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An analytical approach about the general type of step-index optical fiber modes and their variations is presented in this paper. The theoretical model is solved through our analytical method. With the boundary conditions, a composite equation set is established and solved. The precise results of all modes are achieved with a high-precision numerical solution. The modal characteristic contains the distributions of electromagnetic fields, the effective refractive index, and its tendencies. The modal sensitivity is based on the former and the partial derivative of the effective refractive index (neff/ni and neff/ri). The derivative rule of implicit functions and determinant function allows our method to analyze the sensitivity of modes. Furthermore, four qualitative deductions are derived during the process, including the qualitative analysis of modes and their constraints, supporting previous experiments. Our work is beneficial for exploiting new fiber and researching relative fiber sensors.

In this paper, the Sagnac interferometer with a one-way optical fiber ring and a novel dual Sagnac distributed fiber vibration sensor with an asymmetrical structure for disturbance localization is proposed. The two Sagnac interferometers in this system are asymmetrical and equal in the lengths of optical paths. Using time delay estimation based on cross-correlation, the disturbance localization can be calculated from the two demodulated phase signals. The localization precision is ±10 m with a 50 km sensing fiber and the overall localization error is 0.02%. The time error problem possibly existing in the fiber sensing systems based on time delay estimation is firstly studied. Due to the design of equal optical path lengths, the time error problem does not exist in this system, which is a possible reason for high localization precision. The system has application potential in long-distance perimeter security and many other fields.

Equivalent-graded-index photonic-crystal fiber (EGI-PCF) is a modified photonic-crystal fiber (PCF) where the cladding is not required to be periodic. A radial gradient of the equivalent refractive index distribution provides extra freedom to efficiently tailor the dispersion of EGI-PCF. However, such additional complexity makes the manual fiber design much more challenging where the time consumption becomes too much to be afforded eventually. In this paper, we for the first time propose the method of computer-aided inverse fiber design (CAFD) based on empirical dispersion formula to circumvent this hurdle. We apply the differential evolution (DE) genetic algorithm to seek for the optimized EGI-PCF design with a target of specific dispersion profile. In the dispersion oriented EGI-PCF design, the use of empirical formula instead of numerical simulation (e.g., finite-element method) is proved to greatly reduce the run-time of CAFD and simplifies the fitness function evaluation as much as possible. We adopt our method and demonstrate a design of EGI-PCF with a near-zero ultra-flattened dispersion in the whole S+C+L band, which merely costs a few seconds of a laptop to return an optimized fiber design. Thus improvement of efficiency is about three orders of magnitude faster than any previous CAFD attempts as far as we learn. In the end, we use our method to explore an EGI-PCF design with a unique dispersion profile of all-normal dispersion-decreasing along the fiber length centered around 1 μm that plays a key role for the self-similar pulse evolution in a fiber laser/amplifier.

Instead of inscribing the discrete phases into each local period of the seed HLPG, an equivalent approach to realize the phase-only sampled multichannel helical long-period fiber grating (HLPG) has been demonstrated both theoretically and experimentally which is realized by superposing the so-called sampling HLPGs with the seed HLPG in a same region of the fiber. The proposed approach can greatly facilitate the fabrication processes of the multichannel HLPG by using the direct CO2 laser writing technique, meanwhile it enables to provide much more design and fabrication flexibilities for high channel-count HLPG than the previous methods. As examples, a 3-channel and a 5-channel HLPG have been successfully demonstrated. Moreover, the orbital angular momentum (OAM) modes inherently existed at all channels of the fabricated HLPG have also been verified, which highlights that the proposed HLPGs could find application to multi-wavelength OAM mode converter as well.

