Patent Publication Number: US-2002012090-A1

Title: Optical aligning apparatus and method

Description:
BACKGROUND OF THE INVENTION  
       [0001] This invention relates to an optical aligning apparatus of liquid crystals (LCs), and more particularly to an apparatus and a method for optically aligning LCs in a desired direction through control of the polarization direction of light.  
       [0002] To fabricate liquid crystal displays (LCDs) having uniform brightness and high contrast ratio, it should align LC molecules injected between upper and lower glass substrates in a constant direction. It is in general LCDs that LC molecules has been aligned in a constant direction through alignment films which are respectively formed on opposite surfaces of the upper and lower glass substrates. There have been used a conventional rubbing method and an UV alignment method as LC alignment techniques using alignment films. The conventional rubbing method which now is the most widely used as alignment techniques, aligns LCs with linear grooves formed in alignment films in a constant direction. In rubbing methods, polyimide as alignment films is coated on a transparent glass substrate of LCD and rubbed with a rubbing cloth in a constant direction, resulting in inducing physical defects on the surface of the polyimide to form linear grooves.  
       [0003] The UV alignment technique which utilizes polarized light differently from the mechanical rubbing technique, forms polyvinyl resin on a transparent glass substrate of an LCD and irradiates UV light to it, resulting in aligning LCs.  
       [0004] The conventional rubbing method has difficulties in adjusting a pretilt angle and achieving the reproducibility of process. Because the conventional rubbing method forms and rubs with a rubbing cloth polyimide on the surface of the glass substrate where TFT arrays or color filter arrays are arranged, it causes electrical and mechanical damages to the underlying TFT arrays and reduces the life time of LCDs due to particles and static electricity generated in rubbing. The UV alignment methods have difficulties in controlling residuum in polymerization by irradiation of UV light and fabricating uniform alignment films.  
       [0005] In Korean Patent Application No. 96-42514, there is disclosed an alignment method of “Method for aligning polymeric film, LC alignment method using the same, LC cell and fabrication thereof” to solve the problems of the conventional rubbing method and the UV alignment method.  
       [0006] To briefly speaking, the polymeric film alignment method forms the polymeric film doped with the photosensitive compound on a transparent glass substrate and irradiates the circularly polarized light to the polymeric film, resulting in tiltly aligning photosensitive compound with respect to the substrate surface. By using the polymeric alignment film, it is able to tiltly align LCs injected between two glass substrates with tilt alignment of the photosensitive compound contained within the polymeric alignment film. In the polymeric film alignment method, azo dye doped-polymeric alignment film was used for the photosensitive compound and circularly polarized beam was used for the irradiating light to the polymeric film instead of linearly polarized beam.  
       [0007] In order to align LCs using the above polymeric alignment film, there is a urgent need for an optical apparatus that polarizes beam from the light source into circularly polarized beam or elliptically polarized beam and irradiates the polarized light to the polymeric alignment film.  
       SUMMARY OF THE INVENTION  
       [0008] An object of the present invention is to provide an apparatus and method for optically aligning polymeric alignment films by controlling polarization direction of beam irradiated to the polymeric alignment films.  
       [0009] An another object of the present invention is to provide an apparatus and method for optically aligning LCs without rubbing.  
       [0010] A further object of the present invention is to provide an optical alignment apparatus and method capable of obtaining alignment films of excellent reproducibility and uniformity.  
       [0011] A still another object of the present invention is to provide an optical alignment apparatus and method capable of readily fabricating alignment films on LCD substrates of large area.  
       [0012] A still another object of the present invention is to provide an optical alignment apparatus and method capable of readily fabricating alignment films having a multi-domain structure with separate control of optical paths.  
       [0013] A still another object of the present invention is to provide an optical alignment apparatus and method capable of simply fabricating alignment films having a multi-domain structure on LCD substrates of large area.  
       [0014] According to the present invention, there is provided an optical alignment apparatus for aligning an alignment film on one sided surface of a LCD substrate, comprising: a light unit for generating a parallel beam; a beam-splitter for beam-splitting the parallel beam; and a beam regulator for changing the beam spilt from the beam-splitter into a polarized beam and irradiating the polarized beam to the LCD substrate.  
       [0015] In the optical alignment apparatus, the light unit includes a light source for generating a beam such as an Ar laser; and a parallel beam generating mean for changing the beam from the light source into the parallel beam such as a collimator. The LCD substrate is any one of a TFT substrate, color filter, or a LCD module. The polarized beam from the beam regulator of a polarizer irradiated to the LCD substrate is any one of a circularly polarized beam or an elliptically polarized beam. The alignment film is comprised of methyl orange-contained polyvinylalcohol.  
       [0016] The optical alignment apparatus may be any one of a substrate-rotated type that the light unit, the beam-splitter and the beam regulator are fixed and the LCD substrate is rotated on the light unit, beam-splitter and beam regulator or a substrate-fixed type that the LCD substrate is fixed and the light unit, beam-splitter and beam regulator are rotated on the LCD substrate.  
