Source: http://www.google.com/patents/US7110166?ie=ISO-8859-1&dq=7,403,220
Timestamp: 2014-08-01 14:54:11
Document Index: 210541889

Matched Legal Cases: ['art 3', 'art 2', 'Application No. 11', 'art 2', 'art 2', 'art 3', 'art 4', 'art 81', 'art 82', 'art 3', 'art 3', 'art 4']

Patent US7110166 - Raman pump power control for gain flattening - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsThe present invention aims at providing a method for controlling wavelength characteristics of optical transmission powers by Raman amplification, in which the wavelength characteristics of optical transmission powers are automatically compensated without giving any losses to channel lights to thereby...http://www.google.com/patents/US7110166?utm_source=gb-gplus-sharePatent US7110166 - Raman pump power control for gain flatteningAdvanced Patent SearchPublication numberUS7110166 B2Publication typeGrantApplication numberUS 10/892,121Publication dateSep 19, 2006Filing dateJul 16, 2004Priority dateApr 23, 1999Fee statusPaidAlso published asUS6785042, US7446934, US7599110, US20040252999, US20060285198, US20080291529Publication number10892121, 892121, US 7110166 B2, US 7110166B2, US-B2-7110166, US7110166 B2, US7110166B2InventorsMiki Onaka, Susumu KinoshitaOriginal AssigneeFujitsu LimitedExport CitationBiBTeX, EndNote, RefManPatent Citations (13), Non-Patent Citations (10), Referenced by (9), Classifications (38), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetRaman pump power control for gain flatteningUS 7110166 B2Abstract The present invention aims at providing a method for controlling wavelength characteristics of optical transmission powers by Raman amplification, in which the wavelength characteristics of optical transmission powers are automatically compensated without giving any losses to channel lights to thereby improve transmission characteristics, and an apparatus adopting the same. To this end, the method for controlling wavelength characteristics of optical transmission powers by Raman amplification according to present invention supplies Raman pump light to an optical transmission path (Raman amplifying medium); compensates the wavelength characteristics of optical transmission powers caused by transmission of WDM signal light through the optical transmission path, by gain wavelength characteristics of generated Raman amplification; and monitors the wavelength characteristics of optical transmission powers after Raman amplification to thereby control the gain wavelength characteristics of Raman amplification.
2. The optical transmission system of claim 1, wherein the monitoring unit monitors the wavelength characteristics of the output light of the multiplexing unit.
a monitoring unit monitoring the input light of the first amplifier and the second amplifier; and
4. The optical transmission system of claim 3, wherein the monitoring unit monitors the wavelength characteristics of the input light of the first amplifier and the second amplifier.
5. The optical transmission system of claim 3, wherein the monitoring unit monitors the power of the input light of the first amplifier and the second amplifier.
6. An optical apparatus connected to an optical transmission path transmitting wavelength division multiplexed (WDM) light, comprising:
7. The optical apparatus of claim 6, wherein the monitoring unit monitors the wavelength characteristics of the output light of the multiplexing unit.
8. An optical apparatus connected to an optical transmission path transmitting wavelength division multiplexed (WDM) light, comprising:
9. The optical apparatus of claim 8, wherein the monitoring unit monitors the wavelength characteristics of the input light of the first amplifier and the second amplifier.
10. The optical apparatus of claim 8, wherein the monitoring unit monitors the power of the input light of the first amplifier and the second amplifier.
This application is a divisional of application Ser. No. 09/531,015, filed Mar. 20, 2000, now U.S. Pat. No. 6,785,042.
As techniques utilizing Raman amplification, there are known articles of, for example, S. Knoshita et al., OECC, 10B2-3, July, 1997; and Emori et al. entitled �A broadband dispersion compensating Raman amplifier pumped by multi-channel WDM laser diodes�, Technical Report of IEICE, OCS98-58, pp. 7�12, 1998. The techniques described in these articles have contemplated realizing lower loss of dispersion compensation fiber and broader band of optical amplifier, by Raman amplifying a dispersion compensation fiber within an optical amplifier by utilizing a pump light source such as at 1,480 nm band. Further, in Japanese Unexamined Patent Publication No. 10-73852, there is described an optical amplifying transmission system which has contemplated realizing a broader band of signal transmission, making use of Raman amplification.