Recognizing objects directly from optical fiber output images is useful in endoscopic applications when forming a clear image of the object is unnecessary or rather difficult. Conventional fiber-optic systems, such as multicore-fiber-based and multimode-fiber-based systems, suffer from the sensitivity of the fiber to external perturbations. For example, a slight movement of the fiber (a-few-millimeters translation of the tip for meter-long multicore fibers or multimode fibers) can greatly change the output images of the system. In this work, we utilize the light guidance stability of recently proposed glass-air Anderson localizing optical fiber (GALOF) to achieve robust imaging-free objection recognition. We transport five classes of cell images through an 80-cm straight GALOF. A deep convolutional neural network is trained to classify the output images and tested on images never seen, namely, images collected when the fiber is bent or when the fiber facet is placed several millimeters away from the object without any distal optics. Bending-invariant high classification accuracy (86.8% on average) is observed all the way to the maximum bending offset distance of 45 cm (∼74thinsp;° bending angle). High classification accuracy (91.2%) is also preserved when the fiber facet is 0.5 mm away from the object.

Smartphone-based interrogation of a fiber Bragg grating sensor is, to the best of our knowledge, reported for the first time. The smartphone flashlight LED was used as a light source and a transmissive diffraction grating projected the CFBG spectra on the smartphone camera. In order to efficiently couple light from the smartphone LED to the fiber with CFBG, multimode fiber was used for inscription. Interrogation setup consists of a smartphone and low-cost off-the-shelf available components. Measurement principle was illustrated through the fiber strain caused by applied longitudinal force. Attained measurement sensitivity and resolution were validated via comparison with commercial spectrometer and theoretical results based on Cramer–Rao approach. Also, to the best of our knowledge, the influence of modal noise on the smartphone-based fiber optic sensor interrogation system performance is considered for the first time.

Accurate and fast recognition of fiber intrusion signals has always been a fundamental task in the Optical Fiber Pre-warning System (OFPS). However, currently existing recognition models tend to focus on one aspect and lack a comprehensive approach. In this paper, a dropout-based Stochastic Configuration Network (SCN) optical fiber intrusion signal recognition model is first proposed, which is named DropoutSCN. By combining dropout with randomized algorithm models, it not only enhances the fast learning ability, but also improves the generalization performance of the recognition model. In the experiment, compared with traditional Artificial Neural Network (ANN), Random Vector Functional Link (RVFL), and original SCN models, the DropoutSCN model proposed in this paper has the lowest root-mean-square error (RMSE). In terms of time efficiency, it reduces the time delay by about 2.5 times compared with the traditional ANN. In addition, this paper applies dropout to SCN, which provides a feasible thinking and reference for the study of randomized algorithm models.

Universal fiber is an optical fiber that supports both multimode and single-mode transmission. It is a multimode fiber with a mode field diameter of the fundamental mode roughly matching that of a standard single-mode fiber. In today's short-distance communications, both multimode fiber and single-mode fiber are used. Universal fiber can accommodate the needs of single-mode and multimode transmission so that end users can take advantage of the cost and performance benefits of each transmission type. In this paper, we present the design and properties of universal fiber, as well as its transmission performance for 100G systems. We also explore several application scenarios where the fiber can be utilized. In particular, we illustrate how the fiber can be used in 5G wireless fronthaul applications to meet the current needs while providing a path for future upgrades. Testing results and discussions of practical issues are also presented.

Efficient fiber-optic communication requires precise knowledge of the fiber coefficients, but these often change over time due to factors such as aging or bending. We propose a novel algorithm that identifies the average second-order dispersion and Kerr nonlinearity coefficient of a fiber, without employing any special training signals. Instead, ordinary input and output data recorded during normal operation is used. To the best of our knowledge, this is the first such algorithm. The algorithm is based on the nonlinear Fourier spectrum of the signal, which is known to evolve trivially as the signal propagates through an idealized model of the fiber. The algorithm varies the values of the fiber coefficients until the corresponding nonlinear Fourier spectrum at transmitter and receiver match optimally. We test the algorithm on simulated transmission data over a 1600 km link, and accurately identify the fiber coefficients. The identification algorithm is in particular well suited for providing a fiber model for nonlinear Fourier transform-based communication.

