Fabrication of mid-index contrast ring resonators with a well-defined gap is very challenging, while gapless rings suffer from substantial coupling losses. To avoid these issues, we propose a gapless design based on a step-like structuring of the bus/ring waveguides. As we show with numerical simulations, our design allows to spatially confine the modes to the steps formed on the bus/ring waveguides thus mitigating the coupling losses. Additionally, the step on the ring waveguide reduces the bending losses. Finally, we show how varying the heights and widths of the steps allows to tailor the transmittance and quality factor of the ring.
We present a novel method for determining a spectral phase derivative from a single spectral interferogram obtained by using a white-light interferometry technique, which is further used for calculation of chromatic dispersion profile. The method is based on direct calculations of a second derivative of the registered spectral intensity at extremal points. We explain theoretical background of the method, discuss its limitations and evaluate an accuracy by numerical simulations. Additionally, we validate the proposed method in dispersion measurements of the BK7 glass plate and the SMF-28 fiber.
We present two polymer birefringent fibers with enhanced polarimetric sensitivity to hydrostatic pressure. In the first fiber, with birefringence induced by the arrangement of holes in the microstructured cladding, an increased sensitivity to pressure was obtained by enlarging selected holes in the cladding. The second is a side-hole fiber with an elliptical core made of polymethyl metacrylate–polystyrene (PMMA/PS) copolymer and pure PMMA cladding. The fiber core is located in a narrow PMMA bridge separating the holes. The transmission and sensing characteristics of both fibers are compared, including spectral losses, birefringence, polarization cross-talk and polarimetric sensitivity to hydrostatic pressure.
Supercontinuum generation (SG) in photonic crystal fibers (PCFs) usually takes advantage of soliton dynamics, when pump wavelength is located in the anomalous dispersion region near the zero-dispersion wavelength of the fiber. This results in broader bandwidth than pumping in the normal dispersion region (NDR). SG in NDR is of interest, because of its potential for high degree of coherence and low intensity fluctuations. It was experimentally demonstrated in silica fibers and PCFs pumped around 1000 nm, covering the visible and near-infrared. We developed an all-solid PCF with hexagonal lattice made from N-F2 capillaries, with lattice constant Λ=2.275 μm, filling factor d/Λ=0.9, and a solid N-F2 core with 2,5μm diameter. The capillaries were filled with thermally matched borosilicate glass rods with lower refractive index. The PCF has all-normal dispersion, flattened within 1400- 2750 nm (-35 to -29 ps/nm/km) and a local maximum of -29 ps/nm/km at 1550 nm. Measured attenuation in 1500-1600 nm is around 3.2 dB/m. Nonlinear coefficient calculated at 1550 nm is 17/W/m. We numerically investigate the evolution of supercontinuum formation with a maximum bandwidth of 900-2400 nm. Considered pump pulse lengths were between 1 ps and 50 fs, with corresponding peak powers from 20 kW to 200 kW. Measured coupling efficiency using 20× microscope objective was 50%. One-photon-per-mode noise was used to simulate pump noise and multi-shot SG spectra were calculated. Preliminary experimental results are in good agreement with developed model.
In this work we present our results on supercontinuum (SC) generation using a photonic crystal fiber (PCF) fabricated from lead-bismuth-gallium-oxide glass (PBG-08). Due to high refractive index, high nonlinearity and high transmittance, the PBG-08 glass-based fibers seem to be excellent media for broad supercontinuum generation in the infrared spectral region. In our experiment, a short-length piece of PCF (6 cm) is pumped by a femtosecond fiber laser system, delivering 540 fs pulses at 60 MHz repetition rate and 2.75 W of maximum average power. This compact and cost-effective system allows to generate supercontinuum spanning from 900 to 2400 nm.
This paper presents the sensor characteristics of highly birefringent polymer side-hole optical fiber. The fiber core with
greater refractive index was made of copolymer PMMA-PS, while the cladding of pure PMMA. The fabricated fiber
showed relatively low losses of the order of 6 dB/m in the visible range. We measured several sensing characteristics in
the fabricated fiber, including birefringence and polarimetric sensitivity to pressure and temperature. The fiber showed
high polarimetric sensitivity to pressure, which is directly related to the presence of two large holes transferring
symmetrical load applied to the cladding into nonsymmetric stress distribution in the core region. This in turn changes
modal birefringence of the investigated fiber and increases the sensitivity to pressure.
