CN103004111B

CN103004111B - A kind of coherent reception signal method, equipment and system

Info

Publication number: CN103004111B
Application number: CN201280001505.9A
Authority: CN
Inventors: 周雷; 彭桂开
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2012-09-14
Filing date: 2012-09-14
Publication date: 2016-09-28
Anticipated expiration: 2032-09-14
Also published as: WO2014040272A1; CN103004111A

Abstract

The embodiment of the invention discloses a kind of coherent reception signal method, the method extracts the downlink optical signal of direct current no signal modulation by optical filter, and the local oscillator light as downlink optical signal carries out coherent reception to downlink optical signal；Complete the modulation of uplink optical signal by reflection type optical electrical part and amplify.So that terminal is under conditions of the local oscillator laser instrument of no polarization diversity structure and coherent reception, it is possible to realize low cost coherent.

Description

Coherent signal receiving method, device and system

Technical Field

The present invention relates to the field of communications, and in particular, to a method, device, and system for coherent signal reception.

Background

A Passive Optical Network (POS) is becoming a mainstream technology in the field of broadband access, and a typical POS system is formed by connecting a plurality of Optical Network Units (ONUs) to an Optical Splitter (Splitter) through an Optical fiber, and connecting the Optical Splitter to a local end (OLT) through a trunk Optical fiber after aggregation. In the Network upgrading process, an Optical Distribution Network (ODN) needs to be kept unchanged, that is, an ODN structure based on Splitter is unchanged.

In Subcarrier Multiplexing (SCM)/Orthogonal Frequency Division Multiplexing (OFDM), each ONU corresponds to one channel, each channel corresponds to one Subcarrier Frequency SC1, SC2, SC3, … SCN, and data of each ONU is modulated onto the corresponding Subcarrier, and the Modulation format can achieve the purpose of compressing signal bandwidth by using flexible high-order Modulation 16/64/128 Quadrature Amplitude Modulation (QAM). All channels are combined together in an electrical domain, modulated to optical signals, transmitted through optical fibers, subjected to photoelectric conversion at a receiving end, and each terminal selects a subcarrier belonging to the terminal by using an electric filter. Another advantage of SCM is that bandwidth can be scheduled from the subcarrier level among ONUs, and the architecture can be based on Splitter and is compatible with existing ODN networks.

In the prior art, a hybrid PON system using Ultra Dense wavelength Division Multiplexing Orthogonal Frequency Division Multiplexing (UDWDM-OFDM) can transmit more data and improve the bandwidth of an end user by using the Frequency spectrum compression characteristic of OFDM while maintaining the bandwidth of a photoelectric device of UDWDM PON. Meanwhile, the coherent receiving technology can greatly improve the sensitivity of the receiver, overcome the defect of low receiving sensitivity of OFDM and meet the requirement that the system has enough power budget. However, the ONU needs a polarization diversity structure, and the complexity of the device is increased by 2 times; meanwhile, the ONU needs a high-precision tunable laser with high cost as a local oscillator laser for coherent reception, and the two situations cause that the cost of the terminal is too high and the engineering application cannot be realized.

Therefore, how to enable the terminal to realize low-cost coherent reception under the condition of no polarization diversity structure and coherent reception local oscillator laser is a problem which needs to be solved urgently at present.

Disclosure of Invention

In view of this, embodiments of the present invention provide a method, a device, and a system for coherent reception, so that a terminal can implement low-cost coherent reception without a polarization diversity structure and a coherent reception local oscillator.

In a first aspect, a method of coherent reception, comprising:

receiving a first downlink optical signal sent by a local side device to a terminal device, dividing the first downlink optical signal into two paths, wherein one path is used as signal light, the other path is used for generating local oscillator light of the signal light, and the signal light and the local oscillator light are subjected to coherent reception.

In a first possible implementation manner of the first aspect, the method further includes:

and generating an uplink optical signal sent by the terminal equipment to the local side equipment.

With reference to the first aspect or the first possible implementation manner of the first aspect, in a second possible implementation manner, the dividing the first downlink optical signal into two paths, where one path is used as signal light, and a local oscillator light that is used by the other path to generate the signal light specifically includes:

dividing the first downlink optical signal into two paths, wherein one path is used as a second downlink optical signal to be input into the coupler; filtering the other path to obtain a third downlink optical signal without signal modulation;

directly loading the first uplink optical signal to the third downlink optical signal without signal modulation by direct current, and taking the modulated third downlink optical signal as a second uplink optical signal;

and dividing the second uplink optical signal into two paths, wherein one path is output to local side equipment, the other path is subjected to filtering processing to obtain a third uplink optical signal modulated by a direct current no-signal, and the third uplink optical signal modulated by the direct current no-signal is used as local oscillation light of the second downlink optical signal and input to the coupler.

With reference to the first aspect, the first possible implementation manner of the first aspect, or the second possible implementation manner of the first aspect, in a third possible implementation manner, the second uplink optical signal is input to the local side device after being subjected to a deflection processing, so that a deflection state of the deflected second uplink optical signal is perpendicular to a deflection state of the first downlink optical signal.

With reference to the first aspect, the first possible implementation manner of the first aspect, the second possible implementation manner of the first aspect, or the third possible implementation manner of the first aspect, in a fourth possible implementation manner, the dividing the first downlink optical signal into two paths, where one path is used as signal light, and the local oscillator light for generating the signal light by using the other path specifically includes:

dividing the first downlink optical signal into two paths, wherein one path is used as a second downlink optical signal to be input into the coupler; filtering the other path to obtain a third downlink optical signal without signal modulation of direct current, and obtaining an amplified third downlink optical signal without signal modulation of direct current;

dividing the amplified direct-current signal-free modulated third downlink optical signal into two paths according to a certain proportion, wherein one path is used as a local oscillator optical input coupler of the second downlink optical signal; acquiring a second uplink optical signal through the other path;

and directly loading the first uplink optical signal to the other path separated by the amplified direct-current signal-modulation-free third downlink signal, and acquiring the second uplink optical signal and outputting the second uplink optical signal to local side equipment.

With reference to the first aspect, the first possible implementation manner of the first aspect, the second possible implementation manner of the first aspect, the third possible implementation manner of the first aspect, or the fourth possible implementation manner of the first aspect, the method further includes:

and deflecting the second uplink optical signal and inputting the second uplink optical signal into the local side equipment, so that the deflected state of the second uplink optical signal is vertical to the deflected state of the first downlink optical signal.

