Low loss waveguide fiber coupler with a mode modifying element, and corresponding systems, assemblies, and methods

Abstract

The present invention provides an assembly for aligning an optical fiber with an optical waveguide, addressing the challenges of mode mismatch and optical losses at the interface. The assembly comprises a glass substrate with an optical waveguide, an edge positioned adjacent to an optical fiber, and a mode-modifying element disposed on the substrate surface covering the waveguide end at the edge. The mode-modifying element modifies the mode profile of the waveguide to closely align to that of the optical fiber to significantly reduce mode mismatch and optical losses. Additionally, the mode-modifying element minimizes the number of interfaces encountered by light, further reducing optical losses. The assembly enables efficient coupling of light between optical fibers and integrated waveguides in various applications, such as optical communication systems, data centers, and sensing devices.

Description

LOW LOSS WAVEGUIDE FIBER COUPLER WITH A MODE MODIFYING ELEMENT, AND CORRESPONDING SYSTEMS, ASSEMBLIES, AND METHODS RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Application Serial No. 63 / 668,582 filed on July 8, 2024, the content of which is relied upon and incorporated herein by reference in its entirety. FIELD

[0002] Embodiments of the present disclosure relate to optical interconnect assemblies and methods for efficiently aligning an integrated waveguide and an optical fiber. More specifically, some embodiments of the present disclosure pertain to an assembly that utilizes a mode-modifying element to minimize optical losses at one or more interfaces between optical fibers and optical waveguides. BACKGROUND

[0003] Optical fibers are used for routing optical signals over long distances (e.g., wide area networks (WAN), metropolitan area networks (MAN), local area networks (LAN), racks, etc.). By contrast, optical interconnects (e.g., waveguides) are integrated in substrate materials like glass, silicon, or polymers for short-reach data transmission applications, such as in short reach optical interconnects and photonic integrated circuits (PICs) and are suitable for chip-level, module-level, and board-level optical interconnects.

[0004] However, efficiently coupling light between optical fibers and integrated waveguides remains a challenge due to mode mismatch and optical losses at the interfaces. The mode mismatch arises from differences in the size, shape, and refractive index profiles of the optical fiber and the waveguide, leading to poor overlap between their respective modes.

[0005] Optical losses may occur at interfaces due to, for example, a material different than air being placed on top of the optical waveguide – e.g., there is a transition on the top of the optical waveguide from air to another material, such as a lid, adhesive, a front of a connector, or other material. Similar losses can occur at any interface between two materials with different refractive indices, this may include transitions between various components within the optical system. These interfaces can cause scattering, reflection, and absorption of light, reducing the efficiency of the optical coupling.

[0006] Existing solutions, such as spot-size converters, edge couplers, or grating couplers, often involve complex fabrication processes, precise alignment, or have limited bandwidth and coupling efficiency. Furthermore, they may not effectively address the issue of optical losses at interfaces. SUMMARY

[0007] Consequently, there is a need for an improved assembly that can efficiently couple light between optical fibers and integrated waveguides while minimizing mode mismatch and optical losses at interfaces. The assembly may be compatible with standard optical connectors, simple to manufacture, and offer a reliable coupling solution for various applications.

[0008] The present disclosure addresses the above noted challenges by providing an assembly that incorporates a mode-modifying element, such as a top cladding material, to match the mode profiles of the optical fiber and the integrated waveguide and to reduce the number of interfaces encountered by the optical waveguide. By optimizing the mode overlap and minimizing the interfaces, aspects of the present disclosure significantly reduce coupling losses and enhances overall system performance.

[0009] For the optical interface between the optical fiber and integrated waveguides, a connector solution that is standardized, low cost, and high performance is desirable. Some specific types of connectors (e.g., Multi-fiber Termination Push-on (MTP) connectors and Multi-fiber Push-on (MPO) connectors) have been developed that are state-of the art solutions for multi-fiber connectors in datacenters and other applications. Integrated optical waveguides in glass (e.g., Ion-exchange (IOX), laser-direct writing, deposition) or polymer are promising technologies for fabrication of low-loss optical substrates, such as for interposers, packaging substrates, and circuit board optical interconnects. Integrated optical waveguides in silicon, silicon nitrate, and deposited doped fused silica are promising technologies for fabrication of highly integrated photonic circuits, such as for transceivers, multiplexer, splitters, sensors, etc. To enable and deploy the waveguide technology in datacenters, high-performance computers, and other applications, a standard interface is desirable between the optical fiber(s) and integrated waveguides.

[0010] Notably, alignment between the integrated waveguides and optical fiber(s) can be difficult. Further, maintaining a small form factor to enable attachment and management of many different optical fibers is desirable. In this regard, various features may be employed to aid in alignment, however, such features each require alignment and have their own dimensions and geometries that have to be accounted for. This often means that connection using several different components results in intolerances “stacking” on top of each other, leading to additional inaccuracies in alignment. Moreover, mode mismatch between the optical fiber and the integrated waveguide can cause optical losses at the interface, further complicating the alignment process. This mode mismatch arises due to differences in the size, shape, and refractive index profiles of the optical fiber and the integrated waveguide, leading to poor overlap between their respective modes.

[0011] Some current interfaces require active alignment in order to account for such difficulties in obtaining proper alignment. Where active alignment is used, a powered system is required to align the system that transmits optical test signals and seeks to optimize the optical test signals. Active alignment, however, is costly and time-consuming. Furthermore, active alignment systems may not effectively address the issue of mode mismatch and the resulting optical losses at the interface between the optical fiber and the integrated waveguide.

[0012] Assemblies, systems, and methods described herein enable easy and proper alignment of a substrate and waveguides therein / thereon with one or more optical fibers. This may be accomplished through passive alignment, which permits cost-efficient assembly of components. The substrate may, for example, be any type of substrate, such as an electro-optical substrate, optical substrate (optical waveguides but no electrical lines), photonic integrated circuit (PIC) like silicon photonics, planar lightwave circuit (PLC) like optical splitters, fan-out or break out modules, three-dimensional photonic integrated circuits having one or more waveguides buried below the surface, etc.

[0013] The assemblies, systems, and methods described herein incorporate a mode- modifying element to match the mode profiles of the optical fiber and the integrated waveguide, thereby reducing mode mismatch and optical losses at the interface. The mode-modifying element is configured to modify the mode profile of the optical waveguide to closely match the mode profile of the optical fiber, thereby reducing mode mismatch and optical losses at the interface. By optimizing the mode overlap between the optical waveguide and the optical fiber, the mode- modifying element significantly enhances the coupling efficiency and performance of the assembly.

[0014] Various embodiments of the present disclosure provide one or more components for connecting and aligning one or more optical fibers to one or more optical waveguides on a substrate, a PIC, or a planar lightwave circuit (PLC) (e.g., planar glass waveguides, such as IOX, deposited, laser written waveguides comprising polymer, silicon, silicon nitrate, and / or silica material). The connector may comprise a connector housing that abuts and / or envelops a substrate edge of the substrate. The substrate body of the substrate may be processed (e.g., through laser processing, milling, dicing, etching, or lithography) to make an optical facet and / or provide mechanical alignment features for very precise alignment in reference to the waveguides. In some embodiments, the components of the system (e.g., guide pin(s) and the connector housing) may be passively aligned directly to the substrate body by automated machines, enabling high-volume processing which leads to higher yield and cost savings.

[0015] In some embodiments, various features may be processed into a top surface of a substrate body of the substrate, which may lead to large scale panel level processing (cost savings) and quality improvements through inspection (e.g., through top view microscopy) to find non-good parts (out of specifications). Further, in some embodiments, guide pins may be used and may be directly attached to the substrate body, and this may reduce the stack of tolerances and lead to lower coupling loss and better performance.

