Coupled torsional and longitudinal vibrations of piezoelectric fiber actuator with helical electrodes

The vibration characteristics of a piezoelectric fiber actuator with helical electrodes are studied theoretically and experimentally. Its working principle indicates that the torsional, longitudinal, and tangential deformations of the fiber are coupled. A simplified dynamic model is deduced to investigate the properties of the coupled vibrations and their corresponding equivalent circuits are also provided. Resonant frequencies and mechanical coupling coefficients in free-free boundary condition are calculated. The trends of resonant frequencies as functions of the electrode helical angle and fiber length are discussed and validated in experiments.     

New design for a photoelastic modulator

Modulation of the polarization of light can be achieved by a periodical birefringence. A new photoelastic modulator is described in this paper. In comparison with previously described apparatus, the originality of our mounting consists in the production of longitudinal resonance vibrations caused by shear stresses. These are generated by thin ceramics glued to one side of the material, birefringence modulation being thus achieved. Thanks to the use of ceramics, this modulator is much easier to construct than were the previous ones. The stray birefringence is kept very low in this instrument.     

Recirculation fiber loop interferometer with a Faraday reflector

A new optical scheme of the recirculation fiber loop interferometer with a Faraday reflector and a broadband radiation source is suggested. It is experimentally established that this scheme provides for a more than tenfold decrease in the instrument zero response caused by a spurious polarization modulation in the phase modulator. Factors leading to additional shifts in the instrument zero response are revealed.     

Low-cost optical amplitude modulator based on a tapered single-mode optical fiber

A new, to our knowledge, modulator based on a tapered single-mode optical fiber is introduced. The electro-optic device consists of a tapered optical fiber placed on a resonator made of a piezoelectric material. An electrical signal applied to the piezoelectric material makes the taper bend, and that displacement produces a modulation in the intensity of the optical signal traveling through the fiber. This device is very easy to build and is low in cost. Because of its nature, this new device might be very useful in optical fiber sensors. Its performance is analyzed, and the results are discussed.     

铌酸锂光纤型行波调制器研究

以LiNbO3光纤作为通光部分,Si2N2O为衬底分别取代了传统波导电光调制器的中Ti:LiNbO3波导和铌酸锂衬底设计了带宽为95.49 GHz铌酸锂光纤型调制器.今利用有限元法分析SCPS电极结构下该铌酸锂光纤调制器的性能.研究结果表明,该新型调制器可以在很宽的频带内实现调制速度的匹配和阻抗匹配,半波驱动电压为2.56 V,特性阻抗为55.3Ω.     

An economical piezoelectric phase modulator for fiber optic sensors

A homemade piezoelectric phase modulator for interfero-metric fiber optic sensors was fabricated using piezoelectric buzzers as strain elements. Six piezoelectric elements were embedded between the two halves of a bakelite cylinder split along its axis and secured tightly together again to form a cylinder. Single-mode optical fiber was then wound around the cylinder to complete the unit. Up to a frequency of 500 Hz, the phase shift produced by the modulator is linearly proportional to the amplitude of the applied voltage. The sensitivity of the phase modulator is about 3.6 rad/V and has a dynamic range of 1,000 rad, which is sufficient for most phase modulation purposes.     

Optical coupling method utilizing a lensed fiber integrated with a long-period fiber grating

A novel optical coupling scheme that uses a lensed fiber integrated with a long-period fiber grating (LPFG) is proposed. Two experiments are performed to demonstrate the validity of such a scheme in single-mode-fiber-single-mode-fiber (SMF-to-SMF) and laser-diode-single-mode-fiber (LD-to-SMF) coupling setups. The measured results show that for an appropriate lens radius the addition of a LPFG will lead to a higher coupling efficiency over a longer range of working distance than without the LPFG. Coupling efficiencies of ~78% and 35% are achieved for corresponding working distances of ~250 and 110 mum, 1-dB longitudinal tolerances of ~40 and 26 mum, and 1-dB transverse tolerances of ~7.6 and 2.6 mum for SMF-to-SMF and LD-to-SMF, respectively.     

