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The growing demand for enhanced data transmission and network scalability requires connecting multi‐mode fibers (MMFs) to single‐mode fibers (SMFs). However, conventional fiber‐optic connector systems face challenges such as one‐way transmission, alignment issues, and bulkiness. In this study, an all‐dielectric metasurface (MS)‐based fiber‐coupling system engineered to facilitate alignment‐tolerant bidirectional optical interconnect at a communication wavelength of 1550 nm is proposed and demonstrated. The system features meticulously aligned fiber meta‐tips incorporating an MS integrated onto SMF and MMF facets. The MS collimates the divergent beam emitted from the fiber facet and focuses the collimated beam propagating through free space, enabling bidirectional transmission of optical signals between the SMF and MMF. The achieved performance includes a coupling efficiency of −5.6 dB, optimal radial and axial tolerances of 40 and 600 µm, respectively, an extinction ratio of 13.8 dB, and a signal‐to‐noise ratio of 24.3 dB at 10.3 Gb s−1. The proposed fiber meta‐tips highlight the potential of lab‐on‐fiber technology for optical communication, trapping, and biological sensing. [ABSTRACT FROM AUTHOR]

Neural network (NN), also known as artificial neural network (ANN), provides efficient results in every computation, whether it is pattern recognition, forecasting, customer research, data validation, risk management, data mining, etc. In each computation, NN requires a specific dataset, and according to the datasets, a new NN structure is used to compute the results. Thus, these NN structures mostly depend upon the type of datasets. The current study presents a method that comprises a dedicated architecture known as neuromorphic neural network (NNN), which is made up of optical waveguides that enable high communication and data processing speed at the same time. We have also proposed three algorithms for configuring and building distinct ANN structures from the same architecture. These dedicated structures are not dependent on the datasets and employ the necessary processing element (PE) nodes to function as neurons in the hidden layer. Because specialized resources will be employed to perform operations in the hidden layer, these designs may produce more efficient outcomes than the present logical NN. Furthermore, we assessed our proposed architecture in terms of communication latency, deadlock prevention, energy consumption, and power usage. The simulation results show that deadlocks are avoided to the greatest extent possible, power consumption is reduced by up to 95%, and communicational latency is accomplished in the order of femtoseconds while conversing among PE nodes. The proposed architecture and simulation results promise an alternative for logical NN as well as improved results in terms of speed and efficiency. [ABSTRACT FROM AUTHOR]

Non-Abelian Thouless pumps are periodically driven systems designed by the non-Abelian holonomy principle, in which quantized transport of degenerate eigenstates emerges, exhibiting noncommutative features such that the outcome depends on the pumping sequence. The study of non-Abelian Thouless pump is currently restricted to 1D systems, while extending it to higher-dimensional systems will not only provide effective means to probe non-Abelian physics in high-dimensional topological systems, but also expand the dimension and type of associated non-Abelian geometric phase matrix for potential applications. Here, we propose the design and experimental realization of 2D non-Abelian Thouless pumps on a photonic chip with 2D photonic waveguide arrays, where degenerate photonic modes are topologically pumped simultaneously along two real-space directions. We reveal the associated non-Abelian group and experimentally demonstrate the non-Abelian feature by measuring the pumping sequence dependent output. The proposed 2D non-Abelian Thouless pump shows promising applications for robust optical interconnections and optical computing. The authors expand the dimension of non-Abelian Thouless pump from 1D to 2D and realize it using laser written photonic waveguide arrays, which serve as a promising platform for probing non-Abelian physics in high-dimensional topological systems. [ABSTRACT FROM AUTHOR]

Mode‐division multiplexing (MDM) introduces a new dimension to on‐chip optical interconnection, where the multimode optical switch is one of the core components. However, researchers are still struggling to reduce the chip size and response time, despite great efforts being made. Here, a compact, scalable, fast‐response multimode 2 × 2 switch supporting four modes is demonstrated based on the specific inverse design. The device consists of two multimode 2 × 2 CB couplers (including mode converters, multimode interference couplers, and crossings) and a thermo‐optic (TO) phase shifter. It achieves extinction ratios exceeding 15 dB for all modes at the central wavelength of 1.55 µm. All the fundamental components are designed by an improved general shape optimization method, realizing a compact size and a larger manufacturing tolerance (±20 nm). Besides, a hydrogen‐doped indium oxide microheater is introduced as a TO phase shifter to achieve a fast response (≈3.5 µs in average) for all modes. This solution provides an effective avenue toward large‐scale multimode optical switch matrices for the future MDM systems. [ABSTRACT FROM AUTHOR]

Vertical-cavity surface-emitting lasers (VCSELs) are essential for exhibiting single-transverse-mode output characteristics, which are critical for applications in quantum sensing, optical interconnection, and laser printing. In this study, we achieved stable single-transverse-mode lasing using extended-2λ-cavity with an oxide aperture diameter of 7.08 μm. The device demonstrated a high output power of 6.8 mW and a narrow linewidth of 49.8 MHz at room temperature. Additionally, it maintained stable single-mode emission at 794.8 nm and achieved a side-mode suppression ratio (SMSR) exceeding 40 dB within the temperature range of 25 °C~85 °C, thereby meeting the requirements of 87Rb atom quantum sensors. The fabricated device obtained high-power and narrow linewidth single-transverse-mode operation by a monolithic extended cavity without introducing additional processing procedures, which is expected to promote the commercial viability of VCSELs in quantum sensing. [ABSTRACT FROM AUTHOR]

Micro-scale light-emitting diodes (micro-LEDs) have received widespread attention in recent years for applications in display and optical communication. Compared with conventional quantum well active regions, quantum dots (QDs) can increase the carrier concentration at the same current density, which is beneficial for improving the efficiency and bandwidth of LEDs at low current densities. This is exactly what micro-LEDs need for display and communication applications. In this Perspective, we give a general introduction to InGaN QDs and provide an overview of the growth of InGaN QDs by metal-organic chemical vapor deposition. We then discuss the advances in green and red micro-LEDs based on InGaN QDs for display applications. This is followed by recent progress on high-speed blue micro-LEDs, which have great potential for use in chip-to-chip optical interconnections. Finally, we address the remaining challenges for a further improvement in InGaN QD-based micro-LEDs. [ABSTRACT FROM AUTHOR]

