Contact Geometrical Study for Top Emitting 980 nm InGaAs/GaAsP Vertical-Cavity Surface Emitting Lasers

Geometrical contacts of a double mesa structure with 16 rows ×15 columns arrays of top emitting GaAs based 980 nm vertical cavity surface emitting lasers (VCSELs) are fabricated and characterized. In this paper, 5 strained In0.22Ga0.78As/Ga0.9AsP0.1 quantum wells (QWs) within λ/2 thick cavity have been employed. The top and the bottom epitaxially grown mirrors are based on the linear graded Al0.9Ga0.1As/GaAs distributed Bragg reflectors (DBRs) with 20.5 and 37 periods, respectively. Static parameters including threshold currents, rollover currents, maximum optical output power and wall-plug efficiency are extracted from light out power-current-voltage (LIV) of VCSELs with fixed oxide aperture diameter of ∅~ 6 μm and various mesa2 diameters. In addition, spectral emission for 980 nm VCSELs of oxide aperture between ∅~ 6 and 19 μm and with fixed ∅~ 6 μm and different bias currents are analyzed. The highest optical output power of around 33 dBm is observed at bias current of 0.8 mA for short−reach optical interconnect applications

Teacher's Attitude into Different Approach to Providing Feedback to Students in Higher Education

Feedback within higher education has an effective role in teaching staffs mode. The treatise on teachers' methods of feedback is represented to demonstrate how the novel feedback can help the academic staffs to provide an effective feedback for students in their assignments and written draft. The study investigates the academic staff's methods of feedback and their use the traditional pedagogy (Teacher written feedback) or the novel mode (online and peer feedback) at Salahaddin university in Erbil. The data of the study were collected quantitatively and qualitatively in order to reveal teachers pedagogy in the university and how they use methods of feedback in their teaching. The findings showed that some instructors use peer and online feedback (novel approach) which help students to be reflective and critical thinkers while most of them resort to teacher written feedback (old approach). Ultimately, the results shown that the academic staff may provide the novel feedback (online and peer feedback) to their teaching methods in the future. This will help students to be more proactive in learning. Keywords: feedback, online and peer feedback, Teacher written feedback, formative and summative feedback

Empowering Learning: Students and Teachers Outlook on Peer Assessment for Oral Presentation

The main thrust of this study was to examine students and teachers outlook on the use of peer assessment criteria for oral presentation at Soran University. This strategy advocated enhancing student’s involvement in tutorial presentation and contributed to the development of students learning of peer assessment in their faculty. The paper draws on data collected through questionnaires was used to gather a data from a sample of 60 students and 9 academic staff. Findings from the study indicated that students view on peer assessment for presentation depended on the quality of peers language accuracy and competent background. Descriptive statics showed that Student’s sentiment in peer assessment was believed to be uncertain due to problematic issues; however staffs viewed peer assessment as involvement of learners in learning practices and social development, the findings revealed that teachers were disagreed with the idea of peer’s assessment for presentation as a result of inferior level of learners. As a proactive enforcer, peer assessment for presentation must always be achieved in higher education system to produce proactive approach. Keywords: peer assessment, Oral presentation, Assessing tutorial presentation, Pros and Cons of peer assessment

Long-wavelength GaInNAs/GaAs Vertical-cavity Surface-emitting Laser for Communication Applications

This paper presents a comprehensive study of optical and electrical properties of vertical-cavity surface-emitting lasers(VCSELS) for long wavelength communication applications. The device consists of GaInNAs/GaAs multi-quantum wells QWs that enclosed between standard top and bottom epitaxially grown on AlGaAs/GaAs distributed Bragg reflectors. The impact of driven currents and injecting optical powers through QWs layers on the output light emission is addressed. Room temperature spectra measurements are performed at various applied currents using 980 nm pump laser and maximum intensity amplitude at around 21 dB was achieved

Optical Design of Dilute Nitride Quantum Wells Vertical Cavity Semiconductor Optical Amplifiers for Communication Systems

III-V semiconductors components such as Gallium Arsenic (GaAs), Indium Antimony (InSb), Aluminum Arsenic (AlAs) and Indium Arsenic (InAs) have high carrier mobilities and direct energy gaps. This is making them indispensable for today’s optoelectronic devices such as semiconductor lasers and optical amplifiers at 1.3 μm wavelength operation. In fact, these elements are led to the invention of the Gallium Indium Nitride Arsenic (GaInNAs), where the lattice is matched to GaAs for such applications. This article is aimed to design dilute nitride GaInNAs quantum wells (QWs) enclosed between top and bottom of Aluminum (Gallium) Arsenic Al(Ga)As distributed bragg mirrors (DBRs) using MATLAB® program. Vertical cavity semiconductor optical amplifiers (VCSOAs) structures are based on Fabry Perot (FP) method to design optical gain and bandwidth gain to be operated in reflection and transmission modes. The optical model gives access to the contact layer of epitaxial structure and the reflectivity for successive radiative modes, their lasing thresholds, emission wavelengths and optical field distributions in the laser cavity

