PTB News 1/2005 (135 kB) PTB News 1/2005, English edition, Issue May 2005In future optical telecommunication systems bit rates of up to 640 Gbit/s will be achieved. For timely provision of the measurement technology needed to characterize the employed system components PTB has developed an ultra fast optical sampling oscilloscope with a temporal resolution below 100 fs.
As a consequence of the steadily increasing bandwidth requirements for world-wide telecommunications systems, not only the transmission via glass fibres, but also the data distribution in routers and switches will be all-optical. Laboratory applications in optical time division multiplexing today already achieve transmission rates of up to 320 Gbit/s. New ultra fast optical measuring techniques will become necessary.
Hitherto deployed electronic sampling oscilloscopes with a maximal bandwidth of 80 GHz are no longer suitable for future highest-bit-rate systems. Optical sampling oscilloscopes, on the other hand, are suited. In these the light signal is not directly transformed into an electrical signal by a photodetector but first probed with very short light pulses at a low repetition rate. By means of a nonlinear optical process the product of the momentary data signal and the sampling pulse is formed. Repetitive scanning of the data signal at different points in time subsequently yields a highly-resolved image of the time dependent course of the signal.
Precondition is that the sampling pulse is synchronized with the data stream. The PTB optical sampling oscilloscope exploits techniques developed by PTB for high-precision time and frequency measurements. It utilizes a novel synchronisation method with unique properties. In result a temporal resolution below 70 fs is achieved. The timing instability amounts to a few femtoseconds. Need for such optical sampling oscilloscopes is also found in the diagnosis of ultra short pulses, for instance, in femtochemistry.