WO2020151192A1

WO2020151192A1 - Coherent signal receiving method and device, coherent signal transmitting method and device, and coherent passive optical network system

Info

Publication number: WO2020151192A1
Application number: PCT/CN2019/094118
Authority: WO
Inventors: 胡荣
Original assignee: 烽火通信科技股份有限公司
Priority date: 2019-01-22
Filing date: 2019-07-01
Publication date: 2020-07-30
Also published as: CN109818682A; CN109818682B

Abstract

A coherent signal receiving method and device, a coherent signal transmitting method and device, and a coherent passive optical network system, relating to the field of passive optical networks. The system comprises a coherent signal transmitting device and a coherent signal receiving device. The coherent signal transmitting device divides an optical signal of a wide-linewidth light source device into two signals having the same light intensity; each signal serves as an optical carrier of an optical intensity modulator which is driven by means of an electric driving signal to modulate an optical signal; and the two modulated optical signals are sent to an optical distribution network after being polarized and combined. The coherent signal receiving device divides both a local oscillator light and the received optical signal into mutually perpendicular X-polarized light and Y-polarized light, and the optical field intensities of the X-polarized light and Y-polarized light divided from the local oscillator light are equal; two beams of X-polarized light are mixed, and two beams of Y-polarized light are mixed; optical signals output after mixing are each detected by a single-ended photodetector, and are subjected to transimpedance amplification and DC blocking and then to signal recovery by means of envelope detection. By means of the present invention, the overall cost of coherent light detection can be reduced.

Description

Coherent signal transceiving method, device and coherent passive optical network system

Technical field

The invention relates to the field of passive optical networks, in particular to a coherent signal transceiver method, device and coherent passive optical network system.

Background technique

In the field of long-distance optical transmission, coherent optical detection has gradually replaced direct detection and has become the mainstream optical transport network technology. Figure 1 shows a schematic block diagram of a 100Gb/sDP-QPSK (Dual-Polarization Quadrature Phase-Shit Keying, dual-polarization quadrature phase shift keying) modulated coherent optical transceiver system, including: narrow-line width ECL (External Cavity) with adjustable wavelength Laser, external cavity laser), 50:50Splitter (50:50 splitter), Driver (signal driver), DP-IQ-Modulator (Dual-PolarizationIQ-Modulator, dual-polarization IQ modulator), ICR (Integrated Coherent Receiver, integrated Coherent receiver), and digital transceiver ASIC (Application Specific Integrated Circuit, application specific integrated circuit) chip. The narrow linewidth ECL with adjustable wavelength can be used as an optical signal carrier and a local oscillator for coherent detection (generating a local oscillator light source) at the same time. DP-IQ-Modulator is used to generate and send DP-QPSK signals, and ICR is used to receive DP-QPSK signals And for detection, the digital transceiver ASIC chip is used for digital signal transmission and digital signal recovery.

Figure 2 shows the block diagram of the DP-IQ-Modulator, which includes: four double-arm Mach-Zehnder modulators (Mach-Zehnder modulator), two 90°shift (90-degree phase shifters) And a PBC (Polarization Beam Combiner, polarization beam combiner). The optical carrier CW (Continuous Wave, continuous light source) in Figure 2 generally corresponds to one of the signals of the ECL after the Splitter in the coherent light detection system, and the other signal of the ECL after the Splitter is used as the local oscillator light source for the coherent detection. In Figure 2, Output represents the output polarization multiplexed amplitude/phase modulated optical signal.

The single-channel 100-Gb/s DP-QPSK solution based on coherent optical detection has extensive industry chain support. However, in the field of optical access technology, coherent optical detection has not been recognized by the industry, mainly due to higher cost, size and power consumption. Specifically, the shortcomings of coherent light detection are reflected in the following aspects:

1) A narrow linewidth light source must be used, the wavelength of the light source fluctuates within +/-0.01nm, and the control accuracy is high, which increases the cost.

2) The complexity of ICR is relatively high, as shown in Figure 3, which includes two PBS (Polarization Beam Splitters), two 90-degree Optical Hybrids (optical mixers) with four output optical ports, four One BPD (Balanced Photo Detector, balanced detector), and four TIA (Trans-Impedance Amplifier, transimpedance amplifier). The local oscillator light source in Fig. 3 usually corresponds to one of the signals of the ECL after 50:50 Splitter in the coherent light detection system, and the other signal of the ECL after 50:50 Splitter is used as the optical carrier for transmission.

3) At the receiving end, digital signal processing needs to include frequency offset/phase estimation and compensation, and the frequency offset estimation value needs to be fed back to a VCO (Voltage-Controlled Oscillator) to control the frequency value of the local oscillator light source.

To sum up, the overall cost of the existing coherent light detection scheme is relatively high, and it is not suitable for widespread use.

Summary of the invention

In view of at least one defect in the prior art, the purpose of the present invention is to provide a coherent signal transceiving method, device, and coherent passive optical network system to reduce the overall cost of coherent optical detection.

