Abstract: Optical carrier filtering is used with an externally modulated fibre optic link to maintain high dynamic range operation with significantly reduced optical power levels. A spur-free dynamic range of 115 dBHz/sup 2/3/ is achieved for a frequency of 17 GHz with a received optical power of only 1.5 mA. An external filter is used to demonstrate a 10 dB improvement in dynamic range for a fixed optical power level.

Abstract: An all-fiber narrowband transmission filter (FWHM=0.25 nm) that is compact and exhibits high return loss (30 dB or better) is demonstrated using simultaneously written matched-pair, side-by-side Bragg gratings in a Michelson interferometer configuration. >

Abstract: We review the principle of operation and characteristics of all-fiber devices for dispersion compensation based on chirped distributed resonant coupling. These devices are the chirped Bragg grating, the chirped intermodal coupler, and the tapered two-dissimilar-core fiber. We discuss the use of a figure of merit to characterize equalizing filters. Based on a specific example, filter responses are computed and their performance is evaluated with a numerical simulation of an optical fiber link. Finally, design constraints are discussed. >

Abstract: It has proven desirable to use multistage etalons and resonators in lightwave communication systems. The design of these linear structures, however, is made difficult by the manner in which their transfer functions are nonlinear with respect to their composite reflection coefficients. If we interpret the etalons as discrete-time lattice filters, then z-transform techniques may be used to recursively synthesize filters with desirable properties. An algorithm is developed which can be used to design the arbitrary all-pole transfer functions in transmission, and the restricted class of pole-zero transfer functions in reflection, which are possible to implement with this architecture. We present some design examples such as notch, or channel-blocking, filters and flat-top bandpass, or channel-passing, filters which are appropriate for frequency-division multiple access and wavelength-division multiplexed communications systems. The theory predicts, and we show experimentally, how these structures may be used to discriminate, or route, signals based on their modulated or coded characteristics. >

Abstract: Several approaches to multichannel filtering for texture classification and segmentation with Gabor filters have been proposed. The rationale presented for the use of the Gabor filters is their relation to models for the early vision of mammals as well as their joint optimum resolution in time and frequency. In this work we present a critical evaluation of the Gabor filters as opposed to filter banks used in image coding-in both full rate and critically sampled realizations. In the critically sampled case, tremendous computational savings can be realized. We further evaluate the commonly used octave band decomposition versus alternative decompositions. We conclude that, for a texture segmentation task, several filters provide approximately the same results as the Gabor filter and, most important, it is possible to use subsampled filters with only a modest degradation in segmentation accuracy-realizing considerable computational savings.

Abstract: We describe and characterize a narrow bandwidth volume holographic optical filter operating at the Krypton transition line (1s2‐2p8) at 1547.82 nm, which corresponds to the center wavelength of the proposed International Telecommunications Union wavelength standard. A reflectivity of 98% and a bandwidth full width at half‐maximum of 0.18 nm are measured. The filter exhibits clean sideholes with a −20 dB optical response 0.5 nm away from the peak. The filter can be fabricated and operated with an absolute wavelength precision better than 0.005 nm.

Abstract: We demonstrate a novel and powerful device that permits individual and simultaneous control of all the wavelength channels in a WDM system. The device is based on the monolithic integration of two identical waveguide grating routers with semiconductor optical amplifiers. By biasing appropriately the individual amplifier, each WDM channel can be amplified, detected or modulated. The device exhibits a channel bandwidth of 60 GHz, a channel spacing of 195 GHz and a crosstalk of /spl minus/19 dB. >

Abstract: HgCdTe photoconductive detectors can display a nonlinear response when illuminated. In interferometric applications, this behavior must be accounted for in the data transformation process to avoid errors in the measurement of the spectral distribution of the incident radiation. A model for the distortion of the interferogram is proposed and applied to solar observations made by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier-transform spectrometer during orbital sunrise and sunset from the Space Shuttle. Empirical estimation of the dc current level is necessary for this instrument, and satisfactory nonlinearity correction is obtained for several of the primary ATMOS optical filters. For ATMOS broadband optical filters that cover more than one half the alias bandwidth, the model is inadequate because of the presence of antialiasing electronic filters within the instrument, and it is necessary to resort to estimation and subtraction of the residual baseline offset. In either case the remaining baseline offsets are typically smaller than 1%, which is satisfactory, although offset remains a significant systematic source of error in the estimation of the abundance of telluric and solar constituents from the spectra.

Abstract: We describe the design and characteristics of cascaded coupler Mach-Zehnder (CMZ) channel adding/dropping filters that select every nth channel (n=2,3,4,...) from the wavelength-division-multiplexed (WDM) optical signal. Using the truncated binomial coupling weight distribution, which appears to be optimal, such filters achieve low ( >

Abstract: An accurate method of analysis is presented for optically preamplified receivers using an eigenfunction expansion technique in the optical frequency domain. Excluding three conventional simplifying assumptions on optical filters, electrical circuits, and amplified spontaneous emission, our method can give accurate predictions to the bit-error probabilities in real systems where the amplified spontaneous emission is the dominant noise. >

Abstract: This invention provides split-element liquid crystal polarization interference filters in wide-field, bandpass, cut-on, cut-off and notch filter embodiments. The split-element filters of this invention comprise a polarization interference stage defined by a pair of polarizers. Disposed within the stage are a center retarder, and first and a second split-element retarder, the split-element retarders having equal retardances and positioned in series with and on either side of the center retarder. The retarders can be liquid crystal variable retarders or can be fixed retarders used in combination with liquid crystal retarders. Double split-element filters in passive and tunable embodiments are provided comprising, within a polarization interference stage, a center retarder, an inside pair of split-element retarders and an outside pair of split-element retarders.

