A 1×3 thermo-optic switch based on silica / polymer hybrid waveguides and its manufacturing method

Abstract

A 1×3 thermo-optic switch based on a silica / polymer hybrid waveguide and a preparation method thereof belong to the technical field of the preparation of silica / polymer hybrid waveguide optical integration chips. It is composed of an Si substrate, an SiO2 lower cladding layer, a polymer core layer, a polymer upper cladding layer and metal electrodes, and the polymer core layer is coated in the polymer upper cladding layer. Along the light transmission direction, the polymer core layer mainly consists of an input straight waveguide, a 1×3 multimode interferometer, a phase shifter, first to third modulation arm waveguides, a 3×3 multimode interferometer, and first to third output straight waveguides; the first to third modulation arm waveguides are parallel to each other, and first to third metal electrodes parallel to each other are arranged on the first to third modulation arm waveguides. When a modulation voltage is applied to any one of the first to third metal electrodes, the signal light is output from any one of the first to third output straight waveguides, thereby realizing the switching function of three channels through the modulation of the metal electrodes.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing silica / polymer hybrid waveguide optical integrated chips, and particularly relates to a 1×3 thermo-optic switch based on silica / polymer hybrid waveguides and a preparation method thereof. Background Art

[0002] Optical switches are important devices in optical switching networks. With the rapid growth of the demand for information volume in the information society, the number of interactive ports for optical switching has increased rapidly, resulting in a substantial increase in the number of switches in optical cross-connects. Currently, there is a limit to the cooling systems used in optical networks. To increase the scale of optical cross-connects, lower-power optical switches are required. Commercially available silica planar waveguide (Plannar Lightwave Circuit, PLC) devices currently on the market have advantages such as low loss, good stability, and high coupling efficiency. However, due to the low thermo-optic coefficient of silica materials (1.19×10 -5 K -1 ), when preparing active devices, relatively high power consumption is often required, often dozens of milliwatts. At the same time, since silica waveguides are prepared by doping to form the core layer, the refractive index difference between the core and the cladding is relatively small, about Δn = 0.75%, resulting in relatively large device sizes and difficulty in achieving large-scale integration. Polymer materials have a thermo-optic coefficient that is an order of magnitude higher than that of silica (-1.86×10 -4 K -1 ), and are suitable for fabricating active photonic chips such as thermo-optic switches and tunable filters. At the same time, polymers used as the core layer often have a higher refractive index. With silica as the lower cladding, the refractive index difference can reach Δn = 2.5% - 10%, making the device size and bending radius much smaller than those of silica-based planar optical waveguide devices, and facilitating the preparation of large-scale photonic integrated devices. And this structure can achieve mutual switching of three ports, having a higher integration degree compared to 1×2 switches.

[0003] In currently commonly used optical switches, the mainstream 1×2 and 2×2 low-port switching systems can only achieve switching between two ports, with low integration degree and low chip utilization rate. Therefore, it is necessary to develop a new device structure to improve the integration degree of the device without increasing the chip size and process difficulty. Summary of the Invention

[0004] To solve the problems described in the background art, the present invention proposes a 1×3 thermo-optic switch based on silica / polymer hybrid waveguides and a preparation method thereof.

[0005] Such as Figure 1 And Figure 4As shown in the figure, a 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide according to the present invention is composed of an Si substrate (1), an SiO2 lower cladding (2), a polymer core layer (3), a polymer upper cladding (4), and a metal electrode (5) from bottom to top; the polymer core layer (3) and the polymer upper cladding (4) are located above the SiO2 lower cladding (2), and the polymer core layer (3) is coated in the polymer upper cladding (4); along the light transmission direction, the polymer core layer (3) is composed of an input straight waveguide (101), a 1×3 multimode interferometer (300), a first input S-bending waveguide (102), a second input S-bending waveguide (102’), an intermediate input straight waveguide (103), a first phase shifter (104), a second phase shifter (104’), a first modulation arm waveguide (105), a second modulation arm waveguide (106), a third modulation arm waveguide (107), a first output S-bending waveguide (108), a second output S-bending waveguide (108’), an intermediate output straight waveguide (109), a 3×3 multimode interferometer (400), a first output straight waveguide (110), a second output straight waveguide (111), and a third output straight waveguide (112); wherein, the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107) are parallel to each other, and above the polymer upper cladding (4) at the positions of the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107), there are parallel first metal electrode (201), second metal electrode (202), and third metal electrode (203), which together constitute the metal electrode (5).

[0006] According to whether the interference is general, the self-imaging law of the multimode interferometer can be divided into two categories: general interference and restricted interference. Among them, general interference means that all modes in the multimode waveguide are excited, that is, there is no restriction on the excited modes; restricted interference means that some modes in the multimode waveguide are not excited, and thus some other self-imaging laws are obtained. In this sense, restricted interference is only a special type of general interference. And according to the different modes of restricted excitation, restricted interference can be further divided into two categories, namely: paired interference and symmetric interference. Symmetric interference excites odd-order modes, while paired interference excites even-order modes. The multimode interferometer of symmetric interference can only be input at the input position on the symmetry axis parallel to the long side of the multimode interferometer, and it will generate the first N-fold image point at where n eff is the effective refractive index of the waveguide, W MMI is the effective width of the multimode interferometer, and λ is the wavelength of the signal light; the multimode interferometer of paired interference has two symmetric input positions with respect to the symmetry axis parallel to the long side of the multimode interferometer, which are located on both sides of the symmetry axis at the positions, and it will generate at The N - fold image points are generated for the first time; when input at any position other than the above - mentioned three positions, a multimode interferometer that can generate general interference will be formed, and it will generate the N - fold image points for the first time. In a 1×3 thermo - optic switch based on a silica / polymer hybrid waveguide according to the present invention, the 1×3 multimode interferometer (300) adopts an interference type of symmetric interference, and the 3×3 multimode interferometer (400) adopts an interference type of general interference.

