A same fiber same wave optical fiber time transfer device

Abstract

An optical fiber time transfer device with same fiber and same wave includes: a near-end device, a middle downloading device and a far-end device connected by an optical fiber; the near-end device mainly includes a single fiber bidirectional connector, an f0 related signal generator, an f1 related signal generator, an optical transmitter, an optical receiver, an f1 microwave filter and a signal processing unit; the far-end device mainly includes a single fiber bidirectional connector, an f0 related signal generator, an f1 related signal generator, an optical transmitter, an optical receiver, a f0 microwave filter and a signal processing unit; the middle downloading device includes a 2*2 optical coupler OC, an f0 related signal generator, an f1 related signal generator, an f1 microwave filter, a f0 microwave filter, an optical receiver and a signal processing unit. The device can use the same wavelength of optical carrier in the same optical fiber in different directions for time transfer, ensure the symmetry of bidirectional transmission, and effectively suppress the influence of backscattering.

Description

Technical Field

[0001] This invention relates to time comparison and frequency calibration, and in particular to an optical fiber time transfer device with the same fiber and the same wavelength. Background Technology

[0002] Time is one of the seven international base units and is currently the most precisely measured. Precise time and frequency standards play a crucial supporting role in numerous scientific research areas, including the measurement of fundamental physical quantities, gravitational wave detection, and radio telescope arrays. They also play an indispensable role in 5G communications, radar arrays, and the Internet of Things. Thanks to the advantages of optical fiber, such as its large bandwidth, low loss, and resistance to electromagnetic interference, fiber optic time synchronization has become the mainstream solution for constructing time and frequency systems.

[0003] The core of fiber optic time synchronization lies in accurately subtracting the link delay introduced by the transmission of the time signal in the fiber. The mainstream approach is to measure the bidirectional transmission delay of the time signal and take half of the bidirectional transmission delay as the unidirectional link delay. This approach relies on the assumption of symmetry in bidirectional transmission of the fiber; therefore, using different wavelengths for bidirectional transmission introduces some asymmetry, requiring complex link calibration. Furthermore, using the same wavelength for bidirectional time transmission in the same fiber degrades the signal-to-noise ratio and reduces transmission distance. While time-division multiplexing (TDM) technology can avoid these problems, its control method is complex and requires customized repeater devices. Summary of the Invention

[0004] This invention aims to solve the above-mentioned technical problems and proposes a fiber optic time transfer device with the same wavelength on the same fiber, comprising: a near-end device, an intermediate download device, and a far-end device connected by optical fibers; it can use the same wavelength optical carrier in different directions in the same optical fiber for time transfer while ensuring the signal-to-noise ratio.

[0005] The near-end device includes a first f0 correlation signal generator, a first f1 correlation signal generator, a first optical transmitter, a first optical receiver, a first f1 microwave filter, a first signal processing unit, and a first single-fiber bidirectional connector. The first port of the first f0 correlation signal generator is an external time reference input port, and its second port is connected to the first port of the first optical transmitter. The first port of the first f1 correlation signal generator is also an external time reference input port, and its second port is connected to the second port of the first signal processing unit. The second port of the first optical transmitter is connected to the first port of the first single-fiber bidirectional connector. The first port of the first optical receiver is connected to the third port of the first single-fiber bidirectional connector, and its second port is connected to the first port of the first f1 microwave filter. The second port of the first f1 microwave filter is connected to the first port of the first signal processing unit. The second port of the first single-fiber bidirectional connector is connected to an optical fiber that transmits time information.

[0006] The remote device includes a second f0 correlation signal generator, a second f1 correlation signal generator, a second optical transmitter, a second optical receiver, a first f0 microwave filter, a second signal processing unit, and a second single-fiber bidirectional connector. The first port of the second f1 correlation signal generator is an external time reference input port, and its second port is connected to the second port of the second signal processing unit. The second port of the second f1 correlation signal generator is also an external time reference input port, and its second port is connected to the first port of the second optical transmitter. The second port of the second optical transmitter is connected to the first port of the second single-fiber bidirectional connector. The first port of the second optical receiver is connected to the third port of the second single-fiber bidirectional connector, and its second port is connected to the first port of the first f0 microwave filter. The second port of the first f0 microwave filter is connected to the first port of the second signal processing unit. The second port of the second single-fiber bidirectional connector is connected to an optical fiber that transmits time information.

