Search

Vanadium dioxide (VO2) is an interesting material for hybrid photonic integrated devices due to its insulator–metal phase transition. Utilizing the hysteresis of the phase transition in voltage-biased VO2, we demonstrate a compact hybrid VO2–silicon optical memory element integrated into a silicon waveguide. An optical pulse writes the VO2 memory, leading to an optical attenuation that can be read out by the optical transmission in a silicon waveguide. Our on-chip memory cell can be optically written with energy as low as 23.5 pJ per pulse and with a 10–90% rise time of ∼100 ns. This approach is promising for optical data storage in silicon photonic integrated circuits.

We demonstrate power-efficient, thermo-optic, silicon nitride waveguide phase shifters for blue, green, and yellow wavelengths. The phase shifters operated with low power consumption due to a suspended structure and multi-pass waveguide design. The devices were fabricated on 200-mm silicon wafers using deep ultraviolet lithography as part of an active visible-light integrated photonics platform. The measured power consumption to achieve a $\pi$ phase shift (averaged over multiple devices) was 0.78, 0.93, 1.09, and 1.20 mW at wavelengths of 445, 488, 532, and 561 nm, respectively. The phase shifters were integrated into Mach-Zehnder interferometer switches, and $10- 90$\% rise(fall) times of about 570(590) $\mu$s were measured., Comment: Zheng Yong and Hong Chen contributed equally to this work

Laser beam scanning is central to many applications, including displays, microscopy, three-dimensional mapping, and quantum information. Reducing the scanners to microchip form factors has spurred the development of very-large-scale photonic integrated circuits of optical phased arrays and focal plane switched arrays. An outstanding challenge remains to simultaneously achieve a compact footprint, broad wavelength operation, and low power consumption. Here, we introduce a laser beam scanner that meets these requirements. Using microcantilevers embedded with silicon nitride nanophotonic circuitry, we demonstrate broadband, one- and two-dimensional steering of light with wavelengths from 410 nm to 700 nm. The microcantilevers have ultracompact ~0.1 mm2 areas, consume ~31 to 46 mW of power, are simple to control, and emit a single light beam. The microcantilevers are monolithically integrated in an active photonic platform on 200-mm silicon wafers. The microcantilever-integrated photonic circuits miniaturize and simplify light projectors to enable versatile, power-efficient, and broadband laser scanner microchips.

We report multicore fibers (MCFs) with 10 and 16 linearly distributed cores with single-mode operation in the visible spectrum. The average propagation loss of the cores is 0.06 dB/m at λ = 445 nm and < 0.03 dB/m at wavelengths longer than 488 nm. The low inter-core crosstalk and nearly identical performance of the cores make these MCFs suitable for spatial division multiplexing in the visible spectrum. As a proof-of-concept application, one of the MCFs was coupled to an implantable neural probe to spatially address light-emitting gratings on the probe.

We applied an unmatched back projector based deconvolution algorithm to reduce image reconstruction time in light field microscopy. 3D laser written microstructures were fabricated and used to characterize the light field imaging.

Low-loss broadband fiber-to-chip coupling is currently challenging for visible-light photonic-integrated circuits (PICs) that need both high confinement waveguides for high-density integration and a minimum feature size above foundry lithographical limit. Here, we demonstrate bi-layer silicon nitride (SiN) edge couplers that have ≤ 4 dB/facet coupling loss with the Nufern S405-XP fiber over a broad optical wavelength range from 445 to 640 nm. The design uses a thin layer of SiN to expand the mode at the facet and adiabatically transfers the input light into a high-confinement single-mode waveguide (150-nm thick) for routing, while keeping the minimum nominal lithographic feature size at 150 nm. The achieved fiber-to-chip coupling loss is about 3 to 5 dB lower than that of single-layer designs with the same waveguide confinement and minimum feature size limitation.

Significance: Light-sheet fluorescence microscopy (LSFM) is a powerful technique for highspeed volumetric functional imaging. However, in typical light-sheet microscopes, the illumination and collection optics impose significant constraints upon the imaging of non-transparent brain tissues. We demonstrate that these constraints can be surmounted using a new class of implantable photonic neural probes.Aim: Mass manufacturable, silicon-based light-sheet photonic neural probes can generate planar patterned illumination at arbitrary depths in brain tissues without any additional micro-optic components.Approach: We develop implantable photonic neural probes that generate light sheets in tissue. The probes were fabricated in a photonics foundry on 200-mm-diameter silicon wafers. The light sheets were characterized in fluorescein and in free space. The probe-enabled imaging approach was tested in fixed, in vitro, and in vivo mouse brain tissues. Imaging tests were also performed using fluorescent beads suspended in agarose.Results: The probes had 5 to 10 addressable sheets and average sheet thicknesses Conclusions: The neural probes can lead to new variants of LSFM for deep brain imaging and experiments in freely moving animals.

We demonstrate VO2 optical memory integrated onto a silicon waveguide. Optical information is stored in the bistable states of VO2 and read out as the change in the optical transmission of the waveguide.

We demonstrate implantable neural probes with integrated silicon nitride optical phased arrays (OPAs) fabricated on 200mm wafers for wavelengths near 480nm. A free-propagation slab enables the emission of a single steerable beam from an OPA.

We demonstrate silicon nitride waveguide-integrated silicon lateral p-i-n photodiodes at λ=488nm. A 50-µm long device exhibits a dark current of 178pA at -5V, a responsivity of 0.31 ±0.01A/W, and an external quantum efficiency of ~78%.