To achieve the above objectives, on the one hand, a coherent signal transmission method is adopted, which includes the steps of: dividing the optical signal of the wide-linewidth light source device into two paths with the same light intensity, and each path is used as an optical carrier of an optical intensity modulator, and The light intensity modulator is driven by an electric drive signal to perform optical signal modulation, and the two modulated optical signals are polarized and combined and then sent out.

Preferably, the wide linewidth light source device is a distributed feedback laser.

Based on the above transmission method, a coherent signal receiving method is adopted, which includes the steps of: dividing both the local oscillator light and the received optical signal into mutually perpendicular X-polarized light and Y-polarized light, and the local oscillator light is divided into X-polarized light and Y-polarized light The optical field intensity of the light is equal; the two beams of X-polarized light are mixed, and the two beams of Y-polarized light are mixed, and the four optical signals output after mixing are each detected by a single-ended photodetector, amplified and blocked by transimpedance After that, the signal is recovered through envelope detection.

Preferably, the local oscillator light is generated by a distributed feedback laser.

On the other hand, a coherent signal sending device is adopted, including:

Wide linewidth laser source device, used to send continuous light signal;

An optical splitter, used to divide the optical signal into two optical carriers with the same optical intensity;

Two signal drivers, respectively used to amplify one electrical signal to form an electrical drive signal;

Two optical intensity modulators, each optical intensity modulator is used to receive an optical carrier, and modulate the optical signal through an electric drive signal;

The polarization beam combiner is used to combine the optical signals modulated by the two optical intensity modulators to obtain a polarization multiplexed optical intensity modulation signal.

Preferably, the two light intensity modulators are both Mach-Zehnder modulators, the outputs of the two signal drivers are each connected to the radio frequency input port of a Mach-Zehnder modulator, and the working bias voltage of the Mach-Zehnder modulator is set In the linear modulation area.

Preferably, the two light intensity modulators are both electro-absorption modulators, and the working bias voltage of the electro-absorption modulator is set in the linear modulation area, and the outputs of the two signal drivers are each connected to the radio frequency input of the electro-absorption modulator port.

Preferably, the optical splitter is a 50:50 optical power splitter, and the wide linewidth light source device is a distributed feedback laser.

Based on the foregoing sending device, a coherent signal receiving device is provided, including:

Wide linewidth light source device, used to provide local oscillator light;

Two 90-degree optical mixers, each 90-degree optical mixer includes two input ports and two output ports;

Two polarization beam splitters, a first polarization beam splitter and a second polarization beam splitter, the first polarization beam splitter is used to divide the received optical signal into mutually perpendicular X-polarized light and Y-polarized light, and Input the first input ports of two 90-degree optical mixers respectively; the second polarization beam splitter is used to divide the local oscillator light into X-polarized light and Y-polarized light that are perpendicular to each other and the optical field intensity is equal, and input two respectively The second input port of the 90-degree optical mixer;

Four single-ended photodetectors, respectively used to receive one optical signal output by the 90-degree optical mixer;

Four transimpedance amplifiers, respectively corresponding to the output of a single-ended photodetector;

Four DC blockers, respectively corresponding to the optical signal of a transimpedance amplifier, and used to block DC;

Four analog-to-digital converters, which convert the analog signal output by the DC block into digital signals;

Envelope detection module, which is used to receive all digital signals for signal recovery.

Preferably, the four analog-to-digital converters and the envelope detection module are integrated, and the wide linewidth light source device is a distributed feedback laser.

On the other hand, a coherent passive optical network system is provided, including:

Coherent signal sending device, which is used to divide the optical signal of the wide linewidth light source device into two paths with the same light intensity, each path is used as an optical carrier of a light intensity modulator, and the light intensity modulator is driven by an electric drive signal Carry out optical signal modulation, the two modulated optical signals are combined by polarization and sent to the optical distribution network;

Coherent signal receiving device, which is used to divide the local oscillator light and the received optical signal into mutually perpendicular X-polarized light and Y-polarized light, and the optical field intensity of the X-polarized light and Y-polarized light divided into the local oscillator light are equal; Two beams of X-polarized light are mixed, and two beams of Y-polarized light are mixed. The four optical signals output after mixing are each detected by a single-ended photodetector. After transimpedance amplification and blocking, the signal is detected by envelope restore.

Preferably, the coherent passive optical network system includes an optical line terminal and a plurality of optical network units;

At least one coherent signal sending device is provided in the optical line terminal, and one coherent signal receiving device is provided in the optical network unit;

Alternatively, the optical network unit is provided with one coherent signal sending device, and the optical line terminal is provided with at least one coherent signal receiving device.

The optical line terminal includes at least one single-channel signal transceiver module, and each optical network unit includes a single-channel signal transceiver module;

Each single-channel signal transceiver module includes a combiner/demultiplexer plate, a coherent signal transmitting device and a coherent signal receiving device;

The output of the coherent signal sending device and the input of the coherent signal receiving device are respectively connected to two demultiplexing ports of a multiplexer and demultiplexer plate, and the multiplexer ports of the multiplexer and demultiplexer plate are connected to an optical distribution network.

