Polarisation-scrambled Er-doped superfluorescent fibre source with improved mean-wavelength stability

A polarisation scrambling scheme is employed to reduce the pump-polarisation-dependent mean-wavelength change in the Er-doped superfluorescent fibre source for gyroscope application. A PZT-based fibre-optic polarisation modulation is used at the pump port for polarisation scrambling. Changes of mean wavelength owing to pump polarisation variation are suppressed below 1 ppm.     

采用光纤滤波器的高波长稳定性掺铒光纤光源

研究了双程后向结构掺铒光纤光源的平均波长对泵浦功率的赖性。实验结果表明,通过采用掺铒光纤滤波器以及选择合适的泵浦功率,平均波长随泵浦功率的变化能够降低到-9 ppm/mW。在-40~+60℃ 温度范围内,光纤光源的平均波长不稳定性小于33 ppm(峰峰值)。采用5 m 长的掺铒光纤、泵浦功率55mW 与泵浦波长974.2nm 时,光纤光源输出光波的谱宽达到17nm,功率达5.83mW。     

A depolarized Er-doped superfluorescent fiber source with improvedlong-term polarization stability

In a backward Er-doped superfluorescent fiber source (SFS), we report the observation of large mean wavelength variations (>100 ppm) induced by external perturbations of the fiber birefringence. These previously unreported variations, which need to be reduced to the ppm level for high-accuracy fiber-optic gyroscope applications, are shown to originate first from polarization-dependent gain induced by the polarized pump source, and second from a slight polarization dependence of the SFS wavelength division multiplexing (WDM) coupler and fiber isolator. We demonstrate that these effects can be substantially reduced by incorporating two Lyot fiber depolarizers in the source. The new depolarized SFS exhibits short-term mean wavelength stability of ±2.5 ppm and a long-term drift of ±3 ppm. The latter is probably due mostly to slow variations in the Er-doped fiber temperature, which can be eliminated with a simple temperature control to ~0.1°C     

Sensor interrogation technique using chirped fibre grating basedSagnac loop

A novel and simple sensor interrogation scheme for fibre Bragg grating (FBG)-based sensing systems is demonstrated. In this scheme, a chirped FBG-based Sagnac loop is used as a wavelength-dependent receiver, and a stable and linear readout response is realised. It is a significant advantage of this scheme that the sensitivity and the measurement wavelength range can be easily adjusted by controlling the chirp of the FBG or using an optical delay line in the Sagnac loop     

Wide-stopband chirped fibre moire grating transmission filters

Efficient, wide-stopband fibre transmission filters with single narrow transmission bands produced using multiply exposed chirped fibre grating resonators are reported. Tailored combinations of these structures with additional chirped gratings have achieved single passband transmission with an effective finesse of 48. This demonstrates the feasibility of fabricating all-fibre transmission filters with arbitrary passband/stopband combinations     

Continuous photonic microwave true-time delay using tapered chirped fibre Bragg grating

A photonic microwave true-time delay using a tapered chirped fibre Bragg grating is proposed and fabricated. A resistive heating electrode coated on the tapered fibre and a single-wavelength light was incorporated to control the time delay continuously without any mechanical perturbation and moving. It was achieved by adjusting the reflection positions of the optical signal carrying the microwave signal from within the tapered grating via the thermo-optic effect. The measured time delay was /spl sim/120 ps with electrical power consumption of 250 mW.     

A polarization-stable Er-doped superfluorescent fiber source including a Faraday rotator mirror

We report a tenfold stability improvement in the mean wavelength variations induced by polarization fluctuations in an Er-doped superfluorescent fiber source. This was accomplished by replacing the mirror in a double-pass source with a Faraday rotator mirror, thereby nearly eliminating polarization dependent gain. The resulting mean wavelength variations of less than 3.5 parts-per-million (limited by the detection noise floor), approach the requirement for inertial-grade fiber optic gyroscopes.     

抑制掺铒光纤光源强度噪声的方法研究

目前,高精度光纤陀螺普遍采用掺铒光纤光源,对这种陀螺来说检测灵敏度受强度噪声限制.分析了强度噪声的特点及对陀螺的影响,并提出了一种软件实现的方法来抑制强度噪声,经验证随机游走减小了30%.     

高平均波长稳定性超荧光光纤光源

光纤陀螺要求其光源具有高功率、宽谱输出,同时在大温度范围内仍具有好的平均波长稳定性。为了满足-45℃~70℃大温度范围的应用需求,采用双程后向抽运、法拉第旋转反射、带通滤波等技术手段,对光纤材料和器件进行大温区全局优化,以改善超荧光光纤光源的平均波长稳定性。理论分析了不同中心波长和带宽的带通滤波器以及光纤长度等参量对平均波长稳定性的改善效果,以及和光谱带宽的关系。按照设计结果选择滤波、光纤长度等参量,通过对-45℃~70℃全温区范围进行系统全局优化设计,得到输出功率为32mW,功率稳定性为0.65%,光谱带宽为12.5nm,光源平均波长变化量为23.5×10-6。结果表明,平均波长稳定性在0.5×10-6/℃以下的高稳定性超荧光光纤光源中,32mW输出功率非常高;所得的0.2×10-6/℃是115℃大温差范围、30mW以上超荧光光纤光源中非常优异的平均波长稳定性指标,满足光纤陀螺对光纤光源的要求。     

Time delay measurement of chirped fibre grating using bidirectional modulation of Mach-Zehnder modulator

A simple method for time delay measurement of a chirped fibre grating by using bidirectional modulation of a Mach-Zehnder modulator is proposed. The bidirectionally modulated light with time difference produces an interference fringe in the RF domain. The time delay of a chirped fibre grating can be obtained by measuring the period of the RF interference fringe from different wavelengths.     

