掺杂浓度与溶剂对偶氮聚合物薄膜全光开关

用重复旋转涂膜法制备了乙基红(ER)偶氮染料与聚甲基丙烯酸甲酯(PMMA)掺杂聚合物薄膜和乙基橙(EO)与聚乙烯醇(PVA)掺杂聚合物薄膜.测量了两种聚合物薄膜样品全光开关特性,比较分析了薄膜样品的掺杂浓度和溶剂对全光开关效应的影响,实验结果表明:增加掺杂浓度和溶剂,极性薄膜样品的全光开关效应增强且开关的本底信号增大,但对开关的响应速度影响很小;选择合适的掺杂浓度和强极性溶剂,在室温和几个mW的弱功率控制光条件下聚合物薄膜具有毫秒级开关响应时间和40%以上的开关调制深度,最大的调制深度达72%以上.     

Investigation of SOA-assisted Sagnac recirculating shift register switching characteristics

The switching characteristics of a Semiconductor Optical Amplifier (SOA)-assisted Sagnac recirculating shift register with an inverter are investigated by undertaking a numerical analysis that describes the dynamic gain response of the SOA to high speed and strong feedback optical pulses. The key performance parameters are identified and their role in the formation of the switching window is analyzed. The optimum values of these parameters are not unique and must be adapted to the specific all-optical shift register network application. For this reason, they must be properly selected and combined so as to ensure the satisfaction of the desired operating conditions. The technical restrictions that the derived values may impose on the state-of-the-art photonics technology are also discussed and efficient ways of overcoming them are proposed.     

Micromagnetic investigation of all-optical switching

This Letter investigates all-optical magnetization switching from micromagnetic perspective. The influence of circularly polarized light on a magnetic sample was considered to be both directly through the inverse Faraday effect and indirectly aided by thermal induced effects by the laser beam. Dependence of all-optical switching on pulse duration, laser intensity and the magneto-optical susceptibility strength is studied. An important aspect of this investigation is the analysis of how the cooling process influences the successive switches, especially through limiting the successive writing time.     

Permanent light-induced polar orientation via all-optical poling and photothermal cross-linking in a polymer thin film

An epoxy-based crosslinkable polymer functionalized with nonlinear optical (NLO) photochromic dye known as Red Acid Magly was polarly oriented via thermally-assisted all-optical poling to enhance the photostability of the induced order. During the writing (seeding) process the film was cross-linked by heating with a hot-plate and irradiated simultaneously by the coherent superposition of the 1.06 μm fundamental and 0.532 μm second harmonic beams of a nanosecond pulsed Nd:YAG laser. We demonstrate that crosslinking between the polymer matrix and the pendant chromophore groups induced during the thermally-assisted all-optical poling procedure results in a stable light-induced second order susceptibility.     

Phase-controlled all-optical switching based on coherent population oscillation in a two-level system

We theoretically propose a scheme of phase-controlled all-optical switching due to the effect of degenerate four-wave mixing (FWM) and coherent population oscillation (CPO) in a two-level system driven by a strong coupling field and two weak symmetrically detuned fields. The results show that the phase of the FWM field can be utilized to switch between constructive and destructive interference, which can lead to the transmission or attenuation of the probe field and thus switch the field on or off. We also find the intensity of the coupling field and the propagation distance have great influence on the performance of the switching. In our scheme, due to the quick response in semiconductor systems, a fast all-optical switching can be realized at low light level.     

Enhancement of modulation depth of an all-optical switch using an azo dye-ethyl red film

The polymethyl methacrylate (PMMA) film doped with an azo dye ethyl-red (ER) film is employed to demonstrate the properties of an all-optical switch by its photoinduced dichroism and birefringence. We show how to enhance remarkably the modulation depth of all-optical switches almost to 100% by using two linear polarization beams: one beam is inclined at 45o with respect to the probing beam and serves as a pumping beam, and the other beam is perpendicular to the probing beam and used as an erasing beam. Furthermore, a maximum-to-minimum output intensity ratio of 2000:1 is achieved in experiment, which is very useful and important for optical storages and image displays.     

A method of developing all-optical mono-stable multivibrator system exploiting the Kerr non-linearity of medium

Optics has already been established as a potential candidate for conduction of digital logic and arithmetic operation in communication and computation processes. Different proposals have been reported by different scientists to make optics meaningful signal for conduction of the above operations. As it is well known that the memory device is a basic building block of any computation and communication system hence developing systems such as digital memory, multivibrator, etc. are the obvious requirements for optical communication as well as computation systems also. As the role of switching devices is an essential part of any processing system, many proposals were seen where all-optical switches using the combination of linear and non-linear materials were used, to implement the logic elements.In this context, the authors propose a new scheme for implementation of an all-optical mono-stable multivibrator using the non-linear material based switches and high refractive index based material. This multivibrator can generate a time pulse of definite width.     

A novel realization of all-optical dibit represented frequency encoded Boolean and quaternary inverters without switching device

All-optical frequency encoded dibit representation technique conduct real-time operations with ultra high switching speed rather than all conventional optoelectronic, optical and all-optical switches. So, a high degree of parallelism can be exploited from these proposed systems.     

