阅读说明：本技术 一种偏振不敏感的光子辅助毫米波相干接收装置 (Polarization-insensitive photon-assisted millimeter wave coherent receiving device ) 是由 芦启超 陶理 李仁杰 王之立 谭辉 于 2021-06-24 设计创作，主要内容包括：本发明公开了一种偏振不敏感的光子辅助毫米波相干接收装置,光载波中心频率为fc,相位调制器将中心频率为fs毫米波射频信号调制到相位调制器输出的1阶和-1阶边带,利用隔离器和布拉格光纤光栅滤波获取-1阶边带；偏振不敏感零差相干探测单元的一端与布拉格光纤光栅输出端连接,为信号光；偏振不敏感零差相干探测单元的另一端和可调激光器连接,信号光和本振光均经过一个偏振控制装置调整为X偏振态,再对信号进行零差相干探测。本发明方案采用偏振分束、旋转加耦合,解决了传统相干探测方法的缺陷,基于相位调制器的微波光子下变频,进而实现超宽带、高灵敏度毫米波射频信号接收和解调,支撑毫米波无线通信大容量、远距离传输。(The invention discloses a polarization insensitive photon assisted millimeter wave coherent receiving device, wherein the center frequency of an optical carrier is fc, a phase modulator modulates millimeter wave radio frequency signals with the center frequency of fs to 1-order and-1-order sidebands output by the phase modulator, and an isolator and a Bragg fiber grating are utilized for filtering to obtain the-1-order sidebands; one end of the polarization insensitive homodyne coherent detection unit is connected with the output end of the fiber Bragg grating and is signal light; the other end of the polarization insensitive homodyne coherent detection unit is connected with the adjustable laser, the signal light and the local oscillator light are adjusted to be in an X polarization state through a polarization control device, and then homodyne coherent detection is carried out on the signal. The scheme of the invention adopts polarization beam splitting, rotation and coupling, overcomes the defects of the traditional coherent detection method, and realizes the receiving and demodulation of ultra-wideband and high-sensitivity millimeter wave radio frequency signals based on the microwave photon down-conversion of the phase modulator, thereby supporting the large-capacity and long-distance transmission of millimeter wave wireless communication.)

1. A polarization insensitive photon assisted millimeter wave coherent receiving device is characterized by comprising a phase modulator, an isolator, a Bragg fiber grating and a polarization insensitive homodyne coherent detection unit which are sequentially connected, wherein the center frequency of an optical carrier is fc, a millimeter wave radio frequency signal with the center frequency of fs is modulated to 1-order and-1-order sidebands output by the phase modulator by using the phase modulator, and the-1-order sidebands are obtained by filtering by using the isolator and the Bragg fiber grating; one end of the polarization insensitive homodyne coherent detection unit is connected with the output end of the fiber Bragg grating and is signal light fc-fs; the other end of the polarization insensitive homodyne coherent detection unit is connected with the tunable laser, the polarization insensitive homodyne coherent detection unit is local oscillator light, the signal light and the local oscillator light are adjusted to be in the same polarization state through a polarization control device, and then enter a 90-degree Hybird and balance detector to carry out homodyne coherent detection on the fc-fs signal.

2. The polarization insensitive, photon assisted millimeter wave coherent reception device of claim 1, wherein the polarization control device comprises a polarization beam splitter, a polarization rotator, and a polarization maintaining coupler.

3. A polarization insensitive photonic-assisted millimeter wave coherent receiving device according to claim 1 or 2, wherein the 1 st and-1 st sidebands are respectively: fc + fs and fc-fs.

4. A polarization insensitive photon assisted millimeter wave coherent receiving device according to claim 1 or 2, wherein the local oscillator light center frequency is also adjusted to fc-fs.

5. The polarization insensitive photon assisted millimeter wave coherent receiving device according to claim 1 or 2, wherein the signal light is decomposed into two beams with different polarization states having the same polarization state energy after passing through the polarization beam splitter, wherein one beam is adjusted to have an opposite polarization direction by a polarization rotator, and is coupled with the other beam of polarized light output by the polarization beam splitter by a polarization maintaining coupler.

Technical Field

The invention belongs to the technical field of microwave photonics, and particularly relates to a polarization-insensitive photon-assisted millimeter wave coherent receiving device.

Background

In order to realize wireless communication with higher speed and larger bandwidth, communication frequency is evolved to a higher frequency band, and a millimeter wave band is a development direction of future wireless communication due to available spectrum resources of several GHz. The method is restricted by the processing rate of baseband signals and the bottleneck of an analog-digital/digital-analog conversion device, and directly detects millimeter wave radio frequency signals with a logarithmic GHz bandwidth, relates to electric domain frequency mixing and filtering, and has high device cost and great difficulty. Based on the microwave photon down-conversion technology, the millimeter wave radio frequency signal can be directly converted to a baseband by utilizing the coherent detection technology, and the coherent detection has great performance advantage on the detection of the weak light signal, so that the characteristics of large bandwidth, low loss and the like of an optical device can be fully utilized, and the frequency mixing and filtering cost of the high-frequency radio frequency signal can be reduced.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a polarization insensitive photon assisted millimeter wave coherent receiving device, which adopts polarization beam splitting, rotation and coupling to overcome the defects of the traditional coherent detection method, and realizes the receiving and demodulation of ultra-wide band and high sensitivity millimeter wave radio frequency signals based on the microwave photon down-conversion of a phase modulator, thereby supporting the large-capacity and long-distance transmission of millimeter wave wireless communication.

