Phase filter based complex-valued double sideband signal direct detection optical field reconstruction method

Abstract

An optical field reconstruction method for direct detection of complex-valued double-sideband signals based on phase filters is disclosed. This method splits the complex-valued double-sideband signal under test into two paths. One path is directly subjected to photodetection and square-law detection to obtain the in-phase component of the information-carrying signal; the other path undergoes phase filtering followed by photodetection to obtain the quadrature component of the information-carrying signal, thereby achieving optical field reconstruction. This invention avoids the insertion of guard bands at frequency points other than zero frequency, while also avoiding a significant increase in the beat frequency term between signals, thus significantly improving the system's bit error rate performance and spectral efficiency.

Description

Technical Field

[0001] This invention relates to a technology in the field of optical communication, specifically a method for direct detection and optical field reconstruction of complex-valued double-sideband signals based on phase filters. Background Technology

[0002] Existing direct detection techniques for complex-valued double-sideband signals include carrier-assisted differential detection based on delay interference structures and asymmetric self-coherent detection based on dispersive elements. While these techniques can achieve optical field reconstruction and high spectral efficiency, the signal suffers from severe frequency-selective power fading due to the imperfection of the receiver's transfer function. At zero points, the beat frequency term between signals is greatly amplified, thus degrading the system's transmission performance. Therefore, guard bands need to be added at each zero point of the transfer function, and multi-band modulation techniques are employed, which significantly reduces the spectral efficiency of the direct detection system. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, this invention proposes a method for direct detection and optical field reconstruction of complex-valued double-sideband signals based on phase filters. This method avoids the insertion of guard bands at frequency points other than zero frequency, while also avoiding significant enhancement of the beat frequency terms between signals, thereby significantly improving the system's bit error rate performance and spectral efficiency.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for direct detection and optical field reconstruction of complex-valued double-sideband signals based on phase filters. The method involves splitting the complex-valued double-sideband signal to be measured into two paths. One path is directly subjected to photoelectric detection and square-law detection to obtain the in-phase component of the information-carrying signal. The other path is first subjected to phase filtering and then photoelectric detection to obtain the quadrature component of the information-carrying signal, thereby realizing optical field reconstruction.

[0006] The complex double-sideband signal to be tested includes a carrier wave and an information-bearing signal, wherein the information-bearing signal is a complex signal containing in-phase and quadrature components.

[0007] The phase filtering described herein is achieved through a filter that is fully amplitude-pass and only produces phase changes.

[0008] Technical effect

[0009] This invention uses a phase filter with full amplitude pass to achieve direct detection optical field reconstruction of complex-valued double-sideband signals. Compared with existing technologies, it avoids the insertion of guard bands at frequency points other than zero frequency, while not significantly enhancing the beat frequency term between signals, thereby significantly improving the system's bit error rate performance and spectral efficiency. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of a receiver for direct detection of complex-valued double-sideband signals based on a phase filter.

[0011] Figure 2 These are the amplitude-frequency response and phase-frequency response of the phase filter;

[0012] Figure 3 This is a schematic diagram illustrating the application of an example.

[0013] Figure 4 This is a comparison chart of the bit error rate performance of this method and the method using dispersive elements under different optical signal-to-noise ratios in the embodiments. Detailed Implementation

[0014] like Figure 1 and Figure 3 As shown in this embodiment, a receiver for direct detection of complex-valued double-sideband signals based on a phase filter, implementing the above-described method, includes: a beam splitter and parallel in-phase component detection branches and quadrature component detection branches. The in-phase component detection branch includes a first photodetector and a first DC blocker connected in sequence, while the quadrature component detection branch includes a phase filter, a second photodetector, and a second DC blocker connected in sequence. The complex-valued double-sideband signal c+s(t) output by the transmitter is split into two identical parts by the beam splitter, and the photocurrent i1 output in the in-phase component detection branch is |c+s(t)|. 2 -|c| 2 +n1=2cs in-phase +|s(t)| 2 +n1, the in-phase component obtained after reconstruction Photocurrent output from the quadrature component detection branch n2, the orthogonal components obtained after reconstruction are Where: c is the carrier wave, s(t) is the information-carrying signal, and s in-phase and s quadrature Let n1 and n2 be the in-phase and quadrature components of s(t), respectively, and let h(t) be the time-domain impulse response of the phase filter. in-phase and h quadrature Let h(t) be the in-phase and quadrature components. For linear convolution, Re[·] is the real part extraction operation. It is h quadrature The reciprocal in the frequency domain.

[0015] The DC blocking device is implemented using, but is not limited to, an AC-coupled photodetector or a digital signal processor.

