Integrated Optical Circuit Engineering

Practical optical fiber systems, both multimode and single mode, require connectors for terminating components, system configuration, testing, and maintenance. And in all types of system, from the long-haul large-capacity single-mode fiber systems to the large-core multimode fiber systems used in local area networks, the connectors must exhibit low insertion loss while also being cost effective. With the long-haul single-mode fiber systems, where fiber attenuation may be as low as 0.2 dB/km, it is obvious that the connector’s insertion loss can severely limit the distance between repeaters. Besides the connector's coupling efficiency other factors can also limit the span length. Reflections from connectors close to the transmitter may affect the longitudinal mode spectrum and noise characteristics of some laser transmitters and thereby cause system degradation. Also, high-loss connectors may cause higher-order modes to propagate, in short jumper cables, resulting in modal noise and its associated power penalty. Although these single-mode fiber systems usually employ a small number of connectors, for low insertion losses their 5–10-μm core diameters require fiber alignments of submicron accuracy. In contrast to these single-mode systems local area networks are being designed using large-core multimode fibers (at least today). These networks can be very connector intensive with as many as twenty or more connectors being used between transmitters and receivers. In addition, other optical components such as couplers, taps, and switches may also be used, and the combined losses of the components and connectors must be accommodated by the relatively low system gain provided by low-cost LED transmitters and PIN receivers. In these applications the connector’s performance and cost-effectiveness again must be balanced to achieve a practical resolution. A further consideration is that in all practical systems, both single mode and multimode, there exist applications that require both factory and field-installed versions of these connectors. It Is, therefore, important that field-Installable versions are available for all practical connector designs, Including those designed for single-mode fibers.

An analytical form for the lightwave angular frequency (/spl omega/) dependence of the squared value of the differential group delay in concatenated single-mode optical fiber systems is introduced. We show that the dependence can be described by a combination of cosine functions of rotation angles and their sums and differences of the fiber pieces, which are located between the two end pieces of the concatenated system. Using the analytical expression, the /spl omega/ dependence of real fiber systems can be simulated, providing information about the birefringence configuration of the system. Comparison with experimental data taken on real systems yields good qualitative agreement even if only few concatenations are considered.

A new way to dynamically control in-flight pulses in a wavelength division multiplexed (WDM) single-mode fiber system is presented in this paper. This system functionally resembles an optical fiber ribbon cable, except that all the bits pass on one fiber optic waveguide and that the bandwidth and bit temporal pulse alignment are much greater. In a WDM fiber system, where pulses on different wavelength beams may co-propagate in a single-mode fiber the cross phase modulation (CPM) effects caused by the nonlinearity of the optical fiber are unavoidable. In other words, pulses on different wavelength beams can interact with and affect each other through the intensity dependence of the refractive index of the fiber Using this phenomenon, through the introduction of a Shepherd pulse at a separate wavelength, it is possible to manipulate, 'color', and control pulses on co-propagating beams. How this can be accomplished will be demonstrated in this paper.