In a second aspect, a coherent reception signal device includes:

a receiving unit, configured to receive a downlink optical signal input by a central office;

the first processing unit is used for dividing the first downlink optical signal into two paths, wherein one path is used as signal light, and the other path is used for generating local oscillator light of the signal light;

and the coupler is used for carrying out coherent reception on the signal light and the local oscillator light.

With reference to the second aspect, in a first possible implementation manner of the second aspect, the apparatus further includes:

the second processing unit is used for generating an uplink optical signal sent by the terminal equipment to the local side equipment;

with reference to the second aspect or the first possible implementation manner of the second aspect, in a second possible implementation manner of the second aspect, the first processing unit specifically includes:

the first circulator is used for outputting a first downlink optical signal to the first optical splitter;

the first optical splitter is configured to split the first downlink optical signal into two paths, where one path is used as a second downlink optical signal input coupler; the other path is input into a second circulator;

the second circulator is used for transmitting the other path of the first downlink optical signal to the optical filter;

the optical filter is used for processing the other path into which the first downlink optical signal is divided so as to obtain a third downlink optical signal without signal modulation;

the reflective semiconductor optical amplifier is used for directly loading the first uplink optical signal to the third downlink optical signal modulated by the direct current no-signal, and taking the modulated third downlink optical signal modulated by the direct current no-signal as a second uplink optical signal;

the second optical splitter is used for splitting the second uplink optical signal into two paths, wherein one path is input into the first circulator, and the other path is input into the optical filter;

the first circulator is further configured to divide the second uplink optical signal into one path and output the path to the local side device;

the optical filter is further configured to divide the second uplink optical signal into another path for processing, so as to obtain a third uplink optical signal without signal modulation by direct current;

and the second circulator is further configured to input a third uplink optical signal modulated by the direct-current no-signal to the coupler as local oscillation light of the second downlink optical signal.

With reference to the second aspect, the first possible implementation manner of the second aspect, or the second possible implementation manner of the second aspect, in a third possible implementation manner of the second aspect, the first processing unit specifically includes:

With reference to the second aspect, the first possible implementation manner of the second aspect, the second possible implementation manner of the second aspect, or the third possible implementation manner of the second aspect, in a fourth possible implementation manner of the second aspect, the device further includes a polarization rotator, where the polarization rotator is configured to input the second uplink optical signal into the local-end device after performing deflection processing on the second uplink optical signal, so that a deflection state of the deflected second uplink optical signal is perpendicular to a deflection state of the first downlink optical signal.

With reference to the second aspect, the first possible implementation manner of the second aspect, the second possible implementation manner of the second aspect, the third possible implementation manner of the second aspect, or the fourth possible implementation manner of the second aspect, in a fifth possible implementation manner of the second aspect, the first processing unit specifically includes:

a circulator: the first optical splitter is used for outputting a first downlink optical signal to the first optical splitter;

the first optical splitter is configured to split the first downlink optical signal into two paths, where one path is used as a second downlink optical signal input coupler; the other path is input into an optical filter;

the optical filter is used for processing the other path of the first downlink optical signal to obtain a third downlink optical signal without signal modulation;

the semiconductor optical amplifier is used for amplifying the third downlink optical signal modulated by the direct current no-signal to obtain an amplified third downlink optical signal modulated by the direct current no-signal;

the second optical splitter is used for splitting the amplified direct-current non-signal-modulated third downlink optical signal into two paths, wherein one path is used as local oscillation light of the second downlink optical signal and is input into the coupler, and the other path is input into the modulator;

the modulator is used for directly loading the first uplink optical signal to the other path of the amplified direct-current non-signal-modulated third downlink optical signal branch to obtain a second uplink optical signal;

the circulator is further configured to output the second uplink optical signal to a local side device.

With reference to the second aspect, the first possible implementation manner of the second aspect, the second possible implementation manner of the second aspect, the third possible implementation manner of the second aspect, the fourth possible implementation manner of the second aspect, or the fifth possible implementation manner of the second aspect, in a sixth possible implementation manner of the second aspect, the device further includes a polarization rotator, where the polarization rotator is configured to input the second uplink optical signal into the local side device after performing deflection processing on the second uplink optical signal, so that a deflection state of the deflected second uplink optical signal is perpendicular to a deflection state of the first downlink optical signal.

In a third aspect, a central office device includes various features and combinations of features of a coherent signal receiving device as described in the second aspect above.

In a fourth aspect, a terminal device comprises various features and combinations of features of a coherent reception signal device of the second aspect described above.

In a fifth aspect, a passive optical network system includes the local end device according to the third aspect and/or the terminal device according to the fourth aspect.

In the embodiment of the invention, the local oscillator light which is received in coherence with the downlink optical signal is generated from the downlink optical signal by the terminal, and a laser which is expensive in cost and has accurately adjustable wavelength is not required to be used as the local oscillator laser; the local oscillation optical signal wavelength is the downlink optical signal wavelength, because the local oscillation optical signal wavelength is obtained by injecting the downlink optical signal center wavelength into the reflection type photoelectric device, after being coherent with the second downlink optical signal, the intermediate frequency optical signal is 0Hz, the purpose of minimizing the bandwidth required by the subsequent electrical appliance is naturally achieved, and no wavelength control mechanism is needed; the polarization state of the downlink optical signal is transmitted through the ODN and reaches a terminal, the polarization state is random, a common coherent receiving structure is a polarization diversity mode, two sets of same structures are used for respectively receiving two polarization states of the optical signal, in the invention, the local oscillator optical signal is extracted from the downlink optical signal, the polarization state of the local oscillator optical signal is consistent with that of the downlink optical signal, correct coherent receiving can be completed without a polarization diversity structure, and the complexity of a device is reduced by one time; the reflection-type photoelectric device usually operates in a saturation state, and after the reflection-type photoelectric device erases a downlink optical signal, uplink data are modulated onto the reflection-type photoelectric device, because the optical signal injected into the reflection-type photoelectric device is direct current light without modulation, the reflection-type photoelectric device is not required to be saturated (saturation requires higher injected optical power), and the uplink data are directly modulated onto the light, so that the requirement of the injection-type photoelectric device on the optical signal power is reduced, and the downlink optical power budget is obviously improved; a reflection-type photoelectric device + optical filter structure simultaneously completes the functions of generating and amplifying downlink local oscillator direct current light and modulating and sending uplink signals. And an additional laser is not needed to be used as an uplink light source, so that an optical device required by the terminal side is reduced to the minimum, and the cost advantage is achieved.

