Optical signal generator

An optical signal generator provided with a plurality of modulation parts connected in series in a path of an optical signal, and configured to generate a multilevel-coded modulated optical signal by modulating an intensity of an input optical signal from a light source based on a modulation signal, the optical signal generator comprising:

• a plurality of electro-absorption optical modulators are respectively provided to each of the modulation parts, and the electro-absorption optical modulators are switch between an ON state of optical absorption and an OFF state of the optical absorption in accordance with the modulation signal;
• and
• a control section configured to generate a binary control signal used to control switching between the ON state and the OFF state of each of the modulation parts from the modulation signal,
• wherein each of the modulation parts has a respective extinction ratio of the ON state to the OFF state, and the extinction ratios of at least two of the modulation parts are different from each other,
• wherein the modulation parts are located so that the lower the extinction ratio is of the respective modulation part, the closer to the light source the respective modulation part is located,
• wherein the electro-absorption optical modulators of the respective modulation parts are arranged along the path of the optical signal to form an optical semiconductor element, and the optical semiconductor element has an electrode pad disposed between at least two of the electro-absorption optical modulators disposed adjacent to the electrode pad and which is not electrically connected to the at least two of the electro-absorption optical modulators disposed adjacent to the electrode pad, and
• wherein a bonding wire is configured to connect the electrode pad and a direct-current power supply and is disposed between the at least two of the electro-absorption optical modulators disposed adjacent to the electrode pad.

An optical signal generator provided with a plurality of modulation parts connected in series in a path of an optical signal, and configured to generate a multilevel-coded modulated optical signal by modulating an intensity of an input optical signal from a light source based on a modulation signal, the optical signal generator comprising:

• a plurality of electro-absorption optical modulators are respectively provided to each of the modulations parts, and the electro-absorption optical modulators are switched between an ON state of optical absorption and an OFF state of the optical absorption in accordance with the modulation signal;
• and
• a control section configured to generate a binary control signal used to control switching between the ON state and the OFF state of each of the modulation parts from the modulation signal,
• wherein each of the modulation parts has a respective extinction ratio of the ON state to the OFF state, and the extinction ratios of at least two of the modulation parts are different from each other,
• wherein the modulation parts are located so that the lower the extinction ratio is of the respective modulation part, the closer to the light source the respective modulation part is located,
• wherein the electro-absorption optical modulators are provided to an optical semiconductor element formed on a semi-insulating substrate, and
• wherein a plurality of driving electrode pads, including a plurality of positive terminals and a plurality of negative terminals to which a plurality of wires for supplying the electro-absorption optical modulators with drive voltages are connected, are disposed on a principal surface of the optical semiconductor element opposite to the semi-insulating substrate.