The technical scheme adopted by the invention for solving the technical problems is as follows: the polarization insensitive photon-assisted millimeter wave coherent receiving device comprises a phase modulator, an isolator, a Bragg fiber grating and a polarization insensitive homodyne coherent detection unit which are sequentially connected, wherein the center frequency of an optical carrier is fc, a millimeter wave radio frequency signal with the center frequency of fs is modulated to 1-order sideband and-1-order sideband output by the phase modulator by using the phase modulator, and the-1-order sideband is obtained by filtering by using the isolator and the Bragg fiber grating; one end of the polarization insensitive homodyne coherent detection unit is connected with the output end of the fiber Bragg grating and is signal light fc-fs; the other end of the polarization insensitive homodyne coherent detection unit is connected with the tunable laser, the polarization insensitive homodyne coherent detection unit is local oscillator light, the signal light and the local oscillator light are adjusted to be in the same polarization state through a polarization control device, and then enter a 90-degree Hybird and balance detector to carry out homodyne coherent detection on the fc-fs signal.

According to the technical scheme, the polarization control device comprises a polarization beam splitter, a polarization rotator and a polarization-maintaining coupler.

According to the technical scheme, the 1-order sideband and the-1-order sideband are respectively as follows: fc + fs and fc-fs.

According to the technical scheme, the central frequency of the local oscillator light is also adjusted to fc-fs.

According to the technical scheme, the signal light is decomposed into two beams with the same polarization state energy and different polarization states after passing through the polarization beam splitter, wherein one beam is adjusted to be in the opposite polarization direction through a polarization rotator, and is coupled with the other beam of polarized light output by the polarization beam splitter through a polarization-maintaining coupler. The signal light and the local oscillation light are adjusted to be in an X polarization state through the polarization control device.

The invention has the following beneficial effects: the polarization control device is used for adjusting the polarization states of the signal light carrier and the local oscillator light, so that the sensitivity and the conversion efficiency of the microwave photon down-conversion are improved, down-conversion of any millimeter wave radio frequency signal is realized, and the millimeter wave wireless communication large-capacity and long-distance transmission is supported. The invention can be applied to an ultra-wideband millimeter wave wireless communication system, and solves the problem that optical signals in photon-assisted millimeter wave wireless communication are sensitive to polarization.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is a technical schematic diagram of a polarization insensitive photon assisted millimeter wave coherent receiving device according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a prior art method of reception;

FIG. 3 is a schematic diagram illustrating comparison of amplitude performance of baseband signals obtained by polarization insensitive photon-assisted millimeter wave coherent reception and coherent reception in the prior art;

fig. 4 is a schematic diagram of the output amplitude of the polarization insensitive photon assisted millimeter wave coherent reception for signal light of different polarization states according to the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The photon-assisted millimeter wave coherent receiving device insensitive to polarization comprises a fixed wavelength laser, a phase modulator, an isolator and a Bragg fiber grating which are connected in sequence. The central frequency of the optical carrier is fc, the millimeter wave radio frequency signal with the central frequency of fs is modulated to 1-order and-1-order sidebands, fc + fs and fc-fs output by the phase modulator, and the-1-order sidebands, fc-fs, are obtained by filtering by an isolator and a Bragg fiber grating. The microwave photon down-conversion technology based on the Phase Modulator (PM) has more advantages than the microwave photon down-conversion technology based on the push-pull Mach-Zehnder modulator (MZM), and the PM has larger modulation bandwidth to avoid the analog down-conversion of the received wireless millimeter wave signals on higher carrier frequency, so that the structure of a receiving end is simplified. Meanwhile, the optical signal obtained by the electro-optical conversion has a larger optical signal-to-noise ratio (OSNR), thereby being beneficial to realizing higher-quality signal transmission.

One end of the polarization insensitive homodyne coherent detection unit is connected with the output end of a Bragg fiber grating in a down-conversion structure based on a phase modulator, and is signal light fc-fs; the other end of the polarization insensitive homodyne coherent detection unit is connected with the adjustable laser, and is local oscillation light, and the central frequency of the local oscillation light is also adjusted to fc-fs. The signal light and the local oscillator light are adjusted to be in the same polarization state through a polarization control device composed of a polarization beam splitter, a polarization rotation coupler and a polarization maintaining coupler, and then enter 90-degree Hybird and balance detection to realize homodyne coherent detection of the fc-fs signal and complete demodulation of the millimeter wave radio frequency signal to a baseband signal. The signal light is decomposed into two beams of different polarization states with the same polarization state energy after passing through the polarization beam splitter, wherein one beam is adjusted to be in the opposite polarization direction through a polarization rotator, and is coupled with the other beam of polarized light output by the polarization beam splitter through a polarization-maintaining coupler.

