Abstract:
An analyzer operable with an optical network is responsive to a probe signal reflected by a sensor in the network to convey information about targeted matter in air in the sensor. Multiple sensors at different locations in the network can be associated with respective selective optical wavelength filtering thereby enabling the analyzer to associated respective ones of the sensors.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    This application claims priority to provisional application No. 61/978,044, filed Apr. 10, 2014, entitled “Optical Fiber-Based Remote gas leakage Monitoring with Sensor Identifier”, claims priority to provisional application 61/978.048, filed Apr. 10, 2014, entitled “Optical Fiber-Based Remote Gas Leakage Monitoring using Discovery process in PON” and is related to co-pending patent application Ser. No. 14/______, filed Apr. 10, 2015, entitled “Optical Fiber-based Remote Gas leakage Monitoring”, the contents thereof are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to optics, and more particularly, to optical fiber-based remote gas leakage monitoring with sensor identifier. 
         [0003]    Following the rapid growth of the internet traffic, optical fiber is exhaustively deployed especially in metropolitan area as the optical access network infrastructure. In the optical access network, multiple optical channels are launched using a wavelength division multiplexing (WDM) technique following established standards. Wavelength allocation in typical standards, gigabit Ethernet-passive optical network (GE-PON), ten Gigabit Ethernet (10GbE) PON, and future time and wavelength division multiplexing (TWDM) PON are summarized with fiber loss in  FIG. 2 . As shown in  FIG. 2 , upstream (US) and downstream (DS) for 1G, 10G and multiple wavelength (X) channels in TWDM-PON are allocated from 1,280 nm to 1,625 nm. Wavelength region from 1,625 nm to 1,650 nm is reserved for future use. Therefore, a wavelength window longer than 1,650 nm is free in the current standards. 
         [0004]    A challenge for fiber-based remote methane gas leakage monitoring in an optical network is how to identify a particular gas sensor. An optical distribution network in a PON setting has multiple optical fiber lines after a passive optical splitter and the probe signal is returned from multiple sensors. If distance from optical line terminal OLT to one optical network unit ONU is different from the distance from another OLT to another ONU, two probe signal pulses returned from the two different OLTs are distinguishable based on referring difference in the different round-trip times. However, it is hard to identify the two probe signals returned from the two different OLTs from the OLT to their respective ONUs are similar. 
         [0005]    Prior activity of remote methane gas leakage monitoring is limited to use of one optical fiber line for one sensor thereby avoiding a sensor identification problem. Such one optical fiber line use for one sensor is severely limited and cannot be used in existing network infrastructures. 
         [0006]    Accordingly, there is a need for identifying gas leakage sensors in an optical network that overcomes limitations of current capabilities. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to an apparatus that includes an analyzer operable with an optical network including at least one sensor optically responsive to its surrounding air The analyzer can be responsive to a probe signal combinable with and separable from transmission channels moving in the optical network, the probe signal can be reflected by the sensor to convey information about targeted matter in air in the sensor, and the probe signal from the sensor can be converted from optical to electrical form to be processed by the analyzer for information about the targeted matter and identification of the sensor. Multiple ones of the sensor at different locations in the network can be associated with respective selective optical wavelength filtering thereby enabling the analyzer to identify respective ones of the sensor. 
         [0008]    In a similar aspect of the invention, there is provided a method that includes analyzing a probe signal within an optical network including at least one sensor optically responsive to its surrounding air. The probe signal is combinable with and separable from transmission channels moving in the optical network, the probe signal can be reflected by the sensor to convey information about targeted matter in air in the sensor, and the probe signal from the sensor can be converted from optical to electrical form to be processed by the analyzing for information about the targeted matter and identification of the sensor. Multiple ones of the sensor at different locations in the network can be associated with respective selective optical wavelength filtering thereby enabling the analyzing to identify respective ones of the sensor. 
         [0009]    These and other advantages of the invention will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows an exemplary passive optical network PON employing the inventive optical sensor identification associated with a remote sensor on the PON detecting methane gas leakage. 
           [0011]      FIG. 2  shows a plot of fiber loss versus wavelength to summarize fiber loss for wavelength allocation in typical standards, gigabit Ethernet passive optical network (GE-PON), ten Gigabit Ethernet (10GbE) PON, and future time and wavelength division multiplexing (TWDM) PON. 
           [0012]      FIG. 3  illustrates methane gas detection overlaid on an exemplary passive optical network PON, in accordance with the invention. The passive optical network in  FIG. 3  is operationally similar to that of the network discussed with regard  FIG. 1  as a comparison of the descriptions in the legends for the respective reference numerals for both  FIG. 1  and  FIG. 3  confirm substantial similarity between the elements of the two PONs. For the sake of clarity, discussion of  FIG. 3  is limited to aspects of the exemplary PON of  FIG. 3  considered relevant to an understanding of the invention. 
