Y-type junction power divider prepared based on LNOI material

Abstract

The invention discloses a Y-type junction power divider prepared based on an LNOI material. The Y-type junction power divider comprises a silicon dioxide substrate and a lithium niobate waveguide arranged on the substrate, the lithium niobate waveguide comprises an input straight waveguide, an input tapering cone, a first output tapering cone, a second output tapering cone, a first output straight waveguide and a second output straight waveguide, the input tapering cone is arranged in the middle in the coupling area, the first output tapering cone and the second output tapering cone are located on the two sides of the input tapering cone, and gaps are reserved between the first output tapering cone and the input tapering cone and between the second output tapering cone and the input tapering cone; according to the Y-type junction power divider designed based on the LNOI material, the size of the device is effectively reduced, due to the fact that the waveguide is small in size, the waveguide can be interconnected with other optical devices, the waveguide serves as an integratable miniaturizer, the loss of input light within the bandwidth range of 1480-1640 nm can be kept below 0.2 dB, light in the TE mode and the TM mode is supported to be transmitted, low loss is kept in the two modes, and the power divider can be used as an integrated miniaturizer. And the mode of the light is kept unchanged in the propagation process.

Description

Technical Field

[0001] The invention relates to a Y-junction power divider, in particular to a Y-junction power divider prepared based on LNOI material. Background Art

[0002] In recent years, photonic integrated circuits have been widely studied for their applications in quantum photonics, optical interconnects, photonic computing, and optical communications. The integration of multiple photonic components on a photonic chip requires the development of on-chip photonic integrable components, including waveguides, filters, and optical power dividers. An integrated optical power divider is an important photonic building block that splits the optical power into multiple channels, forms an interferometer system, and taps a small portion of the signal. Power dividers are one of the most basic building blocks of complex airborne optical circuits. They are used in optical switches, modulators, programmable optical circuits, and multiplexers, among others. An ideal power divider should have low loss, wide bandwidth, compact size, high tolerance to manufacturing errors, and small deviations from the expected power division ratio. In addition, it is desirable that the minimum feature size of the power divider is large (>100nm) so that they are suitable for mass production in complementary metal oxide semiconductor (CMOS) foundries.

[0003] LNOI (Lithium Niobate On Insulator) is a key material for photonic integrated circuits (PICs), quantum photonic integrated circuits, and programmable quantum processors because of its large electro-optic coefficient (γ33=32pmV-1), high nonlinear coefficient, broadband optical transparency window of 0.35~5.5μm, and high Curie temperature of 1145℃. Recently, thin-film lithium niobate on insulator substrates (TFLN) have been commercialized and used together with nanofabrication technology to realize electro-optic modulators, ultra-low loss beam splitters and waveguides, entangled photon sources, phase shifters, etc.

[0004] In particular, beam splitters based on LNOI materials are one of the basic and important components of quantum photonic circuits, used to separate and combine optical signals, as well as reconfigurable linear optical paths for quantum bit operations. In addition, due to the randomness of the emission wavelength caused by the quantum dot growth mechanism, quantum circuits cover a large bandwidth range across a variety of optical encoding methods. Quantum photonic circuits are more sensitive to losses and have more stringent performance requirements for individual components. Therefore, it is necessary to design low-loss, broadband LNOI power dividers to meet the needs of modern quantum communications in quantum photonic circuits. Summary of the invention

[0005] In response to the needs in the prior art, the present invention provides a Y-junction power divider prepared based on LNOI material, aiming to increase the function of the Y-junction optical power divider and reduce its loss and space occupancy.

