阅读说明：本技术 一种基于亚波长光栅的lnoi模斑转换器和制备方法 (LNOI (Low noise optical insulator) spot size converter based on sub-wavelength grating and preparation method ) 是由 周奉杰 钱广 顾晓文 唐杰 孔月婵 于 2020-12-30 设计创作，主要内容包括：本发明公开了一种基于亚波长光栅的LNOI模斑转换器,包括：顶层锥形波导、底层锥形波导、锥形亚波长光栅、SiO-2倒锥形厚脊波导包层、SiN亚波长光栅薄层和光纤固定槽；制备方法涉及的工艺包括：顶层锥形波导和底层锥形波导制备、锥形亚波长光栅制备、SiO-2倒锥形厚脊波导制备、SiN亚波长光栅制备、光纤固定槽制备。本发明采用双层锥形波导结合锥形亚波长光栅、SiN亚波长光栅和SiO-2倒锥形厚脊波导的结构,通过调节波导芯层以及包层的有效折射率,实现LNOI光波导中小尺寸光模场的放大功能,进而提高LNOI光波导与单模光纤的耦合效率。(The invention discloses an LNOI spot-size converter based on a sub-wavelength grating, which comprises: top layer conical waveguide, bottom layer conical waveguide, conical sub-wavelength grating and SiO 2 The optical fiber fixing structure comprises an inverted cone-shaped thick ridge waveguide cladding, a SiN sub-wavelength grating thin layer and an optical fiber fixing groove; the preparation method relates to a process comprising the following steps: preparation of top layer tapered waveguide and bottom layer tapered waveguide, preparation of tapered sub-wavelength grating and SiO 2 Preparing an inverted conical thick ridge waveguide, preparing a SiN sub-wavelength grating and preparing an optical fiber fixing groove. The invention adopts double-layer tapered waveguide combined with tapered sub-wavelength grating, SiN sub-wavelength grating and SiO 2 The structure of the inverted cone-shaped thick ridge waveguide is realized by adjusting the effective refractive indexes of a waveguide core layer and a cladding layerAnd the LNOI optical waveguide has the function of amplifying a small-size optical mode field, so that the coupling efficiency of the LNOI optical waveguide and the single-mode optical fiber is improved.)

1. An LNOI spot-size converter based on sub-wavelength gratings, characterized by: comprises a top layer tapered waveguide (1), a bottom layer tapered waveguide (2), a tapered sub-wavelength grating (3) and SiO₂Upper cladding (4), SiO₂An inverted cone-shaped thick ridge waveguide cladding (5), a SiN sub-wavelength grating (6), an optical fiber fixing groove (7) and SiO₂An insulating layer (8), a chip substrate (9); the top layer tapered waveguide (1) is positioned on the bottom layer tapered waveguide (2); the tail end of the top layer tapered waveguide (1) is coincided with the tail end of the bottom layer tapered waveguide (2); the thickness of the tapered sub-wavelength grating (3) is consistent with that of the bottom tapered waveguide (2), and the tapered sub-wavelength grating (3) is connected with the tail end of the bottom tapered waveguide (2); SiO 2₂The upper cladding (4) covers the top layer tapered waveguide (1), the bottom layer tapered waveguide (2) and the tapered sub-wavelength grating (3); SiN sub-wavelength grating (6) embedded in SiO₂The inverted cone-shaped thick ridge waveguide cladding (5) covers the top layer tapered waveguide (1) and the bottom layer tapered waveguide (2); the optical fiber fixing groove (7) is arranged on the butt joint end face of the spot size converter and the optical fiber; SiO 2₂An insulating layer (8) is arranged on the chip substrate (9) and SiO₂Between the upper cladding (4).

2. The sub-wavelength grating-based LNOI speckle converter of claim 1, wherein: the waveguide width of the top layer tapered waveguide (1) is 700 nm-2 μm, the waveguide thickness is 200 nm-400 nm, the coupling transition region length is 50 μm-200 μm, and the end width of the tapered waveguide is 30 nm-200 nm;

the waveguide width of the bottom layer tapered waveguide (2) is 4-8 μm, the waveguide thickness is 200-400 nm, the coupling transition region length is 50-300 μm, and the end width of the tapered waveguide is 30-200 nm;

the grating period of the conical sub-wavelength grating (3) is 500 nm-1 mu m, the duty ratio is 0.3-0.7, the width of a waveguide at the tail end of the sub-wavelength grating is 30 nm-200 nm, the period number of the sub-wavelength grating is 10-100, and the length of a conical transition region is 30 mu m-150 mu m;

