Charles C. Bahr

An analysis of the technical and economic essentials for providing video over fiber-to-the-premises networks

This paper presents a cost comparison of two video transport methodologies on a passive optical network (PON): an out-of-band radio frequency (RF) video overlay and in-band video delivered as multicast Internet Protocol (IP) packets. The RF overlay approach has traditionally been favored for video transmission on a PON due to the availability of cable television (CATV)-like components, including CATV-ready televisions, but recently the lower network costs associated with converging voice, data, and video on an all-packet network (so called “Internet Protocol television” [IPTV]) have begun to be recognized. We have quantified the full cost of the RF video overlay, taking into account all the physical parameters that affect the cost of such deployments, allowing an accurate evaluation of the economics of this system under a variety of configurations. Our IP video model estimates the cost of a multicast IP video network, using analysis of viewer data to estimate the actual bandwidth requirements in real-world IPTV deployments. Using these models we compare the cost of RF video overlay and IP video technology for fiber to the premises (FTTP). We show that the choice of the lowest-cost video solution is sensitive to take-rate and channel lineup in particular, but that IPTV is the lowest-cost solution under the majority of likely deployment circumstances.

Oxidation of InxGa1−xAsyP1−y by NO2 studied with Auger electron spectroscopy

Abstract We have studied the oxidation of quaternary InGaAsP materials by NO2, using Auger electron spectroscopy for both elemental and chemical analysis of the surface. We report that NO2 induces a preferential oxidation, forming oxides of Ga, In, and P. The As remains unoxidized. From Ar+ ion milling we find that the oxide layers are fairly thin (less than 10 A), even at high exposures (greater than 1000 L) of NO2, where we obtain a saturation coverage of approximately 0.3 ML (monolayers). We have also measured electron energy loss spectra (EELS) and observe the disappearance of the surface plasmon loss feature upon oxide formation.

Refractive index profiling of optical waveguides using near-field scanning optical microscopy

We present a method in which we take advantage of the high spatial resolution and experimental simplicity afforded by near-field scanning optical microscopy (NSOM) to determine the refractive index profiles of optical waveguides. We use NSOM to measure the near-field intensities of the guided modes in planar waveguides and optical fibers and calculate numerically, from the measured intensities, the refractive index distributions.

Competition between desorption and diffusion at a GaAs(110) surface

Abstract We directly demosntrate for NO 2 on GaAs(110), using time-resolved modulated molecular beam techniques, that desorption is a competitive rate process with surface diffusion. Using defects as markers, we observe a transition from defect-dominated low coverage chemistry to defect insensitive adsorption/desorption near room temperature. We argue that this competition is generic to adsorbates on semiconductors, in distinct contrast to adsorbates on metal surfaces where diffusion lengths are often large ( >10 3 A) for almost all accessible temperatures.

NO2 dissociation and O penetration at a GaAs(110) surface

Abstract We have studied the dissociative adsorption of NO 2 on a high resistance GaAs(11O) crystal surface. We use multiple internal reflection Fourier Transform infra-red Spectroscopy, in conjunction with Auger Spectroscopy, to specify the chemical bonding and the rate processes involved. We show that the dissociation can be accurately followed by monitoring the sample conductance. Both the conductance and the minority carrier lifetime show that a second subsequent rate process occurs which we identify, using vibrational Spectroscopy, as penetration of chemisorbed oxygen in the bulk with the associated development of a deep electronic level. We directly demonstrate the role of defects in the dissociation. We further show that desorption becomes competitive with diffusion to defects at moderate temperatures, in distinct contrast to what is typical on low Miller index metal surfaces.

Refractive index profiling of planar optical waveguides using near-field scanning optical microscopy

The refractive index profile of a straight channel phosphosilicate glass planar optical waveguide is obtained with high spatial resolution (approximately 0.25 micrometers ) using near- field scanning optical microscopy (NSOM). The optical intensity profile of the waveguide mode is measured by NSOM and the refractive index distribution is calculated from the measured intensity. The calculated refractive index distribution is in agreement with that expected from the fabrication procedure and provides evidence for phosphorous diffusion between the core and cladding regions.

Surface science applied to lasers: near-field optical microscpoy

Near-field scattering optical microscopy (NSOM) is used to characterize the emission output and to obtain photoconductivity maps of InGaAsP multiple quantum well lasers. The high spatial resolution of NSOM (approximately (lambda) /20) allows detailed imaging of the laser structure. Emission measurements not only provide direct visualization of the laser mode but also reveal unwanted emission due to InP electroluminescence. Near-field photoconductivity experiments yield high resolution measurement of carrier transport throughout the structure yielding valuable information on current leakage, defect formation, and the quality of p-n junctions.

Enhanced room temperature oxidation of GaAs(100) using NO2

We have monitored the room temperature oxidation of GaAs(100) with NO2 using Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). We report a relatively high dissociative sticking probability (∼ 5%) for NO2 on GaAs(100) at room temperature (compared to that of O2), as was also observed in earlier studies of NO2 oxidation of GaAs(110). We have measured the oxygen coverage as a function of exposure and initial As/Ga composition of the clean (100) surface. We find that both the sputtered (nearly stoichiometric) and the Ga-rich surfaces are oxidized somewhat more effectively than the annealed stoichiometric surface. The initial dissociative sticking probability for NO2 at room temperature for both the (100) and (110) surfaces is very much greater than that of other molecular sources of oxygen, i.e., N2O, NO, and O2.

50th Anniversary Special Feature: The Discovery of Cosmic Microwave Background

In the midst of this communications technology explosion, we look back 50 years to a discovery that provided important insights into an explosion of another sort: the Big Bang. We show that this seminal discovery was the result of investigations into solving a practical problem (radio communications) and it has connections to a multitude of other subsequent innovations and discoveries. As a result, this legacy continues to inspire innovators to come together to invent technologies and methods that push the boundaries of information and communications technology and that will transform the way humans and machines connect and collaborate.

OXIDATION OF GAAS(110) WITH NO2 : A MOLECULAR BEAM STUDY

We describe time‐resolved modulated molecular beam measurements of the adsorption of NO2 on the GaAs(110) surface. These measurements provide a quantitative description of the gas–surface interaction; thermal NO2 has a nearly unity sticking probability, dissociating to form NO (which quickly desorbs) and a surface oxide of ∼1/3 ML saturation coverage. The NO2 dissociation probability is strongly controlled by the defect density, the oxygen coverage, and the surface temperature. We have characterized the competition between the processes leading to oxygen deposition, i.e., desorption and diffusion of NO 2 to reactive defects. The barrier energies Ediff=6±2 kcal/mol and Edes=9±2 kcal/mol provide an interesting example of the transition from defect‐dominated surface chemistry, typical of low Miller index metal surfaces to defect‐ insensitive diffusion‐limited chemistry, which we argue is generic to corrugated semiconductor surfaces.