GB2136146A - Projection Optical System and Optical Scanning Apparatus Comprising a Plurality of Projection Optical Systems - Google Patents

Abstract

A projection optical system for projecting an enlarged image of an object including an optical fiber lens array and convex and concave lenses arranged in object and image spaces, respectively of the optical fiber lens array. The optical fiber lens array and convex and concave lenses are so arranged that a conjugated image of the object with respect to the convex lens and a conjugate image of the enlarged image with respect to the concave lens are formed at such positions that conditions of the optical fiber lens array necessary for projecting an erecting real image of unit magnification are satisfied. When the convex and concave lenses are arranged in the image and object spaces of the optical fiber lens array, a reduced image of the object is projected. An optical scanning apparatus is formed by arranging a plurality of projection optical systems side by side to form a long continuous scanning line. <IMAGE>

Description

SPECIFICATION Projection Optical System and Optical Scanning Apparatus Comprising a Plurality of Projection Optical Systems The present invention relates to an optical system for projecting an image of an object comprising a lens array having a number of micro lens optical systems having optical axes arranged in parallel with each other, each of the micro lens optical systems forming an erecting real image of the object having unit magnification.

There has been developed the projection optical system in which each of a number of micro lenses is consisting of a converging type optical fiber having a core whose refractive index is varied continuously in a radial direction and the micro lenses are arranged side by side in such a manner that their optical axes are made in parallel with each other. Such a projection optical system has an advantage that an elongated object can be projected, while object distance and image distance can be made small, and has been widely used in electrophotographic copying machines.

There has been further developed a projection optical system comprising a micro lens array which includes a plurality of optical systems for projecting an erecting real image of unit magnification and arranged side by side, each optical system comprising a number of spherical micro lenses made of plastic material. Such a spherical micro lens array has been also used in electrophotographic copying machines.

In the known micro lens arrays, it is possible to project an erecting real image of unit magnification, but it is impossible to project an erecting real image having a variable magnification. Therefore, in order to project the image of a variable magnification, there has been used a projection optical system composed of spherical lenses. However, such a projection optical system requires a long optical path length and thus an apparatus using the optical system is liable to be complicated and large.

In a Japanese Patent Application Laid-open Publication No. 154,343/79 published on December 5, 1979, there has been proposed an optical system for projecting an image of a variable magnification comprising an optical fiber lens array and a concave lens. In such a projection optical system, in case of obtaining an enlarged image, the concave lens is arranged in an image space of the optical fiber lens array between an exit plane of the optical fiber lens array and an image plane on which an erecting real image of unit magnification is to be formed. In order to project a reduced erecting real image, the concave lens is arranged in an object space between an entrance plane of the optical fiber lens array and an object plane for obtaining an erecting real image of unit magnification.

However, such a known projection optical system has the following drawbacks. In case of projecting the enlarged image, an optical path length between the object plane and the image plane becomes longer than that in case of projecting the erecting real image of unit magnification. Further, in order to obtain a large magnification, it is necessary to arrange the concave lens closer to the exit plane of the optical fiber lens array, so that aberrations might be increased. It should be noted that the concave lens could not be arranged closer to the exit plane of the optical fiber lens array having a long length.Further, in case of forming the reduced erecting real image, the concave lens forms a reduced erecting virtual image of an object positioned in the object plane for projecting the erecting real image of unit magnification and the optical fiber lens array forms an erecting real image of the erecting real image of a reduced magnification. The reduced erecting virtual image is not formed on the object plane for forming the erecting real image of unit magnification and therefore, the erecting real image having the same magnification as the reduced erecting virtual image and having a good resolution could never be formed by the optical fiber lens array.

Fig. 1 is a schematic view showing a known projection optical system comprising a micro lens array for projecting an erecting real image of an object having unit magnification. The micro lens array L, comprises a number of optical fiber lenses It, 12 and 13 whose optical axes W, X and Y are arranged in parallel with each other. Each of the optical fiber lenses has a core whose refractive index is made smaller outwardly in a radial direction and has a converging property. An object 0, is placed in an object plane and an erecting real image 1, of unit magnification of the object 0, is formed in an image plane.A light flux emanating from an arrow head point of the object 0, forms an inverted real image at a middle of the optical fiber lens array L, and an inverted real image of this inverted real image, i.e. the erecting real image 11 is formed in the image plane. Since a distant from the object plane and the middle point of micro lens array is equal to a distance from the middle point and the image plane, the erecting real image 1, has a unit magnification.

Each of the optical fiber lenses 11, 12,13 composing the micro lens array L, does not have a sufficiently large angle of view for covering the whole object 0,, but the optical fiber lenses cover different regions of the object 0, to form the composite image 1, of the object 01 in the image plane.

In case of changing the distance between the object 0, and the micro lens array Lr, it is impossible to compose a correct image having a varied magnification, because reduced or enlarged images formed by respective optical fiber lenses are not composed correctly.

