CN111464240B - Vector radio frequency signal generation system based on polarization multiplexing intensity modulator - Google Patents

Abstract

The invention belongs to the technical field of wireless communication over light, in particular to a vector radio frequency signal generating system based on a polarization multiplexing intensity modulator. The system of the present invention includes a laser, a polarization beam splitter, a first radio frequency signal source, a second radio frequency signal source, a polarization multiplexing intensity modulator, a polarized beam coupler, an optical amplifier, an optical filter, and a photodetector connected in sequence; The invention uses a polarization multiplexing intensity modulator combined with optical filters and photodetectors to realize the generation of vector radio frequency signals; adopts the method of photon synthesis and uses polarization multiplexing to overcome the crosstalk of different frequency optical signals; a modulator RF signals carrying different frequencies are converted into optical signals and then transmitted by optical fibers. Since the polarization directions of the two RF signals are orthogonal, PD does not interfere with any interference, which effectively improves the system performance of optical fiber wireless converged communication. It will be used in ROF systems in the future. The main access network plays a huge advantage.

Description

Vector RF Signal Generation System Based on Polarization Multiplexing Intensity Modulator

technical field

The invention belongs to the technical field of wireless communication over light, and in particular relates to a vector radio frequency signal generation system based on a polarization multiplexing intensity modulator.

Background technique

Radio-over-Fiber (ROF) technology has attracted much attention due to its high effective bandwidth, good mobility, and low transmission loss, and is expected to emerge in the future access network. At the same time, the vector modulation format can transmit more information in a limited bandwidth due to its high spectral efficiency, which can reduce the bandwidth requirements of optoelectronic devices and improve the sensitivity of the receiver, so it has also been widely studied. The combination of vector modulation and optical wireless communication can greatly increase the system transmission capacity while maintaining its excellent performance, and it is bound to become a key technology in the future. However, how to generate stable and low-cost optical vector RF signals is a major challenge at present, and it is also one of the key technologies to promote the commercialization of ROF systems.

In the prior art, in the ROF system, the optical heterodyne method is used to up-convert the data signal to the millimeter wave frequency band, and the double frequency modulation is realized by using the optical suppressed carrier (OCS) modulation, and the Mach-Zehnder (MZ) modulator is added. The carrier is suppressed and modulated after power-on. After modulation, the optical carrier is eliminated, and the remaining two first-order sidebands beat on the photodetector (PD) to generate a signal whose frequency is twice the frequency of the electrical carrier. However, this method of electrical multiplexing is used to synthesize and then modulate an intensity modulator to generate multi-frequency ROF signals. The synthesis of electrical signals is prone to reflections and other crosstalk. Therefore, it is necessary to propose a new vector radio frequency signal generation system with simple structure, simple implementation and superior performance.

The technical problem to be solved by the present invention is to provide a vector radio frequency signal generation system based on a polarization multiplexing intensity modulator for the above-mentioned deficiencies in the prior art. By adopting the method of photon synthesis, polarization multiplexing is used to overcome the crosstalk of optical signals of different frequencies. The design is reasonable, the structure is simple, and the implementation is convenient, and can be effectively applied to generate vector radio frequency signals in ROF communication, has good use effect, and is convenient for popularization and use.

Contents of the invention

The object of the present invention is to provide a vector radio frequency signal generating system based on polarization multiplexing intensity modulator with simple structure and excellent performance.

The vector radio frequency signal generation system based on polarization multiplexing intensity modulator provided by the present invention includes: laser (LD), polarization beam splitter (PBS), first radio frequency signal source, second radio frequency signal source, polarization multiplexing intensity modulation device, polarizing beam coupler (PBC), optical amplifier, optical filter, photodetector (PD); among them:

The laser (LD) is used to generate a continuous wave laser with a specified frequency for optical fiber communication;

The polarization beam splitter (PBS) performs polarization diversity on the optical signal sent by the laser (LD), and obtains the optical signal in the X polarization direction and the Y polarization direction;

The first radio frequency signal source is used to generate a radio frequency signal with frequency f1, and drive the sub-intensity modulator in the polarization multiplexing intensity modulator: X-Pol IM;

The second radio frequency signal source is used to generate a radio frequency signal with frequency f2, and drive the sub-intensity modulator in the polarization multiplexing intensity modulator: Y-Pol IM;

