Mode extension waveguide and spot size converter for guiding light coupled to optical fiber comprising such mode extension waveguide

Abstract

A waveguide comprising: a first waveguide portion and a second waveguide portion and a third waveguide portion of tapered width, such that along a first direction, the widths of the first waveguide portion and the second waveguide portion gradually increase toward a first end of the third waveguide portion, and a distance between the first waveguide portion and the second waveguide portion in a second direction gradually decreases from the second end of the first waveguide portion to the first end of the first waveguide portion, wherein the second direction is perpendicular to the first direction; and a maximum distance Gmax between the second end of the first waveguide portion and the second end of the second waveguide portion is greater than 0.2 μm and less than 0.48 μm; and the waveguide has a refractive index between 2 and 4 at a wavelength of 1550 nm.

Description

[0001] background

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority under 35 USC §119 to U.S. Provisional Application Serial No. 62 / 854,013, filed on May 29, 2019, the contents of which are based and are incorporated herein by reference in their entirety. Technical Field

[0004] The present disclosure generally relates to a spot size converter between an optical fiber and an optical waveguide, and more particularly to a spot size converter comprising a first waveguide portion and a second waveguide portion connected to a third waveguide portion, wherein a distance between the first waveguide portion and the second waveguide portion gradually decreases, while widths of the first waveguide portion and the second waveguide portion gradually increase, and the spot size converter can be used, for example, to couple a single-mode optical fiber to an optical silicon strip waveguide of a silicon-based photonic integrated circuit (PIC) chip on a silicon-on-insulator (SOI) platform.

[0005] background

[0006] With the development of high-speed and high-capacity optical communication technology, the key technology in optical integrated devices is to achieve effective coupling between waveguides and optical fibers. For example, the optical waveguide can be a silicon ribbon waveguide for silicon-based PIC chips.

[0007] The optical signal needs to be coupled from the single-mode fiber to the silicon waveguide in the silicon-based PIC chip. However, the width of the cross section of the silicon waveguide is at the submicron level, and the diameter of the ordinary single-mode fiber is at the micron level. That is, the size of the cross section of the silicon waveguide is much smaller than the core diameter of the ordinary single-mode fiber. In addition, the silicon waveguide core layer in the silicon-based PIC chip has a relatively high refractive index. The mismatch between the spot size and the effective refractive index of the silicon waveguide and the ordinary single-mode fiber, as well as the mismatch in the mode field diameter (MFD) cause large coupling losses between the silicon-based PIC chip and the optical device.

[0008] For example, a typical silica ribbon waveguide is about 200nm-220nm (0.2 microns to 0.22 microns) thick and 400nm-500nm (0.4 microns to 0.5 microns) wide, while the core diameter of a typical single-mode optical fiber is about 8 microns. This size mismatch results in a large mismatch between the MFD of a single-mode optical fiber and the MFD of a silica ribbon waveguide. For example, a typical standard single-mode optical fiber has an MFD of about 10 μm, and a nanophotonic silica ribbon waveguide has an MFD of less than about 1 μm.

[0009] Due to this mismatch, direct end-to-end coupling between a standard single-mode optical fiber and a nanophotonic silica ribbon waveguide (MFD < 1 μm) results in coupling losses greater than 20 dB.

[0010] End-face coupling is a method for reducing the coupling loss between a silicon-based PIC chip and an optical fiber. In end-face coupling, a spot size converter (SSC) is designed and manufactured at the edge of a silicon-based PIC chip. The mode field in the SSC is coupled to the mode field in an external single-mode optical fiber, and the size of the light mode spot in the SSC can change as it propagates from one end of the SSC to the other. However, a typical end-to-end SSC that minimizes the coupling loss between a silicon-based PIC chip and a single-mode optical fiber is difficult and expensive to manufacture.

[0011] More specifically, since conventional SSCs require submicron features and need to control feature sizes within tens of nanometers, conventional optical deep UV lithography is considered unsuitable for patterning these SSC waveguide structures. Due to the need for high resolution, electron beam lithography is the most commonly used technique for research purposes and prototyping. This electron beam lithography process, which uses a focused electron beam to write structures directly into a photoresist, can be able to define extremely small features. However, since everything is written in a serial manner, typical electron beam processes are usually very slow and are therefore expensive and unsuitable for mass production. In addition, conventional single-tip SSC waveguides provide an extended MFD (i.e., maximum MFD) of only about 3 or 4 microns.

[0012] No admission is made that any reference cited herein constitutes prior art. Applicants expressly reserve the right to challenge the accuracy and pertinence of any cited document. Summary of the invention

[0013] One embodiment of the present disclosure relates to an optical waveguide, comprising: a first waveguide portion (301) with a tapered width, a second waveguide portion (302) with a tapered width, and a third waveguide portion (303), such that a first end of the third waveguide portion (303) is connected to a first end of the first waveguide portion (301) and a first end of the second waveguide portion (302); and along a first direction, the widths of the first waveguide portion and the second waveguide portion gradually increase toward the first end of the third waveguide portion, and a distance between the first waveguide portion and the second waveguide portion in a second direction gradually decreases from the second end of the first waveguide portion to the first end of the first waveguide portion, wherein the second direction is located on a plane where the waveguide is located, and the second direction is perpendicular to the first direction; and wherein a distance Gmax between the second end of the first waveguide portion (301) and the second end of the second waveguide portion (302) is greater than 0.2 μm and less than 0.48 μm; and the waveguide has a refractive index between 2 and 4 at a wavelength of 1550 nm.

[0014] According to some embodiments, a spot size converter includes:

[0015] A substrate layer; a first covering layer disposed above the substrate layer, wherein the first covering layer includes a first material; a single-stage waveguide (300) disposed in contact with the first covering layer, wherein the waveguide includes a third material; wherein the waveguide includes a first waveguide portion (301) with a tapered width, a second waveguide portion (302) with a tapered width, and a third waveguide portion (303), a first end of the third waveguide portion (303) being connected to a first end of the first waveguide portion (301) and a first end of the second waveguide portion (302); and along a first direction, the widths of the first waveguide portion and the second waveguide portion (301, 302) gradually increase toward the first end of the third waveguide portion (303), and the distance between the first waveguide portion (301) and the second waveguide portion (302) in a second direction gradually decreases from a second end of the first waveguide portion (301) to the first end of the first waveguide portion (301), wherein the second direction lies in the plane of the waveguide (300) and the second direction is perpendicular to the first direction; and wherein the distance Gmax between a second end of the first waveguide portion (301) and a second end of the second waveguide portion (302) is greater than 0.2 μm and less than 0.48 μm;

[0016] And Δ% of the third material relative to the first material > 25%. According to some embodiments, Δ% of the third material relative to the first material > 50%.

[0017] According to some embodiments, a gap is located between the first waveguide portion and the second waveguide portion. According to some embodiments, the gap has a trapezoidal cross-section. According to some embodiments, the gap has a V-shaped cross-section. According to some embodiments: (i) the waveguide is a silicon waveguide, (ii) the distance G between a second end of the first waveguide portion and a second end of the second waveguide portion narrows from the second ends of the first waveguide portion and the second waveguide portion to the first ends of the first waveguide portion and the second waveguide portion, thereby forming a tapered gap having a taper with a length Lt such that 300 microns < Lt < 5000 microns, wherein the minimum distance Gmin of the tapered gap is between 50 nm and 150 nm, and the maximum distance Gmax is between 300 nm and 480 nm (e.g., 350 nm to 450 nm, or 400 nm to 450 nm). According to some embodiments, the width of the third waveguide portion is between about 400 nm and about 500 nm (e.g., 450 nm to 500 nm), and the thickness of the third waveguide portion is between 200 nm and 225 nm.

[0018] Additional embodiments of the present disclosure relate to a spot size converter (SSC) including:

[0019] A substrate layer;

[0020] a first covering layer disposed above the substrate layer, wherein the first covering layer comprises a first material;

[0021] an intermediate layer disposed between the substrate layer and the first cover layer, wherein the optional intermediate layer (203) comprises a second material; and

[0022] A single-stage waveguide (300) disposed inside a first cover layer, wherein the waveguide comprises a third material; wherein the waveguide comprises a tapered width first waveguide portion (301), a tapered width second waveguide portion (302), and a third waveguide portion (303), a first end of the third waveguide portion (303) being connected to a first end of the first waveguide portion (301) and a first end of the second waveguide portion (302); such that a tapered gap is located between the first waveguide portion and the second waveguide portion; and

[0023] Along the first direction, the widths of the first waveguide portion and the second waveguide portion (301, 302) gradually increase toward the first end of the third waveguide portion (303), and the distance between the first waveguide portion (301) and the second waveguide portion (302) in the second direction gradually decreases from the second end of the first waveguide portion (301) to the first end of the first waveguide portion (301), wherein the second direction is located on the plane where the waveguide (300) is located, and the second direction is perpendicular to the first direction; and wherein

[0024] A distance Gmax between the second end of the first waveguide portion (301) and the second end of the second waveguide portion (302) is greater than 0.2 μm and less than 0.48 μm; and

[0025] The Δ% of the third material relative to the first material is >25% (eg, >50%).

[0026] Additional embodiments of the present disclosure relate to a spot size converter (SSC), comprising:

[0027] substrate layer;

[0028] a first covering layer disposed above the substrate layer, wherein the first covering layer comprises a first material;

[0029] an intermediate layer disposed between the substrate layer and the first cover layer, wherein the optional intermediate layer (203) comprises a second material; and

[0030] A single-stage waveguide (300) disposed inside the first cover layer, wherein the waveguide comprises a third material; wherein the waveguide comprises a tapered width first waveguide portion (301), a tapered width second waveguide portion (302), and a third waveguide portion (303), a first end of the third waveguide portion (303) being connected to a first end of the first waveguide portion (301) and a first end of the second waveguide portion (302); and

[0031] Along the first direction, the widths of the first waveguide portion and the second waveguide portion (301, 302) gradually increase toward the first end of the third waveguide portion (303), and the distance between the first waveguide portion (301) and the second waveguide portion (302) in the second direction gradually decreases from the second end of the first waveguide portion (301) to the first end of the first waveguide portion (301), wherein the second direction is located on the plane where the waveguide (300) is located, and the second direction is perpendicular to the first direction; and wherein

[0032] A distance Gmax between the second end of the first waveguide portion (301) and the second end of the second waveguide portion (302) is greater than 0.2 μm and less than 0.48 μm; and

[0033] The Δ% of the third material relative to the second material is >25% (eg, >50%).

