Abstract: An optical transmitting apparatus having a first optical amplifier by which quality of an output optical signal after amplified is changed according to an amplification gain, a second optical amplifier by which quality of an output optical signal after amplified is changed according to an input level of an output optical signal from the first optical amplifier, and a controlling means for performing an adaptive control on an amplification gain of the first optical amplifier so that quality of an output optical signal from the second optical amplifier becomes maximum, thereby optimizing signal quality in the optical transmitting apparatus in a hybrid optical amplifier structure.

Abstract: A multi-stage Raman amplifier includes a first Raman amplifier stage having a first sloped gain profile operable to amplify a plurality of signal wavelengths, and a second Raman amplifier stage having a second sloped gain profile operable to amplify at least most of the plurality of signal wavelengths after those wavelengths have been amplified by the first stage. The second sloped gain profile is approximately complementary slope to the slope of the first sloped gain profile. The combined effect of the first and second Raman stages contributes to an approximately flat overall gain profile over the plurality of signal wavelengths.

Abstract: The invention proposes an optical amplifier for the C and L bands having a first stage with an amplification fiber (8) common to the C and L bands, a second stage with a branch (14) for C-band signals and a branch (12) for L-band signals with an amplification fiber (20). According to the invention, most of the power in the C band is created in the common amplification stage. The amplifier has a coupler (24) in the branch for C-band signals coupling pumping light for the amplification fiber of the first stage in the contrapropagating direction. The invention simplifies the structure of the amplifier and limits the number of devices through which L-band signals pass after they are amplified in the common amplification fiber of the first stage. It improves the L-band signal/noise ratio.

Abstract: The optical amplifier realizes EDFA amplification of optical signals in new bands (the S+- and S-bands), at wavelengths of 1450 to 1530 nm. The amplifier uses multiple erbium-doped fibers to amplify optical signals at wavelengths of 1450 to 1530 nm. Each of the multiple optical filters is interposed between the individual erbium-doped fibers. The sum of the transmission characteristics of the multiple filters is identical to an inverted EDF wavelength gain characteristic at wavelengths of 1450 to 1530 nm which is then shifted to the direction that the transmission increases.

Abstract: A method of providing a predetermined insertion loss in an optical fiber amplifier, includes the step of utilizing a predetermined, fixed, spectrally-flat loss compound (insertion loss pad, ILP) to pad total optical fiber amplifier insertion loss up to a predetermined fixed level.

Abstract: It is disclosed a system for gain equalization in an optical communication system, comprising a fiber link with a two-stage EDFA with an inter-stage access, and in the inter-stage a Dispersion Compensating Fiber, a Raman pump source (RMP) in the contra-propagating way, a Variable Optical Attenuator and a gain flattening filter. The Raman pump is adapted to provide a first gain slope with an opposite trend with respect to the filter and VOA, and is further adapted such that the pump power can be controlled so as to modify the gain slope and get the gain equalization.

Abstract: A multiple stage fiber amplifier system having optical coupled first and second amplifier stages with optical isolator between the first and second stages of the amplifier system includes an optical bypass element coupled between the first and second for bypassing the optical isolator between the first and second stages of the amplifier system to filter out any signal wavelengths present in the bypass so as not to lead to multiple path interference (MPI) with these same signals propagating directly from the first stage to the second stage of the amplifier system. The bypass element can comprise a fiber with a small coiled radius that scatters out higher signal wavelengths or a lossy fiber that itself scatters out longer wavelengths that are in the optical signal wavelength range.

Abstract: A multi-wavelength light amplifier includes a first-stage light amplifier which has a first-light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.

Abstract: The effects of optical impairments on optical signal transmission are substantially reduced in a lightwave transmission system by positioning optical amplifiers and network elements in respective upstream-downstream combinations. By placing an optical amplifier at a position upstream from its corresponding network element, sufficient amplification can be provided by the optical amplifier to compensate for losses introduced by its corresponding network element. Advantageously, the corresponding downstream network element provides sufficient attenuation of the forward travelling lightwave signals so that power-dependent nonlinear effects in the optical fiber do not significantly distort the lightwave signals.

