Effect of conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT) nanotubes on electro-optical and dielectric properties of a ferroelectric liquid crystal

A detailed comparative study of the dielectric and electro-optical properties of a ferroelectric liquid crystal (FLC) and FLC after having doped with conducting polymer Poly (3,4-ethylenedioxythiophene) (PEDOT) nanotubes is done. The electro-optic study reveals a lower electrical response time, rotational viscosity and spontaneous polarization in the FLC/PEDOT nanocomposite system. By fitting the capacitance with voltage in a Preisach model, four dipolar species in both FLC and composites system have been obtained. The orientation of the four dipolar species in the composites system is such that the effective dipole moment in the transverse direction of the FLC molecule is less than that in FLC compound.     

Measurement of electro-optical parameters of a high contrast FLC film

We have fabricated a ferroelectric liquid crystal (FLC) film by using a novel ferroelectric mixture. The various ferroelectric parameters such as response time, spontaneous polarization and contrast ratio of the FLC film have been measured. Experimental results show that the FLC film exhibits high contrast ratios and fast optical response. The FLC film has a possibility of the use in display applications because of the performance characteristics.     

Polymer-doped ferroelectric liquid crystal: UV absorbance,fluorescence and electro-optical study

In this study, UV absorption, fluorescence and electro-optical study have been performed for pure ferroelectric liquid crystal (FLC) and its three different concentrations, i.e. 1%, 3% and 5% of fluorescent polymer in the pure FLC. We observed that there is higher value of UV absorption for fluorescent polymer-doped system in comparison to the pure system. We have found excitation wavelength, emission wavelength and quantum yield for all the mixtures. Quantum yield shows the probability of excited state being deactivated by fluorescence rather than non-radiative mechanism. The higher value of spontaneous polarization and faster response has been observed for fluorescent polymer-doped system compared to the pure FLC system. The electro-optical study also suggests that there exists an optimum concentration of fluorescent polymer for which we have found highest spontaneous polarization and least response time.     

Observation of memory behaviour in cadmium sulphide nanorods doped ferroelectric liquid crystal mixture

In this study, cadmium sulphide (CdS) nanorods doped ferroelectric liquid crystal (FLC) sample cells have been prepared and studied. A memory effect has been observed in CdS nanorods (≤0.3?wt%) doped FLC mixture and confirmed by textures, dielectric and optical studies. The addition of nanorods increases the memory behaviour and efficiency. The occurrence of memory behaviour has been explained due to charge transfer from liquid crystal molecules to CdS nanorods and exists there for 5–15?min in 0.1–0.3?wt% CdS nanorods doped samples. An improvement in polarization, switching time, threshold voltage and rise time parameters has also been noticed in CdS nanorods doped FLC samples.     

Surface anchoring effect on guest–host ferroelectric liquid crystal response time – an electro-optical investigation

The effect is reported of surface anchoring on various electro-optical parameters of a pure ferroelectric liquid crystal (FLC) and five mixtures with different concentrations of dye. The Anthraquinone D5 dye was used as guest entity, whereas Felix 17-000 was used as host in this investigation. The presence of dye molecules in the FLC dramatically affects the electro-optical properties compared with those of the pure system. Electro-optical parameters such as spontaneous polarization and rotational viscosity not only change with the addition of dye but they are also strongly dependent on the concentration of dye in pure FLC. The effect of dye molecules on the anchoring energy of the pure FLC system was also investigated. Due to strong anchoring energy on FLC substrate, its effect on response time was also studied. An improvement in the contrast ratio after dye doping was observed. The value of spontaneous polarization increases due to addition of dye, suggesting that molecular alignment improves, which is very useful from the application point of view.     

