First active fiber ring resonator at 2 µm wavelength

The Photonics Systems Laboratory (PHOSL) at EPFL has successfully collaborated with the Laboratory of Physics of Lasers, Atoms and Molecules (PhLAM) at the University of Lille. As part of the Marie Skłodowska-Curie ITN ‘MEFISTA’, PhD student Moritz Bartnick (PHOSL) joined Prof. Arnaud Mussot’s group at PhLAM for three months, where he worked closely with PhD student Stefano Negrini. Together, they achieved the first demonstration of an active fiber ring resonator operating at 2 µm wavelength.

What was accomplished?

Active fiber ring resonators have previously been demonstrated at the 1.55 µm wavelength using an active fiber to compensate propagation and extraction losses in up to 100m long fiber rings. Given that losses are even greater at 2 µm, the use of an intracavity amplifier for loss compensation is particularly intriguing for this wavelength region. Instead of erbium-doped fiber, which is commonly used to amplify 1.55 µm, Moritz and Stefano have used thulium-doped fiber to amplify 2 µm wavelengths. By the end of the secondment, they successfully locked the pump laser's emission wavelength to the cavity resonances and measured spectra of modulation instability.

Why is this research important?

Fiber ring resonators are of great interest for generating temporal solitons and optical frequency combs. The measurement of modulation instability at 2 µm is a crucial step toward soliton generation at this wavelength, since both measurements rely on the same techniques to stabilize lock the laser wavelength to the cavity resonances. While 1.55 µm is the standard wavelength in optical fiber communication, 2 µm soliton sources could enable molecular fingerprinting of atmospheric molecules such as ammonia, carbon dioxide, or water.

Following the secondment, Moritz and Stefano continued their collaboration with simulations that confirmed their experimental results. They have written a scientific article, which has been published in Optics Letters.