Optical disc drive
View Patent ↗When a multilayered optical disc is used, the signal-to-noise ratio of a read signal is decreased as effective reflectance is extremely low due to the influence of reflection and absorption by front recording layers. Further, when a high-frequency modulation technology is used to suppress returned light noise of a laser, the erasure of recorded information is likely to occur on certain types of discs, making it difficult to simultaneously achieve the suppression of returned light noise of a laser and the prevention of the erasure of recorded information. To address the above problems, the present invention includes a section that performs a read by executing a multi-tone demodulation. The present invention also includes a section that controls the position and shape of a read light pulse to be radiated on a recording layer.
1. An optical disc drive comprising:
a laser light source;
a light source drive that pulse-drives the laser light source;
an optical system that irradiates an optical disc with laser light emitted from the laser light source;
a section that converts optical information to an electrical pulsed read signal, the optical information being optically read from the optical disc when the optical disc is irradiated with the laser light;
a section that converts the pulsed read signal to a sampled pulsed read signal;
a section that synchronizes the pulse drive signal of the laser light source with a channel clock;
a section that changes the phase of the sampled pulsed read signal relative to a channel clock signal;
a section that decodes the sampled pulsed read signal to obtain data recorded on the optical disc; and
wherein a pulse drive frequency of the laser light source is not higher than a channel clock frequency and is at least two times the frequency of a maximum frequency component in the information optically read from the optical disc.
2. The optical disc drive according to claim 1 , wherein the pulse drive frequency of the laser light source is at least ½ the channel clock frequency.
3. The optical disc drive according to claim 1 , wherein the pulse drive frequency of the laser light source is at least ⅖ the channel clock frequency.
4. The optical disc drive according to claim 1 , wherein the section that changes the phase adjusts the phase so that a laser pulse is not incident on a recorded mark edge.
5. The optical disc drive according to claim 1 , wherein the optical disc drive is configured to cause the pulse duty of the pulsed read signal to be no higher than ½.
6. The optical disc drive according to claim 1 , wherein the optical disc drive is configured to cause the pulse drive to be performed so that power lower than the peak power of the pulse is radiated before the pulse is radiated.
7. An optical disc drive comprising:
a laser light source;
a light source drive that pulse-drives the laser light source;
an optical system that irradiates an optical disc with laser light emitted from the laser light source;
a section that converts optical information to an electrical pulsed read signal, the optical information being optically read from the optical disc when the optical disc is irradiated with the laser light;
a section that converts the pulsed read signal to a sampled pulsed read signal;
a section that decodes the sampled pulsed read signal to obtain data recorded on the optical disc;
a section that synchronizes the pulse drive signal of the laser light source with a channel clock; and
a section that changes the phase of the sampled pulsed read signal relative to a channel clock signal.
8. An optical disc drive comprising:
a laser light source;
a light source drive that pulse-drives the laser light source;
an optical system that irradiates an optical disc with laser light emitted from the laser light source;
an analog-to-digital converter that generates a sampled pulsed read signal from a pulsed read signal reflected from the optical disc;
a sampling speed multiplier that converts the sampled pulsed read signal to a predefined sampling speed;
an interpolator that changes the sampling speed of the sampled pulsed read signal converted by the sampling speed multiplier; and
a section that decodes an output signal of the interpolator to obtain a bit stream.