一种基于SOI材料的直波导可调谐光衰减器

设计并制造了一种基于SOI材料的直波导可调谐光衰减器,其调制区采用了独特的双脊型PIN结构,增强了注入电流场与光场的重叠,提高电注入效率。该VOA可实现20dB的光功率衰减量,所需要的最大功率为650mW,器件的片内插入损耗约为3．6dB。     

A new micromechanism for transformation of small displacements to large rotations for a VOA

New movement translation micromechanism (MTM) is proposed to transfer and amplify small in-plane displacement or movement into large out-of-plane vertical displacement or rotation. Based on this MTM, we may just apply 3-V dc load to generate 3.1-/spl mu/m in-plane movement, then 26.4/spl deg/ rotation angle of pop-up micromirror can be subsequently derived. An axial aligned fiber-to-fiber variable optical attenuator (VOA) device using the MTM, a U-shaped electrothermal actuator array, and the pop-up micromirror to reflect the attenuated light toward out-of-plane direction is designed and characterized. The proposed new VOA device achieves 37-dB attenuation range under 3-V dc load, while return loss, polarization-dependent loss, and wavelength-dependent loss at attenuation of 3 dB are measured as -45B, 0.05, and 0.28 dB. This new concept of steering a portion of input light toward out-of-plane direction is proven to be feasible for VOA applications.     

熔锥型光纤声光可变衰减器

利用耦合模理论对光纤熔锥声光器件进行了数值模拟,得到了全光纤声光衰减器传输谱和可调谐性。分析了带宽与声波长、耦合长度的关系。数值分析结果表明,声波在光纤熔锥中引起的轴向电介质微扰、耦合长度和工作波长都会对器件的传输谱产生影响,选择合适的设计参数可以制作较为理想的声光衰减器。实验上获得了损耗小于0．2dB,带宽大于200nm,动态范围为20dB的单模光纤熔锥可变衰减器,所得结果与理论分析相符合。这种器件可用于光纤通信及光纤传感。     

High-isolation polarization-insensitive N-port optical circulator

A polarization-insensitive N-port optical circulator is proposed. A four-port and a six-port circulator are assembled and their characteristics are measured. Experiments demonstrate that the circulators have a low insertion loss (/=65.0 dB), and a high return loss (>/=61.3 dB) for any polarization state of input light.     

Stable, low-loss optical waveguides and micromirrors fabricated in acrylate polymers

Acrylate-based optical waveguides have been fabricated with optical loss of 0.5 dB/cm at 1300 nm by means of a new material system that ensures stable optical and mechanical properties over a wide temperature range. No increase in loss was measured after 500 h at temperatures up to 150 degrees C, and there was no significant increase in loss during short (<5 min) temperature excursions to 300 degrees C for bonding. Single-mode waveguides were fabricated with refractive indices for core and clad of 1.505 and 1.500, respectively, so that the mode field is very similar to that of single-mode silica fiber. Guides were fabricated on both planar and structured substrates of Si and GaAs as well as on substrates coated with metals and dielectrics. Fabrication involved spin coating and UV exposure to cross-link the polymer, but the substrate temperature did not exceed 180 degrees C. With this method guides could be fabricated on a range of substrates up to 125 cm in diameter, including those with multilayer metallization for multichip modules, providing optical interconnect capability. Microprism reflecting surfaces were fabricated in the waveguides to couple light out normal to the substrate. All the processing was compatible with normal semiconductor fabrication.     

Long-period grating fabricated by periodically tapering standard single-mode fiber

We fabricated an asymmetric long-period grating (LPG) by periodically tapering a section of standard single-mode fiber using a resistive filament heating. The LPG exhibits large peak transmission attenuation of -30.31 dB with only 22 periods in a 1.0 cm long optical fiber and possesses unique characteristics for sensing applications. The bending and strain sensitivities are 1.74 nm m and 1.11 pm/mu epsilon, respectively. The polarization dependent loss is large, up to 11.65 dB, which is caused by an asymmetric index profile in the cross section of the tapered LPG.     

