Phase noise compensation system and method in optical fiber link

Abstract

A phase noise compensation system in an optical fiber link includes a continuous light source, a first electro-optical modulator, a second electro-optical modulator, a radio frequency signal generator and a 1×2 optical coupler in a local segment, and a double frequency module, a multiplier module, an amplitude normalization module, a filter module, a first photodetector and a second photodetector at a remote end; and a compensation method thereof, which cancels the phase noise in the link based on the phase conjugation principle and completes the phase noise compensation of the transmitted signal. The present invention does not rely on any link status information and system parameters, reduces the complexity of calculation, is more convenient to implement, and thus improves the stability of the system.

Description

Technical Field

[0001] The present invention belongs to the field of optical fiber transmission and sensing, and more specifically, relates to a phase noise compensation system and method in an optical fiber link. Background Art

[0002] In recent years, with the continuous development of science and technology, the stability of optical fiber transmission has been greatly improved. At the same time, many fields such as deep space exploration, particle accelerators, navigation and communication, and defense applications such as array radars have an increasing demand for high-stability frequency sources and long-distance frequency synchronization. However, these high-stability frequency sources are very expensive, usually huge in size and need to operate in an ideal environment. Therefore, long-distance transmission, high-stability frequency signals, and long-distance signal transmission are of great significance. The existing phase compensation schemes have the following shortcomings: 1. It is necessary to accurately and real-time extract the phase noise introduced by link delay jitter, so relatively complex and precise noise extraction and processing modules are required; 2. Many schemes require relatively complex algorithms to convert the extracted phase noise information into control signals for driving the compensation module, which increases the complexity of the system; 3. The production and control of the noise compensation module are relatively complex, and there are insufficient precision, insufficient compensation dynamic range, and the introduction of additional electrical noise.

[0003] Invention patent announcement number CN108282227B discloses a phase conjugation-based quadruple frequency signal optical fiber arbitrary point stable phase distribution system. The invention mainly realizes the stable distribution of any point in the optical fiber during the transmission process, and the output is a quadruple frequency signal, while the present invention compensates for the phase noise after optical fiber transmission, with the purpose of restoring the original transmission signal. The quadruple frequency signal requires a larger bandwidth and higher sampling rate photodetector and acquisition card, which will greatly increase the system cost, and compared with the invention, the present invention uses fewer optoelectronic components to introduce less hardware noise and reduce structural complexity. Summary of the invention

[0004] The purpose of the present invention is to compensate for the phase noise caused by active device noise and external environmental interference in an optical fiber transmission link and improve the stability of the system.

[0005] In order to achieve the above object, the technical solution provided by the present invention is:

[0006] A phase noise compensation system in an optical fiber link is characterized in that it comprises a continuous light source, a first electro-optical modulator, a second electro-optical modulator, a radio frequency signal generator and a 1×2 optical coupler at a local end, and a double frequency module, a multiplier module, an amplitude normalization module, a filter module, a first photodetector and a second photodetector at a remote end;

[0007] The continuous light source is divided into two optical signals by the 1×2 optical coupler, one of which is injected into the first electro-optical modulator, the radio frequency signal output by the radio frequency signal generator is loaded on the modulation end of the first electro-optical modulator, the output end of the first electro-optical modulator is connected to the input end of the first photodetector through the first optical fiber link, the output signal of the first photodetector is converted into a pre-compensation detection signal by the amplitude normalization module and enters the first input end of the multiplier module; the other optical signal enters the second electro-optical modulator; the second output signal of the radio frequency signal generator is converted into a double frequency signal by the double frequency module and then injected into the second input end of the multiplier module;

[0008] The doubled frequency signal and the pre-compensation detection signal are multiplied and mixed in the multiplier module, and the output mixed signal enters the filter module for filtering and then outputs a phase conjugate signal. The phase conjugate signal is phase conjugate with the pre-compensation detection signal and enters the second electro-optical modulator for modulation. The second electro-optical modulator is connected to the second photodetector via a second optical fiber link, thereby offsetting the phase noise in the first optical fiber link and completing the phase noise compensation of the transmitted signal.

