This report captures the initial conclusions of the DOE seven National Lab team collaborating on the “Solving the Information Technology Energy Challenge Beyond Moore’s Law” initiative from the DOE Big Idea Summit III held in April of 2016. The seven Labs held a workshop in Albuquerque, NM in late July 2016 and gathered 40 researchers into 5 working groups: 4 groups spanning the levels of the co-design framework shown below, and a 5th working group focused on extending and advancing manufacturing approaches and coupling their constraints to all of the framework levels. These working groups have identified unique capabilities within the Labs to support the key challenges of this Beyond Moore’s Law Computing (BMC) vision, as well as example first steps and potential roadmaps for technology development.
Stark, Andrew S.; Yang, Benjamin B.; Ward, Chris W.; Brothers, Timothy B.; Wagner, Brent W.; Langston, Jerrod L.; Bottenfield, Christian B.; Saha, Gareeyasee S.; Lavrencik, Justin L.; Ralph, Stephen E.; Paollela, Arthur P.; Middleton, Charles M.; DeSalvo, Richard D.; Gehl, M.; DeRose, Christopher T.; Lentine, Anthony L.
Stark, Andrew S.; Yang, Benjamin B.; Ward, Chris W.; Davis, Kyle D.; Brothers, Tim B.; Wagner, Brent W.; Langston, Jerrod L.; Bottenfield, Christian B.; Saha, Gareeyasee S.; Lavrencik, Justin L.; Ralph, Stephen E.; Paollela, Arthur P.; Middleton, Charles M.; DeSalvo, Richard D.; Gehl, M.; DeRose, Christopher T.; Lentine, Anthony L.
An 11-channel 1-GHz bandwidth silicon photonic AWG was fabricated and measured in the lab. Two photonic architectures are presented: (1) RF-envelope detector, and (2) RF downconvertor for digital systems. The RF-envelope detector architecture was modeled based on the demonstrated AWG characteristics to determine estimated system-level RF receiver performance.
Gehl, M.; Stark, Andrew S.; Ward, Chris W.; Yang, Benjamin B.; Brothers, Tim B.; Langston, Jerrod L.; Bottenfield, Christian B.; Saha, Gareeyasee S.; Lavrencik, Justin L.; Ralph, Stephen E.; Paollela, Arthur P.; Middleton, Charles M.; DeSalvo, Richard D.; Gehl, M.; DeRose, Christopher T.; Lentine, Anthony L.
We present a quantitative analysis of the correlation of resonant wavelength variation with process variables, and find that 50% of the resonant wavelength variation for microrings is due to systematic process conditions. We also discuss the improvement of device uniformity by mitigating these systematic variations.
We present our experimental results of ultra efficient (up to 2.16 nm/mW) thermally tunable modulators with n-Type heaters and the Si substrate removed. To our knowledge, this is the most efficient thermally tunable modulator demonstrated at 1550nm to date. We include results of externally heated modulators with commensurate performance enhancements through substrate removal.
We demonstrate a silicon photonic transceiver circuit for high-speed discrete variable quantum key distribution that employs a common structure for transmit and receive functions. The device is intended for use in polarization-based quantum cryptographic protocols, such as BB84. Our characterization indicates that the circuit can generate the four BB84 states (TE/TM/45°/135° linear polarizations) with >30 dB polarization extinction ratios and gigabit per second modulation speed, and is capable of decoding any polarization bases differing by 90° with high extinction ratios.
We experimentally demonstrate ultrahigh extinction ratio (>65 dB) amplitude modulators (AMs) that can be electrically tuned to operate across a broad spectral range of 160 nm from 1480-1640 nm and 95 nm from 1280-1375 nm. Our on-chip AMs employ one extra coupler compared with conventional Mach-Zehnder interferometers (MZI), thus form a cascaded MZI (CMZI) structure. Either directional or adiabatic couplers are used to compose the CMZI AMs and experimental comparisons are made between these two different structures. We investigate the performance of CMZI AMs under extreme conditions such as using 95:5 split ratio couplers and unbalanced waveguide losses. Electro-optic phase shifters are also integrated in the CMZI AMs for high-speed operation. Finally, we investigate the output optical phase when the amplitude is modulated, which provides us valuable information when both amplitude and phase are to be controlled. Our demonstration not only paves the road to applications such as quantum information processing that requires high extinction ratio AMs but also significantly alleviates the tight fabrication tolerance needed for large-scale integrated photonics.
