A stable self-interference cancellation device and method of phase modulation combined with fiber dispersion

Abstract

The application provides a stable self-interference cancellation device combined with phase modulation and fiber dispersion, and a stable self-interference cancellation method combined with phase modulation and fiber dispersion, and the process is as follows: performing electro-optical modulation on a reference signal; performing electro-optical modulation on a received signal and rotating a 90-degree polarization state; coupling two-way orthogonal polarization optical signals to a central station for amplification and separation; beating the two-way optical signals at a balanced detector to obtain a microwave electrical signal; and tuning a tunable laser wavelength to achieve deep self-interference cancellation. The application is based on the dispersion effect of an optical fiber, and can realize the conversion of a signal from phase modulation to intensity modulation on one hand; on the other hand, by changing the wavelength difference of two lasers, a precise dispersion delay tuning function is introduced, and the self-interference cancellation in a radio frequency domain with a large bandwidth and the long-distance transmission of useful signals can be realized.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonic signal processing technology, specifically relating to a stable self-interference elimination device and method for phase modulation combined with fiber dispersion in an in-band full-duplex ROF system. Background Technology

[0002] Radio over Fiber (ROF) offers advantages such as large information capacity, long transmission distance, and resistance to electromagnetic interference, making it crucial in various applications including broadband wireless communication, radar, and sensor systems. Limited spectrum resources and the ever-growing demand for higher speeds have further spurred the development of in-band full-duplex ROF technology. However, because signals are transmitted and received simultaneously on the same frequency band, in-band full-duplex ROF introduces a significant challenge: self-interference.

[0003] Compared with traditional RF electrical self-interference cancellation schemes, optically assisted RF self-interference cancellation technology can provide greater bandwidth and higher tuning accuracy. In recent years, scholars at home and abroad have proposed a series of optically assisted schemes to solve the self-interference cancellation problem. ([1]Han Sagnac Loop[J]. IEEE Photonics Journal, 2021, PP(99): 1-1.[3]ChenY.A Photonic-Based Wideband RF Self-Interference Cancellation Approach WithFiber Dispersion Immunity[J].Journal of Lightwave Technology, 2020, PP(99):[4]1-1.Zhu Z, Gao C, Zhao S, et. al.Photonics-Assisted Ultrawideband RF Self-Interference Cancellation With Signal of Interest Recovery and FiberTransmission[J].Journal of Lightwave Technology, 2022, 40(3): 655-663.)

[0004] However, the above solutions have certain limitations. References 1 and 2 both use optical bandpass filters, whose performance significantly impacts self-interference cancellation performance. Furthermore, Reference 2 can only change the phase of the reference signal and lacks tuning delay functionality, limiting the self-interference cancellation performance of broadband signals. References 3 and 4 employ DP-BPSK and DPMZM modulators, respectively. DC drift issues can lead to unstable self-interference cancellation performance, and the delay and amplitude in Reference 3 are tuned in the electrical domain. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a stable self-interference cancellation device combining phase modulation and fiber dispersion, comprising a wavelength-tunable laser, a fixed-wavelength laser, a first phase modulator, a second phase modulator, a first polarization controller, a polarization combiner, an optical fiber, an optical amplifier, a second polarization controller, a polarization beam splitter, and a balanced detector; wherein

[0006] At the base station,

[0007] The optical signal generated by the wavelength-tunable laser is injected into the first phase modulator, and the optical signal generated by the fixed-wavelength laser is injected into the second phase modulator.

[0008] A reference signal is loaded onto the first phase modulator, and a received signal containing self-interference signal and useful signal is loaded onto the second phase modulator, which generates an X-polarized light modulation signal.

[0009] The X-polarized light modulation signal output from the second phase modulator is output to the first polarization controller. The first polarization controller rotates the polarization state by 90 degrees, converting the X-polarized light modulation signal into a Y-polarized light modulation signal.

[0010] The Y-polarized light modulation signal output by the first polarization controller is coupled with the output of the first phase modulator in the polarization combiner, and the polarization combined light signal output by the polarization combiner is transmitted to the central station through optical fiber.

