Optical bistability in GaInAsP/InP coupled-circular resonator microlasers

Optical bistability is realized in GaInAsP/InP coupled-circular resonator microlasers, which are fabricated by planar technology. For a coupled-circular resonator microlaser with the radius of 20?μm and a 2?μm-wide bus waveguide, hysteresis loops are observed for the output power coupling into an optical fiber versus the cw injection current at room temperature. The laser output spectra of the upper and lower states of the hysteresis loop indicate that the bistability is related to mode competitions. The optical bistability can be explained as the mode competition between the symmetry and antisymmetry coupled modes relative to the bus waveguide.     

Cavity nonlinear optics at low photon numbers from collective atomic motion

We report on Kerr nonlinearity and dispersive optical bistability of a Fabry-Perot optical resonator due to the displacement of ultracold atoms trapped within. In the driven resonator, such collective motion is induced by optical forces acting upon up to 10(5) 87Rb atoms prepared in the lowest band of a one-dimensional intracavity optical lattice. The longevity of atomic motional coherence allows for strongly nonlinear optics at extremely low cavity photon numbers, as demonstrated by the observation of both branches of optical bistability at photon numbers below unity.     

Absorptive and dispersive bistability in semiconductor injection lasers

Recent progress in the study of both absorptive and dispersive bistability in semiconductor injection lasers is reported. Inhomogeneously excited semiconductor lasers as an absorptive case, and laser diode optical amplifiers and optical injection locking systems of laser diodes as dispersive cases, are described. Applications of bistable semiconductor lasers, such as optical memories, optical regenerative amplifiers and all-optical switching, are also discussed.     

Computer simulations for a common-cavity two section (CCTS) bistable laser

In this paper a computer simulation about the characteristics of steady-state and transient response for a CCTS bistable laser under inhomogeneous electrical injection or external optical injection is reported. The rate equations are analysed in terms of typical parameters, such as electrical injection currents, spontaneous emission coupling factor, external optical injection intensity, etc. It shown that bistability and self-pulsation come mainly from the absorbing section constituting a saturable absorber in this device. A weak optical signal can be amplified by the laser, the amplification factor being dependent on the direction of the incident light. Some interesting results for the transient response under certain external optical injections are also discussed.     

Optical bistability in gold nano-colloid due to thermal lensing effect

In this study, experimental results are concerning “the optical bistability due to thermal lensing effect”, in colloidal solution of gold nanoparticles (Au Nps) which has been studied under CW laser illuminations. Two different CW laser beams (He–Ne and Nd-Yag) were used to interact with a vertical Fabry–Perot interferometer, containing colloid of the Au Nps. Hysteretic loops have been observed with regard to optical bistability and the results were fitted with theoretical curves. The radiated power to the resonator was elevated up to 50 mW for both the laser beams with the same spot size. Also, new method was defined to precise evaluation of the theoretical hysteretic loop which is describing the relation between nonlinear refractive index and the beam intensity inside the resonator. This dependency is due to thermal lensing effect and numerical simulations of this effect were also performed, in order to better understanding of it.     

Polarization Switching Bistability and Dynamics in Vertical-Cavity Surface-Emitting Laser under Orthogonal Optical Injection

Bistability as well as dynamics associated to polarization switching in a vertical-cavity surface-emitting laser (VCSEL) submitted to orthogonal optical injection from an external master laser are investigated. Intensity-polarization switching bistability is studied by increasing and decreasing the intensity of the injected beam and for a fixed frequency detuning, i.e. the frequency offset between master and the free running VCSEL. Depending on the frequency detuning, bistable switching is experimentally found to occur with or without injection locking of the fundamental mode to the master laser frequency. For large positive detuning, injection locking of the first-order transverse mode with a strong depression of the fundamental mode has been observed. The case of frequency – polarization switching bistability, i.e. when the frequency detuning is first decreased and then increased for a fixed injected power, has also been theoretically analyzed. Qualitative comparison with previous experimental work is presented for the dependence of the width of the bistable switching region on the injection strength level. Finally we show an experimental result of complicated dynamics including period doubling route to chaos that accompany polarization switching and which motivates future theoretical investigations.     

Model of lock-in in a ring laser and a semiconductor laser gyro

It is assumed that the process of lock-in in a ring laser has a finite transient time. This assumption serves as a basis for developing a semiconductor laser gyro. A semiconductor optical amplifier is applied as an amplifying medium, and a ring resonator represents a long optical fiber. The injection of an external single-frequency light into a ring resonator with subsequent circulation of counterpropagating waves is used. The light characteristics of the semiconductor laser gyro are discussed, and the rotation sensitivity of the gyro is demonstrated.     

Fast mode-hop-free acousto-optically tuned laser with a simple laser diode

A mode-hop-free tunable external-cavity Littrow diode laser with intracavity acousto-optic modulators (AOMs) has been built. The modes of the red laser diode without a special antireflection coating are shifted by varying the injection current. The external resonator modes and the grating selectivity are independently electrically alterable by two AOMs. Thus, a tuning of the external resonator over up to 1900 GHz is possible. A precise computer control of laser diode and AOMs allowed a single-mode tuning of the whole laser with a tuning range of 225 GHz in 250 s. Additionally, we demonstrated fast tuning over 90 GHz in 190 micros and a repetition rate of 2.5 kHz.     

