A fiber phase-stable transmission apparatus using a two-stage analog direct modulation laser

Abstract

The application discloses a kind of optical fiber stable phase transmission devices using two-stage analog direct laser, comprising: center end module, remote end module and module external device composition, the module external device is connected with center end module, remote end module respectively, the center end module is connected with remote end module by optical fiber disc;The center end module is as a transmitting party, actively detects and pre-compensates the phase noise introduced by optical fiber transmission;The remote end module is as a transmitting party, and forms loop with the center end module to improve signal transmission stability, obtains the frequency signal phase-locked to center end atomic clock.The optical fiber stable phase transmission device uses two-stage analog direct laser as light source, proportional-integral-derivative PID algorithm is used for transmission delay variation measurement and pre-compensation, and the frequency stability of 10 ‑18 / 10 4 s can be realized.

Description

Technical Field

[0001] This invention relates to the field of microwave photonics, and more specifically to a fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser, which can be applied to high-speed communication, optical frequency synthesis, optical sensing, and precision measurement. Background Technology

[0002] The development of fiber optic phase-stable transmission technology can be traced back to the history of fiber optic communication and optical transmission technologies. In the late 1960s, fiber optic communication technology began to emerge, but due to the limitations of fiber optic materials and fabrication techniques at the time, the loss and distortion of optical signals during transmission were significant, restricting the development of fiber optic communication. Dispersion was a major challenge; different frequencies of optical signals propagate at different speeds in optical fibers, leading to differences in phase delay. This phase delay causes the optical pulse to widen during transmission, limiting the transmission distance and speed of fiber optic communication.

[0003] With the continuous development of optical fiber fabrication and optical device technology, in the early 1970s, scientists such as Kao and Hockham proposed the concept of transmitting communication signals with optical fibers and pointed out that by using low-loss optical fiber materials, a transmission distance of hundreds of kilometers could be achieved. This breakthrough marked the beginning and rapid development of optical fiber communication technology.

[0004] However, the dispersion problem in fiber optic communication remains unresolved. Currently, most industry solutions address the impact of dispersion by using dual-wavelength systems, ensuring the emitted laser wavelength differs from the returned wavelength. Other methods include using narrow-linewidth lasers or pulsed lasers for long-distance transmission, as narrower linewidths result in less cumulative effects over long distances. However, all these methods suffer from high manufacturing costs, a critical issue for practical application.

[0005] With the continuous development of fiber optic phase-stable transmission, compensation methods are mainly divided into active compensation and passive compensation. Passive compensation primarily utilizes the symmetry of the link to ensure that the delay is conjugate in the round trip, thus canceling out the link delay. Active compensation, on the other hand, uses high-precision digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) to actively collect the delay on the link. Then, algorithms such as PID control are used to compensate for the delay using a temperature-controlled oscillator (TCO) or a phase-locked loop (PLL) oscillator, achieving a balance in the delay.

[0006] However, passive compensation methods have some problems. While simple in structure, passive methods have a relatively low limit to phase stabilization accuracy, typically around 10. -17 This is on the order of magnitude. Active compensation methods offer higher phase stabilization accuracy and, through specialized algorithms, can resolve noise introduced by both active and passive RF devices. Summary of the Invention

[0007] In view of this, the present invention provides a fiber optic phase-stabilized transmission device using a two-stage analog direct-tuned laser. The device employs a two-stage analog direct-tuned laser as the light source and uses a proportional-integral-derivative PID algorithm for measuring and pre-compensating for transmission delay variations, enabling 10... -18 / 10 4 Frequency stability of s.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser, comprising: a central module, a remote module, and external devices, wherein the external devices are connected to the central module and the remote module respectively, and the central module and the remote module are connected via an optical fiber disk; the central module, as the transmitter, actively detects and pre-compensates for phase noise introduced by fiber optic transmission; the remote module, as the transmitter, forms a loop with the central module to improve signal transmission stability, thereby obtaining a frequency signal whose phase is locked to the atomic clock at the central end.

[0009] Further, the external components of the module include: a rubidium atomic clock, a first bandpass filter BPF1, a second bandpass filter BPF2, a third bandpass filter BPF3, a first power divider PS1, a first mixer, a low-pass filter LPF, a digital multimeter, and a computer. The rubidium atomic clock is connected to the input terminal of the first bandpass filter BPF1, the output terminal of the first bandpass filter BPF1 is connected to the S terminal of the first power divider PS1, and the I terminal of the first power divider PS1 is connected to the input terminal of the second bandpass filter BPF2. The output of bandpass filter BPF2 is connected to the LO terminal of the first mixer, the IF terminal of the first mixer is connected to the input terminal of low-pass filter LPF, and the output terminal of low-pass filter LPF is connected to a digital multimeter and a computer in sequence; the RF terminal of the first mixer is connected to the output terminal of the remote module, the input terminal of the remote module is connected to one end of the fiber optic tray, the other end of the fiber optic tray is connected to the output terminal of the central module, and the input terminal of the central module is connected to terminal 2 of the first power divider PS1 through the third bandpass filter BPF3.

