# US 12,603,705 B2 · Latency equalization for optical filter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,603,705 B2 - Document ID: US12603705B2 - Status: Granted - Kind: B2 - Application number: 18/568,224 - Filed: 2022-06-29 - Published: 2024-09-05 - Granted: 2026-04-14 - Earliest claimed: 2021-06-30 - Assignees: Telefonaktiebolaget LM Ericsson (publ) - Applicants: Telefonaktiebolaget LM Ericsson (publ) - Inventors: Claudio D'Incà; Sergio Mosti; Alberto Deho; Roberto Magri - Web page: https://patentgrep.com/patent/US12603705B2 ## CPC - H04B 10/2507: for the reduction or elimination of distortion or dispersion - H04B: TRANSMISSION ## Abstract A padding unit comprising one or more fiber paddings is provided. Each of the one or more fiber paddings is for a respective one of one or more pairs of coupled channels in an optical device. At each pair of coupled channels, one channel in the pair of coupled channels is used as an upstream channel and the other channel in the pair of coupled channels is used as a downstream channel. Each fiber padding comprises a padding length of fiber configured to offset at least a part of a latency imbalance at the respective pair of coupled channels, the latency imbalance being a difference in latencies between the respective upstream and downstream channels caused by a difference in the multiplexing or demultiplexing path lengths of the respective upstream and downstream channels. ## Claims ### Claim 1 An optical device comprising: one or more pairs of coupled channels, wherein at each pair of coupled channels one of the channels is used as an upstream channel and the other one of the channels is used as a downstream channel; and a padding unit for at least one of the one or more pairs of coupled channels, the padding unit comprising: one or more fiber paddings, wherein each of the one or more fiber paddings is for a respective one of one or more pairs of coupled channels in the optical device, wherein each fiber padding comprises a padding length of fiber configured to offset at least a part of a latency imbalance at the respective pair of coupled channels, wherein the latency imbalance is a difference in latencies between the respective upstream and downstream channels caused by a difference in multiplexing or demultiplexing path lengths of the respective upstream and downstream channels. ### Claim 2 (depends on 1) The optical device of claim 1, wherein the padding unit comprises a plurality of fiber paddings, wherein each of the plurality of fiber paddings is for a respective one of at least a subset of the plurality of pairs of coupled channels in the optical device, and wherein the padding length of fiber at each of the plurality of fiber paddings is configured to offset at least a part of the latency imbalance at the respective pair of coupled channels such that the differences in latency imbalances across the pairs of coupled channels are reduced. ### Claim 3 (depends on 1) The optical device of claim 1, wherein the padding unit comprises a plurality of fiber paddings, wherein each of the plurality of fiber paddings is for a respective one of at least a subset of the plurality of pairs of coupled channels in the optical device, and wherein the padding length of fiber at each of the plurality of fiber paddings is configured to offset at least a part of a latency in at least one channel at the respective pair of coupled channels, such that the latencies across all channels in the plurality of pairs of coupled channels are equalized at a common value. ### Claim 4 (depends on 1) The optical device according to claim 1, wherein the padding length of fiber of each fiber padding is arranged at an exit of the respective pair of coupled channels. ### Claim 5 (depends on 1) The optical device according to claim 1, wherein the padding length of each fiber padding is determined based on a nominal splice length of fibers in the respective pair of coupled channels. ### Claim 6 (depends on 1) The optical device according to claim 1, wherein the padding length of each fiber padding is determined based on a measured difference in path lengths of the upstream channel and the downstream channel in the respective pair of coupled channels, subsequent to splicing of fibers in the respective pair of couple channels. ### Claim 7 (depends on 1) The optical device according to claim 1, wherein the padding length of each fiber padding is determined based on measured delays in the upstream and downstream channels of the respective pair of coupled channels, wherein the delays are caused by the path lengths of the respective upstream and downstream channels. ### Claim 8 (depends on 1) The optical device according to claim 1, wherein the optical device is an optical filter module. ### Claim 9 (depends on 1) The optical device according to claim 1, wherein the optical device is an optical multiplexer or demultiplexer device. ### Claim 10 (depends on 1) A network node comprising an optical device according claim 1. ### Claim 11 (depends on 10) The network node of claim 10, wherein the network node is a fronthaul network node. ### Claim 12 A padding unit comprising one or more fiber paddings, wherein each of the one or more fiber paddings is for a respective one of one or more pairs of coupled channels in an optical device, wherein at each pair of coupled channels, one channel in the pair of coupled channels is used as an upstream channel and the other channel in the pair of coupled channels is used as a downstream