Fig. 2 is a schematic view showing a known projection optical system comprising a micro lens array L, composed of a number of spherical lenses made of plastic material. Spherical lenses having small diameters i4, 17, iao; i5, i8, ia; and i6, 19, i,2 are arranged on optical axes W, X and Y, respectively to form a number of sets of optical systems for projecting erecting real image of unit magnification.In the projecting optical system comprising lenses i4, 17 and lo, an inverted real image of an object 0, is formed by the lens 14 at a position of the lens 17 and an inverted real image of this inverted real image, i.e. an erecting real image 1, of the object 0, is formed in an image plane by means of the lens 1,0. The middle lens 17 serves to deflect a light flux forming the inverted real image so as to be introduced effectively into the third lens lao. Basically, the middle lens 17 does not contribute to the variation of the magnification and image plane.A number of sets of micro lenses are so arranged that their optical axes W, X, Y are made in parallel with each other to form the micro lens array which can project the erecting real image 1, of unit magnification of the object 0, having a long length. However, also in this projection system it is impossible to form a reduced or enlarged erecting image, because reduced or enlarged images formed by respective sets of micro lenses are not composed correctly.

Fig. 3 shows a known projection optical system for projecting a reduced erecting real image of an object 0, comprising a micro lens array L, and a concave lens L2 arranged in an object space. The micro lens array L, is formed by a number of optical fiber lenses, each projecting an erecting real image of unit magnification. The concave lens L2 is arranged in the object space of the micro lens array L, and the object 0, is so arranged that conditions for projecting an erecting real image of unit magnification are satisfied. A virtual image 02 of the object 0, is formed by the concave lens L2.

That is to say, the object 0, and the virtual image 02 are conjugated with each other with respect to the concave lens L2. A light flux emanating from the object 0, is refracted by the concave lens L2 and is considered to emanate from the virtual image 02. Therefore, a reduced erecting real image 1, is formed in an image space at a position nearer to the micro lens array L1 than at a position S at which the erecting real image of unit magnification would be formed, if the concave lens L2 is not provided.

Fig. 4 illustrates a known projection optical system for projecting an enlarged erecting real image. In this system, an object 0, and a micro lens array L, comprising a number of optical fiber lenses la, i2, 13 are so arranged that the necessary conditions for forming an erecting real image of unit magnification are satisfied. A concave lens L2 is arranged between the micro lens array L1 and an image 12 of the object 0, which would be formed if the concave lens L2 is not arranged. Due to the concave lens L2, the image 12 is enlarged and an enlarged erecting real image 1, is formed in an image plane which is far away from the micro lens array L than the image 12. Therefore, the image 12 can be regarded as being conjugated with the image 12 with respect to the concave lens L2.In this system, the formula 1/a+1/b=i/f is applied. In this formula, a is a distance between a principal plane h2 of the concave lens L2 and the image 12, b is a distance between the principal plane h2 and the image 1,, and f is a focal length of the concave lens L2. Therefore, the distance b can be calculated from the above formula if a and f have been determined. Further, the enlarging magnification can be calculated from Ib/al.

In order to construct an optical scanning apparatus which may be used as a writing head or a reading head for optical recording and reproducing system, an array is formed by a number of optical scanning elements. For instance, a LED array is composed by integrating a number of light emitting diodes in an array form.

In another light gate array, each picture element is formed by magneto- or electro-optical effect material whose polarization can be changed by means of an electric signal and an array of the picture elements is arranged between two polarization plates which are arranged in a cross nicols condition, whereby light transmission and cut-off is controlled by the electric signal.

There has been commercially available a light gate array named LISA in which electrodes are arranged on a thin film of magnetic garnet and the polarization plane is rotated under the influence of heat and magnetic field. Such a light gate array is sold by Valvo GmbH, West Germany. There have been also developed light gate arrays using leadlanthanum-zirconium-titanate ceramics or liquid crystal having opto-electronic effect.

As the information reading head, there have been proposed silicon photodiode array, charge transfer device such as CCD, etc.

The above mentioned optical scanning array is formed in a single crystal plate and thus, its length is limited by a length of the single crystal plate.

Moreover, in order to improve yield in manufacturing the scanning element array, it is difficult to form the array having a long length.

Therefore, usually a plurality of optical scanning arrays are aligned to form a long optical scanning apparatus. In this case, in order to obtain a continuous scanning line, images of the light gate arrays are projected on the scanning line by means of projection optical systems. Fig. 5 illustrates such an optical scanning apparatus in which five gate arrays A-l to A-5 are arranged side by side and images l-1 to 1-5 of the gate arrays are formed on a scanning plane F by means of projection optical systems L-1 to L-5, respectively, each projection optical system comprising a spherical lens. Upon the gate arrays A-1 to A-5 is impinged illumination light from a light guide LG comprising a number of optical fibers and glass plates G-1 to G-5.