In the embodiment of the invention, the local oscillator light which is received in coherence with the downlink optical signal is generated from the downlink optical signal by the terminal, and a laser which is expensive in cost and has accurately adjustable wavelength is not required to be used as the local oscillator laser; the local oscillator optical signal wavelength is the downlink optical signal wavelength, because the local oscillator optical signal wavelength is obtained by injecting the downlink optical signal center wavelength into the semiconductor optical amplifier, after being coherent with the second downlink optical signal, the intermediate frequency optical signal is 0Hz, the purpose of minimizing the bandwidth required by the subsequent electrical appliance is naturally achieved, and no wavelength control mechanism is needed; the polarization state of the downlink optical signal is transmitted through the ODN and reaches a terminal, the polarization state is random, a common coherent receiving structure is a polarization diversity mode, two sets of same structures are used for respectively receiving two polarization states of the optical signal, in the invention, the local oscillator optical signal is extracted from the downlink optical signal, the polarization state of the local oscillator optical signal is consistent with that of the downlink optical signal, correct coherent receiving can be completed without a polarization diversity structure, and the complexity of a device is reduced by one time; the structure of the semiconductor optical amplifier, the optical filter and the modulator can simultaneously complete the functions of generating and amplifying the downlink local oscillator direct current light and modulating and sending the uplink signal, an additional laser is not needed to be used as an uplink light source, the optical device needed by the terminal side is reduced to the minimum, and the structure has the advantage of cost; the ONU side is arranged behind the optical filter, the semiconductor optical amplifier is used for amplifying the direct current light and then dividing the direct current light into 2 paths, wherein one path of the direct current light enters the 2 x 2 coupler to be used as local oscillation light of a downlink optical signal, the other path of the direct current light passes through one modulator, and then the uplink signal is modulated onto the light through the modulator, so that the uplink optical signal can be prevented from being filtered by the optical filter again, and the frequency spectrum utilization rate is higher.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without inventive labor.

Fig. 1 is a flow chart of a method for coherent reception of signals according to an embodiment of the present invention;

fig. 2 is a block diagram of a coherent signal receiving apparatus according to an embodiment of the present invention;

fig. 3 is a structural diagram of an OFDM passive optical network system according to an embodiment of the present invention;

fig. 4 is a structural diagram of another OFDM passive optical network system according to an embodiment of the present invention;

fig. 5 is a structural diagram of another OFDM passive optical network system according to an embodiment of the present invention;

fig. 6 is a flow chart of a method for coherent reception of signals according to an embodiment of the present invention;

fig. 7 is a block diagram of a coherent signal receiving apparatus according to an embodiment of the present invention;

fig. 8 is a structural diagram of an OFDM passive optical network system according to an embodiment of the present invention;

fig. 9 is a block diagram of another OFDM passive optical network system according to an embodiment of the present invention;

fig. 10 is a structural diagram of another OFDM passive optical network system according to an 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 above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

The coherent signal receiving method, the coherent signal receiving system and the coherent device provided by the embodiment of the invention enable the terminal to realize low-cost coherent reception under the condition of no polarization diversity structure and coherent reception local oscillator laser. The following description will be made by way of specific examples.

The first embodiment is as follows:

referring to fig. 1, fig. 1 is a flowchart illustrating a method for coherent signal reception according to an embodiment of the present invention. As shown in fig. 1, the coherent signal receiving method may include the steps of:

As a preferable embodiment, the method further comprises:

101. Receiving a first downlink optical signal sent by a local side device to a terminal device;

102, dividing the first downlink optical signal into two paths, wherein one path is used as a second downlink optical signal to be input into the coupler; filtering the other path to obtain a third downlink optical signal without signal modulation;

in this step, a first downlink optical signal passing through the first circulator is divided into two paths, wherein one path is input into the 2 × 2 coupler as a second downlink optical signal; and the other path of the optical signal passes through a second circulator and then is input into an optical filter for processing so as to obtain a third downlink optical signal without signal modulation of direct current.

In the embodiment of the present invention, the office-side first downlink optical signal is an optical signal sent by the office side to the terminal. The local side generates multi-band OFDM electric signals, downlink data information is modulated in a passband, and a certain frequency interval is set between the downlink data information and a baseband (direct current). Here, each subband may correspond to one terminal, or multiple terminals may share one subband, and wideband allocation is completed by using subcarrier scheduling in the subband. The OFDM electric signal modulates a signal on light through a modulator, and a certain frequency interval exists between the wavelength of the signal light and the central wavelength of the laser in the modulated spectrum, and is the same as the frequency interval between a pass band and a baseband of an electric domain. The modulated optical signal passes through the circulator, is sent to the ODN, and reaches each ONU after passing through the splitter.

At the ONU, a first downlink optical signal is divided into two paths after passing through a first circulator, wherein one path directly enters a 2 x 2 coupler, the other path is input into an optical filter after passing through a second circulator, the optical filter is an optical bandpass filter, the central wavelength is the central wavelength of a downlink laser, and the bandwidth only allows a baseband direct current component to pass through. Because a part of energy of the first downlink optical signal is distributed on the center wavelength without signal modulation (the ratio of the center direct current optical carrier without signal modulation to the signal frequency band is 25 dB), after passing through the optical filter, the signal frequency spectrum component is filtered out, and a direct current (i.e. continuous) optical signal without signal modulation is obtained. Such optical signals conform to local optical conditions as coherent reception.

103, directly loading the first uplink optical signal to the third downlink optical signal without signal modulation by the direct current, and taking the modulated third downlink optical signal as a second uplink optical signal;

in this step, the first uplink optical signal is directly applied to the third downlink optical signal without signal modulation through the reflective photoelectric device to obtain a second uplink optical signal.

In the embodiment of the invention, a first downlink optical signal is divided into two paths after passing through a first circulator, wherein one path is used as a second downlink optical signal and is input into a 2 × 2 coupler; and the other path of the optical signal is processed by an input optical filter after passing through a second circulator, so that a third downlink optical signal without signal modulation is obtained. And injecting the direct current light obtained after filtering into the reflection type photoelectric device. The reflective photovoltaic device herein has two functions: firstly, after direct current light is injected into a reflection type photoelectric device, the central wavelength output by the reflection type photoelectric device is consistent with the central wavelength of a first downlink optical signal; second, the upstream OFDM data information is modulated onto the light by the reflective electro-optical device, while the reflective electro-optical device amplifies the upstream signal. The modulation concept of the uplink optical signal is consistent with that of the downlink optical signal, the signal is modulated to a passband, and a certain frequency interval is set with a baseband. And similarly, the obtained uplink optical signal modulation spectrum is output, the central wavelength is still direct current light without signal modulation, and the power is obviously amplified.