Integrated optical polarization splitter based on photobleaching-induced birefringence in azo dye polymers

An integrated optical polarization splitter has been fabricated by utilizing the photobleaching-induced birefringence in an azo dye polymer. It consists of a Y-branch waveguide formed by the reactive ion etching with one of the two arms photobleached. The refractive index of the photobleached arm is decreased for the TE mode and increased for the TM mode. The performance of the splitter was measured as a function of the energy of the photobleaching beam and compared to a wave propagation simulation of the device. The measured cross talks are less than -28 dB for the TM mode and -24 dB for the TE mode at a wavelength of 1310 nm. The measured excess losses for the TE and TM modes, which measure the effect of the Y branch and the photobleaching, are 0.3 and 0.4 dB, respectively. The insertion loss was 5 dB, which includes the input fiber to waveguide coupling loss.     

Comment on the reported fiber attenuations in the visible regime in "Fabrication of glass photonic crystal fibers with a die-cast process"

We comment on the recent paper by Zhou et al. [Appl. Opt.45, 4433 (2006)APOPAI0003-693510.1364/AO.45.004433], in which transmission losses of 0.2-0.3 dB/m were claimed across the wavelength range 420-900 nm in a high-index (n(d)=1.80518 at 587.6 nm) SF6 glass-based photonic crystal fiber fabricated by novel die-cast technique. If confirmed, these losses are at least 1 order of magnitude lower than previous reported losses of SF6 photonic crystal fibers from other fabrication approaches. Here we present a statistic survey on the relationship between the refractive index and the bulk material attenuation, based on a large number of commercial Schott optical glasses with the n(d) ranging between 1.40 and 2.05. It shows that the loss of a high-index (n(d)=1.80) glass optical fiber should be at the levels of 10-50 dB/m at 420 nm and 1-10 dB/m at 500 nm, respectively. Moreover, the material attenuation of such a high-index glass fiber should intrinsically show a large decay, from 10-50 dB/m at 420 nm to the level of 1 dB/m at 700 nm, which arises from the tail on the UV absorption edge of the high-index glass extending to the visible region. Therefore, we conclude that: (1) the low loss of 0.2-0.3 dB/m reported in the cited paper is abnormally one or two magnitudes lower than the material attenuation that a high-index (n(d)=1.80) glass optical fiber should have in the range between 420 and 500 nm and that (2) the flat loss curve between 420 and 700 nm in the cited paper deviates greatly from the intrinsic behavior of a high-index (n(d)=1.80) glass fiber.     

Variable optical attenuator with a polymer-stabilized dual-frequency liquid crystal

A transmission-type variable optical attenuator (VOA) based on a polymer-stabilized dual-frequency liquid crystal (PSDFLC) is demonstrated at gamma = 1.55 microm. The VOA is highly transparent in the voltage-off state but scatters light in the voltage-on state. By using a birefringent beam displacer incorporated with half-wave plates, we can obtain a VOA that is polarization independent and that exhibits a 31 dB dynamic range. The polymer networks and dual-frequency effect together reduce the response time (rise + decay) of a 16 microm PSDFLC cell to 30 ms at room temperature and at a voltage of 24 Vrms.     

新型光隔离器结构设计与实验性能测试

提出一种功能复用光隔离器设计方案。在传统光隔离器中加入了透镜对,两透镜间拥有一个相邻共焦面,具有空间光交叉功能,能实现功能复用光隔离器输入输出多尾纤之间的对应耦合;二者结合组成空间复用功能系统,使光隔离器具有功能复用的作用。该光隔离器的主要性能测量结果表明,所设计的1550nm双通道功能复用光隔离器两个通道的插入损耗分别为0.43dB和0.31dB,隔离度分别为43dB和40dB,两个功能隔离器之间的串扰都大于60dB,达到了隔离器需要满足的性能指标,在低插损、高隔离的基础上具有功能复用效用。     

Effects of mechanical stress on the transmission properties of optical fiber packaged in a composite structure

