Broadband surface coupling

Abstract

A wideband photonic bump (WBB) comprising: a positive taper of a polymer waveguide, a curved mirror formed on a surface of the WBB, and a tilted flat mirror; the positive taper of the polymer waveguide is configured to further expand a light beam from an anti-taper to match a fiber mode of an optical fiber; the curved mirror is configured to reflect the light beam from the optical fiber; the tilted flat mirror is configured to direct the reflected light beam to an external optical fiber, wherein the WBB is coupled on a surface of a photonic integrated circuit (PIC).

Description

[0001] Cross Reference to Related Applications

[0002] This application is a divisional application of application number 201980025948.3, filed on April 17, 2019, entitled “Wideband Surface Coupling”, the parent application is a national stage entry of a PCT application, which international application was filed on April 17, 2019, application number “PCT / US2019 / 027871”, claiming priority to application number No. 62 / 659,376, filed on April 18, 2018, to the United States Patent Office. TECHNICAL FIELD

[0003] The present disclosure relates generally to optical waveguides, and more particularly to waveguide surface coupling. BACKGROUND

[0004] Communication systems and data centers need to handle large amounts of data at ever increasing speeds and at ever decreasing costs. To meet these demands, optical fibers and optical integrated circuits (ICs), such as photonic integrated circuits (PICs) or integrated optical circuits (IOC), are used in tandem with high-speed electronic ICs. A PIC is a device that integrates multiple photonic functions, similar to an electronic IC or a radio frequency (RF) IC. PICs are typically fabricated using silicon, indium phosphide, or silicon dioxide (SiO2), which allows various optical active and passive functions to be integrated on the same circuit.

[0005] Coupling of a PIC to an optical fiber or a laser module is not as advanced as the integration or coupling of electronic ICs. Specifically, the challenges faced by optical connections are different and much more complex compared to connecting electronic ICs to, for example, electrical pads. Some of the difficulties are due to inherent signal loss due to wavelength dependence, polarization dependence, and tight assembly tolerances of optical packaging.

[0006] A major challenge in the design and fabrication of a PIC is to maintain efficient coupling between a compact surface waveguide and an external optical device, such as a fiber or a laser element. In particular, wideband surface coupling remains a challenge for sub-micron sized waveguides made of high refractive index contrast materials, such as semiconductors.

[0007] Current wideband optical coupling is performed at the end of the PIC, thus not allowing surface coupling. Conventional optical coupling is achieved using a low refractive index waveguide “wrap” around the outputted signal on the PIC to expand the optical beam. The top view and side view of such coupling are shown in Figure 4A and Figure 4B As shown, the waveguide 410 extends to the end of the PIC 400. The waveguide 410 expands the less than 1 micron wavelength from the output 420 to about 3 to 5 microns. SUMMARY

[0008] The following is a summary of several example embodiments of the present disclosure. This summary is provided to facilitate a brief understanding of such embodiments and is not an exhaustive overview of the scope of the present disclosure. This summary is not an exhaustive overview of all contemplated embodiments, and is intended, not as a

[0009] Certain embodiments disclosed herein include a wideband photonic bump (WBB) comprising a positive taper of a polymer waveguide configured to further expand a light beam from an inverse taper to match a fiber mode of an optical fiber, a curved mirror formed at a surface of the WBB configured to reflect the light beam from the optical fiber, and a tilted flat mirror configured to direct the reflected light beam to an external optical fiber, wherein the WBB is coupled at a surface of a photonic integrated circuit (PIC). BRIEF DESCRIPTION OF DRAWINGS

[0010] The subject matter disclosed herein is to be particularly pointed out and distinctly claimed in the concluding portion of the specification. The foregoing and the

[0011] Figure 1 FIG. 1 is a schematic diagram illustrating a side view showing placement of a wideband photonic bump (WBB) on a PIC according to an embodiment.

