Highly sensitive and stable probe refractometer based on configurable plasmonic resonance with nano-modified fiber core

A dispersion model is developed to provide a generic tool for configuring plasmonic resonance spectral characteristics.The customized design of the resonance curve aiming at specific detection requirements can be achieved.According to the model,a probe-type nano-modified fiber optic configurable plasmonic resonance(NMF-CPR)sensor with tip hot spot enhancement is demonstrated for the measurement of the refractive index in the range of 1.3332-1.3432 corresponding to the low-concentration biomarker solution.The new-type sensing structure avoids excessive broadening and redshift of the resonance dip,which provides more possibilities for the surface modification of other functional nanomaterials.The tip hot spots in nanogaps between the Au layer and Au nanostars(AuNSs),the tip electric field enhancement of AuNSs,and the high carrier mobility of the WSe_(2)layer synergistically and significantly enhance the sensitivity of the sensor.Ex-perimental results show that the sensitivity and the figure of merit of the tip hot spot enhanced fiber NMF-CPR sensor can achieve up to 2995.70 nm/RIU and 25.04 RIU^(−1),respectively,which are 1.68 times and 1.29 times higher than those of the conventional fiber plasmonic resonance sensor.The results achieve good agreements with numerical simulations,demonstrate a better level compared to similar reported studies,and verify the correctness of the dispersion model.The detection resolution of the sensor reaches up to 2.00×10^(−5)RIU,which is obviously higher than that of the conventional side-polished fiber plasmonic resonance sensor.This indicates a high detection accuracy of the sensor.The dense Au layer effectively prevents the intermediate nanomaterials from shedding and chemical degradation,which enables the sensor with high stability.Furthermore,the terminal reflective sensing structure can be used as a practical probe and can allow a more convenient operation.

Two-dimensional distributed strain sensing with an Archimedean spiral arrangement in optical frequency domain reflectometry

We demonstrate a distributed two-dimensional(2D)strain-sensing system in optical frequency domain reflectometry(OFDR)with an Archimedean spiral arrangement of the sensing fiber.The Archimedean spiral describes a simple relationship between the radial radius and polar angle,such that each circle(the polar angle from0 to 2π)can sense the 2D strain in all directions.The strain between two adjacent circles can also be easily obtained because an Archimedean spiral facilitates sensing of every angle covering the full 2D range.Based on the mathematical relation of Archimedean spirals,we deduce the relationship between the one-dimensional position of the sensing fiber and 2D distribution in polar coordinates.The results of the experiment show that an Archimedean spiral arrangement system can achieve 2D strain sensing with different strain load angles.

Side-polished SMS based RI sensor employing macro-bending perfluorinated POF

A refractive index(RI)sensor based on perfluorinated plastic optical fiber(PF-POF)is introduced in this paper.The PF-POF as multi-mode fiber was side-polished(SP)to form a macro-bending single-mode-multimode-single-mode(SMS)structure.Both ends of the sensor were closely connected to single-mode quartz optical fiber(SMF).The spectral char-acteristics of the sensor are measured,analyzed and discussed.The results show that when the length of PF-POF is 8 cm,the macro-bending radius is 3 cm,and the SP-depth is 20μm.The intensity sensitivity reaches−219.504 dBm/RIU in the range of RI=1.330~1.356.A reference is provided for the application of PF-POF in RI sensor in the future.The sensor is featured with low-cost,good flexibility and high efficiency.

Solution processable transition metal dichalcogenides-based hybrids for photodetection

Transition metal dichalcogenides(TMDs), as one of the most promising two-dimensional(2D) materials, have attracted considerable attention for use in photodetection applications over the past few years due to their distinct properties, such as atomic-scale thickness, tunable direct bandgaps, and decent carrier mobilities at room temperature. Compared with pure 2D TMDs, the construction of hybrids consisting of TMDs and other low-dimensional materials can further improve the performance of photodetectors including their spectral range, responsivity and detectivity, which significantly boosts interest in the development of TMDs-based photodetectors. On the other hand, solution-phase synthesis methods provide a facile strategy for the scalable production of TMD hybrids, opening an exciting avenue to develop low-cost devices. In this review, we summarize the material synthesis, characterizations, and photodetection applications of the solution processable TMDs-based hybrids, as well as provide insights into their prospects.

