Patent Publication Number: US-2021174658-A1

Title: High sensitivity fiber optic based detection

Description:
BACKGROUND 
     Embodiments of this disclosure relate generally to a system for detecting conditions within a predetermined space and, more particularly, to a fiber optic detection system. 
     Conventional smoke detection systems operate by detecting the presence of smoke or other airborne pollutants. Upon detection of a threshold level of particles, an alarm or other signal, such as a notification signal, may be activated and operation of a fire suppression system may be initiated. 
     High sensitivity smoke detection systems may incorporate a pipe network consisting of one or more pipes with holes or inlets installed at positions where smoke or pre-fire emissions may be collected from a region or environment being monitored. Air is drawn into the pipe network through the inlets, such as via a fan, and is subsequently directed to a detector. In some conventional smoke detection systems, individual sensor units may be positioned at each sensing location, and each sensor unit has its own processing and sensing components. 
     Delays in the detecting the presence of the fire may occur in conventional point smoke detectors and also pipe network detection systems, for example due to the smoke transport time. In pipe network detection systems, due to the size of the pipe network, there is a typically a time delay between when the smoke enters the pipe network through an inlet and when that smoke actually reaches the remote detector. In addition, because smoke or other pollutants initially enter the pipe network through a few of the inlets, the smoke mixes with the clean air provided to the pipe from the remainder of the inlets. As a result of this dilution, the smoke detectable from the smoke and air mixture may not exceed the threshold necessary to indicate the existence of a fire. 
     SUMMARY 
     According to an embodiment, a detection system for measuring one or more conditions within a predetermined area includes at least one fiber optic cable for transmitting light, the at least one fiber optic cable defining a plurality of nodes arranged to measure the one or more conditions. A control system is in communication with the at least one fiber optic cable such that scattered light and a time of flight record is transmitted from the at least one fiber optic cable to the control system. The control system includes a detection algorithm operable to identify a portion of the scattered light associated with each of the plurality of nodes and indicate a presence and magnitude of the one or more conditions at each of the plurality of nodes. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the predetermined area includes a plurality of zones. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the control system is configured to parse the time of flight record relative to the plurality of zones. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments each of the plurality of zones is associated with a region of the predetermined area being monitored. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments each of the plurality of zones is associated with at least one of the plurality of nodes. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments comprising a light source for generating light transmitted to plurality of nodes via the at least one fiber optic cable. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the control system further comprises a control unit operably coupled to the light source to selectively control emission of light from the light source. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments comprising a light sensitive device operably coupled to the plurality of nodes, wherein the scattered light is transmitted from the plurality of nodes to the light sensitive device. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the control system further comprises a control unit operably coupled to the light sensitive device. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the light sensitive device converts the scattered light and time of flight record associated with the plurality of nodes into an electrical signal receivable by the control unit. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments the one or more conditions includes at least one of smoke, fire, dust, volatile organic compounds, particle pollutants, biological particles, chemicals, and gases. 
     According to another embodiment, a method of measuring one or more conditions within a predetermined area includes receiving at a control system a signal including scattered light and time of flight information associated with a plurality of nodes of a detection system, parsing the time of flight information into zones of the detection system, identifying one or more features within the scattered light signal, and analyzing the one or more features within the scattered light signal to determine a presence of the one or more conditions within the predetermined area. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments analyzing the one or more features within the scattered light signal includes applying a detection algorithm to the one or more features associated with a single node of the plurality of nodes. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments analyzing the one or more features within the scattered light signal includes applying a detection algorithm to the one or more features associated with a single zone of the plurality of zones. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments analyzing the one or more features within the scattered light signal includes performing a data fusion analysis on the plurality of zones. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments in response to determining that the one or more conditions is present within the predetermined area, initiating an alarm. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments analyzing the one or more features within the scattered light signal includes performing a data fusion analysis on the plurality of nodes. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments performing the data fusion analysis on the plurality of nodes provides information relative to time and spatial evolution of the presence of the one or more conditions within the predetermined area. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments performing a data fusion detects the presence of the one or more conditions within the predetermined area that would not be detectable when analyzing the one or more features to the one or more features associated with each of the plurality of nodes individually. 
     In addition to one or more of the features described above, or as an alternative, in further embodiments performing a data fusion includes applying at least one of a Bayesian Estimation, linear join estimation techniques, non-linear joint estimation techniques and, clustering techniques. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the present disclosure, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is schematic diagram of a detection system according to an embodiment; 
         FIG. 1A  is a schematic diagram of light transmission at a node of a detection system according to an embodiment; 
         FIG. 2A  is a schematic diagram of a detection system according to another embodiment; 
         FIG. 2B  is a schematic diagram of a detection system according to another embodiment; 
         FIG. 3  is a cross-sectional view of a fiber optic node of the fiber harness of  FIG. 1  according to an embodiment; 
         FIG. 4A  is a side view of a fiber harness of a detection system according to an embodiment; 
         FIG. 4B  is a schematic diagram of a fiber harness of a detection system according to an embodiment; 
         FIG. 5  is a schematic diagram of a detection system including a plurality of fiber harnesses according to an embodiment; 
         FIG. 6  is a perspective view of an area within a building to be monitored by a detection system according to an embodiment; 
         FIG. 7  is a schematic diagram of a control system of the detection system according to an embodiment; 
         FIG. 8  is another schematic diagram of a detection system including an avalanche photo diode sensor according to an embodiment; 
         FIG. 9  is a method of operating a detection system according to an embodiment; 
         FIG. 10  is a schematic diagram of process flow for evaluating the signals generated by the light sensitive device according to an embodiment; 
         FIGS. 11A and 11B  are diagrams illustrating the signals recorded by the detection system over time for various predefined conditions or events according to an embodiment; 
         FIG. 12  is another schematic diagram of a detection system; 
         FIG. 13  is yet another schematic diagram of a detection system; 
         FIG. 14  is a schematic diagram of a detection system using lenses; 
         FIG. 15  is a another schematic diagram of a detection system using mirrors; 
         FIG. 16A  is a schematic diagram of a detection system having a splice connection; 
         FIG. 16B  is another schematic diagram of a splice connection for a detection system; 
         FIG. 17  is a schematic diagram of a detection system including an optical amplifier; 
         FIG. 18  is a schematic diagram of a detection system further configured for communication; 
         FIG. 19  is a schematic illustration of a combined detection system and suppression system; 
         FIG. 20  is a graph representing a time of flight associated with various nodes of a detection system relative to time according to an embodiment; 
         FIG. 21  is a graph representing an output of a node of the detection system both with and without spatial reference according to an embodiment; 
         FIG. 22  is a schematic diagram of a detection system having a plurality of zones according to an embodiment; 
         FIG. 23  is a graph representing the time of flight record for a fire test in a protected space and the result of the algorithms processing the time of flight record to determine the possible location of smoke according to an embodiment; 
         FIG. 24  is a perspective view of a detection system associated with a data center according to an embodiment; 
         FIG. 25  is a graph representing a light scattering signal at a different first node and a second node according to an embodiment; 
         FIG. 26  is a graph representing a light scattering signal at a different first node and a second node according to another embodiment; and 
         FIG. 27  is a method of operating the detection system using the time of flight information according to an embodiment. 
