Low-loss and broadband wafer-scale optical interposers for large-scale heterogeneous integration.

We design, fabricate, and demonstrate a low-loss and broadband optical interposer with high misalignment tolerance for large-scale integration of many chips using thermal compression flip-chip bonding. The optical interposer achieves flip-chip integration with photonic integrated circuit die containing evanescent couplers with inter-chip coupling loss of 0.54dB and ±3.53µm 3-dB misalignment tolerance. The loss measurement spectrum indicated wavelength-insensitive loss across O-band and C-band with negligible spectral dependence. Further, we demonstrate 1 to 100 wafer-scale equal power splitting using equal power splitters (EPS) and a path length matching design fabricated using a wafer-scale fabrication technique.

Monolithic silicon photonic 32x32 thin-CLOS AWGR for all-to-all interconnections.

This paper reports the design, fabrication, and experimental demonstration of a monolithic silicon photonic (SiPh) 32×32 Thin-CLOS arrayed waveguide grating router (AWGR) for scalable SiPh all-to-all interconnection fabrics. The 32×32 Thin-CLOS makes use of four 16-port silicon nitride AWGRs, which are compactly integrated and interconnected by a multi-layer waveguide routing method. The fabricated Thin-CLOS has 4 dB insertion loss, < -15 dB adjacent channel crosstalk, and < -20 dB non-adjacent channel crosstalk. System experiments operated on the 32×32 SiPh Thin-CLOS demonstrate error-free communication at 25 Gb/s.

Pericardial diverticulum arising from the right lateral superior aortic recess: a mimicker of cystic anterior mediastinal mass.

AIM: To report the prevalence of pericardial diverticulum of the right lateral superior aortic recess (RSAR) on computed tomography (CT), to analyse the structural CT findings of whether or not the structure is large enough to be seen on chest radiographs, and to describe changes in size and shape of RSAR on follow-up CT. MATERIALS AND METHODS: A well-circumscribed, fluid-attenuation lesion in the anterior mediastinum with the following CT features was defined as a pericardial diverticulum of the RSAR: no enhancing wall, communication with the RSAR, abutment to the heart with an acute angle, and moulding by adjacent structures. Chest CT images of 31 patients with the diverticulum were evaluated, including four selected from 1,130 consecutive patients (0.4%). RESULTS: The diverticulum projected ventrally from the RSAR and its largest size on axial CT ranged between 12-56 mm. Although the RSAR and the largest diverticular portion were usually seen on the same axial image (n=19), the latter sometimes lay above (n=1) or below (n=11) the former. On sagittal images, the last 11 diverticula resembled teardrops hanging from the RSAR by small stems. All of the 24 patients, each with 1-31 follow-up CT examinations, showed size fluctuations ranging between 1-46 mm (mean, 16 mm) during a follow-up period of 0.5-172 months (mean, 65 months). The diverticulum was not identifiable in five cases and was identifiable but did not show a connection with the RSAR in three cases when the diverticulum was smallest in size. CONCLUSIONS: In cases of cystic anterior mediastinal mass, a deliberate search for its connection with the RSAR on all available CT images including previous studies is necessary for the diagnosis of pericardial diverticulum of the RSAR.

Photonic spiking neural networks with event-driven femtojoule optoelectronic neurons based on Izhikevich-inspired model.

