EP1142166A1 - Optical amplifier with power dependent feedback - Google Patents

Optical amplifier with power dependent feedback

Info

Publication number
EP1142166A1
EP1142166A1 EP99967309A EP99967309A EP1142166A1 EP 1142166 A1 EP1142166 A1 EP 1142166A1 EP 99967309 A EP99967309 A EP 99967309A EP 99967309 A EP99967309 A EP 99967309A EP 1142166 A1 EP1142166 A1 EP 1142166A1
Authority
EP
European Patent Office
Prior art keywords
amplifier
optical
power
node
gain
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99967309A
Other languages
German (de)
English (en)
French (fr)
Inventor
Gregory J. Cowle
Douglas W. Hall
Thomas W. Mcnamara
Chia C. Wang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Oclaro North America Inc
Original Assignee
Corning Inc
Oclaro North America Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Corning Inc, Oclaro North America Inc filed Critical Corning Inc
Publication of EP1142166A1 publication Critical patent/EP1142166A1/en
Withdrawn legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/29Repeaters
    • H04B10/291Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
    • H04B10/293Signal power control
    • H04B10/294Signal power control in a multiwavelength system, e.g. gain equalisation
    • H04B10/296Transient power control, e.g. due to channel add/drop or rapid fluctuations in the input power
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01SDEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/1301Stabilisation of laser output parameters, e.g. frequency or amplitude in optical amplifiers
    • H01S3/1302Stabilisation of laser output parameters, e.g. frequency or amplitude in optical amplifiers by all-optical means, e.g. gain-clamping
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04JMULTIPLEX COMMUNICATION
    • H04J14/00Optical multiplex systems
    • H04J14/02Wavelength-division multiplex systems
    • H04J14/0221Power control, e.g. to keep the total optical power constant
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04JMULTIPLEX COMMUNICATION
    • H04J14/00Optical multiplex systems
    • H04J14/02Wavelength-division multiplex systems
    • H04J14/0201Add-and-drop multiplexing
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q11/00Selecting arrangements for multiplex systems
    • H04Q11/0001Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0005Switch and router aspects
    • H04Q2011/0037Operation
    • H04Q2011/0049Crosstalk reduction; Noise; Power budget

Definitions

  • the present invention relates generally to fiber optical WDM transmission systems and optical amplifiers used therein, and more particularly to an optical feedback resonant laser cavity (OFRC), including a power dependent loss element (PDLE) for optical gain control (OGC) or optical power control (OPC), and to a method for implementing such control, which is particularly useful, although not so limited, in amplified wavelength add/drop multiplexed (WADM) transmission nodes.
  • OFRC optical feedback resonant laser cavity
  • PDLE power dependent loss element
  • OGC optical gain control
  • OPC optical power control
  • WADM amplified wavelength add/drop multiplexed
  • Wavelength division multiplexing is a demonstrated technology for increasing the capacity of existing fiber optic networks.
  • a typical WDM system employs multiple optical signal channels, each channel being assigned a particular wavelength or wavelength band.
  • optical signal channels are generated, multiplexed to form an optical signal comprised of the individual optical signal channels, transmitted over a single waveguide, and demultiplexed such that each channel is individually routed to a designated receiver.
  • Multiple optical channels can be amplified simultaneously in optical amplifiers such as erbium doped fiber amplifiers (EDFAs), facilitating the use of WDM systems for long distance transmission.
  • EDFAs erbium doped fiber amplifiers
  • Add-drop multiplexers are used, for instance, at nodes in a WDM communication network to extract one or more channels from the multiplexed stream, letting the remaining channels pass through unaltered to the next node, and to add to the multiplexed stream a new channel for transmission.
  • Another application of such devices is for routing nodes of reconfigurable optical networks, namely rerouting certain information streams as a result of changed traffic conditions or to remedy a failure downstream from the node.
  • a conventional WADM node 120 consists respectively of gain-controlled input and output amplifiers 121, 123, a pair of lxN and Nxl multiplexers/demultiplexers 125, 127, and an array of add/drop switches 129.
  • This type of WADM node is herein referred to as a lxNxl node since there is a single input amplifier and a single output amplifier, both of which are likely gain flattened and gain controlled amplifiers.
  • Wavelength add/drop multiplexing permits signals to be routed from different networks or propagate through different spans. As a result, however, the per channel power after each add/drop switch can vary significantly, say by YdB.
