阅读说明：本技术 一种光子晶体电光调制器及其制作方法 (Photonic crystal electro-optic modulator and manufacturing method thereof ) 是由 熊兵 刘学成 罗毅 孙长征 于 2020-07-22 设计创作，主要内容包括：本发明公开了一种光子晶体电光调制器及其制作方法,包括衬底、在衬底上通过溅射抬离或者电镀形成的电极、在电极与衬底上沉积形成的键合层、对键合层抛光处理后键合形成的电光材料薄膜、在电光材料薄膜上刻蚀形成的光子晶体线缺陷波导、以及填充于光子晶体线缺陷波导中除线缺陷两侧第一排空气孔以外的其余空气孔内的金属柱；位于线缺陷两侧的金属柱之间分别通过相应的电极实现电连接,且位于线缺陷两侧第一排空气孔的下方未设置电极和键合层。本发明可实现光波导区域调制电场的紧束缚,利用光子晶体的慢光效应增强电光相互作用以降低半波电压长度积,实现器件的小型化。采用周期容性负载电极来实现微波与光波的速度匹配,兼顾高频调制特性。(The invention discloses a photonic crystal electro-optic modulator and a manufacturing method thereof, and the photonic crystal electro-optic modulator comprises a substrate, an electrode formed on the substrate through sputtering lift-off or electroplating, a bonding layer formed by deposition on the electrode and the substrate, an electro-optic material film formed by bonding after polishing the bonding layer, a photonic crystal line defect waveguide formed by etching on the electro-optic material film, and metal columns filled in the rest air holes except for a first row of air holes at two sides of the line defect in the photonic crystal line defect waveguide; the metal columns on two sides of the line defect are electrically connected through corresponding electrodes respectively, and the electrodes and the bonding layers are not arranged below the first air exhaust holes on two sides of the line defect. The invention can realize the tight constraint of the modulation electric field of the optical waveguide area, enhance the electro-optic interaction by utilizing the slow light effect of the photonic crystal so as to reduce the half-wave voltage length product and realize the miniaturization of the device. The speed matching of the microwave and the optical wave is realized by adopting the periodic capacitive load electrode, and the high-frequency modulation characteristic is considered.)

1. A photonic crystal electro-optic modulator is characterized by comprising a substrate, electrodes, a bonding layer, an electro-optic material film, a photonic crystal line defect waveguide formed on the electro-optic material film through etching, and metal columns filled in the rest air holes except a first row of air holes at two sides of a line defect in the photonic crystal line defect waveguide; the metal columns on two sides of the line defect are electrically connected through the corresponding electrodes respectively, and the electrodes and the bonding layer are not arranged below the first air exhaust holes on two sides of the line defect.

2. The photonic crystal electro-optic modulator of claim 1, wherein the substrate is made of a material having a relative dielectric constant greater than 7.

3. The photonic crystal electro-optic modulator of claim 1, wherein the electrodes are formed on the substrate by sputtering lift-off or electroplating using a periodic capacitive loading electrode structure.

4. The photonic crystal electro-optic modulator of claim 1, wherein the electrodes comprise a signal electrode, a ground electrode and a T electrode arranged periodically; the signal electrode is positioned in the middle, the ground electrode is positioned on two sides of the signal electrode to form parallel push-pull loading of an electric field, the T electrodes which are periodically arranged are positioned in two electrode gaps formed by the signal electrode and the ground electrode, and the T electrodes are directly connected with the metal columns filled in the photonic crystal line defect waveguide.

5. The photonic crystal electro-optic modulator of claim 1, wherein the electrodes and metal posts have a conductivity greater than 10⁷S/m metal.

6. The photonic crystal electro-optic modulator of claim 1, wherein the bonding layer is deposited or spin coated on the substrate and the electrode and under the thin film of electro-optic material.