Photonic spiking neural networks (PSNNs) potentially offer exceptionally high throughput and energy efficiency compared to their electronic neuromorphic counterparts while maintaining their benefits in terms of event-driven computing capability. While state-of-the-art PSNN designs require a continuous laser pump, this paper presents a monolithic optoelectronic PSNN hardware design consisting of an MZI mesh incoherent network and event-driven laser spiking neurons. We designed, prototyped, and experimentally demonstrated this event-driven neuron inspired by the Izhikevich model incorporating both excitatory and inhibitory optical spiking inputs and producing optical spiking outputs accordingly. The optoelectronic neurons consist of two photodetectors for excitatory and inhibitory optical spiking inputs, electrical transistors' circuits providing spiking nonlinearity, and a laser for optical spiking outputs. Additional inclusion of capacitors and resistors complete the Izhikevich-inspired optoelectronic neurons, which receive excitatory and inhibitory optical spikes as inputs from other optoelectronic neurons. We developed a detailed optoelectronic neuron model in Verilog-A and simulated the circuit-level operation of various cases with excitatory input and inhibitory input signals. The experimental results closely resemble the simulated results and demonstrate how the excitatory inputs trigger the optical spiking outputs while the inhibitory inputs suppress the outputs. The nanoscale neuron designed in our monolithic PSNN utilizes quantum impedance conversion. It shows that estimated 21.09 fJ/spike input can trigger the output from on-chip nanolasers running at a maximum of 10 Gspike/second in the neural network. Utilizing the simulated neuron model, we conducted simulations on MNIST handwritten digits recognition using fully connected (FC) and convolutional neural networks (CNN). The simulation results show 90% accuracy on unsupervised learning and 97% accuracy on a supervised modified FC neural network. The benchmark shows our PSNN can achieve 50 TOP/J energy efficiency, which corresponds to 100 × throughputs and 1000 × energy-efficiency improvements compared to state-of-art electrical neuromorphic hardware such as Loihi and NeuroGrid.

Demonstration of distributed collaborative learning with end-to-end QoT estimation in multi-domain elastic optical networks.

This paper proposes a distributed collaborative learning approach for cognitive and autonomous multi-domain elastic optical networking (EON). The proposed approach exploits a knowledge-defined networking framework which leverages a broker plane to coordinate the operations of multiple EON domains and applies machine learning (ML) to support autonomous and cognitive inter-domain service provisioning. By employing multiple distributed ML blocks learning domain-level features and working with broker plane aggregation ML blocks (through the chain rule-based training), the proposed approach enables to develop cognitive networking applications that can fully exploit the multi-domain EON states while obviating the need for the raw and confidential intra-domain data. In particular, we investigate end-to-end quality-of-transmission estimation application using the distributed learning approach and propose three estimator designs incorporating the concepts of multi-task learning (MTL) and transfer learning (TL). Evaluations with experimental data demonstrate that the proposed designs can achieve estimation accuracies very close to (with differences less than 0.5%) or even higher than (with MTL/TL) those of the baseline models assuming full domain visibility.

Sub-wavelength-pitch silicon-photonic optical phased array for large field-of-regard coherent optical beam steering.

This paper reports on large field-of-regard, high-efficiency, and large aperture active optical phased arrays (OPAs) for optical beam steering in LIDAR systems. The fabricated 5 mm-long silicon photonic OPA with a 1.3 µm waveguide pitch achieved adjacent waveguide crosstalk below -12dB. A relatively large and uniform emission aperture has been achieved with a low-contrast silicon nitride assisted grating (~20 dB/cm) whose emission profile can be further optimized using an apodized design. The fabricated silicon-photonic OPA demonstrated > 40° lateral beam steering with no sidelobes in a ± 33° field-of-regard and 3.3° longitudinal beam steering via wavelength tuning by 20 nm centered at 1550 nm. We have fully integrated the silicon photonic OPA device with electronic controls and successfully demonstrated 2-dimensional coherent optical beam steering of pre-planned far-field patterns. Future improvements include placement of a distributed Bragg reflector (DBR) underneath the grating emitter in order to achieve nearly a factor of two improvement in emission efficiency.

Demonstration of a carrier frequency offset estimator for 16-/32-QAM coherent receivers: a hardware perspective.

We propose and implement a hardware-efficient frequency offset estimator (FOE) optimized for 16- and 32-QAM coherent optical receivers with low hardware cost and high estimation accuracy. The proposed FOE combines a wide-range coarse estimator and a narrow-range highly accurate estimator in a feedforward architecture. We numerically and experimentally investigate the performance of the proposed estimator by using a field-programmable-logic-array (FPGA) based real-time coherent receiver. Compared with other state-of-the-art estimators in literature, the proposed method reduces over 40% of hardware utilizations while maintaining the same level of estimation accuracy in terms of mean-squared-error (MSE) and optical signal-to-noise ratio (OSNR) sensitivity. These results enable the development of next generation DSP circuit capable of supporting high capacity coherent optical communication link with advanced modulation formats.

Interferometric imaging using Si3N4 photonic integrated circuits for a SPIDER imager.