The glass plates G-1 to G-5 serve as substrates for supporting the gate arrays A-1 to A-5, respectively. Therefore, the substrates, i.e. glass plates G-1 to G-5 have to be made larger than the light gate arrays A-l to A-5. Thus, it is impossible to arrange the gate arrays continuously without space therebetween. Then, the enlarged images I 1 to 1-5 of the gate arrays A-1 to A-5 are formed on the scanning plane F by the projection lenses L-1 to L-5 in such a manner that the successive images 1-1 to 1-5 are connected to each other. In this manner, a long continuous scanning line can be obtained.However, in the known optical scanning apparatus, since it is required to arrange the spherical projection lens systems the number of which is equal to that of the gate arrays, the whole apparatus becomes large in size and complicated in construction. Further, in case of using the spherical projection lens, there might be produced a so-called shading and thus it is impossible to obtain the scanning line whose intensity is uniform over its whole length.

Figs. 6A and 6B show another known optical scanning apparatus comprising a plurality of optical scanning element arrays. Fig. 6A is a cross section and Fig. 6B is a developed plan view in which optical systems are turned in directions a and a' and are viewed from a direction b. In Figs.

6A and 6B, reference numerals 1 and 2 designate rows of LED arrays A, to An and B, to Bn. In each row, a plurality of LED arrays are aligned with interposing spacings therebetween. SA-1 to 5A-n and SB~1 to 5B-n represent substrates for the LED arrays A1 to An and B1 to Bnl respectively.

Between the LED array rows 1 and 2 and a scanning line forming region F are inserted optical fiber lens arrays 3 and 4, respectively and images 1A1 to lAn and 1B1 to IBn of the LED arrays A, to An and B, to Bn are formed on the scanning region F.

The LED arrays A, to An and B, to Bn are so arranged that the images 1A1 to lAn and 1B1 to IBn are arranged alternately without spacing therebetween. In this scanning apparatus, since the optical fiber lens arrays 3 and 4 form the images of unit magnification, the resolution of the picture elements in the image could not be made higher than that of the LED arrays. In order to obtain the scanning line having higher resolution, it has been proposed in a Japanese Patent Application Laid-open Publication No. 67,957/82 to project reduced images of the LED arrays by means of the optical fiber lens arrays.However, in case of forming a reduced image by means of the optical lens array, it is impossible to obtain a sharp image, so that it is theoretically impossible to form the scanning line having high resolution.

The present invention has for its object to provide a projection optical system having a micro lens array, which can project an erect real image having a variable magnification, while an optical distance between an object plane and an image plane can be made small and a resolution of the image can be made high.

It is another object of the invention to provide a projection optical system having a micro lens array, in which an erecting real image of a variable magnification can be projected, while an optical distance between an object plane and an image plane can be made equal to that in case of projecting an erecting real image of unit magnification.

It is another object of the invention to provide a projection optical system comprising a micro lens array, in which an erecting real image of a variable magnification can be projected, while aberrations can be reduced.

It is still another object of the invention to provide a projection optical system in which an erecting real image of a variable magnification can be formed, while a long micro lens array can be used.

According to the invention, in a projection optical system for projecting an erecting real image of an object having a variable magnification comprising a micro lens array having a number of micro lens optical systems arranged along a line and having optical axes arranged in parallel with each other, each micro lens optical system projecting an erecting real image of unit magnification, the improvement comprises optical means including at least a convex lens arranged in either an object space or an image space at such a position that a conjugate image of an object plane or an image plane of the micro lens array with respect to the convex lens is formed at such a position that conditions necessary for projecting the erecting real image of unit magnification are satisfied.

The present invention also relates to an optical scanning apparatus comprising a plurality of micro lens arrays arranged to form a single continuous scanning line and has for its object to provide a novel and useful optical scanning apparatus which can be made small in size and simple in construction.

It is another object of the invention to provide an optical scanning apparatus which can form a scanning line having a very high resolution.

According to the invention, an optical scanning apparatus for effecting a scanning along a continuous scanning line comprises a plurality of optical scanning element arrays aligned in at least one row; at least one micro lens array having a number of micro lens optical systems arranged side by side, said micro lens array being arranged in parallel with the optical scanning element array; and optical means comprising a plurality of lenses arranged in an object and/or image spaces of the micro lens array, said lenses being so arranged that conjugate images of the optical scanning element arrays or parts of the scanning line with respect to the lenses are formed at such positions that conditions of the micro lens array necessary for projecting an erecting real image of unit magnification are satisfied.

