High-performance silicon nitride (de)multiplexer based on ring-assisted MZIs.

We present the design and experimental characterization of the first multistage ring-assisted Mach-Zehnder interferometer (RAMZI) lattice (de)multiplexer implemented with silicon nitride optimized for four channels with a spacing of 100 GHz in the L-band. The device comprises two RAMZI stages to provide a sharp box-like response characterized by a shape factor of 0.9, a flat passband over the entire channel, and a crosstalk level better than -14 dB. The maximally flat passband of the demultiplexer enables a passband width twice that of the maximum spectral excursion defined in the NG-PON2 standard.

Inverse-designed silicon nitride reflectors.

Reflectors play a pivotal role in silicon photonics since they are used in a wide range of applications, including attenuators, filters, and lasers. This Letter presents six silicon nitride reflectors implemented using the inverse design technique. They vary in footprint, ranging from 4 µm × 3 µm to 4 µm × 8 µm. The smaller device has an average simulated reflectivity of -1.5 dB, whereas the larger one exhibits an average reflectivity of -0.09 dB within the 1530 to 1625 nm range. The latter also presents a 1-dB bandwidth of 172 nm, spanning from 1508 to 1680 nm. Despite their resemblance to circular gratings, these devices are more intricate and compact, particularly due to their non-intuitive features near the input waveguide, which include rough holes and teeth. The roughness of these features significantly contributes to the performance of the devices. The reflectors were fabricated on a silicon nitride multi-project wafer (MPW) through a streamlined process involving only a single etching step. The 4 µm × 8 µm reflector demonstrates a remarkably high reflectivity of -0.26±0.11 dB across the 1530 to 1600 nm range, rendering it suitable for high-quality factor cavities with direct applications in lasers and optical communications.

Silicon nitride TM-pass polarizer using inverse design.

Integrated silicon nitride polarizers play a critical role in the design of complex integrated devices such as filters, switches, and large Mach-Zehnder interferometer networks. These devices require precise control of both polarizations on a single circuit. In addition, polarizers are essential to accurately characterize these devices, primarily due to the low efficiency and polarization extinction ratio (PER) of the surface coupling gratings used in CMOS-compatible silicon nitride platforms for test-specific optical I/O. In this article, we present the design and experimental performance of six prototypes of TE-reflector/TM-pass polarizers specifically optimized for the C-band. These prototypes resemble subwavelength gratings with several additional intricate aspects. In particular, the longer prototypes feature two distinct regions, one representing non-intuitive tapers and the other showcasing a more distinct subwavelength grating. We achieve a high TM transmission efficiency of -0.28 dB along with a PER of 18.2 dB. These results are obtained with a device occupying an area as low as 11 µm × 2 µm, setting a new performance benchmark for compact polarizers compatible with standard silicon nitride platforms.

Four-bands high-resolution integrated spectrometer.

We present the concept and design of a novel integrated optical spectrometer able to operate over four different optical bands in the infrared that cover over 900 nm of aggregated bandwidth. The device, named integrated optical four bands spectrometer (IOFBS), consists of a single planar concave grating with 4 inputs waveguides, each corresponding to a different wavelength band, and 39 output channels that can be implemented on a silicon nitride platform. The inputs waveguides (IWGs) are optimized so that the echelle grating works in different diffraction orders to create constructive interference at the fixed output waveguides. The grating facets are engineered to maximize the diffraction efficiency of the beam launched from any of the four IWGs. The IOFBS works in the near infrared, the O-band, part of the S&E bands and the L-band. The simulated spectra feature an average insertion loss of -1.69 dB across the four bands and a crosstalk better than -32 dB with a 3-dB resolution as low as 0.37 nm and a channel spacing of ∼2.1 nm. The entire device covers an area of 5 mm x 4 mm. The versatility of the proposed design can reduce the cost of integrated spectrometers and make on-chip spectral analysis more accessible by taking advantage of batch fabrication to build a compact device with numerous potential applications.

Two-axis MEMS positioner for waveguide alignment in silicon nitride photonic integrated circuits.

