Abstract: The invention comprises a method and apparatus for implementing a relatively low cost add/drop multiplexer (OADM) wherein pre-demux and post-mux dispersion compensation is employed in a manner that substantially avoids imparting additional dispersion compensation to pass-through wavelength channels in a WDM system.

Abstract: A method for determining interactions between a number of optical channels in a wavelength division multiplexed signal wherein, given that during broadband optical transmission, the quality of a “Dense Wavelength Division Multiplexed” signal is adversely affected by multiple channel interactions, the method is used to determine the governing effects, the Kerr effect and the non-linear scattering process by evaluating the spectral profile of the Q factor or of the bit error rate.

Abstract: Optical transmission being performed by frequency modulating frequency-division-multiplexed multi-channel signals as a single unit, distortion that is caused by a ripple-shaped group delay deviation in a transmitter 2, a receiver 4 and an optical link 3 is reduced by providing a level adjuster 2a for adjusting the level of frequency-division-multiplexed multi-channel signals input to the FM modulator 2b, and by increasing the input level of multi-channel signals to the FM modulator 2b by level adjusting means 2a to enlarge the bandwidth of FM signal, in the case where the number of channels is small.

Abstract: Both wavelength dispersion and a dispersion slope of a line fiber are simultaneously compensated for by combining two types of dispersion compensators having different characteristics.

Abstract: An optical system includes a delay region having a photonic band structure, a modulated optical signal source, an optical input, and an optical output. The optical input couples modulated input optical signals into a predetermined mode in the delay region such that group velocity of the optical signal is reduced. The optical output includes a wavelength selective element. Input optical signals are coupled into a highly dispersive mode in the delay region in which the group velocity of the optical signal is reduced. The input signal, which has been delayed and dispersed, is recovered at the output of the device using the wavelength selective element.

Abstract: The present invention aims to provide a dispersion compensator which is ultra small in size and low in cost and capable of controlling dispersion compensating values, and an optical transmission system using the dispersion compensator. A dispersion property of light that propagates through defects in a photonic crystal, is used to compensate for each wavelength dispersion. A dispersion compensator comprises a dispersion-compensating-waveguide array in which a plurality of dispersion compensating waveguides having dispersion compensating values different from one another are placed, a drive unit for driving the dispersion-compensating-waveguide array, and optical fibers for inputting/outputting a light signal. Each of the dispersion compensating waveguides comprises regular waveguides and a waveguide made of defects in photonic crystal. The lengths of the waveguides made of the defects in photonic crystal are changed one by one to make dispersion compensating values different from one another.

Abstract: The present invention provides the method and apparatus for multi-pass photonic processors with the use of circulators and multiple-fiber collimators. In one embodiment of the present invention, a circulator and a reflective element are placed at either end of a chain of cascaded processors. The circulator at a first end routes the light signal to be processed and passed from one processor to the next, the reflective element at a second end reflects the light to be reprocessed and passed from one processor to the previous, the light signal eventually reaches the circulator again and exits. In another embodiment of the present invention, multiple fiber strands are connected to the collimator of a photonic processor. Furthermore, all fiber strands are paired in order to reroute the light signals for reprocessing in the photonic processor.

Abstract: The invention relates to a method for compensating signal dispersion in an optical communication network and to an optical communication network. The dispersion compensation is carried out by constructing the network in such a way that a route having an even number of phase conjugating means can be found between any two nodes. The routing is primarily made along a route in which there is the minimum even number of phase conjugating means between the terminal nodes. A preferred embodiment of the invention is a ring network constructed of two concentric rings in such a way that both rings comprise the same node points, but the number of phase conjugating means to be installed in said rings, in the optical fibers between adjacent nodes is, for example, even in the outer ring and odd in the inner ring.

Abstract: A tunable chromatic dispersion and dispersion slope compensator that utilizes a Virtually Imaged Phased Array (VIPA), a rotating transmissive diffraction grating, and a mirror with different curvatures for different cross-sections is disclosed. The compensator in accordance with the present invention provides simultaneous tunable compensation of chromatic dispersion and dispersion slope utilizing a single apparatus. The amount of compensation is accomplished by rotating the transmissive diffracting grating and/or translating the mirror. A system which utilizes the compensator is thus cost effective to manufacture.

