Broadband light sources with liquid core

Carbondisulfide shows non-linear optical effects and high transmission

The coupled, ultrafast light pulse breaks up into solitons only due to non-linear interactions with matter in the optical fiber. In case of liquid core fibers, this means that the optical density of the liquid inside the core changes significantly with the intensity of the incident light. However, not many materials show nonlinear optical effects and, at the same time, exhibit sufficient light transmission in the infrared spectral range. Mario Chemnitz, scientist at Leibniz IPHT and first author of the publication, explains the unusual effect as follows: "The fiber core is filled with carbon disulfide, a liquid chemical compound with a very high refractive index. If we now couple polarized light into the core, the carbon disulfide molecules orient themselves along the electromagnetic field of the light. Due to this molecular orientation, the optical density -- and thus the light propagation in the fiber -- depends on the intensity of the laser light."

Optical memory effect

One unique feature of carbon disulfide is that the molecules orient themselves with a certain time delay. If the incident laser light pulse is much shorter than the time that the molecules require for orientation in the optical field, the research scientists can observe a special, delayed dynamic of the resulting solitons. This was predicted back in 2010, but it was only now, the Jena scientists were able to provide experimental proof and an exact theoretical description of the processes. Mario Chemnitz describes this phenomenon as an optical "memory effect" of the liquid. This unique characteristic of the liquid fiber cores reduces fluctuations in the spectral bandwidth of the supercontinuum light source and makes liquid core fibers a more stable alternative to the known broadband light sources based on optical fibers made from special glasses.