Fabrication of integrated waveguide grating in azo polymers

In this Letter, we have introduced a technique, new to our knowledge, to fabricate gratings on a waveguide of azo-functionalized polymeric films using a slit mask and a fast, direct-writing method. To prevent the destruction of the waveguide by the grating formation on the waveguide, we placed a slit mask on the waveguide. By properly adjusting the resonance, this grating can be used as an integrated wavelength filter. We have produced an attenuation of 13.4?dB at 1562?nm with a FWHM of 3.45?nm. The grating has been fabricated as narrow as the width of the waveguide to couple filtered light into the waveguide by using a slit mask. Any light shifted from the resonance will pass through the waveguide undisturbed.     

Multidimensional angle sensing method using guided-mode resonance

Optical Review - A waveguide grating on a transparent substrate can serve as an optical notch filter owing to guided-mode resonance. The filtering wavelength is highly sensitive to an incidence...     

一种温度不敏感型阵列波导光栅的研究

研究了的一种新型温度不敏感型阵列波导光栅(AWG)。该新型温度不敏感型阵列波导光栅的波导采用混合材料的波导结构，该混合材料波导通过在石英波导芯层上旋涂聚合物材料的上包层，达到改变波导温度特性的目的，使得阵列波导光栅的温度敏感性降低。通过理论分析和有限差分方法研究了其中两种结构：三层混合材料波导构成的阵列波导光栅和四层混合材料波导构成的阵列波导光栅，计算了该新型温度不敏感型阵列波导光栅的温度特性。结果表明，在一定的设计下，温度变化0～50℃时，这两种温度不敏感型阵列波导光栅的最大波长漂移量小于0．03nm，不到无温度控制时常规阵列波导光栅最大波长漂移量的4％。     

Investigation of all-optical analog-to-digital quantization using a chalcogenide waveguide: A step towards on-chip analog-to-digital conversion

We have investigated all-optical analog-to-digital quantization by broadening the pulse spectrum in a chalcogenide (As₂S₃) waveguide and subsequently slicing the measured spectrum using an array of filters. Pulse spectral broadening was measured for 8 different power levels in a 6 cm long As₂S₃ waveguide and used to analyze an 8-level all-optical quantization scheme employing filters with full-width at half-maximum (FWHM) bandwidth of 2 nm. A supercontinuum spectrum with −15 dB spectral width up to 324 nm was observed experimentally at large powers. This large spectral broadening, combined with filtering using a 128 channel arrayed waveguide grating (AWG) with 2 nm filter spacing, has the potential for all-optical quantization with 7-bit resolution. In order to encode the quantized signal we propose an encoder scheme which can be implemented using optical Exclusive-OR gates. Demonstrating all-optical quantization using a planar waveguide is an important step towards realizing all-optical A/D conversion on a chip.     

Adaptive Integrated Optical Bragg Grating in Semiconductor Waveguide Suitable for Optical Signal Processing

This article presents a methodology for an integrated Bragg grating using an alloy of GaAs, AlGaAs, and InGaAs with a controllable refractive index to obtain an adaptive Bragg grating suitable for many applications on optical processing and adaptive control systems, such as limitation and filtering. The refractive index of a Bragg grating is controlled by using an external electric field for controlling periodic modulation of the refractive index of the active waveguide region. The designed Bragg grating has refractive indices programmed by using that external electric field. This article presents two approaches for designing the controllable refractive indices active region of a Bragg grating. The first approach is based on the modification of a planar micro-strip structure of the iGaAs traveling wave as the active region, and the second is based on the modification of self-assembled InAs/GaAs quantum dots of an alloy from GaAs and InGaAs with a GaP traveling wave. The overall design and results are discussed through numerical simulation by using the finite-difference time-domain, plane wave expansion, and opto-wave simulation methods to confirm its operation and feasibility.     

Modelling of finite-size grating waveguide filters on the basis of a free-space diffraction approach

The field reflection coefficientR of a high strength and short length waveguide grating section is obtained by resorting to a free-space diffraction approach whereby the waveguide grating is excited by means of a virtual high index prism. The effective index of the guided mode, the coupling coefficient between contradirectionally propagating modes of the grating waveguide as well as the modal field are first obtained in the case of an infinite grating by interpreting the results given by an exact diffraction solution by means of a three-wave coupled mode formalism. These results are then introduced in the coupled wave analysis of the structure of finite extent to provide the field at the entrance of the waveguide grating section where the usual overlap integral with the incident field delivers the reflection coefficient. We neglect only the result of radiation mode propagation. This assumption can be made when the grating section is longer than the propagating length of all the leaky modes.     