       [0017] The optical alignment apparatus further comprises an alignment mask arranged between the LCD substrate and the beam modulator, for selectively providing the polarized beam from the beam regulator to form multi domains. The alignment mask has a plurality of windows and parts of a plurality of windows are open with the domain number.  
       [0018] According to the present invention, there is provided an optical alignment apparatus for aligning an alignment film having multi domain on a LCD substrate, comprising: a light unit for generating a parallel beam; a beam-splitter for beam-splitting the parallel beam; a polarizer for polarizing the beam split from the beam-splitter into a polarized beam and irradiating the polarized beam to the alignment film on the LCD substrate; and an alignment mask arranged between the polarizer and the LCD substrate, for selectively irradiating the polarized beam to the LCD substrate.  
       [0019] According to the present invention, there is provided an optical alignment apparatus for aligning alignment films formed on one-sided surface of a plurality of LCD substrates, comprising: a light unit for generating a parallel beam; a plurality of beam-splitters for beam-splitting the parallel beam, respectively; and a plurality of polarizers for polarizing the beams split from the respective beam-splitters into polarized beams, respectively; wherein the alignment films on one-sided surface of the LCD substrates are simultaneously optically aligned.  
       [0020] According to the present invention, there is provided an optical alignment apparatus for aligning front alignment films and rear alignment films formed on front and rear surfaces of a plurality of LCD substrates, comprising: a light unit for generating a first parallel beam; a front alignment optical system for polarizing the first parallel beam received from the light unit into a first plurality of polarized beams having the same polarization direction, respectively and irradiating the plurality of polarized beams to the front alignment films on the plurality of LCD substrates; a beam reflection system for reflecting the first parallel beam to generate a second parallel beam which travels in the opposite direction to the first parallel beam; and a rear alignment optical system for polarizing the second parallel beam received from the beam reflection system into a second plurality of polarized beams having the opposite polarization direction to the first polarized beams, respectively and irradiating the second plurality of polarized beams to the rear alignment films on the plurality of LCD substrates; where the front alignment films and front alignment films on the front and rear surfaces of the LCD substrates are simultaneously aligned.  
       [0021] In the optical alignment apparatus, the alignment films on front and rear surfaces of the plurality of LCD substrates can be simultaneously aligned in the desired direction by setting the plurality of LCD substrates in same direction. On the contrary, the alignment films on front and rear surfaces of the plurality of LCD substrates can be aligned in opposite directions each other by setting parts of the plurality of LCD substrates in one direction and setting others in the opposite direction.  
       [0022] According to the present invention, an optical alignment apparatus for aligning an alignment film on one-sided surface of a LCD substrate, comprising: a light unit for generating a parallel beam; a plurality of beam-splitters for beam-splitting the parallel beam; and a plurality of polarizers for polarizing the beam split from the beam-splitters to a plurality of polarized beams having different polarization directions, respectively; wherein the plurality of polarized beams having different polarization directions are irradiated to the LCD substrate, resulting in aligning the alignment film having different alignment directions.  
       [0023] According to the present invention, an optical alignment apparatus for aligning front and rear alignment films on front and rear surfaces of a LCD substrate, comprising: a light unit for generating a first parallel beam; a front alignment optical system for polarizing the first parallel beam from the light unit into a first plurality of polarized beams having different polarization directions and irradiating the first plurality of polarized beams to the front alignment film; a beam reflection system for reflecting the first parallel beam to generate a second parallel beam which travels in the opposite direction to the first parallel beam; and a rear alignment optical system for polarizing the second parallel beam from the beam reflection system into a second plurality of polarized beams having different polarization directions and irradiating the second plurality of polarized beams to the rear alignment film; wherein the front and rear alignment films are simultaneously aligned in the different alignment directions by irradiating the first and second plurality of polarized beams to the front and rear alignment films, respectively.  
       [0024] In the optical alignment apparatus, the LCD substrate is any one of a TFT substrate, a color filter or a LCD module. The polarized beams irradiated to the LCD substrate are any one of circularly polarized beams or elliptically polarized beams. The optical alignment apparatus may be any one of a substrate-rotated type than the light unit, front and rear alignment optical systems and beam reflection system are fixed and the LCD substrate is rotated on the light unit, front and rear alignment optical systems and beam reflection system or a substrate-fixed type that the LCD substrate is fixed and the light unit, front and rear alignment optical systems and beam reflection system are rotated on the LCD substrate.  
       [0025] In the optical alignment apparatus, the front alignment optical system includes: a plurality of beam-splitters for beam-splitting the first parallel beam from the light unit; and a plurality of polarizers for polarizing the beams split from the beam-splitters into the first plurality of polarized beams; the rear alignment optical system includes: a plurality of beam-splitters for beam-splitting the second parallel beam from the beam reflection system; and a plurality of polarizers for polarizing the beams split from the beam-splitters into the second plurality of polarized beams; the beam reflection system includes a first mirror for reflecting the first parallel beam to a beam which travels in the perpendicular direction to the first parallel beam; and a second mirror for reflecting the beam to the second parallel beam which travels in the opposite direction to the first parallel beam and providing the second beam to the rear alignment optical system.  
