Optical signal repeating and amplifying device and optical level adjusting device

Abstract

Disclosed is an optical signal repeating and amplifying device which has: an optical amplifier which amplifies an optical signal to be input thereto and then outputs it; and an optical filter means through which only one wavelength light of the optical signal to be output from the optical amplifier is passed. Also disclosed is an optical level adjusting device which has: an optical demultiplexer which demultiplexes a wavelength-multiplexed optical signal into a plurality of wavelength lights; a plurality of optical attenuators which attenuate separately the demultiplexed plurality of wavelength lights to be output from the optical demultiplexer; and an optical multiplexer which multiplexes the attenuated wavelength lights to be output from the plurality of optical attenuators into a wavelength-multiplexed optical signal and output it.

What is claimed is:  
     
         1 . An optical signal repeating and amplifying device, comprising: 
 an optical amplifier which amplifies an optical signal to be input thereto and then outputs it; and    an optical filter means through which only one wavelength light of the optical signal to be output from said optical amplifier is passed.    
     
     
         2 . An optical signal repeating and amplifying device, according to  claim 1 , wherein: 
 said optical filter means is an array waveguide diffraction grating type optical demultiplexer, an array waveguide diffraction grating type optical multiplexer, an array waveguide diffraction grating type optical demultiplexer-multiplexer, a band-pass optical filter, a fiber-grating type optical demultiplexer, a fiber-grating type optical multiplexer, or a fiber-grating type optical demultiplexer-multiplexer.    
     
     
         3 . An optical signal repeating and amplifying device, according to  claim 1 , wherein: 
 said optical amplifier is a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         4 . An optical signal repeating and amplifying device, according to  claim 3 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         5 . An optical signal repeating and amplifying device, according to  claim 4 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         6 . An optical signal repeating and amplifying device, comprising: 
 a first optical demultiplexer-multiplexer which demultiplexes a wavelength-multiplexed optical signal into a plurality of wavelength lights;    a plurality of optical transmission lines through which said plurality of wavelength lights from said first optical demultiplexer-multiplexer are separately transmitted; and    a second optical demultiplexer-multiplexer which multiplexes the optical signals transmitted through said plurality of optical transmission lines into a wavelength-multiplexed optical signal and outputs it.    
     
     
         7 . An optical signal repeating and amplifying device, according to  claim 6 , wherein: 
 said first optical demultiplexer-multiplexer includes an optical amplifier to amplify said wavelength-multiplexed optical signal on the input side, or a plurality of optical amplifiers to amplify separately said demultiplexed plurality of wavelength lights on the output side.    
     
     
         8 . An optical signal repeating and amplifying device, according to  claim 6 , wherein: 
 said second optical demultiplexer-multiplexer includes an optical amplifier to amplify said wavelength-multiplexed optical signal on the output side.    
     
     
         9 . An optical signal repeating and amplifying device, according to  claim 6 , wherein: 
 said first optical demultiplexer-multiplexer is an optical demultiplexer and said second optical demultiplexer-multiplexer is an optical multiplexer.    
     
     
         10 . An optical signal repeating and amplifying device, according to  claim 6 , wherein: 
 said first and second optical demultiplexer-multiplexers are an array waveguide diffraction grating type or fiber-grating type optical demultiplexer, optical multiplexer, or optical demultiplexer-multiplexer.    
     
     
         11 . An optical signal repeating and amplifying device, according to  claim 7 , wherein: 
 said optical amplifier is a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         12 . An optical signal repeating and amplifying device, according to  claim 8 , wherein: 
 said optical amplifier is a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         13 . An optical signal repeating and amplifying device, according to  claim 11 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         14 . An optical signal repeating and amplifying device, according to  claim 12 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         15 . An optical signal repeating and amplifying device, according to  claim 13 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         16 . An optical signal repeating and amplifying device, according to  claim 14 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         17 . An optical signal repeating and amplifying device, comprising: 
 an optical circulator through which a wavelength-multiplexed optical signal to be input to the input port is output from the input-output port and a wavelength-multiplexed optical signal to be input to the input-output port is output from the output port;    an optical demultiplexer-multiplexer which demultiplexes the wavelength-multiplexed optical signal from said optical circulator into a plurality of wavelength lights and multiplexes a plurality of wavelength lights into a wavelength-multiplexed optical signal;    a plurality of optical transmission lines through which said demultiplexed plurality of wavelength lights to be output from said optical demultiplexer-multiplexer are separately transmitted; and    a plurality of optical reflecting mirrors which reflect separately said demultiplexed plurality of wavelength lights transmitted through said plurality of optical transmission lines to turn them back.    
     
