limited by ﬁber attenuation . The use of ampliﬁcation inthe loop has been suggested as a potential method for extending loop length, enhanc- ing detection sensitivity , but ampliﬁcation inthe interferometer would lead to non-reciprocity inthe Sagnac loop, with small variations in gain causing nonlinear phase diﬀerences between the interfering beams. In this regard, the use of a distributed Raman ampliﬁcation scheme seems partic- ularly promising, thanks to the improved noise performance oﬀered by dis- tributed ampliﬁcation in comparison to lumped ampliﬁer solutions, which would allow the use of relatively low signal powers  andthe minimiza- tion of the potential impact of nonlinear phase diﬀerences. The possibility of using Raman ampliﬁcation to improve the sensitivity of a ﬁber-optic gy- roscope (FOG) was ﬁrst proposed in 1988 by Desurvire et al. , who showed that distributed gain could be used to increase the number of signal recirculations in a relatively short (1200 m), polarization maintaining loop. Over the years, other possibilities have also been considered, such as the use of erbium-doped ﬁber ampliﬁcation within the reentrant path [109, 110], leading to a 6.56-fold increase in rotation response factor in a 200 m gyro- scope. All of these solutions have been always considered inthe context of relatively short gyroscopic sensors, possibly under the assumption that the amount of gain required to compensate losses in a much longer setup would bring with it a larger signal nonlinearities and non-reciprocity inthe loop. As we will see, many of such expectable diﬃculties can be undercut by the use of advanced distributed ampliﬁcation schemes, including those based on ultra long and Random distributed feedback ﬁber lasers.
Wave propagation inoptical fibers is described by a G-NLSE whose particular form depends on the physical effects considered: higher-order dispersion, Raman scattering, background losses, etc. One of the most efficient algorithms to solve G-NLSEs uses the Split- Step Fourier Method (SSFM) . Four recent publications [2-5] focus on the optimization of this method in modeling optical-fibers communications systems. The approaches of these works are quite different. In Ref.  the authors focus on the accuracy and efficiency of different spatial step-size selection criteria. In Ref.  is shown that the fourth-order SSFM scheme provides more efficiency and accurate solutions than the first- and second-order schemes. In Ref.  the authors study the optimization of the simulations involving non- uniformly time-sampled optical pulses employing a novel numerical algorithm (instead of the well-known SSFM), the Split Step Spline Method. Finally, in Ref.  the authors propose a predictor-corrector technique to accelerate SSFM, whose advantage is to retain information on the approximate solution at each of the mesh points z 0 , ,z 1… z j before the approximation at z j+1 .
5. J. Hu, C. R. Menyuk, L. B. Shaw, J. S. Sanghera, and I. D. Aggarwal, “Raman response function and supercontinuum generation in chalco- genide fiber,” in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference andPhotonic Applications Systems Technologies, (Optical Society of America, 2008), p. CMDD2. 6. J. Hu, C. R. Menyuk, L. B. Shaw, J. S. Sanghera, and I. D. Aggarwal, “Maximizing the bandwidth of supercontinuum generation in as_2se_3 chalcogenide fibers,” Opt. Express 18, 6722 (2010).
tion in terms of maximum reach for both unrepeatered and long-haul multichannel coherent transmission systems [82, 83, 84] using advanced modulation formats in combination with nonlinearity compensation techniques such as digital back propagation or optical phase con- jugation [76, 85]. However, extended reach comes at the cost of an increase in required pump power and, more importantly, is limited by the RIN transferred from the FW pump to the signal. In fact, assuming that the SPV is sufficiently low and that deterministic fiber non- linear effects generated during the transmission can be entirely compensated for, the RIN transferred from fiber pump lasers to the signal becomes the most problematic effect when the use of symmetric bidirectional pumping is needed (i.e. in an OPC-based system ) or, in wider terms, whenever a certain amount of FW pump power can be beneficial to reduce SPV and improve OSNR [66, 87]. Nevertheless, recent works [88, 89] have shown that rDFB amplifiers can be suitable for overcoming RIN impairments enabling transmission distances up to 7915 km for a 10 x 116 Gbps DP-QPSK long-haul system by removing the FBG at the input side of an URFL, thus essentially transforming a Fabry-Perot-like closed cavity into an half-open cavity, at the expense of an additional reduction of the FW pumping efficiency.
