Search

One-for-all phototheranostics based on a single molecule is recognized as a convenient approach for cancer treatment, whose efficacy relies on precise lesion localization through multimodal imaging, coupled with the efficient exertion of phototherapy. To unleash the full potential of phototheranostics, advancement in both phototheranostic agents and light delivery methods is essential. Herein, an integrated strategy combining a versatile molecule featuring aggregation-induced emission, namely tBuTTBD, with a modified optical fiber to realize comprehensive tumor diagnosis and "inside-out" irradiation in the orthotopic breast tumor, is proposed for the first time. Attributed to the intense donor-acceptor interaction, highly distorted conformation, abundant molecular rotors, and loose intermolecular packing upon aggregation, tBuTTBD can synchronously undergo second near-infrared (NIR-II) fluorescence emission, photothermal and photodynamic generation under laser irradiation, contributing to a trimodal NIR-II fluorescence-photoacoustic (PA)-photothermal imaging-guided phototherapy. The tumor treatment is further carried out following the insertion of a modified optical fiber, which is fabricated by splicing a flat-end fiber with an air-core fiber. This configuration aims to enable effective in situ phototherapy by maximizing energy utilization for therapeutic benefits. This work not only enriches the palette of NIR-II phototheranostic agents but also provides valuable insight for exploring an integrated phototheranostic protocol for practical cancer treatment., (© 2024 Wiley‐VCH GmbH.)

A compact surface plasmon resonance sensor based on an H-shaped optical fiber is proposed and demonstrated. The H-shaped optical fiber was fabricated experimentally by using hydrofluoric acid to controllably corrode the polarization-maintaining fiber. A satisfactory distance between the outer surface of the fiber and the core can be achieved, and then the surface plasmon resonance effect can be excited by coating a metal film of appropriate thickness on the surface of the fiber. This technology can realize the preparation of multiple samples at one time, compared to the traditional side-polishing technique. The H-shaped optical fiber obtained from corrosion exhibits a high surface quality and short lengths, down to only a few hundred microns. The effects of the proposed H-shaped optical fiber on spectral properties are induced by process parameters, including fiber remaining thickness, coating thickness and fiber length, and were investigated in detail. The prepared sensor was used for the specific detection of human IgG, and the minimum human IgG concentration that the sensor can distinguish is 3.4 μg/mL. Such a compact surface plasmon resonance fiber sensor has the advantages of an easy fabrication, good consistency and low cost, and is expected to be applied in the specific detection of biomarkers.

A surface-plasmon-resonance-based fiber device is proposed for highly sensitive relative humidity (RH) sensing and human breath monitoring. The device is fabricated by using a polyvinyl alcohol (PVA) film and gold coating on the flat surface of a side-polished polymer optical fiber. The thickness and refractive index of the PVA coating are sensitive to environmental humidity, and thus the resonant wavelength of the proposed device exhibits a redshift as the RH increases. Experimental results demonstrate an average sensitivity of 4.98 nm/RH% across an ambient RH ranging from 40% to 90%. In particular, the sensor exhibits a linear response between 75% and 90% RH, with a sensitivity of 10.15 nm/RH%. The device is suitable for human breath tests and shows an average wavelength shift of up to 228.20 nm, which is 10 times larger than that of a silica-fiber-based humidity sensor. The corresponding response and recovery times are determined to be 0.44 s and 0.86 s, respectively. The proposed sensor has significant potential for a variety of practical applications, such as intensive care and human health analysis., Competing Interests: The authors declare no conflict of interest.

