阅读说明：本技术 一种新型3um中红外波段基于狭缝波导偏振无关石墨烯电光调制器结构 (Novel 3um intermediate infrared band is based on slit waveguide polarization irrelevant graphite alkene electro-optic modulator structure ) 是由 陆荣国 林瑞 沈黎明 于 2021-01-12 设计创作，主要内容包括：本发明公开了一种新型3um中红外波段基于狭缝波导偏振无关石墨烯电光调制器结构,该器件包含两部分结构,模式转换结构及狭缝波导调制器结构。其中模式转换结构包括一个宽度逐渐变大的锥形波导结构,实现TM0到TE1模式的转换,以及一个非对称波导耦合器,实现TE1到TE0模式的转换。本发明可以通过一个模式转换结构将TM模式转换为TE模式,从而实现对光波的偏振无关调制,有效的解决了目前石墨烯光调制器对入射光波偏振方向敏感的技术难题,且本发明中的狭缝波导结构相比于传统条形波导结构具有更强的聚光作用及更短的器件尺寸,在制备工艺方面更容易实现,易于集成,并具有调制速率高、功耗低的优点。(The invention discloses a novel 3um intermediate infrared band graphene electro-optic modulator structure based on slit waveguide polarization independence. The mode conversion structure comprises a tapered waveguide structure with gradually-increased width, and realizes the conversion from TM0 to TE1 mode, and an asymmetric waveguide coupler realizes the conversion from TE1 to TE0 mode. The invention can convert TM mode into TE mode through a mode conversion structure, thereby realizing polarization-independent modulation of light wave, effectively solving the technical problem that the existing graphene light modulator is sensitive to the polarization direction of incident light wave, and compared with the traditional strip waveguide structure, the slit waveguide structure has stronger light-gathering function and shorter device size, is easier to realize in the aspect of preparation process, is easy to integrate, and has the advantages of high modulation rate and low power consumption.)

1. A novel 3um mid-infrared band polarization-independent graphene-based electro-optic modulator structure is shown in a schematic diagram of a three-dimensional structure in fig. 1 (c). The device consists of two parts, a slit waveguide modulator structure of fig. 1(a) and a mode conversion structure of fig. 1 (b). Wherein the slit waveguide modulator comprises an optical waveguide substrate layer (1), an optical waveguide wrapping layer (2), two groups of slit waveguides (3) and (4) are arranged on the optical waveguide substrate layer (1), slit layers (5) and (6) are arranged, the upper surface and the lower surface of each slit waveguide (3) (4) are respectively covered by a first graphene layer (7), a second graphene layer (8), a third graphene layer (9) and a fourth graphene layer (10), an isolation layer (11) is arranged between the first graphene layer (7) and the second graphene layer (8), an isolation layer (12) is arranged between the third graphene layer (9) and the fourth graphene layer (10), the first graphene layer (7) and the fourth graphene layer (10) extend out from one side of the upper surface and the lower surface of each slit waveguide and are connected with a first electrode (13), the second graphene layer (8) and the third graphene layer (9) extend out from the other side of the upper surface and the lower surface of each slit ). The mode conversion structure comprises a tapered waveguide structure (15), an asymmetric waveguide coupler structure (16), waveguide arms 1(17), waveguide arms 2(18) and a modulator top view structure (19).

2. The novel 3um mid-infrared band polarization-independent graphene-based electro-optic modulator structure according to claim 1 is characterized by comprising a mode conversion structure and a slit waveguide structure modulator with stronger light gathering capacity, and has better modulation capacity for mid-infrared bands.

3. The novel 3um mid-infrared band polarization-independent graphene-based electro-optic modulator structure according to claim 1, wherein the thickness of the isolation dielectric layers (11), (12) is 20 nm.

4. The novel 3um mid-infrared band polarization-independent graphene-based electro-optic modulator structure according to claim 1, wherein the slit waveguides (3) and (4), the tapered waveguide structure (15), and the asymmetric waveguide coupling structure (16) are made of chalcogenide glass materials with stronger absorption capability for mid-infrared band.

