CN115832855A - Multi-wavelength tunable ultrastable laser system and frequency control method thereof - Google Patents
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Abstract
The invention provides a multi-wavelength tunable ultrastable laser system and a frequency control method thereof, which relate to the technical field of laser frequency stabilization and double-field quantum key distribution. The problem that secondary Rayleigh scattering noise is caused in the optical fiber by the strong phase reference pulse along with the increase of the transmission distance of the TF-QKD is solved, the interference performance of single photons in a long distance is reduced, and the safe coding distance and the coding rate of the TF-QKD are improved.
Description
Technical Field
The application relates to the technical field of laser frequency stabilization and double-field quantum key distribution, in particular to a multi-wavelength tunable ultrastable laser system and a frequency control method thereof.
Background
The double-field quantum key distribution (TF-QKD) protocol can improve the linear relation between the traditional Quantum Key Distribution (QKD) bit rate and the channel transmittance to be related to the square root, so that the transmission distance of the QKD and the bit rate under a long distance can be greatly improved, however, the implementation of the TF-QKD requires long-distance single-photon phase-level interference, and therefore the interference quality of single photons can be reduced by the tiny frequency deviation of light sources of two sides of a sender, any phase jitter of an optical fiber link and detection noise of a system. At present, the TF-QKD usually adopts an optical phase locking mode to accurately control the relative frequency/phase of light sources at two sides and a mode of strong phase reference pulse and quantum light time division multiplexing to calculate the phase jitter of a link, however, with the increase of transmission distance, the interference performance of single photon at a long distance can be reduced by secondary Rayleigh scattering noise caused by the strong phase reference pulse in an optical fiber, and the safe coding distance and the coding rate of the TF-QKD are limited. In order to realize TF-QKD with farther distance and even with the limit distance, a new link phase jitter calculation mode is needed to avoid the influence of the second Rayleigh scattering noise, namely, a strong phase reference pulse and quantum light wavelength division multiplexing mode is adopted to calculate the link phase jitter. Thus, two transmitters respectively need to use two laser sources with different wavelengths, one of which is used for the quantum optical pulse light source and the other is used for the reference pulse light source, and the frequencies of the quantum optical light source and the reference optical light source on the two sides respectively need to be controlled to be the same, that is, the frequency of two or four remote light sources needs to be accurately controlled.
In the TF-QKD encoded by the time division multiplexing mode, the reference light and the quantum light use the same light source, in order to eliminate the phase jitter introduced by the rapid drift of the relative frequency of the light source, generally, two sides of transmitters respectively adopt PDH technology to lock commercial seed lasers on an optical F-P cavity, so that the rapid drift of the relative frequency of the light sources at two sides is reduced by two to three orders of magnitude, and then, the ultrastable light frequencies at two sides are controlled to be the same by using a laser phase servo system. If the method is based on the traditional method, 4 ultrastable laser systems consisting of ultrastable cavities are needed to be adopted for TF-QKD utilizing wavelength division multiplexing, and laser sources for reference light and quantum light need to be locked with each other pairwise so as to ensure the precision of phase compensation. Therefore, the whole system is very complicated, and 4 sets of ultra-stable laser systems locked by PDH and 2 sets of laser phase servo systems are needed to realize the frequency accurate control of two 4 sets of lasers.
Disclosure of Invention
In order to solve the technical problem, the invention provides a method for a multi-wavelength tunable ultrastable laser, which only needs to place an ultrastable cavity at two places respectively, the frequency of four seed lasers is modulated by utilizing a PDH technology, namely the frequency of an external resonant cavity is taken as a standard, the phase modulation technology is utilized to modulate the phase of incident laser, a side frequency band is generated at two sides of the central frequency of the laser respectively, an optical signal reflected by a reference resonant cavity is compared with a modulation signal and filtered and amplified to obtain an error signal of which the laser frequency deviates from the resonant frequency of the reference cavity, a feedback control system is driven by the error signal to adjust the frequency of the laser so that the laser frequency is stabilized on the resonant frequency of the laser, the two ultrastable cavities at two sides are locked, the four ultrastable lasers with tunable wavelengths can be output at two sides, the frequency difference of the two ultrastable lasers at two sides is kept fixed due to being locked on the same ultrastable cavity, and the precise control of the frequency of two places and four lasers can be realized by utilizing a set of laser phase servo system.
