GB2244595A - Optical fibre amplifier with automatic gain control - Google Patents

Optical fibre amplifier with automatic gain control Download PDF

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Publication number
GB2244595A
GB2244595A GB9108174A GB9108174A GB2244595A GB 2244595 A GB2244595 A GB 2244595A GB 9108174 A GB9108174 A GB 9108174A GB 9108174 A GB9108174 A GB 9108174A GB 2244595 A GB2244595 A GB 2244595A
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United Kingdom
Prior art keywords
amplifier
fibre
signal
optical fibre
waveguide
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.)
Granted
Application number
GB9108174A
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GB9108174D0 (en
GB2244595B (en
Inventor
Christopher John Rowe
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.)
British Telecommunications PLC
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British Telecommunications PLC
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Filing date
Publication date
Application filed by British Telecommunications PLC filed Critical British Telecommunications PLC
Publication of GB9108174D0 publication Critical patent/GB9108174D0/en
Publication of GB2244595A publication Critical patent/GB2244595A/en
Application granted granted Critical
Publication of GB2244595B publication Critical patent/GB2244595B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4287—Optical modules with tapping or launching means through the surface of the waveguide
    • G02B6/4289—Optical modules with tapping or launching means through the surface of the waveguide by inducing bending, microbending or macrobending, to the light guide
    • 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
    • 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
    • H01S3/1305—Feedback control systems
    • 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
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • 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

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

Abstract

An optical fibre amplifier with automatic gain control comprises a length of doped optical fibre 1 having a signal input optical fibre 2, a signal output optical fibre 4, a pump laser input optical fibre 3, a pump laser 5, sampling means 6 that samples the level of the signal on the signal output fibre 4, and a control unit 11 that controls the drive current to the pump laser 5 to compensate for variations in the output signal level. The sampling means 6 includes a mandrel and waveguide (7, 8 Fig 2) for tapping light out of the output signal fibre 4, The optical fibre may be erbium doped, and the signal input may be amplitude modulated. <IMAGE>

