Optical recording medium having a relation between groove widths, groove depths and track pitches

1. An information recording medium comprising a recording track formed by a concave-convex pattern, wherein

the recording track comprises a first recording region R 1 , a second recording region R 2 and a recording region transition section Sx arranged between the first recording region R 1 and the second recording region R 2 ;

a track pitch tp 1 , a groove width w 1 and a groove depth d 1 in the first recording region R 1 , and a track pitch tp 2 , a groove width w 2 and a groove depth d 2 in the second recording region R 2 satisfy formula (1), (2) and/or (3):

0 <|tp 1 −tp 2|  (1)

0 <|w 1 −w 2|  (2)

0 <|d 1 −d 2|  (3);

the recording region transition section Sx comprises a track pitch transition section Stp in which the track pitch changes from tp 1 to tp 2 and a groove shape transition section Sg in which the groove width changes from w 1 to w 2 and/or the groove depth changes from d 1 to d 2 ;

the track pitch transition section Stp and the groove shape transition section Sg at least partially overlap to share a region SL; and

provided that a maximum value of normalized push-pull signal amplitude in a non-recorded state is NPP max and a minimum value of the amplitude is NPP min in the first recording region R 1 and the second recording region R 2 , a normalized push-pull signal amplitude NPP satisfies formula (6) in the entire region of the recording region transition section Sx:

NPP min ≦NPP≦NPP max   (6).

2. The information recording medium according to claim 1 , wherein the first recording region R 1 , the second recording region R 2 and the recording region transition section Sx are formed by a physically continuous groove.

3. The information recording medium according to claim 1 or 2 , which comprises a recording layer containing an organic pigment.

4. The information recording medium according to claim 1 or 2 , wherein the reflectivity of a recording mark portion is higher than the reflectivity of non-recorded portion.

5. The information recording medium according to claim 1 or 2 , wherein a groove bottom portion, that is on far side of a concave-convex pattern from a surface of the information recording medium in which recording-reproduction light is incident, is used as the recording track.

6. The information recording medium according to claim 3 , wherein the composition and the film thickness of the recording layer are constant at least among the first recording region R 1 , the second recording region R 2 and the recording region transition section Sx.

7. The information recording medium according to claim 1 or 2 , which is a disc-shaped information recording medium wherein the length Lg of the groove shape transition section Sg along the track is at least the length of one circle of the track in the disc-shaped information recording medium.

8. The information recording medium according to claim 1 or 2 , wherein the groove width and/or the groove depth in the groove shape transition section Sg simply increases or simply decreases along the track.

9. The information recording medium according to claim 1 or 2 , wherein the length Ltp of the track pitch transition section Stp along the track, and the length LL of the region SL shared by the track pitch transition section Stp and the groove shape transition section Sg, satisfy formulae (4) and (5):

0.2 ≦Lg/Ltp≦ 2.5  (4)

0.1 ≦LL/Ltp≦ 1.0  (5).

10. The information recording medium according to claim 1 or 2 , wherein provided that a maximum value of the groove portion reflectivity in non-recorded state in the first recording region R 1 and the second recording region R 2 is Rgv max and its minimum value is Rgv min , a groove portion reflectivity Rgv in a non-recorded state satisfies formula (7) in the entire region of the recording region transition section Sx:

Rgv min ≦Rgv≦Rgv max   (7).

11. The information recording medium according to claim 1 or 2 , wherein the first recording region R 1 is arranged more inside than the second recording region R 2 , and a third recording region having a track pitch tp 3 wider than the track pitch tp 1 of the first recording region R 1 and the track pitch tp 2 of the second recording region R 2 , is arranged more inside than the first recording region R 1 .

12. The information recording medium according to claim 11 , wherein no information is recorded by wobble of groove in the third recording region R 3 .

13. The information recording medium according to claim 11 , wherein a track pitch transition section Stp′ in which the track pitch changes from tp 3 to tp 1 , is provided between the third recording region R 3 and the first recording region R 1 .

14. The information recording medium according to claim 1 or 2 , wherein the first recording region R 1 includes a read only region storing a predetermined information, and the second recording region R 2 includes readable-writable region in which user data is writable.

15. The information recording medium according to claim 14 , wherein the track pitch in the read only region is 0.35 μm, and the track pitch in the readable-writable region is 0.32 μm.

16. The information recording medium according to claim 14 , which satisfies a relation:

NPPAL max /NPPAL min ≦3

provided that the normalized push-pull signal amplitude in the read only region is NPP1, the normalized push-pull signal amplitude in non-recorded state in the readable-writable region is NPP2, the normalized push-pull signal amplitude after recorded in the readable-writable region is NPP2a, the maximum value among maximum values of these parameters is NPPAL max , and the minimum value among the minimum values of these parameters is NPPAL min .

17. The information recording medium according to claim 16 which satisfies a relation:

NPPAL max /NPPAL min ≦2.

18. The information recording medium according to claim 14 , wherein a first wobble modulation method is applied to the read only region, a second wobble modulation method that is different from the first wobble modulation method is applied to the readable-writable region, and the same wobble modulation method as that for the readable-writable region is applied to the recording region transition section Sx.