Preferably, when the optical line terminal includes more than one single-channel signal transceiving module, the multiplexing port of each multiplexing/demultiplexing plate is connected to the demultiplexing port of a wavelength division multiplexing device. The multiplexer port is connected to the optical distribution network.

Preferably, the coherent signal sending device includes:

Wide linewidth laser source device, used to send continuous light signal;

Preferably, the coherent signal receiving device includes:

Wide linewidth light source device, used to provide local oscillator light;

One of the above technical solutions has the following beneficial effects:

(1) For traditional narrow linewidth lasers, the fluctuation range of the light source wavelength is within +/-0.01nm. In the embodiment of the present invention, a wide linewidth light source device is used to generate the local oscillator light source and the signal carrier light source, and the fluctuation range of the light source wavelength can be relaxed to +/-0.1 nm, which can further reduce the cost of the light source.

(2) In terms of coherent signal transmission, polarization multiplexed light intensity modulators are used for modulation, which is far less difficult to design and manufacture than amplitude/phase modulators, which further effectively reduces the device cost of the transmission device.

(3) In terms of coherent signal reception, single-ended photodetectors are used for reception. Compared with the balanced detection scheme, the design complexity of ICR and photodetectors is simplified. Envelope detection is used to recover the received polarization multiplexed intensity modulation signal. Effectively reduce the cost of receiving devices.

Description of the drawings

Figure 1 is a schematic diagram of a 100Gbps DP-QPSK coherent optical detection system;

Figure 2 is a block diagram of the DP-IQ-Modulator in Figure 1;

Figure 3 is a schematic diagram of the structure of the ICR in Figure 1;

4 is a schematic diagram of a coherent signal sending device according to an embodiment of the present invention;

5 is a schematic diagram of a coherent signal receiving device according to an embodiment of the present invention;

Figure 6 is an implementation framework diagram of a secondary digital equalization algorithm according to an embodiment of the present invention;

7 is a schematic diagram of a coherent passive optical network system according to an embodiment of the present invention;

8 is a schematic diagram of a coherent passive optical network system according to another embodiment of the present invention;

Figure 9 is a schematic diagram of a coherent passive optical network system according to another embodiment of the present invention

10 is a schematic diagram of OLT and ODN in a coherent passive optical network system according to an embodiment of the present invention;

FIG. 11 is a schematic diagram of an OLT and an ODN in a coherent passive optical network system according to another embodiment of the present invention.

detailed description

The present invention will be further described in detail below in conjunction with the drawings and embodiments.

The present invention provides an embodiment of a coherent signal transmission method, including the steps of: generating a continuous optical signal through a wide linewidth light source device, and dividing it into two optical signals with the same light intensity, and each optical signal is used as the light of an optical modulator. Carrier, and the light intensity modulator is driven by the electric drive signal to modulate the optical signal, and the two modulated optical signals are combined to generate a polarization multiplexed intensity modulated optical signal to be sent. The wide-linewidth light source device may be a wide-linewidth laser, such as DFB (Distributed Feedback Laser, distributed feedback laser).

Preferably, the generated linewidth is greater than 10MHz, the fluctuation range of the light source wavelength is relaxed to +/-0.1nm, the linewidth of a general narrow linewidth laser is in the range of 10-100KHz, and the wavelength fluctuation range is within +/-0.01nm.

Based on the above sending method, the present invention provides an embodiment of a coherent signal receiving method, which includes the steps of: generating local oscillator light through a wide linewidth light source device, and dividing the received optical signal into two polarized light beams that are perpendicular to each other. , That is, X-polarized light and Y-polarized light, and the intensity of the X-polarized light and Y-polarized light of the local oscillator is equal. Then mix the two beams of X-polarized light and the two beams of Y-polarized light. The four optical signals output after mixing are each detected by a single-ended photodetector. The detected optical signals are amplified and blocked by transimpedance. , To recover the received signal through envelope detection.

As shown in FIG. 4, an embodiment of a coherent signal sending device is provided. The coherent signal sending device includes a wide-linewidth light source device, an optical splitter, two signal drivers (Driver), and two intensity modulators (IM). ) And a PBC (Polarization Beam Combiner, polarization beam combiner). Among them, the wide-linewidth light source device is used to send continuous optical signals, and a wide-linewidth laser, such as DFB, can be used. The splitter can use a 50:50 optical power splitter (50:50 Splitter) to divide the optical signal into two paths with the same light intensity, and each path is used as an optical carrier of an optical booster. The two signal drivers are respectively used to amplify one electric signal to form an electric drive signal, which is used to drive the optical enhancement damper. Each optical intensity modulator is used to receive an optical carrier, and modulate the optical signal through an electric drive signal. The two modulated optical signals are combined to obtain the polarization multiplexed optical intensity signal and sent out.

