CN103454902A

CN103454902A - Atomic clock

Info

Publication number: CN103454902A
Application number: CN2013102524628A
Authority: CN
Inventors: 乔东海; 季磊
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2013-06-24
Filing date: 2013-06-24
Publication date: 2013-12-18
Anticipated expiration: 2033-06-24
Also published as: CN103454902B

Abstract

The invention discloses an atomic clock comprising an electronic system and a physical package. The physical package comprises a laser, a conversion optical path, a 1/4th wave plate, an alkali atomic bulb gas chamber and a photoelectric detector. The atomic clock is characterized in that the conversion optical path includes a four-port fiber coupler, four optical fibers connected with the fiber coupler, a self-focusing lens and a reflection enhancement film; the output end of the laser is connected with the first optical fiber, the second optical fiber is connected to the self-focusing lens, and the third optical fiber is connected with the photoelectric detector; the reflection enhancement film is arranged on the emergent side of the alkali atomic bulb gas chamber and reflects outgoing light back to the alkali atomic bulb gas chamber. The atomic clock has the advantages that the laser and the photoelectric detector are far away from the alkali atomic bulb gas chamber and experience less influence from temperature and magnetic field, and the atomic clock is more stable.

Description

A kind of atomic clock

Technical field

The present invention relates to a kind of atomic clock, belong to frequency standard device field.

Background technology

The developing history of atomic clock can be traced back to before and after World War II the earliest, and it mainly has benefited from the fast development of quantum mechanics and microwave spectroscopy at that time.What early stage microwave clock was used is that incoherent light source is done pumping and surveyed light, and along with the development of laser instrument, Laser Coherent and detection method are applied in atomic clock research, have obtained better effect thereafter.

Along with the develop rapidly of electronic technology and control technology, for the research of atomic clock, mainly concentrate on two aspects: be to explore development accuracy and the higher atomic clock of degree of stability on the one hand.In recent years, many different types of possess the more New type atom clock of pin-point accuracy and degree of stability, such as Cold atomic fountain clock, ion trap clock, light clock etc. have successfully been developed; The approach that realizes high-precision mini engineering atomic clock of actively finding on the other hand, to meet various engineering development needs, for example develop small-sized satellite atomic clock, utilize Coherent Population Trapping imprison principle to develop Miniaturized Coherent Population Trapping imprison (CPT, Coherent Population Trapping) atomic clock.

The Coherent Population Trapping imprison is a kind of quantum interference phenomenon that atom and coherent light interaction produce, utilize the coherence that laser is good, prepare Coherent Population Trapping imprison state in atom system, the novel C PT atomic clock of the chip type that can realize, this is the cutting edge technology of current atomic clock field and navigation field.Its advantage is: on the one hand, do not need microwave cavity, can obviously reduce volume; On the other hand, adopt the relevant bi-coloured light of laser instrument preparation that is subject to the microwave frequency modulation, can reduce optical frequency shift.Although the CPT atomic clock proposed so far time soon from 1998, its development rapidly, has demonstrated superior performance, and also has larger room for improvement.

In prior art, the CPT atomic clock comprises electronic system and physical package, wherein, physical package consists of laser instrument, conversion light path, quarter wave plate, alkaline atom bubble air chamber and photodetector usually, the laser that laser instrument sends becomes directional light by the conversion light path converting, enter alkaline atom bubble air chamber after quarter wave plate forms the entelechy polarized light, finally received by photoconductive detector.Wherein, the conversion light path is generally lens combination.

The performance index of estimating atomic clock are mainly Alan's variances.According to the definition of Alan's variance, the performance of known atomic clock depends primarily on the contrast of absorption line.

In practice, general CPT desktop experimental system is only pursued the aspect of commissioning, does not consider the problem of volume and power consumption, and miniature and even chip-scale CPT atomic clock is focused on the minimizing of volume and power consumption really very much, but inconvenient commissioning.Up to the present realize that CPT atomic clock index is not very high, being mainly manifested in temperature, to float phenomenon more serious, and temperature control causes power consumption larger, and atomic clock stable output signal degree is very low.Its main cause is, in prior art, each part mentioned above is packaged together, and because alkaline atom bubble air chamber remains under the working temperature of 70～90 ℃ usually, laser instrument and photodetector and the close together that alkaline atom steeps air chamber, can be subject to the impact of its temperature,

Therefore, need to reduce temperature and float phenomenon by the improvement of structure, thereby reduce the error of atomic clock.

Summary of the invention

Goal of the invention of the present invention is to provide a kind of atomic clock, by architecture advances, reduces the impact of temperature on atomic clock.

