Photonic RF and microwave reconfigurable filters and true time delays based on an integrated optical Kerr frequency comb source (1802.00057v1)

Abstract: We demonstrate advanced transversal radio frequency (RF) and microwave functions based on a Kerr optical comb source generated by an integrated micro-ring resonator. We achieve extremely high performance for an optical true time delay aimed at tunable phased array antenna applications, as well as reconfigurable microwave photonic filters. Our results agree well with theory. We show that our true time delay would yield a phased array antenna with features that include high angular resolution and a wide range of beam steering angles, while the microwave photonic filters feature high Q factors, wideband tunability, and highly reconfigurable filtering shapes. These results show that our approach is a competitive solution to implementing reconfigurable, high performance and potentially low cost RF and microwave

• The paper demonstrates an integrated CMOS-compatible Kerr comb that enables tunable true-time delays and versatile microwave photonic filtering.
• It achieves high angular resolution for phased array antennas with 21 RF channels and minimal beam squint via broadband comb generation.
• The approach leverages controlled optical comb line shaping to realize reconfigurable filters with extended frequency tunability and enhanced Q factors.

Integrated Kerr Frequency Comb for Photonic RF Signal Processing

This paper presents a significant advancement in the field of photonic microwave and radio frequency (RF) signal processing through the application of an integrated optical Kerr frequency comb source. By utilizing a micro-ring resonator (MRR) to generate optical frequency combs, the researchers achieve high-performance RF functions including tunable true time delays for phased array antennas (PAAs) and reconfigurable microwave photonic filters (MPFs).

The core innovation lies in the use of CMOS-compatible Kerr frequency comb generators which offer a multitude of advantages over conventional discrete laser arrays. These include a reduced physical footprint, increased number of available wavelengths, enhanced performance, and simplified device complexity. Such characteristics are particularly beneficial for RF transversal functions where the number of wavelengths dictates the number of available RF channel time delays. This, in turn, results in improved angular resolution and broader beam-steering angles for PAAs, along with higher QRF factors and more versatile filtering options for MPFs.

Transversal Photonic Microwave and RF Signal Processing

The researchers propose a novel multi-channel RF tunable microwave true time delay line leveraging the aforementioned Kerr frequency combs. The generated broadband comb offers a large number of comb lines, which notably improves device performance while also reducing size and the potential cost of the true time delay solution. This device achieves high angular resolution for the PAA with a minimal beam squint, a challenge often faced with traditional technologies.

Further innovations introduced include microwave photonic filters with extended functionalities such as adaptive low pass, high pass, band-stop, Nyquist, and bandpass filter operations. These filters allow for wide center frequency tunability without necessitating additional hardware tuning devices, primarily through the manipulation of tap weights. The experimental results have shown concordance with theoretical results, validating the proposed approach.

High-Resolution Phased Array Antenna

The phased-array antenna employed in this research enhances performance through true time delays orchestrated by the integrated optical comb. The compactness and ultra-high Q factor (~1.2 million) of the MRR allow for a wide Nyquist zone challenging to achieve with mode-locked or external modulation combs. With a free spectral range (FSR) of 1.6 nm and a generated comb bandwidth over 200 nm, the device implements 21 RF channels, leading to a high angular resolution PAA capable of fine-tuned beam steering without frequency-dependent variations.

Versatility of Microwave Photonic Filters

For MPFs, the paper demonstrates significant advancements achievable solely by shaping optical comb lines directly. The device presented can reach Q factors that surpass traditional architectures by leveraging the many tap coefficients obtainable through the Kerr comb-based approach. The controlled shaping and accurate feedback system ensure precise comb line adjustment, transforming optical signals into RF signals effectively.

Implications and Future Directions

The integration of Kerr frequency combs into photonic RF devices harbors significant potential for applications in radar and communication systems due to the high degree of reconfigurability and performance enhancement achievable. Looking forward, expanding the number of channels and optimizing tap coefficients could lead to even higher performing filter shapes and greater out-of-band rejection. This approach provides a promising avenue toward fully integrated and highly versatile RF and microwave signal processing systems.

In conclusion, the utilization of integrated Kerr frequency combs presents promising opportunities for photonic RF signal processing, offering high performance and versatile functionalities in a potentially cost-effective manner. The research illuminates a pathway for further exploration and optimization in next-generation RF and microwave applications.