Wavelength Tuning Research Articles

Bioinspired Hierarchical Photonic Structures with Controllable Polarization and Color for Optical-Multiplexed Information Encryption.

Optical multiplexing technologies, which integrate multiple optical channels based on photonic structures, offer a significant solution for high-capacity information storage and advanced encryption. However, these photonic materials are limited by their inherent and unswitchable chiral structures, which result in a restricted control over the spatial distribution of light. Here, we propose to construct an integrating optical-multiplexed structure using tunable 1D photonic crystals and orientation texture via a combined self-assembly and shear-aligning approach. In this photonic system, the created diverse orientation structure of ethyl cellulose (EC) offers a wide range of light modulations through phase retardation. When combined with the chromatic layer formed by the self-assembly of EC, tunable wavelength and polarization are achieved. Notably, due to the identical components of the light modulation and chiral photonic crystal layers, the traceless interface between them ensures both high confidentiality and durability. By leveraging these hierarchical structures, photonic slices with well-defined polarization states and structural colors are created, enabling the construction of an advanced photonic platform for multiplexed information storage and multichannel 3D and 4D encryption. This study presents a promising strategy to develop traceless, highly confidential photonic units with controllable polarization and color for advanced encryption technologies.

Investigation to Understand the Role of Phase Variation in Red Emitting Eu3+-Doped Calcium Magnesium Silicate Phosphor for In Vitro Bioimaging.

Eu3+-doped silicate phosphors are gaining significant attention for bioimaging and scaffold development due to their narrow red emission, high color purity, quantum yield (QY), and large Stokes shift. These phosphors offer several advantages over conventional imaging techniques, such as good selectivity and sensitivity, simpler operation, reduced data acquisition time, cost-effectiveness, and nondestructive imaging. The luminescence properties of these phosphors can be enhanced by modifying synthesis methods, annealing conditions, and hosts and introducing multiple dopants. This study explores a novel approach for improving luminescence by modifying the crystal structures of Eu3+ doped calcium magnesium silicate (CMS:Eu3+) phosphors for in vitro bioimaging and potential scaffold development. The synthesized diopside (CaMgSi2O6:xEu3+; x = 10, 15, and 20 mol %), merwinite (Ca3MgSi2O8:15 mol % Eu3+), and akermanite (Ca2MgSi2O7:15 mol % Eu3+) phases of CMS:Eu3+ exhibit distinct coordination environments for Eu3+, leading to unique excitation wavelength tunability from ultraviolet (UV) to the visible region, high emission intensity, decay time, QY > 40%, and color purity >83%. A comparative analysis of their structural and photoluminescence properties reveals the impact of phase modifications on luminescence for in vitro bioimaging by optimizing the dopant concentration. The results indicate that CaMgSi2O6: 15 mol % Eu3+ is the most efficient phosphor for in vitro bioimaging, with the highest relative emission intensity in the red region, decay time ∼2 ms, QY ∼ 77%, and color purity ∼86%. The unique morphology of Ca3MgSi2O8:15 mol %Eu3+ and Ca2MgSi2O7:15 mol % Eu3+ also supports cell adhesion, suggesting their potential in scaffold development. In brief, the study highlights the potential of CMS:Eu3+ phosphors for in vitro bioimaging and scaffold development by modifying phases and dopant concentrations.

Elementally Doped Carbonized Polymer Dots: Control of Optical Properties and Their Versatile Applications

AbstractCarbonized polymer dots (CPDs) are a class of luminescent nanomaterials formed through cross‐linking and polymerization. Owing to their excellent biocompatibility, ease of synthesis, good aqueous dispersion, high chemical stability, unique cross‐linking structure, and modifiable surface properties, CPDs have attracted significant attention. However, pure CPDs exhibit certain limitations in terms of optical performance, particularly in terms of fluorescence intensity, phosphorescence intensity, and emission wavelength tunability, which may not meet the requirements of specific applications. To address these limitations, doping CPDs with various elements, such as nitrogen (N), sulfur (S), and phosphorus (P) to modify their band structure and surface functionalization can significantly enhance their optical properties and photochemical stability, thereby expanding their application potential. This paper reviews the main synthesis methods for elementally doped CPDs, examines the effects of different types of elemental doping on their photochemical properties, and explores promising applications in optoelectronic devices, sensors, and catalysis. Finally, recent advancements in elementally doped CPDs are summarized, along with future development directions and challenges.

