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.

53 GBd PAM-4 fully-integrated silicon photonics transmitter with a hybrid flip-chip bonded laser.

We present a fully-integrated single-lane 53 GBd PAM-4 silicon photonics (SiPh) transmitter (Tx) with a flip-chip bonded laser diode (LD). The LD is butt-coupled to a Si edge coupler including a SiO2 suspended spot-size converter. The coupled power exceeds 10 dBm with a 1 dB allowable misalignment of 2.3 µm. The RF and eye performances of the Tx are evaluated. Extinction ratio >5 dB is obtained at 3.5 Vppd voltage swing. Aided by silicon capacitors, the Tx decouples parasitic inductances leading to remarkable improvements in the eye openings and transmitter dispersion eye closure quaternary by 1.16 dB. By implementing the fully-integrated Tx with driver packaging, we successfully demonstrate 106 Gb/s real-time operation satisfying KP4-FEC threshold at -5 dBm receiver sensitivity.

Active Fano resonance switch using dual-layer graphene in an embedded dielectric metasurface.

We propose an active optical Fano switch (OFS) based on an embedded dielectric metasurface (EDM) including dual-layer graphene (DLG). An EDM is a dielectric grating overlapped by two cladding layers, and it excites a Fano resonance. DLG is positioned inside the upper cladding layer to maximize light-graphene interaction. Thus, with a small change of the chemical potential (µc) of graphene, a resonance wavelength is tuned to switch the OFS on and off. First, a red-parity asymmetric Fano resonance is realized, and a sharp asymmetric lineshape is achieved by controlling the structural parameters of the EDM and the interaction between the Fano resonance and additional weak Fabry-Perot interference for efficient switching. The distance of a peak-to-dip wavelength (Δλp-d) and the change of chemical potential (Δµc) for switching is analyzed by varying the duty cycle (DC) and grating thickness (tg) of the EDM. Furthermore, switching contrast as a figure of merit (FoM) is analyzed. With DC of 0.5 and tg of 70 nm, the OFS requires Δλp-d of 7.3 nm and Δµc of 0.25 eV. The FoM of 0.97 is achieved. By adjusting the two parameters, the switching condition is tuned. In the case of a blue parity, the effect of the two parameters exhibits a similar trend to that of the red parity. The FoM, however, is lower due to the reversed parity.

RoF-based indoor distributed antenna system that can simultaneously support 5G mmWave and 6G terahertz services.

The telecommunication society is paving the way toward ultra-high frequency regions, including the millimeter wave (mmWave) and sub-terahertz (sub-THz) bands. Such high-frequency electromagnetic waves induce a variety of physical constraints when they are used in wireless communications. Inevitably, the fiber-optic network is deeply embedded in the mobile network to resolve such challenges. In particular, the radio-over-fiber (RoF)-based distributed antenna system (DAS) can enhance the accessibility of next-generation mobile networks. The inherent benefits of RoF technology enhance the DAS network in terms of practicality and transmission performance by enabling it to support the 5G mmWave and 6G THz services simultaneously in a single optical transport link. Furthermore, the RoF allows the indoor network to be built based on the cascade architecture; thus, a service zone can be easily added on request. This study presents an RoF-based multi-service DAS network and experimentally investigates the feasibility of the proposed system.

106.25-Gbps PAM-4 bidirectional optical sub-assembly module with in-line arrangement of optical and electrical interfaces.

We successfully demonstrate a 106.25-Gbps PAM-4 bidirectional optical sub-assembly for optical access networks, including a driver amplifier and an electro-absorption modulated laser for a transmitter, a photodiode and transimpedance amplifier for a receiver, and an optical filter block. For its implementation, we propose design strategies providing an in-line arrangement of optical and electrical interfaces while ensuring optical alignment tolerance for easy assembly and reducing electrical crosstalk between the transmitter and receiver. Measured receiver sensitivity was <-11.4 dBm for the KP4 forward error correction limit during transmitter operation, and measured power penalty of 10-km single-mode fiber transmission was <0.9 dB.

Coherent terahertz wireless communication using dual-parallel MZM-based silicon photonic integrated circuits.

Coherent terahertz (THz) wireless communication using silicon photonics technology provides critical solutions for achieving high-capacity wireless transmission beyond 5G and 6G networks and seamless connectivity with fiber-based backbone networks. However, high-quality THz signal generation and noise-robust signal detection remain challenging owing to the presence of inter-channel crosstalk and additive noise in THz wireless environments. Here, we report coherent THz wireless communication using a silicon photonic integrated circuit that includes a dual-parallel Mach-Zehnder modulator (MZM) and advanced digital signal processing (DSP). The structure and fabrication of the dual-parallel MZM-based silicon photonic integrated circuit are systematically optimized using the figure of merit (FOM) method to improve the modulation efficiency while reducing the overall optical loss. The advanced DSP compensates for in-phase and quadrature (IQ) imbalance as well as phase noise by orthogonally decoupling the IQ components in the frequency domain after adaptive signal equalization and carrier phase estimation. The experimental results show a reduction in phase noise that induces degradation of transmission performance, successfully demonstrating error-free 1-m THz wireless transmission with bit-error rates of 10-6 or less at a data rate of 50 Gbps.

