Abstract: In one embodiment, an optical device includes a polarization diversity module configured to receive an optical input signal and output a first optical output signal and a second optical output signal having the same polarization state. This helps ensure light beams propagating in the optical device have the same polarization state, thereby mitigating the effects of polarization-dependent loss in the optical device. In one embodiment, the optical device comprises an optical dynamic gain equalizer with a light modulator.

Abstract: An optical amplifier of the invention comprises first and second optical amplification sections connected in a cascade manner between an input terminal and an output terminal. Optical isolators which block C-band ASE travelling in an opposite direction to L-band signal light, are inserted on the amplification medium of each of the optical amplification sections. A constant gain control section calculates the number of wavelengths based on the input power of signal light, and controls the pumping light power of each optical amplification section at a constant slope with respect to the number of wavelengths, so that the respective gains in the optical amplification sections corresponding to the number of wavelengths each become constant. As a result, it is possible to maintain flat gain wavelength characteristics even when receiving input of WDM light where the number of wavelengths varies rapidly over a wide range.

Abstract: A coordinated method is provided for controlling dynamic gain equalization in an optical transport network. The method includes: detecting a deviation in optical power of an optical signal traversing the optical transport network along a transmission path, adjusting spectral profile of the optical signal at a first network element in the optical transport network, where the first network element is located in the transmission path downstream from the origination point of the deviation; and adjusting spectral profile of the optical signal at a second network element subsequent to the adjustment at the first network element, where the second network element is located in the transmission path downstream from the origination point and the first network element.

Abstract: The present invention relates to an optical amplifier (TDFA) having a configuration which enables to reduce temperature dependence of the gain with reduced power consumption and simple control. The optical amplifier includes, in the order from an input port to an output port, an optical isolator, an optical coupler, an optical amplification fiber, an optical coupler, an optical isolator, an optical gain equalizing filter, a variable optical attenuator, an optical isolator, an optical coupler, an amplification fiber, an optical coupler, and an optical isolator. At least a core region of the optical amplification fiber is doped with Tm element, and signal light in a predetermined wavelength range is amplified by supply of pumping light. The gain equalizing fiber has a loss spectrum which shifts toward the short wavelength side as the temperature of the optical waveguide is higher, thereby equalizing the optical amplification gain of the signal light in the optical amplification fiber.

Abstract: A gain flattening device for an optical fiber amplifier. In the gain flattening device, a first end portion, having first and second ends, receives an amplified optical signal from a first amplification fiber via the first end. A second end portion, having third and fourth ends, outputs the amplified optical signal to a second amplification fiber via the fourth end. A first connector is included for connecting the first end to the third end. A second connector is included for connecting the second end to the fourth end. At least one reflective grating is further included with a predetermined gain curve at a predetermined wavelength band. An optical coupling portion couples the amplified optical signal from the first connector to the second connector in at least one coupling region where the first and second connectors are closer to each other than in any other area, and outputs part of the amplified optical signal reflected from the reflective grating via the second end.

Abstract: The optical amplifier apparatus comprises an optical amplifier (3) which amplifies an input signal light, an output detecting unit (5) which detects an output level of the optical amplifier, an output control unit (6) which controls an output level of the optical amplifier according to an output level detected by the output detecting unit (5), a gain inclination detecting unit (7) which detects a gain inclination relating to a wavelength of the optical amplifier, and a gain inclination control unit (8) which controls a gain inclination of the optical amplifier (3) according to a gain inclination detected by the gain inclination detecting unit (7).

Abstract: A Raman amplifying device includes a plurality of Raman amplifiers having a gain wavelength characteristic with a gain peak at which an amplification gain becomes the largest, including a first Raman amplifier having a gain wavelength characteristic with a plurality of gain peaks including a first gain peak and a second gain peak adjacent to the first gain peak; a second Raman amplifier having a gain wavelength characteristic with at least one gain peak including a third gain peak between the first gain peak and the second gain peak; and a third Raman amplifier having a gain wavelength characteristic with a fourth gain peak between the first gain peak and the third gain peak, the fourth gain peak forming an arithmetic sequence between the first gain peak and the third gain peak.

