Abstract: A limiter for limiting selected frequency components by generating Stokes waves in a stimulated Brillouin scattering medium. The generated Stokes waves create a seed that is provided to another stimulated Brillouin scattering medium. The seed selecting the undesired frequency components to be attenuated.

Abstract: An apparatus containing an integrated optical circuit that enhances phase stability of the injection-locking process of two slave lasers. The integrated optical circuit helps to reduce phase noise by keeping environmental or mechanical perturbations uniform everywhere on that circuit. Also, the integrated optical circuit provides connections for additional components to be coupled, which can monitor and control the performance characteristics of the integrated optical circuit and the injection-locking process.

Abstract: A method for minimizing the generation of interferometric intermodulation distortion in an analog fiber optic link that employs a directly modulated diode laser as its optical source. This is accomplished via the reduction of frequency chirp in the current-modulated diode laser source (32). To reduce frequency chirp, the diode laser (32) is coupled to an external reflector (52), so that an external laser cavity with a long, passive section is formed. Specifically, the frequency chirp of this extended laser cavity is reduced from that of the original diode laser by the ratio of the optical path length in the external cavity to that in the diode. The external reflector (52) can also be integrated, via splicing, to the fiber pigtail (54) of the laser transmitter (50) so that the compact geometric form factor of a diode transmitter is preserved.

Abstract: An apparatus and method for photonically sampling an analog signal and encoding the photonically sampled signal. The two interferometer arms of a Mach-Zehnder interferometer section are directly coupled to the dual input ports of a directional coupler switch section. Optical pulses transmitted through the interferometer arms are phase shifted in proportion to an analog signal applied at the electrical input port of the Mach-Zehnder interferometer section. The phase-shifted pulses in each interferometer arm are coupled in the directional coupler switch section and are directed to the dual output ports of the directional switch section based upon the binary code applied to the electrical input port of the directional coupler switch section. The directional switch section has an optical length designed to provide a net phase shift of 3&pgr;/4.

Abstract: An apparatus and method for photonically sampling an analog signal and encoding the photonically sampled signal. The two interferometer arms of a Mach-Zehnder interferometer section are directly coupled to the dual input ports of a directional coupler switch section. Optical pulses transmitted through the interferometer arms are phase shifted in proportion to an analog signal applied at the electrical input port of the Mach-Zehnder interferometer section. The phase-shifted pulses in each interferometer arm are coupled in the directional coupler switch section and are directed to the dual output ports of the directional switch section based upon the binary code applied to the electrical input port of the directional coupler switch section. The directional switch section has an optical length designed to provide a net phase shift of 3&pgr;/4.

Abstract: A substantially lossless transmissive link, such as an RF fiber optic link, that selectively employs a number of techniques to improve various link parameters. The link may be structured to comprise a high power light source, such as a laser, that provides light output having a high level of optical power. A feedback circuit may be disposed around the light source that reduces relative-intensity-noise levels produced by the light source at low frequencies. A modulator is provided that modulates the light output of the light source. Preferably, a dual output modulator may be used to provide two modulated optical signals whose respective RF modulation is “effectively” 180 degrees out of phase. An optical fiber that transmits the modulated optical signal(s). A photodetector without a load resistor directly on its output that is operable at the high level of optical power, receives the modulated light and recovers the RF signal.

Abstract: Linearly-polarized, single-frequency fiber lasers are realized with optical fibers that have first and second refractive indices in a first fiber grating and third and fourth refractive indices in a second fiber grating. The first and third refractive indices are arranged along a first transverse fiber axis and the second and fourth refractive indices are arranged along a second transverse fiber axis. The grating periods and the first and third refractive indices are selected to generate spectrally-aligned signal reflectances along the first transverse axis and the grating periods and the second and fourth refractive indices are selected to generate spectrally-spaced signal reflectances along the second transverse axis. Thus, a fiber resonator is formed only along the first transverse axis and the fiber laser's output signal is linearly polarized.

Abstract: A method for creating nonuniform grating strengths within fiber optic includes exposing photosensitive fiber optic material to an optical source for various periods of time through a mask. As the fiber optic material is exposed, the grating strength of the fiber changes. By linearly exposing the fiber optic material to different durations of optical energy, nonuniform grating strengths are created within the fiber, thereby creating a fiber optic section having asymmetric grating strengths.