[0011] At the central station,

[0012] The polarization-coupled optical signal output from the optical fiber is amplified by an optical amplifier, and then rotated by a second polarization controller to align with the polarization beam splitter.

[0013] The aligned orthogonally polarized light signal output from the second polarization controller enters the polarization beam splitter, which separates the X-polarized light signal and the Y-polarized light signal and outputs them in two separate paths.

[0014] The X-polarized optical signal and the Y-polarized optical signal output by the polarization beam splitter are input together into a balanced detector for photoelectric conversion, which converts the optical signal into a microwave electrical signal.

[0015] A stable self-interference cancellation method combining phase modulation and fiber dispersion is also provided, which is based on the aforementioned stable self-interference cancellation device combining phase modulation and fiber dispersion. The specific process is as follows:

[0016] For ease of explanation, let's first assume the reference signal is V1sinω. s t, the self-interference signal is V2sinω s (t+τ AThe useful signal is V3sinω. s (t+τ B ); where V1, V2, and V3 are the voltage amplitudes of the reference signal, interference signal, and useful signal, respectively, and τ A τ B ω represents the delay generated by the self-interference signal and the useful signal during their propagation in space, respectively. s The angular frequencies of the reference signal, self-interference signal, and useful signal;

[0017] Step 1: Electro-optic modulation of the reference signal

[0018] The output optical carrier of the wavelength-tunable laser is injected into the first phase modulator. The first phase modulator modulates the reference signal onto the light. Under small-signal modulation, the envelope E of the output optical signal is modulated by the first phase modulator. x (t) is shown in Equation 1

[0019] E x (t)=E c1 exp(j(ω c +ω τ )t)(J0(m1)+J1(m1)exp(jω s t)-J1(m1)exp(-jω s t))(1)

[0020] Among them, E c1 To provide the amplitude of the optical carrier for a wavelength-tunable laser, ω c ω is the input optical carrier frequency at the reference frequency. τ For a tunable laser at the reference frequency ω c The offset frequency is as follows: J0() is a 0th-order Bessel function of the kind, J1() is a 1st-order Bessel function of the kind, and m1=πV1 / V π V is the modulation index of the first phase modulator. π t represents the half-wave voltage of the phase modulator, and t represents time.

[0021] Step 2: Electro-optic modulation of the received signal and rotation of its polarization state by 90 degrees.

[0022] A fixed-wavelength laser outputs an optical carrier wave, which is injected into a second phase modulator. The second phase modulator performs electro-optic modulation on the received signal, which includes self-interference signals and useful signals, and outputs an X-polarized optical modulation signal. A first polarization controller rotates the X-polarized optical modulation signal by 90 degrees to become a Y-polarized optical modulation signal. Under small-signal modulation, after the polarization rotation, the envelope E of the optical signal output by the first polarization controller... y (t) is shown in Equation 2:

[0023] E y(t)=E c2 exp(jω c t)(J0(m2)J0(m3)+J0(m3)J1(m2)exp(jω s (t+τ A ))-J0(m3)J1(m2)exp(-jω s (t+τ A ))+J0(m2)J1(m3)exp(jω s (t+τ B ))-J0(m2)J1(m3)exp(-jω s (t+τ B (2)

[0024] Among them, E c2 The amplitude of the optical carrier provided for a fixed-wavelength laser is given by m² = πV² / V. π m3=πV3 / V π These are the modulation indices for the self-interference signal and the useful signal, respectively.

[0025] Step 3: The two orthogonally polarized light signals are coupled and transmitted to the central station for amplification and then separated.

[0026] The optical signals output from the first phase modulator and the first polarization controller are orthogonally polarized optical signals. These two orthogonally polarized optical signals are coupled by a polarization combiner and then transmitted to the central station via optical fiber. Due to the dispersion effect of the optical fiber, the transmission function of the optical fiber is H(ω)=exp(-αL / 2+jβ2L(ω-ω)). c ) 2 / 2), where α is the attenuation constant, L is the fiber length, β2 is the group velocity dispersion parameter, and ω is the angular frequency; subsequently, the orthogonally polarized light signal is amplified by an optical amplifier; then, it is polarized and aligned with the polarization beam splitter by a second polarization controller; the orthogonally polarized light signal output from the second polarization controller is input to the polarization beam splitter, where it is separated into an X-polarized light signal and a Y-polarized light signal and output in two separate paths; the X-polarized light signal E SMFx (t) and Y-polarized optical signal E SMFy The envelopes of (t) are respectively:

[0027]

[0028] Among them, G OA For the gain of the erbium-doped fiber amplifier, θ(ω)=β2L(ω-ω c ) 2 / 2 represents the phase shift introduced by the radio frequency signal in the fiber dispersion effect;

[0029] Step 4: The two optical signals beat at the balanced detector to obtain the microwave electrical signal.

