| 摘要 |
PROBLEM TO BE SOLVED: To block unwanted wavelength from entering into photodetectors with an inexpensive constitution without providing filters and also without necessitating spaces where the filters are to be provided by forming films having wavelength selectivities which transmit target wavelengths and do not transmit other wavelengths on single surfaces or both surfaces of lenses arranged at the photodetector sides. SOLUTION: After a light which is received via an optical fiber 21 and whose wavelength isλ2 is reflected by branching filters 13, 22, it is received at a photodetector (PD1) 16 with a lens 15. Besides, after a light whose wavelength isλ1 in reflected lights reflected by the branching filter 13 passes through the branching filter 22 to be received at a photodetector (PD2) 18 with a lens 17. Then, dielectric multiple layers having wavelength selectivities are formed on single surfaces or both surfaces of the lenses 15, 17. Thus, wnwanted wavelengths are bolcked from entering into the photodetectors 16, 18 without using filters. |
