Abstract: A fiber optic rotation sensor comprises a fiber optic interferometer loop formed from a highly birefringent optical fiber, and a short coherence length source for introducing light into the inteferometer loop to provide a pair of waves which counter-propogate therethrough. A detector is included to detect the phase difference between the waves after they have traversed the loop to provide an indication of the loop rotation rate, in accordance with the Sagnac effect. Phase errors are reduced by selecting the coherence length of the source and the birefringence of the fiber, so that the loop is comprised of plural fiber coherence lengths. The term "fiber coherence length" should be distinguished from source coherence length. Fiber coherence length is the length of fiber required for the optical path length difference between the two polarization modes of a single mode fiber to equal one coherence length of the light source.

Abstract: A fiber optic rotation sensor comprises a fiber optic interferometer loop formed from a highly birefringent optical fiber, and a short coherence length source for introducing light into the interferometer loop to provide a pair of waves which counter-propogate therethrough. A detector is included to detect the phase difference between the waves after they have traversed the loop to provide an indication of the loop rotation rate, in accordance with the Sagnac effect. Phase errors are reduced by selecting the coherence length of the source and the birefringence of the fiber, so that the loop is comprised of plural fiber coherence lengths. The term "fiber coherence length" should be distinguished from source coherence length. Fiber coherence length is the length of fiber required for the optical path length difference between the two polarization modes of a single mode fiber to equal one coherence length of the light source.

Abstract: In a closed loop fiber optic gyroscope, the counter-propagating lightwaves are phase modulated by a triangular wave modulation with the triangular wave skewed to lock the phase difference between the counter-propagating waves alternately to specific values of phase difference which are greater than and less than the phase difference due to rotation. The difference in elapsed time between the up-slope and down-slope portions of the triangular wave modulation yields a measure of rotation angle, whereas such difference in elapsed time divided by total elapsed time yields a measure of rotation rate. The phase difference is further modulated about the locked values at a higher frequency, such higher frequency phase difference modulation being synchronously detected to produce a rotation rate signal component employed to generate the skewed triangular wave. Various other features are employed to light polarization errors.

Abstract: A fiber optic interferometer provides Kerr effect compensation by intensity modulating counterpropagating waves of unequal intensity such that the average value of the square of the intensity is equal to a constant times the average value of the intensity squared, the constant preferably being equal to about two. The intensity modulation may be achieved by using a modulator in combination with a light source or by using a source in which plural frequencies combine to provide the modulation.

Abstract: A single, continuous strand of fiber optic material is wrapped about a mandrel to form oval-shaped loops having parallel sides and curved ends. A magnet is positioned so that its B-field is substantially parallel to the straight portions of the loops. As light propagates through these straight portions of the loops, its direction of polarization is rotated in accordance with the Faraday effect. The curved portions are formed to create sufficient linear birefrigence to provide a phase difference of 180 degrees between light in the two orthogonal polarization modes of the fiber. This advantageously causes the Faraday rotations in each of the straight portions to add, rather than cancel. The magneto-optic rotator of the present invention is useful in a variety of applications such as an optical isolator, a modulator, and a magnetometer.

Abstract: A fiber optic rotation sensor, employing the Sagnac effect, comprises all fiber optic components, positioned along a continuous, uninterrupted strand of fiber optic material. The rotation sensor includes a detection system utilizing a modulator for phase modulating light waves which counterpropagate through a loop formed in the fiber optic strand. The modulator is operated at a specific frequency to eliminate amplitude modulation in the detected optical output signal. The rotation sensor is mounted in a .mu.-metal housing to shield it from the effects of ambient magnetic fields. An isolator is utilized to prevent the optical output signal from returning to the laser source. This advantageously reduces power losses in the system by eliminating the need for a coupler to couple the output signal to a detector.

