Abstract:
A scheme is described for remote control of the wavelength of a tunable transmitter in a smart small form-factor pluggable (SFP) transceiver, a smart SFP plus (SFP+) transceiver, a smart 10 gigabit small form-factor pluggable (XFP) transceiver, a smart duplex transceiver, a smart bidirectional (BiDi) transceiver, or a smart single wavelength single fiber (SWSF) BiDi-transceiver in a communication system using an operating system with Operation, Administration, and Maintenance (OAM) and Proprietary Protocol (PP) functions; an OAM, PP &amp; Payload Processor; a transceiver; an optical spectrum analyzer; a bit error rate test (BERT); and an optical link in the field.

Description:
FIELD 
     Embodiments of the invention relate to a scheme for remote control of an electro-optical parameter of a smart transceiver in an optical fiber communication system, and more particularly, a scheme for remote control of the wavelength of a tunable transmitter in a smart transceiver. The applications of embodiments of the present invention include a smart transceiver installed in communication systems without optical amplifiers as well as optically amplified wavelength division multiplexing (WDM) communication systems, for example, such as long-haul transmission networks, access networks of fiber to the x (FTTx), passive optical networks (PON), and wireless backhauls between a base station (BTS) and an antenna tower or a remote radio head (RRH), but not limited only to these systems. A smart transceiver is an intelligent transceiver which can execute Ethernet in the First Mile Operation, Administration, and Maintenance (EFM OAM) functions specified in IEEE 802.3ah, including an electrical loopback configuration and the proprietary protocol (PP) functions. The type of the smart transceiver includes a smart small form-factor pluggable (SFP) transceiver, a smart small form factor pluggable plus (SFP+) transceiver, and a smart 10 gigabit small form-factor pluggable (XFP) transceiver, and a Duplex smart transceiver as well as conventional two-wavelength bidirectional (BiDi) smart transceiver and single wavelength, single fiber bidirectional (SWSF BiDi) smart transceiver, all of which are tunable. 
     BACKGROUND 
     An ability to tune the wavelength of a tunable transmitter in a transceiver from a remote site is very desirable for the following applications: 1) the mitigation of the interferometric beat noises (IBN) by avoiding the overlap of the wavelengths of two transmitters in a link where there are finite optical reflections along the link and SWSF BiDi smart transceivers are used, and 2) the link optimization of individual channel of a WDM communication system using duplex type smart transceivers or conventional two-wavelength BiDi smart transceivers. 
     For an optical link using SWSF BiDi transceivers in non-WDM communication systems or WDM, including conventional WDM or dense WDM (CWDM or DWDM) communication systems, the IBN generated, during optical to electrical (O/E) conversion at an optical receiver, between the optical spectral components of the intended signal from one transmitter and the optical spectral components of the unwanted, reflected signal of the other transmitter along the optical link will interfere with an intended signal and degrade signal to noise ratio (S/N) of the intended signal such that the communication optical link may not work properly, or even may be shut down; the IBN becomes biggest when the spectral components of two transmitters are overlapping on each other&#39;s. To suppress this IBN, there are two options: 1) Option #1, use of angled polished connectors (APCs) wherever physical connections with connectors are needed along the optical link to minimize the optical reflection at the connection, and 2) Option #2, use of the wavelength of one transmitter which is outside the wavelength spectra of the other transmitter in the link while allowing the reflections along the optical link. The Option #1 might be neither practical nor appealing to network owners or service providers, considering that 1) almost all the connectors of currently deployed outside plant (OSP) link fibers are polished or ultra polished type connectors (PC or UPC) where an air gap between two connectors at the connection is always possible causing 13 dB to 14 dB of optical reflection and converting all these PC or UPC connectors into APC connectors will be quite expensive, 2) owners of OSP link fibers might not be interested in replacing all the PC or UPC connectors with APC connectors to lease the OSP fibers to the customers, and 3) transceivers with APC connectors cost more than those with PC or UPC connectors. The Option #2, however, is expected to be very attractive to network owners or service providers since this approach allows finite reflections along the optical link and does not require any specific type of connectors such as APC connectors; this offers network owners or service providers, for the first time, their own choice of selection of connector type in their communication systems using SWSF BiDi transceivers while taking full advantage of all the merits of the SWSF BiDi transceivers. With this Option #2, the mitigation of the IBN can be achieved through tuning the wavelength of transmitters such that the wavelength spectra of a transmitter of the SWSF BiDi transceiver at one end of the optical link is not overlapping the wavelength spectra of a transmitter of the SWSF BiDi transceiver at the other end of the optical link. This is particularly important when there are finite optical reflections along the optical link, and the difference in received optical power level, at an optical receiver, between the intended signal and the reflected signal is less than 13 dB. 
