CN114355507B - Micro-ring resonator based on inverted ridge type silicon dioxide/polymer mixed waveguide and preparation method thereof - Google Patents

Abstract

A microring resonator based on an inverted ridge silica/polymer hybrid waveguide and a preparation method thereof, which belongs to the technical field of integrated chip preparation of an inverted ridge silica/polymer hybrid waveguide. From bottom to top, it is composed of Si substrate, SiO ₂ lower cladding layer, strip polymer core layer and polymer flat layer; the strip polymer core layer is composed of a micro-ring resonance part and a coupling part; the micro-ring resonance part is composed of the first The curved waveguide, the first straight waveguide, the second curved waveguide and the second straight waveguide are connected in sequence, which is a racetrack micro-ring structure; the coupling part is composed of the input straight waveguide, the third straight waveguide and the output straight waveguide being connected in sequence. The second straight waveguide and the third straight waveguide constitute a directional coupler. The microring resonator of the present invention has the advantages of low loss, compact structure, simple preparation process, and low cost. It can be used to prepare switches, filters, and modulators in optical networks, and can realize temperature, refractive index, biological Sensing and other sensing functions.

Description

Microring resonator based on inverted ridge silica/polymer hybrid waveguide and its fabrication Preparation method

Technical field

The invention belongs to the technical field of preparing integrated chips of inverted ridge silica/polymer hybrid waveguides, and specifically relates to a microring resonator based on inverted ridge silica/polymer hybrid waveguides and a preparation method thereof.

Background technique

In order to meet the demand for information transmission capacity in people's daily lives, communication methods using light as a medium play an increasingly important role in communication systems. In the research of planar lightwave circuit (PLC) devices, according to different core layer materials, they are mainly divided into three categories: silica-based PLC, indium phosphide PLC and polymer PLC. Among them, polymer PLC has more advantages. The advantages of large thermo-optical coefficient (-1.86×10 ^-4 K ^-1 ), simple preparation process, and extremely low cost are widely used in flat optical waveguide devices, especially variable optical attenuators, optical switches, and tunable Filters and other active planar optical waveguide devices.

Usually, the process for preparing polymer PLC is to form a core layer by wet etching after contact exposure, and then spin-coat the polymer cladding. Through the process of heating, solidification and annealing, the core layer and cladding are in close contact to prepare a waveguide device. . However, the same solvent exists in the polymer core layer and cladding layer, which will cause the core layer and cladding layer to dissolve into each other during the heating and curing process, so that the end side walls are not steep, the core layer becomes rounded, and light spots are introduced. Changes in the mode may cause additional losses at best, or cause device function failure at worst.

Contents of the invention

In order to solve the problems in the background technology, the present invention proposes a microring resonator based on an inverted ridge silica/polymer hybrid waveguide and a preparation method thereof. In the present invention, a groove is first etched in the silicon dioxide lower cladding layer by inductively coupled plasma (ICP) etching, and then a polymer is spin-coated on the groove and the silicon dioxide lower cladding layer. , forming an inverted ridge silica/polymer hybrid waveguide structure. Since the groove structure is made of silica material, it will not react with the core polymer, so the side walls of the core waveguide formed are steep and smooth, forming Device losses are also reduced.

