Jung S. Park

Enhanced room temperature ferromagnetism in Co- and Mn-ion-implanted silicon

The authors report on ferromagnetism at room temperature in cluster-free, cobalt- and manganese-ion-implanted crystalline silicon. Through magnetic and structural analysis it is shown that the ion-implanted Si consists of two layers of Co- and Mn-containing silicon: (1) an amorphous Si layer on the surface and (2) single crystalline Si beneath. The amorphous layer shows very little magnetism by itself but seems to be responsible for partially canceling out or masking the ferromagnetism in the crystalline Si. The authors also observe that etching of the amorphous Si layer dramatically enhances the measured magnetism by as much as 400%.

Quantitative infrared imaging of silicon-on-insulator microring resonators.

There is considerable research activity in multiresonator optical circuits in silicon photonics, e.g., for higher-order filters, advanced modulation format coding/decoding, or coupled-resonator optical waveguide delay lines. In diagnostics of such structures, it is usually not possible to measure each individual microring resonator without adding separate input and output waveguides to each resonator. We demonstrate a non-invasive diagnostic method of quantitative IR imaging, applied here to a series cascade of rings. The IR images contain information on the otherwise inaccessible individual through ports and the resonators themselves, providing an efficient means to obtain coupling, loss, and intensity-enhancement parameters for the individual rings.

Three-way electrical gating characteristics of metallic Y-junction carbon nanotubes

Y-junction based carbon nanotube (CNT) transistors exhibit interesting switching behaviors, and have the structural advantage that the electrical gate for current modulation can be formed by any of the three constituent branches. In this letter, we report on the gating characteristics of metallic Y-CNT morphologies. By measuring the output conductance and transconductance we conclude that the efficiency and gain depend on the branch diameter and is electric field controlled. Based on these principles, we propose a design for a Y-junction based CNT switching device, with tunable electrical properties.

Mid-Infrared Wavelength Conversion in Silicon Waveguides Pumped by Silica-Fiber-Based Source

We discuss the potential of four-wave mixing (FWM) in a cascaded silica-silicon platform for generation of light in the midwave infrared (mid-IR) spectral domain. The motivation for developing light sources in mid-IR is supported by numerous applications, such as free-space communications, light detection and ranging (LIDAR), remote sensing, and medicine. These applications would greatly benefit from narrow linewidth and widely tunable laser sources with modulation capability. In this paper, a summary of existing light sources in mid-IR is given and the potential features that the proposed hybrid silica-silicon source can deliver to mid-IR applications are listed. Silica fiber is a well utilized platform at telecom wavelengths that is supported by an excellent infrastructure including tunable narrow linewidth laser sources, unsurpassed in the other spectral domains, high-bandwidth modulators, and detectors. The capability of this platform has recently been extended to the shortwave IR region (SWIR). On the other hand, silicon suffers from impairments imposed by nonlinear absorption at telecom wavelengths, but it possesses excellent linear and nonlinear optical properties in the SWIR (1.7-2.2 μm) and mid-IR (2.2-5 μm) regions. Therefore, in combination with a silica-based SWIR source, it can be utilized as an efficient FWM platform for mid-IR frequency generation.

Mid-Infrared Four-Wave Mixing in Silicon Waveguides Using Telecom-Compatible Light Sources

We report four-wave mixing in silicon waveguides in the spectral region beyond 2 ?m using infrared signals derived from telecom-compatible fiber-optic sources. We measure a high value of the nonlinear parameter gamma = 103 /(Wm).

Two-Pump Four-Wave Mixing in Silicon Waveguides

We report dual-pump four wave mixing in silicon waveguides and demonstrate generation of up to 10 sidebands with self-seeded higher order pumps. A conversion efficiency of −8.38dB was measured between the signal and phase-conjugated idler.

Tuning of microring resonators

Structural imperfections in fabricated microring resonators make post-fabrication tuning of rings useful in order to obtain desired transmission, phase and delay characteristics. Optical trimming of polymer microrings has been demonstrated using photobleaching. Here we investigate post-fabrication tuning of silicon-on-insulator microrings and microring based devices, including aligning the resonant frequencies of rings, and tuning the coupling coefficients.

Disorder and localization in microresonator arrays

An optical waveguide consisting of coupled identical resonators in a linear array can slow down the propagation of light and act as a delay line. However, such a slow-wave structure offers only a modest improvement in delay per unit length over a spool of optical fiber, as its performance rapidly degrades if the resonators or their spacing are not exactly identical. Here we show that the same degree of functionality can be achieved in a more compact and disorder-immune structure, formed by nesting one resonator inside another, and thereby folding the light path back onto itself.

Light localization in silicon nanophotonic waveguides

We report the first observation of Anderson light localization in compact silicon nanophotonic slow-light waveguides consisting of long sequences of coupled resonators fabricated on a silicon-on-insulator (SOI) chip.

Multi-slot silicon optical waveguides

We describe, fabricate and demonstrate multi-slotted silicon nanophotonic waveguides, comprised of four low index slots etched longitudinally along the waveguide. The computed modal profiles are well described by supermode theory. We have measured the group index of refraction of the waveguide in the TE and TM polarizations.