Abstract: By gradually translating the peak frequency of guiding filters along its length, we create a fiber transmission line that is substantially opaque to noise while remaining transparent to solitons. This trick allows the use of stronger filters, and hence greater jitter reduction, without incurring the usual penalty of exponentially rising noise from the excess gain required to overcome filter loss.

Abstract: : We studied optical processing techniques to detect and track frequency hopped radio signals in a dense electromagnetic environment by using cross-spectrum of two signals obtained from antenna elements spaced by one-half an RF wavelength. We decimate the array by retaining only every Mth element and scan the cross-spectrum past the decimated array. We therefore reduce the circuit complexity, but suffer some loss in system performance because we require more photodetector bandwidth to accommodate the scanning action. An extension of the decimated array concept is to decimate the reference waveform in the heterodyne spectrum analyzer. In this case, we generate only 64 optical probes in the Fourier domain instead of the 2048 that are normally required. The advantage is that all of the optical power in the reference beam can be concentrated into the reduced number of optical probes, thereby offsetting some of the intrinsic loss in performance experienced by the cross-spectrum analyzer. (JHD)

Abstract: The wavelet transform is implemented using an optical multichannel correlator with a bank of wavelet transform filters. This approach provides a shift-invariant wavelet transform with continuous translation and discrete dilation parameters. The wavelet transform filters can be in many cases simply optical transmittance masks. Experimental results show detection of the frequency transition of the input signal by the optical wavelet transform.

Abstract: Optical systems including an optical amplifier and a narrow bandwidth optical filter for removing undesired spontaneous emission. An in-fiber Bragg grating reflector reflects substantially only the input amplified signal back to a circulator port of an optical circulator where the desired amplified signal is coupled from the next circulator port. The undesired emission exits from the grating reflector and is removed from the system. Cascaded grating reflectors are used in a wavelength division multiplexing (WDM) system. A two section narrow band transmission filter with cascaded gratings.

Abstract: The problems of spatial diffraction and optical dispersion in the time domain was extended by analogy to optical ultrafast pulse filtering. An analog setup in the 4-f spatial-filter configuration is proposed, and several applications such as the temporal signal convolver or correlator and the joint transform processor are suggested, followed by ways to generate the temporal filter. The implementation aspects and an example of the speed superiority of this approach are also discussed.

Abstract: The quality of color correction is dependent upon the filters used to scan the image. This paper introduces a method of selecting the scanning filters using a priori information about the viewing illumination. Experimental results are presented. The addition of a fourth filter produces significantly improved color correction over that obtained by three filters.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Abstract: A novel approach for designing optimal multilayer filters based on a real-coded genetic algorithm is presented. Given the total number of layers in the filter, as well as the electrical properties of the materials constituting each layer, the algorithm iteratively constructs multilayers whose frequency response closely matches a desired frequency response. In contrast to existing iterative techniques, this method does not require a preliminary design using classical techniques. Also, the design procedure is independent of the nature of the multilayer as well as the characteristics of the incident and substrate media. The algorithm is applied to the design of various lowpass and high-pass optical filters, operating between practical terminal conditions. The performance of the resulting designs matches or improves on that for filters that were synthesised using semiclassical techniques.

Abstract: The application of optical amplifiers (OAs) to fiber-optic delay line signal processing is demonstrated. Both erbium-doped fiber amplifiers (EDFAs) and semiconductor optical amplifiers (SOAs) are applicable. Analytical results are presented for both amplified and unamplified fiber-optic recirculating delay lines (AFORDLs and UFORDLs). In the AFORDL an OA is inserted in the fiber loop. It is shown that the active AFORDL structure is capable of realizing all-fiber filters not possible with the passive UFORDL. This result is significant because it shows that the OAs can function beyond just the trivial optical loss compensation to provide extra flexibility not available in passive designs. An AFORDL design is presented which has a pole near +1 and a zero at -1 in the Z-plane resulting in useful characteristics in the magnitude and phase responses. The results suggest that extension of the concept to higher-order filters has the potential to lead to the realization of more complex optical processors. >

Abstract: An instrument for determining the concentration of a particular gas that might be present in a sample has no moving parts and is extremely compact and inexpensive. A novel waveguiding structure serves both as an optical element and as the sample chamber. As an optical element, the waveguiding structure collects radiation from a blackbody source located at the entrance end of the waveguiding structure and conducts the radiation through the waveguiding structure, concentrating it on two infrared detectors mounted at the opposite end of the waveguiding structure. As a sample chamber, the waveguiding structure causes the radiation to undergo multiple reflections that result in the average path length being substantially greater than the physical length of the waveguiding structure. Each of the detectors has its own optical filter, and baffling assures that each detector responds only to radiation which has passed through its filter. One filter defines a spectral passband that coincides with the infrared absorption band of the gas to be measured. The other filter defines a non-absorbing or neutral passband. The electrical signals produced by the detectors are processed to provide a ratio, the value of which is related to the concentration of the particular gas to be detected.

