Optimum Phase Measurement in the Presence of Noise
Hosted By: Optoelectronics Technical Group
06 September 2022 10:00 - 11:00
Eastern Time (US & Canada) (UTC - 05:00)Single frequency lasers are an indispensable tool in many areas of scientific and engineering disciplines. The laser phase noise properties directly affect the precision and accuracy of several critical measurement techniques such as high-sensitivity laser-based spectroscopy and interferometry. The magnitude of laser phase noise is also a key limiting factor in applications based on transmitting laser light over an optical fiber, such as high-capacity coherent telecommunication, quantum cryptography and distribution of reference atomic clock signals. Accurate measurement of laser phase noise is therefore a topic of great fundamental and practical importance.
Even though the scientific field of laser phase noise measurement is more than 50 years old, the state-of-the-art measurement techniques still exhibit strong limitations in terms of the measurement sensitivity and the frequency range. The implication of these limitations is that it is not possible to: (i) accurately measure the fundamental laser linewidth (Schawlow-Townes limit), (ii) measure the impact of optical amplifier noise on signal phase - an open problem since 1962, (iii) accurately measure phase noise of ultra-narrow linewidth lasers and (iv) provide a phase noise measurement of the emerging low-power nano-lasers. Advancing phase noise measurement techniques is thus important for providing answers to some of the fundamental questions which could potentially lead to improved laser phase noise performance.
In this webinar hosted by the Optoelectronics Technical Group, Prof. Darko Zibar will propose a fundamentally novel approach for phase noise measurement by combining a heterodyne phase measurement with advanced digital signal processing methods aided by physical models. Prof. Zibar proposes a practical phase noise measurement technique with an ultimate accuracy that surpasses the limitations of the current techniques by several orders of magnitude. The proposed technique provides the theoretically most accurate (optimum) measurement of a laser signal phase and approaches the quantum limit. Compared to state-of-the-art techniques, the proposed measurement technique is not limited by the measurement noise, but rather by the fundamental quantum noise associated with the laser. Prof. Zibar will show that, in contrast to common beliefs, it is possible to measure the phase noise well below the conventional measurement noise floor, greatly enhancing the measurement frequency range and the sensitivity. A record measurement frequency range and sensitivity are achieved. This allows us to finally provide an answer to a longstanding question on the impact of amplifier noise on the signal phase. The method thus holds the potential to become a reference phase noise measurement tool. It will also show how the proposed approach can be extended to phase noise characterization of optical frequency combs.
Finally, Prof. Zibar will introduce a novel method for noise characterization of frequency combs based on Bayesian filtering and subspace tracking. The method allows for the identification and decomposition of noise sources associated with the frequency comb.
What You Will Learn:
- How techniques from the machine learning toolbox can advance phase noise characterization of lasers and frequency combs
- How to approach quantum noise limited optical phase measurement
Who Should Attend:
- Ph.D. students in optics
- Research scientists and engineers in the broad field of photonics
About the Presenter: Darko Zibar, Technical University of Denmark
Darko Zibar is a Professor at the Department of Electrical and Photonics Engineering, Technical University of Denmark and the group leader of Machine Learning in Photonics Systems (M-LiPS) group. He received his MSc degree in telecommunication and his PhD degree in optical communications from the Technical University of Denmark, in 2004 and 2007 respectively. He has been on several occasions (2006, 2008, and 2019) visiting researcher with the Optoelectronic Research Group led by Prof. John E. Bowers at the University of California, Santa Barbara (UCSB). While at UCSB, he has been working on topics ranging from analog and digital demodulation techniques for microwave photonics links and machine learning-enabled ultra-sensitive laser phase noise measurement techniques. In 2018, he was a visiting professor with Optical Communication (Prof. Andrea Carena, OptCom) group, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, working on the topic of machine learning-based Raman amplifier design. His research efforts are currently focused on the application of machine learning techniques to advance classical and quantum optical communication and measurement systems. Some of his major scientific contributions include: record capacity hybrid optical-wireless link (2011), design of the ultra-wideband arbitrary gain Raman amplifiers (2019), record sensitive optical phase noise measurement technique that approaches the quantum limit (2021). He is a recipient of the Villum Young Investigator Programme (2012), the Young Researcher Award by the University of Erlangen-Nurnberg (2016), and the European Research Council Consolidator Grant (2017). He was a part of the team that won the HORIZON 2020 prize for breaking the optical transmission barriers (2016). In 2022, he was the recipient of the Friedrich Wilhelm Bessel International Research Award of the Alexander von Humboldt Foundation.