Abstract: A method and apparatus for reducing transmission penalties associated with ghost pulses in an optical signal in a transmission system includes providing phase modulation to the optical signal in the transmission system with a period of phase modulation greater than a bit period of the transmission system, wherein the phase modulation is applied to the optical signal such that the phases of at least some logical “ones” within a sequence of logical “ones” of the optical signal are modified such that the phases of the individual ghost-pulse fields from each triplet of “ones” are different, either pseudo-randomized or substantially shifted by &pgr;, thereby resulting in a reduction of the total ghost pulse. Advantageously, there is no need to synchronize the timing of the phase modulation with the timing of the power profile of the optical signal.

Abstract: A device and method for compensating for chromatic dispersion in an optical signal. The optical signal is coupled between an optical waveguide of a type having (i) a fundamental-mode waveguide and (ii) a higher-order mode waveguide surrounding the fundamental-mode waveguide, wherein different effective indexes of refraction are associated with the fundamental-mode and higher-order mode waveguides. The device comprises a transmissive, long-period optical grating disposed along a length of the optical waveguide and has a receiving end and a transmitting end. The grating is chirped between the ends along a light conducting axis of the optical waveguide such that different wavelengths of the optical signal are coupled to the fundamental-mode and higher order mode waveguides at different points along the length of the grating so that chromatic dispersion is corrected at the transmitting end.

Abstract: The present invention relates to a dispersion compensating optical fiber (“DC fiber”) having a segmented core and having a negative total dispersion and negative dispersion slope in the C-band. The index profile of the fiber is selected to provide an optical properties suitable for a high performance communication system operating in the C-band wavelength band, i.e., between about 1525 nm to 1565 nm. The DC fiber according to the invention exhibits dispersion slope at 1549 nm more negative than −3.4 ps/nM2-km and has a negative &Dgr;2% that is more negative than −0.4%. Preferably, the DC fiber has a total dispersion more negative than −125 ps/nm2-km. The DC fiber may be optically connected to a Non-Zero Dispersion Shifted Fiber (NZDSF) in the system to compensate for dispersion thereof. Optionally, the transmission system may include a positive dispersion, positive slope trim fiber.

Abstract: To increase the bit rate at which and the distance over which data can be transmitted by optical fiber, polarization dispersion is compensated by means of a polarization controller, a system for generating a differential group delay between two orthogonal modes of polarization and a control unit of the polarization controller. A chromatic dispersion compensator applies compensation which is adjusted dynamically to optimize the quality of the received optical signal. Applications include long-haul optical transmission on standard fibers.

Abstract: Fiber-based dispersion compensation elements are provided for use in optical amplifiers and other optical network equipment that handle optical data signals in fiber-optic communications links. The dispersion compensation elements may include chirped superstructure fiber gratings. Systems and method for fabricating the dispersion compensation elements using ultraviolet light are provided.

Abstract: A WDM system comprising a first WDM module having a first multiplexer unit for multiplexing a WDM optical signal, a second WDM module having a first demultiplexer unit for demultiplexing the WDM optical signal, and wherein the system is arranged, in use, such that optical losses experienced by individual channels of the WDM optical signal in the first multiplexing unit and the first demultiplexing unit and optical losses experienced by the channels during un-amplified transmission between the first and second WDM modules are substantially balanced.

Abstract: A method of and system for estimating the bit error rate of a channel in an optical communication system includes a method of and system for measuring the in-band cross-talk of the channel in a wavelength division multiplexed system. A single channel is selected from the plurality of channels in the optical communication system. The signal in this single channel is passed to a digital signal processor proportional to the time rate of change of a phase of an optical source generating the signal. The digital signal processor converts the filtered signal into the frequency domain, and a spectrum analyzer determines the features of the in-band cross-talk from the signal in the frequency domain. The features of the in-band cross-talk may be combined with other measured noise features, such as the power spectral density, to estimate BER.

