EP0495087A1 - Scanner a laser avec moyen de faconnage par rayon de post-balayage - Google Patents

Scanner a laser avec moyen de faconnage par rayon de post-balayage

Info

Publication number
EP0495087A1
EP0495087A1 EP19910915883 EP91915883A EP0495087A1 EP 0495087 A1 EP0495087 A1 EP 0495087A1 EP 19910915883 EP19910915883 EP 19910915883 EP 91915883 A EP91915883 A EP 91915883A EP 0495087 A1 EP0495087 A1 EP 0495087A1
Authority
EP
European Patent Office
Prior art keywords
hologon
spinner
scanning apparatus
scan
grating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19910915883
Other languages
German (de)
English (en)
Inventor
Badhri Narayan
James E. Roddy
Richard A. Stark
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Eastman Kodak Co
Original Assignee
Eastman Kodak Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Publication of EP0495087A1 publication Critical patent/EP0495087A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/10—Scanning systems
    • G02B26/106—Scanning systems having diffraction gratings as scanning elements, e.g. holographic scanners
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
    • G02B19/0004—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed
    • G02B19/0009—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having refractive surfaces only
    • G02B19/0014—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having refractive surfaces only at least one surface having optical power
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
    • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
    • G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
    • G02B19/0052—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a laser diode
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0938—Using specific optical elements
    • G02B27/095—Refractive optical elements
    • G02B27/0972—Prisms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/12—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using the sheet-feed movement or the medium-advance or the drum-rotation movement as the slow scanning component, e.g. arrangements for the main-scanning
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/12—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using the sheet-feed movement or the medium-advance or the drum-rotation movement as the slow scanning component, e.g. arrangements for the main-scanning
    • H04N1/126—Arrangements for the main scanning
    • H04N1/1265—Arrangements for the main scanning using a holographic scanning element

