Source: http://www.google.com/patents/US5995274?ie=ISO-8859-1&dq=7,346,545
Timestamp: 2015-03-02 01:46:45
Document Index: 656641116

Matched Legal Cases: ['art 1000', 'art 2000', 'art 1000', 'art 2000', 'art 1000', 'art 1000', 'art 2000', 'art 1000', 'art 1000', 'art 2000', 'art 2000', 'art 1000', 'art 1000', 'art 2000', 'art 3000', 'art 3000', 'art 3000', 'art 2000', 'art 1000', 'art 3000', 'art 2000', 'art 3000', 'art 2000', 'art 3000', 'art 1000', 'art 3000', 'art 3000', 'art 3000', 'art 3000', 'art 3000', 'art 3000', 'art 3000', 'art 1000', 'art 2000', 'art 1000']

Patent US5995274 - Multi-wavelength light amplifier - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn 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...http://www.google.com/patents/US5995274?utm_source=gb-gplus-sharePatent US5995274 - Multi-wavelength light amplifierAdvanced Patent SearchPublication numberUS5995274 APublication typeGrantApplication numberUS 09/139,768Publication dateNov 30, 1999Filing dateAug 25, 1998Priority dateMay 2, 1996Fee statusPaidAlso published asCN1121626C, CN1167269A, CN1406016A, CN1406017A, CN1406018A, CN1406019A, CN100477563C, CN100477571C, CN100477572C, CN100477573C, DE69737190D1, DE69737190T2, DE69737802D1, DE69737802T2, DE69737813D1, DE69737813T2, DE69739010D1, EP0805571A2, EP0805571A3, EP0805571B1, EP0902565A2, EP0902565A3, EP0902565B1, EP0902566A2, EP0902566A3, EP0902566B1, EP0902566B9, EP0902567A2, EP0902567A3, EP1578047A1, EP1578047B1, EP2296303A1, EP2296303B1, US5966237, US6025947, US6144485, US6157481, US6198572, US6377395, US6646791, US6865016, US7227681, US7477447, US7969649, US8553319, US20010017729, US20020067538, US20040036958, US20050046927, US20070201876, US20090086310, US20110205620, US20140043675Publication number09139768, 139768, US 5995274 A, US 5995274A, US-A-5995274, US5995274 A, US5995274AInventorsYasushi Sugaya, Susumu KinoshitaOriginal AssigneeFujitsu LimitedExport CitationBiBTeX, EndNote, RefManPatent Citations (16), Non-Patent Citations (8), Referenced by (40), Classifications (41), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetMulti-wavelength light amplifier
US 5995274 AAbstract
1. An optical amplifying apparatus comprising:a first amplifying stage amplifying a light signal, to produce a first stage amplified light signal; a dispersion compensator compensating for dispersion in the first stage amplified light signal, to produce a dispersion compensated light signal; a second amplifying stage amplifying the dispersion compensated light signal; and a controller controlling a power level of the first stage amplified light signal in accordance with a power level of the dispersion compensated light signal before being amplified by the second amplifying stage, wherein the first and second amplifying stages are included in a multi-stage optical amplifying unit. 2. An optical amplifying apparatus as in claim 1, wherein the controller comprises:an attenuator attenuating the power level of the first stage amplified light signal, the controller controlling the attenuation of the attenuator to control the power level of the first stage amplified light signal. 3. An optical amplifying apparatus as in claim 1, wherein the controller comprises:an attenuator attenuating the power level of the first stage amplified light signal; and a control circuit controlling the attenuation of the attenuator, to control the power level of the first stage amplified light signal to compensate for loss in the dispersion compensator. 4. An optical amplifying apparatus as in claim 1, wherein the controller controls the power level of the first stage amplified light signal to maintain a power level at an output of the second amplifying stage at a predetermined level.
5. An optical amplifying apparatus as in claim 1, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 6. An optical amplifying apparatus as in claim 2, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 7. An optical amplifying apparatus comprising:a first amplifying stage amplifying a light signal, to produce a first stage amplified light signal; a dispersion compensator compensating for dispersion in the first stage amplified light signal, to produce a dispersion compensated light signal; a second amplifying stage amplifying the dispersion compensated light signal; an attenuator attenuating the power level of the first stage amplified light signal; and a level control circuit controlling the attenuation of the attenuator in accordance with a power level of the dispersion compensated light signal before being amplifying by the second amplifying stage, wherein the first and second amplifying stages are included in a multi-stage optical amplifying unit. 8. An optical amplifying apparatus as in claim 7, further comprising:a detector detecting the power level of the dispersion compensated light signal and producing a corresponding detection signal, wherein the level control circuit controls the attenuation of the attenuator in accordance with the detection signal, to control the power level of the first stage amplified light signal to compensate for loss in the dispersion compensator. 9. An optical amplifying apparatus as in claim 7, further comprising:a coupler decoupling a portion of the dispersion compensated light signal; and a detector detecting the power level of the dispersion compensated light signal from the decoupled portion, and producing a corresponding detection signal, wherein the level control circuit controls the attenuation of the attenuator in accordance with the detection signal, to control the power level of the first stage amplified light signal to compensate for loss in the dispersion compensator. 10. An optical amplifying apparatus as in claim 7, wherein the second amplifying stage amplifies the dispersion compensated light signal to produce a second stage amplified light signal, the apparatus further comprising:a level control correction circuit controlling the level control circuit to control the attenuation of the attenuator so that a power level of the second stage amplified light signal is maintained at a predetermined level. 11. An optical amplifying apparatus as in claim 7, wherein the second amplifying stage amplifies the dispersion compensated light signal to produce a second stage amplified light signal, the apparatus further comprising:a detector detecting a power level of the second stage amplified light signal and producing a corresponding detection signal; and a level control correction circuit controlling the level control circuit in accordance with the detection signal of the detector to control the attenuation of the attenuator so that a power level of the second stage amplified light signal is maintained at a predetermined level. 12. An optical amplifying apparatus as in claim 7, wherein the second amplifying stage amplifies the dispersion compensated light signal to produce a second stage amplified light signal, the apparatus further comprising:a coupler decoupling a portion of the second stage amplified light signal; a detector detecting a power level of the second stage amplified light signal from the decoupled portion, and producing a corresponding detection signal; and a level control correction circuit controlling the level control circuit in accordance with the detection signal of the detector to control the attenuation of the attenuator so that a power level of the second stage amplified light signal is maintained at a predetermined level. 13. An optical amplifying apparatus as in claim 7, further comprising:a dispersion compensator loss correction circuit controlling the level control circuit to control the attenuation of the attenuator so that the power level of the dispersion compensated light signal is maintained at a predetermined level. 14. An optical amplifying apparatus as in claim 7, further comprising:a detector detecting a power level of the dispersion compensated light signal and producing a corresponding detection signal; and a dispersion compensator loss correction circuit controlling the level control circuit in accordance with the detection signal of the detector to control the attenuation of the attenuator so that the power level of the dispersion compensated light signal is maintained at a predetermined level. 