[0034] According to some exemplary embodiments, the waveguide is configured to provide <2 dB (e.g., <1 dB, or ≤0.5 dB) when coupled to a single-mode fiber, and has a mode field diameter (MFD) at 1550 nm such that MFD≥7 microns. According to some embodiments, the waveguide is configured to provide a coupling loss of <1.5 dB, and MFD≥7 microns. According to some embodiments, the waveguide is configured to provide a coupling loss of <1 dB when coupled to a single-mode fiber, and MFD≥7 microns. According to some embodiments, the waveguide is configured to provide a coupling loss of <1 dB when coupled to a single-mode fiber, and MFD≥8 microns at 1550 nm. According to some embodiments, the waveguide is configured to provide a coupling loss of <1 dB when coupled to a single-mode fiber, and 7.5 microns≤MFD≤10 microns at 1550 nm.

[0035] According to some embodiments of the SSC, at a wavelength of 1550 nm, the absolute value of the difference between the refractive index n2 of the second material and the refractive index n1 of the first material is less than 0.1, and / or at a wavelength of 1550 nm, the absolute value of the difference between the refractive index n3 of the third material and the refractive index n1 of the first material is 0.5. <n3-n1<2.5。

[0036] According to some embodiments:

[0037] The length of the waveguide (300) is L1,

[0038] The lengths of the first waveguide portion (301) and the second waveguide portion are L2, and the length of the third waveguide portion is L3;

[0039] The thicknesses of the first waveguide portion (301), the second waveguide portion (302), and the third waveguide portion (303) are H1,

[0040] The minimum widths of the first waveguide portion (301) and the second waveguide portion (302) are W1min and W2min respectively, the width of the second end of the third waveguide portion (303) is W3, and the distance between the waveguide (300) and the top of the substrate layer (201) or optionally the bottom of the intermediate layer (203) is H3, where 0 < L1 ≤ 500 μm, 0 < L3 ≤ 200 μm, 0 < H1 ≤ 400 nm, H3 > 2 μm (e.g., H3 ≥ 3 μm, or in some embodiments H3 ≥ 5 μm), 50 nm < W1min ≤ 100 nm, 50 nm < W2min ≤ 100 nm, and 200 nm ≤ W3 ≤ 550 nm. According to some embodiments, 0 < L1 ≤ 500 μm, 0 < L3 ≤ 200 μm, H1 + H3 > 3 μm, and H3 > 2.5 μm (e.g., H3 > 3 μm or H3 ≥ 5 μm), 70 nm < W1min ≤ 90 nm, 70 nm < W2min ≤ 90 nm and 400 nm ≤ W3 ≤ 500 nm. According to some embodiments, the maximum gap width Gmax between the first waveguide portion (301) and the second waveguide portion (302) is 200 nm ≤ Gmax ≤ 450 nm. According to some embodiments, the maximum gap width Gmax between the first waveguide portion (301) and the second waveguide portion (302) is 300 nm ≤ Gmax ≤ 450 nm, or 200 nm ≤ Gmax ≤ 400 nm.

[0041] Advantageously, an SSC having the multi-tip waveguide disclosed herein can be fabricated using waveguides with small tip widths (W1, W2) less than 100 microns, and fabricating such an SSC does not require expensive high-resolution lithography.

[0042] Additional features and advantages will be set forth in the following detailed description, which will be partly apparent to those of ordinary skill in the art from the description, or recognized by practicing the embodiments as described in the written description, the claims, and the drawings herein.

[0043] It should be understood that both the foregoing general description and the following detailed description are exemplary only, and they are intended to provide an overview or framework for understanding the nature and characteristics of the claims.

[0044] The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the description serve to explain the principles and operation of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. Figure 1A is a schematic diagram of a spot size converter according to an embodiment of the present invention;

[0046] Figure 1B is a schematic diagram of a spot size converter according to an embodiment of the present invention;

[0047] Figure 2 is a plan view of a waveguide of a spot size converter according to an embodiment of the present invention;

[0048] Figure 3A is a schematic end view of a cross section where a-a' of a spot size converter is located according to an embodiment;

[0049] Figure 3B is based on Figure 3A A schematic end view of a cross section where bb' of a spot size converter of a corresponding embodiment is located;

[0050] Figure 4 Schematic diagram showing coupling to optical fiber and optical waveguide Figure 2 waveguide;

[0051] Figure 5A An exemplary embodiment of a dual tip waveguide 300 is shown;

[0052] Figure 5B Shown in Figure 5A a simulated optical mode expansion of a spot size in one embodiment of a waveguide, wherein the mode expansion is due to a gradual narrowing of a gap region within an input section of the waveguide;

[0053] Figure 6 Shows Figure 4 Mode distribution (ψ SMF (r) and ψ SSC (r)), and Figure 2 and Figure 5A mode distribution of an input section (a section facing the optical fiber) of an optical waveguide;

[0054] Figure 7A-7B Shown for manufacturing Figure 1A , Figure 1B and Figure 2 An exemplary embodiment of a process for forming a waveguide (process 1);

[0055] Figure 7C-7E Shown for manufacturing Figure 1A , Figure 1B and Figure 2 Another exemplary embodiment of a process for forming a waveguide of the invention (process 2); and

[0056] Figure 8 Shows Figure 2 The calculated optical power conversion efficiency of the waveguide. DETAILED DESCRIPTION

[0057] definition:

[0058] The "Relative Refractive Index Percentage" is defined as

[0059] Δ%=100×[n 2 –n 参考 2 )] / n 2 ,

[0060] where n is the refractive index of the material in the region of interest, and n 参考 is the refractive index of the reference material. Unless otherwise specified, the relative refractive index percentages are defined at 1550 nm. In one aspect, the refractive index n 参考 is for silica glass having a refractive index of about 1.45 at 1550 nm. As used herein, unless otherwise indicated, the relative refractive index percentage (also referred to herein as the relative refractive index) is represented by Δ, and the value of the relative refractive index percentage is given in "%". The refractive index in the region is less than the reference index n 参考 In the case where the relative index percentage is negative, the region is referred to as a depressed region or depressed index. 参考 In this case, the relative index percentage is positive and the area can be said to be enhanced or has a positive index.

[0061] For example, the relative refractive index percentage of a silicon waveguide (relative to pure silica glass) is

[0062] Δ%=100×[n 2 –n 参考 2 )] / 2n 2 =100×(3.48 2 +1.45 2 ) / 2×3.48 2 =82.6%.

[0063] “Up-dopant” is considered in this article to be relative to pure undoped SiO 2 A dopant that has a tendency to increase the refractive index. A "downdopant" is considered herein to be a dopant that has a tendency to increase the refractive index relative to pure undoped SiO 2A dopant having a tendency to lower the refractive index. An updopant may be present in a region of the fiber having a negative relative refractive index when accompanied by one or more other dopants that are not updopants. Likewise, one or more other dopants that are not updopants may be present in a region of the fiber having a positive relative refractive index. A downdopant may be present in a region of the fiber having a positive relative refractive index when accompanied by one or more other dopants that are not downdopants.

[0064] With mode field diameter MFD 1 and MFD 2 The coupling efficiency α between two waveguides is defined as:

[0065] α=4×(MFD 1 2 ×MFD 2 2 ) / (MFD 1 2 +MFD 2 2 ) 2

[0066] With mode field diameter MFD 1 and MFD 2 The coupling loss η between two waveguides is defined as:

[0067] η=1-α

[0068] When calculated in db, the coupling loss η (dB) is calculated as

[0069] 10 log 10(η)

[0070] For the purposes of describing and defining the present disclosure, it is noted that the terms "about" and "approximately" are used herein to represent the inherent degree of uncertainty that can be attributed to any quantitative comparison, value, measurement, or other representation. The terms "about" and "approximately" are also used herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0071] Various embodiments will be further illustrated by the following examples.

[0072] Example 1A:

[0073] Figure 1A is a schematic diagram of a spot size converter (SSC) according to an embodiment of the present invention. Figure 1A The spot size converter 200 shown includes: (a) a substrate layer 201 (eg, silicon, or Y 2 O 3(a) a transparent ceramic (refractive index n=1.88+ / -5% at 1550 nm); (b) a first cover layer 202 disposed above the substrate layer 201, wherein the first cover layer comprises a first material (e.g., glass, such as silicon dioxide SiO 2 (c) an optional intermediate layer 203 disposed between the substrate layer 201 and the first cover layer 202, wherein the intermediate layer comprises a second material (eg, silicon dioxide, or doped silicon dioxide glass, or Y 2 O 3 doped ceramic); (d) and a SSC waveguide 300 disposed inside the first cladding layer. Figure 1A The waveguide 300 is at least partially enclosed by the first cover layer 202. The first material and the second material may be, for example, silica-based glasses (e.g., pure silica or doped silica), and may have the same or similar composition. According to some embodiments, the waveguide 300 is a silica waveguide. The substrate layer 201 includes a fourth material (e.g., silicon), and according to some embodiments, the composition of the third material and the fourth material may be the same or substantially the same.

[0074] For example, the substrate layer 201 may be silicon dioxide. The first cover layer 202 may be pure silicon dioxide SiO 2 , the waveguide can be silicon or silicon nitride, and the optional layer can be Y 2 O 3 Doped ceramics.

[0075] Example 1B:

[0076] Figure 1B is a schematic diagram of a spot size converter according to an embodiment of the present invention. A spot size converter is an optical component including an optical waveguide configured to expand or change the size of a mode field diameter (MFD) of an optical signal propagating through the waveguide. Figure 1A The spot size converter 200 shown includes: a substrate layer 201 (e.g., silicon); (b) a first cover layer 202 disposed above the substrate layer 201, wherein the first cover layer includes a first material; (c) an optional intermediate layer 203 disposed between the substrate layer 201 and the first cover layer 202, wherein the intermediate layer includes a second material; and an SSC waveguide 300 disposed on the first cover layer. The substrate layer 201 includes a fourth material (e.g., silicon or Y 2 O 3 transparent ceramic (refractive index at 1550nm is 1.88+ / -5%)), and according to some embodiments, the composition of the third material and the fourth material may be the same or substantially the same. For example, the substrate layer 201 may be silicon dioxide. The first cover layer 202 may be pure silicon dioxide SiO 2 , the waveguide 300 may be silicon or silicon nitride, and the optional layer may be Y2 O 3 Doped ceramics.

[0077] Waveguide 300.