SUMMARY OF THE INVENTION The present invention has been carried out in view of the points as described above, and it is therefore an object of the present invention to provide a method for controlling wavelength characteristics of optical transmission powers utilizing Raman amplification, in which wavelength characteristics of optical transmission powers are automatically compensated without giving loss to each channel light, and transmission characteristics are improved by compensating a loss of transmission path making use of Raman amplification, and a wavelength division multiplexing optical communication system and an optical amplifier adopting the method.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a basic constitution of an apparatus adopting a method for controlling wavelength characteristics of optical transmission powers utilizing Raman amplification according to the present invention;
FIG. 2 is a graph showing a Raman gain peak wavelength relative to a Raman pump wavelength, and FIG. 3 is a graph showing a gain inclination amount of signal light band relative to a Raman pump wavelength. Here, the signal light band is supposed to be such as from 1,530 to 1,560 nm (hereinafter called �C-band�), and respective points in the figures are obtained by plotting those data shown in the known articles. It is noted that a sign of the gain inclination amount is indicated as being �+(plus)� where a gain increases as a wavelength of signal light is lengthened (gain is slanting rightwardly upward relative to wavelength), and as being �−(minus)� where a gain decreases as a wavelength of signal light is shortened (gain is slanting rightwardly downward relative to wavelength).
As shown in FIGS. 2 and 3, it is assumed that gain peak wavelengths relative to pump wavelengths can be represented by a first approximation curve, for Raman amplification. It is also assumed that the gain inclination amount of Raman amplification within the aforementioned signal light band becomes �−(minus)� where the pump wavelength is shorter than 1,450 nm, and becomes �+(plus)� where longer than the same, and that the absolute value of the gain inclination amount becomes larger as the pump wavelength deviates further from 1,450 nm.
In order that the compensation wavelength characteristic has a linearity, a gain peak wavelength of Raman amplification is required to be outside the signal light band. In the aforementioned FIG. 2, the condition required for the gain peak wavelength to be outside the C-band is that the pump wavelength is at a side shorter than 1,435 nm and at a side longer than 1,462 nm. Further, in order that the absolute value of compensation wavelength characteristic is equal to or more than 0.1 dB/nm, pump wavelength shown in the aforementioned FIG. 3 is required to be at a side shorter than 1,447 nm and at a side longer than 1,480 nm. Based on the above consideration, the condition required for realizing the compensation wavelength characteristic making use of Raman amplification is judged to be that: pump wavelength is at a side shorter than 1,435 nm (where a �−� gain inclination is required for tilt compensation) and at a side longer than 1,480 nm (where a �+� gain inclination is required for tilt compensation).
At the tilt monitoring part 3, wavelength characteristics of optical transmission powers are monitored with respect to output light of the Raman amplification generating part 2 as mentioned above. This monitoring of wavelength characteristics of optical transmission powers are performed in general by measuring an optical spectrum of output light, and various techniques have been proposed for specific measuring procedures therefor (for example, refer to an earlier Japanese Patent Application No. 11-54374 of the present applicant, and an article by K. Otsuka et al., ECOC'97, Vol. 2, pp. 147�150(1997)). There will be mentioned hereinafter one example of the aforementioned method, and its overview will be explained.
According to the apparatus having the aforementioned basic constitution, WDM signal light caused with dispersions in its optical transmission powers of respective channels are not given with �loss� differently from the conventional, but given with compensation for the wavelength characteristics of optical transmission powers by preferentially increasing channels of lower powers making use of gain wavelength characteristics of Raman amplification. Thus, there can be avoided degradation of an optical S/N ratio. Further, optical S/N ratio can be rather improved, if compensation is performed by Raman amplification by an amount equal to or greater than an insertion loss at the Raman amplification generating part 2. The gain wavelength characteristics of Raman amplification at the Raman amplification generating part 2 are controlled by providing the tilt monitoring part 3, so that the wavelength characteristics of optical transmission powers can be compensated more assuredly. It is particularly effective to automatically control the gain wavelength characteristics of Raman amplification, for a system in which a number of channel lights to be used and wavelengths are variously changed.
