WO2017028803A1

WO2017028803A1 - Olt optical transceiver module, and method and system for processing a plurality of pons

Info

Publication number: WO2017028803A1
Application number: PCT/CN2016/095945
Authority: WO
Inventors: 匡国华; 李明生; 付志明; 马壮
Original assignee: 中兴通讯股份有限公司
Priority date: 2015-08-20
Filing date: 2016-08-19
Publication date: 2017-02-23
Also published as: CN106470075A; CN112671468A; CN112615674A

Abstract

Provided are an OLT optical transceiver module, and a method and system for processing a plurality of PONs. The OLT optical transceiver module comprises: a second downlink transmitting unit configured to receive a second path of electrical signal and a third path of electrical signal which are sent by an electric connector and convert the second path of electrical signal into a second path of downlink optical signal and the third path of electrical signal into a third path of downlink optical signal, wherein the second path of downlink optical signal and the third path of downlink optical signal adopt a time division multiplexing manner; and a WDM unit configured to conduct wavelength division multiplexing on a first path of downlink optical signal sent by a first downlink transmitting unit and the second path of downlink optical signal and the third path of downlink optical signal which are sent by the second downlink transmitting unit and then output same through an optical interface, wherein the first path of downlink optical signal, the second path of downlink optical signal and the third path of downlink optical signal coexist. By means of the present invention, the problem that a passive optical network cannot be smoothly upgraded is solved, thereby effectively reducing system upgrade costs and operation and maintenance costs of an operator.

Description

OLT optical transceiver integrated module, method and system for processing multiple PONs

Technical field

The present invention relates to the field of optical communication technologies, and in particular, to an optical line terminal (OLT) optical transceiver module, and a method and system for processing multiple PONs.

Background technique

With the rapid development of optical fiber communication technology and the popularization and popularization of optical fiber access technology, the demand for bandwidth has been increasing, making a current commercialized technology unable to meet the needs of the growing broadband service. Therefore, the higher bandwidth fiber access technology has become the solution for the next generation broadband access network.

For products with a large number of commercial applications, the technical solution is mature and stable. Considering the cost and maintenance, the application of higher bandwidth must also consider the smooth upgrade of the system. Therefore, the new scheme of passive optical network should consider the compatibility with the traditional mature technology. The optical distribution network (ONU) can be selected according to the specific application environment.

In the related art, Gigabit-Capable Passive Optical Network (GPON) technology cannot meet the needs of the growing broadband service. The higher bandwidth XGPON1 and XGPON2 technologies become the next generation broadband access network solutions. Among them, XGPON1 is a passive optical network with a downlink rate of 10 Gbps and an uplink rate of 2.5 Gbps. XGPON2 has a downlink rate of 10 Gbps and an uplink rate of 10 Gbps. Passive optical network. In GPON technology, Optical Line Terminal (OLT) is the main equipment used to connect optical fiber trunks. Its OLT optical transceiver module is an important part of GPON fiber communication. The current XGPON1OLT technology solution can achieve an uplink rate of 2.488 Gbps (hereinafter referred to as 2.5G), a downlink rate of 9.95 Gbps (hereinafter referred to as 10G) data transmission, and an XGPON2 OLT technology solution can achieve an uplink rate of 10 Gbps (hereinafter referred to as 10G), downlink The data transmission rate of 9.95 Gbps (hereinafter referred to as 10G) can solve the technical problem of the commercial low-cost solution of the next generation passive optical network.

The GPON technology solution is mature and stable, and has been widely used in commercial applications. Considering the cost and maintenance issues, the application of XGPON1 and XGPON2 must also consider the smooth upgrade of the system. Therefore, the application of the OLT optical transceiver module should be compatible with the traditional GPON technology and XGPON1 and XGPON2 technologies, so that more customers can be based on specific The application environment selects different types of ONUs, but the OLT optical transceiver module in the related art cannot be compatible with the traditional GPON technology and the XGPON1 and XGPON2 technologies.

In view of the technical problem that the passive optical network in the related art cannot be smoothly upgraded, an effective solution has not been proposed yet.

Summary of the invention

The embodiments of the present invention provide an OLT optical transceiver integrated module, a method and a system for processing multiple PONs, to at least solve the technical problem that the passive optical network cannot be smoothly upgraded in the related art.

According to an embodiment of the present invention, an OLT optical transceiver module is provided, including: an electrical connector, an optical interface, a wavelength division multiplexing (WDM) unit, a first downlink transmitting unit, and a second a downlink transmitting unit, a first uplink burst receiving unit, and a second uplink burst receiving unit; wherein the first downlink transmitting unit is configured to receive the first electrical signal sent by the electrical connector, and the first electrical signal is Converting into a first downlink optical signal; the second downlink transmitting unit is configured to receive a second electrical signal and a third electrical signal sent by the electrical connector, and convert the second electrical signal into a second downstream optical signal And converting the third road electrical signal into the third downlink optical signal; wherein, the second downlink optical signal and the third downlink optical signal adopt a time division multiplexing manner; the first uplink burst receiving unit is configured to receive the WDM unit Separating the first uplink optical signal, and converting the first uplink optical signal into a first electrical signal, and outputting the converted first electrical signal to the electrical connector; and the second uplink burst receiving The element is configured to receive the second uplink optical signal and the third uplink optical signal separated by the WDM unit, and convert the second uplink optical signal into the second electrical signal and convert the third upstream optical signal into the third a road electrical signal; and outputting the converted second electrical signal and the third electrical signal to the electrical connector; wherein the second upstream optical signal and the third upstream optical signal are time division multiplexed; the WDM unit, The first downlink optical signal sent by the first downlink transmitting unit and the second downlink optical signal and the third downlink optical signal sent by the second downlink transmitting unit are wavelength division multiplexed and output through the optical interface; The optical signal received by the optical interface is separated into a first uplink optical signal and a second upstream optical signal, where the second uplink optical signal includes: a second uplink optical signal and a third uplink optical signal.

In the embodiment of the present invention, the first downlink transmitting unit includes: a first laser driving unit configured to convert the first road electrical signal into a first laser driving signal; and a first laser configured to receive the first laser The first laser driving signal sent by the driving unit generates the first downlink optical signal under the trigger of the first laser driving signal.

