Discrimination of strain and temperature based on a polarization-maintaining photonic crystal fiber incorporating an erbium-doped fiber

A simple sensing method for simultaneous measurement of temperature and strain is investigated by using a Sagnac fiber loop mirror composed of a polarization-maintaining photonic crystal fiber (PM-PCF) incorporating an erbium-doped fiber (EDF). Amplified spontaneous emission created by a pumped EDF is transmitted to a Sagnac fiber loop mirror. The interference between two counter-propagating signals in a Sagnac fiber loop mirror generates a periodic transmission spectrum with respect to wavelength. When external temperature is increased, the transmission peak power reduces because the amplified spontaneous emission of the EDF is decreased by the applied temperature change (0.04 dB/°C). The peak wavelength is shifted into the shorter wavelength because of the negative temperature dependence of the birefringence of the PM-PCF (0.3 pm/°C). As the applied strain increases, the peak wavelength of the transmission spectrum of the Sagnac loop mirror incorporating the EDF shifts into a longer wavelength (1.3 pm/με) because the phase change of the proposed sensing probe is directly proportional to the applied strain. The transmission peak power, however, is not changed by the applied strain. Since the source and the sensing probe are integrated, the overall system configuration is significantly simplified without requiring any additional broadband light source. Therefore, it is possible to simultaneously measure temperature and strain by monitoring the variation of transmission peak power and peak wavelength, respectively.     

Hybrid configuration of Sagnac and modal interferometer with high extinction ratio

A hybrid configuration of Sagnac and modal interferometer is proposed to obtain high extinction ratio (ER). Firstly, a modal interferometer based on core-offset splicing of three sections of single mode fiber is obtained through manually controlling the fusion parameters. Then the modal interferometer is inscribed into a Sagnac loop, which can obtain a higher ER by carefully adjusting the polarization controller (PC). There is about 10 dB extinction ratio higher than the modal interferometer. The higher the extinction ratio is, the sharper the bottom of waveform will be, so the wavelength shifts can be measured more accurately when sensing temperature, pressure or other parameters. The measured sensitivity of temperature is 48.67 pm/°C in the band of 1550 nm. It also can be applied in strain measurement, vibration measurement and so on.     

Performance of a wavelength-tunable erbium-doped fiber laser using a Sagnac interferometer

We experimentally demonstrate a wavelength-tunable erbium-doped fiber laser that is composed of a ring cavity and a single-mode fiber Sagnac interferometer in a new and simple arrangement. We find that the fiber laser output wavelength is tunable by adjusting the filter effect of the Sagnac fiber loop through a fiber polarization controller set there. The quasi-single-wavelength continuously tunable laser outputs could be achieved within some wavelength range. The multi-wavelength laser outputs could also be observed under some appropriate settings of the polarization controller. A theoretical demonstration of the wavelength tunability about the transmission-type Sagnac loop filter has also been achieved using the Jones calculus theory.     

基于低双折射光子晶体光纤Sagnac干涉仪的超低温度系数扭曲传感器

研究了低双折射光子晶体光纤中由光纤扭曲造成的圆双折射效应,并应用Sagnac干涉仪结构设计了扭曲传感器.在Sagnac环中的光子晶体光纤上施加机械压力引入初始线双折射并产生正弦干涉光谱,再扭曲光纤产生圆双折射使干涉光谱随扭曲角度移动.光谱峰值波长随扭曲角度变化符合Sinc函数关系,理论分析与实验相符.传感器灵敏度为1.00 nm/°,分比率为0.01°,并具有超低的温度系数-0.5 pm/℃.     

Temperature and strain discrimination using two parallel connected Sagnac loops based on character-1 shaped polarization-maintaining fiber

A fiber sensor configuration suitable for discrimination of temperature and strain is presented. The sensor head is composed of two parallel concatenated Sagnac loops based on character-1 shaped polarization-maintaining fiber (PMF). The two Sagnac loops include different sections of character-1 shaped PMFs, and show different sensitivity to temperature and strain. By monitoring the wavelength shift of the two dips in the transmission spectrum, simultaneous measurement of temperature and strain is obtained. The sensitivity for strain and temperature are measured to be 14.46 pm and ? 0.54 nm.     