  • VOA variable optical attenuator
  • the pump power of the output amplifier needs to support (10 ⁇ /10) x (N-1)) + 1 channels of power before the VOA can respond.
  • the pump power penalty to protect the surviving channel is almost YdB if N is large.
  • One suggested approach to address this problem consists of replacing the VOAs and the output amplifier of the lxNxl architecture with multiple parallel power equalization amplifiers (PEAs) as schematically shown in FIG. 2, to form what is referred to herein as a lxNxN architecture because there are N optically controlled outputs.
  • PEAs parallel power equalization amplifiers
  • Each PEA can be designed to operate in its saturation regime so that the output signal power is determined by the pump power and is substantially independent of the input powers. Simulation results have shown that it is possible for the output power of these PEAs to differ by only 0.5dB for an input power difference of 6dB, and a IdB difference has been experimentally demonstrated.
  • this approach is cost effective in that the VOAs and a complex output amplifier are eliminated from the system, and separate pump diodes for each PEA are replaced by a shared pump source, there is a recognized need for transient (as channels are added/dropped ) power control of each of the parallel amplifiers. Without such control the inversion of the amplifier is higher when a channel is dropped, and there is a large transient power spike when another channel is added back into the amplifier.
  • an optical feedback resonant laser cavity (OFRC) in each PEA so that the transient control is individually applied to these parallel amplifiers, even though they commonly share the pump power.
  • the OFRC is configured so that an optical power control (OPC) laser turns on (lases) when a signal channel is dropped from the PEA.
  • OPC optical power control
  • the OPC laser turns off (stops lasing) when a signal channel appears in the PEA, so that the PEA is only saturated by the signal channel and the signal channel extracts all of the available energy provided by the pump power.
  • the OPC laser has to be turned off by a signal channel having the lowest possible channel power.
  • the cavity loss of the OFRC must be high.
  • a high loss produces a low OPC laser power when the laser turns on, and thus a high amplifier inversion.
  • a signal channel with a high power is added into the highly inverted PEA which is saturated by an OPC laser with low power, there will be a transient power spike due to that high inversion.
  • the OFRC requires a lower cavity loss and higher OPC laser power. This presents the paradox of having a high loss and a low loss in the OFRC.
  • the WDM input amplifiers shown in FIG. 1 and FIG. 2 are gain-controlled to reduce steady-state (DC) gain error.
  • DC steady-state
  • WDM optical amplifier involves configuring each amplifier with an OFRC such as an optical gain control (OGC) laser cavity.
  • OGC optical gain control
  • the optical gain must equal the passive loss at the lasing wavelength.
  • the optical gain at all wavelengths in a given spectrum is locked once the gain is fixed at any particular wavelength.
  • the gain spectrum of the amplifier is determined once the OGC laser wavelength and the passive loss at that wavelength are determined.
  • an erbium doped fiber is not a purely homogeneous medium for light amplification; rather, it exhibits a certain degree of inhomogeneity. This circumstance gives rise to the phenomenon of spectral hole burning.
  • the power of the OGC laser is increased, for example, by dropping channels or by increasing the pump power, the spectral hole at the lasing wavelength gets deeper and results in a steady-state (DC) gain error in the signal band. This is illustrated schematically in FIG. 3(a). Accordingly, there is a need to solve the gain error problem caused by spectral hole burning by the OGC laser when signals are added or dropped, or the pump power is changed.
  • An embodiment of the present invention is directed to an optical amplifier that includes a gain medium; a pump source coupled thereto to excite the gain medium; an optical feedback resonant laser cavity (OFRC) coupled to the gain medium; and a power dependent loss element (PDLE) in the OFRC which exhibits a decreasing loss as a function of increasing incident laser power.
  • the OFRC with a PDLE according to the invention provides optical gain control (OGC) for a WDM amplifier or optical power control (OPC) for a single channel amplifier, when either of which are subject to dynamically changing amplifier input conditions.
  • the PDLE is a passive mechanism such as a saturable absorber.
  • the saturable absorber can be a length of rare earth doped fiber, and more preferably an erbium doped fiber.
  • the PDLE can be an active mechanism such as a light intensity modulator, namely an acousto-optic modulator or an electro- optic modulator, with a feedback control.
  • the preferable OFRC is in the form of a ring cavity, or alternatively a linear cavity.
  • the OFRC structure and associated components used to couple the OFRC to the amplifier will substantially determine the lasing wavelength of the laser.
