Concealment of Chaos Time-Delay Signature in Three-Cascaded Vertical-Cavity Surface-Emitting Lasers

Abstract

The time-delay signature and chaos bandwidth in three-cascaded vertical-cavity surface-emitting lasers (VCSELs) has been investigated experimentally. A peak value of autocorrelation coefficient at the feedback round trip time and the ratio between this peak value and its background are used to quantitatively identify the time-delay (TD) signature of chaos. A new conceptpeak to side-peak ratio is introduced for better quantification of the TD signature concealment. The peak to side-peak ratio is defined as the ratio between the peak value of autocorrelation coefficient at the TD and the peak value at a delay time other than the TD and zero delay time. Three injection cases, small bandwidth, intermediate bandwidth and wide bandwidth of the injecting chaos signals, have been used to study the effect of the bandwidth of the injecting chaos on the TD concealment. The experimental results show that the time-delay signature can be totally concealed in the slave laser subject to the intermediate bandwidth of chaotic optical injection over a wide frequency detuning range.

Simultaneous Chaos Time-Delay Signature Cancellation and Bandwidth Enhancement in Cascade-Coupled Semiconductor Ring Lasers

“…Outside the injection locking region, it is possible to cancel TDS and enhance bandwidth in SSRL at the same time, as can be seen from both figures. However, such region for achieving both goals is narrow, which confirms previous observations in cascaded-coupled systems consisting of conventional EELs [35] or VCSELs [34].…”

Enhancing optical-feedback-induced chaotic dynamics in semiconductor ring lasers via optical injection

“…This further confirms that the suppression of TD signatures and complexity enhancement are achieved, providing that the operation of the master-slave system stays away from injection locking. This has also been previously observed and explained for other optically injected laser systems [16,18]. Moreover, one can also notice the difference in complexity between the regions where all time-delays are effectively suppressed and where only the delay multiples can be identified [see Fig.…”

“…Particularly for chaos-based communications, early works on chaotic lasers with feedback showed that even when the TD signature is concealed in the intensity dynamics I(t) [8], it may in some cases still be inferred by applying the same identifiers to the optical phase dynamics ϕ(t) [9]. For these reasons, novel approaches for suppressing the TD signature in chaotic sources have been reported [10][11][12][13][14][15][16][17][18][19]. Optical injection has been shown as a possible way to generate enhanced chaotic signals, exhibiting suppressed TD signatures, improved chaos bandwidth and dynamical complexity.…”

Experimental investigation on the time-delay signature of chaotic output from a 1550 nm VCSEL subject to FBG feedback

“…VCSELs subject to suitable optical feedback can generate high Kaplan-Yorke dimension optical chaotic output and then apply to optical-chaos-based communication [1,2,7]. However, the chaotic output from external cavity feedback VCSELs (ECF-VCSELs) usually retains a time-delay signature (TDS) originated from the optical round trip between the VCSEL and the external feedback mirror [8][9][10][11][12][13][14], which may provide some possibilities to reconstruct the system by adopting time-series analysis techniques for delayed systems [15][16][17] and then threaten the system security. As a result, the TDS suppression has been a research hot spot in the field related to chaos generation and applications based on delayed VCSELs in recent years.…”

“…Liu et al proposed a three cascade-coupled configuration of VCSELs and numerically investigated the TDS and chaotic bandwidth of the output from the VCSELs [13]. Hong et al experimentally verified the performance of the threecascaded VCSELs in suppressing the TDS of chaos as well as the effect of injecting chaotic bandwidth on the TDS suppression [14]. It should be noted that, for the abovementioned schemes, external optical feedback is provided by mirrors.…”