# US 2025/0155643 A1 · Alternating filter stack assembly for multiplexer and demultiplexer applications > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2025/0155643 A1 - Document ID: US20250155643A1 - Status: Published application - Kind: A1 - Application number: 18/510,576 - Filed: 2023-11-15 - Published: 2025-05-15 - Earliest claimed: 2023-11-15 - Assignees: Cisco Technology, Inc. - Applicants: Cisco Technology, Inc. - Inventors: Iman HASSANI NIA - Web page: https://patentgrep.com/patent/US20250155643A1 ## CPC - G02B 6/29362: {Serial cascade of filters or filtering operations, e.g. for a large number of channels} - G02B 6/29367: {Zigzag path within a transparent optical block, e.g. filter deposited on an etalon, glass plate, wedge acting as a stable spacer} - G02B 6/2938: {for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM} - G02B 6/30: for use between fibre and thin-film device - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract A multiplexer and demultiplexer (MDM) is disclosed. In one aspect, an MDM includes a plurality of filters arranged along a propagation direction. Each one of the filters has a thin-film filter (TFF) supported by a substrate. The filters are arranged so that each filter induces an opposite warpage of an optical signal traversing along the propagation direction than an immediately preceding filter. ## Claims ### Claim 1 A multiplexer and demultiplexer (MDM), comprising: a plurality of filters arranged along a propagation direction of an optical signal, each one of the plurality of filters having a thin-film filter (TFF) supported by a substrate, and wherein the plurality of filters are arranged so that each filter of the plurality of filters induces an opposite warpage of the optical signal traversing along the propagation direction than an immediately preceding filter of the plurality of filters. ### Claim 2 (depends on 1) The MDM of claim 1, wherein the plurality of filters are arranged so that the TFFs have alternating concave and convex curvatures relative to the propagation direction. ### Claim 3 (depends on 1) The MDM of claim 1, wherein the plurality of filters are arranged so that adjacent filters of the plurality of filters have opposite radius of curvature. ### Claim 4 (depends on 1) The MDM of claim 1, further comprising: a filter block, and wherein the plurality of filters are arranged along the propagation direction so that the TFF of every other filter of the plurality of filters connects to the filter block. ### Claim 5 (depends on 1) The MDM of claim 1, further comprising: a filter block, and wherein the plurality of filters are arranged along the propagation direction so that the substrate of every other filter of the plurality of filters connects to the filter block. ### Claim 6 (depends on 1) The MDM of claim 1, wherein the plurality of filters are arranged so that each one of the plurality of filters is flipped vertically with respect to any filter of the plurality of filters positioned adjacent thereto. ### Claim 7 (depends on 1) The MDM of claim 1, wherein spectral beams that pass through respective ones of the plurality of filters produce a first pitch and a second pitch, the first pitch and second pitch are different from one another and alternate with one another along the propagation direction. ### Claim 8 (depends on 1) The MDM of claim 1, wherein the plurality of filters are arranged so that the TFFs of adjacent filters of the plurality of filters are vertically offset from one another. ### Claim 9 (depends on 1) The MDM of claim 1, wherein the plurality of filters are arranged so that the TFFs of the plurality of filters are vertically aligned with one another. ### Claim 10 (depends on 9) The MDM of claim 9, wherein spectral beams that pass through respective ones of the plurality of filters produce a uniform pitch. ### Claim 11 (depends on 1) The MDM of claim 1, wherein the substrate of each filter of the plurality of filters has a base and a cap, and wherein each filter of the plurality of filters is arranged so that, for a given filter of the plurality of filters, the TFF is vertically sandwiched between the base and the cap of the given filter. ### Claim 12 (depends on 1) The MDM of claim 1, wherein the plurality of filters are arranged along the propagation direction in at least a first stack and a second stack, the first stack is spaced from the second stack by a filter block. ### Claim 13 (depends on 12) The MDM of claim 12, wherein: the first stack includes at least two filters of the plurality of filters stacked adjacent to one another, the second stack includes at least two filters of the plurality of filters stacked adjacent to one another, and wherein the TFFs of the at least two filters of the first stack each have a positive radius of curvature and the TFFs of the at least two filters of the second stack each have a negative radius of curvature. ### Claim 14 (depends on 12) The MDM of claim 12, wherein: the first stack includes at least two filters of the plurality of filters stacked adjacent to one another, the second stack includes at least two filters of the plurality of filters stacked adjacent to one another, and wherein the at least two filters of the first stack and the at least two filters of the second stack are staggered along the propagation direction. ### Claim 15 (depends on 12) The MDM of claim 12, wherein: the first stack includes at least two filters of the plurality of filters stacked adjacent to one another, the second stack includes at least two filters of the plurality of filters stacked adjacent to one another, and wherein the optical signal traversing along the propagation direction traverses in an alternating manner between one of the at least two filters of the first stack and one of the at least two filters of the second stack. ### Claim 16 (depends on 12) The MDM of claim 12, wherein: the first stack includes at least one filter of the plurality of filters, the second stack includes at least one filter of the plurality of filters, and wherein the MDM further comprises: a first lens array; a first photonic die coupled with the first lens array, and wherein the at least one filter of the first stack is coupled with the first lens array; a second lens array; and a second photonic die coupled with the second lens array, and wherein the at least one filter of the second stack is coupled with the second lens array. ### Claim 17 (depends on 12) The MDM of claim 12, wherein: the first stack includes at least one filter of the plurality of filters, the second stack includes at least one filter of the plurality of filters, and wherein the filter block defines a cutout in which the at least one filter of the second stack is positioned, and wherein the TFF of each one of the at least one filter of the second stack is vertically aligned with a mirror that extends lengthwise parallel to the propagation direction. ### Claim 18 (depends on 12) The MDM of claim 12, wherein: the first stack includes at least two filters of the plurality of filters stacked adjacent to one another, the second stack includes at least two filters of the plurality of filters stacked adjacent to one another, and wherein the at least two filters of the first stack and the at least two filters of the second stack have a same mounting orientation. ### Claim 19 A multiplexer and demultiplexer (MDM), comprising: a plurality of filters arranged along a propagation direction, each one of the plurality of filters having a thin-film filter (TFF) supported by a substrate, and wherein the plurality of filters are arranged so that the TFFs have alternating concave and convex curvatures along the propagation direction. ### Claim 20 A multiplexer and demultiplexer (MDM), comprising: a filter block; and a plurality of filters arranged along a propagation direction of an optical signal in a first stack and a second stack spaced from the first stack by the filter block, each one of the plurality of filters has a thin-film filter (TFF) supported by a substrate, and wherein the optical signal traverses between the first stack and the second stack in an alternating manner, and wherein the plurality of filters are arranged so that a second filter of the plurality of filters arranged in the second stack induces an opposite warpage of an optical signal traversing along the propagation direction than a first filter of the plurality of filters arranged in the first stack.