# US 11,121,797 B1 · Optical system for compensating for signal loss > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,121,797 B1 - Document ID: US11121797B1 - Status: Granted - Kind: B1 - Application number: 16/984,638 - Filed: 2020-08-04 - Granted: 2021-09-14 - Earliest claimed: 2020-08-04 - Assignees: Fujitsu Limited - Applicants: Fujitsu Limited - Inventors: Youichi Akasaka; Tadashi Ikeuchi - Web page: https://patentgrep.com/patent/US11121797B1 ## CPC - H04J 14/0221: {Power control, e.g. to keep the total optical power constant} - H04B 10/2916: {using Raman or Brillouin amplifiers} - H04J 14/0261: {at the optical multiplex section layer} - 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) - H04B: TRANSMISSION ## Abstract An optical system including a transmission fiber to transmit a WDM input optical signal between first and second points; a second order forward Raman pump module positioned along a first region of the transmission fiber proximate to the first point; a first order backward Raman pump module positioned along a second region of the transmission fiber proximate to the second point, the first order backward Raman pump module is configured to generate a first pumping light along the transmission fiber to amplify the WDM input optical signal at the second region of the transmission fiber, wherein the second order forward Raman pump module is configured to generate a second pumping light along the transmission fiber to amplify the first pumping light generated by the first order backward Raman pump module, wherein the amplified first pumping light amplifies the WDM input optical signal at the first region of the transmission fiber. ## Claims ### Claim 1 An optical system for compensating for signal loss, comprising: a transmission fiber to transmit a wavelength division multiplexing (WDM) input optical signal between a first point and a second point, the WDM input optical signal is 1550 nanometers (nm); a second order forward Raman pump module positioned along a first region of the transmission fiber proximate to the first point; and a first order backward Raman pump module positioned along a second region of the transmission fiber proximate to the second point, wherein the first order backward Raman pump module is configured to generate a first pumping light along the transmission fiber to amplify the WDM input optical signal at the second region of the transmission fiber, the first pumping light is 1455 nm, wherein the second order forward Raman pump module is configured to generate a second pumping light along the transmission fiber to amplify the first pumping light generated by the first order backward Raman pump module, the second pumping light is 1365 nm, wherein the amplified first pumping light amplifies the WDM input optical signal at the first region of the transmission fiber, wherein a direction of travel of the first pumping light is opposite to a direction of travel of the WDM input optical signal, wherein the direction of travel of the first pumping light is opposite to the direction of travel of the second pumping light. ### Claim 2 (depends on 1) The optical system of claim 1, wherein the WDM input optical signal is independent of being amplified by the second order forward Raman pump module. ### Claim 3 (depends on 1) The optical system of claim 1, wherein the WDM input optical signal is only amplified by the first order backward Raman pump module. ### Claim 4 (depends on 1) The optical system of claim 1, wherein the second order forward Raman pump module is configured to generate the second pumping light along the transmission fiber to amplify the first pumping light generated by the first order backward Raman pump module at the first region of the transmission fiber. ### Claim 5 (depends on 1) The optical system of claim 1, further comprising a power adjustment computing module to adjust a power ratio between the first order backward Raman pump module and the second order forward Raman pump module. ### Claim 6 (depends on 5) The optical system of claim 5, wherein the power adjustment computing module adjusts the power ratio to have a power of the WDM input optical signal at the first point and the second point the same. ### Claim 7 (depends on 1) The optical system of claim 1, wherein the amplification of the WDM input optical signal at the first and the second regions of the transmission fiber are both less than 15 decibels (dB). ### Claim 8 A method for compensating for signal loss in an optical network, comprising: transmitting a wavelength division multiplexing (WDM) input optical signal between a first point and a second point of a transmission fiber, the WDM input optical signal is 1550 nanometers (nm); generate, by a first order backward Raman pump module positioned along a second region of the transmission fiber proximate to the second point, a first pumping light along the transmission fiber, the first pumping light is 1455 nm; amplify, by the first pumping light, the WDM input optical signal at the second region of the transmission fiber; generate, by a second order forward Raman pump module positioned along a first region of the transmission fiber proximate to the first point, a second pumping light along the transmission fiber, the second pumping light is 1365 nm; amplify, by the second pumping light, the first pumping light along the transmission fiber; and amplify, by the amplified first pumping light, the WDM input optical signal at the first region of the transmission fiber, wherein a direction of travel of the first pumping light is opposite to a direction of travel of the WDM input optical signal, wherein the direction of travel of the first pumping light is opposite to the direction of travel of the second pumping light. ### Claim 9 (depends on 8) The method of claim 8, wherein the WDM input optical signal is independent of being amplified by the second order forward Raman pump module. ### Claim 10 (depends on 8) The method of claim 8, wherein the WDM input optical signal is only amplified by the first order backward Raman pump module. ### Claim 11 (depends on 8) The method of claim 8, wherein the second pumping light amplifies the first pumping light at the first region of the transmission fiber. ### Claim 12 (depends on 8) The method of claim 8, further comprising adjusting a power ratio between the first order backward Raman pump module and the second order forward Raman pump module. ### Claim 13 (depends on 12) The method of claim 12, wherein adjusting the power ratio includes adjusting the power ratio to have a power of the WDM input optical signal at the first point and the second point the same. ### Claim 14 (depends on 8) The method of claim 8, wherein the amplification of the WDM input optical signal at the first and the second regions of the transmission fiber are both less than 15 decibels (dB).