[0007] The intermediate download device includes a 2×2 optical coupler OC, a third f0 correlation signal generator, a third f1 correlation signal generator, a second f1 microwave filter, a second f0 microwave filter, a third optical receiver, a fourth optical receiver, a third signal processing unit, and a fourth signal processing unit. The first port of the 2×2 optical coupler OC is connected to the optical fiber transmitting time information near the near-end device, the second port is connected to the optical fiber transmitting time information near the far-end device, the third port is connected to the first port of the third optical receiver, and the fourth port is connected to the first port of the fourth optical receiver. The first port of the third f0 correlation signal generator is an external time reference input port, and the second port is connected to the second port of the third signal processing unit. The first port of the third f1 correlation signal generator is an external time reference input port, and the second port is connected to the second port of the fourth signal processing unit. The first port of the second f1 microwave filter is connected to the second port of the fourth optical receiver, and the second port is connected to the first port of the fourth signal processing unit. The first port of the second f0 microwave filter is connected to the second port of the third optical receiver, and the second port is connected to the first port of the third signal processing unit.

[0008] The optical transmission of the first single-fiber bidirectional connector and the second single-fiber bidirectional connector is as follows:

[0009] When light enters from the first port of the first single-fiber bidirectional connector and the first port of the second single-fiber bidirectional connector respectively, it is output from the second port of the first single-fiber bidirectional connector and the second port of the second single-fiber bidirectional connector.

[0010] When light enters from the second port, it exits from the third port.

[0011] The optical transmission of the first 2×2 optical coupler OC is as follows:

[0012] If light enters from the first port, it will exit from the second and third ports; if light enters from the second port, it will exit from the first and fourth ports.

[0013] The first f0 correlation signal generator, the second f0 correlation signal generator, and the third f0 correlation signal generator can detect the time information received from the first port, generate a correlation signal s0, and output it from the second port; the correlation signals generated by the first f0 correlation signal generator, the second f0 correlation signal generator, and the third f0 correlation signal generator are cross-correlated signals.

[0014] The first f1 correlation signal generator, the second f1 correlation signal generator, and the third f1 correlation signal generator can detect the time information received from the first port, generate a correlation signal s1, and output it from the second port; the correlation signals generated by the first f1 correlation signal generator, the second f1 correlation signal generator, and the third f1 correlation signal generator c2 are cross-correlated signals, and their spectra do not overlap with the spectrum of the signal s1.

[0015] The passband range of the first f1 microwave filter and the second f1 microwave filter includes the spectrum range of the related signal s1 but does not include the spectrum of the related signal s0.

[0016] The passband range of the first f0 microwave filter and the second f0 microwave filter includes the spectrum range of the related signal s0 but does not include the spectrum of the related signal s1.

[0017] The first signal processing unit, the second signal processing unit, the third signal processing unit, and the fourth signal processing unit are used to perform cross-correlation operations on the input signals and obtain the input time difference between the two signals based on the operation results.

[0018] It can use optical amplifiers to extend the transmission distance and increase the number of intermediate download devices, so multiple intermediate download devices can exist.

[0019] The first optical transmitter and the second optical transmitter use the same optical carrier wavelength.

[0020] In addition, optical splitters can be added at any location on the transmission fiber to increase remote sites, enabling point-to-multipoint distributed time transmission on the same fiber and wavelength.

[0021] The correlation signals (s1, s2, s3…sN) generated by each remote station and the correlation signal (s0) generated by the near station in the system have no spectral overlap.

[0022] The near-end station includes the correlation signal generator and filter corresponding to the correlation signals (s1, s2, s3...sN) generated by each far-end station.

[0023] The optical transmitters at different remote sites use the same optical carrier wavelength.

[0024] Compared with the prior art, the beneficial effects of the present invention

[0025] Using light of the same wavelength in the same optical fiber for bidirectional time transmission maximizes the symmetry of bidirectional transmission, simplifies control, and eliminates the need for customized repeater amplification devices. Attached Figure Description

[0026] Figure 1 This is a structural diagram of an optical fiber time transfer device of the present invention, which uses the same fiber and the same wavelength.

[0027] Figure 2 This is a schematic diagram of the working principle of the signal processing unit of the optical fiber time transfer device system of the present invention.

