Cascaded Solid Spaced Filters for DWDM applications

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Cascaded Solid Spaced Filters for DWDM
applications

• J. Floriot, F. Lemarchand, M. Lequime

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Narrow Bandpass filters Requirements
Transmittance
Example 50GHz Dl -0.5db gt 0.22nm Dl -3db lt
0.3nm Dl -20db lt 0.6nm
l
sharpness
-0.5 dB
-3 dB
Steepness / shape factor
-20 dB
Isolation band
1528-1568nm
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Fabry Perot Cavities
Spacer layer
Incident Light
T(?)
R(?)
substrate
Mirror
Mirror
Higher Spacer thickness Or Better mirror
reflectance
Narrowing the ? bandwidth
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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
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Solid Spaced Filters
Dielectric mirrors 5 to 7 layers
T(?)
FSR
Wafer thickness
Transparent wafer 50 -150µm thick
Low Absorption, low scattering Level, few
sensitive to deposition errors
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Cascaded Solid Spaced Filters
air gap
T(?)
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Experimental Demonstration 2 fused silica wafers
lt 3 arc-second
lt 3 arc-second
108.7µm
146.0µm
1.443
1.443
Refractive index _at_ ?0
?0 1560.86 nm
540L
402L
Both Sides Coated 5 layer Ta2O5 / SiO2 IAD
mirrors
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Measurement set-up
tunable laser source
InGaAs Photodiode amplifier DAC
lightpathTM collimators
? 1520 1570 nm ?? 10 pm w0 250µm
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??-3db 0.79nm Tmax 99.9
??-3db 0.55 Tmax 98.9
Residual Transmission Level -16dB
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??-3db 0.47 Tmax 98.1
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Triple Cavity Filters

• how extending the rejection band ?

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Use of a blocking filter
BW2 gtgtBW1
BW1
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Cavities with different FSR
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Different Phase Dependence Mirrors
M1
M2
M1
M2
RM1(?) ? RM2 (?)
But ?M1 (?) ? ? M2 (?)
FSR1 ? FSR2
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Conclusion
Vs
?

• Number of layers
• errors sensitivity
• Absorption, scattering
• Rejection Band

low high low high low high reduced
broad
Compactness ? Optical contacting