Abstract: A distributed feedback fiber laser having designed asymmetric power output ports is disclosed. The present invention uses nonuniform grating strengths in a laser cavity of an erbium doped fiber optic material to create nonuniform reflection within the cavity. The stronger the grating strength in a particular section of the cavity, the more reflectivity that section has. This construction results in a fiber laser having two output ports with different output intensities. In a method for creating nonuniform grating strengths within the fiber optic material, photosensitive fiber optic material is exposed to an optical source through a mask. As the fiber optic material is exposed, the grating strength of the fiber is changed. By linearly exposing the fiber optic material to different durations of optical energy, nonuniform grating strengths are created within the fiber.

Abstract: An optical heterodyne system provides the radiation source and beam scan control of a millimeter wave (MMW) array antenna. The heterodyne system is an optical feed system to produce the MMW by mixing the optical outputs from two lasers, distribute the signal source to an array of radiating elements through a Rotman lens and optical fibers, generate the differential phase shift for beam scan in the optical domain, change the beam direction by switching the input laser being used to illuminate the Rotman lens or by varying the frequency of one of the laser sources. The feed system includes a plurality n-1 lasers spaced along the transmit side of the lens, and a center laser disposed on the center axis of the transmit side. A l:n switch receives a command input to determine which of the n-1 lasers will operate. The beat frequency between the center laser operating frequency and that of the n-1 lasers is the MMW frequency.

Abstract: An optical receiver with an enhanced power capability and wide bandwidth is implemented by distributing a number of photodetectors along an optical transmission channel to convert respective portions of an optical signal into electrical signals. An electrical transmission line receives and accumulates signal inputs from the photodetectors. A velocity matching is established between the optical and electrical signals, allowing the photodetector outputs to accumulate coherently along the electrical transmission line, by loading the transmission line with distributed capacitance elements. The loading capacitances are preferably inherent in the photodetectors, which are designed and spaced apart from each other to yield the desired velocity matching.

Abstract: Optoelectronic switching apparatus employing optoelectronic switching devices interconnected by optical media having different delay lengths and an multiport optical coupler. The optoelectronic switching apparatus provides for a multibit true-time-delay beamsteerer for beamsteering phased array antennas. The present invention combines two types of optoelectronic devices, lasers and photodiode switches, using an interconnected passive optical network comprising the optical fibers and the optical coupler. The switches, and input and output signal networks coupled to the respective switches, are controlled using a control signal generator. Using this scheme, any input can be independently selected and a signal can be routed to any output. Furthermore, the product of the total number of different interconnect paths (N.times.M) is provided which provides a greater number of delay lengths than is provided by using only one type of switch (i.e. laser (N) or photodiode (M)) alone.

Abstract: A single transmission optical fiber is used to transmit RF signals of the same frequency but different polarization from a source to a polarization diversity receiver without introducing interference between the signals. The incoming signal of one polarization modulates a first laser transmitter operating at one wavelength, and the incoming signal of the other polarization modulates a second laser transmitter operating at a different, second wavelength. The two modulated optical beams are combined in an optical coupler whose output is connected to the transmission fiber leading to the polarization diversity receiver. At the receiver, a wavelength division multiplexing coupler is used to separate out the two modulated optical carriers. The two RF signals used to modulate the laser transmitters are separately recovered via photodiode detectors to provide inputs to the polarization diversity receiver.

Abstract: A time delay network for phased array antenna beam steering employs a waveguide network as the delay element in a monolithic integration with other optical and electronic elements on a single substrate. A plurality of optical time delay stages are cascaded to form the delay network, with each stage having a selectable delay time. Each stage preferably has a reference or nominal time delay branch, and at least one other finite time delay branch. The lengths of the delay waveguides vary from stage to stage, permitting a high time delay resolution with a relatively small number of separate waveguides. The desired time delay is selected either by directing the modulated laser light into only one of the waveguide branches in each stage by means of waveguide switches or by splitting the light into all the waveguide branches of a stage and then activating only the detector connected to the desired delay waveguide. A variety of cascading schemes and waveguide layouts can be used to implement the time delay network.

Abstract: The device provided is a GaInAsP/InP laser, of the buried heterostructure type, fabricated by a two-step liquid-phase epitaxy technique. The active region is defined by a mesa etch to achieve low threshold current and a single transverse optical mode. The mesa is subsequently buried by a second step of liquid-phase epitaxy for optical and current confinement. A low bandgap heterobarrier is employed to reduce leakage current near the active region at high current biases. A contact layer is grown directly over a majority carrier confining clad layer to reduce defects in the crystal face on the side of the clad layer, and thereby further reduce leakage current.