| 摘要 |
PURPOSE:To obtain a photodetecting circuit with low noise in a wide band by using the 1st inductor connected to a photodetector in parallel and the 2nd inductor connecting the photodetector with an amplifier element. CONSTITUTION:Two inductors 3, 4 are used and two resonance frequency components to be tuned with each other are determined as two points to to expand the range of the resonance frequency of the photodetecting circuit. In an equivalent circuit, parallel resonance based upon a parallel circuit consisting of the inductor 3 and capacitors 10, 11 at resonance frequency fr1 and serial resonance based upon a serial circuit consisting of the inductor 4 and the capacitors 10, 11 at resonance frequency fr2 are generated. In case of using the photodetecting circuit as a photodetecting circuit for optical heterodyne, the inductance values L1, L2 of the inductors 3, 4 are adjusted so that respective resonance frequency levels fr1, fr2 approaches intermediate frequency fo obtained by optical heterodyne detection based upon signal light and local oscillation light. When respective resonance frequency components are set up like fr1<fo<fr2 e,g., the influence of the capacitors in the photodetecting circuit is removed near the resonance frequency and the photodetecting circuit with low noise having a wide band can be obtained. |
