Hansuek Lee

Cooperative upconversion and optical gain in ion-beam sputter-deposited Er x Y 2-x SiO 5 waveguides

Single-phase, polycrystalline Er(x)Y(2-x)SiO(5) thin films were deposited by reactive ion-beam sputter deposition and rapid thermal annealing. Due to the crystalline nature, the silicate thin films provide peak Er(3+) emission cross-section of 0.9 +/- 0.02 x 10(-20) cm(2) that is higher than that in silica. Optical gain, with near 60% inversion, is achieved via optical pumping of a single-mode, ridge-type waveguide with the silicate core with an Er concentration of 1.7 x 10(20) cm(-3). Analysis of pump-power dependence of the optical gain and spontaneous emission intensity of Er(3+) indicate that the gain is limited by cooperative upconversion process, whose coefficient is determined to be (8 +/- 3) x 10(-17) cm(3)/sec.

Analysis and experimental demonstration of simplex coding technique for SNR enhancement of OTDR

We demonstrate SNR improvement of OTDR using simplex codes by experiment, for the first time. For this, we proposed a practical algorithm and derived detailed equations. An in-house OTDR board was developed to verify the proposed algorithm, and the experimental results showed excellent agreement with theory. In addition, we analyzed the SNR variation of the simplex code OTDR, caused by band-limited receiver characteristics.

Performance analysis of nanocluster-Si sensitized Er-doped waveguide amplifier using top-pumped 470nm LED

We analyze the performance of nanocrystal-Si (nc-Si) sensitized Er-doped waveguide amplifier using coupled nc-Si-Erbium rate equation, and suggest novel structures / operation methods which can be used to enhance its performance figures. With 2-dimensional modified propagation equation applied for the pump / signal waves along with modest assumptions on design parameters, we show that 10dB of gain with 0dBm input signal can be achieved with currently available pump LED power.

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

Nonlinear phase shift scanning method for the optimal design of Raman transmission systems

In this paper, an efficient algorithm for the search of optimum design parameters and corresponding transmission quality factor (Q) for a Raman amplified transmission system is presented. Taking the nonlinear phase shift (NPS) as the first-order key design parameter for the determination of the remaining secondary system parameters, and solving the nonlinear Schroumldinger equation (NLSE) as a function of NPS to obtain the optimum (Q) factor, the multiparameter, time-consuming fiber Raman amplifier (FRA) system design process can be reduced to a highly efficient and precise semianalytic one-dimensional optimization problem. As an application example for the suggested optimization algorithm, the authors show the design process for the determination of the system design parameters (input powers to single mode fiber (SMF), dispersion-compensating fiber (DCF), distributed Raman gain, and forward Raman pumping ratio) for a single channel 10-Gb/s 2000-km transmission link. In addition, for the first time within the authors knowledge, they assess the requirements of pump relative intensity noise (RIN), as a function of the pumping direction/span-length changes, to study the shift in the optimum design parameters. Results show a Q-factor improvement for the system more than 1.16 dB/4.89 dB at a 100-km/200-km span length with their design method, when compared to previous optimization method. Discussion on the application to dense wavelength division multiplexing (DWDM) system is also presented

Structural detuning of absorption rate in doped fiber for the enhancement of power efficiency

We propose a novel doped fiber structure, for the enhancement of power conversion efficiency (PCE) in an L-band erbium-doped fiber amplifier. With proper adjustment of the doping profiles for the reduction of pump absorption rate, it becomes possible to optimize the pump evolution inside the doped fiber so as to improve the PCE, while suppressing the development of pump-depleting detrimental amplified spontaneous emission. Exemplary analysis shows significant enhancement in the saturation output power of more than 58.5%, when compared to conventional C-band erbium-doped fiber.

Optimization of the material parameters for Silicon nanocluster sensitized Er-doped waveguide amplifier

Recent progress in the effort of realizing nanocluster silicon sensitized, Er-doped silica waveguide amplet is introduced. Approaches for the optimization of key device / material parameters, in terms of numerical assessment and experimental means will be detailed.

Recent advances in nanocrystal-Si sensitized, Er-doped silica waveguide amplifiers

Recent advances in nanocrystal-Si sensitized, Er-doped silica waveguide amplifiers are introduced. A numerical performance analysis demonstrating its comparative advantages and commercial performance is presented, and ultra-broadband luminescence using a single pump-source and Er-Tm codoping is demonstrated.

Er x Y 2−x SiO 5 thin film waveguide for high optical gain per length at 1.53 μm

Ridge-type Er_xY_2-xSiO₅ waveguides were fabricated. Amorphous Er_xY_2-xSiO₅ was deposited using reactive ion beam sputter deposition, and crystallized by high-temperature annealing. The inversion level achieved was 0.4, limited by grain-boundary scattering and multimodedness of waveguide.

Amplification characteristics of nanocluster-Si sensitized Er-doped waveguide amplifier using top-pumped blue-green LED

In this paper, we provide a detailed performance analysis of an nc-Si EDWA for the real application. Optical gain (small signal / saturation regime), noise figure and required pump density has been assessed in terms of the device structure. Results show a high feasibility of achieving 10dBm output power with 0dBm of input signal, using an array of commercially available high-power blue-green LEDs as the top pump. In numerical model section, we suggest simplified coupled rate equation and 2-D propagation equation constructed to investigate amplifier performance. In performance analysis section, firstly, we compared population inversion characteristics for Er with/without nc-Si condition to confirm the widening of high inversion region by introducing nc-Si sensitizer, which means less pump intensity requirement for same input signal power. In addition, to test the feasibility of the NC-EDWA for the metro-network applications, we simulated the amplifier performance for varying the width of amplifier region. With 50x7μm2 active core and bottom mirror, only 15.8 W/cm2 (8.8 W/cm2 for 100μm width) of pump intensity was sufficient to meet the target operating condition. We also compare the inversion distributions of NC-Si EDWA, for the 4 types of EDWA structures under investigation (straight without/with mirror, adiabatic without/with mirror). As another key performance factor, we also calculated noise figures for different NC-Si EDWA structures.