Annan Shang

Bio: Annan Shang is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Materials science & Tantalate. The author has an hindex of 4, co-authored 13 publications receiving 51 citations.

Enhanced electro-optic beam deflection of relaxor ferroelectric KTN crystals by electric-field-induced high permittivity

Abstract: Most applications of a ferroelectric-based electro-optic (EO) beam deflector have been limited by the high applied voltage. In this Letter, we report a dramatically increased EO beam deflection in relaxor ferroelectric potassium tantalate niobate (KTN) crystals by using the electric-field-enhanced permittivity. Due to the existence of the electric-field-induced phase transition in relaxor ferroelectric materials, the dielectric permittivity can be substantially increased by the applied electric field at a certain temperature. Both the theoretical study and the experimental verifications on the enhanced beam deflection and EO effect in the case with the electric-field-induced high permittivity were conducted. The experimental results confirmed that there was a three-fold increase in the deflection angle, which represented a dramatic increase in the deflection angle. By offering a wider deflection range and a lower driving voltage, such a largely enhanced beam deflection is of great benefit to the KTN deflector.

Ruby fluorescence-enabled ultralong lock-on time high-gain gallium arsenic photoconductive semiconductor switch.

Abstract: We report a new type of photoconductive semiconductor switch (PCSS), consisting of a semi-insulating gallium arsenic (GaAs) substrate and a front-bonded ruby crystal. The 532 nm laser pulses from an Nd-YAG laser incident on the front surface of the ruby crystal. A portion of the laser pulse passes through the crystal and reaches the GaAs substrate, and the remaining portion of the laser pulse is absorbed by the ruby crystal. This results in the emission of 694 nm fluorescent light. Furthermore, a portion of emitted fluorescent light also reaches the GaAs substrate. The high-fluence 532 nm short laser pulse with a pulse width around several nanoseconds is used to trigger the PCSS entering the high-gain nonlinear mode, whereas the low-fluence long-lifetime (on the order of a millisecond) 694 nm fluorescent light is used to maintain the lock-on time. Thus, an ultralong lock-on time on the order of millisecond is achieved, which is 3 orders of magnitude longer than a typical lock-on time of high-gain GaAs PCSS.

Anomalous bi-directional scanning electro-optic KTN devices with UV-assisted electron and hole injections

Abstract: In this Letter, we reported anomalous electro-optic potassium tantalate niobate (KTN) devices, in which both electrons and holes were injected into the KTN crystal via ultraviolet (UV) illumination-assisted charge injection. This could not only significantly enhance the performance of electro-optic devices (e.g., a 270% increase in the deflection angle in terms of the KTN deflector) but also enable the new bi-directional scanning capability. The results in this work would be very useful for a variety of devices and applications, such as electro-optic based vari-focal lenses.

Enhanced electro-optic beam deflection of relaxor ferroelectric KTN crystals by electric-field-induced high permittivity

Abstract: Most applications of a ferroelectric-based electro-optic (EO) beam deflector have been limited by the high applied voltage. In this Letter, we report a dramatically increased EO beam deflection in relaxor ferroelectric potassium tantalate niobate (KTN) crystals by using the electric-field-enhanced permittivity. Due to the existence of the electric-field-induced phase transition in relaxor ferroelectric materials, the dielectric permittivity can be substantially increased by the applied electric field at a certain temperature. Both the theoretical study and the experimental verifications on the enhanced beam deflection and EO effect in the case with the electric-field-induced high permittivity were conducted. The experimental results confirmed that there was a three-fold increase in the deflection angle, which represented a dramatic increase in the deflection angle. By offering a wider deflection range and a lower driving voltage, such a largely enhanced beam deflection is of great benefit to the KTN deflector.

A waveguide mode modulator based on femtosecond laser direct writing in KTN crystals

Abstract: We report a novel mode modulator based on a KTN crystal waveguide produced by femtosecond laser (fs-laser) writing. The KTN waveguide is a typical dual-line structure that depends on the decrease of refractive index at the focus area. The propagation loss of the waveguide along the TE polarization is as low as ~0.9 dB/cm at 632.8 nm. The investigation of confocal micro-Raman spectra reveals that the microstructure of the waveguide region has no obvious change during the femtosecond laser direct writing (FsLDW) procedure. Under the applied direct current (DC) electric field, the waveguide modes in the guiding structure can be modulated, resulting in mode conversion from TE00 to TE02. Both the experimental results and the theoretical simulation indicate that the mode modulation phenomenon originates from the space-charge-field induced refractive-index increment between the waveguide core and the bulk substrate. The simplicity and remarkable performance of the demonstrated device paves the way for integrating low-cost and high-efficient electric-optical modulator on photonics circuits.