A highly polarization-sensitive near-infrared photodetector based on two-dimensional germanane/α-CdS heterostructure

Abstract Near-infrared (NIR) photodetectors have been widely used in imaging, remote sensing, communications, and medical fields. Emerging trends in the next-generation NIR photodetectors emphasize small size, low power consumption, and high polarization-sensitivity, thus demanding novel material compositions. Based on first-principles calculations, this paper proposes the two-dimensional Germanane/α-CdS vertically stacked van der Waals heterostructure as a polarization-sensitive NIR photodetector with superior performance. This structure exhibits thermodynamic stability at ambient temperatures, a type II band alignment, a tunable sensitive wavelength spanning 849–2296 nm, strong photocurrent and anisotropy, and remarkable polarization sensitivity with an extinction ratio of 6.74 under a nominal bias voltage of 0.2 V.

Fano Resonant Sensing in MIM Waveguide Structures Based on Multiple Circular Split-Ring Resonant Cavities

In this work, a non-through metal–insulator–metal (MIM) waveguide capable of exciting three Fano resonances was designed and numerically studied using the finite element method. Fano resonances are achieved through the interaction between the modes of multiple circular split-ring resonator cavities and the waveguide. The effect of coupling between different resonators on the Fano resonance peaks is investigated. Independent tuning of the Fano resonance wavelength and transmission rate is accomplished by modifying the structural rotation angle and geometric parameters. After optimizing these parameters, the structure achieves an optimal refractive index sensitivity of 946.88 nm/RIU and a figure of merit of 99.17. The proposed structure holds potential for guiding the design of nanosensors.

Recent Advances and Challenges in Metal Halide Perovskite Quantum Dot-Embedded Hydrogels for Biomedical Application

Metal halide perovskite quantum dots (MHP QDs), as a kind of fluorescent material, have attracted much attention due to their excellent photoluminescence (PL) quantum yield (QY), narrow full width at half maximum (FWHM), broad absorption, and tunable emission wavelength. However, the instability and biological incompatibility of MHP QDs greatly hinder their application in the field of biomedicine. Hydrogels are three-dimensional polymer networks that are widely used in biomedicine because of their high transparency and excellent biocompatibility. This review not only introduces the latest research progress in improving the mechanical and optical properties of hydrogels/MHP QDs but also combines it with the existing methods for enhancing the stability of MHP QDs in hydrogels, aiming to provide new ideas for researchers in material selection and methods for constructing MHP QD-embedded hydrogels. Finally, their application prospects and future challenges are introduced.

High-precision 1.5 µm band tunable single-frequency fluoro-sulfo-phosphate fiber laser based on a self-injection locking scheme

In this paper, a high-precision 1.5 µm band tunable single-frequency Er3+/Yb3+ co-doped fluoro-sulfo-phosphate (EYFSP) fiber laser based on a self-injection locking scheme is experimentally demonstrated. A self-developed 4 cm long EYFSP fiber with a high gain coefficient (3.2–4.7 dB/cm) at the C-band serves as the gain medium for laser output. The single longitudinal mode (SLM) operation is realized via a 15 cm long commercial unpumped gain fiber and a self-injection locking scheme, while flexible wavelength tuning is controlled by a fiber Fabry–Perot tunable filter (FFP-TF). The laser wavelength is tuned from 1528.08 to 1555.55 nm, with a tuning precision of up to 10–18 pm and a tuning speed of 30 nm/s. Throughout the entire tuning range of 27.47 nm, the measured laser linewidth is less than 1.3 kHz, the relative intensity noise remains below −140dB/Hz at frequencies above 3 MHz, and the power fluctuation is as low as 1% over a measurement period of 2 h. These results demonstrate that the high-precision 1.5 µm band tunable single-frequency EYFSP fiber laser is a promising candidate for future coherent optical communication systems and optical fiber sensing.

