A new code for optical code division multiple access systems

A new code structure based on Double-Weight (DW) code families is proposed for Spectral-Amplitude-Coding Optical Code Division Multiple Access (OCDMA) system. The constraint of a constant weight of 2 for the DW code can be relaxed using a mapping technique. By using this technique, codes that have a larger number of weight can be developed. Modified Double-Weight (MDW) Code is another variation of a DW code family that can has a variable weight greater than two. The MDW code possesses ideal cross-correlation properties and exists for every natural number n. A much better performance can be provided by using the MDW code compared to the existing codes such as Hadamard and Modified Frequency-Hopping (MFH) codes. This has been demonstrated from the theoretical analysis and simulation

Experimental demonstration of a flexible and stable semiconductor laser linewidth emulator

We propose and demonstrate experimentally a laser source whose linewidth is adjustable independently of its other characteristics. This source can be used to test whether a particular laser would be suitable in a system, without the need to purchase several different lasers. It also has the advantage that the linewidth is generated digitally so it is extremely stable over time. We demonstrate a dialed-linewidth emulator between 256 kHz to 150 MHz. The narrowest linewidth shown by this technique is the original linewidth of the semiconductor laser source used in the setup. We also investigate the effect of driving our modulator into its nonlinear range

Laser phase noise effect and reduction in self- homodyne optical OFDM transmission system

We present a laser phase noise (PN) induced effect of a phase-modulation-to-intensity-modulation conversion noise and noise pedestals underneath each of the orthogonal frequency division multiplexing (OFDM) subcarriers in a selfcoherent optical OFDM transmission using a self-homodyne technique. We provide a statistical analysis on the received symbols using a histogram to demonstrate the effect of a phase rotation term and inter-subcarrier interference individually and collectively. The PN is then compensated using a simple time delay to realign the phase walk-off of the subcarriers relative to the carrier. Significant quadrature improvements of 6.82 dB using 5 MHz laser linewidth over a 720 km transmission length and 5.38 dB using 20 MHz over 240 km have been obtained with 16 quadrature amplitude modulation (QAM) over 15 GHz OFDM signal bandwidth. The technique also significantly reduced an optical-signal-to-noise ratio requirement at the bit error rate of 1 × 10−3 by 16.15 dB for 64-QAM over 160 km. With the delay, the system can tolerate three times the chromatic dispersion-length product

Design configuration of encoder and decoder modules for modified double weight (MDW) code spectral amplitude coding (SAC) optical code division multiple access (OCDMA) based on fiber Bragg gratings

In this work, we are proposing the serial and parallel configurations of encoder and decoder modules to encode and decode a new developed spectral amplitude coding (SAC) known as modified double weight (MDW) code for optical code division multiple access (OCDMA) system. This coding scheme is designed in a way to decrease the number of FBGs used in the encoder and decoder modules and to maintain the cross-correlation parameter to 1

Light music

Our universe is full of light. Light can be both obvious and mysterious. Some can be seen with our naked eye and some are not. Through its special properties, light wave is used to connect the globe by carrying messages and information, with its superior speed and vast bandwidth

Characteristics of RoF millimeter-wave generation for 5G system

An optical millimeter-wave (mm-wave) generation system is designed to be incorporated with radio over fibre (RoF) system for 5G application. The design employs the dual-sideband optical carrier suppression (DSB-OCS) technique with a dual-electrode Mach-Zehnder modulator (DE-MZM). A mm-wave of 40 GHz is generated with the intention to be used as a wireless carrier for the distribution of 1.25 Gbps data via direct modulation (DM) over a 20 km RoF system. The result shows that the system has a phase noise of -90 dBc at 1kHz frequency offset and achieves bit error rate (BER) of 10 −9 with modulation index, m above a figure of 0.5

Cascaded dual drive MZM and dual parallel MZM architecture for optical linearization of MZM nonlinearity

A cascaded architecture of Dual Drive Mach Zehnder Modulator (DDMZM) and Dual Parallel Mach Zehnder Modulator (DPMZM) for the reduction of Mach Zehnder Modulator Nonlinearity is proposed in this article. The architecture is analyzed using N-channel HFC CATV system based on Carrier to Carrier Triple Beat (C/CTB) ratio. The architecture in comparison with other proposed architecture namely Dual Cascade MZM and Dual Parallel MZM have shown an improved performance in terms of reduced CTB and increased C/CTB ratio at higher modulation index

Wavelength shifting in the Fiber Bragg Grating (FBG) based encoder and decoder modules for SAC-OCDMA system

