Takashi Hiraga (Senior Researcher) of the Photonics Research Institute (Director: Masanobu Watanabe) of the National Institute of Advanced Industrial Science and Technology (President: Hiroyuki Yoshikawa) (hereinafter referred to as AIST) has developed a large-volume, high-speed data distribution system required by hospitals and broadcast stations for transmitting large quantities of image data in collaboration with Dainichiseika Color & Chemicals Mfg. Co., Ltd. (President: Yasushi Takahashi), Trimatiz, Ltd. (President: Yuji Shimada), Spacecreation Co., Ltd. (President: Kuniaki Aoki), Inter Energy Co., Ltd. (President: Yasuo Masuda), and Nissei Electric Co., Ltd. (President: Katsuo Kono).

The current packet transmission (Ethernet) needs standby time and takes time to transmit large volumes of image data, though it has excellent versatility.

This system combines photoregulation-type optical switches and transceivers that transform optical signals to electrical signals, and vice versa. This allows optical communication at speeds of up to 1.5 bps – the data transmission speed of the hard disk of a terminal PC – and allows the user of a terminal PC to feel as if the PC is connected to the central data server (see Figure 1).

This system was exhibited and demonstrated in Electrotest Japan scheduled for January 17-19 and Fiber Optics Expo scheduled for January 24-26, both of which was held at Tokyo Big Sight.

Figure 1. Schematic design of the present system

Usage of image data is increasing, particularly at medical institutions and broadcast stations. Medical institutions take many tomograms using magnetic resonance imaging (MRI) and X-ray computed tomography and present them to patients for explaining diseased parts with the help of three-dimensional rotating image displays. Image data captured by various inspection equipment are stored in a data server, and are used by clinical doctors for analysis and explanations in their examination rooms.

Thus, large volumes of image data are now transmitted via networks, and so the demand for a high-speed large-volume network that can be used without hindrance is growing. Currently, such networks are based on packet communications, the same as used by the backbone, but this is not widespread and only large hospitals have introduced the system due to several reasons including expensive equipment and high power consumption.

In February 2003, AIST and Dainichiseika Color & Chemicals Mfg. jointly developed a photoregulation-type optical switch that uses a perforated mirror and the micro thermal lens effect that forms a cone-shaped lens inside a thin film element when an organic thin-film optical element absorbs an optical control signal.

The switch was successfully downsized for handheld equipment in July 2004, and was improved to allow for operation in the 1.31 µm and 1.55 µm wavebands currently used for digital signals in optical communications. These two improvements paved the way for constructing a new communications system in local area networks inside households, offices, and hospitals.

We developed an optical network capable of transmitting large volumes of data by constructing an optical fiber network that combines several photoregulation-type optical switches (see Figures 2 and 3).

Because this system does not use any electronic parts, it is preferred as an optical network for hospitals that need to eliminate electromagnetic noise, manufacturing plants whose electronic instruments are damaged by electromagnetic nose, and facilities that handle high-level radioactivity.

Figure 2. an outward appearance ofphotoregulation-type optical switche

Figure 3. an inside of photoregulation-type opticalswitche

To utilize the high data transmission speed of 1.5 Gbps of the current serial ATA (eSATA) hard disk, the newly-developed large-volume, high-speed data optical distribution system transforms electron to light at the exit of the data server (eSATA HDD) and distributes the data as an optical signal to each terminal PC (1.31 µm and 1.55 µm wavebands).

If one of the terminal PCs sends (or detects) an order to connect it to the data server through Ethernet, it irradiates control light (wavelength 0.98 µm) to activate the optical distribution network, whereby data transmitted from the data server are stored in the terminal PC. High-speed data exchange is realized because only an optical fiber line is used for data transmission between the terminal PC and the data server, so each user can operate their terminal PC as if it is connected to the data server.

Figure 4. The developed system for Instantaneous Distribution ofLarge-Volume Data at Hospitals and Broadcast Stations

The transmission method most widely used by backbones is Ethernet (packet transmission), and IP telephones (packet transmission) are becoming widespread in public telephone line networks. The packet transmission system is preferred for long-distance phone calls and PC communications that do not transmit much data in comparison with the connection time.

In contrast, the line switching system using a dedicated line is preferred for local area networks that need to transmit large volumes of data like images in a short period of time. For example, it takes only a few seconds for this system to transmit data equivalent to a compact disc (about 650 MBytes). To transmit the same amount of data by 100 Mbps Ethernet would take about one minute and by 1 Gbps Ethernet would take nearly 30 seconds even with the best line conditions.

The transmission speed varies greatly with the overcrowding of the line if data are transmitted by the packet system in a common line. If multiple users transmit large volumes of data by Ethernet simultaneously, the communications speed of other users will slow down considerably, and a complicated system that includes band control is required to prevent this overcrowding. In this system, a specified user occupies the communication line for a few seconds (that is, the line is busy), but another user can use the line as soon as the specified user finishes the communications and frees up the line.

Large-volume, high-speed data optical distribution using the communications infrastructure based on this system is ideal for local area data transmission systems, and is expected to spread to medium-sized hospitals because the risk of leakage of patients’ information is low.

This research was conducted with assistance from the Project to Develop Creative Seeds (Test for Establishing Rights for 2005-2006) of the Japan Science and Technology Agency (JST).

This system is being demonstrated on an experimental basis in a medium-sized hospital in Chiba Prefecture, and we are planning to demonstrate it in broadcast stations. We then aim put into practical use in two or three years after analyzing the data obtained the demonstrations.