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Window Material

Almost any plastic material will work as a window mate-

rial. 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 percent or less for best optical

performance. Light loss should be measured at 875 nm.

Shape of the Window

From an optics standpoint, the window should be flat.

This ensures that the window will not alter either the

radiation pattern of the LED, or the receive pattern of

the photodiode.

Flat Window

(First choice)

If the window must be curved for mechanical or in-

dustrial design reasons, place the same curve on the

back side of the window that has an identical radius as

the front side. While this will not completely eliminate

the lens effect of the front curved surface, it will sig-

nificantly reduce the effects. The amount of change in

the radiation pattern is dependent upon the material

chosen for the window, the radius of the front and back

curves, and the distance from the back surface to the

transceiver. Once these items are known, a lens design

can be made which will eliminate the effect of the front

surface curve.

The following drawings show the effects of a curved

window on the radiation pattern. In all cases, the center

thickness of the window is 1.5 mm, the window is made

of polycarbonate plastic, and the distance from the

transceiver to the back surface of the window is 3 mm.

HSDL-3602 Flat Window

Curved Front and Back

(Second choice)

HSDL-3602 Curved Window

Curved Front, Flat Back

(Do not use)

HSDL-3602 Curved/Flat Window

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Data subject to change. Copyright © 2007 Lite-On Technology Corporation. All rights reserved.