Description

FIBRE AMPLIFIER WITH AUTOMATIC GAIN CONTROL This invention relates to an optical fibre amplifier with automatic gain control.
An optical fibre amplifier is constituted by a length of doped (usually with erbium or neodymium) fibre which is pumped optically by a pump laser via a dedicated optical fibre. Essentially, therefore, a fibre amplifier can be regarded as a black box having three connections, namely a signal input, a pump input and a signal output. The pump input provides the power to amplify a signal at the signal input to give an output at a higher power, typically 15 to 20 dB greater. In an optical system which incorporates one or more amplifiers, the stability of amplifier output is crucial, especially if a number of amplifiers are placed in series. For example, if the outputs of ten amplifiers all drop by ldB, the signal received at the downstream end of the system is reduced by 10 dB, and this can lead to serious problems.
In this specification the term "optical" is intended to refer to that part of the electromagnetic spectrum which is generally known as the visible region together with those parts of the infra-red and ultraviolet regions at each end of the visible region which are capable for example of being transmitted by dielectric optical waveguides such as optical fibres.
The aim of the invention is to provide an optical fibre amplifier having a substantially constant average output.
The present invention provides an optical fibre amplifier with automatic gain control, the amplifier comprising a length of doped optical fibre having a signal input optical fibre, a signal output optical fibre and a pump laser input optical fibre, a pump laser associated with the pump laser input fibre, sampling means for sampling the level of the signal on the signal output fibre, and control means for controlling the drive current to the pump laser to compensate for variations in the output signal level, wherein the sampling means is constituted by a physically non-intrusive device for tapping light out of a curved portion of the output signal fibre.
The use of a physically non-intrusive tapping device (that is to say a tapping device that is effective without having to break the fibre being tapped) for tapping light out of the output signal fibre permits signal sampling without the fibre having to be broken into for, for example, splicing purposes. Consequently, automatic gain control can be accomplished without disruption of the system.
Advantageously, the tapping device is a clip-on device including a waveguide, a mandrel and a photodetector, the waveguide and the mandrel being shaped to bend the output signal fibre therebetween, and the photodetector being positioned to receive light from the waveguide.
Preferably, the control means is constituted by a proportional integral control unit which compares the signal received from the photodetector with a predetermined standard, the control unit being such as to vary the pump laser drive current to compensate for any deviation of the photodetector output signal from said predetermined standard.
The amplifier may further comprise a band pass filter positioned between the waveguide and the photodetector, the band pass filter having its pass range centered on the wavelength of the input signal.
Conveniently, the waveguide is a perspex waveguide, the pump laser is a 50mW 1480nm laser, and the optical fibres are single mode optical fibres.
An optical fibre amplifier constructed in accordance with the invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which: - Fig. 1 is a schematic diagram showing the amplifier; Fig. 2 is a diagram showing a clip-on detector which forms part of the amplifier of Fig. 1; and Fig. 3 is a graph showing the amplifier characteristics.
Referring to the drawings, Fig. 1 shows a fibre amplifier 1 having two input optical fibres 2 and 3 and an output optical fibre 4. The fibres 2, 3 and 4 are all single mode optical fibres. The amplifier 1 is constituted by a length of erbium doped optical fibre. The input fibre 2 is connected to a signal source (not shown) operating at 1536 nm, and the input fibre 3 is connected to a pump laser 5. The laser 5 is a 50mW, 1480nm semiconductor laser, though a higher power laser could be used with advantage.
A clip-on detector 6 is associated with the output fibre 4, the detector being arranged to tap off 0. 5dB (- 10%) of the output signal. As shown in Fig. 2, the detector 6 comprises a mandrel 7, a perspex waveguide 8, an optical filter 9, and a photodiode 10. The output fibre 4 is positioned in a curve between the mandrel 7 and a V-shaped indented portion 8a of the waveguide 8 so that the radius of curvature of the curve is of the order of 5 to 6mm. This tapping out of optical energy occurs as a result of the radiation leak which is inherent in a fibre which is curved to this degree. The light tapped out of the fibre 4 in this way is picked up by the waveguide 8, which directs it to the photodiode 10 via the filter 9.The filter 9 is a dielectric stack, band pass filter having a narrow (lOnm) band pass range centered on 1536nm. It is effective, therefore, to remove any residual pump power reaching the photodiode 10, and also removes substantially all of the spontaneous emission which inevitably occurs in the fibre amplifier 1. The filter 9 does, therefore, effectively limit the light reaching the photodiode 10 to that of the amplified signal.
The output of the photodiode 10 is used to control the drive current applied to the pump laser 5 to modify the gain of the amplifier 1 to compensate for any change in the output signal. This control is effected by a proportional integral (PI) control unit 11 which is positioned in a line 12 leading from the photodiode 10 to the drive current input of the pump laser 5. The PI control unit 11 compares any signal from the photodiode 10 with a standard. Any deviation from this setpoint causes a change in the pump laser drive current, thereby changing the gain of the amplifier 1 to compensate for the deviation in the output signal. The average output power of the amplifier can, therefore, be varied (set) from within the control unit 11.
Fig 3. is a graph showing the fibre amplifier characteristics, and illustrating the automatic gain control. As will be seen, for each of the different power output settings, the power output is constant until maximum gain is reached.
The main advantage of the amplifier described above is that it can be incorporated into an optical fibre network with the minimum of intrusion. In particular, the use of the clip-on detector 6 for tapping off part of the output signal of the amplifier 1 is physically non-intrusive, that is to say there is no need for the output fibre 4 to be broken in order to insert a coupler (or other intrusive device) for tapping off part of the output signal.
Moreover, the clip-on detector 6 (together with the associated feed-back items 12, 11, 5 and 3) could be added to a fibre amplifier already in an optical fibre network to provide automatic gain control for that amplifier.
Another advantage of the amplifier 1 described above is that, by varying the degree of compression of the fibre 4 between the mandrel 7 and the V-shaped indented portion 8a of the waveguide 8, the power coupled out of the fibre can be adjusted. This tunability of the output ratio (i. e.
the ratio of the output signal of the amplifier 1 which is tapped out of the fibre), enables the output of the amplifier to be- monitored and adjusted to suit different applications.
It will be apparent that modifications could be made to the amplifier described above. For example, the dielectric stack, band pass filter 9 could be replaced by a filter having a narrower pass band (for example down to about lnm), thereby reducing still further the effects of spontaneous emission and residual pump. Moreover, it would be possible to amplitude modulate the signal laser with a small (=10 kHz) signal on top of the main signal. This additional signal, whose modulation depth need only be about 5%, does not affect the main system. The control unit 11 would then be modified to detect the frequency of this additional signal, and so disregards the pump (dc) and the effects of spontaneous emissions. In this way, the effects of pump remnants and spontaneous emissions (which are part of the mean amplifier output, and are thus input to the control unit 11) on the operation of the amplifier can be eliminated.

