EP0781661A1

EP0781661A1 - Increased pixel density and increased printing speed in a xerographic line printer with multiple linear arrays of surface emitting lasers

Info

Publication number: EP0781661A1
Application number: EP96308989A
Authority: EP
Inventors: Thomas L. Paoli; Tibor Fisli
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1995-12-22
Filing date: 1996-12-11
Publication date: 1997-07-02
Also published as: JPH09174916A

Abstract

The pixel density along a scan line on a photoreceptor in a xerographic line printer with a structure (300) comprising multiple linear arrays (302, 304, 306, 308, 316, 318) of surface emitting lasers (310, 312, 320, 322) can be increased by providing staggered linear laser arrays (306, 308, 316, 318) within a single structure. The printing speed of the printer with such a structure of multiple linear arrays can also be increased by providing aligned linear laser arrays (302, 304) wherein first linear arrays (306, 316) and second linear arrays (308, 318) are aligned with one another.

Description

This invention relates to a xerographic line printer with a monolithic structure of multiple linear arrays of surface emitting lasers and, more particularly, to increased pixel density and increased printing speed of the xerographic line printer.
US-A-5 337 074 and US-A-5 461 413 disclose using a single linear surface emitting laser array as the light source for a line printer.
Co-pending European patent application nos entitled "COLOR XEROGRAPHIC PRINTER WITH MULTIPLE LINEAR ARRAYS OF SURFACE EMITTING LASERS WITH THE SAME WAVELENGTHS", ............. entitled "COLOR XEROGRAPHIC PRINTER WITH MULTIPLE LINEAR ARRAYS OF SURFACE EMITTING LASERS WITH DISSIMILAR WAVELENGTHS" and entitled "COLOR XEROGRAPHIC PRINTER WITH MULTIPLE LINEAR ARRAYS OF SURFACE EMITTING LASERS WITH DISSIMILAR POLARIZATION STATES AND DISSIMILAR WAVELENGTHS", all filed concurrently herewith and corresponding to US patent application nos. 08/577793, 08/577794 and 08/577792 respectively, describe color xerographic line printers having monolithic multiple linear arrays of surface emitting lasers with either the same wavelength, different wavelengths or different wavelengths and different polarizations. In each case, the xerographic line printer has multiple linear vertical cavity surface emitting laser (VCSEL) arrays.
Each laser linear array will simultaneously expose a complete scan line across a photoreceptor. Thus. multiple laser linear arrays will simultaneously expose multiple complete scan lines across one photoreceptor or complete scan lines across multiple photoreceptors. For the purposes of this application, multiple lines on a single photoreceptor or single lines across multiple photoreceptors or multiple lines across multiple photoreceptors will be treated the same.
Each individual VCSEL or laser emitting element in the linear array is spaced tangentially from the adjacent VCSEL. The resulting emitted spot of light or pixel will be spaced from the adjacent pixel within the scan line on the photoreceptor. The physical structure of the monolithic structure of the linear arrays and the optical elements of the xerographic line printer place limitations on the number or density of spots per inch along the scan line.
The laser linear arrays are spaced in the process (sagittal) direction from each other in the monolithic structure. The beams from these linear arrays, after the optics of the xerographic line printer, will form scan lines on the photoreceptor which are also spaced from each other in the process direction. Again, the physical structure of the monolithic structure of the linear arrays and the optical elements of the xerographic line printer place limitations on the number and spacing of scan lines simultaneously exposed on the photoreceptor. The greater the number of scan lines, the faster the printer speed is.
It is an object of this invention to increase the pixel density along the scan line of a xerographic line printer with a monolithic structure of multiple linear arrays of surface emitting lasers.
It is yet another object of this invention to increase the printing speed of a xerographic line printer with a monolithic structure of multiple linear arrays of surface emitting lasers.
In accordance with one aspect of the present invention, there is provided a xerographic line printer having a structure comprising at least one multiple linear array of surface emitting lasers, at least one of the multiple linear arrays comprising at least:- a first linear array of surface emitting lasers having the same center to center spacing, and a second linear array of surface emitting lasers having the same center to center spacing as the first linear array, characterised in that the surface emitting lasers in the first linear array are spaced from the surface emitting lasers in the second linear array in the process direction of the printer.
In one embodiment of the invention, the surface emitting lasers in the first linear array are aligned with the surface emitting lasers in the second linear array in the process direction of the printer. A third linear array of surface emitting lasers having the same center to center spacing as the surface emitting lasers of the first and second linear arrays may also be provided, the surface emitting lasers in the third linear array also being aligned with the surface emitting lasers of the first and second linear arrays in the process direction of the printer. Additionally, a fourth linear array of surface emitting lasers having the same center to center spacing as the surface emitting lasers of the first, second and third linear arrays is also provided, the surface emitting lasers in the fourth linear array also being aligned with the surface emitting lasers of the first, second and third linear arrays in the process direction of the printer.
In another embodiment of the present invention, the first and second linear arrays are tangentially staggered by a predetermined distance related to the center to center spacing. In this case, the predetermined distance is one half the center to center spacing. If a third linear array of surface emitting lasers having the same center to center spacing as the first and second linear arrays is provided, the surface emitting lasers of the first, second and third linear arrays being tangentially staggered by a predetermined distance equal to one-third the center to center spacing. Similarly, for a fourth linear array of surface emitting lasers having the same center to center spacing as the first, second and third linear arrays, the surface emitting lasers of the first, second, third and fourth linear arrays are tangentially staggered by a distance equal to one-fourth the center to center spacing.
In yet another embodiment of the present invention, a first array including a first linear array of surface emitting lasers having the same center to center spacing, and a second linear array of surface emitting lasers having the same center to center spacing as the first linear array, the first and second linear arrays being tangentially staggered by a distance equal to one half the center to center spacing, and a second array including a third linear array of surface emitting lasers having the same center to center spacing as the first and second linear arrays, and a fourth linear array of surface emitting lasers having the same center to center spacing as the first, second and third linear arrays, the third and fourth linear arrays being tangentially staggered by a distance equal to one half the center to center spacing, the surface emitting lasers in the first array being aligned with the surface emitting lasers in the second array in the process direction of the printer.
It is preferred that the linear arrays are separated by a distance equal to the interline scan pitch times the interlace factor divided by the system magnification.
In accordance with the present invention, the pixel density along the scan line on a photoreceptor from a xerographic line printer with a monolithic structure of multiple linear arrays of surface emitting lasers can be increased by providing tangentially staggered linear laser arrays within a single monolithic structure. The printing speed of a xerographic line printer with a monolithic structure of multiple linear arrays of surface emitting lasers can be increased by providing sagitally aligned linear laser arrays within a single monolithic structure.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description, by way of example only, taken in conjunction with the accompanying drawings, in which:-