[0078] The waveguide 300 is preferably substantially symmetrical along the major axis and comprises a third material. In some embodiments, the waveguide is symmetrical along the major axis. The waveguide 300 has a plurality of tips (eg, 2 tips). Figure 2 One embodiment of a multi-tip waveguide 300 is shown. The principal axis is indicated by the dashed line. Specifically, Figure 2 The exemplary embodiment of the waveguide 300 shown includes a first waveguide portion 301 (terminating at a first tip), a second waveguide portion 302 (terminating at a second tip), and a third waveguide portion 303. The first waveguide portion and the second waveguide portion are tapered, i.e., their widths vary along their lengths. A first end of the third waveguide portion 303 is connected to a first end of the first waveguide portion 301 and a first end of the second waveguide portion 302. According to at least some embodiments, a gap region Gr (also referred to herein as a gap, Gr) between the first waveguide portion and the second waveguide portion is tapered. That is, the gap region Gr has a V-shaped cross-section or a trapezoidal cross-section in the xz plane, i.e., the distance G between the waveguide portion 301 and the waveguide portion 302 (the width of the gap region Gr) is tapered and therefore non-uniform. According to some embodiments, the tapered gap region Gr has a taper with a length Lt, such that 300 microns < Lt < 2000 microns. In Figure 1A , Figure 1B and Figure 2 In the illustrated embodiment, the widths W1 and W2 of the first waveguide portion 301 and the second waveguide portion 302 gradually increase along the first direction (main axis direction) toward the first end of the third waveguide portion 303, and the distance G between the first waveguide portion 301 and the second waveguide portion 302 (i.e., the width G of the gap Gr) gradually decreases from the second end of the first waveguide portion or the second waveguide portion toward the first end of the first waveguide portion 301. That is, the width G of the gap Gr between the first waveguide portion 301 and the second waveguide portion 302 in the second direction gradually decreases toward the first end of the third waveguide portion 303. The second direction is perpendicular to the first direction. Figure 2 An Oxy coordinate system is further shown, where in this embodiment, the first waveguide portion 301 and the second waveguide portion 302 are symmetrical or approximately symmetrical about the y-axis, and the width G of the gap region is measured along the x-axis.

[0079] Figure 3A Schematically shows Figure 2The cross section where a-a' is located in FIG. It shows that the thickness of the first waveguide portion 301 and the thickness of the second waveguide portion 302 are H1, the minimum widths of the first waveguide portion 301 and the second waveguide portion 302 are W1min and W2min, and the distance from the bottom of the first waveguide portion 301 and the bottom of the second waveguide portion 302 to the top of the substrate layer 201 or the bottom of the intermediate layer is H3. Figure 2 In the exemplary embodiment of , the width W1 and the width W2 are equal (W1=W2). In addition, it is assumed that the plane of the cross section where a-a' is located is the xy plane. Figure 3B Schematically shows Figure 2 The cross section where b-b' is located. Figure 3B The thickness of the third waveguide portion 303 is also shown as H1, and the width of the third waveguide portion 303 is W3. It should be noted that in this embodiment, W3 is equal to or substantially equal to, or approximately equal to, the sum of W1, W2, and G. For example, in Figure 2 In the embodiment shown, W3 = W1 + W2 + G. Therefore, in this embodiment, W3 = W1min + W2min + Gmax.

[0080] Preferably, in order to provide more efficient coupling at a wavelength of 1550nm, the absolute value of the difference between the refractive index of the second material and the refractive index of the first material is preferably not greater than 0.1 (i.e., |n2-n1|≤0.1), and / or the difference between the refractive index of the third material and the refractive index of the fourth material is not less than 0.5 (e.g., n3-n1>0.5). For example, |n2-n1| can be 0, 0.02, 0.05, 0.075, 0.09, or therebetween. In addition, for example, at a wavelength of 1550nm, n3-n1 can be 1.5, 1.8, 2, 2.5, or therebetween. The third material can be silicon or silicon nitride, i.e., the waveguide 300 can be made of silicon or silicon nitride. The fourth material (i.e., the substrate layer material) can have a refractive index n4 at a wavelength of 1550nm. In some embodiments, n4=n3 (e.g., both the waveguide 300 and the substrate are made of silicon dioxide). In the embodiments described herein, n4>n2, for example, n4-n2≥0.5, and in some embodiments, n4-n2>1. For example, if the second material is a silica-based glass (e.g., n2 is between 1.8≥n2>1.45), and the fourth material is silicon, such that 4≥n4≥3.5, then n4-n2 can be between about 1.5 and about 3.

[0081] Therefore, according to some embodiments, the spot size converter 200 includes a first waveguide portion 301, a second waveguide portion 302, and a third waveguide portion 303, which together can form a tapered gap in the waveguide 300. Preferably, as Figure 2As shown, the gap Gr in the waveguide 300 has a trapezoidal cross section or a V-shaped cross section in the xz plane. The spot size converter can be used to achieve spot size conversion between an optical fiber (e.g., a single-mode optical fiber) and an optical waveguide (e.g., a silicon ribbon waveguide), and the coupling loss between the optical fiber and the optical waveguide can be reduced by using the spot size converter.

[0082] In this embodiment, the spot size converter 200 can be added and connected to one end of the optical waveguide. Specifically, the spot size converter can be connected to the optical waveguide 500 by using the second end of the third waveguide portion 303. For example, Figure 4 As shown, the second end of the third waveguide portion 303 may be directly connected to the optical waveguide 500, and the second ends of the two optical waveguide portions 301, 302 may be connected or coupled to the optical fiber 400. Other methods of connecting the spot size converter 200 to the optical waveguide 500 may also be used.

[0083] exist Figure 4 In some embodiments, the cross-section of the optical waveguide 500 is rectangular, and the optical waveguide 500 has a width W4 and a height or thickness H4. The optical waveguide 500 can be, for example, an optical silicon ribbon waveguide 500'. In some embodiments, the optical silicon ribbon waveguide 500' can have a width W4 of 0.4 microns to about 0.5 microns and a height or thickness H4 of about 0.2 microns to about 0.22 microns.

[0084] It should be noted that in the embodiments described herein, the cross section refers to a cross section perpendicular to the length direction. Alternatively, it should be understood that the cross section is a cross section perpendicular to the first direction.

[0085] Figure 2 The Oxz coordinate system is further shown. It can be understood that the first direction is the positive direction of the z-axis. In addition, the widths W1 and W2 of the first waveguide portion 301 and the second waveguide portion 302 gradually increase along the positive direction of the z-axis. Preferably, the edges of the first waveguide portion 301 and the second waveguide portion 302 are straight.

[0086] Preferably, if Figure 2 As shown, the cross-sectional shape of the third waveguide portion 303 is rectangular, and the width of the third waveguide portion at the first end of the third waveguide portion 303 is equal to the width at the second end of the third waveguide portion 303. Figure 2 In an embodiment, the width of the waveguide portion 303 is constant or substantially constant (ie, it varies by no more than 5% of its maximum width, and preferably by no more than 2% of its maximum width).

[0087] In addition, it is assumed that the length of the waveguide 300 is L1, the length of the waveguide portions 301, 302 is L2, and the length of the third waveguide portion 303 is L3. It is assumed that the widths of the first waveguide portion 301 and the second waveguide portion 302 are W1 and W2, and the width of the second end of the third waveguide portion 303 is W3. It is assumed that the thickness of the first waveguide portion 301, the thickness of the second waveguide portion 302, and the thickness of the third waveguide portion 303 are all H1. For example, in some embodiments, 0.2 micrometers ≤ H1 ≤ 0.22 micrometers. For example, in some embodiments, H1 is between 0.2 micrometers and 0.5 micrometers (e.g., 0.2 micrometers to 0.3 micrometers).

[0088] Assume that the distance between the bottom of the waveguide 300 and the top of the substrate layer 201 is H3. Preferably, H3>2 microns, and in some embodiments, H3≥3 microns (e.g., 2 microns≤H1≤10 microns, 3 microns≤H1≤10 microns, or 3 microns≤H1≤6 microns). For example, in some embodiments, H1 is between 0.2 microns and 0.5 microns (e.g., 0.2 microns to 0.3 microns), and H3≤5 microns. In some embodiments, 2 microns≤H3≤10 microns, 3 microns≤H3≤10 microns, or 3 microns≤H3≤6 microns. In some embodiments, H1≤5 microns. For example, in some embodiments, 2 microns≤H3≤4 microns, or 2 microns≤H3≤3.5 microns. In some embodiments, H1 is between 0.2 microns and 0.5 microns (e.g., 0.2 microns to 0.3 microns), and H3 is less than 10 microns. In some embodiments, H1 is between 0.2 microns and 0.5 microns (e.g., 0.2 microns to 0.3 microns), and H3 is less than 6 microns or 5 microns. In some embodiments, H1 is between 0.2 microns and 0.5 microns (e.g., 0.2 microns to 0.3 microns), and H3 is between 2 microns and 4 microns.

[0089] It can be understood that in this embodiment, the length is the dimension in the z-axis direction of the coordinate axis, and the width is the dimension in the x-axis direction of the coordinate axis. Accordingly, the thickness is the dimension in the y-axis direction of the coordinate axis (i.e., Figure 2 The dimension in the outward direction).

[0090] Exemplary ranges of the foregoing parameters can be as follows: H3 > 2 μm (e.g., between 2.5 μm and 3.5 μm), 0.1 < H1 ≤ 300 nm (and preferably 200 - 250 nm), 100 μm < L1 (e.g., 100 μm < L1 ≤ 5000 μm, 100 μm < L1 ≤ 2000 μm, or e.g., 1000 μm or 500 μm), 200 < L2 ≤ 2000 μm (e.g., 200 μm to 1500 μm, L2 < L1, L3 > 0 μm (e.g., 200 μm ≤ L3 ≤ 500 μm), the waveguide tip has a width of 10 nm < W1min ≤ 100 nm and 10 nm ≤ W2min ≤ 100 nm (e.g., 10 nm to 40 nm), and 200 nm ≤ W3 ≤ 500 nm (e.g., 400 nm ≤ W3 ≤ 500 nm). The typical tip widths W1min, W2min at the second ends (tips) of the waveguide portions 301, 302 can be about 30 nm to about 40 nm, but can be smaller (e.g., 15 nm, 20 nm or 25 nm) or larger (e.g., 45 nm, 50 nm, 60 nm, 70 nm, 80 mm, 90 nm, 100 nm or in between). In some embodiments, the thickness H of the substrate layer 201 s is about 600 μm to about 700 μm, the thickness H of the first cladding layer 202 c is about 2 μm to about 10 μm (e.g., about 4 μm to 10 μm for the Figure 1A embodiment shown, and about 2 μm to 5 μm for the Figure 1B embodiment shown), and the thickness H of the optional intermediate layer 203 (if this layer exists) O is greater than about 8 μm (e.g., 10 μm to 400 μm).

