We demonstrate stable operation of a thin-film lithium tantalate (TFLT) modulator at very high operating temperatures. We show that the electro-optic modulation and bandwidth of the TFLT modulators are not affected by high-temperature operation, and both waveguide and resonant modulators are DC-bias stable even at 120°C. At higher temperatures, we even observe 10

The recent surge in AI and ML applications within the semiconductor industry necessitates stringent thermal management, driving the need for highly-efficient two-phase cooling mechanisms. Two-phase heat sinks consisting of parallel microchannels offer significantly higher heat transfer efficiency compared to single-phase liquid cooling. However, flow instabilities and local dryout can be triggered by non-uniform heating and severely degrade the thermal performance causing system failure. Therefore, careful characterization of the heatsinks via spatially resolved temperature measurements is crucial for studying the failure modes, such as dryout, for two-phase heat sinks. In this study, we employ a thermal test vehicle (TTV) comprising of 18 silicon dies integrated on a single interposer, functioning as both the heat source and temperature sensor to characterize thermal performance in a custom two-phase heat sink with high-aspect ratio microchannels. The TTV is capable of dissipating 2600 W and measuring high-spatial resolution temperature data via 264 embedded platinum resistance temperature detectors (RTDs). The heat sink ’s performance with the refrigerant R1233zd(E) is assessed under aggressive heat loads intentionally selected to induce dryout. The resulting temperature signatures help deduce the areas over which dryout occurs, demonstrating the utility of the TTV in careful assessment of the thermal performance of two-phase heat sinks, especially under highly demanding thermal loads.

In this paper, we demonstrate the ultra-high-power handling capability and DC bias stability of optical microring and electro-optic (EO) coupling resonators on the thin-film lithium tantalate (TFLT) platform. We show that, with annealing, oxide-cladded TFLT resonators can handle several watts (4W) of circulating power with minimal frequency shift and no observable photo-refractive effect. Furthermore, we demonstrate a compact 2mm coupling modulator achieving a low Vpi of 3V with stable bias and phase control in the telecom C-band.

Driven by recent Artificial Intelligence applications, exponential growth in compute can only be enabled by significant scaling of high bandwidth (BW) optical interconnect. Higher speed, more power efficient integrated optical transceivers are required. Here, we demonstrated for the first time hybrid integration thin-film lithium niobate (TFLN) Mach-Zehnder optical modulator with a commercial open-collector driver through flip-chip bonding. The built assembly demonstrated a Vπ·L of 2.3 V·cm, a measured electro-optic bandwidth of more than 45 GHz, limited by the driver. The measurement results demonstrate minimal interconnect parasitic effects and hence the advantage of closely integrating drivers and modulators in the TFLN transmitter. Also, the thermal performance of the assembly is characterized by a high-resolution infrared camera, and the maximum temperature is ~68°C, without air cooling. The hybrid integrated TFLN transmitter shows high potential for large channel count parallel transceivers for inter/intra datacenter applications.

We present a hybrid assembly of a SiGe driver and TFLN modulator, featuring a novel differential driving scheme achieving low VπL = 1.1 Vcm. We demonstrate 140 GBd PAM-8 modulation with 1.4 pJ/bit energy consumption.

We present the first experimental demonstration of a high-bandwidth thin-film lithium tantalate (TFLT) electro-optic modulator operating at 1 μm, with a Vπ of 2.4 V, and less than 2 dB electro-optic roll-off up to 50 GHz and stable DC bias operation.

We experimentally demonstrate high-extinction optical pulse generation in thin-film lithium tantalate (TFLT), achieving a wide range of pulse widths with sharp rise and fall edges, without measurable distortion or long temporal tails. We further provide a direct one-to-one comparison with thin-film lithium niobate (TFLN) modulators under identical measurement conditions. Our results reveal that the distorted pulse response observed in TFLN originates from charge activation and transport, whereas the distortion-free response in TFLT is enabled by the substantially larger activation energy of defect-related charge carriers. This larger activation barrier suppresses leakage-current-induced charging dynamics, thereby enabling stable and distortion-free pulse generation. The successful generation of high-extinction, distortion-free optical pulses in TFLT can play a significant role in integrated quantum photonic technologies, particularly for qubit preparation, measurement, and fast feedback circuits.

We report a multi-stage racetrack-Mach Zehnder interferometric (MZI) coupler on thin-film lithium niobate (TFLN) with both thermal and electro-optic control. We experimentally show fabrication tolerant electro-optic coupling modulation with a drive voltage of 1.5 V with a 3.75 mm long modulator section.

