CN112532335A

CN112532335A - Wavelength control method for ultra-dense wavelength division multiplexing coherent light access system

Info

Publication number: CN112532335A
Application number: CN202011312417.3A
Authority: CN
Inventors: 胡保民; 唐子坚; 李�浩; 赵华
Original assignee: Shenzhen C-Data Technology Co ltd
Current assignee: Shenzhen C-Data Technology Co ltd
Priority date: 2020-11-20
Filing date: 2020-11-20
Publication date: 2021-03-19
Anticipated expiration: 2040-11-20
Also published as: CN112532335B

Abstract

The invention discloses a wavelength control method of an ultra-dense wavelength division multiplexing coherent light access system, which needs to maintain a wavelength allocation table at an OLT side, maintain a wavelength state table at an ONU side, and then complete the work of ONU registration, wavelength allocation and the like without manual intervention through an OLT downlink GATE frame, a REGISTER frame and a TUNE frame, and an ONU uplink REGISTER _ REQ frame and a REGISTER _ ACK frame.

Description

Wavelength control method for ultra-dense wavelength division multiplexing coherent light access system

Technical Field

The invention relates to the technical field of optical access networks, in particular to a wavelength control method of an ultra-dense wavelength division multiplexing coherent optical access system.

Background

The conventional WDM-PON technology is shown in fig. 1. The Remote Node of fig. 1 uses AWG with only one wavelength on each branch. The wavelength of each ONU (optical network) is fixed (determined by the port of AWG 2), which is inconvenient for opening and maintenance, and the scheme can not reuse the optical splitter widely deployed by operators. To this end, the applicant disclosed on the same day as the present patent application an ultra-dense wavelength division multiplexing system of fig. 2, which can greatly increase the optical power budget due to the introduction of coherent technology, so that the ODN technology (mainly composed of optical splitters and optical fiber cables) that has been widely deployed by operators can be reused. The uplink and downlink wavelengths of the 32 channels on the OLT side of the system shown in fig. 2 are fixed, and the wavelengths on the ONU side are tunable (i.e., colorless), so that the system can be conveniently deployed and maintained. In order to achieve the purpose of automatic wavelength allocation and registration of the ONU and reduce or avoid manual intervention, a wavelength control method is needed, and the present invention is developed based on this.

Disclosure of Invention

The invention provides a wavelength control method of an ultra-dense wavelength division multiplexing coherent optical access system aiming at the problem of automatic wavelength allocation and registration of the ONU of the ultra-dense wavelength division multiplexing coherent optical access system, thereby realizing the ONU registration and wavelength allocation without manual intervention.

In order to achieve the purpose, the specific technical scheme of the invention is as follows:

a wavelength control method of an ultra-dense wavelength division multiplexing coherent optical access system is characterized in that a coherent multi-wavelength MAC control sublayer (CMWMC sublayer) is added between an MAC CLIENT sublayer and an OAM sublayer of an Ethernet protocol stack to coordinate the access of a plurality of ONUs. A CMWMC sublayer needs to maintain a wavelength allocation table at an OLT side, an ONU side maintains a wavelength state table, then downstream OAM frames of the OLT comprise GATE frames, REGISTER frames and TUNE frames, upstream OAM frames of the ONU comprise REGISTER _ REQ frames and REGISTER _ ACK frames, and the ONU registration, wavelength allocation and other work without manual intervention can be completed by combining a timer; the aged wavelength allocation table can be cleaned in time by combining an overtime mechanism of the timer; and by combining the OLT and the ONU nonvolatile memories, the ONU registration and the wavelength allocation can be rapidly realized. The specific scheme is as follows:

(1) the sublayer OLT side maintains a 32-row wavelength allocation table as in the table below. The table may be stored in a non-volatile memory of the OLT, and the "wavelength identifier" and the "access ONU MAC address" retain the last accessed wavelength after the OLT machine is restarted. Each row of data (1-32 wavelengths) is provided with a Tage timer, the timer of the MAC non-empty row is maximized after being electrified, then 1 is continuously reduced, when the timer is reduced to 0, the row is aged (the wavelength is recycled), and all data in the row are emptied; and when the OLT receives an ONU handshake response REGISTER _ REQ or REGISTER _ ACK frame, resetting the local line timer to the maximum value.

