Optical Code Research Articles

Spectral Amplitude Coding Optical CDMA: Performance Analysis on Free Space Optical Channel

In this paper, we investigate the performance of Spectral Amplitude Coding Optical Code Division Multiple Access technique based on Free Space Optical channel. SAC OCDMA is one of the most popular multiplexing techniques since many years and FSO is gaining popularity and is very useful especially in point to point communication. The system presented in this paper utilizes Walsh Hadamard code as signature code. The coder and decoder structures are based on optical filters of fiber Bragg gratings (FBGs). This system focuses on the performance analysis of FSO based systems for subtropical regions. This paper demonstrates the error rate performance in the form of eye diagrams/BER under varying channel gain and link distances. Five cases have been taken which shows that SAC OCDMA FSO system is reliable even for distances sufficient to overcome the last mile problem.

Development of a new high-current triode extraction system for helicon ion source: design and simulation

AbstractThree triode extraction systems are simulated by IBSimu ion optical code for Amirkabir Helicon Ion Source (AHIS). The optimized pierce and suggested parabolic electrodes are introduced for the first time in this paper. The obtained N+beam for parabolic geometry designed for ion implantation has 66 keV energy, and 10.4 mA current. Ion beam emittance and Twiss parameters of the emittance ellipse as the function ofxterm index are calculated for parabolic electrode equation. The simulated triode extraction systems have been evaluated by using of optimized parameters such as the extraction voltage, gap distance, plasma electrode (PE) aperture, and ion temperature. The extraction voltage, gap distance, PE aperture, and ion temperature have been changed in the range of 58–70 kV, 35–39 mm, 4–6 mm, and 0.5–4.4 eV in the simulations, respectively.

Performance Evaluation of Hybrid FSO-SACOCDMA System under Different Weather Conditions

Abstract Spectral amplitude coding optical code division multiple access (SACOCDMA) is a multiplexing technique, which provides faster speed, efficiency, security and unlimited bandwidth. It is widely preferred because of its ability to eliminate multiple access interference (MAI). Free space optics (FSO) provides a wireless link to transmit data securely at higher rates for last mile access. In this work, a 100 Gb/s hybrid FSO-SACOCDMA is designed using direct detection. The performance of FSO using SACOCDMA utilizing NZCC (New Zero Cross Correlation) code is evaluated under different weather conditions (clear weather, haze and fog) for ten users where each user carries 10 Gb/s. The results indicate that in clear weather FSO distance can be extended up to 13 km. Moreover, after using preamplifier in clear weather, FSO enhances the maximum distance to 35 km with acceptable signal to noise ratio and bit error rate. Using an amplifier in the link not only makes the quality of the signal better but it also increases the communication range.

Review on developments in all-optical spectral amplitude coding techniques

The focus of this work is to consolidate a review of accomplished research in the field of optical code division multiple accesses (OCDMA), to outline the state-of-the-art comparison, and to recognize the prominent trends as well as limitations. Code division multiple access (CDMA) has prospered as a vital solution for numerous applications such as cellular mobile communication-based wireless network technology and wired/wireless local area networks that include areas of unlicensed industry, medicine, and science. Due to the commercial utilization of the various advantages of CDMA, it has raised the matter of whether optical technology reliant communications provide the noteworthy advantages to optical networks as well as what are the technologies that facilitate optical chip-based (code division) networks. Aforementioned matter has been addressed in the context of the incorporation of OCDMA in the systems through several experiments of laboratory-based test-bed investigations, field trials, and simulation analysis of multiple users in the recent research works. The performance of OCDMA has an edge over wavelength division multiplexing and offers an unmatched capacity that is seen through simulations. To cater the explosive expansions in internet application, different spectral amplitude codes have been proposed till now. We present a review of the different spectral amplitude codes based on the reported works in spectral amplitude code OCDMA systems. For the purpose of state-of-the-art comparison, parameters considered are data speeds, advanced modulation formats, bit error rate, extinction ratio, decision algorithms, photonic efficiencies of photodetectors, frequency bands, signal-to-noise ratio, forward error correction, photodetector noises, etc., and simulations are carried out in similar input environments. We explore the advantages/limitations of the spectral amplitude codes, recent progress in the technology, practical works on spectral amplitude coding (SAC) throughout the world, encryption–decryption techniques, all-optical methods, literature comparison, future scope, and applications of the SAC-OCDMA codes.

