The develop of 622Mbits/s free space laser communication system

622Mbits/s free space laser communication system is developed. IT's communication rate is 622Mbits/s. The whole system include three parts which are signal in and out circuit laser driver and receive circuit and optical antenna The communication principle is introduced The experiment result shows that the transmission of data and image are satisfied with demands of design. It have a definite market value.

gcs-ma: a group communication system for mobile agents

Reliable messaging is a key component necessary for mobile agent systems. Current researches focus on reliable one-to-one message delivery to mobile agents. But how to implement a group communication system for mobile agents remains an open issue, which is a powerful block that facilitates the development of fault-tolerant mobile agent systems. In this paper, we propose a group communication system for mobile agents (GCS-MA), which includes totally ordered multicast and membership management functions. We divide a group of mobile agents into several agent clusters,and each agent cluster consists of all mobile agents residing in the same sub-network and is managed by a special module, named coordinator. Then, all coordinators form a ring-based overlay for interchanging messages between clusters. We present a token-based algorithm, an intra-cluster messaging algorithm and an inter-cluster migration algorithm to achieve atomicity and total ordering properties of multicast messages, by building a membership protocol on top of the clustering and failure detection mechanisms. Performance issues of the proposed system have been analysed through simulations. We also describe the application of the proposed system in the context of the service cooperation middleware (SCM) project.

VLSI architecture of a K-best detector for MIMO--OFDM wireless communication systems

The K-best detector is considered as a promising technique in the MIMO-OFDM detection because of its good performance and low complexity. In this paper, a new K-best VLSI architecture is presented. In the proposed architecture, the metric computation units (MCUs) expand each surviving path only to its partial branches, based on the novel expansion scheme, which can predetermine the branches' ascending order by their local distances. Then a distributed sorter sorts out the new K surviving paths from the expanded branches in pipelines. Compared to the conventional K-best scheme, the proposed architecture can approximately reduce fundamental operations by 50% and 75% for the 16-QAM and the 64-QAM cases, respectively, and, consequently, lower the demand on the hardware resource significantly. Simulation results prove that the proposed architecture can achieve a performance very similar to conventional K-best detectors. Hence, it is an efficient solution to the K-best detector's VLSI implementation for high-throughput MIMO-OFDM systems.

Long-wavelength SiGe/Si MQW resonant-cavity-enhanced photodetectors (RCE-PD) for application in optical fiber communication network

　

A novel high sensitivity CE-PTHPT for optical fiber communication

Planar punch through heterojunction phototransistors with a novel emitter control electrode and ion- implanted isolation (CE-PTHPT) are investigated. The phototransistors have a working voltage of 3-10V and high sensitivity at low input power. The base of the transistor is completely depleted under operating condition. Base current is zero. The CE-PTHPT has an increased speed and a decreased noise. The novel CE-PTHPT has been fabricated in this paper. The optical gain of GaAlAs/GaAs CE-PTHPT for the incident light power 1.3 and 43nw with the wavelength of 0.8 mu m reached 1260 and 8108. The input noise current calculated is 5.46 x 10(-16) A/H-z(1/2). For polysilicon emitter CE-PTHPT, the optical gain is 3083 at the input power of 0.174 mu w. The optical gain of InGaAs/InP CE-PTHPT reaches 350 for an incident power of 0.3 mu w at the wavelength of 1.55 mu m. The CE-PTHPT detectors is promising as photo detectors for optical fiber communication system.

Long-wavelength Si-based MQW photodetectors for application in optical fiber communication

Si-based SiGe/Si strained MQW long-wavelength photodetectors (PD) with cycle type (Ring Shape) waveguide (CWG) and resonant-cavity-enhanced (RCE) structure have been investigated for the first time for improving the quantum efficiency and response time. The results show that the responsivities are higher than that of conventional PD with a same Ge content reported previously. In addition, RCE-PD has an obvious narrow band response with FWHM less than 6nm.

Investigation on integrated high speed DFB light source and narrow bandwidth RCE photodetector for WDM fiber communication network application

Electroabsorption (EA) modulator integrated with partially gain coupling distributed feedback (DFB) lasers have been fabricated and shown high single mode yield and wavelength stability. The small signal bandwidth is about 7.5 GHz. Strained Si1-chiGechi/Si multiple quantum well (MQW) resonant-cavity enhanced (RCE) photodetectors with SiO2/Si distributed Bragg reflector (DBR) as the mirrors have been fabricated and shown a clear narrow bandwidth response. The external quantum efficiency at 1.3 mum is measured to be about 3.5% under reverse bias of 16 V. A novel GaInNAs/GaAs MQW RCE p-i-n photodetector with high reflectance GaAs/ALAs DBR mirrors has also been demonstrated and shown the selectively detecting function with the FWHM of peak response of 12 nm.

Modal correction for fiber-coupling efficiency in free-space optical communication systems through atmospheric turbulence

High-speed free-space optical communication systems have recently used fiber-optical components. The coupling efficiency with which the received laser beam can be coupled into a single-mode fiber is noticeably limited by atmospheric turbulence due to the degradation of its spatial coherence. Fortunately, adaptive optics (AO) can alleviate this limitation by partially correcting the turbulence-distorted wavefront. The coupling efficiency improvement provided by Zernike modal AO correction is numerically evaluated. It is found that the first 3-20 corrected polynomials can considerably improve the fiber-coupling efficiency. The improvement brought by AO is compared with that brought by a coherent fiber array. Finally, a hybrid technique that integrates AO and a coherent fiber array is proposed. Results show that the hybrid technique outperforms each of the two above-mentioned techniques. (C) 2009 Elsevier GmbH. All rights reserved.

Entanglement dynamics and chaos in the Dicke model

We study dynamical properties of quantum entanglement in the Dicke model with and without the rotating-wave approximation. Specifically, we investigate the maximal entanglement and mean entanglement which reflect the underlying chaos in the system, and a good classical-quantum correspondence is found. We also show that the maximal linear entropy can be more sensitive to chaos than the mean linear entropy.