For a better understanding of the invention, reference is taken to the accompanying drawings, in which: Fig. 1 is a schematic view showing a known optical fibere lens array; Fig. 2 is a schematic view illustrating a known spherical micro lens array; Fig. 3 is a schematic view depicting a known reducing projection optical system; Fig. 4 is a schematic view illustrating a known enlarging projection optical system; Fig. 5 is a schematic view showing a known optical scanning apparatus; Figs. 6A and 6B are schematic cross sectional and plan views depicting a known optical scanning apparatus; Fig. 7 is a schematic view illustrating an embodiment of the reducing projection optical system according to the invention; Fig. 8 is a schematic view showing an embodiment of the enlarging projection optical system according to the invention;; Fig. 9 is a schematic view illustrating another embodiment of the enlarging projection optical system according to the invention; Fig. 10 is a plan view showing the projection optical system shown in Fig. 8; Fig. 11 is a plan view illustrating the projection optical system shown in Fig. 9; Fig. 12 is a schematic view depicting another embodiment of the reducing projection optical system according to the invention; Fig. 13 is a schematic view showing an embodiment of the optical scanning apparatus according to the invention; Fig. 14 is a schematic view illustrating another embodiment of the optical scanning apparatus according to the invention; Fig. 1 5 is a schematic view of another embodiment of the optical scanning apparatus according to the invention;; Figs. 1 6A and 1 6B are schematic cross sectional and plan views depicting another embodiment of the optical scanning apparatus according to the invention; Fig. 1 7 is a schematic plan view showing another embodiment of the optical scanning apparatus according to the invention; Fig. 1 8 is a schematic view showing an embodiment of the projection optical system according to the invention; Fig. 19 is a schematic plan view depicting still another embodiment of the optical scanning apparatus according to the invention; and Fig. 20 is a schematic view illustrating a part of the optical scanning apparatus shown in Fig. 1 7.

Fig. 7 is a schematic view showing an embodiment of the projection optical system according to the invention. In the present embodiment, in order to project a reduced erecting real image of an object 01, a convex lens L3 is arranged in the image space of a micro lens array L1. In the present embodiment, the micro lens array is formed by an optical fiber lens array comprising optical fiber lenses 11, 12, 13 having optical axes W, X, Y parallel to each other, but it should be noted that the micro lens array may be composed of a micro spherical lens array similar to that shown in Fig. 2. If the convex lens L3 is not provided, an image 1, would be formed, because an object 0, is so positioned that the necessary conditions for forming an erecting real image of unit magnification are satisfied.Due to the refracting action of the convex lens L3, the image 1, is reduced and a reduced erecting real image 12 is formed. That is to say, the images 1, and 12 are conjugated with each other with respect to the convex lens L3. The reducing magnification may be derived by measuring heights of the images 1, and 12 and by calculating 12/11. Further, the magnification may be also derived from the imaging formula 1/a+1/b=1/f, wherein a is a distance from a principal plane h3 of the convex lens L3 to the image 11, f is a focal length of the convex lens L3 and b is a distance between the principal plane h3 and the image 12.

Then, the magnification can be derived from la/bl.

Fig. 8 is a schematic view illustrating another embodiment of the projection optical system for projecting an enlarged erecting real image of an object. In this embodiment, a convex lens L3 is arranged in the image space of a micro lens array L comprising an optical fiber lens array L1. In this embodiment, the convex lens L3 is so arranged that an erecting virtual image 02 of an object 0, is formed by the convex lens at such a position that the conditions for projecting the erecting real image of unit magnification are satisfied. That is to say, the object O and virtual image 02 are conjugated with each other with respect to the convex lens L3. Therefore, an enlarged erecting real image 1, of the object 0, is formed on the image space of the micro lens array L1.It should be noted that the enlarged image i1 is formed at such a position that the conditions for projecting the erecting real image of unit magnification are satisfied. In the other words, a distance between the exit plane of the micro lens array L, and the image 1, is determined by the micro lens array to be used. In this embodiment, the enlarging magnification can be derived from the imaging formula 1/a+1/b=1/f, wherein a is a distance from a principal plane h3 of the convex lens L3 and the object 02, b is a distance between the principal plane h3 and the virtual image Oi and f is a focal length of the convex lens L3. The magnification can be calculated from Ib/al.

In the embodiments shown in Figs. 7 and 8, any desired reducing or enlarging magnification can be obtained by suitably determining a, b and f. In this case, the reduced and enlarged images of the object can be formed, while the necessary conditions of the micro lens array for projecting the erecting real image of unit magnification are satisfied. Therefore, it is possible to obtain the reduced and enlarged images high high resolution. Further optical path lengths of the projection optical systems can be made shorter than that of the optical system for projecting the image of unit magnification. Therefore, an apparatus using the projection optical system can be made small.Moreover, in the embodiment illustrated in Fig. 7, a light flux emanating from the object 0, is made incident upon the micro lens array perpendicularly thereto and thus, the decrease in light intensity at end portions can be avoided. It should be further noted that since the convex lens L3 is arranged in the image space, the convex lens can be protected from dust and stain, when the object is positioned outside the apparatus.

Further, in the embodiment shown in Fig. 8, the object 03 is positioned nearer to the micro lens array L,, the optical path length can be further reduced. Further, since the convex lens L3 is arranged in the object space, the convex lens can be protected against toner developer, when the optical system is used in electrophotographic copying machines.

In the embodiments explained above, since the single convex lens is arranged in the object or image space, when the magnification is to be changed largely, the curvature of convex lens has to be large. Then aberrations might be increased.

