Signal generation method and system applied to direct alignment and direct detection optical fiber communication system

Abstract

The invention relates to the technical field of optical fiber communication, and particularly discloses a signal generation method and system applied to a direct-modulation and direct-detection optical fiber communication system, and the method comprises the steps: carrying out the bit mapping and preprocessing of a data stream, generating a single-side-band signal of a baseband, loading the single-side-band signal to an X-polarization state of a set dual-polarization IQ modulator, and obtaining a single-side-band signal; the corresponding first offset point is adjusted to a zero point; connecting an I-path port and a Q-path port of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator with a resistor, and adjusting a corresponding second bias point to a linear working point; and signals in the X polarization state and the Y polarization state output by the dual-polarization IQ modulator are mapped to one polarization state by using a polarizer, a single-side-band optical signal is output through the output end of the polarizer, and arbitrary adjustability of carrier and signal power is realized by modulating the angle of the polarizer and the second bias point.

Description

Technical Field

[0001] The present application relates to the field of optical fiber communication technology, and in particular to a signal generation method and system for use in a direct adjustment and direct detection optical fiber communication system. Background Art

[0002] With the increase of transmission capacity in optical fiber communication systems, the bottleneck in the current optical network has shifted to the optical interconnection between data centers and the optical transmission network of the metropolitan area network. In such networks, a low-cost solution is needed to achieve a transmission rate of at least 100Gb / s, and the transmission distance is at least 100 kilometers. Therefore, in this case, the direct modulation and direct detection method is one of the methods that has received the most attention. However, in order to achieve a transmission distance of more than 100 kilometers, due to the need for low-noise fiber amplifiers, the operating wavelength of the optical fiber communication system needs to be around 1550nm, which means that in the case of direct reception, its performance will be affected by the power damage caused by dispersion, which will seriously limit the transmission distance of the direct modulation and direct detection system. Although the use of dispersion-compensating fiber can effectively overcome the influence of fiber dispersion, it will also affect the flexibility of the optical network and increase the cost of the optical fiber transmission link.

[0003] In order to solve the above problems, researchers have proposed many methods. At present, the more common solution is to use single-sideband modulation. In this way, the carrier and the signal are directly beat in the photodetector at the receiving end to restore the electric field of the electrical signal after transmission, so as to compensate for the effects caused by dispersion. However, the current methods of generating single-sideband signals all require the modulator to be biased to the linear point because there must be an optical carrier at DC. This method causes most of the signal power to be added to the DC, thereby reducing the power utilization and signal-to-noise ratio of the signal, and causing a large loss in energy consumption. Therefore, such a technical solution has great limitations in practical applications. Summary of the invention

[0004] The purpose of the present application is to provide a signal generation method and system for use in a direct modulation and direct detection optical fiber communication system, so as to solve the problem that the single-sideband signal generation method in the prior art causes most of the signal power to be added to the direct current, thereby reducing the power utilization rate and signal-to-noise ratio of the signal and causing great loss in energy consumption.

[0005] To achieve the above-mentioned object, the embodiment of the present application provides a signal generation method applied to a direct modulation and direct detection optical fiber communication system, comprising the steps of: generating a baseband single sideband signal after bit mapping and preprocessing a data stream, and then loading it to the X polarization state of a set dual polarization IQ modulator, and adjusting the corresponding first bias point to zero;

[0006] Connecting resistors to the I and Q ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator, and adjusting the corresponding second bias point to a linear operating point;

[0007] A polarizer is used to map the signals in the X polarization state and the Y polarization state output by the dual polarization IQ modulator to one polarization state, and a single-sideband optical signal is output through the output end of the polarizer. The carrier and the signal power can be arbitrarily adjusted by modulating the angle of the polarizer and the second bias point.

[0008] Optionally, the preprocessing includes: performing Fourier transform on the data stream to obtain a frequency spectrum and then filtering out a sideband.