Abstract: An optical fiber amplifier includes an optical amplifying section having an Er-doped fiber. A gain equalizing section is provided at secondary stage of the optical amplifying section and has an optical filter unit for compensating for wavelength dependency characteristics of a signal gain at the optical amplifying section. The gain equalizing section has a filter rotating device and the optical filter unit has et least two optical filters of transparent multi-layer film in which a layer of high refractive index and a layer of low refractive index are alternately and repeatedly stacked. The optical filter is rotated by the filter rotating device such that the wavelength transmission characteristics of the optical filter are set by changing an angle of incidence of the signal light with respect to the optical filter and the wavelength dependency characteristics of the signal gain are compensated for. The optical filter which is of the multi-layer film and which is rotatably arranged improves wavelength tunability.

Abstract: A molecular absorption filter-based diagnostic technique has been developed to obtain instantaneous, planar velocity measurements in high speed flows. This paper presents the details of the technique and its application in high Reynolds number compressible mixing layers with convective Mach numbers of 0.51 and 0.86. Pressure broadening was used to “tune” the absorption profile of the filter to a given flow field/optical arrangement. It is shown that two filters can be used when background scattering is significant: one as the velocity-discriminating filter, the other to eliminate unwanted background light from the reference camera. Collected images show instantaneous variations in velocity within both the highly organized roller type structures of the M c = 0.51 mixing layer and the unorganized structures found in both mixing layers. An uncertainty analysis showed that the measurement uncertainty was ±8.6% for the current measurements, but improvements to reduce the uncertainty to ±3% are suggested.

Abstract: We report a polarization-independent integrated acousto-optical double-stage wavelength filter in X-cut, Y-propagating LiNbO/sub 3/. The device consists of a combination of four acousto-optical mode converters, a TE- and a TM-pass polarizer, and two polarization splitters; their specific design and properties are discussed. The filter has a bandwidth of 1.4 nm and a tuning range of 76 nm around /spl lambda/1.55 /spl mu/m. Maximum filter transmission is achieved with a RF drive power of only 80 mW; it excites via a single unidirectional transducer a guided surface acoustic wave driving the four polarization converters of both stages. Fiber-to-fiber insertion loss is 4.6 dB for TM- and 4.8 dB for TE-polarized waves. Multiwavelength filtering has been demonstrated. >

Abstract: A new method of modulating the coupling coefficient along the waveguide is proposed. The effect of our method, which uses a nonperiodic sampled grating, is demonstrated both theoretically and experimentally. A Bragg filter is fabricated on an InGaAsP/InP wafer utilizing the method, and the sidelobe level is shown to improve by 7 dB compared with a conventional filter with a uniform coupling coefficient. The experimental results are found to be in good agreement with calculations. >

Abstract: A tunable optical filter for use in wavelength division multiplexing systems. The optical filter contains a plurality of tunable reflection gratings which block all of the channels in the incoming lightwave. An electrode or a heating element is provided for each reflection grating to tune the reflection gratings so that their reflection bands do not coincide with a desired channel or channels thereby allowing the desired channel or channels to pass through the filter.

Abstract: An optical multichannel controller that gives full access to 12 individual wavelength channels is reported. The device consists of two waveguide grating routers integrated with semiconductor optical amplifiers. It exhibits a channel spacing of exactly 3.2 nm (400 GHz) and an off-peak signal rejection of more than 40 dB. The amplifiers compensate for the multiplexer insertion losses. >

Abstract: The liquid of a flow cytometer itself acts as an optical waveguide, thus transmitting the light to an optical filter/detector combination. This alternative apparatus and method for detecting scattered light in a flow cytometer is provided by a device which views and detects the light trapped within the optical waveguide formed by the flow stream. A fiber optic or other light collecting device is positioned within the flow stream. This provides enormous advantages over the standard light collection technique which uses a microscope objective. The signal-to-noise ratio is greatly increased over that for right-angle-scattered light collected by a microscope objective, and the alignment requirements are simplified.

Abstract: To realise a temperature independent narrowband optical filter, a three-dimensional athermal waveguide for which optical path length is independent of temperature is developed. The temperature coefficient of the optical path length is successfully decreased to -2% of that of a conventional waveguide.

