The rapid instantaneous change of (1) signal amplitude, from a reference value to a higher or lower value, and then quickly returns to the reference value.
(2) The rapid transient change of signal characteristics (such as phase and frequency) changes from a reference value to a higher or lower value, and then quickly returns to the reference value.
The pulse shaping program can produce different pulse waveforms, and the optimal pulse waveform is different according to different applications.
(1) square wave
Square wave pulse includes square wave, Boxcar function and rectangular function. In digital signal, the transition from low level to high level is called rising edge, while the transition from high level to low level is called falling edge. If a rising or falling edge is detected in a digital system, or it only works in this case, it is called edge triggering. Digital timing diagram is an example of many square waves.
(2) Nyquist pulse
Nyquist pulse is a pulse that meets the Nyquist intersymbol interference standard and is very important in data transmission. Sinc function is a pulse that meets the Nyquist intersymbol interference standard, so it is very important in signal processing theory. But because of causality, no real signal generator can generate sinc function.
Nyquist pulse is generated at 20 13. The method used is to reduce the size of the pulse in the fiber, because the distance between them is 10 times and the bandwidth is 10 times. The completeness of Nyquist pulse is over 99%, which can be generated by simple laser and modulator.
(3) Gaussian pulse
Gaussian pulse is a pulse whose shape is Gaussian function, which is generated by Gaussian filter. It is the fastest transient pulse without overshoot and minimum group delay.