We report for the first time successful inscription of high reflectivity Bragg grating in nanostructured core active fiber. Nanostructurization of the fiber core allows to separate the active and photosensitive areas and to distribute them all over the core. As a result unfavorable clustering between germanium and ytterbium particles is avoided. The distribution of discrete glass areas with feature size smaller than λ/5 results in effectively continuous refractive index profile of the fiber core. We present a single-mode fiber with built-in Bragg grating for laser application with the core composed of ytterbium and germanium doped silica rods. The core structure is arranged as a regular lattice of 1320 doped with ytterbium and 439 doped with germanium silica glass rods. The average germanium doping level within the core of only 1.1% mol allowed efficient inscription of Bragg grating. The nanostructured core was 8.6 μm and the internal cladding was 112 μm in diameter coated with low index polymer to achieve the double-clad structure. In the first proof-of-concept in the laser setup we achieved 35 % of slope efficiency in relation to launched power for the fiber length of 18 m. The output was single-mode with spectrum width below 1 nm. The maximum output power limited by pumping diode was 2.3 W. The nanostructurization opens new opportunities for development of fibers with a core composed of two or more types of glasses. It allows to control simultaneously the refractive index distribution, the active dopants distribution and photosensitivity distribution in the fiber core.
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.
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 report a development of microscopic size gradient index vortex masks using modified stack-and-draw technique. Vortex mask has a form of tens of microns thick, flat-surface all-glass plate. Its functionality is determined by internal nanostructure composed of two types of soft glass nanorods. Their spatial arrangement ensures that the average refractive index mimics continuous refractive index distribution imposing azimuthal phase modulation of optical beam. The mask of thickness of 40 microns is used to demonstrate generation of optical vortices with charges 1 and 2, in the femtosecond and cw regimes, respectively.
We report on sensing characteristics of the rocking filter fabricated in specially designed microstructured fiber with
enhanced sensitivity to hydrostatic pressure. The filter shows a very high sensitivity to pressure ranging from 16.2 to
32.2 nm/MPa, depending on the resonance order. Extremely low cross-sensitivity between pressure and temperature
27÷66×103 K/MPa has also been recorded and therefore the rocking filter can be used for pressure measurements with
mbar resolution with no need for temperature compensation.
We present sensing characteristics of higher order rocking filters fabricated in highly birefringent microstructured fiber
which resonantly couple polarization modes at several wavelengths. First rocking filter (RF1) shows tree resonances arising
at 855, 1271, and 1623 nm, while in the second filter (RF2) the resonances arise at 908, 1145, 1354 and 1548 nm. We
measured sensitivity to temperature in both filters and to hydrostatic pressure in the RF1. Our results show that both filters
have very low response to temperature ranging from 1.38 to 3.03 pm/K depending on the resonance order. Simultaneously,
the sensitivity to hydrostatic pressure is very high and reaches 6.14 and 3.30 nm/MPa, respectively for the first and the
second resonance in the RF1. These unique sensitivity characteristics make the filters an excellent device for hydrostatic
pressure measurement with no need for temperature compensation.
In this work, we demonstrate the possibility of fabricating short LPGs and rocking filters in highly birefringent Photonic
Crystal Fiber using CO2 laser. In our experiments both kinds of gratings were made in the same Boron doped highly
birefringent PCF using similar exposure parameters. We also present the sensing capabilities of both fabricated gratings
to temperature, strain and hydrostatic pressure by interrogation of the wavelength shifts at the different resonances.
We demonstrate an efficient higher order rocking filter, which resonantly couples polarization modes guided in birefringent
photonic crystal fibers. The grating was inscribed in the birefringent fiber with two large holes adjacent to the core by
periodic mechanical twisting and heating with an arc fusion splicer. Because in photonic crystal fibers the phase
birefringence is very dispersive and increases against wavelength, the phase matching between coupled modes can be
obtained simultaneously at several wavelengths. In particular, we demonstrate that for the grating period Λ =8 mm, resonant
coupling can be obtained at three different wavelengths. The first order coupling (-13dB) is obtained for Λ = LB . This
condition is fulfilled at λ = 856 nm. The second order coupling (-20dB) is obtained for Λ = 2LB at λ =1270 nm and the third
order coupling (- 17dB) occurs for Λ = 3LB at λ =1623 nm. The length of the filter was 9.6 cm, which corresponds to 13
periodic twists. We also present the results of sensitivity measurements of this filter to hydrostatic pressure and temperature.
We present the results of measurements of modal birefringence and temperature sensitivity of birefringent holey fibers fabricated by Fiber Optic Group, University of Marie Curie-Sklodowska (UMCS) in Lublin, Poland. The birefringence measurements were carried out in a wide spectral range of 0.63 - 1.57 μm in two fibers with different hole diameters and pitch distances. Our results show that absolute value of birefringence increases against wavelength and is one order of magnitude greater than in conventional highly birefringent fibers. The measurements of temperature sensitivity carried out for bare fibers show that zero sensitivity can be achieved at certain wavelength.
We investigated theoretically and experimentally the polarimetric sensitivity to temperature of highly birefringent
photonic crystal fibers (HB PCFs) in which the birefringence is induced by two large holes adjacent to the core. We
carried out the sensitivity measurements in a broad spectral range (680-1550 nm) using a spectral domain interferometric
method for two fibers with different pitch distance and hole diameter. Our results show that the polarimetric sensitivity
to temperature in the investigated fibers is highly dispersive and crosses zero at specific wavelengths. Furthermore, we
found good agreement between the measured and the calculated characteristics.