CN108008531B - raman laser optical path matching system based on Mach-Zehnder interferometer - Google Patents
raman laser optical path matching system based on Mach-Zehnder interferometer Download PDFInfo
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Abstract
The invention discloses a Raman laser optical path matching system based on a Mach-Zehnder interferometer, which utilizes the Mach-Zehnder interferometer of an optical fiber to realize optical path matching between two beams of laser in a phase feedback loop, so that the phase feedback loop is consistent with phase noise detected by an atomic group and coming from a laser light source, and the influence of the phase noise of the laser on the Raman laser can be inhibited through the feedback loop.
Description
Technical Field
The invention relates to a Raman laser optical path matching system based on a Mach-Zehnder interferometer, and belongs to the technical field of cold atom gravimeters.
background
The raman laser is two laser beams having a fixed frequency difference and phase difference used for a cold atom gravimeter, and phase noise of beat frequencies of the two laser beams is referred to as phase noise of the raman laser. The cold atom gravimeter can carry out high-precision measurement on gravitational acceleration, gravitational gradient and the like based on the interference effect of matter waves. Ultra-high precision cold atom gravimeters require raman lasers with ultra-low phase noise.
One method is to use two independent lasers to generate two beams of laser, and lock their beat frequency to the output signal of a super-stable crystal oscillator by means of optical phase-locked loop, thereby realizing Raman laser with low phase noise. Another method is to use only one laser and split its output laser into two beams by a beam splitter, where one beam is frequency shifted by an electro-optical modulator driven by a super-stable crystal oscillator to generate two beams with a certain frequency difference. Then, the beat frequencies of the two laser beams are locked to the super-stable crystal oscillator through a phase feedback system so as to suppress noise caused by a laser light source, vibration, temperature change and the like.
there are two modes of operation of the cold atom gravimeter. One is a velocity insensitive mode in which the two laser beams that act on the atomic group have the same propagation direction, and therefore the doppler shifts of the two laser beams due to the falling velocity of the atom are almost the same in magnitude and cancel each other. As a result, the falling speed of the atoms and the velocity distribution of the atomic group itself have little influence on the measurement accuracy of the gravimeter. However, since the two laser beams have the same direction, the direction of photons absorbed and emitted by the atoms is the same, so that the total momentum obtained by the atoms is small. The result is that there is little separation of excited and unexcited atoms in momentum space, resulting in a low sensitivity of the gravimeter.
The other is a velocity sensitive mode in which the two lasers acting on the radicals travel in opposite directions, and the doppler shifts of the two lasers due to the falling velocity of the atoms are almost the same in magnitude but opposite in sign. Therefore, the frequency of one laser needs to be adjusted during operation to counteract the effect of the doppler shift. However, since the two laser beams are opposite in direction, the directions of photons absorbed and emitted by the atoms are also opposite, and thus the total momentum gained by the atoms is large. The result is a large separation of excited and unexcited atoms in momentum space, resulting in a high sensitivity of the gravimeter.
typical cold atom gravimeters use a velocity sensitive mode. In order to realize two laser beams with opposite transmission directions, the two laser beams are generally transmitted through the atomic group in the same direction, and then are reflected perpendicularly by using a mirror and pass through the atomic group again. The laser light interacting with the atoms is the initial one and the reflected other. In this process, the reflected laser light may experience additional optical paths, and the phase jitter accumulated by the laser during its experience of these additional optical paths may deteriorate the phase noise of the raman laser light. Also, since the extra optical path does not occur in the phase feedback loop, the phase noise cannot be suppressed by the phase feedback loop. Finally, the inherent noise of the atomic gravimeter is increased, and the measurement accuracy is reduced.
