Acousto-optic polychromatic light modulator

• US 5,463,493 A
• Filed: 01/19/1993
• Issued: 10/31/1995
• Est. Priority Date: 01/19/1993
• Status: Expired due to Fees

• Current Assignee: MVM Electronics
• Original Assignee: MVM Electronics
• Inventors: Shah, Manhar L.
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): Robbins, Thomas
• Application Number:
  US08/005,992
• Time in Patent Office: 1,015 Days
• Field of Search: 359/309, 359/312, 359/313, 359/308, 359/314
• US Class Current: 359/312
• CPC Class Codes: G02F 1/11 based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves acousto-optical deflection G02F1/33
• CPC Class Codes: G02F 1/332 comprising a plurality of transducers on the same crystal surface, e.g. multi-channel Bragg cell
• CPC Class Codes: G02F 2203/05 wavelength dependent

Abstract

An acousto-optic polychromatic light modulating apparatus employs an acousto-optic medium, and a single piezoelectric transducer, which is driven by a plurality of frequency components, the intensities of which are controlled in response to input electronic data, to produce a color-modulated diffracted polychromatic output beam. The acousto-optic medium and mode as well as acousto-optic interaction length and the geometry of the device are selected such that there is negligible acousto-optic interaction with a given frequency signal on all output optical beam colors except for the one assigned to that frequency, with a high degree of color convergence achieved over a wide wavelength range. The present invention can be used to increase the modulation rate of a polychromatic modulator by selecting the incident optical beam energy propagation direction to be nearly normal to the acoustic wave phase propagation direction with non-parallel tangents at the incident and diffracted optical wave-vector loci. It may also be incorporated within the laser cavity of a discrete line laser and in the laser cavity of a continuous band laser, thereby enabling the selection or tuning of one or more wavelengths simultaneously. The use of a multi-frequency input RF driver enables the laser to be tuned electronically at high speed, without mechanical movement of any physical components.

Claims

1. An acousto-optic polychromatic light modulating apparatus comprising an acousto-optic medium, a piezoelectric transducer attached to said acousto-optic medium and operative to convert electrical signals supplied thereto into ultrasonic waves, said ultrasonic waves being launched from said piezoelectric transducer into said acousto-optic medium for interaction with a substantially collinear polychromatic light beam incident upon and traveling through said acousto-optic medium, an electronic driver which is coupled to said piezoelectric transducer and which generates signals containing a plurality of RF frequencies at respectively controllable amplitudes, thereby selecting a desired combination of wavelengths in a substantially collinear polychromatic output beam diffracted from said acousto-optic medium, and wherein said acousto-optic medium, its mode and acousto-optic interaction length thereof are such that there is effective interaction by respective ones of said plurality of RF frequencies with respectively different predetermined wavelengths contained in said polychromatic output beam.

2. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein said substantially collinear incident light beam is a linearly polarized polychromatic light beam and said substantially collinear diffracted polychromatic output beam is a first order diffracted beam having a polarization orthogonal to the polarization of the incident light beam.

3. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein said substantially collinear incident light beam is a linearly polarized polychromatic light beamand wherein said substantially collinear diffracted polychromatic output beam is a zeroth order beam having a polarization identical to the polarization of the incident light beam.

4. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein said RF driver generates one of a repetitive frequency chirp, noise spectrum, and an impulse-modulated RF, PN sequence-modulated RF output, having a desired frequency content and repetition period, and wherein a tunable RF filter is interposed between said RF driver and said acousto-optic mediumto prevent one or more frequency bands from said RF driver from being output to said transducer.

5. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein said acousto-optic medium is configured and arranged to employ far-off-axis anisotropic Bragg diffraction.

6. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein said acousto-optic medium is configured and arranged to employ parallel tangents to the loci of incident and diffracted optical wave vectors.

7. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein said acousto-optic medium is configured and arranged to employ anisotropic Bragg diffraction, and has an acoustic phase propagation direction substantially along a tangent to a locus of an incident optical wave vector, so as to improve modulation speed.

8. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein said acousto-optic medium has entrance and exit optical faces which are non-parallel by at least 0.5 degrees, so as to accept and output a substantially collinear polychromatic light beam.

9. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein optical rotation of said acousto-optic medium is chosen to define a desired RF drive frequency range and polychromatic modulator characteristics.

10. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein said transducer is an apodized transducer for reducing side lobes or inter-color modulation effects.