[0006] A Y-junction power divider based on LNOI material, comprising a silicon dioxide substrate and a lithium niobate waveguide arranged on the substrate, wherein the silicon dioxide substrate and the lithium niobate waveguide are covered with a silicon dioxide cladding; the lithium niobate waveguide comprises an input straight waveguide, an input taper, a first output taper, a second output taper, a first output straight waveguide and a second output straight waveguide, wherein the input taper, the first output taper and the second output taper form a coupling region, the input straight waveguide is connected to the input taper, the first output taper is connected to the first output taper, the second output taper is connected to the second output straight waveguide, the input taper is centrally arranged in the coupling region, the first output taper is connected to the first output taper, the second output taper is connected to the second output straight waveguide The cone and the second output taper are located on both sides of the input taper and there is a gap between them. The length and thickness of the first output taper, the second output taper and the input taper are the same and the end faces of the three are arranged flush. When the wavelength of the input light is in the range of 1480nm to 1640nm, the input light is in TE mode, and the output light is in TE mode; when the input light is in TM mode, the output light is in TM mode, thereby realizing the polarization-independent function. For this purpose, the angle between the side wall of the lithium nitrate waveguide and the silica substrate is set to 70°; the input light is input by the input straight waveguide, and is output from the first output straight waveguide and the second output straight waveguide after passing through the coupling region.

[0007] Furthermore, the distances between the lower base of the first output taper and the lower base of the second output taper and the corresponding lower base of the input taper are 120 nm-160 nm.

[0008] Further: the distance between the lower base of the first output cone and the lower base of the input cone is called the first coupling gap, and the distance between the lower base of the input cone and the lower base of the second output cone is called the second coupling gap. The first coupling gap and the second coupling gap are both constant from the input side to the output side of the coupling region.

[0009] Furthermore, the cross sections of the input straight waveguide, the input taper, the first output taper, the second output taper, the first output straight waveguide and the second output straight waveguide are all isosceles trapezoidal.

[0010] Furthermore, the thickness of the lithium niobate waveguide is 0.3 μm, and the thickness of the silicon dioxide substrate is 2 μm.

[0011] Beneficial effects of the present invention: The Y-junction power divider designed based on LNOI material effectively reduces the volume of the device. Due to the small size of the waveguide, it can be interconnected with other optical devices. As an integrable miniaturized device, for input light within the bandwidth range of 1480nm~1640nm, the loss can be kept below 0.2dB, and the propagation of light in TE and TM modes is supported. Low loss is maintained in both modes, and the mode of light is kept unchanged during the propagation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention; Figure 2 It is a schematic diagram of the top view structure of the coupling area in the present invention; Figure 3 for Figure 2 1C-1C cross-sectional view; Figure 4 for Figure 2 1D-1D cross-sectional view; Figure 5 for Figure 2 1E-1E cross-sectional view; Figure 6 It is a corresponding relationship diagram of the simulation results of the coupling region length and the power loss under two coupling gap conditions in the TE mode of the present invention; Figure 7 It is a corresponding relationship diagram of the simulation results of the coupling region length and the power loss under two coupling gap conditions in the TM mode of the present invention; Figure 8 A diagram showing the corresponding relationship between the simulation results of the input light and the power loss at different wavelengths of the present invention; Fig. 9 Schematic diagram of the three-dimensional structure of the first comparative example; Fig.10 It is a top view of the coupling area of ​​the first comparative example; Fig.11 for Fig.10 2C-2C cross-sectional view; Fig.12 Schematic diagram of the three-dimensional structure of the second comparative example; Fig.13 It is a top view of the coupling area of ​​the second comparative example; Fig.14 for Fig.13 3C-3C cross-sectional view; Fig.15 for Fig.13 3D-3D cross-sectional view; Fig.16 for Fig.13 3E-3E section view. DETAILED DESCRIPTION

[0013] The present invention is described in detail below in conjunction with the accompanying drawings. The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention. The directional terms such as left, middle, right, top, and bottom in the embodiments of the present invention are only relative concepts or are based on the normal use state of the product, and should not be considered as restrictive.

