Ultra-low insertion loss electro-optic modulator and method based on continuous domain bound state waveguide

Abstract

The present invention discloses an ultra-low insertion loss electro-optic modulator based on a continuous domain bound state waveguide and a method thereof, wherein the electro-optic modulator comprises a ridge waveguide, a slab waveguide and a substrate in order from top to bottom; wherein the refractive index of the ridge waveguide is lower than that of the slab waveguide, so that the discrete state of the transverse magnetic mode TM is in the continuous domain of the transverse electric mode TE; the width of the ridge waveguide is adjusted w The transverse magnetic mode TM is completely decoupled from the transverse electric mode TE. w= 2nπ / k y , n is a positive integer, k y It is a wave vector perpendicular to the waveguide direction. The present invention can realize a low-loss BIC waveguide, make light propagate infinitely close to lossless, and greatly reduce the insertion loss of the modulation device.

Description

Technical Field

[0001] The present invention relates to the field of electro-optic modulators, and in particular to an ultra-low insertion loss electro-optic modulator based on a continuous domain bound state waveguide and a method thereof. Background Art

[0002] The rapid development of the information age has put forward higher requirements for on-chip highly integrated optical chips. As an important component unit in microwave photonics, electro-optic modulator chips need to develop in the direction of integration, high speed, low loss and low power consumption. Among them, electro-absorption modulator is a commonly used modulator type. Indium tin oxide (ITO) has a dielectric constant near zero (ENZ) characteristic in the 1550 nm communication band. It has great absorption of light under appropriate bias voltage and is an emerging electro-absorption modulator material. However, since the material itself has relatively strong absorption of light and will face mode leakage during propagation when forming a waveguide, the device insertion loss is relatively large, generally 0.01dB / μm~1dB / μm. In the face of optical chip applications for transmitting optical information, it is necessary to further reduce the insertion loss of ITO modulators.

[0003] Bound states in the continuum (BIC) refers to a discrete state that is in a continuous domain that radiates outward. By designing the structural parameters of the system to completely decouple the discrete state from the continuous domain, the discrete state can exist completely losslessly in the continuous domain. Since this concept was proposed, it has been confirmed in many fields such as solid elastic waves, sound waves, water waves, and light waves, but it has rarely been applied to electro-absorption modulators. The present invention aims to study the practical application of BIC waveguides in electro-absorption modulators. Summary of the invention

[0004] The main purpose of the present invention is to provide an ultra-low insertion loss electro-absorption modulator based on a continuous domain bound state waveguide and a design method.

[0005] The technical solution adopted by the present invention is:

[0006] Provided is an ultra-low insertion loss electro-optic modulator based on a continuous domain bound state waveguide, which includes a ridge waveguide, a slab waveguide and a substrate from top to bottom; wherein the refractive index of the ridge waveguide is lower than that of the slab waveguide, so that the discrete state of the transverse magnetic mode TM is in the continuous domain of the transverse electric mode TE; the width of the ridge waveguide is adjusted w The transverse magnetic mode TM is completely decoupled from the transverse electric mode TE. w = 2nπ / k y , n is a positive integer, k yis the wave vector perpendicular to the waveguide direction.

[0007] According to the above technical solution, the ridge waveguide includes a dielectric covering layer, an electrically adjustable absorption layer and an insulating layer from top to bottom.

[0008] According to the above technical solution, the widths of the dielectric cover layer, the electrically adjustable absorption layer and the insulating layer are equal.

[0009] According to the above technical solution, the material of the dielectric cover layer is organic glass, the material of the electrically adjustable absorption layer is indium tin oxide, and the material of the insulating layer is hafnium dioxide.

[0010] According to the above technical solution, the material of the planar waveguide is silicon.

[0011] According to the above technical solution, the material of the substrate is silicon dioxide.

[0012] According to the above technical solution, the electrically adjustable absorption layer is a transparent conductive layer, and under the condition of an applied voltage, a carrier gathering area is generated in its shallow surface layer.

[0013] According to the above technical solution, the electrically adjustable absorption layer is used as the cathode and the planar waveguide is used as the anode. The two and the insulating layer form a micro-capacitor structure, and the absorption rate of the electrically adjustable absorption layer is adjusted by an external voltage.

