| 摘要 |
PURPOSE:To enable a control action to be held stable even under the presence of disturbance, by a method wherein the range of frequency of a frequency sweeping light is controlled so that the difference between the sweep starting time of the frequency sweeping light and the generating time of a pulse firstly generated in the reference pulse train which is generated within one time coefficient substantially coincides with a predetermined reference value. CONSTITUTION:A T flip-flop (T.FF) is driven by the first pulse out of the reference pulses which are inputted to the section indicated by a dotted line, and corresponds to both the pulse generated at the starting point of a sweep period and the output pulse of an optical resonator. Then, the output of the T.FF becomes a square wave having a starting point and an ending point which are set by the continuous two pulses. Since the height of the square wave is equal to a logical level EL and constant at all times, the square wave is integrated with an integrator in the next stage, and thereby an output ELDELTAt at corresponding to a time difference DELTAt between the continuous two pulses is obtained. When the time difference DELTAt between the two pulses is in the range of 0<=DELTAt<=t1, t2<=DELTAt, a control loop is closed, and an error signal is fed back to a DBR1. This prevents the first pulse from dissipating and another pulse preceding to the original first pulse from generating. Accordingly, a stable system can be formed in which the control does not fail even under the presence of disturbance. |
