Patent ID: 7551822

Claim:
A nonlinear optical signal-treating apparatus, comprising: (a) a pulse light source for outputting first pulse light into a free space; (b) a first optical fiber having a first end and a second end; (c) a second optical fiber that (c1) has an input end that is spliced with the second end of the first optical fiber; (c2) has a mode-field diameter smaller than that of the first optical fiber; (c3) receives the first pulse light at the input end so as to guide it; and (c4) generates second pulse light having a newly produced wavelength by utilizing a nonlinear optical phenomenon so as to output it; and (d) a light-introducing optical system comprising an aspheric lens, for inputting the first pulse light into the first end of the first optical fiber; the ratio of the peak power of the first pulse light outputted from the first optical fiber to that of the first pulse light inputted into the first optical fiber being at least 0.5 and at most 1.5 and the ratio of the pulse width of the first pulse light outputted from the first optical fiber to that of the first pulse light inputted into the first optical fiber being at least 0.5 and at most 1.5, wherein: the first optical fiber has a mode-field diameter of at least 8 μm at a wavelength of 1.55 μm.