the SiO₂The upper cladding (4) is a rectangular waveguide, the width of the waveguide is 6-10 μm, the length of the waveguide is 200-400 μm, and the thickness of the waveguide is 0.5-2 μm;

the SiO₂The inverted cone-shaped thick ridge waveguide cladding (5), the narrow waveguide end covers the transition region of the top tapered waveguide (1), and the waveguide width is 3-5 μm; the wide waveguide end is the optical fiber access end surface of the spot-size converter, the waveguide width is 6-15 μm, and the thickness is 2-8 μm;

the period of the SiN sub-wavelength grating (6) is 500 nm-2 mu m, the duty ratio is 0.3-0.7, the period number of the grating is 10-100, the thickness of the SiN waveguide is 20 nm-80 nm, the interval between every two layers is 500 nm-1.5 mu m, the width of the waveguide on the coupling end surface of the optical fiber is 4 mu m-8 mu m, the width of the waveguide at the tail end of the grating is 1 mu m-2 mu m, and the length of the conical transition region is 50 mu m-400 mu m.

3. The sub-wavelength grating-based LNOI speckle converter of claim 2, wherein: the SiN sub-wavelength grating (6) is arranged at a position 500 nm-1 mu m above the top layer conical waveguide (1) and the bottom layer conical waveguide (2) in conical transition with SiO₂The inverted cone-shaped thick ridge waveguide cladding (5) is consistent in shape.

4. The sub-wavelength grating-based LNOI speckle converter of claim 1, wherein: the SiN sub-wavelength grating (6) is of a single-layer or double-layer or three-layer structure.

5. The sub-wavelength grating-based LNOI speckle converter of claim 1, wherein: the SiO₂The inverted cone-shaped thick ridge waveguide cladding (5) is of a single-layer or double-layer or three-layer structure.

6. The sub-wavelength grating-based LNOI speckle converter of claim 1, wherein: the optical fiber fixing groove (7) is a V-shaped groove or groove-shaped structure formed on the chip substrate (9) and is manufactured by adopting a corrosion or etching process.

7. The sub-wavelength grating-based LNOI speckle converter of claim 1, wherein: the waveguide widths of the top layer tapered waveguide (1), the bottom layer tapered waveguide (2) and the tapered sub-wavelength grating (3) are gradually narrowed, and the transition region is in a linear or parabolic shape, a square root shape, an exponential shape or a step shape.

8. A preparation method of an LNOI spot-size converter based on a sub-wavelength grating is characterized by comprising the following steps:

step s1, preparing an etching mask of the top-layer tapered waveguide (1);

step s2, etching the top-layer tapered waveguide (1);

step s3, preparing etching masks of the bottom layer tapered waveguide (2) and the tapered sub-wavelength grating (3);

step s4, etching the bottom layer tapered waveguide (2) and the tapered sub-wavelength grating (3);

step s5, SiO₂Growing a medium;

step s6, SiN medium growth;

step s7, preparing the SiN sub-wavelength grating (6);

step s8, SiO₂Growing a medium;

step s9, SiO₂Preparing an inverted conical thick ridge waveguide cladding (5);

step s10, SiO₂Preparing an upper cladding (4);

step s11, fiber securing groove (7) preparation.

9. The method of claim 8, wherein the method comprises:

the thickness of the lithium niobate bottom layer tapered waveguide (2) manufactured by the selected LNOI is 200 nm-500 nm, and SiO is₂The thickness of the insulating layer (8) is 2-3 μm, and the chip substrate (9) is lithium niobate or silicon;

in the step (s3), the etching mask comprises a photoresist and a metal mask, the photoresist comprises an HSQ negative photoresist, a ZEP 520A positive photoresist and a 7908 positive photoresist, and the metal mask is made of Ni or Ti/Ni or Cr/Ni;

in the step (s4), the etching is performed by dry etching process, reactive ion etching or inductively coupled plasma etching, and the etching gas is argon or argon and SF₆The mixed gas of (3);

the SiO₂The medium and the SiN medium are grown by adopting a plasma enhanced chemical vapor deposition method;

the SiO₂The etching of the medium and the SiN medium adopts an F-based dry etching process, and etching gas adopts SF₆Or CHF₃Or SF₆/Ar, or CHF₃/Ar；

When the substrate is silicon, the optical fiber fixing groove (7) is prepared by adopting a wet etching silicon process, wherein the etching solution comprises KOH and TMAH solution; when the substrate is lithium niobate, the optical fiber fixing groove (7) is prepared by adopting an F-based dry etching process, and SF is selected as etching gas₆Or CHF₃Or SF₆/Ar, or CHF₃/Ar。

Technical Field

The invention relates to an LNOI (Low noise on insulator) spot size converter and a preparation method, in particular to an LNOI spot size converter based on a sub-wavelength grating and a preparation method.

