Nevertheless, in the case of (de-)multiplexing OAM modes which has simpler symmetry, there exist more elegant and easy- to-implement spatial transformations known as geometrical coordinate transformations as illustrated in Fig. 6(b) [56, 57]. A log-polar coordinate transformation, in which log-polar coordinates in the input plane are conformally mapped to Cartesian coordinates in the output plane, was introduced for OAM mode sorting . It can be performed with only two phase-masks and a Fourier transformation lens. After propagating through this system, the spiral wave-front of an input OAM mode is transformed to a tilted plane wave-front with the tilt angle proportional to the OAM mode topological charge. OAM modes with different topological charges are hence transformed to plane wave-fronts with different tilt angles which can be focused to distinct positions in the focal plane of the lens. This scheme is a true unitary transformation that maintains its simplicity regardless of mode numbers. However, the log-polar transformation suffers high mode crosstalk due to significant overlap between adjacent demultiplexed modes, as shown in the lower-left part of Fig.6(b). To overcome this problem in principle, the authors proposed and demonstrated a novel ‘spiral transformation’ very recently, which is able to perform the same OAM (de-)multiplexing function with significantly higher resolution and thus lower mode crosstalk, as shown in Fig. 6(b2), also with only two phase masks.
Although, the technological breakthroughs such as WDM had allowed the capacity per fiber to be increased around ten- fold every four years in the past decade, however, the capacity of the optical communication systems based on these transmission technologies is slowly becoming saturated. To satisfy the exponential growth of the Internet traffic, for the next generation short reach systems, including data center transmission and optical interconnect (OI) applications, the space-divisionmultiplexing (SDM) can be a way forward. The SDM technology based on the multicore fiber (MCF) has recently attracted much attention as a potential approach. In this paper, design strategy of computer-compatible 8-core trench-assisted MCF (TA-MCF) is presented to reduce the intercore crosstalk. Moreover, the influence of butt-coupled TA-MCF OI on coupling loss is also discussed. On the other hand, another alternative approach, the modedivisionmultiplexing (MDM) is also showing promise and mode (de)multiplexer is one of the key devices in such a MDM system. Designs of mode splitters using asymmetric directional couplers for the fundamental quasi-TE (TM) mode with the higher order quasi-TE (TM) modes (de)multiplexer including the 𝐇 𝒚 𝟐𝟏 (𝐇 𝒙 𝟐𝟏 ), 𝐇 𝒚 𝟑𝟏 (𝐇 𝒙 𝟑𝟏 , 𝐇 𝒚 𝟒𝟏 (𝐇 𝒙 𝟒𝟏 , and 𝐇 𝒚 𝟓𝟏 (𝐇 𝒙 𝟓𝟏 )
Recent studies show that the capacity limitation of a single modeoptical fiber (SMF) is rapidly approaching the fundamental Shanon limit [1, 2]. Space divisionmultiplexing (SDM) is considered to be an important approach to overcome the capacity limitation of single corebased transmission systems. A multi-core fiber (MCF) or multimode fiber (MMF) has the advantage of boosting the transmission capacity without increasing the fiber count . A few-mode fiber (FMF) has core radius slightly larger than a conventional SMF, which not only enables more guided modes but also results in a larger effective area. This larger effective area of MMF or FMF enhances the power transmission capabilities that may result in longer distance communication and also less sensitive to area reduction due to the external perturbation like bending in fiber [4–6]. However, an important issue arises in FMF transmission system that is the crosstalk or mode coupling between the modes of propagation [7, 8]. The modedivisionmultiplexing in a three-mode fiber using multiple-input multiple-output (MIMO) processing have shown significant transmission capacity improvements over the long distance communication . MIMO based processing techniques are considered necessary to reduce the cross-talk and to reproduce the input signal. However, MIMO introduces latency in the system that further increases with the increased number of modes and also increases the overall complexity of the networks significantly [10,11]. The cross-coupling between the modes is inversely proportional to the effective index difference between these modes and it is more severe between the neighboring modes. A low effective index difference ∆n e f f between the modes may result in energy transfer
The MDM transmission system is considered as a promising solution. However, in the optical MDM system, when the light ray propagates through the MMF; it spreads into multiple paths (modes). Some of these modes (called low-order modes) travel at low angles to the fibre axis. These modes have shorter paths compared to the other modes (high-order modes) which travel at larger angles to the core axis and they have longer paths. Therefore, these modes travel through the fibre with different group velocities (i.e., differential mode group delays (DMGD)), and arrive to the receiver at different times. During propagation of these modes, and due to the fibre manufacturing imperfections (e.g., bending, stresses and twisting), the orthogonality of the modes will damage and the modes will couple with each other, causing the so-called mode coupling . Each time the mode coupling occurs, the power is leaked from one data symbol launched into a particular mode to the adjacent symbol so-called cross-talk. This causes the symbols to spread over time. This phenomenon is known as modal dispersion (MD). The modal dispersion will lead to overlapping the neighboring symbols of signal while it transmits to the receiver. The signal is then no longer
Orthogonal frequency divisionmultiplexing (OFDM) is a method of modulation of digital signal in which a signal is divided into many narrowband channels of different frequencies. This technology was first used in the 1960s for the research to minimize interference between channels which are near to each other with respect to frequency. In some points, OFDM and Frequency DivisionMultiplexing (FDM) are similar to each other. They differ from each other in modulation and demodulation technique of the signal. But in both the cases minimization of the interference, or crosstalk between the channels and symbols forming data stream is given priority and perfection of individual channels is given less importance.OFDM technology is used in European digital audio broadcast services. This technology is also used in digital television and is now being considered as a technique of receiving high-speed digital data over the same conventional telephone lines.