Disclosure of Invention
the invention aims to solve the problems and provides a Raman laser optical path matching system based on a Mach-Zehnder interferometer, which utilizes the Mach-Zehnder interferometer with one optical fiber to realize optical path matching between two beams of laser in a phase feedback loop, so that the phase feedback loop is consistent with phase noise detected by atomic groups and coming from a laser light source, and the influence of the phase noise of the laser on the Raman laser can be inhibited through the feedback loop.
A Raman laser optical path matching system based on a Mach-Zehnder interferometer comprises a laser source, a first 1/2 lambda plate, a first polarization splitting prism, an electro-optic modulator, a first 45-degree reflector, a Fabry-Perot etalon, a second 1/2 lambda plate, a second 45-degree reflector, a third 1/2 lambda plate, a second polarization splitting prism, a first optical fiber coupler, a first polarization maintaining optical fiber, an optical fiber collimator, a laser beam splitter, an acousto-optic modulator, a laser beam expander, a first 1/4 lambda plate, a first atomic group, a second 1/4 lambda plate, a zero degree reflector, a second optical fiber coupler, an optical fiber polarization beam splitter, a second polarization maintaining optical fiber, a third polarization maintaining optical fiber, a high-speed optical switch, a fourth polarization maintaining optical fiber, a fifth polarization maintaining optical fiber, a Y waveguide, an optical fiber polarization beam combiner, a high-speed photoelectric detector, a photoelectric detector, Feedback circuitry.
laser light source output laser enters a first polarization beam splitter prism after passing through a first 1/2 lambda plate, and the first polarization beam splitter prism divides the input laser into transmission laser and reflection laser. The transmission laser which penetrates through the first polarization beam splitter prism enters the electro-optical modulator, and the output laser of the electro-optical modulator consists of a carrier, a required first-order modulation sideband and a high-order modulation sideband. The output laser of the electro-optical modulator is reflected by the first 45-degree reflector and enters the Fabry-Perot etalon, the Fabry-Perot etalon filters redundant laser frequency components, and the output laser is a required first-order modulation sideband. The output laser of the Fabry-Perot etalon is reflected by the second polarization beam splitter prism after passing through the second 1/2 lambda plate, and the reflected laser is input into the first optical fiber coupler; the laser reflected by the first polarization beam splitter prism is reflected by the second 45-degree reflector and then passes through the third 1/2 lambda plate, and the output laser of the third 1/2 lambda plate passes through the second polarization beam splitter prism and then is input into the first optical fiber coupler. The output end of the first optical fiber coupler is connected with the optical fiber collimator through the first polarization maintaining optical fiber, the output laser of the optical fiber collimator enters the laser beam splitter, and the laser beam splitter divides the input laser into the reflected laser with larger power and the transmission laser with smaller power. The reflected laser enters an acousto-optic modulator, and the acousto-optic modulator is used as a high-speed optical pulse modulator to generate required pulse laser. The output laser of the acousto-optic modulator enters a laser beam expander, the output laser of the laser beam expander passes through a first 1/4 lambda wave plate, a first atomic group, a second atomic group and a second 1/4 lambda wave plate in sequence, is reflected by a zero-degree reflector, and then passes through a second 1/4 lambda wave plate, the second atomic group and the first atomic group in sequence; the transmission laser enters the second optical fiber coupler, the output end of the second optical fiber coupler is connected with the input end of the optical fiber polarization beam splitter, and the left output end of the optical fiber polarization beam combiner is connected with the left input end of the optical fiber polarization beam combiner through the second polarization-maintaining optical fiber. The right output end of the optical fiber polarization beam combiner is connected with the input end of the high-speed optical switch through a third polarization-maintaining optical fiber, and the left output end and the right output end of the high-speed optical switch are respectively connected with the left input end and the right input end of the Y waveguide through a fourth polarization-maintaining optical fiber and a fifth polarization-maintaining optical fiber. The output end of the Y waveguide is connected with the right input end of the optical fiber polarization beam combiner, and the output laser of the optical fiber polarization beam combiner enters the high-speed photoelectric detector. The output end of the high-speed photoelectric detector is connected with the input end of the feedback circuit system, and the output end of the feedback circuit system is connected with the modulation signal input end of the electro-optical modulator.