[0016] In an example embodiment, an assembly is provided for aligning an optical fiber with an optical waveguide. The assembly may comprise a glass substrate comprising at least one optical waveguide configured to support a waveguide mode. The waveguide mode has a first light pattern, and wherein the at least one optical waveguide defines an end at an edge of the glass substrate. An optical fiber is configured to be positioned adjacent to the edge to align with the at least one optical waveguide to receive light therefrom or transfer light thereto. The optical fibersupports a fiber mode, the fiber mode having a second light pattern. The assembly for aligning an optical fiber with an optical waveguide further comprises a mode-modifying element disposed on a surface of the glass substrate covering the end of the at least one optical waveguide at the edge of the glass substrate. The mode-modifying element is configured to modify the first light pattern of the waveguide mode to more closely align with the second light pattern of the fiber mode to reduce optical losses between the at least one optical waveguide and the optical fiber.

[0017] In some embodiments, the assembly for aligning an optical fiber with an optical waveguide further comprises a photonic integrated circuit (PIC) positioned on the glass substrate. The optical fiber is configured to be positioned adjacent to the edge to align with the at least one optical waveguide to receive light from the PIC or transfer light to the PIC. The mode- modifying element is configured to reduce optical losses at interfaces between the optical fiber, the at least one optical waveguide, and the PIC.

[0018] In some embodiments, the interfaces of the assembly for aligning an optical fiber with an optical waveguide comprises a first interface between the optical fiber and the at least one optical waveguide at the edge of the glass substrate. The interfaces further comprises a second interface between the at least one optical waveguide and the PIC.

[0019] In some embodiments, the assembly for aligning an optical fiber with an optical waveguide further comprises a lid positioned on the mode-modifying element and the at least one optical waveguide. The lid is configured to provide a protective covering for the at least one optical waveguide and the mode-modifying element.

[0020] In some embodiments, the mode-modifying element of the assembly for aligning an optical fiber with an optical waveguide element is disposed proximate to the at leastone optical waveguide in an extended configuration over an entire length of the at least one optical waveguide.

[0021] In some embodiments, the mode-modifying element of the assembly for aligning an optical fiber with an optical waveguide element comprises a material having a refractive index that is the same or below the glass within a range of 0.05, or below the effective index of the waveguide mode to prevent leakage of light from the at least one optical waveguide.

[0022] In some embodiments, the mode-modifying element of the assembly for aligning an optical fiber with an optical waveguide element is any one of an optical adhesive, optical glass, a combination of an adhesive and a glass, a polymer, or a deposited thin film.

[0023] In some embodiments, the mode-modifying element of the assembly for aligning an optical fiber with an optical waveguide element is configured to modify the first light pattern of the waveguide mode to match the second light pattern of the fiber mode to produce a coupling loss of 0.2 dB or lower.

[0024] In some embodiments, the mode-modifying element of the assembly for aligning an optical fiber with an optical waveguide element is configured to modify the first light pattern of the waveguide mode to match the second light pattern of the fiber mode to produce a coupling loss of 0.1 dB or lower.

[0025] In some embodiments, the assembly for aligning an optical fiber with an optical waveguide further comprising at least one guide pin positioned in a receiving feature of the glass substrate, wherein the at least one guide pin extends outwardly from the glass substrate.

[0026] In some embodiments, the receiving feature of the assembly for aligning an optical fiber with an optical waveguide is a trench. The trench comprises two side edges and abottom surface, and trench is configured so that the at least one guide pin rests against the two side edges without contacting the bottom surface.

[0027] In some embodiments, the assembly for aligning an optical fiber with an optical waveguide further comprising a second lid configured to secure the at least one guide pin within the receiving feature wherein the second lid is positioned adjacent to the first lid.

[0028] In some embodiments, the trench of the assembly for aligning an optical fiber with an optical waveguide is formed using a laser-based or chemical etching, or combination approach.

[0029] In another example embodiment, a system is provided for aligning an optical fiber with an optical waveguide. The system comprises the optical fiber, and a glass substrate comprising at least one optical waveguide configured to support a waveguide mode. The waveguide mode has a first light pattern, wherein the at least one optical waveguide defines an end at an edge of the glass substrate. The optical fiber is configured to be positioned adjacent to the edge to align with the at least one optical waveguide to receive light therefrom or transfer light thereto, wherein the optical fiber supports a fiber mode, the fiber mode having a second light pattern. The system also comprises a mode-modifying element disposed on a surface of the glass substrate covering the end of the at least one optical waveguide at the edge of the glass substrate. The mode-modifying element is configured to modify the first light pattern of the waveguide mode to more closely align with the second light pattern of the fiber mode to reduce optical losses between the at least one optical waveguide and the optical fiber. The system further comprises at least one guide pin defining a first end and a second end, and the glass substrate of the system further comprising a receiving feature configured to receive and connect the first end of the at least one guide pin, wherein the second end for the at least one guide pin extends outwardly from theglass substrate. The system further comprises a connector housing configured to receive the optical fiber comprising at least one receiver portion extending from a first side to a second side, the at least one receiver portion defining a recess. The recess of the at least one receiver portion is configured to receive the at least one guide pin to cause alignment of the optical fiber with the one or more optical waveguides and restrain movement of the optical fiber relative to the waveguide substrate.

[0030] In some embodiments, the system for aligning an optical fiber with an optical waveguide further comprises a photonic integrated circuit (PIC) positioned on the glass substrate. The optical fiber is configured to be positioned adjacent to the edge to align with the at least one optical waveguide to receive light from the PIC or transfer light to the PIC. The mode- modifying element is configured to reduce optical losses at interfaces between the optical fiber, the at least one optical waveguide, and the PIC.

[0031] In some embodiments, the interfaces of the system for aligning an optical fiber with an optical waveguide comprises first interface between the optical fiber and the at least one optical waveguide at the edge of the glass substrate. The interfaces further comprises a second interface between the at least one optical waveguide and the PIC.

[0032] In some embodiments, the system for aligning an optical fiber with an optical waveguide further comprises a lid positioned on the mode-modifying element and the at least one optical waveguide. The lid is configured to provide a protective covering for the at least one optical waveguide and the mode-modifying element.

[0033] In some embodiments, the mode-modifying element of the system for aligning an optical fiber with an optical waveguide element comprises a material having arefractive index that is the same or below the glass within a range of 0.05, or below the effective index of the waveguide mode to prevent leakage of light from the at least one optical waveguide.

[0034] In some embodiments, the mode-modifying element of the system for aligning an optical fiber with an optical waveguide element is any one of an optical adhesive, optical glass, a combination of an adhesive and a glass, a polymer, or a deposited thin film.

[0035] In some embodiments, the receiving feature of the system for aligning an optical fiber with an optical waveguide is a trench. The trench comprises two side edges and a bottom surface, and trench is configured so that the at least one guide pin rests against the two side edges without contacting the bottom surface.

[0036] In some embodiments, the trench of the system for aligning an optical fiber with an optical waveguide is formed using a laser-based or chemical etching, or combination approach.

[0037] In another example embodiment, a method of manufacturing an assembly for aligning an optical fiber with an optical waveguide is provided. The method comprises providing a glass substrate comprising at least one optical waveguide configured to support a waveguide mode, the waveguide mode having a first light pattern. The method further comprises disposing a mode-modifying element on a surface of the edge of the glass substrate covering an end of the at least one optical waveguide. The mode-modifying element is configured to modify the first light pattern of the waveguide mode to more closely align with a second light pattern of a fiber mode of the optical fiber so as to reduce optical losses between the at least one optical waveguide and the optical fiber.

[0038] In some embodiments, the method of manufacturing an assembly for aligning an optical fiber with an optical waveguide further comprises positioning a lid on the mode-modifying element and the at least one optical waveguide. The lid is configured to provide a protective covering for the at least one optical waveguide and the mode-modifying element.

