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The ever-growing demand for miniaturized optical systems presents a significant challenge in revolutionizing their core element – the varifocal lens. Recent advancements in ultra-thin, tunable metasurface optics have introduced new approaches to achieving zoom imaging. However, current varifocal metalens have faced challenges such as low focusing efficiency, limited tunability, and complicated designs. Here, we employ the high-contrast transmit arrays (HCTA) structures to design and fabricate a polarization-independent, single-layer flexible metalens that operates at a wavelength of 940 nm. Using a uniform stretching system, we characterized its optical performance to achieve over 60 % focusing efficiency within a 0 %–25 % stretch range, while the focal length changes align with theoretical predictions. Furthermore, our research also successfully demonstrated the capacity of a metalens with a numerical aperture (NA) of 0.5 to efficiently adjust imaging magnification within a 2× range, achieving imaging results that approach the diffraction limit. This research offers promising prospects for the practical use of compact and miniaturized optoelectronic devices in fields like photography, mixed reality, microscopy, and biomedical imaging.

High beam quality, large-area output, and small footprint are significant pursuing goals for vertical-cavity surface-emitting lasers (VCSELs), which impose strict requirements on tight light confinements with minimized radiation losses. To achieve this, bound states in the continuum (BICs) have been demonstrated as an effective way of trapping light. Here, we combine BICs and photonic bandgaps to realize a quasi-BIC single-mode photonic crystal (PhC) laser on a colloidal quantum dots (CQDs)/silicon oxide (SiO2) hybrid integrated platform. The PhC cavity is a defect-free hexagonal heterostructure with three regions, and the thin CQDs film is embedded within the SiO2 nanopillar planar array as both an optical gain material and a backbone for the PhC. The mode gaps between different regions provide the lateral confinement while the quasi-BICs near the Γ-point generate the small-divergence vertical radiation coupling, resulting in a well-defined emission concentrating within ±1.85° of the normal surface direction and an optical pumping energy density threshold of 216.75 μJ/cm2. Our results demonstrate the design flexibility and versatility of the quasi-BIC laser even with a low contrast of a refractive index between the PhC slab and the substrate, which has potential applications in cavity quantum electrodynamics, nonlinear optics, and integrated photonics.

The introduction of liquid crystals into microcavities has garnered considerable attention for their exceptional tunability and high sensitivity to external perturbation factors within their distinct phase states. Here, a novel light source with both wavelength tunability and an exceptionally narrow linewidth is presented. This innovation is realized by strategically manipulating LC molecules, transitioning them from a well‐aligned state to a disordered state with increasing temperature. The microcavity is tailored to support bound states in the continuum, a cutting‐edge concept in photonic research that allows for light localization with minimal loss. In the pursuit of potential biocompatibility and to reduce cytotoxicity, indium phosphide colloid quantum dots are opted to serve as the emissive carriers within the system. An ultra‐narrow linewidth light emission of 0.039 nm is observed, corresponding to a quality factor reaching 16668, along with a tunable range of 1.21 nm and a temperature sensitivity of 33.52 pm K−1. The invention's compact size and tunable character make it an ideal candidate for a variety of potential applications, such as eco‐friendly sensors with minimal ecological impact, optical modulators with precise control over light, and adaptable photonic devices that can be integrated with a diverse array of materials and configurations. [ABSTRACT FROM AUTHOR]

Liquid crystals are widely used in photonics because of their profound electro–optic properties. However, the slow switching speeds (milliseconds) and the fluid nature of liquid crystals restrict their potential use in integrated photonics. In this work, polymer‐stabilized liquid crystals are utilized as the functional material to improve the response time with a polymer network that helps pre‐orientate the liquid crystal. Additionally, plasmonic slot structures are simultaneously employed to minimize the switch voltage by confining the optical field within the electrode spacing at subwavelength scales. Thanks to the large overlap of the optical and electric fields, the scattering states of the polymer‐stabilized liquid crystal can be effectively manipulated to modulate the loss of the propagating wave, resulting in strong optical attenuation in the integrated photonic platform. Specifically, a plasmonic enhanced polymer‐stabilized liquid crystal photonic device for operation at 1550 nm, which has a length of only 10 µm and shows an extinction ratio of 0.38 dB µm−1, with a power consumption of less than 6 µW and a response time ≈20 µs, resulting in a figure‐of‐merit of 0.012 mW. [ABSTRACT FROM AUTHOR]

We report a new Ag nanoparticle-dispersed polymer nanocomposite for volume holographic recording through acrylic photopolymerization. The initial grating buildup dynamics at the inhibition stage are measured at various Ag nanoparticle concentrations. The refractive index modulation amplitude as large as 0.0069 at 633 nm is seen at the optimum Ag nanoparticle concentration of 1 wt.% with respect to the monomer. Electron paramagnetic resonance measurements show that Ag nanoparticles influence both the generation of alkyl radicals and the scavenging of oxygen in free radical photopolymerization. This mechanism intrinsically determines the molecular weight of polymer being formed and, thereby, affects the refractive index modulation amplitude of the formed grating as a function of Ag nanoparticle concentrations. Moreover, we confirm that two-beam holographic exposure leads to a periodic assembly of dispersed Ag nanoparticles using a dark-field microscopy. Our results suggest a simple way to control the photopolymerization and, therefore, to tailor polymers for practical uses.

