| 摘要 |
PURPOSE:To make the branching loss of a coupling circuit substantially small with respect to signal light and to make the higher outputs of local oscillating light sources less necessary by incorporating the 1st, the 2nd photodetecting parts which detect the 1st, the 2nd coupled beams of light obtained from the 1st, the 2nd exit ends to convert said beams to electrical signals, respectively and a coupling part which couples the electrical signals from the 1st, the 2nd photodetecting parts. CONSTITUTION:When the beam diameters and optical paths of signal light 4 and local oscillation light 9 are adjusted, the 1st signal light 7 and the 1st local oscillation light 13, the 2nd signal light 8 and the 2nd local oscillation light 14 are coupled to form the 1st, the 2nd coupled beams 23, 24 of light. The 1st, the 2nd beams 23, 24 are made incident to the 1st, the 2nd photodetecting parts 17, 18 respectively past the 1st, the 2nd exit ends 15, 16. The 1st, the 2nd parts 17, 18 are constituted of photodiodes, amplifiers, etc., and output the 1st, the 2nd intermediate frequency outputs 19, 20 of a frequency f0 by heterodyne detection from the respective coupled beams of light in the form of electrical signals. The 1st, the 2nd intermediate frequency outputs 19, 20 are electrically coupled in a coupling part 21 to an intermediate frequency output 22. |
