Photonic system

Abstract

The present disclosure provides a photonic system, comprising: a PIC comprising a first SiN waveguide; and a second SiN waveguide vertically tapered by increasing thickness in a direction towards the first SiN waveguide and vertically tapered by decreasing thickness in a direction away from the first SiN waveguide, wherein: the first SiN waveguide comprises a tapered end having a first effective index n1; and the second SiN waveguide and a third SiN waveguide together form first and second low-index contrast sections of an effective index n2 at the ends, a third high-index contrast section between the first and second low-index contrast sections, the third high-index contrast section having a third effective index n3 and a vertical taper that adiabatically couples the first and second low-index contrast sections to the third high-index contrast section, n3 is close to n1 and n3 > n2, and the tapered end of the first SiN waveguide is optically coupled to the third high-index contrast section.

Description

[0001] This invention application is a divisional application of patent application No. 201880085856.X, entitled "Adiabatic Coupled Photonic System with Vertically Tapered Waveguide", filed on December 6, 2018, with international application number PCT / US2018 / 064329, and entered the Chinese national phase on July 8, 2020.

[0002] Cross-references to related applications

[0003] This application claims the benefit and priority of U.S. Provisional Patent Application No. 62 / 595,463, filed December 6, 2017, which is incorporated herein by reference. Technical Field

[0004] The implementation methods discussed in this article relate to multi-level thermally coupled photonic systems. Background Technology

[0005] Unless otherwise stated herein, the materials described herein are not prior art to the claims of this application and are not acknowledged as prior art by virtue of being included in this section.

[0006] A common solution for coupling light into or out of a silicon (Si) photonic integrated circuit (PIC) includes planar couplers or edge couplers. Edge coupling, starting from the edge of the Si PIC, can be implemented to couple light into or out of the Si PIC. However, edge coupling may require a part shape that is sensitive to variations in efficiency that can result from manufacturing tolerances.

[0007] The subject matter claimed herein is not limited to implementations that address any shortcomings or that operate only in environments such as those described above. Rather, this background is provided merely to illustrate an example technical field in which some of the implementations described herein can be practiced. Summary of the Invention

[0008] This summary is provided to introduce a series of concepts in a simplified form, which will be further described in the detailed description below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to help determine the scope of the claimed subject matter.

[0009] Some of the example implementations described in this article generally involve two-stage thermally coupled photonic systems.

[0010] In an example implementation, the photonic system includes a photonic integrated circuit (PIC) comprising a silicon (Si) waveguide and a first silicon nitride (SiN) waveguide. The photonic system may also include an interposer comprising a second SiN waveguide, the second SiN waveguide comprising a vertical tapered portion by increasing the thickness of the second SiN waveguide in the direction toward the first SiN waveguide to allow optical mode transfer, and decreasing the thickness of the second SiN waveguide in the direction away from the first SiN waveguide to suppress optical mode transfer.

[0011] The Si waveguide may include a second lateral tapered portion to allow optical mode transfer from the Si waveguide to the first SiN waveguide. Furthermore, the first SiN waveguide may include a first lateral tapered portion to allow optical mode transfer from the first SiN waveguide to the second SiN waveguide. A vertical tapered portion on the second SiN waveguide of the interposer may be reduced in thickness away from the first SiN waveguide of the PIC to prevent optical mode transfer from the first SiN waveguide to the second SiN waveguide.

[0012] In another example embodiment, the photonic system may include a silicon (Si) waveguide with a first lateral tapered portion at its termination, the Si waveguide being configured to propagate an optical signal in an optical mode. The system may also include a first silicon nitride (SiN) waveguide including a non-tapered portion configured to adiabatically optically couple an optical signal from the lateral tapered portion of the Si waveguide, the first SiN waveguide further including a second lateral tapered portion at its termination. The system may also include a second SiN waveguide including a first vertical tapered portion to increase the thickness of the second SiN waveguide, the first vertical tapered portion being configured to adiabatically couple an optical signal from the first SiN waveguide to the second SiN waveguide, the second SiN waveguide further including a second vertical tapered portion to reduce the thickness of the second SiN waveguide, thereby suppressing optical coupling with the first SiN waveguide.

[0013] The system may also include a third SiN waveguide configured to optically couple signals from the second SiN waveguide. Furthermore, the SiN waveguide and the first SiN waveguide may be configured as part of a photonic integrated circuit (PIC), and the second and third SiN waveguides may be configured as part of an interposer layer for coupling with the PIC. Additionally, the second and third SiN waveguides may include low-contrast portions configured to couple optical signals fiber-to-fiber. The second SiN waveguide may be vertically tapered between a thickness of approximately 20 nm and approximately 250 nm. The second and third SiN waveguides may be spaced approximately 1 μm apart.

[0014] In another embodiment, a method includes propagating an optical signal in a silicon (Si) waveguide including a first lateral tapered end. Additionally, the method may include: firstly, optically coupling the optical signal from the first lateral tapered end of the Si waveguide to a first silicon nitride (SiN) waveguide including a second lateral tapered end. Furthermore, the method may include: secondly, in response to a second SiN waveguide being vertically tapered to an increased thickness near the second lateral tapered end of the first SiN waveguide, optically coupling the optical signal from the second lateral tapered end of the first SiN waveguide to a third SiN waveguide.

[0015] Additionally, the method may further include: in response to the second SiN waveguide becoming vertical away from the first SiN waveguide, optical signal is optically coupled from the second SiN waveguide to the third SiN waveguide. Furthermore, the second and third SiN waveguides may be high-contrast waveguides, wherein the second SiN waveguide has a thickness of approximately 250 nm and the third SiN waveguide has a thickness of approximately 20 nm, and the second and third SiN waveguides are separated by a distance of approximately 1 μm.

[0016] According to one aspect of this disclosure, a photonic system is also provided, comprising: a PIC including a first SiN waveguide; and a second SiN waveguide vertically tapered by increasing thickness in a direction toward the first SiN waveguide to allow adiabatic optical mode transfer between the first SiN waveguides, and vertically tapered by decreasing thickness in a direction away from the first SiN waveguide to allow adiabatic optical mode transfer between the second SiN waveguide and a third SiN waveguide, wherein: the first SiN waveguide includes a tapered end having a first effective refractive index n1; and the second SiN waveguide... The iN waveguide and the third SiN waveguide together form a first and second low refractive index contrast portion with effective refractive index n2 at both ends, and a third high refractive index contrast portion between the first and second low refractive index contrast portions. The third high refractive index contrast portion has a third effective refractive index n3 and a vertical tapered portion that thermally couples the first and second low refractive index contrast portions to the third high refractive index contrast portion between the first and second low refractive index contrast portions. n3 is close to n1 and n3>n2, and the tapered end of the first SiN waveguide is optically coupled to the third high refractive index contrast portion.

[0017] Additional features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from that description, or may be learned by practice of the invention. The features and advantages of the invention can be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the invention will become more fully apparent from the following description and the appended claims, or may be learned by practice of the invention as set forth below. Attached Figure Description

[0018] To further illustrate the above and other advantages and features of the present invention, a more specific description of the invention will be presented with reference to specific embodiments of the invention shown in the accompanying drawings. It should be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit the scope of the invention. The invention will be described and explained with additional features and details using the drawings.

[0019] Figure 1 This is a three-dimensional view of an example optoelectronic system (hereinafter referred to as the "system").

[0020] Figure 2 yes Figure 1 A side view of an example two-stage adiabatic coupled photonic system (hereinafter referred to as the "photonic system").