For several decades silica-based optical fibres have been used for telecommunication and sensor purposes. The single-mode fibre is frequently employed in long-distance networks, whereas the multi-mode fibre is the preferred means of signal transport in campus and in-building networks. Because of the huge bandwidth of optical fibres in comparison to its electrical wireless and copper-based counterparts, the demand for optical fibres keeps increasing. In a competitive market, fibre manufacturers aim to produce ever better fibres that are as cheap and easy to employ as possible. As fibre research, development and manufacturing is a mature discipline, improvements in fibre design can only be achieved through the construction of robust, accurate and efficient numerical fibre models for the computation of those quantities that determine the behaviour of the fibre. We have developed a modular software code, based on Maxwell’s equations, to compute these quantities in a vectorial full-wave way for both single-mode and multi-mode optical fibres. Key is the refractive-index profile, or, more specifically, the dopant profile, as it defines the propagation, splicing and bending-loss characteristics of the fibre. For the single-mode fibre, the fibre quantities that we have concentrated on are dispersion, dispersion slope, mode-field diameter, effective area, bending loss, effective and theoretical cut-off wavelength and MAC-value. We highlight one fibre quantity in particular, viz. the computation of the bending loss in a single-mode fibre. Many approximate modelling techniques have been developed to estimate this loss in a fast way. Our numerical scheme, however, is the first rigorous one, as we have performed a vectorial full-wave analysis of the bent optical fibre. In this context, triple integrals involving products of Bessel functions with large, complex order and argument appear. Due to cancellations in the pertaining computation, a high relative accuracy is needed for the computation of each product. As a result, it takes weeks on a contemporary computer to compute the bending loss as a function of the radius of curvature. We have used the vectorial full-wave bending-loss results to determine the most appropriate approximate method. Subsequently, we have extended that approximate method to compute the bending losses of higher-order modes, since the required effective cut-off wavelength depends on the bending loss of the first higher-order mode. The selected approximate method has been used in the ensuing bending-loss calculations. Since the fibre properties are often conflicting, it is a challenging task to adapt the radial dopant profile to meet a set of predefined design goals. A design goal is a combination of desired values for (some of) the aforementioned fibre quantities, and can mathematically be translated into a cost function. The minimisation of this cost function provides us with the optimal dopant profile for that specific set. For the single-mode fibre, we have performed this minimisation for piecewise-linear profiles, by employing various global and gradient-based local optimisation strategies to speed up the design step considerably. Frequently,these optimisation strategies lead to counter-intuitive dopant profile designs that could not have been contrived otherwise. We have selected a deliberate mix of several optimisation routines and have compared their performances. Perhaps the most important conclusion is that there still appears to be room for improvement in the design of the radial dopant profile of commercially available fibres. For the multi-mode fibre, vectorial full-wave optimisation is not feasible yet because of the long computation times for the large number of propagating modes. Still, our numerical scheme allows for a manual fine-tuning of the popular power-law profile to minimise differential mode delay. Further, we have included mode coupling and differential mode attenuation in our model to obtain intensity patterns that match closely with measurements. We have also analysed the influence of profile variations, e.g. on-axis dips and kinks, on the intensity pattern. A selective excitation of different mode groups in a multi-mode fibre, offers the possibility to create several independent transmission channels, and thus a higher information capacity. Recently, the feasibility of this so-called mode group diversity multiplexing technique has been demonstrated. Simulations provide us with a means to better understand its operation and possibly increase its efficiency. The channel separation may be enhanced by employing a lens between the fibre and the detector, which is called mode-selective spatial filtering. Our numerical simulations of a mode group diversity multiplexing link, with and without mode-selective spatial filtering, are in agreement with the measurements. The above discussion makes clear that the developed software code has a wide range of applicability. Moreover, it is built in a modular way and thus extensions, like the inclusion of more fibre quantities or different profile dopants, are straightforward.

Accurate determination of the zero-dispersion wavelength (/spl lambda//sub 0/) is crucial for high bandwidth performance in single-mode fiber systems. We examine two dispersion measurement systems, based on the frequency-domain phase shift and differential phase shift techniques. Both systems are capable of measuring /spl lambda//sub 0/, with repeatabilities (precisions) of /spl plusmn/0.1 nm; however, their ultimate accuracies have yet to be determined. By comparing the two systems, we get an estimate of potential systematic errors. The systems are used to determine /spl lambda//sub 0/ in standard reference fibers.

The performance of ultra wideband (UWB) signals transmission using radio-over-fiber (ROF) technology is analyzed. UWB signals are directly modulated onto the optical carrier of wavelength 1550 nm for single mode fiber (SMF) system and 850 nm for multimode fiber (MMF) system. Bit error rates (BER) as a function of SMF and MMF lengths are presented. The ranges of SMF length are 0 to 5.5 km and 25.2 km to 31 km and 0 to 700 m for MMF. By varying the attenuation between the UWB transmitter and ROF modulator and between the photo-detector and UWB receiver, BER of less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> is achieved for SMF system. Reliable transmission of UWB signals using ROF technology is thus demonstrated. MMF system achieves a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> for lengths less than 450 m