In the embodiment of the present invention, the second downlink transmitting unit includes: a second laser driving unit configured to receive the second electrical signal and the third electrical signal of different time slots sent by the electrical connector; Converting the electrical signal into a second laser driving signal and converting the third electrical signal into a third laser driving signal; the second laser is configured to receive the second laser driving signal and the third laser driving signal sent by the second laser driving unit And generating a second downlink optical signal under the trigger of the second laser driving signal, and generating a third downstream optical signal under the trigger of the third laser driving signal.

In the embodiment of the present invention, the first uplink burst receiving unit includes: a first photo receiving unit configured to receive the first uplink optical signal separated by the WDM unit, and convert the first uplink optical signal into the first current signal a first amplifying unit configured to receive the first current signal sent by the first photo receiving unit and convert the current signal into a first differential voltage signal; and the second amplifying unit is configured to receive the first differential sent by the first amplifying unit The voltage signal is amplified or limited by the first differential voltage signal and output to the electrical connector.

In the embodiment of the present invention, the first uplink burst receiving unit further includes: a first reset circuit configured to release the residual signal level of the input end of the second amplifying unit after receiving the reset signal.

In the embodiment of the present invention, the second uplink burst receiving unit includes: a second photo receiving unit configured to receive the second uplink optical signal and the third uplink optical signal of different time slots separated by the WDM unit, and Converting the two-way upstream optical signal into a second current signal and converting the third upstream optical signal into a third current signal; the third amplifying unit is configured to receive the second current signal and the third current signal sent by the second photoelectric receiving unit And converting the second current signal into a second differential Pressing the signal and converting the third current signal into a third differential voltage signal; the fourth amplifying unit is configured to receive the second differential voltage signal and the third differential voltage signal sent by the third amplifying unit, and the second differential voltage The signal and the third differential voltage signal are amplified or clipped and output to the electrical connector.

In the embodiment of the present invention, the second uplink burst receiving unit further includes: a second reset circuit configured to release the residual signal level of the input end of the fourth amplifying unit after receiving the reset signal.

In an embodiment of the present invention, the OLT optical transceiver integrated module further includes: a burst receiving optical power RSSI monitoring unit, configured to receive, by the first uplink burst receiving unit, a first uplink optical signal and/or a second separated by the WDM unit. The uplink burst receiving unit receives the second uplink optical signal and/or the third uplink optical signal of different time slots separated by the WDM unit for collecting, processing, and reporting, and monitoring the first uplink optical signal and the second uplink optical signal. The signal strength of the signal and the third upstream optical signal.

In an embodiment of the present invention, the OLT optical transceiver integrated module further includes: a microcontroller, and the first laser driving unit, the second laser driving unit, the second amplifying unit, the fourth amplifying unit, and the burst receiving optical power RSSI monitoring unit. And the electrical connector is connected, and is configured to monitor the first laser driving unit, the second laser driving unit, the second amplifying unit, the fourth amplifying unit, the burst receiving optical power RSSI monitoring unit, and the electrical connector.

According to an embodiment of the present invention, an OLT optical transceiver integrated module is further provided, including: an electrical connector, an optical interface, a wavelength division multiplexing WDM unit, a first downlink transmitting unit, and a second downlink transmitting unit, a three-way downlink transmitting unit, a first uplink burst receiving unit, a second uplink burst receiving unit, and a third uplink burst receiving unit; wherein the first downlink transmitting unit is configured to receive the electrical connector The first electrical signal converts the first electrical signal into a first downstream optical signal; the second downstream transmitting unit is configured to receive a second electrical signal sent by the electrical connector, and the second electrical signal is Converted into a second downlink optical signal; the third downlink transmitting unit is configured to receive a third electrical signal sent by the electrical connector, and convert the third electrical signal into a third downstream optical signal, wherein, the second The downlink optical signal and the third downlink optical signal adopt a time division multiplexing manner; the first uplink uplink receiving unit is configured to receive the first uplink optical signal separated by the WDM unit, and the first uplink optical signal is Converted into a first electrical signal, the converted first electrical signal is output to the electrical connector; the second upstream burst receiving unit is configured to receive the second uplink optical signal separated by the WDM unit, and the second The road upstream optical signal is converted into the second electrical signal; and the converted second electrical signal is output to the electrical connector; the third uplink receiving unit is configured to receive the third uplink optical signal separated by the WDM unit And converting the third uplink optical signal into a third electrical signal; and outputting the converted third electrical signal to the electrical connector, wherein the second upstream optical signal and the third upstream optical signal are time division multiplexed The WDM unit is configured to set the first downlink optical signal sent by the first downlink transmitting unit and the second downlink optical signal sent by the second downlink transmitting unit and the third downlink of the third downlink transmitting unit. The optical signal is wavelength-multiplexed and output through the optical interface; the optical signal received by the optical interface is separated into a first uplink optical signal, a second uplink optical signal, and a third uplink optical signal.

According to an embodiment of the present invention, there is also provided a method for processing a plurality of passive optical networks, the method comprising: receiving a first electrical signal, a second electrical signal, and a third electrical signal transmitted by the electrical connector Converting the first electrical signal into the first downstream optical signal, converting the second electrical signal into the second downstream optical signal, and converting the third electrical signal into the third downstream optical signal; The downlink optical signal, the second downlink optical signal, and the third downlink optical signal are output after wavelength division multiplexing; wherein the second downlink optical signal and the third downlink optical signal are time division multiplexed; To The optical signal is demultiplexed and multiplexed to obtain a first uplink optical signal, a second uplink optical signal, and a third uplink optical signal; the first uplink optical signal is converted into a first electrical signal, and the second uplink is uplinked. The optical signal is converted into the second electrical signal and the third upstream optical signal is converted into the third electrical signal, and the converted first electrical signal, the second electrical signal and the third electrical signal are output to the electrical connection. The second uplink optical signal and the third uplink optical signal are time division multiplexed.

According to an embodiment of the present invention, there is also provided a system for processing a plurality of passive optical networks, a splitter, an optical network unit, and an optical line terminal OLT optical transceiver integrated module in the above embodiment; wherein the optical splitter and the optical The line terminal OLT optical transceiver module is connected, and the optical splitter is connected to the optical network unit.

In an embodiment of the present invention, a computer storage medium is further provided, and the computer storage medium may store an execution instruction for performing the implementation of the method for processing multiple passive optical networks in the foregoing embodiments.

