Optical disk having specified track pitch, and optical disk apparatus

Abstract

An optical disk with sectional trapezoidal pits comprising a substrate having information recorded by a plurality of pit trains formed thereon at a specified track pitch, and a reflective layer formed on the substrate, wherein the information is reproduced by being irradiated with light beam via an objective lens, the track pitch is set within the range of (0.72 to 0.8) α×λ/NA/1.14 μm when a wavelength of the light beam is μ nm and a numerical aperture of the objective lens is NA, each of the pits is a multiplication ratio used to secure allowable disk tilt angles in an upper width within the range of (0.3 to 0.50) α×λ/NA/1.14 μm, a bottom width within the range of (0.2 to 0.32) α×λ/NA/1.14 μm and a depth within the range of (1/4.2×λ/n) to (1/5.2 λ/n) (n: refractive index of said substrate and λ: a wavelength) and obtained by 2.623×10 −7 ×(d/λ) 2 −1.706×10 −4 (d s /λ)+0.934, where d s is thickness of the substrate.

What is claimed is:  
     
       1. An optical disk comprising: 
       a circular substrate having a predetermined diameter and a predetermined thickness, said substrate comprising information recorded as a plurality of pit trains formed on said circular substrate with a track pitch, each said pit train comprising a plurality of pits; and  
       a reflecting layer formed on said substrate;  
       wherein said information is reproduced by said pit trains being irradiated with a light beam via an objecting lens, said objective lens having a numerical aperture NA, and wherein: said track pitch is in the range of (0.72 to 0.8)α×(λ/NA)/1.14 μm when a wavelength of said light beam is λ μm; each of said pits is scaled by the multiplication ratio α, said multiplication ratio α being used to secure allowable tilt angles of said optical disk and being obtained by 2.623×10 −7 × (d s /λ) 2 −1.706×10 −4  (d s /λ)+ 0.934 m , where d   s  is said predetermined thickness in μm and is equal to 600 μm; a radial tilt of said optical disk is not more than 9.5 mrad; and said predetermined diameter is 120 mm.  
     
     
       2. The optical disk according to  claim 1 , further comprising: 
       a secondary substrate comprising secondary information recorded as a plurality of second pit trains formed on said secondary substrate at said track pitch, each said second pit train comprising a plurality of second pits; and  
       a secondary reflecting layer formed on said secondary substrate, said reflecting layer and said secondary reflecting layer being disposed between said substrate and said secondary substrate.  
     
     
       3. The optical disk according to  claim 2 , further comprising a pair of protective films formed on said reflecting layer and said secondary reflecting layer, respectively, and positioned between said reflecting layer and said secondary reflecting layer. 
     
     
       4. The optical disk according to  claim 3 , further comprising an adhesion layer formed between said protective films to adhere said protective films to each other. 
     
     
       5. An optical disk apparatus comprising: 
       an optical disk comprising a circular substrate and a reflecting layer formed on said substrate, said substrate having a predetermined diameter and a predetermined thickness and comprising information recorded as a plurality of pit trains formed on said substrate with a track pitch, each said pit train comprising a plurality of pits;  
       an objective lens disposed so as to face said optical disk, said objective lens having a numerical aperture NA;  
       means for projecting a light beam onto said optical disk via said objective lens; and  
       means for sensing reflected light of said light beam projected onto said optical disk by said projecting means to reproduce said information recorded on said optical disk;  
       wherein: said track pitch is in the range of (0.72 to 0.8)α×(λ/NA)/1.14 μm when a wavelength of said light beam is λ μm; each of said pits is scaled by the multiplication ratio α, said multiplication ratio being used to secure allowable tilt angles of said optical disk and being obtained by 2.623×10 −7 × (d s /λ) 2 −1.706×10 −4  (d s /λ)+ 0.934 m , where d   s  is said predetermined thickness in μm and is equal to 600 μm; a radial tilt of said optical disk is not more than 9.5 mrad; and said predetermined diameter is 120 mm.  
     
     
       6. The optical disk apparatus according to  claim 5 , wherein said sensing means produces a push-pull signal and a playback signal, said push-pull signal representing a difference between signals sensed in at least two areas along a track of said optical disk, and wherein each of said pits has a depth to enable both said push-pull signal and said playback signal to have large levels. 
     
     
       7. The optical disk apparatus according to  claim 5 , wherein said information, when recorded on said substrate, is compressed according to MPEG2, and wherein said sensing means has a function of expanding said information to reproduce said information. 
     
     
       8. An optical disk comprising: 
       a pair of transparent circular substrates with surfaces facing one another, each of said transparent circular substrates having information recorded as a plurality of pit trains formed on a corresponding one of said transparent circular substrates with a track pitch, each said pit train comprising a plurality of pits;  
       a pair of reflecting layers coated on said facing surfaces of said circular substrates, respectively,  
       a pair of protective layers formed on said pair of reflecting layers, respectively; and  
       an adhesive layer formed between said protective layers to adhere said protective layers to one another;  
       wherein said information is reproduced by said pit trains being irradiated with a light beam via an objective lens, said objective lens having a numerical aperture NA, and wherein: said track pitch is in the range of (0.72 to 0.8)α×(λ/NA)/1.14 μm when a wavelength of said light beam is λ μm; each of said pits is scaled by the multiplication ratio α, said multiplication ratio α being used to secure allowable tilt angles of said optical disk and being obtained by 2.623×10 −7 × (d s /λ) 2 −1.706×10 −4  (d s /λ)+ 0.934 m , where d   s  is said predetermined thickness in μm and is equal to 600 μm; a radial tilt of said optical disk is not more than 9.5 mrad; and said predetermined diameter is 120 mm.  
     