Simultaneous measurement of multiparameters using a Sagnac interferometer with polarization maintaining side-hole fiber

A Sagnac interferometer with a section of a polarization maintaining side-hole fiber for multiparameter measurement is proposed. The sensor was experimentally demonstrated to be sensitive to torsion, temperature, and longitudinal strain, simultaneously. The birefringence in the investigated side-hole fiber is induced simultaneously by the elliptical shape of a germanium-doped core and by field overlap with the air holes surrounding the core. The latter effect is purely geometrical and causes high chromatic dispersion of the group birefringence in the long wavelength range, which results in a different period of spectral interference fringes. A different wavelength response is obtained for each interference fringe peak when the fiber is subjected to torsion, temperature, or longitudinal strain. A matrix equation for simultaneous measurement of the three parameters--torsion, temperature, and longitudinal strain--is also proposed.     

All fiber on-axis coupling scheme between single mode fiber and GRIN fiber

In this paper we present a simple and novel method to maximize on-axis coupling efficiency to radially symmetric fibers without the need for extra free space optical elements. The method is based on inserting a segment of step-index multimode fiber (MMF), cleaved to a particular length, between the input fiber and the output fiber (OF). The MMF segment modifies the input field to match the guided modes in the OF. Using this technique we show that, by inserting an appropriate length MMF segment, it is theoretically possible to obtain a coupling coefficient as high as ?0.8 dB between a single mode fiber and a graded index ring-shaped fiber and ?0.32 dB for a multi-shell fiber. Our experimental measurements showed good agreement with theoretical predictions for the ring fiber.     

Sensitive acoustic vibration sensor using single-mode fiber tapers

Optical fiber sensors are a good alternative to piezoelectric devices in electromagnetic sensitive environments. In this study, we reported a fiber acoustic sensor based on single-mode fiber (SMF) tapers. The fiber taper is used as the sensing arm in a Mach-Zehnder interferometer. Benefiting from their micrometer dimensions, fiber tapers have shown higher sensitivities to the acoustic vibrations than SMFs. Under the same conditions, the thinnest fiber taper in this report, with a diameter of 1.7 μm, shows a 20 dB improvement in the signal to noise ratio as compared to that of an SMF. This acoustic vibration sensor can detect the acoustic waves over the frequencies of 30 Hz-40 kHz, which is limited by the acoustic wave generator in experiments. We also discussed the phase changes of fiber tapers with different diameters under acoustic vibrations.     

Compression test of a single carbon fiber in a scanning electron microscope and its evaluation via finite element analysis

A longitudinal compression test for a single polyacrylonitrile-based carbon fiber (T300) was performed using a scanning electron microscope. The compressive stress/strain behavior was initially linear, but subsequently became nonlinear. The longitudinal tangent modulus decreased with increasing compressive strain. A cyclic compression test revealed that the T300 carbon fiber deformed elastically up to ~90% compressive strength. The variability in the compressive strength was evaluated using Weibull analysis. The representative compressive strength of the T300 carbon fiber was nearly the same as the tensile strength. The compressive strength of the T300 carbon fiber was almost same as that of the high-tensile strength T800S carbon fiber. Finite element analysis was performed to investigate the validity of the test method. The results showed that the longitudinal compressive stress on the carbon fiber varied during longitudinal compressive loading. The maximum longitudinal compressive stress in the carbon fiber was slightly higher than the average compressive strength applied at the end. However, the variability in the measured compressive strength was much higher than that in the longitudinal compressive stress on the carbon fiber, which does not affect the former.     

复合型超声马达纵-扭振动固有频率简并研究

纵、扭振动固有频率简并是提高纵-扭复合型超声马达输出力矩的关键问题。然而同一弹性体内的纵振固有频率远高于扭振固有频率．目前对两种振动固有频率的简并缺乏深入的理论研究。纵一扭复合型超声马达振动分析模型都基于一维理论。在此提出了一种纵、扭振动固有频率简并的新方法。通过将纵一扭复合型超声马达设计成双定子对称结构．在定子上附加一个调整环改变定子的力学边界条件。实现纵、扭振动同频共振。应用Hamilton原理建立了考虑泊松效应的定子纵、扭振动理论模型，分析了定子的纵振与扭振第一阶固有频率随调整环质量和位置的变化规律，通过优化马达的几何结构参数获得了纵振与扭振的同频谐振点。     

含金属芯压电纤维的纵向振动研究

建立了悬臂杆结构含金属性芯电纤维的纵向振动模型和动态测试模型。基于第一类压电方程,推导了外加简谐激励电压时,悬臂杆结构含金属芯压电纤维的等效纵向外力;基于纵向振动理论,推导出纵向振动模型;并由电位移,得到表面电荷、电流、导纳,建立了动态测试模型,通过测量共振频率fr、反共振频fa率和低频电容,计算出压电纤维的几个主要参数：弹性柔顺系数 、机电耦合系数 、介电常数 和压电常数 。详细叙述了纵向振动模型和动态测试模型的建立过程,并给出了具体的测试方法,提供了一个实际试样的测试结果。测试结果表明,根据纵向振动模型所建立的动态测试方法可以快速、准确地测量含金属芯压电纤维的主要参数。     

