Programmable photonic circuits
Bogaerts, Wim, Daniel Pérez, José Capmany, David A. B Miller, Joyce Poon, Dirk Englund, Francesco Morichetti, Andrea Melloni
Nature 586, pp 207-216 (2020)
abstractThe growing maturity of integrated photonic technology makes it possible to build increasingly large and complex photonic circuits on the surface of a chip. Today, most of these circuits are designed for a specific application, but the increase in complexity has introduced a generation of photonic circuits that can be programmed using software for a wide variety of functions through a mesh of on-chip waveguides, tunable beam couplers and optical phase shifters. Here we discuss the state of this emerging technology, including recent developments in photonic building blocks and circuit architectures, as well as electronic control and programming strategies. We cover possible applications in linear matrix operations, quantum information processing and microwave photonics, and examine how these generic chips can accelerate the development of future photonic circuits by providing a higher-level platform for prototyping novel optical functionalities without the need for custom chip fabrication.
Full-field swept-source optical coherence tomography and neural tissue classification for deep brain imaging
Felts Almog, Ilan, Fu der Chen, Suhan Senova, Anton Fomenko, Elise Gondard, Wesley D. Sacher, Andres M. Lozano, Joyce K. S Poon
Journal of Biophotonics 13 (2), pp e201960083/1-11 (2020)
abstractOptical coherence tomography can differentiate brain regions with intrinsic contrast and at a micron scale resolution. Such a device can be particularly useful as a realtime neurosurgical guidance tool. We present, to our knowledge, the first full-field swept-source optical coherence tomography system operating near a wavelength of 1310 nm. The proof-of-concept system was integrated with an endoscopic probe tip, that is compatible with deep brain stimulation keyhole neurosurgery. Neuroimaging experiments were performed on ex vivo brain tissues and in vivo in rat brains. Using classification algorithms involving texture features and optical attenuation, images were successfully classified into three brain tissue types.
VO2 electro-optic memory and oscillator for neuromorphic computing
Jeong, Junho, Youngho Jung, Zhongnan Qu, Bin Cui, Ankita Khanda, Ankita Sharma, S. S. P. Parkin, Joyce K. S Poon
CLEO: Science and Innovations 2020, pp STh3R.2 /1-2 (2020)
abstractWe demonstrate optical memory and light-triggered electrical oscillations in a VO2 electro optic micro-wire device for potential applications in neuromorphic computing architectures.
Tunable matched-pair high-order vernier multi-ring filters with > 100 nm FSR
Mak, Jason C. C, Joyce K. S Poon
CLEO: Science and Innovations 2020, pp SM3J.3/1-2 (2020)
abstractWe propose and demonstrate a novel Vernier microring filter achieving an ultra-high out- of-band extinction of -52 dB and large free spectral range > 100 nm. The filter is wavelength-tunable over the O-band.
Wavelength tunable matched-pair Vernier multi-ring filters using derivative-free optimization algorithms
Mak, Jason C. C, Tianyuan Xue, Zheng Yong, Joyce K. S Poon
IEEE Journal of Selected Topics in Quantum Electronics 26 (5), pp 5900212/1-12 (2020)
abstractWe demonstrate matched pairs of multi-ring Vernier filters that mutually suppress the out-of-band resonances resulting from the Vernier effect to increase the free-spectral range (FSR) while achieving high out-of-band extinction ratio. These filters can be aligned to any center wavelength within the Vernier FSR. Both the design methodology and alignment procedure rely on derivative-free optimization methods. We report on an O-band silicon microring optical filter achieving out-of-band extinction of -52 dB over an FSR > 100 nm.
Integration of III-V on silicon gain devices at the backside of silicon-on-insulator wafers for photonic fully integrated circuits
Menezo, Sylvie, Torrey Thiessen, Jason Mak, Jérémy Da Fonseca, Karen Ribaud, Zheng Yon, Christophe Jany, Joyce K. S Poon
CLEO: Science and Innovations 2020, pp SM4J.7/1-2 (2020)
abstractWe present a new platform integrating heterogeneous III-V/silicon gain devices at the backside of silicon-on-insulator wafers. The fabrication relies on commercial silicon photonic processes. The performances of lasers and SOAs fabricated accordingly are reported.