104, dividing the second uplink optical signal into two paths, wherein one path is output to a local side device, the other path is subjected to filtering processing to obtain a third uplink optical signal without direct current signal modulation, and the third uplink optical signal without direct current signal modulation is input to the coupler as local oscillation light of the second downlink optical signal;

in this step, the second uplink optical signal is divided into two paths, wherein one path is output to the OLT through the first circulator, the other path is output to the optical filter to obtain a third uplink optical signal without direct current signal modulation, the third uplink optical signal without direct current signal modulation is used as local oscillation light of the second downlink optical signal, the local oscillation light passes through the second circulator and is input to the 2 × 2 coupler, and the 2 × 2 coupler performs coherent reception on the second downlink optical signal and the local oscillation light of the second downlink optical signal.

In the embodiment of the invention, an optical signal output from a reflection type photoelectric device is divided into two paths, wherein one path is input into a first circulator and is sent to an OLT as an uplink optical signal; and the other path of the optical signal passes through the optical filter again, the uplink signal data information is just filtered by the optical filter to obtain an amplified direct current optical signal, and the amplified direct current optical signal is input into the 2 x 2 coupler through the second circulator to be used as local oscillation light of the second downlink optical signal to perform coherent reception on the second downlink optical signal.

And 105, performing coherent reception on the second downlink signal light and the local oscillator light of the second downlink optical signal.

The embodiment of the invention has the following advantages: firstly, a laser with high cost and accurately adjustable wavelength is not needed to be used as a local oscillator laser at a terminal side; secondly, the local oscillator optical signal wavelength is the downlink optical signal wavelength, because the local oscillator optical signal wavelength is obtained by injecting the downlink optical signal central wavelength into the reflection-type photoelectric device. After the first downlink optical signal is coherent, the intermediate frequency optical signal is 0Hz, so that the purpose of minimizing the bandwidth required by subsequent electrical appliances is naturally achieved without any wavelength control mechanism; third, the polarization state of the downstream optical signal is random after it is transmitted through the ODN and reaches the termination. A common coherent receiving structure is a polarization diversity method, and two sets of the same structure are used to receive two polarization states of an optical signal respectively. In the invention, the local oscillation optical signal is extracted from the downlink optical signal, the polarization state of the local oscillation optical signal is consistent with that of the downlink optical signal, and correct coherent reception can be completed without a polarization diversity structure. The complexity of the device is doubled; fourth, the reflective photoelectric device is normally operated in a saturation state, and after the reflective photoelectric device erases the downlink optical signal, the uplink data is modulated onto the reflective photoelectric device. Here, because the optical signal to the reflective photoelectric device is direct current light without modulation, the reflective photoelectric device is not required to be saturated (saturation requires higher injected light power), and the uplink data can be directly modulated onto the light. The requirements of the injection reflection type photoelectric device on the optical signal power are reduced, and the downlink optical power budget is obviously improved; fifthly, a structure of a reflection type photoelectric device and an optical filter simultaneously completes the functions of generating and amplifying the downlink local oscillator direct current light and modulating and sending the uplink signal. No additional laser is required as an upstream light source. The optical device required by the terminal side is reduced to the minimum, and the cost advantage is very high.

Example two:

referring to fig. 2, fig. 2 is a structural diagram of a coherent signal receiving apparatus according to an embodiment of the present invention. As shown in fig. 2, the coherent reception signal apparatus may include the following:

a first circulator 201 for outputting a first downlink optical signal to a first optical splitter 202;

the first optical splitter 202 is configured to split the first downlink optical signal into two paths, where one path is used as a second downlink optical signal input coupler 203; the other input is a second circulator 204, wherein the coupler can be a 2 × 2 coupler;

the second circulator 204 is configured to transmit the other split path of the first downlink optical signal to an optical filter 205;

At the ONU, the first downlink optical signal is divided into two paths after passing through the first circulator 201, where one path directly enters the 2 × 2 coupler 203, and the other path passes through the second circulator 204 and then enters the optical filter 205, where the optical filter 205 is an optical bandpass filter, the center wavelength is the center wavelength of the downlink laser, and the bandwidth only allows the baseband dc component. Since a part of the energy of the first downlink optical signal is distributed at the center wavelength without signal modulation (the ratio of the center unmodulated dc optical carrier to the signal frequency band is 25 dB), after passing through the optical filter 205, the signal spectrum component is filtered out, and a dc (i.e. continuous) optical signal without signal modulation is obtained. Such optical signals conform to local optical conditions as coherent reception.

The optical filter 205 is configured to process the other path into which the first downlink optical signal is split, so as to obtain a third downlink optical signal without signal modulation by dc;

a reflective photoelectric device 207 for directly applying the first uplink optical signal to the dc non-signal modulated third downlink optical signal to obtain the second uplink optical signal;

in the embodiment of the present invention, the first downlink optical signal is divided into two paths after passing through the first circulator 201, wherein one path is input into the 2 × 2 coupler 203 as the second downlink optical signal; the other path is processed by the second circulator 204 and then input to the optical filter 205, so as to obtain a third downlink optical signal without signal modulation. The direct current light obtained after the filtering is injected into the reflective photoelectric device 207. The reflective photovoltaic device 207 here serves two functions: firstly, after the direct current light is injected into the reflective photoelectric device 207, the central wavelength output by the reflective photoelectric device 207 is consistent with the central wavelength of the first downlink optical signal; second, the upstream OFDM data information is modulated onto light by the reflective photoelectric device 207, while the reflective photoelectric device 207 amplifies the upstream signal. The modulation concept of the uplink optical signal is consistent with that of the downlink optical signal, the signal is modulated to a passband, and a certain frequency interval is set with a baseband. And similarly, the obtained uplink optical signal modulation spectrum is output, the central wavelength is still direct current light without signal modulation, and the power is obviously amplified.

In this embodiment, the optical filter 205 includes a first optical filtering sub-module and a second optical filtering sub-module. The first optical filtering submodule is used for inputting the other path of light into the optical filter after passing through the second circulator so as to filter out a signal spectrum, so as to obtain a third downlink optical signal without signal modulation of direct current. The second optical filtering sub-module is configured to filter a signal spectrum of another path into which the second uplink optical signal is divided by the optical filter, so as to obtain a third uplink optical signal without signal modulation, and input the third uplink optical signal without signal modulation as local oscillation light of the second downlink optical signal to the 2 × 2 coupler through a second circulator.