掺Yb钒酸盐晶体激光振荡中的光学双稳态现象研究

研究了三种掺Yb钒酸盐晶体Yb:LuVO4,Yb:YVO4和Yb:GdVO4的激光振荡中所呈现的光学双稳态效应.以晶体所吸收的抽运功率表征的双稳区宽度ΔPabs可超过1W,在双稳区高功率一侧的边界,即激光振荡的上阈值点,出现激光输出功率的不连续变化或跃变,同时发生亚毫秒时间尺度上的大幅度强度涨落.谐振腔的输出耦合透过率、晶体长度、晶体中的热效应等对双稳态效应均具有重要影响.     

用阈值表达式研究长外腔半导体激光器的双稳特征

利用外腔半导体激光器（ＥＣＬＤ）在不同频率振荡所需的阈值载流子密度的表达式及相关的折射率表达式他它的双稳特性,由此导出了在外腔半导体激光器的ｐ－ｖ（功率－频率）曲线上出现双稳的条件以及双稳环宽度的解析表达式。     

非线性光纤环：2.掺铒光纤全纤光学双稳态实验

利用掺饵光纤和光纤定向耦合器组成全光纤谐振腔，在光学非线性条件下，实现了全纤光学双稳运转，实验双稳阈值与理论相符。     

Stability of nonlinear Fabry-Perot resonators

The stability of folded Fabry-Perot resonators is investigated for the case where the resonator contains a medium with a dispersive third-order nonlinearity. Positive-branch instabilities of Ikeda type are found, with thresholds comparable to optical bistability thresholds. In the unstable region, the internal field is apparently chaotic, though oscillatory behaviour is found in a special case.     

Optical bistability by two laser beams in photorefractive crystals

For a nonlinear medium, a given incident laser beam may produce different transmitted light waves. This phenomenon (the so-called optical bistability) corresponds to multiple solutions of the boundary value problems of the nonlinear Helmholtz equation. Optical bistability can be useful in the design of optical switches. Devices that display this behavior could potentially play a major role in the development of optical communication systems and computing. In this article we present experimental results concerning the optical bistability in photorefractive BaTiO₃:Fe crystal. Two laser beams were used to interact with the photorefractive crystal which resulted in the bistability of the intensity of transmitted wave. This was achieved without the application of any optical resonator. High contrast optical bistability is found experimentally in the pump-ratio dependence of the output intensity.     

Long-term stable thermally induced absorptive optical bistability in MBE-grown ZnSe epilayers

MBE-grown ZnSe epilayers released from their GaAs substrates exhibit thermally induced absorptive optical bistability of high contrast ratios and low switching powers in a wide temperature range up to room temperature. For increasing sample thickness or for enhanced reflection realized by inserting the samples into a resonator, counteracting dispersive switching becomes visible. The interplay of both the absorptive and dispersive effects is studied for different samples and varied experimental parameters. Long-term stability of the samples with regard to all switching effects makes them promising candidates for application studies.     

Optical bistability on a silicon chip

We demonstrate, for the first time to our knowledge, optical bistability on a highly integrated silicon device, using a 5-microm-radius ring resonator. The strong light-confinement nature of the resonator induces nonlinear optical response with low pump power. We show that the optical bistability allows all-optical functionalities, such as switching and memory with microsecond time response and a modulation depth of 10 dB, driven by pump power as low as 45 microW. Silicon optical bistability relies on a fast thermal nonlinear optical effect presenting a 500-kHz modulation bandwidth.     

Switchable lasing in multimode microcavities

We propose the new concept of a switchable multimode microlaser. As a generic, realistic model of a multimode microresonator a system of two coupled defects in a two-dimensional photonic crystal is considered. We demonstrate theoretically that lasing of the cavity into one selected resonator mode can be caused by injecting an appropriate optical pulse at the onset of laser action (injection seeding). Temporal mode-to-mode switching by reseeding the cavity after a short cooldown period is demonstrated by direct numerical solution. A qualitative analytical explanation of the mode switching in terms of the laser bistability is presented.     

有源-吸收分段式脊型波导半导体激光器的光双稳激射特性

本文报道了一种脊型波导有源-吸收分段结构半导体激光器中的光双稳输出特性的实验研究结果及其理论分析.给出了实验中发现的获取最大光滞回线宽度(Hysterisis)、所对应的器件结构参数以及电注入水平.此外,一种光线近似理论模型被采用来求解光输出特性从而得到了与实验近似一致的结果.     

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.     

Noticeable positive Doppler effect on optical bistability in an N-type active Raman gain atomic system

We theoretically investigate the Doppler effect on optical bistability in an N-type active Raman gain atomic system inside an optical ring cavity.It is shown that the Doppler effect can greatly enhance the dispersion and thus create the bistable behaviour or greatly increase the bistable region,which has been known as the positive Doppler effect on optical bistability.In addition,we find that a positive Doppler effect can change optical bistability from the hybrid dispersion-gain type to a dispersive type.     

Analysis of the spectral variation of a dye laser by gain medium inhomogeneity

In this paper, an analysis of spectral variation of a high repetition rate dye laser by an optical inhomogeneity developed inside the gain medium is presented. The passive band-pass, responsible for bandwidth, set (in homogeneous medium) by dispersive optical element in its resonator is modulated by scale length of the inhomogeneity introduced in the gain medium. Inhomogeneities, introduced by temperature in laminar flow (at low Reynolds number) and fractional change in flow-induced scale length (at higher Reynolds number) have an effect on the wavelength of dye laser.