Butler matrix enabled multi-beam optical phased array for two-dimensional beam-steering and ranging

Based on the wavelength transparency of the Butler matrix(BM)beamforming network,we demonstrate a multibeam optical phased array(MOPA)with an emitting aperture composed of grating couplers at a 1.55μm pitch for wavelength-assisted two-dimensional beam-steering.The device is capable of simultaneous multi-beam operation in a field of view(FOV)of 60°×8°in the phased-array scanning axis and the wavelength-tuning scanning axis,respectively.The typical beam divergence is about 4°on both axes.Using multiple linearly chirped lasers,multibeam frequency-modulated continuous wave(FMCW)ranging is realized with an average ranging error of 4 cm.A C-shaped target is imaged for proof-of-concept 2D scanning and ranging.

Ultra-low-loss multi-layer 8×8 microring optical switch

Microring-based optical switches are promising for wavelength-selective switching with the merits of compact size and low power consumption.However,the large insertion loss,the high fabrication,and the temperature sensitivity hinder the scalability of silicon microring optical switch fabrics.In this paper,we utilize a three-dimensional(3D)microring-based optical switch element(SE)on a multi-layer Si_(3)N_(4)-on-SOI platform to realize highperformance large-scale optical switch fabrics.The 3D microring-based SE consists of a Si∕Si_(3)N_(4) waveguide overpass crossing in the bottom and the top layers,and Si_(3)N_(4) dual-coupled microring resonators(MRRs)in the middle layer.The switch is calibration-free and has low insertion loss.With the 3D microring-based SEs,we implement an 8×8 crossbar optical switch fabric.As the resonance wavelengths of all SEs are well aligned,only one SE needs to be turned on in each routing path,which greatly reduces the complexity of the switch control.The optical transmission spectra show a box-like shape,with a passband width of~69 GHz and an average on-state loss of~0.37 dB.The chip has a record-low on-chip insertion loss of 0.52-2.66 dB.We also implement a non-duplicate polarization-diversity optical switch by using the bidirectional transmission characteristics of the crossbar architecture,which is highly favorable for practical applications.100 Gb/s dual-polarization quadrature-phase-shift-keying(DP-QPSK)signal is transmitted through the switch without significant degradation.To the best of our knowledge,this is the first time that 3D MRRs have been used to build highly scalable polarization-diversity optical switch fabrics.

Low temperature sensitivity on-chip Fouriertransform spectrometer based on dual-layer Si_(3)N_(4)spiral waveguides

On-chip Fourier-transform spectrometers(FTSs)based on Mach–Zehnder interferometer(MZI)arrays suffer from severe central wavelength and fringe contrast variation due to fabrication errors.Even though a calibration matrix can be employed to correctly retrieve the input spectra,environmental temperature variation greatly degrades the retrieving performance.In this paper,we devise a dual-layer Si_(3)N_(4) waveguide interferometer to reduce the temperature sensitivity.The beating of the even and odd supermodes in the dual-layer waveguide generates periodic intensity fluctuations in the spectrum.Since these two modes have similar modal profiles,their thermal sensitivity and propagation loss are relatively balanced,leading to a low temperature sensitivity and a high interference extinction ratio.We designed and fabricated a passive FTS based on a 32-channel dual-layer Si_(3)N_(4) waveguide array.Experimental results show that the temperature sensitivity is reduced to 10 pm/°C,which is almost half that of single-layer Si_(3)N_(4) MZI-based FTSs.With this chip,we accurately reconstructed various types of optical spectra,including single and two sparse laser lines,and broadband optical spectra.Our method can fit a wide wavelength range,which is a promising technology to improve the practical applications of on-chip FTSs.

Integrated terahertz vortex beam emitter for rotating target detection

We propose a terahertz(THz)vortex emitter that utilizes a high-resistance silicon resonator to generate vortex beams with various topological charges.Addressing the challenge of double circular polarization superposition resulting from the high refractive index contrast,we regulate the transverse spin state through a newly designed second-order grating partially etched on the waveguide’s top side.The reflected wave can be received directly by a linearly polarized antenna,simplifying the process.Benefiting from the tuning feature,a joint detection method involving positive and negative topological charges identifies and detects rotational Doppler effects amid robust micro-Doppler interference signals.This emitter can be used for the rotational velocity measurement of an on-axis spinning object,achieving an impressive maximum speed error rate of∼2%.This approach holds promise for the future development of THz vortex beam applications in radar target detection and countermeasure systems,given its low cost and potential for mass production.

