Minimization of the shadow patterns produced by periodic mesh grids in extreme ultraviolet telescopes

Thin metallic films are used as passband filters in space telescopes operating in the extreme ultraviolet (EUV). Because of their thinness, typically 100 to 200 nm, they are very sensitive to static pressure differentials and to mechanic and acoustic vibrations. Therefore, they are difficult to manage in all phases of a space program, from manufacturing to vacuum testing to launch. A common solution to this problem is to reinforce them with fine mesh grids with pitches ranging from a few hundred micrometers to a few millimeters. Depending on their location in the optical path, the main effect of these periodic grids is either to diffract light or to cast penumbral shadows on the focal plane. In this paper, we analyze the formation of the shadow modulation patterns and derive design rules to minimize their amplitude. The minimization principle is illustrated by an application to a solar EUV telescope.     

Coupled resonator filter with single-layer acoustic coupler

We discuss the operation of novel coupled-resonator filters with single-layer acoustic couplers. Our analysis employs the physical Mason model for acoustic resonators. Their simpler fabrication process is counterbalanced by the high acoustic attenuation of suitable coupler materials. At high levels of attenuation, both the phase and the acoustic impedance must be treated as complex quantities to accurately predict the filter insertion loss. We demonstrate that the typically poor near-band rejection of coupled resonator filters can be improved at the die level by connecting a small capacitance between the input and output of the filter to produce a pair of tunable transmission minima. We make use of these theoretical findings to fabricate coupled resonators filters operating at 2.45 GHz.     

Automated Synthesis of Wideband Bandpass Filters Based on Slow-wave EBG Structures

This paper is focused on the automated synthesis of wideband bandpass filters operating at microwave frequencies and based on electromagnetic bandgap (EBG) structures. The classical counterpart of such filter consists of a combination of transmission line sections and shunt-connected grounded stubs placed at equidistant positions. By replacing the transmission line sections with capacitively-loaded lines (a kind of EBG-based lines) exhibiting the same phase shift at the lower cutoff frequency and the same characteristic (actually Bloch) impedance, filter size is reduced and the spurious pass bands can be efficiently suppressed. In practice, the loading capacitances are implemented by means of patches, in order to achieve a fully planar filter implementation. The presence of the patches reduces the effective phase velocity of the capacitively-loaded lines, thus providing a slow-wave effect useful for filter miniaturization. Moreover, due to periodicity, such EBG-based lines exhibit wide stop bands, which are used for spurious suppression. Even though such EBG-based filters were previously reported by some of the authors, a systematic synthesis method was not applied for filter design. In this paper, the main aim is to demonstrate the potential of aggressive space mapping (ASM) for that purpose, and it will be shown that such filters can be automatically synthesized.     

Variable narrow-band transmission filters for spectrometry from space. 2. Fabrication process

The optical components described here are variable narrow-band transmission filters, where the transmittance peak varies with the position along the surface of the filter itself. They allow the construction of ultracompact and low-weight spectrometers for space applications. The theoretical behavior of graded filters has been already investigated by the authors, for imaging spectrometry of the Earth surface. The application of graded filters to miniaturized instruments for planetary missions (Mercury) is considered. Experimental results on the fabrication of small-dimension variable transmission filters operating over a wide spectrum, from visible to near infrared, are reported.     

Estimation of safe exposure time from an ophthalmic operating microscope with regard to ultraviolet radiation and blue-light hazards to the eye

Hazards from the optical radiation of an operating microscope that cause damage at the corneal, lenticular, and retinal levels were investigated; we considered, in particular, ultraviolet radiation (UVR) and blue light. The spectral irradiance from a Zeiss operation microscope OPMI VISU 200 was measured in the corneal plane between 300 and 1100 nm. Effective irradiance and radiance were calculated with relative spectral effectiveness data from the American Conference for Governmental and Industrial Hygienists. Safe exposure time to avoid UVR injury to the lens and cornea was found to be 2 h without a filter, 4 h with a UVR filter, 200 a yellow filter, and 400 h with a filter combination. Safe exposure time to avoid retinal photochemical injury was found to be 3 min without a filter and with a UVR filter, 10 min with a yellow filter, and 49 min with a filter combination. The effective radiance limit for retinal thermal injury was not exceeded. The hazard due to the UVR component from the operating microscope is not critical, and operation time can be safely prolonged with the use of appropriate filters. The retinal photochemical hazard appears critical without appropriate filters, permitting only some minutes of safe exposure time. The calculated safe exposure times are for worst-case conditions and maximal light output and include a safety factor.     

Holographic edge-illuminated polymer Bragg gratings for dense wavelength division optical filters at 1550 nm

We discuss the use of holographic photopolymer materials for use as dense wavelength division multiplexing filters in the C-band of the optical communication spectrum. An edge-illuminated hologram configuration is described that effectively extends the grating length to achieve narrow band filters operating near 1550 nm in photopolymers that are 100-200-microm thick. This configuration enables the formation of apodized and cascaded filter systems. Rouard's method is used to examine the properties of both apodization and cascaded gratings and indicates the potential for narrow spectral bandwidths (< 0.2 nm) and high side-lobe suppression (<-- 30 dB). Initial experimental results with a commercially available photopolymer are provided that verify narrowband spectral-transmittance properties (< 0.6 nm) and the ability to apodize the index profile. The primary limitation of the design is the absorption of existing photopolymer materials. Optimizing the polymer chemistry for filter design at 1550 nm may solve this problem.     

