Optical components

Abstract

An optical component for achieving horizontal and vertical spot size conversion to couple light from a thin waveguide to a thick waveguide is disclosed. The component includes: at least one first thin waveguide having: a first section having a first optical mode field, and a horizontal spot size expansion section providing spot size conversion for a first horizontal dimension of the first optical mode field of a light beam propagating in the first waveguide; and at least one second thick waveguide having: a second section having a second optical mode field, and a horizontal spot size reduction section providing spot size conversion for a second horizontal dimension of the second optical mode field of a light beam propagating in the second waveguide. The expansion end of the first waveguide is aligned and rotated to interface with the reduction end of the second waveguide so that the mode fields in the first waveguide and the second waveguide are rotated 90 degrees relative to each other, so that the spot size of the light beam thus coupled between the first waveguide and the second waveguide is expanded or contracted in two lateral dimensions depending on the direction of the light beam.

Description

Technical Field

[0001] The present invention relates to methods of coupling single mode optical fiber arrays to photonic integrated circuits. More particularly, the present invention relates to optical components for implementing a two-dimensional (2D) spot size converter (SSC) between optical mode fields in optical waveguides of different thicknesses and widths. Background Art

[0002] Photonic integrated circuit (PIC) chips typically require optical input and output coupling from and to single-mode fiber (SMF) arrays. However, the waveguides in photonic integrated circuits typically have a much smaller mode field or "spot size" compared to standard single-mode fibers (SSMFs). The smaller the spot size difference, the greater the optical coupling loss between the PIC waveguide and the SMF.

[0003] Arrays of small core fibers, lensed fibers, or tapered fibers are not suitable for coupling light from (or to) large waveguide arrays with small spot sizes because the positions of the fiber cores relative to each other have random variations and it is not possible to align all fibers simultaneously to an array of small PIC waveguides. The variation in the position of the fiber cores in a fiber array is typically about 1 μm due to the variation in the position of the cores within each fiber and the fiber-to-fiber positioning in, for example, a V-groove array.

[0004] A horizontal and vertical spot size converter (SSC) is usually required between the waveguide and the fiber. This 2D converter can be a structure that changes the spot size in both the horizontal and vertical directions simultaneously, or a combination of separate vertical and horizontal converter structures, where the waveguide tapers from one spot size to another in each direction separately.

[0005] A separate spot size converter chip, also called a waveguide interposer, can be used to perform vertical and horizontal spot size conversion between a standard SMF array and an array of small waveguides at the edge of the PIC chip. The advantage is that there is no waveguide-to-waveguide variation in the thin waveguide array, and the array of thin mode fields can be precisely aligned. 2D spot size converters have been achieved by various methods, such as direct writing of waveguides, step etching of thick waveguide layers, grayscale lithography, grinding of waveguides, tapering of optical fibers, lenses, grating couplers, sub-wavelength diffractive structures, and reverse tapers. Horizontal taper is usually not a problem on PICs, but vertical spot size conversion is difficult to achieve with most optical waveguide technologies using wafer-level processing techniques.

[0006] In some applications, there is also a need to couple light between thick and thin waveguides on different PICs, or even within a multilayer PIC, i.e. no optical fiber is part of this coupling task. Both optical fibers and PIC waveguides can be considered "waveguides", so the need for 2D SSC can be considered a general need for spot size conversion between optical mode fields in optical waveguides of different thickness and width. One of these waveguides (usually the thicker one) can be an SMF, or its other end can be coupled to an SMF. Summary of the invention

[0007] No perfect solution has been proposed for coupling light between a thin waveguide array and another thick waveguide array. An ideal coupling concept needs to have a wide transmission spectrum, polarization-independent operation, low insertion loss and small size, as well as low manufacturing and assembly costs of the components.

[0008] The object of the present invention is to find a novel solution to the above mentioned problems, which mitigates the disadvantages of the prior art solutions. The present invention is defined as follows regarding an optical component for achieving horizontal and vertical spot size conversion for coupling light from a thin waveguide to a thick waveguide or vice versa, and various embodiments of the present invention are also defined as follows.

[0009] According to the present invention, waveguides on two different chips or in two different waveguide layers are coupled together so that the optical mode width in one waveguide corresponds to the thickness of the optical mode in the other waveguide, and vice versa. Therefore, each waveguide mode only needs to be expanded in the horizontal direction, but the optical mode field is expanded (or reduced) in both the horizontal and vertical directions. Therefore, the horizontal and vertical spot size conversion between the small optical waveguide and the large optical waveguide is performed by combining two horizontal spot size conversions and by rotating the mode between the two waveguides around the optical axis. This mode rotation can be achieved by an upper reflecting waveguide mirror, a rotation of the waveguide chip, or a combination thereof.