SLMs are versatile and capable of dynamically altering the intensity or/and phase of a beam without moving parts. Adaptive compensation of the wavefront has been demonstrated for real-time micro-alignment of optics in MDM systems, wavefront tuning and interferometry for wavefront verification in MDM systems in order to im- prove the output power coupling into the desired mode [6, 33, 34]. In , an SLM is used to calculate phase masks for each mode using a simulated annealing ap- proach which aims to find the most efficient hologram capable of generating a mode with the highest power coupling efficiency based on the MMF profile. SLMs have also been used for equalization of temporal varia- tions in a MDM system due to the effects of modal dis- persion [36–38]. For better digital control of mode purity and alignment, SLMs have recently been incor- porated into laser cavities directly. In , an inte- grated system containing a diode-pumped solid state (DPSS) laser where the transverse modes are controlled by an intra-cavity spatial light modulator (SLM) is demonstrated.
A FSO MWDM system of seven Laguerre-Gaussian (LG) modes based on DFE has been simulated in OptSim  and exhibited illustratively in Fig. 1. The FSO MWDM system consists of three parts; transmitter, FSO channel, and receiver. The input signal is generated using a pseudo-random binary sequence (PRBS) from the data generator at 3 Gbps. which is modulated to non-return-to-zero (NRZ) sequence, and is connected to a seven-segmented spatial vertical cavity surface emitting laser array with each segment represented as SpVCSELs. The SpVCSELs operate on two wavelengths; 1550.12 nm and 1551.92 nm and seven LG modes; LG 0 0, LG 0
One of the most damaging impairments on Free Space Optical (FSO) system performance is atmospheric turbulence, induced irradiance fluctuations often referred to as scintillation . Scintillation takes place as a result of heating of the surface of earth, resulting in the rise of thermal air masses. The masses combine forming regions with different densities and sizes, which cause differences in refractive indices varying with time. Moreover, these regions cause fluctuations in the irradiance of the received laser beam. A multiple-input multiple-output (MIMO) approach has been investigated as a solution, however in a dispersive channel, inter-symbol interference (ISI) is highly detrimental . The use of OFDM in conjunction with MIMO technique has been suggested to overcome both ISI and the induced fading caused by atmospheric turbulence. MIMO-OFDM is currently used in the 4G wireless  and research has shown that deploying diversity at the receiver is more efficient than at the transmitter side . A comparison of BER performance of both ACO- OFDM and MACO-OFDM techniques in turbulent channels using SIMO configurations is carried out.
Overall, successful demonstration of OTDM up to 400Gb/s has brightened the future of commercial OTDM. This system has the advantage of operating only on a single wavelength. It is possible of running OTDM on a number of existing WDM channels, which improves the overall data capacity. It is purely digital and compliant with the concepts of all-digital network. With rapid advancement in semiconductor technology and integration techniques, it will eventually make possible to manufacture compact, stable and higher performance components for commercial OTDM system [Jeffrey Huang EE558 Spring 99]. Hybrid WDM/OTDM networks have been proposed to move data between WDM and OTDM networks, and various subsystems have been demonstrated at 40 Gbit/s including WDM-to-OTDM and OTDM to-WDM translators, OTDM transmitters, and OTDM add–drop multiplexers [Lavanya1]. OTDM and WDM are considered as the bases of second generation optical networks. OTDM and WDM can be used within the same network. they are complementary technologies in that a single fiber strand can be transmitting a several WDM signals. OTDM multiplexed data can be contained in each single WDM wavelength can contain. All Optical Network (AON ) uses WDM and OTDM together. AON increases the efficiency and throughput while decreases delay and errors. DWDM takes WDM, one of the second- generation optical network technologies, and takes it further.
