Microfiber Knot Resonator Research Articles

Low detection limit of uric acid based on Prussian blue-enhanced photothermal effect with microfiber knot resonator

The human serum uric acid (UA) level is a crucial indicator for diagnosing dementia in middle-aged and elderly individuals, with decreased levels being expressed in patients. Therefore, developing a high-performance sensor for online uric acid detection is of significant research interest. Herein, a microfiber knot resonator (MKR) sensor for quantitative detection of UA levels is reported. Combining polydimethylsiloxane (PDMS) with an adiabatic MKR, the specificity of UA detection in serum is improved using the photothermal effect of Prussian blue-enhanced uricase reaction. During the sensor operation, UA generates the photothermal effect under 650 nm laser irradiation, causing the PDMS film to expand with heat absorption, thereby shifting the resonance spectrum of the PDMS-MKR sensor. Experimental results demonstrate a sensitivity of 0.0559 nm/(μmol/L) within a UA concentration range of 40–120 μmol/L and a detection limit as low as 0.3578 μmol/L. The proposed sensor shows potential applications in clinical point-of-care early diagnosis and prognosis of dementia due to its specificity, fast detection speed, robustness, and high integration.

All-fiber cascade system for high-sensitive temperature monitoring: An exploration of the tunability of Ti3C2-MKRs

A tunable all-fiber optical cascade temperature system is demonstrated with two microfiber knot resonators (MKRs) as sensing device (MKR_s) and reference device (MKR_r), respectively. The temperature monitoring device is prepared by depositing Ti3C2 onto MKR_s by optical deposition. Sufficient experimental evidence for temperature sensing sensitivity of the dual sensor device cascade system (MKR_r + Ti3C2-MKR_s) is 4.33 nm/°C, which is a 10.13-fold increase in sensitivity compared with the temperature sensing sensitivity of 0.427 nm/°C of the Ti3C2-MKR_s. After depositing Ti3C2 materials (∼400 μm) on the bare MKR_r, we further improve the sensitivity of the cascade system (Ti3C2-MKR × 2) to 9.20 nm/°C, which represents a significant 21.5 times improvement in sensitivity compared to Ti3C2-MKR_s. The sensitivity of cascade fiber optic sensors is controlled by varying the modified length of Ti3C2 materials optically deposited on the MKR_r surface. Overall, this study not only enhances device utilization but also provides a new research direction for the preparation of all-fiber sensors with tunable sensitivity.

Spectral characteristic of multi-wavelength random fiber laser using a microfiber knot resonator

We demonstrate a U-band multi-wavelength random Raman fiber laser (RRFL) based on a microfiber knot resonator (MKR). The RRFL has a forward-pump half-open cavity, wherein a 10-km single mode fiber provides both Rayleigh backscattering feedback and Raman gain. A MKR with a 0.18 nm free spectral range is used as the broadband comb filter. Up to 40 and 38 wavelength channels within 3 dB bandwidth were achieved from the intracavity and the end of the RRFL, respectively. The laser showed a good stability with maximum 0.38 and 0.1 dB peak power fluctuation within an hour at the two outputs, respectively. The spectral evolution with two envelopes was observed, and the impact of the MKR was discussed. The MKR is a small-size all-fiber and wavelength-insensitive broadband filter, which suits well with the broadband operation of the RRFL. The proposed RRFL has a simple structure and good potential tunability and provides guidance for flexible multi-wavelength lasers in the U-band and other wavebands, which have great potential in applications.

MXene V2C-coated runway-type microfiber knot resonator for an all-optical temperature sensor.

We present an all-optical temperature sensor device made of an MXene V2C integrated runway-type microfiber knot resonator (MKR) for the first time. MXene V2C is coated on the surface of the microfiber by optical deposition. The experimental results show that the normalized temperature sensing efficiency is ∼1.65 dB °C-1 mm-1. The high sensing efficiency of the temperature sensor we proposed benefits from the efficient coupling of the highly photothermal material MXene and the runway-type resonator structure, which provides a better idea for the preparation of all-fiber sensor devices.