Hydrogen as an antioxidant gas has been widely used in the medical and biological fields for preventing cancer or treating inflammation. However, controlling the hydrogen concentration is crucial for practical use due to its explosive property when its volume concentration in air reaches the explosive limit (4%). In this work, a polymer-based microcantilever (μ-cantilever) hydrogen sensor located at the end of a fiber tip is proposed to detect the hydrogen concentration in medical and biological applications. The proposed sensor was developed using femtosecond laser-induced two-photon polymerization (TPP) to print the polymer μ-cantilever and magnetron sputtering to coat a palladium (Pd) film on the upper surface of the μ-cantilever. Such a device exhibits a high sensitivity, roughly -2 nm % -1 when the hydrogen concentration rises from 0% to 4.5% (v/v) and a short response time, around 13.5 s at 4% (v/v), making it suitable for medical and environmental applications. In addition to providing an ultracompact optical solution for fast and highly sensitive hydrogen measurement, the polymer μ-cantilever fiber sensor can be used for diverse medical and biological sensing applications by replacing Pd with other functional materials.

We demonstrate the microprinting of a novel suspended polymer fiber Bragg grating for high-sensitivity temperature measurements. The proposed sensor was developed using a femtosecond laser-induced multiphoton polymerization technique. The grating was cured in a single-groove silica tube spliced between two single-mode fibers. Its transmission spectrum, mode field, and temperature response were thoroughly investigated. A sensitivity of -220  pm/°C was achieved over a temperature range of 24°C to 40°C, which is meaningful in biosensing applications. This all-in-fiber polymer Bragg grating exhibits high temperature sensitivity, excellent mechanical strength, and ultrahigh integration. As such, a temperature sensing element of this type would be a beneficial tool for biological measurements.

We demonstrated a compact and highly-sensitive curvature sensor based on a Mach-Zehnder interferometer created in a photonic crystal fiber. Such a Mach-Zehnder interferometer consisted of a peanut-like section and an abrupt taper achieved by use of an optimized electrical arc discharge technique, where only one dominating cladding mode was excited and interfered with the fundamental mode. The unique structure exhibited a high curvature sensitivity of 50.5 nm/m -1 within a range from 0 to 2.8 m -1 , which made it suitable for high-sensitivity curvature sensing in harsh environments. Moreover, it also exhibited a temperature sensitivity of 11.7 pm/°C.

We demonstrated a high-sensitivity strain sensor based on an in-fiber Fabry-Perot interferometer (FPI) with an air cavity, which was created by splicing together two sections of standard single-mode fibers. The sensitivity of this strain sensor was enhanced to 6.0  pm/με by improving the cavity length of the FPI by means of repeating arc discharges for reshaping the air cavity. Moreover, such a strain sensor has a very low temperature sensitivity of 1.1  pm/°C, which reduces the cross sensitivity between tensile strain and temperature.

Benefiting from the great advances of the femtosecond laser two-photon polymerization (TPP) technology, customized microcantilever probes can be accurately 3-dimensional (3D) manufactured at the nanoscale size and thus have exhibited considerable potentials in the fields of microforce, micro-vibration, and microforce sensors. In this work, a controllable microstructured cantilever probe on an optical fiber tip for microforce detection is demonstrated both theoretically and experimentally. The static performances of the probe are firstly investigated based on the finite element method (FEM), which provides the basis for the structural design. The proposed cantilever probe is then 3D printed by means of the TPP technology. The experimental results show that the elastic constant k of the proposed cantilever probe can be actively tuned from 2.46 N/m to 62.35 N/m. The force sensitivity is 2.5 nm/µN, the Q-factor is 368.93, and the detection limit is 57.43 nN. Moreover, the mechanical properties of the cantilever probe can be flexibly adjusted by the geometric configuration of the cantilever. Thus, it has an enormous potential for matching the mechanical properties of biological samples in the direct contact mode. [ABSTRACT FROM AUTHOR]