channel, wherein each fiber padding comprises a padding length of fiber configured to offset at least a part of a latency imbalance at the respective pair of coupled channels, wherein the latency imbalance is a difference in latencies between the respective upstream and downstream channels caused by a difference in multiplexing or demultiplexing path lengths of the respective upstream and downstream channels. ### Claim 13 (depends on 12) The padding unit according to claim 12, wherein the padding unit comprises a plurality of fiber paddings, wherein each of the plurality of fiber paddings is for a respective one of at least a subset of the plurality of pairs of coupled channels in the optical device, and wherein the padding length of fiber at each of the plurality of fiber paddings is configured to offset at least a part of the latency imbalance at the respective pair of coupled channels such that the differences in latency imbalances across the pairs of coupled channels are reduced. ### Claim 14 (depends on 12) The padding unit according to claim 12, wherein the padding unit comprises a plurality of fiber paddings, wherein each of the plurality of fiber paddings is for a respective one of at least a subset of the plurality of pairs of coupled channels in the optical device, and wherein the padding length of fiber at each of the plurality of fiber paddings is configured to offset at least a part of a latency in at least one channel at the respective pair of coupled channels, such that the latencies across all channels in the plurality of pairs of coupled channels are equalized at a common value. ### Claim 15 (depends on 12) The padding unit according to claim 12, wherein the padding length of fiber of each fiber padding is for arranging at an exit of the respective pair of coupled channels. ### Claim 16 (depends on 12) The padding unit according to claim 12, wherein the padding length of each fiber padding is determined based on a nominal splice length of fibers in the respective pair of coupled channels. ### Claim 17 (depends on 12) The padding unit according to claim 12, wherein the padding length of each fiber padding is determined based on a measured difference in path lengths of the upstream channel and the downstream channel in the respective pair of coupled channels, subsequent to splicing of fibers in the respective pair of couple channels. ### Claim 18 (depends on 12) The padding unit according to claim 12, wherein the padding length of each fiber padding is determined based on measured delays in the upstream and downstream channels of the respective pair of coupled channels, wherein the delays are caused by the path lengths of the respective upstream and downstream channels. ### Claim 19 A method for manufacturing a padding unit, wherein the padding unit comprises one or more fiber paddings, wherein each of the one or more fiber paddings is for a respective one of one or more pairs of coupled channels in an optical device, and wherein at each pair of coupled channels, one channel in the pair of coupled channels is used as an upstream channel and the other channel in the pair of coupled channels is used as a downstream channel, the method comprising: determining a padding length for each of the one or more fiber paddings, wherein the padding length offsets at least a part of a latency imbalance at the respective pair of coupled channels, the latency imbalance being a difference in latencies between the respective upstream and downstream channels caused by a difference in the multiplexing or demultiplexing path lengths of the respective upstream and downstream channels; and forming the one or more fiber paddings based on the one or more determined padding lengths. ### Claim 20 (depends on 19) The method according to claim 19, wherein the padding unit comprises a plurality of fiber paddings, wherein each fiber padding is for a respective one of at least a subset of a plurality of pairs of coupled channels in the optical device, and wherein the padding length of fiber at each of the plurality of fiber paddings is configured to offset at least a part of the latency imbalance at the respective pair of coupled channels such that the differences in latency imbalances across the pairs of coupled channels are reduced. ### Claim 21 (depends on 19) The method according to claim 19, wherein the padding unit comprises a plurality of fiber paddings, wherein each fiber padding is for a respective one of at least a subset of a plurality of pairs of coupled channels in the optical device, and wherein the padding length of fiber at each of the plurality of fiber paddings is configured to offset at least a part of a latency in at least one channel at the respective pair of coupled channels, such that the latencies across all channels in the plurality of pairs of coupled channels are equalized at a common value. ### Claim 22 (depends on 19) The method according to claim 19, wherein determining the padding length of each fiber padding is based on one of: a nominal splice length of fibers in the respective pair of coupled channels; a measured difference in path lengths of the upstream channel and the downstream channel in the respective pair of coupled channels, subsequent to splicing of fibers in the respective pair of couple channels; and measured delays in the upstream and downstream channels of the respective pair of coupled channels, wherein the delays are caused by the path lengths of the respective upstream and downstream channels.