This PDF file contains the front matter associated with SPIE Proceedings Volume 12427, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

All-optical digital computing has the potential to greatly reduce the latency, power consumption and increasing bandwidth in data center devices. This, however, requires solving 3 fundamental computing paradigms using all-optical methods: data in use, data at rest and data in transit. In this talk we present the current challenges in optical digital logic and discuss the criteria for real-world processing needs (data in use), the challenges in optical memory able to interface with said logic (data at rest) and the challenges facing the overall architectures and interconnects (data in transit). Our goal is to explore how an all-optical digital computer can be realized in the near future by addressing all these challenges and proposing roadmaps for their solution.

In this work, we consider a hybrid-coherent time-delay photonic reservoir, with a coherent input layer and an incoherent output layer, for post-processing signals from a 200 km, 28 GBaud PAM-4 transmission link. The amplitude and the phase of the transmission link are obtained through a coherent receiver and introduced as two independent encoding signals at the input of our photonic reservoir. We use the photodetected intensity of the reservoir’s response to train a linear classifier and perform the data recovery task. This hybrid-coherent reservoir exhibits a bit error rate of 10−4 , three orders of magnitude lower compared to the performance of the same photonic reservoir that processes only the amplitude information at the input.

We have successfully designed and fabricated the silicon photonics integrated circuit for a 1.6 Tbps co-packaged optics, consisting of low-loss crossings, wavelength multiplexers, and optical modulators. The optical insertion losses of siliconnitride crossing structure and wavelength multiplexers were less than 0.2 dB and 3.0 dB, respectively. Those passive components enabled low-loss optical transmitter circuits for four-parallel CWDM4 application.

Rapid developments in computer science have led to the increasing demand for efficient computing systems. Linear photonic systems rose as a favorable candidate for workload-demanding architectures, due to their small footprint and low energy consumption. Mach Zehnder Interferometers (MZI) serve as the foundational building block for several photonic circuits, and have been widely used as modulators, switches and variable power splitters. However, combining MZIs for realizing multiport splitters remains a challenge, since the exponential increase in the number of devices and the consequential increase in losses is limiting the performance of the MZI based multiport device. To overcome such limitations, incorporating alternative and low loss integration platforms combined with a generalized design of the MZI could allow the realization of a robust variable power splitter. In this work, we present for the first time a 4×4 Generalized Mach Zehnder Interferometer (GMZI) incorporated on a Si₃N₄ photonic integration platform and we experimentally demonstrate its operation as a variable power splitter. We developed an analytical model to describe the operation of the 4×4 GMZI, allowing us to evaluate the impact of several parameters to the overall performance of the device and investigate the device’s tolerance to fabrication imperfections and design alternations. Its experimental evaluation as a variable power splitter reveals a controlled imbalance that ranges up to 10 dB in multiple output ports of the device, validating the theoretically derived principles of operation.

We show the computational power of few-mode fibers (FMF) in a 40 Gbps spatiotemporal coincidence detector scheme. We consider a 5.5 m step-index FMF, with a 16.6 μm core diameter, as the medium that introduces various delays to a temporal input pulse, via the supported propagation fiber modes. In our representation, the different group velocities of the excited fiber modes define equivalent optical dendritic branches. A 1550 nm laser’s optical output is modulated by a 40 Gbps binary sequence and coupled to the FMF. The output optical pattern is photodetected by a 3×3 array and used to solve successfully a 6-bit header classification task.

IOCore^TM is a 5 mm × 5 mm silicon photonic micro transceiver with a multimode interface. IOCore features four lanes for transmitting and receiving, and 25 Gbps/lane and 32 Gbps/lane have been released. A Fabry-Perot quantum dot laser in the 1.3 micrometer band is applied as the light source. This facilitates low-cost assembly with a multimode coupling interface and robust connectivity at high temperatures. With the increasing power consumption of IT equipment, there is a need to respond to high temperature operation and excellent cooling capacity using immersion cooling technology. In recent years, it has been proposed to mount the transceiver on the system board or LSI package to achieve high throughput with low power consumption. These transceivers require high reliability because they are difficult to repair. This study summarizes and reports on the design and evaluation of IOCore, which has been partially published previously, including its high temperature operation (105 °C), suitability for immersion systems, and reliability.

In current data-center switches, external fiber-optic connections are terminated in pluggable transceivers at the faceplate of the housing. The signals within the switch are transported electrically via copper traces on printed circuit boards. With increasing data rates, these electrical connections are becoming progressively more lossy, and increasing the electrical power to compensate for this loss negatively impacts the operational cost, electric power infrastructure, and waste heat management. To address these problems, the industry is envisioning placing the transceivers inside the housing very close to where the signals are generated: co-packaged with the switch ASIC. This approach effectively replaces the high-loss copper lanes with low-loss optical-fiber. However, to achieve this low-loss optical connectivity, the optical fibers must be single-mode for short ~0.5 m application lengths to avoid introducing signal impairments due to multi-path interference. It is also desirable that these fibers have good bend performance and mode-field diameters compatible with the installed base of single-mode fiber. In this paper, we will summarize the design of a new fiber optimized for these co-packaged applications and present data on developmental prototypes that demonstrates their suitability for use in short-length optical interconnects. We will also present a novel concept for management of the hundreds to thousands of fibers within the switch housing in which variable lengths of cable are neatly secured inside stackable accumulators. This tailoring of the length for each cable path results in no cable crossovers and will thus facilitate lower-cost and less error-prone assembly and easier maintenance of the switch.

