Electro-optic Q switch of an La3Ga5SiO14 crystal

We study the influence of the electro-optic and optical activity effects of a crystal on the arbitrary linearly polarized light propagating along the optical axis and design an experiment to demonstrate this. According to the theory and the experimental results, we achieve a successful voltage-decreased electro-optic Q switch of the La3Ga5SiO14 crystal.     

Electro-optic routing in a nematic liquid-crystal waveguide

We propose a versatile guided-wave geometry encompassing electro-optic control for signal routing. A zero-gap directional coupler in liquid crystal can switch between two output states in the guide plane, permitting signal rerouting with modulation voltages as small as 70 mV. In the absence of an applied bias, no guiding--hence no modal output--is provided by the structure.     

Intracavity frequency doubling and Q switching in diode-laser-pumped Nd:YVO(4) lasers

A highly efficient and compact Nd:YVO(4) laser is proposed. In cw operation, a single-longitudinal-mode output of 95 mW and a multilongitudinal-mode output of 435 mW have been observed at 1.06 μm with a 1-W diode laser. Using a KTP crystal in the short laser cavity, a green output of 105 mW was generated. A Q-switched pulse with a peak power of 230 W and a pulse width of 8 ns was obtained with the intracavity KTP crystal, which was used as both an electro-optic Q switch and a frequency doubler.     

Complete polarization conversion using one crystal with dual transverse Pockels effect

Based on dual transverse Pockels effect, complete polarization conversion can be achieved by using only one electro-optic crystal and its two externally applied voltages. The electro-optic phase retardation and the azimuth angle of the field-induced principal dielectric axes of the crystal can be independently and linearly controlled by the amplitude and direction of the applied electric field, and the formulas for this correlation are deduced for arbitrary input and output polarization states. The candidate crystals mainly include the uniaxial crystals of 3 m, 62 m, and 32 symmetry groups, and the cubic crystals of 43 m and 23 symmetry groups. Theoretical analysis demonstrates that one crystal exhibiting both dual transverse Pockels effect and optical activity can also be used for complete polarization converter. The continuous polarization rotation of a linearly polarized light from 0 degrees to 180 degrees has been performed experimentally by use of single lithium niobate crystal with four lateral electrodes. In addition the light beam position-dependent polarization conversion by using a bulk electro-optic crystal is also measured in the experiment. This new type of polarization converter will have potential applications in many fields due to its simple configuration, explicit control logic of polarization conversion, and lower power consumption.     

电光晶体研究进展

电光效应就是晶体折射率随外加电场而发生变化的现象。这种效应在光调制领域中有广泛的应用,可以制作激光器件,如高速电光开关、电光偏转器等。介绍了电光晶体的类型,以及电光晶体的研究现状和发展趋势。比较详细地介绍了偏硼酸钡晶体(1985年由我国科学家发现的第一个"中国牌"晶体)、磷酸钛氧钾和磷酸钛氧铷晶体、硅酸镓镧晶体等的特性和应用。最后提出了有关电光晶体研究的建议和展望,指出,必须从理论和实际两个方面来开展对电光晶体的研究,争取有所突破。     

Surface Plasmon-polaritons on an Anisotropic Substrate

Abstract

The case of a surface plasmon-polariton (excited by transverse magnetic light) propagating at the interface between an isotropic metal (silver) and an anisotropic (uniaxial) substrate is considered. The field distribution within the system is illustrated when the optic axis of the substrate is not orthogonal in the plane of light propagation. It is seen that in this case a component of the electric field perpendicular to the plane of propagation exists, and in certain circumstances this can become a propagating transverse electric mode. Thus a transverse electric re-radiation occurs, which is enhanced by the surface plasmon resonance, this could form the basis of an electro-optic switch using the anisotropic properties of a liquid crystal layer.     

