Abstract: A Lyot depolarizer for depolarizing a laser with multiple longitudinal modes comprises two segments of PM fiber optimized for length as a function of the longitudinal mode spacing of the laser source, and not as taught in the prior art as a function of the laser coherence length. The present invention has found secondary coherence peaks in the coherence function of a multiple longitudinal mode source, which can significantly worsen the DoP if the PM fiber lengths are significantly extended beyond optimum, contrary to the teaching in the prior art. The present invention makes use of the periodic structure of the source spectrum by converting half the longitudinal modes to an orthogonal polarization state. As a result a significantly shorter fiber depolarizer is needed than for a single longitudinal mode source. Greater temperature stability is achieved by properly adjusting the lengths of both segments of PM fiber.

Abstract: A Lyot depolarizer for depolarizing a laser with multiple longitudinal modes comprises two segments of PM fiber optimized for length as a function of the longitudinal mode spacing of the laser source, and not as taught in the prior art as a function of the laser coherence length. The present invention has found secondary coherence peaks in the coherence function of a multiple longitudinal mode source, which can significantly worsen the DoP if the PM fiber lengths are significantly extended beyond optimum, contrary to the teaching in the prior art. The present invention makes use of the periodic structure of the source spectrum by converting half the longitudinal modes to an orthogonal polarization state. As a result a significantly shorter fiber depolarizer is needed than for a single longitudinal mode source. Greater temperature stability is achieved by properly adjusting the lengths of both segments of PM fiber.

Abstract: An optical gain device preferably uses stimulated Raman scattering and is in a ring configuration. Fused fiber couplers are used in one embodiment in combination with wavelength selective reflectors to input pump energy to the ring, and to output the desired output wavelengths. The couplers and reflectors are arranged so that the relative phase shifting induced by the couplers allows the optical energy to be directed as desired. The system may also make use of a redirecting reflector at the output wavelength that keeps output light in the ring propagating in the proper direction. A plurality of reflectors may also be used in the ring to select the desired wavelengths at the different Stokes orders being used. In an alternative embodiment, thin film type couplers are used rather than fused fiber couplers.

Abstract: An optical transmission system that employs a Raman amplifier including a Raman pump for introducing depolarized pump light into the fiber. The pump includes an optical source generating a polarized optical pump signal, an optical splitter that splits the pump signal into a first pump portion and a second pump portion, and a beam combiner that combines the first pump portion and the second pump portion into the depolarized pump light. Further, the pump includes a delay device, such as a length of fiber, that causes the first pump portion to propagate farther from the beam splitter to the beam combiner than the second pump portion. The length of fiber is longer than the coherence length of the pump signal.

Abstract: The negative effects of kinking in the L-I characteristics of laser diode operation with respect to feedback control for laser diode current control is suppressed by either (1) combining the output of a plurality of laser diodes together or (2) by imparting a current modulation superimposed on the direct driving current of the laser diode in conjunction with a limited feedback bandwidth, or a combination of both approaches (1) and (2).

Abstract: A multiple stage fiber amplifier system having optical coupled first and second amplifier stages with optical isolator between the first and second stages of the amplifier system includes an optical bypass element coupled between the first and second for bypassing the optical isolator between the first and second stages of the amplifier system to filter out any signal wavelengths present in the bypass so as not to lead to multiple path interference (MPI) with these same signals propagating directly from the first stage to the second stage of the amplifier system. The bypass element can comprise a fiber with a small coiled radius that scatters out higher signal wavelengths or a lossy fiber that itself scatters out longer wavelengths that are in the optical signal wavelength range.

Abstract: An optical transmission system that employs a Raman amplifier including a Raman pump for introducing depolarized pump light into the fiber. The pump includes an optical source generating a polarized optical pump signal, an optical splitter that splits the pump signal into a first pump portion and a second pump portion, and a beam combiner that combines the first pump portion and the second pump portion into the depolarized pump light. Further, the pump includes a delay device, such as a length of fiber, that causes the first pump portion to propagate farther from the beam splitter to the beam combiner than the second pump portion. The length of fiber is longer than the coherence length of the pump signal.

Abstract: Optical couplers functioning, for example, as fiber optic combiners or fiber optic splitters for multimode fibers are disclosed for coupling, for example, the light output of a plurality of multimode laser sources into a multimode output fiber or fibers. Coupling combinations include multimode fibers to multimode fiber or fibers (MMFs/MMF(s)) or multimode fibers/single mode fiber to double clad fiber (MMFs/SMF/DCF). Improvements are disclosed in coupling efficiency and the power distribution uniformity of optical power into an output fiber, such as double clad fiber inner cladding or multimode fiber core, from multiple multimode input fibers.

Abstract: A fiber laser uses a mechanism to prevent a thermally induced shift of the gain spectrum to a range that causes the laser to become destabilized when operated at a first signal wavelength. By establishing a nominal gain spectrum that is further from the undesired range than in a conventional laser, a gain spectrum shift does not reach the undesired wavelength range. This may be accomplished by decreasing the reflectivity of a resonant cavity of the laser, such as by angling the reflective end of the cavity. It may also be accomplished by increasing the population inversion of the laser. Using a pump energy reflector to prevent pump energy from exiting the inner cladding of a double-clad version of the laser the fiber may increase population inversion. The fiber length may also be shortened or the diameter of the inner cladding reduced to increase the population inversion before a laser output is achieved.

