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DC FlexMIL Report Summary

Project ID: 656607
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - DC FlexMIL (Development and Control of Flexible Mode-locked Integrated Laser)

Reporting period: 2016-01-01 to 2017-12-31

Summary of the context and overall objectives of the project

The DC FlexMIL project aims at the development, characterization and control of a novel class of pulsed light source to reach new stable, flexibly shapeable emission properties within an integrable format (i.e. on-chip).

Pulsed light sources have boosted over the past years several important applications including precision metrology, nonlinear microscopy as well as high-capacity telecommunications and are today established devices in optical laboratories. The realization of these sources in compact forms (i.e. their integration on chip) will represent benefits in terms of performances, complexity management, costs, handling and power consumption (fundamental aspects for the development of a commercial technology). These advances in combination with improving the light sources controllability towards highly flexible emission properties (e.g., the temporal and spectral pulse shape, etc.) easily adaptable to various requirements, are necessary for novel applications in e.g. metrology and quantum science and for enabling their out-of-lab operation and widespread use. DC FlexMIL is aimed at advancing the realization of a controllable, integrable pulsed light source technology.

The objectives of DC FlexMIL are therefore the investigation and design of laser concepts allowing radiation control based on nonlinear optical interactions (modulation instabilities, i.e. four-wave mixing) within integrated structures (specifically waveguides and ring cavities), and their implementation towards realizing integrated light sources for classical and non-classical applications. Furthermore, the project objectives include the training of the research fellow in related disciplines to advance their career development towards a successful independent researcher.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Over the two-year period of the project, the activities of DC FlexMIL lead to the realization of novel integrable light sources. Based on the unique characteristics of developed nonlinear integrated microring resonators (i.e. narrow resonance bandwidth and access to high field enhancement promoting nonlinear effects), we were able to demonstrate the first realization of a pulsed passively mode-locked nanosecond laser with a record-low transform-limited spectral bandwidth of 105 MHz [1] - more than one hundred times lower than any pulsed laser to date. To characterize the laser's bandwidth (which was so narrow that it was not accessible with state-of-the-art optical spectrum analyzers), we exploited a coherent beating technique allowing, for the first time, the possibility of measuring the entire spectral characteristics of a mode-locked laser in the radio frequency (RF) domain using widely-available RF electronics only. Furthermore, we realized within the waveguide structures, based on the four-wave mixing effect (i.e. modulation instability), a phase controllable amplification of the light field on multiple independent channels (i.e. frequencies) with a maximum phase sensitive extinction ratio of 24.6dB, allowing a versatile optical control of the field output [2]. Based on the nonlinear field dynamics in guiding structures, we were also able to demonstrate the first realization of controllable Riemann waves up to the generation of a shock wave, and to link it to the solutions of the inviscid Burger's equation [3].
By taking advantage of the properties of the developed ring-resonator structures in combination with the accessible nonlinear four wave-mixing effects, we were successful in applying the developed know-how to enable novel quantum technologies by developing an entirely new kind of non-classical light source. Specifically, we realized for the first time an integrated quantum frequency comb (comprised of equidistantly spaced frequency channels), which allowed the generation of qubits (the quantum analogue to a bit) on multiple channels [4]. With this, we demonstrated the first on-chip realization of entangled multi-photon states [4]. Going further, we were also able to demonstrate the sources usability for the first on-chip generation of non-classical entangled high-dimensional light states (so-called quDits, i.e. d-level states) as well as their coherent control in a compact platform using only integrated and widely available telecommunications components [5]. With this approach, we realized an integrated quantum light source that is capable of generating a 100 dimensional quantum system, equivalent to 6.4 qubits. Combining this expertise with the developed laser concept, we furthermore realized a compact and practical generation scheme for these non-classical frequency combs [6].

The results emerged from the DC FlexMIL project have been widely disseminated through journal publications (6 at this stage), international conference contributions (more than 50 contributions), press releases (see [7]), seminar and workshop presentations as well as outreach activities (see e.g. [8]) and through the project website: Finally, through the DC FlexMIL project and the generated research output the research fellow experienced an exceptional research training expanding his knowledge in relevant fields and gained international experience as well as visibility, important for his career development towards an independent researcher.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The developed nanosecond laser's compact architecture and its modest requirements in terms of power, readily allow for stable and portable operation, while opening up a route towards the full integration of the laser system. The laser concept can be of direct use for efficient molecule excitation. Together with the possibility to resolve the full laser spectrum in the RF domain, such characteristics pave the way towards novel sensing and spectroscopy implementations. The developed non-classical pulsed quantum frequency comb sources are of particular interest for applications in sensing and quantum information processing. We expect that micro-resonator-based entangled photon states and their control can open up new venues for reaching the processing capabilities required for meaningful quantum information science.

[1] M. Kues, et al., "Passively mode-locked laser with an ultra-narrow spectral width," Nature Photonics 11, 159 (2017).
[2] Y. Zhang, et al., "Multi-channel phase-sensitive amplification in a low loss CMOS-compatible spiral waveguide," Optics Letters, 42, 4391 (2017).
[3] B. Wetzel, et al., "Experimental generation of Riemann waves in optics: A route to shock wave control," Physical Review Letters 117, 073902 (2016).
[4] C. Reimer, M. Kues, et al., "Generation of multiphoton entangled quantum states by means of integrated frequency combs," Science 351, 1176 (2016).
[5] M. Kues, et al., "On-chip generation of high-dimensional entangled quantum states and their coherent control," Nature 546, 622 (2017).
[6] P. Roztocki, et al., "Practical system for the generation of pulsed quantum frequency combs," Optics Express 25, 18940 (2017).
[8] "On-chip quantum frequency combs", Optics and Photonics News, December Special Issue (2016).
"Scaling on-chip entangled photon states to higher dimensions," Optics and Photonics News, December Special Issue (2017) - on the cover.

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