Single-step writing of Bragg grating waveguides in fused silica with an externally modulated femtosecond fiber laser

For the first time to our knowledge, high-strength (>30 dB) first-order Bragg grating waveguides were fabricated in bulk fused silica glass in a single-scanning step by modulating a high-repetition-rate femtosecond fiber laser with an external acousto-optic modulator. The modulation induced a waveguide segmentation by delivering controlled bursts of laser pulses to define an array of partially overlapped refractive index voxels. With appropriate choice of modulation frequency and sample scanning speed, low loss waveguides could be formed at high writing speeds to yield sharp Bragg spectral resonances tunable over the 1300 to 1550 nm telecom band. Effects of acousto-optic modulation duty cycle on propagation loss and grating strength are characterized. This modulation method offers facile control and integration of multiwavelength Bragg grating devices to enhance overall functionality of optical circuits in three-dimensional geometries.     

Four-wavelength DBR laser array with waveguide couplers fabricated using selective MOVPE growth

We have developed an integrated multiwavelength laser with waveguide couplers using a novel selective metal-organic vapor-phase epitaxy (MOVPE) technique. The lasing wavelength was controlled by modulating the effective refractive index of distributed Bragg reflector (DBR) waveguides. Array lasing wavelengths were distributed from 1548.0 to 1553.5 nm with an average spacing of 1.8 nm. The propagation loss of the waveguide coupler was about 16 dB for inner ports and 20 dB for outer ports with a 6 dB splitting loss. Four-wavelength laser outputs were coupled into a single-mode fibre.     

Femtosecond laser fabrication of phase-shifted Bragg grating waveguides in fused silica

Phase-shifted Bragg grating waveguides (PSBGWs) were formed in bulk fused silica glass by femtosecond laser direct writing to produce narrowband (22±3) pm filters at 1550 nm. Tunable π and other phase shifts generated narrow passbands in controlled positions of the Bragg stopband, while the accurate placement of multiple cascaded phase-shift regions yielded a rectangular-shaped bandpass filter. A waveguide birefringence of (7.5±0.3)×10(-5) is inferred from the polarization-induced spectral shifting of the PSBGW narrowband filters.     

LiNbO3:Fe晶体中光写入波导时折射率的变化规律

研究了利用光辐照法制作光折变波导时LiNbO3:Fe晶体中折射率变化的规律.分别采用波长为6328nm和532nm的寻常偏振和非常偏振的细激光束和片状激光束，在LiNbO3:Fe晶体中进行了写入波导实验.研究表明，制作波导的写入光宜采用寻常偏振光.在利用由光束辐照LiNbO3:Fe晶体形成的正折射率变化区域作为波导结构时，必须严格控制辐照时间.否则，由于长时间光辐照会带来较强的噪音栅以及折射率变化区域会发生扩展，而难以形成优 质波导.利用片光在“三明治”方式辐照下，以小曝光量制作波导时，可以避免噪音栅的 关键词： 光致折射率变化 光折变波导 光辐照法 LiNbO3:Fe晶体     

Fundamental losses in planar Bragg waveguides

This paper considers a planar Bragg waveguide. The guided modes and their dissipation due to the fundamental absorption are described. In the interacting-wave approximation, an analytical relation between the characteristics of the modes and parameters of the Bragg-waveguide geometry was established. Absorption losses in hollow Bragg waveguides were shown to be significantly lower than in a regular waveguide fabricated from the same material. Quantitative estimates of the fundamental and radiation losses in Bragg waveguides are given for materials used at wavelengths of 1.55, 10.6, and 0.245 μm.     

Directly written monolithic waveguide laser incorporating a distributed feedback waveguide-Bragg grating

We report the fabrication and performance of the first C-band directly written monolithic waveguide laser (WGL). The WGL device was created in an erbium- and ytterbium-doped phosphate glass host and consisted of an optical waveguide that included a distributed feedback Bragg grating structure. The femtosecond laser direct-write technique was used to create both the waveguide and the waveguide-Bragg grating simultaneously and in a single processing step. The waveguide laser was optically pumped at approximately 980 nm and lased at 1,537 nm with a bandwidth of less than 4 pm.     