基于电路级模型的二维铁电液晶系统结构参数研究

提出将电路级模拟器扩展应用到二维铁电液晶(FLC)的光电混合系统。依照铁电液晶的理论模型建立等效电路,通过调整时序脉冲及驱动源波形,灵活地控制晶胞厚度、面积、粘滞系数、入射偏振角和自发极化强度等典型参数,实现了开关响应特性的动态模拟。比较铁电液晶与扭曲向列型液晶(TN)显示盒的差异。结果表明,该技术方法不仅适用于FLC结构参数指标的优化,而且对于其它集成光学器件的仿真技术研究也是一种有益地探索。     

Electro-optic and dielectric behavior of a FLC material having doped with a non-mesogenic polar molecules

Liquid crystal mixtures of non-mesogenic polar molecule with a commercial ferroelectric liquid crystal (FLC) mixture were prepared. Two mixtures were prepared by mixing 0.5% (w/w) and 1% (w/w) of polar molecules with commercial FLC mixture. Comprehensive studies of dielectric and electro-optic properties of the commercial FLC mixture and the polar molecules doped FLC mixtures have been made as a function of temperatures. Our studies reveal a higher tilt angle in lower concentration (0.5%) mixture but in case of 1% mixture tilt angle is decreased in comparison to 0.5% mixture. The spontaneous polarization of the commercial FLC mixture and other two mixtures is almost equal in magnitude at all temperatures. At the lower temperature region of SmC¹ phase, Goldstone mode (GM) dielectric strength of the commercial FLC mixture and low concentration (0.5%) mixture is found almost equal but it is slightly higher in case of high concentration (1%) mixture. With the increase of temperature GM dielectric strength of both the doped mixtures rapidly converges at different temperatures which are much lower than the temperature of transition (T_C) from SmC¹ – SmA phase. The results have been discussed.     

Bidimensional distortion in ferroelectric liquid crystals with strong anchoring in bookshelf geometry

In the last decade, it has been experimentally found that in certain conditions a periodic domain pattern arises in ferroelectric liquid crystals (FLC) in bookshelf geometry. Such a periodic texture appears after switching-off an external electric field, even in strong anchoring conditions. It has a static character and is bidimensional, being dependent on directions normal to both the smectic planes and the cell plates. Here a new model explaining this phenomenon is proposed, valid in the case of FLC with strong anchoring. The model is based on the coupling between the spontaneous polarization field in the first semi-period of its modulation along the cell plates and the same field in the second semi-period. This coupling competes with the FLC medium elasticity and is trapped by the anchoring. According to our model, in the ferroelectric state the biperiodic texture is favored by increasing the values of spontaneous polarization. The critical value of the spontaneous polarization for which the undeformed state becomes unstable is found. It is shown to be proportional to the square root of the ratio between the FLC elastic constant and the cell thickness. Moreover, it is inversely proportional to the sinus of the pre-tilt angle with respect to the cell walls.     

Suppression of relaxation modes in dye dispersed SmC* phase

We report the results of dielectric and electro-optical properties of ferroelectric liquid crystal (FLC), Felix 17/100, exhibiting chiral smectic C phase and dye dispersed FLCs. The polarization measurement on pristine and dye dispersed FLC mixture shows decrease in the value of polarization, indicating the distribution of dye dipole in a direction opposite to the orientation of FLC molecule. The rotational viscosity also decreases accordingly as shown by the measurement of response time. Dielectric measurement shows existence of two relaxation modes both in pure FLC and dye dispersed FLC. The relaxation strength of Goldstone mode decreases with the dispersion of dye and the relaxation frequency of this mode shifts towards the high-frequency side. The second relaxation mode arises due to the formation of domains at the surface interface. The dispersion of dye into FLC suppresses the domains.     

