# US 9,753,222 B2 · Asymmetric optical fiber coupler > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,753,222 B2 - Document ID: US9753222B2 - Status: Granted - Kind: B2 - Application number: 14/765,021 - Filed: 2014-01-31 - Published: 2015-12-31 - Granted: 2017-09-05 - Earliest claimed: 2013-02-01 - Assignees: Polyvalor, Limited Partnership - Applicants: Polyvalor, Limited Partnership - Inventors: Nicolas Godbout; Caroline Boudoux; Wendy-Julie Madore; Simon Lemire-Renaud; Xavier Daxhelet; Mikael Leduc - Web page: https://patentgrep.com/patent/US9753222B2 ## CPC - G02B 6/2835: {formed or shaped by thermal treatment, e.g. couplers} - G02B 6/245: Removing protective coverings of light guides before coupling - G02B 6/2856: {formed or shaped by thermal heating means, e.g. splitting, branching and/or combining elements} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract There is described an optical fiber coupler in which at least one fiber is a multiple-clad fiber, containing a single-mode core supporting a single guiding mode and an inner multi-mode cladding guiding multiple modes. The multiple-clad fiber is fused with a second fiber of a different etendue to create an optical fiber coupler having an enhanced multi-mode signal transmission. ## Claims ### Claim 1 An optical fiber coupler comprising: a first optical fiber having a first cross-talk portion located between a first end and a second end, and having a first single-mode core, at least one inner multi-mode cladding, and a first outer cladding, the first cross-talk portion having a first etendue; a second optical fiber having a second cross-talk portion located between a third end and a fourth end, the second cross-talk portion having a second etendue, the second etendue forming an etendue ratio differing from one relative to the first etendue; and a coupling region where the first cross-talk portion is optically coupled to the second cross-talk portion; wherein the etendue ratio is indicative of an extraction of more than 50% of a multi-mode signal from the at least one inner multi-mode cladding of the first optical fiber at the second end to the third end of the second optical fiber while maintaining a single-mode signal in the first single-mode core, wherein a first cross-sectional area of the at least one inner multi-mode cladding of the first optical fiber is different from a second cross-sectional area of the second optical fiber, and wherein an inner one of the at least one inner multi-mode cladding is tapered to form an inner single-mode cladding, such that a fundamental mode of the first single-mode core is adiabatically transformed into a fundamental mode of the inner single-mode cladding and the inner single-mode cladding is transformed into a single-mode guiding region. ### Claim 2 (depends on 1) The optical fiber coupler of claim 1, wherein the extraction of the multi-mode signal is above 60%. ### Claim 3 (depends on 2) The optical fiber coupler of claim 2, wherein the extraction of the multi-mode signal is above 70%. ### Claim 4 (depends on 1) The optical fiber coupler of claim 1, wherein the etendue ratio is above 1.5. ### Claim 5 (depends on 4) The optical fiber coupler of claim 4, wherein the etendue ratio is above 2. ### Claim 6 (depends on 5) The optical fiber coupler of claim 5, wherein the etendue ratio is above 10. ### Claim 7 (depends on 1) The optical fiber coupler of claim 1, wherein the cross-talk portions are optically coupled to one another along only a portion of their lengths. ### Claim 8 (depends on 7) The optical fiber coupler of claim 7, wherein the first cross-talk portion has a first down-stream portion, a first constant diameter portion and a first up-stream portion; the second cross-talk portion having a second down-stream portion, a second constant diameter portion and a second up-stream portion; and wherein the coupling region optically joins either the first down-stream portion or the first up-stream portion and a certain section of the first constant diameter portion of the first cross-talk portion to a corresponding one of the second up-stream portion or the second down-stream portion and a corresponding portion of the second cross-talk portion. ### Claim 9 (depends on 1) The optical fiber coupler of claim 1, wherein a first numerical aperture of the at least one inner multi-mode cladding of the first optical fiber is different from a second numerical aperture of the second optical fiber. ### Claim 10 (depends on 1) The optical fiber coupler of claim 1, wherein at least a portion of the first cross-talk portion of the first optical fiber is pre-tapered prior to coupling to the second optical fiber. ### Claim 11 (depends on 1) The optical fiber coupler of claim 1, wherein the first outer cladding is removed at least along the first cross-talk portion