     
    
    
     The detailed description explains embodiments of the present disclosure, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION 
     Referring now to the FIGS., a system  20  for detecting one or more conditions or events within a designated area is illustrated. The detection system  20  may be able to detect one or more hazardous conditions, including but not limited to the presence of smoke, fire, temperature, flame, or any of a plurality of pollutants, combustion products, or chemicals. Alternatively, or in addition, the detection system  20  may be configured to perform monitoring operations of people, lighting conditions, or objects. In an embodiment, the system  20  may operate in a manner similar to a motion sensor, such as to detect the presence of a person, occupants, or unauthorized access to the designated area for example. The conditions and events described herein are intended as an example only, and other suitable conditions or events are within the scope of the disclosure. 
     The detection system  20  uses light to evaluate a volume for the presence of a condition. In this specification, the term “light” means coherent or incoherent radiation at any frequency or a combination of frequencies in the electromagnetic spectrum. In an example, the photoelectric system uses light scattering to determine the presence of particles in the ambient atmosphere to indicate the existence of a predetermined condition or event. In this specification, the term “scattered light” may include any change to the amplitude/intensity or direction of the incident light, including reflection, refraction, diffraction, absorption, and scattering in any/all directions. In this example, light is emitted into the designated area; when the light encounters an object (a person, smoke particle, or gas molecule for example), the light can be scattered and/or absorbed due to a difference in the refractive index of the object compared to the surrounding medium (air). Depending on the object, the light can be scattered in all different directions. Observing any changes in the incident light, by detecting light scattered by an object for example, can provide information about the designated area including determining the presence of a predetermined condition or event. 
     In its most basic form, as shown in  FIG. 1 , the detection system  20  includes a single fiber optic cable  28  with at least one fiber optic core. The term fiber optic cable  28  includes any form of optical fiber. As examples, an optical fiber is a length of cable that is composed of one or more optical fiber cores of single-mode, multimode, polarization maintaining, photonic crystal fiber or hollow core. Each cable may have a length of up to 5000 m. A node  34  is located at the termination point of a fiber optic cable  28  and is inherently included in the definition of a fiber optic cable  28 . The node  34  is positioned in communication with the ambient atmosphere. A light source  36 , such as a laser diode for example, and a light sensitive device  38 , such as a photodiode for example, are coupled to the fiber optic cable  28 . A control system  50  of the detection system  20  including a control unit  52 , discussed in further detail below, is utilized to manage the detection system operation and may include control of components, data acquisition, data processing and data analysis. 
     As shown in  FIG. 1A , the light from the light source  36  is transmitted through fiber optic cable  28  and through the node  34  to the surrounding area, illustrated schematically at  21 . The light  21  interacts with one or more particles indicative of a condition, illustrated schematically at  22 , and is reflected or transmitted back to the node  34 , illustrated schematically at  23 . A comparison of the light provided to the node  34  from the light source  36  and/or changes to the light reflected back to the light sensitive device  38  from the node  34  will indicate whether or not changes in the atmosphere, such as particles  22  for example, are present in the ambient atmosphere adjacent the node  34  that are causing the scattering of the light. The scattered light as described herein is intended to additionally include reflected, transmitted, and absorbed light. Although the detection system  20  is described as using light scattering to determine a condition or event, embodiments where light obscuration, absorption, and fluorescence is used in addition to or in place of light scattering are also within the scope of the disclosure. 
     In another embodiment, the detection system  20  can include a plurality of nodes  34 . For example, as illustrated in  FIG. 2A , a plurality of fiber optic cables  28  and corresponding nodes  34  are each associated with a distinct light sensitive device  38 . In embodiments where an individual light sensitive device  38  is associated with each node  34 , as shown in  FIG. 2A , the signal output from each node  34  can be monitored. Upon detection of a predetermined event or condition, it will be possible to localize the position of the event because the position of each node  34  within the system  20  is known. Alternately, as shown in  FIG. 2B , a plurality of fiber optic cables  28 , may be coupled to a single light source  36  and/or light sensitive device  38 . 
     In embodiments where a single light sensitive device  38  is configured to receive scattered light from a plurality of nodes  34 , the control system  50  is able to localize the scattered light, i.e. identify the scattered light received from each of the plurality of nodes  34 . For example, the control system  50  may use the position of each node  34 , specifically the length of the fiber optic cables  28  associated with each node  34  and the corresponding time of flight (i.e. the time elapsed between when the light was emitted by the light source  36  and when the scattered light was received by the light sensitive device  38 ), to associate different portions of the light signal with each of the respective nodes  34  that are connected to that light sensitive device  38 . Alternatively, or in addition, the time of flight may include the time elapsed between when the light is emitted from the node  34  and when the scattered light is received back at the node  34 . In such embodiments, the time of flight provides information regarding the distance of the object or particle relative to the node  34 . 
