A frequency shift keying detection system and method based on optical phase finite-difference

Abstract

The application relates to a frequency shift keying detection system and method based on optical phase finite difference, and belongs to the technical field of optical communication. The system comprises a frequency shift keying optical signal transmitting unit, an optical beam splitter, an optical delay unit, an optical phase diversity receiving unit, an optoelectronic detection unit, an analog-to-digital conversion unit and a digital signal processing unit. By delaying and interfering the frequency shift keying optical signal, a phase difference related to instantaneous frequency is formed, and a corresponding phase diversity optical signal is obtained through the phase diversity receiving unit; the optoelectronic detection unit obtains a phase diversity electrical signal; and the analog-to-digital conversion unit samples the phase diversity electrical signal into a digital signal. The digital signal processing unit constructs a complex signal, extracts a phase and unwraps the phase, so that frequency modulation information is recovered, and frequency shift keying signal detection is realized. The application does not depend on a specific frequency shift keying signal generation mode, is suitable for different frequency modulation structures and different phase diversity receiving structures, realizes low-complexity frequency shift keying detection without a local oscillator light source, and is suitable for a high-speed low-power artificial intelligence data center optical interconnection system.

Description

Technical Field

[0001] This invention belongs to the field of optical communication technology and relates to a frequency shift keying detection system and method based on optical phase finite difference. Background Technology

[0002] Frequency Shift Keying (FSK) modulation has significant application value in high-speed optical interconnect systems due to its characteristics such as constant envelope, good noise immunity, and high receiver sensitivity. With the development of artificial intelligence data centers, high-speed low-power optical interconnects, and multi-level FSK systems, there are increasing demands for high-speed, wide-bandwidth, low-power, and low-complexity FSK signal detection.

[0003] Existing frequency shift keying (FSK) detection methods mainly include electrical domain frequency discrimination methods, frequency-power mapping methods based on optical filters, and coherent frequency discrimination methods. Traditional electrical domain frequency discrimination methods typically rely on devices such as phase-locked loops, electrical mixers, or high-frequency discriminators. In high-speed and high-frequency scenarios, these methods require high bandwidth from electronic components, resulting in complex system implementations and susceptibility to high-frequency link losses and noise. Optical filter-based detection methods convert frequency changes into optical power changes through the frequency response of the optical filter. However, these methods often suffer from nonlinear frequency response, uneven sensitivity, and sensitivity to wavelength drift. As the frequency shift range increases or the modulation order rises, the difficulty of frequency determination in the system further increases.

[0004] On the other hand, although coherent frequency discrimination methods based on local oscillator sources can achieve high-sensitivity frequency recovery, they usually require additional local oscillator sources, complex polarization control structures, and highly complex digital signal processing algorithms, resulting in high system power consumption and implementation costs, which is not conducive to high-speed, low-power optical interconnect applications.

[0005] Therefore, there is an urgent need to develop a frequency shift keying (FSK) detection method that can be applied to different FFS signal generation methods and achieve low-complexity, high-linearity frequency recovery without the need for a local oscillator light source. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a frequency shift keying detection system and method based on optical phase finite difference, so as to solve the problems of the prior art, such as complex system implementation, susceptibility to high-frequency link loss and noise, nonlinear frequency response, uneven sensitivity, sensitivity to wavelength drift, and high system power consumption and implementation cost, which are not conducive to high-speed and low-power optical interconnect application scenarios.

[0007] To achieve the above objectives, the present invention provides a frequency shift keying detection system based on optical phase finite difference, which includes a frequency shift keying optical signal transmitting unit, an optical beam splitter, an optical delay unit, an optical phase diversity receiving unit, a photoelectric detection unit, an analog-to-digital conversion unit, and a digital signal processing unit.

[0008] The frequency shift keying optical signal transmitting unit is used to generate frequency shift keying optical signals; The optical beam splitter is used to split the frequency shift keying optical signal into two optical signals. The optical delay unit is used to delay one of the optical signals in time, so that a phase difference related to the instantaneous frequency is formed between the optical signals at different times; The optical phase diversity receiving unit is used to interfere with time-delayed optical signals and non-time-delayed optical signals to generate optical signals with different phase diversity. The photoelectric detection unit is used to convert optical signals with different phase diversity into electrical signals; The analog-to-digital converter unit is used to convert analog electrical signals into digital signals; The digital signal processing unit is used to perform complex signal construction, digital filtering, phase extraction and phase unwrapping processing on the digital signal, and to recover the frequency modulation information according to the phase change to realize frequency shift keying signal detection.

