光纤投影双频自动轮廓测量术

提出一种双频光纤投影自动轮廓测量技术；用一分二单模光纤耦合器产生正弦光强分布的投影光栅场；将光纤一臂绕在压电陶瓷（ＰＺＴ）环上述旁瓣通过压电陶瓷环引入相移值；以改变出射端两光纤间的距离来发迹投影光栅场的空间频率，用双频光栅技术实现复杂表面自动轮廓测量。     

Virtual Gires-Tournois etalons realized with phase-modulated wideband chirped fiber gratings

We propose and demonstrate novel virtual Gires-Tournois (GT) etalons based on fiber gratings. By introducing an additional phase modulation in wideband linearly chirped fiber Bragg gratings, we have successfully generated GT resonance with only one grating. This technique can simplify the fabrication procedure while retaining the normal advantages of distributed etalons, including their full compatibility with optical fiber, low insertion loss, and low cost. Such etalons can be used as dispersion compensation devices in optical transmission systems.     

Photonic microwave bandpass filter with improved dynamic range

A technique to improve the dynamic range of a photonic microwave bandpass filter is proposed and experimentally demonstrated. The filter is implemented based on phase modulation to intensity modulation conversion using fiber Bragg gratings (FBGs) serving as frequency discriminators, with the optical carriers located at the left or right slopes of the FBGs, to generate positive or negative tap coefficients. The dynamic range of the photonic microwave bandpass filter is increased by reducing the optical-carrier-induced shot noise and relative intensity noise at the photodetector, which is realized by placing the optical carriers at the lower slopes of the FBG reflection spectra. A photonic microwave bandpass filter with an improvement in dynamic range of about 10 dB is demonstrated.     

Visualization of type II fiber Bragg gratings induced in a birefringent fiber with an elliptical stress cladding

Experimental results on visualization of type II fiber Bragg gratings induced in a birefringent fiber with an elliptical stress cladding are presented. The gratings are recorded by a single pulse of an excimer KrF-laser by means of the phase-mask method. Images of the gratings are obtained in a bright field using contrasting techniques such as differential interference contrast and dark field. It is shown that single-pulse recording forms several type II Bragg gratings in the optical fiber. The spatial profile of these gratings corresponds to the phase mask period. Microcracks due to which type II gratings are induced are localized both on the boundaries between the fiber core and claddings surrounding it and at some distance from them.     

Polarization insensitive homodyne detection of optical phase modulation by two-wave mixing in saturable Er-doped fiber

We report linear polarization-insensitive detection of optical phase modulation in an adaptive interferometer based on transient two-wave mixing via dynamic population gratings in saturable Er-doped fiber (EDF). The proposed simple and robust configuration has an all-fiber design based on commercially available elements which makes it promising for applications in optical fiber interferometric sensors and coherent optical communication systems. The experimentally investigated single-mode polarization-maintaining EDF arrangement operated at 1492 nm and demonstrated efficient compensation of the polarization drifts below 100 Hz.     

40Gb/s光时分复用传输光纤光栅补偿色散研究

用精密扫描掩模法写入宽阻带啁啾光纤光栅,掩模板背面两端各10％长度处镀有按4阶高斯函数透过率的膜,写入的啁啾光栅的时延纹波最大值为20ps。为减少写入光纤光栅的偏振模色散,研制了新的低偏振模色散光纤光栅补偿写入法。采用补偿写入法前的平均微分群时延为9．1406 ps;采用补偿写入法后的平均微分群时延为0．1521 ps。并利用低偏振模色散光纤光栅对40Gb／s光时分复用系统在普通G．652光纤传输122km的色散进行了补偿实验,功率代价为1．5dB。     

Novel Technique for All-Optical Clock Extraction Using Fiber Bragg Gratings

We demonstrate a simple passive technique, using phase shifted fibre Bragg gratings, for extraction of optical clock signals from RZ optical data signals . The generation of an optical clock signal at 12.5 GHz from a 12.5 Gbs RZ optical data stream is experimentally demonstrated with simulation of optical clock extraction at 10 GHz fro m 40 Gbs OTDM data streams .     