[0030] The X-polarized signal and the Y-polarized optical signal are simultaneously input into a balanced detector, and the microwave electrical signal I(t) is obtained by beat frequency at the balanced detector.

[0031]

[0032] Where R is the responsivity of the balanced detector;

[0033] Step 5: Tuning the wavelength of the tunable laser to achieve deep elimination of self-interference.

[0034] According to equation (5), by tuning the power and wavelength of the tunable laser, the following relationship can be satisfied to achieve self-interference signal cancellation:

[0035]

[0036] The advantages of this invention are as follows: Based on the dispersion effect of optical fiber, this invention can realize the conversion of signal from phase modulation to intensity modulation; on the other hand, by changing the wavelength difference between the two lasers, a precise dispersion delay tuning function is introduced, which can realize large-bandwidth radio frequency domain self-interference cancellation and long-distance transmission of useful signals. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the stable self-interference cancellation device combining phase modulation and fiber dispersion in the in-band full-duplex ROF system of the present invention.

[0038] Figure 2 This is a simulation diagram of the single-frequency signal cancellation performance of the present invention;

[0039] Figure 3 This is a simulation diagram of the broadband signal cancellation performance of the present invention. Detailed Implementation

[0040] The present invention relates to a stable self-interference cancellation device for phase modulation combined with fiber dispersion in an in-band full-duplex ROF system, such as... Figure 1 As shown, it includes a wavelength-tunable laser, a fixed-wavelength laser, a first phase modulator, a second phase modulator, a first polarization controller, a polarization combiner, an optical fiber, an optical amplifier, a second polarization controller, a polarization splitter, and a balanced detector.

[0041] At the base station, the optical signal generated by the wavelength-tunable laser is injected into the first phase modulator, and the optical signal generated by the fixed-wavelength laser is injected into the second phase modulator. A reference signal is loaded into the first phase modulator, and the received signal (including self-interference signal and useful signal) is loaded into the second phase modulator, which generates an X-polarized optical modulation signal. The X-polarized optical modulation signal output from the second phase modulator is output to the first polarization controller, which rotates the polarization state by 90 degrees, converting the X-polarized optical modulation signal into a Y-polarized optical modulation signal. Then, the Y-polarized optical modulation signal output from the first polarization controller is coupled to the output of the first phase modulator in a polarization combiner, and the polarization-combined optical signal output from the polarization combiner is transmitted to the central station via optical fiber.

[0042] At the central station, the polarization-combined optical signal output from the optical fiber is amplified by an optical amplifier, and then polarized by a second polarization controller to align with the polarization beam splitter. The aligned orthogonally polarized optical signal output from the second polarization controller enters the polarization beam splitter, which separates the X-polarized and Y-polarized optical signals and outputs them in two separate paths. The X-polarized and Y-polarized optical signals output from the polarization beam splitter are input together to a balanced detector for photoelectric conversion, converting the optical signal into a microwave electrical signal.

[0043] By tuning the wavelength and power of a tunable laser, the delay and amplitude alignment of self-interference signals can be achieved, thus eliminating self-interference to a greater extent and ultimately obtaining a useful signal.

[0044] use Figure 1 The device shown implements a stable self-interference cancellation method combining phase modulation and fiber dispersion. The specific process is as follows:

[0045] For ease of explanation, let's first assume the reference signal is V1sinω. s t, the self-interference signal is V2sinω s (t+τ A The useful signal is V3sinω. s (t+τ B Where V1, V2, and V3 are the voltage amplitudes of the reference signal, interference signal, and useful signal, respectively, and τ A τ B ω represents the delay generated by the self-interference signal and the useful signal during their propagation in space, respectively. s The angular frequencies of the reference signal, self-interference signal, and useful signal.

