11 TOPS photonic convolutional accelerator for optical neural networks.

Convolutional neural networks, inspired by biological visual cortex systems, are a powerful category of artificial neural networks that can extract the hierarchical features of raw data to provide greatly reduced parametric complexity and to enhance the accuracy of prediction. They are of great interest for machine learning tasks such as computer vision, speech recognition, playing board games and medical diagnosis1-7. Optical neural networks offer the promise of dramatically accelerating computing speed using the broad optical bandwidths available. Here we demonstrate a universal optical vector convolutional accelerator operating at more than ten TOPS (trillions (1012) of operations per second, or tera-ops per second), generating convolutions of images with 250,000 pixels-sufficiently large for facial image recognition. We use the same hardware to sequentially form an optical convolutional neural network with ten output neurons, achieving successful recognition of handwritten digit images at 88 per cent accuracy. Our results are based on simultaneously interleaving temporal, wavelength and spatial dimensions enabled by an integrated microcomb source. This approach is scalable and trainable to much more complex networks for demanding applications such as autonomous vehicles and real-time video recognition.

Ultra-broadband TM-pass polarizer based on anisotropic metamaterials in lithium niobate on an insulator.

An ultra-broadband TM-pass polarizer is designed, fabricated, and experimentally demonstrated based on subwavelength grating (SWG) metamaterials in a lithium niobate on an insulator (LNOI) platform. According to our simulation, the designed device is predicted to work at a 220 nm wavelength range from 1460 to 1680 nm, covering the S-, C-, L-, U-bands of optical fiber communication. By depositing and subsequently etching a silicon nitride thin film atop the LNOI chip, the SWG structures are formed successfully by using complementary metal-oxide semiconductor (CMOS)-compatible fabrication processes. The measured results show a high polarization extinction ratio larger than 20 dB and a relatively low insertion loss below 2.5 dB over a 130 nm wavelength range from 1500 to 1630 nm, mainly limited by the operation bandwidth of our laser source.

Ridge waveguide couplers with leaky mode resonator-like wavelength responses.

Integrated photonic resonators based on bound states in the continuum (BICs) on the silicon-on-insulator (SOI) platform have the potential for novel, mass-manufacturable resonant devices. While the nature of BIC-based ridge resonators requires the resonators to be extended in the (axial) propagation direction of the resonant mode, the requirement for excitation from the quasi-continuum extends the resonator structures also in the lateral dimensions, resulting in large device footprints. To overcome this footprint requirement, we investigate the translation of BIC-based ridge resonators into a guided mode system with finite lateral dimensions. We draw analogies between the resulting waveguide system and the BIC-based resonators and numerically demonstrate that, analog to the BIC-based resonators, such a waveguide system can exhibit spectrally narrow-band inversion of its transmissive behavior.

Correlated twin-photon generation in a silicon nitride loaded thin film PPLN waveguide.

Photon-pair sources based on thin film lithium niobate on insulator technology have a great potential for integrated optical quantum information processing. We report on such a source of correlated twin-photon pairs generated by spontaneous parametric down conversion in a silicon nitride (SiN) rib loaded thin film periodically poled lithium niobate (LN) waveguide. The generated correlated photon pairs have a wavelength centred at 1560 nm compatible with present telecom infrastructure, a large bandwidth (21 THz) and a brightness of ∼2.5 × 105 pairs/s/mW/GHz. Using the Hanbury Brown and Twiss effect, we have also shown heralded single photon emission, achieving an autocorrelation g H(2)(0)≃0.04.

Adaptive dispersion compensation using a photonic integrated circuit finite impulse response filter.

Optical equalization can be used for chromatic dispersion compensation in optical communication systems to improve the system performance; however, optical signal processing (OSP) is generally specifically designed for transmission channels, that is non-adaptive to dynamic transmission distortions compared with digital signal processing (DSP). In this contribution, we demonstrate optical equalization using a photonic integrated circuit (PIC) filter for chromatic dispersion compensation, with static and adaptive techniques: (a) the static optical equalizer is calibrated based on the known fiber dispersion and length, by using the fractional delay reference method; (b) the adaptive optical equalizer is updated iteratively to compensate transmission impairments based on a least-mean squares (LMS) algorithm. Experimental results show that both the static optical equalizer and the adaptive optical LMS equalizer can give an 18-dB Q-factor for a 14-Gbd QPSK signal transmitting over 30 km. To highlight the capability of the optical equalizers, we use simulations to show the improvement in dispersion compensating characteristics by implementing additional taps.

Ridge resonators with compact guided mode coupling.

