Polarization rotator and manufacturing method thereof

Abstract

The invention discloses a polarization rotator and a manufacturing method thereof. The polarization rotator comprises a first waveguide, a first coupling waveguide, a mode conversion waveguide, a second coupling waveguide and a second waveguide which are sequentially connected in a first direction, the first waveguide is used for introducing external first mode polarized light; the first coupling waveguide is used for coupling the first waveguide and the mode conversion waveguide; the mode conversion waveguide is used for converting the first mode polarized light guided by the first waveguide into second mode polarized light, and the mode conversion waveguide has geometric asymmetry in a first direction; the second coupling waveguide is used for coupling the mode conversion waveguide and the second waveguide; the second waveguide is used for exporting the second mode polarized light converted by the mode conversion waveguide; wherein the first direction is a light propagation direction. According to the polarization rotator and the manufacturing method thereof, the device structure can be effectively shortened, and meanwhile efficient conversion rate is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor device manufacturing, and in particular relates to a polarization rotator and a manufacturing method thereof. Background Art

[0002] With the rapid development of optical communication and photonic integrated circuit technology, polarization control has become one of the key technologies for achieving efficient optical signal processing. As an important functional device in optical communication systems, polarization rotators can convert the polarization state of light from transverse electric (TE) mode to transverse magnetic (TM) mode, or vice versa; they are widely used in the fields of wavelength division multiplexing, optical modulation and optical sensing.

[0003] Traditional polarization rotators are mostly based on symmetric waveguide structure design, and polarization conversion is achieved through mode coupling. This design uses the phase matching conditions of the two polarization modes (TE and TM) in the waveguide to gradually convert the input polarization state to the target polarization state during propagation. However, due to the small difference in the effective refractive index of the two modes in the symmetric waveguide, the mode coupling efficiency is limited, resulting in low polarization conversion efficiency and high insertion loss, which makes it difficult to meet the needs of modern optical integrated systems for high-performance devices.

[0004] In the field of optical communications, the performance of polarization rotators directly affects the transmission quality and integration capabilities of polarization systems. Although the traditional symmetrical waveguide design process is relatively simple, its low efficiency and high loss can no longer meet the needs of high-speed and large-capacity optical communications. Although asymmetric waveguides have theoretical advantages, their complex processing technology and high precision requirements increase production costs and preparation difficulties.

[0005] Therefore, developing a polarization rotator with high conversion efficiency, low insertion loss and controllable process can not only improve the overall performance of the optical communication system, but also has important significance for promoting the large-scale application of photonic integrated circuits.

[0006] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0007] The object of the present invention is to provide a polarization rotator and a manufacturing method thereof, which can effectively shorten the device structure and bring about a high conversion rate.

[0008] In order to achieve the above object, a technical solution provided by a specific embodiment of the present invention is as follows:

[0009] A polarization rotator comprises a first waveguide, a first coupling waveguide, a mode conversion waveguide, a second coupling waveguide and a second waveguide connected in sequence in a first direction;

[0010] The first waveguide is used to introduce external first mode polarized light;

[0011] The first coupling waveguide is used to couple the first waveguide and the mode conversion waveguide;

[0012] The mode conversion waveguide is used to convert the first mode polarized light introduced by the first waveguide into the second mode polarized light, and the mode conversion waveguide has geometric asymmetry in the first direction;

[0013] The second coupling waveguide is used to couple the mode conversion waveguide and the second waveguide;

[0014] The second waveguide is used to guide out the second mode polarized light converted by the mode conversion waveguide;

[0015] The first direction is the light propagation direction.

[0016] In one or more embodiments of the present invention, the first waveguide, the first coupled waveguide, the mode conversion waveguide, the second coupled waveguide, and the second waveguide each include a substrate, a core layer, and a cladding layer integrally arranged along a first direction.

[0017] In one or more embodiments of the present invention, the cross-section of the core layer of the mode conversion waveguide is in the shape of a right-angled trapezoid, wherein the right-angled trapezoid is formed by performing dry etching and wet etching on both sides of the core layer of the mode conversion waveguide respectively.

[0018] In one or more embodiments of the present invention, the substrate of the mode conversion waveguide has a first surface, and the first surface has a first region, a second region, a third region, and a fourth region sequentially distributed in a second direction;

[0019] The first surface of the substrate of the mode conversion waveguide is recessed in a first region relative to the second region, the third region and the fourth region;

[0020] The core layer of the mode conversion waveguide is arranged in the second region and the third region, and the side surface of the core layer of the mode conversion waveguide close to the fourth region is inclined relative to the first surface;

[0021] The cladding of the mode conversion waveguide is arranged on a side of the core layer of the mode conversion waveguide away from the substrate, and the orthographic projection of the cladding of the mode conversion waveguide is located in the second region;

[0022] Wherein, the second direction is perpendicular to the light propagation direction.

