Slave Vertical-cavity Surface-emitting Lasers Research Articles

Evolution of time-delay signature of polarized chaos in a unidirectional-coupling VCSEL system with variable-polarization optical injection.

The evolution characteristics of the time-delay signature (TDS) of polarized chaos is systematically investigated in a unidirectional-coupling vertical-cavity surface-emitting (VCSEL) scheme with variable-polarization optical injection (VPOI), by means of the time series, optical spectra, power spectra, and autocorrelation function. In this scheme, the polarized chaos with TDS from a master VCSEL (M-VCSEL) with the external cavity is unidirectionally injected into another solitary slave VCSEL (S-VCSEL) through VPOI. The numerical results show that the VPOI can exert significant influence on the TDS characteristics of polarized chaos in the S-VCSEL. Under special injection parameters, as the polarization injection angle (θp) of VPOI varies, the TDS evolution for the X polarization component can exhibit almost an opposite evolutionary pattern to that for the Y polarization component in the S-VCSEL. A series of TDSs is mapped in the θp plane, and the injection strength and frequency detuning have been simulated to thoroughly elaborate the TDS evolution of polarization-resolved chaos in the S-VCSEL. Moreover, the optimal parameter spaces with effectively suppressed TDS are also determined for each polarization component in those maps.

Time-delay signature suppression of polarization-resolved wideband chaos in VCSELs with dual-path chaotic optical injections.

The combining investigation on the time-delay signature (TDS) and chaos bandwidth have been theoretically investigated in a vertical-cavity surface-emitting laser (VCSEL) system with dual-path chaotic optical injections. In this scheme, the polarized chaos with the TDS from an external-cavity master VCSEL is routed into two different paths and then unidirectionally injected into another solitary slave VCSEL. With the aid of the autocorrelation function and the effective bandwidth calculation, the TDS and bandwidth of polarized chaos from the chaotic system are quantitatively evaluated. The results show that, in such a dual-path chaotic optical-injection system, the high-quality polarized chaos with the successful TDS suppression and chaotic bandwidth enhancement can be achieved in wider parameter regions in contrast with the case for the single-path chaotic optical injection. Further research also finds that the injected time-delay difference between two injection paths is desired to mismatch the feedback time delay, which is conducive to suppressing TDS and expanding bandwidth of polarized chaos. Besides, the better chaotic quality with low TDS and wide bandwidth can be expected by choosing the appropriate injection strengths of two injection paths.

All-Optical VCSEL-to-VCSEL Injection Based on Cross Gain Modulation for Routing in Multinode Flexible Spectrum Optimization in Optical Fibre Transmission Links

In this paper, we experimentally present a novel, all-optical spectral efficient vertical-cavity surface-emitting laser- (VCSEL-) based technique for routing and spectrum assignment in optical networks. Exploiting all optical VCSEL-to-VCSEL injection to attain cross gain modulation, the optical transmitter is optimized for optical transmission paths to assure quality of service by overcoming blockage for differentiated bandwidth demands during network congestion incidences. A 10 Gbps directly modulated 1549 nm master VCSEL is optically injected into the 1549 nm side modes of a 1550 nm slave VCSEL. The Shannon limit is considered for higher transmission rates with the problem decomposed into degraded routing and spectrum assignment and chromatic dispersion in the optical transmission link penalties. In this work, the proposed technique achieved a 1.3 dB penalty for transmission over a 25 km G.655 nonzero dispersion-shifted single-mode optical fibre, a value within the transmission media and optical system characteristics of 3 dB as recommended by the International Telecommunication Union-Telecommunication (ITU-T). The number of transceivers, switches, and optical transmission links in the network was reduced, increasing the number of satisfied bandwidth requests, thus optimizing the spectral resource utilization.

