All-fiber Devices Research Articles

Isotropically Polarized Bipiezoelectric Polyacrylonitrile-Poly(vinylidene Fluoride) Advanced Triboelectric Nanogenerator for Operation in High-Humidity Environments.

Conventional hybrid piezo-triboelectric nanogenerators (PTNGs) have potential applications as energy supply devices for microelectronic devices, but their low power density and unstable performance under high-humidity conditions are challenges that need to be solved. Here, we report a novel flexible hybrid bifiezo-triboelectric nanogenerator (Bi-PTNG) based on isotropic polarization design of piezoelectric PVDF and PAN nanofiber membranes, which greatly improves power density of devices and performances in high-humidity conditions. The performance enhancement mechanism of the Bi-PTNG was investigated by model analysis, experimental measurements, and simulations. The results showed that the power density output of Bi-PTNG increased by approximately 88% compared to that of a depolarized PAN/PVDF-based triboelectric nanogenerator (TENG). The application studies demonstrated that a 2 × 2 cm2 Bi-PTNG can be directly used to run more than 120 commercial LEDs, and this highly flexible and breathable all-fiber device can be integrated into clothing or insoles to monitor human movement in high-humidity conditions. This work not only provides an effective strategy for enhancing the power output of TENGs and advancing their practical applications but also offers robust guidance for the material selection and optimization of the polarization direction in such nanogenerators.

All-fiber fast acousto-optic temporal control of tunable optical pulses

We demonstrate a new all-fiber electrically tunable modulation method which significantly reduces the response time of a Bragg grating acousto-optic modulator. A 4 cm long device is fabricated with a 1 cm grating inscribed in a suspended core fiber. An acoustic pulse train is switched out of phase along the fiber, damping unwanted natural resonant vibrations inside the grating. The device rise time is decreased from 56 to 9 µs by tuning the duty cycle of the driven electrical signal, contributing to achieve the shortest switching time of 15.6 µs. This tunable temporal response reveals unique features to change the profile of optical pulses. High pulse modulation depths are achieved employing a compact acousto-optic modulator, pointing to fast switching of all-fiber photonic devices.

Low-loss C-band all-fiber FIFO device by novel bridge fiber

Multi-core fibers (MCF) technology is the feasible path to extend the capacity of optical fiber communication systems. However, there is a lack of low-loss and low-crosstalk multi-core fan-in and fan-out (FIFO) devices for MCF communication in the C-band. In this paper, we proposed all-fiber FIFO devices with seven trench-assisted bridge fibers (TABFs). The special structure of the TABFs could facilitate the matching of single-core fiber with MCF during the tapering progress. By using the TABFs, the average taper loss was less than 0.06 dB. The novel method can reduce the insertion loss of FIFO devices. The experiments indicated that the fabricated FIFO devices exhibited lower than 0.50 dB insertion loss and less than −55.2 dB crosstalk in the C-band. This work provides novel TABFs and an efficient way to fabricate low-loss low-crosstalk FIFO devices for MCF communication systems.

Mode-locked thulium-doped fiber laser using a stretched few-mode fiber as a saturable absorber

In this work, an all-fiber saturable absorber (SA) based on nonlinear multimode interference in a short few-mode fiber (FMF) was proposed. Saturable absorption in this all-fiber device was demonstrated with an absorption modulation depth and a saturation fluence of 14.3% and 55.6 μJ cm−2, respectively. A stable mode-locking operation was observed in a thulium-doped passively mode-locked fiber laser using the FMF-based FMF SA. Ultrafast pulses were generated at 1911 nm with a pulse width of 1.96 ps and a 15.69 MHz repetition rate, respectively. The output average power was 2.8 mW, corresponding to a pulse energy of 178 pJ, which was significantly improved compared to graded-index multimode fiber-based SA. The experimental results demonstrate that FMF SA has great potential in eye-safe ultrafast photonics.

All-fiber broadband spectral acousto-optic modulation of a tubular-lattice hollow-core optical fiber.

We demonstrate a broadband acousto-optic notch filter based on a tubular-lattice hollow-core fiber for the first time to our knowledge. The guided optical modes are modulated by acoustically induced dynamic long-period gratings along the fiber. The device is fabricated employing a short interaction length (7.7 cm) and low drive voltages (10 V). Modulated spectral bands with 20 nm half-width and maximum depths greater than 60% are achieved. The resonant notch wavelength is tuned from 743 to 1355 nm (612 nm span) by changing the frequency of the electrical signal. The results indicate a broader tuning range compared to previous studies using standard and hollow-core fibers. It further reveals unique properties for reconfigurable spectral filters and fiber lasers, pointing to the fast switching and highly efficient modulation of all-fiber photonic devices.

