A two-stage amplifier of laser eavesdropping model based on waveguide fiber taper

In order to improve ability of amplification about optical arrival angle in laser eavesdropping system, and enhance receiving field of view (FOV) of laser eavesdropping system, this paper presents a new multistage amplifier laser eavesdropping model based on waveguide fiber taper. First of all, taking about four-quadrant (4QD) laser eavesdropping model as an example, from the theoretical view, analyses factors that, currently, laser eavesdropping system face many restrictive factors during practical applications. Besides, from the receiving FOV and ability of amplification about arrival angle of incoming optical axis angles, systematically analyses advantages of multi-stage amplifier model. What’s more,through constructing laser eavesdropping test platform, we demonstrate Signal to Noise Ratio(SNR) of two stage amplification model is eventually promoted to 6-10 dB compared with one amplifying model,especially in low and high audio level, the advantages is more obvious.

Tapered optical fiber DNA biosensor for detecting Leptospira DNA

Objective: To establish a DNA detection platform based on a tapered optical fiber to detect Leptospira DNA by targeting the leptospiral secY gene.Methods: The biosensor works on the principle of light propagating in the special geometry of the optical fiber tapered from a waist diameter of 125 to 12 μm. The fiber surface was functionalized through a cascade of chemical treatments and the immobilization of a DNA capture probe targeting the secY gene. The presence of the target DNA was determined from the wavelength shift in the optical transmission spectrum.Results: The biosensor demonstrated good sensitivity, detecting Leptospira DNA at 0.001 ng/μL, and was selective for Leptospira DNA without cross-reactivity with non-leptospiral microorganisms. The biosensor specifically detected DNA that was specifically amplified through the loop-mediated isothermal amplification approach.Conclusions: These findings warrant the potential of this platform to be developed as a novel alternative approach to diagnose leptospirosis.

Fabrication and sensing characteristics of intrinsic Fabry–Perot interferometers in fiber tapers

This Letter presents intrinsic Fabry–Perot interferometers in the fiber tapers fabricated by the femtosecond laser micromachining technique. The sensing of temperatures as high as 1000°C based on the fiber device is characterized, with a sensitivity of 15.28 pm∕°C. A nearly linear refractive index sensing is also obtained by using the fringe visibility to characterize, with a sensitivity of 73.05 dB∕RIU. These intrinsic Fabry–Perot interferometers in fiber tapers may be useful in applications of high-temperature and linear refractive index sensing.

Effect of Scanning Beam Profile to Fabricate Fused Fiber Tapers by CO_2 Laser Irradiation Method

Beam uniformity is a crucial building block of CO2 experiments aimed at fusing and stretching optical fibers in a lossless manner. When the irradiation beam is expanded through a galvanometer mirror, ways to achieve beam uniformity are investigated.

Temperature sensor based on a single-mode tapered optical fiber

A temperature sensor is demonstrated and fabricated by coating the single-mode tapered optical fiber with temperature-sensitive silicone rubber. It works on the change of the evanescent fields in the tapered optical fiber. Small changes in the refractive index of coating film greatly influence the power of evanescent fields, which modulate the transmission optical power in the waist region. The range of temperature measured is from -20℃ to 70 ℃. The results show that the temperature sensor has high temperature sensitivity （0.012 mW/℃） and good repeatability.

Experimental measurement and numerical analysis of fused taper shape for optical fiber coupler

To find out the effect of the shape of fused taper region on the optical fiber coupler, the fiber couplers were fabricated at different drawing speeds with a six-axes fiber coupler machine. The results, which were obtained from the shape of fused taper region measured with microscope, show that there is a close correlation between the cone angle and optical performance of fiber coupler. High-performance fiber coupler cannot be obtained until rheological shape is controlled accurately. The numerical analysis model, which was built based on generalized Maxwell viscoelastic theory, is resolved with ANSYS software. The calculated results accord with the experimental data. It can apply a theoretic basis for forecasting the shape of fiber coupler fabricated under the conditions of different technological parameters.

Zinc-oxide/PDMS-clad tapered fiber saturable absorber for passively mode-locked erbium-doped fiber laser

We propose and demonstrate a passively mode-locked erbium-doped fiber laser(EDFL)based on zinc-oxide/polydimethylsiloxane(ZnO/PDMS)saturable absorber(SA)that evanescently interacts with the light on a tapered fiber.The ZnO/PDMS composite is coated on the whole surface of the tapered fiber to guarantee the maximum efficiency of the SA device,with a measured insertion loss of 0.87 dB and a modulation depth of 6.4%.The proposed laser can generate soliton mode-locking operation at a threshold power of 33.07 mW.The generated output pulse yields a repetition rate and pulse width of 9.77 MHz and 1.03 ps,respectively.These results indicate that the proposed ZnO/PDMS-clad tapered fiber could be useful as an efficient,compatible,and low-cost SA device for ultrafast laser applications.