Abstract: Compensating for polarization mode dispersion in a birefringent optical transmission fibre is achieved by controlling the birefringence of the fibre. The difference in group velocity of the orthogonal polarization states of an optical signal transmitted over the fibre is monitored to generate an error signal representing the difference. The birefringence of the fibre is adjusted accordingly to minimize the difference and thereby provide dynamic compensation. Birefringence control may be achieved by a non-linear fibre grating written into the fibre to impose a differential time delay. The fibre may be a side hole fibre (SHF), a holey fibre (HF), a photonic crystal fibre (PCF), or any other suitable microstructure fibre. The fibre may have stressing rods, may be tapered along its length and may be controlled electrically, mechanically, acoustically or thermally by spaced heating elements.

Abstract: An optical transmission system includes a number of corresponding modular multiplexing and demultiplexing units used in transmitting and receiving an optical signal respectively. Additionally, compensation components compensate for optical dispersion experienced by the optical signal. The modular multiplexing and demultiplexing units are assembled in a cascade fashion at the transmit side and the receive side of the optical transmission system, respectively. The dispersion compensation components share dispersion compensation fiber across the cascaded units.

Abstract: A fiber optic communications link having PMD characterization across multiple optical channels to identify PMD problems. The communications link has adaptive PMD controls employed along the optical link, whereby PMD phenomena detected by instruments, such as PMD compensators, are interpreted as being either attributable to perturbation of fiber characteristics at large, or by failure of PMD equipment along the link. The present invention avoids taking unnecessary control or maintenance actions upon PMD related controllers and compensators. PMD notifications from various PMD compensators are correlated to identify which portion of the link has undergone a change in polarization characteristics to further identify PMD related errors and problems.

Abstract: The bidirectional dispersion compensator comprises at least one circulator (Z,Z1,Z2,Z4) and at least one filter-coupler element (F1, etc.). The optical signals (S1,S2) that are emitted in opposite directions are merged and sent to a compensation fiber (LK,LK1, etc.) together, are reflected at the ends of this fiber, and are forwarded in the respective directions of transmission as dispersion-compensated optical signals (SK1 and SK2).

Abstract: An optical channel dispersion compensating and monitoring apparatus when an optical signal transmits from an optical transmitter to an optical receiver through an optical fiber is disclosed. A WDM optical amplifier comprising the optical channel dispersion compensating and monitoring apparatus, for a long distance is also disclosed. A WDM optical channel dispersion compensating and monitoring apparatus comprises a dispersion compensating unit for compensating the optical signal distorted in the optical fiber at each channel when the optical signal transmits from an optical transmitter to an optical receiver through the optical fiber and an optical channel monitoring unit for converting an optical power as the portion of the compensated optical signal to electric signals and monitoring the converted electric signals.

Abstract: An optical communication system transmitting a plurality of channel wavelengths is provided. The system includes a transmitter unit, a receiver unit, and an optical transmission path interconnecting the transmitter and receiver units. The transmission path has a concatonation of optical fibers defining a dispersion map such that each of the channel wavelengths are located at FMX and XPM antiresonances at which FWM and XPM are suppressed.

Abstract: The invention is the novel use of dispersion compensation in a long haul wavelength division multiplexed high capacity optical transport system which has very many channels packed extremely closely together, in order to greatly reduce the deleterious effects of four-wave mixing. Four-wave mixing is an exchange of energy between nominally independent channels, arising from the fundamental fibre non-linearity, which has the effect of degrading transmission quality. Conventional systems make use of fibre dispersion compensating modules to overcome the effects of fibre dispersion. In such systems, it has been discovered that the exact distribution of fibre dispersion along the optical link (the ‘dispersion map’) strongly influences the degree of four-wave mixing, and hence the degradation in transmission quality.

Abstract: A low dispersion comb filter or interleaver assembly has a first interleaver element and a second interleaver element. The first interleaver element is configured so as to provide a dispersion vs. wavelength curve wherein each dispersion value thereof is approximately opposite in value to a dispersion value at the same wavelength for the second interleaver element, so as to mitigate net or total dispersion in the interleaver assembly.