[0014] The present invention also provides an ultra-low insertion loss electro-optical modulation method based on a continuous domain bound state waveguide, comprising the following steps:

[0015] The refractive index of the ridge waveguide is set so that the discrete state of the transverse magnetic mode TM is in the continuous domain of the transverse electric mode TE;

[0016] The effective refractive index n of ridge waveguides with different widths is obtained by mode analysis using simulation software. eff , and calculate the insertion loss of ridge waveguides with different widths IL : ,in λ is the wavelength of light;

[0017] A graph depicting insertion loss;

[0018] According to the insertion loss curve, find the width of the ridge waveguide corresponding to the minimum insertion loss;

[0019] An ultra-low insertion loss electro-optic modulator is manufactured according to the width and refractive index of the ridge waveguide corresponding to the minimum insertion loss.

[0020] Following the above technical solution, the dielectric constant of the electrically adjustable absorption layer in the ridge waveguide is adjusted by applying an external voltage to produce a near-zero effect, so that the electromagnetic field is localized in the electrically adjustable absorption layer and is absorbed maximally by the electrically adjustable absorption layer.

[0021] The beneficial effects of the present invention are as follows: by setting the refractive index of the ridge waveguide in the electro-optic modulator to be lower than that of the substrate slab waveguide, the discrete state of the transverse magnetic mode TM is in the continuous domain of the transverse electric mode TE, and by optimizing the width of the ridge waveguide, the transverse magnetic mode TM is completely decoupled from the transverse electric mode TE, thereby realizing a low-loss BIC waveguide, making the light propagate infinitely close to lossless, and greatly reducing the insertion loss of the modulation device.

[0022] Furthermore, by adjusting the dielectric constant of the electrically adjustable absorption layer material to be close to zero, it is ensured that the electro-optical modulation device has a sufficiently large modulation extinction ratio, thereby obtaining an electrically adjustable absorption device with higher performance.

[0023] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 is a schematic structural diagram of a cross section of a modulator according to an embodiment of the present invention;

[0026] Figure 2 is the TM mode light field distribution in the cross section when the ridge waveguide width w is different in the present invention;

[0027] Figure 3 is a graph of insertion loss of a modulator under different ridge waveguide widths according to an embodiment of the present invention;

[0028] Figure 4 FIG. 1 is a cross-sectional light field distribution of an electro-optic modulation device in an on and off state according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] It should be noted that the diagrams provided in the embodiments of the present invention are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the diagrams only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout type may also be more complicated.

[0031] In the present invention, it is also necessary to explain that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, if the terms "first" and "second" appear, they are only used for description and distinction purposes, and cannot be understood as indicating or implying relative importance.

[0032] Example 1

[0033] like Figure 1 As shown, the ultra-low insertion loss electro-optic modulator based on the continuous domain bound state BIC in the embodiment of the present invention includes a ridge waveguide, a slab waveguide and a substrate from top to bottom. The ridge waveguide includes a dielectric cover layer, an electrically adjustable absorption layer and an insulating layer from top to bottom. The three layers have equal widths and together constitute the ridge waveguide of the electro-absorption modulator.

[0034] The dielectric covering layer may be made of organic glass PMMA, the electrically adjustable absorption layer may be made of indium tin oxide ITO, the insulating layer may be made of hafnium dioxide HfO2, the planar waveguide may be made of silicon Si, and the substrate material may be made of silicon dioxide SiO2.

[0035] By setting the refractive index of the ridge waveguide lower than that of the slab waveguide (Si), a continuous domain bound state BIC is generated in the waveguide, that is, the discrete state of the transverse magnetic mode TM is in the continuous domain of the transverse electric mode TE. By designing the width of the ridge waveguide, the phase of the TM mode field coupled from both sides of the ridge waveguide to the TE mode satisfies the coherent destructive phase, thereby achieving complete decoupling of the TM mode and the TE mode, and realizing ultra-low loss propagation of light in the ridge waveguide.

