Patent Publication Number: US-2016248534-A1

Title: Method for processing optical signal, optical module and optical line terminal

Description:
TECHNICAL FIELD 
     The present disclosure relates to the field of optical communications, and in particular to a method for processing optical signals, an optical module and an Optical Line Terminal (OLT). 
     BACKGROUND 
     With the rapid development of optical fibre communication technologies and the promotion and popularization of optical fibre access technologies, demands of people for bandwidth are unceasingly increased, and a technology capable of providing higher bandwidth becomes a solution for a next generation broadband access network. 
     A technical solution is mature and stable for products which have been largely applied to the business. In consideration of cost and maintenance, the smooth upgrade of a system is also required to be taken into consideration according to a solution for higher bandwidth. However, the problem of smooth upgrade of the system caused by using of the higher bandwidth is not yet solved in the traditional art. The compatibility of a traditional mature technology is not yet considered, and therefore an Optical Network Unit (ONU) can select a solution according to a specific application environment. 
     SUMMARY 
     The present disclosure provides a method for processing optical signals, an optical module and an OLT, which are intended to solve the technical problem of smooth upgrade of a passive optical network. 
     In order to solve the technical problem, an embodiment of the present disclosure provides an optical module of an OLT, which may include two photoelectric transmitter and receiver units and a Wavelength Division Multiplexing (WDM) unit. 
     Each photoelectric transmitter and receiver unit is configured to: generate a downstream optical signal with a corresponding rate and wavelength according to an electric signal, and then output the downstream optical signal to the WDM unit; and receive an upstream optical signal outputted by the WDM unit with a rate and wavelength corresponding to a burst mode, and convert the upstream optical signal into the electric signal. 
     The WDM unit is configured to: after receiving the downstream optical signals outputted by the two photoelectric transmitter and receiver units, perform WDM on the downstream optical signals, and then output the downstream optical signals; and receive the upstream optical signal, de-multiplex the upstream optical signal to obtain upstream optical signals with different rates and wavelengths, and output the upstream optical signals to the corresponding photoelectric transmitter and receiver units respectively. 
     Preferably, each photoelectric transmitter and receiver unit may include: 
     a laser drive unit, configured to receive the corresponding electric signal, convert the electric signal into a laser drive signal, and output the laser drive signal to a laser; and 
     the laser, configured to generate the corresponding downstream optical signal after receiving the laser drive signal. 
     Preferably, each photoelectric transmitter and receiver unit may include: 
     a photoelectric receiving diode, configured to receive the upstream optical signal with the corresponding rate and wavelength outputted by the WDM unit, convert the upstream optical signal into a corresponding current signal, and send the current signal to a trans-impedance amplifier in a burst mode; 
     the trans-impedance amplifier, configured to convert the received current signal into a differential voltage signal, and send the differential voltage signal to a limiting amplifier in a burst mode; and 
     the limiting amplifier, configured to process and output the differential voltage signal. 
     Preferably, each photoelectric transmitter and receiver unit may further include: 
     a RESET bleeder circuit, configured to process a residual signal level of the limiting amplifier after receiving a RESET signal. 
     Preferably, 
     one of the photoelectric transmitter and receiver units may be configured to generate a downstream optical signal which has a first downstream signal rate and is transmitted in a first downstream wavelength continuous mode, and receive an upstream optical signal which has a first upstream signal rate and a first upstream wavelength; 
     the other photoelectric transmitter and receiver unit may be configured to generate a downstream optical signal which has a second downstream signal rate and is transmitted in a second downstream wavelength continuous mode, and receive an upstream optical signal which has a second upstream signal rate and a second upstream wavelength; and 
     the ranges of the first downstream wavelength, the second downstream wavelength, the first upstream wavelength and the second upstream wavelength may be not overlapped. 
     An embodiment of the present disclosure also provides an OLT, which may include the above-mentioned optical module. 
     An embodiment of the present disclosure also provides an optical signal processing method, which may include that: 
     a first downstream optical signal which has a first downstream signal rate and is transmitted in a first downstream wavelength continuous mode is generated, and a second downstream optical signal which has a second downstream signal rate and is transmitted in a second downstream wavelength continuous mode is generated; 
     WDM is performed on the first downstream optical signal and the second downstream optical signal, and then the first downstream optical signal and the second downstream optical signal are output; 
     a first upstream optical signal which has a first upstream signal rate and a first upstream wavelength and a second upstream optical signal which has a second upstream signal rate and a second upstream wavelength are received; and 