     For an optical link using transceivers other than SWSF BiDi transceivers in a WDM (CWDM or DWDM) communication system which is composed of, at both ends of a link, conventional duplex type transceivers (or two-wavelength BiDi transceivers) with a specific wavelength for individual channel of the link, an optical MUX, a link optical fiber, and an optical DEMUX, it is not rare that a service provider encounters occasions of deploying a transceiver the transmitter wavelength of which, set initially by the transceiver supplier, might not be at the center or the optimum of the composite wavelength bandwidth of the optical MUX and DEMUX along each channel. This would result in the link budget very tight without much available operational system margin which must be allocated for any robust communication system, whereas the optimization of wavelength of the transmitter of the transceiver could help each channel of the WDM link with an extra operational system margin. 
     Certain communication systems, therefore, will benefit with a transceiver which is equipped with the adjustability of the wavelength of a transmitter in the transceiver as described above. Since 1) a communication system consists of, at least, two transceivers where the transmitter of one transceiver is transmitting a signal to the receiver of another transceiver, and 2) the optimum wavelength of each transmitter depends solely on the system in which the transceiver is operating, the controllability of the wavelength of the transmitter in one transceiver by another transceiver will be a desirable feature. This is particularly true if two transceivers are physically separated far away from each other. In other words, a remote controllability of the wavelength of a tunable transmitter of one transceiver by another transceiver will be very valuable, considering the facts that 1) the adjustment of its wavelength can be executed by the technician at the CO where all the necessary test equipments are accessible easily and 2) another technician does not have to be present simultaneously at the site of the transceiver which is in need of adjustment of its wavelength; this will save a lot of capital and operating expenditures (CAFEX and OPEX) by the service provider/operator. This necessitates a new, novel approach to achieve this remote controllability of the wavelength of a tunable transmitter in a transceiver. 
     SUMMARY 
     According to embodiments of the present invention, a scheme for remote control of the wavelength of a tunable transmitter in a smart transceiver may comprise a smart transceiver at a first end of the optical link, the optical link, a transceiver, an OAM, PP &amp; Payload processor, an operating system with the OAM and the PP functions, an optical spectrum analyzer at a second end of the optical link, and a Bit Error Rate Tester (BERT). A PP similar to OAM Protocol Data Unit (OAMPDU) of EFM OAM is a message protocol of changing or monitoring the wavelength of the tunable transmitter in the smart transceiver. 
     According to embodiments of the present invention, a smart transceiver at a first end of the optical link can perform the EFM OAM and the PP functions in passive mode including the electrical loopback and the PP functions. The smart transceiver is equipped with 1) a circuitry which can adjust the wavelength of the tunable transmitter and 2) a circuitry which can measure a certain parameter of the Tx representing the wavelength of the Tx indirectly in the smart transceiver upon receiving a commanding message in PP from the transceiver at a second end of the optical link. The type of the smart transceiver may be a smart SFP transceiver, a smart SFP+ transceiver, a smart XFP transceiver, a smart Duplex transceiver, a smart conventional BiDi transceiver, or a smart SWSF BiDi transceiver. 
     According to embodiments of the present invention, an optical link may comprise an optical multiplexer (MUX), optical amplifier(s), optical fiber(s), and an optical demultiplexer (DEMUR). 
     According to embodiments of the present invention, a transceiver at a second end of the optical link can perform the EFM OAM and the PP in active mode. This transceiver can send out a commanding message of the adjustment or measurement of the wavelength of the transmitter in the smart transceiver in a first end of the optical link using a PP. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements. 