Definitions

  • This invention relates to laser scanning apparatus for producing large format high quality images, and more particularly to such apparatus having means for shaping the scanning spot produced by such apparatus subsequent to the scanning means.
  • U.S. patent no. 4,707,055 issued November 17, 1987 to Stark, and U.S. patent no. 4,904,034 issued February 27, 1990 to Narayan, Roddy, Stark and Thompson (which are incorporated herein by reference) describe scanning apparatus for providing a substantially straight line scan of a laser spot having a selected shape.
  • the scanning apparatus shown schematically in Fig. 2 includes a laser beam light source 10, such as a laser diode.
  • Means (not shown) are provided for modulating the output of the laser diode 10 in accordance with information contained in a stream of electronic signals. As such means are well known in the art, no further description is provided herein.
  • the beam 12 from the laser diode 10 is collimated by collimating optics 14, and is incident on a stationary diffraction grating 16, which directs the beam 12 to a rotating holographic beam scanner disc 18, referred to in the art as a hologon spinner.
  • the hologon spinner disc 18 comprises a plurality of holographically produced diffraction grating facets 20 as shown in Fig. 3. As the disc is rotated by a high speed motor 22, the diffraction grating facets 20 cause the beam to scan in a direction perpendicular to the plane of the drawing in Fig. 2.
  • the scanned beam 12' then passes through a pair of beam shaping prisms 2 and 26 which serve as beam expanders for expanding the cross section of the beam in the cross scan direction.
  • the shaped beam 12" then passes through an f- ⁇ lens 28 which focuses the scanning beam onto a target such as a photosensitive element 34 attached to a rotating drum 30.
  • the beam is scanned by hologon spinner 18 in a direction parallel to the axis 32 of the rotating drum 30 to provide a line scan on the photosensitive element 34.
  • a page scan of the element 34 is provided by rotation of drum 30 about axis 32. For optimum exposure of the photosensitive element 34, it is desirable that the spot produced by the laser beam be narrower in the line scan direction than in the page scan direction.
  • the useful duty cycle of the hologon be as large as possible, and for a high resolution scanner (i.e. a small spot at the photosensitive element 34) it is desirable that the beam at the hologon spinner 18 be large.
  • the beam 12 at the hologon spinner 18 be narrower in the page scan direction, as shown in Fig. 3.
  • the prisms 24 and 26 are employed to generate the desired beam shape at the photosensitive element 34.
  • the required size of the f- ⁇ lens 28, which needs to be large to accommodate the large format scan, varies directly with its distance from the hologon scanner 18, and the cost of the f- ⁇ lens increases approximately with the square of the distance to the hologon. Therefore, it can be seen that the presence of the beam shaping prisms 24 and 26 exact a cost in the size of the f- ⁇ lens required by the scanner.
  • the object of the present invention to provide an improved hologon laser scanner of the type having means for post-scanning shaping of the scanning spot that avoids the shortcoming noted above.
  • the object is achieved according to the present invention by providing a planar beam expander means between the f- ⁇ lens and the hologon scanner, whereby the f- ⁇ lens can be moved closer to the 5 hologon scanner, and therefore be made smaller and hence less expensive.
  • either one or both of the beam expander prisms is replaced by a diffraction grating.
  • the planar beam expander is a 0 gradient index optical plate having an index of refraction that continuously increases from one surface to the other.
  • Figure 1 is a schematic diagram of laser scanning apparatus accordingly to the present invention
  • Figure 2 is a schematic diagram of laser scanning apparatus according to the prior art
  • Figure 3 illustrates a radial hologon employed in the apparatus of Figures 1 and 2;
  • Figure 4 is a schematic diagram illustrating a diffraction grating beam expander employed in one embodiment of the present invention
  • Figure 5 is a schematic diagram of a gradient index optical plate beam expander employed in an alternative embodiment of the present invention.
  • Figure 6 is a schematic diagram useful in describing the scanner shown in Figure 1;
  • Figure 7A and B are diagrams useful in describing the orientation of the diffraction grating beam expander with respect to the hologon spinner.
  • Figure BA and B are diagrams useful in describing the incident ray and diffraction ray at the diffraction grating, relating to the signs of their respective angles.
  • FIG. 1 scanning apparatus according to the present invention is shown. Elements corresponding the the elements in the prior art scanner shown in Figure 2 are similarly numbered.
  • the beam expanding prisms 24 and 26 of the prior art have been replaced by a single planar beam expander 36, thereby enabling the f- ⁇ lens 28 to be moved closer to hologon spinner 18, and hence made smaller, realizing considerable cost savings in the f- ⁇ lens.
  • Only a single planar beam expander 36, oriented parallel to the hologon spinner 18, is employed in the example shown in Figure 1 for achieving the maximum space savings and hence maximum size reduction in the f- ⁇ lens 28.
  • the expanded beam 12" is no longer parallel with the output beam 12, as in the apparatus shown in Figure 1.
  • the planar beam expander 36 preferably comprises a diffraction grating 36' employed with a large incidence angle ⁇ . and a small diffraction angle ⁇ , as shown in Figure 4.
  • the planar beam expander 36 comprises a sheet of gradient index material 36" such as doped glass (as shown in Fig. 5), wherein the index of refraction varies continuously from one surface 42 to the opposite surface 44. With the index gradient in the direction of arrow A as shown in Figure 5, parallel rays 46 entering the sheet of gradient index glass 36" will be continuously refracted as they traverse the glass sheet, and will exit parallel as shown by rays 48.
  • a procedure for designing the diffraction grating beam expander 36' shown in Figure 4 will now be described. Design Procedure
  • the initial data needed to begin the diffraction grating design process are: ⁇ : spectral wavelength of the laser light source 10 ⁇ : angle of incidence of the input beam 12 on the spinner 18 G: grating factor for the spinner 18 ⁇ : rotation angle of the spinner corresponding to the position where bow is to be nulled by the output grating. f- i anamorphic beam magnification factor for the output grating.
  • the grating factor G is related to diffraction order number (m), wavelength ( ⁇ ) and groove frequency (f ) by the expression: G - m ⁇ f g (1)
  • the direction cosines of the diffracted beam 12 leaving the hologon spinner 18 are calculated next. These direction cosines are: cos ⁇ ⁇ CB - DA (2) cosfl - - E (3) cos ⁇ ⁇ AB + CD (4) where
  • the beam incidence angle ( ⁇ ..) on the diffraction grating 36' can be either a negative or a positive value.
  • the sign identifies the orientation of the output grating with respect to the hologon spinner 18, as shown in Figures 7A and 7B.
  • Figure 7A illustrates the case where the angle ⁇ . is negative
  • Figure 7B illustrates the case where ⁇ , is positive.
  • the diffraction grating requires a specific grating factor that causes the bow to be nulled when the spinner rotation angle is ⁇ .
  • This grating factor is calculated from the quadratic formula:
  • the required grating factor is calculated from eg. (11).
  • this quadratic equation will give two solutions for the grating factor.
  • the good solution will have RQ ⁇ SP in eq. (15) below, causing cos ⁇ .-O, and this is the condition for zero bow.
  • the bad solution will have RQ « -SP and should be discarded.
  • the calculated grating factors from eg. (11) can be negative. These are acceptable solutions. The negative sign only means that the grating order number (m) used is -1 instead of +1.
  • the direction cosines of the beam leaving the diffraction grating 36 when the spinner rotation is ⁇ are: cos ⁇ .-RQ-SP (15)
  • the diffraction angle ( ⁇ .) can either have the same sign as the incidence angle ( ⁇ .) or the opposite sign. This condition identifies the orientation of the diffracted beam with respect to the incident beam as shown in Figures 8A and 8B. Fig. 8A
  • FIG. 30 illustrates the case where the angles ⁇ , and ⁇ 1 have opposite signs
  • Fig. 8B illustrates the case where they have the same signs.
  • the anamorphic magnification M. of the beam caused by the diffraction grating is:
  • the scan trajectory is calculated from the equations:
  • the groove frequency for the output grating is 413.940139 grooves/mm.
  • the diffraction angle of the beam leaving the diffraction grating (at mid-scan) is calculated from eq. (24). ⁇ . - -33.630999 degrees
  • the scan trajectory i ⁇ found by fir ⁇ t calculating sets of direction cosine ⁇ for the scanning beam at the spinner output using eq. (2-9) for a sequence of spinner rotation angles ⁇ . Then, u ⁇ ing these direction cosines in eq. (15-22), corresponding ⁇ et ⁇ of direction co ⁇ ine ⁇ are generated for the scanning beam leaving the diffraction grating. Finally, the beam angular deflections are calculated from eq. (26-27).
  • the resulting trajectory i ⁇ given in the following table: Hologon
  • a laser scanner according to the present invention is useful for making large format high-quality images, such as graphic arts quality images and is advantageous in that the f- ⁇ lens may be placed closer to the hologon scanner thereby employing a smaller and hence lower cost f- ⁇ lens realizing manufacturing economy in the laser scanner.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Diffracting Gratings Or Hologram Optical Elements (AREA)