Dielectric and electro-optic behavior of pure ferroelectric liquid crystal material and the isomeric mixtures

We report here the dielectric relaxation spectroscopy and electro-optical properties of a ferroelectric liquid crystal (FLC) CB470 (R) and isomeric mixtures containing CB470 (R) and its optical isomer CB480 (S) in two different concentrations. We have studied with two isomeric mixtures: mixing CB470 (R) and CB480 (S) in the ratio 95:5 (w/w) and 90:10 (w/w). With increase of percentage of CB480 (S) in the mixture the spontaneous polarization (P_S) value has been decreased due to cancellation of a part of the dipolar contribution, since the direction of P_S of the two isomers are in opposite direction. The tilt angles of the pure FLC materials and the isomeric mixtures remain almost unchanged. The dielectric strength of Goldstone mode is almost proportional to the spontaneous polarization (P_S). An additional collective mode has been observed in the SmC¹ phase due to the formation of domain with large periodicity in pure FLC material and in one of the isomeric mixtures by unwinding the helical structures, which is known as domain mode. The existence of domain mode has been studied extensively with the variation of P_S in the isomeric mixtures. The result has been discussed.     

Electro-optic and dielectric studies of silica nanoparticle doped ferroelectric liquid crystal in SmC* phase

We present the results based on the electro-optic and dielectric properties of silica nanoparticle (SNP) doped ferroelectric liquid crystal (FLC) in SmC* phase. Switching time, spontaneous polarization and rotational viscosity decreases with increase in the silica concentration. An improvement in switching time after doping the silica nanoparticle is due to enhancement in anchoring energy exist between silica nanoparticle and ferroelectric liquid crystal. We noticed that the dielectric permittivity and dielectric strength decreases with increasing the concentration of silica nanoparticle in SmC* phase. Relaxation frequency increases with increasing the silica concentration and temperature in SmC* and decreases as we approaches towards transition temperature.     

Electro-optic properties of nematic and ferroelectric liquid crystalline nanocolloids doped with partially reduced graphene oxide

Flakes of partially reduced graphene oxide (PRGO) were doped in nematic liquid crystals (NLCs) and ferroelectric liquid crystals (FLCs), respectively. The dielectric and electro-optical properties of NLCs doped with those flakes have been investigated. Threshold voltage and switching times are reduced by 30%–50%. This is primarily due to the decrease of the elastic properties of the nanocolloids compared to the non-doped nematics. The influence of the PRGO flakes on the spontaneous polarization, tilt angle and switching time of FLCs was investigated too. Such flakes reduce the response time by 40%–60%, increases spontaneous polarization by 20%–25% and increase the tilt angle by 15%–20%.     

Integrated Electro-Optic Switches Based on Ferroelectric Liquid Crystal Waveguides

Two integrated electro-optic switches based on smectic C * ferroelectric liquid crystal (FLC) planar waveguides oriented in the bookshelf geometry have been designed and realized. In order to test the first switch, a particular waveguide structure consisting of a three-stage device, having a thin FLC film middle stage and two glass waveguides as other stages, has been designed and realized. The second one is realized by a planar waveguide with a smectic C * ferroelectric liquid crystal overlayer. In this article the design, the realization, and the experimental characterization of electro-optical switches are reported. The electro-optical behavior and the response time of both devices have been studied for different configurations for both TE and TM polarization. Our main aim was to demonstrate the feasibility of an integrated electro-optic device based on a FLC waveguide, and our experimental results provide a number of interesting indications about device optimization and practical applications.     

Effect of barium titanate nanoparticles of different particle sizes on electro-optic and dielectric properties of ferroelectric liquid crystal

A comparative study of two different particle sizes of ferroelectric barium titanate (BaTiO₃) nanoparticles as a dopant on the molecular structure, spontaneous polarization and dielectric behavior of a pure ferroelectric liquid crystal 6F₆T have been studied. It has been found that there is a remarkable decrease in isotropic temperature of both doped samples as compared to the pure 6F₆T sample. The spontaneous polarization also decreases for both the doped samples and the reduction is more pronounced in case of the dopant with large particle size. The dielectric spectroscopy confirms the presence of soft mode as well as Goldstone mode and also shows the decrease in the value of dielectric permittivity ?' as a function of frequency for both doped samples. The improvised properties of liquid crystal host doped with BaTiO₃ nanoparticles mainly depend upon the synthesis method of nanoparticles and also upon the particle size of dopant.     