Vertical cavity surface-emitting laser (VCSEL)-based optical interconnects (OI) are crucial for high-speed data transmission in data centers, supercomputers, and vehicles, yet their performance is challenged by harsh and fluctuating thermal conditions. This paper addresses these challenges by integrating an ordinary differential equation (ODE) solver within the VCSEL communication chain, leveraging the adjoint method to enable effective gradient-based optimization of pre-equalizer weights. We propose a machine learning (ML) approach to optimize feed-forward equalizer (FFE) weights for VCSEL transceivers, which significantly enhances signal integrity by managing inter-symbol interference (ISI) and reducing the symbol error rate (SER). [ABSTRACT FROM AUTHOR]

A Si-based photodetector is the core device of Si-based optical interconnection; its material and performance are the key factors restricting its development. This paper conducts theoretical research on the issues of lattice mismatch between heterogeneous materials and low device responsivity in Si-based InGaAs photodetectors for the 1550 nm optical communication band. The material mismatch issue is addressed through the use of the high-aspect ratio trapping (ART) epitaxial technique, enabling the realization of high-performance Si-based III-V materials. By introducing a dielectric metasurface into the top layer of the structure, the light absorption efficiency is enhanced, realizing broadband optical absorption enhancement for Si-based photodetectors. This paper mainly focuses on designing the optimal parameters of the dielectric metasurface structure based on the finite-difference time-domain (FDTD) Solutions to achieve the performance analysis of a high-responsivity 1550 nm Si-based InGaAs photodetector. The results show that the quantum efficiency of the dielectric metasurface structure is theoretically estimated to be 88.8% and the response rate is 1.11 A/W, which is 2%~16% higher than that of the unetched structure in the whole band. The research results of this paper will provide new ideas for the development of novel, high-performance, and miniaturized Si-based photodetectors and lay a theoretical foundation for Si-based optical interconnection. [ABSTRACT FROM AUTHOR]

Advancements in computer science have propelled society into an era of data explosion, marked by a critical need for enhanced data transmission capacity, particularly in the realm of space-division multiplexing and demultiplexing devices for fiber communications. However, recently developed mode demultiplexers primarily focus on mode divisions within one dimension rather than multiple dimensions (i.e., intensity distributions and polarization states), which significantly limits their applicability in space-division multiplexing communications. In this context, we introduce a neural network-assisted meta-router to recognize intensity distributions and polarization states of optical fiber modes, achieved through a single layer of metasurface optimized via neural network techniques. Specifically, a four-mode meta-router is theoretically designed and experimentally characterized, which enables four modes, comprising two spatial modes with two polarization states, independently divided into distinct spatial regions, and successfully recognized by positions of corresponding spatial regions. Our framework provides a paradigm for fiber mode demultiplexing apparatus characterized by application compatibility, transmission capacity, and function scalability with ultra-simple design and ultra-compact device. Merging metasurfaces, neural network and mode routing, this proposed framework paves a practical pathway towards intelligent metasurface-aided optical interconnection, including applications such as fiber communication, object recognition and classification, as well as information display, processing, and encryption. [ABSTRACT FROM AUTHOR]

Multidimensional multiplexing technologies have been proven to be a promising scheme to meet the demands of high‐capacity optical interconnects and optical processing networks. However, challenges remain to realize multidimensional hybrid multiplexing data transmission and signal processing between few‐mode fiber transmission links and on‐chip optical processing networks, since the optical coupling between fiber and chip is almost exclusively in the single‐mode regime. Here, a multidimensional fiber‐to‐chip optical processing system is proposed and demonstrated for hybrid wavelength‐, mode‐, and polarization‐division multiplexing signals, where multidimensional coupling between few‐mode fiber transmission link and on‐chip multi‐mode processing network is realized by using a 3D photonic integrated (de)multiplexers on a glass chip as well as 2D photonic integrated (de)multiplexers on a silicon chip, and the on‐chip multidimensional optical processing network composed by parallel cascaded micro‐ring resonator array performs a function of reconfigurable optical add/drop multiplexer. By operating wavelength‐division multiplexing in conjunction with mode‐division multiplexing and polarization‐division multiplexing, the communication bandwidth of fiber‐to‐chip optical processing systems can be further scaled. [ABSTRACT FROM AUTHOR]

We demonstrate high-extraction-rate Ta2O5-core/SiO2-clad photonic waveguides on silicon fabricated by the photolithography-assisted chemo-mechanical etching technique. Low-confinement waveguides of larger than 70% coupling efficiency with optical fibers and medium propagation loss around 1 dB/cm are investigated in the experiment. Monolithic microring resonators based on Ta2O5 waveguides have shown the quality factors to be above 105 near 1550 nm. The demonstrated Ta2O5 waveguides and their fabrication method hold great promise in various cost-effective applications, such as optical interconnecting and switching. [ABSTRACT FROM AUTHOR]

Optoelectronic integrated circuit (OEIC) technology has attracted considerable research attention. Studies have achieved numerous breakthroughs in the basic scientific problems, key technologies, demonstration applications, and industrial promotions of OEIC. This study details the technical process, development status, existing problems, and future research trends of the design, manufacturing, and packaging of OEIC to provide a systematic summary of OEIC technology. [ABSTRACT FROM AUTHOR]