[0023] In one or more embodiments of the present invention, a side surface of the core layer of the mode conversion waveguide close to the first region is arranged perpendicular to the first surface; and / or,

[0024] The core width of the mode conversion waveguide decreases away from the substrate.

[0025] In one or more embodiments of the present invention, the width of the first region is equal to the sum of the widths of the third region and the fourth region.

[0026] In one or more embodiments of the present invention, the first surface of the substrate of the mode conversion waveguide is recessed in the first region relative to the second region, the third region and the fourth region by a depth of 0.5 μm to 1 μm.

[0027] In one or more embodiments of the present invention, the cladding width of the first waveguide is greater than the cladding width of the mode conversion waveguide; and / or,

[0028] The cladding width of the second waveguide is greater than the cladding width of the mode conversion waveguide;

[0029] The cladding width of the first coupling waveguide decreases from the first waveguide to the mode conversion waveguide; and / or,

[0030] The cladding width of the second coupling waveguide increases from the mode conversion waveguide toward the second waveguide.

[0031] In one or more embodiments of the present invention, the first waveguide, the first coupled waveguide, the mode conversion waveguide, the second coupled waveguide and the second waveguide each further include a buried layer integrally arranged along the first direction, and the buried layer covers the cladding surface, the core layer surface and the substrate surface.

[0032] In one or more embodiments of the present invention, both the first waveguide and the second waveguide are single-mode waveguides; and / or,

[0033] The first waveguide has geometric symmetry in a first direction, the second waveguide has geometric symmetry in the first direction, and the symmetry axes of the first waveguide and the second waveguide in the first direction coincide with each other.

[0034] A method for manufacturing a polarization rotator, comprising:

[0035] An epitaxial wafer is provided, the epitaxial wafer comprising a substrate and a core layer and a cladding layer stacked on a surface of the substrate, the epitaxial wafer comprising a first waveguide region, a first coupling waveguide region, a mode conversion waveguide region, a second coupling waveguide region and a second waveguide region sequentially distributed in a first direction, and the mode conversion waveguide region of the epitaxial wafer comprises a first region, a second region, a third region and a fourth region sequentially distributed in a second direction;

[0036] forming a first mask layer having a target waveguide pattern on a cladding surface of the epitaxial wafer;

[0037] dry etching the cladding layer not covered by the first mask layer to form an initial ridge waveguide structure;

[0038] forming a second mask layer, wherein the second mask layer does not cover the core layer located in the first region of the mode conversion waveguide region;

[0039] Dry etching the core layer in the first region of the mode conversion waveguide region and etching to the substrate in the first region;

[0040] forming a third mask layer, wherein the third mask layer does not cover the core layer located in the third region and the fourth region in the mode conversion waveguide region;

[0041] Wet etching a portion of the core layer located in the third region and all of the core layer located in the fourth region in the mode conversion waveguide region;

[0042] removing the first mask layer, the second mask layer and the third mask layer to form a buried layer covering the surface of the cladding layer, the surface of the core layer and the surface of the substrate;

[0043] The first direction is the light propagation direction, and the second direction is perpendicular to the light propagation direction.

[0044] In one or more embodiments of the present invention, forming a first mask layer having a target waveguide pattern on the cladding surface of the epitaxial wafer includes:

[0045] forming a photoresist layer on the cladding surface of the epitaxial wafer;

[0046] Photolithography development to expose a target waveguide pattern on the surface of the cladding;

[0047] forming a metal mask layer, wherein the metal mask layer covers the photoresist layer and the exposed surface of the cladding layer;

[0048] The photoresist layer and the metal mask layer on the photoresist layer are stripped off to form a first mask layer having a target waveguide pattern.

[0049] In one or more embodiments of the present invention, the dry etching includes inductively coupled plasma etching; and / or,

[0050] The wet etching solution includes a mixed solution of dilute hydrochloric acid and dilute sulfuric acid.

[0051] Compared with the prior art, the polarization rotator and its manufacturing method of the present invention can accurately control the device size and shorten the length to hundreds of microns through the design of a single waveguide structure (mainly a mode conversion waveguide) with an asymmetric geometric structure, thereby meeting the compactness requirements of integrated photonics and bringing about a high conversion rate.

