Optical nonlinear characteristics of a side-injectionlight-controlled laser diode with a multiple-quantum-well saturableabsorption region

A multiple-quantum-well bistable laser-diode structure in which the input signal is launched into the main laser through an orthogonally configured subwaveguide is proposed. Insensitivity to input light wavelength (28 nm of 3 dB bandwidth) and high isolation of input versus output (over 30 dB) are observed. In addition, reflection of input signal is negligibly small     

Does Globalization Reduce or Enhance Democracy? A Micro Analysis Based on an 18 Country Cross-National Asia-Europe Survey

Does globalization have a positive or negative impact on democracy? One reason this problem has gone unsolved is found in the fact that most studies to date have not made systematic use of empirical data to test propositions concerning the relationship between globalization and democracy. While there have been studies that have made a pioneering systematic contribution through the use of macroeconomic and other aggregate statistics, this article empirically examines whether globalization enhances or constrains democracy by using cross-national survey data collected in 17 countries (the Asia-Europe Survey). Our empirical testing has shown that globalization tends to be positively correlated to democratic activism at the individual level, suggesting the possibility that experiences of globalization strengthen democracy.

     

Investigation of dynamic polarization stability of 850-nmGaAs-based vertical-cavity surface-emitting lasers grown on (311)B and(100) substrates

The polarization stability of 850-nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) under dynamic operation was investigated by comparing the characteristics of VCSELs grown on (311)B and (100) GaAs substrates. Significantly larger suppression ratios of the two orthogonal polarization modes was obtained for VCSELs on (311)B substrates than those on (100) substrates under zero-bias modulation. Time-dependent orthogonal polarization suppression ratio measurements also showed that the polarization direction was more stable in the VCSEL on (311)B substrates than that on (100) substrates. Error-free transmission was realized from VCSELs on (311)B substrates with and without a polarizer in both back-to-back and 100-m multimode fiber transmission     

Start-Bit Detection and Gate-Pulse Generation Using Phase-Modulated Preamble for Asynchronous Packet Processing

Start-bit detection and a single gate pulse generation scheme scalable to high-speed operation for asynchronous packet processing have been achieved. It is based on phase-modulated two-bit preamble for a coder and one-bit-delayed detection combined with a balanced photodetector as exclusive or (xor) function for a decoder. By using pi/2 phase-shifted first-bit and a pi/2 phase-shifted one-bit delay line, a single gate pulse can be generated with high speed, regardless of packet period. We have successfully achieved the single gate-pulse generation with bit rate of 10.72 Gb/s and various packet periods from 12.8 to 120 ns. Amplitude of the gate pulse was almost constant with fluctuation of plusmn5%. Suppression ratio of a gate pulse could be improved up to 9.5 dB via nonlinear absorption characteristics of an electroabsorption modulator. Autonomous gating operation for an optical digital-to-analog converter was also verified for two-bit operation     

AlGaAs/GaAs multiquantum-well (MQW) surface-emitting laser

In the letter the lasing characteristics of a multiquantum-well surface-emitting injection laser with 100 wells at 77 K under pulsed condition is reported. The output light of the device was linearly polarised.<>     

Use of Fourier and Karhunen-Loeve decomposition for fast patternmatching with a large set of templates

We present a fast pattern matching algorithm with a large set of templates. The algorithm is based on the typical template matching speeded up by the dual decomposition; the Fourier transform and the Karhunen-Loeve transform. The proposed algorithm is appropriate for the search of an object with unknown distortion within a short period. Patterns with different distortion differ slightly from each other and are highly correlated. The image vector subspace required for effective representation can be defined by a small number of eigenvectors derived by the Karhunen-Loeve transform. A vector subspace spanned by the eigenvectors is generated, and any image vector in the subspace is considered as a pattern to be recognized. The pattern matching of objects with unknown distortion is formulated as the process to extract the portion of the input image, find the pattern most similar to the extracted portion in the subspace, compute normalized correlation between them at each location in the input image, and find the location with the best score. Searching for objects with unknown distortion requires vast computation. The formulation above makes it possible to decompose highly correlated reference images into eigenvectors, as well as to decompose images in frequency domain, and to speed up the process significantly     

Long-wavelength multiple-quantum-well voltage-controlled bistablelaser diodes

We have investigated static and dynamic characteristics of a multiple-quantum-well (MQW) voltage-controlled bistable laser diode at 1.5 μm. Using the quantum confined Stark effect, the absorption coefficient and the absorption band edge of the saturable absorption region are controlled by applied voltage, resulting in easy change of the hysteresis width and the threshold current. Applied voltage from below the current injection regime to the saturable absorption region, typically the reverse bias voltage, allows faster turn-off switching speed due to the carrier sweep-out by the applied electric field, MQW bistable lasers with InGaAs-InP, InGaAs-InGaAsP and InGaAs-InAlAs systems and several kinds of well numbers were fabricated and their threshold current and switching characteristics are compared. A hysteresis width change of about 20 mA was obtained by changing the applied voltage of about 1 V in each case, Less than 100 ps turn-on switching time with injection light of 1-mW peak intensity was obtained. The device can be switched-on by injection light with about 50 nm bandwidth, and the minimum input light switching intensity of less than 10 μW is achieved around the absorption peak wavelength of the saturable absorber. The InGaAs-InAIAs system has the advantage of low voltage bias at the saturable absorber, because the absorption edge is sharper than other materials due to its high conduction band offset. It has a turn-off switching time of less than 100 ps at the applied voltage height of 2.0 V. And also, memory operation with the repetition rate of 2 GHz has been achieved using input light and the applied voltage     

Optimal approximation of uniformly rotated images: relationshipbetween Karhunen-Loeve expansion and discrete cosine transform

We present the concept that for uniformly rotated images, the optimal approximation of the images can be obtained by computing the basis vectors for the discrete cosine transform (DCT) of the original image in polar coordinates, and that the images can be represented as linear combinations of the basis vectors.     

Parametric amplifiers for high sensitivity receivers sensitivity receivers

The characteristics of parametric amplifiers, including effective input noise temperature, bandwidth, stability, and gain compression are discussed. Two specific amplifiers, a liquid nitrogen cooledL-band unit for a radio astronomy observatory, and a three-channel unit for a satellite vernier auto track systems are described, and the characteristics of these amplifiers are presented.