in a typical raman laser system, in order to eliminate the influence of the laser light source, vibration, temperature, and the like on the phase noise, the phase difference between two laser beams is generally locked to a super-stable crystal oscillator through a phase-locked loop. The optimal scheme is that the phase difference between the atom and the two laser beams detected by the photoelectric detector is completely consistent, so that the phase noise of the Raman laser is completely determined by the phase noise of the super-stable crystal oscillator and the performance of the phase-locked loop. However, a cold atom gravimeter operating in a speed sensitive mode necessarily generates an extra optical path because a certain laser beam undergoes a vertical reflection process; and because the atomic group interacts with the Raman laser twice at the highest point and the lowest point, the extra optical path length has two fixed values. Since the laser light source has phase noise, the extra optical path may cause the phase noise of the laser light source not to cancel each other and thus to be transmitted to the phase noise of the raman laser. For this reason, it is necessary to make an optical path difference between the two laser beams received by the photodetector equal to the extra optical path due to the vertical reflection. And the optical path difference is variable, so that the atomic groups can realize optical path matching at the highest point and the lowest point. At this time, the phase noise detected by the photodetector coincides with the phase noise felt by the radical, so that suppression of the phase noise can be achieved by the feedback circuit system.
the input end of the interferometer separates two input laser beams through the optical fiber polarization beam splitter and then respectively enters two arms of the interferometer, and the right arm of the interferometer can realize rapid switching between two lengths through the micromechanical optical switch. The matching of the optical path difference caused by vertical reflection is realized by setting the optical fiber length difference between the right arm and the left arm, and then the phase noise from the laser source is suppressed by utilizing the phase feedback loop, so that the influence of the phase noise of the laser source on the measurement accuracy of the cold atom gravimeter is suppressed.
the invention has the advantages that:
(1) the optical path matching system of the all-fiber is realized, and the influence of the phase noise of the laser light source on the cold atom gravimeter is inhibited;
(2) The optical path matching is realized by using the optical fiber optical path, and the extra phase noise introduced by the optical fiber optical path matching is very low;
Drawings
FIG. 1 is a block diagram of a Raman laser optical path matching system based on a Mach-Zehnder interferometer;
FIG. 2 is a schematic diagram of optical path matching;
FIG. 3 is a schematic timing diagram of a top-throwing atomic gravimeter;
in the figure:
1-laser light source 2-first 1/2 lambda plate 3-first polarization beam splitter prism
4-electro-optical modulator 5-first 45 degree mirror 6-Fabry-Perot etalon
7-second 1/2 lambda plate 8-second 45 deg. mirror 9-third 1/2 lambda plate
10-second polarization beam splitter prism 11-first optical fiber coupler 12-first polarization maintaining optical fiber
13-optical fiber collimator 14-laser beam splitter 15-acousto-optic modulator
16-laser beam expander 17-first 1/4 lambda plate 18-first radical
19-second radical 20-second 1/4 lambda plate 21-zero degree mirror
22-second optical fiber coupler 23-optical fiber polarization beam splitter 24-second polarization maintaining optical fiber
25-third polarization maintaining fiber 26-high speed optical switch 27-fourth polarization maintaining fiber
28-fifth polarization maintaining optical fiber 29-Y waveguide 30-optical fiber polarization beam combiner
31-high speed photodetector 32-feedback circuitry
Detailed Description
The present invention will be described in further detail below with reference to the accompanying drawings.