[0052] The polarization rotator and the manufacturing method of the present invention prepare a polarization rotator with an asymmetric geometric structure by accurately defining the target waveguide pattern, peeling off to form a mask layer, dry etching for preliminary shaping, and wet etching. The manufacturing method does not need to rely on multi-waveguide coupling, avoids the stringent requirements on spacing and symmetry in the coupled design, and can achieve efficient polarization rotation at a smaller device size. The manufacturing method is simple in process, does not introduce impurities, and the parameters are easy to control. The processing accuracy and manufacturing tolerance are also significantly better than those of the coupled polarization rotator, while improving the production efficiency and device miniaturization capability.

[0053] The polarization rotator and the manufacturing method thereof of the present invention introduce a mask layer to effectively protect the initial structure of the waveguide and increase the overall process tolerance; through the combination of dry etching process and wet etching process, the design deviation caused by the difficulty in controlling the etching depth is effectively solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0055] Figure 1 is a top view of a polarization rotator according to an embodiment of the present invention;

[0056] Figure 2 is the first waveguide cross section of the polarization rotator in one embodiment of the present invention ( Figure 1 Schematic diagram of the cross section of AA in the figure;

[0057] Figure 3 is a mode conversion waveguide of a polarization rotator in one embodiment of the present invention ( Figure 1 Schematic diagram of the cross section of BB;

[0058] Figure 4 is the second coupling waveguide of the polarization rotator in one embodiment of the present invention ( Figure 1 Schematic diagram of the cross section of CC;

[0059] Figure 5 is a process flow chart of a method for manufacturing a polarization rotator in the present invention;

[0060] Figure 6 FIG. 1 is a top view of an epitaxial wafer in a process step of a method for manufacturing a polarization rotator in one embodiment of the present invention.

[0061] Figure 7-Figure 141 is a cross-sectional view of the process steps of a method for manufacturing a polarization rotator according to an embodiment of the present invention, wherein a in each figure is a cross-sectional view of a first waveguide of a polarization rotator ( Figure 6 a) at the AA position in the middle, b) are cross-sectional views of the mode conversion waveguide ( Figure 6 middle BB position). DETAILED DESCRIPTION

[0062] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0063] As mentioned in the background technology, traditional polarization rotators are mostly based on symmetrical waveguide structure design, and polarization conversion is achieved through mode coupling. Coupled polarization rotators are usually prepared by preparing two adjacent waveguides on a substrate, and using the waveguide spacing and length to regulate the coupling efficiency of the TE mode and the TM mode. However, during the processing, it is extremely difficult to accurately control the waveguide spacing. Deviations in deposition thickness or mask alignment errors can cause the waveguide spacing to deviate from the design value, significantly reducing the coupling efficiency. In addition, the coupling length of such devices is usually long, making it difficult to miniaturize the device size, which is inconsistent with the compactness requirements of integrated photonics.

[0064] In order to improve the polarization conversion efficiency, polarization devices based on asymmetric waveguide structures have emerged. Asymmetric waveguides mainly break the symmetry of the waveguide, such as introducing the asymmetry of the cross-sectional geometry or the difference in the refractive index of different materials, to enhance the coupling strength between the TE and TM modes, thereby achieving higher polarization conversion efficiency. For example, skewed slot waveguides or trapezoidal waveguides, or by designing complex geometric shapes to make the effective refractive index of the two modes tend to be consistent, improve the hybridization between the modes, and thus improve the conversion efficiency. However, the complexity of the preparation process of waveguides with asymmetric structures increases significantly with the diversity of structures.

[0065] Traditional methods rely on dry etching (such as reactive ion etching, RIE) or wet etching to form waveguide structures, but dry etching easily introduces sidewall roughness and surface defects, resulting in additional light scattering losses. In addition, asymmetric designs require that the etching depths vary in different areas, but the etching uniformity of existing equipment is limited, and it is difficult to accurately control the depth gradient. Over-etching or under-etching may also destroy the cross-sectional shape of the waveguide and reduce the conversion efficiency. The alignment error of existing ordinary commercial lithography equipment is usually around 0.1 microns. For waveguides with a width of only a few microns, it is easy to cause large process errors, which may lead to deviations from the design value. The isotropy of wet etching makes it difficult to accurately control asymmetric shapes, and the requirements for structural accuracy become a technical difficulty. In addition, the dimensional deviation of the waveguide structure caused by the processing device or the successful non-uniformity of material growth may also weaken the coupling effect between modes, thereby limiting device performance.

[0066] Based on this, the present invention provides a polarization rotator and a method for manufacturing the same. Structurally, a single waveguide structure (mainly a mode conversion waveguide) with an asymmetric geometric structure is designed to accurately control the size of the device and shorten the length to hundreds of microns, thereby meeting the compactness requirements of integrated photonics while bringing about a high conversion rate. Methodologically, by accurately defining the target waveguide pattern, stripping to form a mask layer, performing preliminary forming by dry etching, and combining wet etching, etc., the polarization rotator with precise size, controllable shape, and high optical quality can be manufactured. The manufacturing method is simple, does not introduce impurities, and the process parameters are easy to control. The method is similar to the traditional photonic integrated device processing method, has high compatibility, and high production efficiency.