Abstract: A single, continuous strand of fiber optic material is wrapped about a mandrel to form oval-shaped loops having parallel sides and curved ends. A magnet is positioned so that its B-field is substantially parallel to the straight portions of the loops. As light propagates through these straight portions of the loops, its direction of polarization is rotated in accordance with the Faraday effect. The curved portions are formed to create sufficient linear birefringence to provide a phase difference of 180 degrees between light in the two orthogonal polarization modes of the fiber. This advantageously causes the Faraday rotations in each of the straight portions to add, rather than cancel. The magneto-optic rotator of the present invention is useful in a variety of applications such as an optical isolator, a modulator, and a magnetometer.

Abstract: A fiber optic amplifier as disclosed, comprised of a fiber optic, monomode waveguide which has a core and cladding. Part of the cladding over a predetermined region is removed and replaced by an active medium capable of absorbing light energy at a first wavelength and emitting light energy at a second wavelength. The active medium is a lasing dye which has an index of refraction adjusted to be slightly less than the index of refraction of the fiber core. The amount of cladding which is removed is adjusted such that a predetermined amount of penetration of the evanescent field from a pump light signal coupled into an end of the fiber penetrates the active medium. A probe signal to be amplified causes stimulated emission from the excited dye molecules by penetration of its evanescent field into the dye in the region where the cladding is removed.In the preferred embodiment a recirculating pump is used to circulate dye through a cavity which is placed over the portion of the fiber where the cladding is removed.

Abstract: Apparatus and method of manufacture for coupling optical power between two strands of fiber optic material in a given direction of propagation. The coupler employs generally parallel, intersecting strands of fiber optic material having the cladding removed on one side thereof to within a few microns of the fiber cores in the region of intersection to permit light transfer between the strands.

Abstract: A pair of optical couplers are arranged in series with a pair of outputs from the first optical coupler supplying the pair of inputs to the second optical coupler. At least one of the optical fibers between the first and second couplers is arranged to have a variable length, said variation being at least one-half the wavelength of the light signal utilized within the system. When light is supplied to one input of the first coupler, this light can be switched selectively to either of the outputs of the second coupler by varying the length of one of the optical fibers between the couplers. Thus, a light signal supplied to either of the inputs of the first coupler can be selectively output at either of the outputs of the second coupler or can be made to alternate between these outputs in accordance with the length of the intervening optical fiber.

Abstract: A fiber optic directional coupler comprises a pair of bases, with respective longitudinal, arcuate grooves formed therein on confronting faces thereof, for mounting a pair of optical fibers in close proximity. A portion of the cladding is removed from each of the fibers to form planar facing surfaces which permits the spacing between the fiber cores to be within a predetermined critical zone so that guided modes of the fibers interact, through their evanescent fields, to cause light to be transferred by evanescent field coupling between the fibers. The coupler is "tuned" to a desired coupling efficiency by offsetting the planar facing surfaces to increase the spacing between the fiber cores. A method of manufacture of the coupler includes procedures which permit the coupler halves to be made symmetrical. The method also permits couplers having given coupling characteristics to be reproduced.

Abstract: Apparatus and method of manufacture for coupling optical power between two strands of fiber optic material in a given direction of propagation. The coupler employs generally parallel, intersecting strands of fiber optic material having the cladding removed on one side thereof to within a few microns of the fiber cores in the region of intersection to permit light transfer between the strands.

Abstract: Rotation sensor having a loop of fiber optic material in which counter propagating waves are generated with a phase relationship corresponding to the rate at which the loop is rotated. All fiber optic components are employed in the system for directing the light to and from the loop and establishing, maintaining and controlling proper polarization of the light. In one particularly preferred embodiment, the loop and other components are formed on a single strand of fiber optic material which extends continuously through the system.

Abstract: Apparatus and method for changing the degree of polarization of light in a waveguide such as an optical fiber. A portion of the cladding of a strand of fiber optic material is removed, and a body of birefringent material is mounted in the area in which the material has been removed in close proximity to the core of the fiber. The birefringent material modifies the propagation of two polarization modes within the fiber in such manner that one of the modes is coupled to a bulk wave mode and removed from the guide, while the second mode excites no bulk waves and remains guided.