Field Of Silicon Photonics Research Articles

(Invited) Advanced III-V-on-Si Heterogeneously Integrated Platforms for Next Generation Silicon Photonics Integrated Circuits

The field of Silicon Photonics has experienced a solid and continuous progress over the last few years, gaining in technological maturity, design tools, and new methods [1]. The deployment of low-cost, compact, and power-efficient photonic circuits with a high wafer yield and robustness stands as one of the fundamental pillars that sustain such progress [2]. Presently, photonic circuit technology has diversified its number of available platforms. Despite the fact that indium phosphide (InP) [3] and silicon-on-insulator (SOI) platforms are still considered as the workhorses of integrated photonics in terms of maturity and deployment of active (InP) and passive (SOI) components, other alternatives such as germanium-on-silicon [4], silicon nitride-on-insulator [2] or hybrid solutions combining different functional materials with Si are gaining momentum [5]. A representative example is the heterogeneous III-V/Si platform [6], which has been used to develop compact photonic circuits with on-chip gain. Contrarily to the hybrid integration, the III-V-on-Si heterogeneous integration avoids the constraints of chip-to-chip alignment while enabling the simultaneous integration of hundreds of III-V gain chips in a scalable fashion. Still, the integration methods of such III-V materials on silicon need to be improved to attain the maturity level of the monolithic III-V platform, which benefits from a complete palette of technological solutions not yet available in the III-V-on-Si heterogeneous integration. More recently, an advanced heterogeneous scheme based on wafer-seed-bonding and epitaxial regrowth has emerged [7]–[9]. The ambition is to create a generic integration scheme combining the best offered by the III-V and the Si-photonics platforms. The regrowth capability gives access to the large epitaxial toolkit available in the conventional InP monolithic platform, where several epitaxial steps are often implemented [10][11]. To cite some of them, the epitaxial regrowth of III-V materials to bury III-V lasers bonded onto silicon are object of intense research nowadays to overcome the thermally inefficient buried oxide [12].In this paper, we will review the advances on III-V-on-Si heterogeneous integration through the implementation of several key demonstrators and building blocks for silicon photonics, including on-chip semiconductor optical amplifiers, lasers and electro-absorption modulators. We will discuss the progress and benefits of the direct seed bonding and regrowth as well as new device designs to improve the performance.

A Pick‐and‐Place Technology Enabled, Mechanically Programmable, Spiral Optical Waveguides Integrated Hybrid Circuits from Four Extremely Pseudo‐Plastic Organic Crystals for Visible Spectral Band Tunability

AbstractIn the field of silicon photonics, highly compact and miniature high‐density circuits are achieved by precisely shaping millimeter‐long waveguides into spiral configurations. Organic photonics, on the other hand, takes advantage of mechanically flexible crystal spiral waveguides (SWs) within organic photonic circuits. These SWs offer versatility, enabling precise control over light paths and mechanical programmability. This study introduces an innovative pick‐and‐place technique for constructing various organic spiral waveguides (OSWs) with different geometries, such as Cornu, Archimedean, elliptical, rectangular, four‐sided polygons, and three‐sided polygons. Additionally, this method allows for the creation of optically reprogrammable photonic circuits. Custom‐synthesized flexible crystals are used, including blue‐emitting (Z)−3‐(4‐(9H‐carbazol‐9‐yl)phenyl)−2‐(3,5‐bis(trifluoromethyl)phenyl)acrylonitrile (Cz‐2CF3), green‐emitting (E)−1‐(((5‐bromopyridin‐2‐yl)imino)methyl)naphthalene‐2‐ol (BPyIN), cyan‐emitting 9,10‐dibromo anthracene (DBA), and red‐emitting 4,7‐bis(4‐octylthiophen‐2‐yl)benzo[c][1,2,5]thiadiazole (BTD). Systematically integrating a Cz‐2CF3 OSW (with two ports for optical signal routing in clockwise/counterclockwise directions) with DBA and BTD waveguides produces multi‐color hybrid photonic circuits with customizable optical functions, tailored to specific design needs. The number of output ports can be dynamically adjusted through mechanical programming by coupling crystals tip‐to‐tip when replacing the DBA waveguide with a BPyIN waveguide using the pick‐and‐place technology. This mechanically programmable hybrid spiral photonic circuit seamlessly operates across the entire visible spectral bandwidth, making it valuable for various applications, including high‐fidelity sensing, spectrometer components, and intelligent circuitry.