Noble Metal Coating on Perovskite Microcrystals for Robust and Plasmonic Lasing Applications

AbstractLead halide perovskites (LHP) are solution‐processable semiconductor materials with high optical gain and broad wavelength tunability, making them well‐suited for laser applications. Here, a solution‐based method for the 3D conformal coating of LHP microcrystals with noble metals is presented. A nanoscale metal coating layer is found to significantly enhance both laser performance and environmental stability. This enables gold‐coated CsPbBr3 microcrystals to be delivered into live cells, achieving single‐mode plasmonic lasing under optical pumping. Silver‐coated CsPbBr3 particles demonstrate stable plasmonic lasing in the air. This one‐pot synthesis method opens new possibilities for leveraging LHPs to implant micro‐laser sources into physical, biological, and industrial systems.

Efficient Spin-Light-Emitting Diodes With Tunable Red to Near-Infrared Emission at Room Temperature.

Spin light-emitting diodes (spin-LEDs) are important for spin-based electronic circuits as they convert the carrier spin information to optical polarization. Recently, chiral-induced spin selectivity (CISS) has emerged as a new paradigm to enable spin-LED as it does not require any magnetic components and operates at room temperature. However, CISS-enabled spin-LED with tunable wavelengths ranging from red to near-infrared (NIR) has yet to be demonstrated. Here, chiral quasi-2D perovskites are developed to fabricate efficient spin-LEDs with tunable wavelengths from red to NIR region by tuning the halide composition. The optimized chiral perovskite films exhibit efficient circularly polarized luminescence from 675 to 788nm, with a photoluminescence quantum yield (PLQY) exceeding 86% and a dissymmetry factor (glum) ranging from 8.5 × 10-3 to 2.6 × 10-2. More importantly, direct circularly polarized electroluminescence (CPEL) is achieved at room temperature in spin-LEDs. This work demonstrated efficient red and NIR spin-LEDs with the highest external quantum efficiency (EQE) reaching 12.4% and the electroluminescence (EL) dissymmetry factors (gEL) ranging from 3.7 × 10-3 to 1.48 × 10-2 at room temperature. The composition-dependent CPEL performance is further attributed to the prolonged spin lifetime as revealed by ultrafast transient absorption spectroscopy.

Local Tuning of the Epsilon‐Near‐Zero Condition in Hybrid Silicon Waveguides Using Reactive Laser Annealing

The ability for locally tuning devices in photonic integrated circuits could be an essential function for a wide range of applications requiring reconfigurable photonics. This work demonstrates the application of postgrowth reactive laser annealing to selectively tune the optical properties of tin‐doped indium oxide (ITO) patches integrated in silicon waveguides. ITO stands out due to its distinctive ability to operate in the epsilon‐near‐zero (ENZ) regime at near‐infrared wavelengths. The precise local tuning of the ENZ wavelength in ITO/Si hybrid waveguides by controlling the laser annealing fluence is demonstrated. This technique uniquely allows for the customization of optical constants at critical telecom wavelengths. The findings present a powerful and adaptable method to exploit the exceptional qualities of ITO and, by extension, other transparent conducting oxides, paving the way for the functional diversification of hybrid photonic devices on a singular‐silicon chip.

Detection of Atmospheric NO2 Using Scheimpflug DIAL with a Blue External Cavity Diode Laser Source

Nitrogen dioxide (NO2) is broadly acknowledged as one of the six key air pollutants, posing a significant threat to environmental stability and human health. The profile of atmospheric nitrogen dioxide is required for quantifying NO2 emissions from fossil fuel combustion and industry. In continuous-wave differential absorption lidar (CW-DIAL) systems, the laser sources employed are subject to the issues of varying output characteristics and poor instability. This study presents a CW-DIAL system for remote sensing of atmospheric NO2 that employs a compact grating-based external cavity diode laser (ECDL) and Scheimpflug imaging. The laser in this system utilizes a piezoelectric transducer (PZT) for precise wavelength tuning, emitting at 448.1 nm and 449.7 nm with an output power of 2.97 W and a narrow linewidth of 0.16 nm. Signal capturing was achieved through a Newtonian telescope with a diameter of 200 mm and a 45° inclined CCD image sensor, satisfying the Scheimpflug principle. A case study near road traffic was used to verify the feasibility of ECDL-DIAL, which took place from 1 October to 2 October 2023 over an industrial park. The system generates precise NO2 distribution maps with sub-50 m resolution over 3 km, updating every 10 min.