Wavelength identification	Access ONU MAC	Access time stamp	Aging timer
					1	AA:BB:CC:DD:EE:FF	T1	Tage
2
				…	…	…	…
m
				…	…	…	…
32

(2) The sublayer maintains a 32-row wavelength state table at the ONU side, as in the table below. The table may be stored in the non-volatile memory of the ONU, and the registration success (or historical registration success) status column is kept after the ONU machine restarts, and the attempt registration column is cleared (i.e. 0).

(3) After the OLT is started, the m (m is the wavelength identification value, m is more than or equal to 1 and less than or equal to 32) MAC Client at the OLT side calls the CMWMC sublayer primitive to inquire the m row of the table:

a) if the MAC of the line is found to be null, a timer Tgate of decreasing 1 is set, and the transmit GATE frame broadcasts the following: "is the mth wavelength channel free, is there an ONU to access? ". When the Tgate timer is cleared, the REGISTER _ REQ frame (including the MAC of the response ONU)) is not received, the Tgate is reset, and the GATE frame is continuously sent.

b) If the row MAC is found to be not empty and the MAC address is legal, a REGISTER frame is periodically sent (assuming a period of Talive) to broadcast the following: "is the mth wavelength channel registered by an ONU with MAC address MACm, does other ONUs not tune to the channel, is the MACm ONU online or continuously online? "the ONU should reply with a REISTER _ ACK frame response in time. This process is repeated with a period of Talive.

The GATE frame and the REGISTER frame of the m-th wavelength channel can be monitored only by the ONU tuned to the m-th wavelength channel, and the other ONUs can receive the optical signal through the optical splitter, but cannot know the signal content because the ONU is not tuned to the m-th wavelength channel.

(4) After a certain ONU at a user side is started, the local optical wavelength channel identifier in the nonvolatile memory is checked, if the local optical wavelength channel identifier is not empty, the recording channel is directly tuned, otherwise, the nth optical wavelength channel is randomly tuned, meanwhile, the uplink optical switch is kept to be disconnected by default, and the ONU monitors the downlink broadcast frame of the nth optical wavelength channel of the optical splitter.

a) Monitoring a Gate frame, randomly delaying for a period of time (a binary random evasion algorithm can take a value, the maximum value is Tgate, and the minimum value is Tgate. times. 1/231), closing an uplink optical switch, setting a timing Tack (Tack should be greater than Tgate) which continuously decreases by 1, and replying the following content by using a REGISTER _ REQ frame: "the MAC address of the local machine is MACn, hopes to access the nth wavelength channel, please reply". If the REGISTER frame is not received when the Tack is zero, the uplink optical switch is closed, another wavelength channel y is randomly tuned to (y is not equal to all channel identifiers which are tried before but are not successful), and the monitoring action is repeated.

b) Monitoring a REGISTER frame, and comparing whether the MAC address of the ONU is consistent with the MAC address in the frame: if the MAC addresses are consistent, the uplink optical switch is closed (if the uplink optical switch is closed before, the uplink optical switch is kept unchanged), the ONU nonvolatile memory records the local wavelength channel identifier, and replies a REGISTER _ ACK frame to the OLT to display the local MAC address and the current wavelength channel identifier; if the channel identifiers are inconsistent (the ONU is tuned to the wavelength channel which is allocated and registered by the OLT), the upstream optical switch is disconnected, the ONU is randomly tuned to another wavelength channel y (y is not equal to all the channel identifiers which are tried before but are not successful), and the monitoring action is repeated.

c) And monitoring the TUNE frame (containing the wavelength channel value x required to be tuned), immediately tuning to the wavelength channel x specified by the TUNE frame, maintaining the state of the upstream optical switch unchanged, and repeating the monitoring action.

d) If no frame is monitored, another wavelength channel y is randomly tuned (y ≠ all channel identifiers that have been tried previously but not successfully) and the monitoring action is repeated.

(5) The mth MAC Client (corresponding to a wavelength mark m, wherein m is a certain natural number which is greater than or equal to 1 and less than or equal to 32) on the OLT side performs the following actions:

1) the REGISTER _ REQ frame is monitored and it is checked whether the MAC carried by the frame is present in the wavelength allocation table.

a) If the MAC does not exist in any row and the MAC address of the mth row of the table is empty, the MAC address carried by the frame is filled into the MAC address of the mth row, the current time is filled into the access time stamp, the aging timer is reset to the maximum value, and the REGISTER frame is sent.

b) If the MAC does not exist in any row and the MAC address of the mth row of the table is not null, the system is indicated to be abnormal, an error code is returned, the mth row is cleared, and a Gate frame is sent out.

c) If the MAC exists in row m of the table: filling the current time into an access timestamp and resetting an aging timer to a maximum value; and transmits a REGISTER frame.

d) If the MAC address is present in another wavelength channel row (assuming that the x-th wavelength channel and x ≠ m), it indicates a system abnormality and sends a TUNE frame to notify the ONU "please TUNE to the x-th wavelength channel".