[0046] Step 1: Electro-optic modulation of the reference signal.

[0047] First, the optical carrier output from the wavelength-tunable laser is injected into the first phase modulator. The first phase modulator modulates the reference signal onto the light. Under small-signal modulation, the envelope E of the output optical signal is modulated by the first phase modulator. x (t) is shown in Equation 1

[0048] E x (t)=E c1 exp(j(ω c +ω τ )t)(J0(m1)+J1(m1)exp(jω s t)-J1(m1)exp(-jω s t))(1)

[0049] Among them, E c1 To provide the amplitude of the optical carrier for a wavelength-tunable laser, ω c ω is the input optical carrier frequency at the reference frequency. τ For a tunable laser at the reference frequency ω c The offset frequency is given by J0(), where J0() is a 0th-order Bessel function of the kind and J1() is a 1st-order Bessel function of the kind, and m1 = πV1 / V. π V is the modulation index of the first phase modulator. π t represents the half-wave voltage of the phase modulator, and t represents time.

[0050] Step 2: Electro-optically modulate the received signal and rotate its polarization state by 90 degrees.

[0051] A fixed-wavelength laser outputs an optical carrier wave, which is injected into a second phase modulator. The second phase modulator electro-optically modulates the received signal (including self-interference and the useful signal), outputting an X-polarized optical modulated signal. This X-polarized signal is then rotated by 90 degrees by a first polarization controller to become a Y-polarized optical modulated signal. Under small-signal modulation, after the polarization rotation, the envelope E of the optical signal output by the first polarization controller... y (t) is shown in Equation 2:

[0052] E y (t)=E c2 exp(jω c t)(J0(m2)J0(m3)+J0(m3)J1(m2)exp(jω s (t+τ A ))-J0(m3)J1(m2)exp(-jω s (t+τ A ))+J0(m2)J1(m3)exp(jω s (t+τ B ))-J0(m2)J1(m3)exp(-jωs (t+τ B (2)

[0053] Among them, E c2 The amplitude of the optical carrier provided for a fixed-wavelength laser is given by m² = πV² / V. π m3=πV3 / V π These are the modulation indices for the self-interference signal and the useful signal, respectively.

[0054] Step 3: The two orthogonally polarized light signals are coupled and transmitted to the central station for amplification and then separated.

[0055] The optical signals output from the first phase modulator and the first polarization controller are orthogonally polarized optical signals. These two orthogonally polarized optical signals are coupled by a polarization combiner and then transmitted to the central station via optical fiber. Due to the dispersion effect of the optical fiber, the transmission function of the optical fiber is H(ω)=exp(-αL / 2+jβ2L(ω-ω)). c ) 2 / 2), where α is the attenuation constant, L is the fiber length, β2 is the group velocity dispersion parameter, and ω is the angular frequency. Subsequently, the orthogonally polarized light signal is amplified by an optical amplifier; then, it undergoes polarization rotation alignment with the polarization beam splitter by a second polarization controller; the orthogonally polarized light signal output from the second polarization controller is input to the polarization beam splitter, where it is separated into X-polarized and Y-polarized light signals and output in two separate paths. X-polarized light signal E SMFx (t) and Y-polarized optical signal E SMFy The envelopes of (t) are respectively:

[0056]

[0057] Among them, G OA For the gain of the erbium-doped fiber amplifier, θ(ω)=β2L(ω-ω c ) 2 / 2 represents the phase shift introduced by the radio frequency signal in the fiber dispersion effect.

[0058] Step 4: The two optical signals beat at the balanced detector to obtain a microwave electrical signal.

[0059] The X-polarized signal and the Y-polarized optical signal are simultaneously input into a balanced detector, and the microwave electrical signal I(t) is obtained by beat frequency at the balanced detector.

[0060]

[0061] Where R is the responsivity of the balanced detector.

[0062] Step 5: Tune the wavelength of the tunable laser to achieve deep elimination of self-interference.

