We report on a high speed silicon-waveguide-integrated PIN Ge photodetector of 45 GHz bandwidth, and a high efficiency of 0.3 V·cm silicon optical modulator with a metal-oxide-semiconductor (MOS) junction by applying the low optical loss and high conductivity poly-silicon gate. These OE/EO devices enable low drive voltage of around 1V, which would contribute to a high density optical interposer of the future photonics-electronics convergence system.

This paper reviews the recent progress of quantum-dot semiconductor optical amplifiers developed as ultrawideband polarization-insensitive high-power amplifiers, high-speed signal regenerators, and wideband wavelength converters. A semiconductor optical amplifier having a gain of > 25 dB, noise figure of20 dBm, over the record widest bandwidth of 90 nm among all kinds of optical amplifiers, and also having a penalty-free output power of 23 dBm, the record highest among all the semiconductor optical amplifiers, was realized by using quantum dots. By utilizing isotropically shaped quantum dots, the TM gain, which is absent in the standard Stranski-Krastanow QDs, has been drastically enhanced, and nearly polarization-insensitive SOAs have been realized for the first time. With an ultrafast gain response unique to quantum dots, an optical regenerator having receiver-sensitivity improving capability of 4 dB at a BER of 10-9and operating speed of > 40 Gb/s has been successfully realized with an SOA chip. This performance achieved together with simplicity of structure suggests a potential for low-cost realization of regenerative transmission systems.

The twelve articles in this special issue are devoted to optoelectronc device manufacture based on quantum dot technology.

A new type of nonlinear image processing filters for multimedia applications is proposed. The filters remove small-amplitude fluctuations while keeping edges sharp. The filter algorithm is simply realized by combination of a usual linear filter and a comparator, which is suitable for hardware implementation. Here, two types of multimedia applications are considered, one is to post-process block-based encoded images which contain blocking artifacts, and the other to remove undesirable skin components in facial images, which is useful for facial beautification. Computer simulations verify the high performance of the proposed methods.

A novel digital signal processing technique, fuzzy filtering, is proposed for estimating signals with edges, contaminated with additive white Gaussian noise. In this filter, the concept of fuzzy clustering is utilized for classifying signals. This filter classifies the input signal sequence into a flat part and a changing one ambiguously using a fuzzy-logic membership function. Then, the signal is estimated on the basis of the classification. Fuzzy clustering is more effective than conventional definite classification, since some edges in the signal are ambiguous. Moreover, by combining with median filtering a filter for removing both white Gaussian noise and impulsive noise can be obtained. Computer simulations demonstrate its superior capability.>