Optical frequency distributed amplification device and method

Abstract

The present invention provides an optical frequency distributed amplification device and method, the device comprising: a local oscillator light source, used to output a single-frequency narrow-linewidth laser locked to a time-frequency reference; an optical frequency modulation module, used to modulate an input laser signal; a transmission optical fiber, used to transmit the modulated frequency reference signal to a bidirectional erbium-doped fiber amplifier; a bidirectional erbium-doped fiber amplifier, used to amplify the frequency reference signal; a receiving module, used to receive the optical frequency reference signal and return the optical frequency reference signal; a noise detection module, used to detect the optical frequency reference signal returned from the optical frequency modulation module, generate a modulation signal by separating and comparing high gain noise and low gain noise, and adjust the gain of the bidirectional erbium-doped fiber amplifier according to the modulation signal. Through this scheme, the influence of interference signal ringing and additional broadband noise on the transmission quality of the optical frequency reference signal can be reduced, the optimal setting of the optical fiber amplifier gain can be guaranteed, and the stability and accuracy of the optical frequency reference signal can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of optical communication, and in particular relates to an optical frequency distributed amplification device and method. Background Art

[0002] The frequency accuracy and stability of current optical atomic clocks can reach the order of 10-18. This development has opened up new frequency standards for basic physics, spectroscopy, geodesy, astronomy, and other scientific fields and top technologies. However, optical clocks are extremely complex and expensive devices that are difficult to miniaturize and make portable. In this case, the optical frequency reference signal generated by long-distance distributed optical clocks is an ideal solution.

[0003] Currently, the most promising scheme for optical frequency distribution is to use bidirectionally operated optical fibers equipped with phase stabilization systems to reduce fiber phase and frequency fluctuations caused by temperature changes and vibrations. Since the phase fluctuations loaded on the reverse propagating signal are highly correlated, the phase and frequency fluctuations are usually compensated by detecting the reverse propagating signal. The interference noise of the optical signal depends on various factors, such as the length of the continuous fiber span, the position and amplitude of the reflection and loss, the backscattering characteristics of a specific fiber, the amplitude of vibrations along the fiber, etc. Since these factors are difficult to determine and some of them may change over time, the theoretical calculation or simulation of the interference noise seems to be extremely challenging. In this case, a reasonable solution is to measure the interference noise intensity in real time and determine the optimal gain of the amplifier.

[0004] Existing bidirectional optical amplifier optimization algorithms and correlated noise detection schemes are developed for medium coherence intensity modulated laser source (MHz linewidth) systems and are not suitable for processing signals affected by interference noise and fading. In essence, the main factors limiting the stability and accuracy of frequency transmission are the inherent bandwidth and efficiency limitations of the fiber-induced phase noise cancellation loop, the uncompensated fiber section in the local and remote modules, and the birefringence of the optical path (i.e., polarization mode dispersion). Obviously, the existing schemes are difficult to ensure the optimal amplifier gain setting, which will cause the tracking phase-locked loop to produce periodic jumps, resulting in a serious decrease in the stability and accuracy of the optical frequency reference signal. Summary of the invention

[0005] In view of this, an embodiment of the present invention provides an optical frequency distributed amplification device and method for solving the problem that the optical fiber amplifier gain setting in the existing optical frequency distribution is difficult to achieve the optimal setting, which affects the stability and accuracy of the optical frequency reference signal.

[0006] In a first aspect of an embodiment of the present invention, a method for optical frequency distributed amplification is provided, comprising:

[0007] A local oscillator light source, used to output a single-frequency narrow-linewidth laser locked to a time-frequency reference, and the laser linewidth is less than 100kHz;

[0008] An optical frequency modulation module is used to modulate the input laser signal according to the time code, receive the external modulation signal, realize phase-locked feedback, and output the modulated frequency reference signal;

[0009] Wherein, the output end of the optical frequency modulation module is connected to the first transmission optical fiber and the noise detection module;

[0010] A first transmission optical fiber, used for transmitting the modulated frequency reference signal to the bidirectional erbium-doped optical fiber amplifier;

[0011] A bidirectional erbium-doped fiber amplifier for amplifying the frequency reference signal and compensating for the loss caused by the transmission of the first transmission fiber;

[0012] A second transmission optical fiber, used for transmitting the compensated frequency reference signal to the receiving module;

[0013] A receiving module, used for receiving an optical frequency reference signal and transmitting the optical frequency reference signal back to the optical frequency modulation module;

[0014] The noise detection module is used to detect the optical frequency reference signal transmitted back from the optical frequency modulation module, generate a modulation signal by separating and comparing high gain noise and low gain noise, and adjust the gain of the bidirectional erbium-doped fiber amplifier according to the modulation signal to reduce the influence of interference signal ringing and additional broadband noise on the transmission quality of the optical frequency reference signal.