This paper reports design, fabrication, and experimental demonstration of a silicon nitride photonic integrated circuit (PIC). The PIC is capable of conducting one-dimensional interferometric imaging with twelve baselines near λ = 1100-1600 nm. The PIC consists of twelve waveguide pairs, each leading to a multi-mode interferometer (MMI) that forms broadband interference fringes or each corresponding pair of the waveguides. Then an 18 channel arrayed waveguide grating (AWG) separates the combined signal into 18 signals of different wavelengths. A total of 103 sets of fringes are collected by the detector array at the output of the PIC. We keep the optical path difference (OPD) of each interferometer baseline to within 1 µm to maximize the visibility of the interference measurement. We also constructed a testbed to utilize the PIC for two-dimension complex visibility measurement with various targets. The experiment shows reconstructed images in good agreement with theoretical predictions.

Blind modulation format identification using nonlinear power transformation.

This paper proposes and experimentally demonstrates a blind modulation format identification (MFI) method delivering high accuracy (> 99%) even in a low OSNR regime (< 10 dB). By using nonlinear power transformation and peak detection, the proposed MFI can recognize whether the signal modulation format is BPSK, QPSK, 8-PSK or 16-QAM. Experimental results demonstrate that the proposed MFI can achieve a successful identification rate as high as 99% when the incoming signal OSNR is 7 dB. Key parameters, such as FFT length and laser phase noise tolerance of the proposed method, have been characterized.

Uniform emission, constant wavevector silicon grating surface emitter for beam steering with ultra-sharp instantaneous field-of-view.

We report on uniform emission intensity profile, uniform propagation constant silicon gratings for beam steering application with ultra-sharp instantaneous field-of-view (IFOV). To achieve uniform emission intensity across relatively long emission length, we designed a custom grating with varying Si3N4 width and duty cycle while maintaining a uniform propagation constant for relatively narrow divergence emission pattern. We designed and fabricated the custom Si3N4/Si grating with the varying Si3N4 width/duty cycle together with the reference Si3N4/Si grating with a constant 50:50 duty cycle. The custom grating demonstrated the beam steering angle value of 6.6° by sweeping wavelength between 1530 nm and 1575 nm with the emission length over 1 mm. The measured IFOV based on the 3-dB beamwidth values of the far field patterns for the TE polarization are 0.10° and 0.75° for the custom grating and for the reference grating, respectively. The custom grating also indicates mode-selective behavior due to the perturbation of propagation constant for input modes other than TE polarization. The measured TE-mode to TM-mode suppression ratio for the custom grating is approximately 8.2 dB peak-to-peak measured at far field.

Silicon nitride tri-layer vertical Y-junction and 3D couplers with arbitrary splitting ratio for photonic integrated circuits.

We designed and demonstrated a tri-layer Si3N4/SiO2 photonic integrated circuit capable of vertical interlayer coupling with arbitrary splitting ratios. Based on this multilayer photonic integrated circuit platform with each layer thicknesses of 150 nm, 50 nm, and 150 nm, we designed and simulated the vertical Y-junctions and 3D couplers with arbitrary power splitting ratios between 1:10 and 10:1 and with negligible(< -50 dB) reflection. Based on the design, we fabricated and demonstrated tri-layer vertical Y-junctions with the splitting ratios of 1:1 and 3:2 with excess optical losses of 0.230 dB. Further, we fabricated and demonstrated the 1 × 3 3D couplers with the splitting ratio of 1:1:4 for symmetric structures and variable splitting ratio for asymmetric structures.

Experimental demonstration of interferometric imaging using photonic integrated circuits.

This paper reports design, fabrication, and demonstration of a silica photonic integrated circuit (PIC) capable of conducting interferometric imaging with multiple baselines around λ = 1550 nm. The PIC consists of four sets of five waveguides (total of twenty waveguides), each leading to a three-band spectrometer (total of sixty waveguides), after which a tunable Mach-Zehnder interferometer (MZI) constructs interferograms from each pair of the waveguides. A total of thirty sets of interferograms (ten pairs of three spectral bands) is collected by the detector array at the output of the PIC. The optical path difference (OPD) of each interferometer baseline is kept to within 1 µm to maximize the visibility of the interference measurement. We constructed an experiment to utilize the two baselines for complex visibility measurement on a point source and a variable width slit. We used the point source to demonstrate near unity value of the PIC instrumental visibility, and used the variable slit to demonstrate visibility measurement for a simple extended object. The experimental result demonstrates the visibility of baseline 5 and 20 mm for a slit width of 0 to 500 µm in good agreement with theoretical predictions.

