Ferroelectric materials are widely used in diverse applications, where their performance is strongly dominated by grain size. Here, dense Er-doped lead titanate-based relaxor ferroelectrics were synthesized via spark plasma sintering, enabling precise grain size control from 0.9 to 11.1 μm. Fine-grained ceramics exhibit high defect concentrations and internal stress, stabilizing the tetragonal phase and resulting in weak, disordered polarization with low domain wall density and constrained mobility. At intermediate grain sizes, dense nanodomain networks with narrow walls (∼150 nm) form, allowing sharp and reversible polarization switching. Coarse-grained ceramics develop hierarchical, web-like domains with thicker walls (∼400 nm), reducing the pinning effect and enhancing wall mobility. Both saturation and remanent polarizations increase with grain size up to 5.4 μm before plateauing, while the piezoelectric coefficient rises by 200%, reaching 723 pC N-1. These results demonstrate grain-size engineering as an effective route to optimize domain wall structure and relaxor ferroelectric performance.

While various materials have been explored for the transducer of flexible ultrasound sensors, there remains a significant need for transducer materials that simultaneously achieve both high electromechanical coupling efficiency and mechanical robustness for skin-conformal ultrasound applications. In this study, we present a flexible ultrasound sensor based on novel erbium-doped Pb(Mg0.33Nb0.67)(x)Ti(1-x)O3 (PMNPT) piezo ceramics (x=0.30) , which exhibit an electromechanical coupling coefficient (k(t)) of 58.4%. Simple and cost-effective methods were explored to fabricate soft electronic circuits and to assemble the flexible ultrasound sensor. Acoustic testing further confirms a 6-dB one-way bandwidth of 27.8% at a center frequency of 6.04 MHz, ensuring high resolution. As a proof-of-concept, we demonstrate its capability to capture blood pressure (BP) waveforms directly from the brachial artery, correlating arterial diameter dynamics with localized blood-pressure variations. Additionally, the patch was used to accurately measure different blood-mimicking flow rates (BFRs) in a vessel-mimicking phantom. The novel Er-doped PMNPT ceramics specifically improve the electromechanical coupling coefficient and ultrasound signal bandwidth, which are critical for enhancing the performance of flexible systems intended for high-resolution vascular monitoring.

The nonlinear Fourier transform (NFT) can be utilized to characterize pulses in fiber lasers. For chirp-free sech pulse, NFT works great. However, the presence of chirp significantly affects the reliability of NFT characterization. By modifying the NFT methodology, we demonstrate its applicability for characterizing chirped pulses in dispersion-managed fiber lasers. Numerical simulations reveal that the modified NFT approach effectively captures the pulse dynamics within dispersion-managed cavities. The discrete spectral energy of the recovered solitons can be used to evaluate the credibility of the modified NFT.

A receiver with photonics-enabled simultaneous self-interference cancellation and image rejection for in-band full-duplex communication is proposed and experimentally demonstrated. The carrier suppressed double sideband (CS-DSB) modulation is applied for the conversion of received signals, the reference signal and the local oscillator (LO) signal in optical domain via the dual-polarized quadrature phase shift keying (DP-QPSK) modulator. The sidebands of CS-DSB signals are filtered for photon detection to generate the intermediate frequency (IF) signals. The direct current (DC) biases of the DP-QPSK modulator are utilized to introduce a phase difference of -45 degrees between received signals and the LO signal in the X-polarization to realize the quadrature down-conversion, and a phase difference of 135 degrees between the reference signal and LO signal in Y-polarization to obtain phase inversion for the self-interference cancellation. By regulating the amplitude, phase and time delay of the two polarization CS-DSB signals in optical domain, the image rejection and self-interference cancellation are simultaneously realized in IF band, which has the advantage of dispersion immunity for long fiber transmission. Experimentally, the image and self-interference (SI) are suppressed simultaneously with self-interference cancellation depth of 39, 26, 22 dB and image rejection ratio of 35, 27, 24 dB, corresponding to the bandwidth of 100 MHz, 500 MHz and 1 GHz, respectively. The signal of interest (SOI) with 16-QAM modulation is successfully recovered after 20 km fiber transmission with the SI-to-SOI power ratio of 16.5 dB.

