Performance Of Optical Filters Research Articles

The effect of interface roughness on spectral efficiency of thermophotovoltaics with multi-layer filters

Spectral efficiency is an important parameter to characterize the optical performance of optical filters in thermophotovoltaic systems. The multilayer filters are normally designed by assuming ideally flat interfaces, but realistic structures have a degree of interface roughness present. This work explores the influence of interface roughness on the spectral efficiency, with examples including structures with different materials or number of layers.

Femtosecond laser line-by-line inscription of apodized fiber Bragg gratings.

The reflection spectra of conventional fiber Bragg gratings (FBGs) with uniform index modulation profiles typically have strong sidelobes, which hamper the performance of FBG-based optical filters, fiber lasers, and sensors. Here, we propose and demonstrate a femtosecond laser line-by-line (LbL) scanning technique for fabricating apodized FBGs with suppressed sidelobes. This approach can flexibly achieve various apodized modulation profiles via precise control over the length and/or transverse position of each laser-inscribed index modification track. We theoretically and experimentally studied the influences of the apodization function on the side-mode suppression ratio (SMSR) in the fabricated apodized FBG, and the results show that a maximum SMSR of 20.6 dB was achieved in a Gaussian-apodized FBG. Subsequently, we used this method to fabricate various apodized FBGs, and the SMSRs in these FBGs were reduced effectively. Specifically, a dense-wavelength-division-multiplexed Gaussian-apodized FBG array with a wavelength interval of 1.50 nm was successfully fabricated, and the SMSR in such an array is 14 dB. Moreover, a Gaussian-apodized phase-shifted FBG and chirped FBG were also demonstrated with a high SMSR of 14 and 16 dB, respectively. Therefore, such an apodization method based on a modified femtosecond laser LbL scanning technique is an effective and flexible way to fabricate various FBGs with high SMSRs, which is promising to improve the performance of optical filters, fiber lasers, and sensors.

Performance analysis of waveguide-mode resonant optical filters with stochastic design parameters.

The performance of optical filters with resonant waveguide gratings is investigated numerically in a stochastic context, assuming random fluctuations of various design variables. Specifically, we derive stochastic models based on polynomial chaos expansions, whose involved coefficients are obtained by computing spectral projections via sparse-grid quadrature. The latter exploits purely deterministic results from a rigorous coupled-wave analysis solver and requires less simulation data than standard Monte Carlo (MC) techniques. The statistical moments of the filter's spectral response are calculated reliably, as the comparison against reference results from MC analysis verifies, and the extraction of the Sobol indices reveals the structure's sensitivity with respect to specific design parameters. Moreover, the present analysis clearly points out that neglecting even small geometric variations in the filter design may produce misleading conclusions regarding the corresponding performance, with undesirable consequences in real-life applications.

System Robust Optimization of Ring Resonator-Based Optical Filters

Fabrication variations can have a detrimental effect on the performance of optical filters based on ring resonators. However, by using robust optimization these effects can be minimized and device yield can be significantly improved. This paper presents an efficient robust optimization technique for designing manufacturable optical filters based on serial ring resonators. The serial ring resonator is treated as a system which has computationally expensive (directional coupler section) and cheap components (ring section). Cheap mathematical models are constructed of the directional coupler sections in the resonators. The approximate system response based on the cheap model is then robustly optimized. The robust bandpass filter performance is compared against designs that do not take uncertainties into account. The optimality of the robust solutions is confirmed by simulating it on the expensive physical model as a post-processing step. Results indicate that the employed approach can provide an efficient means for robust optimization of ring resonator-based optical filters.

Modeling and optimum design band pass filter for mid IR region

In this study, we design narrow band pass filter for window (3_5) ?m dependent on the needle optimization method , and a comparison with global designs published -Also, the effect of change parameter design on the optical performance of filter was studded and being able to overcome the difficulties of the design.In this study, the adoption of homogeneous optical properties materials as thin film depositing on a substrate of germanium at wavelength design (? = 4 ?m). For design this kind of filters we used advanced computer program (Matlab )to build a model design dependent both matrix characteristic and Needle technique. In this paper we refer to the type of Mert function , which is used for correct optical performance access to the target in very short time.

Modeling and optimum design band pass filter for mid IR region

In this study, we design narrow band pass filter for window (3_5) ?m dependent on the needle optimization method , and a comparison with global designs published -Also, the effect of change parameter design on the optical performance of filter was studded and being able to overcome the difficulties of the design.In this study, the adoption of homogeneous optical properties materials as thin film depositing on a substrate of germanium at wavelength design (? = 4 ?m). For design this kind of filters we used advanced computer program (Matlab )to build a model design dependent both matrix characteristic and Needle technique. In this paper we refer to the type of Mert function , which is used for correct optical performance access to the target in very short time.

