Three methods for improving an axial strain sensitivity of polarization maintaining fiber loop mirror

Sensitivity is one of the important performances for sensor. Theoretical results show that we can choose a long wavelength monitoring point, a high strain dependent birefringence coefficient polarization maintaining fiber (PMF) and a low birefringence PMF to improve the axial strain sensitivity of PMF loop mirror, and experimental results show that the axial strain sensitivity has respectively been improved by 8.06, 30.73, and 22.26% by these methods. The advantage of these methods is to improve the axial strain sensitivity without increasing system complexity. These results help to improve the temperature, displacement, torsion, curvature and liquid level sensitivities of PMF loop mirror. These results can also be applied in photonic crystal fiber loop mirror.     

Temperature sensitivity of long period fiber grating in SMF-28 fiber

In this paper we have presented long period fiber grating (LPFG) as temperature sensor. Temperature based sensors have found a number of applications in commercial and industrial fields. In LPFG based temperature sensors, they respond to shift in various peak resonant wavelengths corresponding to various attenuation bands of the transmission spectrum. Temperature effect on the various attenuation bands of a LPFG have been investigated to create a highly sensitive measurement device. The temperature sensitivities of various attenuation bands of a LPFG over the wavelength region of 1.1–1.7 μm, for a grating period of 280 μm period, are obtained by monitoring the wavelength shift of each peak resonant wavelength with temperature increment of 20 °C, ranging from 0 °C to 100 °C.     

Comparison of single and double cladding long period fiber grating sensor using an intensity modulation interrogation system

The performance of long period fiber grating (LPFG) sensors written in single cladding and double cladding fibers have been compared by using a fast responding interrogation system based on intensity modulation. Temperature and dynamic strain monitoring using this system have been demonstrated. This system is capable of resolving strain to 0.2 and 0.4 με at a loading frequency of 20 Hz, and temperature resolution to 0.02 and 0.19 °C by using LPFG in the single cladding (SC-LPFG) and double cladding (DC-LPFG), respectively.     

Simultaneous strain and temperature measurement using a highly birefringence fiber loop mirror and a long-period grating written in a photonic crystal fiber

We present a new design for simultaneous strain and temperature measurement using a high-birefringence fiber loop mirror (HiBi-FLM) concatenated with a temperature-insensitive long-period grating (LPG) written in a photonic crystal fiber (PCF). The FLM acts as a sensor head, while the LPG in PCF serves as a filter to convert wavelength variation to optical power change. By measuring the wavelength variation and the power difference of two near peaks in the spectral response of this configuration, simultaneous strain and temperature measurement is obtained.     

Fiber laser switched by a long period grating interferometer as an intra-cavity loss modulator

In this paper we present an actively switched fiber laser with an all-fiber long-period grating-based interferometer used as an intra-cavity loss modulator. The modulator consists of two equal long-period gratings written sequentially in the same piece of a double-clad optical fiber. One of the gratings is fixed onto a piezoceramic cylinder producing fast modulation of the interferometer transmission spectrum. The laser demonstrates a stable regime of pulsed emission at repetition rates in the range of tens of kHz.     

Single-sideband modulated radio-over-fiber system based on long period fiber grating

We present a prototype for optical single-sideband (SSB) modulated radio-over-fiber (RoF) system by employing a long period fiber grating (LPFG). A LPFG with 13.78 nm base width of transmission spectrum and 0?23.2 dB of transmission depth was designed by using commercial software. Then it is used in RoF SSB modulation scheme. In the scheme, a Mach?Zehnder modulator modulates the light wave with millimeter-wave driving signals to realize optical double-sideband (ODSB) modulation, the generated ODSB modulation signals pass through a LPFG. Due to the negative slope in transmission spectrum, the lower sideband experiences higher attenuation than the upper sideband. Thus the conversion from ODSB to optical single sideband with carrier (OSSB + C) can be easily achieved by using only one LPFG. Also, the carrier to sideband ratio (CSR) can be reduced by using a LPFG, results show the CSR can be decreased from 12.49 dB to 1.1 dB.     

Temperature-insensitive strain measurement using differential double Bragg grating technique

A novel differential double Bragg grating sensor for temperature-insensitive strain measurement is presented. The sensor consists of two identical weak measuring and reference gratings separated by some distance. The reference grating is placed inside the silica capillary that made it almost strain insensitive. The basic idea in differential double Bragg grating sensor is to measure the energy of the oscillating term in the reflection spectrum of double Bragg grating structure. The normalized energy of the interference term depends on the pitch difference of the two gratings and does not change when pitch variations of both gratings are equal with temperature variation. Therefore, the normalized energy of the interference term can be used for the temperature-insensitive strain measurement.     

基于长周期光纤光栅的磁场传感方案的实现

长周期光纤光栅是近几年出现的一种新型光纤器件。其耦合机理是前向传输的纤芯基模与前向传输的各阶包层模式之间的耦合 ,这与光纤布喇格光栅明显不同。它对温度、应力、弯曲及外部折射率的变化具有相当高的灵敏度 ,是一种理想的光纤型敏感结构。提出利用长周期光纤光栅谐振波长的移动或移动变化量进行磁场强度的测量 ,并进行了理论推导、仿真实验及分析研究。得出了谐振波长变化量与外界磁场强度的关系模型。分析了设计中应该考虑的因素。     

Temperature-compensating multiple fiber Bragg grating strain sensors with a metrological grating

A novel approach based on multiple fiber Bragg gratings for measuring the distributed strain, which is temperature compensated, is demonstrated. Especially, in order to increase the measurement accuracy, a metrological grating is employed to read out the output of the system. The measurement resolution of the system is less than 0.5 μ.     

