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360 results on '"Alshahrie, Ahmed"'

6. Influence of Asymmetric Gain Suppression on Relative Intensity Noise Properties of Multimode Semiconductor Lasers

Author

Bakry, Ahmed, Alshahrie, Ahmed, Mahmoud, Alaa, Dalir, Hamed, and Ahmed, Moustafa

Subjects
Physics - Optics
Abstract

We introduce modeling and simulation of the noise properties associated with types of modal oscillations induced by scaling the asymmetric gain suppression (AGS) in multimode semiconductor lasers. The study is based on numerical integration of a system of rate equations of 21-oscillating modes taking account of the self- and cross-modal gain suppression mechanisms. AGS is varied in terms of a pre-defined parameter, which is controlled by the linewidth enhancement factor and differential gain. Basing on intensive simulation of the mode dynamics, we present a mapping (AGS versus current) diagram of the possible types of modal oscillations. When the laser oscillation is hopping multimode oscillation (HMMO), the spectra of relative intensity noise (RIN) of the total output and hopping modes are characterized by a sharp peak around the relaxation oscillation (RO) frequency and a broad peak around the hopping frequency. The levels of RIN in the regimes of single-mode oscillation (SMO) are much lower than those under HMMO, and the mode-partition noise is two order of magnitudes lower.

Published
2020
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7. Stabilizing Multimode Hopping Oscillations and Reducing Associated Noise in Long Wavelength Laser Diode Using External Optical Feedback

Author

Ahmed, Moustafa, Bakry, Ahmed, Alshahrie, Ahmed, and Dalir, Hamed

Subjects
Physics - Optics, Physics - Applied Physics
Abstract

We report on converting the multimode hopping oscillation (MHO) in long-wavelength semiconductor laser into single-mode oscillation (SMO) by applying external optical feedback (OFB). We characterize and compare the noise performance of the laser when supporting SMO and multimode oscillations. The study is based on a modified time-delay multimode rate-equation model of the laser that includes mechanisms of spectral gain suppression along with OFB induced due to multiple reflections by an external reflector. The study is applied to 1.55um-InGaAsP laser that exhibits multimode hopping in its solitary version and supports wide bandwidth. The noise is evaluated in terms of the relative intensity noise (RIN). We show that when OFB synchronizes with the asymmetric gain suppression (AGS), it enhances the gain of one longer wavelength mode and supports SMO. In this case OFB improves the noise performance of the laser. On the other hand, when OFB works against AGS, it sustains hopping multimode oscillation (HMMO) and deteriorates the side-mode suppression ratio (SMSR) and the noise performance., Comment: 15 pages, 7 figures

Published
2020

8. Transverse Coupled Cavity VCSEL: Making 100 GHz Bandwidth Achievable

Author

Ahmed, Moustafa, Bakry, Ahmed, Alshahrie, Ahmed, and Dalir, Hamed

Subjects
Physics - Optics
Abstract

Enhancing the modulation bandwidth (MBW) of semiconductor lasers has been the challenge of research and technology to meet the need of high-speed photonic applications. In this paper, we propose the design of vertical-cavity surface-emitting laser integrated with multiple transverse coupled cavities (MTCCs) as a promising device with ultra-high 3-dB bandwidth. The laser features high modulation performance because of the accumulated strong coupling of the slow-light feedback from the surrounding lateral TCCs into the VCSEL cavity. Photon-photon resonance (PPR) is predicted to occur at ultra-high frequencies exceeding 145 GHz due to the optical feedback from short TCCs, which achieves 3-dB MBW reaching 170 GHz. The study is based on the modeling of the VCSEL dynamics under multiple transverse slow-light feedback from the surrounding TCCs. We show that the integration of the VCSEL with four or six feedback cavities is advantageous over the TCC-VCSEL in achieving much higher MBW enhancement under weaker coupling of slow-light into the VCSEL cavity. We also characterize the noise properties of the promising MTCC-VCSEL in the regime of ultra-high bandwidth in terms of the Fourier spectrum of the relative intensity noise (RIN).

Published
2020

19. VCSEL with multi-transverse cavities with bandwidth beyond 100 GHz

Author

Heidari Elham, Ahmed Moustafa, Dalir Hamed, Bakry Ahmed, Alshahrie Ahmed, and Sorger Volker J.

