| 摘要 |
PURPOSE:To reduce distortion included in an optical output of a light emitting element by converting a part of the optical output into an electric signal by a photodetecting element, comparing the electric signal with an original signal, extracting only a distortion component, and feeding back the distortion component to the original signal. CONSTITUTION:It is defined that the gain of a driving circuit 1 is G1, the electric/optical conversion factor of the light emitting element 2 is beta, the coupling efficiency between the light emitting element 2 and the photodetecting element 3 is eta, the optical/ electric conversion factor of the photodetecting element 2 is alpha, and the gains of a feedback amplifier 4 and a signal amplifier 5 are G2 and G3 respectively, a signal is Is, the output of a filter 6 is Ij, and the output of the feedback amplifier 4 is Ib. The filter 6 passes only a signal component out of the output of the signal amplifier 5. When the distortion generated due to non-linearity in the electric/optical conversion characteristics of the light emitting element 2 is defined as DELTA, the optical output P0 is shown in the formula I. If the gain G3 of the signal amplifier 5 is set up so that Ij=alphabetaetaG1Is is formed, the optical output P0 is turned from the formula I to the formula II, so that only the distortion component can be reduced only by the loop gain of feedback without reducing the amplifying degree of the signal component. |
