Abstract: A tunable tandem Fabry-Perot etalon in used in optical systems as a filter between two amplifier stages. The etalon filters the signal going from the preamplifier to the amplifier and provides further filtering as the output of the amplifier also passes through the etalon.

Abstract: An optical communication system uses adjustable dispersion compensating fibers to compensate for dispersion in system fibers. The amount of dispersion introduced by the dispersion compensating fibers is varied depending upon the amount of compensation required. The amount of compensation may be determined automatically and the amount of compensation introduced by the fibers may be adjusted automatically by a controller.

Abstract: Bidirectional transmission over a single optical fiber is obtained in an optical communications system by using a three port circulator in customer premises equipment together with an optical fiber amplifier and a narrow band filter. The fiber amplifier can be locally or remotely pumped. The acousto-optic modulator is advantageously used because it reduces the coherent Rayleigh noise by detuning upstream and downstream wavelengths.

Abstract: A bidirectional optical amplifier uses a four port optical circulator. Optical amplification is obtained in two fiber amplifiers which are connected to the optical circulator.

Abstract: We have discovered that at least some optical waveguide lasers such as Er-doped fiber lasers are subject to excessive output amplitude fluctuations, including severe fluctuations when the laser is subjected to mechanical shock. We have determined that these highly undesirable fluctuations are due to a resonance phenomenon, and that the fluctuations can be at least substantially reduced by means of a feedback loop that makes the amplitude of the output of the pump laser responsive to the amplitude of the output of the waveguide laser. We have also discovered that the operation of a pump laser/waveguide laser combination is frequently improved if an appropriate non-reciprocal element (e.g., an isolator or a tilted wavelength filter) is placed between the two lasers. An exemplary embodiment of the invention comprises the feedback loop as well as the non-reciprocal element.

Abstract: We have discovered that at least some optical waveguide lasers such as Er-doped fiber lasers are subject to excessive output amplitude fluctuations, including severe fluctuations when the laser is subjected to mechanical shock. We have determined that these highly undesirable fluctuations are due to a resonance phenomenon, and that the fluctuations can be at least substantially reduced by means of a feedback loop that makes the amplitude of the output of the pump laser responsive to the amplitude of the output of the waveguide laser. We have also discovered that the operation of a pump laser/waveguide laser combination is frequently improved if an appropriate non-reciprocal element (e.g., an isolator or a tilted wavelength filter) is placed between the two lasers. An exemplary embodiment of the invention comprises the feedback loop as well as the non-reciprocal element.

Abstract: Dispersion compensation is achieved in an optical communications system by using an optical circulator with first, second, and third ports. The first and third ports are connected to system optical fibers. The second port is connected to a dispersion compensating fiber and return means. The signal passes through the dispersion compensating fiber twice permitting shorter dispersion compensating fibers to be used than were previously used. A Faraday rotator may be used compensate for the polarization mode dispersion of the fiber.

Abstract: An amplifier is described which has a two stage arrangement in which the second stage is pumped with the pump signal not used in the first stage.

Abstract: A balanced doped fiber optical amplifier is disclosed which requires only a single wavelength division multiplexer to provide pump and signal inputs to multiple amplifier stages. In particular, a first section of doped fiber is coupled to an "input" port of the multiplexer and a second section of doped fiber is coupled to an "output" port of the multiplexer. First and second pump signals are coupled to the remaining ports to provide a counter-propagating pump signal to the first doped fiber section and a co-propagating pump signal to the second doped fiber section. The parameters of each doped fiber section (e.g., length, dopant concentration, pump power, pump wavelength) may be individually tailored to provide the desired results (pre-amplification or power boosting, for example). A plurality of balanced optical amplifiers may be cascaded to provide multi-stage amplifiers, and the pump signal levels may be controlled to provide gain equalization.

Abstract: A hybrid pumping scheme for rare-earth doped fiber amplifiers is disclosed. In particular, the arrangement utilizes at least two pump sources, operating at different wavelengths, coupled to a section of doped optical fiber, such as erbium-doped optical fiber. Optical multiplexers, such as fused fiber couplers, may be used to couple the message signal desired to be amplified, as well as the pump sources, to the doped fiber section. For certain embodiments, the doped fiber may be segmented into separate components, with the length of each component determined with respect to the wavelength of the associated pump signal.