Optical Code Research Articles

DW-ZCC code based on SAC–OCDMA deploying multi-wavelength laser source for wireless optical networks

In this paper, double weight zero cross correlation (DW-ZCC) code is proposed for spectral amplitude coding optical code division multiple access (SAC–OCDMA) system. DW-ZCC takes the advantages of two previously proposed SAC-codes namely modified double weight (MDW) and zero-cross correlation (ZCC) codes, while providing optimized code length and maximum cross-correlation of zero. Although the proposed code can be utilized in SAC–OCDMA system with any optical medium, this research work focuses on outdoor wireless optical networks (WON) deploying multi-wavelength laser source, where optical bandwidth is much limited. The mathematical and simulation analysis of proposed system employing direct decoding (DD) is developed, considering the influences of turbulence and system noises including relative intensity noise, optical beat interference (OBI) and receiver noises. It is shown that employing DD detection; it is possible to completely avoid OBI which enhances system capability. The results show that SAC–OCDMA–WON system is noticeably improved using DW-ZCC in term of transmission distance by at least 200 m in comparison with MDW and conventional ZCC codes.

Mode-Locked Laser Diodes and Their Monolithic Integration

We describe mode locked laser diodes (MLLDs) operating from 40 GHz to >1 THz. Below 40 GHz, operation at the fundamental cavity frequency is appropriate, but at higher frequencies harmonic mode-locking (HML) is used. To increase output power and control nonlinear behavior, the gain needs to be modified, and an AlGaInAs/InP structure with a three-quantum-well active layer and passive far-field reduction layer is presented. In 40-GHz all-active MLLDs, this structure offers improvements in internal loss, slope efficiency, mode locking (ML) range, RF linewidth, timing jitter, far field pattern, and coupling efficiency to a single-mode fiber. By creating a transparent passive waveguide in part of the cavity, a 490-fs pulse width was achieved, the shortest reported from any quantum well MLLD. Several approaches are described for HML: colliding pulse ML operating up to 240 GHz, coupled cavity ML up to 160 GHz, and sampled Bragg grating constructions up to 1.28 THz. This latter approach offers stable HML over a wide range of bias conditions. Finally, we report a synchronized multicolor ML laser array, containing four 40-GHz lasers with designated wavelength registration for optical code division multiple access or optical time division multiple access applications.

Multiuser MIMO Indoor Visible Light Communication System Using Spatial Multiplexing

Visible light communications is an energy efficient and cost-effective solution for indoor wireless access. In this paper, we propose a multiple input multiple output system using centralized or decentralized transmitted power allocation algorithms with multiple LEDs and photodetectors. The proposed system uses an optical code division multiple-access technique to support multiple users. Time-space minimum mean squared error filters at the receivers are designed to diminish the effect of multiple-access interference. In the centralized power allocation algorithm, all the LED lamps in the room are coordinated and controlled by a central controller; each LED lamp supports all the users within the indoor area. The decentralized power allocation algorithms we propose have similar bit error rate performance yet less computational burden compared to the centralized algorithm. In our decentralized algorithms, users are supported by a subset of the LEDs, and so the optimization problem size can be reduced by as much as $93\%$ . For each receiver, multiple photodetectors with different orientations are employed to improve the signal to interference plus noise ratio. In addition, some practical considerations such as shadowing effects, illumination requirements, dimming control, and transmitted power quantization are taken into account.

Extracting sub-exposure images from a single capture through Fourier-based optical modulation

Through pixel-wise optical coding of images during exposure time, it is possible to extract sub-exposure images from a single capture. Such a capability can be used for different purposes, including high-speed imaging, high-dynamic-range imaging and compressed sensing. In this paper, we demonstrate a sub-exposure image extraction method, where the exposure coding pattern is inspired from frequency division multiplexing idea of communication systems. The coding masks modulate sub-exposure images in such a way that they are placed in non-overlapping regions in Fourier domain. The sub-exposure image extraction process involves digital filtering of the captured signal with proper band-pass filters. The prototype imaging system incorporates a Liquid Crystal over Silicon (LCoS) based spatial light modulator synchronized with a camera for pixel-wise exposure coding.

