CN114460682B - End face coupler - Google Patents
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- CN114460682B CN114460682B CN202011241217.3A CN202011241217A CN114460682B CN 114460682 B CN114460682 B CN 114460682B CN 202011241217 A CN202011241217 A CN 202011241217A CN 114460682 B CN114460682 B CN 114460682B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/12004—Combinations of two or more optical elements
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/241—Light guide terminations
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12133—Functions
- G02B2006/12147—Coupler
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Abstract
The invention provides an end face coupler, which comprises a silicon substrate, an oxygen burying layer and a silica cladding, wherein the silica cladding is internally provided with: the waveguide comprises a strip-shaped central waveguide, a first waveguide section and a second waveguide section, wherein the ends of the first waveguide section and the second waveguide section are connected; the geometric center line of each slab waveguide is arranged in parallel with the geometric center line of the first waveguide section, and a first distance is reserved between the geometric center line of each slab waveguide and the geometric center line of the first waveguide section; the geometric center line of each auxiliary waveguide is arranged in parallel with the geometric center line of the first waveguide section, and a second distance is reserved between the geometric center line of each auxiliary waveguide and the geometric center line of the first waveguide section; the refractive index of the strip-shaped central waveguide is larger than that of each slab waveguide and each auxiliary waveguide, so that a waveguide mode field matched with the mode field of the optical fiber is formed. The end face coupler reduces the mode field matching loss between the optical fiber and the waveguide and improves the coupling efficiency.
Description
Technical Field
The invention relates to the technical field of photoelectric devices, in particular to an end face coupler.
Background
The silicon-based photonic device has the remarkable advantages of compatibility with a Complementary Metal Oxide Semiconductor (CMOS) process, large bandwidth, low delay, low energy consumption, low crosstalk and the like, and can realize on-chip optical interconnection with high performance, low cost, small size and high integration. Silicon and silicon dioxide or air have larger refractive index difference, so that the waveguide taking silicon as a material has strong limiting capacity on an optical field, and high integration can be realized.
The rapid development of optical fiber communication has greatly promoted the development of photonic devices, and in the field of optical communication, a key problem is how to guide light from an optical fiber into a waveguide of an integrated chip. To solve this problem, the connection between the optical fiber and the waveguide is generally realized by using an end-face coupler. However, the end-face coupler has a certain coupling loss, and the coupling loss mainly includes the alignment loss of the mode field of the optical fiber and the waveguide, the mode field matching loss of the optical fiber and the waveguide, the reflection loss of the waveguide end face, the scattering loss of the waveguide end face, and the waveguide mode conversion loss. The alignment loss for the mode field of the fiber and the waveguide depends mainly on the alignment capability of the fiber and the waveguide, and thus can be reduced by aligning the fiber and the waveguide; the scattering loss of the waveguide end face can be reduced by improving the quality of the end face; the reflection loss at the end face of the waveguide can be reduced by dropping a refractive index matching fluid on the end face.
And as the mode field diameter of the optical fiber is about 10.5 μm, and the diameter of the waveguide is generally less than 0.5 μm, the mode field mismatch of the optical fiber and the waveguide exceeds 20dB, so that large mode field matching loss exists between the optical fiber and the waveguide. At present, no ideal end face coupler exists to solve the problem of overhigh mode field matching loss. Therefore, how to smoothly couple light from the optical fiber into the waveguide of the integrated chip and improve the coupling efficiency is an urgent technical problem to be solved.
Disclosure of Invention
Accordingly, the present invention is directed to an end coupler that solves one or more of the problems set forth in the prior art.