Structurally determinable optical soliton molecules enabled by a pre-designed microfiber resonator in a passively mode-locked fiber laser

The temporal structure of an optical soliton molecule (SM) produced in a passively mode-locked fiber laser relies directly on phase relations among the comprised solitons. However, such phase relations are typically determined by many global and local parameters of the fiber cavity. Thus, any parameter disturbance would exert complex distortion on the SM. This is always unpredictable and difficult to manipulate. One factor is the difficulty in deciding what parameter options have enabled the SM’s formation. The second is the coupling effect among the related parameters. Consequently, the produced SMs usually exhibit considerable uncertainty and poor stability. How to obtain pre-defined SMs has long been a sought-after yet technically unsolved issue. Herein, as a preliminary investigation we demonstrate that employing a microfiber knot resonator (MKR) in a mode-locked fiber laser can enable the formation of artificially defined and structure-stabilized SMs. Specifically, the MKR enables the single soliton splitting into several ones through enhancing the local nonlinearity. But more importantly, it meanwhile functions as a notch filter that dominates and tailors the spectral evolution. The tailored spectrum is then mapped to the temporal domain, grouping the randomly split solitons into a structured and stabilized SM. Our results suggest an easy-to-access avenue in producing structure-determinable SMs in fiber lasers.

Ultra-high harmonic mode-locking with a micro-fiber knot resonator and Lyot filter.

We report on ultra-high harmonic mode-locking with a repetition rate of up to ∼1 THz by combining a microfiber knot resonator (MKR) and a Lyot filter. The harmonic mode-locked pulses are tunable by changing the diameter of MKR, which agrees well with the theoretical calculation. Our results indicate that the ultrafast pulse generation mechanism is due to the dissipative four-wave mixing mode-locking technique. This work provides a simple and efficient scheme to generate tunable ultrafast pulses with a high repetition rate for various applications, such as THz generation and ultrafast data communication.

High-Sensitivity Humidity Sensor Based on Microknot Resonator Assisted Agarose-Coated Mach-Zehnder Interferometer

An optical fiber humidity sensor with a microfiber knot resonator (MKR) nested U-shaped Mach-Zehnder (MZ) interferometer based on the Vernier effect is proposed. While the reference arm is protected by cured ultraviolet glue, the sensing arm is coated by agarose. The Vernier effect is realized by superimposing the comb-like transmission spectra of the MKR and MZ interfernce, which are designed to have slightly different free spectral ranges. Experimental results indicate that the proposed sensor can provide a maximum humidity sensitivity of 2.442 nm/%RH with a measurement range from 60% RH to 95% RH. The sensor temperature response, reversibility and repeatability are also investigated. The response time is found to be 102 ms for a change of ∼30% RH. This sensor not only retains key features and merits of the MKR, including low cost and small footprint, but also has a simpler preparation process compared with conventional sensors based on the Vernier effect.

Highly Sensitive Photothermal Fiber Sensor Based on MXene Device and Vernier Effect.

A photothermal fiber sensor based on a microfiber knot resonator (MKR) and the Vernier effect is proposed and demonstrated. An MXene Ti3C2Tx nanosheet was deposited onto the ring of an MKR using an optical deposition method to prepare photothermal devices. An MXene MKR and a bare MKR were used as the sensing part and reference part, respectively, of a Vernier-cascade system. The optical and photothermal properties of the bare MKR and the MXene MKR were tested. Ti3C2Tx was applied to a photothermal fiber sensor for the first time. The experimental results showed that the modulation efficiency of the MXene MKR was 0.02 nm/mW, and based on the Vernier effect, the modulation efficiency of the cascade system was 0.15 nm/mW. The sensitivity was amplified 7.5 times. Our all-fiber photothermal sensor has many advantages such as low cost, small size, and good system compatibility. Our sensor has broad application prospects in many fields. The proposed stable MKR device based on two-dimensional-material modification provides a new solution for improving the sensitivity of optical fiber sensors.

SnSe-Coated Microfiber Resonator for All-Optical Modulation.