[0039] Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating example preferred embodiments of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, which are not necessarily to scale, wherein:

[0041] FIG.1 is a cross sectional schematic view of an example fiber-to-waveguide interface, illustrating the asymmetry mode profile of air cladding, in accordance with some embodiments discussed herein;

[0042] FIG.2 is a top view of an example glass substrate assembly with a glass lid and guide pins, in accordance with some embodiments discussed herein;

[0043] FIG. 3 is a cross sectional view of the glass substrate assembly of FIG. 2 with the guide pins, in accordance with some embodiments discussed herein;

[0044] FIG.4 is a cross sectional schematic view of an example fiber-to-waveguide interface with a glass lid and photonic integrated circuit (PIC) disposed on the surface of the waveguide, illustrating the optical losses at each interface, in accordance with some embodiments discussed herein;

[0045] FIG.5 is a cross sectional schematic view of an example fiber-to-waveguide interface with a mode modifying element disposed on the surface of the waveguide and a glass lid and photonic integrated circuit (PIC) disposed on top of the mode modifying element, illustrating the reduced optical losses at each interface, in accordance with some embodiments discussed herein;

[0046] FIG. 6A is a cross sectional schematic view of an example fiber-to- waveguide interface with a mode modifying element disposed on the surface of the waveguide and a lid disposed on top of the mode modifying element, in accordance with some embodiments discussed herein;

[0047] FIG. 6B is a cross sectional schematic view of an example fiber-to- waveguide substrate interface of FIG. 6A, where a tapered configuration of the mode-modifying element is shown, in accordance with some embodiments discussed herein;

[0048] FIG. 6C is a cross sectional schematic view of an example fiber-to- waveguide interface of FIG.6A, where an extended configuration of the mode-modifying element is shown, in accordance with some embodiments discussed herein;

[0049] FIG. 7A is a perspective view of an example glass substrate assembly with guide pins secured by a second lid, in accordance with some embodiments discussed herein;

[0050] FIG. 7B is a perspective view of a glass substrate body with integrated waveguides of the assembly of FIG.7A, in accordance with some embodiments discussed herein;

[0051] FIG.7C is a perspective view of the glass substrate body of FIG.7B with a first lid bonded to the surface of the glass substrate body, in accordance with some embodiments discussed herein;

[0052] FIG. 7D is a perspective view of the glass substrate body of FIG. 7C illustrating the glass substrate body having a receiving feature, in accordance with some embodiments discussed herein;

[0053] FIG. 7E is a perspective view of the glass substrate body of FIG. 7D after the glass substrate body with the receiving feature and the first lid has been cut through the center, in accordance with some embodiments discussed herein;

[0054] FIG. 8 is a cross sectional view of the glass substrate assembly of FIG.7A, in accordance with some embodiments discussed herein;

[0055] FIG. 9 is a perspective view of an example use of the glass substrate assembly of FIG. 7A with guide pins received within a connector housing, in accordance with some embodiments discussed herein; and

[0056] FIG.10 is a flow chart illustrating operations that may be performed to align a glass substrate with a mode modifying element with an optical fiber, in accordance with some embodiments discussed herein. DETAILED DESCRIPTION

[0057] The following description of the embodiments of the present disclosure is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. The following description is provided herein solely by way of example for purposes of providing an enabling disclosure of the disclosure but does not limit the scope or substance of the disclosure.

[0058] The present disclosure relates to optical coupling assemblies and methods for efficiently coupling light between integrated optical waveguides and optical fibers. Ion-exchange (IOX) is a widely used process for fabricating low-loss optical waveguides in glass substrates. The process involves multiple steps, including lithography, ion-exchange, and post- processing. The resulting waveguides exhibit low propagation losses making them suitable for various applications such as optical communication systems, sensors, and integrated photonics devices. In these applications, the waveguides efficiently confine and guide light.

[0059] The ability to guide light through a waveguide is dependent on modes supported by its structure. When light propagates through a waveguide or fiber, it does so in specific patterns called modes. The term "mode" refers to the spatial distribution of light within the waveguide or fiber, determined by the structure's refractive index profile and geometry. In a single-mode waveguide or fiber, light propagates in a single pattern, which can be described by its polarization: either transverse electric (TE) or transverse magnetic (TM). A single-mode waveguide or fiber supports only one TE mode and one TM mode, which are orthogonal to each other. The TE mode has its electric field perpendicular to the direction of propagation, while the TM mode has its magnetic field perpendicular to the direction of propagation. These modes have distinct spatial distributions and polarization states, which can affect the efficiency of coupling between different waveguide structures.

[0060] Coupling light between an optical fiber and an integrated waveguide presents a challenge due to mode mismatch. This mismatch arises because the modes supported by the optical fiber and the waveguide have different spatial distributions and properties. Efficient coupling requires the modes to overlap and match as closely as possible. However, the geometric and refractive index differences between the fiber and waveguide structures often result in significant mode mismatch, leading to coupling losses and inefficient light transfer.

[0061] FIG.1 illustrates a side view of a typical fiber-to-waveguide interface 100, highlighting this issue. In this example, an optical fiber 102 is positioned adjacent to a glass substrate 104 containing one or more waveguide(s) 111. The waveguide 111 is formed near the surface of the glass substrate 104 with an end 111a of the waveguide corresponding to an edge 104a of the glass substrate, and there is an air cladding 106 above the waveguide. The specific fabrication method for the waveguides may vary depending on the substrate material and the desired waveguide properties. For example, in glass substrates, ion-exchange techniques can be used to create high-quality, low-loss waveguides through selective modification of the glass using an ion-exchange process, laser-writing process, or a deposition and etching process. The waveguide 111 may support a first mode (i.e., waveguide mode) with a distinct spatial distribution of light intensity or light pattern, and the optical fiber 102 may support a second mode (i.e., fiber mode) with a distinct distribution of light intensity of light pattern. The modes supported by the optical fiber 102 and the waveguide 111 have different spatial distributions due to their distinct geometries and refractive index profiles, resulting in mode mismatch and coupling losses when attempting to transfer light between them.

[0062] The optical fiber 102 can be any type of fiber suitable for the specific application, such as a single-mode fiber (SMF), a multimode fiber (MMF), or a polarization- maintaining fiber (PMF). The choice of fiber may depend on factors such as the wavelength of operation, the required bandwidth, and the distance over which the light needs to be transmitted.

[0063] An optical fiber is typically formed of a cylindrical core surrounded by a cladding layer, both made of silica glass with slightly different refractive indices. The refractive index difference between the core and cladding allows the fiber to guide light along its length. Thedimensions of the core and cladding, along with their refractive indices, determine the mode profile of the light propagating through the fiber, which may be symmetric.

[0064] The waveguide 111 is formed by creating a high-refractive-index region within the glass substrate 104. The refractive index profile of the waveguide 111 is determined by the distribution of the exchanged ions within the glass, which may depend on its fabrication process, such as that of the ion exchange process parameters. Unlike the geometry of an optical fiber, the cross-section of the waveguide is typically asymmetric. The proximity of the waveguide to the glass substrate surface and the presence of the air cladding 106 above it further contributes to the asymmetry of the waveguide's mode profile.

[0065] The mismatch between the symmetric mode profile of the optical fiber 102 and the asymmetric mode profile of the waveguide 111 at the interface 103 leads to optical losses when coupling light from the fiber to the waveguide, or vice versa. When light from the optical fiber 102 is coupled into the waveguide 111, some of the light may not be confined within the waveguide core and can leak into the substrate or the air cladding. Similarly, when light from the waveguide 111 is coupled into the optical fiber 102, some of the light may not be captured by the fiber core due to the mode profile mismatch.

[0066] The extent of the mode mismatch depends on several factors, including the specific geometries of the fiber and the waveguide, the refractive index contrast between the core and cladding of the fiber, and the refractive index distribution within the waveguide 111. The mismatch becomes more pronounced when the dimensions and refractive indices of the fiber and the waveguide are significantly different.

[0067] To minimize the optical losses caused by mode mismatch, it is important that the waveguide 111 mode profile closely resembles and aligns to that of the optical fiber 102.This can be achieved by optimizing the fabrication process of the waveguide 111 parameters to control the refractive index distribution and the geometry of the waveguide 111. However, even with optimized designs, there is still a residual mode mismatch that limits the coupling efficiency between the fiber and the waveguide.

[0068] FIG. 2 illustrates a perspective view of a conventional glass waveguide assembly 200 designed for coupling light between an optical fiber and an integrated waveguide. The assembly 200 includes a glass substrate 140 with a glass substrate body 142 that has an upper surface 144 and an edge 146. The substrate body 142 contains the one or more optical waveguides 111 (not shown in this view) formed using techniques such as ion exchange process (IOX).

