Mode Propagation in a Nonuniform Cylindrical Medium (Correspondence)

A simplified form of the coupling coefficient C(/spl beta//sub p/, /spl beta//sub q/) resulting from a coupled mode theory analysis of wave propagation in a nonuniform medium is derived. It is found for most situations of interest that C(/spl beta//sub p/, /spl beta//sub q/) is proportional to 1/(/spl beta//sub p/-/spl beta//sub q/) and the power transfer between two modes is proportional to 1/(/spl beta//sub p/ - /spl beta//sub q/)/sup 4/. /spl beta//sub p/ and /spl beta//sub q/ are the two different modal propagation constants. For a dielectric rod C(/spl beta//sub p/, /spl beta//sub q/) is a simple line integral around the rod boundary. Approximate forms are presented for optical waveguides.     

Hybrid-Frequency Cutoffs in Gyrotropic Waveguides (Short Papers)

The behavior of the Brillouin diagram /spl omega/ versus /spl beta//sub z/ is analyzed for axially magnetized gyrotropic waveguides in the vicinity of the hybrid frequencies /spl omega//sub k/ and /spl omega//sub i/. Starting from the exact dispersion relation for the modes in the waveguides under consideration it is shown that 1) the dispersion curves terminate at discrete cutoff points located along the /spl omega/ = spl omega//sub k/, /spl omega//sub i/ line and 2) the group velocity at these points is zero. These results modify the behavior of the dispersion curves existing in the literature.     

On The General Relation Between /spl alpha/ and Q (Correspondence)

The relation between the quality factor Q and the attenuation constant /spl alpha/ of a transmission line has been known as follows: /spl alpha/ = /spl beta/ / /2Q where /spl beta/ is the phase constant. Recently from the following relation of propagation constant at resonance /spl Gamma/(/spl omega//sub 0/) + /spl part//spl Gamma/ / /spl part//spl omega/ /spl Delta//spl omega//spl cong/ i/spl beta/(/spl omega//sub 0/), where /spl Gamma/(/spl omega//sub 0/) = /spl alpha/(/spl omega//sub 0/) + i/spl beta/(/spl omega//sub 0/). Yeh derived a general relation between Q and /spl alpha/, namely, /spl alpha/ = /spl upsi//sub p/ / /spl upsi//sub g/ /spl beta/ / /2Q where /spl upsi//sub p/, and /spl upsi//sub g/ are the phase velocity and group velocity of the wave respectively. This general relation can be derived very simply from the generally accepted definition of /spl alpha/ and Q.     

Characterization of accumulation layer capacitance for extracting data on high-/spl kappa/ gate dielectrics

A new parameter extraction technique has been outlined for high-/spl kappa/ gate dielectrics that directly yields values of the dielectric capacitance C/sub di/, the accumulation layer surface potential quotient, /spl beta//sub acc/, the flat-band voltage, the surface potential /spl phi//sub s/, the dielectric voltage, the channel doping density and the interface charge density at flat-band. The parallel capacitance, C/sub p/(=C/sub sc/+C/sub it/), was found to be an exponential function of /spl phi//sub s/ in the strong accumulation regime, for seven different high-/spl kappa/ gate dielectrics. The slope of the experimental lnC/sub p/(/spl phi//sub s/) plot, i.e., |/spl beta//sub acc/|, was found to depend strongly on the physical properties of the high-/spl kappa/ dielectric, i.e., was inversely proportional to [(/spl phi//sub b/m/sup *//m)/sup 1/2/K/C/sub di/], where /spl phi//sub b/ is the band offset, and m/sup */ is the effective tunneling mass. Extraction of /spl beta//sub acc/ represented an experimental carrier confinement index for the accumulation layer and an experimental gate-dielectric direct-tunneling current index. /spl beta//sub acc/ may also be an effective tool for monitoring the effects of post-deposition annealing/processing.     

