Optical code readers with holographic optical elements

• US 20020148900A1
• Filed: 04/13/2001
• Published: 10/17/2002
• Est. Priority Date: 04/13/2001
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Nagano, Shinji, Patel, Mehul, Gurevich, Vladimir, Krichever, Mark, Blasczak, Matthew, Vinogradov, Igor R., Bianculli, Thomas D.
• Granted Patent: US 6,651,886 B2
• Time in Patent Office: Days
• US Class Current: 235/462.34
• CPC Class Codes: G02B 26/106 having diffraction gratings as scanning elements, e.g. holographic scanners holographic optical elements G02B5/32, holography G03H
• CPC Class Codes: G06K 7/10663 using hologram

Abstract

Holographic optical elements are configured and deployed in optical imagers and scanners to produce optical modification of output laser beams and light received and detected by the system. In some preferred embodiments electrically switchable holographic optical elements (ESHOEs) are employed for beam tilting, for varying spot size and shape for modifying system focal distance and field of view, for changing laser aiming patterns and/or for color imaging.

Claims

1. An optical code reading system comprising:

a photo sensor employing an array of cells for producing electrical signals responsive to an image directed to said sensor;

an optical system for focusing images corresponding to at least two fields of view which do not completely overlap, the optical system including at least one electrically switchable holographic optical element for switching between said fields of view;

means for electrically controlling said electrically switchable holographic optical element to switch between the fields of view; and

means for decoding data from the electrical signals corresponding to an optical code symbol contained in at least one of the images focused on the photo sensor.

2. The system of claim 1 further comprising processing means for stitching together image portions from at least two of the fields of view to form a composite image with resolution higher than the resolution obtainable with a single exposure of the photo sensor.

3. The system of claim 1 wherein the optical system includes at least one lens through which an input optical path of the system passes and wherein the at least one electrically switchable holographic optical element has transparent plates and is located in the optical path.

4. The system of claim 1 wherein the electrically switchable holographic optical element is formed with a volume hologram which tilts an input optical path of the system when voltage is removed from the plates thereof.

5. An imaging system for reading an optical code symbol comprising:

a photo sensor having a two dimensional array of cells;

an optical system for directing images to the photo sensor, wherein the optical system includes an electrically switchable holographic optical element switchable between two states to vary the optical properties of the images directed to the photo sensor; and

means for switching the electrically switchable holographic optical element to select an image of the optical code symbol which is readily decodable.

6. The imaging system of claim 5 wherein at least two different system magnifications are selectively provided by switching the electrically switchable holographic optical element.

7. The imaging system of claim 5 wherein the electrically switchable holographic element is switched between two states which provides different focal distances.

8. An imager based optical code reading system with a range finder for determining the distance of an object in a field of view of the system comprising:

an image sensor having a primary input optical axis;

an electrically switchable holographic optical element for tilting the input optical axis of the image sensor;

means for detecting a shift in position of an image of the object on the image sensor caused by the tilting of the input optical axis; and

means for determining the distance of the object by triangulation from the detected shift in position.

9. The system of claim 8 wherein the shift in position of the image of the object is detected by detecting a shift in position of an image of an edge of an optical code symbol on the object.

10. The system of claim 8 wherein the shift in position of the image of the object is detected by detecting a shift in position of an image of an aiming spot projected by the system onto the object.

11. The system of claim 8 further comprising means responsive to said distance determining means for adjusting the focal distance of the system.

13. The laser beam source of claim 12 wherein the volume hologram contains an interference pattern simulation of a cylindrical lens to produce an elliptical laser beam spot.

14. The laser beam source of claim 13 wherein the laser beam spot is switchable between an elliptical and a circular shape.

15. The laser beam source of claim 12 wherein the electrically switchable holographic optical element is reflective and functions as a moving mirror for scanning the laser beam across the optical code.

16. The laser beam source of claim 12 wherein plural transmission mode electrically switchable holographic optical elements are stacked together to provide multiple, switchable beam shaping functions.

17. The laser beam source of claim 12 wherein at least one electrically switchable holographic optical element controls beam ellipticity and at least one other electrically switchable holographic optical element controls the location of the narrowest portion of the laser beam waist.

18. The laser beam source of claim 17 wherein a return signal of detected reflections of the laser beam is monitored to determine the appropriate laser beam shape and the electrically switchable holographic optical elements are controlled to produce said appropriate laser beam shape in response thereto.

20. The method of claim 19 wherein the power of the coherent light beam is varied to selectively reduce the power level of the incident light beam a sufficient amount such that the first pattern is visible to a user and the second pattern is too dim to be visible to the user.

21. The method of claim 19 wherein an electronic control switches the power of the coherent light beam to turn off part of the aiming pattern.

22. The method of claim 19 wherein the first pattern is a close range aiming pattern and the second pattern is a long range aiming pattern.

24. The apparatus of claim 23 wherein the color components are red, green and blue light.

25. The apparatus of claim 24 wherein the filter means is an optical stack made up of at least three electrically switchable holographic elements, constituting red, green and blue filters, respectively.

26. The apparatus of claim 23 wherein substantially all of the cells of the photo detector are each used to sequentially detect red, green and blue light.

27. The apparatus of claim 23 wherein at least three electrically switchable holographic optical elements are located on an optical path of the apparatus and wherein

a first electrically switchable holographic optical element is switchable between a first mode where a first wavelength band is reflected to the photo sensor and a second mode where the incident light is directed toward

a second electrically switchable holographic optical element that is switchable between a first mode where a second wavelength band is reflected to the photo sensor and a second mode where the incident light is directed toward

a third electrically switchable holographic optical element that is switchable between a first mode where a third wavelength band is reflected to the photo sensor and a second mode where the incident light is directed toward a light stop.

12. A laser beam source for a laser optical code scanning system comprising:

a laser diode for producing a laser beam;

an electrically switchable holographic optical element in an output beam path of the laser diode formed with a volume hologram for selectively modifying the laser beam shape in response to a control signal; and

control circuitry for switching the holographic optical element to restore and erase the volume hologram formed in the electrically switchable holographic optical element.

19. A method for changing laser aiming patterns used for aiming an optical code reader comprising the steps of

providing a diffractive optical element;

directing a coherent light beam at the diffractive optical element;

using the diffractive optical element to transform incident coherent light into at least two different aiming patterns, wherein a first pattern is projected at a relatively higher optical power and a second pattern is projected at a relatively lower optical power; and

varying the power of the coherent light beam directed at the diffractive optical element to vary the appearance of the projected aiming pattern.

23. An apparatus for producing video signals corresponding to a color image comprising:

a photo sensor employing an array of cells for producing video signals in response to incident light;

an optical system comprising;

means for focusing an image on the photo sensor; and

filter means for selectively directing to the photo sensor different color components of the color image including electrically switchable holographic optical means; and

means for electrically controlling said at least one electrically switchable holographic optical element to sequentially direct the different color components of the color image to the photo sensor.