An optical transfer system comprising: an optical transmission unit including a pulse-signal generation unit that generates a pulse signal having a pulse width equal to or less than Ts/2 with respect to a symbol repetition cycle Ts, a data modulation unit that generates a data modulation signal based on a transmission data signal, and a polarization interleaving unit that generates a polarization-multiplexed signal in which a delay difference between two polarization components that are substantially orthogonal to each other is one-half, Ts/2, of the symbol repetition cycle Ts; an optical reception unit including a local oscillation light source that generates light corresponding to a central wavelength of an optical signal received from the optical transmission unit, an optical interference unit that causes an interference between light generated by the local oscillation light source and an optical signal received from the optical transmission unit, and a photoelectric conversion unit that converts an output from the optical interference unit to an electric signal; a received electric-signal processing unit including an analog-digital conversion unit that converts an electric signal output from the optical reception unit to a digital signal; and a digital-signal processing unit that performs elimination of a delay difference of Ts/2 between polarized signal components and adaptive equalization of a distortion other than the delay difference with respect to the digital signal, wherein the optical transmission unit generates an optical signal in which respective polarization components are alternately present on a time axis, a time period during which the respective polarization components are simultaneously present on the time axis is substantially zero, and a repetition cycle of optical signals of the respective polarization components becomes Ts, and wherein the data modulation unit modulates data of a single-polarization optical signal, and the polarization interleaving unit distributes a data-modulated single-polarization optical signal alternately to two polarization components. an optical transmission unit including a pulse-signal generation unit that generates a pulse signal having a pulse width equal to or less than Ts/2 with respect to a symbol repetition cycle Ts, a data modulation unit that generates a data modulation signal based on a transmission data signal, and a polarization interleaving unit that generates a polarization-multiplexed signal in which a delay difference between two polarization components that are substantially orthogonal to each other is one-half, Ts/2, of the symbol repetition cycle Ts; an optical reception unit including a local oscillation light source that generates light corresponding to a central wavelength of an optical signal received from the optical transmission unit, an optical interference unit that causes an interference between light generated by the local oscillation light source and an optical signal received from the optical transmission unit, and a photoelectric conversion unit that converts an output from the optical interference unit to an electric signal; a received electric-signal processing unit including an analog-digital conversion unit that converts an electric signal output from the optical reception unit to a digital signal; and a digital-signal processing unit that performs elimination of a delay difference of Ts/2 between polarized signal components and adaptive equalization of a distortion other than the delay difference with respect to the digital signal, wherein the optical transmission unit generates an optical signal in which respective polarization components are alternately present on a time axis, a time period during which the respective polarization components are simultaneously present on the time axis is substantially zero, and a repetition cycle of optical signals of the respective polarization components becomes Ts, and wherein the data modulation unit modulates data of a single-polarization optical signal, and the polarization interleaving unit distributes a data-modulated single-polarization optical signal alternately to two polarization components.