Figure 1 is a schematic illustration of the front view of a single linear array of vertical cavity surface emitting lasers (VCSELs) formed according to the present invention;
Figure 2 is a schematic illustration of the front view of two staggered linear arrays of vertical cavity surface emitting lasers (VCSELs) for increasing pixel density formed according to the present invention;
Figure 3 is a schematic illustration of the front view of three staggered linear arrays of vertical cavity surface emitting lasers (VCSELs) for increasing pixel density formed according to the present invention;
Figure 4 is a schematic illustration of the front view of four staggered linear arrays of vertical cavity surface emitting lasers (VCSELs) for increasing pixel density formed according to the present invention;
Figure 5 is a schematic illustration of the front view of two staggered linear arrays of vertical cavity surface emitting lasers (VCSELs) for maintaining pixel density formed according to the present invention;
Figure 6 is a schematic illustration of the front view of three staggered linear arrays of vertical cavity surface emitting lasers (VCSELs) for maintaining pixel density formed according to the present invention;
Figure 7 is a schematic illustration of the front view of four staggered linear arrays of vertical cavity surface emitting lasers (VCSELs) for maintaining pixel density formed according to the present invention;
Figure 8 is a schematic illustration of the front view of two aligned linear arrays of vertical cavity surface emitting lasers (VCSELs) for increasing printing speed formed according to the present invention;
Figure 9 is a schematic illustration of the front view of three aligned linear arrays of vertical cavity surface emitting lasers (VCSELs) for increasing printing speed formed according to the present invention;
Figure 10 is a schematic illustration of the front view of four aligned linear arrays of vertical cavity surface emitting lasers (VCSELs) for increasing printing speed formed according to the present invention; and
Figure 11 is a schematic illustration of the front view of two aligned linear arrays of two staggered linear arrays of vertical cavity surface emitting lasers (VCSELs) for increasing pixel density and for increasing printing speed formed according to the present invention.