[0021] Figures 3A to 3G include Figure 1 and Figure 2 Various views of the different parts of the photon system.

[0022] Figure 4 Graphical representation of simulated optical modes in the intermediate layer waveguide band.

[0023] Figures 5A to 5B A graph showing the relationship between the effective refractive index and modes appearing in the tapered portion of the waveguide is presented.

[0024] Figure 6 The diagram shows a comparison of the tapered section length and coupling efficiency for waveguides in the system.

[0025] Figure 7 The effect of the end dimension of the first SiN waveguide in the system on the coupling loss with the second SiN waveguide is shown.

[0026] Figure 8 include Figure 1 and Figure 2 A view of the various parts of the photonic system according to another embodiment.

[0027] Figure 9 The bonding process for coupling the intermediary layer to the PIC is shown.

[0028] Figure 10 A method for coupling optical signals from a PIC to an SMF is shown. Detailed Implementation

[0029] Some of the implementation methods described herein generally involve light traveling from a silicon (Si) waveguide to an intermediate silicon nitride (Si) waveguide. x N yThis is generally referred to herein as an adiabatic coupling from a SiN waveguide to an interposer waveguide (e.g., a polymer or high-refractive-index glass waveguide), or an adiabatic coupling from an interposer waveguide to a SiN waveguide and then from a SiN waveguide to a silicon (Si) waveguide. For ease of reference in the discussion below, adiabatic coupling is generally discussed in the context of a single Si waveguide-to-SiN waveguide-to-interposer waveguide coupling; however, it should be understood that a given system may include multiple such couplings.

[0030] The Si waveguide can have a first optical mode size, the first SiN waveguide can have a second optical mode size that is substantially larger than the first optical mode size, and the interposer waveguide can have a third optical mode size that is substantially larger than the second optical mode size. For example, the first optical mode size can be about 0.3 μm, or in the range of 0.25 μm to 0.5 μm; the second optical mode size can be about 1 μm, or in the range of 0.7 μm to 3 μm; and the third optical mode size can be about 10 μm, or in the range of 8 μm to 12 μm. The third optical mode size can be substantially similar to the optical mode size of a standard single-mode fiber. For example, a standard single-mode fiber can have an optical mode size of about 10 μm, substantially similar to the third optical mode size.

[0031] Si waveguides can be tapered to a width of approximately 80 nanometers (nm) to increase the size of the optical mode and incorporate it into the cladding of the Si waveguide. A first SiN waveguide can be fabricated on a Si photonic integrated circuit (PIC) including the Si waveguide. The first SiN waveguide can receive light from the inverted Si taper. Similar to the Si waveguide, the first SiN waveguide can be tapered to a width of 80 nm to 300 nm. An interposer waveguide, including a second and third SiN waveguide with a core of approximately 1 μm, can be placed in close optical contact with the first SiN waveguide. Light from the inverted Si waveguide can be progressively and adiabatically coupled to the first SiN waveguide along the propagation direction and then adiabatically coupled to the interposer including the second and third SiN waveguides, and can be completely or substantially completely translated to the interposer. The interposer waveguide can be processed on a separate rigid or flexible substrate and can be attached to the first SiN waveguide using various techniques including thermomechanical attachment or by using a refractive index-matched adhesive. A Si PIC can include modulators, waveguides, detectors, couplers, and other optical components in Si-on-Insulator (e.g., silicon on a box layer of silicon dioxide (SiO2)) on a Si substrate. Integrated circuits (ICs) can be flip-chip bonded (e.g., via copper pillars) to the Si PIC in a portion of the Si PIC away from the first SiN waveguide and where an interposer having a second and third SiN waveguide can be located. The interposer waveguide can be included in the interposer, which can be transparent and / or may have alignment marks to facilitate easy optical alignment of the first SiN waveguide on the Si PIC with the interposer waveguide on the interposer. The interposer waveguide including the second and third SiN waveguides can be passively or actively aligned with the first SiN waveguide.

[0032] A first SiN waveguide can be defined during the fabrication of a Si PIC, wherein a SiN / SiO2 layer portion is added during the Si PIC fabrication process for coupling and passive functionality. A standard Si photonic stack has a Si substrate, a SiO2 oxide layer (referred to as a buried oxide layer (BOX) or SiO2 buried oxide layer), and a Si waveguide layer, wherein the Si waveguide is surrounded by a SiO2 cladding to confine light. The embodiments described herein can add a first SiN layer to this standard stack for two-stage coupling and optionally passive optical functionality. The first SiN layer has a region of a SiN core waveguide surrounded by a SiO2 cladding to confine light. SiN has an intermediate refractive index between that of Si and that of polymers, and thus enables effective thermally adiabatic coupling between two layers with taper widths within the critical dimensions of certain standard complementary metal-oxide-semiconductor (CMOS) wafer fabs. The low loss of SiN and the lower core / cladding refractive index difference of SiN relative to the SiO2 cladding compared to Si and SiO2 enable the fabrication of higher-performance passive components. For example, wavelength division multiplexers (WDM muxes) and demultiplexers (WDM demuxers) in SiN have higher channel isolation than those in Si. Furthermore, the peak wavelength drift of passive components in SiN with temperature is 5 times smaller than that of passive components in Si.

[0033] In some implementations, the transmit (TX) Si waveguide and receive (RX) Si waveguide on the Si PIC can be in a single plane, or accessible at a single-plane interface of the Si PIC, while the MT connector for parallel single-mode fiber can be configured via a multi-source agreement (MSA), where the TX array is in one row and the RX array is in a row below the TX array. TX and RX can also be in the same row but separated from each other. The implementations described herein include an interposer layer that can connect from the first SiN waveguide input / output in the plane of the Si PIC and present itself to, for example, two vertically separated rows of input / output of an MT connector.

[0034] In some embodiments, wavelength division multiplexing or other passive optical functions can be integrated into the same SiN / SiO2 layer forming the first SiN waveguide. Using a SiN / SiO2 layer can be advantageous compared to implementing such optical functions in other layers and / or materials because: due to the low loss of SiN and the small refractive index difference between the core and cladding, the SiN / SiO2 layer can provide lower loss and better channel isolation. Some embodiments described herein can be wavelength-independent in their operating range. For example, some embodiments described herein can be wavelength-independent in their operating range over the 1310 nm standard long-range (LR) standard, while the surface grating coupler can have a relatively narrow passband of 20 nm to 30 nm.

[0035] In some embodiments, light propagating from the Si waveguide to the first SiN waveguide and then to the interlayer comprising the second and third SiN waveguides can travel downwards from the Si waveguide to the first SiN waveguide and then upwards into the interlayer comprising the second and third SiN waveguides. Subsequently, at the interlayer, the light can be coupled into an optical fiber, or the light can propagate along the opposite path. In these and other embodiments, the interlayer waveguide may comprise a polymer or a high-refractive-index glass waveguide having a similar cladding refractive index close to 1.5.

[0036] Numerous embodiments are disclosed in the following discussion. Unless the context otherwise indicates, the various embodiments are not mutually exclusive. For example, unless the context otherwise indicates, part or all of one or more embodiments may be combined with part or all of one or more other embodiments.

[0037] Various aspects of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. It should be understood that the drawings are illustrative and schematic representations of such exemplary embodiments and are not intended to limit the invention, nor are they necessarily drawn to scale.