[0010] According to the present invention, there is provided an optical component for achieving horizontal and vertical spot size conversion to couple light from a thin waveguide to a thick waveguide or vice versa. The component comprises:

[0011] - at least one first thin waveguide having: a first section having a first optical mode field, and a horizontal spot size extension section providing a spot size conversion for a first horizontal dimension of the first optical mode field of a light beam propagating in the first waveguide;

[0012] - at least one second thick waveguide having a second section with a second optical mode field and a horizontal spot size reducing section providing a spot size conversion for a second horizontal dimension of the second optical mode field of a light beam propagating in the second waveguide.

[0013] The expanded end of the first waveguide is aligned and rotated to dock with the reduced end of the second waveguide so that the mode fields in the first waveguide and the second waveguide are rotated 90 degrees relative to each other, so that the spot size of the light beam coupled between the first waveguide and the second waveguide is expanded or contracted in two lateral dimensions depending on the direction of the light beam.

[0014] According to some embodiments, at least two of said first waveguides are placed on a first common planar substrate and at least two of said second waveguides are placed on a second common planar substrate.The substrates may be separate and parallel substrates.

[0015] In some embodiments, the waveguide layers can be stacked on a common substrate.

[0016] According to some embodiments, an upper reflective element is placed at the expanded end of the first waveguide and the reduced end of the second waveguide to reflect light between the first waveguide and the second waveguide.

[0017] In some embodiments, the first waveguide includes: a horizontally curved section for aligning the optical axes of all the first waveguides in the optical assembly to a common optical axis, and an upper reflective element at the interface of the first waveguide for reflecting light from the plane of the first waveguide and coupling light between each pair of the first waveguide and the second waveguide. The optical axis of the second waveguide may be perpendicular to the plane of the first waveguide.

[0018] According to another embodiment, the gap arranged between the butt ends of the first waveguide and the second waveguide can have a size that does not cause significant beam divergence in the gap in either of the two lateral directions of the beam, so that the mode fields of the first waveguide and the second waveguide are directly coupled to each other without any focusing optical device between them.

[0019] Alternatively, the gap provided between the butt ends of the first waveguide and the second waveguide may have a size that results in significant beam divergence in the gap in a lateral direction relative to the length of the first waveguide, thereby focusing or collimating the divergent beam to the second waveguide at the interface of the second waveguide by a convex lens or a concave mirror.

[0020] In some embodiments, the second waveguide includes a horizontal curved section for aligning the optical axes of the first waveguides and the second waveguides in the optical assembly with a common optical axis, so that light is directly coupled between each pair of the first waveguides and the second waveguides without any upper reflective element in the coupling interface. The first waveguide can be placed on a substrate having a groove suitable for accommodating the curved section of the second waveguide so as to align the optical axes of all the first waveguides and the second waveguides in the optical assembly with the common optical axis.

[0021] In some further embodiments, a first waveguide is placed on one substrate and a second waveguide is placed on a different substrate, at least one of the substrates having mechanical alignment features in at least one direction adapted to receive corresponding alignment features or surfaces on the other substrate when the substrates are pressed together. The mechanical alignment features may be patterned by at least partially machining the same material layer used to form the first and / or second waveguides.

[0022] Other embodiments of the invention may include one or more features from the following bulleted list:

[0023] The first, second or both waveguides comprise a horizontal spot size extension waveguide section having a tapered waveguide width;

[0024] The first, second or both waveguides include a slab waveguide region in which an input beam is expanded and a concave waveguide mirror that collimates or focuses the expanded beam into another waveguide having a horizontally expanded mode field relative to the input beam;

[0025] The first, second or both waveguides include a horizontally curved section with a total internal reflection (TIR) ​​mirror;

[0026] • The upper reflective element of the first, second or both waveguides comprises a total internal reflection (TIR) ​​mirror.

[0027] In practical applications of some embodiments of the optical assembly of the present invention, the first waveguide is a component of a photonic integrated circuit (PIC). An array of single-mode fibers (SMF) can be optically coupled to an optical interposer between the PIC and the array of SMFs, the optical applicator comprising an array of the second waveguides. Light can then be coupled from the end face of the second waveguide to the optical fiber array.

