GB2351861A - Power equalising optical amplifier - Google Patents
Power equalising optical amplifier Download PDFInfo
- Publication number
- GB2351861A GB2351861A GB0008851A GB0008851A GB2351861A GB 2351861 A GB2351861 A GB 2351861A GB 0008851 A GB0008851 A GB 0008851A GB 0008851 A GB0008851 A GB 0008851A GB 2351861 A GB2351861 A GB 2351861A
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- United Kingdom
- Prior art keywords
- optical
- amplification unit
- power
- different
- amplifier
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/29—Repeaters
- H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B10/293—Signal power control
- H04B10/294—Signal power control in a multiwavelength system, e.g. gain equalisation
- H04B10/2941—Signal power control in a multiwavelength system, e.g. gain equalisation using an equalising unit, e.g. a filter
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
- H01S3/10023—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by functional association of additional optical elements, e.g. filters, gratings, reflectors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/06754—Fibre amplifiers
- H01S3/06758—Tandem amplifiers
Abstract
A power equalising optical amplifier comprises a first optical amplification unit 404, which amplifies and reflects wavelength division multiplexed optical signals at a variety of positions depending upon their wavelengths, and a second optical amplification unit 406, which amplifies and reflects wavelength division multiplexed optical signals at a variety of different positions depending upon their wavelengths. The two units are connected via a circulator 402. At least one of the units comprises an optical fibre amplifier and a chirped fibre grating, which reflects signals of different wavelengths at different positions, thereby equalising their powers.
Description
2351861 OPTICAL AMPLIFIER The present invention relates to an optical
amplifier, and more particularly, to an optical amplifier which equalizes the power of optical signals having different wavelengths.
Optical amplifiers (OAs) are expected to be widely employed in future communications systems. Erbium doped fiber amplifiers (EDFAs) serve to periodically amplify an optical signal when a great amoun t of data is transferred over great distances via an optical fiber without regeneration, to compensate for 10 attenuation of the optical signal caused by long-distance transmission.
However, there are some new problems (e.g., dispersion) during periodic amplification of an optical signal for long-distance transmission. Wavelength division multiplexing (WDIVI) represents a method of overcoming some of these problems. In WDIVI a great amount of data is transmitted over several carriers, each with a different wavelength, and thus transmission speed and capacity are increased.
Assuming that an optical carrier represents one channel, optical power representing the strength of signals can evolve differently in different channels. These power differences can be very large, if the signals are attenuated and reamplified repeatedly in the optical amplifier, or if they travel through different paths in an optical network.
The power differences can stem from the following reasons.
(1) The gains can be different in different channels. A further difficulty arises in that if the gain of an optical amplifier such as an EDFA is homogeneously broadened and changed, the gains at different wavelengths change by different amounts. Here, the homogeneous broadening represents filling ideal atom positions with all ions in a gain medium, i.e., branching each ion into an ideal energy level by the Stark effect. Furthermore, it can be difficult or even impossible 1 to know which level of gain an OA will operate at, since the gain level may vary with time. Still, EDFAs that are gain-flattened or gain-equalized regardless of wavelengths and channels have been demonstrated, including those that are gain flattened or gain-equalized independently of operating conditions. However, the gain will not be ideally flat or equal. In systems with many concatenated OAs, even small gain differences between channels can be detrimental, and lead to significant power differences.
(2) The signal attenuation due to loss between amplifiers can be different in different channels, resulting in significant power differences. As for the amplification, attenuation can also vary with time, and this variation in attenuation can be different in different channels or wavelengths in an unpredictable way.
It can be concluded that it is very unlikely that the gain will compensate for the attenuation at several wavelengths simultaneously for the majority of operating conditions. (In contrast, for single wavelength systems, this occurs automatically at some wavelength so long as the loss does not exceed the gain available from the OAs.) This is especially difficult since the attenuation between amplifiers conceivably changes with different wavelength dependencies for different reasons.
Examples of the reasons can be splice degradation, incorporation of power splitters or other optical elements into the transmission path, incorporation of dispersion compensating fibers, and increased micro-bending losses. In fact, with such an uncertainty in prediction of signal powers due to the dependence of the loss of the signal powers on the wavelengths, it is impossible to ensure a flat gain as the inter-amplifier loss changes, with hom og eneously-b road en ed amplifiers like the EDFA.