[0038] Figure 1 This is a perspective view of an example optoelectronic system 100 (hereinafter referred to as "System 100") arranged according to at least one embodiment described herein. As shown, System 100 includes a Si PIC 102, an interposer 104, a three-dimensional (3D) stacked region 106, and a flip-chip integrated circuit (IC) 108. The Si PIC 102 and the interposer 104 together form a two-stage thermally adiabatic coupled photonic system 200 (hereinafter referred to as "Photonic System 200").

[0039] Typically, a Si PIC 102 may include one or more optical elements, such as modulators, waveguides, couplers, or other optical elements, on a silicon-on-insulator substrate.

[0040] Typically, the 3D stacked region 106 can provide electrical connections to one or more active optical components in the Si PIC 102. Therefore, the 3D stacked region 106 may include, for example, metallized pillars, traces and / or contacts, as well as insulating dielectrics and / or other materials and elements.

[0041] Typically, the flip-chip bonded IC 108 may include one or more active and / or passive electronics that can be communicatively coupled to one or more active optical components of the Si PIC 102 via the 3D stacking region 106.

[0042] Interposer 104 can be mechanically coupled to Si PIC 102, or layer deposition can be used to integrally form interposer 104 and Si PIC 102. The interposer SiN waveguide of interposer 104, as well as the SiN waveguide and Si waveguide of Si PIC 102, can be configured to thermally couple light into or out of Si PIC 102. As used herein, in the transition interaction region—sometimes referred to herein as the thermally adiabatic coupler region—light can be thermally coupled from one optical component or device (referred to herein as the “initial state” waveguide) to another optical component or device (referred to herein as the final state waveguide). To transfer optical power from the initial state waveguide to the final state waveguide, one or more optical properties of one or both of the initial state waveguide and the final state waveguide, such as width, height, effective refractive index, etc., vary along the optical axis. In this paper, the initial-state waveguide and the final-state waveguide form a system within the transition interaction region, and the light remains in a single mode of the joint system during the physical transition from the initial-state waveguide to the final-state waveguide. The initial-state waveguide and the final-state waveguide can correspond to Si waveguides and SiN waveguides, respectively, and vice versa. Alternatively, the initial-state waveguide and the final-state waveguide can correspond to SiN waveguides and Si waveguides, respectively. Alternatively, the initial-state waveguide and the final-state waveguide can correspond to SiN waveguides and intermediate layer waveguides, respectively, and vice versa. Alternatively, when two components are configured as described herein to form an adiabatic coupler region, the two components can be considered adiabatic coupled together or adiabatic coupled to each other.

[0043] Furthermore, in this document, "light" is generally used to refer to electromagnetic radiation of any suitable wavelength, and light can include light with wavelengths of, for example, about 800 nm to 900 nm, 1200 nm to 1360 nm, 1360 nm to 1460 nm, 1530 nm to 1565 nm, or other suitable wavelengths. Light can also have TE or TM polarization.

[0044] In these and other embodiments, the SiN waveguide in Si PIC 102 can be aligned with and optically coupled to the SiN waveguide in interposer 104. Additionally, the interposer waveguide in interposer 104 can be aligned with and optically coupled to the SiN waveguide in Si PIC 102. The Si waveguide can have a first refractive index n1. The SiN waveguide can have a second refractive index n2. The interposer SiN waveguide can have a third refractive index n3. Typically, the second refractive index n2 of the SiN waveguide is between the first refractive index n1 of the Si waveguide and the third refractive index n3 of the interposer SiN waveguide. Furthermore, n1 > n2 > n3. In some implementations, for a two-stage thermally coupled photonic system with three waveguides, each waveguide has a corresponding refractive index of n1, n2, n3, where the first refractive index n1 can be in the range of 3 to 3.5, the second refractive index n2 can be in the range of 1.8 to 2.2, and the third refractive index n3 can be in the range of 1.49 to 1.6.

[0045] Additionally, the interposer SiN waveguide in interposer 104 can be aligned with and optically coupled to one or more inputs and / or outputs for optical signals. Example input sources may include optical signal sources (e.g., lasers), optical fibers, fiber optic connectors, lenses, or other optical components or devices to which incoming optical signals (e.g., signals directed toward the Si PIC 102) are provided from these example input sources to interposer 104 for input to the Si PIC 102. Example output devices to which outputs can be sent may include lasers, optical receivers (e.g., photodiodes), optical fibers, fiber optic connectors, lenses, or other optical components or devices to which outgoing signals (e.g., signals leaving the Si PIC 102) can be provided through interposer 104. One or more active optical components of the Si PIC 102 can generate outgoing signals or can be sources of outgoing signals output from the photonics system 200 via Si waveguides, SiN waveguides, and interposer waveguides. Alternatively or additionally, one or more active optical components of the Si PIC 102 may be configured to receive and process incoming signals input to the photonic system 200 via intermediate layer waveguides, SiN waveguides, and Si waveguides.

[0046] Figure 2 It is arranged according to at least one embodiment described herein. Figure 1 A side view of the photonic system 200. The photonic system 200 includes a Si PIC 102 and an interposer layer 104. Figure 2 Additionally, a 3D stacked region 106 is shown.

[0047] The Si PIC 102 includes: a Si substrate 202, a SiO2 buried oxide layer 204, a first layer 206 including one or more SiN waveguides 208, and a second layer 210 including one or more Si waveguides 212. In the illustrated embodiment, both the first layer 206 and the second layer 210 are formed over the SiO2 buried oxide layer 204. Specifically, the first layer 206 is formed on (or at least over) the second layer 210, and the second layer 210 is formed on (or at least over) the SiO2 buried oxide layer 204. Alternatively or additionally, a SiN slab 214 may be formed between the first layer 206 and the second layer 210, at least in the region where the Si waveguides 212 are optically coupled to the first SiN waveguide 208. In an example implementation, the first SiN waveguide 208 includes Si3N4 as a waveguide core, which is surrounded along its length by SiO2 or other suitable waveguide cladding on at least both sides.

[0048] Despite Figure 2 Not shown, but the Si PIC 102 may also include one or more active optical components formed in the second layer 210. In these and other embodiments, the Si PIC 102 may also include one or more dielectric layers 216 formed on and / or above the second layer 210 and one or more metallization structures 218 formed in the dielectric layers 216. The metallization structures 218 may extend from the top of the Si PIC 102 through the dielectric layers 216 to make electrical contact with active optical components formed in the second layer 210 or elsewhere in the Si PIC 102. The dielectric layers 216 may include SiO2 or other suitable dielectric materials. The dielectric layers 216 and the metallization structures 218 are generally examples of the 3D stacked region 106.

[0049] Combined with reference Figure 1 and Figure 2 The flip-chip bonded IC 108 can be flip-chip bonded to the 3D stacking region 106. The flip-chip bonded IC 108 may include one or more active and / or passive electronic devices that can be communicatively coupled to one or more active optical components formed in the second layer 210 of the Si PIC 102 via the 3D stacking region 106.

[0050] Intermediate layer 104 may include waveguide strips 222, which include one or more intermediate layer waveguides 224. Each waveguide strip 222 includes: a first intermediate layer core waveguide, designated herein as a second SiN waveguide 224A; an intermediate layer cladding 225 having a different refractive index; and a second intermediate layer core waveguide, designated herein as a third SiN waveguide 224B. The coupler portion of the second SiN waveguide 224A of the intermediate layer may be disposed above and aligned with the lateral tapered end of the first SiN waveguide 208 in the first layer 206, as will be described in more detail below.