     
       9. An optical disk comprising: 
       
         a circular substrate comprising information recorded as a plurality of pit trains formed on said circular substrate with a track pitch, each said pit train comprising a plurality of pits; and  
       
       
         a reflecting layer formed on said substrate;  
       
         wherein said information is reproduced by said pit trains being irradiated with a light beam via an objecting lens, said objective lens having a numeral aperture NA, and wherein said track pitch is in the range of  (   0 . 72  to  0 . 8   ) α× ( λ/NA ) / 1 . 14  μm when a wavelength of said light beam is λ μm; each of said pits is scaled by the multiplication ratio α, said multiplication ratio α being used to secure allowable tilt angles of said optical disk and being obtained by  2 . 623 × 10     −7 ( d   s   /λ ) 2   − 1 . 706 × 10     −4  ( d   s   /λ ) + 0 . 934 , where d   s    is a thickness of said circular substrate in μm; a radial tilt of said optical disk is not more than  9 . 5  mrad.   
     
     
       10. An optical disk apparatus comprising: 
       
         an optical disk comprising a circular substrate and a reflecting layer formed on said substrate, said substrate comprising information recorded as a plurality of pit trains formed on said substrate with a track pitch, each said pit train comprising a plurality of pits;  
       
       
         an objecting lens disposed so as to face said optical disk, said objective lens having a numerical aperture NA;  
       
       
         a projector configured to project a light beam onto said optical disk via said objecting lens; and  
       
       
         a sensor configured to sense reflected light of said light beam projected onto said optical disk by said projecting means to reproduce said information recorded on said optical disk,  
       
         wherein said track pitch is in the range of  (   0 . 72  to  0 . 8   ) α× ( λ/NA ) / 1 . 14  μm when a wavelength of said light beam is λ μm; each of said pits is scaled by the multiplication ratio α, said multiplication ratio being used to secure allowable tilt angles of said optical disk and being obtained by  2 . 623 × 10     −7  ( d   s   /λ ) 2   − 1 . 706 × 10     −4  ( d   s   λ ) + 0 . 934 , where d   s    is a thickness of said circular substrate in μm; a radical tilt of said optical disk is not more than  9 . 5  mrad.   
     
     
       11. An optical disk comprising: 
       
         a circular substrate comprising information recorded as plurality of pit trains formed on said circular substrate with a track pitch, each said pit train comprising a plurality of pits; and  
       
       
         a reflecting layer formed on said substrate;  
       
         wherein said information is reproduced by said pit trains being irradiated with a light beam via an objective lens, said objective lens having a numeral aperture NA, and wherein said track pitch is in the range of  (   0 . 72  to  0 . 8   ) α× ( λ/NA ) / 1 . 14  μm when a wavelength of said light beam is λ μm; each of said pits is scaled by the multiplication ratio α, said multiplication ratio α being used to secure allowable tilt angles of said optical disk and being obtained by  2 . 623 × 10     −9  ( θ   A   d   s   /λ ) 2   − 1 . 706 × 10     −5  ( θ   A   /λ ) + 0 . 934 , where d   s    is a thickness of said circular substrate in μm; and θ   A    is an allowable tilt angle in mrad.   
     
     
       12. An optical disk according to  claim 11 , wherein said substrate has the thickness of  600  μm and a diameter of  120  mm. 
     
     
       13. An optical disk apparatus comprising: 
       
         an optical disk comprising circular substrate and a reflecting layer formed on said substrate, said substrate comprising information recorded as a plurality of pit trains formed on said substrate with a track pitch, each said pit train comprising a plurality of pits;  
       
       
         an objective lens disposed so as to face said optical disk, said objective lens having a numerical aperture NA;  
       
       
         a projector configured to project a light beam onto said optical disk via said objective lens; and  
       
       
         a sensor configured to sense reflected light of said light beam projected onto said optical disk by said projecting means to reproduce said information recorded on said optical disk,  
       
         wherein said track pitch is in the range of  (   0 . 72  to  0 . 8   ) α× ( λ/NA ) / 1 . 14  μm when a wavelength of said light beam is λ μm; each of said pits is scaled by the multiplication ratio α, said multiplication ratio being used to secure allowable tilt angles of said optical disk and being obtained by  2 . 623 × 10     −9  ( θ   A   d   s   /λ ) 2   − 1 . 706 × 10     −5  ( θ   A   d   s   /λ ) + 0 . 934 , where d   s    is a thickness of said circular substrate in μm; and θ   A    is an allowable tilt angle in mrad.   
     
     
       14. An optical disk according to  claim 13 , wherein said substrate has the thickness of  600  μm and a diameter of  120  mm.