Optical circuit boards for system-level interconnection may be fabricated by bonding segments of optical fiber, in the configuration necessary for signal distribution, to a substrate such as a printed wiring board. To measure the effects of mechanical stress on optical transmission, a four-point bend test is applied to prototype optical circuit boards. The results show that flexing a board to a strain of approximately 0.3% leads to a decrease in loss of 0.012 ± 0.002 dB for multimode fiber. Flexing of a thin board, in two directions, around 40-in.- (101.6-cm-) bend-radius mandrels decreases fiber loss by almost 1 dB after 700 cycles. Single-mode fiber bonded to aboard, however, exhibits an increase in loss of 0.11 ± 0.05 dB under an induced strain of 0.3%, a change that is not significant relative to typical loss-per-line budgets in real systems.     

Application of thin-film optical filters to the temperaturecompensation of optical fiber grating-based devices

A major problem currently affecting the implementation of in-fiber refractive-index grating-based optical fiber devices is the drift in wavelength modulation due to the change in the ambient temperature. For accurate and reliable long-term operation of these devices, suitable temperature compensation techniques are a necessity. This paper presents a novel temperature compensation technique for in-fiber refractive index grating-based devices and components. The proposed technique is based on the temperature-dependent spectral characteristics of a dielectric multilayer thin-film interference filter fabricated on the endface of refractive-index grating impressed optical fiber. Temperature compensation is achieved by comparing the reflected intensities at the grating-reflected and the interference filter-reflected wavelengths. The proposed scheme also compensates for light source fluctuations and lead-in fiber bending losses     

Synchronous amplitude and time control for an optimum dynamic range variable photonic delay line

A synchronous-amplitude-controlled and time-delay-controlled photonic controller for phased-array antenna applications is proposed and demonstrated. Amplitude control is based on a variable optical attenuator system that operates in synchronism with the photonic delay line (PDL). This amplitude control system can provide both the signal calibration for the different PDL channels and settings required for driving the antenna elements of a phased-array radar and the optimum optical power levels that impinge on the photodetector for optimum fiber-optic-link performance. Various variable amplitude control modules based on ferroelectric liquid crystals, polymer-dispersed liquid crystals, and photoconductive devices are proposed. We show that the dynamic range loss due to a switched-PDL inherent structure loss can be compensated when we control the optical power from the laser, using the synchronous optical attenuation system. For the first time to our knowledge, full dynamic range loss compensation is demonstrated for an external-modulation-fed 3-bit switched PDL with a structure optical insertion loss of 5.5 dB. A compression dynamic range of 158 dB.Hz was measured at 6 GHz, and a spurious free dynamic range of 111 dB.Hz(2/3) was estimated. Feasibility of the dynamic range compensation technique for multichannel, higher-insertion-loss PDL systems is discussed.     

High-bandwidth, graded-index polymer optical fiber for near-infrared use

We describe graded-index polymer optical fibers with high bandwidth (5.12 GHz for 100-m transmission) and low loss in the near-infrared region (56 and 115 dB/km at wavelengths of 688 and 773 nm, respectively) that we successfully obtained with a new interfacial-gel polymerization technique using an all-deuterated methyl methacrylate monomer and a partially fluorinated acrylate monomer. The necessity for both low attenuation and high bandwidth for a polymer optical fiber is described for its use as a physical media in a high-speed multimedia network.     

聚合物SiON波导的可变光衰减器性能研究

利用弯曲聚合物SiON波导设计了一种新型可变光衰减器,该器件由输入、输出直波导,S型的弯曲波导,以及在聚合物SiON波导弯曲部位镀上的电极组成.通过外加电场的作用来调节波导覆盖层的折射率,从而达到衰减波导中光能量的目的.现采用光束传播法(BPM)对设计的新型光衰减器进行了仿真设计,结果表明,设计的光衰减器具有大的动态可调衰减范围(45.3 dB),低的插入损耗(0.8 dB).     