5. The novel 3um mid-infrared band polarization-independent graphene-based electro-optic modulator structure according to claim 1, wherein the isolation dielectric layers (11), (12) are made of an insulating material, and the insulating material is silicon oxide, silicon oxynitride or boron nitride.

6. The structure of the novel inverted ridge type polarization-independent graphene electro-optic modulator according to claim 1, wherein the first electrode (13) and the second electrode (14) are made of any one or an alloy of any two or more of gold, silver, copper, platinum, titanium, nickel, cobalt and palladium.

Technical Field

The invention relates to an electro-optical modulator, belongs to the technical field of photoelectrons, and particularly relates to a novel 3um intermediate infrared band graphene electro-optical modulator structure based on slit waveguide polarization independence.

Background

Optical modulatorThe module is a module which converts an electric signal into an optical signal and transmits the optical signal into an optical fiber for transmission, and is one of key devices in an optical fiber communication system. The optical fiber has wide application in the fields of short pulse generation, signal demultiplexing, data coding, optical interconnection, wavelength switching, optical add-drop multiplexing and the like, is one of core devices of a future high-speed optical communication system, and has extremely wide application space. Graphene is a honeycomb-shaped two-dimensional hexagonal carbon structure material, is a novel material, has unique and excellent optoelectronic characteristics, and is considered to be an ideal substitute of a traditional semiconductor material in the future. Graphene has 20,000cm at room temperature²The carrier mobility of/Vs, which is about 100 times or more the carrier mobility of silicon material, means that graphene-based electronic devices can operate at ultra high speeds. Under an applied voltage, the photoconductivity of the graphene also changes, so that the refractive index and the absorptivity of the graphene are changed, and meanwhile, the graphene has a zero band gap structure, so that the graphene can play a role in a very wide optical wavelength range. In addition, in the aspect of process, the graphene is compatible with the traditional CMOS process and is easy to integrate. Due to these excellent properties of graphene, graphene materials are considered to have potentially important applications in optoelectronic devices.

Optical modulators based on graphene materials have been extensively studied at present, and most of them are based on the conventional SOI optical waveguide structure, in which a graphene layer is laid on the surface of a waveguide, and a bias voltage is applied to a graphene sheet to change the fermi level of the graphene material itself so as to change the refractive index and absorption rate of the waveguide to incident light, thereby achieving modulation of the phase and amplitude of the incident light (see documents Ming Liu, xiaoo Yin, Ulin-Avila, et al. However, the existing electro-optical modulators based on graphene materials all have a common defect that the electro-optical modulators are polarization-related, i.e., sensitive to the polarization direction of incident light, and only capable of effectively modulating light waves in a specific direction, but not obvious in modulation effect on light waves in other polarization directions, so that the application range of the electro-optical modulator is limited.

Graphene-based polarization-independent electro-optic modulators have been reported, for example, the invention patent with application number 201410370459.0 discloses a graphene-based polarization-independent optical modulator: the substrate, the first graphite alkene ridge waveguide of graphite alkene level embedding, the second graphite alkene ridge waveguide of graphite alkene perpendicular embedding, first graphite alkene ridge waveguide and second graphite alkene ridge waveguide all are located the substrate, and the graphite alkene layer mutually perpendicular of embedding in the graphite alkene layer of first graphite alkene ridge waveguide embedding and the second graphite alkene ridge waveguide.

Just like the structure, one section of optical waveguide simultaneously contains one section of horizontally embedded graphene layer and one section of vertically embedded graphene layer, and the requirement on the aspect of the process is higher, and the realization is difficult.

Also, for example, the invention patent with application number 201510469011.9 discloses a polarization insensitive modulator based on arc graphene, which comprises an optical waveguide substrate layer, a dielectric layer arranged above the optical waveguide substrate layer, a D-shaped waveguide layer arranged above the dielectric layer, a second arc graphene layer coated on the periphery of the D-shaped waveguide layer, a first arc graphene layer coated on the periphery of the second arc graphene layer, a rectangular waveguide layer coated on the periphery of the first arc graphene layer, a rectangular waveguide layer and a first arc graphene layer, all be provided with between first arc graphite alkene layer and the second arc graphite alkene layer and between second arc graphite alkene layer and the D shape wave guide layer and keep apart the dielectric layer, first arc graphite alkene layer extends and is connected with first electrode from one side of D shape wave guide, and second arc graphite alkene layer extends and is connected with the second electrode from the opposite side of D shape wave guide.

