Ferroelectric polymers are well known for their piezoelectric and pyroelectric applications. We have investigated their electro-optic properties using the attenuated total reflection method. Two different polymers were studied. P(VDF-TrFe) is an highly crystalline ferroelectric polymer which presents a well defined Curie temperature (100°C) and which can be polarized at room temperature, while P(VDCN-VAc) is an amorphous polymer which exhibits only a glass transition at 170°C. The high polarization which can be obtained in this polymer led some authors to refer it as a ferroelectric glass. We have shown that the attenuated total reflection allowed us to measure the electro-optic coefficient together with the piezoelectric coefficient. Futhermore, it is possible to separate the primary electrooptic coefficient from the secondary one which is due to the variation of density induced by the piezoelectric effect. Inversed polarization gives electrooptic coefficient with opposite sign. Because of their inherent thermodynamic stability, these ferroelectric polymers are very suitable for applications and their electrooptic coefficient can be surely increased by doping with non-linear active molecules.
The electro-optic effect in an electric-field-aligned side-chain polymer is investigated. The polymer contains dipolar hyperpolarizable molecules as pendant groups. The hyperpolarizable group is 4-oxy-4'-nitrostilbene. The dielectric strength of the polymer material has been measured and is over 200 MV/m. Measurements on the electro-optic coefficients are reported. Two experimental methods are used. From a crossed-polarizers set-up r33-r13=0.58 pm/V is obtained. From an interferometric set-up r13=0.27 pm/V is obtained. Combining the results of both methods yields r33=0.85 pm/V and r33/r13=3.1. The results are in agreement with theoretical predictions based on the isotropic model for electric-field-induced alignment.
A new analog phase modulator operating at 10.6μm using a Nematic Liquid Crystal thin film allows very accurate phase control with a 2π phase shift and response times τup and τdown lower than 300μs for low applied voltages (250V). These performances are achieved with a four electrodes structure generating an electric field whose direction is continuously controlled from 0° to 90° and always forces the NLC molecules in rotation.
A pronounced photorefractive effect in La3Ga5SiO14-Pr3+ crystal has been revealed. This is the first observation of the photorefraction caused by a bulk photovoltaic effect in photosensitive piezoelectrics. Owing to symmetry pecularities of a bulk photovoltaic effect in trigonal La3Ga5Si014, a value and a sign of the photorefraction depend on the orientation of an inducing light polarization vector. Experimental photorefraction data are in good accord with phenomenological description. The discovered phenomenon may lead to advanced application of La3Ga5Si014 crystals in photorefractive recording and holographic adaptive optics.
The photorefractive properties of LiNb03:Fe bulk crystals with different proton concentrations and of proton-exchanged planar waveguides fabricated with LiNb03:Fe substrates are investigated. The saturation values of refractive index change, the photoconductivity, the photorefractive sensitivity and the photovoltaic current density of bulk LiNb03:Fe crystals are only determined by the Fe impurities and do not depend on proton concentration. But the dark conductivity is increased by protons. In Li1-xHxNb03 waveguides we find after fabrication a strong decrease of the saturation value of light-induced refractive index change due to an increase of dark conductivity and a decrease of the electrooptic coefficients. Absorption measurements indicate that mainly Fe3+ ions are present in the waveguide region. After annealing photorefractive index changes increase and the dark conductivity decreases again.
An electrooptic LiNbO3 filter is used for tuning free running oscillation (720-900 nm) and giant pulses (760-820 nm) of a flash lamp pumped Ti:A12O3 laser. The tuning laser characteristics and the peculiarities of electrooptic filters application in tunable laser resonators are analyzed.
