On nonclassical effects in two-photon optical bistability and two-photon laser

We analyse the fluctuations at steady state in the good quality cavity case in two-photon lasers with running wave and two-photon absorptive optical bistability in a ring cavity. In the case of two-photon laser we do not find any nonclassical effect, contrary to expectations. On the other hand, in two-photon optical bistability we find squeezing and antibunching in the low transmission branch. The maximum reduction of fluctuations that can be obtained is slightly larger than by a factor of two.     

Effects of two-photon optical bistability upon phase conjugation

We have investigated phase conjugation by degenerate four-wave mixing, in circumstances where optical bistability can occur by two-photon resonant interaction. The solutions of the probe equation coupled with the two-photon equation of state have been obtained and studied. The two-photon phase-conjugated reflectivity is shown to exhibit multistability as well as hysteresis.     

Stability conditions for two-photon optical bistability in a ring cavity

A stability analysis in the good-cavity and mean-field limits, of two-photon optical bistability arising when two beams at different frequencies interact with a nonlinear medium in a ring cavity, is presented. Another metastable state has been found to occur in the double-absorption case in certain circumstances, and the system may be described as exhibiting a form of tristability.     

The mechanisms for optical bistability in a two-photon resonant system

The categories of optical bistability within a nondegenerate two-beam, two-photon resonant system are presented and discussed.     

Optical bistability due to a two-photon absorption resonance with fluctuations

Using the intensity-dependent complex dielectric function for a two-photon absorption resonance we derive the Langevin equation for the fluctuating light-field in the non-linear resonator. The corresponding Fokker-Planck equation is solved by expanding the distribution function in terms of products of trigonometric functions and generalized Laguerre polynomials. The expansion coefficients are calculated using the method of matrix continued fractions. Numerical results for the stationary case are given.     

Double-beam two-photon optical bistability in a Fabry-Perot cavity with polar molecules

Optical bistability in a micrometre-sized Fabry-Perot cavity, filled with appropriate polar molecules, is analysed after two incident beams (with frequenciesgw ₁ andgw ₂) produce in the system a two-photon resonance at frequencygw ₁ +gw ₂. One-photon resonances at the frequenciesgw ₁ andgw ₂ are discarded. It was not necessary to assume a particular relationship betweengw ₁ andgw ₂, and the single-beam two-photon optical bistability whengw ₁ andgw ₂ are of the same order or equal is emphasized.     

The absorption spectra of optical bistability with dispersion

The absorption spectra of a weak field (Ω) probing the bistable behaviour of a homogeneously broadened medium (ω₀) detuned with respect to the exciting laser light (ω_L) has been investigated. A dispersion like structure superimposed on an inverted peak near the critical threshold is predicted. The frequency response of the differential gain amplifier is also obtained.     

A dynamical model for the increasing absorption optical bistability

By phenomenological analysis with reference to Miller et al. [2a], a specific Hamiltonian for increasing absorption optically bistable systems is proposed and the corresponding coupled dynamical equations are derived.     

The resonance of two-photon absorption in separated optical fields

A beam of molecules interacting with two space-separated light standing waves of light is considered. It is shown that a resonance of two-photon absorption is predicted. The width of the resonance is equal to the reciprocal of the time of flight between the waves.     

Increasing absorption optical bistability operating in the front surface layer of high absorption samples

The increasing absorption optical bistability in a bulk ZnSe sample with quite high absorption has been observed. Our experiments show that the bistability operates only in the front surface layer of sample and that the back layer of sample can be regarded as a linear absorber and heat sink.     

All optical logic NAND gate based on two-photon absorption in semiconductor optical amplifiers

We propose a new scheme to realize all optical logic NAND operating at high speeds up to 250 Gb/s utilizing the ultrafast phase response during two-photon absorption (TPA) process in semiconductor optical amplifiers (SOA). NAND gate is important because other Boolean logic elements and circuits can be realized using NAND gates as basic building blocks. Rate equations for semiconductor optical amplifiers (for input data signals with high intensity) configured in the form of a Mach-Zehnder interferometer have been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The performance of this scheme is analyzed by calculating the quality factor of the resulting data streams. The results show that both AND and NAND operations at 250 Gb/s with good signal to noise ratio are feasible.     

