| 摘要 |
Only the light at an overlapping wavelength of the transmission characteristics of at least two wavelength selecting filters is looped, and at least one of the wavelength selecting filters varies a selected wavelength. Since a loss due to the optical filters is small and there is not a loss caused by a highly reflecting film, the output of an external-resonator variable-wavelength laser can be increased. Optical circuit component (8) divides light input from external device (1) into at least two ports. Loop waveguide (11) interconnects at least ports (9, 10) divided by optical circuit component (8) in the form of a loop. At least two first wavelength selecting filters (12, 13) are inserted in series in a path of loop waveguide (11), and have periodic transmission characteristics on a frequency axis which are different from each other. At least one of first wavelength selecting filters (12, 13) varies the selected wavelength.
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