As noted previously, xerographic line printers can have monolithic multiple linear arrays of surface emitting lasers with either the same wavelength, different wavelengths or different wavelengths and different polarizations. In each case, the xerographic printer has multiple linear arrays of vertical cavity surface emitting lasers (VCSEL). Each individual linear laser array has VCSELs emitting nominally the same wavelength with the same polarization state. As described in the co-pending applications mentioned above, the monolithic structure can be a non-monolithic structure formed from two monolithic structures. For the purposes of this application, the term "monolithic structure" shall encompass the non-monolithic structures.
All of the VCSELs in the linear laser array will be addressed simultaneously so that the linear laser array will simultaneously expose all the pixels in a line on the photoreceptor. The term of art used to describe the entire line of pixels on the photoreceptor is the "scan line", although, technically, in this application the beam is not being scanned along a line. However. this application will conform to conventional nomenclature and describe the simultaneously exposed pixel line on the photoreceptor as a "scan line".
For the sake of clarity, the photoreceptor of the xerographic line printer has a given speed, the optical system of the xerographic line printer has a given magnification and the addressibility of the individual VCSELs is also at a given speed.
Reference is now made to Figure 1 wherein is described the single linear laser array 10 as used in the illustrated embodiments of the present invention.
VCSEL array 10 of Figure 1 consists of a single linear array 12. Individual VCSELs 14 in the single linear array 12 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 16 between the individual VCSELs 14. Each VCSEL 14 emits a light beam of nominally the same wavelength and same or random polarization state. This VCSEL array 10, with a sufficient density of VCSELs 12, is capable of exposing all the pixels across a full page in the printing application. However it is difficult to fabricate and operate closely spaced VCSELs in arrays that will produce pixel densities at 600spi or higher along the scan line of a photoreceptor.
VCSEL array 20 of Figure 2 consists of two adjacent staggered linear arrays 22 and 24. Individual VCSELs 26 in the first linear array 22 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 16 between the individual VCSELs 26. Individual VCSELs 28 in the second linear array 24 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 16 between the individual VCSELs 28. The pitch 16 between the individual VCSELs in the first and second linear arrays 22 and 24 of Figure 2 is the same pitch distance 16 between the individual VCSELs in the single linear array 12 of Figure 1. The two linear arrays 22 and 24 are tangentially staggered or offset in the sagittal or process direction by a distance 30 equal to one-half the pitch 16.
This staggering or offset in the VCSEL array 20 of Figure 2 allows exposure of each line at the same speed as VCSEL array 10 of Figure 1 but doubles the pixel density along the scan line on the photoreceptor. The light spots from the VCSELs 28 in the second linear array 24 expose between the light spots from the VCSELs 26 in the first linear array 22 if the two arrays are exposed along the same scan line by delaying the exposure with one linear array relative to the exposure with the other linear array. The length of the time delay equals the time it takes the photoreceptor to move the first line of exposed spots on the photoreceptor into alignment with the position of the image of the second linear array.
Two staggered arrays are easier to fabricate in a monolithic structure than one tightly spaced array.
VCSEL array 32 of Figure 3 consists of three adjacent staggered linear arrays 34, 36 and 38. Individual VCSELs in each array are still spaced apart by the pitch 16, the same as in Figures 1 and 2. However, the three linear arrays 34, 36 and 38 are tangentially staggered or offset in the sagittal or process direction by a distance 40 equal to one-third the pitch 16.
VCSEL array 42 of Figure 4 consists of four adjacent staggered linear arrays 44, 46, 48 and 50. Individual VCSELs in each array are still spaced apart by the pitch 16, the same as in the previous Figures. However, the four linear arrays 44, 46, 48 and 50 are tangentially staggered or offset in the sagittal or process direction by a distance 52 equal to one-quarter the pitch 16.
The benefits from staggering the arrays are increasing the density of the spots along the scan line on the photoreceptor and the ease of fabrication of staggered linear arrays. The disadvantage to staggering the arrays is the resulting sacrifice of printing speed since multiple arrays are used to expose one scan line rather than multiple scan lines.