Abstract

Dans un scanner à laser du type ayant des moyens de façonnage par rayon de post-balayage utilisant des prismes entre un scanner à hologon et une lentille f-, les prismes sont remplacés par un dispositif d'expansion du rayon plan tel qu'une grille de diffraction, permettant ainsi de positionner la lentille f- plus près de l'hologon, et par conséquent de la faire plus petite et donc moins coûteuse.
EP19910915883 1990-08-03 1991-08-01 Scanner a laser avec moyen de faconnage par rayon de post-balayage Withdrawn EP0495087A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US56234590A 1990-08-03 1990-08-03
US562345 1995-11-22

Publications (1)

Publication Number Publication Date
EP0495087A1 true EP0495087A1 (fr) 1992-07-22

Family

ID=24245902

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19910915883 Withdrawn EP0495087A1 (fr) 1990-08-03 1991-08-01 Scanner a laser avec moyen de faconnage par rayon de post-balayage

Country Status (3)

Country Link
EP (1) EP0495087A1 (fr)
JP (1) JPH05502122A (fr)
WO (1) WO1992002843A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0559492B1 (fr) * 1992-03-05 1996-11-13 Sharp Kabushiki Kaisha Système de balayage holographique

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4410237A (en) * 1980-09-26 1983-10-18 Massachusetts Institute Of Technology Method and apparatus for shaping electromagnetic beams
US4707055A (en) * 1986-04-04 1987-11-17 Eastman Kodak Company Scanning apparatus
US4973112A (en) * 1988-12-01 1990-11-27 Holotek Ltd. Hologon deflection system having dispersive optical elements for scan line bow correction, wavelength shift correction and scanning spot ellipticity correction

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9202843A1 *

Also Published As

Publication number Publication date
JPH05502122A (ja) 1993-04-15
WO1992002843A1 (fr) 1992-02-20

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