Widely tunable optical‐fiber ring laser using high‐performance traveling wave amplifier

Abstract

AbstractA widely tunable optical‐fiber ring laser is fabricated using a traveling wave amplifier (TWA) and an optical‐fiber loop as the gain medium and the external cavity. The wavelength tuning in the wide range of more than 100 nm is obtained using a high‐performance TWA and a low‐loss external cavity.The TWA is made by anti‐reflection (AR) coated on both facets of a VIPS (V‐grooved inner stripe laser on p‐substrate) laser with residual reflectivity less than 10−4∼ 10−6. The length of the TWA is optimized to obtain high gain peak. The gain distribution of more than 16 dB in the wavelength range of 100 nm and the high gain peak of 30 dB are achieved. As the external cavity structure, the use of a diffraction grating and a bandpass filter, as the wavelength selective elements, are investigated and compared with each other.Hence, it is found that when the filter is used, the wavelength tuning range is about 10 nm wider than that of the grating and the fiber output power over 14 mW is achieved. The laser exhibits a very narrow linewidth of 15 kHz (longitudinal mode) and is believed to be a very useful source in optical communications if it is made to become a single‐mode one.