Preferably, the two optical intensity modulators both adopt Mach-Zehnder modulators, and the optical splitter is a 50:50 optical power divider. The specific implementation includes: using DFB as a continuous light source, the line width is usually greater than 10MHz; first, through a 50:50 optical power splitter, two optical carriers with the same intensity are generated; two optical carriers are input into two Mach-Zehnder modulators, Carry out light intensity modulation; the two optical intensity modulation signals from the Mach-Zehnder modulator are then multiplexed by PBC to generate polarization multiplexed light intensity modulation signals. At the circuit end, the two electrical signals are amplified by the signal driver, and then connected to the RF input port of the Mach-Zehnder modulator, and the working bias voltage of the Mach-Zehnder modulator is set in the linear modulation area to generate intensity modulated light signal.

Preferably, the two optical intensity modulators both adopt EAM (Electro Absorption Modulator), and the optical splitter may still be a 50:50 optical power divider. The specific implementation includes: DFB is used as a continuous light source, and its line width is usually greater than 10MHz; first, through a 50:50 optical power divider, two optical carriers with the same intensity are generated; two optical carriers are input two EAMs for optical intensity modulation, modulation The two output light intensity modulation signals are then combined by a polarization beam combiner to generate polarization multiplexed light intensity modulation signals. At the circuit end, the two electrical signals are respectively amplified by the signal driver, and then connected to the radio frequency input port of the electro-absorption modulator, and the working bias voltage of the electro-absorption modulator is set in the linear modulation area.

As shown in FIG. 5, an embodiment of a coherent signal receiving device is provided, which specifically includes a wide linewidth light source device, two 90-degree optical mixers, two PBS (Polarization Beam Splitters, polarization beam splitters), and four Single-ended photodetector (PD, Photo Detector), four transimpedance amplifiers (TIA), four DC blockers (DC Blocker), four analog-to-digital converters (Analog-to-Digital Converter, ADC) and a package Network detection module.

Specifically, the wide-linewidth light source device is used to provide wide-linewidth local oscillator light, and a wide-linewidth laser, such as DFB, can be used. The two PBSs are the first PBS and the second PBS, and each 90-degree optical mixer It has two input ports and two output ports.

The first PBS is used to receive the optical signal and divide it into two mutually perpendicular polarized lights, namely X-polarized light and Y-polarized light, which are respectively input into the first input port 1 of the two 90-degree optical mixers. The two second PBSs are used to divide the local oscillator light into two polarized light beams that are perpendicular to each other and have the same optical field intensity, and are respectively input into the second input ports 2 of the two 90-degree optical mixers. The four optical signals output by the two 90-degree optical mixers are respectively received by a single-ended photodetector, and then all amplified by a TIA, and then blocked by a DC block, and then passed through four analog-to-digital conversions After the converter is converted into a digital signal, it is input to the envelope detection module for signal recovery.

Preferably, the envelope detection module can be implemented by logic chips such as DSP or ASIC, and the four ADCs can be set separately or integrated on the envelope detection module.

In this embodiment, the optical signal received by the coherent signal receiving device comes from the coherent signal sending device. The principle of signal recovery will be described in detail below with reference to FIG. 5.

The two 90-degree optical mixers are divided into a first optical mixer and a second optical mixer, and the output light field of the first optical mixer is expressed as:

In the above formula, t represents time, E _s1 is the component of the optical signal at the input port 1 of the first optical mixer, E _{L1 is} the component of the local oscillator light at the input port 2 of the first optical mixer, E _s1 (t) =A _s1 (t) exp(j2πω _s ·t), E _L1 (t)=A _L1 exp(j2πω _L ·t). A _s1 (t) is the signal component amplitude of the optical signal at the first input port 1 of the first optical mixer, and A _{L1 is} the signal component amplitude of the local oscillator light at the second input port 2 of the first optical mixer, ω _s and ω _L are the angular frequencies of the optical signal and the local oscillator light, respectively.

Similarly, the output light field of the second optical mixer is expressed as:

In the above formula, E _s2 is the component of the optical signal at the first input port 1 of the second optical mixer, E _{L2 is} the component of the local oscillator light at the second input port 2 of the second optical mixer, E _s2 ( t)=A _s2 (t)exp(j2πω _s ·t), E _L2 (t)=A _L2 exp(j2πω _L ·t). Among them, A _s2 (t) is the signal component amplitude of the optical signal at the first input port 1 of the second optical mixer, and A _{L2 is} the signal component of the local oscillator light at the second input port 2 of the second optical mixer Amplitude, ω _s and ω _L are the angular frequencies of the optical signal and local oscillator light respectively.

Here, the light field intensity of E _L1 and E _L2 are equal and constant, that is, A _L1 =A _L2 =A _L. The first optical mixer outputs optical signals E _a and E _b , and the second optical mixer outputs optical signals E _c and E _d .

