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.     

A multichannel energy filter comprising a cylinder with closed ends and an axial filament electrode

A new electrostatic multichannel deflector providing energy filtration of charged particles is proposed. The device comprises a cylinder with closed ends and an axial filament electrode. The potential profile in the system is analytically calculated. The main parameters of the energy filter are calculated for a charged particle beam injected and extracted via grounded end faces. Owing to a small azimuthal beam size compared to the cylinder perimeter, the proposed system is quite compatible with one-to four-channel dynamical monopole mass spectrometers, providing energy-filtered beam deflection to a detector.     

Acousto-optic tunable filter chromatic aberration analysis and reduction with auto-focus system

An acousto-optic tunable filter (AOTF) displays optical band broadening and sidelobes as a result of the coupling between the acoustic wave and optical waves of different wavelengths. These features were analysed by wave-vector phase matching between the optical and acoustic waves. A crossed-line test board was imaged by an AOTF multi-spectral imaging system, showing image blurring in the direction of diffraction and image sharpness in the orthogonal direction produced by the greater bandwidth and sidelobes in the former direction. Applying the secondary-imaging principle and considering the wavelength-dependent refractive index, focal length varies over the broad wavelength range. An automatic focusing method is therefore proposed for use in AOTF multi-spectral imaging systems. A new method for image-sharpness evaluation, based on improved Structure Similarity Index Measurement (SSIM), is also proposed, based on the characteristics of the AOTF imaging system. Compared with the traditional gradient operator, as same as it, the new evaluation function realized the evaluation between different image quality, thus could achieve the automatic focusing for different multispectral images.     

Design of a configurable multispectral imaging system based on an AOTF

In this paper, we present a configurable multispectral imaging system based on an acousto-optic tunable filter (AOTF). Typically, AOTFs are used to filter a single wavelength at a time, but thanks to the use of a versatile sweeping frequency generator implemented with a direct digital synthesizer, the imager may capture a configurable spectral range. Experimental results show a good spectral and imaging response of the system for spectral bandwidth up to a 50 nm.     

Development of an all-sky-scanning spectroradiometer with a visible diode array and a near-infrared acousto-optic tunable filter

A sky scanner was developed that collects spectral radiance data over the wavelength range 390-1732 nm by use of two radiometers, the first being a monochromator with a 512-element silicon diode array and the second being a near-infrared acousto-optic tunable filter (AOTF) coupled to an InGaAs detector. The scanner is capable of completing a set of spectral radiance measurements at 146 points in the sky hemisphere in a period of less than 4 min.     

一种以AOTF为核心的农药荧光检测系统

提出了一种将 AOTF 技术用于农药含量检测的荧光光谱系统。该系统分别采用以α-Quartz,TeO2 晶体作为声光介质的激发和发射色散元件 AOTF,以高压短弧氙灯为激发光源,利用光纤探测并传输荧光,由数据采集卡进行数据接收和 A/D 转换。该系统通过声光调制产生单色光,由超声射频的变化实现光谱扫描,没有机械调谐部件,故波长切换快、结构简单。西维因农药的荧光特性测量结果表明,系统的荧光波长范围为 500-750nm, 光谱分辨率为 10nm。当激发光波长为320nm,荧光波长为 647nm,西维因溶液浓度为 0.0-120.0μg/L 时,系统具有较好的线性关系,线性相关系数 r 为 0.9991。它可用于对粮食作物中的农药残留的检测和荧光光谱分析。     

Numerical analysis of a high-resolution fast tunable filter based on an intracavity Bragg grating

A fast tunable filtering technique is proposed associating a diffraction grating with an intracavity Bragg grating. The bandwidth and the tuning range of this filter can be easily adapted by changing the diffraction grating's orientation, or its period, and its response is uniform over the whole tuning range. A numerical simulation of the filter response to a Gaussian beam has been developed, and it fits the experimental results allowing a calculation of the performances that could be obtained with more specific elements. For example, using a commercial acousto-optic deflector would allow a separation of 500 frequencies. It would then be possible to have a tuning range of 100 nm with a bandwidth of 0.2 nm for optical telecommunications.     

