Source: https://patents.google.com/patent/US20040036958?oq=%22peter+l+basel%22+%22lsi+logic%22
Timestamp: 2018-02-25 18:42:23
Document Index: 117131050

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

US20040036958A1 - Controller which controls a variable optical attenuator to control the power level of a wavelength-multiplexed optical signal when the number of channels are varied - Google Patents
US20040036958A1
US20040036958A1 US10650990 US65099003A US2004036958A1 US 20040036958 A1 US20040036958 A1 US 20040036958A1 US 10650990 US10650990 US 10650990 US 65099003 A US65099003 A US 65099003A US 2004036958 A1 US2004036958 A1 US 2004036958A1
US10650990
US6865016B2 (en )
[0007]FIG. 1 is a diagram illustrating a conventional fiber optic communication system which uses wavelength division multiplexing to transmit, for example, four channels through a single optical fiber. Referring now to FIG. 1, transmitting units 20-1, 20-2, 20-3 and 20-4 transmit individual carriers having wavelengths λ1-λ4, respectively. Each carrier is modulated with information and represents an individual channel. The different carriers are multiplexed together by an optical multiplexer 22 into a wavelength-multiplexed optical signal. The wavelength-multiplexed optical signal is transmitted through an optical fiber 24 to an optical demultiplexer 26. Optical demultiplexer 26 branches the wavelength-multiplexed optical signal into four separate optical signals having the wavelengths λ1-λ4, respectively. The four separate branched optical signals are then detected by receiving units 28-1, 28-2, 28-3 and 28-4, respectively.
[0022]FIG. 1 (prior art) is a diagram illustrating a conventional fiber optic communication system.
[0023]FIG. 2 (prior art) is a diagram illustrating an optical amplifying apparatus for a fiber optic communication system which uses wavelength division multiplexing.
[0024]FIG. 3 is a diagram illustrating an optical amplifying apparatus, according to an embodiment of the present invention.
[0026]FIG. 5 is a diagram illustrating an automatic gain control circuit, according to an embodiment of the present invention.
[0027]FIG. 6 is a diagram illustrating automatic level control circuit, according to an embodiment of the present invention.
[0028]FIG. 7 is a diagram illustrating a switching circuit of the automatic level control circuit in FIG. 6, according to an embodiment of the present invention.
[0029]FIGS. 8 and 9 are diagrams illustrating an automatic level control circuit, according to additional embodiments of the present invention.
[0030]FIG. 10 is a diagram illustrating an optical amplifying apparatus, according to an additional embodiment of the present invention.
[0031]FIG. 11 is a diagram illustrating an optical amplifying apparatus, according to a further embodiment of the present invention.
[0032]FIG. 12 is a diagram illustrating an optical amplifying apparatus, according to an embodiment of the present invention.
[0033]FIG. 13 is a diagram illustrating an optical amplifying apparatus, according to an additional embodiment of the present invention.
[0034]FIG. 14 is a diagram illustrating an optical amplifying apparatus, according to an additional embodiment of the present invention.
[0035]FIG. 15 is a diagram illustrating an optical amplifying apparatus, according to a further embodiment of the present invention.
[0036]FIG. 16 is a diagram illustrating an optical amplifying apparatus, according to a still further embodiment of the present invention.
[0037]FIG. 17 is a diagram illustrating modification to the optical amplifying apparatus illustrated in FIG. 16, according to an embodiment of the present invention.
[0038]FIG. 18(A) is a graph illustrating gain versus wavelength characteristics of a rare-earth-doped optical fiber (EDF) in an optical amplifying apparatus, according to an embodiment of the present invention.
[0039]FIG. 18(B) is a graph illustrating the transmissivity of an optical filter in an optical amplifying apparatus, according to an embodiment of the present invention.
[0040]FIG. 18(C) is a graph illustrating overall gain of the rare-earth-doped optical fiber (EDF) in FIG. 18(A) and the optical filter in FIG. 18(B), according to an embodiment of the present invention.
[0041]FIG. 19 is a diagram illustrating an optical amplifying apparatus, according to an embodiment of the present invention.
[0042]FIG. 20 is a diagram illustrating an optical amplifying apparatus, according to an additional embodiment of the present invention.
[0043]FIG. 21 is a diagram illustrating an optical amplifying apparatus, according to a further embodiment of the present invention.