Further, since the distance between the micro lens array and the object or the image is small, it is difficult to arrange the convex lens having a relatively large thickness for projecting a wide region. Therefore, the region which can be covered by the projection optical system is limited. Moreover, the optical path length of the projection optical system is shorter than that in case of projecting the image having unit magnification. Therefore, when the projection optical system could not be provided in an apparatus in which the unit magnification projection and variable magnification projection can be simply selected at will by selectively moving the convex lens with respect to the optical axis.In such an apparatus the variation in the optical path length has to be compensated for in the short optical path length inherent to the micro lens array, however such a correction could not be easily realized.

Fig. 9 is a schematic view showing another embodiment of the projection optical system according to the invention, which can obviate the inconveniences explained above. In the present embodiment, in order to project an enlarged erecting real image of an object, a convex lens L3 is arranged in the object space of a micro lens array L, and a concave lens L2 is provided in the image space. In the object space, a virtual image O, of an object 0, is formed by the convex lens L3 at such a position that the necessary conditions for forming the erecting real image of unit magnification are satisfied. That is to say the virtual image 02 is conjugated with the object 0, with respect to the convex lens L3.In the image space, an enlarged erecting real image 1, is formed due to the concave lens L2 In this case, the image 1, is conjugated with an image 12 with respect to the concave lens L2 That is to say, the virtual image 03 and the real image 12 are formed at such positions that the necessary conditions of the micro lens array for projecting the erecting real image of unit magnification are satisfied.

Therefore, the resolution of the image 12 is very high. The enlarging magnification can be expressed by a ratio of 0,/1, which is equivalent to a product of a ratio 01/02 and a ratio 12/Il.

Therefore, in the present embodiment, the enlarging function is effected partly by the convex lens L3 and partly by the concave lens L2 In the present embodiment, as compared with the embodiments shown in Figs. 7 and 8 in which only a single convex lens is arranged in the object and image spaces, the curvatures of the lenses L2 and L3 can be made smaller and thus, the aberrations can be reduced. Further, the length of the micro lens array can be made much longer.

This will be further explained with reference to Figs. 10 and 11. In order to cover the long micro lens array L, by means of the single convex lens L3 as illustrated in Fig. 10, the diameter of the lens L3 has to be made longer so that a thickness of the lens L3 becomes larger. Therefore, the object plane 01 might situate within the lens L3. In practice, such a construction could not be adopted. Then, it is necessary to make thin the lens L3 so that the object plane Ol situates outside the lens. To this end, the diameter of the convex lens L3 must be made small and thus, the length of the micro lens array has to be made small accordingly.Further, the optical path length TC2 in case of projecting the enlarged erecting real image becomes always mailer than the optical path length TC, in case of projecting the erecting real image of unit magnification.

Contrary to this, in the embodiment illustrated in Fig. 9, since the enlargement function are effected both in the object and image spaces, the curvatures of the convex and concave lenses L3 and L2 can be made small as shown in Fig. 11.

Therefore, the lenses can be effectively arranged between the object plane 0, and the image plane 1, and thus, the micro lens array L can be made sufficiently long for projecting images of long objects. Moreover, the optical path length TC2 in case of projecting the enlarged image is substantially equal to the optical path length TCa in case of projecting the image having unit magnification. It should be noted that these optical path lengths TC, and TC2 can be easily made equal to each other. That is to say, TC2 may be shortened by decreasing the curvature of convex lens L3 and by increasing the curvature of concave lens L2 and TC2 may be extended by increasing the curvature of convex lens L3 and by decreasing the curvature of concave lens L2 while the enlarging magnification is remained same.

Further, if the lenses L2 and L3 are made further away from the micro lens array L1, the enlarging function is decreased and the positions of the object and image planes are also varied.

Therefore, the setting of the lens positions can be also used for making TC, and TC2 equal to each other.

Fig. 12 is a schematic view showing still another embodiment of the projection optical system according to the invention. The optical system of this embodiment is to project the reduced erecting real image of an object 0,. For this purpose, concave lens L2 and convex lens L3 are arranged in object space and image space of a micro lens array La, respectively. Further, a virtual image 02 of the object 0, due to the concave lens L2 and an erecting real image 12 which is conjugated with an erecting real image 1, with respect to the convex lens L3 are so positioned that the necessary conditions of the micro lens array for projecting the erecting real image of unit magnification are satisfied.In this embodiment, the reducing magnification is derived from a ratio O,/I,. The reducing projection optical system of the present embodiment has the same advantages as those of the optical system shown in Fig. 9.

The present invention is not limited to the embodiments explained above, but many alterations and modifications can be conceived by those skilled in the art. For instance, the convex and concave lenses may be formed by Fresnel lenses. Then, thickness of lenses can be further reduced. Further, convex and concave lenses may be shaped into an elongated form corresponding to the elongated micro lens array. Moreover, the micro lens array may be composed not only of optical fiber lenses shown in Fig. 1, but also of spherical micro lenses shown in Fig. 2.

As explained above in detail, in the projection optical system according to the invention, the convex lens or the convex lens and concave lens are arranged in the object or image spaces in such a manner that an image conjugated with the object or image plane with respect to the lens is formed at such a position that the necessary conditions for projecting the erecting real image of unit magnification are satisfied. Therefore, it is possible to form an enlarged or reduced erecting real image having a high resolution and less aberrations. Further, the optical path length can be made constant in case of projecting the image of unit magnification and in case of projecting the enlarged or reduced image. Further, the length of the micro lens array can be made longer without causing the serious drawbacks.