[0007] As Figure 2 shown, a 1×3 thermo - optic switch based on a silica / polymer hybrid waveguide according to the present invention, wherein the 1×3 multimode interferometer (300) is composed of a first input Taper waveguide (310), a first multimode interference region (320), and three first output Taper waveguides (330). The first input Taper waveguide (310) and the first output Taper waveguide (330) have the same structure and are symmetrically arranged at the input end and the output end of the first multimode interference region (320), and are both formed by cascading two sine - shaped Taper waveguides and a rectangular three - segment Taper waveguide (311, 312, and 313, 331, 332, and 333); the signal light transmitted in the optical fiber is coupled into the input straight waveguide (101), and then input into the first input Taper waveguide (310), and transmitted to the first multimode interference region (320) where the self - imaging effect occurs. When the transmission length of the signal light in the first multimode interference region (320) is, triple images will be generated for the first time, where n eff is the effective refractive index of the waveguide, W MMI is the effective width of the multimode interferometer, and λ is the wavelength of the signal light; the signal light generates three beams of light with the same intensity (the phase of the middle light is different from the phases of the upper and lower lights and will lead ) from the position where the triple images are generated for the first time, and then are respectively output to the three output Taper waveguides (330), and then transmitted to the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107) through the first input S - bent waveguide (102), the middle input straight waveguide (103), and the second input S - bent waveguide (102'); by designing the sine - structured input Taper waveguide (310) and output Taper waveguide (330), the mode output at the self - imaging point of the multimode interference region can be made more matched with the mode in the Taper waveguide, reducing the insertion loss introduced by the multimode interferometer. In the form of a Taper - cascaded waveguide, a more uniform splitting ratio can be achieved, thereby improving the extinction ratio of the thermo - optic switch.

[0008] As Figure 5As shown in the figure, a 1×3 thermo-optic switch based on a silica / polymer hybrid waveguide according to the present invention, wherein the 3×3 multimode interferometer (400) is composed of 3 second input Taper waveguides (410), a second multimode interference region (420), and 3 second output Taper waveguides (430). The second input Taper waveguides (410) and the second output Taper waveguides (430) have the same structure and are symmetrically arranged at the input end and the output end of the second multimode interference region (420), and are each composed of two sine-shaped Taper waveguides and a rectangular-shaped 3-segment Taper waveguide cascaded (411, 412, and 413, 431, 432, and 433); the signal light passing through the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107) respectively passes through the input channels A, B, and C of the first output S-bending waveguide (108), the intermediate output straight waveguide (109), the second output S-bending waveguide (108'), and the second input Taper waveguide (410) to transmit the signal light into the second multimode interference region (420) to generate a self-imaging effect. When the transmission length of the signal light in the multimode interference region is, a triple image will be generated for the first time, where n eff is the effective refractive index of the waveguide, W MMI is the effective width of the multimode interferometer, and λ is the wavelength of the signal light; the signal light generates three beams of light with the same intensity (different phases, and the specific phase difference can be seen in the imaginary term matrix of the transmission matrix of the 3×3 multimode interferometer (400), the i-th column represents the input port, and the j-th row represents the output port) from the position where each input light generates a triple image for the first time (3 beams of input light will generate 3 triple images, which is equivalent to the superposition of the wave functions of three lights here, synthesizing a wave function, thereby changing the enhancement of the output light). Then the three beams of light are respectively output into the 3 output Taper waveguides (430), and then output through the first output straight waveguide (110), the second output straight waveguide (111), and the third output straight waveguide (112); by designing the input / output Taper waveguides with a sine structure, the mode output at the self-imaging point of the multimode interference region can be made more matched with the mode in the Taper waveguide, reducing the insertion loss introduced by the multimode interferometer; by adopting the form of cascaded Taper waveguides, a more uniform splitting ratio can be achieved, thereby improving the extinction ratio of the switch.

[0009] After the signal light is input from the input straight waveguide and passes through the 1×3 multimode interferometer (300), the input light is split into three beams of signal light with the same amplitude. The transmission matrix of the 1×3 multimode interferometer (300) is:

[0010]

[0011] The three input optical beams pass through the middle connection part and modulation part and are connected to a 3×3 multimode interferometer (400). The transmission matrix of the 3×3 multimode interferometer (400) is:

[0012]

[0013] And the transmission matrix of its connection part is:

[0014]

[0015] Where is the phase change of the nth connection part.

[0016] According to the transmission matrix method, the transmission matrix of the entire switch is:

[0017] T = T 3×3 T M T 1×3 (4)

[0018] From formulas (1) to (4), it can be obtained that:

[0019]

[0020] In the actual preparation process, the value of can be calculated according to the light intensities of the three output ports, or can be monitored by a vector network analyzer.