     
         18 . An optical signal repeating and amplifying device, according to  claim 17 , wherein: 
 said optical demultiplexer-multiplexer is of array waveguide diffraction grating type or fiber-grating type.    
     
     
         19 . An optical signal repeating and amplifying device, according to  claim 17 , wherein: 
 said optical circulator includes an optical amplifier on the input port side or on the input-output port side.    
     
     
         20 . An optical signal repeating and amplifying device, according to  claim 17 , wherein: 
 said plurality of optical transmission lines are separately provided with an optical amplifier.    
     
     
         21 . An optical signal repeating and amplifying device, according to  claim 19 , wherein: 
 said optical amplifier is a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         22 . An optical signal repeating and amplifying device, according to  claim 20 , wherein: 
 said optical amplifier is a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         23 . An optical signal repeating and amplifying device, according to  claim 21 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         24 . An optical signal repeating and amplifying device, according to  claim 22 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         25 . An optical signal repeating and amplifying device, according to  claim 23 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         26 . An optical signal repeating and amplifying device, according to  claim 24 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         27 . An optical signal repeating and amplifying device, comprising: 
 a n optical demultiplexer-multiplexer which demultiplexes a wavelength-multiplexed optical signal into a plurality of wavelength lights and multiplexes a plurality of wavelength lights into a wavelength-multiplexed optical signal;    a plurality of optical transmission lines through which said demultiplexed plurality of wavelength lights to be output from said optical demultiplexer-multiplexer are separately transmitted; and    an optical dividing and coupling means through which each of said plurality of wavelength lights transmitted through each of said plurality of optical transmission lines is re-input to said optical demultiplexer-multiplexer while by-passing a different one of said optical transmission lines without overlapping with another wavelength light.    
     
     
         28 . An optical signal repeating and amplifying device, according to  claim 27 , wherein: 
 said optical dividing and coupling means comprises an optical divider and an optical transmission line which are disposed between any two of said plurality of optical transmission lines.    
     
     
         29 . An optical signal repeating and amplifying device, according to  claim 27 , wherein: 
 said optical demultiplexer-multiplexer includes an optical amplifier on the input side or on the output side.    
     
     
         30 . An optical signal repeating and amplifying device, according to  claim 27 , wherein: 
 said plurality of optical transmission lines are separately provided with an optical amplifier.    
     
     
         31 . An optical signal repeating and amplifying device, according to  claim 29 , wherein: 
 said optical amplifier is a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         32 . An optical signal repeating and amplifying device, according to  claim 30 , wherein: 
 said optical amplifier is a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         33 . An optical signal repeating and amplifying device, according to  claim 31 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         34 . An optical signal repeating and amplifying device, according to  claim 32 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         35 . An optical signal repeating and amplifying device, according to  claim 33 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         36 . An optical signal repeating and amplifying device, according to  claim 34 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         37 . An optical signal repeating and amplifying device, according to  claim 27 , wherein: 
 said optical demultiplexer-multiplexer is an array waveguide diffraction grating type or fiber-grating type optical demultiplexer, optical multiplexer, or optical demultiplexer-multiplexer.    
     
     
         38 . An optical signal repeating and amplifying device, comprising: 
 a first optical demultiplexer-multiplexer which demultiplexes a wavelength-multiplexed optical signal into a plurality of wavelength lights;    a plurality of optical filters through which said plurality of wavelength lights from said first optical demultiplexer-multiplexer are separately passed; and    a second optical demultiplexer-multiplexer which multiplexes the optical signals passed through said plurality of optical filters into a wavelength-multiplexed optical signal and outputs it.    
     
     
         39 . An optical signal repeating and amplifying device, according to  claim 38 , wherein: 
 said first optical demultiplexer-multiplexer includes an optical amplifier to amplify said wavelength-multiplexed optical signal on the input side.    
     
