In this study, experimental investigation of fiber-based Fabry-Perot is compared against the theoretical predictions of Fabry-Perot resonators. The special emphasis in this study was placed on testing the perspectives for resonance enhancement by coating the fiber facets by highly reflective surfaces and by replacing the flat surfaces by concave mirrors fabricated by the Two-Photon Polymerization (2PP) 3D nano-printing method. Golden layers of varying thickness were deposited on both flat and concave mirrors of optical fiber Fabry-Perot resonators, which were constructed from simply two optical fiber tips carefully aligned parallel to each other. An improvement of extinction ratio by even 12.5 dB and higher finesse of the resonance signal was registered. The resonance spectra resulting from such modifications were measured and discussed in relation to the assumptions of the theory for free-space Fabry-Perot resonators. It was demonstrated that the most optimal reflectance (R) values of both mirrors for the standard Fabry-Perot cavities (R1 = R2) are not the most optimal in case of fiber Fabry-Perot cavities.
In this study, we present a fiber-tip Fabry-Perot interferometer operating in reflective mode, fabricated on the end faces of standard single-mode optical fibers using the Two-Photon Polymerization 3D nanoprinting method. Theoretical analysis highlights the primary challenge in accurately fitting the geometric dimensions of the cavity due to light beam divergence at the end of a single-mode fiber. Therefore, significant emphasis was placed on creating a compact structure with a high-reflection mirror formed on the printed tip. Various shapes of reflective surfaces were tested, including flat and concave. Additionally, to improve reflection we used the cathode sputtering method to get thin metal films on the printed surfaces. During conducted research, it has been demonstrated that the optimal solution is to cover only one surface of the resonator. This necessitated the development of a structure with a unique shape, enabling the deposition of a thin metallic layer solely on the top surface while simultaneously preventing deposition on the core.
Colloidal liquid crystals offer a route to change physical properties and create micro and nano structures. Optical methods only characterise relatively simple colloidal systems. More complex systems require powerful data analytic methods. We present a new approach using Topological Data Analysis to reveal the structural and morphological features in a nematic liquid crystal doped with gold nanoparticles confined in a thin capillary, including the changes occurring during phase transitions. Our topological framework allows us to identify distinct temperature-induced macroscopic states, obtain a geometric representation of the time-dependent topological states and identify several configurations with different degrees of symmetry and order.
Photonic liquid crystal fibers (PLCFs) have been studied for over a decade as an emerging field of sensing and telecommunication devices. Exciting properties of liquid crystals (LCs) infiltrating photonic crystal fibers (PCFs) can be additionally tuned by doping with various materials that are sensitive to external influences, such as an electric field or temperature. Among them, metallic nanoparticles (NPs) are gathering a great interest, due to their potential applications. NPs can be used to highly influence material properties of LCs as dielectric anisotropy, elastic constants, and viscosity. This may lead to many desirable effects, such as a decrease of the Fredericks threshold voltage or reduction of LC switching times. In this paper we doped a nematic LC with 2-nm gold (Au) and 8-nm silver (Ag) NPs, and infiltrated the prepared mixtures into photonic crystal fibers. We examined the influence of this doping in two different electric field systems, one with two flat copper electrodes, and second with four copper microelectrodes. Our results indicate that metallic NP (both Au and Ag) doping enhances sensitivity of the PLCF-based sensors to an electric field and decreases the threshold voltage. Additionally, due to smaller distances between the electrodes, the proposed four microelectrode system requires lower voltages to effectively tune the PLCF.
Carbon dioxide (CO2) measurement has an important role in atmosphere monitoring. Usually, two types of
measurements are carried out. The first one is based on gas concentration measurement while the second involves gas
exchange rate measurement between earth surface and atmosphere [1]. There are several methods which allow gas
concentration measurement. However, most of them require expensive instrumentation or large devices (i.e. gas
chambers). In order to precisely measure either CO2 concentration or CO2 exchange rate, preferably a sensors network
should be used. These sensors must have small dimensions, low power consumption, and they should be cost-effective.