As mentioned above, the D-shaped waveguide structure has a great difficulty in implementing the D-shaped waveguide manufacturing process to achieve a good polarization independent modulation effect.

As mentioned above, the problems of the conventional electro-optical modulator based on graphene are all problems that those skilled in the art need to solve.

Disclosure of Invention

The invention overcomes the defects of the prior art, provides a novel 3um intermediate infrared band graphene electro-optic modulator structure based on slit waveguide polarization independence, solves the problems that the conventional graphene electro-optic modulator is difficult to realize in the preparation process and sensitive to the polarization direction of incident light waves, and can obtain a more compact device size due to better light condensation effect of the slit waveguide. In order to solve the technical problems, the invention adopts the following technical scheme:

a novel 3um intermediate infrared band polarization-independent graphene electro-optic modulator structure based on a slit waveguide is composed of two parts, wherein one part is a mode conversion structure and comprises a tapered waveguide and a non-stacked waveguide coupler; the other part is a slit waveguide modulator, including the optical waveguide stratum basale, is provided with a set of slit waveguide on the optical waveguide stratum basale, and the upper and lower surface of slit waveguide covers respectively by first, second, third and fourth graphite alkene layer, first and second graphite alkene layer, is provided with the isolation dielectric layer between third and the fourth graphite alkene layer respectively, first, fourth graphite alkene layer extend from one side of slit waveguide upper and lower surface and be connected with first electrode, second, third graphite alkene layer extend from slit waveguide upper and lower surface opposite side and be connected with the second electrode.

As a first optimization scheme of the invention, the slit distance in the slit waveguide is 60 nm.

As a second optimization scheme of the invention, the thickness of the isolation dielectric layer is 20 nm.

As a third optimization scheme of the invention, the material of the waveguide in the slit waveguide and the mode conversion structure is the same, and the material is a chalcogenide glass material which has better absorption effect on the mid-infrared waveguide. .

As a fourth optimized solution of the present invention, the isolation dielectric layer is made of an insulating material, and the insulating material is silicon oxide, silicon oxynitride, or boron nitride.

In a fifth preferred embodiment of the present invention, the first electrode and the second electrode are made of any one or an alloy of any two or more of gold, silver, copper, platinum, titanium, nickel, cobalt, and palladium.

Compared with the prior art, the invention has the beneficial effects that:

1. the mode conversion structure provided by the invention can realize conversion from a TM mode to a TE mode, and realize modulation on the TE mode in the modulation area, thereby realizing modulation irrelevant to light wave polarization and effectively solving the technical problem that the existing graphene light modulator is sensitive to the polarization direction of incident light waves.

2. Compared with the traditional strip waveguide, the slit waveguide has better light-gathering effect, can reduce the size of a device on the premise of obtaining larger extinction ratio (the traditional strip waveguide obtains the extinction ratio higher than 25dB under the condition that the size is 300um, and the slit waveguide obtains the extinction ratio higher than 30dB under the condition that the size is 200 um), and is easy to realize in the aspect of preparation process.

3. The polarization-independent electro-optic modulator can be compatible with the traditional SOI and CMOS processes in the preparation process, is easy to integrate, and has the advantages of high modulation rate and low power consumption.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1(a) is a schematic diagram of the mode conversion structure of the device of the present invention; (b) is a cross section structure diagram of the device slit waveguide modulator; (c) is a schematic three-dimensional structure of the device of the present invention.

FIG. 2(a) is a schematic diagram of the conversion efficiency of a tapered waveguide in a mode conversion structure of a device of the present invention; (b) is a schematic diagram of the conversion efficiency of the asymmetric waveguide coupler in the mode conversion structure of the device.

FIG. 3 shows the variation of the absorption of the graphene to TE and TM modes with the applied voltage in the slot waveguide modulator of the device of the present invention.

FIG. 4 shows the wavelength dependence of the transmittance and the transmittance difference in the TE and TM modes of the device of the present invention in the "ON" and "OFF" states.