15. An optical amplifying apparatus as in claim 7, further comprising:a coupler decoupling a portion of the dispersion compensated light signal; a detector detecting a power level of the dispersion compensated light signal from the decoupled portion, and producing a corresponding detection signal; and a dispersion compensator loss correction circuit controlling the level control circuit in accordance with the detection signal of the detector to control the attenuation of the attenuator so that the power level of the dispersion compensated light signal is maintained at a predetermined level. 16. An optical amplifying apparatus as in claim 7, wherein the second amplifying stage amplifies the dispersion compensated light signal to produce a second stage amplified light signal, the apparatus further comprising:a level control correction circuit controlling the level control circuit to control the attenuation of the attenuator so that a power level of the second stage amplified light signal is maintained at a predetermined level; and a dispersion compensator loss correction circuit controlling the level control circuit to control the attenuation of the attenuator so that a power level of the dispersion compensated light signal is maintained at a predetermined level. 17. An optical amplifying apparatus as in claim 7, wherein the second amplifying stage amplifies the dispersion compensated light signal to produce a second stage amplified light signal, the apparatus further comprising:a first detector detecting a power level of the second stage amplified light signal and producing a corresponding detection signal; a level control correction circuit controlling the level control circuit in accordance with the detection signal of the first detector to control the attenuation of the attenuator so that the power level of the second stage amplified light signal is maintained at a predetermined level; a second detector detecting a power level of the dispersion compensated light signal and producing a corresponding detection signal; and a dispersion compensator loss correction circuit controlling the level control circuit in accordance with the detection signal of the second detector to control the attenuation of the attenuator so that the power level of the dispersion compensated light signal is maintained at a predetermined level. 18. An optical amplifying apparatus as in claim 7, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 19. An optical amplifying apparatus as in claim 10, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 20. An optical amplifying apparatus as in claim 13, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 21. An optical amplifying apparatus as in claim 16, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 22. An optical amplifying apparatus comprising:a first amplifying stage amplifying a light signal, to produce a first stage amplified light signal; a dispersion compensator compensating for dispersion in the first stage amplified light signal, to produce a dispersion compensated light signal; a second amplifying stage amplifying the dispersion compensated light signal; a level control circuit controlling a power level of the first stage amplified light signal; and a dispersion compensator loss correction circuit controlling the level control circuit to control the power level of the first stage amplified light signal in accordance with a power level of the dispersion compensated light signal before being amplified by the second amplifying stage, wherein the first and second amplifying stages are included in a multi-stage optical amplifying unit. 23. An optical amplifying apparatus as in claim 22, wherein the second amplifying stage amplifies the dispersion compensated light signal to produce a second stage amplified light signal, the apparatus further comprising:a level control correction circuit controlling the level control circuit to control the power level of the first stage amplified light signal so that a power level of the second stage amplified light signal is maintained at a predetermined level. 24. An optical amplifying apparatus as in claim 22, wherein the second amplifying stage amplifies the dispersion compensated light signal to produce a second stage amplified light signal, the apparatus further comprising:a detector detecting a power level of the second stage amplified light signal and producing a corresponding detection signal; and a level control correction circuit controlling the level control circuit in accordance with the detection signal of the detector to control the power level of the first stage amplified light signal so that a power level of the second stage amplified light signal is maintained at a predetermined level. 25. An optical amplifying apparatus as in claim 22, wherein the second amplifying stage amplifies the dispersion compensated light signal to produce a second stage amplified light signal, the apparatus further comprising:a coupler decoupling a portion of the second stage amplified light signal; a detector detecting a power level of the second stage amplified light signal from the decoupled portion, and producing a corresponding detection signal; and a level control correction circuit controlling the level control circuit in accordance with the detection signal of the detector to control the power level of the first stage amplified light signal so that the power level of the second stage amplified light signal is maintained at a predetermined level. 26. An optical amplifying apparatus as in claim 22, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 27. An optical amplifying apparatus as in claim 23, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 28. An optical amplifying apparatus comprising:a first amplifying stage amplifying a light signal, to produce a first stage amplified light signal; a dispersion compensator compensating for dispersion in the first stage amplified light signal, to produce a dispersion compensated light signal; a second amplifying stage amplifying the dispersion compensated light signal; a level control circuit controlling a power level of the first stage amplified light signal; and a level control correction circuit controlling the level control circuit to control the power level of the first stage amplified light signal in accordance with a power level of the dispersion compensated light signal before being amplified by the second amplifying stage, wherein the first and second amplifying stages are included in a multi-stage optical amplifying unit. 29. An optical amplifying apparatus as in claim 28, further comprising:a dispersion compensator loss correction circuit controlling the level control circuit to control the power level of the first stage amplified light signal so that the power level of the dispersion compensated light signal is maintained at a predetermined level. 30. An optical amplifying apparatus as in claim 28, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 31. An optical amplifying apparatus as in claim 29, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 32. An optical amplifying apparatus comprising:a first amplifying stage amplifying a light signal, to produce a first stage amplified light signal; a dispersion compensator compensating for dispersion in the first stage amplified light signal, to produce a dispersion compensated light signal; a second amplifying stage amplifying the dispersion compensated light signal; and a controller controlling a power level of the first stage amplified light signal in accordance with the dispersion compensated light signal before being amplified by the second amplifying stage, the first and second amplifying stages included in a multi-stage optical amplifying unit. 33. An optical amplifying apparatus as in claim 32, wherein the controller controls the power level of the first stage amplified light signal so that the power level of the dispersion compensated light signal is maintained at a predetermined level.