     the first upstream optical signal and the second upstream optical signal are de-multiplexed. 
     An embodiment of the present disclosure also provides a computer storage medium in which computer executable instructions are stored. The computer executable instructions are used for executing the above-mentioned method. 
     The embodiments of the present disclosure provide the optical signal processing method, the optical module and the OLT. The OLT can support multiple passive optical networks, particularly a Gigabit Passive Optical Network (GPON) and a 10G PON (XGPON1) which currently exist. The OLT supports a traditional GPON OLT technical solution and also supports an XGPON1 high-rate technical solution. The smooth upgrade of a GPON system can be realized, and the system upgrade cost, operation cost and maintenance cost of an operator are reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an OLT according to an embodiment of the present disclosure; 
         FIG. 2  is a system structure diagram according to an embodiment 1 of the present disclosure; 
         FIG. 3  is a functional principle block diagram according to an embodiment 1 of the present disclosure; 
         FIG. 4  is a system structure diagram according to an embodiment 2 of the present disclosure; and 
         FIG. 5  is a functional principle block diagram according to an embodiment 2 of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In order to make the purpose, technical solution and advantages of the present disclosure clearer, the embodiments of the present disclosure will be described below with reference to the drawings in detail. It is important to note that the embodiments in the present disclosure and the characteristics in the embodiments can be randomly combined with each other under the condition of no conflicts. 
       FIG. 1  is a diagram of an optical module of an OLT according to an embodiment of the present disclosure. As shown in  FIG. 1 , the optical module according to the embodiment includes: two photoelectric transmitter and receiver units and a WDM unit. 
     Each photoelectric transmitter and receiver unit is configured to: generate a downstream optical signal with a corresponding rate and wavelength according to an electric signal, and then output the downstream optical signal to the WDM unit; and receive an upstream optical signal with a rate and wavelength corresponding to a burst mode output by the WDM unit, and convert the upstream optical signal into the electric signal. 
     The WDM unit is configured to: after receiving the downstream optical signals output by the two photoelectric transmitter and receiver units, perform WDM on the downstream optical signals, and then output the downstream optical signals; and receive the upstream optical signal, de-multiplex the upstream optical signal to obtain upstream optical signals with different rates and wavelengths, and output the upstream optical signals to the corresponding photoelectric transmitter and receiver units respectively. 
     The embodiment of the present disclosure provides an OLT which supports coexistence of multiple PONs. The OLT can work in a technical solution for higher bandwidth, and can be compatible with a traditional mature commercial solution, the technical problem of smooth upgrade of a PON is solved, and the system upgrade cost, operation cost and maintenance cost of the operator are reduced. 
     For example, a GPON technology cannot meet increasing demands for broadband services gradually. A higher-bandwidth XGPON1 technology becomes a solution for the next generation broadband access network. In the GPON technology, the OLT is a main device used for connecting an optical fibre main line, and the optical module of the OLT is an important component for realizing GPON optical fibre communication. A current XGPON1 OLT technical solution can realize data transmission at an upstream rate 2.488 Gbps (2.5G for short hereinafter) and at a downstream rate 9.95 Gbps (10G for short hereinafter), thereby solving the technical bottleneck of the XGPON1. 
     The GPON technical solution is mature and stable, and has been largely applied to the business. In consideration of cost and maintenance, the smooth upgrade of the system is also required to be taken into consideration in the application of the XGPON1. Thus, the application of the XGPON1 should be compatible with a traditional GPON technology, so that the ONU can select a solution according to the specific application environment. 
     As shown in  FIG. 2 , the embodiment of the present disclosure designs an OLT optical transmitter and receiver module which supports the coexistence of two PONs. The using of ONUs in two modes is supported in a coexistence system. The coexisting optical transmitter and receiver module of the embodiment can work in two modes via system selection. In a first OLT mode, a first upstream rate and a first upstream wavelength are adopted, and a transmitting part with a first downstream rate and a first downstream wavelength is adopted. In a second OLT mode, a second upstream rate and upstream wavelength and a second downstream rate and downstream wavelength are adopted. 
       FIG. 3  shows a functional principle block diagram according to an embodiment 1 of the present disclosure, which includes: an electric connector, an optical interface, a wavelength multiplexing unit, a first downstream transmitting part, a second downstream transmitting part, a first upstream burst receiving part, a second upstream burst receiving part and other signal processing parts. 
     The electric connector is used for connecting a first electric signal and a second electric signal. 
     The optical interface serves as an input output optical interface for a first upstream optical signal, a second upstream optical signal, a first downstream optical signal and a second downstream optical signal. 