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.     

Novel fiber design for broadband long period gratings

We report a novel fiber design for obtaining long period gratings (LPGs) having a broad transmission spectrum. These gratings are based on guided to guided mode coupling in a staircase profile fiber. Numerical simulations predict 20 dB bandwidths as high as 100 nm and an estimated insertion loss of less than 1 dB. Such broadband LPGs are expected to find applications in many all fiber components.     

Detection and analysis of paraffin oil adulteration in coconut oil using fiber optic long period grating sensor

A fiber optic sensing system for the detection of adulteration of coconut oil by paraffin oil is experimentally demonstrated. The sensing mechanism is based on the sensitive dependence of the resonance peaks of a long period grating (LPG) on the changes of the refractive index of the environmental medium surrounding the cladding surface of the grating. The wavelength shift of the attenuation bands of the LPG was measured with the sensor immersed in a mixture of paraffin oil and pure coconut oil in different proportions. Detection limit of adulteration was found to be 3% for coconut oil-paraffin oil binary mixture.     

Temperature-sensitive dual-segment polarization maintaining fiber Sagnac loop mirror

A new temperature-sensitive fiber Sagnac loop mirror (FLM) is proposed using two segments of polarization maintaining fiber (PMF). The proposed dual-segment FLM provides greater temperature sensitivity in the spectral spacing detuning compared to the conventional single-segment configuration. Besides, the proposed configuration also enables both efficient positive and negative spectral spacing detuning by rising the temperature of one of the PMF segments. The experimental results show that the proposed configuration has achieved a great improvement in increasing spectral spacing variation range by 6.6 times and an increment of temperature sensitivity as much as 337.6% as compared to the conventional configuration.     

Optimization of photonic bandgap fiber long period grating refractive-index sensors

Long period gratings in low-index contrast solid-core photonic bandgap fibers are a promising platform for fiber-based fluid refractive index sensing with very low detection limits. We provide a comprehensive investigation of the possibilities for refractive index sensing using that principle in a commercial photonic crystal fiber filled with a fluid: using an acoustic grating, we map out the cladding bands, and use this data to optimize a long period grating’s sensitivity. We then implement the optimized long period grating, again using an acoustic grating, and directly measure its sensitivity to refractive index. We demonstrate a sensitivity of 17,900 nm/RIU (6.94 nm/°C) which corresponds to a smallest detectable index change of the fluid of 8.4 × 10⁻⁶.     

Study and investigation of long period grating as refractive index sensor

In this paper, we have investigated the response of long period grating (LPG) as refractive index sensor. The response has been studied for refractive index variation ranging from 1 to 1.45. In this work, we found that the sensing mechanism is based on two different aspects. First is the change of coupling power from the guided core mode to other co-propagating cladding modes and second is the wavelength shift of the peak resonant wavelengths from their original positions due the change of refractive index of the environmental (external) medium surrounding the cladding of the grating.     

Dual-resonance long-period grating in fiber loop mirror structure for liquid refractive index measurement

An interferometric structure based on a Dual-Resonance Long-Period Grating (DRLPG) within a Fiber Loop Mirror (FLM) is presented in this paper. Its purpose is to measure the refractive index (RI) of liquid analytes. The grating is the RI sensing probe, while the FLM serves as a band-pass filter. Due to the high extinction ratio of the FLM, amplitude measurements can be obtained, allowing implementation of the differential interrogation method to establish the sensitivity of the device. The use of a polarization controller makes it possible to fine-tune the interferometric peaks with respect to the two notches of the DRLPG. Precisely aligned configuration produces a maximum sensitivity of 3871.5?dB/RIU within the RI range of 1.3333 up to 1.3419 with linear sensor response.     

长周期光栅生物传感器研究进展

长周期光纤光栅是对周围环境比较敏感的一种无源光学器件,由于其具有无后向反射、对折射率灵敏度高、体积小、易于集成化、不受电磁干扰、耐酸碱腐蚀、不需要参比电极等诸多特点,在折射率传感领域备受关注。自从2000年Bentley研究组第一次将长周期光纤光栅用于抗原的检测以来,经过十余年的发展,长周期光栅在生物物质的检测方面取得了很大的进展,已被用于抗原抗体、细菌病毒、蛋白质、DNA、酶及核酸等诸多生物物质的检测。本文对长周期光纤光栅近年来在生物传感领域的研究进展和应用进行了总结和评述,并对长周期光纤光栅在生物物质检测方面的未来发展趋势做了展望。     

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.     

保偏光纤光栅温度传感性能的实验研究

在经过氢敏化处理的保偏光纤上制作了中心波长在1300 nm窗口的光纤布拉格光栅，并对这种保偏光纤布拉格光栅的温度传感特性进行了实验研究与理论分析。结果表明这种光栅可以用作温度传感器，对温度进行测量。和普通的标准单模光纤布拉格光栅一样，它对温度的响应具有很好的线性关系。本实验结果还可以作为对保偏光纤光栅传感特性进一步深入研究的参考。     

Hetero-core fiber Bragg grating for simultaneous measurement of strain and bending based on cladding mode ratiometric detection

A simple but practical method using multimode-single mode fiber Bragg grating (FBG) for cladding mode based simultaneous measurement of strain and bending is proposed and investigated experimentally. Experimental results show that the intensity ratio between cladding mode and FBG resonance of hetero-core FBG show monotonous changes following with the increase of deflection, by which strain and bending discrimination can be achieved by measuring the wavelength shift of FBG resonance and ratiometrically detecting the intensity changes between cladding modes and FBG resonance.