General Dynamics Corporation

General Dynamics Corporation, Electronics Division

Tacan Corporation

Mark E Curran

An optical modulator or laser source has a detector for detecting its output signal and for producing a corresponding output signal. A tapping device is connected to tap off a portion of the input modulation signal as a reference signal. The reference signal is compared and subtracted from the detector output signal by a subtraction unit in order to produce an error output signal which will be proportional to the laser noise/distortion components. This error signal is amplified and connected to an external modulator linked to the laser optical output and intensity modulates the laser output signal by the error signal in order to reduce or cancel the noise and distortion components in the signal.

Optical modulator noise nonlinearity reduction circuit

The fiber optic combiner/splitter is a positive and negative axicon combination which can convert a ring-shaped beam into a solid beam. The positive half of the axicon is effectively a plano-convex lens where the convex surface is generally a shallow cone. The flat surface of the lens abuts each end of an array of single mode fibers which are arranged in a ring configuration around a support member. The negative half of the axicon is effectively a plano-concave lens which is complementary to the positive lens. The focused beams from the positive half of the axicon are combined to form a single beam which is then directed into a single optical fiber. For conversions in the reverse direction, light is taken from a single multimode fiber and expanded into a ring-like pattern. The ring of light is picked up by the ring of single mode fibers. Each single mode fiber receives an equal amount of optical energy or power to provide good efficiency in splitting of the multiplexed beam.

Fiber optic combiner/splitter

A multi-mode optical fiber segment having partially reflecting mirrors on each end functions as a resonant cavity with respect to the modulation frequency when the length of the fiber is equal to one-half the modulation wavelength of the light injected into the fiber. Modulated light is injected through a hole in the mirror at one end, either from a fiber, a waveguide, or directly from a laser diode. The core diameter of the cavity fiber is limited only by the requirement that it must be much larger than the input hole. Light exits though a hole in the mirror opposite the input hole. Upon entry into the resonant cavity, light is subject to multi-modal propagation resulting in dispersion. The resultant output light of the fiber is lower overall in intensity, but its useful frequency response is expanded by the bandpass half-skirt of the fiber-optic filter.

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Oceanside, CA, United States of America

Mark E Curran