[0009] Furthermore, the frequency shift keying optical signal transmitting unit can adopt any optical signal generating structure capable of optical frequency modulation, frequency shifting, or frequency switching. It can be a direct modulation laser, an external modulator, an electro-optic modulator, an acousto-optic modulator, an integrated optical frequency modulation structure, or other structures capable of generating frequency shift keying optical signals.

[0010] Furthermore, the frequency shift keying optical signal includes binary frequency shift keying signal or multi-level frequency shift keying signal.

[0011] In this system, frequency shift keying (FSK) optical signals of different bases are generated by setting different numbers of discrete optical frequency states. For binary FFS signals, input bits "0" and "1" are mapped to two different optical frequency states respectively; for M-ary FFS signals, every log2(M) input bits form a symbol, and different symbols are mapped to M different optical frequency states. Different optical frequency states can be generated by changing the drive current of the direct modulated laser, the drive voltage of the external modulator, or the control signals of other frequency modulation units.

[0012] Furthermore, the delay time of the optical signal by the optical delay unit is less than the symbol period of the frequency shift keying signal.

[0013] Furthermore, the optical phase diversity receiving unit adopts a phase diversity receiving structure including at least two phase numbers or phase intervals, which is used to perform phase diversity interference on time-delayed optical signals and non-time-delayed optical signals and output corresponding optical signals.

[0014] Furthermore, the optical phase diversity receiving unit can generate two-phase diversity optical signals including 0 degrees and 180 degrees; the photoelectric detection unit includes two photodetectors, which receive the two-phase diversity optical signals of 0 degrees and 180 degrees respectively, and output two analog electrical signals after photoelectric conversion; the two analog electrical signals are subtracted by a subtractor to obtain the in-phase component signal; the analog-to-digital conversion unit is used to convert the in-phase component signal into a digital signal, and recover the quadrature component information in the digital domain through Hilbert transform.

[0015] Furthermore, the optical phase diversity receiving unit can generate three-phase diversity optical signals including 0 degrees, 120 degrees, and 240 degrees; the photoelectric detection unit includes three photodetectors that receive the three-phase diversity optical signals of 0 degrees, 120 degrees, and 240 degrees respectively, and output three analog electrical signals after photoelectric conversion; the analog-to-digital conversion unit includes three analog-to-digital converters that synchronously convert the three analog electrical signals into three digital signals, and recover the in-phase and quadrature component information through digital signal processing.

[0016] Furthermore, the optical phase diversity receiving unit can generate four-phase diversity optical signals including 0 degrees, 90 degrees, 180 degrees, and 270 degrees. The corresponding photoelectric detection unit includes four photodetectors, which receive the optical signals of 0 degrees, 90 degrees, 180 degrees, and 270 degrees of phase diversity, respectively. After photoelectric conversion, four analog electrical signals are output. Among them, the two analog electrical signals corresponding to 0 degrees and 180 degrees are subtracted by a subtractor to obtain the in-phase component signal; the two analog electrical signals corresponding to 90 degrees and 270 degrees are subtracted by a subtractor to obtain the quadrature component signal. The analog-to-digital conversion unit includes two analog-to-digital converters for synchronously converting the in-phase component signal and the quadrature component signal into digital signals.

[0017] Another aspect of the present invention provides a frequency shift keying detection method in conjunction with the above-described system, the method comprising: Frequency-shift keying optical signals are generated by a frequency-shift keying optical signal transmitting unit; An optical beam splitter is used to split the frequency shift keying optical signal into two optical signals; An optical delay unit is used to delay one of the optical signals, so that a phase difference related to the instantaneous frequency is formed between the optical signals at different times. By performing phase diversity interference on time-delayed and non-time-delayed optical signals using an optical phase diversity receiving unit, optical signals with different phase diversity can be obtained. Optical signals with different phase diversity are converted into electrical signals through a photoelectric detection unit; Analog electrical signals are converted to digital signals using an analog-to-digital converter (ADC). The digital signal processing unit performs complex signal construction, digital filtering, phase extraction, and phase unwrapping on the digital signal.

[0018] The beneficial effects of this invention are as follows: (1) Based on the principle of optical phase finite difference, this invention converts frequency change into phase change by performing phase diversity interference on time-delayed optical signals and non-time-delayed optical signals, thereby realizing frequency recovery of frequency shift keying signals and having good linear frequency response characteristics.

[0019] (2) This invention can realize frequency shift keying signal detection without introducing a local oscillator light source, which reduces system complexity, system power consumption and implementation cost, and is suitable for high-speed and low-power optical interconnect scenarios.

[0020] (3) This invention does not depend on a specific frequency shift keying signal generation method, is compatible with direct modulation, external modulation and other frequency modulation structures, and has good versatility and scalability.