Chromatic dispersion, or group velocity dispersion (GVD), is primarily the cause of performance limitation in the long haul 10 Gb/s and beyond fibre optic communication systems. As a result of dispersion short light pulses propagating down the fibre become longer, which leads to significant inter-symbol interference (ISI) thereby severely degrading the performance. Single modefibres (SMF) effectively eliminate inter-modal dispersion by limiting the number of modes to just one through a much smaller core diameter. However, the pulse broadening still occurs in SMFs due to intra-modal dispersion.
WDM corresponds to the scheme in which multiple optical carriers at different wavelengths are modulated by using independent electrical bit streams (which may themselves use TDM and FDM techniques in the electrical domain) and are then transmitted over the same fiber. The optical signal at the receiver is demultiplexed into separate channels by using an optical technique. WDM has the potential for exploiting the large bandwidth offered by optical fibers. For example, hundreds of 10-Gb/s channels can be transmitted over the same fiber when channel spacing is reduced to below 100 GHz. The concept of WDM has been pursued since the first commercial lightwave system became available in 1980 .WDM systems first appeared around 1995, and their total capacity exceeded 1.6 Tb/s by the year 2000. Several laboratory experiments demonstrated in 2001 a system capacity of more than 10 Tb/s although the transmission distance was limited to below 200 km. Clearly, the advent of WDM has led to a virtual revolution in designing lightwave systems .
We ask that authors follow some simple guidelines. In essence, we ask you to make your paper look exactly like this document. The easiest way to do this is simply to download the template, and replace the content with your own material. Traditional radio systems are fronting encumbrance in designing due to demand of data for diversity of new services. Researchers have developed a contemporary communication system that reveals the properties of prevailing wireless and optical fiber communication technologies, named as Free Space Optical Communication (FSO) . Contemporary FSO system has been mostly explored to take advantages of existing wired optical communication . FSO concentrate on strengthening of communication by assimilating point to point laser signals. FSO provides huge bandwidth, unregulated spectrum, cost effective implementation and low input power as compared to traditional wired fibers [3-4]. FSO also provides alternate to the locations where the deployment of wired network is hard to reach. Despite all these advantages, FSO system is affected by rain, fog, refractive index variation etc. [5-7]. Many researchers have provided different solution to deal with such issues over the years [8-11]. Another issue that is to be addressed is system capacity. Many researchers have employed different multiplexing schemes and even advanced novel one. One such scheme which is widely used in optical communication is known as wavelength divisionmultiplexing (WDM) [12-48]. In this work, we emphasize on the high speed long reach FSO system. To replicate that we employ return-zero modulation format in two different channels each with data rate of 10 Gbps and wavelengths 1550 nm and 1551 nm. The signal is multiplexed using WDM and the channel used is free space of the range 20 Km. The receiver consist of photo diode followed by low pass filter and bit error rate analyser. The rest of the paper is organized as, Section II consists of system description, result and discussion is presented in Section III and Section IV concludes the paper.
Optical wireless communication is an emerging dynamic research and development area that has generated a vast number of interesting solutions to very complicated communication challenges. The transmission power employed in optical wireless communication configurations (mainly indoors) is limited by numerous factors, including eye safety, physical device limitations and power consumption, in outdoor and free space optical systems. To overcome the attenuation due to fog, one could employ lasers with higher powers, but this is also limited by the eye safety standards. Both Quadrature amplitude modulation on discrete multitones and multilevel pulse amplitude modulation are spectrally efficient modulation schemes suitable for light emitting diode based communications, but are less power efficient. Orthogonal frequency divisionmultiplexing (OFDM) transmission scheme is a type of multichannel systems. It does not use individual band limited filters and the oscillators for each sub-channel and furthermore, the spectra of subcarriers are overlapped for bandwidth efficiency. In this paper, a modulation scheme named interval shift key modulation is implemented to modulate the subcarriers in optical wireless system introduced to enhance the output signal parameters Mat Lab is used to measure the data rate, the spectral efficiency, the power efficiency and bit error rate. The Simulation results obtained indicate the efficiency of the proposed system for OFDM multiplexing.
The paper presents both MILP formulations and heuristic algorithms for the resource allocation problem in three SDM- based modular DC switching schemes. The objective of the resource allocations is upper-bounded by the proposed SEA subproblem and tightly lower-bounded by the proposed heuris- tic algorithms. The trade-off between the number of estab- lished connections and throughput is identified. By plotting the interplay of the two objectives on the throughput–connection plane, we find that the best balance can be achieved at the “elbow point” of the Pareto curve, where both objectives are optimized simultaneously. Moreover, the shape of the Pareto curve is related to the relative traffic load and the SDM switching scheme. Despite A3’s extra flexibility, it has only slightly better performance compared with A1. Whereas A2 has the lowest achievable throughput and number of estab- lished connections due to the large resource granularity of its superchannels. The trade-off persists for all the architectures in random-traffic scenario, with shifts of the Pareto curves introduced by the specific traffic distributions and resource granularity.
