阅读说明：本技术 慢波匹配结构薄膜型电光调制器 (Slow wave matching structure film type electro-optical modulator ) 是由 熊兵 刘学成 罗毅 孙长征 郝智彪 于 2020-04-08 设计创作，主要内容包括：本发明公开了一种慢波匹配结构薄膜型电光调制器,包括：Y分支输入波导、Y分支输出波导和光子晶体线缺陷波导组成的光波导结构以及渐变型周期容性负载电极组成的微波共面波导结构。其中,光子晶体线缺陷波导通过引入线缺陷限制处在禁带区域的光场,通过对光子晶体线缺陷波导的目标排光子晶体晶格施加目标位移,以调控光波群速度和/或获得宽谱慢光,并且增强电光相互作用以降低半波电压；渐变型周期容性负载电极用于减慢微波波速使之与光波群速度匹配从而获得大带宽,感性区到容性区的渐变结构用于降低微波反射,进一步提升高频特性。光波导结构由高介电常数绝缘体电光材料薄膜制得；渐变型周期容性负载电极结构采用高电导率金属材料制得。(The invention discloses a film type electro-optic modulator with a slow wave matching structure, which comprises: the microwave coplanar waveguide structure comprises an optical waveguide structure consisting of a Y-branch input waveguide, a Y-branch output waveguide and a photonic crystal line defect waveguide, and a microwave coplanar waveguide structure consisting of a graded period capacitive load electrode. The photonic crystal line defect waveguide limits an optical field in a forbidden band region through introducing line defects, applies target displacement to a target row photonic crystal lattice of the photonic crystal line defect waveguide to regulate and control the optical wave group speed and/or obtain wide-spectrum slow light, and enhances electro-optic interaction to reduce half-wave voltage; the gradual change type periodic capacitive load electrode is used for slowing down the microwave wave speed to enable the microwave wave speed to be matched with the light wave group speed, so that a large bandwidth is obtained, the gradual change structure from the inductive area to the capacitive area is used for reducing microwave reflection, and the high-frequency characteristic is further improved. The optical waveguide structure is made of a high-dielectric-constant insulator electro-optic material film; the gradual-change type periodic capacitive load electrode structure is made of a high-conductivity metal material.)

1. A thin film type electro-optic modulator of slow wave matching structure, comprising:

a Y-branch input waveguide and a Y-branch output waveguide;

the photonic crystal line defect waveguide is used for limiting an optical field in a forbidden band region through lead-in line defects and applying target displacement to a target row photonic crystal lattice of the photonic crystal line defect waveguide so as to regulate and control the optical wave group speed and/or obtain wide-spectrum slow light, wherein the Y-branch input waveguide, the Y-branch output waveguide and the photonic crystal line defect waveguide are all made of high-dielectric-constant insulator electro-optic material films.

2. The slow wave matching structure thin film type electro-optic modulator of claim 1, wherein the thin film of high dielectric constant insulator electro-optic material comprises: perovskite (ABO)₃) Form crystals, typically lithium niobate (L iNbO)₃) And lithium tantalate (L iTaO)₃) A crystal; crystals of the KDP type, typically monopotassium phosphate (KH2PO4) crystals; sphalerite type crystals.

3. The slow wave matching structure film type electro-optic modulator of claim 1 or 2, wherein the high dielectric constant microwave has a relative dielectric constant greater than 20.

4. The slow wave matching structure thin film type electro-optic modulator of claim 1, wherein the photonic crystal line defect waveguide is an air hole or dielectric hole type photonic crystal line defect waveguide.

5. The slow wave matching structure film type electro-optic modulator of claim 4, wherein said modulator employs a periodic capacitive loading electrode structure, wherein said periodic capacitive loading electrode structure gradually loads T-shaped electrodes according to slow wave requirements.

6. The slow wave matching structure thin film type electro-optic modulator of claim 5, wherein transition structures are added to the main electrode region and the T-shaped electrode region.

7. The slow wave matching structure thin film type electro-optic modulator of claim 5, wherein the transition structure employs a linear, an arc or a function curve satisfying a predetermined condition to perform an inductive-to-capacitive transition from a non-loaded region to a loaded region.

8. The slow wave matching structure thin film type electro-optic modulator of claim 1, further comprising: and the controller is used for adjusting the slow optical group speed by finely adjusting the working optical wavelength to match with the microwave phase speed close to the Bragg boundary, so that a larger modulator bandwidth is obtained.

