Abstract: An optical fiber comprises a core having an elliptical cross section and a cladding having a circular cross section. The core has an aspect ratio between 2 and 40. The core and the cladding have a common central axis with the core being enclosed by the cladding. The difference of a refractive index of the cladding to a refractive index of the core is between 1×10?2 and 1.5×10?1. A trench is located between the core and the cladding. The trench has a uniform width and encircles the core. The refractive index of the trench is lower than the refractive index of the cladding.

Abstract: An optical fiber configured to improve the pump conversion efficiency of an L-band fiber amplifier which uses the multimode pump source. By directly absorbing multimode light including 915 nm, an active fiber core region co-doped with both erbium and ytterbium can provide gain to the L-band signals via stimulated emission. The unwanted C-band amplified spontaneous emission (ASE) light generate from this active fiber core region can be absorbed by another active fiber core region doped with erbium, then provides additional gain to the L-band signals. Active regions and cladding can be configured to match a given spatial mode of the optical signal. Signal-pump combiners with end-coupling or side coupling can be used.

Abstract: An optical fiber comprises a core having an elliptical cross section and a cladding having a circular cross section. The core has an ellipticity between 2 and 40. The core and the cladding have a common central axis with the core being enclosed by the cladding. The difference of a refractive index of the cladding to a refractive index of the core is between 1×10?2 and 1.5×10?1. A trench is located between the core and the cladding. The trench has a uniform width and encircles the core. The refractive index of the trench is lower than the refractive index of the cladding.

Abstract: An improved method and apparatus for optical and radio frequency implementation of a fast frequency hopping spread spectrum communication for code division multiple access systems is disclosed. The method avoids the frequency hopping synthesizer requirements in the transmitter as well as in the receiver. In a system where a pool of CDMA users share a channel characterized by a number of F available frequencies (or frequency bands), each user is assigned a subset of M (M less than or equal to F) frequencies from the F available frequencies, selected and ordered in time as prescribed by his own code (or address). In the transmitter, the information bit sequence modulates a broadband source so that the energy assigned to a data bit is concentrated on just a short interval of the bit period which is less than or equal to the so-called chip interval.

Abstract: An improved method and apparatus for optical and radio frequency implementation of a fast frequency hopping spread spectrum communication for code division multiple access systems is disclosed. The method avoids the frequency hopping synthesizer requirements in the transmitter as well as in the receiver. In a system where a pool of CDMA users share a channel characterized by a number of F available frequencies (or frequency bands), each user is assigned a subset of M (M less than or equal to F) frequencies from the F available frequencies, selected and ordered in time as prescribed by his own code (or address). In the transmitter, the information bit sequence modulates a broadband source so that the energy assigned to a data bit is concentrated on just a short interval of the bit period which is less than or equal to the so-called chip interval.

Abstract: An optical identification friend-or-foe (IFF) system for vehicles comprises an active cooperative identification friend-or-foe (ACTIFF) system wherein a responder optical head is located on each friendly vehicle. That responder optical head comprises a number of small panels arranged in an array with surfaces of adjacent panels being at an angle to each other, the outer surfaces of the panels being coated with laser paint designed to emit radiation at one or more selective wavelengths when subjected to a suitable interrogation pump beam. Those selective wavelengths form an identification code for a vehicle. In operation, an interrogating vehicle would transmit a narrow well-collimated infrared (IR) beam towards a target vehicle causing laser paint on the coated surfaces to emit the selective wavelengths when subjected to that IR beam. These wavelengths can then be detected by the interrogating vehicle for identification purposes.