Optical Fiber-Based Remote Gas Leakage Monitoring

Abstract

The invention uses a point-to-multi-point (P2MP) discovery process conducted in a passive optical network PON system to identify each sensor that returns a probe pulse identified with a respective sensor without adding any equipment at the remote sensors. The sensors provide with the returned signal information indicative of measured gas leakage in the air in the sensor.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to optics, and more particularly, to optical fiber-based remote gas leakage monitoring with sensor identifier.

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 (10 GbE) 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 (λ) 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.

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 the OLT to another ONU, two probe signal pulses returned from the two different ONUs are distinguishable based on referring differences in the different round-trip times. However, it is hard to identify the two probe signals returned from the two different ONUs, to the OLT when distances between their respective ONUs and the OLT are similar.

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.

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

The present invention is directed to an apparatus including an analyzer operable with an optical network including an optical line terminal OLT with a medium access control MAC sub-layer and including at least one sensor associated with a respective optical network unit ONU in the network, the sensor being 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. The analyzer can be responsive to timing information from the MAC sub-layer about round trip of time frames during conducting ONU discovery to relate the information about the target matter in the sensor with the identity of the sensor.

In a similar aspect of the invention, there is provided a method that includes analyzing a probe signal within an optical network including an optical line terminal OLT with a medium access control MAC sub-layer and including at least one sensor associated with a respective optical network unit ONU in the network, the sensor being optically responsive to its surrounding air. The analyzing 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 analyzing for information about the targeted matter. The analyzing can be responsive to timing information from the MAC sub-layer about round trip of time frames during conducting ONU discovery to relate the information about the target matter in the sensor with the identity of the sensor.

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

FIG. 1 shows an exemplary passive optical network PON employing the inventive optical sensor identification associated with a remote sensor, in the PON, for detecting methane gas leakage.

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 (10 GbE) PON, and future time and wavelength division multiplexing (TWDM) PON.

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.

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.

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.

FIG. 6 illustrates flow of frames within the network in FIG. 1 that enables calculation of a round trip time of frames during conducting an ONU discovery process, in accordance with the invention.

FIG. 7 shows flow of frames and time references between flow events within the network in FIG. 5 that enable calculation of a round trip time of frames during conducting an ONU discovery process to enable distinguishing different sensor heads at different ONUs within a network, in accordance with the invention

FIG. 8 is a diagram of an exemplary processor, analyzer or controller for implementing analyzing of probe signals corresponding to remote sensors responsive to methane gas leakage.

DETAILED DESCRIPTION

The present invention includes use of a point to multi point (P2MP) discovery process conducted in a conventional passive PON system to identify each sensor. Each returned probe pulse can be identified without adding any equipment at remote sensors.

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 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 the ONU (108) by a WDM filter (110) and 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.

The probe signal returns back to the OLT (101) 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 photo detector PD (104) through an optical circulator (103).

Media Access Control (MAC) sub-layer block (111) calculates round trip time of frames during conducting ONU discovery process, whose flow is shown in FIG. 6, and sends the timing information to an analyzer or controller (114). When methane gas concentration is high around the sensor head (109), a weak dip is measured on the probe pulse as shown in inset (a) of FIG. 1. By using timing information from MAC block (111), the analyzer or controller (114) relates each returned probe pulse to each sensor.

Wavelength allocation in typical standards, gigabit Ethernet passive optical network (GE-PON), ten Gigabit Ethernet (10 GbE) 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 (λ) 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.

Meanwhile, absorption spectra of methane (CH₄) 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 onto an existing PON 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) (301) 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 (309) via the sensor head (310). The probe signal is reflected and again multiplexed (308) with other communication channels, returned through transmission fiber (306), de-multiplexed (305) from the other channels at the OLT (301), passed through the optical circulator (303) coupled to the laser diode (302) and optical to electrical converted with photo diode (PD) 304 followed by signal processing by an analyzer or controller 311.

The invention enables methane gas leakage information at several monitoring points to be collected at the 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.

A challenge in this fiber-based remote methane gas leakage monitoring system is how to identify a particular gas sensor. An optical distribution network in a PON has multiple optical fiber lines after a passive optical splitter (307), the probe signal is returned from multiple sensors. If a distance from/to the OLT to an ONU (408) is different from the distance from the OLT to ONU (410), like in 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).

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), 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.

When the MAC block (512) calculates round trip times, processing time in the ONU (508) is included, resulting in inaccurate propagation time estimation. Therefore, the ONU (508) calculates processing time taken to a return message, t₂−t₁, to the OLT (501) using an internal clock and sends the processing time information to the OLT as shown in FIG. 7. Using the processing time information inside the ONU (508), the MAC block can estimate propagation delay to the ONU, by calculating (t₃−t₀−(t₂−t₁))/2, with higher accuracy. Propagation delay also depends on chromatic dispersion of the transmission fiber. This difference in the propagation delay can also be taken into account to calculate the propagation delay of the probe signal with higher accuracy.

