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     

Narrowband fiber grating filters

Two techniques for the fabrication of fiber gratings with a narrowband filter response are reported. In the first technique, the reflection bandwidth is reduced by increasing the grating length. Fiber gratings 10 mm long have been made with a bandwidth of ~0.3 nm. In the second technique, a phase shift is incorporated into the grating to form a resonant structure. Fiber resonators with resonant dips in reflection and peaks in transmission having full-width half-maximum (FWHM) bandwidths of ~0.08 nm have been fabricated. A corresponding narrowband transmission peak was also measured     

Fiber Bragg grating fabrication for dispersion slope compensation

Group-delay dispersion slope causes signal deterioration in long-distance high-data-rate communication systems. We report the fabrication of high-quality apodized and chirped fiber gratings with dispersion slopes as high as -1800 ps/nm/sup -2/ over a 0.7-mn bandwidth-sufficient to compensate for the dispersion slope of >25000-km length of standard fiber at a wavelength of 1550 nm. We believe this is the first time that fiber Bragg gratings have been specifically designed and fabricated for dispersion slope compensation. The fabrication technique uses a standard unchirped phase mask and two scans of the inscribing UV beam.     

New diffraction grating profiles in InP for DFB lasers and integrated optics

A bilevel processing technique has been used to obtain sub-micrometer-period InP diffraction gratings. Novel cross-sectional grating profiles with depths of up to 4000 ? have been obtained which should facilitate the fabrication of more efficient Bragg devices.     

啁啾光纤光栅补偿光纤色散的研究

啁啾光纤光栅被认为是目前最有实用价值的色散补偿方案之一。分析了啁啾光纤光栅补偿色散的基本原理,从简单模型出发分析了啁啾光纤光栅的色散补偿能力,用数值法研究了啁啾光纤光栅的时延及色散特性,并比较了变迹型与非变迹型啁啾光纤光栅。结果表明要获得较大的色散,要求光纤光栅有较长的长度和较小的啁啾。同时为了消除色散曲线的振荡还必须采取适当的变迹方法。     

皮秒脉冲在级联光纤光栅中的传输特性研究

基于波分复用(WDM)系统中级联光纤光栅色散特性,研究了皮秒脉冲宽度以及光纤光栅长度和耦合系数等参数对脉冲压缩的影响;以高斯脉冲为例,运用等效色散的方法数值模拟了皮秒脉冲经过常规光纤和级联光纤光栅的演化过程.结果表明,选择合适的参数,级联光纤光栅可以对在普通光纤中色散展宽的脉冲进行色散补偿.还发现,进一步增加光栅长度,可使脉冲得到有效压缩.     

250-W average-power Nd:YAG laser with self-adaptive cavitycompleted by dynamic refractive-index gratings

A high average power laser oscillator with a cavity completed by a nonlinear mirror formed by refractive index gratings which accompany population gratings induced in Nd:YAG laser crystals by generating beams themselves is investigated numerically and experimentally. The role of different noise sources at the initial stage of nonlinear cavity formation is studied. The adaptation of the cavity formed by nonlinear dynamic mirrors to intracavity distortions is demonstrated. The generation of beams with average power up to 250 W, near-diffraction-limited divergence, and long coherence length has been achieved     

Design, Fabrication and Characterization of an InP-Based Tunable Integrated Optical Pulse Shaper

In this paper a tunable integrated semiconductor optical pulse shaper is presented. The device consists of a pair of arrayed waveguide gratings with an array of electrooptical phase modulators in between. It has been fabricated in InP-InGaAsP material for operation at wavelengths around 1.55 mum. Multimode inputs to the waveguide gratings are used to flatten their optical passband. We have used a new short-pulse characterization technique to fully characterize pulse shaping by the device, i.e., both the power and the phase profile. A fourfold decrease in pulse ringing was observed for the devices with flattened passbands. Moreover these devices showed a 25% increase in pulse peak power. The possibilities for using the device as a dispersion (pre-) compensator have been investigated. Pulse reconstruction could be obtained for dispersion values of up to 0.2 ps/nm. The fabrication technology of the pulse shaper is compatible with the fabrication of integrated mode-locked lasers, which makes further integration of complete arbitrary pulse generators possible.     

Temperature dependence of type I-IA dual-fibre Bragg gratings

Fibre Bragg gratings (FBGs) of a new IA type have been reported to show thermal behaviour that is different from that of conventional type I gratings. Given a sufficiently large temperature coefficient difference between the two grating types, a dual-grating sensor formed by both types of gratings could allow simultaneous temperature and strain measurement. Such dual-grating sensors were prepared for the 830 nm wavelength region and tested at temperatures of up to 300/spl deg/C. As far as the variation of the different temperature coefficients is concerned, the temperature coefficient of type IA FBGs and the temperature coefficient of type I FBGs have been found to converge as the temperature increases. The difference in temperature coefficients drops to 1% after annealing at 300/spl deg/C.     