Study of fiber optic code division multiple access Code families for Application in Optical Communication based on weight and bit error rate

This paper investigates on fiber optic code division multiple access (FOCDMA) code families using different sets of parameter. The different code families considered here are generalized multi-wavelength Reed-Solomon code (GMWRSC), complete row-wise orthogonal pairs (CRWOP), row-wise orthogonal pairs (RWOP) and Multiwavelength Optical Orthogonal Code (MWOOC). The parameters under investigation in this work chosen to be number of maximum users (Nmax),Bit error rate(BER),Spreading Factor(Sf),Weight(K’),Number of Wavelengths(WI) and number of time chips(T). By using suitable mathematical formula, computation is made for above said parameters using aforementioned methods At the end a healthy comparison was made to identify efficient one among them just by estimating cardinality of each result. The comparison result revealed that row wise orthogonal pairs (RWOP) code family gives high performance.

Multi-factor product authentication using integrated Quick Response (QR) code pixelated antenna

Abstract A Quick Response (QR) Code style antenna is presented. Such an antenna can provide two-level authentication, both optically through the current QR technology, plus a radio frequency (RF) signature from microstrip patch antenna designed from the QR signature using copper patterning. The antenna is designed through the pixilation of a patch antenna where conductor is present in the dark regions of the optical QR code. The QR based antenna design has a unique frequency and radiation signature and can be used for RF authentication of products. The design process for the pixilation is presented as well as fabrication and measured results of a QR code antenna design. The possibility of using a Genetic Algorithm to create a “library” of acceptable antenna results in accordance with the QR data it represents is also discussed.

Performance Investigation of 2-D Optical Orthogonal Codes for OCDMA

Abstract In this paper, comparative analysis of code performance of dissimilar optical 2-D codes from Optical Orthogonal code family has been studied. Optical 2-D codes considered from OOC family are (n,w,1,2) OOC, SPS/OOC, OCFHC/OOC, EPC/OCS and VWOOC. By utilizing hard limiting error probability (HEP) equations and combinatorial method, code performance of each considered code is evaluated in detail. On the basis of detailed comparative performance analysis, EPC/OCS is concluded as best performing codes among all other optical codes under consideration. EPC/OCS possesses much better correlation properties, along with lower hit probability values which are responsible for its supremacy in performance characteristics to the other OOCs considered.

Development of ZCCC for multimedia service using SAC-OCDMA systems

Abstract Spectral Amplitude Coding – Optical Code Division Multiple Access systems are gaining popularity due to their property of very low multiple access interference. A new code with zero cross correlation, termed as Zero Cross Correlation Code (ZCCC) is proposed. Code construction algorithm is designed with any weight for any number of users having constant, or variable weights. Variable weight (VW) codes give different quality of service, and are suitable, and useful for multimedia applications. The performance of proposed codes is analyzed using direct detection technique. Numerical results show that the use of proposed code yields lower bit error rate, and/or require lower code length than existing codes. Simulation results on OptiSystem 13 also show better performance of proposed code than existing ZCC code (Anuar et al., 2009). Proposed ZCCC requires only two filtering elements irrespective of weight, and construct codes without using mapping as compared to ZCC codes.

Relative Difference Sets Partitioned by Cosets

We explore classical (relative) difference sets intersected with the cosets of a subgroup of small index. The intersection sizes are governed by quadratic Diophantine equations. Developing the intersections in the subgroup yields an interesting class of group divisible designs. From this and the Bose-Shrikhande-Parker construction, we obtain some new sets of mutually orthogonal latin squares. We also briefly consider optical orthogonal codes and difference triangle systems.

