Characteristics Of Optical Bistability Research Articles

Numerical simulation and analysis of dual base transistor laser

AbstractIn this work, characteristics of dual base transistor laser are numerically analyzed for the first time. Active base region of the transistor laser is split into two unequal regions composing of shorter and longer sections, which are biased separately. Static characteristics of transistor laser are evaluated using a rate equation model, which reveals switching action in output optical power for a longer section base current of 9.2 mA with unpumped shorter section. Hysteresis behavior in the optical output is observed for the longer section input current till 1.6 mA. Optical bistable characteristics are studied for various values of gain (longer) and absorber (shorter) section currents. Further slope efficiency is evaluated using P‐I characteristics, before the onset of bistability, for gain lever features under common emitter (CE) configuration. A maximum gain lever of 4.5 dB is observed with the longer section bias current of 1.3 mA.

Nonlinear response of sodium and potassium doped ZnO along with improvement in bandgap structure: A combined physicochemical study

In this study, zinc oxide nanoparticles have been synthesized in the presence of alkali hydroxides (NaOH and KOH) using the Sol-Gel method. The XRD, DLS, Z-scan, and UV–Vis spectroscopy were used to investigate nanoparticles' structural and optical properties. XRD diffraction patterns show enhancement in structural constants by adding sodium and especially potassium atoms. Correspondingly, the bandgap energy reduces because of decreasing the lattice energy. Also, the nonlinear absorption coefficient is measured using the z-scan technique, and it is found that reverse saturable absorption (RSA) is the prominent nonlinear optical phenomenon in this samples upon increasing the power of the incident laser beam and the magnitude of nonlinear absorption coefficient enhance by introducing Na and K atoms into the ZnO (named as NZO and KZO, respectively) crystal lattice. In accordance with the enhancement of nonlinear absorption processes, NZO and KZO are bestowed with optical bistability characteristics, which is beneficial for manufacturing optical switchers.

Contrast ratio and hysteresis width of optical bistability in quantum-dot vertical-cavity semiconductor optical amplifiers integrated with MEMS membrane

The characteristics of optical bistability in quantum dot vertical cavity semiconductor optical amplifier integrated with MEMS membrane have been investigated, and a closed-form model is derived taking into account the effect of the quantum dot discrete states and the membrane deflection and reflectivity. We show that small membrane deflection significantly adjusts the resonant wavelength, the contrast ratios and the hysteresis width. The shape of the input–output characteristics of the device can be adjusted to display clockwise, butterfly and counterclockwise hysteresis loops depending on the membrane deflection and the initial wavelength detuning. Our analysis reveals that the contrast ratios of the upper and lower bistable levels are totally different. Also, it has been shown that the characteristics of the bistability are strong function of the active layer linewidth enhancement factor and the membrane reflectivity.

Bistability characteristics of different types of optical modes amplified by quantum dot vertical cavity semiconductor optical amplifiers

We have studied the characteristics of optical bistability of different types of optical modes amplified by small-size quantum dot vertical cavity semiconductor optical amplifiers operated in reflection. Our analysis reveals that TE01 mode exhibits stronger intensity-dependent non-linearity in small radius devices, which results in stronger optical phase modulation and therefore larger hysteresis width compared with the other modes. The effect of the wavelength detuning of the input signal on the shape of the hysteresis loop is studied. We find that butterfly hysteresis loop exhibits the largest hysteresis width compared with clockwise and counterclockwise loops. Our analysis reveals that doping the quantum dots with p-type doping slightly reduces the hysteresis width while doping the dots with n-type doping clearly increases the hysteresis width for any wavelength detuning. We estimate that the hysteresis width of quantum dot active layer will exhibit higher hysteresis width compared with quantum well active layer having the same threshold gain.