[0028] Figure 3 This is a schematic diagram of an embodiment of the optical fiber time transfer device system of the present invention.

[0029] Figure 4 This is a schematic diagram of the point-to-multipoint structure of Embodiment 2 of the distributed time transfer device of the present invention, which is based on the same fiber and same wave. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0031] In the description of this invention, it should be understood that the term 'proximal end' refers only to the endpoint where the time-frequency reference source is located, and is not a fixed endpoint. The terms 'low frequency' and 'high frequency' refer only to the relative frequency, and do not specifically refer to frequencies higher or lower than a particular frequency.

[0032] The following description, in conjunction with the accompanying drawings, illustrates an optical fiber time transfer device based on the present invention, which operates on the same fiber and wavelength.

[0033] Please refer to Figure 1 , Figure 1 This is a structural diagram of a fiber optic time transfer device of the present invention. As can be seen from the figure, the fiber optic time transfer device of the present invention includes: a near-end device, an intermediate download device, and a far-end device connected by optical fibers; it can use the same wavelength optical carrier in different directions in the same optical fiber to perform time transfer while ensuring the signal-to-noise ratio.

[0034] The near-end device includes a first f0 correlation signal generator, a first f1 correlation signal generator, a first optical transmitter, a first optical receiver, a first f1 microwave filter, a first signal processing unit, and a first single-fiber bidirectional connector. The first port of the first f0 correlation signal generator is an external time reference input port, and its second port is connected to the first port of the first optical transmitter. The first port of the first f1 correlation signal generator is also an external time reference input port, and its second port is connected to the second port of the first signal processing unit. The second port of the first optical transmitter is connected to the first port of the first single-fiber bidirectional connector. The first port of the first optical receiver is connected to the third port of the first single-fiber bidirectional connector, and its second port is connected to the first port of the first f1 microwave filter. The second port of the first f1 microwave filter is connected to the first port of the first signal processing unit. The second port of the first single-fiber bidirectional connector is connected to an optical fiber that transmits time information.

[0035] The remote device includes a second f0 correlation signal generator, a second f1 correlation signal generator, a second optical transmitter, a second optical receiver, a first f0 microwave filter, a second signal processing unit, and a second single-fiber bidirectional connector. The first port of the second f1 correlation signal generator is an external time reference input port, and its second port is connected to the second port of the second signal processing unit. The second port of the second f1 correlation signal generator is also an external time reference input port, and its second port is connected to the first port of the second optical transmitter. The second port of the second optical transmitter is connected to the first port of the second single-fiber bidirectional connector. The first port of the second optical receiver is connected to the third port of the second single-fiber bidirectional connector, and its second port is connected to the first port of the first f0 microwave filter. The second port of the first f0 microwave filter is connected to the first port of the second signal processing unit. The second port of the second single-fiber bidirectional connector is connected to an optical fiber that transmits time information.

[0036] The intermediate download device includes a first 2×2 optical coupler (OC), a third f0 correlation signal generator, a third f1 correlation signal generator, a second f1 microwave filter, a second f0 microwave filter, a third optical receiver, a fourth optical receiver, a third signal processing unit, and a fourth signal processing unit. The first port of the first 2×2 optical coupler (OC) is connected to an optical fiber transmitting time information near the near-end device, the second port is connected to an optical fiber transmitting time information near the far-end device, the third port is connected to the first port of the third optical receiver, and the fourth port is connected to the first port of the fourth optical receiver. The first port of the third f0 correlation signal generator is an external time reference input port, and the second port is connected to the second port of the third signal processing unit. The first port of the third f1 correlation signal generator is an external time reference input port, and the second port is connected to the second port of the fourth signal processing unit. The first port of the second f1 microwave filter is connected to the second port of the fourth optical receiver, and the second port is connected to the first port of the fourth signal processing unit. The first port of the second f0 microwave filter is connected to the second port of the third optical receiver, and the second port is connected to the first port of the third signal processing unit.

[0037] The optical transmission of the first single-fiber bidirectional connector and the second single-fiber bidirectional connector is as follows:

[0038] When light enters from the first port of the first single-fiber bidirectional connector and the first port of the second single-fiber bidirectional connector respectively, it is output from the second port of the first single-fiber bidirectional connector and the second port of the second single-fiber bidirectional connector.

[0039] When light enters from the second port, it exits from the third port.