[0021] By designing the size of the S-bent waveguide (the bending radius is 2500 μm and the horizontal offset is 30 μm) and adding an input phase shifter (104 and 104') in front of the upper and lower two modulation arm waveguides (105 and 107), a phase change of is introduced into the modulation arm. When no voltage is applied to the metal electrode, the output channels ①, ②, and ③ will output light with equal power; when a voltage is applied to a certain metal electrode (201, 202, or 203), the electric power applied to a certain metal electrode (201, 202, or 203) is changed to heat a certain modulation arm waveguide (105, 106, or 107). Due to the thermo-optic effect, the refractive index of the polymer modulation arm changes with the increase of temperature, so that the phase of the light changes. Denote the phase change amount at this time as where n is the nth modulation arm (n = 1, 2, or 3). When the phase change on the first modulation arm waveguide (105) reaches , the light will be output from the output channel ③; when the phase change on the second modulation arm waveguide (106) reaches , the light will be output from the output channel ②; when the phase difference on the third modulation arm waveguide (107) reaches When the time is right, light will be output from output channel ①; thus, the switching functions of the three channels are realized by modulating the metal electrodes.

[0022] The polymer upper cladding material described above is polymethyl methacrylate (PMMA), polyethylene (PE), polyester (PET), polystyrene (PS), EpoClad, etc. Preferably, PMMA is used, and its refractive index at a wavelength of 1550 nm is 1.47606.

[0023] The polymer core material described above is a polymer material with a negative thermo-optic coefficient, such as SU-8 2002, SU-8 2005, EpoCore, etc. Preferably, SU-8 2002 is used, and its refractive index at a wavelength of 1550 nm is 1.5802.

[0024] The metal electrode material described above can be an alloy material composed of one or more of gold, silver, copper, and aluminum.

[0025] The preparation method of the 1×3 optical switch based on the polymer / silica hybrid waveguide described in the present invention is as follows:

[0026] 1) On the silicon wafer substrate (1), a layer of dense silica with a thickness of 10 - 20 μm is grown by thermal oxidation as the lower cladding (2);

[0027] 2) The polymer core material is spin-coated on the silica lower cladding (2), pre-baked to remove the excess solvent in the polymer core material, and then allowed to cool naturally to obtain the polymer core thin film (31);

[0028] 3) Through ultraviolet lithography, development, and post-baking, the pattern on mask Ⅰ that is the same (the polymer core material is a positive photoresist) or complementary (the polymer core material is a negative photoresist) to the polymer core structure to be prepared is transferred onto the polymer core thin film (31), thereby obtaining the polymer core (3). The thickness of the polymer core (3) is 2 - 5 μm. The input straight waveguide (101), the first input S-bending waveguide (102), the second input S-bending waveguide (102’), the intermediate input straight waveguide (103), the first modulation arm waveguide (105), the second modulation arm waveguide (106), the third modulation arm waveguide (107), the first output S-bending waveguide (108), the second output S-bending waveguide (108’), the intermediate output straight waveguide (109), the first output straight waveguide (110), the second output straight waveguide (111), and the third output straight waveguide (112) in the polymer core (3) have the same width of 2 - 5 μm;

[0029] 4) Use a vacuum spin coater to spin coat a polymer upper cladding material on the silica lower cladding (2) and the polymer core layer (3), where the thickness of the polymer upper cladding (4) above the polymer core layer (3) is 2 - 7 μm, and after baking treatment, it is naturally cooled and cured;

[0030] 5) Evaporate a metal thin film (51) with a thickness of 50 - 400 nm on the polymer upper cladding (4);

[0031] 6) Use a vacuum spin coater to spin coat a layer of photoresist (61) on the surface of the metal thin film (51), and after pre-baking to remove the photoresist solvent, it is naturally cooled and cured;

[0032] 7) Through ultraviolet exposure, development, and post-baking, obtain a photoresist pattern (62) on the metal thin film (51) that is the same as the metal electrode structure to be prepared;

[0033] 8) Use the metal etching solution corresponding to the metal to etch the metal thin film (51) covered without the photoresist pattern (62) to obtain the metal electrode (5), and then remove the photoresist (61) covering the metal electrode (5); the metal electrode (5) is located above the polymer upper cladding (4) directly above the positions of the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107). The symmetry center of the metal electrode (5) in the width and length directions is aligned with the symmetry center of the modulation arm waveguide in the width and length directions. The length of the metal electrode (5) is equal to the lengths of the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107), and the width is greater than the widths of the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107), thereby preparing the 1×3 thermo-optic switch based on the silica / polymer hybrid waveguide of the present invention.

[0034] Compared with the prior art, the innovation of the present invention lies in:

[0035] 1. The thermo-optic switch is an organic-inorganic hybrid integrated composite waveguide structure, using silica as the lower cladding, which reduces the device loss;

[0036] 2. Adopting an organic-inorganic hybrid integrated composite waveguide structure, with a polymer as the core layer, the core-cladding refractive index difference Δn = 2.5% - 10%, which can achieve more compact end-face dimensions and bending radii, and prepare large-scale, low-power, and fast planar optical waveguide integrated circuits;

[0037] 3. The thermo-optic switch can complete the device preparation through simple contact exposure, and the required processing cost is extremely low;

[0038] 4. Using a polymer material as the modulation arm waveguide, the power consumption required to achieve the switching function is small;

[0039] 5. The sine-shaped Taper waveguide structure is adopted on the MMI, reducing the loss of the device;

[0040] 6. By adopting the Taper waveguide structure with multiple Taper cascaded waveguides, the power distribution of the power divider can be made more uniform, achieving a high extinction ratio;

[0041] 7. A phase shifter is applied to each of the modulation arm waveguides on both sides, enabling the switch function to be achieved by applying modulation to only one modulation arm each time;

