CN1980098A - Wave-division multi-plexing light accessing system and data receiving-transmitting method - Google Patents

Abstract

The invention discloses a wavelength division multiplexing optical access system, which is composed of an optical line terminal, a remote node and a plurality of optical network units. Among them, the light source unit of the optical line terminal provides a wide-spectrum light source, and the wide-spectrum optical signal sent by it is divided into spectral lines and then sent to the downlink modulated wave-locked light source to provide a seed wavelength optical signal for the transmission of downlink data of the optical line terminal; the optical network The unit inputs the downlink optical signal demultiplexed by the remote node from the optical line terminal to the uplink modulated wave-locked light source to provide the seed wavelength optical signal for the ONU uplink data transmission. The invention also discloses a data sending and receiving method of the wavelength division multiplexing optical access system. The present invention achieves the purpose of using a low-cost wide-spectrum light source to provide a light source for the uplink and downlink data transmission of the system, reducing the system cost; at the same time, because the uplink and downlink data are sent using the same wavelength, the system saves wavelength resources.

Description

A wavelength division multiplexing optical access system and data sending and receiving method thereof

technical field

The invention relates to the field of optical access technology, in particular to a wavelength division multiplexing optical access system and a data sending and receiving method thereof.

Background technique

At present, many Internet services are connected through dial-up modems, asymmetric digital line subscriber lines, cable modems, and very high-speed digital subscriber loops (Very-high-bit-rate Digital Subscriber Loop, VDSL) with rates ranging from 56Kbps to several Mbps. enter. However, in order to provide various video services, such as high-quality video information services, data transmission requires a bandwidth of about 100 Mbps, which cannot be met with the above-mentioned several access methods. Internet demand is growing rapidly. Passive Optical Network (PON) is a user access network that can meet these new business requirements, and is economical and easy to operate and maintain. As shown in Figure 1, a passive optical network generally includes an optical line terminal located in the central office, an optical distribution network and many optical network units (Optical Network Unit, ONU). According to different PON implementations, PON can be divided into different The type of wavelength division multiplexing passive optical network (Wavelength Divided Multiplexing Passive Optical Network, WDM-PON) is one of them.

WDM-PON has the advantages of huge bandwidth capacity, information security similar to point-to-point communication, simple network structure, and low maintenance costs. However, on the other hand, WDM-PON network devices are expensive, and the cost has been high. WDM-PON proposes that the initial ONU adopts a large number of lasers with different wavelengths, but this will lead to a large storage volume of lasers and ONUs, which is not conducive to operation and maintenance and ONU cost reduction. In order to solve the above problems, many alternative fixed wavelengths have emerged. A low-cost light source technology solution for lasers; at the same time, in order to solve the problem that ONUs cannot be used universally, a colorless ONU solution is proposed. The so-called colorless ONU means that the upstream wavelength of the ONU is not determined by the ONU's own hardware, but the optical line terminal provides the ONU with a seed wavelength optical signal of a specific wavelength, and the wavelength of the laser on the ONU locks the wavelength of the seed wavelength optical signal Or the ONU performs reflection amplification on the seed wavelength optical signal, and uses the wavelength-locked or reflection-amplified laser to transmit upstream data, so that the upstream wavelength of the ONU will have nothing to do with the ONU's own hardware, so that the ONU can be used universally.