In order to improve the transmission distance of the TF-QKD and even explore the limit of the transmission distance of the TF-QKD, the invention adopts a multi-wavelength tunable ultrastable laser as a light source, so that the strong phase reference pulse and the quantum pulse of the TF-QKD adopt ultrastable lasers with different wavelengths, therefore, the influence of the secondary Rayleigh scattering noise of the strong phase reference pulse can be eliminated by a filtering mode due to the fact that the wavelength of the secondary Rayleigh scattering noise generated by the strong phase reference pulse in an optical fiber is different from that of the quantum light pulse, the interference quality of single photons under a long distance is improved, and the transmission distance of the TF-QKD is improved.
According to the scheme, two ultrastable cavities are adopted by two senders of the TF-QKD system to lock four commercial seed lasers, four paths of ultrastable lasers with tunable wavelengths are output simultaneously, and a laser phase servo system is additionally arranged, so that the frequency precision control of the four paths of lasers is realized. In the traditional method, if the precise control of the remote frequency of four independent seed lasers is to be realized, four seed lasers need to be respectively locked on four corresponding ultrastable cavities, and then four ultrastable lasers running independently on two sides are mutually locked through three sets of frequency/phase servo control systems, so that the system is very complicated to realize the precise control of the frequency of four independent lasers. This scheme adopts two liang of locks of four seed light on two super steady chambeies, and two laser of locking correspond the different resonant frequency (the different longitudinal mode) in every super steady chamber respectively, and two tunnel wavelengths are exported in every super steady chamber, because the change in chamber arouses different longitudinal mode frequencies unanimous, and then laser wavelength after two tunnel locks changes unanimously, only uses one set of frequency/laser phase servo system can make the longitudinal mode mutual locking in two super steady chambers in addition to realize the accurate control of frequency of four ways laser.
The invention provides a multi-wavelength tunable ultrastable laser system, which comprises: the system comprises a first ultrastable laser system, a second ultrastable laser system, a first radio frequency system, a second dense wavelength division multiplexer, a fourth dense wavelength division multiplexer and a laser phase servo system;
the first ultrastable laser system is used for locking the frequencies of output light of the first seed light system and the second seed light system to first ultrastable frequencies respectively, outputting the frequencies to the second dense wavelength division multiplexer respectively and used for the first double-field quantum key distribution system;
the second ultrastable laser system is used for locking the frequencies of output light of the third sub-optical system and the fourth sub-optical system to second ultrastable frequencies respectively, and outputting the frequencies to the fourth dense wavelength division multiplexer respectively for the second double-field quantum key distribution system;
the first radio frequency system is used for tuning the light source wavelengths of the first seed light system and the second seed light system, so that the difference value of the light source wavelengths of the two seed light systems is fixed; the second radio frequency system is used for tuning the light source wavelengths of the third sub-optical system and the fourth sub-optical system, so that the difference value of the light source wavelengths of the two sub-optical systems is fixed;
the output light after the frequency locking of the second sub-light system and the output light after the frequency locking of the fourth sub-light system are respectively input to the laser phase servo system, and the laser phase servo system is used for controlling the wavelength of the output light after the frequency locking of the second sub-light system to be equal to that of the output light after the frequency locking of the fourth sub-light system, so that the frequency locking of the first ultrastable laser system and the second ultrastable laser system is realized.
Further, the first seed light system comprises a first seed laser, a first acousto-optic modulator and a first electro-optic modulator; the second seed light system comprises a second seed laser, an acousto-optic modulator II and an electro-optic modulator II; the seed light I output by the first seed laser sequentially passes through the acousto-optic modulator I and the electro-optic modulator I for error detection, and the seed light II output by the second seed laser sequentially passes through the acousto-optic modulator II and the electro-optic modulator II for error detection;
the third sub-optical system comprises a third sub-laser, an acousto-optic modulator III and an electro-optic modulator III; the fourth sub-optical system comprises a fourth sub-laser, an acousto-optic modulator IV and an electro-optic modulator IV; and the seed light III output by the third sub laser sequentially passes through the acousto-optic modulator III and the electro-optic modulator III for error detection, and the seed light IV output by the fourth sub laser sequentially passes through the acousto-optic modulator IV and the electro-optic modulator IV for error detection.