The design and photonic generation of power-efficient impulse radio ultra-wideband (IR-UWB) waveforms is a challenging step in the design and development of IR-UWB over fiber (IR-UWBoF) systems with combined optical and wireless transmission. In this paper, the definition of the spectral power efficiency (SPE) and its associated optimization problem are reformulated. Based on this reformulation, a theoretical upper bound for the SPE is derived and applied to two of the most common types of photonically generated IR-UWB waveforms. Accurate closed-form analytical expressions for the SPE upper bounds of these two waveform types are obtained and optimized. The analytical framework presented in this paper can be extended and applied to other waveform types. Simulation results show excellent agreement with the analytically obtained expressions. Accordingly, these analytical expressions can be used as reliable guidelines for precise and efficient design of practical IR-UWBoF systems that guarantee optimal design, generation, and distribution of IR-UWB waveforms.

Optical fiber-based biosensors are an emerging field of research with an extremely broad area of possible applications and a disruptive potential to turn the paradigm known as lab-on-fiber into reality. In the past few years, a variety of system choices has been explored, ranging from the type of sensing fiber, to the optical transducing element, to possible sensing amplification strategies. We revise some of the possible approaches to the design of a biosensor, highlighting their advantages and disadvantages, based on previous literature and on the experience of our research groups. The discussion is focused onto DNA sensing systems, especially in a label-free format, where the hybridization and recognition of the sought DNA sequence is translated directly into a modification of the optical fiber properties.

A novel fiber-optic chaos synchronization system allowing bidirectional long-distance chaos communication is proposed. For this system, chaos synchronization between two response lasers (RLs) is achieved via an identical driven chaotic signal injection from a remote driving laser (DL) over a long-distance fiber. The simulated results show that under suitable operation conditions, high-quality chaos synchronization between the two RLs can be obtained while the synchronization quality between any one of RLs and the DL is bad, which is useful for improving the system security. Using the two synchronized chaos output signals from RLs as two chaotic carriers and adopting a novel message encryption and decryption method, the communication performances, the impact of long-distance fiber channel and the security of this system, have been analyzed. After adopting an optimized system configuration, two 10 Gb/s messages propagating along opposite direction can be effectively decrypted over 100 km fiber channel.

Recent progress on novel long-range coherent optical frequency domain reflectometry is reviewed along with its applications to diagnosing problems with optical fiber cables. The measurement range of a conventional C-OFDR is limited to the coherence length of the laser used as the light source, since the phase noise of the laser degrades the sharpness of the beat spectrum. We have developed phase-noise-compensated optical frequency domain reflectometry (PNC-OFDR) to overcome this limitation by introducing a novel phase-noise compensation technique, and we achieved a very high-resolution measurement over the fiber link length. We describe the principle of PNC-OFDR and recent related developments, and discuss its use in diagnosing issues with fiber networks.

A review of current fiber-based technologies capable of producing slow-light effects is presented, with emphasis on the applicability of these technologies to telecommunications. We begin with a review of the basic concepts of phase velocity, group velocity, and group delay. We then present a survey of some of the figures of merit used to quantify the engineering properties of slow-light systems. We also present a description of several of the physical processes that are commonly used to induce a slow-light effect. Finally, a review of some recent advances in this field is presented.

Maxwell's equation for modeling the guided waves in a circularly symmetric fiber leads to a family of partial differential-equation-eigenvalue systems. In fiber design, one would like to determine the index profile, which is involved in Maxwell's equation so that certain optical properties, which sometimes involve derivatives of the eigenvalues, are satisfied. In this paper, we will discuss how to determine derivatives of the eigenvalue problem and the gradients of the dispersion with respect to design parameters in the model

Novel photonics polymer devices for broadband technologies are described, focusing on the high-bandwidth graded-index plastic optical fiber (GI POF). Based on these photonics polymer device technologies, the concept of "Fiber to the Display" is proposed, where GI POF is directly distributed to display from main server in a building or house. Therefore, real-time face-to-face communication with high-definition-television quality becomes possible, which cannot be achieved by current technologies. The authors believe that new innovative concepts of broadband society in the 21st century will be realized by "the proposal from the material side."