A second optical splitter 206, configured to split the second uplink optical signal into two paths, where one path is input to the first circulator 201, and the other path is input to the optical filter 205;

the first circulator 201 is further configured to divide the second uplink optical signal into one path and output the path to the OLT;

the optical filter 205 is further configured to divide the second uplink optical signal into another path for processing, so as to obtain a third uplink optical signal without signal modulation by dc;

the second circulator 204 is further configured to input a third uplink optical signal modulated by the direct current no-signal as local oscillation light of the second downlink optical signal to the 2 × 2 coupler 203;

the 2 × 2 coupler 203 is configured to perform coherent reception on the second downlink optical signal and local oscillation light of the second downlink optical signal.

In the embodiment of the present invention, the optical signal output from the reflective photoelectric device 207 is divided into two paths, wherein one path is input to the first circulator 201 and is sent to the OLT as an uplink optical signal; the other path passes through the optical filter 205 again, and the uplink signal data information is just filtered by the optical filter to obtain an amplified direct current optical signal, which is input to the 2 × 2 coupler 203 through the second circulator 204 to be used as local oscillation light of the second downlink optical signal to perform coherent reception on the second downlink optical signal.

Example three:

referring to fig. 3, fig. 3 is a structural diagram of an OFDM passive optical network system according to an embodiment of the present invention. As shown in fig. 3, the OFDM passive optical network system may include the following devices:

a terminal comprising the apparatus of figure 2 and an opto-electrical converter, an analogue mixer, a sine wave generator, a digital-to-analogue converter, an orthogonal frequency division multiplexing decoder;

the apparatus of fig. 2 has been described in detail in the second embodiment, and will not be described in detail in the third embodiment.

The photoelectric converter 301 is configured to convert the optical signal output by the 2 × 2 coupler 203 into an analog electrical signal and output the analog electrical signal to the analog mixer 302;

the analog mixer 302 is used for processing the analog electric signal and the sine wave generated by the sine wave generator 303;

the sine wave generator 303 is configured to generate a sine wave to output to the analog mixer 302;

the digital-to-analog converter 304 is configured to convert the analog electrical signal output by the analog mixer 302 into a digital electrical signal and output the digital electrical signal to the orthogonal frequency division multiplexing decoder 305;

the ofdm decoder 305 is used to select a digital electrical signal wave of a specific frequency spectrum.

A local side is used for generating a multi-band OFDM electric signal, and a preset first frequency interval exists between the passband frequency and the baseband frequency of the multi-band OFDM electric signal; modulating the multi-band OFDM electric signal into a downlink optical signal through a modulator, wherein a preset second frequency interval exists between the optical wavelength of the downlink optical signal and the central wavelength of the laser, and the first frequency interval is equal to the second frequency interval; outputting the downlink optical signal to the terminal through a circulator, and receiving an uplink optical signal from the terminal; and dividing a part of downlink laser to be used as local oscillation laser of the uplink optical signal to carry out coherent reception on the uplink optical signal.

Meanwhile, the local side also comprises a polarization diversity structure, a photoelectric converter, a digital-to-analog converter and an orthogonal frequency division multiplexing decoder.

The polarization diversity structure is used for modulating a part of the split laser to be used as the polarization state of the local oscillator light and the polarization state of the uplink optical signal, so that the polarization state of the local oscillator light is consistent with the polarization state of the uplink optical signal, and coherent reception is realized.

In the embodiment of the invention, the local side generates a multi-band OFDM electric signal, downlink data information is modulated in a passband, and a certain frequency interval is set between the passband and a baseband (direct current). Here, each subband may correspond to one terminal, or multiple terminals may share one subband, and wideband allocation is completed by using subcarrier scheduling in the subband. The OFDM electric signal modulates a signal on light through a modulator, and a certain frequency interval exists between the wavelength of the signal light and the central wavelength of the laser in the modulated spectrum, and is the same as the frequency interval between a pass band and a baseband of an electric domain. The modulated optical signal passes through the circulator, is sent to the ODN, and reaches each ONU after passing through the splitter.

The first downlink optical signal is divided into two paths after passing through the first circulator 201, wherein one path is used as a second downlink optical signal and is input into the 2 × 2 coupler 203; the other path is processed by the second circulator 204 and then input to the optical filter 205, so as to obtain a third downlink optical signal without signal modulation. The direct current light obtained after the filtering is injected into the reflective photoelectric device 207. The reflective photovoltaic device 207 here serves two functions: firstly, after the direct current light is injected into the reflective photoelectric device 207, the central wavelength output by the reflective photoelectric device 207 is consistent with the central wavelength of the first downlink optical signal; second, the upstream OFDM data information is modulated onto light by the reflective photoelectric device 207, while the reflective photoelectric device 207 amplifies the upstream signal. The modulation concept of the uplink optical signal is consistent with that of the downlink optical signal, the signal is modulated to a passband, and a certain frequency interval is set with a baseband. And similarly, the obtained uplink optical signal modulation spectrum is output, the central wavelength is still direct current light without signal modulation, and the power is obviously amplified.

An optical signal output from the reflective photoelectric device 207 is divided into two paths, wherein one path is input to the first circulator 201 and is sent to the OLT as an uplink optical signal; the other path passes through the optical filter 205 again, and the uplink signal data information is just filtered by the optical filter to obtain an amplified direct current optical signal, which is input to the 2 × 2 coupler 203 through the second circulator 204 to be used as local oscillation light of the second downlink optical signal to perform coherent reception on the second downlink optical signal.

In this embodiment, after the uplink optical signal reaches the OLT, the uplink optical signal passes through the circulator, because the polarization state of the uplink optical signal is random, a polarization diversity structure is needed, and a part of the downlink Laser is split to be used as a local oscillator Laser of the uplink optical signal, so as to perform coherent reception on the uplink data.