34. An optical amplifying apparatus as in claim 33, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. 35. An optical amplifying apparatus comprising:first amplifying means for amplifying a light signal, to produce a first stage amplified light signal; dispersion compensation means for compensating for dispersion in the first stage amplified light signal, to produce a dispersion compensated light signal; second amplifying means for amplifying the dispersion compensated light signal; and control means for controlling a power level of the first stage amplified light signal in accordance with a power level of the dispersion compensated light signal before being amplified by the second amplifying means, the first and second amplifying means being included in a multi-stage optical amplifying unit. 36. A method comprising the steps of:amplifying a light signal, at a first amplifying stage, to produce a first stage amplified light signal; compensating for dispersion in the first stage amplified light signal, to produce a dispersion compensated light signal; amplifying the dispersion compensated light signal, at a second amplifying stage; and controlling a power level of the first stage amplified light signal in accordance with a power level of the dispersion compensated light before the dispersion compensated light signal is amplified, wherein the first and second amplifying stages are included in a multi-stage optical amplifying unit. 37. An optical amplifying apparatus comprising:a first optical amplifier amplifying an optical signal and outputting a first stage amplified optical signal; an optical level controller receiving the first stage amplified optical signal, controlling an optical power level of the first stage amplified optical signal and outputting a level controlled optical signal; a dispersion compensator receiving the level controlled optical signal, compensating for dispersion in the level controlled optical signal and outputting a dispersion compensated optical signal; and a second optical amplifier amplifying the dispersion compensated optical signal and outputting a second stage amplified optical signal, wherein the optical level controller controls the optical power level of the first stage amplified optical signal in accordance with an optical power level of the dispersion compensated optical signal, and the first and second optical amplifiers are included in a multi-stage optical amplifier unit. 38. An optical amplifying apparatus as in claim 37, wherein the optical level controller comprises:an optical attenuator having a variable optical attenuation and optically attenuating the power level of the first stage amplified optical signal with the optical attenuation varied in accordance with the power level of the dispersion compensated optical signal. 39. An optical amplifying apparatus as in claim 37, wherein the optical level controller further comprises:an optical attenuator having a variable optical attenuation and optically attenuating the power level of the first stage amplified optical signal; and a control circuit varying the attenuation of the optical attenuator in accordance with the power level of the dispersion compensated optical signal to compensate for loss in the dispersion compensator. 40. An optical amplifying apparatus as in claim 37, wherein the optical level controller controls the power level of the first stage amplified optical signal to maintain a power level of the second stage amplified optical signal.
41. An optical amplifying apparatus as in claim 37, further comprising:a first gain controller controlling a gain of the first optical amplifier to be constant; and a second gain controller controlling a gain of the second optical amplifier to be constant. 42. An optical amplifying apparatus comprising:a multi-stage optical amplifying unit including first and second amplifying stages, the first amplifying stage amplifying a light signal, to produce a first stage amplified light signal; an optical level controller controlling an optical power level of the first stage amplified light signal and outputting a level controlled light signal; a dispersion compensator compensating for dispersion in the level controlled light signal and outputting a dispersion compensated light signal, the second amplifying stage amplifying the dispersion compensated light signal to produce a second stage amplified light signal, wherein the optical level controller controls the optical power level of the first stage amplified light signal in accordance with a power level of the dispersion compensated light signal. 43. An optical amplifying apparatus as in claim 42, further comprising:a first gain controller controlling a gain of the first amplifying stage to be constant; and a second gain controller controlling a gain of the second amplifying stage to be constant. Description
This application is a Divisional of application Ser. No. 08/845,847, filed Apr. 28, 1997, now pending.
Referring now to FIG. 2, the optical amplifying apparatus includes a first part 1000 (sometimes referred to herein as a "rare-earth-doped optical fiber amplifier part") and a second part 2000 (sometimes referred to herein as an "electrically-controlled optical device part").
First part 1000 includes a rare-earth-doped optical fiber (EDF) 34, optical branching couplers 361 and 362, optical isolators 381 and 382, photodiodes 401 and 402, an optical wavelength multiplexing coupler 42, a pump laser diode (LD) 44 and an automatic optical gain control circuit (AGC) 46.
Second part 2000 includes optical branching coupler 36 , an electrically-controlled variable optical attenuator (ATT) 48, a photodiode (PD) 403 and an automatic level control circuit (ALC) 50. Optical attenuator 48 is, for example, constructed of a magnetooptical element. However, many different types of variable optical attenuators can be used.
A wavelength-multiplexed optical signal is fed to rare-earth-doped optical fiber 34 via optical branching coupler 361, optical isolator 38 and optical wavelength multiplexing coupler 42. A pump light beam is supplied by pump laser diode 44 to rare-earth-doped optical fiber 38 via optical wavelength multiplexing coupler 42. The wavelength-multiplexed optical signal is amplified by rare-earth-doped optical fiber 34 and input to optical attenuator 48 via optical isolator 382 and optical branching coupler 362.
A portion of the wavelength-multiplexed optical signal branched by optical branching coupler 361 is converted into an electrical signal by photodiode 401 and input to automatic optical gain control circuit 46. A portion of the amplified wavelength-multiplexed optical signal branched by optical branching coupler 362 is converted into an electrical signal by photodiode 402 and input to automatic optical gain control circuit 46. Pump laser diode 44 is controlled so as to maintain a ratio between a level of the input wavelength-multiplexed optical signal and a level of the amplified wavelength-multiplexed optical signal at a predetermined level.
More specifically, optical gain control circuit 46 controls pump laser diode 44 so as to maintain, at a constant level, the ratio between the level of the input wavelength-multiplexed optical signal as converted into an electrical signal by the photodiode 401 and the level of the amplified wavelength-multiplexed optical signal as converted into an electrical signal by the photodiode 402. In this manner, first part 1000 conserves the wavelength dependence by controlling the optical gain at a constant level.
