Optical element and method for manufacturing same, and optical modulator

Abstract

Provided are an optical element which can be inexpensively and easily manufactured and which is capable of adequately reducing or removing a higher mode while keeping loss of a fundamental mode low, amethod for manufacturing the same, and an optical modulator. The present invention has a substrate and first through third optical waveguides formed on the substrate and each having a lower claddinglayer, a core layer, and an upper cladding layer, the core layer having a larger refractive index than the lower cladding layer and the upper cladding layer, the first optical waveguide being optically connected to the second optical waveguide, the second optical waveguide being optically connected to the third optical waveguide, the first through third optical waveguides having a mesa structure in which top parts of at least the upper cladding layer and the core layer protrude on the lower cladding layer, the core height of the third optical waveguide being less than the core height of the first optical waveguide, the core height being the height to the top surface of the core layer from bottom surfaces on both sides of the mesa structure or locations where the inclination of lateral surfaces of the mesa structure becomes discontinuous approaching the bottom surfaces, and the mesa width of the third optical waveguide being less than the mesa width of the first optical waveguide, the mesa width being the width of the middle of the core layer.

Description

technical field [0001] Optical element, manufacturing method of optical element, and optical modulator Background technique [0002] As an optical waveguide, a semiconductor optical waveguide formed on a semiconductor substrate and having a core layer and a cladding layer made of a semiconductor material is known. As a waveguide structure of a semiconductor optical waveguide in an optical functional element or the like, for example, a structure called a high mesa structure is used. An optical waveguide with a high mesa structure has a feature that the waveguide loss is small and the bending radius can be reduced. [0003] The optical waveguide with high mesa structure is difficult to suppress high-order transverse modes due to the very narrow cut-off mesa width. Therefore, optical waveguides with high mesa structures are usually designed to increase the loss of high-order modes. Specifically, the equivalent refractive index of the high-order mode is designed to be smaller...

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Problems solved by technology

As a result, the high-order modes are radiated toward the substrate side, resulting in an increase in the loss of the high-order modes.

[0004] On the other hand, in an optical waveguide with a high mesa structure, if the mesa width is too narrow to increase the high-order mode loss, even the fundamental mode loss will increase.

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