Nonuniformly spaced array imaging

An image reconstruction algorithm for randomly spaced array imaging is developed. Based on the fact that the sampled bistatic Fourier space data can occupy almost the same region as that for rotating object imaging if the angular coverage is suitably defined, the range-Doppler reconstruction method developed in the rotating object imaging can be applied to the uniformly spaced circular array imaging case. When the array elements are randomly spaced, three more steps, a range alignment, a phase compensation, and an interpolation, are required to preprocess the measured signals. Experimental and numerical results have shown the effectiveness of the proposed algorithm     

Extremely low noise InGaAs/InAlAs HEMT grown by MOCVD

MOCVD-grown InGaAs/InAlAs HEMTs with excellent noise performance comparable to that of MBE-grown devices have been successfully fabricated. A minimum noise figure lower than 0.30 dB has been obtained with an associated gain of approximately 15 dB at 12 GHz. Furthermore, devices in ceramic packages have exhibited a minimum noise figure of 0.42 dB.<>     

Resonance in a superstrate-loaded cylindrical-rectangularmicrostrip structure

The complex resonant frequencies of the cylindrical-rectangular microstrip structure loaded with a dielectric superstrate layer is studied using a rigorous full-wave analysis, and the numerical results are obtained using the Galerkin moment method calculation. The numerical convergence for the selected sinusoidal basis functions with and without the edge singularity condition is also discussed. Numerical results for the dependence of the real and imaginary parts of the complex resonant frequencies on the superstrate permittivity and thickness are calculated and analyzed, and are compared with those obtained for the planar microstrip structure     

A wide-bandwidth low-noise InGaAsP-InAlAs superlattice avalanchephotodiode with a flip-chip structure for wavelengths of 1.3 and 1.55μm

The authors reports the fabrication of a flip-chip InGaAsP-InAlAs superlattice avalanche photodiode using gas source molecular beam epitaxy. The incident light reaches the InGaAs photoabsorption layer through the InP substrate and an InGaAsP-InAlAs superlattice multiplication region which are transparent for wavelengths of 1.55 and 1.3 μm. The light reflection by the electrode enables the absorption layer to be as thin as 0.8 μm without significantly reducing the quantum efficiency. A maximum bandwidth of 17 GHz was obtained at a low multiplication factor because the transit time through the absorption layer is reduced     

Dye laser pumped Pr3+-doped fiber lasers: basicparameter investigation, CW operation, and Q-switched operation

An investigation of a Pr³⁺-doped Al₂O₃ -SiO₂ glass fiber is described. The basic material parameters like fluorescence lifetime and stimulated emission cross section, measured around 1048 nm, where the fiber has a strong emission band, are discussed. The pump source was a Rh6G dye laser at 590 nm. Continuous wave (CW,) operation with a slope efficiency of 26% and a pump threshold of 1.2 mW was obtained. The Q-switched operation, yielding a repetition rate up to 10 kHz with a maximum peak power of 30 W and a minimum pulsewidth of 25 ns, is described     

SONET implementation

The status of the synchronous optical network (SONET) infrastructure development and deployment are examined to see whether or not they meet original expectations. Issues arising from deployment, such as the use of new features and the necessary support from operations systems, and future directions of SONET are discussed. These future trends include digital cross connect systems (DCSs), SONET ring architectures, and hybrid ring-DCS networks. New SONET services are also discussed     

Subspace-based signal analysis using singular value decomposition

A unified approach is presented to the related problems of recovering signal parameters from noisy observations and identifying linear system model parameters from observed input/output signals, both using singular value decomposition (SVD) techniques. Both known and new SVD-based identification methods are classified in a subspace-oriented scheme. The SVD of a matrix constructed from the observed signal data provides the key step in a robust discrimination between desired signals and disturbing signals in terms of signal and noise subspaces. The methods that are presented are distinguished by the way in which the subspaces are determined and how the signal or system model parameters are extracted from these subspaces. Typical examples, such as the direction-of-arrival problem and system identification from input/output measurements, are elaborated upon, and some extensions to time-varying systems are given     

Monolithic arrays of surface emitting laser NOR logic devices

Monolithic, cascadable, laser-logic-device arrays have been realized and characterized. The monolithic surface-emitting laser logic (SELL) device consists of an AlGaAs superlattice lasing around 780 nm connected to a heterojunction phototransistor (HPT) in parallel and a resistor in series. Arrays up to 8×8 have been fabricated, and 2×2 arrays show uniform characteristics. The optical logic output is switched off with 40 μW incident optical input     

Application of high Tc superconductors asfrequency selective surfaces: experiment and theory

The use of YBa₂Cu₃O_7-x and Tl₂CaBa₂Cu₂O₈ high-temperature superconducting thin films to fabricate frequency selective surfaces (FSS) at millimeter-wave frequencies (75-110 GHz) is discussed. An analytical/numerical model was applied, using a Floquet expansion and the method of moments, to analyze bandstop superconducting frequency selective surfaces. Experimental results were compared with the model, and showed agreement with resonant frequency prediction with an accuracy of better than 1%. The use of the superconducting frequency selective surfaces as quasi-optical millimeter-wave bandpass filters was also demonstrated     

A floating-gate analog memory device for neural networks

A floating-gate MOSFET device that can be used as a precision analog memory for neural network LSIs is described. This device has two floating gates. One is a charge-injection gate with a Fowler-Nordheim tunnel junction, and the other is a charge-storage gate that operates as a MOSFET floating gate. The gates are connected by high resistance, and the charge-injection gate is small so that its capacitance is much less than that of the charge-storage gate. By applying control pulses to the charge-injection gate, it is possible to charge and discharge the MOSFET floating gate in order to modify the MOSFET current with high resolution over 10 b. The charge injection can be carried out without disturbing the MOSFET output current with high voltage control pulses. This device is useful for on-chip learning in analog neural network LSIs