Abstract: An optical amplifier makes use of a co-propagating fiber amplifier stage and a counter propagating fiber amplifier stage. One of the stages is preferably a low noise stage, while the other is a high gain stage, typically the output stage. The low noise stage may have a small core fiber while the high gain stage has a large core fiber. Pumping energy is introduced into the amplifier by coupling a plurality of laser sources in the same wavelength range using a narrow channel wavelength division multiplexer coupler. In each stage of the amplifier, some portion of the pump energy is transferred from the pumping wavelength to the signal wavelength. In a single polarization optical signal generator embodiment, the optical signal is developed in a distributed Bragg reflector oscillator having an output Bragg grating embedded in a polarization perserving fiber. A polarization controller is used at the amplifier output to restore the single polarization which is developed in the oscillator.

Abstract: An optical amplifier makes use of a co-propagating fiber amplifier stage and a counter propagating fiber amplifier stage. One of the stages is preferably a low noise stage, while the other is a high gain stage, typically the output stage. The low noise stage may have a small core fiber while the high gain stage has a large core fiber. Pumping energy is introduced into the amplifier by coupling a plurality of laser sources in the same wavelength range using a narrow channel wavelength division multiplexer coupler. In each stage of the amplifier, some portion of the pump energy is transferred from the pumping wavelength to the signal wavelength. In a single polarization optical signal generator embodiment, the optical signal is developed in a distributed Bragg reflector oscillator having an output Bragg grating embedded in a polarization perserving fiber. A polarization controller is used at the amplifier output to restore the single polarization which is developed in the oscillator.

Abstract: A method and various structures are described for reducing excess photon noise in short coherence light sources, such as broadband superfluorescent fiber or superluminescent diodes, for example. The method contemplates splitting the light source signal into a plurality of components, thereby splitting, and reducing, the photon noise or "beat noise" as well as the light intensity. Each component travels in a separate path having a unique time delay which is longer than the coherence time of the light source. The light from each separate path is recombined at an output end, prior to detection, causing the signal to get back to its original intensity, while keeping the total beat noise at a reduced level. The paths may be created using different length polarization maintaining (PM) fibers, different length optical fibers, or multi-mode fibers having several propagation modes propagating at different rates.

Abstract: A WDM communication system utilizes a pump-mediated gain-shaped fiber amplifier having a predetermined nominal signal gain bandwidth and is pumped by a plurality of laser pump sources having different wavelength outputs with their outputs combined to provide a scaled power output of a weighted average of their wavelengths for launching into at least one end of the fiber amplifier. The weighted average of the output wavelengths of the individual sources is varied to produced a modified weighted average that broadens the predetermined nominal signal gain bandwidth. The wavelength weighted average of the combined pump sources may be modified by changing the operation of at least one of the pump laser sources, e.g., by changing the power level or the temperature level of one or more of the individual pump sources or by terminating the operation of one or of the individual pump sources.

Abstract: An amplifier method and apparatus for use with optic systems utilizing a fiber optic circulator to direct input signals to a splitter that splits the copropagating pump light and input signals into two equal parts for simultaneous introduction into the two opposite ends of the active gain fiber. Half of the pump light and half of the signal are propagating through the active fiber in a clockwise and counterclockwise direction at the same time. This bidirectional propagation results in a more uniform excitation along the entire length of the active fiber, providing uniform stimulation of photon emission at both ends, causing significantly reduced noise and higher gain of the signal. Two half-amplified signals are combined and supplied to the circulator that provides the amplified output signal without any residual pumping light at the input or the output port of the circulator.

Abstract: A wavelength stabilization apparatus and method for a superfluorescent source comprising a SFS (superfluorescent source) comprising a fiber with a core doped with lazing material. The SFS source produces SFS light with an SFS wavelength when pumped with pump light from a pump light source having a pump light wavelength. An output controller responds to a sample of the SFS light and operates to maximize the power of the sample of SFS light by automatically adjusting the pump light wavelength. The output controller also has a pump power controller responsive to a sample of the pump light from the pump light source for stabilizing the output power of the sample of the pump light with respect to a predetermined reference output power level.

Abstract: A superfluorescent broadband fiber laser source comprises an optical fiber doped with a laser material and having one end pumped with pump light of sufficient intensity to produce amplified spontaneous emission within the fiber and forward and backward waves therefrom. The polarizations of the backward wave experiences a 45.degree. rotation as it travels into and another 45.degree. rotation as it passes back out of a 45.degree. Faraday rotator mirror device. An amplified polarization=rotated beam from the doped fiber is divided into orthogonally polarized beams in a polarization beam splitter coupler. A return polarized signal from an interferometer is passed through the doped fiber, the Faraday rotator mirror device and the doped fiber for producing a polarized output signal that has been amplified by four passes through the doped fiber.

Abstract: A wavelength stabilization apparatus and method for a superfluorescent source comprising a SFS (superfluorescent source) comprising a fiber with a core doped with lzaing material. The SFS source produces SFS light with an SFS wavelength when pumped with pump light from a pump light source having a pump light wavelength. An output controller responds to a sample of the SFS light and operates to maximize the power of th esample of SFS light by automatically adjusting the pump light wavelength. The output controller also has a pump power controller responsive to a sample of the pump light from the pump light source for stabilizing the output power of the sample of the pump light with respect to a predetermined reference output power level.

Abstract: A ring laser gyro is shown which generates two or more laser beams that travel through a gain medium. The laser produces two bias components, one due to Langmuir flow and the second due to a thermal gradient. The invention uses a symmetrically mounted restriction in the gain portion of the laser passageways to control the flow of the gain medium. The non-gain portion of the passageways is also enlarged to reduce the effects of a thermal gradient on the flow of the medium.