Silicon photonics with the advantages of low power consumption and low fabrication cost is a crucial technology for facilitating high-capacity optical communications and interconnects. The graphene photodetectors (GPDs) featuring broadband operation, high speed, and low integration cost can be good additions to the SiGe photodetectors, supporting high-speed photodetection in wavelength bands beyond 1.6 μm on silicon. Here we realize a silicon-integrated four-channel wavelength division multiplexing (WDM) optical receiver based on a micro-ring resonator (MRR) array and four p-n homojunction GPDs. These photo-thermoelectric (PTE) GPDs exhibit zero-bias responsivities of ∼1.1 V W−1 and set-up limited 3 dB-bandwidth >67 GHz. The GPDs show good consistence benefiting from the compact active region array (0.006 mm2) covered by a single mechanically exfoliated hBN/graphene/hBN stack. Moreover, the WDM graphene optical receiver realized 4 × 16 Gbps non-return-to-zero optical signal transmission. To the best of our knowledge, it is the first GPD-array-based optical receiver using high-quality mechanically exfoliated graphene and edge graphene-metal contacts with low resistances. Apparently, our design is also compatible with CVD-grown graphene. This work sheds light on the large-scale integration of GPDs with high consistency and uniformity, enabling the application of high-quality mechanically exfoliated graphene, and promoting the development of the graphene photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Next-generation energy-efficient photonic integrated systems, such as neuromorphic computational chips require efficient heterogeneous integration of ultracompact light sources and photodetectors through highly dense waveguide circuits. However, interconnecting these devices in emitter-receiver communication circuits remains a challenge and an obstacle towards upscaling heterogeneous photonic chips. Here we report on versatile air-cladded free-standing 3D polymer waveguides (OrmoCore, n≈1.5) spanning up to 900 µm in length without intermediate mechanical support structures, microprinted via two-photon polymerization. The presented waveguides are suitable for on-chip out-of-plane light coupling as well as non-connected 3D crossings, needed for high density optical circuits. The waveguides show optical transmission losses of 1.93 dB mm−1 at λ = 635 nm, and of 3.71 dB mm−1 at λ = 830 nm in the wavelength range of GaAs-based microLEDs spectral emission. On-chip imaging for high-precision alignment and TPP microfabrication are performed seamlessly by utilizing the same laser source for both steps, allowing accurate 3D printing on microstructured substrates. As proof of concept, we interconnect two GaAs-based microLEDs via an on-chip microprinted 3D waveguide. Such combined systems can serve as building blocks of future complex integrated heterogeneous photonic networks. [ABSTRACT FROM AUTHOR]

Modulating characteristics of transmissive and reflective Fabry–Perot type multi-nanolayer conductor–dielectric electro-optical modulators (EOMs) for chip-to-chip free space optical interconnection are analyzed via wavelength-scale electromagnetic modelling. For electromagnetic analysis the frequency-domain method of single expression is used. The considered EOM structures consist of an electro-optical spacer of LiNbO3 covered by two thin ITO conducting nano-layers, surrounded by Si/SiO2 distributed Bragg reflectors (DBRs). In the case of transmissive EOM the DBRs are symmetric regarding the spacer, while in the case of reflective EOM they are asymmetric to provide high reflectance for the structure. From four possible types of DBRs the suitable structure has been chosen with layers of higher permittivity adjoining to the ITO nano-layers. ITO nano-layers serving as electric contacts for supplying modulating electrical signal to the electro-optical spacer are parts of the multi-nanolayer structures and are included in the electromagnetic models. An incident radiation from an external laser diode at 1.55 μm wavelength is considered. The optimal configurations of the EOM structures providing a high peak in the transmittance for the transmissive EOM and a narrow dip in the reflectance for the reflective EOM are proposed. Efficiency of optical wave intensity modulation is analyzed by means of influence of electro-optical spacer's permittivity change on the transmittance and the reflectance of the EOM structures. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated a tunable and high transmission efficiency plasmonic power splitter and also a wavelength demultiplexer based on metal–insulator-metal surface. By using Finite Difference Time Domain method, the power splitter exhibits high transmission peaks of about 45% in each output port. Additionally, the simulation results demonstrate that the equal transmitted wavelengths of the two output ports can be easily tuned by changing the geometric parameters of the waveguide. Subsequently, the structure was amended to become a demultiplexer with selecting wavelengths of 1272 and 912 nm, and transmission efficiencies of 76.44 and 88.03%, respectively. Following that, the dependence of demultiplexing wavelengths on geometrical parameters of the structure is investigated. Besides being highly compact and efficient, having narrow-band spectra and low reflectance coefficient are the other main advantages of these devices. The compact power splitter presented in this study is one of the critical components of an integrated processor and hence can be of great interest in a wide range of applications, from highly integrated photonic circuits to on-chip optoelectronic modules and other optical devices such as erbium-doped fiber amplifiers. [ABSTRACT FROM AUTHOR]

This two-part work develops a comprehensive toolbox for the statistical characterization of nonlinear distortions of DAC-generated signal constellations to be transmitted over communication links, be they electronic (wireline, wireless) or photonic, Mach–Zehnder modulator (MZM)-based optical interconnects in particular. The all-analytic toolbox developed here delivers closed-form expressions for the second-order statistics (means, variances) of all relevant constellation metrics of the DACs' building blocks and of DAC-driven MZM-based optical transmitters, all the way to the slicer in the optical receivers over a linear channel with coherent detection. The key impairment targeted by the model is the random current mismatch of the ASIC devices implementing the DAC drivers. In particular the (skew-)centrosymmetry of the DAC metrics is formally derived and explored. A key applicative insight is that the conventional INL/DNL (Integral NonLinearity/Differential NonLinearity) constellation metrics, widely adopted in the electronic devices and circuits community, are not quite useful in the context of communication systems, since these metrics are ill-suited to predict communication link statistical performance. To rectify this deficiency of existing electronic DAC metrics, we introduce modified variants of the INL|DNL, namely the integral error vector (IEV) and the differential error vector (DEV) constellation metrics. The new IEV|DEV represent straightforward predictors of relevant communication-minded metrics: error vector magnitude (EVM) treated here in Part I, and Symbol/Bit Error-Rates (SER, BER) treated in the upcoming Part II of this paper. [ABSTRACT FROM AUTHOR]

Intensity-modulated direct-detection (IM/DD) optical systems are most widely employed in short-reach optical interconnects due to their simple structure and cost-effectiveness. However, IM/DD systems face mixed linear and nonlinear channel impairments, mainly induced by the combination of square-law detection and chromatic dispersion, as well as the utilization of low-cost non-ideal transceivers. To solve this issue, recent years have witnessed a growing trend of introducing machine learning technologies such as neural networks (NNs) into IM/DD systems for channel equalization. NNs usually present better system performance than traditional approaches, and various types of NNs have been investigated. Despite the excellent system performance, the associated high computational complexity is a major drawback that hinders the practical application of NN-based equalizers. This paper focuses on the performance and complexity trade-off of NNs employed in IM/DD systems, presenting a systematic review of the current status of NN-based equalizers as well as a number of effective complexity reduction approaches. The future trends of leveraging advanced NN in IM/DD links are also discussed. [ABSTRACT FROM AUTHOR]