Frequency-stabilized Yb：fiber comb with a tapered single-mode fiber

We demonstrate a stable Yb：fiber frequency comb with supercontinuum generation by using a specially designed tapered single-mode fiber, in which a spectrum spanning from 500 nm to 1500 nm is produced. The carrier-envelope offset signal of the Yb：fiber comb is measured with a signal-to-noise ratio of more than 40 dB and a linewidth narrower than 120 kHz. The repetition rate and carrier-envelope offset signals are simultaneously phase locked to a microwave reference frequency.

Surface-enhanced Raman scattering sensor based on fused biconical taper zone of optical fiber

In this paper, a novel surface-enhanced Raman scattering （SERS） sensor combined with fused biconical taper fiber （FBTF） and film coated with silver sols is proposed. This structure is designed to significantly increase the SERS active surface when the length of the taper is increased and the radius is reduced, since the penetration depth is inversely proportional to the taper radius and proportional to the taper length according to the fiber-optic evanescent-wave theory. Based on the SERS sensing principle, the feasibility of FBTF sensor is analyzed in this paper. As a result, the Raman spectrum of R6G is obtained from the fused biconical taper zone surface coating with the silver sols in our experiments. The detected concentration is up to 10-7mol/L.

High-frequency fused high-voltage arc tapering process power supply for of fiber

The performance of the optical fiber coupler prepared with fused biconical taper method is determined by the quality of fused stretching. Besides, the stable high-temperature heat source is the essential guarantee for fused stretching process to go smoothly. The way of using AC （alternating current） arc as the heat source is proposed in this article. In addition, the paper also introduces high-frequency high-voltage power supply with the characteristics of constant current and restricted voltage, which is composed of preceding voltage regulation part and following inverter.

基于锥形掺镱光纤实现20 kW高光束质量激光输出

锥形光纤能够有效兼顾非线性效应抑制和模式控制,具备实现高功率、高光束质量光纤激光的潜力。近期国防科技大学研制了锥形掺镱光纤,采用1 018 nm光纤激光后向级联泵浦实现了20.2 kW激光输出,光束质量β因子平均值优于2,拉曼抑制比为33 dB。研究结果展示了锥形光纤在实现万瓦级高光束质量激光方面的优势。

基于光纤光栅的多点拉锥光纤柔性曲率传感器

针对现有曲率传感器存在制造工艺繁琐、成本较高的问题,提出了一种基于光纤光栅的反射式拉锥光纤柔性曲率传感器,通过将单模拉锥光纤植入聚二甲基硅氧烷(polydimethylsiloxane,PDMS)材料中实现对曲率的柔性传感,同时,利用光纤布拉格光栅(fiber Bragg grating,FBG)的波分复用特性,将其与多个拉锥光纤曲率传感器级联,实现了多点拉锥光纤柔性曲率传感,可同时感知多点的曲率信息。实验结果表明,薄膜状的PDMS柔弹性良好,拉锥光纤与PDMS膜能同步弯曲,弯曲灵敏度约为0.59348-0.60696 dB/m^(-1)。基于FBG的多点拉锥光纤柔性曲率传感还具有较好的抗串扰能力。进一步地,使用该柔性传感器对喉咙处及手腕处的人体活动监测进行了应用研究,结果表明该传感器不但能检测到人体微小的肌肉变化,也能检测到幅度较大的动作,在人体活动监测领域具有良好的发展前景。

微纳Taper光纤干涉传感器的折射率测量理论研究

利用微纳taper光纤干涉方程和微纳光纤传输模式函数关系,建立了微纳taper光纤干涉波长随环境折射率变化的数学模型,指出微纳taper光纤干涉波长的响应规律由基模高阶模有效折射率差、色散因子和环境折射率3个因素所决定.详细研究了微纳taper光纤传感器的灵敏度变化规律,结果表明,传感器的灵敏度随光纤半径变小而急速增大,并随环境折射率的增大而非线性增加,而且探测波长越长,其灵敏度越大.