Abstract: The present invention has an object to provide a WDM optical transmission system for effectively compensating such as wavelength dispersions of respective wavelength bands, by a simple constitution making use of a hybrid transmission path in case of transmitting a broadband WDM signal light containing a plurality of wavelength bands. To this end, wavelength dispersion characteristics of a hybrid transmission path utilizing a 1.3 &mgr;m zero-dispersion SMF and an RDF in the present WDM optical transmission system, are set such that compensation ratios of wavelength dispersion and dispersion slope become approximately 100% for a reference wavelength band which is one of a plurality of wavelength bands; and dispersion compensation fibers capable of compensating wavelength dispersions caused within the hybrid transmission path are inserted into propagation paths, respectively, within an optical amplifier, for the wavelength bands except for the reference wavelength band.

Abstract: A method and apparatus for managing state-of-polarization (SOP) controllers along an optical communications link. When the polarization-mode dispersion (PMD) in the link exceeds a preset limit as determined by a PMD compensator, the SOP controller is directed to change rotation angle in an arbitrary fashion. This shift is only undertaken after other indicators are examined to determine that PMD is the main problem affecting the link, and not simply a consequence of a separate problem that the SOP controller rotation angle should not try to fix. By reducing unnecessary SOP adjustments which can disrupt data traffic, the reliability of the optical link is improved.

Abstract: The invention relates to the monitoring of polarization mode dispersion (PMD) using heterodyne detection for providing PMD compensation in optical networks, and an apparatus for monitoring PMD. In the present invention, a broadband PMD monitor is disclosed based on heterodyne detection with a tunable laser source which can be fed to a compensator such as an add/drop or other wavelength switch and polarization dependent attenuation means. A signal from a local oscillator is combined with an optical signal and the beat frequency amplitude and phase is analyzed for two orthogonal polarization states simultaneously to obtain a state of polarization. By averaging a plurality of polarization states within a channel, PMD can be estimated for compensation.

Abstract: An operation unit of a PMD compensation module includes a PBS, a compensated part and a combiner. The PBS separates an optical input into a first polarized signal and a second polarized signal. The compensated part includes a fixed prism and a movable prism. The first polarized signal outputted from the PBS travels through the fixed prism and the movable prism in series. The light path of the first polarized signal in the movable prism is elongated or shortened according to a position of the movable prism. A continuously variable delay can thus be applied between the first and second polarized signals. The combiner recombines the first polarized signal received from the compensated part and the second polarized signal received from the PBS into an optical output signal.

Abstract: An optical communication apparatus performs wavelength division multiplexing with respect to signals of a plurality of signal transmission bands. The apparatus includes a first optical unit which effects distributed Raman amplification and has a characteristic that compensates for dispersion of a transmission path to which the optical communication apparatus is connected, with respect to at least one of the signal transmission bands.

Abstract: The present invention offers a polarization mode dispersion compensator and a compensation method for polarization mode dispersion having simple constitution and being strong against external disturbances. The polarization mode dispersion compensator, a representative example of the present invention, is provided with a compensation circuit for polarization mode dispersion, a degree of polarization measuring circuit, and a control circuit. An optical signal is input to the compensation circuit for polarization mode dispersion through an optical fiber, and after the process of compensation for polarization mode dispersion, it is output to an optical fiber. An optical coupler divides a part of the optical signal passing through the optical fiber. The degree of polarization measuring circuit finds the degree of polarization of the divided optical signal.

Abstract: A temperature stabilization package comprises a hollow external housing of a thermally insulating material. The hollow external housing includes a holder and a lid to cover the holder. The holder includes a floor having at least one projection and a separating wall around the projection. An internal surface of the lid has at least one post formed therein. The housing surrounds a container that includes a base and a cover over the base to form an internal cavity inside the container. An outer face of the base has at least one lower socket. The cover includes at least one upper collar so that the container may be coupled inside the hollow external housing by engagement of a lower socket with a projection and an upper collar with a post to hold the container substantially surrounded by, but spaced from, the wall and the hollow external housing.

