Search

We report a silicon-based integrated optical sampling chip. High-repetition-rate optical sampling pulses are generated by interleaving low-repetition-rate input optical pulses with the assistance of wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM). The WDM pulse interleaver is based on a loopback arrayed waveguide grating (AWG) with linearly increasing delays. The amplitude of the interleaved pulses can be adjusted by the attenuators in the loopback waveguides. Two high-order modes in a multimode waveguide are utilized to further increase the pulse repetition rate. With WDM and MDM, the optical pulse sampling rate is increased by 8 times. The optical sampling pulses are then modulated by a multimode Mach-Zehnder modulator with the active arms integrated with L-shaped PN junctions. The sampled pulses are finally separated by mode and wavelength demultiplexers for low-speed parallel processing. The wavelength demultiplexer is made of a dual-ring assisted Mach-Zehnder interferometer (DR-MZI) with high wavelength selectivity. This successful implementation of the high-speed sampling chip marks a significant step forward in the full integration of analog-to-digital converters on a single chip and opens up avenues toward real applications of microwave photonics.

Due to the difficulty of controlling the waveguide loss in the doping region, high-speed silicon micro-ring modulators usually have limited extinction ratio. In this work, we present a mode-division-multiplexing (MDM) resonance-enhanced silicon micro-ring modulator with an ultrahigh extinction ratio. We used a two-mode micro-ring resonator and a mode conversion circular structure to trap the light twice within a single micro-ring resonator. Proof-of-concept high extinction ratio up to 55 dB was obtained. 30 Gb/s PAM-8 and 50 Gb/s PAM-4 signaling with a bit error rate below the hard-decision forward error correction (HD-FEC) threshold were demonstrated with the fabricated modulator, indicating great potential for high-order pulse amplitude modulation (PAM).

Vehicular fog computing (VFC) has become an appealing paradigm to provide services for vehicles and traffic systems. However, high mobility is one of the great challenges to the communication and computation service qualities in VFC. A network model for directional vehicle mobility is proposed in this paper to guarantee the service qualities of vehicles in VFC. In the model, vehicles are configured into three vehicular subnetworks according to their turning directions at the next crossing. For each subnetwork, vehicles communicate with each other via vehicle-to-vehicle communication, and with roadside units via vehicle-to-infrastructure communication. The aim is to minimize the average response time of the tasks originated from vehicles. By carefully choosing neighboring vehicles as task processing helpers, a greedy algorithm is proposed to solve the mentioned optimization problem. Besides, two bipartite matching based algorithms, named BMA1 and BMA2, are proposed by exploiting Kuhn-Munkras approach and minimum-cost maximum-flow approach, respectively. Performance of the proposed model and the offloading algorithms are evaluated on the combined simulation platform by open street map, SUMO and NS-3. Simulation results show that, the proposed model outperforms four existing models in terms of average response time, when the five models have similar number of unsuccessful tasks. Moreover, the proposed BMA1 and BMA2 are superior to the existing greedy algorithm in terms of the average response time of tasks, and the proposed greedy algorithm significantly accelerates the generation of offloading decisions in comparison to BMA1, BMA2 and the existing greedy algorithm.

Sinc-shaped Nyquist pulses have wide applications in optical communications and microwave photonics. The quality of the generated Nyquist pulses has a significant effect on the overall performance of the communication system and the signal processing system. Generating high-quality Nyquist pulses with integrated silicon modulators is however still challenging due to the highly nonlinear response and fabrication-induced discrepancies of the device. We present a model for a silicon dual-parallel modulator with which the best possible quality of the generated optical frequency comb (OFC) and sinc-shaped Nyquist pulses can be obtained. In the model, the phase and amplitude deviations are taken into consideration. Device induced waveform and spectrum distortion can be well described. Based on the guidance of the model, a root-mean-square error of 2.8% is obtained between the experimentally generated signals and the ideal pulses, which proves the high accuracy of the model and its importance for high-quality Nyquist pulse generation.

Silicon nitride (Si3N4) has a higher nonlinear threshold compared to silicon, which reduces the effect of two-photon absorption. However, the low thermo-optic coefficient and the reduced refractive index contrast of thin Si3N4 waveguides lead to a low thermal tuning speed and low thermal efficiency. This paper demonstrates a widely tunable III-V/Si3N4 hybrid-integrated external cavity laser with a relatively faster switching time. The Si3N4 external feedback circuit is based on 800-nm-thick Si3N4 waveguides with an optical confinement factor of 87%. It allows the reduction of the oxide under-cladding layer thickness to 4 μm and the oxide upper-cladding layer to 1.7 μm without additional loss. The switching time between two non-adjacent lasing wavelengths is 60.7 μs. The maximum output power is 34 mW under 500 mA injection current. The side mode suppression ratio is more than 70 dB over the tuning range of 58.5 nm. The laser intrinsic linewidth is 2.5 kHz.