[0051] The Si waveguide 212 (or more specifically, the core of the Si waveguide 212) may have the first refractive index n1 mentioned above. The SiN waveguide 208 (or more specifically, the core of the SiN waveguide 208) may have the second refractive index n2 mentioned above. The intermediate layer waveguide strip 222 (or more specifically, the second SiN waveguide 224A and the third SiN waveguide 224B) may have the third refractive index n3 mentioned above, where n1>n2>n3. Figure 2 The spatial separation of the intermediate layer 104 from the Si PIC 102 illustrates the separation of functional entities, because in at least one embodiment, the intermediate layer 104 can be formed directly on the Si PIC 102 using, for example, a deposition process.

[0052] Figures 3A to 3G Including arrangements according to at least one embodiment described herein Figure 2 Various views of parts of the photonic system 200. In particular, Figure 3A Including top view 300A and longitudinal section view 300B, and Figure 3B Included in respectively by Figure 3A The reference lines 1 to 8 in the diagram represent lateral cross-sections 300C to 300H at some locations.

[0053] According to Figure 3A The xyz coordinate axes are arbitrarily defined in each of views 300A to 300B and in other figures provided herein. Figure 3A Top view 300A shows the relative x-axis and z-axis alignment of the various components with respect to each other. Since all views 300C to 300H have the same orientation, therefore... Figure 3BAll views 300C to 300H provide a single instance of the xyz coordinate axes. The x-direction may sometimes be referred to as the lateral or transverse direction, and terms such as width, transverse, lateral, side, side, etc., may be used to refer to, for example, dimensions, relative positions, and / or movement along the x-direction, unless the context otherwise specifies. The y-direction may sometimes be referred to as the vertical direction, and terms such as height, thickness, vertical, vertically, above, below, up, down, etc., may be used to refer to, for example, dimensions, relative positions, and / or movement along the y-direction, unless the context otherwise specifies. The z-direction may sometimes be referred to as the longitudinal or light propagation direction, and terms such as length, longitudinal, upstream, downstream, forward, backward, front, back, etc., may be used to refer to, for example, dimensions, relative positions, and / or movement along the z-direction, unless the context otherwise specifies.

[0054] Figure 3A The longitudinal section diagram 300B shows example material stacks for various components. Figure 3A The top view 300A includes the outlines or footprints of the individual components at different levels in the material stack. These components may not necessarily be visible when viewed from above, but are shown as outlines or footprints to illustrate the x-alignment and z-alignment of the individual components relative to each other.

[0055] Figure 3A The portion of the photonic system 200 shown in the top view 300A includes a tapered end of a Si waveguide 212. The tapered end of the Si waveguide 212 is relatively wider at reference line 1 than at reference line 2. The tapered end of the Si waveguide 212 can be considered to have a tapered portion or an inverted tapered portion, which are structurally equivalent. As used herein, a waveguide, for example... Figure 3A The Si waveguide 212 in the diagram can be considered to have a tapered portion relative to the outgoing optical signal—for example, an optical signal that enters the waveguide at a relatively wide portion and propagates through the waveguide toward a relatively narrow portion. In contrast, waveguides, for example... Figure 3A The Si waveguide 212 in the diagram can be considered to have an inverted tapered portion relative to the incoming optical signal—for example, an optical signal propagating through the waveguide and exiting it in a direction from narrower to wider. For the sake of simplicity in the following discussion, the term "tapered portion" and its variations should be broadly understood as the variation of the waveguide width along the optical axis. In some embodiments, it may be advantageous to vary the waveguide width linearly or nonlinearly along the optical axis, or in a piecewise manner that is both linear and nonlinear. The width of the tapered portion around the interaction region of the initial-state and final-state waveguides can be varied to optimize coupling or reduce the length of the coupling region to produce physically smaller devices.

[0056] A Si waveguide 212, including a tapered end, can be formed in the second layer 210 and positioned below the first layer 206, which includes the first SiN waveguide 208. For example, the second layer 210 can be positioned below a SiN plate 214, which in turn is positioned below the first layer 206. Figure 3B As shown in view 300C, within the second layer 210, SiO2 can typically be arranged adjacent to the sides of the Si waveguide 212 (e.g., in the positive x and negative x directions) to form a cladding for the Si waveguide 212 serving as the core. In some embodiments, the Si waveguide 212 of the Si PIC 102 and / or other Si waveguides can have a thickness t of approximately 0.3 μm (e.g., in the y direction). Si And a refractive index of approximately 3.4. The specific values ​​of refractive index, thickness, width, length, and other values ​​provided herein are provided by way of example only, and values ​​other than those explicitly stated may still fall within the range of the described embodiments.

[0057] like Figure 3A As shown, the SiN plate 214 may be formed on or otherwise located on the second layer 210 including the Si waveguide 212. In some embodiments, the SiN plate 214 may have a thickness of approximately 0 nm to 50 nm (e.g., in the y-direction).

[0058] Figure 3A View 300B also shows a first SiN waveguide 208. The first SiN waveguide 208 includes both a coupler portion and a tapered end. The coupler portion of the first SiN waveguide 208 typically includes the portion of the first SiN waveguide 208 between reference line 1 and reference line 3, and the tapered end of the first SiN waveguide 208 typically includes the portion of the first SiN waveguide 208 between reference line 4 and reference line 5. The tapered end of the first SiN waveguide 208 is relatively wider at reference line 4 than at reference line 5.

[0059] Within the first layer 206, SiO2 can typically be arranged adjacent to the sides of the first SiN waveguide 208 (e.g., in the positive x and negative x directions) to serve as the cladding of the first SiN waveguide 208, as in... Figure 3B View 300C to Figure 3E As shown in view 300F. In some embodiments, the first SiN waveguide 208 and / or other SiN waveguides of the first layer 206 may have a thickness of approximately 0.5 μm to 1 μm (e.g., in the z-direction) and a refractive index of about 1.99.

[0060] from Figure 3AAs can be seen, although the first SiN waveguide 208 is displaced relative to the Si waveguide 212 in the y direction, the tapered end of the Si waveguide 212 can be aligned with the coupler portion of the first SiN waveguide 208 (basically between reference line 1 and reference line 2) in the x and z directions, so that the tapered end of the Si waveguide 212 establishes the coupler portion of the SiN waveguide 208 in the x and z directions (as seen in view 300A) and is parallel to it (as seen in view 300B).

[0061] Figure 3A An intermediate waveguide strip 222 is also shown. The intermediate waveguide strip 222 includes a second SiN waveguide 224A, a cladding 225, and a third SiN waveguide 224B. The second SiN waveguide 224A includes: a first vertical tapered portion (generally between reference line 2 and reference line 4), a high-contrast coupler portion (generally between reference line 4 and reference line 6), a second vertical tapered portion (generally between reference line 6 and reference line 7), and a low-contrast fiber coupler portion (generally extending beyond reference line 7).

[0062] The photonic system 200 includes a first optical mode portion, typically located to the left of reference line 1, in which an optical signal propagates in an optical mode within Si waveguide 212. The photonic system 200 includes a first coupler portion, typically located between reference lines 1 and 2, within PIC 102, in which the optical mode of the optical signal in Si waveguide 212 is transferred to a first SiN waveguide 208. The photonic system 200 includes a second coupler portion, typically located between reference lines 4 and 5, in which the optical mode of the optical signal in the first SiN waveguide 208 is transferred to a second SiN waveguide 224A in interposer 104. The photonic system 200 also includes a second optical mode portion, typically located between reference lines 5 and 7, in which the optical signal propagates in an optical mode. The photonic system 200 also includes a third coupler section, typically located between reference line 7 and reference line 8, in which the optical signal is converted into fiber mode in both the second Sin waveguide 224A and the third SiN waveguide 224B.