[0091] In addition, the distance (Gmin) between the first end of the first waveguide portion 301 and the first end of the second waveguide portion 302 can be 90 microns to 150 microns, e.g., 90 microns to 110 microns, preferably 95 microns to 105 microns, or 95 microns to 100 microns. In addition, the distance (Gmax) between the second end of the first waveguide portion 301 and the second end of the second waveguide portion 302 can be 200 nm to 480 nm (e.g., 350 nm to 460 nm, 375 nm to 460 nm, 375 nm to 460 nm, or 400 nm to 450 nm). For example, the distance Gmax (i.e., the maximum width of the gap region Gr) can be 220 nm, 320 nm, 350 nm, 400 nm, 425 nm or 450 nm, 460 nm or in between.

[0092] Optionally, in Figure 1A and Figure 1BIn the illustrated spot size converter 200 , the material of the substrate layer 201 may be silicon, the first material may be silicon dioxide, the second material may be silicon dioxide or another material, and the third material may be silicon or silicon nitride.

[0093] In this embodiment, the substrate layer 201 is used to support the waveguide 300. The first cover layer 202 is used to limit the propagation of the optical mode to the waveguide 300. The optional intermediate layer 203 can also be used to limit the propagation of the optical mode to the waveguide 300, so that the optical mode propagating through the waveguide 300 is not coupled into the substrate layer 201.

[0094] The mode spreading provided by the waveguide 300 is based on the use of two tapered waveguide sections 301, 302 to form a waveguide that propagates through a single mode optical fiber (e.g., SMF- The MFD of the waveguide 300 is expanded by separating the two waveguide portions 301, 302 by the tapered gap region Gr, so the waveguide 300 has two legs and two small ends. The greater the separation Gmax, the greater the MFD of the waveguide 300 at the second end of the waveguide portions 301, 302 located adjacent to or close to the optical fiber. Therefore, the waveguide 300 converts the small mode field diameter MFD from the optical waveguide 500 to the large size mode field diameter (MFD) of the single mode optical fiber 400 by using two waveguide portions 301, 302.

[0095] According to some embodiments, the spot size converter 200 includes a waveguide 300, the waveguide 300 being configured to provide a coupling loss of <2 dB when coupled to a single mode fiber, and having a mode field diameter (MFD) at 1550 nm such that the mode field diameter MFD ≥ 7 microns. According to some embodiments, the waveguide 300 is configured to provide a coupling loss of <1.5 dB, and having an MFD ≥ 7 microns at a wavelength of 1550 nm. According to some embodiments, the waveguide 300 is configured to provide a coupling loss of <1 dB (when coupled to a single mode fiber), and MFD ≥ 7 microns at 1550 nm. According to some embodiments, the waveguide 300 is configured to provide a coupling loss of <1 dB, and 7.5 microns ≤ MFD ≤ 10 microns. According to some embodiments, the waveguide 300 is configured to provide a coupling loss between 0.2 dB and 1 dB, and 7.5 microns ≤ MFD ≤ 10 microns. According to some embodiments, the waveguide is configured to provide a coupling loss between 0.2 dB and 0.5 dB, and 7.5 microns ≤ MFD ≤ 10 microns at 1550 nm.

[0096] Figure 4 The waveguide 300 of the spot size converter 200 is schematically shown between the optical fiber 400 and the optical waveguide 500. It can be understood that Figure 1A , Figure 1B and Figure 2 In the waveguide 300 shown, the width W3 of the second end of the third waveguide portion 303 may be equal to the width W4 of the optical waveguide 500, i.e., preferably W3 is substantially the same as W4, or even more preferably W3 = W4. The thickness H1 of the third waveguide portion 303 may be equal to the thickness H4 of the optical waveguide 500, i.e., H1 = H4.

[0097] More specifically, one end of the waveguide 300 is coupled to the optical fiber 400, and the other end of the waveguide 300 is coupled to the optical waveguide 500. In this way, when an output optical signal from the optical fiber 400 (e.g., a single-mode optical fiber) is input to the spot size converter 200 through the second ends of the waveguide portions 301, 302 of the waveguide 300, the optical energy propagating through the waveguide 300 can be distributed between the first waveguide portion 301 (the first leg of the waveguide 300) and the second waveguide portion 302 (the second leg of 300). Then, the optical energy can be coupled into the third waveguide portion 303, and the optical signal is subsequently coupled into the optical waveguide 500.

[0098] Similarly, when an output optical signal of the optical waveguide 500 is provided to the spot size converter 200 by coupling the optical waveguide 500 to the third waveguide portion 303, the optical signal propagates through the third waveguide portion 303 and may then be provided to an optical fiber by the first waveguide portion 301 and the second waveguide portion 302 through an optical field formed between the first waveguide portion 301 and the second waveguide portion 302 of the waveguide 300.

[0099] Figure 5A One embodiment of an exemplary waveguide 300 is shown. In this embodiment, the waveguide 300 has the following parameters: W3 = 500 nm; W1 = W2 = t; W1min = W2min = 40 nm, L1 = 2000 μm, L2 = 1000 μm; H1 = 220 nm; Gmin = 100 nm; Gmax = 420 nm. This exemplary embodiment of the waveguide 300 is made of silicon.

[0100] Figure 5B Shows Figure 5A Simulated mode expansion in the exemplary waveguide 300. Figure 5B The optical mode expansion within the waveguide 300 (which corresponds to the MFD expansion) is shown. Figure 5B At the second ends of the waveguide portions 301, 302 (ie at the tips of these waveguides, Figure 4At position A shown, where t = W1min = W2min = 40 nm), the MFD of the waveguide 300 is about 8-9 microns. This is also the typical MFD of the single-mode fiber 400. Therefore, the waveguide 300 can be advantageously coupled to the single-mode fiber 400 with minimal coupling losses. In contrast, a typical spot size converter with a single-tip tapered waveguide is achieved with an MFD of only 2-3 microns, and therefore its connection to a typical single-mode fiber results in much higher losses.

[0101] Figure 5B It is also shown that as the optical modes travel through the waveguide 300, they expand in diameter (ie, the MFD of the waveguide expands). For example, at position B (see FIG. 1 ) where the width W1 = W2 = 100 nm in this embodiment. Figure 4 ), the MFD of the waveguide 300 is about 3-4 microns, and at position C (closer to the front end of the waveguide portions 301, 302) where the waveguide width W1=W2 is 150 microns, the MFD of the waveguide 300 is about 1 micron. At the second end of the waveguide 300 (where W3=500 nm), the MFD can be even smaller (e.g., 0.8 microns or 0.9 microns).

[0102] Optical mode expansion occurs within the waveguide 300 due to the gradual narrowing of the width G of the gap region Gr inside the input section of the waveguide 300 (i.e., the section facing the optical fiber 400). More specifically, the gradual narrowing of the width of the waveguide portions 301, 302 results in a tapered gap region of width G between the first waveguide portion and the second waveguide portion. In some embodiments, the width W3 is between 400nm and 500nm, while the width G of the tapered gap region Gr changes from a minimum distance or width Gmin of about 100nm (e.g., a Gmin of 90nm, 95nm, 100nm, 110nm, or 120nm) to a maximum distance or width Gmax of greater than 200nm. For example, in some embodiments, Gmin is about 100nm or less, and Gmax>300nm, and in some embodiments, Gmax>350nm. In some embodiments, Gmax>400nm. In some embodiments, 500nm>Gmax>300nm. In some embodiments, 500nm>Gmax>350nm. In some embodiments, 500nm>Gmax>400nm. These waveguide dimensions (or widths) can be achieved via a relatively low resolution complementary metal oxide semiconductor (CMOS) deep ultraviolet lithography (DUVL) process described below. In contrast, typical commercial spot size converters use single tip waveguides (where the waveguide is tapered, the taper width is reduced from 500nm to a tip width of tens of nanometers, and such single tip waveguides are very difficult to manufacture to the required specifications using a lower resolution CMOS DUVL process). Therefore, high resolution lithography processes are required to manufacture such single tip tapered waveguides, making them more expensive to produce.

[0103] Furthermore, embodiments of the waveguide 300 have dual tips that facilitate achieving a greater / stronger MFD extension (to 5 microns or greater, e.g., 6 μm to 10 μm) than that achieved by conventional tapered single-tip spot size converter waveguides, thereby advantageously achieving better (higher) fiber-to-chip coupling efficiency relative to that typically achieved by conventional tapered single-tip waveguides. More specifically, our modeling analysis indicates that the MFD provided by an exemplary embodiment of the waveguide 300 to a typical single-mode optical fiber 400 is nearly twice as great as the MFD provided by a single-tip spot size converter waveguide having a tip width of the same size (e.g., a tip width of 40 microns).

[0104] Furthermore, efficient, low-loss coupling between the large MFD dual-tip spot size converter waveguide 300 and a single-mode optical fiber (MFD ~8 μm to 10 μm) can be achieved with much looser misalignment tolerances than required when coupling a conventional single-tip tapered spot size converter waveguide to the same optical fiber.

[0105] For example, when the tip of a single-mode fiber does not have a lens (lensed fibers are manufactured by creating a lens at the end of the fiber, which is typically done to achieve better coupling between the fiber and the spot size converter waveguide), the misalignment tolerance when coupling the dual-tip spot size converter waveguide 300 to such a single-mode fiber (MFD ~ 8μm to 10μm) is 5 to 15 times looser than the maximum tolerance required to couple a conventional single-tip tapered spot size converter waveguide to the same single-mode fiber. Furthermore, for example, the misalignment tolerance in coupling the dual tip spot size converter waveguide 300 to a typical (non-lensed) single mode fiber (fiber MFD ˜8 μm to 10 μm) is still 2 to 3 times looser than the maximum tolerance allocated for coupling a conventional single tip tapered spot size converter waveguide to a lensed single mode fiber (a lensed single mode fiber is a single mode fiber modified to have a lensed fiber tip with an MFD of about 2.5 μm to 4 μm, which is done to improve the coupling loss between the fiber and the conventional single tip tapered spot size converter waveguide. Thus, the coupling process between the waveguide 300 and the single mode fiber is less time consuming and less expensive than coupling a conventional spot size converter SSC with a single tip tapered waveguide to the same or similar fiber.

[0106] Furthermore, because the MFD in the dual tip waveguide 300 can be extended to match the MFD of a single mode fiber, direct coupling of the waveguide 300 to the single mode fiber 400 can be achieved with low loss and without the need for additional structures. For example, the waveguide 300 is a "single stage" waveguide, and the spot size converter (SSC) 200 for coupling to a single mode fiber does not require a dual stage waveguide spot size converter (SSC) structure (i.e., a structure made of overlapping waveguides placed on top of each other).