Abstract: A sensing system with a multichannel fiber optic bundle (MFOB) sensitive probe for measuring displacement, vibrations, roughness and two angles between a probe tip and light reflected target. The MFOB sensitive probe includes three branches of transmitting and receiving channels. The tip end of the MFOB is arranged in a rectangular 3*3 matrix formation. The other end of the MFOB includes eleven optical tips and connectors for optically connecting the tip of each channel, through optical filters, with light sensors and light sources. The sensing system further includes an electronic portion, having a thermostabilized box, an analog portion of an electronic module, a multifunction input/output board for use with a computer, and a controller for programmably controlling and measuring all parameters using computer analysis.

Abstract: We consider the detection of multiple classes of objects in clutter with 3-D object distortions and contrast differences present. We use a correlator because shift invariance is necessary to locate and recognize one object whose position is not known and to handle multiple objects in the same scene. The detection filter used is a linear combination of the real part of different Gabor filters, which we refer to as a macro Gabor filter (MGF). A new analysis of the parameters for the initial set of Gabor functions in the MGF is given, and a new neural network algorithm to refine these initial filter parameters and to determine the combination coefficients to produce the final MGF detection filter is detailed. Initial detection results are given. Use of this general neural network technique to design correlation filters for other applications seems very attractive.

Abstract: Experiments with varying filter bandwidth in a soliton fiber laser are reported. Continuous tuning over 50 nm was obtained for pulses of >

Abstract: Experimental and theoretical results on single- and double-amplified recirculating delay lines are presented. One of our aims is to emphasize their application as filters, showing a wide flexibility of design. Analysis of their performance in the spectral and time domains have been carried out. A novel method of understanding the behavior of double structures has been developed and successfully tested with experimental results employing Er-doped fiber amplifiers as delay lines. >

Abstract: An Optical filter is provided on a light receiving surface of an image sensor. The filter has a plurality of thin layers alternately laminated. The thin layers alternately consist of a dielectric layer having a high refractive index and a metal layer and each thin layer has its stress σ in a range -5 GPa≦σ<-0.2 GPa.

Abstract: The acquisition of simultaneous dual confocal images with red and far-red light has both advantages (e.g. lower autofluorescence) and limitations. An understanding of these requisites is necessary to acquire high-quality images and to avoid the misinterpretation of experimental data. The poor detection of far-red light mandates a high optical transfer efficiency for the system, thus the transmittance of the objective lens and its axial and lateral chromatic aberration in the far-red are important factors for consideration. This technical note is an attempt to 'demystify' the process of filter set design for confocal microscopy by discussing the considerations that went into the construction of a filter set for use with the reagents cyanine 3.18 (Cy3) and cyanine 5.18 (Cy5), and thus to encourage users to look beyond the multi-purpose designs available commercially. The 568-nm laser line exciting Cy3 is at its emission maximum, which limits the collectable Cy3 fluorescence. High-transmission optical filters with sharp band pass cutoffs are thus desirable for maximum light throughout. Light path mirror efficiency rapidly degrades above 700 nm, but the loss of this portion of the Cy5 emission spectrum is acceptable since the fluorophore is very bright, and these very long wavelengths are also likely to introduce aberration. While resolution is decreased with far-red light, there is also greater penetration and less scattering, and it is thus possible to obtain high-quality images from deeper within the specimen.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract: An tunable optical filter of the kind used, for example, in wavelength-division multiplexing (WDM) optical communication systems and tunable source applications, has an interference filter element which is pivotable to adjust the operating wavelength of the filter. In order to reduce polarization dependency as the angle of the interference filter element changes, the light beam to be filtered is passed through the filter element twice, the second time with its polarization state shifted, specifically orthogonal, relative to the polarization state during the first pass. As a result, polarization dependent effects are equalized. The optical filter comprises a pivotally mounted filter element, an input optical fiber for directing a light beam to be filtered through the filter element in a first direction with a first polarization state, optical elements for rotating the polarization state of the filtered light beam and returning the light beam through the filter element (10) a second time, and an output optical fiber for receiving the light beam following passage of the light beam though the filter element the second time. The optical elements may comprise a reflector for reflecting a light beam emerging from the optical filter element to return through the optical filter element in the opposite direction, and a polarization rotator, such as a quarter-wave plate or a Faraday rotator, for rotating the polarization state of the light beam through 90 degrees before passage in the opposite direction.

Abstract: We consider the detection of candidate objects (regions of interest) in a scene containing high clutter, multiple objects in different classes, independent of aspect view, with hot, cold, bimodal, and partial object variations and with high and low contrast targets. We use three different filters with each designed to produce high probability of detection (PD). We fuse the results from different outputs to reduce the probability of false alarms (PFA). All filters are realizable on an optical correlator.

Abstract: Add-drop filters are demonstrated using silica-on-silicon optical waveguide technology. This device consists of a full directional coupler subdivided by Mach-Zehnder sections. Tapering of the coupling coefficients is experimentally shown to dramatically reduce the filters' sidelobes. Only one photolithographic step is required using the silica planar waveguide technology, yielding accurate wavelength control of the filters. Excellent agreement between measurement and design was achieved. >

Abstract: We present a theoretical framework for the design of optical infinite impulse response filters using fiber devices. A condition for the congruence of these structures is given in addition to a general signal processing form. The letter is concluded with a demonstrative example. >