| 摘要 |
PURPOSE:To improve the receiving sensitivity of light heterodyne detection by using a directionality coupler in which the normalizing propagation constant of two guided wave paths is consistent by the wavelength of a local emitted light and it is different by the wavelength of a signal light. CONSTITUTION:For a directionality coupler 3 of two inputs and two outputs constituting two guided wave paths of optical fibers 1 and 2, the normalizing propagation constant of two guided wave paths is coincident with the wavelength lambda2 of the local light emission and is different by the wavelength lambda1 of a signal light. Consequently, when the signal emitted light lambda1 is inputted from one side guided wave path and the local emitted light lambda2 is inputted from other side guided wave path simultaneously, the difference frequency of the signal light lambda1 and the local emitted light lambda2, the intermediate frequency is emitted only from the output edge of one side guided wave path and the loss due to the power supply of the signal light is eliminated by the directionality coupler 3. Thus, the receiving sensitivity of the detector is improved. |
