| 摘要 |
PURPOSE: To attain automatic frequency control with high accuracy by using a difference-between a 1st and a 2nd optical frequency just after the 1st optical frequency is switched to the 2nd optical frequency. CONSTITUTION: When a channel signal 16 is switched, a reference signal generating section 19 generates a reference signal corresponding to a new channel as a control signal to switch the optical frequency and the reference signal is shaped by a reference signal shaping filter 21 and given to a comparator 23. As a result, the absolute value of the error signal outputted from the comparator 23 is increased and the frequency of a local oscillation light source 3 is controlled by high speed AFC so that the error signal is made zero and then the switching to the new channel is conducted in a short time. |