  • a ring cavity will preferably be coupled to the amplifier via two wavelength selective couplers which transmit the signal band wavelengths and couple the wavelength band of the OGC laser or OPC laser to the feedback cavity.
  • a linear cavity will preferably utilize a grating structure as a cavity end reflector/transmitter with the reflected light corresponding to the lasing wavelength and the transmitted light corresponding to the signal band wavelengths.
  • the amplifier is preferably an EDFA, but alternatively could be a semiconductor amplifier, a Raman amplifier, a Brillouin amplifier, or other type of amplifier operating over conventional or extended optical bandwidths.
  • the preferable OGC or OPC laser cavity is in the form of a ring cavity, or alternatively a linear cavity, and the lasing wavelength is substantially determined by the coupled wavelength.
  • a ring cavity will preferably be coupled to the amplifier via two wavelength selective couplers which transmit the signal band wavelengths and couple the laser wavelength.
  • a linear cavity will preferably utilize a grating structure as a cavity end reflector/transmitter with the reflected light corresponding to the lasing wavelength and the transmitted light corresponding to the signal band wavelengths.
  • the PDLE again is a passive mechanism such as a saturable absorber.
  • the saturable absorber can be a length of rare earth doped fiber, and more preferably an erbium doped fiber.
  • the PDLE similarly can be an active mechanism such as a light intensity modulator, namely, an acousto-optic modulator, with a feedback control.
  • a method for controlling a transient power change in a single channel optical amplifier or reducing a DC gain error in a WDM optical amplifier that are subject to dynamically variable operating conditions at an input of the amplifier, and including an OFRC coupled to a gain medium of the amplifier having an output power that is dynamically dependent upon the operating conditions includes the step of decreasing the cavity loss of the OFRC as the output power of the OFRC increases or vice-versa, whereby the inversion of the amplifier gain medium is dynamically varied to reduce gain or power changes in the amplifier.
  • the invention described herein provides a device and method for improved optical gain or power control.
  • the advantages of optical (in contrast to electronic) control are well appreciated and include the attributes of being passive (that is, substantially independent of gain ripple, signal input powers, and pump power) and self-contained.
  • the invention is especially useful in WADM applications, as well as for soliton propagation systems, in which precise channel powers are important, and which benefit from the power "re-equalization" at each lxNxN node. Since at each lxNxN node the channel power is re-equalized after a PEA such that the output power is independent of the input power, gain ripple does not accumulate along a chain of amplifiers.
  • Fig. 1 is a schematic illustration of a conventional lxNxl WADM node with a single input and output amplifier
  • Fig. 2 is a schematic illustration of a conventional lxNxN WADM node with parallel power equalization amplifiers (PEAs) and a commonly shared pump;
  • Fig. 3(a) is a plot of two gain versus wavelength curves for different signal channel counts without a PDLE according to the invention;
  • Fig. 3(b) is a plot of two gain versus wavelength curves for different signal channel counts with a PDLE according to the invention
  • Fig. 4 is a schematic illustration of an amplifier with an OFRC including a PDLE according to an embodiment of the invention
  • Fig. 5 is a plot of power dependent loss versus incident laser power from an OGC laser for a PDLE according to an embodiment of the invention
  • Fig. 6 is a plot of two sets of data points of gain versus wavelength for optical signals amplified by an OGC amplifier when the OGC cavity loss is fixed (VOA only) and when the OGC cavity contains a PDLE according to an embodiment of the invention
  • Fig. 7 is a set of plots of gain error versus wavelength for eight optical signal channels amplified by an OGC amplifier when seven channels and one channel, respectively, are dropped, when the amplifier has a fixed loss and a PDLE in the OGC cavity according to an embodiment of the invention
  • Fig. 8 is a two plot comparison graph of transient gain error versus time for a 1533nm signal channel when the remaining channels are dropped and added for the OGC amplifier with and without a PDLE according to the invention.
  • Fig. 9 is a three plot comparison graph of output power versus time for a single channel amplifier (PEA) with no control, optical feedback control with a fixed loss, and optical feedback control with a PDLE in the OFRC, when a 1557.2-nm channel with a power of -6dBm is added to the PEA.
  • PEA single channel amplifier
  • optical power control OPC
  • OGC optical gain control
  • a power equalization amplifier as used herein is a single optical signal channel amplifier operated in saturation, in contrast to a WDM amplifier (described below with respect to optical gain control).
