[en] Synchronisation of chaotic systems is a fascinating subject both from the viewpoint of Nonlinear Science as well as for the development of new generation concealed communication technology. Spectacular achievement from the viewpoint of technology development is the real-time successful demonstration of optical chaotic carrier based concealed communications at Gigabits per sec using commercial fibre-optic links. Till recently, the transmitters had been made chaotic by time delayed (optical) amplified opto-electronic feedback. The chaotic transmitter output next carried the signal (in optical form) through the fibre channel to the receiver. An appropriate (optical) amplified opto-electronic injection was made to the receiver that led latter to become chaotic as well as synchronised. The nature of chaos, used for such transmission, can be broadly classified into two categories: weak and strong. The distinction can be made by time series, autocorrelation and spectral analyses of the chaotic dynamics. The noisy periodic temporal dynamics of weak chaos reveals repetitive uniformly spaced secondary peaks in autocorrelation analysis and dominance of repetitive uniformly spaced spectral lines over relatively weak chaotic continuum in Fourier Spectrum. In contrast, in the case of strong chaotic regime, the temporal behavior exhibits noise like dynamics. Consequently, all repetitive secondary peaks disappear in the autocorrelation analysis and the array of spectral lines gets submerged in strong continuum in Fourier analysis. Since, weak chaos poses a serious limitation from the viewpoint of security, the transmitter and receiver lasers should preferably be operated in strong chaotic regime. However, to our knowledge, excellent synchronisation (cross-correlation coefficient 0.9 or more) has not been achieved so far when transmitter has been made strong chaotic by time delayed optical feedback. In this paper, we show experimentally that by injecting from another strong chaotic laser ('drive laser') to the transmitter laser, excellent synchronisation between strong chaotic transmitter and receiver lasers is realisable. (author)