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Modal Analysis of Space-Time Periodic Diffraction Gratings

Ansari Dogaheh, Amir Reza | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55193 (05)
  4. University: Sharif University of Technolog
  5. Department: Electrical Engineering
  6. Advisor(s): Mehrany, Khashayar; Khavasi, Amin
  7. Abstract:
  8. Over the past few years, time-periodic and space-time-periodic media have garnered a considerable amount of attention, thanks to their exotic and unique interactions with electromagnetic phenomena. These media do not generally comport with Lorentz's reciprocity theorem, thus can be utilized in order to implement non-reciprocal amplification and frequency transformation. One class of such media, that have been the subject of less discussion and interest, are space-time periodic diffraction gratings.In this thesis, we aim to develop a series of semi-analytical methods in order to analyze such structures. Our focus will be on a subset of methods which make use of the modal expansion of fields within these structures, thus are aptly called modal methods.In this thesis, after a review of the literature regarding the analysis of diffractions gratings (space, time, or space-time periodic), two modal methods for the analysis of time-periodic diffraction gratings under illumination from an arbitrarily polarized incident wave are presented. The stability and fast convergence of these methods are then assured, after they are appropriately adjusted under proper conditions. Going forward, we will analyze time-periodic diffraction gratings under a number of special conditions, and assure the efficacy of the aforementioned methods under these conditions. Afterwards, we will introduce a discrete mode resonance that occurs in these structures and develop two methods to obtain their corresponding discrete modes. Next, we will expand the two methods used for the analysis of time-periodic media, to the case of space-time periodic media. We will also ensure the stability and fast convergence of these methods by making similar adjustments. Finally, we will expand these methods to the case of three-dimensional from a STP grating with arbitrarily slanted fringes and under arbitrarily polarized incident wave.

  9. Keywords:
  10. Modal Analysis ; Diffraction Gratings ; Fourier Modal Analysis ; Fourier Factorization ; Space-Time Periodic Media ; Time Periodic Media

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