Phase noise measurements of a double-locked laser diode

The double-locked laser configuration used for these measurements is fiber coupled and consists of an optically isolated, dc-biased master laser that optically injects a slave laser through an optical circulator. The lasers operate at a wavelength of approximately 1557 nm. A modulation signal from a microwave frequency synthesizer is added to the dc bias of the slave laser. After passing through the optical circulator, the output of the slave laser is detected by a fast photodiode. The photodiode signal is amplified, split and routed to a microwave spectrum analyzer, a microwave phase noise test set, and a microwave mixer. At the mixer, the signal is compared with the output of the microwave frequency synthesizer.