With the advantages of high speed, small size, and easy integration, the silicon photonic resonant ring modulator has gradually become a critical device for emerging integrated optical platforms. Ring modulators are primarily used in optical communications, optical computing, artificial intelligence, and other fields. In this work, the proposed ring modulator can operate in both the O- and C-bands. The 3 dB electro-optical (EO) bandwidth of the ring modulator is 39 GHz and 34 GHz at −4 V in the O-band and C-band, respectively. The modulation efficiency of the device is 0.92 V·cm and 0.95 V·cm in the O-band and C-band, respectively. The eye diagram of an optical output signal from the device is tested using a 100 Gbit/s non-return-to-zero (NRZ) input signal with a 2.5 Vpp in both the O-band and C-band. The modulation speed can reach 140 Gb/s and 120 Gb/s in the O-band and C-band with four-level pulse amplitude modulation (PAM-4) formats at a voltage swing of 2.5 Vpp, respectively. [ABSTRACT FROM AUTHOR]

Silicon-based optical switches are integral to on-chip optical interconnects, and mode-division multiplexing (MDM) technology has enabled modes to function as carriers in routing, further boosting optical switches' link capacity. However, traditional multimode optical switches, which typically use Mach–Zehnder interferometer (MZI) structures and mode (de)multiplexers, are complex and occupy significant physical space. In this paper, we propose and experimentally demonstrate a novel demultiplexing-free dual-mode 3 × 3 thermal-optical switch based on micro-rings (MRs) and mode exchangers (MEs). All MRs are designed to handle TE1 mode, while the ME converts TE0 mode to TE1 mode, enabling separate routing of both modes. Bezier curves are employed to optimize not only the ME, but also the dual-mode 45° and 90° waveguide bends, which facilitate the flexible and compact layout design. Moreover, our structure can support multiple wavelength channels and spacings by adding pairs of MRs, exhibiting strong WDM compatibility. The switch has an ultra-compact footprint of 0.87 × 0.52 mm2. Under both "all-bar" and "all-cross" configurations, its insertion losses (ILs) remain below 8.7 dB at 1,551 nm, with optical signal-to-noise ratios (OSNRs) exceeding 13.0 dB. Also, 32 Gbps data transmission experiments validate the switch's high-speed transmission capability. [ABSTRACT FROM AUTHOR]

The hardware‐level construction of artificial synapses, mimicking the functionality of biological synapses, is widely acknowledged as a pivotal stride in artificial intelligence systems. Particularly, establishing all‐optical artificial synapses for neuromorphic computing, leveraging on‐chip optical interconnects instead of conventional wired connections, has garnered widespread attention. Here, high‐quality CsPbBr3 single crystals are synthesized, and intriguing relaxation processes associated with reversible photo‐induced phase transition (PIPT) are observed, leading to a corresponding change in the birefringence effect. The birefringence change is systematically analyzed by an optical system. The relaxation time of reversible PIPT is similar to the behavior patterns of biological synapses, enabling the device to mimic synaptic features. The device successfully mimics excitatory/inhibitory synaptic behaviors such as EPSP/IPSP, PPF, SDDP, SFDP, and SIDP by using 1310 nm signal. Furthermore, the device continues to exhibit excitatory/inhibitory synaptic functionality when 940 and 1550 nm signals are applied, achieving multi‐wavelength synaptic behaviors. The all‐optical devices have the advantages of low crosstalk, fast signaling, and wide optical bandwidth, which lays the foundation of all‐optical hardware for neuromorphic computing systems. [ABSTRACT FROM AUTHOR]

A novel bidirectional passive optical interconnection is proposed for data centers (DCs). The interconnection is based on a coupler of arrayed waveguide grating. The nodes distribute on both sides and simultaneously, bidirectional transmission is allowed. Compared with the traditional passive optical interconnected DCs, the scale is doubled, and the throughput is increased. The crosstalk in simultaneously bidirectional transmission is tested and the results show it is very little. The transmission between the nodes on the same side is relayed by one node on the other side. Some relay methods are proposed, and the relay efficiency is evaluated. [ABSTRACT FROM AUTHOR]

A Transimpedance amplifier (TIA)-based optical receiver in active voltage-current feedback topology is designed for optical interconnects at 0.18 μ m CMOS technology. The proposed inductorless TIA incorporates a gain boosting amplifier in its path to achieve high gain and bandwidth. This gain boosting amplifier is based on a regulated gain cascode (RGC) amplifier. The RGC stage raises the g m of the circuit, reducing the input resistance of the input stage; as a result, the bandwidth extends. To further amplify the gain, a common source (CS) stage is used at the output without much effect on the system's overall bandwidth. An analytical model of the proposed TIA is developed and later simulated at room temperature in the Cadence Virtuoso analog design environment. The pre-layout and post-layout simulation results of the proposed TIA have been shown to validate its performance. It achieves a transimpedance gain of 62 d B Ω while consuming power of 14.5 mW from a 1.8 V supply voltage. The bandwidth is extended to 8.2 GHz from 1.83 GHz with an input photodiode capacitance of 300 fF. The current spectral density of input-referred noise is 31 pA/ H z. [ABSTRACT FROM AUTHOR]

On-chip ultra-wideband optical waveguide amplifiers are crucial for short-distance optical interconnections that utilize wavelength division multiplexing (WDM) technology. Silicon optical amplifiers still face significant challenges due to the indirect-band-gap nature and low rare earth solubility of silicon. This paper prepared a series of Er3+-Tm3+ co-doped La 2 O 3 –Al 2 O 3 glasses that are expected to be used in on-chip ultra-broadband optical waveguide amplifiers by aerodynamic levitation (ADL) technique, and further studied their luminescence characteristics and energy transfer process. Research results indicate that the glass composition 5Er 2 O 3 -0.6Tm 2 O 3 -43.4La 2 O 3 –51Al 2 O 3 is an optimal optical waveguide amplifier host material due to its excellent luminescence properties and ultra-broadband flat photoluminescence spectrum extending up to 440 nm. Moreover, positive gain can be obtained with a population ratio greater than 0.2, which further illustrates its feasibility as a matrix material for ultra-broadband optical waveguide amplifiers. The advancement of this material is expected to significantly aid in the fabrication and progress of next-generation ultra-wideband optical waveguide amplifiers. [ABSTRACT FROM AUTHOR]