Fig. 1 3 is a cross section showing an embodiment of the scanning apparatus according to the invention. The scanning apparatus of this embodiment is to be used as a reading head and comprises a plurality of optical scanning element array assemblies 1 a to 11 c having optical element 'arrays 1 2a to 1 2c such as light emitting diode arrays or light gate arrays which are formed on substrates 1 3a to 1 3c, respectively. Necessary circuits such as scanning circuit are also integrally formed in the substrates. The scanning apparatus further comprises a micro lens array 14 which may be composed of an optical fiber lens array or a spherical micro lens array. The micro lens array 1 4 has a sufficient length for covering a scanning line to be formed on a scanning plane F.Between the optical scanning element arrays 1 2a to 1 2c and the micro lens array 14 are arranged convex lenses 1 spa to 1 sic and between the micro lens array 14 and the scanning plane F are provided concave lenses 1 6a to 1 6c. In this manner, each of the convex lenses 1 5a to 1 5c, each of the concave lenses 1 6a to 1 6c and parts of the micro lens array 1 4 constitute the projection optical system shown in Fig. 9 and enlarged erecting real images 1 7a to 1 7c of the optical scanning element arrays 1 2a to 1 2c are formed on the scanning plane F. In this case, the optical scanning element arrays 1 2a to 1 2c are separated from each other by a given distance so that the images 1 7a to 1 7c form a single continuous scanning line.

As is well known in the art, the length of the optical scanning element array is limited to about one inch due to the manufacturing technique and further the scanning elements could not be formed up to the edges of the substrate.

Therefore, it is impossible to form a long and continuous scanning line merely by arranging the scanning element array assemblies side by side.

In the present embodiment, this probem can be solved by arranging the enlarging optical systems between the scanning element array assemblies 1 1 a to licand the scanning plane F.That is to say, the enlarged erecting real images 1 7a to 1 7c of the scanning element arrays 1 2a to 1 2c form the continuous long scanning line.

Fig. 1 4 illustrates another embodiment of the optical scanning apparatus according to the invention. In the present embodiment, only convex lenses 1 spa to 1 sic are arranged between the scanning element arrays 1 2a to 1 2c and the micro lens array 14. Therefore, the convex lens and the micro lens array constitute the projection optical system illustrated in Fig. 8. Also in this embodiment, enlarged erecting real images 1 7a to 1 7c of the scanning element arrays 1 2a to 1 2c are formed on the scanning plane F to form a long continuous scanning line.

Fig. 1 5 is a schematic view showing another embodiment of the optical scanning apparatus according to the invention. In the present embodiment, a plurality of optical scanning blocks 1 8a to 1 8c are arranged side by side. The scanning block 1 8a comprises an optical scanning element array assembly 1 a having a scanning element array 1 2a formed on a substrate 1 3a, a micro lens,array 1 4a and convex and concave lenses 1 spa and 1 6a. The micro lens array 1 4a and convex and concave lenses 1 spa and 1 6a form the projection optical system illustrated in Fig. 9 and project an enlarged erecting real image 1 7a of the optical scanning element array 1 2a. Therefore, by suitably selecting the enlarging magnification of the enlarging projection optical system, it is possible to obtain a long and continuous scanning line by merely arranging the optical scanning blocks 1 spa to 1 8c side by side.

Figs. 1 6A and 1 6B show another embodiment of the optical scanning apparatus according to the invention. In the present embodiment, reduced images of optical scanning element arrays are formed on a scanning plane F. To this end, a first row of optical scanning element array assemblies 31A-1, 31A-2,...31A-n and a second row of optical scanning element array assemblies 31 B-1, 31 ....... 31 B-n are arranged in parallel with each other. Each of the scanning element array assemblies comprises scanning element array 32An1, . . 32A-2,... 32A-n, 32B-i, 32B-2,... .32B- n which is formed in a substrate 33A-1, 33A- 2, . . .33A-n; 33B-1, 33B-2,... 33B-n.Between the first and second rows of the scanning element array assemblies 31 A and 31 B and the scanning plane F are arranged first and second micro lens arrays 34A and 348, respectively. In object space of the first micro lens array 34A are provided concave lenses 35A-1,35A-2, . . .35A-n and between the micro lens array 34A and the scanning plane F are arranged convex lenses 36A-1, 36A-2,... 36A-n. In this manner, the concave lens 35A, convex lens 36A and a part of the micro lens array 34A constitute the reducing projection optical system shown in Fig. 1 2.