[0036] The propagation length of light in a waveguide can be approximately expressed as ,in w is the width of the waveguide, k y is the wave vector perpendicular to the waveguide direction. w = 2nπ / k y (n is a positive integer), sin 2 ( k y w / 2)→0, L→∞, the light can propagate an infinite distance, that is, propagation without insertion loss. In actual simulation, the BIC ridge waveguide width can be obtained by scanning the curve of the change of insertion loss with the ridge waveguide width. The specific method is: using COMSOL simulation software through mode analysis to obtain the effective refractive index n of ridge waveguides with different widths eff , the loss of the ridge waveguide can be expressed by the formula: Calculated, where λ is the wavelength of light. By scanning the ridge waveguide width and calculating the corresponding insertion loss value, the ridge waveguide width corresponding to the minimum insertion loss can be found, that is, the BIC waveguide width.

[0037] The refractive index of the dielectric cover layer is smaller than that of the planar waveguide, and the difference is large, which meets the BIC condition. The width of the ridge waveguide is designed to achieve ultra-low loss propagation of the light field. At the same time, in order to ensure that the applied voltage can efficiently adjust the absorption of the ridge waveguide, the commonly used transparent conductive layer ITO is selected in the present invention. Under the condition of applied voltage, the shallow layer (about 1 nanometer) of ITO will produce a carrier aggregation area. According to the Drude model calculation, the change in carrier concentration will cause the change of the dielectric constant of ITO. Under the appropriate voltage, the real part of its dielectric constant will approach zero, causing the electromagnetic field to be localized in ITO and strongly absorbed by ITO. Therefore, the present invention can use the ITO layer as the cathode, the Si planar waveguide as the anode, and the insulating layer HfO2 (as the dielectric layer) to form a micro-capacitor structure to achieve the regulation of the ITO absorption rate by the external voltage. This micro-capacitor structure is embedded between the dielectric cover layer and the substrate to form an ITO electro-absorption modulator based on the BIC waveguide.

[0038] Example 2

[0039] Preferably, in this embodiment, the dielectric cover layer is made of organic glass PMMA with a thickness of 300 nm, the electrically adjustable absorption layer is made of ITO with a thickness of 10 nm, the insulating layer is made of HfO2 with a thickness of 5 nm, the planar waveguide is made of Si with a thickness of 220 nm, the substrate is made of SiO2 with a thickness of 5 μm, the ridge waveguide width is 1.6 μm, and the initial carrier concentration of the electrically adjustable absorption layer is 1×10 19 cm -3 .

[0040] Furthermore, the electrically adjustable absorption layer serves as the negative electrode of the modulator, and the planar waveguide serves as the positive electrode of the modulator, which is connected to the external radio frequency signal through the GS probe.

[0041] like Figure 2 As shown, this embodiment simulates the TM mode distribution during the light field propagation process under different waveguide widths (the electric field intensity value in the figure is taken as a logarithm for the convenience of distinction). Figure 2In (a) and (c), when the waveguide width is 1μm and 2μm, there is a light field leaked from the ridge waveguide in the slab waveguide, and the propagation loss is large; Figure 2 In (b), when the waveguide width is 1.6 μm, the light is well confined near the ridge waveguide, there is no leakage mode, and the insertion loss is small. This embodiment obtains the propagation loss under different waveguide widths through mode analysis, such as Figure 3 As shown, it can be seen that when w = 1.6μm, the waveguide meets the BIC formation condition and the propagation loss is minimal, so it can achieve an insertion loss much lower than that of the traditional electro-absorption modulator.

[0042] When the waveguide width is 1.6 μm, the insertion loss of this embodiment is only 0.004 dB / μm.

[0043] To demonstrate the performance of electroabsorption modulator based on BIC waveguide, Figure 4 As shown in (a) and (b) in FIG. 1 , the cross-sectional light field of the modulator in the on state and the off state are simulated in this embodiment. There is a significant difference between the two states, and the electro-optic modulation extinction ratio can reach 0.361 dB / μm.

[0044] Specifically, the on state corresponds to an external bias voltage of 0 V, and the off state corresponds to an external bias voltage of 3 V.