[0014] The embodiments disclosed herein operate as a Y-shaped power divider, allowing the optical energy in the input waveguide to be equally divided between two separate output waveguides. The design works on the principle of optical waveguide coupling and requires physical symmetry along the entire length of the device. Different from the traditional straight waveguide, after simulation testing, it was found that in order to make the power divider have a smaller size, the device waveguide can have a sharp tip and a narrow gap, and it was finally decided to set the coupling area waveguide shape to a tapered structure. The device can have extremely low loss, a small footprint, a large operating bandwidth, polarization-independent characteristics, and a high tolerance to manufacturing variations. When the device is used in active devices such as variable optical attenuators (VOAs) or MZIs, electrical isolation is a desired feature because the two output waveguides are not physically connected, thereby providing electrical isolation between the two output waveguides.

[0015] In the embodiments disclosed herein, the waveguide portion is made of LiNbO3 material, which has a strong electro-optic coefficient (r 33 = 30.8 pm / V) and significant second-order optical nonlinearity (d 33 =−33 pm / V) With the advancement of thin film technology and crystal ion slicing technology, LN waveguides on thin film insulators have a large refractive index contrast (Δn~0.7). This gives them enhanced light confinement capabilities and reduced bending losses, and the refractive index of the material is much larger than that of the SiO2 cladding. This power divider can also be used in a series of devices to split or combine light to multiple outputs / inputs. For example, an embodiment can include a splitter tree in which several splitters are cascaded, thus playing a significant role in the field of integrated circuits.

[0016] A Y-junction power divider based on LNOI material, such as Figure 1 and Figure 2As shown, it includes a SiO2 substrate 101, a SiO2 cladding and a LiNbO3 waveguide, the SiO2 cladding covers the silicon dioxide substrate and the lithium niobate waveguide, the LiNbO3 waveguide includes an input straight waveguide 102, a first output taper 103, an input taper 104, a second output taper 105, a first output straight waveguide 106, and a second output straight waveguide 107, wherein the input straight waveguide 102 is connected to the input taper 104, the first output taper 103 is connected to the first output straight waveguide 106, the second output taper 105 is connected to the second output straight waveguide 107, and light is input from the input straight waveguide 102 and output from the first output straight waveguide 106 and the second output straight waveguide 107; The tapered parts of the waveguides, namely the first output taper 103, the input taper 104, and the second output taper 105, together form a coupling region 114. The thickness of the three tapered waveguides is the same, 0.3 μm, and the sidewall inclination angles are all set to 70°. The input taper 104 tapers in width from the input side 109 to the output side 112. In other words, the waveguide width is along Figure 1 The input taper 104 has a structure that gradually narrows in the x-axis direction. The size of the input taper 104 in this power divider is set to be 1.42 μm wide at the input side 109 and 1.22 μm wide at the upper base, 0.42 μm wide at the output side 112 and 0.22 μm wide at the lower base, and has a taper length of 5 μm-30 μm in the coupling region 114. The first output taper 103 and the second output taper 105 are placed close to (usually 100-200 nm or less) the left and right sides of the input taper 104 in the coupling region 114, and have side surfaces generally parallel to and spaced apart from the side surfaces of the input taper 104 in the coupling region 114, and the spacing distance remains constant along the waveguide side wall. The first output taper 103 is tapered in width and gradually widens from the input side 108 to the output side 111, and the second output taper 105 is tapered in width and gradually widens from the input side 110 to the output side 113. In other words, the first output taper 103 and the second output taper 105 have a waveguide width along Figure 1The tapered structure gradually widens in the x-axis direction. The dimensions of the first output taper 103 and the second output taper 105 are set to be 1.42 μm wide at the bottom of the output side and 1.22 μm wide at the top, and 0.42 μm wide at the bottom of the input side and 0.22 μm wide at the top. The first output taper 103 and the second output taper 105 have a taper length equal to that of the input taper 104 (approximately 5 μm-30 μm in the coupling region 114). The input side 108 and the input side 110 of the first output taper 103 and the second output taper 105 are located on the same plane as the input side 109 of the input taper 104, and the output side 111 and the output side 113 of the first output taper 103 and the second output taper 105 are located on the same plane as the output side 112 of the input taper 104. The dimensions provided herein are exemplary only, and other dimensions will be apparent to those of ordinary skill in the art.