A Tunable Repetition Rate Multiplier for Optical Phase Code Sequences

We propose a tunable repetition rate multiplier for optical phase code sequences consisting of a temporal grating and a temporal 4-F system. The temporal 4-F imaging preserves the input code words at the output, while the temporal grating multiplies the code rate by an integer being programed via an arbitrary wave generator. A lower bound and an upper bound are, respectively, set for aperture width of involved active elements and dispersion deviation of involved dispersion elements to control output phase distortion. By numerical simulation, an 8-period-long input sequence of individual phase Barker code with 10 ns code chip width and 2-rad peak phase is multiplied from 4 to 16 MHz corresponding to multiplication factor tuned from one to four. The expected phase preserving feature and tunable capacity are validated. Degradations including leaked ripples and envelop fluctuation are successfully controlled by the aperture-width bound and the dispersion-deviation bound, respectively. The proposed multiplier provides a promising potential for multifunctional photonic-aided continuous-wave radars with enhanced agility and adaptability.

Energy-efficient QoS-based OCDMA networks aided by nonlinear programming methods

One of the advantages of the optical code division multiple access (OCDMA) system networks over other multiple access methods is the ability to provide differentiated classes of quality of service (QoS) for different users. The performance of the OCDMA networks is mainly limited by the multi-access interference (MAI) coming from other users sharing the same spectral resources. The suitable resource allocation in OCDMA networks allows greater capacity and the reliable deployment of the available resources in the network. This work aiming at applying and analyzing four analytical optimization methods applied to energy efficiency (EE) maximization of OCDMA networks. Hence, such optimization methods were applied and their performance-complexity tradeoffs are compared, namely the augmented Lagrangian method (ALM) (Hadi and Pakravan, 2018), sequential quadratic programming method (SQP), majoration-minimization (MaMi) approach (Sun et al., 2017; Stoica, 2004), as well as Dinkelbach’s method (DK). Tests were performed considering practical and realistic OCDMA networks with a wide range of nodes, typically K={8;16;32} nodes. The evaluated optimization methods were able to achieve convergence and perform suitably to solve the optical EE-OCDMA optimization problem. However, in a few specific high loading system configurations, the DK method did not reach full convergence; besides DK processing time was much greater compared to the promising ALM, SQP and MaMi EE-OCDMA optimization approaches.

Study of the Different Optical Filters in SAC-OCDMA System

Abstract Spectral amplitude coding for optical code division multiple access (SAC-OCDMA) networks has received much attention over the last two decades. This article aims to explore the impact of encoder change on different types of optical filters, such as the Gaussian optical filter and the Bessel optical filter, for high data rates and to give an overview on importance of choosing the optimal type of optical filter according to the frequency range selected by the user is 25 and 50 GHz. SAC-OCDMA transmitter utilizes Wavelength Division Multiplexing multiplexer (WDM MUX) as an encoder, to generate a code having low cross-correlation called Random Diagonal code, and spectral direct detection as a detection technique. The change of optical filter, in WDM MUX, directly affects the performance of the system. The results show that the system for 50 GHz, with a WDM MUX, using a Gaussian optical filter has better performance compared to the optical Bessel filter and can reach a bit error rate (BER) of 10−25. SAC-OCDMA system, using a WDM MUX based on Bessel filters with a bit rate of 300Mb/s, achieves a BER of 10−28 which leads us to recommend it for second norm 25 GHz. Moreover, the power received increases by 4 dBm every 20 Km with the increase in the length of the fibre for both filters Bessel and Gaussian. Our work focuses on the two 25 and 50 GHz bands, after a study on the impact of the change of the bandwidth and the order of the different optical filters used according to the BER applied to the different networks of access, such as local area network (LAN).

Effect of atmospheric turbulence on the BER performance of an optical CDMA FSO link with SIK receiver

An analytical approach is presented to evaluate the effect of atmospheric turbulence on the bit error rate (BER) performance of an optical code division multiple access (OCDMA) free space optical (FSO) link using optical domain encoder and sequence inverse keying (SIK) balanced photodetector receiver. The analysis is presented to find the expression of the signal current and multi access interference (MAI) current at the output of the SIK receiver taking into account the effect of atmospheric turbulenceand the channel effect due to pointing error. The conditional BER conditioned on a given atmospheric turbulence is evaluated. The average BER is obtained by averaging the conditional BER over the probability density function (pdf) of the atmospheric turbulence. The results are evaluated for different code length, number of simultaneous user, link distances and other system parameters. It is found that, the performance of an OCDMA system with a SIK receiver is highly degraded due to turbulence effect and suffers significant power penalty at a given BERwhich can be substantially reduced by increasing the code length using SIK receiver. The penalty is found to be 9 dB and 11.5 dB for link distance 3000m with user number 2 and 16 respectively at BER=10−9. The allowable number of simultaneous user at a given BER is also determined for a given code length.