Design, Modeling, and Characterization of Hot Electron Light Emission and Lasing in Semiconductor Heterostructure-VCSOA with Optical Gain up to 36 dB

Vertical-cavity semiconductor optical amplifiers (VCSOAs) are interesting devices for optical communication applications. In this work, we have studied the characteristics of gain spectra and amplifier bandwidth in reflection mode at 1300 nm GaInNAs/GaAs hot electron light emission and lasing in semiconductor heterostructure-VCSOA structure using MATLAB program. The device contains 16 Ga0.7In0.3N0.038As0.962 multiple quantum wells (QWs) in its intrinsic region; the active region is bounded between eight pairs of GaAs/AlAs top distributed Bragg reflectors (DBRs) mirror and 25 pairs of AlAs/GaAs bottom DBRs mirror. Simulation results suggest that the resonance cavity of QW of HILLISH-VCSOA is varied with temperature and number of DBRs periods. We compare the relation between the wavelength and gain at a different single-pass gain in both reflection and transmission modes. The highest gain at around 36 dB is observed in reflection mode. Moreover, we calculated the amplifier bandwidth at different periods of top mirror’s reflectivity, in which when the peak reflection gains increases, the amplifier bandwidth decreases

Ga0.35In0.65 N0.02As0.08/GaAs bidirectional light-emitting and light-absorbing heterojunction operating at 1.3 μm

The Top-Hat hot electron light emission and lasing in semiconductor heterostructure (HELLISH)-vertical-cavity semiconductor optical amplifier (THH-VCSOA) is a bidirectional light-emitting and light-absorbing heterojunction device. The device contains 11 Ga0.35In0.65 N0.02As0.08/GaAs MQWs in its intrinsic active region which is enclosed between six pairs of AlAs/GaAs top distributed Bragg reflectors (DBRs) and 20.5 pairs of AlAs/GaAs bottom DBR mirrors. The THH-VCSOA is fabricated using a four-contact configuration. The wavelength conversion with amplification is achieved by the appropriate biasing of the absorption and emission regions within the device. Absorption and emission regions may be reversed by changing the polarity of the applied voltage. Emission wavelength is about 1,300 nm and a maximum gain at this wavelength is around 5 dB at T = 300 K

Performance Characteristics of Conventional Vertical Cavity Surface Emitting Lasers VCSELs at 1300 nm

Vertical-cavity surface emitting lasers (VCSELs) are interesting devices because of their low-cost manufacturing and testing methods, circularly shaped output beam for high coupling efficiency and suited for use in fiber-optic networks and as optical interconnects. In this paper, experimental results of output light-current-voltage (LIV), optically pumped VCSELs operating at 1320 nm wavelength are presented. The commercial device is biased just below threshold current of 0.84 mA under pump power of 1 mW. An amplified gain at around 20 dB is obtained. In addition, the influence of temperature on the performance of the device is studied

Gain studies of 1.3-μm dilute nitride HELLISH-VCSOA for optical communications

The hot electron light emitting and lasing in semiconductor heterostructure-vertical-cavity semiconductor optical amplifier (HELLISH-VCSOA) device is based on Ga0.35In0.65 N0.02As0.08/GaAs material for operation in the 1.3-μm window of the optical communications. The device has undoped distributed Bragg reflectors (DBRs). Therefore, problems such as those associated with refractive index contrast and current injection, which are common with doped DBRs in conventional VCSOAs, are avoided. The gain versus applied electric field curves are measured at different wavelengths using a tunable laser as the source signal. The highest gain is obtained for the 1.3-μm wavelength when an electric field in excess of 2 kV/cm is applied along the layers of the device

Student’s Perspective on Formative Assessment: Quizzes and Discussion as Ongoing Process in Higher Education

The goal of this article was to investigate student’s angle on quiz and discussion as development of learning process and its effect on learners. This study explored students perspective towards formative assessment in higher education. Ostensibly, to create a generation that preserves to be critical learners. The results of the study gained from students of Soran and Koya University in order to make the distinction between two universities. The aim of this research was to get students perception of process of learning (quiz and discussion) and its effect positively or negatively on learners. The findings set out that Koya University student valued formative assessment (quiz and discussion) in their process of learning more than learners of Soran University; however Koya university students have positive effect to formative assessment during the courses in the class. The finding increases student’s awareness towards formative assessment and its sustainable growth in academic spheres