11. An acousto-optic polychromatic light modulating apparatus according to claim 1, wherein said acousto-optic medium comprises a material selected from the group consisting of TeO₂, Hg_2Cl2, Hg₂ Br₂, Hg₂ I₂, PbCl₂, PbBr₂, Tl₃ AsS₄, Tl₃ VS₄, Tl₃ NbS₄, Tl₃ AsSe₃, Tl₃ TaS₄, Tl₃ TaSe₄, CaMoO₄, LiNbO₃, CaWoO₄, PbMoO₄, and crystalline quartz.

12. An acousto-optic polychromatic light modulating apparatus comprising:

an acousto-optic medium having a first face from which an acoustic wave is to be launched into said medium for interaction with a polychromatic input light beam, a second face upon which multiple color components of said polychromatic input light beam are collinearly incident, and a third face from which a light beam travelling through said acousto-optic medium is diffracted;

a piezoelectric transducer mounted on the first face of said acousto-optic medium and to which a multi-frequency RF input signal is applied, said piezoelectric transducer being operative to launch a multi-frequency acoustic wave into said acousto-optic medium for interaction with said polychromatic input light beam as it travels through said acousto-optic medium; and

a multi-frequency RF signal driver which is operative to generate a plurality of RF signals for selective application to said piezoelectric transducer in order to control the launching of acoustic waves by said transducer, such that a respective one of an RF signal that has been selected from among the plurality of RF signals generated by said RF signal driver for application to said piezoelectric transducer effectively interacts with only a respective one wavelength component of said polychromatic light beam, said respective one wavelength being different from another wavelength component of said polychromatic light beam, thereby modulating the wavelength composition of said polychromatic light beam and producing a color composition-modulated polychromatic output light beam the respective color components of which are collinearly diffracted from said third face of said acousto-optic medium.

13. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said polychromatic input light beam is linearly polarized.

14. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said multi-frequency RF signal driver which is operative to apply a plurality of RF signals to said piezoelectric transducer in order to control the launching of multi-frequency acoustic waves by said transducer, such that each respective RF signal among the plurality of RF signals applied by said RF signal driver to said piezoelectric transducer effectively interacts with a respectively different wavelength component of said polychromatic light beam.

15. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said diffracted polychromatic output light beam is a first order diffracted beam having a polarization orthogonal to the polarization of said input light beam.

16. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said diffracted polychromatic output light beam is a zeroth order beam having a polarization identical to the polarization of said input light beam.

17. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said RF signal driver generates one of a repetitive frequency chirp, noise spectrum, an impulse-modulated RF output and a PN sequence-modulated RF output, having a desired frequency content and repetition period, and wherein a tunable RF filter is interposed between said RF signal driver and said acousto-optic medium to prevent one or more frequency bands from said RF signal driver from being applied to said transducer.

18. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said acousto-optic medium is configured and arranged to employ far-off-axis anisotropic Bragg diffraction.

19. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said acousto-optic medium is configured and arranged to employ parallel tangents to the loci of incident and diffracted optical wave vectors.

20. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said acousto-optic medium is configured and arranged to employ anisotropic Bragg diffraction, and has an acoustic phase propagation direction substantially along a tangent to a locus of an incident optical wave vector, so as to improve modulation speed.

21. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said second and third faces of said acousto-optic medium are non-parallel by at least 0.5 degrees.

22. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein optical rotation of said acousto-optic medium is chosen to define a desired RF drive frequency range and polychromatic modulator characteristics.

23. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said transducer is an apodized transducer.

24. An acousto-optic polychromatic light modulating apparatus according to claim 12, wherein said acousto-optic medium comprises a material selected from the group consisting of TeO₂, Hg₂ Cl₂, Hg₂ Br₂, Hg₂ I₂, PbCl₂, PbBr₂, Tl₃ AsS₄, Tl₃ VS₄, Tl₃ NbS₄, Tl₃ AsSe₃, Tl₃ TaS₄, Tl₃ TaSe₄, CaMoO₄, LiNbO₃, CaWoO₄, PbMoO₄, and crystalline quartz.

25. A method of modulating a polychromatic light beam comprising the steps of:

(a) directing said polychromatic light beam having multiple color components which are collinearly incident upon a first face of an acousto-optic medium, said acousto-optic medium having a second face from which an acoustic wave is to be launched into said medium for interaction with said polychromatic light beam as it travels through said acousto-optic medium, and a third face from which a modulated polychromatic output light beam is diffracted;

(b) generating a plurality of RF signals; and

(c) launching a multi-frequency acoustic wave from said second face into said acousto-optic medium for interaction with said polychromatic light beam as it travels through said acousto-optic medium in accordance with the plurality of RF signals generated in step (b), such that each RF signal among the plurality of RF signals generated in step (b) effectively interacts with a respectively different wavelength component of said polychromatic light beam, thereby modulating respectively different wavelength components of said polychromatic light beam to produce a color composition-modulated polychromatic output light beam the respective color components of which are collinearly diffracted from said third face of said acousto-optic medium.