Ridge resonators are a recently introduced integrated photonic circuit element based on bound states in the continuum (BICs) which can produce a single, sharp resonance over a broad wavelength range with high extinction ratio. However, to excite these resonators, a broad beam of laterally unbound slab mode is required, resulting in a large device footprint, which is not attractive for integrated photonic circuits. In this contribution, we propose and numerically validate a guided-mode waveguide structure that can be analogue to the BIC-based ridge resonators. Our simulations show that the proposed guided-mode waveguide structure can produce resonances with similar characteristics, yet with a significantly reduced footprint. Furthermore, we investigate the influence of the resonator's dimensions on the bandwidth of the resonance, demonstrating that resonances with Q-factors from low to very high (> 10000) are feasible. We believe that the reduced footprint and ability to design filters systematically make the guided-mode waveguide resonators an attractive photonic circuit component with particular value for foundry fabricated silicon photonic circuits.

Minimum complexity integrated photonic architecture for delay-based reservoir computing.

Reservoir computing is an analog bio-inspired computation scheme for efficiently processing time-dependent signals, the photonic implementations of which promise a combination of massive parallel information processing, low power consumption, and high-speed operation. However, most of these implementations, especially for the case of time-delay reservoir computing, require extensive multi-dimensional parameter optimization to find the optimal combination of parameters for a given task. We propose a novel, largely passive integrated photonic TDRC scheme based on an asymmetric Mach-Zehnder interferometer in a self-feedback configuration, where the nonlinearity is provided by the photodetector, and with only one tunable parameter in the form of a phase shifting element that, as a result of our configuration, allows also to tune the feedback strength, consequently tuning the memory capacity in a lossless manner. Through numerical simulations, we show that the proposed scheme achieves good performance -when compared to other integrated photonic architectures- on the temporal bitwise XOR task and various time series prediction tasks, while greatly reducing hardware and operational complexity.

Investigating the thermal robustness of soliton crystal microcombs.

Soliton crystals are a novel form of microcomb, with relatively high conversion efficiency, good thermal robustness, and simple initiation among the methods to generate them. Soliton crystals can be easily generated in microring resonators with an appropriate mode-crossing. However, fabrication defects can significantly affect the mode-crossing placement and strength in devices. To enable soliton crystal states to be harnessed for a broader range of microcomb applications, we need a better understanding of the link between mode-crossing properties and the desired soliton crystal properties. Here, we investigate how to generate the same soliton crystal state in two different microrings, how changes in microring temperature change the mode-crossing properties, and how mode-crossing properties affect the generation of our desired soliton crystal state. We find that temperature affects the mode-crossing position in these rings but without major changes in the mode-crossing strength. We find that our wanted state can be generated over a device temperature range of 25 ∘C, with different mode-crossing properties, and is insensitive to the precise mode-crossing position between resonances.

Integrated lithium niobate optical mode (de)interleaver based on an asymmetric Y-junction.

Lithium niobate on insulator (LNOI) platforms promise unique advantages in realizing high-speed, large-capacity, and large-scale photonic integrated circuits (PICs) by leveraging lithium niobate's attractive material properties, which include electro-optic and nonlinear optic properties, low material loss, and a wide transparency window. Optical mode interleavers can increase the functionality of future PICs in LNOI by enabling optical mode division multiplexing (MDM) systems, allowing variable mode assignment while maintaining high channel utilization and capacity. In this Letter, we experimentally demonstrate an optical mode interleaver based on an asymmetric Y-junction on the LNOI platform, which exhibits an insertion loss of below 0.46 dB and modal cross talk of below -13.0 dB over a wavelength range of 1500-1600 nm. The demonstrated mode interleaver will be an attractive circuit component in future high-speed and large-capacity PICs due to its simple structure, scalability, and capacity for efficient and flexible mode manipulation on the LNOI platform.

Integrated lithium niobate polarization beam splitter based on a photonic-crystal-assisted multimode interference coupler.

Lithium niobate on insulator (LNOI) is a promising platform for high-speed photonic integrated circuits (PICs) that are used for communication systems due to the excellent electro-optic properties of lithium niobate (LN). In such circuits, the high-speed electro-optical modulators and switches need to be integrated with passive circuit components that are used for routing the optical signals. Polarization beam splitters (PBSs) are one of the fundamental passive circuit components for high-speed PICs that can be used to (de)multiplex two orthogonal polarization optical modes, enabling on-chip polarization division multiplexing (PDM) systems, which are suitable for enhancing the data capacity of PICs. In this Letter, we design and experimentally demonstrate a high-performance PBS constructed by a photonic crystal (PC)-assisted multimode interference (MMI) coupler. The measured polarization extinction ratio (ER) of the fabricated device is 15 dB in the wavelength range from 1525 to 1565 nm, which makes them suitable for the high-speed and large data capacity PICs required for future communication systems.