       [0026] According to the present invention, there is provided an optical alignment method, comprising the steps of: providing a LCD substrate which the alignment film is formed on one-sided surface thereof; generating a parallel beam; beam-splitting the parallel beam; polarizing the split beam into a polarized beam; irradiating the polarized beam to the LCD substrate to align the alignment film.  
       [0027] According to the present invention, there is provided an optical alignment method, comprising the steps of: providing a LCD substrate which the front and rear alignment films are formed on front and rear surfaces thereof, respectively; generating a first parallel beam; beam-splitting the first parallel beam; polarizing the split beam into a first polarized beam; irradiating the first polarized beam to the LCD substrate to align the front alignment film; polarizing a second parallel beam which travels in the opposite direction to the first parallel beam to generate a second polarized beam; and irradiating the second polarized beam to the LCD substrate to align the rear alignment film.  
       [0028] In the optical alignment method, the step of generating the second parallel beam includes the steps of: first reflecting the first parallel beam into a beam which travels in the perpendicular direction to the first parallel beam and secondly reflecting the beam into the second parallel beam which travels in the opposite direction to the first parallel beam.  
       [0029] In the optical alignment method, the LCD substrate is any one of a TFT substrate, color filter, or a LCD module and the polarized beam irradiated to the LCD substrate is any one of a circularly polarized beam or an elliptically polarized beam. The alignment film is comprised of methyl orange-contained polyvinylalcohol.  
       [0030] According to the present invention, there is provided an optical alignment method, comprising the steps of: providing a LCD substrate which the alignment film is formed on one-sided surface thereof; generating a parallel beam; beam-splitting the parallel beam into a plurality of split beams; polarizing the plurality of split beams into a plurality of polarized beams having different polarization directions; and irradiating the plurality of polarized beams having different polarization directions to the LCD substrate to align the alignment film having different alignment directions.  
       [0031] According to the present invention, there is provided an optical alignment method, comprising the steps of: providing a LCD substrate which the front and rear alignment films are formed on both sided surfaces thereof; generating a first parallel beam; beam-splitting the first parallel beam into a plurality of split beams; polarizing the plurality of split beams into a first plurality of polarized beams having different polarization directions; irradiating the first plurality of polarized beams having different polarization directions on the from alignment film of the LCD substrate; reflecting the first parallel beam to generate a second parallel beam which travels in the opposite direction to the first opposite direction; beam-splitting the second parallel beam into a plurality of split beams; polarizing the plurality of split beams into a second plurality of polarized beams having different polarization direction; and irradiating the second plurality of polarized beams having different polarization direction to the rear alignment film.  
       [0032] According to the present invention, there is provided an optical alignment method, comprising the steps of: providing a plurality of LCD substrate; generating a first parallel beam; beam-splitting the first parallel beam into a plurality of split beams; polarizing the plurality of split beams into a first plurality of polarized beams; and irradiating the first plurality of polarized beams to the plurality of LCD substrates.  
       [0033] In optical alignment method, alignment films are formed on one sided surface of the plurality of LCD substrates. The first plurality of polarization beams may be any one of circularly or elliptically polarized beams in one polarization direction or any one of circularly or elliptically polarized beams in different polarization directions.  
       [0034] When alignment films are formed on both sided surfaces of the plurality of LCD substrates, respectively, the method further comprising the steps of: reflecting the first parallel beam to generate a second parallel beam which travels in the opposite direction to the first opposite direction; beam-splitting the second parallel beam into a plurality of split beams; polarizing the plurality of split beams into a second plurality of polarized beams having different polarization direction; and irradiating the second plurality of polarized beams having different polarization direction to the rear alignment film. The second plurality of polarization beams may be any one of circularly or elliptically polarized beams in one polarization direction or any one of circularly or elliptically polarized beams in different polarization directions.  