Birefringent photonic crystal fibers with zero polarimetric sensitivity to temperature

We designed, fabricated, and characterized birefringent holey fibers with zero polarimetric sensitivity to temperature. The sensitivity measurements were carried out in a wide spectral range of 0.68–1.55 μm in fibers with different hole and pitch values and with birefringence induced by a pair of large holes adjacent to the core. Our results show that zero sensitivity to temperature can be obtained at certain wavelengths for the bare fibers with properly adjusted geometrical parameters. Moreover, the spectral measurements of the sensitivity to temperature are in good agreement with the modeling results for all the investigated fibers.     

基于PDMS材料的Sagnac干涉光纤挥发性有机物传感器

在一段8cm长的保偏光纤两端分别熔接两段普通的单模光纤,在保偏光纤的侧面均匀地镀上一层聚二甲基硅氧烷材料,聚二甲基硅氧烷材料经该段保偏光纤接入到一个光纤耦合器中,从而形成一个光纤Sagnac干涉仪.聚二甲基硅氧烷材料吸附挥发性有机物分子时,会引起聚二甲基硅氧烷材料体积上的膨胀,导致Sagnac干涉波长的漂移,通过对Sagnac干涉光波长漂移的测量即可实现对挥发性有机物气体的检测.实验测量了传感器对挥发性有机物浓度的响应,结果表明,在0~6 000ppm浓度范围内,传感器的灵敏度为1.03pm/ppm,由光谱仪的最小分辨率为0.02nm可知,该传感器对挥发性有机物的检测下限约为19.4ppm.该传感器相比聚二甲基硅氧烷材料与光纤光栅结合的传感器,灵敏度提高了4 300倍.     

Temperature independent torsion sensor using a high-birefringent Sagnac loop interferometer

A high-birefringent (Hi-Bi) Sagnac loop interferometer for torsion measurement is demonstrated. The sensing head is formed by a section of standard single mode fiber spliced between the output ports of a Hi-Bi coupler at 3 dB. The sensing configuration is characterized in torsion, temperature and strain. The results obtained indicate the viability of a torsion sensor independent of the temperature and strain cross-sensitivity effects. Additionally, in the proposed configuration all measurements are performed without the need of a polarization controller, a device most often required in standard Sagnac loops applied for sensing.     

A Distributed Fibre Bragg Grating Sensor Interrogator Employing a Reformative Arrayed Waveguide Grating

We present an interrogating technique employing a reformative arrayed waveguide grating without output waveguides in combination with a linear charge coupled device. A simple and effective data processing method called area equalized point is used to improve the system resolution. The simulation results show that the wavelength shift of a fibre Bragg grating with temperature can be precisely measured by this interrogation technique. The temperature accuracy and wavelength resolution of the sensor system are smaller than 0.08℃ and 0.8pm, respectively. If the FBG 3dB-bandwidth is 0.2nm with the wavelength spacing between two adjacent FBGs of 1.4 nm, the temperature and wavelength errors caused by crosstalk are respectively 0.01℃ and 0. 1 pm.     

Anti-Stokes Frequency Shift and Evolution in Polarization-Maintaining Photonic Crystal Fiber with Two-Zero Dispersion Wavelengths

Using the tunable pump pulses with about lOO fs pulse duration and 1064 nm central wavelength; the polarization-, wavelength- and power-dependent anti-Stokes lines are generated and modulated simultaneously in a polarization-maintaining photonie crystal fiber （PM-PCF） with two zero-dispersion wavelengths. By accurately controlling the polarization directions, the wavelength and the power of the pump pulse in the fiber anomalous region close to the second zero-dispersion wavelength of the PM-PCF, the output anti-Stokes pulse spectra can be tuned between 563 nm and 603 nm, which is in good agreement with the theoretical simulation. The color conversion of the mode image from yellow to orange is also observed with the different polarization pump pulses. These results can be attributed to the combined interaction between the fiber birefringence （including linear- and nonlinear- birefringence） and dispersion, and are attributed to phase-matching parametric four-wave mixing.     