The output optical signal E _{a of} the first optical mixer passes through the single-ended photodetector, and the detected photocurrent is:

Here, P _s1 (t)=|A _s1 (t)| ² /2; P _L1 =|A _L | ² /2; P _s1 (t) and P _L1 are both intermediate variables, and R represents the response of the photodetector Coefficient; ω _IF represents the difference between the angular frequency of the optical signal and the local oscillator light; θ(t) represents other phase disturbances. Since A _L is a constant, P _L1 is a DC component here, which can be removed after passing through the TIA and the DC block. In a coherent access system, the power of the received optical signal is usually much smaller than the optical power of the local oscillator, so there are the following relationships:

Then, after passing through the TIA and the DC block, the optical signal can also be expressed as:

In the same way, the output optical signal E _{b of} the first optical mixer passes through the single-ended photodetector, and the detected photocurrent is:

Then, after passing through the TIA and the DC block, the optical signal can be expressed as:

The output optical signal E _{c of} the second optical mixer passes through the single-ended photodetector, and the detected photocurrent is:

Here, P _s2 (t)=|A _s2 (t)| ² /2; P _L2 =|A _L | ² /2; R represents the response coefficient of the photodetector; ω _IF represents the angle between the optical signal and the local oscillator light The difference in frequency; θ(t) represents other phase disturbances. Since A _L is a constant, P _L2 here is a DC component, which can be removed after passing through the TIA and the DC block. In the access system, the power of the received optical signal is usually much smaller than the optical power of the local oscillator, so there are the following relationships:

Then, the optical signal after passing through the TIA and the DC block can be expressed as:

Similarly, the second optical mixer output optical signal E _d mono- end photodetector which detects the light current is:

The above four signals (V _a , V _b , V _c , V _d ) are respectively sampled by ADC and form two equalizer input signals in pairs. One complex signal composed of Va and Vb is expressed as:

Similarly, the complex signal input by another equalizer is composed of Vc and Vd, expressed as:

Among them, T represents the sampling period of the signal.

As shown in Figure 6, in this embodiment, a two-stage equalization algorithm (envelope detection) is used to process the above input signals (E _Xin , E _Yin ). The first-stage equalizer is a two-input two-output equalizer, which includes Four equalization units. Since these four equalization units only contain one weight coefficient, they can be represented by scalar symbols, namely: m _XX , m _XY , m _YX , m _YY . The intermediate signal after the first stage equalizer can be expressed as:

E _Xmid = m _XX E _Xin +m _XY E _Yin (15)

E _Ymid = m _YX E _Xin +m _YY E _Yin (16)

The second-level equalizer includes two equalization units, and each equalization unit has multiple weight coefficients, so they are represented by vector symbols, respectively: h _X and h _Y. The equalization unit of the second-level equalizer has multiple weight coefficients, so the input signal and the intermediate signal must be composed of the same number of sampled data, and expressed in vector symbols: the input signal is (E _Xin , E _Yin ), the intermediate signal It is (E _Xmid , E _Ymid ).

The first-stage equalizer coefficient m _XY is updated as follows:

m _XY =m _XY +με _X E _Xout ·A(h _X ,E _Yin ) (17)

Among them, μ is the update coefficient; ε _X is the error amount; E _Xout is the X polarization output signal; A(h _X , E _Yin ) is the correction signal. specific:

ε _X =|E _Xout |-R _X (18)

Here, |E _Xout | represents the modulus of the output signal E _Xout , and R _X represents the transmitted X polarization reference signal. For the intensity modulation signal sent, such as NRZ (Non-Return to Zero), R _X is equal to '0' or '1'; such as PAM4 (4-Level Pulse-Amplitude Modulation, 4-level pulse amplitude) For modulation) signals, R _X is equal to '0', '1', "2", and "3". The correction signal A(h _X ,E _Yin ) is calculated based on the following formula:

A(h _X ,E _Yin )=(h _X ·E _Yin ^T ) ^*

In the above formula, the superscript ‘*’ represents the conjugate of the complex number, and the superscript ‘T’ represents the transposed matrix.

The first-level equalizer coefficient m _XX is updated in the following way:

m _XX =m _XX +με _X E _Xout ·A(h _X ,E _Xin ) (19)

Among them, μ is the update coefficient; ε _X is the error amount; E _Xout is the X-polarized output signal; A(h _X , E _Xin ) is the correction signal. The correction signal A(h _X ,E _Xin ) is calculated based on the following formula:

A(h _X ,E _Xin )=(h _X ·E _Xin ^T ) ^*

The first-level equalizer coefficient m _YX is updated in the following way:

m _YX = m _YX +με _Y E _Yout ·A(h _Y ,E _Xin ) (20)

Among them, μ is the update coefficient; ε _Y is the error amount; E _Yout is the Y polarization output signal; A(h _Y , E _Xin ) is the correction signal. specific:

ε _Y ＝|E _Yout |-R _Y (21)