Further, the first radio frequency system comprises a radio frequency signal source RF1A, a radio frequency signal source RF1B, a radio frequency signal source RF2A and a radio frequency signal source RF2B; the radio frequency signal source RF1B and the radio frequency signal source RF2B respectively output radio frequency signals, signals generated by the radio frequency signal source RF1A and the radio frequency signal source RF2A are respectively modulated in a phase modulation mode, and modulated frequency signals output by the radio frequency signal source RF1A and the radio frequency signal source RF2A respectively enter the first electro-optical modulator and the second electro-optical modulator;
the second radio frequency system comprises a radio frequency signal source RF3A, a radio frequency signal source RF3B, a radio frequency signal source RF4A and a radio frequency signal source RF4B; the radio frequency signal source RF3B and the radio frequency signal source RF4B respectively output radio frequency signals, signals generated by the radio frequency signal source RF3A and the radio frequency signal source RF4A are respectively modulated in a phase modulation mode, and modulated frequency signals output by the radio frequency signal source RF3A and the radio frequency signal source RF4A respectively enter the electro-optical modulator III and the electro-optical modulator IV.
Furthermore, the first ultrastable laser system further comprises a first polarization beam splitter, a first ultrastable cavity, a first dense wavelength division multiplexer, a first photoelectric detector, a second photoelectric detector, a first mixer, a second mixer, a first low-pass filter, a second low-pass filter, a first servo circuit and a second servo circuit;
the optical signals respectively modulated by the first electro-optical modulator and the second electro-optical modulator enter the first polarization beam splitter and the first hyperstable cavity at the same time, and then are reflected back to enter the first dense wavelength division multiplexer; one path of optical signal output by the first dense wavelength division multiplexer passes through a first photoelectric detector, then is mixed with a radio frequency signal output by a radio frequency signal source RF1B in a first mixer, and generates a first error signal after passing through a first low-pass filter; meanwhile, another path of optical signal output by the first dense wavelength division multiplexer passes through a second photoelectric detector, then is mixed with a radio frequency signal output by a radio frequency signal source RF2B in a second mixer, and generates a second error signal after passing through a second low-pass filter;
the first error signal is processed by a first servo circuit and then fed back to a frequency control end of the first seed laser and a first acousto-optic modulator for frequency locking, so that the first seed laser is locked on a first ultrastable cavity; meanwhile, the second error signal is processed by a second servo circuit and then fed back to the frequency control end of the second seed laser and the acousto-optic modulator to be frequency-locked, so that the second seed laser is also locked on the first hyperstable cavity.
Furthermore, the second ultrastable laser system further comprises a second polarization beam splitter, a second ultrastable cavity, a third dense wavelength division multiplexer, a third photodetector, a fourth photodetector, a third mixer, a fourth mixer, a third low-pass filter, a fourth low-pass filter, a third servo circuit and a fourth servo circuit;
the optical signals respectively modulated by the electro-optical modulator III and the electro-optical modulator IV simultaneously enter a second polarization beam splitter and a second hyperstable cavity, and are then reflected back to enter a third dense wavelength division multiplexer; one path of optical signal output by the third dense wavelength division multiplexer passes through a third photoelectric detector, is mixed with a radio frequency signal output by a radio frequency signal source RF3B in a third mixer, and generates a third error signal after passing through a third low-pass filter; meanwhile, another path of optical signal output by the third dense wavelength division multiplexer passes through a fourth photoelectric detector, is mixed with a radio frequency signal output by a radio frequency signal source RF4B in a fourth mixer, and generates a fourth error signal after passing through a fourth low-pass filter;
after being processed by a third servo circuit, the third error signal is fed back to a frequency control end of the third sub-laser and an acousto-optic modulator for frequency locking, so that the third sub-laser is locked on a second ultrastable cavity; meanwhile, after being processed by a fourth servo circuit, the fourth error signal is fed back to the frequency control end of the fourth sub-laser and the acousto-optic modulator for frequency locking, so that the fourth sub-laser is also locked on the second ultrastable cavity.
