We studied numerically 1000 nm, 1 ps pulse width propagation in a PT-symmetric nonlinear directional coupler in the form of dual-core photonic crystal fiber. The base material of the fiber is phosphate glass, while gain and loss channels are implemented by ytterbium-based and copper-based doping, respectively. The propagation models were based on coupled generalized nonlinear Schrödinger equations solved with the Split-Step method: 1) extended model including coupling coefficient dispersion, self-steepening nonlinearity and its spectral dependence, stimulated Raman contribution, cross-phase modulation and Gaussian-like gain and loss coefficient frequency function; 2) simplified model with second-order dispersion term, linear coupling and first-order nonlinearity. We predicted two states of light propagation: 1) linear pulse energy oscillation between gain and loss channels (PT-symmetry state) at 100 pJ; 2) retention of the pulse in the excited gain channel (broken PT-symmetry) at 445 pJ. The presented results open perspective on the demonstration of fiber-based all-optical switching devices.
In recent years the novel active glass materials for optical fibers with broadband emission are of great interest due to potential application in spectroscopy, environmental monitoring or medicine. Development of that kind materials is based on elaborating the glass matrix co-doped with different rare earth ions, e.g. Er, Yb, Ho, Tm. Glasses doped with multiple rare earths characterize with a high number of spectroscopic parameters, due to the presence of energy transfer phenomena between those different rare earth ions. Nonlinear nature of that phenomena varying with the dopants concentration levels, makes the design and development of optical fibers made of glass doped with several active ions not trivial. In this work, we present the nanostructured material composed of several separated glass areas with subwavelength size with individually designed parameters. As a proof-of-concept, we propose the active phosphate fiber with the core consisted of two types of glasses doped with Yb3+ and Er 3+ ions, which exhibit independent performance. The presented phosphate fiber laser operates simultaneously at dual wavelengths at 1.04 μm and 1.535 μm with very good beam quality of M2=1.14 and slope efficiency of 23.0% and 9.8%, respectively. To our knowledge, this kind of fiber has not been demonstrated previously.
Nanostructured GRIN components are optical elements which can have arbitrary refractive index profile while retaining flat-parallel entry and exit facets. They are composed of more than 9000 individually placed glass subwavelength rods made of two types of glass with different refractive indices. They are developed using a standard stack-and-draw method used for fibre drawing. The refractive index profile of the nanostructured GRIN element can be described by the effective refractive index theory when the diameter of the individual rods are sufficiently smaller than the wavelength. In this paper we show that use of glasses designed for high diffusion and high temperatures during drawing process allows to develop parabolic nanostructured GRIN microlenses with rod diameter larger than wavelength. In particular, we have developed a GRIN microlens with diameter of 115 μm composed of 115 rods on diagonal. Our GRIN microlens has a length of 200 μm and a working distance equal to 1.05 mm, with focal spot of 8.5 μm measured for the 658 nm wavelength. We experimentally verified its imaging properties. Image resolution higher than 3.25 μm was measured.
We study optical properties of gradient index vortex masks based on an effective medium approach. We consider masks with single charge developed using two types of nanorods made of thermally matched low and high refractive index glasses. Optical performance of generated vortices are analyzed in terms of glass refractive index difference and spatial dimension of the components. A fabricated vortex mask has been combined with single mode optical fiber. Optical performance of the resulting fiber integrated vortex mask is characterized and discussed.
We study optical properties of the gradient index vortices obtained using effective medium approach. Vorteces with charge +1 has been was developed using two types of nanorods made of thermally matched low and high refractive index glasses. Their optical properties of vortices are analyzed in the context of glass refractive index and size of the components. Consequently vortex has been integrated with single mode optical fiber and such a system is analyzed.
Most of the research work related to photonic crystal fibres has to date been focused on silica based fibres. Only in the recent years has there been a fraction of research devoted to fibres based on soft glasses, since some of them offer interesting properties as significantly higher nonlinearity than silica glass and wide transparency in the infrared range. On the other hand, attenuation in those glasses is usually one or more orders of magnitude higher that in silica glass, which limits their application area due to limited length of the fibres, which can be practically used. We report on the development of single-mode photonic crystal fibres made of highly nonlinear lead-bismuth-gallate glass with a zero dispersion wavelength at 1460 nm and flat anomalous dispersion. A two-octave spanning supercontinuum in the range 700–3000 nm was generated in 2 cm of the fibre. In contrast to the silica glass, various oxide based soft glasses with large refractive index difference can jointly undergo multiple thermal processing steps without degradation. The use of two soft glasses gives additional degrees of freedom in the design of photonic crystal fibres. As a result, highly nonlinear fibres with unique dispersion characteristics can be obtained. Soft glass allow also development of fibres with complex subwavelength refractive index distribution inside core of the fibre. A highly birefringent fibre with anisotropic core composed of subwavelength glass layers ordered in a rectangular structure was developed and is demonstrated
Thermally stable tellurite, lead-bismuth-gallium oxides based boron-silicate and lead-silicate glasses dedicated for multiple thermal processing are presented. The glasses are successfully used for the development of photonic crystal fibers, nanostructured gradient index lenses, all-solid microstructured fibers as well as refractive or diffractive micro-optical elements with ultra-broadband transmission.
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