These examples refer to the so-called sensitivity analysis for DQPSK, RZ-DQPSK and CSRZ-DQPSK modulation formats, shown in OptSim. It means that such examples give the curve of BER vs. the OSNR measured at the receiver. As OSNR we define the Optical Signal-to-Noise Ratio considering the amount of noise measured on an equivalent noise bandwidth equal to the bit-rate. The analysis is carried out using the semi analytical BER estimator based on the Karhunen-Loewe series expansion of noise.
The layout looks like: