Phase-change recording layer optical recording method

1. An optical recording method in which a crystalline state of a phase-change recording layer of a rewritable optical recording medium having said phase-change recording layer is used as unrecorded/erased state, and information is recorded by forming recording marks in an amorphous state with various time lengths nT (where T is a reference clock period, and n is an integer not less than 2), characterized in that:

(M-1) when a recording velocity is within a range of recording velocities at which recorded information in said rewritable optical recording medium can be rewritten,

a plurality of recording marks with the time length of nT are formed;

dividing said time length nT into η 1 T, α 1 T, β 1 T, α 2 T, β 2 T, . . . , α i T, β i T, . . . , α m T, β m T and η 2 T (where m is a pulse dividing number, i is an integer not less than 1 and not larger than m, Σ i (α i +β i )+η 1 +η 2 =n, α i (1≦i≦m) is a real number larger than 0, β i (1≦i≦m−1) is a real number larger than 0, β m is a real number not less than 0, and η 1 and η 2 are real numbers not less than −2 and not larger than 2) in this order, where said pulse dividing number m for at least one time length of the recording marks is not less than 2, and the every time length of recording marks satisfies n/m≧1.25;

applying a recording beam having a recording power Pw i (1≦i≦m) during a time period of α i T;

applying a recording beam having a bias power Pb i (1≦i≦m, Pb i <Pw i , Pb i <Pw i+1 ) during a time period of β i T;

applying a recording beam having an erasing power Pe (Pe is a value not less than any values of m Pb i 's where 1≦i≦m, and is a value smaller than any values of m Pw i 's where 1≦i≦m) on the spaces between said plural recording marks; and

(M-2) when said recording velocity is higher than the recording velocity at which recorded information in said rewritable optical recording medium can be rewritten, and when the phase-change recording layer is beforehand crystallized,

a recording mark with a time length nT is formed with one block pulse in which a recording beam with a recording power PwH and a recording beam with a bias power PbH are applied.

2. The optical recording method according to claim 1 , wherein said bias powers Pb i and PbH are smaller than said erasing power Pe.

3. The optical recording method according to claim 1 further comprising the steps of:

when said recording velocity is higher than the recording velocity at which recorded information in said rewritable optical recording medium can be rewritten,

classifying the nT recording marks (where n is a natural number not less than k 0 , where k 0 is 2 or 3) into recording marks with time lengths of k 0 T, . . . , (k 0 +(k 1 −1))T (where k 1 is an integer) and recording marks with time lengths of not less than (k 0 +k 1 )T, and

allowing γ (where γ is a value not less than 0 and not larger than 2) to be varied according to n;

in the case of recording marks with the time length of k 0 T, . . . , (k 0 +(k 1 −1))T, forming said recording mark by starting radiation of the recording beam having said recording power PwH at a timing delayed by a time period T dk T (where T dk is a value between −1 and 1) from the start timing of said recording mark, and terminating the radiation of the recording beam having said recording power PwH at a timing advanced by a time period γT from the end timing of said recording mark; and

in the case of recording marks with the time length not less than (k 0 +k 1 )T, forming said recording mark by starting radiation of the recording beam having said recording power PwH at the start timing of said recording mark, and terminating the radiation of the recording beam having said recording power PwH at a timing advanced by a time period γT from the end timing of said recording mark.

4. The optical recording method according to claim 1 further comprising the steps of:

when said recording velocity is in a range of recording velocities at which recorded information in said rewritable optical recording medium can be rewritten,

a recording mark with a time length of nT is formed;

dividing a time length (n−j)T (where j is a real number from −2 to 2) in a recording mark of n=2m (where m is a pulse dividing number, and is a natural number not less than 1) into m sections of α i T and β i T, comprised of α 1 T, β 1 T, α 2 T, β 2 T, . . . , α m T and β m T (provided Σ i (α i +β i )=n−j);

dividing a time length (n−k)T (where k is a real number from −2 to 2) in a recording mark of n=2 m+1 into m sections of α i ′T and β i ′T, comprised of α 1 ′T, β 1 ′T, α 2 ′T, β 2 ′T, . . . , α m ′T and β m ′T (provided Σ i (α i ′+β i ′)=n−k);

when m≧4, β i−1 +α i =β i−1 ′+α i ′=2±0.2 (where i is 3 to m−1);

applying a recording beam having said recording power Pw i (where i is an integer not less than 1 and not larger than m) during time periods of said α i T and said α i ′T; and

applying a recording beam having said bias power Pb i (where i is an integer not less than 1 and not larger than m) during time periods of said β i T and said β i ′T.

5. The optical recording method according to claim 1 , wherein said recording power Pw i is a constant value PwL within 1≦i≦m; and

said bias power Pb i is a constant value PbL within 1≦i≦m.

6. The optical recording method according to claim 4 or 5 , wherein at least one among α 1 ≠α 1 ′, β 1 ≠β 1 ′, α 2 ≠α 2 ′, β m−1 ≠β m−1 ′, α m ≠α m ′ and β m ≠β m ′ is satisfied.

7. The optical recording method according to claim 4 or 5 , wherein β m−1 ≠β m−1 ′ and α m ≠α m ′ are satisfied.

8. A rewritable optical recording medium in which information can be recorded in the optical recording method according to claim 1 , characterized in that said phase-change recording layer of said rewritable optical recording medium has a composition containing Sb as a main component.