We experimentally demonstrate optical frequency-modulated continuous-wave (FMCW) signal generation utilizing a silicon dual-parallel Mach-Zehnder modulator (DP-MZM). The sideband suppression ratio (SSR) and the sideband-to-carrier suppression ratio (SCSR) of the single-sideband suppressed carrier (SSB-SC) modulation are higher than 15 dB when RF frequency is lower than 20 GHz. With the generated triangular modulated FMCW signal, we demonstrate simultaneous ranging and velocimetry. The chirp bandwidth is 10 GHz and the chirp period is $1~\mu \text{s}$ , corresponding to a ranging resolution of 13 mm and a velocimetry resolution of 0.5 m/s, consistent with the theoretical calculation. These results show that wideband FMCW signal generation by a silicon DP-MZM is promising for high-resolution light detection and ranging.

Mode-division multiplexing (MDM), which could further increase the capacity and flexibility of the communication systems, has attracted much attention. In this Letter, we demonstrate a proof-of-principle silicon mode-insensitive modulator based on the balanced Mach-Zehnder interferometer that could realize modulation of both TE

In this paper, we demonstrate a method to generate a low-chirp ultra-wideband pulse (UWB) signal based on a silicon single-drive push-pull segmented Mach-Zehnder modulator (SMZM). The concept is analyzed theoretically and demonstrated experimentally. We get positive monocycle pulses with different relative time delays between the two driving signals. The center frequency and fractional bandwidth of the generated positive monocycle pulse is 5.97 GHz and 161% with a relative time delay of 56 ps. By changing the operating point of the SMZM, we can get negative monocycle pulses. We modulate the UWB signals with on-off keying and pulse position formats by properly coding the driving signal. As far as we know, this is the first time to realize low-chirp UWB signals using only one silicon modulator. The successful generation of UWB signals poses a significant step in realizing a compact low-cost and low-chirp UWB generator on the silicon photonics platform.

Analog microwave photonic links require high-linearity electro-optic modulators. We investigate and optimize the linearity performance of a silicon Fano resonance modulator based on a reconfigurable microring-assisted Mach–Zehnder interferometer (MZI). The microring resonator has a tunable coupling coefficient and the reference arm of the MZI is variable in both amplitude and phase, allowing for flexible tuning of the operating point. The on-chip insertion loss of the device is 5 dB. High modulation linearity can be obtained at both Fano resonant and anti-Fano resonant wavelengths, among which the latter has a higher carrier-to-distortion ratio (CDR). However, the Fano resonance has a higher modulation efficiency due to its sharp slope of the resonant transfer function, eventually leading to a larger spurious-free dynamic range (SFDR). Experimental results indicate that the best SFDR of the third-order intermodulation distortion (IMD3) is 111.3 dB·Hz2/3 measured at the 1 GHz frequency, comparable to the commercial lithium niobate modulators.

Compact and integrated microwave pulse generation can benefit various applications in integrated microwave photonics. We demonstrate high-quality microwave pulse generation with multiple pulse shapes based on an integrated silicon dual-parallel Mach–Zehnder modulator. Three typical microwave pulses, including sinc-shaped Nyquist pulses, triangular pulses, and Gaussian pulses, are successfully generated. The device is capable of multi-wavelength operation with a tunable repetition rate. All the generated pulses show a root mean square error below 4%. The comparison with the results based on LiNbO3 modulators and other silicon modulators is also provided to confirm the high quality of generated pulses. Our article demonstrates the high tunability of microwave pulse generation with silicon modulators and shows the potential of an integrated silicon chip to generate high-speed photonic and microwave pulse trains demanded in optical communications and integrated microwave photonics.

We demonstrate nine-line optical frequency comb (OFC) and sinc-shaped Nyquist pulse generation based on two cascaded silicon Mach–Zehnder modulators. The OFC has a flatness of 1.83 dB, a frequency spacing of 5 GHz, and a corresponding Nyquist pulsewidth of ∼22 ps. Moreover, multi-wavelength operation and repetition rate tunability have also been demonstrated, which indicates the potential of our work to generate an on-chip high-speed pulse train demanded in optical communications and microwave photonics applications.

We demonstrate novel phase-coded microwave signal generation based on a two-segment single-drive push–pull silicon Mach–Zehnder modulator. The coding signal and the microwave frequency are each applied to one of the separate segments. The phase-coded microwave signal is generated by properly setting the working point of the modulator. The precise π phase shift is determined by the sign of the coding signal. Both theoretical analysis and experimental demonstration are performed to verify the concept. The modulator successfully generates a 10-GHz (20-GHz) phase-coded microwave signal with a 5-Gb/s (10-Gb/s) coding data rate and the measured pulse compression ratio is 133.0 (156.8).