2) The REGISTER ACK frame is monitored to check if the MAC carried by the frame is present in the wavelength allocation table.

a) If the MAC exists in row m of the table: if the REGISTER _ ACK is received for the first time and the REGISTER _ REQ frame is not received, filling the current time into an access timestamp and resetting the aging timer to the maximum value, otherwise, only resetting the aging timer to the maximum value; a REGISTER frame is sent.

b) If the MAC does not exist in any row, sending a TUNE frame tells the ONU "please TUNE to the 0 th wavelength channel" (i.e. as long as it is not an m wavelength channel).

c) If the MAC address is present in another wavelength channel row (assuming that the x-th wavelength channel and x ≠ m), it indicates a system abnormality and sends a TUNE frame to notify the ONU "please TUNE to the x-th wavelength channel".

The above only illustrates the main flow and the state change, and the operation of the specific table entry and some abnormal states are not described, and the further description is subject to the following specific implementation.

In addition, by way of reference, the system on which the invention is based is illustrated below:

a super-dense wavelength division multiplexing coherent light access system is composed of an optical line terminal OLT, a Remote Node and an optical network unit ONU, wherein the Remote Node is composed of an optical splitter;

the downlink direction is as follows: the OLT generates 32 paths of intrinsic optical signals through a laser and an optical frequency comb, and realizes ultra-dense wavelength division multiplexing signal optical signals of 32 wavelengths of a single optical fiber through IQ modulation and AWG; 32 wavelength signals at a Remote Node are distributed to the ONU through a 1:32 optical splitter; on the ONU side, a part of uplink optical signals are coupled out to be used as local oscillation light for downlink coherent reception, and beat frequency is carried out to generate corresponding wavelength signals;

an uplink direction: the laser of each ONU is tuned to a different wavelength; the 32 ONUs are coupled by a 1:32 optical splitter and then are merged into a single optical fiber; the OLT side beats the 32 wavelength signals through intrinsic optical signals (generated by a downlink laser and an optical frequency comb) by a coherent technology to generate corresponding receiving signals.

According to the scheme, the OLT consists of a sending end OLT Tx, a receiving end OLT Rx and a circulator; at a sending end OLT Tx, a seed source laser generates 32 wavelengths after optical frequency combing, a part of light with each wavelength is separated out through a coupler and is output as local oscillator light of a receiving end OLT Rx, and the other part of light becomes sent signal light after passing through an IQ modulator. Automatic locking of the modulator bias is achieved by a control circuit. The 32-channel high-speed electric signals input by the electric back plate carry out variable-rate modulation on data according to the requirement of access service, and meanwhile, the signals can be selectively pre-compensated. The signal light output by the 32 IQ modulators passes through the AWG and then is used as the downstream signal light of the OLT. At a receiving end OLT Tx, an input wavelength division multiplexing signal light is divided into 32 paths of optical signals after passing through a coupler, the optical signals and input 32 corresponding local oscillator light enter a coherent receiving module together, after the electric signals after coherent receiving are input into an FPGA, a low-complexity self-adaptive equalization algorithm is executed, and then recovered signals are output through a high-speed data output port.

According to the scheme, the ONU consists of a coherent receiver, a tunable laser, a CPU/MAC, a 1:2 optical splitter, an optical switch and a circulator. The tunable laser uses a direct modulation laser for reducing cost, and output light of the direct modulation laser is divided and simultaneously used as local oscillation light for coherent detection. The intrinsic light and the input optical signal are beaten and processed to generate the required downlink electrical signal. Particularly, in order to cooperate with a wavelength control algorithm, an optical switch is added in the uplink output optical direction of the tunable laser, so that the situation that a plurality of ONUs send out the same wavelength laser to generate collision is avoided.