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.

By way of example, a block diagram of a computer or controller or analyzer to support the invention is discussed next in FIG. 8. 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).

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.

From the foregoing, it can be appreciated that the present invention a fiber-based remote methane gas leakage monitoring system that 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.

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.

Claims

1. An apparatus comprising: an analyzer operable with an optical network including an optical line terminal OLT with a medium access control MAC sub-layer and including at least one sensor associated with a respective optical network unit ONU in the network, the sensor being optically responsive to its surrounding air;wherein 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; andwherein the analyzer can be responsive to timing information from the MAC sub-layer about round trip of time frames during conducting ONU discovery to relate the information about the target matter in the sensor with the identity of the sensor.

2. The apparatus of claim 1, wherein the timing information from the MAC sub-layer comprises the ONU calculating a processing time taken to return a message, t2−t1, to the OLT using an internal clock and sending the processing time information to the OLT, the analyzer using the processing time information inside the ONU, MAC sub-layer to estimate propagation delay of the probe signal due to the ONU with higher accuracy, by calculating (t3−t0−(t2−t1))/2, where t0 and t1 represent the OLT to ONU times of a discovery gate step, and t2 and t3 represent ONU to OLT times of a register request step.

3. The apparatus of claim 1, wherein the timing information from the MAC sub-layer can be influenced by a propagation delay depending on chromatic dispersion of a transmission fiber in the optical network and the analyzer being configured to account for this difference in the propagation delay to calculate the propagation delay of the probe signal with higher accuracy.

4. The apparatus of claim 1, wherein the information about the targeted matter in the probe signal comprises changes in the probe signal responsive to concentration levels of the targeted matter in the air, the targeted matter exhibiting respective absorption spectra to light.

5. The apparatus of claim 1, wherein the sensor comprises a sensor head that includes a collimator lens and reflector mirror, the probe signal being interactable with the targeted matter in air between the collimator lens and reflector mirror.

6. The apparatus of claim 1, wherein the sensor comprises am optical circulator, an optical isolator, and a sensor head comprising two collimator lenses with the probe signal being interactable with the targeted matter in air between the collimator lens and reflector mirror.

7. The apparatus of claim 1, wherein the probe signal carrying information about the targeted matter in the sensor is processed by the analyzer to reveal dips in the probe signal responsive to absorption spectra of the targeted matter.

8. A method comprising: analyzing a probe signal within an optical network including an optical line terminal OLT with a medium access control MAC sub-layer and including at least one sensor associated with a respective optical network unit ONU in the network, the sensor being optically responsive to its surrounding air;wherein the analyzing 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 analyzing for information about the targeted matter; andwherein the analyzing can be responsive to timing information from the MAC sub-layer about round trip of time frames during conducting ONU discovery to relate the information about the target matter in the sensor with the identity of the sensor.

9. The method of claim 1, wherein the timing information from the MAC sub-layer comprises the ONU calculating a processing time taken to return a message, t2−t1, to the OLT using an internal clock and sending the processing time information to the OLT, the analyzing using the processing time information inside the ONU, MAC sub-layer to estimate propagation delay of the probe signal due to the ONU with higher accuracy, by calculating (t3−t0−(t2−t1))/2, where t0 and t1 represent the OLT to ONU times of a discovery gate step, and t2 and t3 represent ONU to OLT times of a register request step.

10. The method of claim 1, wherein the timing information from the MAC sub-layer can be influenced by a propagation delay depending on chromatic dispersion of a transmission fiber in the optical network and the analyzing accounting for this difference in the propagation delay to calculate the propagation delay of the probe signal with higher accuracy.

11. The method of claim 1, wherein the information about the targeted matter in the probe signal comprises changes in the probe signal responsive to concentration levels of the targeted matter in the air, the targeted matter exhibiting distinctive absorption spectra to light.

12. The method of claim 1, wherein the sensor comprises a sensor head that includes a collimator lens and reflector mirror, the probe signal being interactable with the targeted matter in air between the collimator lens and reflector mirror.

13. The apparatus of claim 1, wherein the sensor comprises an optical circulator, an optical isolator, and a sensor head comprising two collimator lenses with the probe signal being interactable with the targeted matter in air between the collimator lens and reflector mirror.

14. The apparatus of claim 1, wherein the probe signal carrying information about the targeted matter in the sensor is processed by the analyzing to reveal dips in the probe signal responsive to absorption spectra of the targeted matter.