Detection of changes in the time gap of signals

 

A femto-second accurate measurement of the temporal relation between two optical signals and of an optical and a microwave signal provides a variety of application possibilities. A highly precise synchronisation of various optical and electrical signals and high-resolution applications in metrology are some examples for that.

Fields of Application

  • Telecommunication
  • Navigation systems
  • Data transfer
  • Surveying

Problem

The main problems of the previously used methods for measuring the temporal relation between two pulsed optical signals or a pulsed optical signal and a microwave signal are the low long-term stability on one hand and a very complicated test setup on the other hand.
Presently, each of the optical signals is detected with a photo detector in order to measure the temporal relation between these two pulsed optical signals. A high harmonic of the basic laser frequency is being selected with a band-pass filter from the frequency spectrum and then a phase detector determines the temporal relation between the two signals afterwards. Temperature alteration in each of the three utilized components (photo detector, filter, phase detector) as well as a change of the optical output at the photo detector falsifies the measurement of the time offset.
This problem remains even when measuring the time offset of an optical and a microwave signal is done through a photo detector with a microwave oscillator replacing the filter.

Innovation

The developed method significantly reduces the dependency of the measurement results on the temperature and on the optical output. This method uses only one instead of two photo detectors for measuring the temporal relation between two optical signals so that the changes on the performance of the detector remain the same for both signals. Instead of a temperature-sensitive phase measurement, the performance of one or several laser harmonics (which change along with the temporal offset of both optical signals in this newly developed method) are being measured. As a result, changes in the performance of the optical signals can be distinguished from the changes in the temporal offset.
The developed method utilises an electro-optical amplitude modulator in order to convert changes in the temporal offset into a change in the frequency spectrum when measuring the time offset of an optical and a microwave signal. The temporal offset of the signals results from a performance measurement of the modulated laser spectrum. The temporal measurement resolution is better than 10 fs.