Special Report: Next Generation Internet Applications
2.1.1 Optical Signal Modifiers The proliferation of optical networks, in part, can be attributed to advancements in optical semiconductor research. Advanced optical amplifier design has provided circuit designers with components capable of reducing the size and cost of optical circuit implementations. Tunable lasers have greatly reduced the cost required to operate on various wavelengths within the optical transmission. Special substrate applications have made it possible to filter out the unnecessary components of optical signals to fully realize optical networks. As a result of extensive research in these areas, optical infrastructure development is ahead of projection, laying the foundation for the physical realization of all-optical networks.
2.1.1.1 Optical Amplifiers Optical amplifiers are critical to high-speed optical networks. Historically, long-distance fiber runs utilized optical amplifiers to boost the spectral power of the transmission. Recently, however, research is underway to use optical amplifiers for additional applications such as wavelength conversion. Raman amplifiers operate by means of a pump laser. This pump laser operates at a shorter wavelength than the signal laser. As the pump and signal wavelengths proceed down the optical medium, the pump laser starts scattering photons and losing energy. This energy is absorbed by the signal, since it is at a longer wavelength, resulting in amplification of the signal. The pump laser eventually fades due to this loss of energy. Therefore, Raman amplification provides a means of amplifying optical signals of any wavelength within the transmission line, depending on the wavelength separation of the pump and signal. Raman amplification also reduces the need for costly electrical amplifiers along the transmission path. Multiple Raman amplifiers are necessary when amplification of multiple wavelengths in a fiber is needed. Erbium-Doped Fiber Amplifiers (EDFA) address the scalability problems of Raman amplifiers.
An EDFA consists of fiber doped in Erbium, a rare ion. The addition of the Erbium impurity causes amplification across a broad spectrum of wavelengths when excited by a pump laser. Like Raman amplifiers, EDFAs require no OEO conversion to produce this in-line amplification. While EDFAs amplify a larger number of wavelengths along the transmission line than Raman amplifiers, they do have a long delay time that could hinder their inclusion in optical switches.
Historically used for optical transmission amplification, Semiconductor Optical Amplifiers (SOA) were determined to contain nonlinearities that affected the integrity of the optical signal when used across a broad range of wavelengths. These problems, however, did not mark the end of SOAs. Instead, these nonlinearities make SOAs useful for wavelength conversion techniques as described in section 2.2.3. [4][5][6]
Previous Next Table
of Content for report: Next Generation Internet Applications Home