Performance of Ar/sup +/-milled Ti:sapphire rib waveguides as single transverse-mode broadband fluorescence sources

Rib waveguides have been fabricated in pulsed-laser-deposited Ti:sapphire layers using photolithographic patterning and subsequent Ar/sup +/-beam milling. Fluorescence output powers up to 300 /spl mu/W have been observed from the ribs following excitation by a 3-W multiline argon laser. Mode intensity profiles show high optical confinement and the measured beam propagation factors M/sub x//sup 2/ and M/sub y//sup 2/ of 1.12 and 1.16, respectively, indicate single transverse-mode fluorescence emission. Loss measurements using the self-pumped phase conjugation technique have yielded comparable values (1.7 dB/cm) for the ribs and the unstructured planar waveguide counterparts. The combination of optimum modal properties and strong optical confinement, together with sufficient levels of fluorescence output, make the single-moded Ti:sapphire rib waveguides a very interesting candidate as a fluorescence source for optical coherence tomography applications.     

The rank and kernel of extended 1-perfect /spl Zopf//sub 4/-linear and additive non-/spl Zopf//sub 4/-linear codes

A binary extended 1-perfect code of length n + 1 = 2/sup t/ is additive if it is a subgroup of /spl Zopf//sub 2//sup /spl alpha// /spl times/ /spl Zopf//sub 4//sup /spl beta//. The punctured code by deleting a /spl Zopf//sub 2/ coordinate (if there is one) gives a perfect additive code. 1-perfect additive codes were completely characterized and by using that characterization we compute the possible parameters /spl alpha/, /spl beta/, rank, and dimension of the kernel for extended 1-perfect additive codes. A very special case is that of extended 1-perfect /spl Zopf//sub 4/-linear codes.     

Thickness dependence of Weibull slopes of HfO/sub 2/ gate dielectrics

Breakdown voltage distribution, Weibull slopes, and area scaling factors have been investigated for HfO/sub 2/ gate dielectrics in order to gain a better understanding of the breakdown mechanism. Weibull slope of thick HfO/sub 2/ (e.g., /spl beta//spl ap/4 for EOT=2.5 nm) is smaller than that of SiO/sub 2/ with similar physical thickness, whereas /spl beta/ of the thinner HfO/sub 2/ (e.g., /spl beta//spl ap/2 for EOT=1.4 nm) is similar to that of SiO/sub 2/. The implication of the thickness dependence of /spl beta/ is discussed.     

On /spl Zopf//sub 4/-linear Preparata-like and Kerdock-like codes

We say that a binary code of length n is additive if it is isomorphic to a subgroup of /spl Zopf//sub 2//sup /spl alpha// /spl times/ /spl Zopf//sub 4//sup /spl beta//, where the quaternary coordinates are transformed to binary by means of the usual Gray map and hence /spl alpha/ + 2/spl beta/ = n. In this paper, we prove that any additive extended Preparata (1968) -like code always verifies /spl alpha/ = 0, i.e., it is always a /spl Zopf//sub 4/-linear code. Moreover, we compute the rank and the dimension of the kernel of such Preparata-like codes and also the rank and the kernel of the /spl Zopf//sub 4/-dual of these codes, i.e., the /spl Zopf//sub 4/-linear Kerdock-like codes.     

Monolithically integrated InGaAs-AlGaInAs Mach-Zehnder Interferometer optical switch using quantum-well intermixing

A highly efficient monolithically integrated Mach-Zehnder interferometer (MZI) optical switch based on a 1.5-/spl mu/m InGaAs-AlGaInAs multiple-quantum-well structure is reported. The device was fabricated by integrating phase shifter sections with bandgap-shifted low-loss waveguides obtained by a single step sputtered SiO/sub 2/-annealing quantum-well intermixing technique. Evaluation of the refractive index change induced by current injection (plasma, band-filling, band-shrinkage effects) and applied electric field (quantum confined Stark effect) based on the MZI was investigated. A device with an active length of 400 /spl mu/m in one of the MZI arms had an extinction ratio /spl ges/20 dB with a half-wavelength current (I/sub /spl pi//) and half-wavelength voltage V/sub /spl pi// as low as 3.2 mA and 3.5 V (1.9 V in push-pull configuration), respectively.     

