Optical device and polarization rotator

Abstract

Various embodiments of the utility model provide a polarization rotator and a mode converter of an optical device. The optical device provided by the embodiment of the utility model comprises a polarization rotator and a mode converter. The polarization rotator includes a straight waveguide segment having a first end and a second end, a first widened waveguide segment continuing from the second end, a first tapered waveguide segment continuing from the first widened waveguide segment, a second widened waveguide segment disposed over the first widened waveguide segment, and a second tapered waveguide segment continuing from the second widened waveguide segment. The mode converter includes a third tapered waveguide segment continuing from the second tapered waveguide segment and a third widened waveguide segment disposed over the third tapered waveguide segment. The output end of the polarization rotator is coupled to the input end of the mode converter.

Description

Technical Field

[0001] The embodiments of the utility model relate to an optical device and a polarization rotator. Background Art

[0002] Modern information networks rely heavily on fiber optic communications. Electrical signals are converted to optical signals for transmission through optical fiber networks, and received optical signals are converted back to electrical signals for processing. Although optical signals propagating on optical fibers and waveguides may have transverse electrical (TE) polarization modes and transverse magnetic (TM) polarization modes, photonic components are generally designed to operate with specific polarization modes. This means that when different polarization modes are present, two sets of photonic components may be required to operate on different polarization modes. Polarization beam splitter rotators (PBSR) have been developed to convert optical signals with more than one polarization mode into optical signals with a single polarization mode. With the help of conversion, simpler and more efficient photonic component designs can be achieved. Although existing PBSRs are generally sufficient for their intended use, they are unsatisfactory in some respects. For example, existing PBSRs may be sensitive to temperature changes and the conversion efficiency may not be ideal. Utility Model Content

[0003] In one exemplary aspect, the present disclosure relates to an optical device. The optical device includes a polarization rotator, which includes a straight waveguide segment having a constant width between a first end and a second end along a direction, a first widening waveguide segment continuing the second end of the straight waveguide segment, the first widening waveguide segment having a first width along the direction, the first width linearly increasing from the second end, a first tapered waveguide segment continuing the first widening waveguide segment, the first tapered waveguide segment having a second width along the direction, the second width linearly decreasing from the first widening waveguide segment, the second widening waveguide segment being disposed above the first widening waveguide segment, and the second tapered waveguide segment continuing the second widening waveguide segment. The optical device also includes a mode converter, which includes a third tapered waveguide segment continuing the first tapered waveguide segment, and the third widening waveguide segment is disposed above the third tapered waveguide segment. The output end of the polarization rotator is coupled to the input end of the mode converter.

[0004] In another exemplary aspect, the present disclosure relates to a polarization rotator. The polarization rotator includes a straight waveguide segment having a constant width between a first end and a second end along a direction, at least two bottom inverted tapered waveguide segments sequentially continuing from the second end of the straight waveguide segment, the bottom tapered waveguide segment continuing from the at least two bottom inverted tapered waveguide segments, at least two top inverted tapered waveguide segments disposed above the at least two bottom inverted tapered waveguide segments, and the top tapered waveguide segment continuing from the at least two top inverted tapered waveguide segments and disposed directly above the bottom tapered waveguide segment. The straight waveguide segment, the at least two bottom inverted tapered waveguide segments, the bottom tapered waveguide segment, the at least two top inverted tapered waveguide segments, and the top tapered waveguide segment are disposed in a silicon oxide layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present disclosure will be best understood when the following detailed description is read in conjunction with the attached drawings. It should be emphasized that, in accordance with standard industry practice, various features are not drawn to scale and are for illustration purposes only. In fact, the size of various features may be arbitrarily increased or decreased for clarity of discussion.

[0006] Figure 1 A polarization beam splitter rotator (PBSR) according to a first embodiment of the present disclosure is shown.

[0007] Figures 2 to 6 According to one or more aspects of the present disclosure, Figure 1 Various cross-sectional views across the length of the polarization rotator of the PBSR.

[0008] Figure 7 According to one or more aspects of the present disclosure, Figure 1 A magnified view of the polarization rotator in the PBSR.

[0009] Figure 8 A multi-order polarization rotator according to one or more aspects of the present disclosure is shown.

[0010] Figures 9 to 12 According to one or more aspects of the present disclosure, Figure 8 Various cross-sectional views of the length of a multi-order polarization rotator.

[0011] Fig.13 An Nth-order polarization rotator according to one or more aspects of the present disclosure is shown.

[0012] Fig.14 A circular multi-order polarization rotator according to one or more aspects of the present disclosure is shown.

[0013] Fig.15 A PBSR according to a second embodiment of the present disclosure is shown.

[0014] Fig.16A PBSR according to a third embodiment of the present disclosure is shown.

[0015] Fig.17 A PBSR according to a fourth embodiment of the present disclosure is shown.

[0016] Fig.18 A PBSR according to a fifth embodiment of the present disclosure is shown.

[0017] Fig.19 A flow chart of a method 900 for forming the PBSR and polarization rotator of the present disclosure is shown in accordance with one or more aspects of the present disclosure.

[0018] Figure 20 to Figure 25 According to one or more aspects of the present disclosure, Fig.19 A partial cross-sectional view of a workpiece 1100 undergoing stages of operations in method 900 is shown. DETAILED DESCRIPTION

[0019] The following disclosure provides several different embodiments or examples for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. Of course, these are merely examples and are not restrictive. For example, the formation of a first feature on or above a second feature in the following description may include an embodiment in which the first and second features are formed in direct contact, and may also include an embodiment in which additional features may be formed between the first and second features so that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numbers or letters in various examples. This repetition is for the purpose of simplicity and clarity and does not itself dictate the relationship between the various embodiments or architectures discussed.

[0020] Additionally, for ease of description, spatially relative terms, such as "below," "under," "beneath," "above," "over," and the like, may be used herein to describe the relationship of one element or feature to another element or feature, as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation shown in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptive terms used herein may likewise be interpreted accordingly.

