A method for simultaneous and same-frequency integrated optical transceiver for satellite-to-ground two-way laser communication

Abstract

This invention discloses a simultaneous, same-frequency integrated optical transceiver method for bidirectional satellite-to-ground laser communication. A monolithically integrated electro-absorption modulated laser is used at the satellite payload end, serving as both the transmitter and receiver, enabling simultaneous transmission of uplink and downlink signals in the satellite-to-ground laser link at the same optical carrier frequency. The downlink transmitted electrical signal is fed into the electro-absorption modulated laser via an electrical circulator for electro-optic modulation, while the uplink received optical signal is injected into the electro-absorption modulated laser via an optical circulator for self-coherent detection. The uplink received electrical signal contains self-interference components caused by leakage from the downlink transmitted electrical signal. These self-interference components are canceled out by constructing an inverse signal with the same amplitude as the self-interference signal in the analog domain, and residual self-interference components are eliminated in the digital domain using channel estimation and adaptive filtering. This invention has the advantages of high integration, high spectral efficiency, and strong self-interference suppression capability, making it suitable for high-speed satellite-to-ground laser communication systems.

Description

Technical Field

[0001] This invention relates to the field of free-space laser communication, and more particularly to a method for simultaneous and co-frequency integrated optical transceiver for bidirectional laser communication between space and ground. Background Technology

[0002] With the rapid development of satellite internet, free-space laser communication has gradually become an important means of realizing satellite-to-ground communication due to its advantages such as high data rate, no need for licensed spectrum, simple and quick deployment, and high directionality and security. With the accelerated deployment of mega-constellations, the requirements for satellite payload size, weight, and power consumption (SWaP) are becoming increasingly stringent. Existing satellite-to-ground laser communication systems typically require separate transmitters and receivers, increasing the size, weight, and power consumption of the payload and limiting the miniaturization and lightweight design of low-Earth orbit satellites. Furthermore, uplink and downlink typically employ wavelength division multiplexing (WDM) or time division multiplexing (TDM), making it difficult to achieve efficient utilization of spectrum resources. Summary of the Invention

[0003] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is the low integration and low spectrum utilization of optical transceivers in existing satellite-to-ground laser communication. The present invention provides a simultaneous, same-frequency integrated optical transceiver method for two-way satellite-to-ground laser communication. A monolithically integrated electro-absorption modulated laser (EML) is used as both a transmitter and receiver. Its internal distributed feedback (DFB) laser serves as both the light source and local oscillator. The electro-absorption modulator (EAM) simultaneously performs modulation and detection functions, effectively reducing the size, weight, and power consumption of the transceiver. To address the self-interference problem introduced by the EML transceiver, a balun transformer is used to construct an equal-amplitude, inverse-phase signal to eliminate self-interference in the analog domain. Residual self-interference components are then eliminated through channel estimation and adaptive filtering in the digital domain.

[0004] To achieve the above objectives, the present invention provides a method for simultaneous and co-frequency integrated optical transceiver for bidirectional satellite-to-ground laser communication, comprising the following steps:

[0005] Step 1: At the satellite payload end, an electro-absorption modulated laser is used as an integrated transceiver device. The distributed feedback laser in the electro-absorption modulated laser is used to generate a continuous optical carrier, and the electro-absorption modulator in the electro-absorption modulated laser is used as both an electro-optic modulator and a photodetector.

[0006] Step 2: In the downlink, the transmitted signal is converted from digital to analog and then split into two paths by a balun converter. One path is the drive signal, which is fed into the electroabsorption modulator through an electrical circulator to modulate the continuous optical carrier to generate the downlink transmitted optical signal. The other path is the inverted signal, which is used for analog self-interference cancellation in the subsequent uplink.

[0007] Step 3: The downlink transmitted optical signal is sent to the space link via an optical circulator, while the uplink received optical signal is coupled to the electroabsorption modulated laser via an optical circulator. The two signals have the same carrier frequency and their signal spectra overlap.

[0008] Step 4: In the uplink, the electroabsorption modulated laser performs photoelectric conversion on the received uplink optical signal and outputs a mixed electrical signal containing self-interference signals formed by leakage of the uplink and downlink signals.