[0028] The various embodiments of the present invention are characterized by what has been stated above. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 An embodiment of the photonic integrated circuit of the present invention is shown;

[0030] Figure 2 A second embodiment of the photonic integrated circuit of the present invention is shown;

[0031] Figure 3 Another embodiment of the photonic integrated circuit of the present invention is shown;

[0032] Figure 4 Further exemplary embodiments of the photonic integrated circuit of the present invention are shown. DETAILED DESCRIPTION

[0033] In detail, the exemplary embodiment shown in the figures is based on a horizontal tapering of a first silicon-on-insulator (SOI) waveguide of approximately 3×3 μm (3 μm thick and 3 μm wide) to a size of approximately 3×12 μm, whereby the mode field of the waveguide is horizontally amplified. Throughout the description, the waveguide dimensions are given in the order of height×width. The width of the thin waveguide typically varies in the PIC. In a 3 μm thick SOI waveguide, the width is typically 3 μm or narrower in at least some parts of the PIC. Therefore, reference is made only to the 3×3 μm waveguide as an exemplary input waveguide. In this regard, Figures 1 to 4 The scaling is not perfect and can present waveguide dimensions of approximately 3 × 5 μm.

[0034] As the two waveguide modes rotate relative to each other, light is then coupled to the input end of a 12×3μm second waveguide with a matching mode field. The width of the second waveguide is then tapered from 3μm to 12μm to achieve a target output size of 12×12μm. The light from this 12×12μm waveguide can then be coupled to the core of a standard single-mode fiber (SMF). Obviously, any combination of SOI waveguides of different sizes and other types of optical waveguides can be coupled together by the same inventive principle, which allows light to be coupled from an array of thin waveguide modes to another array of thick waveguide modes without the need for any vertical tapering of the waveguides.

[0035] Figure 1 One embodiment is shown in . It shows a photonic integrated circuit (PIC) 100 comprising three 3 μm thick first waveguides 103 on a silicon substrate 101. The functional components of the PIC are not shown and only three waveguides are selected for visualising the invention. Figure 1 Also shown is an interposer 110, which includes three 12 μm thick second waveguides 105 on a silicon substrate 102. For clarity, the buried oxide (BOX) layer is omitted in the figure. In this embodiment, the thin waveguides 103 and the thick waveguides 105 are both placed horizontally and parallel, and the thick waveguides 105 are inverted on the thin waveguides 103.

[0036] Each thin waveguide 103 consists of a narrow (3×3 μm in some embodiments) input component 103a, 103b or 103c (here each having a different length), a tapered section 103d, a curved section 104 and a 3×12 μm section 103e. The tapered section 103d is a horizontally widening tapered section that performs a first horizontal spot size conversion from a narrow input width (e.g. 3 μm) to a final width (e.g. 12 μm). The horizontal tapering of the thin waveguide 103 can be achieved in many alternative ways and in different components of the PIC 100. For example, it can be achieved by a continuous tapering of the waveguide width, such as Figure 1 As shown, or it can be achieved by a combination of a slab waveguide (where the light expands horizontally) and a curved waveguide mirror (which collimates the expanded light).

[0037] The curved sections may consist of curved waveguides or flat waveguide mirrors 104. The relative positions of the tapered and curved sections may also be swapped or even overlapped. For example, a combination of a flat waveguide and a curved mirror may perform both tapering and bending. In some embodiments of the invention, there may be no curved sections, as circuit layout, location requirements, and other design considerations determine the optimal shape and size of the waveguide in each case. Figure 1 In a specific embodiment, the curved segments may be omitted when the straight segments 103e do not share the same optical axis and the waveguides 103 will therefore not overlap each other.

[0038] After the tapered and curved sections, the light is directed into the 3x12 μm section 103e which ends with the upper mirror 106. Obviously, if the assembly of the PIC 100 and the interposer chip 110 were inverted, the mirror would be the lower mirror.

[0039] A similar upper reflector 107 is located on the interposer chip 110. Between the upper reflector pair 106 and 107, light passes vertically in either direction, as indicated by arrow 108. Figure 1 In FIG. 1 , the upper reflector 107 at the narrow end 105a of the thick waveguide 105 actually reflects the light from these waveguides downwards because the waveguide 105 is inverted under the silicon substrate 102. The thick waveguide 105 also has a horizontal tapered section 105b and a wide (e.g. 12 μm wide) output waveguide section 105c. The upper reflectors 106, 107 are preferably TIR (total reflection) mirrors, but they can also be metallized mirrors or other similar elements. Here, the terms "upper reflector" and "upper reflective element" are used to refer to any upper or lower reflective structure that couples light from the waveguide upward or downward relative to the horizontal plane in which the waveguide lies.