OCDMA and its Applications in Fiber Optics Communication Networks

As multiple accessing technique that can be used to provide access to multiple users to transmit data to same channel simultaneously without any scheduling or delay in transmission, Optical Code Division Multiple Access (OCDMA) has been an alluring for the past few decades. All users share all bandwidth simultaneously and access the network asynchronously. To provide access to multiple users simultaneously, many coding techniques to increase possible users and improve performance has been analyzed for OCDMA systems. In this paper, many different proposed methods of coding are reviewed. Performance, cardinality and capacity of these codes are discussed. Significance of introducing dimensions in optical code is also be discussed.

Performance Analysis of Physical-Layer Security in an OCDMA-Based Wiretap Channel

Based on information-theoretic security, physical-layer security in an optical code division multiple access (OCDMA) system is analyzed. For the first time, the security leakage factor is employed to evaluate the physicallayer security level, and the safe receiving distance is used to measure the security transmission range. By establishing the wiretap channel model of a coherent OCDMA system, the influences of the extraction location, the extraction ratio, the number of active users, and the length of the code on the physical-layer security are analyzed quantitatively. The physical-layer security and reliability of the coherent OCDMA system are evaluated under the premise of satisfying the legitimate user’s bit error rate and the security leakage factor. The simulation results show that the number of users must be in a certain interval in order to meet the legitimate user’s reliability and security. Furthermore, the security performance of the coherent OCDMA-based wiretap channel can be improved by increasing the code length.

Assessment of Optical Coherence Tomography Color Probability Codes in Myopic Glaucoma Eyes After Applying a Myopic Normative Database

To evaluate the optical coherence tomography (OCT) color probability codes based on a myopic normative database and to investigate whether the implementation of the myopic normative database can improve the OCT diagnostic ability in myopic glaucoma. Comparative validity study. In this study, 305 eyes (154 myopic healthy eyes and 151 myopic glaucoma eyes) were included. A myopic normative database was obtained based on myopic healthy eyes. We evaluated the agreement between OCT color probability codes after applying the built-in and myopic normative databases, respectively. Another 120 eyes (60 myopic healthy eyes and 60 myopic glaucoma eyes) were included and the diagnostic performance of OCT color codes using a myopic normative database was investigated. The mean weighted kappa (Kw) coefficients for quadrant retinal nerve fiber layer (RNFL) thickness, clock-hour RNFL thickness, and ganglion cell-inner plexiform layer (GCIPL) thickness were 0.636, 0.627, and 0.564, respectively. The myopic normative database showed a higher specificity than did the built-in normative database in quadrant RNFL thickness, clock-hour RNFL thickness, and GCIPL thickness (P < .001, P< .001, and P < .001, respectively). The receiver operating characteristic curve values increased when using the myopic normative database in quadrant RNFL thickness, clock-hour RNFL thickness, and GCIPL thickness (P= .011, P= .004, P < .001, respectively). The diagnostic ability of OCT color codes for detection of myopic glaucoma significantly improved after application of the myopic normative database. The implementation of a myopic normative database is needed to allow more precise interpretation of OCT color probability codes when used in myopic eyes.

Combinatorial constructions of optimal (m, n, 4, 2) optical orthogonal signature pattern codes

Optical orthogonal signature pattern codes (OOSPCs) play an important role in a novel type of optical code-division multiple-access (CDMA) network for 2-dimensional image transmission. There is a one-to-one correspondence between an $(m, n, w, \lambda)$-OOSPC and a $(\lambda+1)$-$(mn,w,1)$ packing design admitting an automorphism group isomorphic to $\mathbb{Z}_m\times \mathbb{Z}_n$. In 2010, Sawa gave the first infinite class of $(m, n, 4, 2)$-OOSPCs by using $S$-cyclic Steiner quadruple systems. In this paper, we use various combinatorial designs such as strictly $\mathbb{Z}_m\times \mathbb{Z}_n$-invariant $s$-fan designs, strictly $\mathbb{Z}_m\times \mathbb{Z}_n$-invariant $G$-designs and rotational Steiner quadruple systems to present some constructions for $(m, n, 4, 2)$-OOSPCs. As a consequence, our new constructions yield more infinite families of optimal $(m, n, 4, 2)$-OOSPCs. Especially, we shall see that in some cases an optimal $(m, n, 4, 2)$-OOSPC can not achieve the Johnson bound.

