Add/drop channel filter based on two parallel long-period fiber gratings coupler

A wavelength-selective coupler constructed with two parallel long-period fiber gratings (LPFGs) was investigated thoroughly. Both the numerical and experimental results verified that the filter response could be improved by adjusting the UV refractive modulation of the gratings and by controlling the external surrounding. And an add/drop channel filter with high efficiency and good spectral characteristic was achieved even though the claddings of the two gratings were not processed. This feature is very favorable to simplify the fabrication process.     

A compact in-plane photonic crystal channel drop filter

This paper presents a novel in-plane photonic crystal channel drop filter.The device is composed of a resonant cavity sandwiched by two parallel waveguides.The cavity has two resonant modes with opposite symmetries.Tuning these two modes into degeneracy causes destructive interference in bus waveguide,which results in high forward drop efficiency at the resonant wavelength.From the result of numerical analysis by using two-dimensional finite-difference time-domain method,the channel drop filter has a drop efficiency of 96% and a Q value of over 3000,which can be used in dense wavelength division multiplexing systems.     

非对称熔锥法制作光纤光栅辅助耦合器型上下话路滤波器

通过在失配光纤消逝场间的耦合作用中引入光栅调制扰动效应，推导出用于解释光栅辅助耦合器响应特征的耦合模方程，在此基础上全面分析了两光纤间的失配度对上下话路滤波性能的影响.采用非对称熔融预拉锥工艺，调整光纤的结构参数，制成了性能良好的光栅辅助耦合器，实验测试结果与理论计算符合得很好. 关键词： 光纤光栅 光纤耦合器 上下话路滤波器 熔融预拉锥     

Add/drop applications in fiber ring networks based on a reconfigurable optical add/drop multiplexer in a re-circulating loop

A periodic add/drop system in a fiber ring network was investigated using a reconfigurable optical add/drop multiplexer (ROADM) in a re-circulating fiber loop. After seven cascaded add/drop nodes at every 150 km along the transmission, at bit error ratio (BER) equals to 10⁻⁹ and data rate of 10 Gbps, we observed a 2.5 dB power penalty for the passing through channels with 1050 km transmission distance, and 0.3 dB sensitivity penalty variation for the periodic add/drop channels at every 150 km, respectively.     

Holographic reflection gratings in azobenzene polymers

Writing and reading of reflection gratings in films of an azo side-group polymer are reported. The gratings were induced holographically by use of an argon-ion laser at 488 nm. The measured diffraction efficiency was in the range 2-10%. To estimate the scattering of the reflected light within the material, we further characterized the gratings by calculating a characteristic transmission. A distinct minimum for this transmission was observed, which was redshifted farther from the writing wavelength for gratings written in 50-microm polymer samples.     

A channel drop filter in hetero-woodpile-structure

By finite difference time domain method, a channel drop filter with four-port is designed, analyzed, and theoretically simulated in the hetero-woodpile-structure. Hetero-woodpile-structure includes three parts namely, along the propagation direction, the constant lattice in the core woodpile is different from two cladding woodpiles. This channel drop filter is comprised of two straight waveguides separated by an air-cavity in the same layer. Through simulations, we found that adjustment of the resonant-mode in heterostructure can be achieved in various ways, such as only changing the lattice constants, or changing both lattice constants, and the cavity size. The results also show that this structure can realize the energy transfer between bus and drop waveguides.     

A new proposal for PCRR-based channel drop filter using elliptical rings

In this paper using elliptical resonant ring we proposed a channel drop filter based on photonic crystal structures suitable for optical communication applications. The drop efficiency and the quality factor of our proposed filter is 100% and 647. We also investigated the optical properties of different configurations of the proposed photonic crystal ring resonator such as vertical ring, dual ring and triple ring structures. According to the results different configurations show different optical properties, so for vertical, double and triple ring configurations the quality factor will be 387, 865 and 1559, respectively.     

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.     

Waveguide structure optimization of arrayed waveguide gratings concatenation in cascaded optical add/drop multiplexers

The dimensions of input waveguide and output waveguide of arrayed waveguide gratings (AWGs) determine the crosstalk, insertion loss and 1-dB bandwidth. In cascaded optical add/drop multiplexers (OADMs), the value of these parameters will largely affect the power penalty of system. The power penalty of cascaded OADMs is calculated with different waveguide dimensions of AWGs in this paper. Considering of wavelength misalignment, an optimization design of AWGs is obtained.     

Channel drop filter using photonic crystal ring resonators for CWDM communication systems

In this paper, a new optical channel drop filter (CDF) using photonic crystal ring resonators (PCRRs) is presented. Using the two-dimensional (2D) finite-difference time-domain (FDTD) method in triangular lattice photonic crystal (PC) silicon rods, 100% forward dropping efficiency and a quality factor of more than 1000 can be achieved in third communication window while the resonant wavelength is 1550 nm. Through this novel (CDF), a multi-CDF operation with 100% drop efficiencies across all channels can be obtained. The proposed device could be used in future coarse wavelength division multiplexing (CWDM) communication systems.     

