Hybrid integration of two-dimensional materials for photonic devices

Hybrid integration of two-dimensional (2D) materials on photonic integrated circuits (PICs) open a new avenue for integrated photonics because they offer additional functionality beyond those available with the native PIC platform, typically silicon nitride or silicon. For example, the unique properties of 2D materials like layer-tunable bandgap, high optical nonlinearity, direct band light emission, optical modulation, saturable absorption, can be harnessed for functions in PICs. This thesis focuses on the hybrid integration of 2D materials with PICs for optoelectronic applications. The development status of hybrid integrated 2D materials-based photodetectors and modulators is reviewed and gives a background introduction for our work that is discussed in detail in the following chapters.With multiple types of 2D materials, the absorption spectrum of the large 2D family can cover an ultrawide optical bandwidth from ultraviolet to microwave holding great promise for photodetector applications. Here, we propose and experimentally study several 2D materials-based photodetectors. First, we demonstrate a silicon ring resonator integrated graphene-silicon Schottky diode and theoretically study the low power saturation of the diode by modelling the free carrier density. Secondly, a hybrid integration platform for integrating graphene with bound states in the continuum (BICs) PICs is proposed. The integration scheme is applicable to any 2D material onto any dielectric substrate with negligible influence to the material quality and has high fabrication tolerance. As a verification of the theory, we integrated different types of two-dimensional materials onto silicon nitride and lithium niobite substrates. An ultrafast BIC-based waveguide-integrated graphene photodetector is experimentally demonstrated. We also study group-10 transition metal dichalcogenides (TMDs) for high speed optoelectronics in near infrared. A broadband and high speed PtSe2 surface illuminated photodetector and a high-speed BIC waveguide integrated PtSe2 photodetector with low dark current are demonstrated.Optical modulator is one of the most crucial building blocks in photonics. There are several different mechanisms that can induce optical modulation in 2D materials such as thermo-optic, electro-optic and all-optical modulations. Here in this thesis, we study the thermal-optical effect of graphene on BIC ring resonators. By using graphene as a heat generator, a thermal modulation depth of 35 dB is achieved. In addition, we demonstrate a high-speed graphene electro-optic (EO) intensity modulator with the BIC PICs. Platinum diselenide can be grown by chemical vapor deposition as a two-dimensional (2D) material and is relatively stable in air. We experimentally demonstrate a 2D PtSe2 optical modulator at 1550nm wavelength. The modulator was formed by fabricating a capacitor using two layers of PtSe2 separated by a dielectric, and propagating the light along the plane of the 2D materials by using a BIC optical waveguide. The fabricated PtSe2 modulator has a response speed of 4.8 GHz and a modulation depth of 6 dB.Integrated plasmonic structures can concentrate light to deep-subwavelength volumes below the diffraction limit and have been explored in many applications including label-free nanophotonic sensing with single molecule sensitivity, nonlinear conversion, and lasing for enhancing the light matter interaction. However, conversion between the dielectric waveguide mode and the plasmonic mode typically suffers from large mode conversion loss and requires high nanofabrication precision because of the mode mismatch and the precise alignment requirements with the plasmonic slot structure, respectively. In this thesis, we proposed a hybrid structure for enhancing the optical absorption of a 2D material by PSW using a simple fabrication process that has relaxed lithographic alignment tolerance.There are still many possible applications in the integration of 2D materials on PICs. For example, functional devices for optoelectronics and nonlinear applications such as second harmonic generation or parametric conversion could be realized by integrating van der Waals heterostructures with the PICs. Another potential application is to study the nonlinear effects by integrating 2D materials with the deep-subwavelength slot waveguides for the light-matter interaction could be strongly enhanced in the narrow metal slots.二維材料的光子集成為硅基光學和氮化硅平台提供了新的功能器件，並為集成光學的發展開闢了新途徑。二維材料具有其獨特的特性，例如高非線性係數，具有發光的直接帶隙，光調製特性，可飽和吸收等等。這些特性可以被用作實現片上光學的功能器件。本論文主要討論了基於二維材料的片上集成光電器件。我們對當前集成在光波導上的光調製器和光探測器的發展情況進行了回顧，並為後續各章節中詳述的工作提供了背景介紹。二維材料的多樣性使得具有從紫外到微波的超寬帶吸收譜，這為其在光電探測器的應用方面提供了廣闊的前景。在本文中，我們提出並通過實驗實現了幾種基於二維材料的光電探測器。首先，我們介紹了一種集成在硅光環形諧振腔上的石墨烯-硅肖特基結二極管，並通過對石墨烯載流子密度進行建模，從理論上解釋了光探測器在較低功率下的飽和現象。其次，我們還提出了一種用於二維材料的光子集成的基於連續態中的束縛態的混合集成方案。該方案適用於將任何二維材料集成在任何絕緣基底上面，整個製作環節對二維材料的質量影響可以忽略不計。我們將不同種類的二維材料集成在氮化硅和鈮酸鋰基底上來驗證此集成方案，並通過實驗提出了一種基於連續態中的束縛態的超快片上石墨烯光電探測器。最後，我們還研究了Ⅹ族過渡金屬二滷化物在高速光電子器件的應用。我們研究了一種寬帶的高速的二硒化鉑空間光探測器和一種基於連續態中的束縛態的具有低暗電流的高速的集成光電探測器。光調製器是光子學中最關鍵的組成部分之一。通過例如熱光效應，電光效應，全光調製效應等不同機制可以誘發二維材料的光學調製效應。在本文中，我們首先研究了石墨烯對於基於連續態中的束縛態的環形諧振腔的熱光調製效應。通過將石墨烯作為發熱體, 我們實現35 dB的調製深度。此外，我們還實現了石墨烯在基於連續態中的束縛態的光子集成電路中高速電光強度調製器。由於二硒化鉑可以通過化學氣相沉積法大面積生長，並在空氣中可以保持穩定，我們提出了將二硒化鉑用於製作在1550納米波段的光調製器。通過使用被電介質層隔開的兩層二硒化鉑來製作電容器，並在基於連續態中的束縛態的光波導中使光沿著平面進行傳播，從而形成電光調製器。我們製作的二硒化鉑光調製器具有6 dB的調製深度和4.8吉赫茲的調製帶寬。集成的等离激元结构可以将光集中到低于衍射极限的深亚波长范围。由於其可以增强光和物质的相互作用，已被用於许多应用，包括具有单分子灵敏度的无标记纳米光子传感，非线性转换和激光器。然而，介电波导模式和等离子体模式之间的转换通常遭受较大的模式转换损失，并且由于分别存在模式失配和与等离子体狭缝结构的精确对准要求而需要高的纳米制造精度。在这里，我们报道了用于增强二維材料光耦合的，具有大制造公差的等离子缝隙复合结构。通過將二維材料和光子集成電路相結合，光電子學還有許多未來的發展方向。例如，可以通過將范德華異質結結構與光子集成電路相結合來實現用於光電和非線性應用的功能器件，例如二次諧波生成或是參數轉換。由于二維材料和光场的耦合可以在亚波长金属狭缝中显著增强，其另一個潛在應用是利用将二维材料集成在亚波长金属波导上以研究二维材料的非线性效应。Wang, Yi.Ph.D. Chinese University of Hong Kong 2020.Includes bibliographical references.Abstracts also in Chinese.Title from PDF title page (viewed on September 6, 2022)