As shown in FIG. 2 , it is a schematic diagram of an existing low-cost WDM-PON system architecture based on the above principles. In this technical solution, the wide-spectrum light source 2 provides a light source for the transmission of downlink data of the optical line terminal, and the wide-spectrum light source 1 provides a light source for the transmission of ONU’s uplink data, wherein the two wide-spectrum light sources must meet the requirement of arrayed waveguide grating (Arrayed Waveguides Grating, AWG) 1 and Arrayed Waveguide Grating 2 Free Spectral Range (Free Spectral Range, FSR) requirements. Wherein, after the wide-spectrum light output by the wide-spectrum light source 2 is divided by the spectral line of AWG1, it will output seed wavelength optical signals of different wavelengths for each downlink wave-locking light source of the OLT, as shown in Figure 2. The downlink wave-locking light source will lock or Reflect and amplify the input seed wavelength optical signal (λ1~λn), and output the laser for transmitting the downlink data, and at the same time, the downlink data can be directly modulated onto the laser signal and sent out. The transmission of the upstream data of the ONU is similar to the transmission of the downstream data of the optical line terminal, the difference is that the wavelength of the seed wavelength optical signal input to the upstream locking light source of each ONU is different from the wavelength of the seed wavelength optical signal input to the downstream locking light source FSR.

This technical solution uses low-cost wide-spectrum light sources, AWG's spectral line segmentation characteristics, AWG's FSR periodicity characteristics and wave-locked light sources to achieve the purpose of providing light sources for the entire WDM-PON system using only two wide-spectrum light sources , which reduces the cost of the whole system, however, this technical solution also has the following disadvantages:

In this technical solution, the wide-spectrum light source 1 and the wide-spectrum light source 2 must meet the FSR requirements of AWG1 and AWG2, and this special requirement will increase the cost of the wide-spectrum light source.

In addition, in this technical solution, the uplink and downlink data are transmitted using different wavelengths, which occupy more wavelength resources.

Contents of the invention

The technical problem to be solved by the present invention is to provide a wavelength division multiplexing optical access system, which uses a low-cost wide-spectrum light source to realize the provision of seed wavelength optical signals for the downlink data transmission of the optical line terminal and the uplink data transmission of the ONU , and the uplink and downlink data are transmitted at the same wavelength.

In order to solve the above technical problems, the present invention proposes a wavelength division multiplexing optical access system, which includes an optical line terminal, a remote node connected to the optical line terminal with an optical fiber, and multiple an optical network unit; wherein, the optical line terminal includes a downlink modulation transmitting unit, an uplink receiving unit and a light source unit, and the downlink modulation transmitting unit includes a plurality of downlink modulation wave-locking light sources; the remote node includes a first Three arrays of waveguide gratings; each optical network unit includes an uplink modulation transmitting unit and a downlink receiving unit, and the uplink modulation transmitting unit includes an uplink modulation wave-locking light source; wherein:

The light source unit includes a wide-spectrum light source, and the wide-spectrum optical signal generated by it is divided into spectral lines to generate a seed wavelength optical signal;

The downlink modulation and transmitting unit uses the seed wavelength optical signal to generate a downlink optical signal, carries downlink data on the downlink optical signal and transmits it;

The optical network unit receives a downlink optical signal from the optical line terminal via the third arrayed waveguide grating, and the uplink modulation and transmitting unit generates an uplink optical signal by using the downlink optical signal, and carries uplink data on the Uplink optical signal and transmit.

Wherein, the optical line terminal further includes: a transmission control unit, configured to control a downlink modulation-locked light source corresponding to the optical network unit to send a corresponding downlink optical signal according to the online status of the optical network unit.

The downlink modulation transmitting unit further includes: a plurality of encoding units, which are used to respectively perform inverse return-to-zero encoding on multiple channels of downlink data, and then send them to the corresponding plurality of downlink modulation wave-locking light sources respectively.

Correspondingly, the present invention provides a method for transmitting and receiving data in a wavelength division multiplexing optical access system, the method comprising the following steps:

a. The wide-spectrum light output by the wide-spectrum light source is divided into spectral lines and transmitted as a seed wavelength optical signal to each downlink modulated wave-locking light source;

b. The optical line terminal controls the downlink modulation-locked light source corresponding to each optical network unit to send a corresponding downlink optical signal according to the status of each optical network unit;

c. The optical network unit divides the received downlink optical signal into two parts, one part is used to restore the downlink data, and the other part is transmitted to its uplink modulated wave-locked light source as a seed wavelength optical signal;

d. The uplink modulated wave-locking light source emits an optical signal with the same wavelength as the seed wavelength optical signal, and modulates uplink data onto the optical signal for transmission.

