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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SOLISYNTH (Synthesis of Low Noise Microwaves Using Solitons Locked to an Ultra-Stable Cavity)

Teaser

Summary

Low-noise radiofrequency and microwave signals are considered of pivotal importance to a wide range of fundamental research and industrial applications including telecommunication networks, radar and lidar systems, long baseline interferometry and tests of fundamental constants. Conventionally, low-noise microwave signals were provided by bulky and expensive microwave oscillators. Due to the increasing need for compact low-noise microwave sources that are suitable for out-of-door navigation, timekeeping and high-speed communication, various alternative methods have been proposed. Among these proposals, optical-frequency-comb based low-noise microwave generation has shown the promise of generating microwaves with extremely low phase noise level that is only limited by fundamental quantum shot noises.

SOLISYNTH aimed to demonstrate a coherent and compact optical frequency comb based on the platform of optical microresonators with high quality factors. The innovative approach was to use the unique nonlinear dynamics of dissipative cavity solitons to attenuate noises that are induced by various mechanisms. Once the frequency comb in the optical domain is stabilized, the stability can be transferred to the radiofrequency/microwave domain, thus producing low-noise signals at cavity soliton repetition rates with low power consumption and small footprint. Moreover, because dissipative cavity solitons are formed with delicate physics, they exhibit unique characteristics such as relaxation oscillations. To date, these characteristics have not been fully understood, and a careful investigation on this subject is not only of fundamental importance but also critical to the practical applications based on cavity solitons. In this work we have investigated the complex dissipative soliton dynamics with novel excitation approaches and electrooptic comb based ultrafast examination, and we also have studied how the soliton dynamics introduce noises in the generated microwaves. The project consists of two primary phases: (phase I) soliton comb generation with dispersion-engineered microresonators and investigation of the transient soliton dynamics; and (phase II) spectral purification and generation of low-noise microwaves.

Overall, the goal of SOLISYNTH has been fully achieved. Several major objectives, including the generation of broadband and mid-infrared frequency combs based on nano/micro-fabricated resonators and waveguides, the seeding and switching of complex comb states, and the generation of low-noise microwave signals with soliton microcombs, have all been demonstrated. The research results achieved by this project have been published or are currently under review for high-impact journals.

Work performed

Objectives of SOLISYNTH are the following:

1. Generating broadband soliton microcombs and mid-IR frequency combs with dispersion-engineered microresonators and waveguides.
2. Develop strategies to seed and control comb states and to study complex soliton dynamics.
3. Developing low-noise microwave synthesis based on stabilized soliton microcombs

Overall, the project has fully achieved its objectives and milestones for the period. In particular, we have accomplished the following milestones:

(M1) Demonstrate successfully engineered dispersions of crystalline resonators.
(M2) Demonstration of broadband self-referenced soliton Î¼R-OFC.
(M3) Reach fundamental-noise-limited frequency stability of laser locked to an ultrastable cavity.
(M4) Show that the noise levels of synthesized microwaves are comparable to large-scale microwave oscillators.

Deliverables of SOLISYNTH include:

(D1) Publication on â€œFrequency comb based on dispersion-engineered crystalline resonatorsâ€.
(D2) Publication on comb state seeding and switching.
(D3) Publication on stable microwave synthesis with Î¼R-OFC locked to an ultrastable cavity.

The results achieved by this project have produced 5 manuscripts that have been published or are currently under review by high-impact journals. In addition, the beneficiary has attended several academic conferences, giving 6 oral presentations on these research results.

Final results

SOLISYNTH developed low-noise microwave synthesis based on the microresonator dissipative Kerr soliton platform. While microresonator soliton frequency comb technology is a hot topic in the community of nonlinear dynamics and frequency comb spectroscopy, SOLISYNTH represents a significant contribution with its results published in several journal articles and widely disseminated at international conferences.

The impact of this project includes:

1. SOLISYNTH has been situated in a high-impact and fast developing field and thus attracted great attention;

2. The results and objectives we have accomplished within this project have in return provided strong impacts to the community, which will contribute to the development of this field, not only at present but also in the future. In particular, the injection locking technique that was developed within SOLISYNTH can be used in the commercialization of fully integrated compact chip-based frequency comb sources.

To the European Union, SOLISYNTH has also made contributions to the EU H2020 program in excellence research, proving that Europe continues to produce world class science, and being among the first to advance optical frequency comb technologies.