Optical beam steering and distance measurement experiments through an optical phased array and a 3D printed lens

We present beam steering experiments based on the wavelength tuning of edge-coupled 1D optical phased arrays (OPAs) on a 3 µm silicon on insulator (SOI) platform. Two versions of 512-channel OPA with different pitch values, namely 2 µm and 3 µm, are designed, fabricated, and characterized. For the 2 µm pitch, the width of the output array is 1 mm, steering sensitivity is measured to be 1°/nm, and the maximum beam steering angle is 45°. For the 3 µm pitch, the output array is 1.5 mm wide, the steering sensitivity is 0.6°/nm, and the maximum beam steering angle is 30°. Since the chip doesn’t offer vertical collimation, both a cylindrical (2D-shaped) lens and a 3D printed (3D-shaped) lens were tested with the OPA chips. The high number of output channels results in a wide width of the output array, therefore enabling frequency-modulated continuous-wave (FMCW) distance measurements up to a few meters. The ability to achieve precise steering angles and distance measurements with up to 5 cm accuracy improves the efficiency of light detection and ranging (LiDAR) systems in various fields, such as autonomous vehicles, robotics, and environmental mapping.

Broadband stimulated Raman hyperspectral imaging of cells and semiconductors with synchronized fiber and solid-state sources

We demonstrate broadband hyperspectral stimulated Raman scattering (SRS) microscopy covering over 2000 cm−1, which is achieved by two tunable Stokes light sources synchronized with a pump light source. Specifically, a fiber optical parametric oscillator and a fiber laser, both equipped with automatic wavelength tuning capabilities, are employed to acquire SRS signals in the ranges of 270–2040 cm−1 and 2800–3100 cm−1, respectively. Using this system, we perform hyperspectral SRS imaging of live HeLa cells, covering the entire fingerprint and C–H stretching regions. Furthermore, the spectral coverage in the lower fingerprint region (<1000 cm−1) enables SRS signal acquisition of wide bandgap semiconductors. We succeed in obtaining the SRS spectra of 4H-silicon carbide (SiC) and gallium nitride and demonstrate SRS imaging of the longitudinal optical phonon-plasmon coupled mode of 4H-SiC. We anticipate that the present method will further expand the applications of SRS in various scientific fields.

Photofunctional cyclophane host-guest systems.

Modulation of optical properties through smart protein matrices is exemplified by a few examples in nature such as rhodopsin (absorption wavelength tuning) and the green fluorescence protein (emission), but in general, the scope found in nature for the matrix-controlled photofunctions remains rather limited. In this review, we present cyclophane-based supramolecular host-guest complexes for which electronic interactions between the cyclophane host and mostly planar aromatic guest molecules can actively modulate excited-state properties in a more advanced way involving both singlet and triplet excited states. We begin by highlighting photofunctional host-guest systems for on-off fluorescence switching and chiroptical functions using bay-functionalized perylene bisimide cyclophanes. Next, we examine the impact of π-extension in perylene bisimide cyclophanes for multiple guest binding, showcasing photofunctional properties including circularly polarized luminescence (CPL). We then focus on triplet-generating cyclophanes, i.e. coronene bisimide cyclophane, with high intersystem crossing (ISC) rates, where we demonstrate modulation of excited state pathways upon guest encapsulation and triplet sensitization through phosphorescence and thermally activated delayed fluorescence (TADF). Furthermore, using supramolecular strategies, we advance non-covalent designs, involving either heavy-atom-based Pt(acac)2 guests or heavy-atom free charge transfer complexes, for triplet harvesting under ambient conditions and demonstrate the role of supramolecular nanoenvironments in stabilizing triplet excitons in aerated solutions. Additionally, we showcase examples for triplet-triplet annihilation (TTA) upconversion in defined cyclophane complexes in aqueous solutions and the application of host-guest chemistry in organic light-emitting diodes (OLEDs).