Verification of hybrid-integrated 400-Gb/s (4 × 100 Gb/s) CWDM4 ROSA using a bandwidth-improved multilayer board.

We have successfully demonstrated a hybrid-integrated 400-Gb/s (4 × 100 Gb/s) CWDM4 PAM-4 receiver optical sub-assembly (ROSA) with a bandwidth-improved multilayer evaluation board. The proposed ROSA offers packaging simplification through passive optical alignment assembly of main components. In addition, we have proposed a structure to mitigate the bandwidth limitation issue caused by the typical edge connector mounting on the multilayer board, when needed bandwidth exceeds ∼20 GHz. With the bandwidth-improved multilayer board, the 3-dB bandwidth of the ROSA was observed to be >35.7 GHz and its receiver sensitivity was successfully measured to be <-10 dBm at FEC limit, bit error rate of 2.4e-4, for all channels.

Demonstration of photonics-aided terahertz wireless transmission system with using silicon photonics circuit: erratum.

We present an erratum for our recent paper [Opt. Express 28, 23397 (2020)] to include funding information in the funding section.

Demonstration of photonics-aided terahertz wireless transmission system with using silicon photonics circuit.

We experimentally demonstrate the use of silicon photonics circuit (SPC) in the simple and cost-effective photonics-aided Terahertz (THz) wireless transmission system. We perform theoretical investigation (with experimental confirmation) to understand that the system performance is more sensitive to the free space path loss (FSPL) at the THz wireless link than the SPC's insertion loss. The SPC, we design and fabricate, combines two incident optical carriers at different wavelengths and modulates one of two optical carriers with data to transfer, consequently reducing the system footprint that is indeed one of the key challenges that must be tackled for better practicability of the THz communication system. We perform experimental verification to show the feasibility of 40 Gb/s non-return-to-zero (NRZ) on-off-keying (OOK) signal transmission over 1.4 m wireless link for possibly its application in short-reach indoor wireless communication systems utilizing (sub-)THz frequency band such as, e.g., indoor WiFi, distributed antenna/radio systems, rack-to-rack data delivery, etc. The SPC could be further integrated with various photonic elements such as semiconductor optical amplifiers, laser diodes, and photo-mixers, which will enable the path towards all-photonic THz-wave synthesizers.

Realization of real-time DSP for C-band PAM-4 transmission in inter-datacenter network.

We designed and realized real-time pulse amplitude modulation-4 (PAM-4) digital signal processing (DSP) including forward error correction (FEC) for a C-band inter-datacenter network. The PAM-4 DSP is intended to compensate for chromatic dispersion and provide dispersion tolerance. A decision feedback equalizer (DFE) and maximum likelihood sequence equalizer (MLSE) were employed for the dispersion compensation. A low-density parity check (LDPC) code was used to increase coding gain. The soft-decision Viterbi algorithm (SOVA) was adopted to provide probabilistic information to the LDPC code. For implementation in a real-time field programmable gate arrays (FPGAs), we employed fully parallelized structures. In the design, three LDPC cores were operated in parallel, and the equalizers were also operated with 128 PAM-4 symbols. With the DSP, we empirically proved the feasibility of 25 km transmission without error-floor sign, corresponding to a dispersion compensation capacity of 425 ps/nm. We confirmed 35 km ∼ 85 km error-free transmission for inter-datacenter network.

Low-cost and miniaturized 100-Gb/s (2 × 50 Gb/s) PAM-4 TO-packaged ROSA for data center networks.

We design and implement a cost-effective and compact 100-Gb/s (2 × 50 Gb/s) PAM-4 receiver optical sub-assembly (ROSA) by using a TO-can package instead of an expensive box-type package. It consists of an optical demultiplexer, two PIN-PDs and a 2-channel linear transimpedance amplifier. The components are passively aligned and assembled using alignment marks engraved on each part. With a real-time PAM-4 DSP chip, we measured the back-to-back receiver sensitivities of the 100-Gb/s ROSA based on TO-56 to be less than -13.2 dBm for both channels at a bit error rate of 2.4e-4. The crosstalk penalty due to the adjacent channel interference was observed around 0.1 dB.

Suppression of thermal wavelength drift in widely tunable DS-DBR laser for fast channel-to-channel switching.

We present a simple and effective method for suppressing thermally induced wavelength drift in a widely tunable digital supermode distributed Bragg reflector (DS-DBR) laser monolithically integrated with a semiconductor optical amplifier (SOA). For fast thermal compensation, pre-compensatory currents are injected into the gain medium section of the DS-DBR laser and the SOA. This method can be easily applied to existing commercial tunable lasers, since it is implemented without any modification to manufacturing process. Experimental results exhibit that wavelength stability is noticeably improved to ± 0.01 nm. We also experimentally demonstrate a fast channel-to-channel switching in a wavelength-routed optical switching system employing a 90 × 90 arrayed waveguide grating router (AWGR). The measured switching time is less than 0.81 µs.