           [0013]      FIG. 4  illustrates power level variations detected in probe signals from different sensors: in (a) different distances from the sensor head ONUs back to the OLT result in different power levels detected in corresponding probe signals and in (b) similar distances from the sensor head ONUs back to the OLT result in indistinguishable power levels detected in corresponding probe signals. The passive optical network in  FIG. 4  is operationally similar to that of the network discussed with regard to  FIG. 1  as a comparison of the descriptions in the legends for the respective reference numeral legends for both  FIG. 1  and  FIG. 4  confirm substantial similarity between the elements of the two PONs. For the sake of clarity, discussion of  FIG. 4  is limited to aspects of the exemplary PON of  FIG. 4  considered relevant to an understanding of the invention. 
           [0014]      FIG. 5  illustrates the PON configuration of  FIG. 1  modified to address the sensor identification limitation shown in  FIG. 4  ( b ). The passive optical network PON in  FIG. 5  is operationally similar to that of the PON discussed with regard to  FIG. 1  as a comparison of the descriptions in the legends for the respective reference numeral legends for both  FIG. 1  and  FIG. 5  confirm substantial similarity between the elements of the two PONs. For the sake of clarity, discussion of  FIG. 5  is limited to aspects of the exemplary PON of  FIG. 5  considered relevant to an understanding of the invention. 
           [0015]      FIG. 6  shows an example of combining multiple reflection wavelengths for identifying different sensors. In the example shown, eight sensors can be identified with three reflection wavelengths. 
           [0016]      FIG. 7  is a diagram of an exemplary processor or analyzer for implementing analyzing of probe signals corresponding to remote sensors responsive to methane gas leakage. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The present invention includes use of a fiber Bragg grating (FBG) based sensor identifier located near the sensor head, and each FBG has a different grating pattern. By doing so, probe pulse shapes returned from each sensor head become different among each other returned pulse can identify its corresponding sensor in the network. 
         [0018]      FIG. 1  depicts an exemplary form of the proposed invention. A probe optical pulse signal from a laser diode LD ( 102 ) is combined with other communication channels from/to optical line terminal OLT ( 101 ) by a wavelength division multiplexing filter WDM filter ( 105 ) via an optical circulator ( 103 ), coupled to an optical transmission fiber ( 106 ). At the optical network unit ONU ( 108 ) side, the probe signal is de-multiplexed from the other communication channels from/to ONU ( 108 ) by a WDM filter  110 . A particular wavelength component of the probe signal is reflected by a fiber Bragg grating FBG ( 111 ), and the remaining wavelength component of the probe signal is reflected by a sensor head ( 109 ). The sensor head ( 109 ) consists of a collimator lens ( 112 ) and a mirror ( 113 ), and the probe signal is propagated in air between the collimator lens ( 112 ) and the mirror ( 113 ) to have an interaction with methane gas in the surrounding air. 
         [0019]    The probe signal returns back to the OLT side via the WDM filter ( 110 ), a passive splitter ( 107 ), and optical transmission fiber ( 106 ). The returned probe signal is separated from the other communication channels by the WDM filter ( 105 ), and then it is converted from an optical signal to an electrical signal by a PD ( 104 ) through an optical circulator ( 103 ). Due to the fiber Bragg grating FBG ( 111 ), a particular wavelength component is reflected in advance of the remaining wavelength component and the returned probe signal can be measured as shown in inset (a) of figure  FIG. 1 . When methane gas concentration is high enough around the sensor head ( 109 ), a weak dip is measured on the probe pulse. By using FBGs with a different reflection wavelength at each respective sensor, an analyzer or controller ( 114 ) can identify each returned probe pulse to each sensor. 
         [0020]    Wavelength allocation in typical standards, gigabit Ethernet passive optical network (GE-PON), ten Gigabit Ethernet (10GbE) PON, and future time and wavelength division multiplexing (TWDM) PON are summarized with fiber loss shown in  FIG. 2 . As shown in  FIG. 2 , upstream (US) and downstream (DS) for 1G, 10G and multiple wavelength (X) channels in TWDM-PON are allocated from 1,280 nm to 1,625 nm. The wavelength region from 1,625 nm to 1,650 nm is reserved for future use. Therefore, a wavelength window longer than 1,650 nm is free in the current standards. 
         [0021]    Meanwhile, absorption spectra of methane (CH 4 ) exist at 1,651 nm and 1,654 nm. Using the unoccupied wavelength longer than 1,650 nm, methane gas detection service can be overlaid on existing PON service as shown in  FIG. 3 . In this network of  FIG. 3 , a probe signal whose wavelength is changing around 1,651 nm or 1,654 nm from a laser diode (LD)  302  is multiplexed with transmission channels using a WDM filter  305  at the optical line terminal (OLT) side, de-multiplexed from other transmission channels at optical network unit (ONU) ( 301 ) side, and exposed to air to measure methane gas concentration around ONU. The probe signal is reflected and again multiplexed with other communication channels, returned through transmission fiber ( 306 ), de-multiplexed ( 305 ) from the other channels at the OLT ( 301 ), and optical-to-electrical converted with photo diode (PD)  304  followed by signal processing by an analyzer or controller  311 . 