According to one aspect of the invention, the invention discloses an end-face coupler, which comprises a silicon substrate, a buried oxide layer arranged on the silicon substrate and a silica cladding layer positioned on one side of the buried oxide layer far away from the silicon substrate, wherein the silica cladding layer is internally provided with:
a strip-shaped central waveguide extending from one end of the end-face coupler to the other end, the strip-shaped central waveguide including a first waveguide segment and a second waveguide segment, the first waveguide segment and the second waveguide segment being connected at their ends so as to enable optical coupling between the first waveguide segment and the second waveguide segment, one end of the first waveguide segment remote from the second waveguide segment being an optical fiber access end, the cross-sectional area of the second waveguide segment gradually increasing with increasing distance from the optical fiber access end, the cross-sectional shape of the strip-shaped central waveguide being rectangular;
two slab waveguides symmetrically arranged on opposite first and second sides of the first waveguide segment and extending from one end of the end-face coupler towards the other end, a geometric centerline of each of the slab waveguides being arranged parallel to a geometric centerline of the first waveguide segment, a first distance being provided between the geometric centerline of each of the slab waveguides and the geometric centerline of the first waveguide segment;
two auxiliary waveguides symmetrically arranged on opposite third and fourth sides of the first waveguide and extending from one end of the end-face coupler towards the other end, a geometric centerline of each of the auxiliary waveguides being arranged parallel to a geometric centerline of the first waveguide segment, a second distance being provided between the geometric centerline of each of the auxiliary waveguides and the geometric centerline of the first waveguide segment;
the refractive index of the strip-shaped central waveguide is larger than that of each slab waveguide and each auxiliary waveguide, so that a waveguide mode field matched with the optical fiber mode field is formed at the access end of the optical fiber.
In some embodiments of the invention, each of the slab waveguides is parallel to the silicon substrate.
In some embodiments of the present invention, a distance between geometric centerlines of two of the auxiliary waveguides is not less than a width of each of the slab waveguides in a lateral direction perpendicular to an extending direction thereof.
In some embodiments of the present invention, a cross-sectional shape of each of the auxiliary waveguides is rectangular, and a cross-sectional shape of the slab waveguide is rectangular.
In some embodiments of the present invention, a width of each of the slab waveguides in a lateral direction perpendicular to an extending direction thereof is in a range of 15 μm to 30 μm, and a thickness of each of the slab waveguides in a longitudinal direction perpendicular to the extending direction thereof is in a range of 20nm to 30nm.
In some embodiments of the invention, the slab waveguide has a width dimension in a transverse direction perpendicular to its direction of extension that is uniform or that gradually decreases in a direction away from the fiber access end; the auxiliary waveguide has a width dimension in a transverse direction perpendicular to its direction of extension that is uniform or that gradually decreases in the direction of the fiber access end.
In some embodiments of the present invention, the cross-sectional shape of the strip-shaped central waveguide is square, the second waveguide segment is a frustum-shaped waveguide, and the upper bottom surface of the frustum-shaped waveguide completely coincides with the end surface of the first waveguide segment.
In some embodiments of the present invention, a length of the first waveguide segment is equal to a length of each of the slab waveguides and/or each of the auxiliary waveguides; the ratio of the length of the second waveguide segment to the length of the first waveguide segment ranges from 1 to 2.
In some embodiments of the present invention, the difference between the refractive index of the slab waveguide and the refractive index of the slab waveguide is greater than or equal to 50% of the refractive index of the slab waveguide.
In some embodiments of the present invention, the material of the central waveguide is silicon, and the material of each of the slab waveguides and each of the auxiliary waveguides is silicon nitride.
In the end-face coupler in the embodiment of the invention, two slab waveguides and two auxiliary waveguides are symmetrically arranged around a strip-shaped central waveguide at an optical fiber access end of the coupler, and the refractive index of the strip-shaped central waveguide is higher than that of each slab waveguide and each auxiliary waveguide, so that a waveguide mode field matched with an optical fiber mode field is formed at the optical fiber access end; therefore, in the coupling process of the optical fiber and the waveguide, the mode field matching loss of the optical fiber and the waveguide is reduced, and the coupling efficiency is improved; and the cross section area of the second waveguide section of the strip-shaped central waveguide is gradually increased along with the increase of the distance away from the optical fiber access end, so that light can be transmitted stably, and leakage is avoided.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It will be appreciated by those skilled in the art that the objects and advantages that can be achieved with the present invention are not limited to what has been particularly described hereinabove, and that the above and other objects that can be achieved with the present invention will be more clearly understood from the following detailed description.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. For purposes of illustrating and describing some portions of the present invention, corresponding parts of the drawings may be exaggerated, i.e., may be larger, relative to other components in an exemplary apparatus actually manufactured according to the present invention. In the drawings:
fig. 1 is a schematic structural diagram of an end-face coupler according to an embodiment of the present invention.
