| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a photodetector suitable for receiving quantum encryption or the like by reducing a dark count generated by a parasitic photon generated at a signal band by a parametric down-conversion process. <P>SOLUTION: In the photodetector for making the signal light of a wavelength λ<SB>1</SB>and the excitation light of a wavelength λ<SB>2</SB>incident on a nonlinear optical medium converting the signal light to the sum frequency light of a wavelength λ<SB>3</SB>by sum frequency generation generated in the nonlinear optical medium and detecting the sum frequency light converted to the wavelength λ<SB>3</SB>, the periodic inversion structure of the code of the nonlinear constant of the nonlinear optical medium has such a structure that the code of the nonlinear constant is inverted at each period Λ<SB>0</SB>, the ratio of the inverted area and non-inverted area of a periodic modulation structure is changed in the length Λ<SB>0</SB>of a part of the nonlinear optical medium, and the ratio of turning the code of the nonlinear constant to one code increases as approaching both ends of the nonlinear optical medium. <P>COPYRIGHT: (C)2011,JPO&INPIT |
