Surface-emitting Laser Subject Research Articles

Experimental Investigations on Polarization Switching and Bistability in a 1550 nm VCSEL Subject to Orthogonal Optical Injection With Time-Varying Injection Power

Polarization switching (PS) and polarization bistability (PB) characteristics of a 1550 nm vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection (OOI) with time-varying injection power are experimentally investigated for the first time. To implement the optical injection, a Mach-Zehnder modulator (MZM) modulated by a triangular radio wave is adopted, and the influences of some typical parameters on the performances of PS and PB are analyzed. Under suitable operation conditions, PB in the VCSEL subject to OOI with time-varying injection power can be observed only for the input power P0 of MZM locating within a determined range, and the width of hysteresis loop gradually decreases with the increase of P0 from the minimum P0, min to the maximum P0, max. Under different frequency detuning Δ ν between the injection light and the X polarization mode of the VCSEL, the determined ranges of P0 required for PB are different. With the variation of Δ ν from a negative value to a positive value, both P0, min and P0, max present a trend of decrease first and then increase. Additionally, with the increase of the modulation frequency, the hysteresis loop width firstly increases rapidly and then gradually tends saturation.

Frequency-induced polarization switching and bistability in a 1550 nm VCSEL subject to parallel optical injection

We experimentally investigate frequency-induced polarization switching (PS) and bistability (PB) characteristics in a 1550 nm vertical-cavity surface-emitting laser (1550 nm VCSEL) subject to parallel optical injection, for which the polarization direction of the injection light is along with the direction of dominant polarization mode in the solitary 1550 nm VCSEL. The results show that, for a 1550 nm VCSEL under parallel optical injection with frequency detuning ∆ν (= νinj − ν0, where νinj is the frequency of injection light and ν0 is the frequency of dominant polarization mode of the solitary 1550 nm VCSEL), type I PS (the dominant polarization mode switches from Y-polarization mode with a shorter wavelength to X-polarization mode with a longer wavelength) and type II PS (the dominant polarization mode switches from X-polarization mode to Y-polarization mode) can be observed through continuously scanning the frequency of injection light. Moreover, the values of ∆ν required for generating PSs are dependent on the variation route, namely frequency-induced PB phenomenon occurs. In the region with negative ∆ν, there exist two hysteresis loops, whose widths are seriously influenced by the injection power and the biased current.

Polarization Bistability in a 1550 nm Vertical-Cavity Surface-Emitting Laser Subject to Variable Polarization Optical Injection

The polarization bistability (PB) features in a 1550 nm vertical-cavity surface-emitting laser (1550 nm-VCSEL) subject to variable polarization optical injection (VPOI) are experimentally investigated. We have investigated the influence of polarization angle $\theta _{p}$ of optical injection on PBs induced by scanning the power (power-induced PB) and the frequency of injected light (frequency-induced PB) along with different routes. The experimental results show that, for the fixed frequency of the injection laser and by scanning the injection power within a certain region, there exists a determined range of $\theta _{p}$ in which power-induced PB in the 1550 nm-VCSEL subject to VPOI can be observed. For VPOI with $\theta _{p}$ located within the determined range, the power-induced PB possesses larger hysteresis width, as compared with orthogonally polarized optical injection. The hysteresis width will be larger for a smaller value of $\theta _{p}$ . Under the condition of fixed injection power and continuously varying the frequency of the injection laser, two frequency-induced hysteresis cycles can be observed, of which one is located at negative frequency detuning, and the other is located at positive frequency detuning. The variations of the two hysteresis width with $\theta _{p}$ exhibit different trends. Also, when the bias current of the 1550 nm-VCSEL increases, the hysteresis width can be further broadened for the power-induced PB, and the broadening effect is relatively weak for the frequency-induced PB.

Polarization Switching Characteristics of 1550-nm Vertical-Cavity Surface-Emitting Lasers Subject to Double Polarization Pulsed Injection

Based on the spin-flip model, the polarization switching (PS) characteristics of two polarization outputs in a 1550-nm vertical-cavity surface-emitting laser (1550-nm VCSEL) subject to double polarization pulsed injection (DPPI) are investigated theoretically, and the obtained results are compared with the case, in which the 1550-nm VCSEL is simultaneously injected by the pulses of orthogonal polarized light and a continuous wave (CW) parallel polarized light, which is called double optical injection with pulsed orthogonal polarization (DIPOP). The simulated results show that, compared with the DIPOP, the DPPI method is beneficial to improving the PS performance under suitable parameters. The influences of the timing difference (Δt) in the switching of two injection pulses on the PS performance of 1550-nm VCSEL subject to DPPI are analyzed, and the optimized values of At under different bias currents are determined. Furthermore, for optimized At, the dependences of the switching times on the amplitudes of two polarization pulses and the frequency detuning are given.