Rapidly reconfigurable high-fidelity optical arbitrary waveform generation in heterogeneous photonic integrated circuits.

This paper demonstrates rapidly reconfigurable, high-fidelity optical arbitrary waveform generation (OAWG) in a heterogeneous photonic integrated circuit (PIC). The heterogeneous PIC combines advantages of high-speed indium phosphide (InP) modulators and low-loss, high-contrast silicon nitride (Si3N4) arrayed waveguide gratings (AWGs) so that high-fidelity optical waveform syntheses with rapid waveform updates are possible. The generated optical waveforms spanned a 160 GHz spectral bandwidth starting from an optical frequency comb consisting of eight comb lines separated by 20 GHz channel spacing. The Error Vector Magnitude (EVM) values of the generated waveforms were approximately 16.4%. The OAWG module can rapidly and arbitrarily reconfigure waveforms upon every pulse arriving at 2 ns repetition time. The result of this work indicates the feasibility of truly dynamic optical arbitrary waveform generation where the reconfiguration rate or the modulator bandwidth must exceed the channel spacing of the AWG and the optical frequency comb.

Hybrid integration of modified uni-traveling carrier photodiodes on a multi-layer silicon nitride platform using total reflection mirrors.

We demonstrate hybrid integration of modified uni-traveling carrier photodiodes on a multi-layer silicon nitride platform using total reflection mirrors etched by focused ion beam. The hybrid photodetectors show external responsivity of 0.15 A/W and bandwidth of 3.5 GHz for devices with a diameter of 80 µm. The insertion loss of the waveguide is 3 dB and the coupling efficiency of the total reflection mirror is -3 dB. The highest RF output power is -0.5 dBm measured at 3 GHz with 9 mA photocurrent and -9 V bias.

Hematological adverse effects and pharmacokinetics of ribavirin in pigs following intramuscular administration.

Ribavirin (RBV) is a synthetic guanosine analog that is used as a drug against various viral diseases in humans. The in vitro antiviral effects of ribavirin against porcine viruses were demonstrated in several studies. The purposes of this study were to evaluate the adverse effects and pharmacokinetics of ribavirin following its intramuscular (IM) injection in pigs. Ribavirin was formulated as a double-oil emulsion (RBV-DOE) and gel (RBV-Gel), which were injected into the pigs as single-dose IM injections. After injection of RBV, all of the pigs were monitored. The collected serum and whole blood samples were analyzed by liquid chromatography-tandem mass spectrometry and complete blood count analysis, respectively. All of the ribavirin-treated pigs showed significant decreases in body weight compared to the control groups. Severe clinical signs including dyspnea, anorexia, weakness, and depression were present in ribavirin-treated pigs until 5 days postinjection (dpi). The ribavirin-treated groups showed significant decrease in the number of red blood cells and hemoglobin concentration until 8 dpi. The mean half-life of the RBV-DOE and RBV-Gel was 27.949 ± 2.783 h and 37.374 ± 3.502 h, respectively. The mean peak serum concentration (Cmax ) and area under the serum concentration-time curve from time zero to infinity (AUCinf ) of RBV-DOE were 8340.000 ± 2562.577 ng/mL and 16 0095.430 ± 61 253.400 h·ng/mL, respectively. The Cmax and AUCinf of RBV-Gel were 15 300.000 ± 3764.306 ng/mL and 207526.260 ± 63656.390 h·ng/mL, respectively. The results of this study provided the index of side effect and pharmacokinetics of ribavirin in pigs, which should be considered before clinical application.

Tongue-to-palate resistance training improves tongue strength and oropharyngeal swallowing function in subacute stroke survivors with dysphagia.