Autophagy is ubiquitously present in eukaryotes. During this process, intracellular proteins and some waste organelles are transported into lysosomes or vacuoles for degradation, which can be reused by the cell to guarantee normal cellular metabolism. However, the function of autophagy-related (ATG) proteins in oomycetes is rarely known. In this study, we identified an autophagy-related gene, PlATG6a, encoding a 514-amino-acid protein in Peronophythora litchii, which is the most destructive pathogen of litchi. The transcriptional level of PlATG6a was relatively higher in mycelium, sporangia, zoospores and cysts. We generated PlATG6a knockout mutants using CRISPR/Cas9 technology. The P. litchii Δplatg6a mutants were significantly impaired in autophagy and vegetative growth. We further found that the Δplatg6a mutants displayed decreased branches of sporangiophore, leading to impaired sporangium production. PlATG6a is also involved in resistance to oxidative and salt stresses, but not in sexual reproduction. The transcription of peroxidase-encoding genes was down-regulated in Δplatg6a mutants, which is likely responsible for hypersensitivity to oxidative stress. Compared with the wild-type strain, the Δplatg6a mutants showed reduced virulence when inoculated on the litchi leaves using mycelia plugs. Overall, these results suggest a critical role for PlATG6a in autophagy, vegetative growth, sporangium production, sporangiophore development, zoospore release, pathogenesis and tolerance to salt and oxidative stresses in P. litchii.

We demonstrate a multi-channel silicon photonic transmitter based on wavelength division multiplexing (WDM) and mode division multiplexing (MDM). The light source is realized by a silicon nitride (Si3N4) Kerr frequency comb and optical modulation is realized by silicon electro-optic modulators. Three wavelengths and two modes are employed to increase the optical transmission capacity. The accumulated data rate reaches 150 Gb/s. The dense integration of WDM and MDM components with a compact optical comb source opens new avenues for the future high-capacity multi-dimensional optical transmission.

Autophagy is ubiquitously present in eukaryotes. During this process, intracellular proteins and some waste organelles are transported into lysosomes or vacuoles for degradation, which can be reused by the cell to guarantee normal cellular metabolism. However, the function of autophagy-related (ATG) proteins in oomycetes is rarely known. In this study, we identified an autophagy-related gene

We demonstrate a high-efficiency silicon Mach-Zehnder modulator with U-shaped PN junctions. The depletion region of the U-shaped PN junction has a large overlap with the waveguide optical mode, leading to a low drive voltage. The calculated modulation efficiency is 0.33 V·cm at 0 V bias and 0.55 V·cm at −2 V bias. On-off keying (OOK) modulation and four-level pulse amplitude modulation (PAM-4) are achieved at 32 Gb/s and 64 Gb/s data rates under 2 V drive voltage, respectively. The bit error rate for the PAM-4 modulation is below the hard-decision forward error correction threshold of 3.8 × 10−3.

Recently, optical mode-division multiplexing has drawn a lot of attention due to its ability to increase the optical communication capacity in one physical channel with a single wavelength carrier. In this Letter, we demonstrate reconfigurable mode-selective modulation which is potentially useful for on-chip mode-multiplexed photonic systems. The device consists of two mode exchangers and one T E 1 mode modulator. The mode exchanger is based on a Mach–Zehnder interferometer that performs mode exchange between T E 0 and T E 1 modes. The T E 1 mode modulator consists of a pair of 1 × 3 / 3 × 1 multimode interferometers acting as a mode (de)multiplexer. It only selectively modulates the T E 1 mode while bypassing the T E 0 mode. 32 Gb/s on-off keying (OOK) modulation is successfully demonstrated for both input T E 0 and T E 1 modes. This device can be used as a building block for on-chip multimode interconnect networks.

We reported a silicon modulator with L-shaped PN junction for high efficiency modulation based on mode conversion to recycle light twice within the modulator phase shifter. Record low vπ·lπ of 0.37 V·cm was experimentally demonstrated.

