Hak-Seung Han

Optical gain at 1.54 μm in erbium-doped silicon nanocluster sensitized waveguide

Optical gain at 1.54 μm in erbium-doped silicon-rich silicon oxide (SRSO) is demonstrated. Er-doped SRSO thin film was fabricated by electron-cyclotron resonance enhanced chemical vapor deposition of silicon suboxide with concurrent sputtering of erbium followed by a 5 min anneal at 1000 °C. Ridge-type single mode waveguides were fabricated by wet chemical etching. Optical gain of 4 dB/cm of an externally coupled signal at 1.54 μm is observed when the Er is excited via carriers generated in the Si nanoclusters by the 477 nm line of an Ar laser incident on the top of the waveguide at a pump power of 1.5 W cm−2.Optical gain at 1.54 μm in erbium-doped silicon-rich silicon oxide (SRSO) is demonstrated. Er-doped SRSO thin film was fabricated by electron-cyclotron resonance enhanced chemical vapor deposition of silicon suboxide with concurrent sputtering of erbium followed by a 5 min anneal at 1000 °C. Ridge-type single mode waveguides were fabricated by wet chemical etching. Optical gain of 4 dB/cm of an externally coupled signal at 1.54 μm is observed when the Er is excited via carriers generated in the Si nanoclusters by the 477 nm line of an Ar laser incident on the top of the waveguide at a pump power of 1.5 W cm−2.

Coefficient determination related to optical gain in erbium-doped silicon-rich silicon oxide waveguide amplifier

Gain-determining coefficients in Er-doped, nanocrystal-Si (nc-Si) sensitized silica waveguide amplifiers are investigated. Single-mode, Er-doped silica waveguides with nc-Si embedded in them were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition of Er-doped a-Si:Ox (x<2) followed by a high-temperature anneal to precipitate nc-Si. Exciting the Er ions via nc-Si by pumping the waveguide from the top with the 477 nm line of an Ar laser resulted in an enhancement of the transmitted 1535 nm signal of up to 14 dB/cm, indicating a possible net gain of up to 7 dB/cm. From the dependence of the signal enhancement upon the pump power, an emission cross section of 2×10−19 cm2 at 1535 nm and an effective excitation cross section of ⩾10−17 cm2 at 477 nm is obtained.

1.54 μm Er3+ photoluminescent and waveguiding properties of erbium-doped silicon-rich silicon oxide

1.54 μm Er3+ photoluminescent and waveguiding properties of erbium-doped silicon-rich silicon oxide (SRSO) are investigated. Optimum Er3+ luminescence was obtained after an anneal of at least 5 min at 950 °C, and at least 1 at. % excess silicon in SRSO was necessary for the excitation of erbium to be dominated by carriers. The refractive index and the bulk waveguide loss of erbium-doped SRSO film with 0.1 at. % erbium and 1 at. % excess silicon after the optimal anneal treatment was 1.4817 and 4.0 dB/cm, respectively. Fabrication of an erbium-doped SRSO strip waveguide using the standard Si processing techniques and the guiding of internal 1.54 μm Er3+ emission by such a strip waveguide are demonstrated.

1.54 μm Er3+ photoluminescent properties of erbium-doped Si/SiO2 superlattices

The 1.54 μm Er3+ photoluminescent properties of erbium-doped Si/SiO2 superlattices are investigated. Two superlattice films, one with erbium in Si layers and the other with erbium in SiO2 layers, were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition of SiH4 and O2 with cosputtering of erbium and subsequent rapid thermal anneal. Both display Er3+ luminescence, but it is stronger with longer luminescent lifetime and less temperature quenching when erbium is in the SiO2 layer. The results demonstrate that by using quantum structures, nonradiative deexcitation of Er3+ may be suppressed, and that carrier recombination events, which excite Er3+ ions, may be physically separated from Er atoms and still lead to an efficient Er3+ luminescence.

Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs

A review is presented of Si nanocluster sensitization of Er-doped silica for planar optical amplifiers using top-pumping 470-nm light-emitting diodes (LEDs). The motivation and basic physical principles underlying the nanocluster sensitization are first reviewed. The material structures necessary for optimum performances are presented, with emphasis on the need for nanoscale engineering of the composition and structure. Evidence of optical gain using commercial GaN-visible LEDs are presented, and the simulation results of possible device performances described. Finally, some possible future directions for research are discussed

Rare-earth-doped nanocrystalline silicon: excitation and de-excitation mechanisms and implications for waveguide amplifier applications

Excitation and de-excitation mechanisms of rare earth doped nanocrystalline silicon and its implications for waveguide amplifier applications are investigated. Er, Nd, and Pr doped silicon rich silicon oxide (SRSO) thin films were prepared by electron cyclotron resonance enhanced chemical vapor deposition with co-sputtering of target and subsequent anneal at 950 degrees C. Temperature and pump-power dependence of Er3+ photoluminescence shows that carrier-mediated non-radiative de-excitation are strongly suppressed indicating feasibility of population inversion. Detailed investigations of dependence of Er3+ luminescence intensity and lifetime on pump width indicate that exciton-erbium coupling is dominant over carrier- exciton coupling, and that the luminescent Er ions are not inside the Si nanoclusters but in the SiO2 matrix near the clusters. Luminescence properties of Nd-doped SRSO is similar to that of Er-doped SRSO, but the temperature dependence of Nd3+ luminescence intensity is different from that of Er3+ luminescence, an effect which we ascribe to its higher transition energy. In contrast, no luminescence could be observed from Pr-doped SRSO. Erbium-doped SRSO waveguides are fabricated using the standard Si processing techniques, and guiding of 1.55 micrometers light with strong Er luminescence is observed. These results indicate that for rare erath-doped SRSO waveguides to become practical, formation of high density of small Si nanoclusters must be induced.

Optical Gain Using Nanocrystal Sensitized Erbium: Nato-Series

The amount of information being transmitted via optical fibers has been increasing exponentially at a rate exceeding even the vaunted “Moore’s Law” of silicon integrated circuits [1]. One key technology that enabled such rapid growth is erbium-doped fiber amplifiers (EDFA). By using the intra-4f transition of Er3+ (4I13/2 → 4I15/2) to amplify optical signals near 1.54 μm, the absorption minimum of silica-based optical fibers, EDFAs made today’s wideband, all-optical networks possible [2]. However, because EDFAs require expensive lasers tuned to one of the absorption bands of Er3+ for excitation of Er, they remain too expensive to be used widely, thereby hindering the extension of the all-optical network all the way to the individual end-users. Yet neither substituting the fiber for a waveguide nor sensitizing Er3+ with other rare earth ion such as Yb3+ can fundamentally solve this problem. In fact, the high Er3+ concentrations required for waveguide-based amplifiers due to the need to compress long fibers into short waveguides leads to pair-induced quenching [3], necessitating the use of even more powerful and expensive lasers.

Control of Location and Carrier-Interaction of Erbium Using Erbium-Doped Si/SiO 2 Superlattice

The effect of controlling the interaction between the erbium atoms and the carriers of the host matrix is investigated using erbium doped Si/SiO 2 superlattices. Based on the previous finding that controlling the location of the erbium atoms by doping only the SiO 2 layers improves both the Er 3+ photoluminescence intensities and the temperature quenching of the Er 3+ luminescence, we identify controlling the interaction between erbium atoms and the carriers in the Si layer to be the key point. We demonstrate that by further isolating the erbium atoms from the Si layers by depositing thin buffer layers of pure SiO 2 improves the Er 3+ photoluminescence by several orders of magnitude while still allowing efficient excitation by carriers to dominate. Finally, we demonstrate that efficient waveguides can be fabricated using such erbium doped Si/SiO 2 superlattices.