Nowadays, opticalfiber sensors are substituting traditional sensors based on electronic platforms, since they demonstrate the advantages of small size, low power consumption, lightweight, immunity to electromagnetic interference, very high sensitivity, long distance between signal generation and detection (remote operation) and capability to withstand either corrosive and high temperature environments [2, 3]. Many types of sensors also show additional advantages, such as the capability of multiplexing several sensors on a single fiber or the use of simultaneous monitoring systems for more than just a few sensors in operation. A number of approaches have been adopted inopticalfiber sensors to measure changes inthe external environment, such as evanescent field effects, taper effects, Bragg resonances, and multimode interference (MMI) [4, 5, 6]. Among them, sensors based on fiber Bragg gratings have been commonly applied for a wide variety of measurements because of their particular advantages .
PCs can be realized in two different schemes as dielectric rods in air or air holes etched into a dielectric medium. The advantage of the first scheme is that waveguides created by removing a row of holes are single-moded. Therefore, as opposed to “holes in dielectric” scheme, higher order modes cannot be excited at discontunities, such as bends. Highly efficient 90ᵒ bends can be designed in these systems. For example, a 90ᵒ waveguide bend with 95% transmission is reported in square array of dielectric rods . However, “rods in air” scheme does not provide sufficient vertical confinement as “holes in dielectric” scheme and its practical feasibility into opticaldevices is difficult. In “holes in dielectric” scheme, light can be guided through the line-defect by PBG effectandinthe vertical dimension by total internal reflection. It is well known that among different lattice types, triangular lattice of air holes in dielectric medium provide the largest TE PBG .
Multihole capillaries are another type of emerging structures in chemical-sensing devices. They are similar in structure to MOFs, however, their designs are made for sensing purposes only, and thus the guiding principles of optical fibers are not the key parameters in these struc- tures. However, the advantages of their internal structures, similar to MOFs, are employed for high surface-to-volume ratio compared to traditional systems, minimal sample in- troduced, or low diffusion of the samples. Aouani et al. designed a bundle consisting of 6000 individually cladded optical fibers, 50 cm in length, in which polystyrene micro- spheres were deposited in one of the extremes for remote FCS. Alexa Fluor 647 was employed as analyte probe. The intrinsic background fluorescence limited the LOD to 400 nM . Guo et al. employed multihole capil- laries as platforms for ultrasensitive optofluidic SERS de- tection. Metallic nanoparticles were inserted into the wall of the inner holes, and two configurations were proposed. Figure 17A depicts the schemes of both designs. The first, based on transversal detection, andthe second on longitudi- nal detection. The transversal-detection configuration pro- vides inline SERS detection for real-time measurements, whereas the longitudinal-detection configuration accumu- lates theRaman signal along the capillary obtaining high sensitivities. Contrary to the longitudinal detection in HC- PCF, where only the sample injected inthe core interacts with the confined light from a laser, in a multihole capil- lary there is no light confinement and therefore each chan- nel can act independently, increasing the surface area. In addition, all wavelength can be used as there is no need for light confinement. Comparing these structures to SC- PCF, a higher light–matter interaction was achieved, as for the SC-PCF most of the light is confined inthe solid core and only the evanescent field interacts with the aque- ous sample from the surrounding holes of the microstruc- ture. Finally, short lengths were necessary for the multihole capillaries (3 mm) compared to PCFs (usually tens of cm). A multihole capillary with 2700 channels and 117 nm of gold nanoparticles was employed to detect rho- damine 6G molecules, obtaining LODs of 1 × 10 –5 nM. Au