[0067] like Figure 1 As shown, the polarization rotator in one embodiment of the present invention includes a first waveguide A, a first coupling waveguide B, a mode conversion waveguide C, a second coupling waveguide D and a second waveguide E connected in sequence in a first direction. The first direction is the light propagation direction, such as Figure 1 The first waveguide A, the first coupling waveguide B, the mode conversion waveguide C, the second coupling waveguide D and the second waveguide E are integrally arranged.

[0068] The first waveguide A is used to introduce external first mode polarized light. The first coupling waveguide B is used to couple the first waveguide A and the mode conversion waveguide C. The mode conversion waveguide C is used to convert the first mode polarized light introduced by the first waveguide A into a second mode polarized light. The first mode polarized light includes one of TE mode polarized light or TM mode polarized light, and the second mode polarized light includes the other of TE mode polarized light or TM mode polarized light. The second coupling waveguide D is used to couple the mode conversion waveguide C and the second waveguide E. The second waveguide E is used to export the second mode polarized light converted by the mode conversion waveguide C.

[0069] The first waveguide A and the second waveguide E are both single-mode waveguides. Preferably, the first waveguide A and the second waveguide E have the same size, and can stably confine and transmit the light field. The first waveguide A has geometric symmetry in the first direction, and the second waveguide E also has geometric symmetry in the first direction, and the symmetry axes of the first waveguide A and the second waveguide E in the first direction coincide.

[0070] The first coupling waveguide B and the second coupling waveguide D adopt a Trap structure. The Trap structure is a mode limiting technology used in waveguides or optical devices, mainly used to effectively control the propagation mode of light waves or electromagnetic waves, reduce energy leakage, and improve transmission efficiency.

[0071] The mode conversion waveguide C has geometric asymmetry in the first direction and is asymmetric about the symmetry axis in the first direction of the first waveguide A and the second waveguide E. The asymmetry of the mode conversion waveguide C destroys the orthogonality of the TE mode and the TM mode, resulting in hybridization of the TE mode and the TM mode, so that part of the energy of the TE mode is coupled to the TM mode.

[0072] like Figures 1 to 4 As shown, the first waveguide A, the first coupled waveguide B, the mode conversion waveguide C, the second coupled waveguide D and the second waveguide E each include a substrate 100, a core layer 200, a cladding layer 300 and a buried layer 400 integrally arranged along a first direction. The core layer 200 covers the surface of the substrate 100, the cladding layer 300 is arranged on the side of the core layer 200 away from the substrate 100, and the buried layer 400 covers the surface of the cladding layer 300, the surface of the core layer 200 and part of the surface of the substrate 100 (mainly the surface of the substrate 100C of the mode conversion waveguide C).

[0073] The width of the cladding 300A of the first waveguide (in a direction perpendicular to the first direction - Figure 1 The length in the y direction shown is defined as the width, which applies to the following) is greater than the width of the cladding 300C of the mode conversion waveguide. The width of the cladding 300B of the first coupling waveguide decreases from the first waveguide A to the mode conversion waveguide C. The width of the cladding 300E of the second waveguide is greater than the width of the cladding 300C of the mode conversion waveguide. The width of the cladding 300D of the second coupling waveguide increases from the mode conversion waveguide C to the second waveguide E. Preferably, the width of the cladding 300A of the first waveguide is equal to the width of the cladding 300B of the second waveguide.

[0074] The first coupling waveguide B and the second coupling waveguide D can smoothly transition the mode field distribution differences between the first waveguide A and the mode conversion waveguide C, and between the mode conversion waveguide C and the second waveguide E through the width gradient design. This width gradient avoids the mode field mismatch caused by the abrupt interface, thereby significantly improving the mode coupling efficiency. This width gradient design is insensitive to the dimensional deviation in the manufacturing process and reduces the impact caused by lithography or etching errors.

[0075] In this embodiment, the substrate 100 is preferably an N-type InP substrate. The core layer 200 is preferably a high refractive index core layer, and the material includes but is not limited to InGaAsP and AlGaInP. The cladding 300 is preferably a P-type InP cladding. The buried layer 400 is preferably a silicon dioxide buried layer, and the main function of the buried layer 400 is to prevent the loss of light field energy caused by mode leakage.

