Optical transmitting apparatus, optical receiving apparatus, and optical communication system comprising them

An optical transmitting apparatus comprising a phase modulator and a driving signal generator to drive the phase modulator, wherein

• the phase modulator comprises a phase shift unit which provides a proper phase difference between a pair of split optical signals on an optical waveguide, a data modulator which performs a phase modulation of the optical signals on the split optical waveguide and an electrode for superimposing a low-frequency signal, and wherein
• said optical transmitting apparatus further comprises:
• a low-frequency signal superimposer to generate low-frequency signals with a proper phase difference and to provide the low-frequency signals to the electrode on the split optical waveguide;
• a monitor to monitor at least one of maximum power, minimum power and phase of a low-frequency signal or a higher harmonic signal of the low-frequency signal superimposed on the optical signal after coupling of the split optical waveguide;
• and
• a phase difference controller to control the phase shift unit so as to obtain a proper phase difference using the output of the monitor unit by maximizing a frequency component with a same frequency as the low-frequency signal or minimizing a frequency component with a double frequency of the low-frequency signal.

An optical transmitting apparatus comprising a phase modulator and a driving signal generator to drive the phase modulator, wherein

• the phase modulator comprises a phase shifter which provides a proper phase difference between a pair of split optical signals on an optical waveguide, a data modulator with a data input unit on the split optical waveguide and an electrode, provided on a different optical waveguide from the optical waveguide where the phase shifter is configured, for superimposing a low-frequency signal, and wherein
• said optical transmitting apparatus further comprises:
• a low-frequency signal superimposer to generate low-frequency signals with a proper phase difference and to provide the low-frequency signals to the electrode and on a bias input terminal of the phase shift unit;
• a monitor to monitor at least one of maximum power, minimum power and phase of a low-frequency signal or a higher harmonic signal of the low-frequency signal superimposed on the optical signal after coupling of the split optical waveguide;
• and
• a phase difference controller to control the phase shift unit so as to obtain a proper phase difference using the output of the monitor unit by maximizing a frequency component with a same frequency as the low-frequency signal or minimizing a frequency component with a double frequency of the low-frequency signal.

An optical transmitting apparatus comprising a phase modulator and a driving signal generator to drive the phase modulator, wherein

• the phase modulator comprises a phase shifter which provides a proper phase difference between a pair of split optical signals on an optical waveguide and data modulator with a data input unit on a split optical waveguide, and wherein
• said optical transmitting apparatus further comprises:
• a low-frequency signal superimposer to generate low-frequency signals with a proper phase difference and to provide the low-frequency signal to the data input unit of the data modulator;
• a monitor to monitor at least one of maximum power, minimum power and phase of a low-frequency signal or a higher harmonic signal of the low-frequency signal superimposed on the optical signal after coupling of the split optical waveguide;
• and
• a phase difference controller to control the phase shift unit so as to obtain a proper phase difference using the output of the monitor unit by maximizing a frequency component with a same frequency as the low-frequency signal or minimizing a frequency component with a double frequency of the low-frequency signal.

An optical transmitting apparatus comprising a phase modulator and a driving signal generator to drive the phase modulator, wherein

• the phase modulator comprises a phase shifter which provides a proper phase difference between a pair of split optical signals on an optical waveguide and data modulator with a data input unit and a bias input unit on a split optical waveguide, and wherein
• said optical transmitting apparatus further comprises:
• a low-frequency signal superimposer to generate low-frequency signals with a proper phase difference and to provide the low-frequency signal to the bias input unit of the data modulator;
• a monitor to monitor at least one of maximum power, minimum power and phase of a low-frequency signal or a higher harmonic signal of the low-frequency signal superimposed on the optical signal after coupling of the split optical waveguide;
• and
• a phase difference controller to control the phase shifter so as to obtain a proper phase difference using the output of the monitor by maximizing a frequency component with a same frequency as the low-frequency signal or minimizing a frequency component with a double frequency of the low-frequency signal.

