Abstract: Methods and systems for reducing a first tilt of a spectrum of light transmitted via an optical fiber are provided. To reduce the first tilt, an amplifier, such as an erbium doped fiber amplifier, is configured to yield a gain spectrum with an opposite tilt to that of the first tilt. When light traverses the fiber by passing the amplifier, the first tilt of the spectrum and the opposite tilt of the gain spectrum cancel partially or totally, thereby reducing the first tilt.

Abstract: Methods and systems for reducing a first tilt of a spectrum of light transmitted via an optical fiber are provided. To reduce the first tilt, an amplifier, such as an erbium doped fiber amplifier, is configured to yield a gain spectrum with an opposite tilt to that of the first tilt. When light traverses the fiber by passing the amplifier, the first tilt of the spectrum and the opposite tilt of the gain spectrum cancel partially or totally, thereby reducing the first tilt.

Abstract: An Erbium doped fiber amplifier (EDFA) is placed in a laser cavity to clamp the gain of the amplifier. The laser cavity is preferably formed to minimize the effects of relaxation oscillations and of spectral hole burning. In a preferred embodiment, the laser cavity supports a lasing wavelength which makes the saturation energy at the laser wavelength less than that at the signal wavelengths. In an erbium doped fiber implementation, the laser wavelength is shorter than that of the signal wavelengths and is separated from them by no more than approximately 75% of the width of the spectral hole. The compounding of relaxation oscillations may be substantially eliminated by varying the length of the fiber within each laser cavity within a system to change the photon round-trip time within each cavity.

Abstract: An Erbium doped fiber amplifier (EDFA) is placed in a laser cavity to clamp the gain of the amplifier. The laser cavity is preferably formed to minimize the effects of relaxation oscillations and of spectral hole burning. In a preferred embodiment, the laser cavity supports a lasing wavelength which makes the saturation energy at the laser wavelength less than that at the signal wavelengths. In an erbium doped fiber implementation, the laser wavelength is shorter than that of the signal wavelengths and is separated from them by no more than approximately 75% of the width of the spectral hole. The compounding of relaxation oscillations may be substantially eliminated by varying the length of the fiber within each laser cavity within a system to change the photon round-trip time within each cavity.

Abstract: High output power, high gain, and low noise are achieved in a two-stage optical amplifier, suitable for use as a repeater for a long haul lightwave communication system, in accordance with the principles of the invention, by employing a first amplifying stage having a signal gain sufficiently small to prevent self-saturation by amplified stimulated emission (ASE) that uses counter-propagating pump light to cause maximum inversion of the first stage amplifying medium. In an illustrative embodiment of the invention, EDFAs are used in each of two amplifying stages. The length of the EDFA in the first stage is short enough to ensure nearly complete inversion of the EDFA from pump light that counter-propagates with the signal. The counter-propagating pump light allows the invention to advantageously avoid the significant noise figure penalty from the input loss associated with co-propagating pump light.

Abstract: The present invention relates to a method of mitigating gain peaking in a chain of fiber amplifiers by pumping the amplifiers at a predetermined wavelength to produce gain over a specified wavelength range.

Abstract: A technique employing a depolarized optical source to reduce the polarization dependent gain associated with the optical pump signal used to excite doped fiber amplifiers within an optical transmission system. Pumping the doped fiber amplifiers with a signal that has no single predominant linear SOP, equalizes the gain of the amplifiers. A particular embodiment of the invention includes a pump comprised of a passive polarization scrambler coupled to the output of a multifrequency optical laser. The simple, passive arrangement keeps overall system costs to a minimum and increases reliability.

Abstract: An article, such as an optical communication system, which includes a laser formed in an optical waveguide or optical fiber having a rare-earth-doped core or core portion. In one embodiment, the optical resonant cavity of the laser is at least partially defined by a distributed Bragg reflector formed in a portion of the core. In contrast to the prior art, the length of the optical resonant cavity is about 5 cm or less.

Abstract: In an embodiment for obtaining accurate noise figure measurements for any degree of saturation of an optical amplifier, a polarizer is located at the output of the optical amplifier. The amplified spontaneous noise (ASE) produced by an optical amplifier is not polarized, whereas the amplified signal has a well defined state of polarization which is preferably linear. If the amplified signal is not linearly polarized, it can be rendered linearly polarized in one direction by means of a polarization controller located downstream of the polarizer. By setting the polarizer to have its state of polarization orthogonal to that of the linearly polarized amplified signal, the spectral density of the ASE from the polarizer can be measured without associated distortion due to the signal. By sequentially adjusting the polarization controller to minimize and then maximize the signal which it passes, sequential measurements of the ASE spectral density and gain of the optical amplifier can be obtained.

Abstract: A compact all-fiber, electrically tunable ring laser includes a diode-pumped erbium-doped fiber amplifier. The frequency of the laser is tuned by a fiber Fabry-Perot (FFP) etalon that is electrically tuned. An in-line optical isolator is used in conjunction with the FFP to eliminate undesired reflections. A second FPP with a narrow free spectral range (FSR) can be used in conjunction with a first FFP with a wide FSR.

Abstract: A compact all-fiber, electrically tunable ring laser includes a diodepumped erbium-doped fiber amplifier. The frequency of the laser is tuned by a fiber Fabry-Perot(FFP) etalon that is electrically tuned. An in-line optical isolator is used in conjunction with the FFP to eliminate undesired reflections. A second FFP with a narrow free spectral range (FSR) can be used in conjunction with a first FFP with a wide FSR.

Abstract: This invention relates to an Erbium doped fiber amplifier having improved operating characteristics. Parameters which determine the operating characteristics of an erbium doped fiber amplifier are the concentration of erbium in the core of a fiber; the ratio of the radius of the core of the fiber doped with erbium relative to the radius of the core of the fiber, and, the length of the fiber. It is now recognized that improved fiber amplifier performance can be obtained by varying the core-cladding refractive index difference of the fiber. The various parameters are here defined for providing an erbium doped fiber amplifier having optimum gain characteristics.

Abstract: This invention is a rare earth doped optical amplifier with increased gain and lowered pump thresholds. The amplifying scheme is based on a 3 level lasing system rather than the more prevalent 4 level lasing system. Additionally, the transmission mode of the optical fiber at the pump wavelength has a radius which is substantially equal to or greater than the radius of the distribution profile of the rare earth ions in the fiber amplifier core. With the inventive amplifier, a gain of 37 dB and a saturation power of 11.3 dBm has been obtained with only 54 mW of launch power at .lambda.=1.49 .mu.m.

Abstract: In this invention, there is disclosed a new photodiode which comprises a semimetal/semiconductor junction. Distortion of the bands associated with this type of junction result in current flow when an electron hole pair is formed by, for example, a photon impinging upon the junction. The photodiode operates in the photovoltaic mode. However, rather than relying on impurity doping to fabricate a p-n junction, the semimetallic nature of HgTe and its large conduction band offsets with Hg.sub.1-x Cd.sub.x Te are used to create a rectifying Schottky like structure.