Spectrally selective splitters with metal-dielectric-metal surface plasmon waveguides

Spectrally selective splitters with metal-dielectric-metal (MDM) subwavelength waveguides are proposed in this paper. The method is based on the Bragg grating structure with periodically modulated MDM waveguide width, which delivers a stop band effect for the surface plasmon propagating in the waveguide. By adding appropriate Bragg grating structure in one or more arms of the waveguide splitters, light in a certain frequency range can be readily guided into the desired directions, as demonstrated numerically by the finite-difference time-domain method. Dependence and optimization of the geometrical parameters are also considered in this paper.     

电流调谐光纤光栅外腔分布布拉格反射激光器

报道一种新颖的波长可调谐光纤光栅外腔分布拉格反射激光器。把经过金属管封装的光纤面布拉格光栅作为激光二极管的外腔反射镜,得到的单模激光输出不仅线宽窄,边模抑制比高,而且,调节流过金属管的电流,可在5nm范围内的6个不同波长间转换。     

Direct laser written waveguide-Bragg gratings in bulk fused silica

Optical waveguides that incorporate Bragg gratings have been written in bulk fused silica by using the femtosecond laser direct-write method and without the need for lithography or ion-beam techniques. A single manufacturing process is used to create waveguide-Bragg grating reflectors for operation in the C band.     

Integrated optical electric field sensor based on a Bragg grating in lithium niobate

We demonstrate a new sensor concept for the measurement of oscillating electric fields that is based on Bragg gratings in LiNbO₃:Ti channel waveguides. This miniaturized sensor that works in a retroreflective scheme does not require metallic electrodes and can be directly immersed in an oscillating electric field. The electric field induces a shift of the Bragg wavelength of the reflection grating that is due to the electro-optic effect. The operating point of the sensor is chosen by adjusting the laser wavelength to the slope of the spectral reflectivity function of the grating. In this way the magnitude of an external electric field is measured precisely as the amplitude of modulated reflected light intensity by using a lock-in amplifier. The sensor principle is demonstrated by detecting low-frequency electric fields ranging from 50 V/cm to 5 kV/cm without any conducting parts of the sensor head. Furthermore, the ability of the sensor to determine the three-dimensional orientation of an external electric field by a single rotation along the waveguide direction is demonstrated. PACS 42.40.Eq; 42.82.-m; 42.82.Et     

Modelling of photonic crystal waveguides: a simple and accurate approach

We present an improved variational effective index method for reduction of 2-D Bragg grating problems to 1-D and show significant improvements particularly at smaller wavelengths. The method is based on the optimal variational (Vopt) method, which we have earlier used successfully for conventional waveguides. A 1-D transverse profile along with a longitudinal index variation are reduced to a 1-D longitudinal distribution, reflection and transmission spectra of which have been studied for both the TE and TM modes by transfer matrix methods. An accurate modeling for the out of plane scattering losses has been presented which occur when a guided wave propagating in a conventional waveguide impinges on a photonic crystal waveguide. Taking these losses into account brings the results pretty close to those of a rigorous 2-D Helmholtz solver QUEP, improving them remarkably over the variational EIM (vEIM) results.     

Tunable multiwavelength distributed-feedback zirconia waveguide lasers

Simultaneous tuning of multiple-output wavelengths was achieved in Rhodamine 6G-doped distributed-feedback zirconia waveguide lasers. As many as four separate output wavelengths were observed for a planar zirconia waveguide of 2.2-microm thickness. The laser output wavelengths corresponded to the propagation modes allowed in the planar waveguide. Continuous tuning by variation of the period of the optically generated grating was achieved from 584 to 611 nm.     

光纤光栅可调谐半导体单模超短光脉冲的研究

本文利用光纤光栅形成外腔反馈,得到量子阱半导体激光二极管单模超短光脉冲.其光谱线宽约为0.4nm,脉冲宽度约为60ps.并利用调谐装置,改变光纤光栅的反射波长,得到不同波长的超短光脉冲,其波长可长期稳定.     