Dual-channel physical random bits generation by a master-slave vertical-cavity surface-emitting lasers chaotic system

Taking the chaotic output from a master-slave framework chaotic system as chaotic entropy resource, we propose a scheme for acquiring dual-channel high-speed physical random bits (PRBs). For such a scheme, a vertical-cavity surface-emitting laser (VCSEL) under polarization-preserved optical feedback from a fiber Bragg grating is utilized as the master VCSEL (M-VCSEL). Under suitable operating parameters, both X and Y polarization components (X-PC and Y-PC) of the M-VCSEL can output chaotic signals with comparable power and weak time-delay signatures. The chaotic outputs from the X-PC and Y-PC of the M-VCSEL are divided into two parts, and then injected into the corresponding polarized component of another VCSEL (named as slave VCSEL, S-VCSEL) after undergoing different flight-time, and such an injection method is named as dual-path polarization-preserved optical injection (DP-PPOI). The X-PC and Y-PC in the S-VCSEL under DP-PPOI can simultaneously output chaotic signals with enhanced bandwidth, which are quantified by 8-bit analog-to-digital converters and taken as the entropy sources for generating dual-channel bit sequence after adopting m least significant bits (m-LSBs) extraction and logical exclusive-OR post-processing. Finally, the randomness of the bit sequences generated under optimized parameters is tested by NIST SP 800-22 statistical test suite. The results demonstrate that dual-channel random bits at rate of 500 Gbit s−1 can be obtained, and the rate of random bits can be further increased to 1 Tbit s−1 through adopting cross-merging method.

Analysis and characterization of chaos generated by free-running and optically injected VCSELs.

We report on the dynamics of free-running and optically injected VCSELs. In particular, the powerful measures including the 0-1 test for chaos and permutation entropy are used for locating the chaotic dynamics in a free-running VCSEL, which illustrates the effects of some key parameters on the chaotic region. In order to enhance chaotic dynamics, the output of the free-running VCSEL (master) is injected to another free-running VCSEL (slave). Our results show that the chaotic dynamics of the slave VCSEL can be greatly enhanced, i.e., both the bandwidth and complexity, while this occurs only outside of the injection locking region where the correlation between the mater and slave lasers is low. To take advantage of these enhanced chaotic dynamics exhibiting extremely high complexity and broadband bandwidth, a three-laser synchronization scheme is proposed and demonstrated. These findings pave the way to the generation of high-quality chaos (no time-delay signature, high bandwidth and complexity) and notably chaos-based applications based on free-running and optically injected VCSELs.

Complex-enhanced chaotic signals with time-delay signature suppression based on vertical-cavity surface-emitting lasers subject to chaotic optical injection

A chaotic system is constructed on the basis of vertical-cavity surface-emitting lasers (VCSELs), where a slave VCSEL subject to chaotic optical injection (COI) from a master VCSEL with the external feedback. The complex degree (CD) and time-delay signature (TDS) of chaotic signals generated by this chaotic system are investigated numerically via permutation entropy (PE) and self-correlation function (SF) methods, respectively. The results show that, compared with master VCSEL subject to optical feedback, complex-enhanced chaotic signals with TDS suppression can be achieved for S-VCSEL subject to COI. Meanwhile, the influences of several controllable parameters on the evolution maps of CD of chaotic signals are carefully considered. It is shown that the CD of chaotic signals for S-VCSEL is always higher than that for M-VCSEL due to the CIO effect. The TDS of chaotic signals can be significantly suppressed by choosing the reasonable parameters in this system. Furthermore, TDS suppression and high CD chaos can be obtained simultaneously in the specific parameter ranges. The results confirm that this chaotic system may effectively improve the security of a chaos-based communication scheme.

Key distribution based on unidirectional injection of vertical cavity surface emitting laser system

