page_title: Yasuharu Suematsu
section_title: Creation of Dynamic Single Mode Lasers
hierarchical_section_title: Yasuharu Suematsu / Research / Creation of Dynamic Single Mode Lasers
caption_attribution_description: English: Fig.6. A commercial phase shift distributed reflector laser array, with 100\ coin for size reference. By courtesy of Furukawa Electric Co.
context_page_description: Yasuharu Suematsu is researcher and educator in optical communication technology by invention of the Dynamic Single Mode Semiconductor Lasers for actuation and following development of large capacity and long distance optical fiber communications.
context_section_description: Light is the highest frequency of electromagnetic waves that humans can control. It outperforms radio waves by a wide margin in transmitting a large capacity of information. Research into optical communications was undertaken such as in U.S.A., Japan, and England. The nature of optical fiber communication was thought possibly being able to transmit a large capacity of information over a long distance, all over the world. To make it a reality, the focus was on creating a Dynamic Single Mode laser (DSM laser) (Fig.2) which has the following three characteristics:
  (1) operates at a wavelength band which causes minimal loss within the optical fiber to allow for long-distance transmission (1.5 micrometers was discovered to be the ideal wavelength band during the course of following research);
  (2) operates stably at a single wavelength to surmount the problem of transmission capacity reduction due to dispersion on the propagation constant in single mode optical fiber; and
  (3) allows the wavelength to be tuned to adapt to communication in multiple wavelengths.
  First, in 1972-1974, Suematsu and his student proposed a single mode resonator which would consist of refractive index waveguide for the transverse mode, and two distributed reflectors joined together with a phase shift by odd numbers of a half π for the axial single mode operation (Fig.2) . In the meantime, Suematsu pioneered materials for a mixed crystal of GaInAsP/InP for a semiconductor laser that would operate at a wavelength band of 1.5 micrometers—which causes minimal loss inside the optical fiber as Donald A. Keck et al suggested in 1973— and continuously operates at room temperature, in July 1979. 
  Following these preliminary achievements, Suematsu and his co-workers succeeded in creating an integrated laser with built-in distributed reflectors using a material in the band of 1.5 micrometers. In October 1980, Suematsu and his students had built a dynamic single mode laser that stably operates at a single mode even under rapid direct modulation (Fig.3 and Fig.4) , and continuously operates at room temperature. This laser remained in stable operation mode even when the temperature was changed, so that the wavelength could be tuned thermally within the 1.5 micrometers band. Thus, the thermo-tunable dynamic single mode laser was born and triggered to develop 1.5 micrometer high speed fiber system, as cited by such as the 1983 Valdemar Poulsen Gold Medal , the Danish history of optical communication, and the 1986 David Sarnoff Award . Its spectral behavior was investigated profoundly to attain full single mode operation. Meanwhile, research and development progressed at industries in areas such as optical fibers, optical circuits, optical devices, modulation schemes, and system structures. The actualization of the dynamic single mode laser became an impetus to develop high-capacity and long-distance optical fiber communications, and it began to be applied commercially in the end of the 1980s.
caption: Fig.6. A commercial phase shift distributed reflector laser array, with 100\ coin for size reference. By courtesy of Furukawa Electric Co.
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