Owing to the low attenuation of optical fibres, transmission systems with repeater spacings of 10–20 km become feasible. For future high-capacity systems this imposes great demands on the fibre bandwidth. Because of the inherent limitations of multimode fibres, single-mode fibre waveguides have to be taken into account. The transmission properties of single-mode fibres and their dependence on the fibre design are discussed, resulting in recommendations for practical fibre structures and statements of their production tolerances. For efficient coupling between two single-mode fibres the requirements are analysed and methods are described to achieve them in practice. As a transmitter for single-mode fibre systems mainly the GaAlAs-injection laser is considered. Its high speed modulation and spectral behaviour are discussed with reference to high-capacity transmission systems. Also the problem of launching is treated in detail. Finally, fast avalanche-photodiodes are considered as receivers for single-mode fibre transmission systems.

Волоконно-оптичні системи є одним з найбільш перспективних напрямків при розробці фізичної основи інформаційного простору. При реалізації оптоволоконних ліній зв'язку часто виникає необхідність узгодження оптоелектронних компонентів з різними поперечними перетинами випромінюючих і приймаючих областей і різними числовими апертурами. Варіантом такого завдання може бути з'єднання одномодового і багатомодового волокон або випромінювачів і фотоприймачів з волокнами різних типів. Одним з методів такого узгодження є створення каскадних волокон, в яких лінзове волокно і кілька ділянок градієнтних волокон інтегровано в одномодове волокно. Предметом дослідження є технології елементів волоконно-оптичних систем передачі. Метою даної роботи є створення компонентів волоконно-оптичних ліній зв’язку, що дозволяють підвищувати ефективність вводу випромінювання від джерела в оптичних світловод, зокрема одномодовий. Для досягнення поставленої мети необхідно вирішення наступних завдань: розглянути фактори, що впливають на втрати енергії при генерації і вводу випромінювання джерела в оптичне волокно, а також розробити і впровадити систему узгоджуючих елементів і дати послідовність дій для ефективного вводу випромінювання джерела в одномодове волокно. Висновки. Запропонована технічна і технологічна реалізація процесу робить можливим вводити більшу потужність в оптоелектронні лінії передачі інформації, що підвищує ефективність вводу випромінювання до 20 дБ. Визначення точності розташування сполучної площини в пристроях узгодження та взаємного розміщення випромінювачів та оптичного волокна дає можливість знизити втрати в з'єднанні до 0,1 дБ, передавати інформацію з більшою надійністю на більші відстані без регенерації і зберегти працездатність волоконно-оптичної системи в умовах впливу механічних, кліматичних і радіаційних факторів

A simple and accurate theory proposed by Jiang et al. (see Optical and Quantum Electronics, vol.22, p.23, 1990) to calculate the mode partition noise in single-mode fiber systems is shown to be in good agreement with the transmission experiment presented. The 560 Mb/s transmission experiment using the multilongitudinal mode laser diode is described and the result indicates that the transmission distance is limited to 10 km by the mode partition noise when 1-dB power penalty takes place. A statistical method is proposed to determine the k-parameter of laser diodes modulated by quasi-random RZ binary signals. The k-parameter is the most important parameter to describe the mode partition characteristics of laser diodes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bend-induced retardation and twist-induced rotation in single-mode optical fibers are important variables in the design of optical fiber current measurement systems. Bend-induced retardation varies with the square of the curvature and is believed caused by a waveguide geometry effect. Twist-induced rotation varies with the angle through which the fiber is twisted and is produced by torsional strain in the fiber. Both effects were found highly reproducible and to have small temperature dependence. Neither effect should significantly limit the performance of optical measurement systems using single-mode fibers.