Abstract: There is proposed a method and a module for real time control of power per optical channel in a multi-channel optical communication line formed by a group of optical elements connected in a chain by fiber spans. The group of elements comprises one or more optical fiber amplifiers (OFA); each of the spans is characterized by its span loss, while each of the OFA is characterized by its gain and its designed output power per channel. The method comprises steps of calculating an expected total input power value (EIP) for a particular optical amplifier (OFA) in the line, measuring a real total input power (MIP) at the particular optical amplifier, and comparing the values. If a difference between the EIP and the MIP at the OFA exceeds a predetermined value, the method (and the module) ensures adjusting the gain of the OFA to maintain its output power per channel constant.

Abstract: The present invention relates to an optical component and others in structure capable of implementing improved compensation for a gain slope. The optical component is equipped with first and second Mach-Zehnder interferometers. The first Mach-Zehnder interferometer is provided with a first temperature controller for controlling a temperature of at least one of a part of an optical main path and a first optical side path, while the second Mach-Zehnder interferometer 42 is also provided with a second temperature controller for controlling a temperature of at least one of a part of the optical main path and a second optical side path.

Abstract: An optical pulse testing apparatus incorporating an optical pulse generator composed of low cost components. The optical pulse testing apparatus comprises: a ring optical path including an optical fiber 30 with a rare earth element added to; an excitation light source 32 which enters excitation optical pulses into the optical fiber 30; an optical branching filter 38 for branching the circulating optical pulses circulating through the ring optical path to emit output optical pulses; and a photodetector 40 for detecting the circulating optical pulses circulating through the ring optical path to obtain signals indicative of a light intensity and a generation timing of the circulating optical pulses. Thus, the optical pulse generator, and the optical pulse testing apparatus and method using the optical pulse generator require no expensive optical parts and complicated device control.

Abstract: An Optical transmission system (10) is presented that comprises at least one transmitter (12), at least one transmission line (14), at least one optical fiber amplifier (18), and at least one receiver (21), the optical fiber amplifier (18) being designed to show a flat characteristic of output power versus wavelength. The optical fiber amplifier (18) is designed to show the flat output characteristic in response to a flat characteristic of a first input power level versus wavelength. At least one coupler (28) for coupling at least one Raman amplifier (30) to the optical transmission system (10) is provided, the Raman amplifier (30) having a Raman gain that is tilted in a direction opposite to a tilt of the optical fiber amplifier (18) that would occur in response to a flat characteristic of a second input power level versus wavelength. Thereby, an optical transmission system (10) is presented that can be upgraded to improve OSNR while maintaining a flat output characteristic.

Abstract: Devices and methods for equalizing the gain of an optical amplifier are described. For devices including harmonic filters that are controllable by amplitude control voltages and phase control voltages, techniques for controlling the amplitude control voltages and phase control voltages are presented. Additionally, device architectures are described by which an incoming optical signal is equalized to compensate for uneven gain in prior amplifiers or other optical components, and in which the incoming optical signal is received at a beam displacer and separated into orthogonal component beams, wherein the beams are counter-propagated through the equalizer in opposite directions through the same spatial path so as to minimize or eliminate the effects spatially dependent imperfections in the equalizer.

Abstract: A dynamic gain equalizer using amplification instead of attenuation is disclosed. The device relies on integrated semiconductor optical amplifiers in line with a demultiplexer on a single integrated substrate for performing equalization of signals within each of a plurality of channels.

Abstract: A method of automatic gain control for use in an optical amplification device comprising a variable optical attenuator and an optical amplifier connected downstream of the optical attenuator includes the steps of measuring the power at the input of the amplification device, determining the number of channels at the input of the amplification device as a function of the measured power knowing the attenuation value of a span upstream of the device, and modifying the gain of the amplifier as a function of the number of channels determined in this way.

Abstract: A device including an input port configured to receive an input signal is described. The device also includes an output port and a structure, which structure includes a tunneling junction connected with the input port and the output port. The tunneling junction is configured in a way (i) which provides electrons in a particular energy state within the structure, (ii) which produces surface plasmons in response to the input signal, (iii) which causes the structure to act as a waveguide for directing at least a portion of the surface plasmons along a predetermined path toward the output port such that the surface plasmons so directed interact with the electrons in a particular way, and (iv) which produces at the output port an output signal resulting from the particular interaction between the electrons and the surface plasmons.