[0015] In a second aspect of an embodiment of the present invention, an optical frequency distributed amplification system is provided, comprising:

[0016] The local oscillator light source outputs a single-frequency narrow-linewidth laser that is locked to a time-frequency reference;

[0017] Modulate the input laser signal according to the time code, receive the external modulation signal, realize phase-locked feedback, and output the modulated frequency reference signal;

[0018] The modulated frequency reference signal is transmitted to the bidirectional erbium-doped fiber amplifier through the transmission optical fiber, and the frequency reference signal is amplified by the bidirectional erbium-doped fiber amplifier and then transmitted to the receiving end;

[0019] After receiving the optical frequency reference signal, the receiving end transmits the optical frequency reference signal back;

[0020] The returned optical frequency reference signal and the laser signal output by the local oscillator light source are detected, and a modulation signal is generated by separating and comparing the high gain noise and the low gain noise. The gain of the bidirectional erbium-doped fiber amplifier is adjusted according to the modulation signal.

[0021] In the embodiment of the present invention, according to the returned optical frequency reference signal, the high gain noise and the low gain noise are separated and compared by the noise detection module to generate a modulation signal, and the gain of the bidirectional erbium-doped fiber amplifier is adjusted according to the modulation signal, so as to reduce the influence of the interference signal ringing and the additional broadband noise on the transmission quality of the optical frequency reference signal, and ensure the optimal setting of the optical fiber amplifier gain, avoid the periodic jump generated by the tracking phase-locked loop, and thus improve the stability and accuracy of the optical frequency reference signal. At the same time, it can realize the reasonable distribution of the gain between the chain optical fiber amplifiers. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 A schematic diagram of the structure of an optical frequency distributed amplification device provided by one embodiment of the present invention;

[0024] Figure 2 A schematic diagram of the structure of a noise detection module provided by an embodiment of the present invention;

[0025] Figure 3 A schematic flow chart of an optical frequency distributed amplification method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] It should be understood that the term "including" and other similar expressions in the specification or claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions, such as a process, method, system, or device including a series of steps or units is not limited to the listed steps or units. In addition, "first" and "second" are used to distinguish different objects, not to describe a specific order.

[0028] See also Figure 1 , a schematic diagram of the structure of an optical frequency distributed amplification device provided by an embodiment of the present invention, comprising:

[0029] A local oscillator light source 110 is used to output a single-frequency narrow-linewidth laser locked to a time-frequency reference, and the laser linewidth is less than 100 kHz;

[0030] The local oscillator light source 110 is connected to the optical frequency modulation module 120 , and outputs a single-frequency narrow-linewidth laser signal locked to a time-frequency reference to the optical frequency modulation module 120 .

[0031] The optical frequency modulation module 120 is used to modulate the input laser signal according to the time code, receive the external modulation signal, realize the phase-locked feedback, and output the modulated frequency reference signal;

[0032] Wherein, the output end of the optical frequency modulation module 120 is connected to the first transmission optical fiber 130 and the noise detection module 170;

[0033] The optical frequency modulation module 120 receives an external modulation signal, such as a phase stabilization system, and can implement phase-locked feedback, that is, frequency and phase synchronization using feedback control principles, and output a modulated frequency reference signal.

[0034] A first transmission optical fiber 130 is used to transmit the modulated frequency reference signal to the bidirectional erbium-doped optical fiber amplifier;

[0035] The first transmission optical fiber 130 may be a standard communication optical cable with a length greater than 50 km, and is used to transmit the modulated frequency reference signal.

[0036] A bidirectional erbium-doped fiber amplifier 140, used to amplify the frequency reference signal and compensate for the loss caused by the transmission of the first transmission fiber;

[0037] One end of the bidirectional erbium-doped fiber amplifier 140 is connected to the first transmission fiber 130 , and the other end is connected to the second transmission fiber 150 , so as to amplify and compensate the frequency reference signal transmitted by the optical fiber.

[0038] Each bidirectional erbium-doped fiber amplifier 140 has two oppositely pumped semiconductor lasers to provide pumping light and is connected to a transmission optical fiber.