Process Development of Low-Loss LPCVD Silicon Nitride Waveguides on 8-Inch Wafer

Silicon nitride is a material compatible with CMOS processes and offers several advantages, such as a wide transparent window, a large forbidden band gap, negligible two-photon absorption, excellent nonlinear properties, and a smaller thermo-optic coefficient than silicon. Therefore, it has received significant attention in the field of silicon photonics in recent years. The preparation of silicon nitride waveguides using low-pressure chemical vapor deposition methods results in lower loss and better process repeatability. However, due to the higher temperature of the process, when the thickness of the silicon nitride film exceeds 300 nm on an 8-inch wafer, it is prone to cracking due to the high stress generated by the film. Limited by this high stress, silicon nitride waveguide devices are typically developed on wafers with a thickness of 4 inches or less. In this work, we successfully fabricated a 400 nm-thick silicon nitride waveguide on an 8-inch wafer using a Damascene method similar to the CMOS process for copper interconnects and demonstrated propagation losses of only 0.157 dB/cm at 1550 nm and 0.06 dB/cm at 1580 nm.

The High Photoresponse of Stress‐Tuned MoTe2 Optoelectronic Devices in the Telecommunication Band

There are attractive prospects to achieve large photocurrent and high optical response in telecommunication wavelengths for optoelectronic devices. Inspired by the recent experiment [Nat. Photonics 2020, 14, 578], the photocurrent of the devices composed of noncentral inversion symmetric monolayer MoTe2 along the armchair direction under different linearly polarized light by the quantum transport calculation is investigated. The results demonstrate that the maximum photocurrent will increase under the biaxial tensile stress, and importantly, the peak of photocurrent will move toward the direction of lower photon energy owing to the reduction of the bandgap of monolayer MoTe2, which is opposite to the case of applying the bias voltage. Ultimately, it is proved that monolayer MoTe2 devices with large photoresponse can be tuned to the interesting telecommunication band via the imposition of biaxial stress and bias voltage, which makes the devices have potential applications in the field of silicon photonics.

Molecular‐Beam Epitaxy Growth and Properties of AlGaAs Nanowires with InGaAs Nanostructures

Combinations of III–V nanowires (NWs) with quantum dots (QDs) are promising building blocks for quantum light sources. Herein, for the first time, the results of growing AlGaAs NWs with InGaAs QDs by molecular‐beam epitaxy on a silicon substrate are shown. The optimal growth temperature is determined and the physical properties of the grown nanostructures are studied. It is shown that the grown nanostructures exhibit photoluminescence (PL) signal up to room temperature in a wide wavelength range, including 1.3 μm emission which is important for the optical fiber transmission. It is found that in addition to InGaAs QDs radial InGaAs quantum wells are formed inside the NWs as a result of lateral/axial InGaAs growth competition. The proposed technology opens up new possibilities for the integration of direct‐band III–V materials with the silicon platform for various applications in the field of silicon photonics and quantum communication technology.

Investigating the potential of laser-written one-dimensional photonic crystals inside silicon

The field of silicon photonics is based on introducing and exploiting advanced optical functionality. Current efforts in the field are based on conventional micro/nanofabrication methods, leading to optical functionality over wafer surfaces. A complementary and emerging field is introducing analogous optics directly within the wafer using lasers. Here we investigate the theoretical feasibility of a subclass of such optics, photonic crystals. Our efforts will guide future experimental efforts towards in-chip spectral control.

Analysis of stress distribution in microfabricated germanium with external stressors for enhancement of light emission

In the field of silicon photonics, germanium (Ge) is an attractive material for monolithic light sources. Tensile strain is a promising means for Ge based light sources due to enhancing direct band gap recombination. We investigated strain engineering in Ge using silicon nitride (SiNx) stressors. We found that microfabricated Ge greatly improves the tensile strain because SiNx on the Ge sidewalls causes a large tensile strain in the direction perpendicular to the substrate. Tensile strain equivalent to an in-plane biaxial tensile strain of 0.8% at maximum was applied, and the PL emission intensity was improved more than five times at the maximum.

