FREQUENCY SEPARATION LOCKING AND SYNCHRONIZATION FOR FDM OPTICAL SOURCES USING WIDELY FREQUENCY TUNABLE LASER-DIODES

A laser diode (LD) frequency separation locking method (reference pulse method) is proposed. This method has advantageous features for frequency division multiplexing (FDM) networks from the viewpoint of frequency separation stability with strict frequency separation standard, modulation format independency, controllability over a large number of LD’s, and frequency synchronization capability. Frequency locking experiments, using four and ten controlled LD’s, confirm that the control system using the method can stabilize frequency spacing for more than 100 LD’s. The frequency fluctuation is suppressed to less than 10 MHz. The reference pulse method can be applied to modulated LD’s under any modulation format. Frequency synchronization, utilizing the reference pulse method, is also proposed and demonstrated experimentally for two controlled LD groups, each consisting of three LD’s. Frequency discrepancy between two LD groups was only 2.7% of frequency separation. Required frequency-swept light power and controlled LD power at detector input for frequency synchronization indicate that more than 5 × 104 LD groups within 10 km area, each having 100 LD’s, can be synchronized simultaneously. The region can be broadened without considerably reducing the controllable LD group number. The results above indicate that the reference pulse method can be applied to FDM networks. © 1990 IEEE