Design and fabrication of polarization-insensitive hybrid solgel arrayed waveguide gratings

We report on the successful design and fabrication of a polarization-insensitive arrayed waveguide grating (AWG), using solgel-derived silica glass films formed on fused-silica substrates. By controlling the waveguide width and making the propagation constants of the polarizations equal, we have found it possible to fabricate polarization-insensitive solgel-based AWGs. Polarization-insensitive design improves the cross talk by approximately 10 dB in the dynamic range.     

Surface plasmon interference on the surface of an aluminum-covered fiber core array for solgel fabrication of submicrometer gratings

An interesting method to fabricate submicrometer gratings (SMGs) utilizing the interference of surface plasmon waves (SPWs) is presented. The stationary wave field off the aluminum (Al) layer surface of an Al-covered UV fiber core, formed by the interference of the induced SPWs, has been employed as a submicrometer photolithography tool to inscribe SMGs on the surface of a self-processing hybrid HfO(2)/SiO(2) solgel ?lm. Using atomic force microscopy, the period of the fabricated SMGs was measured as 105 nm. The intensity distribution of the stationary wave field was measured by a near-field scanning optical microscope and anastomosed with theoretical values calculated by using FDTD simulations.     

软X射线位相型金透射光栅的设计与制作

根据衍射光栅的标量理论,计算并讨论了金透射光栅在软X波段衍射效率对光栅厚度和占宽比的依赖关系.结果表明,选择合适的光栅槽深和占宽比,高达 21.9%的衍射效率可能被获得,远高于振幅型光栅的+1级衍射效率10.14%.通过全息光刻与电镀转移技术制作的位相型金透射光栅由300nm的聚酰亚胺薄膜支撑,光栅槽深200nm,占宽比为0.55,周期为1μm,面积为20mm×5mm.在国家同步辐射装置上,测得其+1级透射衍射效率在波长λ=7.425nm时获得最大值,约为16%. 关键词： 透射位相光栅 全息光刻 电镀     

Simple reflow technique for fabrication of a microlens array in solgel glass

A simple reflow method for fabrication of refractive microlens arrays in inorganic-organic SiO2-ZrO2 solgel glass is presented. To our knowledge, this is the first report that presents a simple reflow technique for transforming a negatively induced hybrid solgel material into desirable spherical microlenses. It is shown that the microlenses have excellent smooth surfaces and uniform dimensions. The reflow technique is considerably cheaper than use of a high-energy beam-sensitive gray-scale mask and is suitable for mass production.     

Sample-inverted reflow technique for fabrication of a revolved-hyperboloid microlens array in hybrid solgel glass

We propose a novel fabrication method, which is referred to as the sample-inverted reflow technique, to fabricate a refractive microlens array (MLA) with a revolved-hyperboloid profile in a solgel material. The fabricated solgel MLA demonstrates an excellent smooth profile with a fabrication error much less than the difference between the revolved hyperboloid and the spherical surface. In an application of coupling a laser diode (LD) to a single-mode fiber (SMF), we propose a two-MLA coupling scheme in which two revolved-hyperboloid MLAs are used between the LD and the SMF. In this configuration the coupling efficiency achieves 81.7% (-0.88 dB).     

Method of optical pulse characterization using sinusoidal optical phase modulations

A simple noniterative electric field retrieval method using a sinusoidally driven optical phase modulator is demonstrated. We derive an analytic relation between the two-frequency correlation function of the electric field of the optical signal under test and the derivatives of the optical spectrum of the phase-modulated signal with respect to the amplitude of the phase modulation. This relation is used to algebraically reconstruct the electric field of the signal under test. We validate the technique by demonstrating accurate and sensitive characterization of picosecond pulses used in telecommunication.     

一种亚纳米级变栅距衍射光栅制作方法的研究

变栅距(VLS)衍射光栅具有自聚焦、像差校正等独特优点。VLS光栅要求的最小栅距变化量为亚纳米数量级,仅靠提高光栅刻划机的分度精度已很难实现,针对这一问题,提出了一种相位扫描方法用于光栅刻划机的变栅距分度控制,即通过对刻划机分度系统的干涉条纹进行微位移扫描来进行相位控制。实验结果表明,相位扫描方法达到了变栅距光栅所要求的亚纳米级的栅距变化精度。     

Influence of the characteristic curve of the material on the diffraction efficiency of holographic volume phase gratings

The behaviour of the diffraction efficiency of holographic gratings is discussed on the basis of the multiwave coupled-wave approach, taking into consideration the photoinduced change in the refractive index of the recording medium. The cases of Bragg and off-Bragg reconstruction in Bragg and mixed diffraction are considered. The influence of the higher harmonics of the refractive index modulation profile on the diffraction efficiency is shown.     