[0040] Light is coupled from the thin waveguides 103a, 103b, 103c of the PIC circuit 100 to the output end 105c of the optical interposer 110 as follows: The light propagates in the waveguide along the direction of the optical axis of each waveguide segment. The optical axis is perpendicular to the end face of each entry point and exit point of the light into the corresponding waveguide section. When encountering a horizontally curved segment or an upper reflector, such as 104, 106 or 107, the optical axis and the light beam turn.

[0041] exist Figure 1In the case shown, the first parts 103a, 103b, 103c of the three waveguides 103 are parallel. In this example, the waveguide segments 103a, 103b and 103c have different lengths in order to demonstrate the possibility of relatively free positioning of the waveguides on the substrate 101 in some embodiments of the invention. The beam from each waveguide segment 103a-c then enters a tapered segment 103d, which gradually widens the beam to a horizontal configuration of 12 μm width.

[0042] When the light beams hit the horizontal TIR mirror 104, their optical axes turn to become parallel to each other (this is not necessary before the curved section). At the end of the parallel waveguide section 103e, the upper reflector 106 reflects the light vertically upward to the upper reflector 107 of the waveguide 105 placed orthogonally above the upper reflector 106 to efficiently collect the light and reflect it to the narrow end of the thick waveguide 105. The orthogonal placement of the upper reflector pair 106 and 107 means that the polarization of the light is rotated 90° when the light is coupled between the first thin waveguide 103 and the second thick waveguide 105. The light then travels horizontally in the inverted waveguide 105, first through the tall and narrow section 105a that accommodates the horizontally expanded mode field of the waveguide 103 (now turned to the vertical direction by the upper reflector 106). The horizontal tapered section 105b of the waveguide 105 then gradually expands the mode field of the light beam in an orthogonal direction relative to the already expanded mode field. The result is that the thin and narrow optical mode (e.g. 3×3 μm) of the first waveguide 103 has been efficiently coupled to the thick and wide optical mode (e.g. 12×12 μm) of the second waveguide 105 through a combination of two horizontal mode size expansions and a rotation interface between the two waveguides 103, 105. From the output end face (not shown) of the 12×12 μm sized waveguide 105, the light can be coupled to, for example, the core of a standard single mode optical fiber (not shown). The polarization of the light beam is turned so that the horizontal TE polarization of the light beam entering the waveguide 103 is now a vertically oriented TM polarization in the waveguide 105, and vice versa.

[0043] As mentioned above, circuit layout and other design considerations determine the optimum shape and size of the waveguide in each case. Figure 1 In the concept shown, the upper mirror pair can be processed at different locations on the chip, not necessarily along the same line, such as Figure 1 PIC 100 and interposer chip 110 may also be referred to as lower chip 100 and upper chip 110, respectively. When the optical axes of optical waveguide 103 are merged on lower chip 100, the optical waveguides on upper chip 110 may be arranged side by side in a conventional manner, making it easier to align the lower and upper upper mirrors with each other. In particular, wet-etched upper mirrors are usually required to be in a specific direction, and Figure 1 All mirrors in the array do have the same orientation. However, this may not be necessary in some embodiments, as long as Figure 1It is sufficient for each mirror pair 106, 107 to be aligned orthogonally as shown.

[0044] If the thin and thick waveguides 103, 105 are located on two separate chips (lower chip 100 and upper chip 110), as Figure 1 As shown, the upper reflector is preferably placed near the edge of these chips so that the substrate 102 does not overlap the substrate 101 too much. This is helpful if there are flip chip integrated components, wire bonds or other components extending on the substrate 101. The thin and thick waveguides 103, 105 can also be manufactured as 2-layer PICs on a common substrate 101 or 102 (depending on their relative vertical positioning), for example by transferring one waveguide layer on top of the other waveguide layer using layer transfer technology.

[0045] Another embodiment of the present invention is Figure 2 The photonic integrated circuit 200 includes three 3 μm thick first waveguides 203 on a silicon substrate 201. The optical interposer 210 includes three 12 μm thick second waveguides 205 on another silicon substrate 202. In this embodiment, the substrate 202 and the second waveguides 205 are placed vertically relative to the first waveguides 203.