     
         40 . An optical signal repeating and amplifying device, according to  claim 38 , wherein: 
 said second optical demultiplexer-multiplexer includes an optical amplifier to amplify said wavelength-multiplexed optical signal on the output side.    
     
     
         41 . An optical signal repeating and amplifying device, according to  claim 38 , wherein: 
 said first and second optical demultiplexer-multiplexers are an array waveguide diffraction grating type or fiber-grating type optical demultiplexer, optical multiplexer, or optical demultiplexer-multiplexer.    
     
     
         42 . An optical signal repeating and amplifying device, according to  claim 38 , wherein: 
 said plurality of optical filter are a band-pass optical filter in which a wavelength band desired to pass is set.    
     
     
         43 . An optical signal repeating and amplifying device, comprising: 
 an optical divider which divides a wavelength-multiplexed optical signal into a plurality of lights;    a plurality of optical filters through which said plurality of wavelength lights from said optical divider are separately passed; and    an optical coupler which couples the optical signals passed through said plurality of optical filters into a wavelength-multiplexed optical signal and outputs it.    
     
     
         44 . An optical signal repeating and amplifying device, according to  claim 43 , wherein: 
 said optical divider includes an optical amplifier to amplify said wavelength-multiplexed optical signal on the input side.    
     
     
         45 . An optical signal repeating and amplifying device, according to  claim 43 , wherein: 
 said optical divider includes an optical amplifier to amplify said wavelength-multiplexed optical signal on the output side.    
     
     
         46 . An optical signal repeating and amplifying device, according to  claim 43 , wherein: 
 said plurality of optical filter are a band-pass optical filter in which a wavelength band desired to pass is set.    
     
     
         47 . An optical signal repeating and amplifying device, comprising: 
 an optical circulator through which a wavelength-multiplexed optical signal to be input to the input port is output from the input-output port and a wavelength-multiplexed optical signal to be input to the input-output port is output from the output port;    an optical demultiplexer-multiplexer which demultiplexes the wavelength-multiplexed optical signal from said optical circulator into a plurality of wavelength lights and multiplexes a plurality of wavelength lights into a wavelength-multiplexed optical signal;    a plurality of optical filters through which said demultiplexed plurality of wavelength lights to be output from said optical demultiplexer-multiplexer are separately passed; and    a plurality of optical reflecting mirrors which reflect separately said demultiplexed plurality of wavelength lights passed through said plurality of optical filters to turn them back.    
     
     
         48 . An optical signal repeating and amplifying device, according to  claim 47 , wherein: 
 said optical circulator includes an optical amplifier to amplify the wavelength-multiplexed optical signal on the input port side or on the input-output port side.    
     
     
         49 . An optical signal repeating and amplifying device, according to  claim 47 , wherein: 
 said optical demultiplexer-multiplexer is of array waveguide diffraction grating type or fiber-grating type.    
     
     
         50 . An optical signal repeating and amplifying device, according to  claim 47 , wherein: 
 said plurality of optical filter are a band-pass optical filter in which a wavelength band desired to pass is set.    
     
     
         51 . An optical signal repeating and amplifying device, according to  claim 47 , wherein: 
 said plurality of optical filter are a bi-directional optical filter.    
     
     
         52 . An optical signal repeating and amplifying device, comprising: 
 an optical circulator through which a wavelength-multiplexed optical signal to be input to the input port is output from the input-output port and a wavelength-multiplexed optical signal to be input to the input-output port is output from the output port;    an optical divider-coupler which divides the wavelength-multiplexed optical signal from said optical circulator into a plurality of lights and couples a plurality of lights into a wavelength-multiplexed optical signal;    a plurality of optical filters through which said divided plurality of lights to be output from said optical divider-coupler are separately passed; and    a plurality of optical reflecting mirrors which reflect separately said divided plurality of lights passed through said plurality of optical filters to turn them back.    
     
     
         53 . An optical signal repeating and amplifying device, according to  claim 52 , wherein: 
 said optical circulator includes an optical amplifier to amplify the wavelength-multiplexed optical signal on the input port side or on the input-output port side.    
     
     
         54 . An optical signal repeating and amplifying device, according to  claim 52 , wherein: 
 said plurality of optical filter are a band-pass optical filter in which a wavelength band desired to pass is set.    
     