[0076] like Figure 2 As shown, the substrate 100C of the mode conversion waveguide C has a first surface S1, and the first surface S1 has a first area S11, a second area S12, a third area S13 and a fourth area S14 distributed in sequence in the second direction. The second direction is perpendicular to the light propagation direction, as shown in FIG. Figure 1 and Figure 2 Preferably, the width of the first region S11 is equal to the sum of the widths of the third region S13 and the fourth region S14.

[0077] The first surface S1 of the substrate 100C of the mode conversion waveguide is recessed in the first region S11 relative to the second region S12 , the third region S13 , and the fourth region S14 . Preferably, the recess depth is 0.5 μm-1 μm.

[0078] The core layer 200C of the mode conversion waveguide is disposed in the second region S12 and the third region S13. The side surface of the core layer 200C of the mode conversion waveguide close to the fourth region S14 is inclined relative to the first surface S1. The side surface of the core layer 200C of the mode conversion waveguide close to the first region S11 is perpendicular to the first surface S1. The width of the core layer 200C of the mode conversion waveguide gradually decreases from the direction away from the substrate 100C.

[0079] Preferably, the cross section of the core layer 200C of the mode conversion waveguide is in the shape of a right-angled trapezoid, wherein the right-angled trapezoid is formed by dry etching and wet etching on both sides of the core layer 200C of the mode conversion waveguide in the second direction. Dry etching penetrates the cladding and the core layer and over-etches to the substrate to form a vertical sidewall of the right-angled trapezoid; wet etching the core layer to form an inclined sidewall of the right-angled trapezoid. The right-angled trapezoid structure effectively causes the optical axis X / Y to deviate by 47.5 degrees. After the TE / TM polarized light is injected through the first waveguide A, the light forms a mixed mode of light in the mode conversion waveguide C. Due to the deviation of the optical axis, the optical axis is deflected to Y / X after a propagation length of a beat frequency, and the TE / TM polarization is converted to TM / TE polarization.

[0080] The cladding 300C of the mode conversion waveguide is disposed on a side of the core layer 200C of the mode conversion waveguide facing away from the substrate 100C, and an orthographic projection of the cladding 300C of the mode conversion waveguide is located in the second region S12.

[0081] The buried layer 400C of the mode conversion waveguide completely covers the surface of the cladding 300C of the mode conversion waveguide, the surface of the core layer 200C of the conversion waveguide, and the surfaces of the first region S11 and the fourth region S14 of the substrate 100C of the mode conversion waveguide.

[0082] In the polarization rotator of this embodiment, the mode field areas of each waveguide are similar, and no additional coupling loss is caused. While the device length of the polarization rotator is less than 168um, the polarization conversion efficiency in the communication C band is greater than 98%. Among them, the mode field area (MFA) is an important parameter that describes the energy distribution range of the fundamental mode in the optical waveguide. When the mode field areas of different waveguides are similar, the mode mismatch loss can be significantly reduced, which plays a key role in optical interconnection, couplers and integrated photonic devices.

[0083] The polarization rotator of the present invention can precisely control the device size and shorten the length to hundreds of microns through the design of a single waveguide structure (mainly a mode conversion waveguide) with an asymmetric geometric structure, thereby meeting the compactness requirements of integrated photonics and bringing about a high conversion rate.

[0084] like Figure 5 As shown, the present invention also discloses a method for manufacturing a polarization rotator, which specifically includes the following steps:

[0085] S1, providing an epitaxial wafer, the epitaxial wafer comprising a substrate and a core layer and a cladding layer stacked on a surface of the substrate, the epitaxial wafer comprising a first waveguide region, a first coupling waveguide region, a mode conversion waveguide region, a second coupling waveguide region and a second waveguide region sequentially distributed in a first direction, and the mode conversion waveguide region of the epitaxial wafer comprising a first region, a second region, a third region and a fourth region sequentially distributed in a second direction;

[0086] S2, forming a first mask layer having a target waveguide pattern on the cladding surface of the epitaxial wafer;

[0087] S3, dry etching the cladding layer not covered by the first mask layer to form an initial ridge waveguide structure;

[0088] S4, forming a second mask layer, wherein the second mask layer does not cover the core layer located in the first region in the mode conversion waveguide region;

[0089] S5, dry etching the core layer in the first region in the mode conversion waveguide region and etching to the substrate in the first region;

[0090] S6, forming a third mask layer, wherein the third mask layer does not cover the core layer located in the third region and the fourth region in the mode conversion waveguide region;

[0091] S7, wet-etching a portion of the core layer located in the third region and the entire core layer located in the fourth region in the mode conversion waveguide region;

[0092] S8, removing the first mask layer, the second mask layer and the third mask layer to form a buried layer covering the surface of the cladding layer, the surface of the core layer and the surface of the substrate;

[0093] The first direction is the light propagation direction, and the second direction is perpendicular to the light propagation direction.

