Julius Wittmann

Comparison of polarization handling methods in coherent optical systems

The authors compare three polarization handling methods in coherent optical systems. These methods are: endless polarization control, polarization diversity, and data-induced polarization switching. These methods are also compared with active, data-synchronous polarization switching. It is seen that endless polarization control is potentially the most powerful candidate, however, the choice of polarization control devices remain questionable. Polarization diversity is as versatile as polarization control and is potentially the fastest method; however, it yields lower receiver sensitivity. Endless control or a well-designed diversity receiver should be used for coherent trunk systems. Data-induced polarization switching is restricted to frequency-shift-keying (FSK) systems. It promises a loss span similar to that of diversity, but is far simpler, which makes it recommendable for FSK distribution systems. >

Impact of the dual-PIN-photodiode series resistance on the noise of tuned optical receivers

Optical front ends are crucial components for both direct detection and heterodyne systems. Serial tuning1 has proved to be suitable for noise suppression without sacrificing a broadband frequency response2-4 A thorough investigation of the noise performance of a serial tuned high impedance design2 shows that, for a sufficiently high transconductance of the preamplifier transistor, three main sources are contributing to the total noise. In Fig. 1 the corresponding equivalent spectral input noise current densities are shown. Trace 1 is the total input noise density, which is in close agreement with measured values,2 trace 2 represents the noise of the diode series resistance of the dual PIN diode.