Background

The thin film Lithium Niobate (LNOI) material is a new photoelectron integrated material, the structure of which is similar to that of Silicon On Insulator (SOI), and is a three-layer structure, the top layer Lithium Niobate thin film has the advantage of high electrooptical coefficient, and is a preferred material for preparing high-speed electrooptical modulators and optical switches, and the middle insulating layer and the Lithium Niobate have large refractive index difference (delta n ═ n-_LiNbO3-n_SiO22.2-1.44-0.76), device size and waveguide transmission loss can be reduced, and the substrate has many choices, with silicon substrate being the most widely used.

The mode spot converter mainly comprises a grating coupler and an end face coupler, the existing end face coupler mostly adopts a tapered waveguide structure, the limiting capability of the waveguide on an optical mode is weakened along with the narrowing of the width of the waveguide, the mode field of a waveguide core layer can be diffused into a cladding, the optical mode field can be further amplified by adopting the cladding with the refractive index close to that of the waveguide core layer, but the tapered waveguide is generally longer, and the amplifying capability on the optical mode field is limited. By adopting the end-face coupler of the cantilever beam and the three-dimensional tapered waveguide, although the coupling efficiency is improved, the preparation process is difficult, the stability is poor, and the large-scale production of the LNOI optical chip is difficult to realize. Therefore, it is highly desirable to develop a high coupling, low loss, small size and easy to fabricate LNOI mode spot converter.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide an LNOI mode spot converter with high coupling efficiency, low loss and small size and a preparation method.

The technical scheme is as follows: the LNOI spot-size converter comprises a top-layer tapered waveguide, a bottom-layer tapered waveguide, a tapered sub-wavelength grating and SiO₂Upper cladding, SiO₂Inverted cone-shaped thick ridge waveguide cladding, SiN sub-wavelength grating (SWG), optical fiber fixing groove, and SiO₂An insulating layer, a chip substrate; top layer cone waveThe guide is positioned on the conical waveguide at the bottom layer; the tail end of the top layer tapered waveguide is coincided with the tail end of the bottom layer tapered waveguide; the tapered sub-wavelength grating is consistent with the bottom tapered waveguide in thickness, and is connected with the tail end of the bottom tapered waveguide; SiO 2₂The upper cladding covers the top layer tapered waveguide, the bottom layer tapered waveguide and the tapered sub-wavelength grating; SiN sub-wavelength grating embedded SiO₂The inverted cone-shaped thick ridge waveguide cladding layer covers the top layer tapered waveguide and the bottom layer tapered waveguide; the optical fiber fixing groove is positioned on the butt joint end face of the spot size converter and the optical fiber; SiO 2₂The insulating layer is arranged on the chip substrate and SiO₂Between the upper cladding layers.

The waveguide width of the top layer tapered waveguide is 700 nm-2 μm, the waveguide thickness is 200 nm-400 nm, the coupling transition region length is 50 μm-200 μm, and the end width of the tapered waveguide is 30 nm-200 nm; the waveguide width of the bottom layer tapered waveguide is 4-8 μm, the waveguide thickness is 200-400 nm, the coupling transition region length is 50-300 μm, and the end width of the tapered waveguide is 30-200 nm; the grating period of the conical sub-wavelength grating is 500 nm-1 mu m, the duty ratio is 0.3-0.7, the width of a waveguide at the tail end of the sub-wavelength grating is 30 nm-200 nm, the period number of the sub-wavelength grating is 10-100, and the length of a conical transition region is 30 mu m-150 mu m; SiO 2₂The upper cladding is a rectangular waveguide, the width of the waveguide is 6-10 μm, the length of the waveguide is 200-400 μm, and the thickness of the waveguide is 0.5-2 μm; SiO 2₂The inverted cone-shaped thick ridge waveguide cladding layer is provided, the narrow waveguide end covers the transition region of the top tapered waveguide, and the width of the waveguide is 3-5 μm; the wide waveguide end is the optical fiber access end surface of the spot-size converter, the waveguide width is 6-15 μm, and the thickness is 2-8 μm; the period of the SiN sub-wavelength grating is 500-2 mu m, the duty ratio is 0.3-0.7, the period number of the grating is 10-100, the thickness of the SiN waveguide is 20-80 nm, the interval between every two layers is 500-1.5 mu m, the width of the optical fiber coupling end face waveguide is 4-8 mu m, the width of the optical fiber coupling end face waveguide is 1-2 mu m, and the length of the conical transition region is 50-400 mu m.