[0021] (4) The present invention supports phase diversity reception structures with different number of phases or different phase intervals, and can be adapted to two-phase, three-phase, four-phase and multi-phase diversity reception architectures, and has good system compatibility.

[0022] (5) The present invention achieves frequency recovery through phase extraction and phase unwrapping. Compared with the method based on optical filter frequency-power mapping, it reduces the dependence on the frequency response characteristics of the filter and improves the system stability and robustness.

[0023] (6) This invention is applicable to binary frequency shift keying and multi-level frequency shift keying signals, and can support high-speed, multi-modulation format frequency shift keying systems.

[0024] (7) The present invention adopts a combination of optical domain delay interference and digital domain phase recovery, which reduces the bandwidth requirements of traditional electrical domain frequency discrimination methods for high-frequency electronic devices and is conducive to the realization of high-speed broadband frequency shift keying systems.

[0025] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 A schematic diagram of the frequency shift keying detection system based on optical phase finite difference provided by the present invention; Figure 2 This is a schematic diagram of a frequency shift keying detection system based on a direct modulation laser and a four-phase diversity receiver structure, provided in an embodiment of the present invention. Figure 3 A schematic diagram showing the comparison of error vector amplitudes under different rates of OOK\PAM4 and FSK\FSK4 signals and different electric drive powers; Figure 4 A schematic diagram showing the comparison of the error vector amplitude as a function of received optical power for OOK / PAM4 and FSK / FSK4 signals at different rates and with the same electric drive power; Figure 5 A schematic diagram showing the comparison of lower eye diagrams for OOK\PAM4 and FSK\FSK4 signals at different rates; Figure 6 for Figure 2 The illustrated embodiment is a schematic diagram showing the comparison of bit error rate with received optical power for OOK and FSK signals at the same rate. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0028] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0029] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0030] like Figure 2 As shown, an embodiment of the present invention provides a frequency shift keying detection system based on a direct modulated laser and a four-phase diversity receiver structure. In this embodiment, a direct modulated laser is used to generate a frequency shift keying optical signal, and a 90° optical mixer structure is used to realize the detection of the frequency shift keying signal.

[0031] At the transmitting end, a directly modulated laser is used as the light source, and the instantaneous optical power of the optical signal can be expressed as:

[0032] in, This refers to the laser bias power. For modulation amplitude, This is the normalized modulation signal. The output optical signal of a directly modulated laser not only contains an intensity modulation component but also generates frequency chirp. Its output optical field can be expressed as:

[0033] in, Let be the instantaneous phase of the optical signal. The transient frequency chirp is determined by the derivative of the phase with respect to time, i.e.:

[0034] The transient frequency chirp can be composed of the transient chirp term on the left and the adiabatic chirp term on the right, as shown below:

[0035] in, Linewidth enhancement factor is the adiabatic chirp coefficient.

[0036] Under conditions of large modulation depth, i.e. At the falling edge of the signal, i.e. At that time, As the frequency approaches zero, the transient frequency chirp approaches infinity, leading to spectral broadening and signal distortion. In this embodiment, by increasing the laser bias current and employing a small-signal modulation method, the transient frequency chirp approaches infinity. Thus To minimize and suppress the influence of transient frequency chirp, the system operates in a modulation state dominated by adiabatic chirp. Under this condition, the transient frequency chirp can be approximated as:

[0037] Therefore, it can be seen that transient frequency chirp and modulation signal The relationship between them is approximately linear. A non-return-to-zero (NRZ) code signal can be used to form an FSK modulated signal; similarly, when When modulated by four-level pulse amplitude (PAM4), a four-frequency shift keying (FSK4) modulation signal can be formed.

[0038] For other types of frequency shift keying optical signal transmitting units, such as external modulators, electro-optic modulators, acousto-optic modulators, and integrated optical frequency modulation structures, the specific mechanisms for generating discrete optical frequency states differ. For example, electro-optic modulators can map different frequency radio frequency drive signals to different output optical frequency states through single-sideband modulation, carrier suppression, and optical sideband selection; acousto-optic modulators can directly generate corresponding optical frequency shifts using acousto-optic drive signals of different frequencies.

[0039] Different types of frequency shift keying (FSK) optical signal transmitting units require different settings for drive signals, operating biases, and modulation amplitudes based on their modulation mechanisms to generate discrete optical frequency states corresponding to different input symbols. This embodiment uses a directly modulated laser as an example to illustrate the generation process of FFS optical signals; other types of FFS optical signal transmitting units will not be described in detail.

