Apparatus for beam splitting

• US 5,883,746 A
• Filed: 03/20/1997
• Issued: 03/16/1999
• Est. Priority Date: 09/22/1994
• Status: Expired due to Fees

• Current Assignee: Heidelberger Druckmaschinen Ag
• Original Assignee: Linotype-Hell AG (Heidelberger Druckmaschinen Ag)
• Inventors: Zelenka, Thomas
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): BEY, DAWN MARIE
• Application Number:
  US08/809,943
• Time in Patent Office: 726 Days
• Field of Search: 359/629, 359/636, 359/638, 359/726, 359/728, 359/220, 359/221
• US Class Current: 359/629
• CPC Class Codes: G02B 26/10 Scanning systems
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: G02B 7/003 Alignment of optical elements G02B7/001, G02B7/002 take precedence; for mirrors G02B7/1822

Abstract

An apparatus for splitting a light beam into two sub-beams is formed of a stationary light source for generating a light beam, of a first polarization converter and of a deflection unit rotating around the optical axis in which two sub-beams are generated from the light beam. The deflection unit contains a polarization beam splitter, a following, second polarization converter and a reflector that is preferably designed as a prism. An automatic correction of positional offsets of the sub-beams is implemented in the deflection unit since the polarization beam splitter or the deflection unit is tilted and/or the lenses are shifted with adjustment drives. The positional offsets of the sub-beams are measured in their focus plane, and corresponding correction values are transmitted with a transformer to the adjustment drives in the rotating deflection unit.

Claims

1. An apparatus for splitting a light beam into a first and a second sub-beam, comprising:

a stationary light source for generating a light beam on an optical axis;

an objective arranged in the optical axis in front of the light source;

a deflection unit rotatable about the optical axis, said light beam being incident onto said deflection unit;

a polarization beam splitter in said deflection unit arranged on the optical axis for dividing the light beam into a first polarized light component as said first sub-beam reflected by said polarization beam splitter substantially perpendicular to the optical axis and into a second polarized light component transmitted by said polarization beam splitter substantially in a direction of the optical axis, a polarization converter and a reflector being arranged on the optical axis behind said polarization beam splitter for phase turning the second light component by 90°

in phase with respect to a polarization direction and for reflecting the phase-turned second beam component back to the polarization beam splitter at which the phase-turned second beam component is reflected as said second sub beam substantially perpendicular to said optical axis;

respective focusing units in said deflection unit for focusing said first and second sub-beams onto respective surfaces;

for correcting relative positional offsets of the first and second sub-beams relative to one another, the reflector comprising a prism with at least two mirror faces residing at an angle relative to one another for reflecting the phase-turned second beam component back to said polarization converter after the second beam component has passed through the polarization converter to said prism.

2. An apparatus according to claim 1 wherein the two mirror faces reside at an angle of 90°

relative to one another.

3. The apparatus according to claim 1 wherein the prism is designed as a triangle prism.

4. The apparatus according to claim 3 wherein at least two mirror faces of the triangle prism are at an angle of 90°

to one another.

5. The apparatus according to claim 1 wherein the prism is designed as a triple prism.

6. The apparatus according to claim 5 wherein at least two mirror faces of the triple prism are at 90°

relative to one another.

7. The apparatus according to claim 1 wherein the focusing unit for the first sub-beam comprises at least one lens in the beam path of the first sub-beam.

8. The apparatus according to claim 1 wherein the focusing unit for the second sub-beam comprises at least one lens in the beam path of the second sub-beam.

9. The apparatus according to claim 1, further comprising:

means for determining a relative positional offset of at least one of the sub-beams at a reference surface impinged by the sub-beam and for a determining a correction value corresponding to the determined positional offset;

means for transmission of the correction value to the deflection unit; and

means for changing an angle of inclination of the polarization beam splitter of the deflection unit relative to the optical axis depending on the transmitted correction value for correcting relative positional offsets of the sub-beams.

10. The apparatus according to claim 9, wherein:

the angle of inclination of the polarization beam splitter is changeable by tilting the deflection unit relative to the optical axis; and

the means for changing the angle of inclination of the polarization beam splitter is an adjustment drive which is in an interactive connection with the deflection unit and controllable by said transmitted correction value for tilting said deflection unit.

11. The apparatus according to claim 10, wherein the adjustment drive comprises a piezo drive.

12. The apparatus according to claim 10 wherein the adjustment drive comprises a magnetostrictive drive.

13. The apparatus according to claim 9 wherein the means for determining the relative positional offset of the at least one sub-beam and for determining the correction value corresponding to the determined positional offset comprises a position-measuring unit arranged at said reference surface struck by the sub-beam.

14. The apparatus according to claim 13 wherein a differential photo diode is employed as the position-measuring unit.

15. The apparatus according to claim 9 wherein the means for the transmission of the correction value to the deflection unit comprises an electro-magnetic transformer.

16. The apparatus according to claim 1 further comprising:

means for determining a relative positional offset of at least one of the sub-beams at a reference surface impinged by the sub-beam and for determining a correction value corresponding to the determined positional offset;

means for transmission of the correction value to the deflection unit; and

means for shifting a position of said at least one focusing unit depending on the transmitted correction value for correcting relative positional offsets of the sub-beams.