Implement the present invention, have following beneficial effect:

The invention proposes a wavelength division multiplexing optical access system and its data sending and receiving method. The light source unit of the optical line terminal provides a wide-spectrum light source. The light source provides a seed wavelength optical signal for the generation of the downlink optical signal of the optical line terminal; the optical network unit inputs a part of the downlink optical signal demultiplexed by the remote node from the optical line terminal to the uplink modulated wave-locked light source for The transmission of the ONU uplink signal provides a seed wavelength optical signal, thereby realizing the purpose of using a low-cost wide-spectrum light source to provide a light source for the uplink and downlink signal transmission of the system, reducing the system cost; at the same time, because the uplink and downlink signals are sent using are the same wavelength, so that the system saves wavelength resources.

Description of drawings

FIG. 1 is a schematic diagram of the system composition of a passive optical network in the prior art;

FIG. 2 is a schematic diagram of the system composition of WDM-PON in the prior art;

Fig. 3 is a schematic diagram of the composition of the wavelength division multiplexing optical access system in the present invention;

Fig. 4 is a schematic diagram of an optical signal output when NRZ encoding is used for downlink data in the present invention;

5 is a schematic diagram of an optical signal output when downlink data is encoded with IRZ in the present invention;

Fig. 6 is a schematic flow chart of the data sending and receiving method of the wavelength division multiplexing optical access system in the present invention;

FIG. 7 is a schematic flowchart of specific steps of step S6002 in FIG. 6 .

Detailed ways

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

Fig. 3 shows a schematic diagram of the composition of the wavelength division multiplexing optical access system in the present invention. The system is composed of an optical line terminal 1 , a remote node 2 and a plurality of optical network units 3 . The optical line terminal 1 modulates and transmits multiple downlink data, and at the same time multiplexes it into a downlink mixed optical signal and sends it to the remote node 2. The remote node 2 demultiplexes the downlink mixed optical signal into multiple channels of different wavelengths. The optical signals are transmitted to the corresponding optical network units 3 respectively; at the same time, the optical network unit 3 modulates the uplink data to be sent and sends it to the remote node 2, and the remote node 2 multiplexes it into an uplink mixed optical signal and transmits it to Optical line terminal 1. Thus, the uplink and downlink data transmission of the system is completed.

The optical line terminal 1 includes a downlink modulation and transmitting unit 11 for modulating and sending downlink data, an uplink receiving module 12 for receiving and demodulating uplink data, and an uplink receiving module 12 for providing seed wavelength optical signals for the entire wavelength division multiplexing optical access system The light source unit 13. The downlink modulation transmitting unit 11 includes a plurality of downlink modulation wave-locking light sources 111 , an encoding unit 112 , and a first arrayed waveguide grating 113 . The light source unit 13 includes a broadband light source 131 and an optical bandpass filter 132. After the broadband light emitted by the broadband light source 131 undergoes spectral shaping by the optical bandpass filter 132, it is input into the downlink modulation emission unit 11 and passed through the first array The waveguide grating 113 divides the spectral lines to generate narrow-band laser signals with the center wavelengths of λ1~λn respectively, which are respectively input as seed wavelength optical signals to the corresponding n downlink modulation wave-locking light sources 111, and the downlink modulation wave-locking light sources 111 complete the adjustment of the seed wavelengths. After the wavelength optical signal is locked or reflected and amplified, an optical signal with the same wavelength as the seed wavelength optical signal is output. At the same time, the downlink modulation locking light source 111 also has the function of a modulator. The n downlink data are respectively encoded by n encoding units 112 and then input into n downlink modulation locking light sources 111 respectively. The downlink modulation locking light source 111 encodes the encoded data It is modulated onto the optical signal output after its wave-locking or reflection and amplification and then emitted. The first arrayed waveguide grating 113 receives optical signals carrying downlink data from each downlink modulated wave-locking light source 111 , multiplexes them into a downlink mixed optical signal, and sends it to the remote node 2 through an optical fiber.

