Biconical Taper Research Articles

Optimization of the Geometries of Biconical Tapered Fiber Sensors for Monitoring the Early‐Age Curing Temperatures of Concrete Specimens

AbstractIn this article, a geometrical optimization procedure using biconical tapered fiber sensors is proposed for monitoring the early‐age curing temperatures of concrete specimens. The geometries of the sensors are theoretically optimized by the ray‐tracing theory. The results of the theoretical analysis show that the performance of the sensors is heavily influenced by Evanescent Waves, which are due to the tunneling rays and are fully escaped by tapering the fiber. The effects of the geometrical parameters, including the taper ratios, taper lengths, and ray launch angles, as well as the surrounding temperatures, on the behavior of the sensors are studied numerically. The numerical results demonstrate that higher performance of the proposed optimized sensors can be achieved by a longer taper length and smaller taper ratio combined with an initial ray launching angle of 0.01 rad. An experimental study on early‐age curing temperature monitoring of concrete specimens with the biconical tapered fiber sensors was carried out. The experimental measurements agree well with the theoretical results.

Triple and Double Photons Absorption Process and Down-Conversion Laser Emitting Investigation of Er-Ion Doped Microsphere

We report a readily and cheap method to build taper optical fiber-Er3+ doped microsphere platform to investigate upconversion fluorescence emission and down-conversion laser oscillation with low threshold pump power. We demonstrate to dope Er3+ into silica microsphere surface by dipping a single-taper optical fiber into a certain concentration of erbium nitrate solution (Er(NO3)) , then dry it and use the electrical-arc of the optical fiber splicer to melt the tip of taper fiber to form the Er3+-doped silica microsphere due to surface tension induced. We also present a HF acid etching setup to fabricate low loss biconical optical taper fibers. We demonstrate the Er3+ doped silica microsphere triple photons and dual photons absorption process of up-conversion fluorescence emission and down-conversion laser oscillation spectra by using the optical tapered fiber to couple 976 nm/1534 nm pump light source.

基于双“8”字型光纤谐振环的全光纤三端口Interleaver

In order to improve the transmission performance of all-fiber three-channel interleavers,an all-fiber three-channel interleaver was developed by using a new configuration of dual-8-shaped ring resonator.The ring was composed of a planar 3×3 single mode fiber coupler and two 2×2 fiber couplers and was used as an input device.Furthermore,a regular triangle 3×3 fiber coupler was used as output device.The propagation properties of the three-channel interleaver were studied experimentally and theoretically.Obtained result indicates that the sidelobe level of channel of the proposed device is reduced by more than 24 dB and the crosstalk characteristics,channel isolation,the bandwidth of passband/stopband,the rolloff in transition band and the coupling-coefficient tolerance have been improved greatly in comparison with that of the convention all-fiber three-channel interleaver based on a two-stage cascaded Mach-Zehnder interferometer(TCMZI).This kind of interleaver was fabricated with a fused biconical taper technics in an experiment.The experimental results are in good agreement with the analytical ones and it shows that the measured sidelobe level is about-30 dB and the channel isolation is higher than 30 dB.

Development of miniature optical fiber hybrid WDM coupler employing the FBT technology

An innovative technique for fabricating the optical fiber hybrid wavelength-division multiplexing (WDM) coupler is presented. The device is comprised of two components, a wavelength division multiplexer and an optical fiber coupler, in a miniature stainless steel tube. The outstanding features of the ultra-low polarization dependent loss (PDL) under 0.05 dB and the compact size of ∅3.5 × 65 mm for bare-fiber type of package are accomplished by using the pioneering methodology combining the main techniques of twisted and parallel fusion processes in the fused biconical taper (FBT) technology. Besides, its miniaturization is more competitive in both of the applications of optical communication and sensing systems where a compact-sized package is required for extending the flexibility of installation.

Microstructure analysis in the coupling region of fiber coupler with a novel electrical micro-heater

Fused-tapered fiber coupler is widely used in optical-fiber communication, optical-fiber sensor and optical signal processing. Its optical performance is mainly determined by the glass properties in the coupling region. In this study, the effect of fused biconical taper (FBT) process on glass microstructure of fiber coupler was investigated by testing the microstructure of the cross-section of coupling region. The fiber coupler is fabricated with a novel home-designed electrical heater. Our experimental results show that the boundary between fiber core and fiber cladding become vague or indistinct after FBT under transmission electron microscopy (TEM) and Ge 2+ in fiber core diffuses into fiber cladding. Crystallizations are observed in coupling region under scanning electron microscope (SEM) and microscopic infrared (IR), and the micro crystallizations become smaller with the drawing speed increasing. The wave number of fiberglass increases after FBT and it is in proportion to the drawing speed. The analysis of the microstructure in the coupling region explored the mechanism of the improvement in the performance of fiber couplers which can be used for the guidance of fabrication process.

