Multifunctional mixed analog/digital signal processor based on integrated photonics

Photonic signal processing offers a versatile and promising toolkit for contemporary scenarios ranging from digital optical communication to analog microwave operation.Compared to its electronic counterpart,it eliminates inherent bandwidth limitations and meanwhile exhibits the potential to provide unparalleled scalability and flexibility,particularly through integrated photonics.However,by far the on-chip solutions for optical signal processing are often tailored to specific tasks,which lacks versatility across diverse applications.Here,we propose a streamlined chip-level signal processing architecture that integrates different active and passive building blocks in silicon-on-insulator(SOI)platform with a compact and efficient manner.Comprehensive and in-depth analyses for the architecture are conducted at levels of device,system,and application.Accompanied by appropriate configuring schemes,the photonic circuitry supports loading and processing both analog and digital signals simultaneously.Three distinct tasks are facilitated with one single chip across several mainstream fields,spanning optical computing,microwave photonics,and optical communications.Notably,it has demonstrated competitive performance in functions like image processing,spectrum filtering,and electro-optical bandwidth equalization.Boasting high universality and a compact form factor,the proposed architecture is poised to be instrumental for next-generation functional fusion systems.

Versatile photonic molecule switch in multimode microresonators

Harnessing optical supermode interaction to construct artificial photonic molecules has uncovered a series of fundamental optical phenomena analogous to atomic physics.Previously,the distinct energy levels and interactions in such two-level systems were provided by coupled microresonators.The reconfigurability is limited,as they often require delicate external field stimuli or mechanically altering the geometric factors.These highly specific approaches also limit potential applications.Here,we propose a versatile on-chip photonic molecule in a multimode microring,utilizing a flexible regulation methodology to dynamically control the existence and interaction strength of spatial modes.The transition between single/multi-mode states enables the“switched-off/on”functionality of the photonic molecule,supporting wider generalized applications scenarios.In particular,“switched-on”state shows flexible and multidimensional mode splitting control in aspects of both coupling strength and phase difference,equivalent to the a.c.and d.c.Stark effect.“Switched-off”state allows for perfect low-loss single-mode transition(Qi~10 million)under an ultra-compact bend size(FSR~115 GHz)in a foundry-based silicon microring.It breaks the stereotyped image of the FSR-Q factor trade-off,enabling ultra-wideband and high-resolution millimeter-wave photonic operations.Our demonstration provides a flexible and portable solution for the integrated photonic molecule system,extending its research scope from fundamental physics to real-world applications such as nonlinear optical signal processing and sixth-generation wireless communication.

Reliable intracavity reflection for self-injection locking lasers and microcomb generation

Self-injection locking has emerged as a crucial technique for coherent optical sources,spanning from narrow linewidth lasers to the generation of localized microcombs.This technique involves key components,namely a laser diode and a high-quality cavity that induces narrow-band reflection back into the laser diode.However,in prior studies,the reflection mainly relied on the random intracavity Rayleigh backscattering,rendering it unpredictable and unsuitable for large-scale production and wide-band operation.In this work,we present a simple approach to achieve reliable intracavity reflection for self-injection locking to address this challenge by introducing a Sagnac loop into the cavity.This method guarantees robust reflection for every resonance within a wide operational band without compromising the quality factor or adding complexity to the fabrication process.As a proof of concept,we showcase the robust generation of narrow linewidth lasers and localized microcombs locked to different resonances within a normal-dispersion microcavity.Furthermore,the existence and generation of localized patterns in a normal-dispersion cavity with broadband forward–backward field coupling is first proved,as far as we know,both in simulation and in experiment.Our research offers a transformative approach to self-injection locking and holds great potential for large-scale production.