[0107] Figure 6 The normalized optical power distribution at the end of the waveguide 300 adjacent to the second end of the waveguide portions 301, 302 is shown relative to the transverse dimension (micrometers) (solid line), and the normalized optical power distribution of the single-mode optical fiber 400 relative to the transverse dimension (dashed line). More specifically, Figure 6 shows a SMF with tip width t=W1min=W2min=40nm. Mode distribution of optical fiber ψ SMF (r) and the mode distribution ψ of the double-tip SSC waveguide 300 SSC (r) (normalized in power ∫ψ(r)rdr=1). Figure 6 As shown, most of the optical power is located in a spot of about 10 microns in width, which is centered at a lateral position of about 62.5 microns. A typical single-mode optical fiber has an uncoated fiber diameter (i.e., cladding diameter) of about 125 microns. Therefore, in this embodiment, the center of the core is located at a lateral position of 62.5 microns, and as shown in FIG. Figure 6 As shown, most of the power provided by the waveguide 300 to the optical fiber 400 is coupled to the fiber core. For the optical waveguide 300 coupled to the single-mode optical fiber 400, by integrating the overlapping portion of the two normalized optical power distributions (i.e., by integrating the overlapping portion of the two normalized powers), the coupling coefficient between the waveguide 300 and the single-mode optical fiber 400 is calculated to be about 95%.

[0108] Therefore, according to one embodiment, the apparatus for light transmission includes the spot size converter 200 as described above, the spot size converter 200 including the optical waveguide 300. According to some embodiments, the spot size converter 200 is configured to couple an optical signal to the optical waveguide 500, wherein the optical signal is input from the optical fiber 400. According to some embodiments, the spot size converter 200 is connected to the optical waveguide 500 by using the second end of the third waveguide portion 303, and the width of the second end of the third waveguide portion is equal to the width W4 of the optical waveguide 500.

[0109] It will be appreciated that in this embodiment, the waveguide 300 may be formed using electron beam lithography (EBL) or a CMOS compatible process with deep ultraviolet lithography (DUVL). Preferably, the waveguide 300 may be manufactured by removing a tapered region inside the input section of the waveguide using a relatively low resolution CMOS compatible manufacturing technique to create a tapered gap Gr between the two waveguide portions 301, 302 of the waveguide 300. It is advantageous to manufacture the waveguide 300 using CMOS compatible manufacturing techniques because this may result in the production of a cheaper spot size converter 200.

[0110] like Figure 5B As shown and as described above, the larger the width Gmax of the large end of the taper Gr, the greater the achievable mode expansion, and thus the better the coupling of the waveguide 300 to the optical fiber 400.

[0111] In contrast, a conventional SSC (spot size converter) has a tapered waveguide with a single tip, and the taper size of a typical single tip waveguide is reduced from about 500 nm to a tip of about 100 nm. Single tip SSC waveguides with smaller taper sizes (e.g., between 10 nm and 90 nm) cannot be manufactured using conventional CMOS DUVL SSC manufacturing processes because conventional SMOS DUVL technology has relatively low lithographic resolution. In addition, conventional single tip SSC waveguides have a tip size of about 100 nm and provide an extended MFD (i.e., maximum MFD) of only about 3 microns or 4 microns. High resolution lithography is required to make single tip SSC waveguides with smaller tip sizes, and such SSC waveguides are very expensive to manufacture.

[0112] According to one embodiment, the waveguide 300 can also be fabricated on a standard SOI (Silicon On Isolator) wafer by DUVL or EBL and anisotropic plasma dry etching to define the inner tapered region forming the tapered gap Gr and the double tips of the waveguide portions 301, 302. In addition, the waveguide 300 can also be formed by using photolithography techniques.

[0113] Once the waveguide 300 is fabricated, an oxide layer (e.g., silicon dioxide, SiO2) may be deposited on top of the waveguide 300 by PECVD (plasma enhanced chemical vapor deposition). 2 ). The first cladding layer 202 is located directly beside the waveguide 300 and serves as a cladding layer that supports and contains the (signal) light propagating within the waveguide 300. The material of the cladding layer 202 (cladding material) has a refractive index that is less than the refractive index of the material of the waveguide 300 (core material).

[0114] Due to the tapered gap Gr inside the input section of the waveguide 300, the waveguide 300 is advantageously suitable for coupling a SOI waveguide (such as the waveguide 500) and a single-mode optical fiber 400. The tapered gap is created, for example, by a lithography-based manufacturing technique. More importantly, the waveguide 300 has multiple tips (e.g., dual tips) that can provide a greater extension of the MFD (e.g., a maximum MFD ≥ 8 microns) and further achieve low-loss coupling with the single-mode optical fiber 400 without the need for additional stages or additional (multiple) waveguide structures.

[0115] The spot size converter (SSC) 200 described herein may be manufactured by a CMOS-compatible process based on DUVL (deep ultraviolet lithography) or EBL. Figure 7A-7E Two exemplary embodiments of processes for making a multi-tip spot size converter 200 are shown. These methods create a tapered region Gr inside the input section of the waveguide 300, for example, preferably using Fig. 7A and Figure 7B Two exemplary CMOS compatible processes are shown (e.g., single-step Si etching), or Figure 7C-Figure 7E Two-step (Si) etching embodiment shown. According to embodiments described herein, the waveguide 300 and spot size converter (SSC) 200 described herein may be fabricated using commercial CMOS compatible processes.

[0116] The deep ultraviolet lithography process (DUVL) utilizes a deep ultraviolet beam having a wavelength of no more than 300 nm, for example, less than 260 nm, for example, 150 nm to 225 nm, or 200 nm to 255 nm. For example, the irradiation wavelength of DUVL may be 248 nm, 246 nm, 193 nm, or 157 nm. The mask used in the DUVL process may be made of chrome or aluminum, and the exposure time used in the DUVL process may be, for example, less than 10 minutes, and preferably 3 minutes or less (e.g., 1 second to 3 minutes).

[0117] First process ( Fig. 7A , Figure 7B Process 1) shown.

[0118] Summary of the first process:

[0119] During the first process, a resist material is spin-coated onto a wafer 600 (e.g., an SOI wafer) or otherwise deposited onto the wafer. The resist material is a photoresist compatible with DUVL or an electron beam resist compatible with EBL. After exposure (e.g., by DUVL or EBL) and development, the pattern of the waveguide is transferred to the waveguide material layer (e.g., a silicon layer), for example, via plasma dry etching. The resist residue is then removed, for example, by oxygen plasma cleaning. Finally, the oxide (cladding material, e.g., SiO 2 ) can be deposited by plasma enhanced chemical vapor deposition (PECVD) over the resulting waveguide 300. Details of one embodiment of this process are described below.

[0120] First, during step 1, a wafer 600 (eg, a SOI wafer) comprising three layers 602, 604, 606 is manufactured or provided for step 2 of the process. Layer 602 is made of waveguide material, layer 604 is referred to herein as an insulator layer, and layer 606 serves as a wafer substrate layer.

[0121] Insulator layer 604 may be, for example, a silica-based glass (e.g., SiO 2 ). According to some embodiments, layer 602 and layer 606 are silicon layers. According to other embodiments, at least one of layer 602 and layer 606 is silicon nitride. According to some embodiments, one of layer 602 or layer 606 may be silicon and the other layer may be silicon nitride.

[0122] During step 2 of the present embodiment, a resist material 610' is spin-coated onto a wafer 600 (e.g., an SOI wafer), thereby producing a resist layer 610. The resist material 610' can be, for example, a ZEP520A electron beam resist material available from Zeon Corporation, or another etchant material used in a photolithography process (e.g., a DUV photoresist). This type of resist material is considered a "positive resist material," i.e., a resist material that is removed after exposure and development, and unexposed areas remain.

[0123] Step 3 can be performed by DUVL or EBL.

[0124] If EBL is used in step 3 , only the resist areas that need to be removed are exposed to an electron beam and then developed by an electron beam compatible developer to remove unwanted sections of the resist material and form a resist transfer pattern 610 ″. The resulting resist transfer pattern 610 ″ is in the shape of the waveguide 300 .

[0125] If DUVL is used in step 3, a photolithography development process is applied to the resist layer 610 to form a resist layer transfer pattern 610". For example, after the resist layer 610 is exposed to a deep ultraviolet beam and the resist material is developed with a DUVL-compatible developer, a desired pattern is transferred from the mask to the resist layer 610, thereby forming the shape of the waveguide 300 in the resist material (i.e., forming the resist transfer pattern 610" in the shape of the waveguide 300). That is, unwanted portions of the resist material are removed, and the remaining resist material has the shape of the waveguide 300.

[0126] Step 3 is followed by step 4, which includes removing the waveguide material from the wafer except for a portion located under the resist transfer pattern 610″, and thereby forming the waveguide 300. For example, dry plasma etching (step 4) is used to etch and remove (etch away) the layer 602 except for a portion 602′ of the layer 602 located under the resist transfer pattern 610″, thereby forming the waveguide 300 located under the transfer pattern 610″ and on the insulator layer 604 (which corresponds to the layer 202 of the spot size converter 200). The insulator layer 604 has a dielectric constant (D ) of less than 4, preferably less than 3, for example, 1.5 to 2.5, or 1 to 2.5. k ). The insulator layer 604 may be, for example, pure SiO 2 glass or another glass (eg, potassium lithium borosilicate).

[0127] In step 5, the resist residues (resist pattern 610″ located above the portion(s) 602′) are subsequently removed (e.g., by oxygen plasma cleaning), thereby exposing the waveguide 300 located above the insulator layer 604. Such a waveguide and a spot size converter including the waveguide are, for example, Figure 1B Shown in.

[0128] Finally (and optionally), in step 6, a top cladding layer 608 of an oxide (e.g., silicon dioxide) or similar cladding material is deposited over the resulting silicon waveguide 300, for example by PECVD (plasma enhanced chemical vapor deposition), resulting in the waveguide 300 being covered by layer 202, as shown. Figure 1A shown.

[0129] Second process ( Figure 7C-Figure 7E Process 2) shown.

[0130] Summary of the second process: Process 2 is a two-step patterning process. During this process, a photoresist or electron beam resist material is spin-coated on a wafer 600 (e.g., an SOI wafer) and exposed to a deep ultraviolet beam or an electron beam, for example, via a DUVL or EBL process. After the development of the resist material, a waveguide pattern (e.g., a band waveguide pattern) is transferred to a waveguide material layer 602 (e.g., a silicon layer), for example, via anisotropic plasma dry etching. After removing the resist residue, a new resist layer is spin-coated on the wafer again. The waveguide-in-waveguide taper (i.e., the gap region Gr) between the waveguide portion 301 and the waveguide portion 302 is patterned by a second DUVL or EBL. If a DUVL process is used, patterning of the waveguide region between the waveguide portion 301 and the waveguide portion 302 is performed in combination with high-precision mask alignment. Subsequently, the tapered structure of the waveguide portions 301, 302 is formed (e.g., by silicon dry etching). Finally, an oxide (e.g., SiO 2 A top cladding layer of silicon (or another glass) can be deposited on top of the silicon waveguide by plasma enhanced chemical vapor deposition (PECVD). Details of an exemplary embodiment of this process are described below.

