CN103955130A - Differential detection device and method for coherent layout imprisoned magneto-optic effect - Google Patents

Abstract

The invention discloses a differential detection device for trapping magneto-optical effects in a coherent layout, comprising a bias coupler, a laser tube, a solenoid, an alkali metal atom vapor bubble, a polarization beam splitting crystal, a first photocell, and a second photocell. The invention also discloses a differential detection method for the magneto-optic effect of coherent layout trapping. The invention detects the laser signal after the interaction between the linearly polarized light and the atom in the magnetic field. Through this scheme, the laser signal related to the amplitude noise and frequency noise can be suppressed. The combined common-mode noise improves the signal-to-noise ratio of the signal, thereby improving the stability of the output frequency of the coherent population trapped atomic clock. The passive coherent layout trapped atomic clock realized by this scheme has the advantages of simple structure, low cost, and small volume, and is suitable for realizing small and micro atomic clocks. The invention also discloses a differential detection method for coherent layout trapping magneto-optic effect.

Description

Differential detection device and method for magneto-optical effect trapped in coherent layout

technical field

The invention relates to the field of passive coherent layout trapped atomic clocks, in particular to a differential detection device for a coherent layout trapped magneto-optical effect, and a differential detection method for a coherent layout trapped magneto-optic effect.

Background technique

Passive coherent layout captive atomic clock is an electronic device that outputs high-stability frequency signals. It has many characteristics such as small size, low power consumption, light weight, fast start-up, and miniaturization. Technical fields such as engineering measurement, communication, missile guidance and electronic instruments and equipment.

The working principle of the passive coherent layout trapped atomic clock is: two different frequency laser (dual-color laser) fields interact with a three-level atomic system composed of an excited state energy level and two ground state hyperfine energy levels. When the two-frequency laser of the two-color laser Satisfying the frequency of the transition from one ground state to the excited state respectively, and the difference between the two frequencies is strictly equal to the resonance frequency between the two ground state hyperfine energy levels of the atom, the two-color laser field can achieve a coherent layout trapping resonance with the atom, and the two atoms of the atom The ground state is prepared into a coherent superposition state, that is, a coherent structurally trapped state. Atoms in the coherent layout trapped state no longer absorb energy from the laser field, so when the two-color laser beam passing through the atomic medium satisfies the coherent layout trapped resonance condition, the transmitted light is stronger than the light intensity that does not satisfy the resonance condition (electromagnetically induced transparency phenomenon) . The passive coherent layout trapped atomic clock detects the transmitted laser light intensity, and uses the obtained electromagnetically induced transparent signal as a frequency discrimination signal to lock the output frequency of the atomic clock to the resonant frequency between the two ground state hyperfine energy levels of the atom.

The current popular passive coherent layout-confined atomic clock scheme is that the laser beam generated by the laser tube passes through the atomic vapor bubble and the atomic gas in the bubble to achieve coherent layout-confinement resonance, and the photodetector detects the transmitted laser beam to obtain a photoelectric signal. The photoelectric signal obtained by the detector contains the coherent layout trapping signal needed to lock the output frequency of the atomic clock. In addition, the detected signal also includes the absorption signal of atoms to single photons, as well as the laser frequency components that do not participate in the interaction of atoms. The noise corresponding to these signals includes: 1. Laser power noise; 2. Laser frequency noise through atoms to laser The amplitude noise of the absorption signal transformed by absorption; 3. The fluctuation of the atomic number density of the vapor bubble causes the slowly varying amplitude noise of the atomic absorption of the laser, etc. These noises associated with the laser amplitude noise and frequency noise, as well as the slowly changing noise caused by the fluctuation of the atomic number density to the light absorption change affect the signal-to-noise ratio of the coherent layout trapped signal, thereby affecting the frequency stability of the passive coherent layout trapped atomic clock .

The invention provides a device and method for improving the signal-to-noise ratio of obtained coherent layout trapping signals by suppressing noise through differential detection. the

Contents of the invention

The principle of linearly polarized light coherent structure confining magneto-optical rotation is: in a magnetic field environment, the left-handed and right-handed light components of linearly polarized light undergo different dispersion and absorption when they are confined in resonance with alkali metal atoms in a coherent structure. The polarization direction will be rotated after the interaction of neutral atoms.

A polarization beam-splitting crystal is placed behind the atomic vapor bubble. When the angle between the transmission polarization direction of the polarization beam-splitting crystal and the polarization direction of the incident line polarization is 45°, the absorption signal of atoms to single photons and the laser light not participating in the interaction of atoms The polarization of the frequency component does not change, and it is divided into two beams of laser light with equal power by the polarization beam splitting crystal. These signals cancel each other out when differentially detecting the magneto-optical rotation effect of linearly polarized light coherent layout, and the magneto-optical rotation signal whose polarization has rotated can be extracted, so in principle, the noise associated with laser amplitude noise and frequency noise and the gradual noise caused by the fluctuation of the atomic number density to the light absorption change can be greatly reduced. In addition, when parallel linearly polarized light interacts with alkali metal atoms, in addition to the magneto-optic rotation effect of the coherent structure confined resonance, there is also the magneto-optic rotation effect of alkali metal atoms on single-photon transitions. Theoretically, when the magnetic field is on the order of tens of μT, under the working conditions of the passive coherent structure trapped atomic clock, the amplitude of the magneto-optical rotation signal of the alkali metal atom to the single photon transition is smaller than that of the coherent structure trapped resonance. 3 orders of magnitude, and the magneto-optical rotation signal of the single-photon transition is Doppler broadened, so the influence of the magneto-optical rotation signal of the single-photon transition on the magneto-optical rotation signal of the linearly polarized light coherent layout we obtained can be ignored, The magneto-optic rotation signal we detected experimentally is mainly derived from the coherent layout trapped resonance between linearly polarized light and alkali metals.

