Patent ID: 11956070
Assignee: NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Field: Telecommunications (Electrical engineering)
Classification: CPC H  G | IPC H

Claim 0:
1. An optical transmission system, comprising:
an optical fiber with a number of spatial modes being L, where the L is an integer of at least 2;
an optical multiplexer connected to one end of the optical fiber, the optical multiplexer being configured to:
receive M of a transmitted signal beam of light from a transmitter, where the M is a natural number in a range from 1 to L;
convert the M of the transmitted signal beam of light into the L of input signal beams of light; and
input the L of the input signal beams of light to the optical fiber to cause the L of the input signal beams of light to be propagated for each of the spatial modes of the optical fiber as a propagated beam of light;

an optical demultiplexer connected to another end of the optical fiber, the optical demultiplexer being configured to demultiplex the propagated beam of light to generate N of demultiplexed beams of light, where the N is equal to the L;
a receiver configured to:
receive the N of the demultiplexed beams of light from the optical demultiplexer; and
output the N of received signals corresponding to the N of the demultiplexed beams of light;

a signal generation apparatus configured to:
receive the N of the received signals from the receiver; and
convert the N of the received signals into P of a combined signal as a conversion, where the P is an integer of M or more and less than L; and

a P×M multiple-input multiple-output equalizer configured to receive the P of the combined signal from the signal generation apparatus to output the M of a demodulated signal,
wherein the signal generation apparatus is configured to:
either apply phase rotation to or adjust an amplitude of two received signals of the N of the received signals to obtain two modified signals as a first step of the conversion; and
combine the two modified signals as a second step of the conversion to generate one combined signal of the P of the combined signal.