Broadband all-fiber optical phase modulator based on photo-thermal effect in a gas-filled hollow-core fiber

We report broadband all-fiber optical phase modulation based on the photo-thermal effect in a gas-filled hollow-core fiber.The phase modulation dynamics are studied by multi-physics simulation.A phase modulator is fabricated using a 5.6-cm-long anti-resonant hollow-core fiber with pure acetylene filling.It has a half-wave optical power of 289 mW at 100 kHz and an average insertion loss 0.6 dB over a broad wavelength range from 1450 to 1650 nm.The rise and fall time constants are 3.5 and 3.7μs,respectively,2–3 orders of magnitude better than the previously reported microfiber-based photo-thermal phase modulators.The gas-filled hollow-core waveguide configuration is promising for optical phase modulation from ultraviolet to mid-infrared which is challenging to achieve with solid optical fibers.

Design of a Surface-Plasmon-Resonance Sensor Based on a Microstructured Optical Fiber with Annular-Shaped Holes

A novel design is proposed for highly sensitive surface-plasmon-resonance sensors. The sensor is based on a microstructured optical fiber with two layers of annular-shaped holes. A gold layer is deposited on the inner surface of the second hole-layer, in which the holes have several micrometers thickness in size, facilitating analyte infiltration and metal layer deposition. In the first layer of holes, the sector-ring^shaped arms, used as supporting strips, are utilized to tune the resonance depth of the sensor. Numerical results indicate that the sensor operation wavelength can be tuned across the C＋L-band. The spectral sensitivity of 1.0.104 nm. RIU-1 order of magnitude and a detection limit of 1.0.10-4 RIU order are demonstrated over a wide range of analyte refractive index from 1.320 to 1.335.

Microstructured Cantilever Probe on Optical Fiber Tip for Microforce Sensor

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 2.46N/m to 62.35N/m.The force sensitivity is 2.5nm/μN,the Q-factor is 368.93,and the detection limit is 57.43nN.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.

Hollow and filled fiber bragg gratings in nano-bore optical fibers

To combine the technical functions and advantages of solid-core fiber Bragg gratings(FBGs) and hollow-core optical fibers(HCFs), the hollow and filled FBGs in nano-bore optical fibers(NBFs) with nano-bore in the GeO2-doped core are proposed.The fundamental mode field, effective mode index, and confinement loss of NBF with 50 nm–7 μm-diameter hollow and filled nano-bore are numerically investigated by the finite element method.The reflected spectra of FBGs in NBFs are obtained by the transmission matrix method.The hollow FBGs in NBFs can be acheived with ~5% power fraction in the bore and the ~0.9 reflectivity when bore diameter is less than 3 μm.The filled FBGs can be realized with^1% power fraction and 0.98 reflectivity with different fillings including o-xylene, trichloroethylene, and chloroform for 800-nm bore diameter.The feasibility of the index sensing by our proposed NBF FBG is also analyzed and discussed.The experimental fabrication of hollow and filled FBGs are discussed and can be achieved by current techniques.The aim of this work is to establish a principle prototype for investigating the HCFs and solid-core FBGs-based fiber-optic platforms,which are useful for applications such as the simultaneous chemical and physical sensing at the same position.

The Study on the Polycrystal Germanium Dioxide Hollow-core Fiber and Its Performances

A method of fabricating pure germanium dioxide hollow-core fibers has been introduced for the first time. The inner diameter of the fiber is φ0.8mm, with the transmission loss of 1.23dB/m at 10.6μm. The mechanism of transmitting CO_2 laser by the fiber is analyzed. The transmitting performances are discussed and its application fields are envisaged.