Claims (8)

1. An optical fibre amplifier with automatic gain control, the amplifier comprising a length of doped optical fibre having a signal input optical fibre, a signal output optical fibre and a pump laser input optical fibre, a pump laser associated with the pump laser input fibre, sampling means for sampling the level of the signal on the signal output fibre, and control means for controlling the drive current to the pump laser to compensate for variations in the output signal level, wherein the sampling means is constituted by a physically non-intrusive device for tapping light out of a curved portion of the output signal fibre.
2. An amplifier as claimed in claim 1, wherein the tapping device is a clip-on device including a waveguide, a mandrel and a photodetector, the waveguide and the mandrel being shaped to bend the output signal fibre therebetween, and the photodetector being positioned to receive light from the waveguide.
3. An amplifier as claimed in claim 2, wherein the control means is constituted by a proportional integral control unit which compares the signal received from the photodetector with a predetermined standard, the control unit being such as to vary the pump laser drive current to compensate for any deviation of the photodetector output signal from said predetermined standard.
4. An amplifier as claimed in claim 2 or claim 3, further comprising a band pass filter positioned between the waveguide and the photodetector, the band pass filter having its pass range centered on the wavelength of the input signal.
5. An amplifier as claimed in any one of claims 2 to 4, wherein the waveguide is a perspex waveguide.
6. An amplifier as claimed in any one of claims 1 to 5, wherein the pump laser is a 50mW 1480nm laser.
7. An amplifier as claimed in any one of claims 1 to 6, wherein the optical fibres are single mode optical fibres.
8. An optical fibre amplifier substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.
GB9108174A 1990-04-18 1991-04-17 Fibre amplifier with automatic gain control Expired - Fee Related GB2244595B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB909008735A GB9008735D0 (en) 1990-04-18 1990-04-18 Fibre amplifier with automatic gain control

Publications (3)

Publication Number Publication Date
GB9108174D0 GB9108174D0 (en) 1991-06-05
GB2244595A true GB2244595A (en) 1991-12-04
GB2244595B GB2244595B (en) 1994-04-13

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GB9108174A Expired - Fee Related GB2244595B (en) 1990-04-18 1991-04-17 Fibre amplifier with automatic gain control