Fig. 2 is a front view of an end-face coupler according to an embodiment of the present invention.
Fig. 3 is a side view of an end-face coupler according to an embodiment of the present invention.
Fig. 4 is a top view of an end-face coupler according to an embodiment of the present invention.
Fig. 5 is a simulation diagram of optical field distribution at the fiber access end face of the end-face coupler according to an embodiment of the invention.
Fig. 6 is a simulation diagram of optical field distribution of the chip access end surface of the end surface coupler according to an embodiment of the present invention.
Fig. 7 is a simulation diagram of optical field distribution along the optical transmission direction of the end-face coupler according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings. The exemplary embodiments and descriptions of the present invention are provided to explain the present invention, but not to limit the present invention.
It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme according to the present invention are shown in the drawings, and other details not closely related to the present invention are omitted.
It should be emphasized that the term "comprises/comprising/comprises/having" when used herein, is taken to specify the presence of stated features, elements, steps or components, but does not preclude the presence or addition of one or more other features, elements, steps or components.
It should be noted that the terms of orientation and orientation used in the present specification are relative to the position and orientation shown in the drawings; the term "coupled" as used herein may mean not only a direct connection, but also an indirect connection in which an intermediate is present, unless specifically stated otherwise. A direct connection is one in which two elements are connected without the aid of intermediate elements, and an indirect connection is one in which two elements are connected with the aid of other elements.
The invention discloses an end face coupler, aiming at solving the problem of overhigh mode field matching loss in the coupling process of an optical fiber and a waveguide. The whole structure of the end face coupler is based on SOI technology, and can be divided into two sections along the optical transmission direction, wherein the first section is used for capturing and focusing an optical field, and the second section is used for compressing and transmitting the captured optical field into a waveguide of a chip.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, like reference characters designate the same or similar parts throughout the several views.
Fig. 1 is a schematic structural diagram of an end-face coupler according to an embodiment of the present invention, and as shown in fig. 1, the end-face coupler includes a silicon substrate, a buried oxide layer 02, and a silica cladding layer 03. The buried oxide layer 02 is disposed on a silicon substrate and the silica cladding 03 is located on the side of the buried oxide layer 02 remote from the silicon substrate.
A strip-shaped central waveguide extending from one end of the end-face coupler towards the other end is provided within the silica cladding 03. The strip-shaped central waveguide may be specifically located at the center of the silica cladding 03, i.e. the geometric center line of the strip-shaped central waveguide may coincide with the geometric center line of the silica cladding 03. The cross-sectional shape of the strip-shaped central waveguide may be rectangular, and the cross-section refers to a plane perpendicular to the extending direction of the strip-shaped central waveguide. The strip-shaped central waveguide comprises a first waveguide section 331 and a second waveguide section 332, the first waveguide section 331 and the second waveguide section 332 being terminated such that optical coupling is possible between the first waveguide section 331 and the second waveguide section 332. It should be understood that the end-to-end connection of the first waveguide segment 331 and the second waveguide segment 332 includes not only the end-to-end connection of the ends of the first waveguide segment 331 and the second waveguide segment 332, but also the overlapping of a portion of the ends of the first waveguide segment 331 and the second waveguide segment 332 in the longitudinal direction; the longitudinal direction refers to the light transmission direction. Whichever docking method is used, it is sufficient that optical coupling between the first waveguide section 331 and the second waveguide section 332 is ensured. In addition, an end of the first waveguide segment 331 away from the second waveguide segment 332 is an optical fiber access end, specifically, a left end in fig. 1; the second waveguide segment 332 has a gradually increasing cross-sectional area with increasing distance away from the fiber access end, i.e., the second waveguide segment 332 has a gradually increasing cross-sectional area from left to right. The right end of the second waveguide segment 332 is used as a chip waveguide access end, and the cross-sectional area of the second waveguide segment 332 is gradually increased in the optical transmission direction, so that the optical mode field can be stably transmitted to reduce mode field leakage in the coupling process.
