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We propose a power-over-fiber system with a new photovoltaic converter voltage control technology consisting of intermittent operation of a light source based on capacitor voltage estimation to achieve high energy efficiency. This efficiency is made possible by ensuring the photovoltaic converter voltage stays within an appropriate range. However, detecting and controlling the voltage on the photovoltaic converter side would waste power. In our system, a controller on the light source side estimates the voltage of photovoltaic converter side from our circuit model and controls the photovoltaic converter voltage by controlling light source activation/deactivation. Therefore, it is possible to maintain high photoelectric conversion efficiency without wasting power on the photovoltaic converter side. We show that this method can significantly improve energy efficiency from 11.0% to 22.4% compared to a method that controls the voltage on the photovoltaic converter side. We also demonstrate that an optical switch with a power consumption of 130 mW can be driven with 5-mW optical input. Our power-over-fiber system is practical because its optical power is low and safe enough to be used in existing optical access networks.

In this paper, to the best of our knowledge, a new type of hollow-core anti-resonant fiber (HC-ARF) design using hybrid silica/high-index material (HIM) cladding is presented for single-polarization, high-birefringence, and endlessly single-mode operation at 2 μm wavelength. We show that the inclusion of a HIM layer in the cladding allows strong suppression of $x-$polarization, while maintaining low propagation loss and single-mode propagation for $y-$polarization. The optimized HC-ARF design includes a combination of low propagation loss, high-birefringence, and polarization-extinction ratio (PER) or loss ratio of 0.02 dB/m, 1.2 $\times \, 10^{-4}$, and >550 respectively, while the loss of the $x-$polarization is >20 dB/m. The proposed fiber may also be coiled to small bend radii while maintaining low bend-loss of $\approx$0.01–0.1 dB/m, and can potentially be used as polarization filter based on the different gap separations and bend conditions.

We experimentally investigate the problem of monitoring the Kerr-nonlinearity coefficient $\gamma$ from transmitted and received data for a single-mode fiber link of 1600 km length. We compare the accuracy and speed of three different approaches. First, a standard split-step Fourier method is used to predict the output at various $\gamma$ values, which are then compared to the measured output. Second, a recently proposed nonlinear Fourier transform (NFT)-based method, which matches solitonic eigenvalues in the transmitted and received signals for various $\gamma$ values. Third, a novel fast version of the NFT-based method, which only matches the highest few eigenvalues. Although the NFT-based methods do not scale with link length, we demonstrate that the SSFM-based method is significantly faster than the basic NFT-based method for the considered link of 1600 km, and outperforms even the faster version. However, for a simulated link of 8000 km, the fast NFT-based method is shown to be faster than the SSMF-based method, although at the cost of a small loss in accuracy.

The lack of access to broadband services and speeds that allows urban and rural populations to meet the minimum requirements of today’s society creates a lack of economic opportunities and digital inequality. In contrast, regions with adequate broadband infrastructure can attract investors and become the home of tech workers while boosting the local economy. To level the field and promote the expansion and improvement of broadband infrastructure, federal and state agencies in the U.S. provide funding through programs such as the Rural Digital Opportunity Fund, and The Enabling Middle Mile Broadband Infrastructure Program among others. Here, counties assess their broadband infrastructure, identify the funding opportunity, and compete for that funding by submitting grant applications. In this research paper, we present the problems, challenges, and lessons learned during the process of assessment of the broadband infrastructure for Polk County, Florida, USA. In addition, connectivity technologies and physical layer options for broadband internet infrastructure were reviewed and we present our recommendation in terms of technology for the upgrading and expansion of the current network. In particular, we discuss the challenges in determining actual network coverage by contrasting official data of the Federal Communications Commission (FCC) with several crowd-sensing datasets such M-Lab (Measurement Lab), Ookla Open Datasets, and results from the Polk County community broadband survey. We discuss the advantages and limitations of using these publicly available datasets and open-source tools. Finally, we provide guidelines and best practices in terms of data analysis and visualization that may be used by city planners and researchers.

A novel setup for a Double-Taper Mach-Zehnder Interferometer (DTMZI) is presented to measure axial strain and torsion. An epoxy section is added between the two tapers as a fixture to ensure torsion sensing. The modal filtering effect of the epoxy upon the interferometry response is experimentally verified. The transmission spectrum of DTMZI under strain and torsion is modelled and further analyzed through the differential accumulated phase between the beating modes.The experimental spectral observation confirms our estimate. The relationships between the spectral shifts in wavelength and applied displacements are obtained. The sensor shows a very high sensitivity against the applied strain and twists. [ABSTRACT FROM AUTHOR]

A novel interrogation method is presented in the application of strain sensing with a double taper Mach-Zehnder interferometer (DTMZI). The proposed sensing setup comprises a laser source and an optical power meter, which significantly lowers future integration cost and complexity. An analytical coupling model is established to study the sensor's strain-related modal behaviour. The design parameters of the DTMZI device are conditioned to satisfy a single-wavelength measurement. The spectral responses of several fabricated sensors are examined. Our experiments confirm the direct mapping between different strain values and particular transmission measures for the single wavelength case. [ABSTRACT FROM AUTHOR]