To achieve the above object of the invention, the technical solution used in the present invention is: a kind of atomic clock, by electronic system and physical package, formed, and described physical package comprises laser instrument, conversion light path, quarter wave plate, alkaline atom bubble air chamber and photodetector; Described conversion light path comprises four fiber port coupling mechanisms, four optical fiber, GRIN Lens being connected with fiber coupler and increases anti-film, and the output terminal of described laser instrument connects the first optical fiber, and the second optical fiber connects GRIN Lens, and the 3rd optical fiber connects photodetector; Describedly increase the exiting side that anti-film is positioned at alkaline atom bubble air chamber, emergent light is reflected back to alkaline atom bubble air chamber.

In technique scheme, described laser instrument is for take the direct band-gap semicondictor material as gain of light medium, tie injected carrier by pn and realize population inversion, take Fabry-Perot-type cavity or distribution bragg grating is resonator cavity, the diode laser that carries out the stimulated emission light amplification.

Described four fiber port coupling mechanisms are 2 * 2 single-mode optical-fibre couplers.

Described GRIN Lens is the lens pillar that inner refractive index distributes and radially reduces gradually.

The described thickness that increases anti-film equals 1/4th optical maser wavelengths.

Further technical scheme, be provided with the second photodetector, and described the second photodetector connects the 4th optical fiber.

Preferred technical scheme is that described alkaline atom bubble air chamber is arranged in different individual packages from described laser instrument, photodetector.

In technique scheme, described electronic system comprises phase-locked loop, electrically controlled attenuator, micro control system and analog-digital chip, in order to wavelength and the frequency of controlling laser instrument.

It is example that the alkaline atom bubble air chamber of take adopts the caesium chamber, and principle of work of the present invention is explained as follows: laser instrument sends laser, and the 4.596GHz microwave signal of phase-locked loop generation is modulated on the left and right sideband of laser, and Ear Mucosa Treated by He Ne Laser Irradiation is on the caesium chamber; 2 * 2 fiber couplers, between laser instrument and caesium chamber, are attached thereto four optical fiber that have that connect.Wherein the second optical fiber is connected with GRIN Lens, places a quarter-wave plate after GRIN Lens, laser beam is transformed into to circularly polarized light and is irradiated into the caesium chamber; Connect behind the caesium chamber and increase anti-film, light path, through increasing anti-film reflection, enters fiber coupler again, and by the 3rd optical fiber output; Connect photodetector at output port, photodetector is converted to current signal by light signal, and by the micro control system extraction process, micro control system will further produce control signal, until whole atomic clock system is in the lock state.

Further in technical scheme, at the 4th fiber port of fiber coupler, connect the second photodetector, be used for the incident intensity of detecting laser.

In such scheme, the Laser Modulation mode adopts the half-band width modulation, be that the RF modulating frequency equals differential half of two Ground State Energies, it is poor that the difference of first sideband frequency of left and right just equals the hyperfine energy level splitting of ground state, by these two single order sideband pump excitations, realizes CPT resonance.This modulator approach is defined as the half-breadth modulation.

Because technique scheme is used, the present invention compared with prior art has following advantages:

1, the present invention is by arranging the fiber coupler of four ports, arrange and increase anti-film simultaneously, laser instrument is connected with fiber coupler respectively with photodetector, can be so that laser instrument and photodetector, away from alkaline atom bubble air chamber, reduce the impact on it of temperature and magnetic field.

2, owing to adopting optical fiber and fiber coupler to form the conversion light path, can reduce the loss of light.

3, increase the setting of anti-film, on the one hand photodetector can be connected on fiber coupler together with laser instrument, by being reflected again, emergent light enters alkaline atom bubble air chamber on the other hand, can increase light path, make light follow the action time of caesium atom or rubidium atom elongated, improve the degree of stability of atomic clock.

4, the setting of the second photodetector, incident intensity that can detecting laser, in order to observe in time the light intensity of laser change.

The accompanying drawing explanation

Fig. 1 is embodiment Central Plains secondary clock overall system diagram.

Fig. 2 is phase-locked loop system block diagram in embodiment.

Fig. 3 is the laser aligner index path that in embodiment, GRIN Lens and optical fiber form.

Fig. 4 is caesium in the atomic clock physical package/rubidium chamber atmo energy level transition figure.

Fig. 5 is embodiment intermediate ring road filter circuit figure.

Embodiment

Below in conjunction with drawings and Examples, the invention will be further described:

Embodiment 1:

As shown in Figure 1, a kind of atomic clock with GRIN Lens, mainly comprise laser instrument 170, fiber coupler 120 and be attached thereto four optical fiber 121,122,123,124 that connect, GRIN Lens 130, quarter-wave plate 140, caesium chamber 150, increase anti-film 160, photodetector 110 and the second photodetector 180, phase-locked loop 200, electrically controlled attenuator 300, micro control system 500, digital to

analog converter

400 and 600 parts.Wherein laser instrument 170, fiber coupler 120 and be attached thereto four optical fiber 121,122,123,124 that connect, GRIN Lens 130, quarter-wave plate 140, caesium chamber 150, increase anti-film 160, photodetector 110 and the second photodetector 180 form the physical package 100 of atomic clock of the present invention.