Therefore, this creates a great demand for a robust low-power and low-cost CO2 sensor [2,3]. As a solution, we propose
a photonic sensor that can measure CO2 concentration and also can be used to measure gas exchange by using the Eddy
covariance method [1].
A network of photonic CO2 sensors based on distributed sensing elements that are spread around the tested ecosystem area is proposed. Each of the sensing elements is connected to a wireless network with adjacent sensing elements and a base station that collects, archives, and analyzes results of measurements. The sensing element includes a CO2 sensor module for data transmission as well as power supply module that analyzes speed and direction of flow of the air mass within the specified measurement point.
In this work we studied a newly reported class of nonlinear effects observed in 5CB liquid crystals doped with gold nanoparticles (GNPs). The size of the GNP was determined by direct TEM imaging and by X-ray scattering of the diluted NP solution. GNPs was coated by thiols with the ratio of mesogenic to n-alkyl thiols varying from 1:2 to 1:1. The research involved comparing properties of both undoped and doped 5CB (nematic LC) by infiltrating LC cell and microholes of the photonic crystal fiber (PCF) separately. In our experiment the PCF fiber type LMA-10 made by NKT Photonics as host material has been used.
Liquid crystals over the last two decades have been successfully used to infiltrate fiber-optic and photonic structures initially including hollow-core fibers and recently micro-structured photonic crystal fibers (PCFs). As a result photonic liquid crystal fibers (PLCFs) have been created as a new type of micro-structured fibers that benefit from a merge of “passive” PCF host structures with “active” LC guest materials and are responsible for diversity of new and uncommon spectral, propagation, and polarization properties. This combination has simultaneously boosted research activities in both fields of Liquid Crystals Photonics and Fiber Optics by demonstrating that optical fibers can be more “special” than previously thought. Simultaneously, photonic liquid crystal fibers create a new class of fiber-optic devices that utilize unique properties of the photonic crystal fibers and tunable properties of LCs. Compared to „classical” photonic crystal fibers, PLCFs can demonstrate greatly improved control over their optical properties. The paper discusses the latest advances in this field comprising PLCFs that are based on nanoparticles-doped LCs. Doping of LCs with nanoparticles has recently become a common method of improving their optical, magnetic, electrical, and physical properties. Such a combination of nanoparticles-based liquid crystals and photonic crystal fibers can be considered as a next milestone in developing a new class of fiber-based optofluidic systems.
The paper presents numerical analysis compared with experimental data of influence of polymerization shrinkage on highly birefringent (HB) PANDA optical fibers embedded in a composite material. Since polymerization is a chemical process consisting in combining single molecules in a macromolecular compound [1], principal directions of the polymerization shrinkage depend on a number of the composite layers associated with this process. In this paper a detailed analysis of the piezo-optic effects occurring in HB optical fibers before and after the lamination process answers the question to what extent a degree of the material degradation can be properly estimated.
In order to measure strain independently from temperature, hybrid solution based on a polarimetric and chirped Fiber Bragg Grating (FBG) sensors is proposed. The sensor is designed in a reflective configuration, where the chirped FBG is written on a highly birefringent (HB) fiber. The FBG act as a sensing element and also as a mirror for the polarimetric sensor. Information from both polarimetric and FBG part of the sensor can be determined independently from spectral analysis of the reflected light. Strain and temperature sensitivity of the proposed sensor solution is measured. Relation between both sensitivities are different for the FBG and the polarimetric sensor. Taking advantage of this, both temperature and strain can be determined by using only one sensing fiber.
A strain sensor that operates in the intensity domain by converting the wavelength information from the fiber Bragg grating sensor, into intensity variation is presented in this paper. The fiber-optic sensor system involves a highly birefringent fiber as a demodulation system and a FBG sensor which is used for strain measurement.