[0044]FIG. 22 is a diagram illustrating an optical amplifying apparatus, according to a still further embodiment of the present invention.
[0045]FIG. 23 is a diagram illustrating an optical amplifying apparatus, according to an embodiment of the present invention.
[0046]FIG. 24 is a more detailed diagram of a portion of the optical amplifying apparatus in FIG. 23, according to an embodiment of the present invention.
[0047]FIG. 25 is a diagram illustrating a fiber optic communication system employing an optical amplifying apparatus according to an embodiment of the present invention.
[0048]FIG. 26 is a more detailed diagram illustrating the optical amplifying apparatus of FIG. 25, according to an embodiment of the present invention.
[0049]FIG. 27 is a diagram illustrating a transmission line employing a plurality of optical amplifying apparatuses, according to an embodiment of the present invention.
[0050]FIG. 28 is a timing diagram illustrating the operation of an optical amplifying apparatus, according to an embodiment of the present invention.
[0051]FIG. 29 is a diagram illustrating a portion of an optical communication system, according to an embodiment of the present invention.
[0053]FIG. 2 is a diagram illustrating an optical amplifying apparatus for a fiber optic communication system which uses wavelength division multiplexing, and is similar to that disclosed in related to U.S. patent application Ser. No. 08/655,027, which is incorporated herein by reference
[0065]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) 52 1, optical branching couplers 54 1 and 54 2, optical isolators 55 1 and 55 2, an optical wavelength multiplexing coupler 56 1, photodiodes (PD) 58 1 and 58 2, a pump laser diode (LD) 59 1, and an automatic gain control circuit (AGC) 60 1. First part 1000 amplifies a wavelength-multiplexed optical signal while conserving wavelength dependance.
[0088]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 60 1, 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.
[0090]FIG. 6 is a diagram illustrating automatic level control circuit 66, for controlling an optical output at a constant level. Referring now to FIG. 6, automatic level control circuit 66 includes resistors R7-R9, an operational amplifier 78, a transistor 80, a switching circuit (SWC) 82 and a reference voltage circuit 84. Vcc is the power supply voltage, Vref is a reference voltage, G is the earth or ground, and cs1 and cs2 are control signals provided by monitor signal processing circuit 70. A control element 86 is a control element of optical attenuator 64 for controlling the transmissivity of optical attenuator 64.
[0093]FIG. 7 is a diagram illustrating switching circuit 82. Referring now to FIG. 7, switching circuit 82 includes capacitors C1 and C2 which are individually selected with a switch SW that is controlled by the control signal CS2. Therefore, switching circuit 82 controls the frequency characteristic of automatic level control circuit 66. Moreover, switching circuit 82 controls optical attenuator 64 by controlling transistor 80 by following the level of the output wavelength-multiplexed optical signal with a predetermined frequency characteristic. The control signal cs2 from monitor signal processing circuit 70 changes the frequency characteristic by switching between capacitors C1 and C2 of switching circuit 82. The control signal cs1 switches between different levels of the reference voltages in accordance with the number of channels.
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.
[0106]FIG. 9 is a combination of FIGS. 6 and 8. Referring now to FIG. 9, the capacitance CSWC is switched by switching circuit 82 to cause the cut-off frequency fc to be shifted to a low-frequency zone, to thereby slow the filter response. Thereupon, latch circuit 94 controls the attenuation to the average based on a monitored value.
[0112]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) 52 2, an optical branching coupler 54 4, an optical wavelength multiplexing coupler 56 2, optical isolators 55 3 and 55 4, a photodiode (PD) 58 5, a pump laser diode (LD) 59 2 and an automatic gain control circuit (AGC) 60 2. Third part 3000 also shares optical branching coupler 54 3 and the photodiode (PD) 58 3 with second part 2000.
[0118]FIG. 11 is a diagram illustrating an optical amplifying apparatus, according to a further embodiment of the present invention. Referring now to FIG. 11, the optical amplifying apparatus includes first part 1000, second part 2000 and third part 3000, which are the same as that show in FIG. 10. However, the optical amplifying apparatus in FIG. 11 also includes an automatic level control (ALC) correction circuit 98 for controlling and correcting automatic level control circuit 66 of second part 2000.
[0121]FIG. 12 is a diagram illustrating an optical amplifying apparatus, according to an embodiment of the present invention. The optical amplifying apparatus in FIG. 12 is a combination of the optical amplifying apparatuses in FIGS. 10 and 11.