[0009] Step 5: By adjusting the amplitude and delay of the inverted signal, an inverted signal matching the self-interference signal is constructed, and it is combined with the mixed electrical signal in the analog domain through a combiner to cancel the self-interference component in the mixed electrical signal.

[0010] Step six: Sample the analog signal after the above self-interference cancellation and convert the analog signal into a digital signal;

[0011] Step 7: Channel estimation is performed using the self-interference signal in the digital domain, and then the self-interference signal is accurately reconstructed using a digital filter. Finally, the residual self-interference component is subtracted from the digital signal to recover the uplink received signal.

[0012] Furthermore, in step one, the electroabsorption modulated laser includes a distributed feedback laser and an electroabsorption modulator.

[0013] Furthermore, in step two, the differential output characteristics of the balun converter are used to generate two analog signals with equal amplitude and opposite phase, thereby achieving self-interference signal cancellation in the analog domain.

[0014] Furthermore, in step three, an optical circulator is used at the optical port of the electroabsorption modulated laser to achieve transmit-receive isolation.

[0015] Furthermore, in step four, the electro-absorption modulated laser performs self-coherent detection on the received optical signal, the distributed feedback laser provides local oscillator light using injection-locked technology, and the electro-absorption modulator performs photoelectric conversion on the beat frequency components of the local oscillator light and the signal light.

[0016] Furthermore, in step five, analog self-interference cancellation is performed before analog-to-digital conversion to prevent high-power self-interference signals from saturating the analog-to-digital converter.

[0017] Furthermore, in step five, the amplitude and delay of the two self-interference signals are perfectly matched through an adjustable attenuator and a phase shifter in the simulated self-interference cancellation.

[0018] Furthermore, in step six, due to the limited cancellation depth of the analog self-interference cancellation, some self-interference signals still exist in the received signal after analog-to-digital conversion.

[0019] Furthermore, in step seven, the obtained downlink received signal is recovered. It can be represented as:

[0020]

[0021] in, For an ideal downlink transmission signal, The signal is the uplink received signal after analog-to-digital conversion, which contains self-interference components caused by leakage from the downlink transmitted signal. To estimate the impulse response of the self-interference channel, This represents the number of filter taps.

[0022] Furthermore, an adaptive algorithm is employed to analyze the impulse response of the self-interference channel. Estimate and track in real time changes in self-interference path response caused by satellite platform vibration or environmental changes.

[0023] Furthermore, the adaptive algorithm is either the least mean square algorithm or the recursive least squares algorithm.

[0024] Furthermore, a finite impulse response filter is used to accurately reconstruct the self-interference signal, and its tap coefficients are updated in real time based on the channel estimation results.

[0025] Technical effect

[0026] This invention provides a simultaneous, same-frequency integrated optical transceiver method for two-way satellite-to-ground laser communication. It employs an electro-absorption modulated laser to achieve integrated transceiver operation, significantly reducing the size, weight, and power consumption of the satellite payload. The electro-absorption modulated laser performs self-coherent detection of the uplink signal, effectively improving receiver sensitivity without requiring complex frequency offset estimation and phase recovery algorithms. The distributed feedback laser uses injection locking to compensate for Doppler frequency shift, thereby adapting to dynamic changes in the satellite link and effectively improving system stability. By dual suppression of strong self-interference signals in both the analog and digital domains, two-way communication under the same optical carrier frequency is achieved, effectively improving spectrum utilization efficiency.

[0027] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of a satellite payload optical transceiver method for a simultaneous and integrated optical transceiver method for bidirectional laser communication between satellite and ground, according to a preferred embodiment of the present invention.

[0029] Figure 2This is a schematic diagram of the modulation function and absorption function of an electroabsorption modulator for a simultaneous and same-frequency integrated optical transceiver method for two-way laser communication between space and ground, according to a preferred embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram illustrating the principle and structure of analog and digital cancellation in a preferred embodiment of a simultaneous and integrated optical transceiver method for bidirectional laser communication between space and ground.