Alignment is critical for efficient integration of photonic integrated circuits (PICs), and microelectromechanical systems (MEMS) actuators have shown potential to tackle this issue. In this work, we report MEMS positioning actuators designed with the ultimate goal of aligning silicon nitride (SiN) waveguides either to different outputs within a SiN chip or to active chips, such as lasers and semiconductor optical amplifiers. For the proof-of-concept, suspended SiN waveguides implemented on a silicon-on-insulator wafer were displaced horizontally in the direction of light propagation to close an initial gap of 6.92 µm and couple the light to fixed output waveguides located on a static section of the chip. With the gap closed, the suspended waveguides showed ∼ 345 nm out-of-plane misalignment with respect to the fixed waveguides. The suspended waveguides can be displaced laterally by more than ±2 µm. When the waveguides are aligned and the gap closed, an average loss of -1.6 ± 0.06 dB was achieved, whereas when the gap is closed with a ± 2 µm lateral displacement, a maximum average loss of ∼ -19.00 ± 0.62 dB was obtained. The performance of this positioner does not only pave the way for active chip alignment, but it could also be considered for optical switching applications.

Compact silicon nitride interferometers.

We demonstrate a compact silicon nitride interferometer which uses waveguides with the same length and different effective indices instead of similar effective indices and different lengths. In such structures there is no need to have waveguide bends. This not only reduces losses but also results in an order of magnitude smaller footprint and thus enables much higher integration densities. We also study the tunability of this interferometer using thermo-optical effects induced by a simple aluminum heater and show that thermal tuning can compensate for the effects of fabrication variations on the spectral response. The application of the proposed design in a tunable mirror is also briefly discussed.

Aluminum Nitride Out-of-Plane Piezoelectric MEMS Actuators.

Integrating microelectromechanical systems (MEMS) actuators with low-loss suspended silicon nitride waveguides enables the precise alignment of these waveguides to other photonic integrated circuits (PICs). This requires both in-plane and out-of-plane actuators to ensure high-precision optical alignment. However, most current out-of-plane electrostatic actuators are bulky, while electrothermal actuators consume high power. Thus, piezoelectric actuators, thanks to their moderate actuation voltages and low power consumption, could be used as alternatives. Furthermore, piezoelectric actuators can provide displacements in two opposite directions. This study presents a novel aluminum nitride-based out-of-plane piezoelectric MEMS actuator equipped with a capacitive sensing mechanism to track its displacement. This actuator could be integrated within PICs to align different chips. Prototypes of the device were tested over the range of ±60 V, where they provided upward and downward displacements, and achieved a total average out-of-plane displacement of 1.30 ± 0.04 µm. Capacitance measurement showed a linear relation with the displacement, where at -60 V, the average change in capacitance was found to be -13.10 ± 0.89 fF, whereas at 60 V the change was 11.09 ± 0.73 fF. This study also investigates the effect of the residual stress caused by the top metal electrode, on the linearity of the displacement-voltage relation. The simulation predicts that the prototype could be modified to accommodate waveguide routing above it without affecting its performance, and it could also incorporate in-plane lateral actuators.

Using Comic-Based Concussion Discharge Instructions to Address Caregiver Health Literacy in the Emergency Department.

INTRODUCTION: This study compared the effectiveness of comic-based with text-based concussion discharge instructions on improving caregiver knowledge. This study also examined the role of social determinants of health on comprehension instructions. METHODS: This was an observational study of the caregivers of pediatric concussion patients. Caregivers' health literacy and demographics related socioeconomic factors were obtained. After the patients' evaluation in the emergency department, caregivers were given printed comic-based concussion discharge instructions. Caregivers were contacted 3 days later and tested overall knowledge of discharge instructions' content. These survey results were compared with historical controls who received text-based instructions. RESULTS: A total of 120 participants were recruited, and 86 participants completed follow-up procedures. When comparing the caregivers' recall ability with a comic-based vs traditional text-based instructions, caregivers with comic-based content were more likely to accurately recall overall discharge instructions (77.5% vs 44%, P < .001), particularly physical rest and activity restrictions (86.5% vs 63%, P < .001). Caregivers also were less likely to misidentify a red flag symptom (7.5% vs 19%, P < .04). Comic-based instructions did not increase recall of cognitive rest instructions or postconcussive symptoms. When examining demographic factors, caregivers who could not recall 3 postconcussive symptoms were more likely to be Hispanic or Black, less likely to be college educated, and more likely to have low health literacy. DISCUSSION: Novel methods should be explored to adequately prepare caregivers for continuing postconcussive care at home. Discharge instructions must be tailored to address caregivers' baseline health literacy and how caregivers digest and retain information.