Suspended nanomembrane silicon photonic integrated circuits

Leveraging the low linear and nonlinear absorption loss of silicon at mid-infrared(mid-IR)wavelengths,silicon photonic integrated circuits(PICs)have attracted significant attention for mid-IR applications including optical sensing,spectroscopy,and nonlinear optics.However,mid-IR silicon PICs typically show moderate performance compared to state-of-the-art silicon photonic devices operating in the telecommunication band.Here,we proposed and demonstrated suspended nanomembrane silicon(SNS)PICs with light-guiding within deep-subwavelength waveguide thickness for operation in the short-wavelength mid-IR region.We demonstrated key building components,namely,grating couplers,waveguide arrays,micro-resonators,etc.,which exhibit excellent performances in bandwidths,back reflections,quality factors,and fabrication tolerance.Moreover,the results show that the proposed SNS PICs have high compatibility with the multi-project wafer foundry services.Our study provides an unprecedented platform for mid-IR integrated photonics and applications.

Achievable information rate optimization in C‑band optical fber communication system

Optical fber communication networks play an important role in the global telecommunication network.However,nonlinear efects in the optical fber and transceiver noise greatly limit the performance of fber communication systems.In this paper,the product of mutual information(MI)and communication bandwidth is used as the metric of the achievable information rate(AIR).The MI loss caused by the transceiver is also considered in this work,and the bit-wise MI,generalized mutual information(GMI),is used to calculate the AIR.This loss is more signifcant in the use of higher-order modulation formats.The AIR analysis is carried out in the QPSK,16QAM,64QAM and 256QAM modulation formats for the communication systems with diferent communication bandwidths and transmission distances based on the enhanced Gaussian noise(EGN)model.The paper provides suggestions for the selection of the optimal modulation format in diferent transmission scenarios.

Blazed subwavelength grating coupler

Short-wavelength mid-infrared(2–2.5 μm wave band) silicon photonics has been a growing area to boost the applications of integrated optoelectronics in free-space optical communications, laser ranging, and biochemical sensing. In this spectral region, multi-project wafer foundry services developed for the telecommunication band are easily adaptable with the low intrinsic optical absorption from silicon and silicon dioxide materials. However,light coupling techniques at 2–2.5 μm wavelengths, namely, grating couplers, still suffer from low efficiencies,mainly due to the moderated directionality and poor diffraction-field tailoring capability. Here, we demonstrate a foundry-processed blazed subwavelength coupler for high-efficiency, wide-bandwidth, and large-tolerance light coupling. We subtly design multi-step-etched hybrid subwavelength grating structures to significantly improve directionality, as well as an apodized structure to tailor the coupling strength for improving the optical mode overlap and backreflection. Experimental results show that the grating coupler has a recorded coupling efficiency of-4.53 dB at a wavelength of 2336 nm with a 3-dB bandwidth of ~107 nm. The study opens an avenue to developing state-of-the-art light coupling techniques for short-wavelength mid-infrared silicon photonics.

All-silicon dual-cavity fiber-optic pressure sensor with ultralow pressure-temperature cross-sensitivity and wide working temperature range

Pressure-temperature cross-sensitivity and its accompanying temperature-related stability is a nerve-wracking obstruction for pressure sensor performance in a wide temperature range.To solve this problem,we propose a novel(to the best of our knowledge)all-silicon dual-cavity optical Fabry–Perot interferometer(FPI)pressure sensor.The all-silicon structure has high intrinsic reflectivity and is able to eliminate the influence of thermal-expansion-mismatch-induced stress and chemical-reaction-induced gas generation,and therefore,in essence,enhances measurement accuracy.From the experiment results,the pressure-temperature cross-sensitivity is reduced to be∼5.96 Pa/℃,which presents the lowest pressure-temperature cross-sensitivity among the FPI pressure sensors with the capability of surviving high temperatures up to 700℃ thereby opening the way for high-precision pressure monitoring in various harsh and remote environments.