[0031] Figure 4 This is a schematic diagram of the self-interference signal spectrum before and after analog and digital cancellation in a preferred embodiment of a simultaneous and integrated optical transceiver method for bidirectional laser communication between space and ground. Detailed Implementation

[0032] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0033] In the following description, specific details, such as particular internal procedures and techniques, are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will appreciate that the invention may be practiced in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of the invention with unnecessary detail.

[0034] This invention provides a method for simultaneous, same-frequency integrated optical transceiver for bidirectional laser communication between satellite and ground, comprising the following steps:

[0035] Step 1: At the satellite payload end, an electro-absorption modulated laser is used as an integrated transceiver device. The distributed feedback laser in the electro-absorption modulated laser is used to generate a continuous optical carrier, and the electro-absorption modulator in the electro-absorption modulated laser is used as both an electro-optic modulator and a photodetector.

[0036] Step 2: In the downlink, the transmitted signal is converted from digital to analog and then split into two paths by a balun converter. One path is the drive signal, which is fed into the electroabsorption modulator through an electrical circulator to modulate the continuous optical carrier to generate the downlink transmitted optical signal. The other path is the inverted signal, which is used for analog self-interference cancellation in the subsequent uplink.

[0037] Step 3: The downlink transmitted optical signal is sent to the space link via an optical circulator, while the uplink received optical signal is coupled to the electroabsorption modulated laser via an optical circulator. The two signals have the same carrier frequency and their signal spectra overlap.

[0038] Step 4: In the uplink, the electroabsorption modulated laser performs photoelectric conversion on the received uplink optical signal and outputs a mixed electrical signal containing self-interference signals formed by leakage of the uplink and downlink signals.

[0039] Step 5: By adjusting the amplitude and delay of the inverted signal, an inverted signal matching the self-interference signal is constructed, and it is combined with the mixed electrical signal in the analog domain through a combiner to cancel the self-interference component in the mixed electrical signal.

[0040] Step six: Sample the analog signal after the above self-interference cancellation and convert the analog signal into a digital signal;

[0041] Step 7: Channel estimation is performed using the self-interference signal in the digital domain, and then the self-interference signal is accurately reconstructed using a digital filter. Finally, the residual self-interference component is subtracted from the digital signal to recover the uplink received signal.

[0042] Specifically, such as Figure 1 As shown, this method is applicable to space payloads, preferably low-Earth orbit satellites. Its core transceiver component is a monolithically integrated electro-absorption modulated laser (EML), which is a monolithically integrated distributed feedback (DFB) laser and electro-absorption modulator (EAM). When the integrated transceiver is in transmit mode, the DFB laser is biased by a specific current... Driven by [unclear], a continuous optical carrier is generated. The downlink transmit signal is converted into an RF electrical signal by a digital-to-analog converter (DAC), and then sequentially loaded onto the RF port of the EML through an electrical circulator and a DC biaser (Bias-T). The EAM is used under reverse bias voltage [unclear]. The DFB laser's continuous optical carrier, utilizing its electrical absorption characteristics, is intensity-modulated to generate a downlink transmit optical signal, which is then transmitted to the space link via an optical circulator. When the integrated transceiver is in receive mode, the uplink receive optical signal from the space link is injected into the EML's optical port through the optical circulator. The DFB laser uses injection-locked technology to provide the local oscillator light required for coherent detection. The EAM, acting as a photodetector, performs beat frequency processing on the local oscillator light and the uplink signal light and completes photoelectric conversion. Due to the limited physical isolation of the electrical circulator, high-power downlink signals in the transmit link leak into the uplink through the circulator. Therefore, the electrical signal output by the EAM is a mixed current signal consisting of the desired uplink signal and the downlink leakage self-interference signal, which needs to be processed by a subsequent self-interference cancellation module.