In this embodiment, the following advantages are provided at the terminal side: firstly, a laser with high cost and accurately adjustable wavelength is not needed to be used as a local oscillator laser at a terminal side; secondly, the local oscillator optical signal wavelength is the downlink optical signal wavelength, because the local oscillator optical signal wavelength is obtained by injecting the downlink optical signal central wavelength into the reflection-type photoelectric device. After the first downlink optical signal is coherent, the intermediate frequency optical signal is 0Hz, so that the purpose of minimizing the bandwidth required by subsequent electrical appliances is naturally achieved without any wavelength control mechanism; third, the polarization state of the downstream optical signal is random after it is transmitted through the ODN and reaches the termination. A common coherent receiving structure is a polarization diversity method, and two sets of the same structure are used to receive two polarization states of an optical signal respectively. In the invention, the local oscillation optical signal is extracted from the downlink optical signal, the polarization state of the local oscillation optical signal is consistent with that of the downlink optical signal, and correct coherent reception can be completed without a polarization diversity structure. The complexity of the device is doubled; fourth, the reflective photoelectric device is normally operated in a saturation state, and after the reflective photoelectric device erases the downlink optical signal, the uplink data is modulated onto the reflective photoelectric device. Here, because the optical signal to the reflective photoelectric device is direct current light without modulation, the reflective photoelectric device is not required to be saturated (saturation requires higher injected light power), and the uplink data can be directly modulated onto the light. The requirements of the injection reflection type photoelectric device on the optical signal power are reduced, and the downlink optical power budget is obviously improved; fifthly, a structure of a reflection type photoelectric device and an optical filter simultaneously completes the functions of generating and amplifying the downlink local oscillator direct current light and modulating and sending the uplink signal. No additional laser is required as an upstream light source. The optical device required by the terminal side is reduced to the minimum, and the cost advantage is very high.

Example four:

referring to fig. 4, fig. 4 is a structural diagram of another OFDM passive optical network system according to an embodiment of the present invention. As shown in fig. 4, the coherent reception signal system may include the following devices:

the apparatus of fig. 2 has been described in detail in the second embodiment, and will not be described in detail in the fourth embodiment.

Meanwhile, the local side also comprises a photoelectric converter, a digital-to-analog converter and an orthogonal frequency division multiplexing decoder.

The local side in the coherent OFDM passive optical network system further comprises: before the downlink optical signal is output to a terminal through a circulator, modulating the downlink optical signal into a polarization state of a downlink laser, and sending the polarization state down through a polarization beam combiner; before a part of local oscillation laser which is divided from a downlink laser and used as the uplink optical signal is used for carrying out coherent reception on the uplink optical signal, a part of local oscillation laser which is divided from the downlink laser and used as the uplink optical signal passes through a first 90-degree polarization rotator and enters a 2 x 2 coupler of a local side;

the terminal further includes: a second 90-degree polarization rotator is added between the reflective photoelectric device and the circulator 1, so that when the uplink optical signal reaches the polarization beam combiner, the polarization state of the uplink optical signal is perpendicular to the polarization state of the downlink optical signal, and the uplink optical signal is output to the 2 × 2 coupler at the local side from the other port of the polarization beam combiner.

In this embodiment, the downlink data is modulated onto one polarization state (e.g., horizontal polarization direction) of the laser, and sent down through the polarization beam combiner. On the terminal side, a 90-degree polarization rotator is added between the reflective photoelectric device and the first circulator 201, so that when an uplink optical signal reaches the local-side polarization beam combiner, the polarization state is perpendicular to downlink data, and the uplink optical signal is output from the other port of the polarization beam combiner. The downlink laser enters the 2 × 2 coupler after passing through a 90-degree polarization rotator to be coherently received with the uplink optical signal. At this time, the polarization states of the local oscillator light and the signal light are known, and the vibration direction is known. And a polarization diversity structure is not needed, and the complexity of the devices at the local side is reduced.

Example five:

referring to fig. 5, fig. 5 is a structural diagram of another coherent OFDM passive optical network system according to an embodiment of the present invention. The system may include the following devices:

The coherent OFDM passive optical network system also comprises a splitter, wherein the local end is connected with the splitter through an optical distribution network, and the terminal is connected with the splitter.

As a preferable embodiment, the terminal and the local side are connected through a Wavelength Division Multiplexing passive optical network (WDM-PON), a hybrid TDM-WDM PON, or a Coherent PON.

The PON network based on the Splitter is deployed in a large scale, and any upgrade to the network is preferably based on the network architecture and smoothly upgraded. The technology of electric domain high-order modulation such as M-QAM/OFDM is mature, after the large-scale mass production, the technology is realized by ASIC, and the cost is very competitive. The high-order modulation technologies can effectively compress signal frequency spectrums, high-bandwidth signals are compressed and then transmitted and received through the low-bandwidth optical device, and optical cost which occupies the highest PON cost is reduced. Such as 10Gbps with a 2.5G optical system.

Example six:

referring to fig. 6, fig. 6 is a flowchart of a method for coherent signal reception according to an embodiment of the present invention. As shown in fig. 6, the coherent signal receiving method may include the steps of:

601. dividing a first downlink optical signal passing through the circulator into two paths, wherein one path is used as a second downlink optical signal and is input into a 2 multiplied by 2 coupler; and the other path of the optical signal passes through an optical filter to obtain a third downlink optical signal modulated by the direct current no-signal, and passes through a semiconductor optical amplifier to obtain an amplified third downlink optical signal modulated by the direct current no-signal.

In this embodiment of the present invention, the first downlink optical signal is an optical signal sent by the central office to the terminal. The local side generates multi-band OFDM electric signals, downlink data information is modulated in a passband, and a certain frequency interval is set between the downlink data information and a baseband (direct current). Here, each subband may correspond to one terminal, or multiple terminals may share one subband, and wideband allocation is completed by using subcarrier scheduling in the subband. The OFDM electric signal modulates a signal on light through a modulator, and a certain frequency interval exists between the wavelength of the signal light and the central wavelength of the laser in the modulated spectrum, and is the same as the frequency interval between a pass band and a baseband of an electric domain. The modulated optical signal passes through the circulator, is sent to the ODN, and reaches each ONU after passing through the splitter.

At the ONU, the first downlink optical signal is divided into two paths after passing through the circulator, wherein one path is used as a second downlink optical signal and is input into the 2 x 2 coupler; and the other path of the optical signal passes through an optical filter to obtain a third downlink optical signal modulated by the direct current no-signal, and passes through a semiconductor optical amplifier to obtain an amplified third downlink optical signal modulated by the direct current no-signal. The filter is an optical bandpass filter with a center wavelength that is the center wavelength of the downstream laser and the bandwidth is allowed only through the baseband dc component. Because a part of energy of the first downlink optical signal is distributed on the center wavelength without signal modulation (the ratio of the center direct current optical carrier without signal modulation to the signal frequency band is 25 dB), after passing through the optical filter, the signal frequency spectrum component is filtered out, and a direct current (i.e. continuous) optical signal without signal modulation is obtained. Such optical signals conform to local optical conditions as coherent reception.