[0040] At the receiving end, the optical signal is first split into two paths by an optical beam splitter. One path continues to transmit along the original path, while the other path undergoes a time delay introduced by an optical delay unit. , Less than the symbol period. The two optical signals are:

[0041]

[0042] Two optical signals interfere in a 90° optical mixer, and orthogonal electrical signal components are obtained through a balanced detection structure in the photoelectric detection unit. After photoelectric conversion, the in-phase component and the orthogonal component are represented as follows:

[0043]

[0044] in, Phase difference It can be expressed as the integral of the transient frequency chirp over the time window, i.e.:

[0045] in, For the integral variable, when the delay time Less than the symbol period of the frequency shift keying optical signal, and the integration interval When the frequency state switching interval is not crossed, the transient frequency remains approximately constant within the integration interval. Therefore, the above relationship can be approximated as:

[0046] Therefore, there is an approximately linear relationship between the phase difference and the transient frequency chirp, and the detection of the phase difference can realize the detection of the transient frequency chirp.

[0047] In digital signal processing, the in-phase and quadrature components after analog-to-digital conversion are used to construct a complex signal, which is then digitally filtered to obtain the complex signal represented as follows:

[0048] and These represent the in-phase component and the quadrature component after digital filtering, respectively.

[0049] Phase extraction is performed on the complex signal to obtain instantaneous phase information. Due to the periodic phase transition phenomenon, phase unwrapping processing is required to eliminate the transition and obtain continuous phase change. The instantaneous phase difference obtained by digital demodulation is finally expressed as:

[0050] in, For phase unwrapping operation, This is for phase extraction operations.

[0051] Finally, Normalization is performed to eliminate the DC component, ensuring that the phase difference states corresponding to different frequency states are distributed within the range of -1 to 1. For binary frequency shift keying optical signals, 0 is set as the decision threshold; when the normalized phase difference is less than 0, it is determined to be a low-frequency state, and when the normalized phase difference is greater than or equal to 0, it is determined to be a high-frequency state. For multi-level frequency shift keying optical signals with equal frequency intervals, the normalized phase states corresponding to different frequency states are set at equal intervals from -1 to 1, and the median value of every two adjacent normalized phase states is set as a fixed decision threshold. The corresponding frequency state and symbol are determined based on the threshold interval where the normalized phase difference is located, and the original bit sequence is recovered based on the preset mapping relationship between symbols and bit combinations. In this embodiment, to verify the progress of the system of the present invention, a traditional intensity modulation direct detection method is used as a comparison scheme, that is, detecting the on / off keying (OOK) signal or the PAM4 signal. Both schemes use the same receiving structure, devices, and sampling conditions. During the intensity detection process, a single path from the orthogonal signals is selected as the intensity information, and the power loss introduced by this is compensated by 3 dB, thereby eliminating the influence of receiver structure differences on the experimental results.

[0052] like Figure 3 As shown, under 1 Gb / s FSK, 10 Gb / s FSK and 5 GBaud FSK4 transmission conditions, compared with the traditional intensity detection method, the required electric drive power of the present invention is reduced by approximately 6.49 dB, 2.54 dB and 2.61 dB respectively, under the same error vector amplitude.

[0053] like Figure 4 As shown, under the same electric drive power, the average error vector amplitude within the measured received optical power range is improved by approximately 10.23 dB, 1.95 dB, and 3.28 dB, respectively.

[0054] like Figure 5 As shown, the eye diagrams of received signals under different modulation schemes at different transmission rates are compared while keeping the driving power equal. It can be seen that the present invention still maintains clear signal differentiation under low driving voltage conditions, reflecting a large decision margin.

[0055] To further illustrate that the present invention does not sacrifice bit error rate performance while maintaining low drive power, Figure 6 The bit error rate-received optical power curves for 10 Gb / s FSK and 10 Gb / s OOK at electric drive powers of 5.01 dBm and 7.50 dBm, respectively, are further shown. It can be seen that at low received optical power, the present invention even exhibits a lower bit error rate, while at high received optical power, the bit error rate performance of the present invention is almost consistent with that of the traditional intensity modulation direct detection scheme.