     The wavelength multiplexing unit multiplexes the first downstream optical signal and the second downstream optical signal, outputs the first downstream optical signal and the second downstream optical signal to the optical interface, de-multiplexes the first upstream signal and the second upstream signal received by the optical interface, and then outputs the first upstream signal and the second upstream signal to corresponding photoelectric detectors, and the photoelectric detectors convert the optical signals into photoelectric current signal. 
     In the first downstream transmitting part, a first laser drive unit receives the first electric signal transmitted by the electric connector, optimizes a transmitting end electric signal, converts a digital electric signal into a laser drive signal, and drives a first laser to convert the laser drive signal into the first downstream optical signal. 
     In the second downstream transmitting part, a second laser drive unit receives the second electric signal transmitted by the electric connector, optimizes the transmitting end electric signal, converts the digital electric signal into the laser drive signal, and drives a second laser to convert the laser drive signal into the second downstream optical signal. 
     A micro control unit can control modulated currents and bias currents of the first laser drive unit and the second laser drive unit, so that an optical power and an extinction ratio, which are output, maintain current values, and meet system requirements. 
     In the first upstream burst receiving part, a first optical signal received by the optical interface is separated via the WDM unit and then sent to a first photoelectric receiving diode, the first photoelectric receiving diode converts the first optical signal into a current signal and sends the current signal to a first burst mode trans-impedance amplifier, the first burst mode trans-impedance amplifier converts the received current signal into a differential voltage signal, the differential voltage signal passes through a first RESET bleeder circuit and then is sent to a first burst limiting amplifier, and the first burst limiting amplifier performs amplification or limiting reshaping on the received voltage signal, and then outputs the voltage signal to the electric connector. 
     In the second upstream burst receiving part, a second optical signal received by the optical interface is separated via the WDM unit and then sent to a second photoelectric receiving diode, the second photoelectric receiving diode converts the second optical signal into a current signal and sends the current signal to a second burst mode trans-impedance amplifier, the second burst mode trans-impedance amplifier converts the received current signal into a differential voltage signal, the differential voltage signal passes through a second RESET bleeder circuit and then is sent to a second burst limiting amplifier, and the second burst limiting amplifier performs amplification or limiting reshaping on the received voltage signal, and then outputs the voltage signal to the electric connector. 
     A burst Received Signal Strength Indicator (RSSI) monitoring unit collects, processes and reports a first burst receiving optical signal and a second burst receiving optical signal respectively, monitors optical power signal strength in real time, and follows an SFF-8472 protocol and other protocols. 
     According to the RESET burst bleeder circuits, RESET signals are notification signals for notifying that a next group of burst data come. After the RESET bleeder circuits receive the RESET signals, residual signal levels at input ends of the burst limiting amplifiers are cleared in time to ensure accurate receiving of the next group of burst data. A time sequence requirement of the system is met. The two RESET burst bleeder circuits in the embodiment of the present disclosure process the residual signal levels of the limiting amplifiers of two receiving channels respectively, and the time sequence requirement of a coexistence receiving system is met. 
     The micro control unit controls a signal line or an IIC bus to connect a laser driver, the limiting amplifiers, an RSSI circuit and the like so as to monitor, collect and process corresponding data. An externally connected IIC bus interface is also provided, and is connected to a system panel IIC bus interface via an optical module electric interface so as to diagnose and monitor a digital signal of the optical module via the system. 
     As shown in  FIG. 4 , the embodiment of the present disclosure is an optical module in which a GPON OLT and an XGPON1 OLT coexist, and using of the GPON OLT and the XGPON1 OLT is supported in the coexistence system. The coexisting OLT optical module in the embodiment can work in two modes via system selection. One of the modes is a GPON OLT mode, an upstream rate is 1.25 Gbps, burst receiving by using a 1310 nm centre wavelength is performed, a downstream rate is 2.5 Gbps, and a transmitting part in a 1490 nm centre wavelength continuous mode is adopted. The other mode is an XGPON1 OLT mode, an upstream rate is 2.5 Gbps, burst receiving by using a 1270 nm centre wavelength is performed, a downstream rate is 10 Gbps, and a transmitting part in a 1577 nm centre wavelength continuous mode is adopted. 
       FIG. 5  shows a functional principle block diagram according to a preferred embodiment of the present disclosure. The electric connector adopts a 10Gigabit Small Form Factor Pluggable Module (XFP), and pin function definitions are shown in Table 1 in detail. In the embodiment of the present disclosure, an XFP interface is adopted, levels and functions of each pin of the electric interface are defined, requirements of the system are met and requirements of an INF-8077 protocol are met. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Power 
                   
