MARCH5 promotes STING pathway activation by suppressing polymer formation of oxidized STING.

Stimulator of interferon genes (STING) is a core DNA sensing adaptor in innate immune signaling. STING activity is regulated by a variety of post-translational modifications (PTMs), including phosphorylation, ubiquitination, sumoylation, palmitoylation, and oxidation, as well as the balance between active and inactive polymer formation. It remains unclear, though, how different PTMs and higher order structures cooperate to regulate STING activity. Here, we report that the mitochondrial ubiquitin ligase MARCH5 (Membrane Associated Ring-CH-type Finger 5, also known as MITOL) ubiquitinates STING and enhances its activation. A long-term MARCH5 deficiency, in contrast, leads to the production of reactive oxygen species, which then facilitate the formation of inactive STING polymers by oxidizing mouse STING cysteine 205. We show that MARCH5-mediated ubiquitination of STING prevents the oxidation-induced STING polymer formation. Our findings highlight that MARCH5 balances STING ubiquitination and polymer formation and its control of STING activation is contingent on oxidative conditions.

Silicon-Nanowire-Type Polarization-Diversified CWDM Demultiplexer for Low Polarization Crosstalk.

Coarse wavelength division multiplexing (CWDM)-targeted novel silicon (Si)-nanowire-type polarization-diversified optical demultiplexers were numerically analyzed and experimentally verified. The optical demultiplexer comprised a hybrid mode conversion-type polarization splitter rotator (PSR) and a delayed Mach-Zehnder interferometric demultiplexer. Si-nanowire-based devices were fabricated using a commercially available Si photonics foundry process, exhibiting nearly identical spectral responses regardless of the polarization states of the input signals under the PSR. The experiment demonstrated a low insertion loss of 1.0 dB and a polarization-dependent loss of 1.0 dB, effectively suppressing spectral crosstalk from other channels by less than -15 dB. Furthermore, a TM-mode rejection-filter-integrated optical demultiplexer was designed and experimentally validated to mitigate unwanted TM-mode-related polarization crosstalk that arose from the PSR. It exhibited an improved polarization crosstalk rejection efficiency of -25 dB to -50 dB within the whole CWDM spectral range.

Theoretical verification of a silicon-wire flat-spectral-band wavelength filter based on multimode interference couplers with symmetric and asymmetric splitting ratios for the broadband operating range.

A novel, to the best of our knowledge, device scheme for a silicon-nanowire flat-spectral-band wavelength optical filter is proposed and theoretically demonstrated. The proposed wavelength filter is composed of cascade-connected multiple delayed interference optical delay lines, together with several multimode interference couplers with symmetric and asymmetric splitting ratios. Theoretical calculations based on analytic and numerical simulations exhibit flatband spectra over a wavelength range of >80 nm with potentially better production yield for arbitrary channel spacing.

Towards FBG-Based Shape Sensing for Micro-scale and Meso-Scale Continuum Robots with Large Deflection.

Endovascular and endoscopic surgical procedures require micro-scale and meso-scale continuum robotic tools to navigate complex anatomical structures. In numerous studies, fiber Bragg grating (FBG) based shape sensing has been used for measuring the deflection of continuum robots on larger scales, but has proved to be a challenge for micro-scale and meso-scale robots with large deflections. In this paper, we have developed a sensor by mounting an FBG fiber within a micromachined nitinol tube whose neutral axis is shifted to one side due to the machining. This shifting of the neutral axis allows the FBG core to experience compressive strain when the tube bends. The fabrication method of the sensor has been explicitly detailed and the sensor has been tested with two tendon-driven micro-scale and meso-scale continuum robots with outer diameters of 0.41 mm and 1.93 mm respectively. The compact sensor allows repeatable and reliable estimates of the shape of both scales of robots with minimal hysteresis. We propose an analytical model to derive the curvature of the robot joints from FBG fiber strain and a static model that relates joint curvature to the tendon force. Finally, as proof-of-concept, we demonstrate the feasibility of our sensor assembly by combining tendon force feedback and the FBG strain feedback to generate reliable estimates of joint angles for the meso-scale robot.