       [0035] Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0036]FIG. 1 is a schematic diagram of an optical alignment apparatus illustrating a first basic principle of an optical alignment for forming alignment films on an surface of a LCD substrate by moving the LCD substrate;  
     [0037]FIG. 2 is a diagram illustrating a control method of a rotation angle of a LCD substrate in an optical alignment using the optical alignment apparatus of FIG. 1;  
     [0038]FIG. 3 is a schematic diagram of an optical alignment apparatus for simultaneously fabricating alignment films on one side surface of a plurality of substrates, using the first basic principle in accordance with a first embodiment of the present invention;  
     [0039]FIG. 4 is a schematic diagram of an optical alignment apparatus for simultaneously fabricating alignment films on both side surfaces of a plurality of LCD substrates in accordance with a second embodiment of the present invention;  
     [0040]FIG. 5 is a schematic diagram of an optical alignment apparatus for simultaneously fabricating alignment films having different alignment directions on one-side surface of a plurality of LCD substrates in accordance with a third embodiment of the present invention;  
     [0041]FIG. 6 is a schematic diagram of an optical alignment apparatus for simultaneously fabricating alignment films having different alignment directions on both side surfaces of a plurality of LCD substrates in accordance with a fourth embodiment of the present invention;  
     [0042]FIG. 7 is a schematic diagram of an optical alignment apparatus illustrating a second basic principle of an optical alignment for forming alignment films on an surface of a LCD substrate by fixing the LCD substrate;  
     [0043]FIG. 8 is an example of the optical alignment apparatus adapted to LCD modules;  
     [0044]FIG. 9 is a schematic diagram of an optical alignment apparatus using an alignment mask in accordance with a fifth embodiment of the present invention; and  
     [0045]FIG. 10 is an example of the alignment mask of FIG. 10. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0046] An optical alignment apparatus of the present invention which changes molecule arrangement of photosensitive compound contained within an optical alignment film with polarization direction of light and tiltly aligns LCs to an surface of an LCD substrate with the molecule arrangement of the photosensitive compound, can be divided into a substrate-rotated type that an optical system is fixed and the LCD substrate is rotated to the optical system and a substrate-fixed type that the LCD substrate is fixed and the optical system is rotated to the LCD substrate.  
     [0047]FIG. 1 is a schematic diagram illustrating the basic principle of an optical alignment apparatus of the present invention. The optical alignment apparatus of FIG. 1 is a substrate-rotated type for aligning photosensitive compound by rotating a LCD substrate  15  to a fixed optical system. The optical alignment apparatus  10  comprises a light source  11  for generating beam and a parallel beam generating unit  12  for changing the beam from the light source  11  into parallel beam. A collimator is used for the parallel beam generating unit  12 .  
     [0048] The optical alignment apparatus  10  comprises a beam splitter  13  for beam-splitting the parallel beam and a beam regulator  14  for changing the beam split from the beam-splitter  13  into polarized beam and irradiating the polarized beam to the LCD substrate  15 . The beam regulator  14  is composed of a polarizer which polarizes the split beam into circularly polarized beam or elliptically polarized beam and irradiates the polarized beam to the LCD substrate  15 . In substrate-rotated optical alignment apparatus, the LCD substrate  15  mounted on a rotatable stage where the rotation angel is adjustable to the fixed optical system, not shown in drawings, includes a means for controlling the incident angle of the beam from the beam regulator  14 .  
     [0049]FIG. 2 shows the incident angle of the beam irradiated to the LCD substrate  15  which the alignment film  16  is formed thereon. The rotation angel of the LCD substrate  15  is adjusted between the solid angle of a cone  17 . The incident angle of the beam irradiated to the LCD substrate becomes different according to characteristics of LCDs to be manufactured and it should be adjusted according to the physical quality of LCs, alignment direction and the desired pretilt angle. The LCD substrate  15  includes the LC alignment film  16  which is formed thereon and a photosensitive polymeric film such as methyl orange-doped polyvinyl alcohol (MO/PVA) film is used for the LC alignment film  16 .  
     [0050] According to the optical alignment apparatus  10 , the parallel beam generating unit  12  changes the beam  11   a  generated from the light source  11  into the parallel beam  11   b  and the beam-splitter  13  beam-spitters the parallel beam  11   b  from the parallel beam generating unit  12 . The beam regulator  14  polarizes the beam split from the beam-splitter  13  into the circularly polarized beam or elliptically polarized beam and irradiates the polarized beam  11   c  into the LCD substrate  15 . The molecule arrangement of optical alignment film  16  formed on the LCD substrate  15  is changed. For example, in case where the polymeric film containing the photosensitive compound is used for the optical alignment film  16 , if the polarized beam  11   c  is irradiated into the LCD substrate  15  through the beam regulator  14 , molecules of the photosensitive compound contained in the polymeric alignment film  16  is tiltly aligned.  
     [0051] Therefore, by using the optical alignment apparatus, the LC molecules injected between upper and lower substrates can be aligned so as to have a desired pretilt angle with the tilt alignment of molecules of the photosensitive compound.  
     [0052]FIG. 3 is a schematic diagram of an optical alignment apparatus in accordance with a first embodiment of the present invention. The optical alignment apparatus of the first embodiment is a substrate-rotated type for simultaneously aligning alignment films which are respectively formed on the one-sided surface of a plurality of LCD substrates  24   a - 24   d,  for example on the front surface of LCD substrates. The optical alignment apparatus  20  of the first embodiment comprises a light unit  21  for generating parallel beam  21   a,  a plurality of beam-spitters  22   a - 22   d  for beam-splitting the parallel beam  21   a  and a plurality of polarizers  23   a - 23   d  for polarizing the beam split from the respective beam splitters  22   a - 22   d  into a circularly polarized beam or elliptically polarized beam and irradiating the polarized beam  21   b  to the respective LCD substrates  24   a  through  24   d.    