The arrays 20, 32, 42 shown in Figures 2 to 4 show increased pixel density of the spots along the scan line on the photoreceptor with equal center to center spacing or pixel pitch between the individual VCSELs in the adjacent staggered linear arrays. The converse is also true. The pixel density of the spots along the scan line on the photoreceptor can remain the same with increased center to center spacing or pixel pitch between the individual VCSELs in the adjacent staggered linear arrays.
Returning to Figure 1, the individual VCSELs 14 in the single linear array 12 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 16 between the individual VCSELs 14.
VCSEL array 100 of Figure 5 consists of two adjacent staggered linear arrays 102 and 104. Individual VCSELs 106 in the first linear array 102 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 108 between the individual VCSELs 106. Individual VCSELs 110 in the second linear array 104 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 108 between the individual VCSELs 110. The pitch 108 between the individual VCSELs in the first and second linear arrays 102 and 104 of Figure 2 is twice the pitch distance 16 between the individual VCSELs in the single linear array 12 of Figure 1. The two linear arrays 102 and 104 are tangentially staggered or offset in the sagittal or process direction by a distance 112 equal to one-half the pitch 108 or equal to the pitch distance 16 of Figure 1.
This staggering or offset in the VCSEL array 100 of Figure 5 allows exposure of each line at the same speed as VCSEL array 10 of Figure 1 but maintains the pixel density along the scan line on the photoreceptor. The light spots from the VCSELs 110 in the second linear array 104 expose between the light spots from the VCSELs 106 in the first linear array 102 if the two arrays are exposed along the same scan line by delaying the exposure with one linear array relative to the exposure with the other linear array. The resulting pixel density from VCSEL array 100 of Figure 5 will be the same as the pixel density of VCSEL array 10 of Figure 1.
Two staggered arrays are easier to fabricate in a monolithic structure than one tightly spaced array. An array with an increased center to center spacing or pitch is also easier to fabricate in a monolithic structure than a tightly spaced array.
VCSEL array 114 of Figure 6 consists of three adjacent staggered linear arrays 116, 118, 120. Individual VCSELs in each array are spaced apart linearly in the scan direction with equal center to center spacing or pixel pitch 122 between the individual VCSELs. The pitch 122 between the individual VCSELs in the linear arrays 116, 118, 120 of Figure 6 is three times the pitch distance 16 between the individual VCSELs in the single linear array 12 of Figure 1. Adjacent linear arrays 116 and 118, and 118 and 120 are tangentially staggered or offset in the sagittal or process direction by a distance 124 equal to one-third the pitch 122 or equal to the pitch distance 16 of Figure 1.
VCSEL array 126 of Figure 7 consists of four adjacent staggered linear arrays 128, 130, 132 and 134. Individual VCSELs in each array are spaced apart linearly in the scan direction with equal center to center spacing or pixel pitch 136 between the individual VCSELs. The pitch 136 between the individual VCSELs in the linear arrays 128, 130, 132 and 134 of Figure 7 is four times the pitch distance 16 between the individual VCSELs in the single linear array 12 of Figure 1. Adjacent linear arrays 128 and 130, 130 and 132, and 132 and 134 are tangentially staggered or offset in the sagittal or process direction by a distance 138 equal to one-fourth the pitch 136 or equal to the pitch distance 16 of Figure 1.
The benefit to staggering the arrays and maintaining the density of the spots along the scan line on the photoreceptor is the ease of fabrication of staggered linear arrays.
As noted earlier, the disadvantage to staggering the arrays is the resulting sacrifice of printing speed since multiple arrays are used to expose one scan line rather than multiple scan lines. For increased printing speed, VCSEL array 200 shown in Figure 8 consists of two adjacent linear arrays 202 and 204. Individual VCSELs 206 in the first linear array 202 are arranged linearly in the scan direction with equal center to center spacing or pitch 16 between the individual VCSELs 206. Individual VCSELs 208 in the second linear array 204 are arranged linearly in the scan direction with the same equal center to center spacing or pixel pitch 16 between the individual VCSELs 208, as the VCSELs 206 in the first linear array 202 and the individual VCSELs in the single linear array 12 of Figure 1. The VCSELs 206 and 208 in both arrays emit light of nominally the same wavelength and the same polarization state.
The two linear arrays 202 and 204 are aligned in the sagittal or process direction. The two aligned linear arrays 202 and 204 are separated by a distance 210. The distance 210 can be such that with proper magnification and imaging optics in the xerographic line printer the two adjacent linear arrays 202 and 204 simultaneously expose adjacent scan lines on the photoreceptor. The distance 210 can also be increased so that with proper magnification and imaging optics in the xerographic line printer the two adjacent linear arrays 202 and 204 simultaneously expose interlaced scan lines on the photoreceptor with two unexposed scan lines between the exposed scan lines.
