Finite-element solution of nonlinear TM waves inmultiple-quantum-well waveguides

Intensity-dependent characteristics for TM-polarized optical waves guided by multiple-quantum-well (MQW) waveguides with arbitrary nonlinear media are numerically analyzed by the finite element method. In this approach, self-consistent solutions are obtained through a simple iterative procedure. The power-dependent dispersion relations and magnetic-field (H_x) as well as two electric-field ( E_y and E_z) profiles for nonlinear TM waves in MQW waveguides with three different nonlinear mechanisms are presented. It is shown that, for the waveguides with molecular orientational mechanism, a distinct power limiting action for nonlinear TM modes exists     

Maximum heat-sink temperature for CW operation of adouble-heterostructure semiconductor injection laser

Assuming that the temperature dependence of the threshold current for pulsed operation is known, an analytical expression for the maximum heat-sink temperature, T_hm, for CW operation of the laser can be derived. The maximum heat-sink temperature is expressed in terms of the characteristic temperature T₀, the room-temperature threshold current for pulsed operation I₀ , the equivalent effective thermal resistance &thetas;, and the equivalent effective series electrical resistance r of the device. It is shown that the values of T_hm can be enhanced by increasing the value of T₀ or by decreasing the values of I₀, &thetas;, and r     

Integrated waveguide modulator using a LiNbO3TE&rlarr2;TM convertor for electrooptic coherence modulation of light

The authors report a wavelength independent TE-TM mode convertor used as a waveguide electrooptic modulator in a coherence modulated system. The modulation voltages thus obtained (20 V) are about 10 times lower than those previously reported in earlier coherence modulated devices. The modulator is a strip waveguide fabricated on Y-cut Z-propagation, Ti-indiffused LiNbO₃. When used in conjunction with a birefringent plate and polarizers, the modulator is shown to imprint on light a signal encoded into an optical delay greater than the source coherence length. Demonstration of the device is reported using a highly multimode laser diode at 820 nm     

A multiple-state memory cell based on the resonant tunneling diode

The device consists primarily of several molecular-beam-epitaxy (MBE-) grown GaAs/(AlGa)As resonant tunneling diodes connected in parallel. This device exhibits multiple peaks in the I-V characteristic. When a load resistor is connected, the circuit can be operated in a multiple stable mode. With this concept, implementation of three-state and four-state memory cells are made. In the three-state case the operating points at voltages V₀=0.27 V , V₁=0.42 V, and V₂=0.53 V represent the logic levels 0, 1, and 2. Similarly for the four-state memory cell the logic levels voltages are V₀=0.35 V, V₁=0.42 V, V₂=0.54 V, and V ₃=0.59 V. A suggestion of an integrated device structure using this concept is also presented     

Stability analysis and numerical simulation of multideviceamplifiers

Stability analysis of multidevice amplifiers is made on a generalized circuit comprising two n-ports with S-matrices S (active devices) and S' (passive networks) connected at n interface ports. Open-loop transfer functions defined for a signal-flow graph and its (n-1) subgraphs of incident and reflected waves at the interface ports are expressed in terms of det M_n and its minors, where M_n=S'S-I_n and I_n is the n×n identity matrix. it is shown that the Nyquist plots of the n transfer functions completely characterize the number of right-half complex-frequency-plane zeros of det M_n, and hence the amplifier stability. Insertion of an ideal circulator and isolators at the interface ports enables one to calculate the Nyquist plots and voltage distributions of possible instabilities using commercially available linear circuit simulators. Numerical simulations for two types of parallel-operated GaAs FET amplifiers are performed to verify the usefulness of the analysis in design-phase check of multidevice amplifier stability     

A dispersion formula satisfying recent requirements in microstripCAD

A dispersion formula ϵ^*_eff(f)=ϵ^* -{ϵ^*-ϵ^*_eff(0)}/{1+( f/f₅₀)^m}, for the effective relative permittivity ϵ^*_eff(f) of an open microstrip line is derived for computer-aided design (CAD) use. The 50% dispersion point (the frequency f₅₀ at which ϵ^*_eff(f₅₀)={ϵ ^*+ϵ^*_eff(0)}/2}) is used a normalizing frequency in the proposed formula, and an expression for f₅₀ is derived. To obtain the best fit of ϵ ^*_eff(f) to the theoretical numerical model, the power m of the normalized frequency in the proposed formula is expressed as a function of width-to-height ratio w/ h for w/h⩾0.7 and as a function of w /h, f₅₀, and f for w/h⩽0.7. The present formula has a high degree of accuracy, better than 0.6% in the range 0.1<w/h⩽10, 1<ϵ^*⩽128, and any height-to-wavelength ratio h/λ₀     

