DEVICE FOR AN ATOMIC CLOCK

• US 20120256696A1
• Filed: 09/01/2010
• Published: 10/11/2012
• Est. Priority Date: 09/04/2009
• Status: Active Grant

• Current Assignee: Rolex SA
• Original Assignee: CSEM Centre Suisse D'Electronique et de Microtechnique SA
• Inventors: Lecomte, Steve, Haesler, Jacques
• Granted Patent: US 8,816,779 B2
• Time in Patent Office: Days
• US Class Current: 331/94.1
• CPC Class Codes: G04F 5/14 using atomic clocks
• CPC Class Codes: G04F 5/145 using Coherent Population Trapping

Abstract

A device for an atomic clock, including: a laser source (102) generating a laser beam; a quarter-wave plate (105) modifying the linear polarization of the laser beam into a circular polarization and vice versa; a gas cell (106) placed on the laser beam having a circular polarization; a mirror (107) sending the laser beam back toward the gas cell; a first photodetector (108a); means (103, 101a, 107) for diverting the reflected beam of the laser source (102), and a second photodetector (109) placed behind the mirror (107), the mirror being semitransparent and allowing a portion of the laser beam to pass therethrough, the second photodetector (109) being used for controlling the optical frequency of the laser and/or for controlling the temperature of the cell (106).

Claims

1. A device for an atomic clock comprising:

a laser source generating a laser beam,

a quarter-wave plate modifying the linear polarization of the laser beam into a circular polarization and vice versa,

a gas cell passed through by the laser beam with circular polarization,

a mirror sending the laser beam back toward the gas cell,

a first photodetector,

means for preventing the reflected beam from reaching the laser source, and

a second photodetector, placed behind the mirror,

said mirror being semitransparent and allowing a portion of the laser beam to pass,

said second photodetector being used to control the optical frequency of the laser and/or to control the temperature of the cell.

2. The device as claimed in claim 1, wherein the means for preventing the reflected beam from reaching the laser source comprise a splitter placed between the laser source and the mirror and being used to deflect and allow a portion of the laser beam to pass according to a predefined percentage, as well as a polarizer placed between the output of the laser beam and the splitter in order to protect the laser source from the back-reflections from the various optical elements making up the device.

3. The device as claimed in claim 1, wherein the means for preventing the reflected beam from reaching the laser source comprise a splitter placed between the laser source and the mirror and being used to deflect and allow the laser beam to pass depending on the polarization of said beam in such a way that the polarization of the beam from the laser source via the splitter and arriving on the quarter-wave plate is linear according to the first angle and is modified by the quarter-wave plate into circular polarization, and so that the circular polarization of the beam reflected by the mirror and passing a second time through the gas cell is modified into linear polarization according to the second angle by the quarter-wave plate, the splitter directing the backreflected beam to the first photodetector.

4. The device as claimed in claim 1, wherein the means for preventing the reflected beam from reaching the laser source comprise means for inclining the mirror according to an angle that is not perpendicular to the axis of the laser beam, the reflected beam thus being deflected from the axis of the beam emitted by the laser source.

5. The device as claimed in claim 1, wherein the mirror is of concave form, so as to focus the reflected light beam on the first photodetector.

6. The device as claimed in claim 1, wherein the mirror is of concave form and the axis of symmetry of which is off-center relative to that defined by the incident laser beam so as to focus the reflected light beam on the photodetector and prevent the reflected beam from reaching the laser source.

7. The device as claimed in claim 2, which comprises a third photodetector placed after the splitter so that a portion of the laser beam reaches said third photodetector without having passed through the gas cell.

8. The device as claimed in claim 2, which comprises a diaphragm placed between the splitter and the gas cell, this diaphragm reducing the size of the laser beam.

9. The device as claimed in claim 2, which comprises a second diaphragm placed between the splitter and the gas cell, this diaphragm reducing the size of the laser beam.

10. The device as claimed in claim 2, wherein the mirror is of concave form, so as to focus the reflected light beam on the first photodetector.

11. The device as claimed in claim 3, wherein the mirror is of concave form, so as to focus the reflected light beam on the first photodetector.

12. The device as claimed in claim 4, wherein the mirror is of concave form, so as to focus the reflected light beam on the first photodetector.

13. The device as claimed in claim 2, wherein the mirror is of concave form and the axis of symmetry of which is off-center relative to that defined by the incident laser beam so as to focus the reflected light beam on the photodetector and prevent the reflected beam from reaching the laser source.

14. The device as claimed in claim 3, wherein the mirror is of concave form and the axis of symmetry of which is off-center relative to that defined by the incident laser beam so as to focus the reflected light beam on the photodetector and prevent the reflected beam from reaching the laser source.

15. The device as claimed in claim 4, wherein the mirror is of concave form and the axis of symmetry of which is off-center relative to that defined by the incident laser beam so as to focus the reflected light beam on the photodetector and prevent the reflected beam from reaching the laser source.

16. The device as claimed in claim 3, which comprises a third photodetector placed after the splitter so that a portion of the laser beam reaches said third photodetector without having passed through the gas cell.

17. The device as claimed in claim 3, which comprises a diaphragm placed between the splitter and the gas cell, this diaphragm reducing the size of the laser beam.

18. The device as claimed in claim 7, which comprises a diaphragm placed between the splitter and the gas cell, this diaphragm reducing the size of the laser beam.

19. The device as claimed in claim 3, which comprises a second diaphragm placed between the splitter and the gas cell, this diaphragm reducing the size of the laser beam.

20. The device as claimed in claim 7, which comprises a second diaphragm placed between the splitter and the gas cell, this diaphragm reducing the size of the laser beam.