InGaAs/InP DHBTs with 120-nm collector having simultaneously high f/sub /spl tau//, f/sub max//spl ges/450 GHz

InP/In/sub 0.53/Ga/sub 0.47/As/InP double heterojunction bipolar transistors (DHBT) have been designed for increased bandwidth digital and analog circuits, and fabricated using a conventional mesa structure. These devices exhibit a maximum 450 GHz f/sub /spl tau// and 490 GHz f/sub max/, which is the highest simultaneous f/sub /spl tau// and f/sub max/ for any HBT. The devices have been scaled vertically for reduced electron collector transit time and aggressively scaled laterally to minimize the base-collector capacitance associated with thinner collectors. The dc current gain /spl beta/ is /spl ap/ 40 and V/sub BR,CEO/=3.9 V. The devices operate up to 25 mW//spl mu/m/sup 2/ dissipation (failing at J/sub e/=10 mA//spl mu/m/sup 2/, V/sub ce/=2.5 V, /spl Delta/T/sub failure/=301 K) and there is no evidence of current blocking up to J/sub e//spl ges/12 mA//spl mu/m/sup 2/ at V/sub ce/=2.0 V from the base-collector grade. The devices reported here employ a 30-nm highly doped InGaAs base, and a 120-nm collector containing an InGaAs/InAlAs superlattice grade at the base-collector junction.     

High-speed (/spl ges/1 GHz) electrical and optical adding, mixing, and processing of square-wave signals with a transistor laser

This letter reports the common-emitter operation (gain /spl beta/=/spl Delta/I/sub C///spl Delta/I/sub B/>1, 20/spl deg/C, I/sub B/=36 mA, /spl lambda/=970 nm) of a dual-input transistor laser, arranged with a separate base contact on either side of a single emitter, that adds, mixes, and processes high-speed square-wave electrical inputs and delivers separate electrical and optical outputs. Applying a square-wave electrical input X/sub 1/(t) to one base contact and X/sub 2/(t) at a second base input, we obtain, with the pulsewidth modulated because of mixing, an electrical output proportional to /spl beta//spl times/[X/sub 1/(t)+X/sub 2/(t)] and a laser output tracking the electrical output (h/spl nu//spl times/f[X/sub 1/(t)+X/sub 2/(t)]) and exceeding it in bandwidth (pulse sharpness).     

BV/sub CEO/--BV/sub CBO/ separation and sharpness of breakdown in high-speed bipolar transistors

The effect of secondary impact ionization by the noninitiating carrier on the near avalanche behavior of high-speed n-p-n bipolar transistors is studied. We show that secondary collector ionization by generated holes traveling back toward the base layer significantly reduces BV/sub CBO/ if the hole ionization coefficient is higher than that of electrons [/spl beta//sub p/(E)>/spl alpha//sub n/(E)]: positive feedback associated with a strong secondary ionization sharpens the breakdown characteristic by speeding up carrier multiplication and decreases separation between the open-base collector-emitter (BV/sub CEO/) and the open-emitter base-collector (BV/sub CBO/) breakdown voltages. The effect of secondary ionization on the BV/sub CEO/-BV/sub CBO/ separation has not previously been described. Multiplication coefficient comparisons for representative InP, GaAs, and Si collectors indicate all structures can sustain low-current above BV/sub CEO/ operation from a transport (nonthermal) point of view, although the different degrees of secondary ionization in various semiconductors lead to fundamental differences when InP is compared to GaAs and Si since for the latter materials /spl beta//sub p/(E)相似文献   

InGaAs-InP DHBTs for increased digital IC bandwidth having a 391-GHz f/sub /spl tau// and 505-GHz f/sub max/