[0069] Positioned on the upper surface 144 of the substrate body 142 is a glass lid 150. The glass lid 150 provides mechanical protection and support for the optical waveguides and other components on the substrate. It is typically made of the same material as the glass substrate body 142 to minimize thermal stresses, optical loss, and ensure compatibility. The glass lid is bonded to the substrate body 142 using an adhesive or other bonding methods such as thermal compression bonding, direct bonding, or fusion bonding.

[0070] To align an optical fiber with the waveguides, the assembly 200 includes guide pins 154 positioned in receiving features (not visible) formed on the upper surface 144 of the substrate body 142. These guide pins 154 extend outwardly and are designed to engage with corresponding features on a fiber connector or fiber array, ensuring alignment between the optical fiber and the waveguides.

[0071] Notably, the glass lid 150 is positioned slightly back from the edge 146 of the substrate body 142, creating a gap 153 of approximately 0.5 mm. The gap 153 prevents any adhesive used to bond the glass lid 150 from flowing over the edge 146 and interfering with theoptical coupling interface. However, the presence of this gap can have unintended optical performance issues.

[0072] When coupling light between the optical fiber and the integrated waveguide, there is a change in material composition at the edge 146, where the light from the optical fiber is coupled to the integrated waveguide with an air cladding, that may cause scattering and reflection losses as light propagates from the optical fiber to the waveguides. Additionally, the absence of a top cladding material on top of the integrated waveguide in this gap region allows the mode profile of the waveguides to be confined below the glass surface, leading to a mismatch with the mode profile of the optical fiber. This mode mismatch further contributes to reduced coupling efficiency and increased optical losses.

[0073] While providing a basic structure for aligning an optical fiber with integrated waveguides, the conventional assembly in FIG.2 has limitations due to the gap between the glass lid and the substrate edge. This gap, although necessary for preventing adhesive overflow, introduces challenges such as scattering losses and mode mismatch that can degrade the overall efficiency of the optical coupling.

[0074] FIG.3 illustrates a cross-sectional view of the glass substrate assembly 140 introduced in FIG. 2. The assembly comprises a glass substrate body 142 with an upper surface 144, guide pins 154, and a waveguide array 155.

[0075] The guide pins 154 are positioned within receiving features 148 formed on the upper surface 144 of the glass substrate body 142. These receiving features 148 are each configured to receive and removably or permanently connect to secure the first end of a guide pin 154, ensuring accurate alignment between the waveguide array 155 and the optical fibers (not shown) that will be connected to the assembly. These receiving features may be separated by adistance 145, which is designed to optimize the alignment and spacing of the guide pins 154 and the waveguide array 155.

[0076] The dimensions of the glass substrate assembly 140 permit alignment with the connector housing (not shown in this view). This alignment helps in achieving coupling between the optical fibers and the individual waveguides within the waveguide array 155. In some embodiments, each optical fiber may be connected to a single waveguide, while in other cases, multiple optical fibers may align with multiple waveguides.

[0077] The receiving features 148 may be provided as a trench within the glass substrate body 142 and are formed on the upper surface 144 of the glass substrate body 142. The trenches may be formed using methods such as laser ablation. By employing laser ablation techniques, such as those using nanosecond (ns), picosecond (ps), or femtosecond (fs) pulsed lasers, the position of the side edges of the trenches 148 can be defined with sub-micron accuracy. This allows for the guide pins 154 to rest against the two side edges of the trench without contacting the bottom surface.

[0078] Consequently, where a trench is used, the trench may comprise two side edges and a bottom surface, in the specific embodiment shown in FIG.3, the guide pins 154 have a thickness of 550 m, and the trenches 148 have a width 149A of 249.8 m and a depth 149B of 30 m. The trenches 148 are designed to accommodate the guide pin length, ensuring a secure and stable connection. Additionally, the trench may comprise a length of approximately 5 mm to permit approximately 5 mm of the guide pin to be received. The trenches may be offset at 5.3 mm increments. This offset may be measured from a side edge of a trench to the same respective side edge of an adjacent trench as shown. However, it is important to note that these dimensions may vary in other embodiments to suit specific requirements and design constraints.

[0079] Beneath the glass lid 150, alignment grooves 156 are provided to receive and secure the guide pins 154. These alignment grooves 156 under the lid 150 work in conjunction with the receiving features 148 on the upper surface 144 to enable positioning of the guide pins 154 for accurate fiber-to-waveguide alignment.

[0080] In addition to the receiving features 148 and alignment grooves 156, an adhesive 204 is disposed between the glass lid 150 and glass substrate body 142 providing the assembly 200 mechanical stability. The adhesive 204 is used to secure the glass lid 150 to the glass substrate body 142, ensuring a proper bond is formed between the lid 150 and the glass substrate body 142. However, the adhesive's characteristics, such as its refractive index and thickness, also have an impact on the mode matching and optical losses at the interfaces where it is present. Therefore, the refractive index of the adhesive 204 may be chosen to minimize optical losses and ensure efficient coupling of light. Notably, however, the desired characteristics to minimize optical losses of the adhesive is limited by still needing to be an adhesive (e.g., such as opposed to some example cladding materials described herein).

[0081] FIG.3 provides a comprehensive view of the glass substrate assembly 140, emphasizing the importance of the receiving features 148 on the upper surface 144 and the alignment grooves 156 under the glass lid 150 in achieving alignment between the guide pins 154 and the waveguide array 155. However, there are still limitations in this embodiment in delivering efficient and low-loss optical coupling.

[0082] FIG. 4 illustrates a side view of an example embodiment of an assembly 200 depicting a fiber-to-waveguide interface. This view presents the challenges associated with the multiple interfaces encountered by the optical mode as it propagates from the optical fiber 102to the integrated waveguide 111 within the glass substrate 104, and ultimately to the photonic integrated circuit (PIC) 202.

[0083] The optical fiber 102 is positioned adjacent to the glass substrate 104, where the glass substrate 104 contains a waveguide 111 optimized for low-loss light propagation. At the initial interface 103, the symmetrical mode from the fiber 102 couples into the asymmetric mode within the air-clad region 106’ that sits between the interfaces 103 and 105. This mode mismatch between the fiber and waveguide geometries results in the coupling losses.

[0084] To address this issue, a glass lid 150 is assembled on top of the waveguide region. However, as shown in the figure, the glass lid 150 is intentionally offset to the right, creating a distance or gap between the lid and the fiber 102. This offset is designed to prevent any adhesive used for bonding the lid 150 from overflowing onto the coupling interface 103, which could further degrade the optical performance.

[0085] As the optical mode propagates through the waveguide, it encounters multiple interfaces where there are abrupt changes in material and components. At interface 105, the mode transitions from the air-clad waveguide region 106’ into the region under the glass lid 150, causing a change in the mode profile due to the different cladding material. The mode then undergoes another reshaping at interface 107, where it exits the lid region and re-enters the air- clad waveguide region 106’’ that is between interface 107 and 109 within the glass substrate 104.

[0086] Further, an adhesive layer 204 is employed under the glass lid 150 and PIC 202. This adhesive layer acts as an intermediate cladding material for the waveguide in this region, influencing the mode profile based on its refractive index and thickness. It is important to note that while the adhesive layer 204 is typically thin, the adhesive may not have suitable refractive index to effectively control the spatial distribution of light from the fiber 102. The adhesive 204 hasmultiple functions such as a mechanical bond where it may have optical properties that are not optimized for mode control. This limitation of the adhesive layer contributes to the challenges in achieving efficient coupling between the fiber 102 and waveguide 111 as the adhesive 204 may not adequately reshape the mode profile to match that of the waveguide.

[0087] Finally, at interface 109, the optical mode couples from the waveguide 111 into the PIC 202, where the PIC 202 is designed to perform various functions on optical signals, such as modulation, multiplexing, switching, and routing. Despite the use of the adhesive, the air cladding (106’ and 106’’) and the presence of multiple interfaces (103, 105, 107, and 109), each introduce an abrupt change in cladding material or geometry, leading to increased optical losses due to mode mismatch. The assembly 200 serves to further illustrate the challenges posed by such air-cladding interfaces along the optical path.