Integrated neurophotonics: toward dense volumetric interrogation of brain circuit activity - at depth and in real time
Moreaux, Laurent C., Dimitri Yatsenko, Wesley D. Sacher, Jaebin Choi, Changhyuk Lee, Nicole J. Kubat, R. James Cotton, Edward S. Boyden, Michael Z. Lin, Lin Tian, Andreas S. Tolias, Joyce K.S. Poon, Kenneth L. Shepard, Michael L. Roukes
Neuron 108 (1), pp 66-92 (2020)
abstractWe propose a new paradigm for dense functional imaging of brain activity to surmount the limitations of present methodologies. We term this approach "integrated neurophotonic"; it combines recent advances in microchip-based integrated photonic and electronic circuitry with those from optogenetics. This approach has the potential to enable lens-less functional imaging from within the brain itself to achieve dense, large-scale stimulation and recording of brain activity with cellular resolution at arbitrary depths. We perform a computational study of several prototype 3D architectures for implantable probe-array modules that are designed to provide fast and dense single-cell resolution (e.g., within a 1-mm3 volume of mouse cortex comprising  ∼ 100,000 neurons). We describe progress toward realizing integrated neurophotonic imaging modules, which can be produced en masse with current semiconductor foundry protocols for chip manufacturing. Implantation of multiple modules can cover extended brain regions.
Polarization-diverse silicon photonics WDM receiver with a reduced number of OADMs and balanced group delays
Nojic, Jovana, Dominik Schoofs, Saeed Sharif Azadeh, Florian Merget, Jeremy Witzens
Optical Fiber Communications Conference and Exhibition, OFC 2020 - Proceedings, pp M4H.2/1-3 (2020)
abstractWe experimentally validate a 10-channel polarization diverse WDM receiver with only one ring based add-drop multiplexer per channel and on-chip optical delay lines balancing the two polarization paths for speeds up to 28 Gb/s.
Fabrication tolerant high-speed SiP ring modulators and optical add-drop multiplexers for WDM applications
Nojic, Jovana, Saeed Sharif Azadeh, Juliana Müller, Florian Merget, Jeremy Witzens
Proceedings of SPIE - The International Society for Optical Engineering 11285, pp 112850A/1-11 (2020)
abstractSilicon ring resonator modulators (RRMs) have great potential to reduce footprint and power consumption and to increase modulation speeds in wavelength division multiplexed (WDM) transmitters. However, the optical properties of RRMs are highly sensitive to fabrication variations, which makes them challenging to design for volume production or a large number of WDM-channels. In this work, we present an RRM design that was specifically designed and experimentally validated to have reduced sensitivity to fabrication variations. This includes a sensitivity analysis of resist over- and under-exposure (±30 nm lateral dimension deviation) and of etch depth variability (±10 nm depth variation) within the coupling section. For our design, the deviation from the targeted coupling strength is improved twofold. The proposed devices are fabricated on SOI wafers using a standard CMOS-compatible process. We demonstrate RRMs with an extinction ratio above 5 dB, an OMA better that -7 dB (at 2 Vpp) and a 29 GHz electro-optical bandwidth, showing open eye diagrams at 32 Gb/s limited only by our measurement setup. The measured coupling coefficients are in good agreement with the simulated values. Furthermore, we applied the same design modifications to realize low-doped RRMs as well as ring based adddrop-multiplexers (OADMs). The agreement between the simulated and the measured coupling coefficients (that we identified as the main source of device performance variability) further confirms the effectiveness of our design modifications. These results suggest that the proposed design can be exploited to enable reliable fabrication of resonantbased devices on a large scale, especially in WDM systems.