[0056] The above comparison demonstrates that the frequency shift keying (FSK) detection system and method based on optical phase finite difference proposed in this invention can achieve stable signal detection under different modulation rates and modulation formats, verifying the feasibility and effectiveness of the invention. Compared with traditional intensity detection methods, under the condition of a unified receiving structure and devices, this invention maintains good signal quality even under low driving conditions and exhibits good noise immunity and signal recovery capabilities. These results indicate that this invention achieves efficient detection of FSK signals by combining delayed interferometry and phase recovery. It can achieve low-complexity, highly robust frequency recovery without requiring a local oscillator light source or complex receiving structure, making it suitable for high-speed, low-power artificial intelligence optical interconnect networks.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A frequency shift keying detection system based on optical phase finite difference, characterized in that, It includes a frequency shift keying optical signal transmitting unit, an optical beam splitter, an optical delay unit, an optical phase diversity receiving unit, a photoelectric detection unit, an analog-to-digital conversion unit, and a digital signal processing unit; The frequency shift keying optical signal transmitting unit is used to generate frequency shift keying optical signals; The optical beam splitter is used to split the frequency shift keying optical signal into two optical signals. The optical delay unit is used to delay one of the optical signals in time, so that a phase difference related to the instantaneous frequency is formed between the optical signals at different times; The optical phase diversity receiving unit is used to interfere with time-delayed optical signals and non-time-delayed optical signals to generate optical signals with different phase diversity. The photoelectric detection unit is used to convert optical signals with different phase diversity into electrical signals; The analog-to-digital converter unit is used to convert analog electrical signals into digital signals; The digital signal processing unit is used to perform complex signal construction, digital filtering, phase extraction and phase unwrapping processing on the digital signal, and to recover the frequency modulation information according to the phase change to realize frequency shift keying signal detection.

2. The system according to claim 1, characterized in that, The frequency shift keying optical signal transmitting unit is a direct modulation laser, an external modulator, an electro-optic modulator, an acousto-optic modulator, or an integrated optical frequency modulation structure.

3. The system according to claim 1, characterized in that, The delay time of the optical signal by the optical delay unit is less than the symbol period of the frequency shift keying signal.

4. The system according to claim 1, characterized in that, The optical phase diversity receiving unit employs a phase diversity receiving structure including at least two phase numbers or phase intervals, used to perform phase diversity interference on time-delayed optical signals and non-time-delayed optical signals and output corresponding optical signals.

5. The system according to claim 4, characterized in that, The optical phase diversity receiving unit is used to generate two-phase diversity optical signals including 0 degrees and 180 degrees; the photoelectric detection unit includes two photodetectors, which receive the two-phase diversity optical signals of 0 degrees and 180 degrees respectively, and output two analog electrical signals after photoelectric conversion; the two analog electrical signals are subtracted by a subtractor to obtain the in-phase component signal; the analog-to-digital conversion unit is used to convert the in-phase component signal into a digital signal, and recover the quadrature component information in the digital domain through Hilbert transform.

6. The system according to claim 4, characterized in that, The optical phase diversity receiving unit is used to generate three-phase diversity optical signals including 0 degrees, 120 degrees and 240 degrees; the photoelectric detection unit includes three photoelectric detectors, which receive the three-phase diversity optical signals of 0 degrees, 120 degrees and 240 degrees respectively, and output three analog electrical signals after photoelectric conversion. The analog-to-digital conversion unit includes three analog-to-digital converters, which are used to synchronously convert three analog electrical signals into three digital signals, and recover the in-phase and quadrature component information through digital signal processing.

7. The system according to claim 4, characterized in that, The optical phase diversity receiving unit generates four-phase diversity optical signals including 0 degrees, 90 degrees, 180 degrees, and 270 degrees. The photoelectric detection unit includes four photodetectors that receive the optical signals of phase diversity at 0 degrees, 90 degrees, 180 degrees, and 270 degrees, respectively. After photoelectric conversion, four analog electrical signals are output. The two analog electrical signals corresponding to 0 degrees and 180 degrees are subtracted by a subtractor to obtain the in-phase component signal. The two analog electrical signals corresponding to 90 degrees and 270 degrees are subtracted by a subtractor to obtain the quadrature component signal. The analog-to-digital conversion unit includes two analog-to-digital converters to synchronously convert the in-phase component signal and the quadrature component signal into digital signals.

8. A frequency shift keying detection method in conjunction with the system described in any one of claims 1 to 7, characterized in that, The method includes: Frequency-shift keying optical signals are generated by a frequency-shift keying optical signal transmitting unit; An optical beam splitter is used to split the frequency shift keying optical signal into two optical signals; An optical delay unit is used to delay one of the optical signals, so that a phase difference related to the instantaneous frequency is formed between the optical signals at different times. By performing phase diversity interference on time-delayed and non-time-delayed optical signals using an optical phase diversity receiving unit, optical signals with different phase diversity can be obtained. Optical signals with different phase diversity are converted into electrical signals through a photoelectric detection unit; Analog electrical signals are converted to digital signals using an analog-to-digital converter (ADC). The digital signal processing unit performs complex signal construction, digital filtering, phase extraction, and phase unwrapping on the digital signal.

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