Device for simultaneously eliminating noise of optical fibers of multiple optical paths
By designing a device including a laser source, beam splitter, polarization beam splitter prism, optical fiber path, photodetector and phase lock circuit module, the problem of complexity of optical fiber noise cancellation for multiple optical paths in the prior art is solved, efficient and concise fiber noise cancellation is achieved, and the integration of the optical path and the utilization rate of optical components are improved.
Patent Information
- Application Number
- CN202510175338.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-18
- Publication Date
- 2025-05-30
AI Technical Summary
The existing optical fiber noise cancellation optical path construction method is complex, and it is difficult to achieve simultaneous noise cancellation of multiple optical paths, resulting in high complexity, poor integration, and low utilization rate of optical components.
A device including a laser source, a beam splitter, a polarization beam splitter, a fiber optical path, a photodetector and a phase lock circuit module is designed. By processing light-frequency-beating and phase locking circuits of the beam-combining signal light and reference light, the optical fiber noise cancellation of multiple optical paths is achieved.
The optical fiber noise cancellation of multiple optical paths is achieved simultaneously, which simplifies the experimental optical path, improves the simplicity, compactness and integration of the optical path, reduces the use of optical components and optical losses, and reduces manufacturing costs and space occupancy.
Smart Images
Figure CN120074671A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of fiber optic noise cancellation, and particularly relates to a device for simultaneously canceling fiber optic noise in multiple optical paths. Background Art
[0002] In recent years, due to the increasing maturity of cold atom physics and laser technology, optical frequency standards based on narrow linewidth transitions of atoms and ions have achieved rapid development, and their uncertainty has reached 10 --18 or even 10 -19 order of magnitude. High-precision optical frequency standards are widely used in frontier basic physics research and applied technology research, including relativity tests, precise geodetic measurements, searching for dark matter and gravitational waves, timekeeping and navigation, etc. Uncertainty, stability, and reproducibility are the main technical parameters for measuring the performance of an optical frequency standard at present. In order to improve the stability index of the optical frequency standard, it is very important to develop a super-narrow linewidth clock transition laser with high stability. The PDH frequency stabilization technology is currently the most effective way and the main general technology to achieve a sub-hertz order super-narrow linewidth laser. The PDH frequency stabilization technology references the frequency of the laser to be stabilized on a high-finesse Fabry-Perot (F-P) cavity, and compresses its linewidth through a modulation signal and servo feedback, thereby obtaining a narrower linewidth clock transition spectrum line. The ultra-stable clock laser as a local oscillator is the key to improving the stability of the optical clock. In most experimental scenarios, the local oscillator, as an independent module, usually needs to be interconnected with the equipment to be used, involving the transmission of the laser. The transmission of the laser usually includes the transmission of free-space light and the transmission through optical fibers. The fiber optic transmission has been widely used because it is not restricted by space and region. The highly stable and narrow linewidth laser obtained after frequency stabilization is transmitted to multiple experimental platforms such as the optical clock physical system, optical frequency comb, and transmission cavity frequency stabilization module through optical fibers. In addition, in many practical applications, long-distance optical frequency transmission is also required without affecting the original laser frequency stability. However, during the high-precision frequency transmission process, the refractive index and equivalent length of the optical fiber will be affected by environmental factors, including pressure, temperature, vibration, etc., thus generating phase noise. The phase noise introduced by the optical fiber itself will cause the broadening of the laser spectrum, reduce the transmission accuracy of the optical frequency, and lead to a decrease in the laser frequency stability. Therefore, in order to ensure the high-precision transmission of the laser frequency, corresponding fiber optic noise cancellation is required for each fiber optic transmission process.
[0003] The principle of fiber optic noise cancellation is to make the laser frequency signal at the source end transmit back and forth twice in the optical fiber, beat with the reference signal at the source end, and use a photodetector to detect the beat signal of the two beams of light. After beating, the phase noise introduced during fiber optic transmission is obtained. A phase compensation device is used to compensate the fiber optic phase noise of the laser, thereby achieving high-quality transmission of the optical frequency signal. For the optical path setup of fiber optic noise cancellation, while ensuring good noise cancellation effect, the optical path should be made as simple and easy to operate as possible, reducing the use of optical components and the loss caused by light during propagation. Simplifying the experimental optical path is of great significance for improving experimental efficiency and saving experimental resources. However, the existing optical path setup methods based on fiber optic noise cancellation have limitations. Especially for fiber optic noise cancellation of multiple optical paths, it is necessary to set up the fiber optic noise cancellation part on each optical path, resulting in a complex optical path, low integration, and high loss due to multiple propagations of light in multiple optical components, which is not conducive to improving the feasibility of optical path setup and the utilization rate of optical components. From the perspective of commercial and practical applications, a simple and highly integrated fiber optic noise cancellation optical path saves R & D costs, minimizes the use of optical components under the condition of ensuring experimental results, and is more conducive to the industrialization and practical application of the system. Summary of the Invention
[0004] The purpose of the present invention is to provide a device that can simultaneously cancel fiber optic noise for multiple optical paths in view of the above problems existing in the prior art.