(100) oriented PLZT(28/0/100) thin solid films on the amorphous substrates have been deposited by R.F. planar magnetron sputtering with the powder targets. Only (100), (200) peaks were found in the XRD spectrUm. The oriented degree F(100) is about one. Transmission of the thin films is more than 80% in visible spectrum. As-sputtered PLT thin fillms are amorphous. After annealing at 600°C/4hr. in air, the thin films were crystallized and oriented grow along (100) direction on the amorphous substrates. The composition of the target and thin filMs may be different which is depended on the deposition conditions such as substrate temperature, sputtering voltage and so on. The ratio of Pb/La becomes smaller as the substrate temperature goes higher and the ratio of Ti/La becomes larger as substrate temperature goes higher. Stoichiometric PLT thin films were obtained by varying the composition of the target at same deposition conditions.
Polymer electrolyte - based display devices are of growing importance in view of their specific properties compared to liquid devices. One of them is, of course, the possibility to obtain all solid-state devices without leakage and another one, may be more interesting, is the possibility to obtain a strong dependence of the response time of the display on the temperature. Such a property may be conveniently used for the realization of devices with specific applications such as thermal sensors or heated display devices, for instance. The optical response characteristics of amorphous W03/polymeric electrolyte/stainless steel electrochromic display (ECD) devices have been investigated using cyclic voltammetry and chronoamperometry coupled with optical reflection measurements. The variations of both the colouration time and the colouring efficency with temperature are related to both the ionic conductivity of the polymer and the phase diagram of the polymer.
KxMoS2 (0.15 ≤ x ≤ 0.25) thin films have been deposited by electroless deposition technique. As deposited films are p-type.The resistivity and the Hall mobility have been measured over the temperature range 290 to 77K. The optical absorption spectrum has been found to show the absorption edge at ~2.75μm at 77°C. These films have shown superconducting transition at 15-20°K.
Periodically corrugated optical waveguides on glass with non-collinear coupling have been investigated both theoretically and experimentally. For a TE or TM polarized guided mode of a planar waveguide obliquely incident on a grating pad, there are four characteristic angles corresponding to the coupling with TE and TM reflected modes fulfilling the Bragg condition. The reflectivity is obtained by solving the coupled mode equations for the non-collinear case. The modelling shows that integrated passive functions such as polarization splitting and interference can be achieved. The polarization interference element uses the property that the coupling coefficients TM-TE and TE-TE are equal at defined incidence angles. Since the angle between the two reflected TE beams is only a few minutes of arc, the two beams can interfere. The waveguides are made by K+ ion exchange in BK7 glass for 3 hours at 380°C. The structure was designed for use at a wavelength of 633 nm and uses a 485 nm period grating which was fabricated by holographic exposure and plasma etching techniques in a 50 nm TiO2 layer e-beam evaporated onto the glass surface. The reflectivity of the grating structure was studied experimentally and compared with theory. The diffraction angles are within 30 " of arc of the predicted angles. The measured reflectivities reached 20 %. The feasibility of realizing an integrated optic preprocessing circuit for polarization interferometry has been demonstrated.
Recent development of waveguide nonreciprocal devices, i.e. , isolator and circulator, is reviewed. Two major difficulties exist for their fabrication. First, form birefringence must be overcome to obtain high TE-TM mode conversion efficiency. Secondly, both of input and output light must be either TE or TM mode. A variety of methods and device structures have been proposed to solve these difficulties. However, experimental demonstration of waveguide isolator has been limited. After a brief discussion on advantages and drawbacks of proposed methods and device structures, a new fabrication process of waveguide isolator is described. A device structure which ensures TE mode operation was achieved by making adjoining nonreciprocal and reciprocal mode converters by using laser annealing technique. Faraday and Cotton-Mouton effects of Bi-substituted iron garnet film were used for nonreciprocal and reciprocal mode converters, respectively. Growth-induced and stress-induced birefringences of the film were used to cancel the form birefringence. An isolation ratio of 12.5dB was achieved at wavelength of 1.15μm with external magnetic field of 100 Gauss.
A simple procedure has been developped which allows us to obtain the phase matching and the coupling coefficient in multilayer magnetooptical waveguides using the "Transfer Matrix Method". This procedure gives the TE-TM mode conversion parameters of a waveguide without having to solve analytically the non-perturbed system.