[0042] 8. The 1×3 thermo-optic switch realizes the free switching of 3 channels, and is more flexible and has a more compact structure compared with the traditional 1×2 and 2×2 switches. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0044] Figure 1 : Schematic structural diagram of the 1×3 thermo-optic switch of the present invention;

[0045] Figure 2 : Schematic structural diagram of the 1×3 multimode interferometer (300) of the present invention;

[0046] Figure 3 : Transmission spectrum diagram of the 1×3 multimode interferometer (300) of the present invention;

[0047] Figure 4 : Cross-sectional schematic diagram of the 1×3 thermo-optic switch of the present invention;

[0048] Figure 5 : Schematic structural diagram of the 3×3 multimode interferometer (400) of the present invention;

[0049] Figure 6 : Transmission spectrum diagram of the 3×3 multimode interferometer (400) of the present invention when a single channel of input channel A is input;

[0050] Figure 7 : Transmission spectrum diagram of the 3×3 multimode interferometer (400) of the present invention when a single channel of input channel B is input;

[0051] Figure 8 : Process flow chart for preparing the 1×3 thermo-optic switch of the present invention;

[0052] Figure 9 : The optical field diagrams of the 1×3 thermo-optic switch (a) without temperature change, (b) with a 1.4K temperature change applied to the third modulation arm waveguide (107), (c) with a 1.5K temperature change applied to the second modulation arm waveguide (106), and (d) with a 1.4K temperature change applied to the first modulation arm waveguide (105) according to the present invention;

[0053] Figure 10 : The transmission spectrum diagram of the 1×3 thermo-optic switch according to the present invention when a 1.4K temperature change is applied to the third modulation arm waveguide (107);

[0054] Figure 11 : The transmission spectrum diagram of the 1×3 thermo-optic switch according to the present invention when a 1.5K temperature change is applied to the second modulation arm waveguide (106);

[0055] Figure 12 : The transmission spectrum diagram of the 1×3 thermo-optic switch according to the present invention when a 1.4K temperature change is applied to the first modulation arm waveguide (105); Detailed implementation manner

[0056] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0057] Embodiment 1:

[0058] As shown in the attached Figure 1As described above, it is a schematic structural diagram of a 1×3 thermo-optic switch. It consists of an input straight waveguide (101), a 1×3 multimode interferometer (300), a first input S-bend waveguide (102), a second input S-bend waveguide (102'), an intermediate input straight waveguide (103), a first phase shifter (104), a second phase shifter (104'), parallel first modulation arm waveguides (105), second modulation arm waveguides (106), third modulation arm waveguides (107), a first output S-bend waveguide (108), a second output S-bend waveguide (108'), an intermediate output straight waveguide (109), a 3×3 multimode interferometer (400), a first output straight waveguide (110), a second output straight waveguide (111), and a third output straight waveguide (112). Considering the relationship between modulation efficiency and size, the length of the modulation arm is set to 2000 μm. The radius of the S-bend waveguide is 2500 μm, and the horizontal offset is 30 μm. The phase shifter is composed of a waveguide that narrows first and then widens, and then widens first and then narrows. The width of the wide part is 6 μm, the width of the narrow part is 3 μm, and the length is 300 μm. The lengths of the parts where it narrows first and then widens and where it widens first and then narrows are equal.

[0059] The signal light output by the light source is coupled into the input straight waveguide (101). After passing through the 1×3 multimode interferometer (300), the signal light is evenly divided into three beams of light with equal power. The upper and lower beams of light enter the first phase shifter (104) and the second phase shifter (104') respectively through the first S-bend waveguide (102) and the second S-bend waveguide (102') connected to the 1×3 multimode interferometer. The two phase shifters provide phase changes, and then are transmitted to the upper and lower parallel first modulation arm waveguides (105) and third modulation arm waveguides (107) for modulation. The middle beam of light is transmitted through the intermediate input straight waveguide (103) to the second modulation arm waveguide (106) for modulation. The above three beams of signal light then pass through the first S-bend waveguide (108), the second S-bend waveguide (108'), and the intermediate output straight waveguide (109) connected to the modulation arm waveguides to transmit the light into the 3×3 multimode interferometer (400), and finally output from the three output straight waveguides (110, 111, and 112). When only a voltage is applied to the first modulation arm waveguide (105) to change the electric power loaded on the first metal electrode (201) to heat the first modulation arm waveguide (105), due to the thermo-optic effect, the refractive index of the polymer changes with the increase in temperature, resulting in different phase differences when the light reaches the 3×3 multimode interferometer, and the phase of the signal light changes. We denote the phase change caused by heating as where n is the nth modulation arm. When When the time is right, light will be output from output channel ③. When a voltage is applied only to the second modulation arm waveguide (106) to change the electric power loaded on the second metal electrode (202) and heat the second modulation arm waveguide (106), when When the time is right, light will be output from output channel ②. When a voltage is applied only to the third modulation arm waveguide (107) to change the electric power loaded on the third metal electrode (203) and heat the third modulation arm waveguide (107), when When the time is right, light will be output from output channel ①, thus realizing the switching function of the three channels.