Modelling of finite-size grating waveguide filters on the basis of a free-space diffraction approach

The field reflection coefficient R of a high strength and short length waveguide grating section is obtained by resorting to a free-space diffraction approach whereby the waveguide grating is excited by means of a virtual high index prism. The effective index of the guided mode, the coupling coefficient between contradirectionally propagating modes of the grating waveguide as well as the modal field are first obtained in the case of an infinite grating by interpreting the results given by an exact diffraction solution by means of a three-wave coupled mode formalism. These results are then introduced in the coupled wave analysis of the structure of finite extent to provide the field at the entrance of the waveguide grating section where the usual overlap integral with the incident field delivers the reflection coefficient. We neglect only the result of radiation mode propagation. This assumption can be made when the grating section is longer than the propagating length of all the leaky modes.     

减少聚合物阵列波导光栅损耗的蒸气回溶技术

阵列波导光栅(AWG)器件是波分复用(WDM)系统的一种关键器件,其中,聚合物阵列波导光栅由于其制备工艺、器件集成等方面的优势而受到人们的日益关注。侧壁散射损耗是聚合物阵列波导光栅损耗的一个主要因素,减少阵列波导光栅波导的侧壁损耗对制备低损耗阵列波导光栅具有重要意义。一种蒸气回溶技术被用来有效地减少硅基聚合物阵列波导光栅的散射损耗,该技术的机理是饱和溶剂分子融入并软化波导侧壁,增加其流动性,从而降低波导侧壁粗糙度。用扫描电镜方法验证了用该技术能获得更光滑的波导侧壁。对直波导和阵列波导光栅样品进行回溶处理,测试后得到直波导的侧壁散射损耗减少2.1 dB/cm,阵列波导光栅中心信道和周边信道的插入损耗分别减少5.5 dB和6.7 dB,串扰减少2.5 dB。     

Condition for the realization of a temperature-insensitive long-period waveguide grating

We analyze the condition for achieving a temperature-insensitive resonance wavelength of a long-period grating formed in a channel waveguide. We find that by controlling the waveguide cladding thickness, zero temperature sensitivity can be achieved with core and cladding materials that have significantly different thermo-optic coefficients. To verify our finding, we design a polymer long-period waveguide grating (LPWG) according to the zero-sensitivity condition, where the thermo-optic coefficient of the core is twice that of the cladding. The temperature sensitivity of the fabricated grating is within +/-0.15 nm/ degrees C over a temperature range of approximately 15 degrees C, which is more than an order of magnitude lower than those of previously reported LPWGs fabricated with the same materials.     

基于阵列波导光栅的智能服装人体测温解调系统研究

研究并实现了一种应用于智能服装中人体温度测量的阵列波导光栅解调系统。分析了系统的解调原理,搭建了光纤布拉格光栅解调实验平台,采用了强度法解调出光纤光栅的布拉格波长,完成了光纤光栅传感器串联前后解调的实验。结果表明,系统对光纤布拉格光栅的布拉格波长的解调具有高线性度,波长测量精度可达0.001 nm,光纤布拉格光栅传感器间串扰所造成的解调误差为0.000 5 nm,人体温度的测量误差为±0.16 ℃。该解调系统精度高、串扰低,可适用于智能服装中人体温度的测量。     

Volume grating preferential-order focusing waveguide coupler

A volume grating focusing waveguide coupler has been designed, fabricated, and tested. The volume grating is designed to couple a 633-nm wave guided in a single-mode polyimide waveguide preferentially into the air cover. The beam is outcoupled normally to the surface of the waveguide and focused to a line 25 mm above the waveguide. The slanted-fringe volume grating is holographically recorded by the interference of two coherent 364-nm ultraviolet waves focused with a cylindrical lens to produce the chirped grating. The 1-mm-long volume grating coupler exhibits a preferential-coupling ratio of 0.98, a coupling efficiency of 95%, and an almost diffraction-limited focal line with a full width at half-maximum of 10.49mum.     

Ge0.05Si0.95/Si异质结单模共面布拉格反射波导光栅的设计与分析

GeSi/Si异质结布拉格反射光栅是硅基光电集成领域一种重要的集成光学器件,分析GeSi/Si异质结的传光特性和布拉格条件,通过求解布拉格光栅方程,得出耦合系数和耦合效率。利用上述原理设计出入射角为66°,波导层的厚度为2μm,光栅长度为4252μm,槽深为0.05μm,光栅周期为0.456μm,滤波带宽为0.214nm,耦合效率为84.1%的1.3μm Ge_0.05Si_0.95/Si异质结单模共面布拉格反射光栅,并用数值模拟了入射光波电场和反射光波电场的分布。     