Influence of nonlinear absorption effects on optical bistability in semiconductor ring resonators

We present a theoretical investigation of optical bistability in a nonlinear semiconductor ring resonator, by taking into account the two-photon absorption and the free-carrier absorption. By solving the intensity equation within the ring resonator, a parametric formulation is obtained for describing the bistability relation between the input and the output intensities. Numerical results show that the nonlinear absorption effects can affect the critical points and domain of the optical bistability.     

高吸收ZnSe多晶无镜光学双稳的实验观测

本文对具高吸收的ZnSe多晶材料的增加吸收型光学双稳性进行了实验观测,发现在介质的吸收远高于过去提出的理论判据时,仍能获得双稳输出,并测定了阈值开关功率与光斑尺寸及样品厚度的关系.采用分层模型分析实验结果,定性地解释了实验现象.     

All-optical logic gates based on two-photon absorption in semiconductor optical amplifiers

When the two-photon absorption of a high intensity pump beam takes place in a semiconductor optical amplifier there is an associated fast phase change of a weak probe signal. A scheme to realize fast all-optical XOR logic function using two-photon absorption induced phase change has been analyzed. Rate equations for semiconductor optical amplifiers, for input data signals with high intensity, configured in the form of a Mach–Zehnder interferometer has been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The model shows that both XOR operation and pseudo-random binary sequence generation at 250 Gb/s with good signal to noise ratio is feasible.     

Transients in optical bistability

In this paper we report on both a theoretical model for the transients in optical bistability in a Fabry-Perot cavity and the corresponding experimental results. An analytical calculation permits to predict the shape of the transient curves and the order of magnitude of their time duration in the case of a slow sweep of the length of the cavity. The experiment, which uses the nonlinearity arising from a two-photon transition in rubidium, yields results in good agreement with the theoretical calculation.Work supported by the D.R.E.T.     

Piezooptical optical bistability

A glass fiber piezooptical optical bistability device is reported.Basing on pho-toelastic and strain effects of single-mode fiber,we have realized piezooptical modulation andperformed experiments of optical bistability.     

Effects of two-photon absorption on carrier dynamics in quantum-dot optical amplifiers

We investigate ultrafast gain-dynamics in a quantum-dot (QD) semiconductor optical amplifier where two-photon absorption (TPA) occurs in the bulk region of the waveguide during propagation of a sub-picosecond optical pulse, and gain bleaching occurs in the QD active region. Our calculation reveals that TPA provides optical pumping which is quasi-synchronous in time and space with QD carrier depletion, leading to enhancement of carrier capture into the QDs on an ultrafast timescale. The TPA-induced optical pumping, which is qualitatively different from electrical pumping, changes qualitatively carrier recovery dynamics, reducing pattern effects when a train of optical pulses is injected at the ultra-high speed. PACS 85.60.Bt; 42.79.-e; 07.60.-j     

光栅光学双稳态

本文报道了一种光栅光学双稳态装置.利用改变一对对称光栅间相对位移,实现了对透过光强的周期性调制.将这样的系统作为传输部分,分别用He-Ne激光和普通白光完成了光学双稳实验.实验结果与理论分析相符.     

Use of two-photon absorption in a photorefractive crystal for three-dimensional optical memory

We describe the use of two-photon absorption in a photorefractive crystal for recording bit data in multilayered optical memory. A short-pulse near-infrared laser is used for generating the photorefractive effect by two-photon absorption. We succeeded in recording and reading seven layers of data in a LiNbO(3) crystal with a lateral resolution (distance between bits) of 5microm and an axial resolution (distance between layers) of 20 microm .