               
               
                 Pin 
                 Symbol 
                 Level 
                 on order 
                 Functional description 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 GND 
                   
                 1st 
                 Module ground 
               
               
                 2 
                 TX_FAULT 
                 LVTTL-O 
                 3rd 
                 A failure indication is transmitted, a low 
               
               
                   
                   
                   
                   
                 level shows that transmission operation 
               
               
                   
                   
                   
                   
                 is normal, a high level shows that 
               
               
                   
                   
                   
                   
                 transmission is faulty, and the pull-up 
               
               
                   
                   
                   
                   
                 resistance of a mother board is 4.7 to 
               
               
                   
                   
                   
                   
                 10 kilohm 
               
               
                 3 
                 TX_2.5G_P 
                 LVPECL 
                 3rd 
                 A 2.5G transmitting end differential 
               
               
                   
                   
                   
                   
                 input is positive, alternating current 
               
               
                   
                   
                   
                   
                 coupling is performed, and a differential 
               
               
                   
                   
                   
                   
                 swing ranges from 500 to 2400 mV 
               
               
                 4 
                 TX_2.5G_N 
                 LVPECL 
                 3rd 
                 A 2.5G transmitting end differential 
               
               
                   
                   
                   
                   
                 input is negative, alternating current 
               
               
                   
                   
                   
                   
                 coupling is performed, and a differential 
               
               
                   
                   
                   
                   
                 swing ranges from 500 to 2400 mV 
               
               
                 5 
                 TX_DIS 
                 LVTTL-I 
                 3rd 
                 Enabling is transmitted, disabling is 
               
               
                   
                   
                   
                   
                 transmitted in high levels 10G and 
               
               
                   
                   
                   
                   
                 2.5G, and the internal pull-up resistance 
               
               
                   
                   
                   
                   
                 of an optical module is 4.7 to 10 kilohm 
               
               
                 6 
                 Vcc5 
                   
                 2nd 
                 A 5 V power supply is required to be 
               
               
                   
                   
                   