The optical splitter at the 1:32 remote node is only an example, and may be changed to 1: N (N is a natural number, the value of N is not limited to the power M of 2, and M is a natural number greater than or equal to 1) according to the service requirement, and the optical comb at the transmitting end of the corresponding OLT and the optical splitter at the receiving end of the OLT may also be changed to an optical comb at M channels and an optical splitter at 1: M (the value of M is not less than N) according to the service requirement. It should be noted that if the insertion loss of the optical splitter at the receiving end of the OLT is too large, which results in insufficient optical power budget of the link, the AWG and the POS with low splitting ratio may be used instead of the POS with high splitting ratio, for example, the optical splitter of 1:32 may be replaced with the AWG of 1:4 and four POS of 1: 8.

In the system of the present invention, in order to further increase the carrying capacity of a single fiber, a plurality of sets of seed laser light sources and optical frequency combs can be adopted, and the generated wavelengths can be further increased in capacity after being combined and coupled by AWG, which is described in detail below.

Drawings

Fig. 1 is a diagram of a conventional WDM-PON architecture;

FIG. 2 is a diagram of an architecture of an ultra-dense wavelength division multiplexing coherent optical access system;

FIG. 3 is a simplified diagram of an ultra-dense wavelength division multiplexing coherent optical access system;

FIG. 4 is a schematic diagram of a protocol stack structure of a wavelength control method for an ultra-dense wavelength division multiplexing coherent optical access system;

FIG. 5 is a flowchart illustrating the operation principle of the state machine after the OLT is powered on and started;

fig. 6 is a flowchart of the operating principle of the state machine after the ONU is powered on and started;

fig. 7 is a flow chart of a process of registering a new ONU with an OLT wavelength channel.

Detailed Description

In order that those skilled in the art can understand and implement the present invention, the following embodiments of the present invention will be further described with reference to the accompanying drawings.

Fig. 2 is a super-dense wavelength division multiplexing coherent optical access system on which an embodiment of the present invention relies. The OLT consists of a sending end (OLT Tx), a receiving end (OLT Rx) and a circulator. At a sending end of the OLT, the seed source laser generates 32 wavelengths after optical frequency combing, a part of light with each wavelength is separated out through the coupler and is output as local oscillator light LO at a receiving end of the OLT, and the other part of light with each wavelength is transmitted as signal light after passing through an IQ modulator. Automatic locking of the modulator bias is achieved by a control circuit. The 32-channel high-speed electric signals input by the electric back plate carry out variable rate modulation on data according to the requirement of access service, and meanwhile, the signals can be selectively pre-compensated. The signal light output by the 32 IQ modulators passes through the AWG and then is used as the downlink signal light of the OLT. At the receiving end of the OLT, input wavelength division multiplexing signal light is divided into 32 paths of optical signals after passing through a coupler, the optical signals and input 32 corresponding local oscillator light enter a coherent receiving module, after the coherent received electric signals are input into the FPGA, a low-complexity self-adaptive equalization algorithm is executed, and then recovery signals are output through a high-speed data output port. It can be seen that the wavelength of each channel upstream and downstream of the OLT is unique, determined by the channel on which the AWG1 resides and the input eigen-optical wavelength of the coherent receiver, respectively.

The invention mainly focuses on a wavelength control method, the uplink and downlink wavelengths of an OLT end are fixed, and the invention mainly focuses on the wavelength control of an ONU (optical network unit) without the scope of the invention. Fig. 2 and 3 show that the ONU is composed of a coherent receiver, a tunable laser, a CPU/MAC, a 1:2 optical splitter, an optical switch, and a circulator. The tunable laser uses a direct modulation laser in order to reduce the cost, and the output light of the direct modulation laser is used as the local oscillator light of coherent detection after being branched.

The invention mainly controls the wavelength tuning (32-to-1) and the optical switch (open or closed) of the ONU and the registration of the ONU. Referring to fig. 4, the present invention provides a wavelength control method for an ultra-dense wavelength division multiplexing coherent optical access system, in which a coherent multi-wavelength MAC control sublayer (CMWMC sublayer) is added between an MAC CLIENT sublayer and an OAM sublayer in an ethernet protocol stack to coordinate access of a plurality of ONUs. The CMWMC sublayer needs to maintain a wavelength allocation table at an OLT side, maintain a wavelength state table at an ONU side, then complete the work of ONU registration, wavelength allocation and the like without manual intervention by combining a timer through a downlink OAM frame of the OLT comprising a GATE frame, a REGISTER frame and a TUNE frame and an uplink OAM frame of the ONU comprising a REGISTER _ REQ frame and a REGISTER _ ACK frame; the aged wavelength allocation table can be cleaned in time by combining an overtime mechanism of the timer; and by combining the OLT and the ONU nonvolatile memories, the ONU registration and the wavelength allocation can be rapidly realized. The specific implementation mode is as follows:

