Patent ID: 6256140
Filing Date: 2001-07-03
Classification: H04B

Abstract:
An optical amplifying apparatus for transmitting wavelength division multiplexed signal light, comprising:an input terminal into which signal light is entered and said input signal light is made from single signal light, or signal light, the plural different wavelengths of which are division-multiplexed, is entered;an amplifying optical fiber;a pumping light source for outputting pumping light;a wavelength division multiplexer for causing said pumping light to be entered into said amplifying optical fiber, whereby said signal light is optically amplified to output amplified signal light from said optical amplifying apparatus;an amplified signal light reentering unit for branching a portion of said amplified signal light and for reentering the branched/amplified signal light into said amplifying optical fiber from an output side thereof along a backward direction;a branched/amplified signal light level control circuit for controlling the level of said branched/amplified signal light in such a manner that a total output level becomes a predetermined value, and said total output level is obtained by adding an output level of said amplified signal light to an output level of said branched/amplified signal light which has been reentered into the amplifying optical fiber to be optically amplified;an amplifying optical fiber input power detecting circuit for detecting an input level of said signal light and an input level of said branched/amplified signal light before being reentered into said amplifying optical fiber to thereby output an amplifying optical fiber input level;an amplifying optical fiber output power detecting circuit for detecting an output level of said amplified signal light and an output level of said branched/amplified signal light after being reentered into said amplifying optical fiber to be optically amplified; anda gain control circuit for controlling a gain based upon said amplifying optical fiber input level and said amplifying optical fiber output level in such a manner that said gain is maintained at a preselected value.