SiO₂The inverted cone-shaped thick ridge waveguide cladding is of a single-layer or double-layer or three-layer structure.

The SiN sub-wavelength grating is arranged on the top layer of the conical waveguideThe part 500nm to 1 mu m above the bottom layer conical waveguide is in conical transition with SiO₂The inverted cone-shaped thick ridge waveguide cladding has consistent shape; the SiN sub-wavelength grating is of a single-layer or double-layer or three-layer structure.

The optical fiber fixing groove is a structure in which a V-groove or a groove shape is formed on the chip substrate by etching or etching.

The widths of the top layer tapered waveguide, the bottom layer tapered waveguide and the tapered sub-wavelength grating are gradually narrowed, and the shapes of the transition regions are linear or parabolic, square root, exponential or step-shaped.

Preferably, the SiO₂The inverted tapered waveguide is a thick ridge waveguide.

The preparation method of the LNOI spot size converter comprises the following steps:

step s1, preparing a top-layer tapered waveguide etching mask;

step s2, etching the top conical waveguide;

step s3, preparing a bottom layer tapered waveguide and a tapered sub-wavelength grating etching mask;

step s4, etching the bottom layer tapered waveguide and the tapered sub-wavelength grating;

step s5, SiO₂Growing a medium;

step s6, SiN medium growth;

step s7, preparing the SiN sub-wavelength grating;

step s8, SiO₂Growing a medium;

step s9, SiO₂Preparing an inverted conical thick ridge waveguide;

step s10, SiO₂Preparing an upper cladding;

step s11, fiber securing groove preparation.

Preferably, the SiO₂And SiN dielectric are grown by Plasma Enhanced Chemical Vapor Deposition (PECVD).

The thickness of the lithium niobate bottom tapered waveguide manufactured by LNOI is 200 nm-500 nm, and the thickness of SiO is₂The thickness of the insulating layer is 2-3 μm, and the chip substrate is lithium niobate or silicon; the niobiumThe lithium ion waveguide etching mask comprises photoresist and a metal mask, wherein the photoresist comprises HSQ negative photoresist, ZEP 520A positive photoresist and 7908 positive photoresist, and the metal mask is Ni or Ti/Ni or Cr/Ni;

the lithium niobate waveguide etching adopts a dry etching process and adopts reactive ion etching or inductively coupled plasma etching, and etching gas comprises Ar or SF₆Mixed gas of/Ar;

the SiO₂The medium and the SiN medium are grown by Plasma Enhanced Chemical Vapor Deposition (PECVD), and the growth thickness is set according to the design;

the preparation of the etching mask adopts photoresist comprising 7908 positive photoresist, 701 positive photoresist and UV 135 positive photoresist, and the thickness of the photoresist is increased by adopting spin coating of double layers or three layers for etching the thick waveguide;

the SiO₂The etching of the medium and the SiN medium adopts an F-based dry etching process, and etching gas adopts SF₆Or CHF₃Or SF₆/Ar, or CHF₃A gas such as/Ar;

when the substrate is silicon, preparing the optical fiber fixing groove by adopting a wet etching silicon process, wherein an etching solution comprises KOH and TMAH solutions; when the substrate is lithium niobate, the optical fiber fixing groove is prepared by adopting an F-based dry etching process, and etching gas is SF₆Or CHF₃Or SF₆/Ar, or CHF₃and/Ar and the like.

Compared with the prior art, the invention has the following remarkable effects: 1. the structure of the double-layer tapered waveguide and the sub-wavelength grating is adopted, the effective refractive index of the waveguide is reduced, the small-sized optical mode field in the LNOI ridge waveguide is amplified, the coupling efficiency with a single-mode fiber is improved, and the requirements of low insertion loss, high coupling and small size of an LNOI optical waveguide device are met; 2. introduction of SiO₂SiN sub-wavelength grating structure between layers to adjust the effective refractive index (n) of the cladding_SiO2<n_SWG<n_SiN) The refractive index difference between the LNOI waveguide core layer and the cladding layer is reduced, the waveguide core layer with conical transition is combined, the transverse and longitudinal amplification of the optical mode size is realized, and the loss caused by the refractive index mismatching of the cladding layer is reduced; 3. introduction of SiO₂S between layersThe iN sub-wavelength grating structure amplifies the optical field mode iN the lithium niobate waveguide core layer and draws upwards to limit the optical field mode iN SiO₂The inverted-cone-shaped thick ridge waveguide is beneficial to butt joint with an external optical fiber; 4. the optical fiber fixing groove is formed in the position of the optical fiber access end face of the mode spot converter, so that butt joint of the optical fiber and the LNOI optical chip is facilitated, and practical application of the LNOI high-speed tuning chip is facilitated.

