CN111342906A - MZM-based optical communication receiver optical power stabilizing system - Google Patents
MZM-based optical communication receiver optical power stabilizing system Download PDFInfo
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- CN111342906A CN111342906A CN202010200918.6A CN202010200918A CN111342906A CN 111342906 A CN111342906 A CN 111342906A CN 202010200918 A CN202010200918 A CN 202010200918A CN 111342906 A CN111342906 A CN 111342906A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/66—Non-coherent receivers, e.g. using direct detection
- H04B10/67—Optical arrangements in the receiver
- H04B10/671—Optical arrangements in the receiver for controlling the input optical signal
- H04B10/672—Optical arrangements in the receiver for controlling the input optical signal for controlling the power of the input optical signal
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/66—Non-coherent receivers, e.g. using direct detection
- H04B10/67—Optical arrangements in the receiver
- H04B10/671—Optical arrangements in the receiver for controlling the input optical signal
- H04B10/672—Optical arrangements in the receiver for controlling the input optical signal for controlling the power of the input optical signal
- H04B10/674—Optical arrangements in the receiver for controlling the input optical signal for controlling the power of the input optical signal using a variable optical attenuator
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- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optical Communication System (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
The invention discloses an optical power stabilizing system of an optical communication receiver, which sends a receiving signal into a MZM and realizes the stabilization of the output optical power of the MZM by feedback control of a modulation signal of the MZM, and the specific process is as follows: an optical antenna is used for receiving an optical signal from a transmitting end and sending the optical signal into an MZM, at the output end of the MZM, a beam splitter is used for splitting 10% of the optical signal to serve as a feedback control signal, the optical signal is converted into an electric signal through a photoelectric detector, the electric signal is sent into a data processing unit after AD sampling, harmonic extraction is carried out, and MZM bias point control is achieved; when the MZM power amplifier starts to work, the VOA is used for carrying out primary adjustment on signals, and then the feedback control module is used for controlling the magnitude of modulation signals in real time to ensure that the MZM output power is stable. The power control method of the optical communication receiver has simple structure, easy integration and better practicability.
Description
Technical Field
The invention relates to the field of optical communication, in particular to an optical power stabilizing method of an optical communication receiver based on MZM.
Background
The space optical communication technology is a high-speed communication technology taking a space atmosphere channel as a transmission medium, and plays an important role in the fields of future space exploration, satellite networking and the like. However, different from the optical fiber communication technology, spatial optical communication is seriously affected by atmospheric turbulence, so that the power of an optical signal received by a receiving end is randomly jittered, and a signal processing module at the receiving end is difficult to realize correct demodulation of data. In order to ensure that the optical communication receiver can work normally, the intensity of the received signal needs to be controlled in real time so as to be stabilized within a certain range. According to the experimental result of the previous period, the optical power change of the receiving end introduced by the atmospheric turbulence is generally in the magnitude of several dB, and the jitter frequency can reach dozens of Hz, so that the optical power stabilizing module is required to have stronger modulation capability and faster regulation rate. A Mach-Zehnder modulator (MZM) based on a lithium niobate material is a commonly used modulation device for an optical communication system, can realize high-speed modulation of optical signals, and provides an optical power stabilizing method based on the MZM.
Most of the conventional laser signal power control technologies control the output signal power of a laser at a transmitting end to ensure the stability of the output power of the laser. As proposed by researchers at the institute of Chinese academy of technology, the intensity of the output signal of the laser is adjusted by using the photoelectric modulator, so that the final output power of the laser is stabilized. Researchers at the university of compound denier propose a method for stabilizing the output power of a laser by combining a polarizing device with a liquid crystal spatial light modulator, and related personnel improve the method in the later period, but the method has not strong adjusting capability on the light power.