Supercontinuum generation spanning an octave from 900 nm to 2400 nm was obtained in all-solid glass, photonic crystal
fiber, designed with flattened, all-normal dispersion and optimized for pumping in the 1500-1560 nm range. The report
includes designing of microstructure of all-solid glass photonic crystal fiber and relation of dispersion profile to fiber
filling factor d/Λ, numerical and experimental characteristic of fabricated fiber dispersion profile, supercontinuum
generation experiment under 1530 nm pumping with 70 fs pulses, concluded with numerical analysis based on solution
to nonlinear Schrödinger equation. Interplay among self-phase modulation, optical wave breaking and four-wave mixing
is discussed in context of observed pump pulse broadening.
The intermodal sensitivity of a two-mode birefringent holey fiber to strain, temperature and hydrostatic pressure is measured in the spectral domain. In an experimental setup comprising a broadband source, a polarizer, a twomode birefringent holey fiber under a variable physical parameter, an analyzer and a compact spectrometer, the spectral interferograms are resolved. These are characterized by the equalization wavelength at which spectral interference fringes have the largest period due to the zero group optical path difference between the fundamental, the LP01 mode and the higher-order, the LP11 mode. The spectral interferograms are processed to retrieve the phase as a function of the wavelength. From the retrieved phase functions corresponding to different values of the physical parameter, the intermodal sensitivity as a function of wavelength is obtained. Using this approach, the intermodal sensitivity to strain, temperature and hydrostatic pressure is measured for two orthogonal (x and y) polarizations.
Polarimetric sensitivity of a birefringent holey fiber to strain, temperature and hydrostatic pressure is measured in the spectral domain. In an experimental setup comprising a broadband source, a polarizer, a birefringent holey fiber under a variable physical parameter, a birefringent delay line, an analyzer and a compact spectrometer, the spectral interferograms are resolved. These are characterized by the equalization wavelength at which spectral interference fringes have the largest period due to the zero overall group modal birefringence. The spectral interferograms are processed to retrieve the phase as a function of the wavelength. From the retrieved phase functions corresponding to different values of the physical parameter, the polarimetric sensitivity as a function of wavelength is obtained. Using this approach, the polarimetric sensitivity to strain, temperature and hydrostatic pressure is measured.
The spectral dependence of the polarimetric sensitivity of a birefringent side-hole fiber to temperature and hydrostatic pressure was measured using a simple experimental setup comprising a broadband source, a polarizer, a birefringent fiber under test, a birefringent delay line, an analyzer and a compact spectrometer. The spectral interferograms, characterized by the equalization wavelength at which spectral interference fringes have the highest visibility (the largest period) due to the zero overall group birefringence, were processed to retrieve the phase as a function of wavelength. First, from the retrieved phase functions corresponding to different temperatures of the fiber under test, the spectral polarimetric sensitivity to temperature was obtained. Second, from the retrieved phase functions corresponding to different hydrostatic pressures in a chamber with the fiber under test, the spectral polarimetric sensitivity to hydrostatic pressure was obtained.
In this paper, the strain sensitivity of a two-mode birefringent holey fiber is measured in the spectral domain. In a
simple experimental setup comprising a broadband source, a polarizer, a two-mode birefringent holey fiber under
varied elongations, an analyzer and a compact spectrometer, the spectral interferograms are resolved. These are
characterized by a specific wavelength, the equalization wavelength, at which spectral interference fringes have the
highest visibility (the largest period) due to the zero group optical path difference between the fundamental, the
LP01 mode and the higher-order, the LP11 mode. The spectral interferograms with the equalization wavelength
are processed by a new method to retrieve the phase as a function of the wavelength. From the retrieved phase
functions corresponding to different elongations of a two-mode birefringent holey fiber under test, the spectral
strain sensitivity is obtained. Using this approach, the intermodal spectral strain sensitivity was measured for
two orthogonal (x and y) polarizations.
Photonic Crystal Fibres (PCFs) are well known for allowing the implementation of specific waveguiding features that
cannot be achieved with conventional optical fibres. This results from the design flexibility of the holey structure in the
PCF cladding and/or core regions. Today PCFs have found applications for example in supercontinuum generation,
optical sensing and fibre lasers. They are now also being combined with fibre Bragg gratings, more specifically in the
fields of optical fibre sensing and all-fibre laser applications. In this contribution we discuss how we applied micro-optical
design methods based on commercially available software such as MODE Solutions and FDTD Solutions from
Lumerical Solutions, Inc. and COMSOL Multiphysics® combined with MATLAB® scripting and additional
optimization methods to develop microstructured fibres for three different purposes, i.e. PCF structures that facilitate
Bragg grating inscription, PCF structures that enable temperature insensitive pressure measurements and bendable PCFs
with a very large mode area for high power short pulse fibre lasers. For the three cases we describe the fibre design
methods and property simulations as well as the tolerance studies that take into account manufacturing imperfections as
well as possible variations in material parameters.