[0039] It can be understood that the number of frequency standard transmission optical fibers and bidirectional erbium-doped fiber amplifiers can be increased according to different transmission distances, and is not limited to the configuration in the embodiment, and the length of the standard transmission optical fiber can be flexibly adjusted according to the transmission distance, for example, multiple sections of transmission optical fibers and multiple bidirectional erbium-doped fiber amplifiers can be set.

[0040] A second transmission optical fiber 150 is used to transmit the compensated frequency reference signal to the receiving module;

[0041] One end of the second transmission optical fiber 150 is connected to the bidirectional erbium-doped fiber amplifier 140 , and the other end is connected to the receiving module 160 , so as to transmit the frequency reference signal after amplifier compensation to the receiving module 160 .

[0042] The receiving module 160 is used to receive the optical frequency reference signal and transmit the optical frequency reference signal back to the optical frequency modulation module;

[0043] The return signal of the receiving module 160 is compared with the laser signal of the local oscillator light source 110 to generate an error signal, which can control the modulator in the optical frequency modulation module to achieve frequency locking.

[0044] The noise detection module 170 is used to detect the optical frequency reference signal transmitted back from the optical frequency modulation module, generate a modulation signal by separating and comparing the high gain noise and the low gain noise, and adjust the gain of the bidirectional erbium-doped fiber amplifier according to the modulation signal to reduce the influence of the interference signal ringing and the additional broadband noise on the transmission quality of the optical frequency reference signal.

[0045] The optical frequency reference signal transmitted back to the optical frequency modulation module carries various noises generated by the entire transmission link. Through calculation, the modulation signal of the bidirectional erbium-doped fiber amplifier can be generated, and the gain of each bidirectional erbium-doped fiber amplifier in the transmission link can be adjusted one by one.

[0046] If the high gain noise is less than the low gain noise, the gain is set to be reduced, and if the high gain noise is greater than the low gain noise, the gain is set to be increased.

[0047] In one embodiment, Figure 2 As shown, the noise detection module 170 includes a high-speed detector 210, a first bandpass filter 220, an envelope detector 230, an exponential amplifier 240, a second bandpass filter 250, a first analog-to-digital converter 260, a low-pass filter 270 and a second analog-to-digital converter 280.

[0048] Among them, one end of the high-speed detector 210 is connected to the optical frequency modulation module 120, and the other end is connected to the first bandpass filter 220, one end of the first bandpass filter 220 is connected to the envelope detector 230, and the other end of the envelope detector 230 is connected to the exponential amplifier 240, and the output end of the exponential amplifier 240 is respectively connected to the second bandpass filter 250 and the low-pass filter 270, the output end of the second bandpass filter 250 is connected to the first analog-to-digital converter 260, and the output end of the low-pass filter 270 is connected to the second analog-to-digital converter 280.

[0049] The high-speed detector 210 is used to detect the received optical frequency reference signal and the laser signal output by the local oscillator light source.

[0050] The working bandwidth of the first bandpass filter 220 covers the beat frequency signal, and the beat frequency signal includes gain, interference and broadband additional noise.

[0051] The envelope detector 230 is used to distinguish high-frequency components and low-frequency components generated by noise.

[0052] The exponential amplifier 240 is used to control the signal gain according to the input current so that the amplitude modulation depth of each type of noise is directly related to the signal-to-noise ratio.

[0053] The second bandpass filter 250 is used to filter out high-gain noise; and the low-pass filter 270 is used to filter out low-gain noise.

[0054] The first analog-to-digital converter 260 is used to convert the high-gain noise signal from an analog signal to a digital signal; and the second analog-to-digital converter 280 is used to convert the low-gain noise signal from an analog signal to a digital signal.

[0055] The working principle of the noise detection module 170 is:

[0056] The optical frequency reference signal 120 and the laser signal output by the local oscillator light source 110 are simultaneously injected into the high-speed detector 210. The detected information includes the local oscillator light, the transmission return light, and the noise information carried in the transmission link. By selecting the first bandpass filter 220 with a suitable filtering bandwidth, the beat signal consisting of gain, interference, and broadband additional noise near the beat signal is extracted. The beat signal is manifested as a superposition of a series of time domain vibrations in the time domain and as different frequency spectra distributed near the beat signal in the frequency domain. Under the action of the first bandpass filter 220, the broadband noise is converted into bandwidth-limited noise, with the beat signal frequency as the center. During the amplification process, the sinusoidal signal destroyed by the additional bandwidth-limited noise can be regarded as amplitude and phase modulated by the so-called in-phase and orthogonal components of the noise. Since the amplitude modulation depth of each type of noise is directly related to the signal-to-noise ratio, the envelope detector 230 and the exponential amplifier 240 measure the change in the signal-to-noise ratio. At the output of the envelope detector, the two types of noise (related to the low and high amplification mechanisms) can be distinguished in the frequency domain because they produce low-frequency components and relatively wide components, namely high-gain noise and low-gain noise, respectively. In order to separate these two types of noise, the signals output by the exponential amplifier 240 are respectively input to the second bandpass filter 250 and the low-pass filter 270, separated according to frequency, and the output signals of the two filters are digitized using the first analog-to-digital converter 260 and the second analog-to-digital converter 280, and the standard deviation of the two signals is calculated.

[0057] It will be appreciated that, due to the use of exponential amplifier 240, the readings at the two outputs of the noise detector are inversely proportional to the signal-to-noise ratio associated with the particular type of noise, but are independent of the absolute amplitude of the beat frequency signal.

[0058] In this embodiment, only the amplitude noise is separately detected, which has an important advantage, that is, the residual environmental phase noise of the link is not sensitive and will not generate crosstalk with the frequency phase-locked loop to affect frequency locking.

[0059] In another embodiment, the control logic for controlling the gain of multiple optical fiber amplifiers to suppress noise is:

[0060] High-gain and low-gain noise are obtained through the noise detector, and noise amplitude comparison is started in the control circuit. The default optimization start direction is forward amplification link gain optimization; if the high-gain noise is less than the low-gain noise, the gain is set to decrease; if the high-gain noise is greater than the low-gain noise, the gain is set to increase.

[0061] After the setting is completed, the noise is detected through the noise detector. If the gain noise is reduced, it will directly switch to the next amplifier and start optimizing the gain of the next amplifier. If the gain noise remains unchanged or increases, the gain adjustment direction is set to switch, that is, the reverse amplification link gain is optimized. Similarly, first set to obtain high gain and low gain noise, and detect the noise through the noise detector. If the gain noise is reduced, it will directly switch to the next amplifier. If the gain noise is not reduced, it means that the current gain setting is reasonable, enter the fixed amplifier gain setting, and switch to the next amplifier.

[0062] In this embodiment, based on the two-dimensional noise detection module, the contribution of interference signal ringing and additional broadband noise to the frequency spectrum noise can be independently measured. The feedback signal based on noise detection can correctly distribute the required gain between the chain amplifiers to avoid the influence of back noise, shot noise, white noise, etc. At the same time, it has the ability to optimize gain. When initialization or link changes, the gain can be reduced or increased according to the currently dominant noise type. Reducing the reaction time avoids unnecessary periodic jumps and the loss of lock of the amplifier laser or even the entire transmission system. Furthermore, it not only reduces the impact of interference signal ringing and additional broadband noise on the transmission quality of the optical frequency reference signal, but also ensures the optimal setting of the optical fiber amplifier gain, and improves the stability and accuracy of the optical frequency reference signal.

[0063] It should be understood that the serial numbers of the steps in the above embodiments do not imply a sequence of execution, and the execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0064] Figure 3 A schematic flow chart of an optical frequency distributed amplification method provided by an embodiment of the present invention, the method comprising:

[0065] S301, the local oscillator light source outputs a single-frequency narrow-linewidth laser locked to a time-frequency reference;

[0066] S302, modulating the input laser signal according to the time code, receiving the external modulation signal, realizing phase-locked feedback, and outputting the modulated frequency reference signal;

[0067] S303, transmitting the modulated frequency reference signal to the bidirectional erbium-doped fiber amplifier through the transmission optical fiber, amplifying the frequency reference signal through the bidirectional erbium-doped fiber amplifier, and then transmitting it to the receiving end;

[0068] S304, after receiving the optical frequency reference signal, the receiving end returns the optical frequency reference signal;

[0069] S305, detecting the returned optical frequency reference signal and the laser signal output by the local oscillator light source, generating a modulation signal by separating and comparing the high gain noise and the low gain noise, and adjusting the gain of the bidirectional erbium-doped fiber amplifier according to the modulation signal.

[0070] If the high gain noise is less than the low gain noise, the gain is set to be reduced, and if the high gain noise is greater than the low gain noise, the gain is set to be increased.

