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Valley photonic crystals (VPCs) provide an intriguing approach to suppress backscattering losses and enable robust transport of light against sharp bends, which could be utilized to realize low-loss and small-footprint devices for on-chip optical communications. However, there are few studies on how to achieve power-efficient tunable devices based on VPCs, which are essential for implementing basic functions such as optical switching and routing. Here, we propose and experimentally demonstrate a thermally tunable add-drop filter (ADF) based on VPCs operating at telecommunication wavelengths. By leveraging the topological protection of the edge state and the distinct property of negligible scattering at sharp bends, a small footprint of 17.4 × 28.2 μm2 and a low insertion loss of 2.7 dB can be achieved for the proposed device. A diamond-shaped microloop resonator is designed to confine the light and enhance its interaction with the thermal field generated by the microheater, leading to a relatively low power of 23.97 mW needed for switching the output signal from one port to the other. Based on the thermally tunable ADF under the protection of band topology, robust data transmission is implemented with an ultrahigh data rate of 132 Gb/s. Our work shows great potential for developing high-performance topological photonic devices with the thermally tunable silicon-based VPCs, which offers unprecedented opportunities for realizing topologically protected and reconfigurable high-speed datalinks on a chip.

We review the integration techniques for incorporating various materials into silicon-based devices. We discuss on-chip light sources with gain materials, linear electro-optic modulators using electro-optic materials, low-power piezoelectric tuning devices with piezoelectric materials, highly absorbing materials for on-chip photodetectors, and ultra-low-loss optical waveguides. Methodologies for integrating these materials with silicon are reviewed, alongside the technical challenges and evolving trends in silicon hybrid and heterogeneously integrated devices. In addition, potential research directions are proposed. With the advancement of integration processes for thin-film materials, significant breakthroughs are anticipated, leading to the realization of optoelectronic monolithic integration featuring on-chip lasers. [ABSTRACT FROM AUTHOR]

Integrated photonics is demanded in applications operating at ultraviolet to visible wavelengths, such as atomic/quantum systems, on‐chip broadband receivers, and far‐field structured illumination autofluorescence microscopy. A fundamental challenge in these applications is efficient edge coupling from a single‐mode fiber (SMF) to on‐chip photonic components, which is critical for on‐chip integration. In this paper, a high‐efficiency edge coupler based on an alumina‐on‐insulator platform is introduced and experimentally validated. The coupler employs a symmetric double‐tip taper and a multimode interference (MMI)‐based optical combiner. The double‐tip taper effectively expands the mode field diameter at the chip facet to match that of the SMF at the initial stage. Then the MMI‐based combiner efficiently combines the two channels in the taper into a highly confined strip waveguide. A coupling loss of 2.85 dB/facet has been achieved for the transverse magnetic mode at the wavelength of 407 nm, which is the lowest insertion loss for fiber‐chip coupling on this platform to the best of the knowledge. The design can significantly reduce the insertion loss associated with fiber‐chip coupling, offering a key component for diverse areas ranging from atomic/quantum photonic integrated circuits and ultra‐high capacity communications to optical microscopes. [ABSTRACT FROM AUTHOR]

AR enables the integration of virtual digital information on the real world. However, most AR displays suffer from accommodation vergence conflict, which results in 3D visual fatigue. In this work, our works on 3D visual fatigue‐free display techniques would be presented. [ABSTRACT FROM AUTHOR]

A novel non-volatile optical filter with a large bandwidth (BW) and extinction ratio (ER) tunability is first experimentally demonstrated by introducing an all-optical phase change of Ge2Sb2Te5 (GST). The Si-GST hybrid device promises flexible multi-level regulation of essential filter parameters in an ultra-compact footprint of 30 μ m × 13 μ m. Ultra-low power consumption is realised on account of the saving of external static power that is required in other electric-optic or optic-optic-driven filters. The GST is loaded onto two triple-waveguide directional couplers located at the coupling regions of an add-drop microring resonator. By initiating the GST phase transition with pump optical pulses, the transmitted optical power to the cross port of the triple-waveguide coupler is adjustable, hence influencing the coupling efficiency states of the microring filter. Consequently, a tunable on-off ER from 0.7 dB to 18.2 dB and a tunable BW from 0.6 nm to 3.3 nm are experimentally obtained with the aid of optically manipulating the crystallization degree of GST. Our device potentially enables the realisation of high-density photonic integrated circuits, especially in dense wavelength division multiplexing networks. [ABSTRACT FROM AUTHOR]