Phase demodulation method based on a dual-identical-chirped-pulse and weak fiber Bragg gratings for quasi-distributed acoustic sensing

A phase demodulation method for quasi-distributed acoustic sensing(DAS)systems based on a dual-identicalchirped-pulse and weak fiber Bragg gratings(WFBGs)is proposed.Compared to the use of Rayleigh backscattering light in optical fibers,the implementation of WFBGs can contribute to obtaining an optical signal with a higher signal-to-noise ratio(SNR).The dual-identical-chirped-pulse is generated by a time-delay fiber,and the sinusoidal carrier is generated by the interference between the two chirped pulses reflected by adjacent WFBGs.The phase of the sinusoidal carrier represents the dynamic strain change posed on the sensing fiber.Discrete Fourier transform is used to directly retrieve the phase information.The performance of the phase demodulation from interference signals under different sinusoidal carrier frequencies and SNRs is numerically investigated.The piezoelectric transducer is employed to emulate the sound in the experiment to verify the effectiveness of our method.It is shown that the dynamic strain can be well reconstructed at the end of a 101.64 km fiber when the signal SNR is down to 3.234 d B.Our proposed method enables the application of the long-distance sensing in quasi-DAS systems.

Performance improvement approaches for optical fiber SPR sensors and their sensing applications

Optical fiber surface plasmon resonance(SPR) sensors point toward promising application potential in the fields of biomarker detection,food allergen screening,and environmental monitoring due to their unique advantages.This review outlines approaches in improving the fiber SPR sensing performance,e.g.,sensitivity,detection accuracy,reliability,cross-sensitivity,selectivity,convenience and efficiency,and corresponding sensing applications.The sensing principles of SPR sensors,especially the performance indicators and their influencing factors,have been introduced.Current technologies for improving the fiber SPR performance and their application scenarios are then reviewed from the aspects of fiber substrate,intrinsic layer(metal layer),and surface nanomaterial modification.Reasonable design of the substrate can strengthen the evanescent electromagnetic field and realize the multi-parameter sensing,and can introduce the in situ sensing self-compensation,which allows corrections for errors induced by temperature fluctuation,non-specific binding,and external disturbances.The change of the intrinsic layer can adjust the column number,the penetration depth,and the propagation distance of surface plasmon polaritons.This can thereby promote the capability of sensors to detect the large-size analytes and can reduce the full width at half-maximum of SPR curves.The modification of various-dimensionality nanomaterials on the sensor surfaces can heighten the overlap integral of the electromagnetic field intensity in the analyte region and can strengthen interactions between plasmons and excitons as well as interactions between analyte molecules and metal surfaces.Moreover,future directions of fiber SPR sensors are prospected based on the important and challenging problems in the development of fiber SPR sensors.

Multi-channel polarized low-coherence interference synchronous demodulation system based on a matrix charge-coupled device

A multi-channel synchronous demodulation system of a polarized low-coherence interferometer(PLCI) based on a matrix charge-coupled-device(CCD) is proposed and demonstrated. By using special designs, the system allows the signals from different channels to be received and demodulated synchronously. Multichannel air pressure experiments were implemented to verify the effectiveness of the proposed system. The experiment results showed that the Fabry–Perot(F–P) sensors could be demodulated synchronously with a high tolerance for light sources and sensors, which indicated that any sensor and light source that can be demodulated by PLCI were allowed to be employed, leading to a wide application in the field of multichannel synchronous measurement.

Fiber loop ring-down cavity integrated U-bent single-mode-fiber for magnetic field sensing

A novel magnetic field sensing system based on the fiber loop ring-down technique is proposed in this paper. In the fiber loop, a U-bent single-mode-fiber structure coated with magnetic fluid(MF) serves as the sensing head, and an erbium-doped fiber amplifier(EDFA) is introduced to compensate for the intrinsic loss of the cavity. The ring-down time of the system varies with the change of applied magnetic field due to the tunable absorption coefficient and refractive index of the MF. Therefore, measurement of the magnetic field can be realized by monitoring the ringdown time. The experimental results show that the performance of the system is extremely dependent on the interrogation wavelength, because both the gain of the EDFA and the loss of the sensing head are wavelength dependent.We found that at the optimal wavelength, the ratio of the gain to loss attained its maximum. The sensing system was experimentally demonstrated and a sensitivity of-0.5951 μs∕Oe was achieved.