Continuous-variable quantum key distribution with on-chip light sources

Integrated quantum key distribution(QKD)systems based on photonic chips have high scalability and stability,and are promising for further construction of global quantum communications networks.On-chip quantum light sources are a critical component of a fully integrated QKD system;especially a continuous-variable QKD(CVQKD)system based on coherent detection,which has extremely high requirements for the light sources.Here,for what we believe is the first time,we designed and fabricated two on-chip tunable lasers for CV-QKD,and demonstrated a high-performance system based on these sources.Because of the high output power,fine tunability,and narrow linewidth,the involved on-chip lasers guarantee the accurate shot-noise-limited detection of quantum signals,center wavelength alignment of nonhomologous lasers,and suppression of untrusted excess noise.The system’s secret key rate can reach 0.75 Mb/s at a 50 km fiber distance,and the secure transmission distance can exceed 100 km.Our results mark a breakthrough toward building a fully integrated CV-QKD,and pave the way for a reliable and efficient terrestrial quantum-secure metropolitan area network.

Nonvolatile waveguide transmission tuning with electrically-driven ultra-small GST phase-change material

Low-power reconfigurable optical circuits are highly demanded to satisfy a variety of different applications. Conventional electro-optic and thermo-optic refractive index tuning methods in silicon photonics are not suitable for reconfiguration of optical circuits due to their high static power consumption and volatility. We propose and demonstrate a nonvolatile tuning method by utilizing the reversible phase change property of GST integrated on top of the silicon waveguide. The phase change is enabled by applying electrical pulses to the lm-sized GST active region in a sandwich structure. The experimental results show that the optical transmission of the silicon waveguide can be tuned by controlling the phase state of GST.

Multi-party Energy Management of Energy Hub: A Hybrid Approach with Stackelberg Game and Blockchain

In an integrated energy distribution system(IEDS),an energy hub has been introduced and deemed to be a suitable tool for managing and integrating multi-party energy forms.Due to different energies having diverse characteristics and being coupled with each other,it is difficult for an energy hub to implement the optimal scheduling of multiple energy sources.Therefore,an energy optimization management model is proposed based on the Stackelberg game,which considers the exergy conversion of multi-party energy sources in different operation modes.The problem is solved by the two-layer distributed optimization algorithm,in which the energy hub acts as the leader and is followed by the users.Furthermore,in order to alleviate the deception,malicious tampering,subpeption,and other secure risks in energy trading,blockchain is introduced into the energy hub and the concept of exergy coin(EC)is proposed.A credit-based blockchain framework and concurrent block building consensus process is explored to reduce the calculation cost and promote the exergy trading efficiency.Finally,the case study shows how the proposed method can effectively optimize energy scheduling and configure a more reasonable energy solution.

16 × 16 silicon Mach–Zehnder interferometer switch actuated with waveguide microheaters

We experimentally demonstrate a 16 × 16 reconfigurably nonblocking optical switch fabric using a Benes architecture. The switch fabric consists of 56 2 × 2 Mach–Zehnder interferometer based elementary switches, with each integrated with a pair of waveguide microheaters. The average on-chip insertion loss is ~5.2 dB for both of the 'all-cross' and the 'all-bar' states, with a loss variation of 1 dB over all routing paths. The cross talk for all switching states is better than -30 d B. The switching time of the switch element is about 22 μs. The switching functionality is verified by transmission of a 40 Gb∕s quadrature phase-shift keying optical signal.

Modeling and optimization of a single-drive push–pull silicon Mach–Zehnder modulator

We present an equivalent circuit model for a silicon carrier-depletion single-drive push–pull Mach–Zehnder modulator(MZM)with its traveling wave electrode made of coplanar strip lines.In particular,the partialcapacitance technique and conformal mapping are used to derive the capacitance associated with each layer.The PN junction is accurately modeled with the fringe capacitances taken into consideration.The circuit model is validated by comparing the calculations with the simulation results.Using this model,we analyze the effect of several key parameters on the modulator performance to optimize the design.Experimental results of MZMs confirm the theoretical analysis.A 56 Gb/s on–off keying modulation and a 40 Gb/s binary phase-shift keying modulation are achieved using the optimized modulator.

