Window Material
Almost any plastic material will work as a window
material. Polycarbonate is recommended. The surface
nish of the plastic should be smooth, without any
texture. An IR lter 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. Light loss should be measured at 885 nm.
The recommended plastic materials for use as a cosmetic
window are available from General Electric Plastics.
Recommended Plastic Materials:
Material # Light Transmission Haze Refractive Index
Lexan 141 88% 1% 1.586
Lexan 920A 85% 1% 1.586
Lexan 940A 85% 1% 1.586
Note: 920A and 940A are more ame retardant than 141.
Recommended Dye: Violet #21051 (IR transmissant above 625mm)
Shape of the Window
From an optics standpoint, the window should be at.
This ensures that the window will not alter either the
radiation pattern of the LED, or the receive pattern of the
photodiode. If the window must be curved for mechani-
cal or industrial design reasons, place the same curve on
the backside of the window that has an identical radius as
the front side. While this will not completely eliminate the
lens eect of the front curved surface, it will signicantly
reduce the eects. 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 eect of the front surface curve. The
following drawings show the eects 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 polycar-
bonate plastic, and the distance from the transceiver to
the back surface of the window is 3 mm.
Flat Window
(First Choice)
Curved Front and Back
(Second Choice)
Curved Front, Flat Back
(Do not use)
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Avago, Avago Technologies, and the A logo are trademarks of Avago Technologies, Limited in the United States and other countries.
Data subject to change. Copyright © 2007 Avago Technologies Limited. All rights reserved.
AV02-0454EN - June 21, 2007