High-sensitivity low coherence reflectometer using erbium-doped superfluorescent fibre source and erbium-doped power amplifier

A broadband light source with an output of 150 mW at 1536 nm is constructed by using an erbium-doped power amplifier coupled to an erbium-doped superfluorescent fibre source. A nearly shot-noise-limited sensitivity of -161 dB and a dynamic range of 54 dB are achieved with an optical low coherence reflector using this source.<>     

1 Watt Er/Yb singlemode superfluorescent optical fibre source

A singlemode superfluorescent Er/Yb optical fibre source is described, capable of generating >1 W of output power. The spectral bandwidth of the source can be varied between 0.5 and 4 nm by filtering     

Tunable chirped fibre Bragg grating device controlled by variablemagnetic fields

A novel dynamic chirping fibre Bragg grating device based on a magnetic field applied to a magnetostrictive transducer capable of tuning its dispersion is presented. Chirping ranges up to 300 ps/nm have been demonstrated, which are suitable for several applications such as tunable transversal filtering and dynamic dispersion compensation     

Ultrahigh-sensitivity low coherence OTDR using Er/sup 3+/-doped high-power superfluorescent fibre source

The first-known demonstration of an Er/sup 3+/-doped superfluorescent fibre source coupled to a high-resolution OTDR based on low coherence interference (low coherence OTDR) is reported. Linearly-polarised light with 14 mW output from the source achieves a -146 dB minimum detectable reflectivity at 3 Hz bandwidth. The spatial resolution determined by spectral FWHM is 28 mu m for silica-based waveguides.<>     

Dispersion compensation over 270 km at 10 Gbit/s using anoffset-core chirped fibre Bragg grating

A 120 mm long fibre Bragg grating, adjustably chirped by an offset-core technique, compensates for dispersion in a 10 Gbit/s optical communication system operating at 1054 μm over 270 km of non-dispersion-shifted fibre. Simultaneous compensation of fibre dispersion and source chirp in a directly modulated system is also described     

Spectrally flattened phase-locked multi-carrier light generator with phase modulators and chirped fibre Bragg grating

Described is a phase-locked multi-carrier light generator with a flattened spectral envelope that contains two phase modulators and a dispersion medium. By adopting a chirped fibre Bragg grating as a dispersion medium instead of a long normal dispersion fibre, the stability of the optical output spectrum can be increased and the size of the multi-carrier light generator reduced. A prototype has been built with this configuration, that generates a 61 carrier light with a power deviation of less than 8 dB.     

啁啾光栅解调的准分布式光纤Bragg光栅传感器

为了提高光纤Bragg光栅(FBG)的应用范围.提出一种线性啁啾光栅(CFBG)解调的准分布式FBG传感系统.利用波导理论分析了CFBG特性;利用传输矩阵法推导了CFBG反射谱模型及波长与相位延迟的关系,并给出了相位延迟曲线.实验表明:所设计的系统应变测量范围为0～2000 με,温度测最范围为0～80℃;相位变化与被...     

Efficient sidelobe suppression by source power apodisation in fibreoptic microwave filters composed of linearly chirped fibre grating bylaser array

First results are provided on efficiently apodised RF filters based on linearly chirped fibre gratings fed by laser arrays yielding sidelobe reductions of 10-20 dB as compared to uniform (unapodised) filters     

Effect of adding a long period grating in a double-pass backwardEr-doped superfluorescent fiber source

We first demonstrate that by inserting an appropriate long period grating in an Er-doped superfluorescent fiber source (SFS) of double-pass backward (DPB) configuration, the output spectrum can be broadened up to 40 nm. The characteristics of a long period grating (LPG) are then shown to have marked effects on the properties of the SFS. Both measured and simulated results agree well in the trend. The spectrum broadening using an LPG is shown effective over a large pump power range, especially for a single-humped DPB SFS. After the analysis of three types of output spectra, the tolerances of LPG's characteristics are found larger for a single-humped DPB SFS having the dominant band in 1558 nm     

Fabrication of chirped fibre gratings using etched tapers

A technique for fabricating fibre gratings with an accurately controlled chirp profile is demonstrated. The technique involves writing a grating over a section of fibre, the cladding of which has been tapered by etching it in HF acid. A strain gradient along the taper is used to produce the chirp either during or after writing. Linearly chirped gratings with bandwidths up to 4.8 nm have been demonstrated. Transmission filters have also been demonstrated when a step is made in the taper