Fiber optic sensors offer a high-performance alternative because they provide a low-cost solution, resistance to electromagnetic interference, multiplexing capabilities, and high integration. The performance of fiber optic sensors applies to measuring physical parameters such as pressure, bending, and temperature. This study aims to determine the optimal value of using optical fiber types in landslide early detection sensors. The method used is bending in the form of deflection on the optical fiber. The deflection values used are 0 mm - 15 mm, 0 mm - 20 mm, and 0 mm - 25 mm. The optical fiber is placed horizontally in the middle of the bending tool. This bending affects the deflection of the optical fiber, resulting in the attenuation of light in the optical fiber. The deflection phenomenon results in light attenuation in the optical fiber. The sensitivity level of a single-mode fiber optic sensor is higher than a multimode. It shows the greater linearity value in each deflection treatment. Single-mode optical fiber linearity data on deflection variations of 0 - 15 mm, 0 - 20 mm, and 0 - 25 mm, respectively, are 0.9833, 0.9871, and 0.9847. At the same time, the linearity data of multimode optical fiber is 0.8926, 0.9841, and 0.9687. Single-mode optical fiber is more sensitive than multimode optical fiber. It is caused by the core diameter of single-mode optical fiber, which is much smaller than that of multimode optical fiber. The difference in core diameter results in differences in light propagation in the optical fiber. The small diameter of the core has a low dispersion level so that more light intensity is reflected into the core. Light attenuation occurs in a single-mode optical fiber due to macro bending treatment. Meanwhile, the attenuation of light in Multimode fiber optics is due to the bending and dispersion of light. Therefore, a landslide early detection sensor design is more optimal by using a single-mode optical fiber.

We propose the utilization of a Smart In-Package [Micro] ALigner (SIMPAL) to enable fiber optical sensors for thick walled composite structures. Fiber optic coupling is the barrier preventing single mode and multimode fiber optical sensors systems from being incorporated into composite structures. A fiber optic connector that has a MEMS in-package micro aligner, integrated optical detectors, and control electronics is proposed to overcome the incompatibility between structural manufacturing tolerances and fiber optic alignment tolerances. The SIMPAL technology will enable affordable optical connection with sub-micron alignment tolerances to be made after the fiber optics are machined off at the egress point during a standard trimming process. We have demonstrated and described the MEMS actuator part of the SIMPAL. This active part is a 3-axis active fiber optic micro-aligner small enough to fit into current electro-optical packages. The micro-aligner is fabricated on a silicon wafer with the high aspect MEMS/LIGA process technology. The electrically controllable actuators demonstrate the high force and displacements necessary for in-package alignment of a micro-optics. The integration of lenses, optical sensors and control electronics is proposed to realize a smart optical backplane interconnect system.

The special optical fibers, with large mode field, are developed for fabricating high power optical fibers passive components. If a conventional fiber optical laser is used as optical source, the coupling efficiency between special optical fibers and conventional single mode fibers (SMFs) need to be improved. We investigate the specialty optical fibers property and its effect on the coupling efficiency using an electric arc fusion splicer. Improper splicing parameters can lead to coupling efficiency sharply decreased. Several splicing methods are utilized, and all the results are proposed. Comparing these results, we find a set of splicing parameters for reducing the scattering loss at the splice point. It was demonstrated that properly splicing parameters can make coupling efficiency greatly increased; furthermore, a balance between splicing strength and coupling loss was achieved.

We study the problem of coupling partially coherent radially polarized (PCRP) vortex beams into a single-mode optical fiber. Using the well-known concept of the cross-spectral density (CSD) matrix, we derive a general expression for the coupling efficiency of the partially coherent beam into a single-mode fiber. We adopt PCRP vortex beams for incident beams and use our general results to discuss the effects of the coherence, topological charge, and wavelength on the coupling efficiency of an optical beam focused onto a single-mode fiber with a lens. Our results should be useful for any application that requires coupling of partially coherent beams into optical fibers.

Frequency fluctuation in a single-mode optical fiber is briefly discussed, and a preliminary experiment for optical heterodyne communication in a single-mode fiber is carried out with the aid of frequency-stabilized He-Ne lasers operating at a wavelength of 0.633 microm. As a result, we have obtained clear demodulated signals, having sinusoidal, triangular, and rectangular waveforms, through an optical fiber 100 m in length.