Bistable Laser Research Articles

Statistical analysis of bistable feature in a 1.55-[formula omitted] vertical cavity emitting laser

Optical bistability in telecom-band lasers has attracted significant attention because of its immense potential for applications in the fields of optical communications and optical computing. In this paper, we report on an experimental investigation of the statistical properties of a 1.55-μm bistable VCSEL. The VCSEL exhibits mode switching at a current of 5.41 mA and 4.15 mA when the pump continuously increases and decreases, respectively. Both of these switching exhibit a bistable region, indicating a polarization bistability induced by the gain saturation. By calculation of second-order autocorrelation functions with injection current, we identify different regions associated with the dynamics of different dominant modes. In particular, the statistical analysis reveals more properties of the bistable laser, such as the intensity fluctuations induced by different kinds of noise.

Dual-parameter femtosecond mode-locking pulse generation in partially shared all-polarization-maintaining fiber Y-shaped oscillator with a single saturable absorber

We present a design of a mode-locked fiber laser based on a polarization-maintaining (PM) Y-shaped fiber structure, which employs a single semiconductor saturable absorber mirror (SESAM) and a common polarization beam combiner (PBC) to achieve dual- parameter mode-locking femtosecond pulse in two orthogonal polarization states. The two output pulses have different characteristics, such as repetition frequency (87.3 MHz and 91.3 MHz), average output powers (2.1 mW and 1.9 mW), pulse durations (299 fs and 377 fs) and spectral profiles (centered at 1565.6 nm and 1563.6 nm with spectral width of 9.96 nm and 9.93 nm). The properties of the two pulses are experimentally characterized and their potential applications in areas such as bistable frequency lasers and dual femtosecond optical frequency comb is discussed.

Relaxation and Polarization Oscillations in a Wide-Aperture Bistable Laser with a Saturable Absorber

Relaxation and Polarization Oscillations in a Wide-Aperture Bistable Laser with a Saturable Absorber

Unidirectional mode selection in bistable quantum cascade ring lasers.

Ideal ring resonators are characterized by travelling-wave counter-propagating modes, but in practice travelling waves can only be realized under unidirectional operation, which has proved elusive. Here, we have designed and fabricated a monolithic quantum cascade ring laser coupled to an active waveguide that allows for robust, deterministic and controllable unidirectional operation. Spontaneous emission injection through the active waveguide enables dynamical switching between the clockwise and counterclockwise states of the ring laser with as little as 1.6% modulation of the electrical input. We show that this behavior stems from a perturbation in the bistable dynamics of the ring laser. In addition to switching and bistability, our novel coupler design for quantum cascade ring lasers offers an efficient mechanism for outcoupling and light detection.

Mean-field Floquet theory for a three-level cold-atom laser

We present a theoretical description for a lasing scheme for atoms with three internal levels in a $V$ configuration and interacting with an optical cavity. The use of a $V$-level system allows for an efficient closed lasing cycle to be sustained on a dipole-forbidden transition without the need for incoherent repumping. This is made possible by utilizing an additional dipole-allowed transition. We determine the lasing threshold and emission frequency by performing a stability analysis of the nonlasing solution. In the lasing regime, we use a mean-field Floquet method (MFFM) to calculate the lasing intensity and emission frequency. This MFFM predicts the lasing transition to be accompanied by the breaking of a continuous U(1) symmetry in a single Fourier component of the total field. In addition, we use the MFFM to derive bistable lasing and nonlasing solutions that highlight the nonlinear nature of this system. We then test the bistability by studying hysteresis when slowly ramping external parameters across the threshold and back. Furthermore, we also compare our mean-field results to a second-order cumulant approach. The work provides simple methods for understanding complex physics that occur in cold atom lasers with narrow line transitions.