A Raman laser optical path matching system based on a Mach-Zehnder interferometer comprises a laser light source 1, a first 1/2 lambda plate 2, a first polarization splitting prism 3, an electro-optic modulator 4, a first 45-degree reflector 5, a Fabry-Perot etalon 6, a second 1/2 lambda plate 7, a second 45-degree reflector 8, a third 1/2 lambda plate 9, a second polarization splitting prism 10, a first optical fiber coupler 11, a first polarization maintaining fiber 12, an optical fiber collimator 13, a laser beam splitter 14, an acousto-optic modulator 15, a laser beam expander 16, a first 1/4 lambda plate 17, a first atomic group 18, a second atomic group 19, a second 1/4 lambda plate 20, a zero-degree reflector 21, a second optical fiber coupler 22, an optical fiber polarization beam splitter 23, a second polarization maintaining optical fiber 24, a third polarization maintaining optical fiber 25, a high-speed optical switch 26, a third polarization maintaining optical fiber 25, a third polarization maintaining optical fiber, a second optical fiber, a third polarization, A fourth polarization maintaining optical fiber 27, a fifth polarization maintaining optical fiber 28, a Y waveguide 29, an optical fiber polarization beam combiner 30, a high-speed photoelectric detector 31 and a feedback circuit system 32;
Laser light source 1 output laser enters first polarization beam splitter prism 3 after passing through first 1/2 lambda plate 2, and first polarization beam splitter prism 3 divides input laser into transmission laser and reflection laser. The laser light which passes through the first polarization beam splitter prism 3 enters the electro-optical modulator 4, and the output laser light of the electro-optical modulator 4 consists of a carrier, a required first-order modulation sideband and a high-order modulation sideband. The output laser of the electro-optical modulator 4 is reflected by the first 45-degree reflecting mirror 5 and enters the Fabry-Perot etalon 6, the Fabry-Perot etalon 6 filters redundant laser frequency components, and the output laser is a required first-order modulation sideband. The output laser of the Fabry-Perot etalon 6 is reflected by the second polarization beam splitter prism 10 after passing through the second 1/2 lambda plate 7, and the reflected laser is input to the first optical fiber coupler 11; the laser light reflected by the first polarization beam splitter prism 3 is reflected by the second 45 ° mirror 8 and then passes through the third 1/2 λ -plate 9, and the output laser light of the third 1/2 λ -plate 9 passes through the second polarization beam splitter prism 10 and then is input to the first fiber coupler 11. The output end of the first optical fiber coupler 11 is connected with an optical fiber collimator 13 through a first polarization maintaining fiber 12, the output laser of the optical fiber collimator 13 enters a laser beam splitter 14, and the laser beam splitter 14 divides the input laser into a reflected laser with larger power and a transmitted laser with smaller power. The reflected laser beam enters the acousto-optic modulator 15, and the acousto-optic modulator 15 is used as a high-speed optical switch to generate the required pulse laser beam. The output laser of the acousto-optic modulator 15 enters a laser beam expander 16, the output laser of the laser beam expander 16 passes through a first 1/4 lambda plate 17, a first atomic group 18, a second atomic group 19 and a second 1/4 lambda plate 20 in sequence, is reflected by a zero-degree reflector 21, and then passes through a second 1/4 lambda plate 20, the second atomic group 19 and the first atomic group 19 in sequence; the transmission laser enters the second optical fiber coupler 22, the output end of the second optical fiber coupler 22 is connected to the input end of the optical fiber polarization beam splitter 23, and the left output end of the optical fiber polarization beam splitter 23 is connected to the left input end of the optical fiber polarization beam combiner 30 through the second polarization maintaining optical fiber 24. The right output end of the fiber polarization beam splitter 23 is connected with the input end of a high-speed optical switch 26 through a third polarization maintaining fiber 25, and the left and right output ends of the high-speed optical switch 26 are connected with the left and right input ends of a Y waveguide 29 through a fourth polarization maintaining fiber 27 and a fifth polarization maintaining fiber 28, respectively. The output end of the Y waveguide 29 is connected to the right input end of the optical fiber polarization beam combiner 30, and the output laser of the optical fiber polarization beam combiner 30 enters the high-speed photodetector 31. The output terminal of the high-speed photodetector 31 is connected to the input terminal of the feedback circuit system 32, and the output terminal of the feedback circuit system 32 is connected to the modulation signal input terminal of the electro-optical modulator 4.