Today modern optical communication systems, based on single mode fibers, are specially designed to operate at extremely high transmission rates. Unfortunately the achievable data rates are strongly limited by fluctuating perturbations of the semiconductor laser diode used as transmitter. Mainly the perturbations are caused by undesired reflections of light in the optical communication network returning back to the laser diode. This troubling feedback can be eliminated by the application of an integrated optical isolator put between the transmitter diode and the connecting fiber. These isolators should have excellent transmission of light travelling in the forward direction. On the other hand backward travelling waves should be absorbed as completely as possible. The present paper shows the design of a practical device with corresponding properties as mentioned above. For this isolator structure numerical calculations of light propagation and mode conversion effects are demonstrated.
As a part of a fibre optical sensor development project we have made an evaluation of different optical waveguiding techniques to study the properties of thin magnetooptical films. Because of the application the methods are focused on the determination of the Faraday rotation, the linear birefringence and the dynamics and anisotropy of the magnetic properties of the samples. Measurements using holographic grating, prism and edge (end-fire) light coupling to different substituted YIG films are presented. The advantages of the different methods are discussed and it is shown that the launching technique may affect the properties to be measured. Film stress caused by the prism coupling method is found to influence the magnetic anisotropy.
Visualization and quantitative mapping of the static inhomogeneous magnetic fields by means of new magnetooptical method is described. The method is based on domain structure in Bi-substituted iron-garnet films to obtain the distribution of field component normal to film plane and averaged over film thickness. Theory of the method is outlined. Two configurational kinds of the domain structures are defined to gain simple mapping rules and direct visualization of field distribution in film plane. It's shown for example the way of investigation of field produced by miniature permanent magnets.
The capability of magnetooptic microscopy has been improved considerably thanks to the use of CCD cameras and digital image processing. Using Faraday-effect, we observed the evolution of the magnetic domain structure in the dipolar uniaxial ferromagnet LiHoF4 at very low temperatures (below Tc = 1.54 K) and determined its (H, T) magnetic phase diagram. The possibility of digital image averaging and image substraction increases significantly the sensitivity of the microscopic observation. This is illustrated by the ability to visualise the domain structure near Tc, where contrast is very low. Scanning over the depth of the specimen allows, in simple cases, the determination of the 3-dimensional domain shape. We shall discuss the nucleation process of magnetic bubbles in very thick samples (up to 2mm) from spike shaped domains originating near their surface.
The Ca3(Nb,Ga)5012 single crystals with the 1,2509 nm lattice parameter and low absorption in visible and near infrared wavelength range have been grown by the Czochralski technique from a platinum crucible. The growth temperature was about 1430°C. The growth conditions for liquid phase epitaxy of the iron garnet films on the new Ca3(Nb,Ga)5O12 substrates have been investigates using the Pb0-Bi2O3-B2O3 flux system. The general composition garnet films (Y,Lu,Bi)(Fe Ga)5O12 were grown on (110)-oriented substrates. The horizontal modes of diping were used for the film growth. The Bi content in the prepared films was more than 2,0 atoms per formula unit. The present paper reports the film quality, the interface (substrate/layer) properties, as will as the magnetic and magneto-optical properties of these layers. The information about the interface (substrate /layer) was obtained using the results of study of pulsed film remagnetization. The dynamics of magnetic domain walls was studied usins a high photography method.
Epitaxially grown garnet films (R,Bi)3(Fe,Ga,A1)5O12 (R = Tm, Eu, Er or Gd-Tm) with a high g-factor have been investigated. The dynamics of magnetic domain walls was studied using the high-speed photography method. In general the domain wall velocity vs pulse field have three ranges. The first range is the Walker's ones. The second (nonlinear) range occurs if the Gilbert damping parameter is α < 1. In the third range the velocity vs pulse field is linear again, but the differential domain wall mobility in this range is less than the initial (linear) ones. The initial domain wall mobility and peak velocity of domain walls in the first range vs temperature have maximum at the angular momentum compensation point. The g-factor signs below and above this point are opposite.