     In an embodiment, illustrated in the cross-section of the fiber optic cable shown in  FIG. 3 , two substantially identical and parallel light transmission fiber cores  40 ,  42  are included in the fiber optic cable  28  and terminate at the node  34  (not shown in  FIG. 3 ). However, it should be understood that embodiments are also contemplated herein where the fiber optic cable  28  includes only a single fiber core, or more than two cores. In an embodiment, the light source  36  is coupled to the first fiber core  40  and the light sensitive device  38  is coupled to the second fiber core  42 , for example near a first end of the fiber optic cable  28 . The light source  36  is selectively operable to emit light, which travels down the first fiber core  40  of the fiber optic cable  28  to the node  34 . At the node  34 , the emitted light is expelled into the adjacent atmosphere. The light is scattered and transmitted back into the node  34  and down the fiber cable  28  to the light sensitive device  38  via the second fiber core  42 . 
     In more complex embodiments, as shown in  FIGS. 4A and 4B , rather than having a plurality of individual fiber optic cables  28  separately coupled to the control unit  50 , the detection system  20  includes a fiber harness  30 . The fiber harness  30  may be formed by bundling a plurality of fiber optic cables  28 , or the cores associated with a plurality of fiber optic cables  28 , together within a single conduit or sheath for example. However, it should be understood that embodiments where the fiber harness  30  includes only a single fiber optic cable  28  or the cores associated therewith are also contemplated herein. 
     Structural rigidity is provided to the fiber harness  30  via the inclusion of one or more fiber harness backbones  31 . As shown in the FIG., in embodiments where the fiber harness  30  includes a plurality of fiber optic cables  28 , the plurality of cables  28  may be bundled together at one or more locations, upstream from the end of each cable  28 . The end of each fiber optic cable  28 , and therefore the end of each core associated with the cable  28 , is separated from the remainder of the fiber optic cables  28  at an adjacent, downstream backbone  31  formed along the length of the fiber harness  30 . Each of these free ends defines a fiber optic branch  32  of the fiber harness  30  and has a node  34  associated therewith. For example, as best shown in  FIG. 4B , each fiber optic branch  32  includes the free ends of cores  40 ,  42  that define a node  34  of a corresponding fiber optic cable  28 . 
     In the illustrated, non-limiting embodiments of  FIGS. 4A and 4B , the fiber harness  30  additionally includes an emitter leg  33  and a receiver leg  35  associated with each of the plurality of fiber optic branches  32 . The emitter leg  33  may contain the first fiber optic cores  40  from each of the plurality of fiber optic branches  32  and the receiver leg  35  may contain all of the second fiber cores  42  from each of the fiber optic branches  32 . The length of each pair of fiber optic cores  40 ,  42  extending between the emitter leg  33  or the receiver leg  35  and a node  34  may vary in length. As a result, each node  34 , defined by the cores  40 ,  42  at the end of each fiber optic branch  32 , may be arranged at a distinct location along the fiber harness  30 . Accordingly, the position of each of the nodes  34  relative to the fiber harness  30  may be controlled by the length of the cores  40 ,  42  associated with each node  34 . The position of each of the nodes  34  may be set during manufacture, or at the time of installation of the system  20 . With this variation in length and therefore position of each node  34 , only the longest core or pair of cores  40 ,  42  is supported at the final backbone  31  located upstream from the end  37  of the harness  30 . 
     Alternatively, the fiber harness  30  may include a fiber optic cable (not shown) having a plurality of branches  32  integrally formed therewith and extending therefrom. The branches  32  may include only a single fiber optic core. The configuration, specifically the spacing of the nodes  34  within a fiber harness  30  may be arranged at locations substantially equidistant from one another. Alternatively, the distance between a first node and a second node may be distinct than the distance between the second node and a third node. In an embodiment, the positioning of each node  34  may correlate to a specific location within the designated area. It is understood that there is no minimum spacing required between adjacent nodes  34 . 
     With reference now to  FIG. 5 , the detection system  20  may additionally include a plurality of fiber harnesses  30 . In the illustrated, non-limiting embodiment, a distinct light sensitive device  38  is associated with each of the plurality of fiber harnesses  30 , and more specifically with each of the plurality of light transmission cores  42  within the harnesses  30 . However, embodiments where a single light sensitive device  38  is coupled to the plurality of fiber harnesses  30  are also contemplated here. In addition, a single light source  36  may be operably coupled to the plurality of light transmission fiber cores  40  within the plurality of fiber harnesses  30  of the system  20 . Alternatively, the detection system  20  may include a plurality of light sources  36 , each of which is coupled to one or more of the plurality of fiber harnesses  30 . 
     The detection system  20  may be configured to monitor a predetermined area, such as a building for example. In an embodiment, the detection system  20  is utilized for predetermined areas having a crowded environment, such as a server room, as shown in  FIG. 6 . In such embodiments, each fiber harness  30  may be aligned with one or more rows of equipment  46 , and each node  34  therein may be located directly adjacent to one of the towers  48  within the rows  46 . In addition, the nodes  34  may be arranged so as to monitor specific enclosures, electronic devices, or machinery within the crowded environment. Positioning of the nodes  34  in such a manner allows for earlier detection of a condition as well as localization, which may limit the exposure of the other equipment in the room to the same condition. For example, if a hazardous condition such as overheat, smoke and/or fire were to effect one or more specific pieces of equipment in one or more towers  48 , a node  34  physically arranged closest to the tower  48  and/or closest to the equipment may detect the smoke, fire, temperature, and/or flame; Further, since the location of node  34  is known, suppressive or preventative measures may be quickly deployed in the area directly surrounding the node  34 , but not in areas where the hazardous condition has not detected. In another application, the detection system  20  may be integrated into an aircraft, such as for monitoring a cargo bay, avionics rack, lavatory, or another confined region of the aircraft that may be susceptible to fires or other events. 