Constantly refined technology of manufacturing increasingly complex photonic crystal fibers (PCF) leads to new optical fiber sensor concepts. The ways of enhancing the influence of external factors (such as hydrostatic pressure, temperature, acceleration) on the fiber propagating conditions are commonly investigated in literature. On the other hand longitudinal strain analysis, due to the calculation difficulties caused by the three dimensional computation, are somehow neglected. In this paper we show results of such a 3D numerical simulation and report methods of tuning the fiber strain sensitivity by changing the fiber microstructure and core doping level. Furthermore our approach allows to control whether the modes’ effective refractive index is increasing or decreasing with strain, with the possibility of achieving zero strain sensitivity with specific fiber geometries. The presented numerical analysis is compared with experimental results of the fabricated fibers characterization. Basing on the aforementioned methodology we propose a novel dual-core fiber design with significantly increased sensitivity to longitudinal strain for optical fiber sensor applications. Furthermore the reported fiber satisfies all conditions necessary for commercial applications like good mode matching with standard single-mode fiber, low confinement loss and ease of manufacturing with the stack-and-draw technique. Such fiber may serve as an integrated Mach-Zehnder interferometer when highly coherent source is used. With the optimization of single mode transmission to 850 nm, we propose a VCSEL source to be used in order to achieve a low-cost, reliable and compact strain sensing transducer.
Results of our research on embedded highly birefringent polymer microstructured fibers are presented. A composite material sample with fibers embedded between two layers of a multi-layer composite structure is fabricated and characterized. Temperature sensitivities of the polymer fibers are measured in a free space and compared with the
fibers embedded in the composite material. It appeared that highly birefringent polymer microstructured fibers exhibit a strong increase in temperature sensitivity when embedded in the composite material, which is due to the stress-induced changes in birefringence created by thermally-induced strain.
Polarimetric optical fiber sensors belong to phase sensors in which polarization state of the output light depends on birefringence of the fiber. In general, external stresses can change birefringence of the fibers. Hence polarimetric sensors may be used for strain monitoring inside composite materials. Length of the sensing fiber of the polarimetric sensor is relatively high, particularly when used to measure strain in composite material, thus light traveling through the sensing fiber may become depolarized and dynamics η of the sensor diminishes. In the paper it is shown that by the use of compensation, depolarization of the light passing through the sensor is significantly reduced. This allows use of less expensive and more robust light sources than laser diodes which are important when the sensor is designed to operate in harsh environment. A comparison of different light sources and sensing fibers for application in strain measurement in composite materials is presented and discussed and an influence of the lamination process on sensor dynamics is evaluated.
Composite structures are made from two or more constituent materials with significantly different physical or chemical properties and they remain separate and distinct in a macroscopic level within the finished structure. This feature allows for introducing highly birefringent polymer microstructured optical fibers into the composite material. These new fibers can consist of only two polymer materials (PMMA and PC) with similar value of the Young modulus as the composite material so any stresses induced in the composite material can be easily measured by the proposed embedded fiber optic sensors.
Silica-based HB fibers have severe limitations due to their coating layers while embedded into a composite: the hard coating layer easily transmits radial stress to the sensing fiber and changes its birefringence. Two coating layers – hard and soft – attached to the HB fiber do not influence fiber birefringence since the second (soft) layer can easily absorb any lateral force. On the other hand, a soft coating does not provide any proper transmission of the longitudinal strain. Additionally, fused-silica fibers have an upper strain limit of approximately 2% strain. In highly loaded engineering structures structural monitoring strain is becoming increasingly important. Hence, soft polymer materials used in the manufacturing process of highly birefringent microstructured polymer optical fibers (mPOFs) can solve this limitation. In this paper we present interactions between a composite material and mPOFs during the manufacturing process. The lamination process can dramatically change the group birefringence of the mPOFs. Measurements for fiber embedded in composite materials and fiber in free space were made and compared. A simple explanation of these differences is presented at the end of the paper.
The paper presents influence of the HB1500 bow-tie optical fiber coating on the fiber angular sensitivity for
dynamic stress induced by an acoustic wave. An experimental setup is explained and fiber parameters are presented,
what is a step forward to predict and simulate behavior of optical fibers embedded in composite materials. Both
sensitivities of the fiber (with and without coating) are compared versus the angle between the birefringence axis and the
acoustic wave propagation direction. An influence of the fiber coating has also been experimentally examined.