According to the embodiment of the present invention, in the OLT optical transceiver module, the second downlink optical signal and the third downlink optical signal are time division multiplexed, and the second uplink optical signal and the third uplink optical signal are time division multiplexed. The mode and the second downlink optical signal and the second downlink optical signal sent by the second downlink transmitting unit and the third downlink optical signal are in a wavelength division multiplexing manner, so that the OLT optical transceiver module can be compatible with the wavelength division multiplexing. The mode can work in the time division multiplexing mode, and can work in the following three modes: mode 1: the downlink rate and the downlink wavelength of the first downlink optical signal, the uplink rate and the uplink wavelength of the first uplink optical signal. Mode 2: adopt the downlink rate and downlink wavelength of the second downlink optical signal, the uplink rate and the uplink wavelength of the second uplink optical signal; mode 3: adopt the downlink and downlink wavelengths of the third downlink optical signal, and third The uplink rate and the uplink wavelength of the uplink optical signal of the road, that is, the OLT optical transceiver integrated module can implement a high-rate technical solution, and can also be used Low-rate conventional commercial programs to address the problem of passive optical network is not smooth upgrade, effectively reducing the cost of system upgrades and operation and maintenance costs for operators.

DRAWINGS

The drawings described herein are intended to provide a further understanding of the invention, and are intended to be a part of the invention. In the drawing:

FIG. 1 is a schematic diagram of an application scenario according to an embodiment of the present invention; FIG.

2 is a schematic structural diagram of an OLT optical transceiver integrated module according to an embodiment of the present invention;

3 is a schematic structural diagram of an OLT optical transceiver integrated module according to a preferred embodiment of the present invention;

4 is another schematic structural diagram of an OLT optical transceiver integrated module according to an embodiment of the present invention;

5 is a block diagram of an application of an optical transceiver module in which a GPON OLT, an XGPON 1 OLT, and an XGPON 2 OLT coexist in accordance with a preferred embodiment of the present invention;

6 is a structural block diagram of an OLT optical transceiver integrated module of a GPON OLT, an XGPON 1 OLT, and an XGPON 2 OLT according to a preferred embodiment of the present invention.

detailed description

The invention will be described in detail below with reference to the drawings in conjunction with the embodiments. It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other without conflict.

It is to be understood that the terms "first", "second" and the like in the specification and claims of the present invention are used to distinguish similar objects, and are not necessarily used to describe a particular order or order.

1 is a schematic diagram of an application scenario according to an embodiment of the present invention. As shown in FIG. 1 , an embodiment of the present invention aims to design an OLT optical transceiver integrated module that supports multiple passive optical networks, and supports the use in a coexistence system. At least three types of optical network units (ONUs), the OLT optical transceiver integrated module of the present invention can work in three modes through system selection, namely OLT mode one, adopting the first uplink rate and uplink. Wavelength, first downlink rate and downlink wavelength; OLT mode 2, using the second uplink rate and uplink wavelength, the second downlink rate and downlink wavelength; the other is OLT mode 3, using the third uplink rate and uplink Wavelength, third downlink rate and downstream wavelength.

An OLT optical transceiver module is provided in this embodiment. The module is used to implement the foregoing embodiments and preferred embodiments, and details are not described herein. As used below, the term "module" may implement a combination of software and/or hardware of a predetermined function. Although the apparatus described in the following embodiments is preferably implemented in software, hardware, or a combination of software and hardware, is also possible and contemplated.

2 is a schematic structural diagram of an OLT optical transceiver integrated module according to an embodiment of the present invention. As shown in FIG. 2, the module includes: an electrical connector 22, an optical interface 24, a wavelength division multiplexing WDM unit 26, and a first downlink transmission. The unit 28, the second downlink transmitting unit 210, the first uplink burst receiving unit 212, and the second uplink burst receiving unit 214;

In this embodiment, the first downlink transmitting unit 28 is configured to receive the first road electrical signal sent by the electrical connector 22, and convert the first road electrical signal into the first downlink optical signal;

The second downlink transmitting unit 210 is configured to receive the second electrical signal and the third electrical signal sent by the electrical connector 22, and convert the second electrical signal into a second downstream optical signal and a third electrical signal. Converted into a third downlink optical signal; wherein the second downlink optical signal and the third downlink optical signal are time division multiplexed;

The first uplink burst receiving unit 212 is configured to receive the first uplink optical signal separated by the WDM unit 26, and convert the first uplink optical signal into a first electrical signal, and output the converted first electrical signal. To the electrical connector 22;

The second uplink burst receiving unit 214 is configured to receive the second uplink optical signal and the third uplink optical signal separated by the WDM unit 26, and convert the second uplink optical signal into the second electrical signal and the third The road upstream optical signal is converted into a third electrical signal; and the converted second electrical signal and the third electrical signal are output to the electrical connector 22; wherein, the second upstream optical signal and the third upstream optical signal Using time division multiplexing;

The WDM unit 26 is configured to perform wavelength division multiplexing on the first downlink optical signal sent by the first downlink transmitting unit 28 and the second downlink optical signal and the third downlink optical signal sent by the second downlink transmitting unit 210. Outputting through the optical interface 24; and separating the optical signal received by the optical interface 24 into a first uplink optical signal and a second upstream optical signal, where the second upstream optical The signal includes: a second uplink optical signal and a third uplink optical signal.

In the OLT optical transceiver module, the second downlink optical signal and the third downlink optical signal are time division multiplexed, the second uplink optical signal, and the third uplink optical signal are used in the OLT optical transceiver module. The time division multiplexing mode is adopted, and the second downlink optical signal and the second downlink optical signal and the third downlink optical signal sent by the second downlink transmitting unit are subjected to wavelength division multiplexing, so that the OLT optical transceiver module is compatible. The wavelength division multiplexing mode can work in the time division multiplexing mode, and can be compatible with the following three modes: mode 1: the downlink rate and the downlink wavelength of the first downlink optical signal, and the uplink rate of the first uplink optical signal. And the uplink wavelength; mode 2: the downlink rate and the downlink wavelength of the second downlink optical signal, the uplink rate and the uplink wavelength of the second uplink optical signal; and the third mode: the downlink rate and the downlink wavelength of the third downlink optical signal The uplink rate and the uplink wavelength of the third uplink optical signal, that is, the OLT optical transceiver integrated module can implement a high rate technical solution You can use either a traditional low rate of commercialization solutions to solve the problem can not be passive optical network smooth upgrade, thus achieving an effective system upgrades to reduce the effect of the operator's cost and operation and maintenance costs.

