Abstract: This letter proposes and demonstrates a simple all-optical label detection and swapping technique incorporating a fiber Bragg grating (FBG) filter and a double sideband subcarrier multiplexed (DSB-SCM) signal. The optical datagram consisting of a baseband 2.488-Gb/s data payload and a subcarrier multiplexed 622-Mb/s label are optically processed to separate the two components, and then a new label content is encoded by subsequent optical modulation. The optically separated original label is detected by a square law detector without involving any high-frequency subcarrier circuitry. Bit-error-rate measurements confirm a successful and low-penalty label swapping technique, which maintains optical transparency for the data payload.

Abstract: Stacked Crystal Filters, (SCF), are composed of multi-layers of piezoelectric and metal layers. Normally these filters have a complex frequency spectrum containing near-in spurious responses. However, by having the SCF formed in a Solidly Mounted Resonator (SMR) format, the performance of the device is greatly improved by the finite bandwidth of the SMR reflector. The conventional SCF also has a bandwidth that is too small for some wireless applications. This paper will describe the design and performance issues associated with stacked crystal filters using bulk wave thin films with aluminum nitride as the piezoelectric. Filters without spurious responses, filters having wide bandwidths, and filters operating at frequencies up to 8.5 GHz will be described in addition to GPS filters.

Abstract: This paper presents a novel algorithm for the analysis of quasi-optical filters, consisting of thick metal screens perforated periodically with arbitrarily shaped apertures. The algorithm is based on the widely used method of moments (MoM) in conjunction with entire domain basis functions. Its flexibility, accuracy, and rapidity depend on the use of the boundary integral-resonant mode expansion (BI-RME) method in the numerical determination of the basis functions. A computer code has been developed based on this algorithm. The analysis of two different quasi-optical filters operating at 8 GHz and 280 GHz is reported and compared with experimental data as well as with other simulations. In both cases, the whole analysis requires few seconds on a standard workstation and the theoretical results show a very good agreement with the measured data in a wide frequency band. The capability of the MoM/BI-RME approach to handle completely arbitrary shapes is highlighted in the second example. In this case, in fact, the fabrication process causes small deformations of the nominal shape of the apertures, which must be accounted for, since they play an important role in the frequency response of the filter.

Abstract: A promising class of optical filters is introduced, based on diffraction at small apertures. The filters consist of straight pores with diameters in the micrometer regime and a length of up to one millimeter through a silicon wafer. In contrast to Bragg, Woods, or glass filters, the light is not transmitted in matter but in the medium inside the pores. The filters therefore show a true shortpass characteristic. Due to constructive interference between the high number of pores in an array, macropore filters are of high optical quality and may replace conventional filters in imaging systems.

Abstract: An optical spectrometer uses a tapered Fabry-Perot type linear variable optical filter in conjunction with an optical detector array. The filter can be a long-pass, short-pass, or narrow bandpass filter. The stability of the variable optical filter allows high resolution, depending on the number and spacing of the detectors used. In a further embodiment, signal-processing techniques are used to enhance the resolution of the spectrometer beyond the measured response.

Abstract: A multiplexer/demultiplexer optical system component that is passively aligned upon assembly is disclosed. The optical system includes a lens block and a mirror-filter block. In some embodiments, optical filters are positioned and epoxyed to the mirror-filter block using a positioning tool. In some embodiments, optical filters are positioned and epoxyed on a support structure which has been etched to receive the optical filters. The mirror-filter block is a block having flat surfaces, one of which is a flat reflecting surface. The lens block is formed by injection molding and includes a barrel for holding and positioning an optical fiber, placement for a collimating lens, and placements for focusing lenses such that, when assembled, light incident on each of the focusing lenses propagates along the optical axis of the focusing lens. In some embodiments, the collimating lens and the focusing lenses are integrally formed with the lens block. In some embodiments, one or more of the collimating lens or focusing lenses are formed separately and inserted into holders integrally formed with the lens block to receive the lens. In some embodiments, the lens block includes a reflecting surfaces that directs light onto the focusing lenses. Assembly and alignment of the multiplexer/demultiplexer involves positioning a flat surface of the mirror-filter block against a receiving surface of the lens block with the filters between them and epoxying the components in place.

