| 摘要 |
A miniature scan engine for scanning a beam of monochromatic (laser) light across a bar code and receiving return light at a detector that provides electrical signals representing the code, utilizes an integral assembly of a laser (laser diode), the detector and a light collector mounted on flexures and rotated so as to scan the beam and receive the return light from the code. The collector is a body of material transmissive at the laser wavelength. The body presents an orientable surface so that the return light is incident at or close to perpendicular to the surface. In the body, parallel to the surface, is a volume hologram grating having Bragg planes arranged in rings around a center region in alignment with the detector. The angles of the Bragg planes vary progressively and decreases in a direction toward the center region so that light incident on the collector at angles of incidence, which vary from perpendicular to the surface by about + or -5 DEG , are diffracted and propagate by guided mode propagation, including reflections at the internal surfaces of the body and transmission through the grating (because the light propagating along the paths intersects the grating Bragg planes off Bragg that is at an angle other than the Bragg angle) to the detector. Efficient collection of the light returned from the bar code symbol is obtained. The entire scan engine may occupy a volume of less than 1.25 cubic inch, thereby enabling bar code scanning and reading facilities in devices such as hand-held data collection terminals where space is at a premium. |