[0009] Optionally include:

[0010] The received single-sideband optical signal is converted into an electrical signal through a photoelectric detector, and then converted into a digital signal through an analog-to-digital converter, and the data stream is restored through digital signal processing.

[0011] To achieve the above-mentioned purpose, the embodiment of the present application also provides another signal generation method for a direct modulation and direct detection optical fiber communication system, comprising the steps of: bit mapping and preprocessing the data stream, respectively implementing single sideband modulation on the left and right sidebands at the base frequency, and then loading it to the X polarization state of the set dual polarization IQ modulator, and adjusting the corresponding first bias point to zero;

[0012] Connecting resistors to the I and Q ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator, and adjusting the corresponding second bias point to a linear operating point;

[0013] A polarizer is used to map the signals in the X polarization state and the Y polarization state output by the dual polarization IQ modulator to one polarization state, and a dual single-sideband optical signal is output through the output end of the polarizer. The carrier and the signal power can be arbitrarily adjusted by modulating the angle of the polarizer and the second bias point.

[0014] Optionally, the preprocessing includes: moving the upper sideband and lower sideband signals to an intermediate frequency by spectrum shifting.

[0015] Optionally include:

[0016] The received dual single-sideband optical signal first passes through a set circulator, and then passes through a set semi-transparent and semi-reflective fiber grating filter, which transmits part of the carrier and the right-band optical signal, and reflects the remaining carrier and the left-band optical signal back, and then the right-band optical signal and the left-band optical signal enter the two set photoelectric detectors respectively to realize photoelectric conversion, and digital signal processing is performed after analog-to-digital conversion to restore the data stream.

[0017] To achieve the above-mentioned purpose, the embodiment of the present application further provides a signal generating system applied to a direct modulation and direct detection optical fiber communication system, comprising: a single sideband modulation unit, a digital-to-analog converter, a dual polarization IQ modulator, and a polarizer, wherein:

[0018] The input end of the single sideband modulation unit is used to receive a data stream, and the output end of the single sideband modulation unit is connected to the input end of the digital-to-analog converter, and is used to generate a baseband single sideband signal after bit mapping and preprocessing the data stream;

[0019] The input end of the dual-polarization IQ modulator is used to connect to the light outlet of the laser, the output end of the dual-polarization IQ modulator is connected to the input end of the polarizer, the I-path and Q-path ports of the IQ modulator in the X polarization state of the dual-polarization IQ modulator are respectively connected to the two output ends of the digital-to-analog converter, and the I-path and Q-path ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator are connected to resistors.

[0020] To achieve the above-mentioned purpose, the embodiment of the present application also provides another signal generating system for use in a direct modulation and direct detection optical fiber communication system, comprising: a double-sideband modulation unit, a digital-to-analog converter, a dual-polarization IQ modulator, and a polarizer, wherein:

[0021] The input end of the double-sideband modulation unit is used to receive a data stream, and the output end of the double-sideband modulation unit is connected to the input end of the digital-to-analog converter, and is used to implement single-sideband modulation at the left and right sidebands at the base frequency respectively;

[0022] The input end of the dual-polarization IQ modulator is used to connect to the light outlet of the laser, the output end of the dual-polarization IQ modulator is connected to the input end of the polarizer, the I-path and Q-path ports of the IQ modulator in the X polarization state of the dual-polarization IQ modulator are respectively connected to the two output ends of the digital-to-analog converter, and the I-path and Q-path ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator are connected to resistors.

