The development of chalcogenide glasses fibers for application in the infrared wavelength region between 1 and 10
μm is a big opportunity. More particularly, the possibility to generate efficient non linear effects above 2 μm is a real
challenge. We present in this work the elaboration and optical characterizations of suspended core microstructured
optical fibers elaborated from the As2S3 chalcogenide glass. As an alternative to the stack and draw process a
mechanical machining has been used to the elaboration of the preforms. The drawing of these preforms into fibers
allows reaching a suspended core geometry, in which a 2.5 μm diameter core is linked to the fiber clad region by
three supporting struts. The zero dispersion wavelength is thus shifted towards 2 μm. At 1.55 μm our fibers exhibit a
dispersion around -250 ps/nm/km. Their background level of losses is below 0,5 dB/m. By pumping them at 1.55 μm
with a ps source, we observe self phase modulation as well as Raman generation. Finally a strong spectral
enlargement is obtained with an average output power of - 5 dbm.
A chalcogenide optical fiber of special design is proposed to convert a short-wavelength IR radiation (around 2 μm) up
to second transparency window of atmospheric air (around 4.5 μm) by degenerate four-wave mixing. The fiber supports
a small core surrounded by three large air holes. The zero-dispersion wavelength is shifted down to 2 μm in this fiber by
properly tailoring geometry of the fiber core. We demonstrate by solving the nonlinear Schrödinger equation that
efficient wavelength-conversion can be obtained by pumping the fiber with a Tm:SiO2 pulsed fiber laser.
We experimentally demonstrate soliton self-frequency shifts
well-beyond 500 nm in suspended core fibers. We compare
two fibers and show that the dispersive wave generation induced by the presence of a second zero dispersion wavelength
or the OH-absorption peak may limit the soliton shift performance. By measuring the frequency stabilization spectrum of
the shifted soliton, we show that we can simply and accurately evaluate the second zero dispersion wavelength.
The combination of the functionalities of Fiber Bragg Gratings (FBGs) and Photonic Crystal Fibers (PCFs) has unveiled
new potential for FBG based sensors. The fabrication of FBGs in PCFs has been reported in literature. However, using
dedicated PCFs to improve the sensitivity of FBG-based sensors has received only limited attention. In this report we
therefore show how to eliminate some of the drawbacks of FBGs in conventional step-index fibers for sensor
applications by exploiting the design flexibility of PCFs. The added value of PCFs stems from the ability to design an
optical fiber in which an FBG acts as a sensor with a selective sensitivity, e.g. a sensor that is sensitive to strain but not
to temperature. For this purpose we use a PCF with a birefringence on the order of 10-3, which is one order of magnitude
larger than for conventional birefringent fibers. The two FBG reflection peaks are therefore significantly separated from
each other, e.g. 2 nm, which makes these FBGs suited for sensing purposes since both peaks can be unambiguously and
accurately identified. As a conclusion we summarize the advantages and disadvantages of our approach to design and
fabricate selective FBG-based sensors.
We review exceptional properties of the photonic crystal fibres enabling sensing applications of this new class of fibres.
First, the sensing capabilities of highly birefringent index guided fibres are discussed. This includes dispersion
characteristics of phase and group modal birefringence in different fibre structures, and sensitivity of these parameters to
hydrostatic pressures and temperature. We demonstrate that index guided and photonic bandgap holey fibres of specific
construction can be used as wide-band fibre-optic polarizer. We also show that combining of geometrical and stress
effects makes it possible to design the holey fibres with either zero phase or group modal birefringence at virtually any
given wavelength. Finally, different designs and performance of PCFs suitable for gas sensing are overviewed.
We numerically analyzed the polarization effects in birefringent all-solid photonic bandgap fiber with different index
contrast between matrix and circular inclusions. The birefringence in the analyzed fibers is induced by elliptical shape of
the core composed of double defect in the hexagonal lattice of high index inclusions. Our simulations were fully
vectorial and based on a plane wave method and finite element method. We determined location of photonic bandgaps,
spectral dependence of phase and group modal birefringence, and confinement loss characteristics for different
polarization modes in three analyzed structures.
We investigated theoretically and experimentally the wavelength dependences of phase and group modal birefringence
for the fundamental (E11) and the higher order mode (E31) supported by index guiding highly birefringent photonic
crystal fiber. The birefringence in the investigated structure was induced by asymmetrical cladding consisting of one row
of cladding holes with a diameter lower than the other cladding holes. The numerical simulations carried out with use of
the full-vector finite elements method show that the birefringence of the E31 mode can be about 30% higher than of the
fundamental mode. Additionally, we measured the modal birefringence of the both modes using scanning wavelength
method. A comparatively good agreement between the calculation and experimental results was obtained confirming the validity of the theoretical analysis.
