EP1340295A2 - Amplificateur optique et procede d'amplification d'un signal optique - Google Patents

Amplificateur optique et procede d'amplification d'un signal optique

Info

Publication number
EP1340295A2
EP1340295A2 EP01993962A EP01993962A EP1340295A2 EP 1340295 A2 EP1340295 A2 EP 1340295A2 EP 01993962 A EP01993962 A EP 01993962A EP 01993962 A EP01993962 A EP 01993962A EP 1340295 A2 EP1340295 A2 EP 1340295A2
Authority
EP
European Patent Office
Prior art keywords
optical
optical fiber
pump
wavelength
doped
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01993962A
Other languages
German (de)
English (en)
Inventor
Rodolfo Di-Muro
Kevan Jones
Ian Mcclean
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lumentum Technology UK Ltd
Original Assignee
Bookham Technology PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bookham Technology PLC filed Critical Bookham Technology PLC
Publication of EP1340295A2 publication Critical patent/EP1340295A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • 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
    • H01S2303/00—Pumping wavelength
    • 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094003—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre

Definitions

  • the invention relates to an optical amplifier, and more particularly to a doped-fiber optical amplifier using a pump.
  • optical communications systems in which optical signals are transmitted using optical fibers have become widespread.
  • an optical amplifier is required at intervals, for example every 80km or thereabouts.
  • Optical amplifiers may also be required in other applications, for example to compensate for losses in optical modulators or other equipment.
  • Figure 1 schematically illustrates one type of optical amplifier, a doped fiber optical amplifier.
  • the central component is a length of optical fibre 10 doped in this example with Erbium (Er).
  • Er Erbium
  • the fiber 10 may be around 10m long.
  • a pump 20 transmits pump light into the Er-doped optical fiber through an input optical coupler 12 to excite Er atoms into an inverted state.
  • Signal light is passed into the Er-doped optical fiber 10 from an input optical fiber 16 via the input optical coupler 12 and output light is output from the fiber through an isolator 14 to an output optical fiber 18.
  • the isolator 14 prevents light travelling in the reverse direction.
  • the pump light is absorbed by excitation of doping states in the Er-doped optical fiber 10 and causes an inversion. This causes any signal light entering the Er-doped optical fiber 10 to be amplified by stimulated emission in the Er-doped optical fiber.
  • Optical communications systems have traditionally used signals in the C band, a wavelength band between 1530 and 1560 nm.
  • optical amplifiers for signals in the C band use a pump wavelength of 980nm, i.e. the wavelength of the light emitted by the pump 20 and input into the fiber is at 980nm.
  • 980nm is at one absorption peak of the Er-doped fiber, and pumping at this frequency works well for low noise.
  • Another absorption peak of Er-doped fiber is at 1480nm, and pump light in the wavelength range 1474nm to 1483nm is also used, especially for high power at low cost.
  • a first length of Er-doped fiber 10 is provided, pumped by a 980nm pump light source 20, and a second length of Er-doped fiber 22 is provided, pumped by a 1480nm pump light source 24. Since low noise is most important in the first amplification stage, this arrangement combines to some extent the low noise benefits of a 980nm pump with the low-cost power requirements of a 1480nm pump.
  • Known pump light sources include an LED and/or a laser emitting light at a suitable wavelength.
  • Optical amplification in the L band is carried out in generally the same manner as in the C band.
  • the length of Er-doped optical fiber needed to obtain equivalent amplification to a C band amplifier is much longer in the L band so long lengths of Er-doped optical fiber are needed, typically 60m to 110m, in order to obtain sufficient amplification.
  • high pump powers are required; the amplification efficiency is low.
  • an optical amplifier for amplifying L-band optical signals, having an Er-doped optical fiber and an optical pump coupling light having a pump wavelength from 1435nm to 1460nm into the Er-doped optical fiber.
  • Er-doped optical fiber amplifiers have previously used a pump light source with a wavelength that is very close to the absorption of the Er dopant atoms at around 1480nm. Typical pump wavelengths might be 1479nm or 1483nm. When such an Er-doped optical fiber is used to amplify a C-band optical signal a length of Er-doped optical fiber of typically 10m to 20m may be used. A pump wavelength of 1480nm gives good results in this band.
  • An optical fiber amplifier for the L-band may have an Er-doped optical fiber more than 60m long, typically in the range 60m to 110m. Such greater lengths of optical fiber are needed to get sufficient amplification of L-band signals in view of the lower amplification gain achieved with such L-band signals as compared with C-band signals. As mentioned above, high pump powers are required to pump such long lengths of Er-doped optical fibers.