It should be noted that the first uplink optical signal, the second uplink optical signal, the third uplink optical signal, the first downlink optical signal, the second downlink optical signal, and the third downlink optical signal coexist.

3 is a schematic structural diagram of an OLT optical transceiver integrated module according to a preferred embodiment of the present invention, as shown in FIG. 3,

The first downlink transmitting unit 28 may include: a first laser driving unit 32 configured to convert the first electrical signal into a first laser driving signal; and a first laser 34 configured to receive the first laser driving unit 32 to transmit The first laser driving signal generates a first downlink optical signal under the trigger of the first laser driving signal.

The second downlink transmitting unit 210 may include: a second laser driving unit 36 configured to receive the second electrical signal and the third electrical signal of different time slots transmitted by the electrical connector 22; and convert the second electrical signal into a second laser driving signal and converting the third electrical signal into a third laser driving signal; the second laser 38 is arranged to receive the second laser driving signal and the third laser driving signal sent by the second laser driving unit 36, and The second downlink optical signal is generated by the triggering of the second laser driving signal, and the third downstream optical signal is generated under the trigger of the third laser driving signal.

The first uplink burst receiving unit 212 may include: a first photo receiving unit 310 configured to receive the first uplink optical signal separated by the WDM unit 26, and convert the first uplink optical signal into a first current signal; The amplifying unit 312 is configured to receive the first current signal sent by the first photo receiving unit 310 and convert the current signal into a first differential voltage signal. The second amplifying unit 314 is configured to receive the first sent by the first amplifying unit 312. The differential voltage signal is amplified or clipped and output to the electrical connector 22.

In this embodiment, the first uplink burst receiving unit 212 further includes: a first reset circuit 316 configured to release the residual signal level of the input end of the second amplifying unit 314 after receiving the reset signal.

The second uplink burst receiving unit 214 may include: a second photo receiving unit 318 configured to receive the second uplink optical signal and the third uplink optical signal of different time slots separated by the WDM unit 26, and Converting the optical signal into a second current signal and converting the third upstream optical signal into a third current signal; the third amplifying unit 320 is configured to receive the second current signal and the third current signal sent by the second photoelectric receiving unit 318, And converting the second current signal into a second difference The voltage signal and the third current signal are converted into a third differential voltage signal; the fourth amplifying unit 322 is configured to receive the second differential voltage signal and the third differential voltage signal sent by the third amplifying unit 320, and the second differential voltage The signal and the third differential voltage signal are amplified or clipped and output to the electrical connector.

In the embodiment of the present invention, the second uplink burst receiving unit 214 further includes: a second reset circuit 324 configured to release the residual signal level of the input end of the fourth amplifying unit 322 after receiving the reset signal.

In the embodiment of the present invention, the OLT optical transceiver integrated module further includes: a burst receiving optical power RSSI monitoring unit 326, configured to receive, by the first uplink burst receiving unit 212, the first uplink optical signal separated by the WDM unit 26 and / or the second uplink burst receiving unit receives the second uplink optical signal and/or the third uplink optical signal of different time slots separated by the WDM unit 26 for collecting, processing, and reporting, and monitoring the first uplink optical signal, The signal strength of the second uplink optical signal and the third upstream optical signal.

In the embodiment of the present invention, the OLT optical transceiver integrated module further includes: a microcontroller 328, and the first laser driving unit 32, the second laser driving unit 36, the second amplifying unit 314, the fourth amplifying unit 322, and the burst The receiving optical power RSSI monitoring unit 326 and the electrical connector 22 are connected, and are arranged to monitor the first laser driving unit 32, the second laser driving unit 36, the second amplifying unit 314, the fourth amplifying unit 322, and the burst receiving optical power RSSI. Unit 326 and electrical connector 22 are monitored.

In the embodiment of the present invention, the first photo-receiving unit 310 is a photodiode such as an avalanche photodiode or a circuit capable of photoelectric conversion, but is not limited thereto; the first amplifying unit 312 and the third amplifying unit 320 may be trans-resistances. The amplifier may be a circuit that converts the current signal into a differential voltage signal, but is not limited thereto; the second amplifying unit 314 and the fourth amplifying unit 322 may be limiting amplifiers or can amplify, limit, and shape the differential voltage signals. Circuit, but not limited to.

In a preferred embodiment, the first downlink transmitting unit includes: the first laser driving unit receives the first electrical signal transmitted through the electrical connector, optimizes the electrical signal of the transmitting end, and converts the digital electrical signal into a laser The driving signal drives the first laser to be converted into the first downstream optical signal. The second downlink transmitting unit includes: the second laser driving unit receives the second or third electrical signals of different time slots transmitted through the electrical connector, optimizes the electrical signal of the transmitting end, and converts the digital electrical signal into a laser driving signal Driving the second laser to convert into a second or third downstream optical signal. The microcontroller can control the modulation current and the bias current of the first laser driving unit and the second laser driving unit, so that the output optical power and the extinction ratio maintain the target value, which satisfies the system requirements. The first uplink burst receiving unit comprises: the optical signal received by the optical interface is separated by the wavelength division multiplexing unit and sent to the first optical receiving diode, and the first optical receiving diode is converted into a current signal. And sent to the first burst mode transimpedance amplifier; the transimpedance amplifier converts the received current signal into a differential voltage signal and sends it to the first burst limiting amplifier through the first RESET bleeder circuit, the limiting amplifier The received voltage signal is amplified or clipped and output to the electrical connector. The second uplink burst receiving unit comprises: the optical signal received by the optical interface is separated from the second or third optical signal of different time slots by the wavelength division multiplexing unit, and then sent to the second photo receiving diode, the second photoelectric The receiving diode is converted into a current signal and sent to the second burst mode transimpedance amplifier; the transimpedance amplifier converts the received current signal into a differential voltage signal and sends it to the second path through the second reset (RESET) bleeder circuit. The burst limiting amplifier or the third burst limiting amplifier, the limiting amplifier amplifies or limits the received voltage signal and outputs it to the electrical connector. Receive Signal Strength Indicator (RSSI) The monitoring unit separately collects, processes, and reports the burst optical signals of the first channel and the second channel, and performs real-time monitoring of the received optical power signal strength, and complies with protocols such as SFF-8472. RESET burst bleeder circuit, RESET signal is the notification signal of the next set of burst data arrival. After receiving the reset signal, the RESET bleeder circuit clears the residual signal level at the input end of the burst limiting amplifier to ensure the next Accurate reception of a set of bursty data. Meet system timing requirements.