CORNERSTONE’s Silicon Photonics Rapid Prototyping Platforms: Current Status and Future Outlook

The field of silicon photonics has experienced widespread adoption in the datacoms industry over the past decade, with a plethora of other applications emerging more recently such as light detection and ranging (LIDAR), sensing, quantum photonics, programmable photonics and artificial intelligence. As a result of this, many commercial complementary metal oxide semiconductor (CMOS) foundries have developed open access silicon photonics process lines, enabling the mass production of silicon photonics systems. On the other side of the spectrum, several research labs, typically within universities, have opened up their facilities for small scale prototyping, commonly exploiting e-beam lithography for wafer patterning. Within this ecosystem, there remains a challenge for early stage researchers to progress their novel and innovate designs from the research lab to the commercial foundries because of the lack of compatibility of the processing technologies (e-beam lithography is not an industry tool). The CORNERSTONE rapid-prototyping capability bridges this gap between research and industry by providing a rapid prototyping fabrication line based on deep-UV lithography to enable seamless scaling up of production volumes, whilst also retaining the ability for device level innovation, crucial for researchers, by offering flexibility in its process flows. This review article presents a summary of the current CORNERSTONE capabilities and an outlook for the future.

A Sub-kHz Narrow-Linewidth, and Hundred-mW High-Output-Power Silicon-Based Er Silicate Laser With Hybrid Pump and Signal Co-Resonant Cavity

Narrow-linewidth silicon-based lasersplay an important role in the field of silicon photonics. In this paper, we have proposed a high performance narrow-linewidth silicon-based Er silicate laser, based on strip-loaded DFB waveguide with a hybrid pump and signal co-resonant cavity. The saturated output power can reach over 90 mW at 1535 nm, with a maximum power conversion efficiency of 66%. The pump threshold is about 22 mW, and the laser linewidth is also as narrow as about 755 Hz. The results provide a new way for future scale integrated ultra-narrow-linewidth silicon-based lasers application.

Analysis of coupled micro rings resonators and coupled Fabry–Pérot resonators with a single physical view

Coupled micro ring resonators gained a lot of interest in recent years in the field of silicon photonics. Although it is well recognized that coupled ring resonators and coupled Fabry–Pérot resonators operate with similar physical principles, their analysis in the literature is artificially separated, often each resonator type is analysed with different physical arguments, techniques and nomenclature. As a result, coupled rings resonators and coupled Fabry–Pérot resonators appear as two different problems, and the similarity in the physical principles that govern their operation is blurred. What is more unfortunate is that the established physical intuition, familiar from Fabry–Pérot analysis, is lost in notation when dealing with coupled micro rings. Here, we argue how a lossless boundary between two dielectrics and a lossless waveguide-coupler can be viewed as a single entity: an abstract ‘boundary’ that transmits and reflects optical fields according to Stokes relations. Using this view, Fabry–Pérot and micro rings become a single type of resonator. Accordingly, we calculate effective reflection and transmission coefficients of several configurations of coupled Fabry–Pérot and rings resonators. We calculate these coefficient by the intuitive method of summing reflected fields and by the method of transfer matrix. We illustrate that the effective reflection and transmission coefficients of a coupled ring resonator is similar to 3 layers Fabry–Pérot resonator and discuss the subtle difference. It is hoped that the common nomenclature and analysis used for both types of coupled resonators will give the reader a clear and basic understanding of both types of resonators.

Operation of high-speed silicon photonic micro-disk modulators at cryogenic temperatures

Significant progress has been made in the field of silicon photonics over the past two decades. Silicon photonics provides substantial performance advantages in many data processing and transfer applications. Until now, the benefits of active silicon photonics in cryogenic systems have remained unexplored. Here we demonstrate the operation of a high-speed, CMOS compatible silicon micro-disk modulator transmitting data at rates up to 10 Gb/s and at temperatures down to 4.8 K. This opens the door for the use of silicon photonics as an interface to low temperature, bandwidth intensive systems such as high-performance superconducting-based computing and integrated quantum optics circuits interfacing to superconducting single-photon detectors.