Silicon-wire optical demultiplexers based on multistage delayed Mach-Zehnder interferometers for higher production yield.

We report better spectral uniformity in Si-wire-based multistage delayed Mach-Zehnder interferometer (DMZI) type optical multiplexers/demultiplexers (MUX/DeMUX). Based on a 300 mm silicon-on-insulator wafer-scale ArF-immersion lithography process that guarantees higher phase controllability for low insertion loss, spectral flatness, and low crosstalk, we were able to further improve spectral uniformity across the wafer by optimizing the waveguide width within the optical path of each DMZI region. Irrespective of channel spacing in the wavelength domain, it was experimentally demonstrated that the filter spectral center wavelength deviation of the proposed DeMUXs was three times smaller than that of conventional ones. The proposed device scheme would also be attractive for arbitrary channel spacing and channel count, which makes the proposed scheme more practical in high-performance wavelength division multiplexing optical transceivers.

Si-nanowire-based multistage delayed Mach-Zehnder interferometer optical MUX/DeMUX fabricated by an ArF-immersion lithography process on a 300 mm SOI wafer.

We report good phase controllability and high production yield in Si-nanowire-based multistage delayed Mach-Zehnder interferometer-type optical multiplexers/demultiplexers (MUX/DeMUX) fabricated by an ArF-immersion lithography process on a 300 mm silicon-on-insulator (SOI) wafer. Three kinds of devices fabricated in this work exhibit clear 1×4 Ch wavelength filtering operations for various optical frequency spacing. These results are promising for their applications in high-density wavelength division multiplexing-based optical interconnects.

Low-loss, flat-topped and spectrally uniform silicon-nanowire-based 5th-order CROW fabricated by ArF-immersion lithography process on a 300-mm SOI wafer.

We report superior spectral characteristics of silicon-nanowire-based 5th-order coupled resonator optical waveguides (CROW) fabricated by 193-nm ArF-immersion lithography process on a 300-mm silicon-on-insulator wafer. We theoretically analyze spectral characteristics, considering random phase errors caused by micro fabrication process. It will be experimentally demonstrated that the fabricated devices exhibit a low excess loss of 0.4 ± 0.2 dB, a high out-of-band rejection ratio of >40dB, and a wide flatband width of ~2 nm. Furthermore, we evaluate manufacturing tolerances for intra-dies and inter-dies, comparing with the cases for 248-nm KrF-dry lithography process. It will be shown that the 193-nm ArF-immersion lithography process can provide much less excess phase errors of Si-nanowire waveguides, thus enabling to give better filter spectral characteristics. Finally, spectral superiorities will be reconfirmed by measuring 25 Gbps modulated signals launched into the fabricated device. Clear eye diagrams are observed when the wavelengths of modulated signals are stayed within almost passband of the 5th-order CROW.

High-output-power, single-wavelength silicon hybrid laser using precise flip-chip bonding technology.

An Si/III-V hybrid laser oscillating at a single wavelength was developed for use in a large-scale Si optical I/O chip. The laser had an InP-based reflective semiconductor optical amplifier (SOA) chip integrated with an Si wavelength-selection-mirror chip in a flip-chip configuration. A low coupling loss of 1.55 dB at the Si-SOA interface was accomplished by both mode-field-matching between Si-SOA waveguides and accurately controlling the bonding position. The fabricated Si hybrid laser exhibited a very low threshold current of 9.4 mA, a high output power of 15.0 mW, and a high wall-plug efficiency of 7.6% at 20 °C. Moreover, the device maintained a high output power of >10 mW up to 60°C due to the high thermal conductance between the SOA chip and Si substrate. The short cavity length of the flip-chip bonded laser expanded the longitudinal mode spacing. This resulted in temperature-stable single longitudinal mode lasing and a low RIN level of <-130 dB/Hz.

Flat-topped and low loss silicon-nanowire-type optical MUX/DeMUX employing multi-stage microring resonator assisted delayed Mach-Zehnder interferometers.