Similarly concave lenses 35B-1, 35B-2,... 35B-n and convex lenses 36B-1, 36B-2,...36B-n are arranged in object and image spaces of the micro lens array 34B to form the reducing projection optical systems. Then reduced erecting real images 37A-1, 37B-i, 37A-2,37B-2,... 37A-n, 37B-n of the scanning element arrays 32A-1, 328-i, 32A-2, 32B2,... 32A-n, 328An are formed on the scanning plane F. In this case, the pitch of the scanning element arrays 32A and 32B in the rows and the reducing magnification of the projection optical systems are so selected that the reduced images 37A-1, 378-1,37A- 2,... 37A-n, 37B-n form a long continuous scanning line.Therefore, the resolution of the scanning line can be made higher than that of the scanning element arrays. Further, by changing the reducing magnification and the pitch of the scanning element array assemblies 31 A and 31 B, it is possible to obtain the long continuous scanning line having any desired resolution, while a pitch of scanning elements in the arrays is remained constant.

Fig. 1 7 is a schematic view showing another embodiment of the scanning apparatus according to the invention. In the present embodiment, concave lenses 35A-1,35A-2,... 35A-n are arranged between the optical scanning element array assemblies 3 A-1,31 31A-2,... 31 A-n and the micro lens array 34A and concave lenses 35B-1,35B-2,.. .35B-n are provided between the scanning element array assemblies 31B-1, 318-2,... 31B-n and the micro lens array 35B.

Then, reduced erecting real images 37A-1, 378- 1, 37A-2,... 37A-n, 378An of the scanning element arrays 32A-1, 328-1, 32A-2, 328- 2,... 32A-n, 32B-n are formed on the scanning plane F. Also in this embodiment, the reducing magnification and the pitch of the scanning element arrays are so selected that the reduced images 37A-1, 378-1,. . 37A-n, 37B-n form a long continuous scanning line. In the present embodiment, the concave lens and a part of the micro lens array constitute a reducing projection optical system shown in Fig. 1 8.

Fig. 1 8 shows a projection optical system for projecting a reduced erecting real image of an object 0, comprising a micro lens array L1 and a concave lens L2 arranged in an object space. The micro lens array L, is formed by a number of optical fiber lenses 1" 12, 13 having optical axes W, X, Y arranged in parallel with each other, each projecting an erecting real image of unit magnification. The micro lens array L, and an image plane are so arranged that conditions for forming an erecting real image of unit magnification are satisfied. The concave lens L2 is arranged in the object space of the micro lens array L1 and has a principal plane h2.A virtual image O2 of the object 0, is formed by the concave lens L2 That is to say, the object 01 and the virtual image 02 are conjugated with each other with respect to the concave lens L2 A light flux emanating from the object 01 is refracted by the concave lens L2 and is considered to emanate from the virtual image 02. Therefore, when the virtual image 02 is set in an object plane which satisfies the necessary conditions for projecting the erecting real image of unit magnification, there is formed an erecting real image 1, of unit magnification of the virtual image O2 in the image plane.It is apparent that the image 1, has a reduced magnification with respect to the object O,. As is well known in the art, a principal equation of a single lens, i.e.

1/a+1/b=1/f can be applied here, wherein a is a distance between the principal plane h2 and object 0,, b is a distance between the principal plane h2 and virtual image 02 and f is a focal length of the concave lens L2 The distance b is determined when the positions of the micro lens array L, and the concave lens L2 have been determined and the focal length f is determined if the concave lens L2 to be used has been determined. Therefore, the distance a can be calculated from the above equation. Further, when the distance b is determined, it is possible to derive the reducing magnification as la/bl.

Fig. 1 9 is a schematic view illustrating still another embodiment of the optical scanning apparatus according to the invention. In this embodiment, convex lenses 36A-1, 36A- 2,... 36A-n are arranged between the optical scanning element array assemblies 31 A-i, 31 A- 2,...31A-n and the micro lens array 34A, and convex lenses 36B-1,36B-2, . . .36B-n are provided between the optical scanning element array assemblies 31 8-1, 318-2,... 31B-n and the micro lens array 34B. Then a part of the micro lens array and the convex lens form the reducing projection optical system illustrated in Fig. 7 and reduced erecting real images 37A-1, 37B-1, 37A- 2,37B-2, . . 37A-n, 37B-n of the scanning element arrays 32A-1,32B-1,32A-2,32B- 2,... 32A-n, 32B-n are formed on the scanning plane F. These reduced images form a long continuous scanning line having high resolution.

The present embodiment has an advantage that an effective light transmission property can be attained, even if angular distribution of light emitting or receiving characteristics of the scanning element are not good. This will be further explained with reference to Fig. 20.

Fig. 20 shows an end portion of the optical scanning apparatus illustrated in Fig. 17. In this embodiment, the optical scanning element array 32A-1 comprises scanning elements e1,e2,...

such as light emitting diodes. As depicted in Fig.

20, an amount of light emitted from the diode has such a distribution that a large amount of light is emitted in a perpendicular direction, but only a very small amount of light is emitted toward side directions. The concave lens 35A-1 introduces this small amount of light into an optical fiber lens array 34A. Contrary to this, near the optical axis, a large mount of light is introduced into the micro lens array 34A. Therefore, a so-called shading occurs. Contrary to this, in the embodiment shown in Fig.19, since the concave lens is not provided between the optical scanning element array and the micro lens array, a large amount of light emitted from the light emitting elements is introduced into the micro lens array even at its end portions. Therefore, the shading does not occur.