  • PEC optical power control
  • OFRC optical feedback resonant cavity
  • This "turning on” of the OPC laser can be achieved by controlling the loss in the optical feedback cavity. If the amplifier gain at the OPC laser wavelength in the signal-drop state is higher than the optical feedback cavity loss, the OPC laser will turn on (lase) and drive the amplifier gain down to a value equal to the cavity loss when the signal is dropped. The OPC laser then saturates the amplifier and regulates the amplifier inversion. Ideally, the OPC laser will "turn off when a signal channel is added into the amplifier; otherwise, the OPC laser extracts part of the energy provided by the pump source, and the concept of power equalization via saturating the PEA with only the signal is defeated.
  • the signal power may change by a factor such as YdB
  • the loss must be higher than the gain of the amplifier saturated by the lowest possible signal power so that when the signal appears, the OPC laser stops lasing.
  • a high cavity loss means a low OPC laser power and a high amplifier inversion when the signal is dropped. If the added channel has higher power, then there occurs a transient power spike due to the high amplifier inversion. To reduce the transient power spike, the fixed loss in the optical feedback cavity must decrease. If the cavity loss is fixed, there is the paradox of having a high or a low optical feedback cavity loss.
  • the cavity loss decreases resulting in more feedback in the cavity and an increase in the intensity of the ASE fed into the cavity.
  • the power dependent loss becomes low enough that the OPC laser turns on, and the PDLE is driven by the OPC laser to its low loss condition.
  • the cavity has low loss once the OPC laser turns on and the gain medium has a low inversion.
  • the amplifier inversion is comparable to the inversion that is saturated by the highest possible added signal power. Thus the transient power spike resulting from adding a high power signal is reduced.
  • an EDFA is operated in its saturation regime.
  • WDM multichannel
  • OGC optical gain control
  • OFRC optical feedback resonant cavity
  • an optical fiber amplifier 10 includes a gain medium in the form of a length of erbium doped fiber (EDF) 12 coupled to an input 14 and an output 16 of the amplifier.
  • EDF erbium doped fiber
  • An optical isolator 28 preferably determines the direction of the laser signal (the direction of the OGC laser or the OPC laser) which, as shown, travels in a clockwise direction co- directionally with the input signal.
  • a pump source 18 for exciting the EDF gain medium is coupled to an input of the EDF 12 via coupler 20 which is preferably a WDM coupler.
  • the pump source 18 is preferably a 980nm or 1480nm laser diode.
  • the arrangement shown in FIG. 4 provides for a co-propagating signal and pump (left to right in FIG.
  • VOA variable optical attenuator
  • PDLE power dependent loss element
  • the PDLE 34 is characterized such that its loss value (and thus the cavity loss) decreases with increasing incident light intensity from the OGC laser or the OPC laser. This is illustrated in FIG. 5 which schematically shows the power dependent loss characteristic of the PDLE 34. As shown, the loss of the PDLE decreases non-linearly as the incident light intensity to the PDLE increases.
  • the PDLE is a passive structure such as a saturable absorber.
  • an EDF is well suited to this application because of electron dynamics between the I 13/ state and the ground state.
  • the saturable absorber is a length of EDF 12 having a short I ⁇ 3/ state Er ion lifetime, on the order of ⁇ 1 ms.
  • Other saturable absorbers such as dyes, or semiconductor saturable absorbers, are also suitable.
  • the PDLE 34 is an active device that modulates the laser light intensity, such as an acousto- optic modulator with feedback control to adjust the cavity loss dynamically according to the loading condition of the amplifier.
  • the ring geometry OFRC 30 combined with the PDLE 34 according to the invention effectively provides optical gain control (OGC) or optical power control (OPC) for a WDM amplifier or PEA, respectively.
  • OGC optical gain control
  • OPC optical power control
  • an alternative configuration could comprise a linear OFRC geometry (not shown) having appropriate end reflectors such as mirrors, gratings, filters, or other suitable components.
  • the combination of the pump source 18 and the EDF 12 provides a signal amplifying medium in the 1500nm telecommunications window (C-band from about 1520-1565nm and L-band from about 1565-1625nm)
  • the invention is not intended to be so limited; rather, as will be appreciated by one skilled in the art, any suitable spectrally appropriate gain medium may be utilized.
  • Some examples include a semiconductor optical amplifier with a current pump source or a different rare earth doped waveguide of a glass, glass ceramic, hybrid, or other composition or form with an appropriate excitation source.