Wavelength-division multiplexing isolation fiber filter and light source using cascaded long-period fiber gratings

The author has successfully demonstrated a novel all-fiber wavelength-division multiplexing (WDM) isolation filter with more than 20 equally spaced loss peaks within a 60-nm band and a WDM light source with an output of 21 equally spaced wavelengths within 30% amplitude variation.     

Reconfigurable WDM add/drop multiplexer based on optical switches and fibre Bragg gratings

A reconfigurable wavelength-division-multiplexing (WDM) add/drop multiplexer (WADM) is constructed using optical switches (OSWS) and fibre Bragg gratings (FBGs). Selected one or two channel(s) can be added/dropped at the same multiplexer by properly controlling the optical switch pair and fibre Bragg grating arrangement. Afour-channel system is experimentally demonstrated for a data rate of 2.5 Gb s–1 and a single-mode fibre (SMF) distance of 100km. A negligible maximum power penalty of only 0.3dB is observed when compared with back-to-back transmission.     

Technique for characterization of dimensional changes in slanted holographic gratings by monitoring the angular selectivity profile

A method has been developed for retrieving the complete angular selectivity profile of transmission holographic gratings in one step. The method is applied to study in real time the shrinkage and changes in the effective optical thickness of a slanted holographic grating recorded in an acrylamide-based photopolymer. It can form the basis of a holographic sensor of analytes that cause a thickness change in the holographic medium. It can also be useful for the study and optimization of holographic recording materials and for quality control during production of holographic optical elements.     

Modified theory of photoinduced molecular polar alignment in azo polymers

An improvement on the simplified theory of all-optical poling [Chem. Phys. Lett. 286, 415 (1998)] is proposed. In this improvement the influence of the cis isomer is taken into account in the process of photoinduced molecular polar alignment. An analytical expression for the induced polar order in the steady-state regime is derived. This expression shows that, although the contribution to the photoinduced second-order susceptibility from the cis state itself can be neglected, the population of the cis state plays an important role. This result suggests the possibility that one can improve the induced polar order by increasing the poling temperature, so that thermal-assisted optical poling can be explained.     

Fabrication of tapers with Gaussian refractive-index profile in azo polymers

We have fabricated a refractive-index-tapered waveguide by exposing an azo polymer film to a 532-nm wavelength laser beam focused to about 60-μm spot size at the film with no surface deformation. The converging ability of the taper (ability to increase intensity along the taper) was measured to be 5 db/cm while the loss was 0.39 db/cm. According to the data obtained, the power density increases along the taper while loss is nearly constant along the tapered and non-tapered segments.     

Surface relief gratings in photoaddressable polymers generated by cw holography

Surface relief gratings (SRGs) are a widely observed phenomenon in holographic experiments with photoaddressable polymers. This article proposes a model which is able to explain the observed effects in cw experiments. It is based on forces in an electrical field which are caused by the inhomogeneous spatial distribution of the refractive index and the permittivity in the illuminated sample. Received: 11 September 2000 / Revised version: 5 December 2000 / Published online: 21 February 2001     

Diffraction efficiency increase by corona discharge in photoinduced surface-relief gratings on an azo polymer film

The diffraction efficiency of a surface-relief grating (SRG) was dramatically increased by corona discharge. We fabricated this SRG by applying surface modulation to azo polymer films, using laser interference fringes. The electric charge was deposited upon the SRG by a corona discharge in an oven. The first-order diffraction efficiency measured before and after corona discharge above the glass-transition temperature increased from ~2% to ~40% in a SRG written with a circularly polarized beam. The relief depth of the SRG as measured with an atomic-force microscope also increased, from ~130 nm to ~450 nm. The increase in diffraction efficiency was independent of the writing polarization.     

Improving the performance of a photonic crystal ring-resonator-based channel drop filter using particle swarm optimization method

The optical channel drop filters (CDFs) based on photonic crystals (PCs) are believed to be the essential components for compact photonic integrated circuits and WDM systems. One of the promising designs for a PC-CDF is based on the photonic crystal ring resonators (PCRRs). In this study, different parameters of a PCRR based CDF is optimized by using the particle swarm optimization (PSO) method in conjunction with the numerical method of two-dimensional (2D) finite-difference time-domain (FDTD) in a square lattice dielectric-rod 2D-PC. Hence a PC-CDF with ideal drop efficiency, large free spectral range (FSR) and acceptable quality factor will be proposed.     

Self-adaptive spatial filtering by use of azo chromophores doped in low glass-transition-temperature polymers

We report on self-adaptive spatial filtering by combination of the self-adaptive polarization-rotation property of Disperse Red1-doped polymers with low glass-transition-temperature and Fourier-transform operation. Our system can be operated with only an action beam with object information and without a probe beam for image readout. Edge enhancement by the action beam-probe beam is demonstrated as an example of the system's application to spatial filtering.