The remote node 2 includes a third arrayed waveguide grating 21, which receives the downlink mixed optical signal transmitted from the optical line terminal 1, demultiplexes it into n optical signals λ1-λn of different wavelengths, and transmits them to the corresponding The demodulation process is performed in the n optical network units 3, and at the same time, it is also used as a seed wavelength optical signal sent as uplink data.

The optical network unit 3 includes an uplink modulating and transmitting unit 31 and a downlink receiving unit 32 . The uplink modulation transmitting unit 31 includes an uplink modulation wave-locking light source 311 . Here, in order to make the optical signal from the third arrayed waveguide grating 21 not only be used for receiving and demodulating but also be used as the seed wavelength optical signal of the uplink modulation wave-locking light source 311, a coupler 33 can be used to divide the optical signal into two parts, one part It is transmitted to the downlink receiving unit 32 , and the other part is transmitted to the uplink modulating wave-locking light source 311 of the uplink modulating and transmitting unit 31 . The uplink modulation locking light source 311 outputs an optical signal having the same wavelength as the seed wavelength optical signal after locking or reflecting and amplifying the seed wavelength optical signal. It can be seen from this that each uplink modulated wave-locked light source 311 or each optical network unit 3 corresponds to a downlink modulated wave-locked light source 111, and the wavelengths of their seed wavelength optical signals are the same, the difference is that The seed wavelength optical signal of the downlink modulated wave-locked light source 111 is an optical signal of a specific wavelength after the broadband optical signal is divided by spectral lines, and the corresponding seed wavelength optical signal of the uplink modulated wave-locked light source 311 is from the downlink modulated lock An optical signal of the wave source 111 carrying downlink data. The uplink modulation wave-locking light source 311 also has a modulation function, and modulates and sends the uplink data to be sent. The coupler 33 receives the optical signal carrying uplink data and transmits it to the remote node 2 .

The third arrayed waveguide grating 21 of the remote node 2 multiplexes the optical signals transmitted from each optical network unit 3 into an uplink mixed optical signal and transmits it to the uplink receiving unit 12 of the optical line terminal 1 .

The uplink receiving unit 12 includes a second arrayed waveguide grating 121 and a plurality of demodulation units 122 . The second arrayed waveguide grating 121 demultiplexes the uplink wavelength division multiplexed optical signal into a plurality of uplink data-carrying optical signals λ1˜λn of different wavelengths, and respectively inputs n demodulation units 122 for photoelectric conversion and demodulation.

In order to facilitate bidirectional transmission of optical signals in one optical fiber, as an implementation manner, the optical line terminal 1 further includes a first circulator 14 and a second circulator 15 . The first circulator 14 is used to transmit the optical signal from the light source unit 13 to the downlink modulation and transmitting unit 11 , receive the downlink optical signal from the downlink modulation and transmission unit 11 and transmit it to the second circulator 15 . The second circulator 15 receives the downlink optical signal from the first circulator 14 and transmits it to the remote node 2 , receives the uplink optical signal from the remote node 2 and transmits it to the uplink receiving unit 12 .

In practical applications, in order to make the optical power of the downlink optical signal after long-distance transmission greater than the minimum threshold required by the ONU uplink modulated wave-locking light source 311, the downlink optical signal output by the downlink modulated transmitting unit 11 is usually optically amplified, so , the optical line terminal 1 further includes an optical amplifier 17, located between the first circulator 14 and the second circulator 15, for amplifying the downlink mixed optical signal.