Temperature insensitivity of an all-fiber quarter-wave plate device fabricated with a high-birefringence fiber

Temperature insensitivity of an all-fiber quarter-wave plate device fabricated with a high-birefringence fiber

An All-Fiber Multimode Interference Device for Power Splitting in Few Mode Fiber Networks

An All-Fiber Multimode Interference Device for Power Splitting in Few Mode Fiber Networks

Sub-wavelength focused light and optical trapping application based on two-mode interference from an optical micro-/nanofiber

The ability to focus light on a subwavelength scale is essential in modern photonics. Optical microfiber-based sub-wavelength focusing will allow a miniaturized, flexible and versatile tool for many applications such as biomedical imaging and optomechanics. For a separate mode exited from an optical micro-/nanofiber endface, the photons will experience significant diffraction into the free space. This situation can be changed by incorporating two-mode interference along with the specific spatial distributions of both <i> <b>E</b> </i>-field amplitude and phase. Herein we report a novel approach to realizing sub-wavelength focusing based on the two-mode interference exited from an optical microfiber endface. By utilizing specific distributions of <b><i>E</i></b> -field amplitude and phase of two interacting optical modes, interference field patterns with a single focus (e.g., via a two-mode set of HE<sub>11</sub> and HE<sub>12</sub>) or multiple foci (e.g., via a two-mode set of HE<sub>11</sub> and HE<sub>31</sub>) can be obtained. Then, it is proved that the constructed foci will readily facilitate and selective trapping of nanoparticles. Circular polarization of optical mode is utilized in order to bring in angular symmetry of sub-wavelength focusing patterns compared with linear polarized optical modes. Our simulation results show that the smallest focal spot produced from the EH<sub>11</sub> and HE<sub>12</sub> mode interference has a full width at half-maximum (FWHM) of ~ 348 nm (i.e. 0.65<i>λ</i>). Such a subwavelength focusing field is applied to the optical trapping of an 85 nm-diameter polystyrene nanosphere. Further calculation reveals that the stable trapping can be fulfilled with axial and transverse trap stiffness of 11.48 pN/(μm·W) and 64.98 pN/(μm·W), as well as axial and transverse potential well of 101 <i>k</i><sub>B</sub>T/W and 641 <i>k</i><sub>B</sub>T/W via two-mode interference of HE<sub>11</sub> and HE<sub>12</sub>. These values demonstrate the great improvement over conventional tapered fibers. Further investigations show that different foci, via a two-mode set of HE<sub>11</sub> and HE<sub>31</sub>, exhibit unlike trap stiffness and potential wells, justifying the potential for nanoparticle size sorting. Based on the flexible all-fiber device, this subwavelength focusing strategy by two-mode interference may find promising applications in optical manipulation, superresolution optical imaging, data storage and nanolithography.

All-fiber function devices for twisted lights.

Lights carrying orbital angular momentum (OAM), also called twisted lights, have been applied in fields of optical manipulation, imaging, quantum communication, and mode-division-multiplexing (MDM) optical communication systems. Traditional approaches for manipulating twisted lights carrying OAM in free space paths such as Q-plates, spiral phase plates (SPPs), and spatial light modulators (SLMs) that are usually affected by diffraction effect and imperfect alignment between different optical components, limiting the practical applications of twisted lights. Here we design, fabricated, and package all-fiber function devices for twisted light carrying OAM such as all-fiber broadband OAM generator, all-fiber OAM (de)multiplexer, all-fiber OAM & WDM coupler, and all-fiber OAM 1 × 2 coupler. Base on coupled mode theory and phase-matching condition, twisted light can be generated and detected by pre-tapered single mode fiber (SMF) fusing with multi-mode fiber (MMF). The results show that the proposed all-fiber function devices for twist light have large working broadband (at least C band), high purity (above 95%), and low insert loss (less than 3 dB). The proposed devices will open a reliable way for twisted light applied in optical fiber communications and optical interconnections.

Efficient control of light propagation assisted by photothermal effect in a graphene-integrated all-fiber device

Graphene has arisen as an efficient photothermal (PT) nanomaterial owing to the strong light-matter interaction, ultrafast and nonradiative annihilation of the photoexcited carriers, and high thermal conductivity. Combined with the unique optical properties such as universal absorption coefficient at broadband wavelengths, the PT effect in graphene can be synergistically utilized for all-optical control of light. Here, we report an efficient transmission control of propagating light in graphene-covered side-polished fiber through the PT effect of graphene. When the local heat was generated via PT effect in graphene, a significant change in optical transmission was observed through two different mechanisms. The first one was implemented by the absorption change at the graphene layer via the asymmetrical reshaping of the mode-field distribution, resulting in the optical transmission change of up to 25 dB. The other mechanism was realized by the guiding property switching from the radiation mode to the guided mode of the light, resulting in the all-optical transmission control of over 56 dB at 1550 nm. The proposed method proves that the PT effect assists the broadband and efficient all-optical control with great versatility in graphene-integrated all-fiber devices.