A portion of an output wavelength-multiplexed optical signal branched by optical branching coupler 363 is converted into an electrical signal by photodiode 403 and input to automatic level control circuit 50. Optical attenuator 48 is controlled so as to maintain the wavelength-multiplexed optical signal at a predetermined level.
More specifically, automatic level control circuit 50 controls optical attenuator 48 using the electrical signal derived by photodiode 403 from the wavelength-multiplexed optical signal, so as to maintain the output level of the wavelength-multiplexed optical signal at a constant level.
For example, a predetermined output optical power of an amplifier is generally required for each wavelength (channel) so as to ensure a desired S/N ratio in a receiver. Assuming there are a total of N channels, the total optical output Pc of a rare-earth-doped optical fiber amplifier for amplifying a wavelength-multiplexed optical signal is controlled to be N�P. In the presence of a variation of +α or -α in the number of channels N, switching control is effected so that the total optical power is (N�α)P. Because the optical power for individual wavelengths (channels) varies due to the switching control, non-linear degradation or signal-to-noise (S/N) degradation may result.
FIG. 3 is a diagram illustrating an optical amplifying apparatus, according to an embodiment of the present invention. The optical amplifying apparatus includes a first part 1000 and a second part 2000. First part 1000 includes a rare-earth-doped optical fiber (EDF) 521, optical branching couplers 541 and 542, optical isolators 551 and 552, an optical wavelength multiplexing coupler 561, photodiodes (PD) 581 and 582, a pump laser diode (LD) 591, and an automatic gain control circuit (AGC) 601. First part 1000 amplifies a wavelength-multiplexed optical signal while conserving wavelength dependance.
As an example, a wavelength-multiplexed optical signal is typically in the 1.5 μm band. An erbium-doped optical fiber is known to amplify optical signals in this band, and is therefore used as rare-earth-doped optical fiber (EDF) 521. Moreover, to appropriately amplify a wavelength-multiplexed optical signal in the 1.5 μm band travelling through an erbium-doped optical fiber, it is known to use pump light of a 0.98 μm or 1.48 μm pump band. Therefore, pump laser diode (LD) 591 provides pump light in the 0.98 μm or 1.48 μm pump band.
Moreover, FIG. 3 shows a forward pumping construction in which a pump light beam emitted by pump laser diode 591 travels through rare-earth-doped optical fiber 521 in the same direction as the wavelength-multiplexed optical signal. However, a backward pumping construction could also be used, where a laser diode provides a pump light beam which travels through rare-earth-doped optical fiber 521 in the opposite direction as the wavelength-multiplexed optical signal. Further, a bi-directional pumping construction could be used, where two laser diodes provide pump light which travels through rare-earth-doped optical fiber 521 in both directions through rare-earth-doped optical fiber 521. Thus, the present invention is not intended to be limited to any specific type of directional pumping.
Second part 2000 includes an electrically-controlled variable optical attenuator (ATT) 64, an automatic level control circuit (ALC) 66, optical branching coupler 543 and a photodiode (PD) 583. Second part 2000 controls the total optical output of a wavelength-multiplexed optical signal to be at a constant level, without conserving wavelength dependence. More specifically, automatic level control circuit 66 varies the attenuation, or light transmissivity, of optical attenuator 64 so that the power of the wavelength-multiplexed optical signal, as output from first part 1000, is maintained at a constant power level corresponding to the number of channels in the wavelength-multiplexed optical signal.
Moreover, when the number of channels in the wavelength-multiplexed optical signal is being varied, a monitor signal processing circuit 70 causes the attenuation, or light transmissivity, of optical attenuator 64 to be maintained constant. Thus, monitor signal processing circuit 70 temporarily "freezes" the operation of optical attenuator 64. After the number of channels has been changed, monitor signal processing circuit 70 allows the attenuation, or light transmissivity, of optical attenuator 64 to be varied so that the power of the wavelength-multiplexed optical signal is maintained at a constant level in accordance with the new number of channels.
More specifically, the wavelength-multiplexed optical signal input to the optical amplifying apparatus is branched by an optical branching coupler 681. The branched portion is provided to a photodiode (PD) 584. Photodiode (PD) 584 converts the branched portion into an electrical signal and provides the electrical signal to monitor signal processing circuit 70.
A control signal, which warns of a variation in the number of channels in the wavelength-multiplexed optical transmission system, is superimposed on the wavelength-multiplexed optical signal preferably as a low-speed signal through an amplitude modulation process. However, other methods can be used to superimpose the control signal. Monitor signal processing circuit 70 extracts and identifies the control signal. Monitor signal processing circuit 70 then controls optical attenuator 64 or automatic level control circuit 66 in accordance with the extracted control signal. If amplitude modulation is used, it is relatively easy to extract the control signal by demodulating the electrical signal obtained by photodiode 584.
Alternatively, the control signal may be transmitted to monitor signal processing circuit 70 on a dedicated control channel (wavelength). If a dedicated control channel is used, an optical branching filter (not illustrated) should extract the control signal out of the wavelength-multiplexed optical signal (as branched by optical branching coupler 681). For example, by feeding the optical signal extracted by the optical branching filter to photodiode 584 so as to be converted into an electrical signal, it is possible to extract the control signal.
Therefore, a portion of the wavelength-multiplexed optical signal branched by optical branching coupler 681 is converted into an electrical signal by photodiode 584 and fed to monitor signal processing circuit 70. Monitor signal processing circuit 70 "freezes" an operation of optical attenuator 64, when a control signal warning of a variation in the number of channels is extracted and identified.
As can be seen from FIGS. 4(A) and 4(B), optical attenuator 64 is controlled to provide ALC. However, when the number of channels is being changed, ALC is halted. Instead, when the number of channels is being changed, optical attenuator 64 is controlled to provide a constant light transmissivity, or attenuation. The operation of optical attenuator 64 can be described as being "frozen" when the number of channels is being changed between times t1 and t3 in FIGS. 4(A) and 4(B).
