Author ORCID Identifier
https://orcid.org/0000-0003-3312-6729
Biosketch
R.K. Prasath received his B.E. Degree in Electronics and Communication Engineering from Bharathidasan University, Trichy, and M.E. Degree in Wireless Technologies from Thiagarajar College of Engineering, Madurai. Currently, he has been working as an Assistant Professor in the School of Electrical and Electronics Engineering, SASTRA Deemed University, Thanjavur for the past 15 years. He has a teaching experience of 20 years, and industrial experience of 4 years (as Project Trainee in HTSL Madurai and as Senior Software Engineer in Multitech Software Solutions, Bengaluru). He completed his Ph.D. Degree from SASTRA Deemed University. His research area is non-linear optics and wireless communications. He is a Life Member of the Indian Society of Systems for Science and Engineering (ISSE).
Date of Award
11-12-2025
Document Type
Thesis
School
School of Electrical & Electroncis Engineering
Programme
Ph.D.-Doctoral of Philosophy
First Advisor
Dr. Rakesh Kumar Karn
Second Advisor
Dr.S.K.Pandiyan
Keywords
Periodically Polled Lithium Niobate, Internal Field, Quasi-Phase Matching, Second Harmonic Generation, Duty Ratio
Abstract
Periodically Poled Lithium Niobate (PPLN) crystals have attracted interest in optoelectronics and nonlinear optics. The response to the applied electric field is determined by their larger electro-optic and nonlinear optical coefficients. An internal electric field exists in congruent PPLN crystals due to its defects. Its evaluation is important in controlling the electro-optical behavior. A simple nondestructive diffraction method is proposed to estimate the internal electric field present in the congruent lithium niobate crystal.
Due to the presence of an unrelaxed internal field, the as-poled sample acts as an index grating. When a light is incident on such a sample, it diffracts the incident light beam. The refractive index difference (n ~ 1.52x10-4) between the poled and the unpoled domains and the duty cycle error were calculated by analyzing the diffraction patterns. Using the Pockels effect, the internal field (IF) present in the periodically poled lithium niobate crystal is estimated to be 2.56 kV/mm.
Further, the presence of fabrication errors in domain-engineered quasi-phase matching (QPM) devices directly affects their performance in nonlinear optical processes like second harmonic generation (SHG), sum frequency generation (SFG), difference frequency generation (DFG), etc. In addition to the well-known duty cycle and period error, the existence of error in the aspect ratio of domain inversion of the QPM device also affects the conversion efficiency factor.
The effect of aspect ratio errors in the QPM device has been analyzed theoretically. Further, the impact of duty cycle error and incomplete domain inversion is also studied for various grating profiles like under-poled, rectangular and blazed structures. Their generalized phase profile equations representing the nonlinear optical coefficient have been derived, and their corresponding second harmonic efficiency factors are calculated.
Recommended Citation
RK, Prasath Mr, "Evaluation of Internal Field in PPLN and Studies on QPM SHG Efficiency Factor" (2025). Theses and Dissertations. 213.
https://knowledgeconnect.sastra.edu/theses/213