Optimal design of Er/Yb co-doped fiber amplifiers with an Yb-band fiber Bragg grating

In this paper, Er/Yb co-doped fiber amplifiers(EYDFAs) with an Yb-band fiber Bragg grating(FBG) at the pump end to improve the performance of the amplifier is systematically studied. The influence of the reflectivity and center wavelength of the FBG along with the gain-fiber length on the performance of an EYDFA are numerically analyzed. The results show that the wavelength of the FBG has critical influence on the efficiency of the EYDFA,whereas the requirement to its reflectivity is relaxed. It is an effective and promising way to improve the efficiency of a high-power pumped EYDFA by introducing a suitable Yb-band FBG at the pump end. Based on the analysis of the underlying principles, suggestions for the practical design and possible further improvement strategies are also proposed.

Self-copy-shift-based differential phase extracting method for fiber distributed acoustic sensing

A differential phase extracting method based on self-copy-shift for distributed acoustic sensing is proposed.Heterodyne and optical hybrids are used to realize high signal-to-noise ratio in-phase and quadrature-phase(IQ)signal measurement.The measured signals are self-copied and shifted for certain data points,and then they are digitally mixed with the original signals to construct the differential phase.The four produced signals are then combined to carry out IQ demodulation.An experiment with strain having an amplitude modulation waveform is carried out.The results showed that waveform information can be recovered well,and the signal-tonoise ratio achieves 32.8 dB.

Investigation on temperature characteristics of weak fiber Bragg gratings in a wide range

A weak fiber Bragg grating(WFBG) is an ideal quasi-distributed optical fiber sensor. Special attention should be paid to the spectrum and sensing performance of the WFBG at extreme temperatures due to its poor reflection intensity. In this Letter, the temperature characteristics of the WFBG from-252.75°C to 200.94°C are experimentally investigated. Five WFBGs with reflectivity from ~0.25% to ~10% are used in the experiments. The reflectivity variations and wavelength shifts at different temperatures are studied. Experimental results show that the WFBG can survive and work at extreme temperatures, but the performance is affected significantly.The reflectivity is affected significantly by both cryogenic temperature and high temperature. The temperature responses of Bragg wavelengths in the wide temperature range are also obtained.

Recent Progress of Fiber Sensing Technologies in Tianjin University

The up to date progress of fiber sensing technologies in Tianjin University are proposed in this paper.Fiber-optic temperature sensor based on the interference of selective higher-order modes in circular optical fiber is developed.Parallel demodulation for extrinsic Fabry-Perot interferometer(EFPI)and fiber Bragg grating(FBG)sensors is realized based on white light interference.Gas concentration detection is realized based on intra-cavity fiber laser spectroscopy.Polarization maintaining fiber(PMF)is used for distributed position or displacement sensing.Based on the before work and results,we gained National Basic Research Program of China on optical fiber sensing technology and will develop further investigation in this area.

Integrated optoelectronics with two-dimensional materials

As we enter the post-Moore era,heterogeneous optoelectronic integrated circuits(OEICs)are attracting significant attention as an alternative approach to scaling to smaller-sized transistors.Two-dimensional(2D)materials,offering a range of intriguing optoelectronic properties as semiconductors,semimetals,and insulators,provide great potential for developing nextgeneration heterogeneous OEICs.For instance,Fermi levels of 2D materials can be tuned by applying electrical voltages,while their atomically thin geometries are inherently suited for the fabrication of planar devices without suffering from lattice mismatch.Since the first graphene-on-silicon OEICs were demonstrated in 2011,2D-material heterogeneous OEICs have significantly progressed.To date,researchers have a better understanding of the importance of interface states on the optical properties of chip-integrated 2D materials.Moreover,there has been impressive progress towards the use of 2D materials for waveguide-integrated lasers,modulators,and photodetectors.In this review,we summarize the history,status,and trend of integrated optoelectronics with 2D materials.