Abstract: An optical amplifier and communications system for amplifying an input signal and providing an output signal includes a nonlinear light absorber for passively controlling the level of the output signal. The nonlinear light absorber provides an approximately constant output signal level independent of the level of the input signal.

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: A method for controlling an optical amplifier is disclosed. The illustrative method includes inputting a set-point to a controller; receiving a portion of an input signal; receiving a portion of an output signal from a first amplifier stage; receiving a portion of an output signal from an attenuation stage; receiving a portion of an output signal from a second amplifier stage and adjusting the first amplifier stage, the second amplifier stage and the attenuation stage based on the received portions to substantially maintain the set-point.

Abstract: A variable gain optical amplifier, in which homogeneous gain broadening is dominant, has first and second fixed gain rare-earth doped optical waveguide amplifiers (21, 23) optically in series together with an intervening variable attenuation optical attenuator (22). This arrangement circumvents the problem of gain tilt encountered when operating such amplifiers under variable gain conditions. An alternative form of the module has variable gain waveguide amplifiers, but these are co-regulated so that the aggregate of their gain at a wavelength within the gain spectrum is maintained constant. A further alternative form of module is employed in a concatenation of such modules. In such a concatenation, the gain of individual modules is allowed to vary, but the aggregate of the gain, at wavelength within the gain spectrum, of all the waveguide amplifiers of all the modules of the concatenation is maintained constant.

Abstract: A very low noise figure optical amplifier is provided which includes a noise reduction apparatus as part of the structure of the optical amplifier. To improve the signal-to-noise ratio (SNR) of the amplified optical signal, the noise reduction apparatus makes use of the coherence of a coherent component of an amplified optical signal having a coherent signal power and the incoherence of an incoherent component of the amplified optical signal having an incoherent signal power. The amplified optical signal is split in two path signals with each path signal having the same intensity but a different phase. The optical path length the path signals is selected such that coherent path components are combined constructively at a main output while the power of the incoherent path components is divided between the main output and at least one subsidiary output. The result is an increase in the SNR, and a decrease in noise figure (NF) of approximately 3 dB.

Abstract: In a method of amplifying optical input signals over a wide bandwidth, the optical input signals are applied to an optical waveguide made from a rare-earth-doped amorphous yttrium aluminum oxide material (e.g., erbium-doped yttrium aluminum oxide material). The optical input signals include optical signals having wavelengths shorter than 1,520 nanometers and optical signals having wavelengths longer than 1,610 nanometers. Preferably, the wavelengths range from as short as approximately 1,480 nanometers to as long as approximately 1,650 nanometers. Pump light is applied to the optical waveguide to cause the waveguide to provide optical gain to the optical input signals.

Abstract: An apparatus and a method provide gain flattening in communications systems wherein a large number of optical signals at different wavelengths must be amplified while maintaining signal power within an acceptable range. Because of differences in gain of typical optical amplifiers as a function of wavelength and input power, the signals at different wavelengths are not amplified by the same amounts. Thus, when amplified multiple times, certain signals tend to become severely attenuated to the point of being no longer useable. The present gain flattening apparatus and method cause signals having higher gain-power products to be attenuated by a greater amount in response to Kerr-induced phase shifting such that after multiple stages of amplification, all the signal powers converge toward a small range of acceptable output powers.

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: A control method of an optical amplifier apparatus for compensating a gain characteristic of an optical amplifying medium. The control method includes providing an active gain characteristic actively which is a reverse of a characteristic in gain of the optical amplifying medium, and flattening the gain characteristics possessed by the optical amplifier apparatus at a predetermined value.

Abstract: A multi-stage optical fiber amplifier comprises a first gain stage amplifying and optical signal; a pumping source coupled to the first gain stage, a second gain stage coupled to the first gain to further amplifying the optical signal to a desired output signal power, and a second pumping source coupled to the second gain stage. The second pumping source is preferably an erbium-doped fiber laser and has an operating wavelength between about 1520 nm and about 1620 nm. This amplifier achieves good noise figure and high output powers.