Investigations on LGS and LGT crystals to realize BAW resonators

The LGS family are promising materials for the design of high quality bulk acoustic wave resonators. We have manufactured many plano-convex 10 MHz 5th overtone Y-cut resonators using langasite (LGS, La₃Ga₅SiO₁₄) and langatate (LGT, La₃Ga_5.5Ta_0.5O₁₄) crystals. We observed that the quality factor strongly depends on the polishing method, the supplier of the material, and on the energy trapping. For quartz crystals, we have found that resulting IR spectra exhibit absorption peaks more or less deep, linked to defects. These predominant criteria are not surprising, but they have to be defined in manner similar to that used for quartz crystal. A satisfying machining and polishing method has been first applied to elaborate high Q resonators, and a comparison between samples of LGS and LGT materials from different suppliers is established. In addition, LGT resonators are characterized by their motional parameters and frequency-temperature curves. Nevertheless, one of the main results is that the measured Q × f product is not the expected one. We present results of Q-factor versus radius of curvature: it appears that an optimization should be performed and that this last one cannot be directly transposed from that of quartz crystal resonator. Currently, the best resonator that we have made has a Q × f product of 1.4 × 10¹³ on its 5th overtone (1.7 × 10¹³ on its 9th overtone). This result is slightly higher than the similar parameter obtained on a state-of-the-art SC-cut quartz crystal resonator working at the same frequency.     

Reprogrammable optical phase array

A novel reprogrammable optical phase array (ROPA) device is presented as a reconfigurable electro-optic element. One specific application of the ROPA, a 1 x 6 electro-optic space switch, is fully described. Switching angles are within 2 degrees , and switching is achieved through a complementary metal-oxide semiconductor (CMOS) controlled, diffraction based, optical phase array in a bulk BaTiO3 crystal. The crystal is flip-chipped to the CMOS chip, creating a compact fully integrated device. The design, optical simulation, and fabrication of the device are described, and preliminary experimental results are presented.     

Dual in-plane electronic speckle pattern interferometry system with electro-optical switching and phase shifting

A dual in-plane electronic speckle pattern interferometry (ESPI) system has been developed for in situ measurements. The optical setup is described here. The system uses an electro-optical switch to change between the illumination directions for x and y sensitivity. The ability of the electro-optic device to change the polarization of the laser light forms the basis of this switch. The electro-optic device is a liquid-crystal layer cemented between two optically flat glass plates. An electric field can be set up across the layer by application of a voltage to electrodes. The speckle interferometry system incorporates two additional liquid-crystal devices to facilitate phase shifting, and the overall system is controlled by advanced software, which allows switching between the two perpendicular planes in quasi real time. The fact that there are no moving parts is an advantage in any ESPI system for which mechanical stability is vital.     

Double refraction and reflection of sequential interfaces in a crystal and application to integration of 1 × N optical switch

Abstract

The general formulation of double refraction or internal double reflection with different directions of propagation vector and wave vector in a uniaxial crystal is analysed in terms of Huygens' principle. Then double refraction and double reflection along the sequential interfaces in a crystal are discussed. On this basis, a configuration of electro-optic 1 x N optical switch with modulators and birefringent crystal slabs integrated in a single block of crystal is suggested, which is simple and compact in construction, low in loss and insensitive to environment. Finally, calculations are given which lead to a proposed design of a 1 × 4 switch.     

Effect of polarization state on electro-optic coupling and its application to polarization rotation

The effect of the polarization state on electro-optic coupling is studied by using the wave coupling theory of the linear electro-optic effect. The numerical results show that the polarization state obviously influences the electro-optic coupling. The conditions for realizing perfect coupling are emphasized. As an application of perfect coupling, a novel polarization rotator, which can rotate the polarization of a light beam with an arbitrary angle but keep the output intensity unchanged, is presented.     

Optical statistical timer

A new type of light pulses timer allowing a direct locking within the electric oscillation delivered by a clock is presented. The light pulses to be timed cross an electro-optic crystal excited by an oscillating electric field, which modifies the light polarization. A polarimetry at the crystal exit allows deducing the light pulse arrival time. Accuracy in the picosecond range has been experimentally demonstrated     

Advanced Optical Techniques

The development of a digital electro-optic light beam deflector (DLD) is described. Each deflection stage consists of a DKDP polarization switch with a coating of transparent electrodes (longitudinal electro-optic effect) and a calcite prism for angular deflection. Effects which limit the switching frequency and the capacity speed product (i.e. product of the number of resolvable beam directions and the switching frequency) are theoretically investigated. A four-stage solid-state DLD has been realized which operates at switching frequencies up to 10 kHz and at a random access time of 30 μ s. The system is going to be expanded to 8 × 8 stages for the addressing of 256 × 256 beam directions.     