Abstract: An optical transmitter having a function which compensates for wavelength dispersion is provided with a plurality of light sources for outputting light having wavelengths that differ from one another. Before the optical transmission system begins operating, the wavelength of light output to an optical transmission line is varied by changing over the light sources in order to detect a wavelength whose transmission characteristic is optimum with regard to wavelength dispersion exhibited by this optical transmission line. During system operation, the light having the detected optimum wavelength is output to the optical transmission line.

Abstract: An optical signal, which is to become the subject of dispersion compensation, is split by optical combining/splitting unit 2, and each frequency component of the optical signal that is split is reflected by each reflective surface of reflective mirror 40 of reflective means 4 to apply a predetermined phase shift to the respective frequency components. Each reflected frequency component is then combined using optical combining/splitting unit 2, to give dispersion compensated optical signal. Furthermore, in regards to reflective means 4, which is used to apply phase shift to each frequency component of an optical signal, reflective mirror 40 is made a variable movable mirror by reflection position at each reflective surface, which reflects the frequency components, deforming the entire reflective surface. This allows dispersion that is created in an optical signal to be compensated with favorable controllability and high accuracy.

Abstract: The automatic dispersion compensation device of the present invention comprises a unit measuring the transmission quality of incoming optical signals for one or more channels input from a transmission line and a unit separating and detecting the transmission quality degradation due to chromatic dispersion, in the measurement result of the unit from degradation due to other factors and controlling a variable chromatic dispersion compensator (VDC) in such a way as to compensate for that degradation.

Abstract: The invention disclose a device an a method for compensation of polarization mode dispersion comprising following steps: Measuring the degree of polarization of a signal at the receiver, Running an algorithm to find the maximum of degree of polarization, Comparing the degree of polarization with reference values of the compensation system in a data base, Switching the new starting point to the opposite side of the Poincare Sphere, when the reference value is under a definite threshold value and Selecting the new starting point from the data base.

Abstract: A wavelength-division multiplexing optical transmission system for providing a compensating-purpose dispersion D2 to a wavelength-division multiplexing optical signal to be transmitted through an optical transmission path from a transmitter terminal to a receiver terminal. The compensating-purpose dispersion D2 satisfies conditions that at any wavelength “&lgr;” included in the transmission wavelength band, if dD1(&lgr;)/d&lgr;≠0 is established, then {dD1(&lgr;)/d&lgr;}×{dD2(&lgr;)/d&lgr;}<0 is also established, and if dD1(&lgr;)/d&lgr;=0 is established, then dD2(&lgr;)/d&lgr;=0 is also established, where D1 represents a dispersion generated in the wavelength-division multiplexing optical signal during when the wavelength-division multiplexing optical signal is transmitted through the transmission path from the transmitter terminal to the receiver terminal.

Abstract: An optical communication system and method of use thereof which uses dispersion compensators to intentionally create a dispersive condition at the output of subsequent inline optical amplifiers. The present invention reduces four-wave mixing and increases the allowable spacing between optical amplifiers, thus reducing the required number of amplifiers and dispersion compensators for a given length of optical fiber. In one embodiment, dispersion compensators and optical amplifiers are alternately spaced from one another along a length of an optical fiber such that the dispersion compensators render a dispersive condition at the amplifiers allowing each amplifier to be run at a higher power level. In another embodiment, the dispersion compensator is collocated with the amplifier, but is positioned between a pre-amp stage and a high power output stage to overcompensate both the slope and absolute dispersion of the fiber up to that point.

Abstract: A method for compensating signal distortions of signals polarized to each other in an optical wavelength division multiplex transmission system, comprising the steps of providing a first signal being obtained from a first polarized signal and a second signal being obtained from a second polarized signal, the first and second polarized signals being polarized with respect to each other, determining a first signal quality for the first signal, generating a first error signal in dependence of the first signal quality, and subtracting the first error signal from the first signal.