  • FIG. 4 shows an EDFA 10 with an OFRC 30 including a power dependent loss element 34.
  • the PDLE 34 is a lm long EDF 12 which exhibits a power dependent loss characteristic as shown in FIG. 5.
  • the VOA 32 is set at 8.3dB to provide a fixed loss for the laser cavity 30 at a lasing wavelength of 1527nm, and to set the gain spectrum of the amplifier.
  • the optical gains at eight wavelengths (channels) were measured with eight saturating signals having a per channel power of -lOdBm.
  • the gain spectra for the two conditions, shown in FIG. 6, are essentially the same and exhibit an average gain of about 16dB.
  • the required pump power to provide the gain spectra was 20.8 dBm with the PDLE present.
  • Each saturating channel actually represented four channels worth of power assuming the per channel output power is OdBm for a practical metropolitan WADM system.
  • the gain error ( ⁇ G) due to dropping of signal channels for the OGC schemes with and without the PDLE is shown in FIG.
  • the gain error is defined to be the maximal deviation in gain from the fully loaded gain of the EDFA.
  • the gain of the surviving channels increases with the number of the dropped channels due to the increase of the spectral hole depth caused by the increase of the OGC laser power.
  • the gain error is as large as about 1.3dB for the 1533nm channel.
  • all of the channels acquire a negative gain error when one channel is dropped.
  • the channel gain increases.
  • the gain error for the surviving channel reaches the positive maximum.
  • the worst case gain error is about +0.4dB for the 1533nm surviving channel when the remaining seven channels are dropped.
  • FIG. 5 shows the power dependent loss versus the OGC laser power incident on the PDLE, and the operational regime of the PDLE according to the exemplary embodiment.
  • the incident OGC laser power to the PDLE is about -4dBm, and the PDLE has a loss of about 1.4dB.
  • the power dependent loss is reduced to about 0.4dB at the point where there is but one surviving signal channel input to the amplifier. It can be understood from the data curve in FIG. 5 that the power dependent loss is nonlinear relative to the incident OGC laser power (the slope is greater for more surviving channels).
  • the power dependent loss decreases too much to over-compensate for a small change of the OGC laser power and the spectral hole depth, resulting in a negative gain error.
  • the transient response of the 1533-nm channel due to adding or dropping the other seven channels is also characterized, and the results are illustrated in FIG. 8.
  • the output of the amplifier 10 was band-pass filtered (about -20dB over a 3nm bandwidth) to ensure that only the power excursion of the one surviving channel was measured.
  • the gain of the 1533nm channel overshoots the zero level by about IdB after lOO ⁇ sec of the drop transient (dropping the remaining seven channels).
  • the gain error then gradually increases to the steady state value of about 1.3dB.
  • the gain error of the 1533nm channel settles back to zero.
  • the relaxation oscillations of the OGC laser are also shown imprinted on the surviving channel.
  • the transient response of the surviving channel for the case with the PDLE 34 in the OGC cavity 30 is also shown.
  • the gain of the surviving channel increases by 0.5dB (from the zero value on the vertical axis), and then is expected to settle to its steady state gain error of 0.4dB.
  • the surviving-channel gain should recover to the gain value for a fully loaded amplifier and have zero gain error by definition.
  • the gain of the 1533nm channel undershoots the zero gain value by about 0.6dB and then eventually recovers to zero gain error.
  • the undershoot and slow recovery are due to the slow dynamics of the EDF-PDLE.
  • the OGC laser power is decreased and the loss of the PDLE should become larger to increase the amplifier gain.
  • the loss of the PDLE 34 then increases with a time constant of about 10ms (on the order of the L /2 -state lifetime of the EDF PDLE) and recovers the amplifier gain to its fully loaded value.
  • PDLEs with fast dynamics such as short lifetime Er fibers or semiconductor saturable absorbers, would reduce the observed undershoot and improve the transient response.
  • the transient response of a PEA 10 was characterized under three conditions, namely without transient power control, with optical feedback control with a fixed cavity loss, and with optical feedback control with a PDLE 34 in the cavity, as illustrated in FIG. 9.
  • the add/drop signal is at 1557.2nm, and the signal power is -6dBm.
  • An EDF 12 with a length of about 12m was used as the PDLE.
  • the VOA 32 which had an insertion loss of about 0.3dB, was used for fine adjustment of the total loss in the optical feedback cavity 30.
  • the output power was about 6dBm, as shown in the "signal adding" region in FIG. 9.
