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128 results on '"Raja, M. Yasin"'

108. <atl>Polarization and spatial-mode behavior of short-wavelength VCSELs

Author

Raja, M. Yasin Akhtar, Al-Dwayyan, Abdullah, Cao, Yang, and Wang, Charlie X.

Subjects
*OPTICAL polarization, *LASERS
Abstract

We have investigated the packaging introduced feedback and resulting variations in the characteristics of Vertical-cavity surface-emitting lasers (VCSELs). An integrated test and characterization method was developed for both the packaged and bare dies as well as on-wafers chips. Using an ‘integrated test bench (ITB)’ for characterization, packaged and ‘un-packaged’ VCSELs from multiple sources were studied. ITB was used to monitor and measure simultaneously several beam-parameters under various bias conditions including both dc and high-speed pulsed pumping at room-temperature, or at higher-/lower-temperatures that are thermo-electrically controlled. Typical beam parameters included state of polarization (SOP), transverse (spatial) modes, wavelength spectra, and output power. A common observation was that majority of devices are affected by the presence of optical windows capping the package. A shift in longitudinal mode was noticeable in packaged versus ‘un-packaged’ (window-removed) devices. But, SOP and transverse modes in various devices are affected severely and in an unpredictable fashion. [Copyright &y& Elsevier]

Published
2002
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120. In search of photon’s elementary axial magnetostatic field.

Author

Raja, M. Yasin Akhtar, Sisk, Wade N., Yousaf, Mohammad, and Allen, David

Subjects
*PHOTONS, *OPTICAL polarization
Abstract

Experimental investigations of the photon’s B[sup (3)] -field (third longitudinal polarization) are reported. The existence of an “axial magnetostatic field of photon” has been predicted in B[sub π] or B[sup (3)] -theory as the fundamental property of the circularly polarized light, and reported in numerous papers and monographs. High-sensitivity detection has been employed in photomagnetic induction, Faraday, and inverse Faraday effects (IFE) originating from such a field. The results of all three experiments clearly disprove the claims of B[sub π] -theory. Putting together these results and theoretical calculations in perspective, it is concluded that such fields are non-existent. [ABSTRACT FROM AUTHOR]

Published
1997

121. Characteristics of GaAs/AlGaAs vertical-cavity surface-emitting lasers irradiated with gamma rays

Author

Aldwayyan, Abdullah S., Al-Qahtani, Hadi R., Alsalhi, Mohammed, and Raja, M. Yasin Akhtar

Abstract

The effects of gamma radiation on vertical-cavity surface-emitting laser (VCSEL) characteristics are investigated experimentally. Three groups (batches) of oxide-confined VCSELs are investigated. It is found that radiation can change (increase or decrease) the quantum efficiency of VCSELs considerably, depending on their production batch. Small changes in the threshold current are observed for some devices. Shifts to a longer wavelength in the peak-emission profile are noticed after irradiation, which is found to be reversible in some VCSELs by simply increasing the radiation dose. It is also discovered that gamma radiation affects the total number of competing transverse modes depending on the radiation dose. Self-pulsation characteristics in some devices are not affected by the radiation exposure. Knowledge of the behavior of VCSELs under gamma exposure would be useful for their applications in hostile environment. © 2004 Society of Photo-Optical Instrumentation Engineers.

Published
2004
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122. Gain-flattened ultra-wideband fiber amplifiers

Author

Cao, Yang and Raja, M. Yasin Akhtar

Abstract

This paper presents a novel design of a gain-flattened amplifier that covers an ultra-wide band including the S, C, and L bands. The amplifier has a split-band architecture, which amplifies the S-, C-, and L-band signals in separate paths and then recombines the amplified signals for the final output. Using a commercial software package VPI Component Maker™, the design was simulated and tested for optimization. The gain and noise figure of the new amplifier were analyzed by computer simulation. A gain of 29 dB, a ripple factor of about 1.7 dB, a nominal low noise figure <5 dB, and gain-bandwidth products >120 nm can be achieved. © 2003 Society of Photo-Optical Instrumentation Engineers.

Published
2003
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