Simultaneous strain and temperature measurement based on a photonic crystal fiber modal-interference interacting with a long period fiber grating

An alternative all-fiber sensor for simultaneous strain and temperature measurement based on a photonic crystal fiber (PCF) spliced between single-mode fibers cascaded with a long period grating (LPG) is proposed. By collapsing the air holes at two splicing regions along the PCF, a simple but effective modal-interference (MI) is occurred between the core and cladding modes of the PCF. Due to the different responses on the changes of strain and temperature on the MI and the cascaded LPG, the strain and temperature can be measured simultaneously. Experimental results show that the sensing resolution of 9.1 με in strain measurement is experimentally achieved over a range of 2640 με, while the temperature sensing resolution is 0.27 °C within a range of 30-100 °C.     

A cheap and practical FBG temperature sensor utilizing a long-period grating in a photonic crystal fiber

A whole temperature sensor in one package utilizing a fiber Bragg grating (FBG) made in a conventional single-mode fiber and which uses a long-period grating (LPG) made in a photonic crystal fiber is proposed and experimentally demonstrated. The function of the interrogation is that the wavelength change of the FBG with environmental temperature is transferred to the intensity of the output via the LPG. Utilizing the temperature-insensitivity of the LPG in the PCF, the interrogation is stable and enables a cheap and practical temperature measurement system with a wide dynamic range.     

Photonic crystal fiber interferometer composed of a long period fiber grating and one point collapsing of air holes

We present an all-fiber interferometer fabricated with a single piece of an endless single-mode photonic crystal fiber (PCF) by an electric arc discharge. By forming a long period grating (LPG) at a point and collapsing the air holes at another point along the PCF, the simple but effective interferometer could be implemented. The LPG made a strong wavelength selective mode coupling between the core and cladding modes in the interesting wavelength range, while the air-hole collapse induced wavelength independent mode couplings. By cascading them, we could implement the all-fiber interferometer. As a potential application of the proposed all PCF interferometer, strain sensing is experimentally demonstrated.     

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.     

光子晶体光纤长周期光栅的谐振波长特性研究

利用有限差分法和耦合模理论分析了光子晶体光纤结构参数等因素对光栅周期调节长周期光栅谐振波长作用的影响,结果表明:对于同种光纤,可通过增大或减小光栅周期来减小或增大谐振波长;若占空比f增大或减小,可通过减小或增大光栅周期来保持谐振波长不变;若比例系数M增大或减小,可以成正比增大或减小光栅周期来保持谐振波长不变;在只是空气孔层数增加的系列光纤中,在长波处,为取得同一谐振波长,光栅周期需要增大数个m,但在短波处则正好相反;内层气孔对光栅周期调节谐振波长的作用影响较大,而第5层以外各层的影响十分微弱。综合利用这些规律,可以快捷地选择合适的光栅周期,高效率地制备有合适谐振波长的光子晶体光纤长周期光栅。     

Dependence of the brillouin frequency shift on strain and temperature in a photonic crystal fiber

The dependence of the Brillouin frequency shift on strain in a photonic crystal fiber (PCF) was measured at a wavelength of 1320 nm for the first time to the authors' knowledge. Together with measurements of the dependence of the Brillouin frequency shift on temperature in the PCF, we demonstrate the feasibility of the highly precise simultaneous measurement of temperature and strain by use of the PCF in a distributed Brillouin sensing system with a spatial resolution of 15 cm.     

光子晶体光纤中级联长周期光栅双谐振波长干涉的研究

通过分析单模光纤SMF中的LPG对的传输特性及几个因素对干涉透射谱的影响,并结合前期工作,主要研究光子晶体光纤(PCF)中的LPG对在1665 nm附近U波段传输特性.结合光栅耦合强度与波长的关系以及拍长与波长的关系,对PCF中LPG对的参数进行选择设计,得到双谐振波长的干涉谱,级联LPG对构成的MZI干涉光谱在两个谐振波长处由于耦合强度不同而不同.     

Mach-Zehnder interferometer formed in a photonic crystal fiber based on a pair of long-period fiber gratings

We demonstrate implementation of an all-fiber Mach-Zehnder interferometer formed in a photonic crystal fiber (PCF). We formed the all-PCF Mach-Zehnder interferometer by mechanically inducing two identical long-period fiber gratings (LPGs) in the PCF. The spectral properties of a LPG and a LPG pair were investigated. The interference fringe formed within the stop band of the LPG pair varied with the period and the strength of the gratings, and the fringe spacing was decreased with increasing grating separation. From the fringe spacing measurement the differential effective group index of the PCF was calculated to be deltam approximately equal to 2.8 x 10(-3).     