The invention also provides a frequency control method of the multi-wavelength tunable ultrastable laser system, which is used for tuning the multi-wavelength tunable ultrastable laser system and comprises the following steps:
the method comprises the following steps that firstly, seed light of each seed light system is divided into two beams, one beam is used for error detection, and the other beam is used for a double-field quantum key distribution system;
step two, each seed light system changes the output frequency of the seed light through two radio frequency signal sources in the respective system by a secondary modulation technology to realize independent tuning of wavelength frequency;
step three, respectively feeding back the error signal of each seed light system to the frequency control end of each seed laser, changing the frequency of the seed light, respectively locking the frequencies of the output light of the first seed light system and the second seed light system at the first ultrastable frequency, and respectively locking the frequencies of the output light of the third seed light system and the fourth seed light system at the second ultrastable frequency;
step four, tuning the difference value of the light source wavelengths of the first seed light system and the second seed light system to be a fixed value; tuning the second radio frequency system to tune a difference value of light source wavelengths of the third sub-optical system and the fourth sub-optical system to be a fixed value;
and fifthly, controlling the wavelength of the output light of the second sub-optical system after frequency locking to be equal to that of the output light of the fourth sub-optical system after frequency locking by the laser phase servo system, and realizing frequency locking of the first ultrastable laser system and the second ultrastable laser system.
The beneficial technical effects are as follows:
the invention only needs two ultrastable cavities to output four paths of ultrastable laser with independently tunable wavelengths, and is additionally provided with a laser phase servo system, so that the frequency precision control of the four paths of laser can be realized. The problem of secondary Rayleigh scattering noise caused by strong phase reference pulses in the optical fiber along with the increase of the transmission distance of the TF-QKD is solved, the interference performance of single photons under a long distance is reduced, and the safe coding distance and the coding rate of the TF-QKD are improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive labor.
Fig. 1 is a schematic structural diagram of a multi-wavelength tunable ultrastable laser system according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
In the drawings of the embodiments of the present invention, in order to better and more clearly describe the working principle of each element in the system, the connection relationship of each part in the apparatus is shown, only the relative position relationship between each element is clearly distinguished, and the restriction on the signal transmission direction, the connection sequence, and the size, the dimension, and the shape of each part structure in the element or structure cannot be formed.
The invention adopts two parallel processes, the first process is that four seed lasers are paired pairwise and respectively locked on two PF cavities, and the second process aligns the wavelengths of the four seed lasers pairwise, so that four paths of laser are strictly coherent.
Fig. 1 is a schematic structural diagram of a multi-wavelength tunable ultrastable laser system. The ultrastable laser system comprises: the system comprises a first ultrastable laser system, a second ultrastable laser system, a first radio frequency system, a second dense wavelength division multiplexer DWDM2, a fourth dense wavelength division multiplexer DWDM4 and a laser phase servo system.
The first superstable laser system comprises a first sub-light system, a second sub-light system, a first polarization beam splitter, a first superstable cavity, a first dense wavelength division multiplexer, a first photoelectric detector, a second photoelectric detector, a first frequency mixer, a second frequency mixer, a first low-pass filter, a second low-pass filter, a first servo circuit and a second servo circuit.
The second hyperstable laser system comprises a third sub-optical system, a fourth sub-optical system, a second polarization beam splitter, a second hyperstable cavity, a third dense wavelength division multiplexer, a third photoelectric detector, a fourth photoelectric detector, a third frequency mixer, a fourth frequency mixer, a third low-pass filter, a fourth low-pass filter and a third servo circuit.
The first seed light system comprises a first seed laser, an acousto-optic modulator I and an electro-optic modulator I; the second seed light system comprises a second seed laser, an acousto-optic modulator II and an electro-optic modulator II; the third sub-optical system comprises a third sub-laser, an acousto-optic modulator III and an electro-optic modulator III; the fourth sub-optical system comprises a fourth sub-laser, an acousto-optic modulator IV and an electro-optic modulator IV.
The first radio frequency system comprises a radio frequency signal source RF1A, a radio frequency signal source RF1B, a radio frequency signal source RF2A and a radio frequency signal source RF2B; the second radio frequency system comprises a radio frequency signal source RF3A, a radio frequency signal source RF3B, a radio frequency signal source RF4A and a radio frequency signal source RF4B.
The tuning method of the multi-wavelength tunable ultrastable laser system comprises two processes.
In a preferred embodiment, the output wavelengths of the first seed light and the third seed light are 1550.12nm, which is recorded as λ 1 、λ 3 (ii) a The output wavelengths of the second seed light and the fourth seed light are 1549.32nm which is marked as lambda 2 、λ 4 。
The first process is divided into the following steps:
the method comprises the following steps: the four paths of seed optical signals are respectively divided into two beams, one beam is used for error detection, and the other beam is used for a double-field quantum key distribution system.
