Laser light generating apparatus and method

• US 20020171912A1
• Filed: 04/10/2002
• Published: 11/21/2002
• Est. Priority Date: 04/11/2001
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Masuda, Hisashi
• Granted Patent: US 6,862,131 B2
• Time in Patent Office: Days
• US Class Current: 359/326
• CPC Class Codes: G02F 1/3532 Arrangements of plural nonlinear devices for generating multi-colour light beams, e.g. arrangements of SHG, SFG, OPO devices for generating RGB light beams
• CPC Class Codes: G02F 1/3534 Three-wave interaction, e.g. sum-difference frequency generation G02F1/3532 takes precedence
• CPC Class Codes: G02F 1/3542 Multipass arrangements, i.e. arrangements to make light pass multiple times through the same element, e.g. using an enhancement cavity
• CPC Class Codes: G02F 1/37 for second-harmonic generation G02F1/3532 takes precedence

Abstract

A laser light generating apparatus is provided with a laser light source, a phase modulator, a signal generating unit for applying a modulating signal to the phase modulator, and resonators. A nonlinear optical element is provided in the resonator, and an optical path length varying means for changing length of an optical path of each of the resonators is provided. Error signals are obtained using detection signals of photodetectors for receiving light from the resonators, respectively, and the optical path length varying means is controlled by a sideband method, whereby a control circuit having a negative feedback configuration for controlling length of the resonators is formed. Laser light is subjected to phase modulation and then inputted to the resonator, and light generated by the nonlinear optical element is inputted to the resonator so that the plurality of resonators are simultaneously held in a resonant state.

Claims

1. A laser light generating apparatus comprising:

a laser light source for outputting laser light;

a phase modulator and a signal generating unit for generating a modulating signal to be applied to the phase modulator;

a plurality of resonators including a first resonator and a second resonator disposed in a stage succeeding the first resonator;

a nonlinear optical element disposed in the first resonator;

an optical path length varying means for changing length of an optical path of each of the resonators;

an optical system disposed between the laser light source and the resonators and between two resonators for providing coupling between the laser light source and the resonators and between the two resonators;

a photodetector for receiving light from each of the resonators; and

a control circuit having a negative feedback configuration for obtaining an error signal from a detection signal obtained by the photodetector and the modulating signal and controlling the optical path length varying means by an FM sideband method using the error signal;

wherein the laser light is inputted to the phase modulator, subjected to phase modulation, and then inputted to the first resonator, and light generated by the nonlinear optical element is inputted to the second resonator; and

the light from each of the first resonator and the second resonator is detected by the photodetector, and the length of the optical path of each of the resonators is controlled on the basis of the error signal, whereby the plurality of resonators are or can be simultaneously held in a resonant state.

2. A laser light generating apparatus as claimed in claim 1,

wherein one or a plurality of phase modulators to which the modulating signal of different frequencies is applied are disposed on an optical path between the laser light source and the first resonator, and light outputted from the first resonator is inputted to the second resonator without passing through a phase modulator.

3. A laser light generating apparatus as claimed in claim 1,

wherein wavelength conversion is made by the nonlinear optical element disposed in the first resonator.

4. A laser light generating apparatus as claimed in claim 2,

wherein wavelength conversion is made by the nonlinear optical element disposed in the first resonator.

5. A laser light generating apparatus as claimed in claim 3,

wherein laser light of a second wavelength obtained by subjecting the laser light of a first wavelength outputted by the laser light source to the wavelength conversion by the nonlinear optical element is inputted to the second resonator;

and

the first resonator is held in a resonant state for the laser light of the first wavelength and the second resonator is held in a resonant state for the laser light of the second wavelength.

6. A laser light generating apparatus as claimed in claim 4,

wherein laser light of a second wavelength obtained by subjecting the laser light of a first wavelength outputted by the laser light source to the wavelength conversion by the nonlinear optical element is inputted to the second resonator;

and

the first resonator is held in a resonant state for the laser light of the first wavelength and the second resonator is held in a resonant state for the laser light of the second wavelength.

7. A laser light generating apparatus as claimed in claim 2,

wherein the signal generating unit generates the modulating signal having a first frequency component formed by an oscillation signal required to generate an error signal used for maintaining the resonant state of the first resonator and a second frequency component formed by an oscillation signal required to generate an error signal used for maintaining the resonant state of the second resonator, and applies the signal to the one phase modulator or either one of the plurality of phase modulators.

8. A laser light generating apparatus as claimed in claim 7,

wherein the first frequency component is of a higher frequency than the second frequency component.

9. A laser light generating apparatus as claimed in claim 1,

wherein the first resonator has a gain medium therewithin for amplifying the laser light for output.

10. A laser light generating apparatus as claimed in claim 1,

wherein the nonlinear optical element disposed within the first resonator generates a harmonic frequency light.