[0040] The optical transmission of the first 2×2 optical coupler OC is as follows:

[0041] If light enters from the first port, it will exit from the second and third ports; if light enters from the second port, it will exit from the first and fourth ports.

[0042] The first f0 correlation signal generator, the second f0 correlation signal generator, and the third f0 correlation signal generator can detect the time information received from the first port, generate a correlation signal s0, and output it from the second port; the correlation signals generated by the first f0 correlation signal generator, the second f0 correlation signal generator, and the third f0 correlation signal generator are cross-correlated signals.

[0043] The first f1 correlation signal generator, the second f1 correlation signal generator, and the third f1 correlation signal generator can detect the time information received from the first port, generate a correlation signal s1, and output it from the second port; the correlation signals generated by the first f1 correlation signal generator, the second f1 correlation signal generator, and the third f1 correlation signal generator c2 are cross-correlated signals, and their spectra do not overlap with the spectrum of the signal s1.

[0044] The passband range of the first f1 microwave filter and the second f1 microwave filter includes the spectrum range of the related signal s1 but does not include the spectrum of the related signal s0.

[0045] The passband range of the first f0 microwave filter and the second f0 microwave filter includes the spectrum range of the related signal s0 but does not include the spectrum of the related signal s1.

[0046] The first signal processing unit, the second signal processing unit, the third signal processing unit, and the fourth signal processing unit are used to perform cross-correlation operations on the input signals and obtain the input time difference between the two signals based on the operation results.

[0047] It can use optical amplifiers to extend the transmission distance and increase the number of intermediate download devices, so multiple intermediate download devices can exist.

[0048] The first optical transmitter and the second optical transmitter use the same optical carrier wavelength.

[0049] It is important to note that due to the symmetry of time transmission, the positions of the near-end and far-end devices are relative, their functions are equivalent, and they can be interchanged. Optical amplifiers can be used to extend the transmission distance and increase the number of intermediate download devices; therefore, multiple intermediate download devices can exist.

[0050] Figure 2 This is a schematic diagram of the signal processing unit of a fiber optic time transfer device based on the same fiber and wavelength of the present invention. The analog signal is converted into a digital signal, and a cross-correlation operation is performed on the two signals to extract the peak position of the cross-correlation function, which is then converted into the time difference between the two function inputs.

[0051] The cross-correlated signals can be chirped signals, pseudo-random code signals, etc. Let the two cross-correlated signals be... and Since the two signals are correlated, they can be written as:

[0052]

[0053] in yes and The delay time difference of the input processing unit.

[0054] Performing a Fourier transform on it yields:

[0055] ,

[0056] Furthermore, based on the calculation method of the cross-correlation function, we know that:

[0057]

[0058] Combining the convolution theorem, we can obtain:

[0059]

[0060] in Performing an inverse Fourier transform on it yields...

[0061]

[0062] As can be seen from the properties of autocorrelation, The peak of the function occurs at the origin. The peak of the function appears at place, that is and The offset.

[0063] Figure 3 This is a schematic diagram of an embodiment of the fiber optic time transfer device of the present invention. As shown in the figure, the external reference at the near-end station inputs time information to chirped signal generators with center frequencies f1 and f2 respectively (f2>f1, and the spectra of the two chirped signals do not overlap) to generate signals with non-overlapping spectra. The signal with center frequency f2 is input to the signal processing unit. The signal with center frequency f1 is modulated into the optical domain by the optical transmitter and sent into the optical fiber. It is received by the optical receiver at the intermediate download device and the original signal with center frequency f1 is recovered after passing through the f1 filter. It is then cross-correlated with the locally generated signal with center frequency f1 in the signal processing unit and converted into the input time difference of the two signals. The input time difference of the two signals is obtained at the far-end station through a similar process. At the far-end station, the time reference inputs time information to chirped signal generators with center frequencies f1 and f2 respectively to generate signals with non-overlapping spectra. The signal with center frequency f1 is input to the signal processing unit. The signal with a center frequency of f2 is modulated into the optical domain by the optical transmitter and sent into the optical fiber. It is received by the optical receiver in the intermediate download device and the original signal with a center frequency of f2 is recovered after passing through the f2 filter. It is then cross-correlated with the locally generated signal with a center frequency of f2 in the signal processing unit and converted into the input time difference of the two signals. The input time difference of the two signals is obtained at the near-end station through a similar process.