[0010] Furthermore, the fiber optic cable is model G.652, with a link loss of <10dB;

[0011] The rubidium atomic clock outputs a 100MHz signal with an output power of 11–13 dBm and a stability of <10. -14 / s;

[0012] The noise floor of the digital multimeter is ≤100mV, 7 1 / 2 Measurement accuracy.

[0013] Furthermore, the central module includes: a second power divider PS2, a fourth bandpass filter BPF4, a fifth bandpass filter BPF5, a first phase-locked dielectric oscillator DRO1(RF), a phase-locked dielectric oscillator DRO(RF-0.1G) with RF shifted left by 0.1GHz, a phase-locked dielectric oscillator DRO(RF+0.1G) with RF shifted right by 0.1GHz, a second mixer, a third mixer, a fourth mixer, a first temperature-controlled voltage-controlled oscillator OCXO1, a first photodetector PD1, a second photodetector PD2, a two-stage analog direct-modulation laser DML, a hybrid device module, an erbium-doped fiber amplifier EDFA, and a DWDM filter;

[0014] The first terminal of the second power divider PS2 is connected to the input terminal of the fourth bandpass filter BPF4. The output terminal of the fourth bandpass filter BPF4 is connected to the input terminal of the RF-shifted right-by-0.1GHz phase-locked dielectric oscillator DRO(RF+0.1G). The output terminal of the RF-shifted right-by-0.1GHz phase-locked dielectric oscillator DRO(RF+0.1G) is connected to the LO terminal of the third mixer. The IF terminal of the third mixer is connected to the LO terminal of the second mixer.

[0015] The second power divider PS2 is connected to the input of the fifth bandpass filter BPF5. The output of the fifth bandpass filter BPF5 is connected to the input of the RF-0.1G phase-locked dielectric oscillator DRO (RF-0.1G) with a left shift of 0.1GHz. The output of the RF-0.1G phase-locked dielectric oscillator DRO (RF-0.1G) with a left shift of 0.1GHz is connected to the LO terminal of the fourth mixer. The IF terminal of the fourth mixer is connected to the RF terminal of the second mixer.

[0016] The IF output signal of the second mixer calculates the transmission delay using a PID algorithm and inputs the transmission delay into the first isothermal voltage-controlled oscillator OCXO1. The output of the first isothermal voltage-controlled oscillator OCXO1 is sequentially connected to the first phase-locked dielectric oscillator DRO1(RF), the two-stage analog direct-modulation laser DML, and the hybrid device module. The hybrid device module is connected to the output end of the first photodetector PD1, the other end of the fiber optic disk, and the input end of the erbium-doped fiber amplifier EDFA. The power output end of the first photodetector PD1 is connected to the RF end of the fourth mixer. The output end of the erbium-doped fiber amplifier EDFA is connected to one end of the DWDM filter. The other end of the DWDM filter is connected to the output end of the second photodetector PD2. The power output end of the second photodetector PD2 is connected to the RF end of the third mixer.

[0017] Furthermore, the hybrid device module consists of a 1×2 fiber coupler OC1 and a circulator. The 90% optical power output of the 1×2 fiber coupler OC1 is connected to port 1 of the circulator, the 10% optical power output of the 1×2 fiber coupler OC1 is connected to the output end of the first photodetector PD1, port 2 of the circulator is connected to the other end of the G.652 fiber optic disk, and port 3 of the circulator is connected to the input end of the erbium-doped fiber amplifier EDFA. The insertion loss of the 1×2 fiber coupler OC1 is <4dB, and its operating wavelength is in the C-band. The operating wavelength of the circulator is in the C-band, the insertion loss is <1dB, and the isolation between the ports of the circulator is >40dB.

[0018] Furthermore, the two-stage analog direct-modulation laser DML has a maximum output power of ≤5dBm, a modulation bandwidth of ≤18GHz, a slope efficiency of >0.09mW / mA, a linewidth of <1MHz, and a relative intensity noise of <-145dBc;

[0019] The erbium-doped fiber amplifier (EDFA) has a wavelength range in the C-band, an input power of -20dBm to -5dBm, a gain coefficient of 18dB@-10dBm input, and a noise figure of ≤4.5dB.

[0020] The DWDM filter operates at a wavelength of 1545.322 nm, has a bandwidth of <0.1 nm, and an insertion loss of ≤1.0 dB.

[0021] The first power divider PS1 and the second power divider PS2 have an allowable bandwidth of 10 to 250 MHz and an insertion loss of <3 dB.