Ascorbic acid (AA) works as an antioxidant and plays a key role in the regulation of immune system and health maintenance. Low level of AA causes disease like scurvy whereas, its higher-level induces stomach throes in human body. So, for the detection of AA, a sensitive sensor probe is fabricated by splicing a short section of highly germanium (Ge)-doped photosensitive fiber (PSF) to a single-mode fiber. In the present study, PSF’s core is easily expanded by etching with hydrofluoric acid because PSF’s core is 5-times Ge-doped. It also helps in partial removal of cladding. Thereafter, gold nanoparticles (AuNPs) are immobilized over the sensing probe for localized surface plasmon resonance (LSPR) phenomena. Further, graphene oxide (GO) is decorated over the AuNPs-coated sensor probe. The AuNPs and GO helps to increase the sensitivity and biocompatibility of sensor probe. Ascorbate oxidase from Cucurbita species has been used to increase the specificity of the sensor. The developed sensor probe has been characterized by the UV-Visible spectrophotometer, high-resolution transmission electron microscope (HR-TEM), TEM - Energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), field emission scanning electron microscope (FE-SEM), and SEM-EDS. The sensor exhibited a wide linear range of detection from $1~\mu \text{M}$ to 1 mM, with 3.5 %/mM of sensitivity. A detection limit of proposed sensor is found to be $15.12~\mu \text{M}$ , which is lower than the physiological AA level in serum of healthy human body (40 – $120~\mu \text{M}$). The selectivity of sensor probe has been verified by performing the experiments with various other biomolecules present in serum. The proposed LSPR sensor has many advantages such as low cost, less fragile probe, remote sensing, low electromagnetic interference, online monitoring, detection from micro-droplets, low detection limit, fast response, highly sensitive, and high specificity. [ABSTRACT FROM AUTHOR]

Fabrication and experimental validation of a newly developed copper oxide nanoparticles (CuO-NPs) and silver nanoparticles (AgNPs) immobilized SM-MM-SM-MM-SM (SMSMS) in-line Mach–Zehnder interferometer (MZI) fiber structure-based sensor using localized surface plasmon resonance (LSPR) technique are reported in this article. The AgNPs and CuO-NPs are used to improve the biocompatibility and sensitivity of the sensor. The nanoparticles (NPs) and immobilized probe were characterized by UV-Vis spectrophotometer, HR-TEM, SEM, and EDX, revealing superior performance over the existing uric acid (UA) sensors. The proposed optimized structure-based optical fiber sensors (OFSs) exhibit excellent specificity, sensitivity, and limit of detection (LoD) for the detection of UA. Moreover, the developed sensor exhibits linear profile over a very wide range: 1) $10~\mu \text{M}$ –1 mM for detection over UA presents in serum, while the normal range of UA in serum is 100– $400~\mu \text{M}$ and 2) 0.4–10 mM for detection over UA presents in urine, while the normal range of UA in urine is 1.5–4.4 mM. In addition, the developed sensor has a distinguished advantage, such as multicompatibility over the detection of UA presents in both serum and urine along with its high selectivity, reusability, reproducibility, and lowest LoD. The proposed AgNPs and CuO-NPs immobilized and the uricase functionalized SMSMS structure-based LSPR sensor has better compatibility and are potent candidates for medical applications. [ABSTRACT FROM AUTHOR]

A label-free highly sensitive tapered Single-Mode-Multimode-Single-Mode (TSMS) structure-based optical fiber sensors (OFSs) is presented in this study for the detection of L-cysteine (L-Cys). Well studied biocompatible nanomaterials (NMs) including silver nanoparticles (AgNPs) and graphene oxide (GO) were synthesized and immobilized over the surface of the sensing probe using self-assembly method. Configurations involving the excitation of localized surface plasmon resonance (LSPR) phenomena proposed in the work are investigated in detail. Further, a comparative study with tapered multimode fiber (TMMF) OFSs and pioneering investigations on previously reported sensors in this area over the last few years (notable advances only) is also presented in this study. The characterization of NMs and sensing probe are observed using in house high-resolution transmission electron microscope (HR-TEM), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), and atomic force microscopy (AFM) facilities. The proposed method improves the performance of the L-Cys in various fronts, namely: (i) sensitivity, (ii) linearity range, (iii) correlation coefficient, and (iv) limit of detection (LoD). The calibration curve is found to be linear over the range of 10nM to1 mM with an LoD of $63.25~\mu \text{M}$ and sensitivity of 7.0 nm/mM for the proposed TSMS/AgNPs/GO/OFSs. [ABSTRACT FROM AUTHOR]

This study presents a label-free and efficient method for the diagnosis of collagen-IV by using an optical fiber-based Mach-Zehnder interferometer (MZI) structure. The structure of MZI is fabricated by splicing a 2.3 cm long segment of single-mode fiber (SMF) between two ~ 45 cm strands of multi-mode fibers (MMF). Owing to the mismatch of core diameters, cladding of SMF guides the light. SMF’s cladding is partially etched by using 40% hydrofluoric (HF) acid so that a part of propagating energy is released that can interplay with the surroundings. The etched region is immobilized with ~ 10 nm size of gold nanoparticles (AuNPs) and ~ 50 nm size of copper oxide nanoparticles (CuO-NPs) to initiate the influence of localized surface plasmon resonance (LSPR) phenomenon. For a comparative study, two different probes are developed and analyzed. In one probe, CuO NPs are immobilized over the etched part of SMF and named as CuO-NPs probe. In other probe, a monolayer of AuNPs is sandwiched between fiber surface and CuO-NPs and termed as AuNPs/CuO-NPs probe. The characterization of NPs and developed sensor probe are performed using UV-Vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), and energy distribution spectroscopy (EDS). The sensor probes are made very specific towards collagen-IV by functionalizing them with collagenase enzyme obtained from Clostridium histolyticum. A wide range of Collagen-IV solutions of concentrations from 2 $\mu \text{g}$ /ml to 40 $\mu \text{g}$ /ml are sensed through the collagenase functionalized probe. The specificity of the probes are analyzed by sensing other biomolecules present in the human body. [ABSTRACT FROM AUTHOR]

