波分复用加光栅光谱形状复用的FBG传感解调技术

针对光纤布拉格光栅(FBG)传感网络中可复用光栅的数量问题,提出波分复用(WDM)和光栅光谱形状复用结合的方法。通过MATLAB仿真和具体实验表明,WDM和光谱形状复用结合使用,在光谱宽度、测量范围和光栅谱宽一定的条件下,能使可复用的光栅数量比只用WDM时增加1倍,相比于其他多种复用技术结合的传感网络,解调系统更为简单。     

Control of Bragg grating resonant wavelength through its dependenceon the effective index of a waveguide

Fabrication tolerances for control of the Bragg wavelength of gratings in waveguides are studied. Techniques are demonstrated to hold the period of the grating constant to ±0.04 nm over the majority of the exposed wafer area, and ridge waveguides fabricated with standard thin film process equipment are found to have Bragg wavelengths constant to within ±0.2 nm. Additionally, adjacent ridges with differing widths are written in a single photomask/etch process step and found to controllably shift the Bragg wavelength over a 10-20-nm band suitable for a distributed Bragg reflector (DBR) laser array or a monolithic comb filter for wavelength division multiplexing (WDM) filtering/routing arrays     

基于WDM和TDM的串联FBG高速列车定位系统

介绍了一种基于波分复用（WDM）和时分复用（TDM）串联光纤Bragg光栅（FBG）的高速列车定位系统。用快速的光功率监测替代FBG的波长监测,定位时延较小（0．2s）;波长漂移转化为光功率的一对负正脉冲波动,提高了定位自动识别的准确性;同时WDM与TDM相结合的系统结构设计,扩大了列车定位系统监测的总长度。     

Dispersion of cascaded fiber gratings in WDM lightwave systems

Fiber gratings operating in the transmission mode can provide high dispersion at wavelengths close to the Bragg resonance. When multiple gratings are cascaded for wavelength division multiplexing (WDM) applications, the net dispersion between the stop bands of any two consecutive gratings is significantly modified. We discuss the dispersion characteristics of such cascaded fiber gratings and propose a dispersion compensator for simultaneous compensation of group-velocity dispersion (GVD) for multiple channels of a WDM lightwave system. We also discuss the impact of the dispersion possessed by cascaded gratings on grating based add-drop multiplexers     

利用禁忌搜索算法提高FBG传感系统复用能力的研究

为了提高光纤Bragg光栅(FBG)波分复用(WDM)传感系统的复用能力,禁忌搜索(TS)算法被引入到快速识别Bragg波长中.在构造光谱过程中考虑串扰效应,达到识别在同一信道下工作的2只高反射率串联光栅信息的目的,使系统的复用能力提高了2倍.'TS算法利用光谱的峰值作为搜索初值,有效提升了计算效率,与地毯式搜索(CS...     

Control of lasing wavelength in distributed feedback lasers byangling the active stripe with respect to the grating

We proposed and demonstrated a new and very simple technique of varying the lasing wavelength of distributed feedback (DFB) lasers with the need for fabricating gratings with different pitches. This is accomplished by angling the active stripe at an oblique angle with respect to the axis of the grating lines. This technique should be particularly suitable for fine tuning of lasing wavelength, and it eases the stringent demand on precise control of absolute grating pitches. It should be useful and important for dense (wavelength division multiplexing (WDM) applications and monolithic integration of multi-wavelength DFB lasers     

Subpicometer accuracy laser wavelength sensor using multiplexed Bragg gratings

Wavelength- and angle-multiplexed holographic Bragg gratings are used as a highly sensitive wavelength sensor. An absolute wavelength accuracy as high as 0.3 pm has been demonstrated with gratings recorded in an Fe-doped LiNbO/sub 3/ photorefractive crystals of dimension of 5/spl times/5/spl times/4 (mm/sup 3/). This technique provides a simple and accurate solution to laser wavelength measurement in applications such as wavelength division multiplexed (WDM) fiber-optic networks, precision interferometry, Doppler spectroscopy, and others.     