We report low-loss silicon nitride bi-layer fiber-to-chip edge couplers on 200-mm silicon wafers for visible spectrum photonic circuits. The minimum per-facet coupling loss at λ=488nm was ~2.6dB (TM), and polarization-independent coupling was achieved with ~3.2-dB loss.

We demonstrate 10- and 16-core multicore fibers with all cores operating in a single- mode with

We 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.

© 2020 Elsevier Inc. We propose a new paradigm for dense functional imaging of brain activity to surmount the limitations of present methodologies. We term this approach “integrated neurophotonics”; 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. Moreaux et al. describe a new paradigm for dense functional imaging of brain activity that surmounts limitations of present methodologies. It enables functional imaging from within the brain, permitting dense, large-scale brain circuit interrogation with cellular resolution at arbitrary depths.

SignificanceLight-sheet fluorescence microscopy is a powerful technique for high-speed volumetric functional imaging. However, in typical light-sheet microscopes, the illumination and collection optics impose significant constraints upon the imaging of non-transparent brain tissues. Here, we demonstrate that these constraints can be surmounted using a new class of implantable photonic neural probes.AimMass manufacturable, silicon-based light-sheet photonic neural probes can generate planar patterned illumination at arbitrary depths in brain tissues without any additional micro-optic components.ApproachWe develop implantable photonic neural probes that generate light sheets in tissue. The probes were fabricated in a photonics foundry on 200 mm diameter silicon wafers. The light sheets were characterized in fluorescein and in free space. The probe-enabled imaging approach was tested in fixed and in vitro mouse brain tissues. Imaging tests were also performed using fluorescent beads suspended in agarose.ResultsThe probes had 5 to 10 addressable sheets and average sheet thicknesses < 16 μm for propagation distances up to 300 μm in free space. Imaging areas were as large as ≈ 240 μm × 490 μm in brain tissue. Image contrast was enhanced relative to epifluorescence microscopy.ConclusionsThe neural probes can lead to new variants of light-sheet fluorescence microscopy for deep brain imaging and experiments in freely-moving animals.

We 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 Oxide” (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 $^\circ$ C – 60 $^\circ$ 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 $\sim$ 20 mW were measured before the onset of thermal roll-off and operation up to 80 $^\circ$ C was achieved. The characteristic temperatures and thermal impedance of the lasers were evaluated and future improvements are discussed.

We 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.

We 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.

We demonstrate a flip-chip integrated electro-optic transmitter incorporating a high-swing CMOS driver and silicon photonic Mach–Zehnder modulator, and discuss the RF and thermal characteristics of the assembly. The transmitter showed a dynamic extinction ratio of 8 dB, which is the highest to date for 40+ Gb/s-class transmitters using CMOS drivers with silicon modulators. The input reflection coefficient of the module was mostly determined by the input electrical lines, solder bumps, and driver, while the electro-optic transfer function was mostly set by the Mach–Zehnder modulator. Despite the high power consumption of the driver and modulator (553 mW) and the close proximity between the electronic and photonic dies, the thermal simulations show that heat can be efficiently sunk from the bottom side of the silicon photonic die.

Multiport interferometer meshes can be used to implement unitary transformations on input vectors of light in both the classical and quantum domain. In practice, the phase-shifters in a mesh photonic circuit must be calibrated to compensate for phase errors due to fabrication variations. Calibration using photodetectors external to the mesh has been demonstrated for triangular meshes, but not rectangular meshes. Here, we propose an algorithm for the calibration of rectangular meshes using only external photodetectors and simulate it to evaluate its feasibility.

We investigate integrated mode-locked laser diodes with distributed Bragg reflectors fabricated in the JePPIX-Oclaro indium phosphide photonics platform. The optical and radio-frequency (RF) characteristics of passively mode-locked lasers with and without monolithically integrated feedback cavities were measured and compared. The RF linewidth of the mode-locked laser could be reduced by integrating an optical feedback cavity of a particular length and a tunable magnitude of feedback. A maximum linewidth reduction factor of 1.9 was observed near the onset of mode locking, but increasing the laser optical power tended to lead to unstable operation. Increasing the drive current of the design without feedback also reduced the RF linewidth. A reduction factor of 7.6 was observed.

Multivariable controllers, which efficiently manage thermal tuning for large systems, are proposed based on a novel state-space model of the tuning control problem. Worked examples of the controller design method are presented for the $1\times 2^L$ binary tree and $2^L\times 2^L$ router/selector optical switching architectures, where we characterize the performance of the controller in correcting for geometry variations and demonstrating active cancellation of thermal disturbances simultaneously in multiple tuning variables based on a single scalar measurement signal.

We 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.

We demonstrate optical memory and light-triggered electrical oscillations in a VO2 electro optic micro-wire device for potential applications in neuromorphic computing architectures.

The 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. The current state of programmable photonic integrated circuits is discussed, including recent developments in their building blocks, circuit architectures, electronic control and programming strategies, as well as different application spaces.

Optical coherence tomography can differentiate brain regions with intrinsic contrast and at a micron scale resolution. Such a device can be particularly useful as a real‐time 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, which 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., Optical coherence tomography can differentiate brain regions with intrinsic contrast and at a micron scale resolution. 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, which is compatible with deep brain stimulation keyhole neurosurgery. Using classification algorithms involving texture features and optical attenuation, images were successfully classified into three brain tissue types.