Functionalization of Fiber Devices:Materials,Preparations and Applications

Conventional electronic devices with bulky and rigid features cannot fully meet the requirements of fexibility and wearability in wearable applications.Fiber-shaped electronic devices have been intensively pursued in the past decade attributed to their excellent fexibility,weavability and wearability.The innovation of novel functions has been widely recognized as an emerging direction of fber-shaped electronic devices,pursuing a better adaptability and longer lifetime in practical applications.In this Review,we summarize the recent advances of functional fber devices,focusing on the preparation of functional fber electrodes and electrolytes,as well as the formed interfaces.Fiber devices with a variety of novel functions are systematically introduced,including but not limited to stretchability,healability,shape memory and electrochromism.The remaining challenges and opportunities are also discussed to propose future directions for functionalization of fber electronics.

Optical Fiber Devices in WDM Networks

Crystal optics and fiber grating technology are two of the most important optical fiber device technologies. In this paper, we report several new devices developed in Accelink for WDM networks application.

Integrated liquid crystal photonic bandgap fiber devices

Liquid crystal photonic bandgap （LCPBG） fibers provide a versatile and robust platform for designing optical fiber devices, which are highly tunable and exhibit novel optical properties for manipulation of guided light. We review the research progress on design, fabrication and development of integrated LCPBG fiber devices.

1.55 μm Wavelength Operation of E_r^(3+) -Doped Optical Fiber Bistability

An all optical all fiber optical bistability operation has been realized in an all fiber cavity consisted with Er doped fiber and optical fiber loop mirrors. The experimental bistability threshold is consistent with the theory.

Hybrid Fiber Optical Bistability and Optical Signal Processing

A hybrid fiber optical bistable device with electrical feedback has been proposed and analyzed.Bistability operation and some applications for optical signal processing have been realized experimentally .

Multi-direction bending sensing based on spot pattern demodulation of dual-hole fiber

A multi-direction bending sensor based on spot pattern demodulation of a dual-hole fiber(DHF)is proposed.By using the interference and scattering in a DHF,the related multidirectional variations can be captured by the optical field.Furthermore,the multi-directional bending characteristics of the fiber are quantitatively described by the pattern of the output light spot,achieving multidirectional bending sensing.In addition,considering the subtle changes in the deformation patterns over time,a convolutional neural network(CNN)model based on deep learning is introduced for accurate recognition and prediction of the bending angle.The experimental results show that the sensor can perceive different bending angles in four directions.These outstanding results indicate that the multi-directional bending sensor based on dual-hole interference pattern decoding has potential applications in multi-directional quantitative sensing and artificial intelligence perception.

Few-layer MoS2-deposited microfiber as highly nonlinear photonic device for pulse shaping in a fiber laser [Invited]

Two-dimensional（2D） materials have emerged as attractive mediums for fabricating versatile optoelectronic devices. Recently, few-layer molybdenum disulfide（MoS2）, as a shining 2D material, has been discovered to possess both the saturable absorption effect and large nonlinear refractive index. Herein, taking advantage of the unique nonlinear optical properties of MoS2, we fabricated a highly nonlinear saturable absorption photonic device by depositing the few-layer MoS2 onto the microfiber. With the proposed MoS2 photonic device, apart from the conventional soliton patterns, the mode-locked pulses could be shaped into some new soliton patterns, namely,multiple soliton molecules, localized chaotic multipulses, and double-scale soliton clusters. Our findings indicate that the few-layer MoS2-deposited microfiber could operate as a promising highlynonlinear photonic device for the related nonlinear optics applications.

Coupled Mode Characteristics From the Perturbation of 3D Printed Long-Period Fiber Grating Devices

Characteristics of electric field from a coupled mode inside an optical fiber under perturbation by three-dimensional(3D)printed long-period fiber grating(LPFG)device have been observed in this work by the experiment and simulation.The various periodic index differences referring to the weights of perturbation by 3D printed LPFG device are applied on the single-mode fiber.The experimental results show that the resonant wavelength shift is a linear function of the grating period with the maximum coefficient of determination R2 of 0.9995.Some of resonant wavelengths are chosen to run simulations to investigate the electric field distribution.The scattering direction of the electric field states the magnitude of leaking optical power when the light transmits through the grating region applied to the single-mode fiber.Both the experimental and simulation results demonstrate that our proposed scheme can usefully be applied to selective tunable filters,intruder sensors,etc.