This project concentrates on the design of Fiber Bragg Grating (FBG) based encoder and decoder modules for Spectral Amplitude Coding of Optical Code Division Multiple Access (SAC-OCDMA) system. In SAC-OCDMA system, the unique code sequence is formed by using spectral components which are inherently arranged. This is done by multiplexing the Bragg wavelengths from an array of FBGs. However, the Bragg wavelength is largely depends on the strain and temperature experienced by the gratings. This paper presents the effects of the Bragg wavelength shifting of the uniform FBG used in the encoder and decoder modules for an SAC-OCDMA code to the system performance. The results show a sharp increase of bit error rate (BER) from 10-12 and 10 -14 to 10-4 and 10-5 for Channel 1 and Channel 2 respectively at 0.01 nm Bragg wavelength left and right shifts. It shows that the system performance is significantly affected by the shifting of the Bragg wavelength

Effects of the power differences in the AND-subtraction detection technique in SAC-OCDMA system performance

This project concentrates on the effects detection technique to the system performance of spectral amplitude coding optical code division multiple access (SAC-OCDMA). The system employed the encoder and decoder modules based on the fiber Bragg gratings (FBGs) to generate the unique code sequences for the users. These modules are basically designed for the modified double weight (MDW) code which allows higher code weight w in the even number which is greater than two. The study is mainly focusing on the effects of the power differences between the upper and lower branches of the AND-subtraction technique used as the detection technique to the system performance. The results show that the system will achieve the best system performance when the power difference between the upper and lower branches is approximately 5dB

The effect of laser noise on an optical ofdm system

In recent years, researchers and network equipment manufacturers have focused on the development of a 100 Gb/s optical transmission systems to cater the ever increasing demands for bandwidth. To cater the demands, optical orthogonal frequency division multiplexing (O-OFDM) has been proposed. O-OFDM has been shown as a promising technique to increase spectral efficiency with its ability to compensate for chromatic and polarisation mode dispersion. There are two forms of receiver used for long haul O-OFDM links: coherent-OOFDM (CO-OFDM) and direct detection O-OFDM (DDO-OFDM). The CO-OFDM system is known to be limited by the laser’s phase noise, where the system requires a narrow linewidth laser at both transmitter and receiver, where these lasers phase must track one-another. In the DDO-OFDM system, an optical carrier is transmitted along with the subcarriers so both originate from the same laser, and both experience the same degradations along the fibre. Thus, the linewidth, or equivalently phase-noise, requirements are far less stringent than for CO-OFDM systems. However, given that laser phase noise will be converted to intensity noise (PM-to-IM conversion noise) along a dispersive fibre, there will be some effect on performance in a DDO-OFDM system. The question is whether this is significant, given that the fibre dispersion is not optically compensated as in conventional lightwave systems. In this thesis, laser phase noise effect upon detection in a DDO-OFDM system is shown to impose broad noise pedestal around a subcarrier for higher frequency subcarriers when there is a high accumulated dispersion. The noise pedestal can introduce inter-subcarrier-interference between the adjacent subcarriers. This is different in a CO-OFDM system, where the phase noise is independent of the subcarriers’ frequency and common to all subcarriers. This thesis focuses on the DDO-OFDM system using external modulation at the transmitter. A transmission system was developed to study the effects of the laser relative intensity noise (RIN) and phase noise over a long-haul transmission, and to show the importance of the laser’s characteristics. Experimental measurements on a commercial fixed-wavelength distributed feedback (DFB) laser investigated its RIN, linewidth and light vs. current (L-I) characteristics. The effect of external modulation of this laser was investigated. With the externally-modulated transmitter, the laser chirp is ignored. The linewidth measurement was done using self-homodyne technique and validated using a high-resolution spectrophotometer. The measurements showed inter-dependency between the linewidth and RIN, which agreed with theory. A laser linewidth emulator was developed and demonstrated experimentally. This was done by phase modulating a semiconductor’s laser output to broaden its linewidth. With this laser, the linewidth can be made independent from the other laser’s noise characteristics. Simulations and experiments were performed to study the interaction of linewidth and fibre dispersion. The interaction produces noise conversion from phase modulation to intensity modulation, where the noise PSD was obtained. An analytical equation of the PM-to-IM’s upper-bound was derived and plotted on the noise PSD’s amplitude. When the laser was modulated with RF tones, a noise pedestal around each of the tones was obtained. The peak power of the noise is shown to increase with the increased of the tone’s frequency. This is due to the phase walk-off of the high frequency subcarrier from the carrier is larger than the low frequency subcarrier. The peak also increases when a wider linewidth was used. This noise was shown to cause phase rotations of the received symbols and reduces the Q performance of the DDO-OFDM system. To reduce the effect of the linewidth in the DDO-OFDM system, an experiment using a simple delay line to match the delay experienced by the subcarrier was performed. The result shows improvement of the subcarriers’ Q performance. Finally, this thesis also presented the performance of the DDO-OFDM system in transmitting high-speed data of 120 Gbit/s. This experiment involved several important device improvements in order to achieve a good quality and wide RF-signal bandwidth. In this transmission, a variant of the DDO-OFDM system employing self-coherent polarization-diversity receiver design was developed