基于狭缝整形的低损耗飞秒光纤光栅制备

为了解决飞秒激光逐点法制备的光纤布拉格光栅（Fiber Bragg Gratings, FBG）损耗较高的问题,利用逐面法完成飞秒光纤光栅制备的实验研究。运用高斯光束传播的基本理论,通过狭缝整形技术对聚焦的飞秒激光能量分布进行等高宽整形,突破在光纤横截面内诱导产生圆形折射率调制的难点,最终制备得到低损耗的飞秒光纤光栅。开展不同狭缝宽度制备FBG的光谱特性对比实验,结果表明：利用光斑直径为5.0 mm的飞秒激光光束刻写FBG时,采用宽度为1.7 mm的狭缝制备得到的FBG插入损耗降低至0.15 dB,短波损耗降低至0.5 dB,验证了基于狭缝整形的低损耗飞秒光纤光栅制备方法的有效性。针对狭缝法制备的FBG反射率分散问题,提出控制折射率匹配液填充量以及调整飞秒激光能量的方法,并优化光束聚焦流程,成功降低FBG反射率的分散度。本研究对推动飞秒光纤光栅在大容量、高链路损耗等环境中的实际应用具有重要意义。     

Prototype CO2 laser-induced long-period fiber grating variable optical attenuators and optical tunable filters

Prototype devices capable of variable attenuation at a fixed wavelength, wavelength tuning at a constant attenuation, and combinations of these spectral characteristics are demonstrated in CO2 laser-induced long-period fiber gratings (LPFGs). These devices are based on controlled flexure by means of a piezoceramic platform. CO2 laser-induced LPFG characteristics along with the fabrication and testing processes of these gratings are discussed. Devices with a optical attenuation of 13 dB and a wavelength tuning of 7 nm are reported.     

A novel optical device with wide-bandwidth wavelength conversionand an optical sampling experiment at 200 Gbit/s

This paper reports the characteristics of our proposed prototype optical parametric diffuser (OPD). An OPD is based on the theory of four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). However, to improve the conversion bandwidth and FWM efficiency, the gain bandwidth is spread and the gain peak wavelengths are set to a wavelength near the FWM light on the short-wavelength side by combining different MQW active layers. We measured the optical gain characteristics; the fiber-to fiber gain was 16.1 dB and the gain bandwidth over 8 dB was 117 nm when driven at 200 mA dc, and 190 nm when driven by an 800 mA pulse current. In a wavelength-conversion experiment, a high conversion efficiency of ⩾-20 dB was obtained across a detuning wavelength bandwidth of 43 nm. A clear waveform was obtained in an optical sampling experiment to measure 200 Gbit/s optical data sequences     

Liquid-crystal-deflector based variable fiber-optic attenuator

A compact, low-component-count, no-moving-parts variable optical attenuator (VOA) is demonstrated for the first time by means of beam spoiling that is implemented via an electrically reconfigurable nonpixelated nematic liquid-crystal deflector. The VOA design features an in-line alignment polarization-insensitive design that does not use bulky polarization splitting and combining optics. The proof-of-concept VOA at 1550 nm demonstrates a 30-dB attenuation range, a 2.5-dB insertion loss, a < or = 0.8-dB polarization-dependent loss, and a 1-s maximum attenuation reset time. The VOA design can counter performance-reducing environmental effects such as excess-loss increases due to temperature variations.     

Effect of uniaxial deformation on the optical scattering losses of a semicrystalline fluorocopolymer

Both small- and wide-angle light scattering as well as transmission measurements have been used to investigate the optical scattering losses of a vinylidene difluoride-tetrafluoroethylene-hexafluoropropylene copolymer crystallized from the melt. The main origin of the scattering loss is the wide-angle light scattering from the spherulitic superstructure. Uniaxial deformation transforms this structure into a fiber morphology. The attenuation of fibers has been measured for light propagating both parallel and perpendicular to the orientation axis. For both directions, the attenuation decreases with increasing draw ratio. Annealing of the fibers while keeping their ends fixed is an effective method to reduce the attenuation further, to a low value as close to that of the melt.