Polarization Switching Regions of Optically Injected Long-Wavelength VCSELs

We report on an experimental study of the injected optical power required for polarization switching (PS) in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection. This power is found as a function of the frequency detuning between the injected light and suppressed linear polarization of the solitary VCSEL. Increasing the injected power, we found two types of PS when injecting light with wavelength close to the wavelength of the suppressed linear polarization and to that of the linear polarization of the solitary VCSEL. These two types of PS are, respectively: 1) single and double (with two minima of injected power necessary for PS) and 2) double PS (with two islands of PS and a separate region with a single minimum of injected power). Our experimental results confirm the theoretical predictions of Torre et al. Double PS is observed around the elliptically polarized injection locked states found by Lin et al. Different dynamics are found in the route to PS.

Nonlinear Dynamics of 1550-nm VCSELs Subject to Positive Optoelectronic Feedback

We report an experimental investigation on the nonlinear dynamics of a 1550-nm vertical-cavity surface emitting laser subject to positive optoelectronic feedback. A bifurcation diagram of the extrema of output peak series versus the feedback strength is plotted. Various nonlinear dynamical behaviors including regular pulsing, quasiperiodic pulsing, chaotic pulsing, and mode locking (ML) have been experimentally observed. A mapping of dynamical states is presented in the parameter space of bias current and feedback strength, where different states are identified and shown.

Nonlinear dynamics of 1550 nm VCSELs subject to polarization-preserved optical feedback and orthogonal optical injection

Based on spin-flip model (SFM), the nonlinear dynamics of 1550 nm vertical-cavity surface-emitting lasers (VCSELs) subject to polarization-preserved optical feedback (PPOF) and orthogonal optical injection (OOI) are theoretically investigated. The results show that two linear polarization (LP) modes can be simultaneously stimulated and polarization switching (PS) can be observed, which is different from the case that only y LP mode exists in a VCSEL with PPOF. Under the joint action of PPOF and OOI, the two LP modes will exhibit rich dynamical states, such as period one, period two, multiperiod and chaos oscillation. Different evolution routes to chaos can be also observed. Moreover, frequency detuning Δf (Δf = f m − f s, where f m and f s are the center frequencies of free-running master VCSEL and slave VCSEL, respectively) has an obvious influence on the PS. With the increase of the positive frequency detuning PS points shift toward larger injection strengths; meanwhile, a suitable negative frequency detuning value makes the injection strength for PS be the lowest.

Photonic Approach for Generating Randomness-Enhanced Physical Chaos Via Dual-Path Optically Injected VCSELs

The randomness enhancement of physical chaos generated by slave vertical-cavity surface-emitting lasers (S-VCSEL) subject to dual-path polarization-preserved optical injection (DP-PPOI) from single master VCSEL (M-VCSEL) with variable-polarization optical feedback (VPOF) is investigated numerically. The randomness of chaotic signals is evaluated quantitatively by an information-theory-based quantifier, the permutation entropy. The randomness properties for S-VCSEL with DP-PPOI and S-VCSEL with single-path PPOI are compared, as well as the effects of injection strength, frequency detuning, and VPOF are considered. It is shown that, the PE values for S-VCSELs with two different injection schemes are both much higher than those for M-VCSEL, and increase initially and then decrease until they saturate at a constant level. The region of injection parameter space contributing to randomness-enhanced chaos in S-VCSEL can be greatly broadened by adopting DP-PPOI. The generation of randomness-enhanced chaos via photonic approach is highly desirable for high-speed random number generators based on chaotic VCSELs.