Adjusting TADF and Phosphorescence for Tailored Dynamic Time‐Dependent Afterglow Colored Carbon Dots spanning Full Visible Region

Time‐dependent afterglow colored (TDAC) behavior differs from static afterglow by involving wavelength changes, enabling low‐cost, high‐level encryption and anti‐counterfeiting. However, the existing carbon dot (CD)‐based TDAC materials lack a clear mechanistic explanation and controllable wavelength changes, significantly hindering the progress of practical applications in this field. In this study, we synthesized CDs composites with customizable tunable TDAC wavelengths across the visible region. Furthermore, we elucidated the underlying mechanism of TDAC that exhibits sequential weakening and relative strengthening of long‐ and short‐wavelength afterglow centers. This phenomenon arises due to strong emission with a short lifetime originating from long‐wavelength thermally activated delayed fluorescence (TADF), along with weak emission having a longer lifetime originating from short‐wavelength phosphorescence. The presence of surface‐rich carboxyl groups on CDs determines the short‐wavelength afterglow in their dispersed state while their high conjugation degree governs the long‐wavelength afterglow in their aggregated state. Additionally, appropriate doping levels of CDs enhance color change phenomena during afterglow. Finally, by embedding CDs into different rigid matrix, the range of afterglow changes can be tailored arbitrarily within the visible light region. Leveraging these exceptional TDAC characteristics has allowed us to successfully develop advanced 4D coding technologies that facilitate multi‐mode anti‐counterfeiting and dynamic information encryption.

Adjusting TADF and Phosphorescence for Tailored Dynamic Time-Dependent Afterglow Colored Carbon Dots spanning Full Visible Region.

Time-dependent afterglow colored (TDAC) behavior differs from static afterglow by involving wavelength changes, enabling low-cost, high-level encryption and anti-counterfeiting. However, the existing carbon dot (CD)-based TDAC materials lack a clear mechanistic explanation and controllable wavelength changes, significantly hindering the progress of practical applications in this field. In this study, we synthesized CDs composites with customizable tunable TDAC wavelengths across the visible region. Furthermore, we elucidated the underlying mechanism of TDAC that exhibits sequential weakening and relative strengthening of long- and short-wavelength afterglow centers. This phenomenon arises due to strong emission with a short lifetime originating from long-wavelength thermally activated delayed fluorescence (TADF), along with weak emission having a longer lifetime originating from short-wavelength phosphorescence. The presence of surface-rich carboxyl groups on CDs determines the short-wavelength afterglow in their dispersed state while their high conjugation degree governs the long-wavelength afterglow in their aggregated state. Additionally, appropriate doping levels of CDs enhance color change phenomena during afterglow. Finally, by embedding CDs into different rigid matrix, the range of afterglow changes can be tailored arbitrarily within the visible light region. Leveraging these exceptional TDAC characteristics has allowed us to successfully develop advanced 4D coding technologies that facilitate multi-mode anti-counterfeiting and dynamic information encryption.

Cavity Wavelength on Erbium-Doped Fiber Ring Laser Depending on Fabry–Pérot Etalon Steering Angle

This study presents the liquid crystal Fabry–Pérot etalon (LC-FP) as the preferred laser wavelength tuning solution within a erbium-doped fiber ring laser architecture. The laser cavity wavelength can be adjusted by applying varying voltages to the LC-FP. Furthermore, tuning the laser wavelength can be facilitated by modifying the incident light through changes in the steering angle of the LC-FP, which is attributed to the angular dispersion characteristics of the device. The operational range for the steering angle of the LC-FP is ± 4 to 18 degrees. This architectural framework is adept at facilitating the generation of single-wavelength and dual-wavelength lasers within the C band. The tunable range for a single wavelength is approximately 13 nm, while the tunable range for dual wavelengths is around 14 nm, with a wavelength spacing of approximately 17.5 nm. These capabilities are primarily influenced by the operational wavelength of the erbium-doped fiber amplifier (EDFA), the operating wavelength of the collimator that directs the fiber optic beam into the LC-FP, and the fixed thickness of the LC-FP.