Simultaneous measurement of strain and temperature with a long-period fiber grating inscribed Sagnac interferometer

A Sagnac interferometer with a long-period fiber grating (LPG) inscribed in the polarization-maintaining fiber (PMF) is proposed and experimentally demonstrated for simultaneous measurement of strain and temperature. Due to the different responses of the LPG and the Sagnac interferometer to strain and temperature, simultaneous measurement can be achieved by monitoring the wavelength shifts and the intensity changes of a resonance dip of the sensor setup. The experimental results show that the achieved sensitivities to strain and temperature are 6.4 × 10^− 3 dB/με and 0.65 nm/°C, respectively.     

Mach-Zehnder all-fiber interferometer using two in-series fattened fiber gratings

We present an all-fiber Mach-Zehnder interferometer consisting of two consecutive fattened sections of dispersion-shifted fiber that act as in-series long period fiber gratings. The proposed Mach-Zehnder interferometer shows a broad fringe pattern ranging from 1000 to 1500 nm and is stable against changes in temperature and strain. By tapering a section of 5mm in length to 50% diameter between the fattened sections we observe an increased sensitivity to temperature changes. The measured temperature and strain sensitivities were in the range of 9–17 pm/°C and 1.44–2.9 pm/μɛ, respectively.     

Picosecond optical switching of a 1.5 μm active birefringent optical fiber loop filter using 1.3 μm control optical pulses and a 1.3 μm semiconductor optical amplifier

Less than 100ps, polarization-independent switching operation of an active birefringent optical fiber loop filter using 1.3 μm control optical pulses as well as a 1.3 μm semiconductor optical amplifier (SOA) has been demonstrated. In the proposed SOA-based active birefringent filter operating at 1.55 μm wavelength, 1.3 μm SOA is employed to control the polarization-mode dispersion in the loop part. By injecting 1.3 μm ps gain-switched optical control pulses into the SOA, 1.5 μm input signals can be switched from the transmission port to the reflection port with less than 100 ps rise time.     

基于长周期光纤光栅和保偏光纤Sagnac环光谱特性的温度与应变测量研究

提出并研制了一种结构简单、成本低廉的温度与应变同时测量系统,其结构是在保偏光纤Sagnac环内接入一个长周期光纤光栅(LPFG)。利用LPFG对保偏光纤Sagnac环的透射光谱进行调制,通过监测谐振峰波长和强度的变化,发现波长随温度和保偏光纤的应变变化,强度随LPFG的应变变化,因此可以实现温度与应变的区分测量,并且可判断出应变的施加位置。实验得到该系统的温度灵敏度为0.181 81 nm·℃-1,LPFG区的应变灵敏度为0.005 283 dB·με-1,保偏光纤Sagnac环区的应变灵敏度为0.015 72 nm·με-1。实验结果表明该方案可行,并具有一定的实用性。     

基于全光纤萨格纳克干涉仪的温度不敏感磁场测量

研究了双折射磁光光纤萨格纳克 (Sagnac) 干涉仪透射谱的磁场和温度敏感性. 实验表明, 干涉仪透射谱会随着温度的增加向短波长移动 (温度系数为-0.435 nm/℃), 其波长依赖性则随着磁场的增加而降低. 据此, 通过调节干涉仪内偏振控制器状态实现了温度不敏感的磁场测量, 磁场系数为189 mW/T², 实验结果与理论分析一致. 关键词： 磁场测量 磁光效应 双折射 萨格纳克干涉仪     

基于低双折射光子晶体光纤Sagnac干涉仪的超低温度系数扭曲传感器

研究了低双折射光子晶体光纤中由光纤扭曲造成的圆双折射效应,并应用Sagnac干涉仪结构设计了扭曲传感器.在Sagnac环中的光子晶体光纤上施加机械压力引入初始线双折射并产生正弦干涉光谱,再扭曲光纤产生圆双折射使干涉光谱随扭曲角度移动.光谱峰值波长随扭曲角度变化符合Sinc函数关系,理论分析与实验相符.传感器灵敏度为1....     