     The control system  50  of the detection system  20  is utilized to manage the detection system operation and may include control of components, data acquisition, data processing and data analysis. The control system  50 , illustrated in  FIG. 7 , includes at least one light sensitive device  38 , at least one light source,  36 , and a control unit  52 , such as a computer having one or more processors  54  and memory  56  for implementing one or more algorithms  58  as executable instructions that are executed by the processor  54 . The instructions may be stored or organized in any manner at any level of abstraction. The processor  54  may be any type of processor, including a central processing unit (“CPU”), a general purpose processor, a digital signal processor, a microcontroller, an application specific integrated circuit (“AMC”), a field programmable gate array (“FPGA”), or the like. Also, in some embodiments, memory  56  may include random access memory (“RAM”), read only memory (“ROM”), or other electronic, optical, magnetic, or any other computer readable medium for storing and supporting processing in the memory  56 . In addition to being operably coupled to the at least one light source  36  and the at least one light sensitive device  38 , the control unit  52  may be associated with one or more input/output devices  60 . In an embodiment, the input/output devices  60  may include an alarm or other signal, or a fire suppression system which are activated upon detection of a predefined event or condition. It should be understood herein that the term alarm, as used herein, may indicate any of the possible outcomes of a detection. 
     The control unit  52 , and in some embodiments, the processor  54 , may be coupled to the at least one light source  36  and the at least one light sensitive device  38  via connectors. The light sensitive device  38  is configured to convert the scattered light received from a node  34  into a corresponding signal receivable by the processor  54 . In an embodiment, the signal generated by the light sensing device  38  is an electronic signal. The signal output from the light sensing device  38  is then provided to the control unit  52  for processing via the processor  54  using an algorithm  58  to determine whether a predefined condition is present. 
     The signal received by or outputted from the light sensitive device(s)  38  may be amplified and/or filtered, such as by a comparator (not shown), to reduce or eliminate irrelevant information within the signal prior to being communicated to the control unit  52  located remotely from the node  34 . In such embodiments, the amplification and filtering of the signal may occur directly within the light sensing device  38 , or alternatively, may occur via one or more components disposed between the light sensing device  38  and the control unit  52 . The control unit  52  may control the data acquisition of the light sensitive device  38 , such as by adjusting the gain of the amplifier, the bandwidth of filters, sampling rates, the amount of timing and data buffering for example. 
     With reference now to  FIG. 8 , in an embodiment of the system  20 , the light sensitive device  38  may include one or more Avalanche Photodiode (APD) sensors  64 . For example, an array  66  of APD sensors  64  may be associated with the one or more fiber harnesses  30 . In an embodiment, the number of APD sensors  64  within the sensor array  66  is equal to or greater than the total number of fiber harnesses  30  operably coupled thereto. However, embodiments where the total number of APD sensors  64  within the sensor array  66  is less than the total number of fiber harnesses  30  are also contemplated herein. 
     Data representative of the output from each APD sensor  64  in the APD array  66  is periodically taken by a switch  68 , or alternatively, is collected simultaneously. The data acquisition  67  collects the electronic signals from the APD and associates the collected signals with metadata. The metadata as an example can be time, frequency, location or node. In an example, the electronic signals from the APD sensor  64  are synchronized to the laser modulation such that the electrical signals are collected for a period of time that starts when the laser is pulsed to several microseconds after the laser pulse. The data will be collected and processed by the processor  54  to determine whether any of the nodes  34  indicates the existence of a predefined condition or event. In an embodiment, only a portion of the data outputted by the sensor array  66  is collected, for example the data from a first APD sensor  64  associated with a first fiber harness  30 . The switch  68  may therefore be configured to collect information from the various APD sensors  64  of the sensor array  66  sequentially. While the data collected from a first APD sensor  64  is being processed to determine if an event or condition has occurred, the data from a second APD  66  of the sensor array  66  is collected and provided to the processor  54  for analysis. When a predefined condition or event has been detected from the data collected from one of the APD sensors  64 , the switch  68  may be configured to provide additional information from the same APD sensor  64  to the processor  54  to track the condition or event. 
     In an embodiment, a single control unit  52  can be configured with up to 16 APDs and the corresponding light sensitive devices  38  necessary to support up to 16 fiber harnesses  30 , each fiber harness  30  having up to 30 nodes, resulting in a system with up to 480 nodes that can cover an area being monitored of up to 5000 square meters m 2 . However, it should be understood that the system can be reconfigured to support more or fewer nodes to cover large buildings with up to a million m 2  or small enclosures with 5 m 2 . The larger coverage area enables reducing or removing fire panels, high sensitivity smoke detectors and/or control panels. 
     Further, the overall area that can be monitored by a single node  34  of the detection system  20  is typically specified by code such as NFPA/UL/FM/EN/BSI/ISO. Accordingly, a single node  34  as described herein may be operable to monitor an area between about 0.1 m 2  to about 100 m 2  based on the code being applied. In an embodiment, a single node  34  made be operable to monitor an area of up to 40,000 m 2 ; however, this capability is limited by both laser power and collection optics. If eye safety limitations were not applicable, the area monitored by a single node  34  could be increased to up to about 4,000,000 m 2  of open area. 
     A method of operation  100  of the detection system  20  is illustrated in  FIG. 9 . The control unit  52  operably coupled to the light source  36  is configured to selectively energize the light source  36 , as shown in block  102 , and to emit light to a fiber harness  30  coupled thereto as shown in block  104 . Based on the desired operation of the detection system  20 , the control unit  52  may vary the intensity, duration, repetition, frequency, or other properties, of the light emitted. The light is transmitted through the fiber optic cable  28  and emitted at the node/nodes  34  into the protected space or area being monitored. At block  105 , the light emitted into the area being monitored scatters as it interacts with particles or solid objects located within the space. In block  106 , the scattered light is transmitted back through the fiber optic cable  28  via the second fiber cores  42 . The scattered light may include one or more of scattered light that reflects from an interior of the fiber optic branch  32 , and scattered light within the atmosphere adjacent the node  34  which is received by the node  34  and then, as already described, transmitted back through the fiber optic branches  32  via the second fiber cores  42 . The scattered light is transmitted to the at least one light sensing device  38  in block  108 . As shown in block  110 , the light sensing device  38  generates a signal in response to the scattered light received by each node  34 , and provides that signal to the control unit  52  for further processing. 