[0046] exist Figure 2 In the embodiment shown, the travel of light in the first waveguide 203 is similar to Figure 1 As described in FIG. 1 , three thin waveguides 203 include straight, tapered and curved waveguide sections. The tapered section horizontally expands the mode field of the narrow (e.g., 3 μm wide) first waveguide 203 to provide a target width of 12 μm at the output end of each first waveguide 203. The curved section 204 turns the waveguides so that they all share the same optical axis at this point before the light is coupled to the upper reflector 206 at the end of the 3×12 μm waveguide section.

[0047] Here, light is coupled upward from the upper reflector 206 directly to the bottom end face of the 3×12 μm wide section 205a of the second waveguide 205. Therefore, no upper reflector in the second waveguide 205 is needed to couple the light between waveguides 203 and 205 at the gap 207. The light beam will then travel through the tapered waveguide section 205b to reach the target waveguide dimensions of 12 μm thick and 12 μm wide in the straight waveguide section 205c. From there, the light can be coupled to the optical fiber through the waveguide end face 205d.

[0048] The polarization of the light beam is also turned here so that the horizontal TE polarization of the light beam in waveguide 203 becomes a vertically oriented TM polarization in waveguide 205 .

[0049] In a similar Figure 2In the embodiment of FIG. 2 , a 12 μm SOI interposer chip 210 can be placed fairly freely on top of a 3 μm SOIP IC 200. Due to its vertical orientation, the chip 210 will only cover a relatively small area of ​​the PIC 200 and its substrate 201 .

[0050] Another embodiment of the present invention is Figure 3 and Figure 4 In Figure 3 , the PIC 300 again comprises three 3 μm thick first waveguides 303 with tapered and curved sections and an upper mirror on a silicon substrate 301, as in Figure 1 to Figure 2 Three 12 μm thick second waveguides 305 are implemented on another silicon substrate 302 to form an optical interposer 310 placed vertically relative to the 3 μm thick waveguide 303 and its substrate 301, as Figure 2 . Each waveguide 305 consists of a waveguide portion 305b that is 12 μm thick and greater than 3 μm (e.g., 12 μm) wide and a lens 305a that points to the upper reflector 306 of the corresponding waveguide 303. The lens can be manufactured as a component of the waveguide without any separate processing or lithography steps. It is preferably planar in the vertical direction, aligned with or part of the waveguide sidewall, and curved only in the horizontal direction. The light beam reflected upward from the upper reflector 306 diverges as it propagates in the free-space gap between the upper reflector 306 and the lens 305a. This divergence is much faster in the direction where the optical mode field from the thin waveguide 303 is narrow, which corresponds to the width of the thick waveguide 305. The gap is preferably kept small so that the light beam does not diverge significantly in other directions corresponding to the thickness of the second waveguide 305 and the extended width of the first waveguide 303. Therefore, the light beam diverges mainly in only one direction. The lens 305a then collimates the diverging beam and couples it into the waveguide section 305b.

[0051] Likewise, no mirror is needed in the second waveguide 305, and here too the polarization of the light is converted from the horizontal TE polarization entering the waveguide 303 to the vertically oriented TM polarization in the waveguide 305, and vice versa.

[0052] Figure 3 The embodiment shown is relative to Figure 1 to Figure 2 The first main difference is that no tapered sections or narrow (e.g. 3 μm wide) waveguide sections are needed in the second waveguide 305, since the curved input facet of the thick waveguide 305 acts as a lens and performs a horizontal tapering of the light in the free space gap outside the waveguide 305. This allows the second waveguides 305 to be shorter, and they are also easier to manufacture, since the waveguide 305 no longer needs to have a high aspect ratio (i.e. height to width).

[0053] The second main difference is that there may be a finite distance between the upper reflector 306 and the lens 305a. Figure 1 to Figure 2 In the case of a RF beam, the free space gap needs to be minimized as it can cause unwanted beam divergence. Figure 3 In the embodiment shown, a limited gap is used to expand the beam in one direction. This limited distance is very beneficial in PIC testing, for example, where the interposer chip can be kept at a safe distance, such as 15-30 μm, above the PIC wafer or chip to avoid the risk of them scratching each other. In some embodiments of this type, the substrate 302 does not have to be as Figure 3 This limited distance can also be beneficial when making permanent components. In both assembly and testing, when the two waveguide chips 300, 310 are aligned relative to each other using passive or active alignment, the limited distance can help avoid scratching any optical input / output faces.