Silicon high-speed binary phase-shift keying modulator with a single-drive push–pull high-speed traveling wave electrode

We demonstrate binary phase shift keying(BPSK) modulation using a silicon Mach–Zehnder modulator with aπ-phase-shift voltage(Vπ) of-4.5 V.The single-drive push–pull traveling wave electrode has been optimized using numerical simulations with a 3 dB electro-optic bandwidth of 35 GHz.The 32 Gb/s BPSK constellation diagram is measured with an error vector magnitude of 18.9%.

Effect of gestation dietary methionine-to-lysine ratio on methionine metabolism and antioxidant ability of high-prolific sows

The uptake and metabolism of methionine(Met)are critical for epigenetic regulation,redox homeostasis,and embryo development.Our previous study showed that appropriate supplementation of dietary Met promoted the birth weight and placental angiogenesis of high-prolific sows.To further explore the metabolic effect of Met on pregnant sows,we have evaluated the influence of dietary Met level on Met metabolism,and the relationship between metabolites of Met and reproductive performance,antioxi-dant ability,and placental angiogenesis throughout the gestation of high-prolific sows.Sixty sows(the 3rd parity,Large White)were randomly divided into 5 groups that were fed diets with standardized ileal digestible(SID)methionine-to-lysine(Met:Lys)ratios of 0.27(control),0.32,0.37,0.42,and 0.47 from the mating day(gestational d 0,G0d)until the farrowing day.HPLC-MS/MS analysis was used to simulta-neously evaluate the metabolites related to Met,e.g.S-adenosylmethionine(SAM),S-adenosylhomo-cysteine(SAH),homocysteine(Hcy),cysteine(Cys),and glutathione(GSH).The concentration of SAM and SAH in plasma had significant fluctuations,especially in late pregnancy.Increasing dietary Met sup-plementation significantly improved the plasma SAM and methylation potential(SAM-to-SAH ratio)at d 114 of pregnancy(G114d).Moreover,a positive association of the plasma SAM concentration at G114d was observed with the litter weight of born alive(P<0.05;R2=0.58).Furthermore,Hcy concentration in plasma was at the lowest level for 0.37 ratio group at G114d.However,it significantly increased during late pregnancy.Moreover,there were negative correlations between plasma Hcy concentration at G114d(P<0.05)and the placental vascular density in the fold and stroma(P<0.05).Compared with the control group,the expression of vascular endothelial growth factor-A(VEGF-A)in the placenta tissue of 0.37 ratio group increased significantly(P<0.05).Collectively,these findings indicate that dietary Met:Lys ratio(0.37 to 0.57)in the pregnant diet dose not influence the antioxidant ability of the high-prolific sows;however,the improvement of fetal development and placental angiogenesis of high-prolific sows by supplementation of Met are closely associated to the key Met-related metabolite of SAM and Hcy,respectively.

All-optical wavelength converter using a microdisk resonator integrated with p-n junctions

We explore all-optical wavelength conversion in a microdisk resonator integrated with interleaved p-n junctions.Numerical simulation based on temporal coupled mode theory is performed to study the free-carrier dynamics inside the cavity.It reveals that the detuning of pump and probe frequencies and the carrier lifetime have a significant effect on the device performance.Experimental result confirms that the conversion speed can be considerably improved by applying a reverse bias on the p-n junctions.Wavelength conversion at 10 Gb/s data rate is achieved with a pump power of 5.41 dBm and a bias voltage of-6 V.

Integrated optical delay lines:a review and perspective[Invited]

Optical delay lines（ODLs） are one of the key enabling components in photonic integrated circuits and systems.They are widely used in time-division multiplexing, optical signal synchronization and buffering, microwave signal processing, beam forming and steering, etc. The development of integrated photonics pushes forward the miniaturization of ODLs, offering improved performances in terms of stability, tuning speed, and power consumption. The integrated ODLs can be implemented using various structures, such as single or coupled resonators, gratings, photonic crystals, multi-path switchable structures, and recirculating loop structures.The delay tuning in ODLs is enabled by either changing the group refractive index of the waveguide or changing the length of the optical path. This paper reviews the recent development of integrated ODLs with a focus on their abundant applications and flexible implementations. The challenges and potentials of each type of ODLs are pointed out.