Saturable absorption and its consequent effects in bistable erbium-doped fiber ring laser

The linear absorption in erbium-doped fiber (EDF) contributes to its excellent role in EDF amplifiers and lasers. A nonlinear optical contribution in the absorption of EDF is responsible for optical bistable action when it is present in a laser cavity. To quantify this effect, the variation of absorption coefficient is measured at different signal powers at multiple wavelengths in the C-band for different EDF lengths, and saturable absorption parameters such as the saturation power are extracted. Then the modification in the output characteristics of EDF ring laser with change in fiber length and in the presence of self-induced saturable absorption effect within the gain medium, which leads to optical bistability, is measured. By comparing the measured parameters obtained from saturable absorption in EDF and optical bistability in EDF ring laser, we estimated the length of the gain medium which acts as the saturable absorber inside the cavity of the laser. This is useful in constructing bistable lasers with optimized conditions. The temporal evolution of cavity loss and gain with the intra-cavity power and up- and down-thresholds helps in understanding why the down-threshold will be lesser than the up-threshold in bistable laser systems.

Relaxation and polarization oscillations in a wide-aperture bistable laser with a saturable absorber

The regions of stability of homogeneous generation regimes in a wide-aperture laser with a saturable absorber, including a semiconductor laser with a vertical output of radiation, are determined depending on the relative relaxation rate of carriers in active and passive media and on the frequency detunings of working transitions in these media with a resonant frequency of radiation, taking into account its polarization state. The excitation thresholds for relaxation and polarization oscillations are determined within the four-level model. Keywords: wide-aperture laser, saturable absorber, relaxation and polarization oscillations

Amplification of optical signals in a bistable vertical-cavity surface-emitting laser by vibrational resonance.

The paper presents the results of the experimental study of an application of the phenomenon of vibrational resonance (VR) for enhancement of the response of a bistable vertical-cavity surface-emitting laser (VCSEL) to the effect of optical modulating signals. Specifically, two different cases were investigated: (a) the control of all-optical switching caused by a modulated orthogonal optical injection from another VCSEL and (b) the amplification of autodyne signals from a vibrating diffusely reflecting surface in the self-mixing optical interferometry. It is experimentally demonstrated that an application of the phenomenon of VR in both cases studied leads to a strong amplification of the input optical signals by a factor from 10 to 200 depending on the experimental conditions with respect to the initial values. The effect of the asymmetry of a bistable potential on the amplification factor was also studied. The results obtained can be used to improve all-optical switchings for application in communication systems and enhancement of autodyne signals in self-mixing optical interferometry. This article is part of the theme issue 'Vibrational and stochastic resonance in driven nonlinear systems (part 1)'.

Role of Vitamin D Antiviral Plants and Precaution in COVID-19

Energy concentration is essential to create compact, efficient microfluidic optical devices. Polyethylene glycol (PEG) is a suitable fluid for this purpose with its bipolarity (molecular dissolvability), nonvolatility, and high index of refraction (waveguiding). Its distinguished feature is a bistability in the phase transition process; i.e., a mixture of two PEG types (molecular weight: 300 and 2000), for example, takes both the liquid and solid phases in the temperature range of 2�??38 °C. One can use this phase transition to pause a sample flow at a specific position in microchannels. The bistability also realizes a rewritable signboard with a PEG droplet array, since both the clear (liquid) and milk-white (solid) states are stable at room temperature. The strong scattering in the solid phase is useful to confine a light beam (photonic localization). Mirrorless lasers, which have been studied extensively with microdroplets, can be constructed with dye-dispersed PEG, since the confined fluorescence induces a stimulated emission. A bistable laser emission has been demonstrated in the phase transition process of the microfluid. The light confinement is also useful to enhance the absorbance of inorganic materials, which hardly absorb excitation or probe light particularly in a microchannel. Chemists have recently developed organic-inorganic hybrid phosphors with an enhanced excitation efficiency. Spectroscopic analysis of these hybrids needs time-resolved measurements, since both rapid and slow processes occur in organic ligands and metal ions. The time-space conversion spectral measurement is suitable for microfluidic devices, since a nanosecond resolution is attainable with no need for a large pulsed laser.

Study of optical bistability based on hybrid-cavity semiconductor lasers

All-optical flip-flop has been demonstrated experimentally based on our optical bistable hybrid square-rectangular lasers. In this paper, dual-mode rate equations are utilized for studying the optical bistability in the two-section hybrid-coupled semiconductor laser. A phenomenological gain spectrum model is constructed for considering the mode competition in gain section and saturable absorption effect in the absorptive section in a wide wavelength range. The mechanisms of the optical bistability are verified in the aspect of the distribution of carriers and photons in the two-section hybrid-coupled cavity. In addition, we find that with the adjustment of the device parameters, both of the width and biasing current for achieving the bistability can be tuned for a wide range. Furthermore, a dynamic response of all-optical flip-flop is simulated, using a pair of set/reset optical triggering pulses, in order to figure out the laws for faster transition time with lower power consumption.