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Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0517503A2 (en) * 1991-06-03 1992-12-09 Nippon Telegraph And Telephone Corporation Optical amplifier
US5223705A (en) * 1992-08-12 1993-06-29 At&T Bell Laboratories Measurement of an optical amplifier parameter with polarization
GB2262836A (en) * 1991-12-24 1993-06-30 Northern Telecom Ltd Optical pre-amplifier/receiver arrangement.
US5297154A (en) * 1992-05-04 1994-03-22 Alcatel Sel A.G. Fiber-optic amplifier with feedback-insensitive pump laser
EP0618649A2 (en) * 1993-03-30 1994-10-05 Alcatel SEL Aktiengesellschaft Fiber optic amplifier
GB2287148A (en) * 1994-03-02 1995-09-06 Fujitsu Ltd Preventing occurence of surge light in optical amplifier/transmitter apparatus
US5600481A (en) * 1993-12-27 1997-02-04 Nec Corporation Optical fiber amplifier and optical transmission system using the same
FR2755771A1 (en) * 1996-11-13 1998-05-15 France Telecom Transverse Fluorescence Controlled Optical Amplifier for Telecommunications
US5903385A (en) * 1997-03-13 1999-05-11 Fujitsu Limited Remotely pumping type multi-wavelength light transmission system
US5973821A (en) * 1996-03-01 1999-10-26 Fujitsu Limited Variable optical attenuator which applies a magnetic field to a faraday element to rotate the polarization of light signal
US6055092A (en) * 1995-03-09 2000-04-25 Fujitsu Limited Multi-wavelength light amplifier
US6369938B1 (en) 1996-05-28 2002-04-09 Fujitsu Limited Multi-wavelength light amplifier
US6441955B1 (en) 1998-02-27 2002-08-27 Fujitsu Limited Light wavelength-multiplexing systems
US6496300B2 (en) 1998-02-27 2002-12-17 Fujitsu Limited Optical amplifier
US7924499B2 (en) 1998-03-19 2011-04-12 Fujitsu Limited Gain and signal level adjustments of cascaded optical amplifiers

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4165496A (en) * 1977-12-16 1979-08-21 Bell Telephone Laboratories, Incorporated Optical fiber light tap
GB2168838A (en) * 1984-03-30 1986-06-25 Boh Optical Ab Frequency and output regulation in laser diodes
EP0211537A1 (en) * 1985-07-15 1987-02-25 RAYCHEM CORPORATION (a Delaware corporation) Apparatus for coupling light between an optical fiber and a light element
GB2179468A (en) * 1985-08-20 1987-03-04 Pirelli General Plc Optical coupler for an optical fibre

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4165496A (en) * 1977-12-16 1979-08-21 Bell Telephone Laboratories, Incorporated Optical fiber light tap
GB2168838A (en) * 1984-03-30 1986-06-25 Boh Optical Ab Frequency and output regulation in laser diodes
EP0211537A1 (en) * 1985-07-15 1987-02-25 RAYCHEM CORPORATION (a Delaware corporation) Apparatus for coupling light between an optical fiber and a light element
GB2179468A (en) * 1985-08-20 1987-03-04 Pirelli General Plc Optical coupler for an optical fibre