4×4 nonblocking optical switch fabric based on cascaded multimode interferometers

We experimentally demonstrate a 4 × 4 nonblocking silicon thermo-optic(TO) switch fabric consisting of three stages of tunable generalized Mach–Zehnder interferometers. All 24 routing states for nonblocking switching are characterized. The device's footprint is 4.6 mm × 1.0 mm. Measurements show that the worst cross talk of all switching states is-7.2 dB. The on-chip insertion loss is in the range of 3.7–13.1 dB. The average TO switching power consumption is 104.8 mW.

Optical generation of UWB pulses utilizing Fano resonance modulation

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.

Microwave frequency upconversion employing a coupling-modulated ring resonator

We present a method to generate a frequency-doubled microwave signal by employing a coupling-modulated ring resonator. Critical coupling is achieved when the resonator intrinsic loss is perfectly balanced by the external coupling enabled by a Mach–Zehnder interferometer coupler. The high suppression of the carrier leads to a clean two-tone optical signal with the frequency interval two times larger than that of the input microwave frequency.The beating of the two-tone signal at a photodiode generates the frequency upconverted microwave signal.A theoretical model is established to analyze the modulation process and the microwave signal generation.Experimental results show that the electrical harmonic suppression ratio is around ~20 dB(29 dB) for an input microwave signal with 5 dBm(10 dBm) power.

High-speed silicon microring modulator at the 2μm waveband with analysis and observation of optical bistability

Recently,significantly raised interests have emerged for the 2μm waveband as an extended new window for fiber optic communication.Much research progress has been made on the photonic integrated circuits for the 2μm 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 2μm waveband was demonstrated.An L-shaped PN junction was specially designed for 2μm to achieve a high modulation efficiency with V_(π)L of 0.85V·cm.The measured 3 dB bandwidth is 18 GHz,supporting up to 50 Gbps signaling at 2μm.Additionally,optical bistability induced by the thermo-optical effect and nonlinear effects was analyzed theoretically and observed experimentally in the 2μm 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 2μm 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 2μm,drawing a promising prospect for the silicon photonic integration and high-speed interconnection at the 2μm waveband,and it provides the referenceable analysis of optical bistability,which guides the design and experimental investigation of 2μm MRM.

Application of SOl microring coupling modulation in microwave photonic phase shifters

Phase shifter is one of the key devices in microwave photonics. We report a silicon microring resonator with coupling modulation to realize microwave phase shift. With coupling tuning of the Mach-Zehnder interferometer （MZI） coupler to change the resonator from under-coupling to over-coupling, the device can realize a π phase shift on the incoming microwave signal with a frequency up to 25 GHz. The device can also realize 2.5π continuous phase tuning by manipulating the three DC bias voltages applied on the MZI coupler.

Wavelength-mode pulse interleaver on the silicon photonics platform

We report an 8-channel wavelength-mode optical pulse interleaver on a silicon photonic chip.Wavelength-and mode-division multiplexing techniques are combined to increase the repetition rate of the pulses without adding the complexity of a single dimension.The interleaver uses a cascaded Mach–Zehnder interferometer architecture as a wavelength-division(de)multiplexer,an asymmetric directional coupler as a mode(de)multiplexer,and various lengths of silicon waveguides as delay lines.A pulse sequence with a time interval of 125 ps is implemented with the repetition rate being eight times that of the initial one.The demonstrated wavelength-mode multiplexing approach opens a new route for the generation of high-speed optical pulses.

Silicon non-blocking 4×4 optical switch with automated polarization adjustment

We demonstrate a polarization-insensitive silicon 4×4 optical switch based on Mach–Zehnder interferometer(MZI)switch elements.On-chip polarization controllers are integrated before the switch fabric to automatically adjust an arbitrary input polarization to the transverse electric mode.The 4×4 switch fabric is based on a dilated double-layer network architecture to completely cancel the first-order crosstalk.Thermo-optic phase shifters are integrated in the MZI switch elements and the polarization controllers for adjustment of the switching state and polarization,respectively.We develop a polarization control algorithm based on a gradient descent method for automated polarization control.The polarization recovery time is less than 4 ms,and the measured polarization-dependent loss is~2 d B.The scheme provides a new solution for realizing polarization-insensitive silicon optical switches.