Drawings

FIG. 1 is a schematic diagram of an LNOI spot size converter structure of the present invention;

FIG. 2 is a perspective view of the fiber access end face of the LNOI spot-size converter of the present invention, in which 51 is a first layer of SiO₂The inverted tapered cladding 52 being a second SiO layer₂The inverted conical cladding layer 53 is a third SiO layer₂An inverted conical cladding; 61 is a first layer of SiN sub-wavelength grating, 62 is a second layer of SiN sub-wavelength grating;

FIG. 3 is a structural diagram of the transition region of the tapered waveguide of the present invention, wherein (a) is a structural diagram of the linear tapered waveguide, (b) is a structural diagram of the square root tapered waveguide, (c) is a structural diagram of the parabolic tapered waveguide, (d) is a structural diagram of the exponential tapered waveguide, and (e) is a structural diagram of the stepped tapered waveguide;

FIG. 4 is a schematic diagram of an LNOI double-layer tapered waveguide structure of the present invention, in which 8 is SiO₂An insulating layer, 4 is SiO₂An upper cladding layer;

fig. 5 is a cross-sectional view of the fiber access end structure of the LNOI spot-size converter of the present invention, (a) a single-layer structure, (b) a two-layer structure, and (c) a three-layer structure; in the figure, 51 is the first SiO₂Cladding, 52 being a second SiO₂Cladding, 53 being a third SiO₂Cladding, 54 being fourth SiO₂The cladding, 61 is a first layer of SiN sub-wavelength grating, 62 is a second layer of SiN sub-wavelength grating, 63 is a third layer of SiN sub-wavelength grating, and 9 is a chip substrate;

fig. 6 is a schematic diagram of a process for implementing a sub-wavelength grating-based LNOI spot-size converter in accordance with the present invention, wherein,

(a) preparing a top-layer tapered waveguide etching mask for the LNOI and schematically etching the top-layer tapered waveguide;

(b) the schematic diagram of the LNOI bottom layer conical waveguide and the conical sub-wavelength grating etching is shown;

(c) is SiO₂A cladding medium growth schematic diagram;

(d) is a SiN medium growth schematic diagram;

(e) is a schematic end view of a double-layer SiN sub-wavelength grating;

(f) is SiO₂Schematic end face of inverted cone thick ridge waveguide;

(g) a schematic view of an end face of the fiber-securing groove.

Detailed Description

The invention is described in further detail below with reference to the drawings and the detailed description.

FIG. 1 is a schematic structural diagram of an LNOI spot-size converter of the present invention, which includes a top tapered waveguide 1, a bottom tapered waveguide 2, a tapered sub-wavelength grating 3, and SiO₂Upper cladding 4, SiO₂Inverted cone-shaped thick ridge waveguide cladding 5, SiN sub-wavelength grating 6, optical fiber fixing groove 7 and SiO₂An insulating layer 8 and a chip substrate 9. The fiber holding groove 7 is used for holding an external optical fiber, and the optical fiber can be held in the fiber holding groove 7 and aligned with the end face of the spot-size converter using a fiber-curing agent, as shown in FIG. 2, SiO₂Upper cladding layer 4 and SiO₂The inverted cone-shaped thick ridge waveguide cladding 5 adopts the transition design of the thick ridge waveguide and the tapered waveguide, and the transmission loss of an optical field is reduced. SiN sub-wavelength grating 6 embedded in SiO₂In the inverted cone-shaped thick ridge waveguide cladding 5, which is positioned above the top layer conical waveguide 1 and the bottom layer conical waveguide 2, the SiN sub-wavelength grating 6 is used for realizing the transition gradual change (n) of the effective refractive index of the cladding_SiO2<n_SWG<n_SiN) The SiN sub-wavelength grating 6 is in conical transition with SiO₂The inverted tapered thick ridge waveguide cladding 5 is uniform in shape. The tapered waveguide sub-wavelength grating 3 is connected with the tail end of the bottom tapered waveguide 2 of the wide flat plate and is not overlapped with the top tapered waveguide 1, and the tapered waveguide sub-wavelength grating 3 is used for reducing the effective refractive index of the bottom waveguide 2 and amplifying the size of a mode spot. As shown in FIG. 4, the LNOI spot-size converter of the present invention mainly uses a double-layer tapered waveguide in combination with a tapered sub-wavelength grating, an SiN sub-wavelength grating and SiO₂The structure of the inverted cone-shaped thick ridge waveguide is realized by adjusting the core layer of the waveguideAnd the effective refractive index of the cladding layer amplifies a small-sized optical mode field in the LNOI optical waveguide, is used for enhancing mode limitation, reducing optical transmission loss, improving the coupling efficiency of the LNOI optical waveguide and a single-mode fiber, and simultaneously meets the requirements of low insertion loss, high coupling and small size of an LNOI optical chip.