[0021] In addition, when a value or range of values ​​is described with "about," "approximately," or similar terms, it is intended to include values ​​within a reasonable range, such as those of ordinary skill in the art taking into account the inherent variations in the manufacturing process. For example, based on the known manufacturing tolerances associated with the value, the value or range includes a reasonable range including the number, such as within + / - 10% of the number. For example, when the thickness of the material layer is about 5nm and the manufacturing tolerance of the deposited material layer is known to those of ordinary skill in the art to be 15%, the size range included is 4.25nm to 5.75nm.

[0022] Silicon-on-insulator (SOI) structures are a popular choice for photonic integrated circuits (PICs) due to the high refractive index contrast between silicon and silicon oxide. Fibers can be coupled to optical waveguides on PICs using edge coupling or grating coupling. Although silicon is a good waveguide material and can be doped for electrical manipulation, it has a thermal-optic coefficient that makes it sensitive to temperature changes. To address the temperature sensitivity issue, silicon optical waveguide devices may need to be thermally tuned using thermal heaters or feedback control mechanisms. Silicon nitride can also be used as a waveguide because it also has a high refractive index contrast with silicon oxide. Silicon nitride is less sensitive to temperature, but cannot be doped. Both silicon and silicon nitride have strong birefringence. Optical signals propagating on waveguides may have transverse electric (TE) polarization modes and transverse magnetic (TM) polarization modes. In the TE mode, the electric field vector is transverse and perpendicular to the waveguide axis. In the TM mode, the magnetic field is transverse and perpendicular to the waveguide axis.

[0023] TE mode and TM mode give the optical signal a completely different effective refractive index. Since the effective refractive index is an important design parameter, silicon photonics components are usually designed to operate with a specific polarization. This complicates the design of PIC. For example, a polarization beam splitter (PBS) can be used to split the optical signal into TE mode signal and TM mode signal, which are processed by mode-specific components such as demultiplexers (DeMux) respectively. Alternatively, the TM signal can be converted to a TE signal, so only a TE-specific demultiplexer is required. The functions of polarization rotation and mode conversion can be performed by a polarization beam splitter rotator (PBSR).

[0024] The present disclosure provides various structures of PBSR. The PBSR of the present disclosure can be divided into a polarization rotator that rotates a signal in a TM mode to a TE mode and a mode converter that converts a signal in a high-order TE mode (e.g., TE1) to a TE fundamental mode (i.e., TE0). The polarization rotator of the present disclosure includes a lower waveguide layer and an upper waveguide layer. Each of the lower waveguide layer and the upper waveguide layer has at least an inverse-taper segment and a tapered segment. The vertical projection area of ​​the upper waveguide layer completely falls within the vertical projection area of ​​the lower waveguide layer. In some embodiments, at least one inverse-taper segment of the upper waveguide layer or the lower waveguide layer may include a multi-stage inverse taper to reduce signal loss. The present disclosure also discloses a novel structure of a mode converter, which also includes a lower waveguide layer and an upper waveguide disposed above the lower waveguide layer.

[0025] Figure 1 A polarization beam splitter rotator (PBSR) 100 according to a first embodiment of the present disclosure is shown. The PBSR 100 includes a polarization rotator 1001 followed by a first mode converter 1002. That is, the output of the polarization rotator 1001 is coupled to the input of the first mode converter 1002. The polarization rotator 1001 has a lower waveguide layer and an upper waveguide layer disposed directly above the lower waveguide layer. The lower waveguide layer includes a first lower segment 102, a second lower segment 104, and a third lower segment 106. The first lower segment 102 is a straight segment extending longitudinally along the Y direction and has a uniform width along the X direction. The second lower segment 104 continues the first lower segment 102 and is characterized by an inverted taper. The second lower segment 104 extends longitudinally along the Y direction, and its width increases linearly along the X direction starting from the first lower segment 102. It should be noted that both sides of the second lower segment 104 have the same inverted taper angle. The third lower segment 106 continues the second lower segment 104 and is characterized by a taper. As shown in FIG. Figure 1 As shown, the third lower section 106 extends longitudinally along the Y direction, and its width decreases linearly from the second lower section 104 along the X direction.

[0026] The upper waveguide layer of the first polarization rotator 1001 is arranged directly above the lower waveguide layer, and its vertical projection area completely falls within the vertical projection area of ​​the lower waveguide layer. The upper waveguide layer includes a first upper section 124 and a second upper section 126. The first upper section 124 is arranged directly above the second lower section 104. The second upper section 126 is arranged directly above the third lower section 106. The first upper section 124 is characterized by an inverted tapered shape. The first upper section 124 extends longitudinally along the Y direction, and its width increases linearly from the first lower section 102 along the X direction. It should be noted that both sides of the first upper section 124 have the same inverted tapered angle. The second upper section 126 continues the first upper section 124 and is characterized by a tapered shape. Figure 1As shown, the second upper segment 126 extends longitudinally along the Y direction, and its width decreases linearly along the X direction from the first upper segment 124. The shapes (i.e., inverted tapered shapes) of the second lower segment 104 and the first upper segment 124 are configured to rotate a signal having a TE mode and a TM mode to a TE0-TM0 mixed mode. The shapes (i.e., tapered shapes) of the third lower segment 106 and the second upper segment 126 are configured to convert a TM1 mode to a TE1 mode.

[0027] The first mode converter 1002 includes a fourth lower section 108 and a fifth lower section 110. The fourth lower section 108 extends longitudinally along the Y direction and is characterized by being tapered from the polarization rotator 1001. The fourth lower section 108 includes a width along the X direction that decreases linearly from the polarization rotator 1001. The fifth lower section 110 extends longitudinally along the Y direction and is characterized by being inversely tapered along the Y direction. The fifth lower section 110 includes a width along the X direction that increases from the polarization rotator 1001. The fourth lower section 108 and the fifth lower section 110 are also disposed in the lower waveguide layer together with the first lower section 102, the second lower section 104, and the third lower section 106. The first mode converter 1002 includes a bar port 112 that continues the fourth lower section 108 and a cross port 114 that continues the fifth lower section 110. The fifth lower section 110 functions to convert a signal in the TE1 mode into a signal in the TE0 mode. This results in that both the direct port 112 and the cross port 114 output signals in the TE0 mode.

