Effect of chirped gratings on reflective optical bistability in DFBsemiconductor laser amplifiers

We use spatial chirp of the built-in grating to improve optical bistability on reflection from distributed feedback semiconductor laser amplifiers. We show that improvements in the on-off switching ratio occur because spatial chirp greatly affects the saturation behavior of the reflectivity resonances, allowing access to states of low reflection during bistable switching. We also show that spatial chirp modifies the spectral range of the variety of hysteresis shapes that occur on reflection. In doing so, we discover a new type of hysteresis loop that reveals a qualitative difference between the loop-shaped hystereses occurring near the two edges of the stop band. With spatial chirp, the new hysteresis loop can exhibit an on-off switching ratio in excess of 100000     

Highly reflective fiber Bragg gratings written through a vinylether fiber coating

Highly reflective fiber Bragg gratings (reflectivity >99.99%, -45 dB in transmission) have been written through a 55-μm-thick novel polymer fiber coating in a low (5 mole%) germania-doped optical fiber. The coating is based on vinyl ether chemistry using a cationic photoinitiator     

微结构相移光纤光栅的反射谱特性分析

相移光纤光栅作为一种透射型滤波器,在光通信和传感领域有着广泛的应用.文章介绍了一种基于光纤包层刻蚀技术的新型微结构相移光栅,利用光纤双包层理论分析了包层刻蚀深度和环境折射率对纤芯基模有效折射率的影响,并将谐振理论与传输矩阵法相结合,详细分析了刻蚀深度、刻蚀宽度和刻蚀位置与微结构相移光纤光栅的反射谱之间的关系.     

Optical fiber gas sensor based on self-assembled gratings

The electrostatic self-assembled monolayer synthesis process is used to fabricate gas sensors by building up grating sensor elements on the ends of multimode optical fibers. These novel sensors can be designed to operate in the transmission windows of standard optical fibers and implemented using specific reference wavelengths to normalize the output signals. Experimental results for such sensors designed to detect dichloromethane gas are presented     

Optical bistability in nonlinear fiber resonators driven by lasersources of arbitrary coherence

We present a theory of optical bistability for fiber resonators driven by amplitude-stabilized laser sources of arbitrary coherence. The nonlinear wave equation is solved and the results are applied to analyze the effect of the source coherence on the relevant parameters of the structure such as the switch-on and switch-off powers, the critical input power for the onset of bistability and the cavity critical mistuning     

Optical bistability in an L-band dual-wavelength erbium-doped fiber laser with overlapping cavities

The authors investigate the optical bistability in an L-band dual-wavelength erbium-doped fiber (EDF) laser with overlapping cavities. The bistable input-output hysteresis behavior of the two lasing wavelengths evolves in antiphase. The bistable region is tens of milliwatts wide. The bistability is essentially due to the homogeneous saturable absorption of EDF. The cross-gain saturation causes the bistabilities of the two lasing lines to evolve in antiphase with respect to each other. The gain clamping effect helps to widen the bistable region, which may be controlled by the cavity loss and by the EDF length.     

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.     

基于光子晶体光纤长周期光栅的传感器研究

详细研究了光子晶体光纤长周期光栅(LPG-PCF)的应力和温度特性,利用成功制作的温度不敏感PCF-LPG,实现了两种结构简单光纤传感器.在温度不敏感应力传感器中,PCF-LPG作为温度不敏感的应力传感头,当以波长为1553nm的分布反馈(DFB)激光器为入射光源、用分辨率为0.001dB的光功率计测量时,PCF-LP...     

Optical spectral bistability in a semiconductor fiber ring laserthrough gain saturation in an SOA

We demonstrate the operation of optical bistability in a widely tunable semiconductor fiber ring laser, using a semiconductor optical amplifier (SOA). The laser can be operated in two bistable states: the spectrum of the first state has one main lasing peak with very narrow linewidth, and the second state has simultaneous oscillation of two main peaks at different wavelengths. The two bistable states can be switched to each other using either electrical or optical methods. We further explain the bistable operation using the theory of two-mode competition through gain saturation in the SOA     

Large-time-bandwidth-product surface-wave pulse compressor employing reflective gratings

A novel dispersive delay line with a time-bandwidth product in excess of 1500 has been developed. The device uses the reflection of elastic surface waves from sputter-etched gratings on LiNbO3. This reflective-array compressor is relatively free of the spurious signals which limit the performance of inter-digital transducer arrays.     

