利用光栅闪耀特性优化低通滤波器

为了滤除有效光信号中的光噪声,本文提出了一种利用光栅的闪耀特性将噪声和有效信号之间的夹角角度差放大,再通过光阑得到有效光信号的方法。通过分析和仿真,使用光栅的1、2级闪耀对入射时微小角度差进行放大比较适宜。放大倍数会随着闪耀光栅的周期的减小而增大。负斜入射角度差的放大效果比正斜入射的效果更好。     

Performance of a low-pass filter for far-infrared wavelengths

We describe a low-pass filter that provides high in-band transmittance and excellent rejection at ν > 100 cm(-1). The transmittance of the filter components was measured at liquid-helium temperatures from 10 to 10,000 cm(-1). The total transmittance is >50% for ν < 50 cm(-1) and is calculated to be <10(-9) for ν > 300 cm(-1). The filter was successfully used in a liquid-helium-cooled, rocketborne, far-infrared absolute photometer.     

开关电流高阶椭圆低通滤波器的设计

提出了一种新的开关电流高阶椭圆低通滤波器通用综合方法,该法遵循从RLC滤波器到有源RC滤波器,再到开关电容滤波器,最后到开关电流滤波器的顺序进行设计,方法简单易行.文中给出了5阶开关电流椭圆低通滤波器的设计实例,ASIZ仿真频率响应满足所需的频率技术要求.     

Factorizable state-space model for active optical filter structures with two-port couplers

A state-space model (SSM) is developed for an integrated photonic architecture. This particular architecture is composed of two-port couplers and current-controllable semiconductor optical amplifiers (gains) fabricated on the same substrate. This device architecture leads to a new type of lattice filter structure. The SSM is shown to be factorizable into two matrices, one containing structural parameters of the two-port couplers, which are set during manufacturing, and the other containing the tunable gains. The SSM provides a systematic and practical approach to the analysis of the underlying filter structure, which can be easily extended to multiple-input, multiple-output optical filter structures with or without adjustable gains using two- or four-port couplers. A novel method of using the gains as loss compensation elements in addition to their tunable roles is developed.     

Optically tunable optical filter

We experimentally demonstrate an optically tunable optical filter that uses photorefractive barium titanate. With our filter we implement a spectrum analyzer at 632.8 nm with a resolution of 1.2 nm. We simulate a wavelength-division multiplexing system by separating two semiconductor laser diodes, at 1560 nm and 1578 nm, with the same filter. The filter has a bandwidth of 6.9 nm. We also use the same filter to take 2.5-nm-wide slices out of a 20-nm-wide superluminescent diode centered at 840 nm. As a result, we experimentally demonstrate a phenomenal tuning range from 632.8 to 1578 nm with a single filtering device.     

Synchronization of chaotic oscillators coupled via a low-pass filter in a communication channel

The synchronization of two unidirectionally coupled autooscillators with chaotic dynamics under the action of the filtration properties of a communication channel has been studied. The laws of variation of the amplitude and phase of a driven system are analyzed using the results of numerical simulations and calculations of the phase difference variance and the synchronization error function. The effect of a low-pass filter on the dynamics of a driven system is considered in the context of data transmission using chaos generators.     

Negative permittivity meta-material microstrip binomial low-pass filter with sharper cut-off and reduced size

A binomial low-pass filter provides the flattest pass-band response but slow attenuation transition. A design for improving the roll-off performance based on the negative-epsiv property of complementary split-ring resonators is presented, whilst maintaining the filter pass-band performance. By properly designing and integrating the complementary split-ring resonators with the low-pass filter, not only can the roll-off of the filter be significantly improved, but also the filter size further reduced. The measured results indicate that the proposed structure achieves a flat pass-band with no ripples as well as has a selectivity of 32 dB/GHz. This significantly exceeds the 17 dB/GHz selectivity of the conventional design. Furthermore, the proposed filter has a size smaller by 16%.     

Electrically controlled integrated optical filter

The possibility of electric control over the spectral transfer function of an integrated optical filter comprising a reflection Bragg grating in a photorefractive waveguide is demonstrated for the first time. The filter has a spectral selectivity of 0.15 nm, ensures continuous tuning within ～0.1 nm, and can be electrically switched on and off. The proposed method of control is effective and has good prospects for practical applications.     

Stochastic optical active rheology

We demonstrate a stochastic based method for performing active rheology using optical tweezers. By monitoring the displacement of an embedded particle in response to stochastic optical forces, a rapid estimate of the frequency dependent shear moduli of a sample is achieved in the range of 10(-1)-10(3)?Hz. We utilize the method to probe linear viscoelastic properties of hydrogels at varied cross-linker concentrations. Combined with fluorescence imaging, our method demonstrates non-linear changes of bond strength between T cell receptors and an antigenic peptide due to force-induced cell activation.     

Tunable optical filter for colorimetric applications

A temperature-controlled tunable optical filter for use in the visible range and based on the Christiansen effect, in which the solid particles have been substituted with glass fibers, has been fabricated and tested. The construction of the filter and transmission properties are reported. For an operating temperature of 95°C, the peak wavelength was 509.5 nm, with a peak transmission of 50.8% and a FWHM of 71 nm.     

Holmium-doped optical fiber for filter applications

We consider the properties of holmium-doped fibers in filter applications. We give spectral properties and model filter characteristics. Experiments on filtering of Raman spectra are presented. The fiber filters exhibit strong rejection in the stop band and sharp absorption cutoffs.     

Kinoform filter for an incoherent optical processor

Fabrication and testing of a kinoform filter is described, for use in a real-time incoherent optical processor designed for track recognition in high-energy physics experiments. Composition of the filter as a mosaic of kinoforms with different random diffusers improves the quality of the restoration.     

Photonic crystal-based RGB primary colour optical filter

Abstract

We have presented an RGB optical filter, based on photonic crystal (PhC) waveguides, with the hexagonal arrangement of GaP rods in air. It filters out the three primary colours of the visible range, red (R, λ = 648 nm), green (G, λ = 540 nm) and blue (B, λ = 470 nm). The plane wave expansion method is applied for estimating the dispersion curves and finite element method is utilized in examining the propagation characteristics of the designed PhC-based optical filter. Transmittance, extinction ratio and tolerance analysis have further been calculated to confirm the performance of the proposed optical filter to work in the visible range of optical spectrum and filter out the three primary colours (red, green, blue) along different output ports.     

Smoothing and differentiating load–displacement data using a low-pass filter for improved crack opening load estimates

The presence of even small amounts of noise in experimental data significantly influences numerically determined derivatives. Dynamic programming is used to construct a low-pass filter enabling the smoothing and differentiation of noisy data. The filter is used to smooth and differentiate load–displacement data for a propagating fatigue crack to obtain smoothed compliance as a function of applied load. The smoothed compliance is shown to allow for improved subsequent estimates of the crack opening load.     

Realization of an optical communication tunable filter using a diffraction-based optical system

Optical bandpass tunable filters are key elements for dense WDM optical communication systems. Recently, a realization of optical linear transformation using a spatial diffraction optical system was presented and theoretically analyzed [J. Opt. Soc. Am. A21, 732 (2004)]. We present an optical bandpass tunable filter based on this optical system and a spatial light modulator. The mathematical analysis and additional computer simulations for testing the filter's basic parameters using the Fresnel diffraction theory are presented. Some newly obtained laboratory experimental results of the device in the optical visible spectrum will be shown.