Specifically, as shown in fig. 1, the output light λ of the seed light one 1 After passing through the acousto-optic modulator AOM1, the two beams are divided into two beams, one beam enters the electro-optic modulator EOM1 for error detection, and the other beam enters the first double-field quantum key distribution system, namely the double-field quantum key distribution TF-QKD system in the figure.
Output light lambda of seed light two 2 After passing through the second acousto-optic modulator AOM2, the two beams are divided into two beams, one beam enters the second electro-optic modulator EOM2 for error detection, and the other beam is used for a first double-field quantum key distribution system, namely the double-field quantum key distribution TF-QKD system in the figure.
Output light lambda of seed light III 3 After passing through three AOMs 3 of the acousto-optic modulator, the beam is divided into two beams, one beam enters three EOMs 3 of the electro-optic modulator for error detection, and one beam is used for a second double-field quantum key distribution system, namely the double-field quantum key distribution TF-QKD system II in the figure.
Output light lambda of seed light four 4 After passing through the four AOMs 4 of the acousto-optic modulator, the beam is divided into two beams, one beam enters the four EOMs 4 of the electro-optic modulator for error detection, and the other beam is used for a second double-field quantum key distribution system, namely a second double-field quantum key distribution TF-QKD system in the figure.
Step two: the output frequencies of the four paths of seed optical signals are changed by the radio frequency signal source through a secondary modulation technology respectively, so that four wavelength frequencies are independently tuned.
Specifically, as shown in fig. 1, the RF signal source RF1B outputs an RF signal, and modulates the signal generated by the RF signal source RF1A in a phase modulation manner, and the modulated frequency signal output by the RF signal source RF1A is input into an EOM1 of the electro-optical modulator;
the radio frequency signal source RF2B outputs a radio frequency signal, the signal generated by the radio frequency signal source RF2A is modulated in a phase modulation mode, and the modulated frequency signal output by the radio frequency signal source RF2A is input into the electro-optical modulator II EOM 2.
The radio frequency signal source RF3B outputs a radio frequency signal, a signal generated by the radio frequency signal source RF3A is modulated in a phase modulation mode, and a modulated frequency signal output by the radio frequency signal source RF3A is input into the electro-optical modulator III EOM 3;
the radio frequency signal source RF4B outputs a radio frequency signal, the signal generated by the radio frequency signal source RF4A is modulated in a phase modulation mode, and the modulated frequency signal output by the radio frequency signal source RF4A is input into the electro-optical modulator four EOM 4.
Step three: the four paths of error signals are respectively fed back to the frequency control ends of the seed lasers in the respective optical paths, the frequencies of the four seed lasers are changed, and the frequencies of the first seed laser and the second seed laser are respectively locked on the first ultrastable cavity FP 1; and respectively locking the frequencies of the third sub laser and the fourth sub laser on the second super stable cavity FP 2.
Specifically, an optical signal λ 1 modulated by EOM1 and an optical signal λ 2 modulated by EOM2 enter a first polarization beam splitter PBS1 and a first super-stable cavity FP1 at the same time, and are then reflected back to enter a first dense wavelength division multiplexer DWDM1; an optical signal lambda 1 output by the DWDM1 passes through a first photoelectric detector PD1, then is mixed with a radio frequency signal output by a radio frequency signal source RF1B in a first mixer, and generates a first Error signal Error1 after passing through a first low pass filter LPF 1; meanwhile, after passing through the second photodetector PD2, the optical signal λ 2 output by the DWDM1 is mixed with the radio frequency signal output by the radio frequency signal source RF2B in the second mixer, and then passes through the second low pass filter LPF2 to generate a second Error signal Error2.
After being processed by the first servo circuit Servol1, the first error signal is fed back to a frequency control end of a first seed laser for emitting the first seed light and the AOM1 for frequency locking, so that the first seed laser is locked on the first super stable cavity FP 1. The locked optical signal lambda 1 is input to a second dense wavelength division multiplexer DWDM2; meanwhile, after being processed by the second servo circuit Servol1, a second error signal is fed back to a frequency control end of a second seed laser for emitting a second seed light and AOM2 for frequency locking, so that the second seed laser is also locked on the first ultrastable cavity FP1, and a locked optical signal lambda 2 is input into a second dense wavelength division multiplexer DWDM2, namely, the first seed laser and the second seed laser are locked on the same ultrastable cavity.
