Seven kinds of SC-type fixed optical attenuator ranging from 3 to 30 dB have been successfully developed using Co~(2+)-ion doped optical fiber. They have high input power endurance. The main wavelength dependence in attenuation have been reduced by controlling the Co~(2+)-ion doped area in the fiber core. The fluctuation in attenuation with wavelength and PDL degradation caused by the mode coupling were effectively suppressed in highly attenuative attenuators by using GeO_2-doped absorption fibers in the outer part of the cladding. The simple structure allows us to produce these fixed optical attenuators at a lower cost than conventional ones.
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