[0012] Figure 2A FIG. 2 is a schematic diagram illustrating a side view and a top view showing a conventional WDM coupling according to an embodiment. Figure 2B

[0013] Figure 3 FIG. 3 is a schematic diagram illustrating a side view showing a WBB connection with an optical fiber according to an embodiment.

[0014] Figure 4A FIG. 4 is a schematic diagram illustrating a side view and a top view showing a conventional WDM coupling according to an embodiment. Figure 4B DETAILED DESCRIPTION

[0015] ​​It is important to note that the embodiments disclosed herein are merely examples of the many uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed embodiments. Moreover, some statements can apply to some inventive features but not to others. In general, unless otherwise indicated herein, singular elements can be in the plural and vice versa with no loss of generality. In the drawings, like reference numerals indicate like parts through several views.

[0016] The various embodiments disclosed provide an optical module that allows for broadband surface coupling between a photonic integrated circuit (PIC) (e.g., a photonic chip) and other optical elements (e.g., optical fibers and lasers) while ensuring low signal loss and thermal stability. The optical module is referred to hereinafter as a WBB. Furthermore, the disclosed WBB achieves high signal efficiency through easy alignment between the PIC and the optical elements (optical fibers and lasers).

[0017] To this end, the WBB performs a mode conversion function to allow connection to single mode optical fibers and beam deflection. In one embodiment, the WBB further provides an optical interface to a photonic plug. The WBB disclosed herein can be fabricated through photolithography processes such as gray-tone lithography, nanoimprint lithography, etc.

[0018] Figure 1 A schematic diagram showing a side view of a WBB 100 arranged on a photonic integrated circuit (PIC) 110 according to an embodiment. The optical arrangement of the WBB 100 on the surface of the PIC 110 provides surface coupling. Specifically, the WBB 100 is optically connected to an anti-taper 120 (hereinafter referred to as "anti-taper" 120) of a PIC waveguide and deflects a light beam from the anti-taper 120 to eventually reach an optical fiber (not shown in Figure 1 while converting the light beam from a small waveguide mode to a large fiber mode.

[0019] In one embodiment, the anti-taper 120 is adiabatically shrunk to allow the light beam to expand from a width of approximately less than 1 micron at the end point of the waveguide to approximately 3 or 4 microns.

[0020] The anti-taper 120 is part of the PIC 110 and thus is formed during the manufacturing process of the PIC 110. At the other end, the fiber mode is typically 2-3 times larger (e.g., 10 microns) and requires an optical mode matching element.

[0021] As Figure 1 As schematically shown in

[0022] According to an embodiment, WBB100 includes a positive cone of a polymer waveguide (hereinafter referred to as "positive cone 101"), a curved (collimating) mirror 102, and a tilted plane mirror 103. In some embodiments, the positive cone 101 is constructed and positioned after the fabrication of PIC110. The positive cone 101 is used to further extend the beam from the anti-cone 120 to match the fiber mode. The beam is deflected from the positive cone 101 to the plane mirror 103.

[0023] The tilted plane mirror 103 is used to guide the extended beam of light to an external optical fiber via an optical connection through a photonic plug. Figure 1 (Not shown in the image). The optical path of the beam deflected from plane mirror 103 is discussed below. The optical path allows the fiber to be placed parallel to PIC110.

[0024] In one embodiment, the tilted plane mirror 103 is tilted at a predetermined angle. This angle is determined based on the optical path between the optical fiber and the curved mirror 102, for example, as shown below. Figure 3 The optical characteristics are shown. In an embodiment, the tilted plane mirror 103 is formed using, for example, a nanoimprint lithography process that combines grayscale lithography to prepare a master for nanoimprinting.

[0025] A curved mirror 102 is formed on the surface of the WBB100 and is used to reflect the light beam from the photonic plug (neither of which is on the surface of the WBB100). Figure 1 (As shown in the figure). In an embodiment, the curved mirror 102 can be formed on the substrate using grayscale lithography, nanoimprint lithography, or the like. In an embodiment, both the tilting mirror 103 and the curved mirror 102 are coated with a dielectric layer that serves as a mirror (e.g., for a specific wavelength and angle) to improve the reflectivity of the light beam.