Two matrix algorithms aiming at a dynamic gain-spectrum adjustment in a backward-pumped distributed fiber Raman amplifier (B-DFRA) are developed based on the relation between changes in the pump power and the gain spectrum. Characteristic channels are chosen to reduce the dimension of matrices in the algorithm, which can be implemented by built-in microprocessors or DSP chips inside the B-DFRA module. Furthermore, as shown by the theoretical analysis and the numerical simulation, elements in the matrices can be directly and easily measured in deployed fiber plants without information on fiber parameters. These matrix algorithms are capable of adjusting the gain spectrum to fit the arbitrary profile desired in reality, while a wide dynamic range can be achieved by a multistage adjustment using matrices measured under several gain levels

Fiber optic sensor technology has wide-ranging potential in sensing and measurement and the aim of this paper is to explore the factors that determine this potential. The basic principles of fiber sensing are well established and share much with fiber communications. However, the implementation technologies can be radically different and the market characteristics contrast totally with the communications sector. We explore these issues in the context of applications in structural monitoring, electromagnetic measurements, and environmental sensing. We also present very brief accounts of underlying principles and a short discussion concerning evolving technologies for fiber sensing.

A novel and cost-effective method is developed for the roll alignment automation for out-of-plane coupling between a laser and an angled facet single-mode fiber. The method is based on an approximated closed-form analytical formula for the functional dependence of out-of-plane laser-fiber coupling efficiency on relative rotational angle between fiber and laser. In this method, only three measurements are needed to locate maximum optical power coupling position in the presence of initial fiber-laser relative rotational angular misalignments. This intelligent searching method can easily be incorporated into any conventional fiber-optic alignment optimization algorithms and is sufficiently general for alignment automation of even more complicated out-of-plane fiber-optic alignment in the presence of initial nonplanar misalignments.

In this paper, we review the fundamental advantages and drawbacks of 40-Gb/s systems from a fiber manufacturer's perspective. Based on modeling, experimental results, and fundamental understanding, we correlate the fiber design parameters with the expected performance of long-haul systems operating at 40 Gb/s. Nonlinear penalties, dispersion tolerances, modulation formats, polarization-mode dispersion, and Raman amplification are covered. We also present the fiber features required for both metro and submarine networks at this specific data rate.

Image fiber-optic two-dimensional (2-D) parallel data links based upon optical space-code division multiple access (CDMA) is implemented and experimentally demonstrated for the first time to the authors' knowledge. In the experiment, each input 4/spl times/4 bit-plane is optically encoded by an 8/spl times/8 2-D optical orthogonal signature pattern. The encoded bit-planes are spatially multiplexed, and it is transmitted through a 16 m-long image fiber having 3/spl times/10/sup 4/ pixels. Each receiver can properly recover the intended input bit-plane in the optical decoding process. This result will encourage the application of optical space-CDMA to future high-throughput 2-D parallel data links.

Acoustooptics has been shown to provide a powerful and versatile means of controlling and modulating laser radiation in bulk optic components. We discuss the fiber-optic and fiber-compatible versions of several components such as the phase modulator and Bragg cell. In addition, we present general design rules for such components based on the strengths and weaknesses of the various available materials and illustrate by means of a consolidated account of some previously completed results obtained at the Optoelectronics Research Center at Southampton University. Acoustooptic techniques for the control of optical radiation, well established for bulk-optic components, are shown to be equally valuable in the context of fiber-optic components if carefully applied. >