The working process is as follows:
A Raman laser optical path matching system based on a Mach-Zehnder interferometer, the frequency of output laser of a laser light source is omega, the EOM modulation frequency is omega m, assuming that a modulated laser (represented by L up in FIG. 2) excites atoms from bottom to top at time t, an unmodulated laser (represented by L down in FIG. 2) excites atoms from top to bottom after vertical reflection, an extra optical path caused by the vertical reflection is delta L, the optical path difference of the two lasers before beam expansion is ignored, and only the influence of phase noise of the laser light source is considered, then the two lasers interacting with the atoms at the same time can be respectively represented as:
Where E 1 and E 2 are the amplitudes of the laser light exciting the atom from bottom to top and from top to bottom, respectively, phi 0 (t) is the phase jitter of the laser light source, which is a random variable, and τ 0 ═ Δ L/c is the time delay caused by vertical reflection, and c is the speed of light, then the phase difference between the two laser lights felt by the atom is:
ΔΦ(t)＝ωmt+ωτ0+φ0(t)-φ0(t-τ0) (3)
0 0 0 0 0On the other hand, the error term can be fed back to the phase of a certain laser beam through a feedback system to realize real-time tracking compensation of the error term, wherein, firstly, a photoelectric detector is used for detecting beat frequencies of the two laser beams, then the beat frequency signal is subjected to frequency discrimination and phase discrimination with a reference frequency source, the phase error signal is extracted, and then the phase error signal is fed back to a modulation signal of an EOM through a feedback circuit to change the phase of the upper laser beam and eliminate the phase error.
here, the aforementioned L up is used as the reference laser, where E 1 ', E 2' are the amplitudes of the two laser beams received by the photodetector, τ 1 is the time difference between the modulated laser beam reaching the photodetector through the left arm of the fiber mach-zehnder interferometer and the reference laser, and τ 2 is the time difference between the unmodulated laser beam reaching the photodetector through the right arm of the fiber mach-zehnder interferometer and the reference laser, then the phase difference between the two laser beams sensed by the detector is:
ΔΦ′(t)＝ωm(t-τ1)+ω(τ1-τ2)+φ0(t-τ1)-φ0(t-τ2) (6)
Where Δ Φ' is the phase difference between the two laser beams sensed by the detector, ω m t is eliminated during the frequency discrimination, the constant phase term is not considered, and only Φ 0 (t- τ 1) - Φ 0 (t- τ 2) are concerned, in order to make the feedback phase error signal consistent with the phase error sensed by the atom, τ 1 is 0 and τ 2 is τ 0, which requires careful design of the lengths of the two arms of the fiber mach-zehnder interferometer and their optical path difference, which is equal to the optical path length of the unmodulated laser beam due to vertical reflection, considering that the atomic group interacts with the laser beams at the upper and lower two positions respectively, and the switching of the two optical path differences of the fiber mach-zehnder interferometer can be realized by switching the high-speed optical switch, specifically, the fiber-mach-zehnder interferometer is configured as shown in fig. 2, and the lengths of the two arms should satisfy the following formula:
La＝L0+2ΔLa (7)
Lb＝L0+2ΔLb (8)
Wherein, L 0 is the optical path of the left arm of the optical fiber mach-zehnder interferometer, L a and L b are the optical paths of the right arm of the optical fiber mach-zehnder interferometer when the high-speed optical switch is switched on at the left side and the right side respectively, and Δ L a and Δ L b are the distances between the atomic group and the zero-degree mirror when the atomic group is at the highest point and the lowest point respectively.
If the feedback loop gain is K in the frequency band of interest, the phase error term remaining after feedback is approximately:
Where φ r is the residual phase error, the residual phase error is determined only by the loop gain.
