Abstract: The Remote SONET/SDH Loopback (RSL) is an optical network interface device consisting of a facility interface 24, a drop side interface 26, a facility receive signal splitter 12, a drop side receive signal splitter 18, an idle signal generator 16, a command logic assembly 10, and a switching circuit assembly 22. The RSL addresses the need for a low-cost sub-section layer device by efficiently processing the SONET signal to support only loopback and idle signal generation. The RSL may be provisioned to either loopback the facility or generate an idle signal when the drop side of the termination is disconnected, turned-off, or has otherwise failed to generate a valid signal. The SONET signal may also be looped back upon itself when a user controlled loopback command code is detected within the SONET overhead. The RSL otherwise passes the SONET signal unaltered. The RSL may be provisioned by the user to specify the location and characteristics of the embedded loopback command codes.

Abstract: In a long-distance high-speed optical communication scheme in which multiple optical amplifiers are provided at a large number of stages in optical fibers, an optical signal from a light source which has a desired small line width and oscillates at a single wavelength is modulated at a high speed by an external modulator and then transmitted in the fibers which are dispersion shifted optical fibers, the zero-dispersion wavelength in which is set to be larger than the oscillation wavelength of the light source. Therefore, noises and the modulation instability, which would occur due to the phase fluctuation in the oscillation wavelength of the light source, and the influence of a waveform distortion due to the dispersion in the optical fibers can be avoided to make it possible for the first time in history to transmit the optical signals at the high-speed in the long-distance optical communication system employing the optical amplifiers.