                   
                 5 V +− 5 percent 
               
               
                 7 
                 GND 
                   
                 1st 
                 Module ground 
               
               
                 8 
                 Vcc3_Tx 
                   
                 2nd 
                 A transmitting end power supply is 
               
               
                   
                   
                   
                   
                 required to be 3.3 V +− 5 percent 
               
               
                 9 
                 Vcc3_Rx 
                   
                 2nd 
                 A receiving end power supply is 
               
               
                   
                   
                   
                   
                 required to be 3.3 V +− 5 percent 
               
               
                 10 
                 SCL 
                 LVTTL-I 
                 3rd 
                 Two serial interface clock lines are 
               
               
                   
                   
                   
                   
                 provided, and the pull-up resistance of 
               
               
                   
                   
                   
                   
                 a mother board is 4.7 to 10 kilohm 
               
               
                 11 
                 SDA 
                 LVTTL-I 
                 3rd 
                 Two serial interface data lines are 
               
               
                   
                   
                   
                   
                 provided, and the pull-up resistance of 
               
               
                   
                   
                   
                   
                 a mother board is 4.7 to 10 kilohm 
               
               
                 12 
                 MOD_ABS 
                 LVTTL-O 
                 3rd 
                 An indication indicating that a module is 
               
               
                   
                   
                   
                   
                 in place, the interior is grounded, the 
               
               
                   
                   
                   
                   
                 pull-up resistance of a mother board is 
               
               
                   
                   
                   
                   
                 4.7 to 10 kilohm, and a high level shows 
               
               
                   
                   
                   
                   
                 that the module is not in place 
               
               
                 13 
                 RESET_2.5G 
                 LVTTL-O 
                 3rd 
                 A 2.5G burst receiving RESET signal is 
               
               
                   
                   
                   
                   
                 shown, and a rising edge is triggered 
               
               
                 14 
                 RX_2.5G_LOS 
                 LVTTL-O 
                 3rd 
                 A 2.5G receiving signal is lost, the 
               
               
                   
                   
                   
                   
                 pull-up resistance of a mother board is 
               
               
                   
                   
                   
                   
                 4.7 to 10 kilohm, a high level shows that 
               
               
                   
                   
                   
                   
                 a receiving optical power is lower than 
               
               
                   
                   
                   
                   
                 an alarm threshold, and a lower level 
               
               
                   
                   
                   
                   
                 shows that a receiving end optical 
               
               
                   
                   
                   
                   
                 power is higher than the alarm 
               
               
                   
                   
                   
                   
                 threshold 
               
               
                 15 
                 GND 
                   
                 1st 
                 Module ground 
               
               
                 16 
                 GND 
                   
                 1st 
                 Module ground 
               
               
                 17 
                 RD_2.5G_N 
                 LVPECL/CML-O 
                 3rd 
                 A 2.5G receiving end differential output 
               
               
                   
                   
                   
                   
                 is negative, and direct current coupling 
               
               
                   
                   
                   
                   
                 is performed inside a module 
               
               
                 18 
                 RD_2.5G_P 
                 LVPECL/CML-O 
                 3rd 
                 A 2.5G receiving end differential output 
               
               
                   
                   
                   
                   
                 is positive, and direct current coupling 
               
               
                   
                   
                   
                   
                 is performed inside a module 
               
               
                 19 
                 GND 
                   
                 1st 
                 Module ground 
               
               
                 20 
                 RX_1.25G_RSSI_TRIG 
                 LVTTL-O 
                 3rd 
                 1.25G RSSI sampling is triggered, and 
               
               
                   
                   
                   
                   
                 a rising edge is triggered 
               
               
                 21 
                 RX_2.5G_RSSI_TRIG 
                 LVTTL-O 
                 3rd 
                 2.5G RSSI sampling is triggered, and a 
               
               
                   
                   
                   
                   
                 rising edge is triggered 
               
               
                 22 
                 RESET_1.25G 
                 LVTTL-O 
                 3rd 
                 A 1.25G burst receiving RESET signal 
               
