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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. - PowerPoint PPT Presentation
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Cascaded Solid Spaced Cascaded Solid Spaced Filters for DWDM Filters for DWDM
applicationsapplications
J. Floriot, F. Lemarchand, M. LequimeJ. Floriot, F. Lemarchand, M. Lequime
Narrow Bandpass filters: Narrow Bandpass filters: RequirementsRequirements
-0.5 dB
-3 dB
-20 dB
Isolation band
Steepness /shape factor
sharpness Transmittance Example: 50GHz
0.5db > 0.22nm
-3db < 0.3nm
-20db < 0.6nm
1528-1568nm
Fabry Perot CavitiesFabry Perot Cavities
T()R()
Incident Light
Mirror
Spacerlayer
Mirror
Higher Spacer thickness Or Better mirror reflectance
substrate
Narrowing the bandwidth
Single FP cavitiesSingle FP cavities
35 layers – 17 layer mirrors – 2.12µm spacer27 layers – 13 layer mirrors – 11.68µm spacer15 layers – 7 layers mirrors – 107.22µm spacer
nL = 1.46 / nH = 2.09
-40
-30
-20
-10
01520 1530 1540 1550 1560 1570
WAVELENGTH (nm)
TRA
NSM
ITTA
NC
E (d
B)
Solid Spaced FiltersSolid Spaced Filters
Transparent wafer50 -150µm thick
Dielectric mirrors 5 to 7 layers
T()
Wafer thickness
FSR
Low Absorption, low scattering Level, few sensitive to deposition errors
Cascaded Solid Spaced FiltersCascaded Solid Spaced Filters
T()
air gap
Experimental Demonstration: Experimental Demonstration: 2 fused silica wafers2 fused silica wafers
540L
Both Sides Coated : 5 layer Ta2O5 / SiO2 IAD mirrors
< 3 arc-second
108.7µm
< 3 arc-second
146.0µm
Refractive index @ 01.443 1.443
402L0 = 1560.86 nm
Measurement set-upMeasurement set-up
tunable laser source
lightpathTM collimators
InGaAs Photodiode + amplifier+ DAC
1520 – 1570 nm = 10 pmw0 = 250µm
0
0.2
0.4
0.6
0.8
1
1559 1560 1561 1562WAVELENGTH (nm)
TRA
NS
MIT
TAN
CE
-16
-12
-8
-4
0
1520 1530 1540 1550 1560
dB-3db = 0.79nmTmax = 99.9%
-3db =0.55Tmax = 98.9%
Residual Transmission Level = -16dB
0
0.2
0.4
0.6
0.8
1
1559 1560 1561 1562WAVELENGTH (nm)
TRA
NS
MIT
TAN
CE
-3db =0.47Tmax = 98.1%
-40
-30
-20
-10
0
1520 1530 1540 1550 1560 1570
dB
-40
-30
-20
-10
01520 1530 1540 1550 1560 1570
Tran
smitt
ance
(dB)
Triple Cavity FiltersTriple Cavity Filters
howhow extending the rejection band ?extending the rejection band ?
-100
-80
-60
-40
-20
01520 1530 1540 1550 1560 1570
dBUse of a blocking filterUse of a blocking filter
BW2 >>BW1BW1
Cavities with different FSRCavities with different FSR
-80
-60
-40
-20
01520 1530 1540 1550 1560 1570
dB
Different Phase Dependence MirrorsDifferent Phase Dependence Mirrors
M1 M2M1 M2
RM1() RM2 ()
But M1 () ≠ M2 ()
FSR1 ≠ FSR2
-80
-60
-40
-20
01520 1530 1540 1550 1560 1570
dB
ConclusionConclusion
Number of layersNumber of layerserrors sensitivityerrors sensitivity
Absorption, scatteringAbsorption, scatteringRejection BandRejection Band
Vs ?
Compactness Optical contacting
low low high highlow low high highlow low high high
reduced reduced broad broad