Applying mechanical strain and strain engineering to halide perovskites has endowed them with intriguing properties. However, an in-depth understanding of mechanical strain, including residual strain in halide perovskites, remains incomplete, coupled with the critical challenge of decoupling strain effects from other interferences. Here, we examine the relaxation of residual tensile strain in three-dimensional (3D) halide perovskites through 2D/3D perovskite heterojunction formation. The 2D perovskite induces structural fragmentation in 3D perovskites, facilitating plastic relaxation of tensile strain. By isolating extrinsic crystalline phase interference and exciton-related optical disturbances, we observe that 3D perovskites retain high crystallinity only with moderate tensile strain relaxation. This moderate relaxation enhances optoelectronic properties in 3D perovskites, including broadened band-to-band absorption and prolonged charge carrier lifetime, markedly contributing to an increase in the maximum attainable power conversion efficiency in photovoltaic devices. Our findings outline conditions for strain relaxation that optimize optoelectronic properties, advancing strain engineering in halide perovskites.

Multimodal deformation sensing is a key technology in healthcare monitoring, wearable devices, and robotics. However, significant challenges remain in developing devices capable of simultaneously sensing multiple types of stimuli, as such systems typically require complex structural designs or multiple sensing units, which limit their flexibility and scalability. Here, we propose a structurally simple and mechanically flexible sensor made of soft material, where complex deformations can be inferred by learning the output specklegrams. The simplified one sensing mechanism for multimodal deformation stems from the inherent speckle sensitivity of the soft optical waveguide with a decoding strategy based on deep learning. The proposed soft optical waveguide sensor is low-cost, flexible and can be fabricated by rapid 3D printing. By employing a deep convolutional neural network, the proposed deformation sensor accurately differentiates bending, stretching, twisting, and combined deformations, maintaining a high accuracy close to 100% over three days. Our multimodal deformation sensor promises advancements in multi-functional sensing systems for future applications.

Abstract The reverse piezoelectric effect allows for the conversion of an electrical input signal into mechanical displacement and forms the basis for the operation of positioners and actuators. Addressing the practical need for cost-effective sensitive materials, we introduce erbium-doped lead magnesium niobium titanate ceramics which exhibit exceptionally high strain (3.19% bipolar and 0.8% unipolar) under a very low applied field of 2 kV mm−1, resulting in record-breaking piezoelectric coefficients (d 33* values of 15,950 and 4014 pm V−1, respectively). These exceptional properties stem from a combination of factors including the sensitivity of polar nanoregions to the applied field in this relaxor ferroelectric system, the thickness of the sample, and the energetic availability of polymorphs with different polar structures where a change in polarisation direction occurs at the field induced phase transition. Surpassing the performance of single crystal materials, our findings establish a benchmark in piezoelectric performance with implications for many diverse applications.

The past decade has seen a rapid development in metal halide perovskite nanocrystals (NCs), which has been witnessed by their potential applications in nanotechnology. The inimitable chemical nature behind their unique photoluminescence characteristics has attracted a growing body of researchers. However, the low intrinsic stability and surface defects of perovskite NCs have hampered their widespread applications. Therefore, numerous techniques such as doping and encapsulation (polymer matrices, silica coating, salt matrix, etc.) have been examined for the surface modification of perovskite NCs and to increase their efficiency and stability. In this study, we demonstrated the self-passivation method for surface defects by introducing potassium (K) or rubidium (Rb) during the colloidal fabrication of NCs, resulting in the much-improved crystallinity, photoluminescence, and improved radiative efficiency. In addition, K-doped NCs showed a long-term colloidal stability of more than 1 month, which indicates the strong bonding between the NCs and the smaller-sized potassium cations (K+). We observed the enhancement of the radiative lifetime that can also be explained by the prevention of "Frenkel defects" when K+ stays at the interstitial site of the nanocrystal structure. Furthermore, our current findings signify the importance of surface modification techniques using alkali metal ions to reduce the surface traps of perovskite nanocrystals (PeNCs). Comparable developments could be applied to polycrystalline perovskite thin films to reduce the interface trap densities. The findings of this study have several important implications for future light-emitting applications.

Metal halide perovskites have demonstrated exceptional multifunctionality, finding applications in photovoltaics, light-emitting devices and sensors, which has stimulated intense research interest. Recently, their integration into biomimetic devices has emerged as a promising frontier, exploiting the unique optoelectronic properties of perovskites to mimic biological functions. This review provides a comprehensive analysis of recent advances in the use of metal halide perovskites for biomimetic applications, focusing on their role in different device configurations and fabrication techniques. We elucidate the mechanisms that drive their performance and demonstrate their potential as versatile materials for high performance biomimetic devices. By exploring the intricate interplay between material properties and device functionality, we highlight the transformative potential of metal halide perovskites in creating more efficient, adaptable and biologically inspired technologies. Finally, we discuss future research directions to maximise their application scope, with the aim of bridging materials science and bioengineering for innovative device development.