[0045] Example 3

[0046] The present invention also provides an ultra-low insertion loss electro-optical modulation method based on a continuous domain bound state waveguide, comprising the following steps:

[0047] S1. Setting the refractive index of the ridge waveguide so that the discrete state of the transverse magnetic mode TM is in the continuous domain of the transverse electric mode TE;

[0048] S2. Use simulation software to analyze the mode to obtain the effective refractive index n of ridge waveguides with different widths. eff , and calculate the insertion loss of ridge waveguides with different widths IL : in λ is the wavelength of light;

[0049] S3, a graph depicting insertion loss;

[0050] S4. According to the insertion loss curve, find the width of the ridge waveguide corresponding to the minimum insertion loss;

[0051] S5. An ultra-low insertion loss electro-optic modulator is manufactured according to the width and refractive index of the ridge waveguide corresponding to the minimum insertion loss.

[0052] In accordance with the above technical solution, the method further includes the steps of: adjusting the dielectric constant of the electrically adjustable absorption layer in the ridge waveguide by applying an external voltage so that it produces a near-zero effect, localizing the electromagnetic field in the electrically adjustable absorption layer and being maximally absorbed by the electrically adjustable absorption layer.

[0053] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0054] The order of execution of each step in the above embodiment does not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0055] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. An ultra-low insertion loss electro-optic modulator based on a continuous domain bound state waveguide, characterized in that: From top to bottom, it includes ridge waveguide, slab waveguide and substrate. The refractive index of the ridge waveguide is lower than that of the slab waveguide, so that the discrete state of the transverse magnetic mode TM is in the continuous domain of the transverse electric mode TE. The width of the ridge waveguide is adjusted. w The transverse magnetic mode TM is completely decoupled from the transverse electric mode TE. w = 2nπ / k y , n is a positive integer, k y is the wave vector perpendicular to the waveguide direction; The ridge waveguide includes, from top to bottom, a dielectric covering layer, an electrically adjustable absorption layer and an insulating layer of equal width.

2. The ultra-low insertion loss electro-optic modulator based on continuous domain bound state waveguide according to claim 1, characterized in that: The material of the dielectric cover layer is organic glass, the material of the electrically adjustable absorption layer is indium tin oxide, and the material of the insulating layer is hafnium dioxide.

3. The ultra-low insertion loss electro-optic modulator based on continuous domain bound state waveguide according to claim 1, characterized in that: The material of the slab waveguide is silicon.

4. The ultra-low insertion loss electro-optic modulator based on continuous domain bound state waveguide according to claim 1, characterized in that: The material of the substrate is silicon dioxide.

5. The ultra-low insertion loss electro-optic modulator based on continuous domain bound state waveguide according to claim 1, characterized in that: The electrically adjustable absorption layer is a transparent conductive layer, and under the condition of applied voltage, a carrier gathering area is generated in its shallow surface layer.

6. The ultra-low insertion loss electro-optic modulator based on continuous domain bound state waveguide according to claim 1, characterized in that: The electrically adjustable absorption layer serves as the cathode and the planar waveguide serves as the anode. The two and the insulating layer form a micro-capacitor structure. The absorption rate of the electrically adjustable absorption layer is regulated by an external voltage.

7. An ultra-low insertion loss electro-optical modulation method based on continuous domain bound state waveguide, characterized in that: The following steps are involved: The refractive index of the ridge waveguide is set so that the discrete state of the transverse magnetic mode TM is in the continuous domain of the transverse electric mode TE; The effective refractive index n of ridge waveguides with different widths is obtained by mode analysis using simulation software. eff , and calculate the insertion loss of ridge waveguides with different widths IL : ,in λ is the wavelength of light; A graph depicting insertion loss; According to the insertion loss curve, find the width of the ridge waveguide corresponding to the minimum insertion loss; An ultra-low insertion loss electro-optic modulator is manufactured according to the width and refractive index of the ridge waveguide corresponding to the minimum insertion loss, wherein the ridge waveguide includes a dielectric covering layer, an electrically adjustable absorption layer and an insulating layer with equal width from top to bottom.

8. The ultra-low insertion loss electro-optic modulation method based on continuous domain bound state waveguide according to claim 7, characterized in that: The dielectric constant of the electrically tunable absorption layer in the ridge waveguide is adjusted by applying an external voltage, so that it produces a near-zero effect, localizing the electromagnetic field in the electrically tunable absorption layer and being absorbed maximally by the electrically tunable absorption layer.

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