Patent Application
20130045003
This disclosure relates to detecting Stimulated Brillouin Scattering in a fiber of a communication system.
In a communication system, information is transmitted via message signals through a physical medium from a source to a destination. For example, a cable-based system can be used to deliver high-definition digital entertainment and telecommunications such as video, voice, and high-speed Internet services from a headend to subscribers over an existing cable television network. The cable television network can take the form of an all-coax, all-fiber, or hybrid fiber/coax (HFC) network. In an HFC network, for example, an optical transmitter in the headend/hub converts the electrical signals (e.g., data, video, and voice signals) to optical signals. The optical signals are transmitted downstream via a fiber to a fiber node that serves a group of end users (“service group”). The fiber node can include an optical receiver that converts the received optical signals to electrical signals that then are transmitted to the service group, for example, via receiving devices such as cable modems (CMs) and/or settop boxes (STBs).
If the optical power input to a fiber is too high, a phenomenon known as Stimulated Brillouin Scattering (SBS) can occur. With SBS, a portion of the light input to the fiber is reflected and the power level of the light transmitted through the fiber is reduced below the intended input power level, among other deleterious effects. SBS can reduce the quality of the signal output from the fiber and thereby affect the performance of a communication system.
The performance of a communication system, which can be characterized by its carrier to noise ratio (CNR), composite second order (CSO) distortion, composite triple beat (CTB) distortion, among other measurements, can degrade for a variety of reasons including SBS. Traditional methods for determining whether SBS is present in a fiber of a communication system require the use of a spectrum analyzer. For example, to determine whether SBS is present in a fiber of a communication system a technician at the input of the fiber varies the optical power of the light input to the fiber and a second technician at the other end of the fiber analyzes the output signals using a spectrum analyzer. Thus, traditional methods can require multiple technicians and costly equipment. It can be desirable to troubleshoot for SBS in a communication system using less costly means.
Various implementations of this disclosure use cost effective means to determine whether SBS is present in a fiber of a communication system using a circulator and a detector.
If the optical power of the light input to the fiber 112 is too high, SBS can occur, which can reduce the quality of the signal received at the fiber node 130 and thereby affect the performance of the communication system 100.
As discussed above, traditional methods for determining whether SBS is present in a fiber of a communication system require the use of a spectrum analyzer. For the communication system 100 of
To determine whether SBS is present in the fiber 112, the output of the optical transmitter 114 can be connected to port 1 of the circulator 142 and the fiber 112 can be connected to port 2 of the circulator 142. In some implementations, the optical signal output from the optical transmitter 114 is first fed through an amplifier 115 prior to being input to port 1 of the circulator 142. The optical receiver 144 can be connected to port 3 of the circulator 142.
In this way, the optical signal output from the optical transmitter 114 or alternatively amplifier 115 will be received at port 1 of the circulator 142, output from port 2 of the circulator 142, and transmitted on the fiber 112. If SBS is present in the fiber 112, a portion of the light input to the fiber 112 from port 2 of the circulator will be reflected from the fiber 112 and will enter port 2 of the circulator 142. The reflected light then will be output from port 3 of the circulator 142. The optical receiver 144 connected to port 3 of the circulator 142 will receive the reflected light. The optical receiver 144 can convert the reflected light to a D.C. voltage. A voltmeter 150 connected to the optical receiver 144 can received the D.C. voltage and display the optical power of the reflected light (“the SBS power”). If the SBS power reading from voltmeter 150 is of a sufficient level, then it can be determined that SBS has occurred and appropriate action can be taken.
With the SBS detector 140 of
When transmitter 114 is configured for SBS suppression capabilities, the SBS detector 400 can be used to, among other things, verify the ratings of a fiber (e.g., whether the fiber is a standard signal mode fiber).
By using the SBS detectors 140, 440, and 540 of
While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that any described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.
Particular implementations of the subject matter described in this specification have been described. Other implementations are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results, unless expressly noted otherwise. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some implementations, multitasking and parallel processing may be advantageous.
