Wavelength multiplex transmission systems

A wavelength multiplex transmission system having a transmission apparatus and a receiving apparatus connected via an optical transmission line, wherein:

• the transmission apparatus comprises:
• (N+M) optical transmitters (where N is an integer of 2 or more and M is an integer from 1 to N) for transmitting a plurality of input signals as optical signals with different wavelengths,
• M differential dividers for differentially dividing M input signals out of the plurality of input signals, respectively, and inputting the differentially divided signals into 2×M optical transmitters out of the (N+M) optical transmitters, respectively, and
• a wavelength multiplex filter for wavelength multiplexing and outputting the (N+M) optical signals from the (N+M) optical transmitters, and wherein:
• the receiving apparatus comprises:
• a wavelength separation filter for separating the wavelength multiplexed optical signals to output (N+M) optical signals;
• (N+M) optical receivers for receiving the (N+M) optical signals from the wavelength separation filter, respectively, to output (N+M) output signals;
• M differential combiners, each differentially combining the output signals from the two optical receivers receiving a pair of optical signals which have been differentially divided and transmitted, out of the (N+M) optical receivers, to output one signal;
• and
• a delay time controller for adjusting delay time difference between a pair of optical signals on the optical transmission line, at the preceding stage of the differential combiner.

A receiving apparatus for receiving optical signals including differential signals of a signal, comprising:

• optical receiving means for receiving the optical signals;
• optical conversion means for reproducing the differential signals from the optical signals;
• differential combining means for combining the reproduced differential signals;
• and
• time difference control means for adjusting time difference between the reproduced differential signals.

A receiving apparatus comprising:

• a wavelength separation filter for separating a wavelength multiplexed optical signal to output (N+M) optical signals (where N is an integer of 2 or more and M is an integer from 1 to N);
• (N+M) optical receivers for receiving the (N+M) optical signals from the wavelength separation filter, respectively, to output (N+M) output signals;
• M differential combiners, each differentially combining the output signals from two optical receivers receiving a pair of optical signals out of the (N+M) optical receivers, to output one signal;
• and
• a delay time controller for adjusting delay time difference between the pair of two optical signals on the optical transmission line, at the preceding stage of the differential combiner.