Abstract: Devices and methods for equalizing the gain of an optical amplifier are described. For devices including harmonic filters that are controllable by amplitude control voltages and phase control voltages, techniques for controlling the amplitude control voltages and phase control voltages are presented. Additionally, device architectures are described by which an incoming optical signal is equalized to compensate for uneven gain in prior amplifiers or other optical components, and in which the incoming optical signal is received at a beam displacer and separated into orthogonal component beams, wherein the beams are counter-propagated through the equalizer in opposite directions through the same spatial path so as to minimize or eliminate the effects spatially dependent imperfections in the equalizer.

Abstract: A multistage amplifier is disclosed for amplifying light over a wavelength band. A first and second span of amplifying fiber are optically coupled and a gain flattening filter (GFF) in-line with one of two spans of amplifying fiber is provided for attenuating certain wavelengths of amplified light. A first gain spectral response of the first and second spans of amplifying fiber including the GFF are measured over the wavelength band, and the shape of a ripple that oscillates as a function of wavelength in the form of a plurality of peaks or maxima and valleys in the form of minima occur at a plurality of different wavelengths, each different wavelength corresponding to a different channel. A second filter is provided finishing or compensating filter having a second spectral response that has a second plurality of peaks in the form of maxima and valleys in the form of minima is provided.

Abstract: An optical amplifier has a gain flatness which is maintained to be substantially constant regardless of temperature changes. The optical amplifier includes an EDF amplifying section and a Raman amplifying section, the Raman amplifying section having a temperature dependent gain profile which enables compensating for the temperature dependent gain profile of the EDF amplifying section. The Raman amplifying section includes a wavelength lock grating whose transmission wavelengths shift toward the short wavelength side as the temperature increases. The wavelength lock grating is preferably disposed to have the same temperature as that of an EDF of the EDF amplifying section. A method for compensating for temperature dependency of gain flatness of an optical amplifier and an optical transmission path including an optical amplifier are also disclosed.

Abstract: A bi-directional optical transmission system according to the present invention provides transport of x optical channels over n nodes. The system supports two-way transport of the x channels over a single fiber connecting each of the nodes in sequence. The system is advantageous in that only two optical transmission bands are utilized in order to achieve minimal loss in the separation of bands. The use of only two bands permits the utilization of low-loss wide band thin film optical filters to combine and separate the signals at each node. A reflection port of this filter is used to carry oppositely directed signals of the second band from the bi-directional fiber to an optical amplifier for the second band. An alternate arrangement of the optical filters in the two separate bands is chosen to maximize the optical performance of the overall system and significantly reduce insertion losses.

Abstract: Disclosed is a wide band optical fiber amplifier for amplifying C and L-band optical signal components having an economical configuration, high amplification efficiency while exhibiting a low noise figure. The amplifier includes first and second isolators; first, second, and third amplification units; a distributor; a gain flattening filter; and first and second reflectors. The amplifier receives C and L band optical signals and process the signals by: amplifying C and L band signals; gain flattening the only C band signal twice; amplifying C and L band signals for the second time; splitting the C band signal from L band signal; subjecting L band signal to be amplified three more times; and combining resulting C and L band signals.

Abstract: An optical amplifier system is disclosed comprising a Thulium-doped fiber span, a pump system, and a feedback loop. The Thulium-doped fiber span receives input optical signals. The pump system pumps light having a wavelength in the range of 1049 nm to 1060 nm onto the Thulium-doped fiber span. The light amplifies the input optical signals to generate amplified optical signals. The Thulium-doped fiber span transfers the amplified optical signals. The feedback loop receives at least one wavelength of amplified emissions from the Thulium-doped fiber span. The feedback loop generates optical feedback signals based the wavelength or wavelengths of the amplified emissions. The feedback loop adds the optical feedback signals to the input optical signals to provide clamping of a gain in the amplified optical signals.

