Feature Articles: Network Technology for Digital Society of the Futureˇ˝Research and Development of Competitive Network Infrastructure Technologies
Optical Fiber and Optical Device Technology for Innovative Manufacturing
Long-distance transmission of high-quality and high-power laser optics has been achieved for the first time in the world by combining the advanced optical fiber and optical device technologies developed by NTT in the optical communications field with the high-power laser processing technology of Mitsubishi Heavy Industries, Ltd. The use of laser processing technology is spreading rapidly at manufacturing sites in the automobile, aircraft, and other industries. The results of this joint research are expected to be the first step in revolutionizing the concept of manufacturing for a variety of social infrastructures through B2B2X (business-to-business-to-X) initiatives.
Keywords: laser processing, optical fiber, optical device
Laser processing technology such as for metal cutting and welding is finding widespread use these days at manufacturing sites in the automobile, aircraft, and other industries. The laser beams used in laser processing can be generally divided into single mode and multi-mode*1 in terms of properties (Fig. 1). A single-mode laser beam features high directivity. The beam emitted from the optical fiber can be easily focused on a single point, making for high-precision laser processing. The output from the latest single-mode laser oscillators extends to 10 kW (about 10,000 times the optical intensity used in optical communications), which enables high-precision laser processing with good efficiency. However, the transmission distance of a single-mode laser with conventional optical fiber is limited to only a few meters.
In contrast, a multi-mode laser beam can propagate for more than several tens of meters with existing optical fiber technology, but the wide angle of this type of laser beam emitted from the optical fiber limits processing precision. Consequently, if a 10-kW-class single-mode laser beam can be propagated over distances greater than several tens of meters while maintaining processing quality, it should be possible to greatly ease restrictions on processing location or scale of the processing target at the processing site. Furthermore, if the direction and shape of a single-mode, high-output laser beam can be freely controlled, it should be possible to control the shape in cutting and hole forming and achieve efficient overlay processing*2 (Fig. 2).
2. Optical fiber and optical device technology for high-power transmission
We have succeeded in transmitting a 10-kW high-quality laser beam over a distance of 30 m by optimizing photonic crystal fiber previously developed as a low-loss, high-capacity transmission medium by NTT as a high-power transmission medium . Photonic crystal fiber is optical fiber that transmits light by confining it within an area surrounded by countless air holes. Precise control of the diameter and pitch of these air holes makes it possible to maintain a single mode for application to laser processing even for high power input on the order of 10 kW . This joint research also involved a study on the application of potassium tantalate niobate (KTa1-xNbxO3: KTN) crystal , which was developed by NTT for possible application to optical switches and optical memory, and computer holography  to laser processing. The use of KTN crystal and computer holography here enables flexible control of the laser beam direction and shape. We expect the combination of these three technologies—photonic crystal optical fiber, KTN crystal, and computer holography—to enable 10-kW-class laser beams to be delivered to any processing site for performing flexible, high-quality, and high-efficiency laser processing.
3. Future outlook
The initiative described here is aimed at creating new added value by combining the results of research and development of competitive network infrastructure technology with technology from another industry. Going forward, we expect trials that demonstrate the potential of this technology in actual laser processing to drive its growth as a technology that can revolutionize the manufacturing sites of a variety of social infrastructures.