Abstract: A surface-emitting photonic crystal distributed feedback laser apparatus configured to emit an optical beam of light. The apparatus includes a laser cavity bounded by top and bottom optical claddings, an active region configured to produce optical gain upon receiving optical or electrical pumping, a periodic two-dimensional grating having an order higher than the fundamental and configured to induce modulation of a modal refractive index, and lateral pumped gain area contained within an area covered by the grating, the lateral pumped gain area configured to produce gain in one or more lasing modes having a modal index modulated by the grating. The lateral pumped gain area has a substantially circular shape of diameter D, and wherein the pumped gain area is enclosed by an unpumped region contained within the area covered by the grating but not receiving the optical or electrical pumping.

Abstract: An array antenna apparatus for producing a time-delay beamformed RF signal includes a laser, a modulator for RF modulating the laser optical signal, a first plurality of optical paths coupling the modulator output to a dispersive prism, another plurality of optical paths coupling the dispersive prism outputs to a corresponding plurality of time delay trimmers, an attenuator coupled to each time delay trimmer, and an optical switching matrix to which the time delay trimmers outputs are input. The inputs to the optical switching matrix accordingly are time and amplitude adjusted to remove front end errors prior to rerouting. This is repeated in the back end of the apparatus, in which the switching matrix outputs are each applied to a corresponding attenuator, the outputs of which are then each applied to a photodetector to generate a plurality of replica RF signals that are each applied to a time shifter, thereby producing an error-corrected output that is then applied to an antenna array.

Abstract: An NQR apparatus for irradiating a sample with an RF magnetic field and for determining the presence of a target material by detecting an NQR signal includes a transmitter for generating an output signal at a selected frequency, a receiver for detecting the NQR signal, a probe, and a switch coupling the receiver and the transmitter with the probe for alternately connecting and disconnecting the receiver and the transmitter to the probe, thereby switching the NQR apparatus between a transmitting mode and a receiving mode. The probe consists of a resonant circuit that includes a coil array. The coil array includes a first figure-8 coil and a partially overlapping, second figure-8 coil for generating an RF magnetic field in a detecting region outside the probe.

Abstract: A method for defining targets in hyperspectral image data of a scene, has the steps: (1) identifying a target within the scene; (2) fitting a plurality of conjoined hyperplanes about the target in the scene; and (3) fitting a shape to the identified target by shrinkwrapping the hyperplanes about the target by translating and rotating the hyperplanes until a specified fit parameter is satisfied.

Abstract: A control method and system are provided to sustain chaos in a nonlinear dynamic system. A sustained transient that is tracked as a system parameter is substantially varied thereby allowing sustained chaotic transients to exist far away from the crisis parameter values. The method includes targeting points near a chaotic transient once the iterates reach a neighborhood of an undesired attractor. Targeting is done so that the natural dynamics of the system would not engage again the iterations and chaotic motion. A brief parameter fluctuation forces the attractor to be a repeller so that a point which lies on the previously existing chaotic transient can be targeted. Consequently, instead of landing on the attractor, the iterations will reach a region of phase space where a chaotic transient is present, causing the chaotic motion to be reexcited.

Abstract: An optical fiber includes a core doped with a preselected gain material, an inner cladding disposed about the core, an outer cladding, disposed about the inner cladding, that has a section removed to expose a portion of the inner cladding, a notch disposed in the exposed portion of the inner cladding, and a mirror disposed within the notch that includes a high reflectivity surface oriented so as to reflect light launched into the mirror from an outside source into the fiber. The mirror, e.g. a right-angle trihedron, has a high reflectivity (HR) coating on one face, is inserted into the notch, and affixed thereto with an adhesive such as an optical cement. Pump light, e.g. from a laser diode, is launched through a face of the mirror that is antireflection (AR) coated or sufficiently transparent to the light frequency, and after reflecting off the HR face exits through a third face and into the fiber.

Abstract: An apparatus for processing passive acoustic signals received on a horizontal line array that were either emitted from an underwater object or echo returned from an object, is proposed to display a radar-like range-bearing image of the object, thereby showing the location of the object relative to the receiver horizontal line array. The range-bearing images can be created at different water depth to search for an underwater object in a three-dimensional space. The method includes receiving an acoustic signal from the target, determining a beam covariance matrix, determining a replica field for a range-bearing of the target, determining a replica beam from the replica field; and processing the beam covariance matrix and the replica beam to determine range-bearing ambiguity surface and estimate depth ambiguity for selected peaks of the ambiguity surface.