The Development of a Novel Fused Bi-Conical Taper Machine with an Electrical Resistance Micro-Heater

The Development of a Novel Fused Bi-Conical Taper Machine with an Electrical Resistance Micro-Heater

Monitoring of Curing Temperature of Early-Age Cement Paste Using Biconical Tapered Fiber Sensor

In this paper, a biconical tapered fiber sensor is applied to monitor the temperature of cement paste during curing process. A simple sensing principle of the proposed sensor is presented by analyzing the V-number of leaky rays. An experimental is carried out by tapering the plastic multi-mode step-index fiber to measure the temperature of the cement paste. The numerical result shows that the V-number of leaky ray is increasing with the raised in temperature. The experimental results are in agreement with the results from the theoretical analysis.

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.

Movement Realization of a Novel Fused Biconical Taper System Based on Electrical Heater

A novel fused biconical taper system is developed based on electrical heating system. Its movement platforms are designed. The main drawing movement platform, heater movement platform and packaging movement platform are focused on analysis. Motion control program is developed based on Delphi 2006 according to its technological requirements. The experimental results show that the movement of the novel fused biconical taper system is very stable, and the optical fiber couplers fabricated with the novel system have the good optical performance and the good consistency in particular.

광자결정 광섬유기반 광신호 분배기 개발

A broadband optical coupler with a broad bandwidth of 1000 nm based on a photonic crystal fiber (PCF) is investigated. The PCF has 6 layers of air hole structures and a diameter of . The PCF-based coupler is fabricated by using a fused biconical tapering method based on heating and elongation processes. Changing temperature and an elongation length can control the bandwidth and the bandedge wavelength of the PCF-based broadband coupler. The diameter of the fused region in the PCF-based coupler was measured to be . The fabricated PCF-based coupler has a nearly-flat coupling ration of 3-dB in a broad bandwidth of 1000 nm, which is wider than that of the previously reported PCF-based coupler and that of the single-modefiber-based coupler. Since the resolution of optical coherence tomography system is proportional to the bandwidths of both an optical light sources and an interferometer, the fabricated PCF-based broadband optical coupler has a great potential for realization of a broadband interferogram.

Hydrofluoric acid flow etching of low-loss subwavelength-diameter biconical fiber tapers

An etch method based on surface tension driven flows of hydrofluoric acid microdroplets for the fabrication of low-loss, subwavelength-diameter biconical fiber tapers is presented. Tapers with losses less than 0.1 dB/mm are demonstrated, corresponding to an order of magnitude increase in the optical transmission over previous acid-etch techniques. The etch method produces adiabatic taper transitions with minimal surface corrugations. A biconical fiber taper fabricated using this method is used to demonstrate an erbium doped silica microsphere laser.

Performance improvement of optical fiber coupler with electric heating versus gas heating

Gas heating has been widely used in the process of fused biconical tapering. However, as the instability and asymmetric flame temperature of gas heating exist, the performance of the optical devices fabricated by this method was affected. To overcome the problems resulting from gas combustion, an electric heater is designed and manufactured using a metal-ceramic (MoSi(2)) as a heating material. Our experimental data show that the fused-taper machine with an electric heater has improved the performance of optical devices by increasing the consistency of the extinction ratio, excess loss, and the splitting ratio over that of the previous gas heating mode. Microcrystallizations and microcracks were observed at the fused region of the polarization-maintaining (PM) fiber coupler and at the taper region with scanning electron microscopy and atomic force microscopy respectively. The distribution of the microcrystallizations and microcracks are nonuniform along the fiber with gas heating, while their distribution is rather uniform with electric heating. These findings show that the novel optical fiber coupler with an electric heater has improved the performance of optical fiber devices by affecting the consistency of the optical parameters and micromorphology of the surface of PM fiber.

Enhancing sensitivity of biconical tapered fiber sensors with multiple passes through the taper

A single biconical fiber taper is a simple and low-cost yet powerful sensor. With a distinct strength in refractive index RI sensing, biconical tapered fiber sensors can find their place in handheld sensor platforms, especially as biosensors that are greatly needed in health care, environmental protection, food safety, and biodefense. We report doubling of sensitivity for these sensors with two passes through the tapered region, which becomes possible through the use of sensitive and high-dynamic-range photodetectors. In a proof-of-principle experiment, we measured transmission through the taper when it was immersed in isopropyl alcohol-water mixtures of varying concentrations, in which a thin gold layer at the tip of the fiber acted as a mirror enabling two passes through the tapered region. This improved the sensitivity from 0.43 dB/vol % in the single-pass case to 0.78 dB/vol % with two passes through the taper. The refractive index detection limit was estimated to be 1.210 5 RI units RIU and 0.610 5 RIU in the single- and double-pass schemes, respectively. We predict that further enhance- ment of sensitivity may be achieved with a higher number of passes through the taper. © 2010 Society of Photo-Optical Instrumentation

Influence of tapering process on changes of optical fiber refractive index distribution along a structure

AbstractInvestigations of internal structure changes along an optical fiber during the manufacture of biconical taper have been described. Basing on the constant volume theory, classification of biconical structures manufactured on a special set-up is presented and discussed. The interferometric tomography method has been used for determination of 3D geometry and refractive index distribution in manufactured optical fiber tapers. The experiments provide detailed information on external (diameter of cladding) as well as internal (core diameter and refractive index profile) changes along the taper region. The results have been discussed in relation to the parameters of the manufacturing process.