[0054] exist Figure 4 In FIG. 4 , the PIC 400 includes three 3 μm thick first waveguides 403 on a silicon substrate 401. Three 12 μm thick second waveguides 405 are implemented on a silicon substrate 402, and the optical interposer component 410 is vertically placed relative to the three first waveguides 403 and their substrate 401, as shown in FIG. Figures 2 to 3 The substrate 401 is provided with a groove 408 which is etched or machined into the substrate 401 and is designed to receive the end of the waveguide 405. To briefly describe various embodiments of the present invention, Figure 4 Each waveguide 405 in the optical interposer 410 has a different beam coupling device 405a, 405b and 405c. Preferably only one of these coupling device types is selected for use in each optical interposer 410. The beam coupling device is lowered into each receiving slot 408 during assembly (or chip / wafer testing) to align the common optical axis of all straight waveguide portions 403b on the PIC with the optical axes of all coupling devices 405a-c so that all of these optical axes merge together. Proper alignment of the docking waveguide portions can be provided by a post 407 or similar mechanical arrangement. The post 407 can be placed in a patterned recess 409 that provides a mechanical alignment feature, or have some other alignment feature that locks them into a specific position on the substrate 401.

[0055] exist Figure 4 In the embodiment of the present invention, no upper reflector is required at the end face or interface of the interfacing waveguide portion 403b, but the light propagates directly into the coupling device 405a, 405b or 405c. The coupling device 405a includes an interfacing 3 μm wide and 12 μm thick waveguide portion, a tapered waveguide section and a TIR mirror, similar to Figure 1 Items 105a, 105b and 104 in the embodiment. The coupling device 405b has Figure 3 405a in FIG. 406 . A third exemplary coupling device 405c consists of a curved concave mirror that collects the incident light beam and reflects it upward through the waveguide 405. All coupling devices 405a-c collect light from the end face of the first waveguide 403, which is 3 μm thick and 12 μm wide, expand the light beam (spot size) in a direction corresponding to the thickness of the waveguide segment 403b, and turn the light upward orthogonally relative to the substrate 401 of the PIC 400. Expanding the light beam and turning the light upward occurs horizontally relative to the surface of the optical interposer 410. In all Figures 2 to 4 In the embodiment, the optical interposer requires only one lithographic patterning step, which corresponds to the definition of the width of the thick waveguides 205, 305 and 405. In all embodiments, the increase in both the width and the height of the beam (spot size) is achieved by combining the horizontal expansion of the beam with the first 103, 203, 303, 403 and the second 105, 205, 305, 405 waveguides, without any changes in the thickness of the waveguides themselves or their mode fields.

[0056] exist Figures 1 to 4 In the embodiment of the present invention, the chip pairs 100+110, 200+210, 300+310 and 400+410 need to be aligned with each other to ensure that the light is coupled between the waveguide and the reflector as expected with minimal loss. This can be done in a variety of different ways, which are not core to the present invention, but are briefly discussed here.

[0057] The most straightforward approach is to use active alignment, where light transmission through both the thin and thick waveguides and the coupling interface between them is maximized. Sometimes a U-ring can be added to either waveguide chip to maximize transmission of both coupling interfaces simultaneously, such as at the edge of a wide waveguide array, with input and output coupling done through only one waveguide chip. Another common approach to coupling two waveguide chips together is to use passive alignment with machine vision and suitable alignment marks.

[0058] An attractive approach for low-cost mass production is passive mechanical alignment. This can be achieved in a variety of different ways. One option is to etch a V-shaped alignment groove on each chip, for example during fabrication of the upper reflector, and add alignment balls or similar protrusions that align the two V-grooves when they are brought together. It is also possible to implement some kind of monolithic protruding alignment feature on either chip, such as a post, bump or pyramid, which is then passively aligned to a V-groove, inverted pyramid hole or similar feature on the other chip. Already combined with Figure 4One such arrangement is discussed, in which rectangular posts 407 are patterned into a 12 μm thick SOI layer on an optical interposer chip 410 and self-aligned with the 12 μm thick waveguides 405 and their coupling devices 405a-c. With flat end faces, such posts can be used to precisely control the vertical positioning of the two chips 400 and 410. By pressing the flat end face of the post 407 against a flat surface on the chip 400, while pressing the top (or bottom) and left (or right) surfaces of a similar (preferably longer) post against a similar flat surface, the vertical positioning of the two chips 400 and 410 is controlled. Figure 4 Passive alignment can be performed in all three directions on the sidewalls of the etched pit of trench 408 as shown.

