Precise Synthesis of Organic Cocrystal Alloys with Full-Spectrum Emission Characteristics for the Stepless Color Changing Display.

Organic luminescent materials are indispensable in optoelectronic displays and solid-state luminescence applications. Compared with single-component, multi-component crystalline materials can improve optoelectronic characteristics. This work forms a series of full-spectrum tunable luminescent charge-transfer (CT) cocrystals ranging from 400 to 800 nm through intermolecular collaborative self-assembly. What is even more interesting is that o-TCP-Cor(x)-Pe(1-x), p-TCP-Cor(x)-Pe(1-x), and o-TCP-AN(x)-TP(1-x) alloys are prepared based on cocrystals by doping strategies, which correspondingly achieve the stepless color change from blue (CIE [0.22, 0.44]) to green (CIE [0.16, 0.14]), from green (CIE [0.27, 0.56]) to orange (CIE [0.58, 0.42]), from yellow (CIE [0.40, 0.57]) to red (CIE [0.65, 0.35]). The work provides an efficient method for precisely synthesizing new luminescent organic semiconductor materials and lays a solid foundation for developing advanced organic solid-state displays.

Reversible Thermally Driven Phase Change of Layered In2Se3 for Integrated Photonics.

Two-dimensional In2Se3, 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 ß' phases with the assistance of local strain from surface wrinkles and ripples, as well as reversible phase changes within the ß 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 ß'-In2Se3 working as a transparent microheater proves to be a viable option for efficient thermo-optic modulation. This prototype design for layered In2Se3 offers immense potential for integrated photonics and paves the way for multilevel, nonvolatile optical memory applications.

Integrated Flexible Microscale Mechanical Sensors Based on Cascaded Free Spectral Range-Free Cavities.

Photonic mechanical sensors offer several advantages over their electronic counterparts, including immunity to electromagnetic interference, increased sensitivity, and measurement accuracy. Exploring flexible mechanical sensors on deformable substrates provides new opportunities for strain-optical coupling operations. Nevertheless, existing flexible photonics strategies often require cumbersome signal collection and analysis with bulky setups, limiting their portability and affordability. To address these challenges, we propose a waveguide-integrated flexible mechanical sensor based on cascaded photonic crystal microcavities with inherent deformation and biaxial tensile state analysis. Leveraging the advanced multiplexing capability of the sensor, for the first time, we successfully demonstrate 2D shape reconstruction and quasi-distributed strain sensing with 110 µm spatial resolution. Our microscale mechanical sensor also exhibits exceptional sensitivity with a detected force level as low as 13.6 µN in real-time measurements. This sensing platform has potential applications in various fields, including biomedical sensing, surgical catheters, aircraft and spacecraft engineering, and robotic photonic skin development.

Oriented Self-Assembly of Hierarchical Branch Organic Crystals for Asymmetric Photonics.

Organic hierarchical branch micro/nanostructures constituted by single crystals with inherent multichannel characteristics exhibit superior potential in regulating photon transmission for photonic circuits. However, organic branch micro/nanostructures with precise branch positions are extremely difficult to achieve due to the randomness of the nucleation process. Herein, by taking advantage of the dislocation stress field-impurity interaction that solute molecules deposit preferentially along the dislocation line, twinning deformation was introduced into microcrystals to induce oriented nucleation sites, and ultimately organic branch microstructures with controllable branch sites were fabricated. The growth mechanism of these controllable single crystals with an angle of 140° between trunk and branch is attributed to the low lattice mismatching ratio (η) of 4.8%. These as-prepared hierarchical branch single crystals with asymmetrical optical waveguide characteristics have been demonstrated as an optical logic gate with multiple input/out channels, which provides a route to command the nucleation sites and offers potential applications in the organic optoelectronics at the micro/nanoscale.

Polycrystalline silicon 2 × 2 Mach-Zehnder interferometer optical switch.

In this paper, we demonstrate a broadband Mach-Zehnder interferometer optical switch based on polycrystalline silicon (poly-Si), which enables the development of multilayer photonics integrated circuits. The poly-Si is deposited under a low temperature of 620 °C to avoid unexpected thermal stress and influence on optoelectronic performance. By introducing a π/2 phase shifter and a push-pull configuration, the switch achieved low power consumption and loss caused by carrier plasma absorption (CPA). The switch operates effectively in both "Bar" and "Cross" states at voltages of -3.35 V and 3.85 V. The power consumptions are 7.98 mW and 9.39 mW, respectively. The on-chip loss is 5.9 ± 0.4 dB at 1550 nm, and the crosstalk is below -20 dB within the C-band. The switch exhibits a 10%-90% rise time of 7.7 µs and a 90%-10% fall time of 3.4 µs at 1550 nm. As far as we know, it is the first demonstration of a poly-Si switch on an 8-inch wafer pilot-line. The low-temperature deposited poly-Si switch is promising for multilayer active photonic devices and photonic-electronic applications.