Z to S transformation nonuniqueness in tunable switched-filterresponse evaluation and a digital tunable bandpass filter

Computer-aided responses of an electronically tunable bandpass filter by two different methods are presented. Significantly different results are possible for the same circuit if different methods are used due to the nonuniqueness of the Z-to S domain transformation. It is also demonstrated that digital implementation of tunable bandpass filters using the difference equation approach is possible     

A spectroscopic detecting system for measuring the temperaturedistribution of silver breaking arc using a CCD color camera

This paper describes a spectroscopic detecting system that utilizes a CCD color camera to observe the distributions of two spectral intensities along the axis of an arc column. Following this, the distributions of Ag I 421 nm and Ag I 547 mm spectra observed along the axis of an arc column and the arc temperature calculated from the two spectra when silver contacts interrupt a circuit of dc 50 V and 3.3 A are presented. The spectral intensities of excited silver atoms are strongest near the cathode and become weaker with distance from the cathode contact. The temperature in the cross section of an arc column is highest in the axis of the arc column. The temperature along the axis of arc column is highest near the cathode and becomes weaker with distance from the cathode. Furthermore, in this study it is clarified that CN band spectra exist near the anode contact     

Comparison of a CCD and a flat-panel digital system in an Interventional Cardiology Laboratory

We evaluated the performances of angiographic units equipped with a flat-panel (FP) detector and image intensifier (II) charge-coupled device (CCD) in the Interventional Cardiology (IC) Department. Entrance dose rate and dose per image, along with the dose at the II level were measured using 2 mm copper sheets to simulate a patient. Image quality (IQ) was evaluated using a phantom. Doses increased with fluoroscopy level changing from low to high. FP presented higher doses than CCD. Periodic measurements showed differences of up to 35%. Low mode IQ did not significantly differ from normal and high mode for both systems. Low fluoroscopy mode was decided to be used routinely. Both X-ray systems performed within international recommendations for conventional systems with the exception of higher cine radiation doses and II dose rates, stressing the fact that more studies are required to investigate whether dose levels should be adjusted.     

Temperature correction of radiometric and geometric models for an uncooled CCD camera in the near infrared

This paper presents radiometric and geometric models for both temperature and displacement noncontact measurements using an uncooled charge-coupled device (CCD) video camera. Such techniques ("one sensor-two measures") represent an interest in many industrial low cost applications and scientific domains. To benefit from both measurements, we have to use the camera's spectral response in the near infrared spectral band from 0.75 to 1.1 /spl mu/m. In this spectral band, the temperature variations of an uncooled CCD camera are taken into account in the radiometric and geometric models. By using physical models for CCD camera, we quantify detector's quantum efficiency, sensor noise and spatial resolution as a function of the wavelength and of the detector temperature. These models are confirmed by experimental results of calibration with a low cost uncooled camera based on a Sony detector and operating over the detector temperature range of -30 to -50/spl deg/.     

Two-dimensional thermoluminescence dosimetry using planar detectors and a TL reader with CCD camera readout

A novel method of determining two-dimensional (2-D) dose distributions is presented, using in-house developed, large-area (a few cm(2)) thermoluminescent (TL) detectors based on LiF powder plated on Al foil. An in-house developed planar large-area TL reader equipped with a coupled charge device (CCD) camera is used for readout, providing digital images of 2-D dose distributions on the surface of these large-area TL detectors. The capability of the newly developed system is demonstrated by mapping 2-D dose distributions around a brachytherapy source, at dose ranges and source geometries relevant for clinical radiotherapy. Examples of local and dynamic evaluation of TL output from conventional TL detectors are also shown.     

Design and fabrication of a low-cost, multispectral imaging system

This paper reports the design and construction of a low-cost, multispectral imaging system using a single, large format CCD and an array of 18 individual lenses coupled to individual spectral filters. The system allows the simultaneous acquisition of 18 subimages, each with potentially different optical information. The subimages are combined to create a composite image, highlighting the desired spectral information. Because all the subimages are acquired simultaneously, the composite image shows no motion artifact. Although the present configuration uses 17 narrow bandpass optical filters to obtain multispectral information from a scene, the system is designed to be a general purpose, multiaperture platform, easily reconfigured for other multiaperture imaging modes.     