[0017] The coupling region 114 is a region in which the input taper 104 is located at the center of the device, the first output taper 103 and the second output taper 105 are on both sides of the input taper 104, the input taper 104 has no actual contact with the first output taper 103 and the second output taper 105, a certain gap is maintained between the three and the gaps on both sides are equal in size, the light in the input taper is coupled into the output taper through the gaps on both sides, and the optical power entering the output tapers on both sides is basically equal.

[0018] In order to support transverse electro-optical (TE) and transverse magnetic (TM) optical transmission, that is, to achieve polarization-independent function, the sidewall inclination angle is set to 70°. The optical refractive index of lithium nitrate material is No≈2.21 for ordinary light and Ne≈2.13 for extraordinary light. Figure 1 The effective refractive index of the transverse electro-optic (TE) light along the y-axis is almost determined by the ordinary light refractive index No in the lithium nitrate waveguide. The ordinary light refractive index is fixed and will not change due to the incident angle or polarization state of the light. Therefore, whether the sidewall is tilted or not, the transverse electro-optic (TE) light can be transmitted and the field intensity loss is kept small. Figure 1The effective refractive index of the transverse magnetic (TM) light in the z-axis is determined by the extraordinary refractive index Ne, which is variable and changes with the change of the angle between the light and the crystal optical axis. When the angle is 0°, the refractive index reaches the maximum value, which is the Ne value; when the angle is 90°, Ne is equal to No; when the angle is between 0° and 90°, the refractive index changes between No and Ne. When the light propagates in the input straight waveguide 102 and the input taper 104, due to the existence of the side wall inclination angle, the refractive index changes linearly and gradually, thereby reducing the waveguide's mode restriction on the light, resulting in stronger coupling between the waveguides. Since the difference between No and Ne of the lithium nitrate material is small, the mode change of the light is relatively stable when it is transferred in the coupling region 114, so the transverse magnetic (TM) light can be smoothly converted to the first output taper 103 and the second output taper 105. After simulation, it is found that the coupling loss is the lowest when the inclination angle is set to about 70°, so the side wall inclination angle is set to 70°.

[0019] In the coupling region 114, fixed gaps L1 and L2 are defined between the first output taper 103, the input taper 104, and the second output taper 105. The gaps are preferably designed to facilitate the transition of the input light into the first output taper 103 and the second output taper 105 after entering the input taper 104, and to facilitate the continuation of the light during the separation process. The distance between the lower base of the input taper 104 and the lower base of the first output taper 103 is represented by the first gap L1, and the distance between the lower base of the input taper 104 and the lower base of the first output taper 105 is represented by the second gap L2. In this coupling region 114, the coupling gap L1=L2 is set, and the length of the coupling gap does not change from the input side to the output side of the waveguide; If there is no such coupling gap, the two output waveguides are physically connected directly to the input waveguide, so since the optical signal propagates in the input waveguide toward the output waveguide, the sudden separation of the single input waveguide to the two output waveguides causes the back reflection and scattering of light at the vertex of the optical separator. Such a result is produced because the zero-point vertex cannot be reliably or repeatedly formed using known manufacturing techniques, that is, the singular point cannot be formed in silicon. Therefore, the vertex is a section (discontinuity) or surface that scatters and / or reflects light at this point. Another example of a gapless Y-shaped power divider includes a single waveguide that is separated into two waveguides by a gradient separation region. Due to the manufacturing constraints commonly used in the manufacturing process, the gradient separation region is incompatible with CMOS manufacturing. Traditional deposition and etching techniques are not suitable for defining vertical gradient structures that may require grayscale lithography. A Y-junction power divider that does not include a coupling gap relies on physical symmetry to allow light to be transmitted from a single input channel to two branch channels. Because the output waveguide is physically in contact with the input waveguide, symmetry is necessary. Therefore, the output waveguides are not electrically isolated from each other. The lack of electrical isolation is not desirable for active devices such as MZIs.

