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319 results on '"Sahbudin Shaari"'

301. Long-wavelength MQW vertical-cavity surface emitting laser: Effects of lattice temperature

Author

Sahbudin Shaari, Mahamod Ismail, K. Kumarajah, Burhanuddin Yeop Majlis, and P. S. Menon

Subjects
Lattice temperature, Threshold current, Materials science, business.industry, Thermal resistance, Condensed Matter Physics, Laser, Atomic and Molecular Physics, and Optics, Electrical contacts, Vertical-cavity surface-emitting laser, law.invention, Wavelength, Optics, law, Optoelectronics, Electrical and Electronic Engineering, business, Dark current
Abstract

The lattice temperature in a 1.5 μm wavelength InP-based vertical-cavity surface-emiting laser (VCSEL) was varied between 273 K until 353 K using an industrial-based numerical simulator and its effects on the characteristics of the device was analysed. The temperature fluctuation has a direct effect on the gain distribution, causes a peak wavelength shift and is the precursor for various dark current processes within the laser. The device employs InGaAsP multi-quantum wells (MQW) sandwiched between GaAs/AlGaAs and GaAs/AlAs distributed Bragg reflectors (DBRs). The thermal resistance used to model the electrical contacts causes an approximate 13 K temperature rise above the ambient temperature (300 K) at a bias of 3 V and a 50 % increase in the threshold current is observed with temperature increment. Various heat sources elements within the VCSEL device were also analysed upon increment of lattice temperature.

310. Effect of fabrication parameters on luminescent properties of ZnS:Mn nanocrystals

Author

Mohd Syuhaimi Ab-Rahman, Noor Azie Azura Mohd Arif, and Sahbudin Shaari

Subjects
Spin coating, Materials science, Fabrication, Annealing (metallurgy), business.industry, Doping, Analytical chemistry, Ion, Blueshift, Condensed Matter::Materials Science, Nanocrystal, Optoelectronics, Condensed Matter::Strongly Correlated Electrons, Thin film, business, Luminescence
Abstract

In this work, we mainly focused on the luminescence properties of ZnS:Mn nanocrystals. Various samples of ZnS:Mn have been characterized at different doping concentration, annealing temperature, spin speed and time. The present study shows the application of spin speed, spin time, doping concentration and temperature affect the luminescent intensity performance. Luminescent intensity becomes higher with the increasing film thickness. Spin speed and spin time are two major concerns for coating film to a demanded thickness on the glass slide. Film thickness is the main reasons of the increasing intensity with spin speed and time. Temperature dependent PL measurements provide thermally activated energy transfer from other defects to Mn2+ ions. As the temperature increase, the carriers can be trapped at Mn sites, enhancing the luminescence spectra. Meanwhile, the quenching process influenced the PL intensity with doping concentration. This process occurs at high Mn concentration which the energy transfer from Mn ions to the other nearest Mn atom is weak. Therefore, the luminescence of transition from 4T 1 to 6A 1 of ions becomes stronger. From this reason, it is shown that luminescent intensity increased with higher doping concentration but decreased with higher annealing temperature, spin speed and spin time during spin coating process.

313. Twenty two flattened channels L band multi-wavelength erbium doped fiber laser with composite ring cavity.

Author

Siti Narimah Aziz, Norhana Arsad, Ahmad Ashrif Abu Bakar, P Sushita Menon, and Sahbudin Shaari

Abstract

We demonstrated the generation of a multiwavelength laser comb through two different ring cavity designs. The first design, a ring laser with Sagnac filter is being modified to produce a second design known as composite ring cavity. The ASE spectrum obtained from the composite ring cavity is sliced into more than 30 laser lines. From this comb, 22 laser lines are flattened under the 3 dB peak power fluctuation and 25 lines are flattened under the 10 dB peak power fluctuation. The 24 laser lines have a bandwidth value of 10.48 nm and for each of them, the average OSNR value is found to be at 24 dB. The OSNR value distribution among the laser lines is nearly uniform. However, the fineness obtained in this scheme is very low as 2.8. [ABSTRACT FROM AUTHOR]

Published
2015
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314. Performance enhancement of successive interference cancellation scheme based on spectral amplitude coding for optical code-division multiple-access systems using Hadamard codes.

Author

Tawfig Eltaif, Hossam M. H. Shalaby, Sahbudin Shaari, and Mohammad M. N. Hamarsheh

Subjects
PERFORMANCE evaluation, OPTICAL interference, SPECTRUM analysis, HADAMARD matrices, CODE division multiple access, SIMULATION methods & models
Abstract

A successive interference cancellation scheme is applied to optical code-division multiple-access (OCDMA) systems with spectral amplitude coding (SAC). A detailed analysis of this system, with Hadamard codes used as signature sequences, is presented. The system can easily remove the effect of the strongest signal at each stage of the cancellation process. In addition, simulation of the prose system is performed in order to validate the theoretical results. The system shows a small bit error rate at a large number of active users compared to the SAC OCDMA system. Our results reveal that the proposed system is efficient in eliminating the effect of the multiple-user interference and in the enhancement of the overall performance. [ABSTRACT FROM AUTHOR]

Published
2009

315. Analytical comparison of optical code-division multiple-access systems with and without a successive interference cancellation scheme using modified prime-sequence codes.

