Chongjun He

Electrical and optical properties of Nd3+-doped Na0.5Bi0.5TiO3 ferroelectric single crystal

Sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) single crystal doped with Nd3+ was grown by a top-seeded solution growth method. Powder x-ray diffraction revealed a pure perovskite structure with the rhombohedral phase. We found that the dielectric and ferroelectric properties were enhanced by the Nd3+ dopant. After poling along the [1?1?1] direction, transmittance was enhanced dramatically. The Sellmeier dispersion equation and energy band gaps were obtained. The absorption band around 808?nm has high full-width at half-maximum and large absorption cross-section, which is suitable for AlGaAs diode-laser pumping. A strong emission transition band of Nd3+ at around 1066?nm was observed; a long radiation lifetime 324??s shows a low quenching effect. These results indicate that Nd3+-doped NBT crystal could be applied in photonic or integrated optoelectronic devices as a multi-functional crystal.

Composition dependence of dispersion and bandgap properties in PZN-xPT single crystals

Refractive indices and optical transmittance spectra of (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT) single crystals poled along [001] direction have been investigated. Cauchy dispersion equations of the refractive indices were obtained by least square fitting, which can be used to calculate the refractive indices in the low absorption wavelength range. After poled along [001] direction, the transmittance of PZN–12%PT single crystal is more than 65% from 0.5 to 5.8 μm, which is much higher than that of PZN–5%PT and PZN–8%PT single crystals. Optical energy bandgap was obtained from absorption coefficient spectra. Our results show that as the PT content increases, the refractive indices of PZN-xPT single crystals increase, while the optical bandgap decreases.

Composition and orientation dependence of high electric-field-induced strain in Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals

Relaxor based xPb(In1/2Nb1/2)O3–(1-x-y)Pb(Mg1/3Nb2/3)O3–yPbTiO3 single crystals [PIMNTx/(1-x-y)/y] have broader temperature usage range and comparable piezoelectric properties to (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 crystals. In this work, electric-field-induced strain behavior of PIMNT crystals with different orientation and composition was investigated. High strain with low hysteresis was observed in rhombohedral PIMNT25/44/31 crystal oriented along 〈001〉, rather than 〈011〉 and 〈111〉. Ultrahigh strain level up to 0.75% with linear curve can be achieved under 5 kV/mm electric field. The electric field induces phase transformation of PIMNT crystals is much higher than that of PIMNT crystals. These properties make PIMNT crystals promising candidate for high performance solid-state actuators.

Optical transmission and dispersion of 0.25Pb(In1/2Nb1/2)O3- (0.75 − x) Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

Optical transmission spectra and refractive index dispersions of ternary relaxor-based ferroelectric 0.25Pb(In1/2Nb1/2)O3–(0.75 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 [PIMNT0.25/(0.75 − x)/x] single crystals were studied after poled along [001] direction. Sellmeier dispersion equations of the refractive index were obtained by least square fitting, which can be used to calculate the refractive indices in visible and near infrared spectra. The optical transmission of tetragonal PIMNT0.25/0.37/0.38 single crystal is about 70% from 0.5 to 5.8 μm, which is much higher than that of rhombohedral PIMNT0.25/0.45/0.30 and morphotropic phase boundary PIMNT0.25/0.41/0.34 single crystals. Optical interband direct and indirect transitions were investigated by absorption spectra. Our results show that as the PbTiO3 content increases the refractive indices of PIMNT single crystals increase, while the optical band gap decreases.

Reversal construction of polarization-controlled focusing field with multiple focal spots

Abstract. We propose an approach to control the polarization and intensity of the focusing field with multiple focal spots in a high-numerical-aperture imaging system. This focused field is explained as the reversal radiation of the dipole array with presupposed oscillating direction in the focal volume. By engineering the structure of the electric dipole array and reversing the radiation from this dipole array, the local manipulation of intensity and polarization in the focal region is achieved, and the required field at the pupil plane is derived. A focusing field with six vectorial focal spots is created as an example to verify this method. This multifocal field will meet potential application in polarization-dependent optical microscope and optical trapping for multiple particles.