[0123]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 54 5, a photodiode (PD) 58 6, a dispersion compensation fiber (DCF) 100 and a dispersion compensation fiber (DCF) loss correction circuit 102. Optical branching coupler 54 5 and photodiode (PD) 58 6 can be considered to be included in third part 3000.
[0128]FIG. 14 is a diagram illustrating an optical amplifying apparatus, according to an additional embodiment of the present invention. Referring now to FIG. 14, when monitor signal processing circuit 70 extracts and identifies a control signal for giving warning of a variation in the number of channels, the operation of optical attenuator 64 is frozen (that is, the transmissivity or the attenuation is maintained to be constant), so that a rapid variation in the optical signal level is restricted. DCF loss correction circuit 102 controls automatic level control circuit 66 so as to correct a loss that varies depending on the level of dispersion compensation provided by dispersion compensation fiber 100. Thus, the level of the wavelength-multiplexed optical signal input to third part 3000 is maintained within a predetermined range.
[0129]FIG. 15 is a diagram illustrating an optical amplifying apparatus, according to a further embodiment of the present invention. Referring now to FIG. 15, dispersion compensation fiber 100 compensates for dispersion in the transmission optical fiber, DCF loss correction circuit 102 corrects a variation in the loss depending on the level of compensation provided by dispersion compensation fiber 100, and ALC correction circuit 98 controls automatic level control circuit 66 so as to maintain the level of the output wavelength-multiplexed optical signal in third part 3000 within a predetermined range. Thus, the wavelength-multiplexed optical signal in the wavelength-multiplexed optical transmission system is amplified, relayed and transmitted in a stable manner.
[0130]FIG. 16 is a diagram illustrating an optical amplifying apparatus, according to a still further embodiment of the present invention. Referring now to FIG. 16, monitor signal processing circuit 70 controls optical attenuator 64 or automatic level control circuit 66 upon extracting and identifying a control signal for giving warning of a variation in the number of channels, so as to freeze constant-level control of the optical output. In this manner, a rapid variation in the level of the optical output is restricted.
[0132]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 55 2 and optical branching coupler 54 3, at the input of photodiode (PD) 58 2. Also, an optical filter A2 is provided between the output of optical isolator 55 4 and optical branching coupler 54 4, at the input of photodiode (PD) 58 5. 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.
[0133]FIG. 18(A) is a graph illustrating gain versus wavelength characteristics of rare-earth-doped optical fiber (EDF) 52 2 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) 52 2 and optical filter A2 in FIG. 17, according to an embodiment of the present invention.
[0135]FIG. 19 is a diagram illustrating an optical amplifying apparatus, according to an embodiment of the present invention. Referring now to FIG. 19, the positioning of the first part 1000 and the second part 2000 are essentially switched. Therefore, a wavelength-multiplexed optical signal is controlled to have a constant power level by second part 2000, and is then controlled by first part 1000 to have a constant gain.
[0139]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 54 3, photodiode (PD) 58 3 and monitor signal processing circuit 70.
[0143]FIG. 21 is a diagram illustrating an optical amplifying apparatus, according to a further embodiment of the present invention. The optical amplifying apparatus illustrated in FIG. 21 is similar to the optical amplifying apparatus in FIG. 19, but includes ALC correction circuit 98.
[0145]FIG. 22 is a diagram illustrating an optical amplifying apparatus, according to a still further embodiment of the present invention. The optical amplifying apparatus illustrated in FIG. 22 is a combination of the optical amplifying apparatuses illustrated in FIGS. 20 and 21.
[0147]FIG. 23 is a diagram illustrating an optical amplifying apparatus, according to an embodiment of the present invention. Referring now to FIG. 23, instead of controlling (freezing) the optical attenuator 64 so as to provide a constant attenuation when the number of channels is varied, the optical amplifier as a whole is changed to the AGC mode when the number of channels is varied. Such a change can be achieved by controlling the ratio between the input to, and the output from, optical attenuator 64, to be at a constant level. Such an operation is tantamount to maintaining the gain G (0≦G≦1) of optical attenuator 64 or the light transmissivity of optical attenuator 64 at a constant level.
[0149]FIG. 23 also illustrates a laser diode (LD) 105 which is controlled by monitor signal processing circuit 70 to transmit information to downstream optical components, such as downstream optical repeaters. For example, as described in more detail further below, laser diode (LD) 105 can be used by monitor signal processing circuit 70 to transmit information to downstream optical components.
