The demand for high-bandwidth communication networks and higher frequency signal processing has motivated the development of RF photonics, where RF signals are up-converted to the optical domain to be processed by photonic techniques. Over the last two decades, great strides have been made in this field; however, high-resolution processing is a bottleneck preventing low guardbands in data transmission thereby limiting data-transmission capacity. This is due to the lack of narrowband and single-passband photonic processors that can process RF information with high-resolution in the optical domain. Stimulated Brillouin scattering (SBS) is a nonlinear optical process between two counter-propagating optical waves and an acoustic wave, which can alleviate this bottleneck due to its narrow resolution of as low as 3 MHz, while allowing for frequency tuning in excess of 30 GHz. However, SBS is known to suffer from high spontaneously-generated noise, as well as saturation effects that limit the dynamic range of the RF system.
In this work, we demonstrate RF bandpass filtering using the SBS loss response created through the anti-Stokes interaction using a phase-modulated analog photonic link and low optical pump powers. This enables an enhancement of the signal to noise ratio of an RF tone by up to 8 dB and the linearity by up to 3 dB, when compared to using the Stokes component associated with SBS gain. This technique is compatible with analog photonic link optimization techniques, and paves the way for the realization of compact and low-power SBS-based filters based on a photonic chip that can be implemented in practical systems.
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