Yoshinori Arimoto

1.28 terabit/s (32x40 Gbit/s) wdm transmission system for free space optical communications

We review a novel free space optical (FSO) system that represents a significant breakthrough in the area of FSO communications. The system encompasses a pair of novel terminals: these allow direct and transparent optical connection to common single mode fibers and include a dedicated electronic control unit that effectively tracks the signal beam wandering due to atmospheric turbulence and mechanical vibrations. Further improvement in the signal power stabilization is achieved by means of saturated EDFAs. These solutions allow to realize a new FSO system, which is tested in a double-pass FSO link between two buildings in Pisa, Italy. When the terminals are fed by common WDM signals they allow enough power budget and margins to support a record high capacity transmission (32times40 Gbit/s), with a enormous improvement of stability (six hours with no error burst). During day-long transmission, the system behavior has been deeply characterized to correlate any increase of bit error ratio (BER) to the FSO control parameters.

Performance Evaluation of Next Generation Free-Space Optical Communication System

Free-space optical communication systems can provide high-speed, improved capacity, cost effective and easy to deploy wireless networks. Experimental investigation on the next generation free-space optical (FSO) communication system utilizing seamless connection of free-space and optical fiber links is presented. A compact antenna which utilizes a miniature fine positioning mirror (FPM) for high-speed beam control and steering is described. The effect of atmospheric turbulence on the beam angle-of-arrival (AOA) fluctuations is shown. The FPM is able to mitigate the power fluctuations at the fiber coupling port caused by this beam angle-of-arrival fluctuations. Experimental results of the FSO system capable of offering stable performance in terms of measured bit-error-rate (BER) showing error free transmission at 2.5 Gbps over extended period of time and improved fiber received power are presented. Also presented are performance results showing stable operation when increasing the FSO communication system data rate from 2.5 Gbps to 10 Gbps as well as WDM experiments.

1.28-Tb/s (32

We successfully transmitted a 1.28-Tb/s (32 times 40 Gb/s) wavelength-division-multiplexed (WDM) signal over a free-space optic (FSO) link, for the first time. We used a novel pair of FSO terminals, transparently connected to optical fibers, to transmit/receive the WDM channels over a double-pass FSO path between two buildings (2 times 210 m). Limited penalty on all 40-Gb/s channels and high stability was observed. Furthermore, long-term measurements of the system performance indicate a high improvement in reliability, which makes it a promising alternative for future deployment.

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The deterioration and deformation of a free-space optical beam wave-front as it propagates through the atmosphere can reduce the link availability and may introduce burst errors thus degrading the performance of the system. We investigate the suitability of utilizing soft-computing (SC) based tools for improving performance of free-space optical (FSO) communications systems. The SC based tools are used for the prediction of key parameters of a FSO communications system. Measured data collected from an experimental FSO communication system is used as training and testing data for a proposed multi-layer neural network predictor (MNNP) used to predict future parameter values. The predicted parameters are essential for reducing transmission errors by improving the antennas accuracy of tracking data beams. This is particularly essential for periods considered to be of strong atmospheric turbulence. The parameter values predicted using the proposed tool show acceptable conformity with original measurements.

40 Gb/s) Free-Space Optical WDM Transmission System

This paper shows the design and the performance of a new free-space optical communication terminal including the results of the indoor and outdoor demonstration experiments in a short link distance. To provide flexible and high-speed connectivity to the terrestrial free-space optical communications, a new compact laser communication terminal has been developed at NICT. The terminal has a feature to connect the free-space laser beam directly to single mode fiber by using a special fiber coupler to focus the free-space laser beam and couple it into the single mode fiber, fast and accurate fine tracking system and a small refractive-type telescope with diffraction limited performance. The bandwidth of the fine tracking system is more than 5 kHz using an off-the-shelf miniature Galvano mirror actuator and an analog PID controller.

Enhancing performance of next generation FSO communication systems using soft computing based predictions

Next generation laser communication systems will require small optical antennas and fine tracking system. Such optical communication systems might be applied not only to space communications such as optical feeder links, intersatellite links and stratospheric platforms but also optical links for long distance communication on the ground. We have developed a high-speed laser communication system including a small optical antenna which utilizes off-axis free form surface optical system, and a fine tracking system which feeds back an incident angle signal detected by quadrant detector to a small fine positioning mirror. In particular, the available mirror actuator response frequency for tracking is approximately 2kHz. Accordingly, even though the received 1.5μm laser beam experiences angle-of-arrival fluctuation as a result of atmospheric turbulence the antenna with this fine tracking function has a capability coupling the laser beam directly to the single mode fiber.

Compact free-space optical terminal for multi-gigabit signal transmissions with a single-mode fiber

1.28 Terabit/s (32×40 Gbit/s) is transmitted over a double pass free space optical link between two buildings (2×210m), transparently connected to optical fibers. Limited penalty on all 40 Gbit/s channels and high stability is obtained.

Development of optical antennas utilizing free form surface optics for the high speed laser communication systems

High speed and secure optical code division multiple access signals were successfully transmitted over 160 meters free space and 20 km optical fiber links. This shows possibility of covering area where geographical complexities make fiber installation difficult.

1.28 Terabit/s (32×40 Gbit/s) WDM transmission over a double-pass free space optical link

It is envisioned that the next generation of ultrahigh-speed laser communication systems will utilize compact optical antennas equipped with advanced beam tracking and effective fiber coupling mechanisms. Such laser communication systems will be used not only for space communications but also to provide optical links for long-distance terrestrial communications. We present the design of a high-speed laser communication system developed utilizing compact optical antennas with off-axis free-form surface (FFS) mirrors. We describe FFS optical devices and their design contribution in realizing compact optical antennas. Furthermore, an innovative fiber coupling device made from a glass ferrule and fiber is introduced, and with this device it is possible to couple the laser beam seamlessly to a single-mode fiber. We also present a fine tracking mechanism that uses a miniature fine pointing mirror (FPM) incorporated in the antenna. The machanism functions by feeding back the incident angle of the signal detected by a quadrant detector (QD) to the FPM. The achievable actuator response frequency for tracking is approximately 2 kHz, and it has been demonstrated to effectively mitigate the effects of laser beam angle-of-arrival fluctuation as a result of atmospheric turbulence.

First OCDMA Experimental Demonstration over Free Space and Optical Fiber Link

When a free-space optical beam propagates through the atmosphere it experiences deterioration and deformation of its wave-front caused from small scale, randomly localized changes in the atmospheric index of refraction. This results in beam wander and scintillation effects which can reduce the link availability and may introduce burst errors. This paper outlines experimental work on a free-space optical (FSO) communication system which connects an optical beam directly to a single-mode fiber (SMF) without any optical-to-electrical (O-E) conversion. In order to effectively couple the 1550 nm transmitted optical beam to a SMF it is necessary to be able to track and control the beam angle-of-arrival (AOA) changes. To achieve this, we have developed an optical antenna which uses a fine positioning mirror (FPM) capable of performing high-speed beam tracking and steering thus reducing to a great extent the optical power fluctuations of the received beam coupled to the SMF. This optical power fluctuation is partly a result of beam angle-of-arrival fluctuations caused by atmospheric turbulence. In our experiments we have tried to measure and quantify the magnitude of atmospheric turbulence experienced by an optical beam propagating through the atmosphere. First we demonstrate the relation between the AOA fluctuations and the frequency characteristics of the scintillation effects for a free-space optical beam propagating through a turbulent atmosphere. We use this information to determine the optimum antenna FPM tracking speed for improved performance and error free transmission. The results in the improved fiber received power as well as continuous error free transmission are presented.