Zheng-Mao Wu

Suppression of time delay signatures of chaotic output in a semiconductor laser with double optical feedback.

We experimentally and numerically demonstrate the time delay (TD) signature suppression of chaotic output in a double optical feedback semiconductor laser (DOF-SL) system. Two types of TD signature suppression are demonstrated by adjusting the lengths and the feedback power ratios of the two external cavities. One can significantly eliminate all TD signatures of the DOF-SL system and the corresponding power spectrum distribution becomes quite smooth and flat, the other suppresses one of two TD signatures and remains another one.

Dual-channel chaos synchronization and communication based on unidirectionally coupled VCSELs with polarization-rotated optical feedback and polarization-rotated optical injection.

A novel dual-channel chaotic synchronization configuration is proposed. This system is constructed on the basis of two unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs), where a VCSEL subjected to polarization-rotated optical feedback is used as a transmitter and the other VCSEL subjected to polarization-rotated optical injection is used as a receiver. The synchronization and communication performances of such a system are numerically investigated. The results show that, similar to polarization-preserved coupled system with polarization-preserved optical feedback at the T-VCSEL port and polarization-preserved optical injection at the R-VCSEL port, such polarization-rotated coupled system can also realize complete synchronization between each pair of linear polarization (LP) modes and the total output of T-VCSEL and R-VCSEL. Compared with the polarization-preserved coupled system, this proposed system has higher tolerance to mismatched parameters. Furthermore, the average intensities of two orthogonal LP modes are almost the same so that this framework may be used to realize dual-channel chaos communication. Under the additive chaos modulation (ACM) encryption scheme, the encoded messages can be successfully extracted for both of orthogonal LP modes.

Evolution of time delay signature of chaos generated in a mutually delay-coupled semiconductor lasers system.

In this paper, evolution of time delay (TD) signature of chaos generated in a mutual delay-coupled semiconductor lasers (MDC-SLs) system is investigated experimentally and theoretically. Two statistical methods, including self-correlation function (SF) and permutation entropy (PE), are used to estimate the TD signature of chaotic time series. Through extracting the characteristic peak from the SF curve, a series of TD signature evolution maps are firstly obtained in the parameter space of coupled strength and frequency detuning. Meantime, the influences of injection current on the evolution maps of TD signature have been discussed, and the optimum scope of TD signature suppression is also specified. An overall qualitative agreement between our theoretical and experimental results is obtained.

Time delay signature concealment of optical feedback induced chaos in an external cavity semiconductor laser

The time delay (TD) signature concealment of optical feedback induced chaos in an external cavity semiconductor laser is experimentally demonstrated. Both the evolution curve and the distribution map of TD signature are obtained in the parameter space of external feedback strength and injection current. The optimum parameter scope of the TD signature concealment is also specified. Furthermore, the approximately periodic evolution relation between TD signature and external cavity length is observed and indicates that the intrinsic relaxation oscillation of semiconductor laser may play an important role during the process of TD signature suppression.

Theoretical investigations on the polarization performances of current-modulated VCSELs subject to weak optical feedback

Based on the framework of the spin-flip model (SFM) for GHz level modulation frequency, the polarization performances of current-modulated vertical-cavity surface-emitting lasers (VCSELs) subject to weak optical feedback have been theoretically investigated. The results show that, for type 1 polarization switching (PS), the influences of optical feedback intensity and the current modulation amplitude on the high-frequency modulation response is not obvious. For low-frequency modulation, optical feedback will result in the output of a VCSEL having rich dynamics. A new style PS can be obtained under large-signal modulation through adjusting the modulation frequency. For type 2 PS the situation is more complex, and optical feedback increases the probability of polarization conversion and competition, while also affecting the PS point. The modulation amplitude also affects the output dynamics of the VCSEL.

Isochronous Synchronization Between Chaotic Semiconductor Lasers Over 40-km Fiber Links

A long-distance isochronous chaos synchronization system, composed of a driving chaotic semiconductor laser and twin semiconductor lasers, is demonstrated experimentally. Via a driven chaotic signal which is generated by the driving chaotic semiconductor laser subject to external feedback and then injects into the twin semiconductor lasers by a pair of 20-km single-mode fibers, respectively, isochronous synchronization between the twin semiconductor lasers is experimentally observed. Further results show that high-quality isochronous synchronization can still be maintained even though the correlation coefficient between the driving laser and twin lasers is low. In addition, the bandwidth of synchronized chaotic signals is enhanced to more than 10 GHz although the bandwidth of driving signal is about 5.7 GHz.

Time-Delay Signature Suppression of Polarization-Resolved Chaos Outputs from Two Mutually Coupled VCSELs

Time-delay (TD) signature performances of polarization-resolved chaos outputs from two mutually coupled vertical-cavity surface-emitting lasers (MC VCSELs) are investigated through detailed simulations by means of self-correlation function (SF) and permutation entropy (PE). The results show that, under suitable coupling strength (η) and frequency detuning (Δf) between the two MC VCSELs, the TD signatures of two polarization modes from each VCSEL can be suppressed simultaneously. Furthermore, based on the map of TD signature evolution in the parameter space of Δf and η, the optimal parameter region of TD signature suppression has been determined.

Parallel generation of 10 Gbits/s physical random number streams using chaotic semiconductor lasers

In this paper, we have realized experimentally, for the first time to our knowledge, a parallel generation scheme of high speed random numbers by using chaotic laser. In our setup, two broadband chaos signals are obtained experimentally from a mutually coupled semiconductor lasers system. The bandwidths of these signals are over 10 GHz. Next, by using such chaos signals as entropy sources, two 10 Gbits/s physical random number streams are generated concurrently and successfully pass the NIST statistical tests. Our system is scalable and the rate of random numbers could be further enhanced by simply adding more channels.

Simultaneous Generation of Two Sets of Time Delay Signature Eliminated Chaotic Signals by Using Mutually Coupled Semiconductor Lasers

Simultaneous generation of two sets of time delay (TD) signature suppressed chaotic signals is experimentally demonstrated by using a mutually delay-coupled semiconductor laser (MDC-SL) system. The experimental results show that under proper conditions, TD signatures of chaotic output signals in such a system can be eliminated, and two sets of low TD signature chaotic signals can be simultaneously obtained. Furthermore, both the TD signature evolution pattern and the optimum scope for TD signature elimination are experimentally specified by modulating the coupling strength and adjusting frequency detuning between the two mutually coupled lasers.

Crosstalk Noise Analysis and Optimization in 5

Crosstalk noise is an intrinsic characteristic of photonic devices used by optical router which is used in optical networks-on-chip. It also adds a new dimension to the design of the optical router based on the photonic devices. We analyzed crosstalk noise at device level and router level. Based on the detailed analysis, we proposed a general analytical model to study the transmission loss, crosstalk noise, optical signal-to-noise ratio (OSNR), and bit error ratio in the 5 × 5 hitless optical router. For the first time, this paper used the crossing angles of 60° or 120° instead of the conventional 90° crossing angle to design the optical router. It is obtained that by using this method OSNR is improved by about 10 dB.