[0023] The embodiments of the present application have the following advantages:

[0024] Compared with the prior art, the method provided by the above technical solution makes full use of the characteristics of the existing commercial dual-polarization IQ modulator and the modulation range of the IQ modulator to maximize the optical signal. At the same time, the power ratio of the carrier and the optical signal can be flexibly adjusted. The direct modulation and direct detection technology can be effectively promoted to practicality. This solves the problem that the current method of generating single-sideband signals causes most of the signal power to be added to the direct current, thereby reducing the power utilization rate and signal-to-noise ratio of the signal and causing a large loss in energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0026] Figure 1 A schematic diagram of a single-sideband optical signal generation method for a signal generation method in a direct modulation and direct detection optical fiber communication system provided by at least one embodiment of the present application;

[0027] Figure 2 A receiving principle diagram of a single-sideband optical signal generation method for a signal generation method in a direct modulation and direct detection optical fiber communication system provided by at least one embodiment of the present application;

[0028] Figure 3 A schematic diagram of a dual single-sideband optical signal generation method for a signal generation method in a direct modulation and direct detection optical fiber communication system provided by at least one embodiment of the present application;

[0029] Figure 4 A receiving principle diagram of a dual single-sideband optical signal generation method for a signal generation method in a direct modulation and direct detection optical fiber communication system provided in at least one embodiment of the present application. DETAILED DESCRIPTION

[0030] The following is a description of the implementation of the present application by specific specific embodiments. People familiar with the technology can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0031] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0032] The present application provides a signal generation method for a direct modulation and direct detection optical fiber communication system. Figures 1 to 4 ,include:

[0033] like Figure 1 As shown, it is a schematic diagram of the signal generation method based on the dual polarization IQ modulator adopted in this application, which generates a baseband single sideband signal (i.e. Figure 1The single sideband modulation in the circuit) is then loaded onto the X polarization state of the dual polarization IQ modulator, and the corresponding first bias point is adjusted to zero.

[0034] Connecting resistors (e.g., 50 ohm resistors) to the I and Q ports of the dual-polarization IQ modulator in the Y polarization state indicates that there is no modulation signal, and adjusting the corresponding second bias point to a linear working point to control the magnitude of the carrier power in the Y polarization state. At the same time, a polarizer is connected to the output end of the dual-polarization IQ modulator, and the signals in the X polarization state and the Y polarization state output by the dual-polarization IQ modulator are mapped to one polarization state by the polarizer, and a single-sideband optical signal is output through the output end of the polarizer. By modulating the angle of the polarizer and the second bias point, the carrier and signal power can be arbitrarily adjusted.

[0035] In some embodiments, the preprocessing includes: performing Fourier transform on the data stream to convert it into a frequency spectrum and then filtering out a sideband.

[0036] Specifically, the spectrum of the single-sideband optical signal at the transmitting end of the signal generation system is also as follows: Figure 1 shown. Figure 1 The single sideband modulation technology in is implemented in the digital domain. The main process is to filter out one sideband after the data stream is transformed into a spectrum by Fourier transform, such as Figure 1 As shown, the right sideband is retained and the left sideband is filtered out.

[0037] In some embodiments, Figure 1 The schematic diagram of the receiving end of the single-sideband optical signal transmitted by the transmitting end in the reference Figure 2 , including: converting the received single-sideband optical signal into an electrical signal through a photoelectric detector, then converting it into a digital signal through an analog-to-digital converter, and then restoring the data stream through digital signal processing.

[0038] In some embodiments, based on Figure 1 The single sideband signal generation principle diagram is provided. This patent also proposes a signal generation method for a direct modulation and direct detection optical fiber communication system based on a double sideband signal direct modulation and direct detection transmission architecture, including the following steps:

[0039] After bit mapping and preprocessing, the data stream is modulated at the baseband to achieve single sideband modulation (i.e. Figure 3 Double-sideband modulation in the circuit) is then loaded onto the X polarization state of the dual-polarization IQ modulator, and the corresponding first bias point is adjusted to zero.