Bistable 1060-nm High-Power Single-Mode DFB Laser Diode

We report a novel high-power bistable distributed feedback (DFB) semiconductor laser diode operating near 1060 nm, which is realized by inserting a high-bandgap electron barrier layer and a grating layer in a super large optical cavity laser design. Optical and electrical bistable characteristics are both observed for this device. An on-state optical output power of 98 mW and an on-off extinction ratio of 22 dB were demonstrated between the bistable states. A qualitative physical model based on carrier population profile shift is used to explain the switching effect. Optical flip-flop operation was also demonstrated.

Tunable beam focusing based on optical bistability with a composite Kretschmann configuration involving a Kerr medium

A beam focuser with a composite Kretschmann configuration involving a Kerr medium is investigated theoretically. The structure employs a silver film with four slits filled with the Kerr medium. Optical bistability and beam focusing are demonstrated, and changes to the incident intensity result in optical bistability characteristics in the reflection, focused intensity, spot size, and depth of focus. The proposed structure has the potential to be applied for optical switching and nano-illumination.

Optical bistability in side-mode injection locked dual-mode Fabry-Pérot laser diode

In this paper, optical bistability characteristics are demonstrated experimentally based on a dual-mode laser system comprising a multi-mode Fabry-Pérot laser diode (MMFP-LD) and a built-in feedback cavity formed by a fiber facet. The results show that two lasing modes with frequency separation of ∼0.58 THz and comparable peak powers can be achieved by judicious adjustment of the bias current and the operating temperature of the laser chip, which has a peak fluctuation of less than ∼1 dBm over a measurement period of one hour. A combination of appropriate external injection power and wavelength detuning can result in remarkable optical bistability in two oscillation modes, in which the resulting contrast ratio between the unlocked and locked states can be up to 30 dB, and the corresponding hysteresis loop width can be changed by controlling the side-mode injection power and the wavelength detuning.

Optical bistability in the oscillation of an inhomogeneously broadened quasi-three-level laser

A theoretical modeling analysis is presented to study the optical bistability exhibited in the oscillation of an inhomogeneously broadened quasi-three-level laser. All the major characteristics of optical bistability depend on two normalized parameters, f and xa, which are defined by f = Isat,a/Isat,m and xa = 2αa0pa/δ and are related to measurable properties of the laser medium. In comparison with the case of a homogeneously broadened laser, the essential condition for the occurrence of such bistability, f < xa/(xa + 1), turns out to be the same, whereas the intensities at the up- and down-thresholds are substantially increased and the bistability range is reduced.

Analytical model for optical bistability in nonlinear metal nano-antennae involving Kerr materials

Optical bistability at nanoscale is a promising way to realize optical switching, a key component of integrated nanophotonic devices. In this work we present an analytical model for optical bistability in a metal nano-antenna involving Kerr nonlinear medium based on detailed analysis of the correlation between the incident and extinction light intensity under surface plasmon resonance (SPR). The model allows one to construct a clear picture on how the threshold, contrast, and other characteristics of optical bistability are influenced by the nonlinear coefficient, incident light intensity, local field enhancement factor, SPR peak width, and other physical parameters of the nano-antenna. It shows that the key towards low threshold power and high contrast optical bistability in the nanosystem is to reduce the SPR peak width. This can be achieved by reducing the absorption of metal materials or introducing gain media into nanosystems.

Optical Bistability of Spin Coated Poly(3-octylthiophene)/Polymethylmethacrylate Composite Waveguides

Poly(3-octylthiophene)/polymethylmethacrylate (P3OT/PMMA) composite thin films were prepared by spin coating as composing a prism-coupling waveguide. The optical absorption property of the composite thin film was evaluated using UV-visible spectra in the range 300-900 nm. The optical bistable characteristics of the prism-coupling waveguide composed of P3OT/PMMA composite film was measured for different input laser power intensities using optical bistable measuring equipment. The optical bistability of the waveguide was measured using a Nd:YAG laser with a wavelength of 1,064 nm, pulse width of 5 ns and a repetition frequency of 10 Hz. The optical bistable characteristics of P3OT/PMMA composite waveguides for different input power intensities shows good stability and hysteresis characteristics. However, in terms of the input laser power dependence of optical bistability, the switching on-off position shifts with the increase in input power intensity. In addition, the effect of organic gas treatment and PMMA molecular weight on the optical bistable characteristics of P3OT/PMMA composite waveguides was investigated.