Tilted fiber grating accelerometer incorporating an abrupt biconical taper for cladding to core recoupling

We demonstrate a compact power-referenced fiber-optic accelerometer using a weakly tilted fiber Bragg grating (TFBG) combined with an abrupt biconical taper. The electric-arc-heating induced taper is located a short distance upstream from the TFBG and functions as a bridge to recouple the TFBG-excited lower-order cladding modes back into the fiber core. This recoupling is extremely sensitive to microbending. We avoid complex wavelength interrogation by simply monitoring power change in reflection, which we show to be proportional to acceleration. In addition, the Bragg resonance is virtually unaffected by fiber bending and can be used as a power reference to cancel out any light source fluctuations. The proposed sensing configuration provides a constant linear response (nonlinearity < 1%) over a vibration frequency range from DC to 250 Hz. The upper vibration frequency limit of measurement is determined by mechanical resonance, and can be tuned by varying the sensor length. The tip-reflection sensing feature enables the sensor head to be made small enough (20~100 mm in length and 2 mm in diameter) for embedded detection. The polymer-tube-package makes the sensor sufficiently stiff for in-field acceleration measurement.

The Microstructure Evolution in Fused Region and Taper Region of Fibre Coupler

The fused region and the taper region of the optical fibre coupler were tested by atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The results indicated that the surface roughness increased after fused biconical taper (FBT), that is, the fused region possessed the highest toughness (about 70nm), the taper region is in a second position (about 40nm), and the bare fibre was relatively the lowest (about 10nm). Micro crystals were observed at the fused region and the amount of the micro crystals decreased with increasing the drawing speed. Micro cracks were observed at the taper region and the micro cracks became wide and deep with increasing the drawing speed. All these changes affected not only the optical performance such as excess loss and consistence, but also the reliability and stability. Therefore a fibre device with high quality required small drawbacks.

High efficient Tm3+ doped double cladding silica fiber laser with an intracavity biconical taper

A high efficient LD (laser diode) pumped Tm3+ doped double clad silica fiber laser with an intravacity biconical taper was reported. A biconical taper located ∼3 cm from the output end of the fiber laser was fabricated by heating and stretching method with a length 1.5 cm and waist diameter ∼20 µm. The slope efficiency was 49.8% with respected to the launched pump power, and the maximum output power was 1.97 W. Pre and post output laser power ratio was ∼10. This fiber laser was compared with other three biconical tapered fiber lasers (the same fiber with different tapers) and a uniform geometry fiber laser. With intracavity biconical tapers, fiber lasers’ thresholds were ∼1 W higher than the fiber laser without the taper (1.97 W). The pump end’s slope efficiencies of fiber lasers with tapers were 3–5% in contrast with 37.6% of the uniform one. After tapered, the pre and post laser power ratios were much higher than the un-tapered one’s, but not changed much with the launched pump power.

Light beam coupling between standard single mode fibers and highly nonlinear photonic crystal fibers based on the fused biconical tapering technique

We propose and experimentally demonstrate light beam coupling between a single-mode fiber (SMF) and a highly nonlinear photonic crystal fiber (HN-PCF) based on the fused biconical tapering (FBT) technique. In our experiment, a standard SMF is pre-tapered to match its propagation constant to that of a HN-PCF. In order to remove the condensation in the air holes, the temperature is increased gradually to preheat the fibers. An appropriate level of hydrogen flow is administered to avoid the air-hole collapse. As a result, coupling ratio exceeding 90% between the SMF and HN-PCF is achieved. This technique avoids back Fresnel reflection, mode-field diameter (MFD) mismatch and fiber-core misalignment, bubble generation and air-hole collapse in the interface fusion splice.

Product and process optimisation design through Design of Experiments: A case study

Design of Experiments is an effective optimisation methodology. It has been widely used for product and process optimisation design. This paper presents a solution to optimise one of the key quality performances, the isolation of the fused biconical taper wavelength division multiplexer, using Design of Experiments in a communications company in Tianjin, China. The optimum process parameters have been found by response surface optimisation and the isolation has been improved.

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 °C, there exists a drawing speed of 150 μm/s, which makes the device’s performance optimum. Out of this speed region, the optical performance drops quickly. At drawing speed of 200 μm/s, the excess loss is relatively small when the fused temperature is above 1 200 °C. 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.