A communication system comprising: a first optical system comprising a multiplexer configured to multiplex and demultiplex between a first optical line terminal signal, a second optical line terminal signal, and a feeder optical signal comprising the first optical line terminal signal and the second optical line terminal signal, the first optical line terminal signal comprising at least four first upstream wavelengths (λ 1 -λ 4) in a first upstream free spectral range for transmission in an upstream direction and at least four first downstream wavelengths (λ 9 -λ 12) in a first downstream free spectral range for transmission in a downstream direction, and the second optical line terminal signal comprising at least four second upstream wavelengths (λ 5 -λ 8) in a second upstream free spectral range for transmission in the upstream direction and at least four second downstream wavelengths (λ 13 -λ 16) in a second downstream free spectral range for transmission in the downstream direction, whereby all wavelengths are different from each other; an optical feed fiber optically connected with the first optical system and arranged to convey the feeder optical signal; and a second optical system optically connected with the optical feed fiber and configured to multiplex and demultiplex between the feeder optical signal and optical network unit signals (US, US1-USn), each optical network unit signal (US, US1-USn) comprising one of the first upstream wavelengths (λ 1 -λ 4) in the first upstream free spectral range for transmission in the upstream direction, one of the first downstream wavelengths (λ 9 -λ 12) in the first downstream free spectral range for transmission in the downstream direction, one of the second upstream wavelengths (λ 5 -λ 8) in the second upstream free spectral range for transmission in the upstream direction, and one of the second downstream wavelengths (λ 13 -λ 16) in the second downstream free spectral range for transmission in the downstream direction, whereby each optical network unit signal (US, US1-USn) comprises a different wavelength from each free spectral range (B1, B2, B3, B4), wherein the second optical system comprises a cyclical arrayed waveguide grating. a first optical system comprising a multiplexer configured to multiplex and demultiplex between a first optical line terminal signal, a second optical line terminal signal, and a feeder optical signal comprising the first optical line terminal signal and the second optical line terminal signal, the first optical line terminal signal comprising at least four first upstream wavelengths (λ 1 -λ 4) in a first upstream free spectral range for transmission in an upstream direction and at least four first downstream wavelengths (λ 9 -λ 12) in a first downstream free spectral range for transmission in a downstream direction, and the second optical line terminal signal comprising at least four second upstream wavelengths (λ 5 -λ 8) in a second upstream free spectral range for transmission in the upstream direction and at least four second downstream wavelengths (λ 13 -λ 16) in a second downstream free spectral range for transmission in the downstream direction, whereby all wavelengths are different from each other; an optical feed fiber optically connected with the first optical system and arranged to convey the feeder optical signal; and a second optical system optically connected with the optical feed fiber and configured to multiplex and demultiplex between the feeder optical signal and optical network unit signals (US, US1-USn), each optical network unit signal (US, US1-USn) comprising one of the first upstream wavelengths (λ 1 -λ 4) in the first upstream free spectral range for transmission in the upstream direction, one of the first downstream wavelengths (λ 9 -λ 12) in the first downstream free spectral range for transmission in the downstream direction, one of the second upstream wavelengths (λ 5 -λ 8) in the second upstream free spectral range for transmission in the upstream direction, and one of the second downstream wavelengths (λ 13 -λ 16) in the second downstream free spectral range for transmission in the downstream direction, whereby each optical network unit signal (US, US1-USn) comprises a different wavelength from each free spectral range (B1, B2, B3, B4), wherein the second optical system comprises a cyclical arrayed waveguide grating.