Optical transmitter including splitting elements, external modulators, and wavelength multiplexers, and optical transceiver including polarization separation elements, wavelength demultiplexers, polarization rotation elements, and photodetectors

An optical transmitter to split individual continuous wave light signals with N different wavelengths into M signals, where N is an integer equal to or greater than four, and M is an integer which is greater than two, and is a power of two, the optical transmitter comprising:

• a plurality of splitting elements arranged in a plurality of splitting blocks, each splitting block including N splitting elements configured to split an input light signal at one of the N different wavelengths into two signals, the plurality of splitting blocks being arranged in j=log2 M stages;
• N×M external modulators to modulate respective continuous wave light signals obtained via the plurality of splitting elements at a j-th stage of the j=log2 M stages;
• and
• M wavelength multiplexers to multiplex N input light signals at different wavelengths output from the external modulators, wherein
• the plurality of splitting elements are connected in such a manner that an arranging order of N wavelengths of N lanes that are input to an upstream splitting block and an arranging order of N wavelengths of N lanes that are input to each of downstream splitting blocks are identical.