Phase errors and statistical analysis of silicon-nitride arrayed waveguide gratings.

We present a statistical analysis of arrayed waveguide gratings (AWGs) in the presence of phase errors in the optical waveguides caused by fabrication process variations. Important figures of merit, such as the insertion loss, crosstalk, and non-uniformity, are parameterized as a function of the coherence length, a physical parameter that characterizes the accumulated phase errors in optical waveguides and that can be extracted by measuring variations in the resonant wavelengths of Mach-Zehnder interferometers. A die-level coherence length of 23.7 mm is measured for sub-micrometer-thick silicon nitride (SiN) waveguides fabricated using a 200-mm wafer process. Through Monte Carlo simulations using a semi-analytical model, we examine the impacts of phase errors on the performance of AWGs with 200 GHz and 100 GHz channel spacings. Our results show that the waveguide phase errors cause remarkable excess insertion loss and crosstalk in an AWG, and also increase non-uniformity across channels.

Integrated 1 × 3 MEMS silicon nitride photonics switch.

We present a 1 × 3 optical switch based on a translational microelectromechanical system (MEMS) platform with integrated silicon nitride (SiN) photonic waveguides. The fabricated devices demonstrate efficient optical signal transmission between fixed and suspended movable waveguides. We report a minimum average insertion loss of 4.64 dB and a maximum average insertion loss of 5.83 dB in different switching positions over a wavelength range of 1530 nm to 1580 nm. The unique gap closing mechanism reduces the average insertion loss across two air gaps by a maximum of 7.89 dB. The optical switch was fabricated using a custom microfabrication process developed by AEPONYX Inc. This microfabrication process integrates SiN waveguides with silicon-on-insulator based MEMS devices with minimal stress related deformation of the MEMS platform.

Wide-band silicon photonic MOEMS spectrometer requiring a single photodetector.

We propose a novel integrated micro-opto-mechanical-system spectrometer design in a monochromator setup. It consists of a concave grating fabricated in a planar waveguide that is connected to a rotational electrostatic actuator, which enables angular tuning of the grating. The spectrometer covers a wide operational wavelength range (>100 nm), covering partially the E-band and fully covering the S, C, and L-bands (1416.6 nm - 1696.6 nm), and requires a single photodetector to acquire the spectrum. The spectrometer is designed to exhibit low optical losses throughout the range of motion. The spectrum can be acquired at a frequency of 1.76 kHz. The simulated acquired spectrum features an average insertion loss of -1.8 dB and a crosstalk better than -70 dB with a resolution as low as 1.62 nm. The entire device covers an area of 4 mm x 4 mm and is based on a thick silicon-on-insulator platform.

Polarization-insensitive silicon nitride arrayed waveguide grating.

Next-generation passive optical networks require integrated, polarization-insensitive wavelength-division multiplexing solutions, for which the recently emerging low-loss silicon nitride nanophotonic platforms hold great potential. A novel polarization-insensitive arrayed waveguide grating (AWG) built with silicon nitride waveguides is presented in this Letter. Polarization insensitivity is obtained when both the channel spacing and the center wavelength of the two orthogonal polarization states (i.e., the TE and TM waveguide modes) are simultaneously aligned. In our design, the channel spacing alignment between the polarization states is obtained by optimizing the geometry of the arrayed waveguides, whereas the central wavelength polarization insensitivity is obtained by splitting the two polarization states and adjusting their angle of incidence at the input star coupler to compensate for the polarization mode dispersion of the AWG. A 100 GHz 1×8 wavelength-division multiplexer with crosstalk levels below -16 dB is demonstrated experimentally.

Translational MEMS Platform for Planar Optical Switching Fabrics.

