JPH04265017A - Rubidium atom oscillator - Google Patents

Abstract

PURPOSE:To obtain an LD exciting type rubidium atom oscillator of having higher stability by improving the ratio of a level of a resonance signal for detecting a photodetector and a noise level, and detecting the phase inversion point of an exacter resonance signal. CONSTITUTION:Light from a laser diode LD 1 is split into spectral components by a spectral means 5. Subsequently, one is inputted to a light/microwave resonance part 2 and the resonance signal of an output of a first photodetector 3 is inputted to a differential amplifier 7. On the other hand, the other is inputted to a second photodetector 6, and an output is inputted to the amplifier 7. The output of the amplifier 7 decreases a noise and is inputted to a control electronic circuit 4. In such a manner, the ratio of the level of a resonance signal and the level of a noise is improved, and the LD exciting type rubidium atom oscillator having higher stability can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in rubidium atomic oscillators used in fields such as communications, navigation, and broadcasting.

As for the rubidium atomic oscillator, if a laser diode (hereinafter referred to as LD) pumping type is used instead of a lamp pumping type, the coherence of the light source becomes higher and a rubidium atomic oscillator that is more stable than the conventional one can be obtained. Although an LD-excited rubidium atomic oscillator has been developed, it is desired to provide an even more stable rubidium atomic oscillator.

0003

2. Description of the Related Art FIG. 3 is a block diagram of a conventional LD-excited rubidium atomic oscillator. In FIG. 3, the output frequency of the voltage-controlled crystal oscillator 10 of the control electronic circuit 4 is modulated by the output signal of the low-frequency oscillator 17 in the modulator 11, and the modulated signal is multiplied and synthesized in the frequency synthesizer 12. It is added to the light/microwave resonance part 2, and the L
The coherent pumping light of rubidium-87 with a wavelength of 0.78 microns from D1 is the optical/microwave resonance part 2.
The resonant signal obtained by inputting and pumping the transmitted light and detecting the change in the amount of transmitted light with the photodetector 3 is selectively amplified by the selective amplifier 14, synchronously detected by the synchronous detector 15, and then the integrator 16 The integrated voltage is integrated by the voltage controlled crystal oscillator 1.
By adding 0, the frequency of the microwave output from the frequency synthesizer 12 is controlled to always match the transition frequency of rubidium atoms.

Of course, the temperature and flowing current of the LD 1 are controlled to provide a stable light source. In this way, a highly stable rubidium atomic oscillator is obtained.

[0005]

However, in order to obtain an even more stable rubidium atomic oscillator, the ratio between the level of the resonance signal detected by the photodetector 3 and the noise level of the photodetector 3 must be improved. It is necessary to detect the phase inversion point of the resonance signal more accurately.

Possible sources of noise in the photodetector 3 include optical shot noise, noise of the photodetecting element, thermal noise of the amplifier circuit, etc., but optical shot noise is dominant. However, since a certain amount of light intensity is required to obtain a resonance signal, optical shot noise cannot be avoided, and there is a problem that it is impossible to achieve higher stability.

The object of the present invention is to provide a more stable LD-excited rubidium atomic oscillator.

[0008]

[Means for Solving the Problems] FIG. 1 is a block diagram of the principle of the present invention. As shown in FIG. 1, pumping light from an LD 1 that outputs light with a wavelength of 0.87 μm is input to an optical/microwave resonator 2, and a first photodetector 3 detects a change in the amount of pumping light. In the rubidium atomic oscillator, which inputs the resonance signal to the control electronic circuit 4 and generates a microwave equal to the transition frequency of the rubidium atom and inputs it to the optical/microwave resonator 2, the light from the LD 1 is transmitted to the spectroscopic means 5. One side is input to the optical/microwave resonator 2 and the resonance signal output from the first photodetector 3 is input to the differential amplifier 7, and the other side is input to the second photodetector 6. and its output is input to the differential amplifier 7, and the output of the differential amplifier 7 is input to the control electronic circuit 4.