偶氮聚合物薄膜的全光极化研究

报告了分散红共聚物膜HMMM-DR1,HMMM-DR19和偶氮侧链聚合物膜PCN6和PCN2的合成和制备, 并以HMMM-DR1和PCN6为代表比较研究了这两种具有不同吸收性质材料的全光极化特性,研究了他们的实时极化和弛豫过程,对他们的全光极化性质作了最基本的表征.研究了倍频光吸收对薄膜光极化效率的影响,讨论了偶氮聚合物材料光诱导二阶非线性极化率的效率和倍频光透射率之间的折衷关系,这对实用化的全光器件的研制是至关重要的.实验确证了在PCN6薄膜中实现了准相位匹配.对厚膜中光诱导二阶非线性极化率的弛豫抑制效应作出解释.     

Demonstration of an all-optical switching operation using an optical fiber grating coupler

An optical fiber grating coupler (FGC) is a fused optical fiber coupler with a tapered region in which refractive index-modulated gratings are written. In the FGC, the light with specific wavelength satisfying the Bragg condition of the grating can be dropped to one output port and other lights are transmitted to another output port when lights with various wavelengths are launched into the input port. The FGC can operate as an all-optical switch by controlling the Bragg wavelength of the grating using a third order nonlinear optical effect caused by a control light that are launched with a signal light. In this paper, an all-optical switching operation due to a third order nonlinear optical effect in an FGC is first demonstrated for a signal light with 1.55 μm-wavelength to be changed from one port of the FGC to another one by the 720 W peak of a control light from a Nd:YAG laser with 1.06 μm-wavelength. The switching efficiency obtained was 7%. It was clarified that a longer pulse length of the control light compared to the grating length is required to obtain a large Bragg wavelength shift for the switching. It was also clarified that the Bragg wavelength shift is caused by a third order nonlinear effect and a photothermal effect. A contribution of the photothermal effect was estimated. We also estimated the switching efficiency for pump power in the FGC switch.     

Design of high-Q silicon-polymer hybrid photonic crystal nanobeam microcavities for low-power and ultrafast all-optical switching

Owing to the unique optical properties high-Q photonic crystal nanobeam microcavities have been demonstrated in a variety of materials. In this paper the design of high-Q silicon-polymer hybrid photonic crystal nanobeam microcavities is investigated using the three-dimensional plane-wave expansion method and finite-difference time-domain method. We first discuss the design of high-Q nanobeam microcavities in silicon-on-insulator, after which the polymer is introduced into the air void to form the hybrid structures. Quality factor as high as 1 × 10⁴ has been obtained for our silicon-polymer hybrid nanobeam microcavities without exhaustive parameter examination. In addition the field distribution of resonant mode can be tuned to largely overlap with polymer materials. Because of the overwhelmingly large Kerr nonlinearity of polymer over silicon, the application in all-optical switching is presented by studying the shift of the resonant frequency on the change of refractive index of polymer. The minimum switching intensity of only 0.37 GW/cm² is extracted for our high-Q hybrid microcavities and the corresponding single pulse energy is also discussed according to the pumping methods. The total switching time is expected to be restricted by the photon lifetime in cavity due to the ultrafast response speed of polymer. Our silicon-polymer hybrid nanobeam microcavities show great promise in constructing small-sized all-optical devices or circuits with advantages of possessing low-power and ultrafast speed simultaneously.     

Design of an all-optical switch and arbitrary proportion of energy output beam splitter

Based on the Kerr effect of photonic crystal, we design a simple structure of all-optical switch, which can be controlled by the pump intensity. At the same time, the structure can also realize the free control of energy output. It has low insertion loss and crosstalk. Numerical simulation results embody its high efficiency.     

Improvement of all-optical switching performance based on azo dye-doped polymer film using two cross-linearly polarized pump beams

We propose a method for improving the characteristics of all-optical switching based on azo dye-doped polymers. Using alternately two cross-linearly polarized beams (532 nm, continuous light wave (CW)) to pump azo dye–ethyl red (ER) doped polymer methyl methacrylate (PMMA) film, the modulation depth of the all-optical switching reached 96% at the pump powers of 4.8 mW and 1.6 mW and the modulation frequency of 1000 Hz. For comparison, we used respectively the single linearly polarized beam (4.8 mW) and the alternately linear–circular polarized beams (4.8 mW and 1.6 mW) to pump the film at the modulation frequency of 1000 Hz, the obtained modulation depths of the all-optical switching were 36% and 45.8%, respectively. Furthermore, the experimental measurement and analysis showed that the turn off speed of the all-optical switching could be obviously increased by use of our pump method.     