FIG. 5 is a diagram illustrating automatic gain control circuit 601, for controlling an optical gain to be at a constant level. Referring now to FIG. 5, automatic gain control circuit 601 includes a divider 72, an operational amplifier 74, a transistor 76 and resistors R1-R6. Vcc is a power supply voltage, Vref is a reference voltage, and G is the earth or ground.
As illustrated in FIG. 5, photodiode (PD) 58, converts a portion of the wavelength-multiplexed optical signal into an electrical signal which is provided to divider 72. Photodiode (PD) 582 converts a portion of the amplified wavelength-multiplexed optical signal into an electrical signal which is provided to divider 72. In this manner, divider 72 obtains a ratio between the input and the output of rare-earth-doped optical fiber (EDF) 521. The pump light beam emitted by pump laser diode 591 can then be controlled to produce a constant ratio, thereby providing a constant gain. The configuration of automatic gain control circuit 601 in FIG. 5 is just one example of many possible configurations for an automatic gain control circuit.
A portion of the optical signal output from optical attenuator 64 (see FIG. 3) is branched by optical branching coupler 543 and converted into an electrical signal by photodiode (PD) 583. Then, in FIG. 6, operational amplifier 78 compares the electrical signal with the reference voltage (set voltage) Vref supplied by reference voltage circuit 84 in accordance with control signal CS1. A difference obtained as a result of the comparison is used to drive transistor 80. By controlling a current supplied to control element 86, the attenuation provided by optical attenuator 64 is controlled so that the optical output is maintained at a constant level.
fc =1/(2&#960;R9�CSWC 9),
Therefore, depending on the capacitance of the selected capacitor C1 or C2 of switching circuit 82, the filter cut-off frequency in the high-frequency zone con be changed.
For example, when monitor signal processing circuit 70 extracts and identifies a control signal which warns of a variation in the number of channels, control signal cs2 is supplied to switching circuit 82 so that the frequency characteristic of automatic level control circuit 66 is switched to a low frequency zone. As a result, the following performance for following a variation in the signal detected by photodiode (PD) 583 is lowered. That is, the constant-level control of the optical output is temporarily frozen (for example, the light transmissivity of optical attenuator 64 is maintained to be constant). Further, control signal csl corresponds to the number of channels to be included in the optical signal, and monitor signal processing circuit 70 supplies the control signal cs1 to reference voltage circuit 84. Reference voltage circuit 84 then supplies a reference voltage Vref corresponding to the number of channels. Therefore, the total optical output power assumes a level matching the number of channels after the variation in the number of channels. For example, the reference voltage Vref is changed such that, when a total of a channels are added to the total of N original channels, the total optical output becomes (N+α)�P.
More specifically, FIGS. 8 and 9 are diagrams illustrating automatic level control circuit 66, according to additional embodiments of the present invention. Referring now to FIG. 8, a filter 90 for cutting off high frequencies (fc : �10 KHz) and constructed of a capacitor and a resistor is provided between a switch 92 and transistor 80 so that the response of the automatic level control becomes adequate. For example, the time constant, typically on the order of sub-milliseconds, may be changed to the time constant on the order of 10-100 milliseconds.
More specifically, in FIG. 8, a latch circuit 94 which has a low-pass filter (fc : �0.01 Hz) stores a voltage corresponding to an average level of the current in control element 86. During an ALC operation, switching of the control loop occurs so that the control loop for controlling the drive current at a constant level is initiated. That is, when the switching of the control loop occurs, the voltage corresponding to the average level of the current is latched in latch circuit 94 so as to serve as a reference voltage. The term "average level" is used because the bias current has a time-dependent variation in order to maintain the level of the beam input to photodiode (PD) 583 at a constant level. More specifically, the voltage obtained by integration using a more extended integral time than that provided by the time constant of the normal control loop is latched in latch circuit 94.
The control for maintaining the total optical output at a constant level that corresponds to the number of channels may be resumed in a gradual manner. For example, the output signal of photodiode (PD) 583 may be input to operational amplifier 78 via a time constant circuit 96, or reference voltage Vref may be gradually varied to assume a level that corresponds to the number of channels.
While the above-described arrangement ensures that the frequency characteristic is switched as a result of the control effected by switching circuit 82 so that the constant-level control of the optical output is frozen, it is also possible to hold the signal output by photodiode (PD) 583 when the control signal for giving warning of a variation in the number of channels is extracted and identified. In this instance, the held value is input to operational amplifier 78 so that the constant-level control of the optical output is frozen. Other arrangements for freezing the constant-level control of the optical output are also possible. While it is assumed that the electrically-controlled optical device part is constructed using optical attenuator 64, a semiconductor optical amplifier can be used instead of optical attenuator 64. The semiconductor optical amplifier should have a small wavelength dependence. By controlling the semiconductor optical amplifier, the total optical output may be controlled at a constant level.
FIG. 10 is a diagram illustrating an optical amplifying apparatus, according to an additional embodiment of the present invention. Referring now to FIG. 10, the optical amplifying apparatus includes first part 1000, second part 2000 and a third part 3000. Third part 3000 includes a rare-earth-doped optical fiber (EDF) 522, an optical branching coupler 544, an optical wavelength multiplexing coupler 562, optical isolators 553 and 554, a photodiode (PD) 585, a pump laser diode (LD) 592 and an automatic gain control circuit (AGC) 602. Third part 3000 also shares optical branching coupler 543 and the photodiode (PD) 583 with second part 2000.
Therefore, pump laser diode 591 of first part 1000 and pump laser diode 592 of third part 3000 can each have a relatively small capacity, thereby reducing the cost and stabilization of the amplifying apparatus.
Although FIG. 10 shows second part 2000 and third part 3000 sharing optical branching coupler 543 and photodiode (PD) 583, it is also possible to provide a separate optical branching coupler and a separate photodiode in each of the second part 2000 and the third part 3000.
Automatic gain control circuits 601 and 602 may have the same configuration. Moreover, the optical gains provided by first part 1000 and third part 3000 may be identical. Alternatively, the gains may be varied according to the characteristics of a transmission optical fiber used in third part 3000.
