Abstract
A tunable all-optical microwave oscillator, which has no electrical microwave devices as well as photoelectric conversion and electro-optic modulation, is proposed and experimentally demonstrated. In this scheme, a distributed-feedback laser diode is utilized to be a light source and create a seed microwave signal from the period-one (P1) oscillation by a self-delayed optical feedback injection. A semiconductor optical amplifier-based all-optical feedback loop is introduced to perform optical–optical feedback modulation and mode selection. Meanwhile, a short fiber loop is coupled to further suppress the residual side modes. In the experiment, single-mode microwave photonic signals with good quality are obtained, whose frequencies can be tuned from 6.10 to 15.59 GHz by adjusting the optical feedback ratio. The measured single-sideband phase noise is −89 dBc/Hz at 10-kHz offset from a carrier of 10.98 GHz.
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