In this paper, we present a soft optical waveguide sensor designed for characterizing both 2D and 3D shape deformations using deep learning. Our soft optical sensor achieves an accuracy close to 100% for deformation classifications. (c) 2024 The Author(s)

In the domains of biomedical applications, wearable devices, and soft robotics, recent advancements have underscored the potential of soft, stretchable, and biocompatible devices. The design of optical soft devices has emerged as an ideal candidate for many applications owing to their high flexibility and immunity to electromagnetic interference. In this review, recent advances in soft optical waveguides, including advanced material selection, fabrication strategies, and characterization, are discussed. Herein, a comprehensive summary of the soft‐waveguide sensing strategies and actuation approaches are provided. Furthermore, the extensive applications of soft optical waveguides in the fields of biomedicine, wearable devices, and soft robotics are explored. Lastly, the challenges and opportunities for the future of soft optical waveguides, including multimodal sensing, algorithm optimization, and manufacturing scalability, are discussed.

We present a continual deep-learning framework for characterizing a dynamically deformed multimode fiber (MMF). It enables real-time self-adaptive focus control using transmission and reflection synchronously, addressing challenges like imaging system drift and fiber distal access.

Formamidinium lead bromide (FAPbBr3) nanocrystals have emerged as a powerful platform for optoelectronic applications due to their pure green photoluminescence (PL). However, their low colloidal stability under storage and operation reduces the potential use of FAPbBr3 perovskite nanocrystals (PeNCs) in various applications. In this study, we prepared the poly(L–lactic acid) (PLLA) nanofibrous membrane embedded with FAPbBr3 perovskite nanocrystals by electrospinning the perovskite and PLLA precursor solution. This is a simple and low-cost technique for the direct confinement of nano-sized functional materials in the continuous polymer nanofibres. PLLA as a polymer matrix provided a high surface framework to fully encapsulate the perovskite NCs. In addition, we found that FAPbBr3 PeNCs crystallize spontaneously inside the PLLA nanofibre. The resultant PLLA-FAPbBr3 nanofibrous membranes were stable and remained in the water for about 45 days without any evident decomposition. The results of this research support the idea of new possibilities for the production of air-stable FAPbBr3 PeNCs by forming a composite with PLLA polymer. The authors believe this study is a new milestone in the development of highly stable metal halide perovskite-based nanofibres, which allow for potential use in lasers, waveguides, and flexible energy harvesters.

Optical fiber shape sensing are important measurement technologies in applications such as healthcare, structural monitoring and robotics. Current state-of-the-art optical fiber shape sensing requires complex sensor structures and interrogation systems. We recently demonstrated that the multimode fiber (MMF) output speckles contain its geometric shape information of the MMF itself. In this paper, we will introduce our recently progresses in this direction, including using machine learning in a proof-of-concept three-dimensional (3D) multi-point deformation sensing via a single MMF, and soft waveguide-based shape sensing. Our results show that a single MMF/soft waveguide based deformation sensor possesses the advantage in terms of system simplicity and sensitivity. It has the potential in deformation monitoring or shape-sensing applications.

An ultrasound wave is a kind of acoustic signal with a frequency greater than 20 kHz, which is widely used in diverse fields such as medical imaging diagnosis, nondestructive testing and resource exploration. A variety of ultrasound sensors have been developed for ultrasound detection. Particularly for photoacoustic imaging, specialized ultrasound sensors with high sensitivity, small size, and broad bandwidth are needed. However, achieving such sensor perform-ance still poses a great challenge to the current state-of-the-art in ultrasound sensor technology. A recent work pub-lished in Opto-Electronic Advances (DOI: 10.29026/oea.2022.200076) proposes a microfiber-based ultrasound sensor that breaks the limitations of existing ultrasound sensors. Benefiting from the large evanescent field characteristic of mi-crofiber, combined with the coherent detection technology, the proposed sensor realized highly sensitive ultrasound de-tection and demonstrated excellent performance in high-resolution photoacoustic imaging. The highly sensitive and mini-aturized microfiber ultrasound sensor provides a competitive alternative for various applications, such as endoscopic photoacoustic imaging of the intestinal tract and blood vessels in animals.