[0131] More specifically, during step 1, a wafer 600 (e.g., a silicon-on-insulator wafer, SOI) including three layers 602, 604, 606 is manufactured or provided for step 2 of exemplary process 2. The insulator layer 604 may be, for example, a silica-based glass (e.g., SiO 2 ). According to some embodiments, one of the layers 602, 606 may be silicon and the other layer may be silicon nitride.

[0132] During step 2, a resist material 610' is spun onto a wafer 600 (eg, SOI), thereby producing a resist layer 610. The resist material 610' may be, for example, ZEP520A material available from Zeon Corporation or another suitable resist material.

[0133] The waveguide 300 is then created via a two-step patterning process. During the first patterning step (step 3 of the second process), the initial waveguide shape is created in the resist material by a photolithography process. Step 3 of process 2 can be performed by DUVL or EBL.

[0134] If EBL is used in step 3, only the resist areas that need to be removed are first exposed to an electron beam and then developed by an electron beam compatible developer to remove the unwanted sections of the resist material and form a first resist transfer pattern 610″A (also referred to herein as a partial waveguide pattern) on layer 602.

[0135] If DUVL is used in step 3, a photolithography development process is applied to the resist layer 610 to form a first resist layer transfer pattern 610"A. A first mask is placed over the resist layer, and after the resist layer 610 is exposed to a deep ultraviolet beam and the resist material is developed with a DUVL compatible developer, unwanted portions of the resist material are removed and the desired pattern of the waveguide (partial waveguide pattern) is transferred from the mask to the resist layer 610, thereby forming an initial shape of the waveguide 300 in the resist material (i.e., forming a resist transfer pattern 610"A).

[0136] Step 3 is followed by step 4. Step 4 includes removing the waveguide material from the wafer, except for the portion of the waveguide material located under the resist transfer pattern 610". More specifically, step 4 is used to etch and remove the material of the layer 602, except for the portion 602' of the layer 602 located under the resist pattern 610", to form an initial waveguide. Step 4 can be, for example, an anisotropic plasma dry etching step.

[0137] After step 4, resist residues (ie, remaining resist pattern 610"A located over portion(s) 602') may optionally be removed, for example, by oxygen plasma cleaning.

[0138] It should be noted that in the process 2 embodiment, after performing step 3, the resulting resist pattern 610" (partial waveguide pattern) does not include a gap region corresponding to the gap region Gr of the waveguide 300. Therefore, the portion 602' of the waveguide material layer 602 located below the resist pattern 610" forms an initial waveguide that does not include an internal gap Gr located between the two waveguide portions.

[0139] exist Fig.7D During step 5 of the exemplary process 2 shown in , the resist material 610' is again applied (e.g., spin-coated) over portion 602' and over the exposed portion of layer 604, thereby producing a second resist layer 610. The resist material 610' for the second resist layer 610 can be, for example, ZEP520A material available from Rayon or another suitable resist material. The resist material can be, for example, a positive resist material as described above, or a "negative resist material", for example, ma-N 2400 available from MicroChem. The negative resist material remains on its exposed substrate surface, and the developer solution removes only the unexposed areas.

[0140] The taper of the waveguide parts 301, 302 and the gap region Gr inside the waveguide 300 are then patterned inside the initial waveguide by a second patterning step. The second patterning (step 6 of process 2) can be performed by DUVL or EBL.

[0141] If EBL is used in step 6 (with high precision alignment of the electron beam), only the resist areas that need to be removed are exposed to the electron beam and then developed by an electron beam compatible developer to remove unwanted sections of the resist material and form a resist transfer pattern 610". In this embodiment, the layer 602 material corresponding in shape to the shape of the gap Gr is removed from a portion 602' of the waveguide material layer 602.

[0142] Alternatively, the resist material may be a negative photoresist material (NR), and a second photolithography step (step 6 of process 2) may be performed in conjunction with high precision alignment of mask 615A, such as Fig. 7E Schematically shown. For example, in step 6 of process 2, mask 615A is located above the portion of the second resist layer 610 (negative resist material layer) that is above portion 602'. Then, the negative resist layer 610 that is not covered by the mask is irradiated with an ultraviolet light beam (e.g., a deep ultraviolet beam having a wavelength of about 248nm or less, such as a wavelength of 150nm≤λ≤197nm). Because the photolithography developer only removes the unexposed areas of the negative resist material, and mask 615A prevents portions of the resist area from being exposed to deep ultraviolet radiation, the developer subsequently removes the trapezoidal segment of the negative resist material (because the trapezoidal segment is located below the mask) to form a trapezoidal gap pattern in the shape of the gap area Gr in the negative resist material.

[0143] The waveguide material (e.g., silicon) located below the gap portion of the mask 615 is then etched in step 7 of the process. This results in the formation of a gap region Gr within the waveguide 300 and the separated waveguide portions 301, 302. That is, the resulting inner portion of the waveguide 300 is patterned by etching (e.g., removing silicon) of the waveguide material between the waveguide portion 301 and the waveguide portion 302. The mask 615A is tapered (e.g., trapezoidal), that is, the mask 615A has a tapered width. The shape of the mask 615A corresponds to the shape of the gap region Gr. The mask features at the small side of the mask corresponding to the small side of the gap region are, for example, about 100 nm (and can be in the range of from greater than 90-100 nm to about 150 nm) (which corresponds to the minimum gap width Gmin). The large side of the mask is preferably greater than 400 nm. That is, the mask 615A (second mask) has a tapered width with a minimum width Gmin between 90 nm and 150 nm and a maximum width between 350 nm and 450 nm (corresponding to the maximum gap region width Gmax). Therefore, the minimum gap width Gmin between the two waveguide portions 301, 302 of the waveguide 300 is about 90-100 nm, which corresponds to a minimum feature size of the mask 615A that can be achieved with a standard industrial (low resolution) CMOS DUVL process, and which can result in a tip width of, for example, less than 90 nm.

[0144] More specifically, in Fig. 7E and Fig.7D In the illustrated embodiment, a dry plasma etching step (step 7, part A) is used to etch away and remove the waveguide material layer 602 except for the portion 602' corresponding to the waveguide 300. In step 7 (part B), the resist residue (the remaining resist pattern 610" located above the portion(s) 602') is subsequently removed (e.g., by oxygen plasma cleaning) to form the waveguide 300 located above the layer 604. It should be noted that the layer 604 will correspond to the layer 202 of the spot size converter 200. Such a spot size converter is, for example, Figure 1B Finally (and optionally), in step 8, silicon dioxide (SiO 2 ) is deposited on top of the resulting silicon waveguide by PECVD (plasma enhanced chemical vapor deposition), resulting in the waveguide 300 being covered by layer 202, as shown Figure 1A Using a second (negative) resist material layer in conjunction with mask 615A can produce a waveguide 300 having a tip width W1min, W2min of 100 nm or less, such as 20 nm to 90 nm, 10 nm to 90 nm, or 20 nm to 60 nm.

[0145] Alternatively, during step 6 of process 2, the second resist material may be a positive resist material (PR), and a second photolithography step (step 6 of process 2) may be performed in conjunction with mask 615B, such as Fig. 7E Schematically shown in . Mask 615B includes a gap in a trapezoidal shape. After mask 615B is located on the portion of the second (positive) resist layer 610 above portion 602', the positive resist layer 610 not located below the gap section of mask 615B is irradiated by an ultraviolet light beam (e.g., a deep ultraviolet beam having a wavelength of about 248nm or less). As described above, the positive resist material is a resist material that is removed after exposure and development, and the unexposed area remains. Therefore, a photolithography process is applied to the positive resist layer 610 to remove a trapezoidal pattern in the shape of the gap region Gr from the positive resist material. The waveguide material (e.g., silicon) located below the removed resist material is then etched. This results in the formation of a gap region Gr located within the waveguide 300 and located in the separated waveguide portions 301, 302. That is, the resulting inner portion of the waveguide 300 is patterned by etching (e.g., removing silicon) the waveguide material between the waveguide portion 301 and the waveguide portion 302. The use of a second (positive) resist material layer in conjunction with mask 615B can produce a waveguide 300 having a tip width of 90 nm to 100 nm or more. As described above, a smaller waveguide tip width can be achieved by using a negative resist layer with mask 615A.

[0146] In summary, the first process (Process 1) uses a single step (Si) etch to directly pattern the dual tips of the waveguide 300. In order to achieve narrow tip widths W1min, W2min less than 90nm or 100nm (e.g., 70nm, 50nm, or 40nm) with the first process, very high lithography resolution is required. Therefore, the first process should use EBL to achieve such a small tip width.

[0147] However, in the second process embodiment (Process 2, which uses two-step etching), the dual tip configuration of the multi-tip waveguide 300 is created (patterned) by creating a tapered gap region via a second (Si) etching step, wherein the minimum dimension of the tapered mask 615A is about 90-100 nm or larger. Therefore, it is more preferable (and cheaper) to employ the second process for mass production of the spot size converter 200 by using a standard industrial CMOS 193-nm DUVL, wherein the minimum feature dimension of the mask 615A is in the range of about 90 nm or 100 nm to about 150 nm (the minimum feature dimension of the mask 615 corresponds to the minimum gap width Gmin). This allows narrow tip widths W1min, W2min below 90nm or 100nm (e.g., 80nm, 75nm, 70nm, 60nm, 50nm, 45nm, 40nm, 30nm, 20nm, or 10nm to 50nm, or 20nm to 50nm) to be achieved without using very high lithography resolution or without using EBL.