Here, |E _Yout | represents the modulus of the output signal E _Yout , and R _Y represents the transmitted Y polarization reference signal. For the transmitted NRZ signal, R _Y is equal to '0' or '1'. The correction signal A(h _Y ,E _Xin ) is calculated based on the following formula:

A(h _Y ,E _Xin )=(h _Y ·E _Xin ^T ) ^*

The first-level equalizer coefficient m _YY is updated in the following way:

m _YY ＝m _YY +με _Y E _Yout ·A(h _Y ,E _Yin ) (22)

Among them, μ is the update coefficient; ε _Y is the error amount; E _Yout is the Y polarization output signal; A(h _Y , E _Yin ) is the correction signal. The correction signal A(h _Y ,E _Yin ) is calculated based on the following formula:

A(h _Y ,E _Yin )=(h _Y ·E _Yin ^T ) ^*

The output signal of the second stage equalizer can be expressed as:

E _Xout = h _X · E _Xmid ^T (23)

E _Yout = h _Y ·E _Ymid ^T (24)

The second-level equalizer coefficient h _X is updated as follows:

h _X = h _X + με _X E _Xout E _Xmid ^* (25)

h _Y ＝h _Y +με _Y E _Yout E _Ymid ^* (26)

Among them, μ is the update coefficient; ε _X and ε _Y are the amount of error; E _Xout and E _Yout are the output signals of X polarization and Y polarization, respectively; E _Xmid and E _Yout are the intermediate signals passing through the first-stage equalizer, respectively.

The implementation steps of the equalization algorithm are as follows:

1) Initialize equalization coefficients, such as: m _XX , m _XY , m _YX , m _YY , h _X , h _Y ;

2) Calculate the intermediate signals E _Xmid , E _Ymid and the output signals E _Xout , E _Yout according to the input signals E _Xin and E _Yin ;

3) reference signal R _X, R _Y, and calculating the error amount ε _X ε _Y;

4) Update equalization coefficients: m _XX , m _XY , m _YX , m _YY , h _X , h _Y ;

5) Judge whether the error has converged. If yes, go to step 6; if not, go to step 2;

6) After training, a stable equalizer coefficient is obtained.

Finally, the equalizer output signal E _Xout , E _Yout undergoes envelope calculation, namely: |E _Xout |, |E _Yout | to obtain the restored intensity of the transmitted signal, which fully verifies that the digital signal processor can restore the optical signal of the coherent signal receiving device .

The present invention also provides a coherent passive optical network system, which includes an OLT (Optical Line Terminal, optical line terminal), an ODN (Optical Distribution Network, optical distribution network) and multiple ONUs (Optical Network Unit, optical network units), The OLT is connected to multiple ONUs through ODN.

The coherent passive optical network system includes a coherent signal sending device and a coherent signal receiving device.

The coherent signal sending device is used to divide the optical signal of the wide-linewidth light source device into two paths with the same light intensity, each path is used as an optical carrier of an optical intensity modulator, and the optical intensity modulator is driven by an electric drive signal to perform light Signal modulation, the two modulated optical signals are polarized and combined and sent to ODN.

The coherent signal receiving device is used to receive the optical signal from the ODN, and separate the local oscillator light and the received optical signal into two perpendicular X-polarized light and Y-polarized light, and the local oscillator light is divided into X-polarized light and Y-polarized light. The intensity of the light field of the polarized light is equal; the two beams of X-polarized light are mixed, the two beams of Y-polarized light are mixed, and the four optical signals output after the mixing are each detected by a single-ended photodetector, amplified and isolated by a transimpedance After that, signal recovery is performed through envelope detection.

As shown in FIG. 7, in an embodiment, the ODN includes a 1:n optical power divider, which is used to distribute optical signals to the ONU, and only one ONU is shown.

As shown in FIG. 8, in another embodiment, the ODN includes a wavelength division multiplexer for demultiplexing the ONU. FIG. 8 only shows one ONU.

As shown in Figure 9, in another embodiment, the ODN includes both a wavelength division multiplexer and a 1:n optical power splitter, and each output of the wavelength division multiplexer is connected to a 1:n optical power divider. The input of the power divider, and each output of the 1:n optical power divider is connected to an ONU. Figure 9 shows only one ONU and one 1:n optical power splitter.

Based on the foregoing coherent passive optical network system, in one embodiment, at least one of the foregoing coherent signal sending devices is provided in the OLT to send intensity-modulated optical signals to the ODN; the ONU is provided with the foregoing coherent signal receiving device, from the ODN Receive the signal and make a recovery.

In another embodiment, the ONU is provided with the aforementioned coherent signal sending device to send intensity-modulated optical signals to the ODN; and the OLT is provided with at least one aforementioned coherent signal receiving device for receiving and recovering signals from the ODN.

In another embodiment, the OLT includes at least one single-channel signal transceiving module, and each ONU includes a single-channel signal transceiving module. The transceiver equipment further includes a combining and demultiplexing wave plate, the above-mentioned coherent signal sending device and the above-mentioned coherent signal receiving device.

