Optical Transmission System, Optical Transmission Method, Transmitter, and Receiver

An optical transmission method using:

• N directly-modulated lasers configured to convert N-channel first electrical modulated signals into N-channel optical modulated signals and transmit the N-channel optical modulated signals;
• N photodetectors configured to receive the N-channel optical modulated signals and convert the N-channel optical modulated signals into N-channel second electrical modulated signals;
• and
• at least one of a first MIMO equalizer to which the N-channel first electrical modulated signals are input and a second MIMO equalizer to which the N-channel second electrical modulated signals are input,
• the method comprising the steps of:
• setting an arbitrary matrix coefficient in at least one of the first MIMO equalizer and the second MIMO equalizer;
• inputting at least one of the group of the N-channel first electrical modulated signals and the group of the N-channel second electrical modulated signals to at least one of the first MIMO equalizer and the second MIMO equalizer and experimentally measuring N-channel output signals;
• deciding an optimum matrix coefficient such that a means squared error between the measured output signal and a desired output signal is minimized in each channel in equation (A);
• and
• executing, by at least one of the first MIMO equalizer and the second MIMO equalizer, equalization processing using the optimum matrix coefficient for at least one of the group of the N-channel first electrical modulated signals and the group of the N-channel second electrical modulated signals, thereby compensating for crosstalk between signals in at least one of the group of the N-channel first electrical modulated signals and the group of the N-channel second electrical modulated signals,
• [
• Math
• .
• 4
• ]
• 
• Y
• =
• WX
• (
• A
• )
• where X is a vector of one of the group of the N-channel first electrical modulated signals and the group of the N-channel second electrical modulated signals, Y is a vector of the signals that have undergone the equalization processing, and W is the matrix coefficient W.

A transmitter configured to, in an optical transmission system sequentially including the transmitter, a communication channel, and a receiver, transmit N-channel analog optical modulated signals to be received by the receiver via the communication channel, characterized by comprising:

• a MIMO equalizer to which N-channel digital electrical modulated signals are input;
• a DA converter configured to convert the N-channel digital electrical modulated signals into N-channel analog electrical modulated signals;
• N RF drivers to which the N-channel analog electrical modulated signals are input;
• and
• N directly-modulated lasers configured to be driven by the N-channel analog electrical modulated signals input to the N RF drivers and output the N-channel analog optical modulated signals,
• wherein the MIMO equalizer executes equalization processing using a matrix coefficient based on an impulse response for the N-channel digital electrical modulated signals, thereby compensating for crosstalk between the N-channel electrical modulated signals.