An extensional strain sensing mechanosome drives adhesion-independent platelet activation at supraphysiological hemodynamic gradients.

BACKGROUND: Supraphysiological hemodynamics are a recognized driver of platelet activation and thrombosis at high-grade stenosis and in blood contacting circulatory support devices. However, whether platelets mechano-sense hemodynamic parameters directly in free flow (in the absence of adhesion receptor engagement), the specific hemodynamic parameters at play, the precise timing of activation, and the signaling mechanism(s) involved remain poorly elucidated. RESULTS: Using a generalized Newtonian computational model in combination with microfluidic models of flow acceleration and quasi-homogenous extensional strain, we demonstrate that platelets directly mechano-sense acute changes in free-flow extensional strain independent of shear strain, platelet amplification loops, von Willebrand factor, and canonical adhesion receptor engagement. We define an extensional strain sensing "mechanosome" in platelets involving cooperative Ca2+ signaling driven by the mechanosensitive channel Piezo1 (as the primary strain sensor) and the fast ATP gated channel P2X1 (as the secondary signal amplifier). We demonstrate that type II PI3 kinase C2α activity (acting as a "clutch") couples extensional strain to the mechanosome. CONCLUSIONS: Our findings suggest that platelets are adapted to rapidly respond to supraphysiological extensional strain dynamics, rather than the peak magnitude of imposed wall shear stress. In the context of overall platelet activation and thrombosis, we posit that "extensional strain sensing" acts as a priming mechanism in response to threshold levels of extensional strain allowing platelets to form downstream adhesive interactions more rapidly under the limiting effects of supraphysiological hemodynamics.

Arbitrary access to optical carriers in silicon photonic mode/wavelength hybrid division multiplexing circuits.

The manipulation of optical modes directly in a multimode waveguide without affecting the transmission of undesired signal carriers is of significance to realize a flexible and simple structured optical network-on-chip. In this Letter, an arbitrary optical mode and wavelength carrier access scheme is proposed based on a series of multimode microring resonators and one multimode bus waveguide with constant width. As a proof-of-concept, a three-mode (de)multiplexing device is designed, fabricated, and experimentally demonstrated. A new, to the best of our knowledge, phase-matching idea is employed to keep the bus waveguide width constant. The mode coupling regions and transmission regions of the microring resonators are designed carefully to selectively couple and transmit different optical modes. The extinction ratio of the microring resonators is larger than 21.0 dB. The mode and wavelength cross-talk for directly (de)multiplexing are less than -12.8 dB and -19.0 dB, respectively. It would be a good candidate for future large-scale multidimensional optical networks.

Fringe analysis approach for imaging surface undulations on technical surfaces.

Automated defect inspection is becoming increasingly important for advanced manufacturing. The ability to automatically inspect for critical defects early in the production cycle can reduce production costs and resources on unnecessary manufacturing steps. While there are many inspection techniques available, samples from early in a production workflow can prove challenging as they may still have systematic tooling marks, causing preferential scattering and hindering defect extraction. We propose a new imaging technique that exploits the preferential scattering from a technical surface to generate predictable fringe patterns on the sample's surface using only an array of LEDs. The patterns from this adapted fringe projection technique are imaged, and phase shifting algorithms are used to recover surface undulations on the sample. We implement this technique in the context of Hard Disk Drive platters that exhibit tooling marks from the lapping process and show that it is possible to image both highly scattering pits and scratches, as well as slow surface undulations with the same apparatus.

Ridge resonators: impact of excitation beam and resonator losses.

Photonic resonators based on bound states in the continuum are attractive for sensing and telecommunication applications, as they have the potential to achieve ultra-high Q-factor resonators in a compact footprint. Recently, ridge resonators - leaky mode resonators based on a bound state in the continuum - have been demonstrated on a scalable photonic integrated circuit platform. However, high Q-factor ridge resonators have thus far not been achieved. In this contribution, we investigate the influence of excitation beam width and optical losses on the spectral response of ridge resonators. We show that for practical applications, the space required of the excitation beam is the limiting factor on the highest achievable Q-factor.

Integrated photonic high extinction short and long pass filters based on lateral leakage.

In this contribution we present a new approach to achieve high extinction short and long pass wavelength filters in the integrated photonic platform of lithium niobate on insulator. The filtering of unwanted wavelengths is achieved by employing lateral leakage and is related to the bound state in the continuum phenomenon. We show that it is possible to control the filter edge wavelength by adjusting the waveguide dimensions and that an extinction of hundreds of dB/cm is readily achievable. This enabled us to design a pump wavelength suppression of more than 100 dB in a 3.5 mm long waveguide, which is essential for on-chip integration of quantum-correlated photon pair sources. These findings pave the way to integrate multi wavelength experiments on chip for the next generation of photonic integrated circuits.

