S-band amplification challenges developers: Raman amplification is the leading method, but several other techniques are also under investigation to allow the move to the next frontier for optical amplification

摘要

The next logical frontier for optical amplification is the S-band, which the International Telecommunications Union has defined as wavelengths from 1460 to 1530 nm. The S-band FIGURE 1. Raman is adjacent to the standard erbium-fiber a 1410-nm pump p amplifier C-band at 1530 to 1565 nm, without the bend-sensitive losses that become significant beyond the 1625-nm end of the L-band. A few "hero experiments' have already used S-band amplification to transmit extremely high data rates through single fibers. Last year's record-setting demonstration of 10.92-Tbit/s transmission through a single fiber included 85 channels in the S-barid. The collapse of the telecommunications bubble last year eased near-term demand for higher fiber transmission capacity, but progress on S-band amplifiers continues. Developers face some important technical challenges. As defined by the ITU, the S-band spans 70 nm, twice the 35-nm width of the C band in wavelength units (and more than double it in frequency units). It's likely that two types of amplifiers may be needed to span the entire S-band with reasonably uniform gain. Some developers informally recognize that possibility by. splitting off the S+ band at 1450 to 1490 nm from an S-band shortened to 1490 to 1530 nm. So far the leading approaches are Raman fiber amplifiers and thulium-doped fiber amplifiers, which can be combined to make hybrid amplifiers like those used to flatten gain profiles in the erbium-fiber band. A few other approaches are under development, including specially designed erbium-fiber amplifiers.