In addition to the strip-shaped central waveguide, two slab waveguides 31 and two auxiliary waveguides 32 are provided in the silica cladding 03. Two slab waveguides 31 are symmetrically disposed on opposite first and second sides of the first waveguide section 331, and each slab waveguide 31 extends from one end of the end-face coupler toward the other end, similar to a slab center waveguide. In addition, the geometric center line of each slab waveguide 31 is disposed parallel to the geometric center line of the first waveguide segment 331, and the geometric center line of each slab waveguide 31 is a first distance from the geometric center line of the first waveguide segment 331. Similarly, two auxiliary waveguides 32 are symmetrically disposed on opposite third and fourth sides of the first waveguide section 331, and each auxiliary waveguide 32 also extends from one end of the end-face coupler toward the other end; the geometric centerlines of the auxiliary waveguides 32 are each disposed parallel to the geometric centerline of the first waveguide segment 331, and the geometric centerline of each auxiliary waveguide 32 is a second distance from the geometric centerline of the first waveguide segment 331. It should be understood that the geometric centerline refers to the centerline of a plane that can divide each component into two equal parts; for example, for a rectangular slab waveguide 31, its geometric centerline can also be understood as a centerline; for a strip waveguide with a circular cross section, the geometric center line can be understood as the central axis of the cylinder; and for some irregular solid structures, the geometric centerline refers to the centerline of a plane bisecting the irregular solid into two parts.
Further, the refractive index of the strip-shaped central waveguide is larger than the refractive index of each slab waveguide 31 and each auxiliary waveguide 32, so as to form a waveguide mode field matched with the optical fiber mode field at the optical fiber access end. With this end-face coupler, the provision of slab waveguides 31 on opposite first and second sides of the first waveguide section 331 is more advantageous for optical field trapping, thereby reducing mode field leakage. And the first waveguide section 331 and the two slab waveguides 31 and the two auxiliary waveguides 32 located around the first waveguide section 331 can be regarded as first sections of end-face couplers which capture as much optical field as possible during the transmission of light and converge the optical field towards the slab-shaped central waveguide; the second waveguide segment 332 of the strip-shaped central waveguide, which is connected to the first waveguide segment 331, serves as the second segment of the end-face coupler for adiabatically transferring the optical field captured by the first segment into the photonic integrated device.
As for the refractive index of each waveguide, the difference in refractive index between the stripe-shaped center waveguide and each slab waveguide 31 and each auxiliary waveguide 32 may be set to be greater than or equal to 50% of the refractive index of the stripe-shaped center waveguide. For example, the material of the strip-shaped central waveguide may be silicon, and the material of each slab waveguide 31 and each auxiliary waveguide 32 may be silicon nitride; the refractive index of silicon is approximately twice the refractive index of silicon nitride. In addition, the material of the strip-shaped central waveguide may also be of another type than a silicon material, for example by indium phosphide substitution; the silicon nitride can be replaced by nitrogen oxide; as long as the relative refractive index requirements between the strip-shaped center waveguide and each of the slab waveguides 31 and each of the auxiliary waveguides 32 can be satisfied.
Further, the slab waveguide 31 is parallel to the silicon substrate. When the first waveguide segment 331 is specifically a rectangular waveguide in a stripe shape, the first side and the second side respectively refer to the upper side and the lower side of the central waveguide in the stripe shape, and the third side and the fourth side respectively refer to the left side and the right side of the center in the stripe shape, for the up-down and left-right orientation relationship, relative to fig. 3, that is, the upper side of the first waveguide segment 331 refers to the side of the first waveguide segment 331 away from the silicon substrate.