For a long period of time OFDM was the most popular method for broadband wired and wireless communication. The OFDM development started in late 1950’s with the introduction of frequency divisionmultiplexing. OFDM was the popular choice of point to point communication. It faces challenges in implementation of multi user communication network. Orthogonal frequency division multiple access (OFDMA) network was developed for the purpose of implementation of multi user network. In 1966 the structure and concept of OFDM was developed by using orthogonal overlapping multi- tone signals. The target area of development in multi user communication was perfect carrier synchronization between users to avoid overlapping. It created complexity at the receiver side in terms of order of magnitude of signals.
Abstract--Orthogonal frequency-divisionmultiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, DSL Internet access, wireless networks, power line networks, and 4G mobile communications. OFDM is a frequency-divisionmultiplexing (FDM) scheme used as a digital multi-carrier modulation method. A large number of closely spaced orthogonal sub-carrier signals are used to carry data on several parallel data streams or channels. The orthogonality allows high spectral efficiency, with a total symbol rate near the Nyquist rate for the equivalent baseband signal (i.e. near half the Nyquist rate for the double-side band physical passband signal). Almost the whole available frequency band can be utilized. OFDM generally has a nearly 'white' spectrum, giving it benign electromagnetic interference properties with respect to other co- channel users. The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions (for example, attenuation of high frequencies in a long copper wire, narrowband interference and frequency- selective fading due to multipath) without complex equalization filters. In OFDM, the sub-carrier frequencies are chosen so that the sub-carriers are orthogonal to each other, meaning that cross-talk between the sub-channels is eliminated and inter-carrier guard bands are not required. This greatly simplifies the design of both the transmitter and the receiver; unlike conventional FDM, a separate filter for each sub-channel is not required.
Abstract— over the past few years, there has been increasing emphasis on extending the services available on wired public telecommunications networks to mobile non wired telecommunications users. At present, for mobile network users only low-bit- rate of 100 to 150 kbps data services are available. However, demands for wireless broadband multimedia communication systems (WBMCS) are increasing. It is necessary to use high-bit-rate transmission of at least several MBPS for upcoming new technologies. If digital data is transmitted at the rate of several MBPS, the delay time of the delayed waves is greater than 1 symbol time. Using one of the probably solution for adaptive equalizing signal. There are practical difficulties in operating this equalization at several megabits per second with compact, low-cost hardware. To overcome such an issue and to Achieve WBMCS. Orthogonal frequency divisionMultiplexing (OFDM) Apply to parallel-data transmission scheme, which reduces the influence of multipath fading and makes complex equalizers unnecessary.
The first contribution is the research of possible algorithms that can be applied to a pipe-lined divisioncore and creation of a logic design based on this algorithm. Extensive research is com- pleted in the search of algorithms that can be easily pipe-lined and modeled using Boolean logic. The algorithm must also have the ability to scale from different size bits ranging from small to large. In addition, choosing an algorithm that is not as well-known will create a more unique and possibly better divisioncore. From the chosen algorithm, a logic based design is created. This design is modeled using a hardware description language (HDL) which is easily simulated and analyzed.
We propose an RSCA allocation strategy based on service priorities with the trade-off between throughput and blocking rate, which can increase the high-priority service throughput as much as possible under the condition that the blocking rate is similar.
Due to the superiority of optical fiber communication systems for transmitting data around the world, they have played a key role in making the extraordinary growth in carrying the information to be possible. They have immense transmission capacities and highly immunity from the interferences that can disturb electrical telecommunication systems. However, fiber nonlinearity impairments have been considered as the main problem that limits the maximum transmission reach and reduce the capacity of optical fiber communication system [1-5]. To control signal deterioration, coherent detection has been proposed in combination with fiber compensation technicality [6, 7]. In order to overcome the capacity crunch limitations in optical fiber, physical dimensions namely polarization, space, time, and frequency are explored. Based on extensive studies of multicore fibers, many signals are spatially multiplexed by sending them through many cores or fibers. However, signals that modulated with high-order modulation formats exhibit sensitivity to phase noise due to the fiber nonlinearity and laser phase noise . The phase noise due to fiber nonlinearity, such as self-phase modulation (SPM) restricts the performance of spatially divisionmultiplexing (SDM) systems . The nonlinear distortion is limited by power of optical source, transmission length, and number of amplifiers .