Abstract
Optoelectronic oscillators (OEOs) are useful for applications such as radar, time-frequency metrology and light-wave technology, where microwaves with exceptional purity are needed [1]. The purity of microwave signals is achieved thanks to an optical fiber delay-line inserted into the feedback loop providing a quality factor equal to Q = 2π fmT, where fm is the microwave frequency and T the delay. Microwaves with frequencies as large as 75 GHz, and a phase noise lower than −160 dBc/Hz at 10 kHz has been achieved [2]. As Q increases with T, a long delay should improve the performance. However strong parasite ring-cavity peaks at the integer multiples of the round-trip frequency ΩT = 2π/T limiting the region of low phase noise. Alternatives consisting in adding the output of two loops with different delay time has been proposed to lower the phase noise or to reduce the level of parasite ring-cavity peaks [3]. Single-loop OEOs suffer from another severe limitation: increasing the gain the system becomes unstable leading to a modulation of the microwave amplitude and thus to a degradation of the spectral purity [4].
© 2013 IEEE
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