Meanwhile, an optical signal lambda 3 modulated by EOM3 and an optical signal lambda 4 modulated by EOM4 simultaneously enter a second polarization beam splitter PBS2 and a second super stable cavity FP2, and are reflected back to enter a third dense wavelength division multiplexer DWDM3; after an optical signal lambda 3 output by the DWDM3 passes through a third photodetector PD3, the optical signal lambda 3 is mixed with a radio frequency signal output by a radio frequency signal source RF3B in a third mixer, and a third Error signal Error3 is generated after the optical signal lambda 3 passes through a third low pass filter LPF 3; meanwhile, after passing through the fourth photodetector PD4, the optical signal λ 4 output by DWDM3 is mixed with the radio frequency signal output by the radio frequency signal source RF4B in the mixer four, and then passes through the fourth low pass filter LPF4 to generate a fourth Error signal Error4.
And after being processed by a third servo circuit Serpool 3, the third error signal is fed back to a frequency control end of a third sub-laser for transmitting the third seed light and the AOM3 for frequency locking, so that the third sub-laser is locked on the second super-stable cavity FP 2. The locked optical signal lambda 3 is input to a fourth dense wavelength division multiplexer DWDM4; meanwhile, after being processed by the fourth servo circuit Servol4, a fourth error signal is fed back to a frequency control end of a fourth sub-laser for emitting seed light four and the AOM4 for frequency locking, so that the fourth sub-laser is also locked on the second super-stable cavity FP2, and a locked optical signal lambda 4 is input into the fourth dense wavelength division multiplexer DWDM4, namely, the third sub-laser and the fourth sub-laser are locked on the same super-stable cavity.
The second process is divided into the following steps:
step (ii) of firstly, the method comprises the following steps:
radio frequency signal sources RF1A and RF2A are used for tuning the wavelengths of the first seed laser and the second seed laser, respectively, and radio frequency signal sources RF3A and RF4A are used for tuning the wavelengths of the third seed laser and the fourth seed laser, respectively.
By setting the frequencies of the radio frequency signal sources RF1A and RF2A, the optical signal lambda is made 1 And λ 2 With fixed wavelength difference, i.e. λ 1 -λ 2 ＝Δλ 12 Similarly, the wavelength λ of the optical signal is set by setting the frequencies of the RF signal sources RF3A and RF4A 3 And λ 4 Is fixed, i.e. λ 3 -λ 4 ＝Δλ 34 . Simultaneously making optical signal lambda 1 、λ 2 Wavelength difference of (2) and optical signal lambda 3 、λ 4 Are equal in wavelength difference, i.e. Δ λ 12 ＝Δλ 34 ＝0.8nm。
Step (ii) of II, secondly, the method comprises the following steps:
optical signal lambda 2 And λ 4 The lambda is obtained after being input into a laser phase servo system 2 And λ 4 Based on said deviation, the laser phase servo system simultaneously controls the RF signal sources RF4A and RF3A, i.e. the frequency tuning amounts to the RF signal sources RF4A and RF3A are the same, and the optical signal λ is made to be the same 4 Wavelength locked to the optical signal lambda 2 At a wavelength of (i.e.. Lambda.) 4 ＝λ 2 At the same time realize lambda 3 ＝λ 1 And at the moment, the wavelengths of the four seed lasers are aligned in pairs, and finally, the frequency precision control of the four paths of lasers is realized.
The invention provides a double-cavity four-wavelength tunable ultrastable laser method for QKD, which only needs two ultrastable cavities to output four paths of ultrastable laser with independently tunable wavelengths. Because the four paths of ultrastable lasers with the wavelengths respectively come from the two ultrastable cavities, and the frequency difference of the two paths of laser output frequencies from the same ultrastable cavity is kept fixed, the two paths of lasers from the two ultrastable cavities are locked by only one laser phase servo system, and the frequency of the four paths of lasers can be accurately controlled.