[0022] Furthermore, the remote module includes: a Faraday rotator mirror FM, a third photodetector PD3, a fifth mixer, a second phase-locked dielectric oscillator DRO2(RF), a second temperature-controlled voltage-controlled oscillator OCXO2, a third phase-locked dielectric oscillator DRO3(RF), and a sixth bandpass filter BPF6. The 80% mirror reflection power end of the Faraday rotator mirror FM is connected to one end of a G.652 fiber optic disk, the 20% transmitted power end of the Faraday rotator mirror FM is connected to the output end of the third photodetector PD3, and the output end of the third photodetector PD3 is connected to the RF end of the fifth mixer. The fifth mixer's LO terminal is connected to the output terminal of the second phase-locked dielectric oscillator DRO2(RF). The input terminal of the second phase-locked dielectric oscillator DRO2(RF) is connected to the output terminal of the second isothermal voltage-controlled oscillator OCXO2. The signal output from the fifth mixer's IF terminal is calculated using a PID algorithm and input into the second isothermal voltage-controlled oscillator OCXO2. The second isothermal voltage-controlled oscillator OCXO2 is connected to the sixth bandpass filter BPF6 and the third phase-locked dielectric oscillator DRO3(RF), respectively. The sixth bandpass filter BPF6 is connected to the RF terminal of the first mixer.

[0023] The Faraday rotator mirror FM has a center wavelength of 1550 nm, a single-pass rotation angle of 45°, an insertion loss of <0.7 dB, a polarization-dependent loss of <0.05 dB, and a polarization mode dispersion of <0.05 dB.

[0024] Furthermore, the signal output power of the first phase-locked dielectric oscillator DRO1(RF), the phase-locked dielectric oscillator DRO(RF-0.1G) with a radio frequency shift of 0.1 GHz to the left, the phase-locked dielectric oscillator DRO(RF+0.1G) with a radio frequency shift of 0.1 GHz to the right, the second phase-locked dielectric oscillator DRO2(RF), the third phase-locked dielectric oscillator DRO3(RF), the first isothermal voltage-controlled oscillator OCXO1, and the second isothermal voltage-controlled oscillator OCXO2 are all 10 to 17 dBm, and the phase noise is ≤ -110 dBc@1 kHz.

[0025] Furthermore, the first bandpass filter BPF1, the second bandpass filter BPF2, the third bandpass filter BPF3, the fourth bandpass filter BPF4, the fifth bandpass filter BPF5, and the sixth bandpass filter BPF6 operate at frequencies of 95–105 MHz and have a filtering bandwidth of <10 MHz; the low-pass filter LPF operates at a frequency of ≤1 MHz and has an isolation of <30 dB.

[0026] Furthermore, the operating bandwidths of the LO and RF terminals of the first and second mixers are all 0.025-200MHz, the operating bandwidth of the IF terminal is DC-200MHz, and the conversion loss is ≤5dB; the operating bandwidths of the LO and RF terminals of the third, fourth, and fifth mixers are all 3700-10000MHz, the operating bandwidth of the IF terminal is DC-2000MHz, and the conversion loss is ≤6dB.

[0027] The first photodetector PD1, the second photodetector PD2, and the third photodetector PD3 operate in the C-band with a bandwidth of ≥10GHz.

[0028] Compared with existing technologies, this invention has the following advantages: The fiber optic phase-stabilized transmission device using a two-stage analog direct-tuned laser has a simple structure and faster compensation response. Without sacrificing phase-stabilization accuracy, the overall system response can be improved by adjusting the compensation algorithm. The direct mixing method obtains a DC signal by mixing two signals, which has a higher measurement limit in measuring the stability of fiber optic phase-stabilized transmission. Simultaneously, the two-stage analog direct-tuned laser used as the light source in this invention has higher output power, narrower linewidth, and better linearity. Good linearity provides a wider dynamic range. To recover better RF signals, the output signal power of the first phase-locked dielectric oscillator (DRO1) needs to be high; the good linearity of the two-stage analog direct-tuned laser (DML) meets this design requirement. Furthermore, compared to a single-stage powered laser, the two-stage design allows the laser to have better skew efficiency. By using a proportional-integral-derivative (PID) algorithm for measuring and pre-compensating for transmission delay changes, a 10... -18 / 10 4 Frequency stability of s. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in this invention, the accompanying drawings used in the description of this invention will be briefly introduced below. Obviously, the drawings described below are only a part of this invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser, as described in this invention. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the specific embodiments described are only a part of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] like Figure 1 This is a schematic diagram of the fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser, as described in this invention. The device comprises a central module, a remote module, and external components. The external components are connected to both the central and remote modules, which are connected via an optical fiber disk. The central module, acting as the transmitter, actively detects and pre-compensates for phase noise introduced by the fiber optic transmission. The remote module, also acting as the transmitter, forms a loop with the central module to improve signal transmission stability, obtaining a frequency signal whose phase is locked to the atomic clock at the central end. This fiber optic phase-stabilized transmission device has a simple structure and fast compensation response.

[0033] The external components of this invention include: a rubidium atomic clock, a first bandpass filter BPF1, a second bandpass filter BPF2, a third bandpass filter BPF3, a first power divider PS1, a first mixer, a low-pass filter LPF, a digital multimeter, and a computer. The rubidium atomic clock is connected to the input terminal of the first bandpass filter BPF1, the output terminal of the first bandpass filter BPF1 is connected to the S terminal of the first power divider PS1, and the I terminal of the first power divider PS1 is connected to the input terminal of the second bandpass filter BPF2. The output of BPF2 is connected to the LO terminal of the first mixer. The IF terminal of the first mixer is connected to the input terminal of the low-pass filter LPF. The output terminal of the low-pass filter LPF is connected to a digital multimeter and a computer in sequence for measuring phase stability. The RF terminal of the first mixer is connected to the output terminal of the remote module. The input terminal of the remote module is connected to one end of the fiber optic tray. The other end of the fiber optic tray is connected to the output terminal of the central module. The input terminal of the central module is connected to terminal 2 of the first power divider PS1 through the third bandpass filter BPF3.

