Tampere University researchers have developed a novel optical fibre design that allows the generation of rainbow light in the molecular fingerprint electromagnetic area. This new optical fiber has a self-clean beam and can be used in the development of applications such as cancer diagnostics, environmental monitoring and food control. The journal published the findings. Nature Communications.
A high-power, ultrashort pulse light of high power interacts with a material like a glass optical fiber. This causes complex changes in the temporal as well as spectral properties. These interactions can result in the creation of a supercontinuum laser of light, which is commonly called a rainbow light source. Supercontinuum laser light has revolutionized science since its 2000 debut in a special optical fiber.
The current issue with supercontinuum sources is that they are based only on optical fibers which support a single transverse intensity profile or mode. This limits their optical power. Furthermore, conventional optical fibres are made from silica glass and transmit only in the visible and near-infrared regions. The supercontinuum light can be extended to other wavelengths such as the mid infrared using optical fibers made from soft glasses. However, these optical fibers have a lower threshold for damage than silica and limit the supercontinuum beam’s potential power.
Non-silica optical fiber, with a self cleaning beam
A new type of optical fiber that has a constant refractive index across the fiber structure was recently shown to have a dramatic increase in supercontinuum powers while maintaining a smooth beam intensity profile. “The graded-index refractive variation of such optical fibers results in periodic focusing and defocusing the light inside the fiber, which enables coupling between spatial- and temporal nonlinear light–matter interactions. This creates a self-cleaning mechanism that produces supercontinuum, high-power light with a clean beam profile. As well as their many applications, they also provide a means of studying fundamental physics effects such as wave turbulence,” says Professor Goëry Genty, the leader of the research group at Tampere University.
These fibers have been receiving a lot of attention in the recent research community. However, their use has remained limited to the near-infrared and visible. The group of Profs. Buczynski and Klimczak at the University of Warsaw (Poland) and the group of Prof. Dudley in the University of Burgundy France-Comté (France), the Tampere team demonstrated for the first time the generation of a two-octave supercontinuum from the visible to mid-infrared in a non-silica graded-index fiber with a self-cleaned beam.
“This problem was solved by using a specific design that uses two types of lead-bismuth–gallate glass rods with different indices drawn to produce a nanostructured center. Researchers Zahra Eslami and Zahra Eslami say that the result is a graded index fiber with a parabolic refractive profile that transmits up to the mid-infrared.
There is great potential in monitoring and diagnostics
The mid-infrared contains important vibrational transitions for many important molecules.
Genty explains that the new solution will result in more efficient supercontinuum lights sources in mid-infrared, with many potential uses e.g. for pollutant detection, cancer diagnostics and machine vision.
Researchers anticipate that this new fiber type will soon be an important standard material for the generation and use of frequency combs and broadband source.
The research was conducted at Tampere University and the Academy of Finland Flagship for Photonics Research and Innovation.