  • the inversion of the amplifier is high when the signal is dropped because there is only ASE and no saturating signal in the amplifier.
  • the transient power spike is as high as about 17dBm, as shown.
  • This transient power spike is reduced with optical feedback control.
  • it is still 12dBm which is still considered to be 6dB too high.
  • the OPC laser has to be turned off with the appearance of the lowest possible input signal power (-12dBm in the exemplary case).
  • the optical feedback cavity has a fixed loss, that loss must be high enough; in other words, the total optical feedback cavity loss has to be higher than the optical gain at the OPC laser wavelength when the amplifier has a -12dBm input channel as its saturating signal.
  • a high optical feedback cavity loss means a low OPC laser power.
  • the transient spike is almost eliminated with a PDLE 34 in the optical feedback cavity 30 because the cavity loss is adjusted dynamically, as explained above.
  • the VOA in the optical feedback cavity may be replaced by a well calibrated and performed off-set splice as a loss element.
  • WADM wavelength add/drop multiplexed
  • each path 103 includes an optical amplifier 10 as shown in FIG. 4, with the exception that the pump source 18 is commonly shared among the N optical amplifiers 10 via pump paths 121.
  • At least some of the optical amplifiers 10 each incorporate an OFRC 30 which comprises a PDLE 34 as described above, thereby addressing the problem of dynamically variable signal input conditions to the amplifiers resulting from channel adding/dropping.
  • N optical amplifiers 10 are single channel PEAs or WDM amplifiers depending upon the application. If the amplifiers are PEAs, then changing input conditions will cause output power variations. Likewise, if the amplifiers are WDM amplifiers, changing input conditions will cause gain errors at the amplifier output.
  • an input amplifier 121 preferably being a WDM amplifier, is connected to the demultiplexer 105 at an input of the node. Amplifier 121 is preferably equipped with an OFRC 30 including a PDLE 34 according to the invention.
  • node 110 is equipped with an output amplifier 123, preferably a gain-controlled WDM amplifier.
  • a method for controlling a transient power change in a single channel optical amplifier or reducing a DC gain error in a WDM optical amplifier that are subject to dynamically variable operating conditions at an input of the amplifier, and including an OFRC coupled to a gain medium of the amplifier having an output power that is dynamically dependent upon the operating conditions includes the step of decreasing the cavity loss of the OFRC as the output power of the OFRC increases or vice-versa, whereby the inversion of the amplifier gain medium is dynamically varied to reduce gain or power changes in the amplifier.
  • the OFRC 30 functions as an optical gain control (OGC) mechanism for the amplifier 10 as described above.
  • the cavity loss is fixed and the inversion of the EDF gain medium 12 must increase to maintain the optical gain at the bottom of the spectral hole equal to the optical loss at the OGC laser wavelength.
  • the gain of the channels being amplified increases to cause DC gain error.
  • EDF 12 inversion which in turn compensates for the effect of increased inversion caused by the initial spectral hole burning of the OGC laser.
  • the amplifier 10 is a PEA
  • the method provides for optical power control to reduce transient power spikes resulting from changing amplifier input conditions.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Optics & Photonics (AREA)
  • Plasma & Fusion (AREA)
  • General Physics & Mathematics (AREA)
  • Lasers (AREA)
  • Optical Communication System (AREA)
EP99967309A 1999-01-06 1999-12-14 Optical amplifier with power dependent feedback Withdrawn EP1142166A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US11499699P 1999-01-06 1999-01-06
US114996P 1999-01-06
PCT/US1999/029620 WO2000041346A1 (en) 1999-01-06 1999-12-14 Optical amplifier with power dependent feedback

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JP (1) JP2002534815A (ja)
KR (1) KR20010113641A (ja)
CN (1) CN1357180A (ja)
AU (1) AU2361200A (ja)
CA (1) CA2357496A1 (ja)
TW (1) TW459449B (ja)
WO (1) WO2000041346A1 (ja)

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ITMI20010695A1 (it) * 2001-03-30 2002-09-30 Marconi Comm Spa Metodo e dispositivo per la sopravvivenza del traffico in sistemi dwdm con add/drop nel caso di interruzione del collegamento a fibre ottich
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KR20010113641A (ko) 2001-12-28
CN1357180A (zh) 2002-07-03
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TW459449B (en) 2001-10-11
CA2357496A1 (en) 2000-07-13
WO2000041346A1 (en) 2000-07-13

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