Dear Label_Name,

Greetings! I hope you are well.

I am writing on behalf of an international publishing house, Science and Education Publishing, USA (http://www.sciepub.com).

Science and Education Publishing (SciEP) is a multidisciplinary open access publisher of Journals covering the fields of Science, Technology and Medicine. All SciEP publications are subject to high-quality peer review, editorial and production processes and are freely available online.

Welcome to the April, 2013 edition of SciEP newsletter, providing monthly summaries of articles on science & education related topics of interest to scientist and professionals. The mission of our journals is to provide an open access forum for publishing new findings on issues pertinent to scientific and academic field. We also invite you to submit original research papers, review articles, short reports, or case studies are considered for publication in our Multidisciplinary Journals.

American Journal of Public Health Research
DOI: 10.12691/ajphr-1-1-3

The Implementation of a Tele-Homecare System with Service Oriented Architecture and HL7 Message Transmission Standard
Ching-Sung Wang

American Journal of Medical and Biological Research
DOI: 10.12691/ajmbr-1-1-2

The Influence of Ethanol on Pyruvate Kinases Activity in Vivo, in Vitro, in Silico
Lelevich Sergey Vladimirovich, Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Shedogubova Tatyana Aleksandrovna

American Journal of Medical Sciences and Medicine
DOI: 10.12691/ajmsm-1-1-1

Clinical and Histological Features in Wegener Granulomatosis
Li Cavoli Gioacchino, Passantino Rita, Bono Luisa, Tortorici Calogera, Ferrantelli Angelo, Giammarresi Carlo, Rotolo Ugo

American Journal of Infectious Diseases and Microbiology
DOI: 10.12691/ajidm-1-1-2

The Curse of Lymphatic Filariasis: Would the Continual Use of Diethylcarbamazine Eliminate this Scourge in Papua New Guinea?
Anne Lanham, Lillian Mwanri

We have released issues of some journals on February 2013.
American Journal of Public Health Research
American Journal of Medical Sciences and Medicine
American Journal of Medical and Biological Research
American Journal of Pharmacological Sciences
American Journal of Clinical Medicine Research
American Journal of Nursing Research
American Journal of Cancer Prevention
American Journal of Medicine Studies
American Journal of Infectious Diseases and Microbiology
American Journal of Cardiovascular Disease Research
American Journal of Biomedical Research
American Journal of Mechanical Engineering
American Journal of Microbiological Research
Journal of Preventive Medicine
American Journal of Food and Nutrition
American Journal of Hypertension Research
American Journal of Sports Science and Medicine
Journal of Cancer Research and Treatment
American Journal of Zoological Research
Journal of Biomedical Engineering and Technology
American Journal of Microbiological Research
Biomedical Science and Engineering

We are pleased to announce that submissions are now being accepted for peer review for all the journals across all our subject areas in SciEP.

Please submit your manuscript via our online submission system:
http://www.sciepub.com/author/signin

To unsubscribe from our mailing list, please click on the following link: unsubscribe

I am looking forward to hearing from you.

Kind regards,

David Rain
Email:join@sciepub.com
Science and Education Publishing (http://www.sciepub.com)

Further Investigations into the Effects of Temperature on a 975 nm Tapered Laser Bar Using Convolution to Ascertain the Dominant Effect of Temperature on a Laser Bar

Christian Kwaku Amuzuvi*, Kofi Asante

University of Mines and Technology, Department of Electrical and Electronic Engineering, Tarkwa, Ghana

Abstract: Temperature continues to be an issue in the reliability of high power laser diodes. Any effort, therefore, made to understand the dynamics of temperature on the performance of laser diodes is important. This is because it serves as a catalyst for the generation of nonradiative recombination centers, which ultimately kills laser diodes. In this paper, the convolution of simulation results was done to compare it with experimental results, which revealed more details that hitherto, could not have been captured by experiments alone. The inability of experiments to capture these details is due to the limited spatial resolution of the charged-coupled device (CCD) camera, which is approximately 30 μm much larger than the thickness of the quantum well active region used in the experiment. The convolution results showed a further smile-shaped profile within the four groups of array emitters, which in the experimental results, were considered as one emitter due to the limited spatial resolution of the CCD camera. The use of convolution to determine more details was investigated, due to the dominant effect of temperature found across the output power distribution of high power semiconductor laser diode bars.