An optical transmitting apparatus comprising a phase modulator and a driving signal generator to drive the phase modulator, wherein

• the phase modulator comprises a phase shifter which provides a proper phase difference between a pair of split optical signals on an optical waveguide, a data modulator with a data input unit on a split optical waveguide, and an electrode, which is configured in a former stage of the data modulator, to superimpose a low-frequency signal, and wherein
• said optical transmitting apparatus further comprises:
• a low-frequency signal superimposer to generate low-frequency signals with a proper phase difference and to provide the low-frequency signals to the electrode;
• a monitor to monitor at least one of maximum power, minimum power and phase of a low-frequency signal or a higher harmonic signal of the low-frequency signal superimposed on the optical signal after coupling of the split optical waveguide;
• and
• a phase difference controller to control the phase shift unit so as to obtain a proper phase difference using the output of the monitor unit by maximizing a frequency component with a same frequency as the low-frequency signal or minimizing a frequency component with a double frequency of the low-frequency signal.

An optical transmitting apparatus comprising a phase modulator and a driving signal generator to drive the phase modulator, wherein

• the phase modulator comprises a phase shifter which provides a proper phase difference between a pair of split optical signals on an optical waveguide, a data modulator with a data input unit on a split optical waveguide, and an electrode, which is configured in a former stage or later stage of the data modulator to superimpose a low-frequency signal, and wherein
• said optical transmitting apparatus further comprises:
• a low-frequency signal superimposer to generate a low-frequency signal and to provide the low-frequency signal to the electrode configured in an optical waveguide, which is the same as the optical waveguide where the phase shifter or a bias input terminal of the phase shifter is configured or on the electrode configured on an optical waveguide, which is different from the optical waveguide where the phase shifter is configured;
• a monitor to monitor at least one of maximum power, minimum power and phase of a low-frequency signal or a higher harmonic signal of the low-frequency signal superimposed on the optical signal after coupling of the split optical waveguide;
• and
• a phase difference controller to control the phase shifter so as to obtain a proper phase difference using the output of the monitor by minimizing a frequency component with a double frequency of the low-frequency signal.

An optical transmitting apparatus comprising a phase modulator, a driving signal generator to drive the phase modulator and an intensity modulator for modulating an optical output signal from the phase modulator, wherein

• the phase modulator comprises a phase shifter which provides a proper phase difference between a pair of split optical signals on an optical waveguide, a data modulator with a data input unit on a split optical waveguide, and an electrode, which is configured in a later stage of the data modulation unit, to superimpose a low-frequency signal, and wherein
• said optical transmitting apparatus further comprises:
• a monitor to monitor any of the maximum power of the low-frequency signal, the minimum power of a higher harmonic signal with a frequency of twice of the frequency of the low-frequency signal, or the phase of the higher harmonic signal, by extracting the low-frequency signal after coupling of the split optical waveguide;
• a phase shifter controller to provide the low-frequency signals with a proper phase difference to the electrode and to control the phase shifter by bias control so that the proper phase difference can be obtained based on the output from the monitor;
• first and second automatic bias controllers to add the low-frequency signals on each arm of the data modulation unit and to control the data modulator by bias control based on the output of the monitor;
• a third automatic bias controller to add the low-frequency signal on the intensity modulator and to control the intensity modulator by bias control based on the output from the monitor;
• and
• a switch controller comprising a switch to perform the controls in the monitoring in the monitor, the phase shifter controller and the first through the third automatic controller by time division.

An optical transmitting apparatus comprising a phase modulator, a driving signal generator to drive the phase modulator and an intensity modulator for modulating an optical output signal from the phase modulator, wherein

• the phase modulator comprises a phase shifter which provides a proper phase difference between a pair of split optical signals on an optical waveguide, a data modulator with a data inputter on a split optical waveguide, and an electrode, which is configured in a later stage of the data modulator, to superimpose a low-frequency signal, and wherein
• said optical transmitting apparatus further comprises:
• a monitor to monitor at least one of maximum power, minimum power and phase of a low-frequency signal or a higher harmonic signal of the low-frequency signal superimposed on the optical signal after coupling of the split optical waveguide;
• a phase shifter controller to add a first low-frequency signals with a proper phase difference to the electrode, and to control the phase shifter by bias control so as to obtain a proper phase difference based on the output from the monitor;
• first and second automatic bias controllers to add second and third low-frequency signals on each arm of the data modulator and to control the data modulator by bias control based on the output from the monitor;
• a third automatic bias controller to add a fourth low-frequency signal on the intensity modulator and to control the intensity modulator by bias control based on the output from the monitor;
• and
• a collective controller to cause controls in the monitor operation in the monitor, the phase shifter controller , and the first through third automatic bias controllers in parallel.