While 3-D microelectromechanical systems (MEMS) allow switching between a large number of ports in optical telecommunication networks, the development of such systems often suffers from design, fabrication and packaging constraints due to the complex structures, the wafer bonding processes involved, and the tight alignment tolerances between different components. In this work, we present a 2-D translational MEMS platform capable of highly efficient planar optical switching through integration with silicon nitride (SiN) based optical waveguides. The discrete lateral displacement provided by simple parallel plate actuators on opposite sides of the central platform enables switching between different input and output waveguides. The proposed structure can displace the central platform by 3.37 µm in two directions at an actuation voltage of 65 V. Additionally, the parallel plate actuator designed for closing completely the 4.26 µm air gap between the fixed and moving waveguides operates at just 50 V. Eigenmode expansion analysis shows over 99% butt-coupling efficiency the between the SiN waveguides when the gap is closed. Also, 2.5 finite-difference time-domain analysis demonstrates zero cross talk between two parallel SiN waveguides across the length of the platform for a 3.5 µm separation between adjacent waveguides enabling multiple waveguide configuration onto the platform. Different MEMS designs were simulated using static structural analysis in ANSYS. These designs were fabricated with a custom process by AEPONYX Inc. (Montreal, QC, Canada) and through the PiezoMUMPs process of MEMSCAP (Durham, NC, USA).

Rotating Circular Micro-Platform with Integrated Waveguides and Latching Arm for Reconfigurable Integrated Optics.

This work presents a laterally rotating micromachined platform integrated under optical waveguides to control the in-plane propagation direction of light within a die to select one of multiple outputs. The platform is designed to exhibit low constant optical losses throughout the motion range and is actuated electrostatically using an optimized circular comb drive. An angular motion of ±9.5° using 180 V is demonstrated. To minimize the optical losses between the moving and fixed parts, a gap-closing mechanism is implemented to reduce the initial air gap to submicron values. A latch structure is implemented to hold the platform in place with a resolution of 0.25° over the entire motion range. The platform was integrated with silicon nitride waveguides to create a crossbar switch and preliminary optical measurements are reported. In the bar state, the loss was measured to be 14.8 dB with the gap closed whereas in the cross state it was 12.2 dB. To the authors' knowledge, this is the first optical switch based on a rotating microelectromechanical device with integrated silicon nitride waveguides reported to date.

Integrated optical deserialiser time sampling based SiGe photoreceiver.

A novel photoreceiver architecture enabling parallel processing in the electronic domain of a high-speed optical signal is demonstrated. This allows the electronics to operate at significantly lower frequency than the optical signal and hence reduce power consumption and the impact of parasitics. The photoreceiver performs optical time sampling with four integrated SiGe photodetectors connected in series by waveguide delay lines. Four variations of the optical time sampling receiver are designed and demonstrated which differ by the data rate (10 Gb/s and 20 Gb/s) and silicon delay waveguide loss (2.5 dB/cm and 0.2 dB/cm). The bit error rate performance of the photodetectors in the receiver was measured individually and reached a performance below 1 × 10⁻¹° at an input optical power between 4.8 and 6.3 dBm through an off-chip 50 Ω load at the output. After O/E conversion, the electrical signal (one segment of 2¹5 - 1 PRBS data) from each of the photodetector is processed without errors at a quarter of the bit rate, leading to an overall more power efficient receiver front-end.

Wavelength conversion and unicast of 10-Gb/s data spanning up to 700 nm using a silicon nanowaveguide.

We report extremely large probe-idler separation wavelength conversion (545 nm) and unicast (700 nm) of 10-Gb/s data signals using a dispersion-engineered silicon nanowaveguide. Dispersion-engineered phase matching in the device provides a continuous four-wave-mixing efficiency 3-dB bandwidth exceeding 800 nm. We report the first data validation of wavelength conversion (data modulated probe) and unicast (data modulated pump) of 10-Gb/s data with probe-idler separations spanning 60 nm up to 700 nm accompanied with sensitivity gain in a single device. These demonstrations further validate the silicon platform as a highly broadband flexible platform for nonlinear all-optical data manipulation.

Differential role of NF-κB, ERK1/2 and AP-1 in modulating the immunoregulatory functions of bone marrow-derived dendritic cells from NOD mice.