[0088] FIG. 5 addresses the issues presented in the previous figures of mode mismatch and optical losses by introducing a mode modifying element 302 to the example glass substrate assembly 300.

[0089] The optical waveguide 111 is designed to support a first mode (i.e., waveguide mode), which has a first light pattern, or a distinct spatial distribution of light intensity. Similarly, the optical fiber 102 supports a second mode (i.e., fiber mode), which has a second light pattern or its own distinct spatial distribution of light intensity. The first light pattern and second light pattern are determined by the refractive index profiles and geometries of the waveguide 111 and the optical fiber 102, respectively.

[0090] Due to the differences in the refractive index profiles and geometries of the waveguide 111 and the optical fiber 102, the first light pattern of the first mode (i.e., waveguide mode) and the second light pattern of the second mode (i.e., fiber mode) may not perfectly align,resulting in mode mismatch and optical losses at the interface 103 between the waveguide 111 and the optical fiber 102. To address this issue, the mode-modifying element 302 is positioned at the interface 103, covering the end 111a of the waveguide 111 at the edge 104a of the glass substrate 104. The mode-modifying element 302 is designed to reshape the first light pattern of the first mode supported by the waveguide 111, modifying it to more closely align with the second light pattern of the second mode supported by the optical fiber 102.

[0091] By tailoring the refractive index and geometry of the mode-modifying element 302, the light propagating through the waveguide experiences a gradual mode conversion. The element 302 aids in progressively reshaping the first and second modes to expand and become more symmetric as it approaches the fiber interface 103. This mode reshaping minimizes the mode mismatch that would otherwise occur at the fiber-waveguide interface 103, thereby reducing coupling losses. Specifically, the mode-modifying element 302 aims to reduce the fiber to waveguide coupling loss from the typical .3dB down to .1dB or lower.

[0092] The mode-modifying element 302 can be implemented using various materials, including optical adhesives, adhesive-glass combinations, polymers, or deposited thin films. For optimal performance, the refractive index of the material used for the mode modifying element 302 should be the same or below the substrate's refractive index to prevent light from leaking out of the waveguide.

[0093] In some embodiments, the mode-modifying element 302 can be applied over an array of waveguides integrated into the substrate 104, rather than just a single waveguide. This would enable efficient mode-matching and low-loss coupling for multiple fiber-waveguide pairs simultaneously.

[0094] The mode-modifying element 302 can be deposited or bonded onto the substrate surface using various techniques, such as spin coating, dip coating, dispensing, or direct bonding, depending on the material composition. The control over the element's thickness and geometry of the mode-modifying element 302 will help achieve the desired mode reshaping effect.

[0095] As illustrated in FIG. 5, the mode-modifying element 302 extends continuously across the entire length of the waveguide, eliminating the multiple air-cladding interfaces present in the previous assembly shown in FIG. 4. This continuous tailored cladding structure ensures a smooth and gradual transition of the mode profile, minimizing abrupt changes that could lead to additional losses. Additionally, by controlling the refractive index changes, the mode-modifying element 302 can reduce waveguide loss by more than .2 dB.

[0096] By introducing the mode-modifying element 302, the assembly effectively reduces the number of interfaces to just two: the fiber-waveguide interface 303 and the waveguide- PIC interface 309 (if a PIC 202 is integrated). This simplified interface structure, combined with the optimized mode-matching capabilities of the mode-modifying element 302, enables efficient optical coupling between the fiber 102 and the integrated photonic components.

[0097] While the example in FIG. 5 depicts a specific configuration with a glass lid 150 and a PIC 202, the assembly may be adapted to various other embodiments. For instance, in some embodiments, different types of optical fibers (e.g., single-mode, multi-mode) could be employed, depending on the application requirements. Additionally, in some embodiments, alternative lid configurations or materials could be used to provide mechanical protection or facilitate assembly processes. In some embodiments, the mode-modifying element 302 could also be tailored for different waveguide materials or integrated photonic device platforms where therefractive index or geometries of the mode-modifying element are changed for optimized mode- matching capabilities.

[0098] By minimizing mode mismatch and associated losses through the placement and design of the mode-modifying element 302, this enables low-loss optical interconnects, facilitating the integration of fiber-optic communications with advanced photonic integrated circuits across a wide range of applications.

[0099] As mentioned, different embodiments and configurations of the mode- modifying element 302 can be developed, FIGs.6A-6C illustrate a few example configurations of the mode-modifying element and the mode-modifying element’s adaptability in achieving efficient light coupling between optical fibers and integrated waveguides.

[0100] FIG. 6A provides a comprehensive overview of how the mode-modifying element 302, also may be referred to as the top cladding material, can be incorporated into the glass substrate assembly 400. In the example assembly 400 shown, the components that have been introduced in the previous figures are present. These include the optical fiber 102, the glass substrate 104 containing the integrated waveguide 111, and the glass lid 150. The interface 103 between the optical fiber 102 and the waveguide 111 is where the mode mismatch and optical losses typically occur due to the differences in the mode profiles of the fiber and the waveguide.

[0101] To address the issue of optical loss and mode mismatch, the mode- modifying element 302 is positioned at / near the interface 103, sitting directly beneath the glass lid 150 and above the waveguide 111. The mode-modifying element 302 is used to reshape the mode profile of the integrated waveguide, transforming it to closely match the mode profile of the optical fiber 102. By achieving this mode-matching condition, the mode-modifying element 302 minimizes the optical losses that would otherwise occur at the interface 103 due to mode mismatch.

[0102] The placement of the mode-modifying element 302 beneath the glass lid 150 serves multiple purposes. First, it ensures that the mode-modifying element 302 is precisely aligned with the end of the integrated waveguide at the interface 103. This alignment enables optimal mode matching and minimizing optical losses. Second, the glass lid 150 provides mechanical protection for the mode-modifying element 302 and the waveguide end-face, shielding from potential damage or contamination that could degrade the optical performance of the assembly.

[0103] It is important to note that the specific geometry, dimensions, and material properties of the mode-modifying element 302 are to achieve the desired mode-matching effect. The refractive index of the mode-modifying element 302 is typically chosen to be the same or below the glass substrate 104 (within a range of 0.05 of a refractive index of the glass substrate), allowing for a smooth transition of the optical mode from the fiber 102 to the waveguide 111. The thickness and shape of the mode-modifying element 302 are also optimized to ensure efficient mode conversion while minimizing any residual mode mismatch or optical losses.

[0104] FIG. 6B illustrates a side view of another example assembly 500, where the mode-modifying element 302 is implemented in a tapered configuration. Instead of a continuous cladding layer, the mode-modifying element 302 gradually transitions into an air cladding region 506, forming a tapered configuration that transitions into a sloped terminal end 507. This tapered design is to provide a smooth transition between the cladding material and the air cladding, minimizing abrupt changes that could lead to additional losses due to mode mismatch.

[0105] In the tapered configuration, the tapering angle and length can be controlled to achieve the desired mode transition and minimize losses at the interface between the mode modifying element 302 and the air cladding region 506. The tapering angle, which is the angleformed by the terminal end 507 with respect to the waveguide surface, can be optimized to enable a gradual change in the effective refractive index experienced by the propagating mode. Similarly, the tapering length, which is the distance over which the mode modifying element 302 transitions from the mode modifying element to the air cladding, can be adjusted to provide a sufficiently long transition region for the mode conversion. By controlling these parameters, the tapered configuration can effectively suppress mode mismatch and reduce optical losses at the interface.

[0106] FIG.6C presents another embodiment of the mode modifying element 302, illustrating a side view of an assembly 600 where the mode-modifying element 302 extends across the entire surface of the integrated waveguide 111, effectively eliminating any air-cladding interfaces. This extended mode-modifying configuration avoids the need for transitions or tapers, as the waveguide mode is continuously reshaped and guided by the tailored mode modifying element 302 (i.e., cladding material) until it reaches components such as a photonic integrated circuit (PIC) or other photonic devices. By implementing the extended cladding configuration, the assembly 600 eliminates the multiple air-cladding interfaces that were present in the previous discussed assemblies (FIG. 4), reducing the number of abrupt mode transitions and associated losses. This configuration enables a seamless propagation of the reshaped mode from the fiber interface 103 to the subsequent photonic components, minimizing mode mismatch and improving overall coupling efficiency.