Tunable fiber gratings fabricated in photonic crystal fiber by use of mechanical pressure

The mode-coupling properties of tunable long-period fiber gratings (LPGs) formed in photonic crystal fibers (PCFs) are presented. The mode coupling from the fundamental core mode to a cladding mode of a PCF is obtained by use of periodic mechanical pressure. The strength and the wavelength of the resonant peak are tuned by adjusting the grating period and the pressure applied on the PCF. Contrary to the conventional fiber case, the resonant wavelength of the PCF LPG is decreased by increasing the periodicity.     

Deep-notch, ultracompact long-period grating in a large-mode-area photonic crystal fiber

An extremely short long-period grating (LPG) with strong resonance has been developed in a large-mode-area photonic crystal fiber (PCF) by use of the heat source of a CO2 laser. We believe that such a LPG in pure silica PCF is the first example to be obtained with the point-by-point technique. The fabrication method is simple and repeatable. The resulting LPG has 8 periods, written by a CO2 laser, within a 2.8-mm length of fiber, which yields a deep notch of core-cladding mode coupling of -31.5 dB at the telecommunication wavelength of 1529.2 nm, with a FWHM of approximately 0.7 nm. The principal advantages of this LPG are that it is practical, cost effective, and compact.     

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.     

Long period grating cascaded to photonic crystal fiber modal interferometer for simultaneous measurement of temperature and refractive index

We propose and demonstrate a novel and simple dual-parameter measurement scheme based on a cascaded optical fiber device of long-period grating (LPG) and photonic crystal fiber (PCF) modal interferometer. The temperature and refractive index (RI) can be measured simultaneously by monitoring the spectral characteristics of the device. The implemented sensor shows distinctive spectral sensitivities of -30.82 nm/RIU (refractive index unit) and 47.4 pm/°C by the LPG, and 171.96 nm/RIU and 10.4 pm/°C by the PCF modal interferometer. The simultaneous measurement of the temperature and external RI is experimentally demonstrated by the sensor. The temperature shift and RI shift calculated by the sensor matrix agree well with the actual temperature and RI change in the experiment.     

Supercontinuum generation in seven-core photonic crystal fiber pumped by a broadband picosecond pulsed fiber amplifier

We report a supercontinuum source generated in seven-core photonic crystal fibers(PCFs) pumped by a self-made all-fiber picosecond pulsed broadband fiber amplifier. The amplifier's output average power is 60 W at 1150 nm with spectral width of 260 nm, and its repetition rate is 8.47 MHz with pulse width of 221 ps. With two different lengths of seven-core PCF, different output powers and spectra are obtained. When a 10 m long seven-core PCF is chosen, the output supercontinuum covers the wavelength range from 620 nm to 1700 nm, with the output power of 11.7 W. With only 2 m long seven-core PCF used in the same experiment, the wavelength of the supercontinuum spans from 680 nm to 1700 nm,with the output power of 20.4 W. The results show that the pulse width is 385 ps in the 10 m long seven-core PCF and 255 ps in the 2 m long one, respectively, due to the normal dispersion of the PCF.     

利用双周期光纤光栅实现应变和温度同时测量

提出了一种新颖双周期光纤光栅传感器。在同一段氢载光纤上先后写入长周期光纤光栅、短周期布拉格光纤光栅 ,利用长周期光栅和布拉格光栅对应变和温度敏感性的差异 ,可实现应变和温度的同时测量。实验中采用这种灵敏结构的双周期光栅 ,在 0～ 170 0 με和 2 0℃～ 12 0℃范围内 ,测量精度可达到± 16 με和± 0 8℃。     

柚子型微结构光纤Bragg光栅温度和应变传感特性研究

通过对柚子型微结构光纤Bragg光栅的多个反射峰的温度和应变传感特性进行的理论和实验 研究，得出柚子型微结构光纤Bragg光栅的反射波长与温度呈二次关系，且理论和实验二者 吻合较好; 同时发现每个反射峰的温度灵敏度不同.理论分析柚子型微结构光纤Bragg光栅的 反射波长与应变呈线性关系，实验得到了该种Bragg光栅的反射波长与应变的线性关系，实 验结果与理论分析相吻合.由于微结构光纤光栅反射谱中多个峰对温度和应变等物理量敏感 度不一致，这种Bragg光栅更适合应用到多参量传感领域. 关键词： 微结构光纤 光纤Bragg光栅 温度传感 应变传感     