Dispersion and leakage characteristics of coplanar waveguides

The dispersion and leakage characteristics of coplanar waveguides are treated using the spectral-domain approach together with the complex residue technique. To handle the complex propagation constant of the coplanar waveguide, the Fourier transform and Parseval's theorem in the complex plane are extended. A number of numerical results, such as the effective dielectric constant and normalized attenuation constant, are presented to illustrate the characteristics of the coplanar waveguide. Sharp peaks just after leakage together with broad peaks are two interesting phenomena observed in the attenuation characteristics. The physical mechanism of these peaks and the details of transition in the ϵ_eff and α/k₀ curves are still unclear     

A model for fast switching transients in power systems: the nearzone concept

The author presents a simple time-domain model which makes it possible to predict the order of magnitude of the highest di/ dt values generated by closing switches in electrical power systems. The model is based on traveling-wave analysis. It is demonstrated that two different approaches must be applied, according to whether (a) the closing time, T_s, of the switch is faster than twice the traveling time to the first reflection point or (b) T_s is much slower. Under condition (b) the well-known quasistationary approach di/dt_max=U₀/L can be used, where U₀ is the switched voltage and L is the self-inductance of the line between the stray capacitances located to the left and the right of the switching device. Under condition (a) a new formula must be applied: di/dt _max≈2 U₀/ZT_s, where Z is the line impedance of the line in which the switching device is installed and T_s is the time during which the voltage across the switch collapses from U₀ to zero. Experimental results are given from both fast and slow closing switches     

Analysis of a centered-inclined waveguide slot coupler

Integral equations are developed for a centered-inclined coupling slot (including the effect of finite wall-thickness of the common broad-wall) and the slot-aperture electric intensity field is found using the method of moments. Numerical results for resonant length, backscattered wave amplitude, and phase variation off-resonance are presented over a range of values of the waveguide b dimension, wall thickness, slot width, and frequency. It is shown that the resonant length is relatively insensitive to slot tilt, &thetas;, for a standard-height X-band waveguide, whereas its dependence on &thetas; is significant for reduced-height waveguides. The phase variation of scattered TE₁₀ waves in both waveguides off-resonance is less for wider slots and smaller b dimensions. Shunt-series coupling slots exhibit greater phase variation off resonance when compared to a centred-inclined coupling slot. Also, the former has a longer resonant length for a smaller b dimension and for a wider slot. Thus the centred-inclined slot coupler possesses superior characteristics. The higher-order mode coupling between a centred-inclined slot coupler and a pair of straddling radiating slots in the branch waveguide is significant     

On the figures of merit for electroabsorption waveguide modulators

ΓΔα/F and Δα/α₀ (where Δα is the absorption change, α₀ is the residual absorption, F is the applied electric field, and Γ is the optical confinement factor in the waveguide) have been separately proposed as the relevant figure of merit for electroabsorption waveguide modulators. Using a quantitative and systematic argument, the authors show that they are both necessary and important to the total performance of the modulator     

NOTFET: a high-frequency InP nonlinear transistor

A device called the nonlinearly optimized transconductance field-effect transistor (NOTFET) has been developed for nonlinear circuit applications. An InP NOTFET with two g_m peaks based on InGaAs and InAlAs channels was designed fabricated, and tested for harmonic generation up to 12 GHz, demonstrating the device concept and its advantages compared to conventional FETs and HEMTs. Multipeak g_m/V_GS characteristics also can be obtained by using a multiheterojunction material structure with uncoupled quantum wells, a possibility which is under investigation     

New hot-carrier degradation mode in PMOSFETs with W gate electrodes

Hot-carrier degradation of W gate PMOSFETs, which are surface-channel devices because of the work function of W, has been investigated in comparison with polycide (WSi_x/n⁺ poly-Si) ones. In W gate PMOSFETs, transconductance g_m and threshold voltage V_th decrease on the drain avalanche hot-carrier (DAHC) stress, and Δg_m /g_m0 and ΔV_th become minimum at V_G≅V_D/2. By using the charge-pumping technique, it is found that, after stressing at the same stress condition, the interface state density of W gate devices is about 10 times larger than that of polycide ones but the densities of trapped electrons are almost equal. These results indicate that the difference of hot-carrier degradation between W and polycide gate devices is mainly caused by the difference of the interface state density     

Optimized trench MOSFET technologies for power devices

Low-voltage silicon trench power MOSFETs with forward conductivities approaching the silicon limit are reported. Vertical trench power MOSFETs with the measured performances of V_DB =55 V (R_sp=0.2 mΩ-cm², k _D=5.7 Ω-pF) and V_DB=35 V (R_sp=0.15 mΩ-cm², k_D =4.3 Ω-PF) were developed where V_DB is the drain-source avalanche breakdown voltage, R_sp is the specific on-state resistance, and k_D=R _spC_sp is the input device technology factor where C_sp is the specific MOS gate input capacitance. The optimum device performance resulted from an advanced trench processing technology that included (1) an improved RIE process to define scaled vertical silicon trenches, (2) silicon trench sidewall cleaning to reduce the surface damage, and (3) a novel polysilicon gate planarization technique using a sequential oxidation/oxide etchback, process. The measured performances are shown to be in excellent agreement with the two-dimensional device simulations and the calculated results obtained from an analytical model     