Production of optical notch filters with fine parameter control using regenerated fiber Bragg gratings

A new method to create a controlled notch filter for attenuation of signals based on regenerated fiber Bragg gratings is experimentally demonstrated. A fine adjustment of the notch depth is achieved by controlling the time of regeneration phenomenon in strongly saturated Bragg gratings written in standard ITU G.652 single-mode fiber. This method can used to produce tailored notch filters for several photonic applications, such as optical RF filtering, subcarrier processing or radio over fiber systems.     

All-fiber wavemeter and Fourier-transform spectrometer

An all-fiber Fourier-transform spectrometer is proposed and demonstrated, based on the diffraction of light through the side of a standard optical fiber by a UV-induced fiber grating. The interference pattern, whose Fourier transform yields the optical spectrum, is formed by light diffracted from counterpropagating modes in the fiber. The device is simple and compact and functions as a wavemeter, a fiber-optic network monitor, or a tool for fabrication and testing of long fiber Bragg gratings.     

Phase ripple correction: theory and application

Spectral phase ripple associated with novel dispersive devices can distort broadband optical signals. We present a digital postprocessing algorithm to correct for this distortion by exploiting the static deterministic nature of the ripple. This algorithm is demonstrated with empirical data for several systems employing chirped fiber Bragg gratings (CFBGs). We employ this technique in a photonic time-stretch system incorporating CFBGs, improving the signal fidelity by 9 dB. Simulations and experiments show that this algorithm, which can be reduced to a simple interpolation and matrix multiplication, also mitigates additive noise. We see that the act of distortion correction yields signal fidelity superior to that of an ideal dispersive element.     

Dispersion Compensators Based on Overlaped Linearly Chirped Fiber Gratings for DWDM Systems

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Dispersion Compensators Based on Overlaped Linearly Chirped Fiber Gratings for DWDM Systems

By introducing a convergent lens in the phase mask setup and by tilting appropriately the fiber from the phase mask, a linearly chirped fiber grating with an appropriate chirp can be obtained conveniently. Using this method, two groups of fiber gratings, each of them is composed of 8 overlaped linearly chirped fiber gratings but with different center reflection wavelength separations (～0.8 nm and ～1.6 nm, respectively) are fabricated. Experimental results show that, the compensators based on the two groups of fiber gratings can be used to compensate for the dispersion of 8×2.5 Gb/s transmission over 100 km of standard single-mode fiber for multiple channels in optical time-division multiplexing (OTDM) and densed wavelength division multiplexing (DWDM).     

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     

双面曝光长周期光纤光栅偏振相关损耗

研究了采用高频CO2激光脉冲通过单面和双面曝光制作出的长周期光纤光栅(LPFG)的偏振相关损耗特性。单面曝光制作的长周期光纤光栅由于光纤横截面折射率改变不均匀,对入射光偏振态有较强的依赖性,主要表现为偏振相关损耗较大;为了降低偏振相关损耗,在制作长周期光纤光栅的过程中采用双面曝光的方法,以使其横截面折射率调制受高频CO2激光曝光改变均匀。实验数据显示,高频CO2激光脉冲制作的普通单面曝光长周期光纤光栅最大偏振相关损耗高达1.24 dB,而采用双面曝光的相同谐振峰值长周期光纤光栅的偏振相关损耗则可降至0.42 dB。因此,双面曝光制作的长周期光纤光栅能较好地克服入射光偏振态的不良影响,从而满足对偏振敏感的光纤通信和传感系统的应用要求。     

Characterizations at high temperatures of long-period gratings written in germanium-free air-silica microstructure fiber

We report what is to our knowledge the first characterization at high temperatures of long-period fiber gratings written in Ge-free air-silica microstructure fiber. The gratings written with the electric-arc technique suffer a low shift of the resonance wavelengths when the temperature is increased from 20 degrees C to 1200 degrees C. This shift is studied and compared with that of a long-period fiber grating written in a standard single-mode fiber by the same technique. Good thermal stability of the grating and of the fiber after annealing at 1200 degrees C for 1 h is demonstrated.     

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.     

Data storage in optical fibers and reconstruction by use of low-coherence spectral interferometry

We demonstrate optical data storage in optical fibers and reconstruction by use of low-coherence spectral interferometry. The information was stored by means of writing fiber Bragg gratings with different central wavelengths at different locations of the fiber. We need only a single short pulse is needed to read all the stored data. The maximum theoretical reconstruction rate that can be obtained with our technique is 10 Tbits/s. Our storage technique can be useful for identifying users in optical communication networks.