Category Archives: Multimode fiber

Yuhang Wu_AnomalousBC

Beam self-cleaning of femtosecond pulses in the anomalous dispersion regime

Wu, H. Pourbeyram, D. N. Christodoulides, and F. W. Wise, “Weak beam self-cleaning of femtosecond pulses in the anomalous dispersion regime,” Opt. Lett. 46, 3312–3315 (2021).

Kerr beam cleaning in graded-index multimode fiber has been investigated in experiments with sub-nanosecond pulses and in experiments with femtosecond pulses at wavelengths where the dispersion is normal.  We report a theoretical and experimental study of this effect with femtosecond pulses and anomalous dispersion.  In this regime, beam-cleaning is observed experimentally.  Beyond the spatial dynamics, with the increase of input pulse energy, there is a strong temporal self-compression of the pulse from 500 fs down to around 30 fs (a factor of 17). Numerical simulations exhibit the qualitative trends of the experiments. Our study provides a way to enhance beam quality and temporal peak power at the same time in graded-index multimode fiber and the anomalous dispersion regime.


Multimode Mamyshev oscillator

Henry Haig, Pavel Sidorenko, Anirban Dhar, Nilotpal Choudhury, Ranjan Sen, Demetrios Christodoulides, and Frank Wise, “Multimode Mamyshev oscillator,” Opt. Lett. 47, 46-49 (2022)

Regular mode-locked lasers make short light pulses by synchronization or “locking” of many longitudinal cavity modes. It was recently shown that the transverse modes of a cavity can also be synchronized in a similar— but more general— form of mode-locking known as “spatiotemporal mode-locking” (STML). These lasers make ultrafast pulses that have spatial structure due to the many transverse modes involved. Understanding of this phenomenally complex phenomenon is limited: STML has so far been demonstrated a handful of times in relatively similar types of multimode fiber lasers. In this project, we study STML in a very different type of cavity architecture— the Mamyshev oscillator. The laser supports a vast array of mode-locked states. Learning to control these states in a meaningful way is a long-term goal which might enable gigawatt-class fiber lasers, or fiber lasers that generate purposefully-structured light for applications.

Spatiotemporal mode-locking in multimode fiber lasers

Spatiotemporal mode-locking in multimode fiber lasers

L.G. Wright, D.N. Christodoulides, and F.W. Wise (2017) “Spatiotemporal mode-locking in multimode fiber lasers,” Science 358 (6359), 94-97.

Unlike a conventional single-mode, ‘one-dimensional’ laser, the frequencies of a multimode, multidimensional laser are ordinarily very complicated (figure below, top left, where different colors correspond to different spatial modes). However, we showed that, for a properly designed laser (bottom), the laser’s frequencies would adjust automatically into an organized, synchronized pattern (figure top right), corresponding to the emission of a 3D, multimode laser pulse at regular intervals. Pulses from this laser might eventually allow very sophisticated light-matter interactions, especially with complex molecules (different modes of the laser may interact with different ‘modes’, specific transitions, of molecules or other matter). We have some moderately crazy ideas to realize PW or even EW (exawatt) lasers with this approach.

Simple depiction of spatiotemporal mode-locking

Spatiotemporal dynamics of multimode optical solitons

Spatiotemporal dynamics of multimode optical solitons

L. G. Wright, W. H. Renninger, D. N. Christodoulides, and F. W. Wise. “Spatiotemporal dynamics of multimode optical solitons”. Opt. Express 22, 3492-3506 (2015).

We launch pulses into multimode fiber, exciting multiple spatial modes. We show how nonlinear interactions between the modes give rise to a multimode soliton. A multimode soliton is a non-dispersing wavepacket that contains several distinct spatial mode components, and propagates through the fiber without changing its shape due to a balance between nonlinear and linear effects. We observe spatiotemporal soliton fission – the disintegration of an optical pulse into distinct multimode soliton components with different spatiotemporal properties. Lastly, we observe the effect of stimulated Raman scattering on multimode solitons. This causes them to shift to longer wavelengths, while maintaining their multimode soliton characteristics.

Multimode fiber acts as an intermediate-dimensional system. As the size of the fiber becomes infinite, optical dynamics are (3+1)-D (space+time). Meanwhile, as the fiber becomes small it becomes single mode, so that optical dynamics can be described using only (1+1) dimensions. Analytically, stable spatiotemporal solitons are expected for some region (blue) between 1 and 3 spatial dimensions. It is in this regime that multimode solitons are expected.

Ultrabroadband Dispersive Radiation by Spatiotemporal Oscillation of Multimode Waves

Ultrabroadband Dispersive Radiation by Spatiotemporal Oscillation of Multimode Waves

L. G. Wright, S. Wabnitz, D. N. Christodoulides, F. W. Wise “Ultrabroadband Dispersive Radiation by Spatiotemporal Oscillation of Multimode Waves ” Phys. Rev. Lett. 115, 223902 (2015).

We show that intense pulses in multimode fiber oscillate in space and time, and that this creates resonant radiation across the electromagnetic spectrum. This work provides a route to tunable sources of ultrashort pulses from IR to ultraviolet and beyond. Dreaming, this work could lead to a fiber-format alternative to the free-electron laser.

summary figure 1

The resonant dispersive radiation is diffracted off a grating onto a piece of white paper.