Author

Tawfig Eltaif, Hossam M. H. Shalaby, Sahbudin Shaari, and Mohammad M. N. Hamarsheh

Subjects
PROBLEM solving, SIGNALS & signaling, INTERFERENCE microscopes, CANCELLATION theory (Group theory)
Abstract

We analyzed direct-sequence code-division multiple-access system using a successive interference cancellation (SIC) scheme. Modified prime-sequence codes are utilized as signature sequences, and the performance measure studied in this paper takes into account the the effect of imperfect interference cancellation. The basic principle of the SIC scheme is to subtract the strongest received signals from the original signal one by one till all users have been detected and demodulated. In this analysis we have compared optical code-division multiple-access systems with and without the cancellation scheme, and it is shown that the SIC scheme with −20-dBm effective power can suppress multiple-access interference better than the system without cancellation. [ABSTRACT FROM AUTHOR]

Published
2008

316. Construction of a new code for spectral amplitude coding in optical code-division multiple-access systems.

Author

Feras N. Hasoon, Mohamad Khazani Abdullah, S. A. Aljunid, and Sahbudin Shaari

Subjects
OPTICS, SIMULATION methods & models, CODE division multiple access, MULTIPLE access protocols (Computer network protocols)
Abstract

An enhanced code structure for spectral amplitude coding in optical code division multiple access systems based on double weight (DW) code families is proposed. Enhanced double weight (EDW) codes possess ideal cross-correlation properties such as maximum cross correlation of 1 and a weight that can be any odd number greater than 1. It has been observed through theoretical analysis and experimental simulation that EDW codes perform significantly better than Hadamard and modified frequency-hopping (MFH) codes. In this study, point-to-point transmission with three EDW-encoded channels was tested at the bit rate of 10 Gbit/s per channel. [ABSTRACT FROM AUTHOR]

Published
2007

317. Analytical comparison of optical code-division multiple-access systems with and without a successive interference cancellation scheme using modified prime-sequence codes.

Author

Tawfig Eltaif, Hossam M. H. Shalaby, Sahbudin Shaari, and Mohammad M. N. Hamarsheh

Subjects
*PROBLEM solving, *SIGNALS & signaling, *INTERFERENCE microscopes, *CANCELLATION theory (Group theory)
Abstract

We analyzed direct-sequence code-division multiple-access system using a successive interference cancellation (SIC) scheme. Modified prime-sequence codes are utilized as signature sequences, and the performance measure studied in this paper takes into account the the effect of imperfect interference cancellation. The basic principle of the SIC scheme is to subtract the strongest received signals from the original signal one by one till all users have been detected and demodulated. In this analysis we have compared optical code-division multiple-access systems with and without the cancellation scheme, and it is shown that the SIC scheme with −20-dBm effective power can suppress multiple-access interference better than the system without cancellation. [ABSTRACT FROM AUTHOR]

Published
2008

318. Proposal of successive interference cancellation scheme in optical code-division multiple access systems.

Author

Tawfig Eltaif, Hossam M. H. Shalaby, Sahbudin Shaari, and Mohammad M. N. Hamarsheh

Subjects
*INDUSTRY classification, *CLASSIFICATION, *SENSORY perception, *ORTHOGONAL arrays
Abstract

Proposes one of the multiuser detection schemes, a new technique that has the potential to reduce interference or suppress multiple-access interference and, therefore, increase the capacity of optical code-division multiple access (CDMA) systems. It is a successive interference cancellation (SIC) scheme known as a low-complexity multiuser detection method for direct sequence CDMA systems. A SIC scheme is analyzed using an optical orthogonal code, with a different power for each user, that takes into account the impact of imperfect interference cancellation. [ABSTRACT FROM AUTHOR]

Published
2008

319. Construction of a new code for spectral amplitude coding in optical code-division multiple-access systems.

Author

Feras N. Hasoon, Mohamad Khazani Abdullah, S. A. Aljunid, and Sahbudin Shaari

Subjects
*OPTICS, *SIMULATION methods & models, *CODE division multiple access, *MULTIPLE access protocols (Computer network protocols)
Abstract

An enhanced code structure for spectral amplitude coding in optical code division multiple access systems based on double weight (DW) code families is proposed. Enhanced double weight (EDW) codes possess ideal cross-correlation properties such as maximum cross correlation of 1 and a weight that can be any odd number greater than 1. It has been observed through theoretical analysis and experimental simulation that EDW codes perform significantly better than Hadamard and modified frequency-hopping (MFH) codes. In this study, point-to-point transmission with three EDW-encoded channels was tested at the bit rate of 10 Gbit/s per channel. [ABSTRACT FROM AUTHOR]

Published
2007

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