Over the past 20 years silicon photonics has made a successful transition from academic research field to industrial ecosystem. Transceiver products thrive in the market. Industrial foundries offer mature process flows and PDKs. EDA-companies offer photonic IC design tools. Nevertheless, in many ways, silicon photonics is still a small niche field in the semiconductor industry. Meanwhile, both the research community and a multitude of start-up companies are preparing the next wave in silicon photonics, with scientific achievements and innovative products in a dozen new applications and markets, some of which may become large volume. The value proposition is clear. But the diversity of applications requires new functionalities and new – more heterogeneous - process flows. Will the business proposition follow and become sustainable?

The prevalent and complex AI-based services have caused the rapid growth of demand for high performance computing (HPC). The conventional accelerators such as graphic processing units (GPU) have faced obstacles regarding energy efficiency and computational resources. Optical approach, utilizing silicon photonic integrated chip provide solutions in terms of speed, parallelism, and energy efficiency. In this work, we propose a photonic processor with coupling ratio variable micro-ring resonators (MRR), consisting of asymmetric Mach-Zehnder Interferometers (MZI) as variable couplers. Considering the number of channels, the coupling ratio variable MMR customizes the FWHM, maximizing the bit resolution while minimizing the error rate. Also, the resonant wavelength is fixed during the entire process which facilitates significant increase in channel density. The entire calibration process is successfully verified with 4-channel photonic processor fabricated with the Si photonic foundry service.

Novel computational techniques such as photonics inverse design, along with new nanofabrication approaches, play a crucial role in building scalable integrated photonics. While initial inverse design demonstrations focused on individual small footprint devices, recent developments enable rapid optimization of large footprint structures in 3D, with linear dimensions over 100 microns, and fully compatible with foundry fabrication. We illustrate this with recent demonstrations of powerful integrated photonic systems for application such as optical interconnects. To enable all necessary functionalities, future photonic systems also require integration of traditional and non-traditional photonic materials, including silicon, silicon-carbide, diamond, sapphire, and strong electro-optic materials such as lithium niobate, strontium and barium titanate. We show that compact and efficient lasers, isolators, electro-optic modulators, and detectors can all be integrated on silicon platform.

We report on the investigation of an optical M-by-N switch implementated as a photonic integrated circuit (PIC) in silicon on insulator. The switch relies on a star coupler for non-blocking routing of multiple optical signals. The latter are carried into and out of the star coupler in multi-core dielectric waveguides that support multiple modes. Routing is controlled by applying different optical-phase delays to the individual cores comprising the waveguide. We investigate theoretically and experimentally the viability of the architecture for routing optical signals in a PIC. In addition to signal routing, MASTR switch may be used for general matrix multiplication.

The development of quantum photonic technologies will fuel a paradigm shift in data processing and communication protocols. A controlled generation of non-classical states of light is a challenging task at the heart of such technologies. Epitaxially grown self- assembled semiconductor quantum dots (QDs) offer the advantages of deterministic generation of single photons and prospects of device integration. By growing such QD structures only in designated locations on (001) Si substrate, the quantum properties of the emitted photons could be tuned with the built-in thermal stress for generating highly entangled photon pairs.

We present a GaSb based micro transfer printed (µTP) gain devices for integration with a 3 µm silicon-on-insulator platform and demonstrate integration to a reflective distributed Bragg reflector (DBR) forming a functional single frequency external cavity laser at 1960 nm. Previously used on InP and GaAs, we transferred the technique on GaSb, that allows the expansion of applications from telecommunication to sensing, such as environmental gas detection. In addition, we introduce a test device series and a methodology to measure and analyze the effects µTP design specific features, such as etched facets, to assess the transfer print process quality.

In this talk we present on recent advancements in hybrid-glass waveguides on silicon photonic platforms. We describe novel monolithic hybrid integration approaches and waveguide designs for functional glass claddings on silicon-on-insulator (SOI). We describe our results on low-loss hybrid tellurite-silicon waveguides, high-Q resonators, and amplifiers and lasers and our recent efforts to optimize their performance and utility in silicon photonic systems. Such devices are promising for new functionalities in sensing, metrology, computing, and communications applications.

We present an angled multimode interferometer (AMMI) wavelength division (de)multiplexer on a 220 nm silicon-on-insulator platform, which is designed and operated for C-band wavelengths. The length of the AMMI is 855 µm, and can provide a channel spacing of 15 nm and a crosstalk suppression of 7 dB. Through inverse design, the length of the AMMI is reduced to 300 µm with a channel spacing at 8 nm; also to be operated at C band wavelengths. In addition, using shape optimization on a 2x2 multimode interferometer, the length of the device is reduced from 158 µm to 40 µm with improved performance in terms of transmission variation across the C-band.

Integrated electro-optic modulators offer huge potential to meet communications and computations' rapidly growing bandwidth requirements. Devices based on silicon allow high-volume, low-cost CMOS fabrication, and co-integration with the CMOS circuits. They are promising candidates for mass-producible Tb/s-scale inter-rack and intra-rack interconnects. This talk will focus on our advancement of silicon-based optical modulators: (1) miniaturized all silicon MOSCAP modulators for co-packaged optics and its integration with low voltage drivers, allowing low optical power consumption of 2 pJ/bit. (2) Novel carrier absorption enhanced electro-optical modulation in MOSCAP ring resonators towards integration with ultra-low voltage (<1V) CMOS drivers; (3) Carrier depletion ring unity device for large scale and high bandwidth density error-free links; (4) Linear DC-Kerr effect dominated silicon modulators towards lidar and quantum applications.

