Giant Brillouin gain in frozen CS2 capillaries

Abstract

Stimulated Brillouin-Mandelstam scattering offers exceptional capabilities for photonic signal processing, but current platforms demand performance trade-offs between long interaction lengths, high gain, low optical losses, and practical implementation. Here, we demonstrate a novel platform based on the reversible freezing of a carbon disulfide filled liquid-core optical fiber. This approach delivers a giant in-fiber Brillouin gain of 434 W-1m-1 with a linewidth of 24 MHz, while maintaining low propagation losses in a fully spliced architecture and providing the potential for meter-scale interaction lengths. Leveraging this gain, as a proof of principle, we realize an optoacoustic memory operating at sub-nanojoule pulse energies - more than two orders of magnitude lower than state-of-the-art implementations. This power reduction is universal for Brillouin-based fiber applications in general and will enable low-power photonic signal processing and neuromorphic computing, efficient microwave photonics and sensing, as well as in-fiber quantum optomechanics-based technologies.

Figures (10)

• Figure 1: Schematic of Brillouin Scattering in frozen liquid-core optical fiber. A pump photon ($\omega_p$) is back-scattered from an acoustic phonon ($\Omega_B$) resulting in a back-scattered Stokes downshifted by $\Omega_B$. The back scattered Stokes generated in the frozen section reveals an exceptionally high nonlinearity.
• Figure 2: Measurement of Brillouin gain of frozen LiCOF. Brillouin response of liquid (green) and solid (blue) phase demonstrates the up-shift in BFS and increase in Brillouin gain achieved through freezing. Dots correspond to raw measurement data, while the blue line shows the Lorentzian fit of the main peak in the solid phase. The inset shows the exponential increase of the on-off gain with increasing pump power, acquired in a different measurement, and compares it to the theoretical prediction based on the measured $G_B$. On the right, the different features of the frozen LiCOFs spectral response are attributed to different combinations of optical and acoustic modes.
• Figure 3: (a) Tuning Brillouin response of frozen LiCOF by heating a fraction $L_\mathrm H$, thus increasing the global pressure, before freezing. (b) BFS of frozen LiCOF as a function of the temperature used for heating $L_\mathrm H$. Pressure difference computed via temperature difference from 25℃.
• Figure 4: (a) Experimental measurement of the write and read process for a control-pulse energy of 0.205nJ. Gray dashed lines show the reference taken without control pulses. The inset zooms into the readout to show the signal surpassing three standard deviations of the noise above the noise level. (b) Memory process for a control-pulse energy of 2.05nJ. (c) Area under the curve of data and readout pulses computed from the individual measurements for increasing control pulse energies in comparison to the theory.
• Figure S1: Schematic of Setups. (a) Setup used for gain measurements. DFB laser: distributed feedback laser, SSBM: single-sideband modulator, RF Source: radio-frequency source, VOA: variable optical attenuator, FPC: fiber polarization controller, Circulator: fiber-integrated optical circulator, EDFA: erbium-doped fiber amplifier, BPF: band-pass filter. (b) Experiment configuration with connections to optical setup. Heater to increase pressure, liquid nitrogen to freeze LiCOF.