As understood from FIG. 27, noise figure is about 7dB over an entire region of C-band in the absence of Raman pump light supply, while noise figure is remarkably improved at a shorter wavelength side in case of pump light supply at 1,430 nm. Noise figure at a longer wavelength side is not improved by supplying pump light at 1,430 nm only, and is conversely degraded to a slight degree corresponding to the insertion loss of the WDM coupler 22 b. To improve the transmission characteristic at the longer wavelength side, it is advisable to supply pump lights including both of 1,430 nm and 1,485 nm with required proportions, respectively, in the aforementioned manner shown in FIG. 18. In this way, there can be realized a wavelength characteristic having: an inclination similar to that of gain wavelength characteristic of Raman amplification which is obtained when pump light at 1,430 nm only is supplied; and a gain increased over the whole of signal light band. Thus, the compensation is performed up to a degree equal to or more than the insertion loss of WDM coupler 22 b, thereby realizing reduction of noise figure over the entire region of C-band as shown in FIG. 27.
Meanwhile, in case of Raman amplifying a transmission path in the aforementioned manner, the transmission path is input with pump light having a power of as large as several hundreds mW, giving importance to consider safety such as of a worker. Concretely, as shown in FIG. 30, it is required such as to provide a function for reducing a light power to a safety level when there is disconnected a connector (point �a�) at a position where Raman pump light is input into a transmission path from the WDM coupler 22 b. In the constitutional example of FIG. 30, there is provided a branching coupler between the WDM couplers 22 a, 22 b, so as to branch a light reflected back from the point �a� and lights transmitted from pump LD's, respectively, such that these lights are received by photodiodes (PD) such as via attenuators (ATT). Further, received light powers of respective photodiodes are sent to the Raman amplification controlling part 4. Upon judgment of disconnection of the connector at point �a� based on a ratio between the transmitted light and the reflected light, there is cut off a power source of the Raman pump LD's so that the light level at point �a� is reduced to a safety level.
Provided between an output end of former stage optical amplifying part 81 and the optical isolator 86B is a WDM coupler 22 b, so that Raman pump light at wavelength 1,430 nm output from a pump LD 23 is supplied from the backward side of the EDF 81 a, via the WDM coupler 22 b. There are arranged an optical coupler 3A between the latter stage optical amplifying part 82 and an output port OUT, as well as a tilt monitoring part 3 for monitoring wavelength characteristics of optical transmission powers making use of branched light of the optical coupler 3A. A monitored result of this tilt monitoring part 3 is sent to a Raman amplification controlling part 4 which transmits a controlling signal to the pump LD 23.
In the aforementioned system, WDM signal light propagated through the optical transmission path 7 is input into the port P1 of optical circulator 100, and then sent from the port P2 the EDF 81 a. To this EDF 8 a, there are supplied pump light of wavelength 1.43 μm from the pump LD 23 1 and pump light of wavelength 1.48 μm from the pump LD 23 2 via the WDM couplers 22 a, 22 b. Thus, the WDM signal light is amplified by a stimulated emission effect of pumped Erbium, and simultaneously therewith, Raman amplification is also generated by pump lights of respective wavelengths. The WDM signal light amplified by the EDF 81 a passes through the WDM coupler 22 b and is then sent to the optical isolator 86B, while a part of the WDM signal light is reflected such as by connecting points of optical elements and is propagated in a reverse direction within the EDF 81 a. This reflected backward light of the WDM signal light and the pump lights of respective wavelengths passed through the EDF 81 a are input into the port P2 of optical circulator 100 and then sent from the port P3 to the WDM coupler 101. At the WDM coupler 101, the output light from the port P3 is demultiplexed into a signal light component and a pump light component, and the thus demultiplexed signal light component is terminated thus suppressed. On the other hand, the pump light component is reflected by the medium 103 and sent back to the port P3 of optical circulator 100 via the WDM coupler 101. The pump light component sent back to the port P3 is sent to the optical transmission path 7, and generates Raman amplification within optical transmission path 7.