Recently, lumped Mach-Zehnder Modulators (MZMs) have received renewed attention due to their potential for low power consumption and compact size. However, the practicality of lumped MZMs with conventional lumped electrodes (C−LEs) is limited by their lower electro−optical (EO) bandwidth. The reduction in EO bandwidth results from the inherent trade−off between EO bandwidth and half−wave voltage length product ( V π L ) within the C−LE architecture. This paper proposes a thin−film lithium niobate (TFLN)−based lumped MZM with capacitively−loaded lumped electrodes (CL−LEs). The purely linear EO effect of the LN eliminates the parasitic capacitance in the doped PN junction and enhances the EO bandwidth. Furthermore, the CL−LE structure can break the limitation between EO bandwidth and V π L inherent in the C−LE design. Simulations show the proposed device achieves a high EO bandwidth of 32.4 GHz and a low V π L of 1.15 V·cm. Due to the reduced capacitance and lower V π L , the power consumption of the device is as low as 0.1 pJ/bit. Simulation results indicate that the open−eye diagrams are achieved at 64 Gb/s for 1.5 mm TFLN lumped MZM, with an ER of 2.97 dB. Consequently, the proposed device architecture substantially enhances the performance of lumped MZMs, showing promise for application in short−reach optical interconnects within data centers. [ABSTRACT FROM AUTHOR]

Processor fault diagnosis is intended to identify faulty processors of a multicomputer system, guaranteeing its high reliability and availability. The g -good-neighbor conditional diagnosability is a novel fault diagnosis method for various networks. Under the PMC model and comparison model, the g -good-neighbor conditional diagnosabilities of hypermesh optical interconnection networks are determined, respectively. Directly applying the results, the g -good-neighbor conditional diagnosabilities of hypercubes are derived under the PMC and comparison models. [ABSTRACT FROM AUTHOR]

Several types of silicon-nanowire-based optical demultiplexers (DeMUXs) for use in short-reach targeted datacenter applications were proposed and their spectral responses were experimentally verified. First, a novel 100-GHz-spaced 16λ polarization-diversified optical DeMUX consisting of 2λ delayed interferometer (DI) type interleaver and 8λ arrayed waveguide gratings will be discussed in the spectral regimes of C-band, together with experimental characterizations showing static and dynamic spectral properties. Second, a novel 800-GHz-spaced 8λ optical DeMUX was targeted for use in LR (long reach) 400 Gbps Ethernet applications. Based on multiple cascade-connected DIs, by integrating the extra band elimination cutting area, discontinuous filtering response was analytically identified with a flat-topped spectral window and a low spectral noise of <−20 dB within an entire LR-8 operating wavelength range. Finally, a 20-nm-spaced 4λ coarse wavelength division multiplexing (CWDM)-targeted optical DeMUX based on polarization diversity was experimentally verified. The measurement results showed a low excessive loss of 1.0 dB and a polarization-dependent loss of 1.0 dB, prominently reducing spectral noises from neighboring channels by less than −15 dB. Moreover, TM-mode elimination filters were theoretically analyzed and experimentally confirmed to minimize unwanted TM-mode-oriented polarization noises that were generated from the polarization-handling device. The TM-mode elimination filters functioned to reduce polarization noises to much lower than −20 dB across the entire CWDM operating window. [ABSTRACT FROM AUTHOR]

Efficient energy transfer is crucial in electromagnetic communication. Therefore, producing a waveguide coupler that achieves broadband, nonreflective transmission is a challenging task. With the advancement of silicon-based integrated photonic circuits, fiber-to-chip coupling has become increasingly important. Although various couplers have been developed for fiber-to-chip coupling, they often have limitations such as long coupling length, low coupling efficiency, and narrow bandwidth. This is due to the inability to eliminate reflections between the two waveguides. Here, we introduce a method using universal impedance matching theory and transformation optics to eliminate reflections between two waveguides. The coupler, called the universal impedance matching coupler, using this method has the shortest subwavelength coupling length, a 99.9 % coupling efficiency, and a broad bandwidth. [ABSTRACT FROM AUTHOR]

Grating couplers that interconnect photonic chips to off-chip components are crucial for various optoelectronics applications. Despite numerous efforts in past decades, the existing grating couplers are still far from optimal in energy efficiency and thus hinder photonic integration toward a larger scale. Here, we propose a strategy to achieve ultralow-loss grating couplers by using unidirectional guided resonances (UGRs), suppressing the useless downward radiation with no mirror on the bottom. By engineering the dispersion and apodizing the geometry of grating, we experimentally realize a grating coupler with a record-low loss of -0.34 dB and 1-dB bandwidth exceeding 30 nm at the telecom wavelength of 1550 nm and further demonstrate an optic via with a loss of only -0.94 dB. Given that UGRs ubiquitously exist in a variety of grating geometries, our work sheds light on a systematic method to achieve energy-efficient optical interconnect and paves the way to large-scale photonic integration. [ABSTRACT FROM AUTHOR]

The electro‐optic (EO) modulator is a crucial device for achieving high‐speed optical communication and optical interconnection by loading the high‐frequency electrical signals onto the optical carrier. To date, modern communication technique demands for a low energy consumption for green data center establishment. In this work, a thin‐film BaTiO3 crystal waveguide Mach–Zehnder interferometer (MZI) type EO intensity modulator is experimentally implemented and its dynamic‐polarization interference process involving a phase‐polarization modulation (PPM) scheme other than conventional optical phase modulation (OPM) is carefully analyzed. Its findings show that the PPM scheme can efficiently reduce the half‐wave voltage (Vπ${V}_\pi$) and the equivalent half‐wave voltage (Veπ${V}_{e\pi }$) of the modulator. Then, a new theory of deriving the bit energy (BE) from Veπ${V}_{e\pi }$ is put forward, which has proven that the BE value under PPM is lower than the OPM counterpart. The EO modulator prototype featuring a length of 1.4 mm, Veπ${V}_{e\pi }$= 3.0 V and BE = 1.2 pJ/bit match well with the numerical calculations, thus validating the feasibility to achieve a BE<0.2 pJ/bit for an EO modulator through optimization of the electrode gap and state‐of‐the‐art fabrication techniques in the near future. [ABSTRACT FROM AUTHOR]