Highly reconfigurable silicon integrated microwave photonic filter towards next-generation wireless communication

Integrated microwave photonic filters(IMPFs)are capable of offering unparalleled performances in terms of superb spectral fineness,broadband,and more importantly,the reconfigurability,which encounter the trend of the next-generation wireless communication.However,to achieve high reconfigurability,previous works should adopt complicated system structures and modulation formats,which put great pressure on power consumption and controlment,and,therefore,impede the massive deployment of IMPF.Here,we propose a streamlined architecture for a wideband and highly reconfigurable IMPF on the silicon photonics platform.For various practical filter responses,to avoid complex auxiliary devices and bias drift problems,a phase-modulated flexible sideband cancellation method is employed based on the intensity-consistent single-stage-adjustable cascadedmicroring(ICSSA-CM).The IMPF exhibits an operation band extending to millimeter-wave(≥30 GHz),and other extraordinary performances including high spectral resolution of 220 MHz and large rejection ratio of 60 d B are obtained.Moreover,Gb/s-level RF wireless communications are demonstrated for the first time towards real-world scenarios.The proposed IMPF provides broadband flexible spectrum control capabilities,showing great potential in the next-generation wireless communication.

Submilliwatt, widely tunable coherent microcomb generation with feedback-free operation

Microcombs are revolutionizing optoelectronics by providing parallel, mutually coherent wavelengthchannels for time-frequency metrology and information processing. To implement this essential function inintegrated photonic systems, it is desirable to drive microcombs directly with an on-chip laser in a simpleand flexible way. However, two major difficulties have prevented this goal: (1) generating mode-lockedcomb states usually requires a significant amount of pump power and (2) the requirement to align laser andresonator frequency significantly complicates operation and limits the tunability of the comb lines. Here, weaddress these problems by using microresonators on an AlGaAs on-insulator platform to generate dark-pulsemicrocombs. This highly nonlinear platform dramatically relaxes fabrication requirements and leads to arecord-low pump power of <1 mW for coherent comb generation. Dark-pulse microcombs facilitated bythermally controlled avoided mode crossings are accessed by direct distributed feedback laser pumping.Without any feedback or control circuitries, the comb shows good coherence and stability. With around150 mW on-chip power, this approach also leads to an unprecedentedly wide tuning range of over one freespectral range (97.5 GHz). Our work provides a route to realize power-efficient, simple, and reconfigurablemicrocombs that can be seamlessly integrated with a wide range of photonic systems.

16-channel photonic–electric co-designed silicon transmitter with ultra-low power consumption

A hybrid integrated 16-channel silicon transmitter based on co-designed photonic integrated circuits(PICs) and electrical chiplets is demonstrated. The driver in the 65 nm CMOS process employs the combination of a distributed architecture, two-tap feedforward equalization(FFE), and a push–pull output stage, exhibiting an estimated differential output swing of 4.0V_(pp). The rms jitter of 2.0 ps is achieved at 50 Gb/s under nonreturnto-zero on–off keying(NRZ-OOK) modulation. The PICs are fabricated on a standard silicon-on-insulator platform and consist of 16 parallel silicon dual-drive Mach–Zehnder modulators on a single chip. The chip-on-board co-packaged Si transmitter is constituted by the multichannel chiplets without any off-chip bias control, which significantly simplifies the system complexity. Experimentally, the open and clear optical eye diagrams of selected channels up to 50 Gb/s OOK with extinction ratios exceeding 3 dB are obtained without any digital signal processing. The power consumption of the Si transmitter with a high integration density featuring a throughput up to 800 Gb/s is only 5.35 p J/bit, indicating a great potential for massively parallel terabit-scale optical interconnects for future hyperscale data centers and high-performance computing systems.