[0063] Intermediate waveguide strip 222 includes intermediate waveguides 224A and 224B, and typically includes portions of intermediate waveguides 224A and 224B between reference line 1 and reference line 8, and may extend away from the coupler portion (e.g., to...). Figure 3A (Right side). Intermediate waveguides 224A and 224B can be formed and thus coupled together with one or more potential other intermediate waveguides to... Figure 2The Si PIC 102. In some embodiments, the intermediate waveguide 224A may have a thickness t (e.g., in the y-direction) varying between, for example, 20 nm and 250 nm. 224A Furthermore, the refractive index of the intermediate waveguide 224A is approximately 1.986, and the refractive index of the intermediate cladding 225 is approximately 1.446. The intermediate waveguide 224B may have a thickness t of, for example, 20 nm (e.g., in the y-direction). 224B Furthermore, the refractive index of intermediate waveguide 224B is approximately 1.986, and the refractive index of intermediate cladding 225 is approximately 1.446. Additionally, the refractive indices of intermediate waveguides 224A and 224B are greater than that of intermediate cladding 225, and intermediate waveguides 224A and 224B can have an effective refractive index in the range of 1.50 to 1.65. The effective refractive index is defined as the overlap integral of the refractive index distribution of the waveguide with the optical field. Consider a SiN waveguide with a SiO2 cladding. Importantly, since a large portion of the optical mode overlaps with the surrounding lower refractive index SiO2, the effective refractive index decreases as the width of the SiN waveguide tapers. Note that the lower limit of the effective refractive index range of the intermediate waveguide mode is determined by the minimum taper end width provided by the SiN fabrication process, which is assumed here to be on the order of 200 nm. For example, the minimum taper end width of the SiN waveguide could be 180 nm. If this process allows for a smaller end width of the SiN waveguide, it will correspondingly allow for a lower refractive index of the interposer. This is because an adiabatic coupling transition occurs when the effective refractive index of the SiN waveguide and the effective refractive index of the interposer waveguide are essentially the same. Reducing the end width of the SiN waveguide lowers its effective refractive index, thus resulting in a lower refractive index for the interposer material.

[0064] from Figure 3A As can be seen, although the second intermediate waveguide 224A and the third intermediate waveguide 224B are displaced relative to the first SiN waveguide 208 in the y direction, the coupler portions of the intermediate SiN waveguides 224A and 224B are still aligned with the tapered end of the first SiN waveguide 208 in the x and z directions, such that the coupler portion of the intermediate waveguide 224A overlaps with the tapered end of the SiN waveguide 208 (as seen in view 300A) and is parallel to it (as seen in view 300B).

[0065] Figure 3B Views 300C to 300H depict the tapered ends of each of Si waveguide 212 and SiN waveguides 208 and 224A, and SiN waveguide 224B, respectively. Figure 3AThe width (e.g., in the x-direction) at reference lines 1 to 8. For example, as can be seen from view 300C, the width of Si waveguide 212 is approximately 0.32 μm at reference line 1. Si1 Tapered to a width of approximately 0.08 μm (or 80 nm) at reference line 2. Si2 Additionally, the thickness of the second SiN waveguide 224A varies from approximately 20 nm. 224A1 Tapering (i.e., vertically increasing) to an intermediate thickness t less than 0.25 μm. 224A3 Furthermore, the thickness of the third SiN waveguide 224B remains constant at approximately 20 nm throughout all reference lines 1 to 8. The oxide SiO2 225 separating the second SiN waveguide 224A and the third SiN waveguide 224B remains constant at approximately 1 μm throughout all reference lines 1 to 8.

[0066] Furthermore, as can be seen from views 300E and 300F, the width of the first SiN waveguide 208 extends from approximately 1.0 μm at reference line 4. SiN1 Tapered to a width of approximately 0.20 μm (or 200 nm) at reference line 5. SiN2 As another design example, the width w is at reference line 4. SiN1 It can be approximately 1.5 μm, tapered to a width of approximately 0.08 μm at reference line 5. SiN2 .

[0067] The tapered ends of Si waveguide 212 and SiN waveguide 208 provide an adiabatic transition for optical signals propagating from Si waveguide 212 to the first SiN waveguide 208 and from the first SiN waveguide 208 to the second SiN waveguide 224A, or for optical signals propagating in the opposite direction. The adiabatic transition can be achieved by changing the structure and / or effective refractive index of the tapered ends of Si waveguide 212 and the first SiN waveguide 208 in a sufficiently slow manner, so that when light is incident on the tapered end, it does not scatter from its mode, and when it leaves the tapered end and enters the coupler portion of the second SiN waveguide 224A on the interposer layer, it continues to propagate in the same mode. That is, light can undergo a gradual transition between the tapered ends of Si waveguide 208 or the first SiN waveguide 212 and the adjacent coupler portions of the first SiN waveguide 208 or the second SiN waveguide 224A with a y-axis shift, such that the mode does not change and no significant light scattering occurs. Therefore, the tapered end of the Si waveguide 212, which is coupled to the coupler portion of the first SiN waveguide 208, is an example of an adiabatic coupler region. The tapered end of the first SiN waveguide 208 and the coupler portion of the second SiN waveguide 224A are another example of an adiabatic coupler region.

[0068] Furthermore, as can be seen from views 300G and 300H, the thickness t of the second SiN waveguide 224A is from line 6 to line 7. 224A6 The thickness t at reference line 6 is approximately 250 nm. 224A6 The thickness t, tapered to approximately 20 nm at reference line 7. 224A7 The second SiN waveguide 224A and the third SiN waveguide 224B are composed of a thickness t. SiO1 Separated by SiO2 particles of approximately 1 μm.

[0069] Furthermore, according to view 300H, from extending to Figure 3A Starting from reference line 7 on the right, the second SiN waveguide 224A and the third SiN waveguide 224B participate in optical coupling, so that SiN waveguides 224A and 224B participate in the conversion from optical mode to fiber mode for coupling to fiber such as single-mode fiber (SMF) 390.

[0070] like Figures 3A to 3G As shown, the second SiN waveguide 224A is tapered or varied in thickness. This variation in waveguide thickness provides a higher refractive index interlayer, which ensures an improved effective refractive index matching the first SiN waveguide 208 of the Si PIC102. Furthermore, this variation in waveguide shape improves TM mode coupling performance. Additionally, thermally adiabatic tapered portions are required for coupling between the Si waveguide 212 and the first SiN waveguide 208, and for coupling between the first SiN waveguide 208 and the second SiN waveguide 224A. Such tapered portions can terminate with a finite end dimension that can be varied with process control. Tapering and reverse tapering of the waveguide thickness are more resistant to process variations. Furthermore, adjusting the waveguide thickness can further provide a better coefficient of thermal expansion (CTE).

[0071] A technique for thickness taper of waveguides, such as the second SiN waveguide 224A, can be performed using the following techniques: an example of such techniques could be LioniX's TriPleX. TM Process.

[0072] In operation, the structure, refractive index, and / or other properties of an optical medium determine its effective refractive index. The effective refractive index is somewhat analogous to energy levels in quantum mechanics. A higher effective refractive index is analogous to a lower energy level. Therefore, given two adjacent optical media with different effective refractive indices, light tends to propagate through the medium with the higher effective refractive index.