Fast wavelength-switching of a diode-pumped solid-state disk laser

The functionality of two experimental setups for fast wavelength-switching of an Yb:YAG disk laser is tested and characterized. The first setup consists of two resonators sharing one disk. Both resonators are alternately opened by a chopper disk. Each resonator is tuned independently by a set of a two-stage Lyot filter and an etalon. Up to 1500 Hz the setup can switch between two freely selectable wavelengths (linewidth (fwhm) ≪1 pm) within the complete Yb:YAG tuning range (from 1020 nm to 1055 nm) emitting a maximum average power of 105 mW. The power of both resonators differs by a factor of 0.7. Their pointing stability amounts to 20 μrad. The second setup consists of a single tunable resonator (two-stage Lyot filter, etalon) additionally equipped with an electro-optical device (Faraday rotator or Pockels cell) providing a high pointing stability of better than 1 μrad. The wavelength switches occur stepwise and are predetermined by the etalon (about 90 pm or multiples thereof). The Faraday rotator suffers from its high thermal load and operates for some few 10 s only at 0.5 Hz. The resonator with the Pockels cell provides long term stability at 1000 Hz, switching steps up to 1.1 nm and a power ratio of 0.83 for the selected wavelengths.     

Tuneable Sagnac comb filter including two wave retarders

In this paper we study theoretically and experimentally a wavelength-tuneable Sagnac birefringence filter. The device is a Sagnac interferometer including a symmetric fibre coupler and a length of high-birefringence fibre in the loop. A wave retarder is inserted at each end of the birefringent fibre for absolute wavelength tuning. We show theoretically that wavelength tuning through wave plate orientation ensuring constant amplitude of the filtering function is possible only if a minimum of two wave retarders are included in the setup. The position of the transmission peaks then varies linearly with the angle of one of the retarders and can be adjusted over one entire channel spacing. This happens only when a quarter-wave retarder and a half-wave retarder are used, if the former is oriented at 45° with respect to the fibre birefringence axes, while the orientation of the latter serves as the adjustment parameter. The theoretical predictions are confirmed by the experimental results.     

A near-infrared zero-order achromatic retarder

Phase retarders normally show strong wavelength dependence. Achromatic retarders which exhibit nearly identical characteristics over a wide wavelength spectrum is used in polychromatic light. The present investigation deals with a technique to design and study the characteristics of an achromatic combination of birefringent plates in 800–2000 nm range. The retarder has been designed using calcite, crystalline quartz and ADP. The thicknesses of the plates are 19.38 μm, 446.14 μm and 12.57 μm respectively. The new arrangement of three birefringent plates proposed has the promise of producing a zero-order quarter wave achromatic combination with fairly good accuracy.     

Optical fiber strain and temperature sensor based on an in-line Mach–Zehnder interferometer using thin-core fiber

We propose and demonstrate a fiber in-line Mach–Zehnder interferometer using thin-core fibers. This in-line interferometer is composed of a short section of thin-core fiber inserted between two single mode fibers (SMF), and demonstrated as a strain and temperature sensor in this study. A strain sensitivity of ?1.83 pm/με with a measurement range of 0?2000 με, and the temperature sensitivity of ?72.89 pm/°C with a temperature variation of 50 °C are achieved. We also discussed that the influence of strain and temperature change on the relative power ratios among the excited cladding modes in thin-core fibers.