Optical properties and local structure of Dy^(3+)-doped chalcogenide and chalcohalide glasses

Dy^3＋-doped Ge-Ga-Se chalcogenide glasses and GeSe2-Ga2Se3-CsI chalcohalide glasses were prepared. The absorption, emission properties, and local structure of the glasses were investigated. When excited at 808 nm diode laser, intense 1.32 and 1.55 μm near-infrared luminescence were observed with full width at half maximum （FWHM） of about 90 and 50 nm, respectively. The lifetime of the 1.32 μm emission varied due to changes in the local structure surrounding Dy^3＋ ions. The longest lifetime was over 2.5 ms, and the value was significantly higher than that in other Dy^3＋-doped glasses. Some other spectroscopic parameters were calculated by using Judd-Ofelt theory. Meanwhile, Ge-Ga-Se and GeSe2-Ga2Se3-CsI glasses showed good infrared transmittance. As a result, Dy^3＋-doped Ge-Ga-Se and GeSe2-Ga2Se3-CsI glasses were believed to be useful hosts for 1.3 μm optical fiber amplifier.

Mid-infrared all-optical modulators based on an acetylene-filled hollow-core fiber

We report all-optical mid-infrared phase and intensity modulators based on the photo-thermal effect in an acetylene-filled anti-resonant hollow-core fiber.Optical absorption of the control beam promotes the gas molecules to a higher energy level,which induces localized heating through non-radiative relaxation and modulates the refractive index of the gas material and hence the accumulated phase of the signal beam propagating through the hollow-core fiber.By modulating the intensity of the control beam,the phase of the signal beam is modulated accordingly.By use of a 1.53μm near-infrared control beam,all-optical phase modulation up to 2.2πrad is experimentally demonstrated at the signal wavelength of 3.35μm.With the phase modulator placed in one arm of a Mach-Zehnder interferometer,intensity modulation with on-off ratio of 25 dB is achieved.The gas-filled hollow-core-fiber modulators could operate over an ultra-broad wavelength band from near-to mid-infrared and have promising application in mid-infrared photonic systems.

Ultraflat, broadband, and highly coherent supercontinuum generation in all-solid microstructured optical fibers with all-normal dispersion

High flatness, wide bandwidth, and high-coherence properties of supercontinuum(SC) generation in fibers are crucial in many applications. It is challenging to achieve SC spectra in a combination of the properties, since special dispersion profiles are required, especially when pump pulses with duration over 100 fs are employed. We propose an all-solid microstructured fiber composed only of hexagonal glass elements. The optimized fiber possesses an ultraflat all-normal dispersion profile, covering a wide wavelength interval of approximately 1.55 μm. An SC spectrum spanning from approximately 1030 to 2030 nm(corresponding to nearly one octave) with flatness<3 dB is numerically generated in the fiber with 200 fs pump pulses at 1.55 μm. The results indicate that the broadband ultraflat SC sources can be all-fiber and miniaturized due to commercially achievable 200-fs fiber lasers. Moreover, the SC pulses feature high coherence and a single pulse in the time domain, which can be compressed to 13.9-fs pulses with high quality even for simple linear chirp compensation. The Fourier-limited pulse duration of the spectrum is 3.19 fs, corresponding to only 0.62 optical cycles.