  • the inventors have investigated the transmission of 1480nm pump light in a long optical fiber amplifier, and have deteimined that the light is absorbed over a short length of fiber, leaving a long length of fiber that does not have significant inversion. Since the non-inverted fiber is lossy at the signal wavelength, loss to the signal can occur in this non-inverted region. Thus, the high pump power used in conventional approaches is used to compensate for this loss.
  • the inventors propose using pump light at a wavelength that is not at the usual wavelength. Rather, the wavelength proposed is a little away from this wavelength which reduces the absorption in the fiber per unit length so that the light is absorbed over a much longer length of fiber. This increases the length of optical fiber that has significant inversion. Contrary to what might be supposed, the reduction in the efficiency with which the pump light is absorbed increases the overall efficiency by reducing rather than increasing the total pump power requirement.
  • the undoped optical fiber has an absorption peak due to water at 1380nm, so that the chosen pump wavelength has to be away from this peak.
  • the pump wavelength must remain able to excite the doped atoms, and so although it should not be at the absorption peak some absorption must still be obtained.
  • optical fibers are likely to carry both C-band and L- band signals, possibly also S-band (lower wavelength) signals, and the pump wavelength should be kept away from the signal wavelengths.
  • substantially no pump light above this frequency range i.e. from 1465nm to 1510nm, is coupled into the optical fiber.
  • a pump wavelength in the range 1490nm to 1510 nm, rather than 1435nm, is employed.
  • the input light signal may be brought in on a signal input optical fiber.
  • An optical coupler may be provided to couple the light from the signal input optical fiber and the pump into the Er- doped optical fiber.
  • An isolator may be provided on the Er-doped optical fiber to prevent back reflections.
  • a second stage of amplification may be provided, having a second-stage Er-doped optical fiber and a second-stage pump source.
  • the second-stage pump source may emit at a wavelength of 1480nm.
  • a second-stage optical coupler may couple the outputs from the first Er-doped optical fiber and the second pump source into the second Er-doped optical fiber.
  • An isolator may be provided between the first Er-doped optical fiber and the second-stage optical coupler to prevent light in the second Er-doped optical fiber having an effect on the first optical fiber.
  • a variable optical attenuator (NOA) may be provided in front of the second-stage optical coupler.
  • a C-band optical amplifier may be provided in parallel to the L-band optical amplifier described above.
  • the invention is also directed to a method by which the described apparatus operates and including method steps for carrying out every function of the apparatus.
  • a preferred embodiment provides a method of amplifying an L-band optical signal including pumping an Er-doped optical fiber with a pump signal at 1435nm to 1455 nm and feeding an L- band optical signal through the Er-doped optical fiber to amplify the L-band optical signal.
  • an optical amplifier having a doped length of optical fiber having dopant atoms which absorb light in an absorption wavelength band having a maximum absorption at a maximum absorption wavelength, a pump hght source for providing pump light at a pump wavelength, an optical coupler, having a signal input, for coupling the pump light source and the signal input to the doped length of optical fiber, wherein the doped length of optical fiber is sufficiently long that pump hght at the said maximum absorption wavelength is substantially absorbed and inversion occurs along only part of the length of optical fiber, and the pump wavelength is at the edge of the absorption wavelength band away from the maximum absorption wavelength so that inversion occurs along a greater length of the optical fiber than for a pump light at the said maximum absorption wavelength.
  • the wavelength may differ by at least 1% from the maximum absorption wavelength.
  • Figure 1 is a schematic of a conventional optical amplifier
  • Figure 2 is a schematic of a conventional 2-stage optical amplifier
  • Figure 3 is a schematic of a first embodiment of an optical amplifier according to the invention.
  • Figure 4 is a graph of the inversion in an Er-doped optical fiber as a function of distance down the fiber
  • Figure 5 is an expanded view of a section of the graph of Figure 4;
  • Figure 6 is a graph of the total inversion and the amplifier gain of an Er-doped fiber amplifier as a function of pump wavelength;
  • Figure 7 is a graph of amplifier gain of an Er-doped fiber amplifier as a function of signal wavelength for a number of different pump wavelengths
  • Figure 8 is a schematic of a second embodiment of the invention.
