Natural and artificial light-harvesting systems utilizing the functions of carotenoids

Carotenoids are essential pigments in natural photosynthesis. They absorb in the blue–green region of the solar spectrum and transfer the absorbed energy to (bacterio-)chlorophylls, and so expand the wavelength range of light that is able to drive photosynthesis. This process is an example of singlet–singlet energy transfer and so carotenoids serve to enhance the overall efficiency of photosynthetic light reactions. Carotenoids also act to protect photosynthetic organisms from the harmful effects of excess exposure to light. In this case, triplet–triplet energy transfer from (bacterio-)chlorophyll to carotenoid plays a key role in this photoprotective reaction. In the light-harvesting pigment–protein complexes from purple photosynthetic bacteria and chlorophytes, carotenoids have an additional role, namely the structural stabilization of those complexes. In this article we review what is currently known about how carotenoids discharge these functions. The molecular architecture of photosynthetic systems will be outlined to provide a basis from which to describe the photochemistry of carotenoids, which underlies most of their important functions in photosynthesis. Then, the possibility to utilize the functions of carotenoids in artificial photosynthetic light-harvesting systems will be discussed. Some examples of the model systems are introduced.     

All- optical phase encoded 4-to-1 phase multiplexer using four wave mixing in semiconductor optical amplifier

Optics has already showed its potency over its electronic complements in case of superfast computing and communication systems. Semiconductor optical amplifier, (SOA) with its several nonlinear properties, plays a very crucial role in the development of high-speed all-optical processor. Multiplexer and demultiplexer are the extremely important element of the processor which takes part in utilizing different actions like encoding, decoding, routing, and the different process of data conversion and generation, etc. In this paper, the authors have proposed a scheme of phase encoded all-optical phase multiplexer using four wave mixing (FWM) property of semiconductor optical amplifier. Thus, the improved tolerance against fiber-nonlinearity and higher receiver sensitivity of phase encoding method with the fast occurring processes like FWM in SOA offers higher speed in this proposed scheme of multiplexing.     

Designs of all-optical NOR gates using SOA based MZI

The paper investigates the non-linear behavior of semiconductor optical amplifier with Mach–Zehnder interferometer (SOA-MZI) configuration which makes it to work as a logic gate. The two designs of NOR gate based on SOA-MZI have been verified. The basic principal of both designs are same. The summation of data pulses have been taken and inverted to perform a NOR operation. In the design, the first 3 dB coupler creates a phase difference of π/2 in clock pulse and data pulse while passing through two interferometer arms. The clock and data pulses pass through SOA which attenuates the clock pulse wherever the data pulse is present. After passing through second 3 dB coupler a phase difference of π/2 is again created. Therefore, if the clock pulse is in the same phase will be added and if it is out of phase, will be canceled. The designs have been investigated at different bit-rates to achieve higher extinction ratio (ER), Q-factor and bit-error rate (BER) for different pump currents of SOA.     

Generation of new longitudinal modes in an amplifying dye solution

A novel phenomenon is reported for the first time that the generation of the newlongitudinal modes in amplifying multi-longitudinal mode laser in a dye amplifier.The newmodes are located on the violet side within the gain band of the amplifing medium.The phe-nomenon is explained by the theory of third-order nonlinear polarization in the case of four-wave resonances.The intensity of the new modes created are comparable with or even higherthan that of the original modes.The effect can be expected to serve as a new method for ex-tention of spectral tuning ranges of laser.     

Relaxation times effects on the four wave-mixing signal for π-conjugated push-pull molecules within the two-state valence-bond charge-transfer model

We have theoretically studied the four wave-mixing signal for π-conjugated push-pull molecules in the context of the simple valence-bond charge-transfer model. In particular, we address the effect of modify the rate between the longitudinal and transversal relaxation times on this signal considering the variation of the parameter f (fraction of the charge-transfer resonance structure of the ground state). Our results show notable changes in intensity of the peaks of the four wave-mixing (FWM) spectrum with relation to the variation in the ratio of the relaxation times.     

非相干光作用下的Ce：BaTiO3自泵浦相位共轭镜特性

地Ｃｅ：ＢａＴｉＯ３晶体的自泵浦相位共竟然非相干光作用下自泵浦相位共轭反射率增强的特性进行了研究。实验是在Ｈｅ－Ｎｅ激光产生稳态自泵浦相位共轭输出后，用非相干光平行ｃ轴照射来获得这一增强特性的，当水平移动非相干光入射位置，发现有两个区域非相干光作用能使相位共轭反射率增加，本文对此进行了相应的分析和讨论。     

汞蒸汽中双光子共振四波和频产生125nm的相干辐射

利用汞原子6~1S_0—7~1S_0双光子共振四波和频产生了125nm的相干辐射.对双光子共振增强效应、双光子共振克尔(Kerr)效应进行了研究.讨论了平面波和聚焦情况下最佳相位匹配的条件.实验中还观测到了四波参量振荡和四波差频的信号输出.     

Four Wave Mixing of the Signal and ASE Noisein Long Distance Optical Communication System

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Studies on multi-wavelength fiber Bragg grating laser strain sensor

A novel stable multi-wavelength fiber Bragg grating laser is achieved and its sensing characteristic with the strain is studied. The beat signals generated by the multi-wavelength fiber laser are measured under different strains. Four-wave mixing (FWM) is firstly observed in such a short-cavity fiber laser.     

Simulation of high capacity 40 Gb/s long haul DWDM system using different modulation formats and dispersion compensation schemes in the presence of Kerr's effect

In this paper, simulative analysis of 40 Gb/s long haul (500-2000 km) DWDM system with ultra high capacity upto 1.28 Tb/s has been carried out for carrier-suppressed return-to-zero (CSRZ), duobinary return-to-zero (DRZ) and modified duobinary return-to-zero (MDRZ) modulation formats. The DWDM system has been analyzed for the pre, post and symmetrical dispersion compensation schemes for 16 Channels with 25 GHz channel spacing in order to find the optimum modulation format for a high bit rate optical transmission system. The effect of variation in input power and transmission distances is observed in terms of Q value and eye opening for various formats. It is found that symmetrical compensation is superior to pre and post dispersion compensation schemes. It has also been observed that the performance of DWDM system is severely limited by the four-wave mixing (FWM) effect and is determined that MDRZ format seems to be the best choice for the transmission distance beyond 1550 km despite slightly more complex transmitter and receiver configuration. Further, symmetrical compensation scheme has been investigated for 32×40 Gb/s MDRZ format for faithful transmission over 1450 km.