Fiber-optic biosensors have garnered significant attention and witnessed rapid development in recent years owing to their remarkable attributes such as high sensitivity, immunity to electromagnetic interference, and real-time monitoring. They have emerged as a potential tool in the realm of biomarker detection for low-concentration and small molecules. In this paper, a portable and cost-effective optical fiber biosensor based on surface plasmon resonance for the early detection of breast cancer is demonstrated. By utilizing the aptamer human epidermal growth factor receptor 2 (HER2) as a specific biomarker for breast cancer, the presence of the HER2 protein can be detected through an antigen-antibody binding technique. The detection method was accomplished by modifying a layer of HER2 aptamer on the flat surface of a gold-coated D-shaped polymer optical fiber (core/cladding diameter 120/490 μm), of which the residual thickness after side-polishing was about 245 μm, the thickness of the coated gold layer was 50 nm, and the initial wavelength in pure water was around 1200 nm. For low-concentration detection of the HER2 protein, the device exhibited a wavelength shift of ~1.37 nm with a concentration of 1 μg/mL (e.g., 5.5 nM), which corresponded to a limit of detection of ~5.28 nM. Notably, the response time of the biosensor was measured to be as fast as 5 s. The proposed biosensor exhibits the potential for early detection of HER2 protein in initial cancer serum and offers a pathway to early prevention of breast cancer. [ABSTRACT FROM AUTHOR]

A three-parameter sensor based on a point-by-point fiber Bragg grating (PBP-FBG) is proposed. The fabricated sensor is 40 mm long. The spectrum loss at 1336.15 nm is selected to measure the surrounding liquid level. The sensitivity for liquid level sensing is −0.046 dB/mm. The temperature is measured using the Bragg dip shifts with sensitivity of 10.06 pm/ °C. The cut-off mode shift is used to measure the surrounding refractive index with sensitivity of 535.14 nm/RIU. As a benefit of femtosecond laser direct inscription fabrication, the grating length is controllable and the liquid level sensing range is expandable. This sensor provides a simple, reliable method for accurate liquid level, temperature and refractive index measurements in hazardous environments. [ABSTRACT FROM AUTHOR]

A type of encoded FBG array for use as an optical fiber tag is inscribed using a femtosecond laser line-by-line technique. Each tag included two labels and several codes formed by grating fragments with a predetermined length. Encoded information was characterized by measuring the backscattered optical signal. Local spectra from the internal grating fragments were then used to enlarge the encoding capacity or encrypt the encoded FBG. The insertion loss of the device is as low as <0.1 dB. [ABSTRACT FROM AUTHOR]

An ultra-compact cascaded Fabry Perot (F-P) interferometer in fiber, which exhibits a high-visibility and enhanced detection limit, has been developed by chemical-assisted femtosecond laser micromachining. The reflection spectrum of the cascaded F-P interferometer shows stronger and narrower resonance than single F-P cavity. The liquid refractive index (RI) measurement demonstrates that the wavelength sensitivity and the dip intensity sensitivity are ∼888 nm/RIU and −882 dB/nm/RIU, respectively, and the obtained detection limit is 4.22 × 10−5 RIU in RI range 1.325–1.330, which is higher than that of the conventional single F-P cavity in optical fibers based on wavelength modulation (10−4 RIU). Moreover, the gas pressure measurement demonstrates that the wavelength sensitivity is 2.86 nm/MPa and the detection limit reaches 1.311 × 10−2  MPa in pressure range 1.5–2.0 MPa. The proposed in-fiber cascaded F-P interferometer will find potential applications in chemical and biological sensors, biomedical probes, and low-cost care products. [ABSTRACT FROM AUTHOR]