In summary, it can be seen that in the present invention, the downlink optical signal carrying the downlink data can be used as the seed wavelength optical signal of the ONU uplink modulated wave-locking light source 311 . Since the optical network unit 3 itself does not generate laser light of a specific wavelength required for sending uplink data, the ONU uplink modulates the wave-locking light source 311 only when there is injected light (seed wavelength optical signal) and the optical power of the seed wavelength optical signal is greater than the minimum threshold In this case, the laser with a specific wavelength for sending uplink data can be output. If the encoding unit 112 of the optical line terminal 1 adopts general non-return to zero encoding (Not Return to Zero, NRZ) for the downlink data, as shown in Figure 4, then when the downlink data bit is "0", the downlink modulation locks The light source 111 will have no light output (or only have a very small power light output, which is related to the extinction ratio), at this time, the optical power of the seed wavelength optical signal injected into the ONU uplink modulation wave-locking light source 311 will be lower than its required minimum threshold As a result, there is no laser output. Therefore, the optical network unit 3 can only modulate the uplink data when the downlink data bit is "1" (the uplink modulation wave-locking light source 311 only has laser output when the downlink data bit is "1"), so that the optical network unit 3 It becomes very difficult to send uplink data. In order to solve this problem, in the present invention, the encoding unit 112 of the optical line terminal 1 adopts an encoding method called Inverse Return to Zero (IRZ) for downlink data, as shown in FIG. 5 , by encoding Make the downlink modulation locking light source 111 of the optical line terminal 1 have a strong enough laser output regardless of whether the downlink data bit is "0" or "1", so that the ONU uplink modulation locking light source 311 no matter whether the downlink data bit is "0" Whether it is "1" or "1" has a laser output, so that the transmission of uplink data is not limited to whether the downlink data bit is "0" or "1".

In addition, since the generation of the uplink optical signal of the optical network unit 3 depends on the presence or absence of downlink data, when a certain downlink modulated wave-locking light source 111 has no downlink data to send, it needs to be controlled to send idle frames, and its corresponding optical The network unit 3 provides the optical signal of the seed wavelength to realize the sending of its uplink data until it goes offline. In addition, since the optical network unit 3 itself has no light source, in order to find that the optical network unit 3 is online in time, when the optical network unit 3 is offline, the downlink modulation locking light source 111 corresponding to the optical network unit 3 must periodically send a discovery frame, thereby The seed wavelength optical signal is provided for the optical network unit 3 to send a network access request to the optical line terminal 1 .

Therefore, in practical applications, the optical line terminal 1 further includes a transmission control unit 16, as shown in FIG. The optical signal is used to ensure that the uplink data of the optical network unit 3 is sent out in time. The emission control unit 16 further includes a detection unit 161 and a control unit 162 . The detection unit 161 is used to detect whether the downlink modulation locking light source has downlink data transmission and whether the optical network unit 3 is online, and sends the detection result to the control unit 162; the control unit 162 is used to generate a pair with the optical network unit 3 according to the detection result Corresponding downlink modulation control command of the wave-locking light source 111; when the detection result is online and there is downlink data to send, control it to send a wavelength division multiplexing optical signal carrying downlink data to the optical network unit 3; when the detection result is online but When the downlink modulated wave-locked light source 111 corresponding to the optical network unit 3 has no downlink data to send, the control unit 162 controls the downlink modulated wave-locked light source 111 to send an idle frame signal; 3 Send a discovery frame. The discovery frame can be sent periodically, and the length of the period can be set according to the needs of the user, for example, it can be several seconds or several minutes.