The polarization multiplexing intensity modulator includes two sub-intensity modulators, denoted as X-Pol IM and Y-Pol IM, respectively receiving optical signals in the X polarization direction and Y polarization direction from the polarization beam splitter (PBS); the The modulator has two orthogonal polarization states, and each sub-intensity modulator contains a polarization state, so the output signals of the two sub-intensity modulators are orthogonal, and finally synthesized into one output through the polarization beam coupler PBC;

The polarized beam coupler (PBC) couples two beams of orthogonally polarized light into an optical fiber, and then inputs it into an optical amplifier;

The optical amplifier is used to amplify the optical signal in the optical fiber link, and input the optical signal into the optical filter;

The optical filter is used to filter out the single sideband signal; and input the signal into the photodetector (PD);

The photodetector (PD) realizes the photoelectric conversion of the optical signal, and converts the optical signal into an electrical signal.

In the present invention, X-Pol IM and Y-Pol IM work at the orthogonal point respectively;

In the present invention, the optical amplifier is an erbium-doped optical fiber amplifier;

In the present invention, the optical filter can be a tunable optical fiber filter, a wavelength division multiplexing filter, an optical interleaver, etc.;

The working process of the vector radio frequency signal generating system of the present invention is as follows: the laser outputs a continuous wave optical carrier of a specified frequency, and injects into a polarization multiplexing intensity modulator after performing polarization diversity through a polarization beam splitter PBS. The first and second radio frequency signal sources with frequencies f1 and f2 are respectively used to drive X-Pol IM and Y-Pol IM (both set at the orthogonal point), so that they carry two independent radio frequency signals of different frequencies, and then Through the polarization beam coupler PBC, two beams of orthogonally polarized light are coupled into an optical fiber, and then the optical signal is amplified by the optical amplifier, and then passed through the optical filter in the optical fiber link to filter out the single sideband signal, and finally injected into the In the photodetector PD, the photoelectric conversion of the optical signal is realized, and the vector radio frequency signal is generated.

Wherein, the first radio frequency signal source is: after the local oscillator signal passes through the frequency doubler and the I/Q baseband signal is up-converted in the IQ mixer, after being amplified by the electric amplifier, it is used to drive the X-Pol IM. The second radio frequency signal source is: the local oscillator signal and the I/Q baseband signal are up-converted in the IQ mixer, and after being amplified by the electric amplifier, they are used to drive the Y-Pol IM.

The invention realizes the generation of the vector radio frequency signal by using a polarization multiplexing intensity modulator combined with devices such as an optical filter and a photodetector. By adopting the method of photon synthesis, polarization multiplexing is used to overcome the crosstalk of different frequency optical signals. A modulator carries RF signals of different frequencies into optical signals and then transmits them through optical fibers. Because the polarization directions of the two RF signals are orthogonal, PD does not have any interference. It effectively improves the system performance of optical fiber and wireless converged communication, and will play a huge advantage in the access network based on the ROF system in the future.

Description of drawings

Fig. 1 is a structural diagram of a vector radio frequency signal generation system based on a polarization multiplexing intensity modulator in the present invention.

Fig. 2 is a schematic diagram of the structure of the first radio frequency signal source in the present invention.

Fig. 3 is a schematic diagram of the structure of the second radio frequency signal source in the present invention.

Fig. 4 is a schematic illustration of the system output in the present invention.

Numbers in the figure: 1 is the laser (LD), 21 is the first radio frequency signal source, 22 is the second radio frequency signal source, 3 is the polarization beam splitter (PBS), 4 is the polarization beam coupler (PBC), 5 is the polarization Multiplexing intensity modulator, 61 is the first sub-intensity modulator (X-Pol IM), 62 is the second sub-intensity modulator (Y-Pol IM), 7 is the optical amplifier, 8 is the optical filter, and 9 is the photoelectric Detector (PD); 101 and 102 are local oscillator signals, 11 is a frequency doubler, 121 and 122 are I/Q baseband signals, 131 and 132 are IQ mixers, 141 is an electric amplifier, and 142 is an electric amplifier.

detailed description

Below in conjunction with accompanying drawing, the present invention will be further described.