[0005] The above object of the present invention is achieved by the following technical means:
[0006] A device for simultaneously canceling fiber optic noise for multiple optical paths includes a laser source, a first beam splitter, a second polarization beam splitter prism, a first fiber optic path, a second fiber optic path, a photodetector, and a phase-locked loop circuit module. The laser source outputs the original laser, and the original laser is input into the first beam splitter. The first beam splitter splits the original laser into a reference light and a signal light. The reference light returns to the first beam splitter after passing through a first quarter-wave plate, a first mirror, and a first quarter-wave plate in sequence. The signal light passes through a second half-wave plate and a second polarization beam splitter prism in sequence. The second polarization beam splitter prism splits the signal light into a first signal light and a second signal light. The first signal light is input into the first fiber optic path, and the first fiber optic path reflects the first frequency-modulated signal light back to the second polarization beam splitter prism. The second signal light is input into the second fiber optic path, and the second fiber optic path reflects the second frequency-modulated signal light back to the second polarization beam splitter prism. The second polarization beam splitter prism combines the first frequency-modulated signal light and the second frequency-modulated signal light into a combined signal light, and the combined signal light passes through a second half-wave plate and a first beam splitter in sequence.
[0007] The combined signal light and the reference light converge at the first beam splitter. After convergence, the combined signal light and the reference light sequentially pass through the fourth mirror and the convex lens and then are focused onto the detection end face of the photodetector. The photodetector performs optical beat frequency on the combined signal light and the reference light to obtain a first mixed electrical signal. The first mixed electrical signal is input into the phase-locked circuit module. The phase-locked circuit module outputs a first fiber optic noise signal to the first fiber optic light path. The first fiber optic light path eliminates noise from the first signal light according to the first fiber optic noise signal; the phase-locked circuit module outputs a second fiber optic noise signal to the second fiber optic light path. The second fiber optic light path eliminates noise from the second signal light according to the second fiber optic noise signal.
[0008] As described above, the phase-locked circuit module includes a power amplifier, a mixer, a power splitter, a first filter, a second filter, a first signal generator, a second signal generator, and a third signal generator. The first signal generator outputs a first mixing signal referenced to the hydrogen clock frequency. The first mixed electrical signal is amplified by the power amplifier and then input into the mixer together with the first mixing signal for mixing to obtain a second mixed electrical signal. The mixer inputs the second mixed electrical signal into the power splitter. The power splitter divides the second mixed electrical signal into two parts. One part of the second mixed electrical signal is input into the first filter for filtering to obtain a first down-converted signal. The other part of the second mixed electrical signal is input into the second filter for filtering to obtain a second down-converted signal;
[0009] The first down-converted signal is input into the second signal generator. The second signal generator divides the frequency of the first down-converted signal and locks the frequency-divided signal to the hydrogen clock frequency to obtain a first fiber optic noise signal and outputs it to the first acousto-optic modulator. The first acousto-optic modulator shifts the frequency of the first signal light; the second down-converted signal is input into the third signal generator. The third signal generator divides the frequency of the second down-converted signal and locks the frequency-divided signal to the hydrogen clock frequency to obtain a second fiber optic noise signal and outputs it to the second acousto-optic modulator. The second acousto-optic modulator shifts the frequency of the second signal light.
[0010] As described above, the first fiber optic light path includes a second mirror, a first acousto-optic modulator, a second quarter-wave plate, a third half-wave plate, and a first optical fiber. The first signal light is reflected by the second mirror and then enters the first acousto-optic modulator. After the first signal light is frequency-shifted by the first acousto-optic modulator, the first-order diffracted light of the first signal light is output. The first-order diffracted light of the first signal light sequentially passes through the second quarter-wave plate and the third half-wave plate and then is coupled into the first optical fiber. The first optical fiber reflects part of the first-order diffracted light of the first signal light to obtain a first reflected signal light. The first reflected signal light sequentially passes through the third half-wave plate, the second quarter-wave plate, and the first acousto-optic modulator. The first acousto-optic modulator frequency-shifts the first reflected signal light and then outputs a first frequency-modulated signal light. The first frequency-modulated signal light is reflected by the second mirror again and then reaches the second polarization beam splitter prism.
[0011] As described above, the second optical fiber optical path includes a second acousto-optic modulator, a third reflector, a third quarter-wave plate, a fourth half-wave plate, and a second optical fiber. The second signal light is frequency-shifted by the second acousto-optic modulator and then outputs the first-order diffracted light of the second signal light. The first-order diffracted light of the second signal light sequentially passes through the third reflector, the third quarter-wave plate, and the fourth half-wave plate and then is coupled into the second optical fiber. The second optical fiber reflects a part of the first-order diffracted light of the second signal light to obtain a second reflected signal light. The second reflected signal light sequentially passes through the fourth half-wave plate, the third quarter-wave plate, and the third reflector and then is input into the second acousto-optic modulator. The second acousto-optic modulator frequency-shifts the second reflected signal light and then outputs a second frequency-modulated signal light to the second polarization beam splitter prism.