大孔柚子型微结构光纤探针的表面增强拉曼散射性能研究

随着光纤制备工艺以及纳米材料制备技术的发展,光纤探针已成为一种新型的表面增强拉曼散射(SERS)基底,通过在普通单模光纤或多模光纤上制备不同的结构并修饰相应的纳米材料,可以得到多种类型的光纤表面增强拉曼散射探针,并实现较好的检测效果。但受限于光纤本身的结构,普通光纤仅能利用端面或侧表面提供拉曼检测的“热点”区域,限制了其SERS性能的进一步提高。因此制备了大孔柚子型微结构光纤(MSF)表面增强拉曼散射(SERS)探针,其中大孔柚子型MSF SERS探针结构通过一段阶跃多模光纤与柚子型微结构光纤熔接制得。实验分别对自制的纳米银溶胶基底以及大孔柚子型MSF SERS探针的SERS性能进行检测。采用溶胶自组装法制备负载银纳米颗粒的MSF SERS探针,通过控制自组装时间制备不同光纤SERS探针(Ag/MSF-x,其中x为自组装时间,分别为15、30、45、60 min)。采用溶液检测方法,利用Ag/MSF-x探针对10^(-3) mol·L^(-1)的亚甲基蓝(MB)探针分子进行检测,通过比较相同条件下的增强效果筛选得到Ag/MSF-45探针。为进一步检测Ag/MSF-45探针的SERS性能,制备不同浓度的MB溶液,分别利用纳米银溶胶基底和Ag/MSF-45探针对其进行检测。实验结果表明,纳米银溶胶基底对MB的检测限(LOD)为10^(-6) mol·L^(-1),Ag/MSF-45探针对MB的检测限(LOD)为10^(-7) mol·L^(-1);拉曼信号的再现性结果表明纳米银溶胶基底以及Ag/MSF-45探针在各个特征峰处的RSD值均在合理范围内;在1619 cm^(-1)拉曼位移处对纳米银溶胶基底以及Ag/MSF-45探针检测MB的拉曼强度和浓度进行对数转换拟合,纳米银溶胶基底的拟合优度R2达0.91628,Ag/MSF-45探针的拟合优度R2达0.98848;纳米银溶胶基底和Ag/MSF-45探针的再现性结果表明,其在各个特征峰处的RSD值均处于合理范围,但Ag/MSF-45探针的各特征峰RSD值均小于纳米银溶胶基底,最大为13.89%;利用10^(-6) mol·L^(-1)的MB对Ag/MSF-45探针的增强因子(AEF)进行计算,Ag/MSF-45探针的AEF达到6.09×10^(6),表现出良好的增强效果。因此,基于大孔柚子型MSF SERS探针凭借独特的空气孔结构使其具有较高的灵敏度以及良好的再现性,且其SERS性能均优于纳米银溶胶基底,在农业、化学分析、生物检测等领域及大分子物质检测等方面应用前景广泛。

孔助光纤(Hole-assisted lightguide fiber)色散和双折射特性的研究

通过改变包层中空气孔的参数,孔助光纤(holeassistedlightguidefiber)具有比传统光纤更容易调节的色散和双折射特性.采用有限差分法研究了包层空气孔数目、大小和位置等参数对孔助光纤色散和双折射特性的影响.数值计算结果表明增加空气孔的数目和尺寸以及减小空气孔到纤芯的距离都能够使得零色散向短波长方向移动,减小空气孔与纤芯的距离有助于获得更大的双折射.

Reseach Progress of Photonic Crystal Fibers in China

Photonic Crystal Fibers have attracted worldwideinterest within the last decade due to their uniqueoptical properties and because they exhibit a muchhigher degree of design freedom compared to conventionaloptical fibers.In this article, the fabricationtechnologies of photonic crystal fibers and theirapplications at home and abroad were formulated atlength, especially in the following fields, such aslarge mode area active photonic crystal fibers andfiber lasers, birefringence fibers and sensors, highnonlinear photonic crystal fibers and frequencytransformation, dispersion compensation PCFs anddispersion compensation for telecommunicationsystems, and photonic band-gap fibers. Finally, accordingto the above analysis, the prospects anddeveloping trends of photonic crystal fibers in thefuture were presented.

Characteristics of Bragg Gratings in All-Solid Photonic Bandgap Fiber

We report on fiber Bragg gratings in all-solid photonie bandgap fiber that was composed of a triangular array of high-index Ge-doped rods in pure silica background with fluorine-doped index-depressed layer surrounding the Ge-doped rod. Fiber Bragg gratings were photowritten with 193 nm ArF excimer laser and characterized for their response to strain, temperature, bending, and torsion. These gratings couple light from the forward core mode to not only backward core mode but also backward rod modes. This results in multiple resonance peaks in the reflection spectrum. All resonance wavelengths exhibited the same temperature and strain response with coefficient similar to that of Bragg gratings in standard single-mode fiber. The strength of the resonance peaks corresponding to the backward rod modes showed high sensitivity to bending and torsion.