The detailed parameters are as follows:

the LNOI double-layer tapered waveguide of the present invention: the waveguide width of the top layer tapered waveguide 1 is 700 nm-2 μm, the waveguide height is 200 nm-400 nm, the coupling transition region length is 50 μm-200 μm, and the tapered waveguide end width is 30 nm-200 nm; the waveguide width of the bottom layer tapered waveguide 2 is 4-8 μm, the waveguide width is 200-400 nm, the coupling transition region length is 50-300 μm, and the tapered waveguide end width is 30-200 nm; the transition region of the LNOI top-layer tapered waveguide 1 and the LNOI bottom-layer tapered waveguide 2 is in the shape of a line, a parabola, a square root, an exponential, a staircase and the like, as shown in fig. 3.

The period of the conical sub-wavelength grating 3 is 500 nm-1000 nm, the duty ratio is 0.3-0.7, the width of a waveguide at the tail end of the sub-wavelength grating is 50 nm-200 nm, the period number of the grating is 10-100, and the length of a conical transition region is 30 mu m-150 mu m; the transition region of the tapered sub-wavelength grating 3 is in a shape of a line, a parabola, a square root, an exponential, a staircase and the like, as shown in fig. 3.

SiO₂The upper cladding 4 is a rectangular waveguide with a waveguide width of 6-10 μm, a waveguide length of 200-400 μm, and a waveguide thickness of 1-2 μm.

SiO₂The narrow waveguide end of the inverted cone-shaped thick ridge waveguide 5 covers the transition region of the top layer conical waveguide 1, the waveguide width is 3-5 μm, the wide waveguide end is the optical fiber access end face of the spot size converter, the waveguide width is 6-15 μm, and the waveguide thickness is 2-8 μm.

SiN sub-wavelength grating 6 embedded in SiO₂In the inverted cone-shaped thick ridge waveguide 5, the part of 500 nm-1 mu m above the conical waveguide sub-wavelength grating 3 is covered, the period of the SiN sub-wavelength grating 6 is 500 nm-2 mu m, the duty ratio is 0.3-0.7, the grating period number is 10-100, the waveguide thickness is 20 nm-80 nm, the width of the optical fiber coupling end face waveguide is 4 mu m-8 mu m, and the width of the tail end of the SiN sub-wavelength grating 6 is1-2 μm, the length of the taper transition region is 50-400 μm, the SiN sub-wavelength grating 6 is a single-layer or double-layer or three-layer structure, as shown in FIG. 5, the interval between each layer of the SiN sub-wavelength grating 6 is 500 nm-1.5 μm.

The optical fiber fixing groove 7 is arranged on the optical fiber end face of the spot size converter and is etched to remove the corresponding SiO₂Upper cladding layer 4 and SiO₂And the insulating layer 8 is etched or etched on the chip substrate 9 to form a V-shaped groove or a groove and the like.

Fig. 6 shows the process steps of the method for manufacturing the LNOI spot-size converter according to the present invention, which includes the following steps:

step s1, etching mask preparation of the top-layer tapered waveguide 1. The waveguide etching mask comprises photoresist and a metal mask, wherein the photoresist comprises HSQ negative photoresist, ZEP 520A positive photoresist and 7908 positive photoresist, and the metal mask is made of Ni or Ti/Ni or Cr/Ni.

Step s2, the top tapered waveguide 1 is etched. The waveguide etching adopts dry etching process, adopts reactive ion etching or inductively coupled plasma etching, and uses Ar or SF as etching gas₆Mixed gas of/Ar.

And step s3, preparing the bottom layer tapered waveguide 2 and the tapered sub-wavelength grating 3 by etching masks.

Step s4, the bottom tapered waveguide 2 and the tapered sub-wavelength grating 3 are etched.

Step s5, SiO₂And (3) medium growth: SiO growth by PECVD₂，SiO₂The thickness is 1-2 μm.

Step s6, SiN dielectric growth: SiN is grown by PECVD, and the thickness of the SiN is 20 nm-80 nm.