     Using one or more algorithms  58  executed by the processor  54 , each signal representing the scattered light received by each of the corresponding nodes  34  is evaluated to determine whether the light at the node  34  is indicative of a predefined condition, such as smoke for example. With reference to  FIG. 10 , a schematic diagram illustrating an example of a flow path for processing the signals generated by each of the nodes  34  is illustrated. As shown, the signal indicative of scattered light  69  is parsed, shown at block  70 , into a plurality of signals based on their respective originating node  34 . In the illustrated, non-limiting embodiment, background signals, illustrated schematically at  72 , are subtracted from the data before the pulse features are evaluated for each of the individual signals. Through integration, pulse compression, and/or feature extraction, shown at block  74 , one or more characteristics or features (pulse features) of the signal may be determined. Examples of such features include, but are not limited to, a peak height, an area under a curve defined by the signal, statistical characteristics such as mean, variance, and/or higher-order moments, correlations in time, frequency, space, and/or combinations thereof, and empirical features as determined by deep learning, dictionary learning, and/or adaptive learning and the like. 
     In an embodiment, the time of flight record is parsed and features are extracted. The time of flight record can cover a period of time. For example, a time of flight record can record light intensity over 0.001-1,000,000 nanoseconds, 0.1-100,000 nanoseconds, or 0.1-10,000 microseconds. The features extracted from the signal can include, but are not limited to height, full width at half maximum, signal pick up time, signal drop off time, group velocity, integration, rate of change, mean, and variance for example. 
     As best shown with reference to  FIG. 20 , successive time of flight records may be shifted from the expected time by tens of nanoseconds due to the electronic jitter within the electronics that arises at one or more of the processing components, such as the clock, processor, or the circuit boards for example. Accordingly, replacement of electronic components that contribute to this shifting of the time of flight record, may facilitate a reduction in this electronic jitter. Another method for processing time of flight data includes using spatial referencing within the time of flight record. As best shown in  FIG. 21 , a fixed point within the field of view of the node  34 , such as feature or position located on a wall or other object that does not move relative to the node  34 , will provide a signal return that can be used as reference in the time of flight record. In an embodiment, the fixed point can be in the protected space, furniture, or on a wall. Alternatively, the fixed point can be within the detection system  20 , such as an attachment to the end of the node  34 , the node  34  itself, within the fiber or fiber harness, or as a separate fiber loop with known distance. The fixed point provides the reference signal return in the time of flight record. The time in the time of flight record is then adjusted based on the reference signal return. This enables signal accumulation having a narrower distribution, which enables better resolution of events being monitored within the protected space. 
     With reference to  FIGS. 22 and 23 , in an embodiment, signal indicative of the scattered light, and therefore the corresponding time of flight record, is parsed via the processor  54  of the control unit  52  to form a plurality of zones. The parsing may be performed based on the duration of the time of flight and/or based on the originating node of the signal. Each zone may be associated with one or more specific detectors or node  34 , or alternatively, may be associated with a region of the space being monitored, which may include a single node or multiple nodes  34 . In an embodiment, one or more pieces of equipment, such as the air handling units shown in  FIG. 22  for example, are located within each of the respective zones. As shown in  FIG. 23 , evaluation of a predetermined event or condition can be performed based on each zone to more efficiently identify the location of the event. In the illustrated graph, an alarm has been generated based on the scattered light identified within the second zone, and one or more particles indicating the presence of smoke have also been identified at the third zone. By parsing the time of flight record into zones associated with one or more corresponding nodes  34 , if smoke or another event occurs within a zone, a change in the light scattering will be detected within the zone. 
     Returning to  FIG. 10 , through application of the data processing, illustrated schematically at block  76 , the features may then be further processed by using, for example, smoothing, Fourier transformation or cross correlation. In an embodiment, the processed data is then sent to the detection algorithm at block  78  to determine whether or not the signal indicates the presence and/or magnitude of a condition or event at a corresponding node  34 . This evaluation may be a simple binary comparison that does not identify the magnitude of deviation between the characteristic and a threshold. The evaluation may also be a comparison of a numerical function of the characteristic or characteristics to a threshold. The threshold may be determined a priori or may be determined from the signal. The determination of the threshold from the signal may be called background learning. Background learning may be accomplished by adaptive filtering, model-based parameter estimation, statistical modeling, and the like. In some embodiments, if one of the identified features does not exceed a threshold, the remainder of the detection algorithm is not applied in order to reduce the total amount of processing performed during the detection algorithm. In the event that the detection algorithm indicates the presence of the condition at one or more nodes  34 , an alarm or fire suppression system may, but need not be activated. It should be understood that the process for evaluating the data illustrated and described herein is intended as an example only and that other processes including some or all of the steps indicated in  FIG. 10  are also contemplated herein. 
     The process for evaluating the data set forth in steps  70 - 78  of  FIG. 10  may also advantageously employ classifiers including those that may be learned from the signal via deep learning techniques including, but not limited to deep neural networks, convolutional neural networks, recursive neural networks, dictionary learning, bag of visual/depth word techniques, Support Vector Machine (SVM), Decision Trees, Decision Forests, Fuzzy Logic, and the like. The classifiers may also be constructed using Markov Model techniques, Hidden Markov Models (HMM), Markov Decision Processes (MDP), Partially Observable MDPs, Markov Decision Logic, Probabilistic Programming, and the like. 
     In addition to evaluating the signals generated from each node  34  individually, the processor  54  may additionally be configured to evaluate the plurality of signals or characteristics thereof collectively, such as through a data fusion operation to produce fused signals or fused characteristics. The data fusion operation may provide information related to time and spatial evolution of an event or predetermined condition. As a result, a data fusion operation may be useful in detecting a lower level event, insufficient to initiate an alarm at any of the nodes  34  individually. For example, in the event of a slow burning fire, the light signal generated by a small amount of smoke near each of the nodes  34  individually may not be sufficient to initiate an alarm. However, when the signals from the plurality of nodes  34  are reviewed in aggregate, the increase in light returned to the light sensitive device  38  from multiple nodes  34  may indicate the occurrence of an event or the presence of an object not otherwise detected. In an embodiment, the fusion is performed by Bayesian Estimation. Alternatively, linear or non-linear joint estimation techniques may be employed such as maximum likelihood (ML), maximum a priori (MAP), non-linear least squares (NNLS), clustering techniques, support vector machines, decision trees and forests, and the like. 