As shown in Figure 1, the vector radio frequency signal generation system based on polarization multiplexing intensity modulator, each component and function are described as follows:

Laser 1 is used to generate a continuous wave optical carrier with a specified frequency for optical fiber communication. The first radio frequency signal source 21 generates a radio frequency signal with a frequency f1. The second radio frequency signal source 22 generates a radio frequency signal with a frequency f2. The polarization beam splitter 3 (PBS) performs polarization diversity on the optical signal to obtain optical signals in the X polarization direction and the Y polarization direction. Polarizing Beam Coupler 4 (PBC), couples two beams of orthogonally polarized light into one fiber. The polarization multiplexed intensity modulator 5 includes two sub-intensity modulators, namely a first intensity modulator 61 (X-Pol IM) and a second intensity modulator 62 (Y-Pol IM). The modulator has two orthogonal polarization states, and each sub-intensity modulator contains a polarization state, so the output signals of the two sub-intensity modulators are orthogonal, and finally synthesized into one output through the polarization beam coupler 4 (PBC). The optical amplifier 7 is used to amplify the optical signal in the optical fiber link. The optical filter 8 is used to filter out single sideband signals. The photodetector 9 realizes the photoelectric conversion of the optical signal, and converts the optical signal into an electrical signal.

The laser 1 outputs a continuous wave optical carrier of a specified frequency, which is injected into the polarization multiplexed intensity modulator 5 after polarization diversity is performed through the polarization beam splitter 3 (PBS). The first radio frequency signal source 21 with frequency f1 is used to drive the first intensity modulator 61 (X-Pol IM), and the second radio frequency signal source 22 with frequency f2 is used to drive the second intensity modulator 62 (Y-Pol IM ), so that the polarization multiplexing intensity modulator 5 carries two independent radio frequency signals of different frequencies (X-Pol IM and Y-Pol IM are both set at the orthogonal point), and then through the polarization beam coupler 4 (PBC), the two A beam of orthogonally polarized light is coupled into an optical fiber, and then the optical signal is amplified by the optical amplifier 7, and then passed through the optical filter 8 in the optical fiber link to filter out the single sideband signal, and finally injected into the photodetector 9 (PD ), realize the photoelectric conversion of the optical signal, and generate the vector radio frequency signal.

Wherein, the first radio frequency signal source 21 is: after the local oscillator signal passes through the frequency doubler 11 and the I/Q baseband signal 121 realizes up-conversion in the IQ mixer 131, after being amplified by the electric amplifier 141, it is used to drive the X- Pol IM. The second radio frequency signal source 22 is: the local oscillator signal and the I/Q baseband signal 122 are up-converted in the IQ mixer 132 and amplified by the electric amplifier 142 to drive the Y-Pol IM.

The specific connection method in Figure 1 is as follows:

The output end of the laser 1 is connected to the input end of the polarization beam splitter 3 (PBS), the output end of the polarization beam splitter 3 (PBS) is connected to the optical input end of the polarization multiplexing intensity modulator 5, and the polarization multiplexing intensity modulator The optical output end of 5 is connected to the input end of the polarization beam coupler 4 (PBC), the output end of the polarization beam coupler 4 (PBC) is connected to the input end of the optical amplifier 7, and the output end of the optical amplifier 7 is connected to the optical filter 8 The input end of the optical filter 8 is connected with an optical fiber, and the output end of the optical filter 8 is connected with the input end of the photodetector 9 with an optical fiber. The first radio frequency signal source 21 is connected to the electrical input end of the first sub-intensity modulator 61 (X-Pol IM) with a cable, and the first radio frequency signal source 22 is connected to the electrical input terminal of the second sub-intensity modulator 62 (Y-Pol IM). The input is connected with a cable.

Figure 2 The connection method is as follows: All components are connected with cables.

The specific connection method in Figure 3 is as follows: All components are connected with cables.

The generation of vector radio frequency signals is an important part of the optical fiber wireless fusion communication system. The vector radio frequency signal generation system based on the polarization multiplexing intensity modulator adopts the method of photon synthesis and uses polarization multiplexing to overcome the interference of different frequency optical signals. Crosstalk has reasonable design, simple structure, and convenient implementation. It can be effectively applied to generate vector radio frequency signals in ROF communication and improve system performance.

