Abstract: Accurate and efficient synchronization of two pulsed radiation sources (e.g. iwo mode locked lasers) is accomplished in stages. Rough synchronization is accomplished by synchronizing (for example) the fundamental repetition rate of the two lasers. Fine synchronization is accomplished by synchronizing high harmonics of the two lasers. More accurate synchronization may be accomplished by adding more stages, by utilizing light out of a nonlinear laser in which the two beams are crossed, or by utilizing heterodyne beats of the two laser beams. A dc offset signal may added to the control signal generated by the synchronization stages.

Abstract: Apparatus for collecting light from an LED and transmitting it in a near-uniform column incudes a conical reflector about the base of the LED for collecting light emitted to the sides of the LED, and a lens specially designed to focus the collected light into a near-collimated beam. The lens has opposite, substantially elliptical surfaces to collect and collimate the rapidly diverging light from the LED and the reflector, and each lens surface includes a flat spot to prevent shadows from forming, thereby producing a more uniform beam.

Abstract: A laser amplifier system amplifies pulses in a single “stage” from ˜10−9 joules to more than 10−3 joules, with average power of 1-10 watts, and beam quality M2<2. The laser medium is cooled substantially below room temperature, as a means to improve the optical and thermal characteristics of the medium. This is done with the medium inside a sealed, evacuated or purged cell to avoid moisture or other materials condensing on the surface. A “seed” pulse from a separate laser is passed through the laser medium, one or more times, in any of a variety of configurations including single-pass, multiple-pass, and regenerative amplifier configurations.

Abstract: A precise, tunable, low loss add/drop filter for use in fiber optic communication systems utilizes a cascaded system of Mach Zender-like stages, along with reflective elements to return passed channels to the output pass+add signal while transmitted signal(s) appear at the drop port. The optional add signal follows the reverse path of the drop signal and is added to the pass signal.

Abstract: A digital hearing aid according to the present invention is capable of measuring its own performance. The hearing aid includes a test signal generator for feeding a test signal into the hearing aid amplifier. The response to the test signal is acquired at a specific point in the hearing aid, depending upon what aspect of performance is to be measured. Various elements of the hearing aid and/or the hearing aid feedback may be bypassed. The hearing aid further includes the capability of initializing hearing aid parameters based upon the performance measurements. The measurement and initialization capability may be entirely integral to the hearing aid, or an external processor may be used to download the measurement program and the run time program, and assist in computing the parameters.

Abstract: A polarization insensitive tunable optical filter system combines an interference filter or the like with a quarter wave plate and a retro-reflector. The retro-reflector is situated and aligned to intercept light reflected from the filter, and the quarter wave plate is disposed between the filter and the retro-reflector. Hence, the pass signal reflected off the filter a first time passes through the quarter wave plate a first time, reflects off of the retro-reflector, passes through the quarter wave plate a second time, and reflects off of the filter a second time.

Abstract: A fuel cell using fuel and oxidant resulting in the production of water and heat in addition to electrical power. The fuel cell employs an evaporative cooler and has methods to adjust the moisture and temperature for the fuel and oxidant flows to improve the fuel cell efficiency. The water produced by the fuel cell is used to provide the water for wet channels of the evaporative cooler. The evaporative cooler has separate product channels and dry working channels that are cooled by heat transfer across a heat exchanger plate. The heat exchanger plate forms part of each wet working channel on the wet side of the heat exchanger plate and part of the product channel and the dry working channel on the dry side. The fuel passes first through the dry working channel then the wet working channel becoming humidified by the evaporation therein and cooling the heat exchanger plate before going to the anode of the fuel cell.

Abstract: The present invention relates to a method and an apparatus for providing enhanced indirect evaporative cooling of air, water, fuel, or other fluids while controlling the humidity. The design makes cooling down to the dew point possible without energy input other than the energy to produce the fluid flow needed. The design makes use of stacked composite plates (7) with channels (1, 2) for fluid flow between adjacent plates. On opposing surface areas of these plates, there are wet areas (4) or dry areas (3). The wet areas (4) provide cooling by conventional evaporation which is in turn used to cool the fluids in contact with the dry areas (3). The benefit is controlled heat transfer, which allows selected cooling of fluid flow such that the temperature as low as dew point are reachable.

Abstract: Apparatus and methods for imaging multiple fluorescent sample particles in a flow channel. A flow channel defines a flow direction for samples in a flow stream and has a viewing plane perpendicular to the flow direction. A clear volume between the illuminated flow volume and the imaging optics is provided. A beam of illumination is formed as a column having a size effective to cover the viewing plane, and illuminates the flow nearly end on, or from the side. Imaging optics are arranged to view the focal plane to form an image of the multiple fluorescent sample particles in the flow stream. A camera records the image formed by the imaging optics. A computer detects and enumerates the particles in the flow.