All-fiber tunable devices based on high-index photonic crystal fibers filled with liquid crystals.

In this paper we present all-in fiber tunable devices based on specially designed and optimized high-index photonic crystal fibers filled with nematic liquid crystals. A special host microstructured optical fibers have been designed and manufactured to ensure low-loss index guiding and mode field diameter matching to SMF-28 fiber, ensuring low losses on interconnections with leading in-out FC/PC connectorized pigtails. We present four types of tunable all-fiber devices: tunable retarders with tuning range as high as 20 λ, tunable polarizers with variable axis of polarization and continuously tunable polarization dependent losses, tunable and fully controllable polarization controller and finally indeterministic depolarizer in which depolarization is caused by random thermodynamic process. We also present a cost-effective method to achieve change in the direction of the steering electric field, which was controlled by custom-made programable controllers. Finally, we present a method for effective packaging for the proposed devices.

Online trace detection of mercury ions with enhanced fluorescence excitation within metal-lined hollow-core fiber.

In this Letter, we present a portable all-fiber fluorescent detection system based on metal-lined hollow-core fiber (MLHCF) for the ultra-sensitive real-time monitoring of mercury ions (Hg2+). The system employs a rhodamine derivative as the probe. The hollow core of the MLHCF serves as both the flow channel of the liquid sample and the waveguide of the optical path. The metal coating in the intermediate layer between the capillary and the polyimide (PI) coating in the MLHCF provides good light confinement, enhancing the interaction between the sample and the incident light for better fluorescence excitation and collection efficiency. Additionally, further enhancement is achieved by placing an inserted filter along the light path to reflect the excitation light back to the MLHCF. A 3-cm length of MLHCF enables simultaneous excitation of a 40-µL sample volume and collection of most of its fluorescent signal in all directions, thereby significantly contributing to its exceptional sensitivity with a limit of detection (LOD) of 2.3 ng/L. The all-fiber fluorescence-enhanced detection device also shows rapid response time, excellent reusability, and selectivity. This system presents an online, reproducible, and portable solution for the trace detection of Hg2+ and provides a promising way for detecting other heavy metal ions.

Optical-fiber-integrated high-speed organic phototransistor with broadband imaging capacity.

Fiber optic communication is becoming the central pillar of modern high-speed communication technology, which involves the abundant fiber components. Currently, most of photodetectors are fabricated on the silicon chip, so mass fiber-to-chip interfaces increase the complexity of advanced optoelectronic system, and also grow the risk of optical information loss. Here, we report an all-fiber organic phototransistor by employing rubrene single crystal and few-layer graphene to realize the "plug-to-play" operation. The device shows a broadband photoresponse from the ultraviolet to visible range, with fast response times of approximately 130/170 µs and reasonable specific detectivity of 6 × 109 Jones, which is close to the level of commercial on-chip device. Finally, several imaging applications are successfully demonstrated by deploying this all-fiber device. Our work provided an efficient strategy for fabricating all-fiber organic devices, and confirmed their significant potential in future optical fiber optoelectronics.

Surface lattice resonance of circular nano-array integrated on optical fiber tips

As metallic nanoparticles are arranged to form a 2D periodic nano-array, the coupling of the localized surface plasmonic resonance (LSPR) results in the well-known phenomenon of surface lattice resonances (SLRs). We theoretically investigate the SLR effect of the circular nano-array fabricated on the fiber tips. The difference between the 2D periodic and circular periodic arrays results in different resonant characteristics. For both structures, the resonant peaks due to the SLRs shift continuously as the array structures are adjusted. For some specific arrangements, the circular nano-array may generate a single sharp resonant peak with extremely high enhancement, which originates from the collective coupling of the whole array. More interestingly, the spatial pattern of the vector near-field corresponding to the sharp peak is independent of the polarization state of the incidence, facilitating its excitation and regulation. This finding may be helpful for designing multifunctional all-fiber devices.

Light manipulation for all-fiber devices with VCSEL and graphene-based metasurface.