[0059] Okay, especially for Figures 2 to 4 In the embodiment, a V-shaped alignment groove is wet-etched on the 3μm SOI chip and a photolithographically patterned V-shaped tip extending from the edge of the 12μm SOI layer is dry-etched. When the 12μm SOI chip is vertically placed on top of the 3μm SOI chip, the V-shaped tip immediately falls into the V-shaped groove on the 3μm SOI.

[0060] Similar mechanical alignment features can be added to Figures 2 to 3 In the assembly shown, various alignment features etched into the 12 μm SOI layer can pass through various holes patterned into the PIC chip. In some cases, this may require the alignment features to protrude beyond the edge of the substrate (202, 302, 402), such as Figure 4 As shown, see item 407. This can be achieved by etching down the Si substrate or by using, for example, a cavity SOI wafer.

[0061] In some applications, it may not be desirable to place the fiber vertically relative to the PIC. To avoid this, the thicker waveguide 205, 305, 405 can be bent to have a horizontal bend section (similar to Figure 2 204 or Figure 4 405a-c) to turn them from a vertical orientation to a horizontal orientation relative to the PIC 200, 300, 400. If the output surfaces of these curved waveguides (such as Figure 2 205d) is coupled to an SMF array, each fiber of the SMF array is in a horizontal direction, and the individual fibers in the array are located on top of each other. It is also possible to have an upper reflector in the thick waveguide to enable the fibers to be placed orthogonally relative to the substrate of the thick waveguide. This allows horizontal fiber arrays to be added to Figures 2 to 4 Alternatively, a vertical fiber array may be added to Figure 1 implementation method.

[0062] The present invention is not intended to be limited to the use of any particular material or waveguide size. References to silicon, SOI, 3 or 12 μm thick waveguides are only specific embodiments of the present invention and should not limit the scope of the present invention. In addition, any reference to "thin", "thick", "narrow" and "wide" waveguides refers to the relative thickness and width of the optical mode field in these waveguides, rather than the size of the waveguide itself, because the mode field size also depends on the materials and shapes used in the waveguide: sometimes the mode field even expands as the waveguide becomes smaller. References to "vertical", "orthogonal" and "parallel" do not refer to exact angles, because the present invention can also be expected to be applied and / or work with slight variations relative to the exact angle given in theory. For example, the waveguide faces can be slightly tilted to reduce back reflections, which causes light to be refracted in these faces. Similarly, the upper reflective element can reflect light upward (or downward) in some non-orthogonal direction, which also reduces back reflections. These small deviations from the nominal angle also allow the two waveguide chips to be placed in slightly non-parallel or non-orthogonal orientations relative to each other. The terms "upper", "lower", "horizontal" and "vertical" have also been used to explain specific embodiments of the invention, and the invention is obviously applicable to other orientations where these directions are reversed or rotated to some other directions. It is also possible within the scope of the invention to rotate some components by 180° or to map them relative to a certain point or plane. Some embodiments of the invention may have been explained under the assumption that light propagates from a thin waveguide to a thick waveguide, but the invention is obviously also applicable to the opposite case, where any reference to terms such as "input" or "output" should be interchanged.

Claims

1. An optical component for achieving horizontal and vertical spot size conversion to couple light between an extended end of a thin waveguide and one end of a thick waveguide, the component comprising: - at least one first waveguide having: a first section having a first optical mode field, and a horizontal spot size extension section providing a spot size conversion for a first horizontal dimension of the first optical mode field of a light beam propagating in the first waveguide, the first waveguide being a thin waveguide; - at least one second waveguide having: a second section having a second optical mode field, and a horizontal spot size reduction section providing a spot size conversion for a second horizontal dimension of the second optical mode field of a light beam propagating in the second waveguide, the second waveguide being a thick waveguide; in The extended end of the first waveguide is aligned and rotated to dock with the one end of the second waveguide, so that the mode fields in the first waveguide and the second waveguide are rotated 90 degrees relative to each other, so that the spot size of the light beam coupled between the first waveguide and the second waveguide is expanded or contracted in two lateral dimensions depending on the direction of the light beam.