用于裂隙光源的侧面发光塑料光纤散射点设计

设计一种侧面发光塑料光纤表面正四棱锥形微结构散射点,使侧面发光塑料光纤可用作裂隙灯显微镜的裂隙光源,以减小裂隙光源的体积.采用光学仿真软件分析光纤上表面(有散射点)和光纤下表面(无散射点)的散射率,当塑料光纤直径为1 mm时,得到优化后的正四棱锥散射点的底边宽度和深度均为80μm.仿真结果表明,光纤下表面散射光的光束发散角在垂直于光纤方向约为40°,在平行于光纤方向约为110°,经过焦距为50 mm的投射镜会聚后的光带宽度约为0.3 mm,可以满足裂隙灯显微镜的要求.

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.

A new generation of plastic optical fibers and its functional exploiting

A major problem of plastic optical fibers(POFs) is large transmission loss in comparison with silica fibers.After adopting a new optical fiber structure,hollow-core Bragg fiber with cobweb-structured cladding,which can suppress the absorption losses of constituent materials by a factor of about 104―106,the problem of POFs with large losses is solved ultimately.With the advantage of flexibility and easy bending,the POFs with this structure can guide light with low transmission loss for information and energy in the wavelength range of visible light to terahertz(THz) wave(0.4―1000 μm).This new generation of POFs will find many applications.

Deep-learning cell imaging through Anderson localizing optical fiber

We demonstrate a deep-learning-based fiber imaging system that can transfer real-time artifact-free cell images through a meter-long Anderson localizing optical fiber.The cell samples are illuminated by an incoherent LED light source.A deep convolutional neural network is applied to the image reconstruction process.The network training uses data generated by a setup with straight fiber at room temperature(∼20°C)but can be utilized directly for high-fidelity reconstruction of cell images that are transported through fiber with a few degrees bend or fiber with segments heated up to 50°C.In addition,cell images located several millimeters away from the bare fiber end can be transported and recovered successfully without the assistance of distal optics.We provide evidence that the trained neural network is able to transfer its learning to recover images of cells featuring very different morphologies and classes that are never“seen”during the training process.

Toward a compact fiber comb with 1.66×10^(-12)instability based on acetylene-filled photonic microcells

We demonstrated an optical fiber frequency comb stabilized to an acetylene-filled photonic microcell.The short-term instability of the comb at 1 s gate time was 1.66×10^(-12)for a 4.2-h measurement in a laboratory environment with air conditioning.This is the best short-term stability reported for a compact fiber comb stabilized to an acetylene-filled photonic microcell at telecom wavelengths.It is particularly significant in the development of compact fiber combs with target instability of 10^(-13).Such a device has the potential to serve as an alternative to GPS in areas lacking signal coverage,including remote locations,regions with adverse weather conditions,and military intelligence areas.

Numerical Investigation Into a Surface Plasmon Resonance Sensor Based on Optical Fiber Microring

A reflective surface plasmon resonance （SPR） sensor based on optical fiber microring is proposed. In such a sensor, plasmons on the outer surface of the metallized channels containing analyte can be excited by a fundamental mode of a thin-core fiber （TCF）. The refractive index （RI） sensing can be achieved as the surface plasmons are sensitive to changes in the refrective index of the analyte. Numerical simulation results show that the resonance spectrum shifts toward the shorter wavelength gradually when the analyte refractive index increases from 1.0 to 1.33, whereas it shifts toward the longer wavelength gradually when the analyte refractive index increases from 1.33 to 1.43, and there is a turning point at the refractive index value of 1.33. The highest sensitivity achieved is up to 2.30×10^3nm/RIU near the refractive index value of 1.0. Such a compact sensor has potential for gaseous substance monitoring.

Grating Writing in Structured Optical Fibers

Grating writing in structured optical fibers is reviewed. Various laser sources have been used including UV and near IR nanosecond and femtosecond lasers, each enabling different material processing regimes. The issue of scattering is modeled through simulation and compared with experiment. Good agreement has been established.

Pure germanium dioxide hollow-core fiber for transmitting CO_2 laser

A method of fabricating pure germanium dioxide hollow-core fibers has been introduced for the first time. The output power of the fabricated fiber can come to 18 W, with the transmission loss of 1.23 dB/m at 10.6 μm. The mechanism of transmitting CO2 laser by the fiber is analyzed, the transmitting loss is further discussed and its application fields are envisaged.