There are many implementation manners for the detection unit 161 to detect whether the optical network unit 3 is online, and here only one preferred implementation manner is taken as an example for illustration. In this preferred embodiment, when the ONU 3 goes online, it will send a network access request message to the OLT 1, and when it is offline normally, it will send an offline notification message to the OLT 1. The detection unit 161 is connected to the uplink receiving unit 12, and when it finds that the uplink receiving unit 12 has received a network access request sent by a certain optical network unit 3, it records the state of the optical network unit 3 as online, and simultaneously notifies the control Unit 162; similarly, when it finds that the uplink receiving unit 12 has received an offline notification sent by a certain optical network unit 3, it records the state of the optical network unit 3 as offline, and notifies the control unit 162 at the same time. For the situation that the optical network unit 3 is offline abnormally, there is another detection method: there are timers corresponding to each optical network unit 3 in the uplink receiving unit 12; when the uplink receiving unit 12 finds that there is no The signal sent by a certain optical network unit 3 starts the timer corresponding to the optical network unit 3, if the uplink receiving unit 12 has not received the optical signal of the optical network unit 3 within the time preset by the timer, then The detection unit 161 considers that the optical network unit 3 is offline, records its status as offline, and notifies the control unit 162 at the same time. In addition, the detection unit also monitors in real time the sending buffers of the downlink modulating wave-locking light sources in the downlink modulating and transmitting unit, and will notify the control unit when it detects that the optical network unit 3 is online but there is no downlink data waiting to be sent in its sending buffer 162 Fill the sending buffer with idle frame data, so as to control the downlink modulation wave-locking light source to send downlink idle frames.

In addition, in order to better improve the performance of the optical line terminal 1 receiving the uplink data of the optical network unit 3 and reduce the bit error rate of uplink data reception, the downlink receiving unit 32 of the optical network unit 3 also includes a clock extraction unit 321, the The uplink modulation and transmitting unit 31 also includes a sending synchronization unit 312 . The clock extraction unit 321 is used to extract the clock signal in the downlink data and send it to the transmission synchronization unit 312; the transmission synchronization unit 312 is used to control the transmission of the uplink data according to the clock signal, so as to synchronize the transmission of the uplink data and the downlink optical signal.

As an implementation manner, the downlink modulated wave-locked light source 111 and the uplink modulated wave-locked light source 311 in the present invention may use wavelength-locked F-PLD lasers.

As another implementation manner, the downlink modulated wave-locked light source 111 and the uplink modulated wave-locked light source 311 in the present invention may use RSOA lasers.

Different lasers may be used for the downlink modulated wave-locked light source 111 and the uplink modulated wave-locked light source 311 .

Correspondingly, the present invention provides a method for realizing data transmission and reception on the above-mentioned wavelength division multiplexing optical access system, as shown in FIG. 6 . The method includes the following steps:

Step S6001: The wide-spectrum light output by the wide-spectrum light source is divided into spectral lines and then transmitted as a seed wavelength optical signal to each downlink modulated wave-locking light source.

The wide-spectrum light source emits wide-spectrum light, and the wide-spectrum light generates multiple narrow-band laser signals with different central wavelengths after being divided by spectral lines, which are respectively input to each downlink modulated wave-locking light source as seed wavelength optical signals.

Step S6002: The optical line terminal controls its corresponding downlink modulation-locked light source to send corresponding downlink optical signals according to the state of each optical network unit.

The downlink modulated wave-locking light source locks or reflects and amplifies the seed wavelength optical signal, and outputs a downlink optical signal with the same wavelength as the seed wavelength optical signal. However, in order to enable the data of the corresponding ONU to be sent out in time, the OLT needs to control the downlink modulation wave-locking light source to send different downlink optical signals to the ONU according to the online status of the ONU, so as to timely The optical network unit provides the required seed wavelength optical signal.

As an implementation, the optical line terminal can multiplex the optical signals of each downlink modulated wave-locking light source into a mixed downlink optical signal for long-distance transmission on the optical fiber, and then demultiplex and send it to the corresponding optical network unit .

Step S6003: the optical network unit divides the received downlink optical signal into two parts, one part is used to restore downlink data, and the other part is transmitted to its uplink modulation locking light source as a seed wavelength optical signal.

Step S6004: The uplink modulated wave-locking light source emits an optical signal with the same wavelength as the seed wavelength optical signal, and modulates uplink data onto the optical signal for transmission.