The present invention is not limited to the embodiments explained above, but may be modified in various ways. For instance, in the embodiments shown in Figs. 13, 14, 1 5, 1 6, 17 and 19, the optical scanning element array is formed by the light emitting diode array, but it may be composed of a light receiving element array such as CCD array and silicon photodiode array. Further, the convex and concave lenses may be formed by Fresnel lenses having a small thickness.

Claims (19)

1. In a projection optical system for projecting an erecting real image of an object having a variable magnification comprising a micro lens array having a number of micro lens optical systems arranged along a line and having optical axes arranged in parallel with each other, each micro lens optical system projecting an erecting real image of unit magnification, the improvement comprising optical means including at least a convex lens arranged in either an object space or an image space at such a position that a conjugate image of an object plane or an image plane of the micro lens array with respect to the convex lens is formed at such a position that conditions necessary for projecting the erecting real image of unit magnification are satisfied.

2. A system according to claim 1, wherein said optical means comprises a convex lens arranged in the image space of the micro lens array at such a position that an image conjugated with a reduced erecting real image of object with respect to the convex lens is formed at such a position that the necessary conditions for projecting the erecting real image of unit magnification are satisfied.

3. A system according to claim 1, wherein said optical means comprises a convex lens arranged in the object space of the micro lens array at such a position that a virtual image of the object conjugated with the object with respect to convex lens is formed at such a position that the necessary conditions for projecting the erecting real image of unit magnification are satisfied.

4. A system according to claim 1, wherein said optical means comprises convex and concave lenses arranged in the object and image spaces, respectively at such positions that a virtual image conjugated with the object with respect to the convex lens and a virtual image conjugated with an enlarged erecting real image with respect to the concave lens are formed at such positions that the necessary conditions for projecting the erecting real image of unit magnification are satisfied.

5. A system according to claim 1, wherein said optical means comprises concave and convex lenses arranged in the object and image spaces of the micro lens array, respectively at such positions that a virtual image conjugated with the object with respect to the concave lens ànd,a virtual image conjugated with a reduced erecting real image of the object with respect to the convex lens are formed at such positions that the necessary conditions for projecting the erecting real image of unit magnification are satisfied.

6. A system according to claim 1, wherein said micro lens array is consisting of an optical fiber lens array.

7. A system according to claim 1, wherein said micro lens array is consisting of a spherical micro lens array.

8. An optical scanning apparatus for effecting a scanning along a continuous scanning line comprising a plurality of optical scanning element arrays aligned in at least one row; at least one micro lens array having a number of micro lens optical systems arranged side by side, said micro lens array being arranged in parallel with the optical scanning element array; and optical means comprising a plurality of lenses arranged in an object and/or image spaces of the micro lens array, said lenses being so arranged that conjugate images of the optical scanning element arrays or parts of the scanning line with respect to the lenses are formed at such positions that conditions of the micro lens array necessary for projecting an erecting real image of unit magnification are satisfied.

9. An apparatus according to claim 8, wherein said optical scanning element arrays are arranged along a line at a given pitch.

10. An apparatus according to claim 9, wherein said optical means comprises a plurality of convex lenses each arranged between respective optical scanning element arrays and the micro lens array, and a plurality of concave lenses each arranged between respective parts of the scanning line and the micro lens array.

ii. An apparatus according to claim 9, wherein said optical means comprises a plurality of convex lenses each arranged between respective optical scanning element arrays and the micro lens array.

12. An apparatus according to claim 8, wherein each of the optical scanning element arrays, each of the lenses and a part of the micro lens array are formed as a block and a plurality of blocks are arranged side by side to form the continuous scanning line.

13. An apparatus according to claim 8, wherein first and second rows of optical scanning element arrays and first and second micro lens arrays are arranged in parallel with the scanning line in such a manner that parts of the scanning line corresponding to the optical scanning element arrays of first and second rows are alternately arranged to form the continuous scanning line.

14. An apparatus according to claim 13, wherein said optical means comprises first and second arrays of reducing projection optical systems respectively inserted between the first and second optical scanning element array rows and the scanning line.

1 5. An apparatus according to claim 14, wherein each of said reducing projection optical system comprises a concave lens arranged between an optical scanning element array and a micro lens array and a convex lens inserted between the micro lens array and the scanning line.

16. An apparatus according to claim 14, wherein each of said projection optical system comprises a concave lens arranged between an optical scanning element array and the micro lens array.

1 7. An apparatus according to claim 14, wherein each of said projection optical system comprises a convex lens arranged between an optical scanning element array and the micro lens array.

18. A system as claimed in any one of claims 1 to 7, substantially as hereinbefore described with reference to any one of Figures 7 to 20 of the accompanying drawings.

19. Apparatus as claimed in any one of claims 8 to 17, substantially as hereinbefore described with reference to any one of Figures 1 3 to 20 of the accompanying drawings.