Alternatively, the distance between the geometric centerlines of the two auxiliary waveguides 32 is not smaller than the width of each slab waveguide 31 in the lateral direction perpendicular to the extending direction thereof. The width of the slab waveguide 31 in the lateral direction perpendicular to the extending direction thereof refers to the dimension of the slab waveguide 31 in the horizontal direction shown in fig. 3; at this time, that is, the two auxiliary waveguides 32 are respectively located at the left and right sides of the slab waveguide 31, and the distance between the geometric center lines of the auxiliary waveguides 32 is greater than the size of the slab waveguide 31 in the horizontal direction. In addition, the distance between the geometric center lines of the auxiliary waveguides 32 may be equal to the dimension of the slab waveguide 31 in the horizontal direction, and the geometric center lines of the auxiliary waveguides 32 and the left and right side surfaces of the slab waveguide 31 are located in the same vertical plane. In addition, when the width dimension of the slab waveguide 31 in the transverse direction is large enough, the distance between the geometric center lines of the auxiliary waveguides 32 may be smaller than the width of the slab waveguide 31 in the transverse direction, as long as it is ensured that the mode fields formed by the two slab waveguides 31 and the two auxiliary waveguides 32 match the mode field of the optical fiber.
Further, the auxiliary waveguide 32 is specifically a rectangular waveguide whose cross section perpendicular to the extending direction thereof is rectangular in shape. Similarly, the cross-sectional shape of the slab waveguide 31 may also be rectangular. The cross section means a plane perpendicular to the extending direction of the auxiliary waveguide 32 or the slab waveguide 31. In addition, the cross-sectional shapes of the auxiliary waveguide 32 and the slab waveguide 31 may also be other shapes, such as an isosceles trapezoid.
The slab waveguide 31 having a rectangular cross-sectional shape includes at least two cases where the slab waveguide 31 has a uniform width dimension in a transverse direction perpendicular to an extending direction thereof or gradually decreases in a direction away from the optical fiber access end. The uniform width dimension is understood to mean that the dimension of the slab waveguide 31 in the y-direction shown in fig. 1 is equal in the direction away from the fiber access end, i.e., the whole slab waveguide 31 has a rectangular parallelepiped structure. The width dimension gradually decreasing in a direction away from the fiber access end may be a projection of the slab waveguide 31 in the Z direction in a wedge shape or a trapezoid shape. It should be understood that, for the slab waveguide 31 of the above-described structural shape, the thicknesses thereof are equal, the thickness being the dimension of the slab waveguide 31 in the Z direction. Further, in the case where the slab waveguide 31 is uniform in width dimension in the lateral direction perpendicular to the extending direction thereof, the width thereof in the lateral direction perpendicular to the extending direction thereof ranges from 15 μm to 30 μm, and the thickness thereof in the longitudinal direction perpendicular to the extending direction thereof ranges from 20nm to 30nm; in addition, when the width dimension of the slab waveguide 31 in the transverse direction perpendicular to the extending direction thereof is gradually decreased in the direction away from the optical fiber access end, the thickness thereof in the longitudinal direction perpendicular to the extending direction thereof ranges from 20nm to 30nm, and the width thereof in the end face near the optical fiber access end ranges from 15 μm to 30 μm; the width in the lateral direction perpendicular to the extending direction thereof refers to the Y-axis direction shown in fig. 1, and the thickness in the longitudinal direction perpendicular to the extending direction thereof refers to the Z-axis direction shown in fig. 1.
Similarly, the auxiliary waveguide 32 specifically includes the following two cases: the auxiliary waveguide 32 has a width dimension in a transverse direction perpendicular to its direction of extension that is uniform or gradually decreases in a direction away from the fiber access end. The width in the lateral direction perpendicular to the extending direction thereof refers to the dimension in the Y direction shown in fig. 1. When the width dimension of the auxiliary waveguide 32 is uniform, the entire auxiliary waveguide 32 can be regarded as a rectangular parallelepiped structure; and when the width of the auxiliary waveguide 32 is gradually reduced in a direction away from the optical fiber access end, the auxiliary waveguide 32 has a wedge shape or a trapezoidal shape projected in the Z direction shown in fig. 1.