Researchers of the university of vinpochology have intensively developed a technology for stabilizing the received optical power of optical communication based on a liquid crystal spatial light modulator, in which a polarizer is used to convert a received signal into linearly polarized light, then a liquid crystal device is used to control the rotation angle of the linearly polarized light, and finally an analyzer is used to filter light, thereby realizing the control of the output power. The method generally requires that the change of the optical power is within 30 percent, the regulation rate of the liquid crystal device is not high, and the method is not beneficial to system integration due to the fact that the liquid crystal device is a spatial light modulation device. Researchers have also proposed a method for controlling the received optical power by using a polarizer in combination with an optical rotator, which also uses the birefringence of an optical crystal to change the polarization state of a light beam passing through the crystal, and thus change the intensity of an optical signal passing through an analyzer, in the same principle as the liquid crystal modulation method.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a system that has a simple structure and is easy to integrate, and can realize real-time control of the receiving optical power of an optical communication receiver, and only one MZM and its feedback control module are needed to realize real-time control of the receiving optical power.
The technical scheme adopted by the invention is as follows:
an optical power stabilizing system of an optical communication receiver based on MZM comprises an optical antenna, a single-mode fiber, a Mach-Zehnder modulator MZM, a variable optical attenuator VOA, an optical splitter, a photoelectric converter, an AD and a signal processing and feedback controller;
the optical antenna is used for receiving the optical signal and coupling the received optical signal into the single-mode optical fiber positioned at the focal point of the optical antenna;
the single-mode fiber is used for sending the received optical signal to the input end of the Mach-Zehnder modulator (MZM);
the Mach-Zehnder modulator MZM is used for modulating the optical signal, and the modulated optical signal is output to the optical splitter; the system can automatically assign values to the modulation signal and the bias voltage during initial work, and after stable work, under the control of the signal processing and feedback controller, the MZM works at an orthogonal bias point and keeps the output optical power stable;
the variable optical attenuator VOA is used for manually adjusting the optical power;
the optical splitter is used for separating a part of the modulated optical signals, performing photoelectric conversion on the part of the modulated optical signals through the photoelectric converter, outputting the part of the modulated optical signals to the signal processing and feedback controller after AD sampling, and sending the other part of the separated optical signals to the optical power meter;
the signal processing and feedback controller is used for generating a perturbation signal, obtaining the optical power variation and the harmonic component of the perturbation signal according to the data obtained by AD sampling, and controlling the modulation signal and the bias voltage of the Mach-Zehnder modulator MZM to stabilize the output power of the Mach-Zehnder modulator MZM;
the optical power meter is used for measuring the power of an output optical signal of the Mach-Zehnder modulator MZM.
The variable optical attenuator VOA can be arranged between the receiving antenna and the Mach-Zehnder modulator MZM, or between the Mach-Zehnder modulator MZM and the optical splitter, or between the optical splitter and the optical power meter; for primarily adjusting the power of the output optical signal.
The initial value of the modulation signal of the Mach-Zehnder modulator MZM during initial operation is greater than one fourth of the half-wave voltage of the MZM.
The selection of the mach-zehnder modulator MZM is recommended to set the magnitude of the modulation signal to be one-half of the half-wave voltage of the MZM during initial operation.
Compared with the prior art, the invention has the following advantages:
the stable receiving optical power of the optical communication receiver is realized by using the MZM, the advantage of high response speed of the MZM is fully exerted, and the real-time control of the receiving optical power can be realized; compared with the technology of adjusting the optical power based on a polarization device, the MZM has the advantages of large adjustment range of the received optical power and high adjustment precision; compared with a method for realizing optical power control by using a spatial light modulator, the method provided by the invention realizes the adjustment and control of the optical power in the optical fiber and the MZM, and is convenient to realize and easy to integrate.
Drawings
Fig. 1 is a schematic block diagram of the present invention.
FIG. 2 is a schematic diagram of the MZM structure employed in the present invention.
FIG. 3 is a schematic of the MZM transfer function sampled in accordance with the present invention.
Detailed Description
The following describes the implementation process of the present invention in detail with reference to the accompanying drawings and embodiments.