InP-In/sub 0.53/Ga/sub 0.47/As-InP double heterojunction bipolar transistors (DHBT) have been designed for use in high bandwidth digital and analog circuits, and fabricated using a conventional mesa structure. These devices exhibit a maximum 391-GHz f/sub /spl tau// and 505-GHz f/sub max/, which is the highest f/sub /spl tau// reported for an InP DHBT-as well as the highest simultaneous f/sub /spl tau// and f/sub max/ for any mesa HBT. The devices have been aggressively scaled laterally for reduced base-collector capacitance C/sub cb/. In addition, the base sheet resistance /spl rho//sub s/ along with the base and emitter contact resistivities /spl rho//sub c/ have been lowered. The dc current gain /spl beta/ is /spl ap/36 and V/sub BR,CEO/=5.1 V. The devices reported here employ a 30-nm highly doped InGaAs base, and a 150-nm collector containing an InGaAs-InAlAs superlattice grade at the base-collector junction. From this device design we also report a 142-GHz static frequency divider (a digital figure of merit for a device technology) fabricated on the same wafer. The divider operation is fully static, operating from f/sub clk/=3 to 142.0 GHz while dissipating /spl ap/800 mW of power in the circuit core. The circuit employs single-buffered emitter coupled logic (ECL) and inductive peaking. A microstrip wiring environment is employed for high interconnect density, and to minimize loss and impedance mismatch at frequencies >100 GHz.     

Electrooptic modulation of multisilicon-on-insulator photonic wires

This paper proposes and analyzes electrically modulated submicrometer-size high-index-contrast waveguides (photonic wires) based on a multisilicon-on-insulator (MSOI) platform. Metal-oxide-semiconductor junctions are used to control the effective refractive index of the waveguides. The electrooptic structures are electrically and optically modeled. The performances of the studied configurations are analyzed and compared in terms of phase modulation efficiency, optical losses, and operation speed, and the feasibility of their fabrication is discussed. Calculations indicate that the proposed schemes can be used to achieve highly efficient phase shifters (V/sub /spl pi//L/sub /spl pi//<1 V-cm) based on photonic wires on MSOI, with data transmission rates ranging from 3 to 10 Gb/s.     

Low-power low-voltage CMOS A/D sigma-delta modulator for bio-potential signals driven by a single-phase scheme

Since the 1970's, the analog switches in switched-capacitor (SC) circuits are operated by nonoverlapping bi-phase control signals (/spl phi//sub 1/, /spl phi//sub 2/). The nonoverlapping of these two phases is essential for successful SC operation since, a capacitor inside an SC circuit can discharge if two switches, driven by /spl phi//sub 1/ and /spl phi//sub 2/, are turned on simultaneously. Moreover, since 1983, two additional phases are generally used in many SC circuits, which consist of advanced versions of /spl phi//sub 1/ and /spl phi//sub 2/. These two additional phases overcome the problem of signal-dependent charge injection. This paper presents a low-power and low-voltage analog-to-digital (A/D) interface module for biomedical applications. This module provides an A/D conversion based on a mixed clock-boosting/switched-opamp (CB/SO) second-order sigma-delta (/spl Sigma//spl Delta/) modulator, capable of interfacing with several different types electrical signals existing in the human body, only by re-programming the output digital filter. The proposed /spl Sigma//spl Delta/ architecture employs a novel single-phase scheme technique, which improves the dynamic performance and highly reduces the clocking circuitry complexity, substrate noise and area. Simulated results demonstrate that the signal integrity can be preserved by exploring the gap between the high conductance region of pMOS and nMOS switches at low power-supply voltages and the fast clock transitions that exist in advanced CMOS technologies. The mixed CB/SO architecture together with the overall distortion reduction resulting from using the proposed single-phase scheme, result that the dynamic range of the modulator is pushed closer to the theoretical limit of an ideal second-order /spl Sigma//spl Delta/ modulator.     