In the embodiment of the present invention, the two RESET burst bleed circuits respectively process the residual signal levels of the limiting amplifiers of the two receiving channels to meet the timing requirements of the coexistence receiving system. The microcontroller is connected to the laser driver, the limiting amplifier, the RSSI circuit through the control signal line or the IIC bus to monitor, collect and process the corresponding data. It also has an external integrated circuit bus (Inter-integrated Circuit (IIC) interface, and is connected to the system board IIC bus interface through the optical module electrical interface to realize the digital signal diagnosis and monitoring of the optical module.

It should be noted that each of the above units may be implemented by software or hardware. For the latter, the foregoing may be implemented by, but not limited to, the foregoing modules are all located in the same processor; or, the modules are located in multiple In the processor.

The embodiment of the present invention further supports OLT mode 1, OLT mode 2, and OLT mode 3 are wavelength division multiplexing modes, as shown in FIG. 4, FIG. 4 is another structure of an OLT optical transceiver integrated module according to an embodiment of the present invention. The schematic diagram includes an electrical connector 42, an optical interface 44, a wavelength division multiplexing WDM unit 46, a first downlink transmitting unit 48, a second downlink transmitting unit 410, a third downlink transmitting unit 412, and a first uplink burst. The receiving unit 414, the second uplink burst receiving unit 416, and the third uplink burst receiving unit 418;

The first downlink transmitting unit 48 is configured to receive the first electrical signal sent by the electrical connector 42 and convert the first electrical signal into the first downstream optical signal;

The second downlink transmitting unit 410 is configured to receive the second electrical signal sent by the electrical connector 42 and convert the second electrical signal into the second downstream optical signal;

The third downlink transmitting unit 412 is configured to receive the third electrical signal sent by the electrical connector 42 and convert the third electrical signal into a third downstream optical signal, wherein the second downstream optical signal and the third The downlink optical signal of the road adopts time division multiplexing mode;

The first uplink burst receiving unit 414 is configured to receive the first uplink optical signal separated by the WDM unit 46, and convert the first uplink optical signal into a first electrical signal, and convert the converted first electrical signal. Output to the electrical connector 42;

The second uplink burst receiving unit 416 is configured to receive the second uplink optical signal separated by the WDM unit 46, and convert the second uplink optical signal into a second electrical signal; and convert the second electrical circuit The signal is output to the electrical connector 42;

The third uplink burst receiving unit 418 is configured to receive the third uplink optical signal separated by the WDM unit 46, and convert the third uplink optical signal into a third electrical signal; and convert the third electrical circuit The signal is output to the electrical connector 42, wherein the second upstream optical signal and the third upstream optical signal are in a time division multiplexing manner;

The WDM unit 46 is configured to send the first downlink optical signal sent by the first downlink transmitting unit 48 and the second downlink optical signal sent by the second downlink transmitting unit 410 and the third downlink transmitting unit 412. Down the road The wavelength is multiplexed and outputted through the optical interface 44. The optical signal received by the optical interface 44 is separated into a first uplink optical signal, a second uplink optical signal, and a third uplink optical signal.

In the OLT optical transceiver module, the first downlink optical signal, the second downlink optical signal, and the third downlink optical signal are in a wavelength division multiplexing manner, so that the OLT optical transmission and reception is performed. The integrated module can work in the following three modes: mode 1: the downlink rate and the downlink wavelength of the first downlink optical signal, the uplink rate and the uplink wavelength of the first uplink optical signal; and mode 2: the second downlink light is adopted. The downlink rate and the downlink wavelength of the signal, the uplink rate and the uplink wavelength of the second uplink optical signal; mode 3: the downlink rate and the downlink wavelength of the third downlink optical signal, and the uplink and uplink wavelengths of the third uplink optical signal That is, the OLT optical transceiver integrated module can realize a high-rate technical solution, and can also use the traditional low-rate commercialization solution to solve the problem that the passive optical network cannot be smoothly upgraded, thereby effectively reducing the operator's system upgrade. The effect of cost and operation and maintenance costs.

In the embodiment of the present invention, the electrical connector 42 is used as a physical connection interface for inputting and outputting the first, second, and third electrical signals, respectively. The optical interface 44 is used as an input/output physics of the first uplink optical signal, the second uplink optical signal, the third uplink optical signal, the first downlink optical signal, the second downlink optical signal, and the third downlink optical signal. Optical interface. The wavelength division multiplexing WDM unit 46 multiplexes the first downlink optical signal and the second downlink optical signal, and outputs the same to the optical interface 44, and receives the first uplink signal and the second signal received by the optical interface 44. The third uplink signal of the road is demultiplexed and output to the corresponding photodetector.

5 is a block diagram of an application of an optical transceiver module in which a GPON OLT, an XGPON 1 OLT, and an XGPON 2 OLT coexist, according to a preferred embodiment of the present invention. As shown in FIG. 5, GPON ONU, XGPON 1 ONU, and XGPON 2 ONU are supported in the coexistence system. In a preferred embodiment of the present invention, the coexisting OTL optical module can work in three modes through system selection, one is GPON OLT mode, the uplink rate is 1.25 Gbps, and the burst reception is performed at a center wavelength of 1310 nm, and the downlink rate is 2.5 Gbps. 1490nm central wavelength continuous mode transmission part; the second is XGPON1 OLT mode, uplink rate 2.5Gbps, burst reception with 1270nm center wavelength, downlink rate 10Gbps, 1577nm ZTE wavelength continuous mode transmission part; the other is XGPON2OLT mode The uplink rate is 10 Gbps, and the same 1270 nm center wavelength burst reception as XGPON1 is adopted. The time division mode is multiplexed, and the downlink rate is 10 Gbps. The transmission portion of the same 1577 nm ZTE wavelength continuous mode as XGPON1 is used, and is multiplexed by time division mode.