Packet Loss Rate Differentiation in slotted Optical Packet Switching OCDM/WDM

We propose a multi-class mechanism for Optical Code Division Multiplexing (OCDM), Wavelength Division Multiplexing (WDM) Optical Packet Switch (OPS) architecture capable of supporting Quality of Service (QoS) transmission. OCDM/WDM has been proposed as a competitive hybrid switching technology to support the next generation optical Internet. This paper addresses performance issues in the slotted OPS networks and proposed four differentiation schemes to support Quality of Service. In addition, we present a comparison between the proposed schemes as well as, a simulation scheduler design which can be suitable for the core switch node in OPS networks. Using software simulations the performance of our algorithm in terms of losing probability, the packet delay, and scalability is evaluated.

Effect of Pointing Error on BER Performance of a Multi-wavelength OCDMA FSO System with SIK Dual Detector Receiver

Abstract A novel analytical approach is presented to evaluate the bit error rate (BER) performance of a multi-wavelength optical code division multiple access (MW-OCDMA) free space optical (FSO) system using optical domain encoder and sequence inverse keying (SIK) balanced photodetector direct detection receiver taking the effect of pointing errors into considerations. The analysis is carried out to find the expression for the signal, multi-access interference (MAI) and crosstalk at the output of the SIK receiver in presence of pointing error. The BER performance results are evaluated for different values of standard deviation of pointing error, code length, number of simultaneous user and other system parameters. It is found that, MW-OCDMA system offers improved BER performance over single wavelength OCDMA FSO system. However, the performance of an MW-OCDMA system is degraded due to the effect of pointing error between the laser transmitter and optical receiver and the system suffers significant power penalty at a given BER of 10−9. The penalty is found to be 11.0 dB, 24.0 dB and 30 dB for jitter standard deviation of 1.3, 1.8 and 2.5 respectively when code length is 512 and number of user is 8 for number of wavelength 8. Further, the penalty can be greatly reduced by increasing the code length for a given number of user and number of wavelength.

Spectral/spatial optical CDMA code based on Diagonal Eigenvalue Unity

Abstract A new two dimensional Diagonal Eigenvalue Unity (2D-DEU) code is developed for the spectral⧹spatial optical code division multiple access (OCDMA) system. It has a lower cross correlation value compared to two dimensional diluted perfect difference (2D-DPD), two dimensional Extended Enhanced Double Weight (2D-Extended-EDW) codes. Also, for the same code length, the number of users can be generated by the 2D-DEU code is higher than that provided by the others codes. The Bit Error Rate ( BER ) numerical analysis is developed by considering the effects of shot noise, phase induced intensity noise (PIIN), and thermal noise. The main result shows that BER is strongly affected by PIIN for the higher source power. The 2D-DEU code performance is compared with 2D-DPD, 2D-Extended-EDW and two dimensional multi-diagonals (2D-MD) codes. This comparison proves that the proposed 2D-DEU system outperforms the related codes.