[0148] Figure 8 The calculated optical power conversion efficiency of an exemplary embodiment of a dual tip SSC (spot size converter) waveguide 300 at a transmission wavelength of 1550 nm is shown. The dual tip SSC (spot size converter) waveguide 300 consists of a 200 nm deep by 500 nm wide Si (silicon) waveguide portion 303 and two waveguide portions 301, 302. In this embodiment, the waveguide portion 301 and the waveguide portion 302 are tapered and each waveguide portion 301, 302 has a tip that is 220 nm deep and 90 nm wide, resulting in a separation (Gmax) of 320 nm between the waveguide tips. In this embodiment, the Si waveguide 300 is located on a low refractive index (1.44-1.46) buried oxide layer and is covered by a low temperature silicon oxide with a similar refractive index deposited on top. The initial width (Gmin) of the tapered gap is 100 nm. Figure 8 It is shown that an optical power conversion efficiency (also referred to herein as coupling efficiency α) greater than 0.9 (i.e., a loss less than ˜0.5 dB) can be achieved with a length Lt greater than 600 microns. Thus, the design of the waveguide 300 allows for the realization of an efficient and compact mode converter (spot size converter 200) with a minimum feature size corresponding to a Gmin of about 100 nm, which is well within the current capabilities of the DUVL CMOS process. Therefore, the spot size converter 200 can be advantageously manufactured by an embodiment of process 2.

[0149] Alternatively, in one embodiment, when the width W4 of the optical waveguide 500 is 500 nm and the thickness H4 of the optical waveguide 500 is H4=220 nm, the parameter values ​​of the waveguide 300 of the spot size converter 200 may be as shown in Table 1.

[0150] Table 1

[0151]

[0152] In the embodiment of Table 1, the spot size converter 200 includes a waveguide 300, and the waveguide 300 has a first waveguide portion 301, a second waveguide portion 302, and a third waveguide portion 303. The spot size converter 200 of Table 1 can be used to achieve spot size conversion between the optical fiber 400 and the optical waveguide 300, and the coupling loss between the optical fiber 400 and the optical waveguide 300 can be reduced by using the spot size converter 200.

[0153] For example, if Figure 1A or Figure 1B The spot size converter 200 shown is disposed between the optical fiber 400 and the optical waveguide 500, and the optical signal output from the optical fiber 400 can be coupled to the spot size converter 200. There is an optical field distributed between the first waveguide portion 301 and the second waveguide portion 302. Then, the optical signal can be coupled to the third waveguide portion 303, and further coupled to the rear optical waveguide 500, as shown in FIG. Figure 4 shown.

[0154] Alternatively, for example, the parameters of the spot size converter use the values ​​shown in Table 1. SMF- The outer diameter of the exemplary single-mode optical fiber 400 is about 125 μm, and its core diameter is about 8.2 μm. The mode field (normalized mode distribution) of the optical signal output from the optical fiber 400 is about 125 μm. Figure 6 3 and can be understood as the mode field of the input optical signal of the spot size converter 200. The spot diameter of the mode field is about 10 μm (i.e., the MFD provided by the waveguide 300 of the present embodiment is about 10 μm). Therefore, when a single-mode optical fiber is used with the spot size converter 200 provided in the present embodiment, there is a relatively large alignment tolerance. Therefore, by using the spot size converter 200 provided in the present embodiment instead of a conventional spot size converter, the alignment requirements between the optical fiber 400 and the spot size converter 200 can be greatly relaxed.

[0155] It can be understood that in the aforementioned embodiments, the waveguide in the spot size converter 200 is symmetrical or substantially symmetrical in structure, and the symmetry plane is a plane perpendicular to the width direction, or the symmetry plane can be understood as a yz plane.

[0156] Therefore, one embodiment of the present disclosure relates to an optical waveguide, comprising: a first waveguide portion (301) with a tapered width, a second waveguide portion (302) with a tapered width, and a third waveguide portion (303), wherein a first end of the third waveguide portion (303) is connected to a first end of the first waveguide portion (301) and a first end of the second waveguide portion (302); and along a first direction of a main axis, the widths of the first waveguide portion and the second waveguide portion gradually increase toward a first end of the third waveguide portion, and a distance between the first waveguide portion and the second waveguide portion in a second direction gradually decreases from a second end of the first waveguide portion to a first end of the first waveguide portion, wherein the second direction is located on a plane where the waveguide is located, and the second direction is perpendicular to the first direction; and wherein a distance Gmax between a second end of the first waveguide portion (301) and a second end of the second waveguide portion (302) is greater than 0.2 μm and less than 0.48 μm; and the waveguide has a refractive index between 2 and 4 at a wavelength of 1550 nm.

[0157] According to some embodiments, a spot size converter includes:

[0158] A substrate layer; a first covering layer, the first covering layer is arranged above the substrate layer, wherein the first covering layer comprises a first material; a single-stage waveguide (300), the single-stage waveguide (300) is arranged to contact the first covering layer, wherein the waveguide is symmetrical or approximately symmetrical along a main axis, and the waveguide comprises a third material; wherein the waveguide comprises a first waveguide portion (301) with a tapered width, a second waveguide portion (302) with a tapered width, and a third waveguide portion (303), a first end of the third waveguide portion (303) is connected to a first end of the first waveguide portion (301) and a first end of the second waveguide portion (302); and along a first direction of the main axis, the first waveguide The widths of the first waveguide portion and the second waveguide portion (301, 302) gradually increase toward the first end of the third waveguide portion (303), and the distance between the first waveguide portion (301) and the second waveguide portion (302) in a second direction gradually decreases from the second end of the first waveguide portion (301) to the first end of the first waveguide portion (301), wherein the second direction is located on a plane where the waveguide (300) is located, and the second direction is perpendicular to the first direction; and the distance Gmax between the second end of the first waveguide portion (301) and the second end of the second waveguide portion (302) is greater than 0.2 μm and less than 0.48 μm; and

[0159] The Δ% of the third material relative to the first material is greater than 25%. According to some embodiments, the Δ% of the third material relative to the first material is greater than 50%.

[0160] According to some embodiments, a gap is located between the first waveguide portion and the second waveguide portion. According to some embodiments, the gap has a trapezoidal cross-section. According to some embodiments, the gap has a V-shaped cross-section. According to some embodiments: (i) the waveguide is a silicon waveguide, (ii) the distance G between the second ends of the first waveguide portion and the second waveguide portion narrows from the second ends of the first waveguide portion and the second waveguide portion to the first ends of the first waveguide portion and the second waveguide portion, thereby forming a tapered gap having a taper with a length Lt such that 300 microns < Lt < 5000 microns, wherein the minimum distance / width Gmin of the tapered gap is between 50 nm and 150 nm, and the maximum distance / width Gmax is between 300 nm and 480 nm (e.g., between 350 nm and 450 nm, or between 400 nm and 450 nm). According to some embodiments, the width of the third waveguide portion is between about 400 nm and about 500 nm (e.g., between 450 nm and 500 nm), and the thickness of the third waveguide portion is between 200 nm and 225 nm.

[0161] Additional embodiments of the present disclosure relate to a spot size converter (SSC) comprising:

[0162] a substrate layer;

[0163] a first cladding layer disposed above the substrate layer, wherein the first cladding layer comprises a first material;

[0164] an intermediate layer disposed between the substrate layer and the first cladding layer, wherein the optional intermediate layer (203) comprises a second material; and

[0165] a single-stage waveguide (300) disposed within the first cladding layer, wherein the waveguide is symmetric (or approximately symmetric) along the main axis, and the waveguide comprises a third material; wherein the waveguide comprises a first waveguide portion (301) with a tapered width, a second waveguide portion (302) with a tapered width, and a third waveguide portion (303), and the first end of the third waveguide portion (303) is connected to the first ends of the first waveguide portion (301) and the second waveguide portion (302); such that a tapered gap is located between the first waveguide portion and the second waveguide portion; and

[0166] along a first direction of the main axis, the widths of the first waveguide portion and the second waveguide portion (301, 302) gradually increase towards the first end of the third waveguide portion (303), and the distance between the first waveguide portion (301) and the second waveguide portion (302) in a second direction gradually decreases from the second end of the first waveguide portion (301) to the first end of the first waveguide portion (301), wherein the second direction lies in the plane of the waveguide (300) and the second direction is perpendicular to the first direction; and wherein

[0167] A maximum distance (maximum width) Gmax between the second end of the first waveguide portion (301) and the second end of the second waveguide portion (302) is greater than 0.2 μm and less than 0.48 μm; and

[0168] The Δ% of the third material relative to the first material is >25% (eg, >50%).

[0169] Additional embodiments of the present disclosure relate to a spot size converter (SSC), comprising:

[0170] substrate layer;

[0171] a first covering layer disposed above the substrate layer, wherein the first covering layer comprises a first material;

[0172] an intermediate layer disposed between the substrate layer and the first cover layer, wherein the optional intermediate layer (203) comprises a second material; and

[0173] A single-stage waveguide (300) disposed inside a first covering layer, wherein the waveguide is symmetrical along a main axis and comprises a third material; wherein the waveguide comprises a first waveguide portion (301) having a tapered width, a second waveguide portion (302) having a tapered width, and a third waveguide portion (303), wherein a first end of the third waveguide portion (303) is connected to a first end of the first waveguide portion (301) and a first end of the second waveguide portion (302); and

[0174] Along a first direction of the main axis, the widths of the first waveguide portion and the second waveguide portion (301, 302) gradually increase toward the first end of the third waveguide portion (303), and the distance between the first waveguide portion (301) and the second waveguide portion (302) in a second direction gradually decreases from the second end of the first waveguide portion (301) to the first end of the first waveguide portion (301), wherein the second direction is located on a plane where the waveguide (300) is located, and the second direction is perpendicular to the first direction; and wherein

[0175] A distance Gmax between the second end of the first waveguide portion (301) and the second end of the second waveguide portion (302) is greater than 0.2 μm and less than 0.48 μm; and

[0176] The Δ% of the third material relative to the second material is >25% (eg, >50%).

[0177] According to some exemplary embodiments, the waveguide is configured to provide a coupling loss of <2 dB (e.g., <1 dB, or ≤0.5 dB) to a single-mode optical fiber and has a mode field diameter (MFD) at 1550 nm such that MFD≥7 microns. According to some embodiments, the waveguide is configured to provide a coupling loss of <1.5 dB and MFD≥7 microns. According to some embodiments, the waveguide is configured to provide a coupling loss of <1 dB and MFD≥7 microns. According to some embodiments, the waveguide is configured to provide a coupling loss of <1 dB at 1550 nm when coupled to a single-mode optical fiber and has MFD≥8 microns at 1550 nm. According to some embodiments, the waveguide is configured to provide a coupling loss of <1 dB when coupled to a single-mode optical fiber and 7.5 microns≤MFD≤10 microns at 1550 nm.