[0028] The lower waveguide layer and the upper waveguide layer are both disposed in the dielectric layer. Figure 1 The partial cross-sectional views along the lines A-A', B-B', C-C', D-D' and E-E' are shown in Figures 2 to 6 middle. Figure 2 Shown along Figure 1 FIG. 1 is a partial cross-sectional view of the first lower segment 102 along the line AA' in FIG. The first lower segment 102 is disposed in a dielectric layer 103, which may include silicon oxide. Along the Z direction, the first lower segment 102 has a first thickness T1. Figure 3 Shown along Figure 1 FIG. 1 is a partial cross-sectional view of the second lower segment 104 and the first upper segment 124 along the line BB' in FIG. The second lower segment 104 and the first upper segment 124 are also disposed in the dielectric layer 103. Along the Z direction, the second lower segment 104 has a first thickness T1, and the first upper segment 124 has a second thickness T2. The bottom surface of the first upper segment 124 is separated from the top surface of the second lower segment 104 by a portion of the dielectric layer 103 at the gap G. Figure 4 Shown along Figure 11001. A partial cross-sectional view of the third lower segment 106 and the second upper segment 126 along the line CC' in FIG. The third lower segment 106 and the second upper segment 126 are also disposed in the dielectric layer 103. Along the Z direction, the third lower segment 106 has a first thickness T1, and the second upper segment 126 has a second thickness T2. According to experimental results and computer simulations, when the lower waveguide layer includes silicon nitride (SiN) and the upper waveguide layer includes silicon (Si), the first thickness T1 should be less than 0.8 μm, and the second thickness T2 should be less than 0.4 μm. The gap G should be less than 0.3 μm, otherwise the polarization rotator 1001 may not work properly.

[0029] Figure 5 and 6 Shown along Figure 1 1 is a partial cross-sectional view of the fourth lower segment 108 and the fifth lower segment 110 along the lines D-D' and EE' in FIG. The fourth lower segment 108 and the fifth lower segment 110 are both disposed in the lower waveguide layer and are both disposed in the dielectric layer 103. The fourth lower segment 108 and the fifth lower segment 110 both comprise a first thickness T1. Figures 5 and 6 As shown, the width of the fifth lower segment 110 along the X direction is smaller than that of the fourth lower segment 108 close to the third lower segment 106 , but the difference between the two decreases as the distance from the third lower segment 106 increases.

[0030] Figure 7 include Figure 1 Magnified top view of the polarization rotator 1001 of PBSR100. Figure 7 Intended to illustrate the difference and variation in width between different segments. The first lower segment 102 has a first width W1 along the X direction. The second lower segment 102 has a first length L1 along the Y direction. The width of the second lower segment 104 starts from the first width W1 adjacent to the first lower segment 102 and increases to a second width W2 adjacent to the third lower segment 106. The width of the first upper segment 124 starts from the third width W3 adjacent to the first lower segment 102 and increases to a fourth width W4 adjacent to the third lower segment 106. The third lower segment 106 and the second upper segment 126 include a second length L2 along the Y direction. According to experimental results and simulations, when the lower waveguide layer includes silicon nitride (SiN) and the upper waveguide layer includes silicon (Si), the first width W1 is about 1.25 to about 2 times the first thickness T1, the second width W2 is about 1.1 to about 3 times the fourth width W4, and the fourth width W4 is about 1.1 to 4 times the second thickness T2. In addition, when the lower waveguide layer includes silicon nitride (SiN) and the upper waveguide layer includes silicon (Si), the third width W3 should be less than 0.2 μm to reduce undesired optical reflection. The first length L1 is greater than the second length L2. When the lower waveguide layer includes silicon nitride (SiN) and the upper waveguide layer includes silicon (Si), the first length L1 may be between about 200 μm and about 300 μm, and the second length L2 may be between about 40 μm and about 60 μm.

[0031] In some of the above examples, the lower waveguide layer (including the first lower segment 102, the second lower segment 104, the third lower segment 106, the fourth lower segment 108, and the fifth lower segment 110) includes silicon nitride (SiN) or consists essentially of silicon nitride, and the upper waveguide layer (including the first upper segment 124 and the second upper segment 126) includes silicon (Si) or consists essentially of silicon. In other embodiments, the lower waveguide layer and the upper waveguide layer can be formed of other materials. In one example, both the lower waveguide layer and the upper waveguide layer can include the same material, such as silicon (Si), silicon nitride (SiN), III-V semiconductor materials (e.g., gallium nitride (GaN)), or polymers (e.g., polyimide (PI), polymethyl-methacrylate (PMMA), polystyrene (PS), or polycarbonate (PC)). In another example, the lower waveguide layer includes silicon (Si) and the upper waveguide layer includes silicon nitride (SiN). In yet another example, the lower waveguide layer may include a Group III-V semiconductor and the upper waveguide layer includes a polymer or vice versa.

[0032] It should be noted that although PBSR100 is described as having multiple lower segments and multiple upper segments, multiple segments in the same layer can be continuous structures or patterned from continuous structures. For example, the first lower segment 102, the second lower segment 104, the third lower segment 106, and the fourth lower segment 108 can be continuous structures, such as continuous silicon nitride (SiN) structures. Nothing in the present disclosure requires or suggests that multiple segments must be formed independently or be discontinuous. The segments used in the present disclosure are intended to describe structural features or width differences.

[0033] Figure 8A multi-order polarization rotator 2001 is shown. In some embodiments where the signal contains a range of wavelengths, a single-order polarization rotator may experience losses because wavelength signals outside the range may not be able to enter the hybrid mode (or hybridization mode) and their polarization will not be rotated. The multi-order polarization rotator 2001 is intended to reduce such losses due to the wider range of signal wavelengths. In the described embodiment, the multi-order polarization rotator 2001 also includes a lower waveguide layer and an upper waveguide layer directly above the lower waveguide layer. The lower waveguide layer of the multi-order polarization rotator 2001 includes a first lower segment 202, a second lower segment 204, a third lower segment 206, a fourth lower segment 208, a fifth lower segment 210, and a sixth lower segment 212. The upper waveguide layer of the multi-order polarization rotator 2001 includes a first upper segment 224, a second upper segment 226, a third upper segment 228, a fourth upper segment 230, and a fifth upper segment 232. The first lower section 202, the second lower section 204, the third lower section 206, the fourth lower section 208, the fifth lower section 210, and the sixth lower section 212 are continuous. The first upper section 224, the second upper section 226, the third upper section 228, the fourth upper section 230, and the fifth upper section 232 are continuous.