Step s7, preparing an etching mask of the SiN sub-wavelength grating 6: the SiN etch mask uses photoresists that include 7908 positive photoresist, 701 positive photoresist, and UV 135 positive photoresist.

Step s8, etching the SiN sub-wavelength grating 6: the SiN medium etching adopts dry etching process, and etching gas adopts SF₆Or CHF₃Or SF₆/Ar, or CHF₃and/Ar and the like.

Step s9, SiO₂Preparing the inverted conical thick ridge waveguide 5: SiO 2₂The etching mask is made of photoresist and is made of silicon nitride,comprises 7908 positive photoresist, 701 positive photoresist and UV 135 positive photoresist, and adopts spin coating double-layer or three-layer technique to increase photoresist thickness for thick SiO₂And (5) waveguide etching. SiO 2₂The etching adopts a dry etching process, and etching gas adopts SF₆Or CHF₃Or SF₆/Ar, or CHF₃and/Ar and the like.

Step s10, SiO₂Preparing an upper cladding 4 rectangular waveguide: SiO 2₂The etching process is the same as step s 9.

Step s11, fiber fixation groove 7 preparation: when the substrate is silicon, preparing the optical fiber fixing groove 7 by adopting a wet etching silicon process, wherein an etching solution comprises KOH and TMAH solutions; when the substrate is lithium niobate, the optical fiber fixing groove 7 is prepared by adopting a dry etching process, and the etching gas is SF₆Or SF₆Mixed gas of/Ar.

Example one

Selecting a 3-inch x-cut LNOI wafer, wherein the thickness of the lithium niobate film is 600nm and SiO is₂The thickness of the insulating layer is 2 μm, the substrate is made of Si material, and the preparation process comprises the following steps:

A1) preparing an etching mask of the top-layer tapered waveguide 1: spin coating negative photoresist HSQ at 2000rpm/min, and baking at 150 deg.C on a hot plate for 120 s.

A2) Etching the top layer tapered waveguide 1: and performing ICP etching by using Ar plasma, wherein the waveguide etching depth is 300 nm.

A3) Preparing an etching mask of the bottom layer conical waveguide 2 and the conical sub-wavelength grating 3: spin coating negative photoresist HSQ at 2000rpm/min, and baking at 150 deg.C on a hot plate for 120 s.

A4) Etching the bottom-layer tapered waveguide 2 and the tapered sub-wavelength grating 3: and performing dry etching by adopting Ar plasma ICP, wherein the waveguide etching depth is 300 nm.

A5) First SiO₂Growing the medium of the cladding 51: PECVD (plasma enhanced chemical vapor deposition) growth of SiO₂And the thickness of the cladding medium is 1 mu m.

A6) Growing a first layer of SiN sub-wavelength grating 61 medium: SiN was grown by PECVD to a thickness of 20 nm.

A7) Preparation of the first layer of SiN sub-wavelength grating 61: spin-coating photoresist 7908 at 3000rpm/min, baking at 110 deg.C for 110 s, exposing and developing, and adopting ICP dry etching with CHF as etching gas₃Etching power is 100W, etching depth is 20nm, and removing the photoresist by using acetone after etching.

A8) Second SiO₂Growth of medium of the cladding 52: PECVD (plasma enhanced chemical vapor deposition) growth of SiO₂And the thickness of the cladding medium is 2 mu m.

A9)SiO₂Preparing the inverted conical thick ridge waveguide 5: spin-coating the photoresist 701 at 1500rpm/min and baking at 110 deg.C on a hot plate for 110 seconds. Performing ICP dry etching after exposure and development, wherein the etching gas is CHF₃The etching power is 200W, the etching depth is about 2.5 mu m, and the etching material comprises second SiO₂Cladding 52, first layer of SiN sub-wavelength grating 61, and first SiO₂Cladding 51, remaining SiO₂About 0.5 μm is SiO₂And (4) etching the upper cladding layer, and removing the residual photoresist by using acetone.

A10)SiO₂Preparing an upper cladding 4 rectangular waveguide: spin-coating the photoresist 701 at 1500rpm/min and baking at 110 deg.C on a hot plate for 110 seconds. Performing ICP dry etching after exposure and development, wherein the etching gas is CHF₃The etching power is 200W, the etching depth is about 0.5 mu m, and the etching material is residual SiO₂(about 0.5 μm) and removing the remaining photoresist with acetone after etching.

