Rotational transition based clock, rotational spectroscopy cell, and method of making same

• US 9,529,334 B2
• Filed: 03/31/2015
• Issued: 12/27/2016
• Est. Priority Date: 03/31/2015
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Herbsommer, Juan Alejandro, Cook, Benjamin S., Nadeau, Phillip, Jacobs, Simon Joshua, Trombley, Django Earl
• Primary Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US14/674,197
• Publication Number:
  US 20160291549A1
• Time in Patent Office: 637 Days
• Field of Search: 331/3, 331/94.1
• US Class Current: 1/1
• CPC Class Codes: G01N 29/36 Detecting the response signal , e.g. electronic circuits specially adapted therefor
• CPC Class Codes: G01N 29/44 Processing the detected response signal , e.g. electronic circuits specially adapted therefor digital signal processing per se G06F17/00
• CPC Class Codes: G04F 5/14 using atomic clocks
• CPC Class Codes: G04F 5/145 using Coherent Population Trapping
• CPC Class Codes: H03L 7/26 using energy levels of molecules, atoms, or subatomic particles as a frequency reference

Abstract

Described examples include a millimeter wave atomic clock apparatus, chip scale vapor cell, and fabrication method in which a low pressure dipolar molecule gas is provided in a sealed cavity with a conductive interior surface forming a waveguide. Non-conductive apertures provide electromagnetic entrance to, and exit from, the cavity. Conductive coupling structures formed on an outer surface of the vapor cell near the respective non-conductive apertures couple an electromagnetic field to the interior of the cavity for interrogating the vapor cell using a transceiver circuit at a frequency that maximizes the rotational transition absorption of the dipolar molecule gas in the cavity to provide a reference clock signal for atomic clock or other applications.

Claims

1. A clock apparatus, comprising:

a vapor cell, including;

a cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity,

a dipolar molecule gas inside the sealed interior of the cavity,

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture, and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture; and

a transceiver circuit for providing an alternating electrical output signal to the first conductive coupling structure for coupling an electromagnetic field to the interior of the cavity, for receiving an alternating electrical input signal from the second conductive coupling structure representing the electromagnetic field received from the cavity, for selectively adjusting a frequency of the electrical output signal to reduce the electrical input signal, and for providing a reference clock signal at the frequency of the electrical output signal;

wherein the cavity extends along a non-linear axis from a first end to a second end, wherein the first non-conductive aperture is proximate the first end, and wherein the second non-conductive aperture is proximate the second end.

2. A clock apparatus, comprising:

a vapor cell, including;

a cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity,

a dipolar molecule gas inside the sealed interior of the cavity,

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture, and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture; and

a transceiver circuit for providing an alternating electrical output signal to the first conductive coupling structure for coupling an electromagnetic field to the interior of the cavity, for receiving an alternating electrical input signal from the second conductive coupling structure representing the electromagnetic field received from the cavity, for selectively adjusting a frequency of the electrical output signal to reduce the electrical input signal, and for providing a reference clock signal at the frequency of the electrical output signal;

wherein the cavity includes a third non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing another electromagnetic field entrance to the cavity, and a fourth non-conductive aperture spaced from the second non-conductive aperture in the interior cavity surface for providing another electromagnetic field exit from the cavity;

wherein the first conductive coupling structure is proximate the first and third non-conductive; and

wherein the second conductive coupling structure is proximate the second and fourth non-conductive apertures.

3. A clock apparatus, comprising:

a vapor cell, including;

a cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity,

a dipolar molecule gas inside the sealed interior of the cavity,

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture, and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture;

a transceiver circuit for providing an alternating electrical output signal to the first conductive coupling structure for coupling an electromagnetic field to the interior of the cavity, for receiving an alternating electrical input signal from the second conductive coupling structure representing the electromagnetic field received from the cavity, for selectively adjusting a frequency of the electrical output signal to reduce the electrical input signal, and for providing a reference clock signal at the frequency of the electrical output signal; and

at least one conductive electronic bandgap structure formed on the outer surface of the vapor cell spaced from and between the first and second conductive coupling structures for attenuating electromagnetic wave coupling along the outer surface of the vapor cell.