Coexistence of bound soliton and harmonic mode-locking soliton in an ultrafast fiber laser based on MoS2-deposited microfiber photonic device

As the typical material of two-dimensional transition metal dichalcogenides（TMDs）, few-layered MoS2 possesses broadband saturable absorption and a large nonlinear refractive index, which could be regarded as a promising candidate for dual-function photonic device fabrication. In this work, the coexistence of a bound soliton and harmonic mode-locking soliton was demonstrated in an ultrafast fiber laser based on a MoS2-deposited microfiber photonic device. Through a band-pass filter, each multi-soliton state was investigated separately. The bound soliton has periodic spectral modulation of 1.55 nm with a corresponding pulse separation of 5.16 ps.The harmonic mode-locking soliton has the repetition rate of 479 MHz, corresponding to the 65th harmonic of the fundamental repetition rate. The results indicated that there exist more possibilities of different multi-soliton composites, which would enhance our understanding of multi-soliton dynamics.

All-fiber ultrafast laser generating gigahertz-rate pulses based on a hybrid plasmonic microfiber resonator

Ultrafast lasers generating high-repetition-rate ultrashort pulses through various mode-locking methods can benefit many important applications,including communications,materials processing,astronomical observation,etc.For decades,mode-locking based on dissipative four-wave-mixing(DFWM)has been fundamental in producing pulses with repetition rates on the order of gigahertz(GHz),where multiwavelength comb filters and long nonlinear components are elemental.Recently,this method has been improved using filter-driven DFWM,which exploits both the filtering and nonlinear features of silica microring resonators.However,the fabrication complexity and coupling loss between waveguides and fibers are problematic.We demonstrate a tens-to hundreds-of gigahertz-stable pulsed all-fiber laser based on a hybrid plasmonic microfiber knot resonator device.Unlike previously reported pulse generation mechanisms,the operation utilizes the nonlinear-polarization-rotation(NPR)effect introduced by the polarization-dependent feature of the device to increase intracavity power for boosting DFWM mode-locking,which we term NPRstimulated DFWM.The easily fabricated versatile device acts as a polarizer,comb filter,and nonlinear component simultaneously,thereby introducing an application of microfiber resonator devices in ultrafast and nonlinear photonics.We believe that our work underpins a significant improvement in achieving practical low-cost ultrafast light sources.

Fiber gas sensor-integrated smart face mask for roomtemperature distinguishing of target gases

Wearable gas sensors that are lightweight, portable, and inexpensive have great potential application in the real-time detection of human health and environmental monitoring. In this work, we fabricated flexible fiber gas sensors with single-walled carbon nanotube （SWCNT）, multi-walled carbon nanotube （MWCNT）, and ZnO quantum dot-decorated SWCNT （SWCNTs@ZnO） sensing elements. These flexible fiber gas sensors could be operated at room temperature to detect target gases with good sensitivity and recovery time. They also exhibited superior long-term stability, as well as good device mechanical bending ability and robustness. Integrating these flexible gas sensors into face masks, the fabricated wearable smart face masks could be used to selectively detect CaHsOH, HCHO, and NH3 by reading the corresponding LEDs with different colors. Such face masks have great potential application in the Internet of Things and wearable electronics.

Harmonic mode-locked fiber laser based on microfiber-assisted nonlinear multimode interference

A novel harmonic mode-locked fiber laser based on nonlinear multimode interference(NL-MMI) in a microfiber-assisted ultrafast optical switch is proposed in this Letter.The microfiber-assisted ultrafast optical switch can be obtained by tapering the splicing point of the graded-index multimode fiber(GIMF) and single-mode fiber,which not only helps to shorten the self-imaging period in GIMF to relax the strict requirement of NL-MMI on the length of multimode fiber,but also improves the harmonic order.In the experiment,with the waist diameter of ~15 μm,the repetition rates of the fiber laser can be stably locked at 285 MHz,corresponding to the 16 th-order harmonic mode-locking,with the pulse duration of 1.52 ps.Our results provide novel insight into the design of a high-repetition-rate laser and the application of microfibers in the modelocking device.