     [0053] The molecules of optical alignment films  25   a - 25   d  which are respectively formed on the front surfaces of the plurality of LCD substrates  24   a - 24   d  are simultaneously tiltly aligned in the desired direction, when the polarized beams  21   b  from the plurality of the polarizers  23   a - 23   d  are irradiated to the front surfaces of the LCD substrates  24   a  through  24   d,  respectively. In optical alignment apparatus of FIG. 3, all the alignment films  25   a - 25   d  of the LCD substrates  24   a - 24   d  are aligned in one direction, provided that all the LCD substrates are set in the same direction as shown in FIG. 3. On the contrary, provided that parts of the plurality of LCD substrates  24   a - 24   d  are set in the first direction as shown in FIG. 3 and the others are set in the second direction opposite to the first direction, it enables the alignment films on the LCD substrates arranged in the first direction and the alignment films on the LCD substrates arranged in the second directions to be aligned in the opposite directions each other.  
     [0054] The light unit  21 , not shown in FIG. 3, is composed of a light source for generating a beam and a parallel beam generating unit for changing the beam into the parallel beam  21   a.  An Ar +  laser and a collimator are used for the light source and the parallel beam generating unit, respectively. Herein, each of a plurality of LCD substrates may be a TFT substrate, a color filter substrate or a LCD module.  
     [0055]FIG. 4 is a schematic diagram of an optical alignment apparatus in accordance with a second embodiment of the present invention. The optical alignment apparatus of the second embodiment is a substrate-rotated type for simultaneously aligning alignment films formed on both-sided surfaces of a plurality of LCD substrates  34   a - 34   d.  The optical alignment apparatus  30  of the second embodiment provides a plurality of LCD substrates  34   a - 34   d  which a first plurality of alignment films  35   a - 35   d  are formed on the front surfaces thereof, respectively and a second plurality of alignment film  36   a - 36   d  are formed on the rear surfaces thereof, respectively. Polarized beams  31   b - 31   e  and  31   g - 31   j  are irradiated to the first plurality of alignment films  35   a - 35   d  and the second plurality of alignment films  36   a - 36   d  formed on the both-sided surfaces of the LCD substrates  34   a - 34   d,  respectively.  
     [0056] The optical alignment apparatus of the second embodiment comprises a light unit  31  for generating a parallel beam  31   a,  a front alignment optical system  310  for polarizing the parallel beam  31   a  received from the light unit  31  into circularly polarized beams or elliptically polarized beams and irradiating the polarized beams  31   b - 31   e  to the first plurality of the alignment films  35   a - 35   d  formed on the front surfaces of the LCD substrates  34   a - 34   d,  respectively and a rear alignment optical system  320  for polarizing the parallel beam  31   a  received from the light unit  31  into circularly polarized beams or elliptically polarized beams and irradiating the polarized beams  31   g - 31   j  to the second plurality of the alignment films  36   a - 36   d  formed on the rear surfaces of the LCD substrates  34   a - 34   d,  respectively.  
     [0057] The front alignment optical system  310  comprises a plurality of beam-splitters  32   a - 32   d  for beam-splitting the parallel beam  31   a  received from the light unit  31  and a plurality of polarizers  33   a - 33   d  for polarizing the respective beams split from the beam-splitters  32   a - 32   d  into circularly polarized beams or elliptically polarized beams and irradiating the polarized beams  31   b - 31   e  to the respective alignment films  35   a - 35   d  on the front surfaces of the LCD substrates  34   a - 34   d.    
     [0058] Similarly, the rear alignment optical system  320  comprises a plurality of beam-splitters  37   a - 37   d  for beam-splitting the parallel beam  31   a  received from the light unit  31  and a plurality of polarizers  38   a - 38   d  for polarizing the beams split from the respective beam-splitters  37   a - 37   d  into circularly polarized beams or elliptically polarized beams and irradiating the polarized beam  31   g - 31   j  to the respective alignment films  36   a - 36   d  on the rear surfaces of the LCD substrates  34   a - 34   d.    
     [0059] The optical alignment apparatus  30  further comprises a beam reflection system  330  for reflecting the parallel beam  31   a  received from the light unit  31  and providing the reflected beam  31   f  which travels in the opposite direction to the parallel beam  31   a  to the rear alignment optical system  320 . The beam reflection system  330  includes a first mirror  39   a  for reflecting the parallel beam  31   a  received from the light unit  31  to a parallel beam  31   k  which travels in perpendicular direction to the parallel beam  31   a  and a second mirror  39   b  for reflecting the parallel beam  31   k  to the parallel beam  31   f  perpendicular to the parallel beam  31   k,  thus the parallel beam  31   f  which travels in the opposite direction to the parallel beam  31   a  and providing the parallel beam  31   f  to the beam-splitters  37   a - 37   d  of the rear alignment optical system  320 .  