The distance 210 is the interline array pitch, or distance between the two lines of the two arrays. The interline array pitch equals the interlace factor times the interline scan pitch divided by the system magnification. The interlace factor is the multiple of scan pitch between simultaneously exposed scan lines. The system magnification is the xerographic printing systems optical magnification. The interlace factor in general can be any odd number for an even number of scan lines and an even number for any odd number of scan lines.
This dual aligned array gives twice the printing speed to the xerographic line printer since two scan lines are simultaneously printed if both arrays are addressed simultaneously. This dual aligned array 200, with a sufficient density of VCSELs 206 and 208, is capable of simultaneously exposing two adjacent or two interlaced pixel lines across a full page in the printing application. The dual aligned monolithic array provides easier fabrication than a nonmonolithic structure for spots aligned sagittally. The disadvantage to aligned laser arrays is that the aligned arrays do not increase the pixel density along the scan line on the photoreceptor.
VCSEL array 212 of Figure 9 consists of three adjacent aligned linear arrays 214, 216 and 218. Individual VCSELs in each array are still spaced apart by the pitch 16, the same as in the previous Figures. However, the three linear arrays 214, 216 and 218 are separated by a distance 210.
VCSEL array 220 of Figure 10 consists of four adjacent staggered linear arrays 222, 224, 226 and 228. Individual VCSELs in each array are still spaced apart by the pitch 16, the same as in the previous Figures. However, the four linear arrays 222, 224, 226 and 228 are separated by a distance 210.
The distance 210 can be determined to provide adjacent simultaneous pixel lines along the photoreceptor or simultaneous interlaced pixel lines along the photoreceptor.
The arrays 20, 32, 42 shown in Figures 2 to 4 show increased pixel density with adjacent staggered linear arrays of VCSELs. The arrays 200, 212, 220 shown in Figures 8 to 10 show increased printing speed with adjacent aligned linear arrays of VCSELs. A VCSEL array 300 shown in Figure 11 shows both increased pixel density and increased printing speed with adjacent aligned linear arrays of adjacent staggered linear arrays of VCSELs.
VCSEL array 300 of Figure 11 consists of two aligned arrays 302 and 304. The first aligned array 302 consists of two adjacent staggered linear arrays 306 and 308. Individual VCSELs 310 in the first linear array 306 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 16 between the individual VCSELs 310. Individual VCSELs 312 in the second linear array 308 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 16 between the individual VCSELs 312. The pitch 16 between the individual VCSELs in the first and second linear arrays 306 and 308 of Figure 11 is the same pitch distance 16 between the individual VCSELs in the single linear array 12 of Figure 1. The two linear arrays 306 and 308 are tangentially staggered or offset in the sagittal or process direction by a distance 314 equal to one-half the pitch 16.
The second aligned array 304 consists of two adjacent staggered linear arrays 316 and 318. Individual VCSELs 320 in the third linear array 316 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 16 between the individual VCSELs 320. Individual VCSELs 322 in the fourth linear array 318 are arranged linearly in the scan direction with equal center to center spacing or pixel pitch 16 between the individual VCSELs 322. The pitch 16 between the individual VCSELs in the third and fourth linear arrays 316 and 318 of Figure 11 is the same pitch distance 16 between the individual VCSELs in the single linear array 12 of Figure 1. The two linear arrays 316 and 318 are staggered or offset in the sagittal or process direction by a distance 314 equal to one-half the pitch 16.
Array 302 is aligned with array 304 and thus the first linear array 306 is aligned with the third linear array 316 while the second linear array 308 is aligned with the fourth linear array 318.
As discussed previously with regard to Figures 2 to 4, the first linear array 302 doubles the pixel density along a first scan line on the photoreceptor. The second linear array 304 doubles the pixel density along a second scan line on the photoreceptor. Since arrays 302 and 304 are aligned, the two scan lines are simultaneously printed. The separation distance between the two arrays can be either in pitch or interlaced, as discussed previously with regard to Figures 8 to 10.
In the aligned, staggered configuration of the multiple linear arrays of vertical cavity surface emitting lasers, the number of linear arrays that are staggered can be different than the number of arrays that are aligned. The staggered arrays determine the pixel density while the aligned arrays determine printing speed.
US-A-5 233 367 provides the basic mathematical formula for spacing between adjacent lines in interlacing.
Thus, the VCSEL array can consist of :-