2. The optical assembly according to claim 1, wherein: At least two of said first waveguides are placed on a first common planar substrate, and at least two of said second waveguides are placed on a second common planar substrate.

3. The optical assembly according to claim 1, wherein: An upper reflective element is placed at the extended end of the first waveguide and the one end of the second waveguide to reflect light between the first waveguide and the second waveguide.

4. The optical assembly according to claim 3, wherein: The first waveguide and the second waveguide are placed on two separate parallel substrates.

5. The optical assembly according to claim 3, wherein: The first waveguide and the second waveguide are placed on two stacked waveguide layers on a common substrate.

6. The optical assembly according to claim 1, wherein: The first waveguide includes: a horizontally bent section, the horizontally bent section being used to align optical axes of all the first waveguides in the optical assembly with a common optical axis; and an upper reflective element at an interface of the first waveguide, the upper reflective element being used to reflect light from a plane of the first waveguide and to couple light between each pair of the first waveguide and a second waveguide, the optical axis of the second waveguide being perpendicular to the plane of the first waveguide.

7. The optical component according to any one of claims 1 to 6, wherein: A gap arranged between the butt ends of the first waveguide and the second waveguide has a size that does not cause significant beam divergence in the gap in either of the two lateral directions of the beam, so that the mode field of the first waveguide and the mode field of the second waveguide are directly coupled to each other without any focusing optical device between them.

8. The optical component according to any one of claims 1 to 6, wherein: A gap disposed between the butting ends of the first waveguide and the second waveguide has a size that results in significant beam divergence in the gap in a lateral direction corresponding to the width of the second waveguide, thereby focusing or collimating the divergent beam to the second waveguide by a convex lens at the interface of the second waveguide.

9. The optical component according to any one of claims 1 to 6, wherein: A gap provided between the butting ends of the first waveguide and the second waveguide has a size that results in significant beam divergence in the gap in a lateral direction corresponding to the width of the second waveguide, thereby focusing or collimating the divergent beam to the second waveguide by a concave mirror at the interface of the second waveguide.

10. The optical component according to any one of claims 1 to 6, wherein: The second waveguide includes a horizontally bent section for aligning optical axes of the first waveguide and the second waveguide in the optical assembly to a common optical axis so that light is directly coupled between each pair of the first waveguide and the second waveguide.

11. The optical assembly according to claim 10, wherein: The first waveguides are placed on a substrate having a groove adapted to accommodate the curved section of the second waveguides so as to align the optical axes of all of the first and second waveguides in the optical assembly with a common optical axis.

12. The optical component according to any one of claims 1 to 6, wherein: The first waveguide, the second waveguide, or both include a horizontal spot size expansion waveguide section or a horizontal spot size reduction waveguide section, respectively, having a tapered waveguide width.

13. The optical component according to any one of claims 1 to 6, wherein: The first waveguide, the second waveguide, or both, respectively, include a horizontal spot size expansion section or a horizontal spot size reduction waveguide section having a slab waveguide region in which an input beam is expanded and a concave waveguide mirror that collimates or focuses the expanded beam to the second waveguide or the first waveguide, respectively, having a horizontally expanded mode field relative to the input beam.

14. The optical component according to any one of claims 1 to 6, wherein: The first waveguide, the second waveguide, or both include a horizontally curved section having a total internal reflection (TIR) ​​mirror.

15. An optical assembly according to any one of claims 3 to 6, wherein: The upper reflective element of the thin waveguide, the thick waveguide, or both comprises a total internal reflection (TIR) ​​mirror.

16. The optical component according to any one of claims 1 to 6, wherein: The first waveguide is part of a photonic integrated circuit (PIC).

17. An optical assembly according to any one of claims 1 to 6, wherein: An array of single mode fibers (SMF) is optically coupled to an optical interposer between the PIC and the SMF array, the optical interposer comprising the array of the second waveguides.

18. The optical assembly according to claim 17, wherein: Light is coupled from the end face of the second waveguide to the optical fiber array.

19. The optical assembly according to any one of claims 1 to 6, wherein: The first waveguide is placed on one substrate and the second waveguide is placed on a different substrate, at least one of the substrates having mechanical alignment features in at least one direction adapted to receive corresponding alignment features or surfaces on the other substrate when the substrates are pressed together.

20. The optical assembly of claim 19, wherein: The mechanical alignment features are patterned by at least partially machining the same layer of material used to form the first and / or second waveguides.

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