               
                   
                   
                   
                   
                 is shown, and a rising edge is triggered 
               
               
                 23 
                 GND 
                   
                 1st 
                 Module ground 
               
               
                 24 
                 RD_1.25G_N 
                 LVPECL/CML-O 
                 3rd 
                 A 1.25G receiving end differential 
               
               
                   
                   
                   
                   
                 output is negative, and direct current 
               
               
                   
                   
                   
                   
                 coupling is performed inside a module 
               
               
                 25 
                 RD_1.25G_P 
                 LVPECL/CML-O 
                 3rd 
                 A 1.25G receiving end differential 
               
               
                   
                   
                   
                   
                 output is positive, and direct current 
               
               
                   
                   
                   
                   
                 coupling is performed inside a module 
               
               
                 26 
                 RX_1.25G_LOS 
                 LVTTL-O 
                 3rd 
                 A 1.25G receiving signal is lost, the 
               
               
                   
                   
                   
                   
                 pull-up resistance of a mother board is 
               
               
                   
                   
                   
                   
                 4.7 to 10 kilohm, a high level shows that 
               
               
                   
                   
                   
                   
                 a receiving optical power is lower than 
               
               
                   
                   
                   
                   
                 an alarm threshold, and a lower level 
               
               
                   
                   
                   
                   
                 shows that a receiving end optical 
               
               
                   
                   
                   
                   
                 power is higher than the alarm 
               
               
                   
                   
                   
                   
                 threshold 
               
               
                 27 
                 GND 
                   
                 1st 
                 Module ground 
               
               
                 28 
                 TX_10G_N 
                 CML-I 
                 3rd 
                 A 10G transmitting end differential input 
               
               
                   
                   
                   
                   
                 is negative, alternating current coupling 
               
               
                   
                   
                   
                   
                 is performed inside a module, and an 
               
               
                   
                   
                   
                   
                 acceptable differential input amplitude 
               
               
                   
                   
                   
                   
                 of an input end is 200 to 1600 mV 
               
               
                 29 
                 TX_10G_P 
                 CML-I 
                 3rd 
                 A 10G transmitting end differential input 
               
               
                   
                   
                   
                   
                 is positive, alternating current coupling 
               
               
                   
                   
                   
                   
                 is performed inside a module, and an 
               
               
                   
                   
                   
                   
                 acceptable differential input amplitude 
               
               
                   
                   
                   
                   
                 of an input end is 200 to 1600 mV 
               
               
                 30 
                 GND 
                   
                 1st 
                 Module ground 
               
               
                   
               
            
           
         
       
     
