GB2278230A - Optical amplifier - Google Patents

Optical amplifier Download PDF

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Publication number
GB2278230A
GB2278230A GB9310207A GB9310207A GB2278230A GB 2278230 A GB2278230 A GB 2278230A GB 9310207 A GB9310207 A GB 9310207A GB 9310207 A GB9310207 A GB 9310207A GB 2278230 A GB2278230 A GB 2278230A
Authority
GB
United Kingdom
Prior art keywords
wavelength
amplifier
optical
pump source
emission
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Withdrawn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
GB9310207A
Other versions
GB9310207D0 (en
Inventor
Andrew Niall Robinson
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.)
Nortel Networks Ltd
Original Assignee
Northern Telecom Ltd
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 Northern Telecom Ltd filed Critical Northern Telecom Ltd
Priority to GB9310207A priority Critical patent/GB2278230A/en
Publication of GB9310207D0 publication Critical patent/GB9310207D0/en
Publication of GB2278230A publication Critical patent/GB2278230A/en
Withdrawn legal-status Critical Current

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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
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/1301—Stabilisation of laser output parameters, e.g. frequency or amplitude in optical amplifiers
    • H01S3/13013—Stabilisation of laser output parameters, e.g. frequency or amplitude in optical amplifiers by controlling the optical pumping
    • 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
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
    • H01S5/0612—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature controlled by temperature
    • 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
    • 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
    • H01S3/094011—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre with bidirectional pumping, i.e. with injection of the pump light from both two ends of the fibre
    • 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
    • H01S3/094076—Pulsed or modulated pumping
    • 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
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
    • 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
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/068—Stabilisation of laser output parameters
    • H01S5/0683—Stabilisation of laser output parameters by monitoring the optical output parameters
    • H01S5/0687—Stabilising the frequency of the laser

Landscapes

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

Abstract

The emission wavelength of the pump laser (5) of an erbium doped fibre amplifier is locked to the peak in the absorption characteristic of its amplifier fibre (4) by means of a feedback loop employing a photodiode (8) to monitor the proportion of the pump power transmitted through the amplifier fibre while the wavelength of the laser is being dithered by means of a tone generator 11. The output of the photodiode 8 is applied to a phase sensitive detector 12. The output of the latter is smoothed by an integrator 13 and is then used to regulate the temperature of the pump laser 5. <IMAGE>