17. The apparatus according to claim 16 wherein the means for changing the angle of inclination of the focusing units comprises an adjustment drive at each focusing unit controllable by the correction value.

18. The apparatus according to claim 17 wherein the adjustment drive comprises a piezo drive.

19. The apparatus according to claim 17 wherein the adjustment drive comprises a magnetostrictive drive.

20. The apparatus according to claim 16 wherein the means for determining the relative positional offset of the at least one sub-beam and for determining the correction value corresponding to the determined positional offset comprises a position-measuring unit arranged at the reference surface of the sub-beam.

21. The apparatus according to claim 20 wherein a differential photo diode is employed as the position-measuring unit.

22. The apparatus according to claim 16 wherein the means for transmission of the correction value to the deflection unit comprises an electro-magnetic transformer.

23. The apparatus according to claim 1 wherein the light source generates a circularly polarized light beam.

24. The apparatus according to claim 1 wherein:

the light source generates a linearly polarized light beam; and

a further polarization converter for converting the linear polarization of the light beam into a circular polarization is arranged on the optical axis between the light source and the rotating deflection unit.

25. The apparatus according to claim 24 wherein the polarization converter and the further polarization converter are designed as birefringent plates.

26. The apparatus according to claim 23 wherein the birefringent plates are λ

/4 plates.

27. The apparatus according to claim 1 for increasing luminous power of the respectively active first and second sub-beams further comprising:

a further polarization converter stationarily arranged in the optical axis in front of the deflection unit and controllable by a control signal for switching over a rotational direction of a circular polarization of a circular polarized light beam depending on said control signal;

another polarization converter arranged in the optical axis and on the deflection unit in front of the polarization beam splitter for converting said circular polarized light beam into a linear polarized light beam having a first polarization plane or a second polarization plane depending on a respective rotational direction of the circular polarization of the circular polarized light beam;

the converted linear polarized light beam having said first polarization plane is reflected by the polarization beam splitter as said first polarized light component for generating said active first sub-beam, but is not transmitted as said second polarized light component to generate said second sub-beam; and

the converted linear polarized light beam having said second polarization plane is transmitted through the polarization beam splitter as said second polarized light component for generating said active second sub-beam, but is not reflected as said first polarized light component to generate said first sub-beam.

28. The apparatus according to claim 27 wherein the controllable further polarization converter is designed as an electro-optical modulator.

29. The apparatus according to claim 27 wherein the further converter is designed as a wave plate.

30. The apparatus according to claim 27 wherein an angular momentum generator is coupled with the deflection unit for generating the control signal for the further polarization converter, the control signal determining a working interval in which one of the sub-beams is activated and the other sub-beam is de-activated in every revolution of the deflection unit.

31. An apparatus for splitting a light beam into first and second sub-beams, comprising:

a light source for generating a light beam along an optical axis;

an objective arranged on the optical axis in front of the light source;

a deflection unit receiving the light beam passing through the objective and rotatable around the optical axis, said deflection unit having;

a polarization beam splitter for dividing the polarized light beam into a reflective, polarized light component as said first sub-beam that proceeds substantially perpendicular to the optical axis, and into a polarized light component that is allowed to pass and proceeds substantially in a direction of the optical axis;

a polarization converter and a reflector after the polarization converter arranged on the optical axis behind the polarization beam splitter, the polarization converter turning the light component as it passes through the converter by 90°

in phase with respect to the polarization direction, and the reflector reflecting the light component passing through the polarization converter back through the polarization converter and to the polarization beam splitter where it is reflected at the polarization beam splitter to form said second sub-beam; and

the reflector comprising a three sided triangular prism having a face running perpendicular to the optical axis and facing the polarization converter, said reflector being designed such that the light beam incident at an arbitrary angle in turn emerges from the prism parallel to the incident light beam and deflected by 180°

.

32. The apparatus according to claim 31, wherein said triangular prism has at least two mirror faces at 90°

relative to one another.

33. An apparatus for splitting a light beam into first and second sub-beams, comprising:

a light source for generating a light beam along an optical axis;

an objective arranged on the optical axis in front of the light source;

a deflection unit receiving the light beam passing through the objective and rotatable around the optical axis, said deflection unit having;

a polarization beam splitter for dividing the polarized light beam into a reflective, polarized light component as said first sub-beam that proceeds substantially perpendicular to the optical axis, and into a polarized light component that is allowed to pass and proceeds substantially in a direction of the optical axis;

a polarization converter and a reflector arranged on the optical axis behind the polarization beam splitter, the polarization converter turning the light component as it passes through the converter by 90°

in phase with respect to the polarization direction, and the reflector reflecting the light component passing through the polarization converter back through the polarization converter and to the polarization beam splitter where it is reflected at the polarization beam splitter to form said second sub-beam;

respective focusing units for the first and second sub-beams;

a position measuring unit for determining a relative positional offset of at least one of the sub-beams on a reference surface and for determining a correction value corresponding to the determined positional offset; and

a unit for changing at least one of angle of inclination of the polarization beam splitter relative to the optical axis or position of the focusing units for the sub-beams dependent on the correction value for correcting relative positional offset of the sub-beams.

34. The apparatus according to claim 33 wherein the reflector has at least two mirror faces arranged at 90°

relative to one another.