         FIG. 1  shows a configuration for a scheme for remote control of the wavelength of a transmitter in a smart duplex transceiver. 
         FIG. 2  shows a detail functional block diagram of a smart duplex transceiver. 
         FIG. 3  shows a procedure for the remote control of the wavelength of a tunable transmitter in a smart transceiver. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , a scheme for remote control of the wavelength of a transmitter in a smart transceiver includes an operating system with OAM and PP functions  100 , an OAM, PP &amp; Payload Processor  101 , a duplex transceiver  102 , a pair of optical fiber jumpers  103  and  108 , an optical link  104 , a pair of optical fiber jumpers  105  and  107 , and a smart duplex transceiver  106 , an optical spectrum analyzer  109  and a BERT  110 . The OAM, PP &amp; Payload Processor  101  can execute a built-in-system-test (BIST) procedure  150 . 
     As shown in  FIG. 2 , a smart duplex transceiver includes an optical receiver  200 ; an electrical path  201 ; an OAM, PP &amp; Payload Processor  202 ; a Loopback circuit  203 ; an electrical path  204 ; a Tx wavelength control circuit  205 ; electrical paths  206 ,  207 , and  208 ; a Tx wavelength monitoring circuit  209 ; an electrical path  210 ; and an optical transmitter  211 . 
     The following is a procedure for the remote control of the wavelength of a transmitter in a smart duplex transceiver  106 . 
     It is assumed, but not required, during this procedure that the transmission is error free in either direction, from the transceiver  102  to the smart transceiver  106 , or from the smart transceiver  106  to the transceiver  102 , because the PP messages of controlling the transmitter wavelength are to be exchanged between transceivers  102  and  106 . This is typically met since almost all the systems in service are designed to run in error free region with even an extra system margin of few dB. 
     Sometimes the transmission with default settings of the communication system over the optical link  104  might not be error free. In this case, all the PP messages might need to be sent repeatedly to make sure that the PP messages are received correctly by the transceiver at the receiving side. 
     Operation One 
     The following is the first operation  301 . It is necessary, first of all, to configure the smart duplex transceiver  106  in a loopback mode to find the bit error rate (BER) with the current settings of the transceiver. For this, a loopback OAM Protocol Data Unit (OAMPDU) generated at the operating system with OAM and PP functions  100  is sent to an OAM, PP &amp; Payload Processor  101  where the loopback OAMPDU is encapsulated serially with the payload, if there is any. During this period, the output from the BERT  110  is disabled. The output is sent to the transceiver  102 , where the electrical signal of the loopback OAMPDU message is converted into an optical signal. Then the optical signal of the loopback message is transmitted through the optical jumper  103 , the optical link  104 , and an optical jumper  105 , and arrives at the smart duplex transceiver  106 . 
     The optical signal arriving at the smart duplex transceiver  109  is then converted into an electrical signal at the receiver  200 . The electrical signal is transmitted through the electrical path  201 , and arrives at an OAM, PP &amp; Payload Processor  202 , where the loopback OAMPDU message is separated and executed. Now only the remaining payload, if there is any, passes through the OAM, PP &amp; Payload Processor  202  and an electrical path  207 , and arrives at the optical transmitter  211 , where the electrical payload signal is converted into an optical signal. 
     The optical signal of the payload from the smart transceiver  106  is transmitted through an optical jumper  107 , the optical link  104 , and an optical jumper  108 , and arrives at the transceiver  102  where the optical signal is converted into an electrical signal. The electrical signal transmits to the OAM, PP &amp; Payload Processor  101 . This completes the configuration in the loopback mode. 
     Operation Two 
     The following is the second operation  302 . The output from the BERT  110  is enabled and a pseudo-random (PRN) bit stream is sent out at the same data rate of the communication system to the OAM, PP &amp; Payload Processor  101 . During this transmission period, there is no sending out of any OAMPDU&#39;s and PP&#39;s in the data stream. This pseudo-random data signal will be transmitted through the path described above during the preparation of the loopback mode and then will return to the error detector of the BERT for the BER measurement. The measured BER is recorded. 
