Abstract: A method and apparatus for compensating, in the electrical domain, for chromatic dispersion of an optical signal is disclosed. An optical signal is converted to an electrical signal comprised of components which are recoverable and components which are not directly recoverable. A first approximation of the output is derived by applying a transfer function to the electrical signal. The components of the electrical signal which are not directly recoverable are then estimated by applying a second transfer function to the first approximation. After removing these components a second approximation of the output is obtained by re-applying the first transfer function to the result. The optical signal may have a suitably small extinction ratio to improve compensation. The square root of the electrical signal may be taken to improve compensation. A better approximation may be achieved by re-applying the above method iteratively.

Abstract: An optical communication system which includes a transmission path through which a light is transmitted to a specific point, such as to a receiver. The transmission path includes a plurality of sections so that the light travels through the sections to the specific point. Each section overcompensates for dispersion produced in the respective section for the light so that an amount of dispersion for the light at the specific point is substantially zero.

Abstract: An optical preamplifier with an amplification unit is for amplifying an optical signal and compensating dispersion of the optical signal after receiving the optical signal from an optical transmitter, and thereof for supplying the optical signal to an optical receiver.

Abstract: A method of amplifying, transmitting and receiving a signal light. The method includes multiplexing the signal light and a pumping light from a pumping light source so as to output the signal light and the pumping light, and amplifying the signal light by utilizing the pumping light and providing an output of amplified signal light. The amplified signal light and the pumping light are received and the amplified signal light and the pumping light are separately outputted. The outputted amplified signal light is received and a waveform of the amplified signal light is modified so as to compensate for waveform distortion of the signal light along a transmission path of the signal light and an output of a waveform modified signal light is provided. The waveform modified signal light which is received and the pumping light which is received is multiplexed so as to output the waveform modified signal light and the pumping light.

Abstract: The specification describes an optical transmission system for high speed, high capacity digital pulse transmission, i.e. at least 10 Gb/s at a duty cycle of at least 10%, which uses transmission fiber with a dispersion value greater than 20 ps/(nm-km) or more negative than −5 ps/(nm-km). The system operates in the pseudo-linear transmission mode (PLTM). In the PLTM it was discovered that pulse distortion decreases, i.e. eye closure penalty actually decreases, as the dispersion value increases. System performance actually improves by increasing the value of absolute dispersion of the transmission fiber.

Abstract: A dispersion-compensating fiber amplifier having a Raman pumped dispersion-compensating fiber and a distributed optical amplifier. The dispersion-compensating fiber is pumped such that the noise contribution of the dispersion-compensating fiber is reduced.

Abstract: The object of this invention is to improve SNR in the Raman amplification. An optical fiber (10) consists of a dispersion shift fiber in which a zero dispersion wavelength is shifted to the 1.55 &mgr;m band, and an optical fiber (12) consists of a single mode optical fiber having the effective core area of 100 &mgr;m2 which is larger than that of the optical fiber (10). An optical coupler 14 is disposed at the optical signal emission end of the optical fiber (12). A laser diode (16) outputs the laser light of 1455 nm as a Raman pumping light source. The output light from the laser diode (16) is introduced into the optical fiber (12) from the back, namely in the opposite direction to that of the optical signal propagation. The ratio of the Raman gain coefficient of the optical fiber (12) to that of the optical fiber (11) should be 1/1.08 or less, preferably 1/1.1 or less.

Abstract: An optical amplifier, or optical repeater, for amplifying wavelength division multiplexed (WDM) light. A first demultiplexer demultiplexes the WDM light into first and second lights corresponding to different wavelengths in the WDM light. First and second optical amplifiers amplify the first and second lights, respectively. A first multiplexer multiplexes the amplified first and second lights into a multiplexed light. A dispersion compensator compensates for dispersion in the multiplexed light. A second demultiplexer demultiplexes the dispersion compensated, multiplexed light into the first and second lights. Third and fourth optical amplifiers amplify the demultiplexed first and second lights, respectively. A second multiplexer multiplexes the amplified first and second lights from the third and fourth optical amplifiers into a WDM light. The optical amplifier can be configured so that the first and second lights travel through the dispersion compensator in opposite directions.