In an embodiment of the present invention, the cross section of the strip-shaped central waveguide is square, and the cross section refers to a plane of the strip-shaped central waveguide perpendicular to the extending direction (light transmission direction) of the strip-shaped central waveguide. The second waveguide section 332 of the strip-shaped central waveguide may in particular be a truncated pyramid waveguide. The upper bottom surface of the truncated pyramid waveguide completely coincides with the end surface of the first waveguide section 331 to prevent light leakage during coupling. Illustratively, the frustum waveguide has a regular frustum structure, in which the side length of the upper bottom surface of the frustum waveguide is equal to the side length of the end surface of the first waveguide segment 331; the reason why the side length of the upper bottom surface of the truncated pyramid waveguide is equal to the side length of the end surface of the first waveguide segment 331 is to ensure that the end surface of the first waveguide segment 331 and the end surface of the second waveguide segment 332 are completely overlapped and butted, and in addition, the side length of the upper bottom surface of the truncated pyramid waveguide can be slightly larger than the side length of the end surface of the first waveguide segment 331 under the condition of ensuring the optical coupling efficiency. The frustum waveguide can be other common frustum except for the frustum pyramid besides the frustum pyramid; if the upper and lower bottom surfaces of the waveguide are rectangular, the cross-sectional shape of the first waveguide section 331 should be rectangular, which is identical to the upper bottom surface of the waveguide.
In an embodiment of the present invention, as shown in fig. 2 and 4, the length of the first waveguide section 331 is equal to the length of each slab waveguide 31 and/or each auxiliary waveguide 32. The ratio of the length of the second waveguide segment 332 to the length of the first waveguide segment 331 ranges from 1 to 2; a specific alternative is 1, i.e., the length of the second waveguide segment 332 is equal to the length of the first waveguide segment 331. The length refers to the dimension in the extending direction of the first waveguide section 331, each slab waveguide 31, and each auxiliary waveguide 32. It should be understood that the lengths of the slab waveguides 31 and/or the auxiliary waveguides 32 may be greater than the length of the first waveguide section 331, but in order to match the mode field at the output end of the end-coupler to the device waveguide mode field, it is ensured that the lengths of the slab waveguides 31 and the auxiliary waveguides 32 are less than the sum of the lengths of the first waveguide section 331 and the second waveguide section 332.
To describe the structure of the end-face coupler in more detail, the dimensions of the various portions of the end-face coupler will be described in more detail below with reference to fig. 1-4 by way of a specific embodiment.
The end-face coupler is sequentially provided with an SOI substrate 01, a BOX buried oxide layer 02 and a silica cladding 03 from bottom to top, wherein a strip-shaped central waveguide, two slab waveguides 31 respectively positioned at the upper side and the lower side of the strip-shaped central waveguide and auxiliary waveguides 32 respectively positioned at the other two sides of the strip-shaped central waveguide are arranged in the silica cladding 03. In fig. 1, the X direction is the longitudinal direction, the Y direction is the width direction, and the Z direction is the thickness direction. The thickness of the SOI substrate 01 is greater than 7 μm and the width is 30 μm; the thickness of the BOX buried oxide layer 02 is 3 μm, and the width is 30 μm; the silica cladding 03 has a total thickness of 30 μm and a width of 30 μm. The first distance between the two slab waveguides 31 and the slab center waveguide may range from 5 μm to 15 μm, and the second distance between the two auxiliary waveguides 32 and the slab center waveguide may also range from 5 μm to 15 μm; the two slab waveguides 31 located at the upper and lower sides of the strip-shaped central waveguide have a thickness of 20nm and a width of 20 μm; the two auxiliary waveguides 32 have a thickness of 450nm and a width of 550nm; the first waveguide segment 331 has a thickness of 120nm and a width of 120nm, and the second waveguide segment 332 has a regular quadrangular frustum structure with an upper bottom surface of a square with a side length of 120nm and a lower bottom surface of a square with a side length of 450 nm. The length of the first waveguide section 331 is 100 μm; the lengths of each slab waveguide 31 and each auxiliary waveguide 32 are equal to the length of the first waveguide section 331, and are also 100 μm; the length of the second waveguide segment 332 is 260 μm.