Silicon micro-ring modulator with 18-GHz electro-optic bandwidth and

In this paper, we reported an integrated method to generate ultra-wideband (UWB) pulses of different orders based on a reconfigurable silicon micro-ring resonator-coupled Mach-Zehnder interferometer. Under proper operating conditions, the device can produce Fano resonances with a peak-to-valley extinction ratio of above 20 dB. UWB monocycle and doublet signals with picosecond pulse widths are produced when the microring resonator is modulated by square and Gaussian electrical pulses, respectively. With our Fano resonance modulator on silicon photonics, it is promising to foresee versatile on-chip microwave signal generation. [Image: see text]

Optical beam-forming networks (OBFNs) based on optical true-time delay lines (OTTDLs) are well known as the promising candidate for solving the bandwidth limitation of traditional electronic phased array antennas (PAAs) due to beam squinting. Here we report, to the best of our knowledge, the first monolithic 1 × 8 microwave photonic beamformer, based on switchable OTTDLs on the silicon-on-insulator platform. The chip consists of a modulator, an eight-channel OBFN, and eight photodetectors, thus including hundreds of active and passive components in total. It has a wide operating bandwidth from 8 to 18 GHz, which is almost two orders larger than that of electronic PAAs. The beam can be steered to 31 distinguishable angles in the range from − 75.51 ∘ to 75.64°, based on the beam pattern calculation with the measured radiofrequency response. The response time for beam steering is 56 µs. These results represent a significant step toward the realization of integrated microwave photonic beamformers that can satisfy compact-size and low-power consumption requirements for the future radar and wireless communication systems.

Recently, significantly raised interests have emerged for the 2 µm waveband as an extended new window for fiber optic communication. Much research progress has been made on the photonic integrated circuits for the 2 µm waveband, especially on the CMOS-compatible silicon-on-insulator wafer. In this work, a silicon integrated microring modulator (MRM) with record high-speed performances at the 2 µm waveband was demonstrated. An L-shaped PN junction was specially designed for 2 µm to achieve a high modulation efficiency with V π L of 0.85 V · cm . The measured 3 dB bandwidth is 18 GHz, supporting up to 50 Gbps signaling at 2 µm. Additionally, optical bistability induced by the thermo-optical effect and nonlinear effects was analyzed theoretically and observed experimentally in the 2 µm MRM for the first time to our knowledge. Nonlinear coupled mode theory and the Runge–Kutta method were used to simulate the behaviors of bistability in the 2 µm MRM. The simulation and experimental results indicate that, when the MRM is launched by a high optical power, the distorted resonant spectrum under an optical bistable state deteriorates the modulation efficiency and signal performances. This work breaks the record of high-speed silicon MRM at 2 µm, drawing a promising prospect for the silicon photonic integration and high-speed interconnection at the 2 µm waveband, and it provides the referenceable analysis of optical bistability, which guides the design and experimental investigation of 2 µm MRM.

Optical signaling without a high voltage driver for electric-optic modulation is in high demand to reduce power consumption, packaging complexity, and cost. In this work, we propose and experimentally demonstrate a silicon mode-loop Mach–Zehnder modulator (ML-MZM) with record-high modulation efficiency. We used a mode-loop structure to recycle light twice in the phase shifter. With an L-shaped PN junction, a comparably large overlap between the PN junction and optical modes of both TE 0 and TE 1 was achieved to lower the driving voltage or decrease the photonic device size. Proof-of-concept high-efficiency modulation with low V π L of 0.37 V · cm was obtained. Subvoltage V π can be realized with a millimeter’s length phase shifter by this scheme, which makes the realization of CMOS-compatible driverless modulation highly possible. 40 Gb/s signaling with a bit error rate below the 7% forward-error-correction threshold was then demonstrated with the fabricated ML-MZM, indicating great potential for high-speed optical communication.

We report a reconfigurable optical filter chip based on the Si3N4 waveguide platform. Microwave filtering is realized using a device with optical-to-electrical mapping. The filter chip is based on a lattice structure with the dual-ring-coupled Mach-Zehnder interferometers (DR-MZIs) as the basic elements. Both the lattice and ring couplers are tunable, making the chip reconfigurable to various filter functions. A theoretical model is developed to analyze its optical filtering performance. Measurement reveals that the filter passband can reach hundreds of megahertz in the lower limit and several gigahertz in the upper limit. Various orders of infinite impulse response filters are implemented with a tailorable passband. The flexibility in tuning filter center frequency and passband makes it suitable in high-resolution adaptable microwave signal front-end processing.

We experimentally demonstrate optical single-sideband modulation with a variable RF frequency. The sideband suppression ratio for the carrier-remained and carrier-suppressed modulation is more than 38 dB and 13 dB from 1 to 24 GHz, respectively. © 2020 The Author(s)

We report a high-linearity silicon electro-optic modulator based on single ring-assisted Mach-Zehnder Interferometer (MZI). The best spurious-free dynamic range (SFDR) of the third-order intermodulation distortion (IMD3) is 109 dB•Hz2/3. The linearity is comparable to the commercial lithium niobate modulators. The device can find potential applications in microwave photonic systems.

We demonstrated an III-V/silicon nitride hybrid external cavity laser (ECL). The ECL exhibits a tuning range of 45 nm, a side-mode suppression ratio (SMSR) of 60 dB, and a linewidth of round 100 kHz.