hsdl3208 Avago Technologies, hsdl3208 Datasheet - Page 17

• Manufacturer Part Number: hsdl3208
• Description: Ultra Small Profile Package Irda Data Compliant Low Power 115.2 Kbit/s Infrared Transceiver - Agilent Hewlett-packard
• Manufacturer: Avago Technologies

17
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. Light loss should be
measured at 875 nm.
The recommended plastic
materials for use as a cosmetic
window are available from General
Electric Plastics.
Recommended Plastic Materials:
Material
Number
Lexan 141L
Lexan 920A
Lexan 940A
Note: 920A and 940A are more flame retardant than 141L.
Recommended Dye: Violet #21051 (IR transmissant above 625 nm).
Flat Window
(First Choice)
Figure 24. Shape of windows.
Light
Transmission
88%
85%
85%
Haze
1%
1%
1%
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.
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 the
Curved Front and Back
(Second Choice)
Refractive
Index
1.586
1.586
1.586
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.
Curved Front, Flat Back
(Do Not Use)