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Journal of Applied Physics

Achieving optical gain in waveguide-confined nanocluster-sensitized erbium by pulsed excitation

Gerald M. Miller, Ryan M. Briggs, Harry A. Atwater

Published Sep 15, 2010• 22 citations
Publisher

Abstract

We use a rate equation approach to model the conditions for optical gain in nanocluster sensitized erbium in a slot waveguide geometry. We determine the viability of achieving net gain for the range of reported values of the carrier absorption cross section for silicon nanoclusters. After accounting for the local density of optical states modification of the emission rates, we find that gain is impossible in continuous wave pumping due to carrier absorption, regardless of the carrier absorption cross section. We, therefore, propose a pulsed electrical operation scheme which mitigates carrier absorption by taking advantage of the short lifetime of silicon nanoclusters compared to erbium. We show that pulsed excitation of a 10 nm layer achieves a modal gain of 0.9 dB/cm during each pulse. Furthermore this gain can be increased to 2 dB/cm by pumping a 50 nm layer.

DOI
10.1063/1.3465120

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Applied Physics Letters•Apr 14, 2006•36 citations
We use a rate equation approach to model the conditions for optical gain in nanocluster sensitized erbium in a slot waveguide geometry. We determine the viability of achieving net gain for the range of reported values of the carrier absorption cross section for silicon nanoclusters. After accounting for the local density of optical states modification of the emission rates, we find that gain is impossible in continuous wave pumping due to carrier absorption, regardless of the carrier absorption cross section. We, therefore, propose a pulsed electrical operation scheme which mitigates carrier absorption by taking advantage of the short lifetime of silicon nanoclusters compared to erbium. We show that pulsed excitation of a 10 nm layer achieves a modal gain of 0.9 dB/cm during each pulse. Furthermore this gain can be increased to 2 dB/cm by pumping a 50 nm layer.
Energy transfer in erbium doped optical waveguides based on silicon This thesis describes the energy transfer processes\noccurring in materials that can be used for the fabrication of silicon compatible optical integrated circuits, operating at 1.54 mm.The thesis consists of three parts: Part I discusses energy transfer in optical waveguide amplifiers on silicon. The waveguide amplifiers use an intra-4f transition of the rare earth ion erbium occurring at 1.54 mm. To achieve significant amplification, high\n Er concentrations (> 10 20 cm -3 ) are required. At these concentrations Er ions can interact, resulting in co-operative\n upconversion, in which one excited Er ion is excited into a higher energy state, while a neighboring Er ion returns to the ground\n state. In Part I this and other gain limiting effects are investigated. In particular, it is shown that the atomic-scale Er distribution\n is of crucial importance for the performance of Er doped waveguide amplifiers. Part II discusses the energy transfer processes\n occurring in Er doped silicon. It is shown that Er in silicon can be excited by electron-hole pair recombination in an\n impurity-Auger effect. This effect may be used to fabricate an electrically pumped Er doped waveguide amplifier. The reverse\n process can also occur: an excited Er ion can de-excite and generate an electron-hole pair in the silicon, due to a non-radiative\n backtransfer process. This process has an efficiency of 70% at room temperature. This observation enables the fabrication of an\n Er doped photo-detector in a Si waveguide operating at 1.54 mm. The performance of such a detector is discussed. Part III\n discusses the interaction between Er and silicon nanocrystals embedded in SiO2. Si nanocrystals efficiently absorb visible light,\n resulting in the generation of quantum confined electron-hole pairs. The electron-hole pairs efficiently transfer energy to Er.\n Due to the energy transfer, the effective Er absorption cross section is five orders of magnitude larger than for direct optical\n excitation. Silicon nanocrystals may thus be used to increase the pumping efficiency of an Er doped waveguide amplifier. It is\n shown that a single nanocrystal can excite ~1 Er ion at a time and that an optical gain of 0.6 dB/cm may be achieved in a typical\n nanocrystal sensitized waveguide amplifier. Due to the broad absorption band of Si nanocrystals, a broad band light source can\n be used as pump source in such a nanocrystal sensitized Er doped waveguide amplifier.
Abstract—In this article the details of Erbium doped Fiber Amplifier (EDFA) in presence of Silicon nanocrystal (Si-Nc) is investigated. In this analysis Si-Nc and Er ions in matrix of fiber are assumed two and five levels respectively. For this structure rate equation for transient and steady state analysis is considered. The range of Er (+3) concentration and pump intensity at 488 nm are considered [10 17 − 10 21]1/cm 3 and [10 17 − 10 23] photon/cm 2 · sec respectively in this paper. Based on numerical simulation of this problem we observed that with increasing of concentration of the Si-Nc the fiber length for given optical gain is decreased. For example in the case of 40 dB optical gain, we calculated fiber length to be 1.1 × 10 5 cm without Si-Nc and 5 × 10 2 cm for σCCa = 1 × 10 −17 cm 2 (confined carrier absorption cross-section) and 5 cm for σCCa =1 × 10 −19 cm 2 respectively. Our simulations show that for second level with increasing pump intensity the population rise and fall times are decreased. But, for third level the population rise time is decreased and fall time is depends to level of Er ion interactions. We observed that with increasing Er ions optical net gain is increased and finally has a maximum. After this special value of Er ions because of increasing in interaction between ions the net gain finally begin to decrease. In this analysis we let to Er ions have inhomogeneous distribution. Also, we observed that in this case with increasing of the distribution peak, the net gain is increased, interaction between ions is increased, the coupling coefficient to the Si-Ncs is increased and losses due to Si-Ncs are decreased. Finally effect of Kexiton (maximum number of exciton in single Si-Nc) on amplification process is considered and we observed that in the case of Kexiton = 2 the optical gain considerably and introduced losses due to Si-Nc are increased. 28 Rostami and SalmanOgli 1.
Here we report on measurements of optical gain at 1.5μm in crystalline silicon. Gain is achieved by the incorporation of the rare earth erbium in silicon. A method was developed to enable the gain measurement in short silicon waveguides. Crucially, gain values obtained are significantly greater than previously supposed. We have measured a lower limit for the optical cross section for Er3+ of 5×10−19cm2, 30 times higher than previously anticipated. Given these higher values, this system now offers a realistic route to the production of electrically pumped silicon optical amplifier and laser devices using standard silicon process technology.
Net optical gain in silicon nanocrystals (Si-nc) has been measured by pump and probe transmission experiments. Si-nc active layers have been produced by plasma enhanced chemical vapor deposition on transparent quartz substrates. Continuous and pulsed pump and probe transmission measurements have shown clear evidences of net probe amplification with fast (nanosecond) response time. Transfer matrix and rate equations modeling of the nonlinear signal transmission allowed to extract the gain spectra for different pump intensities yielding good qualitative agreement with the experimental data. Gain cross sections per nanocrystals of the order of 3×10−16cm2 have been deduced. The physical origin of the optical amplification is interpreted within a four level recombination model describing the dynamics of strongly localized excitons at the Si-nc∕SiO2 interface.
Absorption coefficient (αabs) of Er3+ ions coupled to Si nanoclusters (Si-nc) in SiO2 has been determined by optical transmission measurements in rib-loaded waveguides characterized by different refractive indices, thus gauging an Er3+ absorption cross section (σabs) of 0.4–1.2×10−20cm2 at 1534nm. Although no significant enhancement due to the presence of Si-nc was observed, a clear dependence on the refractive index has been found. Measurements of the decay lifetime permit one to model the behavior as due to both local and mean field variations caused by the composite nature of the core waveguide layer.