Reconfigurable WDM add/drop multiplexer based on optical switches and fibre Bragg gratings

A reconfigurable wavelength-division-multiplexing (WDM) add/drop multiplexer (WADM) is constructed using optical switches (OSWS) and fibre Bragg gratings (FBGs). Selected one or two channel(s) can be added/dropped at the same multiplexer by properly controlling the optical switch pair and fibre Bragg grating arrangement. Afour-channel system is experimentally demonstrated for a data rate of 2.5 Gb s–1 and a single-mode fibre (SMF) distance of 100km. A negligible maximum power penalty of only 0.3dB is observed when compared with back-to-back transmission.     

Polymer optical fibre Bragg gratings based fibre laser

For the first time the fibre laser constructed from a polymer optical fibre Bragg grating is reported. The single frequency laser with the peak power of −5 dBm and signal to noise ratio greater than 45 dB has been achieved. Further examination demonstrates the excellent characteristics of the fibre laser. First, the fibre laser can be easily tuned over 35 nm by the simple axial tension method. Second, the fibre laser has the high strain sensitivity of 1.48 pm/με with the dynamic measurement range as large as 2.37%.     

Growth dynamics of Bragg gratings in multimode optical fibre

The spectrum of a Bragg grating in a multimode optical fiber can be controlled by the number of irradiation pulses during the writing procedure. Hence, a single mode grating can be fabrication readily within a multimode fiber. The width of the stop band of the grating can also be controlled by means of the number of irradiation pulses. A tilted grating leads to the coupling of core mode to cladding mode, and when the tilt is sufficiently large, eventually to radiation mode. In the case of small tilt, the grating spectrum is the sum of the core-core mode spectrum and the core-cladding mode spectrum.     

Investigation of a multiwavelength raman fiber laser based on few-mode fiber Bragg gratings

We propose and experimentally demonstrate a simple multiwavelength Raman fiber laser based on few-mode fiber Bragg gratings without additional multichannel filters. The multiwavelength Raman laser output has a high extinction ratio of more than 45 dB. The multiwavelength output is so stable that the peak power fluctuation is less than 0.5 dB. The number of lasing wavelengths can be adjusted, corresponding to the properties of few-mode Bragg gratings with multiple resonant wavelengths. By the thermal tuning method, the lasing wavelength of each channel can be effectively controlled, and the laser's tunability is measured to be 10.5 pm/ degrees C.     

Applications of optical fibre Bragg gratings sensing technology-based smart stay cables

Stay cable is one of the most critical structural components of a bridge. However, it readily suffers from fatigue damage, corrosion damage, and their coupled effects. Thus, health monitoring of stay cables is important for ensuring the integrity and safety of a bridge. A smart stay cable assembled with optical fibre Bragg grating (OFBG) strain and temperature sensors was proposed in this study. To protect the OFBG sensors against breakage in application, the OFBG sensors were first incorporated into a glass-fibre-reinforced polymer (GFRP) bar (GFRP-OFBG bar) when the bar was fabricated. To fabricate cables assembled with OFBG sensors, several GFRP-OFBG bars were inserted into the hollows of steel wires and fixed with the steel wires together at the anchorages of the cable. Therefore, the GFRP-OFBG bars can consistently deform with the steel wires in a cable and the smart stay cable can sense its own strain and temperature through OFBG sensors. The fabrication procedure of the smart stay cable was developed and the self-sensing property of the smart stay cable was calibrated. Finally, the application of the smart stay cables on the Tianjing Yonghe Bridge was demonstrated. The fatigue accumulative damage of the smart stay cables was evaluated based on field monitoring strain.     

Picosecond linear optical pulse shapers based on integrated waveguide Bragg gratings

We demonstrate a general linear pulse-shaping technique based on integrated III-V Bragg gratings (BGs). Such a technique allows for the synthesizing of complex waveforms with picosecond resolution using a compact single-waveguide design. This approach is experimentally demonstrated by fabricating and testing a series of integrated ultrafast optical pulse shapers based on BG geometries acting as time-domain code generators operating at 500 Gbits/s.     