Influence of mode competition on the fast wavelength switching ofan SG-DBR laser

Because the sampled grating distributed Bragg reflector (SG-DBR) laser is among the most attractive sources for wavelength division multiplexing (WDM) systems, it is important and necessary to investigate its wavelength switching characteristics. This behavior will set the capability limits for reallocation in wavelength-routed optical networks. In this paper, that mode competition plays an important role in the wavelength switching dynamics of DBR-type tunable lasers is confirmed experimentally. By using a time-resolved spectrum technique, the loss-dependent mode competition behavior has been directly observed, for the first time, from measurements of wavelength switching on an SG-DBR laser     

Robust optical FFH-CDMA communications: coding in place offrequency and temperature controls

In wavelength division multiplexing (WDM), transmitters require stringent and complex frequency control loops to avoid wavelength drifts due to temperature fluctuations. This makes the transmitters heavy, bulky, and inappropriate for local- and short-haul communications networks, as well as for manufacturing locales and other open areas where temperature control is not feasible. We propose and analyze a technique we call robust fast frequency hopping code division multiple access (FFH-CDMA), particularly suitable for severe, hostile, noncontrollable environments. This approach avoids all conditioning and frequency stabilization loops in the transmission end. We develop a modified version of extended hyperbolic congruence codes to achieve environment-resistant codes. We present expressions for the auto- and cross-correlation functions for optical implementation of the codes. We simulate the encoding/decoding operations with parameters from real Bragg gratings. We evaluate probability of error for a single user and as an average over all users versus capacity (the number of simultaneous users). Robust FFH-CDMA is an efficient access technique for hostile environments. It avoids the frequency and temperature control problems of WDM and nonrobust FFH-CDMA at the cost of lower overall capacity in terms of number of simultaneous users     

Cascade self-induced holography: a new grating fabricationtechnology for DFB/DBR lasers and WDM laser arrays

A method of fabricating submicron gratings for optoelectronic devices from a glass mask was proposed and demonstrated. The glass mask has gratings on both sides with a period of at least four times the final feature size. By introducing an offset to the grating periods on the mask, one can achieve multiple-period gratings with a very fine period spacing for advanced wavelength-division multiplexing (WDM) devices. In this paper, we demonstrated 0.5-μm second-order gratings for 1.55-μm DFB lasers and gratings with a 6-Å period difference for a four-channel WDM laser array using only optical sources. The Moire pattern caused by the spatial frequency beating was also observed and discussed. The Moire pattern could serve as an effective tool to measuring wavelength channel spacing between devices with an unprecedented (0.1 Å) resolution     

重叠写入啁啾光纤光栅型滤波器的研究进展

高性能的波分复用器是密集波分复用系统的核心器件之一,重叠写入啁啾光纤光栅型带通滤波器充分发挥了光纤光栅优良的波长选择特点,是一种低成本的新型全光纤波分复用器件.综合评述了各种不同结构的重叠写入啁啾光纤光栅型滤波器的工作原理、基本特点及其应用.     

啁啾光纤光栅法布里-珀罗传感器波分频分复用

实现了一种具有大容量复用潜力的啁啾光纤光栅(CFBG)法布里-珀罗(F-P)传感器复用系统。该传感器复用系统的建立基于波分频分复用方法,即中心波长相同的传感器利用腔长不同空间频率不同来实现空间频分的复用,采用不同中心波长的传感器阵列与频分复用方法相结合就可实现波分频分复用。描述了该光纤光栅法布里-珀罗传感器复用系统的结构、原理及应变实验结果。实验结果表明,该方法可以大大地提高光纤光栅法布里-珀罗应变传感器的复用能力,理论上可复用数百个光纤光栅法布里-珀罗应变传感器;实验中应变测量精度好于±10με,可满足大部分实际应用的要求。     

Lasing wavelength changes due to degradation in buriedheterostructure distributed Bragg reflector lasers

Changes in the wavelength and lamp characteristics due to the degradation of distributed Bragg reflector (DBR) lasers are investigated and the lasers are confirmed to be reliable enough for application as the light sources in WDM systems. The change in wavelength characteristics is due to degradation of the DBR or phase control region and the change in lamp characteristics is due to the degradation of active region. These changes in the characteristics are caused by diminished recombination carrier lifetime. The wavelength stability is strongly correlated with the injected current density. The lamp characteristics is confirmed to be almost as stable as in conventional Fabry-Perot lasers. The applicability of DBR lasers as the light source for wavelength division multiplexing (WDM) systems is demonstrated for actual-use conditions     