This paper presents the optimized optical fiber sensor as a device allowing real-time monitoring of rotation of industrial
machines parts such as shafts, impellers, compressors, mixers, etc. With proper configuration it is possible to
continuously monitor the rotation frequency and phase, and thus synchronize the work of separate parts of machinery.
The main principle or work is similar to standard open-head reflective sensors, but in this case head is shielded by
special protective glass and immersive layer. In the paper, response curves for the different head models were shown.
Also, the results of measuring and comparing the shape of the rotor blades were shown. Authors demonstrated sensor
ability to measure the frequency and amplitude of the additional vibration of the rotor. For comparison, we also
demonstrated a low amplitude micro-vibration measurement with a piezoelectric plate as other test object.
Fiber-optic sensors based on highly birefringent (HB) polarization-maintaining (PM) fibers represent a promising
generation of sensing devices also known as polarimetric fiber sensors. They utilize polarization (phase) modulation
within fibers to sense external perturbations [1]. HB polarimetric sensors can be made temperature insensitive but to
measure strain they require means for setting a zero strain reference. Composite structures are made from two or more
constituent materials with significantly different physical or chemical properties and they remain separate and distinct in
a macroscopic level within the finished structure. This feature allows for the introduction of an optical fiber sensors
matrix into the composite material. In this paper we present experimental evidence that the interactions between the
composite material and optical fibers during manufacturing process are very significant. The lamination process can
dramatically change the strain sensitivity of the highly birefringent (HB) fibers.
This paper is a continuation of our earlier works on remote measurement tools for supporting the research on novel photonic materials. The scope of this particular work encompasses especially a brief review of present exemplary implementations of remote access methods to measurement equipment, followed by proposing a design for a system management web-based application and related databases, selection of optimal software technologies and their implementation. Case-study for a real-time working system has been developed and proposed, which utilizes apparatus available at three collaborating laboratories located at Warsaw University of Technology and dedicated to photonics research.
In the paper we present a new method of analysis of the optical fiber Lyot depolarizer based on application of an additional depolarization matrix in the MuellerStokes equation. As a result we found that the degree of depolarization of the light coming out of the Lyot depolarizer depends not only on length and birefringence of the highly birefringent (HB) fibers used as the Lyot depolarizer but also on coherence and polarization of the light coupled into the depolarizer.
Photonic Crystal Fibers, optical fibers with regular structure of micro-holes running along the axial direction, have
ability to change their optical properties through inserting different materials into their holes. The paper presents our
latest experimental results of the influence of external electric field and hydrostatic pressure on propagation properties of
the photonic crystal fibers infiltrated with liquid crystals clearly indicating great potential for electric field and
hydrostatic pressure sensing applications. Operating range of both electric field and hydrostatic pressure sensors can be
tailored by different combination of a host photonic crystal fiber and a liquid crystal used for infiltration. Moreover, by
changing the operating wavelength different sensor responses can be obtained.
Partially temporary coherent light might be depolarized during propagation in birefringent media. The depolarization depends on coherency of light source DL, birefringence of medium Dn, and azimuth of light beam versus fast and slow axes of medium birefringence (Ex/Ey). Depolarization is caused by polarization mode dispersion, also responsible for spreading light pulses and lowering bandwidth in binary transmission in optical fibers. The depolarization of temporal coherent light is also known in liquid crystals. In this paper we present the results of investigation on depolarization of light in optical fiber structures infiltrated with a liquid crystal.
Polarization mode dispersion (PMD) in telecommunication fibers is caused by their random birefringence and depends
on temporary coherence of the light coupled into the fibers. This phenomenon resulting in light pulses broadening
decreases bite rate in telecommunication lines and is expressed in terms of differential group delay (DGD). Measurement
of the DGD can be used to estimate the value of PMD, and also for compensation of the PMD value. In this paper the
results of PMD compensation by using the Faraday rotator and a longitudinally strained highly birefringent fiber are
presented. By controlling simultaneously the longitudinal strain and the Faraday rotator current during DGD
measurements almost total compensation of PMD for a 30-km-long telecommunication optical fiber has been achieved.