Technical Field

The invention relates to the technical field of low half-wave voltage and ultrahigh-speed Mach-Zehnder electro-optic modulators, in particular to a slow-wave matching structure film type electro-optic modulator.

Background

Fiber optic communications is one of the major pillars of modern communications. With the explosive growth of data communication services, people put higher and higher requirements on communication bandwidth, and the single-wavelength bandwidth of the current optical fiber communication system is moving from 2.5Gb/s and 10Gb/s to higher bandwidth. Loading information onto the laser is divided into inner and outer modulations. The chirp caused by the internal modulation is large, its transmission distance is limited due to the dispersion effect of the fiber, and the modulation bandwidth is also not high. The external modulation mainly comprises an electro-absorption amplitude modulator and an electro-optic phase modulator, the electro-absorption modulator has large inherent loss, the modulator is easily saturated due to the shielding effect of a modulation electric field caused by a photon-generated carrier, and only amplitude change is difficult to apply to a high-level modulation format; the electro-optical modulator mainly comprises lithium niobate, organic polymers, semiconductors and the like, which cannot simultaneously meet the requirements of modern communication on large bandwidth, low half-wave voltage, low insertion loss, miniaturization and integration; the thin-film lithium niobate material is prepared by ion slicing and bonding processes, and has great potential in the aspect of electro-optical modulators.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.

Therefore, the invention aims to provide a thin-film type electro-optical modulator with a slow wave matching structure, which can realize large bandwidth while greatly increasing electro-optical interaction, is expected to realize low half-wave voltage and ultrahigh bandwidth on a very small device length, and is simple and easy to realize.

In order to achieve the above object, an embodiment of the present invention provides a thin film type electro-optical modulator with a slow wave matching structure, including: a Y-branch input waveguide and a Y-branch output waveguide; the photonic crystal line defect waveguide is used for limiting an optical field in a forbidden band region through lead-in line defects and applying target displacement to a target row photonic crystal lattice of the photonic crystal line defect waveguide so as to regulate and control the optical wave group speed and/or obtain wide-spectrum slow light, wherein the Y-branch input waveguide, the Y-branch output waveguide and the photonic crystal line defect waveguide are all made of high-dielectric-constant insulator electro-optic material films, such as thin-film lithium niobate typically.

The slow wave matching structure thin-film type electro-optic modulator provided by the embodiment of the invention is based on a thin-film lithium niobate/lithium tantalate material system, the speed matching of microwave slow waves and light wave slow waves is realized by utilizing a periodic capacitive load electrode and a slow wave optical waveguide structure, the electro-optic interaction is enhanced to reduce half-wave voltage, a graded periodic capacitive load electrode is used for slowing the microwave wave speed to match with the light wave group speed so as to obtain a large bandwidth, a graded structure from a sensitive area to a capacitive area is used for reducing microwave reflection, the high-frequency characteristic is further improved, the large bandwidth is realized while the electro-optic interaction is greatly increased, and finally the electro-optic modulator with the large bandwidth and the low half-wave voltage is obtained.

In addition, the slow-wave matching structure thin-film type electro-optical modulator according to the above embodiment of the present invention may further have the following additional technical features:

further, in one embodiment of the present invention, the high-k insulator electro-optic material film comprises: perovskite (ABO)₃) Form crystals, typically lithium niobate (L iNbO)₃) Crystal (relative dielectric constant 28) and lithium tantalate (L iTaO)₃) Crystal (relative permittivity 44); KDP type crystals, typically monopotassium phosphate (KH2PO4) crystals (relative dielectric constant 20); sphalerite type crystals.

Further, in one embodiment of the present invention, the high permittivity insulator electro-optic material film has a microwave relative permittivity greater than 20.

Further, in one embodiment of the present invention, the photonic crystal line defect waveguide is an air hole or dielectric hole type photonic crystal line defect waveguide.

Further, in an embodiment of the present invention, the modulator employs a periodic capacitive load electrode structure, wherein the periodic capacitive load electrode structure gradually loads the T-shaped electrode according to the requirement of slow wave.

Further, in an embodiment of the present invention, wherein a transition structure is added in the main electrode region and the T-shaped electrode region.

Further, in an embodiment of the present invention, the transition structure adopts a linear, an arc or a function curve satisfying a preset condition to perform inductive-to-capacitive transition from the non-loading region to the loading region.