[0064] Figure 4 This is a schematic diagram of a point-to-multipoint distributed time transfer device according to Embodiment 2 of the present invention. The external reference at the near-end station inputs time information to chirped signal generators with center frequencies f0, f1, f2…fn (the spectra of all chirped signals do not overlap), and modulates the f0 cross-correlation signal into the optical domain, sending it to different optical fibers through optical splitters. Optical splitters can be located at various positions on the optical fibers of the transmission system, thereby realizing point-to-multipoint distributed time transfer. Furthermore, a 2×2 coupler can be connected to each link to achieve intermediate downloading. The cross-correlation signals generated by different far-end stations are different from each other and correspond one-to-one with the near-end station.

Claims

1. A fiber optic time transfer device with the same fiber and wavelength, characterized in that, include: The near-end device, intermediate download device and far-end device are connected in sequence by optical fiber; The near-end device, intermediate download device, and far-end device each include at least two correlated signal generators, optical receivers, and signal processing units with different center frequencies. The near-end device and far-end device also include an optical transmitter and a single-fiber bidirectional connector. At least one of the correlation signal generators of the proximal device, intermediate download device and remote device generates a cross-correlated correlation signal s0; at least one of the correlation signal generators of the proximal device, intermediate download device and remote device generates a cross-correlated correlation signal s1, and the spectrum of signal s0 and the spectrum of s1 do not overlap. The correlation signal generator of the near-end device is used to receive external time reference information and generate at least two signals with non-overlapping spectra. One of the signals is modulated into the optical domain by the optical transmitter and sent into the optical fiber to be received by the optical receiver of the intermediate download device. The other signals and the cross-correlation signal generated by the correlation signal generator of the far-end device are cross-correlated by the signal processing unit of the near-end device and converted into the input time difference of the two signals. The correlation signal generator of the intermediate download device is used to receive external time reference information, generate a signal with non-overlapping spectrum, and perform cross-correlation operation with the received correlation signal with the same center frequency through the signal processing unit of the intermediate download device, and convert it into the input time difference of the two signals. The correlation signal generator of the remote device is used to receive external time reference information and generate at least two signals with non-overlapping spectra. One of the signals is modulated into the optical domain by the optical transmitter and sent into the optical fiber to be received by the optical receiver of the intermediate download device. The other signals and the cross-correlation signal generated by the correlation signal generator of the near-end device are cross-correlated by the signal processing unit of the remote device and converted into the input time difference of the two signals.

2. The optical fiber time transfer device with the same fiber and same wavelength according to claim 1, characterized in that, The near-end device includes a first f0 correlation signal generator, a first f1 correlation signal generator, a first optical transmitter, a first optical receiver, a first f1 microwave filter, a first signal processing unit, and a first single-fiber bidirectional connector. The first port of the first f0 correlation signal generator is an external time reference input port, and its second port is connected to the first port of the first optical transmitter. The first port of the first f1 correlation signal generator is also an external time reference input port, and its second port is connected to the second port of the first signal processing unit. The second port of the first optical transmitter is connected to the first port of the first single-fiber bidirectional connector. The first port of the first optical receiver is connected to the third port of the first single-fiber bidirectional connector, and its second port is connected to the first port of the first f1 microwave filter. The second port of the first f1 microwave filter is connected to the first port of the first signal processing unit. The second port of the first single-fiber bidirectional connector is connected to an optical fiber that transmits time information. The remote device includes a second f0 correlation signal generator, a second f1 correlation signal generator, a second optical transmitter, a second optical receiver, a first f0 microwave filter, a second signal processing unit, and a second single-fiber bidirectional connector. The first port of the second f1 correlation signal generator is an external time reference input port, and its second port is connected to the second port of the second signal processing unit. The second port of the second f1 correlation signal generator is also connected to the first port of the second optical transmitter. The second port of the second optical transmitter is connected to the first port of the second single-fiber bidirectional connector. The first port of the second optical receiver is connected to the third port of the second single-fiber bidirectional connector, and its second port is connected to the first port of the first f0 microwave filter. The second port of the first f0 microwave filter is connected to the first port of the second signal processing unit. The second port of the second single-fiber bidirectional connector is connected to an optical fiber that transmits time information. The intermediate download device includes a 2×2 optical coupler, a third f0 correlation signal generator, a third f1 correlation signal generator, a second f1 microwave filter, a second f0 microwave filter, a third optical receiver, a fourth optical receiver, a third signal processing unit, and a fourth signal processing unit. The first port of the 2×2 optical coupler is connected to an optical fiber near the near-end device for transmitting time information, the second port is connected to an optical fiber near the far-end device for transmitting time information, the third port is connected to the first port of the third optical receiver, and the fourth port is connected to the first port of the fourth optical receiver. The first port of the third f0 correlation signal generator is an external time reference input port, and the second port is connected to the second port of the third signal processing unit. The first port of the third f1 correlation signal generator is an external time reference input port, and the second port is connected to the second port of the fourth signal processing unit. The first port of the second f1 microwave filter is connected to the second port of the fourth optical receiver, and the second port is connected to the first port of the fourth signal processing unit. The first port of the second f0 microwave filter is connected to the second port of the third optical receiver, and the second port is connected to the first port of the third signal processing unit. The first f0 correlation signal generator, the second f0 correlation signal generator, and the third f0 correlation signal generator detect the time information received at their respective first ports, generate cross-correlated f0 signals s01, s02, and s03, and output them from their respective second ports; the first f1 correlation signal generator, the second f1 correlation signal generator, and the third f1 correlation signal generator detect the time information received at their respective first ports, generate cross-correlated f1 signals s11, s12, and s13, and output them from their respective second ports; the spectra of the f0 signals s01, s02, and s03 do not overlap with the spectra of the f1 signals s11, s12, and s13.