received signals are naturally ﬁltered by the transmission scheme and no electronic ﬁlters were used. Inset (a) in Figure 6, illustrates the multiplexed 6.8 and 8.25 GHz subcarriers. The system ﬁltering effect is observed as the modulated spectra are conﬁned around the center microwave frequencies. The laser noise level is at least 20 dB below the 6.8 GHz subcarrier level. As the 8.25 GHz subcarrier is the strongest signal, it has been chosen for demodulation to base-band by homodyne mix- ing, Figure 7. The graphs show the main lobes of the data sig- nals, which can be recuperated by further signal processing. Theoptical link introduced an attenuation equivalent to 30 dB. The received optical signal was ampliﬁed and compared to the elec- trical microwave subcarrier after this one was attenuated by 30 dB. This comparison is illustrated in Figure 7(a), where both electrical andoptical signals show the same spectral distribution. To recuperate the base-band digital data, the 8.25 GHz subcar- rier was detected by synchronous homodyne mixing. In this stage, the received 8.25 GHz data-modulated subcarrier was mixed with an 8.25 GHz signal from a local oscillator. The resulting signal is the 34 Mbps base-band data stream, as depicted in Figure 7(b). The base-band signal was not further processed as this aspect was beyond the scope of this article. Work is in progress for integrating a complete data receiver [by adding the dashed line blocks in Fig. 7(b)], to evaluate the sys- tem performance, including parameters such as SNR, the BER, the dispersion power penalty, and so forth.
This thesis deals with the analysis of the nonlinear phase noise in NLDFCs and a noveloptical nonlinearity compensation technique to partially mitigate SPM in OFC systems. In general, in this thesis the SCF fundamentals and limits as the guided modes characteristics, nonlinear phase noise, SPM, supercontinuum generation, andthe size effects of thefiber cores are revisited and extended to a NLDFC, as the simplest MCF coupler, described as a collection of two coupled SCFs. In this sense, a NLDFC is used to study the impact of the linear coupling on the nonlinear mechanisms as SPM and nonlinear phase shift, including the situation when the incoming signal is noisy. We show that the simpler setup of a NLDFC gives more fundamental information and physical insight about theeffect of the linear coupling on the nonlinear mechanisms as SPM and nonlinear phase noise instead of using more complex MCFs.
However, there have been recent renewed interest and efforts because of the need to solve critical bottlenecks inoptical communication systems. For example, the electro-optic and opto- electronic conversions that limit the overall performance, or the nonlinear optical processing functions required to handle complex optical signals in sophisticated ways, are presently critical problems. In addition, potential applications in fields such as bio-medicine (nonlinear imaging, diagnostics), sensing (femtosecond light pulse interrogation), instrumentation (ultra-fast real time measurements), computing (quantum optics) or fundamental science (photon storage) are attracting researchers’ and engineers’ attention. More specifically, nonlinear opticaldevices, either directly fiber-based or implemented in integrated photonic version in various material systems (e.g. semiconductors), offer a potential for establishing higher-level processing as well as sensing functionalities; functionalities that go well beyond basic functions such as straight sensing of a physical quantity, multiplexing multichannel signals, or direct modulation and demodulation. Examples of expected functionalities implemented with noveldevices are optical mixing, wavelength conversion, optical limiting, broadband traveling-wave-type modulation, tunable and adaptive filtering, wide tunable lasers, semiconductor femtosecond lasers, smart optical sensing, optical switching, andoptical storage.
Management and nutrition of animals grazing on native grass (graminaceae Holcus, Bromus, Dactylo, Poa and Lolium; and legumes, Trifolium and Vivia, to a lesser extent) is the traditional sys- tem for mothers and herds over 4 months old, us- ing little balanced supplementation in adults, and some grain stalks (oat, barley, maize). Supple- mentation with zinc and selenium, as additional minerals inthe diet was offered to measure their effects on height at the withers, weight, alpaca fi- ber diameter, and residual effects on blood, stools and urine.