4. A clock apparatus, comprising:

a vapor cell, including;

a cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity,

a dipolar molecule gas inside the sealed interior of the cavity,

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture, and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture; and

a transceiver circuit for providing an alternating electrical output signal to the first conductive coupling structure for coupling an electromagnetic field to the interior of the cavity, for receiving an alternating electrical input signal from the second conductive coupling structure representing the electromagnetic field received from the cavity, for selectively adjusting a frequency of the electrical output signal to reduce the electrical input signal, and for providing a reference clock signal at the frequency of the electrical output signal;

wherein the transceiver circuit includes;

a signal generator with an output electrically coupled with the first conductive coupling structure for providing the alternating electrical output signal to the first conductive coupling structure and for providing the reference clock signal at the frequency of the electrical output signal;

a lock-in amplifier with an input electrically coupled with the second conductive coupling structure for receiving the alternating electrical input signal and providing an error signal representing a difference between the electrical input signal and the electrical output signal; and

a loop filter for receiving the error signal and providing a control output signal to the signal generator for selectively adjusting the frequency of the electrical output signal to maintain the frequency of the electrical output signal at a peak absorption frequency of the dipolar molecule gas inside the sealed interior of the cavity.

5. A clock apparatus, comprising:

a vapor cell, including;

a cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity,

a dipolar molecule gas inside the sealed interior of the cavity,

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture, and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture; and

a transceiver circuit for providing an alternating electrical output signal to the first conductive coupling structure for coupling an electromagnetic field to the interior of the cavity, for receiving an alternating electrical input signal from the second conductive coupling structure representing the electromagnetic field received from the cavity, for selectively adjusting a frequency of the electrical output signal to reduce the electrical input signal, and for providing a reference clock signal at the frequency of the electrical output signal;

wherein the vapor cell includes;

a first substrate including a first side, at least one cavity sidewall extending inward of the first side, and a cavity bottom; and

a second substrate including a first side and a second side including a cavity top, the second side of the second substrate mounted to the first side of the first substrate to form the cavity including the sealed interior with the conductive interior cavity surface extending at least partially along the at least one cavity sidewall, the cavity bottom, and the second side of the second substrate;

wherein the first and second non-conductive apertures are formed in the interior cavity surface on the second side of the second substrate for providing the electromagnetic field entrance and exit, respectively; and

wherein the first and second conductive coupling structures are formed on the first side of the second substrate.

6. A clock apparatus, comprising:

a vapor cell, including;

a cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity,

a dipolar molecule gas inside the sealed interior of the cavity,

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture, and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture; and

a transceiver circuit for providing an alternating electrical output signal to the first conductive coupling structure for coupling an electromagnetic field to the interior of the cavity, for receiving an alternating electrical input signal from the second conductive coupling structure representing the electromagnetic field received from the cavity, for selectively adjusting a frequency of the electrical output signal to reduce the electrical input signal, and for providing a reference clock signal at the frequency of the electrical output signal;

wherein the dipolar molecule gas is at a pressure of approximately 1 mbar or less inside the sealed interior of the cavity.

7. The clock apparatus of claim 6, wherein the dipolar molecule gas is at a pressure of approximately 0.1 mbar or less inside the sealed interior of the cavity;

and wherein the dipolar molecule gas is at a pressure of approximately 0.01 mbar or more inside the sealed interior of the cavity.