[0063] As can be seen from equation (5), by tuning the power and wavelength of the tunable laser, the following relationship can be satisfied to achieve self-interference signal cancellation:

[0064]

[0065] Thus, the three key factors for achieving self-interference cancellation—amplitude, delay, and inversion—are achieved by tuning the power and wavelength of the tunable laser and the inversion function of the balanced detector, respectively.

[0066] The features of this invention are:

[0067] 1. Using a phase modulator with a simpler structure and more stable performance, it does not require DC bias control compared to other types of modulators, and also avoids DC drift problems.

[0068] 2. Due to the dispersion effect in optical fibers, signals propagating through the fiber generate additional phase. On one hand, after transmission through the fiber, phase modulation can be converted into intensity modulation, generating a first-harmonic electrical signal; on the other hand, after transmission through the fiber, a reference signal is introduced into the signal, β2Lω. τ The delay can be precisely matched with the delay of the self-interference signal by tuning the wavelength of the tunable laser to change the wavelength difference between it and the reference wavelength.

[0069] 3. The delay and amplitude tuning methods are simpler and more compact, and do not require electro-optic delay and amplitude tuning components. Self-interference elimination can be achieved simply by changing the wavelength and power of the tunable laser.

[0070] To verify the elimination performance of the present invention, simulation was performed using OptiSystem 14.0.

[0071] The self-interference signal was set as a single-frequency signal with a center frequency of 14 GHz and a power of 30 dBm. A fixed-wavelength laser with a frequency of 193.4 THz, a power of 10 dBm, a linewidth of 0.1 MHz, a single-mode fiber length of 20 km, an erbium-doped fiber amplifier gain of 10 dB, and a noise figure of 4.5 dB were used. With a self-interference signal delay of 0.8 ns and an attenuation of 1 dB, the frequency of the tunable laser was tuned to 1553.0814 THz, and the power to 9.57 dBm. After this process, the single-frequency self-interference signal cancellation performance was 46.58 dB. Figure 2 As shown. The self-interference signal is replaced with a broadband signal with a bandwidth of 400MHz. Simultaneously, a single-frequency useful signal of 14GHz with a power of 7dBm is introduced, while other parameters remain unchanged. At this point, the self-interference cancellation depth is 42.1dB, as shown. Figure 3 As shown.

Claims

1. A stable self-interference cancellation device combining phase modulation and fiber dispersion, characterized in that, It includes a wavelength-tunable laser, a fixed-wavelength laser, a first phase modulator, a second phase modulator, a first polarization controller, a polarization combiner, an optical fiber, an optical amplifier, a second polarization controller, a polarization beam splitter, and a balanced detector; in At the base station, The optical signal generated by the wavelength-tunable laser is injected into the first phase modulator, and the optical signal generated by the fixed-wavelength laser is injected into the second phase modulator. A reference signal is loaded onto the first phase modulator, and a received signal containing self-interference signal and useful signal is loaded onto the second phase modulator, which generates an X-polarized light modulation signal. The X-polarized light modulation signal output from the second phase modulator is output to the first polarization controller. The first polarization controller rotates the polarization state by 90 degrees, converting the X-polarized light modulation signal into a Y-polarized light modulation signal. The Y-polarized light modulation signal output by the first polarization controller is coupled with the output of the first phase modulator in the polarization combiner, and the polarization combined light signal output by the polarization combiner is transmitted to the central station through optical fiber. At the central station, The polarization-coupled optical signal output from the optical fiber is amplified by an optical amplifier and then rotated by a second polarization controller to align with the polarization beam splitter. The aligned orthogonally polarized light signal output from the second polarization controller enters the polarization beam splitter, which separates the X-polarized light signal and the Y-polarized light signal and outputs them in two separate paths. The X-polarized optical signal and the Y-polarized optical signal output by the polarization beam splitter are input together into a balanced detector for photoelectric conversion, which converts the optical signal into a microwave electrical signal.

