Patent ID: 8160458

Claim:
An optical phase modulation evaluating device, comprising: an optical input unit for inputting, as an optical phase modulation signal, a signal modulated in phase by a data signal at a designated symbol rate; an optical dividing unit for dividing said optical phase modulation signal inputted by said optical input unit into a first light beam and a second light beam; a beam splitter for splitting said first light beam into a third light beam and a fourth light beam, and splitting said second light beam into a fifth light beam and a sixth light beam; a first mirror for reflecting said third light beam to output a reflected light beam as a seventh light beam, and reflecting said fifth light beam to output a reflected light beam as an eighth light beam; a second mirror for reflecting said fourth light beam to output a reflected light beam as a ninth light beam, and reflecting said sixth light beam to output a reflected light beam as a tenth light beam; a synthesizer for combining said eighth light beam with said tenth light beam to synthesize a first light intensity conversion signal and a second light intensity conversion signal differing in phase by π radian from said first light intensity conversion signal, and combining said seventh light beam with said ninth light beam to synthesize a third light intensity conversion signal and a fourth light intensity conversion signal differing in phase by π radian from said third light intensity conversion signal, the change in phase of said optical phase modulation signal being converted to the change in light intensity of said first and second light intensity conversion signals and the change in light intensity of said third and fourth light intensity conversion signals and by said synthesizer; a bit delay device for adding, to said optical phase modulation signal, the delay of one bit with respect to said symbol rate on two optical paths from said beam splitter to said synthesizer through said first mirror or two optical paths from said beam splitter to said synthesizer through said second mirror; an optical phase difference setting means located on two optical path from said beam splitter to said synthesizer through said first mirror or two optical path from said beam splitter to said synthesizer through said second mirror, and adapted to add a designated delay to the phase of said optical phase modulation signal; a first light receiving unit for converting at least one of said first and second light intensity conversion signals to an electric signal; a second light receiving unit for converting at least one of said third and fourth light intensity conversion signals to an electric signal; and a signal processing unit for analyzing said optical phase modulation signal on the basis of output signals of said first and second light receiving units.