A 0-40 GHz RF tunable receiver based on photonic direct conversion and digital feed-forward lasers noise cancellation

This paper presents the architecture of a compact, robust, and broadly tunable RF receiver based on photonic direct conversion and digital feed-forward lasers noise cancellation. In the proposed solution, the incoming RF signal is filtered and down converted to baseband by means of an optical direct conversion (i.e., I/Q) receiving scheme (named here as signal receiver) fed by two free-running semiconductor lasers. At the same time, the beat noise of the free-running lasers is acquired by a second down-converter (reference sensor) fed by the same lasers. Then, the noise information is used by the digital feed-forward noise cancelling algorithm to enhance the frequency resolution provided by the signal receiver. The proposed strategy avoids complex lasers feedback-locking mechanisms, such as electrical/optical phased-locked loop or optical injection locking, as well as bulky RF components such as filters banks and synthesizers. An experimental validation shows an RF input range of 0-40 GHz, instantaneous bandwidth of 2 GHz, carrier noise of ∼-120 dBc/Hz (@ 4 kHz), out-of-band rejection >80 dB, and tuning response <10 μs. Implementing the scheme through integrated photonics technologies should enable increased environmental stability and a chip-scale form factor.