Abstract: A long-distance optical transmission system comprising pulse emitter and receiver means (1, 2) and an optical line (3) which extends between said emitter and receiver means (1, 2) and which comprises alternating segments (3a, 3b) of dispersive fibers having chromatic dispersion of opposite signs, and also having a plurality of amplifiers (4), the system being characterized in that the optical line (3) comprises a plurality of pairs of dispersive fiber segments (3a, 3b) having chromatic is dispersion of opposite signs between successive amplifiers (4), and in that the cumulative dispersion C over the majority of the segments of the optical line satisfies the relationship (R)|C|&Dgr;&ngr;2<0.3 where C is expressed in ps/nm and where &Dgr;&ngr; is the half-height spectral value of the pulses expressed in Thz.

Abstract: An optical device for detecting chromatic dispersion is described. The optical device includes a receiver, which converts an optical signal into an electrical signal having a plurality of frequency components. A bandpass section separates the plurality of frequency components and a gain section amplifies each of the plurality of frequency components of the electrical signal. Each of the spectral components has a corresponding voltage level and each voltage level may be compared to known voltage levels of a signal having little or no chromatic dispersion. From this comparison, the amount of chromatic dispersion may be determined. The optical device may be used as an element of a chromatic dispersion compensation device, or as a stand-alone device for measuring the amount of chromatic dispersion in an optical signal. A method of compensating for chromatic dispersion in real-time based on the optical device and dispersion compensator is also described.

Abstract: Optical amplifier equipment for operation in fiber-optic communications networks is provided. The optical amplifier equipment may include one or more gain, stages based on rare-earth-doped fiber or Raman-pumped fiber. The gain stages may be optically pumped using diode lasers. Optical monitors may be used to measure optical signals in the optical amplifier equipment. Input signals and output signals may be measured. A control unit may adjust the pump powers in the gain stages based on the measured optical signals to suppress gain transients. An optical delay line may be used to provide additional time for the control unit to process the optical signals before adjusting the pump powers. A midstage module including dispersion-compensating fiber may be installed in the optical amplifier equipment. The control unit may automatically detect the amount of optical delay associated with the installed module and may control the pump powers accordingly during transient control operations.

Abstract: The invention is a double chirped mirror and a method of constructing a double chirped mirror for a frequency range of electromagnetic radiation, comprising specifying a design including a plurality of layers, the plurality of layers being transparent to the electromagnetic radiation and having refractive indices which vary between layers in the plurality of layers, and wherein for a first set of layers the optical thickness of alternate layers in the set of layers varies monotonically and the total optical thickness of a layer and the two adjacent half layers in the set of layers varies monotonically. The design is optimized by adjusting the optical thickness of layers in the plurality of layers.

Abstract: A system and method for resolving polarization mode dispersion (PMD) in a span of optical fiber is described. The method involves three main stages: (1) launch two co-polarized optical signals to generate respective four-wave mixing product fields at the Stokes wavelength &lgr;S or the anti-Stokes wavelength &lgr;A sequentially in each part of the fiber to calculate chromatic dispersion; (2) repeatedly launch two optical signals at various states of polarization (SOP) using methods of stage (1) to calculate overall dispersion (i.e., a combination of chromatic dispersion and PMD); and (3) resolve from the overall dispersion calculated at stage (2) the PMD based on the known chromatic dispersion calculated at stage (1). In an ideal case, the PMD can be calculated from two separate measurements at different co-polarized states of polarization, where group velocity is calculated from a measured dispersion map, as a function of wavelength, at the SOPs and the difference is calculated to resolve PMD.

Abstract: The invention provides an optical fiber amplifier which assures stable operation of a pump light source and efficiently makes use of residual pump power to achieve improvement in conversion efficiency. The optical fiber amplifier includes a rare earth doped fiber. Pump light from a pump light source is introduced into one end of the rare earth doped fiber by way of a first optical coupler, and residual pump light originating from the pump light and arriving at the other end of the rare earth doped fiber is applied to the other rare earth doped fiber amplifier or the loss compensation of a dispersion compensating fiber by Raman amplification.