The purpose of the present invention is to provide a differential detection device with a coherent layout that traps the magneto-optical effect. This device can not only suppress the laser power noise caused by the temperature of the laser tube, the driving current, and the input microwave power, but also suppress the laser frequency noise through the atomic The amplitude noise converted from the absorption spectrum and the noise of the laser absorption caused by the temperature change of the steam bubble can improve the signal-to-noise ratio of the coherent layout trapping signal, thereby improving the stability of the output frequency of the passive coherent layout trapping atomic clock. Moreover, the device has simple structure, low cost and small volume, and is suitable for small and miniature atomic clocks.

In order to achieve the above object, the present invention provides a differential detection device for trapping magneto-optical effects in a coherent layout. The device includes a bias coupler that couples microwave signals and DC signals into modulation signals, a laser tube driven by the modulation signal, Alkali metal atom vapor bubbles, polarizing beam splitting crystals and first photocells are arranged in sequence in the direction of the laser beam emitted by the tube, and a second photocell is arranged in the reflection direction of the polarizing beam splitting crystals, and the alkali metal atom vapor bubbles are placed in the solenoid . The buffer gas in the atomic steam bubble is an inert gas, the pressure is 3-5Torr, and the temperature is controlled at 40-60°C. The alkali metal atomic steam bubble is provided with an axial magnetic field of 5-15μT by the solenoid, and the outermost layer of the solenoid Magnetically shielded with high-permeability materials. The angle between the polarization direction of the laser emitted by the laser tube and the transmission polarization direction of the polarization beam splitting crystal is 45°, and the transmitted light is divided into two beams with equal power by the polarization beam splitting crystal. The first photocell is arranged in the transmission direction of the polarization beam splitting crystal, and the second photocell is arranged in the reflection direction of the polarization beam splitting crystal.

Correspondingly, the present invention also provides a differential detection method for coherent layout trapping magneto-optical effects, including:

Step 1. The microwave signal and the DC signal are coupled to each other through the bias coupler, and the coupled signal drives the laser tube to emit multi-color frequency linearly polarized light;

Step 2. In the magnetic field environment of 5-15uT, the multi-color FM linearly polarized laser beam interacts with the alkali metal atoms in the alkali metal atom vapor bubble to obtain the magneto-optical rotation effect;

Step 3. Divide the laser beam passing through the alkali metal atom vapor bubble into two beams with perpendicular polarization and equal power;

Step 4: detecting the optical power of the two laser beams respectively, and subtracting the optical power signals of the two laser beams to obtain the magneto-optical rotation signal trapped by the coherent layout of the linearly polarized light.

Compared with the current popular passive coherent layout trapped atomic clock scheme, the differential detection device of coherent layout trapping magneto-optic effect basically maintains the same volume, power consumption and cost, and can be applied to small and micro passive coherent layout trapped atomic clocks.

The present invention will become clearer through the following description in conjunction with the accompanying drawings, which are used to explain the embodiments of the present invention.

the

Description of drawings

Fig. 1 is a structural schematic diagram of the device of the present invention.

Fig. 2 is a comparison of the noise spectrum of the differential signal generated by the device of the present invention and the noise spectrum of a single photocell signal.

Fig. 3 is a flowchart of the method of the present invention.

In the figure: 1-bias coupler; 2-laser tube; 3-alkali metal atom vapor bubble; 4-polarization beam splitting crystal; 5-first photocell; 6-second photocell; 7-solenoid.

Detailed ways

Embodiments of the present invention will now be described with reference to the drawings, in which like reference numerals represent like elements.

As shown in Figure 1, the microwave signal and the DC signal pass through the bias coupler 1, the frequency range of the bias coupler should include the frequency of the input microwave, the coupled modulated signal drives the laser tube 2, and the laser emitted along the laser tube The outgoing direction of the beam is sequentially arranged with the alkali metal atom vapor bubble 3 , the polarizing beam splitting crystal 4 , the first photoelectric cell 5 and the second photoelectric cell 6 placed in the solenoid 7 . The angle between the polarization direction of the laser light emitted by the laser tube 2 and the transmission polarization direction of the polarization beam splitting crystal 4 is 45°, and the splitting into two beams with equal power is ensured by adjusting the polarization angle of the laser light emitted by the laser tube. The first photocell 5 is arranged in the transmission direction of the polarization beam splitting crystal, and the second photocell 6 is arranged in the reflection direction of the polarization beam splitter crystal 4. The first photocell 5 and the second photocell 6 can be selected from the S-25VL photocell of OSI Optoelectronics Company. The alkali metal atom vapor bubble 3 placed in the solenoid requires the solenoid 7 to provide an axial magnetic field of 5-15uT, and the outermost layer needs to be magnetically shielded with a material with high magnetic permeability to reduce the influence of stray magnetic fields, and the high magnetic The conductivity material can be Permalloy. The buffer gas in the atomic vapor bubble is inert gas or nitrogen, the pressure should be 3-5 Torr, and the temperature should be controlled at 40-60°C

