JPS63168620A - Variable step type optical attenuator - Google Patents

Abstract

PURPOSE:To obtain an optical attenuator which is free from difficulty of optical axis alignment for production and has a satisfactory vibration-proof characteristic to have a high stability, by providing two waveguides different in propagation loss formed on the surface of a substrate and a pair of optical switches which select one of these waveguides. CONSTITUTION:A waveguide 2 which is unified in one end and is branched into two twice to become four parallel waveguide parts 21-24 and is coupled twice to be unified in the other end is formed on the surface of a substrate 1. Loaded metallic films 31-34 for loss adjustment are provided on parallel waveguide parts 21-24, and the waveguide loss is different by the length of the metallic film loaded on each of parallel waveguide parts 21-24. Electrodes 4 are formed in respective Y-shaped branch parts to form Y branch type optical switches which use the electrooptic effect due to voltage application to electrodes. Either of waveguide parts is selected by the switch in each Y-shaped branch part to select one of four parallel waveguide parts 21-24.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an optical attenuator that can vary the amount of attenuation of transmitted light in steps.

[Conventional technology]

Optical attenuators are devices that attenuate the amount of light that passes through them.In addition to fixed optical attenuators that have a fixed amount of attenuation and have a medium with a constant transmittance placed on the optical path, there are also variable attenuators that can change the amount of attenuation. A type optical attenuator is used. Conventionally, this variable optical attenuator uses a rotatable disk-shaped filter whose transmittance gradually changes in the circumferential direction as the attenuating section, and an optical fiber for the input/output section, which controls the input light. The main configuration is that the light from the fiber is sent to the above-mentioned attenuation section through an optical system such as a rod lens, and the light that has passed through this attenuation section is made to enter the output optical fiber again through an optical system such as a rod lens. It is taken by. Therefore, since this variable optical attenuator uses optical fibers for the light input/output section, there is no need for troublesome alignment during use, and it is sufficient to simply connect the optical fibers with each other using a connector etc. Very convenient.

[Problems to be solved by the invention]

However, in the conventional variable optical attenuator as described above, the optical system that inputs the light emitted from the input optical fiber to the attenuator and the optical system that inputs the light emitted from the attenuator to the output optical fiber. Since the optical axes must be aligned, there is a problem in that manufacturing is not easy. In addition, it is not easy to fix these optical fibers, optical systems, and attenuation parts with high precision, and even if they can be fixed with high precision, it is difficult to maintain the fixation precision when vibrations are applied, making them earthquake resistant. This is also a problem in terms of characteristics. An object of the present invention is to provide a step variable optical attenuator that is free from difficulties in optical axis alignment during manufacturing, has good seismic characteristics, and is highly stable.

[Means to solve the problem]

The step-variable optical attenuator of the present invention includes at least two waveguides having mutually different propagation losses formed on the surface of a substrate, and one of these waveguides provided at both ends of the waveguide on the surface of the substrate. and a pair of optical switches for selection.

[Operation] By selecting one of a plurality of waveguides with different propagation losses using a pair of optical switches, the amount of attenuation can be varied stepwise. Since a plurality of waveguides with different losses and a pair of switches are formed on the surface of one substrate, seismic characteristics and stability are essentially good. In addition, there is no need for optical axis alignment, and manufacturing is easy.

【Example】

A step variable optical attenuator according to an embodiment of the present invention is formed on one substrate 1, as shown in the figure. That is, a pattern as shown in the figure is formed on the surface of the substrate 1, that is, there is one waveguide at one end, but it branches twice in a Y-shape to become four parallel waveguides 21 to 24, again in a Y-shape.
A waveguide 2 is formed in a pattern in which the waveguides are grouped together and become one at the curved end. Then, the parallel waveguide section 21~
Loaded metal films 31 to 34 are provided on top of 24 for loss adjustment. The lengths of the metal films loaded on each of the parallel waveguides 21 to 24 are different, and the waveguide loss is made to vary depending on the length. Furthermore, an electrode 4 is formed in each of the Y-shaped branch parts, and a Y-branch type optical switch is formed that utilizes the electro-optic effect produced by applying a voltage to this electrode. By selecting one of the four parallel waveguide sections 21 to 24 at the Y-shaped branch section using these switches, one of the four parallel waveguide sections 21 to 24 can be selected, and in this case, the amount of attenuation can be changed in four stages. Groove blocks 5.6 in which grooves are formed in advance are fixed to both ends of the substrate 1, and optical fibers 7.8 are fixed to the V grooves on the input side of the waveguide 2. and is optically coupled to the output end. To explain an example of a method for manufacturing such a step-variable optical attenuator, the substrate 1 has a thickness of, for example, 500 mm.
Using a .mu.m LiNbO3 substrate, a Tt film is sputtered on the surface using a lift-off method using a mask, and then thermal diffusion is performed to diffuse Ti to a width of about 7 .mu.m to form the waveguide 2 with the above pattern. do. Next, the loaded metal film 3
1 to 34 and the switch electrode 4 are similarly formed of At using the lift-off method. In this case, the loaded metal film 31~
34 and the switch electrode 4 are not necessarily made of the same metal, and the relationship between loading length and loss differs depending on the type of metal, but using the same metal material requires fewer manufacturing steps and is advantageous in terms of manufacturing. It is. (2) For the groove block 5.6, for example, a 500 μm thick Si wafer, which is the same thickness as the substrate 1 described above, is used, and this is etched with a 30% KO3 etching solution to form a V-groove. This is cut to the same width as the substrate 1, butted against the substrate 1, and fixed with adhesive. In this embodiment, the length of the parallel waveguide sections 21 to 24 is 50 mm.
0am, AI loading metal film 31.32.33.34
The respective lengths of Ottm, 100 μm, 200 μm, 3
00μm, the relative output is OdB, -1,2d
B, -2.5 dB, and -3°8 dB, so these four levels of attenuation can be selected by changing the switch. In the above embodiments, a Y-branch type optical switch was used, but a directional coupling type or an X-type optical switch may be used, and the present invention is not limited to the embodiments.

【Effect of the invention】

According to the step variable optical attenuator of the present invention, 1
Since it has a structure in which a waveguide and a switch are formed on one substrate, it has high mechanical stability and good earthquake resistance, and it is easy to manufacture because there is no need for optical axis alignment.

[Brief explanation of the drawing]

The figure is a schematic perspective view of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Waveguide, 21-24... Parallel waveguide part, 31-34... Metal film, 4... Switch electrode, 5.6... ■Groove block, 7.8...Optical fiber.

Claims (2)

[Claims] (1) At least two waveguides having mutually different propagation losses formed on the substrate surface, and a pair of waveguides for selecting one of these waveguides provided at both ends of the waveguides on the substrate surface. A step variable optical attenuator comprising an optical switch. (2) The step variable optical attenuator according to claim 1, wherein V-groove members for positioning the optical fiber are fixed to both ends of the substrate.