HSDL-3210 Datasheet, PDF (23/24 Pages) Agilent(Hewlett-Packard) – IrDA Compliant Low Power 1.15 Mbit/s Infrared Transceiver

Window Material
Almost any plastic material will
work as a window material. Poly-
carbonate 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. Light loss
should be measured at 875 nm.
The recommended plastic
materials for use as a cosmetic
window are available from
General Electric Plastics.
Shape of the Window
From an optics standpoint, the
window should be flat. This en-
sures 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
mechanical or industrial 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 significantly reduce the
effects. The amount of change in
Recommended Plastic Materials:
Material
Number
Light
Haze
Transmission
Refractive
Index
Lexan 141L 88%
1%
1.586
Lexan 920A 85%
1%
1.586
Lexan 940A 85%
1%
1.586
Note: 920A and 940A are more flame retardant than 141L.
Recommended Dye: Violet #21051 (IR transmissant above 625 nm).
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 win-
dow is 1.5 mm, the window is
made of polycarbonate plastic,
and the distance from the trans-
ceiver to the back surface of the
window is 3 mm.
Flat Window
(First Choice)
Figure 29. Shape of windows.
Curved Front and Back
(Second Choice)
Curved Front, Flat Back
(Do Not Use)