Optical intensity and phase modulators in an optical transmitter apparatus

An optical transmitter apparatus, comprising a light source for signal transmission, a Mach-Zehnder type intensity modulator, a transmit signal generator, a digital logic circuit and an intensity modulator driver circuit,

• wherein a transmit signal generated by said transmit generator is inputted to said digital logic circuit, two output signals of which are inputted to said intensity modulator driver circuit, and said Mach-Zehnder type intensity modulator modulates the light beam sent from said signal source in respect to intensity and phase to thereby output an optical signal for transmission, and
• wherein said two signals outputted from said digital logic circuit are combined such that said two output signals assume levels of "1" and "0" or levels of "0" and "1", respectively, when said transmit signal is "0" while said two output signals assume "1, 1" and "0, 0" in an alternating sequence or in a random sequence when said transmit signal is "1", said intensity modulator driver circuit outputs two levels of "V-" and "V+" in correspondence to the outputs "0" and "1", respectively, of said digital logic circuit, and said Mach-Zehnder type intensity modulator generates an optical signal output of substantially minimum intensity in response to the output combinations of (V+ and V-) and (V- and V+) of said intensity modulator driver circuit while generating an optical signal output having a substantially maximum intensity and a positive optical phase in response to an output combination of (V+ and V+) of said intensity modulator driver circuit, and an optical signal output having a substantially maximum intensity and a negative optical phase is generated by said Mach-Zehnder type intensity modulator in response to an output combination of (V- and V-) of said intensity modulator driver circuit.

An optical transmission system, comprising an optical transmitter apparatus, an optical fiber for optical signal transmission and an optical receiver apparatus, said optical transmitter apparatus including a light source for optical signal transmission, an intensity modulator, a phase modulator, a transmit signal generator incorporating a clock generator circuit and a data generator circuit, and an signal generator,

• wherein an output signal of said signal generator is supplied to said phase modulator and said clock generator circuit incorporated in said transmit signal generator, the output of said clock generator circuit being supplied to said data generator circuit whose output is supplied to said intensity modulator as the output of said transmit signal generator, and
• wherein a light beam emitted from said light source passes through said intensity modulator and said phase modulator to be modulated in intensity upon passing through said intensity modulator while modulated in phase upon passing through said phase modulator to be thereby spread in spectrum, the output optical signal of said phase modulator being sent out to said optical fiber as an optical signal to be transmitted, which signal is received by said optical receiver,
• wherein period of the clock signal of said clock generator circuit is adjusted in accordance with the output signal of said signal generator so that periodical timing at which said optical signal arrives at said optical receiver is substantially constant.

An optical transmission system, comprising an optical transmitter apparatus which includes a light source for optical signal transmission, an intensity modulator, a phase modulator, an intensity modulator driver circuit, a phase modulator driver circuit and a transmit signal generator, an optical fiber and an optical receiver,

• wherein a signal to be transmitted is generated by said transmit signal generator and inputted to said intensity modulator driver circuit and said phase modulator driver circuit, output of said intensity modulator driver circuit being supplied to said intensity modulator while output of said phase modulator driver circuit is supplied to said phase modulator, and wherein a light beam emitted from said light source is sent out as an optical signal to be transmitted from said optical transmitter apparatus after having passed through said intensity modulator and said phase modulator, said optical signal being transmitted through said optical fiber to be inputted to said optical receiver,
• wherein intensity modulation of said optical signal is effected upon passing through said intensity modulator, while upon passing through said phase modulator, the optical signal undergoes such phase modulation that deterioration of waveform of said optical signal due to dispersion encountered during transmission through said optical fiber can be suppressed to a possible minimum by generating an inverse chirping corresponding to a negative .alpha.-parameter.

An optical transmission system, comprising an optical transmitter apparatus which includes a light source for optical signal transmission, an intensity modulator, a phase modulator and a modulator driver circuit and a transmit signal generator, an optical fiber and an optical receiver,

• wherein a signal to be transmitted is generated by said transmit signal generator and inputted to said modulator driver circuit, outputs of positive and negative polarities generated by said modulator driver circuit being supplied to said intensity modulator and said phase modulator, respectively, and wherein a light beam emitted from said light source is sent out as an optical signal to be transmitted from said optical transmitter apparatus after having passed through said intensity modulator and said phase modulator, said optical signal being transmitted through said optical fiber to be inputted to said optical receiver,
• wherein intensity modulation of said optical signal is effected upon passing through said intensity modulator, while upon passing through said phase modulator, the optical signal undergoes such phase modulation upon passing through said phase modulator that a phase shift due to said feeble phase modulation by said intensity modulator can be compensated, whereby said optical signal which is not modulated in phase but is modulated in intensity is provided as an output optical signal of said optical transmitter apparatus.