More specifically, a portion of the wavelength-multiplexed optical signal output by optical attenuator 64 is branched by optical branching coupler 543, converted into an electrical signal by photodiode (PD) 583 and input to automatic level control circuit 66. Automatic level control circuit 66 controls optical attenuator 64 so that the total optical output power of the wavelength-multiplexed optical signal is maintained at a constant level. However, the optical output power of the output wavelength-multiplexed optical signal in third part 3000 is not fed to automatic level control circuit 66. Therefore, it cannot be ensured that the total optical output in the third part 3000 is maintained within a predetermined range.
Accordingly, a portion of the output wavelength multiplexed optical signal in the third part 3000 is converted into an electrical signal by photodiode (PD) 585 and input to ALC correction circuit 98 as well as to automatic gain control circuit 602. ALC correction circuit 98 determines whether or not the total optical output power is maintained within the predetermined range. If the total optical output power is not within the predetermined range, ALC correction circuit 98 controls automatic level control circuit 66 which, in turn, cortrols optical attenuator 64 to maintain the total optical output power within the predetermined range. If a semiconductor optical amplifier is used in place of optical attenuator 64, automatic level control circuit 66 controls the gain of the semiconductor optical amplifier so that the total optical output in third part 3000 is maintained within the predetermined level.
FIG. 13 is a diagram illustrating an optical amplifying apparatus, according to an additional embodiment of the present invention. The optical amplifying apparatus in FIG. 13 operates in a similar manner as previously described embodiments of the present invention, but also includes an optical branching coupler 545, a photodiode (PD) 586, a dispersion compensation fiber (DCF) 100 and a dispersion compensation fiber (DCF) loss correction circuit 102. Optical branching coupler 545 and photodiode (PD) 586 can be considered to be included in third part 3000.
Therefore, a portion of the wavelength-multiplexed optical signal output by dispersion compensation optical fiber 100 and branched by optical branching coupler 545 is converted into an electrical signal by photodiode (PD) 586. The electrical signal is input to DCF loss correction circuit 102 as well as to automatic gain control circuit 602. DCF loss correction circuit 102 determines whether or not the level of the wavelength-multiplexed optical signal output by dispersion compensation fiber 100 is within a predetermined range. If the level is outside the predetermined range, DCF loss correction circuit 102 supplies a correction signal to automatic level control circuit 66. For example, the reference voltage (set voltage) for constant control of the optical output is corrected such that the optical output power is within the predetermined range. Therefore, a variation in insertion loss that results in a construction where dispersion compensation fiber 100 compensates for the dispersion in the transmission optical fiber is corrected, and a predetermined output level of the amplified wavelength-multiplexed optical signal is obtained.
FIG. 17 is a diagram illustrating modification to the optical amplifying apparatus illustrated in FIG. 16, according to an embodiment of the present invention. More specifically, in FIG. 17, an optical filter A1 is provided between the output of optical isolator 552 and optical branching coupler 542, at the input of photodiode (PD) 582. Also, an optical filter A2 is provided between the output of optical isolator 554 and optical branching coupler 544, at the input of photodiode (PD) 585. Optical filters A1 and A2 are optical filters as disclosed, for example, in U.S. patent application Ser. No. 08/655,027, which is incorporated herein by reference, for correcting wavelength dependency of the gain.
FIG. 18(A) is a graph illustrating gain versus wavelength characteristics of rare-earth-doped optical fiber (EDF) 52. in FIG. 17, FIG. 18(B) is a graph illustrating the transmissivity versus wavelength of optical filter A2 in FIG. 17, and FIG. 18(C) is a graph illustrating overall gain of rare-earth-doped optical fiber (EDF) 522 and optical filter A2 in FIG. 17, according to an embodiment of the present invention.
If, for example, rare-earth-doped optical fiber (EDF) 522 has a wavelength-dependent gain characteristic as shown in FIG. 18(A), wherein the gain is higher in the long wavelength range, providing a gain correction optical filter A2 at the input of photodiode (PD) 585 ensures that the amplifier has an even gain with respect to wavelength. Providing optical filter A2 ensures that photodiode (PD) 585 receives the corrected multi-wavelength signal so that the unfavorable sensitivity characteristic, wherein the signal sensitivity is low in the short wavelength range and high in the long wavelength range, is corrected. Optical filters A1 and/or A2 may or may not be provided, depending on the use of rare-earth-doped optical fibers (EDF) 521 and 522.
More specifically, an input wavelength-multiplexed optical signal is transmitted to optical attenuator 64. The wavelength-multiplexed optical signal output from optical attenuator 64 is transmitted to rare-earth-doped optical fiber 521 via optical isolator 551 and optical wavelength multiplexing coupler 561. The amplified wavelength-multiplexed optical signal is output via optical isolator 552 and optical branching coupler 542.
A portion of the wavelength-multiplexed optical signal branched by optical branching coupler 541 is converted into an electrical signal by photodiode 581 and fed to automatic level control circuit 66 and automatic gain control circuit 601. Automatic level control circuit 66 controls the optical attenuation provided by optical attenuator 64 so that the wavelength-multiplexed optical signal has its level controlled to be within a predetermined range and is then transmitted to first part 1000.
A portion of the wavelength-multiplexed optical signal branched by optical branching coupler 542 is converted into an electrical signal by photodiode 582 and transmitted to automatic gain control circuit 601. Automatic gain control circuit 601 controls pump laser diode 591 so that a ratio between a level of the wavelength-multiplexed optical signal input to, and output from, rare-earth-doped optical fiber 521 is maintained at a constant level.
Therefore, second part 2000 causes the power level of the wavelength-multiplexed optical signal to be constant even when a signal input via a transmission optical fiber varies greatly. As a result, a wavelength-multiplexed optical signal having a constant level is input to first part 1000. Accordingly, automatic gain control circuit 601 may have a small control zone and a relatively simple construction. Further, since the power level of the optical signal input to rare-earth-doped optical fiber 521 is prevented from exceeding a predetermined level, it is not necessary to raise the level of the pump laser beam supplied by pump laser diode 591. That is, pump laser diode 591 may have a small capacity.