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.
Two spectral interferometric techniques employing a supercontinuum source are used for dispersion characterization
of birefringent microstructured and specialty optical fibers over a broad spectral range (e.g. 500-1600 nm).
First, a technique employing an unbalanced Mach-Zehnder interferometer is used for measuring the chromatic
dispersion and zero-dispersion wavelength of one polarization mode supported by a microstructured optical fiber.
Second, a technique employing a tandem configuration of a Michelson interferometer and a fiber under test is
used for measuring the group modal birefringence dispersion of the fiber and the chromatic-dispersion difference
as a function of wavelength. From these measurements, the chromatic dispersion and the zero-dispersion
wavelength of the other polarization mode supported by the microstructured optical fiber are retrieved. We
revealed from four measurements the dependence of the zero-dispersion wavelength on the geometry of air-silica
microstructured optical fiber. We also measured by the second technique the zero-chromatic-dispersion difference
wavelength for elliptical-core optical fibers. We revealed from four measurements that the dispersion parameter
can be tuned by the fiber geometry.
Chromatic dispersion of polarization modes in holey fibers is measured over a broad spectral range (e.g. 500-1600 nm) using two white-light spectral interferometric techniques. First, a technique employing an unbalanced
Mach-Zehnder interferometer with a fiber in the test arm is used to measure the wavelength dependence of the
differential group effective index, or equivalently the chromatic dispersion of one polarization mode supported
by the fiber. Second, a technique employing a tandem configuration of a Michelson interferometer and the
optical fiber under test is used to measure the group modal birefringence in the fiber. From these measurements,
the chromatic dispersion of the other polarization mode supported by the fiber is retrieved. We measured by
these techniques the chromatic dispersion of polarization modes in four air-silica holey fibers and revealed the
dependence of zero-dispersion wavelength on the geometry of the holey fiber.
We present two white-light spectral interferometric techniques for measurement of the chromatic dispersion of
polarization modes in holey fibers over a broad spectral range (e.g. 500-1600 nm). First, a technique employing
an unbalanced Mach-Zehnder interferometer with a fiber in the test arm is used to measure the wavelength
dependence of the differential group effective index, or equivalently the chromatic dispersion of one polarization
mode supported by the fiber. Second, a technique employing a tandem configuration of a Michelson interferometer
and the optical fiber under test is used to measure the group modal birefringence in the fiber. From these
measurements, the chromatic dispersion of the other polarization mode supported by the fiber is retrieved. We
measured by these techniques the chromatic dispersion of polarization modes in three air-silica holey fibers and
revealed the dependence of zero-dispersion wavelength on the geometry of the holey fiber.
We present the results of measurement of dispersion characteristics of two-mode highly birefringent (HB) fibers
by three spectral interferometric techniques. First, a technique employing a tandem configuration of a Michelson
interferometer and HB fiber under test is used for a broad spectral range measurement (e.g. 500-1300 nm) of
the group modal birefringence for two spatial modes supported by the fiber. Second, a method of a lateral
point-like force acting on the fiber and based on spectral interferometry is used for measuring the phase modal
birefringence at one wavelength for the fundamental mode only. The measured value is combined with the
dispersion of the group modal birefringence to obtain the phase modal birefringence over a broad wavelength
range. Third, a spectral interferometric technique employing an unbalanced Mach-Zehnder interferometer with
HB fiber in the test arm is used for measuring the wavelength dependence of the chromatic dispersion of the one
of the polarization modes supported by the HB fiber over a broad wavelength range (e.g. 500-1400 nm). From
this dependence and from the chromatic-dispersion difference, which is obtained from the measured group modal
birefringence, the chromatic dispersion of the other polarization mode supported by the HB fiber is retrieved.
We measured by these techniques dispersion characteristics of two HB fibers, including elliptical-core HB fiber
and microstructured HB fiber.
We experimentally characterized a birefringent microstructured polymer fiber of specific construction, which allows for
single mode propagation in two cores separated by a pair of large holes. The fiber exhibits high birefringence in each of
the cores as well as relatively weak coupling between the cores. Spectral dependence of the group and the phase modal
birefringence was measured using an interferometric method. We have also measured the sensing characteristics of the
fiber such as the polarimetric sensitivity to hydrostatic pressure and temperature.
