High performance RF filters via bandwidth scaling with Kerr micro-combs

Xingyuan Xu,David J Moss,Sai T Chu,Brent E Little,Arnan Mitchell,Roberto Morandotti,Mengxi Tan,Jiayang Wu,Thach G Nguyen

doi:10.1063/1.5080246

Abstract

We demonstrate high-resolution photonic RF filters using an RF bandwidth scaling approach based on integrated Kerr optical micro-combs. By employing both an active nonlinear micro-ring resonator (MRR) as a high-quality micro-comb source and a passive high-Q MRR to slice the shaped comb, a large RF instantaneous bandwidth of 4.64 GHz and a high resolution of 117 MHz are achieved, together with a broad RF operation band covering 3.28 to 19.4 GHz (L to Ku bands) using thermal tuning. We achieve programmable RF transfer functions including binary-coded notch filters and RF equalizing filters with reconfigurable slopes. Our approach is an attractive solution for high performance RF spectral shaping with high performance and flexibility.

Highlights

Radio frequency (RF) filters are one of the most basic and commonly used components in modern radar and satellite communications systems.1–5 While electronics is subject to bandwidth bottlenecks,6 photonic techniques can realize high performance RF filters, offering wide bandwidths and low loss and strong immunity to electromagnetic interference.Several approaches have been used for photonic RF filters, including mapping the optical filters’ responses onto the RF domain, highlighted by on-chip stimulated Brillouin scattering.7–9 This approach has achieved extremely high performance in terms of RF resolution—as high as 32 MHz—and a stopband rejection >55 dB, it faces challenges in achieving highly reconfigurable transfer functions
We found that the RF tuning range varies from 3.28 to 19.4 GHz (L to Ku bands)
To realise a mismatch between the comb spacing and the free spectral range (FSR) of the passive micro-ring resonator (MRR) for RF spectral channelizing, we used orthogonal polarization modes38,39 of the active and passive MRRs (TE mode of the active MRR and TM mode of the passive MRR) since they had slightly different effective indices—a result of the non-symmetric waveguide cross sections (∼3 μm × 2 μm) that lead to polarization dependent FSRs

Summary

INTRODUCTION

Radio frequency (RF) filters are one of the most basic and commonly used components in modern radar and satellite communications systems. While electronics is subject to bandwidth bottlenecks, photonic techniques can realize high performance RF filters, offering wide bandwidths and low loss and strong immunity to electromagnetic interference. Several approaches have been used for photonic RF filters, including mapping the optical filters’ responses onto the RF domain, highlighted by on-chip (waveguide based) stimulated Brillouin scattering.7–9 This approach has achieved extremely high performance in terms of RF resolution—as high as 32 MHz—and a stopband rejection >55 dB, it faces challenges in achieving highly reconfigurable transfer functions. The use of electro-optic combs introduces drawbacks such as the need of high-frequency RF sources to drive the modulators This in turn results in a limited number of wavelengths that limit the operational bandwidth. We found that the RF tuning range (controlled via thermal tuning) varies from 3.28 to 19.4 GHz (L to Ku bands) This approach is attractive for high performance photonic RF systems

OPERATION PRINCIPLE

EXPERIMENTAL RESULTS

CONCLUSION