A fiber refractometer with large dynamic range from 1.316 to 1.61 RIU has been realized using a hybrid configuration of a single-mode fiber (SMF) coupled to a stripped-cladding multimode fiber (MMF) as sensing element. An extended analysis of the diffraction principle of a Gaussian beam is specifically developed for this sensor configuration to determine the injected power density into the MMF which, when subsequently combined with ray optics, analytical wave optics and Fresnel equations, enables the sensor response to be comprehensively estimated. Simulation results have been experimentally corroborated to very high agreement for a 2-cm and a 5-cm decladded section of multimode fiber used as the sensing element. The results show, for the shorter sensor (2 cm), a very high sensitivity of ~ −250 a.u./RIU being achieved in the Zone II operating regime, i.e. for indices between the cladding and core indices together with a resolution of $2.76\times 10^{-{6}}$ RIU being attained. In addition, the developed models have been used to accurately predict the response of sensing elements of various lengths, hence demonstrating the potential capability of this research to be exploited for optimizing bespoke design of fiber refractometers of any arbitrary sensing lengths or dimensions. As an example, we present the design of a refractometer achieving a maximum sensitivity of 300 a.u./RIU with a potential resolution of $2.26\times 10^{-{6}}$ RIU. [ABSTRACT FROM AUTHOR]

A newly developed localized surface plasmon resonance (LSPR) phenomenon-based cholesterol (Cho) sensor is reported in this article. Functional test of the proposed sensor over an ultra-wide-range of Cho concentration (0.1–10 mM) which covers the Cho concentration in human serum (∼5.17 mM), revealing great performance is executed. Further, different structures such as multimode-photosensitive-multimode (MPM) and single-photosensitive-single (SPS), also called core mismatch fiber structure are presented here for the effective detection of Cho. The proposed sensors are immobilized with different sizes of gold nanoparticles (AuNPs) (∼10 nm and ∼30 nm) followed by zinc oxide NPs (ZnO-NPs). The characterization and functional test of nanomaterials (NMs) and immobilized probes are observed using a UV-Vis spectrophotometer, HR-TEM, AFM, SEM, and EDS. A noticeable improvement is recorded in the all-important sensing parameters of proposed sensors, such as i) sensitivity (0.6898 nm/mM), ii) linearity (0.1–10 mM), iii) limit of detection (LoD) (0.6161 mM), and iv) correlation coefficient (0.9754) on the course of the immune binding of Cho to a specific cholesterol-oxidase (ChOx) functionalized probe, exhibiting great potential for future practical applications. [ABSTRACT FROM AUTHOR]

An optofluidic chip of the single-mode fiber variable optical attenuator (VOA) is proposed. This chip has a simple structure, and it utilizes microfluid and air to regulate the optical attenuation, where air acts as a shutter. Here, the single-mode characteristics of the VOA chip are discussed at 1310 nm and 1550 nm. The experiment results indicate that it is feasible to regulate optical attenuation using the proposed chip. The VOA with this chip has a large optical attenuation range (82 dB) and a very wide operation waveband from visible to near infrared wavelengths. The measured insertion loss is 0.68 dB at 1310 nm and 0.92 dB at 1550 nm, and the measured return loss is 47.8 dB at 1310 nm and is 47.67 dB at 1550 nm.

The combination of 850 nm vertical-cavity surface-emitting laser (VCSEL) with standard single-mode fiber (SSMF) presents an effective and low-cost interface to increase the reach provided by multi-mode fiber links. At 850 nm, SSMF propagates two modes, and in this study, it has been experimentally shown that the different commercially available SSMF's present dissimilar values of differential mode delay. To cope with this unequal behavior of modal dispersion, we propose a scheme based on bidirectional decision feedback equalization (BiDFE) to overcome limited performance of other solutions as mode filtering or classical equalizers. A single span SSMF cabling model, including a measurement-derived statistical characterization of optical connectors, is simulated to evaluate the reach provided by the equalizer attending to both the conditions of the fiber excitation and the characteristics of the VCSEL. A minimum 1.45 km link length at 10 Gb/s is achieved if a linear combining BiDFE (LC-BiDFE) equalizer is included in the receiver, whatever laser launching condition and employing a single-transverse mode VCSEL. If a multi-transverse mode VCSEL is used, the reach provided by LC-BiDFE is slightly reduced but assuring a minimum coverage of 1.15 km. [ABSTRACT FROM PUBLISHER]