     As illustrated and described above, the processor  54  is configured to analyze the signals generated by at least one light sensing device  38  relative to time. In another embodiment, the detection algorithm may be configured to apply one or more of a Fourier transform, Wavelet transform, space-time transform, Choi-Williams distribution, Wigner-Ville distribution and the like, to the signals to convert the signals from a temporal domain to a frequency domain. This transformation may be applied to the signals when the nodes  34  are being analyzed individually, when the nodes  34  are being analyzed collectively during a data fusion, or both. 
     The relationship between the light scattering and the magnitude or presence of a condition is inferred by measuring a signal&#39;s causality and dependency. As an example, the measure of a causality utilizes one or more signal features as an input and determines one or more outputs from a calculation of a hypothesis testing method, foreground ratio, second derivative, mean, or Granger Causality Test. Similarly, one or more signal features may be used as an input to evaluate the dependency of a signal. One or more outputs are selected from a calculation of a correlation, fast Fourier transform coefficients, a second derivative, or a window. The magnitude and presence of the condition is then based on the causality and dependency. The magnitude and presence of a condition may be calculated utilizing one or more evaluation approaches: a threshold, velocity, rate of change or a classifier. The detection algorithm may include utilizing the output from the calculation causality, dependency or both. This is used to indicate the presence of the condition at one or more nodes  34  and initiate a response. 
     When smoke is present within the ambient environment adjacent a node  34 , the frequency effects of the light vary within a small range, such as from about 0.01 Hz to about 10 Hz for example. As a result, the evaluation of the frequency of the signals of scattered light may effectively and accurately determine the presence of smoke within the predetermined space  82 . The detection algorithm may be configured to evaluate the signals in a fixed time window to determine the magnitude of the frequency or the strength of the motion of the smoke. Accordingly, if the magnitude of a frequency component exceeds a predetermined threshold, the algorithm  58  may initiate an alarm indicating the presence of a fire. In an embodiment, the predetermined threshold is about 10 Hz such that when the magnitude of the optical smoke frequency exceeds the threshold, a determination is made that smoke is present. 
     In an embodiment, the algorithm  58  is configured to distinguish between different events or conditions based on the rate of change in the light scattered by the atmosphere near the node  34  and received by one or more of the nodes  34  over time. With reference to  FIGS. 11A and 11B , graphs of the signals recorded from a node  34  over time with respect to different events are illustrated.  FIG. 11A  indicates the change in the light signal received by a node  34  as a person walks through the area being monitored by the node  34 . As shown in the graph, the movement of one or more persons through the area appears as one or more blocks or steps, each of which has an increased and constant magnitude relative to a baseline measurement. These steps indicate the temporary presence of a person and his or her proximity to the node  34 .  FIG. 11B , which represents the detection of smoke from a smoldering fire, appears graphically as a continuously changing signal having an accelerating increase in the change in light signal received by a node  34  over time. It should be understood that the graphs illustrated are examples only. Accordingly, each predefined event detectable by the detection system  20  has one or more unique parameters associated therewith such that the control unit  52  of the detection system  20  can distinguish between and identify multiple types of events. 
     With reference now to  FIG. 24 , an example of a detection system  20  deployed in a data center is illustrated. As shown, the space being protected or monitored, illustrated at  150 , by the detection system  20  contains a plurality of equipment cabinets  46 , such as server racks or other equipment for example. In an embodiment, at least a portion of the detection system  20  is located near one or more vents  152  located within the protected space  150 . In order to accomplish the monitoring of the protected space  150 , two or more dissimilar nodes  34  may be used. A first node  34  may provide information about the overall state of the protected space  150 , while a second node provides detailed spatial information about part of the protected space  150 . The information collected by the first and second nodes  34  will be analyzed via a detection algorithm  58  to determine whether the light at the node  34  is indicative of a predefined condition, such as smoke for example. 
     The light scattering information collected from each node  34 , may be evaluated individually to determine a status at each the node  34 , and initiate an alarm if necessary. Alternatively, or in addition, the data from each node  34  may be analyzed in aggregate, such as via cooperative data fusion for example, to perform a more refined analysis when determining whether to initiate an alarm, sometimes referred to as “object refinement.” 
     Cooperative data fusion is performed via an algorithm which uses a state estimator to relate the data from two or more nodes  34 . One example of a state estimator is a Kalman filter. For example, if smoke is generated and detected at both a first and second node  34 , as shown in  FIG. 25 , but detection at the second node  34 , or a second zone containing a second node  34 , occurs prior to detection at the first node  34  or a first zone including the first node  34 , the smoke can be localized to the second zone of the region being monitored by the second node  34 . However, if smoke arrives at or is only detected at the second node and not at the first node, as shown in  FIG. 26 , the smoke can be localized to a region that is not monitored by the first node  34 . 
     The cooperative data fusion method can also be extended to evaluate time delay. If the delay time between detection of the smoke at the second node and detection of smoke at the first node is compared in the cooperative data fusion algorithm, the smoke source can be further localized based on transport time of the smoke. Another embodiment can use the plurality of nodes and cooperative data fusion to improve the false alarm rate. For example, in an embodiment the cooperative data fusion algorithm may require two or more nodes to provide light scattering data indicative of the same event in order for an alarm to be generated. 
     In another embodiment, two or more nodes  34  may cooperate to refine detected events. Event refinement can be achieved when the scattered light indicative of one event is detected at a first node and another node detects a different event. The events are combined and the output is considered a third event. For example, at least one node may detect smoke, and another node may detect a hand being waved within the protected space  10 . The data fusion algorithm may be configured to combine the events and issue a warning to inspect the location within the protected space  10  for trapped occupants. 