The microring resonator based on the inverted ridge silicon dioxide/polymer hybrid waveguide of the present invention consists from bottom to top of Si substrate (1), SiO ₂ lower cladding layer (2), strip polymer core layer ( 3) and a polymer flat layer (4); the strip polymer core layer (3) is covered in the SiO ₂ lower cladding layer (2), and the upper surface of the polymer core layer (3) is in contact with the SiO ₂ lower cladding layer. The upper surface of the cladding (2) is located on the same plane; the strip polymer core layer (3) is composed of a microring resonance part (100) and a coupling part; wherein the microring resonance part (100) is composed of the first curved waveguide (101 ), the first straight waveguide (102), the second curved waveguide (103) and the second straight waveguide (104) are connected in sequence, forming a racetrack-type micro-ring structure; the coupling part consists of the input straight waveguide (201), the third straight waveguide (104) and the second straight waveguide (104). The waveguide (202) and the output straight waveguide (203) are connected in sequence, and the second straight waveguide (104) and the third straight waveguide (202) form a directional coupler (200); the input end of the second curved waveguide (103) is connected to The output end of the second straight waveguide (104) is connected, the output end of the second curved waveguide (103) is connected with the input end of the first straight waveguide (102), and the output end of the first straight waveguide (102) is connected with the first curved waveguide (102). 101), the output end of the first curved waveguide (101) is connected to the input end of the second straight waveguide (104); the optical signal output by the wide-spectrum light source is coupled into the input straight waveguide (201), and passes through the directional coupler (200 ) is divided into two beams of light, one part of the light is coupled into the second straight waveguide (104) and then enters the microring resonant part (100), and the other part of the light is output from the output straight waveguide (203); it is coupled into the microring resonant part ( 100) of light, in which the light of a wavelength that satisfies the microring resonance condition (the light whose phase changes for one cycle is an integral multiple of 2π when transmitted in the microring resonance part (100)) will be transmitted in the ring and will no longer pass through the directional coupler ( 200) is coupled into the third straight waveguide (202); light with wavelengths that do not meet the microring resonance conditions will be coupled into the third straight waveguide (202) through the directional coupler (200), and the light intensities of the same wavelength are linearly superimposed. Output from the output straight waveguide (203).

The polymer core layer and the polymer flat layer are made of the same material, which is a polymer material with a negative thermo-optical coefficient, including SU-8 2002, SU-8 2005, EpoCore, etc.

The preparation method of the microring resonator based on the inverted ridge silica/polymer hybrid waveguide according to the present invention has the following steps:

1) On the silicon wafer substrate, grow a dense 12-18 μm thick silicon dioxide lower cladding layer through thermal oxidation method;

2) Use a vacuum leveling machine to spin-coat the photoresist layer on the silica lower cladding, and then cool down and solidify naturally after pre-baking;

3) Through UV lithography, development, and post-baking, the structure of the strip-shaped polymer core waveguide to be prepared on the mask plate is the same (the photoresist layer is positive photoresist) or complementary (the photoresist layer is negative) (Plastic photoresist) pattern is transferred to the photoresist layer to form a photoresist layer waveguide structure for masking;

4) Through the ICP etching method, under the mask of the photoresist layer waveguide structure, a groove for filling the polymer core layer material is prepared on the silicon dioxide lower cladding, and then the silicon dioxide lower cladding is removed. photoresist layer on the layer;

5) Use a vacuum leveling machine to spin-coat the polymer core layer and flat layer on the silica lower cladding, and then go through pre-baking, ultraviolet photolithography, and post-baking to prepare the inverted ridge silica of the present invention. /Polymer hybrid waveguide microring resonator; the size of the polymer core layer is consistent with the size of the silicon dioxide groove, with a width of 2 to 5 μm and a thickness of 2 to 5 μm; the thickness of the polymer flat plate layer is determined by adjusting the polymer material and spin coating speed. Depending on the application field of the device, a thickness of 0~5μm can be achieved.

Compared with the existing technology, the innovations of the present invention are:

1. The waveguide is an inverted ridge silica/polymer hybrid waveguide. By filling the silica grooves, the side walls of the polymer core layer obtained are steep, which reduces device loss;

2. The waveguide is an inverted ridge silica/polymer hybrid waveguide. The polymer material is used as the waveguide core layer. The core-clad refractive index difference is large, which can achieve a more compact end face size and bending radius, which is conducive to the preparation of large-scale flat optical waveguides. integrated circuit;

3. The waveguide is an inverted ridge silicon dioxide/polymer hybrid waveguide. The device can be prepared through simple contact exposure, and the required processing cost is extremely low;

4. The device structure adopts a runway-type micro-ring structure, which is compact in structure, has a large extinction ratio, and is easy to be integrated on a large scale.