[0043] In bidirectional transmission systems, the EAM serves as both a modulator and a detector. However, the bias voltage of the EAM... The optimal value varies depending on the operating condition. Therefore, it is necessary to select an appropriate bias voltage. This allows for a trade-off between modulation and detection performance. For example... Figure 2 The diagram shown is a schematic representation of the modulation and absorption functions of the electro-absorption modulator according to an embodiment of the present invention. The nonlinear transfer function of EAM is also shown. With bias voltage The relationship is exponential and can be expressed as:

[0044]

[0045] in To achieve the minimum extinction ratio, Due to inherent losses, and These are the fitting parameters. Figure 2 The transmission curve in is when , , and The modulation function of the EAM (Electronic Amplifier) ​​decreases gradually with increasing reverse bias voltage until the optical signal is completely absorbed and converted into photocurrent. Therefore, the absorption function of the EAM can be expressed as: The absorption curve obtained after normalization is as follows: Figure 2 As shown. To achieve both good modulation and detection performance, an intermediate bias voltage is generally selected.

[0046] Since the EML has only one RF port, high-power transmitted signals will be mixed into the low-power received signal, therefore, it is necessary to eliminate the high-power self-interference signal. For example... Figure 3 The diagram illustrates the principle and structure of analog and digital cancellation according to an embodiment of the present invention. In the analog domain, the downlink transmitted signal, after digital-to-analog conversion and electrical amplification, is split into two signals with equal amplitude and opposite phase by a balun transformer. One signal uses an electrical circulator at the RF port of the EML to partially suppress crosstalk between the uplink and downlink signals; the other signal uses an attenuator and a delay line to adjust the amplitude and delay of the self-interference signal, ensuring that the delay and amplitude of the two self-interference signals are equal when combined, thereby subtracting the leaked transmitted signal from the received signal. In the digital domain, an adaptive algorithm is used to address the impulse response of the self-interference channel. The self-interference signal is estimated and then accurately reconstructed using a finite impulse response (FIR) filter. The tap coefficients are updated in real-time based on the channel estimation results. Finally, the residual self-interference component is subtracted from the digital signal to recover the uplink received signal. , can be represented as: .

[0047]

[0048] in, For an ideal downlink transmission signal, The signal is the uplink received signal after analog-to-digital conversion, which contains self-interference components caused by leakage from the downlink transmitted signal. To estimate the self-interference channel impulse response, This represents the number of filter taps. Adaptive algorithms can employ either the least mean square algorithm or the recursive least squares algorithm.

[0049] like Figure 4 The diagram shown illustrates the spectrum of the self-interference signal before and after analog and digital cancellation according to an embodiment of the present invention. Taking a 400 MHz OFDM signal as an example, Figure 4 (a) and (b) demonstrate the offsetting effects of analog elimination and digital elimination, respectively. For example... Figure 4 As shown in (a), analog self-interference cancellation effectively reduces the power of the self-interference signal, with a cancellation depth of approximately 20 dB. Based on this, channel estimation and digital filtering achieve accurate reconstruction of the residual self-interference signal, and digital self-interference cancellation achieves a cancellation depth of approximately 30 dB, as shown in (a). Figure 4 As shown in (b). Therefore, by adopting a two-stage self-interference cancellation scheme in the analog and digital domains, the crosstalk problem introduced by the EML transceiver can be effectively solved, with a cancellation depth of up to 50dB, thereby realizing simultaneous and integrated optical transceiver at the same frequency.

[0050] As can be seen from the above embodiments, the present invention can achieve high integration, high spectrum utilization and strong self-interference suppression capability by using a monolithic integrated electro-absorption modulated laser, and can achieve simultaneous co-frequency integrated transmission and reception. It is suitable for satellite-to-ground two-way laser communication systems with increasingly stringent requirements for the size, weight and power consumption of satellite payloads.