7. The photonic crystal electro-optic modulator of claim 1, wherein the thin film of electro-optic material is formed by polishing the bonding layer and then bonding electro-optic material to the bonding layer.

8. The photonic crystal electro-optic modulator of claim 1, wherein the photonic crystal line defect waveguide is a tetragonal W1 photonic crystal line defect waveguide.

9. The photonic crystal electro-optic modulator of claim 1, wherein the electro-optic material film is made of any one of lithium niobate, lithium tantalate, and barium titanate.

10. A method for fabricating a photonic crystal electro-optic modulator according to any one of claims 1 to 9, comprising the steps of:

(1) firstly, forming an electrode on a substrate by a sputtering lift-off or electroplating method, wherein the electrode is a periodic capacitive load electrode;

(2) depositing a bonding layer on the electrode and the substrate, and bonding the electro-optic material film on the bonding layer after polishing treatment;

(3) aligning and etching the electro-optic material film and the bonding layer to form a plurality of rows of air holes on two sides of the line defect in the photonic crystal line defect waveguide, and ensuring that the lower parts of the first rows of air holes on the two sides of the line defect are not covered by the electrode and the lower parts of the rest air holes are covered by the electrode;

(4) electroplating the residual air holes except the first row of air holes on the two sides of the line defect to realize metal filling to form a metal column;

(5) and removing the bonding layer below the first air exhaust holes on two sides of the line defect by using a buffer oxide etching solution.

Technical Field

The invention relates to a low half-wave voltage and broadband ultra-compact Mach-Zehnder electro-optic modulator, in particular to a photonic crystal electro-optic modulator and a manufacturing method thereof.

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, the transmission distance is limited due to the dispersion effect of the optical fiber, and the bandwidth of the internal modulation is 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.

In the currently reported thin-film lithium niobate modulator, the waveguide structure is a straight waveguide structure, and the electrodes are all parallel electric field loading realized by adopting common coplanar waveguide traveling wave electrodes with a G-S-G structure. The minimum value of the reported piezoelectric length product is 2.2V cm, the length of the device is in the order of cm, and the low half-wave voltage and the miniaturization of the device cannot be simultaneously met.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a photonic crystal electro-optic modulator and a preparation method thereof. The invention can realize the tight constraint of the modulation electric field of the optical waveguide area, and simultaneously further enhance the electro-optic interaction by utilizing the slow light effect of the photonic crystal, thereby reducing the length product of half-wave voltage and further realizing the miniaturization of the device. In the aspect of electrodes, a periodic capacitive load electrode structure is adopted to realize the speed matching of microwaves and optical waves and give consideration to high-frequency modulation characteristics. It is expected to realize low half-wave voltage and large modulation bandwidth on a device length within 1 mm.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a photonic crystal electro-optic modulator which is characterized by comprising a substrate, an electrode, a bonding layer, an electro-optic material film, a photonic crystal line defect waveguide formed on the electro-optic material film through etching, and metal columns filled in the rest air holes except for a first row of air holes at two sides of a line defect in the photonic crystal line defect waveguide; the metal columns on two sides of the line defect are electrically connected through the corresponding electrodes respectively, and the electrodes and the bonding layer are not arranged below the first air exhaust holes on two sides of the line defect.

The invention also provides a manufacturing method of the photonic crystal electro-optic modulator, which is characterized by comprising the following steps of:

(1) firstly, forming an electrode on a substrate by a sputtering lift-off or electroplating method, wherein the electrode is a periodic capacitive load electrode;

(2) depositing a bonding layer on the electrode and the substrate, and bonding the electro-optic material film on the bonding layer after polishing treatment;

(3) aligning and etching the electro-optic material film and the bonding layer to form a plurality of rows of air holes on two sides of the line defect in the photonic crystal line defect waveguide, and ensuring that the lower parts of the first rows of air holes on the two sides of the line defect are not covered by the electrode and the lower parts of the rest air holes are covered by the electrode;

(4) electroplating the residual air holes except the first row of air holes on the two sides of the line defect to realize metal filling to form a metal column;

(5) and removing the bonding layer below the first air exhaust holes on two sides of the line defect by using a buffer oxide etching solution.