In order to achieve compatibility problems of the above three modes, FIG. 6 is a structural block diagram of an OLT optical transceiver integrated module of a GPON OLT, an XGPON 1 OLT, and an XGPON 2 OLT according to a preferred embodiment of the present invention. As shown in FIG. 6 , the electrical connector is defined by XFP. The optical interface uses the SC Receptacle mode. The OLT optical transceiver integrated module further includes a wavelength division multiplexing WDM part, a 10G transmitting part, a 2.5G transmitting part, a 10G receiving part, a 2.5G receiving part, a 1.25G receiving part, and other signal processing parts.

In the preferred embodiment, the wavelength division multiplexing section multiplexes the 10G 1577 nm center wavelength emission optical signal and the 2.5G 1490 nm center wavelength emission optical signal and outputs it to the SC Receptacle optical interface. At the same time, the received 2.5G 1270nm center wavelength, 10G 1270nm center wavelength and 1.25G 1310nm center wavelength optical signal are demultiplexed and output to 10G avalanche photodiode APD receiving part and 1.25G avalanche photodiode (Avalanche Photo Diode, respectively). APD) Receive part.

In the preferred embodiment, the 10G transmitting portion includes: a 10G clock data recovery unit, a 10G electro-absorption modulated laser (EML) laser driver unit, and a 10G 1577 nm laser, wherein the 10G 1577 nm laser includes a TEC control unit. And the microcontroller section. Among them, the 10G 1577nm laser uses an EML laser, and the 10G EML laser driver unit uses an EML driver chip. The 10G clock data recovery unit performs jitter optimization on the transmitter electrical signal and sends the data to the 10G EML laser driver unit to drive the laser and convert it into an optical signal. The microcontroller part controls the drive current output from the 10G EML laser driver unit, so that the optical signal indicators meet the corresponding standards and remain stable and reliable. The TEC control unit controls the TEC in the 10G 1577nm laser to keep the laser output wavelength stable and meet system requirements.

The 2.5G transmitter section includes a 2.5G laser driver unit, a 2.5G laser, and a microcontroller section. In the preferred embodiment, a 2.5G DML DFB laser driver chip and a 2.5G 1490 nm Distributed Feedback (DFB) laser are used. The 2.5G laser driver unit receives the 2.5G data signal transmitted by the electrical connector and converts the digital signal into a laser drive signal to drive the 2.5G laser into an optical signal. The microcontroller part controls the output current of the 2.5G laser driver unit to make the 2.5G optical signal index stable and meet the system requirements.

The 10G and 2.5G receiving sections include: 10G avalanche photodiode APD, boost circuit, 10G burst transimpedance amplifier, RESET bleeder circuit, 10G 2.5G burst limiting amplifier, burst receive optical power monitoring unit (RSSI) and Microcontroller section. In the preferred embodiment, the avalanche photodiode converts the 10G or 2.5G 1270nm center wavelength optical signal demultiplexed by the wavelength division multiplexing unit into a current signal and sends it to the 10G burst transimpedance amplifier; since XGPON1 and XGPON2 The uplink adopts the time division multiplexing mode, and the optical signal received by the OLT is a burst mode, and the received current signal is quickly converted into a differential voltage signal by a burst transimpedance amplifier and sent to the RESET bleeder circuit. The RESET signal is a notification signal for the arrival of the next set of burst data. After the reset signal is received by the RESET bleeder circuit, the residual signal level of the input of the 10G or 2.5G burst limiting amplifier is cleared in time to ensure the next Accurate reception of burst data. The burst limiting amplifier amplifies or limits the received voltage signal to output to a 2.5G electrical signal and a 10G electrical signal, respectively, and is connected to the electrical connector.

The 1.25G receiving section includes: 1.25G avalanche photodiode, boost circuit, 1.25G burst transimpedance amplifier, RESET bleeder circuit, 1.25G burst limiting amplifier, burst receive optical power monitoring unit (RSSI) and micro control Part. The GPON uplink 1.25G 1310nm center wavelength optical signal demultiplexed by the wavelength division multiplexing unit is input to the 1.25G receiving part. The signal processing principle is similar to the 10G receiving part, and the channel bandwidth is constrained to a suitable 1.25G signal rate, so that the receiving sensitivity is obtained. Handle the best point. The 1.25G signal is output to the electrical connector after passing through the transimpedance amplifier, the RESET bleeder circuit, and the limiting amplifier.

The boost circuit described above outputs an optimum bias voltage for the optimum sensitivity required for the avalanche photodiode. The output voltage range is controlled by the microcontroller to meet the optimum bias voltage variation caused by the avalanche photodiode as a function of temperature.

The burst receive optical power (RSSI) unit collects, processes, and reports burst received optical signals. In this embodiment, an avalanche photodiode photocurrent mirror and a burst sample-and-hold circuit are used, and the microcontroller performs digital conversion and calibration on the analog signal of the sample-and-hold circuit, and then reports the system. This embodiment includes a 2-way RSSI processing unit that performs received optical power monitoring on the 10G and 2.5G receiving portions and the 1.25G receiving portion, and performs real-time monitoring of the burst received optical power signal strength according to the SFF-8472 and INF-8077 protocols.

RESET burst bleeder circuit, RESET signal is the notification signal of the next set of burst data arrival. After receiving the reset signal, the RESET bleeder circuit clears the residual signal level at the input end of the burst limiting amplifier to ensure the next Accurate reception of a set of bursty data. Meet system timing requirements. The RESET burst bleeder circuit of the embodiment satisfies the residual level processing before the burst signal reception for the 10G and 2.5G receiving portions and the burst limiting input terminal of the 1.25G receiving portion, respectively, to ensure the accuracy of the three-way burst data. receive.

The preferred embodiment adopts an XFP interface, and defines the level and function of each pin of the electrical interface to meet the system requirements. Meet the requirements of the INF-8077 agreement.

Through the above preferred embodiments, the OLT optical transceiver integrated module is provided to support both the traditional GPON OLT technical solution and the XGPON1 and XGPON2 high-rate technical solutions, thereby achieving smooth upgrade of the GPON system and reducing the system upgrade operation of the operator. Dimensional cost.

