| CPC H04J 14/02 (2013.01) [G02B 6/293 (2013.01)] | 19 Claims | 

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               1. An optical transmission system comprising: 
            an optical filter configured to selectively pass, as an output light, at least one wavelength component of multiple wavelength components included in an input light, the optical filter comprising a movable element to change a passband; and 
                a controller configured to adjust the passband by controlling the movable element based on power of light corresponding to the output light measured by a power monitor, 
                wherein the optical filter is configured as a bandpass filter having a first amplitude-frequency characteristic in a first wavelength band and having a second amplitude-frequency characteristic in a second wavelength band, 
                wherein the first wavelength band includes a center wavelength of the passband, 
                wherein the second wavelength band is adjacent to the first wavelength band and is more away from the center wavelength than the first wavelength band, 
                wherein in the first wavelength band, the first amplitude-frequency characteristic is that a gain curve corresponds to a convex function defined by a Gaussian function or a super Gaussian function and having a peak at the center wavelength, and 
                wherein in the second wavelength band, the second amplitude-frequency characteristic is that the gain curve shows a steeper slope than the convex function. 
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