Conventionally, in a case where the center frequency of a laser in an external cavity single mode is continuously swept, a center wavelength is set by altering the operation temperature of the laser. However, there is a problem in that oscillation wavelengths become discontinuous due to mode hopping at changes in temperature. In addition, a response time to a change in the center wavelength resulting from the changes in temperature is about a few seconds, which makes it impossible to achieve high speed changes.
Accordingly, as a conventional method of avoiding the mode hopping, there has been proposed a configuration in which an optical filter or an external cavity length is variably set in accordance with the changes in the center wavelength (see, Patent Document 1, for example).
USPTO Backgrounds
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