ASDL-3023 datasheet(23/26 Pages) LITEON

23 / 26 page

Window Material

Almost any plastic material will work as a window

material. Polycarbonate is recommended. The surface

finish of the plastic should be smooth, without any

texture. An IR filter dye may be used in the window to

make it look black to the eye, but the total optical loss

of the window should be 10% or less for best optical

performance.Lightlossshouldbemeasuredat875nm.

Therecommendedplasticmaterialsforuseasacosmetic

windowareavailablefromGeneralElectricPlastics.

Recommended Plastic Materials:

Material #

Light Transmission

Haze

Refractive Index

Lexan141

88%

1.586

Lexan920A 85%

1.586

Lexan940A 85%

1.586

Note:920Aand940Aaremoreflameretardantthan141.

RecommendedDye:Violet#21051

(IRtransmissantabove625mm)

Shape of the Window

From an optics standpoint, the window should be flat.

This ensures that the window will not alter either the

radiationpatternoftheLED,orthereceivepatternofthe

photodiode.Ifthewindowmustbecurvedformechani-

calorindustrialdesignreasons,placethesamecurveon

thebacksideofthewindowthathasanidenticalradiusas

thefrontside.Whilethiswillnotcompletelyeliminatethe

lenseffectofthefrontcurvedsurface,itwillsignificantly

reducetheeffects.Theamountofchangeintheradiation

pattern is dependent upon the material chosen for the

window,theradiusofthefrontandbackcurves,andthe

distance from the back surface to the transceiver. Once

theseitemsareknown,alensdesigncanbemadewhich

will eliminate the effect of the front surface curve. The

followingdrawingsshowtheeffectsofacurvedwindow

ontheradiationpattern.Inallcases,thecenterthickness

ofthewindowis1.5mm,thewindowismadeofpolycar-

bonate plastic, and the distance from the transceiver to

thebacksurfaceofthewindowis3mm.

Flat Window, (First Choice)

Curved Front and Back, (Second Choice)

Curved Front, Flat Back, (Do not use)

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