The schematic diagram is shown in fig. 1, and mainly includes the following modules:
the optical antenna receives the space signal light, finishes signal collection and couples the signal into the single-mode optical fiber positioned at the focal point of the optical antenna;
the single-mode optical fiber is used for transmitting the signal received by the antenna into the MZM;
MZM, made up of two-way optical waveguide, realize the signal modulation by changing the phase difference of two-way;
the optical splitter divides the optical signal output by the MZM into two paths of signals with the proportion of 10% and 90%;
the photoelectric converter is used for converting the optical signal obtained by the optical splitter into an electric signal;
AD, performing discrete sampling on the obtained electric signal;
the VOA is used for manually adjusting the optical power attenuation amount;
and the signal processing and feedback control unit generates a perturbation signal, obtains the optical power variation and the harmonic component of the perturbation signal according to the data obtained by AD sampling, and further controls the modulation signal and the bias voltage signal of the MZM to stabilize the output power of the MZM.
The following describes a detailed implementation procedure of the present invention by taking a space optical communication receiver as an example.
As shown in fig. 1, the optical signal collected by the receiving antenna enters the MZM through a single mode fiber. The input end of the MZM can be regarded as a 3dB optical splitter, which splits the input optical signal into two identical paths (assuming that the device is ideal), wherein one path is modulated by the modulation signal and then combined with the other path at the output end of the MZM. The final output optical power of the MZM is:
where η denotes the insertion loss, P, of the MZMiFor input optical power, Δ φ1And delta phi2The phase shift introduced by the optical signal passing through the upper arm and the lower arm of the MZM is respectively
Δφ2＝φw(3)
Wherein, VmFor the modulation signal added to the upper arm of the MZM, VdcFor the DC bias signal applied to the upper arm of the MZM, VπIs the half-wave voltage of MZMwFor MZM upper and lower arm pair transmissionThe inherent phase shift introduced by the optical signal. For the convenience of analysis, it is assumed above that the intrinsic phase shifts introduced by the upper and lower arms of the MZM are the same and are both phiw。
It can be seen from fig. 3 that when the operating point of the MZM is at the quadrature bias points, i.e., Q-and Q + bias points, the output signal power of the MZM is most sensitive to changes in the modulation signal and the linearity is the best, so Q-or Q + should be selected as the bias point of the MZM. In order to accurately control the bias point of the MZM, a perturbation signal bias point control method may be used. The specific implementation mode is as follows: a sinusoidal perturbation signal Asin (ω t) is added to the bias signal of the MZM, where A is the amplitude of the perturbation signal and ω is the angular frequency of the perturbation signal. The amplitude and frequency of the perturbation signal are typically small in order not to affect the normal operation of the modulator.
After adding the perturbation signal, the output optical power of MZM is
The right side of equation (4) is expanded, and the term containing Asin (ω t) in equation (4) can be subjected to taylor series expansion at point 0, considering that the phase shift introduced by the perturbation signal to the incident light is small. The formula (4) can be simplified into
The first row in equation (5) is a constant term, the second row is a first-order term of the perturbation signal, and the third row is a second-order term of the perturbation signal.
As can be seen from equation (5), when the MZM is operated at a quadrature bias point, i.e.
The item is
The amplitude of the first order of the perturbation signal reaches the maximum and the amplitude of the second order of the perturbation signal reaches the maximumAnd the sign of the primary term of the perturbation signal can be used to judge whether the MZM works at the Q-bias point or the Q + bias point.
The above process can be considered as an MZM bias point control process, where the modulation signal is set to one-half of the half-wave voltage of the MZM and remains unchanged. And after the working point of the MZM is stable, observing whether the signal intensity output by the MZM meets the requirement of an optical receiver on the intensity of the received signal through an optical power meter, and if not, adjusting the intensity of the received signal by using the VOA until the power of the output signal of the MZM is close to a target value. When the power of the received signal is jittered due to the disturbance of the atmospheric channel, the stability of the output optical power of the MZM is ensured by adjusting the magnitude of the modulation signal in real time through the signal processing and feedback control module.