The labels in the figures are: 1-an optical waveguide substrate layer; 2-optical waveguide cladding layer; 3 slit waveguide-; 4-a slit waveguide; 5-a slit layer; 6-a slit layer; 7-a first graphene layer; 8-a second graphene layer; 9-a third graphene layer; 10-a fourth graphene layer; 11-an isolation layer; 12-an isolation layer; 13-a first electrode; 14-a second electrode; 15-tapered waveguide structures; 16-asymmetric waveguide coupler structure.

Detailed Description

The present invention will be further described with reference to the following drawings, and embodiments of the present invention include, but are not limited to, the following examples.

Examples

As shown in fig. 1, a novel 3um mid-infrared band polarization-independent graphene-based electro-optic modulator structure is composed of two parts, i.e., a slit waveguide modulator structure in fig. 1(a) and a mode conversion structure in fig. 1 (b). Wherein the slit waveguide modulator comprises an optical waveguide substrate layer (1), a group of slit waveguides (3) and (4) are arranged in the optical waveguide substrate layer (1), the upper surface and the lower surface of each slit waveguide (3) (4) are respectively covered with a first graphene layer (7), a second graphene layer (8), a third graphene layer (9) and a fourth graphene layer (10), an isolation layer (11) is arranged between the first graphene layer (7) and the second graphene layer (8), an isolation layer (12) is arranged between the third graphene layer (9) and the fourth graphene layer (10), the first graphene layer (7) and the fourth graphene layer (10) extend out from one side of the upper surface and the lower surface of the slit optical waveguide and are connected with a first electrode (13), the second graphene layer (8) and the third graphene layer (9) extend out from the other side of the upper surface and the lower surface of the slit waveguide and are connected with a second electrode (14). The mode conversion structure comprises a tapered waveguide structure (15), an asymmetric waveguide coupler structure (16), two waveguide arms 1(17) and two waveguide arms 2(18), wherein one slit waveguide is correspondingly connected with each waveguide arm, and a modulator overlooking structure (19).

A novel 3um mid-infrared band based on slit waveguide polarization does not have a relation graphite alkene electro-optic modulator structure, its characterized in that comprises a mode conversion structure and a slit waveguide structure modulator that spotlight ability is stronger, and has better modulation ability to the mid-infrared band.

The width of the slit layers (5) and (6) is 60 nm.

The thicknesses of the isolation dielectric layers (11) and (12) are 20 nm.

The narrow-slit waveguides (3) and (4), the tapered waveguide structure (15) and the asymmetric waveguide coupling structure (16) are made of chalcogenide glass materials with stronger absorption capacity for the middle infrared band.

The isolation medium layers (11) and (12) are made of insulating materials, and the insulating materials are silicon oxide, silicon oxynitride or boron nitride.

The first electrode (13) and the second electrode (14) are made of any one or more than two of gold, silver, copper, platinum, titanium, nickel, cobalt and palladium.

The working principle of the optical modulator of the invention is as follows: when incident light passes through the mode conversion structure, the tapered waveguide structure converts a TM0 mode into a TE1 mode, and then converts a TE1 mode into a TE0 mode through an asymmetric waveguide coupling structure, in the process, the TE0 mode of the incident light is not influenced by the mode conversion structure, so that the incident TE0 and TM0 modes are converted into the TE0 mode through the mode conversion structure and then enter a modulation region through two waveguide arms, and each waveguide arm is correspondingly connected with one slit waveguide. When the slit waveguide optical modulator works, a bias voltage is added on the first graphene layer 7, the second graphene layer 8, the third graphene layer 9 and the fourth graphene layer 10 through electrodes, and the dielectric coefficients of the first graphene layer 7, the second graphene layer 8, the third graphene layer 9 and the fourth graphene layer 10 are dynamically tuned by changing the bias voltage, so that the change of the effective real part and the imaginary part of the transmission mode in the optical waveguide is influenced. The real part of the effective index corresponds to the change in the phase of the light and the imaginary part corresponds to the absorption of the light. Since graphene is a two-dimensional material and only optical signals tangential to the surface of graphene generate strong interaction, the graphene in the structure modulator has stronger absorption capacity for the TE0 mode, which is also consistent with our operation of converting both TE0 and TM0 modes into TE0 mode through a mode conversion structure before modulation. When the bias voltage is changed to another specific value, the optical loss of the TE mode becomes larger, so that the TE mode light is absorbed and the optical signal cannot pass through. Therefore, a voltage bias point can be tuned, polarization-independent modulation of an optical signal is realized, and high-speed light wave modulation can be realized due to the ultrahigh carrier mobility of the graphene.