[0051] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for simultaneous, same-frequency integrated optical transceiver for bidirectional satellite-to-ground laser communication, characterized in that, Includes the following steps: Step 1: At the satellite payload end, an electro-absorption modulated laser is used as an integrated transceiver device. The distributed feedback laser in the electro-absorption modulated laser is used to generate a continuous optical carrier, and the electro-absorption modulator in the electro-absorption modulated laser is used as both an electro-optic modulator and a photodetector. Step 2: In the downlink, the transmitted signal is converted from digital to analog and then split into two paths by a balun converter. One path is a drive signal, which is fed into the electroabsorption modulator through an electrical circulator to modulate the continuous optical carrier to generate a downlink transmitted optical signal. The other path is an inverted signal, which is used for analog self-interference cancellation in the subsequent uplink. Step 3: The downlink transmitted optical signal is sent to the space link via an optical circulator, and the uplink received optical signal is coupled to the electroabsorption modulated laser via an optical circulator. The two signals have the same carrier frequency and their signal spectra overlap. Step 4: In the uplink, the electroabsorption modulated laser performs photoelectric conversion on the received uplink optical signal and outputs a mixed electrical signal containing self-interference signals formed by leakage of the uplink and downlink signals. Step 5: By adjusting the amplitude and delay of the inverted signal, an inverted signal matching the self-interference signal is constructed, and it is combined with the mixed electrical signal in the analog domain through a combiner, thereby canceling the self-interference component in the mixed electrical signal. Step six: Sample the analog signal after the above self-interference cancellation and convert the analog signal into a digital signal; Step 7: Channel estimation is performed using the self-interference signal in the digital domain, and then the self-interference signal is accurately reconstructed using a digital filter. Finally, the residual self-interference component is subtracted from the digital signal to recover the uplink received signal.

2. The method for simultaneous and same-frequency integrated optical transceiver for two-way laser communication between satellite and ground as described in claim 1, characterized in that, In step one, the electro-absorption modulated laser includes a distributed feedback laser and an electro-absorption modulator.

3. The method for simultaneous and same-frequency integrated optical transceiver for two-way satellite-to-ground laser communication as described in claim 1, characterized in that, In step two, the differential output characteristics of the balun converter are used to generate two analog signals with equal amplitude and opposite phase, thereby achieving self-interference signal cancellation in the analog domain.

4. The method for simultaneous and same-frequency integrated optical transceiver for two-way laser communication between satellite and ground as described in claim 1, characterized in that, In step three, an optical circulator is used at the optical port of the electroabsorption modulated laser to achieve transmit-receive isolation.

5. The method for simultaneous and same-frequency integrated optical transceiver for two-way laser communication between satellite and ground as described in claim 1, characterized in that, In step four, the electroabsorption modulated laser performs self-coherent detection on the received optical signal, the distributed feedback laser provides local oscillator light using injection-locked technology, and the electroabsorption modulator performs photoelectric conversion on the beat frequency components of the local oscillator light and the signal light.

6. The method for simultaneous and same-frequency integrated optical transceiver for two-way satellite-to-ground laser communication as described in claim 1, characterized in that, In step five, analog self-interference cancellation is performed before analog-to-digital conversion to prevent high-power self-interference signals from saturating the analog-to-digital converter.

7. The method for simultaneous and same-frequency integrated optical transceiver for two-way laser communication between satellite and ground as described in claim 1, characterized in that, In step five, the amplitude and delay of the two self-interference signals are perfectly matched through an adjustable attenuator and a phase shifter in the simulated self-interference cancellation process.

8. The method for simultaneous and same-frequency integrated optical transceiver for two-way satellite-to-ground laser communication as described in claim 1, characterized in that, In step six, due to the limited cancellation depth of the analog self-interference cancellation, some self-interference signals still exist in the received signal after analog-to-digital conversion.

9. The method for simultaneous and same-frequency integrated optical transceiver for two-way laser communication between satellite and ground as described in claim 1, characterized in that, In step seven, the recovered downlink received signal It can be represented as: ， in, For an ideal downlink transmission signal, The signal is the uplink received signal after analog-to-digital conversion, which contains self-interference components caused by leakage from the downlink transmitted signal. To estimate the impulse response of the self-interference channel, This represents the number of filter taps.

10. The method for simultaneous and same-frequency integrated optical transceiver for satellite-to-ground two-way laser communication as described in claim 9, characterized in that, An adaptive algorithm is used to analyze the impulse response of a self-interference channel. Estimate and track in real time changes in self-interference path response caused by satellite platform vibration or environmental changes.

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