Wavelength division multiplexing optical transmission apparatus and wavelength division multiplexing optical transmission method

1. A wavelength division multiplexing optical transmission apparatus comprising:

a plurality of polarization multiplexing optical modulation units that generate a plurality of polarization multiplexed optimodulation signals having different wavelengths;

a polarization-maintaining optical multiplexing unit that multiplexes the wavelengths of the plurality of polarization multiplexed optical modulation signals to generate a wavelength multiplexed optical signal; and

a delay adjustment unit that adjusts a delay in such a manner that light intensities of polarization multiplexed optical modulation signals having adjacent wavelengths in the wavelength multiplexed optical signal vary inversely with respect to each other, wherein:

the delay adjustment unit includes a plurality of delay circuits disposed between the polarization-maintaining optical multiplexing unit and the plurality of polarization multiplexing optical modulation units, and

the plurality of delay circuits respectively adjust delay times of the plurality of polarization multiplexed optical modulation signals.

2. The wavelength division multiplexing optical transmission apparatus according to claim 1 , wherein:

the delay adjustment unit imparts a time shift of T/2 bits between polarization multiplexed optical modulation signals having adjacent wavelengths in the wavelength multiplexed optical signal, and

the T represents a one-bit time slot at a symbol rate.

3. A wavelength division multiplexing optical transmission apparatus, comprising:

a plurality of polarization multiplexing optical modulation units that generate a plurality of polarization multiplexed optical modulation signals having different wavelengths;

a polarization-maintaining optical multiplexin unit that multiplexes the wavelengths of the plurality of polarization multiplexed optical modulation signals to generate a wavelength multiplexed optical signal; and

a delay adjustment unit that adjusts a delay in such a manner that light intensities of polarization multiplexed optical modulation signals having adjacent wavelengths in the wavelength multiplexed optical signal vary inversely with respect to each other, wherein:

the delay adjustment unit adjusts a delay in such a manner that the plurality of polarization multiplexed optical modulation signals in the wavelength multiplexed optical signal become polarization multiplexed optical modulation signals of a polarization bit interleaving system and light intensities of components having the same polarization plane of polarization multiplexed optical modulation signals having adjacent wavelengths in the wavelength multiplexed optical signal vary inversely with respect to each other,

wherein the plurality of polarization multiplexing optical modulation units each include:

an optical coupler that splits output light from a laser diode into X-polarization and Y-polarization;

an X-polarization modulator that generates an X-polarization modulation signal based on the X-polarization and an X-polarization data signal;

a Y-polarization modulator that generates a Y-polarization modulation signal based on the Y-polarization and a Y-polarization data signal; and

a polarization beam combiner that performs polarization multiplexing of the X-polarization modulation signal and the Y-polarization modulation signal and generates a polarization multiplexed optical modulation signal as one of the plurality of polarization multiplexed optical modulation signals, and

the delay adjustment unit includes:

an inter-wavelength delay circuit that adjusts a delay time in the plurality of polarization multiplexed optical modulation signals; and

an inter-polarization delay circuit that adjusts a delay time between the X-polarization data signal and the Y-polarization data signal.

4. A wavelength division multiplexing optical transmission apparatus, comprising:

a plurality of polarization multiplexing, optical modulation units that generate a plurality of polarization multiplexed optical modulation signals having different wavelengths;

a polarization-maintaining optical multiplexing unit that multiplexes the wavelengths of the plurality of polarization multiplexed optical modulation signals to generate a wavelength multiplexed optical signal; and

a delay adjustment unit that adjusts a delay in such a manner that light intensities of polarization multiplexed optical modulation signals having adjacent wavelengths in the wavelength multiplexed optical signal vary inversely with respect to each other, wherein:

the delay adjustment unit adjusts a delay in such a manner that the plurality of polarization multiplexed optical modulation signals in the wavelength multiplexed optical signal become polarization multiplexed optical modulation signals of a polarization bit interleaving system and light intensities of components having the same polarization plane of polarization multiplexed optical modulation signals having adjacent wavelengths in the wavelength multiplexed optical signal vary inversely with respect to each other, and

the delay adjustment unit includes:

a plurality of inter-wavelength delay circuits that adjust delay times in the plurality of polarization multiplexed optical modulation signals, respectively; and

a plurality of inter-polarization delay circuits that adjust delay times in the plurality of polarization multiplexed optical modulation signals, respectively.