We present a novel fiber tip thermometer based on a compact fiber interferometer structure. The sensor tip is formed by splicing the end of two abreast conventional single-mode fibers (SMFs) together, one SMF as the lead-in fiber and the other as the lead-out fiber. Through controlling the splicing parameters, a series of sensor tips with different shapes were made. Due to fiber end enlargement induced by discharge, the coupling occurs between two parallel fiber cores. In addition, the light reflected by the fused end face can be coupled back the fiber core, where the core–core coupling light interfere with the reflected light. Therefore, the different optical paths of the lights form a modal interferometer. A sensor prototype is fabricated and temperature sensing is realized by measuring the wavelength shift of the resonance dips in the reflection spectrum. In the temperature range of 60 °C–300 °C, the corresponding temperature sensitivities are 11 and 10.93 pm/°C for the heating and cooling processes, respectively. Considering that the wavelength resolution of the optical spectrum analyzer is 20 pm, the resolution of the temperature measurement is estimated to be 1.8 °C. Because of its compactness, ease of fabrication, good sensitivity, easy connectivity to other in-fiber optical components, and low cost, this thermometer could find various applications in temperature sensing. [ABSTRACT FROM PUBLISHER]

An approach to obtain single-mode operation on a semirectangular large core area Flat Fiber (FF) slab waveguide is proposed. A new design of FF with two defect eye holes is presented, and its single-mode guiding is analyzed by simulation. To validate the simulation results, a proof of concept FF with a core area > 1200\rm\ \mu \rmm^2 was fabricated, and its modal behavior was examined. It was found that higher order propagation modes could be discriminated from the large core area by introducing a high-refractive index region in the FF eye holes. Experimental results confirmed a single Gaussian mode profile (mode field diameter of \approx745\rm\ \mu m) output of this large core FF, thus validating the simulation results. [ABSTRACT FROM PUBLISHER]

An optofluidic chip of the single-mode fiber variable optical attenuator (VOA) is proposed. This chip has a simple structure, and it utilizes microfluid and air to regulate the optical attenuation, where air acts as a shutter. Here, the single-mode characteristics of the VOA chip are discussed at 1310 nm and 1550 nm. The experiment results indicate that it is feasible to regulate optical attenuation using the proposed chip. The VOA with this chip has a large optical attenuation range (82 dB) and a very wide operation waveband from visible to near infrared wavelengths. The measured insertion loss is 0.68 dB at 1310 nm and 0.92 dB at 1550 nm, and the measured return loss is 47.8 dB at 1310 nm and is 47.67 dB at 1550 nm. [ABSTRACT FROM PUBLISHER]

We reported an erbium-doped fiber ring laser (FRL) displacement sensor based on a single-mode fiber (SMF) loop tied into the laser cavity. The proposed fiber loop structure acts as the sensing head as well as the filter of the FRL. A good linear relationship is obtained both in principle and in experiments between the displacement of one end of the loop and the central wavelength of the proposed FRL. The average sensitivity of this sensor reaches 227.5 pm/mm in the displacement range of 0–30 mm. High optical signal-to-noise ratio ( $\sim 52$ dB) and narrow 3-dB bandwidth (<0.7 nm) are also achieved due to the FRL structure. Moreover, the macrofiber loop, as the key sensor head of the proposed sensing system, is tied with simple SMF without removing the coating, which has obvious advantages of firm structure with a wide range of displacement measurement and easy fabrication with low-cost SMF. [ABSTRACT FROM PUBLISHER]

A nonlinear crystal fiber converter for terahertz (THz) difference frequency generation (DFG) is proposed. This axisymmetric structure consists of a periodically inverted GaAs core clad with index-matched chalcogenide glass, which functions as a single-mode fiber for THz radiation to prevent its diffraction and achieve efficient optical-to-THz conversion. The process of DFG between ps-pulses in the crystal fiber is investigated by developing the guided-wave coupled-mode equations for quasi-monochromatic pulses. The output power, spectral power density, and brightness are analyzed, based on the calculations of the dynamic of energy conversion and the characteristics of the THz beam focusing. High output power as well as excellent beam quality contributes to the high brightness of the presented THz crystal fiber source. [ABSTRACT FROM PUBLISHER]

We review the field we describe as “single-mode fiber optofluidics” which combines the technologies of microfluidics with single-mode fiber optics for delivering new implementations of well-known single-mode optical fiber devices. The ability of a fluid to be easily shaped to different geometries plus the ability to have its optical properties easily changed via concentration changes or an applied electrical or magnetic field offers potential benefits such as no mechanical moving parts, miniaturization, increased sensitivity, and lower costs. However, device fabrication and operation can be more complex than in established single-mode fiber optic devices. [ABSTRACT FROM PUBLISHER]

We propose a measurement system based on optical time-domain reflectometry (OTDR) that offers high-sensitivity detection of bend location in a standard single-mode (SM) fiber. This technique, which employs 1-μm-band probe pulse, i.e., below the cut-off wavelength of SM fiber, enables us to individually observe the fundamental (LP01 ) and the second-order (LP11) modes of the backscattered light generated in the two-mode region of the SM fiber, using a key technical advance is a mode-selective coupler designed for optimal 1-μm-band operation. Analyzing the loss distribution of the backscattered LP11 mode realizes the high-sensitivity detection of the fiber bend location without suffering degradations from the modal dispersion. We perform experiments for the four kinds of widely-used SM fibers, and demonstrate the proof-of-concept; a comparison is made with the conventional OTDR operating at the wavelength of 1650 nm. [ABSTRACT FROM PUBLISHER]

