After presenting all kinds of calibrating methods to calibrate the magnitude response and risetime of the digital
oscilloscope, this paper describes the method that by using femto-second laser pulse to illuminate high-speed
photo-detector ultra-fast electrical pulses with only 10ps risetime which are supposed to calibrate the oscilloscope can be
generated. In experiment the 12GHz real-time digital oscilloscope has been calibrated successfully. This method has
some advantages such as simple structure, convenience in using and great application potential.