Volume 39, Issue 4 -

The aim of this paper was to propose and design an all optical four-channel demultiplexer using two-dimensional photonic crystals. To do so a resonant cavity was created by reducing the radius of the two adjacent rods. The radius of these defect rods was about 85 nm. The resonant cavity has a resonant mode at 1,557 nm. Then by using four resonant cavities with different radius values a four-channel optical demultiplexer was designed. The demultiplexer has four optical channels at λ 1 =1,537 nm, λ 2 =1,546 nm, λ 3 =1,553 nm and λ 4 =1,560 nm.

Polarization dependency imposes great limitations for application of optical device in optical networks and systems. In this paper, we are going to design and propose a 1*2 all optical polarization independent power splitter based on photonic crystal structures. For designing such a device we should employ a fundamental photonic crystal structure which has joint photonic band gap. The obtained results show that at 1,560 nm wavelength the final structure has transmission efficiency equal to 45 % for outputs in both TE and TM modes.

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).

This paper proposes the Nonlinear Adaptive Filter bank–based artificial bee colony Optimizer (NAFO) based on Wiener filter for inverse modeling of nonlinear fiber link. Here a third-order inverse Volterra-based nonlinear equalizer (VNLE) is used to compensate the fiber nonlinearities using MATLAB Simulink. In the novel method the Mean Square Error (MSE) of the optical link is measured and compared with IIR-filter based technique. The MSE is reported to be 10 –14 value lesser in the novel experimental setup consequently the proposed technique shows enhanced and efficient performance.

This paper reports an interesting phenomenon of optical modulation enhancement produced by CW optical sideband injection locking of a directly modulated Fabry-Perot Laser Diode (FPLD) lasing at 1557.1 nm wavelength, the modulation being sinusoidal in nature and effected at 300 kHz and 3 MHz. This investigation is carried out for direct modulation of the FPLD effected in the RF region at 300 kHz and 3 MHz in contradistinction to earlier studies being conducted with the modulation in the microwave frequency band. A nonlinear analysis has been carried out which corroborates experimental observation on modulation enhancement. At low level of optical Intensity Modulation (IM) index, not exceeding 20 %, typical modulation enhancement of 2 % at 300 kHz and 11 % at 3 MHz modulation frequency have been observed. Larger modulation enhancement is expected at higher values of IM indices of the slave FPLD and for medium to high power laser diodes. This circuit can have direct application in Wavelength Division Multiplexed-Passive Optical Network (WDM-PON).

In this paper, a hybrid DWDM/multiple-beam free space optics (FSO) communication link has been proposed consisting of 16 channels with the channel spacing of 100 GHz (0.8 nm) each transmitting at 2.5 Gbps bit rate. At the receiver terminal, an erbium-doped fiber amplifier (EDFA) is used to amplify the received signal. The results show an improved performance of hybrid DWDM/multiple-beam FSO link in terms of Q factor, received power, and link distance under rain attenuation of 19.2 dB/km. The proposed link design was able to transmit data from 16 channels, each transmitting at a bit rate of 2.5 Gbps along a link length of 2,300 m in FSO link under heavy rain weather conditions.

This paper describes an useful scheme of ultra-dense wavelength division multiplexed-passive optical network (UDWDM-PON) meant for the bidirectional transmission of analog video signals to the users in the Optical Network Unit (ONU). Each user has a dedicated wavelength which carries a group of analog video channels. This PON scheme is bidirectional with a long distance of transmission of 100 km typically over a single optical fiber. The video channels designated for a particular user in the ONU can be continuously tuned by a post-detection tunable bandpass filter. Intermodulation distortion (IMD) resulting from a mixing of analog video channels carried by a single wavelength has been calculated for a group of three video channels which lies in the range of –30 dB to –85 dB typically for a set of values of parameters used in practice. This IMD level is fairly acceptable for analog video signal transmission and reception in practice. The novelty of this scheme is that it is long reach.

The existing radio frequency technologies face the bandwidth limitation due to the increase in the number of devices being used inside the indoor environment. though, the backbone networks are capable of carrying a large amount of data to the tune of several hundreds of gigabits per second, the last mile techniques, especially the indoor connectivity, continue to pose a challenge in terms of handling large data capacity. The indoor optical wireless communication could be one such promising technology that is potentially capable of handling large amount of data transmission within the indoor environment. The receiver mobility may largely affect the key communication parameters which undergo spatial variations. Therefore, in this paper, we investigate several parameters especially the channel capacity, bit error rate, received pulse power, pulse delay spread and signal-to-noise ratio pertaining to receiver mobility.

Orthogonal frequency division multiplexing (OFDM) is used with visible light communication (VLC) systems to reduce the effects of inter-symbol interference (ISI) and to achieve communication with high speed of data transmission and huge bandwidth. However, OFDM-based VLC systems suffer from high peak-to-average power ratios (PAPRs). This paper proposes a new hybrid PAPR reduction technique based on signal transformation combined with clipping. The Hadamard transform is used in the proposed technique due to its advantages in reducing the PAPR without affecting the bit error rate (BER) of VLC systems. The optimum clipping threshold at which we can simultaneously reduce the PAPR and improve the BER of VLC systems is also determined. In this paper, we also propose a new OFDM structure based on using discrete cosine transform (DCT) precoding before inverse fast Fourier transform (IFFT) stage to further improve the PAPR reduction capability and BER performance. Several experiments are carried out to test the performance of the proposed technique in terms of complementary cumulative distribution function (CCDF) and the BER. The obtained results show that the proposed technique can simultaneously reduce the PAPR and achieve good BER performance when compared to the original OFDM-based VLC system.

Visible light communication (VLC) is an emerging optical communication technology, and indoor positioning of moving target devices is one of most important issues in the VLC system. In this study, we focused on LED base station location planning to improve the accuracy of the positioning method based on the received signal strength intensity (RSS) and the Kalman filter (KF). We developed a new base station location-planning scheme called equilateral triangle distribution. We proved theoretically that the equilateral triangle distribution scheme reduced the positioning error area when compared with the rectangular distribution scheme. The simulation results showed that the measuring error of the equilateral triangle distribution method using KF was less than 5 cm, even when the receiver was located at the boundary of the room. Our method verified that the VLC indoor positioning accuracy can be improved when LED base stations are distributed according to our equilateral triangle distribution scheme.

Radio over Fiber (RoF) is one of the solutions to the “last mile” because of its bandwidth advantage offered by fiber and the mobility and flexibility of wireless systems. In this paper, the transmission performance of DSB, SSB and OCS with three modulation formats is established, and a new single-sideband modulation single-mode optical fiber transmission model is proposed, and simulated analysis is done to the system. In this paper, 40 GHz millimeter-wave signal was generated by external modulation, and the received signal is received by coherent demodulation. In this paper, Matlab and VPI are used for combine programming simulation, DCF method was used to compensate the chromatic dispersion. Through the analysis of dispersion performance, Q value and bit error rate, we can see that the modified SSB modulation has the best transmission performance for 120 km links.

In this manuscript, we have analyzed a Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA) System. The system performance is enhanced by reducing the effect of Multiple Access Interference (MAI) using uniform Fiber Bragg Gratings (FBGs) encoders and decoders at central office and subscriber’s end. The results are verified through a mathematical model and Modified Double Weight (MDW) codes for the proposed system using Adomian Decomposition Method (ADM). Further, we have demonstrated SAC-OCDMA system for transmission of 40 Gbps data rate up to a distance of 80 km by increasing the number of FBGs. The proposed system has been analyzed in terms of distance, bit error rate (BER) and Quality Factor.