In the above embodiments, the implementation may be wholly or partially realized by software, hardware, firmware, or any combination thereof. When implemented in software, it may be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. The procedures or functions described in accordance with the embodiments of the application are all or partially generated when the computer program instructions are loaded and executed on a computer. The computer may be a general purpose computer, a special purpose computer, a network of computers, or other programmable device. The computer instructions may be stored in or transmitted over a computer-readable storage medium. The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device, such as a server, a data center, etc., that incorporates one or more of the available media. The usable medium may be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid State Disk (SSD)), among others.
While the invention has been described with reference to specific embodiments, the scope of the invention is not limited thereto, and those skilled in the art can easily conceive various equivalent modifications or substitutions within the technical scope of the invention. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (6)
1. A multi-wavelength tunable ultrastable laser system, comprising: the system comprises a first ultrastable laser system, a second ultrastable laser system, a first radio frequency system, a second dense wavelength division multiplexer, a fourth dense wavelength division multiplexer and a laser phase servo system;
the first ultrastable laser system is used for locking the frequencies of output light of the first seed light system and the second seed light system to first ultrastable frequencies respectively, outputting the frequencies to the second dense wavelength division multiplexer respectively and used for the first double-field quantum key distribution system;
the second ultrastable laser system is used for locking the frequencies of output light of the third sub-optical system and the fourth sub-optical system to second ultrastable frequencies respectively, and outputting the frequencies to the fourth dense wavelength division multiplexer respectively for the second double-field quantum key distribution system;
the first radio frequency system is used for tuning the light source wavelengths of the first seed light system and the second seed light system, so that the difference value of the light source wavelengths of the two seed light systems is fixed; the second radio frequency system is used for tuning the light source wavelengths of the third sub-optical system and the fourth sub-optical system, so that the difference value of the light source wavelengths of the two sub-optical systems is fixed;
the output light after the frequency locking of the second sub-light system and the output light after the frequency locking of the fourth sub-light system are respectively input to the laser phase servo system, and the laser phase servo system is used for controlling the wavelength of the output light after the frequency locking of the second sub-light system to be equal to that of the output light after the frequency locking of the fourth sub-light system, so that the frequency locking of the first ultrastable laser system and the second ultrastable laser system is realized.
2. The multi-wavelength tunable ultrastable laser system of claim 1, wherein the first seed optical system comprises a first seed laser, a first acousto-optic modulator, a first electro-optic modulator; the second seed light system comprises a second seed laser, an acousto-optic modulator II and an electro-optic modulator II; the seed light I output by the first seed laser sequentially passes through the acousto-optic modulator I and the electro-optic modulator I for error detection, and the seed light II output by the second seed laser sequentially passes through the acousto-optic modulator II and the electro-optic modulator II for error detection;
the third sub-optical system comprises a third sub-laser, an acousto-optic modulator III and an electro-optic modulator III; the fourth sub-optical system comprises a fourth sub-laser, an acousto-optic modulator IV and an electro-optic modulator IV; and the seed light III output by the third sub-laser sequentially passes through the acousto-optic modulator III and the electro-optic modulator III for error detection, and the seed light IV output by the fourth sub-laser sequentially passes through the acousto-optic modulator IV and the electro-optic modulator IV for error detection.
3. The multi-wavelength tunable ultrastable laser system of claim 2, wherein the first radio frequency system comprises a radio frequency signal source RF1A, a radio frequency signal source RF1B, a radio frequency signal source RF2A, a radio frequency signal source RF2B; the radio frequency signal source RF1B and the radio frequency signal source RF2B respectively output radio frequency signals, signals generated by the radio frequency signal source RF1A and the radio frequency signal source RF2A are respectively modulated in a phase modulation mode, and modulated frequency signals output by the radio frequency signal source RF1A and the radio frequency signal source RF2A respectively enter the first electro-optical modulator and the second electro-optical modulator;
the second radio frequency system comprises a radio frequency signal source RF3A, a radio frequency signal source RF3B, a radio frequency signal source RF4A and a radio frequency signal source RF4B; the radio frequency signal source RF3B and the radio frequency signal source RF4B respectively output radio frequency signals, signals generated by the radio frequency signal source RF3A and the radio frequency signal source RF4A are respectively modulated in a phase modulation mode, and modulated frequency signals output by the radio frequency signal source RF3A and the radio frequency signal source RF4A respectively enter the electro-optical modulator III and the electro-optical modulator IV.