Keywords: by-emitter, emitter, quantum well, defect, non-radiative recombination, degradation, temperature, thermal crosstalk, spatial resolution, convolution, interpolation, charged-coupled device camera

Received March 13, 2014; Revised May 03, 2014; Accepted May 28, 2014

Citation: Christian Kwaku Amuzuvi, Kofi Asante, Further Investigations into the Effects of Temperature on a 975 nm Tapered Laser Bar Using Convolution to Ascertain the Dominant Effect of Temperature on a Laser Bar. American Journal of Electrical and Electronic Engineering, 2 (3). 117-120. January 2014. doi:10.12691/ajeee-2-3-9

1. Introduction

The demand for improved performance and reliability of high-power laser diodes has led to the growth of the industry over the past decade [1]. Apart from the use of high-power laser diodes to pump solid-state lasers, many other applications such as materials processing, printing, medicine, and entertainment have emerged [1,2]. Temperature is one of the main factors limiting the performance of laser bars. Consequently, further investigations into the effects of temperature on the degradation of laser bars have become imperative. Menzel et al. [3] investigated the effect of temperature on facet degradation, where reductions in the performance and lifetime were found to be as a result of nonradiative surface recombination. Xia et al. [4], Tomm et al. [5], and Bull et al. [6] all used a detailed “by-emitter” performance analysis of each emitter to understand the behaviour and degradation of the individual emitters. When emitter temperatures rise, thermal crosstalk between emitters becomes more significant [7]. This paper therefore, seeks to further investigate the effects of temperature on a 975 nm tapered laser bar using convolution to ascertain the dominant effect of temperature on a laser bar. This is necessary, since using experimental results alone may be inadequate, due to the limited spatial resolution of the CCD camera [8].

2. Materials and Methods

The concept of Barlase showing the communication between emitters is shown in Figure 1, which has already been described elsewhere [8]. It is considered as a monolithic block of multiple emitters connected in parallel with each other with a common voltage connected across them shown in Figure 2. Each emitter is biased with a common voltage, but the emitter currents and powers change depending on the details of the individual emitters and their environment.

Figure 1. Flow chart showing the communication between emitters in Barlase for the sixteen emitter 975 nm tapered laser bar

Figure 2. The representation of the sixteen emitter 975 nm tapered laser bar

A hypothetical 8-emitter 975 nm tapered laser bar was used to test for the correctness of the interpolated result, prior to the analysis of the real 16-emitter 975 nm tapered laser bar in Figure 2. Figure 3 shows the graphs of the original and interpolated simulated results, which indicate the successful implementation of the interpolation. The interpolated result phase is needed in order to transform the original simulated result from its non-uniform mesh to a uniform mesh, which is a necessary requirement for the convolution to be performed.

Figure 3. A hypothetical 8-emitter 975 nm tapered laser bar to test the correctness of the interpolated result

3. Results and Discussion

As the thermal camera has a limited spatial resolution, which is much larger than the active region of the laser and because the substrate is transparent to infrared light, the measured temperature underestimated the active region temperature by a factor A. This means that the actual temperature, Treal, is calculated from Treal−Tref = A(Tmeasured−Tref), where Tmeasured is the measured temperature and Tref is the heatsink temperature. Measurements of the emission wavelength shift and measurements at elevated temperatures give A∼1.4 [7]. Theoretical work, where simulated temperature profiles are convolved with the spatial response function of the thermal camera give a value of A∼1.1, but this did not consider the transparency of the substrate to infrared emission.

A further investigation of the temperature measurement was carried out using simulation results of the 975 nm tapered bars by convolution. The convolution routine consists of two parts. The first part interpolates the temperature profile generated by Barlase (which is on a non-uniform mesh) onto a uniform mesh. This is done by the griddata.m [9] function in Matlab. Once the temperature is on a uniform mesh, a 2D convolution is performed using Matlab’s conv2.m function. The conv2.m function only operates on a uniform mesh, hence the interpolation step using the griddata.m function used. Figure 4 shows the graphs for the thermal data for the original (simulation), interpolation, convolution and experimental results being compared. The experimental results were taken at a Tref of 25C and that of the original, interpolation, and convolution at a Tref of 20C, hence the temperature difference between them.

Analysing the details of the simulation and the experimental data reveals that, low spatial resolution of the camera has some effect on the accuracy of the measured results as seen in the comparison done between them. There is a change of ~ 0.35 K between the convoluted data from two peaks at ~ 3000 μm.