The specific parameters described above are only one preferred embodiment of the present disclosure, wherein the width of the SOI substrate 01, the BOX buried oxide layer 02 and the silica cladding 03 can be set in the range of 20 μm to 40 μm, and the length of the entire coupler (the first waveguide segment 331+ the second waveguide segment 332) can be in the range of 260 μm to 1000 μm. It should be noted that the greater the overall length of the coupler, the greater its coupling efficiency but the less integrated; conversely, if the overall length of the coupler is smaller, the coupling efficiency is correspondingly reduced and the integration level is improved; the dimensions of the various components of the coupler can be adjusted specifically to the application requirements.
Fig. 5, 6 and 7 are schematic diagrams of simulations during the coupling test. In the experimental process, the optical fiber accessed to the optical fiber access end of the end face coupler is an SMF-28 standard optical fiber, the diameter of a mode field is about 10.5 mu m, and input light waves are single-mode light waves. FIG. 5 is a graph of the optical field distribution near one end of the fiber for an end-face coupler; FIG. 6 is a graph of the optical field profile of the end-face coupler near one end of the chip; fig. 7 is a diagram of the optical field distribution of light in the direction of light transmission within the end-face coupler. As can be seen from fig. 5 to 7, the end-face coupler can achieve better effects of converging and capturing an optical field, and the captured optical field can be efficiently coupled into the second waveguide segment 332, and the coupling efficiency reaches about 91% after being tested.
Through the embodiment, the end face coupler disclosed by the invention has the advantages that the two slab waveguides and the two auxiliary waveguides are symmetrically arranged around the strip-shaped central waveguide at the optical fiber access end of the coupler, the slab waveguides can capture an optical field better, and the refractive index of the strip-shaped central waveguide is higher than that of each slab waveguide and each auxiliary waveguide, so that a waveguide mode field matched with an optical fiber mode field is formed at the optical fiber access end; therefore, in the coupling process of the optical fiber and the waveguide, the mode field matching loss of the optical fiber and the waveguide is reduced, and the coupling efficiency is improved; and the cross section area of the second waveguide section of the strip-shaped central waveguide gradually increases along with the increase of the distance away from the optical fiber access end, so that light can be stably transmitted, leakage is avoided, and the coupling efficiency is further improved.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments in the present invention.
The above-mentioned embodiments illustrate and describe the basic principles and main features of the present invention, but the present invention is not limited to the above-mentioned embodiments, and those skilled in the art should make modifications, equivalent changes and modifications without creative efforts to the present invention within the protection scope of the technical solution of the present invention.