[0020] The gap is defined by etching the layer to finally form each waveguide during the manufacturing process. The horizontal taper is compatible with traditional deposition and etching techniques (e.g., CMOS manufacturing). The current etching process can be used to define a gap with a width of 100nm-200nm. The interval of 100nm-200nm width is considered sufficient to achieve the features disclosed herein. After simulation, it was found that it is not the case that the smaller the gap, the smaller the power loss of the device or the better the performance. Setting L1 and L2 between 100-200nm will produce the best coupling efficiency. Since the light energy in the input waveguide is divided equally between the two separate output waveguides, it is required that this power divider is physically symmetrical along the input direction of the light, that is, the input taper 104 maintains a certain gap with the first output taper 103 and the second output taper 105 and the gaps on both sides are equal, that is, L1=L2.

[0021] Figure 3-Figure 5 1 is a cross-sectional view of various locations of the LiNbO 3 waveguide in the optical separator 100 . Figure 3 The cross sections of the input side 109 of the input taper 104, the input side 108 of the first output taper 103 and the input side 110 of the second output taper 105 are shown. It can be seen that the waveguides shown in the cross sections have an ideal quadrilateral, but rounded corners may appear due to manufacturing constraints. Figure 4 A cross section of the waveguide in the middle of the coupling region 114 is shown. Figure 5 A cross section of the waveguide output side is shown. Figure 3-5It can be seen that the coupling gap L1=L2, and the coupling gap length does not change from the input side to the output side. For this Y-junction power divider, the thermal insulation can be above 99.8%, which ensures that the separation ratio will not be worse than 55 / 45. The 5-30μm taper length also makes the separation ratio resilient to changes in device layer thickness (i.e., height) with thickness variations of up to + / -10nm for a bandwidth of ~50nm or up to + / -5nm for a bandwidth of 100nm. Wider bandwidths and tighter separation ratio ranges can be achieved by increasing the taper length to achieve higher levels of thermal insulation.

[0022] The working principle of the Y-junction power divider based on LNOI material proposed in the present invention is as follows: the light wave is compressed into the coupling region through the input straight waveguide. Along the propagation direction, the light in the central waveguide gradually transforms into a leakage mode due to the narrowing of the waveguide width. The central waveguide taper (input taper 104) and the two external reverse tapers (first output taper 103 and second output taper 105) are used as two directional couplers (DC) to split the light field. Then, the split light waves at the tip of the end waveguide are coupled to the two external inverted cones. The LiNbO3 material used is conducive to the coupling of light compared to traditional silicon materials, combining it with a tapered structure and greatly shortening the coupling length to 30μm or less. Finally, two output waveguides (first output straight waveguide 106 and second output straight waveguide 107) are used to extract the split light beams.

[0023] The advantage of the power divider shown in this embodiment is that the tapered structure enables the LiNbO3 waveguide to strongly confine light, making the waveguide width gradually narrower or wider, and suppressing the reduction of conversion efficiency while reducing the wavelength and polarization dependence of the conversion efficiency. The waveguide in the coupling region 114 is constructed in a tapered shape to control the effective refractive index, so that the waveguide gradually widens or narrows from the starting point to the end point, thereby controlling the mode field of the light propagating through the LiNbO3 waveguide, and the effective refractive index and mode field of the light propagating through the input taper 104 are close to the effective refractive index and mode field of the light propagating through the first output taper 103 and the second output taper 105. As a result, while reducing the coupling loss between the input taper 104 and the first output taper 103 and the second output taper 105, the length of the coupling region 114 can be shortened.

[0024] In addition, the coupling region 144 of the optical device 100 has a structure with a coupling gap L1=L2 and the length of the coupling gap does not change from the input side to the output side. By coupling without any actual physical contact, electrical isolation between the output waveguides is achieved, and light is evenly transferred from the input taper 104 to the first output taper 103 and the second output taper 105 along the input waveguide of the taper structure, thereby greatly improving the coupling efficiency of the optical separator 100.