高度方向性多光束有机激光

采用DFB分布反馈结构的有机激光由于其自身优点备受关注,而利用高阶布拉格反馈的多光束有机激光及其原理鲜有报道。不同于以往的低阶布拉格反馈形成单波导或单光束激光,本文通过在平面有机半导体波导引入高阶布拉格反馈分别制备了红色和蓝色多束有机激光器。利用四阶布拉格反馈和PVK：DCJTI薄膜实现三光束红光激光器,出射角度为±53°和0.5°。利用五阶布拉格反馈和PS：DSA-ph薄膜实现四光束蓝光激光器,出射角度为±18°和±75°。融合平面波导与光栅耦合的机理,研究了高阶布拉格光栅反馈与器件特性之间的关系。结果表明,理论计算的光束耦合角度和实际测试相符,结果在一定程度上为多光束有机激光器件的设计提供了参考。     

Dual wavelength erbium-doped fiber laser with a lateral pressure-tuned Hi-Bi fiber Bragg grating

Tunable dual wavelength erbium-doped fiber laser (EDFL) with stable oscillation at room temperature is proposed and demonstrated. This laser utilizes a Bragg grating fabricated in a high birefringence fiber as the wavelength-selective component, and then achieves the stable dual wavelength oscillation by introducing the polarization hole burning effect. Furthermore, by applying lateral strain upon the fiber Bragg grating (FBG), the space of the laser dual wavelengths can be tuned continuously.     

A novel dual-wavelength fiber Bragg grating and its application in fiber ring laser

A novel method for fabricating dual-wavelength fiber Bragg gratings (FBGs) by using one phase mask is developed. The method is based on a double-exposure technique. Our technique lends itself to writing gratings with controllable reflectivity and separation of two Bragg wavelengths. A grating with two equal transmission peaks of 20.25 dB is obtained by this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, we demonstrate a dual-wavelength erbium-doped fiber ring laser whose interval of the two peaks is 0.8 nm. The laser's peak powers can get 3.1 mW above and have a good stability.     

Multi-waveguide excitation in fs laser written waveguide arrays

We introduce a new technique to excite multiple waveguides in fs laser written waveguide arrays. Using a microstructured grating, we were able to couple almost all of the power of the laser beam into multiple waveguides in one- and two-dimensional lattices. Tilting the sample a defined phase shift between adjacent waveguides can be obtained, which allows anomalous diffraction and refraction to be studied. PACS 42.79.-e; 42.79.Gn; 42.82.Et; 42.25.Kb     

Numerical analyses of optical couplers for planar waveguides

The paper presents the results of numerical analyses of optical structures realized in the form of planar waveguides made of materials with high values of the refractive index n ??1.85. The analysed structures consist of a waveguide and input-output systems. Input-output couplers are realized in the form of prisms as well as Bragg??s grating couplers. Numerical investigations were carried out by applying the finite difference time domain (FDTD) method.     

编码式光纤光栅传感阵列解调方案的论证

介绍了编码式光栅传感阵列的结构及其传感信号的特点。采用梳状结构对编码式光纤光栅传感阵列进行解调，利用被测光谱通过阵列波导光栅不同通道时输出的不同光强的比值确定被测光的波长。该文分别从理想状态和存在背景反射的状态论证了本文提出的方案的可行性，分析了噪声引起的误差。该系统不但适合于解调大容量的波长信息，而且在解调时不存在任何机械移动部分便可以快速、同时测量多个波长。     

A simple linear cavity dual-wavelength fiber laser using AWG as wavelength selective mechanism

In this paper, a simple design of linear cavity dual-wavelength fiber laser (DWFL) is proposed. Operating in the C-band region stretching from 1538.3 nm to 1548.6 nm, an arrayed waveguide grating (AWG) is used to generate the dual-wavelengths output together with a broadband fiber Bragg grating as a back reflector and an optical circulator with a 10% output coupling ratio which acts as a front mirror. The measured average output power of the DWFL is about −5.66 dBm and with a side mode suppression ratio (SMSR) of 53.1 dB. The spacing between the two output wavelengths can be varied from 0.8 nm to 10.3 nm with a stable output and minimum power fluctuations.