[0034] Continue to refer Figure 8 , the first lower segment 202 is a straight segment extending longitudinally along the Y direction and has a uniform width along the X direction. The second lower segment 204, the third lower segment 206, the fourth lower segment 208, and the fifth lower segment 210 are characterized by an inverted tapered shape. Each of the second lower segment 204, the third lower segment 206, the fourth lower segment 208, and the fifth lower segment 210 extends longitudinally along the Y direction and has a width that increases linearly from the first lower segment 202 along the X direction, although the inverted tapered angles used are different. That is, the side walls of the second lower segment 204, the third lower segment 206, the fourth lower segment 208, and the fifth lower segment 210 are not aligned to form a straight line. On the contrary, the aforementioned side walls undergo a gradual slope change at the interface of two adjacent lower segments. The sixth lower segment 212 is characterized by tapering, and its width decreases along the X direction from the fifth lower segment 210.

[0035] Each of the first upper segment 224, the second upper segment 226, the third upper segment 228, and the fourth upper segment 230 extends longitudinally along the Y direction and has a width that increases linearly from the first lower segment 202 along the X direction, although the reverse taper angles adopted are different. That is, the side walls of the first upper segment 224, the second upper segment 226, the third upper segment 228, and the fourth upper segment 230 are not aligned to form a straight line. Instead, the aforementioned side walls undergo a gradual slope change at the interface between two adjacent upper segments. The fifth upper segment 232 is characterized by a tapered shape, and its width decreases linearly from the fifth lower segment 210 along the X direction. The gradual reverse taper of the multi-order polarization rotator 2001 enables it to rotate signals of a wider range of wavelengths, reduce rotation losses, and improve rotation efficiency.

[0036] In some embodiments, the lower waveguide layer (including the first lower segment 202, the second lower segment 204, the third lower segment 206, the fourth lower segment 208, the fifth lower segment 210, and the sixth lower segment 212) includes silicon nitride (SiN) or consists essentially of silicon nitride, and the upper waveguide layer (including the first upper segment 224, the second upper segment 226, the third upper segment 228, the fourth upper segment 230, and the fifth upper segment 232) includes silicon (Si) or consists essentially of silicon. In other embodiments, the lower waveguide layer and the upper waveguide layer can be formed of other materials. In one example, both the lower waveguide layer and the upper waveguide layer can include the same material, such as silicon (Si), silicon nitride (SiN), III-V semiconductor materials (e.g., gallium nitride (GaN)), or polymers (e.g., polyimide (PI), polymethyl methacrylate (PMMA), polystyrene (PS), or polycarbonate (PC)). In another example, the lower waveguide layer includes silicon (Si) and the upper waveguide layer includes silicon nitride (SiN). In yet another example, the lower waveguide layer may include a Group III-V semiconductor and the upper waveguide layer includes a polymer, or vice versa.

[0037] Although not explicitly depicted in the drawings, the multi-order polarization rotator 2001 may be used with Figure 1 To form a PBSR, the output of the multi-order polarization rotator 2001 is coupled to the input of the first modal converter 1002. In some embodiments, the lower waveguide layer representing the multi-order polarization rotator 2001 is continuous with the lower waveguide layer of the first modal converter 1002.

[0038] Figures 9 to 12 Shown along Figure 8 Various partial cross-sectional views of the length of the multi-order polarization rotator 2001. Figures 9 to 12 As shown, the first lower segment 202, the second lower segment 204, the third lower segment 206, the fourth lower segment 208, the fifth lower segment 210, the sixth lower segment 212, the first upper segment 224, the second upper segment 226, the third upper segment 228, the fourth upper segment 230, and the fifth upper segment 232 are set in the dielectric layer 103 which may include silicon oxide. Fig. 9 Shown along Figure 8 A partial cross-sectional view of the first lower section 202 along line AA' in FIG. Fig.10 Shown along Figure 8 A partial cross-sectional view of the second lower segment 204 and the first upper segment 224 taken along line BB′ in FIG. Fig.11 Shown along Figure 8 A partial cross-sectional view of the third lower segment 206 and the second upper segment 226 along the line CC' in FIG. Fig.12 Shown along Figure 81-1 . A partial cross-sectional view of the fourth lower segment 208 and the third upper segment 228 along the line D-D' in FIG. Along the Z direction, each of the first lower segment 202, the second lower segment 204, the third lower segment 206, the fourth lower segment 208, the fifth lower segment 210, and the sixth lower segment 212 has a first thickness T1. Along the Z direction, each of the first upper segment 224, the second upper segment 226, the third upper segment 228, the fourth upper segment 230, and the fifth upper segment 232 has a second thickness T2. The bottom surface of the upper waveguide layer is separated from the top surface of the lower waveguide layer by a portion of the dielectric layer 103 at the gap G. According to experimental results and computer simulations, when the lower waveguide layer includes silicon nitride (SiN) and the upper waveguide layer includes silicon (Si), the first thickness T1 should be less than 0.8 μm and the second thickness T2 should be less than 0.4 μm. The gap G should be less than 0.3 μm, otherwise the multi-order polarization rotator 2001 may not work properly.