[0025] In order to verify the beneficial effects of the present invention, the following simulation experiment was conducted: The experiment used the time-domain finite difference method for calculation and analysis. The main parameters used in the simulation calculation included: the thickness of the LiNbO3 waveguide was 0.3 μm, the width of the straight waveguide was 1.41838 μm, the parameters of the tapered waveguide were as described above, the thickness of the silicon dioxide substrate was 2 μm, and the length of the three tapered waveguides, that is, the length of the coupling region 114, was set to be the same as L in the simulation modeling. Y ,L Y The simulation results are 5μm, 10μm, 15μm, 20μm, 25μm and 30μm, the coupling gaps L1 and L2 are 120nm and 160nm, and the input light center wavelength is 1560nm. Figure 6 and Figure 7 In the simulation modeling, the tapered waveguide length is 30μm, the coupling gaps L1 and L2 are 160nm, and the input light wavelength range is 1480∼1640nm.

[0026] like Figure 6 As shown, due to the symmetry of the device, we take the output result of the first output straight waveguide 106 as the observation object. Figure 6 is the transmission spectrum obtained when light is input into the power divider in TE mode, according to Figure 6 It can be seen that the loss of the device is kept below 0.4dB when the coupling gaps L1 and L2 of the device are 120nm and 160nm, and the loss is lower when the coupling area is larger than 10μm and the minimum feature size is 120nm.

[0027] like Figure 7 As shown, due to the symmetry of the device, we take the output result of the first output straight waveguide 106 as the observation object. Figure 7 is the transmission spectrum obtained when light is input into the power divider in TM mode, according to Figure 7 It can be seen that under the condition that the coupling gaps L1 and L2 of the device are 120nm and 160nm, the loss of the device is kept below 0.24dB, and the loss is lower when the coupling gaps L1 and L2 are 120nm.

[0028] like Figure 8 As shown, we choose the length L of the coupling region 114 Y The power divider with a coupling gap L1 and L2 of 30μm and 160nm is simulated. Figure 8 The transmission spectrum obtained when light is input into the power divider in TE and TM modes, where the dotted line represents the loss of the TE mode and the solid line represents the loss of the TM mode. Figure 8It can be seen that when the wavelength of the input light is in the range of 1480nm to 1640nm, the insertion loss of the device is lower than 0.2dB, and the loss of the TE mode is lower than the loss of the TM mode.

[0029] Comparative Example 1 Fig. 9 is an isometric view showing an optical power splitter 200 according to a comparative embodiment 1 disclosed herein. Fig.10 yes Fig. 9 1 is a plan view of Comparative Example 1 shown in FIG. First, the optical power splitter 200 of this embodiment will be described with reference to the combination of these drawings. The power splitter 200 includes a SiO2 substrate 201, a SiO2 cladding and a LiNbO3 waveguide. The LiNbO3 waveguide includes an input straight waveguide 202, a first coupling region output straight waveguide 203, a coupling region input straight waveguide 204, a second coupling region output straight waveguide 205, a first output straight waveguide 206, and a second output straight waveguide 207.

[0030] In addition, the optical power splitter 200 has a part of the same structure as the optical power splitter 100, and the same parts are not described separately. The optical device 200 according to the second embodiment is different from the optical device 100 according to the first embodiment in that the three waveguides in the coupling region 214 are changed from the cone in the optical splitter 200 to a vertical waveguide with equal length and width from the input side to the output side. The first coupling region output straight waveguide 203 is a vertical waveguide with a constant width from the starting point 208 to the end point 211, the coupling region input straight waveguide 204 is a vertical waveguide with a constant width from the starting point 209 to the end point 212, and the second coupling region output straight waveguide 205 is a vertical waveguide with a constant width from the starting point 210 to the end point 213.