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: A high power optical amplifier with a multiple-tap output includes a preamplifier stage (such as an EDFA), followed by a power amplifier comprises a concatenated set of co-doped optical amplifier stages. Each amplifier stage includes a tap/power extractor for removing a portion of the amplified input signal, allowing for the pump signal(s) and remaining amplified input signal to be applied as an input to the following stage.

Abstract: Optical amplifiers and methods for manufacturing optical amplifiers are provided that allow amplifiers to be fabricated to match design expectations. Optical amplifiers may be manufactured by assembling passive optical components in the amplifier before assembling active optical components such as doped fiber coils. Passive losses may then be characterized and used to calculate the lengths of the fibers that should be used in the amplifier gain stages. Following corrections to the nominal doped-fiber lengths based on the measured passive losses, the passive and active components of the amplifier may be assembled and characterized. Final corrections may be made to the amplifier assembly based on these characterizations. For example, the lengths of one or more of the doped fibers may be adjusted. If desired, such length adjustments may be made to fiber coils in the mid-stage portion of the amplifier, so that the impact on the operating characteristics of the amplifier are minimized.

Abstract: The present invention is to provide an optical fiber amplifier for clamping and equalizing gain in optical communication systems comprising: a gain clamping amplifier unit for clamping the gain, so as to make input signals have the same output power for each channel by applying a compensating signal; a second isolator for passing the input signal light from said gain clamping amplifier unit and isolating the light coming from the opposite direction; a gain equalizing filter for equalizing the output gain spectrum from the input signal from said second isolator; and a post-amplifier unit for amplifying the signal from said gain equalizing filter. Thus, the optical fiber amplifier is capable of clamping gain automatically by maintaining the same population inversion, and capable of maintaining the same gain equalization for the wide signal gain band to achieve the high transmission capacity, in cases that the number of channel varies in the input signal, while providing a high output signal power.

Abstract: The optical amplifier includes a first gain medium having an optical host that contains a rare earth dopant and a first pump that supplies optical energy at a first wavelength into this first gain medium. The first pump operates at a pump wavelength that has a lower inversion saturation than the highest wavelength of absorption of the first gain medium. The optical amplifier further comprises a second gain medium operatively coupled to the first gain medium and a second pump that supplies optical energy into the second gain medium.

Abstract: An optical amplifying apparatus for widening the input dynamic range and lowering noises. The optical amplifying apparatus comprises a first optical amplifier, an optical attenuator, a second optical amplifier and a controller. The first optical amplifier changes the target value of output light when the variance amount of input light reaches a predetermined value. The controller changes the attenuation amount of attenuator in accordance with a difference between the target value and the changed target value of the output light level of the first optical amplifier, when the target value of the output light level of the first optical amplifier is changed.

Abstract: Amplifiers having multiple gain stages are provided. Some of the gain stages provide gain in a first wavelength band and some of the gain stages provide gain in a second wavelength band. The gain stages that provide gain in the first band are interleaved with the gain stages that provide gain in the second band. The gain stages may be based on rare-earth-doped fiber amplifiers, Raman-pumped fiber amplifiers, or other suitable optical amplifiers. Gain stages may be used that include parallel amplifier branches. Each of the parallel branches may handle a separate wavelength range.

Abstract: The present invention aims at providing an optical amplification apparatus for improving noise characteristics by controlling an amplification operation by assuming a noise figure of the overall apparatus and by taking influences of noise light due to Raman amplification into consideration, and a controlling method of the optical amplification apparatus.

Abstract: An optical amplifier comprises: at least first and second amplifier stages, each stage comprising a doped fiber and a pump source for providing pump light to the fiber. The input and output power of the amplifier is measured to enable automatic gain control. The input and output power is processed in order to derive target pump source levels for achieving a substantially constant gain, and the temporal response of the gain control loop is varied in dependence on the target pump source levels. The response time of the gain control loop is thus matched to the open loop gain of the amplifier, taking into account the combination and settings of the amplifier stages.