[0094] In step S1, the substrate of the epitaxial wafer is preferably N-type indium phosphide, and the core layer material grown on the N-type indium phosphide substrate can be a lattice matching material such as InGaAsP and AlGaInP, depending on specific application requirements.

[0095] In step S2, first, a photoresist layer is formed on the cladding surface of the epitaxial wafer; secondly, photolithography is performed to expose the target waveguide pattern on the cladding surface; then, a metal mask layer is formed, and the metal mask layer covers the photoresist layer and the exposed cladding surface; finally, the photoresist layer and the metal mask layer on the photoresist layer are stripped to form a first mask layer with the target waveguide pattern. The material of the photoresist layer can be a thin film material such as LOR3A, AR80, and is easy to strip. The photolithography method can be contact lithography, projection lithography, electron beam lithography, etc. The metal mask layer can be a metal with good adsorption, such as chromium, gold, nickel, etc., and the hard mask formed by it can effectively protect the initial structure of the waveguide in the subsequent process steps and increase the process tolerance of the photolithography.

[0096] In step S3 and step S5, dry etching includes but is not limited to inductively coupled plasma etching. Among them, the dry etching in step S3 can be a low-temperature process, and the etching rate can be slowed down by changing parameters such as chamber pressure and power, and the etching depth of the epitaxial wafer cladding and core layer is required to reach the design expectation. The dry etching in step S5 can be a high-temperature process, and the etching rate can be accelerated by changing parameters such as etching gas selection and radio frequency power, and the substrate of the epitaxial wafer is required to be over-etched to meet the etching depth.

[0097] In step S6 , the third mask layer may be a photoresist mask, a dielectric mask, a metal mask, or the like.

[0098] In step S7, the wet etching solution includes but is not limited to a mixed solution of dilute hydrochloric acid and dilute sulfuric acid.

[0099] In step S8 , the first mask layer, the second mask layer and the third mask layer may be removed by using a hydrogen fluoride aqueous solution or a mixed solution of hydrogen fluoride and ammonium fluoride.

[0100] Figure 7-Figure 14 FIG. 1 is a process step diagram of a method for manufacturing a polarization rotator in an embodiment of the present invention, wherein a in each figure is a cross-sectional diagram of a first waveguide of a polarization rotator, and b is a cross-sectional diagram of a mode conversion waveguide. Figure 7-Figure 14 , the method for manufacturing the polarization rotator of the present invention is further described in detail.

[0101] refer to Figure 6 and Figure 7 As shown, a cleaned indium phosphide epitaxial wafer 10 is provided. The epitaxial wafer 10 includes a substrate 100 and a core layer 200 and a cladding layer 300 stacked on the surface of the substrate 100. The epitaxial wafer 10 includes a first waveguide region 10A, a first coupling waveguide region 10B, a mode conversion waveguide region 10C, a second coupling waveguide region 10D and a second waveguide region 10E distributed in sequence in a first direction. Figure 7 As shown in b, the mode conversion waveguide region 10C of the epitaxial wafer 10 includes a first region S11, a second region S12, a third region S13 and a fourth region S14 sequentially distributed in the second direction.

[0102] A silicon dioxide layer 11 is formed on the surface of the epitaxial wafer 10 by a chemical vapor deposition process or a thermal oxidation process.

[0103] refer to Figure 8 As shown, a lithography pattern having a target waveguide pattern is defined on the surface of the epitaxial wafer 10 by a stepper lithography process.

[0104] Specifically, a layer of photoresist 12 is first coated using a coating machine. The material of the photoresist 12 can be a thin film material such as LOR3A, AR80, etc. The photoresist 12 is photolithographically processed using contact photolithography, projection photolithography, or electron beam photolithography to define a photolithographic pattern having a target waveguide pattern. After photolithography, a 2.38% developer is used for development to expose the target waveguide pattern on the surface of the silicon dioxide layer 11.

[0105] refer to Fig. 9 As shown, an electron beam evaporation device is used to evaporate a layer of Cr / Ni metal on the surface of the photoresist 12, and N-methylpyrrolidone is used to soak and ultrasonically strip the residual metal to form a first mask layer 13. The first mask layer 13 formed in this step can effectively protect the initial structure of the waveguide in subsequent process steps and increase the process tolerance of photolithography.

[0106] refer to Fig.10 As shown, an inductively coupled plasma etching process is performed, wherein the gas composition is chlorine / methane / nitrogen and the temperature is 60 degrees Celsius. The area not covered by the first mask layer 13 is quickly etched; the etching depth is precisely controlled by the process parameters, and the uncovered cladding 300 is completely etched to form the initial structure of the ridge waveguide. The etching rate can be slowed down by changing the parameters such as chamber pressure and power, and the etching depth of the cladding is required to reach the design expectation.