Specifically, the polychromatic linearly polarized light driven by the laser tube 2 driven by the modulated signal coupled by the microwave signal and the DC signal through the bias coupler 1 interacts with the atoms to form a coherent layout trapped state, and in the axial direction provided by the solenoid Under a magnetic field environment, due to the magneto-optical rotation effect, the left-handed and right-handed components of linearly polarized light experience different dispersion and absorption when interacting with atoms. After passing through the alkali metal vapor bubble 3, the laser beam is divided into two laser beams with similar power by the polarization beam splitting crystal 4, which are respectively detected by the first photocell 5 and the second photocell 6, and the detection signals are subtracted to obtain linearly polarized light Coherent layout confinement Magneto-optical rotation signal.

Fig. 2 is a comparison of the noise spectrum of the differential signal generated by the device of the present invention and the noise spectrum of a single photocell signal. The gray line is the noise spectrum of a single photocell signal, and the black line is the noise spectrum of the differential signal produced by the device. In the frequency band of 0.1Hz-1kHz, the noise suppression of the latter is more than 20dB than that of the former, which proves that the present invention can indeed suppress the noise associated with Noise associated with laser amplitude noise and frequency noise, as well as ramp noise to light absorption changes caused by atomic number density fluctuations.

Fig. 3 is a flowchart of the method of the present invention.

The differential detection method of coherent layout trapping magneto-optic effect of the present invention comprises the following steps:

Step 1. The microwave signal and the DC signal are coupled to each other through the bias coupler, and the coupled signal drives the laser tube to emit multi-color frequency linearly polarized light;

Step 2. In the magnetic field environment of 5-15uT, the multi-color FM linearly polarized laser beam interacts with the alkali metal atoms in the alkali metal atom vapor bubble to obtain the magneto-optical rotation effect;

Step 3. Divide the laser beam passing through the alkali metal atom vapor bubble into two beams with perpendicular polarization and equal power;

Step 4: detecting the optical power of the two laser beams respectively, and subtracting the optical power signals of the two laser beams to obtain the magneto-optical rotation signal trapped by the coherent layout of the linearly polarized light.

The present invention has been described above in conjunction with the best embodiments, but the present invention is not limited to the above-disclosed embodiments, but should cover various modifications and equivalent combinations made according to the essence of the present invention.

Claims (5)

1. The differential detection device of coherent layout trapping magneto-optical effect is characterized in that it includes a bias coupler that couples microwave signals and DC signals into modulation signals, a laser tube driven by the modulation signal, and a laser beam emitted along the laser tube. Alkali metal atom vapor bubbles, polarization beam splitting crystals and first photocells are arranged in sequence in the outgoing direction, and a second photocell is arranged in the reflection direction of the polarization beam splitting crystals, and the alkali metal atom vapor bubbles are placed in the solenoid. 2. The differential detection device for coherent layout trapping magneto-optical effect according to claim 1, characterized in that the angle between the polarization direction of the laser light emitted by the laser tube and the transmission polarization direction of the polarization beam splitting crystal is 45°. 3. The differential detection device for coherent layout trapping magneto-optical effect according to claim 1, characterized in that, the buffer gas provided in the said alkali metal atom vapor bubble is an inert gas, the pressure is 3-5 Torr, and the temperature is controlled At 40-60°C, the alkali metal atom vapor bubble is provided with an axial magnetic field of 5-15μT by the solenoid, and the outermost layer of the solenoid is magnetically shielded by a material with high magnetic permeability. 4. Utilize the device described in claim 1 to carry out the differential detection method of coherent layout trapping magneto-optic effect, comprising: Step 1. The microwave signal and the DC signal are coupled to each other through the bias coupler, and the coupled signal drives the laser tube to emit multi-color frequency linearly polarized light; Step 2. In the magnetic field environment of 5-15uT, the multi-color FM linearly polarized laser beam interacts with the alkali metal atoms in the alkali metal atom vapor bubble to obtain the magneto-optical rotation effect; Step 3. Divide the laser beam passing through the alkali metal atom vapor bubble into two beams with perpendicular polarization and equal power; Step 4: detecting the optical power of the two laser beams respectively, and subtracting the optical power signals of the two laser beams to obtain the magneto-optical rotation signal trapped by the coherent layout of the linearly polarized light. 5. The differential detection method of coherent layout trapping magneto-optical effect according to claim 4, characterized in that, the buffer gas provided in the alkali metal atom vapor bubble is an inert gas, the pressure is 3-5 Torr, and the temperature is controlled at 40-60°C.