Abstract: A cascadable optical amplifier arrangement having a modular base amplifier arrangement (BVA) that is constructed in single-mode technology and has at least one amplifier stage (VS1 to VS4). At least one high-power amplifier stage (HVS1) that has its own active fiber (AF) and at least one pump signal source (PSQ1, PSQ2) is connected to the at least one amplifier stage (VS4) of said base amplifier arrangement (BVA). In this way, a stepwise increase of the output power of an already existing base amplifier arrangement (BVA) can be achieved.

Abstract: Disclosed are an optical amplifier and an optical transmission system using the same in which not only can the dispersion of optical waveguide paths for optical amplification be easily and sufficiently compensated, but also the waveform degradation of signal light can be restrained. An optical amplifier according to one embodiment of the present invention comprises at least two erbium-doped fibers 10 and 20, having erbium doped to optically amplify signal light with the pump light, and having dispersion different from each other in sign, and being connected together in series, and two pump light sources 11 and 12 for supplying pump light to them.

Abstract: In an optical amplifier for wavelength-multiplexing transmission of this invention, signals of a plurality of wavelengths in a 1.55-&mgr;m wavelength band, which is input to an input terminal, sequentially passes through an optical isolator and optical coupler, and is input to an amplification optical fiber to be amplified. The signals amplified by and output from the amplification optical fiber sequentially passes through an optical isolator, optical coupler, optical isolator, and optical coupler, and is input to a further amplification optical fiber to be amplified. The signals amplified by and output from the further amplification optical fiber sequentially passes through an optical coupler, optical isolator, and optical coupler and is output from an output terminal. Each of an input-side optical amplifier and output-side optical amplifier performs constant output control.

Abstract: An optical network and an optical amplifier system provide flattened gain, constant per channel output power, and compensation for variable span losses. The optical amplifier system is disposed in a transmission line of the optical network. The optical amplifier includes a first and second stage optical feedback loop amplifiers.

Abstract: Optical fiber amplifiers with a simple composition than can accurately flatten optical output power in a fixed range are provided. Main optical amplifiers and first gain equalizers connected to these amplifiers are disposed between input port and output port. The main optical amplifiers comprise first EDFs which function as first amplification optical fibers, pumping light sources for providing pumping to drive the first EDFs using amplification characteristics, and second isolators. It is preferable for the second isolators to be isolators that can eliminate optical pumping power. The first gain equalizers are comprised by second absorption EDF. This second EDF operates such that the gain of the optical signal decreases in a non-pumping state or in a slight pumping state. The amplification characteristics used by the first EDF to amplify the optical signal power are opposite to the absorption characteristics used by the second EDF to absorb the optical signal power.

Abstract: The invention is directed to a multistage optical amplifier having a gain stage between two gain flattening filters. According to illustrative embodiments, a gain flattened optical amplifier system comprises a plurality of optical gain stages and a plurality of gain flattening filter stages arranged serially in an alternating manner.

Abstract: A multi-wavelength light amplifier includes a first-stage light amplifier which has a first light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.

Abstract: An amplifier system includes: (i) a distributed Raman fiber amplifier adapted to amplify C and L-band signals and; (ii) a discrete Raman fiber amplifier module that includes a C-band amplification stage and an L-band amplification stage. The discrete Raman fiber amplifier module is operatively connected to the distributed Raman fiber amplifier and amplifies signals received from the distributed Raman fiber amplifier. In one embodiment the distributed Raman fiber amplifier and the discrete Raman fiber amplifier share optical pump power provided by the shared pump.

Abstract: An optical transmission system that includes an optical amplifier coupled to the input of an optical modulator having at least two complementary output ports for providing complementary modulated optical output signals can be used such that the relative intensity noise (RIN) associated with the optical amplifier is coupled into the modulated optical output signals as common mode noise and can therefore be eliminated using a differential detection scheme. Removing the RIN associated with the optical amplifier advantageously increases the carrier to noise ratio (CNR) for the optical transmission system.

Abstract: A multi-wavelength light amplifier includes a first-stage light amplifier which has a first light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.