[0031] The coupling region 214 includes a first coupling region output straight waveguide 203, a coupling region input straight waveguide 204, and a second coupling region output straight waveguide 205. The coupling region input straight waveguide 204 is located between the first coupling region output straight waveguide 203 and the second coupling region output straight waveguide 205, and the coupling gap L1=L2 between the three. Since the cross-sectional shape of the coupling region waveguide along the light transmission direction is the same, only one cross-sectional view is made. Fig.11 The cross-sections of the waveguide input side 209, input side 208 and input side 210 are shown, including the first coupling region output straight waveguide 203, the coupling region input straight waveguide 204, and the second coupling region output straight waveguide 205. It can be seen that three waveguides of the same shape are placed side by side.

[0032] In this embodiment, the standard vertical waveguide with unchanged cross-sectional area makes the device easier to process and manufacture, thereby allowing more devices to be formed on a single substrate or mold. However, in the coupling region 213 of the optical power divider 200, the confinement of light in the three vertical waveguides is weak, so the radiation loss at the starting point 205 of the first output straight waveguide 203 and the starting point 207 of the second output straight waveguide 204 included in the LiNbO3 waveguide increases. In addition, the length of the coupling region 214 where the vertical waveguides have space between each other needs to be somewhat extended, so to achieve better performance, the size of the optical power divider must be increased.

[0033] Comparative Example 2 Fig.12 is an isometric view showing an optical power splitter 300 according to a comparative embodiment 2 disclosed herein. Fig.13 yes Fig.12 2 is a plan view of Comparative Example 2 shown in FIG. First, the optical power separator 200 of this embodiment will be described with reference to a combination of these drawings. The power separator 300 includes a SiO2 substrate 301, a SiO2 cladding and a LiNbO3 waveguide, the LiNbO3 waveguide includes an input straight waveguide 302, a first output taper 303, an input taper 304, a second output taper 305, a first output straight waveguide 306, and a second output straight waveguide 307, wherein the input straight waveguide 302 is connected to the input taper 304, the first output taper 303 is connected to the first output straight waveguide 306, the second output taper 305 is connected to the second output straight waveguide 307, and light is input from the input straight waveguide 302 and output from the first output straight waveguide 306 and from the second output straight waveguide 307; In addition, the optical power splitter 300 is partially similar to the optical power splitter 100 in structure, and the same parts are not described separately. The optical device 300 according to the third embodiment is different from the optical device 100 according to the first embodiment in that the gaps between the three tapered waveguides in the coupling region gradually widen linearly from the input side to the output side, and the coupling gaps L1A and L2A located at the starting point of the coupling region, that is, the input side, are set to be narrower than the coupling gaps L1B and L2B located at the end point of the coupling region, that is, the output side.

[0034] The coupling region 314 in the optical device 300 of the third embodiment is configured to have the following structure. The first coupling gap L1 and the second coupling gap L2 gradually widen linearly from the input side to the output side. The distance between the lower bases of the input side 308 of the first output taper 303 and the input side 309 of the input taper 304 at the starting point of the coupling region 314 is denoted as the first coupling gap L1A. The distance between the input side 309 of the input taper 304 and the input side 310 of the second output taper 305 is denoted as the second coupling gap L2A. The distance between the lower bases of the output side 311 of the first output taper 303 and the output side 312 of the input taper 304 at the end point of the coupling region 314 is denoted as the first coupling gap L1B. The distance between the output side 312 of the input taper 304 and the output side 313 of the second output taper 305 is denoted as the second coupling gap L2B. Then, regarding the relationship between the first gap L1 and the second gap L2, L1A = L2A < L1B = L2B holds.