Calibration of a Circular HV Magnetron Sputtering Source for in-Situ RE Doping of Ecr-PECVD Si-Based Thin Films

Rare-Earth doped silicon based luminescent materials have become an attractive solution in some key areas of technological development. For instance, in the field of silicon photonics there is a drive to replace electronic on-chip components with photonic counterparts [1-2]. One of the major challenges thus far has been to provide the monolithic integration of an efficient reliable electrically driven light source. Such an element could also be used for solid state lighting, and avoid expensive III-V compounds that cannot be fully integrated into electronic drivers in a CMOS line [3]. In-situ doping of Eu3+ions in silicon oxides and oxynitrides fabricated by electron-cyclotron-resonance plasma enhanced chemical vapour deposition (ECR-PECVD) is performed. Doping is achieved by using a Circular High Vacuum Magnetron sputtering source attached to the ECR-PECVD tool. The doping concentration is varied by varying the distance of the sputtering source to the target. The hot matrix composition is varied through varying oxygen and nitrogen gas flows. The effects on the doping concentrations of the sputtering source distance to target is determined through Rutherford Backscattering Spectrometry and Variable Angle Spectroscopic Ellipsometry. Preliminary luminescence measurements are discussed. [1] Jalai, B., and Fothpour, S. “Silicon photonics,” Journal of Lightwave Technology 24, 4600-4615(2006) [2]Liu, A. Jones, R., Liao, L., Samarah-Rubio, Rubin, D., Cohen, O. Nicolaescu, R., and Paniccia, M., “A high-speed silicon optical modulator based on a metaloxide-semiconductor capacitor,” Nature 427, 615-618 (2004) [3] Ponce, F.A., Bour, D.P., “Nitride-based semiconductors for blue and green light-emitting devices”, Nature 386 (6623), 351-359 (1997)

Localised Tuneable Composition Single Crystal Silicon-Germanium-on-Insulator for Low Cost Devices

The realisation of high quality silicon-germanium-on-insulator (SGOI) is a major goal for the field of silicon photonics because it has the potential to enable extremely low power active devices functioning at the communication wavelengths of 1.3 μm and 1.55 μm. In addition, SGOI has the potential to form faster electronic devices such as BiCMOS transistors and could also form the backbone of a new silicon photonics platform that extends into the mid-IR wavelengths for applications in, amongst others, sensing and telecoms. In this paper, we present a novel method of forming single crystal, defect-free SGOI using a rapid melt growth technique. We use tailored structures to form localised uniform composition SGOI strips, which are suitable for the state-of-the-art device fabrication. This technique could pave the way for the seamless integration of electronic and photonic devices using only a single, low cost Ge deposition step.

Progress in silicon platforms for integrated optics

AbstractRapid progress has been made in recent years repurposing CMOS fabrication tools to build complex photonic circuits. As the field of silicon photonics becomes more mature, foundry processes will be an essential piece of the ecosystem for eliminating process risk and allowing the community to focus on adding value through clever design. Multi-project wafer runs are a useful tool to promote further development by providing inexpensive, low-risk prototyping opportunities to academic and commercial researchers. Compared to dedicated silicon manufacturing runs, multi-project-wafer runs offer cost reductions of 100× or more. Through OpSIS, we have begun to offer validated device libraries that allow designers to focus on building systems rather than modifying device geometries. The EDA tools that will enable rapid design of such complex systems are under intense development. Progress is also being made in developing practical optical and electronic packaging solutions for the photonic chips, in ways that eliminate or sharply reduce development costs for the user community. This paper will provide a review of the recent developments in silicon photonic foundry offerings with a focus on OpSIS, a multi-project-wafer foundry service offering a silicon photonics platform, including a variety of passive components as well as high-speed modulators and photodetectors, through the Institute of Microelectronics in Singapore.

Polymer-embedded colloidal lead-sulfide nanocrystals integrated to vertically slotted silicon-based ring resonators for telecom applications

The main drawback of the rapidly evolving field of silicon photonics lies in the absence of efficient monolithically integrated radiation sources as a consequence of the indirect bandgap of Si and Ge. Relevant alternatives based on the hybrid combination of Si with optically active materials have to be technologically simple, temporally stable, and provide efficient coupling to the Si waveguides. Lead-sulfide nanocrystals (NCs) were blended into a polymer resist suitable for deep-UV- and electron-beam lithography and integrated into Si-based vertically slotted waveguides and ring resonators. The polymer both stabilizes the NC’s photoluminescence emission against degradation under ambient conditions and allows lithographic patterning of this compound material. After integration into the optoelectronic structures and upon optical pumping, intense photoluminescence emission from ring resonators was recorded at the output of bus-waveguides. The resonator quality factors were investigated for polymer-NC compounds with NC concentrations in the range between 0.1 and 8 vol%. The spontaneous emission rate enhancement for vertically slotted resonators was estimated to be a factor of two higher as compared to unslotted ones. The stable integration of colloidal NCs as well as the improved light coupling to silicon circuits is an important step in the development of silicon-based hybrid photonics.