Cited By (36)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0517503A2 (en) * 1991-06-03 1992-12-09 Nippon Telegraph And Telephone Corporation Optical amplifier
US5245690A (en) * 1991-06-03 1993-09-14 Nippon Telegraph And Telephone Corporation Optical fiber amplifier including rare earth doped fiber and feedback pump light source control
EP0517503A3 (en) * 1991-06-03 1994-01-12 Nippon Telegraph & Telephone Optical amplifier
GB2262836A (en) * 1991-12-24 1993-06-30 Northern Telecom Ltd Optical pre-amplifier/receiver arrangement.
US5297154A (en) * 1992-05-04 1994-03-22 Alcatel Sel A.G. Fiber-optic amplifier with feedback-insensitive pump laser
US5223705A (en) * 1992-08-12 1993-06-29 At&T Bell Laboratories Measurement of an optical amplifier parameter with polarization
EP0618649A2 (en) * 1993-03-30 1994-10-05 Alcatel SEL Aktiengesellschaft Fiber optic amplifier
EP0618649A3 (en) * 1993-03-30 1994-11-30 Sel Alcatel Ag Fiber optic amplifier.
US5471342A (en) * 1993-03-30 1995-11-28 Alcatel N.V. Fiber optical amplifier having a detector for measuring scattered light at a splice
US5600481A (en) * 1993-12-27 1997-02-04 Nec Corporation Optical fiber amplifier and optical transmission system using the same
US5808785A (en) * 1993-12-27 1998-09-15 Nec Corporation Optical fiber amplifier and optical transmission system using the same
GB2287148A (en) * 1994-03-02 1995-09-06 Fujitsu Ltd Preventing occurence of surge light in optical amplifier/transmitter apparatus
US5570227A (en) * 1994-03-02 1996-10-29 Fujitsu Limited Method and apparatus for preventing occurrence of surge light in optical amplifier/transmitter apparatus
GB2287148B (en) * 1994-03-02 1997-12-10 Fujitsu Ltd Method and apparatus for preventing occurrence of surge light in optical amplifier/transmitter apparatus
US6055092A (en) * 1995-03-09 2000-04-25 Fujitsu Limited Multi-wavelength light amplifier
US6333806B1 (en) 1996-03-01 2001-12-25 Fujitsu Limited Variable optical attenuator which applies a magnetic field to a Faraday element to rotate the polarization of a light signal
US5973821A (en) * 1996-03-01 1999-10-26 Fujitsu Limited Variable optical attenuator which applies a magnetic field to a faraday element to rotate the polarization of light signal
US6717713B2 (en) 1996-03-01 2004-04-06 Fujitsu Limited Variable optical attenuator which applies a magnetic field to a faraday element to rotate the polarization of a light signal
US6570699B2 (en) 1996-03-01 2003-05-27 Fujitsu Limited Variable optical attenuator which applies a magnetic field to a Faraday element to rotate the polarization of a light signal
US6369938B1 (en) 1996-05-28 2002-04-09 Fujitsu Limited Multi-wavelength light amplifier
US6400499B2 (en) 1996-05-28 2002-06-04 Fujitsu Limited Multi-wavelength light amplifier
US8004752B2 (en) 1996-05-28 2011-08-23 Fujitsu Limited Multi-wavelength light amplifier
US6480329B2 (en) 1996-05-28 2002-11-12 Fujitsu Limited Multi-wavelength light amplifier
US8699126B2 (en) 1996-05-28 2014-04-15 Fujitsu Limited Multi-wavelength light amplifier
US8320040B2 (en) 1996-05-28 2012-11-27 Fujitsu Limited Multi-wavelength light amplifier
US7224517B2 (en) 1996-05-28 2007-05-29 Fujitsu Limited Multi-wavelength light amplifier
US7474459B2 (en) 1996-05-28 2009-01-06 Fujitsu Limited Multi-wavelength light amplifier
FR2755771A1 (en) * 1996-11-13 1998-05-15 France Telecom Transverse Fluorescence Controlled Optical Amplifier for Telecommunications
US6507431B1 (en) 1997-03-13 2003-01-14 Fujitsu Limited Remotely pumping type multi-wavelength light transmission system
US5903385A (en) * 1997-03-13 1999-05-11 Fujitsu Limited Remotely pumping type multi-wavelength light transmission system
US6441955B1 (en) 1998-02-27 2002-08-27 Fujitsu Limited Light wavelength-multiplexing systems
US6919987B2 (en) 1998-02-27 2005-07-19 Fujitsu Limited Light wavelength-multiplexing systems
US6496300B2 (en) 1998-02-27 2002-12-17 Fujitsu Limited Optical amplifier
US7969648B2 (en) 1998-03-19 2011-06-28 Fujitsu Limited Gain and signal level adjustments of cascaded optical amplifiers
US7924499B2 (en) 1998-03-19 2011-04-12 Fujitsu Limited Gain and signal level adjustments of cascaded optical amplifiers
US8547629B2 (en) 1998-03-19 2013-10-01 Fujitsu Limited Gain and signal level adjustments of cascaded optical amplifiers

Also Published As

Publication number Publication date
GB9008735D0 (en) 1990-06-13
GB9108174D0 (en) 1991-06-05
GB2244595B (en) 1994-04-13

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PCNP Patent ceased through non-payment of renewal fee

Effective date: 19950417