Abstract: An optical device including dynamic channel equalization is provided. In an exemplary multiplexer or line amplifier configuration the device includes a plurality of separate optical paths, each of which receiving a separate group of optical signals. Each group of optical signals is provided to an associated variable optical attenuator. Separate inputs of an optical combiner are each coupled to an output of an associated one of the variable optical attenuators. The optical combiner has an output providing the separate groups of optical signals in an aggregated form on an aggregate optical signal path. An optical performance monitor is coupled to the aggregate optical signal path, and is configured to detect an optical signal to noise ratio of each of the separate groups. The monitor supplied a feedback signal to corresponding ones of the variable optical attenuators for adjusting a respective attenuation associated with each of the attenuators in dependence of the detected optical signal to noise ratios.

Abstract: A method and apparatus for controlling the pump powers of a broadband DWDM optical system using Raman amplification which determines pump settings that advantageously minimize the peak-to-peak ripple of the channel powers with respect to a given per-channel target. The illustrative method and apparatus first formulates a linear programming optimization problem, and then solves the formulated linear program in order to derive a new set of pump powers to be applied to the Raman amplification pumps. Illustratively, the linear program may be solved with use of any conventional linear programming solution technique, such as, for example, the simplex method.

Abstract: A three stage optical amplifier is disclosed having a substantially flat gain profile. The amplifier includes a variable optical attenuator coupled between second and third stages of the amplifier and a dispersion compensating element. The attenuation of the optical attenuator is adjusted in accordance with the loss across dispersion compensating element and the optical power input to the amplifier to thereby obtain a substantially flattened gain profile. An offset value can also be used to refine the variable optical attenuator control and minimize nonflatness. The first and second stages are preferably pumped to provide high gain and a low noise figure and the third stage is preferably pumped to provide a high optical conversion efficiency. In an additional example, received optical powers associated with each of the channels in a WDM system are monitored and the attenuators within each amplifier in the system are controlled so that the received powers are substantially equal.

Abstract: An optical gain flattening filter for attenuating the wavelength power levels of an optical beam to a threshold value. The filter has a series of volume phase gratings which each have a loss spectrum. The sum of the loss spectra for the volume phase gratings is about equal to the opposite of the gain spectrum of the optical amplifier. As the optical beam passes through the volume phase gratings, the sum of the loss spectra is added to the gain spectrum of the optical amplifier such that the optical beam is attenuated to the threshold value.

Abstract: The present invention relates to a white light source. This white light source comprises a plurality of amplified spontaneous emission light generating sections each comprising at least an active fiber. At least two of the amplified spontaneous emission light generating sections are connected together in series. The plurality of amplified spontaneous emission light generating sections generate amplified spontaneous emission lights having at least partially overlapping wavelength ranges. Furthermore, a white light source of the present invention includes amplified spontaneous emission light generating sections each comprising at least an active fiber. At least one of the amplified spontaneous emission light generating sections comprises a mirror.

Abstract: There are provided a plurality of optical adjusting sections, a wavelength-multiplexing section, and a control section. The plurality of optical adjusting sections, which are provided for respective wavelength bands, amplifies light beams in the respective wavelength bands. The wavelength-multiplexing section wavelength-multiplexes amplified light beams in the respective wavelength bands. The control section controls the outputs of the respective optical amplifying sections so that optical powers of the respective wavelength bands will become approximately identical at a predetermined point when wavelength-multiplexed light of the light beams in the respective wavelength bands travels to the predetermined point. This configuration makes it possible to eliminate optical power deviations between wavelength bands that would otherwise occur when an optical signal of a plurality of wavelength bands is transmitted, and to thereby make optical SNRs uniform.

Abstract: An optical amplifier is provided for performing amplification of optical signals of two wavelength bands, where deterioration in the optical SN ratio relative to one wavelength band is reduced, with a simple construction which can deal with restrictions on installation space, power consumption and the like. To this end, the present optical amplifier has a C/L band optical amplifying section for amplifying respective optical signals of a C band and an L band, a demultiplexer for demultiplexing output light from the C/L band optical amplifying section into the C band and the L band, an L band optical amplifying section for amplifying L band optical signals which have been demultiplexed by the demultiplexer, and a multiplexer for multiplexing the C band optical signals which have been demultiplexed by the demultiplexer and the L band optical signals which have been amplified by the L band optical amplifying section.

