3D Time-of-flight distance measurement with custom - Universität ...

IMAGING TOF RANGE CAMERAS 165
Power density in uW/cm^2
Intensity profile at 2m distance
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Position in cm
Power density in uW/cm^2
Intensity profile at 7.5m distance
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Position in cm
Figure 6.11 Vertical beam profile: profile perpendicular to the optical line-sensor
plane (measured with Newport 840 HandHeld optical power
meter).
In spite of the use of a cylindrical lens, only a small fraction of the modulated light is
effectively used for the range measurement. With a total size of light sensitive pixel
area of 16 µm (H) x 13 µm (V) and a focal length of 4 mm, the projected
observation area of 1 pixel at 7.5 m distance is 30 mm (H) x 25 mm (V). Compared
to the vertical beam profile (Figure 6.11) one can estimate that only about 4% of
the optical power is imaged onto the light sensitive pixel area.
The optical setup for the line sensor is therefore not ideal, since a lot of “expensive”
optical power is lost. In the application of this line sensor one would be better using
a more narrow illumination plane (e.g. a 1D expanded laser beam) or modified
imaging optics instead of the standard lens we are currently using. The reason we
did not further improve this setup nor evaluate the use of laser illumination is that
we regard this line camera as the first step towards the development of the 3D
camera introduced in Section 6.3. For the 3D application the problem of
illuminating only a small strip disappears.