Noise Characterization of a Waveguide-Coupled MSM Photodetector Exceeding Unity Quantum Efficiency

In the field of silicon photonics, it has only recently become possible to build complex systems. As system power constraints and complexity increase, design margins will decrease - making understanding device noise performance and device-specific noise origins increasingly necessary. We demonstrate a waveguide-coupled germanium metal-semiconductor-metal photodetector exhibiting photoconductive gain with a responsivity of 1.76 A/W at 5 V bias and 10.6±0.96 fF capacitance. Our measurements indicate that a significant portion of the dark current is not associated with the generation of shot noise. The noise elbow at 5 V bias is measured to be approximately 150 MHz and the high-frequency detector noise reaches the Johnson noise floor.

Theoretical Study of the Emission of Light Stimulated by Phonons in Indirect Bandgap Semiconductor

Microelectronic device integration has progressed to the point where complete ‘systems-on-a-chip’ have been realized. The development of Complementary Metal-Oxide-Semiconductor (CMOS) technology during the 20th century has permitted the mass-manufacture of high-performance electronic devices on silicon at low cost. However, electronic integration on silicon has encountered some limits mainly due to the heat generated by the high-speed of data transmission required in modern communications. This is the main reason why CMOS-microelectronics giants such as IBM or Intel have included optical interconnects within their chip manufacturing roadmaps in order to ensure the performance of the Moore's law in the next decades. To this end, several basic building blocks with high performance must be developed fully in silicon and employing CMOS processes. Most of these building blocks (waveguides, filters, photodetectors) have been already developed, as mentioned before, within the field of silicon photonics. However, the issue of efficient generation of light in such photonic circuits remains unsolved. The possible induction of light emission from Si, an indirect bandgap material in which radiative transitions are unlikely, raises several interesting and technologically important possibilities, especially the fabrication of a truly integrated optoelectronic microchip. As a consequence, an electrically-pumped laser working at optical communications wavelengths and at room-temperature fully built using silicon is perhaps the most pursued challenge within photonics [1].

Introduction to the Special Issue on Silicon Photonics

The 39 papers in this special issue focus on the field of silicon photonics.

Silicon photonics: the optical spice rack

Silicon is evolving as a versatile photonics platform with multiple functionalities that can be seamlessly integrated. The toolbox is rich, starting from the ability to guide and switch multiple wavelength sources at gigahertz bandwidths, to optomechanical MEMS and opto-fluidics devices. Some of the challenges in the field of silicon photonics are discussed; among them are the decrease of losses in silicon waveguides and the integration of silicon photonics with current CMOS microelectronics.

Introduction to the Issue on Silicon Photonics

field of silicon photonics, which seeks to develop and integrate photonic components that are compatible with Si integrated circuit technology. Silicon photonics has the potential of leveraging the enormously successful infrastructure developed for the semiconductor industry. Mass production of reliable and inexpensive components and systems that can be readily integrated with silicon microelectronics may become possible, thereby extending the reach of photonics, and revolutionizing the industry by providing a solution to the heat and the data-transfer bottleneck that is threatening the continued advance of Si information technology. Recent developments in the areas of light sources including light-emitting devices and Raman lasers, modulators, switches, photonic crystals, waveguides, photodetectors, and subsystem prototypes demonstrate that silicon photonics is becoming a reality. This issue gathers, for the first time, a large number of papers that have undergone peer review. In all, 14 invited papers and 34 contributed papers, authored by academic, industrial, and governmental scientists and engineers from many countries, cover all the key aspects of silicon photonics. For convenience, the papers have been organized into four groups: 1) passive microphotonic components; 2) active microphotonic components (including modulators, switches, and photodetectors); 3) light emission, LEDs, and lasers (both