[0073] In the embodiments described herein, and particularly with reference to Figures 3A to 3GSi waveguides typically have a higher effective refractive index than SiN waveguides. By taperling the ends of a Si waveguide, the effective refractive index can decrease along the length of the taper until the effective refractive index of the Si waveguide approximately matches that of a y-axis-shifted SiN waveguide, or even becomes less than that of the SiN waveguide, for example in... Figures 3A to 3G As shown in the diagram. Therefore, light propagating through Si waveguide 212 and exiting through its tapered end can leave the tapered end of Si waveguide 212 and enter the first SiN waveguide 208 near the point where the effective refractive index of the tapered end of Si waveguide 212 matches the effective refractive index of the first SiN waveguide 208. Similarly, the first SiN waveguide 208 can be tapered at its ends until its effective refractive index approximately matches or even becomes less than the effective refractive index of the y-axis-displaced third SiN waveguide 224B, for example, in... Figures 3A to 3G As shown in the diagram. Therefore, light propagating through the first SiN waveguide 208 and exiting through its tapered end can leave the tapered end of the first SiN waveguide 208 and enter the second SiN waveguide 224A on the interposer near the point where the effective refractive index of the tapered end of the first SiN waveguide 208 matches the effective refractive index of the second SiN waveguide 224A.

[0074] Such fine dimensions may be achievable for some foundries / manufacturers and / or may be inconsistent with their existing processes. Additionally, smaller Si waveguides typically have higher insertion losses than relatively larger Si waveguides, making them disadvantageous. The thermal coupling length between Si waveguides and polymer waveguides can be on the order of 2 mm, at which point such narrow Si waveguides will introduce unwanted optical losses.

[0075] The embodiments described herein achieve two-stage adiabatic coupling, wherein the first SiN waveguide has an intermediate refractive index between the refractive index of the Si waveguide and the refractive index of the second SiN waveguide. This allows the effective refractive index of the Si waveguide to be matched to the effective refractive index of the second SiN waveguide by fabricating a larger SiN waveguide and / or its tapered end. This larger size can be achieved by the wafer fab / manufacturer and allows the use of a larger, lower-loss SiN waveguide. Here, the adiabatic coupling length from the Si waveguide to the first SiN waveguide can be very small, for example, from about 50 μm to 200 μm. In this case, the higher loss of a small, approximately 80 nm wide Si waveguide does not introduce significant loss, and this loss is significantly less than the loss of a narrower Si waveguide of 2 mm or more as described above. The adiabatic coupler region between the first and second SiN waveguides can be about 2 mm, wherein the lower loss of the second SiN waveguide relative to the first Si waveguide results in less loss compared to direct adiabatic coupling between the Si waveguide and the interposer waveguide.

[0076] Figure 4 include Figure 3G A graphical representation of the simulated optical modes of TE and TM polarized light in the intermediate layer waveguide strip 222, including the second SiN waveguide 224A and the third SiN waveguide 224B. Figure 402 shows... Figure 3G A diagram showing the TE mode coupling between the SMF 390 and the intermediate waveguide strip 222. As shown, the TE mode is coupled to the SMF with approximately 85% mode overlap, which corresponds to approximately 0.7 dB. Furthermore, Figure 404 shows... Figure 3G The diagram shows the TM mode coupling between the SMF 390 and the intermediate waveguide strip 222. As shown, the TM mode is coupled to the SMF with approximately 92% mode overlap, which corresponds to approximately 0.36 dB.

[0077] Figure 5A It shows the relationship with Figure 3A The effective refractive index and mode-related diagrams appear between reference numerals 4 and 5 in the figures. Mode distribution diagram 504 shows the modes in the second SiN waveguide 224A, and mode distribution diagram 506 shows the modes in the first SiN waveguide 208. Note that the second SiN waveguide 224A is shown as a cross-sectional view of the waveguide, while the first SiN waveguide 208 is shown as a top view to illustrate the taper relationship between the two waveguides.

[0078] exist Figure 5A In Figure 508, coupling region 510 is shown, where the effective refractive index for the TE mode is compatible with evanescence coupling between the first SiN waveguide 208 and the second SiN waveguide 224A. Figure 5B In Figure 512, the coupling region 514 is shown, wherein the effective refractive index for the TM mode is compatible with the evanescent coupling between the first SiN waveguide 208 and the second SiN waveguide 224A.

[0079] Figure 6 A comparison of tapered portion length and coupling efficiency is shown. The length of each tapered portion provides further optimization of coupling efficiency. Generally, increasing the tapered portion length can improve coupling efficiency for various modes. Tapered portion I relates to the vertical tapered portion of the second SiN waveguide 224A, and tapered portion II relates to the horizontal tapered portion of the first SiN waveguide 208. Figure 6 In one example shown, when the length of tapered portion I of the second SiN waveguide 224A is approximately 1.5 mm and the length of tapered portion II of the first SiN waveguide 208 is approximately 1 mm, the conversion loss of the TE mode is approximately 0.013 dB and the conversion loss of the TM mode is approximately 0.04 dB. Furthermore, Figure 6The diagram illustrates that most couplings occur relative to the basic mode.

[0080] Figure 7 The effect of the end dimension of the first SiN waveguide 208 on the coupling loss with the second SiN waveguide 224A is shown. As illustrated, since the coupling loss is negligible for end widths as large as approximately 300 nm, the process does not require excessive precision to accommodate very small end widths.

[0081] Figure 8 The above shows the relative Figure 3A Alternative embodiments of the interposer and waveguide described in the other related figures. Typically, this embodiment shows a vertically tapered second SiN waveguide 224A′ that continues to taper vertically to zero, resulting in a third SiN waveguide 224B′ optically coupled to the SMF.

[0082] Figure 8 The top view 800A shows the topological view 800A and the longitudinal section view 800B, which further shows example material stacks for the individual components, with most of the components on top relative to... Figure 3A Described.

[0083] exist Figure 8 A portion of the photonic system 200′ shown in view 800A includes an intermediate waveguide strip 222′. The intermediate waveguide strip 222′ includes a second SiN waveguide 224A′, a cladding 225′, and a third SiN waveguide 224B′. Furthermore, the second SiN waveguide 224A′ includes: a first vertically tapered portion (substantially between reference line 2 and reference line 4), a high-contrast coupler portion (substantially between reference line 4 and reference line 6), a second vertically tapered portion (substantially between reference line 6 and reference line 7), and a portion not extending beyond reference line 7. The length of the second vertically tapered portion can be, for example, between 0.5 mm and 1.5 mm.

[0084] Photonic system 200' includes a first optical mode portion, typically located to the left of reference line 1, in which an optical signal propagates in an optical mode within Si waveguide 212. Photonic system 200' includes a first coupler portion, typically located between reference lines 1 and 2, within PIC 102, in which the optical mode of the optical signal in Si waveguide 212 is transferred to a first SiN waveguide 208. Photonic system 200' includes a second coupler portion, typically located between reference lines 4 and 5, in which the optical mode of the optical signal in the first SiN waveguide 208 is transferred to a second SiN waveguide 224A' within interposer 104'. Photonic system 200' also includes a second optical mode portion, typically located between reference lines 5 and 7, in which the optical signal propagates in an optical mode. The photonic system 200' also includes a third coupler section, typically located between reference line 7 and reference line 8, in which the optical signal is converted into fiber mode in both the second SiN waveguide 224A' and the third SiN waveguide 224B'.