     [0060] By using the optical alignment apparatus  30  of the second embodiment, the first plurality of the alignment films  35   a - 35   d  on the front surfaces of the LCD substrates  34   a - 34   d  are simultaneously aligned, provided that the polarized beams  31   b - 31   e  are respectively irradiated to the alignment films  35   a - 35   d  through the front alignment optical system  310 . At the same time, the second plurality of the alignment films  36   a - 36   d  are simultaneously aligned, provided that the parallel beam  31   a  received from the light unit  31  is reflected through the beam reflection system  330  and polarized through the rear alignment optical system  320  and then the polarized beam  31   g - 31   k  are irradiated to the alignment films  36   a - 36   d.    
     [0061] Accordingly, the optical alignment apparatus  30  of the second embodiment is capable of simultaneously aligning the alignment films  35   a - 35   d  and  36   a - 36   d  on the front and rear surfaces of the LCD substrates  34   a - 34   d  on the same optical axis. It is also capable of simultaneously aligning the alignment films formed on the upper and lower substrates under the assembly of a LCD module.  
     [0062] Besides, the optical alignment apparatus of the second embodiment can simultaneously align all the alignment films formed on the front and rear surfaces of the LCD substrates  24   a - 24   d  in one direction as shown in FIG. 4 by setting all the LCD substrates in the same direction. As well as it can align alignment films formed on the LCD substrates in the different directions by setting part of the LCD substrates in the same direction as shown in FIG. 4 and setting the others in the opposite direction.  
     [0063] The light unit  31 , not shown in FIG. 4, is composed of a light source for generating a beam such as an Ar +  laser and a parallel beam generating unit for changing the beam into the parallel beam  31   a  such as a collimator. Herein, each of a plurality of LCD substrates may be a TFT substrate, a color filter substrate or a LCD module.  
     [0064]FIG. 5 is a schematic diagram of an optical alignment apparatus in accordance with a third embodiment of the present invention. The optical alignment apparatus  40  of the third embodiment is a substrate-rotated type for aligning an alignment film  45  formed on one-sided surface of a LCD substrate  44  in the different polarization directions.  
     [0065] The optical alignment apparatus  40  of the third embodiment comprises a light unit  41  generating a parallel beam  41   a,  a plurality of beam-splitters  42   a - 42   d  for beam-splitting the parallel beam  41   a,  respectively and a plurality of polarizers  43   a - 43   d  for polarizing the beam split from the respective beam-splitters  42   a - 42   d  into circularly or elliptically polarized beams having different polarization directions, respectively and simultaneously irradiating the polarized beams  41   b - 41   e  to the alignment film  45  of the LCD substrate  44 . At this time, the alignment film  45  is formed on only one-sided surface of the LCD substrate  44  and the polarized beams  41   b - 41   e  from the beam regulators  43   a - 43   d  are irradiated to the alignment film  45  with different polarization directions.  
     [0066] By using the optical alignment apparatus  40  of FIG. 5, it can form the alignment film  45  having partially different optical characteristics on one LCD substrate, provided that the polarized beams  41   b - 41   e  having different polarization directions are irradiated to the alignment film  45  formed on one-sided surface, for example the upper surface of the LCD substrate  44  through polarizers  43   a - 43   d.  The light unit  41 , not shown in FIG. 5, is composed of a light source for generating a beam such as an Ar +  laser and a parallel beam generating unit for changing the beam into the parallel beam  41   a  such as a collimator. Herein, the LCD substrate  44  may be a TFT substrate, a color filter substrate or a LCD module.  
     [0067]FIG. 6 is a schematic diagram of an optical alignment apparatus in accordance with a fourth embodiment of the present invention. The optical alignment apparatus  50  of the fourth embodiment is a substrate-rotated type for simultaneously aligning alignment films  55  and  56  formed on both-sided surfaces of a LCD substrate  54  in the different polarization directions.  
     [0068] Referring to FIG. 6, the optical alignment apparatus  50  of the fourth embodiment provides a LCD substrate  54  which alignment films  55  and  56  are formed on both-sided surfaces thereof. Beams  51   b - 51   e  and  51   f - 51   i  of having different polarization directions, which are one of circularly polarized beams or elliptically polarized beams, are respectively irradiated to the alignment films  55  and  56  formed on the front and rear surfaces of the LCD substrate  54 . The optical alignment apparatus  50  comprises a light unit  51  generating a parallel beam  51   a,  a front alignment optical system  510  and a rear alignment optical system  520 .  
     [0069] The front alignment optical system  510  polarizes the parallel beam  51   a  received from the light unit  51  into circularly or elliptically polarized beams  51   b - 51   e  in the first polarization direction and irradiates the polarized beams  51   b - 51   e  to the alignment film  55  formed on the front surface of the LCD substrate  54 . The rear alignment optical system  520  polarizes the parallel beam  51   k  into circularly or elliptically polarized beams  51   f - 51   i  in the second polarization direction and irradiates the polarized beams  51   f - 51   i  to the alignment film  56  formed on the rear surface of the LCD substrate  54 . The polarized beams  52   f - 51   i  have a different polarization direction from the polarized beam  51   b - 51   d  from the front alignment optical system.  