Fully automated high-performance signal-to-noise ratio enhancement based on an iterative three-point zero-order Savitzky-Golay filter

The automated processing of data from high-throughput and real-time collection procedures is becoming a pressing problem. Currently the focus is shifting to automated smoothing techniques where, unlike background subtraction techniques, very few methods exist. We have developed a filter based on the widely used and conceptually simple moving average method or zero-order Savitzky-Golay filter and its iterative relative, the Kolmogorov-Zurbenko filter. A crucial difference, however, between these filters and our implementation is that our fully automated smoothing filter requires no parameter specification or parameter optimization. Results are comparable to, or better than, Savitzky-Golay filters with optimized parameters and superior to the automated iterative median filter. Our approach, because it is based on the highly familiar moving average concept, is intuitive, fast, and straightforward to implement and should therefore be of immediate and considerable practical use in a wide variety of spectroscopy applications.     

Transmission features of frequency-selective components in the far infrared determined by terahertz time-domain spectroscopy

Transmission and phase-shift characteristics of dichroic high-pass filters with cutoff frequencies as high as 1.11 THz and of a cross-shaped grid bandpass filter with a resonance frequency of 280 GHz were measured with an electro-optic sampling terahertz time-domain spectrometer operating between 0.1 and 2 THz. Good agreement with transmission theories is found. We also compare the transmission performance of cascaded dichroic filters with that of cross-shaped grid bandpass filters. Both types of bandpass filter permit frequency-selective ultrafast experiments in the far-infrared spectral region. In the millimeter and the submillimeter wavelength regions, which are difficult to access by conventional means, knowledge of the frequency response of frequency-selective components is important for applications in frequency mixing, multiplying, and multiplexing in quasi-optical systems.     

Plasmonic Color Filters for CMOS Image Sensor Applications

We report on the optical properties of plasmonic hole arrays as they apply to requirements for plasmonic color filters designed for state-of-the-art Si CMOS image sensors. The hole arrays are composed of hexagonally packed subwavelength sized holes on a 150 nm Al film designed to operate at the primary colors of red, green, and blue. Hole array plasmonic filters show peak transmission in the 40-50% range for large (>5 × 5 μm(2)) size filters and maintain their filtering function for pixel sizes as small as ～1 × 1 μm(2), albeit at a cost in transmission efficiency. Hole array filters are found to robust with respect to spatial crosstalk between pixel within our detection limit and preserve their filtering function in arrays containing random defects. Analysis of hole array filter transmittance and crosstalk suggests that nearest neighbor hole-hole interactions rather than long-range interactions play the dominant role in the transmission properties of plasmonic hole array filters. We verify this via a simple nearest neighbor model that correctly predicts the hole array transmission efficiency as a function of the number of holes.     

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.     

Ultra-miniature coupled resonator filter with single-layer acoustic coupler

Coupled resonator filters designed using a singlelayer coupler require coupling materials with an acoustic impedance less than 5.0 MRayl. Carbon-doped oxide, with an acoustic impedance of 4.8 MRayl and an acoustic attenuation of 200 to 600 dB/cm at 1 GHz, can be used as a single-layer coupler to produce a competitive 2-stage coupled resonator filter for cellular handset applications in the gigahertz frequency range. The electrical response of our filter is superior to that of coupled resonator filters using a traditional acoustic mirror as the coupling element. We present an ultra-miniature 0.58 mm x 0.38 mm coupled resonator filter operating at a frequency of 2.15 GHz.     

Design of all-optical tunable filter based on two-dimensional photonic crystals for WDM (wave division multiplexing) applications

In this paper, all-optical tunable filters based on two-dimensional photonic crystals with very small dimensions for optical telecommunication of WDM technology are designed and simulated. The structure is made of air holes in a dielectric background. The tuning is done by changing resonant defect angle. The channels obtained for this structure will be set in wavelength range of 1550 nm. Created channels are at wavelengths of 1550, 1551, 1552, and 1565 (16 channels); the distance between adjacent channels is 1 nm. Design and simulation of this filter is done by RSOFT software. Quality factor, transmission efficiency, and band gap shows that filter performance is very good.     

Optical filters consisting of metallic waveguide arrays

We demonstrate high-pass optical filters with cutoffs in the 0.3-10-micron spectral region. These filters consist of uniform arrays of hollow metallic waveguides, obtained by coating wafers of the previously developed channel-glass (CG) materials with a thin metal film. In these filters the channel diameter controls the cutoff frequency, the channel length controls the sharpness of the cutoff, and the channel density determines the transmission efficiency at cutoff. All of these parameters can be controlled in the CG starting material. The properties of the metal coatings that influence the filter properties are also discussed. Cutoff wavelengths near 300 nm have been achieved to date by using CG materials with submicrometer channel diameters. At all channel diameters, the transmission spectra include a peak just above the cutoff wavelength, where the transmission value can exceed that expected on the basis of the geometrical open area of the CG structure.     