基于LiNbO_3的长周期波导光栅可调谐耦合器的设计

设计了一种基于LiNbO_3的长周期波导光栅可调谐耦合器.该耦合器利用长周期光栅的独有特性将输入波导的导模经包层模耦合至输出波导导模.由于LiNbO_3的电光效应,波导光栅芯层与包层的有效折射率随外加电压变化,从而耦合器的谐振波长及耦合效率可由外加电压调谐.分析了光栅周期与耦合器的长度对耦合器带宽和耦合效率调谐范围的影响,以及波导尺寸对谐振波长调谐灵敏度的影响.结果表明光栅周期越短,耦合器长度越长,则耦合器的带宽越窄,耦合效率调谐范围也越大.此外,谐振波长调谐灵敏度随波导宽度的增加而减小,而波导厚度对谐振波长调谐灵敏度的影响可以忽略.对光栅周期为94μm、长度为3.52cm的耦合器进行仿真,结果表明,谐振波长灵敏度为26.2pm/V,3dB带宽可达4.5nm,当外加电压从0变化到200V时,谐振波长变化5.24nm,耦合效率可在1到0.15之间进行调谐.     

Bandpass engineering of lithographically scribed channel-waveguide Bragg gratings

We propose and demonstrate a powerful approach to spectral bandpass engineering (apodization) of one-dimensional channel-waveguide Bragg reflectors. Bandpass engineering is accomplished by precise photolithographic control of the length and the longitudinal placement of individual grating lines, which provides unique line-by-line diffractive amplitude and phase control. Channel-waveguide gratings that exhibit complex filtering functions have been fabricated and modeled. When a second-order apodization effect that comprises effective waveguide refractive-index variation with grating-line length is included in the simulation, extraordinary agreement between predicted and observed spectral passband profiles is obtained.     

TE0导模干涉刻写周期可调亚波长光栅理论研究

通过棱镜耦合激发非对称金属包覆介质波导结构中的TE₀导波模式, 利用两束TE₀模的干涉从理论上实现了周期可调的亚波长光栅刻写. 分析了TE₀模式的色散关系, 刻写亚波长光栅的周期与激发光源、棱镜折射率、光刻胶薄膜厚度及折射率之间的关系. 用有限元方法数值模拟了金属薄膜、光刻胶薄膜和空气多层结构中TE₀导模的干涉场分布. 研究发现, 激发光源波长越短, TE₀ 模干涉刻写的亚波长光栅周期越小; 光刻胶越厚, 刻写的亚波长光栅周期越小; 高折射率光刻胶有利于更小周期亚波长光栅的刻写. 相较于表面等离子体干涉光刻, 基于TE₀ 模的干涉可在厚光刻胶条件下通过改变激发光源、棱镜折射率、光刻胶材料折射率、特别是光刻胶薄膜的厚度等多种方式实现对亚波长光栅周期的有效调控.     

Two-dimensional non-spatial filtering based on holographic Bragg gratings

The filter made up of two gratings performs as a two-dimensional non-spatial filtering. This paper reports that the volume Bragg gratings are fabricated by interfering two collimated coherent laser beams in photopolymer. Diffraction efficiency of a single grating is up to 78% in Bragg's condition, then a two-dimensional non-spatial filter, which consists of two volume Bragg gratings and a half-wave plate, enables the laser beam filtered in two dimensions with the diffraction efficiency of 54%. The Bragg's condition and effect of polarisation on performances of the two-dimension filter are also discussed.     

Real propagation speed of the ultraslow plasmonic THz waveguide

A graded metallic grating structure can not only work as a wave trapping system, but also work as an ultraslow terahertz (THz) waveguide. The depth of the grating waveguide is partial graded and partial fixed. The real propagation speed of such a system is calculated. Different frequencies of THz waves can be propagated at a designed propagation speed, even close to zero.     

Perfect absorption in a monolayer graphene at the near-infrared using a compound waveguide grating by robust critical coupling

We present a perfect graphene absorber with a compound waveguide grating at the near-infrared. The analytical approach is mainly based on the coupled leaky mode theory, which turns the design of the absorber to finding out the required leaky modes supported by the grating structure. Perfect absorption occurs only when the radiative loss of the leaky mode matches the intrinsic absorption loss, which is also named the critical coupling condition.Furthermore, we also demonstrate that the critical coupling of the system can be robustly controlled, and the perfect absorption wavelength can be easily tuned by adjusting the parameters of the compound waveguide grating.     

长周期波导光栅窄带光滤波器特性的模拟

利用两路平行的刻有长周期光栅(LPWG)波导间耦合的理论模型,研究了LPWG波导光滤波器,利用弱耦合实现高耦合效率和窄带滤波的方法,设计了一个窄带光滤波器。仿真结果表明,在1 530~1 560 nm范围,能实现单一的带通、带阻互补滤波输出,3 dB带宽为1 nm,耦合效率高达98%。     

Spatial vector solitons consisting of counterpropagating fields

We present the experimental observation of a spatial vector soliton formed by counterpropagation of coherent optical fields. This is to our knowledge the first observation of a vector soliton in which the induced waveguide (potential) is periodic in the propagation direction. This vector soliton induces a waveguide and a thick grating within the waveguide, which can be used as a tunable optical waveguide filter.