Even if the gain and loss were always balanced for all channels, i.e., even if the sum of the gain and loss were OdB for all channels, this does not ensure that the powers in all channels would be equal. Unequal powers can still result for the following reasons.
(1) The signal powers applied to the system may be different at different wavelengths.
(2) Different signals may travel through different channels in a complex network with routing. When the channels are combined again, their powers will 2 most likely be different from each other, unless some form of power control is employed for each individual channel.
(3) Tunable optical taps may be used, which may attenuate the channels selectively in an unpredictable way.
For many applications, it would be better if the 0As could make the power of the different channels equal (automatic power equalization) rather than make the gain equal. At least, power differences should be kept within certain bounds.
This requires that the gain of a channel with a low input power outside the bounds should be higher than the gains of channels with powers inside the bounds.
Commercially available EDFAs cannot equalize the power differences between WIDIV1 channels because the gain of the EDFAs is homogeneously broadened at room temperature (normal temperature). As a consequence, the gain at one wavelength is almost the same as the gains at all other wavelengths.
Thus, it cannot be said that the gain of a high power channel is smaller than that is of a low power channel. In other words, gains depend on the wavelengths of channels.
In contrast, in a non-homogeneously broadened amplifier, the gain at one wavelength is partially independent of the gains at other wavelengths. Here, the non-homogeneous broadening means that a Stark branch changes for each individual lasing ion. in long distance WDIVI, provided that the gain at other wavelengths is not affected, at least to some extent, the signal gain at one wavelength is reduced if the signal power at that wavelength becomes large. This is termed gain compression or gain saturation. On the other hand, if there is a strong signal compressing the gain at another wavelength, the gain can remain high at the first wavelength.
Several methods have been proposed to equalize the inter-WDM power differences.
One method relies on the cooling of a gain medium, i.e., an EDF, to very low temperatures. An erbium gain can be essentially and non-homogeneously broadened by cooling the EDF to a liquefied nitrogen temperature, resulting in a reduction in the uniform erbium line-width. While this method is reported to work quite well, the added complexity in devices resulting from the cooling is a significant drawback.
3 In another method, the erbium gain -can remain' 'essentially and homogeneously broadened, and the EDFA gain can be non-homogeneously broadened as a whole by amplifying other signal wavelengths in other portions of the EDFA. Thus, the EDF can operate at room temperature. In a method using a twin-core EDFA as an example, paths traversed by different wavelengths are spatially separated, and a gain medium is thus effectively non- homogeneously broadened as a whole, although each and every point in the gain medium is predominantly homogeneously broadened. This method also suffers from some drawbacks. The twin-core EDFA is known to generate more noise than that of a single-core EDIA, an undesired polarization dependence may arise, considerable amounts of power are lost, and fabrication of the twin-core fiber can be difficult.
In yet another method, wavelengths for different channels are decoupled by wavelength-selective couplers (WSCs), and amplified in different EDFs. The gains of the different channels can thus be decoupled from each other, which corresponds to a non-homogeneous broadening. Drawbacks of this approach are that the amplifier becomes more complicated, and pumping power is not used in an effective way.
Claims (6)
1. Here, the grating arrangement of the second power equalization amplification unit 406 is different from that of the first power equalization amplification unit 404.
For example, if the gratings 1, 2, 3 and 4 of the first power equalization amplification unit 404 sequentially reflect optical signals of different wavelengths, V the gratings of the second power equalization amplification unit 406 can be arranged in the sequence 2-3-4"1, 3-4-1-2, 4-1-2-3, 2-4-1-3, 4-2-3-1, 1-3- 2-4, or 3 1-4-
2.
FIG. 5 shows a third embodiment of the present invention. Referring to FIG. 5, an optical amplifier includes a first optical circulator 500, a first power equalization amplification unit 502, a communications optical fiber 504, a second optical circulator 506, and a second power equalization amplification unit 508.
