Method of and device for pulse-mode driving a semi-conductor laser

Claim 3

A method as claimed in claim 8 wherein the pedestal current pulse is switched on gradually.

Claim 4

A method as claimed in claim 1, wherein the pedestal current pulse is switched off gradually.

Claim 5

A driving device for a semiconductor laser wherein the laser emits laser light when a current greater than a laser-threshold current passes through the laser, said device comprising: first and second switchable current sources coupled in parallel to said semiconductor laser with the first switchable current source arranged to supply a pedestal current to said laser which is lower than said laser threshold current, the second switchable current source being arranged to supply information current pulses to said laser such that the sum of the pedestal current and the information current pulses exceed said laser threshold current, first and second pulse shapers connected to said first and second switchable current sources, respectively, a signal source coupled to said first and second pulse shapers so that the first and second pulse shapers generate first and second switching pulses to switch the first and second current sources, respectively, in response to a pulse originating from the signal source, wherein the first and second pulse shapers are further arranged such that commencement of the second switching pulse is delayed with respect to commencement of the first switching pulse and the lenth of the first switching pulse is at least equal to the sum of the length of the second switching pulse and the length of a time interval between the commencement of the two switching pulses.

Claim 6

A driving device for a semiconductor laser wherein the laser emits laser light when a current greater than a laser-threshold current passes through the laser, said device comprising: first and second switchable current sources coupled in parallel to said semiconductor laser with the first switchable current source arranged to supply a pedestal current to said laser which is lower than said laser threshold current, the second switchable current source being arranged to supply information current pulses to said laser such that the sum of the pedestal current and the information current pulses exceed said laser threshold current, first and second pulse shapers connected to said first and second switchable current sources, respectively, a signal source coupled to said first and second pulse shapers so that the first and second pulse shapers generate first and second switching pulses to switch the first and second current sources, respectively, in response to a pulse originating from the signal source, wherein the first and second pulse shapers are further arranged such that commencement of the second switching pulse is delayed with respect to commencement of the first switching pulse and the lenth of the first switching pulse is at least equal to the sum of the length of the second switching pulse and the length of a time interval between the commencement of the two switching pulses.

Claim 7

A driving device as claimed in claim 4 wherein the first current source is switched on gradually.

Claim 8

A driving device as claimed in claim 4 wherein the first current course can be switched off gradually.

Claim 9

A driving device as claimed in claim 4 characterized in that at least one current source comprises a capacitor.

Claim 10

A driving device as claimed in claims 5 or 6 wherein at least one of said current sources comprises a capacitor.

Claim 11

A laser-writing apparatus comprising a semiconductor laser, an optical system for focusing laser radiation generated by the semiconductor laser to a radiation spot on a radiation-sensitive surface of an optical record carrier, means for moving the radiation spot and the radiation-sensitive surface with respect to each other, and a pulse-mode driving device as claimed in any one of claims 10, 4, 5, or 6 coupled to drive the semiconductor laser.

Claim 12

A pulse-mode drive device for a semiconductor laser that emits laser light when it receives a current greater than a laser-threshold current level, said device comprising: a source of signal information, first and second current sources, switching means for selectively coupling said first and second current sources to the semiconductor laser, said first current source supplying a pedestal current for said semiconductor laser which is lower than said laser-threshold current level, said second current source supplying an information current of a level whereby the sum of the pedestal current and the information current exceeds said laser-threshold current level, and delay means coupling said signal source to said switching means so as to selectively switch said first and second current sources to the semiconductor laser such that the second current source supplies a current pulse to the semiconductor laser that is delayed relative to commencement of a current pulse supplied to the semiconductor laser from the first current source.

Claim 13

A pulse-mode drive device for a semiconductor laser that emits laser light when it receives a current greater than a laser-threshold current level, said device comprising: a source of signal information, first and second current sources, switching means for selectively coupling said first and second current sources to the semiconductor laser, said first current source supplying a pedestal current for said semiconductor laser which is lower than said laser-threshold current level, said second current source supplying an information current of a level whereby the sum of the pedestal current and the information current exceeds said laser-threshold current level, and delay means coupling said signal source to said switching means so as to selectively switch said first and second current sources to the semiconductor laser such that the second current source supplies a current pulse to the semiconductor laser that is delayed relative to commencement of a current pulse supplied to the semiconductor laser from the first current source.

Claim 14

A drive device as claimed in claim 10 wherein said delay means comprise pulse shaping means for producing first and second switching pulses for said switching means with the second switching pulse delayed relative to the first switching pulse and wherein the length of the first switching pulse is at least equal to the sum of the length of the second switching pulse and the length of a time interval between commencement of the two switching pulses.

Claim 15

A device as claimed in claim 10 wherein said first and second current sources comprise first and second capacitors, respectively, DC coupled to a source of supply voltage.