In summary, the inverted ridge silica/polymer hybrid waveguide microring resonator proposed by the present invention has the advantages of low loss, compact structure, simple preparation process, low cost, etc., and plays an important role in optical domain optimization and optimization in optical networks. It has functions such as routing, protection and power equalization. In the field of sensing, it can also realize multi-functional sensing functions such as temperature, refractive index, and biological sensing, and has broad application prospects.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1: Schematic cross-sectional view of the inverted ridge microring resonator according to the present invention;

Figure 2: Schematic structural diagram of the inverted ridge microring resonator according to the present invention;

Figure 3: Flow chart of the preparation process of the inverted ridge micro-ring resonator according to the present invention;

Figure 4: Schematic cross-section of the silicon dioxide groove of the inverted ridge microring resonator according to the present invention;

Figure 5: A schematic cross-sectional view of the inverted ridge microring resonator after polymer filling according to the present invention;

Figure 6: Schematic diagram of the near-field light spot of the inverted ridge microring resonator according to the present invention;

Figure 7: Normalized transmission power spectrum of the inverted ridge microring resonator of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on this The embodiments in the invention and all other embodiments obtained by those of ordinary skill in the art without exerting creative efforts belong to the protection scope of the invention.

Example 1:

As shown in Figure 1, it is a schematic cross-sectional view of an inverted ridge microring resonator. From bottom to top, it consists of Si substrate (1), SiO ₂ lower cladding layer (2), polymer core layer (3), and polymer flat plate. Composed of layer (4). The SiO ₂ lower cladding layer (2) can be grown using a thermal oxidation method or a (Plasma Enhanced Chemical Vapor Deposition, PECVD) deposition method. In this embodiment, thermal oxidation is used to grow SiO ₂ with a refractive index of 1.4456. The polymer core layer (3) and the polymer flat layer (4) are made of the same material, and polymer materials with negative thermo-optical coefficients can be used, including SU-8 2002, SU-8 2005, EpoCore, etc., in In this embodiment, SU-8 2002 material is used as the material of the polymer core layer (3), with a refractive index of 1.573. In order to reduce mode crosstalk and polarization-related losses within the waveguide and reduce process difficulty, the size of the waveguide in the polymer core layer (3) is designed to be a square waveguide of 2.5 μm × 2.5 μm. The thickness of the polymer flat layer (4) is 2 μm.

As shown in Figure 2, it is a schematic structural diagram of an inverted ridge microring resonator. The microring resonant part (100) is composed of a first curved waveguide (101), a first straight waveguide (102), a second curved waveguide (103) and a second straight waveguide (104); in order to prepare a compact microring device, the The bending radius of the first curved waveguide (101) and the second curved waveguide (103) is 1400 μm. The first curved waveguide (101) and the second curved waveguide (103) are semicircular structures; the coupling part is composed of the input straight waveguide (201) , a third straight waveguide (202) and an output straight waveguide (203), where the directional coupler (200) is composed of a second straight waveguide (104) and a third straight waveguide (202); in order to prepare a compact microring device, Considering process reasons, the gap (Gap) between the second straight waveguide (104) and the third straight waveguide (202) is 1.5 μm; in order to achieve a high extinction ratio device, after calculation, the directional coupler length is determined to be 1400 μm. That is, the lengths of the first straight waveguide (102), the second straight waveguide (104) and the third straight waveguide (202) are all 1400 μm. The input end of the second curved waveguide (103) is connected to the output end of the second straight waveguide (104), the output end of the second curved waveguide (103) is connected to the input end of the first straight waveguide (102), and the first straight waveguide (102) The output end of 102) is connected to the input end of the first curved waveguide (101), and the output end of the first curved waveguide (101) is connected to the input end of the second straight waveguide (104); the optical signal output by the wide-spectrum light source is coupled into the input straight waveguide. The waveguide (201) is divided into two beams of light through the coupling effect of the directional coupler (200). One part is coupled into the second straight waveguide (104) and thus enters the microring resonance part (100), and the other part is output from the straight waveguide (203) Direct output. The light coupled into the microring resonance part (100), the light with a wavelength that satisfies the microring resonance condition, that is, the light whose phase changes in one cycle of the microring resonance part (100) to an integer multiple of 2π, will be transmitted in the ring, If it is no longer coupled into the third straight waveguide (202) through the directional coupler (200) and output from the output straight waveguide (203), and does not meet the microring resonance conditions, it will be coupled into the third straight waveguide (202) through the directional coupler (200) again. Waveguide (202), the light intensity of the same wavelength is linearly superimposed and output from the output straight waveguide (203).

