Fibercore (United Kingdom)

We review here our recent work in achieving mid-infrared (MIR) fibre lasing beyond 5 µm wavelength in Ce3+-doped selenide-chalcogenide fibre, as well as the observed photoluminescence in samples of the same composition but in particulate and bulk glass form as well as unstructured fibre and in the SIF (step index fibre) in which fibre lasing took place.

This Letter, to the best of our knowledge, reports mid-infrared fiber lasing beyond 5 µm at room temperature for the first time, Ce3+-doped, chalcogenide glass, step index fiber employed in-band pumping with a 4.15 µm quantum cascade laser. The lasing fiber is was 64 mm long, with a calculated numerical aperture of 0.48 at the lasing wavelengths. The core glass was Ge15As21Ga1Se63 atomic % (at. %), doped with 500 parts-per-million-by-weight Ce, with a 9 µm core diameter. The cladding glass was Ge21Sb10Se69 at. % with a 190 µm outer diameter. As pump power increases continuous wave lasing corresponding to the 2F7/2→2F5/2, transition in the Ce3+ ion occurs at 5.14 µm, 5.17 µm, and 5.28 µm.

With the possible exception of nonsilica glasses, each time a new fiber technology has emerged, someone has applied it to FOGs and reported beneficial results. The development of the FOG has essentially tracked that of commercial optical fibers for more than 40 years, running parallel since 1976, when Vali and Shorthill first demonstrated the concepts originally proposed by Pircher and Hepner in early 1967. The nine-year gap between first proposal and experimental demonstration was undoubtedly caused because, in 1967 practical, single-mode fibers simply did not exist, and even by 1976 they were in their infancy and confined to a handful of research laboratories around the globe. FOG technology received a further boost at the beginning of the 1980s when stress-birefringent polarization-maintaining (PM) fibers were developed almost simultaneously by multiple commercial and academic institutions, including NTT, Corning, Hitachi, Bell Laboratories, and the University of Southampton. It was the advent of PM fibers that paved the way for commercial FOG development by delivering practical immunity to environmental variations such as vibration and temperature. To this day, precisionwound coils of PM fiber dominate the FOG industry. Nevertheless, with FOG technology challenging the ring laser gyro (RLG) in navigation-grade sensors and even making in-roads into strategic levels of precision, virtually every new development in fiber technology has been investigated extensively to discover if theoretical performance advantages in FOGs may be realized.

Fiber based sensors have come of age commercially and are now increasing in volume deployment. The sensors are used to measure acceleration, pressure, electric current and more. To achieve the performance required from the sensor requires improvements over key performance aspects of a standard telecommunication fiber such as SMF28. Key design considerations are addressed, reduction of bend loss, joining two fibers, reliability, in particular the fiber lifetime, and mechanical stiffness together with features of birefringence or photosensitivity. Application areas such as Fiber Optic Gyroscope (FOG), acoustic and seismic sensors and sensing of electric current have specific demands of specialist optical fibers and these areas are used to illustrate the technical design considerations.