Spectral narrowing of a long-wavelength VCSEL using a fiber Bragg grating and wavelength-division multiplexing

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A vertical-cavity surface-emitting laser (VCSEL) is a laser that emits light vertically from the semiconductor substrate. The output beam is circular and therefore suitable for coupling with optical fibers. Also, it is possible to arrange many devices two-dimensionally, which is suitable for parallel optical transmission. The wavelengths of VCSELs have been limited to the 800-nm band. However, these wavelengths are not suitable for high-speed large-capacity optical fiber transmission. Recently, VCSELs in the 1300 or 1550 nm band have been developed, and become commercially available last year. These long wavelength VCSELs are suitable for high-speed large-capacity transmission. However, spectral narrowing of long-wavelength VCSELs has not been performed.In the present study, we have coupled a fiber Bragg gratings with a long wavelength VCSEL and demonstrated the spectral narrowing. In 2004, we used conventional 800-nm VCSELs and demonstrated spectral narrowing including direct coupling without a lens. In 2005, we obtained the long-wavelength VCSEL diode (Ray Can) with 1310-nm oscillation wavelength. We fabricated a fiber Bragg grating in singlemode fiber with a reflectivity of 47%, and coupled with the VCSEL. As a result of the experiment, when the grating temperature was 50℃, the spectral width without using an FBG was 85 pm FWHM, then the spectral width decreased to 64 pm by using an FBG. This shows that wavelength selection by the FBG as an external cavity. The achieved maximum reduction in the spectral halfwidth was 25% of that from 85 pm to 64 pm. Data transmission characteristics are to be investigated.We also studied the fabrication process of fiber Bragg grating related with hydrogen. Hydrogen loading is indispensable for grating fabrication. We studied the diffusion of hydrogen in the fiber glass by the finite-element-method analysis and by fabrication of long-period gratings experimentally.