Figure 4. The graphs for the thermal data for the original, interpolation, convolution and experimental results; (a) for a spatial resolution of 70 microns, (b) 30 microns and (c) 17.3 microns being compared

Figure 5 also shows a further investigation made on portions of the graphs of Figure 4, on the central emitters (8, 9 and 10) [10] at different spatial resolutions for the CCD camera (17.3, 30 and 70 microns) for the thermal data for the simulation, interpolation and convolution results being compared. It reveals some disparities, Δx₁ and Δx₂, when the spatial resolution of the CCD camera is varied. This goes to buttress the point that, the spatial resolution of the CCD camera can affect the accuracy of the experimental results.

Figure 5. Portions of the graphs for the thermal data for the simulation, interpolation and convolution results for central emitters (8, 9 and 10) magnified for; (a) when the spatial resolution is 70 microns, (b) 30 microns and (c) 17.3 microns being compared

Figure 6. Convolution results for different spatial resolutions of 30 and 70 microns compared

Figure 6 shows the convolution results at different spatial resolutions of 30 and 70 microns being compared to further evaluate the effect of poor spatial resolution in the measurement of temperature.

To resolve the peaks, lots of points are needed. The finest spacing in the non-uniform mesh is around 0.5 microns. Therefore, N points in the Matlab file needs to be around 3 mm/0.5 microns = 6000 points in the uniform mesh in the x-direction. The computer resources available during this simulation, could handle only 2200 points in the x-direction, which makes the convolution analysis inconclusive. This shortcoming, notwithstanding, the emulation tool Barlase, has demonstrated its versatility in addressing numerous challenges high power laser diodes may have, in the bid of understanding and resolving them. This research work is still evolving and promises to reveal many more interesting results in the quest to making laser diodes more reliable and durable.

4. Conclusion

It is established that, more details and understanding can be derived with the increase in computer power to perform such simulations. Investigation of the measured temperature was carried out with the simulation results of the 975 nm tapered bars by convolution. The convolution routine consists of two parts. The temperature profile generated by Barlase, which is on a non-uniform mesh, is first interpolated to transform it onto a uniform mesh to allow, secondly, the profile to be convolved. Theoretical work, where simulated temperature profiles are convolved with the spatial response function of the thermal camera give a value of A∼1.1, without considering the transparency of the substrate to infrared emission. In a nutshell, more information can be gathered with enhanced computer power to further investigate the effect of temperature on the reliability of semiconductor high power laser bars.

Acknowledgement

CKA thanks the University of Mines and Technology, Tarkwa, Ghana and the GetFund for their support.

References

[1]   | Overton, G., S. G. Anderson, D. A. Belforte, and T. Hausken, Laser Focus World, 47, 40 (2011).
[2]   | Horn, W., Laser Tech. J., 4, 62 (2007).
[3]   | Menzel, U., R. Puchert, A. Barwolff, and A. Lau, Microelectron. Reliab., 38, 821 (May 1998).
[4]   | Xia, R., E. C. Larkins, I. Harrison, S. R. A. Dods, A. V. Andrianov, J. Morgan, and J. P. Landesman, IEEE Photon. Technol. Lett., 14, 893 (2002).
[5]   | Tomm, J. W., A. Gerhardt, T. Elsaesser, D. Lorenzen, and P. Hennig, Appl. Phys. Lett., 81, 3269 (2002).
[6]   | Bull, S., J. W. Tomm, M. Oudart, J. Nagle, C. Scholz, K. Boucke, I. Harrison and E. C. Larkins, J. Appl. Phys., 98, 063101 (2005).
[7]   | Amuzuvi, C. K., Bull S., Tomm J.W., Nagle J., Larkins E. C., Sumpf B., Erbert G., Michel N., and Krakowski M., “The impact of temperature and packaging-induced strain on current competition and emitter power in laser bars” Applied Physics Letter, June 2011.
[8]   | Amuzuvi, C. K., 2013. Emulation and By-Emitter Degradation Analysis of High Power Lasers: Lap Lambert Academic Publishing, Saarbrücken, Germany.
[9]   | Heinz Stockinger, Flavia Donno, Erwin Laure, Shahzad Muzaffar, Peter Kunszt. “CERN Grid Data Management in Action: Experience in Running and Supporting Data Management Services in the EU DataGrid Project”, European Organization for Nuclear Research, 2003.
[10]   | J. Tomm and J. Jiménez, Quantum-Well Laser Array Packaging, McGraw-Hill Professional; 1 edition (2006).