A new multiharmonic loading method for large-signal microwave andmillimeter-wave transistor characterization

A multiharmonic loading method for nonlinear microwave and millimeter-wave transistor characterization using six-port techniques is presented. The system allows independent load tuning of an excitation signal and its harmonics. Load-pull measurements on a MESFET which have been performed at the fundamental frequency f₀ and at the second (2f₀) and third (3f₀ ) harmonics are discussed. The results highlight the importance of such measurement in designing and modeling nonlinear devices and circuits. The experimental results are found to be directly applicable for optimizing efficiency and output power in high-power MESFET amplifiers and MESFET frequency multipliers     

A physical model for the gate current injection in p-channelMOSFET's

A quantitative physical model for calculating the hot-electron injection probability, I_G/I_SUB, for both buried and surface p-channel MOSFETs is presented. The model utilizes the two-dimensional potential contours generated by PISCES, and integrates the probability of substrate hot-electron injection across the high-field region near the drain. The known phenomenon that buried-channel (BC) PMOS has higher hot-electron injection probability but lower channel field (I_SUB/I_D) than a similar surface-channel (SC) device is successfully modeled. This phenomenon can be attributed to the larger energy band hump-up near the drain and the larger oxide field (and thus greater barrier lowering) at a given bias condition for the buried-channel device. The I_G characteristics can be obtained from the calculated I_G /I_SUB ratio, using readily available I_SUB values     

Effect of conduction-band discontinuity on lasing characteristicsof 1.5 μm InGaAs/In(Ga)AlAs MQW-FP lasers

The characteristic temperature (T₀), relaxation frequency (f_r), differential gain (dg /dn) and nonlinear gain coefficient (ϵ) of 1.5-μm InGaAs/In(Ga)AlAs multiple-quantum-well (MQW) Fabry-Perot (FP) lasers grown by gas source molecular beam epitaxy (GSMBE) are reported. It is found that T₀ is little affected by the difference in the conduction band discontinuity. A maximum T₀ value of 86 K is obtained. The dg/dn and ϵ∈ were calculated from the slope of the f_r versus √ power plot and the damping K-factor. It is demonstrated that dg/dn and ϵ of InGaAs/In(Ga)AlAs MQW lasers increase with an increase in the conduction band discontinuity     

An optical integrated circuit for time-division 2-D velocitymeasurement

An LiNbO₃ optical integrated circuit pigtailed with two single-mode fibres, which allows time-division two-dimensional velocity measurement, is discussed. To detect time-division multiplexed beat signals corresponding to velocity components v_X and v_γ of a moving object, a waveguide switch is integrated on a Z-propagating LiNbO₃ substrate of 28×7 mm² in addition to a waveguide interferometer with a frequency shifter. In the optical IC, either v_X or v_γ could be measured selectively with signal-to-noise ratio of 20 dB by driving an electronic gate placed after a photodiode in synchronization with the waveguide switch     

Electromagnetic fields induced in a person due to devices radiatingin the 10 Hz to 100 kHz range

Using dipole and image theory with prolate spheroid models, a qualitative evaluation is made of the electric, E, and magnetic, H¯, fields induced at selected points inside a person due to external electric, E¯₀, and magnetic, H¯₀, fields within the 10 Hz to 100 kHz range. Amplitude measurements of the E¯₀ and H¯₀ vectors are made at selected points in the region with the person absent. The evaluation is valid for any field radiating device if the amplitude and phase angles of the external fields are measured in accordance with the stated protocol     

Analytical stability analysis of dark and bright self-guided wavesin layered self-defocusing nonlinear media

We present an analytical stability analysis on dark (black and gray) self-guided waves and the fundamental state of the bright self-guided waves with nonzero intensity background trapped in a thin self-defocusing nonlinear film bounded by an infinite self- defocusing medium of different nonlinearity. It is found that the gray self-guided wave and the fundamental state of the bright self-guided waves with nonzero intensity background are stable to both symmetric and asymmetric perturbations, whereas the black self-guided wave is stable to symmetric perturbation but unstable to asymmetric perturbation (in contrast to the corresponding one in a uniform self-defocusing medium). For the nonlinear waveguides with the linear refractive index n_c, in the cladding smaller than that n_f the film the instability of the black self-guided waves is shown to result from the presence of the complex growth rate, while the instability for that trapped in a hollow waveguide (n_cc>n_f) may arise from the presence of either real or complex growth rate, depending on the waveguide parameters