The co-packaging of optics and electronics provides a potential path forward to achieving beyond 50 Tbps top of rack switch packages. In a co-packaged design, the scaling of bandwidth, cost, and energy is governed by the number of optical transceivers (TxRx) per package as opposed to transistor shrink. Due to the large footprint of optical components relative to their electronic counterparts, the vertical stacking of optical TxRx chips in a co-packaged optics design will become a necessity. As a result, development of efficient, dense, and wide alignment tolerance chip-to-chip optical couplers will be an enabling technology for continued TxRx scaling. In this paper, we propose a novel scheme to vertically couple into standard 220 nm silicon on insulator waveguides from 220 nm silicon nitride on glass waveguides using overlapping, inverse double tapers. Simulation results using Lumerical’s 3D Finite Difference Time Domain solver are presented, demonstrating insertion losses below -0.13 dB for an inter-chip spacing of 1 μm; 1 dB vertical and lateral alignment tolerances of approximately 2.6 μm and ± 2.8 μm, respectively; a greater than 300 nm 1 dB bandwidth; and 1 dB twist and tilt tolerances of approximately ± 2.3 degrees and 0.4 degrees, respectively. These results demonstrate the potential of our coupler for use in co-packaged designs requiring high performance, high density, CMOS compatible out of plane optical connections.

Optical interconnects using a silicon-on-insulator integrated circuit platform have become the basis for many modern communications platforms. One limiting factor in interconnect technology is creating a consistent, reliable method for measuring the amount of coupled light from optical fibers into waveguides in a photonic integrated circuit. Monitoring the coupling efficiency before, during, and after would be the ideal scenario for fiber bonding. Using a foundry compatible engineered scattering element developed by our lab, we have been able to monitor the degree of fiber alignment by recording the relative power scattered by the engineered element. Recorded powers are then compiled to generate a heat map of the optimal fiber position for coupling. These scattering elements are also polarization sensitive, thus allowing for the fast axis of polarization maintaining fibers to be monitored and optimized for coupling.

Efficient fiber-to-waveguide coupling is critical for photonic integrated circuits. However, it is very challenging because of the mode mismatch and high sensitivity to misalignment between the fiber and the waveguide. To address this challenge, various coupling mechanisms have been exploited using sophisticated coupler designs involving complex light interactions with structures from the microscale to the macroscale. Simulations of these complex interactions are essential for the coupler design. Here, we are introducing a multi-scale simulation workflow to design the coupler making use of the interoperability between Ansys Lumerical and Ansys Zemax OpticStudio.

The functionality of Free Space Optical (FSO) communication links is highly influenced by meteorological conditions such as precipitation, snowfall, and fog. In this study, we establish an FSO link and conduct experimental measurements to evaluate the link performance under extreme winter conditions in the city of Astana, with the goal of facilitating secure 5G applications. During the measurement period, the lowest recorded temperature was -19.3 °C, with an average of -7 °C. We present the path loss for a link with a distance of 212 meters under various weather conditions (snow, clear sky, cloudy, overcast), visibility, humidity, and air pressure levels. We also record wind speed and snowfall rate. The obtained path loss data is subsequently compared with analytical approximations previously reported in the literature.

Recently special gas-adsorbing materials have been developed to capture gaseous contaminants such as moisture, organics and hydrogen in Optical Transceivers, multiplexers, and laser diodes that otherwise may be detrimentally affected by these gases. Hermetically sealed, or semi-hermetic packages are often used to protect High-Reliability Opto-electronic devices from possible damages due to atmospheric gases and harsh environment, aiming for higher performances and longer lifetime of the modules. Nevertheless, sealed devices may experience issues from internal outgassing of gas species like H2O, H2, and VOCs (Volatile Organic Compounds) released by inner materials or components. As reported in MIL-STD-883, the moisture limit of 5,000 ppm is specified as the critical concentration for which evident corrosion mechanisms are observed in integrated circuits and hybrid components. Moisture can be a problem in several PIC (Photonic Integrated Circuits) devices. It is also known that moisture and hydrogen may have negative effects in High Speed Optical Transceivers or that VOCs may cause problems in Laser Diode modules. Special Getter Materials integrated in the packages – especially in their lids – can successfully fix these issues. New getter materials have been developed to sorb the detrimental gases. In particular they have been designed to cope with MIL requirement for moisture and to ensure very low water concentration, even well below 1,000 ppm. Depending on the device and on the amounts of detrimental gases to be sorbed the getter can be selected and properly sized. It is usually activated by heating in vacuum or nitrogen, immediately before the sealing of the device package.

Computational study of optical coupling efficiencies of selected passive optical alignment options has done. Passive placement of fiber array optical alignment in V-grooves, and high-precision pick & place aligners have immense potential applicable for high-volume manufacturing with the benefits of advancement of low-tolerance fabrication of SiPIC, micro-optic parts, and fiber array. The tight 1dB- and 3dB-loss alignment tolerances in lateral direction of the fiber array in V-groove array and focusing lens & fiber array can be improved by using beam collimation approach. Combined optical packaging of passive alignment of micro optics such as micro lens array and active alignment of fiber array or refocusing lens-attached fiber array can compensate the cycle time achieving sufficient coupling efficiency. Dedicated design of passive optical alignment structure and process using Si-PIC, fiber array block, and micro optics is a homework of individual developer utilizing currently available techniques to mitigate tight acceptable tolerances.