Acousto-optically induced single-frequency Nd:YAG ring laser based on double corner cube retroreflectors

Using an acousto-optic modulator (AOM) to enforce the unidirectional operation of a Nd:YAG ring laser based on double corner cube retroreflectors (CCRs) was demonstrated for the first time, to the best of our knowledge. By tilting the AOM with RF applied to deviate from the Bragg angle, a different diffraction loss was introduced between the counterpropagating beams in the ring cavity. A continuous wave single-frequency laser with a maximum output power of 2.99 W was successfully obtained at 1064.5 nm, with a tunable wavelength range from 1064.3 nm to 1064.7 nm. The experimental results indicated the unidirectional operated ring cavity comprising the double CCRs performed significant tolerance to the misalignment of the cavity. By changing the RF to pulsed mode and adjusting the angle of the AOM closer to the Bragg angle, the unidirectional Q-switched operation was achieved with the increase of the diffraction loss of the oscillating light. At the repetition frequency of 110 Hz, a 0.882 mJ single-frequency pulse energy with a pulse width of 70.2 ns was obtained, corresponding to a peak power of 12.6 kW. Sngle-frequency pulses with energy of 0.761 mJ and pulse width of 72.4 ns were also obtained at the repetition frequency of 1 kHz, corresponding to a peak power of 10.5 kW.

Al and Zn Doping in InON Thin Films and Their Optical, Electrical, and Electrochromic Properties.

Indium oxynitride (InON) is a promising material for various applications due to its notable properties, including high mobility, stability, and visible light transparency. Despite its potential, research on InON's electrochromic (EC) properties, especially after doping, remains limited. This study employed DC magnetron sputtering to prepare InON films under various doping conditions. A comprehensive investigation was conducted to examine the impacts of aluminum (Al) and zinc (Zn) doping on the composition, structure, morphology, optical, electrical, and EC characteristics of the InON films. The results indicated that Al doping increased surface amino groups, roughness, and optical band gap while enhancing redox activity. Zn doping introduced ZnO crystalline peaks, smoothed the surface, and reduced the optical bandgap and electrochemical performance. Both doping types negatively affected optical modulation but enabled the tuning of EC response peaks and wavelength ranges. This research underscores the significant role of doping in optimizing the EC performance of InON films, highlighting their potential for advanced applications.

Efficient Time‐dependent Dual‐Model Room Temperature Phosphorescent Carbon Quantum Dots/ Boron Nitride Carbide Oxide Matrices

AbstractRoom temperature phosphorescence (RTP) materials have broad applications in the field of optical devices due to tunable wavelengths and lifetimes. However, creating efficient RTP materials that possess multiple optical properties remains a challenge. Herein, a novel approach is developed to in situ form carbon quantum dots (C‐dots) embedded in boron nitride carbide oxide (B‐N‐C‐O) matrices by introducing nitrogen, phosphorus, and boron dopants into C‐dots (P/B/N doped C‐dots), enabling dual RTP emissions and time‐dependent afterglow. P/B/N doped C‐dots are synthesized by a vacuum‐assisted gradient heating approach using ethylenediamine, phosphoric acid, and boric acid as precursors with a yield of 20 g per batch. The introduction of P/B/N dopants provided multiple triplet states, which enable the C‐dots to have dual RTP emissions and, a long phosphorescent lifetime ranging from 0.98 to 1.30 s. The in situ formation of matrices surrounding the C‐dots enables ultrahigh quantum yield of up to 50%, surpassing the most recently reported RTP C‐dots. To demonstrate the potential applications of the RTP C‐dots, they are used as anti‐counterfeiting ink and phosphorescent dyes for security codes and phosphorescent polyester yarn, showing their suitability for high‐level security applications. This work provides an effective route for large‐scale synthesis of highly efficient RTP materials and preparation of high‐performance optical devices.