Generation of a compact high-power high-efficiency normal-dispersion pumping supercontinuum in silica photonic crystal fiber pumped with a 1064-nm picosecond pulse

Broadband normal dispersion pumping supercontinuum （SC） generation in silica photonic crystal fiber （PCF） is investigated in this paper. A 1064-nm picosecond fiber laser is used to pump silica PCF for the SC generation. The length of PCF is optimized for the most efficient stimulated Raman scattering process in the picosecond pump pulse region. The first stimulated Raman Stokes peak is located in the anomalous dispersion regime of the PCF and near the zero dispersion wavelength; thus the SC generation process can benefit from both a normal dispersion pumping scheme and an anomalous dispersion pumping scheme. The 51.7-W SC spanning from about 700 nm to beyond 1700 nm is generated with an all-fiber configuration, and the pump-to-SC conversion efficiency is up to 90%. In order to avoid the output fiber end face damage and increase the stability of the system, an improved output solution for the high power SC is proposed in our experiment. This high-efficiency near-infrared SC source is very suitable for applications in which average output power and spectral power density are firstly desirable.     

基于激光器激射特性的新型应变传感系统

报道了一种基于掺铒光纤激光器瞬态特性的新型应变传感系统.用光纤环反射镜和光纤Bragg光栅(FBG)构成Fabry-Perot线型腔.腔内插入一个长周期光纤光栅(LPG)，其透射谱的中心波长为1574.4nm.FBG的带宽为0.23nm，不受力时其反射波长为1557.98nm，位于LPG的透射谱左沿；当FBG受力时激射波长向长波方向移动，激光通过LPG时透射损耗增大，腔损耗的增加将使激光激射延迟时间增加.因此，应变的大小可以通过激光产生的延迟时间来测量.这种新型应变传感器的分辨率和灵敏度由抽运光脉冲的高、 关键词： 应变传感 光纤激光器 时域测量 光纤Bragg光栅     

Measurement of temperature and refractive index based on surface long-period gratings deposited onto a D-shaped photonic crystal fiber

We propose a surface long-period grating (LPG) based on a D-shaped photonic crystal fiber (PCF). The D-shaped PCF is fabricated by a side-polishing technique. The surface LPG based on periodic patterns of photoresist (PR) is formed by using the spin-coating and the standard contact lithography methods. Resonant coupling is created by the surface PR-LPG in the D-shaped PCF. The resonant peak shifts to longer wavelength as the ambient index is increased and shifts to shorter wavelength as the temperature is increased. The total wavelength shift is measured to be 122 nm in the refractive index range from 1 to 1.45 and the temperature sensitivity is measured to be −0.3 nm/°C in the temperature range from 30 to 100°C.     

Room temperature multiwavelength erbium-doped fiber ring laser using a highly nonlinear photonic crystal fiber

A multiwavelength laser source is demonstrated with a high power erbium-doped fiber amplifier as the gain medium. A highly nonlinear photonic crystal fiber (PCF) is inserted in the ring cavity to provide nonlinear gain by four-wave mixing. A Sagnac loop is incorporated in the ring cavity serving as a comb-like multichannel filter. The comparison between fiber ring laser without PCF and with PCF shows that the highly nonlinear PCF can generate a larger number of excited wavelengths and help stabilize the output power.     

环形光子晶体光纤中涡旋光的传输特性研究

由于涡旋光具有轨道角动量,将它应用于光纤通信领域可以有效提高信息传输速率.设计了一种环形光子晶体光纤,利用COMSOL Multiphysics软件对其涡旋光TE01,HE±21和TM01模式特性进行模拟计算,它们之间有效折射率差分别为4.59×10~(-4)和3.62×10~(-4);其中,TE01模式的涡旋光在入射光波长范围为1650—1950 nm时,色散值在44.18—45.83 ps·nm~(-1)·km~(-1)之间平坦;入射光波长在1550 nm时,TE01模式的涡旋光的非线性系数为1.37 W~(-1)·km~(-1).该结构的光子晶体光纤的涡旋光具有损耗小、色散平坦等特性,对光纤中传输涡旋光、将涡旋光应用于超连续谱等方面的研究具有重要意义.