[0026] The positive cone 101, through the inverted cone 120, performs mode matching on the beam extracted from the substrate of the PIC 110 to match the fiber mode. As described above, the positive cone 101 can perform mode matching (e.g., from 1 micrometer to 10 micrometers). According to an embodiment, the shape and material type of the positive cone 101 are selected to allow this optical mode matching. In another embodiment, the cone 101 is made of a material having a refractive index lower than that of the inverted cone 120. In an embodiment, the shape of the cone 101 is as follows: Figure 2A and 2B As shown.

[0027] Figure 2AA side view of the arrangement of the inverse taper 120 and the positive taper 101 according to an embodiment is shown. The inverse taper 120 is fabricated on the PIC, and is used to extract the optical beam (optical signal) from the substrate of the PIC 110 to the waveguide channel 210. The channel 210 is not tapered, and is also made of polymer, and can be used to expand the extracted optical beam, for example, from less than 1 micron to 3-5 microns.

[0028] The positive taper 101 is designed to expand the optical beam to the fiber mode, i.e., adiabatically transform the extracted optical beam to satisfy the optical mode of the fiber. In an example implementation, the height (hi) at the end of the positive taper 101 is about 10-13 microns, and the height (h2) at the beginning of the waveguide channel is about 1-3 microns.

[0029] A top view of the arrangement of the inverse taper 120 and the positive taper 101 is shown in Figure 2B .

[0030] It should be noted that the WBB 100 allows surface optical coupling of the PIC and the fiber. Since the coupling is not performed at the edges of the mold of the PIC, the disclosed WBB 100 allows wafer level testing.

[0031] Figure 3 A side view of the WBB 100 connected with the fiber 320 according to an embodiment is shown. Figure 3 The shown assembly includes the connection of the WBB 100 with the photonic plug 300.

[0032] The photonic plug 300 provides optical connection between the PIC 310 and the fiber 320. In an embodiment, the photonic plug 300 includes a spacer 301 connected between the PIC 310 and the fiber 320, a curved mirror 302, and a tilted flat mirror 303. The photonic plug 300 can also include a fiber trench (not shown) in the spacer 301. Figure 3 .

[0033] The fiber 320 and the photonic plug 300 are stacked below a substrate layer 370. In an embodiment, the curved mirror 302 and the tilted flat mirror 303 are both fabricated in the substrate 370. The substrate 370 can be made of the same or different type of material as the substrate of the PIC 310. In an example embodiment, the substrate layer 370 can be made of silicon dioxide (Si02), plastic, etc. In another embodiment, the curved mirror 302 and the tilted flat mirror 303 are both fabricated in the spacer 301 and bonded, instead of in the substrate 370.

[0034] According to one embodiment, the spacer 301 can be made of any transparent and non-conductive material, such as glass, polydimethylsiloxane, air, or any other material with a matching refractive index. The structure of the photonic plug 300 is disclosed in more detail in U.S. Patent No. 9,804,334, assigned to a common assignee, which is incorporated herein by reference.

[0035] According to the disclosed embodiment, WBB100 is disposed on PIC310. When spacer 301 is made of solid material, a cavity is formed in spacer 301 to allow photonic plug 300 to be placed in the cavity.

[0036] exist Figure 3 In the arrangement shown, beam 380-1 is deflected from WBB100. The source of beam 380-1 is a conical shape ( Figure 1 (101 in the middle). The curved mirror 302 reflects the beam 380-1 into a parallel beam 380-2. The parallel beam 380-2 reaches the curved mirror of WBB100 ( Figure 1 In section 101), the curved mirror reflects beam 380-3 back to the tilted plane mirror 303. Plane mirror 303 guides beam 380-3 to optical fiber 320. It should be noted that all beams 380 pass through spacer 301. It should also be noted that light can propagate in the opposite direction.