     [0070] The front alignment optical system  510  comprises a plurality of beam-splitters  52   a - 52   d  for beam-splitting the parallel beam  51   a,  respectively and a plurality of polarizers  53   a - 53   d  for polarizing the beam split from the respective beam-splitters  52   a - 52   d  into circularly or elliptically polarized beams  51   b - 51   e,  respectively and simultaneously irradiating the polarized beams  51   b - 51   e  to the alignment film  55  on the front surface of the LCD substrate  54 . Similarly, the rear alignment optical system  520  comprises a plurality of beam-splitters  57   a - 57   d  for beam-splitting the parallel beam  51   k  and a plurality of polarizers  58   a - 58   d  for polarizing the beam split from the respective beam-splitters  57   a - 57   d  into circularly or elliptically polarized beams, respectively  51   f - 51   i  and irradiating the polarized beam  51   f - 51   i  to the alignment film  56  on the rear surface of the LCD substrate  54 .  
     [0071] The optical alignment apparatus  50  further comprises a beam reflection system  530  for reflecting the parallel beam  51   a  received from the light unit  51  and providing the reflected parallel beam  51   k  which travels in the opposite direction to the parallel beam  51   a  to the rear alignment optical system  520 . The beam reflection system  530  includes a first mirror  59   a  for reflecting the parallel beam  51   a  received from the light unit  51  to a parallel beam  51   j  which travels in perpendicular direction to the parallel beam  51   a  and a second mirror  59   b  for reflecting the parallel beam  51   j  to the parallel beam  51   k  perpendicular to the parallel beam  51   j,  thus the parallel beam  51   k  which travels in the opposite direction to the parallel beam  51   a  and providing the parallel beam  51   k  to the beam-splitters  57   a - 57   d  of the rear alignment optical system  520 .  
     [0072] In the optical alignment apparatus  50  of the fourth embodiment, the alignment films  55  and  56  having different alignment directions each other are formed on both-sided surfaces of the LCD substrate  54 . The polarized beams  51   b - 51   e  having the same polarization direction from the polarizers  53   a - 53   d  of the front alignment optical system  510  are irradiated to the alignment film  55  and the polarized beams  51   f - 51   i  from the polarizers  58   a - 58   d  of the rear alignment optical system  520  having the same polarization direction which is different from the polarized beams  51   b - 51   e,  are irradiated to the alignment film  56 .  
     [0073] Accordingly, the optical alignment apparatus  50  of FIG. 6 can form the alignment films  55  and  56  having different optical characteristics on both-sided surfaces of the LCD substrate  54  by irradiating the polarized beams  52   b - 51   e  and  51   f - 51   i  having different polarization directions each other to the alignment films  55  and  56 .  
     [0074] The light unit  51 , not shown in FIG. 6, is composed of a light source for generating a beam such as an Ar −  laser and a parallel beam generating unit for changing the beam into the parallel beam  51   a  such as a collimator. Herein, the LCD substrate  54  may be a TFT substrate, a color filter substrate or a LCD module.  
     [0075]FIG. 7 illustrates another basic principle of the optical alignment of the present invention. An optical alignment apparatus  60  according to another basic principle is a substrate-fixed type for optically aligning an alignment film  66  on a LCD substrate  65  by rotating a light source  61  and an optical system  610  on the fixed LCD substrate  65 . Thus, so as to optically align, the substrate-fixed optical alignment apparatus  60  irradiates a polarized beam  61   c  to the LCD substrate  65  by rotating the light source  61  and the optical system  610  on condition that the LCD substrate  65  is fixed. By using the substrate-fixed optical apparatus  60 , it can align alignment films in like manners as FIG. 3 through FIG. 6.  
     [0076] The optical alignment apparatus  60  provides the fixed LCD substrate  65  which the alignment film  66  is formed on one-sided surface thereof, a light source  61  for generating a beam  61   a  and a rotatable optical system  610  for irradiating a circularly or elliptically polarized beam  61   c  to the fixed LCD substrate  65 . In substrate-fixed optical alignment apparatus  60 , not shown in drawings, the light source  61  and optical system  610  are rotatable to the fixed LCD substrate  65  and the rotation angle of the light source  61  and the optical system  610  and the incident angle of the beam  61   c  to the LCD substrate  65  are adjustable.  
     [0077] The optical system  610  comprises a parallel beam generating unit  62  for changing the beam  61   a  into a parallel beam  61   b,  a beam-splitter  63  for beam-splitting the parallel beam and a beam regulator  64  for changing the beam split from the beam-splitter  63  into a polarized beam  61   c  and irradiating the polarized beam  61   c  to the alignment film  66  on the LCD substrate  65 . An Ar −  laser and a collimator are used for the light source  61  and the parallel beam generating unit  62 , respectively. The beam regulator  64  is a polarizer which polarizes the beam from the beam-splitter  63  to the circularly or elliptically polarized beam  61   c.    
