Programmable photonic signal processor chip for radiofrequency applications (1505.00094v1)

Abstract: For the abstract, please see the submitted article.

• The paper introduces a photonic analog to electronic FPGAs by employing a two-dimensional mesh of tunable Mach-Zehnder couplers.
• The paper demonstrates wideband RF filtering with a 14 GHz free spectral range and continuous frequency coverage from 1.6 to 6 GHz.
• The paper offers flexible circuit architectures, including tapped-delay-line filters and ring resonators, paving the way for scalable photonic processing solutions.

Overview of the Programmable Photonic Signal Processor Chip for Radiofrequency Applications

This paper presents a pioneering approach to integrated microwave photonics, addressing the pressing need for adaptable, wideband, and efficient analog processing solutions in modern radio frequency (RF) systems. The proposed solution is a programmable photonic signal processor chip designed to function analogously to electronic field-programmable gate arrays (FPGAs). It leverages a grid of tunable Mach-Zehnder (MZ) couplers arranged in a two-dimensional mesh network to achieve versatile RF signal processing.

Key Contributions

• Photonic Analog of FPGAs: The paper introduces the concept of photonic signal processors that mirror the flexibility of electronic FPGAs. This innovation allows for the programming of photonic chips into various circuit architectures, significantly reducing the cost and time associated with designing custom photonic integrated circuits for specific applications.
• Wideband RF Filters: The paper demonstrates a programmable photonic chip with a free spectral range of 14 GHz, offering continuous, over-two-octave frequency coverage from 1.6 to 6 GHz. The chip exhibits capabilities in variable passband shaping, achieving a range from a 55-dB-extinction notch filter to a 1.6-GHz-bandwidth flat-top filter.
• Circuit Architecture Flexibility: The arrangement of MZ couplers allows for the easy synthesis of diverse circuit architectures, such as tapped-delay-line filters and ring resonators for various signal processing tasks. The mesh network's dimensions facilitate extensive functionality, hinting at potential multi-task photonic processors.

Experimental Demonstration

The experimental section provides a proof of principle using a dual-cell mesh network configuration, highlighting the programmability of the chip in terms of both amplitude and phase. Various circuit configurations were demonstrated, including a single-ring notch filter and dual-ring bandpass filter, validated by their corresponding frequency response measurements.

Implications and Future Directions

The implications of this research are manifold. Practically, it aims to enhance RF technologies, such as cognitive radios, by offering high-spectrum-efficiency RF filters with significant frequency agility and tunability. Theoretically, it opens new avenues for scalable and flexible photonic signal processing solutions, potentially leading to the development of more complex and multifunctional photonic circuits.

The paper speculates on future developments, emphasizing the potential to scale the network dimension for implementing more intricate functions and the integration of multiple independent functionalities on a single chip. This necessitates improvements in photonic waveguide technology for greater miniaturization and FSR enhancement.

Challenges and Considerations

Key challenges include the inherent complexity in scaling up mesh networks, which may complicate calibration and control due to potential crosstalk and initial offsets. The paper suggests that advancements in optoelectronic components and control algorithms are essential to overcome such difficulties, particularly regarding efficient electric-to-optic signal conversion and improved tuning rates for circuit reconfigurations.

Conclusion

This work represents a significant stride in the field of integrated microwave photonics, offering a flexible and cost-effective solution for RF signal processing. The programmable chip's versatility promises to extend the capabilities of conventional RF systems while presenting a robust platform for future research and technological advances in photonic signal processing.