| 摘要 |
PROBLEM TO BE SOLVED: To provide an automatic power control (APC) which keeps an extinction ratio constant even if light emission efficiency of an LD lowers. SOLUTION: An APC circuit 20 stores a first control data 34 which decides a modulation current to a bias current so that an extinction ratio of an LD 12 becomes a fixed value under targeted light output. An operation part 30 decides a bias current and a modulation current based on a measurement value of light output and the first control data. A signal generator 32 generates a control signal showing the bias current and the modulation current, and outputs it to a current supply circuit 18. The APC circuit also stores a second control data 36 which decides a correction value in accordance with an ambient temperature of the LD. The operation part obtains a measurement value of an ambient temperature before deciding a bias current, decides a correction value corresponding to the measurement value following the second control data, and corrects targeted light output. Thereafter, a bias current is calculated based on the targeted light output. COPYRIGHT: (C)2007,JPO&INPIT
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