Monolithic, Ultralow Jitter, High Frequency Microwave Synthesizer

• Applicant: Professor Dr.-Ing. Franz Xaver Kärtner
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392199472

• Final Report Year: 2022

Final Report Abstract

Within this collaboration, photonic microwave synthesizers with ultra-low phase noise based on modelocked lasers have been developed and characterized. Initially, we followed the approach laid out in the proposal. The Peking University (PKU) team lead by Professor Zhigang Zhang developed Yb-based mode-locked fiber lasers with up to 1 GHz repetition rate and 1 W of output power. The latest versions of the oscillator, with the fiber glued into a plexiglass frame showed also very low timing jitter. In parallel, the Universität Hamburg team lead by Professor Franz Kärtner improved already prefabricated balanced-optical-microwave phase detectors (BOMPDs) that enable the read-out of microwave signals at an arbitrary harmonic of the mode-locked laser without noise degradation due to amplitude to phase noise conversion processes. These devices were finished and pushed to an exceptionally high timing/phase resolution about 70 times better than a corresponding microwave mixer setup. With the help of a student from Peking University visiting Hamburg at the end of 2019 to spring 2020, we tried to use the lasers and co-integrate them with the BOMPDs, however, it turned out that the high power fiber lasers where rather fragile and often failed and also the timing jitter of those lasers was not as low as expected. Nevertheless interesting high power amplification experiments could be implemented and published. Due to the COVID-pandemic the PKU-student had to leave early which hampered the further development of the system. In parallel, we made great advances in demonstrating very high resolution balanced integrated waveguide optical cross-correlators, developed within a collaboration with the Company AdvR in Montana, USA, for several years. The new devices lead to a hundred-fold improvement in timing resolution when compared with bulk-devices resolving sub-attosecond level time delays. The new devices enable the use of fiber links, developed earlier by the Kärtner group using bulk devices, as very robust and high-resolution optical delay references. The fiber delay line together with the high resolution timing detector opens up a new approach to ultra-low timing jitter pulsed optical sources and photonic microwave synthesizers. Using robust commercial 216 MHz and 1 GHz solidstate lasers at 1550 nm first versions of such delay stabilized low jitter optical sources have been implemented and highly phase stable microwave signals were extracted using uni-traveling-carrier photodiodes. This scheme was also successfully patented and has a high potential for commercialization. In parallel, we also investigated the noise performance of mode-locked fiber lasers using nonlinear-amplifying loop mirrors and explained their exceptional low relative intensity noise by operating them at the saturation point of the equivalent saturable absorption. Such sources can become ideal pulsed sources for the demonstrated low phase noise photonic microwave oscillators once scaled further in power and energy.

Publications

• “Robust 700 MHz mode-locked Yb:fiber laser with a biased nonlinear amplifying loop mirror,” Opt. Express 26, 26003 (2018)
  G. Y. Liu, X. H. Jiang, A. M. Wang, G. Q. Chang, F. X. Kärtner, and Z. Zhang
  
• “Timing jitter reduction through relative intensity noise suppression in high-repetition-rate modelocked fiber lasers,” Opt. Express 27, pp. 11273-11280 (2019)
  Y. Wang, H. Tian, D. Hou, F. Meng, Y. X. Ma, H. Xu, F. X. Kärtner, Y.J. Song and Z. Zhang
  
• “Timing Stability Comparison Study of RF Synthesis Techniques”, in Proc. FEL'19, Hamburg, Germany, Aug. 2019, pp. 325-327
  E. Cano Vargas, F. X. Kärtner, A. Berlin, H. P. H. Cheng, A. Dai, J. Derksen, P. Schiepel, K. Shafak
  
• „Balanced Optical-Microwave Phase Detector for 800-nm Pulsed Lasers with Sub-Femtosecond Resolution,” in Proc. FEL'19, Hamburg, Germany, Aug. 2019, pp. 322-324
  K. Şafak, H. P. H. Cheng, A. Dai, P. Schiepel, E. Cano, J. Derksen, A. Berlin, F. X. Kärtner
  
• “All-polarization-maintaining divided pulse fiber oscillator mode-locked with the optical Kerr effect,” Opt. Lett. 46:(24), 6083-6086 (2021)
  M. Edelmann, Y. Hua, K. Safak, and F. X. Kärtner
  
• “Intrinsic amplitude-noise suppression in fiber lasers mode-locked with nonlinear amplifying loop mirrors,” Opt. Lett. 49:(7) 1752-1755 (2021)
  M. Edelmann, Y. Hua, K. Şafak, and F.X. Kärtner
  
• “Method and apparatus for controlling a pulse repetition rate of a pulsed laser beam, and pulsed laser oscillator with stabilized pulse repetition rate,” EU Patent EP21171191 (granted April 2021)
  K. Shafak, A. Dai, E. Cano and F. X. Kärtner
  
• “Nonlinear Fiber System for Shot-Noise Limited Intensity Noise Suppression and Amplification,” Opt. Lett. 46, 3344 - 3347 (2021)
  M. Edelmann, Y. Hua, K. Şafak, and F.X. Kärtner
  
• „Amplification of 1.08 GHz repetition rate femtosecond laser pulses to 97 W average power by a fiber amplifier,” OSA Continuum 4, 1571-1576 (2021)
  Y. Wang, Y. Liu, Z. Zhang, and F. X. Kärtner
  
• "Extreme-Timing-Resolution with Waveguide-Based Balanced Optical Cross- Correlators," 2022 Conference on Lasers and Electro-Optics (CLEO), 2022, pp. 1-3
  K. Şafak, Anan Dai, Ming Xin, Philip Battle, Tony D. Roberts, Todd Hawthorne and F. X. Kärtner