[0037] Since the tilted plane mirror 303 is used to guide the beam from the bump 100 to the optical fiber 320, it allows the optical fiber 320 to be placed parallel to the PIC 310.

[0038] It should be understood that, due to the specific position and shape of the curved mirror and photonic plug relative to each other in the bump, the disclosed arrangement of the photonic plug 300 and WDM photonic bump 100 achieves high signal efficiency through easy alignment between the PIC 310 and the fiber optic cable 320. The position of this curved mirror can be determined at least relative to the source / drain of the beam. In the embodiment, the shape of the curved mirror is such that all beams are reflected and collimated at a certain angle at the center of the curved mirror 302 and focused onto the drain after the curved mirror in the WDM photonic bump 100.

[0039] Further attention should be paid to, for reference Figure 3 The photonic plugs 300 and WBB100 discussed allow for connection between a single fiber and the PIC310. However, in a typical arrangement, multiple photonic plugs and bumps can be used to allow surface coupling of multiple fibers to the PIC300.

[0040] This document has discussed various optical couplers with reference to specific embodiments having a curved mirror for propagating a light beam. However, the disclosed embodiments can be implemented using other reflecting or focusing elements such as optical lenses, zone plates (e.g., Fresnel zone plates).

[0041] It should be understood that any reference to an element herein using a designation such as "first," "second," and so forth does not generally limit the quantity or order for that element. Rather, these designations are used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements can be employed, or that the first element must precede the second element. Also, unless otherwise specified, a set of elements includes one or more elements. Furthermore, to the extent that the terms "comprises," "comprising," "includes," "including," or the like are used in the detailed description or claims, such terms are intended to be inclusive in a manner similar to that of the terms "comprise" "comprising," "includes," "including" or "have" "having" as an aid in separating embodiments or examples from other embodiments or examples that differ from the specific embodiment or example. Further, to the extent that the phrase "at least one of" is used herein in the detailed description or claims, such a phrase is intended to mean the at least one of a single element or combination of elements, i.e., that at least one of element A or element B is either element A or element B.

[0042] All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the present disclosure and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

Claims

1. A broadband surface coupling device comprising: A first waveguide having an anti-conical shape for extending the beam on a first reference plane; A second waveguide, configured to receive a beam of light from the first waveguide, the second waveguide including a first positive cone on a second reference plane perpendicular to the first reference plane; A curved mirror, horizontally spaced from the second waveguide, configured to reflect the light beam onto an optical fiber; and An inclined plane mirror is positioned between the curved mirror and the second waveguide to guide a light beam from the second waveguide.

2. The apparatus according to claim 1, wherein, The second waveguide also includes a second conical shape on the first reference plane.

3. The apparatus according to claim 1, wherein, At the endpoint of the first waveguide, the inverted cone thermally shrinks from a first width to a second width.

4. The apparatus according to claim 1, wherein, The conical body in the first reference plane changes from a first height to a second height, wherein the first height is higher than the second height.

5. The apparatus according to claim 1, wherein, The curved mirror and the tilted plane mirror are manufactured on the spacer.

6. The apparatus according to claim 1, further comprising: A photonic plug, perpendicularly spaced from the first waveguide and the second waveguide, the photonic plug having an optical fiber connected to the photonic plug, the photonic plug comprising: The second curved mirror; and The second tilted plane mirror, The second curved mirror and the second tilted plane mirror connect the light beam to the curved mirror.

7. The apparatus according to claim 5, wherein, The spacer is transparent to the wavelength of the light beam.

8. The apparatus according to claim 1, wherein, The tilted plane mirror is tilted at a predetermined angle relative to the second waveguide so that the light beam is connected to the second waveguide.

9. The apparatus according to claim 1, wherein, The inverted cone narrows in a first direction, while the upright cone widens in the first direction.

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