Advance Method for Security Enhancement in Optical Code Division Multiple Access System

This paper proposes a new design of encoder and decoder with novel code design for one–dimensional (1D) (spectral domain) and two-dimensional (2D) (spectral and time domain) optical code divisions multiple access system. The suggested code has a zero cross-correlation property in 1D and 2D modes, so multiple-access interference (MAI) is totally eliminated. In proposed new encoder, code reconfiguration is achieved within two users in each group at the transmitter end with defined sequence. This approach degrades the code detection probability at the receiving end against the eavesdropper in the presence of single user in network. Another switching improves the code security against the on–off energy-level detection at the transmitter end. The mathematical and simulation analysis is performed for the proposed code. The probabilities of code estimation at the transmitter and receiver ends are analysed which shows a better confidentiality. The mathematical analysis shows that the proposed code has a better performance than the existing 1D random diagonal, 1D modified double-weight, 2D perfect difference, and 2D diluted perfect difference codes.

Construction and Analysis of a Novel SAC-OCDMA System with EDW Coding using Direct Detection Technique

Abstract Spectral amplitude coding optical code division multiple access (SAC-OCDMA) is a promising innovation for burst and asynchronous environment. This paper endeavors to analyze the efficacy of the proposed optimum SAC-OCDMA system by utilizing enhanced double-weight (EDW) code for six users operating at a bit rate of 60 Gb/s (10×6 Gb/s). Also, an algorithm is designed for EDW code with mapping technique for any weight that can be greater than two. The EDW code is analyzed for bit error rate (BER) and Q-factor using direct detection technique. Further, the system is compared with three dispersion compensating techniques (pre, post and symmetrical). The results indicate that by using symmetrical compensation the maximum usable distance increases to more than twice as compared to without compensation for the targeted BER (10−9), whereas by using p- and post-compensation the BER value increases to 10−13 as compared to without compensation whose BER value is 10−5. The comparison results show acceptable performance improvement.

Synthesis of lanthanum doped carbon dots for detection of mercury ion, multi-color imaging of cells and tissue, and bacteriostasis

This work describes a hydrothermal method for the preparation of multi-functional carbon quantum dots of the type La-CQDs. The La-CQDs are 4.3±0.3nm in diameter and have a good dispersion and exhibit excellent emission property and high stability, as well as excitation-dependent emission behavior with typical excitation/emission peaks at 350/460nm. They can also be used as an effective fluorescent probe for the quenchometric determination of mercury ion in aqueous solution with a detection limit of 0.1µM. The particles are readily internalized by liver epithelial HepG2 cells and enable multi-color fluorescence imaging by displaying green and red emission if excited with 488 and 543nm light, respectively. Intravenous injection of the quantum dots in nude mice, in turn, enabled tissue imaging. The La-CQDs possess abundant phosphate, hydroxyl, pyridinic, pyridine-like and pyrrole-like nitrogen groups. Therefore, they can exhibit strong fluorescence, improve the accuracy as an optical monitoring code both in vitro and in vivo, and enhance blood compatibility. In vitro investigations show that La-CQDs do not exhibit significant apoptotic effects on NIH3T3 cells even at a high concentration (2.5mg/mL) while they exhibit improved antibactericidal capacity of the La-CQDs against gram-positive S. aureus and gram-negative E. coli bacteria was also observed. No apparent pathological damages are observed in all organs during the 30-day period, which suggests that La-CQDs do not produce detectable long-term toxicological responses.

Managing Dispersion-Affected OCDMA Auto-Correlation Based on PS Multiwavelength Code Carriers Using SOA

Distortion of the optical code division multiple access (OCDMA) auto-correlation width by fiber chromatic dispersion can severely influence incoherent OCDMA transmission based on picosecond multiwavelength pulses. To the best of our knowledge, we report for the first time the use of a semiconductor optical amplifier (SOA) for manipulation of the OCDMA auto-correlation consisting of multiwavelength code carriers in order to provide needed compensation. The OCDMA transmission system was based on two-dimensional wavelength-hopping time-spreading codes with 8&#x00A0;ps multiwavelength pulses as the code carriers. Different techniques deploying an SOA for auto-correlation width adjustments were investigated and their effectiveness was subsequently verified on the OCDMA transmission through a 17&#x00A0;km long fiber-optic testbed connecting Strathclyde and Glasgow Universities.