Integrated Bragg grating filters based on silicon-Sb2Se3 with non-volatile bandgap engineering capability.

Integrated optical filters show outstanding capability in integrated reconfigurable photonic applications, including wavelength division multiplexing (WDM), programmable photonic processors, and on-chip quantum photonic networks. Present schemes for reconfigurable filters either have a large footprint or suffer from high static power consumption, hindering the development of reconfigurable photonic integrated systems. Here, a reconfigurable hybrid Bragg grating filter is elaborately designed through a precise, modified coupling mode theory. It is also experimentally presented by integrating non-volatile phase change material (PCM) Sb2Se3 on silicon to realize compact, low-loss, and broadband engineering operations. The fabricated filter holds a compact footprint of 0.5 µm × 43.5 µm and maintains a low insertion loss of < 0.5 dB after multiple levels of engineering to achieve crystallization. The filter is able to switch from a low-loss transmission state to the Bragg reflection state, making it a favorable solution for large-scale reconfigurable photonic circuits. With a switching extinction ratio over 30 dB at 1504.85 nm, this hybrid filter breaks the tradeoff between insertion loss and tuning range. These results reveal its potential as a new candidate for a basic element in large-scale non-volatile reconfigurable systems.

Ultra-compact scalable spectrometer with low power consumption.

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 µm2, 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.

Flexible waveguide integrated thermo-optic switch based on TiO2 platform.

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 (TiO2) 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 TiO2 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.

Waveguide-Integrated PdSe2 Photodetector over a Broad Infrared Wavelength Range.

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 PdSe2 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 PdSe2 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.

Hierarchical Integration of Organic Core/Shell Microwires for Advanced Photonics.

The combination of multiple components or structures into integrated micro/nanostructures for practical application has been pursued for many years. Herein, a series of hierarchical organic microwires with branch, core/shell (C/S), and branch C/S structures are successfully constructed based on organic charge transfer (CT) cocrystals with structural similarity and physicochemical tunability. By regulating the intermolecular CT interaction, single microwires and branch microstructures can be integrated into the C/S and branch C/S structures, respectively. Significantly, the integrated branch C/S microwires, with multicolor waveguide behavior and branch structure multichannel waveguide output characteristics, can function as an optical logic gate with multiple encoding features. This work provides useful insights for creating completely new types of organic microstructures for integrated optoelectronics.

Fast thermo-optical modulators with doped-silicon heaters operating at 2 µm: erratum.

We correct the errors in the performance of the MRR modulator in our paper [Opt. Express29, 23508, (2021)10.1364/OE.430756]. The FWHM of the MRR device should be 0.22nm instead of 0.11nm. And thus, the Q factor, power consumption, and FOM need to be corrected. After the correction, the performance of our devices was still the best among 2µm-waveband TO modulators. All the conclusions are not changed.

Flexible passive integrated photonic devices with superior optical and mechanical performance.

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.

High-performance silicon PIN diode switches in the 2-µm wave band.

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.

Waterproof molecular monolayers stabilize 2D materials.

Two-dimensional van der Waals materials have rich and unique functional properties, but many are susceptible to corrosion under ambient conditions. Here we show that linear alkylamines n-C m H2m+1NH2, with m = 4 through 11, are highly effective in protecting the optoelectronic properties of these materials, such as black phosphorus (BP) and transition-metal dichalcogenides (TMDs: WS2, 1T'-MoTe2, WTe2, WSe2, TaS2, and NbSe2). As a representative example, n-hexylamine (m = 6) can be applied in the form of thin molecular monolayers on BP flakes with less than 2-nm thickness and can prolong BP's lifetime from a few hours to several weeks and even months in ambient environments. Characterizations combined with our theoretical analysis show that the thin monolayers selectively sift out water molecules, forming a drying layer to achieve the passivation of the protected 2D materials. The monolayer coating is also stable in air, H2 annealing, and organic solvents, but can be removed by certain organic acids.

Optical Temperature Sensor Based on Polysilicon Waveguides.

Traditional temperature detection has limitations in terms of sensing accuracy and response time, while chip-level photoelectric sensors based on the thermo-optic effect can improve measurement sensitivity and reduce costs. This paper presents on-chip temperature sensors based on polysilicon (p-Si) waveguides. Dual-microring resonator (MRR) and asymmetric Mach-Zehnder interferometer (AMZI) sensors are demonstrated. The experimental results show that the sensitivities of the sensors based on AMZI and MRR are 86.6 pm/K and 85.7 pm/K, respectively. The temperature sensors proposed in this paper are compatible with the complementary metal-oxide-semiconductor (CMOS) fabrication technique. Benefitting from high sensitivity and a compact footprint, these sensors show great potential in the field of photonic-electronic applications.