Temporal dissipative solitons have been widely studied in optical systems, which exhibit various localized structures and rich dynamics, and have shown great potential in applications including optical encoding and sensing. Yet, most of the soliton states, as well as the switching dynamics amongst, were fractionally captured or via self-evolution of the system, lacking of control on the soliton motion. While soliton motion control has been widely investigated in coherently seeded optical cavities, such as microresonator-based dissipative solitons, its implementation in decoherently seeded systems, typically the soliton mode-locked lasers, remains an outstanding challenge. Here, we report the universal dynamics and deterministic motion control of temporal dissipative solitons in a mode-locked fibre laser by introducing a scanned spectral filtering effect. We investigate rich switching dynamics corresponding to both the assembly and the disassembly of solitons, revealing a complete and reversible motion from chaotic states to soliton and soliton-molecule states. Significant hysteresis has been recognized in between the redshift and blueshift scan of the motorized optical filter, unveiling the nature of having state bifurcations in dissipative and nonlinear systems. The active soliton motion control enabled by filter scanning highlights the potential prospects of encoding and sensing using soliton molecules.

Imaging through scattering media has become an important aspect in optical imaging. To achieve this, different approaches have been presented to recover the phase of an imaging object from its scattered speckle behind a scattering medium. However, all these algorithms require initial parameters which are obtained based on prior knowledge of the imaging object. This is impractical, as prior knowledge of the imaging object is not always available in real imaging applications. In this paper, we propose using a Particle Swarm Optimization algorithm to find these optimal parameters without requiring prior knowledge of the imaging object. These optimal values are then adopted in the Phase Retrieval algorithm based on object-modulated speckles for object image reconstruction behind a scattering medium in a single-shot imaging system. The obtention of the values for the standard deviation for Gaussian filter and the threshold control allows Phase Retrieval to converge faster and avoids the need for running the algorithm more than once in the search for the best reconstruction.

With the continuous study of metal halide perovskite,geometry-confined technologies have been widely applied to reduce the material dimensionality and to produce pre-designed structures,which can tune optical reflectance,scattering,and absorption,thereby optimizing the performance of perovskite-based optoelectronic devices and improving their commercial competitiveness.The morphologies of perovskite active layer play a pivotal role in optoelectronic properties and the resulting device performances.In this review,we systematically summarized recent progress in the preparation and manufacture of various perovskite geometry-confined morphologies,as well as their promising advances in different optoelectronic applications,including photodetectors,solar cells(SCs),lasers,and light-emitting diodes(LEDs).In addition,the remaining challenges and further improvements of preparation unique geometry-confined perovskite morphologies for next-generation high quality optoelectronic devices are discussed.

Lingjie Kong1,2,∗, Conor Evans, Lei Su, Daniel S Elson and Xunbin Wei6,∗ 1 State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Beijing 100084, People’s Republic of China 2 IDG/McGovern Institute for Brain Research, Tsinghua University, Beijing 100084, People’s Republic of China 3 Wellman Center for Photomedicine, Harvard Medical School, Massachusetts General Hospital, Charlestown, MA 02129, United States of America 4 School of Engineering and Materials Science, Queen Mary University of London, London, United Kingdom 5 Hamlyn Centre for Robotic Surgery, Department of Surgery and Cancer, Imperial College London, London, United Kingdom 6 Biomedical Engineering Department, Peking University, Beijing 100191, People’s Republic of China E-mail: konglj@tsinghua.edu.cn and xwei@bjmu.edu.cn This special issue on ‘Translational Biophotonics’ was initiated when COVID-19 started to spread worldwide in early 2020, with the aim of introducing the advances in optical tools that have the ability to transform clinical diagnostics, surgical guidance, and therapeutic approaches that together can have a profound impact on global health. This issue achieves this goal comprehensively, covering various topics including optical techniques for clinical diagnostics, monitoring and treatment, in addition to fundamental studies in biomedicine.

Semiconductors in their optical-fiber forms are desirable. Single-crystal organometallic halide perovskites have attractive optoelectronic properties and therefore are suitable fiber-optic platforms. However, single-crystal organometallic perovskite optical fibers have not been reported before due to the challenge of one-directional single-crystal growth in solution. Here, we report a solution-processed approach to continuously grow single-crystal organometallic perovskite optical fibers with controllable diameters and lengths. For single-crystal MAPbBr3 (MA = CH3NH3+) perovskite optical fiber made using our method, it demonstrates low transmission losses (<0.7 dB/cm), mechanical flexibilities (a bending radius down to 3.5 mm), and mechanical deformation-tunable photoluminescence in organometallic perovskites. Moreover, the light confinement provided by our organometallic perovskite optical fibers leads to three-photon absorption (3PA), in contrast with 2PA in bulk single crystals under the same experimental conditions. The single-crystal organometallic perovskite optical fibers have the potential in future optoelectronic applications.