Abstract: The dispersion managed solution for long haul, high speed D/WDM systems according to the invention operates on three closely related aspects of the communication system. One is provision of a new type of dispersion managed (DM) optical cable with improved dispersion performance over the existing unidirectional and bidirectional cables. Another aspect considered is providing a communication path implemented over DM cable with distributed Raman amplification, to obtain a transmission reach of 2000 km and more, without regeneration. Still another aspect of the dispersion management solution according to the invention is to provide ways of managing the end-to-end dispersion of a communication path, using the DM cable and taking into consideration all active and passive network elements in the respective path. Consideration is also given to the evolution of the path from simple to complex, as the user demand on more services grow.

Abstract: An optical communication system having a transmitting station for outputting WDM (wavelength-division multiplexing) signal light, an optical fiber transmission line, a receiving station, and an optical repeater including an optical amplifier. The transmitting station includes a supervisory circuit for detecting the number of channels of the WDM signal light and transmitting supervisory information including the number of channels to the optical repeater. The optical repeater further includes a circuit for controlling the optical amplifier so that the output level of the optical amplifier becomes a target level. The target level is set according to the supervisory information. According to the structure, it can be possible to provide a system which can easily respond to a change in the number of WDM channels.

Abstract: An optical communication system which includes a transmission path through which a light is transmitted to a specific point, such as to a receiver. The transmission path includes a plurality of sections so that the light travels through the sections to the specific point. Each section overcompensates for dispersion produced in the respective section for the light so that an amount of dispersion for the light at the specific point is substantially zero.

Abstract: Multiple function bandwidth management systems. Bandwidth-management systems for an optical network are easily assembled by concatenating a plurality of intelligent, miniaturized, bandwidth-management modules (BMM's) together. The BMM's subdivide the wide available spectrum into narrow band segments. Each individual BMM is designed to overcome loss and optimize dispersion, gain, and power or gain equalization for a few channels at a time. Each device includes optical connectors and filters, as well as any other components necessary to direct the band of optical channels through the device's optical path while passing other optical channels within the spectrum to additional devices which can be connected without disturbing existing bandwidth-management modules. Each BMM also includes a digital control module that operates the BMM in any one of a plurality of selectable operating modes.

Abstract: Optical amplifiers are provided that have dispersion-compensating fiber that is pumped with an optical source to produce Raman gain. Removable modules of dispersion-compensating fiber, which may be separate from the Raman-pumped dispersion-compensating fiber, may be used to adjust the amount of dispersion compensation provided by a given amplifier. The Raman pump may be formed using fiber-Bragg-grating-stabilized diode lasers or other suitable pump sources. Two cross-polarized diode lasers may be used for the Raman pump to reduce the dependence of the Raman gain on the polarization of the pump. If desired, the dispersion-compensating fiber may be Raman pumped using a two-pass configuration in which pump light reflects off of a reflector to produce additional gain. The reflector may be a Faraday rotator to minimize polarization-dependent pump effects.

Abstract: The invention relates to a hybrid fiber amplifier in which a dispersion compensating Raman amplifier is associated with an erbium doped fiber amplifier to enhance the amplifier efficiency. It is an object of the invention to provide a dispersion compensating Raman amplifier(DCRA) by inducing Raman pump light into a dispersion compensating fiber to obtain a Raman gain in which a depolarizer is used to eliminate the pump light polarization dependent Raman gain, and a hybrid fiber amplifier in which the DCRA is associated with an erbium doped fiber amplifier(EDFA) to enhance the efficiency.

Abstract: An optical amplifier for a 4-fiber system having two inputs and outputs is provided that makes use of a single amplifier rather than two separate amplifiers. The optical amplifier node makes use of an interleaver before and after the single amplifier to demultiplex and multiplex even and odd channel signals traveling in opposite directions. The optical amplifier node can be combined with other like amplifier nodes to provide more complex amplifier solutions at reduced costs due to the need for only half of the typical number of amplifiers. The optical amplifier node can also be combined with, e.g., variable optical attenuators, L/C filters, channel add/drop, and dispersion compensation modules to modify the optical signals as desired.

Abstract: The dependency on a wavelength makes it difficult to lengthen the distance as trying to make the density of the wavelength division multiplexing higher but to enhance the density of the wavelength as trying to make the distance longer. In order to overcome such difficulty, the present invention is arranged to provide an optical signal expander module having a group of wavelength bands in a transmission system. This expander is served to solve the problem of the dispersion and realize both the long distance and the high density of the wavelength division multiplexing that can be traded off.