Optical Bistability of Poly(3-octylthiophene)/Polymethylmethacrylate Composite Waveguides Prepared by Spin Coating

Poly(3-octylthiophene)/Polymethylmethacrylate (P3OT/PMMA) composite waveguides were prepared by spin coating method as composing a prism-coupling waveguide. The UV-vis spectrum of P3OT/PMMA thin film was recorded in the range 300-900 nm using spectrophotometer to determine the optical absorption property of the composite thin film. The prepared P3OT/PMMA waveguide was treated with organic gas for 25 hrs to smoothing the surface of the thin film. An Nd: YAG laser with a wavelength of 1064 nm, a pulse width of 5 ns and a repetition frequency of 10 Hz was used for optical bistability measurement. The optical bistable characteristics of prism coupling waveguide comprising with P3OT/PMMA composite thin film was measured for different laser power intensities using optical bistable measuring equipment. The measured optical bistability displaced good stability and hysteresis characteristics. The input power dependence of optical bistability was observed and the switching on-off position shifted with the increase of input power intensity. In addition, the effects of organic gas treatment on the optical bistability of P3OT/PMMA composite waveguides were analyzed.

Wall thickness dependent double optical bistability in gold nanotube: A physical mechanism based on local field enhancement

The intrinsic optical bistability (OB) in a two-phase composite, a nonlinear gold nanotube embedded in a linear dielectric host, is investigated by theoretical calculation. Based on quasistatic approximation and Kerr nonlinearity, we obtain the local electric field in a certain position of the gold nanotube as a function of the incident field. In addition to the single OB, the appearance of double OB and optical tristability are also reported. It is shown that both wavelength and wall thickness can dramatically affect the optical bistable behavior of gold nanotube. Both the critical wavelength and the region of double OB decrease obviously with increasing the wall thickness. Thus double OB only appears in the thinner gold tube and is absent as the wall thickness exceeds the critical value. Furthermore, all these OB characteristics have been explained by the local field enhancement effect.

End-pumped optical bistability Tm,Ho:YLF laser

We experimentally demonstrate strong optical bistability in a 2 μm continuous wave Tm,Ho:YLF laser with a bulk crystal. The laser is end-pumped by a 792 nm fiber-coupled laser diode. The bistable region is as wide as 1.6 W and the jump power at the turning point is as high as 82.5 mW when the temperature of the laser crystal is kept at 253 K. The influences of the cavity length and the transmission of the output coupler on the characteristics of optical bistability are obtained. The theoretical analysis shows that the bistable output in the Tm,Ho:YLF lasers comes from the combined effects of the nonlinear saturation of ground state reabsorption, the energy transfer upconversion, and the excited state absorption.

Optical bistability at angular incidence in a one-dimensional photonic crystal containing single negative materials

Nonlinear wave propagation is studied theoretically in a one-dimensional photonic band gap structure containing single negative materials. It is found that Kerr nonlinearity is greatly enhanced near the lower edge of a recently explored angular gap for transverse magnetic polarized light. Consequently, optical bistability is achieved at very low values of input intensity in a periodic structure composed of only a few repeating units. The characteristics of optical bistability are affected only slightly with the variation of the incident angle and thickness ratio of the layers. The effect of losses is also found to be relatively insignificant in such a small structure.

