An optical source (10) comprising: a first laser (12) arranged to generate a first optical signal (14) having a first state of polarization and a first optical frequency; a second laser (16) arranged to generate a second optical signal (18, 48, 78) having a second state of polarization, substantially orthogonal to the first state of polarization, and having a second optical frequency, different to the first optical frequency by a preselected frequency difference, ; a polarization beam coupler (20) arranged to combine the first optical signal and the second optical signal into a composite optical signal comprising both the first optical signal and the second optical signal having said substantially orthogonal states of polarization; and an output (22) arranged to output the composite optical signal (24).

An optical source (10) comprising: a first laser (12) arranged to generate a first optical signal (14) having a first state of polarization and a first optical frequency; a second laser (16) arranged to generate a second optical signal (18, 48, 78) having a second state of polarization, substantially orthogonal to the first state of polarization, and having a second optical frequency, different to the first optical frequency by a preselected frequency difference, ; a polarization beam coupler (20) arranged to combine the first optical signal and the second optical signal into a composite optical signal comprising both the first optical signal and the second optical signal having said substantially orthogonal states of polarization; and an output (22) arranged to output the composite optical signal (24).

A method for overlapping spectrum amplification includes receiving an optical signal and splitting the optical signal into a first split signal having a first wavelength band and a second split signal having a second wavelength band. The splitting results in a band gap between the first wavelength band and the second wavelength band. The method further includes delaying the first split signal by a threshold period of time relative to the second split signal and combining the first split signal and the second split signal, resulting in a combined signal having the first wavelength band and the second wavelength band without the band gap therebetween. The path difference between the first split signal along the first signal path and the second split signal along the second signal path is within a threshold multipath interference compensation range.

A method for overlapping spectrum amplification includes receiving an optical signal and splitting the optical signal into a first split signal having a first wavelength band and a second split signal having a second wavelength band. The splitting results in a band gap between the first wavelength band and the second wavelength band. The method further includes delaying the first split signal by a threshold period of time relative to the second split signal and combining the first split signal and the second split signal, resulting in a combined signal having the first wavelength band and the second wavelength band without the band gap therebetween. The path difference between the first split signal along the first signal path and the second split signal along the second signal path is within a threshold multipath interference compensation range.

The present invention relates to signal processing in an optical receiver, in particular to equalization performed in coherent optical receivers. A multiple-input multiple-output (MIMO) equalizer receives and equalizes a plurality of real value signals, for example four sampled electrical baseband tributaries (HI, HQ, VI, VQ). The outputs of the multiple-input multiple-output (MIMO) equalizer provide equalized real or imaginary components of complex signals. The complex signals including the real and imaginary components are then each and individually equalized to remove chromatic dispersion.

A method for overlapping spectrum amplification includes receiving an optical signal and splitting the optical signal into a first split signal having a first wavelength band and a second split signal having a second wavelength band. The splitting results in a band gap between the first wavelength band and the second wavelength band. The method further includes delaying the first split signal by a threshold period of time relative to the second split signal and combining the first split signal and the second split signal, resulting in a combined signal having the first wavelength band and the second wavelength band without the band gap therebetween. The path difference between the first split signal along the first signal path and the second split signal along the second signal path is within a threshold multipath interference compensation range.

A method for overlapping spectrum amplification includes receiving an optical signal and splitting the optical signal into a first split signal having a first wavelength band and a second split signal having a second wavelength band. The splitting results in a band gap between the first wavelength band and the second wavelength band. The method further includes delaying the first split signal by a threshold period of time relative to the second split signal and combining the first split signal and the second split signal, resulting in a combined signal having the first wavelength band and the second wavelength band without the band gap therebetween. The path difference between the first split signal along the first signal path and the second split signal along the second signal path is within a threshold multipath interference compensation range.

An amplitude adjustment circuit includes a memory that stores correspondence information between frequency distributions of an amplitude and adjustment coefficients, a processor configured to generate a frequency distribution of amplitude of data for which adaptive equalization processing has been executed, acquire the correspondence information between frequency distributions of the amplitude and adjustment coefficients from the memory, select the adjustment coefficient based on a result of comparison between the frequency distributions included in the correspondence information acquired by the acquiring unit and the frequency distribution generated by the generating unit, and adjust a gain of the data based on the adjustment coefficient selected by the selecting unit.

An amplitude adjustment circuit includes a memory that stores correspondence information between frequency distributions of an amplitude and adjustment coefficients, a processor configured to generate a frequency distribution of amplitude of data for which adaptive equalization processing has been executed, acquire the correspondence information between frequency distributions of the amplitude and adjustment coefficients from the memory, select the adjustment coefficient based on a result of comparison between the frequency distributions included in the correspondence information acquired by the acquiring unit and the frequency distribution generated by the generating unit, and adjust a gain of the data based on the adjustment coefficient selected by the selecting unit.

According to an example aspect, there is provided an apparatus comprising a first optical converter coupled to a fibre interface and to two waveguides, a dual rail encoder configured to encode dual rail form light from the two waveguides with payload information, and wherein the dual rail encoder is coupled to the first optical converter or to a second optical converter disposed between the dual rail encoder and the fibre interface, and wherein the first optical converter or the second optical converter is coupled so as to provide polarization encoded light into the fibre interface.