As shown in Figure 10, the OLT includes a single-channel signal transceiver module. The multiplexer/demultiplexer plate includes two demultiplexer ports and one multiplexer port. The output of the coherent signal transmitting device is the same as the input of the coherent signal receiving device. The two demultiplexing ports of a multiplexer/demultiplexer plate are respectively connected, and the multiplexer ports of the multiplexer/demultiplexer plate are connected to the ODN. Therefore, the downstream optical signal generated by the coherent signal transmission device passes through a demultiplexing port of the multiplexer/demultiplexer plate, and then comes out of the multiplexer port of the multiplexer/demultiplexer plate and enters the ODN; while the OLT receives the upstream optical signal from the ODN and passes The multiplexer port of the demultiplexer enters, and then exits from the other port of the multiplexer and demultiplexer, and enters the coherent signal receiving device. In the coherent passive optical network system, the same transceiver device in this embodiment can also be installed in the ONU.

As shown in Fig. 11, it is the case that the OLT includes more than one single-channel signal transceiver module. Each single-channel signal transceiver module has the same structure as in Figure 10, but the multiplexer port of each multiplexer/demultiplexer plate is connected to the demultiplexer port of a WDM device, and the multiplexer port of the WDM device is connected ODN. In the case of multi-channel signal transceiving, the downstream optical signal generated by each single-channel signal transceiving module is input through each demultiplexing port of the wavelength division multiplexing device and converged into a downstream optical signal of wavelength division multiplexing. Use the multiplexing port of the device to come out and enter the ODN. The wavelength division multiplexed uplink optical signal from the ODN is wavelength demultiplexed through the multiplexing port of the wavelength division multiplexing device, and then comes out of the demultiplexing ports of the wavelength division multiplexing device, and is input to each single-channel signal transceiver module for processing. Coherent signal reception.

In the above embodiment, the light source generated by the wide linewidth light source device is used as the local oscillator and the signal carrier light source, and the light intensity modulator, single-ended photodetector, and envelope detection are adopted, which can effectively reduce the overall coherent light detection. cost.

The present invention is not limited to the above-mentioned embodiments. For those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also regarded as the protection of the present invention. Within range. The content not described in detail in this specification belongs to the prior art known to those skilled in the art.

Claims

A method for transmitting coherent signals is characterized in that it comprises the steps:

The optical signal of the wide linewidth light source device is divided into two paths with the same light intensity, each path is used as an optical carrier of a light intensity modulator, and the light intensity modulator is driven by an electric drive signal to perform optical signal modulation. The light signal after polarization is combined and sent out.
8. The coherent signal sending method according to claim 1, wherein the wide linewidth light source device is a distributed feedback laser.
A coherent signal receiving method based on the method of claim 1, characterized in that it comprises the steps of:

The local oscillator light and the received optical signal are divided into mutually perpendicular X-polarized light and Y-polarized light, and the optical field intensity of the X-polarized light and Y-polarized light divided into the local oscillator light is equal;

Mix two beams of X-polarized light and two beams of Y-polarized light. The four optical signals output after mixing are each detected by a single-ended photodetector. After being amplified and blocked by transimpedance, they are detected by envelope detection. Restore the signal.
The coherent signal receiving method according to claim 3, wherein the local oscillator light is generated by a distributed feedback laser.
A coherent signal sending device is characterized by comprising:

Wide linewidth laser source device, used to send continuous light signal;

An optical splitter, used to divide the optical signal into two optical carriers with the same optical intensity;

Two signal drivers, respectively used to amplify one electrical signal to form an electrical drive signal;

Two optical intensity modulators, each optical intensity modulator is used to receive an optical carrier, and modulate the optical signal through an electric drive signal;

The polarization beam combiner is used to combine the optical signals modulated by the two optical intensity modulators to obtain a polarization multiplexed optical intensity modulation signal.
The coherent signal sending device according to claim 5, wherein the two light intensity modulators are both Mach-Zehnder modulators, and the outputs of the two signal drivers are each connected to the radio frequency input port of a Mach-Zehnder modulator , And the working bias voltage of the Mach-Zehnder modulator is set in the linear modulation area.
The coherent signal transmitting device according to claim 5, wherein the two light intensity modulators are both electro-absorption modulators, and the working bias voltage of the electro-absorption modulator is set in the linear modulation area, and the two signal The output of the driver is connected to the RF input port of an electro-absorption modulator.
7. The coherent signal sending device according to any one of claims 5-7, wherein the optical splitter is a 50:50 optical power splitter, and the wide linewidth light source device is a distributed feedback laser.
A coherent signal receiving device based on the device of claim 5, characterized in that it comprises:

Wide linewidth light source device, used to provide local oscillator light;

Two 90-degree optical mixers, each 90-degree optical mixer includes two input ports and two output ports;