Tolerogenic dendritic cells represent a promising immunotherapy in autoimmunity. However, the molecular mechanisms that drive tolerogenic DCs functions are not well understood. We used GM-CSF or GM-CSF+IL-4 to generate tolerogenic (GM/DCs) and immunogenic (IL-4/DCs) BMDCs from NOD mice, respectively. GM/DCs were resistant to maturation, produced large amounts of IL-10 but not IL-12p70. GM/DCs displayed a reduced capacity to activate diabetogenic CD8(+) T-cells and were efficient to induce Tregs expansion and conversion. LPS stimulation triggered ERK1/2 activation that was sustained in GM/DCs but not in IL-4/DCs. ERK1/2 and AP-1 were involved in IL-10 production in GM/DCs but not in their resistance to maturation. Supershift analysis showed that NF-κB DNA binding complex contains p52 and p65 in GM/DCs, whereas it contains p52, p65 and RelB in IL-4/DCs. ChIP experiments revealed that p65 was recruited to IL-10 promoter following LPS stimulation of GM/DCs whereas its binding to IL-12p35 promoter was abolished. Our results suggest that immunoregulatory functions of GM/DCs are differentially regulated by ERK1/2, AP-1 and NF-κB pathways.

Simultaneous wavelength conversion of ASK and DPSK signals based on four-wave-mixing in dispersion engineered silicon waveguides.

We experimentally demonstrate four-wave-mixing (FWM)-based continuous wavelength conversion of optical differential-phase-shift-keyed (DPSK) signals with large wavelength conversion ranges as well as simultaneous wavelength conversion of dual-wavelength channels with mixed modulation formats in 1.1-cm-long dispersion-engineered silicon waveguides. We first validate up to 100-nm wavelength conversion range for 10-Gb/s DPSK signals, showcasing the capability to perform phase-preserving operations at high bit rates in chip-scale devices over wide conversion ranges. We further validate the wavelength conversion of dual-wavelength channels modulated with 10-Gb/s packetized phase-shift-keyed (PSK) and amplitude-shift-keyed (ASK) signals; demonstrate simultaneous operation on multiple channels with mixed formats in chip-scale devices. For both configurations, we measure the spectral and temporal responses and evaluate the performances using bit-error-rate (BER) measurements.

IFN regulatory factors 4 and 8 expression in the NOD mouse.

Dendritic cells (DCs) contribute to islet inflammation and its progression to diabetes in NOD mouse model and human. DCs play a crucial role in the presentation of autoantigen and activation of diabetogenic T cells, and IRF4 and IRF8 are crucial genes involved in the development of DCs. We have therefore investigated the expression of these genes in splenic DCs during diabetes progression in NOD mice. We found that IRF4 expression was upregulated in splenocytes and in splenic CD11c(+) DCs of NOD mice as compared to BALB/c mice. In contrast, IRF8 gene expression was higher in splenocytes of NOD mice whereas its expression was similar in splenic CD11c(+) DCs of NOD and BALB/c mice. Importantly, levels of IRF4 and IRF8 expression were lower in tolerogenic bone marrow derived DCs (BMDCs) generated with GM-CSF as compared to immunogenic BMDCs generated with GM-CSF and IL-4. Analysis of splenic DCs subsets indicated that high expression of IRF4 was associated with increased levels of CD4(+)CD8α(-)IRF4(+)CD11c(+) DCs but not CD4(-)CD8α(+)IRF8(+)CD11c(+) DCs in NOD mice. Our results showed that IRF4 expression was up-regulated in NOD mice and correlated with the increased levels of CD4(+)CD8α(-) DCs, suggesting that IRF4 may be involved in abnormal DC functions in type 1 diabetes in NOD mice.

Continuous-wave mid-infrared frequency conversion in silicon nanowaveguides.

We report the first demonstration of cw wavelength conversion from the telecommunications band to the mid-IR (MIR) region via four-wave mixing in silicon nanowaveguides. We measure a parametric bandwidth of 748 nm by converting a 1636 nm signal to produce a 2384 nm idler and show continuously tunable wavelength conversion from 1792 to 2116 nm. This report indicates that the advantages of silicon photonics may be leveraged to create devices for a large range of MIR applications that require cw operation.