1. the OLT maintains a 32-row wavelength allocation table, as in the table below. The table may be stored in a non-volatile memory of the OLT, and the "wavelength identifier" and the "access ONU MAC address" are reserved after the OLT machine is restarted. Each row of data has a Tage timer, the timer of the MAC non-empty row is maximized after being electrified, then 1 is continuously reduced, when the value is reduced to 0, the row is aged, and all data in the row are emptied; and when the OLT receives an ONU handshake response REGISTER _ REQ or REGISTER _ ACK frame, resetting the local line timer to the maximum value.

2. The ONU maintains a 32-row wavelength state table, as shown in the table below. The table may be stored in a non-volatile memory of the ONU, and after the ONU machine restarts, the registration success (or historical registration success) status column is kept, and the attempt registration column is cleared (i.e. 0).

3. The OAM frames related in the downstream OAM frame of the OLT and the upstream OAM frame of the ONU are defined in 5 types, which are described as follows:

4. the OLT is powered on and operates 32 wavelength channels in parallel, and taking the mth wavelength channel as an example, the state machine is shown in fig. 5. After the ONU is powered on and started, the state machine is as shown in fig. 6.

In general, the process of registering a new ONU with an OLT wavelength channel is shown in fig. 7:

(1) sending a Gate frame by an m-th wavelength channel (OLT channel for short) of the OLT, stating that the current OLT channel is idle, and tuning to the m-th wavelength channel (ONU channel for short) of the ONU;

(2) monitoring a Gate frame, randomly delaying for a period of time (a binary random evasion algorithm can take a value, the maximum value is Tgate, and the minimum value is Tgate. times. 1/231), closing an uplink optical switch, setting a timing Tack (Tack should be greater than Tgate) which continuously decreases by 1, and replying the following content by using a REGISTER _ REQ frame: "the local MAC address is MACn, hope to access the mth wavelength channel, please reply".

(3) Before the Tack returns to zero, the ONU channel should receive the REGISTER frame of the OLT channel, broadcast the single MACm address allowed to access and request for reply;

(4) and the ONU channel sends a REGISTER _ ACK frame, reports the MAC address MACm to the OLT channel and finishes the registration process.

The following process is a heartbeat keep alive process:

(5) the OLT channel sends out a REGISTER frame, broadcasts a single MACm address which is allowed to be accessed, and requests for reply;

(6) and after receiving the channel of the ONU, sending a REGISTER _ ACK frame and reporting the MAC address MACm to the channel of the OLT.

Through the configuration of the invention, ONU registration and wavelength allocation without manual intervention can be achieved.

The following is a detailed description of the system on which the invention is based, with reference to the accompanying drawings:

referring to fig. 2-3, the core idea of the ultra-dense phase-coherent access system of the present invention is: the OLT generates 32 paths of intrinsic optical signals through a laser and an optical frequency comb, and realizes ultra-dense wavelength division multiplexing signal optical signals with 32 wavelengths of a single optical fiber through IQ modulation and AWG; 32 wavelength signals at a Remote Node are distributed to the ONU through a 1:32 optical splitter; and on the ONU side, a part of the uplink optical signal is coupled out to be used as local oscillation light for downlink coherent reception, and the beat frequency generates a corresponding wavelength signal. An uplink direction: the laser of each ONU is tuned to a different wavelength; the 32 ONUs are coupled by a 1:32 optical splitter and then are merged into a single optical fiber; the OLT side beats the 32 wavelength signals through intrinsic optical signals (generated by a downstream laser and an optical frequency comb) by a coherent technology to generate corresponding receiving signals. The light in the up and down directions is directionally separated and combined by the circulator.

