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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39744 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Bahrampour, Alireza
  7. Abstract:
  8. By employing the image theory the Er doped microsphere coupled to an external cavity made by a metallic mirror is simulated by a bimicrosphere laser. The symmetric structure causes the formation of odd and even modes corresponding to the TE and TM mode of the microsphere and splitting the oscillation frequencies. The oscillation frequencies are dependent on the coupling coefficient. The coupling coefficient is obtained near the mirror-microsphere distance. The ohmic mirror loss also is determined as a function of the mirror distance. The total optical loss experienced in these resonators is exceptionally low. In fact,quality factor as high as 108 − 1011 have already been demonstrated for microspheres compared to typical values of 103−105 for ring resonators in the 1550 nm wavelength. This extraordinary high Q-factor translates directly into an ultra-narrow resonant optical linewidth that can be employed in a variety of extremely precise measurement tasks. A microsphere doped with optically active erbium ions shows lasing at the 4I13 2 → 4I15 2 transition of Er+3 around 1550nm. Due to themirror symmetries, when an erbium doped microsphere situated near a mirror new resonance frequencies are appeared. Each mode of the microsphere split in to two separate modes with even and odd symmetries. The distance between the new frequencies from the microsphere resonance frequencies is dependent on the distance of microsphere from the mirror. A homogeneous mode is presented and it is shown that even and odd mode frequencies have red and blue shifts respectively. In addition to the intrinsic loss of the microsphere several mechanisms of loss in the microsphere-mirror coupling exist. The title of this thesis is:”Optical sensors based on Er-doped microsphere coupled to an external mirror”.in this study we survey the effects of an external mirror feedback on sensitivity. and show that the presence of this external mirror enhances the sensitivity for both frequencies
  9. Keywords:
  10. Quality Factor ; Silica Microspheres ; Whispering Gallery Mode

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