[0012] As described above, the first beam splitter uses a first half-wave plate and a first polarization beam splitter prism. The original laser sequentially passes through the first half-wave plate and the first polarization beam splitter prism. The first polarization beam splitter prism splits the original laser into a reference light and a signal light.
[0013] As described above, a Faraday rotator is further provided between the first polarization beam splitter prism and the second half-wave plate, and a fifth half-wave plate and a third polarization beam splitter prism are further provided between the first polarization beam splitter prism and the fourth reflector. The combined beam signal light and the reference light after convergence sequentially pass through the fifth half-wave plate and the third polarization beam splitter prism. The third polarization beam splitter prism outputs the combined beam signal light and the reference light with the same polarization to the fourth reflector.
[0014] As described above, both the first optical fiber and the second optical fiber use an optical fiber with an APC beveled end face at one end and a PC flat end face at the other end. The first-order diffracted light of the first signal light enters from the APC beveled end face of the first optical fiber. A part of the first-order diffracted light of the first signal light exits from the PC flat end face of the first optical fiber, and another part of the first-order diffracted light of the first signal light is reflected back by the PC flat end face of the first optical fiber; The first-order diffracted light of the second signal light enters from the APC beveled end face of the second optical fiber. A part of the first-order diffracted light of the second signal light exits from the PC flat end face of the second optical fiber, and another part of the first-order diffracted light of the second signal light is reflected back by the PC flat end face of the second optical fiber.
[0015] As described above, both the first optical fiber and the second optical fiber use single-mode polarization-maintaining fibers.
[0016] The present invention has the following beneficial effects compared with the prior art:
[0017] The device of the present invention can not only ensure that the frequency-stabilized laser does not affect the original frequency stability after being transmitted through the optical fiber, but also solves the complex problem that for multiple optical fibers, it is necessary to build an optical fiber noise elimination device for each path. It can achieve simultaneous optical fiber noise elimination for multiple optical paths, solve the problem of simultaneously eliminating the noise introduced by several optical fibers, and only requires a set of noise elimination systems to achieve multi-path noise elimination, greatly simplifying the complexity of the experimental optical path, making the optical path highly concise, compact, and well-integrated, with strong practicality. The device of the present invention uses fewer optical components, reduces unnecessary optical losses caused by light propagation, improves the utilization rate and efficiency of optical components, saves manufacturing costs and space occupancy to a great extent, and has very important significance and value in the engineering applications of optical clocks and optical fiber transmission. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 It is a schematic structural diagram of the device according to an embodiment of the present invention;
[0019] Figure 2 It is a schematic structural diagram of the device according to another embodiment of the present invention;
[0020] Figure 3 It is a schematic structural diagram of the phase-locked circuit module according to Embodiment 2 of the present invention;
[0021] Reference numerals and corresponding component names:
[0022] 1 - Laser source; 2 - First beam splitter; 3 - First quarter-wave plate; 4 - First mirror; 5 - Second half-wave plate; 6 - Second polarization beam splitter prism; 7 - Second mirror; 8 - First acousto-optic modulator; 9 - Second quarter-wave plate; 10 - Third half-wave plate; 11 - First optical fiber; 12 - Second acousto-optic modulator; 13 - Third mirror; 14 - Third quarter-wave plate; 15 - Fourth half-wave plate; 16 - Second optical fiber; 17 - Fourth mirror; 18 - Convex lens; 19 - Photoelectric detector; 20 - Power amplifier; 21 - Phase-locked circuit module; 22 - First signal generator; 23 - Mixer; 24 - Power splitter; 25 - First filter; 26 - Second signal generator; 27 - Second filter; 28 - Third signal generator; 29 - First half-wave plate; 30 - Faraday rotator; 31 - Fifth half-wave plate; 32 - Third polarization beam splitter prism; 33 - First polarization beam splitter prism. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0023] In order to facilitate the understanding and implementation of the present invention by those of ordinary skill in the art, the present invention will be further described in detail below with reference to the embodiments. The embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.