Gap detection and the auditory filter: phase effects using sinusoidal stimuli

Psychometric functions were determined for the detection of temporal gaps in sinusoidal signals at center frequencies between 0.2 and 2.0 kHz. A continuous notched-noise masker was used to restrict listening to the signal frequency region. The gap always started when the signal was at a positive-going zero crossing. There were three different conditions for the starting phase of the signal at the termination of the gap. In the standard-phase condition the signal restarted at a positive-going zero crossing, in the reversed-phase condition at a negative-going zero crossing, and in the preserved-phase condition at the phase the signal would have had if the gap had not been present. In the standard-phase and reversed-phase conditions the psychometric functions were nonmonotonic, showing oscillations with a period equal to that of the signal; maxima in the functions for the standard-phase condition coincided with minima in the functions for the reversed-phase condition, and vice versa. In the preserved-phase condition the psychometric functions were monotonic and the 75% points were roughly independent of center frequency, having a value of about 5 ms. The general form of the results can be modeled by a filter bank followed by a square-law device and a temporal integrator, but good agreement between the data and the model could not be attained across the whole range of gap durations. The deviations between data and model suggest that subjects are sensitive to the brief transitions in phase (or, equivalently, in frequency) in some conditions.     

用于位移传感器的全息平面变间距光栅设计与制作研究

简述了全息变间距光栅的几何理论.利用遗传算法对记录光路进行了优化计算，提出在目标函数中考虑记录参数误差的影响，推导了目标函数的积分形式，提高了计算效率.针对用于位移传感器的平面变间距光栅，分别计算了球面波干涉及球面波与非球面波干涉情况下的全息记录参数，给出了线密度误差曲线.制作出全息平面变间距光栅，并成功应用于位移传感器中. 关键词： 全息光栅 变间距光栅 遗传算法     

Optical testing of ultrasonic phase gratings using a Fresnel diffraction method

A simple optical method is proposed for studying the Raman-Nath parameter of plane, sinusoidal, ultrasonic beams. The Fresnel diffraction field of a continuous ultrasonic grating illuminated by a collimated laser beam is measured by a photodetector placed mid-way between the self-image planes of the grating. Measurement of the amplitude of the fundamental of the output signal enables the absolute determination of the depth of phase modulation. A comparison of the proposed method with the techniques discussed in the literature is presented.     

衍射光栅位相拼接的计算分析

从光学远场衍射的原理出发 ,研究了两块具有完全相同参数的衍射光栅间相互拼接时不同的位相与谱线强度变化的特性关系 ,建立了相应的数学模型 ,并利用计算机进行了模拟计算。计算的结果表明 :拼接出的光栅比其中单一一块光栅在增加了光强的同时也提高了分辨率 ,为通过采用拼接方法来获取大面积光栅提供了理论依据。     

大口径反射镜加工机床在线检测高精度对准方法

本文提出了基于特殊点对靶标的快速对准装置,实现机床加工臂和检测臂初始扫描位置自动高精度复位。靶标由外围区域四组放大倍率标定点对和中心区域大小对准点对组成;对准装置经初次使用前的畸变校正后,每次自动识别靶标区域完成自动对焦;根据外围点对进行放大倍率标定;自动识别中心大小点对并对其进行坐标定位;根据当前点对靶标位置计算与理想位置角度量和平移量偏差,指导机床转台和导轨互相配合,迭代调整直至完成精确对准。实验表明该方法对准精度约为5 μm,优于几十μm的机械定位精度,更利于实现超高精度光学加工的快速收敛,提高大口径反射镜加工效率。     

Correction of systematic errors in the fabrication of fiber Bragg gratings

We suggest a novel method for significant improvement of fiber Bragg grating (FBG) spectral characteristics based on compensation of repeatable errors during the grating writing process. The method is based on an open loop scheme in which a test grating is written first and then a corrected design is obtained and implemented by writing another (compensated) grating. The results are presented for a FBG dispersion compensator.     

Modelling of strongly nonlinear sinusoidal Bragg gratings by the Method of Single Expression

The one-dimensional problem of plane EM wave interaction with strongly nonlinear sinusoidal Bragg gratings is exactly solved using the new Method of Single Expression (MSE). The basic point of the method is the presentation of the electrical field in the modulated medium (Bragg grating) in the form of a single expression, contrary to the traditional counter-propagating waves approach. The spectral characteristics of linear Bragg gratings of different length are presented. The influence of loss or gain on the spectral characteristics of Bragg gratings is considered. The electrical field amplitude distributions along a grating at the wavelengths corresponding to the minima and maxima of reflectivity in the vicinity of the Bragg resonance are illustrated. Bistable and multistable dependences of reflectivity on the incident electrical field amplitude are obtained for negative and positive nonlinearities.     

Diffraction testing of ultrasonically-produced phase gratings using a double beam illumination method

An optical far-field method is described for studying ultrasonically-produced phase gratings with very small phase variations. An ultrasonic grating is illuminated by two plane waves mutually inclined at an angle properly matched to the diffraction angle of the inspected grating. The expressions for the time-dependent irradiance in the far-field diffraction orders are derived. They enable the extraction of the Raman-Nath parameter of a progressive ultrasonic beam. The application of the technique to pulsed ultrasound beams is proposed.     

Measurement of nonlinear phase of a SOA using an asymmetric loop mirror

We use a setup based on an asymmetric Sagnac interferometer to demonstrate an experimental methodology to characterize the nonlinear phase of a semiconductor optical amplifier as a function of input intensity.