In this work we investigate the application and optimization of GaSb buffers on Silicon for improved device performance in the mid-wave infrared (MWIR). In particular, we examine the nucleation process of AlSb to create a template for growth of the GaSb buffer, as well as the use of defect filtering layers for reducing residual threading dislocations in the buffer layer. The location of the defect filtering layer plays a role in its effectiveness. Threading dislocation densities as low as mid-10^7 defects/cm^2 have been achieved. This study includes analysis from photoluminescence spectroscopy, transmission electron microscopy, temperature-dependent x-ray diffraction studies, and x-ray diffraction reciprocal space mapping.

Silicon photonics has proved itself to be the most promising platform for the next generation photonic technologies and products, ranging from AI accelerators and quantum photonic integrated circuits to consumer healthcare. Conventionally, various sub-micron waveguide platforms are in use, having high propagation and coupling loss. In contrast, VTT’s 3-µm thick-SOI platform offers a more promising alternative, owing to its ultra-low propagation (3 dB/m), SMF coupling loss, and negligible polarization sensitivity. On this platform, we report a proof-of-principle demonstration of a high-speed electro-optic phase modulator based on electro-optic Kerr effect (or DC Kerr effect) as well as its wafer-scale manufacturability.

We successfully demonstrated the 4-channel Ge waveguide photodetectors with an MZI WDM as an O-band CWDM receiver to receive the 212-Gbps NRZ-OOK and 480-Gbps 16-QAM-DMT data streams without digital signal processing compensation in a 2-km SMF link for satisfying the IEEE 802.3bs and 802.3cu standards.

SWIR and MWIR photodetector technologies are mainly served by III-V and II-VI materials such as InSb, InGaAs, and HgCdTe which are costly, require cooling, and face manufacturing and scalability challenges. GeSn is an attractive group IV material that is Si-compatible with the potential to circumvent these challenges by enabling the fabrication of SWIR and MWIR detectors on a scalable and cost-effective Si platform. In this work, material development and optoelectrical properties of a set of heterostructures made of Si/Ge/GeSn are presented. The material properties and its potential application in photodetectors are discussed. For instance, at a low Sn content (below 5 at.%), we found that GeSn-based photoconductive devices display unexpectedly a low dark current and exhibit a room-temperature cutoff wavelength of 1.75 um and a responsivity of 0.52 A/W at 1.55 um. Results from microscopic and spectroscopic studies are also presented. Finally, capacitance devices are fabricated to extract unintentional doping concentrations from CV measurements.

Silicon microring modulator (Si-MRM) plays an essential role in optical communication and optical computation. Typically, the Si-MRM is modulated by a reversed PN junction that controls the depletion zone width to achieve high-speed operation. A different approach is to drive the Si-MRM with a metal-oxide-semiconductor capacitor (MOSCAP) and utilize accumulated charges to modulate the refractive index. In this work, we demonstrate a Si-MRM with MOSCAP consisting of high mobility transparent conducting oxide (HMTCO)/hafnium oxide insulator/p-type Si, which achieved sub-volt driving voltage and 25Gb/s modulation.

Time-gated image sensors with (sub-) nanosecond gating times enable applications in multiple domains. Commercial Intensified CCD cameras or the more recent time-gated SPAD image sensors suffer from low Quantum Efficiency. We present an imaging system based on the tauCAM, a compact time-gated camera with our new 128x128-pixel CAPS sensor. The higher resolution is achieved with a new pixel architecture, yielding an improved fill factor. The capabilities of the new imaging system are demonstrated in a pre-clinical experimental setup. In vivo imaging in subcutaneous mice tumor models reveal that FLT imaging with the tauCAM provides additional contrast between tumor and healthy tissue, in particular for tracers sensitive to their physiological environment.

We present an on-chip LED based on native Si, fabricated in an open foundry CMOS node. This LED has remarkable characteristics such as its sub-wavelength emission area, broad spectrum, high spatial intensity, high bandwidth, and high reproducibility, which make it an ideal light source for various imaging and sensing systems. Two prototypes, a holographic microscope and a LIDAR, are built employing this LED. Our work demonstrates the possibility of integrating monolithic light sources with other photonic and electronic components on a single photonic chip.

Optoelectronic devices operating in the extended short-wave infrared (e-SWIR) covering the 1.4-3.0 μm wavelength range provide valuable information that can not be gathered in the visible wavelengths. For instance, e-SWIR penetrates fog, haze, and smog. The current e-SWIR technologies utilize predominantly expensive III-V and II-VI semiconductors, hindering the large-scale use of e-SWIR devices. Herein, we introduce GeSn devices monolithically integrated on Si wafers as a low-cost, scalable, and CMOS-compatible e-SWIR technology. E-SWIR imaging through fog is demonstrated utilizing the grown GeSn PIN photodetectors. To record the images, focused light from a broadband source was directed through a silicon (Si) wafer and an artificial fog toward the GeSn photodetector. Using raster scanning and a single GeSn photodiode epitaxially grown on Si wafer, full images were composed. The latter showed a clear contrast between the illuminated and the dark zones. This capacity to properly detect objects through obscurants opens a range of opportunities for real-life applications in e-SWIR imaging.

O-band surface-grating-coupled Si wavelength demultiplexing filter using cascaded directional couplers with 30-nm passband linewidth, 6-dB insertion loss and 23.4-dB polarization extinction is demonstrated for 64-Gbit/s NRZ-OOK with WDM channel extinction enhanced from 8.9-dB@1330nm to 14.6-dB@1325 nm.