[0085] Intermediate waveguide strip 222′ includes intermediate waveguides 224A′ and 224B′, and typically includes the portions of intermediate waveguides 224A′ and 224B′ between reference line 1 and reference line 8, and may extend away from the coupler portion (e.g., to...). Figure 8 (Right side). Intermediate waveguides 224A′ and 224B′ can be formed and thus coupled together with one or more potential other intermediate waveguides to... Figure 2 The Si PIC 102 is mentioned. In some embodiments, the intermediate waveguide 224A′ can have a thickness t that varies (e.g., in the y-direction) between, for example, 20 nm and 250 nm. 224A Furthermore, the refractive index of the interposer SiN waveguide 224A′ is approximately 1.51, and the refractive index of the interposer cladding 225′ is approximately 1.5. The interposer waveguide 224B′ may have a thickness t (e.g., in the y-direction) of, for example, 20 nm to 25 nm. 224B Furthermore, the refractive index of the intermediate SiN waveguide 224B′ is approximately 1.51 and the refractive index of the intermediate cladding 225′ is approximately 1.5.

[0086] Furthermore, the refractive indices of the interposer SiN waveguides 224A′ and 224B′ are greater than that of the interposer cladding 225′, and the refractive indices of the interposer waveguides 224A′ and 224B′ can range from 1.509 to 1.52. Note that the lower limit of the refractive index range of the interposer is determined by the minimum taper end width provided by the SiN fabrication process, which is assumed here to be on the order of 200 nm. For example, the minimum taper end width of the SiN waveguide can be 180 nm. If the process allows for a smaller end width of the SiN, then the refractive index of the interposer can be correspondingly lower. This is because when the effective refractive indices of the SiN waveguide and the interposer waveguide are substantially the same, an adiabatic coupling transition occurs. Reducing the SiN end width lowers the effective refractive index of the SiN waveguide, thereby resulting in a lower refractive index of the interposer material.

[0087] from Figure 8 It can be seen that the second SiN waveguide 224A′ terminates at reference line 7, and the third SiN waveguide 224B′ can be tapered horizontally or laterally from the first width (e.g. 8 μm) at reference line 7 to the second width (e.g. 7 μm) at reference line 8 or at the intermediate reference line (not shown) between reference line 7 and reference line 8.

[0088] Figure 9 A bonding process for coupling the interposer 900 to the PIC 902 is illustrated. In one embodiment, one or more trenches 904 can be formed in the interposer 900 using various techniques including etching via chemical or mechanical processes. The trenches 904 can form reservoirs for an adhesive such as epoxy resin 906. The trenches 904 can accommodate excess epoxy resin 906 and can provide further lateral support between the interposer 900 and the PIC 902. The trenches 904 are also adapted to form a thin epoxy bonding line between the second SiN waveguide 224A and the first SiN waveguide 208, which helps reduce optical coupling loss.

[0089] Figure 10 A method 1000 for coupling an optical signal from a PIC to an SMF is illustrated. Method 1000 includes step 1002: propagating an optical signal in a silicon (Si) waveguide including a first lateral tapered end. Method 1000 further includes step 1004: firstly, optically coupling the optical signal from the first lateral tapered end of the Si waveguide to a first silicon nitride (SiN) waveguide including a second lateral tapered end. Method 1000 further includes step 1006: secondly, in response to a second SiN waveguide being vertically tapered to an increased thickness near the second lateral tapered end of the first SiN waveguide, optically coupling the optical signal from the second lateral tapered end of the first SiN waveguide to a third SiN waveguide.

[0090] With regard to virtually any use of plural and / or singular terms herein, those skilled in the art can convert plural to singular and / or singular to plural depending on the context and / or application. For clarity, various singular / plural substitutions may be explicitly described herein.

[0091] The invention may be practiced in other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments are to be considered illustrative rather than restrictive in all respects. Therefore, the scope of the invention is indicated by the appended claims rather than by the foregoing description. All modifications falling within the equivalent meaning and scope of the claims should be included within their scope.

[0092] This technology can also be configured as follows.

[0093] (1) A photonic system comprising:

[0094] Photonic integrated circuit (PIC), comprising a first silicon nitride (SiN) waveguide; and

[0095] An interposer layer includes a second SiN waveguide, which is vertically tapered by increasing its thickness in the direction toward the first SiN waveguide to allow adiabatic optical mode transfer between the first SiN waveguides and by decreasing its thickness in the direction away from the first SiN waveguide to allow adiabatic optical mode transfer between the second SiN waveguide and a third SiN waveguide.

[0096] (2) The photonic system according to (1) further includes: a Si waveguide, the Si waveguide having a tapered portion at one end for thermally coupling light between the Si waveguide and the first SiN waveguide.

[0097] (3) The photonic system according to (1), wherein the second SiN waveguide of the intermediate layer terminates after the thickness is reduced.

[0098] (4) The photonic system according to (1), wherein the first SiN waveguide includes a first transverse tapered portion to allow optical mode transfer between the first SiN waveguide and the second SiN waveguide.

[0099] (5) The photonic system according to (1), wherein the third SiN waveguide is adjacent to the second SiN waveguide and the third SiN waveguide is configured to allow optical mode transfer between the second SiN waveguide and the third SiN waveguide.

[0100] (6) The photonic system according to (5), wherein the second SiN waveguide and the third SiN waveguide are configured as high-contrast waveguides, wherein the second SiN waveguide and the third SiN waveguide have thicknesses of about 250 nm and 20 nm respectively and are spaced apart by about 1 μm, and the second SiN waveguide and the third SiN waveguide are configured to facilitate optical mode transfer with the first SiN waveguide.

[0101] (7) The photonic system according to (6), wherein the second SiN waveguide and the third SiN waveguide are configured as low-contrast waveguides, wherein the second SiN waveguide and the third SiN waveguide have a thickness of about 20 nm and are spaced apart by about 1 μm, and the second SiN waveguide and the third SiN waveguide are configured to suppress optical mode transfer with the first SiN waveguide.

[0102] (8) According to the photonic system described in (1), wherein,

[0103] The first SiN waveguide includes a tapered end having a first effective refractive index n1; and

[0104] The second SiN waveguide and the third SiN waveguide together form a first low-refractive-index contrast portion and a second low-refractive-index contrast portion at both ends with effective refractive indices n2, and a third high-refractive-index contrast portion between the first low-refractive-index contrast portion and the second low-refractive-index contrast portion. The third high-refractive-index contrast portion has a third effective refractive index n3 and a vertically tapered portion. The vertically tapered portion thermally couples the first low-refractive-index contrast portion and the second low-refractive-index contrast portion to the third high-refractive-index contrast portion between the first low-refractive-index contrast portion and the second low-refractive-index contrast portion.

[0105] Wherein, n3 is close to n1 and n3>n2, and the tapered end of the first SiN waveguide is optically coupled to the third high refractive index contrast portion of the intermediate layer.

[0106] (9) A photonic system comprising:

[0107] A silicon (Si) waveguide, which includes a first transverse tapered portion at its termination, the Si waveguide being configured to propagate an optical signal in an optical mode;

[0108] A first silicon nitride (SiN) waveguide includes a non-tapered portion configured to thermally optically couple an optical signal from a first transverse tapered portion of the SiN waveguide, the first SiN waveguide further including a second transverse tapered portion at its termination; and

[0109] The second SiN waveguide includes a first vertical tapered portion to increase the thickness of the second SiN waveguide for thermally coupling optical signals between the first SiN waveguide and the second SiN waveguide. The first SiN waveguide terminates before the second transverse tapered portion. The second SiN waveguide also includes a second vertical tapered portion to reduce the thickness of the second SiN waveguide.