The paper presents a modular fiber optic hydrostatic pressure sensing system based on a polarimetric highly birefringent photonic crystal fiber (HB PCF) operating at infrared wavelengths and utilizing a replaceable fiber-optic head, which allows simple fitting to the measured range of hydrostatic pressure. We propose also an all-fiber built-in analyzer that is based on polarization properties of the photonic crystal fiber filled with a liquid crystal. The output characteristics of the modular sensing system have been optimized in view of enhancing their measurement capabilities and in order to minimize disturbing environmental effects.
The paper discusses polarization phenomena occurring in highly birefringent (HB) photonic liquid crystal fibers based on the
Blazephotonics HB photonic crystal fiber infiltrated with a liquid crystal. We report on the latest experimental polarization
characteristics of microstructured photonic crystal fibers filled with two types of nematic liquid crystals: with low (of the
order ~ 0.05) or medium (of the order ~ 0.2) material birefringence. Electrically and temperature-induced tuning of
polarization properties have been demonstrated.
The paper presents a modular fiber optic sensing system to measure temperature, hydrostatic pressure and/or strain based on polarimetric highly birefringent fiber operating at infrared wavelengths. The main idea of such a system is a new replaceable fiber-optic head, which allows adjusting the measuring system both to the required range and type (strain, pressure or temperature) of the external measurand. The outputs of the modular sensing system characteristics have been optimized in view of enhancing their measurement capabilities and in order to minimize disturbing
environmental effects.
The paper presents construction of a simple fiber-optic color sensor designed for recognition of objects from a set comprising an a prori defined, limited number of colors. Color sensing is based on diffusive reflectivity of examined surfaces measured in several separate spectral channels. Number and positions of channels depend on predetermined set of colors. The channels are fed by selected LED's sequentially, i.e. in Time-Division Multiple Access mode. Collected serially analogue signals are converted onto digital data enabling some processing variants. In order to extend the performance capability of such a sensor and to enable measurements of others colors, a simple neural network was applied.
The paper analyzes polarization properties and presents the latest experimental results on polarization phenomena occurring in microstructrured photonic liquid crystal fibers (PLCFs) in which only selected micro holes or holes areas were filled with prototype nematic liquid crystal guest materials that are characterized by either extremely low (of the order ~ 0.05) or relatively high (of the order ~ 0.3) material birefringence. The photonic crystal fiber host structure was a commercially available highly birefringent PCF (Blazephotonics). The PLCFs under investigation have been powered by a tunable laser operating at infrared. Due to anisotropic properties of the microstructured PLCFs, switching between different guiding mechanisms as well as electrically and temperature-induced tuning of both light propagation and fiber birefringence has been demonstrated.
Microstructured optical fibers have ability to change their optical properties through inserting different materials into their holes. Filling the microstructured fibers with liquid crystals opens up a possibility of dynamic switching between different guiding mechanisms. In this paper we present the influence of electrical field on propagation properties of microstructured photonic crystal fibers filled with either low or highly birefringent nematic liquid crystals. Depending on the liquid crystal material introduced into the micro holes different propagation mechanism controlled by external electric field have been observed. This creates great potential in fiber optic sensing and optical processing application.
Selected perturbation effects on polarization mode dispersion (PMD) in highly birefringent (HB) fibers are reported. In particular, simultaneous twist and longitudinal strain effects on PMD in HB fibers have been investigated. External twist has been found to modify both modal birefringence and differential group delay (DGD) in HB fibers, and in particular to influence the range of DGD changes under longitudinal strain. These results suggest a great potential for a perspective all fiber variable-delay PMD compensator.
The paper reports on thermal and spectral effects in polarimetric fiber optic strain sensors based on new types of highly birefringent (HB) fibers operating at infrared wavelengths. Spectral and temperature characteristics of the HB fibers have been optimized in view of enhancing their sensing capabilities and in order to minimize disturbing environmental effects. Longitudinal strain sensitivity was found to be independent on both the source bandwidth and temperature.