As shown in fig. 1, wherein ECL denotes an external cavity laser, PM denotes an optical phase modulator, ISO denotes an optical isolator, FBG denotes a bragg fiber grating, TL denotes a tunable laser, PBS denotes an optical polarization beam splitter, PBR denotes an optical polarization rotator, and PM-OC denotes a polarization maintaining coupler. The polarization control device is used for adjusting the polarization states of the signal light carrier and the local oscillator light, so that the sensitivity and the conversion efficiency of the microwave photon down-conversion are improved, down-conversion of any millimeter wave radio frequency signal can be realized, and the millimeter wave wireless communication large-capacity and long-distance transmission is supported. The polarization insensitivity in the embodiments of the present invention means: the light source in the system can be in any polarization state, and the polarization state of the light source does not influence the output of the receiving end. Photon-assisted fingers in embodiments of the invention: signals carried by the millimeter wave radio frequency carrier waves are converted to an optical domain firstly, and then are directly converted to a baseband from the optical domain.

Firstly, a continuous light wave fc generated by an External Cavity Laser (ECL) is injected into a light phase modulator PM, the phase modulator modulates a millimeter wave signal fs to generate an upper sideband fc ± fs and a lower sideband fc ± fs, the upper sideband fc ± fs is injected into an optical Isolator (Isolator, ISO), the ISO is connected with a Fiber Bragg Grating (FBG), and then an optical signal output by the Fiber Bragg Grating (FBG) is expressed by formula (1):

E_sig＝E_c{J₁(β_PM)cos[2π(f_c-f_s)t] (1)

where Ec is the output electric field strength of the light source, fc is the optical carrier frequency, fs is the millimeter wave signal center frequency, where AM1 ═ pi (Vs/V pi) (V pi is the half-wave voltage of PM, Vs is the average voltage of the single-tone signal), and is used to characterize the modulation index of the first PM; j1 characterizes a first class of bezier functions with order 1. It can be seen that the output of the first PM is theoretically only a signal-containing polarized light with frequency fc-fs after ISO and FBG filtering.

The output of the FBG port is signal light with a modulation signal, and assuming that the energy of the X and Y Polarization states of the signal are the same, the signal passes through a Polarization Beam Splitter (PBS) and then outputs two beams of polarized light, which is expressed as follows:

E_sig-x＝0.5E_c{J₁(β_PM)cos[2π(f_c-f_s)t] (2)

E_sig-y＝0.5E_c{J₁(β_PM)cos[2π(f_c-f_s)t] (3)

then, the light with the Y Polarization direction is adjusted to the X Polarization direction by a Polarization Beam Rotator (PBR), and is coupled with the X Polarization light output by the PBS by a Polarization maintaining coupler, so as to obtain pure X Polarization signal light. The principle of the local oscillator light is the same as that of the signal light, so that the pure X-polarized local oscillator light can be obtained. The signal light and the certificate can be directly connected to a 90-degree Hybird and a balance detector for homodyne detection, and then the demodulation of the signal can be realized. The baseband signal modulation mode is 8PSK or 16QAM modulation.

In fig. 2, AM denotes an intensity modulator, and TOF denotes a tunable laser. The traditional optical coherent detection method needs to perform primary polarization beam splitting on signal light into two signal lights in X and Y polarization directions, the two signal lights respectively enter 90 degrees Hybird and then are output to a balance detector to obtain baseband signals, and the method respectively utilizes energy of the signal lights in the X and Y polarization directions to further respectively output signals under X polarization and signals under Y polarization. If the polarization directions of the signal light and the local oscillator light are completely vertical, the method has no output, and the signal cannot be detected. In addition, the energy of signal light cannot be completely utilized by the method, and the loss of signal-to-noise ratio can be caused, so that the demodulation thresholds of the millimeter wave signals by the receiver are different, and the ultra-wideband transmission of millimeter waves is not facilitated.

Fig. 3 shows a comparison between the typical case result implemented by the present invention and the performance of the conventional method, and a millimeter wave wireless communication system is built, the millimeter wave radio frequency is 35GHz, the modulation format adopts Quadrature Phase Shift Keying (QPSK), the system baud rate is 5Gbaud, and the receiver detection mode is homodyne coherent detection.

By adopting the technical scheme of polarization-insensitive photon-assisted millimeter wave coherent reception shown in fig. 1 and comparing the performance with the millimeter wave reception scheme adopting the microwave photon down-conversion structure shown in fig. 2, fig. 3 shows the intensity comparison of output signals after down-conversion of two photons, it can be seen that after adopting the polarization-insensitive photon-assisted millimeter wave coherent reception technology provided by the invention, the output response of the signals is obviously enhanced, the overall insertion loss of the system is small, and fig. 4 shows the output intensity performance of the system to signals in different polarization states, it can be seen that the system can keep stable output to input in different polarization states.

It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.