Quantum effect on characteristics of semiconductor ring laser

A bistable semiconductor ring laser (SRL) with two counter propagation modes has been triggered by optical pulse injection which added to the initial nonlasing mode. As the optical pulse injection (OPI) has an important role in switching and lasing of SRL, we have to find a reliable area to achieve its amplitude and frequency. Numerical results show an increase in amplitude of OPI leading to switching time decreasing as well as an increase to amplitude oscillation. It is shown that in order to prevent the oscillation in laser output characteristic, the OPI power must be less than 2 mW. We have also investigated the effect of quantum wells on active region structure of SRL. It is obvious by increasing the quantum well numbers the output optical power has been increased and the switching time has been decreased. The main advantage of this research work is to apply separate confinement heterostructure (SCH) to multi quantum well (MQW) structure to extract numerical model for amplitude and phase of SCH-SRL. Using SCH in MQW-SRL active region will increase the output power to 0.8 mW and decrease threshold current to 12 mA.

Theoretical and experimental investigation of polarization coexistence and switching in an optical bistability Tm,Ho:LLF laser.

We first investigate the polarization coexistence and switching between the orthogonal π- and σ-polarization states in a free running optical bistability Tm,Ho:LLF laser. The output performances of the optical bistability Tm,Ho:LLF laser is numerically simulated, based on a new rate equation theory model taking into account the influences of polarization-dependent gain and losses. The simulation results show the polarization coexistence and switching of output laser in the process of decreasing pump power. The physical mechanism of polarization coexistence and switching is clarified by analyzing the polarization-dependent net-gain coefficients. Furthermore, the polarization coexistence and switching are experimentally realized in the optical bistability Tm,Ho:LLF laser, which validates the theoretical analysis. The theoretical model can be applied to analyze the polarization coexistence and switching in other kinds of (quasi-) three-level optical bistable lasers.

Digital Signal Extraction by Means of Nonlinear Stochastic Filtration

The results of noise immunity analysis for digital communication systems using methods of nonlinear filtering are given. Nonlinear filtration is based on stochastic resonance effect. The stochastic resonance is given to a phenomenon that is manifest in nonlinear systems where by generally feeble input information (such as a weak signal) can be amplified and optimized by the assistance of noise. The stochastic resonance has been observed in a large variety of systems, including bistable ring lasers, semiconductor devices, chemical reactions, and mechanoreceptor cells in the tail fan of a crayfish. Numeral simulation of response at affecting input of the system on additive mixture of harmonic signal and white Gaussian noise are given. Amplitude spectrum of this output signal has been investigated. Results of the output signal-to-noise ratio calculation of the stochastic filter for the additive sum of a harmonic signal and white Gaussian noise for different values of the input noise dispersion are given. It is shown that the output signal-to-noise ratio of the system will peak at a certain value of noise intensity under a action of the input signal and noise. It is shown that the stochastic resonance effect provides separation of a digital signal from the white Gaussian noise. The comparative analysis of noise immunity of the matched filter and nonlinear stochastic filter for input square pulses are given. The effects of signal distortions in nonlinear processing with a stochastic filter are considered. Calculations of the coefficient of nonlinear distortions of a rectangular pulse are performed. It is shown that nonlinear distortions lead to a decrease in the signal-to-noise ratio at the output of the filter.

Hybrid-cavity semiconductor lasers with a whispering-gallery cavity for controlling Q factor

Hybrid cavities composed of a Fabry-Perot (FP) cavity and awhispering-gallery mode (WGM) microcavity have been proposed anddemonstrated for modulating mode $Q$ factor to realize singlemode and optical bistable lasers. In this article, we report hybrid cavity lasers witha pentagon microcavity and a square microcavity, respectively. Thereflectivity spectra of different microcavities are simulated to selectmicrocavities for hybrid cavities. Mode coupling with mode $Q$ factor enhancement is investigated numerically and experimentally.Stable single mode operations with a high coupling efficiency to a singlemode fiber are realized for a hybrid cavity laser with a square microcavity.Furthermore, optical bistability hybrid lasers are investigated as themicrocavity is unbiased, due to saturable absorption in the microcavity andmode competition, respectively. All-optical flip-flop is demonstrated usingtrigger optical pulses with a width of 100 ps for mode competitionbistability. The stable single mode operation and optical bistability ofhybrid cavity lasers may shed light on the applications for photonicintegrated circuits and optical signal processing.