Identical-dual-bandpass sampled fiber Bragg grating and its application to ultranarrow filters

We have theoretically proposed and experimentally demonstrated a new kind of ultranarrow identical-dual-bandpass sampled fiber Bragg gratings (SFBGs) with a pi phase shift technique. The spacing of two bandpasses of the proposed grating can be flexibly adjusted by changing the sampled period, and any desired spacing can be achieved in principle. An experimental example shows that the transmission peaks of two narrow transmission-band are near 1549.1 and 1550.1 nm. Based on the proposed SFBG, an ultranarrow identical-dual-channel filter is designed. Two channels of the proposed filter have an equal bandwidth, an even strength, and the same group delay. The bandwidth of each channel of our filter is as small as 1 pm and up to 10(-3) pm (corresponding to approximately 0.1 MHz), which is less than the bandwidth of the conventional SFBG filters by a factor of 10(2)-10(4). The proposed grating and filter can find potential applications with slow light and dual-wavelength single-longitudinal-mode fiber lasers.     

Frequency characteristics of feeler profilometers

Conclusions Simple RC filters are considerably inferior in their characteristics to filters with amplifiers, but they are much simpler than the latter type. In view of the fact that an RC filter with an amplifier and characteristic similar to the one shown in Fig. 3 (curvef) is complicated and equal in size to the whole amplifying device of a portable workshop probing instrument, it is advisable in standardizing the frequency characteristics of filters to adopt, for portable instruments with an error exceeding ±15%, simple two-stage RC filters with a coefficient y=3–4; and for precision instruments, with an error smaller than ±15%, filters with amplifiers. Moreover, the slope of the characteristic of these filters at frequencies below the critical should be the same as for RC filters with two similar sections (12 db per octave).A further, more detailed, study of the frequency characteristics of complex filters with amplifiers is required. This problem should be solved by developing a filter with an amplifier which is as simple and reliable as possible.     

18.2nm正入射显微成像系统滤光片的研究

18．2nm正人射显微成像系统用多层膜可极大地提高18．2nm的反射率，但它对紫外、可见和红外光也产生很高的反射。显微成像系统用的激光等离子体光源会在红外到敦X射线产生大量的辐射，18．2nm正入射显微系统用的胶片对所有光谱都十分敏感。因此，182nm正人射显微成像系统需要用滤光片滤除不需要的光辐射并对18．2nm的软X射线有较大的透射比，这样才能获得18．2nm的软X射线像。本文讨论了18．2nm正入射显微成像系统用滤光片的设计、制作及其特性。为了去除滤光片膜中的应力，用交替蒸镀Al和C多层膜的方法来制备法光片，铝和碳膜是用磁控溅射法制备的。针孔透过率和成像实验表明，所制备的滤光片满足了18．2nm正入射显微成像系统对滤光片的要求，并且为进一步制备其他薄膜滤光片打下了基础。     

Ultrahigh-efficiency, very narrowpassband, tunable optical filter

Recently developed technologies have been uniquely integrated to produce optical filters with unprecedented performance. The precise design and fabrication of narrow-passband and high-efficiency optical filters with a central frequency of 532 nm are reported. Measurements with these filters demonstrate a performance that accurately mirrors the design specification, with one filter having a passband of 70 pm and an efficiency greater than 90% and the second filter having a passband of 7 pm and an efficiency greater than 80%.     

Synthesis of the low-temperature co-fired ceramic bandpass filters and diplexer with transmission zeros

The multilayered microwave filters are developed with the assistance of two transmission zeros. Besides a coupled line connected to one capacitor, another capacitor cross coupled between the source and load ports is utilised for the proposed filters. By properly adjusting the coupling coefficients between the coupled line and two capacitors, two transmission zeros would appear on the lower side, the higher side or on both sides of the passband skirt. Thus, the characteristics can be employed for diplexers or dual-band filters to make dual-mode portable telephones. Moreover, to miniaturise the circuit sizes and improve their performances, multilayered structure and the low-temperature co-fired ceramic technology are adopted for filter fabrication. The theorem of filter synthesis and procedures of filter design are also presented. Finally, the proposed structure is validated by an agreement between measured results of fabricated filters and the electromagnetic simulation.     

Resonant metal-mesh bandpass filters for the far infrared

The spectral performance of freestanding resonant metal-mesh bandpass filters operating with center frequencies ranging from 585 GHz to 2.1 THz is presented. These filters are made up of a 12-μm-thick copper film with an array of cross-shaped apertures that fill a circular area with a 50-mm diameter. The filters exhibit power transmission in the range 97-100% at their respective center frequencies and stop-band rejection in excess of 18 dB. The theoretically predicted nondiffracting properties of the meshes are experimentally verified through high-resolution beam mapping. Scalability of the filter spectra with mesh dimensions is demonstrated over a wide spectral range. Several modeling methods are considered, and results from the models are shown.