# US 11,309,964 B1 · Method to reduce optical signal fading in signal receive aperture > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,309,964 B1 - Document ID: US11309964B1 - Status: Granted - Kind: B1 - Application number: 17/123,795 - Filed: 2020-12-16 - Granted: 2022-04-19 - Earliest claimed: 2020-12-16 - Assignees: Raytheon Company - Applicants: Raytheon Company - Inventors: Andrew Kowalevicz; Gary M. Graceffo; Benjamin P. Dolgin - Web page: https://patentgrep.com/patent/US11309964B1 ## CPC - H04B 10/112: Line-of-sight transmission over an extended range - H04B 10/2572: {due to forms of polarisation-dependent distortion other than PMD} - G02B 6/4204: {the coupling comprising intermediate optical elements, e.g. lenses, holograms (encapsulated active devices H01S5/02208)} - H04B 10/0795: {Performance monitoring; Measurement of transmission parameters} - H04B 10/40: Transceivers - H04B: TRANSMISSION - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract Free space optical systems and methods of controlling the same for reducing signal fading of encoded optical beams transmitted in a communication channel are provided. Adjacent pairs of a plurality of apertures are separated by a distance being at least greater than the coherence width of the propagation medium of the communication channel. Due to averaging of the beams, variation in power at an optical receiver is reduced. By using an optical resonator in the optical receiver, the beams are converted into an intensity modulation on a non-interfering basis, thereby permitting recovery and decoding of the signal. ## Claims ### Claim 1 A method of reducing signal fading in a free space optical system, comprising acts of: providing a plurality of transmit apertures, a receive aperture, and an optical resonator coupled to the receive aperture; transmitting each respective optical beam of a plurality of optical beams of an optical signal through each aperture of the plurality of transmit apertures; receiving each transmitted optical beam at the receive aperture; and providing each received optical beam to the optical resonator that produces an intensity-modulated output signal from the received optical beams. ### Claim 2 (depends on 1) The method of claim 1, further comprising separating each transmit aperture by a predetermined distance greater than the coherence width of a propagation medium. ### Claim 3 (depends on 1) The method of claim 1 further comprising: accumulating each received beam in the optical resonator by partially reflecting optical signal energy of each received beam between two semi-reflective surfaces to approach a steady state of accumulated optical energy; outputting optical signal energy from the accumulated optical signal energy having an intensity modulation that is proportional to an average of the accumulated optical signal energy; and detecting the output optical signal energy. ### Claim 4 (depends on 1) The method of claim 1 further comprising: dividing a total amount of power of the optical signal from at least one optical source between the optical beams to be transmitted through the plurality of transmit apertures. ### Claim 5 (depends on 4) The method of claim 4, further comprising: evenly distributing the total amount of power between the optical beams to be transmitted through the plurality of transmit apertures; or unevenly distributing the total amount of power between the optical beams to be transmitted by the plurality of transmit apertures. ### Claim 6 (depends on 1) The method of claim 1, further comprising receiving data and encoding the optical signal with the data. ### Claim 7 (depends on 1) The method of claim 1, further comprising receiving data and encoding each optical beam with the data. ### Claim 8 (depends on 1) The method of claim 1 further comprising providing the optical signal with a single source and dividing the optical signal into the plurality of optical beams. ### Claim 9 (depends on 1) The method of claim 1 further comprising: providing a plurality of optical sources; providing each optical beam of the optical signal by a respective optical source of the plurality of optical sources; determining if each optical source is operating nominally; determining a total number of nominally operating optical sources; and distributing a total amount of power of the optical signal between the transmitted beams of the nominally operating sources. ### Claim 10 (depends on 9) The method of claim 9 further comprising increasing the total amount of power between the nominally operating optical sources in response to determining the total number of nominally operating sources is greater than a predetermined value. ### Claim 11 A free space optical system for reducing signal fading comprising: a plurality of transmit apertures; a controller configured to transmit each respective optical beam of a plurality of optical beams of an optical signal through each aperture of the plurality of transmit apertures; a receive aperture configured to receive each transmitted optical beam; and an optical resonator configured to produce an intensity-modulated output signal from the received optical beams. ### Claim 12 (depends on 11) The system of claim 11 wherein each transmit aperture is separated by a predetermined distance greater than the coherence width of a propagation medium. ### Claim 13 (depends on 11) The system of claim 11 wherein the optical resonator is further configured to: accumulate each received beam by partially reflecting optical signal energy of each received beam between two semi-reflective surfaces to approach a steady state of accumulated optical energy; and output optical signal energy from the accumulated optical signal energy having an intensity modulation that is proportional to an average of the accumulated optical signal energy. ### Claim 14 (depends on 11) The system of claim 11 further comprising a controller configured to divide a total amount of power of the optical signal from at least one optical source between the optical beams to be transmitted through the plurality of transmit apertures. ### Claim 15 (depends on 14) The system of claim 14 wherein the controller is further configured to: evenly distribute the total amount of power between the optical beams to be transmitted through the plurality of transmit apertures; or unevenly distribute the total amount of power between the optical beams to be transmitted through the plurality of transmit apertures. ### Claim 16 (depends on 15) The system of claim 15 wherein the controller is further configured to receive data and encode the optical signal with the data. ### Claim 17 (depends on 16) The system of claim 16 wherein the controller is further configured to receive data and encode each optical beam with the data. ### Claim 18 (depends on 16) The system of claim 16 wherein the controller is further configured to provide the optical signal with a single source and divide the optical signal into the plurality of optical beams. ### Claim 19 (depends on 16) The system of claim 16 wherein the at least one optical source includes a plurality of optical sources, and the controller is further configured to: provide each optical beam of the optical signal by a respective optical source of the plurality of optical sources; determine if each optical source is operating nominally; determine a total number of nominally operating optical sources; and distribute the total amount of power between the transmitted beams of the nominally operating sources. ### Claim 20 (depends on 19) The system of claim 19 wherein the controller is further configured to increase the total amount of power between the nominally operating optical sources in response to determining the total number of nominally operating sources is greater than a predetermined value.