         [0022]    The invention enables methane gas leakage information at several monitoring points to be collected at OLT ( 301 ) with passive sensor heads located at ONUs. As the sensor head is completely passive, this scheme is beneficial in terms of cost, maintenance, and ease of installation. This gas leakage monitoring system is even safer than commercial natural gas alarms for home use, because this system enables continuous gas leakage monitoring even when residents are out of home, in the case of power outage, and gas alarm equipment failure. 
         [0023]    A challenge in this fiber-based remote methane gas leakage monitoring system is how to identify particular gas sensor. As optical distribution network in PON has multiple optical fiber lines after a passive optical splitter ( 307 ), the probe signal is returned from multiple sensors. If distance from/to the OLT to an ONU ( 408 ) is different from the distance from the OLT to an ONU ( 410 ), like  FIG. 4(   a ), two probe signal pulses returned from ONU ( 408 ) and ONU ( 410 ) are distinguishable based on differences in their respective round-trip times. However, it is hard to distinguish between different gas leakage sensors at different ONUs, and therefore identify them individually, if the distances from the OLT to each different ONU are similar, see  FIG. 4(   b ). 
         [0024]    The configuration in  FIG. 5 , addresses the situation where returned probe signals have similar path distances back to the OLT. The remote sensor consists of a circulator ( 511 ), an optical isolator ( 509 ), an FBG ( 512 ), and a sensor head ( 513 ). The sensor head ( 513 ) consists of two collimator lenses ( 514 ,  515 ) and the probe signal is propagated in air between these lenses. In this configuration, a wavelength component reflected by the FBG ( 512 ) is terminated by an optical isolator ( 509 ), and no advance optical pulse is measured at a PD ( 504 ), see inset figure  FIG. 5(   a ) compared to the inset in  FIG. 1(   a ). 
         [0025]    The FBG based sensor identification of the present invention can be used to identify respective multiple sensors in a PON based environment. An exemplary application of the inventive FBG-based sensor identification is shown in  FIG. 6 . By combining multiple reflection wavelengths, for example eight sensors can be identified with three reflection wavelengths resulting in different dip patterns in the returned probe signals when methane gas leakage is detected by corresponding sensor heads in the PON. 
         [0026]    The invention may be implemented in optical components, controller/computer or analyzer components that include hardware, firmware or software, or a combination of the three as well as optical components. Preferably, data processing or analyzing aspects of the invention is implemented in a processing executed on a programmable processor or a controller having a processor, a data storage system, volatile and non-volatile memory and/or storage elements, at least one input device and at least one output device. More details are discussed in U.S. Pat. No. 8,380,557, the content of which is incorporated by reference. 
         [0027]    By way of example, a block diagram of a computer or controller or analyzer to support the invention is discussed next in  FIG. 7 . The computer or controller preferably includes a processor, random access memory (RAM), a program memory (preferably a writable read-only memory (ROM) such as a flash ROM) and an input/output (I/O) controller coupled by a CPU bus. The computer may optionally include a hard drive controller which is coupled to a hard disk and CPU bus. Hard disk may be used for storing application programs, such as the present invention, and data. Alternatively, application programs may be stored in RAM or ROM. I/O controller is coupled by means of an I/O bus to an I/O interface. I/O interface receives and transmits data in analog or digital form over communication links such as a serial link, local area network, wireless link, and parallel link. Optionally, a display, a keyboard and a pointing device (mouse) may also be connected to I/O bus. Alternatively, separate connections (separate buses) may be used for I/O interface, display, keyboard and pointing device. Programmable processing system may be preprogrammed or it may be programmed (and reprogrammed) by downloading a program from another source (e.g., a floppy disk, CD-ROM, or another computer). 
         [0028]    Each computer program is tangibly stored in a machine-readable storage media or device (e.g., program memory or magnetic disk) readable by a general or special purpose programmable computer, for configuring and controlling operation of a computer when the storage media or device is read by the computer to perform the procedures described herein. The inventive system may also be considered to be embodied in a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner to perform the functions described herein. 
         [0029]    From the foregoing, it can be appreciated that the present invention can be applied to invention, fiber-based remote methane gas leakage monitoring system can be overlaid on existing PON infrastructure, and methane gas leakage can be monitored at each remote sensing point without inducing monitoring point identification error. Moreover, as the sensor head is completely passive even after applying the proposed invention, the monitoring system can be low cost, easily installed, and needs less maintenance. 
         [0030]    The foregoing is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the Detailed Description, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. It is to be understood that the embodiments shown and described herein are only illustrative of the principles of the present invention and that those skilled in the art may implement various modifications without departing from the scope and spirit of the invention. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the invention.