We show that multi-tap equalization can significantly enhance the tolerance to laser frequency instability and phase noise in optical fast orthogonal frequency division multiplexing (OFDM) systems. We demonstrate the transmission of a 38-Gb/s 16 quadrature amplitude modulation coherent optical fast OFDM signal over 1000-km single-mode fiber using different types of lasers. It is shown that with this technique, the receiver sensitivity can be greatly improved and overhead for carrier frequency offset estimation to track the wavelength can be reduced for commercial lasers. This verifies the benefits of the technique in a continuous-mode optical communication system. We also show that the performance of multi-tap equalization in optical fast OFDM can be better than that in conventional OFDM, and an experiment using lasers with frequency modulation to emulate frequency oscillating effect during wavelength transition shows that optical fast OFDM can be a more potential multicarrier solution for wavelength-selective optical packet networks. [ABSTRACT FROM PUBLISHER]

In this letter, a pair of regenerated gratings with Bragg wavelengths of 1547 and 1304 nm in a single piece of singlemode fiber has been fabricated for simultaneous monitoring of temperature and strain in ultrahigh temperature environment. A 3 × 3 matrix is used to characterize the cross sensitivity of the proposed sensor in which the strain sensitivity varies with temperature change. The proposed structure exhibits the deviation of 28.3 με and 4.1 °C at the ranges of 0-1000 με and 25 °C- 900 °C, respectively. [ABSTRACT FROM PUBLISHER]

In this letter, we present a novel fiber-optic Mach-Zehnder interferometer based on leaky-mode generation from fiber bending and experimentally demonstrate it that is used as a fiber-optic refractometer. The interferometer is simply constructed using a standard single-mode fiber with two fiber bending regions connected by a section of straight fiber. The phase difference is from the optical path difference between the core mode and leaky modes from the designed bending fiber structure. Refractive index (RI) sensors with different parameters have been fabricated and tested in NaCl solutions with different RIs in the range of 1.3288-1.3696, and a maximum RI sensitivity of -204-nm/RIU (refractive index unit) is achieved on a sensor with a 4-cm straight fiber length and 5-mm bending radius. Experimental results have confirmed that there are two dominant cladding modes interfering with the core mode. The RI sensitivities of the sensors with a uniform bending radius are independent of the straight fiber length; as a result, precise control of the fiber length is not required, which makes the sensor production cost-effective. [ABSTRACT FROM PUBLISHER]

By using a Mach-Zehnder intensity modulator (MZM)-based Q-factor enhanced 40-GHz optoelectronic oscillator (OEO) loop, a self-starting pulsed encoder is demonstrated to generate 40-Gbit/s return-to-zero on-off-keying (RZ-OOK) data-stream. By nonlinearly driving the MZM with an OEO circuitry via a proper setting on the intra-loop delay, both the RF and optical output of the OEO at 40 GHz can be extracted to deliver the clock with a Q-factor of up to 2×108, and trigger the synthesizer-free 40-Gbit/s RZ-OOK data-stream. The maximal output power and the carrier-to-noise ratio of the RF output from the OEO are 20 dBm and 62 dB, respectively. Moreover, the single side-band phase noise is suppressed to -120 dBc/Hz at 100-kHz offset frequency by lengthening the single-mode fiber in the OEO loop up to 900 m. In addition, the pulsed RZ carrier with a pulsewidth of 10.5 ps provides a jitter as low as 120 fs and an on/off extinction ratio of 7.7 dB, which is particularly suitable for the RZ-OOK transmission at 40 Gbit/s. The back-to-back transmitted synthesizer-free 40-Gbit/s RZ-OOK data with a pattern length of 223-1 reveals a receiving power sensitivity of -15.2 dBm at the requested bit error rate of 10-9. [ABSTRACT FROM AUTHOR]

A proof-of-principle demonstration of a multiple input-multiple output (MIMO) dense wavelength division multiplexing (DWDM) system is reported. It uses standard uncooled distributed feedback lasers with intensity modulation-direction detection (IM-DD), in which the temperature of each laser is allowed to drift independently within a 50 °C temperature range. A feedback-based laser bias control algorithm is introduced to guarantee acceptable wavelength spacing and a postphotodetection minimum mean square error decoder is applied to cancel the interchannel crosstalk. The relative sensitivity of the MIMO receiver in both a random laser temperature drift scenario and a worst-case scenario are investigated by simulations in MATLAB. Experimental results for a 40-channel × 12.5 Gb/s DWDM system transmitting over 28 km of single-mode fiber with worst possible wavelength distribution prove the feasibility of the technique. [ABSTRACT FROM PUBLISHER]

A tunable erbium-doped fiber (EDF) laser based on random distributed feedback through backward Rayleigh scattering in a 20-km-long single-mode fiber and a tunable fiber Fabry-Perot interferometer filter is demonstrated. It has a broad wavelength tuning range up to 40 nm (from 1525 to 1565 nm) with a narrow linewidth of ~0.04 nm. Due to the half-opened laser cavity design and the efficient gain from the pumped EDF, the measured threshold power is only 13 mW, and the pump efficiency is up to 14%. [ABSTRACT FROM PUBLISHER]

A new device for improving the free-space optical monitoring and coupling into a single mode fiber is proposed. It consists of a fiber taper, which can easily be drawn from a suitable fiber with large core radius. The taper acts as a mode filter discarding higher order modes. A first device is fabricated. Measurements show that lateral tolerances increase linearly with the taper input core radius and longitudinal tolerances increase with the square of the input core radius. [ABSTRACT FROM PUBLISHER]