Optical generation of tunable millimeter-wave based on dual-beam optical injection Locked 1550 nm vertical-cavity surface-emitting laser

Based on the spin-flip model, the nonlinear dynamics of a 1550 nm vertical-cavity surface-emitting laser (1550 nm-VCSEL) subject to dual-beam optically injection is investigated theoretically. The results show that a slave 1550 nm-VCSEL (S-VCSEL) under the injection of dual-beam output from two master VCSELs (M-VCSELs) can be driven to enter into an injection locking state under suitable injection parameters. In this case, the outputs of both X and Y polarization modes of the S-VCSEL exhibit periodic oscillation whose frequency is equal to the frequency detuning between the two M-VCSELs, and its optical spectrum contains only two main frequency components and possesses a single sideband spectrum structure. As a result, two mutually orthogonal optical millimeter-waves can be obtained based on the periodic oscillation in a VCSEL subject to dual-beam optically injected locking. Through adjusting the frequency detuning between the two M-VCSELs, the frequency of the millimeter-wave can be tuned continuously in a large range, while the power and modulation depth can also be controlled by adjusting the system parameters.

Optical generation of high-quality millimeter-wave based on an optically injected VCSEL subject to polarization-rotated external optical feedback

A scheme of optical generation of high-quality millimeter-wave based on the optically injected vertical-cavity- surface-emitting laser (VCSEL) subject to polarization-rotated optical feedback is proposed in this paper. Based on the spin-flip model (SFM), wich external disturbances taken into account, the performances of the millimeter-wave generated by this scheme are numerically investigated. The results show that under suitable operation conditions, a slave VCSEL (S-VCSEL) injected by a master VCSEL (M-VCSEL) will operate in a period-one (P1) oscillation state and the output optical intensity of S-VCSEL looks like being modulated by a microwave signal. By adjusting the injection strength iand the frequency detuning between S-VCSEL and M-VCSEL, a millimeter-wave, whose frequency can be continuously adjusted in a large range from 30 GHz to 60 GHz, is obtained. After introducing polarization-rotated optical feedback, the linewidth of millimeter-wave can be obviously narrowed by adjusting the feedback strength i and the feedback delay time . For a millimeter-wave with a linewidth of 5.509 MHz, generated by the optically injected VCSEL, its linewidth can be reduced to 230.2 kHz under optimum feedback parameters. The results obtained in this paper are helpful for acquiring high-quality millimeter-wave used in high speed Radio-over-Fiber (RoF) system.

Optimization of VCSELs for Self-Mixing Sensing

We have simulated the variations in optical output power from a vertical-cavity surface-emitting laser (VCSEL) subject to self-mixing feedback, which is very important for applications in sensing. In order to maximize the self-mixing signal for a given feedback we have optimized the epitaxial design of the VCSEL. The most important parameters are the number of quantum wells (gain), the number of Bragg mirrors (reflection), and the detector position.

Very Wide Hysteresis Cycles in 1550-nm VCSELs Subject to Orthogonal Optical Injection

A first experimental observation of three different types of frequency-induced polarization bistabilities in 1550-nm single transverse and polarization mode vertical-cavity surface-emitting lasers (VCSELs) subject to orthogonal optical injection is described. The hysteresis width of the bistable region that appears at longer wavelegth detunings increases as the injected power or the VCSEL current increases. Very large hysteresis widths are obtained. These widths are more than seven times larger than previously reported widths.

Mapping of two-polarization-mode dynamics in vertical-cavity surface-emitting lasers with optical injection

We report theoretically on the interplay between polarization switching and bifurcations to nonlinear dynamics in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection. Qualitatively different bifurcation scenarios leading to polarization switching are found and mapped out in the plane of the injection parameters, i.e., the frequency detuning vs injection strength plane. A Hopf bifurcation mechanism on the two-polarization-mode solution determines the injection-locking boundaries and influences polarization switching induced by optical injection. We furthermore report on a torus bifurcation emerging from a two-linearly polarized (LP) mode time-periodic dynamics before polarization switching and injection locking appear. It corresponds to an interesting combination of relaxation oscillation dynamics in the x -LP mode together with wave mixing dynamics in the injected y -LP mode. In agreement with recent experiments, we unveil a period-doubling route to chaos that involves both VCSEL orthogonal LP modes. The corresponding region of chaotic dynamics coincides with abrupt changes in the polarization switching boundaries in the plane of the injection parameters.

Wavelength Polarization Switching and Bistability in a 1550-nm VCSEL Subject to Polarized Optical Injection

Different forms of wavelength polarization switching and bistability are experimentally reported for a 1550-nm vertical-cavity surface-emitting laser (VCSEL) subject to optical injection with different input polarization angles to that of the solitary VCSEL.

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.