In the constitutional example of FIG. 38, the optical isolator 86A is provided at a position where the optical circulator 100 used in the fifth embodiment is inserted, and WDM couplers 104, 105 are inserted in front and in rear of the optical isolator 86A, respectively, so that Raman pump light is sent to the optical transmission path 7 while bypassing the optical isolator 86A. Each of WDM couplers 104, 105 is adapted to demultiplex the light input into a port at one side of the WDM coupler into a signal light component and a pump light component, and to output them to two ports at the other side of the WDM coupler, respectively. Here, the output ports for signal light component of both WDM couplers are connected to the optical isolator 86A, and output ports for the pump light component are connected to each other. In this way, WDM signal light input into the optical amplifier 8 from the optical transmission path 7 is sent to the EDF 81 a, after serially passing through the WDM coupler 104, optical isolator 86A and WDM coupler 105. Further, Raman pump light and the reflected backward-light of WDM signal light both passed through the EDF 81 a are demultiplexed by the WDM coupler 105 into a signal light component and a pump light component, and the signal light component is sent to the optical isolator 86A and attenuated thereby. Contrary, the pump light component demultiplexed by the WDM coupler 105 is bypassed around the optical isolator 86A, and then sent to the optical transmission path 7 via the WDM coupler 104. Note, in case of adopting the above constitution, the number of optical elements to be inserted in the main signal route is increased. Thus, concerning optical SNR, the constitution utilizing an optical circulator is advantageous.
Further, the gain wavelength characteristics of Raman amplification have been explained based on the assumption that a gain characteristic per unit wavelength at a wavelength region excluding a gain peak basically has a relatively excellent linearity. However, there has been confirmed an existence of �waviness� independent of Raman pump light power as shown in FIG. 39( a), when carefully considering the linearity of gain characteristic. This deviation in linearity can be considered as being in the order of �0.5 dB as shown in FIG. 39( b).
In case of necessity for cancelling such waviness of gain wavelength characteristics of Raman amplification, it is effective to use such as an optical filter having fixed wavelength loss characteristics. As a specific example, in case of controlling tilt by Raman amplifying a dispersion compensation fiber within an optical amplifier such as described in the third embodiment, if an optical filter to be applied for negating the gain wavelength characteristics of EDF for the latter stage optical amplifying part (such an optical filter has not been used in the third embodiment, but frequently used generally) is designed with taking into account an amount of waviness of the gain wavelength characteristics of Raman amplification, it becomes possible to exile both of the gain wavelength characteristics of EDF and the waviness of gain wavelength characteristics of Raman amplification by means of a single optical filter. It is also a useful way to increase the number of pump wavelengths. For example, in FIG. 39, the gain at 1,550 nm is lower than those at other wavelengths. As such, the �waviness� can be reduced by Raman amplification by adding a pump wavelength (such as 1,450 nm) having its gain peak at this 1,550 nm.