حسن كامل باقر الموسوي

Graphene nanosheets were fabricated on a metal (Al) substrate by using a chemical spray method. Annealing process has been applied to reducing the concentration of carbon and to increase the sheet hardness. Surface morphology measured by metallurgical microscope Device Corporation, X 1600. Thermal camera was used to measure the performance of coated heat sink. The temperature was measured from the two sides, one from heat sink side, and the other one is from power transistor side. The results showed that the temperature of the transistor was decreased by about 4.3 °C in the case of heat sink coating with 80 μm layer thickness while decreased by 6.9 °C in the case of the heat sink coating with 120 μm layer thickness.

This paper reports on an experimental investigation into the influence of current modulation on the properties of a vertical-cavity surface-emitting laser (VCSEL) with a direct square wave modulation. The optical output power response, as a function of the pumping current, modulation frequency, and amplitude, is measured for an 850 nm VCSEL. We demonstrate that modulation frequency and amplitude play important roles in reducing the VCSEL’s power consumption for optical generation. Indeed, even when the biasing current is below the static threshold, the VCSEL emits optical power under the square wave modulation. The power consumed by the device to generate light is significantly reduced to > 50%, which is below the threshold current, in response to both the modulation frequency and amplitude. An operating VCSEL device at low power is very desirable for less thermal effects, which are essential for a high-speed modulation bandwidth.

This paper presents a novel structure to simulate and achieve the all-optical plasmonic logic gates. We show how the use of dielectric-metal-dielectric (DMD) plasmonic waveguides with four nanorings and three slots can realize the complete family of logic gates; including NOT, OR, AND, NOT-OR, NAND, exclusive-OR, and exclusive-NOR using the constructive and destructive optical interferences between a control signal and input signal(s). We have adopted two optical wavelengths, namely 900 nm and 1330 nm, which are used for optical communication systems. Performance has been measured using the transmission level which registered more than 100 % for all of the seven gates of both wavelengths except NOT and NOT-OR logic gates. In addition, high extinction ratio of more than 20 dB in NOT and exclusive-NOR gates has been achieved using our novel structure.

This paper demonstrates a hybrid radio over multimode fibre and free space optics (RoMMF-FSO) system that can be used to extend the transmission range of the fourth generation long-term evolution (4G-LTE) signal in access networks. A single mode filtering technique (SMFT) is used to enhance 4G-LTE performance. The proposed scheme is evaluated in terms of the system transfer function, laser beam profile, and error vector magnitude (EVM). We show that using SMFT increases the RoMMF-FSO system bandwidth by 2 GHz and improves the received optical power by 13.6 dB. Moreover, the proposed system enhances the EVM by 4%. The measured results show that by using a 1 km MMF instead of a 1 km SMF will marginally increase the measured EVM from ~6.6% to ~7% with a 0.2 dB power penalty with respect to the LTE EVM limit of 12.5% as is specified for 16-quadrature amplitude modulation. The proposed system is validated practically under atmospheric turbulence conditions to mimic the outdoor environment. Measured EVM results are verified theoretically through transmitting LTE signals with turbulent using log-normal model. We also show that for a FSO link span of 500 m to meet the EVM target of 12.5% the SNR power penalties are ~2 dB and ~11 dB for Rytov variance of 1.2 × 10 -4 and 0.1, respectively, compared with no turbulence.

The 4th generation- long term evolution (4G-LTE) mobile technology is widely adopted that offer both higher capacity and efficient bandwidth usage at a global level. However, considering that in cellular networks the major data traffic mostly occurs indoor, providing high quality can be a daunting task. 4G-LTE provides strong support for both outdoor and indoor coverage by adopting enhanced NodeB (eNB) and home eNB (HeNB), respectively. This research work presents (i) a single-mode filtering technique (SMFT) as a simple design, low cost scheme to degrade the dispersion behaviour of the hybrid radio over the multi-mode fibre (MMF) and free space optics (RoMMF-FSO); (ii) the hybrid radio-over-fibre and radio-over-FSO (RoF-FSO) system as a solution to extend the indoor coverage of 4G-LTE; and (iii) the use of perfluorinated graded-index polymer-optical fibre (PF-GI-POF) for in-building networks. The results show that SMFT may increase RoMMF-FSO bandwidth by 2 GHz and enhance the error vector magnitude (EVM) performance by 4%. The proposed system was also made to experience weak turbulence and thick fog for transmission of 67.2 Mbps 16-QAM 4G-LTE. A design for the residential gateway is proposed as the interface between the 1550 and 850 nm wavelengths. The 100 m of PF-GI-POF is adopted as in-building network with 4G-LTE being transmitted over the proposed hybrid radio-over-POF and FSO (RoPOF-FSO) link under the thick fog condition. The proposed system can transmit 4G-LTE at a data rate of up to 33.6 Mbps and 100.8 Mbps, with the latter encountering a power penalty of ~8 dB to compensate for the induced fog loss. Furthermore, the successful transmission of 60 Mbps at 2.6 GHz was reported to have achieved the EVM of 3.5% and BER 10-5 for 300 m of PF-GI-POF.

This paper proposes an optimum hybrid radio over multi-mode fiber and free space optics (RoMMF-FSO) system to enhance the last mile bottleneck issues of wireless communication systems. Single mode fiber (SMF) and gradient index (GRIN) lenses are used as mode filtering techniques to optimize the system performance by mitigating the modal effects produced by multimode optical fiber networks. We characterize the system based on the beam profile, transfer function, and error vector magnitude (EVM) measurements. The results reveal that both techniques can improve the EVM performance significantly by ~19% and ~30% using a SMF filter and SMF-GRIN lenses, respectively. Furthermore, the analysis of the obtained measurements show the SMF-GRIN lenses is more effective than SMF only with lower EVM values and negligible difference in the optical launch power.