Photosensitivity and grating development in trans-4-stilbenemethanol-doped poly(methyl methacrylate) materials

This paper reports the photosensitivity of poly(methyl methacrylate) (PMMA) and its copolymer doped with trans-4-stilbenemethanol. UV irradiation of the doped-PMMA at 325 nm induced the trans- to cis-isomerization of the dopant. This process was confirmed by ¹H NMR spectra of trans-4-stilbenemethanol in CDCL₃ solvent before and after irradiation. The isomerization can be initiated by the irradiation with an intensity of 0.62 mW/cm². Photo-induced refractive index change of −0.0024 was obtained when a PMMA copolymer film doped with 5.1 wt% dopant was exposed to 325 nm light. Lorentz-Lorenz equation was used to estimate the refractive index of a trans-4-stilbenemethanol-PMMA composite and a trans-4-stilbenemethanol-PMMA copolymer composite from the mole refraction and van der Waals volume of each component. A slight elevation of molecular packing coefficient (K) for PMMA and its copolymer containing the dopant implies a denser aggregation as compared to the polymer without the dopant. Long period gratings were created in doped-PMMA films and doped-PMMA copolymer fibers using amplitude mask technique. Gratings were confirmed by microscopic observation and diffraction patterns.     

多层光纤布拉格光栅的理论与实验研究

从理论和实验两方面研究了在非周期性多层光纤上写入布拉格光栅的光学特性。从耦合模理论出发,讨论了光纤具有多于一个光敏层的情况。在实验室自制的两类多层光纤上写入光栅的实验也表明,该类光栅具备有一般光栅的普遍光学特性,说明在使用多层光纤作为关键部分构建器件时,需要的各类光栅部件能够通过直接在该类光纤上写入光栅实现。紫外光在氢载掺铒多层光纤上写入光栅的实验说明分层的异种元素掺杂将导致芯区应力增加,从而辅助提高光纤的光敏性。     

Birefringent azopolymer long period fiber gratings induced by 532 nm polarized laser

Based on the photoinduced birefringence in azo materials, the model of the birefringent long period fiber gratings (BLPFGs) has been proposed and the transmission of such birefringent fiber gratings was further simulated by the coupled mode theory. In order to obtain the optimum condition for making birefringent azopolymer optical fiber (APOF) gratings the photoinduced birefringence of azo dye and methyl methacrylate (MMA) copolymers was systematically studied. After photosensitivity study of azo samples, using Teflon technique, azo dye containing single mode polymer optical fiber (POF) was fabricated. Finally, BLPFGs can be fabricated in azopolymer fiber using polarized 532 nm laser. A 120 μm LPFG with a 50% duty cycle has been successfully written within the core of the fiber with 532 nm laser by an amplitude mask method. Under polarized microphotography, the grating was observed when the optical axis was set at 45° with the direction of the first polarizing lens of the polarization microscope.     

Real-time holographic reflection gratings in volume media of azo-dye-doped poly(methyl methacrylate)

Real-time formation of holographic reflection gratings is experimentally demonstrated in thick media of Disperse Red 1- (DR-1) doped poly(methyl methacrylate) at a nonresonant wavelength (647 nm). Our diffraction efficiencies of 30% and 23% are achieved for reflection gratings inscribed by spatial modulation of intensity and polarization, respectively, and are believed to be the highest achieved for a dye-doped polymer. In addition to the recording of amplitude and phase, the polarization state is also recorded and reconstructed.     

石英基掺Tm3+包层抽运光纤激光器

在MCVD车床上利用“湿法”掺杂方法研制出纤芯高掺Ge的石英基掺Tm³⁺光纤预制棒,采用侧面研磨和抛光工艺制成横截面为正六边形的光纤预制棒.经拉丝,内层涂覆低折射率材料后制成包层抽运光纤.测试其吸收谱,并对光纤参数进行优化.通过在光纤两端紫外写入光纤Bragg光栅,制成线形光学谐振腔,在工作波长793nm的激光抽运下,获得工作波长1947.1031nm、功率2.05W的激光输出.由此证明这种光纤具有优异的光学特性. 关键词： 3+光纤')" href="#">石英基掺Tm³⁺光纤 光纤Bragg光栅 包层抽运 光纤激光器     

Profiles in volume phase holograms in Cp2TiCl2:PMMA

A method for measuring depth profiles in volume phase gratings recorded in doped poly-(methyl methacrylate) (PMMA) is demonstrated. The profiles are the product of photosensitivity and light distribution. Photosensitivity is governed by the distribution of residual monomer. Insensitive PMMA samples may be sensitized by in-diffusion of monomer. The photoinitiator bis(cyclopentadienyl)-titanium-dichloride (Cp₂TiCl₂) is found to be moisture sensitive.     