Surface stress and lattice dynamics in oxide ultrathin films
Premper, Jörg, Florian O. Schumann, Anita Dhaka, Sebastian Polzin, Krassimir Kostov, Veronica Goian, Dirk Sander, Wolf Widdra
Physica Status Solidi B 257 (7), pp 1900650/1-10 (2020)
abstractThe lattice misfit between the substrate and an epitaxial film leads in general to static forces, which define the interface stress, and dynamic responses that modify the thin-film lattice dynamics. Although these are both fundamental concepts that are important for film growth and thin-film properties, they have not been investigated in a combined way so far. Therefore, herein, surface stress experiments in combination with surface phonon studies for three different, cubic oxide ultrathin film systems are reviewed. Within the class of binary oxides, NiO(001) grown on Ag(001) is chosen, which exhibits a -2.2% lattice mismatch, and BaO(001) on Pt(001), a system with a negligible lattice mismatch. For the ternary oxides, perovskite thin films of BaTiO3 grown epitaxially on Pt(001) with a lattice mismatch of -2.3% are focused upon. The surface stress experiments are conducted with an optical two-beam curvature technique under in situ growth conditions. Surface and thin-film phonons are determined by high-resolution electron energy loss spectroscopy. Surface stress and lattice dynamics are discussed in the range from the oxide monolayer to thin films of about 20 unit cell in thickness.
Power-efficient lumped-element meandered silicon Mach-Zehnder modulators
Sharif Azadeh, Saeed, Jovana Nojic, Alvaro Moscoso-Mártir, Florian Merget, Jeremy Witzens
Proceedings of SPIE - The International Society for Optical Engineering 11285, pp 112850C/1-11 (2020)
abstractDriving electro-optic modulators in lumped-element (LE) configuration allows for small footprint, reduced power consumption, and improved high-speed performance. The main shortcoming of conventional rectilinear LE modulators are the required high drive-voltages, resulting from their shortened phase-shifters. To address this, we introduce a Mach-Zehnder modulator with meandered phase shifters (M-MZM), which can be driven in LE configuration, while keeping the optical phase shifter length in the same order as traveling-wave modulators (TW-MZMs). A design limitation that needs to be taken into account consists in the optical transit time of the device, that limits the overall electro-optic bandwidth. First, we review the overall power consumption improvement as well as the bandwidth enhancement in LE modulators compared to TW-MZMs, also taking the driver output impedance and parasitics from wire- or bump-bonds into account. Then, we report on the design, implementation, and experimental characterization of carrier-depletion based M-MZMs fabricated on silicon-on-insulator (SOI) wafers using standard CMOS-compatible processes. The fabricated M-MZMs, provided with low (W1), moderately (W2) and highly (W3) doped junctions, require 9.2 Vpp, 5.5 Vpp, and 3.7 Vpp for full extinction, with optical insertion losses of 5 dB, 6.3 dB and 9.1 dB. For all three M-MZMs, open eye diagrams are recorded at 25 Gb/s using a 50Ω driver and termination. For unterminated M-MZMs, higher data rates could be achieved, provided that a low output impedance driver be wire- or bump-bonded to the modulators. Finally, we compare the power consumption of the M-MZMs with TW-MZMs and show that the M-MZMs feature a 4X reduced power consumption at 25 Gb/s.
Reconfigurable frequency-selective resonance splitting in chalcogenide microring resonators
Shen, Bin, Hongtao Lin, Saeed Sharif Azadeh, Jovana Nojic, Myungkoo Kang, Florian Merget, Kathleen Richardson, Juejun Hu, Jeremy Witzens
ACS Photonics 7 (2), pp 499-511 (2020)
abstractThis paper reports a method to enable, for the first time, reconfigurable control of resonance splitting of one or multiple arbitrarily selected azimuthal orders in a microring resonator. This is accomplished by inscribing Bragg gratings in photosensitive Ge23Sb7S70 chalcogenide microring resonators via a novel cavity-enhanced photoinscription process, in which injection of light at the targeted C-band resonance frequency induces a spatially varying refractive index change. The so formed Bragg grating precisely matches the selected resonance order without introducing optical losses. Long-term room temperature stability of the photoinscribed Bragg gratings has been verified in darkness and during operation with reduced optical power levels. The Bragg gratings can be reconfigured by first erasure with flood illumination of visible light at 561 nm and subsequent reinscription. We also report controlled splitting of multiple resonances by inscribing superimposed Bragg gratings.