Abstract: The present invention relates to a tunable optical filter having a variable wavelength characteristic of transmittance. The tunable optical filter includes first and second polarizers each having a transmission axis determining a polarization axis of transmitted polarized light, a birefringent element having an optic axis determining a phase difference given between two orthogonal components of transmitted polarized light, and a Faraday rotator for giving a variable Faraday rotation angle to transmitted polarized light. The birefringent element and the Faraday rotator are provided between the first and second polarizers. The order of arrangement of the birefringent element and the Faraday rotator, and the relative positional relation between the optic axis of the birefringent element and the transmission axis of each polarizer are set so that the shape of a characteristic curve giving a wavelength characteristic of transmittance changes along a transmittance axis according to a change in the Faraday rotation angle.

Abstract: A Gaussian approach (GA), which takes into account the influence of arbitrary optical and electrical filters, is proposed to analytically evaluate the performance of optically preamplified receivers. This GA also takes into account the effects of waveform distortion in the signal and in the signal-amplified spontaneous emission beat noise. Exact expressions for the mean and variance of the current at the decision circuit input are derived, which explicitly present the dependence on the optical and electrical filter transfer functions and take into account the presence or absence of a polariser. This GA is computationally much faster and simpler than more rigorous methods and the accuracy of its sensitivity estimates is investigated for different optical and electrical filters. It is shown that the GA predicts the optimal optical filter bandwidth very reasonably. Discrepancies below 1.2 dB are found between its sensitivity estimates and rigorous estimates. The assessment of the optical filter detuning impact on the receiver sensitivity is also investigated with this GA. Discrepancies less than 1 dB are found between the GA estimates and rigorous estimates. The GA sensitivity estimate's accuracy is also investigated in the presence of intersymbol interference (ISI) and very accurate predictions are obtained by the GA for significant ISI.

Abstract: The present invention provides a three-dimensional measuring apparatus comprising a light projector for projecting light to an object, a light receiving element, a light receiving optical system for leading light projected on and then reflected by the object to the light receiving element, and a calculator for obtaining measured data for three-dimensional shape measurement based on signals output from the light receiving element. The light receiving optical system includes a first optical filter which transmits only light having substantially the same range of wavelengths as that of the light projected from the light projector, at least one second optical filter which transmits light having a different range of wavelengths as that of the first optical filter and a filter selector which selectively locates one of the first optical filter or the second filter or filters at an optical path of the light receiving optical system.

Abstract: We demonstrate a multigigahertz tunable transversal notch filter based on two uniform fiber Bragg gratings as slicing elements of a broad-band optical source. The tunability of the filter is achieved by wavelength tuning of the fiber gratings to adjust the basic time delay provided by a dispersive element.

Abstract: Optical filters and their manufacture, as well as the use of the optical filters in optical devices, such as polarizers and mirrors are described. The optical filters typically include a first reflective multilayer film, a second reflective multilayer film, and a lossy element disposed between the first and second reflective multilayer films.

Abstract: A tunable optical notch filter employing a Fabry-Perot etalon has a first partially reflective mirror and a second mirror with variable effective reflectivity Both the gap of the etalon and the effective reflectivity of the second mirror can be controlled, eg by TAB actuators, enabling a control of the central wavelength and the depth (loss) of the notch of the spectral response of the filter

Abstract: The authors present detailed, yet largely analytical, models for gain, optical bandwidth, and saturation power of vertical-cavity semiconductor optical amplifiers (VCSOAs) in reflection and transmission mode. Simple formulas for the gain-bandwidth product are derived. The saturation model considers a sublinear material gain, gain enhancement by the standing-wave effect, and all relevant carrier recombination mechanisms. Excellent agreement with measurements on novel 1.3-/spl mu/m VCSOAs is obtained. The models are used to analyze device performance and to investigate optimization options. Parameter plots are given which allow for an easy exploration of the VCSOA design space, matching desired performance data with the required mirror reflectivity and pump current.