Fiber laser with combined feedback of core and cladding modes assisted by an intracavity long-period grating

We present a fiber laser made in a single piece of conventional doped-core fiber that operates by combined feedback of the fundamental core mode LP((0,1)) and the high-order cladding mode LP((0,10)). The laser is an all-fiber structure that uses two fiber Bragg gratings and a long-period grating to select the modes circulating in the cavity; the laser emits at the coupling wavelength between the core mode LP((0,1)) and the counterpropagating cladding mode LP((0,10)) in the Bragg gratings. This work demonstrates the feasibility of high-order mode fiber lasers assisted by long-period gratings.     

异戊二烯与甲基丙烯酸甲酯交替共聚物及其嵌段共聚物的13C-NMR研究

本文以¹³C-NMR方法研究了异戊二烯(IP)和甲基丙烯酸甲酯(MMA)的交替共聚物Poly (IP-a-MMA)及其与苯乙烯(ST)和丙烯酸甲酯(MA)交替共聚物Poly (ST-a-MA)的嵌段共聚物Poly[(ST-a-MA)-b-(IP-a-MMA)-b-(ST-a-MA)]的微观结构,结果表明在完全交替的共聚物中,IP单元主要以反-1,4-结构存在。IP和MMA以"头-头"和"头-尾"两种方式共聚,而以前者为主。     

Optimization of multiplexed holographic gratings in PQ-PMMA for spectral-spatial imaging filters

Holographic gratings formed in thick phenanthrenquinone- (PQ-) doped poly(methyl methacrylate) (PMMA) can be made to have narrowband spectral and spatial transmittance filtering properties. We present the design and performance of angle-multiplexed holographic filters formed in PQ-PMMA at 488 nm and reconstructed with a LED operated at approximately 630 nm. The dark delay time between exposure and the preillumination exposure of the polymer prior to exposure of the holographic area are varied to optimize the diffraction efficiency of multiplexed holographic filters. The resultant holographic filters can enhance the performance of four-dimensional spatial-spectral imaging systems. The optimized filters are used to simultaneously sample spatial and spectral information at five different depths separated by 50 microm within biological tissue samples.     

Polymer waveguides from alicyclic methacrylate copolymer fabricated by deep-UV exposure

We have investigated the fabrication of waveguides from alicyclic methacrylate copolymer based on refractive-index modification by deep-UV exposure. By optimizing the UV-exposure process, we were able to obtain single-mode waveguides with a propagation loss of 0.8 dB/cm at 1550 nm, which is due only to material losses in this wavelength range. The loss obtained here is comparable with that of poly(methyl methacrylate) (PMMA) waveguides fabricated by deep-UV exposure. The fabricated waveguide is also single mode at 808 nm, and its propagation loss is 0.6 dB/cm. This alicyclic methacrylate copolymer is a promising material for the fabrication of polymer waveguides by use of deep-UV exposure.     

Photochromic polymers for the optical homodyne detection of ultrasonic surface displacements

We present a novel scheme with which to detect small ultrasonic surface displacements by use of a photochromic polymer instead of a photorefractive material as an adaptive beam combiner in a two-wave mixing geometry. Poly(methyl methacrylate) is doped with a derivative of zinc tetrabenzoporphyrin that possesses a long-lived triplet state that can be efficiently populated in a reversible manner. The resulting dynamic hologram consists of local absorption and refractive-index gratings, which can process speckled beams reflected from rough surfaces. We believe that this is the first use of a local nonlinear medium for adaptive homodyne detection of ultrasonic surface displacements.     

甲基丙烯酸甲酯—萘乙烯共聚物的NMR研究Ⅱ.甲基丙烯酸甲酯—萘乙烯共聚物的核弛豫研究

用核弛豫研究了溶液中甲基丙烯酸甲酯-萘乙烯共聚物体系中高分子链间的凝聚态结构．通过对溶液中甲基丙烯酸甲酯-萘乙烯共聚物的变温13CNMR自旋-晶格弛豫的研究，发现此体系具有类似小分子在溶液中的弛豫特性．变温1HNMR自旋-自旅弛豫呈现出双指数特性，弛豫快的部分随温度升高而减少对应于聚合物链间凝聚缠结的解缠，当温度继续升高时，主链的这种组分又开始增加，说明主链中形成新的缠结．研究结果还表明，在这种共聚物中，例基萘环的叠加较少．     

Fabrication and amplified spontaneous emission of Eu(DBM) <Subscript>3</Subscript>Phen doped step-index polymer optical fiber

A step-index polymer optical fiber (SI POF) with a core of poly(methyl methacrylate) (PMMA) containing Eu(DBM)₃Phen has been fabricated by a preform technique. Fluorescence analysis showed that there is not obvious change in the local environment around Eu³⁺with the increase of Eu(DBM)₃Phen doping concentration. Amplified spontaneous emission (ASE) phenomenon of the doped SI POF by end-pumping with an Ar⁺-laser of 457.9 nm at ambient temperature was observed. The threshold of the pump power for the onset of ASE is found to be 120 mW for the doped SI POF with a length of 50 cm, the length is also found to be the optimal length for maximum ASE power under the input power of 200 mW. The maximum quantum conversion efficiency of the fiber is about 40%.     