[0016] like Figure 2As shown, when the phase filter is an amplitude-pass phase filter, a phase shift is applied only to the information-carrying signal. The optimal angle of this phase shift is obtained through iterative adjustment based on the actual transmission system. Specifically, the angle of the phase shift is continuously changed to obtain the corresponding bit error rate. The optimal angle is obtained when the bit error rate is minimized.

[0017] Due to h quadrature There is only one zero at zero frequency, therefore h quadrature At frequencies other than zero, the enhancement of the beat frequency term between the signal and the signal is minimal, which avoids the need to insert guard bands at other frequencies, thereby improving the receiver's spectral efficiency. The reconstructed original signal contains not only in-phase and quadrature components, but also second-order terms of the signal s(t), which are eliminated using, but not limited to, the convolutional neural network technique described in "Deep-learning-enabled Direct Detection with Reduced Computational Complexity and High Electrical-spectral-efficiency" (Journal of Lightwave Technology, early access, 2023).

[0018] like Figure 3 As shown, in a laboratory setting, the transmitter is configured to output a 50 GBuad pulse-shaped complex-valued double-sideband 16-QAM pulse-shaped signal with a roll-off factor of 0.01. A 6 GHz guard band (-3 GHz to 3 GHz) is inserted at the zero frequency of the complex-valued double-sideband signal.

[0019] An additive white Gaussian noise channel is set on the complex-valued double-sideband 16-QAM signal to simulate an optical fiber channel.

[0020] In a laboratory setting, a complex-valued double-sideband signal direct detection receiver based on a phase filter is used to convert optical signals into electrical signals. In the digital signal processing at the receiver, a convolutional neural network is used for optical field reconstruction, followed by matched filtering and bit error rate calculation to obtain the following result: Figure 4 The error rate performance is shown.

[0021] like Figure 4 As shown, to achieve a 25% forward error correction (FEC) threshold, the required optical signal-to-noise ratios (SNRs) for the phase filter and dispersive element are 21.6 dB and 26 dB, respectively. In contrast, this invention reduces the required SNR by 4.4 dB, effectively improving system performance.

[0022] In summary, under the same optical signal-to-noise ratio and guard band conditions, the present invention can significantly reduce the bit error rate; under the same bit error rate and guard band conditions, the present invention can significantly reduce the optical signal-to-noise ratio; under the same optical signal-to-noise ratio and bit error rate conditions, the prior art requires the use of a larger guard band, while the present invention can significantly improve the spectral efficiency.

[0023] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A receiver for direct detection of complex-valued double-sideband signals based on a phase filter, characterized in that, include: The beam splitter includes parallel in-phase and quadrature component detection branches. The in-phase component detection branch comprises a first photodetector and a first DC blocker connected in sequence. The quadrature component detection branch comprises a phase filter, a second photodetector, and a second DC blocker connected in sequence. The complex-valued double-sideband signal c+s(t) output from the transmitter is split into two identical parts by the beam splitter. The photocurrent output from the in-phase component detection branch... The in-phase components obtained after reconstruction The photocurrent output by the orthogonal component detection branch The orthogonal components obtained after reconstruction are Where: c is the carrier wave, s(t) is the information-carrying signal, and s in-phase and s quadrature Let n1 and n2 be the in-phase and quadrature components of s(t), respectively, and let h(t) be the time-domain impulse response of the phase filter. in-phase and h quadrature Let h(t) be the in-phase and quadrature components. For linear convolution, To perform the real part operation, It is h quadrature The reciprocal in the frequency domain; The aforementioned direct detection of complex-valued double-sideband signals refers to: splitting the complex-valued double-sideband signal to be tested into two paths, one of which is directly subjected to photoelectric detection and square-law detection to obtain the in-phase component of the information-carrying signal; the other path is first subjected to phase filtering and then photoelectric detection to obtain the quadrature component of the information-carrying signal, thereby realizing optical field reconstruction; The complex double-sideband signal to be tested includes a carrier wave and an information-bearing signal, wherein the information-bearing signal is a complex signal containing in-phase and quadrature components.

2. The receiver for direct detection of complex-valued double-sideband signals based on a phase filter according to claim 1, characterized in that, The phase filtering described herein is achieved through a filter that is fully amplitude-pass and only produces phase changes.

3. The receiver for direct detection of complex-valued double-sideband signals based on a phase filter according to claim 1, characterized in that, When the phase filter is an amplitude-pass phase filter, a phase shift is applied only to the information-carrying signal, and the optimal angle of this phase shift is obtained through iterative adjustment based on the actual transmission system.

4. The receiver for direct detection of complex-valued double-sideband signals based on a phase filter according to claim 3, characterized in that, By continuously changing the phase shift angle, the corresponding bit error rate is obtained, and the optimal angle is obtained when the bit error rate is minimized.

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