Claims (3)

1. A vector radio frequency signal generating system based on polarization multiplexing intensity modulator, is characterized in that, comprises: laser device, polarization beam splitter, the first radio frequency signal source, the second radio frequency signal source, polarization multiplexing intensity modulator, Polarizing beam couplers, optical amplifiers, optical filters, photodetectors; where: The laser is used to generate a continuous wave laser with a specified frequency for optical fiber communication; The polarization beam splitter performs polarization diversity on the optical signals sent by the laser to obtain optical signals in the X polarization direction and the Y polarization direction; The first radio frequency signal source is used to generate a radio frequency signal with frequency f1, and drive the sub-intensity modulator in the polarization multiplexing intensity modulator: X-Pol IM; The second radio frequency signal source is used to generate a radio frequency signal with frequency f2, and drive the sub-intensity modulator in the polarization multiplexing intensity modulator: Y-Pol IM; The polarization multiplexing intensity modulator includes two sub-intensity modulators, denoted as X-Pol IM and Y-Pol IM, respectively receiving the optical signals in the X polarization direction and the Y polarization direction from the polarization beam splitter; the modulator has Two orthogonal polarization states, each sub-intensity modulator contains a polarization state, so the output signals of the two sub-intensity modulators are orthogonal, and finally synthesized into one output through the polarization beam coupler PBC; The polarized beam coupler couples two beams of orthogonally polarized light into an optical fiber, and then inputs it into an optical amplifier; The optical amplifier is used to amplify the optical signal in the optical fiber link, and input the optical signal into the optical filter; The optical filter is used to filter out the single sideband signal; and input the signal into the photodetector; The photodetector realizes the photoelectric conversion of the optical signal, and converts the optical signal into an electrical signal; The connection relationship of each component is as follows: the output end of the laser is connected to the input end of the polarization beam splitter, the output end of the polarization beam splitter is connected to the optical input end of the polarization multiplexing intensity modulator, and the optical output end of the polarization multiplexing intensity modulator end is connected with the input end of the polarized beam coupler, the output end of the polarized beam coupler is connected with the input end of the optical amplifier, the output end of the optical amplifier is connected with the input end of the optical filter 8 with an optical fiber, and the output end of the optical filter is connected with the input end of the optical filter 8 The input end of the photodetector is connected with an optical fiber; the electrical input end of the first sub-intensity modulator X-Pol IM in the first radio frequency signal source and the polarization multiplexing intensity modulator is connected with a cable, and the first radio frequency signal source is connected with the polarization multiplexing intensity modulator. Connect with the electrical input terminal of the second sub-intensity modulator Y-Pol IM in the intensity modulator with a cable; Wherein, the first radio frequency signal source is: after the local oscillator signal passes through the frequency doubler and the I/Q baseband signal is up-converted in the IQ mixer, after being amplified by the electric amplifier, it is used to drive the X-Pol IM; The second radio frequency signal source is: the local oscillator signal and the I/Q baseband signal are up-converted in the IQ mixer, and after being amplified by the electric amplifier, they are used to drive the Y-Pol IM; The two sub-intensity modulators X-Pol IM and Y-Pol IM in the polarization multiplexing intensity modulator work at orthogonal points respectively; The working process of the system is as follows: the laser outputs a continuous wave optical carrier of a specified frequency, and injects it into the polarization multiplexing intensity modulator after polarization diversity is performed through a polarization beam splitter; the first and second radio frequency signal sources generate radio frequencies of f1 and f2 The signal source respectively drives the two sub-intensity modulators X-Pol IM and Y-Pol IM in the polarization multiplexing intensity modulator, so that they carry two independent radio frequency signals of different frequencies, and then through the polarization beam coupler, the two positive beams The cross-polarized light is coupled into an optical fiber, and then the optical signal is amplified by the optical amplifier, and the single-sideband signal is filtered out through the optical filter in the optical fiber link, and finally injected into the photodetector to realize the photoelectric conversion of the optical signal and generate Vector radio frequency signal. 2. The vector radio frequency signal generation system based on polarization multiplexing intensity modulator according to claim 1, characterized in that, the optical amplifier is an erbium-doped fiber amplifier. 3. The vector radio frequency signal generation system based on polarization multiplexing intensity modulator according to claim 1, wherein the optical filter is a tuned fiber filter, a wavelength division multiplexing filter or an optical interleaver.

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