Variable focal length lens device and variable focal length lens control method

1. A variable focal length lens device comprising:

a lens system whose refractive index changes in accordance with an inputted drive signal; and

a resonance-lock controller configured to lock the drive signal to a variable and temperature-dependent resonance frequency of the lens system, wherein

the resonance-lock controller is configured to tune a frequency of the drive signal to a peak position of a voltage-current phase difference between a voltage of the drive signal and a drive current of the lens system, and to raise or lower the frequency of the drive signal based on the drive current when the voltage-current phase difference is changed.

2. A variable focal length lens device comprising:

a lens system whose refractive index changes in accordance with an inputted drive signal; and

a resonance-lock controller configured to lock the drive signal to a variable and temperature-dependent resonance frequency of the lens system, wherein

the resonance-lock controller is configured to set a target effective power that is lower than a peak value of an effective power of the lens system, to tune a frequency of the drive signal to a frequency at which the target effective power is provided, and to raise or lower the frequency of the drive signal in accordance with an increase or decrease in the effective power when the effective power is changed.

3. A variable focal length lens device comprising:

a lens system whose refractive index changes in accordance with an inputted drive signal; and

a resonance-lock controller configured to lock the drive signal to a variable and temperature-dependent resonance frequency of the lens system, wherein

the resonance-lock controller is configured to set a target voltage-current phase difference that is lower than a peak value of a voltage-current phase difference between a voltage of the drive signal and a drive current of the lens system, to tune a frequency of the drive signal to a frequency at which the target voltage-current phase difference is provided, and to raise or lower the frequency of the drive signal in accordance with an increase or decrease in the voltage-current phase difference when the voltage-current phase difference is changed.

4. A method of controlling a variable focal length lens device comprising: a lens system whose refractive index changes in accordance with an inputted drive signal; and a resonance-lock controller configured to lock the drive signal to a variable and temperature-dependent resonance frequency of the lens system, the method comprising:

tuning a frequency of the drive signal to a peak position of a voltage-current phase difference between a voltage of the drive signal and a drive current of the lens system; and

raising or lowering the frequency of the drive signal in accordance with the drive current when the voltage-current phase difference is changed.

5. A method of controlling a variable focal length lens device comprising: a lens system whose refractive index changes in accordance with an inputted drive signal; and a resonance-lock controller configured to lock the drive signal to a variable and temperature-dependent resonance frequency of the lens system, the method comprising:

setting a target effective power that is lower than a peak value of an effective power of the lens system;

tuning a frequency of the drive signal to a frequency at which the target effective power is provided; and

raising or lowering the frequency of the drive signal in accordance with an increase or decrease in the effective power when the effective power is changed.

6. A method of controlling a variable focal length lens device comprising: a lens system whose refractive index changes in accordance with an inputted drive signal; and a resonance-lock controller configured to lock the drive signal to a variable and temperature-dependent resonance frequency of the lens system, the method comprising:

setting a target voltage-current phase difference that is lower than a peak value of a voltage-current phase difference between a voltage of the drive signal and a drive current of the lens system;

tuning a frequency of the drive signal to a frequency at which the target voltage-current phase difference is provided; and

raising or lowering the frequency of the drive signal based on an increase or decrease in the voltage-current phase difference when the voltage-current phase difference is changed.

7. The variable focal length lens device according to claim 1 , wherein the drive signal is at least one of a sinusoidal, triangular, saw-tooth, and rectangular waveform.

8. The variable focal length lens device according to claim 2 , wherein the drive signal is at least one of a sinusoidal, triangular, saw-tooth, and rectangular waveform.

9. The variable focal length lens device according to claim 3 , wherein the drive signal is at least one of a sinusoidal, triangular, saw-tooth, and rectangular waveform.

10. The method of controlling a variable focal length lens device according to claim 4 , wherein the drive signal is at least one of a sinusoidal, triangular, saw-tooth, and rectangular waveform.

11. The method of controlling a variable focal length lens device according to claim 5 , wherein the drive signal is at least one of a sinusoidal, triangular, saw-tooth, and rectangular waveform.

12. The method of controlling a variable focal length lens device according to claim 6 , wherein the drive signal is at least one of a sinusoidal, triangular, saw-tooth, and rectangular waveform.