Abstract: A trigger circuit is provided for a trigger system for a Marx generator column. The column includes a plurality of metal electrode pairs wherein the electrodes of each pair are spaced to form a spark gap therebetween and a capacitor is connected across each gap. The trigger system includes a three electrode (trigatron) spark gap switch forming the first spark gap of the Marx generator column. The triggering circuit includes a trigger transformer having primary and secondary windings. The secondary winding is connected through a connecting cable to a blocking capacitor of an input circuit of the trigatron switch. A charging capacitor is connected to an oscillator power supply so as to be charged thereby to the output voltage (e.g., 345 volts) of the oscillator power supply. An electronic switch (e.g.

Abstract: An apparatus for phase coherent underwater communications includes a transmitter; a receiver, including a processor for jointly performing coherent diversity combining, carrier recovery, channel equalization and synchronization; and an antenna array that includes a plurality of antenna sub-arrays for alternately transmitting a signal generated by the transmitter and for receiving an incoming signal. Each of the antenna sub-arrays includes a plurality of underwater sensors positioned such that each of the sensors is spaced at about one half the wavelength of the receiver/transmitter operating frequency from any adjacent sensor in the same sub-array. At least one of the sub-arrays has a centerpoint vertically spaced apart from a centerpoint of an adjacent sub-array at a distance about equal to or larger than a vertical correlation length of a received signal. The individual sub-arrays are beamformed, e.g. using a plane-wave delay-and-sum (or phase-steering) method.

Abstract: A new optical sensing device containing fiber Bragg gratings, a scanning bandpass filter, an interferometer and multiple photodetectors is disclosed. The present invention also describes a new system and method for fibre Bragg grating (FBG) sensor interrogation and multiplexing. The new system combines a scanning Fabry-Perot (SFP) bandpass filter used to wavelength-multiplex multiple gratings in a single fiber, and an unbalanced Mach-Zehnder fibre interferometer made with a 3×3 coupler to detect strain-induced wavelength shifts. A passive technique for interferometer drift compensation using non-sensing FBGs is included in the system. A complete prototype system interrogates four gratings in a single fiber at a Nyquist sampling rate up to 10 kHz, with a noise floor measured near 4 n&egr; Hz−1/2 above 0.1 Hz. The inclusion of the interferometer drift compensation technique is shown to make quasi-static measurements feasible.

Abstract: The present invention describes a system for counteracting countermeasures against radar detection. Two known countermeasures are “phase front tilting” and “isotropic scattering.” The invention accomplishes this counteraction by deliberately producing a tilt in the phase front of the transmitted energy. This causes the phase front tilting countermeasure itself to become a tracking signal source for the radar system. The isotropic scatterer types of countermeasures are insensitive to the phase front of the transmitted energy and hence produce return signals which may be distinguished from a true radar echo return signal which is highly sensitive to the phase front of the transmitted energy. Thus this invention provides a radar system having a high degree of immunity to radar countermeasure devices.

Abstract: An apparatus for measuring the amount of motion of the surface of a microscopic object includes a light source, an optical fiber for transmitting the light, and a collection objective. The optical fiber emits the light output through an aperture tapered to a diameter in the range of from 20 nm to 200 nm. The collection objective is positioned to receive both the direct component of the fiber light output and the Doppler-shifted reflected light of the fiber light output from the surface of the object. The direct component and the Doppler-shifted reflected light combine in the collection objective to form an interfered light signal that is output to a photo-receiver. The intensity of the interfered light signal is modulated by the relative phase shift between the two interfering beams and is proportional to the out-of-plane displacement caused by the surface motion of the object surface.

Abstract: An apparatus for receiving optical pump radiation having a wavelength &lgr;p and transmitting pump light to an active region. The apparatus includes a first and second reflector, each reflector being reflective at the wavelength &lgr;p, disposed on opposite sides of the active region, where the separation between the reflectors creates a cavity that is resonant at the pump wavelength &lgr;p. The separation distance is preferably about m&lgr;p/2n cos &thgr;, where n is the average index of refraction of the material having an active region, &thgr; is the angle that the pump beam transverses relative the normal of said reflectors, and m is any positive integer. The apparatus provides low cost, high power, optically pumped edge emitting and surface emitting lasers which can be operated at elevated temperatures or power levels. The apparatus further provides mid-IR, high power optically pumped semiconductor lasers with high pump absorbance, long pump wavelength, and a thin active layer.