[0024] Embodiment 1:
[0025] An apparatus for simultaneously eliminating the noise of optical fibers in multiple optical paths, comprising a laser source 1, a first beam splitter 2, a second polarization beam splitter prism 6, a first optical fiber path, a second optical fiber path, a photodetector 19, and a phase-locked circuit module 21. The laser source 1 outputs original laser light, which is input into the first beam splitter 2. The first beam splitter 2 splits the original laser light into a reference light and a signal light. The reference light is reflected by a first mirror 4 after passing through a first quarter-wave plate 3, and then returns to the first beam splitter 2 after passing through the first quarter-wave plate 3 again. Since the reference light passes through the first quarter-wave plate 3 twice, the reference light changes from vertically polarized light to horizontally polarized light. Therefore, the reference light returning to the first beam splitter 2 directly transmits through the first beam splitter 2. The signal light sequentially passes through a second half-wave plate 5 and the second polarization beam splitter prism 6. The second polarization beam splitter prism 6 splits the signal light into a first signal light and a second signal light. The combination of the half-wave plate and the polarization beam splitter prism can achieve the effect of splitting ratio, and the variable splitting ratio of the laser can be realized by rotating the second half-wave plate 5. The first signal light is input into the first optical fiber path, and the first optical fiber path reflects the first frequency-modulated signal light back to the second polarization beam splitter prism 6. The second signal light is input into the second optical fiber path, and the second optical fiber path reflects the second frequency-modulated signal light back to the second polarization beam splitter prism 6. The second polarization beam splitter prism 6 combines the first frequency-modulated signal light and the second frequency-modulated signal light into a combined signal light. The combined signal light sequentially passes through the second half-wave plate 5 and the first beam splitter 2;
[0026] The combined signal light and the reference light converge at the first beam splitter 2. The combined signal light and the reference light after convergence sequentially pass through a fourth mirror 17 and a convex lens 18 and then are focused onto the detection end face of the photodetector 19. The photodetector 19 performs optical beat frequency on the combined signal light and the reference light to obtain a first mixed electrical signal. The first mixed electrical signal is a mixed electrical signal of a first beat frequency electrical signal and a second beat frequency electrical signal. Among them, the first beat frequency electrical signal is the optical beat frequency signal between the first frequency-modulated signal light in the combined signal light and the reference light, and the second beat frequency electrical signal is the optical beat frequency signal between the second frequency-modulated signal light in the combined signal light and the reference light. The photodetector 19 inputs the first mixed electrical signal into the phase-locked circuit module 21. The phase-locked circuit module 21 outputs a first optical fiber noise signal to a first acousto-optic modulator 8, and the first acousto-optic modulator 8 shifts the frequency of the first signal light according to the first optical fiber noise signal, thereby realizing the noise elimination of the first signal light. The phase-locked circuit module 21 outputs a second optical fiber noise signal to a second acousto-optic modulator 12, and the second acousto-optic modulator 12 shifts the frequency of the second signal light according to the second optical fiber noise signal, thereby realizing the noise elimination of the second signal light.
[0027] The first optical fiber optical path includes a second reflector 7, a first acousto-optic modulator 8, a second quarter-wave plate 9, a third half-wave plate 10, and a first optical fiber 11. The first signal light is reflected by the second reflector 7 and then enters the first acousto-optic modulator 8. After the first signal light is frequency-shifted by the first acousto-optic modulator 8, the first-order diffracted light of the first signal light is output. The first-order diffracted light of the first signal light sequentially passes through the second quarter-wave plate 9 and the third half-wave plate 10 and then is coupled into the first optical fiber 11. The first-order diffracted light of the first signal light enters from the APC beveled end face of the first optical fiber 11. A part of the first-order diffracted light of the first signal light exits from the PC flat end face of the first optical fiber 11. Then, another part of the first-order diffracted light of the first signal light is reflected by the PC flat end face of the first optical fiber 11. The part of the first-order diffracted light of the first signal light after reflection is denoted as the first reflected signal light. The first reflected signal light returns along the original path and sequentially passes through the third half-wave plate 10, the second quarter-wave plate 9, and the first acousto-optic modulator 8. After the first acousto-optic modulator 8 frequency-shifts the first reflected signal light, the first-order diffracted light of the first reflected signal light is output, denoted as the first frequency-modulated signal light. The first frequency-modulated signal light is reflected by the second reflector 7 and then enters the second polarization beam splitter prism 6;
[0028] The second optical fiber optical path includes a second acousto-optic modulator 12, a third reflector 13, a third quarter-wave plate 14, a fourth half-wave plate 15, and a second optical fiber 16. After the second signal light is frequency-shifted by the second acousto-optic modulator 12, the first-order diffracted light of the second signal light is output. The first-order diffracted light of the second signal light sequentially passes through the 45° third reflector 13, the third quarter-wave plate 14, and the fourth half-wave plate 15 and then is coupled into the second optical fiber 16. The first-order diffracted light of the second signal light enters from the APC beveled end face of the second optical fiber 16. A part of the first-order diffracted light of the second signal light exits from the PC flat end face of the second optical fiber 16. Then, another part of the first-order diffracted light of the second signal light is reflected by the PC flat end face of the second optical fiber 16. The part of the first-order diffracted light of the second signal light after reflection is denoted as the second reflected signal light. The second reflected signal light returns along the original path and sequentially passes through the fourth half-wave plate 15, the third quarter-wave plate 14, the third reflector 13, and the second acousto-optic modulator 12. After the second acousto-optic modulator 12 frequency-shifts the second reflected signal light, the first-order diffracted light of the second reflected signal light is output, denoted as the second frequency-modulated signal light. The third reflector 13 inputs the second frequency-modulated signal light into the second polarization beam splitter prism 6;
[0029] In this embodiment, both the first optical fiber 11 and the second optical fiber 16 are single-mode polarization-maintaining fibers with an APC beveled end face at one end and a PC flat end face at the other end. Since a small part of the light will be returned along the original path by the PC flat end face of the optical fiber, the APC beveled end face is selected as the incident end face, and the PC flat end face is selected as the exit end face; the third half-wave plate 10, the second quarter-wave plate 9, the fourth half-wave plate 15, and the third quarter-wave plate 14 are all used to match the polarization direction of the laser and the single-mode polarization-maintaining fiber; the first acousto-optic modulator 8 and the second acousto-optic modulator 12 can both form heterodyne detection in a frequency-shifting manner and can also be used as phase compensation devices to compensate for fiber noise.