Integrated non-blocking optical router harnessing wavelength- and mode-selective property for photonic networks-on-chip.

In this paper, we propose and demonstrate a 4×4 non-blocking optical router utilizing 8 mode (de)multiplexers and a 4×4 microring-based grid network, which can passively assign signals carried by optical wavelength and mode channels from an arbitrary input port to corresponding output ports without additional switch time, realizing the non-blocking property. The proposed device is fabricated on a silicon-on-insulator platform using the standard Complementary Metal-Oxide-Semiconductor (CMOS) fabrication processes. The insertion loss is lower than 5.7 dB including the loss of the auxiliary mode (de)multiplexers (AMUXs), while the crosstalk is lower than -15.6 dB for all routing states. Moreover, the transmission spectra from the input ports to the next cascading device are also measured to demonstrate the feasibility of further expanding via cascading multiple blocks, with the insertion loss and crosstalk lower than 7.1 dB (including the mode coupling loss of AMUXs) and -16.4 dB, respectively. The 12 Gbps dynamic transmission experiment is demonstrated with clear and open eye diagrams, illustrating the utility of the device. The device has high geometrical symmetry and good scalability, we exhibit all solutions to expand the 4×4 optical router to 8×8 and 16×16 optical routers with the advantages and deficiencies of each solution discussed.

Demonstration of various optical directed logic operations by using an integrated photonic circuit.

Optical directed logic is a novel logic operation scheme that employs electrical signals as operands to control the working states of optical switches to perform the logic operations. In this Letter, we propose and demonstrate an integrated photonic circuit which can implement five different optical logic operations by utilizing two optical modes. The proposed device is fabricated on a silicon-on-insulator substrate by using electron beam lithography and inductively coupled plasma etching processes. The static experimental results show that the fabricated device can implement five different operations correctly-XOR, XNOR, NOR, NOT, and AND-from which we can see that the signal-to-noise ratios are larger than 17.6 dB over the entire C band for all five logic functions. At last, all five logic operations with the speed of 10 Kbps are demonstrated. The proposed device with simple structure, large bandwidth, and versatility would be a promising candidate for information processing in optical mode division multiplexing networks.

High-speed electro-optic modulator based on silicon nitride loaded lithium niobate on an insulator platform.

Electro-optic (EO) modulators, which convert signals from the electrical to optical domain plays a key role in modern optical communication systems. Lithium niobate on insulator (LNOI) technology has emerged as a competitive solution to realize high-performance integrated EO modulators. In this Letter, we design and experimentally demonstrate a Mach-Zehnder interferometer-based modulator on a silicon nitride loaded LNOI platform, which not only takes full advantage of the excellent EO effect of LiNbO3, but also avoids the direct etching of LiNbO3 thin film. The measured half-wave voltage length product of the fabricated modulator is 2.24 V·cm, and the extinction ratio is ∼20dB. Moreover, the 3 dB EO bandwidth is ∼30GHz, while the modulated data rate for on-off key signals can reach up to 80 Gbps.

On-chip switchable and reconfigurable optical mode exchange device using cascaded three-waveguide-coupling switches.

Data exchange between different data channels can offer more flexible and advanced functions for many optical networks. In this paper, we propose a switchable and reconfigurable data exchange device for arbitrary two optical mode channels based on three-waveguide-coupling (TWC) switches in mode-division multiplexing (MDM) networks. The working principle of the TWC switches is numerically analyzed using the coupled supermode theory. As a proof of concept, switchable data exchange between arbitrary two mode channels among the first three-order quasi-transverse electric modes is experimentally demonstrated successfully. The insertion losses of the device are less than 5.6 dB, including the coupling loss of the multiplexer and demultiplexer, while the mode crosstalk is less than -13.0 dB for all functions. The proposed device is expected to offer more flexibility to on-chip MDM networks due to its low loss, low crosstalk and good scalability.

On-chip biochemical sensor using wide Gaussian beams in silicon waveguide-integrated plasmonic crystal.

An on-chip biochemical sensor based on two-dimensional waveguide-integrated plasmonic crystal formed by a nanogap tile (NGT) array is realized. By using on-chip optical lenses, an ultra-wide collimated Gaussian beam is launched, coupled with surface plasmonic crystals and collected with relatively low additional insertion loss, allowing a large sensing area. The optical field enhancement and stop-band shift of the NGT device for biochemical sensing are numerically and experimentally demonstrated with sensitivity reaching up to ${\sim}{260}\;{\rm nm/RIU}$∼260nm/RIU. Our sensor is demonstrated with monolayer thiol molecules illustrating that it can be functionalized with this class of molecule which is commonly used with bulk surface plasmon resonance sensors.