Optical interconnects are being discussed as a replacement for conventional electrical interconnects and are expected to be applied for future generations of high-performance supercomputers and data centers. Benes networks have attracted much attention because they require only 2 × 2 optical switches, which reduce the cost of rearrangeable nonblocking. However, optical power imbalances can significantly challenge receiver sensitivity. In this work, insertion loss (IL) fairness has been proposed and applied to the field of switches to achieve a relative balance of optical path data transmission in Benes networks. Fairness can be achieved when the port count is small (4 × 4) if the IL between ports is balanced. When the number of ports is moderate (8 × 8), we must use a suitable algorithm or determine the appropriate operating wavelength to minimize the power imbalance. An efficient two-step algorithm (ETS) has particular advantages in solving the path fairness problem and mitigating the power imbalance. As the number of ports increases, the switch states and topology jointly deteriorate the power imbalance. Finally, the ETS algorithm narrows the dynamic range requirement to 13.66 dB, with a 2 dB improvement. It achieves an extinction ratio of 24 dB and a bandwidth of 375 GHz, which outperforms the conventional 32 × 32 Benes network, respectively. [ABSTRACT FROM AUTHOR]

This paper demonstrates with FDTD simulations a silicon nitride polarization independent coarse wavelength division multiplexing (CWDM) receiver platform based on square waveguides for optical interconnects at 1 $\mu$m. Here, the channel spacing of the demultiplexers is much smaller than standard CWDM systems (25 nm) and is set to 8 nm. To avoid high waveguide propagation and radiation losses, several waveguide dimensions were considered. The 450 nm (width) × 450 nm (height) waveguide presented a good tradeoff between low loss and single-mode behavior and was therefore selected. The demultiplexer has a simulated polarization dependence on the waveguide’s width variations of 0.17 nm/nm. In addition, we present edge coupler designs with coupling loss within 2.5 dB for TE and TM polarization.

This article demonstrates with simulations two polarization independent wavelength division multiplexing receiver platforms based on thin silicon nitride waveguides for optical interconnects at 1 $\mu$m. The chosen waveguide base geometry (width = 900 nm × height = 160 nm) is a good tradeoff between mode confinement and propagation loss. We first propose a design using a polarization splitter with an 1×4 demultiplexer based on an arrayed waveguide grating (AWG). This receiver has a reduced size and requires only one etching step. We later propose another simplified receiver design using a polarization splitter-rotator with two identical 1×4 demultiplexers based on cascaded Mach-Zehnder interferometers. The rotator is based on a thicker waveguide (width = 500 nm × height = 400 nm) and is partially etched to rotate the electric field by 90$^{\circ }$. Thus, it requires the use of mode size converters at the in/output ports. To keep the fabrication complexity as low as possible for the second design, we limited ourselves to only two etching steps. Therefore, the thickness of the slab of the mode converters and of the rotator is the same as for the main 900 nm (wide) × 160 nm (thick) waveguide. The simulated extinction ratio of the polarization splitter at 1035 nm is 18 dB and the calculated TM-TE and TE-TM polarization conversion efficiency of the polarization rotator at 1035 nm is 99.9$\%$.

The exponential growth of global data traffic is driven by the unprecedented digitalization of the world. To meet the demands of next‐generation high‐capacity data communication systems, innovative solutions are required. Silicon photonics has gained significant attention due to its ability to integrate multiple core functions of optical interconnects into small‐scale chips, offering cost‐effective and scalable manufacturing capabilities. By leveraging silicon photonics, it becomes possible to address the challenge of scaling system complexity while reducing size, cost, and energy consumption. Despite its advantages, silicon has inherent limitations that restrict its application range, such as the weak plasma dispersion effect and relatively large bandgap. Recently, graphene has emerged as a promising solution for traditional silicon photonics because of its exceptional electrical and optical properties. For instance, graphene on a silicon chip enables nearly pure phase modulation and ultrafast photodetection beyond 500 GHz. Moreover, the demonstrated compatibility of graphene with wafer‐level integration paves the way for mass production of graphene‐based silicon photonic devices, offering improved yield, scalability, and cost‐effectiveness. In this work, a comprehensive review is provided, focusing on graphene‐based silicon photonic devices and their applications in optical interconnects, aiming to explore the potential of graphene in advancing silicon photonic technology. [ABSTRACT FROM AUTHOR]

We report a continuous-wave, O-band quantum-dot semiconductor comb laser for WDM optical interconnects exhibiting a 2.2 THz optical bandwidth with up to 89 comb wavelengths spaced at 25 GHz, over 30% peak ex-facet electrical-to-optical power conversion efficiency, up to 270 mW of usable laser power, relative intensity noise below − 135 dB/Hz per individual mode, individual laser mode linewidth of 140 kHz, mode beating linewidths of 50 kHz across all modes, and stable far-field output with 75% coupling efficiency to PM fiber in a butterfly package. [ABSTRACT FROM AUTHOR]

Intensity modulation/direct detection (IM/DD) optical interconnect systems are susceptible to waveform distortion caused by complex nonlinearities. To reduce the effect of waveform distortion on signal transmission accuracy, in this paper, a random forest (RF) equalization algorithm based on decision tree (DT) integration is proposed for cost-sensitive IM/DD systems, which has the characteristics of nonlinear classification and regression. The performance of the RF equalizer is verified by simulation experiments on a 120 Gbps 8-level pulse amplitude modulation (PAM8) transmission system using an electro-absorption-modulated laser (EML). Simulation studies show that whether it is a back-to-back (B2B) transmission system or a 10 km optical fiber transmission system, the RF equalization scheme can achieve much better bit error rate (BER) performance than the traditional equalization scheme. In addition, in both transmission cases, the RF equalization scheme enables efficient classification of signals and is much less simpler than the artificial neural network (ANN) equalization scheme. [ABSTRACT FROM AUTHOR]