[0034] In this invention, the fiber optic disk is model G.652, with a link loss of <10dB; the rubidium atomic clock outputs a 100MHz signal with an output power of 11-13dBm and a stability of <10. -14 / s; Digital multimeter noise floor ≤100mV, 7 1 / 2 Measurement accuracy.

[0035] The central module of this invention includes: a second power divider PS2, a fourth bandpass filter BPF4, a fifth bandpass filter BPF5, a first phase-locked dielectric oscillator DRO1(RF), a phase-locked dielectric oscillator DRO(RF-0.1G) with RF shifted left by 0.1GHz, a phase-locked dielectric oscillator DRO(RF+0.1G) with RF shifted right by 0.1GHz, a second mixer, a third mixer, a fourth mixer, a first temperature-controlled voltage-controlled oscillator OCXO1, a first photodetector PD1, a second photodetector PD2, a two-stage analog direct-modulation laser DML, a hybrid device module, an erbium-doped fiber amplifier EDFA, and a DWDM filter;

[0036] The first terminal of the second power divider PS2 is connected to the input terminal of the fourth bandpass filter BPF4. In order to obtain the phase fluctuation and stability measurement introduced by the signal during the transmission of the optical fiber link, the optical fiber phase-stable transmission device also needs a phase-locked dielectric oscillator DRO(RF+0.1G) with the phase locked to the right by 0.1GHz and a phase-locked dielectric oscillator DRO(RF-0.1G) with the phase locked to the left by 0.1GHz respectively to generate an error signal to feed back the auxiliary signal controlling the phase of the first isothermal voltage-controlled oscillator OCXO1. The output terminal of the fourth bandpass filter BPF4 is connected to the input terminal of the phase-locked dielectric oscillator DRO(RF+0.1G) with the phase locked to the right by 0.1GHz. The output terminal of the phase-locked dielectric oscillator DRO(RF+0.1G) with the phase locked to the right by 0.1GHz is connected to the LO terminal of the third mixer. The IF terminal of the third mixer is connected to the LO terminal of the second mixer.

[0037] The second power divider PS2 is connected to the input of the fifth bandpass filter BPF5. The output of the fifth bandpass filter BPF5 is connected to the input of the RF-0.1G phase-locked dielectric oscillator DRO (RF-0.1G) with RF shifted left by 0.1GHz. The output of the RF-0.1G phase-locked dielectric oscillator DRO (RF-0.1G) with RF shifted left by 0.1GHz is connected to the LO terminal of the fourth mixer. The IF terminal of the fourth mixer is connected to the RF terminal of the second mixer.

[0038] The IF output signal of the second mixer calculates the transmission delay using a PID algorithm, and inputs the transmission delay into the first isothermal voltage-controlled oscillator (OCXO1). The phase of the first OCXO1 is controlled by feedback to compensate for phase noise in the transmission link. The output of the first OCXO1 is sequentially connected to a first phase-locked dielectric oscillator (DRO1(RF)), a two-stage analog direct-modulation laser (DML), and a hybrid device module. The two-stage analog direct-modulation laser (DML) outputs laser light, which is fed into the hybrid device module. The hybrid device module is connected to the first... The output end of photodetector PD1, the other end of the fiber optic disk, and the input end of erbium-doped fiber amplifier EDFA are connected. In order to further obtain the error signal for feedback control of the phase of the first isothermal voltage-controlled oscillator OCXO1, the output end of the first photodetector PD1 is connected to the RF end of the fourth mixer, the output end of erbium-doped fiber amplifier EDFA is connected to one end of DWDM filter, the other end of DWDM filter is connected to the output end of the second photodetector PD2, and the output end of the second photodetector PD2 is connected to the RF end of the third mixer.

[0039] The hybrid device module consists of a 1×2 fiber coupler OC1 and a circulator. To further compensate for the phase noise introduced by external devices such as the two-stage analog direct-modulated laser DML in a single transmission path to the 1×2 fiber coupler OC1 during laser transmission, the 10% optical power output of the 1×2 fiber coupler OC1 is connected to the output end of the first photodetector PD1 for demodulation to obtain the phase information of the external devices. The 90% optical power output of the 1×2 fiber coupler OC1 is connected to port 1 of the circulator, port 2 of the circulator is connected to the other end of the G.652 fiber optic disk, and port 3 of the circulator is connected to the input end of the erbium-doped fiber amplifier EDFA. The insertion loss of the 1×2 fiber coupler OC1 is <4dB, and its operating wavelength is in the C-band. The circulator operates in the C-band, with an insertion loss of <1dB, and the isolation between the ports of the circulator is >40dB. The use of the hybrid device module reduces the connection loss between fiber flanges, which is helpful in compensating for the optical power loss caused by a 50km long link.