Synthesis of direct-coupled-resonators bandpass filters for WDMsystems

A simple technique for the exact synthesis of selective bandpass filters for wavelength division multiplexing (WDM) systems is presented. The filters consist of direct-coupled ring resonators or cascaded Bragg gratings. The proposed technique permits the calculation of the physical dimensions of the optical structures given the desired frequency response of the filter in terms of bandwidth, free spectral range, out-of-band rejection, and frequency characteristic. The technique, explained in detail for Butterworth and Chebyshev frequency responses, is exact, uses closed-form formulae, and is physically well based. The resulting devices are very compact, have a high out-of-band attenuation, and are suitable for high-density integrated optics. Several filters for applications such as channel add-drop, channel selection, demultiplexing, multichannel filtering, and interleavers are designed, analyzed, and discussed in the paper     

Simple multiwavelength device fabrication technique using a single-grating holographic exposure

A simple technique, using a single-grating holographic exposure associated with localized selective etching steps, has been developed for multiwavelength device fabrication. Four-wavelength DBR laser arrays with a 5 nm Bragg wavelength spacing have been fabricated for wavelength division multiplexing (WDM) applications with this method. These devices exhibit uniformly low-threshold currents (10-15 mA), high-output powers (15 mW) and wide tunabilities (12 nm), leading to an overall accessible wavelength domain of 28 nm for the array.     

Tuning Bragg wavelength by writing gratings on prestrained fibers

Bragg gratings at a specific wavelength are made using an excimer KrF laser and a phase mask. The wavelength can be varied for fine tuning and multiplexing applications by straining the optical fiber during UV illumination. When the strain is removed, the grating formed is at a smaller wavelength than that dictated by the phase mask for the unstrained fiber. This technique was demonstrated by writing two gratings located at the same point in the optical fiber. The transmission from the first grating was used as a means for in situ absolute wavelength tuning. The second grating made with approximately 0.2% axial strain was at 1534.54 nm. Once the grating was made, the strain was removed from the fiber leaving the second grating tuned to 1532.04 nm, a wavelength shift of 2.5 nm     

Integrated dielectric wavelength filters on InGaAs PIN photodetectors

There is an increasing desire to employ wavelength division multiplexing (WDM) techniques in optical communication systems to increase the useable capacity of optical fibre links. WDM transmitters usually consist of several narrow linewidth lasers, with their operating wavelengths suitably spaced. WDM demultiplexers or receivers employ either discrete gratings or discrete transmission filters to separate the various wavelengths. The disadvantage of such demultiplexers is that precise mechanical alignment of the many components is required. Together with the high cost of components such as gratings this makes such demultiplexers unsuitable for mass production. The authors describe a method of producing a dielectric wavelength filter integrated onto an InGaAs PIN photodiode for use in WDM systems and give results for the transmission characteristics of the filters and quantum efficiency of the whole structure.<>     

利用光纤光栅研制分插复用器

在波分复用的光纤通信系统中,分插复用技术需要低损耗、小型化的、稳定的、可靠的器件。使用光纤光栅,可以 制作多种结构的分插复用器,本文对多种基于光纤光栅的分插复用器的结构和原理进行了研究。     

Long-phase error-free fiber Bragg gratings

Stitching errors in the phase mask degrade the spectral response of fiber Bragg gratings fabricated with the phase mask technique. We successfully fabricated a stitching error-free phase mask and applied it to the fabrication of fiber Bragg gratings (FBGs). The gratings have no observable excess sidelobes in the reflectivity and show excellent wavelength selectivity     

Simultaneous OCDM signal transmission over multiple WDM channels using Mach-Zehnder interferometric selector

Proposed is an easy technique for overlaying multiple wavelength division multiplexing (WDM) signals on optical code division multiplexing (OCDM) signals. The approach results in a broad coding spectrum for OCDM signals, and thus provides highly secure services in WDM-based networks. The technique is validated experimentally using an OCDM signal and two WDM signals.