Oscillators – Molecular or particle resonant type
Reexamination Certificate
2002-09-27
2004-11-02
Kinkead, Arnold (Department: 2817)
Oscillators
Molecular or particle resonant type
C331S003000, C332S176000, C332S176000, C332S176000
Reexamination Certificate
active
06812800
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an atomic oscillator, and in particular to a passive-type atomic oscillator of an optical pumping system.
Recently, digital networking of information has been advanced, whereby a clock source with high accuracy/high stability becomes indispensable. While an atomic oscillator such as a rubidium atomic oscillator draws attention as the clock source, downsizing/slimming is expected for mounting form on a system.
2. Description of the Related Art
FIG. 7
schematically shows a rubidium atomic oscillator having a light-microwave resonator as known in the prior art.
This atomic oscillator is composed of a pumping light source
16
, a cylindrical cavity resonator
40
having light passage holes (apertures)
15
a
and
15
b
for receiving a pumping light from the light source
16
, a doughnut-shaped dielectric
41
contained in the resonator for downsizing the cavity resonator
40
, a gas cell
42
for enclosing rubidium atoms further contained in the dielectric
41
, a light detector
14
for detecting the pumping light passing through the gas cell
42
, a frequency control circuit
17
for detecting the output of the light detector
14
and for obtaining a fixed frequency, an antenna
43
for inputting a microwave from the frequency control circuit
17
and for exiting the microwave within the cavity resonator
40
, a tuning screw
44
for tuning the resonance frequency of the cavity resonator
40
to the resonance frequency of the rubidium atom, a temperature control circuit
19
for keeping a temperature fixed by detecting the temperature of the gas cell
42
with a thermal element
21
such as a thermistor and by controlling a current which flows through a heater resistor
18
, and a transistor
20
controlled by the temperature control circuit
19
.
In operation, when the microwave cavity resonator
40
is excited with 6834.682 . . . MHz that is the resonance frequency of the rubidium atom from the frequency control circuit
17
through the antenna
43
, the rubidium atoms within the gas cell
42
absorb the light received from the pumping light source
16
. This phenomenon can be confirmed by the output decrease of the light detector
14
.
Accordingly, the frequency control circuit
17
controls the above-mentioned microwave frequency excited by the microwave cavity resonator
40
to the microwave frequency by which the output of the light detector
14
decreases, whereby an output signal of a frequency with high stability synchronized with the resonance frequency of the rubidium atom can be obtained.
In such a prior art example, the cavity resonator
40
easily available has been used since the dielectric
41
containing the gas cell
42
is required to be provided within the resonator
40
. In order to realize downsizing the cavity resonator
40
, various attempts have been made, and devices such as a change of an accessible resonance mode and a high dielectric material charge have been performed.
In the prior art example shown in
FIG. 7
, by using a basic mode of the cylindrical cavity resonator TE
111
, and by having a built-in alumina ceramic dielectric
41
, the cavity resonator
40
of 16 mm in diameter and 25 mm in length is realized. By utilizing this cavity resonator
40
, a rubidium atomic oscillator of 23 mm (95 cc) in thickness (height) is on the market.
However, the market demands further downsizing and cost-reduction. It is difficult for the atomic oscillator using the prior art cavity resonator as mentioned above to meet the market demands as follows:
In order to meet the market demands, a microwave resonator which is substituted for the cavity resonator requiring a large space is necessary. As one example, a rubidium atomic oscillator (18 mm in thickness) using “half coaxial resonator” has begun to be offered from foreign manufacturers.
However, since a mechanism accuracy of this half coaxial resonator directly influences the resonance frequency, it is natural that a frequency adjustment mechanism should be added. For this reason, the structure of the mechanism becomes complicated and the price becomes expensive.
Also, the adjustment of the resonance frequency is necessary, and the cost increases in proportion to adjustment man-hours etc. Furthermore, in order to excite the resonator, a mechanical antenna or a probe becomes necessary, so that the mechanism becomes complicated even in this point, which causes a cost increase.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide an inexpensive atomic oscillator of an optical pumping system, enabling downsizing, and excluding resonance frequency adjustments, antenna, and probe.
FIG. 1
is a diagram showing an electromagnetic field distribution in a well-known slot line. A metal conductor
2
is formed (metallized) on a high dielectric substrate
1
. If the metal conductor
2
is peeled (removed) by a certain slit to form a slot line
3
, electric fields concentrate on the edge of the metal conductor
2
of the ground potential so that a transmission line is formed. The electromagnetic field distribution forms a magnetic field line
4
and an electric field line
5
, which forms a mode similar to a basic mode of a square waveguide, TE
10
.
On the other hand, a microstrip line is frequently used in a circuit of a microwave band. This is because a line section structure is simple, and also, since the ground conductor is arranged on the backside of the dielectric in which much of the electromagnetic field is distributed inside, a distribution characteristic becomes small, a passage loss is little, and a crosstalk or the like is relatively little so that the integration is easy.
A microwave resonator using such a microstrip line has been already realized. However, since it is characterized in that the magnetic field does not influence the outside as mentioned above, the application thereof to the atomic oscillator is difficult.
On the contrary, the electromagnetic field of the slot line is distributed in a wide area as mentioned above, and has a feature that the dispersion characteristic is large. This means that the passage loss is large, and unnecessary coupling of a crosstalk or the like is required to be prevented, so that it is difficult to use the slot line for a transmission line.
However, from another viewpoint, “applications of atomic oscillator to microwave resonator”, there are found many advantages in the slot line as follows:
{circle around (1)} “Dispersion characteristic is large”→Magnetic coupling with atoms is easy.
{circle around (2)} “TE wave”→Since only the distribution of the magnetic field exists along a line axis (direction of propagation), it becomes possible to widely secure an optical pumping area.
{circle around (3)} “Making MMIC (or MMICization) is easy”→Since a resonance frequency is basically determined by the length of the slot line, it is possible to make the resonance frequency adjustment-free.
{circle around (4)} “Coupling with a different kind of line is easy”→Since coupling with a microstrip line or the like is easy, MMICization including an input/output coupling circuit can be easily realized.
In the present invention, a resonator using a slot line as a microwave resonator is arranged in the portion where atoms are excited, thereby enabling an atomic oscillator downsized/slimmed, and low-cost, not requiring a resonance frequency adjustment to be realized.
FIG. 2
shows an arrangement of a resonator using a slot line. In this slot line resonator
10
, an upper surface of the dielectric substrate
1
is preferably metallized with the metal conductor
2
. The surface of the metal conductor
2
is peeled to form the slot line
3
of e.g. “W” in width and &lgr;
s
/2 in length. It is to be noted that &lgr;
s
indicates 1 wavelength corresponding to a resonance frequency 6834.682 . . . MHz of e.g. the rubidium atom calculated from an rms dielectric constant on the slot line.
Also, a microstrip line
6
passing through the center of the slot line
3
Atsumi Ken
Koyama Yoshito
Matsuura Hideyuki
Sakai Minoru
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Kinkead Arnold
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