The invention has the characteristics and beneficial effects that:

the invention is based on a film type electro-optic material system, typically a film of lithium niobate. The method is characterized in that a line defect photonic crystal waveguide is formed on thin-film lithium niobate through etching, then metals which are mutually and electrically connected are filled in air holes formed by partial etching, and a modulation electric field is tightly bound in a lithium niobate area, so that the electro-optic interaction is further enhanced, low half-wave voltage is realized on a very short device size, and the length of the device is reduced by one order of magnitude compared with the level reported in the existing literature. Meanwhile, the periodic capacitive load electrode on the high dielectric constant substrate is utilized to slow down the microwave so as to match with the optical group velocity to obtain large modulation bandwidth.

Drawings

Fig. 1 is a three-dimensional view of the overall structure of a photonic crystal electro-optic modulator according to an embodiment of the present invention.

Fig. 2 is a top view of the modulator of fig. 1.

Fig. 3 is a cross-sectional schematic diagram of the modulator shown in fig. 1.

Fig. 4 is a schematic diagram of the structure of the electrodes in the modulator of fig. 1.

Fig. 5 (a) - (d) are diagrams respectively illustrating the effect of increasing the electro-optical overlap factor caused by the tight confinement of the electric field by the metal filling in the modulator according to the embodiment of the present invention; the optical field distribution diagram is obtained by (a) adopting optical field distribution before metal filling for the square lattice air hole type photonic crystal waveguide, (b) adopting electric field distribution before metal filling for the square lattice air hole type photonic crystal waveguide, (c) adopting optical field distribution diagram of the square lattice metal filling photonic crystal waveguide, and (d) adopting electric field distribution diagram of the square lattice metal filling photonic crystal waveguide.

Fig. 6 is a three-dimensional view of the overall structure of an M-Z modulator comprised of the electro-optic modulator of fig. 1.

Fig. 7 is a top view of a metal-filled photonic crystal waveguide structure in the M-Z modulator of fig. 6.

Fig. 8 is a graph of the light transmission spectrum and slow group velocity of the light from the optical waveguide structure shown in fig. 2.

Fig. 9 (a) and (b) are schematic diagrams of the speed matching and the electro-optic frequency response of the microwave transmission line structure shown in fig. 4, respectively.

FIG. 10 is a schematic diagram of a modulator fabrication process according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the detailed description and specific examples, while indicating the scope of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

For better understanding of the present invention, the following detailed description describes an application example of a photonic crystal electro-optic modulator and a method for manufacturing the same.

The structure of a photonic crystal electro-optic modulator of the embodiment of the invention is shown in fig. 1-4, and the photonic crystal electro-optic modulator comprises a substrate 1, an electrode 2, a bonding layer 3, an electro-optic material film 4, a photonic crystal line defect waveguide 5 formed on the electro-optic material film 4 through etching, and metal columns 6 filled in the rest air holes of the photonic crystal line defect waveguide 5 except for a first row of air holes 52 at two sides of a line defect 51; the metal posts 6 on both sides of the line defect 51 are electrically connected to each other through corresponding electrodes 2 (the electrodes include three electrodes of a T electrode, a signal electrode and a ground electrode, and the T electrode is directly connected to the metal posts), and the electrodes 2 and the bonding layer 3 are located below the first air holes 52 on both sides of the line defect 51, see fig. 3, and air is located between the lower portions of the first air holes and the substrate 1.

The specific implementation and functions of the components in this embodiment are described as follows:

the substrate 1 is made of a high dielectric constant (relative dielectric constant greater than 7) material, such as silicon and lithium niobate, and is used for reducing the transmission speed of microwaves in the modulator to match the slow optical group velocity in the photonic crystal line defect waveguide 5, and plays a role in providing physical support for the rest of components in the modulator.

