• Journal of the Korean Vacuum Society
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• v.15 no.2
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• pp.194-200
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• 2006

Self-assembled InAs/InAl(Ga)As quantum dots (QDs) were grown on InP substrates by a molecular-beam epiaxy, and their structural and optical properties were investigated by atomic force microscopy (AFM), transmission electron microscopy (TEM), and room-temperature photoluminescence (PL). AFM images indicated that the InAs quantum structures showed various shapes such as quantum dashes, asymmetric and symmetric QDs mainly caused by the initial surface conditions of InAl(Ga)As with the intrinsic phase separation. For the buried InAs QDs in an InAlGaAs matrix, the average lateral size and height of QDs were 23 and 2 nm, respectively. By changing the growth conditions for the QD samples, the emission wavelength of $1.55{\mu}m$ was obtained, which is one of the wavelength windows for fiber optic communications.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.294-300
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• 2006

We fabricated the distributed feedback (DFB) InP/InGaAs/InP grating structures on InP (100) substrates by metal-organic chemical vapor deposition, and their structural properties were investigated by atomic force microscopy and scanning electron microscopy. Self-assembled InAs/InAlGaAs quantum dots (QDs) were grown on the InP/InGaAs/InP grating structures by molecular beam epitaxy, and their optical properties were compared with InAs/InAlGaAs QDs without grating structure. The duty of the grating structures was about 30%. The PL peak position of InAs/InAlGaAs QDs grown on the grating structure was 1605 nm, which was red-shifted by 18 nm from that of the InAs/InAlGaAs QDs without grating structure. This indicates that the formation of InAs/InAlGaAs QDs was affected by the existence of the DFB grating structures.

• Korean Journal of Optics and Photonics
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• v.31 no.3
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• pp.142-147
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• 2020

In this paper, we report highly efficient second harmonic generation of continuous-wave Yb fiber lasers incorporating a periodically poled LiTaO₃ device (MgO:PPSLT) as a frequency converter. The seed laser output from a Yb fiber master oscillator using a Fabry-Perot feedback cavity was amplified in a Yb fiber amplifier stage, yielding 28.5 W of linearly polarized output at 1064 nm in a beam with beam quality, M², of ~1.07. Second harmonic generation was achieved by passing the laser beam through MgO:PPSLT. Under optimized conditions, we obtained 11.1 W of green laser output at 532 nm for an incident signal power of 25.0 W at 1064 nm, corresponding to a conversion efficiency of 44.4%. The detailed investigation to find the optimized operating conditions and prospects for further improvement are discussed.