[0107] In addition to the continuous, tapered, and extended configurations discussed in FIGs. 6A-6C, there are other embodiments of the mode-modifying element 302 that can be employed to achieve efficient mode matching between the optical fiber and the integrated waveguide.

[0108] One such embodiment is a segmented configuration, where the mode- modifying element 302 comprises multiple discrete sections with varying refractive indices or geometries. Each section is designed to progressively reshape the waveguide mode, gradually transforming it to match the fiber mode. This segmented approach allows for a stepwise mode conversion, which can be advantageous in certain applications or fabrication processes.

[0109] Furthermore, the mode-modifying element 302 can be designed to have a non-uniform cross-sectional geometry along the propagation direction. For example, the width or height of the mode modifying element 302 can be tapered or varied to gradually adjust the confinement of the propagating mode. This geometric variation can be used in conjunction with the refractive index to achieve optimal mode matching and minimize losses.

[0110] The ability to customize the mode-modifying element 302 based on the characteristics of the optical fiber, integrated waveguide, and photonic components allows for optimal performance and the efficiency and functionality of a wide range of photonic applications, from telecommunications and data communications to sensing and computing.

[0111] FIGs. 7A-7E illustrate operations that may be involved in the assembly process for the fiber-to-waveguide interface of an example glass substrate assembly, as it directly impacts the performance, reliability, and manufacturability of the optical coupling system. This assembly process provides a guide to understand the sequence of operations and the integration of various components.

[0112] The glass substrate assembly 700, as shown in FIG.7A, incorporates several components, including a glass substrate body 742, one or more integrated waveguide(s) (not shown), a mode-modifying element (e.g., a top cladding material), a first lid 150, and the guidepins 154. In this embodiment, a second lid 750 is also introduced to enhance the mechanical stability and protection of the assembly.

[0113] The glass substrate body 742 serves as the foundation for the assembly, providing a platform for the integration of the optical components. The substrate body 742 has an upper surface 744, a bottom surface 743, and an edge 746, as illustrated in FIG. 7B. In some embodiments, the glass substrate body 742 can be made of various materials other than glass, such as silicon, or polymer, depending on the specific application and the desired optical and mechanical properties.

[0114] The assembly process may begin with the fabrication of the one or more integrated waveguide(s) within the substrate body 742. The waveguides are designed to guide light from an optical fiber to the desired locations on the substrate, enabling efficient optical signal transmission. The specific fabrication method for the waveguides may vary depending on the substrate material and the desired waveguide properties. For example, in glass substrates, ion- exchange techniques can be used to create high-quality, low-loss waveguides through selective modification of the glass using an ion-exchange process, laser-writing process, or a deposition and etching process. Once the waveguides are formed within the substrate, their layout and geometry can be defined in various ways.

[0115] The waveguide layout may be defined by a mask layer formed on the top surface 744 of the glass substrate 742 prior to the ion-exchange process. Alternatively, waveguide layouts can be defined through the position of a focused laser by sequential laser writing, without the need for a mask layer.

[0116] The resulting waveguides can take various forms, including straight waveguides, curved waveguides, and complex geometries that may include optical features orcomponents such as tapers, crossings, splitters, combiners, and arcs. In certain embodiments, these optical components can be combinable in fan-out or fan-in arrays.

[0117] Importantly, the path of each waveguide need not run in a straight line and need not run in a given x-y plane within the substrate. The waveguides may also be designed to support single-mode or multi-mode operation, depending on the application requirements.

[0118] In certain embodiments, the back-end waveguide facets, which interface with other optical components or fibers, may define respective optical quality end faces. These end faces can be formed by polishing techniques, such as laser polishing or mechanical polishing, or through a score-and-break process, like diamond wheel scoring or laser scoring followed by separation.

[0119] Following the waveguide fabrication, the mode-modifying element, e.g., a cladding material, is deposited above the waveguides on the upper surface 744 of the substrate body 742. This cladding material optimizes the waveguide mode that the mode profile of the integrated waveguides would match that of the optical fiber, minimizing mode mismatch and optical losses at the fiber-waveguide interface (e.g., easing a transition from a first light pattern to a second light pattern). The composition and thickness of the mode modifying element are optimized based on the refractive index of the substrate material, the waveguide dimensions, and the operating wavelength of the optical signals.

[0120] FIG.7C illustrates an example operation in the assembly process, where the first lid 150 is bonded to the upper surface 744 of the substrate body 742. The lid 150 may be composed of a plastic or glass material and serves multiple purposes, including protecting the waveguides and mode modifying element from environmental factors, providing a flat and stable surface for subsequent bonding steps, and facilitating the alignment of the guide pins 154.

[0121] The bonding of the first lid 150 to the substrate body 742 may be achieved through various methods, such as adhesive bonding, thermal compression bonding, fusion bonding, laser bonding or direct bonding. The choice of bonding method depends on factors such as the material properties of the lid and substrate, the desired bonding strength, and the thermal and mechanical stability requirements of the assembly. In some embodiments, a thin layer of adhesive or other material (e.g., SiO2, SiON) with a refractive index within 0.1 to that of the refractive index of glass may be used to ensure a reliable bond between the lid and the substrate, where the adhesive or other material may also act as a mode modifying element.

[0122] Following the bond of the first lid 150, the assembly 700 may undergo a process to create receiving features on the upper surface 744 of the substrate body 742. The receiving features are designed to securely position and align guide pins 154 with the integrated waveguides. As shown in FIG. 7D, the receiving features take the form of trenches 148 in this embodiment. However, the receiving features may also be implemented as grooves, V-grooves, or other geometric profiles, depending on the specific requirements and fabrication techniques employed.

[0123] The receiving features, whether trenches 148 or alternative geometries, are positioned and dimensioned to enable accurate alignment of the guide pins 154 with the integrated waveguides. Their placement and sizing help for achieving optimal coupling between the optical fiber and the one or more waveguide(s).

[0124] Several techniques can be employed to form the trenches 148, depending on the substrate material and the desired trench properties. Laser ablation is a commonly used method, particularly for glass substrates, as it allows for the creation of high-precision trencheswith minimal damage to the surrounding material. Other trench formation methods include etching, mechanical machining, or a combination of these techniques.

[0125] FIG. 7E illustrates the substrate assembly 700 after the trenches 148 have been formed and the first lid 150 has been cut through the center. This cut exposes the optical interface surface of the substrate body 742, where the integrated waveguides and cladding material are located. The exposed surface enables direct coupling between the optical fiber and the waveguides, facilitated by the refractive index matching properties of the cladding material.

[0126] The distance 145 between the trenches 148 illustrates the spacing between the guide pins 154 and, consequently, the alignment of the optical fiber with the integrated waveguides. This distance may be designed based on the dimensions of the optical fiber, the waveguide pitch, and the tolerances of the assembly process. In some embodiments, the guide pins 154 may be provided having a thickness of 550 m, and where the trench 148 have a trench width of 249.8 m, and the trench may have a depth of 30 m. Additionally, the trench may comprise a length of approximately 5 mm to permit approximately 5 mm of the guide pin to be received. The trenches 148 may be offset at 5.3 mm increments, measured from a side edge of a trench to the same respective side edge of an adjacent trench.

[0127] In the final operation of the assembly process, as shown in FIG. 7A, the guide pins 154 are inserted into the trenches 148, and the second lid 750 is added using the adhesive 204. The guide pins 154 enable aligning the optical fiber with the integrated waveguides, enabling efficient coupling, and minimizing optical losses. The second lid 750 may be designed to press and hold guide pins 154 in the appropriate position, where the second lid 750 may be formed at least partially of a plastic or glass material. The second lid 750 also provides an additional layer of protection and mechanical support for the assembly.

[0128] The adhesive 204 may be used to permanently connect the second lid 750 and the guide pins 154. The adhesive 204 may be selected based on its compatibility with the lid materials, its bonding strength, and its ability to withstand the operating conditions of the assembly. In some embodiments, other bonding methods, such as thermal compression bonding or direct bonding, may be used instead of adhesive bonding, depending on the specific requirements of the application.