Two polarization beam splitters, a first polarization beam splitter and a second polarization beam splitter, the first polarization beam splitter is used to divide the received optical signal into mutually perpendicular X-polarized light and Y-polarized light, and Input the first input ports of two 90-degree optical mixers respectively; the second polarization beam splitter is used to divide the local oscillator light into X-polarized light and Y-polarized light that are perpendicular to each other and the optical field intensity is equal, and input two respectively The second input port of the 90-degree optical mixer;

Four single-ended photodetectors, respectively used to receive one optical signal output by the 90-degree optical mixer;

Four transimpedance amplifiers, respectively corresponding to the output of a single-ended photodetector;

Four DC blockers, respectively corresponding to the optical signal of a transimpedance amplifier, and used to block DC;

Four analog-to-digital converters, which convert the analog signal output by the DC block into digital signals;

Envelope detection module, which is used to receive all digital signals for signal recovery.
9. The coherent signal receiving device of claim 9, wherein the four analog-to-digital converters and the envelope detection module are integrated, and the wide linewidth light source device is a distributed feedback laser.
A coherent passive optical network system is characterized in that it comprises:

Coherent signal sending device, which is used to divide the optical signal of the wide linewidth light source device into two paths with the same light intensity, each path is used as an optical carrier of a light intensity modulator, and the light intensity modulator is driven by an electric drive signal Carry out optical signal modulation, the two modulated optical signals are combined by polarization and sent to the optical distribution network;

Coherent signal receiving device, which is used to divide the local oscillator light and the received optical signal into mutually perpendicular X-polarized light and Y-polarized light, and the optical field intensity of the X-polarized light and Y-polarized light divided into the local oscillator light are equal; Two beams of X-polarized light are mixed, and two beams of Y-polarized light are mixed. The four optical signals output after mixing are each detected by a single-ended photodetector. After transimpedance amplification and blocking, the signal is detected by envelope restore.
11. The coherent passive optical network system of claim 11, wherein the coherent passive optical network system comprises an optical line terminal and a plurality of optical network units;

At least one coherent signal sending device is provided in the optical line terminal, and one coherent signal receiving device is provided in the optical network unit;

Alternatively, the optical network unit is provided with one coherent signal sending device, and the optical line terminal is provided with at least one coherent signal receiving device.
11. The coherent passive optical network system of claim 11, wherein the coherent passive optical network system comprises an optical line terminal and a plurality of optical network units;

The optical line terminal includes at least one single-channel signal transceiver module, and each optical network unit includes a single-channel signal transceiver module;

Each single-channel signal transceiver module includes a combiner/demultiplexer plate, a coherent signal transmitting device and a coherent signal receiving device;

The output of the coherent signal sending device and the input of the coherent signal receiving device are respectively connected to two demultiplexing ports of a multiplexer and demultiplexer plate, and the multiplexer ports of the multiplexer and demultiplexer plate are connected to an optical distribution network.
The coherent passive optical network system according to claim 13, wherein when the optical line terminal includes more than one single-channel signal transceiver module, the multiplexer port of each multiplexer/demultiplexer plate is connected to one wave The demultiplexing port of the wavelength division multiplexing device and the multiplexing port of the wavelength division multiplexing device are connected to the optical distribution network.
The coherent passive optical network system according to any one of claims 11-14, wherein the coherent signal sending device comprises:

Wide linewidth laser source device, used to send continuous light signal;

An optical splitter, used to divide the optical signal into two optical carriers with the same optical intensity;

Two signal drivers, respectively used to amplify one electrical signal to form an electrical drive signal;

Two optical intensity modulators, each optical intensity modulator is used to receive an optical carrier, and modulate the optical signal through an electric drive signal;

The polarization beam combiner is used to combine the optical signals modulated by the two optical intensity modulators to obtain a polarization multiplexed optical intensity modulation signal.
The coherent passive optical network system according to any one of claims 11-14, wherein the coherent signal receiving device comprises:

Wide linewidth light source device, used to provide local oscillator light;

Two 90-degree optical mixers, each 90-degree optical mixer includes two input ports and two output ports;

Two polarization beam splitters, a first polarization beam splitter and a second polarization beam splitter, the first polarization beam splitter is used to divide the received optical signal into mutually perpendicular X-polarized light and Y-polarized light, and Input the first input ports of two 90-degree optical mixers respectively; the second polarization beam splitter is used to divide the local oscillator light into X-polarized light and Y-polarized light that are perpendicular to each other and the optical field intensity is equal, and input two respectively The second input port of the 90-degree optical mixer;

Four single-ended photodetectors, respectively used to receive one optical signal output by the 90-degree optical mixer;

Four transimpedance amplifiers, respectively corresponding to the output of a single-ended photodetector;

Four DC blockers, respectively corresponding to the optical signal of a transimpedance amplifier, and used to block DC;

Four analog-to-digital converters, which convert the analog signal output by the DC block into digital signals;

Envelope detection module, which is used to receive all digital signals for signal recovery.