Improvement of all-optical switching effect based on azobenzene-containing polymer films

A method for improving the quality of all-optical switching is presented. Pumping poly(methyl methacrylate) (PMMA) films doped with azobenzene chromophore Disperse Red 1 (DR1) with two beams (a linearly and a circularly polarized), all-optical switching effects with very low background and high stability are demonstrated. High frequency switching, which is hard to be realized under pump of a single beam, is obtained. The circularly polarized pump beam can erase the photoinduced birefringence and quicken the relaxation process, thus lowering the background and improving the stability and the extinction ratio of the switching signal. PACS 42.70.Jk; 42.25.Lc; 82.30.Qt; 78.20.Fm; 77.80.Fm     

Implementation of an all-optical binary comparator based on material nonlinearity and polarization encoded light signal

Bitwise comparison and classification of binary data is an essential requirement in digital signal and image processing applications. Here in this paper a new method of a one bit all-optical binary comparison scheme is proposed. This scheme is developed by the proper use of optical nonlinear material and also polarization encoding technique. Very high speed performance can be adopted easily in this mechanism. The scheme can be used to compare any two bits such as 0 and 0, 0 and 1, 1 and 0, 1 and 1.     

An all-optical switch/photodetection at 1550 nm,based on a micro-ring resonator array

In this paper, a photodetector based on InGaAs micro-ring resonator array with 5 μm radius, in telecommunication wavelength region has been investigated. Then for the first time to our knowledge, with the change of refractive index due to optical nonlinear effects (such as: Kerr effect, two photon absorption, free carrier dispersion and free carrier absorption), an all-optical switch, based on pump-probe configuration using this photodetector have been proposed. So, the suggested device, will introduce a dual functionality that is important from view point of economically purposes and in term of integration. By numerically solving the light propagation equations, with FDTD and Crank–Nicolson methods, in addition to steady state and transient response, also we have found the frequency response, in both configurations. With increasing reverse bias voltage, and optimizing the free carrier transportation from absorption region, switching frequency can be increased up to 200 GHz. Also by optimal choosing of parameters such as the number of rings and spaces between two adjacent rings and so on, the box-like spectral response of photodetector with high efficiency is achievable.     

A novel method of developing all-optical frequency encoded memory unit exploiting nonlinear switching character of semiconductor optical amplifier

The very fast running optical memory and optical logic gates are the basic building blocks for any optical computing data processing system. Realization of a very fast memory-cell in the optical domain is very challenging. In the last two decades many methods of implementing all-optical flip-flops have been proposed. Most of these suffer from speed limitation because of low switching response of the active devices. In our present communication the authors propose a method of developing a frequency encoded memory unit based on the switching action of semiconductor optical amplifier (SOA). Nonlinear polarization rotation characters of SOA and ‘SOA based Mach-Zehnder Interferometer’ switch, i.e. ‘SOA-MZI’ switch, are exploited for the purpose of some switching action with least switching power (<−3 dB_m) and high switching contrast ratio (20 dB). Here two logic states (‘0’ state and ‘1’ state) of the memory is encoded by two different frequencies, which will remain unchanged throughout the data communication irrespective of loss of light energy due to reflection, refraction, attenuation, etc. Though the SOA based switch runs with the operational speed 100 Gb/s, still due to the presence of the other optical components in the memory unit, the overall speed of the proposed system will come down to 10 Gb/s.     

Fabrication of high-quality colloidal photonic crystals with sharp band edges for ultrafast all-optical switching

Application of the pressure controlled isothermal heating vertical deposition method to the fabrication of colloidal photonic crystals is systematically investigated in this paper. The fabricated samples are characterized by scanning electron microscope and transmission spectrum. High-quality samples with large transmissions in the pass bands and the sharp band edges are obtained and the optimum growth condition is determined. For the best sample, the transmission in the pass bands approaches 0.9 while that in the band gap reaches 0.1. More importantly, the maximum differential transmission as high as 0.1/nm is achieved. In addition, it is found that the number of stacking layers does not increase linearly with concentration of PS spheres in a solution, and a gradual saturation occurs when the concentration of PS spheres exceeds 1.5 wt.%. The uniformity of the fabricated samples is examined by transmission measurements on areas with different sizes. Finally, the tolerance of the fabricated samples to baking was studied.     

Effect of amplified spontaneous emission on semiconductor optical amplifier based all-optical logic

The performances of all-optical logic gates XOR, AND, OR, NOR and NAND based on semiconductor optical amplifier (SOA) have been simulated including the effects of amplified spontaneous emission (ASE). For the parameters used, all-optical logic gates using SOA are capable of operating at speed of 80 Gb/s.     

Static and dynamic analysis of an all-optical inverter based on a Vertical Cavity Semiconductor Optical Amplifier (VCSOA)

We report the static and dynamic properties of an all-optical inverter based on an 850 nm Vertical Cavity Semiconductor Optical Amplifier (VCSOA). The inverter exhibits low switching power requirements (~ 15 μW), large on/off contrast ratio (> 11 dB), and high speed operation (~ 1.4 GHz). Large and small signal measurements show that the speed of operation and the on/off contrast ratio improve with increased bias current. This holds important prospects for the development of VCSOA-inverters for high-speed, low-power optical logic applications. Finally, a theoretical model of the VCSOA-inverter has been employed giving good agreement with experiments.