2. A method for stabilizing self-interference cancellation by combining phase modulation with fiber dispersion, based on the stable self-interference cancellation device for combining phase modulation with fiber dispersion as described in claim 1, characterized in that, The specific process is as follows: First, assume the reference signal is V1sinω. s t, the self-interference signal is V2 sinω s (t+τ A The useful signal is V3sinω. s (t+τ B ); where V1, V2, and V3 are the voltage amplitudes of the reference signal, self-interference signal, and useful signal, respectively, and τ A τ B ω represents the delay generated by the self-interference signal and the useful signal during their propagation in space, respectively. s The angular frequencies of the reference signal, self-interference signal, and useful signal; Step 1: Electro-optic modulation of the reference signal The output optical carrier of the wavelength-tunable laser is injected into the first phase modulator. The first phase modulator modulates the reference signal onto the light. Under small-signal modulation, the envelope E of the output optical signal is modulated by the first phase modulator. x (t) is shown in Equation 1 A x (t)=E c1 exp(j(ω c +ω τ )t)(J0(m1)+J1(m1)exp(jω s t)-J1(m1)exp(-jω s t)) (1) Among them, E c1 To provide the amplitude of the optical carrier for a wavelength-tunable laser, ω c ω is the input optical carrier frequency at the reference frequency. τ For a tunable laser at the reference frequency ω c The offset frequency is as follows: J0() is a 0th-order Bessel function of the kind, J1() is a 1st-order Bessel function of the kind, and m1=πV1 / V π V is the modulation index of the first phase modulator. π t represents the half-wave voltage of the phase modulator, and t represents time. Step 2: Electro-optic modulation of the received signal and rotation of its polarization state by 90 degrees. A fixed-wavelength laser outputs an optical carrier wave, which is injected into a second phase modulator. The second phase modulator performs electro-optic modulation on the received signal, which includes self-interference signals and useful signals, and outputs an X-polarized optical modulation signal. A first polarization controller rotates the X-polarized optical modulation signal by 90 degrees to become a Y-polarized optical modulation signal. Under small-signal modulation, after the polarization rotation, the envelope E of the optical signal output by the first polarization controller... y (t) is shown in Equation 2: A y (t)=E c2 exp(jω c t)(J0(m2)J0(m3)+J0(m3)J1(m2)exp(jω s (t+τ A )) -J0(m3)J1(m2)exp(-jω s (t+τ A ))+J0(m2)J1(m3)exp(jω s (t+τ B ))-J0(m2)J1(m3)exp(-jω s (t+τ B ))) (2) Among them, E c2 The amplitude of the optical carrier provided for a fixed-wavelength laser is given by m² = πV² / V. π m3=πV3 / V π These are the modulation indices for the self-interference signal and the useful signal, respectively. Step 3: The two orthogonally polarized light signals are coupled and transmitted to the central station for amplification and then separated. The optical signals output from the first phase modulator and the first polarization controller are orthogonally polarized optical signals. These two orthogonally polarized optical signals are coupled by a polarization combiner and then transmitted to the central station via optical fiber. Due to the dispersion effect of the optical fiber, the transmission function of the optical fiber is H(ω)=exp(-αL / 2+jβ2L(ω-ω)). c ) 2 / 2), where α is the attenuation constant, L is the fiber length, β2 is the group velocity dispersion parameter, and ω is the angular frequency; subsequently, the orthogonally polarized light signal is amplified by an optical amplifier; then, it is polarized and aligned with the polarization beam splitter by a second polarization controller; the orthogonally polarized light signal output from the second polarization controller is input to the polarization beam splitter, where it is separated into an X-polarized light signal and a Y-polarized light signal and output in two separate paths; the X-polarized light signal E SMFx (t) and Y-polarized optical signal E SMFy The envelopes of (t) are respectively: Among them, G OA For the gain of the erbium-doped fiber amplifier, θ(ω)=β2L(ω-ω c ) 2 / 2 represents the phase shift introduced by the radio frequency signal in the fiber dispersion effect; Step 4: The two optical signals beat at the balanced detector to obtain the microwave electrical signal. The X-polarized signal and the Y-polarized optical signal are simultaneously input into a balanced detector, and the microwave electrical signal I(t) is obtained by beat frequency at the balanced detector. Where R is the responsivity of the balanced detector; Step 5: Tuning the wavelength of the tunable laser to achieve deep elimination of self-interference. According to equation (5), by tuning the power and wavelength of the tunable laser, the following relationship can be satisfied to achieve self-interference signal cancellation:

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