     An alternative embodiment is as follows. A built-in-system-test (BIST) procedure  150  of the OAM, PP &amp; Payload processor  101  is enabled and transmits a pseudo-random (PRN) bit stream to the smart transceiver  106 . The smart transceiver  106  then transmits the PRN bit stream back to the OAM, PP &amp; Payload processor  101  for bit error (BER) measurement. The measured BER is then recorded. 
     Operation Three 
     The following is the third operation  363 . The output of the BERT  110  is disabled. 
     Operation Four 
     The following is the fourth operation  304 . The loopback configuration of the smart transceiver  106  is disabled using the operation 1) above with a disable loopback OAM Protocol Data Unit (OAMPDU). 
     Operation Five 
     The following is the fifth operation  305 . A wavelength monitoring PP message generated at the operating system with OAM and PP functions  100  is sent to the OAM, PP &amp; Payload Processor  101 . The output is sent to the transceiver  102  where the electrical signal of the wavelength monitoring PP message is converted into an optical signal. Then the optical signal of the wavelength monitoring PP message is transmitted through the optical jumper  103 , the optical link  104 , and an optical jumper  105 , and arrives at the smart duplex transceiver  106 . This PP message is for requesting the wavelength monitoring circuit  209  to measure the parameter representing the Tx wavelength and, for example, the Tx temperature, and then sending it to the transceiver  102  in another PP message generated in the transceiver  106 . 
     The optical signal arriving at the smart duplex transceiver  106  is then converted into an electrical signal at the receiver  200 . The electrical signal is transmitted through the electrical path  201  and arrives at the OAM, PP &amp; Payload Processor  202 , where the wavelength monitoring PP message is separated. An execution message of the wavelength monitoring PP message is sent to the Tx wavelength monitoring PP message circuit  209 , which measures the parameter representing the wavelength of the transmitter  211  accordingly. The measured parameter representing Tx wavelength is processed in the OAM, PP &amp; Payload Processor  202  and sent along the electrical path  207  to the transmitter  211 , with the payload where it is converted into an optical signal. 
     The optical signal is transmitted through the optical jumper  107 , the optical link  104 , and the optical jumper  107 , and arrives at the receiver of the transceiver  102  where the optical signal is converted back into an electrical signal. This signal is processed at the OAM, PP &amp; Processor  101 , and the measured parameter representing Tx wavelength is read out at the Operating System w/OAM and PP Functions  100 . The parameter representing Tx wavelength is then recorded. 
     Operation Six 
     The following is the sixth operation  306 . The wavelength out of the fiber jumper  108  is measured using the Optical Spectrum Analyzer  109 . 
     Operation Seven 
     The following is the seventh operation  307 . A wavelength adjustment PP message, a message that sets the Tx wavelength at a specified value, generated at the operating system with OAM and PP functions  100 , is sent to the OAM, PP &amp; Payload Processor  101 . The output is sent to the transceiver  102 , where the electrical signal of the wavelength adjustment PP message is converted into an optical signal. Then the optical signal of the wavelength adjustment PP message is transmitted through the optical jumper  103 , the optical link  104 , and an optical jumper  105 , and arrives at the smart duplex transceiver  106 . 
     The optical signal arriving at the smart duplex transceiver  106  is then converted into an electrical signal at the receiver  200 . The electrical signal is transmitted through the electrical path  201  and arrives at an OAM, PP &amp; Payload Processor  202 , where the wavelength adjustment PP message is separated. An execution message of the wavelength adjustment is sent to the Tx wavelength control circuit  205 , which adjusts the wavelength of the transmitter  211  accordingly. 
     Operation Eight 
     The following is the eighth operation  308 . Operation 5) is repeated to read out the parameter representing Tx wavelength at the new setting. The parameter is recorded. 
     Operation Nine 
     The following is the ninth operation  309 . Operation 7) is repeated. Operation 5) is repeated and the Tx wavelength is recorded. A check is done to see that the Tx wavelength is consistent with what was set or expected. 
     Operation Ten 
     The following is the tenth operation  310 . Operation 3) and operation 9) are repeated if needed. 
     Operation Eleven 
     The following is the eleventh operation  311 . Operation 1) and operation 2) are repeated. A confirmation is done to see if the measured BER is indeed what is expected. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.