Speckle reduction in optical coherence tomography by adaptive total variation method

An adaptive total variation method based on the combination of speckle statistics and total variation restoration is proposed and developed for reducing speckle noise in optical coherence tomography (OCT) images. The statistical distribution of the speckle noise in OCT image is investigated and measured. With the measured parameters such as the mean value and variance of the speckle noise, the OCT image is restored by the adaptive total variation restoration method. The adaptive total variation restoration algorithm was applied to the OCT images of a volunteer’s hand skin, which showed effective speckle noise reduction and image quality improvement. For image quality comparison, the commonly used median filtering method was also applied to the same images to reduce the speckle noise. The measured results demonstrate the superior performance of the adaptive total variation restoration method in terms of image signal-to-noise ratio, equivalent number of looks, contrast-to-noise ratio, and mean square error.

Controlled focus shaping with generalized cylindrical vector beam

An optical system is proposed for the controlled focus shaping of generalized cylindrical vector beams by a high-numerical-aperture lens. A segmented electro-optical filter with four concentric belts is introduced and works with a double-λ/2-plate. By controlling the rotational angle of the plate and the voltage applied to the filter with proper azimuth angle, a three-dimensional engineered focusing field, such as an electrically controlled axial-shifted focus, extended depth of focus, and a diffraction-limited optical tube, can be achieved. The main advantage of this focusing system is that the focused field can be adjusted and formed by the applied voltage and the rotational angle of the half-wave plates. It can provide a new focus shaping technique with free adjustability and flexibility.

Orientation dependence of dispersion and band gap of PIMNT single crystals

As piezoelectric materials, optical properties of xPb(In1/2Nb1/2)O3–(1-x-y)Pb(Mg1/3Nb2/3)O3–yPbTiO3 single crystals were not perfectly known. Here refractive indices and optical transmission of 0.25Pb(In1/2Nb1/2)O3–0.42Pb(Mg1/3Nb2/3)O3– 0.33PbTiO3 (PIMNT) single crystal are investigated after poled along different directions. Cauchy dispersion equations of the refractive indices were obtained by least square fitting, which can be used to calculate the refractive indices in the low absorption wavelength range. After poled along [011] direction, the optical transmission of PIMNT single crystal is more than 65% above 0.5 μm, which is much higher than that of [001] and [111] directions. Energy band gap was obtained from absorption coefficient.

Optical properties of (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3single crystals

Optical properties of (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT, x=5%, 9% and 12%) single crystals have been comprehensively investigated. The PZN-xPT single crystals used in this study were grown using a high temperature flux method. Refractive indices (nij) were measured by the Brewster’s angles (θB=tan-1n) at different wavelengths. Dispersion equations of refractive indices were obtained. After poled along [001] direction, the transmittance of PZN–12%PT single crystal is more than 65% from 0.5 to 5.8 μm, which is much higher than that of PZN–5%PT and PZN-9%PT single crystals. PZN–12%PT has a tetragonal phase, its spontaneous polarization PS is along [001] direction. After poling, it could form a single domain structure. Orientation and temperature dependences of the electro-optic coefficient were investigated at He-Ne laser by the Senarmont compensator method. Large effective electro-optic coefficient (γc = 430 pm/V) was observed in [001]-poled PZN-9%PT crystal. More importantly, γc of tetragonal PZN-12%PT is about 130 pm/V, which is almost unchanged in a temperature range -20~80 °C. The γc of PZN-xPT single crystals are much higher than that of widely used electro-optic crystal LiNbO3 (γc = 20 pm/V). These excellent optical properties make the PZNxPT single crystals promising candidates for electro-optic modulation applications.

Optical properties of (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 single crystals

Optical properties of (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT, x=5%, 9% and 12%) single crystals have been comprehensively investigated. The PZN-xPT single crystals used in this study were grown using a high temperature flux method. Refractive indices (nij) were measured by the Brewster’s angles (θB=tan-1n) at different wavelengths. Dispersion equations of refractive indices were obtained. After poled along [001] direction, the transmittance of PZN–12%PT single crystal is more than 65% from 0.5 to 5.8 μm, which is much higher than that of PZN–5%PT and PZN-9%PT single crystals. PZN–12%PT has a tetragonal phase, its spontaneous polarization PS is along [001] direction. After poling, it could form a single domain structure. Orientation and temperature dependences of the electro-optic coefficient were investigated at He-Ne laser by the Senarmont compensator method. Large effective electro-optic coefficient (γc = 430 pm/V) was observed in [001]-poled PZN-9%PT crystal. More importantly, γc of tetragonal PZN-12%PT is about 130 pm/V, which is almost unchanged in a temperature range -20~80 °C. The γc of PZN-xPT single crystals are much higher than that of widely used electro-optic crystal LiNbO3 (γc = 20 pm/V). These excellent optical properties make the PZNxPT single crystals promising candidates for electro-optic modulation applications.