An apparatus comprising: a first heterodyne detector configured to convert a received modulated optical signal into a first intermediate-frequency signal by mixing the received modulated optical signal with an optical local-oscillator signal, the intermediate-frequency signal being converted to an intermediate frequency electrical signal, the received modulated optical signal having (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 different from the first carrier frequency; a first band-pass filter configured to generate a first filtered electrical signal by passing a first spectral band of the first intermediate-frequency electrical signal, said first spectral band being centered at a first intermediate frequency; a second band-pass filter configured to generate a second filtered electrical signal by passing a second spectral band of the first intermediate-frequency electrical signal, said second spectral band being centered at a second intermediate frequency different from the first intermediate frequency such that an absolute value of a frequency difference between the first and second intermediate frequencies is smaller than the selected baud rate; and an electronic frequency diversity MIMO equalizer configured to generate a plurality of equalized electrical signals by applying equalization processing to a first digital baseband signal corresponding to the first filtered electrical signal and to a second digital baseband signal corresponding to the second filtered electrical signal; and wherein the apparatus is configured to recover the first data stream and the second data stream based on the plurality of equalized electrical signals. a first heterodyne detector configured to convert a received modulated optical signal into a first intermediate-frequency signal by mixing the received modulated optical signal with an optical local-oscillator signal, the intermediate-frequency signal being converted to an intermediate frequency electrical signal, the received modulated optical signal having (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 different from the first carrier frequency; a first band-pass filter configured to generate a first filtered electrical signal by passing a first spectral band of the first intermediate-frequency electrical signal, said first spectral band being centered at a first intermediate frequency; a second band-pass filter configured to generate a second filtered electrical signal by passing a second spectral band of the first intermediate-frequency electrical signal, said second spectral band being centered at a second intermediate frequency different from the first intermediate frequency such that an absolute value of a frequency difference between the first and second intermediate frequencies is smaller than the selected baud rate; and an electronic frequency diversity MIMO equalizer configured to generate a plurality of equalized electrical signals by applying equalization processing to a first digital baseband signal corresponding to the first filtered electrical signal and to a second digital baseband signal corresponding to the second filtered electrical signal; and wherein the apparatus is configured to recover the first data stream and the second data stream based on the plurality of equalized electrical signals.