Further, in an embodiment of the present invention, the method further includes: and the controller is used for adjusting the slow optical group speed by finely adjusting the working optical wavelength to match with the microwave phase speed close to the Bragg boundary, so that a larger modulator bandwidth is obtained.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic diagram of a slow-wave matching structure thin-film type electro-optic modulator according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a G-S-G electrode structure according to an embodiment of the invention;

FIG. 3 is a diagram illustrating the effect of a novel gradual change structure according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a slow-wave matching structure thin-film type electro-optic modulator according to a first embodiment of the present invention;

FIG. 5 is a diagram showing a dispersion curve and a broad-spectrum slow light region of a photonic crystal waveguide according to a first embodiment of the present invention;

FIG. 6 is a graph of the effective refractive index curve and the normalized frequency response obtained under the optimized parameters of the slow-wave electrode according to the first embodiment of the present invention;

FIG. 7 is a schematic structural diagram of a slow-wave matching structure thin-film type electro-optic modulator according to a second embodiment of the present invention;

FIG. 8 is a diagram showing a dispersion curve and a broad-spectrum slow light region of a photonic crystal waveguide according to a second embodiment of the present invention;

FIG. 9 is a graph of the effective refractive index curve and the normalized frequency response obtained under the optimized parameters of the slow-wave electrode according to the first embodiment of the present invention;

FIG. 10 is a diagram illustrating a waveguide structure replaced with a grating waveguide slow wave structure according to a third embodiment of the present invention;

fig. 11 is a diagram illustrating a waveguide structure replaced with a curved waveguide slow wave structure according to a fourth embodiment of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

The present application is based on the recognition and discovery by the inventors of the following problems:

according to the description of the background art, the theoretical limit of performance of the thin-film lithium niobate modulator reported at present exists, and aiming at the problem, the embodiment of the invention adopts a method for matching an optical wave slow-wave structure and a microwave slow-wave structure, provides the slow-wave matching structure electro-optical modulator based on the thin-film lithium niobate, and is expected to realize low half-wave voltage and ultrahigh bandwidth on a very small device length.

The embodiment of the invention adopts an optical slow wave waveguide structure and aims to: the optical slow wave structure can enhance the electro-optic effect by the enhancement factor ofWhereinIs the optical wave group velocity of the bulk material,is the optical group velocity in the slow wave waveguide.

However, the currently reported photonic crystal electro-optic modulator generally uses silicon-based materials and adopts a lumped electrode structure, and the bandwidth of the photonic crystal electro-optic modulator is limited by the optical wave transit time and the RC time constant, so that the requirement of large bandwidth cannot be met. The embodiment of the invention adopts a thin-film lithium niobate/lithium tantalate platform and uses a traveling wave electrode structure. It has the advantages that: the electro-optic coefficient of the lithium niobate is very high and can reach 29pm/v under the communication wavelength of 1550 nm; secondly, the microwave dielectric constant of lithium niobate is very high (28), and the matching of the microwave and the light wave slow wave speed is easily realized by matching with a periodic capacitive load electrode; the adoption of the thin-film lithium niobate material is easy to manufacture slow-wave structures such as photonic crystal line defect waveguides and the like, and the limitation to light is enhanced; and lithium niobate is an insulator, and the periodic capacitive load electrode structure manufactured on the lithium niobate does not need to be electrically isolated between load electrodes.

A slow wave matching structure thin film type electro-optical modulator proposed according to an embodiment of the present invention is described below with reference to the accompanying drawings.

Fig. 1 is a schematic structural diagram of a slow-wave matching structure thin-film type electro-optic modulator according to an embodiment of the present invention.

As shown in fig. 1, the slow wave matching structure thin film type electro-optical modulator includes: y-branch input waveguide, Y-branch output waveguide and photonic crystal line defect waveguide.

The photonic crystal line defect waveguide is used for limiting an optical field in a forbidden band region through introducing line defects, and applying target displacement to a target row photonic crystal lattice of the photonic crystal line defect waveguide to regulate and control the optical wave group speed and/or obtain wide-spectrum slow light (slow light group refractive index n)_g>Bulk material optical group refractive index n_bulk) And the Y-branch input waveguide, the Y-branch output waveguide and the photonic crystal line defect waveguide are all made of insulator electro-optic material films with high dielectric constants (the microwave relative dielectric constant is more than 20). Hair brushThe modulator of the embodiment of the invention can realize large bandwidth while greatly increasing electro-optical interaction, is expected to realize low half-wave voltage and ultrahigh bandwidth on very small device length, and is simple and easy to realize.