[0035] Figure 14-16 It is a cross-sectional view of each position of the LiNbO3 waveguide in the optical splitter 300. Fig.14 It shows the cross-sections of the input side 309 of the input taper 304, the input side 308 of the first output taper 303, and the input side 310 of the second output taper 305. It can be seen that since it is located on the input side, the cross-sectional area of the input taper 304 is larger than that of the first output taper 303 and the second output taper 305. The input taper 304 is a regular isosceles trapezoid, and the first output taper 303 and the second output taper 305 are trapezoids with one long and one short hypotenuse. Fig.15 It shows the cross-section of the waveguide at the middle position of the coupling region 314. Fig.16 It shows the cross-section of the output side of the coupling region 314. At this time, the areas of the first output taper 103 and the second output taper 105 are larger than that of the input taper 104. From Figure 14-16 It can be seen that the coupling gaps L1 = L2, and the length of the coupling gap widens from the input side to the output side.

[0036] Although the waveguide of the optical splitter 300 has a tapered structure in the coupling region 314, since the first output taper 303 and the second output taper 305 gradually move away from the input taper 304, and the first coupling gap L1 and the second coupling gap L2 gradually widen linearly from the input side to the output side, as a result of the structural change of the LiNbO3 waveguide in the coupling region 314, the refractive index distribution of light gradually changes, resulting in light scattering loss and reducing the coupling efficiency of the optical splitter 300.

[0037] Summary In summary, the Y-junction power divider prepared based on LiNbO3 material provided by the present invention can realize the function of transmitting light polarization-independently, and has a small insertion loss at coupling gaps of 120nm and 160nm. Compared with traditional power dividers, it can transmit light with a wider bandwidth and can tolerate larger manufacturing errors. As a power divider prepared based on LNOI material, it has a smaller device structure than the existing solution, and thus has better effects when applied to optical switches, modulators, programmable optical circuits and multiplexers and other on-chip integrated optical systems.

[0038] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A Y-junction power divider based on LNOI material, characterized in that: The invention comprises a silicon dioxide substrate and a lithium niobate waveguide arranged on the substrate, wherein the silicon dioxide substrate and the lithium niobate waveguide are covered with a silicon dioxide cladding; the lithium niobate waveguide comprises an input straight waveguide, an input taper, a first output taper, a second output taper, a first output straight waveguide and a second output straight waveguide, wherein the input taper, the first output taper and the second output taper form a coupling region, the input straight waveguide is connected to the input taper, the first output taper is connected to the first output taper, the second output taper is connected to the second output straight waveguide, the input taper is centrally arranged in the coupling region, the first output taper and the second output taper are located at the input taper, and the first output taper and the second output taper are located at the input taper. Gaps are left on both sides of the input taper and between the input taper, the lengths and thicknesses of the first output taper, the second output taper and the input taper are the same, and the end faces of the three are arranged flush. When the wavelength of the input light is in the range of 1480nm to 1640nm, the input light is in TE mode, and the output light is in TE mode; when the input light is in TM mode, the output light is in TM mode, thereby realizing the polarization-independent function. For this purpose, the angle between the side wall of the lithium nitrate waveguide and the silica substrate is set to 70°; the input light is input by the input straight waveguide, and is output from the first output straight waveguide and the second output straight waveguide after passing through the coupling region.

2. The Y-junction power divider based on LNOI material according to claim 1, characterized in that: The distances between the lower bases of the first output taper and the second output taper and the corresponding lower bases of the input taper are 120 nm to 160 nm.

3. The Y-junction power divider based on LNOI material according to claim 2, characterized in that: The distance between the lower base of the first output cone and the lower base of the input cone is called the first coupling gap, and the distance between the lower base of the input cone and the lower base of the second output cone is called the second coupling gap. The first coupling gap and the second coupling gap are both constant from the input side to the output side of the coupling region.

4. The Y-junction power divider based on LNOI material according to claim 1, characterized in that: The cross sections of the input straight waveguide, the input taper, the first output taper, the second output taper, the first output straight waveguide and the second output straight waveguide are all isosceles trapezoidal.

5. The Y-junction power divider based on LNOI material according to claim 1, characterized in that: The thickness of the lithium niobate waveguide is 0.3 μm and the thickness of the silicon dioxide substrate is 2 μm.

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