[0150]FIG. 24 is a more detailed diagram of the optical amplifying apparatus in FIG. 23. Referring now to FIG. 24, the operation is as follows:
[0160]FIG. 25 is a diagram illustrating a fiber optical communication system employing an optical amplifying apparatus according to embodiments of the present invention. Referring now to FIG. 25, a transmitter (Tx) 108 transmits an SV light beam to a receiver (Rx) 110, where an SV light beam is light that is wavelength-multiplexed with a main signal. The main signal is used to transmit information downstream. An optical amplifier (O-AMP) 112 amplifies the SV light beam. Main signal control 114 and monitor signal processing 116 are performed.
[0161]FIG. 26 is a more detailed diagram illustrating an optical amplifying apparatus which includes optical amplifier 112, main signal control 114 and monitor signal processing 116 of FIG. 25. The optical amplifying apparatus in FIG. 26 is similar to the optical amplifying apparatus in FIG. 3, but includes laser diode (LD) 105 for sending an SV light beam downstream.
[0163]FIG. 27 is a diagram illustrating a transmission line employing a plurality of optical amplifying apparatuses, according to embodiments of the present invention. Referring now to FIG. 27, a wavelength-multiplexed optical communication system includes transmitters Tx 120, wavelength-multiplexed optical fiber amplifiers/repeaters OAMPs 122 and receivers Rx 124. When a variation in the number of channels is processed, all the OAMPs 122 in the upstream (or downstream) line in the system are set into a constant optical gain control.
[0181]FIG. 28 is a timing diagram illustrating the above-described operation flow.
an optical amplifier which amplifies a light signal having a variable number of channels; and
a controller which controls a power level of the amplified light signal in response to variations in the number of channels in the light signal.
prior to, and subsequent to, varying the number of channels in the light signal, the controller passes the amplified light signal with a varying light transmissivity so that the power level of the amplified light signal is maintained at an approximately constant level in accordance with the number of channels in the light signal, and,
while the number of channels in the light signal is being varied, the controller passes the amplified light signal with a constant light transmissivity to thereby control the power level of the amplified light signal.
prior to, and subsequent to, varying the number of channels in the light signal, the controller maintains the power level of the amplified light signal at an approximately constant level in accordance with the number of channels in the light signal, and,
while the number of channels in the light signal is being varied, the controller amplifies the amplified light signal with an approximately constant gain.
prior to, and subsequent to, varying the number of channels in the light signal, passes the amplified light signal with a varying light transmissivity so that a power level of the amplified light signal is maintained at an approximately constant level in accordance with the number of channels in the light signal, and,
while the number of channels in the light signal is being varied, passes the amplified light signal with a constant light transmissivity.
prior to varying the number of channels in the light signal, the controller passes the amplified light signal with a varying light transmissivity so that the power level of the amplified light signal is maintained at a level which depends on the number of channels in the light signal prior to varying the number of channels, and,
subsequent to varying the number of channels in the light signal, the controller passes the amplified light signal with a varying light transmissivity so that the power level of the amplified light signal is maintained at a level which depends on the number of channels in the light signal subsequent to varying the number of channels.
6. An apparatus as in claim 4, wherein the optical amplifier is a rare-earth-doped optical fiber amplifier which amplifies the light signal with a constant gain.
7. An apparatus as in claim 4, wherein the controller comprises:
an optical attenuator for passing the amplified light signal and which has a variable light transmissivity; and
an automatic level control unit which, prior to, and subsequent to, varying the number of channels in the light signal, varies the light transmissivity of the optical attenuator so that the power level of the amplified light signal is maintained at an approximately constant level in accordance with the number of channels in the light signal.
8. An apparatus as in claim 4, wherein the controller comprises an optical attenuator for providing a light transmissivity which can be varied or maintained constant.
9. An apparatus as in claim 4, wherein
the controller receives a warning signal indicating when the number of channels in the light signal will be varied, and,
upon receipt of the warning signal, the controller begins passing the amplified light signal with a constant light transmissivity and continues passing the amplified light signal with a constant light transmissivity until after the number of channels is varied.
10. An apparatus as in claim 9, wherein the warning signal is included in the light signal, and the controller extracts the warning signal from the light signal.