It can be understood that the modulator of the embodiment of the invention comprises an optical waveguide structure consisting of a Y-branch input waveguide, a Y-branch output waveguide and a photonic crystal line defect waveguide, and a microwave coplanar waveguide structure consisting of a graded-period capacitive load electrode. The photonic crystal line defect waveguide limits an optical field in a forbidden band region through introducing line defects, and applies target displacement to a target row photonic crystal lattice of the photonic crystal line defect waveguide to regulate and control the optical wave group speed and/or obtain wide-spectrum slow light and enhance electro-optic interaction to reduce half-wave voltage; the gradual change type periodic capacitive load electrode is used for slowing down the microwave wave speed to enable the microwave wave speed to be matched with the light wave group speed, so that a large bandwidth is obtained, the gradual change structure from the inductive area to the capacitive area is used for reducing microwave reflection, and the high-frequency characteristic is further improved. The Y-branch input waveguide, the Y-branch output waveguide and the photonic crystal line defect waveguide are all made of high-dielectric-constant insulator electro-optic material films; the gradual-change type periodic capacitive load electrode structure is made of a high-conductivity metal material.

Wherein the high dielectric constant insulator electro-optic material film mainly comprises: perovskite (ABO)₃) Form crystals, typically lithium niobate (L iNbO)₃) Crystal (relative dielectric constant 28) and lithium tantalate (L iTaO)₃) Crystal (relative permittivity 44); KDP type crystals, typically monopotassium phosphate (KH2PO4) crystals (relative dielectric constant 20); sphalerite type crystals.

Specifically, as shown in fig. 1, fig. 1(a) is a top view of the overall structure of the device, and mainly includes the following parts: y branch input waveguide, Y branch output waveguide and photonic crystal line defect waveguide, and these optical waveguide structures are based on lithium niobate/lithium tantalate film material system. The photonic crystal line defect waveguide adopts an air hole type photonic crystal, and the optical field in a forbidden band region is limited by introducing line defects. Wherein the air holes may be filled with a low dielectric constant material such as silicon dioxide. By aligning the n-th row photonic crystal latticeApplying a displacement X_nThe method can regulate and control the group velocity of the optical waves and obtain the broad-spectrum slow light.

Further, in an embodiment of the present invention, the modulator employs a periodic capacitive load electrode structure, wherein the periodic capacitive load electrode structure gradually loads the T-type electrode according to the requirement of slow waves, transition structures are added in the main electrode region and the T-type electrode region, and the transition structures employ linear, arc or function curves meeting preset conditions to perform inductive-to-capacitive transition from the non-loading region to the loading region.

Specifically, the electrode structure adopts a G-S-G electrode parallel push-pull form, and is different from the traditional G-S-G electrode structure such as a figure 2(a), the invention adopts a novel periodic capacitive load electrode structure, and the periodic capacitive load electrode structure figure 2(b) refers to: the T-shaped electrode is periodically loaded on the basis of the traditional G-S-G electrode structure, when the distance between a signal line and a ground wire is larger, better electric field loading is realized due to the T-shaped electrode, meanwhile, the conduction current along the transmission line is reduced, and the microwave loss is reduced. And the periodic capacitive load electrode structure can realize microwave slow wave transmission so as to realize the matching with the optical wave group velocity.

However, as the wave velocity is reduced, the reflection of the conventional capacitive load electrode increases, which greatly affects the high-frequency characteristics of the device. The reflection of the slow wave is mainly from the impedance mismatch between a loaded area and an unloaded area, and therefore, a periodic capacitive load electrode structure diagram 2(c) of a gradually-changing loaded T-shaped electrode is designed to meet the requirement of the scheme of the embodiment of the slow wave. The obtained effect is shown in fig. 3, and the embodiment of the invention adopts a novel gradual change structure to reduce the electrode reflection by more than 10 dB.

Further, in an embodiment of the present invention, the modulator of the embodiment of the present invention further includes: and a controller. The controller adjusts the slow optical group speed by finely adjusting the working optical wavelength to match with the microwave phase speed close to the Bragg boundary, so that larger modulator bandwidth is obtained.

Specifically, in order to obtain a further microwave slow wave, the embodiment of the present invention utilizes the characteristic that the refractive index of the microwave is increased near the microwave bragg frequency, and performs the velocity matching between the optical wave and the microwave in the region near the microwave bragg frequency, thereby further increasing the bandwidth of the device.

The slow-wave matching structure thin-film type electro-optic modulator will be further described by the following specific embodiments.