In this paper, we aimed to address the accommodation‐vergence conflict by developing a liquid crystal (LC) lens that provides faster and more responsive visual effects. Specifically, we used the azo‐dye SD1 based on photoalignment techniques and fabricated a fast‐response Pancharatnam‐Berry (PB) phase LC lens using a single‐exposure photoalignment method. The response time of the LC lens was approximately 1ms. [ABSTRACT FROM AUTHOR]

High‐speed electro‐optic modulators are key components in modern communication networks and various applications that require chip‐scale modulation with large bandwidth, high modulation efficiency, and compact footprint. However, fundamental trade‐offs make it challenging to achieve these metrics simultaneously, and thus new methodologies must be explored. To this end, a Mach–Zehnder modulator harnessing slow‐light waveguides and capacitively loaded slow‐wave electrodes are presented on silicon‐nitride‐loaded lithium niobate on an insulator platform. The increased group index and reduced microwave loss significantly improve the modulation efficiency. With the 1‐mm‐length modulation section, a low half‐wave voltage length product Vπ·L of 0.21 V cm is obtained, which is one order of magnitude smaller than that of conventional thin film lithium niobate Mach–Zehnder modulators, and a modulation bandwidth of surpassing 110 GHz is achieved. The digital signal processor‐free non‐return‐to‐zero signal and eight‐level pulse amplitude modulation signal of up to 180 and 300 Gbps, respectively, are generated by the modulator, which provides ultra‐large bandwidth, ultra‐high efficiency, and a compact solution for next‐generation electro‐optic systems. [ABSTRACT FROM AUTHOR]

Guided by brain‐like temporal processing and event‐driven manner, neuromorphic computing has emerged as a competitive paradigm to realize artificial intelligence with high energy efficiency. Silicon photonics offers an ideal hardware platform with mutual foundry fabrication process and well‐developed device libraries, however, its huge potential to build integrated neuromorphic systems is significantly hindered due to the lack of scalable on‐chip photonic spiking neurons. Here, the first integrated electrically‐driven spiking neuron based on a silicon microring under the carrier injection working mode is reported, which is capable of emulating fundamental neural dynamics including excitability threshold, temporal integration, refractory period, controllable spike inhibition, and precise time encoding at a speed of 250 MHz. By programming time‐multiplexed spike representations, photonic spiking convolution is experimentally realized for image edge feature detection. Besides, a spiking convolutional neural network is constructed by combining photonic convolutional layers with a software‐implemented fully‐connected layer, which yields a classification accuracy of 94.1% on the benchmark Modified National Institute of Standards and Technology database. Moreover, it is theoretically verified that it's promising to further improve the operation speed to a gigahertz level by developing an electro‐optical co‐simulation model. The proposed microring neuron constitutes the final building block of scalable spike activation, thus representing a great breakthrough to boost the development of on‐chip neuromorphic information processing. [ABSTRACT FROM AUTHOR]

On‐chip optical polarizer can extract the desired polarized light signal while filtering out the other polarized light signal, which plays a key role in integrated photonic circuits for purifying the desired polarized signal and reducing polarization crosstalk. However, most of the reported optical polarizers can only work for fundamental modes. With the rapid development of on‐chip multimode processing systems, arbitrary high‐order mode optical polarizers are more desirable. In this contribution, a TM‐pass optical multimode polarizer is proposed and demonstrated using subwavelength grating‐based anisotropic manipulation, which can achieve the polarizing of arbitrary TM high‐order mode theoretically, and the experimental results show the lowest polarization extinction ratio of the fabricated device can reach up to 21.2 dB under working for four‐mode (TM0, TM1, TM2, and TM3) system. The dynamic data transmission with the data rate of 64 Gbit s−1 has also been demonstrated to verify its potential for systematized applications in the future. [ABSTRACT FROM AUTHOR]

Integrated electro-optic (EO) modulators are the core components of the optoelectronic information technology, and lithium niobate is currently the most widely used crystalline thin film material; however, finite EO coefficients limit the modulation efficiency of the modulators. In this Letter, we present an integrated EO modulator using a microring resonator on the lead zirconate titanate (PZT) and silicon nitride (SiN) heterogeneous platform. The microwave attenuation is reduced by using low loss tangent and dielectric constant SiN as the electrode substrate, achieving an EO bandwidth of 33 GHz. Thanks to the high quality of the PZT film deposition and the substantial EO overlap of our structure, ultrahigh modulation efficiency with the half-wave voltage-length product of 0.7 V·cm is achieved. In addition, as a remarkable result, an 80-Gbps on-off keying signal is generated using the modulator.