The increasing thermal demands of high-performance computing in AI datacenters, 5G radio access networks (RAN), and edge compute nodes necessitate the use of advanced cooling solutions beyond conventional air cooling. Multi-chip modules (MCMs), integrating CPUs, GPUs, and high-bandwidth memory (HBM) in 2.5D and 3D architectures, are now drawing power more than 1000 W. Assessing the efficiency of cooling solutions capable of dissipating such high heat loads requires developing a high-power thermal test vehicle (TTV) capable of mimicking the heat maps of the state-of-the-art and next generation CPUs and GPUs. This study demonstrates the high heat dissipation capacity of TTV while cooling it with a two-phase microchannel heatsink. At the core of the developed TTV is a multi-chip module consisting of six emulated logic dies (20 mm x 20 mm) and twelve emulated HBM stacks (10 mm x 10 mm) on a low-temperature co-fired ceramic (LTCC) interposer, capable of dissipating more than 2600 W with localized hotspots reaching 314 W/cm(2) (817 W/cm(2) over the heater resistor area). The module consists of 264 platinum resistive temperature detectors (RTDs) for high-resolution thermal monitoring and enables independent power control across 60 heater regions, facilitating diverse spatial heat maps. The TTV was integrated into a pumped refrigerant cooling system utilizing the low-global-warming-potential (GWP) refrigerant R1233zd(E) in a heat sink with embedded microchannels. Two-phase cooling successfully handled heat fluxes up to 314 W/cm(2) over a 46 mm(2) hotspot on each logic die while maintaining thermal resistances below 0.013 K/W, demonstrating its ability to prevent dryout and thermal runaway at extreme power densities. The experiments also highlighted the superior thermal performance of two-phase cooling over single-phase approaches, achieving up to a 2.8x reduction in mean junction-to-heatsink inlet saturation thermal resistance and reducing peak chip temperatures by up to 25 degrees C. This study demonstrates the utility of the TTV for emulating next-generation high-power computing platforms and the use of two-phase cooling as an advanced thermal management solution for future AI, 5G, and edge computing infrastructures.

We demonstrate a compact, high power tunable laser based on free-space hybrid integration of indium phosphide gain chips with thermally tuned low loss silicon etalons. By optimization of filter fabrication and laser cavity design we achieve 17.6 dBm output power. Integrated thermal control elements enable accurate and wide tuning without the typical external optical feedback or wavelength locking components.

We demonstrate a TFLN travelling-wave Mach-Zehnder modulator suspended on a thin dielectric membrane on silicon substrate with large selectively-removed pockets. The component shows high performance despite the high permittivity of the substrate with a 3-dB EO BW > 110 GHz and V pi = 3.3 V.

Diamondlike carbon (DLC) thin films have been deposited by plasma-enhanced chemical vapor deposition on silicon wafers with methane as a precursor gas and nitrogen as a balancing gas. The optimization of DLC deposition was carried out by varying the experimental parameters of chamber pressure, rf plasma power, and flow rate of the precursor gas. Energy-dispersive spectroscopy of the layers was used to determine the elemental analysis of the DLC thin films. Micro-Raman spectroscopy was used to determine the ratio of disordered graphite from the DLC in the films and to identify the optimal deposition conditions. The surface morphology for the optimum reaction condition was investigated by atomic force microscopy. Chemical stability tests have been performed systematically and have shown that the DLC films are chemically stable with common semiconductor processing chemicals. The films can be removed using oxygen plasma treatment. Ion-coupled plasma/reactive ion etching was performed on the films having almost vertical sidewalls with no trenching at the corners of the pattern. Our DLC films are, therefore, a great candidate as a hard mask for plasma etching.

We demonstrate a transceiver with optics and electronics directly assembled on a low cost Printed Circuit Board (PCB) instead of the conventional TO-can. The PCB has a cut-in cavity for the electro-absorption modulated Laser (EML) which is thermally stabilized by a micro-TEC separated from the driver/TIA on the PCB. In this way, we show greatly reduced power consumption of the module whilst shortening the RF interconnect to the laser and improving the electro-optic (EO) bandwidth of the transmitter. The transceiver operates at 25 Gbps NRZ with less than 0.4 dB optical power variation when the ambient temperature varies from 25C to 75C. BER link performance is unaffected by transceiver operating temperature.

Surface-normal electroabsorption modulators (SNEAMs) are devices with unique characteristics, such as small size, wide bandwidth and polarization insensitive behavior; however, due to the surface-normal configuration and since they operate in reflection, it is challenging to package fiber arrays to SNEAM arrays with many channels. Here, we present a novel approach to package fiber arrays to SNEAM arrays based on passive alignment. We realize an expanded-beam, multi-channel, optical coupling scheme by using a prism lens array and a lens array in between a SNEAM array chip and a standard single mode fiber array. We use this approach to assemble a SNEAM array engine with 8 channels without any active optical alignment. We show that our SNEAM array engine has coupling loss from the fiber inputs to the SNEAMs ranging from 1.2 dB for the best channel to 1.7 dB for the worst channel. Also, we validate our passive alignment packaging scheme by modulating the channels at 25 Gbit/s NRZ-OOK and show that the fiber array is pluggable into the SNEAM array engine. Finally, our approach is independent of the specific SNEAM design, and potentially can be extended to other surface-normal devices, such as lasers or photodiodes.