In this study, a tin monoselenide (SnSe)-based all-optical modulator is firstly demonstrated with high tuning efficiency, broad bandwidth, and fast response time. The SnSe nanoplates are deposited in the microfiber knot resonator (MKR) on MgF2 substrate and change its transmission spectra by the external laser irradiation. The SnSe nanoplates and the microfiber are fabricated using the liquid-phase exfoliation method and the heat-flame taper-drawing method, respectively. Due to the strong absorption and enhanced light–matter interaction of the SnSe nanoplates, the largest transmitted power tunability is approximately 0.29 dB/mW with the response time of less than 2 ms. The broad tuning bandwidth is confirmed by four external pump lights ranging from ultraviolet to near-infrared. The proposed SnSe-coated microfiber resonator holds promising potential for wide application in the fields of all-optical tuning and fiber sensors.

Systematic investigation of spectral characteristics and sensing characteristics of microfiber knot resonator

In this work, we systematically study the transmission spectral characteristics of the microfiber knot resonator (MKR) both in simulation and in an experiment. The transmission spectrum shows several possible phenomena, including dominating resonance, dominating interference, the coexistence of resonance and interference with different intensity ratios, and resonance with Vernier effect. The transmission spectra with various shapes are obtained in simulation by adjusting parameters like fractional coupling intensity loss, intensity coupling ratio, and propagation constants of different modes. The relationship between the transmission spectrum and the size of the resonant ring is studied by reducing the diameter of the resonant ring and analyzing the corresponding transmission spectrum. The performance of a polydimethylsiloxane-coated MKR in refractive index and temperature measurement is also investigated, and the responses of the transmission spectrum, the extracted interference spectrum, the extracted resonance spectrum, the extracted envelope spectrum of Vernier effect are all analyzed, indicating that these spectra have similar responses to the variation of refractive index or temperature. Linear fit indicates that the sensitivities of the transmission spectrum to refractive index and temperature are about 1264.09 nm RIU−1 and −2.60 nm/°C, respectively. This systematic and comprehensive study will provide a helpful guideline for understanding, analyzing and designing MKR-based devices with desired spectral characteristics to meet different application requirements.

Enhanced-sensitive dual microfiber knot resonators based sensor with vernier effect for simultaneous measurement of refractive index and temperature

In this paper, an sensitive-enhanced dual microfiber knot resonators (DMKRs) sensor based on Vernier effect for simultaneous sensing of Refractive index (RI) and temperature has been proposed and demonstrated. Because the spectral characteristics of the two resonators satisfy the production conditions of Vernier effect, the enhanced RI sensitivity of − 12523 nm/ RIU can be obtained by demodulating the Vernier envelope, which is 40 times of that for single microfiber knot resonator (MKR) sensor. However, the crosstalk of saline water temperature is also amplified to 0.91998 nm/℃. Based on the different response sensitivities of Vernier dip, high frequency dip and the sensitivity matrices, we realized the simultaneous detection of RI and temperature. This sensor demonstrated here show the advantages of easy fabrication, low cost and provides an excellent detection option for high sensitivity and small size in RI detection.

Temperature Sensing Characteristics of an MKR in a Microfiber Taper Based on Mechanisms of Interference and Resonance with Vernier Effect

In this work, spectral characteristics and temperature sensing characteristics of an in-line microfiber Mach-Zehnder interferometer (MZI) with an embedded microfiber knot resonator (MKR) is investigated. The microfiber MZI with an MKR (MZIKR) has a dual-effect composite spectrum with comb-like spectrum of the MKR loaded on the dominant interference spectrum. Vernier effect is generated by the MKR via superposition of resonant spectra with three resonant modes circulating in the MKR. This is the first time that Vernier effect is generated in a single MKR, which has advantages of easy fabrication and compact structure compared to the traditional resonant structures with Vernier effect such as two cascaded MKRs. Fast Fourier transform (FFT) and FFT filter are used to analyze and extract the different components of the transmission spectrum of the MZIKR. Temperature sensing characteristics of the different components of the polydimethylsiloxane-coated MZIKR are studied, showing that the interference dip of the MZI spectrum and the envelope dip of the MKR Vernier spectrum achieve a high temperature sensitivity of about -1.8 nm/ °C and about -3.5 nm/ °C, respectively. The proposed sensor has the advantages of easy fabrication, robust structure, and high sensitivity in temperature measurement. The MZIKR with dual-effect composite spectrum may have potential in two-parameter measurement and narrow-band filtering.