Microstructured fibers (MOF), also called photonic crystal fibers (PCF), constitute a class of optical fibers, which
has a large potential for number of novel applications either in the telecom or in the sensing domain. However, some of
the applications require the use of specialty fibers with a doped core. We have made a preliminary exploration of PCF
with doped regions and with inscribed Bragg gratings. The extensive study of the fiber cross-section structure in respect
to possibilities of writing the Bragg gratings and the sensitivities of PCF Bragg gratings was our main concern.
Selective measurement of strain without temperature compensation is achieved with fiber Bragg grating (FBG) in
highly birefringent (HB) PCF, since such grating is characterized by two reflection bands corresponding to the two
polarization modes generated due to the fiber birefringence. The measurement range of such FBG in HB fiber sensor
depends on how strong is the separation of the polarization modes, which is expressed as phase birefringence.
In next step, we have modeled, designed and fabricated specialty PCF with Ge doped core in such way that after
writing the Bragg grating into the fiber we have obtained a sensors exhibiting low sensitivity to any temperature drifts.
Traditional optical fiber sensors are not able to make such a distinction between stress and temperatures and require
complex temperature compensation mechanisms.
We present the results of theoretical and experimental analysis of waveguiding in a two-mode birefringent holey
fiber in which the birefringence is induced by two large holes adjacent to the fiber core. First, using a full-vector
finite-element method we modeled the wavelength dependence of the phase and group effective indices for the
fundamental and higher-order linearly polarized (LP) modes in two orthogonal polarizations. Then we evaluated
the wavelength dependence of the phase and group modal birefringences for both LP modes and the intermodal
dispersion in two orthogonal polarizations as well. Second, we used different interferometric techniques, including
time-domain and spectral-domain ones and a lateral force method, to measure in a broad spectral range the
wavelength dependence of the phase and group modal birefringences for the fundamental and higher-order LP
modes. Employing a white-light spectral interferometric method, we also measured the wavelength dependence
of the intermodal dispersion for two orthogonal polarizations of the two LP modes. Furthermore, using an
unbalanced Mach-Zehnder interferometer we measured the wavelength dependence of the relative group effective
index for the fundamental mode.
We have experimentally characterized three polarizing photonic crystal fibers manufactured by the Laboratory of Optical
Fiber Technology, Maria Curie-Sklodowska University, Lublin, Poland. In the investigated structures the dissimilarity in
the cut-off wavelengths is induced by a pair of large air holes adjacent to the fiber core. Because of different geometry,
the investigated fibers have different polarization ranges. In the first structure, the polarization dependent loss (PDL) of
3 dB/m is observed at 1300 nm and further increases against wavelength. In the two other fibers, the polarization
bandwidth is shifted towards longer wavelengths. We have also investigated the effect of bending on polarization
characteristics. It was experimentally demonstrated that for bent fiber the attenuation of the LPy01 increases for shorter
wavelengths, which results in wider polarization bandwidth. Moreover, we have numerically analyzed and optimized for
maximum operation bandwidth two constructions of the index guided PCFs, whose polarization properties are induced
by unequal diameters of the cladding holes.
Paper presents technology manufacturing and basics parameters of photosensitive high birefringent photonic crystal fiber made from high silica glasses. It was especially elaborated for Bragg gratings inscriptions. Common photonic optical fibers have cores made from nondoped silica glasses. Therefore Bragg gratings inscriptions are difficult or impossible. In photosensitive photonic optical fibers cores are made from germanium doped silica glasses. In presented fiber core glass was made with MCVD method. Technology of manufacturing of high birefringent photonic crystal fibers are analogous to technology of manufacturing of common low birefringent holey fibers.
Fast, frequent, accurate and reliable measurements of physical factors such as temperature, stress or strain play a key role when it comes to ensuring the smooth operation of processes in many domestic, commercial and industrial constructions or devices. For example, most fabrication devices and production process rely on temperature and stress measurements to operate; and most large buildings depend on a series of temperature sensors to control the heating or cooling to maintain the temperature.
Photonic crystal fibres (PCF), constitute a class of optical fibres, which has a large potential for number of novel applications either in the telecom or in the sensing domain. Analysis of sensing characteristics of different photonic crystal fibre structures, including effective index and mode field distribution, photonic bandgap, chromatic dispersion, phase and group modal birefringence, confinement and bending losses, sensitivity to temperature, hydrostatic pressure, and other physical parameters are revealed.