Abstract: Methods and apparatus are disclosed for detecting manufacturing defects on unpopulated printed circuit boards under test (BUT) utilizing reliable single point current measurement. In a first set of preferred embodiments, an AC signal generator is connected to a signal plate placed under the BUT for applying an electrical field and thereby generating signals in conductors of the BUT. An array of pins mounted on an assembly on top of the BUT at fixed intervals samples currents from the test points on the BUT. In a second set of preferred embodiments, the AC signal generator is connected to the pin array, and the pins apply test signals into the conductive elements of the BUT at fixed intervals. The signal plate detects the electrical field on the BUT. The detected signals are analyzed to discern board faults.

Abstract: Methods and apparatus are disclosed for detecting manufacturing defects on unpopulated printed circuit boards under test (BUT) utilizing reliable single point current measurement. In a first set of preferred embodiments, an AC signal generator is connected to a signal plate placed under the BUT for applying an electrical field and thereby generating signals in conductors of the BUT. An array of pins mounted on an assembly on top of the BUT at fixed intervals samples currents from the test points on the BUT. In a second set of preferred embodiments, the AC signal generator is connected to the pin array, and the pins apply test signals into the conductive elements of the BUT at fixed intervals. The signal plate detects the electrical field on the BUT. The detected signals are analyzed to discern board faults.

Abstract: An improved method and apparatus for indirect evaporative cooling of a fluid stream to substantially its dew point temperature. Plate heat exchanger has perforations (11) and channels (3, 4 and 5) for gas on a dry side and wet side. There is a trough formed in a portion of the plate that temporarily holds evaporative fluid which is in contact with the wick material on the wet side surface of the plate. The evaporative fluid flows through the trough by way of liquid perforations into the next trough. The trough of a plate with a wet side up, the liquid perforations are on the side creating a reservoir to wet the opposing wick materials. As streams flow across the dry side (9), transferring heat to the plate. Working gas stream (2) flows across the dry side and through perforations to channels (5) on wet side (10), which it then cools by evaporative cooling as well as conductive and radiative transfer of heat from plate.

Abstract: By construction of heat pipes with two phase heat carrying fluid, an efficient heat transfer system is available. The heating section is used to create, within the heat pipe, build up of vapor pressure which causes the heat carrying fluid to move which then allows for dissipations of the heat into the cooling section. Additions to the system allow for storage of kinetic energy to enhance or regulate the flow, and by introduction of heating elements or porous surfaces, the mechanic can be improved or regulated.

Abstract: A 1×N optical switch according to the present invention switches between output fibers without the need for active alignment by utilizing two beam deflecting stages, for example first passing the input beam through a translating element and then through a beam angle adjusting element. The translating element directs the input beam toward the selected fiber, and the angle adjusting element directs the beam toward the core of the selected fiber.

Abstract: Apparatus and methods for switching an optical signal between a first path and a second path, where the switching occurs continuously such that substantially all of the optical signal passes through the first path or the second path during switching.

Abstract: Apparatus and methods for audio compression and frequency shifting retain the spectral shape of an audio input signal while compressing and shifting its frequency. The fast Fourier transform of the input signal is generated, to allow processing in the frequency domain. The input audio signal is divided into small time segments, and each is subjected to frequency analysis. Frequency processing includes compression and optional frequency shifting. The inverse fast Fourier transform function is performed on the compressed and frequency shifted spectrum, to compose an output audio signal, equal in duration to the original signal. The output signal is then provided to the listener with appropriate amplification to insure audible speech across the usable frequency range.

Abstract: An optical sensing system for detecting welds and defects in metal brightly illuminates a broad section of the metal and images a swath of the metal onto a multi-element detector array, generating voltage signals representing the reflectivity of the swath of the metal as it passes under the detector. A processor system detects areas of low reflectivity and indicates a defect. A slit mask placed in front of the detector array narrows the imaged swath to reduce false accepts. A color filter in front of the detector array reduces ambient light interference. The processor system incorporates an auto-calibration function to compare the current signal to an averaged reference signal.

Abstract: The proposed holographic particle image velocimetry (HPIV) system employs holograms of two time-separated particle fields, illuminated by separate reference beams on a single recording medium. 90-degree scattering is utilized for the object wave, in order to improve Numerical Aperture and resolve the third dimension of the hologram. The proposed HPIV system then uses substantially the same optical geometry for the reconstruction process. A CCD camera is utilized to extract particle subimages, thin slice by thin slice, and a centroid-finding algorithm is applied to extract centroid locations for each volume. The concise cross correlation (CCC) algorithm for extracting velocity vector fields from the centroid data is an important enabling feature of the proposed system. Correlations are calculated between subsets of centroids representing the images or cubes, and velocity vectors are computed from the individual correlations.

Abstract: A technique for correcting higher order delta sigma modulators in audio components, which use mutually nonlinear feedback and feed forward functions. Methods and apparatus are provided to correct jitter and spread in the delta sigma converter due to quantization error, to permit the processing of data streams entering the converter at a different clock rate from that of the modulator, and to permit step up ratios to be changed on the fly in order to reduce radio frequency interference from the output signal.