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InGaAs-based well - island composite quantum confined structure with super-wide and uniform gain distribution for great enhancement of semiconductor laser performance Qingnan Yu, Xue Li, yan jia, wei lu, ming zheng, xing zhang, yongqiang ning, and Jian Wu ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.8b01048 • Publication Date (Web): 01 Nov 2018 Downloaded from http://pubs.acs.org on November 9, 2018
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ACS Photonics
InGaAs-based well - island composite quantum confined structure with super-wide and uniform gain distribution for great enhancement of semiconductor laser performance Qingnan Yu1, Xue Li2, Yan Jia1, Wei Lu1, Ming Zheng1, Xing Zhang2, Yongqiang Ning2 and Jian Wu1,* *Corresponding Author: E-mail: (
[email protected]) Department of Applied Physics, Beihang University, Beijing, 100191, China. Key Laboratory of Luminescence and Application, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 130033, Changchun, China. 2State
ABSTRACT: In the development of semiconductor lasers, it has been a dream all along to simultaneously obtain extremely-wide and uniform gain distribution, because such a gain configuration can greatly enhance semiconductor laser performance. Hence, it has also been a huge challenge how to realize this dream so far. In this paper, we are reporting a special InGaAs-based well-island composite quantum confined structure, with which the best results to date in achieving both super-wide and very uniform gain and power distributions are obtained. The spectral flatness of the output power can reach 0.1dB and the gain bandwidth is broadened to 6-folds broader than FWHM (full width at half the maximum) of the standard gain spectrum from a classic InGaAs quantum well under the same carrier density. The formation of the well-island composite quantum confined structure is associated with the Indium-rich island effect in the material growth. The great significance of this work lies in that it is making the above dream to come true, since not only can it tremendously increase the spectral tuning range of an InGaAs-based semiconductor laser, but also exhibit a great potential on achieving uniform output power over the full spectral tuning range of the laser.
KEYWORDS: tunable semiconductor lasers, well-island composite quantum confined structure, InGaAs/GaAs material, gain characteristics, flat top, Indium-rich islands
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It has been well known that semiconductor lasers are taking important roles in many application fields.1-4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
However, the current quantum confined structures provide semiconductor lasers with the very limited bandwidth and non-uniform distribution of gains, such as the typical gain spectrum of a single InGaAs/GaAs quantum well, which is described in Figure 1a. This leads to a narrow spectral tuning range and non-uniform output power on all cavity modes due to nature of the structure so that the further enhancement of semiconductor laser performance is restricted. Tunable diode lasers are a typical example, in which lasing power is apparently reduced at both ends of the spectral tuning range, apart from the finite wavelength tuning range. This is illustrated in Figure 1b. This problem actually exists in other types of tunable lasers as well, which is shown in Figure 1c. Hence, the great enhancement of both spectral tuning range and uniformity of the lasing power is always expected for the tunable lasers. For this reason, scientists have been seeking for new techniques to obtain more uniform (flat-top) gain distribution with a broader bandwidth for tunable semiconductor lasers.5-21 This work is still on the way and no effective approach or new quantum confined structure has been found to significantly change the current situation so far. In all existing techniques, only a few approaches have shown a certain improvement on both gain uniformity (flatness) and bandwidth. In order to evaluate the capacity of the quantum confined structure achieving and broadening flat-top of gain or power spectrum, a flat-top broadening factor, RSW is defined as a measure of the broadening degree here. It is a ratio of the flat-top width of the broadened gain or power spectrum to the bandwidth (FWHM) of the standard gain or power spectrum from a typical single quantum confined structure based on the same materials and similar operation conditions. One common approach on improvement of both uniformity and bandwidth of the gain or power spectrum is the longitudinal combination of multiple quantum wells or quantum dot layers along the growth direction. These wells or dot layers have different band-gaps to produce mutually offset gain or power spectra and their superposition.17-21 This approach can properly increase the bandwidth and uniformity of the total gain or power spectrum due to the superposition effect. For example, RSW reached 3.8 with the flatness of 3dB for ASE spectrum of the InAs quantum dot structure20 and RSW was about 2.5 with the flatness of 1.2dB for ASE spectrum of the InGaAsP/InP multiple quantum-well structure19 to date, where ASE denotes the amplified spontaneous emission and flatness denotes the ripple of the flat-top of gain or power spectrum. These results show that the simultaneous improvement on both RSW and flatness of the gain or power spectrum is still limited and difficult. The theoretical simulation on the gain superposition of the InGaAs/GaAs/GaAsP multiple quantum wells using PICS3D software computation shows that it is hardly possible to realize both super-wide and uniform gain distributions (e.g. RSW 6.0 and ACS Paragon Plus Environment
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