An electronically controlled optical swept source at 1550 nm using mode locking in a dispersive ring cavity is described. Active mode-locking was achieved by directly modulating the current of a semiconductor optical amplifier (SOA) used as a gain medium. In the static regime, parameters such as linewidth, tuning bandwidth, and contrast were measured, whereas the axial range was determined dynamically. Two types of fiber, dispersion compensation and single mode, are employed in the laser ring cavity. It is demonstrated that the relative lengths of the two types of fiber have little effect on the linewidth, whereas more control on the linewidth is obtained via the frequency of the signal driving the SOA. Linewidths less than 60 pm and over 1 nm were measured in the static regime while driving the SOA at 50-500 MHz. The narrowest linewidths were achieved where the proportion of dispersion compensation fiber in the cavity was 80%-90% of the total length. The optical source is developed to respond to the demands of several optical coherence tomography applications that do not necessarily need long coherence length swept sources. [ABSTRACT FROM PUBLISHER]

Recent advances in short reach 100 Gb/s intensity modulation and directed detection systems are briefly reviewed. As an illustrative example of using digital signal processing enabled transmitters and receivers to allow relatively modest symbol rates, the generation and detection of 112 Gb/s 16-QAM half-cycle Nyquist subcarrier modulation are considered using dual-polarization, single-carrier and single-polarization, dual-carrier implementations. High bandwidth directly modulated passive feedback lasers are used to generate the optical signals and pre-amplified receivers are used to detect the received signals in a back-to-back system and after transmission over 4 km of single-mode fiber. [ABSTRACT FROM PUBLISHER]

A kind of magnetic field sensor based on mode interference effect is proposed. The sensing arm consists of two special up-tapered joints formed on the traditional single-mode fiber by fusion tapering technique. Magnetic fluid is used as the cladding of the structure. The interference valley wavelength or the transmission loss of the sensing structure is sensitive to the external magnetic field, which is utilized for magnetic field sensing. The sensitivity of shift of interference valley wavelength with magnetic field can be up to 325.3 pm/mT in the range of 0-16 mT. The variation of transmission loss at valley wavelength with magnetic field has a sensitivity of -0.2121 dB/mT in the range of 2-30 mT. [ABSTRACT FROM PUBLISHER]

This letter presents a novel broadcast scheme using a double sideband with optical carrier suppression (DSBCS) modulation. Broadcast data and unicast data are delivered simultaneously by a DSBCS and an optical carrier from a single wavelength, whose states of polarization are orthogonal, respectively. The broadcast data and the unicast data modulate DSBCSs and an optical carrier using a reflective semiconductor optical amplifier, respectively, at the optical line terminal, and are detected at the optical network unit without resorting to any polarization tracking. The broadcasted data can be applied for both wireless and wireline services. The transmitting broadcast data and unicast data over a 25-km single-mode fiber are experimentally demonstrated with a power penalty at the bit error rate (BER) = 10-9 of below 1 dB and is sufficiently independent in a single wavelength channel. [ABSTRACT FROM PUBLISHER]

Long-haul mode-division multiplexing (MDM) employs adaptive multi-input multi-output (MIMO) equalization to compensate for modal crosstalk and modal dispersion. MDM systems must typically use MIMO frequency-domain equalization (FDE) to minimize computational complexity, in contrast to polarization-division-multiplexed systems in single-mode fiber, where time-domain equalization (TDE) has low complexity and is often employed to compensate for polarization effects. We study two adaptive algorithms for MIMO FDE: least mean squares (LMS) and recursive least squares (RLS). We analyze tradeoffs between computational complexity, cyclic prefix efficiency, adaptation time and output symbol-error ratio (SER), and the impact of channel group delay spread and fast Fourier transform (FFT) block length on these. Using FDE, computational complexity increases sublinearly with the number of modes, in contrast to TDE. Adaptation to an initially unknown fiber can be achieved in ~3-5 μs using RLS or ~15-25 μs using LMS in fibers supporting 6-30 modes. As compared to LMS, RLS achieves faster adaptation, higher cyclic prefix efficiency, lower SER, and greater tolerance to mode-dependent loss, but at the cost of higher complexity per FFT block. To ensure low computational complexity and fast adaptation in an MDM system, a low overall group delay spread is required. This is achieved here by a family of graded-index graded depressed-cladding fibers in which the uncoupled group delay spread decreases with an increasing number of modes, in concert with strong mode coupling. [ABSTRACT FROM PUBLISHER]

A fiber-optic strain and curvature sensor based on no-core fiber has been proposed and demonstrated. The sensor is fabricated using a multimode fiber without cladding, known as the no-core fiber with a thinner diameter. The jointing point between the no-core fiber and single-mode fiber is a taper, which will improve the sensitivity of the sensor. The peak wavelength shift of the sensor exhibits an excellent response for strain and curvature changes. [ABSTRACT FROM PUBLISHER]

Although the quest for high-power, diffraction-limited, semiconductor lasers has arguably met with limited success, the drive for higher brightness diode lasers continues, driven by fiber laser systems. Using tailored refractive-index and injection-current profiles, broad-area laser beam propagation method simulations predict simultaneous suppression of free-carrier-induced self-focusing and far-field mode compression at high powers. Asymmetric gain from tailored current profiles generate unconventional, null-less modes and lead to distributed gain- and loss-filtering mechanisms for increased beam quality output. A 5.2-7.7 W of filament-free power enables high-efficiency (70%) coupling into SMF-28, resulting in 3.1-5.5 W of fiber-coupled power for erbium-doped fiber amplifiers pumping with 0.72-W/A slope efficiency. The concept is shown to be robust against the shape of the profiles, inhomogeneities in both injection current and refractive index, and thermal lensing with proper submount design. [ABSTRACT FROM PUBLISHER]