In the embodiment of the present invention, a method for processing multiple passive optical networks is also provided, and the method includes the following steps:

Step S702, receiving a first road electrical signal, a second road electrical signal, and a third electrical signal sent by the electrical connector; converting the first electrical signal into a first downstream optical signal, and converting the second electrical signal into The second downlink optical signal and the third electrical signal are converted into the third downlink optical signal; and the converted first downlink optical signal, the second downlink optical signal, and the third downlink optical signal are subjected to wavelength division After multiplexing, the second downlink optical signal and the third downlink optical signal are time division multiplexed;

Step S704, the received optical signal is demultiplexed and multiplexed to obtain a first uplink optical signal, a second uplink optical signal, and a third uplink optical signal; and the first uplink optical signal is converted into a first electrical signal. Converting the second upstream optical signal into a second electrical signal and converting the third upstream optical signal into a third electrical signal, and converting the converted first electrical signal, second electrical signal, and third circuit The electrical signal is output to the electrical connector, wherein the second uplink optical signal and the third upstream optical signal are time division multiplexed;

It should be noted that the first downlink optical signal, the second downlink optical signal, and the third downlink optical signal are three different optical signals. Similarly, the first uplink optical signal and the second uplink optical signal, The three-way upstream optical signal is three different optical signals.

The multiple passive optical networks may include the following: mode 1: downlink rate and downlink wavelength of the first downlink optical signal, uplink rate and uplink wavelength of the first uplink optical signal; mode 2: using the second downlink The downlink rate and the downlink wavelength of the optical signal, the uplink rate and the uplink wavelength of the second uplink optical signal; mode 3: the downlink rate and the downlink wavelength of the third downlink optical signal, and the uplink rate and uplink of the third uplink optical signal The wavelength is obtained by using the first downlink optical signal, the second downlink optical signal, and the third downlink optical signal by using the wavelength division multiplexing method, and the second downlink optical signal and the third downlink optical signal are adopted. In the time division multiplexing mode, the first uplink optical signal, the second uplink optical signal, and the third uplink optical signal are in wavelength division multiplexing mode, and the second uplink optical signal and the third uplink optical signal are time division multiplexed. This method can be compatible with the above three modes, and solves the problem that the passive optical network cannot be smoothly upgraded, thereby achieving an effective reduction of the operator's system. The effect of costs and operation and maintenance costs.

It should be noted that the foregoing method for processing multiple passive optical networks may be implemented by the OLT optical transceiver of the foregoing embodiment. The module implementation can also be implemented by other devices, and is not limited thereto.

In the embodiment of the present invention, there is also provided a system for processing a plurality of passive optical networks, the system comprising a beam splitter, an optical network unit, and an optical line terminal OLT optical transceiver integrated module described in the foregoing embodiment; wherein the splitting The device is connected to the optical line terminal OLT optical transceiver integrated module, and the optical splitter is connected to the optical network unit.

It will be apparent to those skilled in the art that the various modules or steps of the present invention described above can be implemented by a general-purpose computing device that can be centralized on a single computing device or distributed across a network of multiple computing devices. Alternatively, they may be implemented by program code executable by the computing device such that they may be stored in the storage device by the computing device and, in some cases, may be different from the order herein. The steps shown or described are performed, or they are separately fabricated into individual integrated circuit modules, or a plurality of modules or steps thereof are fabricated as a single integrated circuit module. Thus, the invention is not limited to any specific combination of hardware and software.

The above description is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Industrial applicability

The foregoing technical solution provided by the embodiment of the present invention can be applied to the process of processing multiple passive optical networks, and the second downlink optical signal and the third downlink optical signal are time division multiplexed in the OLT optical transceiver module. The second uplink optical signal and the third uplink optical signal adopt a time division multiplexing manner, and the first downlink optical signal and the second downlink optical signal sent by the second downlink transmitting unit and the third downlink optical signal adopt a wave. The sub-multiplexing mode enables the OLT optical transceiver module to be compatible with the wavelength division multiplexing mode and the time division multiplexing mode, and can be compatible with the following three modes: mode 1: using the downlink of the first downlink optical signal Rate and downlink wavelength, the uplink rate and the uplink wavelength of the first uplink optical signal; Mode 2: the downlink rate and the downlink wavelength of the second downlink optical signal, and the uplink and uplink wavelengths of the second uplink optical signal; : adopting the downlink rate and the downlink wavelength of the third downlink optical signal, and the uplink rate and the uplink wavelength of the third uplink optical signal, that is, the O The LT optical transceiver module can realize high-speed technical solutions, and can also use the traditional low-rate commercialization solution to solve the problem that the passive optical network cannot be smoothly upgraded, and effectively reduce the system upgrade cost and operation and maintenance cost of the operator.

Claims

An optical line terminal OLT optical transceiver integrated module comprises: an electrical connector, an optical interface, a wavelength division multiplexing WDM unit, a first downlink transmitting unit, a second downlink transmitting unit, a first uplink burst receiving unit, and a second Uplink burst receiving unit; wherein

The first downlink transmitting unit is configured to receive a first road electrical signal sent by the electrical connector, and convert the first road electrical signal into a first downlink optical signal;

The second downlink transmitting unit is configured to receive a second electrical signal and a third electrical signal sent by the electrical connector, and convert the second electrical signal into a second downstream optical signal and a The third road electrical signal is converted into a third downlink optical signal; wherein the second downlink optical signal and the third downlink optical signal are time division multiplexed;

The first uplink burst receiving unit is configured to receive a first uplink optical signal separated by the WDM unit, and convert the first uplink optical signal into the first electrical signal, and convert the converted Transmitting the first electrical signal to the electrical connector;

The second uplink burst receiving unit is configured to receive the second uplink optical signal and the third uplink optical signal separated by the WDM unit, and convert the second uplink optical signal into the second path And converting the third uplink optical signal into a third electrical signal; and outputting the converted second electrical signal and the third electrical signal to the electrical connector; wherein The second uplink optical signal and the third uplink optical signal adopt a time division multiplexing manner;

The WDM unit is configured to set the first downlink optical signal sent by the first downlink transmitting unit and the second downlink optical signal and the third road sent by the second downlink transmitting unit The downlink optical signal is wavelength-multiplexed and then output through the optical interface; the optical signal received by the optical interface is separated into the first uplink optical signal and the second upstream optical signal, where the second uplink optical signal The method includes: the second uplink optical signal and the third uplink optical signal.
The OLT optical transceiver module according to claim 1, wherein the first downlink transmitting unit comprises:

a first laser driving unit configured to convert the first electrical signal into a first laser driving signal;

