Lennart Wevers

Bio: Lennart Wevers is an academic researcher. The author has contributed to research in topics: Photonics & Photonic integrated circuit. The author has an hindex of 5, co-authored 14 publications receiving 243 citations.

Low-Loss Si3N4 TriPleX Optical Waveguides: Technology and Applications Overview

Abstract: An overview of the most recent developments and improvements to the low-loss TriPleX Si3N4 waveguide technology is presented in this paper The TriPleX platform provides a suite of waveguide geometries (box, double stripe, symmetric single stripe, and asymmetric double stripe) that can be combined to design complex functional circuits, but more important are manufactured in a single monolithic process flow to create a compact photonic integrated circuit All functionalities of the integrated circuit are constructed using standard basic building blocks, namely straight and bent waveguides, splitters/combiners and couplers, spot size converters, and phase tuning elements The basic functionalities that have been realized are: ring resonators and Mach–Zehnder interferometer filters, tunable delay elements, and waveguide switches Combination of these basic functionalities evolves into more complex functions such as higher order filters, beamforming networks, and fully programmable architectures Introduction of the active InP chip platform in a combination with the TriPleX will introduce light generation, modulation, and detection to the low-loss platform This hybrid integration strategy enables fabrication of tunable lasers, fully integrated filters, and optical beamforming networks

Flip-Chip Integration of InP to SiN Photonic Integrated Circuits

Abstract: We present our hybrid InP to SiN TriPleX integration interface with a novel alignment technique and its application to complex photonic integrated circuits. The integration interface comprises vertical alignment stops, which simplify the alignment process and allow for array integration with the same simplicity as for single dies. Horizontal alignment is carried out by utilizing optical backscatter reflectometry to get an active feedback signal without the need to operate the chip. Thus, typical contacting limitations of active flip-chip alignment are overcome. By using this method, we demonstrate the integration of InP DFB lasers with more than 60 mW of optical power coupled to a SiN waveguide with an averaged coupling loss of -2.1 dB. The hybrid integration process is demonstrated for single dies as well as full arrays. We evaluate the feasibility of the assembly process for complex photonic integrated circuits by integrating an InP gain chip to a SiN TriPleX external cavity. The process proves to be well suited and allows monitoring chip quality during assembly. A fully functional hybrid integrated tunable laser is fabricated, which is capable of full C-band tuning with optical output power of up to 60 mW.

Ultra-low-power stress-optics modulator for microwave photonics

Abstract: In this work, we demonstrate the first stress-optic modulator in a silicon nitride-based waveguide platform (TriPleX) in the telecommunication C-band. In our stress-optic phase modulator the refractive index of the waveguiding materials is controlled by the stress-optic effect induced by actuating a 2 μm thick PZT layer on top of the TriPleX waveguide geometry. The efficiency of the modulator is optimized by, amongst others, focusing the applied stress in the waveguide core region through a local increase of the top cladding. Using a Mach-Zehnder interferometer, we measured a half-wave voltage, Vπ, at 34 V at a wavelength of 1550 nm using a modulator with a total length of 14.8 mm. The measured static power consumption of our stress-optic modulator is in the μW-region as it is only determined by small leakage currents (< 0.1 μA), while the dynamic power consumption at a rise time of 1 ms (1 kHz excitation) is less than 4 mW per modulator. The stress optical modulator goes with an excess loss of 0.01 dB per modulator only. This is in line with the typical low loss characteristics of TriPleX waveguides, being < 0.1 dB/cm at a wavelength of 1550 nm. These specifications make stress-optic modulators an excellent choice for next generation optical beam forming networks with a large number of actuators in silicon photonics in general and in the TriPleX platform in particular.

Flip-Chip Integration of InP and SiN

Abstract: We present an interface for hybrid flip-chip integration of InP-based laser sources to silicon-nitride-based photonic platforms. The design enables efficient high optical power coupling over a wide temperature range. The optical modes of laser and SiN chip are expanded using integrated tapers allowing for high alignment tolerance. The chips comprise physical alignment stops for vertical alignment. In the horizontal direction, the integration interface is optimized for active and/or visual alignment with high precision using precise visual alignment marks. The hybrid integrated chip shows a waveguide coupled optical power of more than 40 mW and can operate at elevated temperatures up to 85 °C.

Broadband True Time Delay Microwave Photonic Beamformer for Phased Array Antennas

Abstract: In this paper, we present results on true time delay-based, broadband, and continuously tunable photonic beamforming modules for phased array antennas. The RF beamforming module is based on hybrid optical integration of TriPleX and InP chips. We present two types of analog photonic links (APLs) to achieve true time delay (TTD) beamforming. The parameters of the individual integrated components and their impact on the APL are discussed together with the theory for the two APLs. The measurement results of two 1x4 TTD beamforming architectures are presented. The first is based on step wise delays with a bandwidth of 10 GHz and a link gain of about -46.4 dB. The second is based on continuously tunable delays with a bandwidth of 3.5 GHz and a link gain -39.8 dB.

Integrated microwave photonics

Abstract: Recent advances in photonic integration have propelled microwave photonic technologies to new heights. The ability to interface hybrid material platforms to enhance light–matter interactions has led to the development of ultra-small and high-bandwidth electro-optic modulators, low-noise frequency synthesizers and chip signal processors with orders-of-magnitude enhanced spectral resolution. On the other hand, the maturity of high-volume semiconductor processing has finally enabled the complete integration of light sources, modulators and detectors in a single microwave photonic processor chip and has ushered the creation of a complex signal processor with multifunctionality and reconfigurability similar to electronic devices. Here, we review these recent advances and discuss the impact of these new frontiers for short- and long-term applications in communications and information processing. We also take a look at the future perspectives at the intersection of integrated microwave photonics and other fields including quantum and neuromorphic photonics. This Review discusses recent advances of microwave photonic technologies and their applications in communications and information processing, as well as their potential implementations in quantum and neuromorphic photonics.