     A method of operation  200  of the detection system  20  using time of flight information is shown in more detail in  FIG. 27 . In block  202 , one or more signals including scattered light and raw time of flight information are received by the control unit  52  from a light sensitive device  38 . In response to this information, the control unit  52 , as shown in block  204 , may be configured to parse the time of flight information into information associated with individual zones and/or nodes of the detection system  20 . The control unit  52  may also be configured to process the scattered light information contained within each signal, as shown in block  206 , to identify one or more features within the scattered light. These features can then be used by a detection algorithm to process the information associated with a single node or zone, as shown in block  208 , or alternatively or additionally, data fusion may be performed to analyze the information from several nodes or zones in block  210 . The output from either or both processing steps  208 ,  210  is then used to determine an alarm status in block  212 , and, as shown in block  214 , in instances where the alarm status would prompt initiation of an alarm, e.g. based upon comparison of the alarm status to known or pre-populated conditions within a table (or other suitable data structure), initiate an alarm. 
     To reduce the noise associated with each signal, the light emitting device  36  may be modulated such that the device  36  is selectively operated to generate modulated light in a specific pattern. In an embodiment, the light within the pattern may vary in intensity, duration, frequency, phase, and may comprise discrete pulses or may be continuous. The specific pattern of light may be designed to have desirable properties such as a specific autocorrelation with itself or cross-correlation with a second specific pattern. When the light is emitted in a specific pattern, the light scattered back to a corresponding light sensing device  38  should arrive in the substantially same pattern. Use of one or more specific and known patterns provides enhanced processing capabilities by allowing for the system  20  to reduce overall noise. This reduction in noise when combined with the signal processing may result a reduction of false positives and improved device sensitivity, e.g. with an improved signal to noise ratio the total number of false events or conditions detected will decrease, and the device sensitivity may be improved. Improvement of device sensitivity may further increase the functional limits of the detection system  20 . By cross-correlating one or more second patterns, specific causes of transmitted or reflected signals may be distinguished, e.g. by Bayesian estimation of the respective cross-correlations of the received signal with the one or more second patterns. 
     In addition, modulation of the light signal emitted by the light source  36  may provide improved detection by determining more information about the event or condition causing the scatter in the light signal received by the node  34 . For example, such modulation may allow the system  20  to more easily distinguish between a person walking through the designated area adjacent a node, as shown in  FIG. 11A , and a smoldering fire adjacent the node  34 . 
     Referring now to  FIG. 12 , in some embodiments the system  20  includes one or more optical enhancement devices  80 , such as a bandpass filter, a polarizer, an antireflective coating, a wave plate, and/or other optical features to reduce interference from non-event signals, or other non-desired signals, such as ambient light from either sunlight or lighting in the space, or from solid objects in the predetermined space  82 . Further, the optical enhancement devices  80  may be utilized to reduce undesired wavelengths and/or intensities transmitted from the light source  36 . The optical enhancement  80  is placed in the system  20  downstream of the light source  36 , in some embodiments a laser diode, and upstream of the light sensitive device  38 , in some embodiments the photodiode. The optical enhancement device  80  is placed so that light scattered and reflected back to the light sensitive device  38  is passed through the optical enhancement device  80  to filter or differentiate events or other conditions to be sensed from other signals due to, for example, ambient light, solid objects, bugs, dust, or water vapor. 
     With further reference to  FIG. 12 , in some embodiments the optical enhancement  80  is located at the light sensitive device  38  and/or is a component of, integral to or embedded within the light sensitive device  38 . Further, the light sensitive device  38  may be configured such that the optical enhancement device  80  is readily removable and/or replaceable with another optical enhancement  80  to filter or disseminate different conditions in the scattered/reflected signal. 
     While in the embodiment of  FIG. 12 , the optical enhancement device  80  is located at the light sensitive device  38  or embedded in the light sensitive device  38 , in other embodiments the optical enhancement device  80  is located at other locations, such as at the node  34  as shown in  FIG. 13 . This allows for node-specific placement of optical enhancement devices  80  such that different optical enhancement devices  80  may be placed at different nodes  34 . Further, in some embodiments, combinations of optical enhancement devices  80 , such as combinations of bandpass filters and polarizers, may be utilized to filter or disseminate certain conditions of the scattered/reflected light. Further, in systems  20  where the nodes  34  include two or more cores  40 ,  42 , optical enhancements  80  may be located at an individual core  40 ,  42  or at two or more of the cores  40 ,  42 . 
     Referring now to  FIG. 14 , in some embodiments the system  20  includes focusing or expanding optical elements to increase range, sensitivity or field of view of the detection system  20  in detecting smoke/gas or other conditions or events. A focusing optical element can be placed at the node or between the control system and fiber harness to increase range and sensitivity by converging or collimating light. Also, an expanding optical element can be placed in similar locations to increase the field of view of the node by diverging the light. By way of example, optical elements may include mirrors, focusing lenses, diverging lenses, and diffusers, along with the integration of antireflective coatings on the optical elements or components thereof. 
     As shown in  FIG. 14 , the optical elements may be one or more lenses  84  located at the node  34 . The lens  84  reduces divergence of the outgoing beam transmitted from the light source  36 , while also increasing the amount of scattered light accepted by the node  34  for transmission to the light sensitive device  38 . In some embodiments, the lens  84  is fused to the end of cores  40 ,  42  at the node  34  to reduce scattering of the light off of the lens  84  face, thereby enhancing light collection efficiency of the node  34 . Further, in some embodiments, cores  40 ,  42  may have lensed and tapered fibers, which do not require fusing and function as a lens  84 . Further, the lens  84  may include beam steering features, such as a solid state material which is utilized to change the refractive index of incident light to steer the light along the cores  40 ,  42 . The beam steering feature may also be a photonic integrated circuit, which utilizes patterned silicon to control the directional emission of light. 
     Referring now to  FIG. 15 , in some embodiments the optical elements may include a parabolic mirror  86  located at the node  34 . The parabolic mirror  86  is located off-angle relative to a node axis  88 . As with the lens  84 , the parabolic mirror  86  reduces divergence of the outgoing beam transmitted from the light source  36 , while also increasing an amount of scattered light accepted by the node  34  for transmission to the light sensitive device  38 . In some embodiments, the parabolic mirror  86  is configured to rotate about a rotational axis during operation of the system  20  to further increase a coverage area of the node  34 . 