(1) a single linear array, with a density sufficient to expose all pixels across a full page,
(2) N linear arrays with elements tangentially staggered in the process (sagittal) direction from array to array, capable of exposing all pixels across a full page at N times the density of each linear array,
(3) M separated arrays with elements aligned in the process (sagittal) direction, capable of simultaneously exposing all pixels in multiple interlaced or adjacent lines, and
(4) M separated arrays, each of which consists of N linear arrays with elements tangentially staggered in the process direction from array to array, capable of exposing all the pixels across a full page at N times the density of each linear array and capable of simultaneously exposing all pixels in multiple interlaced or adjacent lines.

In each case, the imaging lens forms a magnified image of the VCSEL array on the photoreceptor.
While the invention has been described in conjunction with specific embodiments, it is evident to those skilled in the art that many alternatives, modifications and variations will be apparent in light of the foregoing description. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.

Claims

A xerographic line printer having a structure (20; 32; 42; 100; 114; 126; 200; 212; 220) comprising at least one multiple linear array (22, 24; 34, 36, 38; 44, 46, 48, 50; 102, 104. 116, 118, 120; 128, 130, 132, 134; 202, 204; 214, 216, 218; 222, 224, 226, 228; 302, 304, 306, 308, 316, 318) of surface emitting lasers (26, 28; 106, 110; 206, 208; 310, 312, 320, 322), at least one of the multiple linear arrays (22, 24; 34, 36, 38; 44, 46, 48, 50; 102, 104. 116, 118, 120; 128, 130, 132, 134; 202, 204; 214, 216, 218; 222, 224, 226, 228; 302, 304, 306, 308, 316, 318) comprising at least:-
a first linear array (22; 34; 44; 102; 116; 128; 202; 214; 222; 302, 304, 306, 316) of surface emitting lasers (26; 106; 206; 310, 320) having the same center to center spacing (16; 108; 122; 136), and