X-ray Topography of Piezoelectric La/sub 3/Ta/sub 0.5/Ga/sub 5.5/O/sub 14/ Crystal Grown by Czochralski Method

We performed synchrotron X-ray topography on a La₃Ta_0.5Ga_5.5O₁₄ (LTG) crystal grown by the Czochralski method. Since a synchrotron X-ray source can provide high-energy X-rays, one can detect bulk structures by X-ray topography. LTG is one of the most attractive piezoelectric crystals along with La₃Ga₅SiO₁₄ (LGS) because of its excellent acoustic properties (temperature compensation of acoustic losses). Since LTG single crystals can be grown from a stoichiometric melt, it was expected that single crystals with better quality than the LGS crystal, which cannot be grown from a stoichiometric system but only from a congruent melt, can be obtained. However, 60 keV X-ray topography revealed that the LTG crystal quality was not as high as the LGS crystal quality. The crystal quality of the central region was lower than that of the surrounding region.     

X-ray topography of piezoelectric La(3)Ta(14)Ga(5.5)O(14) crystal grown by Czochralski Method.

We performed synchrotron X-ray topography on a La(3)Ta0(0.5)Ga (5.5)O(14) (LTG) crystal grown by the Czochralski method. Since a synchrotron X-ray source can provide high-energy X-rays, one can detect bulk structures by X-ray topography. LTG is one of the most attractive piezoelectric crystals along with La(3)Ga(5)SiO(14) (LGS) because of its excellent acoustic properties (temperature compensation of acoustic losses). Since LTG single crystals can be grown from a stoichiometric melt, it was expected that single crystals with better quality than the LGS crystal, which cannot be grown from a stoichiometric system but only from a congruent melt, can be obtained. However, 60 keV X-ray topography revealed that the LTG crystal quality was not as high as the LGS crystal quality. The crystal quality of the central region was lower than that of the surrounding region.     

Double refraction and reflection of sequential crystal interfaces with arbitrary orientation of the optic axis and application to optimum design

The general formulation of double refraction or internal double reflection for any directions of incidence and arbitrary orientation of the optic axis in a uniaxial crystal is analysed in terms of Huygens’ principle. Then double refraction and double reflection along the sequential interfaces in a crystal are discussed. On this basis, if the parameters of the interface are chosen appropriately, the range of angular separation between the ordinary ray and extraordinary ray can be much greater. It is useful for crystal element design. Finally, as an example, an optimum design of the output end interface for a 2?×?2 electro-optic switch is given.     

Field-of-view analysis of a polarization interference Fourier transform imaging spectrometer

The Fourier transform imaging spectrometer (FTIS) is an important tool for the measurement of spectral information in a scene. Advances in electro-optic crystal systems have led to the advent of the FTIS based on polarization interference filters. The operation of these devices as spectrometers has been well characterized, but the imaging capabilities have yet to be thoroughly explored. We explore the field-of-view limitations that occur when using this particular type of FTIS.     

Temperature Characteristics of Surface Acoustic Waves Propagating on La3Ga5SiO4 Substrates

Langasite (LGS) is a novel piezoelectric crystal. The authors numerically analyses the temperature stability of surface acoustic waves (SAW) and the relation of SAW propagation with temperature on certain optimal cuts on LGS in this paper. The results show that LGS has better temperature stability than traditional piezo crystals. The results also demonstrate that the velocity of SAW decrease with temperature, the electro-mechanical coupling constant (k2) and temperature coefficient of frequency increases parabolically and the power flow angle increases linearly on certain optimal cuts of LGS. The calculation result compared with the experimental and show good agreement.     

Effects on skylight at South Pole Station, Antarctica, by ice crystal precipitation in the atmosphere

Measurements of the radiance and polarization of the skylight at South Pole Station, Antarctica, were made for clear cloud-free skies and cloudless skies with ice crystal precipitation. The measurements were made at six narrowband wavelengths from 321 to 872 nm in the principal plane. The data show that scattering by ice crystals increases the radiance in the backscatter plane, decreases it in the solar plane, and shifts the radiance minimum to a point closer to the sun. The crystals decrease the maximum value of linear polarization and shift the position of the maximum away from the sun. The influence of ice crystal scattering is greatest at the longer wavelengths.     

Digital imaging of clear-sky polarization

If digital images of clear daytime or twilight skies are acquired through a linear polarizing filter, they can be combined to produce high-resolution maps of skylight polarization. Here polarization P and normalized Stokes parameter Q are measured near sunset at one inland and two coastal sites. Maps that include the principal plane consistently show that the familiar Arago and Babinet neutral points are part of broader areas in which skylight polarization is often indistinguishably different from zero. A simple multiple-scattering model helps explain some of these polarization patterns.