A11) Preparing an optical fiber fixing groove 7: spin-coating photoresist 7908 at 3000rpm/min, baking on a hot plate at 110 deg.C for 110 s, exposing and developing, and etching the silicon substrate with 5% TMAH solution diluted by volume in 85 deg.C water bath for about 1 hr.

Example two

Selecting a 3-inch x-cut LNOI wafer, wherein the thickness of the lithium niobate film is 600nm and SiO is₂The thickness of the insulating layer is 2 μm, the substrate is made of Si material, and the main preparation process comprises the following steps:

B1) preparing an etching mask of the top-layer tapered waveguide 1: spin-coating the photoresist 7908, evaporating metal Ti/Ni20/150nm after exposure and development, soaking the photoresist in acetone, ultrasonically removing the photoresist, ultrasonically treating the photoresist in ethanol for 5 minutes, washing the photoresist clean by deionized water, and finally spin-drying the photoresist in a spin dryer.

B2) Etching the top layer tapered waveguide 1: and performing ICP etching by using Ar plasma, wherein the waveguide etching depth is 300 nm.

B3) Preparing an etching mask of the bottom layer conical waveguide 2 and the sub-wavelength grating 3: spin-coating a photoresist 7908, evaporating metal Ti/Ni20/150nm after exposure and development, soaking the photoresist in acetone, ultrasonically removing the photoresist, ultrasonically treating the photoresist in ethanol for 5 minutes, washing the photoresist clean by deionized water, and finally spin-drying the photoresist in a spin dryer.

B4) Etching the bottom layer conical waveguide 2 and the sub-wavelength grating 3: and adopting Ar plasma ICP etching, wherein the waveguide etching depth is 300 nm.

B5) First SiO₂Growing the medium of the cladding 51: PECVD (plasma enhanced chemical vapor deposition) growth of SiO₂The thickness was 1 μm.

B6) Growing a first layer of SiN sub-wavelength grating 61 medium: SiN was grown by PECVD to a thickness of 20 nm.

B7) Preparation of the first layer of SiN sub-wavelength grating 61: spin-coating photoresist 7908 at 2500rpm/min, baking on a hot plate at 110 deg.C for 110 s, exposing and developing, and dry etching with ICP (inductively coupled plasma) with CHF (CHF) as etching gas₃Etching power is 150W, etching depth is 20nm, and removing the photoresist by using acetone after etching.

B8) Second SiO₂Growth of medium of the cladding 52: PECVD (plasma enhanced chemical vapor deposition) growth of SiO₂The thickness was 2 μm.

B9) And medium growth of a second layer of SiN sub-wavelength grating 62: SiN was grown by PECVD to a thickness of 20 nm.

B10) Preparation of the second layer of SiN sub-wavelength grating 62: spin-coating photoresist 7908 at 3000rpm/min, baking on a hot plate at 110 deg.C for 110 s, exposing, developing, and dry etching with ICP (inductively coupled plasma) with CHF (CHF) as etching gas₃Etching power is 150W, SiN etching depth is 20nm, and after etching, removing the photoresist by using acetone.

B11) Third SiO₂Growing the medium of the cladding 53: PECVD (plasma enhanced chemical vapor deposition) growth of SiO₂The thickness was 2 μm.

B12)SiO₂Preparing the inverted conical thick ridge waveguide 5: spin-coating a bilayer photoresist 701 at 1500rpm/min, and baking on a hot plate at 110 ℃ for 110 seconds. Performing ICP dry etching after exposure and development, wherein the etching gas is CHF₃The etching power is 200W, the etching depth is about 4.5 mu m, and the etching material comprises third SiO₂Cladding 53, firstTwo-layer SiN sub-wavelength grating 62 and second SiO₂Cladding 52, first layer of SiN sub-wavelength grating 61, and first SiO₂Cladding 51, remaining SiO₂About 0.5 μm is SiO₂And (4) etching the upper cladding layer, and removing the residual photoresist by using acetone.

B13)SiO₂Preparing an upper cladding 4 rectangular waveguide: spin-coating the photoresist 701 at 1500rpm/min and baking at 110 deg.C on a hot plate for 110 seconds. Performing ICP dry etching after exposure and development, wherein the etching gas is CHF₃The etching power is 200W, the etching depth is about 0.5 mu m, and the etching material is residual SiO₂About 0.5 μm, and removing the remaining photoresist with acetone after etching.

B14) Preparing an optical fiber fixing groove 7: spin-coating photoresist 7908 at 3000rpm/min, baking on a hot plate at 110 deg.C for 110 s, exposing and developing, and etching the silicon substrate with 5% TMAH solution diluted by volume in 85 deg.C water bath for about 1 hr.