Subjects
optical feedback, transverse coupled cavity, vcsel, Physics, QC1-999
Abstract

To fulfill the demands of high-speed photonic applications, researchers, and engineers have been working to improve the modulation bandwidth (MBW) of semiconductor lasers. We extend our prior work on modeling a vertical-cavity surface-emitting laser (VCSEL) with multiple transverse-coupled-cavities (MTCCs) to evaluate the feasibility of boosting MBW beyond 100 GHz in this study. Because of the strong coupling of slow-light feedback from nearby lateral transverse coupled cavities (TCCs) into the VCSEL cavity, the laser has a high modulation performance. The intensity modulation response of the VCSEL design using one, two, four, and six TCCs is compared. Due to the optical-feedback (OFB) from short TCCs, which achieves 3 dB MBW reaching 170 GHz, photon–photon-resonance (PPR) is projected to occur at ultra-high frequencies beyond 145 GHz. In terms of the Fourier spectrum of the relative intensity noise (RIN), we characterize the noise features of the MTCC-VCSEL in the ultra-high bandwidth domain.

Published
2021
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21. Scattering properties of PT-symmetric objects

Author

Miri, Mohammad-Ali, Eftekhar, Mohammad Amin, Facao, Margarida, Abouraddy, Ayman F., Bakry, Ahmed, Razvi, Mir A. N., Alshahrie, Ahmed, Alù, Andrea, and Christodoulides, Demetrios N.

Subjects
Physics - Optics
Abstract

We investigate the scattering response of parity-time (PT) symmetric structures. We show that, due to the local flow of energy between gain and loss regions, such systems can deflect light in unusual ways, as a function of the gain/loss contrast. Such structures are highly anisotropic and their scattering patterns can drastically change as a function of the angle of incidence. In addition, we derive a modified optical theorem for PT-symmetric scattering systems, and discuss its ramifications., Comment: 13 pages, 6 figures

Published
2016
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27. Conducting Polymer Nanocomposites as Gas Sensors

Author

Ansari, Mohammad Omaish, Ansari, Sajid Ali, Cho, Moo Hwan, Ansari, Shahid Pervez, Abdel-wahab, Mohamed Shaaban, Alshahrie, Ahmed, Jafar Mazumder, Mohammad Abu, editor, Sheardown, Heather, editor, and Al-Ahmed, Amir, editor

Published
2019
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44. Suppressing the thermal conductivity to enhance the thermoelectric performance of SnSe2using the high-energy ball milling in a pressurised N2atmosphere

Author

Salah, Numan, Abdullahi, Shittu, Salah, Yousef N., Alshahrie, Ahmed, and Koumoto, Kunihito

Abstract

Two-dimensional (2D) layered dichalcogenides possess excellent thermoelectric (TE) properties. Among them, tin diselenide (SnSe2) exhibits n-type semiconducting properties with attractive TE performance near room temperature (RT). However, its high thermal conductivity and relatively low electrical conductivity have limited its TE performance for practical applications. In this study, we significantly suppressed the thermal conductivity and enhanced the TE performance of 2D layered SnSe2polycrystalline structures by reducing the particle size to the nano-scale using the high-energy ball milling (BM) technique in a pressurised N2atmosphere. The particle size was reduced from ∼2 μm to 100 nm after 15 h of BM. TE results of a highly pressed compact leg made from the TE-optimised BM sample (e.g. 7 h) showed that at RT, the electrical conductivity increased by a factor of 9, whereas the Seebeck coefficient was reduced by only 40%. Consequently, the power factor increased from 12 to 42 μW/m·K2. In addition, the thermal conductivity decreased from 5.72 to 0.40 W/m·K, resulting in a significant increase in the figure of merit by a factor of 40 times higher than that of the non-BM SnSe2leg. This study also demonstrated power generation using single-leg modules made from these structures at ΔTvalues above and below RT. The TE power generation of the BM module was found to be much higher than that of the non-BM module, particularly below RT. The 7-h BM module generated 2600 nW at ΔT = 45 K above RT, but when the same ΔTwas applied below RT, the generated power reached 8000 nW. This enhancement in power generation below RT is remarkable, suggesting that the BM SnSe2compact may be useful for generating measurable TE power in cold environments.

Published
2024
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