     
         55 . An optical signal repeating and amplifying device, according to  claim 52 , wherein: 
 said plurality of optical filter are a bi-directional optical filter.    
     
     
         56 . An optical signal repeating and amplifying device, comprising: 
 an optical divider-coupler which divides the wavelength-multiplexed optical signal from said optical circulator into a plurality of lights and couples a plurality of lights into a wavelength-multiplexed optical signal;    a plurality of optical transmission lines which said divided plurality of lights to be output from said optical divider-coupler are separately transmitted;    a plurality of optical filters through which said divided plurality of lights from said plurality of optical transmission lines are separately passed; and    an optical dividing and coupling means through which each of said plurality of lights passed through each of said plurality of optical filters is re-input to said optical divider-coupler while by-passing a different one of said optical transmission lines without overlapping with another light.    
     
     
         57 . An optical signal repeating and amplifying device, according to  claim 56 , wherein: 
 said optical dividing and coupling means comprises an optical divider and an optical transmission line which are disposed between any two of said plurality of optical transmission lines.    
     
     
         58 . An optical signal repeating and amplifying device, according to  claim 56 , wherein: 
 said optical divider-coupler includes an optical amplifier on the input side or on the output side.    
     
     
         59 . An optical signal repeating and amplifying device, according to  claim 56 , wherein: 
 said plurality of optical filter are a band-pass optical filter in which a wavelength band desired to pass is set.    
     
     
         60 . An optical signal repeating and amplifying device, according to  claim 56 , wherein: 
 said plurality of optical filter are a bi-directional optical filter.    
     
     
         61 . An optical level adjusting device, comprising: 
 an optical demultiplexer which demultiplexes a wavelength-multiplexed optical signal into a plurality of wavelength lights;    a plurality of optical attenuators which attenuate separately said demultiplexed plurality of wavelength lights to be output from said optical demultiplexer; and    an optical multiplexer which multiplexes said attenuated wavelength lights to be output from said plurality of optical attenuators into a wavelength-multiplexed optical signal and output it.    
     
     
         62 . An optical level adjusting device, according to  claim 61 , wherein: 
 said optical attenuators are an optical variable attenuator or an optical fixed attenuator.    
     
     
         63 . An optical level adjusting device, according to  claim 61 , wherein: 
 said optical attenuators are separately disposed on a plurality of optical transmission lines which connect between said optical demultiplexer and said optical multiplexer to transmit separately said demultiplexed plurality of wavelength lights.    
     
     
         64 . An optical level adjusting device, according to  claim 61 , wherein: 
 said optical demultiplexer is of array waveguide diffraction grating type or fiber-grating type.    
     
     
         65 . An optical level adjusting device, according to  claim 61 , wherein: 
 said optical multiplexer is of array waveguide diffraction grating type or fiber-grating type.    
     
     
         66 . An optical level adjusting device, according to  claim 61 , wherein: 
 said optical attenuators are replaced by optical amplifiers or include optical amplifiers to be in series connected thereto.    
     
     
         67 . An optical level adjusting device, comprising: 
 an optical circulator through which a wavelength-multiplexed optical signal to be input to the input port is output from the input-output port and a wavelength-multiplexed optical signal to be input to the input-output port is output from the output port;    an optical demultiplexer-multiplexer which demultiplexes the wavelength-multiplexed optical signal from said optical circulator into a plurality of wavelength lights and multiplexes a plurality of wavelength lights into a wavelength-multiplexed optical signal;    a plurality of optical attenuators which attenuate separately said demultiplexed plurality of wavelength lights to be output from said optical demultiplexer-multiplexer; and    a plurality of optical reflecting mirrors which reflect separately said attenuated plurality of wavelength lights passed through said plurality of optical attenuators to turn them back through said plurality of optical attenuators to said optical demultiplexer-multiplexer.    
     
     
         68 . An optical level adjusting device, according to  claim 67 , wherein: 
 said optical demultiplexer-multiplexer is of array waveguide diffraction grating type or fiber-grating type.    
     
     
         69 . An optical level adjusting device, according to  claim 67 , wherein: 
 said optical attenuators are an optical variable attenuator or an optical fixed attenuator.    
     