Silicon microring modulator plays a critical role in energy-efficient optical interconnect and optical computing owing to its ultra-compact footprint and capability for on-chip wavelength-division multiplexing. However, existing silicon microring modulators usually require more than 2 V of driving voltage (Vpp), which is limited by both material properties and device structures. Here, we present a metal-oxide-semiconductor capacitor microring modulator through heterogeneous integration between silicon photonics and titanium-doped indium oxide, which is a high-mobility transparent conductive oxide (TCO) with a strong plasma dispersion effect. The device is co-fabricated by Intel's photonics fab and our in-house TCO patterning processes, which exhibits a high modulation efficiency of 117 pm/V and consequently can be driven by a very low Vpp of 0.8 V. At a 11 GHz modulation bandwidth where the modulator is limited by the RC bandwidth, we obtained 25 Gb/s clear eye diagrams with energy efficiency of 53 fJ/bit. Silicon microring resonator plays crucial role in optical computing owing to the compact footprint and energy-efficiency, yet existing modulators require >2 V to drive it. Here, the authors present a solution to this by using metal-oxide-semiconductor capacitor microring that brings down the driving voltage to 0.8 V. [ABSTRACT FROM AUTHOR]

Optical communication has become a research hotspot in modern non‐contact communication systems, and high‐performance photodetectors, as a key component, are crucial for achieving high‐fidelity signal transmission. Photoconductive devices (PCDs) are expected to find applications in the field of optical communication due to their advantages in high gain. However, it is difficult to achieve an effective balance between high responsiveness and fast response times in PCDs, leading to significant challenges in their commercial applications in the field of optical communication. In this paper, by employing both the mask method and channel width tuning method, a high‐performance PCD is developed based on the Ag‐MAPbI3‐Ag structure, demonstrating a high responsivity of 45.5 A W−1, a high detectivity of 7 × 1012 Jones, and a fast response time of 0.35 ms. Finally, this device is integrated into an optical communication system using embedded technology, effectively achieves byte transmission, and demonstrates the practical application of single‐crystal MAPbI3 PCD as a signal receiver in the system. This research provides a noteworthy approach to facilitating the seamless integration and commercialization of optical communication systems utilizing perovskite single‐crystal devices, while also paving the way for optical interconnects based on perovskite. [ABSTRACT FROM AUTHOR]

We present a high-efficiency silicon grating coupler design based on a left–right mirror-symmetric grating and a metal mirror. The coupler achieves nearly perfect 90-degree vertical coupling. When two SOI chips are placed face to face with a vertical working distance of 50 μm, the chip-to-chip interlayer coupling efficiency reaches as high as 96%. When the vertical working distance ranges from 45 μm to 55 μm, the coupling loss remains below 1 dB. We also verified the effectiveness of our designed vertical coupler through 3D FDTD full-model simulation. The results demonstrate that our proposed vertical coupling structure represents a high-efficiency solution for 3D optical interconnects. The integration of multiple photonic chips in a 3D package with vertical optical and electrical interconnects is also feasible in the foreseeable future. [ABSTRACT FROM AUTHOR]

We optimized and fabricated an ultra-bend-resistant 4-core simplex cable (SXC) employing 4-core multicore fiber (MCF) suitable for short-reach dense spatial division multiplexing (DSDM) optical transmission in the O-band. The characteristics of transmission loss, macro-bending and cross-talk (XT) between adjacent cores after cabling were firstly clarified. By introducing the trapezoid index and optimizing the cabling process, the maximum values of added XT of 1.17 dB/km due to 10 loops with a bending radius of 6 mm imposed over the 4-core SXC and a macro-bending loss of 0.37 dB/10 turns were, respectively, achieved.P Then, the optical transmission with low bit error rate (BER) was presented using a 100GBASE-LR4 transceiver over the 1.2 km long 4-core SXC. The excellent bending resistance of the 4-core SXC may pave the way for a reduction in space pressure and increase in access density on short-reach optical interconnect (OI) based on DSDM. [ABSTRACT FROM AUTHOR]

Photonic integrated circuits (PICs) are coupled with the laser to create active devices for optical communication, optical interconnection, and optical computing. Consequently, the light source remains a focal point of extensive research and development. Currently, the utilization of carbon quantum dots as a gain medium in photonic cavity lasers is accomplished and suggested as a viable approach for achieving active PICs. Nevertheless, challenges persist in achieving narrowband lasing beam output in one direction that is real‐time tunable while minimizing energy losses. These issues represent an active area of ongoing research. This article presents a self‐assembled microstructure and proposes a method for obtaining tunable, narrowband, unidirectional lasing beams. The objective is to stimulate further development in integration of PICs with lasers, extending beyond these applications, to realize substantial performance gains, eco‐friendly solutions, and efficient mass production. [ABSTRACT FROM AUTHOR]

In recent datacenters, considerable data communication has been performed between servers and storages; therefore, an optical interconnection with a wider band is required. Silicon photonics has attracted attention as a technology that places optical engines closer to switch application‐specific integrated circuits and realizes broadband optical interconnection. To utilize silicon photonics, it is necessary to overcome high‐precision alignment between silicon waveguides and single‐mode fibers (SMFs) having vastly different mode field diameters. Optical self‐coupling using light‐induced self‐written (LISW) optical waveguide technology is a potential solution. Previously, near‐infrared (NIR) LISW optical waveguides are fabricated using an SMF with an approximate 10 μm core through irradiation with 10 μW NIR light (1310 and 1550 nm). However, the cladding is liquid, which motivates to fabricate all‐solid LISW optical waveguides. In this study, all‐solid NIR LISW optical waveguides are produced using a core‐selective polymerization method, and single‐mode LISW optical self‐coupling between two SMFs is realized. To enhance the performance of the waveguides, additional resins are incorporated into the high‐refractive‐index base monomer during the cladding formation process. Through the experimentation, the potential for achieving even greater loss reduction by optimizing the hybridization between the base monomer and the supplementary resins is demonstrated. [ABSTRACT FROM AUTHOR]

