# US 2022/0286201 A1 · Detection of ambient disturbances using dispersive delays in optical fibers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2022/0286201 A1 - Document ID: US20220286201A1 - Status: Published application - Kind: A1 - Application number: 17/580,202 - Filed: 2022-01-20 - Published: 2022-09-08 - Earliest claimed: 2021-03-04 - Assignees: Nokia Solutions and Networks Oy - Applicants: Nokia Solutions and Networks OY - Inventors: Mikael Mazur; Nicolas Fontaine - Web page: https://patentgrep.com/patent/US20220286201A1 ## CPC - H04B 10/07: Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems - H04B 10/2572: {due to forms of polarisation-dependent distortion other than PMD} - G01H 9/004: {using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125)} - H04J 14/06: Polarisation multiplex systems - G01V 1/01: Measuring or predicting earthquakes - G01V 1/226: {Optoseismic systems} - H04B: TRANSMISSION - G01H: MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) - G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02) ## Abstract A fiber-optic communication system having two optical channels characterized by different respective group velocities. In an example embodiment, the system comprises an optical receiver capable of measuring a difference in the time of arrival thereto, by way of the two optical channels, of the corresponding signal disturbances caused by a remote ambient event, such as an earthquake or a lightning strike. A signal processor of the receiver can then use the measured time-of-arrival difference to estimate the distance, along the fiber, to the location of the remote ambient event. In some example embodiments, the two optical channels may be different wavelength channels or different spatial modes of a multimode fiber. In some example embodiments, at least one of the two channels may be a payload-data-bearing channel. ## Claims ### Claim 1 An apparatus, comprising: a first optical receiver configured to optically connect to an end segment of an optical fiber to perform a temporal sequence of measurements of a first optical signal received therefrom, the first optical signal having a first carrier wavelength; and a second optical receiver configured to optically connect to the end segment of the optical fiber to perform a temporal sequence of measurements of a second optical signal received therefrom, the second optical signal having a different second carrier wavelength; and wherein, from the measurements, the apparatus is configured to estimate a location of an ambient event based on a difference between receipt times of respective disturbed temporal segments of the first and second optical signals. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the first and second optical receivers are synchronized using a common clock signal. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the difference is caused, at least in part, by effects of chromatic dispersion in the optical fiber. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the ambient event is one of: arrival of a seismic wave at the location along the optical fiber; a lightning strike at the location along the optical fiber; and mechanical vibration at the location along the optical fiber. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein the apparatus is configured to detect the disturbed temporal segments by identifying a disturbance of optical phases of the first and second optical signals. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein the apparatus is configured to detect the disturbed segments by identifying a disturbance of a polarization of the first and second optical signals. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein at least one of the first and second optical receivers is a polarization-sensitive coherent optical receiver. ### Claim 8 (depends on 1) The apparatus of claim 1, further comprising an optical wavelength demultiplexer connected between the end segment of the optical fiber and the first and second optical receivers. ### Claim 9 (depends on 8) The apparatus of claim 8, further comprising a plurality of third optical receivers connected to the optical wavelength demultiplexer to receive therethrough, from the end segment of the optical fiber, respective data-modulated optical signals. ### Claim 10 (depends on 1) The apparatus of claim 1, further comprising a synchronization circuit configured to generate a common clock signal for synchronizing the first and second optical receivers. ### Claim 11 (depends on 1) The apparatus of claim 1, wherein the first and second optical receivers are synchronized using a GPS clock source. ### Claim 12 (depends on 1) The apparatus of claim 1, wherein the first optical receiver is configured to recover data encoded in the first optical signal. ### Claim 13 (depends on 12) The apparatus of claim 12, wherein the second optical receiver is configured to recover data encoded in the second optical signal. ### Claim 14 (depends on 1) The apparatus of claim 1, wherein the estimate does not rely on optical-signal measurements at another end of the optical fiber. ### Claim 15 (depends on 1) The apparatus of claim 1, further comprising a digital signal processor configured to identify the respective disturbed temporal segments of the first and second optical signals by processing the measurements to obtain time-resolved estimates of a selected signal characteristic of the first and second optical signals. ### Claim 16 A method of environmental sensing, comprising: performing a temporal sequence of measurements of a first optical signal received by a first optical receiver from an end segment of an optical fiber, the first optical signal having a first carrier wavelength; performing a temporal sequence of measurements of a second optical signal received by a second optical receiver from the end segment of the optical fiber, the second optical signal having a different second carrier wavelength; and estimating a location of an ambient event based on a difference between receipt times of respective disturbed temporal segments of the first and second optical signals. ### Claim 17 (depends on 16) The method of claim 16, further comprising synchronizing the first and second optical receivers using a common clock signal. ### Claim 18 (depends on 16) The method of claim 16, further comprising detecting the disturbed temporal segments by identifying a disturbance of optical phases of the first and second optical signals. ### Claim 19 (depends on 16) The method of claim 16, further comprising detecting the disturbed segments by identifying a disturbance of a polarization of the first and second optical signals. ### Claim 20 (depends on 16) The method of claim 16, further comprising identifying the respective disturbed temporal segments of the first and second optical signals by processing the measurements to obtain time-resolved estimates of a selected signal characteristic of the first and second optical signals.