The first optical circulator 500 outputs an input optical signal to the first power equalization amplification unit 502, and receives an optical signal power equalized and amplified by the first power equalization amplification unit 502 and outputs the same to the next port via the communications optical fiber 504. The second circulator 506 outputs an optical signal input via the communications optical fiber 504 to the second power equalization amplification unit 508, and receives an optical signal power-equalized and amplified by the second power equalization amplification unit 508 and outputs the same to the next port.
The first and second power equalization amplification units 502 and 508 have the same structure as the power equalization amplification unit 130 of FIG. 1, and are different from each other in their grating arrangements, similar to the case of FIG. 4.
FIG. 6 is a block diagram of the structure of an optical amplifier which power equalizes continuous spectral optical signals, according to the present invention. Referring to FIG. 6, an optical amplifier includes a preamplifier 600, a prefilter 610, an optical circulator 620, a power equalization amplification unit 630, a channel monitor 640, a postfilter 650, and a postamplifier 660.
11 The preamplifier 600 and the prefilter 610 amplifies and bandpass-filters continuous spectral input optical signals. The optical circulator 620 outputs the amplified and filtered optical signal to the power equalization amplification unit 630, and receives back an optical signal power-equalized by the power equalization amplification unit 630 and outputs the received signal to the postfilter 650. The postfilter 650 and the post amplifier 660 band pass-fi iters and amplifies the power-equalized continuous spectral optical signals. The channel monitor 640 connected to the power equalization amplification unit 630 shows the add/drop state of channels.
The power equalization amplification unit 630 includes an EDF 631, a bandpass filter 632, a chirped grating 633, a first pumping diode 634, and a second pumping diode 635.
The chirped grating 633 reflects an optical signal of a continuous wavelength band at different positions of gratings. Here, the reflection wavelength band is 20nm, and its length is about lnm. When an optical signal is reflected by the chirped grating, the chirped grating includes a long period grating or a blazed grating on its upper portion to attenuate the optical signal. It is preferable that the EDF 631 also has loss. For example, an optical fiber doped with samarium is appropriate.
However, since the chirped grating usually disperses an optical signal, for example, two identical gratings chirped in opposite directions to each other can be included to compensate for the dispersion.
The power equalization amplification unit 630 can be applied to the power equalization amplification units 404, 406, 502, and 508 of the optical fibers shown in FIGS. 4 and 5. In this case, two chirped gratings used in the power equalization amplification unit of each of the optical amplifier can be chirped in opposite directions to each other.
All the characteristics, methods, or process steps disclosed in the present specification can be combined with each other, excluding mutually exclusive elements. Each property disclosed in the present specification can be even replaced by an alternative for accomplishing the same, equivalent, or similar object. Therefore, each disclosed property is just an example, and the present invention is not limited to the above embodiments. The present invention is 12 broadened up to novelty of the disclosed characteristics or a combination of the novelties, and likewise for the steps of a method or process.
According to the present invention, in a lossy system such as a system for long-distance transmission, optical signals of different wavelengths are reflected at different positions, and amplified by gain media, thus making power equalization possible. Also, optical amplifiers for optical signal transmission are cascaded, thus allowing power equalization upon long-distance transmission.
CLAIMS 1. An optical amplifier comprising: a first optical amplification unit for amplifying and reflecting a plurality of wavelength optical signals at first selected positions according to wavelengths; a second optical amplification unit for amplifying and reflecting a plurality of wavelength optical signals at second selected positions according to the wavelength, which second selected positions are different to the first selected portions of the first optical amplifier thereby providing different amplification and reflection positions for said first and second optical amplifier for respective wavelengths signals; the first or second optical amplification unit comprising: a pumping optical source, an optical fiber amplifier for amplifying continuous spectral optical signals using pumping light generated by the pumping optical source, and a chirped grating connected in series with said optical fiber amplification for reflecting the amplified continuous spectral optical signals at different wavelengths at different positions and outputting the result to the optical fiber amplifier, wherein when the power of the continuous spectral optical signals are different at different wavelengths, the optical signal powers are equalized by amplifying and reflecting the optical signals at different positions with different amplification gains; an optical circulator for outputting input optical signals to the first optical amplification unit, outputting optical signals reflected by the first optical amplification unit to the second optical amplification unit, and outputting input optical signals reflected by the second optical amplification unit to a transmission path.
