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Cascaded Solid Spaced Filters for DWDM applications

Cascaded Solid Spaced Filters for DWDM applications. J. Floriot, F. Lemarchand, M. Lequime. Narrow Bandpass filters: Requirements. Transmittance. Example: 50GHz Dl - 0.5db > 0.22nm Dl -3db < 0.3nm Dl -20db < 0.6nm. l. sharpness. -0.5 dB. -3 dB. Steepness / shape factor. -20 dB.

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Cascaded Solid Spaced Filters for DWDM applications

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  1. Cascaded Solid Spaced Filters for DWDM applications J. Floriot, F. Lemarchand, M. Lequime

  2. Narrow Bandpass filters: Requirements Transmittance Example: 50GHz Dl -0.5db > 0.22nm Dl -3db < 0.3nm Dl-20db < 0.6nm l sharpness -0.5 dB -3 dB Steepness / shape factor -20 dB Isolation band 1528-1568nm

  3. Fabry Perot Cavities Spacer layer Incident Light T() R() substrate Mirror Mirror Narrowing the  bandwidth Higher Spacer thickness Or Better mirror reflectance

  4. Single FP cavities nL = 1.46 / nH = 2.09 35 layers – 17 layer mirrors – 2.12µm spacer 27 layers – 13 layer mirrors – 11.68µm spacer 15 layers – 7 layers mirrors – 107.22µm spacer

  5. Solid Spaced Filters Dielectric mirrors5 to 7 layers T() FSR Wafer thickness Transparent wafer 50 -150µm thick Low Absorption, low scattering Level, few sensitive to deposition errors

  6. Cascaded Solid Spaced Filters air gap T()

  7. Experimental Demonstration: 2 fused silica wafers < 3 arc-second < 3 arc-second 108.7µm 146.0µm 1.443 1.443 Refractive index @ 0 0 = 1560.86 nm 402L 540L Both Sides Coated : 5 layer Ta2O5 / SiO2 IAD mirrors

  8. Measurement set-up tunable laser source InGaAs Photodiode + amplifier+ DAC lightpathTMcollimators  1520 – 1570 nm  = 10 pm w0 = 250µm

  9. -3db = 0.79nm Tmax = 99.9% -3db =0.55 Tmax = 98.9% Residual Transmission Level = -16dB

  10. -3db =0.47 Tmax = 98.1%

  11. Triple Cavity Filters • howextending the rejection band ?

  12. Use of a blocking filter BW2 >>BW1 BW1

  13. Cavities with different FSR

  14. Different Phase Dependence Mirrors M1 M1 M2 M2 RM1()RM2 () But M1 () ≠ M2 () FSR1 ≠ FSR2

  15. Conclusion Number of layers errors sensitivity Absorption, scattering Rejection Band Vs ? low high low high low high reduced broad • Compactness  Optical contacting

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