[Paper Review] An optical micro-comb with a 50GHz free spectral range for photonic microwave true time delays

Xingyuan Xu, Jiayang Wu+7 more|arXiv (Cornell University)|Oct 30, 2017

Advanced Fiber Laser Technologies30 references3 citations

TL;DR

This paper presents an integrated micro-ring resonator (MRR) Kerr optical comb source with a 50 GHz free spectral range (FSR), enabling a compact, low-cost photonic microwave true time delay line (TTDL). The 81-channel comb across the C-band provides high angular resolution and wide beam steering range in phased array antennas, significantly enhancing performance while reducing system size and complexity.

ABSTRACT

We demonstrate significantly improved performance of a microwave true time delay line (TTDL) based on an integrated micro-ring resonator (MRR) Kerr optical comb source with a channel spacing of 49GHz, corresponding to 81 channels over the C-band. The broadband microcomb, with a record low free spectral range of 49GHz, results in a large number of comb lines for the TTDL, greatly reducing the size, cost, and complexity of the system. The large channel count results in a high angular resolution and wide beam steering tunable range of the phased array antenna (PAA). The enhancement of PAA performance matches well with theory, corroborating the feasibility of our approach as a competitive solution towards implementing compact low-cost TTDL in radar and communications systems.

Motivation & Objective

• To develop a compact, low-cost photonic microwave true time delay line (TTDL) for use in radar and communication systems.
• To address the limitations of conventional TTDLs, such as large size, high cost, and complex architecture.
• To leverage integrated micro-comb technology to achieve high channel count and fine frequency resolution in a single chip.
• To demonstrate feasibility of using a low-FSR micro-comb for high-performance beam steering in phased array antennas (PAA).

Proposed method

• Utilized a silicon nitride micro-ring resonator (MRR) to generate a Kerr optical frequency comb with a 49 GHz channel spacing.
• Achieved a free spectral range (FSR) of 49 GHz, corresponding to 81 comb lines across the C-band (1530–1565 nm).
• Employed a broadband microcomb source to excite multiple optical carriers for microwave signal processing.
• Implemented a photonic TTDL architecture where time delays are induced by phase shifts across comb lines.
• Used the comb's high channel count to enable fine angular resolution and wide tunable beam steering in phased array antennas.
• Validated system performance through theoretical modeling and simulation, aligning with observed experimental trends.

Experimental results

Research questions

• RQ1 Can a micro-comb with a 50 GHz FSR enable a compact, low-cost photonic TTDL for microwave beamforming?
• RQ2 How does a high channel count (81 lines) in a micro-comb improve angular resolution and beam steering range in phased array antennas?
• RQ3 To what extent does the integrated MRR-based micro-comb reduce system size, cost, and complexity compared to conventional TTDLs?
• RQ4 What is the theoretical and practical performance gain in beam steering when using a low-FSR micro-comb source?
• RQ5 Is the performance of the micro-comb-based TTDL consistent with theoretical predictions for phased array systems?

Key findings

• The micro-comb achieved a record-low free spectral range of 49 GHz, enabling 81 comb lines across the C-band.
• The high channel count significantly enhances angular resolution and beam steering tunable range in phased array antennas.
• The system demonstrated a compact, low-cost solution for photonic microwave TTDLs, reducing hardware complexity.
• Theoretical predictions of beam steering performance matched experimental results, validating the design approach.
• The integrated MRR-based micro-comb enables scalable, chip-level implementation of high-performance TTDLs.
• The 50 GHz FSR micro-comb supports wideband microwave signal processing with minimal phase ripple and high stability.