Abstract: Dispersion compensation values are set so as to be transmittable to any path groups in a WDM optical communication system having OADM nodes, which includes transmitting-end and receiving-end terminal nodes; a WDM optical communication transmission line including a plurality of spans each having an optical fiber, the plurality of spans joining the transmitting-end and receiving-end terminal nodes; and a plurality of add drop multiplexing (OADM) nodes disposed on the optical communication transmission line; wherein when taking as the reference a residual dispersion target value of between the transmitting-end terminal and receiving-end terminal nodes, a residual dispersion target value for a node segment between one of the terminal nodes and one of the add drop multiplexing (OADM) nodes and a residual dispersion target value for a node-to-node segment between two of the add drop multiplexing (OADM) nodes are set so as to be proportional to ratios of the span counts in the node segment and in the node-to-node se

Abstract: In accordance with the invention, a WDM optical communication system includes a new tunable multi-channel dispersion compensating filter having low loss, low polarization dependence and capable of compensating many channels over a large wavelength range. In essence, the filter comprises an optical cavity with a near 100% reflector on one side and a variable partial reflector on the other side. The device acts as a tunable all-pass filter.

Abstract: In order to compensate for chromatic dispersion ad dispersion slope over an entire wavelength band of the optical signal, the wavelength band is split into a plurality of bands, and chromatic dispersion compensation is made to make chromatic dispersion in a central wavelength of each of the bands zero.

Abstract: The invention relates to a wavelength division multiplex transmission (WDM) system or a polarisation division multiplex division system with an optical transmitter (OT), an optical receiver (OR) and an optical transmission fiber (TF), the receiver (OR) showing means for measuring dispersion characteristics while transmitting optical signals over the transmission fiber (TF), the transmitter (OT) comprising means for sending correlation signals (CP) on at least two different wavelength or polarisation channels and the receiver (OT) comprising means for performing a correlation determination

Abstract: A transmission of optical signals generated by multi-line optical sources is provided via multichannel WDM optical network. Each multi-line optical source generates optical spectral lines within designated spectral range associated with the spectral window allocated for corresponding WDM channel, and comprises a plurality of spectral lines. Spectral lines are substantially narrower than the spectral separation between the lines.

Abstract: An optical communication system has an optical transmitter, an optical transmission line in optical communication with the optical transmitter, an optical receiver in optical communication with the optical transmission line, and a dispersion compensator disposed between the optical transmitter and the optical receiver along the optical transmission line. The optical transmitter is adapted to transmit an optical signal that includes multilevel encoding. The optical transmission line causes a first dispersion of the optical signal and the dispersion compensator causes a second dispersion of the optical signal. The second dispersion at least partially cancels the first dispersion.

Abstract: A programmable optical add/drop multiplexer (OADM) implements add/drop function of optical signals from a number of cross-connected optical systems while treating issues of coherent cross-talk, chromatic dispersion, slope of dispersion and amplitude equalization. Input WDM (wavelength division multiplexed) optical signals from a number of optical systems are each de-multiplexed into a number of optical path signal that are routed through switches and then multiplexed into a number of output WDM optical signals. Problems with coherent cross-talk in optical path signals are eliminated by introducing equivalent optical path lengths between paths through which the optical path signals propagate and by introducing dead-bands between consecutive optical path signals.

Abstract: The wavelength multiplex transmission device of the present invention includes a block band unit (block dispersion compensating unit etc.) for subjecting a plurality of signal lights of different wavelengths to dispersion compensation on a band basis and outputting the compensated signal lights, a CW light output unit (CW light source unit etc.) for outputting a CW light which supplements power of the signal light, a band multiplexing unit for multiplexing all the signal lights output from the block band unit together with the CW light output from the CW light output unit, and a total band optical amplifier for amplifying all the signal lights multiplexed by the band multiplexing unit in the lump and transmitting the amplified signal lights to a transmission path.

Abstract: A compensation system for adaptive equalization of an optical signal, wherein an optical filter, whose complex coefficients are adjustable, is used for signal equalization. The quality of the optical signal is used, after conversion to an electrical data signal, as a control criterion. The compensation device can largely compensate for distortion produced by dispersion, polarization mode dispersion or self phase modulation. An optical compensation filter with a wide free spectral range is used to compensate for the wavelength-dependent dispersion in a wavelength-division multiplexed system. The setting of the filter may be fixed, or may be adjusted adaptively in a closed control loop.