Conventional grating-inscription technology usually inscribes only one fiber Bragg grating (FBG) in the core of an optical fiber. A novel femtosecond laser point-by-point technology was demonstrated to parallel-inscribe multiple FBGs, i.e., so-called parallel-integrated FBGs (PI-FBGs), with either different or the same reflection wavelengths in the core of a standard single-mode fiber. Single- or multiwavelength PI-FBGs exhibited one or multiple peaks in the reflection spectrum, respectively. The length of PI-FBGs can be shortened to hundreds of micrometers to increase the spatial resolution of the FBG-based sensors. Our ultrashort PI-FBGs with a length of 500 μm could be used to realize ultrahigh temperature sensing with a high spatial resolution of less than 1 mm, a linear sensitivity of 15.0 pm/°C, and a large measurement range of up to 1100 °C, which overcomes the shortcomings of conventional FBG-based sensors with a low spatial resolution of more than 1 cm and a small measurement range of up to 300 °C. Moreover, the grating parameters, such as reflectivity, reflection wavelength, polarization-dependent loss, and full width at half maximum, can be improved to achieve desired PI-FBGs by changing the spatial distribution and grating number of the PI-FBGs. The PI-FBGs are insensitive to bending, which reduces bend-induced measurement errors. Therefore, our PI-FBGs will find potential applications in the fields of optical fiber sensors, communications, and lasers. [ABSTRACT FROM AUTHOR]

A Fabry–Perot interferometer (FPI) composed of a miniature fiber collimator is proposed and demonstrated for high-sensitivity bend measurements. The device consists of a quarter-pitch graded index fiber (GIF) spliced with a section of silica tube, which is interposed between single-mode fibers. The divergence angle of the included miniature fiber collimator was 0.058 rad, which was found to enhance the sensitivity of the proposed FPI to –3.353 dB/degree over the applied angle range. In comparison, the divergence angle without the collimator was 0.130 rad and FPI sensitivity was –0.618 dB/degree over the applied angle range. The fiber bend sensors demonstrated in this paper are compact, robust, and highly sensitive, and hence, are promising in various biomedical applications. [ABSTRACT FROM AUTHOR]

We demonstrated femtosecond laser inscription of fiber Bragg gratings (FBGs) in a twin-core few-mode fiber (TC-FMF) for directional bend sensing. An FBG was selectively inscribed in one core of the TC-FMF by using an 800 nm femtosecond laser through a phase mask. Three resonance peaks at the wavelengths of 1549.05, 1547.65, and 1546.08 nm were observed in the reflection spectrum of the TC-FM FBG, and were generated by the LP01 mode resonance, LP01–LP11 mode cross-coupling resonance, and LP11 mode resonance, respectively. Moreover, the TC-FM FBG exhibited the capability of directional bend sensing and achieved a maximum bend sensitivity of −37.41 pm/m−1. Hence, the proposed TC-FM FBG directional bend sensors could further be developed as promising solutions for detecting vectorial seismic or acoustic waves and 3-D shape sensing. [ABSTRACT FROM PUBLISHER]

We experimentally demonstrate an automatic arc discharge technology for inscribing high-quality helically twisted long period fiber gratings (H-LPFGs) with greatly improved inscription efficiency for single mode fibers. The proposed technology has been developed by implementing an embedded program in a commercial fusion splicer, which employs an ultraprecision motorized translation stage while the tensioning mass required by conventional inscribing technology is eliminated. More significantly, the arc-induced H-LPFGs have been reported to have potential usage as sensors in temperature, refractive index, twist stress, and strain. [ABSTRACT FROM PUBLISHER]

We report a new fiber optic sensor for temperature measurement at a temperature range of up to 900  °C with excellent stability and repeatability. The sensing head is comprised of a short hollow-core fiber segment spliced between two single-mode fibers using a commercial splicer. Optical power from the lead-in fiber is partly coupled to silica cladding of the hollow-core fiber with the remainder propagating in air core by short distance. The two beams are then re-coupled to the core of the lead-out fiber, owing to the offset splicing joint. Due to the effective index difference between the two beams, an interference pattern in the transmission spectrum is obtained. The distinct thermo-optic coefficients between silica and air result in a high-temperature sensitivity of 41 pm/ °C, and the enclosed structure ensures its immunity to the external refractive index. [ABSTRACT FROM PUBLISHER]

