Kayo Ogawa

Measurement and simulation of the effect of snowfall on free-space optical propagation

We measured the time variation of a received laser signal level during snowfall over a distance of 72 m. The signal level dropped sharply for up to 10 ms when a snowflake crossed the laser beam. The probability distribution of the variation due to snowfall was calculated by assuming it to be the linear superposition of the light diffracted by snowflakes. The measured distributions could be reproduced by assuming reasonable snowflake size distributions. Furthermore, the probability distributions due to snowfall over a 1 km distance were calculated, and the expected bit errors during snowfall and the transmitted beam sizes were evaluated.

Real-time typing action detection in a 3D pointing gesture interface

In this paper, we propose a method to detect typing actions in the air by applying principal component analysis and linear discriminant analysis on time-series finger scale data in real time. The proposed method was implemented to an experimental system of in-air typing interface, and a preliminary user study using a keyboard typing application was conducted. The results showed about 95% of the detection rate of typing actions and more than 80% of the input recognition rate.

Recognition of typing motions on AR typing interface

We have proposed Augmented Reality (AR) Typing Interface as a new input interface for mobile devices. By using this interface, users can utilize a wide space in the air in inputting texts. This interface uses a camera which is attached to the back of the device. A virtual keyboard is overlaid on the image captured by a camera using AR technology. In this paper, we propose a new method to recognize typing motions more precisely. In this method, feature vectors are generated by using information of time-series optical flows. Typing motions are recognized by using support vector machine (SVM). We confirmed that the proposed method was able to recognize typing motions with about 90% accuracy for the recorded video of typing in the air.

Optimization to reduce influence of the scintillation in optical wireless communication

In this study, we have examined the optimum combination of optical variables including wavelength, the beam radius of a transmitter, and diameter of receiver aperture, to reduce the effects of scintillation, which is one of the factors that deteriorate the quality of optical wireless communication. Moreover, we have examined the modulation method that is resistant to the decrease in light intensity and the propagation mode of carriers that results in retaining the light intensity. As a result of the examinations, the optimum beam radii of transmitters and the optimum diameter of receiver apertures have been successfully found. Furthermore we have found that the effects of the scintillation can be reduced by using of the Laguerre–Gaussian beam wave as the carrier.

Input action classification in a 3D gesture interface for mobile devices

In this research we propose a new motion classification method to improve operability of a 3D gesture interface that assists text input on mobile devices. A certain range of time-series finger scale data is cropped and is classified using linear discriminant analysis. To confirm possibility of linear separation, data were visualized using principle component analysis. Experimental result with changing cropping ranges and sampling rates showed that the recognition rate improved when the cropped time is longer, and more than 97.9% recognition rates were achieved with cropping time of 0.77s/0.38s from both/one sides of the peak.

Fast and multi-level liquid crystal spatial light modulator using anti-ferroelectric liquid crystal

Due to technological advances in the optical information processing and optical communication fields, the demands for higher performance in spatial light modulator. The anti-ferroelectric liquid crystal (AFLC) has a possibility of achieving multi-tone control by applied voltage similar to nematic LCD. The AFLC was developed as a new spatial light modulator, and furthermore, a high-speed drive method with polarization properties was proposed. From this, a high-speed drive of 500 μsec was confirmed. In addition, basic studies were conducted on necessary functions required for phase modulators, and phase modulation due to the effect of voltage control was verified. From these results, the feasibility for a high-speed multi-level spatial light modulator with the effect of AFLC was verified.

Investigation of mode demultiplexer for Laguerre-Gaussian mode multiplexing in free space

With the rapid increase in communication traffic, the capacities of existing multiplexing methods have reached the limits of expandability. Therefore, the mode multiplex communication method using orbital angular momentum (OAM) has recently attracted attention as a new method. The OAM is a part of Laguerre-Gaussian (LG) beam. LG beam which possesses modes determined by the radial order n and the azimuth order m. The OAM is modes when the radial order n is equal to zero. Transmission capacity and spectral efficiency are expected great increase significantly from the combination of existing multiplexing method and mode multiplexing. In the future, a further increase in transmission capacity is expected because devices connected to the Internet are rapidly increasing with the spread of the Internet of Things. Therefore, in order to further increase transmission capacity, it is necessary to expand the radial order n. In this study, we investigate the mode multiplexing communication method using LG mode extending the radial order n. To realize mode multiplexing with increased the amount of multiplexing, technological developments in demultiplexing are particularly significant. In previous studies, mode-demultiplexers have been considered interferometric method and holographic filter. However, these methods have problems such as the complex of optical system and the reduction in diffraction efficiency. Therefore, we design the computer generated hologram that can extract multiple modes with one filter as the mode-demultiplexer. Through the above examination, we aim to realize simplification and high efficiency of the mode-demultiplexer.

Propagation characteristics of Laguerre-Gaussian beams through atmospheric turbulence in optical wireless communication

The scintillation and bit error rate performance of optical wireless communication systems employing Laguerre-Gaussian (LG) beams were evaluated considering the size of the transmitted beam and receiving aperture. As a result, it was found that the system employing LG beams with a high radial number can reduce the effect of scintillation and improve communication quality.

Visualizing Learning Management System data using Context-Relevant Self-Organizing Map.

In the last few years, many form of Learning Management Systems (LMS) have been introduced in many educational institutions with the main objective of obtaining meaningful information from the accumulated learning data to be then utilized for increasing the quality of the educations in those institutions. One of the most popular techniques for extracting information is by visualizing the high dimensional data that characterize the information. In this study, we propose to utilize Context-Relevant Self Organizing Map, a unique visualization algorithm that preserves not only the topographical characteristics of high dimensional data but also their context, for visualizing LMS data. Our preliminary experiments with real world LMS data show that the Context-Relevant Self-Organizing map is able to provide visual information which cannot be provided by the conventional Self-Organizing Map.

Considerations for application of Laguerre-Gaussian beam wave in optical wireless communication

Effect of scintillations is a serious problem in optical systems which require atmospheric propagation, and various examinations have been implemented to keep communication quality. But combination of optical conditions to optimize communication capability has not been examined. In this paper, optimization of the combination of optical variables, for example transmission beam radius of carrier wave and diameter of receiving aperture, is conducted by using the lognormal distribution model in weak turbulence and the gamma-gamma distribution model, which is suitable for weak to strong turbulence, in moderate to strong turbulence with considering aperture averaging. As a result of the examination, the optimum combination have been successfully found. Moreover, to investigate the propagation mode of carrier wave, comparison of propagation attenuation between Gaussian beam wave and Laguerre-Gaussian beam wave and evaluation of communication quality in optimized optical condition obtained from above-mentioned examination, will be done. The result is that the propagation loss of any of the Laguerre-Gaussian beam waves are smaller than those of the Gaussian beam waves. It is also observed that the propagation loss of (5, 1) Laguerre-Gaussian beam wave is particularly small among those.