Incoherent addition of three monochromatic laser sources is used to create four distinctive power levels to match the profile of standard quaternary pulse amplitude modulation (PAM4). The proposed PAM4 signal generation results in a lower symbol error rate as compared to standard PAM4 systems. This design improves the signal-to-noise ratio as compared to existing PAM4 schemes and can reduce the cost and power consumption of existing 200 G or higher optical transceivers. [ABSTRACT FROM AUTHOR]

Efficient mode conversion is crucial for hybrid photonic systems. We present efficient light transition from a standard single-mode fiber (SMF) to a subwavelength-diameter microfiber via a relatively short tapered fiber. Numerical simulations were performed to design the tapered morphology with high transmittance (approximately 86%) for the fundamental modes. The designed tapered fiber was successfully fabricated on the top of a cleaved SMF tip by the direct laser writing (DLW) method. For the 1550 nm wavelength, the transmittance from the standard SMF to the subwavelength-diameter microfiber was determined to be 77%, accompanied by a change in the effective mode area from 38 μm2 to 0.47 μm2 within a very short length of 150 μm. Our result demonstrated the versatility of the DLW technique for boosting the mode conversion efficiency of fiber-to-chip devices, enabling various applications in the future. [ABSTRACT FROM AUTHOR]

The growth of artificial intelligence applications demands ever larger and more complex deep learning models, dominating today's—and tomorrow's—data center and high-performance computing systems. While traditional electronics are failing to keep pace with application demands, silicon photonic (SiPh) interconnects have emerged as a necessary technology to support these systems. SiPh-driven wavelength-division multiplexing (WDM) offers a particularly promising path toward supporting incredibly high-aggregate link bandwidth in a compact and efficient form factor. One of the basic building blocks of these integrated WDM interconnects is the SiPh resonator. Their inherent wavelength selectivity and compact footprint allow for efficient data transmission multiplexed across dozens of carrier wavelengths. Used as add-drop (AD) filters, SiPh resonators are critical to constructing integrated tunable wavelength-selective optical circuit switches as well as for demultiplexing the different carrier wavelengths toward independent wavelength-insensitive photodiodes in a dense wavelength-division multiplexing receiver. Resonators in the all-pass (AP) configuration are widespread as well, allowing for wavelength-selective modulation to drive aggregate link bandwidths far beyond the individual channel data rate. Unlike SiPh Mach–Zehnder modulators (MZM), resonant modulators can be driven using low, complementary metal-oxide-semiconductor drive voltages, allowing for tight co-integration between photonic integrated circuits, fabricated with larger process node technologies, and electronic integrated circuits, designed to exploit the advantages of the latest node. To push toward practical peta-scale interconnects, a comprehensive review of SiPh resonators is required, addressing bottlenecks and design constraints at both the architecture and device levels. We first describe the predominant integrated link architectures and identify their limits. We then discuss the device-level design considerations that can be made for both AD and AP configuration resonators to overcome the system level limits with novel resonator device designs. Analytical models and numerical simulation of resonators are validated by experimental measurement of devices fabricated in a commercial 300-mm foundry, showing a clear path toward volume manufacturing. The demonstrated resonant modulators and filters support the feasibility of increasing the aggregate bandwidth of resonator-driven SiPh interconnects into the peta-scale regime. [ABSTRACT FROM AUTHOR]

Machine learning using the ANN approach is presented in this paper to design 101 channels of optical DEMUX in the range of 1300–1400 nm. This work is used to envisage the optical parameters of silicon grating structure such as the thickness of SiO and Si which are the decisive factors to allow the desired signal through the structure to realize optical DEMUX. This is accomplished by training an ANN model with a few pre-defined optical DEMUX parameters which are obtained beforehand by the plane wave expansion method. Here, the ANN model is implemented in the Tensor Flow framework of Google Colaboratory Network (Colab) which consists of five hidden layers of ReLU activation besides the input and output linear activation nodes. Besides this, the optical parameters collected from the ANN model are used to simulate through the PWE method for validation by observing the reflectance characteristics curve and found that most of the values are satisfied to realize the optical VLSI DEMUX. The outcomes of the present work could be beneficial in the field of optical VLSI systems pertaining to the optical interconnect. [ABSTRACT FROM AUTHOR]

Mode-division multiplexing (MDM) is a promising multiplexing technique to further improve the transmission capacity of optical communication and on-chip optical interconnection systems. Furthermore, the multimode optical switch is of great importance in the MDM system, since it makes the MDM system more flexible by directly switching multiple spatial signals simultaneously. In this paper, we proposed a mode-independent optical switch based on the graphene–polymer hybrid waveguide platform that could process the TE11, TE12, TE21 and TE22 modes in a few-mode waveguide. The presented switch is independent of the four guided modes, optimizing the buried position of graphene capacitors in the polymer waveguide to regulate the coplanar interaction between the graphene capacitors and spatial modes. The TE11, TE12, TE21 and TE22 modes can be regulated simultaneously by changing the chemical potential of graphene capacitors in a straight waveguide. Our presented switch can enable the independent management of the spatial modes to be more flexible and efficient and has wide application in the MDM transmission systems. [ABSTRACT FROM AUTHOR]

Mode division multiplexing (MDM) technology is an effective solution for high-capacity optical interconnection, and multimode power splitters, as essential components in MDM systems, have attracted widespread attention. However, supporting a wide range of modes and arbitrary power splitting ratios with large bandwidth in power splitters remains a significant challenge. In this paper, we designed a power splitter based on a subwavelength grating (SWG) structure with tilted placement on a silicon-on-insulator (SOI) substrate. We achieve arbitrary TE0–TE9 mode-insensitive power distribution by altering the filling coefficient of the SWG. Thanks to our specific selection of cladding materials and compensatory design for the optical wave transmission and reflection shifts induced by SWG, our device demonstrates low additional loss (EL < 1.1 dB) and inter-mode crosstalk (−18.8 < CT < −60 dB) for optical modes ranging from TE0 to TE9, covering a wavelength range from 1200 nm to 1700 nm. Furthermore, our proposed device can be easily extended to higher-order modes with little loss of device performance, offering significant potential in MDM platforms. [ABSTRACT FROM AUTHOR]