In this embodiment, the semiconductor optical amplifier has two functions: firstly, after direct current light is injected into a semiconductor optical amplifier, the central wavelength output by the semiconductor optical amplifier is consistent with the central wavelength of a first downlink optical signal; second, the semiconductor optical amplifier amplifies the direct current unmodulated downlink optical signal.

602. Dividing the amplified direct-current signal-free modulated third downlink optical signal into two paths according to a certain proportion, wherein one path is used as local oscillation light of a second downlink optical signal and is input into a 2 x 2 coupler, and the 2 x 2 coupler coherently receives the second downlink optical signal and the local oscillation light of the second downlink optical signal; and inputting the other path of the optical signal into the modulator to obtain a second uplink optical signal.

As a preferable embodiment, the amplified dc non-signal modulated third downlink optical signal is divided into two paths according to a ratio of 1:9, wherein one tenth of the amplified dc non-signal modulated third downlink optical signal is input to a 2 × 2 coupler as local oscillation light of a second downlink optical signal, and the 2 × 2 coupler coherently receives the second downlink optical signal and the local oscillation light of the second downlink optical signal; and inputting the ninth amplified direct-current non-signal-modulated third downlink optical signal into a modulator to obtain a second uplink optical signal.

603. And directly loading the first uplink optical signal to the other path separated from the amplified direct-current signal-free modulated third downlink signal through the modulator, thereby acquiring a second uplink optical signal and outputting the second uplink optical signal to the OLT.

The embodiment of the invention has the following advantages: firstly, a laser with high cost and accurately adjustable wavelength is not needed to be used as a local oscillator laser at a terminal side; secondly, the local oscillator optical signal wavelength is the downlink optical signal wavelength, which is obtained by injecting the downlink optical signal center wavelength into the SOA. After the first downlink optical signal is coherent, the intermediate frequency optical signal is 0Hz, so that the purpose of minimizing the bandwidth required by subsequent electrical appliances is naturally achieved without any wavelength control mechanism; third, the polarization state of the downstream optical signal is random after it is transmitted through the ODN and reaches the termination. A common coherent receiving structure is a polarization diversity method, and two sets of the same structure are used to receive two polarization states of an optical signal respectively. In the invention, the local oscillation optical signal is extracted from the downlink optical signal, the polarization state of the local oscillation optical signal is consistent with that of the downlink optical signal, and correct coherent reception can be completed without a polarization diversity structure. The complexity of the device is doubled; fourthly, a SOA + optical filter + modulator structure simultaneously completes the functions of generating and amplifying the downlink local oscillator direct current light and modulating and sending the uplink signal. No additional laser is required as an upstream light source. The optical device required by the terminal side is reduced to the minimum, and the cost advantage is extremely high; fifthly, after the ONU side is behind the optical filter, the SOA is used for amplifying the direct current light, and then the direct current light is divided into 2 paths, wherein one path enters the 2 x 2 coupler to be used as local oscillation light of the downlink optical signal, and the other path passes through one modulator, and then the uplink signal is modulated onto the light through the modulator, so that the uplink optical signal can be prevented from being filtered by the optical filter again, and the spectrum utilization rate is higher.

Example seven:

referring to fig. 7, fig. 7 is a structural diagram of a coherent signal receiving apparatus according to an embodiment of the present invention. As shown in fig. 7, the coherent reception signal apparatus may include the following:

the circulator 701: for outputting a first downlink optical signal to the first optical splitter 702;

the first optical splitter 702 is configured to split the first downlink optical signal into two paths, where one path is input to the 2 × 2 coupler 706 as a second downlink optical signal; the other path is input to an optical filter 703;

the optical filter 703 is configured to process the other split path of the first downlink optical signal to obtain a third downlink optical signal without signal modulation by dc;

the semiconductor optical amplifier 704 is configured to amplify the dc non-signal modulated third downlink optical signal to obtain an amplified dc non-signal modulated third downlink optical signal;

At the ONU, the first downlink optical signal is divided into two paths after passing through the circulator 701, where one path is input to the 2 × 2 coupler 706 as a second downlink optical signal; the other path passes through an optical filter 703 to obtain a dc non-signal modulated third downlink optical signal, and passes through a semiconductor optical amplifier 704 to obtain an amplified dc non-signal modulated third downlink optical signal. The filter 703 is an optical bandpass filter whose center wavelength is the center wavelength of the downstream laser and whose bandwidth allows only the baseband dc component to pass through. Because a part of energy of the first downlink optical signal is distributed on the center wavelength without signal modulation (the ratio of the center direct current optical carrier without signal modulation to the signal frequency band is 25 dB), after passing through the optical filter, the signal frequency spectrum component is filtered out, and a direct current (i.e. continuous) optical signal without signal modulation is obtained. Such optical signals conform to local optical conditions as coherent reception.

In this embodiment, the semiconductor optical amplifier 704 has two functions: firstly, after direct current light is injected into a semiconductor optical amplifier, the central wavelength output by the semiconductor optical amplifier is consistent with the central wavelength of a first downlink optical signal; second, the semiconductor optical amplifier amplifies the direct current unmodulated downlink optical signal.

A second optical splitter 705, configured to split the amplified dc non-signal modulated third downlink optical signal into two paths, where one path is input to the 2 × 2 coupler 706 as local oscillation light of the second downlink optical signal, and the other path is input to a modulator 707;

the modulator 707 is configured to directly load the first uplink optical signal to another branch of the amplified dc non-signal modulated third downlink optical signal to obtain a second uplink optical signal;

the circulator 701 is further configured to output the second uplink optical signal to the OLT;

and a 2 × 2 coupler 706, configured to perform coherent reception on the second downlink optical signal and the local oscillator light of the second downlink optical signal.