[0030] The phase-locked circuit module 21 includes a power amplifier 20, a mixer 23, a power splitter 24, a first filter 25, a second filter 27, a first signal generator 22, a second signal generator 26, and a third signal generator 28. The first signal generator 22 outputs a first mixing signal referenced at the hydrogen clock frequency. The first mixed electrical signal is input into the power amplifier 20. The amplified first mixed electrical signal and the first mixing signal are input into the mixer 23 for mixing to obtain a second mixed electrical signal. The second mixed electrical signal is a mixed signal of a first down-converted signal and a second down-converted signal. Among them, the first down-converted signal is a mixed signal of a first beat frequency electrical signal and the first mixing signal, and the second down-converted signal is a mixed signal of a second beat frequency electrical signal and the first mixing signal. The mixer 23 inputs the second mixed electrical signal into the power splitter 24. The power splitter 24 divides the second mixed electrical signal into two parts. One part of the second mixed electrical signal is input into the first filter 25 for filtering to obtain the first down-converted signal, and the other part of the second mixed electrical signal is input into the second filter 27 for filtering to obtain the second down-converted signal;
[0031] The first signal generator 22, the second signal generator 26, and the third signal generator 28 all adopt DDS signal generators. Since the DDS signal generator has a frequency division upper limit, the amplified first mixed electrical signal is down-converted by the first mixing signal output by the first signal generator 22 referenced at the hydrogen clock frequency, so as to meet the requirement of the frequency division upper limit of the DDS of the signal generator.
[0032] The first down-converted signal is input into the second signal generator 26. The second signal generator 26 divides the frequency of the first down-converted signal and locks the divided signal to the hydrogen clock frequency, thereby obtaining the first optical fiber noise signal. The second signal generator 26 outputs the first optical fiber noise signal to the first acousto-optic modulator 8 to shift the frequency of the first signal light, so that when the frequency-shifted first signal light is output from the PC flat-end face of the first optical fiber 11, the optical fiber noise can be cancelled out; the second down-converted signal is input into the third signal generator 28. The third signal generator 28 divides the frequency of the second down-converted signal and locks the divided signal to the hydrogen clock frequency, thereby obtaining the second optical fiber noise signal. The third signal generator 28 outputs the second optical fiber noise signal to the second acousto-optic modulator 12 to shift the frequency of the second signal light, so that when the frequency-shifted second signal light is output from the PC flat-end face of the second optical fiber 16, the optical fiber noise can be cancelled out, and thus the elimination of optical fiber noise for multiple optical paths is achieved simultaneously.
[0033] Assume that the frequency of the original laser is F, and the driving frequencies of the first acousto-optic modulator 8 and the second acousto-optic modulator 12 are f 1 , f 2 , respectively. The frequency jitters caused by the first optical fiber 11 and the second optical fiber 16 are δ 1 , δ 2 , respectively. Then the frequencies of the first frequency-modulated signal light and the second frequency-modulated signal light are F + 2f 1 + 2δ 1 , F + 2f 2 + 2δ 2 , respectively. The first mixed electrical signal output by the photodetector 19 includes a first beat electrical signal with a frequency of 2f 1 + 2δ 1 and a second beat electrical signal with a frequency of 2f 2 + 2δ 2 . It includes both the driving frequencies of the first acousto-optic modulator 8 and the second acousto-optic modulator 12 and the frequency jitters caused by the two optical fiber noises. After down-converting the first beat electrical signal and the second beat electrical signal in the first mixed electrical signal and then locking them to the hydrogen clock frequency respectively, the first optical fiber noise signal with frequencies of 2δ 1 and the second optical fiber noise signal with frequencies of 2δ 2 are obtained. According to the first optical fiber noise signal, the frequency of the first signal light is shifted, so that when the frequency-shifted first signal light is output from the first optical fiber 11, the optical fiber noise can be cancelled out, thereby eliminating the optical fiber noise; according to the second optical fiber noise signal, the frequency of the second signal light is shifted, so that when the frequency-shifted second signal light is output from the second optical fiber 16, the optical fiber noise can be cancelled out, thereby eliminating the optical fiber noise simultaneously; when there are multiple optical paths, in the same way, only a polarization beam splitter prism and a half-wave plate need to be added for beam splitting, and an acousto-optic modulator is added to the branch path, thereby eliminating the optical fiber noise and ensuring that the frequency stability of the light remains unchanged.
