Frequency shifter and optical displacement measurement apparatus using the same

• US 5,629,793 A
• Filed: 07/07/1995
• Issued: 05/13/1997
• Est. Priority Date: 07/11/1994
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Takamiya, Makoto, Kadowaki, Hidejiro
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US08/499,125
• Time in Patent Office: 676 Days
• Field of Search: 354/278, 354/279, 356/356, 356/358, 356/28.5
• US Class Current: 359/278
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 7/4814 of transmitters alone
• CPC Class Codes: G01S 7/4911 Transmitters
• CPC Class Codes: G01S 7/4917 superposing optical signals in a photodetector, e.g. optical heterodyne detection
• CPC Class Codes: G02F 1/0305 Constructional arrangements G02F1/0327 - G02F1/05 take precedence

Abstract

A frequency shifter for modulating the frequency of an incident light beam is disclosed. This frequency shifter includes an electro-optic crystal portion to be arranged at an incident position, an electrode arranged on the electro-optic crystal portion, a voltage application unit for applying a voltage to the electro-optic crystal portion via the electrode, and a unit which is arranged at least at a portion of the electro-optic crystal portion to uniformize the temperature of the electro-optic crystal portion.

Claims

1. A frequency shifter for modulating a frequency of an incident light beam, said shifter comprising:

an electro-optic crystal portion to be arranged at an incident position;

an electrode arranged on said electro-optic crystal portion;

voltage application means for applying a voltage to said electro-optic crystal portion via said electrode; and

means, arranged at least at a portion of said electro-optic crystal portion, for uniformizing a temperature of said electro-optic crystal portion, wherein

said means for uniformizing the temperature is arranged over portions, of said electro-optic crystal portion, on which two light beams are respectively incident.

2. A shifter according to claim 1, wherein said electrode is arranged at only an area through which one of the two light beams, which are incident on said electro-optic crystal portion, is transmitted.

3. A shifter according to claim 1, wherein said electro-optic crystal portion includes two electro-optic crystals in areas through which the two incident light beams are transmitted, said electro-optic crystals having crystallographic axes arranged in opposite directions.

4. A shifter according to claim 3, wherein said electrode is commonly arranged for said two electro-optic crystals.

5. A shifter according to claim 4, wherein said means for uniformizing the temperature is constituted by a good heat conductor and also serves as said electrode.

6. An apparatus for optically detecting displacement information of an object, said apparatus comprising:

light source means for emitting at least one light beam;

a frequency shifter for modulating a frequency of at least one light beam emitted from said light source means, said frequency shifter including;

i) an electro-optic crystal portion to be arranged at an incident position,

ii) an electrode arranged on said electro-optic crystal portion,

iii) voltage application means for applying a voltage to said electro-optic crystal portion via said electrode, and

iv) means, arranged at least at a portion of said electro-optic crystal portion, for uniformizing a temperature of said electro-optic crystal portion; and

a photodetecting portion for detecting light from the object irradiated with at least one light beam frequency-modulated by said frequency shifter, wherein

said light source means emits two light beams, said frequency shifter causes the two light beams to be incident on said electro-optic crystal portion and modulates at least one of the two light beams, and said photodetecting portion detects light from the object irradiated with the two light beams.

7. An apparatus according to claim 6, wherein said means for uniformizing the temperature is arranged over portions, of said electro-optic crystal portion, on which the two light beams are respectively incident.

8. A frequency shifter for modulating a frequency of an incident light beam, said shifter comprising:

an electro-optic crystal portion to be arranged at an incident position, said electro-optic crystal portion having two electro-optic crystals in areas through which two incident light beams are respectively transmitted, and said two electro-optic crystals having crystallographic axes arranged in opposite directions with respect to an axis perpendicular to a direction of arrangement of said two electro-optic crystals;

an electrode arranged on said electro-optic crystal portion to apply voltages to said two electro-optic crystals in the same direction; and

voltage application means for applying a voltage to said electro-optic crystal portion via said electrode.

9. A shifter according to claim 8, wherein said electrode is commonly arranged for said two electro-optic crystals.

10. A frequency shifter for modulating a frequency of an incident light beam, said shifter comprising:

an electro-optic crystal portion to be arranged at an incident position, said electro-optic crystal portion having two electro-optic crystals in areas through which two incident light beams are respectively transmitted, and said two electro-optic crystals having crystallographic axes arranged in opposite directions;

an electrode arranged on said electro-optic crystal portion to apply voltages to said two electro-optic crystals in the same direction;

voltage application means for applying a voltage to said electro-optic crystal portion via said electrode; and

means, arranged at least at a portion of said electro-optic crystal portion, for uniformizing a temperature of said electro-optic crystal portion.

11. A shifter according to claim 10, wherein said means for uniformizing the temperature is constituted by a good heat conductor and also serves as said electrode.

12. An apparatus for optically detecting displacement information of an object, said apparatus comprising:

light source means for emitting at least one light beam;

a frequency shifter for modulating a frequency of at least one light beam emitted from said light source means, said frequency shifter including;

i) an electro-optic crystal portion to be arranged at an incident position, said electro-optic crystal portion having two electro-optic crystals in areas through which two incident light beams are respectively transmitted, and said two electro-optic crystals having crystallographic axes arranged in opposite directions with respect to an axis perpendicular to a direction of arrangement of said two electro-optic crystals,

ii) an electrode arranged on said electro-optic crystal portion to apply voltages to said two electro-optic crystals in the same direction, and

iii) voltage application means for applying a voltage to said electro-optic crystal portion via said electrode; and

a photodetecting portion for detecting light from the object irradiated with at least one light beam frequency-modulated by said frequency shifter, thereby detecting displacement information of the object.

13. An apparatus according to claim 12, wherein said electrode is commonly provided for said two electro-optic crystals.