[0129] The assembly process described in FIGs.7A-7E is just one example of how the glass substrate assembly may be constructed. There are various embodiments and modifications to the assembly process, aimed at optimizing performance, manufacturability, and cost-effectiveness.

[0130] For instance, the mode-modifying element (e.g., cladding material) can be designed to have different geometries, such as tapered, extended, or segmented configurations, to better match the mode profiles of the waveguides and the optical fiber. The composition of the mode-modifying element can also be varied, using materials with different refractive indices or gradient-index profiles, to achieve the desired mode-matching properties.

[0131] Similarly, the trench formation process can be adapted to create trenches with different cross-sectional shapes, such as V-grooves or U-grooves, to accommodate guide pins of various sizes and geometries. The depth, width, and pitch of the trenches can be optimized based on the specific requirements of the application, such as the optical fiber diameter, the alignment tolerance, and the desired mechanical stability.

[0132] In some embodiments, additional features or components may be incorporated into the assembly process to enhance its functionality or performance. For example, the second lid 750 may be designed with integrated heatsinks or thermal management structuresto dissipate heat generated by active optical components, such as lasers or modulators, integrated into the substrate.

[0133] Furthermore, the assembly process can be scaled up to accommodate larger substrate sizes or higher numbers of optical channels, enabling the fabrication of high-density, high-bandwidth optical interconnects. This scalability is facilitated by the use of automated assembly techniques, such as pick-and-place machines or robotic assembly systems, which can accurately position and bond the various components with high throughput and repeatability.

[0134] There may be various embodiments and modifications to this assembly process, aimed at optimizing performance, manufacturability, and cost-effectiveness. By designing and integrating the components, and by employing the discussed assembly techniques, enables the fabrication of a reliable fiber-to-waveguide interfaces for a wide range of applications in optical communication, sensing, and data processing.

[0135] FIG. 8 illustrates a cross-sectional view of the glass substrate of FIG. 7A, providing insights into the layered structure and components facilitating this optical coupling.

[0136] Starting from the bottom of the assembly 700, is the glass substrate body 742 comprising the upper surface 744. Integrated onto this upper surface 744 are one or more waveguide(s) 155, designed and fabricated to guide light signals from an optical fiber to desired locations on the substrate. The one or more waveguide(s) 155, as mentioned, can be formed through various techniques, such as ion-exchange processes, laser writing, or deposition and etching processes. The waveguides 155 can take various forms, including of an array, or of a straight, curved, or complex geometries incorporating optical features like tapers, crossings, splitters, combiners, and arcs, combinable in fan-out or fan-in configurations. Importantly, thewaveguide paths need not run in straight lines or be confined to a specific plane within the glass substrate body 742.

[0137] Positioned above the one or more waveguide(s) 155 is the mode-modifying element 302, where the mode-modifying element is a tailored cladding material to help reshape the waveguide mode profile, minimizing mode mismatch and associated losses when coupling to an optical fiber mode. The mode-modifying element 302 can comprise materials like optical adhesives, adhesive-glass combinations, polymers, or deposited thin films or any other material that has a refractive index that matches to that of glass. Specifically, the refractive index of the mode modifying element 302 is optimized to be same or below the glass substrate's refractive index to prevent leakage of light from the waveguide.

[0138] Covering the mode-modifying element 302 is the first lid 150, providing mechanical protection and support. The lid may be of any material such as a plastic or glass lid. The first lid 150 can be bonded to the mode-modifying element 302 through various bonding methods such as adhesive bonding, thermal compression bonding, fusion bonding, laser bonding or direct bonding.

[0139] A second glass lid 750 is introduced on top of the first lid 150, further enhancing mechanical stability. This second lid 750 is secured using an adhesive 204 or through bonding methods like thermal compression bonding, fusion bonding, laser bonding or direct bonding. The second lid 750 may comprise receiving features or grooves 756 on its bottom surface, designed to securely receive and align the guide pins 154.

[0140] In some embodiments, the receiving features 756 on the bottom of the second lid 750 may be implemented as grooves or trenches, analogous to the trenches 148 described for the upper surface 744. These receiving features 756 may be formed on the bottomsurface of the lid 750 and can span along its length. In certain embodiments, the receiving feature 756 may extend across the entire length of the lid 750, while in other embodiments, the receiving feature 756 may extend only partially into the lid 750.

[0141] The dimensions and geometry of these receiving features 756 can be constructed such to facilitate optimal alignment and secure positioning of the guide pins 154. For instance, the receiving features 756 may have a width and depth that allows to easily receive and secure the guide pins 154, with the side edge positioned closer to the center of the lid 750 spaced at a specific distance from the center, enabling accurate alignment with the waveguide array 155 and the optical fiber.

[0142] Furthermore, the guide pins 154 extend outwardly from the glass substrate body 742 through receiving features or trenches 148 formed on the upper surface 144. These trenches 148 enable accurate alignment with the waveguide array 155. In some embodiments, the guide pins 154 may be provided having a thickness of 550 m, and where the trench 148 have atrench width 151A of 250 m, and the trench may have a depth 151B of 30 m. The trench widthis dependent on the depth of the waveguide and can be smaller or larger. Additionally, the trench may comprise a length of approximately 5 mm to permit approximately 5 mm of the guide pin to be received. The trenches 148 may be offset at 5.3 mm increments, measured from a side edge of a trench to the same respective side edge of an adjacent trench.

[0143] The assembly 700 further allows for various embodiments and modifications. Alternative lid configurations, materials, or bonding methods could be explored for the lids 150 and 750. The mode-modifying element 302 can be tailored for different waveguide materials or integrated photonic device platforms by optimizing its refractive index and geometric profile, enabling adaptation across diverse applications.

[0144] FIG. 9 illustrates a perspective view of a glass substrate assembly 800, where guide pins 154 are received within a connector housing 760. This configuration represents an embodiment where the assembly 800 is coupled to optical fibers 768 through the connector housing 760, facilitating optical coupling between the fibers 768 and integrated waveguides within the assembly 800.

[0145] The assembly 800 comprises a substrate body 742 with an upper surface 744 and an edge 746. The second lid 750 is positioned on the upper surface 744. In the embodiment shown, the first glass lid (not visible) is present beneath the second lid 750, covering the one or more waveguide(s) and a mode-modifying element.

[0146] In some embodiments, the assembly 800 may comprise only a single lid assembly instead of a two-lid assembly. In such configurations, the single lid would cover the integrated waveguides, along with the guide pins, and mode-modifying.

[0147] The mode-modifying element is applied to reshape the waveguide mode profile to more closely align with the mode of the optical fibers 768, thereby reducing mode mismatch and associated optical losses at the fiber-waveguide interface. In one embodiment, the mode-modifying element may have a tapered configuration, gradually transitioning into an air cladding region to provide a smooth mode transition with minimal abrupt changes. In another embodiment, the mode-modifying element may extend continuously across the entire waveguide length in an extended configuration, eliminating air-cladding interfaces altogether.

[0148] The connector housing 760 securely holds the optical fibers 768, restricting their movement relative to the housing. The connector housing 760 comprises one or more guide holes 764, which may extend completely through the housing or partially into the housing. Theseguide holes 764 receive the second ends of the guide pins 154 extending outwardly from the substrate body 742.

[0149] As the guide pins 154 are received within the guide holes 764, the movement of the assembly 800 is constrained relative to the connector housing 760. This constraint helps facilitate alignment between the optical fibers 768 and the waveguides within the assembly 800 to aid in efficient optical coupling. This coupling between the assembly 800 and the connector housing 760 is achieved at the interface 752, where the waveguide mode is reshaped with the aid of the mode modifying element to closely align with the optical fibers 768.

[0150] The assembly 800 and the connector housing 760 permit alignment, while the mode-modifying element enables optimal mode-matching for low-loss optical coupling. In certain embodiments, a single optical fiber 768 may connect to a single waveguide, while in other embodiments, multiple optical fibers 768 may align with multiple waveguides simultaneously, accommodating various fiber and waveguide array configurations.