With continued reference to fig. 2-3, the OLT consists of a transmitting end (OLT Tx) and a receiving end (OLT Rx) and a circulator. At a sending end of the OLT, the seed source laser generates 32 wavelengths after optical frequency combing, a part of light with each wavelength is separated out through the coupler and is output as local oscillator light of the OLT receiving end, and the other part of light becomes sent signal light after passing through the IQ modulator. Automatic locking of the modulator bias is achieved by a control circuit. The 32-channel high-speed electric signals input by the electric backboard can carry out variable-rate modulation on data according to the access service requirement, and meanwhile, the signals can be selectively pre-compensated. The signal light output by the 32 IQ modulators passes through the AWG and then is used as the downstream signal light of the OLT. At the receiving end of the OLT, input wavelength division multiplexing signal light is divided into 32 paths of optical signals after passing through a coupler, the optical signals and input 32 corresponding local oscillator light enter a coherent receiving module, after the coherent received electrical signals are input into the FPGA, a low-complexity self-adaptive equalization algorithm is executed, and then recovered signals are output through a high-speed data output port.

With continued reference to fig. 2, the ONU consists of a coherent receiver, a tunable laser, a CPU/MAC, a 1:2 splitter, an optical switch, and a circulator. The tunable laser uses a direct modulation laser for reducing cost, and output light of the direct modulation laser is divided and simultaneously used as local oscillation light for coherent detection. The intrinsic light and the input optical signal are beaten and processed to generate the required downlink electrical signal. In particular, in order to cooperate with a wavelength control algorithm, an optical switch is added in the upstream output optical direction of the tunable laser, so that a plurality of ONUs can be prevented from sending the same wavelength laser to generate collision.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, many variations and modifications can be made without departing from the spirit of the invention, and these are within the scope of the invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A wavelength control method of ultra-dense wavelength division multiplexing coherent light access system is characterized in that,

a coherent multi-wavelength MAC control sublayer (CMWMC) is added between MAC CLIENT sublayers and an OAM sublayer of an Ethernet protocol stack, a wavelength allocation table is maintained on an OLT side and a wavelength state table is maintained on an ONU side by the CMWMC sublayer, and then ONU registration and wavelength allocation are carried out by combining an OLT downlink OAM frame and an ONU uplink OAM frame with a timer, so that the access of a plurality of ONUs is coordinated.

2. The wavelength control method of ultra-dense wavelength division multiplexing coherent optical access system according to claim 1,

the downstream OAM frame of OLT includes GATE frame, REGISTER frame and TUNE frame;

wherein, the GATE frame is used for declaring that a certain channel in a wavelength allocation table at the OLT side is idle;

the REGISTER frame is used for declaring that a certain channel is registered and occupied by an ONU (optical network unit) of a certain MAC (media access control) address, and replying a REGISTER _ REQ frame or automatically initiating heartbeat keep-alive;

the TUNE frame is used to indicate that a particular or all addressed ONUs TUNE to a particular channel or a non-current channel;

the ONU uplink OAM frame comprises a REGISTER _ REQ frame and a REGISTER _ ACK frame;

wherein, the REGISTER _ REQ frame is used for replying the GATE frame, reporting the MAC address of the ONU, and requesting confirmation when the ONU wants to access the wavelength channel indicated by the GATE frame;

REGISTER _ ACK is used to reply to the REGISTER frame, echoing the wavelength channel identification and the native MAC address.

3. The wavelength control method of ultra-dense wavelength division multiplexing coherent optical access system according to claim 2,

the wavelength distribution table maintained by the OLT side is stored in a nonvolatile memory, and the list information of the table comprises a wavelength identifier, an access ONU MAC address, an access timestamp and an aging timer;

after the power is on, the aging timer of the MAC non-empty line is maximized, then 1 is continuously reduced, when the aging timer is reduced to 0, the line is aged, and all data in the line are emptied; when the OLT receives an ONU handshake response REGISTER _ REQ or REGISTER _ ACK frame, the local line aging timer is reset to the maximum value;

the wavelength state table maintained by the ONU side is stored in a nonvolatile memory, and the column information comprises wavelength identification, successful registration/successful history registration and attempted registration;

and after the ONU is restarted, the status column of successful registration or successful historical registration is reserved, and the attempted registration column is cleared to be 0.

4. The wavelength control method of claim 1, wherein the aged wavelength allocation table is cleared by using a timeout mechanism of a timer.

5. The wavelength control method of ultra-dense wavelength division multiplexing coherent optical access system according to claim 3,

after the OLT is started, calling a CMWMC sublayer primitive by an mth MAC Client at the OLT side to inquire the MAC information of an mth row of a wavelength allocation table;

when the MAC of the mth row is found to be non-empty and legal by inquiry, a REGISTER frame is periodically sent out by taking the Talive as a period so as to declare that the mth wavelength channel is registered and occupied by the ONU with the MAC address as MACm;

when the MAC of the mth row is found to be empty by inquiry, setting a timer Tgate which is continuously decreased by 1 in an aging timer column of the mth row, and sending GATE frame information to declare that a channel of the mth row is idle; if the REGISTER _ REQ frame is not received when the timer Tgate is cleared, the timer Tgate is reset and GATE frame information continues to be transmitted.