14 2. The optical amplifier as claimed in Claim 1, wherein the chirped gratings of the first or second optical amplification unit are chirped in the opposite direction to each other.
3. An optical amplifier comprising; a first optical circulator; a first optical amplification unit connected to the first optical circulator, for amplifying and reflecting a plurality of wavelength optical signals at different positions'at different wavelengths; a second optical amplification unit for amplifying and reflecting a plurality of wavelength optical signals at different positions at different wavelengths, which is different from the first optical amplifier in the amplification and reflection positions depending on the wavelengths; and a second optical circulator for receiving optical signals output by the first optical circulator and transmitted via a transmission optical fiber from the first optical amplification unit and outputting the received signal to the second optical amplification unit, and outputting optical signals reflected by the second optical amplification unit to a transmission path.
4. The optical amplifier as claimed in Claim 3, wherein the first or second optical amplification unit comprises:
a pumping optical source; a plurality of optical fibers connected in series for amplifying optical signals of a plurality of wavelengths using pumping light generated by the pumping optical source; and a plurality of gratings interspersed between the optical fibers, for reflecting an optical signal of a specific channel wavelength among different wavelength optical signals amplified by the optical fibers, wherein when optical signals for channels of different wavelength have different powers, the optical signal powers for the channels are 15 equalized by amplifying and reflecting the optical signals at different positions with different amplification gains.
5. The optical amplifier as claimed in Claim 3 or 4, wherein the first or second optical amplification unit comprise: a pumping optical source; an optical fiber amplifier for amplifying continuous spectral optical signals using pumping light generated by the pumping optical source; and a chirped grating connected in series with said optical fibre amplification for reflecting the amplified continuous spectral optical signals at different wavelengths at different positions and outputting the result to the optical fiber amplifier, wherein when the powers of the continuous spectral optical signals are different at different wavelengths, the optical signal powers are equalized by amplifying and reflecting the optical signals at different positions with different amplification gains.
6. The optical amplifier as claimed in Clairn 5, wherein the chirped gratings of the first or second optical amplification unit are chir-ped in the opposite direction to each other.
Z-7-
6. The optical amplifier as claimed in Claim 5, wherein the chirped gratings of the first or second optical amplification unit are chirped in the opposite direction to each other.
7. An optical amplifier substantially as herein described with reference to the accompany drawings.
16 1 B. An optical amplifier comprising:
2 a pumping optical source; 3 a plurality of optical fibers for amplifying optical signals of a plurality of 4 wavelengths using pumping light generated by the pumping optical source; and a plurality of gratings alternately connected to the optical fibers, for 6 reflecting an optical signal of a specific wavelength among different wavelength 7 optical signals amplified by the optical fibers, 8 wherein when optical signals for channels have di fferent powers, the optical 9 signal power for each individual channel is equalized by amplifying and reflecting the optical signals at different positions with different amplification gains.
1 9. The optical amplifier as claimed in claim 1, further comprising a 2 plurality of bandpass filters connected respectively to the gratings to give losses to 3 optical signals passing through the gratings.
1 10. The optical amplifier as claimed in claim 1, further comprising a 2 plurality of attenuators connected respectively to the gratings to give losses to 3 optical signals passing through the gratings.
1 11. The optical amplifier as claimed in claim 1, further comprising a 2 plurality of erbium doped fibers (EDF) doped with samarium connected 3 respectively to the gratings to give a loss to optical signals passing through the 4 gratings.
1 12. The optical amplifier as claimed in claim 1, wherein the plurality of 2 optical fibers enable the gain swing of EDFs in a specific channel wavelength to 3 be large and the gain swing in the wavelengths of other channels existing in a 4 segment where the specific channel power is higher than other channel powers, when an optical fiber and a grating connected to that optical fiber are set as a 6 segment.