An optical transmitting apparatus comprising a phase modulator to perform phase modulation according to input data signal, an intensity modulator to perform intensity modulation on an optical output signal from the phase modulator, and a driving signal generator to drive the phase modulator and the intensity modulator, comprising:

• a monitor to monitor at least one of maximum power, minimum power and phase of a low-frequency signal or a higher harmonic signal of the low-frequency signal superimposed on the optical signal after coupling of the split optical waveguide;
• an automatic bias controller to add a low-frequency signal on the phase modulator and the intensity modulator and to control the phase modulator and the intensity modulator by bias control using the output from the monitor;
• and
• a controller to cause the bias control in the monitor operation of the monitor unit and the automatic bias control unit by time division.

An optical transmitting apparatus for transmitting an optical signal modulated corresponding to a data signal, comprising:

• a phase shifter to control a phase of at least one of a first optical signal and a second optical signal, acquired by splitting an optical input, so that the first and the second optical signals have a predetermined phase difference on an optical waveguide;
• a data modulator to modulate the phases of the first and the second optical signals by using the data signal on the optical waveguide;
• a monitor to monitor average optical power of a modulated optical signal acquired by coupling the first and the second optical signals modulated by the data modulator;
• and
• a controller to control the phase shifter using an output of the monitor, wherein the data modulator is a Mach-Zehnder modulator and comprises a phase adder to add a prescribed phase to a phase determined according to the data signal, and
• the phase adder is realized by providing a phase modulation region to form an electrode for applying voltage to one waveguide of the Mach-Zehnder modulator so that the electrode reaches the coupled waveguide in the output side of the Mach-Zehnder modulator.

An optical transmitting apparatus for transmitting an optical signal modulated corresponding to a data signal, comprising:

• a phase shifter to control a phase of at least one of a first optical signal and a second optical signal, acquired by splitting an optical input, so that the first and the second optical signals have a predetermined phase difference on an optical waveguide;
• a data modulator to modulate the phases of the first and the second optical signals by using the data signal on the optical waveguide;
• a monitor to monitor average optical power of a modulated optical signal acquired by coupling the first and the second optical signals modulated by the data modulator;
• and
• a controller to control the phase shifter based on an output of the monitor,
• wherein the data modulator is a Mach-Zehnder modulator and comprises a phase adder to add a prescribed phase to a phase determined according to the data signal, and
• the phase adder is an attenuation element for causing difference in amplitudes of a pair of data signals provided for the Mach-Zehnder modulator from each other.

An optical transmitting apparatus for transmitting an optical signal modulated corresponding to a data signal, comprising:

• a phase shifter to control a phase of at least one of a first optical signal and a second optical signal, acquired by splitting an optical input, so that the first and the second optical signals have a predetermined phase difference on an optical waveguide;
• a data modulator to modulate the phases of the first and the second optical signals by using the data signal on the optical waveguide;
• a monitor to monitor average optical power of a modulated optical signal acquired by coupling the first and the second optical signals modulated by the data modulator;
• and
• a controller to control the phase shifter based on an output of the monitor,
• wherein the data modulator is a Mach-Zehnder modulator and comprises a phase adder to add a prescribed phase to a phase determined according to the data signal, and
• the phase adder is a delay element to cause difference in timings of a pair of data signals provided for the Mach-Zehnder modulator from each other.

An optical transmitting apparatus for transmitting an optical signal modulated corresponding to a data signal, comprising:

• a mark rate unbalancer to unbalance mark rate of the data signal in such a way that an appearance rate of each symbol value becomes unbalanced;
• a phase shifter to control a phase of at least one of a first optical signal and a second optical signal, acquired by splitting an optical input, so that the first and the second optical signals have a predetermined phase difference on an optical waveguide;
• a data modulator to modulate the phase of the first and the second optical signals by using a data signal with its mark rate adjusted on the optical waveguide;
• a monitor to monitor average optical power of a modulated optical signal acquired by coupling the first and the second optical signals modulated by the data modulator;
• and
• a controller to control the phase shifter based on the output of the monitor.