Semiconductor optical modulator

A Mach-Zehnder semiconductor optical modulator comprising:

• an input optical waveguide;
• two interference optical waveguides branched from the input optical waveguide, in which a refractive index of a core is modulated by an electrical signal;
• and
• an output optical waveguide for multiplexed modulated light from the two interference optical waveguides,
• wherein in each of the interference optical waveguides,
• a first n-type clad layer,
• a p-type electron barrier layer,
• a first buffer layer,
• a multi quantum well layer constituting the core,
• a second buffer layer, and
• a second n-type clad layer, are arranged, on a substrate surface equivalent to a (100) plane of a semi-insulating InP semiconductor crystal substrate, in an order named from the InP semiconductor crystal substrate to an upper layer, and
• the first buffer layer contains only As as a V group element.

A Mach-Zehnder semiconductor optical modulator comprising:

• an input optical waveguide;
• two interference optical waveguides branched from the input optical waveguide;
• and
• an output optical waveguide for multiplexed modulated light from the two interference optical waveguides,
• wherein each of the interference optical waveguides comprises:
• a first n-type clad layer;
• a p-type electron barrier layer doped with carbon as a p-type dopant;
• an undoped layer comprising a multi quantum well layer that forms a core, the undoped layer being free of an InGaAsP diffusion stop layer between the p-type electron barrier layer and the multi quantum well layer;
• and
• a second n-type clad layer,
• wherein the undoped layer contains only As as a V group element in a region between the p-type electron barrier layer and the multi quantum well layer.

A method of manufacturing a Mach-Zehnder semiconductor optical modulator, comprising:

• sequentially depositing, on a substrate surface equivalent to a (100) plane of a semi-insulating InP semiconductor crystal substrate by organic metal vapor phase growth:
• a first n-type clad layer;
• a p-type electron barrier layer doped with carbon;
• a first buffer layer containing only As as a V group element;
• a multi quantum well layer;
• a second buffer layer;
• and
• a second n-type clad layer;
• forming an input optical waveguide, two interference optical waveguides branched from the input optical waveguide, and an output optical waveguide for multiplexed modulated light from the two interference optical waveguides;
• and
• forming a capacitive load type traveling-wave electrode above the two interference optical waveguides.