| 摘要 |
PURPOSE:To reduce a modal noise in multi-mode fiber transmission by controlling the amplitude of a superimposed high frequency current in matching with the change in a bias current supplied from an automatic optical output power control circuit to semiconductor laser. CONSTITUTION:An input signal IS from a signal input terminal 1 is added to a current output iRF of a high frequency oscillator 8 attenuated by a variable attenuator 9 and a DC output IB of a bias supply circuit 11 by a coupling circuit 3 and a semiconductor laser 4 is subject to direct intensity modulation by the added current. A loop comprising the semiconductor laser 4, a photodiode 5, a comparator amplifier 7, the bias supply circuit 11 and the coupling circuit 3 acts like keeping a mean output power of the laser 4 constant, the variable attenuator 9 is controlled by a control signal of the bias supply circuit 11 and the optical output of the laser 4 is a pulse amplitude modulation wave having 9 period equal to the period of the high frequency current. |