We present the results of interferometric measurements of chromatic dispersion of polarization modes in holey
fibers over a broad spectral range (e.g. 500-1600 nm). First, a spectral interferometric technique employing an
unbalanced Mach-Zehnder interferometer with a birefringent holey fiber in the test arm is used for measuring the
wavelength dependence of the differential group effective index of the one of the polarization modes supported
by the fiber. We apply a five-term power series fit to the measured data and by its differentiation we obtain
the chromatic dispersion. Second, a spectral interferometric technique employing a tandem configuration of a
Michelson interferometer and the holey fiber under test is used for measuring the group modal birefringence in
the fiber. From the measurements, the differential group effective index and the chromatic dispersion of the
other polarization mode supported by the fiber are retrieved. We confirmed that the measurement results agree
well with that specified by the manufacturer. We also measured by these techniques the chromatic dispersion in
other birefringent holey fiber.
We have systematically measured the differential stress-optic coefficient, ΔC, and Young's modulus, E, in a number of
PMMA fibers drawn with different stress, ranging from 2 up to 27 MPa. Effect of temperature annealing on those
parameters was also investigated. ΔC was determined in transverse illumination by measuring the dependence of
birefringence on additional axial stress applied to the fiber. Our results show that ΔC in PMMA fibers has a negative sign
and ranges from -4.5 to -1.5×10-12 Pa-1 depending on the drawing stress. Increase of the drawing stress results in greater
initial fiber birefringence and lower ΔC. The dependence of ΔC and initial birefringence upon drawing stress is nonlinear
and gradually saturates for higher drawing stress. Moreover, we find that ΔC is linearly proportional to initial fiber
birefringence and that annealing the fiber has no impact on the slope of this dependence. On the other hand, no clear
dependence was observed between the fiber drawing stress and the Young's modulus of the fibers as measured using
microscopic digital image correlation with the fibers tensioned using an Instron tension tester.
In this paper we report on the fabrication of a non-symmetric double core microstructured fiber made of in-house
synthesized silicate glass. The micro-structured fiber uses three rings of holes around two cores separated with a single
hole. This fiber has a birefringence of about 10-3 at 1.5 μm and zero dispersion wavelengths at 1.3- 1.5 nm range.
For experimental verification of nonlinear properties of the fiber we use a femtosecod Ti:Sapphire oscillator emitting in
the range of 750-900 nm in the normal dispersion regime of the pumped fiber. Measurements we performed with
excitation of one of the core and readout at the output from both cores separately. Registered spectra show a strong
coupling between cores and there is no evident difference between signals for excited or other core. Generated spectrum
is flat and relatively narrow, which is a result of pumping in normal region of fiber dispersion as we predicted with
simulations.
In this paper we report on the fabrication and characterization of a double glass micro-structured fiber with low index core and photonic cladding made of high index micro-rods. Micro rods are made of lead-oxide F2 commercially available glass (SCHOTT Inc.) with a refractive index nD=1.619, while as background we use a borosilicate NC21 glass with a refractive index nD=1.533. The fiber cladding is composed of 8 rings of F2 glass micro rods ordered in hexagonal lattice. A core is created by replacement of seven F2 rods with NC21 rods. A fabricated fiber has a linear filling factor of 0.75 and micro rods diameter of 1.2 μm. A core has a diameter of 3.7 μm while cladding and total fiber diameter are 42,6μm and 120 μm, respectively.
Using supercontinuum source we have measured transmission properties of the fabricated fiber. Based on measurements of the fiber samples of 18-80 cm long we have identified two photonic band gaps. Fist band gap is localized in visible range at 610 nm central wavelength. The second broadband photonic band gap is localized in near infrared and it is 80 nm wide at 840 nm central wavelength.
We report on experimental investigations towards application of birefringent microstructured fibers as active elements of
fiber optic sensors for measurements of different physical parameters. The sensing characteristics including spectral
behavior of phase and group modal birefringence, polarimetric sensitivity to temperature, hydrostatic pressure and
elongation are presented for three different index guiding microstructured fibers and hollow core photonic bandgap fiber
with residual birefringence.