[0060] As shown in the Figure 2 accompanying figure, it is a schematic structural diagram of a 1×3 multimode interferometer (300). Considering the device size and actual fabrication difficulty comprehensively, in this example, the first input Taper waveguide (310) of the 1×3 multimode interferometer (300) adopts a cascaded form of 2 equi-length sinusoidal-shaped Taper waveguides (311 and 312) and a rectangular-shaped Taper waveguide (313). The total length of the cascaded Taper waveguides is 132.2 μm. The starting widths of the cascaded Taper waveguides (311, 312, and 313) from far to near the first multimode interference region (320) are 3 μm, 6.8 μm, and 7 μm respectively, and the termination width of the third-stage cascaded Taper waveguide (313) is 7 μm. The first output Taper waveguide (330) adopts a cascaded form of 2 equi-length sinusoidal-shaped Taper waveguides (332 and 333) and 1 rectangular-shaped Taper waveguide (331). The total length of the cascaded Taper waveguides is 132.2 μm. The starting widths of the cascaded Taper waveguides (333, 332, and 331) from far to near the first multimode interference region (320) are 3 μm, 6.8 μm, and 7 μm respectively, and the termination width of the third-stage cascaded Taper waveguide (331) is 7 μm. The width of the first multimode interference region (320) is 30 μm and the length is 322 μm. The center spacing of the three output Taper waveguides is 10.18 μm. The side structure of the sinusoidal-shaped Taper waveguide uses the difference between half of the wide-side width and half of the narrow-side width as the amplitude of the sine. After experiencing the first 1 / 4 sine period, the width of the Taper waveguide changes from the narrow-side width to the wide-side width.

[0061] As shown in the Figure 3 accompanying figure, it is the transmission spectrum diagram of the 1×3 multimode interference region (300). It can be found that at 1550 nm, the light splitting of the three channels is uniform. At wavelengths from 1500 nm to 1630 nm, the loss of each channel is less than 5.1 dB.

[0062] As shown in the Figure 4As described above, it is a cross-sectional view of an inorganic / polymer organic material hybrid waveguide. From bottom to top, there are a silicon substrate (1), a silica lower cladding (2), a polymer core layer (3), a polymer upper cladding (4), and a metal electrode (5). In this example, a dense layer of silica is grown by thermal oxidation, and its refractive index is 1.4448. The polymer core layer material (3) used is a negative photoresist of SU-8 2002, and its refractive index at a wavelength of 1550 nm is 1.5802. The polymer upper cladding material used is polymethyl methacrylate (PMMA), and its refractive index at a wavelength of 1550 nm is 1.47606. In this example, in order to reduce crosstalk between modes and at the same time reduce the difficulty of the manufacturing process, we designed the size of the straight waveguide (all waveguides except the multimode interferometer are 3 μm × 3 μm, and the thickness of the multimode interferometer is 3 μm; the width of the phase shifter first linearly changes from 3 μm to 6 μm, and then from 6 μm to 3 μm, with a total length of 112 μm, where the lengths from narrow to wide and from wide to narrow are the same, both 56 μm.) to be 3 μm × 3 μm.

[0063] As shown in the Figure 5 attachment, it is a schematic structural diagram of a 3×3 multimode interferometer (400). Considering the device size and the actual manufacturing difficulty comprehensively, in this example, each second input Taper waveguide (410) of the 3×3 multimode interferometer (400) adopts a cascaded form of 2 equal-length sinusoidal-shaped Taper waveguides (411 and 412) and 1 rectangular-shaped Taper waveguide (413). The total length of the cascaded Taper waveguides is 132.2 μm. The starting widths of the cascaded Taper waveguides (411, 412, and 413) from far to near the second multimode interference region (420) are 3 μm, 6.8 μm, and 7 μm respectively, and the termination of the third-stage cascaded Taper waveguide (413) is 7 μm. The second output Taper waveguide (430) adopts a cascaded form of 1 rectangular-shaped Taper waveguide (431) and 2 equal-length sinusoidal-shaped Taper waveguides (432 and 433). The length of the cascaded Taper waveguides is 132.2 μm. The starting widths of the cascaded Taper waveguides (433, 432, and 431) from far to near the second multimode interference region (420) are 3 μm, 6.8 μm, and 7 μm respectively, and the termination of the third-stage cascaded Taper waveguide (431) is 7 μm. The width of the second multimode interference region (420) is 30 μm and the length is 1288 μm. The center spacing of the three second input / output Taper waveguides is 10.18 μm. The side structure of the sinusoidal-shaped Taper waveguide uses the difference between half of the wide-side width and half of the narrow-side width as the amplitude of the sine. After experiencing the first 1 / 4 sine cycle, the width of the Taper waveguide changes from the narrow-side width to the wide-side width.

[0064] As shown in theFigure 6 As shown, the transmission spectrum diagram of the 3×3 multimode interferometer (400) of the present invention when a single channel of input channel A is input. At wavelengths from 1500 nm to 1630 nm, the loss of each channel is less than 7 dB.

[0065] As attached Figure 7 As shown, the transmission spectrum diagram of the 3×3 multimode interferometer (400) of the present invention when a single channel of input channel B is input. At wavelengths from 1500 nm to 1630 nm, the loss of each channel is less than 8.5 dB.