Description

OPTICAL AMPLIFIER This invention relates to optically pumped optical amplifiers, particularly, but not necessarily exclusively, to erbium doped optical fibre amplifiers.
The relatively high pump powers currently obtainable from pump laser diodes designed for emission in the region of 980 nm makes it generally attractive to pump erbium doped optical fibre amplifiers in this absorption band.
For efficient use of the available pump power, there is a need for pump power emission wavelength to be registered reasonably precisely with the peak in the amplifiers absorption band. The absorption band at 980 nm that provides the requisite amplification in an erbium doped fibre amplifier is relatively narrow, typically being only a few nanometers wide.
The present invention is directed to obtaining spectral registering between the emission wavelength of the pump and the absorption peak of the amplifier.
According to the present invention there is provided, in an optically pumped optical amplifier, a method of maintaining the alignment of the mean wavelength of emission of a wavelength tuneable optical pump source with an absorption peak of an optical amplifying element optically pumped by that source, wherein the emission wavelength of the source is modulated, and the resulting amplitude modulation of the pump power transmitted through the amplifying element is monitored to provide a control signal employed in a feedback control loop adapted to regulate the mean wavelength of emission of the optical pump source.
The invention also provides an optical amplifier having an optically amplifying element adapted to be optically pumped by a wavelength tuneable optical pump source, which amplifier includes regulation means for controlling the mean emission wavelength of the optical pump source, an electrical oscillator adapted to modulate the emission wavelength of the optical pump source, detector means adapted to provide a measure of the amplitude of the optical pump power of the optical pump source that is transmitted through the amplifying element, and a feedback loop adapted to drive the regulation means so as to minimise the amplitude of the component in the output of the detector means at the frequency of the electrical oscillator.
In principle spectral registry could have been achieved by a method that involved the construction of an optical filter with a narrow passband at the required point in the spectrum, and arranging for a portion of the output of the pump source to be incident upon a photodetector via this filter. Then a feedback system could be constructed to control the pump source emission wavelength, using the photodetector current as a feedback control signal. A primary difficulty with this approach is the construction of a suitable filter with a spectral characteristic centred at just the right wavelength and with a narrow enough pass-band.The present invention avoids having to have recourse to the construction of such a filter, and instead employs the spectral characteristics of the amplifier itself, thereby automatically selecting both the requisite part of the spectrum and the requisite spectral width.
There follows a description of an optically pumped optical amplifier embodying the present invention in a preferred form. The description refers to the accompanying drawings, in which: Figure 1 is a block diagram of the amplifier, and Figure 2 is a graphical diagram illustrating how wavelength modulation is converted to amplitude modulation by the absorption characteristic of the amplifier.
Referring to Figure 1, the signal to be amplified by this amplifier is applied to an input port 1 from where it passes through an optical isolator 2 and a 2x2 fused fibre wavelength multiplexing tapered coupler 3, and from there into a length of erbium doped optically amplifying fibre 4. The amplifier has a laser diode pump source 5 that emits at a wavelength in the region of 980 nm. Associated with this laser diode 5 is a temperature controller 6 by means of which the temperature of the diode may be regulated so as to regulate its emission wavelength. The output of the pump laser diode 5 is applied to the amplifying fibre 4 via the wavelength multiplexer 3. At the far end of the amplifying fibre there is a further 2x2 fibre coupler 7 which taps off some residual pump power transmitted through the amplifier fibre, and feeds it to a photodetector 8.Meanwhile amplified signal power is transmitted through a second optical isolator 9 and on to an output port 10. The 2x2 coupler 7 may be a wavelength multiplexing coupler so that only pump power, and substantially no power at the signal wavelength, is diverted to the photodetector 8. Alternatively it may be designed just to tap only a very small proportion of the total power for diversion to the photodetector.
A tone generator 11 dithers the d.c. drive applied to the pump laser diode, thereby dithering its emission wavelength. As can be deduced from a consideration of Figure 2, if the centre wavelength of the dithered laser emission does not register with the peak in the absorption characteristic of the amplifier fibre, the dither in the emission wavelength produces a corresponding dither in the photocurrent produced at the output of the photodetector 8. In Figure 2, curve 20 depicts the absorption per unit length of the amplifier 4, expressed as a function of wavelength, in the neighbourhood of 980 nm.By way of example, if the dither modulates the emission wavelength, as depicted at 21, between wavelengths 22 and 23, then the absorption provided by the amplifier is modulated, as depicted at 24, between absorption levels 25 and 26. (In Figure 2 the modulation has, for convenience of illustration, been represented as square-wave modulation, but in practice it is generally preferred to use sine-wave modulation). From this Figure 2 it will be seen that, if the centre wavelength of the emission from the laser diode is caused to shift through to longer wavelengths, the resulting amplitude modulation of the photocurrent will first of all diminish, pass through zero, and then begin to increase again, but with the phase reversed.
The output of the photodetector therefore provides a signal that can be used in a feedback control loop to regulate the temperature of the pump laser diode 5 so as to maintain its centre wavelength in registry with the peak in absorption characteristic 20 of the amplifier fibre 4. To this end the output of the photodetector 8 is fed, together with a signal from the tone generator, to a phase sensitive detector 12 to provide an output which is smoothed by an integrator 13 before being applied to the temperature controller 6.
The foregoing specific description has related to a construction of amplifier using only a single pump, this being employed in a copumping configuration. Merely reversing the roles of the input and output ports, and the directionality of the isolators 2 and 9, would convert it into a construction employing a counter-pumping configuration. The design may be further modified to include more than one pump, in which case each pump will have its own emission wavelength control, its own tone generator, and its own feedback loop.
The different tone generators will need to be arranged to operate at different frequencies. By this means the invention can be applied to further configurations, such as bidirectional pumping configurations and also those employing polarisation diversity. For multiple copumped configurations, a single tap 7 and a single photodetector 8 can be shared between the different feedback loops. The same situation applies in respect of multiple counter-pumping configurations, but for bidirectional pumping configurations, a separate tap at each end of the amplifier fibre will be required.
For a 2 nm FWHM absorption characteristic, a wavelength shift of the order of 0.02 nm would result in a modulation depth in the absorption characteristic of the order of 0.5 to 1% of pump light, sufficient for the synchronous detection scheme proposed. A 15-20 mA control tone will provide 0.02 nm wavelength modulation of the pump. The frequency produced by the tone generator may conveniently be in the region of 100 kHz.

