Supercontinuum fiber laser - Principle and Applications

Since the invention of the laser in 1960, one of the major challenges has been to develop efficient methods for converting laser light into new wavelengths. Supercontinuum (SC) generation, first observed in 1970 in bulk materials, and then in 1976 in optical fibers [IN 122] , quickly established itself as an elegant, high-performance solution. By considerably broadening the monochromatic spectrum of lasers, while preserving a spatially coherent, high-power output, this new white light source has revolutionized many fields of application. Supercontinuum sources generate a continuous, ultra-wide electromagnetic spectrum, spanning several octaves in frequency, from the visible to the infrared, while remaining fiber-optically guided. They thus combine the brilliance of a laser with the broad spectral coverage of a lamp, offering great potential for replacing many traditional light sources in optical metrology, spectroscopy and microscopy. Thanks to their versatility, SC lasers are exploited in a variety of fields, including biomedical imaging, optical coherence tomography (OCT) [E 4 155] , materials processing, optical sensing, absorption spectroscopy and optical frequency comb (OFC) metrology. The advantages of supercontinuum light lie not only in its brilliance, which is several orders of magnitude greater than that of blackbody radiation, but also in its remarkable coherence properties. These characteristics enable the use of relatively simple interferometric and heterodyne detection schemes, guaranteeing outstanding performance in a wide range of applications.

The most advanced commercial SC sources are mainly based on microstructured silica optical fibers [RE 43] . They deliver several watts of power across the entire transmission window of silica fibers, from 400 to 2,400 nm. Today, a dozen companies around the world market SC lasers, with notable success. These include LEUKOS in France and NKT Photonics in Denmark. Dedicated mid-infrared (MIR) sources, based on fluoride fibers and offering spectra down to 4 µm, or even 4.8 µm in some cases,...