Abstract: In accordance with some embodiments of the present disclosure, a method for spectrally spacing carrier waves comprises determining a frequency offset between a first frequency of a first optical carrier wave and a second frequency of a second optical carrier wave. The method further comprises adjusting the second frequency of the second optical carrier wave according to the frequency offset. The method additionally comprises combining a first optical signal associated with the first carrier wave and a second optical signal associated with he second carrier wave into a multi-frequency signal.

Abstract: The optical transmitter includes a light source; a signal processor; an optical modulator that modulates output light from the light source in accordance with a transmitting signal subjected to digital signal processing in the signal processor and outputs the modulated light as a light signal to a transmission path; and a control circuit that controls a carrier-wave frequency of the light signal output from the optical modulator, the signal processor including a mapping circuit that maps the transmitting signal to electric-field information according to a modulating scheme, and a phase rotating circuit that provides a phase rotation having a constant cycle to an electric-field phase of the electric-field information to which the mapping circuit maps the transmitting signal, the control circuit controlling the cycle of the phase rotation that the phase rotating circuit provides and thereby controlling the carrier-wave frequency of the light signal output from the optical modulator.

Abstract: [Problem] This invention aims at solving the problem of how a subscriber premises-side optical network unit can be switched to an evaluation mode without the use of a jig board. [Means for Solving the Problem] The invention refers to a subscriber premises-side optical network unit (ONU 10) which is connected to a center-side optical network unit (OLT 1a) via an optical transmission line (optical fiber 2, 4) and to an external device (switch 6) via an electric signal line (electric signal line 5); comprising a memory (memory switch 15a) the stored content of which can be directly or indirectly rewritten by the external device; a detection part (CPU 15) for detecting that the content of the memory has been rewritten; and a control part (CPU 15) for performing, when the detection part detects that the stored content of the memory has been rewritten, a control whereby the optical sending part which sends optical signals to the optical transmission line is put into a continuous light emission state.