11. An apparatus as in claim 4, wherein prior to, and subsequent to, varying the number of channels in the light signal, the controller passes the amplified light signal with a varying light transmissivity so that the power level of the amplified light signal is maintained within a predetermined range.
12. An apparatus as in claim 4, further comprising:
a dispersion compensation optical fiber (DCF) through which the amplified light signal travels,
wherein the controller detects variations in loss due to the DCF and controls the power level of the amplified light signal to compensate for the detected variations.
13. An apparatus as in claim 7, further comprising:
a dispersion compensation optical fiber (DCF) through which the amplified light signal travels; and
a loss correction circuit which detects variations in loss due to the DCF and controls the light transmissivity of the optical attenuator to compensate for-the detected variations.
14. An apparatus as in claim 13, wherein the loss correction circuit controls the light transmissivity of the optical attenuator to maintain the power level of the amplified light signal within a predetermined range.
15. An apparatus as in claim 4, wherein, while the number of channels in the light signal is being varied, the controller passes the amplified light signal with a constant light transmissivity for a predetermined time period and, after the predetermined time period lapses, begins to pass the amplified light signal with a varying light transmissivity.
16. An apparatus as in claim 4, wherein
the controller receives a completion signal indicating when a variation in the number of channels in the light signal is completed, and,
upon receipt of the completion signal, the controller begins passing the amplified light signal with a varying light transmissivity so that the power level of the amplified light signal is maintained at an approximately constant level.
17. An apparatus as in claim 4, wherein, after the controller begins to pass the amplified light signal with a varying light transmissivity subsequent to a variation in the number of channels in the light signal, the controller causes a completion signal to be transmitted downstream to indicate that the controller has completed control in response to the variation in the number of channels.
18. An apparatus as in claim 4, wherein the controller receives a warning signal indicating when the number of channels in the light signal will be varied, the warning signal for use by the controller to determine when to pass the amplified light signal with a constant light transmissivity, the apparatus further comprising:
a plurality of downstream optical amplifiers, the warning signal being transmitted downstream for use in controlling an output of each of the downstream optical amplifiers.
19. An apparatus as in claim 4, further comprising a plurality of optical amplifiers, wherein, for each optical amplifier, an identification signal is transmitted downstream to identify the optical amplifier.
20. An apparatus as in claim 18, wherein, after the controller begins to pass the amplified light signal with a varying light transmissivity subsequent to a variation in the number of channels in the light signal, the controller causes a completion signal to be transmitted downstream to indicate that the controller has completed control in response to the variation in the number of channels.
21. An apparatus as in claim 18, wherein, for each optical amplifier, an identification signal is transmitted downstream to identify the optical amplifier.
22. An apparatus as in claim 20, wherein, while the number of channels in the light signal is being varied, the controller passes the amplified light signal with a constant light transmissivity for a predetermined time period and, after the predetermined time period lapses, begins to pass the amplified light signal with a varying light transmissivity.
23. An apparatus as in claim 20, wherein, for each optical amplifier, an identification signal is transmitted downstream to identify the respective optical amplifier.
24. An apparatus as in claim 18, wherein, while the number of channels in the light signal is being varied, the controller passes the amplified light signal with a constant light transmissivity for a predetermined time period and, after the predetermined time period lapses, begins to pass the amplified light signal with a varying light transmissivity.
25. An apparatus as in claim 17, wherein, while the number of channels in the light signal is being varied, the controller passes the amplified light signal with a constant light transmissivity for a predetermined time period and, after the predetermined time period lapses, begins to pass the amplified light signal with a varying light transmissivity.
26. An apparatus as in claim 17, further comprising a plurality of optical amplifiers, wherein, for each optical amplifier, an identification signal is transmitted downstream to identify the respective optical amplifier.
27. An apparatus as in claim 4, further comprising:
a demultiplexer which demultiplexes the light signal, after being passed by the controller, into individual signals; and
an automatic level control unit which controls the power level of a respective individual signal so that the power level of the individual signal is maintained to be approximately constant when the controller passes the amplified light signal with a constant light transmissivity.
28. An apparatus as in claim 4, further comprising:
a demultiplexer which demultiplexes the light signal, after being passed by the controller, into individual signals which correspond, respectively, to the number of channels in the light signal; and
receivers corresponding, respectively, to the individual signals, each receiver receiving the corresponding individual signal; and
an automatic level control unit which controls the power level of a respective individual signal before being received by the corresponding receiver, so that the power level of the individual signal is maintained to be approximately constant when the controller passes the amplified light signal with a constant light transmissivity.
an optical amplifier which amplifies a light signal having a variable number of channels;
a controller which controls the amplified light signal in response to variations in the number of channels in the light signal;
a demultiplexer which demultiplexes the controlled, amplified light signal into individual signals; and
an automatic level control unit which controls the power level of a respective individual signal so that the power level of the individual signal is maintained to be approximately constant.