Analysis and design of weighted MPC in incoherent synchronous OCDMA network

In this paper, a novel spreading code design in incoherent synchronous Optical Code Division Multiple Access networks is introduced. This new code is designed by remodeling and improvising the existing concept of Modified Prime Code (MPC) sequences. In addition, it has been generated at optimum code weight and sufficient code length with respect to the new MPC, Uniform Cross-Correlation MPC, Double Padded MPC and Enhanced MPC. The proposed new code is named as Weighted MPC (WMPC). The used technique to generate the WMPC sequences is based on XOR operation between code words of MPC and then rearranging between them. Such operation is performed to increase code weight. The proposed coding technique has a capability to provide better correlation results, higher throughput, minimum Multiple User Interference and good network performance. Furthermore, the auto and cross-correlation properties of WMPC sequences were investigated, where the results were compared with the correlation results of other Prime Codes family.

Optical CDMA Coded STBC Based on Chaotic Technique in FSO Communication Systems

Free-Space Optical (FSO) can provide high-speed communications when the effect of turbulence is not serious. However, Space-Time-Block-Code (STBC) is a good candidate to mitigate this seriousness. This paper proposes a hybrid of an Optical Code Division Multiple Access (OCDMA) and STBC in FSO communication for last mile solutions, where access to remote areas is complicated. The main weakness effecting a FSO link is the atmospheric turbulence. The feasibility of employing STBC in OCDMA is to mitigate these effects. The current work evaluates the Bit-Error-Rate (BER) performance of OCDMA operating under the scintillation effect, where this effect can be described by the gamma-gamma model. The most obvious finding to emerge from the analysis is that the BER can be enhanced by orders of magnitude for different numbers of users and different values of scintillation effects using a MIMO channel as compared to Single-Input-Single-Output (SISO) one. The theoretical analysis of the derived BER, which is based on gamma-gamma model, is validated through the Monte Carlo simulation.

Optimization of space-charge dominated injection beam line of high current proton RFQ

Design of a space charge dominated proton beam-line from an ECR ion source to a high current RFQ has been carried out using analytical formulation. The parameters of the beam-line consisting of two solenoids, a slit for selecting H+ and rejecting H2+, and buncher are optimized to match the proton beam with the acceptance of RFQ . Analytical formulation for multispecies beam instead of conventional optical code has helped in simultaneously achieving different objectives within a compact but optimum length. Disc model having finite input energy width for longitudinal calculations and K-V transverse envelope equations for individual macro-discs including the bunching effect has been used. Selected parameters have been further corroborated by particle tracking using the 3D field of buncher and RFQ . Efficient selection/rejection of species has been verified with different type of input particle distributions in particle tracking. Finally the transmitted H+ and remaining H2+ has been tracked through the RFQ . The ratio of H+ to H2+, which is roughly 7:3 at exit of ECRIS could be reduced to 32:1 after the slit, while through RFQ remaining H2+ gets only transmitted but without any acceleration.

Implement Algorithm to Reduce Effect of Snowy Weather in North of Iraq on Fso Signal

Free space optic (FSO) is now a well-established access technology that commonly start using in wireless data transmission because of its large advantage like cost effective and Line-Of-Sight (LOS) permission which lead this technology to be more secure and get own to everyone. While radio frequency (RF) travels using optical fiber through weather atmospheric, large phenomena like (Rain-fog/haze-snow and temperature) works to block laser beam from reaching its receiver. Optical code division multiple access (OCDMA) is a hot topic due to its large advantage such as permitting large number of user to transmit large amount of data using single optical laser beam , but multiple users share single laser beam lead to increase multiple access interference (MAI) which primary deteriorates the performance of OCDMA. Sub-Carrier Multiplexing (SCM) is used in the system to multiplex multiple data stream on single laser beam. Spectral Amplitude Coding (SAC) technique used to enhance FSO signal by allocate own spectrum to each user, this technique generate code called Multi-Diagonal (MD) code that allow zero interaction between user data. This paper focused on the effect of snowy weather in north of Iraq on the FSO signal by using (SCM-SAC-OCDMA) based on multi-diagonal code and determined the distance between the transverse with approach bit error rate (BER) in the receiver side. Based on the system result data can travel through [0.4 - 4] Km as transmission distance under different snow rate with BER between [].