Claims (2)
1. A Raman laser optical path matching system based on a Mach-Zehnder interferometer comprises a laser source, a first 1/2 lambda plate, a first polarization splitting prism, an electro-optic modulator, a first 45-degree reflector, a Fabry-Perot etalon, a second 1/2 lambda plate, a second 45-degree reflector, a third 1/2 lambda plate, a second polarization splitting prism, a first optical fiber coupler, a first polarization maintaining optical fiber, an optical fiber collimator, a laser beam splitter, an acousto-optic modulator, a laser beam expander, a first 1/4 lambda plate, a first atomic group, a second 1/4 lambda plate, a zero degree reflector, a second optical fiber coupler, an optical fiber polarization beam splitter, a second polarization maintaining optical fiber, a third polarization maintaining optical fiber, a high-speed optical switch, a fourth polarization maintaining optical fiber, a fifth polarization maintaining optical fiber, a Y waveguide, an optical fiber polarization beam combiner, a high-speed photoelectric detector, a photoelectric detector, Feedback circuitry;
Laser output by the laser source passes through a first 1/2 lambda wave plate and then enters a first polarization beam splitter prism, and the first polarization beam splitter prism divides the input laser into transmission laser and reflection laser; the laser which penetrates through the first polarization beam splitter prism enters an electro-optic modulator, and the output laser of the electro-optic modulator consists of a carrier, a required first-order modulation sideband and a high-order modulation sideband; the output laser of the electro-optical modulator is reflected by a first 45-degree reflector and then enters a Fabry-Perot etalon, the Fabry-Perot etalon filters redundant laser frequency components, and the output laser is a required first-order modulation sideband; the output laser of the Fabry-Perot etalon is reflected by the second polarization beam splitter prism after passing through the second 1/2 lambda plate, and the reflected laser is input into the first optical fiber coupler; the laser reflected by the first polarization beam splitter prism is reflected by the second 45-degree reflector and then transmits through the third 1/2 lambda plate, and the output laser of the third 1/2 lambda plate is input into the first optical fiber coupler after transmitting through the second polarization beam splitter prism; the output end of the first optical fiber coupler is connected with an optical fiber collimator through a first polarization maintaining optical fiber, output laser of the optical fiber collimator enters a laser beam splitter, and the laser beam splitter divides input laser into reflected laser and transmitted laser; the reflected laser enters an acousto-optic modulator which is used as a high-speed optical switch to generate required pulse laser; the output laser of the acousto-optic modulator enters a laser beam expander, the output laser of the laser beam expander passes through a first 1/4 lambda wave plate, a first atomic group, a second atomic group and a second 1/4 lambda wave plate in sequence, is reflected by a zero-degree reflector, and then passes through a second 1/4 lambda wave plate, the second atomic group and the first atomic group in sequence; the transmission laser enters a second optical fiber coupler, the output end of the second optical fiber coupler is connected with the input end of an optical fiber polarization beam splitter, and the left output end of the optical fiber polarization beam splitter is connected with the left input end of an optical fiber polarization beam combiner through a second polarization-maintaining optical fiber; the right output end of the optical fiber polarization beam splitter is connected with the input end of the high-speed optical switch through a third polarization-maintaining optical fiber, and the left and right output ends of the high-speed optical switch are respectively connected with the left and right input ends of the Y waveguide through a fourth polarization-maintaining optical fiber and a fifth polarization-maintaining optical fiber; the output end of the Y waveguide is connected with the right input end of the optical fiber polarization beam combiner, and the output laser of the optical fiber polarization beam combiner enters the high-speed photoelectric detector; the output end of the high-speed photoelectric detector is connected with the input end of the feedback circuit system, and the output end of the feedback circuit system is connected with the modulation signal input end of the electro-optical modulator.