     
         70 . An optical level adjusting device, according to  claim 67 , wherein: 
 said optical attenuators are replaced by optical amplifiers or include optical amplifiers to be in series connected thereto.    
     
     
         71 . An optical level adjusting device, according to  claim 67 , wherein: 
 said optical attenuators are separately disposed on a plurality of optical transmission lines which connect between said optical demultiplexer-multiplexer and each of said optical reflecting mirrors to transmit separately said demultiplexed plurality of wavelength lights.    
     
     
         72 . An optical level adjusting device, comprising: 
 an optical demultiplexer-multiplexer which demultiplexes a wavelength-multiplexed optical signal into a plurality of wavelength lights and multiplexes a plurality of wavelength lights into a wavelength-multiplexed optical signal;    a plurality of optical transmission lines through which said demultiplexed plurality of wavelength lights to be output from said optical demultiplexer-multiplexer are separately transmitted;    an optical dividing and coupling means through which each of said plurality of wavelength lights transmitted through each of said plurality of optical transmission lines is re-input to said optical demultiplexer-multiplexer while by-passing a different one of said optical transmission lines without overlapping with another wavelength light; and    a plurality of optical attenuators which are disposed between any two of said optical transmission lines to attenuate separately said demultiplexed plurality of wavelength lights to be transmitted therebetween.    
     
     
         73 . An optical level adjusting device, according to  claim 72 , wherein: 
 said optical demultiplexer-multiplexer is of array waveguide diffraction grating type or fiber-grating type.    
     
     
         74 . An optical level adjusting device, according to  claim 72 , wherein: 
 said optical attenuators are an optical variable attenuator or an optical fixed attenuator.    
     
     
         75 . An optical level adjusting device, according to  claim 72 , wherein: 
 said optical dividing and coupling means is an optical divider, an optical coupler or optical divider-coupler.    
     
     
         76 . An optical level adjusting device, according to  claim 72 , wherein: 
 said optical attenuators are replaced by optical amplifiers.    
     
     
         77 . An optical signal repeating and amplifying device, comprising: 
 a first optical demultiplexer-multiplexer which demultiplexes a wavelength-multiplexed optical signal to be input thereto into a plurality of different wavelength lights;    a plurality of optical amplifiers which amplify separately said demultiplexed plurality of different wavelength lights; and    a second optical demultiplexer-multiplexer which multiplexes said amplified wavelength lights to be output from said plurality of optical amplifiers into a wavelength-multiplexed optical signal.    
     
     
         78 . An optical signal repeating and amplifying device, according to  claim 77 , wherein: 
 said plurality of optical amplifiers are inserted into optical transmission lines to connect between said first and second optical demultiplexer-multiplexers.    
     
     
         79 . An optical signal repeating and amplifying device, according to  claim 77 , wherein: 
 said plurality of optical amplifiers are a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         80 . An optical signal repeating and amplifying device, according to  claim 77 , wherein: 
 said first optical demultiplexer-multiplexer is an optical demultiplexer, and said second optical demultiplexer-multiplexer is an optical multiplexer.    
     
     
         81 . An optical signal repeating and amplifying device, according to  claim 77 , wherein: 
 said first and second optical demultiplexer-multiplexers are of array waveguide diffraction grating type.    
     
     
         82 . An optical signal repeating and amplifying device, according to  claim 77 , wherein: 
 said first and second optical demultiplexer-multiplexers are of fiber-grating type.    
     
     
         83 . An optical signal repeating and amplifying device, comprising: 
 an optical circulator through which a wavelength-multiplexed optical signal to be input to the input port is output from the input-output port and a wavelength-multiplexed optical signal to be input to the input-output port is output from the output port;    an optical demultiplexer-multiplexer which demultiplexes the wavelength-multiplexed optical signal from said optical circulator into a plurality of wavelength lights and multiplexes a plurality of wavelength lights into a wavelength-multiplexed optical signal;    a plurality of optical amplifiers which amplify separately said demultiplexed plurality of different wavelength lights to be output from said optical demultiplexer-multiplexer; and    a plurality of optical reflecting mirrors which reflect separately said plurality of wavelength lights to be output from said plurality of optical amplifiers to turn them back through said plurality of optical amplifiers to said optical demultiplexer-multiplexer.    
     