The demand for fast distributed acoustic sensing (DAS) over long ranges, for applications such as non-destructive evaluation of large structures, early detection of damage or surrounding environmental activity, or detection of intrusions over large perimeters, has propelled a recent trend of renewed interest towards Rayleigh-based techniques , , , particularly phase-sensitive (φ)OTDR. Since this technique avoids the need for the previously mentioned averaging due to the moderately high SNR achievable using single-shot data, the sampling rate is ultimately limited by the time-of-flight of the light signal inside thefiber, thus allowing sampling rates as high as 1 kHz for lengths as large as 100 km. Although extremely powerful, conventional schemes of φOTDR present important shortcomings, i.e., they are severely limited by power trace fading points and fail in providing even SNR along the sensing fiber. Recently, a novel interrogation method has been proposed by Pastor-Graells et al. , which addresses both problems in a conventional single-mode fiber with minimal alterations to the conventional setup, i.e., by simply introducing a linear chirp to the propagated light pulse.
Here we review our recent work on chirped-pulse ΦOTDR systems . These systems use linearly chirped pulses in a ΦOTDR to achieve a frequency-to-time mapping of thefiber response over long lengths andin a single-shot. The technique uses only intensity detection, and no frequency scan or local oscillator is needed. The system does not present fading positions unlike the phase-measuring ΦOTDR. With the proposed method, it is possible to combine the best features of ΦOTDR which had been previously demonstrated by separate: fast measurements with a bandwidth only limited by thefiber size, and measurement of temperature/strain variations with resolutions which can be several orders of magnitude below those provided by e.g. Brillouin. Since the measurement is relative, the total range of temperature/strain variation is in principle not limited, being in practice determined only by how the cumulative errors are handled. The technique allows measurements at kHz rates, while maintaining reliability over several hours. The sensitivity can also be tuned by acting on the chirp of the pulses. Temperature/strain resolutions of mK/(4n ε ) have been readily demonstrated.
The interferometer has been encapsulated between two ITO-coated glasses using SMFs as spacers. In this way, an electric field across the fibers may be applied by applying voltage to the ITO electrodes. Both glasses have been preconditioned to anchor the LC molecules parallel to the surface in absence of an electric field. When a field is applied to the cell, the LC molecules will reorient to become parallel to the field (i.e., perpendicular to the glasses). Upon reorientation the LC intends to reach a minimum energy state that depends on the field strength andthe anchoring force that try to keep the molecules parallel to the substrates. This reorientation can be therefore modulated, making it possible to modify the effective refractive index ‘seen’ by the evanescent field of the propagating light waves.
A study was conducted in 2011 to determine the mechanical properties, especially the flexural strength, of a restorative material combining ceramic and BG. Leucite porcelain (k) was used at between 50 and 70%, and it was found that it is possible to obtain a material with appropriate mechanical properties without losing bioactivity. Mechanical properties improve as the content of ceramic inthe material increases (46) . Later studies concluded, despite the limitations of in vitro research, that the ideal composition for good mechanical properties without losing bioactivity is 20% of BG and 80% ceramic (27) . An interesting aspect of this composite material would be the potential formation of a gingival attachment around full-crown restorations, facilitated by the bioactive behavior and its composition, which is similar to tooth enamel. This attachment would seal the tooth-restoration interface, thus eliminating the potential for dissolution and degradation for the cement used for fixation, recurrence of caries and a possible restoration failure (46-47) .