[0039] Fig.13 An N-th order polarization rotator 3001 is shown. Although Figure 8 The multi-order polarization rotator 2001 in the embodiment includes four inverse tapering stages, but the present disclosure contemplates a generalized N-order polarization rotator 3001, such as Fig.13 As shown in . As the name implies, the N-order polarization rotator 3001 includes N reverse tapered stages, including lower segments LS1, LS2, LS3, LS4 to LSN and upper segments US1, US2, US3, US4 to USN. In some instances, N is between 5 and 20, for example between 5 and 10. Although more reverse tapered stages can be included, too many stages may cause the device to be undesirably large or bloated. Each of the lower segments LS1, LS2, LS3, LS4 to LSN is characterized by a different reverse tapered angle. In some embodiments, the reverse tapered angle of each lower segment increases segment by segment starting from the straight line segment 302. The same applies to the upper segment. Each of the upper segments US1, US2, US3, US4 to USN is characterized by a different reverse tapered angle. In some embodiments, the reverse tapered angle of each upper segment increases segment by segment starting from the straight line segment 302. As Fig.13 As shown, each of the upper sections US1, US2, US3, US4 to USN is arranged directly above the corresponding lower sections LS1, LS2, LS3, LS4 to LSN. In addition, the vertical projection area of ​​each of the upper sections US1, US2, US3, US4, US4 to USN completely falls within the vertical projection area of ​​the corresponding one of the lower sections LS1, LS2, LS3, LS4 to LSN. After N reverse tapering stages, the lower waveguide layer includes the lower tapered section LT, and the upper waveguide layer includes the upper tapered section UT. The vertical projection area of ​​the upper tapered section UT completely falls within the vertical projection area of ​​the lower tapered section LT.

[0040] Although not explicitly depicted in the drawings, the N-th order polarization rotator 3001 may be used with Figure 1 3001 are combined with the first mode converter 1002 shown in to form a PBSR. For the combination, the output of the N-order polarization rotator 3001 is coupled to the input of the first mode converter 1002. In some embodiments, this means that the lower waveguide layer of the N-order polarization rotator 3001 is continuous with the lower waveguide layer of the first mode converter 1002.

[0041] Fig.14 A smooth multi-stage polarization rotator 4001 is shown. Figure 8 Compared to the multi-order polarization rotator 2001 shown in , the smooth multi-order polarization rotator 4001 is characterized by having non-straight or non-linear inverted tapered or tapered sidewalls. The smooth multi-order polarization rotator 4001 includes a lower waveguide layer and an upper waveguide layer disposed directly above the lower waveguide layer. The lower waveguide layer of the smooth multi-order polarization rotator 4001 includes a first lower section 402, a second lower section 404, a third lower section 406, a fourth lower section 408, and a fifth lower section 410. The upper waveguide layer of the smooth multi-order polarization rotator 4001 includes a first upper section 424, a second upper section 426, a third upper section 428, and a fourth upper section 430. The first lower section 402, the second lower section 404, the third lower section 406, the fourth lower section 408, and the fifth lower section 410 are continuous. The first upper section 424, the second upper section 426, the third upper section 428, and the fourth upper section 430 are continuous.

[0042] Continue to refer Fig.14, the first lower segment 402 is a straight segment extending longitudinally along the Y direction and has a uniform width along the X direction. Each of the second lower segment 404, the third lower segment 406 and the fourth lower segment 408 is characterized by a nonlinear inverse taper. Each of the second lower segment 404, the third lower segment 406 and the fourth lower segment 408 extends longitudinally along the Y direction and has a width that increases polynomially from the first lower segment 402 along the X direction, although the inverse taper angles adopted are different. The sidewalls of the lower waveguide layer undergo a gradual slope change at the interface of two adjacent lower segments. The fifth lower segment 410 is characterized by a taper and its width decreases polynomially from the fourth lower segment 408 along the X direction. Each of the first upper segment 424, the second upper segment 426 and the third upper segment 428 is characterized by a nonlinear inverse taper. Each of the first upper segment 424, the second upper segment 426, and the third upper segment 428 extends longitudinally along the Y direction and has a width that increases polynomially from the first lower segment 402 along the X direction, although the reverse taper angles adopted are different. The sidewalls of the upper waveguide layer of the smooth multi-order polarization rotator 4001 experience a gradual slope change at the interface of two adjacent upper segments. The fourth upper segment 430 is characterized by a tapered shape, and its width decreases polynomially from the third upper segment 428 along the X direction. Because the reverse tapers and tapered shapes of the multiple segments in the smooth multi-order polarization rotator 4001 are modeled by or can be expressed as polynomial functions, all segments have a smooth or curved profile in a top view along the Z direction.

[0043] In some embodiments, the lower waveguide layer (including the first lower segment 402, the second lower segment 404, the third lower segment 406, the fourth lower segment 408, and the fifth lower segment 410) includes silicon nitride (SiN) or consists essentially of silicon nitride, and the upper waveguide layer (including the first upper segment 424, the second upper segment 426, the third upper segment 428, and the fourth upper segment 430) includes silicon (Si) or consists essentially of silicon. In other embodiments, the lower waveguide layer and the upper waveguide layer can be formed of other materials. In one example, both the lower waveguide layer and the upper waveguide layer can include the same material, such as silicon (Si), silicon nitride (SiN), III-V semiconductor materials (e.g., gallium nitride (GaN)), or polymers (e.g., polyimide (PI), polymethyl methacrylate (PMMA), polystyrene (PS), or polycarbonate (PC)). In another example, the lower waveguide layer includes silicon (Si) and the upper waveguide layer includes silicon nitride (SiN). In yet another example, the lower waveguide layer may include a Group III-V semiconductor and the upper waveguide layer includes a polymer, or vice versa.

[0044] Although not explicitly depicted in the drawings, a smooth multi-stage polarization rotator 4001 can be used with Figure 11002 to form a PBSR. For the combination, the output of the smooth multi-order polarization rotator 4001 is coupled to the input of the first mode converter 1002. In some embodiments, this means that the lower waveguide layer of the smooth multi-order polarization rotator 4001 is continuous with the lower waveguide layer of the first mode converter 1002.

[0045] Fig.15 A PBSR 500 according to a second embodiment of the present disclosure is shown. Fig.15 The PBSR500 includes Figure 1 The polarization rotator 1001 and the second mode converter 5002 shown in PBSR500 are coupled to each other. In other words, the output of the polarization rotator 1001 in PBSR500 is coupled to the input of the second mode converter 5002. Figures 1 to 4 The details of the polarization rotator 1001 are described in detail, so the description of the polarization rotator 1001 in the PBSR 500 is omitted. The second mode converter 5002 includes a lower waveguide layer and an upper waveguide layer disposed above the lower waveguide layer. Fig.15 In some embodiments shown, the second mode converter 5002 includes a lower tapered member 502 and an upper inverted tapered member 504 disposed directly above the lower tapered member 502. The lower tapered member 502 extends longitudinally along the Y direction and has a width that decreases linearly along the X direction from the polarization rotator 1001. The upper inverted tapered member 504 extends longitudinally along the Y direction and has a width that increases linearly along the X direction from the polarization rotator 1001. The lower tapered member 502 has a direct port 512, and the upper inverted tapered member 504 has a cross port 514. The shape of the upper inverted tapered member 504 (i.e., an inverted tapered shape) is configured to convert a TE1 mode signal from the polarization rotator 1001 into a TE0 mode signal. This results in both the direct port 512 and the cross port 514 outputting signals in the TE0 mode.