a second linear array (24; 36; 46; 104; 118; 130; 204; 216; 224; 302, 304, 308, 318) of surface emitting lasers (28; 110; 208; 312, 322) having the same center to center spacing (16; 108; 122; 136) as the first linear array (22; 34; 44; 102; 116; 128; 202; 214; 222; 302, 304, 306, 316),
characterised in that the surface emitting lasers (26; 106; 206; 310, 320) in the first linear array (22; 34; 44; 102; 116; 128; 202; 214; 222; 302, 304, 306, 316) are spaced from the surface emitting lasers (28; 110; 208; 312, 322) in the second linear array (24; 36; 46; 104; 118; 130; 204; 216; 224; 302, 304, 308, 318) in the process direction of the printer.
A printer according to claim 1 wherein the surface emitting lasers (206; 310, 320) in the first linear array (202: 214; 222; 302, 304, 306, 316) are aligned with the surface emitting lasers (208; 312, 322) in the second linear array (204; 216; 224; 302, 304, 308, 318) in the process direction of the printer.
A printer according to claim 2 further including a third linear array (218; 226) of surface emitting lasers having the same center to center spacing (16) as the surface emitting lasers of the first and second linear arrays (214, 216; 222, 224), the surface emitting lasers in the third linear array (218; 226) being aligned with the surface emitting lasers of the first and second linear arrays (214, 216; 222, 224) in the process direction of the printer.
A printer according to claim 3 further including a fourth linear array (228) of surface emitting lasers having the same center to center spacing (16) as the surface emitting lasers of the first, second and third linear arrays (222, 224, 226), the surface emitting lasers in the fourth linear array (228) being aligned with the surface emitting lasers of the first, second and third linear arrays (222, 224, 226) in the process direction of the printer.
A printer according to claim 1 wherein the first linear array (22; 34; 44; 102; 116; 128; 302, 304, 306, 316) and the second linear array (24; 36; 46; 104; 118; 130; 302, 304, 308, 318) are tangentially staggered by a predetermined distance (30; 40; 52; 112; 124; 138; 314) related to the center to center spacing (16; 108; 122; 136).
A printer according to claim 5 wherein the predetermined distance (30; 112) is one half of the center to center spacing (16; 108).
A printer according to claim 5 further including a third linear array (38; 120) of surface emitting lasers having the same center to center spacing (16; 122) as the first and second linear arrays (34, 36; 116, 118), the surface emitting lasers of the first, second and third linear arrays (34, 36, 38; 116, 118, 120) being tangentially staggered a predetermined distance (40; 124) which is equal to one-third the center to center spacing (16; 122).
A printer according to claim 7 further including a fourth linear array (50; 134) of surface emitting lasers having the same center to center spacing (16; 136) as the first, second, third and fourth linear arrays (44, 46, 48, 50; 128, 130, 132, 134) 16; 136), the surface emitting lasers of the first, second and third linear arrays (34, 36, 38; 116, 118, 120) being tangentially staggered a predetermined distance (52; 138) which is equal to one-fourth the center to center spacing (16; 136).
A printer according to claim 1 or 2 comprising:-
a first array (302) including a first linear array (306) of surface emitting lasers (310) having the same center to center spacing (16), and a second linear array (308) of surface emitting lasers (312) having the same center to center spacing (16) as the first linear array (306), the first and second linear arrays (306, 308) being tangentially staggered by a distance (314) equal to one half the center to center spacing (16), and

a second array (304) including a third linear array (316) of surface emitting lasers (320) having the same center to center spacing (16) as the first and second linear arrays (306, 308), and a fourth linear array (318) of surface emitting lasers (322) having the same center to center spacing (16) as the first, second and third linear arrays (306, 308, 316), the third and fourth linear arrays (316, 318) being tangentially staggered by a distance (314) equal to one half the center to center spacing (16), the surface emitting lasers (310, 312) in the first array (302) being aligned with the surface emitting lasers (320, 322) in the second array (304) in the process direction of the printer.
A printer according to any one of the preceding claims wherein the linear arrays (22, 24; 34, 36, 38; 44, 46, 48, 50; 102, 104. 116, 118, 120; 128, 130, 132, 134; 202, 204; 214, 216, 218; 222, 224, 226, 228; 302, 304, 306, 308, 316, 318) are separated by a distance (210) equal to the interline scan pitch times the interlace factor divided by the system magnification.
A printer according to any one of claims 5 to 8, wherein N linear arrays of surface emitting lasers having the same center to center spacing, the N linear arrays being tangentially staggered by a distance equaling the center to center spacing divided by N.
A printer according to any one of claims 2 to 4 or 11, wherein M linear arrays of surface emitting lasers having the same center to center spacing, the M linear arrays being aligned in the process direction of the printer.