Two-channel tunable monochromatic illuminator with a concave diffraction grating and an original scanning system

A two-channel monochromatic illuminator with only one diffraction grating and an original scanning system has been designed for multiple applications. This scanning system consists of two rotational plane mirrors that reflect light diffracted by a concave diffraction grating to the ?1 orders of the spectrum. The light reflected by the mirrors goes to two exit slits that correspond to two channels of the device. The positions of the centers of rotation of the mirrors are selected to produce minimal deviation of the direction of the light reflected during the scanning. The aberration characteristics of some variations in the optical mounting of the device made by use of spherical and toroidal holographic diffraction gratings recorded in stigmatic and astigmatic beams, the possibilities for application of the device for measuring the color sensitivity of the human eye, and the possibilities for measuring the efficiency of concave diffraction gratings, are also discussed.     

CMOS monolithic metal-oxide sensor system comprising a microhotplate and associated circuitry

A gas sensor system fabricated in industrial CMOS technology is presented, which includes, for the first time, a microhotplate and the necessary driving and control circuitry on a single chip. Post-complementary-metal-oxide-semiconductor (CMOS) fabrication steps, such as micromachining of the membrane structure, the deposition of noble metal on the electrodes, and the processing of the sensitive metal-oxide layer, have been developed to be fully compatible with the industrial CMOS process. Temperatures up to 350/spl deg/C were reached on the hotplates using a low-voltage power supply (5 V). A symmetric hotplate design with a temperature homogeneity of better than 2% in the heated area was realized. The integrated temperature controller regulates the membrane temperature with a resolution of /spl plusmn/0.3/spl deg/C in the tracking mode. The temperature increase on the bulk chip owing to heat transfer through the membrane is less than 2% of the respective membrane operation temperature (6/spl deg/C at 350/spl deg/C membrane temperature). The gas sensing performance of the sensor was assessed by test measurements with carbon monoxide (CO). The gas tests evidenced a limit of detection of less than 5 ppm CO.     

Theory and design of a simple tunable Sagnac loop filter for multiwavelength fiber lasers

We present a novel design for a Sagnac loop filter (SLF) whose periodic output spectrum can be fully controlled by cascading a small-birefringence loop (SBL) with a high-birefringence loop (HBL). We develop a detailed theoretical analysis, using the Jones vector method, to calculate the transfer function of the tunable SLF. It has been quantitatively shown that both the transmission coefficient and the phase of the SLF can be controlled by adjusting the orientation angle of the birefringent axes of the SBL in the plane of polarization. The theory has been confirmed by experimental results where a stress-induced SBL was mechanically rotated to tune both the wavelength and the power of a periodic output spectrum. Such a tunable SLF is used in the design of a multiwavelength erbium-doped fiber laser in the C band.     

Acousto-optic tunable filter as a polychromator and its application in multidimensional fluorescence spectrometry.

Acousto-optic tunable filter (AOTF) is an electronically driven dispersive device which operates on the principle of acousto-optic interaction in an anisotropic medium. Incident white light will be diffracted by the AOTF into a specific wavelength when a specific rf is applied to it. The diffracted light needs not be a monochromatic light. Multiwavelength light can be diffracted from the AOTF when several rf signals are simultaneously applied into the filter. Compared to conventional polychromators, advantages of this electronic AOTF polychromator include its ability to individually amplitude-modulate each wavelength of the diffracted multiwavelength light at different frequency. This is accomplished by individually and sinusoidally modulating each applied rf signal at the desired frequency. This feature makes it possible to develop a novel AOTF-based multidimensional fluorimeter in which the sample was simultaneously excited by two different wavelengths (514.5 and 488.0 nm) whose amplitudes were sinusoidally modulated at two different frequencies (100 and 66 Hz). Multicomponent samples, e.g., mixtures of rhodamine 6G and rhodamine B, were successfully analyzed using this novel fluorimeter and the developed data analysis.     

A multichannel energy filter comprising a cylinder with closed ends and axial filament electrode: Part II

This paper continues theoretical investigation of a new electrostatic multichannel deflector performing energy filtration of charged particles is proposed. The device comprises a cylinder with closed ends and an axial filament electrode. An analytical expression is obtained for a potential distribution formed in the device when a retarding potential (equal to that on the filament) is applied to the rear end wall, while the cylinder and the front wall are grounded. The energy filter operating in this regime provides a sharper focusing of the particle beam as compared to the previously considered case of operation with a grounded rear wall. This circumstance allows the beam intensity to be increased 2–2.5 times at the same exit slit width or the energy filtration to be improved 1.5 times at the same beam intensity.