The first laser is configured to receive the first laser driving signal sent by the first laser driving unit, and generate the first downstream optical signal under the trigger of the first laser driving signal.
The OLT optical transceiver module according to claim 1, wherein the second downlink transmitting unit comprises:

a second laser driving unit configured to receive a second electrical signal and a third electrical signal of different time slots transmitted by the electrical connector; and convert the second electrical signal into a second laser driving signal and Converting the third electrical signal into a third laser driving signal;

a second laser, configured to receive the second laser driving signal and the third laser driving signal sent by the second laser driving unit, and generate the second downlink under the trigger of the second laser driving signal The third downlink optical signal is generated by the optical signal and triggered by the third laser driving signal.
The OLT optical transceiver module according to claim 1, wherein the first uplink burst receiving unit comprises:

The first photo receiving unit is configured to receive the first uplink optical signal separated by the WDM unit, and convert the first uplink optical signal into a first current signal;

a first amplifying unit configured to receive the first current signal sent by the first photo receiving unit, and convert the current signal into a first differential voltage signal;

The second amplifying unit is configured to receive the first differential voltage signal sent by the first amplifying unit, and perform amplification or limiting shaping on the first differential voltage signal to output to the electrical connector.
The OLT optical transceiver module according to claim 4, wherein the first uplink burst receiving unit further comprises:

The first reset circuit is configured to release the residual signal level of the input terminal of the second amplifying unit after receiving the reset signal.
The OLT optical transceiver module according to claim 1, wherein the second uplink burst receiving unit comprises:

a second photo receiving unit configured to receive a second uplink optical signal and a third uplink optical signal of different time slots separated by the WDM unit, and convert the second uplink optical signal into a second current signal and Converting the third uplink optical signal into a third current signal;

a third amplifying unit configured to receive the second current signal and the third current signal sent by the second photo receiving unit, and convert the second current signal into a second differential voltage signal and Converting the third current signal into a third differential voltage signal;

a fourth amplifying unit configured to receive the second differential voltage signal and the third differential voltage signal sent by the third amplifying unit, and perform the second differential voltage signal and the third differential voltage signal After amplification or limiting shaping, output to the electrical connector.
The OLT optical transceiver module according to claim 6, wherein the second uplink burst receiving unit further comprises:

The second reset circuit is configured to release the residual signal level of the input terminal of the fourth amplifying unit after receiving the reset signal.
The integrated OLT optical transceiver module according to claim 4 or 6, wherein the OLT optical transceiver integrated module further comprises:

a burst receiving optical power RSSI monitoring unit, configured to receive, by the first uplink burst receiving unit, the first uplink optical signal separated by the WDM unit and/or the second uplink burst receiving unit to receive the WDM Collecting, processing, and reporting the second uplink optical signal and/or the third uplink optical signal of different time slots separated by the unit, and monitoring the first uplink optical signal, the second uplink optical signal, and the The signal strength of the third uplink optical signal.
The OLT optical transceiver integrated module according to any one of claims 1 to 8, wherein the OLT optical transceiver integrated module further comprises:

a microcontroller, connected to the first laser driving unit, the second laser driving unit, the second amplifying unit, the fourth amplifying unit, the burst receiving optical power RSSI monitoring unit, and the electrical connector, configured to drive the first laser The unit, the second laser driving unit, the second amplifying unit, the fourth amplifying unit, the burst receiving optical power RSSI monitoring unit, and the electrical connector perform monitoring.
An optical line terminal OLT optical transceiver integrated module comprises: an electrical connector, an optical interface, a wavelength division multiplexing WDM unit, a first downlink transmitting unit, a second downlink transmitting unit, and a third downlink transmitting unit, first a channel uplink burst receiving unit, a second uplink burst receiving unit, and a third uplink receiving unit; wherein

The first downlink transmitting unit is configured to receive a first electrical signal sent by the electrical connector, and convert the first electrical signal into a first downlink optical signal;

The second downlink transmitting unit is configured to receive a second electrical signal sent by the electrical connector, and convert the second electrical signal into a second downstream optical signal;

The third downlink transmitting unit is configured to receive a third electrical signal sent by the electrical connector, and convert the third electrical signal into a third downstream optical signal, where the second road The downlink optical signal and the third downlink optical signal adopt a time division multiplexing manner;

The first uplink burst receiving unit is configured to receive the first uplink optical signal separated by the WDM unit, and convert the first uplink optical signal into the first electrical signal, which will be converted The first electrical signal is output to the electrical connector;

The second uplink burst receiving unit is configured to receive a second uplink optical signal separated by the WDM unit, and convert the second uplink optical signal into the second electrical signal; and convert The second electrical signal is output to the electrical connector;

The third uplink burst receiving unit is configured to receive a third uplink optical signal separated by the WDM unit, and convert the third uplink optical signal into the third electrical signal; and convert The third electrical signal is output to the electrical connector, wherein the second uplink optical signal and the third upstream optical signal are time division multiplexed;

The WDM unit is configured to set the first downlink optical signal sent by the first downlink transmitting unit and the second downlink optical signal sent by the second downlink transmitting unit, and the third The third downlink optical signal sent by the downlink downlink transmitting unit is wavelength-multiplexed and then output through the optical interface; the optical signal received by the optical interface is separated into the first uplink optical signal and the second road Line light signal, third line up light signal.
A method of processing a plurality of passive optical network PONs, comprising:

Receiving a first electrical signal, a second electrical signal, and a third electrical signal sent by the electrical connector;

Converting the first electrical signal into a first downlink optical signal, converting the second electrical signal into a second downstream optical signal, and converting the third electrical signal into a third downstream optical signal ;

Passing the first downlink optical signal, the second downlink optical signal, and the third downlink optical signal to a wave And outputting after multiplexing; wherein, the second downlink optical signal and the third downlink optical signal are time division multiplexed;

Demultiplexing the received optical signal to obtain a first uplink optical signal, a second uplink optical signal, and a third uplink optical signal; converting the first uplink optical signal into the first electrical circuit a signal, converting the second uplink optical signal into the second electrical signal and converting the third upstream optical signal into a third electrical signal;

Outputting the converted first electrical signal, the second electrical signal, and the third electrical signal to the electrical connector, wherein the second upstream optical signal and the third The uplink optical signal of the road adopts time division multiplexing.
A system for processing a plurality of passive optical network PONs, comprising: a beam splitter, an optical network unit, and an optical line termination OLT optical transceiver integrated module according to any one of claims 1 to 10; wherein said splitting The device is connected to the optical line terminal OLT optical transceiver module, and the optical splitter is connected to the optical network unit.