Abstract: Recent reports from our laboratory have described a method for all-optical multivariate chemometric prediction from optical spectroscopy. The concept behind this optical approach is that a spectral pattern (a regression vector) can be encoded into the spectrum of an optical filter. The key element of these measurement schemes is the multivariate optical element (MOE), a multiwavelength interference-based spectral discriminator that is tied to the regression vector of a particular measurement. The fabrication of these MOEs is a complex operation that requires precise techniques. However, to date, no quantitative means of determining the allowable design/ manufacturing errors for MOEs has existed. The purpose of the present report is to show how the spectroscopy of a sample is used to define the accuracy with which MOEs must be designed and manufactured. We conclude this report with a general treatment of spectral tolerance and a worked example. The worked example is based on actual experimental measurements. We show how the spectral bandpass is defined operationally in a real problem, and how the statistics of the theoretical regression vector influence both the bandpass and the minimum tolerances. In the experimental example, we demonstrate that tolerances range continuously between 1 (totally tolerant) to approximately 10–3 (0.1% T) in this problem.

Abstract: Improved designs of optical multiplexing/demultiplexing module are disclosed for use in multiplexing a composite optical signal into respective individual channels or wavelengths or demultiplexing individual channels or wavelengths into a composite optical signal. According to one embodiment, the optical multiplexing/demultiplexing module comprises an array of collimators, an array of optical filters and an array of mirrors. The collimators are boned to a common substrate after being aligned with a respect optical filter. Different from the prior art devices, the aligned positions of the collimators are secured or help up by preformed wedges. A bonding agent is then applied only to respective contacts between the collimators and the wedges. The wedges are further bonded to a common substrate to secure the collimators.

Abstract: A color measuring sensor assembly includes an optical filter such as a linear variable filter, an optical detector array positioned directly opposite from the optical filter a predetermined distance, and a coherent fiber faceplate having a plurality of optical fibers interposed between the optical filter and the detector array. A light beam propagating through the fiber faceplate from the optical filter to the detector array projects an upright, noninverted image of the optical filter onto a photosensitive surface of the detector array. Each optical fiber in the fiber faceplate is of limited aperture to control the tendency of light to diverge and to increase the resolution capabilities of the sensor assembly. The color measuring sensor assembly can be incorporated with other components into a spectrometer device such as a portable calorimeter having a compact and rugged construction.

Abstract: Eyewear include lenses having spectral transmittances selected for viewing an object with respect to a background. The spectral transmittances are selected to provide a natural feel to scenes viewed with the eyewear. In one example, a lens for viewing a white golf ball includes an object-contrast spectral window that transmits radiation at wavelengths of about 440 nm, a background window that transmits wavelengths at about 550 nm, and a spectral-width window that transmits wavelengths between about 620 nm and 700 nm. Similar eyewear can be configured for other activities. Methods for selecting filters and lenses for such eyewear are also provided.

Abstract: New photonic filter structures for interference mitigation of microwave signals are presented. These fiber filters have a parallel topology, and comprise a grating based photonic bandpass filter, or a dual offset cavity structure based on a new noncommensurate delay-line approach. The new topologies overcome the problem of synthesizing both a narrow stopband and a very-wide and flat passband, to simultaneously excise interference with minimal impact on the wanted signal over a wide microwave range. Results demonstrate stopbands of around 1% of center frequency, wide-band flat transmission, and a shape factor of 10.5 that is the lowest reported for a photonic notch filter, in excellent agreement with predictions.

Abstract: A three-dimensional imaging method and system illuminates an object to be imaged with a light pattern that is formed from two or more light sub-patterns. The sub-patterns can each encompass the visible light spectrum or can be spatially varying intensity sub-patterns that each correspond to a red, green, or blue component. The light pattern is generated by a slotted planar member or an optical filter.