[0040] In this invention, the two-stage analog direct-modulation laser DML has an output power of ≤5dBm, a modulation bandwidth of ≤18GHz, a slope efficiency of >0.09mW / mA, a linewidth of <1MHz, and a relative intensity noise of <-145dBc. The output power of the two-stage analog direct-modulation laser DML is set to ≤5dBm to avoid stimulated Brillouin scattering caused by the transmission link. The linewidth of less than 1MHz reduces the influence of light dispersion during transmission. At the same time, the modulation bandwidth covers the entire X-band, and the low relative intensity noise reduces the stability test limit of the entire phase-stable transmission device. The erbium-doped fiber amplifier (EDFA) has a wavelength range in the C-band, an input power of -20dBm to -5dBm, a gain of 18dB at -10dBm input, and a noise figure of ≤4.5dB. The DWDM filter operates at a wavelength of 1545.322nm, has a bandwidth of <0.1nm, and an insertion loss of ≤1.0dB. The first power divider (PS1) and the second power divider (PS2) have allowable bandwidths of 10 to 250MHz and insertion losses of <3dB.

[0041] The remote module of this invention includes: a Faraday rotator mirror FM, a third photodetector PD3, a fifth mixer, a second phase-locked dielectric oscillator DRO2(RF), a second temperature-controlled voltage-controlled oscillator OCXO2, a third phase-locked dielectric oscillator DRO3(RF), and a sixth bandpass filter BPF6. To compensate for the phase noise introduced by the fiber optic link during transmission, the 80% mirror reflection power end of the Faraday rotator mirror FM is connected to one end of a G.652 fiber optic disk, allowing a portion of the light to return via the original path. The 20% transmittance power end of the Faraday rotator mirror FM is connected to the output of the third photodetector PD3. The third photodetector PD3 is connected to the RF terminal of the fifth mixer. The LO terminal of the fifth mixer is connected to the output terminal of the second phase-locked dielectric oscillator DRO2(RF). The input terminal of the second phase-locked dielectric oscillator DRO2(RF) is connected to the output terminal of the second isothermal voltage-controlled oscillator OCXO2. The signal output from the IF terminal of the fifth mixer is calculated by the PID algorithm and input into the second isothermal voltage-controlled oscillator OCXO2. The second isothermal voltage-controlled oscillator OCXO2 is connected to the sixth bandpass filter BPF6 and the third phase-locked dielectric oscillator DRO3(RF). The sixth bandpass filter BPF6 is connected to the RF terminal of the first mixer.

[0042] In this invention, the center wavelength of the Faraday rotator mirror FM is 1550nm, the single-pass rotation angle is 45°, the insertion loss is <0.7dB, the polarization correlation loss is <0.05dB, and the polarization mode dispersion is <0.05dB. The signal output power of the first phase-locked dielectric oscillator DRO1(RF), the phase-locked dielectric oscillator DRO(RF-0.1G) shifted left by 0.1GHz, the phase-locked dielectric oscillator DRO(RF+0.1G) shifted right by 0.1GHz, the second phase-locked dielectric oscillator DRO2(RF), the third phase-locked dielectric oscillator DRO3(RF), the first isothermal voltage-controlled oscillator OCXO1, and the second isothermal voltage-controlled oscillator OCXO2 are all 10-17dBm, and the phase noise is ≤-110dBc@1KHz. The first bandpass filter BPF1, the second bandpass filter BPF2, the third bandpass filter BPF3, the fourth bandpass filter BPF4, the fifth bandpass filter BPF5, and the sixth bandpass filter BPF6 operate at frequencies of 95–105 MHz with a filtering bandwidth of <10 MHz. The low-pass filter LPF operates at a frequency ≤1 MHz with an isolation of <30 dB. The first and second mixers have operating bandwidths of 0.025–200 MHz at their LO and RF terminals, and a DC–200 MHz operating bandwidth at their IF terminals, with a conversion loss ≤5 dB. The third, fourth, and fifth mixers have operating bandwidths of 3700–10000 MHz at their LO and RF terminals, and a DC–2000 MHz operating bandwidth at their IF terminals, with a conversion loss ≤6 dB. The first photodetector PD1, the second photodetector PD2, and the third photodetector PD3 operate in the C-band with a bandwidth ≥10 GHz. The fiber optic phase-stabilized transmission device of this invention integrates the Faraday rotator mirror FM and the 1×2 fiber coupler OC2 for the first time. Through special processing, 80% of the light entering the Faraday rotator mirror FM is reflected and 20% is transmitted. This design reduces the use of fiber flanges, increases optical power, and makes the phase of the returned signal and the back Rayleigh scattering signal orthogonal, thereby reducing the signal noise floor and improving the signal-to-noise ratio.

