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Diffractive Components for Gravitational Wave Detectors

This research paper discusses diffractive components, such as cavity couplers and mirrors, for use in gravitational wave detectors. It explores the design considerations, properties, and optimization techniques for these components. The study suggests using resonant waveguide gratings as mirrors and the concept of HR-Stacks replaced by resonant waveguide gratings. The technical implementation and future possibilities are also discussed.

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Diffractive Components for Gravitational Wave Detectors

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  1. Diffractive Components for Gravitational Wave Detectors Stefanie Kroker Institute of Applied Physics Friedrich Schiller University Jena S. Kroker

  2. Cavity Couplers Mirror S. Kroker

  3. Outline Introduction 2-Port Cavity Couplers 3-Port Cavity Couplers Conclusion S. Kroker

  4. Grating Equation -1 R 0 R Incident Ray d… period ni… refractive index medium of incidence nj… refractive index propagation medium of diffracted light a… angle of incidence b… diffraction angle l… wavelength m=0,±1, ±2,… 1 R 1 T 0 T -1 T Born, Wolf: Principles of Optics S. Kroker

  5. -1R 0R Incident Ray -1R 0R -2R Incident Ray Littrow Configuration Second Order Littrow Configuration 2-Port Cavity Coupler 3-Port Cavity Coupler S. Kroker

  6. Cavity 0R -1R Incident Ray 0R -2R -1R Incident Ray Mirror Mirror Cavity S. Kroker

  7. Mirrors Resonant Waveguide Grating HR-Stack S. Kroker

  8. Incident Ray 0R -1R Cavity Mirror highly efficient 2-Port Cavity Coupler Highly efficient reflection grating in Littrow mount. Desirable Properties: R-1≈97% R0 ≈3% T as low as possible! S. Kroker

  9. Resonant Waveguide Grating as Mirror Low Index Material High Index Material nL nH Optimized for diffraction angle! Resonant Waveguide Grating Normal incidence: Period upper grating 2 Period waveguide grating S. Kroker

  10. Typical Properties Calculations: R ≥ 97% T ≈0.05% At least achievable S. Kroker

  11. Cavity 0R -2R -1R Incident Ray Mirror 3-Port Cavity Coupler 2nd order Littrow mount: Desireable properties: R0≈95% R-1≈5% R-2, T as low as possible S. Kroker

  12. Resonant Waveguide Grating as Mirror Low Index Material High Index Material nL nH l=1550 nm : d~600…700 nm Waveguide Grating: Period upper grating 3 Period waveguide grating S. Kroker

  13. Upper Grating 3 Ports: d≥l At least 3 diffraction orders in grating material! Problem: Waveguide grating needs to be highly efficient @ q0, ±q1 S. Kroker

  14. Angular Tolerance of Silicon-Grating on SiO2 l=1550 nm Waveguide Grating dWG= 633 nm Upper Grating d3P=1899 nm Diffraction Angle for m=±1 in SiO2 Need to increase angular tolerance! q1 ≈±34° S. Kroker

  15. Stack RWG1RWG2 Reflectivity RWG 2 RWG 1 Angle of Incidence Idea: Stack of Resonant Waveguide Gratings S. Kroker

  16. H ll Grating Grooves Silicon Silica TM-Polarization S. Kroker

  17. S. Kroker

  18. E ll Grating Grooves Silicon Silica TE-Polarization S. Kroker

  19. 3-Port Grating: R0≈94.3% R-1 ≈5.3% R-2 ≈0.3% T ≈0.016% S. Kroker

  20. Conclusion • - new concept for grating couplers: HR-Stacks replaced by • resonant waveguide gratings • 2-port couplers: RWG optimized for diffraction angle of • upper grating • 3-port couplers: angular tolerance of single RWG not • sufficient to provide low transmission, • stack of two or more RWGs can be used • (can also be used to decrease transmission • of 2-port couplers) • technical implementation under investigation (T-shape • considered) S. Kroker

  21. Thank you very much for your attention! S. Kroker

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