17 1 13. The optical ampFfier as cl3i-ned in claim 5, whereii an optical fiber 2 among the plurality of optical fibers is one selected from the group consisting of a 3 phosphosilicate EDF, an alum ino-phosp hosilicate EDF, a samarium-added 4 phosphosilicate EDF, and a samarium-added alumino-phosphosilicate EDF.
1 14. The optical amplifier as claimed in claim 6, wherein one of the optical 2 fibers is an optical fiber selected from the group consisting of a germanosilicate 3 EDF, and a samarium-added germanosilicate EDF.
15. The optical amplifier as claimed in claim 7, wherein one of the optical fibers is an optical fiber selected from the group consisting of an aluminosilicate EDF, and a samarium-added aluminosilicate EDF.
16. An optical amplifier comprising:
a pumping optical source-, 3 an optical fiber for amplifying continuous spectral optical signals using 4 pumping light generated by the pumping optical source; and a chirped grating for reflecting the amplified continuous spectral optical 6 signals according to different wavelengths at different positions and outputting the 7 result to the optical fiber amplifier, 8 wherein when the powers of the continuous spectral optical signals are 9 different at different wavelengths, the optical signal powers are equalized by amplifying and reflecting the optical signals at different positions with different amplification gains.
17. The optical amplifier as claimed in claim 9, wherein the optical fiber has a loss.
18. The optical amplifier as claimed in claim 10, wherein the optical fiber 2 is doped with samarium.
18 1 19. The optic.,.1 ampift,:-.r as claimed in claim 9, wherein the chirped 2 grating includes a long period grating on its upper portion to attenuate optical 3 signals when reflected.
20. The optical amplifier as claimed in claim 9, wherein the chirped 2 grating includes a blazed grating on its uppr portion to attenuate an optical signal 3 when reflected.
1 21. The optical amplifier as claimed in claim 9,. wherein the chirped 2 grating further includes a grating chirped in the opposite direction to the chirped 3 grating to compensate for dispersion of optical signals caused by the chirped 4 grating.
1 2 3 4 5 6 7 11 12 2 3 4 5 19 Amendments to the claims have been filed as follows CLALMS 1 An optical amplifier comprising:
a first optical amplification unit for amplifying and reflecting a plurality of wavelength optical signals at first selected positions according to wavelengths; a second optical amplification unit for amplifying and reflecting a plurality of wavelength optical signals at second selected positions according to the wavelength, which second selected positions are different to the first selected portions of the first optical amplifier thereby providing different amplification and reflection positions for said first and second optical amplifier for respective wavelengths signals; the first or second optical amplification unit comprising: a pumping optical source, an optical fiber amplifier for amplifying continuous spectral optical signals using pumping light generated by the pumping optical source, and a chirped grating connected in series with said optical fiber amplification for reflecting the amplified continuous spectral optical signals at different wavelengths at different positions and outputting the result to the optical fiber amplifier, wherein when the power of the continuous spectral optical signals are different at different wavelengths, the optical signal powers are equalized by amplifying and reflecting the optical signals at different positions with different amplification gains; an optical circulator for outputting input optical signals to the first opticalamplification unit, outputting optical signals reflected by the first optical amplification unit to the second optical amplification unit, and outputting input optical signals reflected by the second optical amplification unit to a transmission path.
2-<:) 2. The optical amplifier as claimed in Claim 1, wherein the chirped gratings of the first or second optical amplification unit are chirped in the opposite direction to each other.
3. An optical amplifier comprising; a first optical circulator; a first optical amplification unit connected to the first optical circulator, for amplifying and reflecting a plurality of wavelength optical signals at different positions at different wavelengths; a second optical amplification unit for amplifying and reflecting a plurality of wavelength optical signals at different positions at different wavelengths, which is different from the first optical amplifier in the amplification and reflection positions depending on the wavelengths; and a second optical circulator for receiving optical signals output by the first optical circulator and transmitted via a transmission optical fiber from the first optical amplification unit and outputting the received signal to the second optical amplification unit, and outputting optical signals reflected by the second optical amplification unit to a transmission path.