On-chip photonic devices such as modulators and photodetectors are essential building blocks for integrated photonics, enabling a wide range of applications in optical communication, sensing, and other emerging fields. Generally, optical modulation and photodetection are accomplished by two discrete devices in integrated photonic circuits, prohibiting the expansion of device functionality and the miniaturization of photonic systems. In this work, we demonstrate graphene/MoTe2 heterojunction integrating with microring resonators (MRRs) to serve as an optical modulator under positive bias voltage and a photodetector under negative bias voltage at the telecom band. Such a device primarily benefits from graphene's optoelectronic characteristics, including broadband absorption and electrostatically tunable refractive index. The obtained dual-functional MoTe2/graphene heterojunction devices demonstrate a modulation depth of ∼26.7 dB, a bandwidth of 7.0 GHz, and a self-driven, wavelength-sensitive optoelectronic response at the telecom C band. Our studies indicate that combining graphene van der Waals heterojunction with MRRs paves the way to emerging photonic applications such as neuromorphic computing while expanding the freedom for miniaturized photonic circuits. [ABSTRACT FROM AUTHOR]

The ever-growing demand for miniaturized optical systems presents a significant challenge in revolutionizing their core element – the varifocal lens. Recent advancements in ultra-thin, tunable metasurface optics have introduced new approaches to achieving zoom imaging. However, current varifocal metalens have faced challenges such as low focusing efficiency, limited tunability, and complicated designs. Here, we employ the high-contrast transmit arrays (HCTA) structures to design and fabricate a polarization-independent, single-layer flexible metalens that operates at a wavelength of 940 nm. Using a uniform stretching system, we characterized its optical performance to achieve over 60 % focusing efficiency within a 0 %–25 % stretch range, while the focal length changes align with theoretical predictions. Furthermore, our research also successfully demonstrated the capacity of a metalens with a numerical aperture (NA) of 0.5 to efficiently adjust imaging magnification within a 2× range, achieving imaging results that approach the diffraction limit. This research offers promising prospects for the practical use of compact and miniaturized optoelectronic devices in fields like photography, mixed reality, microscopy, and biomedical imaging. [ABSTRACT FROM AUTHOR]

The interlayer coupler is one of the critical building blocks for optical interconnect based on multilayer photonic integration to realize light coupling between stacked optical waveguides. However, commonly used coupling strategies, such as evanescent field coupling, usually require a close distance, which could cause undesired interlayer crosstalk. This work presents a novel interlayer slope waveguide coupler based on a multilayer chalcogenide glass photonic platform, enabling light to be directly guided from one layer to another with a large interlayer gap (1 µm), a small footprint (6 × 1 × 0.8 µm3), low propagation loss (0.2 dB at 1520 nm), low device processing temperature, and a high bandwidth, similar to that in a straight waveguide. The proposed interlayer slope waveguide coupler could further promote the development of advanced multilayer integration in 3D optical communications systems. [ABSTRACT FROM AUTHOR]

Flexible photodetectors are pivotal in contemporary optoelectronic technology applications, such as data reception and image sensing, yet their performance and yield are often hindered by the challenge of heterogeneous integration between photoactive materials and flexible substrates. Here, we showcase the potential of an electrostatic force-assisted transfer printing technique for integrating Si PIN photodiodes onto flexible substrates. This clean and dry process eliminates the need for chemical etchants, making it a highly desirable method for manufacturing high-performance flexible photodetector arrays, expanding their widespread applications in electronic eyes, robotics, and human-machine interaction. As a demonstration, a 5 × 5 flexible Si photodetector focal plane array is constructed for imaging sensors and shaped into a convex semicylindrical form to achieve a π field of view with long-term mechanical and thermal stability. Such an approach provides a high yield rate and consistent performance, with the single photodetector demonstrating exceptional characteristics, including a responsivity of 0.61 A/W, a response speed of 39.77 MHz, a linear dynamic range of 108.53 dB, and a specific detectivity of 2.75 × 10 12 Jones at an applied voltage of -3 V at 940 nm.

