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T. Kataoka , S. E. Day, D. R. Selviah, A. Fern á ndez

Polarization-Insensitive Liquid-Crystal Fabry-Perot Tunable Optical Filter. T. Kataoka , S. E. Day, D. R. Selviah, A. Fern á ndez Department of Electronic and Electrical Engineering University College London, U.K. Content

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T. Kataoka , S. E. Day, D. R. Selviah, A. Fern á ndez

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  1. Polarization-Insensitive Liquid-Crystal Fabry-Perot Tunable Optical Filter T. Kataoka, S. E. Day, D. R. Selviah, A. Fernández Department of Electronic and Electrical Engineering University College London, U.K. • Content • Motivation and Aim • LC-FPF with Extra Birefringent layers • ● A Single Quarter-Wave Plate (QWP) • ●A Pair of Quarter-Wave Plates (QWPs) • 3. Conclusion

  2. LC-FPF for Optical Fiber Communication Systems • Electrically tunable filter with low voltage • Wide Tuning Range • 60 nm ( = Free Spectral Range, FSR) • (M. W. Maeda., et al, Bellcore, 1990) • Narrow Band(Full Width of Half Maximum, FWHM) • 0.17 – 0.35 nm ( = 21.23 – 43.70 GHz) • (K. Hirabayashi., et al, NTT, 1991) Advantage Problem • Dependence on Polarization States

  3. Transmission Spectra of a Conventional LC-FPF with Variable Birefringence of LC Unpolarized incident light, 9 dielectric layer mirror, LC layer (HWP, no=1.50, ne=1.70, second-order = 19.38 μm) design λ = 1550 nm no ne ne no ne S P P S

  4. Design & Optimization LC-FPF Insensitive to Input Polarization Attempt Solution Coinciding Two Sets of Orthogonal Polarization Peaks LC-FPF with Extra Birefringent Layers Tuning Peaks At the Same Rate Aim

  5. Structure LC-FPF with A single QWP LC-FPF with A pair of QWPs LC is homogeneously aligned nematic Calculation and Analysis Transmitted Intensity Output Polarization Properties Two Types of LC-FPFs with Extra Birefringent Layers

  6. Polarization parallel to the optic axis of LC Polarization normal to the optic axis of LC ~ Structure of LC-FPF with a Single QWP in the Cavity Dielectric mirrors ITO ITO The optic axis of LC Substrate AR coat Incident light Transmitted light X Z Y Reflected light LC layer Alignment layer Quarter-wave plate A.C

  7. Transmission Spectra of LC-FPF with a Single QWP in the Cavity Unpolarized incident light, 9 dielectric layer mirror QWP (no=1.50, ne=1.70, first-order = 9.69 μm), design λ = 1550 nm LC layer (HWP, no=1.50, ne=1.70, second-order = 19.38 μm) ne 12 nm

  8. Polarized Transmission Spectra of LC-FPF with a Single QWP with a +45º / -45º Polariser Unpolarized incident light, 9 dielectric layer mirror QWP (no=1.50, ne=1.70, first-order), LC layer (HWP, no=1.50, ne=1.70, second-order) +45º -45º +45º -45º +45º -45º ne

  9. Polarization parallel to the optic axis of LC Polarization normal to the optic axis of LC Structure of LC-FPF with a Pair of QWPs in the Cavity The optic axis of LC Incident light Transmitted light X Z Y Reflected light Crossed Quarter-wave plates

  10. Transmission Spectra of LC-FPF with Two QWPs in the Cavity Unpolarized incident light, 9 dielectric layer mirror, QWPs (no=1.50, ne=1.70, first-order = 9.69 μm), design λ = 1550 nm LC layer (HWP, no=1.50, ne=1.70, second-order = 19.38 μm) ne

  11. Polarized Transmission Spectra of LC-FPF with a Pair of QWPs with a +45º / -45º Polariser Unpolarized incident light, 9 dielectric layer mirror, QWPs (no=1.50, ne=1.70, first-order), LC layer (HWP, no=1.50, ne=1.70, second-order) ne +45º -45º +45º -45º +45º -45º -45º +45º

  12. +45º / -45º Linearly Polarized Incident Beam Traveling Through LC-FPF Filter The optic axis of first QWP The optic axis of second QWP Incident light Transmitted light +45ºX Z LC layer (HWP) +45ºY Reflected light Crossed Quarter-wave plates

  13. No splitting peak At 1550 nm The optical path difference between the polarizations the integral multiple to the incident wavelength Two different sets of peaks +45º / -45º polarization encounters only either the fast or the slow axis of the QWPs Started splitting No longer the integral multiple when the birefringence of LC is changed Cause for Splitting of Peaks of LC-FPF with a Pair of QWPs

  14. Transmission Spectra of LC-FPF with Two QWPs in the Cavity Unpolarized incident light, 9 dielectric layer mirror, QWPs (no=1.50, ne=1.70, first-order = 9.69 μm), design λ = 1550 nm LC layer (HWP, no=1.50, ne=1.70, second-order = 19.38 μm) ne

  15. No splitting peak At 1550 nm The optical path difference between the polarizations the integral multiple to the incident wavelength Two different sets of peaks +45º / -45º polarization encounters only either the fast or the slow axis of the QWPs Started splitting No longer the integral multiple when the birefringence of LC is changed Cause for Splitting of Peaks of LC-FPF with a Pair of QWPs

  16. Conclusion • LC-FPF with a single QWP • All peaks tuned by external electric field with unpolarized incident light • Spectrometer for Gas sensing systems. • LC-FPF with a pair of QWPs • Polarization-insensitive operation • A tuning range of 7 nm at near 1550 nm. • A Splitting of peaks caused by the birefringence of QWPs. Acknowledgements • K. Wang in the Optical Devices and Systems Group, UCL. • SID, IEE, EPSRC, UCL Graduate School for Travel Grants.

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