4. The optical amplifier as claimed in Claim 3, wherein the first or second optical amplification unit comprises:
a pumping optical source; a plurality of optical fibers connected in series for amplifying optical signals of a plurality of wavelengths using pumping light generated by the pumping optical source; and a plurality of gratings interspersed between the optical fibers, for reflecting an optical signal of a specific channel wavelength among different wavelength optical signals amplified by the optical fibers, wherein when optical signals for channels of different wavelength have different powers, the optical signal powers for the channels are --2- ( equalized by amplifying and reflecting the optical signals at different positions with different amplification gains.
5. The optical amplifier as claimed in Claim 3 or 4, wherein the first or second optical amplification unit comprise: a pumping optical source; an optical fiber amplifier for amplifying continuous spectral optical signals using pumping light generated by the pumping optical source; and a chirped grating connected in series with said optical fibre amplification for reflecting the amplified continuous spectral optical signals at different wavelengths at different positions and outputting the result to the optical fiber amplifier, wherein when the powers of the continuous spectral optical signals are different at different wavelengths, the optical signal powers are equalized by amplifying and reflecting the optical signals at different positions with different amplification gains.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
KR1019970060016A KR100424772B1 (en) | 1997-11-14 | 1997-11-14 | Optical amplifier system |
GB9824915A GB2331420B (en) | 1997-11-14 | 1998-11-16 | Optical amplifier |
Publications (3)
Publication Number | Publication Date |
---|---|
GB0008851D0 GB0008851D0 (en) | 2000-05-31 |
GB2351861A true GB2351861A (en) | 2001-01-10 |
GB2351861B GB2351861B (en) | 2001-02-21 |
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ID=26314668
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
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GB0008854A Expired - Fee Related GB2351862B (en) | 1997-11-14 | 1998-11-16 | Optical amplifier |
GB0008851A Expired - Fee Related GB2351861B (en) | 1997-11-14 | 1998-11-16 | Optical amplifier |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
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GB0008854A Expired - Fee Related GB2351862B (en) | 1997-11-14 | 1998-11-16 | Optical amplifier |
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GB (2) | GB2351862B (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2003043249A1 (en) * | 2001-08-03 | 2003-05-22 | Huawei Technologies Co., Ltd. | An implementation method for equalizing a power of densed wavelength division multiplex (dwdm) system |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2293936A (en) * | 1994-10-05 | 1996-04-10 | Northern Telecom Ltd | Optical amplifiers |
US5572357A (en) * | 1994-02-14 | 1996-11-05 | Sumitomo Electric Industries, Ltd. | Optical system for amplifying signal light |
WO1997034379A1 (en) * | 1996-03-13 | 1997-09-18 | Hitachi, Ltd. | Optical communication system |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2161612B (en) * | 1984-07-11 | 1988-02-03 | Stc Plc | Optical fibre transmission systems |
GB9411061D0 (en) * | 1994-06-02 | 1994-07-20 | Northern Telecom Ltd | Optical waveguide amplifiers |
-
1998
- 1998-11-16 GB GB0008854A patent/GB2351862B/en not_active Expired - Fee Related
- 1998-11-16 GB GB0008851A patent/GB2351861B/en not_active Expired - Fee Related
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5572357A (en) * | 1994-02-14 | 1996-11-05 | Sumitomo Electric Industries, Ltd. | Optical system for amplifying signal light |
GB2293936A (en) * | 1994-10-05 | 1996-04-10 | Northern Telecom Ltd | Optical amplifiers |
WO1997034379A1 (en) * | 1996-03-13 | 1997-09-18 | Hitachi, Ltd. | Optical communication system |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2003043249A1 (en) * | 2001-08-03 | 2003-05-22 | Huawei Technologies Co., Ltd. | An implementation method for equalizing a power of densed wavelength division multiplex (dwdm) system |
US6833948B2 (en) | 2001-08-03 | 2004-12-21 | Huawei Technologies Co., Ltd. | Method for implementing power equalization of dense wavelength division multiplexing system |
Also Published As
Publication number | Publication date |
---|---|
GB2351861B (en) | 2001-02-21 |
GB0008851D0 (en) | 2000-05-31 |
GB2351862A (en) | 2001-01-10 |
GB2351862B (en) | 2001-02-21 |
GB0008854D0 (en) | 2000-05-31 |
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PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20061116 |