Abstract: The optical amplifier according to the present invention is constructed such that the amount of the electric current fed to the power feeding line 2a is first detected by the current detection means, and then a setting signal is generated to each of the bypass circuits 22 and 23 in accordance with the thus detected amount of the fed current, and thereafter the output level of each of the optical repeater circuits 11 and 12 is controlled respectively by the bypass circuits 22 and 23, so that the output level of these repeater circuits 11 and 12 can be controlled in accordance with the amount of the current fed to the power feeding line 2a.

Abstract: An optical amplifying apparatus which includes an optical amplifier, an optical attenuator and a controller. The optical amplifier amplifies a light signal having a variable number of channels. The optical attenuator passes the amplified light signal and has a variable light transmissivity. Prior to varying the number of channels in the light signal, the controller varies the light transmissivity of the optical attenuator so that a power level of the amplified light signal is maintained at an approximately constant level that depends on the number of channels in the light signal prior to the varying the number of channels. While the number of channels in the light signal is being varied, the controller maintains the light transmissivity of the optical attenuator to be constant.

Abstract: An optical link comprises a first optical amplifier having a first gain spectrum with a first gain ripple and a second optical amplifier having a second gain spectrum with a second gain ripple. A combined gain spectrum of the first and second gain spectra is substantially flat and has a gain ripple that is substantially less than either the first gain ripple or the second gain ripple over a particular wavelength range.

Abstract: A method for dynamically compensating for signal loss and dispersion in an optical signal traversing though an optical network. The method includes providing a dynamic gain equalization filter (DGEQ) having a dynamically adjustable transfer function, and providing a first optical amplifier and a second optical amplifier interconnected by the DGEQ to form a dynamic amplifier site in the optical network. The method further includes controlling spectral power profile of the optical signal at an output of the dynamic amplifier site by dynamically adjusting a transfer function associated with the DGEQ.

Abstract: The invention discloses a method for implementing power equalization of a DWDM system, comprises: Measure and calculate, respectively, a gain spectrum characteristic curve of an optical power booster amplifier unit and a loss spectrum characteristic curve of a loss device with related wavelengths in the DWDM system; Subtracting the loss spectrum characteristic curve from the gain spectrum characteristic curve to obtain a difference curve, taking the complement curve of the difference curve as a loss characteristic target curve of a GFF; Setting in the optical power booster amplifier unit a GFF having loss characteristic curve coinciding with the loss characteristic target curve. The invention synthetically considers gain spectrum of an optical power booster amplifier unit and loss spectrum of a loss device with relating wavelengths to define a loss characteristic curve which a GFF should have. In this way, optical power flatness of every channel is effectively guaranteed.

Abstract: An airgap type etalon has a higher degree of design freedom of a wavelength-temperature characteristic so that such a wavelength-temperature characteristic can be freely adjusted. The airgap type etalon includes a fixing block having one flat surface, and a transparent parallel flat plate having parallel flat surfaces formed with an antireflection coating and a reflection augmenting coating thereon, respectively. The flat surface at the antireflection coating side is joined to the flat surface of the fixing block. A parallel flat spacer has a thickness greater than that of the transparent parallel flat plate and an expansion coefficient different from that of the transparent parallel flat plate. One of the flat surfaces of the parallel flat spacer is joined to the flat surface of the fixing block. A transparent flat plate has opposite flat surfaces formed with an antireflection coating and a reflection augmenting coating thereon, respectively.

Abstract: The present invention relates to a method for gain equalization, for example. First, an optical transmission line including an optical amplifier having a gain changing nonlinearly with wavelength is provided (step (a)). Secondly, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength (step (b)). Finally, gain equalization of the optical transmission line is performed so as to obtain a gain remaining substantially unchanged with wavelength (step (c)). According to this method, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength. Accordingly, variations in equalization error due to changes in system condition can be easily suppressed.

Abstract: An all fiber optical filter is formed by stretching an optical fiber. The all fiber filter includes a core, an inner cladding, and an outer cladding. A core index of refraction is greater than an outer cladding index of refraction. The outer cladding index of refraction is greater than an inner cladding index of refraction. The all fiber optical filter attenuates a portion of an optical signal by transferring optical energy from the core to the outer cladding by evanescent coupling. The all fiber optical filter has a compact structure, which prevents bending and provides stable temperature performance. The all fiber optical filter is preferably used in Wavelength Division Multiplexing (WDM) systems for gain flattening of gain responses from Erbium Doped Fiber Amplifiers (EDFAs). Alternatively, the all fiber optical filter is used in other applications where optical filtering or attenuation is needed.