[0110] (10) The photonic system according to (9) further includes:

[0111] The third SiN waveguide, wherein, when the second SiN waveguide and the third SiN waveguide are configured as high-contrast waveguides, the second SiN waveguide and the third SiN waveguide are configured to facilitate optical mode transfer with the first SiN waveguide.

[0112] (11) The photonic system according to (10), wherein, when the second SiN waveguide and the third SiN waveguide are configured as low-contrast waveguides, the second SiN waveguide and the third SiN waveguide are configured to suppress optical mode transfer with the first SiN waveguide.

[0113] (12) The photonic system according to (10), wherein the Si waveguide and the first SiN waveguide are configured as part of a photonic integrated circuit (PIC), and the second SiN waveguide and the third SiN waveguide are configured as part of an intermediary layer for coupling with the PIC.

[0114] (13) The photonic system according to (10), wherein the second SiN waveguide is vertically tapered between a thickness of about 20 nm and about 250 nm.

[0115] (14) The photonic system according to (10), wherein the second SiN waveguide and the third SiN waveguide are separated by a distance of about 1 μm.

[0116] (15) A method comprising:

[0117] Optical signals propagate in a silicon (Si) waveguide including a first transverse tapered end;

[0118] First, the optical signal is optically coupled from the first transverse tapered end of the Si waveguide to a first silicon nitride (SiN) waveguide including a second transverse tapered end; and

[0119] Secondly, in response to the second SiN waveguide being vertically tapered to an increased thickness near the second transverse tapered end of the first SiN waveguide, the optical signal is optically coupled from the second transverse tapered end of the first SiN waveguide to the second SiN waveguide.

[0120] (16) The method according to (15) further includes: again, in response to the second SiN waveguide being vertically tapered to a reduced thickness away from the first SiN waveguide, optically coupling the optical signal from the second SiN waveguide to the third SiN waveguide.

[0121] (17) According to the method of (16), wherein the second SiN waveguide and the third SiN waveguide are configured as high-contrast waveguides for optical mode transfer, wherein the second SiN waveguide has a thickness of about 250 nm, the third SiN waveguide has a thickness of about 20 nm, and the second SiN waveguide and the third SiN waveguide are separated by a distance of about 1 μm.

[0122] (18) The method according to (16) further includes: coupling the optical signal from the second SiN waveguide and the third SiN waveguide fiber mode to an optical fiber.

[0123] (19) According to the method of (18), wherein the second SiN waveguide and the third SiN waveguide are configured as low-contrast waveguides for suppressing optical mode shift, the second SiN waveguide and the third SiN waveguide each having a thickness of about 20 nm and being spaced apart by about 1 μm.

[0124] (20) The method according to (19) further includes: overlapping the optical fiber with the second SiN waveguide and the third SiN waveguide by a distance of about 3 μm.

Claims

1. A photonic system, comprising: A photonic integrated circuit (PIC) comprising a first SiN waveguide; as well as A second SiN waveguide is vertically tapered by increasing its thickness in the direction toward the first SiN waveguide to allow adiabatic optical mode transfer between the first SiN waveguides, and vertically tapered by decreasing its thickness in the direction away from the first SiN waveguide to allow adiabatic optical mode transfer between the second SiN waveguide and a third SiN waveguide. The second SiN waveguide is located above the first SiN waveguide, and the third SiN waveguide is located above the second SiN waveguide. in: The first SiN waveguide includes a tapered end having a first effective refractive index n1; and The second SiN waveguide and the third SiN waveguide together form a first low-refractive-index contrast portion and a second low-refractive-index contrast portion at both ends with effective refractive indices n2, and a third high-refractive-index contrast portion between the first low-refractive-index contrast portion and the second low-refractive-index contrast portion. The third high-refractive-index contrast portion has a third effective refractive index n3 and a vertically tapered portion. The vertically tapered portion thermally couples the first low-refractive-index contrast portion and the second low-refractive-index contrast portion to the third high-refractive-index contrast portion between the first low-refractive-index contrast portion and the second low-refractive-index contrast portion. n3 is close to n1 and n3>n2, and the tapered end of the first SiN waveguide is optically coupled to the third high-refractive-index contrast portion.

2. The photonic system according to claim 1, further comprising: A Si waveguide, located below the first SiN waveguide and including a tapered portion at one end, is used for thermally insulating optical coupling between the Si waveguide and the first SiN waveguide.

3. The photonic system according to claim 1, wherein, The second SiN waveguide terminates after the thickness is reduced.

4. The photonic system according to claim 1, wherein, The first SiN waveguide includes a first lateral tapered portion to allow optical mode transfer between the first SiN waveguide and the second SiN waveguide.

5. The photonic system according to claim 1, wherein, The third SiN waveguide is adjacent to the second SiN waveguide, and the third SiN waveguide is configured to allow optical mode transfer between the second SiN waveguide and the third SiN waveguide.

6. The photonic system according to claim 5, wherein, When the second SiN waveguide and the third SiN waveguide are configured as high-contrast waveguides, wherein the second SiN waveguide and the third SiN waveguide have thicknesses of approximately 250 nm and 20 nm respectively and are spaced apart by approximately 1 μm, the second SiN waveguide and the third SiN waveguide are configured to facilitate optical mode transfer with the first SiN waveguide.

7. The photonic system according to claim 6, wherein, When the second SiN waveguide and the third SiN waveguide are configured as low-contrast waveguides, wherein the second SiN waveguide and the third SiN waveguide each have a thickness of about 20 nm and are spaced about 1 μm apart, the second SiN waveguide and the third SiN waveguide are configured to suppress optical mode transfer with the first SiN waveguide.

8. The photonic system according to claim 1, further comprising: A silicon (Si) waveguide, which includes a first transverse tapered portion at its termination, the Si waveguide being configured to propagate an optical signal in an optical mode; The first SiN waveguide includes a non-tapered portion configured to thermally optically couple optical signals from the first transverse tapered portion of the SiN waveguide. The first SiN waveguide also includes a second transverse tapered portion at its termination. The first SiN waveguide terminates before the second transverse tapered portion.

9. The photonic system according to claim 8, wherein, When the second SiN waveguide and the third SiN waveguide are configured as high-contrast waveguides, the second SiN waveguide and the third SiN waveguide are configured to facilitate optical mode transfer with the first SiN waveguide.

10. The photonic system according to claim 9, wherein, When the second SiN waveguide and the third SiN waveguide are configured as low-contrast waveguides, the second SiN waveguide and the third SiN waveguide are configured to suppress optical mode transfer with the first SiN waveguide.

11. The photonic system according to claim 9, wherein, The Si waveguide forms part of the photonic integrated circuit (PIC), and the second SiN waveguide and the third SiN waveguide are configured as part of an intermediary layer for coupling with the PIC.

12. The photonic system according to claim 9, wherein, The second SiN waveguide is vertically tapered between a thickness of approximately 20 nm and approximately 250 nm.

13. The photonic system according to claim 9, wherein, The second SiN waveguide and the third SiN waveguide are separated by a distance of approximately 1 μm.

14. The photonic system according to claim 1, wherein, The effective refractive index of the second SiN waveguide changes as the second SiN waveguide tapers vertically by increasing its thickness in the direction toward the first SiN waveguide, and also as the second SiN waveguide tapers vertically by decreasing its thickness in the direction away from the first SiN waveguide.

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