[0046] In some embodiments, the lower tapered member 502 of the second mode converter 5002 includes silicon nitride (SiN) or is substantially composed of silicon nitride, and the upper inverted tapered member 504 of the second mode converter 5002 includes silicon (Si) or is substantially composed of silicon. In other embodiments, the lower tapered member 502 and the upper inverted tapered member 504 can be formed of other materials. In one example, both the lower tapered member 502 and the upper inverted tapered member 504 can include the same material, such as silicon (Si), silicon nitride (SiN), III-V semiconductor materials (e.g., gallium nitride (GaN)), or polymers (e.g., polyimide (PI), polymethyl methacrylate (PMMA), polystyrene (PS), or polycarbonate (PC)). In another example, the lower tapered member 502 and the upper inverted tapered member 504 include silicon nitride (SiN). In yet another example, the lower tapered member 502 includes a III-V semiconductor and the upper inverted tapered member 504 includes a polymer, or vice versa.

[0047] Fig.16 PBSR600 according to the third embodiment of the present disclosure is shown. It should be understood that Fig.15 The second modal converter 5002 shown in FIG. 5 may also be suitable for Figure 8 The multi-order polarization rotator 2001 shown in Fig.13 The N-order polarization rotator 3001 shown in Fig.14 For example, the PBSR 600 includes a multi-order polarization rotator 2001 that cooperates with a second mode converter 5002 , wherein the lower tapered member 502 is continuous with the lower waveguide layer of the multi-order polarization rotator 2001 .

[0048] Fig.17 FIG. 7 shows a PBSR 700 according to a fourth embodiment of the present disclosure. The PBSR 700 includes two Figure 1 The PBSR100 shown in FIG. 7 is used to improve conversion efficiency and reduce loss. Unlike the polarization rotator that forms multiple inverted tapered stages, the PBSR700 connects one PBSR100 in series with another PBSR100. The downstream PBSR100 is used to convert the signal that is not converted by the upstream PBSR100.

[0049] Fig.18 FIG. 8 shows a PBSR 800 according to a fifth embodiment of the present disclosure. The PBSR 800 includes two Fig.15 The PBSR500 shown in FIG. 8 is used to improve conversion efficiency and reduce loss. Unlike the polarization rotator that forms multiple inverted tapered stages, the PBSR800 connects one PBSR500 in series with another PBSR500. The downstream PBSR500 is used to convert the signal that is not converted by the upstream PBSR500.

[0050] Fig.19 A flow chart of a method 900 for manufacturing the polarization beam splitter rotators 100, 500, 600, 700, and 800, the polarization rotator 1001, the multi-order polarization rotator 2001, the N-order polarization rotator 3001, or the smooth multi-order polarization rotator 4001 described above is shown. The method 900 is merely an example and is not meant to limit the scope of the present disclosure to what is explicitly depicted in the method 900. Additional steps may be provided before, during, and after the method 100, and some of the steps described may be replaced, eliminated, or moved for additional embodiments of the method. For simplicity, not all steps are described in detail herein. The following is combined with Figure 20 to Figure 25 Describing method 900 , the figures are partial cross-sectional views showing a workpiece 1100 at various stages of manufacture according to an embodiment of method 900 .

[0051] refer to Fig.19 and Fig. 20 , method 900 includes block 902, wherein a first dielectric layer 1104 is deposited over a substrate 1102. In one embodiment, substrate 1102 may be a silicon (Si) substrate. In some embodiments, substrate 1102 may include other semiconductors such as germanium (Ge), silicon germanium (SiGe), or III-V semiconductor materials. Example III-V semiconductor materials may include gallium arsenide (GaAs), indium phosphide (InP), gallium phosphide (GaP), gallium nitride (GaN), gallium arsenic phosphide (GaAsP), aluminum indium arsenide (AlInAs), aluminum gallium arsenide (AlGaAs), gallium indium phosphide (GaInP), and indium gallium arsenide (InGaAs). Substrate 1102 may also include a buried insulating layer, such as a buried silicon oxide layer, to have a silicon-on-insulator (SOI) structure. The first dielectric layer 1104 may include silicon oxide and may be deposited over the substrate 1102 using chemical vapor deposition (CVD), flowable CVD (FCVD), spin coating, or a suitable deposition method.

[0052] refer to Fig.19 and Fig.21 , method 900 includes block 904, where a lower waveguide layer 1106 is deposited over the first dielectric layer 1104. In some embodiments, the lower waveguide layer 1106 may include silicon nitride, silicon, or a III-V semiconductor material (eg, GaN). The lower waveguide layer 1106 may be deposited using CVD.

[0053] refer to Fig.19 and Fig. 22, method 900 includes block 906, where the lower waveguide layer 1106 is patterned. The patterning at block 906 may include photolithography and etching processes. In an exemplary process, at least one hard mask layer is deposited over the lower waveguide layer 1106. The at least one hard mask layer may include silicon oxide, silicon nitride, or a combination thereof. A photoresist layer is deposited over the at least one hard mask layer. After soft baking, mask alignment, exposure, post-exposure baking, development, rinsing, drying (e.g., spin drying and / or hard baking), the photoresist layer is patterned. The patterned photoresist layer is then used as an etching mask to etch the at least one hard mask layer using a dry etching process (e.g., RIE etching). The patterned hard mask layer is then used as an etching mask to etch the lower waveguide layer 1106 to form Figures 1 to 18 The pattern shown in .