Abstract: It is shown that optical amplifiers (OAs) can provide extra flexibility for unique fibre-optic filter designs, not available in passive configurations. Results are presented for both amplified and unamplified fibre-optic recirculating delay lines (AFORDL and UFORDL) indicating that the AFORDL is capable of realising filters not possible with the UFORDL.

Abstract: This invention disclosure describes the application of a polarization insensitive acoustically-tuned optical filter used in a multichannel WDM system to equalize variations in the power level of the WDM channels. The invention also describes a simple means for providing a low frequency control system which enables the equalizer to determine the signal levels of N optical carriers prior to equalizing the signals.

Abstract: Plastic hollow waveguides (used as fibers) for infrared (IR) transmission were made from plastic tubes covered, on the internal wall, with a metal layer (Ag) and growing a dielectric thin (AgI) overlayer by direct iodination on it. The existence of several absorption lines at given wavelengths in the middle infrared (mid‐IR) region is predicted theoretically and measured experimentally. From the wavelengths of absorption lines the thickness of the AgI film has been computed. The average thickness of the AgI in the hollow waveguide increased with the iodination time and with the concentration of the iodine solution. The crystal size of the AgI was increased with the increase of the AgI thickness. By controlling the iodination process it was possible to make waveguides which can be employed as filters for various wavelengths of the transmitted mid‐IR radiation.

Abstract: A design for a birefringent filter is described, which is suitable for tunable femtosecond lasers. Using a single plate, which has a steeply diving optic axis, two-octave tunability is attained with negligible deterioration of the stopband rejection. For a specific wavelength region, it means that the filter's bandwidth can be changed by a factor of four. Another characteristic of the design is that, for the same bandwidth, the proposed plate is five times thicker than a conventional plate in which the optic axis is parallel to the surface. Thus, etalon effects can be avoided. Tuning characteristics of color center lasers utilizing the new filter are also presented. >

Abstract: The spatial resolution limit of noncollinear acousto-optic tunable filters used for imaging with incoherent light is derived based on phase-matching requirements. It is shown that the noncollinear filter can achieve near diffraction limited imaging. This conclusion was verified experimentally.

Abstract: The authors report for the first time a grating in GeO 2 -SiO 2 planar waveguides formed by exposure to UV radiation. The grating gave a reflectivity or 44% with a bandwidth or 1.1 nm, which indicates an index modulation or at least 2.0×10 -4 . The waveguide material was made sensitive to the UV radiation by annealing in H 2 , which significantly enhanced the 240 nm absorption band

Abstract: We measured cesium magneto-optic line filter spectra at 455 nm for several field orientations. When optimized to achieve the narrowest passbands and the highest transmission, the Faraday filter (B along k) exhibited near-unity transmission peaks of 0.7-GHz bandwidth with an integrated transmission of ∼3 GHz. A transmission calculation that includes the field angle was confirmed experimentally and used to show that the Faraday filter field of view is >60°. We devised a new type of magneto-optic atomic line filter that uses a transverse magnetic field, which we call the Voigt filter.

Abstract: An acoustooptic tunable filter is used to compensate for the gain spectrum variations in multiwavelength lightwave systems containing cascaded fiber amplifiers. Demonstrations of such systems using a circulating loop containing a fiber amplifier and an acoustooptic tunable filter have shown that differential gain compensations of up to 14 dB can be achieved for two arbitrary injected wavelengths. >

Abstract: An interferometric tunable optical filter selects a predetermined wavelength or wavelengths from a wavelength division multiplexed signal. The optical filter splits an input signal into a plurality of waveguide branches. In each branch, the amplitude and phase of the signal can be individually controlled. The signals are then recombined. The resulting interference gives a wavelength dependent transmission spectrum that can be adjusted as desired.

Abstract: The original minimum average correlation energy (MACE) filter is addressed by using a new database (strategic relocatable objects, missile launchers) and including noise performance, depression angle, and resolution effects on the number of training set images that are required. Major attention is given to our new MACE filter algorithms for distortion-invariant pattern recognition: shifted-MACE filters (to suppress large false correlation peaks), minimum variance-MACE filters (for improved noise performance), multiple symbolic encoded filters (to reduce the effect of false correlation peaks), and Gaussian-MACE filters (to improve noise performance and intraclass recognition and reduce the training set size).

