USA As Represented by Secretary of the Navy

Howard E Rast

Richard C Adams

Sam DiVita

Hubert H Caspers

A continuously variable fiber-optic delay line is created from a deformable polymeric fiber in which lighter density elements, e.g. hydrogen, boron, carbon or oxygen, are diffused through the outer surface of the fiber. The diffusion of the lighter elements creates a non-light transmissive cladding that is of a refractive index that increases from the surface of the fiber towards its axis. The cladding longitudinally surrounds a light transmissive core and has a maximum refractive index that is less than any refractive index of the core. A single-mode, graded-index polymeric fiber is thereby created. By applying a reversible and controllable pressure to the exterior of the deformable fiber, the refractive index of the fiber can be changed accordingly. This change in refractive index permits one to continuously vary the time delay of a signal transmitted through a fixed length of the fiber.

Continuously variable fiber optic delay line using compressible media

A method for communicating with a decreased probability of detection by an unintended listening party uses frequency hopping and two substantially identical linearly polarized antennas whose polarization vector is synchronized to frequency. Synchronization of polarization with frequency is accomplished through specifically designed conductor-backed spiral antennas. For these conductor-backed spiral antennas, a change in frequency is synchronized to a change in the polarization vector of the communication signal. Since the receiving station will be programmed to alter its reception frequencies in accordance with those being transmitted, the second spiral antenna will automatically change its polarization upon making these frequency changes. A rapid change of polarization increases the difficulty in detecting and intercepting the communication by parties for whom the message was not intended.

Method for secure communications using spiral antennas

A direction finding apparatus and method for an RF signal are described which provide a variable time delay in fiber optic cables. A tunable transmitter launches optical emissions of several wavelengths into a plurality of fiber optic cables. Since the waveguide material of each cable exhibits anomalous dispersion of the optical emissions, large changes in group refractive index are provided as a function of the different wavelengths of the optical emissions. As a consequence, only small changes in the different wavelengths of the optical emissions produce large changes in the time delay of the different wavelengths of the optical emissions within a fixed length of the optical fiber cables. This apparatus and method produce sensitive angle of arrival determinations for RF signals.

Direction finding apparatus using tunable fiber optic delay line

A system automatically measures the strength of optical fibers by initiating a series of breaks in an optical fiber delivered from a supply spool. The fiber is stressed to failure in an automatically displacable jaw mechanism and the fiber is advanced and the measurement repeated. A computer-controller advances the fiber, records data and monitors jaw mechanism fracture parameters so that the strength distribution of a length of optical fiber is reliably determined.

Automated system for measuring the strength of optical fibers

A method detects incomplete coverage of hermetic coatings applied to opti fibers during in-line optical fiber fabrication procedures as well as off-line applications. A fluorescent material surrounds the core region of the optical fiber prior to the formation of the hermetic coating on the optical fiber and energy is radiated in the optical fiber to propagate in the cladding mode. This causes an excitation of the fluorescent material to fluoresce in response to the propagated energy. An appropriately disposed detector detects levels of emitted fluorescence along the length of the optical fiber to indicate where the hermetic coating is incomplete or where pinholes in the hermetic coating are located. Optionally, the fluorescent material is located outside of the cladding layer, inside of the cladding layer near its outer surface or throughout the cladding region to fluoresce when excited by the propagated energy. Different wavelengths of radiation can be used which excite different fluorescent materials so that pinholes or incomplete coating coverage can be detected in hermetic coatings that have different chemical compositions.

Method for detecting pinholes and incomplete coverage of hermetic

An optical gain control device limits the light intensity incident on a podetector or photomultiplier. A fluorescent medium is interposed between a monitored source of electromagnetic energy and the detector and is irradiated by a local oscillator. The irradiation is absorbed by the fluorescent material which undergoes an electronic transition from the ground state to a first excited state. Photons impinging on the fluorescent material from the monitored electromagnetic source cause another transition to a second, more excited state. When the relaxation occurs from the higher state back to the ground, the material fluoresces. Because the magnitude of the local oscillator irradiation is kept within prescribed limits, the number of ions in the fluorescing material which are brought to the first excited state stay within certain limits. Consequently, the impinging monitored electromagnetic energy cannot excite more ions to the second higher state than were irradiated to the first excited state. Thus, high energy bursts of the monitored electromagnetic energy will not be transmitted to the detection device. Including a blocking filter having one passband which directly receives the monitored electromagnetic energy and another filter having a different passband which is located between the fluorescing material and the detection device, the transmission of dangerous levels of electromagnetic energy is further prevented. Protection of the detection device is automatic and does not depend on any mechanical coaction to assure quick response and long-term high reliability.

Optical gain control device

A passive, high-speed, automatic shutter for controlling the transmission light energy of known wavelengths along a predetermined optical axis is provided to protect imaging devices against sudden, undesirable optical overload which may cause damage. A large plurality of contiguously positioned micro-channel optical waveguides is axially aligned parallel with the optical axis to intercept the light energy. The large plurality of micro-channel optical waveguides provides desirable maximization of resolution for transmitting the image to the imaging device. The micro-channel optical waveguides include a saturable absorber material which is selected for its property of absorbing the known wavelengths of light energy up to a determinable level of intensity and transmitting the known wavelengths of light energy when that determinable level of intensity is exceeded. When the determinable level of intensity is not exceeded, optical images are transmitted through the large plurality of micro-channel waveguides to the imaging device which may desirably be positioned in an off-axis, angular disposition. However, when the determinable level of intensity of the known wavelengths of light energy is exceeded, the large plurality of micro-channel optical waveguides including the saturable absorber material becomes effectively transparent and transmits all such light energy along its initial optical axis so that the excess level of intensity of light energy does not reach the off-axis imaging device.

Passive high-speed automatic shutter for imaging devices

Narrow-band detection of optical signals over a large field of view wherein the selective reflecting power of metallic vapors is employed. A modulated carrier signal to be detected is directed to a Brewster window of an enclosure containing a vapor such as mercury. Only the incident light of interest is reflected through an exit window and detected by means of a photo-multiplier.

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Solana Beach, CA, United States of America

Howard E Rast