| 摘要 |
PURPOSE:To obtain desired characteristics with smaller degrees by using one among the inputs to an N-to-N star coupler as a signal output and one among the outputs as a filter output and feeding each of the remaining outputs through optical fibers of respectively different lengths and an attenuator to the remaining inputs. CONSTITUTION:The light coming in from an input terminal 1 passes through an input fiber 2 and is inputted to a star coupler 3 in the case of 3X3N to N, N=3. The 1st output of the coupler 3 is outputted through the optical fiber to a terminal 5. The 2nd output of the star coupler passes through the optical fiber having the length l and through the attenuator 8 and is inputted to the 2nd input of the coupler 3. The 3rd output of the star coupler passes through the optical fiber 7 having the length 2l and through the attenuator 9 and is inputted to the 3rd input of the coupler 3. The length l of the optical fiber is simply required to be so determined that the propagation time of the light signal coincides with one symbol time. The effect of permitting the realization of the desired characteristics with the less degrees (the number of the attenuators) as compared to the conventional transversal type (non-recursive type) is thus obtd. |
