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