一种结构新颖的L波段掺铒光纤激光器

提出了一种结构新颖的L波段环形腔掺铒光纤激光器。用掺铒光纤作为增益介,采用980nm激光器作为前向抽运源,利用起偏器和偏振控制器获得L波段激光,利用光环形器将后向的放大自发辐射再引入铒光纤的前端,重复利用。当抽运功率为103mW时得到了阈值功率约为23．87mW,输出功率达6．34mW的激光输出,斜率效率约为8．05％,与没有重复利用后向放大自发辐射谱的掺铒光纤激光器做比较,该结构对L波段掺铒光纤激光器的性能有明显的提升作用。对于长度不合适的铒纤,在没有重复利用后向放大自发辐射谱时没有获得激光输出;而在利用后向放大自发辐射后,在阈值功率约为88mW时得到了激光输出,从而很好地证明了上述结论。     

Effect of dichroic azo-dye doped on ferroelectric liquid crystals

In order to study the effect of mixing dye in ferroelectric liquid crystal （FLC） materials, the phase transition temperature and electro-optical properties of azo dye doped FLC samples have been investigated. All the properties have been found to be changed drastically. The results have revealed that not only the SmC^＊- SmA^＊ transition temperature decreased markedly by the addition of azo-dye, but also dye-doped FLC had lower threshold voltage and saturation voltage than the pure FLC.     

Gd 3+ -F − dimer centers in the ferroelectric lead germanate

The Gd³⁺ centers formed in lead germanate doped with fluorine have been studied using electron paramagnetic resonance. The parameters of the triclinic spin Hamiltonian are found at room temperature. The center is shown to be a gadolinium ion having the nearest environment in which the fluorine ion is substituted for the oxygen ion. The Gd-F dimer binding energy relative to the energy of a single gadolinium ion is determined. The interaction of the dimer center with the spontaneous polarization is lower than the measurement error.     

Dielectric and electro-optical studies of a nickel-ferrite-nanoparticle- doped ferroelectric liquid crystal mixture

Effect of magnetic nanoparticles (nickel ferrite) doping on the dielectric and electro-optical properties of a ferroelectric liquid crystal mixture has been studied. In a doped ferroelectric liquid crystal mixture, dispersion of a small amount (0.25 wt.%) of nickel ferrite nanoparticles decreases the polarization and improves the response time compared to an undoped mixture. The significant changes in the polarization and response time are explained on the basis of dipole–dipole interaction and anchoring phenomena. Dielectric permittivity also increases with increasing the temperature of the SmC* phase and shows a reduction in dielectric loss in a doped sample. A Goldstone mode is clearly observed at ～200 and ～500 Hz in an undoped and a doped sample, respectively.     

Characteristic behaviour of spontaneous polarization and dielectric constant of barium titanate containing cobalt ions

The temperature dependence of the dielectric constant and the spontaneous polarization as well as the effect of their thermal history has been investigated for BaTiO₃ crystals doped with Co. Experimental evidence for diffuse phase transitions (DPT) is found. Results are interpreted taking into account that in the crystal exists a relatively large amount of disorder which can be pictured as a change in the local configuration of substituted Co-ions.     

Novel liquid crystal multistage circular polarization switch for three-dimensional laser pico projectors

Crosstalk is one of the most important factors affecting the image quality of polarization switching three-dimensional (3D) projectors. The variation in the phase difference of a polarization switch owing to dispersion degrades crosstalk performance. We propose a novel multistage circular polarization switch comprising liquid crystal devices using a ferroelectric liquid crystal (FLC) in-plane fast switch and a thick nematic liquid crystal (NLC) retarder. In this paper, we present a proof-of-concept model of a 3D laser pico projector using a scanning MEMS head in combination with the polarization switch. We also evaluate the crosstalk and 3D performance of the projector.