[0066] As attached Figure 8 As shown, the preparation method of the 1×3 thermo-optic switch based on a silica / polymer hybrid waveguide of the present invention is as follows:

[0067] 1) On a silicon wafer substrate (1), a dense 15-μm-thick silica undercladding (2) is grown by thermal oxidation;

[0068] 2) Use a vacuum spin coater to spin coat SU-8 2002 photoresist on the surface of the silica undercladding. First, pre-bake at 60 °C for 10 minutes, 90 °C for 20 minutes and then cool naturally to cure. Then, by controlling the rotation speed of 600 revolutions per minute and the spin coating time of 20 s, a 3-μm-thick SU-8 photoresist layer (3) is formed;

[0069] 3) Place the device in step 2) under a 365-nm ultraviolet light lithography machine with a light power of 23 mW / cm 2 , perform alignment lithography. The structure and shape of the used mask I are complementary to the structure and shape of the SU-8 core layer waveguide to be prepared. The exposure time is 3.5 s. Then, post-bake at 65 °C for 10 minutes and 95 °C for 20 minutes, cool to room temperature, put it into a PGMEA (Propyleneglygol-monomethylether-acetate) developer for development, then rinse in isopropyl alcohol to remove the remaining glue, and wash the reaction solution with deionized water; then, at 120 °C, harden the film for 30 minutes to form an SU-8 2002 core layer. In order to be polarization insensitive, the width and height of the strip-shaped SU-8 core layer (3) are the same, both being 3 μm;

[0070] 4) Use a vacuum spin coater to spin coat a PMMA polymer upper cladding (4) with a thickness of 7 μm on the chip, where the thickness of the PMMA polymer upper cladding (4) on the SU-8 core layer waveguide is 4 μm. Then, cure at 120 °C for 30 minutes and cool to room temperature;

[0071] 5) Evaporate a 100-nm-thick metal Al film (51) on the PMMA polymer upper cladding (4);

[0072] 6) Adopt the spin-coating process to spin-coat the positive photoresist BP212 (61) with a thickness of 1.5 μm on the metal Al film (51), and bake it at 87 °C for 20 minutes;

[0073] 7) Place the sample under the ultraviolet lithography machine, and closely contact it with the mask plate II for alignment lithography. The structure and shape of the used mask plate II are the same as those of the metal electrode to be prepared. The structure of the mask plate II is larger than the SU-8 core layer waveguide. Expose for 2 s, remove the mask plate II, and after developing with a NaOH solution with a mass concentration of 5 wt‰, bake it at 90 °C for 20 minutes to transfer the pattern on the mask plate II that is the same as the structure of the metal electrode to be prepared onto the BP212 photoresist layer (62);

[0074] 8) Use a NaOH solution with a mass concentration of 5 wt‰ to remove the metal Al film not masked by the photoresist, expose again for 10 s, and use an ethanol solution to remove the remaining BP212, exposing the Al metal electrode (51), thereby preparing a 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide. The width of each metal modulation electrode (201, 202, 203) is 21 μm, and the distance between every two metal modulation electrodes is 19 μm, aiming to leave enough alignment error range during the preparation of the electrode and the waveguide to reduce the process difficulty.

[0075] 9) As shown in Figure 9 (a), the optical field diagram of the 1×3 thermo-optic switch of the present invention without voltage applied. When no voltage is applied, the output channels ①, ②, and ③ can be approximately regarded as having equal power output.

[0076] As shown in Figure 9 (b), the optical field diagram of the 1×3 thermo-optic switch of the present invention when a voltage is applied to the third modulation arm waveguide (107) resulting in a temperature change of 1.4K. This diagram shows that when a temperature change of 1.4K is applied to the third modulation arm waveguide (107), the light will output from the output channel ①. At this time, the simulated loss at a wavelength of 1550 nm is -0.08233 dB, and the extinction ratio is greater than 33 dB.

[0077] As shown in Figure 9 (c), the optical field diagram of the 1×3 thermo-optic switch of the present invention when a voltage is applied to the second modulation arm waveguide (106) resulting in a temperature change of 1.5K. This diagram shows that when a temperature change of 1.5K is applied to the second modulation arm waveguide (106), the light will output from the output channel ②. At this time, the simulated loss at a wavelength of 1550 nm is -0.07787 dB, and the extinction ratio is greater than 38 dB.

[0078] As shown in Figure 9As shown in (d), the optical field diagram of the 1×3 thermo-optic switch of the present invention when a voltage is applied to the first modulation arm waveguide (105) resulting in a temperature change of 1.4K. This diagram shows that when a temperature change of 1.4K is applied to the first modulation arm waveguide (105), light is output from output channel ③. At this time, the simulated loss at a wavelength of 1550nm is -0.08233dB, and the extinction ratio is greater than 33dB.

[0079] As shown in the appendix Figure 10 As shown, the transmission spectrum diagram of the 1×3 thermo-optic switch of the present invention when a voltage is applied to the third modulation arm waveguide (107) resulting in a temperature change of 1.4K. This diagram shows the transmission spectrum from 1500nm to 1630nm. It can be known from the spectrum diagram that the bandwidth with a device crosstalk less than 20dB is 105nm, from 1505nm to 1610nm.

[0080] As shown in the appendix Figure 11 As shown, the transmission spectrum diagram of the 1×3 thermo-optic switch of the present invention when a voltage is applied to the second modulation arm waveguide (106) resulting in a temperature change of 1.5K. This diagram shows the transmission spectrum from 1500nm to 1630nm. It can be known from the spectrum diagram that the bandwidth with a device crosstalk less than 20dB is 55nm, from 1525nm to 1580nm.

[0081] As shown in the appendix Figure 12 As shown, the transmission spectrum diagram of the 1×3 thermo-optic switch of the present invention when a voltage is applied to the first modulation arm waveguide (105) resulting in a temperature change of 1.4K. This diagram shows the transmission spectrum from 1500nm to 1630nm. It can be known from the spectrum diagram that the bandwidth with a device crosstalk less than 20dB is 105nm, from 1505nm to 1610nm.