A novel localized surface plasmon resonance (LSPR) fiber sensor was proposed. This LSPR fiber sensor was primarily constructed by conducting etching of the cladding layer and core layer on a single-mode fiber, followed by plating of 1444 nanometal rings. Sensor design and relevant calculations were conducted using a semi-analytical simulation method, which integrated the exact mode solver for the cylindrical coordinate and eigenmode expansion method. It was examined that the current metallic patterns in the fiber sensor can trigger the LSPR by the electric field Er of the core mode HE11, and this is the main reason why this novel fiber sensor can obtain high performance. After performing algorithms, images showed evident excitation of the LSPR. The LSPR fiber sensor designed in this paper possesses excellent attributes of short length (185.173 μm), high resolution (approximately - 70 dB), and high sensitivity (approximately 34 257 nm/RIU). [ABSTRACT FROM PUBLISHER]

Wavelength reuse in a symmetric ultra-wideband (UWB) over wavelength-division-multiplexing passive optical network based on injection locking of a Fabry-Pérot laser diode (FP-LD) and polarization multiplexing is proposed and experimentally demonstrated. In the proposed scheme, the downstream UWB signal and baseband signal are generated and polarization multiplexed in the central station and sent to a base station (BS) over an optical fiber. At the BS, one of the downstream signals is selected to injection lock the FP-LD. It is demonstrated theoretically and experimentally that the upstream service performance is less sensitive to the modulation depth of the downstream UWB signal than the baseband signal, and the use of the downstream UWB signal as the injection signal would contribute to a better transmission performance for both the downstream and upstream services. Thus, the downstream UWB signal is selected as the injection signal. An experiment is performed. When the FP-LD is injection locked by a downstream UWB signal, a clear optical carrier is generated which is reused for upstream UWB and baseband transmission. A bidirectional point-to-point transmission of 1.25 Gb/s UWB signal and 10 Gb/s baseband signal over 25-km single-mode fiber using a single wavelength is demonstrated. The bit error rate performances and the eye diagrams for both downstream and upstream transmissions are measured. [ABSTRACT FROM PUBLISHER]

The “Gigabit access passive optical network using wavelength division multiplexing” project aims to implement 64-Gb/s data transmission over 20-km single-mode fiber. Per-user symmetric data rates of 1-Gb/s will be achieved using wavelength division multiplexing passive optical network (WDM-PON) architecture with a 1:64 user split per PON segment. Enabling technologies being developed within the scope of the project include tunable transceivers and athermal 50-GHz array waveguide grating multiplexer devices. The future-proof WDM architecture will enable convergence triple-play (telephony, TV, and broadband internet) service over existing optical infrastructure, and also facilitate cost-effective dense wavelength division multiplexing for metro aggregation and mobile backhaul networks. [ABSTRACT FROM PUBLISHER]

Distributed temperature sensing based on time-correlated two-photon excited fluorescence (TPF) in doped optical fiber is described. Counter-propagating laser pulses generate a TPF flash at the position of their overlap which is scanned along the fiber by a variable relative time delay. The flash is transmitted to one end where it is detected and analyzed to yield the temperature from its thermal dependence. To identify suitable dopants, the two-photon excitation spectra of glass doped with various rare-earths were recorded. Preliminary results on TPF in praseodymium doped single-mode fiber are presented. [ABSTRACT FROM PUBLISHER]

Simulated and measured results are presented for the coupling loss from free space into a large mode area (LMA) photonic crystal fiber. The total measured loss (using bulk optics) for a signal (lambda = 1.55 mum) going in and out of a 1-m-long fiber was -2.15 dB. It was also observed that the fiber is not that sensitive to lateral misalignment compared that to the conventional single-mode fiber. Due to the low loss, this type of fiber could be used to create long delays in optical true-time-delay engines based on the White cell concept and others. The above loss can be further reduced by using field lenses or lensed LMA. [ABSTRACT FROM PUBLISHER]

We analyze numerically an erbium-doped segmented-cladding fiber (SCF) for optical amplification. The fiber has a uniform high-index core and a leaky cladding consisting of alternating high and low refractive-index angular segments of equal size, where erbium is doped in the core and the high-index cladding segments. By choosing the fiber parameters properly, the fiber can offer effective single-mode operation at both the signal (1530 nm) and pump (980 nm) wavelengths with an ultralarge core. We calculate the mode-field distributions in the fiber at these two wavelengths with a full-vector finite-element method. We obtain the gain characteristics and the pump threshold of the fiber by solving the propagation rate equations. With a typical erbium-ion concentration of 0.7 times 1025 ions/m3 , an input pump power of 280 mW, and an input signal power of 0.1 muW, the maximum gain achievable varies from ~ 14 dB to ~ 37 dB with an optimal fiber length of several meters, when the core diameter varies from 40 mum to 28 mum. The threshold pump power required is of the order of 100 mW at 0.1-muW input signal power, and the saturation output signal power is of the order of 100 mW at 280-mW input pump power. The noise figure is ~ 4 dB. Our analysis suggests that, by using a high enough pump power, a few meters of erbium-doped ultralarge-core SCF can provide a small-signal gain comparable with that of a conventional erbium-doped fiber. [ABSTRACT FROM PUBLISHER]