[0043] The working process of the fiber optic phase-stabilized transmission device of this invention is as follows: The phase-stabilized transmission device mainly uses a first photodetector PD1 to collect the link delay caused by the link between the circulator and the two-stage analog direct-modulation laser DML, and a second photodetector PD2 to collect the signal round-trip delay caused by the 50km long link transmission. The collected delay information is extracted by the PID algorithm at the central end and the delay is compensated in the next transmission. The third photodetector PD3 at the remote end demodulates the signal transmitted through the long link, and after passing through the PID algorithm, the second isothermal voltage-controlled oscillator OCXO2 self-recovers a stable signal for user use.

[0044] This invention employs a direct mixing method to measure the transmission delay variation. The LO input of the first mixer is the reference frequency standard, and the RF input is the phase detection signal. Both have the same frequency but a phase difference Δφ(t). Since the amplitude change of the output signal during mixing cannot be accurately derived, the amplitude of its beat frequency signal is represented by C, D is the DC potential in the IF output, and V(t) is the real-time measurement value from a high-precision digital multimeter. First, by artificially altering the phase of the stable phase signal, Δφ(t) undergoes a 2π phase change. When Δφ(t) takes values ​​of 0 and π, the measured value will exhibit a maximum value Vmax and a minimum value Vmin, respectively. Through simple calculations, C and D can be represented using known maximum and minimum values. Therefore, the phase difference Δφ(t) can be deduced from the voltage measurement value of the IF signal, and the corresponding relative time delay fluctuation Δφ(t) can also be calculated.

[0045]

[0046] It is also used for frequency stability calculations.

[0047] Compared to existing technologies, the fiber optic phase-stable transmission device of this invention features a simpler structure and faster compensation response; all components in the system are commercially available, making implementation easy, and the direct mixing method for measuring the stability of fiber optic phase-stable transmission has a higher measurement limit. Furthermore, this invention employs a two-stage analog direct-modulated laser as the light source and a proportional-integral-derivative PID algorithm for measuring and pre-compensating for transmission delay variations, enabling 10... -18 / 10 4 Frequency stability of s.

[0048] Example

[0049] In this embodiment, a fiber-optic phase-stabilized transmission device using a two-stage analog direct-modulation laser is employed. The output power of the 100MHz signal from the rubidium atomic clock is set to 12.26dBm, and the stability is 5×10⁻⁶. -15 / s; The two-stage analog direct-modulated laser DML has a maximum output power of 4.53dBm, a modulation bandwidth of 9.1GHz, a slant efficiency of 0.091mW / mA, and a linewidth of 800KHz; The first phase-locked dielectric oscillator DRO1(RF), the second phase-locked dielectric oscillator DRO2(RF), and the third phase-locked dielectric oscillator DRO3(RF) all have a signal output power of 16.8dBm and a phase noise of -125dBc@1KHz; The phase-locked dielectric oscillator DRO(RF-0.1G) with a 0.1GHz left-shifted RF has a signal output power of 15.1dBm and a phase noise of -121dBc@1KHz; The phase-locked dielectric oscillator DRO(RF+) with a 0.1GHz right-shifted RF has a signal output power of 15.1dBm and a phase noise of -121dBc@1KHz; The phase-locked dielectric oscillator DRO(RF+) with a 0.1GHz right-shifted RF has a signal output power of 16.8dBm and a phase noise of -125 ... The signal output power of the 0.1G unit is 14.8dBm, and the phase noise is -119dBc@1KHz; the signal output power of the first temperature-controlled oscillator OCXO1 and the second temperature-controlled oscillator OCXO2 are both 10.1dBm, and the phase noise is -124dBc@1KHz; the operating frequency of the first bandpass filter BPF1, the second bandpass filter BPF2, the third bandpass filter BPF3, the fourth bandpass filter BPF4, the fifth bandpass filter BPF5, and the sixth bandpass filter BPF6 is 100MHz, and the filtering bandwidth is 5MHz; the operating frequency of the low-pass filter LPF is 1MHz, and the isolation is 25dB; the allowable power of the first power divider PS1 and the second power divider PS2 is... All have a bandwidth of 100MHz and an insertion loss of 2.8dB. The first and second mixers have a LO and RF bandwidth of 100MHz and a DC bandwidth at the IF end, with a conversion loss of 4.8dB. The third, fourth, and fifth mixers have a LO bandwidth of 9.0GHz, a RF bandwidth of 9.1GHz, and a IF bandwidth of 100MHz, with a conversion loss of 5.1dB. The 1×2 fiber coupler OC1 has an insertion loss of 3.2dB and an operating wavelength of 1550nm. The circulator operates at a wavelength of 1550nm with an insertion loss of 0.82dB, and the isolation between the ports of the circulator is 45dB±2dB. The fiber optic tray is of model G. The 652 has a link loss of 9.2dB; the erbium-doped fiber amplifier (EDFA) operates at a wavelength of 1550nm, with an input power of -19.8dBm, a gain of 18dB@-10dBm input, and a noise figure of 4dB; photodetectors PD1, PD2, and PD3 all operate at a wavelength of 1550nm and have a bandwidth of 10.3GHz; the DWDM filter operates at a wavelength of 1545.322nm, has a bandwidth of 0.088nm, and an insertion loss of 0.98dB; the Faraday rotator mirror (FM) has a center wavelength of 1550nm, a single-pass rotation angle of 45°, and an insertion loss of 0.55dB; and the digital multimeter has a noise floor of 100mV.

