Development of optical semiconductor devices for long-distance and high-capacity optical communications

InGaAsP-DFB-DC-PBH single wavelength semiconductor laser

Fig.1 InGaAsP-DFB-DC-PBH single wavelength semiconductor laser

Cross sectional view of InGaAs/InP-PLEG highly sensitive planar APD

Fig.2 Cross sectional view of InGaAs/InP-PLEG highly sensitive planar APD

    Recently, development of optical communication systems are progressing toward realization of high-capacity and long-distance transmission after a first stage of feasibility study and commercialization of transmission systems by effectively utilizing low-loss wavelength band of silica single mode optical fibers, i.e., 1.3-1.5um. A most important key factor to realize such communication systems is development and commercialization of stable single longitudinal mode semiconductor lasers and highly sensitive photo-detectors.

    Conventional multi-longitudinal mode semiconductor lasers have to be replaced by single wavelength semiconductor lasers for transmitting Gbits/s signals over several tens km optical fiber with wavelength dispersion. Kohroh Kobayashi and Ikuo Mito engaged in R&D of InGaAsP/InP distributed feedback (DFB) semiconductor lasers just after its lasing was confirmed. In 1983, they have succeeded to achieve the light output power of 20mW under single wavelength cw operation, which is highly enough for the average power level for practical use. In 1985, they have recorded the maximum cw light output power of 103mW. They have led the R&D of single wavelength light sources in the world by showing the high potential of DFB lasers as a practical single wavelength light source among various candidates. They have also revealed experimentally that a lasing threshold gain difference between the main mode and the sub mode of a DFB laser significantly affects the optical fiber transmission characteristics. They have developed DFB lasers with a phase shift periodic corrugation which has the highest threshold gain difference, resulting in the establishment of the stability of the single wavelength operation under high-speed direct modulation of Gbits/s.

    Kenko Taguchi engaged in R&D of InGaAs/InP avalanche photo-diode (APD). In 1982, he started crystal thin layer growth for photo-detectors using hydride-transport vapor-phase epitaxy method suitable for crystal growth of highly pure epitaxial layers and achieved the impurity concentration as low as 1015 /cm3, which is necessary for the avalanche multiplication. A most important issue for APD where a high electric field is applied on the photo-receiving area of several tens um in diameter is to suppress edge breakdown near the photo-receiving area where a curvature of the pn junction becomes maximum. He succeeded to solve the problem by designing and fabricating a new preferential lateral extended guard ring (PLEG) structure, where the curvature of the pn junction at the guard ring was made small by doubly ion implanting Be atoms near the edge of the photo-receiving area, resulting in the increase in the breakdown voltage difference between the photo-receiving area and the guard ring area. This led the gain bandwidth product, a quality factor of APD, as high as 70GHz and also led improvement of the productivity and the reliability.

    InGaAsP DFB semiconductor lasers and InGaAs APDs they have developed have made possible to transmit 10 Gbits/s signals over 80km in 1988. These devices were installed in commercial optical fiber communication systems with 565Mbit/s, 1.12Gbits/s and 1.6Gbits/s signal bit rates. They are also planned to be used in submarine optical cable communication systems with supposed repeater distance of about 100km, because their high reliability has been confirmed.


[1] Kohroh Kobayashi and Ikuo Mito、High Light Output-Power Single-Longitudinal-Mode Semiconductor Laser Diodes、1985、J. Lightwave Tech., vol.LT-3. no.6, pp.1202-1210, Dec. 1985
[2] Kohroh Kobayashi and Ikuo Mito、Single Frequency and Tunable Laser Diodes、1988、J. Lightwave Tech., vol.6, no.11, pp.1623-1633, Nov. 1988
[3] Kenko Taguchi, Toshitaka Torikai, Yoshimasa Sugimoto, Kikuo Makita, and Hisahiro Ishihara、Planar-Structure InP/InGaAsP/InGaAs Avalanche Photodiodes with Preferential Lateral Extended Guard Ring for 1.0-1.6 um Wavelength Optical Communication Use、1988、J. Lightwave Tech., vol.6, no.11, pp.1643-1655, Nov. 1988

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