optical control device optically connected to the optical waveguide are different, particularly, the curvature of the inner curved optical waveguide.
For the radius, the light control for the internal bent optical waveguide
By using a configuration in which the radius of curvature of the externally bent optical waveguide located farther from the control device is small, excess loss in each of the optical control device and the optical waveguide can be reduced, and the radius of curvature of the externally bent optical waveguide can be reduced. By reducing the size, the size of the integrated optical circuit can be reduced, and moreover, the effective length of the electrodes in the optical control device can be increased to achieve operation at a low voltage.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a 4 × 4 matrix optical switch according to an embodiment of the present invention.

FIG. 2 is a plan view of a Mach-Zehnder type optical switch element.

FIG. 3 is a configuration diagram of an 8 × 8 matrix optical switch according to an embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a bending radius and a radiation loss in a bent optical waveguide.

FIG. 5 is a diagram showing a relationship between a bent optical waveguide and excess loss in a switching element of a Mach-Zehnder type optical switch element.

FIG. 6 is a diagram showing a relationship between a bending radius of a bent optical waveguide and a radiation loss in the example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical switch element (Mach-Zehnder interference system) 2 Externally bent optical waveguide 11 Phase shifter part 12 Coupler part 13 Internally bent optical waveguide

Claims (4)

(57) [Claims] An optical waveguide for guiding an optical signal to a substrate made of a translucent material, and an optical control device for controlling the intensity or propagation direction of light are formed, and these optical waveguide and the optical control device are formed. In an integrated optical circuit optically connected, an internally bent optical waveguide constituting the optical control device
For the radius of curvature of the inner bend optical waveguide than the
The light control device is located on a side remote from the light control device;
External bend of optical waveguide Formed with small radius of curvature of optical waveguide
Integrated optical circuit, characterized in that it is. Wherein said inner curved optical waveguide included in the optical control device, before being connected to the light control device
Serial integrated optical circuit according to claim 1 which direction is being matched at the connections with the outside bend optical waveguide. Wherein the light control device, and a phase shift portion and the coupler portion are connected by the inner curved optical waveguide,
3. The electrode according to claim 2, wherein the electrode constituting the phase shift portion is extended to at least a part of the internally bent optical waveguide.
An integrated optical circuit as described . Wherein said light control device is an optical switch element, the matrix switch is claim 1 comprised of a plurality of optical switch elements and a plurality of optical waveguides
4. The integrated optical circuit according to any one of the items 3 above .