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS4616898Sep 28, 1983Oct 14, 1986Polaroid CorporationOptical communication systems using raman repeaters and components thereforUS5083874Apr 10, 1990Jan 28, 1992Nippon Telegraph And Telephone CorporationOptical repeater and optical network using the sameUS6292288 *Mar 17, 2000Sep 18, 2001The Furukawa Electric Co., Ltd.Raman amplifier, optical repeater, and raman amplification methodUS6342965Mar 19, 1996Jan 29, 2002Fujitsu LimitedOptical fiber amplifier and dispersion compensating fiber module for optical fiber amplifierUS6344922 *Feb 19, 1999Feb 5, 2002Corvis CorporationOptical signal varying devicesJP2000098433A Title not availableJPH1073852A Title not availableJPH01230130A Title not availableJPH06169122A Title not availableJPH08248455A Title not availableJPH09179152A Title not availableJPH09197452A Title not availableJPS60236277A Title not available* Cited by examinerNon-Patent CitationsReference1"A Broadband Dispersion Compensating Raman Amplifier Pumped by Multi-Channel WDM Laser Diodes", Emori, et al., Technical Report of IEICE, OCS98-58, Nov. 1998).2"A High-Performance Optical Spectrum Monitor with High-Speed Measuring Time for WDM Optical Networks", K Otsuka et al., ECOC97, Conference Publication, No. 448.3"Capacity Upgrades of Transmission Systems by Raman Amplification", P.B. Hansen, et al., IEEE Photonics Technology Letters, vol. 9, No. 2.4"Fiber Raman Amplifiers for 1520 nm Band WDM Transmission", Kani et al., Electronic Information Communication Academy Society Congress, B-10-160.5"Raman Amplification of Dispersion Compensating Fiber for Loss Reduction and Enlargement of WDM Wavelength Range", S. Kinoshita et al., OECC97 Technical Digest, Seoul, Korea.6"Wide-Band and Low Noise Optical Amplification Using Distributed Raman Amplifiers and Erbium-Doped Fiber Amplifiers", Masuda et al., Electronic Information Communication Academy Electronics Society Congress, B10-161.7Japanese Office Action mailed Nov. 18, 2003 in Japanese Application H11-375092.8 *Marhic et al. Suppression of fiber nonlinearities in HFC systems by distributed fiber Raman Amplification. 1999 Digest of LEOS Summer Topical Meetings. 7/26/199-Jul. 30, 1999. pp. IV53-IV54.9Stimulated Raman Scattering Effects in WDM Transmission Systems Employing Non-zero Dispersion Shifted Fibers, T. Hoshida et al.10 *Takeda et al. Active Gain-Tilt Equalization by Preferentially 1.43 microns or 1.48 microns Pumped Raman Amplification. OSA Tops. vol. 30. Optical Amplifiers and Their Applications. Jun. 9-11, 1999. pp. 101-105.* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS7355786 *Mar 27, 2006Apr 8, 2008The Furukawa Electric Co., Ltd.Raman amplifying device and raman amplifying systemUS7446934 *Aug 25, 2006Nov 4, 2008Fujitsu LimitedRaman, pump power control for gain flatteningUS7554721Jul 2, 2004Jun 30, 2009Fujitsu LimitedRaman amplifier and Raman amplifier adjustment methodUS7567378Feb 25, 2008Jul 28, 2009The Furukawa Electric Co., Ltd.Raman amplifying device and Raman amplifying systemUS7599110Jun 27, 2008Oct 6, 2009Fujitsu LimitedRaman pump power control for gain flatteningUS7725032 *Dec 29, 2005May 25, 2010Fujitsu LimitedOptical transmission apparatusUS8213078Aug 31, 2010Jul 3, 2012Fujitsu LimitedRaman amplifier and raman amplifier adjustment methodUS8339698Sep 1, 2010Dec 25, 2012Fujitsu LimitedRaman amplifier and raman amplifier adjustment methodUS8564876Jul 30, 2012Oct 22, 2013Fujitsu LimitedRaman amplifier and raman amplifier adjustment method* Cited by examinerClassifications U.S. Classification359/334, 359/349International ClassificationH01S3/06, H01S3/13, H04J14/00, H04J14/02, G02F1/35, H01S3/30, H04B10/2525, H04B10/296, H01S3/067, H04B10/2519, H04B10/2537, H04B10/07, H04B10/29, H01S3/00Cooperative ClassificationH01S2301/02, H01S2301/04, H04B10/2916, H04B10/296, H01S3/06758, H04B10/2942, H01S3/1305, H01S3/09415, H01S3/10015, H01S3/06725, H01S3/302, H04B10/294, H01S3/094096, H01S3/1301, H01S3/094011European ClassificationH01S3/13A, H01S3/30F, H04B10/294, H04B10/2916, H04B10/296, H04B10/2942, H01S3/067G2Legal EventsDateCodeEventDescriptionFeb 19, 2014FPAYFee paymentYear of fee payment: 8Mar 3, 2010FPAYFee paymentYear of fee payment: 4Jan 30, 2007CCCertificate of correctionRotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google