[0107] refer to Fig.11 As shown, a thinner silicon dioxide layer 14 is evaporated again by chemical vapor deposition process to protect subsequent devices from being etched. Secondary overlay is performed by step-by-step photolithography process to form a second mask layer 15 to define the pattern of the area that does not need to be etched subsequently. The area that does not need to be etched subsequently includes the first waveguide area 10A, the first coupling waveguide area 10B, the second area S12, the third area S13 and the fourth area S14 of the mode conversion waveguide area 10C, the second coupling waveguide area 10D and the second waveguide area 10E, refer to Fig.11 As shown in b.

[0108] refer to Fig.12 As shown, an inductively coupled plasma etching process is performed, wherein the gas composition is chlorine / methane / hydrogen, the temperature is 150 degrees Celsius, and the first area S11 of the mode conversion waveguide area 10C not covered by the second mask layer 15 is etched. Fig.12 By using process parameters, rapid etching is performed and the etching depth is controlled to completely etch the core layer 200 of the first region S11 of the mode conversion waveguide region 10C, and overetch 0.5 μm-1 μm to the substrate 100. In this step, the second mask layer 15 and the silicon dioxide layer 14 are also etched to a certain extent.

[0109] refer to Fig.13As shown, a stepper lithography machine is used to define and protect the photoresist pattern of the first waveguide region 10A, the first coupling waveguide region 10B, the first region S11 of the mode conversion waveguide region 10C, the second region S12, the second coupling waveguide region 10D and the second waveguide region 10E to form a third mask layer 16. A mixed solution of dilute hydrochloric acid and dilute sulfuric acid is used to wet-etch the core layer 200 of the third region S13 and the fourth region S14 of the mode conversion waveguide region 10C not covered by the third mask layer 16. Fig.13 As shown in b, a triangular slope structure is formed in the third area S13, and the core layer 200 in the fourth area S14 is completely etched away.

[0110] refer to Fig.14 As shown, the above structure is rinsed with a dilute hydrofluoric acid solution to remove the residual mask layer and silicon dioxide layer, and then a thicker silicon dioxide buried layer 400 is evaporated again through a chemical vapor deposition process.

[0111] Compared with the prior art, the polarization rotator and its manufacturing method of the present invention can accurately control the device size and shorten the length to hundreds of microns through the design of a single waveguide structure (mainly a mode conversion waveguide) with an asymmetric geometric structure, thereby meeting the compactness requirements of integrated photonics and bringing about a high conversion rate.

[0112] The polarization rotator and the manufacturing method of the present invention prepare a polarization rotator with an asymmetric geometric structure by accurately defining the target waveguide pattern, peeling off to form a mask layer, dry etching for preliminary shaping, and wet etching. The manufacturing method does not need to rely on multi-waveguide coupling, avoids the stringent requirements on spacing and symmetry in the coupled design, and can achieve efficient polarization rotation at a smaller device size. The manufacturing method is simple in process, does not introduce impurities, and the parameters are easy to control. The processing accuracy and manufacturing tolerance are also significantly better than those of the coupled polarization rotator, while improving the production efficiency and device miniaturization capability.

[0113] The polarization rotator and the manufacturing method thereof of the present invention introduce a mask layer to effectively protect the initial structure of the waveguide and increase the overall process tolerance; through the combination of dry etching process and wet etching process, the design deviation caused by the difficulty in controlling the etching depth is effectively solved.

[0114] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0115] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A polarization rotator, characterized in that: comprising a first waveguide, a first coupling waveguide, a mode conversion waveguide, a second coupling waveguide and a second waveguide sequentially connected in a first direction; The first waveguide is used to introduce external first mode polarized light; The first coupling waveguide is used to couple the first waveguide and the mode conversion waveguide; The mode conversion waveguide is used to convert the first mode polarized light introduced by the first waveguide into the second mode polarized light, and the mode conversion waveguide has geometric asymmetry in the first direction; The second coupling waveguide is used to couple the mode conversion waveguide and the second waveguide; The second waveguide is used to guide out the second mode polarized light converted by the mode conversion waveguide; The first direction is the light propagation direction.

2. The polarization rotator according to claim 1, wherein: The first waveguide, the first coupled waveguide, the mode conversion waveguide, the second coupled waveguide and the second waveguide each include a substrate, a core layer and a cladding layer integrally arranged along a first direction.