A novel planarization technique for a high-Tc multilevelIC process

A novel technique has been developed to planarize insulating layers which may be used in a YBa₂Cu₃O_7-δ (YBCO) IC process. The technique, called complementary mask planarization (CoMP), has been successfully implemented to planarize line gratings etched in an SrTiO ₃ insulator. The average surface roughness of the line gratings as measured by an atomic force microscope (AFM) was reduced from 3000 to 250 Å after planarization. Films of YBCO were the posited and patterned in the form of narrow strips over the line gratings to simulate insulated crossovers in IC structures. The I-V characteristics of the YBCO strips over planarized line gratings showed that the critical current density is higher by two orders of magnitude than those over unplanarized gratings     

光折变晶体全息图的热固定特性优化的研究

采用红光对单、双掺铌酸锂晶体中全息光栅的热固定效率及光擦除和暗存储寿命的特性进行了深入的实验研究。实验中高掺杂和强还原晶体难以显影出离子光栅 ;对于较少掺杂的未还原晶体 ,获得离子光栅的热固定效率达 5 0 % ;高掺杂晶体中离子光栅的暗存储寿命达 4个月 ,比热固定前电子光栅的暗存储寿命提高了十几倍。实验表明热固定效率和光栅的暗存储寿命不能同时提高 ,这与理论预期一致。     

Spatial frequency doubling lithography (SFDL) of periodicstructures for integrated optical circuit technology

A novel technique for fabricating gratings useful for integrated optical circuits (IOCs) is described. The technique combines optical projection lithography, partially coherent illumination, and spatial filtering. With this technique, only the first two orders diffracted by the mask grating are allowed to pass through the lens. This produces a grating pattern in the image plane that has a high contrast (near 100%), a large depth of focus, and a period half of what would have been obtained in normal imaging. Gratings of different periods, sizes, locations, orientations, and configurations (chirped, phase-shifted, etc.) can all be produced on the same chip with a single exposure. Using a deep UV lens with 248-nm KrF excimer laser for illumination, the authors printed high-quality 0.5-μm period gratings in an oxide layer on 10 mm×10 mm silicon chips. Extended depth of focus was observed. This technique opens up the possibility of high-volume production of IOC chips with Bragg filters using standard IC fabrication facilities     

相位掩模法制造光纤光栅的理论分析

推导出了用相位掩模法制造光纤光栅的理论根据，得出相位掩模法中常见的一些有用公式，并报道了实验结果。     

Line-Tunable Singly Resonant Optical Parametric Oscillator in Mid-Infrared Spectral Range Based on KTA Crystal

Line-tunable narrow-linewidth mid-infrared radiation in 3–5-$mu$m spectral range by singly resonant optical parametric oscillation technique based on a KTA crystal pumped by 1.064-$mu$ m radiation from a $Q$ -switched Nd:YAG laser using different gratings has been demonstrated. Thresholds of oscillation energy at different cavity lengths and at different idler wavelengths with different gratings have been measured. Energy of the generated radiation at 3.6 $mu$ m as a function of pump beam energy at different cavity lengths with different gratings have been measured. Maximum energy obtained at 3.6-$mu$m radiation with a grating having grooves density 85 l/mm at 55-mm cavity length is 4.6 mJ when the cavity was pumped by 42.6-mJ energy, which corresponds to conversion efficiency from pump beam energy to generated idler beam energy 10.8% and maximum slope efficiency achieved was 23.6%. The linewidth obtained with a grating having grooves density 600 l/mm at 3.7 $mu$m was 0.53 cm $^{- 1}$.      

基于光纤光栅谐振腔的双包层光纤激光器

理论分析了线型腔双包层光纤激光器的输出特性,包括光纤长度、光纤损耗及后腔镜反射率对激光输出功率和阈值泵浦功率的影响.设计了基于光纤光栅谐振腔的双包层光纤激光器,采用锥度光纤实现了泵浦模块与双包层光纤之间的低损耗连接,实现了全光纤化的掺Yb3 双包层光纤激光器,其阈值泵浦功率为300 mW,在泵浦入纤功率为17 W时达到了10.5 W的最大激光输出功率,斜率效率为62%.     

利用动态相位掩膜板法制作光纤光栅

在相位掩膜板法光纤Bragg光栅(FBG)制作系统中,通过高精度陶瓷压电(PZT)促动器对相位掩膜板进行运动控制,实现对光栅折射率交流调制量和相位的任意调制,从而实现相移、切趾和啁啾等FBG的制作,从而提高FBG制作工艺的灵活性。     

Low-threshold, self-tuned and passively mode-locked coupled-cavity all-fiber lasers

Low threshold, self-tuned, and passively mode-locked fiber lasers with compact all-fiber coupled-cavity structures have been investigated experimentally. It is shown that the Bragg gratings used in a coupled-cavity fiber laser must be matched in their spectral characteristics for the mode-locking of the laser. Stable mode-locked optical pulses as short as 60 ps at a repetition rate of 213 MHz have been generated without the need of cavity length stabilization.     

Tuning and chirping fiber Bragg gratings by deep etching

We have demonstrated a new method for tuning and chirping fiber gratings. It relies on etching of a fiber down to very small cladding diameter, so that the propagating optical mode in the fiber interacts with the surrounding media. A tuning range of 4.5 nm has been demonstrated with a potential of much larger tuning range by optimization of fibers. Chirped gratings were also demonstrated with this technique. These chirped gratings are very important for use in fiber dispersion compensation and optical pulse shaping.