Telemedicine, defined by the World Health Organization as ‘integrative part of telecommunica- tion systemsinthe promotion of public health’, generates different positive results: more efficiency, less costs, better patient’s quality of life. Thanks to the advances in diagnostic technologies, infor- mation technologies, remote monitoring and long-distance care, telemedicine have increased the viability of home-based care, even for patients with serious conditions. At the same time we observe the increase inthe elderly population suffering from pluripatologyand chronic diseases, that causes an increasing recourse to medical and hospital care; but prolonged hospital stay can determine loss of function and psychophysical disorders. Telemedicine is ‘the investigation, monitoring and man- agement of patients and education of patients and staff using systems which allow ready access to expert advice and patient information, no matter where the patient or relevant information is locat- ed’. We are empowering in different areas new biomedical and information technology as a support to clinical practice. The goal is to make a case study and to use for future analysis. Inthe experi- mental phase 4 patients were followed on hemodialysis and 4 in peritoneal dialysis, previously eval- uated for clinical, social, logistical and psychological conditions. It is estimated that today there are 50.000 patients on dialysis and about 10.000 new cases a year only in Italy. Naturally there are threats to solve because users face difficulties, in terms of interaction with robots, in their usual con- text of life.The right methodology needs to coordinate the entire hospital, different professionals, patients, providing tools for care givers that follow patients, training technicians, aligning data col-
On the other hand, thin films of polyaniline (PANI) and polypyrrole (PPy) have been shown to respond to pH and to the redox state of a solution, thereby undergoing spectral changes inthe visible and near infrared. They also may serve as a matrix for enzyme immobilization. PANI films are easily prepared, and spectral changes depending on analyte concentration occur at wavelengths at which low cost lasers and LEDs are available. PANI and PPy are conductive organic polymers that can be driven between different oxidation states by chemical or electrochemical methods. PANI has two redox equilibriums associated with the polymer chain, andtheoptical properties of the polymer are functions of the state of protonation andthe oxidation state. Since protons and electrons are directly involved inthe polymer redox reaction, changes inoptical spectra (e.g. absorbance) can be attributed to the concentration of protons or the number of electrons produced in an enzymatic reaction. PANI films of good optical quality can be produced by chemical means on almost any desired support including polystyrene, polycarbonate or glass. However, both opticaland electrochemical PANI sensors tend to drift (in terms of conductivity or absorbance) inthe order of 1% of the background signal per day. This makes daily recalibration necessary prior to measurements. Microtiterplates (micro-well) assays offer an alternative to conventional sensing because calibrators can be placed in one or more wells while actual assays are performed inthe residual wells. This is one of the reasons why micro-well assays are commonly employed in routine analysis. In this way, a technique for coating the wells of microtiterplates with polyaniline layers and with polyaniline/enzyme layers is presented by Piletsky et al. . The resulting wells are shown to be useful for assaying enzyme substrates (as exemplified for glucose via pH) and hydrogen peroxide (via the redox properties of the film). Analyte detection is based on monitoring the absorption spectra of the polyaniline, which turn purple as a result of redox processes, or green on formation of acids, by enzymatic reactions. Hydrogen peroxide (a species produced by all oxidases) and glucose (which yields protons on enzymatic oxidation) have been determined inthe millimolar to micromolar concentration range.
In 1959 Richard P. Feynman gave a lecture at an American Physical Society meeting at Caltech called There’s plenty of room at the bottom . In his talk, Feynman discussed the possibilities derived from designing devicesin progressively smaller and smaller scales and envisaged great advances in science and technology when we were able to accurately manipulate atoms themselves. He was aware of the implicit advantages of miniaturization regarding not only the reduced size of thedevices or their portability, but also their faster operation speed, lower raw materials requirements and cost. In short, Feynman tried to inspire physicists and engineers to reach the submicroscopic scale, as he called it. Fifteen years had to pass before Norio Taniguchi ( 谷口紀男) coined the word nanotechnology in 1974 .
achieved by the use of two concepts. The first one, Physical Device, defines each device or system using its control specific characteristics. The second one, Logical Device, is used to group and control different devices by their common functionalities or physical location. For instance, the set of lights which are located closer to a window can be controlled altogether independently of the rest of the lights within the room, by creating a Logical Device for them. Logical and Physical Devices are associated to one or more Parameters. Each Parameter represents a physical quantity or state (such as temperature, brightness level or on/off state) which can be directly modified by these devices. Technology Manager provides a way for external applications to interact with Parameters (i.e. physical magnitudes within the building) instead of over Physical or Logical Devices, abstracting the specific function details of each device.