Optical modulator, semiconductor laser device equipped with an optical modulator, and optical communication system

An optical modulator comprising:

• a semiconductor substrate of a first conductivity type;
• a light absorption layer on the semiconductor substrate and having a multiple quantum well structure, the multiple quantum well structure comprising
• a plurality of first well layers,
• barrier layers sandwiched between the first well layers and having a thickness at which carriers bind together between the first well layers in response to an electric field corresponding to an extinction voltage, and
• a plurality of second well layers, the first and second well layers having respective absorption spectra with respective peak wavelengths, the peak wavelength of the absorption spectrum of the second well layers being shorter than the peak wavelength of the absorption spectrum of the first well layers;
• and
• a semiconductor cladding layer of a second conductivity type on the light absorption layer.

An optical modulator comprising:

• a semiconductor substrate of a first conductivity type;
• a light absorption layer on the semiconductor substrate and having a multiple quantum well structure, the multiple quantum well structure comprising
• a first well layer,
• a plurality of second well layers,
• a first barrier layer interposed between the first well layer and one of the second well layers, the first and second well layers having respective absorption spectra with respective peak wavelengths, the peak wavelength of the absorption spectrum of the second well layers being shorter than the peak wavelength of the absorption spectrum of the first well layer, and
• second barrier layers having a band-gap wavelength, wherein the first barrier layer has a width thicker than the second barrier layers, the second barrier layers are sandwiched between pairs of the second well layers, and the first barrier layer has a band-gap wavelength no longer than the band-gap wavelength of the second barrier layers;
• and
• a semiconductor cladding layer of a second conductivity type on the light absorption layer.