     The optical interface adopts an SC mode. A WDM part, a 10G transmitting part, a 2.5G transmitting part, a 2.5G receiving part, a 1.25G receiving part and other signal processing parts are further provided. 
     In the embodiment, the WDM unit multiplexes a 10G 1577 nm centre wavelength transmitting optical signal and a 2.5G 1490 nm centre wavelength transmitting optical signal, and outputs the signals to an SC Receptacle optical interface. Meanwhile, a 2.5G 1270 nm centre wavelength optical signal and a 1.25G 1310 nm centre wavelength optical signal, which are received, are de-multiplexed and output to avalanche photodiodes of a 2.5G receiving part and a 1.25G receiving part respectively. 
     In the embodiment, the 10G transmitting part includes: a 10G clock data recovery unit, a 10G laser driver unit, a 10G laser, a Thermo Electric Cooler (TEC) control unit and a micro control unit part. 
     In the embodiment, the 10G laser adopts an Electro-absorption Modulated Laser (EML), and the 10G laser driver unit adopts an EML drive chip. The 10G clock data recovery unit performs jitter optimization on a transmitting end electric signal, sends data into a 10G EML laser driver unit, drives the laser, and converts the signal into an optical signal. The micro control unit part controls a drive current output by the drive unit, so that an optical signal index is in accordance with a corresponding standard and keeps stable and reliable. The TEC control unit controls a TEC in the EML, keeps an output wavelength of the laser stable, and meets the requirements of the system. 
     In the embodiment, the 2.5G transmitting part includes: a 2.5G laser driver unit, a 2.5G laser and a micro control unit part. In the embodiment of the present disclosure, a 2.5G Distributed Feed Back (DFB) laser and a 2.5G DFB laser drive chip are adopted. The driver unit receives a 2.5G data signal transmitted by the electric connector of the optical module, and converts a digital signal into a laser drive signal, and drives the 2.5G DFB laser to convert the laser drive signal into an optical signal. The micro control unit part performs drive output current control on a driver chip, so that a 2.5G optical signal index is stable and meets the requirements of the system. 
     In the embodiment, the 2.5G receiving part includes: an avalanche photodiode, a booster circuit, a 2.5G burst trans-impedance amplifier, a RESET bleeder circuit, a 2.5G burst limiting amplifier, a burst RSSI monitoring unit and a micro control unit part. In the embodiment of the present disclosure, the avalanche photodiode converts an optical signal with a 2.5G 1270 nm centre wavelength, which is de-multiplexed by the WDM unit, into a current signal, and sends the current signal to the 2.5G burst trans-impedance amplifier; and due to the fact that an XGPON1 upstream adopts a time division multiplexing mode, the optical signal received by the OLT is in a burst mode, and the received current signal is quickly converted into a differential voltage signal by using the burst trans-impedance amplifier, and the differential voltage signal is sent to the RESET bleeder circuit. A RESET signal is a notification signal for notifying that a next group of burst data come. After the RESET bleeder circuit receives the RESET signal, a residual signal level at an input end of the 2.5G burst limiting amplifier is cleared in time to ensure accurate receiving of the next group of burst data. The 2.5G burst limiting amplifier performs amplification or limiting reshaping on the received voltage signal, and then outputs the voltage signal to the electric connector. 
     In the embodiment, the 1.25G receiving part includes: an avalanche photodiode, a booster circuit, a 2.5G burst trans-impedance amplifier, a RESET bleeder circuit, a 2.5G burst limiting amplifier, a burst RSSI monitoring unit and a micro control unit part. An optical signal with a 1.25G 13100 nm centre wavelength, which is de-multiplexed by the WDM unit, is input to the 1.25G receiving part. A signal processing principle of the 1.25G receiving part is similar to that of the 2.5G receiving part. Channel bandwidth is restricted to be suitable for a 1.25G signal rate, so that a receiving sensitivity is at an optimum point. A 1.25G signal passes through the trans-impedance amplifier, the RESET bleeder circuit and the burst limiting amplifier, and then is output to the electric connector. 
     In the embodiment, the booster circuit outputs an optimum bias voltage of an optimum sensitivity needed by the avalanche photodiode, and an output voltage range is controlled by the micro control unit so as to make it meet an optimum bias voltage variation of the avalanche photodiode along with a temperature variation. In the embodiment, two booster circuits are provided to provide bias voltages for the avalanche photodiodes of the 2.5G receiving part and the 1.25G receiving part, and each booster circuit includes a switching power supply and a charge pump composed of a diode, an inductor and a capacitor. 
     The burst RSSI unit collects, processes and reports burst receiving optical signals. In the embodiment, an avalanche photodiode photoelectric current mirroring and burst sampling retaining circuit is adopted, and the micro control unit performs digital conversion calibration on an analogue signal of the sampling retaining circuit, and then reports the signal to the system. In the embodiment, two RSSI processing units monitor receiving optical powers of the 2.5G receiving part and the 1.25G receiving part respectively, and monitor burst receiving optical power signal strengths in real time according to an SFF-8472 protocol and an INF-8077 protocol. 