Fast thermo-optical modulators with doped-silicon heaters operating at 2 µm.

The 2-µm-waveband has been recognized as a potential telecommunication window for next-generation low-loss, low-latency optical communication. Thermo-optic (TO) modulators and switches, which are essential building blocks in a large-scale integrated photonic circuit, and their performances directly affect the energy consumption and reconfiguration time of an on-chip photonic system. Previous TO modulation based on metallic heaters at 2-µm-waveband suffer from slow response time and high power consumption. In this paper, high-performance thermo-optical Mach-Zehnder interferometer and ring resonator modulators operating at 2-µm-waveband were demonstrated. By embedding a doped silicon (p++-p-p++) junction into the waveguide, our devices reached a record modulation efficiency of 0.17 nm/mW for Mach-Zehnder interferometer based modulator and its rise/fall time was 3.49 µs/3.46 µs which has been the fastest response time reported in a 2-µm-waveband TO devices so far. And a lowest Pπ power of 3.33 mW among reported 2-µm TO devices was achieved for a ring resonator-based modulator.

High-speed Fourier ptychographic microscopy for quantitative phase imaging.

Fourier ptychographic microscopy (FPM), as an emerging computational imaging method, has been applied to quantitative phase imaging with resolution bypassing the physical limit of the detection objective. Due to the weak illumination intensity and long image acquisition time, the achieved imaging speed in current FPM methods is still low, making them unsuitable for real-time imaging applications. We propose and demonstrate a high-speed FPM method based on using laser illumination and digital micro-mirror devices for illumination angle scanning. In this new, to the best of our knowledge, FPM method, we realized quantitative phase imaging and intensity imaging at over 42 frames per second (fps) with around 1 µm lateral resolution. The quantitative phase images have revealed membrane height fluctuations of red blood cells with nanometer-scale sensitivity, while the intensity images have resolved subcellular features in stained cancer tissue slices.

Broadband couplers for hybrid silicon-chalcogenide glass photonic integrated circuits.

We report on the design, fabrication and testing of three types of coupling structures for hybrid chalcogenide glass Ge23Sb7S70-Silicon (GeSbS-Si) photonic integrated circuit platforms. The first type is a fully etched GeSbS grating coupler defined directly in the GeSbS film. Coupling losses of 5.3 dB and waveguide-to-waveguide back-reflections of 3.4% were measured at a wavelength of 1553 nm. Hybrid GeSbS-to-Si butt couplers and adiabatic couplers transmitting light between GeSbS and Si single-mode waveguides were further developed. The hybrid butt couplers (HBCs) feature coupling losses of 2.7 dB and 9.2% back-reflection. The hybrid adiabatic couplers (HACs) exhibit coupling losses of 0.7 dB and negligible back-reflection. Both HBCs and HACs have passbands exceeding the 100 nm measurement range of the test setup. GeSbS grating couplers and GeSbS-to-Si waveguide couplers can be co-fabricated in the same process flow, providing, for example, a means to first couple high optical power levels required for nonlinear signal processing directly into GeSbS waveguides and to later transition into Si waveguides after attenuation of the pump. Moreover, GeSbS waveguides and HBC transitions have been fabricated on post-processed silicon photonics chips obtained from a commercially available foundry service, with a previously deposited 2 µm thick top waveguide cladding. This fabrication protocol demonstrates the compatibility of the developed integration scheme with standard silicon photonics technology with a complete back-end-of-line process.

Engineering third-order optical nonlinearities in hybrid chalcogenide-on-silicon platform.

We demonstrated a class of highly nonlinear hybrid waveguide structures based on infiltration of As2S3 chalcogenide glass into silicon slot waveguides. The nonlinear properties of the hybrid waveguides were precisely quantified via a bidirectional top-hat D-scan method, enabling a direct comparison between properties measured using different device geometries. We experimentally demonstrate hybrid As2S3-Si slot waveguides with a two-photon absorption (TPA) figure of merit exceeding 2 at near infrared wavelengths. These waveguides largely satisfy the critical criterion for efficient nonlinear integrated photonics (FOMTPAwg>1), allowing phase shifts greater than π with minimal overall losses. These results pave the way for efficient and robust ultrafast all-optical devices and circuits in large-scale silicon photonics technology.

Low-loss photonic device in Ge-Sb-S chalcogenide glass.

Low-loss waveguides constitute an important building block for integrated photonic systems. In this work, we investigated low-loss photonic device fabrication in Ge23Sb7S70 chalcogenide glass using electron beam lithography followed by plasma dry etching. High-index-contrast waveguides with a low propagation loss of 0.5 dB/cm and microdisk resonators with an intrinsic quality factor (Q-factor) of 1.2×106 were demonstrated. Both figures represent, to the best of our knowledge, the best low-loss results reported thus far in submicrometer single-mode chalcogenide glass devices.