[0034] In one embodiment, the first beam splitter 2 uses a first beam splitting prism. The original laser sequentially passes through the first half-wave plate 29 and the first polarization beam splitting prism 33. The first polarization beam splitting prism 33 splits the original laser into a reference light and a signal light. Using the first beam splitting prism to achieve beam splitting, the splitting ratios of different splitting ratios are fixed and non-tunable. For example, the first beam splitting prisms with reflection-to-transmission ratios of 10:90, 30:70, and 50:50. Taking the first beam splitting prism with a ratio of 30:70 as an example, assuming the incident light source is 1, 30% of the incident light source is reflected from the surface of the first beam splitting prism as the reference light and does not pass through the optical fiber. 70% of the signal light passes through the BS, returns from the end face of the optical fiber after passing through a series of optical components. After the returned combined signal light returns to the first beam splitting prism, it is reflected by the first beam splitting prism at a ratio of 30% and enters the photodetector 19 together with the reference light. The optical fiber return light entering the photodetector 19 is only 21% of the incident light source. Similarly, after passing through the first beam splitting prism twice, the reference light beam entering the photodetector 19 is also only 21% of the incident light source. The collection efficiency of the effective light of the photodetector 19 is not high. However, the number of optical components used is small, which not only saves resources but also reduces the optical losses caused by the propagation of light in each optical component.
[0035] In another embodiment, the first beam splitter 2 uses the first half-wave plate 29 and the first polarization beam splitting prism 33. The original laser is incident on the first half-wave plate 29 at an angle of 45°. The ratio of the horizontally polarized light to the vertically polarized light can be changed by adjusting the first half-wave plate 29 in front of the first polarization beam splitting prism 33, and the ratio is adjustable and controllable.
[0036] A Faraday rotator 30 is also provided between the first polarization beam splitter prism 33 and the second half-wave plate 5. A fifth half-wave plate 31 and a third polarization beam splitter prism 32 are also provided between the first polarization beam splitter prism 33 and the fourth mirror 17. The polarization of the signal light rotates by 45° after passing through the Faraday rotator 30. Since the signal light passes through the Faraday rotator 30 once and the combined signal light passes through the Faraday rotator 30 again, the polarization of the combined signal light rotates by 90° relative to the initial signal light, and the combined signal light becomes vertically polarized light. After being reflected by the first polarization beam splitter prism 33, the combined signal light converges with the reference light transmitted through the first polarization beam splitter prism 33. The combined signal light and the reference light after convergence pass through the fifth half-wave plate 31 and the third polarization beam splitter prism 32 in sequence. The fifth half-wave plate 31 and the third polarization beam splitter prism 32 select the combined signal light and the reference light with the same polarization direction according to a set ratio (such as 50%:50%). The combined signal light and the reference light with the same polarization direction pass through the fourth mirror 17 and the convex lens 18 in sequence and are then focused on the detection end face of the photodetector 19. The ratio of the horizontally polarized light to the vertically polarized light can be changed by adjusting the first half-wave plate 29 in front of the first polarization beam splitter prism 33, and the ratio is adjustable and controllable. Therefore, the effective light collection efficiency of the light entering the photodetector 19 depends on the splitting ratio of the fifth half-wave plate 31 and the third polarization beam splitter prism 32.
[0037] The device of the present invention can achieve fiber noise cancellation for multiple optical paths simultaneously, solves the problem of simultaneously canceling the noise introduced by several fibers, and only requires a set of noise cancellation systems to achieve multi-path noise cancellation, greatly simplifying the complexity of the experimental optical path, making the optical path highly concise, compact, and well integrated, with strong practicability. The device of the present invention uses fewer optical components, reduces unnecessary optical losses caused by light during propagation, improves the utilization rate and efficiency of optical components, saves manufacturing costs and space occupancy to a great extent, and has very important significance and value in the engineering applications of optical clocks and fiber transmission.