Fiber Bragg gratings for optical telecommunications

Bragg gratings photoimprinted in optical fibers have become essential for flattening the gain of amplifiers, stabilizing the wavelength of pumps or sources, and for fiber lasers. Advantages are low insertion loss, very low polarization sensitivity and an extremely flexible design. Those advantages make gratings also very attractive candidates for applications of complex filtering or precise chromatic dispersion compensation. This article briefly describes the different types of Bragg gratings as well as several examples of applications in optical telecommunications. To cite this article: I. Riant, C. R. Physique 4 (2003).     

Development of a multiwavelength Raman fiber laser based on phase-shifted fiber Bragg gratings for long-distance remote-sensing applications

We propose a simple and flexible multiwavelength Raman fiber laser based on phase-shifted fiber Bragg gratings (FBGs) and a tunable chirped FBG. Using a simple multiwavelength Raman laser configuration with a single phase-shifted FBG and a tunable chirped FBG, we readily achieved simultaneous two-channel sensing probes with a high extinction ratio of more than 50 dB over a 50-km distance. The multiwavelength output was stable and the peak fluctuation was less than 0.5 dB. The temperature and strain sensitivities are estimated to be 10.1 pm/degrees C and 7.5 pm/microstrain, respectively.     

Fiber-fault monitoring technique for passive optical networks based on fiber Bragg gratings and semiconductor optical amplifier

A novel monitoring method for in-service fault indemnification in passive optical networks (PONs) is proposed and demonstrated experimentally. The proposed monitoring technique is based on fiber Bragg grating (FBG) sensors and fiber laser scheme, and a semiconductor optical amplifier (SOA) is used to serve as a gain medium. By detecting the number of the wavelength lasing, the fiber-fault can be monitored without affecting the in-service channels. Moreover, the strain behavior on the FBGs has also been discussed.     

低功耗非线性光纤光栅全光开关

全光开关是未来全光通信和光计算机的关键器件.已经研究过的全光开关的种类很多,其中光纤光栅全光开关最容易与光纤系统匹配.文章首先陈述两种基于普通石英光纤的单光栅全光开关,即光纤布拉格光栅(FBG)全光开关和长周期光纤光栅(LPFG)全光开关,这两种低非线性的光开关要求千瓦量级的高开关功率,故不宜应用;然后重点介绍两种高非线性的光纤光栅全光开关,它们分别由单个高非线性FBG和用高非线性光纤连接的LPFG对构成.文章所介绍的非线性光纤材料是以掺稀土石英光纤为例.这两种高非线性的光纤光栅全光开关具有毫瓦量级的低开关功率,有可能获得实际应用.     

低功耗非线性光纤光栅全光开关

光开关是未来全光通信和光计算机的关键器件.已经研究过的全光开关的种类很多,其中光纤光栅全光开关最容易与光纤系统匹配.文章首先陈述两种基于普通石英光纤的单光栅全光开关,即光纤布拉格光栅（FBG）全光开关和长周期光纤光栅（LPFG）全光开关,这两种低非线性的光开关要求千瓦量级的高开关功率,故不宜应用;然后重点介绍两种高非线性的光纤光栅全光开关,它们分别由单个高非线性FBG和用高非线性光纤连接的LPFG对构成.文章所介绍的非线性光纤材料是以掺稀土石英光纤为例.这两种高非线性的光纤光栅全光开关具有毫瓦量级的低开关功率,有可能获得实际应用.     

Bragg gratings in defect-free germanium-doped optical fibers

Bragg gratings have been written in germanium-doped optical fibers that have been treated to remove the UV absorption bands associated with oxygen-deficient defects. When one is using high-intensity 193-nm light from an ArF excimer laser to fabricate the gratings, the refractive index increases and the grating transmission spectra are similar to those obtained in standard (untreated) fiber.     