The invention is further illustrated below with reference to specific experimental data:

as shown in fig. 1, the intermediate infrared light wave with a wavelength of 3um is used, the materials of the slit waveguide and the waveguide in the mode conversion structure are chalcogenide glass, the optical refractive index of the chalcogenide glass is 2.7796, the size of each of two parts forming the slit waveguide is 720nm x 500nm, and the distance between the slits is 60 nm. The optical waveguide substrate layer, the wrapping layer and the slit layer are made of SiO2 (optical refractive index is 1.444), and the isolation medium layers 8 and 9 are made of hexagonal boron nitride hBN material (optical refractive index is 1.98) with the thickness of 20nm to isolate the first graphene layer 7 from the second graphene layer 8, and to isolate the third graphene layer 9 from the fourth graphene layer 10. The first electrode 13 and the second electrode 14 are made of palladium metal, and a layer of gold is plated on the palladium metal.

Fig. 2 is a schematic diagram of the conversion efficiency and the mode conversion electric field of the mode conversion structure of the optical modulator according to the embodiment of the present invention, and to achieve the highest conversion efficiency, we analyze the influence of the tapered waveguide length and the asymmetric waveguide coupling length on the mode conversion efficiency, respectively, and can find that when the asymmetric waveguide coupling length is 50um, the mode conversion efficiency is close to 0.98; for the tapered waveguide we divide it into three parts and by analysis we find that the largest impact on the conversion efficiency is the second part, which is higher than 0.9 when the three parts are 10um, 40um, 10um in size.

FIG. 3 is a schematic diagram of absorption for TE and TM modes in an optical modulator optical waveguide as a function of applied voltage according to an embodiment of the present invention. It is evident from the figure that the absorption of the TE mode is larger than that of the TM mode, so we use the principle of converting the TM mode into the TE mode to achieve polarization independent modulation. When the applied voltage is 0.1eV, the absorption of the TE mode reaches a peak value, and at this time, the optical waveguide has a strong absorption effect on the TE mode, so that an optical signal cannot pass through the TE mode, and the TE mode can be used as an OFF state point of the modulator. When the applied voltage is 0.8eV, the absorption of TE mode in the waveguide approaches the lowest value and changes smoothly, and at this time, the absorption of light by the waveguide is very weak, so that the optical signal can pass through and can be used as the 'ON' state point of the modulator.

FIG. 4 is a graph illustrating the normalized transmittance of the TE and TM modes in the waveguide as a function of wavelength for the TE and TM modes at the ON and OFF state points in the optical waveguide of an optical modulator according to an embodiment of the present invention. It can be seen from fig. 3 that in the wavelength range of 2.95um to 3.05um, the variation curves of the normalized transmittance in TE and TM modes are almost consistent when in the "ON" and "OFF" states, respectively, i.e. polarization-independent modulation is achieved, and the extinction ratio is greater than 30 dB.

Simulation calculation results show that the extinction ratio of the 20 um-length optical modulator to TE and TM modes is larger than 35dB, and the modulation bandwidth of the 3dB structured optical modulator is higher than 10 GHz.

The above description is an embodiment of the present invention. The foregoing is a preferred embodiment of the present invention, and the preferred embodiments in each preferred embodiment can be combined and used in any combination if not contradictory or prerequisite to a certain preferred embodiment, and the specific parameters in the embodiments and examples are only for the purpose of clearly illustrating the inventor's invention verification process and are not intended to limit the patent protection scope of the present invention, which is to be determined by the claims and the equivalent structural changes made by the contents of the description and the drawings of the present invention are also included in the protection scope of the present invention.