Claims (11)

CLAIMS.
1. In an optically pumped optical amplifier, a method of maintaining the alignment of the mean wavelength of emission of a wavelength tuneable optical pump source with an absorption peak of an optical amplifying element optically pumped by that source, wherein the emission wavelength of the source is modulated, and the resulting amplitude modulation of the pump power transmitted through the amplifying element is monitored to provide a control signal employed in a feedback control loop adapted to regulate the mean wavelength of emission of the optical pump source.
2. A method as claimed in claim 1, wherein the optical pump source in a laser diode, the mean wavelength of whose emission is regulated by the feedback control loop by regulation of the temperature of the diode.
3. A method as claimed in claim 1 or 2, wherein the amplifying element is an erbium doped fibre, and the optical pump source is regulated to emit at a wavelength aligned with an absorption peak of the fibre in the spectral vicinity of 980 nm.
4. In an optically pumped optical amplifier, a method of maintaining, substantially as hereinbefore described with reference to the accompanying drawings, the alignment of the mean wavelength of emission of a wavelength tuneable optical pump source with an absorption peak of an optical amplifying element pumped by that source.
5. An optical amplifier having an optically amplifying element adapted to be optically pumped by a wavelength tuneable optical pump source, which amplifier includes regulation means for controlling the mean emission wavelength of the optical pump source, an electrical oscillator adapted to modulate the emission wavelength of the optical pump source, detector means adapted to provide a measure of the amplitude of the optical pump power of the optical pump source that is transmitted through the amplifying element, and a feedback loop adapted to drive the regulation means so as to minimise the amplitude of the component in the output of the detector means at the frequency of the electrical oscillator.
6. An amplifier as claimed in claim 5, wherein the amplifying element is an optical fibre.
7. An amplifier as claimed in claim 6, wherein the optical fibre is erbium doped.
8. An amplifier as claimed in claim 5, 6 or 7, wherein the optical pump source is a laser diode.
9. An amplifier as claimed in claim 8 wherein the laser diode is provided with a temperature controller adapted to regulate the mean emission wavelength of the laser diode by regulation of its temperature.
10. An amplifier as claimed in claim 8 or 9 wherein the laser is adapted to emit in the spectral vicinity of 980 nm.
11. An optical amplifier having an optically amplifying element adapted to be optically pumped by a wavelength element adapted to be optically pumped by a wavelength tuneable optical pump source, which amplifier is substantially as hereinbefore described with reference to the accompanying drawings.
GB9310207A 1993-05-18 1993-05-18 Optical amplifier Withdrawn GB2278230A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9310207A GB2278230A (en) 1993-05-18 1993-05-18 Optical amplifier

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9310207A GB2278230A (en) 1993-05-18 1993-05-18 Optical amplifier

Publications (2)

Publication Number Publication Date
GB9310207D0 GB9310207D0 (en) 1993-06-30
GB2278230A true GB2278230A (en) 1994-11-23