6. The wavelength control method of ultra-dense wavelength division multiplexing coherent optical access system according to claim 3,

after the ONU at the user side is started, inquiring a wavelength state table stored in a local nonvolatile memory to acquire the identification information of an optical wavelength channel of the local ONU;

when the identification information of the optical wavelength channel of the local machine is found to be non-empty by inquiry, the tunable laser is directly tuned to the recorded channel;

when the identification information of the optical wavelength channel of the optical splitter is found to be empty, randomly tuning to the nth wavelength channel, simultaneously keeping an uplink optical switch disconnected by default, and monitoring a Gate frame sent by the nth wavelength channel of the optical splitter;

when monitoring a Gate frame sent by an nth wavelength channel, closing an uplink optical switch, setting a timer Tack which continuously decreases 1, sending a REGISTER _ REQ frame to report the MAC address of the ONU, and requesting to access the wavelength channel indicated by the Gate frame;

if the timer Tack returns to zero and does not receive any frame information, tuning to another wavelength channel, and repeating the monitoring action;

if the REGISTER frame is received before the timer Tack is reset to zero, the consistency between the MAC address of the local ONU and the MAC address in the REGISTER frame is checked,

if the MAC addresses are consistent, closing the uplink optical switch, and recording the wavelength channel identifier of the local machine in an ONU nonvolatile memory; meanwhile, sending a REGISTER _ ACK frame reply to the OLT to display the MAC address of the local machine and the current wavelength channel identifier;

if the MAC addresses are not consistent, the uplink optical switch is disconnected, another wavelength channel y is randomly tuned, and the monitoring action is repeated;

if the TUNE frame is received before the timer Tack is reset to zero, the wavelength channel of the local ONU is tuned to the wavelength channel appointed by the TUNE frame, the upstream optical switch is kept disconnected, and the monitoring action is repeated.

7. The wavelength control method of ultra-dense wavelength division multiplexing coherent optical access system according to claim 6,

monitoring a REGISTER _ REQ frame when an mth MAC Client at an OLT side calls a CMWMC sublayer primitive to inquire MAC information of an mth row of a wavelength allocation table;

when monitoring a REGISTER _ REQ frame, checking whether the MAC address carried in the monitored REGISTER _ REQ exists in a wavelength allocation table;

if the MAC address in the REGISTER _ REQ frame does not exist in the wavelength allocation table and the MAC address of the mth row is null, filling the MAC address carried by the REGISTER _ REQ frame into the MAC address of the mth row, filling the current time into an access timestamp and resetting an aging timer to the maximum value, and sending out a REGISTER frame;

if the MAC address in the REGISTER _ REQ frame does not exist in the wavelength allocation table and the MAC address of the mth row is not null, clearing the mth row and sending out a Gate frame;

if the MAC address in the REGISTER _ REQ frame exists in the mth row of the wavelength allocation table, filling the current time into an access timestamp, resetting an aging timer to the maximum value, and sending a REGISTER frame;

a TUNE frame is issued if the MAC address in the REGISTER _ REQ frame is present in the other row of the wavelength allocation table.

8. The wavelength control method of the ultra-dense wavelength division multiplexing coherent optical access system according to claim 6, wherein a REGISTER _ ACK frame is monitored when the mth MAC Client on the OLT side calls a CMWMC sublayer primitive to query the MAC information of the mth row of the wavelength allocation table;

when monitoring a REGISTER _ ACK frame, checking whether an MAC address carried by the REGISTER _ ACK frame exists in a wavelength allocation table;

if the MAC address in the REGISTER _ ACK frame does not exist in the wavelength allocation table, sending out a TUNE frame;

if the MAC address in the REGISTER _ ACK frame exists in the mth row of the wavelength allocation table, resetting the aging timer to the maximum value and sending out a REGISTER frame; if the first time REGISTER _ ACK is received, filling the current time into an access time stamp;

a TUNE frame is issued if the MAC address in the REGISTER _ ACK frame is present in the other row of the wavelength allocation table.