A New Code Family for QS-CDMA Visible Light Communication Systems

Visible light communication (VLC) is a promising technology for wireless communication networks. Optical code division multiple access (OCDMA) is a strong candidate for VLC-based applications. The predominant source of bit error in OCDMA is the multiple access interference (MAI). To eliminate MAI in synchronous OCDMA, zero cross correlation (ZCC) codes have been proposed. However, synchronization problems and multipath propagation introduce relative non-zero time delays. Therefore, the zero correlation zone (ZCZ) concept was introduced. In this paper, we propose a new method for generating ZCC codes. The proposed construction can accommodate any number of users with flexible Hamming weight. The numerical results obtained show that the proposed codes significantly reduce MAI, compared to ZCC, as well as ZCZ codes.

Collective compensation of an inter-chip intensity discrepancy for a 4ch QPSK FE-SOCDM system with Si-based ODFT and electrical DFT

An intensity-sloped optical code with an optical chip-pulse stream generated by Si-based ODFT suffers from crosstalk and signal-to-noise (SNR) degradation. To mitigate these problems related to code-orthogonality reduction, we propose a simple intensity-discrepancy-compensation scheme that involves adjusting the chip-level intensity in the digital-domain. We numerically show a 0.1 dB SNR improvement for 40 Gb/s quadrature phase-shift keying (QPSK) Fourier-encoded synchronized optical code division multiplexing (FE-SOCDM) signal when multiplexing 1 dB/chip intensity-sloped optical codes. A proof-of-principle experiment achieves a 0.3 dB received power improvement using intensity-discrepancy compensation for two optical code multiplexing signals with 1.5 dB/chip.

A modified topology achieved in OFDM/SAC-OCDMA-based multi-diagonal code for enhancing spectral efficiency

In this paper, a modified topology-based orthogonal frequency division multiplexing–spectral amplitude coding in optical code division multiple access (OFDM–SAC-OCDMA) has been introduced. Such analysis aims to explain the effect of spectral efficiency with respect to multi-diagonal (MD) code. The new proposed technique introduces a fusion system between the two-code keying scheme and the forward error correction (FEC). The introduced analysis has targeted the effect of signal-to-noise ratio, bit error rate, and spectral efficiency with the presence of beat noise, phase incoherent intensity noise, and thermal noise. Numerical simulations have been utilized and tested in order to illustrate the validation of the (MD) code method to eliminate dominant noise. The calculation results show the following; the SNR and BER for MD under the presence of the previous discussed signal degradation is equal 161 and 1.2 × 10−10, respectively, according to a predefined number of users 150 comparing with some existing codes such as: modified frequency hopping code, Hadamard (HD) code, modified quadratic congruence code. The proposed unipolar encoding with direct detection technique-based OFDM/SAC-OCDMA scheme achieves an enhancement in the performance of SE over the unipolar encoding with direct detection technique-based SAC-OCDMA technique by 3.455 dB. The proposed two keying scheme-based OFDM/SAC-OCDMA introduces an enhancement in the performance of the SE over the unipolar encoding with direct detection technique-based OFDM/SAC-OCDMA technique by 2.8859 dB. FEC has been applied in order to increase the spectral efficiency for different BERs, which the numerical results show that FEC provides 1.7457 dB. Finally, the total enhancement for SE was about 8.0866 dB.

Optimal 2-D $$(n\times m,3,2,1)$$ ( n × m , 3 , 2 , 1 ) -optical orthogonal codes and related equi-difference conflict avoiding codes

This paper focuses on constructions for optimal 2-D $$(n\times m,3,2,1)$$ -optical orthogonal codes with $$m\equiv 0\ (\mathrm{mod}\ 4)$$ . An upper bound on the size of such codes is established. It relies heavily on the size of optimal equi-difference 1-D (m, 3, 2, 1)-optical orthogonal codes, which is closely related to optimal equi-difference conflict avoiding codes with weight 3. The exact number of codewords of an optimal 2-D $$(n\times m,3,2,1)$$ -optical orthogonal code is determined for $$n=1,2$$ , $$m\equiv 0 \pmod {4}$$ , and $$n\equiv 0 \pmod {3}$$ , $$m\equiv 8 \pmod {16}$$ or $$m\equiv 32 \pmod {64}$$ or $$m\equiv 4,20 \pmod {48}$$ .

