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

0

1520 1530 1540 1550 1560 1570

WAVELENGTH (nm)

TR

AN

SM

ITT

AN

CE

(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)

TR

AN

SM

ITT

AN

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)

TR

AN

SM

ITT

AN

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

Tra

nsm

itta

nce (

dB

)

Triple Cavity FiltersTriple Cavity Filters

howhow extending the rejection band ?extending the rejection band ?

-100

-80

-60

-40

-20

0

1520 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

0

1520 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

0

1520 1530 1540 1550 1560 1570

dB

ConclusionConclusion

Number of layersNumber of layers

errors sensitivityerrors sensitivity

Absorption, scatteringAbsorption, scattering

Rejection BandRejection Band

Vs ?

Compactness Optical contacting

low low high high

low low high high

low low high high

reduced reduced broad broad