[0178] According to some embodiments of the SSC, at a wavelength of 1550 nm, the absolute value of the difference between the refractive index n2 of the second material and the refractive index n1 of the first material is less than 0.1, and / or at a wavelength of 1550 nm, the absolute value of the difference between the refractive index n3 of the third material and the refractive index n1 of the first material is 0.5. <n3-n1<2.5。

[0179] According to some embodiments:

[0180] The length of the waveguide (300) is L1,

[0181] The lengths of the first waveguide portion (301) and the second waveguide portion are L2, and the length of the third waveguide portion is L3;

[0182] The thickness of the first waveguide portion (301), the thickness of the second waveguide portion (302) and the thickness of the third waveguide portion (303) are H1,

[0183] The minimum widths of the first waveguide portion (301) and the second waveguide portion (302) are W1min and W2min respectively, the width of the second end of the third waveguide portion (303) is W3, and the distance between the waveguide (300) and the top of the substrate layer (201) or the bottom of the optional intermediate layer (203) is H3, where 0 < L1 ≤ 500 μm, 0 < L3 ≤ 200 μm, 0 < H1 ≤ 400 nm, H3 > 2 μm (for example, H3 ≥ 3 μm, or in some embodiments H3 ≥ 5 μm), 50 nm < W1min ≤ 100 nm, 50 nm < W2min ≤ 100 nm, and 200 nm ≤ W3 ≤ 550 nm. According to some embodiments, 0 < L1 ≤ 500 μm, 0 < L3 ≤ 200 μm, H1 + H3 > 3 μm, and H3 > 2.5 μm (for example, H3 > 3 μm or H3 ≥ 5 μm), 70 nm < W1min ≤ 90 nm, 70 nm < W2min ≤ 90 nm and 400 nm ≤ W3 ≤ 500 nm. According to some embodiments, the maximum gap width Gmax between the first waveguide portion (301) and the second waveguide portion (302) is 200 nm ≤ Gmax ≤ 450 nm. According to some embodiments, the maximum gap width Gmax between the first waveguide portion (301) and the second waveguide portion (302) is 300 nm ≤ Gmax ≤ 450 nm, or 200 nm ≤ Gmax ≤ 400 nm.

[0184] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention. Since those skilled in the art can conceive of modifications, combinations, sub - combinations, and variations of the disclosed embodiments that include the spirit and substance of the invention, the invention should be understood to cover all of the scope of the appended claims and their equivalents.

Claims

1. A single - stage waveguide (300) comprising: A first waveguide section (301) with a tapered width, a second waveguide section (302) with a tapered width, and a third waveguide section (303), such that A first end of the third waveguide section (303) is connected to a first end of the first waveguide section (301) and a first end of the second waveguide section (302); and In a first direction, the widths of the first waveguide section (301) and the second waveguide section (302) gradually increase towards the first end of the third waveguide section (303), and The distance between the first waveguide section (301) and the second waveguide section (302) in a second direction gradually decreases from a second end of the first waveguide section (301) to the first end of the first waveguide section (301), Where the second direction lies in the plane of the waveguide (300) and the second direction is perpendicular to the first direction; and the waveguide has a refractive index between 2 and 4 at a wavelength of 1550 nm, and The distance G between the first waveguide section (301) and the second waveguide section (302) narrows from the second ends of the first and second waveguide sections to the first ends of the first and second waveguide sections, thereby forming a tapered gap region having a taper with a length Lt such that 300 microns < Lt < 2000 microns, and where the minimum distance Gmin of the tapered gap region is between 50 nm and 150 nm, and the distance Gmax between the second end of the first waveguide section (301) and the second end of the second waveguide section (302) is between 300 nm and 450 nm, and the sum of the width W1min of the second end of the first waveguide section (301), the width W2min of the second end of the second waveguide section (302), and the distance Gmax is equal to the width W3 of the third waveguide section (303).

2. The waveguide according to claim 1, characterized in that The gap region between the first waveguide section and the second waveguide section has a trapezoidal cross - section.

3. The waveguide according to claim 1, characterized in that: The waveguide is a silicon waveguide.

4. The waveguide according to claim 1, 2 or 3, characterized in that: (i) The width W3 of the third waveguide section is from 450 nm to 500 nm, and (ii) The third waveguide section has a thickness H1, and the thickness H1 of the third waveguide section is between 200 nm and 225 nm.

5. A spot size converter, characterized in that: The spot - size converter comprises: A substrate layer, where the material of the substrate layer is silicon; A first cladding layer, the first cladding layer is disposed above the substrate layer, where the first cladding layer comprises a first material; A single-stage waveguide (300), the single-stage waveguide (300) being arranged in contact with the first covering layer, wherein the waveguide comprises a third material; wherein the waveguide comprises a first waveguide portion (301) having a tapered width, a second waveguide portion (302) having a tapered width, and a third waveguide portion (303), a first end of the third waveguide portion (303) being connected to a first end of the first waveguide portion (301) and a first end of the second waveguide portion (302); and Along the first direction, the widths of the first waveguide portion (301) and the second waveguide portion (302) gradually increase toward the first end of the third waveguide portion (303), and the distance between the first waveguide portion (301) and the second waveguide portion (302) in the second direction gradually decreases from the second end of the first waveguide portion (301) to the first end of the first waveguide portion (301), wherein The second direction is located on the plane where the waveguide (300) is located, and the second direction is perpendicular to the first direction; and wherein, A distance Gmax between the second end of the first waveguide portion (301) and the second end of the second waveguide portion (302) is between 300 nm and 450 nm, and a sum of a width W1min of the second end of the first waveguide portion (301), a width W2min of the second end of the second waveguide portion (302), and the distance Gmax is equal to a width W3 of the third waveguide portion (303); and The relative refractive index percentage Δ% of the third material relative to the first material is greater than 25%.

6. The spot size converter according to claim 5, characterized in that: The relative refractive index percentage Δ% of the third material relative to the first material is greater than 50%.

7. The spot size converter according to claim 5, characterized in that: The waveguide (i) is configured to provide a coupling loss of less than 2 dB when coupled to a single mode optical fiber; and (ii) has a mode field diameter MFD at a wavelength of 1550 nm such that MFD ≥ 7 microns.

8. The spot size converter according to claim 7, wherein: The waveguide is configured to provide a coupling loss of less than 1.5 dB at 1550 nm when the waveguide is coupled to the single mode optical fiber.

9. The spot size converter according to claim 8, characterized in that: (i) The waveguide is configured to provide a coupling loss of less than 1 dB at 1550 nm when the waveguide is coupled to the single-mode optical fiber.

10. The spot size converter according to claim 8, characterized in that: The waveguide is configured to provide a coupling loss of less than 1 dB at 1550 nm when the waveguide is coupled to a single mode optical fiber; and 7.5 microns ≤ MFD ≤ 10 microns.

11. The spot size converter according to claim 10, wherein: The waveguide is configured to provide a coupling loss between 0.2 dB and 1 dB at 1550 nm. 12 . The spot size converter according to claim 5 , wherein a difference between a refractive index n3 of the third material and a refractive index n1 of the first material is 2.5>n3-n1>0.

5.

13. The spot size converter according to any one of claims 5 to 12, characterized in that: The length of the single-stage waveguide is L1, the length of the first waveguide portion (301) is L2, the length of the second waveguide portion is L2, and the length of the third waveguide portion is L3; The thickness of the first waveguide portion, the thickness of the second waveguide portion (302) and the thickness of the third waveguide portion are H1, the minimum widths of the first waveguide portion and the second waveguide portion are W1min and W2min, and the distance between the waveguide (300) and the substrate layer is H3, wherein 0 μm < L1 ≤ 500 μm; 0 μm < L3 ≤ 200 μm; 0 μm < H1 ≤ 400 nm; H3 >2 μm; 50 nm < W1min ≤ 100 nm; 50 nm< W2min ≤ 100 nm; and 200 nm ≤ W3 ≤ 550nm.

14. The spot size converter according to claim 13, characterized in that: 200 μm < L1 ≤500 μm; H3>3 μm; 70 nm< W1min ≤ 90 nm; and 400 nm≤W3 ≤500 nm.

15. The spot size converter according to claim 13, characterized in that: Gmax=W3-2W1min.

16. The spot size converter according to any one of claims 9 to 12, characterized in that: The first material is silicon dioxide, and the third material is silicon or silicon nitride.

17. The spot size converter according to claim 14, further comprising an intermediate layer arranged between the substrate layer and the first cover layer, wherein the intermediate layer (203) comprises a second material; and wherein a relative refractive index percentage Δ% of the third material relative to the second material is greater than 25%.

18. The spot size converter according to claim 17, characterized in that: The relative refractive index percentage Δ% of the third material relative to the second material is greater than 50%.

19. A spot size converter, characterized in that: The spot size converter comprises: substrate layer; a first covering layer, the first covering layer being disposed above the substrate layer, wherein the first covering layer comprises a first material; an intermediate layer, the intermediate layer being arranged between the substrate layer and the first covering layer, wherein the intermediate layer (203) comprises a second material; and A single-stage waveguide (300), the single-stage waveguide (300) being arranged in contact with the first cover layer, wherein the waveguide comprises a third material; wherein the waveguide comprises a first waveguide portion (301) of tapered width, a second waveguide portion (302) of tapered width, and a third waveguide portion (303), a first end of the third waveguide portion (303) being connected to a first end of the first waveguide portion (301) and a first end of the second waveguide portion (302); and Along a first direction, the widths of the first waveguide portion (301) and the second waveguide portion (302) gradually increase toward the first end of the third waveguide portion (303), and the distance between the first waveguide portion (301) and the second waveguide portion (302) in a second direction gradually decreases from the second end of the first waveguide portion (301) to the first end of the first waveguide portion (301), wherein the second direction is located on a plane where the waveguide (300) is located, and the second direction is perpendicular to the first direction; and wherein A distance Gmax between the second end of the first waveguide portion (301) and the second end of the second waveguide portion (302) is between 300 nm and 450 nm, and a sum of a width W1min of the second end of the first waveguide portion (301), a width W2min of the second end of the second waveguide portion (302), and the distance Gmax is equal to a width W3 of the third waveguide portion (303); and The relative refractive index percentage Δ% of the third material relative to the second material is greater than 25%.

20. The spot size converter according to claim 19, characterized in that: The relative refractive index percentage Δ% of the third material relative to the second material is greater than 50%.

21. A device for optical transmission, characterized in that: The device comprises: A spot size converter as claimed in any one of claims 5 to 12 or claim 19; an optical waveguide; and The spot size converter is configured to couple an optical signal to the optical waveguide, wherein the optical signal is input from an optical fiber.

22. The device according to claim 21, characterized in that The spot size converter is connected to the optical waveguide by using a second end of a third waveguide portion, and a width of the second end of the third waveguide portion is equal to a width of the optical waveguide.

23. The device according to claim 21, characterized in that The thickness H1 of the third waveguide portion is equal to the thickness H4 of the optical waveguide.

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