prior to the coupling to the second optical fiber. ### Claim 12 (depends on 1) The optical fiber coupler of claim 1, wherein the second optical fiber is one of a multi-mode optical fiber, a single-mode optical fiber, a double-clad optical fiber, a multiple-clad optical fiber and a coreless optical fiber. ### Claim 13 (depends on 1) Use of the optical fiber coupler of claim 1 in one of an optical coherent tomography system and a multimodal detection system. ### Claim 14 (depends on 1) The optical fiber coupler of claim 1, wherein the etendue ratio is above one and the multi-mode signal in the at least one inner multi-mode cladding of the first optical fiber is transmitted to the second optical fiber. ### Claim 15 An optical fiber coupler comprising: a first fiber having a first end, a second end, a first middle portion therebetween and a first cross-section, and having a first core supporting a single guiding mode and a first inner cladding larger than the first core for guiding multiple modes; a second fiber having a third end, a fourth end, and a second middle portion therebetween, and having a second cross-section different from the first cross-section in at least one of structure and dimension, whereby a dimension of the second cross-section is different than a dimension of the first cross-section; and a fused region composed of the first middle portion fused to the second middle portion for a single mode signal to remain in the first core of the first fiber from the first end to the second end, and for more than half (50%) of a multi-mode signal in the first inner cladding of the first fiber to be extracted to the second fiber; wherein the first fiber is a pre-tapered double-clad fiber and a fundamental mode of the first core is adiabatically transformed into a fundamental mode of a reduced first inner cladding by pre-tapering of the first fiber, and the reduced first inner cladding is transformed into a single-mode guiding region. ### Claim 16 (depends on 15) The optical fiber coupler of claim 15, whereby a dimension of the second cross-section is greater than a dimension of the first cross-section. ### Claim 17 (depends on 16) The optical fiber coupler of claim 16, wherein more than 60% is extracted from the first fiber to the second fiber. ### Claim 18 (depends on 17) The optical fiber coupler of claim 17, wherein more than 70% is extracted from the first fiber to the second fiber. ### Claim 19 (depends on 15) The optical fiber coupler of claim 15, wherein the fused region is limited to either a down-tapered or an up-tapered portion of the first and the second fibers. ### Claim 20 (depends on 15) The optical fiber coupler of claim 15, wherein the outer cladding of the first middle portion of the first fiber is removed prior to the process of fusing the first fiber and the second fiber together. ### Claim 21 A method for making an optical coupler comprising: providing a first optical fiber having a first end, a second end, a first cross-talk portion therebetween, and having a first core, at least one inner cladding, and a first outer cladding, the first cross-talk portion having a first etendue; providing a second optical fiber having a third end, a fourth end, a second cross-talk portion therebetween, the second cross-talk portion having a second etendue, the second etendue differing from the first etendue; tapering at least the first cross-talk portion; positioning at least a certain section of the first cross-talk portion of the first optical fiber in contact and along a certain section of the second cross-talk portion of the second optical fiber; and providing heat to both certain sections of the first and second cross-talk portions in a manner forming a fused region; wherein the fused region allows a single-mode signal to remain in the first core between the first end and the second end of the first optical fiber, and for more than half of a multi-mode signal in one of the at least one inner cladding of the first optical fiber to be extracted to the second optical fiber. ### Claim 22 (depends on 21) The method of claim 21, wherein said providing a second optical fiber further comprises tapering at least the second cross-talk portion prior to the steps of positioning and providing. ### Claim 23 (depends on 21) The method of claim 21, wherein said providing a first optical fiber further comprises chemically etching the first outer cladding at least along a certain portion of the first cross-talk portion prior to the steps of positioning and providing. ### Claim 24 (depends on 21) The method of claim 21, wherein said providing a second optical fiber further comprises chemically etching an outer cladding of the second optical fiber at least along a certain portion of the second cross-talk portion prior to the steps of positioning and providing.