ABSTRACT
Recent experiments have revealed that the order of the electro-optic (EO) effect depends on the frequency of electric field in paraelectric nanodisordered KTa1-xNbxO3 (KTN) crystal. Through the dielectric frequency spectrum under the bias electric field, enormous linear and quadratic EO effects were discovered at the resonance frequencies, which changed the perception that only the quadratic EO effect exists. Applying just a small AC electric field of 6 V/mm, the effective linear EO coefficient reached 478 pm/V at 609 kHz, and the effective quadratic EO coefficient reached 4.39*10-13m2V-2at 302 kHz. The reason why an extremely low electric field results in an enormous EO coefficient is attributed to the resonance between the polar nanoregions (PNRs) and the electric field, induced by the field-driven reorientation of free dipoles on the boundary of the PNRs. In addition, the order of EO effect depending on the frequency of electric field was attributed to the motion modes of the PNR. This finding improves the understanding of how the EO effect is caused by field-driven PNR dynamics, but also provides a basis for the development of EO devices.
ABSTRACT
The electric-field-enhanced effect of permittivity can improve the performance of electro-optic modulators and deflectors. A theoretical model of super electro-optic modulation based on the field-enhanced effect of the permittivity was proposed. Results showed that a strong field-enhanced effect can greatly reduce the half-wave voltage and increase the modulation depth as a result of increased relative dielectric permittivity and permittivity gradient to the electric field. For bulk paraelectric KTN:Cu near the Curie temperature, we found a novel phenomenon that the response of relative dielectric permittivity to the bias electric field was closely related to the frequency, including attenuation, invariance, and enhancement. We effectively selected the frequencies corresponding to the strong field-enhanced effect by measuring the dielectric-frequency spectrum under the bias voltage. At these frequencies, a phase retardation of π was achieved through 2Vpp AC modulation voltage, indicating that the half-wave voltage was reduced by one order of magnitude.
ABSTRACT
An innovative 3D ladar that utilizes potassium tantalate niobate (KTN) crystal as a polarization modulator is proposed in this Letter. The optical isotropy of KTN in cubic phase can effectively suppress the range errors induced by the incident angles of collected beams in 3D imaging. The giant quadratic electro-optic coefficient can dramatically lower the voltage that is required to modulate the polarization so that a high voltage amplifier with less noise can be used to improve the ranging performances. By virtue of these two advantages, a range error of 4.8 cm and a range precision of 4.4 cm at 15 m have been achieved under a large field of view of 20° (about 0.35 rad) and a maximum detection range without ambiguity of 60 m.
ABSTRACT
Two high resolution flash LIDAR systems based on polarization modulation are demonstrated in this paper. One utilizes a polarization beam splitter (PBS) and two charge coupled device (CCD) arrays; the other utilizes a micro-polarizer array and a CCD array. Compared with the traditional flash LIDAR systems, the main advantage of the presented flash LIDAR systems is replacing high bandwidth detectors with a polarization modulator and low bandwidth detectors. The polarization modulator is used to modulate the polarization state of the received laser pulse in time and the range information can be mapped into the intensity received by the low bandwidth detectors. The distance between the target and the system can be derived from intensity images that can be read out using low bandwidth detectors. Comparisons of the two systems indicate that they have the same range precision. Both demonstrated systems can achieve a high range precision of several millimeters. The system using a PBS and two CCD arrays can obtain higher resolution images, but it is crucial to align the two CCD arrays precisely.