[0009] For the convenience of description, a standard signal is generated by a highly stable frequency source at the local end. The signal V1 is generated by a radio frequency signal generator and can be expressed as:

[0010]

[0011] Where A is the RF signal amplitude, w 0 is the RF signal frequency, is the initial phase of the RF signal, expressed as a cosine signal. By modulating the optical carrier, V1 is transmitted to the remote end through the optical fiber link, and after passing through the first photoelectric detector and the amplitude normalization module, the amplitude normalization signal V2 can be expressed as:

[0012]

[0013] In the formula, It represents the total phase noise introduced by the optical device, environment and fiber delay during the transmission process, which is superimposed on the phase of the transmitted signal. At the same time, the RF signal V1 is converted into a double frequency signal V3 through the double frequency module, which can be expressed as:

[0014]

[0015] The frequency doubling signal V3 and the amplitude normalization signal V2 are input into the multiplier module, and the mixed signal V4 is output, which can be expressed as:

[0016]

[0017] After the mixed signal V4 passes through the filter module, a phase conjugate signal V5 can be obtained:

[0018]

[0019] V5 is modulated onto an optical carrier and then enters the second optical fiber. Since the phase conjugate signal V5 and the amplitude normalized signal V2 have a phase conjugate relationship, the phase error can be offset by transmitting the phase conjugate signal V5 in the new link, thereby compensating for the phase noise.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The phase noise in the link is offset based on the phase conjugation principle to complete the phase noise compensation of the transmitted signal.

[0022] (2) By using different optical carriers, the symmetry of the optical fiber link is improved; by using remote multiplier modules and filter modules, the impact of the environment and active devices on the link and signal stability can be effectively suppressed. At the same time, the improved solution can effectively solve the problem of complex structure and the introduction of too many optoelectronic components.

[0023] (3) The detection signal does not need to be introduced into the algorithm or optical path, which reduces the structural complexity.

[0024] (4) There is no need to introduce too many optoelectronic components, and the double frequency module and filter module do not require additional sampling rate and photodetector, which can effectively reduce system costs.

[0025] (5) Multiple links can be combined as needed to form a multi-core optical fiber link to compensate for the phase noise in multiple links, effectively improving the flexibility of the compensation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure of the phase noise compensation system in the optical fiber link of the present invention;

[0027] Figure 2 is the initial RF signal.

[0028] Figure 3 This is the Lissajous figure of the pre-compensation signal and the initial signal.

[0029] Figure 4 This is the Lissajous figure of the compensated signal and the initial signal. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below in conjunction with the accompanying drawings:

[0031] Figure 1 An improved phase noise compensation system and method of the present invention comprises a continuous light source 1, a first electro-optical modulator 2, a second electro-optical modulator 3, a radio frequency signal generator 4, a 1×2 optical coupler 13 at the local end, a double frequency module 5, a multiplier module 6, an amplitude normalization module 7, a filter module 8, a first photodetector 9, and a second photodetector 10 at the remote end. At the local end, the output end of the continuous light source 1 is connected to the 1×2 optical coupler 13 and is divided into two light signals, wherein the first output end is connected to the input end of the first electro-optical modulator 2, the radio frequency signal generator 4 outputs a radio frequency signal V1 which is loaded on the modulation port of the first electro-optical modulator 2, the output end is connected to the first optical fiber 11, and the signal enters the first photodetector 9 at the remote end after transmission, and the output signal enters the amplitude normalization module 7 and is converted into a detection signal V2 before compensation, and the output end is connected to the first input end of the multiplier module 6. At the same time, the second output end of the RF signal generator 4 is connected to the input end of the double frequency module 5 and converted into a double frequency signal V3. The output end is connected to the second input end of the multiplier module 6, and the double frequency signal V3 and the pre-compensation detection signal V2 are multiplied and mixed to obtain a mixed signal V4. After the output, the signal enters the filter module 8 to obtain a signal V5 that is phase conjugated with the pre-compensation detection signal V2. The phase conjugated signal V5 enters the modulation end of the second electro-optical modulator 3. The second signal output by the 1×2 optical coupler 13 enters the input end of the second electro-optical modulator 3, and the output end is connected to the second optical fiber 12. After transmission, it is received and output by the second photodetector 10. The phase noise in the link is offset based on the phase conjugation principle to complete the phase noise compensation of the transmitted signal.