[0151] While FIG. 9 depicts a specific configuration, the assembly 800 and connector housing 760 can incorporate various embodiments and modifications, such as alternative lid configurations, waveguide geometries, mode-modifying element materials and configurations (e.g., tapered or extended), and bonding methods, enabling optimization for diverse applications in optical interconnects, telecommunications, and data communications.

[0152] Various approaches may be taken to create an assembly for aligning an optical fiber with an optical waveguide. FIG. 10 is one example flow chart illustrating operations that may be performed to align a fiber with a waveguide. At operation 910, a substrate with integrated optical waveguides, receiving features and a mode modifying element deposited above the optical waveguides may be provided. The substrate may be similar to those described above.At operation 920, a first end of at least one guide pin may be secured into the receiving feature of the waveguide substrate. At operation 930, a first lid is positioned directly on the optical waveguides and mode-modifying element. At operation 940, a second lid is positioned directly above the first lid and using an adhesive to secure the guide pins and the second lid. At operation 950, a connector housing with at least one receiver portion defining a recess is provided. At operation 960, the second end of the guide pins are inserted into the recess of the receiver portion of the connector housing to align the optical fiber with the optical waveguides. The operations described herein may be performed in any order unless otherwise noted. Further, additional operations may be performed (such as separating the connector housing and substrate), and some operations may be omitted.

[0153] It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications, and equivalent arrangements.

Claims

WHAT IS CLAIMED IS:

1. An assembly for aligning an optical fiber with an optical waveguide, the assembly comprising: a glass substrate comprising at least one optical waveguide configured to support a waveguide mode, the waveguide mode having a first light pattern, wherein the at least one optical waveguide defines an end at an edge of the glass substrate, wherein the optical fiber is configured to be positioned adjacent to the edge to align with the at least one optical waveguide to receive light therefrom or transfer light thereto, wherein the optical fiber supports a fiber mode, the fiber mode having a second light pattern; and a mode-modifying element disposed on a surface of the glass substrate covering the end of the at least one optical waveguide at the edge of the glass substrate, wherein the mode-modifying element is configured to modify the first light pattern of the waveguide mode to more closely align with the second light pattern of the fiber mode to reduce optical losses between the at least one optical waveguide and the optical fiber.

2. The assembly of claim 1, further comprising a photonic integrated circuit (PIC) positioned on the glass substrate, wherein the optical fiber is configured to be positioned adjacent to the edge to align with the at least one optical waveguide to receive light from the PIC or transfer light to the PIC, and wherein the mode-modifying element is configured to reduce optical losses at interfaces between the optical fiber, the at least one optical waveguide, and the PIC.

3. The assembly of claim 2, wherein the interface comprises: a first interface between the optical fiber and the at least one optical waveguide at the edge of the glass substrate; and a second interface between the at least one optical waveguide and the PIC.

4. The assembly of any of claims 1-3, further comprising a lid positioned on the mode- modifying element and the at least one optical waveguide, wherein the lid is configured to provide a protective covering for the at least one optical waveguide and the mode-modifying element.

5. The assembly of any of claims 1-4, wherein the mode-modifying element is disposed proximate to the at least one optical waveguide in an extended configuration over an entire length of the at least one optical waveguide.

6. The assembly of any of claims 1-5, wherein the mode-modifying element comprises a material having a refractive index that is the same or below the glass within a range of 0.05, or below the effective index of the waveguide mode to prevent leakage of light from the at least one optical waveguide.

7. The assembly of any of claims 1-6, wherein the mode-modifying element is any one of an optical adhesive, optical glass, a combination of an adhesive and a glass, a polymer, or a deposited thin film.

8. The assembly of any of claims 1-7, wherein the mode-modifying element is configured to modify the first light pattern of the waveguide mode to match the second light pattern of the fiber mode to produce a coupling loss of 0.2 dB or lower.

9. The assembly of any of claims 1-7, wherein the mode-modifying element is configured to modify the first light pattern of the waveguide mode to match the second light pattern of the fiber mode to produce a coupling loss of 0.1 dB or lower.

10. The assembly of any of claims 1-9, further comprising at least one guide pin positioned in a receiving feature of the glass substrate, wherein the at least one guide pin extends outwardly from the glass substrate.

11. The assembly of claim 10, wherein the receiving feature is a trench, wherein the trench comprises two side edges and a bottom surface, and wherein the trench is configured so that the at least one guide pin rests against the two side edges without contacting the bottom surface.

12. The assembly of any of claims 10-11, further comprising a second lid configured to secure the at least one guide pin within the receiving feature, wherein the second lid is positioned adjacent to the first lid.

13. The assembly of claim 11, wherein the trench is formed using a laser-based or chemical etching, or combination approach.

14. A system for aligning an optical fiber with an optical waveguide, the system comprising: the optical fiber; a glass substrate comprising at least one optical waveguide configured to support a waveguide mode, the waveguide mode having a first light pattern, wherein the at least one optical waveguide defines an end at an edge of the glass substrate, wherein the optical fiber is configured to be positioned adjacent to the edge to align with the at least one optical waveguide to receive light therefrom or transfer light thereto, wherein the optical fiber supports a fiber mode, the fiber mode having a second light pattern; a mode-modifying element disposed on a surface of the glass substrate covering the end of the at least one optical waveguide at the edge of the glass substrate, wherein the mode-modifying element is configured to modify the first light pattern of the waveguide mode to more closely align with the second light pattern of the fiber mode to reduce optical losses between the at least one optical waveguide and the optical fiber; at least one guide pin defining a first end and a second end; and the glass substrate further comprising a receiving feature configured to receive and connect the first end of the at least one guide pin, wherein the second end for the at least one guide pin extends outwardly from the glass substrate; and a connector housing configured to receive the optical fiber comprising:at least one receiver portion extending from a first side to a second side, the at least one receiver portion defining a recess, wherein the recess of the at least one receiver portion is configured to receive the at least one guide pin to cause alignment of the optical fiber with the one or more optical waveguides and restrain movement of the optical fiber relative to the waveguide substrate.

15. The system of claim 14 further comprising a photonic integrated circuit (PIC) disposed on the glass substrate, wherein the optical fiber is configured to be positioned adjacent to the edge to align with the at least one optical waveguide to receive light from the PIC or transfer light to the PIC, and wherein the mode-modifying element is configured to reduce optical losses at interfaces between the optical fiber, the at least one optical waveguide, and the PIC.

16. The system of claim 15, wherein the interfaces comprise: a first interface between the optical fiber and the at least one optical waveguide at the edge of the glass substrate; and a second interface between the at least one optical waveguide and the PIC.

17. The system of any of claims 14-16 further comprising a lid positioned on the mode- modifying element and the at least one optical waveguide, wherein the lid is configured to provide a protective covering for the at least one optical waveguide and the mode-modifying element.

18. The system of any of claims 14-17, wherein the mode-modifying element comprises a material having a refractive index that is the same or below the glass within a range of 0.05, or below the effective index of the waveguide mode of the glass substrate to prevent leakage of light from the at least one optical waveguide.

19. The system of any of claims 14-18, wherein the mode-modifying element is any one of an optical adhesive, optical glass, a combination of an adhesive and a glass, a polymer, or a deposited thin film.

20. The system of claim 14, wherein the receiving feature is a trench, wherein the trench comprises two side edges and a bottom surface, and wherein the trench is configured so that the at least one guide pin rests against the two side edges without contacting the bottom surface.

21. The system of claim 19, wherein the trench is formed using a laser-based approach.

22. A method of manufacturing an assembly for aligning an optical fiber with an optical waveguide, the method comprising: providing a glass substrate comprising at least one optical waveguide configured to support a waveguide mode, the waveguide mode having a first light pattern; disposing a mode-modifying element on a surface of the edge of the glass substrate covering an end of the at least one optical waveguide, wherein the mode- modifying element is configured to modify the first light pattern of the waveguide mode to more closely align with a second light pattern of a fiber mode of the optical fiber so as to reduce optical losses between the at least one optical waveguide and the optical fiber.

23. The method of claim 22 further comprising: positioning a lid on the mode-modifying element and the at least one optical waveguide, wherein the lid is configured to provide a protective covering for the at least one optical waveguide and the mode- modifying element.

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