We demonstrate an ultrasensitive temperature sensor based on a unique fiber Fabry–Pérot interferometer (FPI) that was created by means of splicing a mercury-filled silica tube with a single-mode fiber. The air cavity of the fiber FPI was formed by the surface of the mercury column and the endface of the single-mode fiber. Moreover, the mercury-based fiber FPI exhibits an ultrahigh temperature-sensitivity of up to −41.9 nm/°C, which is about one order of magnitude higher than that of the ordinary FPI-based fiber-tip sensors reported so far. Hence, such a mercury-based fiber FPI temperature sensor could be used for highly sensitive ambient temperature sensing applications. [ABSTRACT FROM PUBLISHER]

This paper presents a review of our work concerning the recent progress in fabrications and applications of heating-induced long period fiber gratings (LPFGs). Firstly, three kinds of heating fabrication techniques based on CO2 laser, hydrogen–oxygen flame and arc discharge are demonstrated to fabricate LPFGs, i.e., standard LPFGs (SLPFGs) and helical LPFGs (HLPFGs), in different types of optical fibers such as conventional fibers, photonic crystal fibers, and photonic bandgap fibers. Secondly, the all-fiber orbital angular momentum (OAM) mode converters based on heating-induced SLPFGs and HLPFGs in different types of fibers are studied to increase the transmission capacity. Finally, the heating-induced SLPFGs and HLPFGs are investigated to develop various LPFG-based strain, pressure, torsion and biochemical sensors. [ABSTRACT FROM AUTHOR]

• Optical fiber microcavity in-line Mach-Zehnder interferometers (µIMZI) are reviewed. • Impact of microcavity shape on capability for investigation of liquids is studied. • Despite different shapes, µIMZI may offer very high refractive index sensitivity. • The shape has an impact on performance of µIMZI in microfluidic systems. • Depending on application different microcavity shape should be chosen. In this work, we review microcavity in-line Mach-Zehnder Interferometers (µIMZI) obtained in optical fibers using femtosecond (fs) laser micromachining. These structures can be considered as a great solution satisfying the requirements mentioned above for small-volume RI sensing applicable in label-free biosensing. Furthermore, application of the femtosecond laser facilitates tailoring of the microcavity's shape with high degree of flexibility. Over the years, various µIMZI have been reported, where RI sensing has been mainly analyzed but no impact of the microcavity shape has been shown up to date. Thus, on top of the review on µIMZIs, in this work, we discuss the impact of the shape of the on the sensing performance of the device. We use two representative examples of microcavity shapes, i.e., U-shape and V-trench, made in a standard single-mode fiber. Despite different shapes, both structures offer similar and high RI sensitivity (exceeding 13,000 nm/RIU in the RI range 1.333–1.340 RIU). However, the performance of the structures in microfluidic systems is different. Based on the experimental results and numerical simulations, the advantages and disadvantages of different shapes are discussed for their application in investigations of liquids and biosensing. [ABSTRACT FROM AUTHOR]

• A new method for doughnut shaping based on 3D nanoprinted microlens on fiber tip is proposed. • The microlens was designed and optimized based on illumination optics, and it was fabricated by femtosecond laser induced two-photon polymerization. • Compared with diffractive optical elements, our proposed method has a larger manufacturing tolerance. • Both simulation and experiment show that the microlens can successfully transfer the Gaussian beam output into doughnut beam. Spatial beam intensity shaping is of great significance in many applications, such as laser fabrication and medical treatment. In this study we present a new method for doughnut beam shaping based on 3D nanoprinted microlens on fiber tip. The optical structure of the microlens was first designed and optimized based on illumination optics in software, and then the microlens was fabricated on a single-mode-fiber tip by femtosecond laser induced two-photon polymerization. Both simulation and experiment results have demonstrated that the Gaussian beam output from a single-mode fiber can be successfully transferred to a high-quality doughnut beam by using the fiber-tip microlens. The proposed microlens shows larger tolerance in fabrication resolution compared with optical diffraction beam shaping elements. Our research shows that the femtosecond laser induced two-photon polymerization provides a new and flexible method for the integration of micro-scaled beam shaping elements on optical fibers. [ABSTRACT FROM AUTHOR]