All-fiber 6-mode multiplexers based on fiber mode selective couplers.

All-fiber 6-mode multiplexer composed of two consecutive LP11-mode selective couplers (MSC), two LP21-MSCs and an LP02-MSC is fully characterized by wavelength-swept interferometer technique. The MSCs are fabricated by polished-type fiber couplers coupling LP01 mode of a single mode fiber into a higher-order mode of a few mode fiber. A pair of the mode multiplexers has minimum mode dependent loss of 4 dB and high mode group selectivity of over 15 dB. Mode division multiplexed transmission enabled by the all-fiber mode multiplexers is demonstrated over fiber spans of 117 km employing an in-line multi-mode optical amplifier. 6 modes of 120 Gb/s dual polarization quadrature phase shift keying signals combined with 30 wavelength channels are successfully transmitted.

Highly alignment tolerant and high-sensitivity 100Gb/s (4 × 25Gb/s) APD-ROSA with a thin-film filter-based de-multiplexer.

We investigate and demonstrate a 100-Gb/s (4x25-Gb/s) receiver optical sub-assembly (ROSA) based on avalanche photodiodes and a thin-film filter-based de-multiplexer. The overall alignment tolerances of the ROSA are relaxed to have larger than ± 25 µm by improving optical coupling structure. The receiver sensitivity of each lane is also measured to be less than -22.2 dBm, a record minimum to our knowledge, at the bit error ratio of 10-12 for 25.78-Gb/s NRZ signal.

Changes in the first-pass success rate with the GlideScope video laryngoscope and direct laryngoscope: a ten-year observational study in two academic emergency departments.

OBJECTIVE: The aim of this study was to assess the success rate of the GlideScope video laryngoscope (GVL) and direct laryngoscope (DL) over ten years in two academic emergency departments. METHODS: We used adult intubation data using DL and GVL collected from airway management registries at two academic emergency departments. We analyzed changes in first-pass success (FPS) rate by device and operator training level. We conducted a multivariate logistic regression analysis to predict the FPS according to time period. RESULTS: Over the study period (2006 to 2010, season I; 2013-2015, season II) the DL usage rate dropped from 91.6% to 45.0% while the GVL usage rate increased from 8.4% to 55.4%. The FPS rate using DL also declined from 90.8% in 2007 to 75.5% in 2015. On the other hand, the FPS rate using GVL increased from 87.8% to 95.2%. With DL, all operators' FPS rate declined by approximately 10% in season II compared to season I. The FPS rate with GVL was significantly higher in the providers of postgraduate year over 3 years (P=0.043). Multivariate logistic regression analysis revealed an adjusted odds ratio for GVL FPS of 0.799 during season I (P=0.274). However, the adjusted odds ratio for GVL FPS was 3.744 during season II (P<0.001). CONCLUSION: We found that the FPS rates of GVL have slightly increased but DL's FPS rate has significantly decreased during the last ten years.

Experimental demonstration of wavelength domain rogue-free ONU based on wavelength-pairing for TDM/WDM optical access networks.

In this study, we propose and experimentally demonstrate a wavelength domain rogue-free ONU based on wavelength-pairing of downstream and upstream signals for time/wavelength division-multiplexed optical access networks. The wavelength-pairing tunable filter is aligned to the upstream wavelength channel by aligning it to one of the downstream wavelength channels. Wavelength-pairing is implemented with a compact and cyclic Si-AWG integrated with a Ge-PD. The pairing filter covered four 100 GHz-spaced wavelength channels. The feasibility of the wavelength domain rogue-free operation is investigated by emulating malfunction of the misaligned laser. The wavelength-pairing tunable filter based on the Si-AWG blocks the upstream signal in the non-assigned wavelength channel before data collision with other ONUs.

Analysis of dimensional tolerance for an optical demultiplexer of a highly alignment tolerant 4 × 25 Gb/s ROSA module.

We have developed a 4 × 25 Gb/s ROSA (receiver optical sub-assembly) module for 100G Ethernet optical transceiver. This ROSA module has very large alignment tolerance of more than ± 250 µm between the optical DMUX (demultiplexer) and four photodiodes, for the reason it has the advantage of being easily assembled. The large alignment tolerance can be attributed to the dimensional tolerant optical DMUX, which is composed of four thin film filters attached to a parallelogram-shaped optic block. Since it is important to define the fabrication specifications for the dimension of the optic block, we analyze dimensional tolerance for the optic block using three-dimensional simulation. This parallelogram-shaped optical DMUX permits length tolerance of ± 300 µm and angular tolerance of ± 0.1°. The fabricated optical DMUX is estimated to have the angular error of less than 0.09°.