Laser induced phase noise in optically injection locked oscillator

The spectral purity of a microwave reference signal, distributed by a fiber optic link to a subharmonically injection locked-oscillator can be degraded by laser large-signal noise. The authors present the noise conversion process leading to the increase of FM noise in the frequency reference. The analysis is based on the noise of the laser diode under large-signal modulation. The theoretical results show that the noise spectrum density of the reference signal is increased under a certain modulation of the laser diode, and that this increase in the noise level of the reference degrades the FM noise of the subharmonically injection locked oscillator. The phase noise measurement of a free-space optical link with the second subharmonic injection locked local oscillator verified the analysis.<>