Claims

1. A 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide, characterized in that: It consists of an Si substrate (1), a SiO2 lower cladding (2), a polymer core layer (3), a polymer upper cladding (4), and a metal electrode (5) from bottom to top; the polymer core layer (3) and the polymer upper cladding (4) are located above the SiO2 lower cladding (2), and the polymer core layer (3) is covered by the polymer upper cladding (4); along the light transmission direction, the polymer core layer (3) is composed of an input straight waveguide (101), a 1×3 multimode interferometer (300), a first input S-bending waveguide (102), a second input S-bending waveguide (102'), an intermediate input straight waveguide (103), a first phase shifter (104), a second phase shifter (104'), a first modulation arm waveguide (105), a second modulation arm waveguide (106), a third modulation arm waveguide (107), a first output S-bending waveguide (108), a second output S-bending waveguide (108'), an intermediate output straight waveguide (109), a 3×3 multimode interferometer (400), a first output straight waveguide (110), a second output straight waveguide (111), and a third output straight waveguide (112); among them, the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107) are parallel to each other, and on the polymer upper cladding (4) at the positions of the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107), there are parallel first metal electrode (201), second metal electrode (202), and third metal electrode (203), which together constitute the metal electrode (5). Among them, the 1×3 multimode interferometer (300) consists of a first input Taper waveguide (310), a first multimode interference region (320), and 3 first output Taper waveguides (330). The first input Taper waveguide (310) and the first output Taper waveguides (330) have the same structure and are symmetrically arranged at the input end and the output end of the first multimode interference region (320). They are both composed of two sinusoidal-shaped Taper waveguides and a rectangular-shaped 3-segment Taper waveguide cascaded (311, 312, and 313, 331, 332, and 333); the signal light transmitted in the optical fiber is coupled into the input straight waveguide (101), and then input into the first input Taper waveguide (310), and transmitted to the multimode interference region (320) where the self-imaging effect occurs; when the transmission length of the signal light in the multimode interference region (320) is, a triple image will be generated for the first time, where is the effective refractive index of the waveguide, is the effective width of the multimode interferometer, and is the wavelength of the signal light; the signal light generates three beams of light with the same intensity from the position where the triple image is generated for the first time and is respectively output to the 3 output Taper waveguides (330), and then transmitted to the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107) through the first input S-bending waveguide (102), the intermediate input straight waveguide (103), and the second input S-bending waveguide (102') respectively. The 3×3 multimode interferometer (400) consists of three second input taper waveguides (410), a second multimode interference region (420), and three second output taper waveguides (430). The second input taper waveguides (410) and the second output taper waveguides (430) have the same structure and are symmetrically arranged at the input end and the output end of the second multimode interference region (420). They are each formed by cascading two sine-shaped taper waveguides and a rectangular three-segment taper waveguide (411, 412, and 413, 431, 432, and 433). The optical signal passing through the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107) is respectively transmitted to the multimode interference region (420) through the input channels A, B, and C of the first output S-bend waveguide (108), the intermediate output straight waveguide (109), the second output S-bend waveguide (108'), and the second input taper waveguide (410), where self-imaging effect occurs. When the transmission length of the optical signal in the multimode interference region is, triple images are generated for the first time, where is the effective refractive index of the waveguide, is the effective width of the multimode interferometer, and is the wavelength of the optical signal. The optical signal generates three beams of light with the same intensity from the position where triple images are generated for the first time for each input light and is then respectively output to the three output taper waveguides (430), and then output through the first output straight waveguide (110), the second output straight waveguide (111), and the third output straight waveguide (112) respectively; When a modulation voltage is applied to the first metal electrode (201), the second metal electrode (202), or the third metal electrode (203), the phase of the optical signal changes, and the optical signal is output from the first output straight waveguide (110), the second output straight waveguide (111), or the third output straight waveguide (112), thereby realizing the switching function of three channels through the modulation of the metal electrode (5).

2. The 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide according to claim 1, characterized in that: The phase changes introduced by the phase shifters (104 and 104') to the modulation arms. When a voltage is applied only to the first modulation arm waveguide (105), the phase of the optical signal changes. When, the light is output from the third output straight waveguide (112). When a voltage is applied only to the second modulation arm waveguide (106), the phase of the optical signal changes. When, the light is output from the second output straight waveguide (111). When a voltage is applied only to the third modulation arm waveguide (107), the phase of the optical signal changes. When, the light is output from the first output straight waveguide (110).

3. The 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide according to claim 1, characterized in that: The material of the polymer upper cladding (4) is polymethyl methacrylate, polyethylene, polyester, polystyrene, or EpoClad.

4. The 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide according to claim 1, characterized in that: The material of the polymer core layer (3) is SU-8 2002, SU-8 2005, or EpoCore.

5. The 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide according to claim 1, characterized in that: The material of the metal electrode (5) is an alloy material composed of one or more of gold, silver, copper, and aluminum.

6. The 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide according to claim 1, characterized in that: The thickness of the silica lower cladding (2) is 10 - 20 μm; the thickness of the polymer core layer (3) is 2 - 5 μm. In the polymer core layer (3), the input straight waveguide (101), the first input S-bend waveguide (102), the second input S-bend waveguide (102'), the intermediate input straight waveguide (103), the first modulation arm waveguide (105), the second modulation arm waveguide (106), the third modulation arm waveguide (107), the first output S-bend waveguide (108), the second output S-bend waveguide (108'), the intermediate output straight waveguide (109), the first output straight waveguide (110), the second output straight waveguide (111), and the third output straight waveguide (112) have the same width of 2 - 5 μm; the thickness of the polymer upper cladding (4) is 2 - 7 μm; the thickness of the metal electrode (5) is 50 - 400 nm.

