About RYU Laboratory

Ryu Laboratory (Ryu Labs) started research on April 2016 immediately after S. Ryu joined Meiji University.
Ryu Lab is conducting research on optical fiber communication systems, optical wireless communication systems, and optical fiber-related measurement technologies.
The laboratory is located on the Nakano Campus of Meiji University, which is close to JR Nakano Station, to conduct cutting-edge research in an environment.

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Research fields

The current research focuses on the following contents.
1. 1. Research on optical wireless communication systems
2. Research on long-distance coherent optical fiber communication systems
3. Research on optical measurement technology

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1. Optical Wilreless Communication Systems

Due to the development of video distribution services, the current mobile phone network has insufficient communication capacity with only the originally allocated radio frequency resources, and the Wi-Fi network is used as a means to supplement this.
However, at event venues and train stations where many people gather, even if Wi-Fi is used, the communication capacity is tight.
As a means to overcome this situation, we are researching an optical wireless communication method that puts data for mobile phones on the light emitted from familiar lighting. Since the data is placed on the light, the coined word 'Li-Fi', which replaces the 'L' in the English word 'Light', which represents light, with the 'W' in 'Wi-Fi' has also appeared, and is a technology that has been attracting attention these days.
However, since optical wireless communication technology uses spatial propagation of light, there is an essential problem that communication is blocked if there is something that physically blocks it. Therefore, in order to overcome such problems, our laboratory is studying the diversity transmission/reception method. We are also conducting research on MIMO (Multi-Input Multi-Output) technology for the purpose of increasing the capacity and functionality of optical wireless communication systems. MIMO technology has already been put to practical use in wireless communication technology, but our laboratory is conducting research to apply it to optical wireless communication systems.

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2. Long-haul coherent optical fiber communication systems

Research on long-haul high capacity systems has been improved significantly recetly. Using the present state-of-the-art digital coherent optical communication systems technology, 100-Gbit/s per wavelength using QPSK format and 200-Gbit/s per wavelength using 16QAM format have been commercialized. Coherent optical communication systems use optical phase of light to carry data streams.
Coherent optical communication systems using optical phase modulation is essentially susceptible to optical phase noise caused by, e.g., optical fiber nonlinearities. Optical phase noise have not been paid so much attention in traditional optical communication systems since the systems just used 'intensity modulation' of light.
We are doing research on optical phase noise caused in the fibers to clarify the effect of the phase noise characteristics on the transmission performance

Furthermore, as the capacity of coherent optical fiber communication systems increases, the power consumption of the electronic circuits used in the systems has become problematic, and technology to reduce the burden on the global environment is required.
To address this problem, using all-optical circuits that process only optical signals instead of electronic circuits can significantly reduce power consumption compared to when electronic circuits are used.
Please see this article for more information on reducing power consumption using all-optical circuits (Meiji University website).

3. Optical Measurement Technology

Coherent heterodyne detection technology has long been used in the field of optical measurement technology, but analog signal processing has been the main focus. However, since the 21st century, when research on digital coherent optical communication methods has become active, research on applying digital signal processing to optical measurement technology has become active.
By using digital signal processing, so-called offline processing has become possible, and it has become possible to actually confirm phenomena in optical fibers that were previously invisible.
In our laboratory, we are conducting research on measurement technology that combines coherent heterodyne detection technology and digital signal processing. In particular, we are focusing on the following research.
・ Rayleigh scattered light measurement technology
　strain measurement, vibration measurement, birefringence distribution measurement due to stress applied to optical fiber
・ Brillouin scattered light measurement technology
　strain measurement and vibration measurement due to stress applied to optical fiber