[0038] Embodiment 2:
[0039] In this embodiment, the driving frequency of the first acousto-optic modulator 8 is +77 MHz, and the driving frequency of the second acousto-optic modulator 12 is +82 MHz. The frequencies of the first beat signal and the second beat signal detected by the photodetector 19 are +154 MHz (for sideband cooling SBC of ions) and +164 MHz (for spectral line searching SP of ions), respectively. After being amplified in power by a 33 dB power amplifier 20, they are mixed with the output signal of the first mixer signal output by the first signal generator 22 (DDS1, +104 MHz, 7 dBm) referenced to the hydrogen clock, so as to achieve frequency down-conversion. After the 154 MHz signal is mixed with the 104 MHz reference signal, a first down-converted signal with a frequency difference of 50 MHz is obtained. After the 164 MHz signal is mixed with the 104 MHz reference signal, a second down-converted signal with a frequency difference of 60 MHz is obtained. The first down-converted signal and the second down-converted signal are separated by a power splitter 24, and the respective unwanted components in these two paths of signals are filtered out by trackers (both the first filter 25 and the second filter 27 in this embodiment adopt trackers), so as to achieve the distinction of the two paths of signals. Then they enter the second signal generator 26 (DDS2) and the third signal generator 28 (DDS3) respectively. The second signal generator 26 and the third signal generator 28 used in this embodiment have a proportional-integral-derivative (PID) frequency locking function. By setting the interiors of the second signal generator 26 and the third signal generator 28, the first down-converted signal and the second down-converted signal can be processed and calculated to make the first down-converted signal and the second down-converted signal match the frequency of the reference source signal of the 10 MHz hydrogen clock: The first down-converted signal ( Figure 3 RF In of the second signal generator 26 in) enters the second signal generator 26 after passing through the first filter 25. Through internal setting, the 50 MHz signal is divided by 5 to be 10 MHz, which can just beat with the hydrogen clock reference signal with a frequency of 10 MHz ( Figure 3 REF In of the second signal generator 26 in), and then is output to the first acousto-optic modulator 8 (AOM1) to drive the first acousto-optic modulator 8 at +77 MHz. Finally, the laser is used for sideband cooling of ions; Similarly, the second down-converted signal ( Figure 3 RF In of the third signal generator 28 in) enters the third signal generator 28 after passing through the second filter 27. Through the internal setting of the third signal generator 28, the 60 MHz signal is divided by 6 to be 10 MHz, which beats with the hydrogen clock reference signal with a frequency of 10 MHz ( Figure 3 REF In of the third signal generator 28 in), and then is output to the second acousto-optic modulator 12 (AOM2) to drive the second acousto-optic modulator 12 at +82 MHz for spectral line searching of the ion clock transition. It should be noted here that the integration of the circuit part is much easier than that of the optical path part, and the stability of the circuit part is higher and the cost is lower.
[0040] It should be noted that the embodiments described in the present invention are only illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described embodiments or use similar means for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.
Claims
1. A device for simultaneously eliminating noise from multiple optical fibers, comprising a laser source (1), characterized in that: The invention also comprises a first beam splitter (2), a second polarization beam splitting prism (6), a first optical fiber optical path, a second optical fiber optical path, a photodetector (19), and a phase-locked circuit module (21). The laser source (1) outputs original laser light, which is input into the first beam splitter (2). The first beam splitter (2) splits the original laser light into reference light and signal light. The reference light passes through the first quarter wave plate (3), the first reflector (4), and the first quarter wave plate (3) in sequence and then returns to the first beam splitter (2). The signal light passes through the second half wave plate (5) and the second polarization beam splitter in sequence. The first signal light is input into the first optical fiber optical path, and the first optical fiber optical path reflects the first frequency modulated signal light back to the second polarization beam splitter prism (6); the second signal light is input into the second optical fiber optical path, and the second optical fiber optical path reflects the second frequency modulated signal light back to the second polarization beam splitter prism (6); the second polarization beam splitter prism (6) combines the first frequency modulated signal light and the second frequency modulated signal light into a combined signal light, and the combined signal light passes through the second half wave plate (5) and the first beam splitter (2) in sequence; The combined signal light and the reference light are combined at the first beam splitter (2). The combined signal light and the reference light are sequentially passed through the fourth reflector (17) and the convex lens (18) and then focused on the detection end face of the photodetector (19). The photodetector (19) performs optical beat frequency on the combined signal light and the reference light to obtain a first mixed electrical signal. The first mixed electrical signal is input into a phase-locked circuit module (21). The phase-locked circuit module (21) outputs a first optical fiber noise signal to the first optical fiber optical path. The first optical fiber optical path performs noise elimination on the first signal light according to the first optical fiber noise signal. The phase-locked circuit module (21) outputs a second optical fiber noise signal to the second optical fiber optical path. The second optical fiber optical path performs noise elimination on the second signal light according to the second optical fiber noise signal.