Lab-on-Fiber Technology： a New Avenue for Optical Nanosensors

The ＂lab-on-fiber＂ concept envisions novel and highly functionalized technological platforms completely integrated in a single optical fiber that would allow the development of advanced devices, components and sub-systems to be incorporated in modem optical systems for communication and sensing applications. The realization of integrated optical fiber devices requires that several structures and materials at nano- and micro-scale are constructed, embedded and connected all together to provide the necessary physical connections and light-matter interactions. This paper reviews the strategies, the main achievements and related devices in the lab-on-fiber roadmap discussing perspectives and challenges that lie ahead.

Injectable Fiber Electronics for Tumor Treatment

Electrochemical therapy emerged as a low-cost and efective method for tumor ablation.However,it has challenges such as the production of toxic byproducts and the use of rigid electrodes that damage soft tissues.Here,we report a new injectable and tissue-compatible fber therapeutic electronics for safe and efcient tumor treatment.The design of aligned carbon nanotube(CNT)fber as electrodes endowed the device with high softness and enabled mini-invasive implantation through injection.Under a mild voltage(1.2 V),the fber device released hydroxyl ions to alter the local chemical environment of the tissues without additional toxic products/gases,leading to immediate death of tumor cells.The fexible fber device could form stable interface with tissues and showed good biocompatibility after implantation for 30 days.The in vitro experimental results showed the fber device could efciently kill 90.9%of QGY-7703 cancer cells after a single treatment in a few minutes.The tumor-bearing animal models proved that the fber therapeutic device could efectively inhibit the growth of tumor tissues,indicating it is a safe,efective,controllable and low-cost method for tumor therapy.

Two-Dimensional Tunable and Temperature-Insensitive Lyot Filter for FM-to-AM Compensation

Utilizing polarization maintaining photonic crystal fiber(PM-PCF)with the low temperature coefficient of birefringence,a two-dimensional tunable and temperature-insensitive Lyot filter aiming to compensate the frequency modulation to amplitude modulation(FM-to-AM)conversion in high power laser facility is demonstrated.The Jones matrix is applied to analyze the relationship between optical characteristics of the filter and physical parameters(including amplitude ratio,phase delay,and susceptibility of the birefringence to temperature)of the polarization optical field.Both the transmission peak wavelength and extinction ratio of the spectral transmission are able to be changed simultaneously,hence,it shows more efficient FM-to-AM compensation ability.Besides,the transmission peak shift is about 18pm/°C with the PM-PCF configuration,which is about two orders of magnitude less than the normal polarization maintaining fiber(PMF)configuration.The demonstrated filter presents a practical application potential in large scale laser driven facility.

Sharp tunable and additional noise-free optical filter based on Brillouin losses

In this paper, we propose an additional noise-free, independent center frequency and bandwidth tunable optical filter based on stimulated Brillouin scattering(SBS) losses. By suppressing the out-of-band signal with two broadened symmetric SBS losses, tunable pass bandwidths from 500 MHz to 9.5 GHz and the independent center frequency tunability are demonstrated. Considering the limited SBS interaction in the center frequency range,a flat-top response with minimum 0.3 dB ripple is achieved. Assisted by the extra suppression from polarization pulling, a maximum selectivity of 20 dB and an ultrahigh 250 dB∕GHz roll-off are reached. A gain-based SBS filter adds noise to the filtered signal. However, for our proposed filter setup, no additional noise is detected due to the transparency in the passband. Considering the wide independent bandwidth and center frequency tunability, flat-top response, and low-noise characteristic, our proposed filter can be perfectly used as a supplement of most commercialized conventional tunable optical single bandpass filters, whose minimum bandwidth is limited by 10 GHz.