Abstract: A novel type of filter based on D fibre with an overlay grating is proposed. The fabrication and characterisation of the device are described and its use in an erbium doped fibre amplifier to obtain a flatter gain spectrum is discussed.

Abstract: The multi-colored electrophoresis pattern reading system compares the patterns of electrophoresis without a warp to be caused upon electrophoresis by reading the patterns of electrophoresis which is carried out concurrently for plural samples and by labelling the samples with fluorescent substances having different fluorescent wavelengths. The patterns of electrophoresis are read by allowing fluorescence to emit from the plural samples. In reading the fluorescent patterns, optical signals are received by the light receiving section and then the fluorescence having a predetermined wavelength is separated by the fluorescent-wavelength separating section from the optical signals with the aid of an optical filter capable of controlling an angle of incidence relative to the optical axis of the optical filter. The optical signals passed through the fluorescent-wavelength separating section is then subjected to optoelectrical conversion into electric signals which in turn are subjected to signal processing, thereby converting the electric signals into a desired form of data representation.

Abstract: A new type of noncollinear acousto-optic tunable filter (AOTF) suitable for fibre optic communication is described. The AOTF interaction geometry offers the advantages of narrow bandwidth and low drive power. Theoretical analysis of the TeO2 filter shows that optical passband of 1nm and drive power of 12mW are obtainable.

Abstract: Experimental and theoretical results on single and double amplified recirculating delay lines are presented. Their application as fibre-optic filters are discussed, showing a wide flexibility of design, by appropriate choice of their main parameters: loop length, gain and coupling ratio of the coupler.< >

Abstract: Broadband chirped fibre Bragg filters centred at 980nm and 1480nm with reflectivities as high as 99% and reflection bandwidths up to 22nm are reported. The filters have a low transmission loss of <0.5 db between 1.51 and 1.56μm and their application to reject and recycle unabsorbed pump light from a fibre amplifier is demonstrated.

Abstract: Frequency chirp in semiconductor lasers that are directly modulated through carrier injection not only induces dispersion in long-haul single-mode fiber communication systems, but also causes energy loss and signal distortion when frequency selective elements such as Fabry-Perot filters are present. This effect is significant for high-bit-rate channels in a dense wavelength-division-multiplexed system in a LAN/MAN environment which requires narrow-band filters to suppress crosstalk from adjacent channels. A simulation approach is used to determine the channel capacity in the presence of chirp and crosstalk. The results show that a minimal channel spacing of less than 37 and 10 GHz with each channel operating at 2 Gb/s using OOK and FSK, respectively, can be achieved by a dense wavelength division multiple access system. It is also shown that this system performance can be optimized through adjusting various parameters of the laser and the filter. >

Abstract: A single-stage low-sidelobe weighted-coupled integrated acoustooptic tunable filter (IAOTF) operating at the optical wavelength of 131 mu m has been realized on a Y-cut X-propagating LiNbO/sub 3/ substrate for the first time The weighted-coupling, which enabled the achievement of low-sidelobe levels, was facilitated by focused surface acoustic waves generated by a curved interdigital transducer First sidelobe levels as low as -176 dB have been obtained Optical bandwidth of 4 nm and tuning range of 170 nm for an interaction length of 6 mm were also accomplished >

Abstract: Signals encoded as highly stable spatial (or temporal) dark solitons can be used in nonlinear-optical devices such as logic gates, interconnects, multiplexers, and filters. The formation of these waves with the use of simple diffracting (dispersing) elements in prototypical devices is analyzed by using the direct-scattering method, which is also outlined. Noncollisional dark-soliton XOR and AND gates and dark-soliton level splitting and bands are also described.

Abstract: Two types of double-stage, acousto-optical wavelength filters have been fabricated in X-cut, Y-propagating LiNbO/sub 3/ by an integration of TE- and TM-pass polarisers and acousto-optical mode convertors in a doubly confined acoustical/optical singlemode waveguide. Filter characteristics with narrow bandwidth ( >

Abstract: An optical filter 10 for filtering spatial frequencies from an output of an optical imaging system comprises a substantially transparent, or reflective, optical element 12 having a plurality of light refracting, or reflecting, segments 18 arranged on a surface thereof. Each of the plurality of segments 18 is provided with a predetermined angle of refraction, or reflection, distinct from adjacently located segments 18, wherein the different angles of refraction, or reflection, and the arrangement of the segments 18 on the optical element 12, are determined based on a desired spatial frequency transfer function for the filter 10. The optical spatial filter 10 reduces errors in optically formed images by accurately confining a broadened Point Spread Function (PSF) to a desired spot size.