Patent ID: 6842464

Claim:
A wavelength tunable light source comprising: an external resonator light source having a wavelength selection structure and an isolator, and oscillating at a wavelength selected by the wavelength selection structure, the wavelength selection structure being moveable to vary the wavelength selected thereby; and a light path changer directing at least part of the light emitted from the external resonator light source, which includes a spontaneous emitted light ingredient from the light source, to said wavelength selection structure so that a first wavelength of said light, emitted from said external resonator light source, travels along a first optical path, and a second wavelength of light, reflected by the light path changer to the wavelength selection structure, travels along a second optical path, wherein the light path changer adjusts an angle of incidence of the second wavelength of light such that the first wavelength of said light and the second wavelength of light become synchronized.