[0050] In this embodiment, the maximum and minimum voltage values ​​measured by the digital multimeter are Vmax = 270mV and Vmin = -271mV, respectively, and the phase detection signal frequency band f0 = 100MHz. The corresponding relative time delay fluctuations satisfy the following relationship:

[0051]

[0052] The relative time delay fluctuation value calculated using the measurement data of V(t) from a single experiment is -0.0439 ps, indicating that the second stability of the steady-state transmission device reaches 10. -14 At this level, with a decrease of one octave, the stability of the phase-stabilized transmission device will reach 10 when it reaches the point of being stable for 100,000 seconds (i.e., extremely stable). -19 This level of performance and stability has surpassed most levels in the industry.

[0053] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser, characterized in that, include: The system consists of a central module, a remote module, and external devices. The external devices are connected to the central module and the remote module, respectively. The central module and the remote module are connected via an optical fiber disk. The central module acts as the transmitter, actively detecting and pre-compensating for phase noise introduced by optical fiber transmission. The remote module acts as the transmitter, forming a loop with the central module to improve signal transmission stability and obtain a frequency signal whose phase is locked to the central atomic clock. The central module includes: a second power divider PS2, a fourth bandpass filter BPF4, a fifth bandpass filter BPF5, a first phase-locked dielectric oscillator DRO1 for radio frequency, a phase-locked dielectric oscillator DRO(RF-0.1G) shifted left by 0.1GHz, a phase-locked dielectric oscillator DRO(RF+0.1G) shifted right by 0.1GHz, a second mixer, a third mixer, a fourth mixer, a first temperature-controlled voltage-controlled oscillator OCXO1, a first photodetector PD1, a second photodetector PD2, a two-stage analog direct-modulation laser DML, a hybrid device module, an erbium-doped fiber amplifier EDFA, and a DWDM filter; The first terminal of the second power divider PS2 is connected to the input terminal of the fourth bandpass filter BPF4. The output terminal of the fourth bandpass filter BPF4 is connected to the input terminal of the RF-shifted right-by-0.1GHz phase-locked dielectric oscillator DRO(RF+0.1G). The output terminal of the RF-shifted right-by-0.1GHz phase-locked dielectric oscillator DRO(RF+0.1G) is connected to the LO terminal of the third mixer. The IF terminal of the third mixer is connected to the LO terminal of the second mixer. The second power divider PS2 is connected to the input of the fifth bandpass filter BPF5. The output of the fifth bandpass filter BPF5 is connected to the input of the RF-0.1G phase-locked dielectric oscillator DRO (RF-0.1G) with a left shift of 0.1GHz. The output of the RF-0.1G phase-locked dielectric oscillator DRO (RF-0.1G) with a left shift of 0.1GHz is connected to the LO terminal of the fourth mixer. The IF terminal of the fourth mixer is connected to the RF terminal of the second mixer. The IF output signal of the second mixer calculates the transmission delay using a PID algorithm, and inputs the transmission delay into the first isothermal voltage-controlled oscillator OCXO1. The output of the first isothermal voltage-controlled oscillator OCXO1 is sequentially connected to the first radio frequency phase-locked dielectric oscillator DRO1, the two-stage analog direct-modulation laser DML, and the hybrid device module. The hybrid device module is connected to the output end of the first photodetector PD1, the other end of the fiber optic disk, and the input end of the erbium-doped fiber amplifier EDFA. The power output end of the first photodetector PD1 is connected to the RF end of the fourth mixer. The output end of the erbium-doped fiber amplifier EDFA is connected to one end of the DWDM filter. The other end of the DWDM filter is connected to the output end of the second photodetector PD2. The power output end of the second photodetector PD2 is connected to the RF end of the third mixer. The hybrid device module consists of a 1×2 fiber coupler OC1 and a circulator. The 90% optical power output end of the 1×2 fiber coupler OC1 is connected to port 1 of the circulator, the 10% optical power output end of the 1×2 fiber coupler OC1 is connected to the output end of the first photodetector PD1, port 2 of the circulator is connected to the other end of the G.652 fiber optic disk, and port 3 of the circulator is connected to the input end of the erbium-doped fiber amplifier EDFA. The remote module includes: a Faraday rotator mirror FM, a third photodetector PD3, a fifth mixer, a second phase-locked dielectric oscillator DRO2 for radio frequency (RF), a second temperature-controlled voltage-controlled oscillator OCXO2 for RF, a third RF phase-locked dielectric oscillator DRO3 for RF, and a sixth bandpass filter BPF6. The 80% mirror reflection power end of the Faraday rotator mirror FM is connected to one end of a G.652 fiber optic disk, the 20% transmittance power end of the Faraday rotator mirror FM is connected to the output end of the third photodetector PD3, and the power output end of the third photodetector PD3 is connected to the RF end of the fifth mixer. The LO terminal of the fifth mixer is connected to the output terminal of the second phase-locked dielectric oscillator DRO2 of the radio frequency. The input terminal of the second phase-locked dielectric oscillator DRO2 of the radio frequency is connected to the output terminal of the second isothermal voltage-controlled oscillator OCXO2. The signal output from the IF terminal of the fifth mixer is calculated by a PID algorithm and input into the second isothermal voltage-controlled oscillator OCXO2. The second isothermal voltage-controlled oscillator OCXO2 is connected to the sixth bandpass filter BPF6 and the third phase-locked dielectric oscillator DRO3 of the radio frequency. The sixth bandpass filter BPF6 is connected to the RF terminal of the first mixer.