Light manipulation for all-fiber devices has played a vital role in controllable photonic devices. A graphene-based metasurface is proposed to realize light manipulation. A row of VCSEL-based optical engines with low crosstalk is used as the control light to modulate the signal transmitted in the microstructured fiber. In this configuration, the proposed device can work independently of the wavelength division multiplexing (WDM) system. With an insertion loss of only 0.28 dB, evanescent wave coupling to graphene layers is polarisation-insensitive. The device could be effectively manipulated for a few days (not less than 72 hours), which possesses the capacity to dynamically modulate the signal light with both low-temperature sensitivity and low-wavelength sensitivity. The 35 nm wavelength interval results in a change of only about 0.1 dB in the output light intensity of the microstructured fiber when the wavelength changes from 1530 nm to 1565 nm. Moreover, the modulation depth is approximately 2 dB when the modulating voltage is 2.2 V, which may open avenues for channel detection techniques and have deep implications in top tuning applications.

Tunable microsecond Q-switched fiber laser using an all-fiber deionized water saturable-absorber

We experimentally demonstrated a tunable microsecond passively Q-switched fiber laser using deionized water (DIW) as a saturable absorber (SA). The DIW-SA was integrated into an all-fiber device by filling the gap between two cleaved fiber facets with DIW, which were enclosed in a glass ferrule. We observed a high nonlinear transmission through DIW-SA and implemented it in an erbium-doped fiber ring laser cavity. Microsecond Q-switched pulse trains were produced tunable from 1564.3 to 1603.4 nm using a fiber-optic Fabry-Perot interference filter within the cavity, avoiding peak water absorption while maintaining stable operation. Tunable and robust Q-switching of a fiber laser using water would open a new avenue of nonlinear aqua-photonics.

All-fiber device for single-photon detection

Fiber components form the standard not only in modern telecommunication but also for future quantum information technology. For high-performance single-photon detection, superconducting nanowire single-photon detectors (SPDs) are typically fabricated on a silicon chip and fiber-coupled for easy handling and usage. The fiber-to-chip interface hinders the SPD from being an all-fiber device for full utilization of its excellent performance. Here, we report a scheme of SPD that is directly fabricated on the fiber tip. A bury-and-planar fabrication technique is developed to improve the roughness of the substrate for all-fiber detectors’ performance for single-photon detection with amorphous molybdenum silicide (MoSi) nanowires. The low material selectivity and universal planar process enable fabrication and packaging on a large scale. Such a detector responds to a broad wavelength range from 405 nm to 1550 nm at a dark count rate of 100 cps. The relaxation time of the response pulse is ~ 15 ns, which is comparable to that of on-chip SPDs. Therefore, this device is free from fiber-to-chip coupling and easy packaging for all-fiber quantum information systems.

Advanced fiber in-coupling through nanoprinted axially symmetric structures

Here, we introduce and demonstrate nanoprinted all-dielectric nanostructures located on fiber end faces as a novel concept for the efficient coupling of light into optical fibers, especially at multiple incidence angles and across large angular intervals. Taking advantage of the unique properties of the nanoprinting technology, such as flexibly varying the width, height, and gap distance of each individual element, we realize different polymeric axial-symmetric structures, such as double-pitch gratings and aperiodic arrays, placed on the facet of commercial step-index fibers. Of particular note is the aperiodic geometry, enabling an unprecedentedly high average coupling efficiency across the entire angular range up to 80°, outperforming regular gratings and especially bare fibers by orders of magnitude. The excellent agreement between simulation and experiment clearly demonstrates the quality of the fabricated structures and the high accuracy of the nanoprinting process. Our approach enables realizing highly integrated and ready-to-use fiber devices, defining a new class of compact, flexible, and practically relevant all-fiber devices beyond the state-of-art. Applications can be found in a variety of cutting-edge fields that require highly efficient light collection over selected angular intervals, such as endoscopy or quantum technologies. Furthermore, fiber functionalization through nanoprinting represents a promising approach for interfacing highly complex functional photonic structures with optical fibers.

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.

All-fiber optical nonreciprocity based on parity-time-symmetric Fabry-Perot resonators

Nonreciprocal light transmission in an all-fiber platform is critical in modern optical communication systems, which can avoid the packaging and integration process required in current devices based on magneto-optical or nonlinear materials. Here we propose and demonstrate an all-fiber device with remotely tunable isolation ratio and switchable isolation direction by constructing two mutually coupled Fabry-Perot (FP) resonators with identical geometry and balanced gain and loss. By controlling the pumping power, strong optical nonreciprocity is achieved due to gain saturation nonlinearity that is enhanced by the broken parity-time symmetry. Nonreciprocal light transmission with an isolation ratio of 8.58 dB at 1550 nm and an insertion loss of 2.5 dB is demonstrated. The isolation bandwidth is 125 MHz, which is determined by the bandwidths of the two coupled FP resonators. The proposed approach provides an all-fiber solution for a remotely tunable and optically controlled isolator, which may find applications in software-defined optical networks.