Optical modulator

Abstract

This optical modulator includes a substrate and a phase modulation unit on the substrate, said phase modulation unit including: a first traveling-wave electrode, a second traveling-wave electrode, and an optical waveguide configured from a first cladding layer, a semiconductor layer, which is laminated on the first cladding layer, and has a refractive index that is higher than that of the first cladding layer, and a second cladding layer, which is laminated on the semiconductor layer, and has a refractive index that is lower than that of the semiconductor layer. The semiconductor layer is provided with: a rib section, which is formed in the optical axis direction of the optical waveguide, and is to be the core of the optical waveguide; a first slab section formed in the optical axis direction on one side of the rib section; a second slab section formed in the optical axis direction on the other side of the rib section; a third slab section formed in the optical axis direction on the first slab section side opposite to the rib section; and a fourth slab section formed in the optical axis direction on the second slab section side opposite to the rib section. The first slab section is formed thinner than the rib section and the third slab section, and the second slab section is formed thinner than the rib section and the fourth slab section.

Description

technical field [0001] The invention relates to an optical modulator used in an optical communication system and an optical information processing system, in particular to a Mach-Zehnder type optical modulator which operates at low voltage and has small waveguide loss. Background technique [0002] The Mach-Zehnder type (MZ type) optical modulator has the following structure: the light incident on the optical waveguide is split into two waveguides through the optical splitter, and after the split light is propagated for a fixed length, it is passed through the optical combination oscillator to combine them again. Phase modulators are installed in the two optical waveguides that are branched to change the phase of the light transmitted to each optical waveguide, change the interference conditions of the combined light, and modulate the intensity or phase of the light. [0003] LiNbO is used as a material for the optical waveguide constituting the MZ-type optical modulator 3...

AI Technical Summary

Problems solved by technology

In this way, there is a problem that the resistance value of the Si semiconductor layer 203 cannot be reduced by making the medium-concentration p-type semiconductor region 203-1 and the medium-concentration n-type semiconductor region 203-2 thick, and the phase inversion voltage Vπ cannot be reduced.

[0020] In addition, as described above, the doping concentration near the rib A0 (core of the optical waveguide) of the Si semiconductor layer 203 cannot be set to a high concentration, so the pn junction or pin junction of the semiconductor constituting the Si semiconductor layer 203 cannot be greatly reduced. resistance value

Therefore, there is also a problem that the resistance value of the Si semiconductor layer 203 causes high-frequency electrical signal loss, and the voltage applied to the pin junction or pn junction is attenuated, so that the phase inversion voltage Vπ cannot be reduced.

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