Optical Bistability of Spin Coated Poly(3-hexylthiophene)(P3HT)/PMMA Composite Thin Film

In the present work, Poly(3-hexylthiophene)/Polymethylmethacrylate [P3HT/PMMA] composite thin film was prepared using spin coating method on the top of triangular prism as composing a prism coupling waveguide. The optical bistable characteristics of prism coupling waveguide comprising with P3HT/PMMA composite film was measured for different input laser power intensity using optical bistable measuring equipment. Also the effect of organic gas treatment on the optical bistable behavior of P3HT/PMMA quasi-waveguide has been investigated. The measured optical bistabilities have excellent stability and hysteresis characteristics. In the input laser power dependence of optical bistability, the on-off position shifts with the increase of input laser power intensity. A Nd:YAG laser with a wavelength of 1064 nm, a pulse width of 5 ns and a repetition frequency of 10 Hz was used for this measurement.

ポリ（３‐ヘキシルチオフェン）を用いた光双安定素子の作成とその性能評価

Optical bistable devices have attracted much attention for application to optical-optical switch and so forth. We have prepared an optical bistable device of quasi-waveguide constituted comprise of a triangular prism and a poly (3-hexylthiophene)/poly (methyl methacrylate) composite thin film. The thin film was prepared by the spin coating method and drop casting method. With both the thin films, optical bistability was clearly distinguished. The optical bistable characteristics of the quasi-waveguide prepared by the spin coating method can be observed with lower laser power intensity than that by the drop casting method.

Optical bistability effects in a Tm,Ho:YLF laser at room temperature

We demonstrate strong optical bistability in a 2 microm continuous-wave Tm,Ho:YLF laser pumped by a 792 nm laser diode near room temperature. The bistable region is as much as 100 mW wide at 283 K and can be controlled by the temperature of the laser crystal. The influence of crystal temperature on the characteristics of optical bistability is obtained. The influence of the pump-to-mode ratio on the bistable characteristics of the laser is also discussed. To our knowledge this is the first report of optical bistability effects in Tm,Ho:YLF lasers.

Modeling reflective bistability in vertical-cavity semiconductor optical amplifiers

The characteristics of optical bistability in a vertical-cavity semiconductor optical amplifier (VCSOA) operated in reflection are reported. The dependences of the optical bistability in VCSOAs on the initial phase detuning and on the applied bias current are analyzed. The optical bistability is also studied for different numbers of superimposed periods in the top distributed bragg reflector (DBR) that conform the internal cavity of the device. The appearance of the X-bistable and the clockwise bistable loops is predicted theoretically in a VCSOA operated in reflection for the first time, to the best of our knowledge. Moreover, it is also predicted that the control of the VCSOA's top reflectivity by the addition of new superimposed periods in its top DBR reduces by one order of magnitude the input power needed for the assessment of the X- and the clockwise bistable loop, compared to that required in in-plane semiconductor optical amplifiers. These results, added to the ease of fabricating two-dimensional arrays of this kind of device could be useful for the development of new optical logic or optical signal regeneration devices.

Optical Bistable Characteristics of Optical Quasi-waveguide Prepared with Host-Guest Thin Film

The host-guest thin film using nonlinear optical material was fabricated by the spin coat method on the bottom face of a right-angled prism dropped down the solution of tershari-Butyl Vanadyl-phthalocyanine ((t-Bu)nVOPc) and PMMA. To improve the nonlinear optical characteristics, the host-guest thin film was treated with organic gas. Optical bistable characteristics were evaluated by using the optical quasi-waveguide prepared with host-guest thin film after and before organic gas treatment. After and before organic gas treatment, optical bistable characteristics were observed by changing the incident angles of laser beam to prism. Optical bistable characteristics after organic gas treatment were compared with before treatment. After treatment, optical bistable behavior is more sensitive than that before treatment. Moreover, the organic gas treating time dependences of optical bistability were investigated by using the measuring equipment of optical bistability.

A Hybrid Optical Bistable Device Based on a Fibre Bragg Grating

We propose a hybrid optical bistable device based on a fibre Bragg grating.The experimental set-up is designed by using realcommunication components. The optical bistable characteristics aresimulated. The feedback nonlinearity and the delay time of the deviceare emphasized. We discuss the potential of such a device in sensor applications.