Disruption of oligodendrogenesis impairs memory consolidation in adult mice
Steadman, Patrick E., Frances Xia, Moriam Ahmed, Andrew J. Mocle, Amber R.A. Penning, Anna C. Geraghty, Hendrik W. Steenland, Michelle Monje, Sheena A. Josselyn, Paul W. Frankland
Neuron 105 (1), pp 150-164.e6 (2020)
abstractThe generation of myelin-forming oligodendrocytes persists throughout life and is regulated by neural activity. Here we tested whether experience-driven changes in oligodendrogenesis are important for memory consolidation. We found that water maze learning promotes oligodendrogenesis and de novo myelination in the cortex and associated white matter tracts. Preventing these learning-induced increases in oligodendrogenesis without affecting existing oligodendrocytes impaired memory consolidation of water maze, as well as contextual fear, memories. These results suggest that de novo myelination tunes activated circuits, promoting coordinated activity that is important for memory consolidation. Consistent with this, contextual fear learning increased the coupling of hippocampal sharp wave ripples and cortical spindles, and these learning-induced increases in ripple-spindle coupling were blocked when oligodendrogenesis was suppressed. Our results identify a non-neuronal form of plasticity that remodels hippocampal-cortical networks following learning and is required for memory consolidation.
Back-side-on-BOX heterogeneously integrated III-V-on-silicon O-Band distributed feedback lasers
Thiessen, Torrey, Jason C. C Mak, Jeremy Da Fonseca, Karen Ribaud, Christophe Jany, Joyce K. Poon, Sylvie Menezo
Journal of Lightwave Technology 38 (11), pp 3000-3006 (2020)
abstractWe introduce a new III-V-on-Silicon (Si) heterogeneous integration platform, where the III-V material is bonded to the back of a processed Si photonic wafer. This "Back-Side-on-Buried Oxid" (BSoBOX) process is fully compatible with active, multilayer Si photonics platforms. This article describes the process flow and reports on O-band hybrid distributed feedback (DFB) lasers of various grating periods fabricated on this platform. A comprehensive set of measurements show that the quarter-wave shifted DFB lasers have comparable performance to front-side platforms. Single-mode emission with a side mode suppression ratio around 50 dB was measured between 20°C - 60°C. The DFB lasers had threshold currents as low as 32 mA and produced output powers in the Si waveguide from a single-end of about 15 mW at 170 mA before the devices began to mode hop. Output powers of  ∼ 20mW were measured before the onset of thermal roll-off and operation up to 80°C was achieved. The characteristic temperatures and thermal impedance of the lasers were evaluated and future improvements are discussed.
Back-side-on-BOX heterogeneously integrated III-V-on-silicon O-band discrete-mode lasers
Thiessen, Torrey, Sylvie Menezo, Christophe Jany, Jason C. C Mak, Joyce K. S Poon
Optics Express 28 (26), pp 38579-38591 (2020)
abstractWe demonstrate foundry-fabricated O-band III-V-on-silicon discrete-mode lasers. The laser fabrication follows the back-side-on-buried-oxide laser integration process and is compatible with complex, multilayer, silicon-on-insulator based platforms. A series of devices were characterized, with the best devices producing on-chip powers of nearly 20 mW with Lorentzian linewidths below 20 kHz and a side mode suppression ratio of at least 60 dB.
High-efficiency photo detection at 2μm realized by GeSn/Ge multiple-quantum-well photodetectors with photon-trapping microstructure
Zhou, Hao, Shengqiang Xu, Yiding Lin, Yi-Chiau Huang, Bongkwon Son, Wei Li, Xin Guo, Lin Liu, Kwang Hong Lee, Xiao Gong, Chuan Seng Tan
CLEO: Science and Innovations 2020, pp STh4L.1/1-2 (2020)
abstractPhoton-trapping microstructure was designed and incorporated into GeSn/Ge multiple-quantum-well photodetectors to enhance the optical absorption. A four times higher responsivity of 0.11 A/W was achieved at a wavelength of 2μm.