Influence of scattering and two-photon absorption on the optical loss in GaAs-Al/sub 2/O/sub 3/ nonlinear waveguides measured using femtosecond pulses

The influence of scattering and two-photon absorption on the optical loss in GaAs-Al/sub 2/O/sub 3/ semiconductor nonlinear waveguides has been studied using femtosecond pulses. By deploying a scattering technique, loss coefficients were evaluated over an extended wavelength range of 1.3-2.1 /spl mu/m in the near-infrared. A systematic study involving intensity and wavelength dependence of the loss revealed the presence of two-photon absorption for wavelengths below 1.6 /spl mu/m. A simple nonlinear transmission study enabled the separation of the two-photon absorption coefficient from scattering and linear absorption. The calculated two-photon absorption coefficients were /spl sim/9-20 cm/GW.     

RF HBT oscillators with low-phase noise and high-power performance utilizing a (/spl lambda//4/spl plusmn//spl delta/) open-stubs resonator

This paper presents a new type of transmission-line resonator and its application to RF (microwave and millimeter-wave) heterojunction bipolar transistor (HBT) oscillators. The resonator is a parallel combination of two open stubs having length of /spl lambda//4/spl plusmn//spl delta/(/spl delta//spl Lt//spl lambda/), where /spl lambda/ is a wavelength at a resonant frequency. The most important feature of this resonator is that the coupling coefficient (/spl beta//sub C/) can be controlled by changing /spl delta/ while maintaining unloaded Q-factor (Q/sub u/) constant. Choosing a small value of /spl delta/ allows us to reduce /spl beta//sub C/ or equivalently to increase loaded Q-factor (Q/sub L/). Since coupling elements such as capacitors or electromagnetic gaps are not needed, /spl beta//sub C/ and Q/sub L/ can be precisely controlled based on mature lithography technology. This feature of the resonator proves useful in reducing phase noise and also in enhancing output power of microwave oscillators. The proposed resonator is applied to 18-GHz and 38-GHz HBT oscillators, leading to the phase noise of -96-dBc/Hz at 100-kHz offset with 10.3-dBm output power (18-GHz oscillator) and -104-dBc/Hz at 1-MHz offset with 11.9 dBm (38-GHz oscillator). These performances are comparable to or better than state-of-the-art values for GaAs- or InP-based planar-circuit fundamental-frequency oscillators at the same frequency bands.     

Explanation of anomalously high current gain observed in GaN based bipolar transistors

The potential applications of GaN-based bipolar transistors have suffered a setback from poor ohmic contacts and leakage currents. We show in this work that the extrinsic current gain /spl beta//sub EXT/ measured at a low current level can be erroneously attributed to the gain of the intrinsic transistor. By accounting for leakage current coupled with poor ohmic contacts, we show that the observed very high /spl beta//sub EXT/ at low current levels can be modeled accurately. The real gain of the intrinsic transistor /spl beta//sub INT/ is generally much lower. As the current is increased, the effect of leakage currents is diminished, and /spl beta//sub EXT//spl rarr//spl beta//sub INT/. This model is satisfactorily applied to explain our experimental results.     

Low-Loss Two-Dimensional GaAs Epitaxial Waveguides at 10.6-/spl mu/m Wavelength

The successful fabrication of low-loss two-dimensional GaAs epitaxial waveguides by chemical etching for use in integrated optics at 10.6 /spl mu/m is reported. Selective excitation of specific E/sub pq//sup y/ modes was observed by placing the prism at specific angles in the horizontal plane. Loss measurements showed no increase in attenuationfor lower order E/sub pq//sup y/ modes (as compared to corresponding one-dimensional waveguide modes) when the guide width is 50 /spl mu/m. As the guide width is reduced, there is a significant increase in attenuation as p increases.     

TM-pass polymer modulators with poling-induced waveguides and self-aligned electrodes

Transverse magnetic (TM) mode selective polymer Mach-Zehnder modulators with self-aligned electrodes were fabricated for the first time in the electro-optic polymer material APC-CPW1 by employing a poling-induced (PI) writing method. The waveguides support only a TM polarisation, when an arbitrarily polarised optical source is incident. Modulators with a single 3 cm long driving electrode show a V/sub /spl pi// of 3.5 V at 1.55 /spl mu/m.