Random source is important for the security of key distribution. In this paper, a novel secure key distribution scheme based on unidirectional injection of vertical cavity surface emitting laser (VCSEL) system is proposed. In the proposed scheme, a chaotic signal without time delay signature is generated by a VCSEL subject to unidirectional optical injection, which is regarded as a master laser. The chaotic signal generated by the master VCSEL is further injected into two slave VCSELs to obtain synchronized bandwidth-enhanced chaotic signals. After that, by sampling, quantizing and XOR operation on the two synchronized chaotic signals, two key streams can be obtained. Based on the well-known spin-flip model, the time delay signature of chaotic signals generated by master VCSEL and the synchronization performance between the master VCSELs and two slave VCSELs are numerically investigated in detail. It is shown that by the unidirectional injection, the chaotic outputs can be achieved in the master VCSEL in a wide range of frequency detuning and coupling strength. More importantly, no time delay signature can be observed in the auto correlation function of the chaotic intensity time series generated by the master VCSEL. Besides, we find that high quality synchronization is achieved between the bandwidth-enhanced chaotic signals generated by two slave VCSELs under the common driving of master VCSEL. The synchronization coefficient between two slave VCSELs increases up to 0.99, and the synchronization coefficient between master VCSEL and salve VCSEL is only 0.74. Note that such a high quality synchronization between two slave VCSELs while relatively low quality synchronization between the master and slave VCSEL is conducible to ensuring the security of key distribution. In addition, the effects of tunable parameters on key bit error rate are considered, and two quantization methods are employed for comparison. Numerical simulation results show that the key bit error rate between two legitimate users is as low as 1%, and the key bit error rate between legitimate user and eavesdropper is higher than 10% in the single-threshold case; the bit error rate can even be as low as 10-6 in the double-threshold case. The influence of parameter mismatch on key bit error rate is also discussed, and it is suggested that two salve VCSELs should be finely matched to ensure low bit error rate. Finally, NIST randomness test is performed for the generated key streams. Hence, the proposed scheme enhances the security of key distribution, which is valuable for further developing the chaos communication systems.

Wideband Polarization-Resolved Chaos With Time-Delay Signature Suppression in VCSELs Subject to Dual Chaotic Optical Injections

Both the polarization-resolved chaotic bandwidth enhancement and time-delay signature suppression have been numerically investigated based on a slave vertical-cavity surface-emitting laser (S-VCSEL) driven by dual chaotic optical injections (DCOIs) from two master VCSELs (M-VCSELs) under optical feedbacks. The bandwidth and time-delay signature of polarization-resolved chaos generated in VCSELs are evaluated quantitatively via the effective bandwidth and autocorrelation function, respectively. The results show that, in contrast to the polarization-resolved chaos generated from S-VCSEL subject to single chaotic optical injection, for the equivalent injection conditions, the chaos generated by the DCOI configuration can simultaneously realize the bandwidth enhancement and time-delay signature suppression in the distinctly wider injection parameter spaces of injection strength and frequency detuning. By further exploring the influences of different injection parameters from two injection M-VCSELs on the bandwidth and time-delay signature of chaos, it is found that for the DCOI, the moderate injection strengths and relatively larger frequency detuning of two different injection paths are preferred to obtain the desired wideband polarization-resolved chaos with successful time-delay signature suppression.

Anticipation in the Polarization Chaos Synchronization of Uni-Directionally Coupled Vertical-Cavity Surface-Emitting Lasers With Polarization-Preserved Optical Injection

We investigate numerically the anticipated synchronization in the two uni-directionally coupled vertical-cavity surface-emitting lasers (VCSELs) as master and slave configuration. The master VCSEL is rendered chaotic state by an isotropic optical feedback and master’s chaotic output uni-directionally injected to a slave VCSEL under polarization-preserved optical injection. The synchronization quality and lag time between lasers are obtained by performing cross-correlation analysis. When the laser’s parameters are identical, a regime of anticipatory synchronization is found in both of the linearly polarized mode dynamics of the master and slave lasers, if the feedback delay time is greater than the coupling time. Anticipation is robust to a small variation in injection rate, frequency detuning, and laser’s internal parameter mismatches, but the synchronization is not complete. Injection-locking synchronization regime occurs between master and slave lasers for higher injection, positive detuning, and larger mismatch in the internal parameters. We show the mapping of synchronization quality, sustenance of anticipatory synchronization and switching of regimes in the injection rate and parameter mismatch plane. The anticipation maintained even for higher injection rates if mismatch is introduced in certain internal parameters.

Real-time multi-target ranging based on chaotic polarization laser radars in the drive-response VCSELs.

According to the principle of complete chaos synchronization and the theory of Hilbert phase transformation, we propose a novel real-time multi-target ranging scheme by using chaotic polarization laser radar in the drive-response vertical-cavity surface-emitting lasers (VCSELs). In the scheme, to ensure each polarization component (PC) of the master VCSEL (MVCSEL) to be synchronized steadily with that of the slave VCSEL, the output x-PC and y-PC from the MVCSEL in the drive system and those in the response system are modulated by the linear electro-optic effect simultaneously. Under this condition, by simulating the influences of some key parameters of the system on the synchronization quality and the relative errors of the two-target ranging, related operating parameters can be optimized. The x-PC and the y-PC, as two chaotic radar sources, are used to implement the real-time ranging for two targets. It is found that the measured distances of the two targets at arbitrary position exhibit strong real-time stability and only slight jitter. Their resolutions are up to millimeters, and their relative errors are very small and less than 2.7%.