[0054] refer to Fig.19 and Fig.23 , method 900 includes block 908, where a second dielectric layer 1108 is deposited over the patterned lower waveguide layer 1106. In some embodiments, the second dielectric layer 1108 may have the same composition as the first dielectric layer 1104. That is, the second dielectric layer 1108 may include silicon oxide and may be deposited using CVD, FCVD, spin coating, or a suitable method.

[0055] refer to Fig.19 and Fig.23 , method 900 includes block 910, wherein an upper waveguide layer 1110 is deposited over the second dielectric layer 1108. In some embodiments, the upper waveguide layer 1110 may include silicon, silicon nitride, or a polymer (e.g., polyimide (PI), polymethyl methacrylate (PMMA), polystyrene (PS), or polycarbonate (PC)). When the upper waveguide layer 1110 includes silicon or silicon nitride, it may be deposited using CVD. When the upper waveguide layer 1110 includes a polymer, it may be deposited using FCVD or spin coating.

[0056] refer to Fig.19 and Fig.24 , method 900 includes block 912, wherein the upper waveguide layer 1110 is patterned. The patterning at block 912 may include photolithography and etching processes. In an exemplary process, at least one hard mask layer is deposited over the upper waveguide layer 1110. The at least one hard mask layer may include silicon oxide, silicon nitride, or a combination thereof. A photoresist layer is deposited over the at least one hard mask layer. After soft baking, mask alignment, exposure, post-exposure baking, development, rinsing, drying (e.g., spin drying and / or hard baking), the photoresist layer is patterned. The patterned photoresist layer is then used as an etching mask to etch the at least one hard mask layer using a dry etching process (e.g., RIE etching). The patterned hard mask layer is then used as an etching mask to etch the upper waveguide layer 1110 to form Figures 1 to 18The pattern shown in .

[0057] refer to Fig.19 and 25 , the method 900 includes a block 914, in which a third dielectric layer 1112 is deposited over the patterned upper waveguide layer 1110. In some embodiments, the third dielectric layer 1112 may have the same composition as the first dielectric layer 1104. That is, the third dielectric layer 1112 may include silicon oxide and may be deposited using CVD, FCVD, spin coating, or a suitable method.

[0058] In one exemplary aspect, the present disclosure relates to an optical device. The optical device includes a polarization rotator, which includes a straight waveguide segment having a constant width between a first end and a second end along a direction, a first widening waveguide segment continuing the second end of the straight waveguide segment, the first widening waveguide segment having a first width along the direction, the first width linearly increasing from the second end, a first tapered waveguide segment continuing the first widening waveguide segment, the first tapered waveguide segment having a second width along the direction, the second width linearly decreasing from the first widening waveguide segment, the second widening waveguide segment being disposed above the first widening waveguide segment, and the second tapered waveguide segment continuing the second widening waveguide segment. The optical device also includes a mode converter, which includes a third tapered waveguide segment continuing the first tapered waveguide segment, and the third widening waveguide segment is disposed above the third tapered waveguide segment. The output end of the polarization rotator is coupled to the input end of the mode converter.

[0059] In some embodiments, a vertically projected area of ​​the second widening waveguide segment falls completely within a vertically projected area of ​​the first widening waveguide segment, and a vertically projected area of ​​the second tapered waveguide segment falls completely within a vertically projected area of ​​the first tapered waveguide segment. In some implementations, the straight waveguide segment, the first widening waveguide segment, the first tapered waveguide segment, the second widening waveguide segment, the second tapered waveguide segment, the third tapered waveguide segment, and the third widening waveguide segment consist essentially of silicon. In some embodiments, the straight waveguide segment, the first widening waveguide segment, the first tapered waveguide segment, the second widening waveguide segment, the second tapered waveguide segment, the third tapered waveguide segment, and the third widening waveguide segment consist essentially of silicon nitride. In some implementations, the straight waveguide segment, the first widening waveguide segment, the first tapered waveguide segment, the second widening waveguide segment, the second tapered waveguide segment, the third tapered waveguide segment, and the third widening waveguide segment comprise III-V semiconductor materials. In some examples, the straight waveguide section, the first widening waveguide section, the first tapered waveguide section, the second widening waveguide section, the second tapered waveguide section, the third tapered waveguide section, and the third widening waveguide section include a polymer material. In some embodiments, the straight waveguide section, the first widening waveguide section, the first tapered waveguide section, and the third tapered waveguide section are substantially composed of silicon, and the second widening waveguide section, the second tapered waveguide section, and the third widening waveguide section are substantially composed of silicon nitride. In some examples, the straight waveguide section, the first widening waveguide section, the first tapered waveguide section, the second widening waveguide section, the second tapered waveguide section, the third tapered waveguide section, and the third widening waveguide section are disposed in a silicon oxide layer. In some embodiments, the top surface of the first widening waveguide section, the top surface of the first tapered waveguide section, and the top surface of the third tapered waveguide section are respectively separated from the bottom surface of the second widening waveguide, the bottom surface of the second tapered waveguide section, and the bottom surface of the third widening waveguide section by a portion of the silicon oxide layer.

[0060] In another exemplary aspect, the present disclosure relates to a polarization rotator. The polarization rotator includes a straight waveguide segment having a constant width between a first end and a second end along a direction, at least two bottom inverted tapered waveguide segments sequentially continuing from the second end of the straight waveguide segment, the bottom tapered waveguide segment continuing from the at least two bottom inverted tapered waveguide segments, at least two top inverted tapered waveguide segments disposed above the at least two bottom inverted tapered waveguide segments, and the top tapered waveguide segment continuing from the at least two top inverted tapered waveguide segments and disposed directly above the bottom tapered waveguide segment. The straight waveguide segment, the at least two bottom inverted tapered waveguide segments, the bottom tapered waveguide segment, the at least two top inverted tapered waveguide segments, and the top tapered waveguide segment are disposed in a silicon oxide layer.