     [0078] The alignment films on the LCD substrate can be optically aligned by using the substrate-fixed type optical alignment apparatus of FIG. 7, in like manners as FIG. 3 through FIG. 6.  
     [0079]FIG. 8 illustrates an application example of an optical alignment apparatus of the present invention to a LCD module. The optical alignment apparatus  70  provides a light unit  71 , an optical system  710  and a LCD module  720 . The optical alignment apparatus  70  can any one of a substrate-rotated type that rotates the LCD module  720  on the light unit  71  and the optical system  710  or a substrate-fixed type that rotates the light unit  71  and the optical system  710  on the fixed LCD module  720 . Not fully shown in FIG. 8, LCs are injected between upper and lower substrates  74  and  75  of the LCD module  720 .  
     [0080] In case where it aligns a single LCD module, the optical alignment apparatus  70  may comprise the optical system including a beam-splitter  72  and a beam modulator  73  and a single LCD module  720 . In case where it aligns plural LCD modules, the optical alignment apparatus may be comprises the optical system  710  including a plurality of beam-splitters  72   a - 72   d  for beam-splitting the parallel beam  71   a  received from the light unit  71  and a plurality of beam regulators  73   a - 73   d  and a plurality of LCD modules  720 . The light unit  71 , not shown in FIG. 8, is comprised of a light source for generating a beam such as an Ar +  laser and the parallel beam generating unit for changing the beam to the parallel beam  71   a.  Each of the beam regulators is a polarizer which polarizes the beam from the beam-splitter to the circularly or elliptically polarized beam  71   b - 71   e.  Provided that the optical alignment apparatus  70  irradiates each polarized beams  71   b - 71   e  to each LCD modules  720 , molecules of alignment films on upper and lowers substrates  74  and  75  are arranged with the polarization direction of the beams  71   b - 71   e  and then LC molecules between the upper and lower substrates  74  and  75  are optically aligned with the molecule arrangement of the alignment film.  
     [0081]FIG. 9 shows an optical alignment apparatus  80  for forming multi domains in one pixel of a LCD substrate. The optical alignment apparatus  80  of FIG. 9 comprises a light source for generating beam  81   a,  an optical system  810  for irradiating a polarized beam  81   c  to a LCD substrate  85  which an alignment film  86  is formed thereof and an alignment mask  87  which is arranged between the optical system  810  and the LCD substrate  85 , for selectively providing the polarized beam  81   c  to the LCD substrate  85 . The alignment mask  87  has plural windows where parts are open.  
     [0082] The optical system  810  has the same construction and operation as the optical systems of above embodiments and the required number of windows formed in the alignment mask  87  is determined by the number of domains which are formed in one pixel. For example, the alignment mask  87  of FIG. 10 is forming 4-domains in one pixel PX and has 4 windows  87 - 1  through  87 - 4 .  
     [0083] The method for forming 4 domains in one pixel PX by using the optical alignment apparatus  80  including the alignment mask  87  is as follows. If the circularly or elliptically polarized beam  81   c  is irradiated to the LCD substrate  85  through the optical system  810  on condition that one  87 - 1  of 4 windows  87 - 187 - 4  is open and the other windows  87 - 2  through  87 - 4  are not open, the polarized beam  81   c  is irradiated to the LCD substrate  85  through the window  87 - 1 , resulting in forming a first domain only in the exposed area of the pixel PX corresponding to the window  87 - 1 .  
     [0084] Subsequently, the window  87 - 1  opened of the alignment mask  87  is shifted to the next domain-forming area of the pixel PX and the polarized beam  81   c  from the optical system  810  is irradiated to the LCD substrate  85  through the alignment mask  87 , resulting in forming a second domain in the exposed area of the pixel PX corresponding to the window  87 - 1 . If above process is repeatedly carried out, it is capable of forming multi domains for example, 4 domains in one pixel. The windows which are open are determined with the domain number.  
     [0085] As above described, by using the optical alignment apparatus of the present invention, molecules of the alignment films can be optically aligned and the LCs injected between upper and lower substrates can be optically aligned so as to have a desired pretilt angle with the molecule arrangement.  
     [0086] According to the present invention, it is capable of forming defect-free and uniform alignment films and obtaining an excellent reproducibility by rubbing-free alignment technique. Because LCs are aligned by controlling the polarization direction of light, it can simplify the fabrication processes and readily form multi domains, resulting in simplifying the fabrication process of wide-viewing angle LCDs. The optical alignment apparatus makes possible LC alignment before and after assembly of LC modules and fabrication of mass-producible LCDs of high quality.  
     [0087] The foregoing description shows only a preferred embodiment of the present invention. Various modifications are apparent to those skilled in the art without departing from the scope of the present invention which is only limited by the appended claims. Therefore, the embodiment shown and described is only illustrative, not restrictive.