Thermally tunable microfiber knot resonator with flexible graphene heater

Efficiently tuning the output intensity of an optical device is of vital importance for the establishment of optical interconnects and networks. Thermo-optical modulation is an easily implemented and convenient approach and has been widely employed in photonic devices. In this paper, we proposed a novel thermo-optical modulator based on a microfiber knot resonator (MKR) and graphene heater. Upon applying voltage to graphene, the resonant property of the MKR could be thermally tuned with a maximum phase shift of 2.1π. Intensity modulation shows a fast optical response time thanks to the high thermal conductivity of graphene and the thin microfiber diameter of the MKR.

A Highly-Sensitive Temperature-Sensor Based on a Microfiber Knot-Resonator Packaged in Polydimethylsiloxane

In this paper, a microfiber knot resonator (MKR) was encapsulated in polydimethylsiloxane (PDMS), and its capability to sense temperature was experimentally evaluated. A very high sensitivity of -12 nm/°C was recorded for the MKR device, with a microfiber diameter of 2μm and a ring diameter of 95 μm. However, light-loss was significant in the small MKR. We attribute this to the low ratio of ring-length to microfiber-diameter. A stable temperature-sensing performance and sensitivity of negative 8.48 nm/°C were obtained for the MKRs with a microfiber diameter of 3 μm and a ring diameter of 3 mm. A MKR device with a non-uniform microfiber (in diameter) was also fabricated and studied. This compact and miniature temperature-probe will be a promising candidate for wearable devices.

Broadband tunable single-longitudinal-mode erbium-doped fiber ring laser based on a microfiber knot resonator.

We propose and demonstrate a broadband tunable single-longitudinal-mode (SLM) erbium-doped fiber laser based on a microfiber knot resonator (MKR). The MKR is made from a double-ended fiber taper and employed for SLM filtering based on the Vernier effect. An unpumped erbium-doped fiber is used in the fiber laser cavity to suppress mode-hopping for a stabilized SLM laser operation. When combined with an optical fiber filter, widely tunable SLM laser generation is achieved. The proposed SLM laser can be tuned from 1545 to 1565 nm with a high side-mode suppression ratio of about 55 dB and a high stability.

Microfiber-Knot-Resonator-Induced Energy Transferring From Vector Noise-Like Pulse to Scalar Soliton Rains in an Erbium-Doped Fiber Laser

We report on scalar soliton rains (SRs) shedding from vector square-wave noise-like pulse (NLP) by introducing a microfiber-knot-resonator (MKR) into an erbium-doped fiber (EDF) laser. The EDF laser has an ultralong cavity of ∼3.07 km and a large anomalous cavity-dispersion, facilitating the formation of NLP. Once an MKR was further incorporated, comb-like filtering effect could be clearly observed on the emission spectrum. Apart from that, SRs shedding from the NLP were observed, which resulted from the MKR-induced energy transferring effect from the NLP to SRs. It was further found that the SRs existed only along a particular polarization direction, whereas the NLPs could be found in any pair of orthogonal polarization directions, despite some differences in pulse peak power. These suggest that the SRs possess scalar feature, whereas the co-circulating NLP is a package of vector pulses. Our results represent the first observation of MKR-induced pulse energy transferring effect and also the first observation of the co-existence of scalar and vector pulses in a single fiber system. Besides enriching the dynamics and interactions of optical pulses in fiber lasers, our results extend the applications of MKR to the area of pulse manipulations through spectral tailoring and local nonlinearity engineering.