[0061] In some embodiments, the straight waveguide segment, at least two bottom inverted tapered waveguide segments, and the bottom tapered waveguide segment are substantially composed of silicon, and at least two top inverted tapered waveguide segments and the top tapered waveguide segment are substantially composed of silicon nitride. In some embodiments, the straight waveguide segment, at least two bottom inverted tapered waveguide segments, and the bottom tapered waveguide segment include a first thickness, and at least two top inverted tapered waveguide segments and the top tapered waveguide segment include a second thickness less than the first thickness. In some embodiments, the first thickness is between about 0.4 μm and about 0.8 μm, and the second thickness is between about 0.2 μm and about 0.4 μm. In some embodiments, the straight waveguide segment extends longitudinally along a first direction and has a width along a second direction perpendicular to the first direction, and the ratio of the width to the first thickness is between about 1.25 and about 2. In some embodiments, at least two bottom inverted tapered waveguide segments include a first length along the first direction, the bottom tapered waveguide segment includes a second length along the first direction, and the first length is greater than the second length. In some embodiments, the top surfaces of at least two bottom inverted tapered waveguide segments are spaced apart from the bottom surfaces of at least two top inverted tapered waveguide segments by a gap. The top surfaces of the bottom tapered waveguide segments are spaced apart from the bottom surfaces of the top tapered waveguide segments by a gap between about 0.4 μm and about 3 μm.

[0062] In yet another exemplary aspect, the present disclosure is directed to a method. The method includes depositing a first dielectric layer over a substrate, depositing a lower waveguide layer over the first dielectric layer, patterning the lower waveguide layer to form a straight waveguide segment having a constant width along a direction, a first widened waveguide segment continuing the straight waveguide segment, a first tapered waveguide segment continuing the first widened waveguide segment, and a second tapered waveguide segment continuing the first tapered waveguide segment, depositing a second dielectric layer over the patterned lower waveguide layer, depositing an upper waveguide layer over the second dielectric layer, patterning the upper waveguide layer to form a second widened waveguide segment disposed over the first widened waveguide segment, a third tapered waveguide segment continuing the second widened waveguide segment, and a third widened waveguide segment disposed over the second tapered waveguide segment, and depositing a third dielectric layer over the patterned upper waveguide layer.

[0063] In some embodiments, the lower waveguide layer includes silicon nitride. In some implementations, the upper waveguide layer includes silicon. In some examples, the first dielectric layer, the second dielectric layer, and the third dielectric layer include silicon oxide.

[0064] The features of several embodiments are summarized above so that those skilled in the art can better understand various aspects of the present invention. Those skilled in the art should understand that they can easily use the present invention as a basis for designing or modifying other processes and structures to achieve the same purposes and / or achieve the same advantages of the embodiments described herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of the present invention, and they can make various changes, substitutions and modifications herein without departing from the spirit and scope of the present invention.

Claims

1. An optical device, characterized in that: include: Polarization rotator, comprising: a straight waveguide segment having a constant width along a direction between a first end and a second end; a first widened waveguide section, continuing from the second end of the straight waveguide section, the first widened waveguide section having a first width along the direction, the first width increasing linearly from the second end; a first tapered waveguide section, continuing from the first widened waveguide section, the first tapered waveguide section having a second width along the direction, the second width linearly decreasing from the first widened waveguide section; A second widened waveguide section disposed above the first widened waveguide section; and a second tapered waveguide section, continuing from the second widened waveguide section; and Modal converter, including: a third tapered waveguide section, continuing from the first tapered waveguide section; and A third widening waveguide section is arranged above the third tapered waveguide section, The output of the polarization rotator is coupled to the input of the mode converter.

2. The optical device according to claim 1, wherein the vertical projection area of ​​the second widened waveguide section completely falls within the vertical projection area of ​​the first widened waveguide section, The vertical projection area of ​​the second tapered waveguide section completely falls within the vertical projection area of ​​the first tapered waveguide section.

3. The optical device according to claim 1, wherein the straight waveguide segment, the first widening waveguide segment, the first tapered waveguide segment, the second widening waveguide segment, the second tapered waveguide segment, the third tapered waveguide segment, and the third widening waveguide segment are disposed in a silicon oxide layer.

4. The optical device according to claim 3, wherein a top surface of the first widening waveguide segment, a top surface of the first tapered waveguide segment, and a top surface of the third tapered waveguide segment are respectively separated from a bottom surface of the second widening waveguide, a bottom surface of the second tapered waveguide segment, and a bottom surface of the third widening waveguide segment by a portion of the silicon oxide layer.

5. A polarization rotator, characterized in that: include: a straight waveguide segment having a constant width along a direction between a first end and a second end; at least two bottom inverted tapered waveguide sections, sequentially continuing from the second end of the straight waveguide section; a bottom tapered waveguide section, continuing the at least two bottom inverted tapered waveguide sections; at least two top inverted tapered waveguide segments disposed above the at least two bottom inverted tapered waveguide segments; as well as a top tapered waveguide section, continuing the at least two top inverted tapered waveguide sections and disposed directly above the bottom tapered waveguide section, The straight waveguide segment, the at least two bottom inverted tapered waveguide segments, the bottom tapered waveguide segment, the at least two top inverted tapered waveguide segments and the top tapered waveguide segment are arranged in a silicon oxide layer.

6. The polarization rotator according to claim 5, wherein the straight waveguide segment, the at least two bottom inverted tapered waveguide segments, and the bottom tapered waveguide segment comprise a first thickness, Wherein the at least two top inverted tapered waveguide segments and the top tapered waveguide segment comprise a second thickness that is less than the first thickness.

7. The polarization rotator according to claim 6, wherein the first thickness is between 0.4 μm and 0.8 μm, The second thickness is between 0.2 μm and 0.4 μm.

8. The polarization rotator according to claim 6, wherein the straight waveguide section extends longitudinally along a first direction and has a width along a second direction perpendicular to the first direction, Wherein a ratio of the width to the first thickness is between 1.25 and 2.

9. The polarization rotator according to claim 8, wherein the at least two bottom inverted tapered waveguide sections comprise a first length along the first direction, wherein the bottom tapered waveguide section comprises a second length along the first direction, The first length is greater than the second length.

10. The polarization rotator according to claim 5, wherein the top surfaces of the at least two bottom inverted tapered waveguide sections are spaced apart from the bottom surfaces of the at least two top inverted tapered waveguide sections by a gap, wherein a top surface of the bottom tapered waveguide section is spaced apart from a bottom surface of the top tapered waveguide section by the gap, The gap is between 0.4 μm and 3 μm.

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