An ultra-compact on-chip spectrometer was demonstrated based on an array of add-drop micro-donut resonators (MDRs). The filter array was thermally tuned by a single TiN microheater, enabling simultaneous spectral scanning across all physical channels. The MDR was designed to achieve large free spectral ranges with multimode waveguide bends and asymmetric coupling waveguides, covering a spectral range of 40 nm at the telecom waveband with five physical channels (which could be further expanded). Benefiting from the ultra-small device footprint of 150 µm 2 , the spectrometer achieved a low power consumption of 16 mW. Additionally, it is CMOS-compatible and enables mass fabrication, which may have potential applications in personal terminals and the consumer industry.

Two-dimensional In 2 Se 3 , an unconventional phase-change material, has drawn considerable attention for polymorphic phase transitions and electronic device applications. However, its reversible thermally driven phase transitions and potential use in photonic devices have yet to be explored. In this study, we observe the thermally driven reversible phase transitions between α and β' phases with the assistance of local strain from surface wrinkles and ripples, as well as reversible phase changes within the β phase family. These transitions lead to changes in the refractive index and other optoelectronic properties with minimal optical loss at telecommunication bands, which are crucial in integrated photonic applications such as postfabrication phase trimming. Additionally, multilayer β'-In 2 Se 3 working as a transparent microheater proves to be a viable option for efficient thermo-optic modulation. This prototype design for layered In 2 Se 3 offers immense potential for integrated photonics and paves the way for multilevel, nonvolatile optical memory applications.

Mechanically flexible photonic devices are critical components of novel bio-integrated optoelectronic and high-end wearable systems, in which thermo-optic switches (TOSs) as optical signal control devices are crucial. In this paper, flexible titanium oxide (TiO 2 ) TOSs based on a Mach-Zehnder interferometer (MZI) structure were demonstrated around 1310 nm for, it is believed, the first time. The insertion loss of flexible passive TiO 2 2 × 2 multi-mode interferometers (MMIs) is -3.1 dB per MMI. The demonstrated flexible TOS achieves power consumption (Pπ) of 0.83 mW, compared with its rigid counterpart, for which Pπ is decreased by a factor of 18. The proposed device could withstand 100 consecutive bending operations without noticeable degradation in TOS performance, indicating excellent mechanical stability. These results provide a new perspective for designing and fabricating flexible TOSs for flexible optoelectronic systems in future emerging applications.

Hybrid integration of van der Waals materials on a photonic platform enables diverse exploration of novel active functions and significant improvement in device performance for next-generation integrated photonic circuits, but developing waveguide-integrated photodetectors based on conventionally investigated transition metal dichalcogenide materials at the full optical telecommunication bands and mid-infrared range is still a challenge. Here, we integrate PdSe 2 with silicon waveguide for on-chip photodetection with a high responsivity from 1260 to 1565 nm, a low noise-equivalent power of 4.0 pW·Hz -0.5 , a 3-dB bandwidth of 1.5 GHz, and a measured data rate of 2.5 Gbit·s -1 . The achieved PdSe 2 photodetectors provide new insights to explore the integration of novel van der Waals materials with integrated photonic platforms and exhibit great potential for diverse applications over a broad infrared range of wavelengths, such as on-chip sensing and spectroscopy.

Flexible integrated photonics is a rapidly emerging technology with a wide range of possible applications in the fields of flexible optical interconnects, conformal multiplexing sensing, health monitoring, and biotechnology. One major challenge in developing mechanically flexible integrated photonics is the functional component within an integrated photonic circuit with superior performance. In this work, several essential flexible passive devices for such a circuit were designed and fabricated based on a multi-neutral-axis mechanical design and a monolithic integration technique. The propagation loss of the waveguide is calculated to be 4.2 dB/cm. In addition, we demonstrate a microring resonator, waveguide crossing, multimode interferometer (MMI), and Mach-Zehnder interferometer (MZI) for use at 1.55 µm, each exhibiting superior optical and mechanical performance. These results represent a significant step towards further exploring a complete flexible photonic integrated circuit.

The 2-µm wave band has attracted significant research interest due to its potential applications for next-generation high-capacity optical communication and sensing. As the key component, fast optical switches are essential for an advanced and reconfigurable optical network. Motivated by this prospect, we propose and demonstrate two typical silicon PIN diode switches at 2 µm. One is based on a coupled microring resonator (CMRR), and the other is based on a Mach-Zehnder interferometer (MZI) with a push-pull-like configuration. The measured insertion loss of the CMRR switch is <2.5 dB, and the cross talk is <-10.8 dB. The insertion loss of the MZI switch is <2 dB, and the cross talk is <-15.6 dB. The switch times of these two structures are both lower than 12.5 ns.

We report a new polymer/colloidal-quantum-dot (CQD) film with a nanostructured interface, which is fabricated through a template-assisted photopolymerization method, toward the use of amplified spontaneous emission. It is experimentally demonstrated that the amplified spontaneous emission of CQDs is able to be manipulated by changing the nanostructured polymeric interface with a weak scattering ability. The dependences of emission wavelength and threshold on the size of the nanostructure and CQD layer thickness are investigated.