Performances of time-delay signature and bandwidth of the chaos generated by a vertical-cavity surface-emitting laser under chaotic optical injection

Time-delay signature (TDS) and effective bandwidth (EBW) are two key performance indexes to evaluate a chaos signal generated by a laser system including delay-time feedback. In this paper, we propose and simulate a technical scheme to optimize the TDS and EBW of chaotic signal generated by a slave vertical-cavity surface-emitting laser (S-VCSEL) under chaotic optical injection from a master vertical-cavity surface-emitting laser (M-VCSEL), which is subjected to double external-cavity feedback. First, based on the spin-flip model of a VCSEL subjected to two double external-cavity feedback, the time series of two orthogonal polarization components (referred to as X-component (X-PC) and Y-component (Y-PC), respectively) in the M-VCSEL can be obtained. Furthermore, with the help of self-correlation function (SF) analysis method, the TDSs of X-PC and Y-PC can be evaluated. The results show that through selecting suitable system operation parameters, X-PC and Y-PC in the M-VCSEL can simultaneously output chaotic signals with equivalently average intensity and weak TDS. Under optimized operation parameters, the peak values of the SF (σ) of the chaotic signal are 0.20 for X-PC and 0.16 for Y-PC, respectively, and the EBWs of the chaotic signal are 10.72 GHz for X-PC and 10.10 GHz for Y-PC, respectively. The chaotic signals output from the M-VCSEL under optimized operation parameters are injected into the S-VCSEL for further weakening TDS and enhancing EBW. Through examining the evolution rules of TDS and EBW of polarization-resolved chaotic signals in the parameter space composed of injection strength and frequency detuning, the ranges of optimizing injection parameters are determined for achieving two-channel chaotic signals with well suppressed TDS (σ 15 GHz).

Reconfigurable high-speed optical fibre networks: Optical wavelength conversion and switching using VCSELs to eliminate channel collisions

Abstract We experimentally provide an alternative solution to channel collisions through up-wavelength conversion and switching by using vertical cavity surface-emitting lasers (VCSELs). This has been achieved by utilizing purely optical wavelength conversion on VCSELs at the low attenuation, 1550 nm transmission window. The corresponding transmission and bit error-rate (BER) performance evaluation is also presented. In this paper, two 1550 nm VCSELs with 50–150 GHz channel spacing are modulated with a 10 Gb/s NRZ PRBS 2 7 -1 data and their interferences investigated. A channel interference penalty range of 0.15–1.63 dB is incurred for 150–50 GHz channel spacing without transmission. To avoid channel collisions and to minimize high interference penalties, the transmitting VCSEL with data is injected into the side-mode of a slave VCSEL to obtain a new up converted wavelength. A 16 dB extinction ratio of the incoming wavelength is achieved when a 15 dBm transmitting beam is injected into the side-mode of a −4.5 dBm slave VCSEL. At 8.5 Gb/s, a 1.1 dB conversion and a 0.5 dB transmission penalties are realized when the converted wavelength is transmitted over a 24.7 km G.655 fibre. This work offers a low-cost, effective wavelength conversion and channel switching to reduce channel collision probability by reconfiguring channels at the node of networks.

Photonic generation of polarization-resolved wideband chaos with time-delay concealment in three-cascaded vertical-cavity surface-emitting lasers.

Optical chaos generated by chaotic lasers has been widely used in several important applications, such as chaos-based communications and high-speed random-number generators. However, these applications are susceptible to degradation by the presence of time-delay (TD) signature identified from the chaotic output. Here we propose to achieve the concealment of TD signature, along with the enhancement of chaos bandwidth, in three-cascaded vertical-cavity surface-emitting lasers (VCSELs). The cascaded system is composed of an external-cavity master VCSEL, a solitary intermediate VCSEL, and a solitary slave VCSEL. Through mapping the evolutions of TD signature and chaos bandwidth in the parameter space of the injection strength and frequency detuning, photonic generation of polarization-resolved wideband chaos with TD concealment is numerically demonstrated for wide regions of the injection parameters.