계층적 분석 과정을 이용한 다중 속성의 금융통장 인식용 광학 필터의 최적 설계

Department of Industrial Engineering, Seoul National University of Science and Technology, Seoul 139-743, Korea(Received April 28, 2014; Revised May 16, 2014; Accepted May 20, 2014)Abstract: Five factors are identified, which affect the performance of optical filter: 1) type of optical glass, 2) existence of Fe, 3) photo pic coating type, 4) coating form, and 5) coating thickness. If we consider all the levels of five factors, there are 360 possible candidates. We determined five evaluation criteria, which can be used to evaluate possible candidates. For the performance measures we selected white-state avearge voltage, black-state average voltage, and black-state error rate. And we added economic criterion and quality and maintenance criterion. Through the two-step statistical analysis of white-state avearge voltage, black-state average voltage, and black-state error rates, we selected final four candidates. Based on the five criteria we finally determined optimal optical filter using AHP.Keywords: Delphi, AHP (analytic hierarchy process), Black voltage, White voltage, HEA (high efficiency), VLR (value low reflector), VLRW (value low reflector wide)

Enhanced Incidence Angle Based Spectrum Tuning by Using One-Dimensional Ternary Photonic Band Gap Structures

This paper demonstrates a novel way to enhance the incident angle based output spectrum tuning in one-dimensional (1D) photonic band gap (PBG) material by using a ternary periodic structure (i.e., three material layers constituting a period of lattice). The incidence angle sensitive wavelength band shift of binary periodic structure was significantly enhanced when the structure was modified to ternary periodic structure by sandwiching a thin new material layer between every two layers, constituting a period of lattice. When the thickness of sandwiched layer was increased, further enhancement in tunable wavelength band shift was observed. These 1D ternary PBG structures can be substituted in place of 1D binary PBG structures for enhancing the tuning performance of optical filters.

Dispersion implementation in optical filter design by the Fourier transform method using correction factors

The Fourier transform method to design graded-index optical filters, that relates the desired reflection spectrum and the index profile through the use of a Q function, has two important drawbacks: (1) It relies on approximate Q functions, and (2) it does not account for the dispersion of the index of refraction. The former is usually addressed by an iterative correction process. We propose to address the latter by scaling the wavelength in the Fourier transform by the optical thickness of the filter and to multiply the Q function by a wavelength-dependent correction factor. We demonstrate the high effectiveness of this approach by the performance of optical filters designed with such correction factors using the optical properties of SiO2/TiO2 mixtures.

A generalized approach for modeling and analysis of ring-resonator performance as optical filter

A generalized approach for determination of transmittance (transfer function) in Z-domain of optical waveguide based ring resonator is introduced in the present article. Delay line signal processing technique, developed by a few previous researchers, is used to develop the signal flow graph of different ring resonator architectures, and a rule, already established by a previous investigator, is implemented to determine its overall transmittance. Frequency responses of three different ring resonator architectures are presented in the article. The parameters describing the performance of optical filter can be directly estimated from the frequency response plot. The simulated results of single and double ring architectures are compared with those of previously published results. A waveguide based triple ring resonator architecture is proposed, and its frequency response analysis is carried out in the article.

Evaluation method of optical filters used in fluorescence detectors

A calculation method for evaluating UV optical filters, suitable for fluorescence detectors (FD), such as the one from the Auger Project and other similar cosmic ray observatory setups, is presented. We have considered the adopted geometry of a telescope based on a spherical mirror and a camera consisting of a photomultiplier pixel array. In the calculations, an angular weighting factor is introduced, which affects the results of the optical filter performance. Two optical filters, of the interference and absorption type, are evaluated using this method. Experimental measurements of the spectral transmittance of the filters for various angles of incidence are made by a double beam spectrophotometer. To calculate an overall performance, the most dominant spectral lines of the atmospheric fluorescence are used, modified by the atmospheric transmission coefficients. This performance is determined by the detection efficiency of the pixel detector (photomultiplier) with the optical filters used.

