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Parametric fiber-based Mid-IR Swept-Source

Final Report Summary - MIRSS (Parametric fiber-based Mid-IR Swept-Source)

The EU funded research project MIRSS is focused on the investigation of middle infrared (2 um wavelength and above) light generation in fluoride based fibers through parametric amplification. The middle infrared (mid-IR) wavelength region is in great demand due to a wide variety of applications such as spectroscopy, detection of hazardous material, LIDAR. In addition, the 2 um spectral band is also envisioned as the next generation band for optical communication resulting in a strong research push for the development of light source, modulators, and optical amplifiers within this band. The demand for high quality mid-IR light source has significantly increased over the last decades and a rapid wavelength swept source would result in an invaluable tool for many applications.
MIRSS aims at investigation an all-fiber swept source around the 2.2 um wavelength. As the transparency of silica hinders light propagation beyond 2.1 um, we are exploring the potential of heavy metal fluoride glass such as ZBLAN. As these glasses, with a transparent widow extending towards 4 um, can be easily drawn into fibers we are aiming for a robust all fiber system. Our approach to the generation of a short wave infrared swept source is to combine ZBLAN fibers near infrared (near-IR) to mid-IR phase matching inside an optical parametric amplifier to generate mid-IR swept light. To that end, we are exploring dispersion properties, phase matching conditions and nonlinearities of ZBLAN fibers.
We have put together a solid road map towards understanding dispersion characteristics in such fibers: depending on the fiber composition, numerical aperture, core diameter we can now theoretically predict precisely the dispersion characteristics of the fiber. We identified during the first phase that the material dispersion of our ZBLAN composition (52 ZrF4-24 BaF2-5 AlF3-4 LaF4-15 NaF mol %) was strongly normal at the telecom wavelength. Since our goal is to pump the ZBLAN waveguide in the telecom band (1550 -1600 nm) where mature technology such as lasers, amplifiers, modulators is available, the dispersion needs to be tailored. The study showed that it is possible to find some commercially available combination of numerical aperture and core size that would enable the waveguide dispersion to compensate the large material dispersion. After identification of a suitable fibre, experimental work on its characterization was performed: the loss was measured, and the first experiments on four-wave mixing in ZBLAN were carried. A pulsed telecom pump was coupled with a tunable O-band (1250 nm to 1350 nm) signal. We observed for the first time, the generation of an idler wave with a conversion efficiency around -10 dB within the 2 micron. Furthermore this conversion was observed over a wide range of wavelength indicating that the ZBLAN fiber is indeed a good candidate for the generation of 2 micron light through parametric processes. The system is being further optimized and characterized to detect conversion efficiency peaks as predicted from the theory. Indeed, the absence of conversion efficiency peak might be caused by several reasons that originate from imperfections of the drawn fibre (variation of the fibre geometry over the length, and deviations from nominal fibre profile). We are therefore modifying the experimental setup to sweep a wider range of wavelength since the phase matching point could have been shifted from its theoretical value. The impact of the waveguide imperfection is therefore being studied and should lead to a more mature understanding of these waveguides for future applications.
The EU funded research project MIRSS enabled the re-integration of Prof. Camille-Sophie Brès. Her laboratory is now state of the art in Switzerland for non-linear waveguide optics and short-wave/mid-infrared light generation.