Spherical Optics
Spherical lenses are specialized forms of double convex lenses. They have a good light incidence area and a short focal length. Such a sensor design is seen in Fig. 1.
The sphere is split in half for diffuse sensors to separate the reception from the emission channels.
Fig. 1
The emitter and receiver chips are positioned off the optical axis and as near as feasible to the sphere's surface (see Fig. 1). This results in a small sensing range, but a virtually cylindrical detection zone since the produced beam intersects the receiver's sensing range at a certain distance from the device.
A cylindrical detection zone might be pretty helpful when detecting objects through narrow holes or gaps.
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