2. A device for simultaneously eliminating noise from multiple optical fibers according to claim 1, characterized in that: The phase-locked circuit module (21) comprises a power amplifier (20), a mixer (23), a power divider (24), a first filter (25), a second filter (27), a first signal generator (22), a second signal generator (26), and a third signal generator (28), wherein the first signal generator (22) outputs a first mixing signal referenced to the hydrogen clock frequency, the first mixed electrical signal is amplified by the power amplifier (20) and then input into the mixer (23) for mixing with the first mixing signal to obtain a second mixed electrical signal, the mixer (23) inputs the second mixed electrical signal into the power divider (24), the power divider (24) divides the second mixed electrical signal into two parts, wherein one part of the second mixed electrical signal is input into the first filter (25) for filtering to obtain a first frequency reduction signal, and the other part of the second mixed electrical signal is input into the second filter (27) for filtering to obtain a second frequency reduction signal; The first frequency reduction signal is input into the second signal generator (26), the second signal generator (26) divides the first frequency reduction signal and locks the divided signal to the hydrogen clock frequency, obtains a first optical fiber noise signal and outputs it to the first acousto-optic modulator (8), the first acousto-optic modulator (8) shifts the frequency of the first signal light; the second frequency reduction signal is input into the third signal generator (28), the third signal generator (28) divides the second frequency reduction signal and locks the divided signal to the hydrogen clock frequency, obtains a second optical fiber noise signal and outputs it to the second acousto-optic modulator (12), the second acousto-optic modulator (12) shifts the frequency of the second signal light.
3. The device for simultaneously eliminating noise from multiple optical fibers according to claim 2, characterized in that: The first optical fiber optical path comprises a second reflector (7), a first acousto-optic modulator (8), a second quarter wave plate (9), a third half wave plate (10), and a first optical fiber (11); the first signal light passes through the second reflector (7) and is reflected into the first acousto-optic modulator (8); the first signal light passes through the first acousto-optic modulator (8) and is frequency-shifted to output first-order diffracted light of the first signal light; the first-order diffracted light of the first signal light passes through the second quarter wave plate (9) and the third half wave plate (10) in sequence and is coupled into the first optical fiber (11); the first optical fiber (11) reflects part of the first-order diffracted light of the first signal light to obtain first reflected signal light; the first reflected signal light passes through the third half wave plate (10), the second quarter wave plate (9), and the first acousto-optic modulator (8) in sequence; the first acousto-optic modulator (8) shifts the frequency of the first reflected signal light and outputs a first frequency-modulated signal light; the first frequency-modulated signal light passes through the second reflector (7) and is reflected to the second polarization beam splitting prism (6).
4. The device for simultaneously eliminating noise from multiple optical fibers according to claim 3, characterized in that: The second optical fiber optical path comprises a second acousto-optic modulator (12), a third reflector (13), a third quarter wave plate (14), a fourth half wave plate (15), and a second optical fiber (16); the second signal light is frequency-shifted by the second acousto-optic modulator (12) and outputs first-order diffracted light of the second signal light; the first-order diffracted light of the second signal light sequentially passes through the third reflector (13), the third quarter wave plate (14), and the fourth half wave plate (15) and is coupled into the second optical fiber (16); the second optical fiber (16) reflects part of the first-order diffracted light of the second signal light to obtain second reflected signal light; the second reflected signal light sequentially passes through the fourth half wave plate (15), the third quarter wave plate (14), and the third reflector (13) and is input into the second acousto-optic modulator (12); the second acousto-optic modulator (12) frequency-shifts the second reflected signal light and outputs second frequency-modulated signal light to the second polarization beam splitting prism (6).
5. The device for simultaneously eliminating noise from multiple optical fibers according to claim 4, characterized in that: The first beam splitter (2) uses a first half-wave plate (29) and a first polarization beam splitting prism (33); original laser light passes through the first half-wave plate (29) and the first polarization beam splitting prism (33) in sequence; the first polarization beam splitting prism (33) splits the original laser light into reference light and signal light.
6. The device for simultaneously eliminating noise from multiple optical fibers according to claim 5, characterized in that: A Faraday rotator (30) is also provided between the first polarization beam splitter prism (33) and the second half-wave plate (5), and a fifth half-wave plate (31) and a third polarization beam splitter prism (32) are also provided between the first polarization beam splitter prism (33) and the fourth reflector (17). The combined signal light and the reference light are sequentially passed through the fifth half-wave plate (31) and the third polarization beam splitter prism (32), and the third polarization beam splitter prism (32) outputs the combined signal light and the reference light with the same polarization to the fourth reflector (17).
7. A device for simultaneously eliminating noise from multiple optical fibers according to claim 6, characterized in that: The first optical fiber (11) and the second optical fiber (16) are both optical fibers with an APC beveled end face at one end and a PC flat end face at the other end; the first-order diffraction light of the first signal light enters from the APC beveled end face of the first optical fiber (11), a portion of the first-order diffraction light of the first signal light is emitted from the PC flat end face of the first optical fiber (11), and the other portion of the first-order diffraction light of the first signal light is reflected back by the PC flat end face of the first optical fiber (11); the first-order diffraction light of the second signal light enters from the APC beveled end face of the second optical fiber (16), a portion of the first-order diffraction light of the second signal light is emitted from the PC flat end face of the second optical fiber (16), and the other portion of the first-order diffraction light of the second signal light is reflected back by the PC flat end face of the second optical fiber (16).
8. The device for simultaneously eliminating noise from multiple optical fibers according to claim 7, characterized in that: The first optical fiber (11) and the second optical fiber (16) are both single-mode fiber-conserving.