autocorrelators

Autocorrelators are devices or software used to measure the autocorrelation of a signal, which is the correlation of a signal with a delayed version of itself as a function of that delay. They are employed in many fields to analyze periodicity, timing, or pulse shape, and they can be physical instruments or computational tools that produce the autocorrelation function from sampled data.

In digital signal processing, an autocorrelator multiplies the input signal by a version of itself shifted in time and integrates (or sums) the result over a suitable window. This can be done in real time with analog hardware or in software on digital samples. The resulting autocorrelation function reveals repeating patterns or characteristic time scales and is related to the signal’s spectral content through the Fourier transform.

Optical autocorrelators are specialized instruments used to characterize ultrafast laser pulses. They typically split a pulse into two copies, introduce a controllable delay between them, and recombine them in a nonlinear medium or interferometer. The detected signal as a function of delay yields the intensity autocorrelation, from which pulse duration can be inferred. More detailed information about the electric field can require techniques such as frequency-resolved optical gating (FROG) or SPIDER, which extract phase information beyond the intensity autocorrelation.

Limitations of autocorrelation measurements include the loss of phase information, meaning the autocorrelation does not uniquely determine the original waveform. In optical applications, recovering full pulse shape often requires additional measurements. Autocorrelators are widely used in communications, radar, lidar, spectroscopy, and pulse characterization, illustrating their role in both analysis and measurement of time-domain signals.