Generation of polarization-resolved wideband unpredictability-enhanced chaotic signals based on vertical-cavity surface-emitting lasers subject to chaotic optical injection.

A system framework is proposed and analyzed for generating polarization-resolved wideband unpredictability-enhanced chaotic signals based on a slave vertical-cavity surface-emitting laser (S-VCSEL) driven by an injected optical chaos signal from a master VCSEL (M-VCSEL) under optical feedback. After calculating the time series outputs from the M-VCSEL under optical feedback and the S-VCSEL under chaotic optical injection by using the spin-flip model (SFM), the unpredictability degree (UD) is evaluated by permutation entropy (PE), and the bandwidth of the polarization-resolved outputs from the M-VCSEL and S-VCSEL are numerically investigated. The results show that, under suitable parameters, both the bandwidth and UD of two polarization components (PCs) outputs from the S-VCSEL can be enhanced significantly compared with that of the driving chaotic signals output from the M-VCSEL. By simulating the influences of the feedback and injection parameters on the bandwidth and UD of the polarization-resolved outputs from S-VCSEL, related operating parameters can be optimized.

Control of the polarization switching and the nonlinear dynamic behaviors of vertical cavity surface-emitting lasers with external optical injection

For polarization switching (PS) and nonlinear dynamic behaviors (NDBs) of an optically injected laser system composed of a master vertical-cavity surface-emitting laser (VCSEL) and a slave VCSEL, we put forward a novel manipulation scheme by means of electro-optic (EO) modulation with quasi-phase matched technology. It is found that the PS of the slave VCSEL subject to parallel or orthogonal optical injection takes on a change of periodic oscillation with the applied transverse electric field. The optically injected slave VCSEL can experience different NDBs evolutions when the light from the master laser is modulated by the linear EO effect.

Analyses of the time-delay signature and bandwidth of the chaotic output from a master-slave vertical-cavity surface-emitting laser dynamical system

The time-delay signature (TDS) and the bandwidth (BW) are two important performance indexes to assess the chaos signal from a delayed laser system. Based on the spin flip model of vertical-cavity surface-emitting laser (VCSEL), we numerically investigate the characteristics of chaos dynamics in a master-slave VCSEL system, where a chaotic signal generated by a master VCSEL (M-VCSEL) under external optical feedback is unidirectionally injected into a slave VCSEL (S-VCSEL). The influences of injection strength, frequency detuning between M-VCSEL and S-VCSEL, and feedback strength of M-VCSEL on chaos TDS (including intensity TDS (I-TDS) and phase TDS (P-TDS)) and BW are investigated. The results show that by adjusting the injection strength and the frequency detuning, both I-TDS and P-TDS of two polarization components (referred to as X-PC and Y-PC respectively) of the chaotic output from the system can be suppressed simultaneously. Through further analyzing the influences of the injection strength and frequency detuning on the BW of chaotic signal, we find that the BWs of both X-PC and Y-PC of chaotic outputs can simultaneously exceed 30 GHz within a large negative frequency detuning range. Furthermore, by combining the evolution characteristics of the TDS and BW of chaotic outputs in the parameter space of injection strength and frequency detuning, the parameter region for generating the chaotic signals with wide BW and low TDS can be determined. In addition, by reasonably adjusting feedback strength, the quality of chaotic signal from the system can be further optimized.

Manipulation of the polarization switching and the nonlinear dynamic behaviors of the vertical-cavity surface-emitting laser subjected to optical injection by EO modulation