2. The fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser according to claim 1, characterized in that, The external components of the module include: a rubidium atomic clock, a first bandpass filter BPF1, a second bandpass filter BPF2, a third bandpass filter BPF3, a first power divider PS1, a first mixer, a low-pass filter LPF, a digital multimeter, and a computer. The rubidium atomic clock is connected to the input terminal of the first bandpass filter BPF1, the output terminal of the first bandpass filter BPF1 is connected to the S terminal of the first power divider PS1, and the I terminal of the first power divider PS1 is connected to the input terminal of the second bandpass filter BPF2. The output of filter BPF2 is connected to the LO terminal of the first mixer, the IF terminal of the first mixer is connected to the input terminal of the low-pass filter LPF, and the output terminal of the low-pass filter LPF is connected to a digital multimeter and a computer in sequence; the RF terminal of the first mixer is connected to the output terminal of the remote module, the input terminal of the remote module is connected to one end of the fiber optic tray, the other end of the fiber optic tray is connected to the output terminal of the central module, and the input terminal of the central module is connected to terminal 2 of the first power divider PS1 through the third bandpass filter BPF3.

3. The fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser according to claim 2, characterized in that, The fiber optic cable is model G.652, with a link loss of <10dB; The rubidium atomic clock outputs a 100MHz signal with an output power of 11~13dBm and a stability of <10. -14 / s; The noise floor of the digital multimeter is ≤100mV, 7 1 / 2 Measurement accuracy.

4. The fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser according to claim 2, characterized in that, The insertion loss of the 1×2 fiber coupler OC1 is <4dB, and the operating wavelength is C-band; the operating wavelength of the circulator is C-band, the insertion loss is <1dB, and the isolation between the ports of the circulator is >40dB.

5. A fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser according to claim 2, characterized in that, The two-stage analog direct-modulation laser DML has a maximum output power of ≤5dBm, modulation bandwidth of ≤18GHz, slant efficiency of >0.09mW / mA, linewidth of <1MHz, and relative intensity noise of <-145dBc. The erbium-doped fiber amplifier (EDFA) has a wavelength range in the C-band, an input power of -20dBm to -5dBm, a gain of 18dB at -10dBm input, and a noise figure of ≤4.5dB. The DWDM filter operates at a wavelength of 1545.322 nm, has a bandwidth of <0.1 nm, and an insertion loss of ≤1.0 dB. The first power divider PS1 and the second power divider PS2 have an allowable bandwidth of 10~250MHz and an insertion loss of <3dB.

6. The fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser according to claim 2, characterized in that, The Faraday rotator mirror FM has a center wavelength of 1550 nm, a single-pass rotation angle of 45°, an insertion loss of <0.7 dB, a polarization-dependent loss of <0.05 dB, and a polarization mode dispersion of <0.05 dB.

7. A fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser according to claim 6, characterized in that, The signal output power of the first phase-locked dielectric oscillator DRO1, the phase-locked dielectric oscillator DRO(RF-0.1G) shifted left by 0.1GHz, the phase-locked dielectric oscillator DRO(RF+0.1G) shifted right by 0.1GHz, the second phase-locked dielectric oscillator DRO2, the third phase-locked dielectric oscillator DRO3, the first isothermal voltage-controlled oscillator OCXO1, and the second isothermal voltage-controlled oscillator OCXO2 are all 10~17dBm, and the phase noise is ≤-110dBc@1KHz.

8. A fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser according to claim 2, characterized in that, The first bandpass filter BPF1, the second bandpass filter BPF2, the third bandpass filter BPF3, the fourth bandpass filter BPF4, the fifth bandpass filter BPF5, and the sixth bandpass filter BPF6 operate at frequencies of 95~105MHz and have a filtering bandwidth of <10MHz; the low-pass filter LPF operates at a frequency of ≤1MHz and has an isolation of <30dB.

9. A fiber optic phase-stabilized transmission device using a two-stage analog direct-modulation laser according to claim 6, characterized in that, The first and second mixers have operating bandwidths of 0.025-200MHz at their LO and RF terminals, and DC-200MHz at their IF terminals, with a conversion loss ≤5dB. The third, fourth, and fifth mixers have operating bandwidths of 3700-10000MHz at their LO and RF terminals, and DC-2000MHz at their IF terminals, with a conversion loss ≤6dB. The first photodetector PD1, the second photodetector PD2, and the third photodetector PD3 operate in the C-band with a bandwidth of ≥10GHz.

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