The paper presents our latest experimental results on influence of temperature on the propagation properties of photonic
liquid crystal fibers. We used solid-core photonic crystal fibers filled either with a low-birefringence prototype 1550
liquid crystal mixture or with PCB. It appeared that direction of temperature tuning in PLCFs is strongly dependent on
thermal characteristics of both refractive indices.
Spectral and polarization properties of microstructured photonic crystal fibers filled with nematic liquid crystals characterized by either extremely low (of the order ~ 0.05) or higher (of the order ~ 0.3) material birefringence have been investigated. The photonic crystal fiber used as a host material was manufactured in Lublin, Poland and the nematic liquid crystals were introduced into the micro holes of the photonic crystal fiber by the capillary effect. Due to anisotropic properties of the obtained microstructured photonic liquid-crystal fiber, switching between different guiding mechanisms as well as novel spectral and polarization phenomena have been observed.
The paper presents the latest experimental results on influence of temperature and external electrical fields on propagation properties of a photonic liquid-crystal fiber composed of a photonic crystal fiber infilled with a nematic liquid rystal characterized by either extremely low (of the order ~0.05) or relatively high (of the order ~0.3) material birefringence. The nematic liquid crystal was introduced into the micro holes of the photonic crystal fiber by the capillary effect. Due to anisotropic properties of the obtrained photonic liquid-crystal fiber, switching between different guiding mechanisms has also been demonstrated.
In this paper propagation properties in photonic crystal fibers (PCFs) filled with extremely low-birefringence nematic liquid crystal (LC) mixtures have been investigated. The low-birefringence nematic LC compositions included multicomponents esters mixtures and were characterized by extremely low ordinary no = 1.46-1.45 and extraordinary ne = 1.478-1.505 refractive indices at room temperature. Due to reorientation possibilities of nematic molecules within the fiber holes, propagation properties of the obtained photonic liquid crystal fibers could be easily modified.
The paper discusses influence of longitudinal strain on polarization mode dispersion in highly birefringence fibers. It appeared that polarization mode dispersion could be diminished owing to longitudinal strain. The compensating configuration based on dynamically induced longitudinal strain in the HB bow-tie fiber was proposed.
Polarization maintaining photonic crystal fibers constitute a new class of birefringent optical fibers with strong separation of polarization modes and large possibilities of tailoring different parameters. These advantages appear to be perfect for designing optical fiber sensor, so we decided to test this type of fiber. A plane-wave method was used to numerically calculate the effective refractive indices and the field distribution of the propagation modes. The simulation results were compared with experimental measurements of the birefringence and finally the fiber was experienced as a sensor with fully automated set-up. The verification of temperature sensitivity simulations was performed too.
Polarization-maintaining highly birefringent (HB) photonic crystal fibers (PCFs) are a completely new range of optical fibers potentially offering new polarization properties and possibilities. In this paper, we discuss polarization properties of HB PCFs and present initial experimental data. A novel experimental method has been adapted for beat length measurement in various HB fibers.
Polarization mode dispersion (PMD) is a major limitation in optical fiber transmission systems. The paper presents a new method of PMD compensation based on the use of highly birefringent (HB) bow-tie fibers. The method relies on the application of dynamically induced longitudinal strain that modifies differential group delay (DGD) responsible for effective PMD compensation.
Initial results of fiber-optic non-invasive sensing of ignition and combustion process in the inner combustion engine are presented. An optical signal from a polarimetric fiber sensor is studied. Optical sensing is immune to high voltage of the ignition system and to some extent to temperature gradients arising close to the engine.
Initial results of study a lateral stress, static and dynamic, on a light propagation in a high birefringent fiber are presented. A permanent birefringence in optical fiber arises due to large thermal stress in the core. Ambient parameters like temperature and hydrostatic pressure influence the stress anisotropy and thus the light propagation. The parameters can be assumed as uniform and the optical response does not depend on the position of the fiber birefringent axes. For a stress (lateral pressure) the optical response of a fiber reveals an azimuth dependence on mutual direction of an exerted pressure and birefringent axes. With dynamic perturbation, even slowly varying, some additional effects like strain can not be avoided. The effective optical response is composed and strongly depends on the direction of stress.
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