Frequency-diversity mimo processing for optical transmission

An apparatus comprising:

• a first optical transmitter configured to generate a first modulated optical carrier having encoded thereon a first data stream at a selected baud rate, said first modulated optical carrier having a first carrier frequency;
• a second optical transmitter configured to generate a second modulated optical carrier having encoded thereon a second data stream at the selected baud rate, said second modulated optical carrier having a second carrier frequency, wherein the first and second carrier frequencies are separated from one another by a frequency interval that is smaller than the selected baud rate;
• and
• an optical combiner configured to combine the first modulated optical carrier and the second modulated optical carrier for transmission over a fiber-optic link.

An apparatus comprising:

• a plurality of electrical intermediate-frequency generators, each configured to generate a respective electrical carrier wave having a respective intermediate frequency, wherein spacing between neighboring intermediate frequencies is smaller than a selected baud rate;
• a plurality of electrical modulators, each configured to modulate the respective electrical carrier wave, at the selected baud rate and using a respective one of a plurality of data streams to generate a respective one of a plurality of modulated electrical carriers;
• an electrical signal combiner configured to combine the plurality of modulated electrical carriers to generate a modulated multi-carrier electrical signal;
• and
• an optical modulator configured to generate a modulated optical signal by modulating an optical carrier wave based on the modulated multi-carrier electrical signal.

An apparatus comprising:

• an optical detector configured to generate a first filtered electrical signal and a second filtered electrical signal based on a received modulated optical signal, wherein the received modulated optical signal has (i) a first modulated optical carrier having encoded thereon a first data stream at a selected baud rate, said first modulated optical carrier having a first carrier frequency, and (ii) a second modulated optical carrier having encoded thereon a second data stream at the selected baud rate, said second modulated optical carrier having a second carrier frequency;
• and
• a signal processor configured to:
• convert the first filtered electrical signal into a first electrical baseband signal;
• convert the second filtered electrical signal into a second electrical baseband signal;
• apply MIMO equalization processing to the first and second electrical baseband signals to mitigate an effect of inter-carrier interference due to partial spectral overlap of the first modulated optical carrier and the second modulated optical carrier, said MIMO equalization processing configured to receive, as a first input, the first electrical baseband signal, and further configured to receive, as a second input, the second electrical baseband signal, wherein said MIMO equalization processing is configured to generate a first equalized electrical signal, as a first output thereof, and a second equalized electrical signal, as a second output thereof;
• recover the first data stream based on the first equalized electrical signal;
• and
• recover the second data stream based on the second equalized electrical signal.