11 TOPS photonic convolutional accelerator for optical neural networks

Abstract: Convolutional neural networks, inspired by biological visual cortex systems, are a powerful category of artificial neural networks that can extract the hierarchical features of raw data to provide greatly reduced parametric complexity and to enhance the accuracy of prediction. They are of great interest for machine learning tasks such as computer vision, speech recognition, playing board games and medical diagnosis1–7. Optical neural networks offer the promise of dramatically accelerating computing speed using the broad optical bandwidths available. Here we demonstrate a universal optical vector convolutional accelerator operating at more than ten TOPS (trillions (1012) of operations per second, or tera-ops per second), generating convolutions of images with 250,000 pixels—sufficiently large for facial image recognition. We use the same hardware to sequentially form an optical convolutional neural network with ten output neurons, achieving successful recognition of handwritten digit images at 88 per cent accuracy. Our results are based on simultaneously interleaving temporal, wavelength and spatial dimensions enabled by an integrated microcomb source. This approach is scalable and trainable to much more complex networks for demanding applications such as autonomous vehicles and real-time video recognition. An optical vector convolutional accelerator operating at more than ten trillion operations per second is used to create an optical convolutional neural network that can successfully recognize handwritten digit images with 88 per cent accuracy.

Silicon Nitride in Silicon Photonics

Abstract: The silicon nitride (Si3N4) planar waveguide platform has enabled a broad class of low-loss planar-integrated devices and chip-scale solutions that benefit from transparency over a wide wavelength range (400–2350 nm) and fabrication using wafer-scale processes. As a complimentary platform to silicon-on-insulator (SOI) and III–V photonics, Si3N4 waveguide technology opens up a new generation of system-on-chip applications not achievable with the other platforms alone. The availability of low-loss waveguides (<1 dB/m) that can handle high optical power can be engineered for linear and nonlinear optical functions, and that support a variety of passive and active building blocks opens new avenues for system-on-chip implementations. As signal bandwidth and data rates continue to increase, the optical circuit functions and complexity made possible with Si3N4 has expanded the practical application of optical signal processing functions that can reduce energy consumption, size and cost over today’s digital electronic solutions. Researchers have been able to push the performance photonic-integrated components beyond other integrated platforms, including ultrahigh Q resonators, optical filters, highly coherent lasers, optical signal processing circuits, nonlinear optical devices, frequency comb generators, and biophotonic system-on-chip. This review paper covers the history of low-loss Si3N4 waveguide technology and a survey of worldwide research in a variety of device and applications as well as the status of Si3N4 foundries.

Low-Loss Si3N4 TriPleX Optical Waveguides: Technology and Applications Overview

Abstract: An overview of the most recent developments and improvements to the low-loss TriPleX Si3N4 waveguide technology is presented in this paper The TriPleX platform provides a suite of waveguide geometries (box, double stripe, symmetric single stripe, and asymmetric double stripe) that can be combined to design complex functional circuits, but more important are manufactured in a single monolithic process flow to create a compact photonic integrated circuit All functionalities of the integrated circuit are constructed using standard basic building blocks, namely straight and bent waveguides, splitters/combiners and couplers, spot size converters, and phase tuning elements The basic functionalities that have been realized are: ring resonators and Mach–Zehnder interferometer filters, tunable delay elements, and waveguide switches Combination of these basic functionalities evolves into more complex functions such as higher order filters, beamforming networks, and fully programmable architectures Introduction of the active InP chip platform in a combination with the TriPleX will introduce light generation, modulation, and detection to the low-loss platform This hybrid integration strategy enables fabrication of tunable lasers, fully integrated filters, and optical beamforming networks

Review of Silicon Photonics Technology and Platform Development

Abstract: Many breakthroughs in the laboratories often do not bridge the gap between research and commercialization. However, silicon photonics bucked the trend, with industry observers estimating the commercial market to close in on a billion dollars in 2020 [45] . Silicon photonics leverages the billions of dollars and decades of research poured into silicon semiconductor device processing to enable high yield, robust processing, and most of all, low cost. Silicon is also a good optical material, with transparency in the commercially important infrared wavelength bands, and is a suitable platform for large-scale photonic integrated circuits. Silicon photonics is therefore slated to address the world's ever-increasing needs for bandwidth. It is part of an emerging ecosystem which includes designers, foundries, and integrators. In this paper, we review most of the foundries that presently enable silicon photonics integrated circuits fabrication. Some of these are pilot lines of major research institutes, and others are fully commercial pure-play foundries. Since silicon photonics has been commercially active for some years, foundries have released process design kits (PDK) that contain a standard device library. These libraries represent optimized and well-tested photonic elements, whose performance reflects the stability and maturity of the integration platforms. We will document the early works in silicon photonics, as well as its commercial status. We will provide a comprehensive review of the development of silicon photonics and the foundry services which enable the productization, including various efforts to develop and release PDK devices. In this context, we will report the long-standing efforts and contributions that previously IME/A*STAR and now AMF has dedicated to accelerating this journey.