More specifically, if the MZM is operated at the Q-bias point, the output optical power of the MZM is reduced by increasing the modulation signal voltage when the output of the photodetector is greater than the reference value; and when the output of the photoelectric detector is smaller than the reference value, the output optical power of the MZM is increased by reducing the voltage of the modulation signal. If the MZM works at the Q + bias point, when the output of the photoelectric detector is larger than the reference value, the output optical power of the MZM is reduced by reducing the voltage of the modulation signal; and when the output of the photoelectric detector is smaller than the reference value, the output optical power of the MZM is increased by increasing the voltage of the modulation signal. The above-mentioned adjustment process can be realized only by a simple comparison circuit, and certainly, the working efficiency of the signal processing and feedback control module can also be improved by adopting a random parallel gradient descent (SPGD) algorithm.
In the above technical solution, when the bias point of the MZM is controlled, the magnitude of the modulation signal is always kept unchanged;
in the above technical solution, it is recommended that the initial value of the modulation signal is selected to be one half of the half-wave voltage of the MZM, and theoretically, the initial value of the modulation signal may be any value larger than the one-quarter half-wave voltage of the MZM.
In the above technical solution, the VOA may be placed between the receiving antenna and the MZM, between the MZM and the optical splitter, or between the optical splitter and the optical power meter.
In the above technical solution, the detection of the harmonic component of the perturbation signal can be implemented by using a filter.
According to the optical signal power control method, the accurate control of the optical receiver signal power can be realized by using simpler devices and algorithms.
The above description is only a preferred implementation of the present invention, but the scope of the present invention is not limited thereto. Any modifications or substitutions that can be easily made by those skilled in the art within the technical scope of the present disclosure should be covered within the scope of the present disclosure.
Claims (4)
1. An optical power stabilizing system of an optical communication receiver based on MZM is characterized by comprising an optical antenna, a single-mode fiber, a Mach-Zehnder modulator (MZM), an optical splitter, a photoelectric converter, an AD and a signal processing and feedback controller;
the optical antenna is used for receiving the optical signal and coupling the received optical signal into the single-mode optical fiber positioned at the focal point of the optical antenna;
the single-mode fiber is used for sending the received optical signal to the input end of the Mach-Zehnder modulator (MZM);
the Mach-Zehnder modulator MZM is used for modulating the optical signal, and the modulated optical signal is output to the optical splitter; the Mach-Zehnder modulator MZM automatically assigns values to modulation signals and bias voltage during initial work, and enables the Mach-Zehnder modulator MZM to work at an orthogonal bias point and keep output optical power stable under the control of a signal processing and feedback controller after stable work;
the optical splitter is used for separating a part of the modulated optical signals, performing photoelectric conversion on the part of the modulated optical signals through the photoelectric converter, performing AD sampling on the part of the modulated optical signals, outputting the part of the modulated optical signals to the signal processing and feedback controller, and outputting the other part of the modulated optical signals to the optical power meter;
the signal processing and feedback controller is used for generating a perturbation signal, obtaining optical power variation and harmonic component of the perturbation signal according to data obtained by AD sampling, and controlling a modulation signal and bias voltage of the Mach-Zehnder modulator MZM to enable the Mach-Zehnder modulator MZM to work at an orthogonal bias point and keep output power stable;
the optical power meter is used for measuring the power of an output optical signal of the Mach-Zehnder modulator MZM.
2. The MZM-based optical communication receiver optical power stabilization system of claim 1, further comprising a variable optical attenuator; the variable optical attenuator is arranged between the receiving antenna and the Mach-Zehnder modulator MZM, or between the Mach-Zehnder modulator MZM and the optical splitter, or between the optical splitter and the optical power meter; for adjusting the power of the output optical signal.
3. The MZM-based optical communication receiver optical power stabilization system of claim 1, wherein an initial value of the modulation signal of the mach-zehnder modulator (MZM) is set to be greater than one-quarter of a half-wave voltage of the MZM at an initial operation.
4. The MZM-based optical communication receiver optical power stabilization system of claim 3, wherein the initial value of the modulation signal of the Mach-Zehnder modulator (MZM) during initial operation is set to one-half the MZM half-wave voltage.
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| CN115208469A (en) * | 2022-09-09 | 2022-10-18 | 长春理工大学 | Optical power stable receiving method and device based on reciprocity of atmospheric channels |
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