Abstract: A new type of frequency-tunable active notch filter achieves frequency selectivity through interaction among input derived signal components that are passed through parallel signal channels in a forward-only direction. The notch filter differs from earlier channelized notch filters by using multiple, instead of just one, bandpass channels that maintain required forward signal flow in the main, passband-determining signal path without signal distortion at passband frequencies. The new approach has been experimentally verified with a hybrid-integrated three-channel filter whose 40-dB-deep band-reject notch can be continuously tuned, with the help of voltage-controlled variable-capacitance elements, from 9.5 to 10.5 GHz. A single-pole bandpass filter tunes in frequency with the help of only one variable capacitance element, yet still maintains constant passband width across the tuning span.

Abstract: A method and system are provided for obtaining acoustic data for use in determining fish populations in shallow waters. The system includes an acoustic source comprising a buoyancy unit, anchor, and a broadband acoustic transmitter, and a cable which connects the buoyancy unit to the anchor and supports the transmitter. The system also includes one or more acoustic receivers employing hydrophones and including a similar buoyancy unit, anchor, and cable. When the source and receiver are (separately) deployed, the respective cables are released so that the buoyancy units rise in the water. Thus, with the source and receiver anchored to the bottom the transmitter and hydrophones are suspended at a depth near the bottom (below the thermocline if there is a thermocline) determined by the cable length released. At this time, acoustic signals are transmitted from the acoustic transmitter to the hydrophones for recording.

Abstract: A signal processing apparatus for providing electrical frequency measurements of input signals. In one embodiment, a power splitter divides an RF input signal into first and second input signals. An RF channelizer having a filter bank receives the first input signal and determines a coarse frequency measurement. An optical modulator modulates an optical carrier signal with the second input signal, and a beam splitter divides the modulated carrier signal into a plurality of optical signals that each feed into one of a plurality of optical frequency discriminators (“OFD”). Each OFD uses a fiber optic delay line and spatial domain sampling techniques to extract a phase measurement. An ambiguity resolver receives the phase measurement from each OFD and determines a single, absolute phase measurement, which is translated to a fine frequency measurement. A frequency encoder combines the coarse and fine frequency measurements to produce a final frequency measurement having increased resolution.

Abstract: A method and apparatus for increasing the upper frequency range of an optical communication system, particularly one designed to communicate over, repeaterless, distances. A series of temporally interleaved optical solitons of different frequencies are generated, and transmitted and detected by wavelength division multiplexing. An adiabatic transmission line forms part of the transmission link, and serves to narrow the bandwidth of the pulses during propagation. As a result, one can generate the solitons with substantially overlapping spectra, thus increasing the rate at which they are produced, but, because of the narrowed spectra, still resolve them in frequency at the system's receiver.

Abstract: A new pipeline method and apparatus for photonic analog-to-digital converters (ADCs) utilizing wavelength division multiplexing (WDM) and distributed phase modulation is disclosed. The analog-to-digital conversion is performed within the optical system of the ADC, and thus the optical output is a digital bit pattern. The optical output of this system thus facilitates ADC conversion at much higher speeds than available with conventional electronic ADCs. Phase modulators and polarization-based optics are used to map an input analog waveform into a binary output.

Abstract: Various embodiments of low-mass sound generators each having a wide frequency band are disclosed. In some embodiments, the acoustic transducer acting as the sound generator is constructed of four layers of PVDF film. The top and bottom bi-laminate members are separately formed in a pre-curved manner to form a rippled geometry.

Abstract: A method and apparatus for interrogating a resonator to monitor its resonance characteristics (e.g. resonant frequency) in an especially energy efficient manner, particularly changes to the characteristics over time. The resonator is pulsed and the response thereto sampled. By comparison of samples of the response to sequential pulses, sampled at the same times after pulse initiation, one can infer phase changes between the responses, and hence infer changes in resonance characteristics. Preferably, one calibrates the resonator's time response initially as a reference, which permits subsequent determination of the resonance state with only one digital sample per pulse. In one embodiment, the invention this detection scheme is used as a chemical detector. The resonator is an electo-acoustic device, having plural Bragg gratings, with a different adsorptive material atop each grating which adsorbs one selected chemical particularly well.