     
         84 . An optical signal repeating and amplifying device, according to  claim 83 , wherein: 
 said optical demultiplexer-multiplexer is of array waveguide diffraction grating type.    
     
     
         85 . An optical signal repeating and amplifying device, according to  claim 83 , wherein: 
 said optical demultiplexer-multiplexer is of fiber-grating type.    
     
     
         86 . An optical signal repeating and amplifying device, according to  claim 85 , wherein: 
 said fiber-grating type optical demultiplexer-multiplexer comprises a fiber grating disposed on an optical transmission line, and an optical circulator disposed on the optical transmission line, said optical circulator inputting and outputting selectively an optical signal from said fiber grating or an optical signal to said fiber grating.    
     
     
         87 . An optical signal repeating and amplifying device, according to  claim 83 , wherein: 
 said plurality of optical amplifiers are inserted into optical transmission lines to connect between said optical demultiplexer-multiplexer and said plurality of optical reflecting mirrors.    
     
     
         88 . An optical signal repeating and amplifying device, according to  claim 83 , wherein: 
 said plurality of optical amplifiers are a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         89 . An optical signal repeating and amplifying device, according to  claim 88 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         90 . An optical signal repeating and amplifying device, according to  claim 84 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         91 . An optical signal repeating and amplifying device, comprising: 
 an optical demultiplexer-multiplexer which demultiplexes the wavelength-multiplexed optical signal to be input thereto into a plurality of wavelength lights and multiplexes a plurality of wavelength lights into a wavelength-multiplexed optical signal;    a plurality of first optical transmission lines which are connected with the input-output ports on the demultiplex side of said optical demultiplexer-multiplexer;    a plurality of optical divider-couplers which are connected to the ends of said plurality of first optical transmission lines;    a plurality of second optical transmission lines which connect between different two of said plurality of optical divider-couplers, the connecting not to be in parallel to another connecting; and    a plurality of bi-directional optical amplifiers which are inserted into said plurality of second optical transmission lines and amplify an optical signal to transmit therethrough.    
     
     
         92 . An optical signal repeating and amplifying device, according to  claim 91 , wherein: 
 said plurality of second optical transmission lines are separately provided with an optical isolator.    
     
     
         93 . An optical signal repeating and amplifying device, according to  claim 91 , wherein: 
 said plurality of optical amplifiers are a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         94 . An optical signal repeating and amplifying device, according to  claim 93 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         95 . An optical signal repeating and amplifying device, according to  claim 94 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         96 . An optical signal repeating and amplifying device, according to  claim 91 , wherein: 
 said optical demultiplexer-multiplexer is of array waveguide diffraction grating type.    
     
     
         97 . An optical signal repeating and amplifying device, according to  claim 91 , wherein: 
 said optical demultiplexer-multiplexer is of fiber-grating type.    
     
     
         98 . An optical level adjusting device, comprising: 
 a first optical demultiplexer-multiplexer which demultiplexes a wavelength-multiplexed optical signal to be input thereto into a plurality of different wavelength lights;    a plurality of optical amplifiers which amplify separately said demultiplexed plurality of different wavelength lights; and    a second optical demultiplexer-multiplexer which multiplexes said amplified wavelength lights to be output from said plurality of optical amplifiers into a wavelength-multiplexed optical signal; and    means for controlling separately the gain of said plurality of optical amplifiers.    
     
     
         99 . An optical level adjusting device, according to  claim 98 , wherein: 
 said plurality of optical amplifiers are inserted into optical transmission lines to connect between said first and second optical demultiplexer-multiplexers.    
     
     
         100 . An optical level adjusting device, according to  claim 98 , wherein: 
 said plurality of optical amplifiers are a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         101 . An optical level adjusting device, according to  claim 98 , wherein: 
 said first optical demultiplexer-multiplexer is an optical demultiplexer, and said second optical demultiplexer-multiplexer is an optical multiplexer.    
     
     
         102 . An optical level adjusting device, according to  claim 98 , wherein: 
 said first and second optical demultiplexer-multiplexers are of array waveguide diffraction grating type.    
     
     
         103 . An optical level adjusting device, according to  claim 98 , wherein: 
 said first and second optical demultiplexer-multiplexers are of fiber-grating type.    
     