Relationship between rheological manufacturing process and optical performance of optical fiber coupler

Through theoretical analysis and experiments, the viscoelastic mechanical model of optical fiber coupler in the process of fused biconical taper was established, and the numerical analysis in non-uniform temperature field was made. The results show that the rheological parameters, such as drawing speed and fused temperature, have a tremendous influence on stress distribution and performance of optical fiber coupler, especially the influence of fused temperature. The change of fused temperature by 5℃ can lead to the change of the maximum stress by 30% and stress difference by 20% in the same cross section. The change of temperature gradient by 3% can result in the change of stress difference by 90%. In the present condition of rheological technology, rheological defects such as crystallizations and microcracks are easy to generate in the optical fiber coupler.

新型钉型刺辊针布设计及应用

为了减少纤维损伤、实现高效梳理,介绍刺辊针布梳理性能要求,分析传统刺辊针布使用存在锐度衰减快和短绒增长率高的原因,提出优化齿型设计、棱角锥齿化处理、减小齿顶面积、齿体表面强化处理等措施,开发出新型钉型刺辊针布;详细阐述新型钉型刺辊针布的设计原理、技术特征,对比分析其与传统刺辊针布梳理机采棉、纤维素纤维、再生聚酯纤维的成纱质量指标。指出:新型钉型刺辊针布具有齿体强度高、耐磨性好、衰减周期长、适纺范围广等优势;相比传统刺辊针布,新型钉型刺辊针布可减少纤维损伤,降低纱疵和落棉率,提升梳理质量。

Realization of Tapered Waveguide by Stretching the Rod Waveguide

By stretching the rod waveguide with different velocities in opposite directions,the tapered waveguide can be fabricated.In condition of taking no account of volume expansion caused by heating and under the assumptions of volume conservation,the rod waveguide can be stretched freely in the heated region without being stretched outside of the heated region. A model,which shows the relation of the transition shape and the two factors,that is the ratio of two velocity and the heated region length,is presented for the shape of the taper transition through mathematic deduction.Based on this model,a desired tapered waveguide can be fabricated.The tapered waveguide are widely used for fabricating tapered fiber couplers and sensors.In addition,the conclusion can be used for fabricating fused fiber coupler.

Structure analysis of optical fiber coupler with infrared spectrometry

To obtain excellent performance optical fiber couplers, the structural difference of SiO2 in couplers with different manufacturing techniques was investigated. With 740-FT-IR infrared spectrometric analyzer, the infrared absorption spectrum of SiO2 in couplers at different drawing velocities was measured, and two characteristic peaks in the wavenumber range of 6502000 cm-1 were observed. One characteristic peak is at about 943 cm-1, which is （attributed） to Si—O—Si bond asymmetric stretching vibration, the other is at about 773 cm-1, which is attributed to （Si—O—Si） bond symmetric stretching vibration. From the infrared spectrum, it is found that the intensity and wavenumber of the characteristic peaks are related to the manufacturing technique of couplers. The characteristic peak at （about） 943 cm-1 becomes steeper when increasing the drawing velocity. At the drawing velocity of 150 μm/s, the distance between the two characteristic peaks is maximum, and then the optical fiber coupler has excellent performance, indicating that the performance of the optical fiber coupler has a close relationship with the wavenumber of the two characteristic peaks.

Switchable multi-wavelength fiber laser based on modal interference

A comb fiber filter based on modal interference is proposed and demonstrated in this paper. Here two cascaded uptapers are used to excite the cladding mode, and a core-offset jointing point is used to act as an interference component.Experimental results show that this kind of structure possesses a comb filter property in a range of the C-band. The measured extinction ratio is better than 12 dB with an insertion loss of about 11 dB. A switchable multi-wavelength erbium-doped fiber laser based on this novel comb filter is demonstrated. By adjusting the polarization controller, the output laser can be switched among single-, dual-, and three-wavelengths with a side mode suppression ratio of better than 45 dB.

Effect of technological parameters on optical performance of fiber coupler

To find out the influence of technological parameters on optical performance of fused optical fiber device, the fiber coupler was served as subject investigated by using the fused biconical taper machining as experimental setup. Fused fiber coupler's optical performances such as insertion loss, excess loss, directivity and uniformity were tested with the optical test system that was constituted of tunable laser and optical spectrum analyzer. Especially the relationship between optical performance and drawing speed was investigated. The experimental results show that the optical performance is closely related to process conditions. At fused temperature of 1 200 ℃, there exists a drawing speed of 150 μms, which makes the device's performance optimum. Out of this speed region, the optical performance drops quickly. At drawing speed of 200 μms, the excess loss is relatively small when the fused temperature is above 1 200 ℃. So the technological parameters have close relationship with optical performance of the coupler, and the good performance coupler can't get until the drawing speed and fused temperature match accurately.