FIG. 20 is a diagram illustrating an optical amplifying apparatus, according to an additional embodiment of the present invention. The optical amplifying apparatus illustrated in FIG. 20 is similar to the optical amplifying apparatus in FIG. 19, but also includes optical branching coupler 543, photodiode (PD) 583 and monitor signal processing circuit 70.
Referring now to FIG. 20, a wavelength-multiplexed optical signal supplied via a transmission optical fiber is input to variable optical attenuator 64 and has a portion branched by optical branching coupler 543, converted into an electrical signal by photodiode 583 and input to monitor signal processing circuit 70.
Therefore, in FIG. 23, a switch 104 is controlled by monitor signal processing circuit 70 to switch between automatic level control provided by automatic level control circuit 66 and automatic gain control provided by an automatic gain control circuit 603. More specifically, for example, as illustrated in FIG. 4 (A), monitor signal processing circuit 70 causes switch 104 to select automatic level control circuit 66 prior to, and subsequent to, a variation in the number of channels. While the number of channels is being varied, monitor signal processing circuit 70 causes switch 104 to select automatic gain control circuit 603.
(2) When monitor signal processing circuit 70 receives a signal warning of a change in the number of channels, a gain monitoring signal 107 of automatic gain control circuit 603 is read so that an average gain (attenuation) with respect to a time constant on the order of 10-100 ms is determined.
(3) A reference voltage VAGC corresponding to the average gain determined in (2) is output from monitor signal processing circuit 70 to automatic gain control circuit 603.
(8) Switch 104 selects automatic level control circuit
More specifically, monitor signal processing circuit 70 inserts, in the SV light beam, information indicating when the attenuation, or light transmissivity, of the optical attenuator 64 will be held constant, or "frozen". The SV light beam, carrying that information, is transmitted by laser diode (LD) 105 to the transmission line.
(3) Each OAMP starts "freezing" the operation of the associated optical attenuator.
FIG. 28 is a timing diagram illustrating the abovedescribed operation flow.
According to the above embodiments of the present invention, a rare-earth doped optical fiber used in an optical amplifier, where the dopant is erbium (Er). However, the present invention is not intended to be limited to an erbium (Er) doped optical fiber. Instead, other rare-earth-doped optical fibers, such as a neodymium(Nd)-doped optical fiber or a praseodymrium(Pd)-doped optical fiber, may also be used, depending on the wavelength involved. Further, for example, the various photodiodes disclosed herein can be replaced by phototransistors.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS4644145 *Apr 30, 1985Feb 17, 1987Standard Elektrik Lorenz AktiengesellschaftOptical receiver with electrically variable attenuatorUS5280383 *Dec 2, 1992Jan 18, 1994At&T Bell LaboratoriesDual-stage low power optical amplifierUS5436760 *Jul 14, 1994Jul 25, 1995Nec CorporationOptical fiber amplifier with gain equalizing circuitUS5457811 *Jun 13, 1994Oct 10, 1995Southwestern Bell Technology Resources, Inc.System for controlling signal level at both ends of a transmission sink based on a detected valueUS5463487 *Jul 29, 1994Oct 31, 1995Northern Telecom LimitedOptical transmission systemUS5510926 *Jan 11, 1995Apr 23, 1996Alcatel N.V.Transmission method and an optical link using multiplexing with applicationUS5539563 *May 31, 1994Jul 23, 1996At&T Corp.System and method for simultaneously compensating for chromatic dispersion and self phase modulation in optical fibersUS5664131 *Sep 20, 1995Sep 2, 1997Fujitsu LimitedLight amplifierUS5805322 *Jan 17, 1996Sep 8, 1998Fujitsu LimitedMultiplex optical communication systemUS5831754 *May 1, 1995Nov 3, 1998Hitachi, Ltd.Optical amplifierGB2294170A * Title not availableJPH03206427A * Title not availableJPH05241209A * Title not availableJPH07212315A * Title not availableJPS6074593A * Title not availableWO1996029627A1 *Mar 20, 1995Sep 26, 1996Hitachi LtdOptical fiber amplifier* Cited by examinerNon-Patent CitationsReference1Japanese Publication "Er:Doped Fiber Amplifier for WDM Transmission Using Fiber Gain Control", Technical Report of IEICE, OCS94-66, OPE94, Nov. 1994. (Nov. 1994. (including English language Abstract).2 *Japanese Publication Er:Doped Fiber Amplifier for WDM Transmission Using Fiber Gain Control , Technical Report of IEICE, OCS94 66, OPE94, Nov. 1994. (Nov. 1994. (including English language Abstract).3 *Nakabayashi, et al, Tech. Report of IEICE. OCS 94 66, OPE94 89 (1994 11) pp. 31 36 and 1 15.4Nakabayashi, et al, Tech. Report of IEICE. OCS-94-66, OPE94-89 (1994-11) pp. 31-36 and 1-15.5 *Nakabayashu et al, Tech. Report of IEICE, OCS94 66, OPE 94 89, pp. 31 36, English Translation, Nov. 1994.6Nakabayashu et al, Tech. Report of IEICE, OCS94-66, OPE 94-89, pp. 31-36, +English Translation, Nov. 1994.7 *Sugaya et al, OAA 95 Paper FC3, Jun. 16, 1995, 5 pages.8Sugaya et al, OAA '95 Paper FC3, Jun. 16, 1995, 5 pages.* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS6137605 *Jan 20, 1998Oct 24, 2000Nec CorporationOutput power control system for optical amplification repeaterUS6292291 *Nov 24, 1999Sep 18, 2001Samsung Electronics Co., Ltd.Optical fiber amplifier having constant output power for each channel and amplifying method thereofUS6337764 *Nov 24, 1999Jan 8, 2002Samsung Electronics Co., Ltd.Optical fiber amplifier for controlling gain flatnessUS6366393 *Aug 25, 1999Apr 2, 2002Lucent Technologies Inc.Fast gain control for optical amplifiersUS6373625 *Nov 1, 1999Apr 16, 2002Fujitsu LimitedMethod, apparatus, and system for optical amplificationUS6377396 *Nov 6, 2000Apr 23, 2002Onetta, Inc.Optical amplifiers with variable optical attenuation for use in fiber-optic communications systemsUS6414788 *Nov 15, 2000Jul 2, 2002Onetta, Inc.Optical amplifier system with transient controlUS6469824 *Feb 2, 2001Oct 22, 2002Oki Electric Industry, Co., Ltd.Bi-directional pumped optical fiber amplifier with fault detection means and novel pump controlUS6496302 *Sep 3, 1999Dec 17, 2002Nec CorporationOptical amplifierUS6603596 *Mar 9, 1999Aug 5, 2003Fujitsu LimitedGain and signal level adjustments of cascaded optical amplifiersUS6757099Aug 15, 2001Jun 29, 2004Pts CorporationOptical power transient control scheme for EDFA amplifiersUS6856454Jun 20, 2003Feb 15, 2005Pts CorporationDynamic optical spectral control scheme for optical amplifier sitesUS6865016 *Aug 29, 2003Mar 8, 2005Fujitsu LimitedController which controls a variable optical attenuator to control the power level of a wavelength-multiplexed optical signal when the number of channels are variedUS7061666Apr 16, 2003Jun 13, 2006Fujitsu LimitedGain and signal level adjustments of cascaded optical amplifiersUS7061669 *Sep 28, 2004Jun 13, 2006Fujitsu LimitedOptical apparatus with loss compensation capability and optical amplifier for loss compensationUS7227681Oct 4, 2004Jun 5, 2007Fujitsu LimitedController which controls a variable optical attenuator to control the power level of a wavelength-multiplexed optical signal when the number of channels are variedUS7362925 *Jun 6, 2005Apr 22, 2008Fujitsu LimitedControl method and control apparatus of optical deviceUS7400443 *Nov 20, 2003Jul 15, 2008Ciena CorporationMethod and apparatus for optical amplifying device gain control with gain thresholdUS7453628 *Jan 3, 2006Nov 18, 2008Fujitsu LimitedOptical amplifier having wide dynamic rangeUS7477447Apr 30, 2007Jan 13, 2009Fujitsu LimitedController which controls a variable optical attenuator to control the power level of a wavelength-multiplexed optical signal when the number of channels are variedUS7480092 *Aug 26, 2003Jan 20, 2009Fujitsu LimitedOptical amplification method and device usable with bands other than the C-bandUS7554720 *Apr 20, 2006Jun 30, 2009Fujitsu LimitedOptical transmission apparatus with automatic gain control and automatic level control mode selectionUS7880960Jun 23, 2009Feb 1, 2011Fujitsu LimitedOptical amplifier and abnormality detection method for the sameUS7924499Jun 24, 2010Apr 12, 2011Fujitsu LimitedGain and signal level adjustments of cascaded optical amplifiersUS7969648Apr 19, 2006Jun 28, 2011Fujitsu LimitedGain and signal level adjustments of cascaded optical amplifiersUS7969649Dec 4, 2008Jun 28, 2011Fujitsu LimitedController which controls a variable optical attenuator to control the power level of a wavelength-multiplexed optical signal when the number of channels are variedUS8004752Mar 24, 2009Aug 23, 2011Fujitsu LimitedMulti-wavelength light amplifierUS8031396 *Oct 29, 2009Oct 4, 2011Imra America, Inc.Modular, high energy, widely-tunable ultrafast fiber sourceUS8064771 *Jun 22, 2006Nov 22, 2011Infinera CorporationActive control loop for power control of optical channel groupsUS8164826 *Mar 13, 2008Apr 24, 2012Nec CorporationMulti-stage optical amplifier and method of controlling the sameUS8320040Jul 6, 2011Nov 27, 2012Fujitsu LimitedMulti-wavelength light amplifierUS8429594May 17, 2010Apr 23, 2013Fujitsu LimitedVia design apparatus and via design method based on impedance calculationsUS8547629Mar 8, 2011Oct 1, 2013Fujitsu LimitedGain and signal level adjustments of cascaded optical amplifiersUS8548321Mar 30, 2009Oct 1, 2013Fujitsu LimitedOptical transmission apparatusUS8553319Apr 29, 2011Oct 8, 2013Fujitsu LimitedController which controls a variable optical attenuator to control the power level of a wavelength-multiplexed optical signal when the number of channels are variedUS8570646Jul 21, 2011Oct 29, 2013Imra America, Inc.Modular, high energy, widely-tunable ultrafast fiber sourceUS8670176 *Nov 5, 2009Mar 11, 2014Fujitsu LimitedOptical amplifying deviceUS8699126Oct 25, 2012Apr 15, 2014Fujitsu LimitedMulti-wavelength light amplifierUS20100123949 *Nov 5, 2009May 20, 2010Fujitsu LimitedOptical amplifying deviceWO2003017439A2 *Aug 14, 2002Feb 27, 2003Ceyba IncOptical power transient control scheme for edfa amplifiers* Cited by examinerClassifications U.S. Classification359/337, 359/341.42, 359/337.5, 359/341.41, 359/337.11, 398/92International ClassificationG02B6/06, H04J14/00, H01S3/10, H01S3/06, H04B10/58, H04B10/07, H04B10/296, H04B10/29, H04B10/54, H04B10/2543, H04B10/2525, H04B10/564, H01S3/13, H04J14/02, H01S3/067Cooperative ClassificationH01S3/1003, H01S3/10015, H01S2301/04, H01S3/06758, H04B10/2942, H04B10/296, H01S3/1301, H04B2210/003, H04B10/2912, H04B10/2931, H04B10/291, H04J14/0221European ClassificationH04B10/296, H04B10/2912, H04B10/2931, H04B10/2942, H04B10/291, H01S3/067G2, H04J14/02B, H01S3/13ALegal EventsDateCodeEventDescriptionApr 27, 2011FPAYFee paymentYear of fee payment: 12May 4, 2007FPAYFee paymentYear of fee payment: 8May 6, 2003FPAYFee paymentYear of fee payment: 4Feb 5, 2002CCCertificate of correctionMay 22, 2001CCCertificate of correctionRotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services