3. The polarization rotator according to claim 2, characterized in that The cross section of the core layer of the mode conversion waveguide is in a right-angled trapezoidal shape, wherein the right-angled trapezoidal shape is formed by performing dry etching and wet etching on both sides of the core layer of the mode conversion waveguide respectively.

4. The polarization rotator according to claim 2, wherein: The substrate of the mode conversion waveguide has a first surface, and the first surface has a first area, a second area, a third area and a fourth area sequentially distributed in a second direction; The first surface of the substrate of the mode conversion waveguide is recessed in a first region relative to the second region, the third region and the fourth region; The core layer of the mode conversion waveguide is arranged in the second region and the third region, and the side surface of the core layer of the mode conversion waveguide close to the fourth region is inclined relative to the first surface; The cladding of the mode conversion waveguide is arranged on a side of the core layer of the mode conversion waveguide away from the substrate, and the orthographic projection of the cladding of the mode conversion waveguide is located in the second region; Wherein, the second direction is perpendicular to the light propagation direction.

5. The polarization rotator according to claim 4, characterized in that The side surface of the core layer of the mode conversion waveguide close to the first region is arranged perpendicular to the first surface; and / or, The core width of the mode conversion waveguide decreases away from the substrate.

6. The polarization rotator according to claim 4, characterized in that The width of the first region is equal to the sum of the widths of the third region and the fourth region.

7. The polarization rotator according to claim 4, characterized in that The first surface of the substrate of the mode conversion waveguide has a recessed depth of 0.5 μm-1 μm in the first region relative to the second region, the third region and the fourth region.

8. The polarization rotator according to claim 2, wherein: The cladding width of the first waveguide is greater than the cladding width of the mode conversion waveguide; and / or, The cladding width of the second waveguide is greater than the cladding width of the mode conversion waveguide; The cladding width of the first coupling waveguide decreases from the first waveguide to the mode conversion waveguide; and / or, The cladding width of the second coupling waveguide increases from the mode conversion waveguide toward the second waveguide.

9. The polarization rotator according to claim 2, wherein: The first waveguide, the first coupled waveguide, the mode conversion waveguide, the second coupled waveguide and the second waveguide each further include a buried layer integrally arranged along the first direction, the buried layer covering the cladding surface, the core surface and the substrate surface.

10. The polarization rotator according to claim 1, wherein: The first waveguide and the second waveguide are both single-mode waveguides; and / or, The first waveguide has geometric symmetry in a first direction, the second waveguide has geometric symmetry in the first direction, and the symmetry axes of the first waveguide and the second waveguide in the first direction coincide with each other.

11. A method for manufacturing a polarization rotator, characterized in that: include: An epitaxial wafer is provided, the epitaxial wafer comprising a substrate and a core layer and a cladding layer stacked on a surface of the substrate, the epitaxial wafer comprising a first waveguide region, a first coupling waveguide region, a mode conversion waveguide region, a second coupling waveguide region and a second waveguide region sequentially distributed in a first direction, and the mode conversion waveguide region of the epitaxial wafer comprises a first region, a second region, a third region and a fourth region sequentially distributed in a second direction; forming a first mask layer having a target waveguide pattern on a cladding surface of the epitaxial wafer; dry etching the cladding layer not covered by the first mask layer to form an initial ridge waveguide structure; forming a second mask layer, wherein the second mask layer does not cover the core layer located in the first region of the mode conversion waveguide region; Dry etching the core layer in the first region of the mode conversion waveguide region and etching to the substrate in the first region; forming a third mask layer, wherein the third mask layer does not cover the core layer located in the third region and the fourth region in the mode conversion waveguide region; Wet etching a portion of the core layer located in the third region and all of the core layer located in the fourth region in the mode conversion waveguide region; removing the first mask layer, the second mask layer and the third mask layer to form a buried layer covering the surface of the cladding layer, the surface of the core layer and the surface of the substrate; The first direction is the light propagation direction, and the second direction is perpendicular to the light propagation direction.

12. The method for manufacturing a polarization rotator according to claim 11, characterized in that: Forming a first mask layer having a target waveguide pattern on the cladding surface of the epitaxial wafer, comprising: forming a photoresist layer on the cladding surface of the epitaxial wafer; Photolithography development to expose a target waveguide pattern on the surface of the cladding; forming a metal mask layer, wherein the metal mask layer covers the photoresist layer and the exposed surface of the cladding layer; The photoresist layer and the metal mask layer on the photoresist layer are stripped off to form a first mask layer having a target waveguide pattern.

13. The method for manufacturing a polarization rotator according to claim 11, characterized in that: The dry etching includes inductively coupled plasma etching; and / or, The wet etching solution includes a mixed solution of hydrochloric acid and sulfuric acid.

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