For the polarization switching (PS) and the nonlinear dynamic behaviors (NDBs) of the optically injected laser system composed of master vertical-cavity surface-emitting laser (M-VCSEL) and slave vertical-cavity surface-emitting laser (S-VCSEL), we put forward a novel manipulation scheme and explore their control law by means of electro-optic (EO) modulation with quasi-phase matched technology in periodically poled LiNbO3. It is found that the PS of the S-VCSEL subjected to parallel or orthogonal optical injection undergoes a change of periodic oscillation with the applied transverse electric field. The envelope trajectory of the oscillation peak appears to be a cosine curve, and that of the oscillation wave trough becomes a sine curve. Besides, the PS of the S-VCSEL only depends on the applied transverse electric field and the bias current of the M-VCSEL, and is independent of the bias current of the S-VCSEL. When the bias current of the M-VCSEL takes a different value, the PS of the S-VCSEL shows a different evolution law in one period of the applied electric field. For a certain fixed bias current of the M-VCSEL, the optically injected S-VCSEL can emit an arbitrary polarization mode and its NDBs experience different evolutions when the light from the M-VCSEL goes through EO intensity modulation. If the output light of the M-VCSEL is subjected to EO intensity modulation and EO phase modulation simultaneously, while the bias current of the S-VCSEL is fixed at 1.06, that of the M-VCSEL is fixed at 1.18, and the optical injection strength is set at 5 ns-1, then the output polarization of the S-VCSEL is in turn switched from the y-LP to the left-handed elliptic polarization (EP), then the right-handed EP circular polarization, and lastly the left-handed EP. And its NDB shows in turn a single period, four doubled periods, chaos, four doubled periods, and chaos with the increase of the applied electric field.

Two channel photonic microwave generation based on period-one oscillations of two orthogonally polarized modes in a vertical-cavity surface-emitting laser subjected to an elliptically polarized optical injection

Previous investigations demonstrated that a semiconductor laser subjected to optical injection can realize period-one (P1) oscillation output under suitable operational parameters, which can be used to obtain high quality photonic microwave. In this paper, we propose a scheme for simultaneously generating two channel photonic microwave based on the P1 oscillations of two orthogonally polarization modes in a vertical-cavity surface-emitting laser (VCSEL) subjected to an elliptical polarization optical injection, and the relevant characteristics of obtained photonic microwave are numerically simulated and analyzed. The results show that under suitable operational parameters, a free-running VCSEL (named master VCSEL, M-VCSEL) can output an elliptical polarization light in which both X and Y polarization components of the elliptical polarization light oscillate at the same frequency. By using the elliptical polarization light from the M-VCSEL as an injection light into another VCSEL (named slave VCSEL, S-VCSEL), both two polarization components of the S-VCSEL can be driven into P1 oscillation through selecting suitable injection strength under a fixed frequency detuning between the M-VCSEL and the S-VCSEL. Based on the P1 oscillation, two orthogonally photonic microwave signals can be obtained. With the increase of the injection strength from the M-VCSEL, the frequency of photonic microwave shows a gradually increasing trend while the power of photonic microwave displays an increasing process accompanied by slight ripples. Combining the distribution mappings of the frequency, the power, and the amplitude difference between the first sideband and the second sideband of the photonic microwave in the parameter space of the injection strength and the frequency detuning, certain regions with optimally operational parameters can be determined for acquiring high quality photonic microwave.

All-VCSEL Transmitters With Remote Optical Injection for WDM-OFDM-PON

We report on a novel scheme that uses vertical cavity surface emitting lasers (VCSELs) and remote optical injection technique in the hybrid wavelength division multiplexing orthogonal frequency division multiplexing (OFDM) passive optical network. In the proposed scheme, 1.55- μm VCSELs are used as low-cost, directly modulated upstream and downstream transmitters. The slave VCSEL at the optical network unit is remotely injection-locked by modulated downstream signals, and no need for additional injection-locking optical sources and external modulators. In our experiment, bidirectional transmission of 1.25 Gb/s 4-quadrature amplitude modulation (4QAM)-OFDM signal over 26-km single mode fiber has been successfully demonstrated. Moreover, we investigate the residual amplitude modulation (RAM) caused by the conversion of injected AM into slave AM. In addition, the experimental results show that due to this RAM, the power penalty of the 1.25 Gb/s 4QAM-OFDM upstream transmission is deteriorated by 2 dB.

Optical Injection Locking of Polarization Modes in VCSELs Emitting at 1.3 $\mu{\rm m}$ Wavelength

Injection locking of polarization modes of 1.3 μm wavelength vertical-cavity surface-emitting lasers (VCSELs) fabricated via wafer fusion is investigated. Maps of the injected modes in the frequency-power plane reveal the detailed response of the slave VCSEL to the optical injection, in agreement with numerical simulations of the system.