30. An apparatus for amplifying a light signal, comprising:
an automatic level control unit which maintains a power level of the light signal to be approximately constant and produces a corresponding output signal; and
an optical fiber amplifier which amplifies the output signal of the automatic level control unit with a constant gain.
31. An apparatus as in claim 30, wherein the light signal includes a variable number of channels, the apparatus further comprising:
prior to, and subsequent to, varying the number of channels in the light signal, passes the amplified output signal of the optical fiber amplifier with a varying light transmissivity so that a power level of the amplified output signal is maintained at an approximately constant level in accordance with the number of channels in the light signal, and,
while the number of channels in the light signal is being varied, passes the amplified output signal of the optical fiber amplifier with a constant light transmissivity.
32. An apparatus as in claim 31, wherein prior to, and subsequent to, varying the number of channels in the light signal, the controller passes the amplified output signal of the optical fiber amplifier so that the power level of the amplified output signal is maintained within a predetermined range.
33. An apparatus as in claim 31, wherein the controller receives a warning signal indicating when the number of channels in the light signal will be varied, the warning signal for use by the controller to determine when to pass the amplified light signal with a constant light transmissivity.
34. An apparatus as in claim 31, wherein the controller receives a completion signal indicating when a variation in the number of channels in the light signal is completed, the completion signal for use by the controller to determine when to pass the amplified output signal with a varying light transmissivity, the apparatus further comprising:
a plurality of downstream optical amplifiers, the completion signal being transmitted downstream for use in controlling an output of each of the downstream optical amplifiers.
35. An apparatus as in claim 31, wherein, after the controller begins to pass the amplified light signal with a varying light transmissivity subsequent to a variation in the number of channels in the light signal, the controller causes a completion signal to be transmitted downstream to indicate that the controller has completed control in response to the variation in the number of channels.
36. An apparatus as in claim 33, wherein, after the controller begins to pass the amplified light signal with a varying light transmissivity subsequent to a variation in the number of channels in the light signal, the controller causes a completion signal to be transmitted downstream to indicate that the controller has completed control in response to the variation in the number of channels.
37. An apparatus as in claim 31, wherein, while the number of channels in the light signal is being varied, the controller passes the amplified light signal with a constant light transmissivity for a predetermined time period and, after the predetermined time period lapses, begins to pass the amplified light signal with a varying light transmissivity.
38. An apparatus as in claim 33, wherein, while the number of channels in the light signal is being varied, the controller passes the amplified light signal with a constant light transmissivity for a predetermined time period and, after the predetermined time period lapses, begins to pass the amplified light signal with a varying light transmissivity.
39. An apparatus as in claim 35, wherein, while the number of channels in the light signal is being varied, the controller passes the amplified light signal with a constant light transmissivity for a predetermined time period and, after the predetermined time period lapses, begins to pass the amplified light signal with a varying light transmissivity.
40. An apparatus as in claim 36, wherein, while the number of channels in the light signal is being varied, the controller passes the amplified light signal with a constant light transmissivity for a predetermined time period and, after the predetermined time period lapses, begins to pass the amplified light signal with a varying light transmissivity.
41. An apparatus as in claim 31, further comprising a plurality of optical amplifiers, wherein, for each optical amplifier, an identification signal is transmitted downstream to identify the respective optical amplifier.
42. An apparatus as in claim 33, further comprising a plurality of optical amplifiers, wherein, for each optical amplifier, an identification signal is transmitted downstream to identify the respective optical amplifier.
43. An apparatus as in claim 35, further comprising a plurality of optical amplifiers, wherein, for each optical amplifier, an identification signal is transmitted downstream to identify the respective optical amplifier.
44. An apparatus as in claim 36, further comprising a plurality of optical amplifiers, wherein, for each optical amplifier, an identification signal is transmitted downstream to identify the respective optical amplifier.
prior to, and subsequent to, varying the number of channels in the light signal, maintains a power level of the amplified light signal at an approximately constant level in accordance with the number of channels in the light signal, and,
while the number of channels in the light signal is being varied, amplifies the amplified light signal with an approximately constant gain.