Recently we have fabricated at Institute of Electronic Materials Technology (ITME) a microstrucuted fiber made of silicate glass NC21A synthesized in-house at ITME. Fabricated fiber is build of three rings of holes around slightly elliptical core (2.6 μm x 3.4 μm). Dispersion properties of the fiber are calculated based on real structure with biorthonormal basis method. Fabricated fiber has a birefringence at the level of 10-3 at 1.5 μm. A zero dispersion is achieved for the wavelengths 860 nm and 870 nm, respectively.
In this fiber, pumped with 100 fs pulses with energy of nJ level, ultra broadband supercontinuum generation in the range 400 - 1600 nm has been achieved.
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 demonstrate that bending loss in large mode area photonic crystal fiber (LMA PCF) reveals a strong dependence of
the amplitude and location of the loss peaks on the bend radius and on the fiber angular orientation. To do so we
measured bending induced loss in LMA PCF as a function of wavelength in a broad spectral range (800-1500 nm) for
different bend radii and for different angular orientations of the fiber with respect to the bending plane. The oscillations
of bending loss with the bend radius and orientation are particularly well pronounced when the radiative component of
the fundamental mode is reflected from the flat boundary of the holey cladding. We also show the good agreement
between our measurement results and earlier simulations relying on a finite element method with perfectly matched
layers and equivalent index model.
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.
In this paper we report on the fabrication of a micro-structured fiber made of in-house synthesized silicate glass, with a
nonlinear Kerr refractive index of 4.0 10-15 cm2/W. The micro-structured fiber uses three rings of holes around a slightly
elliptical core with dimensions 2.6 μm x 3.4 μm. This fiber has a birefringence of about 10-3 at 1.5 μm and zero
dispersion wavelengths at 860 nm and 870 nm. Using this fiber we have demonstrated ultra broadband supercontinuum
generation in the range 400 - 1600 nm for 19.5 cm fiber sample pumped with 100 fs pulses with central wavelength of
755 nm and energy of 2 nJ. Broadband generation of 200 nJ in the range 650-850 nm with pulse energy on the level of
0.5 nJ is also observed with the same structure.
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.
In this paper we report on progress in optimization of the material and structure of photonic crystal fibers for use as an
element of fiber sensor of strain and temperature. The fabricated photonic structures consist of elliptical-like holes
ordered in rectangular lattice. The rectangular lattice is applied to obtain global asymmetry of photonic structure with
two-fold geometry and to create birefringence of fiber. Elliptical air holes allows to increase birefringence in the
structure up to the order of 10 -2 for wavelength of 1.55 μm, theoretically. Additionally, rectangular lattice gives a better
control of elliptical air holes uniformity during fabricating process. For fabrication of the fibers we use NC21 borosilicate
glass. Use of high quality glass allows omitting problems with very high attenuation of the previously fabricated
highly birefringent photonic crystal fibers made of SK222 glass. With full vector plane-wave expansion method an
influence of structure parameters such as ellipticity of air holes and aspect ratio of rectangular lattice on birefringence
and modal properties of the fiber is studied. In this paper we present optimization of the fiber structure design, which
takes into account technological limits of fabrication of elliptical holes in fibers. Theoretical birefringence is compared
with experimental measurements. Experimental results already obtained allows to predict birefringence at the order of 10
-3 for wavelength of 1.55 μm for optimized photonic cladding of the fibers.
In this paper, different interferometric techniques were used for measuring dispersion characteristics of specialty
optical fibers, including Corning PMF-38 highly birefringent fiber. We measured the wavelength dependence of
both the phase and group modal birefringences for two lowest-order linearly polarized (LP) modes. The phase
modal birefringence was measured by a lateral force method. The group modal birefringence was measured by a
method of spectral-domain tandem interferometry. The latter method was also used to measure the intermodal
group dispersion for two orthogonal polarizations of the LP modes. The experiment revealed a distinct dispersion
splitting between X-polarized and Y-polarized LP modes.
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.
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 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.
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 theoretical and experimental studies of both scalar and polarization or modal pump-divided parametric
amplification in photonic crystal fibers. In the scalar case, we discuss broadband parametric amplification at telecom
wavelengths near 1550 nm. With a pump-divided scattering process, we discuss the possibility of widely tunable
frequency conversion and four-wave mixing gain at visible wavelengths. We confirmed the theory by experiments where
intense, linearly polarized pump pulses at wavelengths ranging from 532 to 625 nm led to the spontaneous generation of
modulation instability sidebands with frequency shifts ranging from 3 up to 63 THz. The observations were in good
agreement the experimental characterization and theoretical modelling ofthe linear and nonlinear properties of the PCF.
