Frontiers in Guided Wave Optics and Optoelectronics

Abstract

To accommodate rapidly increasing quantities of information and communication, optical fiber transmission technology with high-speed high-capacity is demanded. The development of an optical gain medium and fiber amplifiers to cover the 1250~1650 nm region, which is the entire optical telecommunication windows of silica fiber, becomes an important issue for ultra-wide broadband optical communication. Bismuth-doped glasses exhibit a broadband luminescence in the near infrared region. Thus, they are potential gain media for extending the spectral bandwidth of the current erbium-doped silica fiber amplifiers. There are several reports on an infrared luminescence from bismuth-doped glasses such as germanate, phosphate, borate et al. (Meng et al., 2005ab; Peng et al., 2005abc; Suzuki & Ohishi, 2006). According to their research, bismuth-doped glasses are therefore very promising for creating broadband amplifiers for fiber telecommunication lines and tunable or femto-second lasers. There are two useful wavelengths for optical communication. One is the 1550 nm, erbium- doped fiber amplifiers (EDFAs) working wavelength, which has minimum losses. EDFA developments within the third telecommunication window have contributed to the rapid growth of wavelength division multiplexing (WDM) transmission systems. The L-band (1570~1605 nm) of EDFA can be used in WDM systems in conjunction with C-band (1530~1560 nm). However, efforts to use WDM techniques to exploit this capability have been hampered by nonlinear fiber effects such as four-wave mixing. In addition, the amplification bandwidth of silica-based EDFA is as small as ~70 nm (Yamada et al., 1998). A broadband amplifier with a gain bandwidth of more than 70 nm was reported by the integration of EDFA with thulium-doped fiber amplifiers or fiber Raman amplifiers (FRAs) (Yamada et al., 1998). The other useful wavelength (1300 nm) for optical communication is O-band, between 1260 and 1360 nm, which is the natural zero-dispersion region of silica glass fiber where the temporal distortion of transferred optical pulses can be minimized. For example, praseodymium-doped fluoride fiber amplifiers (PDFFAs) and FRAs have been successfully used for 1300 nm amplification, but it also suffer from narrow bandwidth (~25 nm) in operating wavelength and low efficiency (Miyajima et al., 1991; Whitley, 1995). In addition, a PDFFA normally made from fluoride glass, which is very brittle and cannot be fusion spliced to the silica glass fiber. An alternative core fiber material and fiber amplifier for 1300 nm amplification is expected.