  • Figure 9 is a schematic of an embodiment of a combined C- and L- band amplifier.
  • an input optical coupler 12 has a signal input 36 to which a signal optical fiber 16 is connected, and a pump input 34 to which a pump light source 32 is connected.
  • the input optical coupler 12 couples both inputs 34, 36 to an output 38 coupled to an 80m coiled length of Er-doped optical fiber 10.
  • the pump light source 32 is a semiconductor laser emitting at 1450nm. Any other suitable light source may also be used, such as a semiconductor LED.
  • the pump light emitted by the pump light source 32 is absorbed by dopant atom energy states in the Er-doped optical fiber 10 which causes an inversion there.
  • the fiber amplifies signal light transmitted on the input optical fiber 16 by stimulated emission.
  • the inventors have investigated inversion in an Er-doped optical fiber.
  • a 200mW pump is injected into a 60m length of Er-doped fiber at 0m.
  • the amount of inversion as a function of -1 distance along the fiber is shown in Figure 4 for a number of different pump wavelengths.
  • Figure 5 shows in greater detail the portion of this graph between 30 and 50m from the pump injection point.
  • Figure 6 shows the total inversion and the total amplifier gain in an 80m length of Er-doped optical fiber as a function of pump wavelength. Unexpectedly, the best gain is obtained with a pump wavelength of 1450nm, which is at the edge of the Er absorption line.
  • a simple explanation of increased gain using pump light at 1450nm is as follows.
  • the pump light of wavelength 1450nm is at the edge of the 1480nm absorption band and so absorbs much less efficiently in a short length of fiber than light at 1480nm.
  • Pump light at 1480nm accordingly only efficiently inverts a short length of fiber, of order 10m, before being substantially absorbed, whereas pump light at 1450nm is capable of inverting a much longer length of fiber.
  • optical fiber Since optical fiber is lossy, long lengths of non-inverted fiber will produce no amplification of the signal but instead simply result in losses. Thus, by using a pump wavelength of 1450nm the loss to the signal in long lengths of non-inverted fiber may be minimised. It turns out that this effect improves the overall gain.
  • Figure 7 shows the total gain of an 80m Er-doped fiber optical amplifier as a function of the input wavelength for different pump wavelengths.
  • An approximately ldB increase in gain using a pump at 1450nm as compared to 1480nm is achieved over almost all of the L-band.
  • the amplifier with the 1450nm pump was tested again, reducing the optical pump power until the same gain as was achieved with a 200mW 1470nm pump.
  • a pump power of 155mW was required which is a saving of 45mW, i.e. 23%.
  • Figure 8 illustrates a two-stage optical amplifier using the invention.
  • the first stage corresponds to the optical fiber amplifier as described above with reference to Figure 3.
  • the output of the optical fiber 10 is input through an optical isolator 14 to a second-stage optical coupler 26 driven by a second- -stage optical pump 24.
  • the second-stage optical amplifier includes a second-stage optical fiber 22 that is also doped with Er.
  • the output of the second-stage Er-doped optical fiber passes through an output isolator 14 as in the embodiment described with reference to Figure 3.
  • the first optical pump 32 has a wavelength of 1450nm, whereas the second optical pump is less critical and has a wavelength of 1480nm.
  • 1450nm pump light could be used in both stages.
  • an optical signal is amplified by C- and L-band optical amplifiers in parallel.
  • the input signal of an input optical fiber 16 is passed to a splitter 50 which splits the signal to pass through an L-band optical amplifier 52 and a C-band optical amplifier 54.
  • the amplified signals are then combined in an optical combiner 56 to produce the final signal.
  • the L-band optical amplifier 52 may be an optical amplifier as described above. This approach makes use of the ready availability of C band optical amplifiers.
  • the invention is not limited to the above embodiments.
  • the invention may also find application to optical amplifiers doped by different materials such as neodymium or thulium.
  • the technique of pumping optical fibers with a wavelength that is different to the wavelength of the maximum absorption in the optical fiber may have application in any doped-fiber optical amplifier, especially to those of lower gain where long lengths of doped optical fiber are required.
  • the pump hght source 32 may be any suitable light source that emits light at the required wavelength.
  • the pump light source 32 may be an LED, a laser, for example a semiconductor laser, or a number of LEDs or lasers.
  • pump arrangements may be used, such as counter pumping, i.e. pumping the Er- doped optical fiber 10 in the reverse direction to the signal direction.
  • the input optical coupler may be of any suitable type, such as a fused fiber coupler.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