Abstract: An apparatus and method are described for exploiting almost the full almost 25TH% of bandwidth available in the low-loss window in optical fibers (from 1430 nm-1620 nm) using a parallel combination of optical amplifiers. The low-loss window at about 1530 nm-1620 nm can be amplified using erbium-doped fiber amplifiers (EDFAs). However, due to the inherent absorption of the erbium at shorter wavelengths, EDFAs cannot be used below about 1525 nm without a significant degradation in performance. For the low-loss window at approximately 1430-1530 nm, amplifiers based on nonlinear polarization in optical fibers can be used effectively. A broadband nonlinear polarization amplifier (NLPA) is disclosed which combines cascaded Raman amplification with parametric amplification or four-wave mixing. In particular, one of the intermediate cascade Raman order wavelengths &lgr;r should lie in close proximity to the zero-dispersion wavelength &lgr;0 of the amplifying fiber.

Abstract: The present invention provides an all-optical dynamic gain equalizer of an open-loop design using nonlinear optical materials for equalizing channel power without the need of complex electronics and close-loop control, and provides pulse reshaping and in some embodiments noise reduction at no extra cost. The invention achieves restoration of spectral power uniformity by employing nonlinear optical limiters with desirable power transfer function curves to each of the optical signals to be equalized. The invention provides the highly desirable functions of dynamic gain equalization, and optical pulse reshaping. Some embodiments constructed according to the invention provide signal dynamic range control by biasing the nonlinear optical limiter with a biasing optical signal.

Abstract: A multi-port optical amplifier chip has an inner cladding layer sandwiched between a pair of outer cladding layers, a plurality of active core elements disposed substantially within the inner cladding layer to receive optical signals at respective input ports and transmit amplified optical signals at respective output ports, a pair of reflecting surfaces on opposing sides of the inner cladding and at least one pump source. The pump source directs pump light into the inner cladding layer where it is confined to bounce back-and-forth across the active core elements thereby enhancing the absorption of pump light into the core elements, hence increasing gain. Greater than 5 dB over the C-band (1930 nm-1965 nm) in less than 10 cm is expected with a phosphate glass material co-doped with greater than 2 weight percent Erbium and 10 weight percent Ytterbium. A number of fiber drawing based approaches are contemplated for manufacturing the amplifiers to achieve this performance and reduce cost.

Abstract: Raman amplification pumping light output from a pumping light source unit is supplied to a Raman amplification optical fiber through an optical circulator. The remaining Raman amplification pumping light is detected by a light-receiving element through an optical circulator and bandpass filter. Signal light that has reached a Raman amplifier propagates through the Raman amplification optical fiber while being Raman-amplified. A control section controls the power or spectral shape of Raman amplification pumping light output from each of N pumping light sources included in the pumping light source unit on the basis of the power of the remaining Raman amplification pumping light, which is detected by the light-receiving element. Hence, a Raman amplifier capable of easily controlling gain spectrum flattening in the signal light wavelength band can be obtained.

Abstract: Optical systems of the present invention include a plurality of optical processing nodes in optical communication via a plurality of signal varying devices. A first signal varying device includes an optical fiber configured to produce Raman scattering/gain in a signal wavelength range and a first signal variation profile. A first pump source is configured provides sufficient pump power in a plurality of first pump wavelengths to stimulate Raman scattering/gain in the optical fiber within the signal wavelength range. A second signal varying device is provided having a second signal variation profile to produce a cumulative signal variation profile that differs from the first and second signal variation profiles.

Abstract: Optical systems of the present invention include amplifiers configured to achieve maximum signal channel in a span downstream of the transmitter and amplifier site and to decrease the interaction between the wavelengths at high signal channel powers. In addition, the system can include various types of optical fiber positioned in the network to provide for increased signal channel powers and higher gain efficiencies in the system.