7. The 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide according to claim 6, characterized in that: The lengths of the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107) are 2000 μm; the thickness of the silica lower cladding (2) is 15 μm; the thickness of the polymer core layer (3) is 3 μm. In the polymer core layer (3), the input straight waveguide (101), the first input S-bend waveguide (102), the second input S-bend waveguide (102'), the intermediate input straight waveguide (103), the first modulation arm waveguide (105), the second modulation arm waveguide (106), the third modulation arm waveguide (107), the first output S-bend waveguide (108), the second output S-bend waveguide (108'), the intermediate output straight waveguide (109), the first output straight waveguide (110), the second output straight waveguide (111), and the third output straight waveguide (112) have the same width of 3 μm; the thickness of the polymer upper cladding (4) is 4 μm; the thickness of the metal electrode (5) is 100 nm.

8. The 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide according to claim 7, characterized in that: The total length of the first input Taper waveguide (310) is 132.2 μm. The starting widths of the cascaded Taper waveguides (311, 312, and 313) from far to near the multimode interference region (320) are 3 μm, 6.8 μm, and 7 μm respectively, and the termination width of the third-stage cascaded Taper waveguide (313) is 7 μm; the total length of the first output Taper waveguide (330) is 132.2 μm. The starting widths of the cascaded Taper waveguides (333, 332, and 331) from far to near the multimode interference region (320) are 3 μm, 6.8 μm, and 7 μm respectively, and the termination width of the third-stage cascaded Taper waveguide (331) is 7 μm; the width of the 1×3 multimode interference region (320) is 30 μm and the length is 322 μm, and the center spacing of the three first output Taper waveguides (330) is 10.18 μm; among them, the side structure of the sine-shaped Taper waveguide uses the difference between half of the wide-side width and half of the narrow-side width as the amplitude of the sine. After experiencing the first 1 / 4 sine period, the width of the Taper waveguide changes from the narrow-side width to the wide-side width.

9. The 1×3 thermo-optic switch based on a polymer / silica hybrid waveguide according to claim 7, characterized in that: The total length of the second input Taper waveguide (410) is 132.2 μm. The starting widths of the cascaded Taper waveguides (411, 412, and 413) from far to near the multimode interference region (420) are 3 μm, 6.8 μm, and 7 μm respectively, and the termination of the third-stage cascaded Taper waveguide (413) is 7 μm. The total length of the second output Taper waveguide (430) is 132.2 μm. The starting widths of the cascaded Taper waveguides (433, 432, and 431) from far to near the multimode interference region (420) are 3 μm, 6.8 μm, and 7 μm respectively, and the termination of the third-stage cascaded Taper waveguide (431) is 7 μm. The width of the 3×3 multimode interference region (420) is 30 μm and the length is 1288 μm. The center spacing of the three second output Taper waveguides (430) is 10.18 μm. For the side structure of the sine-shaped Taper waveguide, the amplitude of the sine is the difference between half of the wide-side width and half of the narrow-side width, and the width of the Taper waveguide changes from the narrow-side width to the wide-side width over the first 1 / 4 sine period.

10. A method for preparing a 1×3 thermo-optic switch based on the polymer / silica hybrid waveguide according to any one of claims 1 to 9, the steps are as follows: 1) On a silicon wafer substrate (1), a layer of dense silica with a thickness of 10 - 20 μm is grown by thermal oxidation as the lower cladding (2); 2) A polymer core layer material is spin-coated on the silica lower cladding (2), pre-baked to remove the excess solvent in the polymer core layer material, and then naturally cooled to obtain a polymer core layer thin film (31); 3) Through ultraviolet lithography, development, and post-baking, transfer the pattern on the mask I that is the same (the polymer core layer material is a positive photoresist) or complementary (the polymer core layer material is a negative photoresist) to the polymer core layer structure to be prepared onto the polymer core layer film (31), thereby obtaining the polymer core layer (3). The thickness of the polymer core layer (3) is 2 - 5 μm, and the width is 2 - 5 μm; 4) Use a vacuum spin coater to spin-coat the polymer upper cladding material on the silica lower cladding (2) and the polymer core layer (3). Among them, the thickness of the polymer upper cladding (4) above the polymer core layer (3) is 2 - 7 μm, and after baking treatment, it is naturally cooled and cured; 5) Evaporate a metal film (51) with a thickness of 50 - 400 nm on the polymer upper cladding (4); 6) Use a vacuum spin coater to spin-coat a photoresist (61) on the surface of the metal film (51), and after pre-baking to remove the photoresist solvent, it is naturally cooled and cured; 7) Through ultraviolet exposure, development, and post-baking, a photoresist pattern (62) identical to the metal electrode structure to be prepared is obtained on the metal thin film (51). 8) The metal thin film (51) covered without the photoresist pattern (62) is etched using the metal-corresponding metal etching solution to obtain the metal electrode (5), and then the photoresist (61) covering the metal electrode (5) is removed. The metal electrode (5) is located above the polymer upper cladding (4) at the positions of the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107). The symmetry center of the metal electrode (5) in the width and length directions is aligned with the symmetry center of the modulation arm waveguides in the width and length directions. The length of the metal electrode (5) is equal to the lengths of the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107), and the width is greater than the widths of the first modulation arm waveguide (105), the second modulation arm waveguide (106), and the third modulation arm waveguide (107), thereby preparing a 1×3 thermo-optic switch based on a silica / polymer hybrid waveguide.

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