8. A clock apparatus, comprising:

a vapor cell, including;

a cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity,

a dipolar molecule gas inside the sealed interior of the cavity,

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture, and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture; and

a transceiver circuit for providing an alternating electrical output signal to the first conductive coupling structure for coupling an electromagnetic field to the interior of the cavity, for receiving an alternating electrical input signal from the second conductive coupling structure representing the electromagnetic field received from the cavity, for selectively adjusting a frequency of the electrical output signal to reduce the electrical input signal, and for providing a reference clock signal at the frequency of the electrical output signal;

wherein the conductive interior cavity surface is plated with a metal material extending at least partially along the at least one cavity sidewall, the cavity bottom, and the second side of the second substrate, the metal material having a thickness greater than a skin depth at the frequency of the electrical output signal.

9. A vapor cell, comprising:

a cavity formed in at least one substrate, the cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity;

a dipolar molecule gas inside the sealed interior of the cavity;

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture; and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture;

wherein the cavity extends along a non-linear axis from a first end to a second end, wherein the first non-conductive aperture is proximate the first end, and wherein the second non-conductive aperture is proximate the second end.

10. A vapor cell, comprising:

a cavity formed in at least one substrate, the cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity;

a dipolar molecule gas inside the sealed interior of the cavity;

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture; and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture;

wherein the cavity includes a third non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing another electromagnetic field entrance to the cavity, and a fourth non-conductive aperture spaced from the second non-conductive aperture in the interior cavity surface for providing another electromagnetic field exit from the cavity;

wherein the first conductive coupling structure is proximate the first and third non-conductive apertures; and

wherein the second conductive coupling structure is proximate the second and fourth non-conductive apertures.

11. A vapor cell, comprising:

a cavity formed in at least one substrate, the cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity;

a dipolar molecule gas inside the sealed interior of the cavity;

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture;

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture; and

at least one conductive electronic bandgap structure formed on the outer surface of the vapor cell spaced from and between the first and second conductive coupling structures for attenuating electromagnetic wave coupling along the outer surface of the vapor cell.

12. A vapor cell, comprising:

a cavity formed in at least one substrate, the cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity;

a dipolar molecule gas inside the sealed interior of the cavity;

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture;

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture;

a first substrate including a first side, at least one cavity sidewall extending inward of the first side, and a cavity bottom; and

a second substrate including a first side and a second side including a cavity top, the second side of the second substrate mounted to the first side of the first substrate to form the cavity including the sealed interior with the conductive interior cavity surface extending at least partially along the at least one cavity sidewall, the cavity bottom, and the second side of the second substrate;

wherein the first and second non-conductive apertures are formed in the interior cavity surface on the second side of the second substrate for providing the electromagnetic field entrance and exit, respectively; and

wherein the first and second conductive coupling structures are formed on the first side of the second substrate.

13. A vapor cell, comprising:

a cavity formed in at least one substrate, the cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity;

a dipolar molecule gas inside the sealed interior of the cavity;

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture; and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture;

wherein the dipolar molecule gas is at a pressure of approximately 1 mbar or less inside the sealed interior of the cavity.

14. The vapor cell of claim 13, wherein the dipolar molecule gas is at a pressure of approximately 0.1 mbar or less inside the sealed interior of the cavity;

and wherein the dipolar molecule gas is at a pressure of approximately 0.01 mbar or more inside the sealed interior of the cavity.

15. A vapor cell, comprising:

a cavity formed in at least one substrate, the cavity including a sealed interior with a conductive interior cavity surface, a first non-conductive aperture in the interior cavity surface for providing an electromagnetic field entrance to the cavity, and a second non-conductive aperture spaced from the first non-conductive aperture in the interior cavity surface for providing an electromagnetic field exit from the cavity;

a dipolar molecule gas inside the sealed interior of the cavity;

a first conductive coupling structure formed on an outer surface of the vapor cell proximate the first non-conductive aperture; and

a second conductive coupling structure formed on the outer surface of the vapor cell proximate the second non-conductive aperture;

wherein the conductive interior cavity surface is plated with a metal material having a thickness greater than a skin depth at the frequency of the electrical output signal.