Abstract: An optical amplifier arrangement having at least one optical amplifier stage (V1, V2) and a variably settable attenuator (VDL), whose attenuation spectrum (DV2, DV3, DV5, DV6) assumes an attenuation profile (DV2, DV3, DV5, DV6) that increases or decreases proportionally to wavelength. To reduce tilt of the channel level spectrum of an optical transmission signal, the profile of the attenuation spectrum (DV2, DV3, DV5, DV6) is variably settable. An advantageous structure of the variably settable attenuator according to the invention is furthermore specified.

Abstract: An Optical transmission system (10) is presented that comprises at least one transmitter (12), at least one transmission line (14), at least one optical fiber amplifier (18), and at least one receiver (21), the optical fiber amplifier (18) being designed to show a flat characteristic of output power versus wavelength. The optical fiber amplifier (18) is designed to show the flat output characteristic in response to a flat characteristic of a first input power level versus wavelength. At least one coupler (28) for coupling at least one Raman amplifier (30) to the optical transmission system (10) is provided, the Raman amplifier (30) having a Raman gain that is tilted in a direction opposite to a tilt of the optical fiber amplifier (18) that would occur in response to a flat characteristic of a second input power level versus wavelength. Thereby, an optical transmission system (10) is presented that can be upgraded to improve OSNR while maintaining a flat output characteristic.

Abstract: The present invention relates to a method for gain equalization, for example. First, an optical transmission line including an optical amplifier having a gain changing nonlinearly with wavelength is provided (step (a)). Secondly, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength (step (b)). Finally, gain equalization of the optical transmission line is performed so as to obtain a gain remaining substantially unchanged with wavelength (step (c)). According to this method, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength. Accordingly, variations in equalization error due to changes in system condition can be easily suppressed.

Abstract: An optical amplifier, provided in a WDM transmission system, contains an amplification medium for amplifying WDM light, a measurement part for measuring at least one input optical power of the WDM light on both input and output sides of the amplification medium, a variable gain equalizer for variably setting a passing-wavelength characteristic, a database for holding data representing wavelength characteristics that respectively correspond to transmission line types, an arithmetic part for computing an inverted passing-wavelength characteristic resulting from a passing-wavelength, based on an acquired transmission line type, the optical power measured by the measurement part, and the data held in the database, and a setting part for setting a passing-wavelength characteristic of the variable gain equalizer, based on the inverted passing-wavelength characteristic computed by the arithmetic part, and with this, capable of controlling optical filters more quickly and amplifying optical signals more efficiently i

Abstract: A method is provided for determining and setting the tilting of the spectrum of light signals in an optical fiber of an optical data transmission path having at least one part for varying the tilting of the spectrum, wherein the light signals are amplified by at least one optical amplifier and a portion of the amplified light signals is extracted, the extracted light signals are then partially guided through an influencing element with a known frequency-dependent intensity influence, the influencing element being an amplifier, a waveguide structure or a fiber with an amplifying action, the total intensity of the extracted light signals is then measured upstream and downstream of the influencing element prior to the extracted light signals being guided through the influencing element, and the control criterion is determined, based on the known frequency-dependent intensity influence of the influencing element and the measured total intensity, for setting the tilting via which the part for varying the tilting i

Abstract: The present invention is directed to a gain equalizer having a preferable equalization characteristic and a structure that can be easily fabricated. The gain equalizer flattens a spectrum of light in a predetermined wavelength range inputted through an input terminal and outputs the light from an output terminal, and comprises a coarse-tunable equalizing section and a fine-tunable equalizing section connected in series. The coarse-tunable equalizing section coarsely flattens the spectrum of the light in the predetermined wavelength range, and includes a plurality of filters each having a large loss and a small reflectance as compared with the fine-tunable equalizing section. The fine-tunable equalizing section flattens the spectrum of the light in a wavelength range where the coarse-tunable equalizing section can not flatten at a predetermined value or less among the predetermined wavelength range.

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: An optical amplifier system for amplifying an input wavelength division multiplexed (WDM) optical signal with a first optical coupler to extract a portion of the power of the input signal, an erbium-doped fiber amplifier to generate an output signal and a second optical coupler to extract a portion of the power of the output signal. A spectral monitoring unit having a volume phase grating separates the extracted input and output signals into spectral components. A photo-detector array of the spectral monitoring unit determines the power level of the spectral components. The system further includes a controller operative to control the operation of the amplifier in response to the power levels of the spectral components.