Abstract: An optical demultiplexer to reduce the number of expensive dispersion compensators when compensating secondary dispersion during demultiplexing. By providing optical circulators, dispersion compensators, and optical filters that reflect specified wavelengths and transmit wavelengths other than the specified wavelengths from among the outputs of the dispersion compensators, and causing specified wavelengths to make round trips of the dispersion compensators, the dispersion volume of the dispersion compensators is reduced.

Abstract: An optical demultiplexer to reduce the number of expensive dispersion compensators when compensating secondary dispersion during demultiplexing. By providing optical circulators, dispersion compensators, and optical filters that reflect specified wavelengths and transmit wavelengths other than the specified wavelengths from among the outputs of the dispersion compensators, and causing specified wavelengths to make round trips of the dispersion compensators, the dispersion volume of the dispersion compensators is reduced.

Abstract: In an optical wavelength multiplexing system capable of multiplexing 16 wavelengths at maximum, when only a part of wavelengths are used in an initial operation in a newly established system, the operation of an optical amplifier causes the level of an optical signal per wavelength to be too high, thereby deteriorating the waveform of an optical signal by the nonlinear effect in a transmission line, etc. As a result, the transmission quality is lowered because the system is established based on 16 multiplexed wavelengths. Therefore, when only a part of the 16 waves are used as signal wavelengths, a light having a wavelength &lgr;c different from the signal wavelength is transmitted with the optical signal so that a total level of a light propagated in a transmission line can be equal to the level obtained when 16 waves are wavelength-multiplexed. Thus, the level of the optical signal having each wavelength is approximately adjusted.

Abstract: A light amplifier device includes a module body to which an exciting light source, an optical multiplexer and an optical isolator are attached, and an optical fiber having a light amplifying function, the optical fiber being wound around the module body.

Abstract: The present invention provides a light signal transmission system comprising: a first optical fiber for transmitting a light signal sent from a first terminal station to a second terminal station; a second optical fiber for transmitting a light signal sent from the second terminal station to the first terminal station; first and second optical amplification fibers, inserted along the route of the first and the second optical fiber respectively; first and second excitation light sources, being located away from the first and the second optical amplification fibers respectively, for supplying excitation light to the first optical amplification fibers; first and second control means for controlling first and second excitation level of the excitation light output from the first and second excitation light sources respectively in accordance with a difference between a first reception level of the light signal received by the first terminal station and a second reception level of the light signal received by the se