[0071] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and modules described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0072] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0073] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optical frequency distributed amplification device, characterized in that: include: A local oscillator light source, used to output a single-frequency narrow-linewidth laser locked to a time-frequency reference, and the laser linewidth is less than 100kHz; An optical frequency modulation module is used to modulate the input laser signal according to the time code, receive the external modulation signal, realize phase-locked feedback, and output the modulated frequency reference signal; Wherein, the output end of the optical frequency modulation module is connected to the first transmission optical fiber and the noise detection module; A first transmission optical fiber, used for transmitting the modulated frequency reference signal to the bidirectional erbium-doped optical fiber amplifier; A bidirectional erbium-doped fiber amplifier for amplifying the frequency reference signal and compensating for the loss caused by the transmission of the first transmission fiber; A second transmission optical fiber, used for transmitting the compensated frequency reference signal to the receiving module; A receiving module, used for receiving an optical frequency reference signal and transmitting the optical frequency reference signal back to the optical frequency modulation module; The noise detection module is used to detect the optical frequency reference signal transmitted back from the optical frequency modulation module, generate a modulation signal by separating and comparing high gain noise and low gain noise, and adjust the gain of the bidirectional erbium-doped fiber amplifier according to the modulation signal to reduce the influence of interference signal ringing and additional broadband noise on the transmission quality of the optical frequency reference signal.

2. The device according to claim 1, characterized in that The noise detection module includes a high-speed detector, a first bandpass filter, an envelope detector, an exponential amplifier, a second bandpass filter, a first analog-to-digital converter, a low-pass filter, and a second analog-to-digital converter; Among them, one end of the high-speed detector is connected to the optical frequency modulation module, and the other end is connected to the first band-pass filter, one end of the first band-pass filter is connected to the envelope detector, and the other end of the envelope detector is connected to the exponential amplifier, the output end of the exponential amplifier is respectively connected to the second band-pass filter and the low-pass filter, the output end of the second band-pass filter is connected to the first analog-to-digital converter, and the output end of the low-pass filter is connected to the second analog-to-digital converter.

3. The device according to claim 2, characterized in that The high-speed detector is used to detect the optical frequency reference signal received back and the laser signal output by the local oscillator light source.

4. The device according to claim 2, characterized in that The working bandwidth of the first bandpass filter covers the beat frequency signal, and the beat frequency signal includes gain, interference and broadband additional noise.

5. The device according to claim 2, characterized in that The envelope detector is used to distinguish high-frequency components and low-frequency components generated by noise.

6. The device according to claim 2, characterized in that The exponential amplifier is used to control the signal gain according to the input current so that the amplitude modulation depth of each type of noise is related to the signal-to-noise ratio.

7. The device according to claim 2, characterized in that The second bandpass filter is used to filter out high-gain noise; and the low-pass filter is used to filter out low-gain noise.

8. The device according to claim 2, characterized in that The first analog-to-digital converter is used to convert the high-gain noise signal from an analog signal to a digital signal; the second analog-to-digital converter is used to convert the low-gain noise signal from an analog signal to a digital signal.

9. The device according to claim 1, characterized in that The method of generating a modulation signal by separating and comparing high gain noise and low gain noise, and adjusting the gain of the bidirectional erbium-doped fiber amplifier according to the modulation signal comprises: If the high gain noise is less than the low gain noise, the gain is set to decrease; if the high gain noise is greater than the low gain noise, the gain is set to increase.

10. An optical frequency distributed amplification method using the optical frequency distributed amplification device according to any one of claims 1 to 9, characterized in that: include: The local oscillator light source outputs a single-frequency narrow-linewidth laser that is locked to a time-frequency reference; Modulate the input laser signal according to the time code, receive the external modulation signal, realize phase-locked feedback, and output the modulated frequency reference signal; The modulated frequency reference signal is transmitted to the bidirectional erbium-doped fiber amplifier through the transmission optical fiber, and the frequency reference signal is amplified by the bidirectional erbium-doped fiber amplifier and then transmitted to the receiving end; After receiving the optical frequency reference signal, the receiving end transmits the optical frequency reference signal back; The returned optical frequency reference signal and the laser signal output by the local oscillator light source are detected, and a modulation signal is generated by separating and comparing the high gain noise and the low gain noise. The gain of the bidirectional erbium-doped fiber amplifier is adjusted according to the modulation signal.

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