The benefits of PCF allow fabrication of different types of specialty microstructured fibres such as endlessly single mode, double clad, germanium or rare earth doped, highly birefringent, and many other microstructured fibres as sensor components. The developed characterization techniques of specialty microstructured fibres are reviewed as well. Finally, the new microstructured fibres and fibre component for sensing applications which were designed, fabricated and characterized will be presented. One of the demonstrated components is the effective Bragg grating written in highly birefringent and single mode photonic crystal fibre.
Paper described fabrication methods of high birefringence index guided holey fibers made from silica and high
silica glasses. Several kinds of high birefringence holey fibers are described in the point of view their fabrication
technology and basic characterization. There are: triple defect fiber with shape induced birefringence, two kinds of
fibers with filling factor asymmetry induced birefringence, fibers with filling factor asymmetry induced birefringence
and germanium doped core designed for Bragg gratings writing, fiber with filling factor asymmetry induced
birefringence and neodymium doped core designed for fiber amplifiers and lasers, dual core fiber with circular and
weakly separated cores.
Methods of manufacturing we used were: MCVD method for silica and high silica glass preparation as optical
fiber preform manufacturing and OVD method for porous silica glass fabrication including additional processes as
hydroxylation, impregnation with suitable salts solutions, thermal decomposition, dehydroxylation and sintering lead to
silica, high silica and rare earth doped glass preparation in the form of elements for microstructured fiber preforms
compose.
We present the results of experimental and theoretical analysis of dispersion characteristics of a two-mode birefringent holey fiber, in which the birefringence is induced by two large holes adjacent to the fiber core. Different interferometric techniques were used to measure in a broad spectral range the wavelength dependences of the
phase and the group modal birefringence for the fundamental and the higher-order linearly polarized (LP) spatial modes. We also measured the wavelength dependence of the intermodal dispersion for two orthogonal polarizations of the fundamental and the higher-order LP spatial modes employing a white-light spectral interferometric
method. Furthermore, we calculated all the dispersion characteristics using a full-vector finite-element method and confirmed good agreement between experimental and theoretical results.
We report on experimental studies of polarimetric sensitivity to temperature and hydrostatic pressure in two highly birefringent index guided photonic crystal fibers. Our results confirm earlier theoretical predictions indicating that polarimetric sensitivity to temperature in highly birefringent PCF with specific constriction can be very low. Proper choice of constructional parameters of the PCF can lead to complete temperature desensitization. On the other hand, relatively high polarimetric sensitivity to hydrostatic pressure in the analyzed structures make them good candidates for applications as active elements in hydrostatic pressure sensors.
We proposed and theoretically analyzed birefringent holey fibers of new construction. The birefringence in these fibers is induced by a highly asymmetrical cladding, which is composed of only two rows of large holes separated by one row of small holes The fiber cores have the form of single defects made of pure silica or containing GeO2 doped circular inclusion The geometries of both fibers were preliminarily optimized in order to assure minimum number of structural elements, while keeping the confinement losses of the fundamental mode below 1 dB/km. We used an edge finite element method to calculate the spectral dependence of the confinement losses and the phase birefringence. Due to small number of the cladding holes, the proposed fiber construction with GeO2 doped inclusion in the core region may be especially useful for inscription the Bragg gratings.
In this communicate, we present a numerical approach allowing to model propagation characteristics of the large core birefringent holey fibers with stress applying elements. The main advantage of the proposed method is that it takes into account simultaneously both geometry of the holey region as well as material birefringence induced by stress applying elements. Using this approach, we calculated the spectral dependence of phase and group modal birefringence for different geometry of the analyzed fiber. Furthermore, the spectral dependence of polarimetric sensitivity to temperature was determined. The calculation results were compared with experimental data published earlier.
We numerically analyzed the polarization properties of two birefringent photonic bandgap holey fibers with different geometries. Our calculation method is fully vectorial and uses a hybrid edge/nodal finite element approach with PML absorbing boundary conditions. In both structures, we determined the spectral dependence of the phase modal birefringence and the spectral dependence of the losses for the fundamental modes of orthogonal polarizations. Our results show that the dependence of losses upon mode polarization is so high that both structures can be used as fiber polarizers.
We report on research towards application of birefringent photonic crystal fibers as active and passive elements of fiber optic sensors for measurements of different physical parameters. Using experimental and theoretical methods, the sensing characteristics of different photonic structures are studied, including spectral behavior of phase and group modal birefringence, polarization dependent losses, sensitivity to temperature and hydrostatic pressure.