[0040] Connecting resistors (e.g., 50 ohm resistors) to the I and Q ports of the dual-polarization IQ modulator in the Y polarization state indicates that there is no modulation signal, and adjusting the corresponding second bias point to a linear working point to control the magnitude of the carrier power in the Y polarization state. At the same time, a polarizer is connected to the output end of the dual-polarization IQ modulator, and the signals in the X polarization state and the Y polarization state output by the dual-polarization IQ modulator are mapped to one polarization state by the polarizer, and a dual single-sideband optical signal is output through the output end of the polarizer. By modulating the angle of the polarizer and the second bias point, the carrier and signal power can be arbitrarily adjusted.

[0041] In some embodiments, the preprocessing includes: shifting the upper sideband and lower sideband signals to the intermediate frequency by spectrum shifting, thereby ensuring that there is no signal at the low frequency.

[0042] Specifically, the principle diagram of the dual single-sideband optical signal generation method is as follows: Figure 3 As shown. Similar to the generation of single-sideband optical signals, here a polarization IQ modulator is used to implement single-sideband modulation on the left and right sidebands respectively. Through digital signal preprocessing, single-sideband modulation is implemented on the left and right sidebands at the baseband respectively, and at the same time a certain protection band is retained at the baseband so that the left and right sidebands do not overlap and generate crosstalk. After this method is modulated onto the light, the spectrum of the dual single-sideband optical signal is also as shown Figure 3 shown. Figure 3 The dual single-sideband modulation technology in the present invention is implemented in the digital domain. The difference from the conventional double-sideband modulation is that the present invention shifts the upper sideband and lower sideband signals to the intermediate frequency by means of spectrum shifting, thereby ensuring that there is no signal at the low frequency.

[0043] In some embodiments, for receiving dual single-sideband optical signals, the schematic diagram is as follows: Figure 4 As shown. It includes: the received dual single-sideband optical signal first passes through a circulator, and then passes through a semi-transparent and semi-reflective fiber grating filter, which can transmit part of the carrier and the right-side band optical signal, and reflect the remaining carrier and the left-side band optical signal back, and its corresponding spectrum is shown as follows Figure 4 Then the right-side optical signal and the left-side optical signal enter two photoelectric detectors respectively to realize photoelectric conversion, and after analog-to-digital conversion, the next digital signal processing process is performed to restore the data stream.

[0044] The present application describes a new method for generating single-sideband optical signals in a direct modulation and direct detection optical fiber communication system: first, a dual-polarization IQ modulator is used at the transmitting end. The modulator has three electrical interfaces for each polarization state (x polarization and y polarization), corresponding to the I path, Q path and bias point adjustment. The transmitted bit stream data (i.e. Figure 1 and Figure 2 The data stream in the dual-polarization IQ modulator is pre-processed by the single-sideband modulation module to form the single-sideband I and Q signals, and is directly loaded onto a polarization IQ modulator. The bias point is adjusted to zero to maximize the power of the optical signal. On the other polarization IQ modulator, no electrical signal is loaded on its I and Q ports. The signal light power on the other polarization IQ modulator is adjusted by adjusting the position of the bias point, which also corresponds to the carrier power. A polarizer is connected to the optical output end of the dual-polarization IQ modulator to map the two polarizations of light to one polarization state and adjust the carrier and optical signal power ratio. The dual-polarization IQ modulator is connected in parallel, and the laser light is transmitted to the optical input end of the dual-polarization IQ modulator respectively.

[0045] In summary, compared with the prior art, the method provided by the present application makes full use of the characteristics of the existing commercial dual-polarization IQ modulator and the modulation range of the IQ modulator to maximize the optical signal. At the same time, the power ratio of the carrier and the optical signal can be flexibly adjusted. The direct modulation and direct detection technology can be effectively promoted to practicality. This solves the problem that the current method of generating single-sideband signals causes most of the signal power to be added to the direct current, thereby reducing the power utilization rate and signal-to-noise ratio of the signal, and causing a large loss in energy consumption.

