| 摘要 |
A wavelength filter includes a first waveguide with a transmission band of a predetermined basic mode and a second waveguide, arranged in at least one location of the first waveguide, with a transmission band whose cutoff frequency corresponds to a finite value included in the transmission band of the basic mode. A pair of optical couplers constituting a Mach-Zehnder interferometer is connected to the opposite ends of a filter unit including the first waveguide and the second waveguide. When a plurality of wavelength filters is cascaded, the wavelength filters can be each varied in terms of the cutoff frequency of the second waveguide.
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