In this paper, we numerically investigate the performance of orthogonal optical chaotic division multiplexing (OOCDM) based on active–passive decomposition utilizing semiconductor lasers. To the best of our knowledge, it is the first time that two necessary conditions including chaotic synchronization condition and orthogonal condition of chaotic carriers are defined to quantify the performance of OOCDM. The chaotic characteristics of the output optical powers, including time traces, RF power spectra, and auto-correlation function, are numerically analyzed. The effects of spontaneous emission noise and the following internal and external parameter mismatch on the performance of OOCDM are analyzed in detail, which include gain saturation coefficient, photon lifetime, carrier decay rate, carrier number at transparency, differential gain, linewidth enhancement factor, and pumping current. The numerical results show that the proposed OOCDM system is robust towards spontaneous emission noise and parameter mismatch for certain relative mismatch ratios.
Chaotic optical communications is an encryption protocol for fiber-optic communications at the physical layer. For this encryption protocol, a message is embedded within a chaotic carrier generated by a transmitter, and recovered by a receiver upon synchronization with chaotic transmitter [1]. Chaotic carrier generation and chaotic synchronization have been realized utilizing CO2 lasers, fiber lasers, solid-state lasers, semiconductor lasers and so on. Due to the following merits of semiconductor lasers: low cost, small size, high efficiency, low power consumption, and so on, chaotic optical communications using semiconductor lasers has attracted extensive research interest during the past decade [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13] and [14]. Argyris et al. successfully realized a field trial chaotic optical communications for transmission rate of 1 Gbits/s, and bit error rate of 10−7 in a 120-km commercial single optical fiber [1]. This is a milestone opening the door to the practical applications of chaotic optical communications. During recent years, the practical issues for chaotic optical communications mainly focus on the chaotic photonic integrated circuits (PICs) [15], multiplexing [16], bidirectional communications [17], bandwidth enhancement [18], security analysis [19] and [20], transmission rate increase [21], generation of novel chaotic carriers [22], [23] and [24], etc.
Multiplexing is an important aspect for this technique, which can realize multiple-channel transmission in a single optical fiber to economize link resources. WDM for chaotic optical communications includes two aspects: WDM between chaotic optical channel and conventional optical channel, and WDM among multiple chaotic optical channels. For the former, Zhang et al. numerically studied the DWDM transmission between chaotic optical channel and conventional optical channel [25]. Argyris et al. experimentally demonstrated the corresponding results [26]. For the later, Zhao et al. studied the performance for DWDM among triple chaotic optical channels [27]. However, the orthogonal optical chaotic division multiplexing (OOCDM) can obviously economize the optical link resources. Rontani et al. pointed out that OOCDM can be realized utilizing active–passive decomposition (APD) [28]. Nevertheless, to the best of our knowledge, the orthogonal performance of optical chaotic division multiplexing, including necessary conditions, robust orthogonality, chaotic synchronization against parameter mismatch, has not yet been analyzed in detail.
In this paper, the performance for OOCDM based on APD is demonstrated numerically. The necessary conditions for OOCDM are proposed and analyzed by quantifying the system performance with the variation of the parameter values of the transmitters and spontaneous emission noise
In this paper, we numerically study the performance of the OOCDM based on semiconductor lasers. The active–passive decomposition method is adopted to achieve OOCDM. Two necessary conditions for the orthogonal multiplexing are proposed. The effect of spontaneous emission noise and parameter mismatch including gain saturation coefficient, photon lifetime, carrier decay rate, carrier number at transparency, differential gain, linewidth enhancement factor, and pumping current on the orthogonal multiplexing is analyzed in detail. The results show that the system is very robust against parameter variation. The results presented in this paper are important for the practical application of chaotic optical communications. The future research of OOCDM will focus on message transmission performance utilizing the system. These issues may include message encryption protocols, bit rate, and the chaos-pass filtering effect for receivers.