Abstract: We present a tunable interference filter for infrared and visible light that scans the desired part of the optical spectrum within milliseconds. A single pixel detector measures serially the intensity at selected wavelengths. This concept avoids expensive linear detectors as used for grating spectrometers. The tunable optical interference filter is fabricated by a new porous silicon batch technology using only two photolithography steps. The refractive index of this filter microplate is gradually modulated in depth to create a Bragg mirror or a Fabry-Perot bandpass filter for a transmission wavelength between 400 run and 6 gm. Two thermal bimorph micro-actuators tilt the plate by up to 90 degrees, changing the incidence angle of the beam to be analyzed. This tunes the wavelength transmitted to the detector by a factor of 1.25, e.g. from 4 to 5 mum. The filter area can be chosen between 0.27 mm x 0.70 mm and 2.50 mm x 3.00 mm, its thickness is typically 30 pm. The spectral finesse Delta lambda/lambda, of 25 is sufficient for most diagnosis applications, e.g. detection of CO2 and CO in combustion processes by their IR absorption bands. Online colorimetry and color correction of desktop printers can be envisaged. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: This paper overviews the properties and possible applications of long wavelength vertical-cavity semiconductor optical amplifiers (VCSOAs). A VCSOA operating in the 1.3-/spl mu/m wavelength region is presented. The device was fabricated using wafer bonding; it was optically pumped and operated in reflection mode. The reflectivity of the VCSOA top mirror was varied in the characterization of the device. Results are presented for 13 and 12 top mirror periods. By reducing the top mirror reflectivity, the amplifier gain, optical bandwidth, and saturation output power were simultaneously improved. For the case of 12 top mirror periods, rye demonstrate 13-dB fiber-to-fiber gain, 0.6 nm (100 GHz) optical bandwidth, a saturation output power of -3.5 dBm and a noise figure of 8.3 dB. The switching properties of the VCSOA are also briefly investigated. By modulating the pump laser, we have obtained a 46-dB extinction ratio in the output power, with the maximum output power corresponding to 7-dB fiber-to-fiber gain. All results are for continuous wave operation at room temperature.

Abstract: Spectroscopic system and spectrometers including an optical bandpass filter unit consisting of a plurality of bandpass regions and a spatial encoding unit for encoding discrete frequencies of light passing through the optical filter. The incorporation of the encoding unit allows the spectrometer system to use a detector consisting of one or a small number of elements, rather than using a more expensive detector array as is commonly used with filter-based spectrometers. The system can also include an integrating chamber that collects the light that is not transmitted through the bandpass filter unit and is substantially reflected, and redirects this light to strike the filter unit again, resulting in a significant increase in the optical power passing through the filter. The integrating chamber maximizes the return of the reflected light to the filter assembly and minimizes optical losses. The integrating chamber may be an orthogonal design to preserve the optical geometric characteristics of the light entering the chamber, even after multiple reflections from the optical filter.

Abstract: We propose a hollow optical waveguide with metal coating or dielectric multilayer coating to achieve sufficient reflectivity at guiding walls. Low-loss and polarization-insensitive propagation characteristics are predicted. The propagation constant is independent of the temperature, resulting in temperature-insensitive photonic waveguide devices, such as optical filters and grating optical demultiplexers. We demonstrate a hollow optical waveguide with metal-coated walls on a GaAs substrate, which was fabricated using dry etching. The propagation loss including the coupling loss with an input fiber was 2.6 dB/cm and 7.3 dB/cm for transverse electric (TE) mode and transverse magnetic (TM) mode, respectively.

