Some wavelength converters generate converted light having a wavelength different from that of input light by using a nonlinear optical phenomenon, such as four-wave mixing, that occurs in an optical fiber.  Non-patent Document 1 (M. Onishi, et al.:  Proc.  23rd ECOC, 1997, vol.  2, p. 115) discloses that a desired wavelength conversion characteristic can be obtained by adjusting the wavelength of pump light, which is input to an optical fiber, in accordance with the zero-dispersion wavelength of the optical fiber.  Non-patent Document 2 (K. Inoue, et al.:  IEEE Photonics Technology Lett.,  vol.  6 (1994) 1451) discloses a wavelength-tunable light source that can be used for such a purpose.  A wavelength converter using the wavelength-tunable light source has a complex structure and is expensive. 
On the other hand, attempts have been made to obtain a desired wavelength conversion characteristic by adjusting the zero-dispersion wavelength of an optical fiber.  For example, Non-patent Document 3 (M. Takahashi et al.:  Proc.  32nd ECOC 2006 Th.1.5.1) discloses a method for shifting the zero-dispersion wavelength of a highly nonlinear fiber by stretching the fiber.  However, Non-patent Document 3 does not disclose a specific method for applying tension to the fiber.  In particular, a method for repeatedly changing tension is not examined in Non-patent Document 3.     Non-patent Document 1: M. Onishi, et al.:  Proc.  23rd ECOC, 1997, vol.  2, p. 115.     Non-patent Document 2: K. Inoue, et al.:  IEEE Photonics Technology Lett.,  vol.  6 (1994) 1451.     Non-patent Document 3: M. Takahashi et al.:  Proc.  32nd ECOC 2006 Th.1.5.1.     Non-patent Document 4: T. Okuno, et al.:  IEEE J. Select.  Topics in Quantum Electron.  Vol.  5 (1999) 1385.     Non-patent Document 5: T. Okuno, et al.:  Electron.  Left.  vol.  39 (2003) 972.