Mid-infrared chalcogenide microfiber knot resonators

A novel type of mid-IR microresonator, the chalcogenide glass (ChG) microfiber knot resonator (MKR), is demonstrated, showing easy fabrication, fiber-compatible features, resonance tunability, and high robustness. ChG microfibers with typical diameters around 3 μm are taper-drawn from As 2 S 3 glass fibers and assembled into MKRs in liquid without surface damage. The measured Q factor of a typical 824 μm diameter ChG MKR is about 2.84 × 10 4 at the wavelength of 4469.14 nm. The free spectral range (FSR) of the MKR can be tuned from 2.0 nm (28.4 GHz) to 9.6 nm (135.9 GHz) by tightening the knot structure in liquid. Benefitting from the high thermal expansion coefficient of As 2 S 3 glass, the MKR exhibits a thermal tuning rate of 110 pm · ° C − 1 at the resonance peak. When embedded in polymethyl methacrylate (PMMA) film, a 551 μm diameter MKR retains a Q factor of 1.1 × 10 4 . The ChG MKRs demonstrated here are highly promising for resonator-based optical technologies and applications in the mid-IR spectral range.

All‐Optical Control of Microfiber Knot Resonator Based on 2D Ti2CTx MXene

AbstractAll‐optical devices based on 2D materials have attracted great attention for desirable applications, such as communications and signal processing. However, the previously reported all‐fiber all‐optical devices utilizing the interferometer structures greatly limit their practical applications due to the poor anti‐interference ability and slow modulation rate. In this work, an all‐optical device has been demonstrated based on a microfiber knot resonator (MKR) deposited with Ti2CTx MXene, exhibiting a large photothermal conversion efficiency and high thermal conductivity. Experimental results show that the proposed all‐optical device is capable of producing a high‐performance phase and intensity modulation with a high modulation efficiency, fast response time, and good stability. Therefore, it is anticipated that the MKR‐based all‐optical devices based on 2D materials can pave the way to a new design of high‐performance all‐optical devices and have great potentials in the future optical information processing.

Relative Humidity Sensors Based on Microfiber Knot Resonators-A Review.

Recent research and development progress of relative humidity sensors using microfiber knot resonators (MKRs) are reviewed by considering the physical parameters of the MKR and coating materials sensitive to improve the relative humidity sensitivity. The fabrication method of the MKR based on silica or polymer is briefly described. The many advantages of the MKR such as strong evanescent field, a high Q-factor, compact size, and high sensitivity can provide a great diversity of sensing applications. The relative humidity sensitivity of the MKR is enhanced by concerning the physical parameters of the MKR, including the waist or knot diameter, sensitive materials, and Vernier effect. Many techniques for depositing the sensitive materials on the MKR surface are discussed. The adsorption effects of water vapor molecules on variations in the resonant wavelength and the transmission output of the MKR are described regarding the materials sensitive to relative humidity. The sensing performance of the MKR-based relative humidity sensors is discussed, including sensitivity, resolution, and response time.

PDMS packaged microfiber knot resonator used for sensing longitudinal load change

In this paper, we proposed a sensitive load sensor probe based on microfiber resonator. The microfiber was prepared from the common single mode fiber by one-step heating-stretching method and used to fabricate a microfiber knot resonator (MKR) by micromanipulation technique. This MKR was packaged later by polydimethylsiloxane (PDMS) film layer in two glass slides. The load sensing performance have been explored and compared for the bare MKR structure and PDMS packaged MKR probe. The longitudinal load sensing characteristics were experimentally demonstrated with a small sensitivity of 6 p.m./N, due to the large Young's modulus and low elasto–optical effect of silica materials. In order to increase the longitudinal load sensitivity and stability of bare MKR, we chose PDMS to encapsulate MKR due to its small Young's modulus and large Poisson's ratio. The strain sensing performance of both a bare and PDMS packaged silica MKR were experimentally demonstrated and compared. The experiment results revealed a sensitivity of 94.5 p.m./N. The simple structure, low loss and easily fabrication process pave its way to a miniature strain sensor chip.