EXFO PSO-200 Optical Modulation Analyzer - Manual (Page 268)

Measurement Definitions
260 PSO-200
Measurements for Eye Diagrams
Duty Cycle
The duty cycle is defined only for RZ formats as the ratio between the pulse
width (read at 50 % of the one level) and the pulse repetition time.
Duty Cycle Distortion
The duty cycle distortion (DCD) is a measurement of the time separation of
the rising and falling edge of the eye at the center (50 %) level. It is defined
in percentage of the symbol period as:
In a “perfect” eye with no timing and amplitude jitter, and a 50 % crossing,
the DCD is zero.
Pulse width
Pulse repetition time
DCD 100%
T
rise,center
T
fall,center
–
symbol period
------------------------------------------------------ =
Symbol period
DCD time