Advanced electro-optic beam steering devices based on KTN crystals
Restricted (Penn State Only)
- Author:
- Lee, Yun Goo
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 06, 2023
- Committee Members:
- Julio Urbina, Major Field Member
Qi Li, Outside Unit & Field Member
Victor Pasko, Major Field Member
Shizhuo Yin, Chair & Dissertation Advisor
Madhavan Swaminathan, Program Head/Chair - Keywords:
- Electro-optic
Beam deflector
KTN
Potassium tantalate niobate
Beam steering - Abstract:
- In this dissertation, we systematically investigated the structural optimization of KTN (KTa1-xNbxO3) beam scanners which significantly improved their deflection performance. With the increasing demand for high-speed and wide-range optical beam scanners, potassium tantalate niobate [KTa1-xNbxO3 (KTN)] has been widely investigated due to its extraordinarily large EO effect. However, the area of structural optimization of KTN beam deflectors needs to be further investigated, especially to overcome some challenges based on their fundamental properties. To overcome these challenges, first, we studied the effect of the naturally embedded compositional gradient of KTN deflectors on their beam deflection. The existence of a compositional gradient of KTN due to the top-seeded growing (TSSG) method can greatly alter the Curie temperature (T_C) of the KTN crystal. It shifts the maximum permittivity region due to the altered Curie temperature, eventually preventing the KTN deflectors from working at their highest functionalities. We investigated this effect in detail and proposed a temperature gradient working condition to compensate for the compositional gradient effect in the light propagation direction of the KTN deflecting system. It showed three times higher beam deflection compared to the conventional uniform temperature operation. Secondly, other challenges in KTN beam deflectors are that their deflection is polarization-dependent and generates substantial heat at high-frequency operation. These challenges limit the KTN beam deflector from reaching its naturally high-speed (ns range) capability, as well as intensity drop and bulky system due to the polarizers. To handle this problem, we suggested a compact reflective-type KTN beam deflector model that can function with any polarized light. Theoretical derivation of the resultant deflection angle in our model proves that outcome beam deflection can indeed be polarization independent. Also, based on our calculation of the temperature rise due to the dielectric heating at a high-frequency regime, our model suffers much less in terms of the heating effect for high-speed operation. Finally, we conducted a quantitative simulation and showed that surface topology on the electrode of KTN can significantly increase the charge injection over the KTN deflector, resulting in a higher deflection angle compared to the conventional model. For high-speed deflection in KTN scanners, lower external bias is always preferable not only because of dielectric heating increases but also because of the limitation of commercial high-speed voltage amplifiers. With a surface topology on the electrode, we could verify that the local electric field substantially increased, as did the deflection angle.