The principle of work of whole system: at first micro control system 500 carries out initialization to phase-locked loop 200, make phase-locked loop lock onto that on the frequency of atom hyperfine levels transition, (used herein is the half-band width modulation, the frequency that phase-locked loop produces is 4.596GHz), the hyperfine energy level difference of caesium atom is 9.2GHz, the electric current that micro control system 500 enters electrically controlled attenuator 300 by control is controlled the microwave power that enters physical package 100, makes the CPT harmonic peak reach maximum.Judge that whether harmonic peak reaches the most direct maximum method is the current signal that extracts physical encapsulation interior lights electric explorer feeds back, after the phase-locked amplifying circuit in periphery, error signal is fed back to micro control system 500, now 500 pairs of phase-locked loops 200 of micro control system adjustment of programming, the electric current of laser instrument is regulated simultaneously, until system CPT harmonic peak reaches maximum, make the whole system locking.

As shown in Figure 2, the phase-locked loop arrived 200 involved in the present invention, mainly comprise temperature compensating crystal oscillator 210, frequency synthesizer 220, third order PLL path filter 230, voltage controlled oscillator 240.The groundwork mode is as follows: temperature compensating crystal oscillator 210 provides benchmark 10MHz frequency, initialized frequency synthesizer 220 is the fractional frequency division frequency multiplier, carry out frequency and phase discrimination generation error current according to the frequency after voltage controlled oscillator 240 feedback signal frequency divisions and reference frequency, pass through again the charge pump output error signal to voltage controlled oscillator, until phase-locked loop system locks onto (4.596GHz) on needed frequency.Wherein loop filter 230 is even more important, and it will affect the phase noise of radio frequency output, so the design of loop filter 230 is very important, physical circuit designs as shown in Figure 5.

As shown in Figure 3, involved in the present invention to collimating apparatus mainly comprise optical fiber 300, GRIN Lens 310.The function of GRIN Lens 310 is to obtain needed parallel beam, will be re-aggregated in fiber coupler 120 and from optical fiber 122 and output to photodetector 110 from increasing light that anti-film 160 reflects simultaneously.

As shown in Figure 4, under the effect of low-intensity magnetic field, the caesium atomic energy level splits into hyperfine energy level, and for caesium, this energy level difference is 9.2GHz.What the present invention relates to is semi-wave modulated, and the frequency that peripheral radio frequency loop produces equals 4.596GHz.Through ovennodulation, laser will produce two sidebands, and the difference on the frequency of these two sidebands is just in time 9.2GHz, and now the caesium atom will be trapped on hyperfine energy level, will no longer absorb light, and peak value will appear in the light intensity that now shines photodetector.For the rubidium element, the energy level difference that is hyperfine energy level is different, and the energy level difference of rubidium is 6.8GHz.

Claims

1. an atomic clock, by electronic system and physical package, formed, described physical package comprises laser instrument, conversion light path, quarter wave plate, alkaline atom bubble air chamber and photodetector, it is characterized in that: described conversion light path comprises four fiber port coupling mechanisms, four optical fiber, GRIN Lens being connected with fiber coupler and increases anti-film, the output terminal of described laser instrument connects the first optical fiber, the second optical fiber connects GRIN Lens, and the 3rd optical fiber connects photodetector; Describedly increase the exiting side that anti-film is positioned at alkaline atom bubble air chamber, emergent light is reflected back to alkaline atom bubble air chamber.

2. atomic clock according to claim 1, it is characterized in that: described laser instrument is for take the direct band-gap semicondictor material as gain of light medium, tie injected carrier by pn and realize population inversion, take Fabry-Perot-type cavity or distribution bragg grating is resonator cavity, the diode laser that carries out the stimulated emission light amplification.

3. atomic clock according to claim 1, it is characterized in that: described four fiber port coupling mechanisms are 2 * 2 single-mode optical-fibre couplers.

4. atomic clock according to claim 1 is characterized in that: described GRIN Lens is the lens pillar that inner refractive index distributes and radially reduces gradually.

5. atomic clock according to claim 1, it is characterized in that: the described thickness that increases anti-film equals 1/4th optical maser wavelengths.

6. atomic clock according to claim 1, is characterized in that: be provided with the second photodetector, described the second photodetector connection the 4th optical fiber.

7. according to the described atomic clock of claim 1 or 6, it is characterized in that: described alkaline atom bubble air chamber is arranged in different individual packages from described laser instrument, photodetector.