We experimentally show an electro-optic tunable Fabry-Perot cavity on thin-film lithium niobate (TFLN). Instead of tuning the cavity phase and thus resonant frequency, we demonstrate modulation of the FP cavity by tuning the cavity mirrors via the electro-optic effect in the couplers. We enable full tuning of a low-Q FP cavity with only 3.5 V Vpi and a very short 3.5 mm long Mach-Zehnder interferometer (MZI) mirror.

Future optical communication systems will exploit increasingly wide optical wavelength bands to continue scaling capacity per installed fiber. Currently, optical components such as tunable lasers and modulators are designed to operate in a single wavelength band only and multiple designs are therefore needed for a single system. Improved tunable lasers operating seamlessly over these wider bands would both simplify system deployment and management. Increasing the laser tuning range requires improved wavelength selection mechanisms to simplify calibration and improve performance. We report a tunable laser with an 11THz tuning range and 14 mW output power. This laser is based on what we believe to be a novel silicon optical bench platform augmented with thermal membranes to enable both low tuning power consumption and low crosstalk laser tuning. Reduction of crosstalk simplifies both calibration and control of the laser frequency. The total power consumption of the tunable laser is only 700 mW. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Oscillating heat pipes (OHPs) typically consist of a meandering or serpentine channel or tube that contains alternating liquid slugs and vapor plugs distributed along the length of the channel. Heat transport into and out of the channels results in fluid motion due to vapor bubble generation and growth (heat input) and vapor bubble shrinkage and collapse (heat removal), which, respectively, occur at the so-called evaporator and condenser sections of the OHP. OHPs are commonly used to transport heat laterally from a heat source to a heat sink. However, they can also be employed to effectively spread heat laterally within the plane of the OHP from hotspots on one side of the OHP to a heat sink on the opposite side; we refer to this configuration as a vertical heat spreading stack. The local vaporization and condensation processes inherent to OHPs allow them to mitigate unfavorable effects associated with high heat fluxes and localized hot spots where, for example, concentrated heat sources can result in large temperature spikes when relying on a purely conduction-based approach. This work focuses on evaluating the performance of OHPs in managing localized areas of high heat flux. Potential applications include electronics cooling and in-package thermal management. A vertical heat spreading test apparatus is developed to characterize the thermal performance of the aluminum OHPs with hotspots of sizes 4 mm x 4 mm and 4 mm x 10 mm and heat fluxes of up to 100 W/cm 2 . The effects of different working fluids and fluid fill ratios are studied. A performance map of the OHPs is presented that explores the dependence of thermal resistance on the hotspot size, location, heat flux, working fluid and fluid fill ratio.

The relentless traffic growth of passive optical networks (PONs) requires high-performance optical transceivers capable of operating over legacy installed fiber links designed for much lower data rates. New methods of increasing launched optical power and received optical sensitivity are required while reducing the cost of these transceivers. We present a compact silicon optical bench 10Gb/s XGS-PON platform demonstrating E1 class performance over 29dB link loss. The integration approach is suited to high volume automated assembly for low cost.

In this paper, we introduce the design and fabrication of a high-power thermal test vehicle (TTV) equipped with a two-phase cooling system, targeting improved thermal management in Multi-Chip Modules (MCMs) for AI datacenters, 5G RAN, and EDGE compute nodes. With the rise in device integration and component power densities, conventional cooling methods fall short, prompting the need for innovative approaches to achieve efficient heat dissipation. The TTV utilizes advanced heterogeneous integration techniques on a low-temperature co-fired ceramic (LTCC) substrate, designed to reliably dissipate over 1000 W of heat. This provides a robust platform for testing advanced two-phase cooling strategies to effectively remove heat from densely packed silicon dies, thus addressing the thermal challenges inherent in modern electronics.We elaborate on the fabrication of two variations of the TTV: the first comprising six X1 MCM modules, each measuring 25 mm × 38 mm, and the second a single X6 module measuring 76 mm × 76 mm, showcasing the robustness of the process. These TTVs are engineered to manage power dissipation of up to 1008 W, with logic chips experiencing background power densities of approximately 34 W/cm^2 and hotspots peaking at 400W/cm^2, while HBM stack chips exhibit a heat flux of 16 W/cm^2. The logic chips, measuring 20 mm x 20 mm, and the HBM stacks, measuring 10 mm x 10 mm, closely replicate the specifications of cutting-edge AI hardware.The importance of this work lies in its capacity to offer a scalable and dependable testing platform for advanced thermal management strategies in high-performance computing. By leveraging two-phase cooling, it paves the way toward more reliable and efficient computing infrastructures, effectively addressing the challenges posed by high power and heat flux in contemporary electronic devices.

We fabricate and measure compact 45 mode spatial mode multiplexers based on multi-plane light conversion technology compatible with wafer scale manufacturing and measurement. The devices measure 2×4.8×1mm in dimension, fibers can be directly attached and work over 200 nm bandwidth around 1550 nm.