2. A Raman laser optical path matching system based on Mach-Zehnder interferometer according to claim 1, wherein the frequency of the output laser of the laser light source is omega, the EOM modulation frequency is omega m, assuming that the modulated laser excites atoms from bottom to top at time t, and the unmodulated laser excites atoms from top to bottom after vertical reflection, the extra optical path caused by the vertical reflection is represented as DeltaL, and considering only the influence of the phase noise of the laser light source, the two beams of laser light interacting with the atoms at the same time are respectively represented as:
Wherein E 1 and E 2 are the amplitudes of the laser for exciting the atoms from bottom to top and from top to bottom respectively, phi 0 (t) is the phase jitter of the laser light source, tau 0 is the time delay caused by vertical reflection, c is the speed of light, and the phase difference of the two lasers sensed by the atoms is as follows:
ΔΦ(t)＝ωmt+ωτ0+φ0(t)-φ0(t-τ0) (3)
0 0 0Firstly, using a photoelectric detector to detect the beat frequency of the two laser beams, then carrying out frequency discrimination and phase discrimination on the beat frequency signal and a reference frequency source, extracting phase error signals of the two laser beams, and then feeding the phase error signals of the two laser beams back to a modulation signal of an EOM (electro-optical modulator) through a feedback circuit, thereby changing the phase of the laser beam on the upper path and realizing the elimination of the phase error;
specifically, at the same time as the atom, the phases of the two beams of laser light received by the photodetector are respectively:
Let L up be reference laser, E '1 and E' 2 be amplitudes of two laser beams received by a photoelectric detector respectively, τ 1 is a time difference between modulated laser beams reaching the photoelectric detector through a left arm of an optical fiber Mach-Zehnder interferometer and the reference laser beams, τ 2 is a time difference between unmodulated laser beams reaching the photoelectric detector through a right arm of the optical fiber Mach-Zehnder interferometer and the reference laser beams, and a phase difference between the two laser beams sensed by the detector is:
ΔΦ′(t)＝ωm(t-τ1)+ω(τ1-τ2)+φ0(t-τ1)-φ0(t-τ2) (6)
wherein, Δ Φ' is the phase difference of the two laser beams sensed by the detector, and ω m t is eliminated in the frequency discrimination process;
Switching the optical path difference between the optical fiber Mach-Zehnder interferometers by switching the high-speed optical switch so that τ 1 is equal to 0 and τ 2 is equal to τ 0, specifically, the lengths of the two arms of the optical fiber Mach-Zehnder interferometer should satisfy the following formula:
La＝L0+2ΔLa (7)
Lb＝L0+2ΔLb (8)
Wherein, L 0 is the optical path of the left arm of the optical fiber Mach-Zehnder interferometer, L a and L b are the optical paths of the right arm of the optical fiber Mach-Zehnder interferometer when the high-speed optical switch is conducted on the left side and on the right side respectively, and Δ L a and Δ L b are the distances between the atomic groups at the highest point and the lowest point and the zero-degree reflector respectively;
If the feedback loop gain is K in the frequency band of interest, the phase error term remaining after feedback is approximately:
where φ r is the residual phase error, and the residual phase error is determined by the loop gain only.
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| CN103401135A (en) * | 2013-08-02 | 2013-11-20 | 北京工业大学 | Method and device for amplifying laser by adopting raman frequency conversion |
| CN103701022A (en) * | 2013-12-19 | 2014-04-02 | 北京工业大学 | Double-resonant-cavity all-optical-fiber mode-locked pulse laser |
| CN104298045A (en) * | 2014-08-19 | 2015-01-21 | 北京航空航天大学 | Raman laser system and optical path difference automatic adjusting method based on frequency modulation continuous wave |
| CN104682187A (en) * | 2015-03-09 | 2015-06-03 | 北京航空航天大学 | Automatic compensation device of phase noise of Raman laser system based on closed loop feedback and method thereof |
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