We propose a novel silicon-nanowire-type multiplexer (MUX) / demultiplexer (DeMUX) based on multi-stage microring resonator assisted delayed Mach-Zehnder interferometers. It is theoretically shown that spectral flatness of DeMUX spectra can be accomplished by incorporating nonlinear phase behaviors of microring resonators into the multi-stage delayed Mach-Zehnder interferometers. We experimentally demonstrate flat-topped 400GHz-spacing 1 × 4Ch demultiplexing operation in the fabricated device with silicon-nanowire waveguides. Furthermore, by integrating the micro-heaters on the top cladding layer of the fabricated device, the DeMUX performance is upgraded in terms of excess loss (<0.8dB) and crosstalk (<-10dB) without any degradation of filter spectral flatness at each channel grid.

Optical 60° hybrid for demodulating six-level DPSK signal.

We propose and demonstrate an optical 60° hybrid for demodulating optical signals with six-level DPSK modulation format. The proposed device consisting of a paired-interference 2∶6MMI coupler, phase shifters, and 2∶2MMI couplers with an asymmetric splitting ratio of 72∶28 exhibited hexagonal phase response over a C-band range.

Optical 45 degrees hybrid for demodulating 8-ary DPSK signal.

We propose a novel optical 45 degrees hybrid employing a 2 x 8 paired interference based multimode interference (MMI) coupler, three phase shifters and three 2 x 2 optical couplers. Since the proposed 45 degrees hybrid can demodulate an 8-ary differential phase shift keyed (8-DPSK) signal with only one delayed Mach-Zehnder interferometer (DMZI), the demodulator has simpler configuration and much smaller device dimensions than conventional 8-DPSK demodulators consisting of four pairs of DMZIs and 2 x 2 optical couplers. We calculate and experimentally demonstrate octagonal phase response of the proposed 45 degrees hybrid with a relative phase deviation of < +/- 5 degrees over 32-nm-wide spectral range.

Compact optical 90 degrees hybrid employing a tapered 2x4 MMI coupler serially connected by a 2x2 MMI coupler.

We propose a novel optical 90 degrees hybrid employing a paired-interference-based tapered 2x4 multimode interference coupler and a 2x2 multimode interference coupler. It was experimentally shown that the proposed 90 degrees hybrid has very short device length of less than 227 mum and is never accompanied by any waveguide intersections for coupling to balanced photodiodes. The proposed device exhibited quadrature phase response with a common-mode rejection ratio of more than 20dB and a phase deviation of less than 5 degrees over C-band spectral range.

Optical 90 degree hybrid with broad operating bandwidth of 94 nm.

We propose an optical 90 degree hybrid where no waveguide intersection in coupling to balanced photodiodes is required for coherent detection. The proposed device consisting of a paired-interference 2x4 multimode interference (MMI) coupler, a phase shifter, and a 2x2 MMI coupler exhibited quadrature phase response over a 94-nm-wide spectral range.

Analysis and demonstration of single-passband response and tuning characteristics in a chirped ladder interferometric filter for a widely tunable laser diode.

We have designed and demonstrated a chirped ladder-type tunable filter and discussed its potential application for a tunable diode laser. A ladder interferometric filter normally has a periodic passband, which makes it impossible to stabilize laser oscillation frequency. To overcome this drawback, we have designed, fabricated, and characterized a novel chirped tunable ladder filter. We have successfully demonstrated a single-passband response in the fabricated device. Furthermore, a tuning operation of more than 30 nm was achieved by introducing a current injection structure and optimizing electrode lengths at each single-stage ladder interferometer.

All-optical wavelength conversion in a GaInAsP/InP optical gate loaded with a Bragg reflector.

All-optical wavelength conversion employing a GaInAsP/InP nonlinear distributed-feedback waveguide switch is investigated. The device has the advantages of simple structure, compactness, polarity-noninverted operation, and feasibility of integration with other photonic devices such as semiconductor optical amplifier and modulators. We show that the device exhibits constant conversion efficiency around -9.2 dB in a signal-wavelength range of 1530-1560 nm. Furthermore, this device can potentially be made polarization independent.