Frequency-induced polarization bistability in vertical-cavity surface-emitting lasers with orthogonal optical injection

We report theoretically on a pure frequency-induced polarization bistability in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection, i.e., the master laser light polarization is orthogonal to that of the slave VCSEL. As the frequency detuning is scanned from negative to positive values and for a fixed injected power, the VCSEL exhibits two successive and possibly bistable polarization switchings. The first switching (from the slave laser polarization to the injected light polarization) exhibits a bistable region whose width is maximum for a given value of the injected power. Such a dependency of hysteresis width on the injected power is similar to that recently found experimentally by Hong et al.[Electron. Lett. 36, 2019 (2000)]. The bistability accompanying the second switching (from the injected light polarization back to the slave laser free-running polarization) exhibits, however, significantly different features related to the occurrence of optical chaos. Interestingly, the width of the bistable region can be tuned over a large range not only by modifying the injection parameters but also by modifying the device parameters, in particular the VCSEL linewidth enhancement factor.

Analysis of Bit-Error Rate of Vertical-Cavity Surface-Emitting Lasers Modulated at High Speed

A theoretical study of single and multimode vertical-cavity surface-emitting lasers (VCSELs) subject to pseudorandom modulation of the current at a rate of 10 Gb/s is performed. Eye diagrams, probability density functions of the power at the decision time, averaged turn-on delay, and timing jitter are analyzed for different values of the on- and off-state currents. Bit sequences where errors occur are identified. Extensive simulations have been performed to obtain the bit-error rate (BER) for the back-to-back configuration. We find that the BER performance of single-mode VCSELs is better than the one obtained with multimode VCSELs when the off-state current is smaller than the threshold current. The same result is obtained when the off-state current is larger than the threshold value, providing that the on-state current is large enough. However, BER in single-mode VCSELs is greater than in multimode VCSELs when the off-state current is equal to the threshold current. BER performance is also better for multimode VCSELs when the off-state current is larger than the threshold value, if the on-state current is small enough.

Static and dynamic characteristics of VCSELs with polarisation-selective optical feedback

Static and dynamic characteristics of birefringent vertical-cavity surface-emitting lasers (VCSELs) subject to both isotropic and polarisation-selective optical feedback are investigated theoretically. The model considers two orthogonally polarised transverse modes; moreover, the spatial dependences of photon density, carrier density and injection current are taken into account. For a short external cavity, the two-mode VCSELs can be forced to operate with one mode by introducing the polarisation-selective optical feedback. It is further shown that the phase of feedback light determined by the external cavity length affects the laser operation characteristics greatly, that is, when the external cavity length is chosen, the reflected light strengthens (weakens) the optical field in the laser cavity, the mode that has the same polarisation direction can be enhanced (suppressed), while the other mode is suppressed (enhanced) correspondingly. For a relatively long external cavity, the continuous wave operation of VCSELs is destabilised and rich non-linear dynamics are excited. By increasing the external cavity length, the VCSELs follow a period-halving route to chaos. It is also found that the evolution of dynamics shows periodic repetition with respect to the external cavity length, and the period is half of the lasing wavelength. Further investigation shows that, for isotropic feedback, both modes exhibit the same dynamics and similar mode intensity; for polarisation-selective feedback, though similar non-linear behaviours are observed, the modal strengths are quite different, that is, the feedback light enhances one mode while greatly suppressing the orthogonally polarised mode.

Pure frequency-polarisation bistability in vertical cavity surface-emitting semiconductor laser subject to optical injection

Pure frequency-polarisation bistability in a vertical cavity surface-emitting semiconductor laser subject to optical injection has been observed. It was found that the width of the bistability loop may be enhanced by increasing the injection power.

Polarization selection and sensitivity of external cavity vertical-cavity surface-emitting laser diodes

A theoretical analysis has been undertaken of the polarization properties of birefringent vertical-cavity surface-emitting lasers (VCSELs) subject to weak optical feedback in an external cavity configuration. Attention is focussed on the competition between two orthogonal polarizations of the fundamental (LP/sub 01/) transverse mode of the device. It is shown that control of the emission polarization can be exercised even for very small external reflectivities (10/sup -4/%) by appropriate choice of optical feedback delays. The polarization selectivity is shown to be dependent upon the strength of optical feedback. Polarization is also shown to be highly sensitive to small changes in optical feedback delay. Thermally induced wavelength shift is shown to affect polarization behaviour.