We have designed and experimentally demonstrated radio-over-fiber (ROF) systems to simultaneously generate optical millimeter-wave (mm-wave) and centralized lightwaves using one low-bandwidth intensity modulator (IM) with low-frequency local oscillator (LO) signals while simplifying the transmission design and reducing the cost of the base station (BS). The techniques based on double-sideband (DSB) and single-sideband (SSB) signals for ROF systems are discussed in detail in terms of architecture efficiency, bandwidth requirement, and fiber transmission performance. The repetitive frequency of the optical mm-wave carriers are four times of that of the LO in central office (CO) by using DSB scheme. Full-duplex transmission services have been successfully realized over 20-km single-mode fiber (SMF) based on wavelength-reuse technique. In order to mitigate chromatic dispersion, the SSB technique has also been investigated in this paper. We had realized an ROF system that attained dispersion-free transmission and a negative power penalty by using SSB generation. We also quantified the optical carrier-to-sideband ratio (CSR) of downstream transmission in this ROF link and established that the performance of ROF system can be significantly improved when the optical signals are transmitted at a CSR value of 0 dB. The proposed architectures require much less bandwidth of the modulators, receiver sensitivity, system operation efficiency, and reliability. [ABSTRACT FROM PUBLISHER]

We present extensive numerical simulations of an optical link deploying four electroabsorption modulated lasers (EMLs) at 25 Gb/s over up to 40 km of standard single-mode fiber. The receiver comprises a semiconductor optical amplifier (SOA) as a preamplifier. We analyze the bit error ratio (BER) along different link lengths under varying conditions such as output power and extinction ratio of the EML transmitters, the noise figure of the SOA preamplifier and the bit and word alignment of the four wavelength channels. We demonstrate that the EML transmitters require a minimum extinction ratio of 8 to 10 dB and a minimum output power of +2 to +4 dBm in order to meet the BER requirements for 100 Gigabit Ethernet (100 GbE) using 4 times 25-Gb/s physical media dependent (PMD) devices. Furthermore, we show that single-channel performance analyses can be used to estimate the behavior for multichannel amplification in the SOA preamplifier. [ABSTRACT FROM PUBLISHER]

This paper reviews optical fiber design evolution for transmission systems over the past three decades, including both multimode and single-modes fibers. Key fiber attributes related to fiber transmission systems and how fiber designs have evolved to improve these attributes to enable higher and higher transmission data rate are discussed. Major fiber design change milestones in the past are covered. Also discussed are recent new developments in optical fiber technology. [ABSTRACT FROM PUBLISHER]

The development of metrology to support the optical fiber communications industry is an excellent case study of how stakeholders-fiber manufacturers, their customers, standards-developing organizations, and (in the U.S.) the Federal Government-worked together to develop product specification standards that facilitated the growth of an industry. This paper reviews some of that history, primarily from the perspective of the National Institute of Standards and Technology, which worked with the industry to provide independent research and neutral coordination of many industry studies and measurement comparisons. [ABSTRACT FROM PUBLISHER]

Soliton self-frequency shift (SSFS), a consequence of Raman self-pumping that continuously red-shifts a soliton pulse, has been widely studied recently for applications to fiber-based sources and signal processing. In this paper, the fundamentals of SSFS are reviewed. Various fiber platforms for SSFS (single-mode fiber, microstructured fiber, and higher order mode fiber) are presented and experimental SSFS demonstrations in these fibers are discussed. Observation of Cerenkov radiation in fibers exhibiting SSFS is also presented. A number of interesting applications of SSFS, such as wavelength-agile lasers, analog-to-digital conversion, and slow light, are briefly discussed. [ABSTRACT FROM PUBLISHER]

In this paper, we design, analyze, and demonstrate experimentally U.S. Federal Communications Commission (FCC)- compliant power-efficient ultrawideband (UWB) waveforms generated by optical pulse shaping. The time-domain pulse shape is written in the frequency domain, and a single-mode fiber performs the frequency-to-time conversion. The waveform is inscribed in the frequency domain by the fiber Bragg grating (FBG). A significant challenge for this approach is elimination of an unwanted, positive rectangular pulse superimposed on the desired waveform. Our innovative use of balanced photodetection eliminates this pedestal, assuring compliance with the FCC mask at low frequency. Three UWB pulses with duration of 0.3,0.6, and 1.2 ns are designed and tested experimentally. Whereas an excellent match between the optimized and measured pulses is achieved for the simpler, shorter duration waveforms, the noise in the fabrication process of FBGs limits the generation of the more complex, longer duration waveforms. [ABSTRACT FROM PUBLISHER]

The performance of different electronic equalization and processing schemes for 40- and 10-Gb/s optical transmission over single-mode fiber (SMF) are discussed, from the point of their ability to compensate chromatic dispersion (CD) and polarization mode dispersion (PMD). In addition, the impact of fiber nonlinearity and modulation format on equalization is also investigated. The main objective of this paper is to present an overview and a comparison of the performances rather than a detailed explanation of the principles of the different equalization schemes. The equalizers which will be covered are analog equalizer (feedforward and decision feedback type), maximum likelihood sequence estimator (MLSE), electronic precompensation, coherent/intradyne detection with digital signal processing (DSP) equalization, DSP-based optical orthogonal frequency division multiplexing (OFDM), and turbo equalization. [ABSTRACT FROM PUBLISHER]