L'invention concerne un amplificateur optique à fibre dopée à l'erbium en bande L ayant une longueur de fibre optique dopée comprise entre 60m et 110m. La gamme de longueurs d'onde de la lumière pompée est comprise entre 1435nm et 1460nm. Il n'y a sensiblement aucune lumière dans la gamme comprise entre 1465nm et 1505nm dans la fibre. Le gain de l'amplificateur est supérieur à celui obtenu lorsque l'on utilise une lumière pompée de 1480nm.
EP01993962A 2000-11-09 2001-11-08 Amplificateur optique et procede d'amplification d'un signal optique Withdrawn EP1340295A2 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US71037200A 2000-11-09 2000-11-09
US710372 2000-11-09
PCT/GB2001/004944 WO2002039552A2 (fr) 2000-11-09 2001-11-08 Amplificateur optique et procede d'amplification d'un signal optique

Publications (1)

Publication Number Publication Date
EP1340295A2 true EP1340295A2 (fr) 2003-09-03

Family

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EP01993962A Withdrawn EP1340295A2 (fr) 2000-11-09 2001-11-08 Amplificateur optique et procede d'amplification d'un signal optique

Country Status (3)

Country Link
EP (1) EP1340295A2 (fr)
AU (1) AU2002220816A1 (fr)
WO (1) WO2002039552A2 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1811616B1 (fr) * 2005-12-16 2017-01-04 OFS Fitel, LLC Fibres optiques du type multi-mode dopées aux terres rares et dispositifs
US12278693B2 (en) 2022-12-06 2025-04-15 Ciena Corporation Stretched single optical span communications system and method avoiding hazardous power levels

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3670434B2 (ja) * 1996-04-22 2005-07-13 ルーセント テクノロジーズ インコーポレーテッド 多段光ファイバ増幅器を有するシステム
US6122298A (en) * 1996-11-01 2000-09-19 Tyco Submarine Systems Ltd. Multi-wavelength optical pump
US5936763A (en) * 1996-11-15 1999-08-10 Matsushita Electric Industrial Co., Ltd. Optical fiber amplifier, semiconductor laser module for pumping and optical signal communication system
DE69725840T2 (de) * 1997-06-06 2004-07-22 Avanex Corp., Fremont Faseroptisches Telekommunikationssystem
AU1101500A (en) * 1998-10-05 2000-04-26 Optigain, Inc. Ultra-wide bandwidth fiber based optical amplifier
US6307669B1 (en) * 1998-11-20 2001-10-23 Corning Incorporated L-band amplification with detuned 980nm pump

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO0239552A3 *

Also Published As

Publication number Publication date
WO2002039552A2 (fr) 2002-05-16
WO2002039552A3 (fr) 2002-12-27
AU2002220816A1 (en) 2002-05-21

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