As shown in Figure 7, step S6002 in the aforementioned Figure 6 specifically includes the following steps:

Step S7001: the optical line terminal detects whether the optical network unit is online, if the detection result is yes, execute step S7002, otherwise, execute step S7005.

Step S7002: the optical line terminal judges whether the downlink modulated wave-locking light source corresponding to the optical network unit has downlink data to be sent, if the judgment result is yes, execute step S7003, otherwise, execute step S7004.

Step S7003: the optical line terminal controls the downlink modulation-locked light source to modulate the coded downlink data onto the optical signal sent by it and emit it.

This step also includes: performing reverse return-to-zero coding on the downlink data by the optical line terminal.

Step S7004: the optical line terminal controls the downlink modulated wave-locked light source to emit an idle frame optical signal.

Step S7005: the optical line terminal controls the downlink modulated wave-locked light source to transmit the discovery frame optical signal.

The discovery frame can be transmitted periodically, and the length of the period can be set according to the needs of the user, for example, it can be several seconds or several minutes.

The above disclosures are only preferred embodiments of the present invention, and certainly cannot limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (13)

1. A wavelength division multiplexing optical access system, comprising an optical line terminal, a remote node connected to the optical line terminal with an optical fiber, and a plurality of optical network units connected to the remote node with an optical fiber; wherein, the The optical line terminal includes a downlink modulation transmitting unit, an uplink receiving unit and a light source unit, the downlink modulation transmitting unit includes a plurality of downlink modulation wave-locking light sources; the remote node includes a third arrayed waveguide grating; each optical The network unit includes an uplink modulation and transmitting unit and a downlink receiving unit, and the uplink modulation and transmitting unit includes an uplink modulation and wave-locking light source; it is characterized in that: The light source unit includes a wide-spectrum light source, and the wide-spectrum optical signal generated by it is divided into spectral lines to generate a seed wavelength optical signal; The downlink modulation and transmitting unit uses the seed wavelength optical signal to generate a downlink optical signal, carries downlink data on the downlink optical signal and transmits it; The optical network unit receives the downlink optical signal from the optical line terminal through the third arrayed waveguide grating, the uplink modulation and transmitting unit generates an uplink optical signal by using the downlink optical signal, and carries the uplink data on the and transmit the above-mentioned uplink optical signal. 2. The wavelength division multiplexing optical access system according to claim 1, wherein the optical line terminal further comprises: The transmission control unit is configured to control the downlink modulation-locked light source corresponding to the optical network unit to send a corresponding downlink optical signal according to the online status of the optical network unit. 3. The wavelength division multiplexing optical access system according to claim 2, wherein the transmission control unit further comprises a detection unit and a control unit, wherein: The detection unit is used to detect the online status of the optical network unit, and send the detection result to the control unit; The control unit is used to generate a control command for the downlink modulation wave-locking light source according to the detection result; when the detection result is online and there is downlink data waiting to be sent, control the downlink modulation wave-locking light source to transmit the modulated A downlink optical signal of downlink data; when the detection result is offline, control the downlink modulated wave-locked light source to send a discovery frame optical signal. 4. The wavelength division multiplexing optical access system according to claim 3, wherein when the detection result is online, but the downlink modulated wave-locked light source corresponding to the optical network unit has no downlink data waiting to be sent, the The control unit controls the downlink modulated wave-locked light source to send an idle frame optical signal. 5. The wavelength division multiplexing optical access system according to any one of claims 1 to 4, wherein the optical line terminal further includes a first circulator and a second circulator, wherein: The first circulator is used to transmit the optical signal output by the broadband light source to the downlink modulation and transmitting unit, and is used to receive the downlink optical signal output by the downlink modulation and transmission unit, and transmit it to the second circulator; The second circulator is used to receive the downlink optical signal and transmit it to the remote node, and is used to receive the uplink optical signal sent from the remote node and transmit it to the uplink receiving unit. 6. The wavelength division multiplexing optical access system according to any one of claims 1 to 4, wherein the downlink modulation and transmitting unit further includes: A plurality of encoding units are configured to respectively perform inverse-return-to-zero encoding on multiple channels of downlink data, and then send them to the corresponding plurality of downlink modulated wave-locking light sources respectively. 