Elton Marchena

Integrated tunable CMOS laser

An integrated tunable CMOS laser for silicon photonics, operating at the C-band, and fabricated in a commercial CMOS foundry is presented. The III-V gain medium section is embedded in the silicon chip, and is hermetically sealed. The gain section is metal bonded to the silicon substrate creating low thermal resistance into the substrate and avoiding lattice mismatch problems. Optical characterization shows high performance in terms of side mode suppression ratio, relative intensity noise, and linewidth that is narrow enough for coherent communications.

Free-carrier absorption modulation in silicon nanocrystal slot waveguides.

Free-carrier absorption (FCA) has proven to be an important obstacle in the development of a silicon-based laser; however, FCA may serve as a potential advantage in active silicon-based switches or modulators. In this work, we present FCA modulation in slot waveguides with silicon nanocrystals (Si-ncs) embedded in SiO(2) as the low-index slot material. Slot waveguides were fabricated with and without Si-ncs, and the presence of Si-ncs was shown to increase the pump-induced FCA loss in the waveguides by a factor of 4.5. We modeled the Si-nc material using a four-level rate equation analysis to estimate the excited population of Si-ncs, allowing us to extract a value of 2.6 × 10(-17) cm(2) for the FCA cross section of the Si-nc material.

Comparison of raised-microdisk whispering-gallery-mode characterization techniques

We compare the two prevailing raised-microdisk whispering-gallery-mode (WGM) characterization techniques, one based on coupling emission to a tapered fiber and the other based on collecting emission in the far field. We applied both techniques to study WGMs in Si nanocrystal raised microdisks and observed dramatically different behavior. We explain this difference in terms of the radiative bending loss on which the far-field collection technique relies and discuss the regimes of operation in which each technique is appropriate.

Mitigation of Si nanocrystal free carrier absorption loss at 1.5 μm in a concentric microdisk structure

We study the mitigation of Si nanocrystal (Si-nc) free carrier absorption (FCA) loss at telecom wavelengths in a concentric microdisk design. The concentric microdisk design relies on using the Si-nc emission as an optical pump for the surrounding Er-based lasing media without subjecting the lasing mode to the FCA loss present in the Si-ncs. We analyze the FCA loss as a function of overhang width in this design and show that for large enough overhang width the FCA loss is negligible. We also compute the FCA cross section from the FCA loss and number of excited Si-ncs, modeled by a four-level system, and show sigma(FCA)=1.08 +/- 2.3 x 10(-17) cm(2), which is in good agreement with reported cross sections for similar films.

Fabrication and characterization of optimized corner-cut square microresonators

In this paper we report the fabrication and characterization of waveguide coupled square resonators with modified corners, in particular the corner-cut square resonator. We employ rigorous FDTD analysis to identify an optimal corner-cut length and compare this with our experimental findings. Two- and three dimensional FDTD analysis is also used to optimize the coupling gap and the width of the coupling waveguide. Fabrication of the square microresonators on silicon-on-insulators by conventional E-beam lithography and dry etching techniques will be discussed in detail. The characterization of these corner-cut square microresonators shows good performance and excellent agreement with the rigorous electromagnetic simulations.

Pulsed pumping of silicon nanocrystal light emitting devices

Typical silicon nanocrystal light emitting devices (LEDs) operate under direct current (DC) biasing conditions that require high electric fields or high current densities. The electroluminescence (EL) under these conditions relies on impact excitation that can be damaging to the material. In this work, we present bipolar injection into silicon nanocrystal LEDs using a pulsed pumping scheme. We measured the frequency dependence of the integrated and time-resolved EL of the LEDs. The frequency dependent behavior of the time-resolved characteristics is used to explain the integrated EL measurements. In addition, the light output of the device was measured under pulsed excitation and was found to increase by a factor of 18 as compared to the case of DC excitation.

Coupling Si nanocrystal microdisk emission to whispering-gallery modes in a concentric SiO2 ring.

We present a concentric microdisk design in which luminescence from an inner disk of Si nanocrystals (Si-ncs) contributes to resonant modes in an outer ring of SiO2. Photoluminescence from fabricated structures reveals the excitation of whispering-gallery modes (WGMs) with quality factors as high as 2850, limited by the spectral resolution of our spectrometer. Two-dimensional finite-difference time-domain simulations provide insight into the WGM properties and the role of disk and ring geometry. The presented concentric disk structure provides a means to use the efficient visible luminescence of Si-ncs as an optical pump for an extrinsic lasing material such as Er:SiO2.

High power, narrow linewidth, low noise, integrated CMOS tunable laser for long haul coherent applications

An integrated-CMOS-tunable-laser with 15-dBm output power is presented. Fabrication is realized in commercial CMOS foundry. Laser shows high power, low RIN, and ultra-narrow linewidth. Performance over fiber is comparable with best-in-class, market-leading ITLA, proving suitability for long haul coherent applications.

Modeling of light amplification and enhanced spontaneous emission in silicon nanocrystals

Based on coupled quantum electrodynamics the light propagation in active silicon nanocrystals was reported in this paper. The classical electron oscillator model was employed to bridge the link between the rate equations of the four-level atomic system of the active medium and the electromagnetic interaction. With the assistance of auxiliary differential equations we numerically solved the system by using the Finite-difference Time-domain (FDTD) method. Both stimulated and spontaneous emissions were taken into account in the active medium system. Light amplification characteristics due to stimulated emission were investigated under various pumping rates. To enhance the spontaneous emission, microcavities based on one-dimensional photonic crystals were designed to maximize the nonlinear interaction between the active medium and electromagnetic waves. Preliminary experimental investigation of the cavity-enhanced luminescence was performed to demonstrate the validation of the proposed simulation scheme.

Silicon multiple exciton generation/pn junction hybrid solar cell

The concept of a nanostructured-surface/pn junction hybrid solar cell has been modeled to incorporate multiple excitons generation effects. Using the mature silicon solar cell as a base, a nanostructured surface can be made to increase efficient absorption of high energy light by impact ionization induced multiple exciton effects. The nanostructured surface has additional benefits including anti-reflection and a surface field at the quantum confined regions. An ideal detailed-balance efficiency of 41.2% is found for the hybrid solar cell under one sun illumination. This is reduced to 33% when taking into account non-idealities yet both models increase rapidly with concentration as discussed thus motivating a search for the best nanostructured surface to yield multiple excitons generation. A preliminary design of such a surface has been chosen and fabrication is shown.