A thermally tunable, silicon-based optical filter

Abstract A novel silicon MEMS-based concept for tunable optical filters used in wavelength-division multiplexing (WDM) systems is presented. Such a filter is essential for monitoring and reconfiguring optical networks. The device is based on a Fabry–Perot interferometer employing a silicon cavity and silicon-based dielectric Bragg mirrors and is fabricated as a free-standing membrane. Wavelength tuning is achieved through thermal modulation of the resonator’s optical thickness. Measurement of optical filter performance and tunability as well as numerical simulation results of its steady-state and transient thermal behavior are presented.

InAlGaAs bulk micromachined tunable Fabry–Pérot filter for dense WDM systems

In this work we report on micromechanically tunable Fabry–Pérot filter concepts for wavelength division multiplexing (WDM) systems. The optical resonator is designed for a cavity length around 30 μm in order to increase the filter selectivity while relaxing the demands on the required mirror reflectance. The introduction of micromechanical actuators, utilizing electrothermal and electrostatic principles, allows wavelength tuning of the filter over a range of more than 40 nm in the 1.55 μm wavelength regime. The movable Bragg mirror, designed as suspended membrane and fabricated with an InP bulk-micromachining technology, consists of a molecular beam epitaxy-grown InAlGaAs quarter-wavelength multilayer stack. The influence of micromechanical actuation and the effect of intrinsic mechanical stress on the mirror deformation has been investigated systematically to optimize the optical filter performance. Filter losses induced by the light absorption within the epitaxial Bragg mirror have been minimized using a highly doped InGaAs/InAlAs composition. Furthermore, low-loss Fabry–Pérot filters have been fabricated using InAlGaAs/InAlAs Bragg mirrors. The measured full-width at half-maximum (FWHM) is 0.24 nm and a filter insertion loss of 2.8 dB has been observed. The FWHM is kept below 0.35 nm over an entire tuning range of 40 nm for an actuation power of 1.3 mW. The bulk-micromachining technology presented here is open for the future development of WDM components, e.g. tunable receivers or laser diodes.

Effects of random phase and amplitude errors in optical fiber Bragg gratings

This paper studies the influence of random phase and amplitude fabrication errors on the performance of optical filters based on fiber Bragg gratings (FBG's). In particular, we analyze two effects of particular importance for optical communications: the excess crosstalk induced in apodized gratings commonly used in wavelength-division-multiplexing (WDM) systems, and the time-delay fluctuations that appear in chirped gratings employed to compensate the fiber dispersion. A statistical model is presented to explain these effects in terms of the coherence length of the grating fabrication procedure.

On the performance of optical filters for the XMM focal plane CCD-camera EPIC

Optical filters have been developed for the X-ray astronomy project XMM (X-ray Multi Mirror Mission) [1] of ESA, where specific CCDs will serve as focal plane cameras on board the observatory. These detectors are sensitive from the X-ray to the NIR (near infrared) spectral region. For observations in X-ray astronomy an optical filter must be placed in front of the CCD, suppressing visible and UV (ultraviolet) radiation of stars by more than 6 orders of magnitude while being highly transparent at photon energies above 100 eV. The flight model filter is designed to have an effective area of 73 mm diameter without making use of a supporting grid. Efforts have been made to utilize plastic foils to tailor filters meeting these specific requirements. It was found, that a typical filter could be composed, e.g., of a polypropylene foil of 20 μg/cm 2 thickness serving as a carrier, coated with metallic films of Al or Al and Sn of about 20–25 μg/cm 2 thickness. Other possible carriers are polycarbonate (Lexan, Macrolon) and poly-para-xylylene (Parylene N) films of similar thicknesses. The preparation and characterization of these three types of carrier foils as well as of two sample filters is described, including mechanical tests as well as optical transmission measurements in the photon energy range from 1 eV to 2 keV.

THIN-FILM MULTILAYER OPTICAL FILTERS; SENSIIVITY ANALYSIS

Thin-film multilayer optical filters play an important role in many aeronautic applications. The selection of a specific wavelength signal is very important for aircraft communication, guidance and control. Aerial imaging and reconnaissance require optical filters to reject background radiation. The performance of optical filters is affected by many parameters: The materials' indices of refraction, the layers' thicknesses and the anges of incidence are the most important parameters. During production, these parameters have tolerances within which they can be produced. Here, a sensitivity study is done to show the effect of these parameters on the filter performance. The study covered single-layer, two-layer and three-layer filters. For all the investigated filters neither a variation of up to 5% of the indices of refraction and the thickness of layers nor angles of incidence up to 100 showed considerable effect on both the peak transmission and the shape of transmission curve. The sensitivity analysis helps greatly in studying the mutual relationship between the filter performance and the tolerance of its parameters.