article posted 1 April 2016/em>
Byoungjin So is a is a graduate student under PhD in materials science and engineering department of Pohang University of Science and Technology(POSTECH), Republic of Korea. Before that he obtained his Bachelors degree in Materials Science and Engineering in Inha University, Korea in 2012.
Buried Active Waveguides Containing Lead Sulphide Quantum Dots
Byoungjin So* & Jong Heo
Department of Materials and Engineering and Division of Advanced Nuclear Engineering, Pohang University of Science and Technology (POSTECH), South Korea
Glasses containing various rare-earth ions such as praseodymium, thulium and erbium are being investigated for optical amplification. In this case, it is necessary to develop suitable glass composition for each rare-earth ion if one were to cover the entire telecommunication window. The other hand, glasses containing semiconductor quantum dots (QDs) have advantages of size-tunable optical properties, i.e. the emission wavelength can be controlled by simply changing the sizes of QDs in glasses. Therefore, they provide potentials for broad-band optical amplification. In particular, lead sulfide QDs emits near-infrared radiation since they have a narrow energy bandgap (e.g. PbS=0·41 eV at 298 K) with a strong quantum confinement effect and a large Bohr radius of 18 nm. Emission windows of PbS QDs also match with the optical telecommunication window (1·3 µm ~1·55 µm) . Attempts were also made to fabricate the fibers and waveguides containing QDs. Drawing of a glass fiber containing QDs has been difficult due to the uncontrolled precipitation of QDs during the drawing process . Ion-exchanged waveguide using PbS doped glasses suffer optical losses on the surface due to partially buried structure .
In this study, waveguides containing PbS QDs were fabricated by irradiating the laser with a wavelength of 532 nm. Ag nanoparticles play an important role to convert the photon energy of a laser to thermal energy in the transparent glasses through the surface plasmon resonance process . Silicate glasses containing PbO and ZnS were ion-exchanged inside the AgNO3
meet at 300°C. Ag nanoparticles were then formed by heat treatment at 400°C. The 532 nm CW laser of 0·6 W power was irradiated on the ion-exchanged region and waveguides of ~30 µm in diameter were written by moving of the stage parallel to the laser beam (Fig. 1.). Scanning electron microscope showed that diameters of QDs were ~200 nm at the center of the waveguides and decrease to <1 nm at the periphery. Elemental analysis of waveguides using the electron probe micro analyzer showed the redistribution of elements due to the laser irradiation. Luminescence from PbS QDs inside the waveguides were recorded and optical losses of the waveguides were measured. Light guiding and amplification were investigated for characterization of active waveguide.
Figure 1: Optical microscope image of waveguide written by translation of the specimen parallel to incident laser beam
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