The electrode 2 adopts a periodic capacitive load electrode structure, the electrode 2 is formed on the substrate 1 by a sputtering lift-off or electroplating method, the effective refractive index of the microwave of the modulator can be further increased to be matched with the refractive index of the optical group, and therefore, the large modulation bandwidth is obtained. Referring to fig. 4, the electrode 2 specifically includes a signal electrode 22, a ground electrode 23, and T electrodes 21 arranged periodically; wherein, the signal electrode 22 is located in the middle, the ground electrode 23 is located at two sides of the signal electrode 22 to form parallel push-pull loading of an electric field, and the T electrodes 21 are periodically arrangedIn the two electrode gaps formed by the signal electrode 22 and the ground electrode 23, the T electrode 21 is directly connected to the metal pillar 6 filled in the photonic crystal line defect waveguide 5. The electrode 2 adopts high-conductivity metal (the conductivity is more than 10)⁷S/m metal), typically gold. The thickness of the electrode 2 is 100nm or more.

And the bonding layer 3 is arranged above the substrate 1 and the electrode 2 and below the electro-optical material film 4 in a deposition or spin coating mode. The bonding layer 3 can be benzocyclobutene (BCB) or silicon dioxide (SiO)₂) Or the like, preferably silicon dioxide in this embodiment, for bonding the thin film 4 of electro-optic material. The thickness of the bonding layer 3 between the electrode 2 and the film 4 of electro-optic material is 10nm-2000 nm.

The electro-optical material film 4 is formed by polishing the bonding layer 3 and then bonding the electro-optical material on the bonding layer 3. The electro-optical material is a material with electro-optical effect, and in this embodiment, lithium niobate, lithium tantalate or barium titanate is used. The typical lithium niobate thin film has a very high electro-optic coefficient, the electro-optic coefficient under the communication wavelength of 1550nm can reach 29pm/V, and the thin film technology is mature;

the photonic crystal line defect waveguide 5 is formed by etching on the thin film of electro-optic material 4. The photonic crystal line defect waveguide 5 is preferably a tetragonal lattice W1 photonic crystal line defect waveguide. The other air holes except the first air exhaust hole 52 on both sides of the line defect 51 are respectively filled with metal to form metal columns 6, the lower parts of the metal columns 6 on both sides of the line defect 51 are respectively contacted with the T electrodes to realize the electrical connection between the metal columns, namely, the metal columns on each side are respectively electrically conducted with the microwave transmission line signal electrode 22 or the ground electrode 23 through the T electrode 21, and the metal columns 6 adopt the conductivity more than 10⁷S/m metal. Because the optical field of the photonic crystal line defect waveguide 5 is mainly concentrated in the defect region and the first air exhaust hole region, the metal is filled in the residual air holes, so that the additional loss of the metal to light can be reduced to the maximum extent; in addition, as can be seen from the optical field and electric field distribution in the lithium niobate region shown in fig. 5, the air holes can tightly bind the electric field having the modulation effect in the region where the optical field is located after being filled with metal, which brings about smaller sizeThe electrode spacing and the larger electro-optic overlap factor can enhance the electro-optic interaction and reduce the half-wave voltage length product; another function of the photonic crystal line defect waveguide 5 is: the photonic crystal line defect waveguide 5 is a slow light waveguide, which can further enhance electro-optic interactions, according to document 1(Roussey M, Baida F I, Bernal MP. Experimental and the optical interference of the slow light effect on accessible photonic crystal [ J ]]The theoretical and experimental results in the Journal of the Optical Society of America B,2007,24(6): 1416-1422) show that the enhancement factors are:

wherein the content of the first and second substances,is the optical wave group velocity of the bulk material,is the optical wave group velocity in the slow wave waveguide, and f is the slow light enhancement factor of the photonic crystal waveguide.