[0046] An embodiment of the present application further provides a signal generating system for use in a direct modulation and direct detection optical fiber communication system, comprising: a single sideband modulation unit, a digital-to-analog converter, a dual polarization IQ modulator, and a polarizer, wherein:

[0047] The input end of the single sideband modulation unit is used to receive a data stream, and the output end of the single sideband modulation unit is connected to the input end of the digital-to-analog converter, and is used to generate a baseband single sideband signal after bit mapping and preprocessing the data stream;

[0048] The input end of the dual-polarization IQ modulator is used to connect to the light outlet of the laser, the output end of the dual-polarization IQ modulator is connected to the input end of the polarizer, the I-path and Q-path ports of the IQ modulator in the X polarization state of the dual-polarization IQ modulator are respectively connected to the two output ends of the digital-to-analog converter, and the I-path and Q-path ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator are connected to resistors.

[0049] An embodiment of the present application also provides another signal generating system used in a direct modulation and direct detection optical fiber communication system, comprising: a double-sideband modulation unit, a digital-to-analog converter, a dual-polarization IQ modulator, and a polarizer, wherein:

[0050] The input end of the double-sideband modulation unit is used to receive a data stream, and the output end of the double-sideband modulation unit is connected to the input end of the digital-to-analog converter, and is used to implement single-sideband modulation at the left and right sidebands at the base frequency respectively;

[0051] The input end of the dual-polarization IQ modulator is used to connect to the light outlet of the laser, the output end of the dual-polarization IQ modulator is connected to the input end of the polarizer, the I-path and Q-path ports of the IQ modulator in the X polarization state of the dual-polarization IQ modulator are respectively connected to the two output ends of the digital-to-analog converter, and the I-path and Q-path ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator are connected to resistors.

[0052] The specific implementation method is referred to the above method embodiment and will not be described again here.

[0053] The entire system uses a dual-polarization IQ modulator at the transmitting end. This modulator is currently the main modulator used in 100Gb / s coherent optical communication systems, with the characteristics of large shipments and low cost. By modulating the signal on one polarization state and not modulating the signal on the other polarization but only loading the carrier, the generation of a single-sideband signal is achieved. In order to achieve the beat frequency of two signals with different polarizations in the photodetector, a polarizer is used at the output end of the modulator to convert the two polarization signals to one polarization state, so that direct reception can be achieved. This method can effectively utilize the power of the transmitted signal and improve the transmission performance of the system.

[0054] Note that, unless otherwise directly stated, all features disclosed in this specification (including any attached claims, abstracts and drawings) may be replaced by alternative features for achieving the same, equivalent or similar purposes. Therefore, unless otherwise explicitly stated, each feature disclosed is only an example of a group of equivalent or similar features. Where used, further, preferably, further and more preferably are simple beginnings for elaborating another embodiment based on the aforementioned embodiment, and the content of the further, preferably, further or more preferably followed by the combination with the aforementioned embodiment constitutes a complete construction of another embodiment. Several further, preferably, further or more preferably settings following the same embodiment can be arbitrarily combined to form another embodiment.

[0055] In the implementation of functions and steps, the corresponding functions and steps in various embodiments may also occur in a different order than shown. For example, two consecutive functions and steps may actually be performed or implemented substantially in parallel, and they may sometimes be performed or implemented in the opposite order, depending on the functions involved.

[0056] Although the present application has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made to the present application. Therefore, these modifications or improvements made without departing from the spirit of the present application all fall within the scope of protection claimed in the present application.

Claims

1. A signal generation method used in a direct modulation and direct detection optical fiber communication system, characterized in that: Includes steps: The data stream is bit-mapped and pre-processed to generate a baseband single-sideband signal, which is then loaded onto the X-polarization state of the dual-polarization IQ modulator, and the corresponding first bias point is adjusted to zero; Connecting resistors to the I and Q ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator, and adjusting the corresponding second bias point to a linear operating point; A polarizer is used to map the signals in the X polarization state and the Y polarization state output by the dual polarization IQ modulator to one polarization state, and a single-sideband optical signal is output through the output end of the polarizer. The carrier and the signal power can be arbitrarily adjusted by modulating the angle of the polarizer and the second bias point.

