Field-induced And Nanodisordered Ktn Crystals: Properties, Devices, And Applications

Open Access
Author:
Chang, Yun-ching
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 25, 2014
Committee Members:
  • Shizhuo Yin, Dissertation Advisor
  • Shizhuo Yin, Committee Chair
  • James Kenneth Breakall, Committee Member
  • Victor P Pasko, Committee Member
  • Zi Kui Liu, Committee Member
Keywords:
  • Electro-optics
  • KTN
  • Kovacs effect
  • waveguide
Abstract:
Potassium tantalate niobate [KTa1−xNbxO3 (KTN)] crystal has the largest electro-optic (EO) coefficients among all Kerr mediums. As other perovskites relexors, KTNs also exhibit extraordinary thermal hysteresis on the dielectric and EO properties. This study conducted transient observations of the EO effect in cooling and heating processes. The disordered polar nano-regions (PNRs), which minimize optical depolarization and scattering, strongly impact the characteristics of nanodisordered KTNs. Our investigation showed that the super cooling process effectively suppress the influence from PNRs formation. An enormous transient EO coefficient was thus observed, and made the single-crystal KTN a good candidate as a free-space optical (FSO) switch. The large EO coefficient reduces the driving voltage of the large aperture switch. A device with a large aperture, a wide FOV, and a very fast speed is demonstrated. In addition, by taking advantage of the Kovacs effect, the driving voltage can be further reduced. Furthermore, this dissertation introduces a novel technique to manipulating the guiding waves inside the EO crystal. A field-induced dynamic optical waveguide is locally induced and controlled by an external electric field. Based on this discovery, a field-induced 1 × 2 KTN EO switch is proposed, which possesses low power dissipation, low cross-talk, and broad bandwidth. The performance of the fabricated device also shows good agreement with the proposed model. This research suggests that the nanodisordered KTN based devices can improves the performance of existing EO applications. Moreover, the controllable field-induced KTN waveguide can potentially benefit next generation high speed data centers and communication networks of the future.