As shown in Figure 3, the process flow chart for preparing the inverted ridge microring resonator of the present invention has the following steps:

1) On the silicon wafer substrate (1), grow a dense 15 μm thick silicon dioxide lower cladding layer (21) through thermal oxidation method;

2) Use a vacuum leveling machine to spin-coat Micro Chem's SU-8 2002 photoresist on the surface of the silicon dioxide lower cladding (21). First, it needs to be baked at 60°C for 10 minutes and 90°C for 20 minutes. Natural cooling and solidification, by controlling the rotation speed to 600 rpm and the spin coating time to 20 seconds, a 3 μm thick SU-8 photoresist layer is formed (51);

3) Place the device in step 2) under a 365nm ultraviolet lithography machine with a light power of 23mW/cm ² and perform photolithography. The structure of the mask I used is consistent with the strip-shaped polymer core waveguide to be prepared ( 3) The structure is complementary, the exposure time is 3.5s, and then post-baked at 65°C for 10 minutes and 95°C for 20 minutes, cooled to room temperature, put into PGMEA (Propyleneglygol-monomethylether-acetate) developer for development, and then placed in Rinse in isopropyl alcohol to remove residual glue, and wash the reaction solution with deionized water; then harden the film at 120°C for 30 minutes to form an SU-8 photoresist layer (52), which is used as a mask for etching;

4) Using the ICP etching method, prepare a silicon dioxide groove on the silicon dioxide lower cladding layer (21) under the mask of the SU-8 photoresist layer (52), with a depth of 2.5 μm and a width of 2.5 μm. ;In order to ensure that the side walls of the waveguide are steep, the gas passed through the ICP is C ₄ F ₈ /SF ₈ mixed gas, and then the SU-8 photoresist layer (52) on the silicon dioxide lower cladding layer (2) is removed; The cross-sectional view of the silicon dioxide groove of the inverted ridge microring resonator is shown in Figure 4;

5) Use a vacuum leveling machine to spin-coat Micro Chem's SU-8 2002 photoresist on the surface of the silica lower cladding (2). First, it needs to be baked at 60°C for 10 minutes and 90°C for 20 minutes. Natural cooling and solidification, by controlling the rotation speed to 3000 rpm and spin coating time for 20 seconds, fill the silica grooves to form the polymer core layer (3). Since SU-8 has a self-leveling type, a 2 μm thick flat layer will be formed. SU-8 polymer flat layer (4); place the device under a 365nm UV lithography machine with a light power of 23mW/cm ² and an exposure time of 5s, followed by 10 minutes at 65°C and 20 minutes at 95°C. After several minutes of post-baking and cooling to room temperature, the formed inverted ridge micro-ring resonator has a cross-sectional view after polymer filling, as shown in Figure 5;

As shown in Figure 6, it is a schematic diagram of the near-field light spot of the inverted ridge microring resonator of the present invention. Light with a wavelength of 1550 nm is coupled into the waveguide, and a round light spot can be observed by the near-field infrared CCD.

As shown in Figure 7, it is the normalized transmission power spectrum diagram of the inverted ridge microring resonator of the present invention. The circles are the measured values. Through Lorentz fitting, the fitting curve is obtained. The fitting effect is good, and we get The half-wave width is 74pm, and the current resonance peak center wavelength is 1500.154 nm. The calculated Q value of the current resonance front is the ratio of the resonance peak center wavelength to the half-wave width, which is 20272, indicating that the device of the present invention has a high Q value.

