FEMTOSECOND LASER ON A CHIP

Project Information

FEMTOCHIP

Grant agreement ID: 965124

DOI

10.3030/965124

Project closed

EC signature date 27 January 2021

Start date 1 March 2021

End date 31 August 2024

Funded under

• EXCELLENT SCIENCE - Future and Emerging Technologies (FET)

Total cost

€ 3 418 525,00

EU contribution

€ 3 418 525,00

Coordinated by

DEUTSCHES ELEKTRONEN-SYNCHROTRON DESY
Germany

Periodic Reporting for period 2 - FEMTOCHIP (FEMTOSECOND LASER ON A CHIP)

Reporting period: 2022-03-01 to 2024-08-31

Summary of the context and overall objectives of the project

Femtosecond lasers have enabled the direct measurement of optical frequencies and the realisation of optical clocks. Femtosecond lasers present a high potential for a wide range of applications. However, the technology’s large size and high cost restrict its deployment. The aim of the EU-funded FEMTOCHIP project is a fully integrated chip-scale mode-locked laser with pulse energy, peak power and jitter specifications of a shoebox-sized fibre laser system. The innovation will enable many applications ranging from on chip femtosecond laser frequency combs, chip-scale atomic clocks, seeding of large femtosecond laser systems to high-speed high resolution analog-to-digital conversion . The project will address key challenges to facilitate high pulse peak power and suppress Q-switching instabilities. Ultrashort pulse production is supported by on-chip dispersion compensation and artificial saturable absorption to achieve stable femtosecond pulse generation from a chip-scale device.

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

Extensive simulation studies have led to a first design of a mode-locked laser and its sub-components like integrated apodized chirped waveguide gratings or nonlinear artificial saturable absorbers as well as the rare earth doped amplifier have been developed on the LIGENTEC Silicon Photonics fabrication platform and the University of Twente rare-earth doped Al2O3-film deposition tool.

Specifically, we have demonstrated the concept of large mode area (LMA) waveguides in integrated photonics. We have developed successfully Tm-doped Al2O3-waveguides in connection with the LMA waveguide amplifiers and demonstrated ultra-compact amplifiers with record high output power directly from an integrated amplifier producing as much as 2 W output power. Similar amplifiers were used to demonstrate on chip femtosecond pulse amplification. We also demonstrated successful fabrication of all components of the integrated femtosecond laser and demonstrated a Q-switched laser producing high energy pulses similar to those from fiber lasers. We also fabricated the complete integrated femtosecond laser up to the gain deposition step, since gain deposition became unfortunately unavailable for the more than the last year of the program because of necessary upgrading of the corresponding deposition system. Unfortunately, the upgrade could not be completely finished during the project lifetime even with the half year extension. Nevertheless, the fabricated chips were characterized with respect to device performance. Apodized chirped Bragg gratings with superb performance with respect to bandwidth and smoothness of the generated group delay dispersion were demonstrated. In addition, a six stage on chip interleaver, based on the ultralow-loss SiN-process developed at EPFL, was demonstrated. Since gain deposition was always considered as the highest risk in this project, we also looked into an alternative gain material based on Atomic Layer Deposition (ALD).

Overall, the results achieved constitute a major progress in integrated photonics and is a major step forward towards an on-chip femtosecond laser. The results have been published in many high impact papers.
Dissemination via peer reviewed journal publications, selected publications only:

1. Rosa, J.; Lahtinen, J.; Julin, J.; Sun, Z.; Lipsanen, H., “Tuning of Emission Wavelength of CaS:Eu by Addition of Oxygen Using Atomic Layer Deposition,” Materials 2021, 14, 5966. https://doi.org/10.3390/ ma14205966
2. Singh, N. and Kärtner, F. X., "Nonlinear Mach-Zehnder interferometer isolator," Opt. Express 30, 5973-5980 (2022), https://doi.org/10.1364/OE.447205
3. Ji, Xinru, et al. "Compact, spatial-mode-interaction-free, ultralow-loss, nonlinear photonic integrated circuits." arXiv preprint arXiv:2109.06764 (2021). https://doi.org/10.48550/ arXiv.2109.06764
4. Ji, X., Liu, J., He, J. et al. Compact, spatial-mode-interaction-free, ultralow-loss, nonlinear photonic integrated circuits. Commun Phys 5, 84 (2022). https://doi.org/10.1038/ s42005-022-00851-0
5. Liu. Y., et al., "A photonic integrated circuit based erbium-doped amplifier", SCIENCE 376, pp. 1309-1313 (2022). https://doi.org/10.1126/ science.abo2631
6. Yang Liu et al. ,A photonic integrated circuit–based erbium-doped amplifier.Science376,1309-1313(2022). https://doi.org/10.1126/ science.abo2631
7. Gaafar, M. A. et al.,"Photonic-chip integrated large-mode-area high-power CW optical amplifier", EPJ Web Conf., 287 (2023) 01009. https://doi.org/10.1051/ epjconf/202328701009
8. Singh, N. et al., “Silicon photonics-based high-energy passively Q-switched laser”, Nat. Photonics (2024). https://doi.org/10.1038/ s41566-024-01388-0
9. Singh, N. et al., “Watt-class CMOS-compatible optical high power amplifier,” Nat. Photonics (2025). https://doi.org/10.1038/s41566-024-01587-9

Exploitation and target application requirements:

• Femtosecond seed laser for ultrafast lasers with higher powers (e.g. for material processing)

• Frequency combs for metrology, spectroscopy and low noise microwave generation

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)

There are numerous applications for the integrated low-noise femtosecond laser that will be developed in FEMTOCHIP. For brevity, we concentrate on few examples with commercial applications, with a large market volume that can benefit from the integrated technology: Currently, analogue-to-digital converters (ADCs), which are core elements in high-bandwidth ground- and space-based communication technologies, are limited by timing jitter related to the on-chip clocking, which is slightly below 100 fs. This timing jitter limits the sampling speed-resolution-product. The FEMTOCHIP (timing jitter < 1 fs) system can immediately boost ADC performance by 2 orders of magnitude. Other applications with large markets are high-resolution LIDAR and RADAR systems for autonomous systems.

Although a final functioning mode-locked laser could not be achieved during the grant period, because of delays in gain layer deposition, we demonstrated beyond state of the art performance of amplifiers delivering more than 2 W of output power directly from a silicon photonics based amplifier. We also demonstrated all sub-components of mode-locked laser with excellent performance, especially also very broadband apodized chirped Bragg gratings for dispersion compensation inside a femtosecond laser and also for pulse compression in general.

Further obvious benefits:
-The FEMTOCHIP demonstrations will enlarge the market opportunities for LIGENTEC (especially in design and manufacturing of low-loss waveguides), with the existing customers and for all potential new end-users.
-FEMTOCHIP will provide the prerequisite laser system for many SMEs in their design and manufacturing process or as a source for their applications.

FEMTOCHIP Illuminating structure