     According to the RESET burst bleeder circuit, a RESET signal is a notification signal for notifying that a next group of burst data come. After the RESET bleeder circuit receives the RESET signal, a residual signal level at an input end of the burst limiting amplifier is cleared in time to ensure accurate receiving of the next group of burst data. A time sequence requirement of the system is met. The RESET burst bleeder circuits in the embodiment process residual levels of the input ends of the burst limiting amplifiers of the 2.5G receiving part and the 1.25G receiving part respectively before burst signals are received, and it is ensured that two burst data are accurately received. 
     In the embodiment of the present disclosure, an OLT which supports the coexistence of the GPON and the XGPON1 is preferred as an embodiment, and both the traditional GPON technical solution and the XGPON1 high-rate technical solution are supported. 
     Based on the optical module of the OLT provided by the embodiment of the present disclosure, an embodiment of the present disclosure provides an optical signal processing method, which includes the steps as follows. 
     S 11 : An optical module of an OLT generates a first downstream optical signal which has a first downstream signal rate and is transmitted in a first downstream wavelength continuous mode, and a second downstream optical signal which has a second downstream signal rate and is transmitted in a second downstream wavelength continuous mode. 
     S 12 : The optical module of the OLT multiplexes the first downstream optical signal and the second downstream optical signal, and then outputs the first downstream optical signal and the second downstream optical signal. 
     S 21 : The optical module of the OLT receives a first upstream optical signal which has a first upstream signal rate and a first upstream wavelength, and receives a second upstream optical signal which has a second upstream signal rate and a second upstream wavelength. 
     S 22 : The optical module of the OLT de-multiplexes the first upstream optical signal and the second upstream optical signal. 
     An embodiment of the present disclosure also provides a computer storage medium in which computer executable instructions are stored. The computer executable instructions are used for executing the above-mentioned method. 
     Each unit can be realized by a Central Processing Unit (CPU), a Digital Signal Processor (DSP) or a Field-Programmable Gate Array (FPGA) in an electronic device. 
     Those skilled in the art should understand that the embodiments of the present disclosure can provide a method, a system or a computer program product. Thus, forms of hardware embodiments, software embodiments or embodiments integrating software and hardware can be adopted in the present disclosure. Moreover, a form of the computer program product implemented on one or more computer available storage media (including, but not limited to, a disk memory, an optical memory and the like) containing computer available program codes can be adopted in the present disclosure. 
     The present disclosure is described with reference to flowcharts and/or block diagrams of the method, the device (system) and the computer program product according to the embodiments of the present disclosure. It should be understood that each flow and/or block in the flowcharts and/or the block diagrams and a combination of the flows and/or the blocks in the flowcharts and/or the block diagrams can be realized by computer program instructions. These computer program instructions can be provided for a general computer, a dedicated computer, an embedded processor or processors of other programmable data processing devices to generate a machine, so that an apparatus for realizing functions assigned in one or more flows of the flowcharts and/or one or more blocks of the block diagrams is generated via instructions executed by the computers or the processors of the other programmable data processing devices. 
     These computer program instructions can also be stored in a computer readable memory capable of guiding the computers or the other programmable data processing devices to work in a specific mode, so that a manufactured product including an instruction apparatus is generated via the instructions stored in the computer readable memory, and the instruction apparatus realizes the functions assigned in one or more flows of the flowcharts and/or one or more blocks of the block diagrams. 
     These computer program instructions can also be loaded to the computers or the other programmable data processing devices, so that processing realized by the computers is generated by executing a series of operation steps on the computers or the other programmable devices, and therefore the instructions executed on the computers or the other programmable devices provide a step of realizing the functions assigned in one or more flows of the flowcharts and/or one or more blocks of the block diagrams. 
     The above is only a preferred embodiment of the present disclosure. Certainly, the present disclosure may also have other embodiments. Those skilled in the art can make various corresponding variations and modifications according to the present disclosure without departing from the spirit and essence of the present disclosure, but these corresponding variations and modifications shall fall within the protection scope of attached claims of the present disclosure.