Claims (8)
1. An end face coupler comprising a silicon substrate, a buried oxide layer disposed on the silicon substrate, and a silica cladding layer disposed on a side of the buried oxide layer remote from the silicon substrate, wherein:
a strip-shaped central waveguide extending from one end of the end-face coupler to the other end, the strip-shaped central waveguide including a first waveguide segment and a second waveguide segment, the first waveguide segment and the second waveguide segment being connected at their ends so as to enable optical coupling between the first waveguide segment and the second waveguide segment, one end of the first waveguide segment remote from the second waveguide segment being an optical fiber access end, the cross-sectional area of the second waveguide segment gradually increasing with increasing distance from the optical fiber access end, the cross-sectional shape of the strip-shaped central waveguide being rectangular, the first waveguide segment being a strip-shaped rectangular waveguide;
two slab waveguides symmetrically arranged on opposite first and second sides of the first waveguide segment and extending from one end of the end-face coupler towards the other end, a geometric centerline of each of the slab waveguides being arranged parallel to a geometric centerline of the first waveguide segment, a first distance being provided between the geometric centerline of each of the slab waveguides and the geometric centerline of the first waveguide segment;
two auxiliary waveguides symmetrically arranged on opposite third and fourth sides of the first waveguide and extending from one end of the end-face coupler towards the other end, a geometric centerline of each of the auxiliary waveguides being arranged parallel to a geometric centerline of the first waveguide segment, a second distance being provided between the geometric centerline of each of the auxiliary waveguides and the geometric centerline of the first waveguide segment;
the refractive index of the strip-shaped central waveguide is greater than that of each slab waveguide and each auxiliary waveguide, so that a waveguide mode field matched with the optical fiber mode field is formed at the access end of the optical fiber;
the distance between the geometric center lines of the two auxiliary waveguides is not less than the width of each flat waveguide in the transverse direction perpendicular to the extending direction of the flat waveguide;
the width range of each flat waveguide in the transverse direction perpendicular to the extending direction of the flat waveguide is 15-30 micrometers, and the thickness range of each flat waveguide in the longitudinal direction perpendicular to the extending direction of the flat waveguide is 20-30nm;
the length of the first waveguide segment is equal to the length of each of the slab waveguides and/or each of the auxiliary waveguides.
2. The end-face coupler of claim 1, wherein each of the slab waveguides is parallel to the silicon substrate.
3. The end-face coupler of claim 1, wherein each of said auxiliary waveguides has a rectangular cross-sectional shape and said slab waveguide has a rectangular cross-sectional shape.
4. The end-face coupler of claim 3, wherein the slab waveguide has a width dimension in a transverse direction perpendicular to its direction of extension that is uniform or that gradually decreases in a direction away from the fiber access end; the auxiliary waveguide has a width dimension in a transverse direction perpendicular to its direction of extension that is uniform or that gradually decreases in a direction away from the fiber access end.
5. The end-face coupler of claim 1, wherein the cross-sectional shape of the strip-shaped central waveguide is square, the second waveguide segment is a frustum-shaped waveguide, and the upper bottom surface of the frustum-shaped waveguide completely coincides with the end surface of the first waveguide segment.
6. The end-face coupler of claim 1, wherein the ratio of the length of the second waveguide segment to the length of the first waveguide segment is in the range of 1~2.
7. The end-face coupler according to any of claims 1 to 6, wherein the difference between the refractive index of the slab waveguide and the refractive index of the slab waveguide is 50% or more of the refractive index of the slab waveguide.
8. The end-face coupler of claim 7, wherein the material of the slab center waveguide is silicon and the material of each slab waveguide and each of the subsidiary waveguides is silicon nitride.
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| US11747559B2 (en) * | 2021-08-25 | 2023-09-05 | Globalfoundries U.S. Inc. | Photonic integrated circuit structure with supplemental waveguide-enhanced optical coupling between primary waveguides |
| US11747560B2 (en) | 2021-08-25 | 2023-09-05 | Globalfoundries U.S. Inc. | Photonic integrated circuit structure with a tapered end portion of one waveguide adjacent to a v-shaped end portion of a different waveguide |
| US11733458B2 (en) * | 2021-10-04 | 2023-08-22 | Globalfoundries U.S. Inc. | Edge couplers with confining features |
| CN114966966B (en) * | 2022-05-24 | 2023-05-16 | 北京邮电大学 | Nonlinear tapered coupler based on auxiliary waveguide |
| CN114924348B (en) * | 2022-06-06 | 2023-06-09 | 吉林大学 | Three-dimensional edge coupler based on silicon dioxide optical waveguide |
| CN116661060B (en) * | 2023-07-28 | 2023-10-31 | 中天通信技术有限公司 | End face coupler and optical module |
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| CN110658586A (en) * | 2019-11-19 | 2020-01-07 | 华进半导体封装先导技术研发中心有限公司 | End face coupler and preparation method thereof |
| CN111552029A (en) * | 2019-02-08 | 2020-08-18 | 菲尼萨公司 | Optical waveguide routing structure and method thereof |
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