Abstract: The invention is an optoelectronic (OE) crossbar switch ( 10 ) for both digital and analog signals, used either separately or combined, whose functions are reconfigurable and distributed. The invention allows multiple senders to be connected with multiple receivers simultaneously. The invention uses optical filters for wavelength division multiplexing and demultiplexing (WDM and WDD). A single fiber module input/output port carries multiple bi-directional signals that are optically filtered out in the module using WDM/WDD filters ( 12 ) at each sender/receiver and then selected after optical filtering using photodiode detectors ( 15 ) as detectors and switches. Laser transmitters ( 14 ), photodiode detectors ( 15 ), and smart electronics ( 18 ) are used to implement the crossbar switch functions. In addition to optical filters, the use of time division multiplexing (TDM) and code division multiple access (CDMA) implemented either electrically or optically are taught to increase the number of independent users that the distributed switch handles. The switch can be cascaded with other switches using optical bridging circuits ( 100 ) to create a scaleable interconnect fabric. An arbitration technique can be used which allows signals to be sent only when the intended receiver is capable of accepting these signals.

Abstract: In optoelectronic systems, package moisture can affect stress levels in dielectric coatings on MEMS devices. Specifically, as the moisture content in these dielectric coatings changes, there are concomitant changes in the material stress. These changes in material stress can affect the operation of the overall MEMS device. Specifically, in the context of tunable filters, moisture can lead to a drift in the size of the optical resonant cavity over time as changes in material stress affect the MEMS structures. According to the invention, a getter is added to the package to absorb moisture, and thereby stabilize the operation of the optical filter, and specifically prevent uncontrolled drift in the size of its optical cavity.

Abstract: A new topology for a tunable microwave photonic notch filter, which achieves a wide and continuous tuning range of FSR/2, is presented. The novel principle of tuning is based on changing optical variable attenuators only; consequently, a fixed wavelength laser can be used as the optical source. Experimental filter tuning results demonstrate a wide fractional tuning range of 50%, continuous tuning capability, and a notch filter shape that does not change as it is tuned, in very good agreement with predictions.

Abstract: A digital camera is provided with an optical filter unit 43 which is movable in the slide direction SL in front of the CCD 41 , and infrared light emitters 25 and 32 for emitting near-infrared light. The optical filter 43 has an infrared cut filter 45 for cutting light in the infrared range, and a visible light cut filter for selectively transmitting light of the infrared range by cutting light in the visible light range. While maintaining the identicalness of the main object, the infrared cut filter 45 is disposed above the CCD 41 to acquire visible light image data via the CCD 41 , and the object is irradiated with infrared light emitted from the infrared emitters 25 and 32 , and the visible light cut filter is disposed above the CCD 41 to acquire infrared image data, i.e., non-visible light image data, by the CCD 41 . As a result, a visible light image and a non-visible light image are easily acquired of the same object.

Abstract: A multi-channel optical device includes a first plurality of optical structures formed simultaneously using vapor deposition on different regions of a common substrate. Each optical structure in the plurality is comprised of a plurality of thin-film layers. The thickness of each layer in a given optical structure corresponds to a wavelength associated with one of the channels. A reflector has a surface parallel to the common substrate, and a transport region is disposed between the first plurality of optical structures and the reflector. An aperture is disposed at one end of the transport region, and the first plurality of optical structures are disposed along a length of the transport region. When an input optical signal is provided to the aperture, the device functions as an optical demultiplexer and output optical signals associated with different ones of the channels are generated at separate positions along a length of the transport region. When input optical signals are applied to separate positions along the length of the transport region, the device functions as an optical multiplexer and those input optical signals are combined in the transport region and output as a combined optical output signal at the aperture.

Abstract: Optical filters in, for example, a wavelength division multiplexing (WDM) fiber optic system or an optical waveguide device are utilized and provided The optical waveguide device comprises a lower substrate layer, an insulating dielectric layer and a waveguide ribs layer The insulating dielectric layer, having a first refractive index, is positioned above the lower substrate layer The waveguide ribs layer, having a second different refractive index, is positioned above the dielectric layer An optical waveguide is formed from the waveguide ribs layer for transmission of light In the waveguide ribs layer, an optical filter structure formed, wherein the optical filter structure is integrated onto the same substrate as the optical waveguide