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.
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 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 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 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.
Two different measurement techniques based on tandem interferometry are used to measure the dispersion of group and phase modal birefringence in elliptical-core optical fibers. The first technique is based on time-domain tandem interferometry and uses processing of a series of interferograms at different wavelengths recorded in a tandem interferometer placed at the output of the optical fiber under test. The second technique is based on spectral-domain tandem interferometry and employs a low-resolution spectrometer. It uses a series of the spectral interferograms recorded at the output of a tandem configuration of a Michelson interferometer and the optical fiber under test to resolve the so-called equalization wavelengths, at which the overall group optical path difference is equal to zero. This technique enables the direct dispersion measurements of the group modal birefringence over a wide spectral range. The results obtained by both measurement methods are compared each other and good agreement is confirmed. We also modeled the dispersion of phase and group modal birefringence in the optical fibers using the modified perturbation approach first proposed by Kumar.
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.
A spectral-domain white-light interferometric technique employing a low-resolution spectrometer at the output of a tandem configuration of the compensated (non-dispersive) Michelson interferometer and a two-mode highly birefringent optical fiber is used to measure intermodal dispersion characteristics of the optical fiber. The technique utilizes the fact that the spectral interference fringes are resolved in this configuration only in the vicinity of the so-called equalization wavelength at which the optical path difference (OPD) in the interferometer is the same as the intermodal group (OPD). The white-light spectral interferometric technique is used to measure the wavelength dependences of both the difference between propagation constants of X-polarized and Y-polarized LP modes and the intermodal group OPDs for an elliptical-core (highly birefringent) optical fiber. The measured intremodal dispersion characteristics of the optical fiber are compared with those corresponding to the results of an adequate theoretical analysis using the known parameters of the optical fiber.
Spectral domain characteristics and parameters of optical fibers such as losses and their wavelength dependence, cutoff wavelengths for different fiber modes, wavelength dependencies of both the beat length and intermodal dispersion, etc., are important from the point of view of the development of new types of optical fibers. More
recently, a new spectral domain white light interferometric technique employing a low resolution spectrometer has been used in measurement of the intermodal dispersion in optical fibers. The technique utilizes the fact that the spectral interference fringes are resolved at the output of a tandem configuration of the compensated
(non-dispersive) Michelson interferometer and a few-mode optical fiber only in the vicinities of the so called equalization wavelengths at which the optical path difference (OPD) in the interferometer is the same as the intermodal group OPDs. Thus in the case of a two mode optical fiber the OPD adjusted in the interferometer and measured as a function of the equalization wavelength gives directly the spectral dependence of the intermodal group OPD in the optical fiber. The aim of this work is to use the new spectral domain white light interferometric technique to measure the intermodal dispersion in three different optical fibers. The aim of the work is also to perform an adequate theoretical analysis using a model of a weakly guiding, step-index optical fiber and to compare the corresponding results with the measured intermodal dispersion.
A new spectral-domain white-light interferometric technique employing a low-resolution spectrometer is used for dispersion characterization of optical fibers. The technique utilizes the fact that the spectral interference fringes are resolved at the output of a tandem configuration of the compensated (non-dispersive) Michelson interferometer and a two-mode optical fiber only in the vicinities of so-called equalization wavelengths at which the optical path difference (OPD) in the interferometer is the same as the intermodal group OPDs. Processing of these interference fringes in case of a two-mode optical fiber and measuring the OPD adjusted in the interferometer as a function of the equalization wavelength serve for dispersion characterization including the spectral dependence of both the difference between propagation constants of modes and the intermodal group OPD in the optical fiber. The white-light spectral interferometric technique is used for both circular-core and elliptical-core (highly birefringent) optical fibers. The measured dispersion characteristics of the optical fibers are compared with those corresponding to the results of an adequate theoretical analysis using the known parameters of the optical fibers.
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.
The results of modeling spectral characteristics of modal birefringence and its sensitivity to temperature using different approaches for calculation the residual thermal stress are presented. The modeling was carried out using the modified perturbation approach first proposed by Kumar.
Spectral properties of two elliptical core fibers were investigated using interferometric methods. Phase and group modal birefringences were measured versus wavelength in the spectral range from 633 nm to 830 nm. We also measured sensitivity of phase and group modal birefringence to temperature and hydrostatic pressure in the same spectral range. Strong wavelength dependence of modal birefringence and its sensitivity to external parameters was detected in investigated fibers.
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