26. A method according to claim 25, wherein said polychromatic light beam is linearly polarized and wherein said diffracted polychromatic output light beam is a first order diffracted beam having a polarization orthogonal to the polarization of said polychromatic light beam.

27. A method according to claim 25, wherein said polychromatic light beam is linearly polarized and wherein said diffracted polychromatic output light beam is a zeroth order beam having a polarization identical to the polarization of said polychromatic light beam.

28. A method according to claim 25, wherein step (b) comprises generating one of a repetitive frequency chirp, noise spectrum, an impulse-modulated RF output, and a PN sequence-modulated RF output, having a desired frequency content and repetition period, and coupling the generated one of the repetitive frequency chirp, noise spectrum, impulse-modulated RF output, and PN sequence-modulated RF output, through a tunable RF filter disposed in a signal application path to said acousto-optic medium, so as to prevent one or more RF frequency bands from being contained in the multi-frequency acoustic wave launched from said second face into said acousto-optic medium in step (c).

29. A method according to claim 25, wherein said acousto-optic medium is configured and arranged to employ far-off-axis anisotropic Bragg diffraction.

30. A method according to claim 25, wherein said acousto-optic medium is configured and arranged to employ parallel tangents to the loci of incident and diffracted optical wave vectors.

31. A method according to claim 25, wherein said acousto-optic medium is configured and arranged to employ anisotropic Bragg diffraction, and has an acoustic phase propagation direction substantially along a tangent to a locus of an incident optical wave vector.

32. A method according to claim 25, wherein said first and third faces of said acousto-optic medium are non-parallel by at least 0.5 degrees.

33. A method according to claim 25, wherein said acousto-optic medium has an optical rotation which defines a desired RF drive frequency range and polychromatic modulator characteristics.

34. A method according to claim 25, wherein step (c) comprises launching said multi-frequency acoustic wave from an apodized transducer mounted upon said second face of said acousto-optic medium.

35. A method according to claim 25, wherein said acousto-optic medium comprises a material selected from the group consisting of TeO₂, Hg₂ Cl₂, Hg₂ Br₂, Hg₂ I₂, PbCl₂, PbBr₂, Tl₃ AsS₄, Tl₃ VS₄, Tl₃ NbS₄, Tl₃ AsSe₃, Tl₃ TaS₄, Tl₃ TaSe₄, CaMoO₄, LiNbO₃, CaWoO₄, PbMoO₄, and crystalline quartz.

36. A polarization independent acousto-optic polychromatic light modulating apparatus comprising at least one birefringent plate, an acousto-optic medium having an entrance face and an exit face, said birefringent plate being placed in the vicinity of either the entrance face, the exit face or both the entrance and exit faces of said acousto-optic medium, a piezoelectric transducer attached to said acousto-optic medium and operative to convert electrical signals supplied thereto into ultrasonic waves, said ultrasonic waves being launched from said piezoelectric transducer into said acousto-optic medium for interaction with a substantially collinear randomly polarized polychromatic light beam incident upon and traveling through said birefringent plate and said acousto-optic medium, an electronic driver which is coupled to said piezoelectric transducer and which generates signals containing a plurality of RF frequencies at respectively controllable amplitudes, thereby selecting a desired combination of wavelengths as well as polarization states in no more than two individually substantially collinear polychromatic output beams diffracted from said acousto-optic interaction medium, and wherein said acousto-optic medium, its mode and acousto-optic interaction length thereof are such that there is effective interaction by a respective one of said plurality of RF frequencies with only a predetermined wavelength contained in said polychromatic output beam.

37. An acousto-optic polychromatic light modulating apparatus comprising an acousto-optic medium, an acoustic wave launching transducer attached to said acousto-optic medium and operative to simultaneously receive a plurality of RF signals having respectively different RF frequencies and, in response thereto, to simultaneously launch a plurality of acoustic waves having respectively different frequencies associated with the respectively different RF frequencies applied thereto, said acousto-optic medium receiving a substantially co-linear polychromatic light beam incident upon and travelling through said acousto-optic medium and exiting said acousto-optic medium, such that respectively different ones of said plurality of acoustic waves associated with respectively different RF frequencies launched by said transducer interact with respectively different optical wavelength components of said polychromatic light beam, so as define a composite color output polychromatic light beam having color components thereof defined in accordance with said respectively different RF frequencies.