In this paper, we introduce a physics-guided deep learning approach for high-quality, real-time Fourier-domain optical coherence tomography (FD-OCT) image reconstruction. Unlike traditional supervised deep learning methods, the proposed method employs unsupervised learning. It leverages the underlying OCT imaging physics to guide the neural networks, which could thus generate high-quality images and provide a physically sound solution to the original problem. Evaluations on synthetic and experimental datasets demonstrate the superior performance of our proposed physics-guided deep learning approach. The method achieves the highest image quality metrics compared to the inverse discrete Fourier transform (IDFT), the optimization-based methods, and several state-of-the-art methods based on deep learning. Our method enables real-time frame rates of 232 fps for synthetic images and 87 fps for experimental images, which represents significant improvements over existing techniques. Our physics-guided deep learning-based approach could offer a promising solution for FD-OCT image reconstruction, which potentially paves the way for leveraging the power of deep learning in real-world OCT imaging applications., Competing Interests: The authors declare no conflicts of interest., (© 2024 Optica Publishing Group.)

Emotion recognition in conversation (ERC) is a vital task that requires deciphering human emotions through analysis of contextual and multimodal information. However, extant research on ERC concentrates predominantly on investigating multimodal fusion while overlooking the model's constraints in dealing with unimodal representation discrepancy and speaker dependencies. To address the aforementioned problems, this paper proposes a Hierarchical decision fusion-based Local-Global Graph Neural Network for multimodal ERC (HiMul-LGG). HiMul-LGG employs a hierarchical decision fusion strategy to ensure feature alignment across modalities. Moreover, HiMul-LGG also adopts a local-global graph neural network architecture to reinforce inter-modality and intra-modality speaker dependency. Additionally, HiMul-LGG utilizes a cross-modal multi-head attention mechanism to promote interplay between modalities. We evaluate HiMul-LGG on two emotion recognition datasets, IEMOCAP and MELD, where HiMul-LGG outperforms existing methods. The results of the ablation study also imply the effectiveness of the proposed hierarchical decision fusion strategy and local-global structure of Graph construction., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

In this Letter, we report a second-order silicon photonic (SiP) coupled resonator optical waveguide (CROW) filter with an ultra-narrow 10-dB bandwidth of 1.75 GHz and a high extinction ratio (ER) of ∼50 dB. By utilizing this CROW filter, we demonstrated an innovative self-coherent detection, called carrier-extracted self-coherent (CESC) detection. By effectively suppressing signal components with the narrow-bandwidth CROW, full-field recovery can be achieved without expensive coherent lasers and sophisticated iteration algorithms. The performance of the CROW filter-based CESC system was further experimentally verified by retrieving 100 Gb/s QPSK signals.

In cost-sensitive application scenarios, increasing the data rate per channel under a limited receiver bandwidth is critical, and thus, the transceivers with low costs and high electrical spectral efficiencies (ESEs) are highly desirable. In this Letter, we demonstrate a modified silicon photonic (SiP) carrier-assisted differential detection (CADD) receiver with a record ESE for single polarization. The ESE of the conventional CADD is mainly limited by the transfer function that originated from the optical delay and hybrid. We modify the transfer function of the CADD by placing an additional delay in parallel to the original delay path. Consequently, the modified transfer function exhibits a sharper slope around the zero frequency, leading to a higher ESE. Here we employ complementary metal-oxide-semiconductor-compatible SiP integration to further reduce the cost and footprint of the modified CADD receiver. In the experiment, 280-Gb/s raw rate (net 226-Gb/s) 16-QAM OFDM signal after 80-km SMF transmission was detected using a 36.5-GHz SiP modified CADD receiver, with a bit error ratio below the 24% SD-FEC threshold. To our best knowledge, we achieve a record net 6.2-b/s/Hz ESE for an integrated single-polarization DD receiver with a 16-QAM format.