JPS63168619A - 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 is easily miniaturized and has a high mechanical stability, by providing two curved waveguides different in curvature radius 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 go to four curved waveguide parts 21-24 and is coupled twice to be unified in the other end is formed on the surface of a substrate 1. Curved waveguide parts 21-24 are formed on concentric circles so that they are different in curvature radius, and the waveguide loss is different by each curvature radius. Electrodes 3 are formed in respective Y-shaped branch parts to form Y branch optical switches which use the electrooptic effect due to voltage application to electrodes 3, and either of curved waveguides is selected by the switch in each Y-shaped branch part to select one of four curved 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]

An optical attenuator attenuates the amount of light that passes through it, but instead of a fixed type optical attenuator that has a fixed amount of attenuation and has a medium with a constant transmittance placed on the optical path, there is a variable type that can change the amount of attenuation. A type optical attenuator is used. Conventionally, this variable optical attenuator uses a rotatable circular filter whose transmittance gradually changes in the circumferential direction as the attenuation section, and an optical fiber for the input/output section. The configuration is such that the light from the optical fiber is sent to the above-mentioned attenuator through an optical system such as a rod lens, and the light that has passed through the attenuator is made to enter the output optical fiber again through the rod lens or other optical system. It is mainly taken. Therefore, since this variable optical attenuator uses optical fibers for the light input and output parts, 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 into the attenuation section and the optical system that inputs the light emitted from the attenuation section to the output optical fiber are Since the optical axis must be aligned, there is a problem 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. SUMMARY OF THE INVENTION An object of the present invention is to provide a step-variable optical attenuator that does not have difficulty in aligning optical axes during manufacturing, is easily miniaturized, and has high mechanical stability.

[Means to solve the problem]

The step-variable optical attenuator of the present invention includes at least two curved waveguides with different bending radii formed on the surface of a substrate, and one of these waveguides provided at both ends of the curved waveguide on the surface of the substrate. and a pair of optical switches for selecting one.

[For production]

When a waveguide is curved, mode conversion of the propagating light occurs, increasing transmission loss, and radiation loss occurs when light radiates outward from the waveguide at the bend. Determined according to the bending radius. Therefore,
Multiple curved waveguides with different bending radii are formed,
Selecting one of the waveguides using a pair of optical switches:
The amount of attenuation can be varied in stages. This is because a plurality of waveguides with different bending radii and a pair of optical switches are formed on the surface of one substrate. Mechanical stability and seismic properties are inherently good and miniaturization is easy. 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 curved waveguides 21 to 24, again forming two groups in a Y-shape. A waveguide 2 is formed in a pattern in which the waveguides are coupled and become one at the other end. Then, the curved waveguide section 2
1 to 24 are formed concentrically with different bending radii, and the waveguide loss varies depending on each bending radius. Furthermore, an electrode 3 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 the electrode 3. Depending on which one of the four curved waveguide sections 21 to 24 is selected at the Y-shaped branch section, one of the four curved waveguide sections 21 to 24 can be selected.
The amount of attenuation can be changed in stages. 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 μm LiNbO3 substrate, a Ti film was sputtered on the surface by the riff I-off method using a mask, and then thermal diffusion was performed to diffuse Ti to a width of about 7 Bm to form the pattern described above. A waveguide 2 is formed. Next, like the switch electrode 3, it is formed by AI using the lift-off method. In this example, the bending radius of each of the curved waveguide sections 21 to 24 was set to 4 mm, 3 mm, 2 mm, and 1 mm, and the respective attenuation amounts were measured to be 1.05 dB and 2.30 dB.
B, 3.65 dB, and 5.20 dB, so these four levels of attenuation can be selected by changing the switch. Incidentally, although not shown, by fixing groove blocks in which V grooves are formed in advance on both ends of this substrate 1, and fixing optical fibers to these V grooves, the input side and output side ends of the waveguide 2 are fixed. It is desirable that the input optical fiber and the output optical fiber be optically coupled to each other. This V-groove block has a thickness of 500 μm, which is the same thickness as the substrate 1 described above.
This Si wafer is etched with a 30% KO3 etching solution to form a groove.This is cut to the same width as the substrate 1, butted against the substrate 1, and fixed with an adhesive. Further, 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 above embodiments.

【Effect of the invention】

According to the step variable optical attenuator of the present invention, 1
Because it has a structure in which the waveguide and optical switch are formed on one substrate, it has high mechanical stability, good earthquake resistance, and can be made very compact, making it unnecessary to align the optical axis. It is easy to manufacture.

[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... Curved waveguide part, 3... Switch electrode.

Claims (1)

[Claims] (1) At least two curved waveguides with different bending radii formed on the substrate surface, and a method for selecting one of these waveguides provided on the substrate surface at both ends of the curved waveguide. A step variable optical attenuator comprising a pair of optical switches.