Optical bistability in semiconductor periodic structures

A theoretical demonstration of optical bistability in periodic layered media, particularly in long-period GaAs/AlAs superlattices is presented. The proposed structure consists of a periodic multilayer system, as opposed to previously demonstrated nonlinear bistable devices which employed Fabry-Perot etalons. The optical resonance effect which is essential for bistable devices is, in this case, induced by a refractive index modulation. The nonlinear active medium is distributed in the whole structure rather than placed between the two mirrors of a Fabry-Perot cavity. It is shown by a complete calculation of wave propagation in the periodic nonlinear medium that a multiple valued feature appears in the structure's nonlinear reflectivity spectrum. The input/output characteristics of the structure exhibit bistable hysteresis similar to that of a nonlinear Fabry-Perot etalon     

光学双稳态及其应用

本文综述了光学双稳态的物理概念、光学双稳器件的发展及其可能的应用。     

Optical bistability from three-level atoms

A novel mechanism is proposed for optical bistability utilizing the population trapping which may occur in a coherent superposition of sublevels in a three-level system. The resulting bistability does not require atomic saturation and is insensitive to Doppler and laser bandwidth effects.     

二元相位取样光纤Bragg光栅型光分插复用器方案

结合马赫-曾德干涉仪(MZI)和二元相位取样光纤布拉格光栅(BP-SFBG)构造出了一种具备多信道处理功能的光分插复用器(OADM).首先利用传输矩阵法建立了OADM的理论模型,再结合传输矩阵法和Chebyshev恒等式实现对BP-SFBG的快速分析和计算;最后给出了一个仿真设计的实例,数值结果表现出了良好的性能,为具体器件的研制提供了有益的参考.     

基于反射光栅的超精密定位系统研究

应用光学理论研究了一种μm级位移分辨率的反射型双级光栅测量系统,建立了反射莫尔信号与对应位移的数学模型,通过计算机仿真分析了反射莫尔信号的位移特性,进而设计了一套基于反射光栅的精密定位系统。系统取反射的0次激光莫尔信号为控制信号,由微机控制实现高精度位置检测及超精密自动定位;采用的修正莫尔技术,极大地提高了位置检测信号的灵敏度及定位精度;通过粗定位和精定位相结合的两段式复合定位,实现高速高精度定位。实验结果表明,基于反射光栅的精密定位系统可获得±10nm的定位精度。     

Optical bistability in a radially varying mode

The theory of optical bistability in an interferometer with a nonlinear absorber is treated, including radial variation in the mode function. Dispersive effects and inhomogeneous broadening are included in the resulting analytic state equations. These realistic equations requite much greater cooperativity (or atomic absorption), relative to the plane-wave theory, before bistability exists.     

Optical bistability in a nonlinear directional coupler

In the nonlinear directional coupler, the optical field and the nonlinear material usually interact in a spatially and temporally local fashion and the device exhibits a nonlinear transmission characteristics, but it is not bistable. In this paper, it is shown theoretically that optical bistability in the input optical power is possible for the nonlinear directional coupler if the local phase change of the optical mode propagating through tile coupler is influenced by the excitation over the whole coupler. This condition can be satisfied in a coupler based on biased-pin-diodes comprising coupled asymmetric quantum wells in the i-region, Calculations show that in this configuration, the nonlinear directional coupler can exhibit sharp switching characteristics, low switching optical powers, optical bistability or bifurcation     

Step-changed long-period fiber gratings

The spectral characteristics of a new type of long-period grating (LPG) structure, step-changed LPG, are investigated theoretically and experimentally. It is shown that the spectral profile of such gratings can be tailored by adjusting the step parameters. A good agreement between simulated results and measured spectra is obtained. This type of LPG has potential applications in gain flattening of erbium-doped fiber amplifiers