2. The signal generation method used in a direct modulation and direct detection optical fiber communication system according to claim 1, characterized in that: The preprocessing includes: transforming the data stream into a frequency spectrum through Fourier transform and then filtering out a sideband.

3. The signal generation method used in a direct modulation and direct detection optical fiber communication system according to claim 1, characterized in that: include: The received single-sideband optical signal is converted into an electrical signal through a photoelectric detector, and then converted into a digital signal through an analog-to-digital converter, and the data stream is restored through digital signal processing.

4. A signal generation method used in a direct modulation and direct detection optical fiber communication system, characterized in that: Includes steps: After bit mapping and preprocessing, the data stream is subjected to single sideband modulation at the left and right sidebands at the baseband, and then loaded into the X polarization state of the dual polarization IQ modulator, and the corresponding first bias point is adjusted to zero; Connecting resistors to the I and Q ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator, and adjusting the corresponding second bias point to a linear operating point; A polarizer is used to map the signals in the X polarization state and the Y polarization state output by the dual polarization IQ modulator to one polarization state, and a dual single-sideband optical signal is output through the output end of the polarizer. The carrier and the signal power can be arbitrarily adjusted by modulating the angle of the polarizer and the second bias point.

5. The signal generation method used in a direct modulation and direct detection optical fiber communication system according to claim 4, characterized in that: The preprocessing includes: moving the upper sideband and lower sideband signals to the intermediate frequency by spectrum shifting.

6. The signal generation method used in a direct modulation and direct detection optical fiber communication system according to claim 4, characterized in that: include: The received dual single-sideband optical signal first passes through a set circulator, and then passes through a set semi-transparent and semi-reflective fiber grating filter, which transmits part of the carrier and the right-band optical signal, and reflects the remaining carrier and the left-band optical signal back, and then the right-band optical signal and the left-band optical signal enter the two set photoelectric detectors respectively to realize photoelectric conversion, and digital signal processing is performed after analog-to-digital conversion to restore the data stream.

7. A signal generating system used in a direct modulation and direct detection optical fiber communication system, characterized in that: include: Single sideband modulation unit, digital-to-analog converter, dual polarization IQ modulator, polarizer, among which, The input end of the single sideband modulation unit is used to receive a data stream, and the output end of the single sideband modulation unit is connected to the input end of the digital-to-analog converter, and is used to generate a baseband single sideband signal after bit mapping and preprocessing the data stream; The input end of the dual-polarization IQ modulator is used to connect to the light outlet of the laser, the output end of the dual-polarization IQ modulator is connected to the input end of the polarizer, the I-path and Q-path ports of the IQ modulator in the X polarization state of the dual-polarization IQ modulator are respectively connected to the two output ends of the digital-to-analog converter, and the I-path and Q-path ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator are connected to resistors.

8. A signal generating system used in a direct modulation and direct detection optical fiber communication system, characterized in that: include: Double-sideband modulation unit, digital-to-analog converter, dual-polarization IQ modulator, polarizer, among which, The input end of the double-sideband modulation unit is used to receive a data stream, and the output end of the double-sideband modulation unit is connected to the input end of the digital-to-analog converter, and is used to implement single-sideband modulation at the left and right sidebands at the base frequency respectively; The input end of the dual-polarization IQ modulator is used to connect to the light outlet of the laser, the output end of the dual-polarization IQ modulator is connected to the input end of the polarizer, the I-path and Q-path ports of the IQ modulator in the X polarization state of the dual-polarization IQ modulator are respectively connected to the two output ends of the digital-to-analog converter, and the I-path and Q-path ports of the IQ modulator in the Y polarization state of the dual-polarization IQ modulator are connected to resistors.

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