7. The wavelength division multiplexing optical access system according to any one of claims 1 to 4, wherein the downlink modulation and transmitting unit includes: The first arrayed waveguide grating is used to divide the spectral line of the broadband optical signal output by the broadband light source into a plurality of optical signals of different wavelengths, which are respectively transmitted to the corresponding plurality of downlink modulated wave-locking light sources, and used for receiving The downlink optical signals from the plurality of downlink modulated wave-locked light sources are multiplexed into one downlink mixed optical signal and then transmitted. 8. The wavelength division multiplexing optical access system according to any one of claims 1 to 4, wherein the uplink receiving unit includes a second arrayed waveguide grating and multiple demodulation units, wherein: The second arrayed waveguide grating is used to receive the uplink optical signal from the remote node, demultiplex it into a plurality of optical signals of different wavelengths, and transmit them to the plurality of demodulation units respectively; The demodulation unit is used for performing photoelectric conversion and demodulation processing on the received optical signal. 9. The wavelength division multiplexing optical access system according to any one of claims 1 to 4, wherein the optical network unit includes: The coupler is used to receive the optical signal from the third arrayed waveguide grating, divide it into two optical signals, and transmit them to the downlink receiving unit and the uplink modulating wave-locking light source of the optical network unit respectively. 10. The wavelength division multiplexing optical access system according to any one of claims 1 to 4, characterized in that, the downlink receiving unit also includes a clock extraction unit, and the uplink modulation transmitting unit also includes a transmission synchronization unit unit, where: The clock extraction unit is used to extract the clock signal in the downlink data and send it to the sending synchronization unit; The sending synchronization unit is used for controlling the sending of uplink data according to the clock signal. 11. A method for transmitting and receiving data in a wavelength division multiplexing optical access system, characterized in that the method comprises the following steps: a. The wide-spectrum light output by the wide-spectrum light source is divided into spectral lines to form a seed wavelength optical signal, and is transmitted to each downlink modulated wave-locking light source; b. The optical line terminal controls the downlink modulation-locked light source corresponding to each optical network unit to send a corresponding downlink optical signal according to the status of each optical network unit; c. The optical network unit divides the received downlink optical signal into two parts, one part is used to restore the downlink data, and the other part is transmitted to its uplink modulated wave-locked light source as a seed wavelength optical signal; d. The uplink modulated wave-locking light source emits an optical signal with the same wavelength as the seed wavelength optical signal, and modulates uplink data onto the optical signal for transmission. 12. The method for transmitting and receiving data in a wavelength division multiplexing optical access system according to claim 11, wherein said step b specifically comprises the following steps: b1. The optical line terminal detects whether the optical network unit is online, and if the detection result is yes, execute step b2; otherwise, the optical line terminal controls the downlink modulated wave-locking light source corresponding to the optical network unit to transmit a discovery frame optical signal; b2. The optical line terminal judges whether the downlink modulating wave-locking light source corresponding to the optical network unit has downlink data to be sent, if the judgment result is yes, execute step b3, otherwise, execute step b4; b3. The optical line terminal controls the downlink modulation-locked light source to modulate the encoded downlink data onto the optical signal sent by it and emit it; b4. The optical line terminal controls the downlink modulated wave-locked light source to transmit an idle frame optical signal. 13. The method for transmitting and receiving data in a wavelength division multiplexing optical access system according to claim 12, characterized in that said step b3 further comprises: said optical line terminal performing reverse return-to-zero encoding on downlink data.

Images