4. The multi-wavelength tunable ultrastable laser system of claim 2, wherein the first ultrastable laser system further comprises a first polarization beam splitter, a first ultrastable cavity, a first dense wavelength division multiplexer, first and second photodetectors, a first mixer, a second mixer, first and second low pass filters, and first and second servo circuits;
the optical signals respectively modulated by the first electro-optical modulator and the second electro-optical modulator enter the first polarization beam splitter and the first hyperstable cavity at the same time, and then are reflected back to enter the first dense wavelength division multiplexer; one path of optical signal output by the first dense wavelength division multiplexer passes through a first photoelectric detector, then is mixed with a radio frequency signal output by a radio frequency signal source RF1B in a first mixer, and generates a first error signal after passing through a first low-pass filter; meanwhile, another path of optical signal output by the first dense wavelength division multiplexer passes through a second photoelectric detector, then is mixed with a radio frequency signal output by a radio frequency signal source RF2B in a second mixer, and generates a second error signal after passing through a second low-pass filter;
the first error signal is processed by a first servo circuit and then fed back to a frequency control end of the first seed laser and a first acousto-optic modulator for frequency locking, so that the first seed laser is locked on a first ultrastable cavity; meanwhile, the second error signal is processed by a second servo circuit and then fed back to the frequency control end of the second seed laser and the acousto-optic modulator to be frequency-locked, so that the second seed laser is also locked on the first hyperstable cavity.
5. The multi-wavelength tunable ultrastable laser system according to claim 2, wherein said second ultrastable laser system further comprises a second polarization beam splitter, a second ultrastable cavity, a third dense wavelength division multiplexer, a third and a fourth photodetector, a third mixer, a fourth mixer, a third and a fourth low-pass filter, a third and a fourth servo circuit;
the optical signals respectively modulated by the electro-optical modulator III and the electro-optical modulator IV simultaneously enter a second polarization beam splitter and a second hyperstable cavity, and are then reflected back to enter a third dense wavelength division multiplexer; one path of optical signal output by the third dense wavelength division multiplexer passes through a third photoelectric detector, is mixed with a radio frequency signal output by a radio frequency signal source RF3B in a third mixer, and generates a third error signal after passing through a third low-pass filter; meanwhile, another path of optical signal output by the third dense wavelength division multiplexer passes through a fourth photoelectric detector, is mixed with a radio frequency signal output by a radio frequency signal source RF4B in a fourth mixer, and generates a fourth error signal after passing through a fourth low-pass filter;
after being processed by a third servo circuit, the third error signal is fed back to a frequency control end of the third sub-laser and an acousto-optic modulator for frequency locking, so that the third sub-laser is locked on a second ultrastable cavity; meanwhile, after being processed by a fourth servo circuit, the fourth error signal is fed back to the frequency control end of the fourth sub-laser and the acousto-optic modulator for frequency locking, so that the fourth sub-laser is also locked on the second ultrastable cavity.
6. A frequency manipulation method of a multi-wavelength tunable ultrastable laser system for tuning the multi-wavelength tunable ultrastable laser system of any one of claims 1-5, comprising the steps of:
the method comprises the following steps that firstly, seed light of each seed light system is divided into two beams, one beam is used for error detection, and the other beam is used for a double-field quantum key distribution system;
step two, each seed light system changes the output frequency of the seed light through two radio frequency signal sources in the respective system by a secondary modulation technology to realize independent tuning of wavelength frequency;
step three, respectively feeding back the error signal of each seed light system to the frequency control end of each seed laser, changing the frequency of the seed light, respectively locking the frequencies of the output light of the first seed light system and the second seed light system at the first ultrastable frequency, and respectively locking the frequencies of the output light of the third seed light system and the fourth seed light system at the second ultrastable frequency;
step four, tuning the difference value of the light source wavelengths of the first seed light system and the second seed light system to be a fixed value; tuning the second radio frequency system to tune a difference value of light source wavelengths of the third sub-optical system and the fourth sub-optical system to a fixed value;
and fifthly, controlling the wavelength of the output light of the second sub-optical system after frequency locking to be equal to that of the output light of the fourth sub-optical system after frequency locking by the laser phase servo system, and realizing frequency locking of the first ultrastable laser system and the second ultrastable laser system.
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| CN117375833B (en) * | 2023-12-07 | 2024-03-08 | 济南量子技术研究院 | Transmitting end full-on-chip TF-QKD system based on chip optical comb |
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