     In some embodiments, both lens  84  and mirror  86  may be utilized at node  34 . Further, while in the embodiments illustrated in  FIGS. 14 and 15  optics are utilized at each node  34 , in other embodiments, optics may be utilized only at selected nodes  34  to provide their benefits to the selected nodes  34 , such as increasing detection range at selected nodes  34  due to, for example, constraints in placement of nodes  34  in the protected space. In other embodiments, the optical elements can be placed at the light source  36  or light sensitive device to enhance the detection system  50 . 
     In addition to smoke or dust, the system  20  may be utilized to monitor or detect pollutants such as volatile organic compounds (VOC&#39;s), particle pollutants such as PM2.5 or PM10.0 particles, biological particles, and/or chemicals or gases such as H 2 , H 2 S, CO 2 , CO, NO 2 , NO 3 , or the like. Multiple wavelengths may be transmitted by the light source  36  to enable simultaneous detection of smoke, as well as individual pollutant materials. For example, a first wavelength may be utilized for detection of smoke, while a second wavelength may be utilized for detection of VOC&#39;s. Additional wavelengths may be utilized for detection of additional pollutants, and using multiple wavelength information in aggregate may enhance sensitivity and provide discrimination of gas species from false or nuisance sources. In order to support multiple wavelengths, one or more lasers may be utilized to emit several wavelengths. Alternatively, the control system can provide selectively controlled emission of the light. Utilization of the system  20  for pollutant detection can lead to improved air quality in the predetermined space  82  as well as improved safety. 
     In some embodiments, such as shown in  FIG. 16A , the fiber optic branches  32  are each operably connected to the fiber harness backbone  31 , which may only include a single fiber optic core, via a coupling  132 . In some embodiments, the coupling  132  is one of a splice connection, a fused connection or a solid state switching device. Utilizing couplings  132  allows nodes  34  to be added to the fiber harness  30  after installation of the fiber harness  30 , or removal or relocation of the nodes  34  once the fiber harness  30  is installed. The couplings  132  therefore increase adaptability of the fiber harness  30  and the system  20 . 
     In another embodiment, such as shown in  FIG. 16B , a first fiber optic core  40  is operably coupled to a first node  34 , while a second node  34  is operably coupled to a second fiber optic core  42 . In such embodiments, the first fiber optic core  40  is utilized for transmission of light from the light source  36 , while the second fiber optic core  42  receives scattered light and conveys the scatter light to the light sensitive device  38 . In some embodiments, a first coupling  132   a  coupling the first fiber optic core  40  to the first node  34  is the same as a second coupling  132   b  coupling the second fiber optic core  42  to the second node  34 , while in other embodiment the first coupling  132   a  is different from the second coupling  132   b.    
     Further, as an alternative to or in addition to the splice connection, fused connections, one or more solid state switching devices, and/or optical amplifiers  96  may be placed along the fiber harness  30  to amplify signals proceeding through the fiber harness  31 . The optical amplifier  96  may be located, for example as shown in  FIG. 17 , between nodes  34 , or between the light detection device  38  and the fiber harness  30 . Further, in some embodiments, coupling  132  may be located at other locations along the fiber harness  30 , for example, between the fiber harness  30  and the light source  36 , and/or between the fiber harness  30  and the light sensitive device  38 . 
     Referring now to  FIG. 18 , the control system  50  is configured for multiple inputs and/or multiple outputs for communication of information through the fiber optic cables  28  and the nodes  34 . In some embodiments, the multiple inputs and outputs may include an Internet connection  140 , a building network or management system  142 , and/or a fire panel  134  of the building or enclosed space. The fire panel  134  is configured for communications with, for example, a fire department, and/or is configured to transmit alarms through the building or space in the event of detection of smoke, fire or other substance by the system  20 . In the embodiment shown in  FIG. 18 , some or all of the fiber optic cables  28  (not shown) within the fiber harness  30  are further utilized for the communication of alarms, alerts and other information, such as system diagnostic information through the building. The control system  50  is able to both measure the condition in the predetermined area  82  and provide communication. For example, once the control system  50  determines that a condition is present based on detection signals received from one or more nodes  34 , the control system  50  transmits one or more alarm signals from the fire panel  134  along fiber optic cables  28  to one or more alarm units  138  in the building or space which may initiate an alarm or alert based on the received alarm signals. The control system  50  is able to do this in a fiber optic harness  30  by combining frequency and amplitude modulation of the light. In some embodiments, the alert or alarm is an audible sound or sounds, while in other embodiments the alert or alarm is a light, or a combination of light and sound. Further, the control system  50  may be configured to send and/or receive communication through the fiber optic cables  28  and the nodes  34  to communicate with one or more building infrastructure or local devices in the space via modulated light transmitted along the cables  32 . In some embodiments, this communication is via Li-Fi protocol. 
     Referring now to  FIG. 19 , shown is an enclosure  122 , for example, a server housing, with one or more electronic components  124  located therein. A detection system  20  is installed in the enclosure  122 , along with a suppression system  126 . The suppression system  126  may include, for example, a suppressant supply  128  and one or more suppressant outlets  130  located at, for example, nodes  34  of the detection system  20 . The detection system  20 , the suppression system  126  and the one or more electronic components  124  are connected to the control unit  52  of the detection system  20 . In the event of detection of fire or smoke at a node  34  of the detection system  20 , the control unit  52  triggers the suppression system  126  to activate the suppressant outlet  130  at the node  34  location to provide localized suppression in the enclosure  122 . Further, the control unit  52  may command powering down of electronic components  124  in the node  34  region to prevent further damage to the particular electronic components  124 . Localized detection and suppression, such as described herein via detection system  20  and suppression system  126 , provides protection of electronic components  124  from fire and smoke, while localizing suppression to protect such components not subjected to fire and smoke from exposure to suppressant, thus reducing damage to those components and further reducing cost and expense of suppressant cleanup after an event. 
     While the disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.