基于啁啾布喇格光栅的液位传感器

设计了一种基于啁啾光纤布喇格光栅的新型液位传感器,该传感器主要由矩形悬臂梁构成的传感机构和光纤光谱仪组成。导出了啁啾光纤布喇格光栅的反射谱带宽与液位的关系;通过光谱仪检测啁啾光纤布拉格光栅反射谱的带宽,就可以得到被测液位的高度。并对设计的传感器系统进行了实验验证,实验结果表明,该啁啾光纤布拉格光栅反射谱带宽对温度变化不敏感,且在测量范围内,反射谱带宽与被测液位间有很好的线性关系。     

Optimisation of superimposed chirped fibre Bragg gratings for the generation of ultra-high speed optical pulse bursts

Compact superstructure fibre Bragg gratings for the generation of ultra-high speed optical pulse bursts are reported. The gratings are equivalent in response to multi-pass superimposed chirped fibre Bragg gratings (SI-CFBGs), but an arbitrary sequence of consecutive gratings can be replicated in a single fabrication step using a simple trigonometric amplitude-phase function. SI-CFBGs are fabricated in photosensitive optical fibre and the time-resolved reflection of a 10 GHz picosecond pulse train is measured via frequency-resolved optical gating and optical sub-harmonic sampling detection techniques. The experimental results are compared to the theoretically simulated grating response and good agreement is found.     

Design of multi-channel optical code-division multiple-access encoders and decoders based on sampled fiber Bragg gratings

An encoding/decoding scheme of multi-channel optical code-division multiple-access (OCDMA) system using sampled fiber Bragg gratings (SFBGs) is proposed and numerically investigated. A multiple-phase-shift (MPS) technique based SFBG is first developed as a dense wavelength-division multiplexing (DWDM) device to accommodated multiple channels. The OCDMA scheme is achieved through phase coding/encoding on each individual channel of the SFBG and the auto correlative ratio for each user is larger than 14.3 dB. The whole system exhibits enhanced performance in terms of the capacity and security since the OCDMA technique is simultaneously implemented for all channels using the single SFBG.     

光致折变布拉格光栅实验研究

本文介绍了 2 48nm、Kr F准分子激光经过石英相位掩膜版的空间调制 ,在载氢增敏处理过的通信光纤与 B/Ge光纤上分别写入光致折变布拉格光栅的实验研究。经实验测定 ,在光栅布拉格波长上 (λH2 =15 46 .45 5 4nm ,λB/Ge=15 45 .15 5 nm) ,两种光栅反射率均大于 99% ,3d B带宽分别为 0 .12 9nm和 0 .182 nm。经比较 ,B/ Ge光纤比氢载光纤具有更好的光敏性和热稳定性     

Coupling characteristics of photo-induced Bragg gratings in depressed- and matched-cladding fibre

Experimental transmission spectra of ultraviolet (u.v.)-written Bragg gratings in depressed- and matched-cladding fibre are characterized and compared. In particular, we discuss how the location and strength of the spectral features vary with the degree of blazing, or angular tilt of the grating. The fine-structure detail on the short-wavelength side of the fundamental Bragg line is attributed to power coupling between the forwardpropagating fundamental (LP₀₁) mode and discrete, backward-propagating cladding modes. Resonances corresponding to backward-propagating LP_0n and LP_1n modes are identified, and their relative strengths are compared with theoretical overlap calculations. Physical arguments are presented that explain the pronounced ghost-grating notch that appears in the transmission spectra of blazed, fibre Bragg gratings in depressed-cladding fibre.     

Relative humidity sensor with optical fiber Bragg gratings

A novel concept for an intrinsic relative humidity (RH) sensor that uses polyimide-recoated fiber Bragg gratings is presented. Tests in a controlled environment indicate that the sensor has a linear, reversible, and accurate response behavior at 10-90% RH and at 13-60 degrees C. The RH and temperature sensitivities were measured as a function of coating thickness, and the thermal and hygroscopic expansion coefficients of the polyimide coating were determined.