Detecting nanometric vibrations of a liquid surface by a metal-coated fiber tip

Optical radiation emitted from a metal-coated fiber tip apex when it emerges from a liquid into the air was measured. A strong enhancement of the output radiation and its strong dependence on the relative position of the tip to a liquid surface were observed. This phenomenon permits in situ recording of nanometric vibrations of the liquid and provides a basis for development of various ultrasensitive vibration detecting sensors.     

Piezoelectric fiber optic phase modulator with a reduced level of spurious polarization modulation

It is experimentally demonstrated that a tenfold decrease in the level of spurious polarization modulation can be achieved in a fiber optic phase modulator comprising two fiber sections featuring the polarization mode conversion, arranged on the same piezoelement.     

Multifrequency erbium-doped fiber laser operating at room temperature

A method to realize room-temperature operation of a multifrequency Er-doped fiber laser with low-frequency shift feedback placed within a linear laser cavity is theoretically proposed and experimentally demonstrated. Simultaneous multiwavelength lasing with 0.5 nm wavelength spacing is experimentally demonstrated by applying a sinusoidal signal of 10 kHz to a fiber phase modulator inserted within the linear cavity to prevent single wavelength steady-state oscillation. In the linear cavity, an all-polarization-maintaining fiber Sagnac loop is used as a periodic filter, and a single-mode fiber loop with a polarization controller is used as a partial reflector and also as an output port.     

The Ni-plated carbon fiber as a tracer for observation of the fiber orientation in the carbon fiber reinforced plastic with X-ray CT

Microfocus X-ray computed tomography (XCT) is effective to evaluate the 3-dimensional (3D) structure (position and orientation) of the fillers in the composites. However, the observation of the carbon fiber (CF) in resin by XCT is not easy due to the small difference between X-ray attenuation coefficient of CF and that of resin. We conducted XCT scanning of carbon fiber reinforced plastics (CFRPs) containing Ni-plated CF. The fiber orientation can be clearly observed in CT images due to a large X-ray attenuation coefficient of Ni-plating. Ni-plated CF essentially showed the same fiber orientation as that of normal CF. We also carried out the 3D characterization of the fiber orientation in an injection-molded dumbbell specimen with weld line. The fibers around the weld line are oriented perpendicular to the longitudinal direction of the specimen.     

A fiber optic phase modulator with an optical frequency shift of up to 20 GHz

A fiber optic phase modulator is described in which the phase of a light wave traveling in an optical fiber is modulated by a composite electromechanical resonator with Q≌1000. The instantaneous frequency of the wave at the modulator output varies according to a harmonic law. The interval of tuning of the instantaneous light wave frequency achieved in the experiment is 20 GHz, which corresponds to a modulation index of ≌10⁶. It is demonstrated that a maximum value of the frequency tuning range is determined by the elastic limit of the resonator material.     

All-fiber spot-size transformer for efficient free-space optical interconnecting devices

A new concatenated configuration of optical fibers is proposed to improve misalignment tolerance and working distance in a free-space optical interconnection. The structure is composed of three segments: a thermally expanded core fiber, a coreless silica fiber, and a claddingless graded-index fiber. A numerical analysis for the design of each fiber segment is performed completely, and the device characteristics are experimentally evaluated in terms of the tolerances for a 1-dB coupling-loss increment against longitudinal, transverse, and angular misalignments.     

Modeling of capillary flow in shaped polymer fiber bundles

Moisture transporting in fiber assembly is one of the critical factors affecting physiological comfort. In this study, we investigated at the capillary flow in complex geometries representative of the void spaces formed between fibers in shaped polymer fiber bundles. Dynamic process of liquid creeping in capillary is analyzed based on Reed and Wilson vertical wicking model. Critical equivalent radius values of capillary tubes in polymer fiber assembly are discussed here. In the cases of round, criss-cross and triangle shape fiber, Reed and Wilson model is integrated with shaped fiber bundle mathematical simulation model (MFB) to calculate the dynamic curve of liquid arising. Instantaneous wicking velocity, wicking height, wicking flux, and characters are compared to figure out that the wicking effect of shaped polymer fiber is quite better than normal round one.