Tongue function can affect both the oral and pharyngeal stages of the swallowing process, and proper tongue strength is vital for safe oropharyngeal swallowing. This trial investigated the effect of tongue-to-palate resistance training (TPRT) on tongue strength and oropharyngeal swallowing function in stroke with dysphagia patients. This trial was performed using a 4-week, two-group, pre-post-design. Participants were allocated to the experimental group (n = 18) or the control group (n = 17). The experimental group performed TPRT for 4 weeks (5 days per week) and traditional dysphagia therapy, whereas the control group performed traditional dysphagia therapy on the same schedule. Tongue strength was measured using the Iowa Oral Performance Instrument. Swallowing function was measured using the videofluoroscopic dysphagia scale (VDS) and penetration-aspiration scale (PAS) based on a videofluoroscopic swallowing study. Experimental group showed more improved in the tongue strength (both anterior and posterior regions, P = 0·009, 0·015). In addition, the experimental group showed more improved scores on the oral and pharyngeal phase of VDS (P = 0·029, 0·007), but not on the PAS (P = 0·471), compared with the control group. This study demonstrated the effectiveness of TPRT in increasing tongue muscle strength and improving swallowing function in patients with post-stroke dysphagia. Therefore, we recommend TPRT as an easy and simple rehabilitation strategy for improving swallowing in patients with dysphagia.

Highly efficient chip-scale III-V/silicon hybrid optical amplifiers.

We discuss the design and demonstration of highly efficient 1.55 µm hybrid III-V/Silicon semiconductor optical amplifiers (SOA). The optimized III-V wafer stack consists of Al(0.10)In(0.71)Ga(0.18)As multiple quantum wells (MQW) and Al(0.48)In(0.52)As electron stop layers to realize SOAs with high wall-plug efficiency (WPE). We present various designs and experimentally determine WPE values for 2 mW and 0.1 mW input power amplification. The 400 µm long flared SOA achieved the highest WPE value of 12.1% for output power > 10mW and the 400 µm long straight SOA achieved the highest WPE value of 7.3% for output power < 10mW. These are the highest WPE values ever obtained for 1.55 µm SOAs.

Low-loss compact multilayer silicon nitride platform for 3D photonic integrated circuits.

We design, fabricate, and demonstrate a silicon nitride (Si(3)N(4)) multilayer platform optimized for low-loss and compact multilayer photonic integrated circuits. The designed platform, with 200 nm thick waveguide core and 700 nm interlayer gap, is compatible for active thermal tuning and applicable to realizing compact photonic devices such as arrayed waveguide gratings (AWGs). We achieve ultra-low loss vertical couplers with 0.01 dB coupling loss, multilayer crossing loss of 0.167 dB at 90° crossing angle, 50 µm bending radius, 100 × 2 µm(2) footprint, lateral misalignment tolerance up to 400 nm, and less than -52 dB interlayer crosstalk at 1550 nm wavelength. Based on the designed platform, we demonstrate a 27 × 32 × 2 multilayer star coupler.

Athermal silicon ring resonators clad with titanium dioxide for 1.3µm wavelength operation.

We investigate the athermal characteristics of silicon waveguides clad with TiO(2) designed for 1.3 µm wavelength operation. Using CMOS-compatible fabrication processes, we realize and experimentally demonstrate silicon photonic ring resonators with resonant wavelengths that vary by less than 6 pm/°C at 1.3 µm. The measured ring resonance wavelengths across the 20-50°C temperature range show nearly complete cancellation of the first-order thermo-optical effects and exhibit second-order thermo-optical effects expected from the combination of TiO(2) and Si.

Mode-multiplexed transmission over conventional graded-index multimode fibers.

We present experimental results for combined mode-multiplexed and wavelength multiplexed transmission over conventional graded-index multimode fibers. We use mode-selective photonic lanterns as mode couplers to precisely excite a subset of the modes of the multimode fiber and additionally to compensate for the differential group delay between the excited modes. Spatial mode filters are added to suppress undesired higher order modes. We transmit 30-Gbaud QPSK signals over 60 WDM channels, 3 spatial modes, and 2 polarizations, reaching a distance of 310 km based on a 44.3 km long span. We also report about transmission experiments over 6 spatial modes for a 17-km single-span experiment. The results indicate that multimode fibers support scalable mode-division multiplexing approaches, where modes can be added over time if desired. Also the results indicate that mode-multiplexed transmission distance over 300 km are possible in conventional multimode fibers.