All-Fiber Spectroscope with Second-Order Fiber Bragg Grating for Rotational Raman Lidar

Owing to the second-order fiber Bragg grating possessing narrower reflectivity bandwidth than first-order, an all-fiber spectroscopic filter with several second-order fiber Bragg gratings and optical fiber couplers in the visible region is designed to extract interest rotational Raman spectra. Considering the inference fringe visibility of inscribing fiber Bragg grating and the fiber core index dispersion effect, numerical simulations are made by the improved mathematical model based on an exponential photorefractive dynamic, and its simulative results show better agreement with the experimental data. We propose an all-fiber spectroscopic configuration, which could balance lidar sensitivity against signal-to-noise ratio for optimizing remote sensing performance by fiber Bragg gratings serially. Simulative results show that the thumb principle for fabricating second-order fiber Bragg grating is the increasing gratings length, and that this all-fiber spectroscope can achieve >70 dB suppression to elastic scattering and efficiently extract the rotational Raman signal for profiling atmospheric temperature.     

Comment on "microstructured polymer fiber laser"

We comment on the recent Letter by Argyros et al. [Opt. Lett. 29, 1882 (2004)] in which a microstructured polymer fiber doped with the dye Rhodamine 6G was discussed as a possible fiber laser source. We suggest that the lasing action at 632 nm was due to stimulated Raman scattering in the poly(methyl methacrylate) host material.     

New nanosecond Q-switched Nd:VO4 laser fifth harmonic for fast hydrogen-free fiber Bragg gratings fabrication

We demonstrate the fabrication of fiber Bragg gratings using a novel high-repetition rate nanosecond Q-switched Nd:VO₄ laser fifth harmonic (213 nm) source for the first time in boron and hydrogen-free, Ge doped fiber. Strong gratings are rapidly obtained with the phase mask technique in hydrogen-free B/Ge doped photosensitive fiber with relatively low average power (100 mW), as well as in standard Corning SMF28 fiber. The evolution of the refractive index change during UV-exposure is presented. Photosensitivity of fibers to the 213 nm light is compared to the fourth harmonic (266 nm) light, as well as picosecond 213 nm radiation and is shown to be significantly higher than both. We believe that the photosensitivity of SMF28 fiber is due to a single-photon rather than two-photon absorption process.     

Monolithic fluoride-fiber laser at 1480 nm using fiber Bragg gratings

We report what we believe is the first monolithic fluoride-fiber laser making use of fiber Bragg gratings written directly in the doped fluoride-fiber core. The Tm(3+):ZBLAN fiber laser is upconversion pumped at 1070 nm and emits at 1480 nm. Using two different all-fiber cavities, we observed a threshold as low as 75 mW and a conversion efficiency of up to 40% with respect to launched pump power.     

Running holograms in azopolymer films

We report investigations on running holograms recorded in an azopolymer film made of a poly(methyl methacrylate) matrix doped with Disperse Red 1. Two-wave mixing experiments were carried out in the symmetrical transmission geometry. A stabilization technique was employed for active control of the phase shift between the real-time hologram and the interference pattern. Depending on the imposed phase shift, a running hologram propagates in the material in the form of an isomerization wave created by a continuous erasing–rewriting process. Diffraction efficiencies and the hologram velocities were measured as functions of the holographic phase shift at the wavelengths 515 and 488 nm. The experimental results were compared to theoretical curves obtained from a simplified model of the isomerization kinetics. The selective contributions of the phase and the amplitude gratings to the whole hologram were also determined.     

Dispersion copolymerization of methyl methacrylate and styrene in supercritical carbon dioxide

A method for producing finely dispersed powders of methyl methacrylate (MMA)-styrene copolymer by radical polymerization in a supercritical carbon dioxide medium (SC-CO₂) was proposed, studied, and experimentally implemented. The dispersing agent (surfactant), which made it possible to obtain nearly monodisperse size distribution of polymer particles, was poly(dimethylsiloxane methacrylate), a SC-CO₂-soluble substance. The copolymer, synthesized with a molecular mass of M _w ～ 36000 in the form of spherical particles with a characteristic size of ～1 μm, exhibited a higher thermal stability as compared to poly(methyl methacrylate) with a similar molecular mass. Varying the percentage ratio between MMA and styrene monomers, it was possible effectively control the integral hydrophobicity and physicomechanical characteristics of the methacrylate-styrene copolymer.     

光纤光栅温度应变智能传感原理及增敏技术研究

文章分析了光纤光栅对温度和应变传感的响应机理，对光纤光栅的纤芯材料选择、光纤光栅的写入方法及封装方法等方面进行了综合评述，在此基础上讨论了实现光纤光栅对温度和应变传感增敏的基本原理和方法，介绍了长周期光纤光栅与光纤布拉格（Bragg)光栅融合测量和如何选用对温度和应变灵敏的纤芯材料，研究了超短脉冲激光直接写入法和如何选用热膨胀系数和弹性模量不同的特种聚合材料对光纤光栅进行封装处理。