[0009]

[Operation] In the present invention, the output of the first photodetector 3 is the sum of the resonance signal A and the optical shot noise B, that is, A+B, and the output of the second photodetector 6 is the optical shot noise C. In addition, since the output light of the LD 1 has high coherence, the phases of the optical shot noises B and C are approximately equal, and the output of the differential amplifier 7 becomes A+B-C, resulting in a reduction in noise.

[0010] Then, the ratio between the level of the resonance signal detected by the photodetector 3 and the noise level of the photodetector 3 is improved, so that a more accurate phase inversion point of the resonance signal can be detected, resulting in higher stability. A LD-excited rubidium atomic oscillator can be obtained.

[0011]

Embodiment FIG. 2 is a block diagram of an LD-excited rubidium atomic oscillator according to an embodiment of the present invention.

The difference between FIG. 2 and the conventional example shown in FIG. 3 is that LD1
The outputs of the two are separated, one is inputted to the photodetector 6, the outputs of the photodetectors 3 and 6 are added to the differential amplifier 7, and the output is inputted to the control electronic circuit 4. , this different point will be mainly explained below.

In FIG. 2, the coherent pumping light of rubidium-87 with a wavelength of 0.78 microns from the LD 1 is separated by a half mirror 5-1, and one is added to the optical/microwave resonator 2 and pumped. The sum of the resonance signal A obtained by detecting the change in the amount of pumping light with the photodetector 3 and the optical shot noise B of the photodetector 3 is applied to one input terminal of the differential amplifier 7, and the half mirror 5-1 is added to one input terminal of the differential amplifier 7. The other part of the spectrum is changed direction by a prism 5-2 and inputted to a photodetector 6.
The output optical noise C is applied to the other input terminal of the differential amplifier 7, and the output of the differential amplifier 7 is input to the control electronic circuit 4.

In this case, since the output light of the LD 1 has high coherence, the phases of the optical shot noises B and C of the photodetectors 3 and 6 are approximately equal, so that the output of the differential amplifier 7 has optical shot noises B and C of the optical detectors 3 and 6. This means that the noise of the photodetector 3 has been reduced by the difference in C, and the ratio between the level of the resonance signal and the noise level of the photodetector 3 has improved, making it possible to more accurately detect the phase inversion point of the resonance signal. Therefore, a more stable LD-excited rubidium atomic oscillator can be obtained.

[0015]

Effects of the Invention As explained in detail above, according to the present invention, the noise of the photodetector 3 is reduced, and the ratio between the level of the resonance signal and the noise level of the photodetector 3 is improved. Since it becomes possible to accurately detect the phase inversion point of the resonance signal, there is an effect that a more stable LD-excited rubidium atomic oscillator can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the principle of the present invention.

FIG. 2 is a block diagram of an LD-excited rubidium atomic oscillator according to an embodiment of the present invention;

FIG. 3 is a block diagram of a conventional LD-excited rubidium atomic oscillator.

[Explanation of symbols]

1 is a laser diode, 2 is an optical/microwave resonance part, 3 and 6 are photodetectors; 4 is a control electronic circuit; 5 is a spectroscopic means; 5-1 is a half mirror, 5-2 is a prism, 7 is a differential amplifier, 10 is a voltage controlled crystal oscillator; 11 is a modulator; 12 is a frequency synthesizer; 14 is a selection amplifier; 15 is a synchronous detector; 16 is an integrator, 17 indicates a low frequency oscillator.

Claims (1)

[Claims] [Claim 1] Pumping light from a laser diode (1) that outputs light with a wavelength of 0.87 μm is input to an optical/microwave resonator (2), and is detected by a first photodetector (3). Changes in the amount of pumping light are detected and a resonance signal is input to the control electronic circuit (4), which generates microwaves equal to the transition frequency of rubidium atoms and activates the optical/microwave resonator (
In the rubidium atomic oscillator input to 2), the light from the laser diode (1) is separated into spectra by the spectrometer (5), and one is input to the optical/microwave resonator (2) and the first A differential amplifier (
7), the other is input to the second photodetector (6), and the output is input to the differential amplifier (7);
A rubidium atomic oscillator, characterized in that the output of the control electronic circuit (4) is inputted to the control electronic circuit (4).