Evidence of a Critical Phase Transition in Purely Temporal Dynamics with Long-Delayed Feedback.

Experimental evidence of an absorbing phase transition, so far associated with spatiotemporal dynamics, is provided in a purely temporal optical system. A bistable semiconductor laser, with long-delayed optoelectronic feedback and multiplicative noise, shows the peculiar features of a critical phenomenon belonging to the directed percolation universality class. The numerical study of a simple, effective model provides accurate estimates of the transition critical exponents, in agreement with both theory and our experiment. This result pushes forward a hard equivalence of nontrivial stochastic, long-delayed systems with spatiotemporal ones and opens a new avenue for studying out-of-equilibrium universality classes in purely temporal dynamics.

Bistable lasing in parity-time symmetric coupled fiber rings

We propose a parity-time (PT) symmetric fiber laser composed of two coupled ring cavities with gains and losses, which operates both in PT-symmetric and symmetry-broken regimes depending on the static phase shifts. We perform analytical and numerical analysis by the transfer matrix method taking into account gain saturation and predict laser bistability in the PT-symmetric regime in contrast to a symmetry-broken single-mode operation. In the PT-broken regime, the generation power counterintuitively increases with an increase of the cavity losses.

Amplification of an Autodyne Signal in a Bistable Vertical-Cavity Surface-Emitting Laser with the Use of a Vibrational Resonance

For the first time, it is demonstrated experimentally that a vibrational resonance in a polarization-bistable vertical-cavity surface-emitting laser can be used to increase the laser response in autodyne detection of microvibrations from reflecting surfaces. In this case, more than 25-fold signal amplification is achieved. The influence of the asymmetry of the bistable potential on the microvibration-detection efficiency is studied.

All-optical flip-flop based on hybrid square-rectangular bistable lasers.

A compact, simple, and bistable hybrid square-rectangular laser is experimentally demonstrated as an all-optical flip-flop memory. Controllable bistability is induced by two-mode competition, together with the saturable absorption at the square microcavity section. The all-optical set and reset operations are realized by injecting signal pulses at two-mode wavelengths, with the response times of 165 and 60ps at the triggering pulse width of 100ps and switching energies of 2.7 and 14.2fJ, respectively. The robust hybrid-cavity design has an active area of 660 μm2 and permits efficient unidirectional single-mode lasing, low-power flip-flop operation, and superior fabrication tolerance for monolithic photonic integration.

Splitting in the pinning-depinning transition of fronts in long-delayed bistable systems.

We investigate the formation of localized domains through front pinning in a periodically forced, bistable semiconductor laser with long-delayed optoelectronic feedback. At difference with 1D spatially extended systems, the transition from the pinning to the propagation regime occurs via two separated bifurcations, each corresponding to the unpinning of one of the fronts surrounding the localized domain. The bifurcation splitting is systematically explored, unveiling the crucial role played by the forcing frequency. The experimental results are reproduced and interpreted by means of a prototypical model of our system.

All-Optical Shift Register Using Polarization Bistable VCSEL Array

We investigated all-optical shift register operations using 1.55-μm polarization bistable vertical-cavity surface-emitting lasers (VCSELs) formed in an array. The VCSEL array consisted of VCSELs that oscillated with single longitudinal and transverse modes at room temperature. The lasing wavelengths were tuned by adjusting the driving currents of each VCSEL. A VCSEL in the array exhibited polarization flip-flop operation by injection of the orthogonally polarized set-reset input pulses. By injection of the VCSEL output light into another VCSEL in the same array through a polarizer and an optical gate, the second VCSEL also exhibited polarization flip-flop operation according to the polarization state of the first VCSEL. The shift register operation has been successfully demonstrated using two adjacent VCSELs in the array. The optical power needed for polarization switching is usually lower than the VCSEL output power. Thus, this shift register operation was achieved without optical amplifiers.