     
         104 . An optical level adjusting device, according to  claim 98 , wherein: 
 said optical amplifiers are replaced by optical attenuators or include optical attenuators to be in series connected thereto.    
     
     
         105 . An optical level adjusting device, comprising: 
 an optical circulator through which a wavelength-multiplexed optical signal to be input to the input port is output from the input-output port and a wavelength-multiplexed optical signal to be input to the input-output port is output from the output port;    an optical demultiplexer-multiplexer which demultiplexes the wavelength-multiplexed optical signal from said optical circulator into a plurality of wavelength lights and multiplexes a plurality of wavelength lights into a wavelength-multiplexed optical signal;    a plurality of bi-directional optical amplifiers which amplify separately said demultiplexed plurality of different wavelength lights to be output from said optical demultiplexer-multiplexer;    a plurality of optical reflecting mirrors which reflect separately said plurality of wavelength lights to be output from said plurality of optical amplifiers to turn them back through said plurality of optical amplifiers to said optical demultiplexer-multiplexer.    means for controlling separately either the gain of said plurality of optical amplifiers or the reflectivity of said plurality of optical reflecting mirrors.    
     
     
         106 . An optical level adjusting device, according to  claim 105 , wherein: 
 said plurality of optical amplifiers are inserted into optical transmission lines to connect between said optical demultiplexer-multiplexer and said plurality of optical reflecting mirrors.    
     
     
         107 . An optical level adjusting device, according to  claim 105 , wherein: 
 said plurality of optical amplifiers are a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         108 . An optical level adjusting device, according to  claim 107 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         109 . An optical level adjusting device, according to  claim 108 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         110 . An optical level adjusting device, according to  claim 105 , wherein: 
 said optical amplifiers are replaced by optical attenuators or include optical attenuators to be in series connected thereto.    
     
     
         111 . An optical level adjusting device, according to  claim 105 , wherein: 
 said first and second optical demultiplexer-multiplexers are of array waveguide diffraction grating type.    
     
     
         112 . An optical level adjusting device, according to  claim 105 , wherein: 
 said first and second optical demultiplexer-multiplexers are of fiber-grating type.    
     
     
         113 . An optical level adjusting device, comprising: 
 an optical demultiplexer-multiplexer which demultiplexes the wavelength-multiplexed optical signal to be input thereto into a plurality of wavelength lights and multiplexes a plurality of wavelength lights into a wavelength-multiplexed optical signal;    a plurality of first optical transmission lines which are connected with the input-output ports on the demultiplex side of said optical demultiplexer-multiplexer;    a plurality of optical divider-couplers which are connected to the ends of said plurality of first optical transmission lines;    a plurality of second optical transmission lines which connect between different two of said plurality of optical divider-couplers, the connecting not to be in parallel to another connecting;    a plurality of bi-directional optical amplifiers which are inserted into said plurality of second optical transmission lines and amplify an optical signal to transmit therethrough; and    means for controlling separately the gain of said plurality of bi-directional optical amplifiers.    
     
     
         114 . An optical level adjusting device, according to  claim 113 , wherein: 
 said plurality of second optical transmission lines are separately provided with an optical isolator.    
     
     
         115 . An optical level adjusting device, according to  claim 113 , wherein: 
 said plurality of optical amplifiers are a semiconductor optical amplifier or an impurity-doped optical fiber amplifier.    
     
     
         116 . An optical level adjusting device, according to  claim 116 , wherein: 
 said impurity-doped optical fiber amplifier is a rare-earth-element-doped optical fiber amplifier.    
     
     
         117 . An optical level adjusting device, according to  claim 117 , wherein: 
 said rare-earth-element-doped optical fiber amplifier is an erbium-doped optical fiber amplifier, a neodymium-doped optical fiber amplifier, or a praseodymium-doped optical fiber amplifier.    
     
     
         118 . An optical level adjusting device, according to  claim 113 , wherein: 
 said optical demultiplexer-multiplexer is of array waveguide diffraction grating type.    
     
     
         119 . An optical level adjusting device, according to  claim 113 , wherein: 
 said optical demultiplexer-multiplexer is of fiber-grating type.    
     
     
         120 . An optical level adjusting device, according to  claim 113 , wherein: 
 said optical amplifiers are replaced by optical attenuators or include optical attenuators to be in series connected thereto.