Independent Biaxial Scanning Light Detection and Ranging System Based on Coded Laser Pulses without Idle Listening Time.

The goal of light detection and ranging (LIDAR) systems is to achieve high-resolution three-dimensional distance images with high refresh rates and long distances. In scanning LIDAR systems, an idle listening time between pulse transmission and reception is a significant obstacle to accomplishing this goal. We apply intensity-modulated direct detection (IM/DD) optical code division multiple access (OCDMA) using nonreturn-to-zero on-off keying to eliminate the idle listening time in scanning LIDAR systems. The transmitter records time information while emitting a coded laser pulse in the measurement angle derived from the pixel information as the measurement direction. The receiver extracts and decodes the reflected laser pulses and estimates the distance to the target using time-of-flight until the pulse is received after being transmitted. Also, we rely on a series of pulses and eliminate alien pulses via several detection decision steps to enhance the robustness of the decision result. We built a prototype system and evaluated its performance by measuring black matte and white paper walls and assessing object detection by measuring a watering can in front of the black matte paper wall. This LIDAR system eliminated both shot and background noises in the reception process and measured greater distances with improvements in accuracy and precision.

Performance enhancement of the 3D OCDMA system by using dynamic cyclic shift and multi-diagonal codes

A new three-dimensional (3D) code is developed for spectral/time/spatial optical code division multiple access (OCDMA) system namely 3D dynamic cyclic shift/multi-diagonal (3D-DCS/MD). Its construction is based on the dynamic cyclic shift code for spectral and temporal encoding and multi-diagonal code for spatial one. The data of users are retrieved correctly using the MAI cancelation property. Compared with the OCDMA systems using 3D perfect/multi-diagonal, and 3D perfect difference, the 3D-DCS/MD system has a low phase-induced intensity noise. Hence, this system overcomes these codes in terms of data rate, required source power and spectral width. Also, it can accommodate more than 200 users at 622 Mbps.

Performance Estimation of Advanced Intensity Modulation Formats Using Hybrid SAC-OCDMA through IsOWC Channel

Abstract Spectral amplitude coding optical code division multiple access (SAC-OCDMA) is one of the most important multiplexing schemes of OCDMA that has turned out to be a stimulating investigating area in optical communication due to its increased privacy, network capacity and its flexibility in allocating the channels and asynchronous environment. On the other hand, Inter-satellite optical wireless communication (IsOWC) which is a favorable area of research in optical communication is useful for bursty transmissions and long-distance communications. In this paper, we have designed a hybrid SAC-OCDMA system through IsOWC channel using ZCC code for advanced intensity modulation formats (CSRZ, Db, and AMI). The investigation is done for four users at a bit rate of 40(4×10) Gb/s using a direct detection technique. Further, on comparing the proposed system using advanced intensity modulation formats, the result shows that system using CSRZ format is better in terms of BER, Q-factor, SNR and the eye diagram with respect to AMI and Db.

Facile Access to Wearable Device via Microfluidic Spinning of Robust and Aligned Fluorescent Microfibers.

Microfluidic spinning technology (MST) has drawn much attention owing to its ideal platform for ordered fluorescent fibers, along with their large-scale manipulation, high efficiency, flexibility, and environment friendliness. Here, we employed the MST to fabricate a series of uniform fluorescent microfibers. By adjusting the microfluidic spinning parameters, the as-prepared microfibers of different diameters are successfully obtained. For more practice, these regular arranged fibers could be formed to versatile fluorescent codes by using various microfluidic chips. Also, these versatile fluorescent fibers could be further weaved into a white fluorescent film via continuous and cross-spinning process, which could be applied in a white light emitting diode (WLED) and a wearable device. Besides, we investigated the MST-directed microreactors to carry out green synthesis of CdSe quantum dots (QDs) fibers by the knot of Y-type microfluidic chip. The as-prepared CdSe QDs show nice optical property and are good candidate as phosphors in WLED. This strategy offers a facile and environment-friendly route to fluorescent hybrid microfibers and might open their potential application in optical devices, security, and fluorescent coding.