46. An apparatus as in claim 45, wherein the controller comprises:
an optical attenuator which passes the amplified light signal and has a variable light transmissivity; and
47. An apparatus as in claim 46, wherein, while the number of channels in the light signal is being varied, the automatic level control unit maintains the light transmissivity of the optical attenuator to be constant.
48. An apparatus as in claim 45, wherein the controller comprises:
an optical amplifier which further amplifies the amplified light signal; and
an automatic level control unit which, prior to, and subsequent to, varying the number of-channels in the light signal, varies the gain of the optical amplifier of the controller so that the power level of the light signal, as amplified by the optical amplifier of the controller, is maintained at an approximately constant level in accordance with the number of channels in the light signal.
49. An apparatus as in claim 45, wherein
upon receipt of the warning signal, the controller begins amplifying the amplified light signal with an approximately constant gain and continues amplifying the amplified light signal with an approximately constant gain until after the number of channels is varied.
50. An apparatus as in claim 49, wherein the warning signal is included in the light signal, and the controller extracts the warning signal from the light signal.
51. An apparatus as in claim 45, further comprising:
52. An apparatus as in claim 45, wherein, while the number of channels in the light signal is being varied, the controller amplifies the amplified light signal with an approximately constant gain for a predetermined time period and, after the predetermined time period lapses, begins to maintain the power level of the amplified light signal at an approximately constant level.
53. An apparatus as in claim 45, wherein
the controller receives a completion signal indicating when a variation in the number of channels in the light signal is completed.
54. An apparatus as in claim 45, wherein, after the controller begins to maintain the power level of the amplified light signal at an approximately constant level subsequent to a variation in the number of channels in the light signal, the controller causes a completion signal to be transmitted downstream to indicate that the controller has completed control in response to the variation in the number of channels.
55. An apparatus as in claim 45, further comprising:
a demultiplexer which demultiplexes the light signal from the controller into individual signals; and
an automatic level control unit which controls the power level of a respective individual signal so that the power level of the individual signal is maintained to be approximately constant when the controller amplifies the amplified light signal with an approximately constant gain.
prior to varying the number of channels in the light signal, varies the light transmissivity of the optical attenuator so that a power level of the amplified light signal is maintained at an approximately constant level that depends on the number of channels in the light signal prior to the varying the number of channels,
while the number of channels in the light signal is being varied, maintains the light transmissivity of the optical attenuator to be constant, and
subsequent to varying the number of channels in the light signal, varies the light transmissivity of the optical attenuator so that a power level of the amplified light signal is maintained at an approximately constant level that depends on the number of channels in the light signal subsequent to the varying the number of channels.
57. A method for controlling a light signal having a variable number of channels and amplified by an optical amplifier, the method comprising the steps of:
prior to, and subsequent to, varying the number of channels in the light signal, passing the amplified light signal with a varying light transmissivity so that a power level of the amplified light signal is maintained at an approximately constant level in accordance with the number of channels in the light signal, and,
while the number of channels in the light signal is being varied, passing the amplified light signal with a constant light transmissivity.
58. A method for controlling a light signal having a variable number of channels and amplified by an optical amplifier, the method comprising the steps of:
prior to, and subsequent to, varying the number of channels in the light signal, maintaining a power level of the amplified light signal at an approximately constant level in accordance with the number of channels in the light signal, and,
while the number of channels in the light signal is being varied, amplifying the amplified light signal with an approximately constant gain.
US10650990 1996-05-02 2003-08-29 Controller which controls a variable optical attenuator to control the power level of a wavelength-multiplexed optical signal when the number of channels are varied Expired - Lifetime US6865016B2 (en)
US10057866 Division US6646791B2 (en) 1996-05-02 2002-01-29 Controller which controls a variable optical attenuator to control the power level of a wavelength-multiplexed optical signal when the number of channels are varied
US10956107 Division US7227681B2 (en) 1996-05-02 2004-10-04 Controller which controls a variable optical attenuator to control the power level of a wavelength-multiplexed optical signal when the number of channels are varied
US20040036958A1 true true US20040036958A1 (en) 2004-02-26
US6865016B2 US6865016B2 (en) 2005-03-08
WO2005099135A1 (en) * 2004-04-06 2005-10-20 Bookham Technology Plc Voa control