Digital tracking and focus servo system with TES to FES crosstalk calibration

1. A method of calibrating a crosstalk correction for a tracking error signal (TES) to a focus error signal (FES) crosstalk, comprising:

choosing a cross-talk gain from a set of cross-talk gains, the cross-talk gain determining a fraction of a tracking error signal from a tracking servo system to subtract from a focus error signal in a focus servo system to form an adjusted focus error signal in the crosstalk correction;

performing a Bode calculation to obtain a frequency component of the adjusted focus error signal at a frequency in response to a perturbation of the tracking servo system at the frequency;

comparing the component with components resulting from previous values of the cross-talk gain, each of the previous values of the cross-talk gain being of the set of cross-talk gains; and

replacing an optimized cross-talk gain with the cross-talk gain if the component is lower than previous components.

2. The method of claim 1 , wherein the frequency is a tracking cross-over frequency.

3. The method of claim 1 , wherein performing the Bode calculation includes

providing a disturbance to the tracking servo loop at the frequency;

measuring the adjusted focus error signal; and

calculating the component of the adjusted focus error signal at the frequency.

4. A method of obtaining an optimum crosstalk gain, comprising:

obtaining a Bode component of an adjusted focus error signal to a disturbance of a tracking error signal for each of a set of crosstalk gains; and

setting the optimum crosstalk gain as the crosstalk gain of the set of crosstalk gains that provides the lowest Bode component.

5. The method of claim 4 , wherein obtaining the Bode component includes

perturbing the tracking error signal at a frequency;

measuring the adjusted focus error signal; and

setting the Bode component to be a single frequency discrete Fourier transform of the adjusted focus error signal.

6. The method of claim 4 , wherein the adjusted focus error signal is the focus error signal less a tracking error signal from the tracking servo loop multiplied by the crosstalk gain.

7. The method of claim 5 , wherein the frequency is a tracking cross-over frequency.

8. A servo system, comprising:

an optical pick-up unit;

an analog processor coupled to receive signals from detectors in the optical pick-up unit and provide digital signals;

at least one processor coupled to receive the digital signals, the processor calculating a control signal; and

a driver coupled to control a position of the optical pick-up unit in response to the control signal,

wherein the at least one processor executes an algorithm that obtains a Bode component of an adjusted focus error signal to a disturbance of a tracking error signal for each of a set of crosstalk gains, and

sets an optimum crosstalk gain as the crosstalk gain of the set of crosstalk gains that provides the lowest Bode component.

9. The system of claim 8 , wherein obtaining the Bode component is obtained by

perturbing the tracking error signal at a frequency;

measuring the adjusted focus error signal; and

setting the Bode component to be a single frequency discrete Fourier transform of the adjusted focus error signal.

10. The system of claim 8 , wherein the adjusted focus error signal is a focus error signal less a tracking error signal from the tracking servo loop multiplied by the crosstalk gain.

11. The system of claim 9 , wherein the frequency is a tracking cross-over frequency.