An in-service fiber line identification scheme based on high-resolution fiber line length measurement is proposed and demonstrated for single star, survivable, and passive double star architectures to meet the demands of in-service cable reconstruction. In the proposed scheme, a reference fiber is assigned just after the fiber network has been constructed and differences in length between the constructed fiber lines and the reference fiber are measured by OFDR. The measured values are recorded as identification ranges, which include the measurement errors, as unique values of the actual lines. The OFDR length measurement system can measure a wide range of length differences from 4 cm to 3 km. The lines were successfully identified in all three kinds of architecture by the proposed scheme. The scheme is based on the line length, which is an actual property representing the whole line. Therefore, the line data can be verified simply and effectively, according to the actual information on the line. >

This paper proposes architecture for a novel automatic fiber line testing system with an optical time-domain reflectometer (OTDR) and describes the system requirements, the design method, and the system evaluation. The results of a trial on a manufactured system and an evaluation of its characteristics are presented with evidence that an in-service optical fiber can be tested with no degradation in communication quality and the desired measurement accuracy and system component characteristics can be realized. In addition, it is confirmed that a failure between an optical fiber cable and a digital service unit (DSU) can be identified with 100% accuracy. >

This paper discuss past, present, and future use of fiber optics and optoelectronics, in conjunction with coaxial communications networks, to provide enhanced communications and networking capabilities. The role of network architectures and various options regarding wavelengths and modulation techniques are discussed and compared, as are several scenarios of fiber to the neighborhood, service area, curb, and home.

The ability to integrate the Laguerre-Gauss functions in closed form is exploited to allow a simple but accurate evaluation of single-mode fiber spot size using Galerkin's method. The method avoids the need for numerical integration in a broad class of refractive-index profiles. Its simplicity depends on the use of a pattern-matching algorithm to avoid the numerical integration normally called for. The algorithm is very fast and gives exact results. The development of symbolic computer languages makes this approach especially easy. A symbolic program was used to predict the spot size and the far-field radiation pattern, and the results are compared with the exact values, getting excellent results. >

The paper by R. L. Gallawa, J. Lightwave Technology, vol. 1, p. 192, 1993; describes the use of Ritz-Galerkin method for evaluating single mode fiber parameters e.g.: spot size, launch efficiency integral and far-field distribution; that require the integration of the modal field over an infinite cross-section. To sum up, although the numerical results in the paper are correct they have been obtained in a manner which leads to an intricate technique to compute single mode parameters. >

This paper reviews the state-of-the-art of fiber cable technology used in the public network, and discusses some of the advances required to extend the fiber network into the subscriber loop for the cost-effective implementation of the Broad-band Integrated Services Digital Network (BISDN) of the future. Emphasis is placed on identifying cable structures which are optimized for the different parts of the public network, such as the trunk, loop-feeder, and distribution plant. The technologies addressed include fiber and coating design, cable structures, installation, splicing, connectorization, and reliability issues.

Optical coherent multicarrier systems with highly selective tunable optical heterodyne receivers can be used for transmission and switching of broadband signals. Some technical solutions for coherent bidirectional subscriber lines, a ten-channel distribution system, and a switching setup with computer-controlled receiver tuning are presented. The laboratory experiments, including carrier-frequency stabilization, multiplexing, and demultiplexing, as well as the fiber components used, are described. The influence of fiber nonlinearities on multicarrier transmission is considered. >

For the first time in the history of communications technology, single-mode fiber offers the possibility of truly transparent communications systems. In this paper we consider the application of single-mode fiber technology to optical networks and the evolution of the technology to all optical networks based on space or wavelength switching. Also discussed is the progress towards some early experimental networks.

This paper presents a statistical analysis to the end-to-end chromatic dispersion budgeting in single-mode fiber links which employ multilongitudinal-mode laser transmitters around 1.3 or 1.55 μm regions. This is a novel approach which is relevant for upgrading the "bit rate × distance" of those already installed 400- and 565-Mbit/s fiber links.