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The study of nonlinear dynamical systems is a subject of much interest, one application being in secure communication systems realized through the synchronization of chaotic dynamical systems. In this paper optical coupling is used to effect synchronization between two diode lasers in a master-slave configuration, and we study the effect of frequency detuning between the master and slave lasers on the character of the observed synchronization. Experimental conditions are found under which the synchronization plot ͑formed by plotting the output power of the slave laser against that of the master at each instant in time͒ makes a transition from a positive gradient to a negative gradient. The appearance of such a negative gradient is a new phenomenon, to our knowledge, which we term ''inverse synchronization.'' A rate-equation model is proposed which accounts for light injection into the slave laser, and which agrees with the experimental results. Using this model, we etablish that inverse synchronization is caused by nonresonant coupling between the master and slave lasers.

Known hybrid orthogonal frequency division multiplexing-digital filter multiple access (OFDM-DFMA) PONs show promise of seamless and cost-effective convergence of optical and mobile networks for 5G and beyond. This paper reports, for the first time, a new hybrid OFDM-DFMA PON based on intensity modulation and direct detection (IMDD), obtained by modifying digital signal processing (DSP) algorithms embedded in both the OLT and ONUs. The proposed PON allows two spectrally overlapped sub-bands to occupy each individual sub-wavelength spectral region to independently transmit upstream ONU information. A model of the proposed PON is developed and its upstream transmission performances are numerically explored for different application scenarios. Compared with the previously published PON, the proposed PON doubles the number of supported ONUs and provides >1.7-fold aggregate upstream signal transmission capacity increases with <1.5dB upstream power budget degradations. Alternately, for the same ONU count, >2.2-fold aggregate upstream signal transmission capacity increases and >0.7dB upstream power budget improvements are achievable. The performance improvements vary by <18% for a transmission distance range as large as 50km. In addition, the proposed PON is tolerant to finite digital filter tap length-induced channel interferences.

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