3. The optical fiber time transfer device with the same fiber and same wavelength according to claim 2, characterized in that, When light enters from the first port of the first single-fiber bidirectional connector, it is output from the second port of the first single-fiber bidirectional connector; when light enters from the second port of the first single-fiber bidirectional connector, it is output from the third port of the first single-fiber bidirectional connector. When light enters from the first port of the second single-fiber bidirectional connector, it is output from the second port of the second single-fiber bidirectional connector; when light enters from the second port of the second single-fiber bidirectional connector, it is output from the third port of the second single-fiber bidirectional connector.

4. The optical fiber time transfer device with the same fiber and same wavelength according to claim 2, characterized in that, When light is input from the first port of the 2×2 optical coupler, it is output from the second and third ports of the 2×2 optical coupler respectively; when light is input from the second port of the 2×2 optical coupler, it is output from the first and fourth ports of the 2×2 optical coupler respectively.

5. The optical fiber time transfer device with the same fiber and same wavelength according to any one of claims 2-4, characterized in that, The passband range of the first f1 microwave filter and the second f1 microwave filter includes the spectrum range of the related signal s1 but does not include the spectrum of the related signal s0; the passband range of the first f0 microwave filter and the second f0 microwave filter includes the spectrum range of the signal s0 but does not include the spectrum of the related signal s1.

6. The optical fiber time transfer device with the same fiber and same wavelength according to any one of claims 2-4, characterized in that, The first signal processing unit, the second signal processing unit, the third signal processing unit, and the fourth signal processing unit are used to perform cross-correlation operations on the input signals and obtain the input time difference between the two signals based on the operation results.

7. The optical fiber time transfer device with the same fiber and same wavelength according to any one of claims 2-4, characterized in that, The intermediate download device can be one or more, and the transmission distance can be extended by optical amplifiers.

8. The optical fiber time transfer device with the same fiber and same wavelength according to any one of claims 2-4, characterized in that, The first optical transmitter and the second optical transmitter use the same optical carrier wavelength.

9. The optical fiber time transfer device with the same fiber and same wavelength according to claim 1, characterized in that, It also includes an optical splitter installed on the transmission optical fiber between the near-end device and the far-end device to realize point-to-multipoint distributed time transfer on the same fiber and the same wavelength. That is, the far-end device includes multiple correlation signal generators with different center frequencies to generate correlation signals s1, s2, s3...sN, and their spectra do not overlap with the correlation signal s0 generated by the near-end site. The near-end device includes correlation signal generators and filters corresponding to the correlation signals s1, s2, s3...sN generated by each far-end site.

10. The optical fiber time transfer device with the same fiber and same wavelength according to claim 9, characterized in that, The optical transmitters at different remote sites use the same optical carrier wavelength.

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