The embodiment of the invention has the following advantages: firstly, a laser with high cost and accurately adjustable wavelength is not needed to be used as a local oscillator laser at a terminal side; secondly, the local oscillator optical signal wavelength is the downlink optical signal wavelength, because the local oscillator optical signal wavelength is obtained by injecting the downlink optical signal center wavelength into the semiconductor optical amplifier. After the first downlink optical signal is coherent, the intermediate frequency optical signal is 0Hz, so that the purpose of minimizing the bandwidth required by subsequent electrical appliances is naturally achieved without any wavelength control mechanism; third, the polarization state of the downstream optical signal is random after it is transmitted through the ODN and reaches the termination. A common coherent receiving structure is a polarization diversity method, and two sets of the same structure are used to receive two polarization states of an optical signal respectively. In the invention, the local oscillation optical signal is extracted from the downlink optical signal, the polarization state of the local oscillation optical signal is consistent with that of the downlink optical signal, and correct coherent reception can be completed without a polarization diversity structure. The complexity of the device is doubled; fourthly, a structure of a semiconductor optical amplifier, an optical filter and a modulator completes the functions of generating and amplifying the downlink local oscillator direct current light and modulating and sending the uplink signal at the same time. No additional laser is required as an upstream light source. The optical device required by the terminal side is reduced to the minimum, and the cost advantage is extremely high; fifthly, after the optical filter is arranged on the ONU side, the semiconductor optical amplifier is used for amplifying the direct current light and then dividing the direct current light into 2 paths, wherein one path enters the 2 x 2 coupler to serve as local oscillation light of the downlink optical signal, and after the other path passes through one modulator, the uplink signal is modulated onto the light through the modulator, so that the uplink optical signal can be prevented from being filtered by the optical filter again, and the spectrum utilization rate is higher.

Example eight:

referring to fig. 8, fig. 8 is a structural diagram of an OFDM passive optical network system according to an embodiment of the present invention. As shown in fig. 8, the OFDM passive optical network system may include the following devices:

a terminal comprising the apparatus of figure 7 and an opto-electrical converter, an analogue mixer, a sine wave generator, a digital-to-analogue converter, an orthogonal frequency division multiplexing decoder;

the apparatus of fig. 7 has been described in detail in embodiment 7, and will not be described in detail in the eighth embodiment.

The photoelectric converter 801 is configured to convert the optical signal output by the 2 × 2 coupler 706 into an analog electrical signal and output the analog electrical signal to the analog mixer 802;

the analog mixer 802 is configured to process the analog electrical signal and a sine wave generated by the sine wave generator 803;

the sine wave generator 803 is configured to generate a sine wave and output the sine wave to the analog mixer 802;

the digital-to-analog converter 804 is configured to convert the analog electrical signal output by the analog mixer 802 into a digital electrical signal and output the digital electrical signal to the orthogonal frequency division multiplexing decoder 805;

the ofdm decoder 805 is used for selecting a digital electrical signal wave of a specific frequency spectrum.

Example nine:

referring to fig. 9, fig. 9 is a structural diagram of another OFDM passive optical network system according to an embodiment of the present invention. As shown in fig. 9, the passive optical network system may include the following devices:

the apparatus of fig. 7 has been described in detail in the seventh embodiment, which will not be reiterated in the ninth embodiment.

Example ten:

referring to fig. 10, fig. 10 is a structural diagram of another coherent OFDM passive optical network system according to an embodiment of the present invention. The system may include the following devices:

the apparatus of fig. 7 has been described in detail in the seventh embodiment, and will not be described in detail in the tenth embodiment.

As a preferable embodiment, the Coherent OFDM passive optical network system is configured such that the terminal and the central office are connected through a WDM-PON, a Hybird TDM-WDM PON, or a Coherent PON.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method of coherently receiving a signal, the method comprising:

receiving a first downlink optical signal sent by a local side device to a terminal device, and dividing the first downlink optical signal into two paths, wherein one path is used as signal light, the other path is used for generating local oscillator light of the signal light, and the signal light and the local oscillator light are subjected to coherent reception;

the dividing of the first downlink optical signal into two paths, where one path is used as signal light, and the local oscillator light for generating the signal light from the other path specifically includes: dividing the first downlink optical signal into two paths, wherein one path is used as a second downlink optical signal to be input into the coupler; filtering the other path to obtain a third downlink optical signal without signal modulation; directly loading the first uplink optical signal to the third downlink optical signal without signal modulation by direct current, and taking the modulated third downlink optical signal as a second uplink optical signal; dividing the second uplink optical signal into two paths, wherein one path is output to local side equipment, the other path is subjected to filtering processing to obtain a third uplink optical signal without direct current signal modulation, and the third uplink optical signal without direct current signal modulation is input to the coupler as local oscillation light of the second downlink optical signal;

or,

the dividing of the first downlink optical signal into two paths, where one path is used as signal light, and the local oscillator light for generating the signal light from the other path specifically includes:

dividing the first downlink optical signal into two paths, wherein one path is used as a second downlink optical signal to be input into the coupler; filtering the other path to obtain a third downlink optical signal without signal modulation of direct current, and obtaining an amplified third downlink optical signal without signal modulation of direct current; dividing the amplified direct-current signal-free modulated third downlink optical signal into two paths according to a certain proportion, wherein one path is used as a local oscillator optical input coupler of the second downlink optical signal; acquiring a second uplink optical signal through the other path; and directly loading the first uplink optical signal to the other path separated by the amplified direct-current signal-modulation-free third downlink signal, and acquiring the second uplink optical signal and outputting the second uplink optical signal to local side equipment.

2. The method of claim 1, further comprising:

3. The method of claim 1, further comprising:

4. The method of claim 2, further comprising:

5. An apparatus for coherent reception of a signal, the apparatus comprising:

a receiving unit, configured to receive a first downlink optical signal input by a central office;

the coupler is used for carrying out coherent reception on the signal light and the local oscillator light;

wherein, the first processing unit specifically comprises: the first circulator is used for outputting a first downlink optical signal to the first optical splitter;

the second circulator is further configured to input a third uplink optical signal modulated by the direct-current no-signal to the coupler as local oscillation light of the second downlink optical signal;

or,

the first processing unit specifically includes: a circulator: the first optical splitter is used for outputting a first downlink optical signal to the first optical splitter;

6. The apparatus of claim 5, further comprising:

and the second processing unit is used for generating an uplink optical signal sent by the terminal equipment to the local side equipment.

7. The apparatus according to claim 5, further comprising a polarization rotator, configured to perform a deflection process on the second uplink optical signal and input the second uplink optical signal to the local-side apparatus, so that a deflection state of the deflected second uplink optical signal is perpendicular to a deflection state of the first downlink optical signal.

8. The apparatus according to claim 6, further comprising a polarization rotator, configured to perform a deflection process on the second uplink optical signal and input the second uplink optical signal to the local-side apparatus, so that a deflection state of the deflected second uplink optical signal is perpendicular to a deflection state of the first downlink optical signal.

9. A terminal device, characterized in that it comprises a device according to any one of claims 5-8.

10. A passive optical network system comprising a terminal device according to claim 9.