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4446524A1 (en) * 1994-12-24 1996-06-27 Sel Alcatel Ag Fiber optic amplifier
WO1997026722A1 (en) * 1996-01-18 1997-07-24 Northern Telecom Limited Self-stimulation signal detection in an optical transmission system
GB2322228A (en) * 1997-02-17 1998-08-19 Northern Telecom Ltd Optical amplifiers and WDM transmission systems
EP0859435A2 (en) * 1997-02-17 1998-08-19 Corning Incorporated Pump wavelength tuning of optical amplifiers and use of same in wavelength division multiplexed systems
WO2000036713A2 (en) * 1998-12-17 2000-06-22 Alliedsignal Inc. Method for controlling the wavelength of an optical fiber-based light source
US6144486A (en) * 1998-01-30 2000-11-07 Corning Incorporated Pump wavelength tuning of optical amplifiers and use of same in wavelength division multiplexed systems
US6320693B1 (en) 1998-06-30 2001-11-20 Corning Incorporated Thermal tuning of optical amplifiers and use of same in wavelength division multiplexed systems
US6715436B2 (en) 1998-09-24 2004-04-06 Stolt Offshore Limited Sea-going vessel and hull for sea-going vessel
CN100388114C (en) * 2000-07-21 2008-05-14 住友电气工业株式会社 Raman amplifier

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4554510A (en) * 1983-09-12 1985-11-19 The Board Of Trustees Of Leland Stanford Junior University Switching fiber optic amplifier
EP0517503A2 (en) * 1991-06-03 1992-12-09 Nippon Telegraph And Telephone Corporation Optical amplifier

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4554510A (en) * 1983-09-12 1985-11-19 The Board Of Trustees Of Leland Stanford Junior University Switching fiber optic amplifier
EP0517503A2 (en) * 1991-06-03 1992-12-09 Nippon Telegraph And Telephone Corporation Optical amplifier

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4446524A1 (en) * 1994-12-24 1996-06-27 Sel Alcatel Ag Fiber optic amplifier
US5822094A (en) * 1996-01-18 1998-10-13 Northern Telecom Limited Self-stimulation signal detection in an optical transmission system
WO1997026722A1 (en) * 1996-01-18 1997-07-24 Northern Telecom Limited Self-stimulation signal detection in an optical transmission system
US5859716A (en) * 1996-01-18 1999-01-12 Northern Telecom Limited Self-stimulation signal detection in an optical transmission system
EP0859435A2 (en) * 1997-02-17 1998-08-19 Corning Incorporated Pump wavelength tuning of optical amplifiers and use of same in wavelength division multiplexed systems
EP0859435A3 (en) * 1997-02-17 1999-01-07 Corning Incorporated Pump wavelength tuning of optical amplifiers and use of same in wavelength division multiplexed systems
GB2322228A (en) * 1997-02-17 1998-08-19 Northern Telecom Ltd Optical amplifiers and WDM transmission systems
AU745834B2 (en) * 1997-02-17 2002-04-11 Corning Incorporated Pump wavelength tuning of optical amplifiers and use of same in wavelength division multiplexed systems
US6144486A (en) * 1998-01-30 2000-11-07 Corning Incorporated Pump wavelength tuning of optical amplifiers and use of same in wavelength division multiplexed systems
US6320693B1 (en) 1998-06-30 2001-11-20 Corning Incorporated Thermal tuning of optical amplifiers and use of same in wavelength division multiplexed systems
US6715436B2 (en) 1998-09-24 2004-04-06 Stolt Offshore Limited Sea-going vessel and hull for sea-going vessel
WO2000036713A2 (en) * 1998-12-17 2000-06-22 Alliedsignal Inc. Method for controlling the wavelength of an optical fiber-based light source
WO2000036713A3 (en) * 1998-12-17 2000-08-03 Allied Signal Inc Method for controlling the wavelength of an optical fiber-based light source
US6327277B1 (en) 1998-12-17 2001-12-04 Honeywell International Inc. Method for controlling the wavelength of an optical fiber-based light source
CN100388114C (en) * 2000-07-21 2008-05-14 住友电气工业株式会社 Raman amplifier

Also Published As

Publication number Publication date
GB9310207D0 (en) 1993-06-30

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