11. A laser light generating apparatus as claimed in claim 1,

wherein a nonlinear optical element disposed within the second resonator is an optical mixing element and generates light of a sum frequency or a difference frequency by mixing two pieces of laser light.

12. A laser light generating apparatus as claimed in claim 1,

wherein the laser light passed through the phase modulator to which the modulating signal is applied, and then subjected to wavelength conversion by the nonlinear optical element disposed in the first resonator is sequentially inputted to a plurality of resonators without being passed through another phase modulator;

and

the FM sideband method using error signals generated from the modulating signal and light detection signals for the plurality of resonators simultaneously holds the resonators in a resonant state.

13. A laser light generating apparatus as claimed in claim 1,

wherein transmission width of the first resonator is wider than transmission width of the second resonator.

14. A laser light generating apparatus as claimed in claim 1,

wherein frequency of a phase modulation signal used to maintain the resonant state of the second resonator is substantially equal to or lower than a frequency corresponding to transmission width of the first resonator, and is substantially equal to or higher than a frequency corresponding to transmission width of the second resonator.

15. A laser light generating apparatus as claimed in claim 1,

wherein frequency of a phase modulation signal used to maintain the resonant state of the first resonator is higher than a frequency corresponding to transmission width of the first resonator;

and

frequency of a phase modulation signal used to maintain the resonant state of the second resonator is equal to or lower than the frequency corresponding to the transmission width of the first resonator.

17. A laser light generating method as claimed in claim 16,

wherein the laser light phase-modulated by the phase modulator to which the modulating signal of different frequencies is applied is inputted to the first resonator, and light outputted from the first resonator is inputted to the second resonator without passing through a phase modulator.

18. A laser light generating method as claimed in claim 16,

wherein the laser light is subjected to wavelength conversion by the nonlinear optical element disposed in the first resonator.

19. A laser light generating method as claimed in claim 18,

wherein laser light of a second wavelength obtained by subjecting laser light of a first wavelength outputted by a laser light source to the wavelength conversion by the nonlinear optical element is inputted to the second resonator;

and

the first resonator is held in a resonant state for the laser light of the first wavelength and the second resonator is held in a resonant state for the laser light of the second wavelength.

20. A laser light generating method as claimed in claim 16,

wherein the original modulating signal applied to the phase modulator, a harmonic frequency light signal of the original modulating signal, a sum frequency signal of the harmonic frequency light signal and the original modulating signal, or a difference frequency signal of the harmonic frequency light signal and the original modulating signal is used as the modulating signal for the FM sideband method.

21. A laser light generating method as claimed in claim 16,

wherein a first frequency component formed by an oscillation signal required to generate the error signal used for maintaining the resonant state of the first resonator and a second frequency component formed by an oscillation signal required to generate the error signal used for maintaining the resonant state of the second resonator are included in the modulating signal applied to the phase modulator, or a sum frequency signal, a difference frequency signal, or a harmonic frequency light signal of the modulating signal.

22. A laser light generating method as claimed in claim 21,

wherein the first frequency component is set to be of a higher frequency than the second frequency component.

23. A laser light generating method as claimed in claim 16,

wherein after the phase modulation, the laser light converted in wavelength by the nonlinear optical element disposed in the first resonator is sequentially inputted to a plurality of resonators without being passed through another phase modulator;

and

the FM sideband method using error signals generated from the modulating signal and light detection signals for the plurality of resonators simultaneously holds the resonators in a resonant state.

24. A laser light generating method as claimed in claim 16,

wherein transmission width of the first resonator is set wider than transmission width of the second resonator.

25. A laser light generating method as claimed in claim 16,

wherein frequency of a phase modulation signal used to maintain the resonant state of the second resonator is set substantially equal to or lower than a frequency corresponding to transmission width of the first resonator, and is set substantially equal to or higher than a frequency corresponding to transmission width of the second resonator.

26. A laser light generating method as claimed in claim 16,

wherein frequency of a phase modulation signal used to maintain the resonant state of the first resonator is higher than a frequency corresponding to transmission width of the first resonator;

and

frequency of a phase modulation signal used to maintain the resonant state of the second resonator is equal to or lower than the frequency corresponding to the transmission width of the first resonator.

16. A laser light generating method of phase-modulating laser light, then inputting the phase-modulated light to a plurality of resonators, detecting light obtained from each of the resonators, obtaining an error signal from a detected signal and a modulating signal used for the phase modulation, and thereby variably controlling length of an optical path of each of the resonators by an FM sideband method, said laser light generating method comprising the steps of:

inputting the laser light phase-modulated by a phase modulator to a first resonator and then inputting light generated by a nonlinear optical element disposed within the first resonator to a second resonator; and

detecting light from each of the first resonator and the second resonator, generating an error signal from each of detected signals and the modulating signal, and thereby controlling the length of the optical path of each of the resonators, whereby the plurality of resonators are simultaneously held in a resonant state.