[0032] Figure 2 The initial RF signal in the improved phase noise compensation system and method of the present invention is a cosine signal with an amplitude of 1V. The total phase noise introduced by the simulated environmental interference and time delay is pi / 6. At this time, the received signal before compensation is obtained. The Lissajous figure is drawn using the signal and the initial signal to obtain Figure 3 .from Figure 3 It can be seen from the figure that the ellipse shows a 30° deviation, indicating that the phase difference between the two signals is 30°, proving that the received signal has phase noise. Subsequently, an improved phase noise compensation system and method of the present invention is used for compensation, and the compensated signal is then compared with the initial signal to form a Lissajous figure to obtain Figure 4 ,from Figure 4 It can be seen that the graph is a monotonically increasing straight line, indicating that the phase difference between the two signals is 0, that is, the simulated phase noise is compensated and the phase information of the original signal is restored.

[0033] Experiments have shown that in the fiber modulation structure of the present invention, a detection signal is used for loop transmission. During the link transmission process, phase noise will be generated due to delay jitter and environmental disturbance; at the receiving end, the detection signal and the transmitted signal are mixed, doubled and filtered to obtain a set of new transmission signals that are phase-conjugated with the transmitted signal. Finally, the phase conjugation principle is used to offset the phase noise in the same new link, thereby completing the phase noise compensation of the transmitted signal. At the same time, the method can be superimposed and combined as needed to form a multi-core optical fiber link to compensate for the phase noise in multiple links. The present invention does not rely on any link status information and system parameters, reduces the complexity of the calculation, is more convenient to implement, and thus improves the stability of the system.

[0034] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A phase noise compensation system in an optical fiber link, characterized in that: It comprises a continuous light source (1), a first electro-optical modulator (2), a second electro-optical modulator (3), a radio frequency signal generator (4) and a 1×2 optical coupler (13) at the local end, and a double frequency module (5), a multiplier module (6), an amplitude normalization module (7), a filter module (8), a first photodetector (9) and a second photodetector (10) at the remote end; The continuous light source (1) is divided into two optical signals through the 1×2 optical coupler (13), one of which is injected into the first electro-optical modulator (2), the radio frequency signal generator (4) outputs a radio frequency signal V1 which is loaded on the modulation end of the first electro-optical modulator (2), the output end of the first electro-optical modulator (2) is connected to the input end of the first photoelectric detector (9) through a first optical fiber link (11), the output signal of the first photoelectric detector (9) is converted into a pre-compensation detection signal V2 through the amplitude normalization module (7) and enters the first input end of the multiplier module (6); the other optical signal enters the second electro-optical modulator (3); the second output signal of the radio frequency signal generator (4) is converted into a double frequency signal V3 through the double frequency module (5) and then injected into the second input end of the multiplier module (6); The doubled frequency signal V3 and the pre-compensation detection signal V2 are multiplied and mixed in the multiplier module (6) to output a mixed signal V4, which enters the filter module (8) for filtering and outputs a phase conjugate signal V5. The phase conjugate signal V5 is phase conjugated with the pre-compensation detection signal V2 and enters the second electro-optical modulator (3) for modulation. The second electro-optical modulator (3) is connected to the second photodetector (10) via a second optical fiber link (12), thereby offsetting the phase noise in the first optical fiber link and completing the phase noise compensation of the transmitted signal.

2. A method for compensating phase noise in an optical fiber link, characterized in that: The specific steps of this method are as follows: Local end: The RF signal generator (4) generates a RF signal V1 as a standard signal, and the formula is as follows: Where A is the RF signal amplitude, w0 is the RF signal frequency, is the initial phase of the RF signal, expressed as a cosine signal; By modulating the optical carrier, the radio frequency signal V1 is transmitted to the remote end via the first optical fiber link, and after passing through the first photoelectric detector (9) and the amplitude normalization module (7), a pre-compensation detection signal V2 is obtained, which is expressed as: In the formula, It represents the total phase noise introduced by optical devices, environment and fiber delay during transmission. The radio frequency signal V1 is converted into a double frequency signal V3 through the double frequency module (5), which is expressed as: The double frequency signal V3 and the amplitude normalized signal V2 are input into the multiplier module (6), and the mixed signal V4 is output, which is expressed as: After the mixed signal V4 passes through the filter module (8), a phase conjugate signal V5 is obtained, which is expressed as: The phase conjugated signal V5 is modulated onto an optical carrier and then enters the second optical fiber link (12). Since the phase conjugated signal V5 and the amplitude normalized signal V2 have a phase conjugated relationship, the conjugated signal V5 is transmitted in the new link to offset the phase error, thereby compensating for the phase noise.

Images