Arrayed waveguide gratings provide flexible spectral filtering functionality for integrated photonic applications. Achieving narrow channel spacing requires long optical path lengths which can greatly increase the footprint of devices. High index contrast waveguides, such as those fabricated in silicon-on-insulator wafers, allow tight waveguide bends which can be used to create much more compact designs. Both the long optical path lengths and the high index contrast contribute to significant optical phase error as light propagates through the device. Therefore, silicon photonic arrayed waveguide gratings require active or passive phase correction following fabrication. Here we present the design and fabrication of compact silicon photonic arrayed waveguide gratings with channel spacings of 50, 10 and 1 GHz. The largest device, with 11 channels of 1 GHz spacing, has a footprint of only 1.1 cm2. Using integrated thermo-optic phase shifters, the phase error is actively corrected. We present two methods of phase error correction and demonstrate state-of-the-art cross-talk performance for high index contrast arrayed waveguide gratings. As a demonstration of possible applications, we perform RF channelization with 1 GHz resolution. Additionally, we generate unique spectral filters by applying non-zero phase offsets calculated by the Gerchberg Saxton algorithm.
We demonstrate a silicon photonic transceiver circuit to implement polarization encoding/decoding for DV-QKD. The circuit is capable of encoding BB84 states with >30 dB PER and decoding with >20 dB ER.
We design, fabricate and demonstrate the operation of a compact, 1 GHz resolution silicon arrayed waveguide grating. Active phase correction allows for low channel cross-talk, enabling the demonstration of spectral shaping and RF signal analysis.
We experimentally demonstrate amplitude modulators (AMs) with >65 dB extinction across over a 160 nm spectral range. The output optical phase response is also characterized when the amplitude is modulated.
We demonstrate the operation of silicon micro-disk modulators at temperatures as low as 3.8K. We characterize the steady-state and high-frequency performance and look at the impact of doping concentration.
We demonstrate compact silicon photonic arrayed waveguide gratings with channel spacing down to 1 GHz using active phase correction. The relative phase of each path within the device is directly measured using an interferometer, and two methods of phase optimization are implemented and compared.
A two-part silicon photonic variable optical attenuator is demonstrated in a compact footprint which can provide a high extinction ratio at wavelengths between 1520 nm and 1620 nm. The device was made by following the conventional p-i-n waveguide section by a high-extinction-ratio second-order microring filter section. The rings provide additional on-off contrast by utilizing a thermal resonance shift, which harvested the heat dissipated by current injection in the p-i-n junction. We derive and discuss a simple thermal-resistance model in explanation of these effects.
We describe the challenge of implementing optical interconnect for beyond Moore's electronic devices. In particular, we developed a simple link model and calculated the optical communications energy for logic voltages down to 10 mV. The results of this link model show a limit to the minimum communications energy that depends on the achievable extinction ratio of the devices. This work gives some insight into the tact that should be taken for improved optical devices to have an impact in future computing systems using ultra-low voltage transistor devices.
Tunable silicon microring resonators with small, integrated micro-heaters which exhibit a junction field effect were made using a conventional silicon-on-insulator (SOI) photonic foundry fabrication process. The design of the resistive tuning section in the microrings included a "pinched" p-n junction, which limited the current at higher voltages and inhibited damage even when driven by a pre-emphasized voltage waveform. Dual-ring filters were studied for both large (>4.9 THz) and small (850 GHz) free-spectral ranges. Thermal red-shifting was demonstrated with microsecond-scale time constants, e.g., a dual-ring filter was tuned over 25 nm in 0.6 μs 10%-90% transition time, and with efficiency of 3.2 μW/GHz.