Abstract:
The design and optimisation of optical communication systems requires methods
of measuring the intensity and phase of ultra-short (<10ps), high bit rate (10-
40GHz) optical pulses. Conventional methods of ultra-short pulse characterisation
are based on nonlinear optical processes. For high duty cycle pulse trains, such as
those used in communication systems, the sensitivity of instruments based on these
nonlinear processes is very poor. This has Ied to the development of linear phasesensitive
measurement techniques based on high speed optical modulators. This
thesis presents the implementation and comparison of several of these linear phase
sensitive methods of ultra-short optical pulse characterisation. Several applications
of these techniques in the measurement of optic communication grade pulses have
been investigated and developed.
A self-contained, real-time linear Spectrographic pulse measurement apparatus
has also been developed. The instrument employed an Electroabsorption Modulator
(EAM) followed by an electrically tunable fibre Fabry-Perot filter and a IOMHz
InGaAs detector. Together with purpose developed software, the instrument could
acquire and invert spectrograms at 8Hz. This allowed the real-time optimisation
of pulses and systems. The instrument was tested by measuring a range of Cband,
10-40GHz optical pulses with widths down to 2.4ps. The use of electro-optic
intensity and phase modulators in place of the EAM was trialled and found to be
a viable alternative. This significantly extends the useable wavelength range of the
instrument.
Three other phase-sensitive measurement techniques were implemented and used
to verify the results from the linear Spectrographic setup. These included Second-
Harmonic Generation Freqnency Resolved Optical Gating (SHG-FROG), interferometric
and tomographic pulse measurements. The results from the four methods
showed good agreement.
The linear Spectrographic setup was also used successfully and with great benefit
in three different applications, including high speed optical modulator characterisation
and pulse compression.