Claims (3)

1. A micro-ring resonator based on a hybrid inverted-ridge silica and polymer waveguide, characterized in that: from bottom to top, from Si substrate (1), siO ₂ The strip-shaped polymer core layer (3) consists of a lower cladding layer (2) and a polymer panel layer (4); the strip-shaped polymer core layer (3) is coated on SiO ₂ The upper surface of the polymer core layer (3) and SiO in the lower cladding layer (2) ₂ The upper surfaces of the lower cladding layers (2) are positioned on the same plane; the strip-shaped polymer core layer (3) consists of a micro-ring resonance part (100) and a coupling part; the micro-ring resonance part (100) is formed by sequentially connecting a first bending waveguide (101), a first straight waveguide (102), a second bending waveguide (103) and a second straight waveguide (104), and is of a runway type micro-ring structure; the coupling part is formed by sequentially connecting an input straight waveguide (201), a third straight waveguide (202) and an output straight waveguide (203), and the second straight waveguide (104) and the third straight waveguide (202) form a directional coupler (200); the optical signal output by the wide-spectrum light source is coupled into an input straight waveguide (201), is divided into two beams of light through the coupling action of a directional coupler (200), one part of the light is optically coupled into a second straight waveguide (104) so as to enter a micro-ring resonance part (100), and the other part of the light is output from an output straight waveguide (203); light coupled into the micro-ring resonating section (100), wherein light of a wavelength satisfying the micro-ring resonating condition, i.e., light transmitted in the micro-ring resonating section (100) for one revolution with a phase change of an integer multiple of 2 pi, will be transmitted in the ring and no longer coupled into the third straight waveguide (202) by the directional coupler (200); light with a wavelength which does not meet the micro-ring resonance condition is coupled into a third straight waveguide (202) through a directional coupler (200), and light rays with the same wavelength are outputted from an output straight waveguide (203) after being overlapped;

wherein SiO is ₂ The thickness of the lower cladding layer (2) is 12-18 mu m; the width of the strip-shaped polymer core layer (3) is 2-5 mu m, and the thickness is 2-5 mu m; the thickness of the polymer plate layer is more than 0 mu m and less than or equal to 5 mu m; the strip-shaped polymer core layer (3) and the polymer flat layer (4) are made of the same material and are polymer materials with negative thermo-optic coefficientsMaterials SU-8 2002, SU-8 2005 or EpoCore.

2. A micro-ring resonator based on a hybrid inverted-ridge silica and polymer waveguide as defined in claim 1, wherein: siO (SiO) ₂ The thickness of the lower cladding layer (2) is 15 mu m; the width of the strip-shaped polymer core layer (3) is 2.5 mu m, and the thickness is 2.5 mu m; the thickness of the polymer plate layer is 2 μm; the bending radius of the first bending waveguide (101) and the second bending waveguide (103) is 1400 mu m, and the first bending waveguide (101) and the second bending waveguide (103) are in a semicircular structure; the spacing between the second straight waveguide (104) and the third straight waveguide (202) is 1.5 μm; the directional coupler has a length of 1400 μm, i.e. the first straight waveguide (102), the second straight waveguide (104) and the third straight waveguide (202) are each 1400 μm in length.

3. A method of manufacturing a micro-ring resonator based on a hybrid inverted-ridge silica and polymer waveguide as claimed in claim 1 or 2, comprising the steps of:

1) Growing a layer of compact silicon dioxide lower cladding layer on a silicon wafer substrate by a thermal oxidation method;

2) Spin coating a photoresist layer on the silicon dioxide lower cladding layer by using a vacuum spin coater, and naturally cooling and solidifying after pre-baking treatment;

3) Transferring the patterns which are the same as or complementary to the strip polymer core layer waveguide structure to be prepared on the mask plate to the photoresist layer through ultraviolet lithography, development and post-baking to form the photoresist layer waveguide structure for the mask;

4) Preparing a groove for filling a polymer core layer on the silicon dioxide lower cladding layer under a mask of the photoresist layer waveguide structure by an ICP etching method, and then removing the photoresist layer on the silicon dioxide lower cladding layer;

5) And spin-coating a polymer core layer and a polymer slab layer on the silicon dioxide lower cladding layer by using a vacuum spin coater, and then performing pre-baking, ultraviolet lithography and post-baking to prepare the micro-ring resonator based on the inverted-ridge silicon dioxide and polymer mixed waveguide.