Optical coherent dot-product chip for sophisticated deep learning regression

Optical implementations of neural networks(ONNs)herald the next-generation high-speed and energy-efficient deep learning computing by harnessing the technical advantages of large bandwidth and high parallelism of optics.However,due to the problems of the incomplete numerical domain,limited hardware scale,or inadequate numerical accuracy,the majority of existing ONNs were studied for basic classification tasks.Given that regression is a fundamental form of deep learning and accounts for a large part of current artificial intelligence applications,it is necessary to master deep learning regression for further development and deployment of ONNs.Here,we demonstrate a silicon-based optical coherent dot-product chip(OCDC)capable of completing deep learning regression tasks.The OCDC adopts optical fields to carry out operations in the complete real-value domain instead of in only the positive domain.Via reusing,a single chip conducts matrix multiplications and convolutions in neural networks of any complexity.Also,hardware deviations are compensated via in-situ backpropagation control provided the simplicity of chip architecture.Therefore,the OCDC meets the requirements for sophisticated regression tasks and we successfully demonstrate a representative neural network,the AUTOMAP(a cutting-edge neural network model for image reconstruction).The quality of reconstructed images by the OCDC and a 32-bit digital computer is comparable.To the best of our knowledge,there is no precedent of performing such state-of-the-art regression tasks on ONN chips.It is anticipated that the OCDC can promote the novel accomplishment of ONNs in modern AI applications including autonomous driving,natural language processing,and scientific study.

Hybrid-integrated high-performance microwave photonic filter with switchable response

The integrated microwave photonic filter(MPF),as a compelling candidate for next-generation radio-frequency(RF)applications,has been widely investigated for decades.However,most integrated MPFs reported thus far have merely incorporated passive photonic components onto a chip-scale platform,while all necessary active devices are still bulk and discrete.Though few attempts to higher photonic integration of MPFs have been executed,the achieved filtering performances are fairly limited,which impedes the pathway to practical deployments.Here,we demonstrate,for the first time to our knowledge,an all-integrated MPF combined with high filtering performances,through hybrid integration of an In P chip-based laser and a monolithic silicon photonic circuit consisting of a dual-drive Mach–Zehnder modulator,a high-Q ring resonator,and a photodetector.This integrated MPF exhibits a high spectral resolution as narrow as 360 MHz,a wide-frequency tunable range covering the S-band to K-band(3 to 25 GHz),and a large rejection ratio of>40 d B.Moreover,the filtering response can be agilely switched between the bandpass and band-stop function with a transient respond time(48μs).Compared with previous MPFs in a similar integration level,the obtained spectral resolution in this work is dramatically improved by nearly one order of magnitude,while the valid frequency tunable range is broadened more than twice,which can satisfy the essential filtering requirements in actual RF systems.As a paradigm demonstration oriented to real-world scenarios,high-resolution RF filtering of realistic microwave signals aiming for interference rejection and channel selection is performed.Our work points out a feasible route to a miniaturized,high-performance,and cost-effective MPF leveraging hybrid integration approach,thus enabling a range of RF applications from wireless communication to radar toward the higher-frequency region,more compact size,and lower power consumption.

An ultra-compact polarization-insensitive slot-strip mode converter

Integrated waveguides with slot structures have attracted increasing attention due to their advantages of tight mode confinement and strong light-matter interaction.Although extensively studied,the issue of mode mismatch with other strip waveguide-based optical devices is a huge challenge that prevents integrated waveguides from being widely utilized in large-scale photonic-based circuits.In this paper,we demonstrate an ultra-compact low-loss slot-strip converter with polarization insensitivity based on the multimode interference(MMI)effect.Sleek sinusoidal profiles are adopted to allow for smooth connection between the slot and strip waveguide,resulting reflection reduction.By manipulating the MMI effect with structure optimization,the self-imaging positions of the TE0 and TM0 modes are aligned with minimized footprint,leading to low-loss transmission for both polarizations.The measurement results show that high coupling efficiencies of−0.40 and−0.64 dB are achieved for TE_(0) and TM_(0) polarizations,respectively.The device has dimensions as small as 1.1μm×1.2μm and composed of factory-available structures.The above characteristics of our proposed compact slot-strip converter makes it a promising device for future deployment in multi-functional integrated photonics systems.