We measured and calculated the spectral dependence of the polarimetric sensitivity to temperature (dB/dT) in a photonic crystal holey fiber. The birefringence in this fiber is induced by the elliptical shape of the core, which consists of a triple defect in the hexagonal structure. Comparison of the temperature sensitivity measured for the bare fiber and for the fiber with polymer coating shows that the stress induced by the thermal expansion of the polymer contributes significantly to the overall temperature response. Measurements carried out for the bare fiber demonstrate that the temperature sensitivity has a positive sign and strongly increases vs. wavelength. Additionally, we present the results of calculations of the spectral dependence of dB/dT obtained using a finite element method. The calculated and measured values of dB/dT show relatively good agreement.
We present a numerical investigation of fundamental and higher order modes propagating in doped core birefringent holey fiber. The conditions for the co-existence of two competing light guiding mechanisms, their consequences on the mode propagation and the potentialities for Bragg grating applications with this are discussed.
We analysed spectral dependence of modal birefrincence and susceptibility to temperature and to strain in two birefringent photonic bandgap fibers. The birefringence in these fibers is induced by the elliptical shape of either the core or the cladding holes. We show that in one of the fibres, the sensitivity to temperature nad to strain reaches zero in the center of the photonic bandgap. Our calculation method is fully vectorial and based on a hybrid edge/nodal finite element approach.
We investigated theoretically and experimentally an impact of hydrostatic pressure on phase modal birefringence in birefringent photonic crystal holey fiber of new construction. The birefringence in this fiber is induced by highly elliptical shape of the core, which consists of triple defect in the hexagonal structure. Using finite element method, we first calculated the stress components and deformations induced by hydrostatic pressure in the fiber cross-section. In the second step, the distribution of the stress-related corrections of refractive index were determined. Finally, we calculated the sensitivity of the phase modal birefringence (dB/dp) to hydrostatic pressure versus wavelength. The contribution of the geometrical effects related only to deformation of the holey structure as well as the stress-related contribution to the overall pressure sensitivities were analyzed separately. Our results show that these two factors decrease the phase modal birefringence, which results in negative sign of dB/dp. We also measured the pressure sensitivity for several wavelengths using polarimetric technique. The experimental and theoretical values of dB/dp show very good agreement.
A construction of the polarizing holey fiber was optimized in order to assure maximum single polarization bandwidth. We demonstrated that the polarization bandwidth of the holey fiber can be increased up to 480 nanometers by properly choosing the fiber constructional parameters. A single-polarization operation in the analyzed structure was achieved by introducing a pair of air holes adjacent to the fiber core and having diameters greater than the cladding holes. Similarly to traditional polarizing fibers, the operation principle of the analyzed holey fiber is related to the difference in cut-off wavelengths of the two orthogonally polarized fundamental modes.
We present and compare two numerical approaches to analysis of photonic crystal fibers, i.e., finite element method based on triangular elements and Fourier decomposition method. The two methods were employed to determine propagation constants in hexagonal photonic fiber by solving vectorial and scalar wave equations. The results obtained with different methods shows very good agreement. We also demonstrated that coupling coefficients between orthogonally polarized modes in fully vector wave equation are negligible for this type of structure and for this reason they can be disregarded. Such a simplification saves computational time and hardware resources without loosing the precision of calculations. We also compared the efficiency of scalar and vectorial approach in calculations of cut-off wavelength. Our results show that scalar approach is not accurate enough for modeling fibers with large filling factor.
Applying an effective index method, we determined the dependence of propagation constants upon temperature in photonic crystals holey fibers with hexagonal and elliptical cores. Our analyiss shows that modal birefringence increases with temperature and wavelength in photonic crystal fibers with elliptical core, which is an effect opposite to taht observed in classical elliptical-core fibers. Some of the calculations were carried out for the fibers recently manufactured at Laboratory of Optical Fiber Technology, MCS University in Lublin, Poland.
In this paper we analyzed the influence of hydrostatic pressure on modal birefringence in photonic crystal holey fibers. We calculated the spectral dependence of modal birefringence B(λ) and its sensitivity to hydrostatic pressure dB(λ)/dp in the holy fiber with birefringence induced by the lack of hexagonal symmetry in the cladding. The contribution of geometrical effect related to deformation of the holey structure as well as the stress-related contribution to the overall pressure sensitivity were analyzed separately. Our results show that both factors decrease modal birefringence, which results in negative sign of pressure sensitivity. Furthermore, we show that the pressure sensitivity of the analyzed structure is of the same order as sensitivities of the commercially available highly birefringent fibers with stress applying elements like Panda or Bow-Tie.
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